Aluminium Design and Construction John Dwight

Type 4 fillers
The advantage of these, when used for welding 1xxx, 3xxx or 6xxx-series
material, is their ability to prevent cracking. The normally preferred version
is 4043A (�5% Si). When crack control is paramount, as in a highly restrained
joint, the 4047A (�12% Si) filler may be specified instead, but with some
loss in corrosion resistance. Type 4 fillers provide no protection against
cracking when employed for welding parent metal containing over 2%
Mg, and are therefore unsuitable for use with most 5xxx and 7xxx materials.
Type 5 fillers
When a joint is to be made in 7xxx-series alloy or the strongest form of
5xxx (such as 5083), and the prime requirement is weld-metal strength,
the best filler alloy is 5556A (or equivalent). For other 5xxx-series parent
alloys, the precise choice of filler tends to be less critical. As a general
rule, the filler composition should broadly match that of the parent
metal. A lower amount of magnesium will produce a weaker weld,
whereas a more highly alloyed filler may lead to trouble in potentially
corrosive environments.
3.3.5 Weld inspection
The required amount of inspection at a welded joint depends on the
level of weld quality that the designer wants to achieve, and BS.8118
recognizes three such levels [9].
1. Minimum quality. This is acceptable when the force transmitted by
the joint under factored loading is not more than one-third of its
factored static resistance, and fatigue is not a factor.
2. Normal quality is called for in non-fatigue situations when the transmitted
force is too high for minimum quality to be allowed, or under fatigue
conditions when the required fatigue class is 20 or below.
3. Fatigue quality applies when fatigue is a factor in the design of the
joint, and the required fatigue class is 24 or over.
Table 3.2 Filler wire types for welding dissimilar parent alloys
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