Formation of Manganese-Containing PEO Coatings on Aluminum Alloys

This chapter introduces the investigation of Al alloys plasma electrolytic oxidizing (PEO) and analysis of process characteristics. The research directs to set regularity of electrochemical obtaining (forming or formation) of nanostructured coatings mono- and mixed oxides which are incorporated with transition metals namely manganese. It is shown that the alloys surface and bulk composition heterogeneity complicates the alloys processing to produce a uniform layer of oxides. Electrolytes containing K4P2O7 and KOH as the basic component were used to homogenize the outer surface layer of aluminum alloys and to form uniform conversion covers, predominantly oxides. PEO in these electrolytes in the range of current densities 5…20 A/dm2 allows obtaining mixed oxide coatings which contained both matrix and doping metal oxides. It was found that the rising of both the permanganate concentration in the electrolyte and current density of treatment allows to enrich the surface layer of the coatings with oxides. The X-ray analysis confirms the incorporation of MnOx into the matrix of aluminum oxide. The modes for PEO of aluminum alloys have been proposed for producing conversion coatings containing Mn up to 36 wt%. Mixed oxide covers exhibit a developed surface and increased catalytic properties and corrosion stability. The complex of functional properties determines the possibility of their usage as promising materials for emission control technologies and also in systems of ICE waste gas purification.