Mgo/Mg 3 (PO 4 ) 2 /CePO 4 coating on AZ31 alloy improves wear and corrosion resistance

A MgO/Mg3(PO4)2/CePO4 composite coating was prepared on AZ31 magnesium alloy via a one-step in-situ micro-arc oxidation (MAO) process. The addition of Ce(Ac)3 to the electrolyte greatly enhanced the wear and corrosion resistance of the MAO coating. Ce(Ac)3 increased the breakdown and final voltages during MAO, and decreased the coating porosity from 3.689% to 2.081%. At 5 g/L Ce(Ac)3, the composite coating exhibited an average friction coefficient of 0.2891, a wear volume of 0.6284 mm3, and a corrosion current density of 7.318 × 10−7 A/cm2, which was three orders of magnitude lower than that of AZ31 alloy and two orders lower than that of a conventional MAO coating, owing to the lubricating effect of lamellar CePO4. After immersion in 3.5 wt.% NaCl solution for 14 days, dense aggregated products formed near the surface pores, sealing coating defects and forming a secondary corrosion barrier to improve long-term corrosion resistance. This work optimises the microstructure of MAO coatings on AZ31 alloy, clarifies the synergistic mechanism of microstructure evolution, self-lubrication and secondary passivation on tribological and anti-corrosion properties, and provides a feasible method for developing high-performance MAO composite coatings on magnesium alloys.