A treatment solution for a method for producing a corrosion-protective coating layer and concentrate of such a treatment solution

摘要

A treatment solution for a method of forming a corrosion protective overcoat layer on a metallic surface, wherein the surface to be treated is contacted with a treatment solution containing - a chromium (III) ion source, - a phosphate source, - a zinc ion source, and - a citrate source wherein the molar ratio of chromium (III) ions to zinc ions is 1: at least 1.65 and the molar ratio of chromium (III) ions to citrate 1: at least 1.4, and the treatment solution is substantially free of polymers which are free from Reaction - one or more alkoxysilanes of the formula R4-xSi (OR1) x wherein the radicals R are the same or different from each other and each represents a substituted or unsubstituted hydrocarbon group having 1 to 22 carbon atoms, x is 1, 2 or 3 and R1 is a substituted or unsubstituted hydrocarbon group having 1 to 8 carbon atoms, and - one or more alkoxides of the formula Me (OR2) n wherein Me is Ti, Zr, Hf, Al, Si and n is the oxidation state of Me and R2 is a substituted or unsubstituted hydrocarbon group of 1 to 8 carbon atoms.