Effect of current density on microstructure, mechanical behavior and corrosion resistance of black MAO coating on 6063 aluminum alloy

Black micro-arc oxidation (MAO) coatings were prepared on 6063 aluminum alloy using alkaline silicate electrolyte at different current densities. Effect of current densities on the microstructure, mechanical behavior and corrosion resistance of black ceramic coatings was studied. The experimental results indicated that the current density could increase the process voltage, enhance the MAO reaction, increase the coating thickness, reduce the poriness, increase the surface roughness, and improve the mechanical properties (hardness, adhesion, friction and wear). The black MAO coating prepared in the current density with 6A/dm² had the best corrosion resistance in 3.5 wt% NaCl solution, as manifested by a corrosion current density of 3.713 × 10⁻⁷ A/cm² that was 2 orders of magnitude less than that of the 4A/cm². The corrosion resistance results were further confirmed through an immersion corrosion test.