Micro-hardness evolution in Friction Stir Processed 7475 aluminium plate

Friction Stir Process (FSP) is an efficient way to refine microstructure of aluminium alloys and improve the damage resistance. The intense plastic deformation driven by the FSP tool leads to smaller and equiaxial recrystallized grains. However, the heat generated during the processing can strongly affect the precipitation state in case of age-hardening aluminium alloys. Considering FSP with 7XXX aluminium series is thus a compromise between grain refinement and hardening precipitation evolution. As-FSPed samples are usually softened due to dissolution and/or coarsening of the hardening phases. Studying Vickers micro-hardness mapping in the thickness of processed 7475 aluminium plates is a way of easily tracking precipitate evolution during FSP for a large number of heat treatment conditions