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Page 1

The welding of
aluminium and

its alloys

Gene Mathers

Cambridge England

Page 2

Published by Woodhead Publishing Limited, Abington Hall, Abington
Cambridge CB1 6AH, England

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.

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Page 121

autogenous and a wire feed is not required, although this can be easily pro-
vided from a spool of wire fed from a cold wire feed unit. The wire should
be fed into the leading edge of the weld pool at a similar angle to that used
in manual welding. Both the start of the wire feeding and carriage travel
should be delayed until the weld pool is well established. When ending the
weld the current should be tapered down and the wire feed speed adjusted
to provide crater filling.

DCEN helium TIG is ideally suited to mechanisation since full advan-
tage can be taken of the increase in travel speed, which may be up to 10
times that of an argon shielded AC-TIG weld. It is also possible to weld
thick plates, up to 18mm thick, in a single pass, square edge preparation
with no filler metal, making this a very cost-effective method. The high
travel speeds possible with the technique may lead to undercutting, partic-
ularly if the welding current is increased in the expectation that this will
permit even higher travel speeds to be achieved. Short arc lengths are nec-
essary when autogenous welding, typically 0.8–1.5mm, and in some cir-
cumstances the electrode tip may be below the surface of the plate with the
arc force depressing the weld pool surface. Contraction during cooling will
cause upsetting to occur, resulting in a local thickening of the joint and
providing sufficient excess weld metal that the joint is not underfilled.

6.4 TIG spot and plug welding

By overlapping two plates a spot weld can be achieved by using the DCEN
TIG process to fuse through the top plate and melt into the lower plate.
Initial use of the process was carried out without a filler wire but hot crack-
ing problems with the alloys meant that it was confined to pure aluminium
up to 2mm thick. The development of automatic wire feeding systems
capable of feeding wire into the weld pool as the weld is terminated has
helped in extending the range of alloys that could be welded. Even with
this improvement, however, it has been found that the critical nature of the
surface condition causes welding defects such as oxide films.This means that
the process does not find general use because of low strength and poor

Further work has taken place using fully automated equipment and
helium shield gas and with low-frequency AC. These improvements have
resulted in a wider use of the process but MIG spot welding tends to be
preferred as providing better and more consistent quality.

TIG welding 115

Page 122

7.1 Introduction

The metal arc inert gas shielded process,EN process number 131,also known
as MIG, MAGS or GMAW, was first used in the USA in the mid 1940s. Since
those early days the process has found extensive use in a wide range of indus-
tries from automotive manufacture to cross-country pipelines. It is an arc
welding process that uses a continuously fed wire both as electrode and as
filler metal, the arc and the weld pool being protected by an inert gas shield.
It offers the advantages of high welding speeds, smaller heat affected zones
than TIG welding, excellent oxide film removal during welding and an all-
positional welding capability. For these reasons MIG welding is the most
widely used manual arc welding process for the joining of aluminium.

7.2 Process principles

The MIG welding process, illustrated in Figs. 7.1 and 7.2, as a rule uses direct
current with the electrode connected to the positive pole of the power
source, DC positive, or reverse polarity in the USA. As explained in
Chapter 3 this results in very good oxide film removal. Recent power source
developments have been successful in enabling the MIG process to be also
used with AC. Most of the heat developed in the arc is generated at the
positive pole, in the case of MIG welding the electrode, resulting in high
wire burn-off rates and an efficient transfer of this heat into the weld pool
by means of the filler wire. When welding at low welding currents the tip
of the continuously fed wire may not melt sufficiently fast to maintain the
arc but may dip into the weld pool and short circuit.This short circuit causes
the wire to melt somewhat like an electrical fuse and the molten metal is
drawn into the weld pool by surface tension effects. The arc re-establishes
itself and the cycle is repeated. This is known as the dip transfer mode of
metal transfer. Excessive spatter will be produced if the welding parame-
ters are not correctly adjusted and the low heat input may give rise to lack-

MIG welding


Page 241

Laser Welding, P.A. Hilton et al., Woodhead Publishing Limited. ISBN 1-85573-

Laser Welding – A Practical Guide, C.T. Dawes, Woodhead Publishing Limited.
ISBN 1-85573-034-0.

Chapter 9
AWS C 1.1M Recommended Practices for Resistance Welding. Author and pub-

lisher American Welding Society. ISBN 0-87171-601-0.

Chapter 10
Guidelines for Quality Assurance in Welding Technology, Author and publisher

International Institute of Welding. ISBN 0-85300-229-0.
Quality Assurance of Welded Construction, N.T. Burgess et al., Elsevier Science

Publishers Ltd. ISBN 1-85166-274-X.

Chapter 11
ANSI/AWS B1.11 Guide for the Visual Examination of Welds.Author and publisher

American Welding Society. ISBN 0-87171-625-9.
ANSI/AWS B1.10 Guide for the Non-Destructive Examination of Welds. Author

and publisher American Welding Society. ISBN 0-87171-259-8.
ASM Handbook Vol.8. Mechanical Testing and Evaluation. Author and publisher

American Society for Materials. ISBN 0-87170-389-0.
Introduction to the Non-Destructive Testing of Welded Joints, R. Halmshaw,

Abington Publishing. ISBN 1-85573-314-5.
Welding Inspection Handbook, Author and publisher American Welding Society.

ISBN 0-87171-560-0.

Useful contact names and addresses
The Aluminium Association, 900 19th Street NW, Washington, DC 20006, U.S.A.
Aluminium Federation, Broadway House, Calthorpe Road, Five Ways, Birmingham,

West Midlands, B15 1TN, United Kingdom. Tel +44(0)121 4561103.

American Society for Materials, 9639 Kinsman Road, Materials Park, Ohio, OH
44073-0002, U.S.A.

American Society of Mechanical Engineers, Three Park Avenue, New York, NY
10016-5990, U.S.A.

American Welding Society, 550 N.W. LeJeune Road, Miami, Florida, 33126, U.S.A.

British Institute of Non-Destructive Testing, 1 Spencer Parade, Northampton, NN1
5AA United Kingdom. Tel +44(0)1604 630124.

British Standards Institution, 389, Chiswick High Road, London, W4 4AL. United
Kingdom. Tel +44(0)20 8996 9001.

Institute of Materials, 1 Carlton House Terrace, London, SW1Y 5DB, United
Kingdom. Tel. +44(0)20 7451 7300.

Bibliography 233

Page 242

TWI Ltd, Granta Park, Abington, Cambridge, CB1 6AL, United Kingdom. Tel
+44(0)1223 891162.

Woodhead Publishing Limited (includes Abington Publishing), Abington Hall,
Abington, Cambridge, CB1 6AL, United Kingdom. Tel +44(0)1223 891358.

234 Bibliography

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