| 摘要 |
The resistance of chromated zinc surfaced steel objects, particularly plates and sheets, to extraction of hexavalent chromium by alkaline degreasing solutions used on the chromated objects, can be substantially increased by utilizing an aqueous acidic liquid chromating composition containing (A) about 9.6 to about 96 g/L, expresse d as its stoichiometric equivalent as chromic acid, of total chromium; (B) about 2 to about 35 g/L of trivalent chromium ions; (C) a bout 1 to about 128 g/L of phosphate ions; and (D) about 0.3 to about 4 g/L of fluorozirconate ions, with the chromium rati o in the aqueous acidic liquid composition being about 0.41 to about 0.70, the chromic acid/fluorozirconate weight ratio being ab out 10 to about 40, and the PO4/Cr +3 ratio being greater than about 0.03, greater than or equal to about {(9.2)(the chromium rati o)- 4.0}, and less than or equal to about {(9.2)(the chromium ratio) -1.2}. The corrosion resistance of the coatings forme d can be further improved if the chromating composition also contains about 0.1 to about 200 g/L of dispersed silica.
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