Ceramic coatings have been produced on 6061 Al alloy substrates in a weak alkaline-silicon electrolyte under different AC voltage at 60 Hz combined with a 200 V DC voltage for 5 minutes by a plasma electrolytic oxidation process. The surface morphology, composition, structure and microhardness analysis of layers were carried out by an X-ray diffractormetor, optical microscopy, scanning electron microscopy, an energy dispersive X-ray spectrometer and a microhardness tester. Analysis shows that a two-layer structure coating consist of different states of α-Al2O3, β-Al2O3 and γ-Al2O3, where Si concentrates in the hard outer layer, and Cl predominates in the soft internal layer. The influence of deposition AC voltages on the kinetics of coating formation, coating microhardness, the number and size of the discharging channels was investigated.

Keywords: Plasma Electrolytic Oxidation, Ceramic Coating; Al Alloy, Weak Alkaline-Silicon Electrolyte, Voltages.