Composition and process for chromating galvanized steel and like

Details Composition and process for chromating galvanized steel and like Composition and process for chromating galvanized steel and like

1990-09-27

1992-02-25

Bell, Mark L.

Metal treatment

Process of modifying or maintaining internal physical...

Processes of coating utilizing a reactive composition which...

148258, 148267, 106 1412, C23C 2248

Patent

active

050910230

ABSTRACT:
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, expressed as its stoichiometric equivalent as chromic acid, of total chromium; (B) about 2 to about 35 g/L of trivalent chromium ions; (C) about 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 ratio in the aqueous acidic liquid composition being about 0.41 to about 0.70, the chromic acid/fluorozirconate weight ratio being about 10 to about 40, and the PO.sub.4 /Cr.sup.+3 ratio being greater than about 0.03, greater than or equal to about {(9.2) (the chromium ratio)-4.0}, and less than or equal to about {(9.2) (the chromium ratio)-1.2}. . . The corrosion resistance of the coatings formed can be further improved if the chromating composition also contains about 0.1 to about 200 g/L of dispersed silica.

REFERENCES:
patent: 4749418 (1988-06-01), Saeki et al.

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