The Welding Of Aluminum & Its Alloys - Gene Mathers.pdf

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The welding of
aluminium and
its alloys
Gene Mathers
Cambridge England
188267550.001.png
Published by Woodhead Publishing Limited, Abington Hall, Abington
Cambridge CB1 6AH, England
www.woodhead-publishing.com
Published in North America by CRC Press LLC, 2000 Corporate Blvd,NW
Boca Raton FL 33431, USA
First published 2002, Woodhead Publishing Ltd and CRC Press LLC
© 2002, Woodhead Publishing Ltd
The author has asserted his moral rights.
This book contains information obtained from authentic and highly regarded
sources. Reprinted material is quoted with permission, and sources are indicated.
Reasonable efforts have been made to publish reliable data and information, but
the author and the publishers cannot assume responsibility for the validity of all
materials. Neither the author nor the publishers, nor anyone else associated with
this publication, shall be liable for any loss, damage or liability directly or
indirectly caused or alleged to be caused by this book.
Neither this book nor any part may be reproduced or transmitted in any form
or by any means, electronic or mechanical, including photocopying, microfilming
and recording, or by any information storage or retrieval system, without
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The consent of Woodhead Publishing and CRC Press does not extend to
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resale. Specific permission must be obtained in writing from Woodhead Publishing
or CRC Press for such copying.
Trademark notice: Product or corporate names may be trademarks or registered
trademarks, and are used only for identification and explanation, without intent to
infringe.
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library.
Library of Congress Cataloging in Publication Data
A catalog record for this book is available from the Library of Congress.
Woodhead Publishing ISBN 1 85573 567 9
CRC Press ISBN 0-8493-1551-4
CRC Press order number: WP1551
Typeset by SNP Best-set Typesetter Ltd., Hong Kong
Printed by TJ International, Padstow, Cornwall, England
Preface
Engineering is not an exact science and, of the many disciplines within engi-
neering, welding is probably one of the most inexact – rather more of an
art than a science. Much of the decision-making is based on experience and
a ‘gut feel’ for what is or is not acceptable. When the difficulties of shop
floor or site control are taken into account and the occasional vagaries of
the welder and the sometimes inadequate knowledge of supervisory staff
are added, the problems of the practising shop floor engineer can appear
overwhelming. I hope that some of this uncertainty can be dispelled in this
book, which is aimed at those engineers with little or no knowledge of
metallurgy and perhaps only the briefest acquaintance with the welding
processes. It does not purport to be a metallurgical or processes textbook
and I make no apology for this. Having lectured fairly extensively on
welding technology, I have come to realise that most engineers think of
metals as being composed of a large number of small billiard balls held
together by some form of glue. I have attempted to describe the metallur-
gical aspects of the aluminium alloys in these terms. I have therefore kept
the contents descriptive and qualitative and have avoided the use of
mathematical expressions to describe the effects of welding.
The book provides a basic understanding of the metallurgical principles
involved in how alloys achieve their strength and how welding can affect
these properties. I have included sections on parent metal storage and prepa-
ration prior to welding and have also described the more frequently encoun-
tered processes. There are recommendations on welding parameters that
may be used as a starting point for the development of a viable welding pro-
cedure. Also included are what I hope will be useful hints and tips to avoid
some of the pitfalls of welding these sometimes problematic materials.
I would like to thank my colleagues at TWI, particularly Bob Spiller,
Derek Patten and Mike Gittos, for their help and encouragement during
the writing of this book – encouragement that mostly took the form of
‘Haven’t you finished it yet?’. Well, here it is. Any errors, inaccuracies or
omissions are mine and mine alone.
Gene Mathers
ix
Contents
Preface
ix
1
Introduction to the welding of aluminium
1
1.1
Introduction
1
1.2
Characteristics of aluminium
4
1.3
Product forms
6
1.4
Welding: a few definitions
6
2
Welding metallurgy
10
2.1
Introduction
10
2.2
Strengthening mechanisms
10
2.3
Aluminium weldability problems
18
2.4
Strength loss due to welding
31
3
Material standards, designations and alloys
35
3.1
Designation criteria
35
3.2
Alloying elements
35
3.3
CEN designation system
36
3.4
Specific alloy metallurgy
40
3.5
Filler metal selection
46
4
Preparation for welding
51
4.1
Introduction
51
4.2
Storage and handling
51
4.3
Plasma-arc cutting
52
4.4
Laser beam cutting
58
4.5
Water jet cutting
63
4.6
Mechanical cutting
64
4.7
Cleaning and degreasing
66
v
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vi
Contents
5
Welding design
69
5.1
Introduction
69
5.2
Access for welding
70
5.3
Welding speed
71
5.4
Welding position
72
5.5
Edge preparation and joint design
72
5.6
Distortion
84
5.7
Rectification of distortion
88
5.8
Fatigue strength of welded joints
89
6
TIG welding
97
6.1
Introduction
97
6.2
Process principles
97
6.3
Mechanised/automatic welding
114
6.4
TIG spot and plug welding
115
7
MIG welding
116
7.1
Introduction
116
7.2
Process principles
116
7.3
Welding consumables
130
7.4
Welding procedures and techniques
135
7.5
Mechanised and robotic welding
141
7.6
Mechanised electro-gas welding
143
7.7
MIG spot welding
144
8
Other welding processes
147
8.1
Introduction
147
8.2
Plasma-arc welding
147
8.3
Laser welding
150
8.4
Electron beam welding
155
8.5
Friction welding
160
9
Resistance welding processes
166
9.1
Introduction
166
9.2
Power sources
167
9.3
Surface condition and preparation
169
9.4
Spot welding
171
9.5
Seam welding
175
9.6
Flash butt welding
176
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