ALUMINIUM AND ITS ALLOYS CALYPSO WORKS. ALUMINIUM AND ITS ALLOYS THEIR PROPERTIES, THERMAL TREATMENT AND INDUSTRIAL APPLICATION BY C. GRARD LIEUTENANT-COLONEL TRANSLATED BY C. M. PHILLIPS (NATURAL SCIENCES TRIPOS, CAMBRIDGE) AND H. W. L. PHILLIPS, B.A.(CANTAB.), A.I.C (LATE SCHOLAR OF ST. JOHN'S COLLEGE, CAMBRIDGE) NEW YORK D. VAN NOSTRAND COMPANY EIGHT WARREN STREET 1922 PRINTED IN GREAT BRITAIN TRANSLATORS' NOTE IN this translation of Col. Grard's book on " Aluminium and its Alloys," the original text has been adhered to, with the exception of certain of the appendices. Certain of the con- ditions of the French aeronautical specifications, dealing with sampling and identification of material, have not been con- sidered of sufficient interest to English readers to warrant their inclusion, but the clauses dealing with methods and results of tests have been given. The centigrade scale of temperatures has been retained throughout the book. In statistics of a general nature as, for instance, in the case of approximate output the tonne and ton have been regarded as equivalent. In exact statistics, however, an accurate conversion has been made, and both sets of values given. Where prices are given, the rate of exchange has been taken as twenty-five francs to the pound sterling, whatever the date of the statistics in question. The Tensile Strength and Elastic Limit are expressed in kilogrammes per square millimetre and in tons per square inch at the express wish of the author, both sets of values are given throughout the book, in the tables and diagrams. In the case of Hardness and Cupping Tests, no conversion has been attempted, the metrical values being in general use in this country. As regards Shock Resistance also, no con- version has been attempted. On the Continent the term " Resilience " is employed to denote the energy absorbed in impact, expressed in kilogramme-metres per square centimetre of cross section of the test piece at the bottom of the notch, whilst in this country, it is employed to denote a different property. The area of cross section at the foot of the notch vii viii ALUMINIUM AND ITS ALLOYS is not taken into consideration, but the Shock Resistance is expressed simply by the energy, in foot-pounds, absorbed by impact upon a test piece of standard dimensions. Assuming that the conversion from kilogramme-metres per square centimetre to foot-pounds is an arithmetical possi- bility, the figures would still not be comparable, as the numerical value depends to a very great extent on the precise form of the test piece employed, especially on the angle and radius at the foot of the notch, which is different in British and Continental practice. The translators would wish to express their thanks to Dr. A. G. C. Gwyer, Chief Metallurgist to the British Alu- minium Co., Ltd., for his valuable advice and for his assistance in the reading of proofs. C. M. PHILLIPS. H. W. L. PHILLIPS. WABBINGTON, November, 1920, AUTHOR'S NOTE FOE carrying out the numerous tests required for this work, we have utilised the following Government laboratories : Le Laboratoire d'Essais du Conservatoire national des Arts et Metiers (chemical analyses, mechanical tests'). Le Laboratoire d'Essais de la Monnaie et des Medailles (chemical analyses). Le Laboratoire de la Section technique de I'Artillerie (chemical analysis). Le Laboratoire de 1'Aeronautique de Chalais-Meudon (mechanical tests and micrography). The results, from which important deductions have been made, possess, therefore, the greatest reliability. We must also thank the following private laboratories : Les Laboratoires de la Societe Lorraine-Dietrich (heat treatments and mechanical tests), Les Laboratoires de 1'Usine Citroen (mechanical tests and micrography), for the readiness with which they have placed their staff and laboratory material at the disposal of the Aeronautique. By their assistance tests were multiplied, inconsistencies removed, and the delays, incidental to the carrying out of this work, minimised. Thanks also to the courtesy of the Societe de Commentry- Fourchambault, M. Chevenard, engineer to the Company, has investigated, by means of the differential dilatometer of which he is the inventor, the critical points of certain alloys, whose thermal treatment (quenching and reannealing) is of vital importance. INTRODUCTION GENERAL ARRANGEMENT OF CONTENTS THE chief characteristic of aluminium is its low density, being second only to magnesium, and, for this reason, it is valuable for aircraft. Aluminium would be ideal if this lightness could be combined with the mechanical properties of the Ferrous metals. The ore, from which alumina, for the preparation of the metal, is extracted, is widely distributed, and France is particularly favoured in this respect. Whatever the method of working and thermal treatment, pure aluminium only possesses a low strength, which prohibits its use for articles subjected to great stresses. Fortunately, certain of the mechanical properties of the metal can be improved by the addition of other constituents, and in some of the alloys thus formed the density is little changed. These are the so-called light alloys, in which aluminium is a main constituent, and which can be divided into : (i) Light alloys of low strength, (ii) Light alloys of great strength. In others, aluminium is present in such small quantity that the alloy loses its characteristic lightness, to the advantage of some of the mechanical properties. The most important are those in which copper is the principal constituent. These are (iii) Heavy alloys of great strength. The alloys of aluminium, which can thus be divided into three groups, are very numerous, and there can be no question of considering them all. In each group we shall study the ones which seem the most interesting those in which aluminium plays an important part. We shall not lay much xi xii ALUMINIUM AND ITS ALLOYS stress upon those in which aluminium is of minor import- ance. Adopting the classification here given, arbitrary, no doubt, but which, from the aviator's point of view, has its value, since it puts side by side the properties of lightness and strength, we shall consequently arrange this work according to the following scheme : Book I. Aluminium, comprising two parts : Part I. Production of aluminium. Part II. Properties of aluminium. Book II. Alloys of aluminium, comprising three parts : Part III. Light alloys for casting purposes. Part IV. Light alloys of great strength. Part V. Heavy alloys of great strength. Throughout, a large number of tests has been made on each type. In particular, an exhaustive study has been carried out on the properties as functions of cold work and annealing, and on the hardness at all temperatures. The reliability of the results is guaranteed by the standard of the testing laboratories, and by the reputation of the experimenters. CONTENTS PAGE TRANSLATORS' NOTE , ., ._ ... . . . . vii AUTHOR'S NOTE . . . * . . . . . ix INTRODUCTION '* 3d BOOK I ALUMINIUM PART I PRODUCTION OF ALUMINIUM CHAPTER I. METALLURGY OF ALUMINIUM . . . , . ' . -' 3 II. WORLD'S PRODUCTION . ,. * . ....... 9 PART II PROPERTIES OF ALUMINIUM I. PHYSICAL PROPERTIES . * . . ' . T . V . 15 II. CHEMICAL PROPERTIES ANALYSIS AND GRADING . . 16 III. MECHANICAL PROPERTIES / . . . ,.. . 18 A. TENSILE PROPERTIES (i) Variation in Tensile Properties with amount of Cold Work 20 (ii) Variation in Tensile Properties with Annealing Tempera- ture * - V . . . 29 B. HARDNESS AND SHOCK RESISTANCE (i) Variation of these Properties with amount of Cold Work . 36 (ii) Variation of these Properties with Annealing Temperature 39 C. CUPPING VALUES DEPTH OF IMPRESSION AND BREAKING LOAD (i) Variation of these Properties with amount of Cold Work . 41 (ii) Variation of these Properties with Annealing Temperature 44 D. SUMMARY . . . . . . . 47 E. CONTEMPORARY LITERATURE . > ,* . . 51 IV. MICROGRAPHY OF ALUMINIUM ... . . . . 56 V. PRESERVATION OF ALUMINIUM . . * , > . 58 VI. SOLDERING OF ALUMINIUM . . > . , . . 62 tt xiv ALUMINIUM AND ITS ALLOYS BOOK II ALLOYS OF ALUMINIUM PAGE CLASSIFICATION . 67 PABT III LIGHT ALLOYS OF ALUMINIUM FOR CASTING PURPOSES 71 PART IV LIGHT ALLOYS OF GREAT STRENGTH ... 87 CHAPTER I. (a) VARIATION IN MECHANICAL PROPERTIES WITH AMOUNT OF COLD WORK 89 (b) VARIATION IN MECHANICAL PROPERTIES WITH ANNEALING TEMPERATURE . . . . . . . .91 II. QUENCHING .......... 96 Effect of Quenching Temperature ..... 96 Rate of Cooling . " 101 Ageing after Quenching . . . . . . .103 III. VARIATION IN MECHANICAL PROPERTIES WITH TEMPERATURE ' OF REANNEAL AFTER QUENCHING . . . . .110 IV. RESULTS OF CUPPING TESTS AFTER VARYING THERMAL TREAT- MENT . . . . . . . . .114 V. HARDNESS TESTS AT HIGH TEMPERATURES . . . .116 PART V CUPRO-ALUMINIUMS OR ALUMINIUM BRONZES . 117 I. GENERAL PROPERTIES . . . . . . . .118 II. MECHANICAL PROPERTIES ....... Alloy Type I (90 % Cu, 10 % Al) . . . . Alloy Type II (89 % Cu, 10 % Al, 1 % Mn) .... Alloy Type III (81 % Cu, 11 % Al, 4 % Ni, 4 % Fe) IH. MICROGRAPHY ......... APPENDICES APPENDIX I. ANALYTICAL METHODS ........ II. EXTRACTS FROM THE FRENCH AERONAUTICAL SPECIFICATIONS FOR ALUMINIUM AND LIGHT ALLOYS OF GREAT STRENGTH III. REPORT OF TESTS CARRIED OUT AT THE CONSERVATOIRE DES ARTS ET METIERS ON THE COLD WORKING OF ALUMINIUM IV. REPORT OF THE TESTS CARRIED OUT AT THE CONSERVATOIRE DES ARTS ET METIERS ON ANNEALING THIN SHEET ALUMINIUM AFTER COLD WORK ........ V. REPORT OF TESTS CARRIED OUT AT THE CONSERVATOIRE DES ARTS ET METIERS ON THE ANNEALING OF THICK (10 MM.) SHEET ALUMINIUM AFTER COLD WORK .... VI. PAPER SUBMITTED TO THE ACADEMIE DES SCIENCES BY Lr.-CoL. GRARD, ON THE THERMAL TREATMENT OF LIGHT ALLOYS OF GREAT STRENGTH LIST OF PLATES Calypso Works * ." .' * .' . ". . Frontispiece BOOK I ALUMINIUM PART I PRODUCTION AND METALLURGY PLATE TO FACE PAGE I Norwegian Nitrides and Aluminium Company . . ,. . 13 Photograph 1. Works at Eydehavn near Arendal 2. Works at Tyssedal on the Hardanger Fjord II. Saint Jean de Maurienne o , . .* . . . . 13 Photograph 1. Cylindrical dam 2. Aqueduct across the Arc III. Engine-room at Calypso ~". . . . . . .13 PART II PROPERTIES OF ALUMINIUM I AND II. Micrography of Aluminium . . . . . .57 Photograph 1. Aluminium ingot, chill cast (R. J. Anderson) 2. Aluminium ingot, sand cast (R. J. Anderson) 3. Aluminium, cold worked (50 %) 4. Aluminium, cold worked (100 %) 5. Aluminium, cold worked (300 %) 6. Aluminium, cold worked (300 %) and subsequently annealed at 350 for 10 minutes 7. Aluminium annealed at 595 for 60 minutes (R. J. Anderson) 8. Aluminium annealed at 595 for 4 hours (R. J. Anderson) BOOK II ALLOYS OF ALUMINIUM PART III CASTING ALLOYS III AND IIlA. Micrography of casting alloys ..... 86 Photograph 1. Copper 4 %, aluminium 96 % 2. Copper 8 %, aluminium 92 % 3. Copper 12 %, aluminium 88 % 4. Copper 3 %, zinc 12 %, aluminium 85 % Copper 11 %, tin 3 %, nickel 1 %, aluminium 85 % xv xvi ALUMINIUM AND ITS ALLOYS PLATE TO FACE PAGE PART V CUPRO-ALUMINIUMS I. Micrography of cupro-aluminium, Type I, forged and annealed 143 Photograph 1. As forged. X 60 2. As forged. X225 3. Forged and subsequntly annealed at 300. X60 4. Forged and subsequently annealed at 300. X225 IB. Micrography of cupro-aluminium, Type I, showing eutectic structure ......... 143 Photograph A. Etched with alcoholic FeCl 3 . X 500 ( Porte vin) B. Etched with alcoholic FeCl 3 . X 870 (Portevin) ,, C. Etched with alcoholic FeCl 3 , showing cellular and lamellar formations. X 500 (Por- tevin) D. Etched with alcoholic FeCl 3 , showing eutectic 4--y. Hypereutectoid alloy. X 200 (Portevin) II. Micrography of cupro-aluminium, Type I, forged and subse- quently annealed. . . . . . .143 Photograph 5. Forged and subsequently annealed at 700. X60 6. Forged and subsequently annealed at 700. X225 7. Forged and subsequently annealed at 900. X60 8. Forged and subsequently annealed at 900. X225 III. Micrography of cupro-aluminium, Type I, forged and subse- quently quenched . . . . . . .143 Photograph 9. Forged and subsequently quenched from 500. x 60 10. Forged and subsequently quenched from 500. X 225 11. Forged and subsequently quenched from 600. X 60 12. Forged and subsequently quenched from 600. X 225 IV. Micrography of cupro-aluminium, Type I, forged and subse- quently quenched (Breuil) . . . . . .143 Photograph 13. Forged and subsequently quenched from 700. X 60 14. Forged and subsequently quenched from 700. X 225 15. Forged and subsequently quenched from 800. X 60 16. Forged and subsequently quenched from 800. X 225 LIST OF PLATES xvii PLATE TO FACE FAQE V. Micrography of cupro-aluminium, Type I, forged and subse- quently quenched (Breuil) . . . . . .143 Photograph 17. Forged and subsequently quenched from 900. X 60 18. Forged and subsequently quenched from 900. X 225 VI. Micrography of cupro-aluminium, Type I, forged, quenched, and reannealed .144 Photograph 19. Forged, quenched from 900, reannealed at 300. X 60 20. Forged, quenched from 900, reannealed at 300. X 225 21. Forged, quenched from 900, reannealed at 600. X 60 22. Forged, quenched from 900, reannealed at 600. x 225 VII. Micrography of cupro -aluminium, Type I, forged, quenched, and reannealed . "4 '" . * ; .* '* , . 144 Photograph 23. Forged, quenched from 900, reannealed at 700. X 60 24. Forged, quenched from 900, reannealed at 700. X225 25. Forged, quenched from 900, reannealed at 800. X 60 26. Forged, quenched from 900, reannealed at 800. x 225 VIII. Micrography of cupro-aluminium, Type I, cast and annealed . 144 Photograph 27. As cast. x 60 28. As cast. x225 29. Cast and annealed at 800. X 60 30. Cast and annealed at 800. X 225 IX. Micrography of cupro-aluminium, Type I, cast and annealed . 144 Photograph 31. Cast and annealed at 900. X 60 32. Cast and annealed at 900. X 225 X. Micrography of cupro-aluminium, Type I, cast and quenched 144 Photograph 33. Cast and quenched from 500. X 60 34. Cast and quenched from 600. X 60 35. Cast and quenched from 700. x 60 36. Cast and quenched from 800. x 60 37. Cast and quenched from 900. x 60 XI. Micrography of cupro-aluminium, Type II, forged and an- nealed . . . * . . . . .144 Photograph 38. As forged. x 60 39. As forged. x 225 40. Forged and subsequently annealed at 8CO. X60 41. Forged and subsequently annealed at 800. x225 6 xviii ALUMINIUM AND ITS ALLOYS PLATE TO FACE PAGE XII. Micrography of cupro-aluminium, Type II, quenched and re- annealed ......... 144 Photograph 42. Quenched from 900, reannealed at 600. X60 43. Quenched from 900, reannealed at 600. X225 XIII. Micrography of cupro-aluminium, Type III, forged and an- nealed 144 Photograph 44. As forged. x 60 45. As forged. x 225 46. Forged and annealed at 600. x 60 47. Forged and annealed at 600. x 225 XIV. Micrography of cupro-aluminium, Type III, forged and an- nealed 144 Photograph 48. Forged and annealed at 800. x 60 49. Forged and annealed at 900. x 225 XV. Micrography of cupro-aluminium, Type III, forged and quenched ......... 144 Photograph 50. Quenched from 500. x 60 51. Quenched from 500. x 225 52. Quenched from 800. x 60 53. Quenched from 800. X 225 XVI. Micrography of cupro-aluminium, Type III, forged and quenched ......... 144 Photograph 54. Quenched from 900. x 60 55. Quenched from 900. X 225 XVII. Micrography of cupro-aluminium, Type III, quenched and reannealed . . . . . . . . . 144 Photograph 56. Quenched from 900, reannealed at 500. X60 57. Quenched from 900, reannealed at 500. X225 58. Quenched from 900, reannealed at 600. X60 59. Quenched from 900, reannealed at 600. X225 LIST OF ILLUSTRATIONS IN TEXT BOOK I ALUMINIUM PART I PRODUCTION AND METALLURGY FIGURE PAGE 1. Melting-point curve of mixtures of cryolite and alumina . . 5 2. World's production of bauxite .,' . ?.- f ^-* \ ..-. \ . 9 3. Map of the South of France, showing distribution of bauxite and situation of aluminium and alumina factories , . . 11 PART II PROPERTIES 4. Variation in mechanical properties (tensile) of thin aluminium sheet (1 mm. thick) with cold work .. * ^ \. . .23 5. Variation in mechanical properties (tensile) of thick aluminium sheet (10 mm. thick) cut longitudinally to the direction of rolling, with cold work . .. - .,.*, ~- v ,. *V^ v; %^ %*, . 26 6. Variation in mechanical properties (tensile) of thick aluminium sheet (10 mm. thick) cut transversely to the direction of rolling, with cold work . . , . . . .27 7. Variation in mechanical properties (tensile) of aluminium with annealing temperature. Test pieces 0-5 mm. thick. Prior cold work 50 %. Y . . .-'".," . Y Sv . . 28 8. Variation in mechanical properties (tensile) of aluminium with annealing temperature. Test pieces 0-5 mm. thick. Prior cold work 100 % . . . J. 29 9. Variation in mechanical properties (tensile) of aluminium with annealing temperature. Test pieces 0-5 mm. thick. Prior cold work 300 % '. . ' .*' 30 10. Variation in mechanical properties (tensile) of aluminium with annealing temperature. Test pieces 2-0 mm. thick. Prior cold work 50 % . . . . . . . . . .31 11. Variation in mechanical properties (tensile) of aluminium with annealing temperature. Test pieces 2-0 mm. thick. Prior cold work 100 % 32 xix xx ALUMINIUM AND ITS ALLOYS FIGUBE PAGE 12. Variation in mechanical properties (tensile) of aluminium with annealing temperature. Test pieces 2-0 mm. thick. Prior cold work 300 % 3 13. Variation in mechanical properties (tensile) of aluminium with annealing temperature. Test pieces 10 mm. thick. Prior cold work 100 % 35 14. Variation in mechanical properties (tensile) of aluminium with annealing temperature. Test pieces 10 mm. thick. Prior cold work 300% 36 15. Variation in mechanical properties (hardness and shock) with cold work. Test pieces 10 mm. thick . . . . . .37 16. Variation in mechanical properties (hardness and shock) on anneal- ing after 100 % cold work. Test pieces 10 mm. thick . 3 1 7. Variation in mechanical properties (hardness and shock) on anneal- ing after 300 % cold work. Test pieces 10 mm. thick . . 40 18. Pereoz apparatus for cupping tests ...... 42 19. Cupping tests. Variation in breaking load and depth of impression with cold work. Test pieces 2-0, 1-5, 1-0, 0-5 mm. thick . . 43 20. Cupping tests. Variation in breaking load and depth of impression with thickness at specified amounts of cold work (0, 50, 100, and 300 %) 44 21. Cupping tests. Variation in breaking load and depth of impression on annealing after 50 % cold work. Test pieces 0-5 mm. thick 45 22. Cupping tests. Variation in breaking load and depth of impression on annealing after 100 % cold work. Test pieces 0-5 mm. thick 46 23. Cupping tests. Variation in breaking load and depth of impression on annealing after 300 % cold work. Test pieces 0-5 mm. thick 47 24. Cupping tests. Variation in breaking load and depth of impression on annealing after 50 % cold work. Test pieces 20 mm. thick 48 25. Cupping tests. Variation in breaking load and depth of impression on annealing after 100 % cold work. Test pieces 2-0 mm. thick 49 26. Cupping tests. Variation in breaking load and depth of impression on annealing after 300 % cold work. Test pieces 2-0 mm. thick 50 27. Cupping tests. Variation in depth of impression with thickness. Annealed aluminium sheet (R. J. Anderson) .... 53 28. Cupping tests. Variation in depth of impression with thickness. Cold worked aluminium sheet (R. J. Anderson) ... 54 29. Aluminium sheet. Effect of annealing for different lengths of time at 430 (R. J. Anderson) 55 LIST OF ILLUSTRATIONS IN TEXT xxi BOOK II ALLOYS OF ALUMINIUM FIGURE PAGE 30. Equilibrium diagram of copper-aluminium alloys (Curry) . . 69 PART III CASTING ALLOYS 306. Hardness of aluminium at high temperatures (500 kg. load) . 73 31. Hardness of aluminium -copper alloy (4 % Cu) at high tempera- tures (500 and 1000 kg.) . . ..;. : > . 77 32. Hardness of aluminium-copper alloy (8 % Cu) at high tempera- tures (500 and 1000 kg.) . . . . . * , . 77 33. Hardness of aluminium -copper alloy (12 % Cu) at high tempera- tures (500 and 1000 kg.) . .-,. . 1. . .. . 79 34. Variation in hardness with copper content (load 500 kg. ) Tem- peratures 0, 100, 200, 300, 350, 400 . . , . * . 79 35. Hardness of aluminium -zinc -copper alloy (12 % Zn, 3 % Cu) at high temperatures (500 and 1000 kg. load) . ,. . . 81 36. Hardness of aluminium-copper-tin-nickel alloy (11% Cu, 3 % Sn, 1 % Ni) at high temperatures (500 and 1000 kg. load) . . 83 37. Melting-point curve for zinc -aluminium alloys . ... 83 PART IV LIGHT ALLOYS OF GREAT STRENGTH 38. Tensile test piece (thick sheet) . v .. ' .' 'i. . ': . 89 39. Tensile test piece (thin sheet) . t> 4 .'; , ,/ . ' ,, . 89 40. Variation in mechanical properties (tensile and shock) of duralumin with cold work. Metal previously annealed at 450 and cooled in air. Test pieces cut longitudinally to direction of rolling . 90 41 . Variation in mechanical properties (tensile and shock) of duralumin with cold work. Metal previously annealed at 450 and cooled in air. Test pieces cut transversely to direction of rolling . . 91 42. Variation in mechanical properties (tensile, hardness, and shock) of duralumin, with annealing temperature. Metal subjected to 50 % cold work, annealed, and cooled very slowly. Longitudinal test pieces . . . . . . .92 43. Variation in mechanical properties (tensile and shock) of duralumin, with annealing temperature. Metal subjected to 50 % cold work, annealed, and cooled in air. Longitudinal test pieces . '. *'.- V *. ' j ' . . . . 93 44. Variation in mechanical properties (tensile, hardness, and shock) of duralumin, with annealing temperature. Metal subjected to 50 % cold work, annealed, and cooled very slowly. Transverse test pieces . . . . .' . I*' . .93 45. Variation in mechanical properties (tensile and shock) of duralumin, with annealing temperature. Metal subjected to 50 % cold work, annealed, and cooled in air. Transverse test pieces . . , . . . . . . . 94 xxii ALUMINIUM AND ITS ALLOYS FIGURE PAGE 46. Duralumin compared with pure aluminium, using dilatometer . 96 47. Variation in mechanical properties of duralumin with time after quenching (from 300) 97 48. Variation in mechanical properties of duralumin with time after quenching (from 350) 98 49. Variation in mechanical properties of duralumin with time after quenching (from 400) ........ 99 50. Variation in mechanical properties of duralumin with time after quenching (from 450) ........ 99 51. Variation in mechanical properties of duralumin with time after quenching (from 500) 100 52. Variation in mechanical properties of duralumin with time after quenching (from 550) 100 53. Variation in mechanical properties of duralumin with quenching temperature (after 8 days) . . . . . . .101 54. Variation in mechanical properties of duralumin with time after quenching from 475 (during first 48 hours) . . . .103 55. Variation in mechanical properties of duralumin with time after quenching from 475 (during first 8 days) . . . .104 56. Variation in mechanical properties of duralumin with annealing temperature. Metal quenched from 475, reannealed, and cooled very slowly. . . . . . . . . .110 57. Variation in mechanical properties of duralumin with annealing temperature. Metal quenched from 475, reannealed, and cooled in air . . . . . . . . . .111 58. Variation in mechanical properties of duralumin with annealing temperature. Metal quenched from 475, reannealed, and quenched in water . . . . . . . .112 59. Duralumin. Cupping tests. Variation in breaking load and depth of impression with annealing temperature. Anneal followed by cooling at various rates . . . . . . .114 60. High temperature hardness tests (500 kg.) on duralumin quenched from 475 116 PART V CUPRO-ALUMINITJMS 61. Tensile test piece (round bars) ....... 62. Aluminium bronze, Type I, critical points .... 63. Aluminium bronze, Type I, allowed to cool in furnace 64. Aluminium bronze, Type I, slow cooling ..... 65. Aluminium bronze, Type I, temperature not exceeding Ac 3 66. Variation in mechanical properties (tensile and impact) with an- nealing temperature. Cast aluminium bronze, Type I (Cu 90 %, Al 10 %) . . LIST OF ILLUSTRATIONS IN TEXT xxiii FIGURE PAGE 67. Variation in mechanical properties (tensile and impact) with an- nealing temperature. Forged aluminium bronze, Type I .124 68. Variation in mechanical properties (tensile and impact) with quenching temperature. Cast aluminium bronze, Type I . 125 69. Variation in mechanical properties (tensile and impact) with quenching temperature. Forged aluminium bronze, Type I . 126 70. Variation in mechanical properties (tensile and impact) with temperature of reanneal after quenching from 700. Forged aluminium bronze, Type I . . * , . , , 127 71. Variation in mechanical properties (tensile and impact) with temperature of reanneal after quenching from 800. Forged aluminium bronze, Type I . . . . . ? . 128 72. Variation in mechanical properties (tensile and impact) with temperature of reanneal after quenching from 900. Forged aluminium bronze, Type I. * . ., , ,129 726. High -temperature hardness tests (500 kg.) on aluminium bronze, Type I, as cast, worked, and heat treated ... . . 131 73. Aluminium bronze, Type II, critical points * ... 132 74. Aluminium bronze, Type II . . . ... . . 132 75. Variation in mechanical properties (tensile and impact) with annealing temperature. Forged aluminium bronze, Type II (Cu 89 %, Mn 1 %, Al 10 %) . 133 76. Variation in mechanical properties (tensile and impact) with quenching temperature. Forged aluminium bronze, Type II . 134 77. Variation in mechanical properties (tensile and impact) with temperature of reanneal after quenching from 800. Forged aluminium bronze, Type II . * . . . . .135 78. Variation in mechanical properties (tensile and impact) with temperature of reanneal after quenching from 900. Forged aluminium bronze, Type II .. . . . . .135 786. High -temperature hardness tests (500 kg.) on aluminium bronze, Type II. Quenched from 900, reannealed at 600. , .136 79. Aluminium bronze, Type III, critical points (dilatometer) . . 137 80. Aluminium bronze, Type III, critical points, temperature time curve . . . . . . . ^ . . 138 81. Variation in mechanical properties (tensile and impact) with annealing temperature. Forged aluminium bronze, Type III (Cu 81 %, Ni 4 %, Fe 4 %, Al 11 %) . ... . . 138 82. Variation in mechanical properties (tensile and impact) with quenching temperature. Forged aluminium bronze, Type III 139 83. Variation in mechanical properties (tensile and impact) with temperature of reanneal after quenching from 900. Forged aluminium bronze, Type III . .' i' .' . ' . 140 836. High -temperature hardness tests (500 kg.) on aluminium bronze, Type III. Annealed at 900 . .... 141 BOOK I ALUMINIUM Aluminium and its Alloys PART I PRODUCTION OF ALUMINIUM CHAPTER I METALLURGY OF ALUMINIUM ALUMINIUM is prepared by the electrolysis of alumina dissolved in fused cryolite. The electric energy is derived from water- power. The essential materials for the process are therefore (i) Alumina, (ii) Cryolite. ALUMINA. Alumina is prepared from bauxite [(Al, Fe) 2 8 2H 2 0] or from certain clays [Al 2 O 3 .2Si0 2 ]. (a) From Bauxite. Bauxite is a clay-like substance, whitish when silica is pre- dominant, or reddish when oxide of iron is largely present. It is found in great quantity in France, in the neighbourhood of the village of Baux, near Aries (hence the name, bauxite), and more commonly in the Departments of Bouches-du- Rhone, Gard, Ariege, Herault, and Var. It is found in Calabria, Iceland, Styria, Carniola, and in the United States of America in Georgia, Arkansas, Alabama, and Tennessee. Commercial bauxite has the following composition : * Alumina (A1 2 O 8 ) . 57 % A premium of -20 to 40 francs per kilo (roughly Id. to 2d. per Ib.) was, in 1909, paid for each per cent over 60 %. Silica (SiO,) . 3 % If below 2 %, a premium of -20 fr. per kg. (roughly Id. per Ib.) was paid per -1 %. * Lodin, " Annales des Mines," Nov., 1909. ALUMINIUM AND ITS ALLOYS Iron Oxide (Fe 2 3 ) . 14 % For each per cent above this value, up to the maximum allowed, 17 %, -20 fr. per kg. (roughly Id. per Ib.) was de- ducted. Some works allow as much as 25 % Fe 2 3 . White bauxites are chiefly used for the production of aluminium sulphate and the alums. Red bauxites form the raw material for the preparation of alumina, and therefore of aluminium. Intermediate or refractory bauxites, fused in an electric furnace, give artificial corundum. Bauxite is treated either by Deville's method or by that of Bayer, the latter being almost exclusively employed. A third method depends upon the production of aluminium nitride. This is obtained by heating bauxite in air to 1800-1 900 in an electric furnace. It is then decomposed in an autoclave in presence of soda solution, giving (i) ammonia, used as a manure in the form of its sulphate, (ii) sodium aluminate, from which commercially pure alumina can be obtained. (b) From Clay. Clays are treated either by the Cowles-Kayser or by the Moldentrauer process, yielding alumina from which aluminium is prepared by electrolysis. CRYOLITE. Cryolite, which is so called on account of its high fusibility, is a double fluoride of aluminium and sodium of the formula Al 2 F 6 .6NaF. It is obtained from Western Greenland, where it occurs in beds up to one metre thick, but the high price of this material has led to the manufacture of synthetic cryolite, using calcium fluoride (fluor-spar), which is found in con- siderable quantities. ELECTRIC FURNACES. The furnace consists of a vat, containing electrodes (anodes), and a conducting hearth (the cathode) sloping towards the tapping hole. Aluminium, formed by electrolysis of the alumina, collects on the floor of the vat ; oxygen is liberated at the anode, which it attacks, forming carbon monoxide and finally carbon dioxide. The current is used at a potential difference of 8 to 10 volts, and at a density of 1 -5 to 3 amps, per square centimetre of electrode. The furnace is regulated by raising or lowering the electrodes, or by varying the quantity of alumina. When METALLURGY OF ALUMINIUM the latter is present in small quantities, the fluorides decom- pose, and the voltage (normally 8-10 volts) rises. This is indicated by the change in intensity of a lamp. In this case sodium is formed at the cathode, and has deleterious effects on the quality of the metal. METHOD OF TAPPING ALUMINIUM. Since aluminium is very easily oxidised, it cannot be sub- jected to a final refining process, but must possess, at this early stage, its commercial purity. It is therefore essential to avoid oxidation during the manufacturing process, and the cryolite, iooo c 975 950 925^ 9001 O 5 10 15 20 FIG. 1. Melting-point Curve of Mixtures of Al 2 F 6 .6NaF and A1 2 O 3 . (Pryn.) containing alumina in solution, furnishes the means to that end. The metallic aluminium must not float, but sink to the bottom of the vat, where the fused salts protect it against oxidation. The salts must have, therefore, a lower density than the metal. The theory of the preparation of the metal is made clear by a study of the melting-point curve of mixtures of cryolite (Al 2 F 6 .6NaF) and alumina, due to Pryn.* Pure cryolite melts at 1000, and the mixture of maximum fusibility (915) consists of 95 % cryolite with 5 % alumina. As the alumina content increases from 5 to 20 %, the melting point rises from 915-1015, the curve of fusibility consisting of portions of straight lines of varying slope. * Pryn, " Mineral Industry," Vol. XV, p. 19. 6 ALUMINIUM AND ITS ALLOYS Certain definite mixtures of cryolite, calcium fluoride or aluminium fluoride, and alumina have still lower melting points, the limiting value being 800 (Hall). In practice the melting point of the bath ranges from 900-950 ; it is there- fore evident that the manufacturer has a choice of mixtures which will fulfil these conditions. The respective densities of the cryolite mixture and of aluminium are : Cryolite mixture . f solid > 2 ' 92 lliquid, 2-08 Aluminium , /solid, 2-6 lliquid, 2-54 which satisfy the conditions above mentioned. The furnace is tapped about every forty-eight hours. The liquid flows first into a receiver, in which the fluorides carried over are retained in the solid state, and from this vessel into moulds, giving ingots which can easily be divided. OUTPUT. According to Flusin, the output is as follows : 210 kg. to 275 kg. of aluminium per kilowatt-year (i.e. 4631b.-606-l Ib. per kw. year), or, 154-200 kg. per " Force de cheval " year (i.e. 344-1-447 Ib. per horse-power year), which works out at : 31-41 kilowatt hours per kg. of aluminium (i.e. 14-1-18-7 kw. hours per Ib.), assuming an average efficiency of 70 %, and a maximum efficiency of 78 %. CONSUMPTION OF MATERIAL. Alumina per kg. of aluminium : theoretically 1-888 kg. practically 2-0 kg. ; formerly this figure was higher, but then the voltage was 15 to 20 v. (i.e. 1-888 tons and 2-0 tons of alumina per ton of aluminium, respectively). Cryolite, per kg. of aluminium 0-150 kg. on an average (i.e. 3 cwt. cryolite per ton of aluminium). Calcium and aluminium fluorides, per kg. of aluminium, 0-200 kg. (i.e. 4 cwt. per ton of aluminium). Anodes, per kg. of aluminium, 0-8 to 1-0 kg. (i.e. 16 cwt,-l ton per ton of aluminium), METALLURGY OF ALUMINIUM From these data we can draw the following conclusions con- cerning the cost price. For the production of a ton of alu- minium two tons of alumina are required and also one ton of carbon for the electrodes ; while, for the production of the alumina itself, six tons of carbon are required. Since alumina is made near the spot where bauxite is found, it is necessary to consider the effect of the following transport charges upon the cost price : (i) Carriage qf carbon to alumina works, (ii) Carriage of carbon to aluminium works, (iii) Carriage of alumina to aluminium works. It is evident that those aluminium works which can obtain only hydraulic power locally, so that the transport charges, just mentioned, are heavy, are at a disadvantage in competing with works more favourably situated. The French aluminium works are especially favoured in this respect.* ROLLING OF ALJJMINIUM. The ingots of aluminium are first melted in a furnace often a revolving furnace, heated by gaseous fuel. The aluminium is then cast into slabs, which, in France, usually are of the following dimensions : (1) S0kg.=0-55m. xO-65m. xO-08m.(21-6in. x25-5in. x3-15in.) (2) 55 kg.=0-56m. x 0-66m. x 0-055m.(22-0in. X 25-9in. X 2-16in.) (3) 27 kg.=0-35m. x 0-7m. X 0-04m.(13-8in. X 27-5in. X l-57in.) * Lodin established in the following manner the cost price in 1909 : Alumina . 1 -950 kg. per kg. of Al at 0-3 fr. per kg. Cryolite . . 0-125 kg. 0-6 Electrodes . 0-800 kg. 0-35 Labour . . 0-025 ,, 5 Electrical energy 40 kw. at -006 fr. per kw. Total 0-585 fr. 0-075,, 0-280,, 0-125,, 0-240,, l-305fr. per kg. of aluminium (i.e. roughly 6d. per lb.), to which, in general, transport charges must be added. In the United States of America, the cost price of aluminium in 1906 would be, according to "The Mineral Industry," roughly 7d. per lb. The price of aluminium has varied in a very noticeable manner since 1855, having passed through the following stages : Fr. per kg. 1855 . 1886 . 1890 . 1900 . 1908 (end of Heroult patents) 1908-1914 1916 . 1230 78 19 2-5 2 1-5-21 6-8-7-0 Price per lb. 22 5 3 183 6 10 11 -9 2/6-2/6| 8 ALUMINIUM AND ITS ALLOYS Aluminium is often cast into billets, frequently cylinders of 3 kg. in weight, 80 cm. high and 4 cm. in diameter (31-5 in. X 1 -57 in.). The slabs or billets are cast from a mixture of ingots, and therefore a fresh analysis must be carried out to give the quality. The temperature of casting is usually 750-775, and the temperature of rolling 400-450, roughly the temperature of smouldering wood. ROLLING OF ALUMINIUM INTO THIN SHEETS.* Aluminium can be rolled into sheets '01 cm. thick (-0039 in.), similar to tinfoil. The process has been carried out by Drouilly a strip initially 0-35 cm. thick (-138 in.) is rolled in the cold to 0-04 cm. (-016 in.); the reduction is made in six passes with intermediate annealing. The second stage consists in reducing the sheets to a thickness of -01 cm., either by means of blows from a 150 kg. (roughly 3 cwt.) pneumatic hammer, giving 300 blows per minute, or by further rolling. EXTRUSION. Tubes and sections can be obtained by extrusion.! ALUMINIUM DUST. Powdered aluminium, in the form of paint, is applied to finished metallic goods, resulting in a galvanisation effect. For literature on this subject, the work of Guillet (loc. cit.) should be consulted. * For details of process, see Guillet, " Progres des Metallurgies autreque la Siderurgie et leur Etat actuel en France," pp. 264-268. (Dunod et Pinat, 1912.) t Cf. Breuil, " Genie Civil," 1917. Nos. 23 and 24. CHAPTER II WORLD'S PRODUCTION I. BAUXITE. THE French Minister of Commerce gives the following par- ticulars concerning the world's production of bauxite : * U.S.A. France Great Britain Italy Tonnes Tons Tonnes Tons Tonnes Tons Tonnes Tons 1910 1911 1912 1913 152,070 158,107 162,685 213,605 149,698 155,610 160,110 210,228 196,056 254,831 258,929 309,294 193,358 250,800 254,836 304,410 4,208 5,103 5,882 6,153 4,142 5,022 5,789 6,056 6,952 6,842 It is therefore evident that up to 1914, there were only two important centres in the world for the production of bauxite, namely, France and the United States of America. POSITION IN 1913. The distribution of bauxite in 1913 (527,536 tons) is shown in the following diagram (Fig. 2) : Scale 10,000 Tons O FIG. 2. Distribution of Bauxite. "Vol. I, "Rapport general sur I'industrie francaise, sa situation, son avenir," based on the work of sections of the "Comite consultatif des Arts et Manufactures " and of the "Direction des Etudes techniques," April, 1919. (Director: M. Guillet). 9 10 ALUMINIUM AND ITS ALLOYS Sixty -five per cent of the French production was exported, half of which (i.e. 32 %) was sent directly or indirectly to Germany, approximately 15 % to Great Britain, and a certain proportion to the United States, which is rapidly falling off, as the new beds are developed in that country, in Tennessee and North Carolina. Of the 7365 tons (7483 tonnes) of alumina exported, 80 % goes to supply the Swiss factories. The Report of the French Minister of Commerce (loc. cit.) shows the influence of the war on the production of bauxite. (a) France. Bauxite for Aluminium Bauxite for other purposes Total Tonnes Ton Tonnes Tons Tonnes Tons 1915 1916 1917 37,894 68,866 101,748 37,296 67,779 100,150 48,628 37,334 19,168 47,860 36,743 18,865 86,522 106,200 120,916 85,156 104,520 119,015 The diminution in production is clearly due to the large falling off of exports. (b) United States. 1915 293,253 tons (297,961 tonnes) of bauxite. 1916 . 1917 . (c) Great Britain. 1915 . 1917 418,640 559,750 (425,359 (568,690 11,726 tons (11,914 tonnes) of bauxite. 14,714 (14,950 ) The whole of this amount was imported from the French beds at Var. The discovery of beds in British Guiana, where there are large waterfalls, will probably affect the British production very considerably. (d) Italy. Position unchanged. (e) Germany. Germany has been unable to import French bauxite, and has, therefore, since the war, begun to work the beds at Frank- fort-on-Main. (f) Austria-Hungary. Austria-Hungary has supplied the needs of Germany during the war. Just when war was declared, very important beds WORLD'S PRODUCTION 11 12 ALUMINIUM AND ITS ALLOYS (20,000,000 tons) were discovered in Hungary (Siebenbergen). The bauxite was sent to Germany, and works were erected, on the spot, for treating the mineral. In addition, there are mines in Dalmatia, Herzegovina, Istria and Croatia, which are either being worked or are ready to be worked. The quality of this bauxite seems on the whole very inferior to that of the French. II. ALUMINIUM. A statement of production figures can only be made with caution, discriminating between possible and actual output. The latter, a fraction of the former, depends upon the demand, and also upon the possibility of obtaining materials for the production of other substances for instance, the manufacture of aluminium replacing that of chlorates, and conversely. Statistics, from this point of view, are often lacking in clear- ness. Nevertheless, bearing in mind these two considerations, we can consider the following figures as sufficiently accurate, referring to an average annual production. (a) France. France, as is shown in the accompanying map (Fig. 3), is favourably situated for the production of aluminium. The close proximity of the bauxite beds, the alumina works, and the water power necessary for the electro-metallurgy, forms a unique combination, and, in addition, carbon can be easily conveyed to the works. Actual output, 12,000-15,000 tons per annum. Possible output, 18,000-20,000 tons per annum. ALUMINIUM WORKS. The French works are amalgamated, forming " L' Aluminium fran9aise," and are grouped into companies : (i) The " Societe Electro-metallurgique fran9aise," with works at Praz, and at St. Michel de Maurienne in the valley of the Arc, and at Argentiere in the valley of the Durance. (ii) The " Compagnie des Produits chimiques d'Alais et de la Camargue," possessing the Calypso works (at St. Michel de Maurienne), and works at St. Jean de Maurienne in the valley of the Arc. (iii) The " Societe d'Electro-chimie," works at Premont, in the valley of the Arc. (iv) " La Societe Electro-chimique des Pyrenees," with works at Auzat (Ariege). PLATE I. PHOTOGRAPH 1. NORWEGIAN NITRIDES AND ALUMINIUM COMPANY. Works at Eydehavn near Arendal (25,000 H.P.), situated on an arm of the sea. PHOTOGRAPH 2. NORWEGIAN NITRIDES AND ALUMINIUM COMPANY. Works at Tyssedal (35,000 H.P.) on the Hardanger Fjord. To face page 1 PLATE III. ENGINE-ROOM AT CALYPSO. To face page 13 WORLD'S PRODUCTION 13 ALUMINA WORKS. The alumina works are situated near the bauxite beds in Herault, Var, and Bouches-du-Rhone, at Gardanne and La Barasse (Bouches-du-Rhone) and at Salindres (Gard). (b) Great Britain. Output about 6000 tons. There are two companies : (i) The British Aluminium Company (Scotland and Norway), (ii) The Aluminium Corporation (works at Dolgarrog, North Wales). (c) Italy. Output 1500-2000 tons. (d) Switzerland. Output 12,000-13,000 tons, from works at Neuhausen (canton of Schaffhausen) and at Chippis and Martigny (canton of Valais). It is noticeable that in Switzerland there are no works for the preparation of alumina from bauxite, hence the materials required for the manufacture of aluminium, alumina and cryolite are imported. (e) Nonuay. The Norwegian output has been : 1913 . . approximately 1000 tons 1917 ... 7000 1918 . . 6000 Its possible production may be about 15,000-16,000 tons. Alumina is imported mainly from the works at Menessis (Somme) and Salzaete (Belgium), belonging to L'Aluminium fran9aise, which have been damaged during the war. (f ) United States and Canada. The output of the United States and of Canada in recent years has been about 30,000 tons; it is capable of great development, but it is difficult to give precise details on the subject. The " Rapport sur 1'Industrie frangaise " of the Minister of Commerce gives, as a probable figure for 1917, 70,000 tons, which might rise to 80,000 with further increase in prospect. The two large American companies are the Aluminium Company of America, and the Northern Aluminium Company 14 ALUMINIUM AND ITS ALLOYS of Canada, having their main works at Niagara Falls, at Massena, at Quebec and at Schawinigan Falls respectively. (g) Germany and Austria. It is really difficult to give precise returns on the capacity for production of these two countries. It has been given as approximately 10,000 tons, though it is not possible actually to verify this figure. In conclusion, the following table of actual world's production may be given, omitting all more or less hypothetical specula- tions : United States and Canada . . 70,000 tons (?) France 15,000 Switzerland .... 12,000 Great Britain .... 6,000 Norway . . . . 6,000 Italy 2,000 Germany and Austria . . . 10,000 (?) Total, about 1 20,000 tons PART II PROPERTIES OF ALUMINIUM CHAPTER I PHYSICAL PROPERTIES Density : 2-6 (as annealed), 2-7 (as worked, or when impurities (iron and copper) are present). This places aluminium among the lightest metals (lead, 11-4; nickel, 8-94; iron, 7-8; tin, 7-3; zinc, 7; anti- mony, 6). Atomic Weight : 26-9. Specific Heat : 0-22, increasing with rise of temperature. It finally reaches 0-308 at about the melting point. Thermal Conductivity : 36 (silver=100). Aluminium is a substance, therefore, having a great specific heat, and a high thermal conductivity, which renders it particularly suitable for the manufacture of cooking utensils. Electrical Conductivity and Resistance. The electrical conductivity is very high, being about 60 % of that of copper. Its specific resistance is 2-78 microhms per centimetre cube. Melting Point : about 650. 16 CHAPTER II ANALYSIS AND GRADING THE division of aluminium into grades is based upon the amount of impurities present. The chief impurities are : Group I : Iron and silicon. Group II : Carbides, sulphides, copper, zinc, tin, sodium, nitrogen, boron, titanium. Group III : Alumina. The electrodes, in particular the anodes, form the principal source of the impurities. The anodes can be made of petroleum coke, anthracite, or gas carbon, using tar as a binding material. All manufacturers prefer petroleum coke, which, before the war, contained 1 % of ash, and during the war, 2-3 %. The other materials, anthracite and gas carbon, contain 4-5 % of ash. Group I : Iron and silicon. The presence of more than 1 % of iron usually causes faulty castings which are useless. As a rule, the amount of silicon is about one-third of that of the iron, and rarely exceeds one- half. Group II : Various impurities, other than alumina. These impurities, with careful working, are present only in relatively small quantities, less than 1 %, but their estimation is necessary, since, owing to some accident during the working, they may attain abnormal proportions. Group III : Alumina. It is impossible to emphasise too much the importance of this impurity. For a long time, it was customary to estimate the iron, silicon and other impurities, and, ignoring the alumina, to determine the aluminium by difference. This method, in which alumina is returned as metallic aluminium, is unsatisfactory, for experience has shown that excessive 16 ANALYSIS AND GRADING 17 quantities of alumina are very harmful on account of its infusibility at casting temperatures,* its higher density,! and its insolubility in the molten metal. This impurity must therefore be estimated. Furthermore, a high percentage of alumina seems to favour the formation of blow-holes. For these reasons, the melting up of aluminium scrap, more or less oxidised, gives poor results. GRADES OF ALUMINIUM. As already stated, the usual industrial practice is to estimate only iron and silicon, the aluminium content being determined by difference this obviously gives a fictitious value. Grade I : Aluminium nominally 99-5 %. i.e. the total amount of iron and silicon being equal to or less than 0-5 %. Grade II : Aluminium nominally 99-0 %. i.e. the total amount of iron and silicon being equal to or less than 1-0 %. Grade III : Aluminium nominally 98-99 %. i.e. the total amount of iron and silicon being equal to or less than 2 %. Though retaining this long-established system of classifica- tion, the foregoing grading should be modified, so as to take into account the impurities of the second group as well as those of the first, still, however, ignoring the alumina. We then have the following grades : J Grade I : Aluminium content (by difference) 99-5 % or over. Grade II : Aluminium 99-99-5 %. Grade III : Aluminium 98-99 %. In the first two grades, the impurities of the second group (carbides, sulphides, copper, zinc, tin, sodium, nitrogen, boron, and titanium) should not exceed 0-3 % ; in the third grade these impurities should not exceed 0-4 %, the iron 1 %, and the silicon 0-6 %. Alumina is not considered in calculating the purity, but should not exceed 0-4 % for Grade I, 0-6 % for Grade II, and 0-8 % for Grade III. These are safe limits to allow, without interfering with, or reducing, the production. * Melting point of alumina 3,000 C., of aluminium 650 C. t Density of alumina 3-75, of aluminium 2-6. j This system of grading is adopted in the French Aeronautical Specifica- tions, and the analytical methods are given in Appendix I. A variation of 0-25 % in the aluminium content is allowed in Grade I, 0-50 % in Grade II, and 0-75 % in Grade III. C CHAPTER III MECHANICAL PROPERTIES THE mechanical properties can be grouped as follows : A. Tensile Properties: Tensile Strength, Elastic Limit, and Elongation. B. Hardness and Shock Resistance. C. Cupping Value : Depth of Impression and Breaking Load. Tests have been carried out on metal of varying thickness, as shown below : 0-5 mm. sheet : Tensile and Cupping Tests. 2 mm. sheet : Tensile, Cupping, and Hardness (scleroscope) Tests. 10 mm. sheet : Tensile, Shock, and Hardness Tests. The variations in these properties with (i) different amounts of cold work ; (ii) different anneals subsequent to varying degrees of work, have been investigated. An account of the experiments and results will be given in the following form : A. TENSILE PROPERTIES. (i) Variation in tensile properties with the amount of cold work. (a) Thin test pieces. (b) Thick test pieces. Discussion of Results. (ii) Variation in tensile properties with increasing annealing temperature, following varying amounts of cold work. (a) Thin test pieces. (b) Thick test pieces. Discussion of results. B. HARDNESS AND SHOCK RESISTANCE. (i) Variation of these properties (Brinell Hardness and Shock Resistance) with amount of cold work, using test pieces 18 MECHANICAL PROPERTIES 19 of 10 mm. thick sheet, and variation of Scleroscope Hardness with the amount of cold work for sheets of the thin series. Discussion of results. (ii) Variation of Brinell Hardness and Shock Resistance with increasing annealing temperature, after varying amounts of cold work, using test pieces from sheets 10 mm. thick (thick series). Discussion of results. C. CUPPING VALUE. Depth of impression and breaking load, using test pieces of metal comprising the thin series only. (i) Variation of these properties with amount of cold work. (ii) Variation of these properties with increasing annealing temperature following varying amounts of cold work. Discussion of results. D. FINAL SUMMARY. E. CONTEMPORARY LITERATURE ON THE SUBJECT. A. TENSILE PROPERTIES Thin Series Dimensions of test pieces. TYPE IA. (Length 100mm. Between shoulders | Breadth 20 mm. (Thickness 0-5 mm. Area of cross section 10 sq. mm.* Gauge length (for measuring elongation) = \/66 -67s = 30 mm. TYPE IB. [Length 100 mm. Between shoulders -[ Breadth 20 mm. [Thickness 1 mm. Area of cross section 20 sq. mm. Gauge length = V^G-GTs^SG mm. TYPE Ic. [Length 100 mm. Between shoulders -j Breadth 20 mm. 'Thickness 1-5 mm. Area of cross section 30 sq. mm. Gauge length = V 66 '67s=45 mm. * These values are only approximate. In each case the breadth and thickness were measured to the nearest -01 mm., and the exact cross section calculated from these figures. 20 ALUMINIUM AND ITS ALLOYS TYPE ID. (Length 100 mm. Between shoulders -I Breadth 20 mm. [Thickness 2 mm. Area of cross section 40 sq. mm. Gauge length = V66-67s=50 mm. Thick Series TYPE II. [Length 100mm. Between shoulders J Breadth 15mm. [Thickness 10 mm. Area of cross section 150 sq. mm. Gauge length=V66-67s=100 mm. TESTING LABORATORIES. The experiments on the variation of mechanical properties with cold work (thin series) and the cupping tests (both in the worked and annealed states) were carried out at the " Chalais Meudon " Laboratory. The experiments on the effect of annealing at different temperatures after cold work were carried out at the Conservatoire des Arts et Metiers. Reports of the latter experiments are given in the appendices. I. Variation of the Tensile Properties (Tensile Strength, Elastic Limit, and Elongation) with the amount of cold work. DEFINITION OF COLD WORK. A metal, which, as the result of work " in the cold," i.e. at relatively low temperatures, has undergone permanent defor- mation, is said to be " cold worked " or " work hardened." The properties of the metal, thus treated, are changed, and the amount of this change is a measure of the cause the so-called cold work. A metal which has been completely annealed has, by definition, zero cold-work. If S be the initial section of a bar in the annealed state and if s be the final section after cold work (drawing or rolling), the cold work may be defined in terms of the deformation as follows : * Cold work S (initial) s(final) ;%) s(final) xioo. As has been pointed out in the author's work on " Copper and Cartridge Brass," the " percentage cold work " given by the above formula is a function of the deformation only, and does not give any indication of the value of the mechanical MECHANICAL PROPERTIES 21 properties. The latter may actually remain stationary, while the percentage of deformation continues to increase with the deformation itself. We can therefore distinguish two values : (a) The cold work in terms of deformation (theoretical cold work). (6) The cold work in terms of the change in mechanical properties (effective cold work). In this book, unless otherwise stated, it is always the former that is meant, and this allows of easy evaluation in course of manufacture. (a) Thin Series The tests on the thin series were carried out on test pieces cut respectively from sheets of the thicknesses specified : Type la . . Thickness 0-5 mm. 16 . . 1-0 mm. Ic . . 1-5 mm. Id . 2-0 mm. Sheets of each of the above thicknesses were subjected to the following amounts of cold work, and the results investigated. Cold work % Ratio S/s (completely annealed) 50% 1-5 100% 2 300 % 4 Method of working sheets and slabs so as to obtain required amounts of cold work. Two methods were employed in the preliminary working of the sheets and slabs. FIRST METHOD. Annealed Metal. A slab 40 mm. thick at an initial tempera- ture of 450 is reduced to the required thickness by hot rolling, without intermediate reheating, and is finally annealed at 350. Cold-Worked Metal. Assuming that 100 % cold work is desired, a sheet 40 mm. thick is reduced by hot rolling, without intermediate reheating, to double the final thickness required. It is then annealed at 350, and cold rolled so as to reduce the section by one-half. A similar process is employed for the other degrees of cold work investigated. 22 ALUMINIUM AND ITS ALLOYS SECOND METHOD. A slab 40 mm. thick, at an initial temperature of 450, is reduced to a uniform thickness of 8 mm. by hot rolling. Annealed Metal. The sheet, 8 mm. thick, is reduced to the required thickness by cold rolling, with intermediate annealing at 350 every 2 mm. reduction, and is finally annealed at 350. Cold-Worked Metal. Assuming that 100 % cold work is desired, the sheet, 8 mm. thick, is reduced by cold rolling, with intermediate annealing every 2 mm. reduction, to double the final thickness required. It is then annealed at 350, and cold rolled so as to reduce the section by one-half. A similar process is employed for the other degrees of cold work in- vestigated. A comparative study of the cold working of thin sheets was carried out by both these methods, w r hereas in the study of the cold working of thick sheets, and in the study of annealing alone, the second method only was employed. Although the second method is more uniform and more sound, it has not given results superior to those of the first. As will be seen below, it seems as if, up to a certain limit, large amounts of cold work need not be avoided in manufacture, provided that this is only an intermediate stage, and is followed by a re-softening anneal. ANALYSIS Cold work % Thickness 0-5 mm. 1mm. 1-5 mm. 2mm. Iron . . 0-93% 0-82% 0-98% 0-95% Silicon . . 0-56 0-52 0-56 0-45 Cold work 50 % Iron . . 0-88 0-84 0-97 0-93 Silicon . . 0-25 0-26 0-39 0-41 Alumina . . 0-36 0-30 0-26 0-34 Cold work 100 % Iron . . 0-81 0-83 0-70 0-81 Silicon . . 0-32 0-38 0-23 0-23 Alumina . . 0-24 0-29 0-26 0-24 Cold work 300 % Iron . . 0-88 0-77 0-85 0-72 Silicon . . 0-31 0-46 0-56 0-46 Alumina . 0-17 0-16 0-24 0-22 MECHANICAL PROPERTIES 23 NUMBER OF TESTS. For each degree of cold work, two sheets were used for the tensile tests, and in each sheet three test pieces were cut longitudinally and three transversely. THIN SERIES (Sheet 1mm. thick) -13 50 100 150 200 Cold Work 250 FIG. 4. Variation in Mechanical (tensile) Properties with Cold Work. RESULTS OF TESTS. Fig. 4 summarises the results for test pieces of the Type Ib (I mm. thickness) cut longitudinally. After discussing the results obtained for this type, we will point out the variations observed, due to the different thick- nesses of the sheets comprising the thin series, and to the 24 ALUMINIUM AND ITS ALLOYS direction, longitudinal or transverse, in which the test pieces were cut. Cold work % (annealed state) : Elastic Limit : 4-5 kg. per sq. mm. (2-86 tons per sq. in.). Tensile Strength : 9-0 kg. per sq. mm. (5-72 tons per sq. in.). Elongation : 40 %. Cold work 50 % : Elastic Limit : 12-0 kg. per sq. mm. (7-62 tons per sq. in.). Tensile Strength : 14-0 kg. per sq. mm. (9-09 tons per sq. in.) Elongation: 11%. Cold work 100 % :- Elastic Limit : 14-0 kg. per sq. mm. (8-89 tons per sq. in.). Tensile Strength : 15-0 kg. per sq. mm. (9-52 tons per sq. in.) Elongation : 9 %. Cold work 300 % :- Elastic Limit : 17-5 kg. per sq. mm. (11-11 tons per sq. in.). Tensile Strength: 18-0 kg. per sq. mm. (1 1 -43 tons per sq. in.). Elongation : 6 %. (i) Merely cold working to the extent of 50 % has completely changed the properties of aluminium, and the Elongation has been reduced to a quarter of its original value. Consequently, if work hardening is undesirable, even a very small amount of deformation must be avoided, since the changes in the properties take place very markedly from the outset. (ii) The maximum cold work, beyond which deterioration and disintegration may set in, is reached when the Tensile Strength is approximately doubled. (iii) If cold work be expressed, no longer in terms of the deformation, but in terms of the changes in the properties, then, choosing as variable the Tensile Strength, and employing the formula Cold work= - where R= Tensile Strength (cold worked) r= Tensile Strength (annealed) we have, in the case of the thin series, the following results : Cold work (deformation) % Cold w r ork (effective) 3> 5J ^O /Q ,, ,, -3 100% f 300% 1 MECHANICAL PROPERTIES 25 It seems, therefore, that 200-300 % cold work is the maximum for the working of aluminium, giving what might be called the " Maximum Effective Cold Work." INFLUENCE OF THICKNESS (THIN SERIES). The variation in thickness between 0-5 mm. and 2-0 mm. exerts only a slight effect on the results, so that the mean curve given for test pieces of 1-mm. thickness may be taken as the curve for all the thin series. EFFECT ON TENSILE PROPERTIES OF THE DIRECTION IN WHICH TEST PIECES WERE CUT. The Elongation in the transverse test pieces is less than that in the longitudinal. Cold work % Difference 10 % Cold work 50 % and above Maximum difference 40 % In the Tensile Strength and Elastic Limit there is practically no difference. (b) Thick Series The tests on the " Thick Series " have been carried out on test pieces of Type II, thickness 10 mm., cut from sheets of this thickness. The following different amounts of cold work were investi- gated : Cold work % Ratio : ^ liti f Q Section = (completely Final Section annealed) 50% 1-5 M 100% 2 300% 4 ANALYSIS. Cold work % : Aluminium . . . 99-00 % Iron 0-64 % Silicon .... 0-33 % Carbon . . . . 0-03 % Alumina .... traces. Cold work 50%: Aluminium . . . . 98-80 % Iron 0-72 % Silicon .... 0-35 % Carbon . . . .0-08 % Alumina . . . traces. 26 ALUMINIUM AND ITS ALLOYS Cold work WO %: Aluminium Iron . Silicon Carbon Alumina 98-60 % 0-84 % 0-41 % 0-07 % traces. THICK SERIES (Longitudinal ) 40 250 300% 100 150 200 Cold Work FIG 5. Variation in Mechanical Properties with Cold Work. Cold work 300 % : Aluminium .... 99-01% Iron 0-61 % Silicon .... 0-33 % Carbon . . . .0-03 % Alumina traces. MECHANICAL PROPERTIES 27 Figs. 5 and 6 summarise the variations in properties in the case of the thick series (sheets 10 mm. thick).* FIG. 5. TESTS ON LONGITUDINAL TEST PIECES. As can be seen, the variations in the properties with cold work (deformation) are similar to those of the thin series. THICK SERIES (Transverse) II 50 250 100 150 200 Cold Work FIG. 6. Variation in Mechanical Properties with Cold Work. In every case the minima and maxima are approximately the same. Tensile Strength. Minimum, 10 kg. per sq. mm. (6-35 tons per sq. in.). Maximum, 16 kg. per sq. mm. (10-16 tons per sq. in.). * Cf. Appendix III. Report of the Conservatoire des Arts et Metiers. No. 13456, February 5th, 1919. 28 ALUMINIUM AND ITS ALLOYS Elongation. Minimum, 8 %. Maximum, 38 %. In the case of aluminium in thin sheets as compared with thick, (i) The cold work, whatever its amount, is more homogeneous throughout the thickness. (ii) The effect of annealing is more complete. THIN SERIES (Test Pieces 0.5 mm. thick) 100 200 300 400 Temperature 500 600C FIG. 7. Variation in Mechanical Properties on Annealing at different Temperatures after 50 % Cold Work. FIG. 6. TESTS ON TRANSVERSE TEST PIECES. The Tensile Strength and Elastic Limit are little affected by the direction in which the test pieces are cut, but, on the other hand, the Elongation undergoes variations of the order of 15 to 20 %. MECHANICAL PROPERTIES 29 II. Variation of Tensile Properties with increasing Annealing Temperature following varying amounts of Cold Work. (a) Thin Series EXPERIMENTAL DETAILS OF THE TESTS. ' The tests were carried out on two series of tensile test pieces from sheets of aluminium, the one 0-5 mm. thick, Type la, THIN SERIES (Test Pieces O'Smm. thick) 100 200 300 400 Temperature 500 600 C FIG. 8. Variation in Mechanical Properties on Annealing at different Temperatures after 100 % Cold Work. the other, 2-0 mm. thick, Type Id. Each of these series includes metal in three degrees of cold work, 50, 100, and . 300 %. 30 ALUMINIUM AND ITS ALLOYS INVESTIGATION OF THE DURATION OF TIME NECESSARY FOR COMPLETE ANNEAL AT VARIOUS TEMPERATURES. Preliminary tests have been carried out with a view to determining the minimum time necessary to give the properties characterising each temperature.* Kg. per THIN SERIES (Test Pieces O'Smm. thick) 11 40 100 500 eoc 200 300 400 Temperature FIG. 9. Variation in Mechanical Properties on Annealing at different Temperatures after 300 % Cold Work. The following results were obtained for the two series : Bath Temperature Duration of Time Oil ... 100 150 200 250 300 5 minutes. Sodium nitrite . 350 400 450 500 3 minutes. Potassium nitrate . 550 600 1 minute. * Cf. Appendix IV. Report of the Conservatoire des Arts et Metiers. No. 13357, January 24th, 1919. MECHANICAL PROPERTIES 31 TEST PIECES 0-5 mm. THICK. TYPE IA. Figs. 7, 8, and 9 summarise the results obtained. STAGES or ANNEALING. Whatever the amount of work, the following stages can be distinguished : (i) Region of cold work, (ii) Region of softening, (iii) Region of complete anneal, (iv) Region of falling-off of Elongation. THIN SERIES (Test pieces 2mm.thick) 11 10 100 500 600 C 200 300 400 Temperature FIG. 10. Variation in Mechanical Properties on Annealing after 50 % Cold Work. (i) Region of Cold Work ; 0-150. W ithin this range, the properties remain similar to those which the metal possesses in the particular cold-worked state, 32 ALUMINIUM AND ITS ALLOYS as given in Fig. 4. The effect of temperatures up to 150 is therefore insignificant. (ii) Region of Softening ; 150-350. This is a transition stage, in which the aluminium becomes softer, and gradually acquires the properties of completely annealed metal. THIN SERIES (Teot Pieces 2mm. thick) 100 200 300 400 Temperature 500 600 C FIG. 11. Variation in Mechanical Properties on Annealing after 100 % Cold Work. (iii) Region of Complete Anneal ; 350-450. This is the region in which the extent of anneal remains approximately constant ; that is to say, in which the properties of the metal are almost the same after annealing at any tempera- ture within this range. MECHANICAL PROPERTIES 33 350 to 450 is, therefore, the optimum annealing range of temperature. (iv) Region of Falling-off of Elongation ; 450-500. In this region there is a decrease in the Elongation, without any appreciable change in the Tensile Strength and Elastic Limit. THIN SERIES (Test Pieces 2mm. thick) 100 500 600C 200 300 400 Temperature Fio. 12. Variation in Mechanical Properties on Annealing after 300 % Cold Work. NOTES ON THE RESULTS. (i) The softening is the more abrupt as the original cold work increases. (ii) The 'temperature of complete anneal (characterised by maximum elongation) becomes lower as the cold work increases. D 34 ALUMINIUM AND ITS ALLOYS Amount of Original Cold Work 50 % . 100 % . 300 % Temperature of Maximum Elongation 425 400 350 (iii) The values of the properties in the completely annealed state increase with the amount of original cold work, up to 300 %. Amount of Cold Work Tensile Strength Elastic Limit % . Elongation Kg. /mm. a Tons /in. z Kg. /mm. 2 Tons /in. 2 50% 100 % 300 % 10-8 6-8G 11-0 6-99 11-2 7-11 4-8 3-05 4-5 2-86 5-2 3-31 34-0 37-5 40-0 This shows that, in the treatment of aluminium, it is advisable to employ extensive cold work, up to a maximum amount varying between 200 % and 300 %, always provided that the work is followed by an anreal adequate in duration and at a suitable temperature. Large amounts of cold work (i) lower the length of time necessary for complete anneal, (ii) lower the temperature of complete anneal, (iii) improve the properties. TEST PIECES 2 mm. THICK. TYPE ID. Figs. 10, 1 1, and 12 summarise the results. The same regions are noticeable as in Figs. 7, 8, and 9, and lie, approximately, within the same limits of temperature, and the same remarks may be made as to the results obtained after varying cold work. (b) Thick Series EXPERIMENTAL DETAILS OF TESTS. Tests were carried out on test pieces (Type No. II, 10 mm. thick) taken from sheets of that thickness having been cold worked to the extent of 100 and 300 %. INVESTIGATION or THE DURATION or TIME NECESSARY FOR COMPLETE ANNEAL AT VARIOUS TEMPERATURES. As in the case of the thin test pieces, preliminary tests were carried out with a view to determining the time required to give the properties characterising each temperature.* * Of. Appendix V. Report of the Conservatoire dee Arts et Metiers. No. 13463. MECHANICAL PROPERTIES The results are as follows : Bath oil . Sodium nitrite . Potassium nitrate Temperature 100-125-150-175-200-225-250 275-300-325-350-375-400-^25-450 475-500-525-550-575-600 35 Duration of Time 6 minutes. 4 2 Figs. 13 and 14 summarise the variations in mechanical properties for the thick series (sheets 10 mm. thick). THICK SERIES 100 200 300 400 Temperature 500 600C FIG. 13. Variation in Mechanical Properties on after 100 % Cold Work. FIGS. 13 (100 % COLD WORK) AND 14 (300 % COLD WORK). As in the case of the thin series, the same regions are notice- able, and a comparison of the two figures leads to the same conclusions as to the effect of initial cold work on the results obtained after a subsequent anneal. 36 ALUMINIUM AND ITS ALLOYS B. HARDNESS AND SHOCK RESISTANCE I. Variation of the Brinell Hardness and Shock Resistance with the amount of cold work, using test pieces taken from sheets 10 mm. thick, and of the Shore scleroscope hardness, with the amount of cold work, for sheets of the thin series. HARDNESS TESTS. (a) Brinell Tests on thick sheets. These were carried out under a load of 500 kg. and 1000 kg. respectively, using a ball 10 mm. in diameter. The results are shown in Fig. 15. THICK SERIES (Test Pieces 1 0mm. thick) 160 200 300 400 500 600*C Temperature FlQ. 14, Variation in Mechanical Properties on Annealing after 300 % Cold Work.] MECHANICAL PROPERTIES 37 As is evident from a comparison of Fig. 15 and Fig. 5, the curves of Tensile Strength and Elastic Limit plotted against cold work are of the same general form as the hardness curves 42 4 40 Shock 39 Resistanc 38 37 36 35 34 2 .33 30 m 29 28 27 26 25 24 23 22 21 20 THICK SERIES Brine!/ 'Hardness Shock Resistance (transuerse 50 100 1 50 200 Cold Work 250 300% FIG. 15. Variation in Mechanical Properties (Hardness and Shock) with Cold Work. under 500 kg. and 1000 kg. These hardness curves under 500 and 1000 kg. deviate very little from each other, and the divergences, for which experimental errors are partly re- sponsible, need no comment. 38 ALUMINIUM AND ITS ALLOYS Annealed aluminium possesses a Brinell Hardness of 23 under 500 or 1000 kg., corresponding with a Tensile Strength of approximately 10 kg. per sq. mm. (6-35 tons per sq. in.). In the case of the thick series, the maximum hardness, as also the maximum Tensile Strength, occurs at 200 % cold work. (b) Shore Scleroscope Tests on thin sheets. As ball tests are impossible on thin sheet, rebound tests were made, using the Shore apparatus, on sheets of the thin series, possessing respectively 50 %, 100 %, and 300 % cold work. The average scleroscope numbers of sheets 1 and 2 mm. thick are as follows : Average scleroscope number Test pieces 1 mm. thick 2 mm. thick As annealed . . 4-5 5-5 50 % cold work . 16-0 11-5 100% cold work . 24-0 14-0 300 % cold work . 28-0 16-0 The scleroscope numbers vary with the thickness, but, whatever the thickness, the scleroscope number of completely annealed metal varies between 4 and 6, providing, therefore, a convenient means of verifying the extent of anneal. SHOCK TESTS. These were carried out on test bars, 55 x 10 x 10 mm., with a Mesnager notch of 2 mm. depth, using a 30 kg. m. charpy pendulum of the Conservatoire des Arts et Metiers. The results are also shown in Fig. 15. If the Shock Resistance curves (longitudinal and transverse) of Fig. 15 be compared with the Elongation curves of Figs. 5 and 6, it will be seen that they are of identical shape. At 50 % cold work, the Shock Resistance reaches almost its minimum value. In the annealed state, the Shock Resistance varies between 8 and 8-5 kilogramme-metres per sq. cm., without any appreciable difference between test pieces cut longitudinally or transversely. This difference, however, becomes more marked as the cold work increases. Minimum Shock Resistance, 300 % cold work (longitudinal) 5 kg. m. per sq. cm. Minimum Shock Resistance, 300 % cold work (transverse) 3 kg. m. per sq. cm. MECHANICAL PROPERTIES 39 II. Variation of Brinell Hardness and Shock Resistance with increasing annealing temperature after varying amounts of cold work, using test pieces taken from sheets 10 mm. thick. Figs. 16 and 17, corresponding with 100 % and 300 % cold work respectively, summarise the results. THICK SERIES (Test Pieces 10mm. thick) WOO Kg 100 200 300 400 Temperature 500 FIG. 16. Variation in Mechanical Properties (Hardness and Shock) on Annealing after 100 % Cold Work. HARDNESS. The hardness curves under 1000 kg. and 500 kg. are shown in the figures. These curves diverge little ; they are practically identical in the region of cold work, and diverge chiefly in the region of anneal, where the hardness under 1000 kg. is slightly greater than that under 500 kg. The object in obtaining 40 ALUMINIUM AND ITS ALLOYS these curves is not so much to compare the actual hardness numbers under 500 and 1000 kg., as to gain some indication of the trend of these values under two different loads. The advantage of this is evident ; for instance, in the case of higJi temperature tests, where the determination of hardness under WOO Kg THICK SERIES (Test Pieces 1 0mm. thick) Shock Resistance Shock Resistance Kg.m Per 200 300 400 500 600C Temperature FIG. 17. Variation in Mechanical Properties (Hardness and Shock) on Annealing after 300 % Cold Work. 1000 kg. would not be possible, the hardness must be determined under 500 kg. Since we have all the necessary data, we may then extend our results, and make such deductions as are useful. It is evident from Figs. 16 and 17 that the hardness curves exhibit the same regions as the curves for the Tensile properties, as noted above. MECHANICAL PROPERTIES 41 SHOCK RESISTANCE. It should be observed that in the cold- work region (0-150 c.) the Shock Resistance remains approximately constant, having a value of about 4 kg. m. per sq. cm. for 300 % cold work. It rises gradually in the softening region, and in the completely annealed zone it reaches 8 kg. m. per sq. cm. on annealing at 400 c. after 100 and 300 % cold work. It continues to increase slowly up to 9 kg.m. per sq. cm. on annealing at 600 after 100 % cold work, and even to 10 kg. m. per sq. cm. on annealing at this temperature after 300 % cold work. C. CUPPING TESTS Depth of Impression and Breaking Load EXPERIMENTAL DETAILS. Cupping tests were carried out on sheet metal by means of the Persoz apparatus (Fig. 18) in the Chalais laboratory. This apparatus consists, essentially, of a graduated rod furnished at one end with a plate and at the other with a ball 20 mm. in diameter. This ball rests on a circle 90 mm. in diameter taken from the sheet to be tested and gripped between two serrated annular rings of 50 mm. internal diameter. By subjecting the whole apparatus to a compressional stress between the two plates of a testing machine, steadily increasing pressures can be applied to the centre of the circle, through the ball. This compression is continued right up to the point of rupture of the dome which forms, in the sheet, under the pressure of the ball. The breaking load, and the depth of the impression made in the sheet, at the point of rupture, can thus be measured. The apparatus permits the measurement of the depth of impression with a maximum error of -02 to -03 mm. I. Variation of Depth of Impression and Breaking Load with the amount of Cold Work. Figs. 19 and 20 summarise the results. The values depend upon two variables : (i) The percentage of cold work, (ii) The thickness of the sheets. The degrees of cold work investigated were % (annealed), 50 %, 100 %, and 300 %, and the sheets, on which tests were 42 ALUMINIUM AND ITS ALLOYS I FIG. 18. Persoz Apparatus for Cupping Tests. MECHANICAL PROPERTIES 43 carried out, were those comprising the thin series ; 0-5 mm., 1-0 mm., 1-5 mm., and 2-0 mm. in thickness respectively. Fig. 19 shows for each thickness the variation of the Depth of Impression and Breaking Load with cold work. THIN SERIES 100 150 200 Cold Work 250 300% FIG. 19. Cupping Tests : Variation in Breaking Load and Depth of Impression with Cold Work. Test pieces of thickness specified (2-0, 1-5, 1-0, and 0-5 mm.). It shows clearly that the very slight increase in the Breaking Load due to the cold work is only obtained at the expense of the Depth of Impression at rupture. We may therefore deduce the following general conclusion : 44 ALUMINIUM AND ITS ALLOYS The absolute minimum cold work should be specified for sheet aluminium required for pressing or other work of a similar nature. The amount of cupping, which annealed sheet will stand, is clearly superior to that which sheet, worked even very little, can support. THIN SERIES 1000 Kg. Breaking Load 16 15 . 14 13 vt I o J= 4-1 Q. & 900 800 700 600 500 400 100% Cold 50 % Work 300 //, 200 100 0-5 i-o 1-5 Thickness of Sheet 2-0 mm. FIG. 20. Cupping Tests : Variation in Breaking Load and Depth of Impression with thickness, at specified amounts of Cold Work (0, 50, 100 and 300 %). Fig. 20, which is derived from Fig. 19, shows the variation of Breaking Load and Depth of Impression with thickness in the case of test pieces having been subjected to %, 50 %, 100 %, and 300 % cold work respectively. It shows that an increase of thickness must be resorted to, if an increased cupping value is desired. CONCLUSION. Whatever the thickness, all sheet destined for pressing should be annealed, and this condition should be included in specifications. II. Variation of Depth of Impression and Breaking Load with increasing annealing temperature, after varying amounts of Cold Work. Investigations were made on test pieces of the thin series : Type la (0-5 mm.) and Type Id (2-0 mm.), taken from sheet cold MECHANICAL PROPERTIES 45 worked to 50 %, 100 %, and 300 %. Figs. 21, 22, and 23 summarise the results obtained on Type la (0-5 mm. thick). They show that the maximum values of the Depth of Impres- sion and Breaking Load are reached in the region 375-425, and these values remain approximately constant up to 600. THIN SERIES (Test Pieces O^mm. thick) 15 14 13 12 c 11 10 S. 8 ! a Is Q 4 3 Breaking Load Kg 210 200 Uepth of Impression 190 180 170 160 150 Breaking Load 100 500 600C 200 300 400 Temperature FIG. 21. Cupping Tests : Variation in Breaking Load and Depth of Impression on Annealing after 50 % Cold Work. They show, further, that the final results (Depth of Impression and Breaking Load) are higher as the initial cold work is greater. The following table summarises the results : Initial Cold Work 50% 100 % 300 % SHEETS 0-5 mm. THICK After Complete Anneal Breaking Load Depth of Impression 185kg. llmm. 195 kg. 12 mm. 200kg. 12-5 mm. 46 ALUMINIUM AND ITS ALLOYS Figs. 24, 25, and 26 give the results for Type Id (2-0 mm. thick). They show that for sheet 2-0 mm. thick, as in the case of sheet 0-5 mm. thick, the Depth of Impression and Breaking Load reach their maximum values in approximately the same temperature range, but slightly extended (375-450), THIN SERIES (Test Pieces O'Smm. thick) 200 300 400 Temperature 600C FIG. 22. Cupping Tests : Variation in Breaking Load and Depth of Impression on Annealing after 100 % Cold Work. and these values remain approximately constant up to 600. The same remarks as before apply as to the relation between the initial cold work and the final values (Breaking Load and Depth of Impression at rupture). The following table may therefore be drawn up : SHEETS 2-0 mm. THICK After Complete Anneal Initial Cold Work Breaking Load Depth of Impression 50% 850kg. 16mm. 100% 880kg. 16-2 mm. 300% 950kg. 16-4 mm. MECHANICAL PROPERTIES 47 D. FINAL SUMMARY In this chapter the following properties have been con- sidered : (a) Tensile properties. (b) Hardness and Shock Resistance. (c) Cupping properties. THIN SERIES Breaking (Test Pieces 0'5mm. thick) Depth of 15 Breaking x 14 Load Kg 13 12 s 11 1 Impression nf vj 00 & / S / f J <40. (Robert J. Anderson.) PHOTOGRAPH 2. ALUMINIUM INGOT. SAND CAST. X50. (Robert J. Anderson.) :;V:v^.^?^' --- ^' PHOTOGRAPH 3. ALUMINIUM. COLD WORKED (50 %). XlOO. PHOTOGRAPH 4. ALUMINIUM. COLD WORKED (100 %): XlOO. To face page 57 PLATE II. PHOTOGRAPH 5. ALUMINIUM. COLD WORKED (300 %). X60. PHOTOGRAPH 6. ALUMINIUM. COLD WORKED (300 %) AND SUBSEQUENTLY ANNEALED AT 350 FOR 10 MINUTES. XlOO. i aw?./? f WMm PHOTOGRAPH 7. ALUMINIUM. ANNEALED AT 595 FOR 60 MINUTES. X50. (Eobert J. Anderson.) PHOTOGRAPH 8. ALUMINIUM. ANNEALED AT 595 FOR 4 HOURS. X50. (Robert J. Anderson.) To face page 57 MICROGKAPHY OF ALUMINIUM 57 acid (HF), as suggested by Brislee, employing a mixture of one part of fuming hydrofluoric acid and eight parts of water. The section is plunged into this liquid, and the blackening of the surface is removed by immersing for some seconds in con- centrated nitric acid. Hydrogen fluoride vapour may equally well be employed for etching. To give good results, the hydro- fluoric acid should be chemically pure, and should be preserved and used in vessels coated with paraffin. RESULTS. Micrographs of aluminium are given in Plates I and II. Photographs 1 and 2, taken from the work of R. J. Anderson, refer to chill and sand castings. The first shows the dendritic structure, well known in cast metals. The second shows crystals of aluminium surrounded by segregations. Photographs 3, 4, and 5 refer to aluminium cold worked to 50,; 100, and 300 % respectively. The flow lines in the direction of rolling are evident. Photographs 6, 7, and 8 show the effect of annealing after cold work. Photograph 6 shows the result of annealing, at 350 for 10 minutes, aluminium previously cold worked to 300 %. The lines of flow due to cold work have not dis- appeared, but underneath these striations, still visible, a fine cellular network, characteristic of annealed metal, can be seen. The striations due to cold work only disappear on heating either for a longer period or to a higher temperature. Photo- graphs 7 and 8 show the characteristics of a metal whose Elongation has diminished as a result of over-annealing. The thermal and mechanical treatment of aluminium can thus be controlled, up to a certain limit, by micrographic examination, as can also the purity of the metal and the absence of dross. CHAPTER V PRESERVATION OF ALUMINIUM WE have thought it best to consider, in a special chapter, the subject of the preservation of aluminium, or, if it be preferred, of its changes under the influence of physical, chemical, or mechanical agencies. The explanation of this change refers, partly, to indisputable phenomena, and partly to hypotheses which probably have the advantage of lying very near the truth. It is a fact that aluminium changes under certain conditions. Ditte, H. Le Chatelier, Ducru, Heyn and Bauer have made investigations and published papers on this subject. EFFECT OF ATMOSPHERIC AGENCIES The effect of atmospheric agencies can be summarised as follows : Am. Sheets of aluminium were protected from the rain, and exposed to the atmosphere by Heyn and Bauer, and after two hundred days had not changed in appearance. Ditte explains this apparent unchangeability by the fact that a very thin film of alumina is formed, which protects the rest of the metal from all change. WATER. Aluminium is attacked by distilled water, hydrated alumina being deposited. According to Ditte, this thin layer of alumina protects the aluminium from further oxidation. AIR AND WATER. Air and ordinary water, acting alternately, have less effect than water alone. AIR AND SALT WATER. The views of Ditte upon this subject are as follows : " Whenever aluminium is in contact with the atmosphere, salt water, sea water, or brackish water, the metal becomes 58 PRESERVATION OF ALUMINIUM 59 coated with a more or less compact layer of alumina, possibly mixed with other soluble salts. After the aluminium has been removed from the liquid, the change will continue to take place, if the metal has not been entirely freed from this coating and has not been sufficiently washed so as to remove from it all traces of alkali. Wherever the external surface of the metal has allowed a trace of the sea salt to penetrate, the action will slowly con- tinue, proceeding the more rapidly as the oxidised substance is more hygroscopic, and permits the possible chemical re- actions to take place more easily." In these results, the molecular state of the metal (anneal, degree of cold work, etc.) has not been taken into account. Then the following questions arise : Are these changes solely due to chemical actions, oxidations, tending to change the composition of the metal ? Are they due to disintegrations, depending upon the mole- cular state of the aluminium ? Are they due to the ill-effects of cold work, giving rise to a sort of spontaneous anneal, accompanied by disintegrations and cracks ? We have particularly studied this phenomenon in the brasses, whose preservation was irretrievably endangered, if, after cold working, a certain minimum anneal (350) had not been previously carried out. Cartridge cases and artillery shells suffered very largely from this fault before the remedy, just described, was applied. In other words, is the disintegration of aluminium connected with chemical causes or mechanical causes or does it not depend on these two causes together ? The following literature, referring to different cases of alteration, will enable us to see, up to a certain point, what are the respective parts played by these two types of phenomena. Ducru* observed the alterations of aluminium for the first time about 1894 in the case of wires of this metal, used as telegraph wires in the Congo or Dahomey from the coast to the interior. In a month, the wire, which had a Tensile Strength of 23 kg. per sq. mm. (14-6 tons per sq. in.), had become grey, and changed to an extremely weak substance. Chemical ^ analysis showed no oxidation. Hence there was no change of 1 a chemical nature. 4 * See 2nd Report, 1911, of the meeting of the French and Belgian members of the International Association for testing materials, March 25th, 1911. Burdin, Angers. 60 ALUMINIUM AND ITS ALLOYS The same phenomena were observed in the case of a sheet of aluminium at Havre, exposed alternately to air and sea water ; in this instance, at the end of three months, there was superficial oxidation. This changed layer was removed by planing so as to leave only the sound portion. Tests on this showed that the Tensile Strength had fallen from 22 to 4 kg. per sq. mm. (14 to 2-54 tons per sq. in.). At all events, there was an initial cold work clearly indicated. In 1897, Ducru observed the alteration of aluminium in utensils made by pressing. This alteration took place on the bottom of the utensil in the following manner : There was a diminution in the metallic lustre of the alu- minium, and the appearance of a grey colour, becoming more pronounced. The altered portion possessed no strength, while analysis showed only 4 to 5 % of the metal to be changed to alumina. Similar observations were made about 1911, on utensils, 1 mm. in thickness, made by pressing, and intended for domestic and culinary purposes. The same changes were apparent, and the bottom of the vessel could be pierced by simple pressure of the finger. Analysis showed that 2-7 %, 3-7 %, and 3-5 %, according to the sample, was changed to alumina, and Ducru drew the following conclusions : " In conclusion, the alteration of aluminium appears, at least in certain cases, to have one peculiar characteristic, namely, that it is not an oxidation effect, for that seems to affect only a small portion of the metal, and it is, on the other hand, accompanied by a diminution in mechanical strength, which causes serious trouble." Then, if the phenomena be investigated more closely, it is evident that the unfortunate incidents mentioned have occurred in the case of excessively cold-worked aluminium wires, sheets, or pressed utensils. The external agencies play the part of accelerators, assisting the breakdown of equilibrium, which, in their absence, would probably only have been delayed. We have, ourselves, verified these disintegrations due to cold work. We have not carried out experiments on alu- minium, but the investigations we have made on the cold working of brass lead us to infer that the working of aluminium cannot be irrelevant to these disintegrations. From the micrographic standpoint, worked aluminium, similarly to worked brass, assumes a striated appearance, PRESERVATION OF ALUMINIUM 61 showing crystalline deformation in the direction of the mechani- cal work a condition in which instability is probable. For aeronautical use, where security is essential, the need for an anneal is clearly proved, a conclusion supported by the arguments already given. For strengths higher than that of annealed aluminium, resource must be had to its alloys. For purposes in which safety is not of prime consideration, and in which the high strength obtained by the working of aluminium is desirable, the problem takes on another aspect. The practical durability of cold-worked aluminium will be a predominant factor to be considered in solving the problem of the practical and economical uses of which it is capable (for wires and cables for electrical conductors). CHAPTER VI SOLDERING OF ALUMINIUM AFTER having discussed the physical, chemical, and mechanical properties, we may say a few words about the soldering of aluminium. This soldering is not without difficulties, which are both of a physical and chemical nature. (a) PHYSICAL DIFFICULTIES. Coefficient of Expansion. Aluminium possesses a high coefficient of expansion, which must be taken into considera- tion in order to avoid breakdowns. As its tenacity is low at high temperatures, there is a possibility of rupture occurring owing to the relative contraction as the joint cools down. Melting Point. The low melting point of aluminium, 650, is also a disadvantage. If the temperature of the blowpipe (generally high) is not very carefully regulated, the melting point of the metal may be reached or even exceeded, thus damaging the articles to be soldered, to say nothing of the deterioration of properties resulting from overheating, which cannot be remedied by subsequent cold work, followed by an anneal at a suitable temperature and for an appropriate time. (b) CHEMICAL DIFFICULTIES. These difficulties arise from the impurities of the metal and of the soldering alloys. Impurities. The impurities have been divided into three groups : Group I. Iron-Silicon Group. Iron and silicon have harmful effects in aluminium solders. It is impossible to eliminate these impurities completely, but their amount must be restricted according to the specifi- cations we have laid down. The alloys of iron and silicon with aluminium are very weak and constitute the weakest parts in the article. The over- heating, due to the soldering, facilitates, therefore, the forma- tion of a very weak system, consisting of the alloys of these 62 SOLDERING OF ALUMINIUM 63 impurities with the aluminium, which is liable to lead to rupture. Hence a metal must be used which does not contain larger amounts of impurities than the maxima previously specified. Group II. Minor Impurities. If these do not exceed the maxima stipulated, they do not cause any serious incon- veniences. Group III. Alumina. The formation of alumina is un- avoidable during soldering, and this gives rise to the most serious difficulties. The presence of alumina between the two sheets to be soldered hinders the soldering, if means are not taken, during the operation, to remove it. For this pur- pose, a flux is used, which must fulfil certain prescribed technical conditions. The following flux is recommended by " L'Union de la Soudure Autogene " : Lithium chloride . . ;.; 15% Potassium chloride . . . 45 % Sodium chloride . r . . 30% Potassium fluoride . , 7% Sodium bisulphate . , 3 % The bisulphate of soda, under the action of heat, reacts with the chlorides and fluorides forming hydrochloric and hydrofluoric acids, which attack the alumina, producing the volatile chloride and fluoride of aluminium. SOLDERING ALLOYS. Generally, the alloys for soldering aluminium are not satis- factory. In order to effect soldering, i.e. for alloying to take place, the temperature must be relatively high and then the disadvantages pointed out as a result of overheating are to be feared. Galvanic couples, in presence of salt solutions, may lead to disintegrations of the metal. To sum up, we are forced to the following conclusions concerning the soldering of aluminium : (1) The metal used must be as pure as possible. (2) A flux must be employed to remove the alumina, which hinders soldering. (3) Preferably, autogenous welding should be used. BOOK II '^/ALLOYS OF ALUMINIUM CLASSIFICATION OF ALLOYS As regards abridged notation and nomenclature of alloys, we shall conform to the methods prescribed by the Permanent Commission of Standardisation in Paper A2, July 28th, 1919, on " The Unification of Nomenclature of Metallurgical Products." Thus, for example, the abridged notation of an alloy may be Al Gun Sn, Nil showing that we are dealing with an alloy of aluminium containing n % copper 3 % tin. 1 % nickel. According to the classification adopted (see page xi), we have to consider (1) Light alloys of aluminium for casting purposes. (2) Light alloys of aluminium of great strength (Tensile Strength greater than 35 kg. per sq. mm. (22-22 tons per sq. in.)). A typical light alloy of these two classes has a density less than 3-5, and in the majority of light alloys, as we shall see, the density is less than 3. (3) Heavy alloys of which aluminium is a constituent, comprising especially the "cupro-aluminiums," that is to say, alloys of copper and aluminium containing 1-20 % of aluminium with less than 1 % of other im- purities. Copper being the principal constituent, an alloy of copper con- taining 10 % of aluminium, for example, would be represented by the symbol CuAl 10 and the special cupro-aluminium alloy con- taining 9 % of aluminium and 1 % of manganese by CuAlsMnj. These alloys are often known as aluminium bronzes, though the name aluminium bronze should be restricted to alloys of copper and tin containing aluminium, such as the aluminium bronze for bearings whose symbolic notation is CuSn 44 Al 3 . 67 68 ALUMINIUM AND ITS ALLOYS Moreover, in the nomenclature of alloys, we shall invariably put first the principal metal, followed by the other metals which are present as added constituents. Thus the name " aluminium-zinc alloys " refers to those rich in aluminium and which therefore come under the heading of light alloys, while the name " zinc-aluminium alloys " refers to those rich in zinc, which are not, therefore, classed as light alloys, but as heavy alloys. These heavy alloys are only of value in aeronautical construction if some special properties compensate for their weight. After dealing with the alloys of the three groups of which we have made a special investigation, we shall summarise shortly, in a special section, the properties of the principal alloys in the group which have been studied by previous investigators. Before discussing, in the following chapters, the investigations on these alloys, we think it advisable to recall the important part played by copper in the alloys of aluminium. Since the majority of the alloys of these three groups are affected by this constituent, it seems suitable to consider it separately, before entering into a detailed study of each. EQUILIBRIUM DIAGRAM OF COPPER- ALUMINIUM ALLOYS. The diagram was first established by H. Le Chatelier, then by Campbell and Mathews, Carpenter and Edwards, Gwyer, and Curry. There are few differences between these various diagrams. We give Curry's diagram (Fig. 30), and the results of the micrographic examination may be summarised as follows : Three regions may be distinguished : First Region. Alloys rich in copper (100 %-86 % by weight of copper). In the region extending from 100 %-92 % of copper, the alloy consists of a solid solution, known as a, while from 92 %- 86 % of copper the solid solutions a and y are present. The latter region can be further divided into two, namely : ( solution a 92 %-88 % copper + leutectic (a+y) / solution y 88 %-86 % copper + \ eutectic (a+y) CLASSIFICATION OF ALLOYS 69 At 88 % of copper, therefore, the alloy consists of the eutectic (a+y), formerly called jS. This use of the name j8 is incorrect, since the constituent j3 corresponds with austenite in steels we shall not employ it. The solution a would correspond, in steels, with a iron, the solution y with cementite, and the eutectic (a +y) with pearlite. noo 1000 900 800 700 600 500 100 90 80 70 60 50 40 30 20 10 100%Cu 90 80 70 60 50 40 30 20 10 0%(by weight) Fio. 30. Copper- Aluminium Diagram (after Curry). The heavy alloys of great strength, that is, the cupro-alu- miniums, or aluminium bronzes, are contained, approximately, in the region from 92 % to 88 % of copper, i.e. the region corre- sponding with the solution a and the (a-fy) eutectic. Second Region. This is a middle zone, extending from 86 % to 54 % of copper, in which a certain number of constituents exist which have been differently named by the various in- vestigators. The corresponding alloys are weak and of no industrial importance. 70 ALUMINIUM AND ITS ALLOYS Third Region. This extends from 54 % to % of copper. The alloys consist of the constituents CuAl 2 and 77, the latter being a solid solution of copper in aluminium containing a very low percentage of copper. This region may be divided into two : (a) Between 54 % and 30 % of copper, in which the con- stituents CuAl 2 and eutectic occur, the eutectic being (b) Between 30 % and % of copper, in which the con- stituent 77 and the eutectic just mentioned occur. It must be noted that, for low amounts of copper, the constituent 77 is present alone, without any eutectic. At 30 % of copper the alloy would consist only of the (CuAl 2 -f 77) eutectic. The only part of this region which is of industrial importance is that extending from 12 % to % of copper, which corresponds with the light alloys of low strength for casting purposes. Hence we shall only deal with the two extremities of the equilibrium diagram of the copper-aluminium alloys. PART III LIGHT ALLOYS OF ALUMINIUM FOR CASTING PURPOSES WE have no intention of considering the details of the casting of aluminium, and have no wish to discuss all the possible alloys of aluminium used, or usable for this purpose. We shall simply give the results of experiments carried out on a certain number of these, particularly those which have been used in aeronautical work. We shall conclude this account with a summary of the properties of certain other alloys, as investi- gated and tested in France and other countries. First of all we shall summarise the different legitimate requirements as regards the quality of aluminium and its alloys used for casting. PROPERTIES OF ALUMINIUM CASTING ALLOYS. The following are the most important, especially from the aeronautical standpoint. (1) Lightness. (2) Minimum of blowholes and porosity. (3) A sufficiently great Tensile Strength, Elastic Limit, and Hardness. And, for articles used at high temperatures, such as pistons, motor cylinders, etc. : (4) A certain minimum hardness throughout the range of temperature experienced. (5) Maximum thermal conductivity and specific heat. We may say at once that pure aluminium will not satisfy all these requirements, and that it is even difficult to find an alloy that will completely fulfil all these con- ditions, which we shall discuss in turn. (1) Lightness. The pure metal best satisfies this condition, the alloys rich in magnesium alone being superior in this respect. 71 72 ALUMINIUM AND ITS ALLOYS The addition of other constituents, however, ought not to deprive the alloy of the lightness due to the aluminium. One of the great advantages of the low density consists in the removal of the critical period of vibration* outside the regular period of the moving system. A critical period of vibration obtains, when there is coincidence between the frequency of the particular part in question and the displace- ment frequency of the system of which it forms a part a persistence of these conditions may lead to rupture. If aluminium be substituted for steel, and the area of cross section be doubled, there is still a reduction in weight and a vibration frequency four times greater which displaces the critical resonance range a certain number of octaves, thus making harmful coincidences more improbable. A maximum density of 3 should be specified. (2) Minimum of Blowholes and Porosity. The cast article must be sound, having as few blowholes as possible. A high percentage of alumina seems to cause blowholes in the cast aluminium article, and hence renders it useless. Porosity must be avoided. In the pistons of aeroplane engines, porosity invariably leads to erosion, on account of the hot gases being continually forced through the article. Porosity also prevents watertightness. It is detected by special tests and is usually avoided by the skill of the founder. (3) A sufficiently great Tensile Strength, Elastic Limit, and Hardness. Pure cast aluminium has, in the cold, the following properties : Tensile Strength (average )j= 7 kg. per sq. mm. (445 tons per sq. in.). Elastic Limit =3-5 kg. per sq. mm. (2-22 tons per sq. in.). % Elongation = 7 Shock Resistance = 2 kg. m. per sq. cm. Brinell Hardness = 23 and is unsuitable for most articles. It is obvious that a Tensile Strength comparable with that obtained after forging or rolling cannot be expected in a cast alloy. * Cf. Fleury and Labruy^re, " Des emplois de 1' Aluminium dans la con- struction des Machines " (Dunod and Pinat, 1919). LIGHT ALLOYS OF ALUMINIUM 73 From this point of view the requirements must be modest, varying between 8 and 20 kg. per sq. mm. (5-08 and 12-7 tons per sq. in.), according to the added constituents and the method of casting (chill or sand). The Elastic Limit is generally very near the Tensile Strength, and is sometimes indistinguishable from it. The Elongation is always very low, and the Hardness varies as does the Tensile Strength. Very little must be expected as regards Shock Resistance also, no cast alloy having, to our knowledge, an appreciable shock resistance ; they are all more or less brittle. It is essential to take this fact into consideration in speci- fying the method of working for cast articles. For articles subjected to high temperatures, which is the case in the majority of parts of machines, the following proper- ties are required : (4) A certain Minimum Hardness up to the Maximum Tempera- ture reached. Pure aluminium does not possess sufficient hardness as the temperature rises. Parts of engines, such as cylinders and pistons, may reach a temperature of 200-300. 100 90 80 70 5 E 60 3 Z 50 1 40 (D 30 20 10 100 500 600 C 200 300 400 Temperature FIG. 306. Hardness of Aluminium at High Temperatures under 500 Kg. load. In order to avoid collapse, those parts subjected to stress should possess, throughout the whole range of temperature experienced during working, certain minimum properties. 74 ALUMINIUM AND ITS ALLOYS As regards hardness, this can be expressed approximately by a Brinell number of about 30 under a load of 500 kg. This number is greater than that of aluminium in the cold, and necessitates an original hardness of 50 to 60. Tests have been carried out on a certain number of alloys in order to examine these properties at high temperatures. Fig. 30& shows the hardness of aluminium at different temperatures, and enables us to see how the hardness is in- creased by the addition of various constituents. (5) A Maximum Thermal Conductivity and Specific Heat. A high conductivity prevents local heating, which rapidly causes deterioration, and renders the article useless. Alloys of aluminium possess great advantages in this respect. We know that the conductivity of aluminium is 36, that of silver being 100 and of copper 75-11 it is third as regards thermal conductivity. This fact is of very great importance ; it renders the employment of aluminium alloys for pistons very successful. On the other hand, the specific heat of aluminium is very high, which reduces the rise in temperature. This property, added to the high thermal conductivity, causes aluminium pistons to become far less heated in use than pistons of cast iron. The temperature reached is lower than that of decomposition of the lubricating oils, so that carbonaceous deposits, similar to those produced on cast-iron pistons, are not formed on pistons of alloys of aluminium for this reason fouling and seizing do not occur. After this short discussion we will consider individually the alloys which we have investigated or met with in practice. ALLOYS OF ALUMINIUM FOR CASTING PURPOSES. The following alloys have been considered : (a) Binary aluminium-copper alloys the study of the part of the equilibrium diagram of the aluminium-copper alloys extending from 100 % to 88 % of aluminium. (b) Ternary alloys aluminium-copper-zinc. (c) Quaternary alloys aluminium-copper-tin-nickel. We conclude the account of the tests carried out on these alloys by referring, in a special section, to certain other alloys belonging to the group, namely : LIGHT ALLOYS OF ALUMINIUM 75 Alloys of aluminium and tin. Alloys of aluminium and zinc. Alloys of aluminium and magnesium. As far as possible, we shall compare the properties of the cast alloys with those of the same alloys when forged or rolled. These alloys have been worked in the following manner : (1) Casts. Some heats were cast directly into chills without runners. Ten casts were made for each alloy in cylinders 50 mm. hi diameter and 50 mm. in length. In five casts two tensile and two shock test pieces were made per cast, the operation being carried out in such a way as to obtain a tensile test piece at one end and a shock test piece at the other end of the heat, and one tensile and one shock test piece towards the middle of the heat. In the other casts, cylindrical bars were made for hardness tests at high temperatures. These were carried out, using a 10 mm. ball and loads of 500 and 1000 kg. (2) Test Pieces. These were cast, on the one hand in chills, and on the other hand by bottom pouring, the test pieces being fed by lateral runners. These two types of tests, the one on sand cast, and the other on chill cast test pieces, seemed indispensable in order to show the different results obtained by the two methods. In general, casting is carried out by the latter method, while the real and intrinsic properties of the alloy are revealed by the former. We should render ourselves liable to error, if we took, as the figure for Tensile Strength, that determined on the sand cast samples. Tests on the sand cast test pieces indicate the success or failure of the alloy, but do not show the true properties possessed by the chill cast article. (a) BINARY ALLOYS ALUMINIUM-COPPER. The following types are considered : Type I . ... 4 % copper. II y ; v 8% ,, in . , * 12 % 76 ALUMINIUM AND ITS ALLOYS TYPE I (4 % COPPER) Analysis Aluminium, alumina . . . 94-25 Copper 4-70 Iron . . . . . . 0-57 Silicon 0-48 Density: 2-75 Mechanical Properties (as cast). The average mechanical properties may be summarised as follows : (a) Tests on Sand Castings. Tensile Strength = 11 kg. per sq. mm. (6-98 tons per sq. in.). % Elongation =3 Shock Resistance =0-6 kg. m. per sq. cm. (b) Tests on Chill Cast Bars. Tensile Strength= 13-7 kg. per sq. mm. (8-70 tons per sq. in.) % Elongation =3-8 The Elastic Limit is approximately the same as the Tensile Strength. In the forged or rolled state, this same alloy may giye : Tensile Strength =20 kg. per sq. mm. (12-7 tons per sq. in.) Elastic Limit = 8 kg. per sq. mm. (5-08 tons per sq. in.) % Elongation =10 Hardness at High Temperatures. The results of the hardness tests at high temperatures are shown in Fig. 31. TYPE II (8 % COPPER) Analysis Aluminium, alumina . . .90-07 Copper 8-65 Iron 0-84 Silicon 0-44 Density: 2-92 Mechanical Properties (as cast). The average mechanical properties may be summarised as follows : LIGHT ALLOYS OF ALUMINIUM 77 O 50 TOO 150 200 250 300 350 400C Temperature FIG. 31. Hardness of Copper- Aluminium Alloy, containing 4 % Copper, at High Temperatures under 500 and 1000 Kg. load. 50 100 150 200 250 300 Temperature FIG. 32. Hardness of Copper-Aluminium Alloy, containing 8 % Copper, at High Temperatures under 500 and 1000 Kg. load. 78 ALUMINIUM AND ITS ALLOYS (a) Tests on Sand Castings. Tensile Strength = 1 1 kg. per sq. mm. (6-98 tons per sq. in.) % Elongation =0-7 Shock Resistance =0-3 kg. m. per sq. cm. (b) Tests on Chill Cast Bars. Tensile Strength =12-3 kg. per sq. mm. (7-81 tons per sq. in.) % Elongation =0-7 The Elastic Limit is approximately the same as the Tensile Strength. The results of the hardness^ tests at high temperatures are summarised in Fig. 32. TYPE III (12 % COPPER) Analysis Aluminium, alumina . . . 86-24 Copper 12-65 Iron 0-88 Silicon 0-43 Density: 2-95. Mechanical Properties (as cast). The average mechanical properties may be summarised as follows : (a) Tests on Sand Castings. Tensile Strength = 13 kg. per sq. mm. (8-25 tons per sq. in.) % Elongation =0-8 Shock Resistance =0-2 kg. m. per sq. cm. (b) Tests on Chill Cast Bars. Tensile Strength = 13-6 kg. per sq. mm. (8-64 tons per sq. in.) % Elongation =1 The Elastic Limit is approximately the same as the Tensile Strength. The results of the hardness tests at high temperatures are summarised in Fig. 33. The variations in the hardness at high temperatures with the copper content are shown in Fig. 34. Allowing, with a view to avoiding the possibility of collapse, a minimum Brinell hardness of 30, it is evident that the alloy LIGHT ALLOYS OF ALUMINIUM 79 150 140 130 120 110 1 100 1 30 z 300 350 400C 50 100 150 200 250 Temperature FIG. 33. Hardness of Copper-Aluminium Alloy, containing 12 % Copper, at High Temperatures under 500 and 1000 Kg. load. WOC FIG. 34. Variation in Hardness under 500 Kg. load, with Copper content at Temperatures 0, 100, 200, 300, 350, and 400 C. 80 ALUMINIUM AND ITS ALLOYS containing 4 % copper can be used for the range of temperature 0-275, the alloy having 8 % copper over the range 0-310, and the alloy having 12 % copper over the range 0-320. It must be noted that cold working cannot be employed to increase the hardness, since its effect must be nullified by the rise in temperature. (b) TERNARY ALLOYS ALUMINIUM-COPPER-ZINC (12-13 % ZINC, 3 % COPPER). Analysis Aluminium, alumina . . . 83-75 Copper 3-10 Zinc 11-60 Lead 0-22 Iron 0-88 Silicon 0-55 Density: 2-94. Mechanical Properties (as cast). The average mechanical properties may be summarised as follows : (a) Tests on Sand Castings. Tensile Strength = 11 kg. per sq. mm. (6-98 tons per sq. in.) % Elongation =0-3 Shock Resistance =0-6 kg. m. per sq. cm. (b) Tests on Chill Cast Bars. Tensile Strength =16-5 kg. per sq. mm. (10-48 tons per sq. in.) % Elongation =2-8 For the same copper content, the Elastic Limit is approxi- mately the same as the Tensile Strength. If the amount of zinc be increased to 13 %, the values become : Tensile Strength =18-4 kg.per sq.mm.(l 1 -68 tons per sq. in.) % Elongation =4 The results of the hardness tests at high temperatures are summarised in Fig. 35, which shows the rapid falling off in hardness as the temperature is increased. The hardness at ordinary temperatures, however, is greater than that of the majority of other casting alloys. LIGHT ALLOYS OF ALUMINIUM 81 (c) QUATERNARY ALLOYS Analysis Aluminium, alumina Copper .... Tin .... Nickel .... Iron Silicon V" Density: 2-98 84-93 10-14 3-20 0-86 0-48 0-27 50 100 300 350 400C 150 200 250 Temperature FIG. 35. Hardness of Zinc -Copper- Aluminium Alloy, con- taining 12 % Zinc, 3 % Copper, at High Temperatures under 500 and 1000 Kg. load. Mechanical Properties (as cast). The average mechanical properties may be summarised as follows : (a) Tests on Sand Castings. Tensile Strength = 13 kg. per sq. mm.(8-25 tons per sq. in.) % Elongation =1 Shock Resistance =0-3 kg. m. per sq. cm. (b) Tests on Chill Cast Bars. Tensile Strength =12-6 kg. per sq.mm.(8-00 tons per sq. in.) % Elongation =0-5 82 ALUMINIUM AND ITS ALLOYS The Elastic Limit is approximately the same as the Tensile Strength. The results of the Hardness tests at high temperatures are summarised in Fig. 36. B. PROPERTIES OF OTHER ALLOYS, GIVEN FOR REFERENCE IN A SUPPLEMENTARY SECTION (1) ALLOYS OF ALUMINIUM AND ZINC. (a) Aluminium-Zinc Alloys. The alloys of this group, which are easily utilised, are those corresponding with the shaded portion of the fusibility curve of aluminium -zinc alloys (Fig. 37). These are alloys containing to 30 % zinc. The following table due to Jean Escard* summarises the properties of chill cast bars, of bars forged at 350, and of bars annealed at 300 for one hour after forging : Tensile Elastic Alloy Strength Limit Elon- % % j- r c aiiii cut Kg tons Kg tons Bo/Lion Al. Zn. mm. 2 in. a mm. 2 in. 2 f As cast 7-9 5-01 4-2 2-67 8-8 94-7 5-3 } Forged 13-6 8-64 11-3 7-18 19-0 V Forged & annealed 9-6 6-10 2-5 1-59 30-0 Used for casting c As cast 9-3 5-91 6-5 4-13 2-5 and rolling 89-8 10-2 J Forged 18-2 11-56 16-7 10-60 33-5 ( Forged & annealed 14-8 9-40 4-5 2-86 38-0 84-0 16-0 r As cast J Forged V. Forged & annealed 17-1 10-86 25-4 16-13 23-2 14-73 10-4 6-60 18-1 11-49 7-5 4-76 2-0 23-0 28-0 \Used especially j for casting f As cast 18-4 11-68 17-1 10-86 1-0 79-0 21-0 { Forged \. Forged & annealed 31-3 19-87 31-5 20-00 22-4 14-22 27-6 17-53 14-0 14-5 f Kosenhain and 75-0 25-0 Forged 42-0 26-67 89-0 24-76 16-5 \ Archbutt: v Density : 3-2 All these alloys are brittle and fail under repeated impact : the brittleness is increased by rise of temperature. For ex- ample, the breaking of gear boxes of motors. EFFECT OF TEMPERATURE (Rosenhain and Archbutt). The Tensile Strength diminishes very rapidly with rise of temperature. The Tensile Strength of the alloy containing 25 % zinc changes from 43-3 kg. per sq. mm. (2749 tons per sq. in.) at the ordinary temperature to 28-5 kg. per sq. mm. (18-10 tons per sq. in.) at 100, and the rate of this diminution increases with the temperature. We have noted in Fig. 35, referring to the ternary alloy aluminium-zinc-copper, the rapid decrease in hardness with rise * Jean Escard, " L' Aluminium dans 1'Industrie " (Dunod and Pinat, 1918). LIGHT ALLOYS OF ALUMINIUM 83 150 140 130 120 110 100 90 80 70 60 5-0 40 30 20 10 00 Kg. WOO Kg? 50 100 150 200 250 Temperature 300 350 400 C FIG. 36. Hardness of Copper -Tin-Nickel-Aluminium Alloy, con taining 11 % Copper, 3 % Tin, and 1 % Nickel, at High Temperatures under 500 and 1000 Kg. load. TOO 80 700i 60 40 20 C 600 500 400 300 200 Netting Point V m Industrial Alleys, 0%Zn. '0 20 40 60 80 100.% AT Fia. 37. Melting-point Curve of Zinc-Aluminium Alloys. 84 ALUMINIUM AND ITS ALLOYS of temperature. The Brinell number for this alloy falls from 85 under a load of 500 kg. at the normal temperature, to 56 under the same load at 100. Cadmium is sometimes added to alloys of aluminium and zinc (1-40 % zinc) (patented by Bayliss and Clark, England) in the proportions of 0-001 to 10 respectively, an addition which confers great malleability, and facilitates working and stamping. At other times, 0-5 % to 1 % of copper is added, or even 2 %, forming for aluminium-zinc alloys the soldering metal of the following composition : Aluminium . 88 % Zinc . . . 10% Copper . 2 % (b) Zinc-Aluminium Alloys. Investigations on the alloys rich in zinc have been carried out by Leon Guillet and Victor Bernard.* The following alloys, among others, were studied : (1) Binary zinc-aluminium alloys containing 1, 2, 3, or 5 % of aluminium. (2) Ternary zinc-aluminium-copper alloys containing 2 % of aluminium and 2, 4, 6, or 8 % of copper ; 4 % of alu- minium and 2, 4, 6, or 8 % copper ; 8 % of aluminium and 4 % of copper (German type of alloy). The following results were obtained : (1) The cast alloys are of no value, the Elongation and Shock Resistance being approximately zero. (2) The rolled alloys have low elongations and almost no Shock Resistance. Extruded alloys generally have considerably increased elongations. This extrusion gave the following properties for the alloy containing 8 % of copper and 4 % of aluminium : Tensile Strength =30 to 31 kg. per sq. mm. (19-05-19-68 tons per sq. in.) % Elongation =27-29 Shock Resistance =2 kg. m. per sq. cm. This is the most interesting of the zinc -aluminium alloys, but its Shock Resistance is very low. * " Revue de Mdtallurgie," Sept.-Oct., 1918. LIGHT ALLOYS OF ALUMINIUM 85 (2) ALUMINIUM-TIN ALLOYS. The alloy, containing 3 % of tin, having a density 3-25, should be mentioned, as it is very suitable for casting. Tin is frequently added in foundry practice, in order to facili- tate the casting of alloys. (3) ALLOYS OF ALUMINIUM AND MAGNESIUM. It is clear that these alloys, from the point of view of light- ness, are more important the more magnesium (density : 1-75) they contain. (a) Aluminium-Magnesium Alloys. Magnalium, which con- tarns 5-25 % of magnesium, has, for an average content of magnesium, a density of about 2-80 in the cast state. MECHANICAL PROPERTIES OF ALUMINIUM-MAGNESIUM ALLOYS. Jean Escard, in the work just quoted, gives the following values for alloys containing 2 % and 10 % of magnesium : Tensile Strength Elonga- Magnesium Treatment A s tion Kg./mm.* Tons/in/ 0' .0 10% Sand cast . . . 12-6 8-00 3 Cast and rapidly cooled . 20-1 12-76 2 Cast and quenched . 28-1 17-84 1 Sand cast . .15 9-52 2-4 Cast and rapidly cooled . 23-6 14-99 3-4 Cast and quenched , 43 27-30 4-2 The effect of quenching on alloys containing magnesium is marked, but we shall discuss this more fully in connection with the alloys of the second group (light alloys of great strength). A very small quantity of magnesium (0-5 to 1 %) is sufficient to increase the hardness after quenching in a most remark- able manner ; the presence of 30 % to 50 % of magnesium renders the alloy hard and brittle. (b) Magnesium-Aluminium Alloys. The magnesium-alu- minium alloys, that is to say, alloys rich in magnesium, have been worked out by the Germans during the war, and the Zeppelin L 49, brought down at Bourbonne, possessed several parts made of similar alloys. The alloy would be of the type " Elecktron," known before the war, whose density is 1-8, and whose conductivity is of the same order as that of zinc ; it contains 90-92 % of magnesium. These alloys are very difficult to roll, and generally contain numerous holes and flaws. 86 ALUMINIUM AND ITS ALLOYS The alloy containing 90 % of magnesium and 10 % of aluminium possesses the following properties, as cast : Elastic Limit = 8 kg. per sq. mm. (5-08 tons per sq. in.) Tensile Strength = 1 1 kg. per sq. mm. (6-98 tons per sq. in.) % Elongation =1 Shock Resistance = zero Their most striking property is lightness, and they should not be overlooked by aviation authorities, who should take an interest in perfecting their manufacture. MICROGRAPHY OF CASTING ALLOYS OF ALUMINIUM. The five photographs in Plates III and IIlA show the micrographic appearance of the five casting alloys of aluminium that have been studied. The first three refer to aluminium-copper alloys. These alloys contain the constituent 77 (this being, as we have seen, pure aluminium or a solid solution of copper and aluminium with a very low content of copper) plus the eutectic (CuAl 2 -h??). Photograph 1, Plate III, referring to the alloy containing 4 % of copper, shows solution 77 almost pure. Photographs 2 and 3, Plate III, referring to alloys containing 8 % and 12 % of copper respectively, show, to a slight extent, the eutectic previously described. Photographs 4 and 5, Plate H!A, refer to the ternary and quaternary alloys containing about 3 % and 11 % of copper respectively. PLATE III. -~^<*.-.< \ PHOTOGRAPH 1. Copper, 4 % ; Aluminium, 96 %. / -^ & PHOTOGRAPH 2. Copper, 8 % ; Aluminium, 92 %. :.&' ^ PHOTOGRAPH 3. Copper, 12 % ; Aluminium, 88 %. To face page 86 PLATE IIlA. .'-,~: ; -''V .; " : & VX- -. PHOTOGRAPH 4. Copper, 3 ; Zinc, 12 % ; Aluminium, 85 . PHOTOGRAPH 5. Copper, 1 1 ; Tin, 3 % ; Nickel, 1 % ; Aluminium, 85 . To face page 86 PART IV LIGHT ALLOYS OF GREAT STRENGTH THE group of light alloys of great strength comprises complex alloys containing copper, magnesium, manganese, and zinc, in addition to the aluminium ; iron, silicon, and alumina are present as impurities, having been introduced with the alu- minium. These alloys have, as a rule, the following typical com- positions : ALUMINIUM-COPPER-MAGNESIUM ALLOYS. Copper . . . . " . . 3-5-4 % Magnesium . ... . about 0-5 % Manganese . . . ' . . 0-5-1 % Aluminium and impurities . . (difference) ALUMINIUM-COPPER-ZlNC-MAGNESIUM ALLOY. Copper . . . . . . 2-5-3% Zinc V . . . . . 1-5-3% Magnesium . . . . 0-5 % Manganese . ' * . . . 0-5-1 % Aluminium and impurities . . (difference) The remarkable property of hardening after cooling, which these alloys possess, is due to the presence of the magnesium, or of the magnesium and zinc. This hardening is more pro- nounced as the cooling is more rapid. The mechanical proper- ties, which the alloy possesses immediately after more or less rapid cooling, are changed completely after a certain interval of time. Without entering into a detailed discussion of the causes which bring about this transformation, we will study from a practical point of view, the results obtained by mechani- cal work and thermal treatment and from them deduce useful practical conclusions. Tests have been carried out on light alloys, aluminium- copper-magnesium, having the average composition already given and corresponding with the light alloy known as duralumin. 87 88 ALUMINIUM AND ITS ALLOYS A description of this work is given in the following form : Chapter I. (a) Variation in the mechanical properties (Tensile Strength, Elastic Limit, Elongation, Shock Resistance, and Hardness) with the amount of cold work, (b) Variation in these mechanical properties with annealing temperature (after cold work). Chapter II. Quenching Quenching Temperature, Rate of Cooling, and Ageing after Quenching. Chapter III. Reannealing after Quenching. Chapter IV. Cupping tests, after thermal treatment. Chapter V. High temperature tests. CHAPTER I (a) VARIATION OF THE MECHANICAL PROPERTIES (TENSILE STRENGTH, ELASTIC LIMIT, ELONGATION, SHOCK RESIS- TANCE, AND HARDNESS) WITH THE AMOUNT OP COLD WORK. TEST pieces were cut from sheets, 10 mm. thick, subjected to the required degree of cold work under the conditions already stated (see Fig. 38). 15 MOi 100- FIG. 38. Tensile Test Piece (thick sheet). 20 10 -100- FIG. 39. Tensile Test Piece (thin sheet). Test pieces were also prepared from thin sheet (see Fig. 39). This research was carried out upon metal which had been annealed in a bath of sodium nitrite and potassium nitrate at 450 C., and cooled in air. The reason for this initial treat- ment will be discussed later. In its annealed condition the alloy possessed the following properties : Tensile Strength Kg/mm * Tons /in * Elastic Limit Kg/mm * Tons /in * Elongation % Shock Resistance Kg.m/cm s Longitudinal Transverse 32 2032 26 16-51 13 8-25 12 7-62 18 10 3 2-5 90 ALUMINIUM AND ITS ALLOYS The variations in these properties with the amount of cold work are shown in Figs. 40 and 41. Discussion of Fig. 40 (test pieces cut longitudinally to direction of rolling). Tensile Strength. This property decreases to a minimum at 15-20 % cold work, and then slowly increases. DURALUMIN ( Longitudinal) XU3 C _0 LU Kg.m 6 per 28 24 20 y ' K 12 \ \ /0 Tensile Strength^ Elastic Limit Elongation Resistance "**- : 10 20 30 %Co!d Work 15 <0 10 a V) c o 40 FIG. 40. Variation in Mechanical Properties (Tensile and Impact) with Cold Work. Metal previously annealed at 450 and cooled in air. Elastic Limit. This increases and, after 20 % cold work, is nearly equal to the Tensile Strength. Elongation. This decreases very rapidly, falling from 18 % to 4 % as the cold work increases from 18 % to 20 %. The value remains constant from 20 % to 40 % cold work, and finally, at 50 % cold work, becomes extremely small (less than 1 %) Shock Resistance. This falls from 3 kg. m. per sq. cm. to less than 1 kg. m. per sq. cm., while the cold work changes from to 50 %. VARIATION IN MECHANICAL PROPERTIES 91 Fig. 41 (test pieces cut transversely to direction of rolling). The same general remarks apply, but there is an inflexion in the Elongation curve. CONCLUSIONS. For sheets of thickness 10 mm. or above, cold work to the amount of 50 % seems to be the maximum possible ; further DURALUMIN Kg 36 (Transverse) per mrrr 32 20 28 Tensile / X X^^ Strength^? c 24 ^^^^^ .s* in ^ 15 *****~?2~~~' Elastic Limit rf 20 ,'" CM no s c c s O 7 s . (J 16 / 10 Q. 0^ s (/) / E Kg.m6 12 ^ per cm 2 5 V 4 8\ % Elongation 5 X 3 ... V \. 2 4" \. Shock "*** ri? '*.^ ,.'*^ 1 o ""* 10 20 30 40 5C %Cold Work FIG. 41. Variation in Mechanical Properties (Tensile and Impact) with Cold Work. Metal previously annealed at 450 and cooled in air. work beyond this point leads to a cracking of the sheets. Moreover, a stronger plant is required than that usually employed for working this alloy a point which does not arise in the working of thin sheets. (6) VARIATION OF THESE MECHANICAL PROPERTIES WITH ANNEALING TEMPERATURE. The material, upon which these tests were carried out, had been cold worked to the extent of 50 %, and test pieces were cut from it longitudinally and transversely to the direction of rolling. Up to 300 C. the metal was annealed 92 ALUMINIUM AND ITS ALLOYS in oil and from 300 to 500 C. in the nitrate-nitrite bath. Since the rate of cooling has an effect, which will be discussed later, two standard rates have been used : (i) Cooling very slowly in the furnace or liquid bath itself (100 degrees per hour maximum rate), (ii) Cooling in air. The metal was allowed to age for eight days after cooling before being tested. DURALUMIN K e g r (Longitudinal) mm? 32 20 % Elongation 28 ^~ Tensile /^ Strength/ Kg. Elastic^ ^^v^./ 1 5 100 90 80 ^ per cm? 9 8 20 Limit \ x^\ \ /% \ \ '.Elongation / 16 \! \ / CM. C 10 | % 70 I 60 Z 50 1 40 7 6 5 4 _Brjnell < woo Kg.) i > ^" // ..-- i"?i- Hardness \ 1 \ ...-"" 12 .C500/rg.> \' \ ,-~ : \ ....,<-> ^tY -#' s i -4 v \ M 1 5 CO 30 3 // w 20 2 4 y /SAocft 10 1 ^^f;^.*' Resistance n rt^"--"" 7 ... o 100 200 300 Annealing Temperature 400 500 C FIG. 42. Variation in Mechanical Properties (Tensile, Hardness, and Impact) with Annealing Temperature. Metal subjected to 50 % Cold Work, annealed, and cooled very slowly. The results are shown in Figs. 42, 43, 44, and 45. Fig. 42, Longitudinal, Rate of cooling, (i) (furnace). Fig. 43 ,, Rate of cooling, (ii) (air). Fig. 44, Transverse Rate of cooling, (i) (furnace). Fig. 45 Rate of cooling, (ii) (air). It is evident from these figures, that, whatever the rate of cooling and in whatever direction the test pieces ar$ cut, VARIATION IN MECHANICAL PROPERTIES 93 2 ui jod stioj. o ||ouug 3 ui uad suoj_ CM J-LUO jod -ui -9x 94 ALUMINIUM AND ITS ALLOYS there are two particularly interesting annealing temperatures, i.e. (1) 350-375, (2) 475-500. The following table summarises the results obtained on the longitudinal test pieces for these temperatures, after 50 % cold work : Anneal Tensile Strength Elastic Limit Shock Temperature Rate of Kg. tons Kg. tons tion Resistance Kg.m. (degrees C.) Cooling mm. 4 in. 8 mm. 2 in.* % cm. 8 350 (i) 20 12-7 6 3-81 20 6 (ii) 20 12-7 7 4-45 20 4-5 475 (i) 28 17-78 12 7-62 16 4 (ii) 32 20-32 18 11-43 18 4 DURALUMIN Kg. per (Transverse) mm. 2 32 20 c 28 o +J I Tensile. / 15 5A. --_-.. """--"^^ Strength/ LJ "^^ ^v / UJ 20 Elastic\ \ I Limit \ \ / c ^ ^-^ 'jr \ 450, 500, and 550 C. DURALUMIN 32 Kg. pp 20 mm 2 70 28 % Elongation 60 24 15 Tensile Strength 50 $o"~ ^ s. _.* D /"//?// *"""""*^'*""-.-..v.*?Z/. Ci I ..-' Hardness c: |40 | N Kg. m c P # 3 ~7 W ~~E/astic Limit Y2 ^ ^Elongation . 10 | 4 | CO ,**^"" ^. , f \ 20 : 8 \ ^X 5 Resistance 10 i 4 u o . Days 02468 Time after Quenching FIG. 47. Variation in Mechanical Properties with Time after Quenching (from 300). Figs. 47-52 (inclusive) summarise the results obtained after quenching in water at 20 C. which we will call rate of cooling (iii) the tests being carried out Immediately after quenching 48 hours 4 days ,, 5 days ,, 8 days 98 ALUMINIUM AND ITS ALLOYS Fig. 53 shows the variation of mechanical properties with quenching temperature after a uniform ageing of eight days. NOTES. (I) Influence, of Time. The effect of the interval of time after quenching is noticeable from a temperature of 300 upwards, and is particularly marked above 400. DURALUMIN 70 80 50 Kg.m H per cm 2 10 32 Kg. per 28 % Elongation 24 Tensile Strength 7000 Kg. Brinell No. 500 Kg.-...- 20 15 2 4 . v ; 6 Time after Quenching 8 Days FIG. 48. Variation in Mechanical Properties with Time after Quenching (from 350). (2) Influence of Temperature. From 200 upwards, certain molecular changes take place and Fig. 63 reveals two particularly noticeable quenching temperatures, 350 and 475, producing the following properties in the metal : Quenching from 350 Tensile Strength . . 20 kg./mm. 2 or 12-7 tons/in. 2 Elastic Limit . . 9 kg./mm. 2 or 5-61 tons/in. 2 % Elongation . .15 Shock Resistance . . 3 kg.m./cm. 2 QUENCHING 99 N CM 2--UI tied SUOJL !2 2 *> o | \ \ ^"e* \ S.^ i \ CO o *t m ct r~ CO CM LUO add LU O o o> o 00 o 1^ o (O 10 o ^- o co o CM o o * 100 ALUMINIUM AND ITS ALLOYS 2 ui tied SUOJL I ii uji K\ 8 II ll 'ill' z"! ID O :> LJ O O CD O . ^ o\ ||9uug E t CD Q.O if r QUENCHING Tensile Strength . Elastic Limit % Elongation Shock Resistance . Quenching from 475 . 40 kg. /mm. 2 or 25-4 tons /in. 2 . 20 kg. /mm. 2 or 12-7 tons /in. 2 . 20 .- 3-5kg.m./cm. 2 Remembering that quenching is nothing more than heating followed by very rapid cooling (rate iii), it is evident that, in DURALUMIN 100 90 SO 1 70 60 \ 50 . GO Kg.m P er 2 cm. 3BC IK 40 Kg per mm 36 % Elongation 32 23 24 Brinell v-.... Hardness.. """ ^""-'.'.'.' .**"" V 1 6 .....- (500 Kg} 12 // v-. / A M / v'-y--' ./x^y 8 ^//oc/f Resistance //*'' L" ----y - xo Elongation 100 200 300 400 Temperature 500 25 20 10 600C FIG. 53. Variation in Mechanical Properties with Quenching Temperature (after 8 days). this chapter and the preceding one, we have studied the variations of the worked alloy with the temperature of annea' after cold work, and with the rate of cooling following this anneal. The anneals at 350 and 475 have been pointed out as being especially interesting, whatever the rate of cooling. 1X>*2 ; : v.AIiUMINIUM AND ITS ALLOYS The following table gives a summary of the results : Anneal Tensile Strength Elastic Limit Elonga- tion % Shock Resistance Kg.m. cm.* Temperature (degrees C.) Bate of Cooling Kg. tons mm. 3 in." Kg. tons mm. 4 in. a 350 (i)(100p.h.) (ii) (air) (iii) (quenched in water) 20 12-7 20 12-7 20 12-7 6 3-81 7 4-45 9 5-61 20 20 15 6 4-5 3 475 (i)(100p.h.) (ii) (air) (iii) (quenched in water) 28 17-78 32 20-32 40 25-4 12 7-62 18 11-43 20 12-7 16 18 20 4 4 4 These two annealing temperatures correspond with a soften- ing treatment and a final treatment. The treatment which yields maximum softening consists in annealing at 350, and cooling very slowly (rate (i), furnace). The final treatment, i.e. that which gives the alloy maximum strength, consists in annealing at 475 and cooling extremely rapidly (rate (iii), quenching in water). Other methods of treatment annealing at 350 followed by more rapid cooling (rate (ii) or (iii)), or heating at 475 and cooling more slowly (rate (i) or (ii)) serve respectively to soften and harden the metal but to a less degree than the two treatments mentioned, which are, therefore, preferable. Finally, Fig. 53 shows that quenching from above 550 produces a falling off in all properties. Quenching from 550 gives the following properties : Tensile Strength . . 27 kg./mm. 2 or 17-14 tons/in. 2 Elastic Limit . . 19 kg./mm. 2 or 12-06 tons/in. 2 % Elongation . . 2 Shock Resistance . . 2-5 kg.m./cm. 2 QUENCHING OF CAST DURALUMIN. The properties of cast duralumin are as follows : Sand Cast. Tensile Strength . (average) 1 1 kg. /mm. 2 or 6-98 tons /in. 2 % Elongation . approx. zero. Shock Resistance . approx. zero. Sand Cast, after Quenching. Tensile Strength . (average) 14 kg. /mm. 2 or 8-89 tons /in. 2 % Elongation . approx. zero. Shock Resistance . approx. zero. QUENCHING Chill Cast. Tensile Strength (average) % Elongation Shock Resistance 103 10 kg. /mm. 2 or 6-35 tons /in. 2 approx. zero, approx. zero. Chill Cast, after Quenching. Tensile Strength (average) % Elongation . Shock Resistance 15 kg./mm. 2 or 9-52 tons/in. 2 approx. zero, approx. zero. It can be seen that unworked, cast duralumin is not affected by quenching. Kg. per mm. 2 r40 % Elongation 36 32, Brinell Number 120 110 100 90 80 70 60 50 40 30 20 10 Kg. m per cm? 9 20 10 o 024 6 8 10 12 14 16 18 20 22 24 2 28 SO 32 34 36 38 4O 42 44 46 413 5O Hours Time after Quenching FIG. 54. Variation in Mechanical Properties with Time after Quenching from 475 (during first 48 hours). (c) VARIATION OF MECHANICAL PROPERTIES WITH DURATION OF TIME AFTER QUENCHING. A constant temperature of quenching has been chosen, 475. Four hundred bars of duralumin and the same number of shock test pieces were treated simultaneously, i.e. heated to 475 in the nitrate-nitrite bath and quenched in water. Tensi e tests, hardness tests, and shock tests were carried out under the following conditions : 104 ALUMINIUM AND ITS ALLOYS 1st day . 6 an hour throughout the 24 hours. I 4 an hour during the first 12 hours, y ' 1 2 an hour during the second 12 hours. 3rd and 4th days . 2 an hour. 5th 6th, 7th, and I 2 2 hours . 8th days J For the following week . 2 every morning. For the next fortnight . 2 a week. These tests can be continued for a very long time on some test pieces kept in reserve. DURALUMIN 130 120 m. per cm TOO 10 c 00 I OJ I 70 r: eo .E 5 i "t CO 20 10 Kg Kg. per mm 2 40% Elongation Tensile 'Strength 23 24 ^ r\-. ^ Elastic Limit ' i'0x fc ~^- -" x Hardness Resistance Hours ~4O 50 60 TO 8*0 35~~i6o tlo 1 4o 130 lio 1^6 1^0 1 f Pay* 25 20 15.E (L o Q. 3 01^34567 Time after Quenching Fia. 55. Variation in Mechanical Properties with Time after Quenching from 475 (during first 8 days). VARIATION DURING THE FIRST EIGHT DAYS. The results of the tests during the first twenty-four hours are accurately shown in Fig. 54. Fig. 55 shows the results for the first eight days. Two distinct periods are noticeable : (a) First four days. (b) Second four days. QUENCHING 105 (a) First four days. The curves for this period are characterised by very marked oscillations, which cannot be attributed to experimental errors, and which evidently are due to notable molecular changes. (b) Second four days. During this period, the oscillations become less pronounced, and the wavy curves flatten out, tending to an equilibrium state. GENEBAL FORM OF CURVES. The following conclusions may be drawn from a considera- tion of the general form of the curves lying most evenly through the points. (1) Tensile Strength. The Tensile Strength increases in an oscillatory manner, changing from 30 kg. per sq. mm. to 38 kg. per sq. mm. (19-05 tons/in 2 to 24-13 tons/in. 2 ) in the first four days. The varia- tions during the last four days are included between the limits of 38 to 40 kg. per sq. mm. (24-13 to 25-40 tons per sq. in.). The most considerable increase occurs during the first ten hours when the value rises from 30 to 36 kg. per sq. mm. (19-06 to 22-86 tons per sq. in.). (2) Elastic Limit. This curve is of the same general form as that of the Tensile Strength, and in a similar manner increases from 10 to 23 kg. per sq. mm. (6-35 to 14-61 tons per sq. in.) in the first four days. The variations during the last four days, lie between the limits of 22 to 24 kg. per sq. mm. (13-97 to 15-24 tons per sq. in.). The greatest increase occurs during the first twenty-one hours when the value rises from 10 to 22 kg. per sq. mm. (6-35 to 13-97 tons per sq. in.). (3) Elongation. The Elongation oscillates very considerably during the first four days, but, at the end of eight days, the value is not appre- ciably altered. It varies about a mean value of 20 %. (4) Shock Resistance. The same remarks apply as for the Elongation. (5) Brinell Hardness. The curves of Hardness under a load of 1000 kg. and 500 kg. respectively are similar in form to those of Tensile Strength and Elastic Limit. 106 ALUMINIUM AND ITS ALLOYS Brinell No. (1000kg.) originally 80 after 24 hours 110 after 48 hours 100 after 8 days 100 (500 kg.) originally 61 after 24 hours 85 after 48 hours 80 after 8 days 75 The following table summarises these variations : Elastic Limit Tensile Strength Elonga- tion % Shock Resistance Kg.m. cm. 8 Ke. mm. 3 tons in. 8 Kg mm. tons in." Immediately after quenching Four days after quenching Eight days after quenching 10 22 22 6-35 13-97 13-97 30 38 38 19-05 24-13 24-13 20 22 20 4-5 3-4 3-0 VARIATIONS AFTER EIGHT DAYS. A further investigation of the variations in the properties of duralumin with the length of time after quenching can be carried out on the test pieces which were kept in reserve. The tests carried out during the first three months do not reveal any important variations other than those which have been already noted at the end of eight days. It is advisable, however, to continue these tests for a very long period, and on a very considerable number of test pieces to minimise the effect of individual experimental errors, and to give a trust- worthy value to the inferences drawn from the tests. While these systematic tests are being carried out, we have attempted to find an alloy of high strength, prepared as long ago as possible, whose original properties had been accurately determined and whose date of manufacture was definitely known. We approached the firm of Breguet, who possess samples taken from the consignments from the works on dates definitely known. Tests had been carried out at the time of manufacture on test pieces taken from the samples. It must be noted that these samples have been kept in store and there is therefore no question of the alloy having been subjected to the strain of flight. We could thus see how the alloy had behaved during storage and investigate whether any ageing had taken place, i.e. an alteration of properties. QUENCHING The following table summarises the results : 107 Properties as determined in Properties as determined in Date original tests Date final tests Type of . Sample of Original Elastic Limit Tensile Strength Elon- of Final Elastic Limit Tensile Strength Elon- test tests Kg. tons Kg. tons jaiion % Kg. tons Kg. tons fallOn % mm.* in.* mm. 1 in, 1 mm. 1 in. 1 mm. * in. * Rectangular tube 25-0 15-87 44-0 27-94 17-8 of 65/35 mm.. 1916 22 13-97 37 23-49 15 Oct. 7 23-3 14-80 42-6 27-05 11-05 thickness 0-2 mm. 1919 23-0 14-60 42-5 26-99 26-6 16-89 44-0 27-94 17-08 Rectangular tube 40 25-4 20 of 65/35 mm.. Mar. 23-5 14-92 38 24-13 15 25 15-87 40 25-4 17-3 thickness 0-25 mm 1918 25 15-87 37-5 23-81 20 25-3 16-07 37-8 24-0 20 Torpedo tube of Oct. 23-5 14-92 39 24-76 14 tt 26-6 16-89 43-5 27-62 17 82/35 mm. 1917 26-6 16-89 43-5 27-62 15-2 Bound tube of 75 mm. diam.. June 24 15-24 38 24-13 14 tt 26 16-51 41 26-03 15-2 thickness 0-2 mm. 1916 27 17-14 44-6 28-32 15-2 Bound tube of 55 mm. diam.. Oct. 23-5 14-92 38 24-13 14 M 29 18-41 41 26-03 15-2 thickness 0-2 mm. 1916 28-6 18-16 42-6 27-05 15-2 Bound tube of 40 mm. diam.. Oct. 24 15-24 38 24-13 15 m 25 15-87 41 26-03 17-5 thickness 0-1 mm. 1918 27-5 17-46 40 25-4 17-5 This table shows that all the metal of this consignment has the following properties : Elastic Limit . (231) kg. per sq. mm. ((14-6-63) tons per sq. in.) Tensile Strength. (38 1) kg. per sq. mm. ((24-13 -63) tons per sq. in.) % Elongation . 14-5 0-5 After a lapse of time varying from one to three years, the properties lie between the following limits : Elastic Limit . (26 3) kg. per sq. mm. ((16-51 1-9) tons per sq. in). Tensile Strength. (41 3) kg. per sq. mm. ((26-03 1-9) tons per sq. in). % Elongation . 15-20. With the exception of one test piece giving 1 1 -05 % Elonga- tion, an increase in the value of all the properties can be observed. These particular tests, then, do not reveal any deterioration of the metal, but, on the contrary, a slight general improvement. In order to draw a reliable conclusion, we must await the final results of the methodical experiments now in hand experi- ments in which the values of the original properties are reliable on account of the number of the tests and the particular care 108 ALUMINIUM AND ITS ALLOYS taken in carrying them out. These experiments will allow us to find out definitely whether there is any gradual improvement in the properties. VARIATION or THE TIME REQUIRED TO REACH EQUILIBRIUM, WITH THE TEMPERATURE AFTER QUENCHING. The preceding tests constitute an investigation of the time required to reach Equilibrium after quenching, in which the changes after quenching have been allowed to take place at the normal temperature. The effect of the temperature after quenching on the attainment of Equilibrium has been investi- gated by means of supplementary experiments. The following temperatures were employed : - 20 C. 0C. + 20 C. + 100C. 150 200 250 300 350 Immediately after quenching, test pieces were maintained at each of these temperatures for 1, 2, 3, 4, 5, and 6 hours respectively, i.e. some at 20, others at 0, other at +20, etc. Tensile tests were carried out after each of these periods of time, after warming up or cooling to air temperature. The results can be summarised as follows : Temperature 20 After six hours there is no change in properties. ,, No change after six hours. ,, +20 After six hours the Tensile Strength has increased by 4 kg. per sq. mm. (2-54 tons per sq. in.) to the value 34 kg. per sq. mm. (21-6 tons per sq. in.). ,, 100 After six hours the Tensile Strength has increased by 8 kg. per sq. mm. (5-08 tons per sq. in.) and become 38 kg. per sq. mm. (24-13 tons per sq. in.). All the properties have attained their mean normal values. QUENCHING 109 Temperature 150 All the properties have attained their mean normal values after two hours. 200 The process is simply an anneal and and above the rate of cooling has a pronounced effect. The results obtained are strictly con- cordant with those drawn dia- grammatically in Fig. 57 (variation of mechanical properties with tem- perature of reanneal after quenching from 475). From these tests the following conclusions may be drawn : Changes after quenching are retarded by low temperature. They become more rapid as the temperature immediately after quenching is raised between the limits of and 150, temperatures above 150 causing, after similar cooling to air temperature, changes in the properties. If the alloy be im- mersed in boiling water, for example a very practical pro- cedure Equilibrium is reached much more rapidly. Immediately after quenching. Tensile Strength =30 kg. per sq. mm. (19-05 tons per sq. in.) Elastic Limit = 10 kg. per sq. mm. (6-35 tons per sq. in.) % Elongation =18 After immersion in boiling water for one hour after quenching. Tensile Strength =35-5 kg. per sq. mm. (22-54 tons per sq. in.) Elastic Limit =17-5 kg. per sq. mm. (1 1-10 tons per sq. in.) % Elongation =20 After immersion in boiling water for two hours after quenching. Tensile Strength =37 kg. per sq. mm. (23-49 tons per sq. in.) Elastic Limit = 18-5 kg. per sq. mm. (5-40 tons per sq. in.) % Elongation =20 After six hours under these conditions. Tensile Strength =37 kg. per sq. mm. (23-49 tons per sq. in.) Elastic Limit =20 kg. per sq. mm. (12-7 tons per sq. in.) % Elongation =20 Values which remain approximately un- changed after further immersion in boiling water. Thus, by immersion in boiling water after quenching, Equilibrium is reached more rapidly an effect which is of interest from the industrial point of view. CHAPTER III VARIATION OF MECHANICAL PROPERTIES WITH THE TEMPERATURES OF REANNEAL AFTER QUENCHING THE metal, in every case quenched from 47 5 , was reannealed at a series of temperatures every fifty degrees from the normal up to 500 and cooled. The three rates of cooling already defined were employed : rate (i), cooling very slowly in the bath ; rate (ii), cooling in air ; rate (iii), cooling by quenching in water. Kg per* mm 2 DURALUMIN 25 100 200 300 400 500 Annealing Temperature FIG. 56. Variation in Mechanical Properties with Annealing Tempera- ture. Metal quenched from 475, reannealed, and cooled very slowly. 110 VARIATION IN MECHANICAL PROPERTIES 111 The results for the three rates of cooling are shown in Figs. 56, 57, and 58 respectively. All the properties show a minimum at a temperature which varies with the rate of cooling as shown in the following table : E ate of Cooling Temperature of Minimum Values corresponding with the minimum Tensile Strength Elastic Limit Elonga- tion % Shock Resistance Kg. in. cm.* Kg. tons mm.* in.* Kg. tons mm.* in.* (i) (") (iii) 330-360 290-320 275-300 20 12-7 25 15-87 24 15-24 7 4-4 11 6-98 9 5-71 14 14 14 4-5 5 5 These minima do not afford any particular interest. DURALUMIN Kg. per 140 130 120 no 100V) GO 505 40 30J3 202 10 1 2.4jf/asf/c Limit " *"-^ 23 20 (1000'KgT / : \ .6.. Hardness GOO Kg j --..... ion .Shock Resistance \\\ \\ \\ 100 200 25 20 15 c* c s. etl :r TOO 10 808 70 7 O .E 50 5 . 00 404 303 202 10 1 Hardness ; 16 (SOOKg -^Elongation \\ \ V\ \ -... " 12 12 Shoch Resistance 20 TOO 200 300 400 Annealing Temperature 500C Fio. 58. Variation in Mechanical Properties with Annealing Tern- perature. Metal quenched from 475, reannealed, and quenched in water. This is a softening treatment, giving values approximately equal to those produced by the softening process previously described but entailing a more complicated method of working. VARIATION IN MECHANICAL PROPERTIES 113 Fig. 57. Quenching from 475, reannealing, followed by cooling in air (rate (ii)). No particular advantage. Fig. 58. Quenching from 475, reannealing and quenching in water (rate (iii)). The most interesting values are those corresponding with the range of annealing temperatures 475-500. This is simply a process of double quenching and gives the alloy the following properties : Tensile Strength =40 kg. per sq. mm. (25-4 tons per sq. in.) Elastic Limit =23 kg. per sq. mm. (14-6 tons per sq. in.) % Elongation =22 Shock Resistance=5 kg. m. per sq. cm. It is clear from these values that a double quenching is superior to a single one. Two quenchings improve the Elastic Limit, the Elongation, and the*Shock Resistance, and should therefore be employed if the maximum values of these proper- ties are required in the finished metal. CONCLUSION. From the practical point of view, this type of light alloy can be subjected, after cold work, to three treatments : (1) Annealed at 350 and cooled very slowly (rate (i)), giving the most suitable intermediate state from the point of view of further mechanical work. This is the softening process. (2) Annealed at 475 and quenched, yielding the hardened or final state. (3) Annealed at 475, quenched, reannealed at 475-500, and quenched again. This process double quenching yields the optimum final state. CHAPTER IV RESULTS OF CUPPING TESTS AFTER VARYING THERMAL TREATMENT THE experimental methods were the same as those described already for the cupping tests on aluminium (page 41). The circles to be tested were taken from sheets, 2 mm. thick, having been cold worked to the extent of 40 %. DURALUMIN (Cupping Tests) C 7 O a 10 ests t 50 45 40 35 30 c c. 25 o 20 H 15 Z/7C0 10 400 500 600 700 800 900C Quenching Temperature FIG. 76. Variation in Mechanical Properties (Tensile and Impact) with Quenching Temperature. Forged Aluminium Bronze, Type II (Cu 89 %, Mn 1 %, Al 10 %). (1) Reanneal after Quenching from 800. The results are summarised in Fig. 77. The anneal which produces the best Tensile Strength and Elastic Limit is one at about 400, when the values are : Tensile Strength =70 kg. per sq. mm. (44-45 tons per sq. in.) Elastic Limit 28 kg. per sq. mm. (17-78 tons per sq. in.) % Elongation =14 Shock Resistance = 3 kg. m. per sq. cm. On the other hand, the anneal producing the best Elongation and Shock Resistance is one at 750, when the values are : Tensile Strength = 54 kg. per sq. mm. (34-29 tons per sq. in.) Elastic Limit =22 kg. per sq. mm. (13-97 tons per sq. in.) % Elongation =38 Shock Resistance=14 kg. m. per sq. cm. MECHANICAL PROPERTIES 135 100 200 300 400 500 600 700 800 900C Annealing Temperature FIG. 77. Variation in Mechanical Properties (Tensile and Impact) with Temperature of Reanneal after Quenching from 800. Forged Aluminium Bronze, Type II (Cu 89 %, Mn 1 %, Al 10%). 80y 100 200 300 400 500 600 700 800 900 C Annealing Temperature Fio. 78. Variation in Mechanical Properties (Tensile and Impact) with Temperature of Reanneal after Quenching from 900. Forged Aluminium Bronze, Type II (Cu 89 %, Mn 1 %, Al 10 %). 136 ALUMINIUM AND ITS ALLOYS (2) Reanneal after Quenching from 900. The results are summarised in Fig. 78. The best Tensile Strength and Elastic Limit are produced by an anneal at about 350, which does not cause any important changes in the alloy. 100 200 300 400 500 Temperature 600 700 800 C FIG. 786. High-temperature Hardness Tests (500 Kg.) on Aluminium Bronze, Type II, Quenched from 900, Reannealed at 600. The best Elongation and Shock Resistance are produced by an anneal at about 750, when the values are : Tensile Strength = 54 kg. per sq. mm. (34-29 tons per sq. in.) Elastic Limit =20 kg. per sq. mm. (12-7 tons per sq. in.) % Elongation =45 Shock Resistance=14 kg. m. per sq. cm. This cupro-aluminium, containing 1 % manganese, acquires, as a result of this treatment, very remarkable properties. The Tensile Strength and Elastic Limit, approaching those of the tempered steels, are surpassed in importance by the great Elongation and unusual Shock Resistance. CONCLUSION. The optimum thermal treatment for cupro-aluminium con- taining 1 % of manganese, i.e. Type II, is as follows : quenching from 900, followed by reannealing at 750. MECHANICAL PROPERTIES 137 (/) HARDNESS AT HIGH TEMPERATURES. The hardness tests at high temperatures were carried out under the same conditions as for Type I, and the results are shown in Fig. 786. They were carried out only on the heat-treated alloy (quenched from 900 and reannealed at 600). They reveal a greater hardness than that of Type I for all temperatures between and 500, but a slightly lower hard- ness for temperatures above 500. 010 100 200 300 400 500 600 7QO . FIQ, 79. Aluminium Bronze, Type III (Dilatometer). III. TYPE in 81 % Copper, 11 % Aluminium, 4 % Nickel, 4 % Iron (a) CHEMICAL ANALYSIS. Copper Aluminium Manganese Iron Nickel Lead Tin . Difference 80-95 10-60 0-45 4-40 3-55 nil nil 0-05 100-00 (6) INVESTIGATION OF THE CRITICAL POINTS. Neither the expansion curve nor the curve of temperature plotted against time indicates the slightest transformation (see Figs. 79 and 80). 138 ALUMINIUM AND ITS ALLOYS ,*ui SUOJL s. VAVJV/ r-'-vT".'- W^>su. iM' !l^ ? ?^^^^7?S^K^J^ PHOTOGRAPH 38. CUPRO-ALUMINIUM. A3 FORGED. X60. PHOTOGRAPH 39. CUPRO-ALUMINIUM. As FORGED. X225. PHOTOGRAPH 40. CUPBO-AUTMXNIUH. FORGED AND SUBSEQUENTLY ANNEALED AT 800. X60. PHOTOGRAPH 41. CUPRO-ALUMINIUM. FORGED AND SUBSEQUENTLY ANNEALED AT 800 X225. To face page 1-44 PLATE XII. TYPE II. QUENCHED AND REANNEALED. PHOTOGRAPH 42. CUPRO-ALTJMINITJM. QlJEXCHED FROM 900 REAXNEALED AT 600. X60. rv^r v ^ \,f< ^?T ^>-.^i/^V_. ^, fe-^ ' , .^^ PHOTOGRAPH 43. CUPRO-ALUMINIUM. QUENCHED FROM 900, REA3JNEALED AT 600. X 225. To face page 144 PLATE XIII. TYPE III. FORGED AND ANNEALED. PHOTOGRAPH 44. CUPRO- ALUMINIUM. As FORGED. X60. PHOTOGRAPH 45. CUPRO- ALUMINIUM. As FORGED. X225. PHOTOGRAPH 46. CUPRO -ALUMINIUM. FORGED AND ANNEALED AT 600. X60. PHOTOGRAPH 47. CUPRO-ALUMINIUM. FORGED AND ANNEALED AT 600. X225. To face page 144. PLATE XIV. TYPE III. FORGED AND ANNEALED. PHOTOGRAPH 48. CUPRO-ALUMINIUM. FORGED AND ANNEALED AT 800. x60. PHOTOGRAPH 49. CUPRO-ALUMINIUM. FORGED AND ANNEALED AT 900. x225. TV. faon r.a 111 PLATE XV. "".J-'V:* TYPE III. FORGED AXD QUENCHED. PHOTOGRAPH 50. CUPRO- ALUMINIUM. QUENCHED FROM 500. X60. PHOTOGRAPH 51. CUPRO- ALUMINIUM. QUENCHED FROM 50( X225. PHOTOGRAPH 52. CL-PRO- ALUMINIUM. QUENCHED FROM 800. X60. PHOTOGRAPH 53. CUPRO -ALUMINIUM. QUENCHED FROM 8(K X225. To face page 144. PLATE XVI. **- , TYPE III. FORGED AND QUENCHED. PHOTOGRAPH 54. CUPRO-ALUMINITJM. QUENCHED FROM 900 C X60. PHOTOGRAPH 55. CUPRO-ALUMINIUM. QUENCHED FROM 900. X225. To face page 144. PLATE XVII. TYPE III. QUENCHED AND REANXEALED." PHOTOGRAPH 56. CCPRO-ALUMINIUM. QUENCHED FROM 900' REANNEALED AT 500. X60. PHOTOGRAPH 57. CIJPRO- ALUMINIUM. QUENCHED FROM 900, REANNEALED AT 500. X225. PHOTOGRAPH 58. PHOTOGRAPH 59. CPRO-AO-.MINirM. Q( EXCHED FROM 900, CUPRO-ALUMINIUM. QUENCHED FROM 900 REANNEALED AT 600. REANNEALED AT 600 i 2 mm. thick. Bars > 16 mm. in diameter and<36 mm. in diameter. Tensile Strength : 36 kg. per sq. mm. (22-8 tons/in. 2 ) Elastic Limit : 20 kg. per sq. mm. (12-7 tons /in. 2 ). For bars>36 mm. in diameter : Tensile Strength : 33 kg. per sq. mm. (20-9 tons/in. 2 ) Elastic Limit : 19 kg. per sq. mm. (12-1 tons /in. 2 ) % Elongation : 13 %. Class (6). Sections < 2 mm. thick. Bars (specified Drawn) of any diameter and bars < 16 mm. in diameter. Tensile Strength : 38 kg. per sq. mm. (24-1 tons per sq. in.) Elastic Limit : 22 kg. per sq. mm. (14-0 tons per sq. in.) % Elongation : 16 %, or 14 % in the case of bars and sections so thin that straightening is necessary. CUPPING TESTS. Cupping tests are required for pure aluminium, sheet and strip. The prescribed method is that described on page 41 , and the * The Cahiers des Charges Unifies Franais specify a minimum Tensile Strength of 36 kg./mm. (22-8 tons /in 8 .). 154 ALUMINIUM AND ITS ALLOYS following minimum depth of impression at rupture should be obtained : Thickness . . 0-5 mm. 1-0 mm. 1-5 mm. 2-0 mm. 020 in. -039 in. -059 in. -079 in. Depth of impression . llmm. 13mm. 14mm. 15mm. Cold Bending Tests are prescribed for light alloy sheet and strip, and the following method should be adopted wherever possible : The test is carried out at ordinary temperatures, and in a special machine giving a gradually increasing pressure, without shock. The bend is formed in two operations. First Operation. The test piece, which should be 100 mm.X 20 mm. if possible, is placed on a V-shaped block, whose surfaces are inclined to each other at an angle of 60 ; the opening should be 125 mm. at least. A wedge (whose edge should be rounded off with a radius at least equal to that which the bend should have at the completion of the test) is applied to the middle of the test piece, and depressed mechanically until the test piece is in contact with the faces of the V. Second Operation. Using a spacer, the test piece should be bent slowly, by mechanical means, into the form of the letter U. No cracks should appear. The distance between the two interior surfaces of the arms of the U is specified in the following table : Thickness* Longitudinal. Transverse. Less than 1-5 mm. (-059 in.) SJxthickness 4xthickness =or>l-5mm. (-059in.) 4 xthickness Sxthickness Drifting Tests. Prescribed for light alloy tubes. A conical, hardened steel mandrel, having an angle of 45, is forced axially into a short length of tube until the first split appears. This should not occur until the diameter has increased by 11 %.| Crushing Tests. Prescribed for light alloy tubes. A short length of tube is flattened by means of a hammer moving in a direction parallel to the principal axis. The tube is supported on a piece of steel to avoid localisation of stress. No fissure should appear until the reduction in length of the principal axis of the tube has reached or exceeded 40 %. * The Cahiers des Charges Unifies Frangais specify the following dis- tances : Thickness. Longitudinal. Transverse. < 1 -5 mm. 4-5 x thickness 5 X thickness = or> 1 -5 mm. 5-5 X thickness 6 X thickness f Cahiers Unifies Franais specify 9 %. APPENDIX III LAB OR AT GERE D'ESSAIS MECANIQUES, PHYSIQUES, CHIMIQUES ET DE MACHINES. 292 Rue Saint Martin, Paris. REPUBLIQUE FRANC AISE. Ministere du Commerce, de Tin* dustrie, des Postes et des Tele- graphes. Conservatoire des Arts et Metiers. Paris, Feb. 5th, 1919. Report of Test No. 13456 on the requisition of Major Grard, technical inspector of metallurgical aviation materials, Paris. Registered, Jan. 18th, 1919. Object. Tensile and Shock tests at a temperature of 15 on test pieces of sheet aluminium possessing various degrees of cold work. RESULTS. Dimensions of test pieces. (a) Tensile Test Pieces. (Length ; . . 100mm. Between shoulders -/Breadth . * . 15mm. (Thickness . . , { 10 mm. Approximate area of cross section . . 150 sq. mm. (accurately measured for each test piece) Gauge length = ^66-678 . .'* . = 100mm. (b) Shock Test Pieces. Bars : 55x10x10 mm. with a 2-mm. round notch. Apparatus : 30 kg. m. Charpy pendulum. 155 156 ALUMINIUM AND ITS ALLOYS xxxxxxxxxxxx XXXXXXXXXXXX cocpcoocpocococococpco cbobcbcccbcbGbGbi>GQGbGb coGOGocoGococococoooGOGo CO CO CO CO CO CO CO CO CO CO CO CO OOOOOOOOOOOO Or-H 1OOOOOOOOOOOO J CO CO CO CO CO CO CO CO CO CO CO CO OOOOOOOOOOOO CiO5GOO5GOOOOOO5O5C5O5O5 0*010*010*0000*010*0 CDt>-COlOt-O5! IrHi (OCCOO eococoiocoeoeoeococoeoco 00 GO CO GO GO GO O Oi t** O5 OS O C5O5O5OJOiO5GOGOGOGOGOGO COCOrt~ i r~ ' -,c cc c-i i> i rr^ri^rtccM^ccecso 1 obooccocsosoocics x r: o ^ ri * o r< 5v| CO CC CO CC CC CO CO C5O Oi i(MC5-^OCOt-QOOSO ooooooooooo 3 APPENDIX IV LABORATOIBE D'ESSAIS REPUBLIQUE FRANQAISE. MECANIQUES, PHYSIQUES, Ministere du Commerce, de Tin CHIMIQUES ET DE MACHINES. dustrie, des Postes et des Tele- graphes. Conservatoire des Arts et Metiers. Paris, Jan. 2th, 1919. Report, No. 7, of Test No. 13357 on the requisition of Major Grard, technical inspector of metallurgical aviation materials, Paris. Registered, Nov. 27th, 1918. Object. Tensile tests on test pieces of sheet aluminium after thermal treatment. NATURE OF SAMPLES SUBMITTED. Two series of tensile test pieces in sheet aluminium : (1) 0-5 mm. thick marked 5. (2) 2-0 mm. thick marked 20. Each of these series consists of metal having three degrees of cold work, namely : rt n/ , , ^ J 50 % marked B. 100 % marked C. 300 % marked D. Metal of each of the above thicknesses and degrees of cold work has been annealed under the following conditions : All the test pieces requiring the same anneal were pierced with a hole at one end and threaded on to the same piece of wire, 6-8 mm. apart, so as to be immersed simultaneously in the annealing bath, which was continuously stirred. Sheets 40 mm. square and circles 90 mm. in diameter, for micro- graphic examination and cupping tests respectively, were subjected to the same anneal at the same time as the tensile test pieces. RESULTS. Dimensions of Test Pieces. Between shoulders I *f "^J 1 , ' ' mm ' { Breadth . . 20 mm. Approximate area of cross section : * (1) Test pieces 0-5 mm. thick . . 10 sq. mm. (2) Test pieces 2-0 mm. thick . . 40 sq. mm. Gauge length =<\/Gfr~61S : (1) Test pieces 0-5 mm. thick gauge length =30 mm. (2) Test pieces 2*0 mm. thick gauge length =50 mm. * In each case the breadth and thickness were measured to the nearest 01 mm., and the exact cross section calculated from these figures. 158 APPENDICES 159 *! UhfttHC.) p IQ o co cb eo o o o -i (N ) CO O O _ Temperature (degrees C.) Duration (minutes) Marks Kg tons mm* in* Kg tons mm* in* tion % J\C* marks B7 5-5 3-49 11-2 7-11 35-0 . B8 3-9 2-48 10-8 6-86 31-7 C7 4-1 2-60 12-5 7-94 33-4 (2) C8 4-3 2-73 12-1 7-68 40-0 D7 4-4 2-79 11-8 7-49 36-6 D8 3-8 2-41 12-0 7-62 36-0 398 1 ,B7 3-4 2-16 9-8 6-22 38-6 I B8 3-6 2-29 9-9 6-29 38-0 on)C7 3-5 2-22 10-2 6-48 37-4 20 C8 3-0 1-90 10-2 6-48 44-0 (D7 31 1-97 10-6 6-73 40-0 V D8 3-4 2-16 10-6 6-73 37-0 B9 5-2 3-30 10-1 6-41 34-4 (BIO 43 2-73 10-9 6-92 33-3 *J C9 54 343 11-2 7-11 36-4 icio 5-2 3-30 11-8 7-49 36-7 D9 4-0 2-54 11-6 7-37 35-0 V D10 4-7 2-98 11-7 7-43 38-4 403 3 B9 31 1-97 9-7 6-16 38-6 BIO 3-0 1-90 9-7 6-16 36-8 9ft C9 3-0 1-90 10-4 6-60 40-4 /U CIO 2-6 1-65 10-4 6-60 38-4 D9 34 2-16 10-8 6-86 38-0 X D10 36 2-29 10-8 6-86 364 Bll 5-1 324 11-5 7-30 36-0 B12 4-8 3-05 114 7-24 333 Cll 49 3-11 11-7 7-43 34-0 C12 53 337 12-2 7-75 38-4 Dll 34 2-16 11-4 7-24 38-4 D12 3-6 2-29 11-5 7-30 37-0 393 5 Bll 31 1-97 9-6 6-10 39-0 B12 2-9 1-84 9-7 6-16 39-0 9ft Cll 3-4 2-16 10-6 6-73 39-4 4() C12 4-2 2-67 10-8 6-86 41-0 Dll 3-6 2-29 10-7 6-79 36-0 D12 3-8 2-41 10-8 6-86 36-4 X B13 3-9 2-48 11-6 7-37 333 [ B14 33 2-10 11-5 730 32-6 )C13 4-2 2-67 11-8 7-49 36-8 5 )C14 3-4 2-16 11-7 7-43 36-8 [D13 32 2-03 11-1 7-05 384 V D14 3-8 2-41 11-2 7-11 36-8 549 0-5 B13 2-8 1-78 9-9 6-29 39-6 B14 3-1 1-97 10-2 6-48 38-0 9ft C13 3-2 2-03 11-1 7-05 37-8 Z\J C14 3-6 2-29 10-8 6-86 34-0 D13 31 1-97 10-9 6-92 39-6 D14 33 2-10 10-9 6-92 37-0 162 ALUMINIUM AND ITS ALLOYS A. PRELIMINARY TESTS continued Am Temperature (degrees C.) leal Duration (minutes) Marks Apparent Elastic Limit Kg tons Tensile Strength Kg tons Elonga- tion % Re- marks mm 3 in 2 mm* in 2 .B15 4-2 2-67 11-2 7-11 34-4 [B16 4-1 2-60 11-0 6-98 34-4 6 \C15 4-8 3-05 11-7 743 35-0 5 C16 3-8 2-41 12-3 7-81 31-7 f D15 3-7 2-35 12-0 7-62 34-4 550 1 \D16 ,B15 5-0 3-17 2-9 1-84 11-6 7-34 10-2 6-48 35-0 38-6 (BIG 2-8 1-78 10-0 6-35 36-0 20 )ci5 3-3 2-10 11-0 6-98 32-0 ^ U )C16 3-4 2-16 11-3 7-18 36-0 f D15 3-2 2-03 10-9 6-92 39-0 V D16 31 1-97 10-8 6-86 356 B17 5-0 3-17 11-8 7-49 33-3 [B18 4-8 3-05 12-2 7-75 32-7 5 )C17 5-0 3-17 13-2 8-38 33-3 5 )C18 4-7 2-98 11-9 6-56 30-0 f D17 4-4 2-79 11-5 7-30 35-0 551 2 V D18 4-4 2-79 11-8 7-49 37-4 B17 2-9 1-84 10-1 6-41 35-6 B18 2-6 1-65 9-9 6-29 36-6 20 C17 2-8 1-78 11-3 7-18 35-6 ZU C18 3-2 2-03 11-2 7-11 35-0 D17 3-3 2-10 11-0 6-98 36-0 D18 3-4 2-16 11-0 6-98 41-6 B. FINAL EXPERIMENTS Am Temperature (degrees C.) ical Duration (minutes) Marks Apparent Elastic Limit Kg tons mm 8 in* Tensile Strength Kg tons mm 2 in* Elonga- tion % Be- marks B64 13-4 8-51 13-9 8-83 6-7 B65 13-1 8-32 14-5 9-21 9-7 B66 13-3 8-45 14-6 9-27 12-7 C64 14-3 9-08 15-1 9-59 11-7 5 C65 14-4 9-14 15-4 9-78 12-3 C66 13-8 8-76 15-4 9-78 10-0 (1) D64 17-3 10-99 17-3 10-99 33 (1) D65 17-0 10-79 17-0 10-79 6-0 Zero metal unannealed D66 /B64 B65 17-8 11-30 11-5 7-30 11-4 7-24 17-8 11-30 12-0 7-62 12-2 7-75 6-3 10-0 11-0 B66 11-4 7-24 12-4 7-87 10-6 C64 13-1 8-32 13-7 8-70 14-4 20^ C65 12-8 8-13 13-8 8-76 11-2 C66 13-0 8-25 13-4 8-51 11-6 D64 15-8 10-03 16-3 10-35 7-0 D65 15-9 10-10 16-6 10-54 8-0 D66 15-5 9-84 17-2 10-92 6-6 APPENDICES B. FINAL EXPERIMENTS continued 163 Apparent Tensile Anneal Elastic Limit Strength Elonga- T? Q Temperature (degrees C.) Duration (minutes) Marks Kg tona mm* In* Kg tona mm* in* tion % Jtv6" marks rB31 12-9 8-19 14-0 8-89 12-7 B32 13-8 8-76 13-8 8-76 130 B33 13-1 832 15-4 9-78 133 C31 14-8 9-40 14-8 9-40 11-7 5- C32 14-5 9-21 15-0 9-52 10-0 C33 14-2 9-02 14-6 9-27 8-3 (1) D31 17-1 10-87 17-6 11-18 6-0 D32 15-4 9-78 15-4 9-78 33 ID33 16-9 10-73 17-3 10-99 5-0 (1) 103 5 fB31 11-5 7-30 12-0 7-62 13-6 B32 11-1 7-05 12-0 7-62 14-0 B33 11-1 7-05 12-0 7-62 12-0 C31 12-1 7-68 13-5 8-57 14-6 20- C32 12-4 7-87 13-7 8-70 10-0 (1) C33 12-4 7-87 13-6 8-64 13-0 D31 14-9 9-46 16-0 10-16 7-6 (1) D32 13-9 8-83 15-8 10-03 6-0 (1) D33 13-7 8-70 16-0 10-16 6-0 (1) fB34 12-1 7-68 13-4 8-51 133 B35 13-8 8-76 13-6 8-64 15-0 B36 13-0 8-25 13-48 8-56 15-0 C34 10-4 6-60 14-7 9-33 10-0 5- C35 13-5 8-57 14-6 9-27 10-0 C36 12-9 8-19 14-9 9-46 63 (1) D34 12-5 7-94 16-13 10-24 33 (1) D35 13-9 8-83 14-5 9-21 33 (1) 160 5 ID36 'B34 12-3 7-81 10-6 6-73 14-9 9-46 12-1 7-68 33 13-6 (1) B35 10-9 6-92 12-4 7-87 14-0 B36 10-6 6-73 12-0 7-62 13-6 C34 12-1 7-68 13-0 8-25 U-0 20 - C35 11-7 7-43 13-1 8-32 15-0 C36 11-5 7-30 133 845 12-0 D34 12-9 8-19 15-4 9-78 8-2 D35 14-0 8-89 15-6 9-91 6-2 (1) .D36 13-2 8-38 15-5 9-84 7-4 fB37 12-0 7-62 12-2 7-75 153 B38 11-5 7-30 13-2 8-38 16-6 B39 11-8 7-49 13-2 8-38 10-4 (1) C37 13-0 8-25 14-4 9-14 10-0 (1) 5. C38 13-4 8-51 15-2 9-65 15-0 (1) C39 13-4 8-51 14-1 8-95 7-7 D37 13-7 8-70 16-5 10-48 6-7 (1) D38 14-2 9-02 17-6 11-18 73 199 5 D39 13-5 8-57 17-0 10-79 5-0 (1) rB37 9-6 6-10 11-5 730 16-2 B38 10-3 6-54 12-0 7-62 16-0 B39 10-0 6-35 11-6 737 16-2 C37 12-0 7-62 13-0 8-25 18-0 20- C38 12-0 7-62 13-2 8-38 16-4 C39 11-0 6-98 12-8 8-13 17-6 D37 13-8 8-76 15-4 9-78 10-0 D38 13-2 8-38 15-3 9-72 8-0 iD39 13-9 8-83 15-3 9-72 9-0 164 ALUMINIUM AND ITS ALLOYS B. FINAL EXPERIMENTS continued Anneal Apparent Elastic Limit Tensile Strength Elonga- Re- Temperature (degrees C.) 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