Corrosion Resistance Enhancement of AZ91 Magnesium Alloy Using Ni-P Interlayer and Electrophoretic Deposited 3YSZ Coating

The zirconia stabilized by 3mol % Y2O3 (3YSZ) was applied onto the surface of the magnesium alloy AZ91D using electrophoretic deposition (EPD) from a non- aqueous solution. A Ni-P interlayer between the substrate and YSZ coating was also prepared by electroless plating. Finally, coatings were heat treated in control atmosphere at 400 °C. The preparation, microstructure and corrosion resistance of the coatings were investigated. Scanning electron microscope (SEM) was used to investigate the morphology of coatings. In addition, compositions of surface were determined by X-ray diffraction (XRD). The corrosion resistance of the coatings was evaluated by electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. Also, the stability of coating was investigated by the Rockwell C indentation test (VDI 3198 norm). The results indicate that Ni-P interlayer can improve the quality of zirconia coating on the surface. Also, the Ni-P interlayer and YSZ coating increase the charge-transfer resistance of AZ91D surface in chloride solution.