Influence of Sodium Tungstate and Sealing Treatment on Corrosion Resistance of Coatings Formed on AZ31 Magnesium Alloy by Plasma Electrolytic Oxidation

W-containing ceramic coatings were fabricated on AZ31 magnesium alloy by plasma electrolytic oxidation (PEO) in an aluminate-based electrolyte with the addition of sodium tungstate (Na2WO4·2H2O). The addition of Na2WO4·2H2O not only increased the growth rate and surface roughness of the coatings but also improved the corrosion resistance of the PEO coating. The relationship between the corrosion resistance of the PEO coating and the concentration of Na2WO4·2H2O was studied, and the coating obtained in 10 g l-1 Na2WO4·2H2O showed the best corrosion resistance. Ce-based sealing followed by Al(H2PO4)3 sealing treatment was further carried out to improve the corrosion resistance of the coatings. It was found that the number and size of pores and micro-cracks decreased after sealing. Potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) measurements indicated that the corrosion resistance of the PEO coatings was effectively improved by the two-step sealing method.