Effects of oxidation time on corrosion resistance of plasma electrolytic oxidation coatings on magnesium alloy

Abstract

Abstract The plasma electrolytic oxidation (PEO) technique was used to coat AZ31 magnesium alloy in a phosphate-based electrolyte. Effects of oxidation time on the morphology, phase structure, and corrosion resistance of the ceramic coatings were systematically investigated by scanning electron microscopy, X-ray diffraction, potentiodynamic polarization and electrochemical impedance spectroscopy testing. The main components of the resulting coatings were MgO, MgF2 and t-ZrO2. It was also found that there was a significant influence of the oxidation time on the corrosion resistance of the coatings. The coating obtained under the oxidation time of 10 min exhibited a corrosion current of 3.89 × 10−6 A cm−2 in 3.5 wt.% NaCl solution, which was a significant decrease compared with the uncoated magnesium alloy. The results of the corrosion tests indicated that the PEO coating formed at 10 min demonstrates a higher corrosion resistance compared to the samples formed at 5, 15 and 20 min.