Effect of severe shot peening on corrosion behavior of AZ31 and AZ91 magnesium alloys

Abstract

Severe shot peening (SP) was performed on the AZ31 and AZ91 Mg alloys to obtain a nanostructured surface layer. The microstructure, micro-hardness and corrosion behavior of AZ31 and AZ91 Mg alloys after SP treatment were studied using transmission electron microscopy, micro-hardness tester and corrosion tests, respectively. Results showed that SP treatment produced a plastic deformation layer with α-Mg grains at the nanometer scale in the surface of AZ31 and AZ91 Mg alloys. After SP treatment, the micro-hardness in the near surface region displayed an obvious increase for two alloys, owing to the combination of the grain refinement and the work-hardening. The corrosion resistance of AZ31 alloy was improved by SP treatment, because a relatively compact passive film formed rapidly on the nanostructured surface. Unfortunately, SP treatment played a minor role in enhancing the corrosion resistance of AZ91 alloy, because it had little effect on size and distribution of β-phases.