Corrosion resistance of composite coating on magnesium alloy using combined microarc oxidation and inorganic sealing

The combined microarc oxidation (MAO) and inorganic sealing process was used to deposit a composite coating to improve the corrosion resistance of AZ31 magnesium alloy. The surface morphologies of the resulting duplex coatings were studied by SEM. Furthermore, the corrosion resistance of the coated Mg alloy substrates was investigated using electrochemical workstation and dropping corrosion test. The results show that the composite coating surface consists of Mg, Si, O and Na. It is difficult to deposit inorganic coating on a thick MAO coating surface. As the composite coating was solidified by CO2 under 175 degrees C, it exhibits a better corrosion resistance than the MAO monolayer, owing to the thick and compact inorganic coating.