Through-thickness microstructure and mechanical properties in stationary shoulder friction stir processed AA7075

Stationary shoulder friction stir processing of high strength thick AA7075 aluminium alloy demonstrated tiny gradient in the microstructure refinement across the thickness, which was attributed to the less heat input and small temperature gradient by the stationary shoulder. Stationary shoulder produced a very smooth surface finish with a little amount of flash throughout the processing area. Probe-dominated stir zone (SZ) resulted in uniform grain refinement as well as hardness distribution across the SZ thickness. The ductility in SZ increased by 48% in comparison to the unprocessed material without costing tensile strength. This tensile behaviour trend maintained throughout the thickness in SZ.