Microstructure and mechanical property studies of AA6056 friction stir welded plate

The microstructure and mechanical properties of a friction stir welded 6056-T6 aluminum alloy plate were investigated by using polarized optical and transmission electron microscopy techniques. The microstructure revealed different grain morphologies in the thermo-mechanically affected zones, in proximity of the weld nugget; the advancing side had fairly elongated, bent grains, whilst the broader retreating side had more elongated, narrower grains. On both sides in approach to the nugget zone, grain subdivision rose with shear strain despite rising temperature. Overaged precipitates in both thermo-mechanically affected zones are associated with minima in hardness. Tensile tests showed yield and ultimate strength slightly lower across the weld compared to the parent material as well as a reduction in ductility of the weld region.