Effect of positive pulse voltage on color value and corrosion property of magnesium alloy black micro-arc oxidation ceramic coating

Abstract To improve the corrosion resistance of the magnesium alloy and to extend its applications in light absorption field, black anti-corrosion and absorption integrated ceramic coatings were prepared on AZ31 magnesium alloy by asymmetric bipolar pulse micro-arc oxidation (MAO) technique. The effect of applied positive pulse voltage on the color value and corrosion properties of the coatings were investigated. The results showed that the Cu2+ ions were dissolves into MgO lattice to form the substitutional solid solution (Mg1-XCuXO) during MAO of magnesium alloys. The color value was mainly determined by the effect of the content of Cu2+ ions on the band gap of MgO. On the premise of constant negative pulse voltage, with the increase of positive pulse voltage, the solid solubility of Cu2+ ions in ceramic coating increased first and then remained unchanged, while the color value decreased first and then kept constant. The average absorption rate of black ceramic coating to visible light could be up to 95%. Moreover, the rising positive pulse voltage increased the thickness and decreased the density of the black ceramic coating, resulting the anti-corrosion property increases first and then decreases.