Effect of warm shot peening treatments on surface properties and corrosion behavior of AZ31 magnesium alloy

Magnesium alloys are considered as a suitable choice for temporary biodegradable implants due to their biocompatible and biodegradable properties, able to avoid a second surgery when implant removal is needed. Nevertheless, nowadays one of the shortcomings of magnesium-based materials is their poor corrosion resistance and the associated high corrosion rate. This fact considerably hinders their application in biomedical field. The aim of this work is to induce a severe plastic deformation on the upper layer of the AZ31 Mg alloy in order to modulate its surface properties to slow down the kinetics of the corrosion damage. Specimens were submitted to conventional and severe shot peening treatments at room temperature, 240 degrees C (near recrystallization temperature) and 360 degrees C (above recrystallization temperature); the specimens were then analyzed in terms of grain refinement, surface roughness, work hardening, and residual stresses. Potentiodynamic polarization tests were also performed to evaluate the influence of the shot peening treatments on the specimens' corrosion resistance. The results evidenced surface roughness as the most influential factor in corrosion behavior, although for the specimens with similar roughness, also the effect of grain size is notable.