Corrosion resistance enhanced by an atomic layer deposited Al2O3 /micro-arc oxidation coating on magnesium alloy AZ31

Low corrosion resistance becomes one of the major limitations for applications of magnesium (Mg) alloys. Atomic layer deposition (ALD) was applied to fabricate an Al2O3 nanofilm on micro-arc oxidation (MAO) coating of AZ31 alloys. FE-SEM, XPS, and XRD were used to characterize surface morphologies and chemical compositions of the coatings. The corrosion resistance of the MAO/Al2O3 composite coatings were evaluated via polarization, electrochemical impedance spectroscopy (EIS), and hydrogen evolution. The results demonstrated that the Al2O3 deposited for 1000 cycles completely sealed the pores of MAO coatings. And the corrosion current density of composite coatings decreased by three orders of magnitude compared to the bare MAO coatings. The formation and corrosion resistance mechanisms of the composite coating were proposed.