Process for phosphating metallic surfaces

Abstract

A process is disclosed for phosphating metallic surfaces, particularly electrolytically or hot dipped galvanized steel strip surfaces, by dip or spray processing the metallic surfaces with acidic aqueous phosphating solutions, wherein the workpieces are cathodically treated at the same time with a direct current. The process is characterized by (a) the use of phosphating solutions that contain the following components: Zn.sup.+2 cations in a range from 0.1 to 5 g/l; PO.sub.4.sup.-3 anions in a range from 5 to 50 g/l; NO.sub.3.sup.- anions in a range from 0.1 to 50 g/l; as well as Ni.sup.+2 cations in a range from 0.1 to 5 g/l and/or Co.sup.+2 cations in a range from 0.1 to 5 g/l; (b) the observance of the following conditions: pH value of the phosphating solutions in a range from 1.5 to 4.5; temperature of the phosphating solutions in a range from 10.degree. to 80.degree. C.; duration of treatment in a range from 1 to 300 sec, (c) simultaneous cathodic treatment of the workpiece during phosphating with a direct current having a density in the range from 0.01 to 100 mA/cm.sup.2.

Dependencies are inferred from the claim text.