Effect of Various Additives on Performance of Plasma Electrolytic Oxidation Coatings Formed on AZ31 Magnesium Alloy in the Phosphate Electrolytes

Abstract

Plasma electrolytic oxidation (PEO) coatings were prepared on AZ31 magnesium alloy using alkaline phosphate as base electrolyte system, and with the addition of sodium silicate (Na₂SiO₃), sodium aluminate (NaAlO₂) and potassium fluorozirconate (K₂ZrF₆) as additives. The microstructure, phase composition and element composition as well as surface profile of the PEO coatings were analyzed by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and threedimensional (3D) optical profilometry. The corrosion and wear properties were evaluated by electrochemical potentiodynamic polarization in 3.5 wt% NaCl solution and ball-on-disc wear tests, respectively. The results showed that the anions of the additives effectively participated in the coating formation influencing its microstructural features, chemical composition, corrosion resistance and tribological behaviour. It was observed that the sample treated by PEO in the electrolyte solution containing K₂ZrF₆ as an additive showed better corrosion and abrasive resistance.

Keywords

magnesium alloy / plasma electrolytic oxidation / additives / microstructure / corrosion resistance

References

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