Materials
Why do my aluminium welds crack?
Quick answer
Aluminium welds crack from centreline hot cracking: wrong filler (or no filler), too-constrained joints, or cracking impurities. The fix: use ER4043/ER5356 filler at proper dilution, design joints with room to move, and don't weld pure aluminium with mismatched filler.
The three real causes
- No or low filler dilution — the pool's own chemistry cracks as it freezes
- High restraint — the joint can't shrink as it cools, so it tears
- Wrong filler for the parent alloy — chemistry matters more on ally than any other common metal
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