Effect of cold spraying on residual stress and mechanical properties of friction stir welded 2219 aluminum alloy joint

In order to improve the residual stress and mechanical properties of friction stir welded aluminum alloy joints, the cold spraying process was carried out on the upper surface of 4 mm thick friction stir welded 2219 aluminum alloy joint. The changes of residual stress and mechanical properties of the joint before and after cold spraying were studied. The results show that the longitudinal residual stress of the as-welded joint presents an asymmetric “M” shape distribution, and the peak of residual stress was located at the advancing side near the shoulder outer. After cold spraying, the residual stress of the joint was greatly reduced, and the peak of residual stress was reduced from 186 MPa to 43 MPa. The thickness of the coating is about 200 μm, and the large plastic deformation occurred at the interface between the coating and the substrate. What’s more, the grains near the interface are refined. Because of the shot peening effect during cold spraying, the microhardness of the upper surface of the joint was increased by 25 HV on average, and the affected depth was about 1 mm. The tensile properties of the joint were also significantly improved, with the tensile strength increased by 6.3% and the elongation increased by 78.6%. Both as-welded and coated tensile specimens fractured near the heat affected zone at the advancing side of the joint. It is consistent with the characteristics of fracture in the weak zone.