Effects of Electrolyte Parameters on Properties of Ceramic Coatings Formed on Aluminum Alloy 7075 by Plasma Electrolytic Oxidation

Four electrolyte (aluminate, silicate, borate and phosphate) solutions were optimized for using in surface treatment of 7075 aluminum alloy by plasma electrolytic oxidation. Microstructure, phase composition and corrosion resistance of ceramic coatings on the surface were analyzed by SEM, X-ray diffraction as well as electrochemical work station. It was showed that ceramic coatings prepared in aluminate solution had excellent continuity, compact structure with micro hardness of HV0.1 1100. The major portion of all coatings consisted of γ-Al2O3 and bits of α-Al2O3, the corrosion potential was increased by a small extent while the corrosion current density was significantly reduced.