Effects of the ratio of anodic and cathodic currents on the characteristics of micro-arc oxidation ceramic coatings on Al alloys

•Ra of the ceramic coatings decreases with the decrease of the ratio ra/ca.•Hardness of the ceramic coatings increases with the decrease of the ratio ra/ca.•H and Hout decrease with the decrease of the ratio ra/ca while Hin increases.•The proportion of the inner compact layer in the total ceramic coatings increases with the decrease of the ratio ra/ca.•The inner compact layer is compact and uniform. The micro-arc oxidation (MAO) has increasingly gained attention as a novel and unique technique for depositing thick, dense, and ultra-hard ceramic coatings on aluminum and its alloys substrates. For the MAO technology, discharge parameter, especially the cathodic current, has an important effect on the characteristics of ceramic coatings. But the effects of the ratio of anodic and cathodic currents on properties of the ceramic coatings on Al alloys are rarely studied. This work investigates the effects of the ratio of anodic and cathodic currents under the constant current density on morphology, phase composition, microstructure, and properties of ceramic coatings on 6061 Al alloys. It is found that the ceramic coatings surface roughness Ra is decreasing, and the hardness of ceramic coatings is increasing with the decrease of the ratio. The ceramic coatings are mainly composed of a large amount of α-Al2O3 and γ-Al2O3. The content of α-Al2O3 in the ceramic coatings increases with the decrease of the ratio.