Study on scanning micro-arc oxidation technology applied to 2024 aluminum alloy

The ceramic coating was formed on the part of the impaired surface of the 2024 alloy sample by scanning micro-arc oxidation using low pulsating power supply. It proposed a solution for local repairing impaired part of big workpiece using micro-arc oxidation technique. Microstructure and phase composition of coating were characterized by SEM, XRD and EDS. The nano indentation hardness and elastic modulus of coatings were tested by nano indenter. The corrosion resistance properties of coatings were determined by potentiodynamic polarization. The results show that under the continuous current mode, the bath voltage of scanning micro-arc oxidation (SMAO) raise fast and go into micro-arc oxidation stage immediately. The thickness of the coating formed by SMAO is 17 μm after a single scanning, indicating SMAO has high film efficiency. The coating, mainly composed of α-Al₂O₃ and γ-Al₂O₃, is dense in the inner layer and porous in the outer layer. There are a large number of micropores and micro-cracks on its surface. The nano indentation test results show that the nano indentation hardness and elastic modulus of coatings firstly increase and then decrease from interface to surface. The potentiodynamic polarization indicates that the SMAO and MAO coatings all have effective corrosion protective effect to 2024 aluminium alloy. And the MAO coating's performance is better than that of SMAO coating.