Development of Potentiostatically Deposited Cerium Conversion Coating for Mg Alloys

Abstract

In this work, cerium conversion coating (CeCC) was deposited on AZ91D Mg alloy using potentiostatic polarization method combined with phosphate pore-sealing treatment. Initially, the optimum deposition parameters to obtain a crack-free surface were found. The characterization of coating revealed the presence of a nodular morphology of cerium oxide deposits. Next, the electrochemical behavior of the coated surface was assessed using potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5 wt% NaCl solution. Based on electrochemical characterization, the coating exhibited a fivefold increase in the charge transfer resistance and a corresponding 76% reduction in corrosion rate, when compared to the bare surface. Furthermore, the conversion coating exhibited improved corrosion resistance when evaluated using the immersion test. Therefore, these findings demonstrate the feasibility of the potentiostatic method for creating nearly crack-free CeCC on Mg alloys, unlike conventional conversion coatings. Moreover, this approach holds great potential for effectively mitigating the corrosion issues in Mg alloys.