Effect of Plasma Electrolytic Oxidation Process as a Pretreatment on Corrosion Resistance of Polymeric Coatings Applied on Mg Alloy

In this study, Plasma Electrolytic Oxidation (PEO) at three frequencies of 500, 1000 and 3000 Hz was applied on Mg surface and the effect of PEO surface preparation on protective behavior of three types of epoxy, fusion bond epoxy (FBE) and polyurethane coatings was investigated. The microstructural and protective properties of PEO coatings were studied by SEM, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that the coating formed at frequency of 3000 Hz had smaller pore size and better protection properties. EIS test in 3.5 Wt.% NaCl solution was also used to investigate the protective behavior of the two-layered coatings. The results showed that PEO process had a favorable effect on the protective behavior of the polymer layers. Moreover, the best protection behavior was related to the PEO/FBE coating system.