Effect of Cerium Nitrate on the Protective and Adhesion Properties of PEO/Epoxy Coating Applied on Mg alloy

In this study the effect of cerium nitrate existing in the structure of plasma electrolytic oxidation (PEO) coating on the protective behavior and adhesion strength of PEO/epoxy duplex coating applied on AZ31 Mg alloy was investigated. PEO coating was considered as the pretreatment for applying the epoxy layer. The presence of Ce additive affected the morphology of the surface of the PEO coating and its corrosion resistance. Embedding Ce in the structure of the PEO layer showed that the PEO structure, in addition to its pretreatment role, acts as the container of cerium. The results of the electrochemical impedance spectroscopy (EIS) test and the pull-off adhesion test in dry and wet conditions on duplex coatings revealed that the presence of Ce improves the protective behavior of the epoxy layer and its adhesion strength. Formation of cerium hydroxide in chathodic regions leads to improvement in the protection properties of duplex coating system.