The effect of electrolyte on the microstructure and corrosion properties of plasma electrolytic oxidation coating on AA7075

Document Type : Original Articles

Authors

Erfan Pirhadi nori ¹

Saeed Reza Allahkaram ¹

mehrnaz gharagozlou ²

¹ School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran

² Department of Nanomaterials and Nanocoatings

10.22067/jmme.2025.89503.1153

Abstract

Abstract: Plasma electrolytic oxidation (PEO) is an effective method to improve the corrosion resistance of 7075 aluminum alloy. Electrolyte plays a crucial role in determining the properties of the final coating. In this research, the effect of electrolyte on plasma electrolytic oxidation (PEO) coatings formed on AA7075 alloy in silicate, phosphate, and silicate-phosphate electrolytes was investigated. The thickness of the coatings was measured by an Eddy-current thickness gauge. It was found that increasing the concentration of silicate increases the growth rate of the coating. Increasing the silicate concentration from 5 to 10 g/L led to a coating thickness increase from 7 to 14.5 µm. The microstructure and constituent elements of the coatings were examined by SEM equipped with an EDS detector. The presence of sodium phosphate in the electrolyte slows the coating's growth rate and reduces its porosity by 10.6 percent. The corrosion resistance of coatings was evaluated in 3.5% NaCl solution by EIS test. It was found that |Z| is 89% higher for the silicate-phosphate coating than the silicate coating. Silicate-phosphate electrolyte showed the best corrosion resistance behavior due to its lower porosity.

Keywords

AA7075

Plasma Electrolytic Oxidation

Corrosion

Subjects

• Corrosion and Oxidation

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