Plasma electrolytic oxidation (PEO) is a promising surface treatment to generate adherent and thick anti-corrosive coating on light-weight metals (Al, Mg, Ti, etc.) using an eco-friendly alkaline electrolyte. High energy plasma, however, inevitably generates porous structures that limit their practical performance. The present study proposes a straight-forward simple method by utilizing sub-zero electrolyte (268 K) to alter the plasma characteristics during formation of the protective coating on AZ31 Mg alloy via PEO with a comparison to the electrolyte at room temperature (298 K). In refrigerated electrolyte, the formation of micro-defects is suppressed relatively at the expense of low coating growth, which is measured to be twice lower than that at 298 K due to the temperature-dependent soft plasma discharges contributing to the development of the present coating. As a consequence, corrosion resistance of the sample processed at 268 K is superior to that of 298 K, implying that the effect of coating thickness is less dominant than that of compactness. This phenomenon is interpreted in relation to the ionic movement and oxide solidification controlled by soft plasma discharges arising from the temperature gradient between electrolyte and surface of the substrate during PEO.

等离子电解氧化 (PEO) 是一种很有前景的表面处理方法，可使用环保的碱性电解液在轻质金属（Al、Mg、Ti 等）上生成粘附且厚的防腐蚀涂层。然而，高能等离子体不可避免地会产生限制其实际性能的多孔结构。本研究提出了一种直接的简单方法，即利用低于零的电解质（268 K）改变通过 PEO 在 AZ31 镁合金上形成保护涂层期间的等离子体特性，并与室温下的电解质（298 K）进行比较. 在冷冻电解液中，微缺陷的形成相对受到抑制，但涂层生长速度较慢，由于与温度相关的软等离子体放电有助于本涂层的发展，其测量值比 298 K 时的值低两倍。因此，在 268 K 下处理的样品的耐腐蚀性优于 298 K，这意味着涂层厚度的影响不如致密性占主导地位。这种现象被解释为与离子运动和氧化物凝固有关，这些离子运动和氧化物凝固是由 PEO 期间电解质和基板表面之间的温度梯度引起的软等离子体放电控制的。