Effect of surface mechanical attrition treatment on corrosion fatigue behavior of AZ31B magnesium alloy

Surface mechanical attrition treatment (SMAT) is considered as an effective technology to influence fatigue and corrosion resistance as these properties are largely related to surface structure and property. Despite the increasing number of studies that report the effects of SMAT on separate fatigue or corrosion behaviors, the impact of SMAT on fatigue property under corrosive environment is left unexplored. In this paper, the corrosion fatigue properties of AZ31B magnesium alloy before and after SMAT process are investigated. Hydrogen evolution tests and potentiodynamic polarization tests are carried out to obtain the corrosion resistance, and it is found that SMAT promotes corrosion rate. The surface roughness of SMATed specimen also increases, which accelerates corrosion rate. In terms of fatigue properties, the fatigue life of SMATed specimen is found to be higher, in both air and 3% NaCl solution. And the larger the size of stainless steel balls used during processing SMAT specimens, the longer the fatigue life. Under 3% NaCl corrosive environment, the beneficial effects induced by SMAT process gradually emerge with increasing stress amplitude during fatigue tests. Reduced fatigue life of SMATed specimen under corrosive environment is attributed to roughened interface between deformed surface layer and bulk material. Nevertheless, the crack initiation sites for SMAT specimens are the same in both air and NaCl solution, all located at the subsurface area.