Characterization of the ceramic coating formed on 2024 Al alloy by scanning plasma electrolytic oxidation

Scanning plasma electrolytic oxidation (SPEO) was used to prepare ceramic coating on 2024 Al alloy. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to examine the coating morphologies and phase compositions. Polarization curves were used to evaluate the anti-corrosion properties of the coated samples. The results revealed that a ceramic coating with the largest thickness of 30 μm was formed in a very short period of time, exhibiting high efficiency of coating formation. During the initial stage of the SPEO process under fixed-current mode, the anodic voltage rapidly increased to a steady value. In the stable stage, general anodization, spark oxidation, and micro-arc oxidation stages appeared at the same time in different places, which were generally found in different periods for the traditional plasma electrolytic oxidation (PEO) process. The coating was mainly composed of α-Al ₂ O ₃ and γ-Al ₂ O ₃ . The treated sample exhibited better corrosion resistance than the uncoated substrate in the 3.5% NaCl solution.