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Chromate passivation treatment of self tapping screw screw machining is a method for using metal or metal coating immersed with some additive chromate or chromate solution, chemical or electrochemical, chromate coating forming process including trivalent chromium and chromium six in six metal surfaces. The commonly used zinc coating (zinc plating, hot-dip galvanizing, zinc alloy) and cadmium plated layer have been treated to improve corrosion resistance, but they can also be used as the surface of other metals, such as aluminum, copper, tin, magnesium, nickel and their alloy corrosion. Close the chromate film structure, adhesion, good chemical stability, film after drying no hole, can be used as a barrier to prevent water from entering the bottom of the metal isolation, reliable protection function in the corrosive environment of metal surface.

The main component of a self - tapping screw chromate coating is a compound containing trivalent chromium and six valence chromium and chromate, a base metal or metal coating. The insoluble trivalent aluminum compound consists of a membrane skeleton that gives the film a certain thickness, and its stability is high, so the film has very good strength. Six valence chromium compounds have a good filling effect, soluble, scattered in the interior of the film, the film is scratching, can make passivation again, inhibit, and prevent metal corrosion. In salt spray test and temperature test, the corrosion resistance of chromate coating on galvanized layer is ten times or even ten times higher than that without coating.

Solutions for chromate treatment of basic metals, films and films, are also different in composition. In chromate solutions, Cr 6 / SO4 2 is more than the film that directly affects the color and thickness, and the concentration of sulfuric acid is constant, with a high content of trivalent chromium and a quantity of chromate coating. Aluminate film cannot be formed in chromate solution without addition of acid or base.