材料期刊网

The polarization curves of magnesium alloy AZ91D with a micro-arc oxidation (MAO) coating showed several typical patterns caused by differences in the composition and structure of the coating. The pattern of the polarization curve of magnesium alloy AZ91D with a MAO coating depends on the primary composition and structure of the MAO coating and many experimental factors, such as the concentration of chloride ions, pH of the electrolyte, degree of cathodic polarization, and the exposed area of the specimen. These factors change the pattern of polarization curve of magnesium alloy AZ91D with MAO coating by affecting the main composition and structure of the MAO coating because of its instability in aqueous solution. Compositional and structural changes in the MAO coating on magnesium alloy AZ91D were investigated by Fourier transform infrared microscopic mapping and the corresponding optical photographs, respectively. A model was proposed to describe the transformation of the MAO coating in aqueous NaCl solution. For magnesium alloy AZ91D with a MAO coating immersed in NaCl solution, the rate determining steps of the anodic and cathodic reactions are the mass diffusion and charge transfer steps, respectively. As a result, the corrosion current density fitted from the polarization curve is not an accurate corrosion rate.