Characteristics of sealed plasma electrolytic oxidation coatings with electrochemical impedance spectroscopy

Plasma electrolytic oxidation (PEO) coatings are prepared on aluminium with graphite powders added into the electrolyte. The scanning electron microscopy (SEM) coupled with an energy dispersive x-ray analysis system (EDX) is used to characterize the surface and the cross-section morphologies of the coatings. The electrochemical impedance spectroscopy (EIS) is used not only to evaluate the corrosion resistance but also to analyse the structure of the coating. Results show that graphite powders are embedded in the PEO coating. The corrosion resistances of both the inner barrier and the outer porous layer are greatly improved, and the EIS could give some valuable detailed information about the coating structure.