Structure and properties of ceramic coating on Al alloy by plasma microarc oxidation

Microarc oxidation (MAO) coating on 7075 Al alloy were prepared in Na₂SiO₃ electrolytes with and without Na₂WO₄ addition. The effects of Na₂WO₄ with different concentrations on the surface morphology, cross-sectional microstructure and micro-hardness of ceramic coatings have been studied by using SEM and micro-hardness tester, respectively. The results show that the microarc oxidation surface treatment can form a dense ceramic coating on 7075 Al alloy, which has good adhesion with Al alloy substrate. The concentration of Na₂WO₄ solution has significant influence on the color, surface morphology, density and micro-hardness of ceramic coating, but has not much influence on the thickness of the ceramic coating. The addition of Na₂WO₄ into the base Na₂SiO₃ electrolyte resulted in the increase of the microhardness of the ceramic coating.