The Study of Surface Microgeometry and Morphology of Plasma Electrolytic Oxidation Dielectric Coatings on Aluminum Alloys

The article focuses on the results of the surface microgeometry and morphology research of the plasma electrolytic oxidation (PEO) coatings produced in the alkaline-silicate electrolytes in various electricity modes-galvanostatic (GS) and arbitrarily falling power (AFP) in alternating current modes. PEO coatings were formed on the samples of wrought aluminum alloys, which are normally used for the manufacturing of the diamond grinding wheels bodies. The influence of PEO factors on R-a roughness index as well as porosity, shape and size of the structural particles of the coatings surface was studied. It was established that PEO increases the reference R-a value by a factor of 2 ... 6, depending upon the electrolyte composition and the processing mode. The "liquid glass" (a technical-grade sodium silicate solution) concentration is the key driver of R-a index, its decrease from 12 to 6 g/L leads to roughness reduction by 25 ... 40%. An extreme dependence of R-a index on anode current density in GS mode is identified in the electrolytes with the minimal concentration of the alkaline component of KOH solution. It was demonstrated that the morphology research results qualitatively correlate with the microgeometric and functional coating characteristics.