Abstract: There is disclosed a process and apparatus for carrying out plasma electrolytic oxidation of metals and alloys, forming ceramic coatings on surfaces thereof at a rate of 2-10 microns per minute. The process comprises the use of high-frequency current pulses of a certain form and having a given frequency range, combined with the generation of acoustic vibrations in a sonic frequency range in the electrolyte, the frequency ranges of the current pulses and the acoustic vibrations being overlapping. The process makes it possible to introduce ultra-disperse powders into the electrolyte, with the acoustic vibrations helping to form a stable hydrosol, and to create coatings with set properties. The process makes it possible to produce dense hard microcrystalline ceramic coatings of thickness up to 150 microns. The coatings are characterised by reduced specific thickness of an external porous layer (less than 14% of the total coating thickness) and low roughness of the oxidised surface, Ra 0.6-2.1 microns.

Abstract: This invention relates to the sphere of plasma electrolyte oxide coating of aluminium alloys. The method incorporates anode-cathode oxide coating in an alkaline electrolyte at a temperature of 15-50° C., using 50-60 Hz frequency alternating current. In the initial stage of the process oxide coating is carried on for 5-90 seconds at a current density of 160-180 A/dm2, then the current density is dropped to 3-30 A/dm2 and the process is continued in a regimen of spontaneous diminution of power demand without on-line adjustment of the regimen until the set coating thickness is achieved. The alkaline electrolyte used is an aqueous solution of alkaline metal hydroxide at 1-5 g/l, an alkaline metal silicate at 2-15 g/l, an alkaline metal pyrophosphate at 2-20 g/l and peroxide compounds at 2-7 g/l (in terms of H2O2—30%).