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 center dot 2H(2)O). The addition of Na2WO4 center dot 2H(2)O 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 center dot 2H(2)O was studied, and the coating obtained in 10 g 1(-1) Na2WO4 center dot 2H(2)O 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.