Study Of Preparing Process And Performance Of Micro-arc Oxidation Black Coating On AZ91D Magnesium Alloy

The anodized oxide film of magnesium alloy has many defects (poor bond strength, low wear and corrosion resistance, easy fading, uneven color, etc) in traditional surface coloring technology. These defects have largely limited the applications of magnesium alloy. In this paper, black ceramic film with uniform color, smooth surface, compact structure and excellent corrosion resistance on AZ91D alloy was successfully obtained by micro-arc oxidation(MAO).Three electrolytic solution systems (silicate, organic amineâ… , organic amineâ…¡)were worked out through a large number of study. The influences of termination voltage and oxidation time in the same electrolyte were further studied.The differences between thickness, roughness and blackness of MAO films were compared. Salt fog corrosion test and accelerated weathering test were used to compare the differences of corrosion resistance and aging resistance. The result shows that micro-arc oxidation process in three electrolytic liquid systems can greatly increase the corrosion resistance and aging resistance of AZ91D alloy and the Organic amineâ…¡system is the best.XRD and SEM tests show that the elements and phase composition of ceramic film are related with the composition of magnesium alloy and electrolyte types, and coloring salt plays an important role. With the increase of terminal voltage and oxidation time the proportion of coloring salt in MAO film increased. The surface of the films produced in three electrolytic solutions system exhibits a net-pore shaped morphology. The pore radius and porosity of MAO film obtained in organic amine system are much better than that in silicate system.