Development of microarc oxidation process to improve corrosion resistance on AZ91HP magnesium alloy

A new anodizing process,which does not contain chromate but can improve the corrosion resistance of magnesium alloys significantly,was developed using a microarc power supply. Surface morphology was observed and the coating was compact and ceramic-like. In addition,the corrosion resistance of samples before and after anodization by the new process and a method in US Patent 5470664 was compared by potentiodymaic polarization curves,electrochemical impedance spectroscopy (EIS) and salt spray test. The results show that the anodization can improve the corrosion resistance of magnesium alloy. The samples obtained by the new process and the method mentioned in the US Patent 5470664 achieve 9 and 7 rates after 336 h salt spray test,respectively.