Effect of EDTA on microstructure and corrosion performance of MAO coating on 6061 Al alloy

In this work, micro-arc oxidation (MAO) technology was employed to fabricate oxide ceramic coatings on an aluminum alloy substrate. The additive ethylenediaminetetraacetic acid disodium (EDTA-2Na) was introduced into a silicate-based electrolyte to investigate its influence on the microstructure and properties of the MAO coatings. The results revealed that the coating containing EDTA-2Na (MAO/EDTA-2Na) exhibited a smoother and denser surface, along with significant improvements in thickness, hardness, wear resistance, and corrosion resistance compared with the additive-free coating. Electrochemical test results showed that the self-corrosion current density of the MAO/EDTA-2Na decreased by approximately three orders of magnitude. In addition, the corrosion potential of the coating shifted positively by 0.88 V. The impedance arc radius measured by electrochemical impedance spectroscopy was significantly larger than that of the aluminum alloy, further confirming that the coating effectively hindered the corrosion reaction process. Furthermore, the salt spray test results showed that the MAO/EDTA-2Na exhibited no obvious corrosion phenomena after 240 h of exposure to a neutral salt spray environment, in comparison with the bare aluminum alloy and the MAO coating. This study provided insights into the formation and growth mechanism of the ceramic layer, offering theoretical and technical support for improving surface protection of metallic alloys.