Investigation of the influence of electrolyte composition on the structure and properties of coatings obtained by microarc oxidation

Abstract

Aluminum alloys, along with positive properties - low density, high specific strength, electrical conductivity, ductility, viscosity and others, have disadvantages: low hardness, modulus of elasticity, wear resistance and high chemical activity in many inorganic acids. The method of microarc oxidation (MАO) can eliminate these shortcomings. The transformation of the surface layers of the workpiece into high-temperature oxides of aluminum will strengthen the surface and increase its protective properties. The properties of MАO coatings depend on many factors, one of which is the composition of the electrolyte. According to the literature, the most widely used alkaline-silicate electrolytes, which have shown the greatest efficiency in MАO of aluminum alloys. The data available in the literature on the use of multicomponent electrolytes containing sodium aluminate NaAlO2 and sodium hexametaphosphate Na6P6O18 do not allow to elucidate their role in the formation of MАO coatings. Studies of the use of hexametaphosphate to alkaline silicate electrolyte have shown that Na6P6O18 promotes the formation of a thicker coating. The rate of thickness formation in the absence of hexametaphosphate is 0.5 ,7 0.7 μm / min, and at a hexametaphosphate content of 10 g / l - 0.9 ÷ 1.1 μm / min. As for the effect on the phase composition, the effect was not detected. It was studied that the addition of aluminate-silicate electrolytes of sodium aluminate in the amount of up to 13 g / l does not have a significant effect on the thickness of the coating, but affects the phase composition of the coating.