Characterization and Corrosion Behavior of PEO Coatings Formed on AZ۳۱ Magnesium Alloy at Different Electrolytes

In this study, the process of applying plasma electrolyte oxidation (PEO) coating on AZ۳۱ 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 ۳.۵ %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 Mg۲SiO۴. 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 Mg۲SiO۴ phase as well as its relatively low porosity.

کلیدواژه ها:

AZ۳۱ Magnesium alloy ، plasma electrolytic oxidation (PEO) ، corrosion behavior ، sodium silicate ، sodium polyphosphate ، sodium aluminate ، آلیاژ منیزیم AZ۳۱ ، اکسیداسیون پلاسمای الکترولیتی (PEO) ، رفتار خوردگی ، سدیم سیلیکات ، سدیم پلی فسفات ، سدیم سیلیکات ،