Structuring and passivation of high-strength steels through plasma electrolytic oxidation for the application in material compounds

• Applicant: Professor Dr.-Ing. Thomas Lampke
• Subject Area: Coating and Surface Technology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 464291298

Plasma electrolytic oxidation (PEO) has great potential for the corrosion protection of high-strength steels and simultaneously enables an excellent adhesion of polymer matrices in modern material composites for lightweight construction. However, basic knowledge is currently missing for this approach. As part of this project, the fundamental mechanisms of passivation and layer formation are investigated in order to realize the passivation and surface structuring of steels using PEO. The addition of passivators (e.g. silkates, aluminates) to the electrolyte is necessary for the anodic passivation of unalloyed and low-alloyed steels and the ignition of the PEO process. Therefore, the passivation and ignition behavior is first investigated with the help of potential-controlled ramp tests. The passivators also largely determine the chemical composition of the PEO layer. The influence of the current regime on the distribution and intensity of the microarc discharges and the resulting layer microstructure is assessed by means of an instrumented experimental set-up. Additionally, the optical and electrical process monitoring are used to monitor the oxide growth in order to stop the process after a comparatively thin, porous PEO layer has formed. Pronounced undercuts are also created on the metal side before the PEO, in order to realize a highly stressable metal-polymer bonding by mechanical interlocking. This pre-structuring takes place in the same bath through anodic metal dissolution below the passivation potential. The effect of the layer microstructure and the surface topography on the PEO layer adhesion, the metal-polymer shear strength and the corrosion behavior are characterized using mechanical and electrochemical methods.

• DFG Programme: Research Grants