Enhanced corrosion resistance of AZ91 magnesium alloy through refinement and homogenization of surface microstructure by friction stir processing

Highlights: • Friction stir processing leads to significant enhancement in corrosion resistance of AZ91alloy. • Corrosion behavior is evaluated by electrochemical, hydrogen evolution and mass loss measurements. • The effect of microstructure modification on the corrosion behavior is analyzed. • Beneficial effect of texture and stable β layer on corrosion resistance is documented. - Abstract: Friction stir processing (FSP) is applied to modify the surface microstructure of cast AZ91 magnesium alloy. The electrochemical and hydrogen evolution measurements reveal that the corrosion rate of processed alloy in 3.5 wt% NaCl solution is significantly decreased. This is mainly attributed to the alteration of corrosion process induced by modification on the morphology and distribution of β-Mg₁₇Al₁₂ phase via FSP. It is originally reported that the formation of a compact and continuous β phase layer on the FSPed surface owing to the segregation of fine β phase effectively enhances the stability and passivity of corrosion product film.