Stress corrosion of laser-remelted MAO coating on AZ31B Mg alloy

To improve the stress corrosion cracking (SCC) resistance of AZ31B magnesium alloy, ceramic coatings were fabricated via micro-arc oxidation (MAO) combined with laser remelting (LR). The results reveal that LR effectively optimizes the microstructure of MAO coatings, reducing porosity by 70.86%, lowering coating thickness, and promoting the formation of the MgO phase. The LR treatment enhances the adhesion strength and electrochemical corrosion resistance of MAO coatings. Slow strain rate tensile (SSRT) tests conducted in simulated body fluid (SBF) demonstrate that both MAO and MAO-LR treatments decrease the SCC susceptibility of AZ31B alloy. Benefiting from its dense and uniform microstructure, the MAO-LR coating achieves a low SCC susceptibility index of 16.77%, which is 43.54% lower than that of the bare substrate (29.70%). Fractographic observations further verify that the optimized MAO-LR coating effectively isolates corrosive media and inhibits crack propagation, thus substantially enhancing the alloy's SCC resistance.