Electrodeposition of zinc on AZ91D magnesium alloy pre-treated by stannate conversion coatings

A stannate chemical conversion process followed by an activation procedure was employed as the pre-treatment process for AZ91D magnesium alloy substrate. Zn was electroplated onto the pre-treated AZ91D magnesium alloy surface from pyrophosphate bath to improve the corrosion resistance and the solderability. The surface morphologies of conversion coating and zinc coating were examined with scanning electron microscope (SEM). The phase composition of conversion coating was investigated by X-ray diffraction (XRD). The electrochemical corrosion behavior of the coatings in the corrosive solution was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The experimental results showed that the activated stannate chemical conversion coating provided a suitable interface between zinc coating and the AZ91D magnesium alloy substrate. The corrosion resistance of the AZ91D substrate was improved by the zinc coating.