PROCESS FOR COATING AND/OR TOUCHING UP COATINGS ON 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 leastequal the original coating in corrosion protection by use of a dry-in-placeaqueous acidic liquid comprising: fluorometallate anions; acomponent selected from the group consisting of phosphorus-containinginorganic oxyanions and phosphonate anions; and an oxidizingagent, preferably a mixture of hexavalent and trivalent chromium. Otherpreferred optional active ingredients include free fluoride ions,which stabilize the fluorometallate ions against the formation ofprecipitates, and a fluorinated surfactant. The same composition also formsan effective protective coating over previously uncoated metal, particularlyaluminum. The compositions do not contain any substantialamount of silica, which has often been previously used in compositions forsimilar purposes.