Corrosion resistance property of the ceramic coating obtained through microarc oxidation on the AZ31 magnesium alloy surfaces

Microarc oxidation is a recently developed surface treatment technology under anodic oxidation. The magnesium alloy offers various possibilities of application in industry, but its poor property in corrosion resistance, wear resistance, hardness and so on, limited its application. Through microarc oxidation, ceramic coating is directly formed on the surface of magnesium alloy, by which its surface property is greatly improved. In this paper, a dense ceramic oxide coating approximately 20 μm thick was prepared on a AZ31 magnesium alloy through microarc oxidation in a Na2SiO3-Na2WO4-KOH-Na2EDTA electrolytic solution. The property of corrosion resistance of ceramic coating was studied by CS300P electrochemistry-corrosion workstation, and the main impact factor of the corrosion resistance was also analyzed. Microstructure and phase composition were analyzed by SEM and XRD. The microhardness of the coating was also measured. The basic mechanism of microarc coating formation is explained. The results show that the corrosion resistance property of microarc oxidation coating on the AZ31 magnesium surface is superior to the original samples in the 3.5 wt% NaCl solutions. The microarc oxidation coating is relatively dense and uniform, mainly composed of MgO, MgAl2O4 and MgSiO3. The microhardness of the AZ31 magnesium alloy surface attained 410HV, which was much larger than that of the original AZ31 magnesium alloy without microarc oxidation.