Patent ID: 8394208

Claim:
A process for forming a passivating layer on a metal surface comprising the following steps: (i) cleaning the metal surface to remove oils, fats and dirt, (ii) optionally washing the cleaned metal surface, (iii) optionally pickling the metal surface to remove rust or other oxides, (iv) optionally washing the pickled metal surface with water, and (v) forming the passivating layer on the metal surface by contacting the metal surface with a Cr (VI) free composition having a pH value of 1 to 6, comprising: a) at least one terpolymer synthesized from 20 to 80% by weight of (meth)acrylic acid, 10 to 40% by weight of maleic anhydride, and 0.1 to 20% by weight of vinyl phosphonic acid as component A; b) water or a mixture of water and another water miscible solvent, the fraction of water in such a mixture is at least 75% by weight, which is capable of dissolving, dispersing, suspending or emulsifying the terpolymer of component A, as component B; c) at least one acid or one alkali metal or alkaline earth metal salt of said acid selected from the group consisting of phosphoric acid, sulfuric acid, sulfonic acids, formic acid, acetic acid, nitric acid, hydrofluoric acid, and hydrochloric acid, as component F; and d) compounds of Ce, Ni, Co, V, Fe, Zn, Zr, Ca, Mn, Mo, W, Cr and/or Bi, as component H.