Phase constituency effect of ternary Al2O3-SiO2-MgO coating on coating morphology and corrosion resistance of Mg alloy AE44

Broader engineering applications of magnesium‑aluminum alloys are limited by their relatively low hardness and inadequate corrosion resistance. To address these shortcomings, surface modification techniques such as plasma electrolytic oxidation (PEO) are employed to form protective oxide layers that enhance surface performance. Previous studies primarily focused on plasma temperature and soft discharge to analyze the discharge behavior during PEO process, while relatively less attention has been paid to the subsequent solidification process. In this study, PEO coatings containing binary and ternary phases were produced using mixed aluminate-silicate electrolytes with varying concentrations. The Al 2 O 3 -SiO 2 -MgO ternary phase diagram was employed to investigate phase evolution during solidification. Different primary phases and their corresponding liquidus temperatures were revealed to understand the formation of phase constituents and their compositions. It was found that the electrolyte composition significantly influenced the primary phases formed in the coatings, thereby affecting their liquidus temperatures and, consequently, the microstructure, morphology, and corrosion resistance. In particular, increasing the silicate content from 0 g/L to 6 g/L in the mixed electrolyte reduced the liquidus temperature of the primary phases, enhanced the fluidity of the coating material during solidification and led to a decrease in surface porosity (by up to 30% difference) on the coating surfaces through densifying the coating microstructure and sealing the pores, ultimately improving the polarization corrosion resistance (up to 110.34 kΩ · cm 2 ) of the coated alloy, compared to the uncoated Mg alloy (1.161 kΩ · cm 2 ). More research is needed for studying long-term corrosion behavior.