Page 80 - Welding of Aluminium and its Alloys

5

Welding design

5.1 Introduction
In all constructional applications where welded connections are used either
a stress analysis is carried out or ample experience of acceptable perfor-
mance exists for the specific joint design. The principles of stress analysis
are outside the scope of this chapter – it deals instead with those shop-floor
fabrication activities that the designer directly influences. There are many
national and international specifications dealing with the design aspects of
specific structures. For instance, BS 8118 deals with the structural use of alu-
minium, as does the US specification D 1.2. Pressure vessel design is
covered by BS PD 5500 and ASME VIII. For advice on the design of such
structures the designer can do no better than consult the relevant specifi-
cations. For a list of relevant specifications see Appendix A at the end of
this book.
The objective of the designer is to provide an assembly with adequate
strength for the specific application with the least amount of weld metal
and the minimum number of joints. This requires the designer to plan for
a smooth flow of stresses through the joint, to compensate for any strength
loss due to welding, to design the component such that there is sufficient
access for welding and to select the metal to be welded with optimum weld-
ability in mind. As mentioned in Chapter 2 there is little that can be done
to improve the strength of the weldment to match that of the cold worked
or precipitation-hardened alloy.All that the designer can do to compensate
for the loss is to thicken the component, either overall or locally, or to move
the weld to an area of low stress. For advice consult British Standard BS
8118 or the AWS Structural Design Code D 1.2, as mentioned above.
There are a number of factors that the designer needs to take into
account that are specific to designs in aluminium. Some of these have been
mentioned in earlier chapters and include such physical properties as the
high coefficients of thermal conductivity and expansion, the major loss
of strength of certain alloys in the HAZ and the low Young’s modulus. In

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