Influence of grain refinement and grain orientations on residual stress and wear behaviour of friction stir processed Al6061 alloys

The present study investigates the effect of microstructure evolution, including grain refinement and grain orientation, on the surface residual stresses of friction stir processed (FSP) Al6061 alloy. Grain rotation, dynamic recrystallization (DRX), and grain boundary migration are all induced by the FSP process, which results in notable microstructural alterations. According to EBSD analysis, the original S-rolling texture changes into Brass and Goss textures while grain size decreases and high-angle grain boundaries (HABs) increase. The residual stress distribution measured at various depths is correlated with these microstructural alterations, because of the severe plastic deformation and thermal cycles after FSP, residual stresses close to the surface become extremely compressive, reaching a maximum negative value of −564 MPa at 500 µm depth. Residual stresses change from compressive to tensile at deeper depths; at 2000µm and reaches 375 MPa. The relationship between residual stress redistribution and microstructural evolution shows that stable textures and finer grains lead to a more advantageous residual stress state. FSP significantly reduced wear depth and coefficient of friction by fine-tuning the grain structure and increasing the high-angle grain boundary content. Following FSP, SEM images revealed smoother surfaces with minimal damage.