Development of Microarc Oxidation/Sputter CeO₂ Duplex Ceramic Anti-Corrosion Coating for AZ31B Mg Alloy

A duplex CeO₂/MAO coating was deposited on AZ31B magnesium alloy through microarc oxidation and reactive radio frequency magnetron sputtering. The microstructure and chemical composition of the proposed coating were investigated through scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The CeO₂/MAO coating was approximately 580 nm in thickness and showed fewer micropores and defects than those the MAO coating presented. The properties of corrosion resistance were assessed using the polarization test, electrochemical impedance spectroscopy, and the neutral salt spray test. The CeO₂/MAO duplex coating had the lowest corrosion current density of 3.25×10⁻⁹ A/cm² and the highest polar resistance, approximately four orders of magnitude higher than that of the uncoated sample. Electrochemical measurements suggested that CeO₂ coating can serve as a strong physical barrier between the corrosion medium and the Mg alloy.