extrusion of 2024 aluminium alloy sections by jaya subramaniyan

266 Pages·2016·12.89 MB·English

2.
EXTRUSION OF 2024 ALUMINIUM ALLOY SECTIONS
BY
JAYA SUBRAMANIYAN
A Thesis submitted for PhD of London University
John Percy Group
Department of Materials
Imperial College
London SW7 2BP.
March 1989
TO MY PARENTS,
MICHAEL CLODE &
RAGHUNATHAN
1
Abstract
Extrusion of 2024 aluminium alloy sections
The Aluminium Association alloys designated 2XXX have extensive application in
the aerospace and transport industries. Their hot working range is limited because
their high temperature flow properties are relatively strong and the alloys are
prone to incipient melting at higher extrusion temperatures.
Much work has been accomplished on the production of limit diagrams for
axi-symmetric rod extrusion which allows the prediction of pressure limits,
surface acceptability structure and properties. The work is, however, not generally
applicable to the production of shaped extrusions which constitute the bulk of output
in the industrial environment.
The project seeks to relate both direct and indirect modes axi-symmetric and
shaped sections by considering the geometrical variables involved (e.g. the aspect
ratio and circumscribing circle diameter) in order to produce the pressure and
surface limitation loci on the limit diagram. The project also involved a detailed
investigation of the structure and substructure at all stages of processing from the as
cast to the final heat treated extrudates. Also studied was the variation of structure
within the direct and indirect deformation zones and across and along the extruded
sections. Such work allowed the introduction of the structure loci on the limit
diagram. Four different sections (round, square, T-shape and U-shape) were
investigated both by the direct and indirect route.
The pressure, surface quality, recrystallisation (particularly in the outer band)
and the structural loci were quantified in terms of the material constants contained
in the high temperature constitutive equation and/or the temperature compensated
strain rate. Conclusions are presented regarding the possibility of structure and
property control in the extrusion process using the results from the the
experimental matrix designed to establish the interaction of the process variables
and strength, ductility, fracture toughness etc.
2
ACKNOWLEDGMENTS
The author would like to express his sincere thanks to Professor Terry Sheppard
for his initiation of the project and his supervision, guidance and encouragement
throughout the course of this work.
The author would also like to express his appreciation to Alcan International Ltd.,
for their financial and material support experimental facilities and useful
discussions and technical advice notably Dr. A. J. Bryant and Dr. Nick Parson. I am
also grateful to the Overseas Reasearch Scholarship Fund for providing partial
financial assistance.
Sincere thanks are also expressed to present and past members of the John Percy
Research Group and in particular Drs. Henry McShane, Mike Clode, N. Raghunathan
for their useful discussions, suggestions, patience and willingness to help. Also I
would like to thank Alison Mew and Dr. Efklidis loannidis for their help with the
corrections and Apple Macintosh respectively. Sincere thanks to The JPDC for
making every Friday afternoon eventful.
Technical assistance from Mr. Alec Neve, Mr Melvyn Andrews, and Mr. Roy
Baxter and his colleagues in the workshop are also greatly appreciated.
Thank also to Ian and Alison Metcalfe and the lads at Garden Hall for making my
stay there extremely enjoyable. I would also like to thank Mr. and Mrs Ludden for all
their encouragement and help throughout this PhD programme.
And finally to my parents for all their love and support.
3
CONTENTS
Abstract 1
Acknowledgements 2
Contents 3
List of figures 7
List of tables 11
Chapter 1 Introduction
1.0 Introduction 1 4
Chapter 2 Literature Survey
2.1 The Al-Cu-Mg system 1 7
2.2 The effect of alloying elements 1 9
2.3 Preheat treatment 20
2.3.1 Homogenisation 20
2.3.2 Solution treatment 22
2.3.3 The mechanisms of age-hardening 22
2.3.4 The effect of age hardening 25
2.4 Hot working 27
2.4.1 Empirical relationships 27
2.4.2 Structural aspects of hot working 29
2.4.3 Restoration processes 30
2.4.4 Static restoration processes 31
2.5 Substructure strengthening 31
2.6 Extrusion 33
2.6.1 Direct extrusion 33
2.6.2 Indirect extrusion 36
2.6.3 Limit diagrams 37
2.6.4 Structure produced by extrusion 39
4
2.6.5 Shaped extrusion 4 0
Chapter 3 Theory
3.1 Introduction 4 3
3.2.1 Torsion analysis 4 3
3.3 Extrusion analysis 4 4
3.3.1 Temperature rise 4 4
3.3.2 Strain rate 4 4
3.4 Evaluation of the billet container friction in direct extrusion 4 5
Chapter 4 Experimental
4.1 Introduction 4 8
4.2 The extrusion press 4 8
4.2.1 Tooling 5 0
4.3 Material 5 0
4.4 Examination of extrudates 5 3
4.4.1 Heat treatment of extrudates 5 3
4.4.2 Hardness tests 5 3
4.4.3 Optical microscopy 5 4
4.4.4 Electron microscopy 5 5
4.4.5 Tensile testing 5 5
4.4.6 Fracture toughness tests 5 6
4.5 Torsion testing 5 6
4.6 Partially extruded billets 5 8
4.7 Surface quality 5 8
Results and Discussion
Chapter 5 Torsion Analysis
5.1 Torsion data analysis 61
5.2 Torque/twist curves 61
5.3 Flow stress characteristics 6 3
5
5.4 Constitutive equations 6 7
5.5 Torsion structures 6 9
5.6 Conclusion 7 0
Chapter 6 Extrusion Analysis
6.1 Extrusion data analysis 7 2
6.2 Load-displacement curves 7 2
6.3 Effect of extrusion parameter on the pressure to extrude 7 4
6.3.1 Extrusion temperature 7 4
6.3.2 Extrusion ratio 7 9
6.4 The variation of peak pressure with Z 8 2
6.5 Variation of AP with Ln (Zp) 8 6
6.6 Evaluation of the friction conditions 8 9
6.7 General pressure equation 9 5
6.8 The effect of section shape on the pressure 1 01
6.8.1 Effect of section shape on Peak pressure 1 01
6.8.2 Effect of section shape on APeak pressure 1 0 6
6.9 Geometrical considerations 106
6.10 Surface quality of extrudates 113
6.11 Conclusion 120
Chapter 7 Structural Analysis
7.1 The evolution of structure and substructure 123
7.1.1 As-cast structure 123
7.1.2 Homogenised structure 125
7.2 Structural variations with extrusion conditions 128
7.2.1 Extrudate structures 128
7.2.2 Substructural variation with extrusion conditions 136
7.2.3 Effect of process conditions on the steady state substructure 142
7.2.4 Variation of substructures across and along extrudates 1 45
7.3 Material flow during steady state extrusion 146
7.4 Development of substructure during extrusion 153
7.5 The effect of solution treatment on extrudate microstructures 1 61
7.6 The effect of ageing on the microstructure 171
7.7 Conclusion 174
Chapter 8 Room Temperature Properties
8.1 Room temperature properties of extrudates 177
8.1.1 Effect of extrusion conditions on the hardness properties 177
8.1.2 Variation of hardness along extrudate length 179
8.1.3 Variation of hardness across the extrudate 182
8.1.4 Effect of solution treatment on the hardness 182
8.2 Ageing characteristics of alloy 2024 extrudates 184
8.3 Tensile properties of 2024 alloy extrudates 190
8.3.1 Stress-strain characteristics of alloy 2024 1 90
8.3.2 T1-Temper 1 93
8.3.3 T6-Temper 1 99
8.3.4 T5-Temper 201
8.3.5 The effect of a preageing stretch on the tensile properties 201
8.4 Fracture toughness properties of alloy 2024 202
8.5 Limit diagrams 207
8.6 Conclusion 213
Chapter 9 Conclusions
9.1 Major conclusions 215
9.2 Recommendation for further work 217
Appendices
1 Extrusion data 220
2 Ageing data 232
3 Tensile data 235
4 Short rod fracture toughness data 237
5 Experimental errors 238
6 Modification to calculations involving jx 240
References 243
7
List of figures
Fig. 2.1 Phase diagram of aluminium-copper 24
Fig. 2.2 Principles of direct and indirect extrusion 34
Fig. 2.3 Idealised load-displacement curve for direct and indirect extrusion 35
Fig. 2.4 Extrusion ratio vs extrusion temperature limit diagram 37
Fig. 4.1 General layout of press and extrusion tooling 49
Fig. 4.2 The dies used for rod extrusion 51
Fig. 4.3 The dies used for shaped extrusion 52
Fig. 4.4 Short rod fracture toughness test sample 57
Fig. 5.1 Schematic torque vs twist curves 62
Fig. 5.2 Stress-strain curves for torsion (strain rate =16.0/s) 64
Fig. 5.3 Stress-strain curves for torsion (strain rate =5.0/s) 65
Fig. 5.4 Stress-strain curves for torsion (strain rate =0.16/s) 66
Fig. 6.1 Typical load-displacement trace for direct extrusion of alloy 2024 at
high and low temperatures 73
Fig. 6.2 Typical load-displacement trace for direct and indirect extrusion of
alloy 2024 73
Fig. 6.3 Peak pressure vs initial billet temperature for direct extrusion 75
Fig. 6.4 Peak pressure vs initial billet temperature for indirect extrusion 76
Fig. 6.5 Peak pressure vs Ln R for direct extrusion 80
Fig. 6.6 Peak pressure vs Ln R for indirect extrusion 81
Fig. 6.7 Peak pressure vs Ln (Z) for direct and indirect extrusion 84
Fig. 6.8 Peak pressure vs Ln (Z/A) for direct and indirect extrusion 85
Fig. 6.9 Tangential construction for AP evaluation 87
Fig. 6.10 A Peak Pressure vs Ln Z for extrusion 88
Fig. 6.11 Peak pressure vs billet length for direct extrusion alloy 2024 90
Fig. 6.12 Peak pressure vs predicted pressure calculated using equation 6.12 for
both modes of extrusion 98
Fig. 6.13 Effect of die geometry on load displacement curves for both modes of
extrusion 102
8
Fig. 6.14 Graph of peak pressure vs Ln Zj for shaped sections (direct mode) 103
Fig. 6.15 Graph of peak pressure vs Ln Zj for shaped sections (indirect mode) 104
Fig. 6.16 Graph of APeak pressure vs Ln Zj for shaped sections (direct mode) 107
Fig. 6.17 Graph of APeak pressure vs Ln Zj for shaped sections (indirect mode) 108
Fig. 6.18 Graph of peak pressure vs Ln Zj (direct mode) 111
Fig. 6.19 Graph of peak pressure vs Ln Zj (indirect mode) 112
Fig. 6.20 Predicted pressure from general pressure equation vs experimental
extrusion pressure for shaped sections 114
Fig. 6.21 Typical examples of extrudate surfaces of alloy 2024 116
Fig. 6.22 Ln Zj vs initial billet temperature for surface conditions - direct and
indirect extrusion of alloy 2024 119
Fig. 7.1 As cast microstructure 124
Fig. 7.2 Homogenised material microstructure 126
Fig. 7.3 Heat treatment profile given prior to extrusion 127
Fig. 7.4 Extrudate microstructure 129
Fig. 7.5 Shaped microstructure 131
Fig. 7.6 Volume % recrystallised vs initial billet temperature for direct
extrudates 132
Fig. 7.7 Volume % recrystallised vs initial billet temperature for direct
extrudates 132
Fig. 7.8 Recrystallised layer thickness vs Ln Zj for direct shapes 134
Fig. 7.9 Recrystallised layer thickness vs Ln Zj for indirect shapes 134
Fig. 7.10 Comparison of substructures in transverse plane for direct and indirect
extrusion of alloy 2024 137
Fig. 7.11 Comparison of substructures in transverse plane for direct and indirect
extrusion of alloy 2024 rod section 140
Fig. 7.12 Comparison of substructures in transverse plane for direct and indirect
extrusion of alloy 2024 U-section 141
Fig. 7.13 Influence of strain on subgrain size 142
Fig. 7.14 Inverse subgrain size (d'1) vs Ln Zc relationship 143
Fig. 7.15 Inverse subgrain size (d"1) vs Ln Zj relationship 143