Wear and Corrosion Behaviours of PEA Alumina Coatings on Gray Cast Iron

Alumina (Al₂O₃) thin film coatings are applied on Al alloys using Plasma Electrolytic Oxidation (PEO) method to reduce the wear and corrosion problems. Plasma Electrolytic Aluminating (PEA) is a technique which could generate Alumina coatings on cast iron, mild steel and copper alloys. In this study, the aim is to explore the anti-wear and anti-corrosion behaviours of PEA Alumina coatings on gray cast iron. The dry sliding tribology test data was obtained from Pin-on-Disk (POD) tests against SAE 52100 steel and Tungsten Carbide (WC) counterfaces. Comparing with the PEO Alumina coatings, the PEA Alumina coating has much lower Coefficient of Friction (COF) and less wear. The microstructure, chemical composition and phase composition of this coating were investigated with Scanning Electron Microscope (SEM), Energy-Dispersive X-Ray Spectroscopy (EDX) and X-Ray Diffraction (XRD), respectively. There was FeO (or FeAl₂O₄) found on the PEA Alumina coating. To figure out the relationship between FeO and the COF, 500 °C heat treatment was conducted on PEA Alumina coated samples, in which FeO could be fully oxidized into Fe₂O₃ by heat treatments. Differences between unheated and heated samples in chemical composition and wear behaviours were observed. The co-existence of FeO (or FeAl₂O₄) compounds in PEA Alumina coating is an important factor which introduce relative low COF. The corrosion resistance was evaluated by electrochemical tests. It could be observed and be calculated that the PEA Alumina coated gray cast iron has much better corrosion resistance than uncoated samples. Since the PEA coating can also be applied onto steel materials, the coating technology can be used to protect the hinges of doors and other joint parts from frequent wear and corrosion issues.