Relationship between welding conditions, abnormal grain growth and mechanical performance in friction-stir welded 6061-T6 aluminum alloy

In this work, a relationship between welding conditions, annealing behavior, and mechanical performance of friction-stir welded (FSWed) 6061-T6 aluminum alloy was examined. In the entire studied FSW range, the welded material was found to be unstable against abnormal grain growth during post-weld solutionizing treatment. However, a lowering of the FSW heat input tended to inhibit this undesirable phenomenon. In addition to the stir zone, the abnormal microstructural coarsening was also observed in the heat-affected zone, whereas the thermo-mechanically affected zone experienced static recrystallization. In all cases, the abnormal grain growth was found to result in similar to 25-35 degrees <110> rotation of the original crystallographic texture. Hence, this process was suggested to be governed by the orientation-growth mechanism. Due to the relatively high strain-hardening ability intrinsic to the coarse-grained materials, the abnormal grains suppressed tensile strain in the stir zone during transverse tensile tests thus degrading weld ductility.