Abstract
This study examines the effects of one-sided laser shock peening (LSP) on friction-stir-welded (FSW) 7075 aluminium alloy joints. It compares depth-dependent grain refinement, residual stress and local hardness in the nugget zone and relates these measurements to the transverse tensile response of the whole joint. Electron backscatter diffraction measurements at corresponding depths showed that the largest measured grain-size difference occurred 100 μm below the treated surface, where the mean grain size was 7.95 μm in the untreated joint and 1.54 μm after LSP. This difference diminished with depth. The weld-longitudinal residual stress changed from tensile to compressive at the treated surface, reaching approximately −280 MPa. It changed sign at a depth of 0.5–0.6 mm, while the treated and untreated stress profiles approached each other at approximately 0.9 mm. At a depth of 0.5 mm, microhardness increased from 126.8 to 135.6 HV. In transverse tension, mean yield strength increased from 346.8 to 383.9 MPa, ultimate tensile strength from 381.2 to 419.8 MPa, and elongation after fracture from 5.47% to 7.13%. These results show that LSP produced depth-dependent microstructural and residual stress changes, accompanied by local hardening and improvements in the tensile response of the joint.