Study On Microstructure And Properties Of Ceramic Coating Prepared On Magnesium Alloy By Micro-arc Oxidation

Ceramic coatings were formed on the Mg alloy (AZ91D) by using the self-designed equipment, the solution formulae of silicate-phosphate system, the starting voltage, current density, oxidation time were optimized through contrast, orthogonal and synthesized analysis means. The growing rules, phase structure and the micro-structure of ceramic coating were characterized by scanning electronic micro-telephone (SEM) and x-ray diffraction (XRD); the cohesion, corrosion and wear behaviors of ceramic coating were studied by scratch, electrochemical and ball-and-disk scar tests. The Al₂O₃ powders were added into the optimized solution, and the current density and oxidation time were also optimized; besides, the morphology, cohesion and corrosion resistance of ceramic coating, which obtained without and with addition of Al₂O₃ powders in the optimum parameter, were contrasted.The results indicated that a multilayer structure was formed on the AZ91D, an outer loosed layer and an inner compact layer. Owing to the metallurgical bonding, the inner layer had good interfacial connection with the substrate; the outer layer was porous. The surface of coating disposed ununiformly many fused mass, which is volcano-like particles and whose top accompanied with micro-holes, also some cracks were existed on the surface. With the oxidation time extending, the sizes of fused mass...