Effect of Shot Peening on the Ballistic Performance of Friction Stir Welded Magnesium Alloy (AZ31B) Joints

The influence of shot peening (SP) on the ballistic performance of base metal (BM) and friction stir welded (FSWed) AZ31B magnesium alloy joints has been investigated. The defect-free welded joints of AZ31B magnesium alloy were prepared by using the optimum weld parameters, and the joints were shot peened by using steel balls of 2 mm in diameter. In order to investigate the effect of SP on the microstructure, SEM analyses were done at several regions of the top and bottom surfaces of the BM and stir zone (SZ) regions of the FSWed joints. Improved microhardness values of 75 and 70 HV were observed at the top surface of SP-treated BM and SZ regions. The effect of SP on the ballistic performance of AZ31B magnesium alloy joints was determined by conducting high velocity ballistic experiments. Steel core projectiles of 7.62 mm in diameter were used to impact the welded joints. Aluminium alloy AA6062 plates of 25 mm thickness were used as a back plate along with the target. The depth of penetration of the projectile into the target and the back plate was measured to determine the ballistic performance. Among the various regions tested, the SP-treated BM target offered improved ballistic performance compared to the SZ of the SP target. Post investigation of the projectile penetrated regions of the SP targets indicated the absence of voids and micro-cracks compared to non-treated targets.