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24

Technical Services

Common Causes and Cures

There are two types of cracks that can occur in aluminum welds:

stress cracks and hot cracks

.

Weld Cracking

Stress cracks

occur when the weld is simply unable to withstand the forces applied to it. This can be due to a poor joint

design that is welded as designed, a weld that is just not strong enough for the application (not designed properly) or an

improper weld. Images 1A and 1B show fillet weld examples. Image 1A shows the profile of an acceptable weld. Image 1B

shows an excessively concave weld that failed through the effective throat (refer to Image 2). If the weld is inadequate for

any of the above mentioned reasons, it is very possible it will not withstand service conditions.

Hot cracks

are a result of the chemistry. It can be the chemistry of the base alloy, the filler alloy or the combination

making the weld itself. The graph that follows shows the hot cracking sensitivity for some of the most common aluminum

alloy groups; Silicon (4XXX), Copper (2XXX), Magnesium (5XXX), and Magnesium-Silicide (6XXX).

Image 1A

Image 1B

Image 2