Synthesis of eutectic Al–18Ce alloy and effect of cerium on the PEO coating growth

Abstract

Plasma electrolytic oxidation (PEO) is an attractive technique for enhancing the wear resistance, hardness and aqueous medium corrosion of aluminum alloys. Phase composition, microstructure and elemental distribution determine the mechanical-corrosion properties of coating. In this study, Al–18Ce binary alloys were synthesized and the effect of Ce (cerium) on the formation mechanism of PEO coating was investigated. The pure Al and eutectic Al–18Ce binary alloy were coated by PEO for 15 min and the effect of Ce content on behavior and properties of the coatings were examined. α-Al and Al11Ce3 phases were observed in the XRD pattern of Al–Ce alloy. The average values of hardness on Al11Ce3 precipitate and the hardness values of Al/Al11Ce3 regions were found to be 365 ± 35 HV and 75.5 ± 2.5 HV, respectively. It was found that the eutectic Al–Ce alloy microstructure contained α-Al, the fine eutectic Al11Ce3 lamellar and needle-like Al11Ce3 precipitates. While α-Al2O3, γ-Al2O3 and 3Al2O3·2SiO2 phases were identified on all the coatings, CeO2 phase was identified on the coatings of Al–18Ce alloy. The α-Al2O3 phase was detected on the coating synthesized on the pure Al, while the increased amount of Ce in Al alloys reduced the formation of α-Al2O3 phase. The size and the number of porosity levels of the coatings increased with increasing amount of Ce in Al. The microhardness profile throughout the coating/substrate interface to surface of the coating decreased for the coatings. The diameter of tiny globular particles on the coating/substrate (C/S) interface for Al–Ce alloy was found to be approximately 0.5–1.5 μm.