A New Eco-friendly Anticorrosion Strategy for Ferrous Metals: Plasma Electrolytic Aluminating

To avoid possible eco-disadvantages of phosphating and zinc plating used for corrosion protection of ferrous metals, this work was to develop an alternative coating technique, called plasma electrolytic aluminating (PEA) process, which can be environmentally friendly in terms of the process itself, and eco-friendly with respect to the coating materials. The PEA process was to form a metal aluminate coating on the metallic surfaces through plasma discharging in an aluminate-based electrolyte when a high voltage was applied to the metals. The aluminating mechanism was investigated using scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction (XRD). The research revealed that the hercynite film formed on the metallic surface was indispensable for initiation of the aluminating process. Only after a continuous hercynite film fully covered the metallic surface could the stable plasma discharges be established to sinter the film into a strong ceramic coating. The XRD analysis indicated that a prolonged PEA treatment would result in a hercynite–alumina composite coating. Hardness tests and electrochemical corrosion tests showed that the composite coating could provide the gray cast iron (as an example of ferrous metals) with excellent wear and corrosion protection. With the benign coating process and safe ceramic coating materials, the plasma electrolytic aluminating approach could be used as an eco-friendly and cost-effective strategy for anticorrosion of ferrous metals.