In this study, a high-hardness and wear-resistant ceramic coating was prepared on the surface of 319S aluminum alloy using the micro-arc oxidation (MAO) technique. The effects of pulse width, negative voltage, and KOH concentration on the MAO coating were investigated, and the microhardness and surface roughness of the coating were measured. The morphology, elemental distribution, and phase composition of the coating were analyzed using SEM, EDS, XRD, and digital microscopy. The influence of the MAO coating on the wear of the 319S aluminum alloy was evaluated using a friction-wear tester. The results showed that in the sodium silicate solution system, with an increase in pulse width, the thickness of the coating gradually increased and the surface hardness initially increased and then decreased. With an increase in negative voltage, the density of the coating first increased and then decreased, the thickness of the dense layer initially increased and then decreased, and the surface hardness initially increased and then decreased. With an increase in the KOH concentration, the coating thickness increased and the roughness initially decreased and then increased. When the pulse width was 3000 ms, the negative voltage was 130 V, and the KOH concentration was 1 g/L, the coating exhibited the best density, with the highest surface hardness of 1426.8 HV and the thickest dense layer of 55 μm. The reduction in surface cracks and improvement in density indicated an enhancement in the hardness and wear resistance of the coating. The decrease in width and depth of the wear scars demonstrated the excellent wear resistance of the coating.

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 shows 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

This study investigates the characteristics and performance of ceramic coatings fabricated on 2024 aluminum alloy surfaces using the scanning plasma electrolytic oxidation (SPEO) process. The effects of various scanning parameters, including discharge gap, scanning frequency, scanning speed, and overlap rate, on coating properties were systematically examined. The coatings were characterized using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), microhardness testing, roughness analysis, and thickness measurement. The results reveal that optimizing scanning parameters significantly enhances coating performance. The SPEO process enables efficient localized coating deposition through progressive scanning, achieving performance comparable to that of conventional full-surface PEO. Although the high current density associated with the SPEO process generates more surface pores and microcracks, which slightly affect hardness, roughness, and corrosion resistance, the differences are minimal and acceptable for most applications. Furthermore, the SPEO process demonstrates high efficiency in repairing large or complex components, highlighting its significant potential for industrial applications.

Currently, research on the edge effect issue in the micro-arc oxidation process primarily focuses on investigating process conditions and enhancing additives. However, some scholars have utilized finite element analysis software to simulate the edge effect during the simulation process, overlooking the investigation of the morphology of the auxiliary cathode. This study analyzes the growth characteristics of the oxide film on aluminum alloy 2A12 during micro-arc oxidation. Additionally, the inter-electrode discharge electric field is simulated using the finite element analysis method. The auxiliary cathode is optimized to mitigate the influence of the edge effect on the film layer. The findings indicate that employing a cylindrical shape as the auxiliary cathode instead of a rectangular groove leads to an increased thickness of the micro-arc oxidation film. However, it also results in an augmented length of the film layer affected by the edge effect at both ends of the workpiece. Decreasing the distance between the auxiliary cathode and the workpiece surface leads to a higher thickness of the obtained micro-arc oxidation film. Decreasing the length of the auxiliary cathode results in a reduction in both the thickness of the film layer on the workpiece surface and the area affected by the edge effect. Increasing the eccentric cone ratio of the auxiliary cathode enhances the uniformity of the micro-arc oxidation film layer. In this study, we present a novel auxiliary cathode model that incorporates a smaller cylindrical shell at the center and eccentric cone shells on each side. This model has the potential to enhance the optimization rate of the micro-arc oxidation film layer on cylindrical workpieces by 17.77%.