Microstructural, protective, inhibitory and semiconducting properties of PEO coatings containing CeO2 nanoparticles formed on AZ31 Mg alloy

The aim of this study is to investigate the effects of presence of cerium oxide nanoparticles on the microstructure, protective properties and inhibitory properties, while also enquiring into plasma electrolytic oxidation (PEO) coatings semiconductors properties, which were formed in a phosphate electrolyte solution, applied on AZ31 Mg alloy. According to the SEM/elemental map, Ce has been deposited in the oxide coating structure, and results in the changing of the morphology and coating thickness. According to the results of potentiodynamic polarization (PDS) and electrochemical impedance spectroscopy (EIS), during the short and long immersion period of up to 16 days, the presence of optimum level of CeO2 in the phosphate electrolyte solution (3 g/l) results in the highest protection properties for PEO coating. Furthermore, the EIS test following the PDS, indicated the inhibitory effects of the cerium products, while the results of Mott-Schottky (M-S) test indicated a decrease in the donor concentration with presence of optimum CeO2 and thus, a drop in the tendency to undergo corrosion reactions. Thermodynamic investigations have shown that the formation of corrosion products which contain Ce is possible and stable, hence leading to the improvement of the protective properties of PEO coatings.