Structure and corrosion resistance of electron-beam-strengthened and micro-arc oxidized coatings on magnesium alloy AZ31

Micro-arc oxidation (MAO) is very effective to enhance the corrosion performance of Mg alloys. However, the micro-pores in MAO coatings provide a channel for the corrosion medium to reach the alloy matrix. In this work, electron beam strengthening (EBS) is performed to improve the microstructure of the Mg alloy and the MAO coating is prepared subsequently to improve the corrosion performance. The crystalline size of the Mg alloy decreases, the roughness improves, and the corrosion resistance increases. Furthermore, refinement of the grain size by EBS improves the discharge in MAO. The noticeable effect of EBS on the microstructure of the coating lies in the improvement of density, such as porosity reduction by 47.8%. The compactness of the coatings also increases significantly, subsequently improving the corrosion resistance. The corrosion mechanism is proposed.