The characteristics, such as roughness, thickness, microhardness and corrosion resistance, of plasma electrolytic oxide coatings
on AZ91D alloy were investigated under the processing condition of various coating times. The coatings on AZ91D alloy consisted
of MgO, MgAl2O4 and Mg2SiO4 oxides. The surface roughness and thickness of coatings became larger with increasing the coating
time. The microhardness in cross section of coatings was much higher than not only that in surface but that in the conventional
anodic oxide coatings, which increased progressively as the coating time increased. After being immersed in 3.5%NaCl solution and
methyl alcohol, the corrosion resistance of AZ91D alloy was markedly improved by plasma electrolytic oxidation coating treatment,
and the AZ91D alloy coated for 50min revealed excellent corrosion resistance.