The effect of high energy shot peening on microstructure and joining strength of TIG welded AZ31B weldment

The effects of high energy shot peening on the microstructure and mechanical properties of TIG welded AZ31B magnesium (Mg) alloy joints were investigated. The surface characteristics, surface residual stress, tensile strength, grain size and dislocation density were characterized by the experimental observations. Results show that the surface defects were eliminated, tensile residual stress was turned into compressive residual stress and superior joining strength were obtained after HESP treatment under the pressure of 0.15 MPa. A nanoscale layer was obtained in the surface layer and the hardness was significantly increased in the surface layer. Large amounts of dislocations also generated with the aid of HESP treatment. All these factors contributed to the significant improvement in mechanical performance of the Mg alloy joints, leading to a notable enhancement (14.0%) in tensile strength of treated joints to 262.3 MPa over the joints without HESP treatment (230.08 MPa).