Aluminum-Manganese Work Hardening
Increase in strength of unalloyed or low-alloy Al-Mn sheets through plastic cold working without phase transformation. The blocking of dislocations leads to an increase in hardness.
Work hardening simply means: the sheet has become harder and more brittle through bending or forming. That happens because dislocations pile up in the structure – the material gets stronger but loses ductility. When welding, this causes trouble: the structure is no longer in equilibrium, and you risk hot cracks in the weld or in the heat-affected zone. Especially with aluminum-manganese sheets, you need to be careful. If you have to weld such a part, anneal it first. That means: controlled heating and slow cooling to let the structure relax. After that, it welds like normal material, and the weld holds cleanly.