Formation of MAO-Coatings on the Substrate of Carbon Structural Steels in Solutions with Finely Dispersed Corundum

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The possibility of formation of high-quality MAO-coatings on structural carbon steels by complex treatment including a liquid aluminizing and microarc oxidation in solutions with finely dispersed corundum powder has been shown. It is ascertained that a metal Al coatings are formed on the steel substrates during aluminizing. The outer layers of these coatings are composed of Al and the inner layers consist of Al and Fe. MAO-coatings are formed as a result of oxidation of aluminum coatings and introduction of microparticles of corundum from the solution into growing alumina layer. Ultrasound treatment is found to strengthen the process of introduction of corundum microparticles in alumina. It is shown that the MAO process must be completed before the aluminum oxidation begins in the inner layers of the metal Al coating, since otherwise Fe can fall into the MAO-coating, which leads to a change in the structure and degradation of physicomechanical properties of MAO-coatings. The conditions for obtaining thicker MAO-coatings with increased hardness, wear resistance, and also higher electrical resistivity and breakdown voltage are determined.