EFFECT of COPPER ADDITIONS on DEFORMATION PROCESSING of ALUMINIUM ALLOYS by RICHARD PAUL VIEROD, B.Sc (ENG), A.R.S.M. a Thesis S
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EFFECT OF COPPER ADDITIONS ON DEFORMATION PROCESSING OF ALUMINIUM ALLOYS BY RICHARD PAUL VIEROD, B.Sc (ENG), A.R.S.M. A Thesis submitted for the Degree of Doctor of Philosophy of the University of London John Percy Research Group Department of Metallurgy and Material Science Royal School of Mines Imperial College London, SW7 2BP May 1983 1 * ABSTRACT The effect of an increase in copper content from 1 wt% Cu to 5 wt% Cu on the hot working characteristics of a 2000 series alloy based on AA2014 have been investigated, as well as a binary 4 wt% Cu alloy. The torque twist data generated from the hot torsion tests has been analysed using a * graphical and mathematical minimisation technique, the temperature during testing being allowed for in the latter technique. The development of a strain dependent constitutive equation used in the temperature- rise model has been investigated. k The dependence of the direct extrusion peak pressure and peak height on extrusion ratio, billet temperature and Zp the temperature compensated strain rate has been investigated in the 2000 series alloys and for direct and indirect extrusion of the 2014 alloy. The effect of container temperature and billet length on the peak pressure has also been investigated. The development of a general f pressure equation applicable over a wide range of extrusion conditions and to a complete alloy system is investigated in the 2000 series alloys and a non heat treatable 5052 alloy. A solution preheat treatment determined from hot torsion tests has been used on the 2014 alloy to investigate whether surface cracking can be reduced during direct extrusion. > The structures in the 2000 series alloys have been investigated at all stages of processing from the as cast to the steady state quenched extrusion and torsion specimens using optical and transmission electron microscopy. The effect of process conditions on the hot worked substructure and the variation of structure within the direct and I indirect deformation zones and across and along the extrudes has been investigated. The effects of direct and indirect extrusion, and the solution soak treatment on the structures of the solution treated (T6) and press quenched and aged (T5) 2014 alloy have been investigated. The mechanical properties of the Tl, T6 and T5 2014 ^ alloy have been evaluated using hardness, tensile, fracture toughness and stress corrosion cracking tests. The effect of Cu content on the Tl and T6 tensile properties has also been established. Limit diagrams for ±11 the alloys and extrusion modes are presented. i 2 CONTENTS Page ABSTRACT 1 CONTENTS 2 LIST OF PLATES 6 LIST OF TABLES 7 LIST OF FIGURES 10 INTRODUCTION 16 CHAPTER 1 LITERATURE SURVEY 1.0 Introduction 18 1.1 Commercial Aluminium - Copper - Magnesium 18 System 1.2 Effect of Alloying Elements 19 1.3 Heat Treatments Applied to the Al-Cu System 21 1.3.1 Ageing Mechanism 21 1.3.2 The Effects of Ageing and Second Phase 24 Particles on the Room Temperature Properties 1.4 Hot Working 26 1.4.1 Empirical Relationships 27 1.4.2 Structural Aspects of Hot Working 30 1.4.3 Restoration Processes 30 1.5 Substructure Strengthening 33 CHAPTER 2 THEORY 2.1 Introduction 37 2.2 Torsion Analysis 37 2.2.1 Temperature Rise During Torsion Testing 37 2.2.2 Evaluation of the Hot Working Constants 42 2.2.2.1 Mathematical Minimisation 42 2.2.2.2 Graphical Analysis 43 2.3 Extrusion Analysis 48 2.3.1 Temperature Rise at Peak Load 48 2.3.2 Temperature Rise During Extrusion 49 2.3.3 Strain Rate Evaluation 50 2.3.4 Evaluation of the Billet Container 50 Friction CHAPTER 3 EXPERIMENTAL 3.1 Introduction 53 3-2 The Extrusion Press 53 3.2.1 Container Heating 54 Page 3.2.2 Billet Preheat 54 3.2.3 Extrusion Data Recording 56 3.2.4 Direct Extrusion Tooling 57 3.2.5 Indirect Extrusion Tooling 58 3.2.6 Water Quench 59 3.2.7 Experimental Procedure 59 3.2.8 Direct Extrusion 59 3.2.9 Indirect Extrusion 60 3.3 Materials 61 3.4 Partially Extruded Billets 63 3.5 Heat Treatment of Extrudes 63 3.6 Examination of Extrudes 64 3.6.1 Hardness Tests 64 3.6.2 Tensile Tests 65 3.6.3 Fracture Tests 65 3.6.4 Optical Microscopy 66 3.6.5 Electron Microscopy 66 3.6.6 Surface Quality 67 3.6.7 Stress Corrosion Testing 67 3.7 Torsion Tests 68 CHAPTER 4 RESULTS AND DISCUSSION 4.1 Torsion Data Analysis 71 4.1.1 Torque Twist Curves 71 4.1.2 Temperature Rise During Testing 73 4.1.3 Flow Stress Characteristics 78 4.1.3.1 Graphical Analysis 80 4.1.3.2 Mathematical Minimisation 86 4.1.4 Strain Dependency of the Hot Working 99 Characteristics 4.1.5 Torsion Ductility 107 4.2 Extrusion Data Analysis 111 4.2.1 Extrusion Parameter Measurement 111 4.2.2 Load Displacement Curves 112 4.2.3 Variation of Peak Pressure With Extrusion 115 Ratio 4.2.4 Variation of Peak Pressure With Initial 117 Billet Temperature 4.2.5 Effect of Container Temperature on the 121 Peak Pressure 4.2.6 Evaluation of the Friction Conditions 126 4.2.7 The Variation in Peak Pressure with Zp 132 4.2.8 The Variation ofAP with Zp 137 4.2.9 General Pressure Equation 140 4.2.10 Extrude Surf•-e Condition 153 4.2.10.1 Evaluation of the Presolution Soak Flow 155 Stress and Extrusion Characteristics 4.2.10.2 Evaluation of the Surface Condition 164 4 Page 4.3 Structural Investigation 170 4.3.1 Introduction 170 4.3.2 As Cast Structure 170 4.3 ^3 Homogenised Structure 173 4.3.4 Extrusion Structures 174 4.3.5 The Variation in Steady State Substructures 178 in Extrusion and Torsion 4.3.5.1 Extrude Substructures 178 4.3.5.2 Torsion Substructures 181 4.3.5.3 The Effect of Process Conditions on the 183 Steady State Substructure 4.3.6 Material Flow During Steady State Extrusion 196 4.3.6.1 Flow Characteristics During Steady State 196 Direct and Indirect Extrusion 4.3.6.2 Substructural Variations Within the 198 Deformation Zones 4.3.6.3 Variation in Substructure Across and Along 206 the Direct and Indirect Extrude of the 2014 Alloy 4.3.7 Heat Treated Structures 210 4.3.7.1 Solution Treated Structures 210 4.3.7.2 Aged Microstructures 220 4.4 Room Temperature Properties 226 4.4.1 Introduction 226 4.4.2 Effect of Extrusion Condition on the 226 Hardness Properties 4.4.3 Ageing Characteristics 228 4.4.4 Tensile Tests 232 4.4.5 Stress Strain Curves 232 4.4.6 Tensile Properties of the 2014 Alloy 234 4.4.6.1 T1 Temper 234 4.4.6.2 T6 Temper 238 4.4.6.3 T5 Temper 244 4.4.7 The Effect of Cu Content on the Tensile 249 Properties 4.4.8 Fracture Toughness Properties of the 2014 254 Alloy 4.4.9 Stress Corrosion Resistance of the 2014 Alloy 264 4.4.10 Limit Diagrams 267 4.4.11 Process Conditions vs Properties 276 CHAPTER 5 5.1 Conclusions 279 5.2 Recommendations for Further Work 284 APPENDICES I Torsion Data 287 II Extrusion Data 290 III Room Temperature Mechanical Properties 298 IV Grain Size Measurements 303 Page V Calibration Curves and Experimental Errors 304 VI Computer Programmes 306 NOMENCLATURE 315 REFERENCES 317 ACKNOWLEDGEMENTS 319 6 List of Plates Plate No Title I General Layout of the Extrusion Press II Direct and Indirect Tooling III Surface Cracking of 2014 Alloy IV As Cast Microstructures of 1$ Cu and Cu Alloys V Homogenised Microstructures VI Typical Microstructures of the Press Quenched Extrudes - 2% Cu VII Substructures Observed in the Longitudinal Plane of the Press Quenched Direct Extrudes of the 1$ Cu, 3# Cu and Cu Alloys VIII Substructures Observed in the Longitudinal Plane in the Periphery of the as-quenched Torsion Specimens of the 1$ Cu, Cu and Cu Alloys VIII b) Presolution soak steady state torsion substructures - 2014 alloy IX Macrosections of Partially Extruded Billets of the Cu Alloy Development of Substructure along the Flowline during Steady State Direct Extrusion of the Cu Alloy XI Development of Substructure along the Flowline during Steady State Indirect Extrusion of the 1% Cu Alloy XII Substructures Observed in the Longitudinal Plane of the Press Quenched Direct and Indirect Extrudes of the 2014 Alloy XIII Solution Treated and Aged Structures of the 2014 Alloy XIV T6 Solution Treated and Aged Microstructures of the Direct and Indirect 2014 Alloy - Longitudinal Plane XV T5 and T6 Microstructures of the 2014 Alloy CH Direct, Indirect and SS Direct Extrudes XVI Fracture Surfaces of T6 and T5 Extrudes of 2014 Alloy just below the Fatigue Crack XVII Stress Corrosion Structures in the Longitudinal Plane of the Indirect Extrudes of 2014 Alloy - Unetched 7 List of Tables Table No Title 1.1 Composition Limits for 2014 3.1 Alloy Compositions 3.2 Classification of Heat Treatments Used 4.1 Initial and Temperature Corrected Hot Working Constants at Homologous Strains of 1.0, 0.75 and 0.5 4.2 Area Average Temperature Rises, Flow Stress Data and Hot Working Constants in the 1% Cu and 3$ Cu Alloys 4.3 Comparison of the Evaluated Temperature Rises in Torsion 4.4 Empirical Constants Derived from the Graphical Analysis 4.3 Hot Working Constants Derived from the Graphical Analysis 4.6 Hot Working Characteristics of the 4% Cu 2014 Alloy 4.7 Quoted Values of the Hot Working Constants 4.8 Empirical peak pressure-process parameter relationships for direct extrusion of the 2000 series alloys.