Structure and Properties of Black Ceramic MAO Coatings on Aluminum Alloys

The existing processes for obtaining black wear-resistant coatings include chemical methods, anodic oxidation followed by painting in aniline dyes, electrochemical deposition, vacuum plasma treatment, microarc oxidation (MAO). Of great interest for the formation of light-absorbing coatings is the MAO method, which is characterized as a reliable and environ-mentally friendly process, which provides the formation of a hard ceramic-like oxide layer with high corrosion resistance and good adhesion to the substrate. Therefore, the development of methods for obtaining high-quality black MAO coatings with both high optical and mechanical characteristics is currently an urgent task. The paper presents the results of a study of the structure and properties of black ceramic coatings on aluminum alloy AMg(2) obtained by microarc oxidation using silicate-alkaline and silicate-phosphate electrolytes containing potassium ferrocyanide and sodium tungstate as coloring components. Sodium tungsten acid and potassium ferrocyanide with a concentration of 0.5 to 2.0 g/l were added to the electrolytes as additional components that ensured the coloring of the coatings. It has been established that the most saturated black coatings in a silicate-alkaline electrolyte are formed with the addition of 1.5-2.0 g/l of sodium tungstate, and in a silicate- phosphate electrolyte with the addition of 1.5 g/l of potassium ferrocyanide. The use of an electrolyte containing sodium tung- state makes it possible to form coatings with a lower microroughness height (Ra 0.97-1.11 mu m) compared to coatings obtained in an electrolyte containing potassium ferrocyanide (Ra up to 4.20 mu m). The maximum wear resistance of the resulting coatings (wear rate (0.38-0.59)center dot 10(-4) mm(3)/(m center dot N)) is achieved by treatment in the studied electrolytes with a duration of 10 min. In this case, the thickness of the coatings is 21-31 mu m. A further increase in the duration of processing does not have a significant effect on the wear rate.