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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.degree. 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/dm.sup.2, then the current density is dropped to 3-30 A/dm.sup.2 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 H.sub.2 O.sub.2 --30%). The method enables the protective properties of ceramic oxide coatings to be enhanced through an increase in the micro-hardness, density and strength of adhesion to the substrate without any additional energy outlay or time required.

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