Preparation and Corrosion Behavior in Marine Environment of MAO Coatings on Magnesium Alloy

To improve the corrosion performance of magnesium alloys in the marine environment, the MAO, MAO–Cu(2)CO(3)(OH)(2)·H(2)O and MAO–Cu(2)P(2)O(7) ceramic coatings were deposited on AZ91D magnesium alloys in basic electrolyte and the discoloration mechanism of the Cu-doped MAO coatings and the corrosion behavior of the three MAO coatings in the artificial seawater solution were investigated by SEM, EDS and XPS. The results indicated that the formation and discoloration mechanism of the brown MAO ceramic coatings were attributable to the formation of Cu(2)O in the coatings. Though the three MAO coatings had a certain protective effect against the corrosion of AZ91D substrate in the artificial seawater, the distinctive stratification phenomenon was found on the MAO–Cu(2)P(2)O(7) coated sample and the corrosion model of the MAO–Cu(2)P(2)O(7) coatings in the immersion experiment was established. Therefore, the brown Cu-doped MAO coatings were speculated to significantly reduce the risk of the magnesium parts in marine environments.