Cerium conversion coatings for AZ91D magnesium alloy in ethanol solution and its corrosion resistance

Golden-yellow-colored cerium conversion coatings on AZ91D magnesium alloy were obtained by immersion in ethanol solution and post-treated in 3.0 wt.% Na3PO4 aqueous solution. SEM revealed that the coatings deposited more heavily on α phase than on β phase. XPS results showed that the coatings consist of CeO2, Ce2O3, CePO4, Al2O3, Mg3(PO4)2 and MgO. Corrosion tests indicated that the coatings with post-treatment significantly reduced the corrosion rate of AZ91D alloy in NaCl solution. The post-treatment is necessary for better corrosion resistance. The corrosion resistance of the coatings with post-treatment is superior to that of DOW No.1 coating.