Design of Micro-Arc Oxidation Process for Rare Earth Magnesium Alloys and Research on Their Corrosion Resistance

The influences of electrolyte compositions and electrical parameters on the microstructure, elemental composition, thickness, roughness, hardness and corrosion resistance of the surface coatings of VW63 rare earth magnesium alloys during micro-arc oxidation are investigated, the growth characteristics of surfacing coatings in the micro-arc oxidation process are revealed, and the factors influencing the overall performances of the surface coatings are systematically analyzed. The results show that the best electrolyte compositions are of 25.0 g/L sodium silicate, 15.0 g/L sodium fluoride, 15.0 g/L sodium hydroxide, and 15.0 g/L triethanolamine, and that the best electrical parameters are 450 V of voltage, 500 Hz of frequency, 20% of duty cycle, and 20 min of duration. The thickness of the surface coating by micro-arc oxidation optimized is uniform, the hardness can reach 472HV0.01, and the interfacial bonding strength between the surface coating and the base material can reach 50.0 MPa. Compared with the magnesium alloy untreated, the corrosion resistance of the magnesium alloy treated by micro-arc oxidation is promoted significantly.