Laser and shot peening effects on fatigue crack growth in friction stir welded 7075-T7351 aluminum alloy joints

The influence of shot and laser peening on the fatigue crack growth behavior of friction stir welded (FSW) aluminum alloy (AA) 7075-T7351 sheets was investigated. The alterations resulting from this surface modification on the fatigue crack growth of FSW were characterized and evaluated for two different crack configurations. A systematic investigation of the various peening effects indicated a significant decrease in fatigue crack growth rates resulting from using laser peening compared with native welded and unwelded specimens. In contrast, shot peened specimens did not result in a significant reduction in fatigue crack growth. The fatigue striation spacings for the laser peened specimens were assessed and found to be small compared with the unpeened, and shot peened specimens. The reduction in striation spacing indicates a slower fatigue crack growth rate and is partially attributed to the deeper compressive residual stresses induced by the laser peening.