Layer formation mechanisms during plasma-anodising of magnesium in dependence of the electrolyte composition

镁等离子阳极氧化过程中的层形成机制与电解质成分的关系

基本信息

批准号：
258050305
负责人：
Professor Dr.-Ing. Thomas Lampke
金额：
--
依托单位：
Professur Werkstoff- und Oberflächentechnik
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2014
资助国家：
德国
起止时间：
2013-12-31 至 2016-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/258050305?language=en
关键词：
Layer formation mechanisms during plasma

项目摘要

The potential field of application of magnesium materials is far greater than the application range covered today facilitating a further reduction of energy consumption in mobile systems. However, its poor corrosion and wear resistance is a drawback to many applications, which can be overcome by surface modification. Plasma electrolytic anodic oxidation (PAO) allows for the formation of ceramic oxide coatings on the magnesium substrate improving the corrosion resistance even though a post-treatment (e.g. sealing) is mostly required. There is a lack of knowledge with regard to the interactions of the electrolyte and the magnesium substrate during the PAO process precluding the development of wear resistant coatings or corrosion resistant coatings, which do not require a post-treatment. The interactions between electrolyte, magnesium substrate and formed oxide layers are insufficiently established at the present state of research especially regarding the effect of single electrolyte components and different combinations of them. Thus, electrolytes for PAO are solely designed on an empirical basis and success is highly dependent on the experience of the experimenter. Electrolytes used for PAO of magnesium almost exclusively contain electrolyte components in low concentrations (< 50 g/l). This is perceived as unfavourable by the applicants of the present project because magnesium oxide, which has unfavourable characteristics like low hardness, strength and chemical resistance, is mainly produced during PAO in low-concentrated aqueous solutions. Further, the dissolution of substrate and coating material in the aqueous electrolyte under high polarisation is competing against the coating formation. Preliminary tests showed a strong passivation of the magnesium substrate and the formed oxide layer in high concentrated electrolytes (> 100 g/l of a single component). Thus, the voltage rise in the first seconds of the process is promoted and a wider range of electrical process parameters becomes accessible. Further, both literature and preliminary test results indicate the favourable formation of non-magnesium-oxides or spinels, which leads to better coating characteristics. The proposed research project aims to investigate the passivation and dissolution behaviour of magnesium substrate in the solutions of single electrolyte components and different combinations of them. Using polarisation and electrochemical impedance techniques, the interactions between electrolyte and substrate are systematically analysed and the understanding of the influence on coating growth mechanisms (substrate passivation, discharge evolution, dissolution) is raised. The gained knowledge allows for the composition of electrolytes for a PAO process that aims at attaining defined coating characteristics.

镁材料的潜在应用领域远远大于目前所涵盖的应用范围，有助于进一步降低移动系统的能耗。然而，其较差的耐腐蚀性和耐磨性是许多应用的一个缺点，这可以通过表面改性来克服。等离子电解阳极氧化 (PAO) 可以在镁基材上形成陶瓷氧化物涂层，从而提高耐腐蚀性，即使主要需要进行后处理（例如密封）。对于 PAO 工艺过程中电解质和镁基体的相互作用缺乏了解，阻碍了不需要后处理的耐磨涂层或耐腐蚀涂层的开发。目前的研究水平尚未充分确定电解质、镁基体和形成的氧化物层之间的相互作用，特别是关于单一电解质组分及其不同组合的影响。因此，PAO 电解质完全是根据经验设计的，成功很大程度上取决于实验者的经验。用于镁 PAO 的电解质几乎只含有低浓度（< 50 g/l）的电解质成分。本项目的申请人认为这是不利的，因为氧化镁主要是在低浓度水溶液中的PAO过程中产生的，具有低硬度、低强度和耐化学性等不利特性。此外，在高极化下，基材和涂层材料在水性电解质中的溶解与涂层的形成竞争。初步测试表明，在高浓度电解液（> 100 g/l 单组分）中，镁基材和形成的氧化层发生强烈钝化。因此，促进了该过程的第一秒内的电压上升，并且可以获取更广泛的电过程参数。此外，文献和初步测试结果都表明有利于形成非镁氧化物或尖晶石，从而获得更好的涂层特性。拟议的研究项目旨在研究镁基材在单一电解质成分及其不同组合的溶液中的钝化和溶解行为。利用极化和电化学阻抗技术，系统地分析了电解质和基材之间的相互作用，并加深了对涂层生长机制（基材钝化、放电演变、溶解）的影响的理解。所获得的知识可用于 PAO 工艺的电解质成分，旨在获得规定的涂层特性。