TREATMENT SOLUTION CONTAINING CHROMIUM(III) FOR A METHOD FOR PRODUCING AN ANTI-CORROSION COATING LAYER, CONCENTRATE OF SUCH A TREATMENT SOLUTION, AND METHOD FOR PRODUCING AN ANTI-CORROSION COATING LAYER

The invention relates to a treatment solution for a method for producing an anti-corrosion coating layer on a metal surface, wherein the surface to be treated is brought in contact with a treatment solution, which contains a chromium(III) ion source, a phosphate source, a zinc ion source, and a citrate source, wherein the amount-of-substance ratio of chromium(III) ions to zinc ions is 1 to at least 1.65 and the amount-of-substance ratio of chromium(III) ions to citrate is 1 to at least 1.4 and the treatment solution is substantially free of polymers that can be obtained by reacting one or more alkoxysilanes of the formula: R4-xSi(OR1)x, wherein the groups R are the same or different from each other and each represent a substituted or unsubstituted hydrocarbon group having 1 to 22 hydrocarbon atoms, x is equal to 1, 2, or 3, and R1 stands for a substituted or unsubstituted hydrocarbon group having 1 to 8 hydrocarbon atoms, and one or more alkoxides of the formula: Me(OR2)n, wherein Me stands for Ti, Zr, Hf, Al, Si and n stands for the oxidation number of Me and R2 represents a substituted or unsubstituted hydrocarbon group having 1 to 8 hydrocarbon atoms.