Microstructural and mechanical properties of alumina coatings produced by microarc oxidation technique on 7039 aluminum alloy substrate

Abstract

Aluminum alloy (7039) was coated using a microarc oxidation (MAO) process in an alkali solution. To vary the coating's microstructure and thickness, various current densities and duration were used. The microstructure was studied using a scanning electron microscope and X-Ray Diffraction. Surface roughness was measured using a surface profilometer. Micro hardness measurements on the coated layer, and tribological investigation in biofluids were also performed. The results showed that the coating consists of alpha-Al2O3, gamma-Al2O3 and mullite phase. It was found that the high hardness and thickness are associated with the high concentration of alpha-Al2O3, resulted from the increased current density. MAO coatings typically exhibit micro hardness gradient across the coating thickness. Results also showed that the thicker the coating, the higher the surface roughness. Tribological experiments indicated that this coating is stable and relatively wear resistant in synthetic biofluids.