Effect of Morphological Features on Dielectric Properties of Plasma Electrolytic Oxidation Coatings on D16T Aluminum Alloy

The article focuses on the results of the surface morphology and dielectric properties research of the plasma electrolytic oxidation (PEO) coatings produced in the alkaline-silicate electrolytes in galvanostatic (GS) mode using rectified anode current. PEO coatings were formed on the samples of wrought aluminum alloy D16Tused normally for the manufacturing of the diamond grinding wheels bodies. The influence of PEO factors on the porosity (quantity, shape, size, structure and its distribution on the surface) and dielectric properties (volume resistivity, electrolytic strength) was studied. It was established that through porosity increases in the series of solutions: 12 g/L LG ("liquid glass" (LG), a technical-grade sodium silicate solution) < 1 g/L.OH + 6 g/L LG (alkaline-silicate solution) < 2 g/L.OH + 12 g/L LG. The accordingly sizes of pores are 10.15 mu m, up to 1 mu m and 2.10 mu m. The through porosity increases in each electrolyte with increasing of anode current density from 5 to 15 A/dm(2). The smallest relative increase in porosity is observed in the samples oxidated in sodium liquid glass solution 12 g/L LG. It was demonstrated that the dielectric properties research results qualitatively correlate with the micro geometric and morphology characteristics. The electrolyte composition is a major factor affecting the volume resistivity and electrolytic strength. The coatings produced in 12 g/l LG technical-grade sodium solution have the best dielectric properties, corresponding to the smallest through the porosity of these samples.