PROCESS FOR COATING AND/OR TOUCHING UP COATINGS ONPROCESS FOR COATING AND/OR TOUCHING UP COATINGS ON METAL SURFACES METAL SURFACES

摘要

Defects in an initial protective coating, particularly a conversion coating, on a metal substrate can be touched up so as to at least equal the original coating in corrosion protection by use of a dry-in-place aqueous acidic liquid comprising: fluorometallate anions; a component selected from the group consisting of phosphorus-containing inorganic oxyanions and phosphonate anions; and an oxidizing agent, preferably a mixture of hexavalent and trivalent chromium. Other preferred optional active ingredients include free fluoride ions, which stabilize the fluorometallate ions against the formation of precipitates, and a fluorinated surfactant. The same composition also forms an effective protective coating over previously uncoated metal, particularly aluminum. The compositions do not contain any substantial amount of silica, which has often been previously used in compositions for similar purposes.