Black ceramic coatings prepared in phosphate-based electrolyte containing Fe3+ complexes on ZK61M Mg alloy by micro-arc oxidation

Black micro-arc oxidation (MAO) coatings were fabricated on ZK61M Mg alloy in alkaline electrolyte containing sodium phosphate, ferric citrate, and potassium glucose. The formation process of Fe3+ complexes in the electrolyte and the phase composition and coloration mechanisms of the MAO coatings were investigated. The results showed that Fe3+ complexes move to the anode and are liable to thermal decomposition continuously in the location of spark discharges, resulting in the formation of iron oxide and magnetite incorporated in the black ceramic coatings.