Effect of stress shot peening on the microstructure and residual stress of Al18B4O33 whisker reinforced aluminum matrix composite

This work systematically studied the effects of stress shot peening (SSP) on the microstructure, residual stress and hardness of the ultrafine-grained Al18B4O33 whisker reinforced Al -Mg -Si matrix composite (Al18B4O33w/Al-Mg- Si) by the modified Warren-Averbach method, X-ray diffraction stress equipment, transmission electron microscopy and hardness tester. The results showed that conventional shot peening generated a gradient deformation layer of the Al18B4O33w/Al-Mg-Si with ultrafine grains (200-400 nm) near the surface layer. By contrast with conventional SP, SSP effectively induced superior microstructures at the deformed zone with finer crystalline size and more dislocations. In parallel, SSP effectively enhanced the compressive residual stress (CRS) distribution with a higher magnitude of surface CRS (-83 MPa) and maximum CRS (-152 MPa) value and deeper affected depth along the loading direction. The fragmentized whisker during SSP acted as the pinning role on the dislocation movements, which was beneficial for grain refinement and CRS improvement. It is concluded that SSP technique can be regarded as an effective process of improving the surface properties of ultrafine-grained Al18B4O33w/Al composite.