Effect of treatment time on a PEO-coated AZ31 magnesium alloy

Plasma electrolytic oxidation (PEO) coatings were formed in a phosphate-silicate-based electrolyte containing K2ZrF6 on an AZ31 Mg alloy. The physical and chemical properties of the coatings were investigated using scanning electron microscopy, atomic force microscopy, X-ray diffraction (XRD), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The results showed that the thickness of the PEO coatings increased linearly with increased treatment times. Additionally, the micropores on the coating surfaces increased in size, but decreased in porosity with increased PEO treatment time. The XRD results showed that the coatings were mainly composed of MgO, MgF2, MgSiO3, and ZrO2, and the electrochemical tests revealed that the corrosion resistance of the coatings increased with increased treatment time. Besides, the EIS results correlated well with the potentiodynamic polarization test results.