Patent ID: 7815751

Claim:
A process for forming a conversion coating on a ferrous metal surface, the process comprising: exposing the ferrous surface to an aqueous composition comprising zirconium as ZrF 6 2− ions, vanadium as a part of vanadium/oxygen ions, fluoride as a part of the ZrF 6 2 — ions, nitrate ions and phosphate ions in a ratio and a concentration effective for providing the ferrous metal surface with a protective conversion coating, the aqueous composition comprising from 90 to 185 ppm zirconium, from 178 to 360 ppm fluoride, from 50 to 110 ppm vanadium, and from 50 to 180 ppm phosphate ions, the aqueous composition having a pH in the range of from 2.0 to 5.0, the aqueous composition forming the protective conversion coating which includes zirconium and vanadium throughout the pH range and forming a protective conversion coating on the metal surface which includes zirconium, vanadium and phosphate at a pH of from about 4 to about 5, the aqueous composition being substantially free of an organic film forming composition and tannins, the ratio of fluoride to zirconium in the aqueous composition at least 6 fluoride to one zirconium, the ratio of zirconium to vanadium in the range of 1:2 to 2:1 to provide the conversion coating on the ferrous metal surface, the conversion coating including at least zirconium and vanadium on the ferrous metal surface and the conversion coating on the metal surface consisting essentially of zirconium, vanadium, oxygen and phosphate when the ferrous metal surface is exposed to the aqueous composition at a pH of from about 4 to about 5.