Electrolytic MgO/ZrO2 duplex-layer coating on AZ91D magnesium alloy for corrosion resistance

•An MgO/ZrO2 coating has been prepared by electrolytic deposition and annealing.•Better adhesion of the MgO layer is achieved using a ZrO2 intermediate layer.•The ZrO2 layer can prevent the formation of corrosion product Mg2(OH)3Cl·4H2O.•An MgO/ZrO2 coating enhances more corrosion resistance on AZ91D than an MgO coating.

By a two-step fabrication process of electrolytic deposition and annealing treatment, an MgO/ZrO2 duplex-layer coating has been prepared on AZ91D magnesium alloy as a protective film against corrosion. Owing to the chemical bonding formed after the condensation of precursory hydroxides, the adhesion strength, thickness and compactness of MgO coating on the substrate are significantly enhanced by the intermediate ZrO2 layer which prevents the formation of corrosion product Mg2(OH)3Cl·4H2O. As a result, the MgO/ZrO2 duplex-layer coated specimen reveals relatively high corrosion resistance and superior stability in 3.5 wt% NaCl solution with respect to the MgO single-layer coated specimen.