The preparation and characterization of a nano-CeO2/phosphate composite coating on magnesium alloy AZ91D

A nano-CeO2 modified phosphate composite coating was prepared on magnesium alloy AZ91D by chemical conversion. The nano-CeO2/phosphate composite coating was composed of Zn3(PO4)2·4H2O, Zn2Mg(PO4)2 and CeO2, with less mud-cracks and pores. With nano-CeO2 modification, the corrosion resistance and the mechanical performance of the nano-CeO2/phosphate composite coating were improved significantly compared with those of the single phosphate coating. The coating resistance and the corrosion current density for the composite coated alloy were respectively larger and lower than those for the single phosphated alloy, particularly for the alloy with the composite coating containing 1.02 wt% CeO2, which was formed in the treatment bath containing 2.0 g/L nano-CeO2. The adhesive force and the micro-hardness of the nano-CeO2/phosphate composite coating were higher than those of the single phosphate coating. The mechanism of nano-CeO2 modification on the electrochemical and physical properties was very closely associated with the effects of nano-CeO2 particles on the grain refinement and the dispersion strengthening.