Influence of high temperature thermal treatment on grain stability and mechanical properties of medium strength aluminium alloy friction stir welds

A heat treatment of 2h at 535°C was applied to 6082T6 friction stir welds. One of the effects of post-welding heat treatment on microstructure was abnormal grain growth. The presence, in the same nugget, of zones with different grain size, is the key factor to understand why, after exposure at 535°C for 2h, abnormal grain growth is locally observed. The ductility substantially increased and tensile strengths remained comparable to those of as-friction stir welded samples. Particle evolution influenced microhardness values and determined deformation to fracture, even if abnormal grain growth appeared in the nuggets.