Mechanical characterization of AZ31B magnesium alloy treated by severe shot peening

Recent developments in shot peening demonstrate that it can be applied using unconventional parameters in order to obtain nanocrystals on a thin surface layer of the treated material. In last few years, the interest on Magnesium and its alloys is growing. In this study, four series of AZ31B magnesium alloy specimen, not-peened, conventional shot peened, severe shot peened and severe shot peened with re-peening treatment, were mechanically characterized. The treated material surfaces were first investigated in terms of surface topography, grain size, depth of refined grains layer and roughness. Then, the effects induced by the treatment on material mechanical behaviour were analyzed performing hardness test and residual stresses determination. Finally, the effects of the induced surface modifications were investigated in terms of wettability. The surface morphology and roughness are deeply changed by severe shot peening due to the media imprints leaved on the surface. A refined grains layer was detected in all shot peened samples, but with different features among different treatments. Severe shot peening enhances both compressive residual stress field and hardness in terms of absolute value and depth. A better wettability was obtained. By slightly grinding the surfaces of the wettability test samples, the effects of varying substrate grain size were separated from those of varying surface roughness. Ultimately, this study demonstrated the mechanical features enhancement led by severe shot peening. Re-peening treatment shows better characteristics were smoother surface is an important factor.