Aluminium Design and Construction John Dwight

3xxx, 5xxx same as for MIG;
6xxx reduce MIG value by 0.05;
7xxx reduce MIG value by 0.2.
6.8.3 Extent of the softened zone for TIG welding
With the present dearth of information, we would tentatively suggest that
the extent of the nominal HAZ at a TIG weld should be found by making
the following arbitrary adjustment to the predicted extent for MIG:
Welds on thin material. Increase Az by 50%.
Welds on thick material. Increase s by 25%.
A problem arises when an original MIG weld is repaired using TIG.
This will locally increase the width of the HAZ by an amount that is
very hard to quantify.
6.9 HAZ AT FRICTION-STIR WELDS
At the time of writing, it is too soon to provide comprehensive HAZ
data for joints made by the new friction-stir process. However, from a
study of some hardness surveys provided by Hydro-Aluminium in
Norway, using 6xxx-series specimens, it is possible to make the following
observations for material welded in the T6 condition.
1. The pattern of softening will be of the same general form as that
shown in Figure 6.2.
2. The severity of softening is comparable to that with MIG.
3. The extent of the softened zone relates to the shoulder radius of the
welding tool.
4. The softened area will tend to be rather less than that obtained with
MIG.
Note, however, that it is possible to FS-weld together extruded sections
in the T4-temper, and then apply post-weld ageing to bring them up to
full T6 properties. Then there is no HAZ region worth speaking of and
the ductility is good. Such a procedure is readily carried out in an
extrusion plant where long ageing furnaces already exist.
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