A Zn/Al–Mn/Al multilayer coating on AZ31B magnesium alloy with enhanced corrosion resistance and interfacial adhesion

Magnesium alloys suffer from poor corrosion resistance and unsatisfactory surface appearance, limiting their broader applications in aerospace and 3C electronics. Conventional coatings, such as micro-arc oxidation coatings and electroless nickel plating, have drawbacks including low thermal conductivity, high porosity, weak adhesion and unsatisfactory aesthetics. To overcome these issues, an Al–Mn/Al multilayer coating was developed via ionic liquid electrodeposition on zincated magnesium alloy. The Al–8.5 at.% Mn transition layer provides a dense, smooth barrier that significantly enhances adhesion to the zincated Mg substrate and prevents interfacial voids defects observed with pure Al coatings. Electrochemical tests show that the multilayer coating reduces corrosion current density by five orders of magnitude and increases corrosion potential. Subsequent anodizing of the Al layer further improves corrosion resistance by another two orders of magnitude, enabling the coating to withstand over 600 h of salt spray without corrosion and blistering failure, while maintaining an aesthetically pleasing metallic appearance. This study proposes a promising corrosion-resistant coating strategy to expand the practical applications of magnesium alloys in demanding environments.