Mechanisms of the plasma electrolytic oxidation of light-metal-based material compounds

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Weight reduction is fundamental for achieving the technically and socio-politically motivated decrease of the energy consumption of technical systems, which are in motion during service. Multi-material design as well as functional integration are becoming a focus of technological efforts concerning both lightweight materials and lightweight construction. Associated therewith, both the complexity of parts and structures and the complexity of load regimes on materials and their surfaces increase. The application of various materials within one part or assembly represents a challenge in terms of surface treatment. Each material requires specific methods for the adjustment and improvement of its surface properties. Various materials in a material compound cannot be separated for the surface treatment, which traditionally takes place at the end of the process chain. For an aluminium/magnesium compound material, preliminary studies showed the suitability of the plasma electrolytic oxidation method (PEO) to treat the surface of dissimilar metals present in a material compound. The acting mechanisms of multi-material PEO, however, have not been established, yet. Especially the concurring chemical and electrochemical reactions during the simultaneous coating formation (oxide formation and dissolution or destruction by discharges) on dissimilar metals are of major scientific concern. Further, a lack of knowledge exists regarding the distribution of the energy input during PEO to facilitate the formation of functional oxide coatings on dissimilar metallic components of a material compound. Preliminary studies indicate that the electrolyte, which is used for the PEO, is a crucial parameter.This research project aims at the elucidation of the interactions between the material compound and the electrolyte under the characteristic conditions of the PEO process (discharges, high overpotentials, alternating polarization) for aluminium/magnesium and aluminium/steel material compounds. The utilisation of model experiments and electrochemical measurements as well as the analysis of the formed oxide coatings generates fundamental knowledge of the behaviour of material compounds in the PEO process. Thus, the surfaces of light-metal-based material compounds can perspectively be protected against various, complex loads by PEO.