Influence of Alternating Current Density on the Mechanical Behavior and Microstructure of PEO-Coated 7075 Aluminum Alloy

Abstract

The objective of the study was to investigate the characteristics of coatings formed on 7075 Al alloy using a plasma electrolytic oxidation (PEO) method in silicate electrolytes under alternating current conditions. The properties of the coatings were evaluated based on the current density applied during the experimental process. To analyze the samples, the surface and cross-sectional images of the coatings were observed using scanning electron microscopy. The results showed that the PEO coatings were between 25–102 µm in thickness, and the thickness was found to be dependent on the applied current density. The hardness values of the PEO coatings were found to be significantly, approximately three times, higher than the uncoated alloy. Wear analysis revealed that the PEO coatings formed under current densities of 8.8 A/dm2 and 17.8 A/dm2 exhibited the best wear resistance among all the coatings. In addition, the PEO coatings also displayed good corrosion resistance, with the resistance of the coatings formed under the current densities of 13.5 A/dm2 and 17.8 A/dm2 being significantly improved compared to that of the bare Al alloy. The most effective anticorrosion PEO coating was found to be the one formed under a current density of 17.8 A/dm2. The wear depths of the PEO coatings formed under current densities of 8.8 A/dm2 and 17.8 A/dm2 were low, resulting in high wear resistance. Among all the PEO coatings, the coating formed under a current density of 17.8 A/dm2 showed the best overall anticorrosion and mechanical properties. Overall, the study highlights the potential of PEO coatings in significantly improving the corrosion and wear resistance of 7075 Al alloy. The results of the study provide useful information for the selection of current density for the PEO coating process on 7075 Al alloy to achieve desired properties. © 2023 by the authors.