Black decorative anticorrosion coatings obtained on AA2024 alloy by plasma–electrolytic treatment and inhibitionстатья
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Дата последнего поиска статьи во внешних источниках: 26 января 2022 г.
Аннотация:This research work is concerned with developing a model of black anticorrosion coatings growthduring plasma electrolytic treatment of a widely used industrial alloy AA2024 and investigationof corrosion inhibitor use efficiency depending on a coating thickness. The inhibitor used in thisstudy is an equimolar composition of sodium oleoyl sarcosinate and sodium flufenamate.Assuring that addition of 1.5 g/l Co(OH)3 into an alkaline aqueous solution (pH~12.6),containing 5 g/l of technical water glass, leads to the formation of visually black coatings withhigher anticorrosion properties, the following assumptions were made: 1) the visual black colorof a coating is mainly provided with the existence of CoO and Co3O4 oxides; 2) the increase inthe anticorrosive properties of the coatings is caused by the filling of many open pores in thecoatings with cobalt orthosilicate which is more fusible than aluminum oxide. Major filling ofthe pores with the double oxide takes place on the surface of a forming inner layer prior to itsintensive growth under the outer layers of the coatings. As a result, a coating with a thicknessof 17 μm has higher anticorrosion properties than the ones with thicknesses of 38 and 70 μm.Results of energy dispersive X-ray spectroscopy and review of the data given in the publishedscientific works confirm the possibility of the abovementioned hypothesis. The efficiency of thecorrosion inhibitor is also higher for a coating with a thinner inner layer, when it has alreadystarted to be formed under porous outer layers of the coating. The black coating with an averagethickness of 17 μm, loaded with the mixed inhibitor, shows the maximum decrease (byapproximately 467.4 times) in the corrosion current density, i.e., the greatest protection ofAA2024 alloy against corrosion.