Characterisation Method of the Passivation Mechanisms during the pre-discharge Stage of Plasma Electrolytic Oxidation Indicating the Mode of Action of Fluorides in PEO of Magnesium
Characterisation Method of the Passivation Mechanisms during the pre-discharge Stage of Plasma Electrolytic Oxidation Indicating the Mode of Action of Fluorides in PEO of Magnesium
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DOI：
10.3390/coatings10100965
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发表时间：
2020-10
期刊：
影响因子：
3.4
通讯作者：
F. Simchen;M. Sieber;T. Mehner;T. Lampke
中科院分区：
文献类型：
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作者：
F. Simchen;M. Sieber;T. Mehner;T. Lampke
等离子体电解氧化(PEO)是一种在金属轻质建筑材料表面获得保护性涂层的方法。在这里，工件在合适的水溶液中受到强烈的阳极极化，这导致了钝化层和气态外壳的形成。然后，等离子体电解放电出现在基板表面，并将其转化为陶瓷层。钝化层的性能受所选择的衬底/电解液组合的影响，对于PEO工艺的启动和特性是必不可少的。在这项工作中，提出了一种新的方法，系统地研究了预放电阶段的衬底/电解液相互作用。该过程通过极化实验进行，并允许基于小电解液体积对钝化行为进行定量表征。通过对不同的镁铝材料的交叉比较，该方法被用来研究在镁上形成的钝化膜的导电机理。此外，还考虑和量化了磷酸盐、甘油和氟化物对AZ31镁合金在碱性环境中钝化行为的影响。这些结果为电解液中有毒氟化物对镁表面PEO膜形态的积极影响提供了一种解释方法。
Plasma electrolytic oxidation (PEO) is a method to obtain protective coatings on metallic light-weight construction materials. Here, the workpiece receives a strong anodic polarisation in a suitable aqueous electrolyte, which leads to the formation of a passive layer and a gaseous shell. Afterwards, plasma electrolytic discharges appear on the substrate surface and convert it into a ceramic layer. The properties of the passive layer are influenced by the selected substrate/electrolyte combination and are essential for the PEO process-initiation and characteristics. In this work, a new method for the systematic investigation of the substrate/electrolyte interactions during the pre-discharge stage is presented. The procedure is carried out by a polarisation experiment and allows for a quantitative characterisation of the passivation behavior, based on a small electrolyte volume. The method is used to investigate a literature-known electrical conduction mechanism on passive films formed on magnesium, by cross-comparison between different Mg and Al materials. In addition, the influence of phosphate, glycerol, and fluoride on the passivation behaviour of the Mg alloy AZ31 in an alkaline environment is considered and quantified. The results provide an explanatory approach for the positive influence of toxic fluorides within the electrolyte on the morphology of PEO layers on magnesium.