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In this study, the process of applying plasma electrolyte oxidation (PEO) coating on AZ31 magnesium alloy was performed in different alkaline electrolytes based on sodium silicate (SE), sodium polyphosphate (PE) and sodium aluminate. The morphology, chemical composition and phase structure of coatings were investigated via scanning electron microscopy (SEM) equipped with the energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction, respectively. The corrosion behavior of coatings was examined by polarization and electrochemical impedance spectroscopy tests in a solution containing 3.5 %wt sodium chloride. Microscopybased investigations indicated that the thickness of the formed coating in the phosphate electrolyte was approximately two times greater than that of those formed in the other electrolytes, while the relative porosity percentage was higher than other two electrolytes. The phase investigations of the coatings implied that the MgO was the dominant phase of AE and PE coatings while the major phase of the SE coating was Mg2SiO4. Additionally, electrochemical investigations demonstrated that the corrosion resistance of the produced coating in the silicate electrolyte was dramatically higher than other coatings which could be attributed to the presence of the dense and stable Mg2SiO4 phase as well as its relatively low porosity.

Keywords: AZ31 Magnesium alloy, plasma electrolytic oxidation (PEO), corrosion behavior, sodium silicate, sodium polyphosphate, sodium aluminate

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