Tribological and Corrosion Properties of Coatings Produced by Plasma Electrolytic Oxidation on the ZA27 Alloy

In this paper, a continuous and dense coating was deposited on samples of the ZA27 alloy through the plasma electrolytic oxidation (PEO) process to improve its wear and corrosion performance. A nontoxic and environmentally friendly inorganic salt, Na₂SiO₃, is chosen as electrolytes with different concentrations. The effect of the concentration of Na₂SiO₃ aqueous solutions on the coating performances was investigated. The coatings with 3Al₂O₃·2SiO₂ (mullite), Zn₂SiO₄ and Al₂O₃ (either crystal phase or with some amorphous SiO₂ phases) were formed by the PEO processes. It was found that the coating thickness increased with the increase in electrolyte concentration. However, the wear and corrosion resistance performance of the coatings did not improve as the coating’s thickness increased. This was due to the fact that the coating produced with electrolytes of 10 g/L has a porous structure with large pore size. Among all the samples, coating produced by 15 g/L Na₂SiO₃ has the best wear and corrosion resistance, which is attributed to its continuous and dense structure with thickness of about 47 μm.