Some of the magnesium alloys can be use as implantations in human body. The lack of sufficient corrosion resistance in physiologic environments is one of the disadvantageous of these materials. Plasma Electrolytic Oxidation (PEO) is one of the promising treatments which can enhance the corrosion and wear resistance of these alloys. Mg AZ31 is one of these biocompatible alloys that we used as substrate in this research. PEO coatings were obtained in baths containing Trisodium Phosphate and KOH and also DC bipolar and unipolar currents used to coating these materials. In the first part of experiments the coatings were obtained under 1 kHz DC bipolar current and three concentrations of 0, 0.05 and 0.25 g/l Calcium Acetate additive in order two producing Tri-Calcium Phosphate containing coatings. The second part coatings were obtained under DC unipolar by 1, 2, 3 kHz frequencies and 0, 0.05 g/l Calcium Acetate concentrations. Electron microscopy, X-Ray diffraction and electrochemical tests were conducted on samples to characterizing their properties. Electron microscopy analysis showed higher thickness for coatings obtained under DC unipolar. The electrochemical analysis showed better corrosion resistance for DC unipolar samples. Also the X-Ray diffraction showed Tri-Calcium Phosphate in coated samples under unipolar condition but this phase didn’t verified in bipolar coated samples. It is concluded that DC unipolar currents are sufficient for PEO coatings on Mg AZ31 alloy and also we can get Tri-Calcium Phosphate by adding Calcium Acetate in coating electrolyte which is beneficial to biocompatibility of the coating. Keywords: Magnesium Alloy, AZ31, Corrosion, Electrochemical Impedance, Polarization, Open Circuit Potential, Calcium Acetate
