Improving wear and corrosion properties of alumina coating on AA7075 aluminum by plasma electrolytic oxidation: Effects of graphite absorption

An alumina coating with a thickness of 20-50 mu m was deposited by plasma electrolytic oxidation (PEO) on an AA 7075 Al alloy in an alkali-aluminate electrolyte using a 5 kW DC power supply. After the formation of the coating, the effects of current density, electrolyte concentration, and process time on the coating characteristics were investigated comprehensively. In order to achieve improved tribological and corrosion properties, the prepared samples were evaluated by means of various characterization techniques including scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses, micro-hardness, thickness and roughness measurements, corrosion potentio-dynamic, and pin-on-disk wear tests. Electrophoretic graphite absorption was subsequently carried out on the samples, which resulted in the desirable experimental results to boost the coating in terms of roughness, tribological, and corrosion properties. The positive effects of graphite absorption on the PEO coatings were also elaborated in detail.