Extrusion of Aluminium Alloys

427 Pages·1999·10.03 MB·English

by  Professor Terry Sheppard (auth.)

EXTRUSION OF ALUMINIUM ALLOYS
EXTRUSION OF
ALUMINIUM ALLOYS
PROFESSOR T. SHEPPARD
D.Se, Ph.D., F.I.M., C.Eng., F.I.Meeh.E.
Department of Product Design and Manufacture,
Boumemouth University
SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.
A c.I.P. Catalogue record for this book is available from the Library of Congress
ISBN 978-1-4419-4728-4 ISBN 978-1-4757-3001-2 (eBook)
DOI 10.1007/978-1-4757-3001-2
AII Rights Reserved
© 1999 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 1999
Softcover reprint ofthe hardcover 1s t edition 1999
No par! of the material protected by this copyright notice may be reproduced ar
utilized in any form or by any means, electronic ar mechanical,
including photocopying, recarding, or by information storage and
retrieval system, without written permis sion from the copyright owner.
Contents
Preface Xl
1 Introduction 1
1.1 Brief history of the extrusion process
1.1.1 The origin of extrusion 2
1.1.2 Extrusion presses for sheathing electric cables 3
1.1.3 Application of extrusion to copper alloys 3
1.2 The therrnomechanical process 6
1.3 Direct and indirect extrusion 7
1.3.1 Direct extrusion 8
1.3.2 Indirect extrusion 11
1.4 Extrusion of rods and solid shapes 12
1.5 Extrusion of hollow sections 14
1.6 The extrusion press 16
1.6.1 Direct presses 16
1.6.2 Indirect presses 20
2 Continuum principles 24
2.1 Yielding and ductility 24
2.2 Constitutive equations 27
2.3 The extrusion pressure 29
2.3.1 Bulk analysis 30
2.3.2 The upper-bound theorem 31
2.3.3 Finite-element solutions 37
2.3.4 Comparison of finite-element modelling
with upper-bound and slip-line field techniques 38
2.4 The friction coefficient 48
2.5 Temperature models 49
2.5.1 Temperature profile in the heated billet 49
2.5.2 Heat balance in extrusion 50
2.5.3 Finite-element modelling predictions 53
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EXTRUSION OF ALUMINIUM ALLOYS
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2.5.4 Thermal balance during extrusion predicted
by integral profile techniques 55
2.6 Diffusion 61
2.6.1 Fick's laws of diffusion 62
2.6.2 Solutions to the diffusion equation 63
2.6.3 Problems in which D varies with composition 66
3 Metallurgical features affecting the extrusion of aluminium alloys 69
3.1 Aluminium-alloy systems 69
3.1.1 The 1XXX system 69
3.1.2 The 2XXX system 70
3.1.3 The 3XXX system 72
3.1.4 The 4XXX system 72
3.1.5 The 5XXX system 72
3.1.6 The AA6XXX system 76
3.1.7 The AA7XXX system 81
3.1.8 Aluminium-lithium alloys 86
3.2 The DC cast state 90
3.3 Homogenization 93
3.3.1 Atomic movements and D 95
3.3.2 Metallurgical consideration of homogenization 102
3.4 Thermal activation 110
3.5 Recovery and recrystallization 113
3.5.1 Dynamic recovery and dynamic recrystallization 114
3.5.2 Microstructure 115
3.6 Recrystallization and layer thickness after solution soaking 116
3.7 Quench sensitivity 119
4 Extrusion processing 127
4.1 Introduction 127
4.2 The Zener-Hollomon parameter and flow stress 127
4.2.1 Flow stress 127
4.2.2 Theoretical considerations 129
4.2.3 Comparison of compression and torsion
in material assessment 130
4.3 Material flow in extrusion 136
4.3.1 The three types of flow 136
4.4 The pressure/displacement diagram 140
4.5 The strain rate during extrusion 141
4.6 Extrusion pressure - practical considerations 143
4.6.1 The effect of friction 144
4.6.2 The effect of the temperature-compensated strain rate 144
4.6.3 The effect of section shape 146
4.7 Surface quality considerations 151
CONTENTS vii
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4.8 Process-structure relationships 156
4.9 Recrystallization 160
4.9.1 Structure after extrusion 160
4.9.2 Volume fraction recrystallization in the F-temper
and after solution soaking 166
4.10 The relationship between process parameters and properties 170
4.11 Material flow and inhomogeneity - structural considerations 176
4.11.1 Development of structure in the extrusion container 176
4.11.2 Substructural considerations 179
4.11.3 Extrudate structure 183
4.11.4 Subgrain size 184
4.11.5 Development of dislocation structure related to
peak: pressure 185
4.12 Press quenching and press solutionizing 186
4.12.1 Introduction 186
4.12.2 Metallurgical aspects 188
4.12.3 Technological problems 191
4.13 Limit diagrams 198
5 Homogenization and extrusion conditions for specific alloys 205
5.1 Introduction 205
5.2 lXXX alloys 206
5.3 2XXX alloys 208
5.4 3XXX alloys 216
5.5 4XXX alloys 219
5.6 5XXX alloys 221
5.7 6XXX alloys 227
5.8 7XXX alloys 227
5.8.1 AI-Zn-Mg alloys 227
5.8.2 AI-Zn-Mg-Cu alloys 232
5.9 Aluminium-lithium alloys 236
5.10 Extrudability, limit and productivity diagrams 238
5.10.1 Extrudability 238
5.10.2 Limit diagrams 240
5.10.3 Productivity diagrams 245
6 Processing of 6XXX alloys 253
6.1 Homogenization 253
6.1.1 General principles of heat treatment 253
6.2 Alloys for specific applications 261
6.2.1 High extrudability, general purpose alloys 261
6.2.2 Medium-strength alloys 263
6.3 Factors affecting quench sensitivity 267
6.3.1 Cooling rate 267
viii I EXTRUSION OF ALUMINIUM ALLOYS
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6.3.2 Recrystallization inhibitors 269
6.3.3 Toughness 270
6.3.4 Structural sensitivity 270
6.3.5 Quench sensitivity in welding 270
6.4 Surface problems and surface generation 272
6.4.1 Introduction 272
6.4.2 Surface features 274
6.4.3 Extrusion topology (limit) diagrams 291
6.4.4 Summary 293
6.5 Alternative metallurgical diagrams 295
6.5.1 Possible phase transformations 296
6.6 Texture 301
6.7 Extrusion defects 303
6.7.1 Metallurgical factors affecting press productivity 303
6.7.2 Recovery related defects 307
6.7.3 Metallurgical defects visible after anodizing 317
7 Plant utilization 323
7.1 Introduction 323
7.2 The modem extrusion plant 323
7.2.1 The extrusion press 324
7.2.2 Ancillary equipment 327
7.2.3 The extrusion process and parameter optimizing 330
7.3 Press requirements 331
7.3.1 Reliability 332
7.3.2 Mechanics 332
7.3.3 Hydraulics 335
7.3 4 Control and monitoring 335
7.4 Isothermal extrusion 340
7.4.1 Process optimization 342
7.4.2 Features required in a comprehensive process optimization 343
7.4.3 Results of process optimization 345
7.5 Expert systems 351
7.5.1 An expert system applied to an extrusion press 353
7.5.2 A typical system description 354
7.6 Aspects of die design and correction 357
7.6.1 Die stack considerations 360
7.6.2 Die design steps 360
7.6.3 Process factors to consider before modifying the die 370
7.7 Tool failure 374
7.7.1 Characteristics 374
7.7.2 Preventative measures 374
7.8 Scrap losses 375
7.8.1 Extrusion losses 376
CONTENTS ix
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7.8.2 Billet scrap 378
7.9 Extrusion control in manufacturing profiles of complex shapes 380
7.9.1 Classification of complex shapes 380
7.9.2 Improvement of billet quality 381
7.9.3 Extrusion press alignment 381
7.9.4 Extrusion condition 382
7.10 Product tolerance 382
7.10.1 Die section 382
7.10.2 Extrusion section 384
7.10.3 Billet section 385
7.10.4 Extrusion conditions 385
7.10.5 Improvements in yield 385
Appendix 1 International alloy designations and chemical composition
limits for wrought aluminium and wrought aluminium alloys 389
Appendix 2 Conversion factors for some common units 401
Appendix 3 Temper designations 405
Index 409
Preface
Aluminium extrusions have become much more widely used in the last decade.
The largest expansion being in the archtectural field but in both aerospace and in
automotive applications significant advances have been achieved. Significantly
this expansion has been accompanied by a demand for increased quality both in
dimensional tolerance and in property specification. Much research has been pub
lished especially in Germany and the United Kingdom and the research groups at
SINTEF, Trondheim and at Imperial College, London have been recognized as
producing significant contributions. The large extrusion companies have also
published and the author recognizes the excellent work published by Norsk
Hydro, Alcan International, Alussuisse, Reynolds Pechenet and Alcoa.
Individuals in each of these companies have been invaluable in discussions on
various topics and for this I express my sincere thanks.
The aim of this book is to view the extrusion process as a thermomechanical
event: hence individual press design is not considered although the more impor
tant and relevant features of both design and essential practice are discussed at
length in the final chapter. I also consider it necessary to give the reader the
opportunity to study the continuum plasticity, metallurgy and diffusion back
ground theory and to show how this may be applied in practice. Hence individual
chapters are introduced to cover these subjects. Extrusion may now be considered
in a theoretical manner and I am hopeful that this text will assist the practical
extruder as well as those working in research centres and Universities to approach
the process to achieve the required dimensional and property requirements.
Each group of aluminium alloys are considered separately with a separate
chapter devoted to the 6XXX alloys which are the most widely produced. I am
deeply indebted to Dr Nick Parsons of Alcan International and to Dr Mike Clode
for assistance in preparing this chapter. In this context I also recognize the con
tribution of Comalco research laboratories in Melbourne where I was fortunate to
spend several months stretched over three years.
Each of my research students have contributed via their thesis, but special
thanks are due to Dr. A.F. Castle, Dr. M.G.Tutcher, Dr. S.J. Patterson and to the
input of Professor H M Flower to the theses.
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I must also recognize the very important role played by the Aluminum
Association, Washington DC who, together with the American Extruders
Council, have organized conferences every four years. In the same context, the
input of Bob Werner to these conferences has been outstanding. The proceedings
of these conferences have provided a rich source of reference material.
Finally my thanks to all the countless journals for pennission to use illustra
tions and to SMS Schloemann for their assistance with Chapter 7.
Terry Sheppard, Bournemouth, June 1998.