Corrosion Performance of Composite MAO/TiO2 Sol–Gel Coatings on Magnesium Alloy AZ91D

In this paper, the composite coatings on the surface of magnesium alloy were successfully prepared by the combination of micro-arc oxidation (MAO) and sol–gel method. Oxide ceramic layers were formed on AZ91D magnesium alloy using MAO process. The sol–gel layers were coated on MAO ceramic layers. The composition of the composite coatings was analyzed by x-ray diffraction and x-ray photoelectron spectroscopy. The microstructure of the composite coatings was analyzed by scanning electron microscope. The results show that the composite coatings can reduce the gap membrane effectively. The polarization curves and electrochemical impedance spectroscopy were used to evaluate the corrosion resistance. The results of corrosion tests show that the sol–gel layer enhances the corrosion resistance of the magnesium alloys significantly.