Painting of magnesium alloys based on microarc electrodeposition
LIU Yuangang, ZHANG Wei, GAO Jin, TU Yunhua, LI Jiuqing Materials Science and Engineering School, University of Science and Technology Beijing, Beijing 100083, China
A painting method based on a microarc oxidation (MAO) coating was applied to protect magnesium alloys. The MAO coating was simultaneously electrodeposited on the anode and cathode of AZ91D magnesium cast alloy with AC symmetric pulse method in composite silicate solution. Salt spraying tests were used to investigate the corrosion resistance of sol-gel, polysilicone, and organic epoxy primer and polyurethane acrylic topcoat coverings, which were considered as three post-coating methods to MAO specimens. After painted with epoxy primer and polyurethane acrylic topcoat, the barrier property of MAO samples was compared with that of Mg/paint and traditional Mg/chromate conversion coating (CCC)/paint specimens by salt spraying tests and electrochemical impedance spectroscopy (EIS). It was demonstrated that sol-gel, polysilicone and organic coatings all bear some validity, especially epoxy primer with polyurethane acrylic topcoat worked so well that no corrosion happened after 480 h of salt spraying. The shielding property of Mg/MAO/Paint was better than that of Mg/paint and Mg/CCC/paint.