Characterization and corrosion behaviour of a phosphate-based plasma electrolytic oxidation coating on extruded EV31 magnesium alloy

Abstract This paper is focused on evaluating the surface properties of protective coating prepared by plasma electrolytic oxidation on magnesium alloy EV31. Plasma electrolytic oxidation was performed in DC mode with a constant current density of 0.05 A cm −2 for 14 min. Evolution of voltage was measured and depicted graphically in order to describe the growth of the plasma electrolytic oxidation coating. Morphology and thickness of the plasma electrolytic oxidation coating were examined together with corrosion resistance of the coating by measurements of electrochemical characteristics using electrochemical impedance spectroscopy and potentiodynamic polarization after 1 h in 0.1 M NaCl. Results from potentiodynamic polarization showed decrease in corrosion current density i corr from 10.50 μA cm −2 (substrate) to 1.02 μA cm −2 (plasma electrolytic oxidation coated) and results from electrochemical impedance spectroscopy showed increase in R p by one order of magnitude for plasma electrolytic oxidation coated sample after both 1 h and 168 h exposure times.