Effects of tannic acid on properties of anodic coatings obtained by micro arc oxidation on AZ91 magnesium alloy

► Tannic acid can promote the coating formation and change the coating color. ► Tannic acid can increase the coating thickness. ► Insoluble magnesium-tannate is formed in anodic coatings in the solution with tannic acid. ► Tannic acid can improve the corrosion resistance of the anodized magnesium alloy.