Study on corrosion protection behavior of magnesium alloy/micro-arc oxidation coating in neutral salt spray environment

To study the corrosion behavior of wrought and cast Mg alloys protected by a micro-arc oxidation layer, a neutral salt spray test was used to accelerate the corrosion of the samples. The results showed that the surface of the wrought Mg alloy/micro-arc oxidation system was relatively smooth up to 720 h, and there was no obvious change in the alloy. However, the corrosion products were observed on the surface after 960 h. Corrosion products appeared in the cast Mg alloy/micro-arc oxidation system after 240 h of testing. Electrochemical impedance spectroscopy results and failure analyses of the scratched samples indicated that in the early stage of corrosion, a large number of corrosion products were formed on the substrate and accumulated in the micro-arc oxidation layer, which blocked the pores and gradually enhanced the impermeability of the two Mg alloys/micro-arc oxidation systems. After 480 h, the impermeability of the micro-arc oxidation layer in the cast Mg alloy/micro-arc oxidation system decreased as the number of pores, cracks, and other defects in the layer increased. This resulted in a decrease in the damage position of the micro-arc oxidation layer.