Patent ID: 8241745

Claim:
A substantially chromium-free process for passivating metallic surfaces of Zn, Zn alloys, Al or Al alloys by treating the surface with an acidic aqueous formulation having a pH of from 1 to 6 of a polymer comprising —COOH groups and/or salts thereof wherein the formulation (Z) used for the treatment at least comprises (a) at least one substantially noncrosslinked, water-soluble copolymer (A) comprising at least 50% by weight of (meth)acrylic acid units and 5 to 40% by weight of at least one comonomer which comprises acidic groups but is other than (meth)acrylic acid, in a concentration of from 0.1 g/l to 200 g/l, and (b) water or an aqueous solvent mixture (B) comprising at least 80% by weight of water, and the surface is further treated with at least one water-soluble crosslinker, the crosslinker comprising at least 2 crosslinking groups selected from the group consisting of azirane, oxirane, and thiirane groups and joined to one another by means of a linking group (X) comprising at least 2 carbon atoms, the number-average molecular weight M n of the crosslinker being from 112 to 5000 g/mol, the solubility of the crosslinker in water being at least 10 g/l, and the treatment with the crosslinker being carried out before, after or simultaneously with the treatment with the formulation (Z), wherein a passivating layer on the metallic surface is obtained whose thickness is from 0.01 to 3 micrometer, and wherein the pH of the formulation is controlled by the nature and concentration of the (meth)acrylic acid units and the at least one comonomer which comprises acidic groups but is other than (meth)acrylic acid.