Microstructure and Texture-Driven Enhancement of Surface Properties in Water-Cooled Friction Stir Processed AA6061 Alloy

Abstract The current study investigates the effect of microstructure and microtexture evolution on the surface residual stresses, hardness, and tribological behavior of AA6061 processed via water-cooled friction stir processing (FSP). The electron backscatter diffraction results revealed a significant grain size reduction from 90 µm in the base metal to 2.8 µm in the stir region, accompanied by an increase in high-angle grain boundaries from 38% to 74%. This transformation, mainly driven by continuous dynamic recrystallization and particle-stimulated nucleation, is supported by the development of dominant shear textures, copper ({112}<111>) and brass ({110}<112>), in place of the base metal's rolling texture. The FSP sample exhibited improved compressive residual stresses (up to –330 MPa) and a depth-dependent increase in the microhardness. Tribological studies confirmed a remarkable reduction in the wear-rate and the coefficient of friction under both 20 N and 40 N loads. Scanning electron microscopy analysis of worn surfaces exhibited minimal surface damage, showing a shift from adhesive to mild abrasive wear.