Microstructure and Properties of Micro-Arc Oxidization Coatings on Surface of High Purity Magnesium Prepared in Different Electrolyte Systems

The surface of pure magnesium was treated by micro-arc oxidation in three electrolyte systems of silicate system, aluminate system, silicate and aluminate composite system. The microstructure and properties of micro-arc oxidation coatings were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and electrochemical testing. The results show that the micro-arc oxidation coating obtained in the silicate system had the thickest thickness of 34.54 μm, the structure was relatively dense and uniform, and the coating was mainly composed of MgO and Mg₂SiO₄. The micro-arc oxidation coating obtained in the composite electrolyte system was composed of MgO, Mg₂SiO₄ and MgAl₂O₄, and had the lowest surface roughness of 0.19 μm and a dense and uniform structure. The micro-arc oxidation coating obtained in the aluminate system was also composed of MgO and Mg₂SiO₄, and had the worst compactness in three electrolyte systems. The coating obtained in the silicate system had the best corrosion resistance, whose free corrosion current density was one order of magnitude less than that of magnesium substrate.