Chemical and electrical interaction mechanisms during the plasma electrolytic (PEO) mixed oxide formation on magnesium

镁是最轻的金属工程材料，因此在移动系统中具有巨大的减重潜力。除此之外，镁很容易回收。优异的铸造工艺性能和对电磁和机械振荡的良好阻尼能力，决定了镁材料用于制造机器外壳以及用于感官、光学和娱乐电子设备的框架和外壳。尽管镁合金具有良好的加工和应用性能，但由于其耐腐蚀性和摩擦学应力较低，镁合金的应用范围目前受到限制。等离子体电解氧化是一种很有前途的环保表面处理工艺，可以应对这些技术挑战。一个已经成功完成的dfg项目关注的是在放电开始之前和过程中衬底/电解质的相互作用，以及将电解质成分插入生成的peop涂层中的目标。结果表明，采用高浓度电解液制备的混合氧化物（化学成分以电解液成分为主，而非基体成分为主）涂层硬度明显超过氧化镁层。然而，由于其形貌受到局部缺陷的影响，这种涂层将对所得的耐腐蚀性和耐磨性产生负面影响。这揭示了进一步研究的需要。在等离子体电解质涂层过程中，复杂涂层形成过程的特征以及化学和电气过程参数的相互作用只能通过经验手段来实现，根据目前的技术水平和缺乏一致的过程模型。因此，拟建项目旨在研究混合氧化物形成下等离子体电解氧化镁过程中化学和电相互作用过程的作用机制。为了达到这个目标，需要详细地描述和理解这个过程。为此，涂层形成所需的脉冲电荷吞吐量将被分解为电和等离子体化学部分，并且需要系统地记录涂层愈合软火花和阴极放电等具体过程阶段。在此基础上，混合脉冲模式调整到各个过程阶段将被开发。项目期间生成的数据基础随后将用于创建描述底层机制的模型概念。根据得到的结论和使用环保电解质，将在镁基体上生成粘附性和低缺陷的混合氧化物涂层，并符合腐蚀性和摩擦学要求。

Magnesium is the lightest metallic engineering material and therefore offers an enormous potential to save weight in mobile systems. Beyond that, magnesium is easy to recycle. Excellent casting process properties and a good damping capacity towards electromagnetic and mechanical oscillations predestine magnesium materials for the construction of machine casings as well as framework and encasements for sensible sensory, optical and entertainment electronic devices. Despite the positive processing and application properties listed here, the application spectrum of magnesium alloys is currently limited due to their low resistance towards corrosive and tribological stress. Plasma electrolytic oxidation is a promising and environmentally friendly surface treatment process to encounter these technical challenges. An already successfully finished DFG-project was concerned with the substrate/electrolyte interaction before and during the discharge initiation, as well as the aimed insertion of electrolyte components into the generated PEOcoating. It was shown that by employing highly concentrated electrolytes, very hard and chemically resistant mixed oxide (chemical compositions dominated by electrolyte components rather than substrate components) coatings are producible, which hardness exceed that of MgO layers significantly. However, due to their morphology being afflicted with local defects, such coatings will negatively affect the resulting corrosion- and wear resistance. This reveals further research needs. A characterisation of the complex coat-forming processes as well as the interactions of chemical and electrical process parameters during the plasma electrolyte coating procedure is only possible by empirical means, according to the state of the art and in lack of a consistent process model. Therefore, the proposed project is aiming towards the research of action mechanisms of interacting chemical and electrical processes during the plasma electrolytic oxidation of magnesium under formation of mixed oxides. To reach this goal, the process needs to be characterised and understood in detail. For that, the charge throughput of the pulses necessary for coating formation are to be broken down into electro- and plasma-chemical parts, and specific process stages like the coat-healing Softsparking and cathodic discharges need to be systematically recorded. On this basis, hybrid pulse patterns adjusted to the individual process stages will be developed. The data foundation generated during the project will subsequently be used to create a model concept which describes the underlying mechanisms. Based on the obtained conclusions and using environmentally friendly electrolytes, adherent and low-defect mixed oxide coatings are to be generated on magnesium substrates and to be qualified for corrosively and tribologically demanding applications.