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AssigneeMcGean-Rohco, Inc.
InventorsCraig V. Bishop, Marlinda J. Thomay, Billie J. Page
Estimating the term…
A method is described for preparing a black chromium-containing conversion coating on a zinc-nickel alloy surface containing at least about 8% nickel in the alloy or on a zinc-iron alloy surface. The method of the invention comprises contacting said surfaces with an aqueous acidic solution comprising trivalent chromium and an amount of a phosphorus acid selected from phosphoric acid, phosphorous acid, hypophosphorous acid, and mixtures thereof effective to provide a solution having a pH of from about 1.0 to about 2.5. Metal articles having zinc-nickel alloy surfaces containing at least about 8 % nickel in the alloy or having zinc-iron alloy surfaces which have been treated in accordance with the method of the invention exhibit the desired blackened surfaces and are characterized by improved corrosion resistance.
A method of depositing a black chromium-containing conversion coating on a zinc-nickel alloy surface containing at least about 8% nickel in the alloy, or on a zinc-iron alloy surface which comprises contacting said surfaces with a hexavalent chromium-free aqueous acidic solution at a temperature of from about 20.degree. C. to about 35.degree. C., said solution comprising trivalent chromium, and an amount of a phosphorus acid selected from phosphoric acid, phosphorous acid, hypophosphorous acid, and mixtures thereof which is effective to provide a solution having a pH of from about 1.0 to about 2.5.
The method of claim 3 wherein the chromium phosphate is selected from CrPO.sub.4, Cr(H.sub.2 PO.sub.4).sub.3, Cr.sub.2 (HPO.sub.4).sub.3 and Cr.sub.3 (HPO.sub.4).sub.3 (PO.sub.4).
A method of depositing a black chromium-containing conversion coating on a zinc-nickel alloy surface containing at least about 8% nickel in the alloy or on a zinc-iron alloy surface which comprises contacting said surfaces with a hexavalent chromium-free aqueous acidic solution at a temperature of from about 20.degree. C. to about 35.degree. C., said solution comprising Cr(H.sub.2 PO.sub.4).sub.3 and an amount of a phosphorus acid selected from phosphoric acid, phosphorous acid, hypophosphorous acid, and mixtures thereof effective to provide a solution having a pH of from about 1 to about 2.
Dependencies are inferred from the claim text.