Plasma electrolytic oxidation (PEO) is innovative approach for fabricating ceramic coatings on metallic substrates. Traditionally, an aqueous electrolyte is used in PEO; however, the size of the treated sample is limited because of the system heating, and production of the undesired components in the coating. To overcome these drawbacks, a PEO process in molten salt was designed and implemented. The growth mechanism of the coating formation has not yet been studied. In the present work, an aluminum oxide coating was created on an Al-Cu 2024 alloy using PEO at various current frequencies in molten salt. Chemical and phase compositions, coatings morphology, X-ray photoelectron spectroscopy, and X-ray diffraction were studied. Potentiodynamic polarization method and electrochemical impedance spectroscopy were used to analyze a corrosion behavior of the coated alloys. The results revealed the formation of a double-layered aluminum oxide coating free of any undesired components. To achieve the highest corrosion resistance, the current frequency should be intermediate; high frequencies produce a non-uniform oxide inner layer, and low frequencies produce a thin oxide inner layer. Finally, based on the observations, a coating growth mechanism for PEO at high and low current frequencies was proposed.

等离子体电解氧化（PEO）是在金属基材上制造陶瓷涂层的创新方法。传统上，PEO使用水性电解质。然而，由于系统加热以及涂层中不希望的组分的产生，处理样品的尺寸受到限制。为了克服这些缺点，设计并实施了熔盐中的PEO工艺。尚未研究涂层形成的生长机理。在目前的工作中，使用PEO在熔盐中以各种电流频率在Al-Cu 2024合金上创建了氧化铝涂层。研究了化学和相组成，涂层形态，X射线光电子能谱和X射线衍射。用电位动力极化法和电化学阻抗谱法分析了涂层合金的腐蚀行为。结果表明形成了不含任何不希望有的组分的双层氧化铝涂层。为了获得最高的耐蚀性，电流频率应该是中间的。高频产生不均匀的氧化物内层，而低频产生薄的氧化物内层。最后，基于这些发现，提出了高电流频率和低电流频率下PEO的涂层生长机理。低频产生薄的氧化物内层。最后，基于这些发现，提出了高电流频率和低电流频率下PEO的涂层生长机理。低频产生薄的氧化物内层。最后，基于这些发现，提出了高电流频率和低电流频率下PEO的涂层生长机理。