Green Cerate Based Surface Treatment for Improving the Corrosion Resistance of Magnesium Alloy AZ91D in Marine Environments

摘要

The corrosion behavior of AZ91D treated with ceria conversion coatings was studied in 3.5% NaCl solution. The effect of surface preparation prior to ceria treatment was also studied. Electrochemical Impedance Spectroscopy (EIS) and polarization measurements have been used to evaluate the corrosion behavior. The optimum conditions under which ceria can provide acceptable localized corrosion protection to the magnesium substrate were determined. Generally, ceria can be used as a localized corrosion inhibitor for AZ91D. The level of inhibition strongly depends on the ceria concentration. According to the EIS and polarization measurements, alkaline etching prior to ceria coatings is more effective in reducing the pitting corrosion of AZ91D than acidic one. It was found that alkaline solution plays an important role in inhibiting the active surface sites, rejecting the chloride ions from the surface and forming uniformly distributed oxide film.