Effect of Working Voltage on Microstructure and Corrosion Resistance of Micro-Arc Oxidization Coating on MB5 Magnesium Alloy
YAO Mei-yi, ZHOU Bang-xin, WANG Jun-an(Institute of Materials, Shanghai University, Shanghai 200072, China)
Micro-arc oxidation coatings of various compositions were prepared on the surface of MB5 magnesium alloy at different working voltages (102～200 V). The microstructure of the resulting micro-arc oxidization coatings was studied by means of scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD). The corrosion resistance of the micro-arc oxide coatings was investigated using electrochemical test. The results showed that the working voltage had significant effects on the microstructure and composition of the oxide coating, which in turn directly affected the corrosion resistance of the magnesium alloy. During the micro-arc oxidation process, both the ions in solution and alloy elements in the magnesium alloy participated in the physico-chemical reaction in the micro-arc zone. The oxide coating was composed of α-MgF_2, MgO, Mg_2SiO_4 and MgAl_2O_4, while the content of MgO in the oxide coating greatly increased with increasing working voltage.