Novel Cyanide-Free Electroplating Process for Zinc and Zinc Alloy Die-Cast Components
The proposed invention comprises a process for plating upon zinc die cast articles without the use of cyanide in the plating solution The process proposes the plating of the zinc die cast articles with a zinc alloy layer first, followed by plating with copper, nickel, chromium, tin or brass. The preferred zinc alloy initial coating is zinc-nickel.
1 . A process for plating upon a zinc die-cast article, said process comprising:
(a) cleaning said article;
(b) electroplating said article in an aqueous solution comprising (i) zinc ions, (ii) nickel ions, and (iii) counter ions, by making said article a negative cathode in said solution to produce a zinc-nickel alloy coating thereon; and
(c) electroplating said article with a metal selected from the group consisting of copper, nickel, chromium, tin, and alloys of the foregoing.
2 . (canceled)
3 . (canceled)
4 . A process according to claim 1 wherein the article is made cathodic prior to contacting it with the aqueous solution of step (b).
5 . A process according to claim 18 wherein the article is made cathodic prior to contacting it with the aqueous solution of step (b).
6 . A process according to claim 1 , wherein the source of the nickel ions in step (b) is selected from the group consisting of nickel chloride, nickel sulfate and nickel acetate.
7 . A process according to claim 6 , wherein the nickel ions are present in the aqueous solution of step (b) at a concentration of between about 10 g/l and about 100 g/l.
8 . A process according to claim 7 , wherein the nickel ions are present in the aqueous solution of step (b) at a concentration of between about 50 g/l and about 55 g/l in the aqueous solution in step (b).
9 . A process according to claim 1 wherein the source of the zinc ions in step (b) is a water soluble zinc salt.
10 . A process according to claim 9 wherein the water soluble zinc salt is selected from the group consisting of zinc chloride, zinc sulfate, zinc acetate and alkali metal zincates.
11 . A process according to claim 9 wherein the aqueous solution of step (b) comprises a buffering compound selected from the group consisting of ammonium ions and borate ions.
12 . A process according to claim 9 wherein the water soluble zinc salt is present in the aqueous solution of step (b) at a concentration of between about 10 g/l and about 100 g/l.
13 . A process according to claim 12 wherein the water soluble zinc salt is present in the aqueous solution of step (b) at a concentration of between about 45 g/l and about 50 g/l.
14 . A process according to claim 1 wherein the source of the zinc ions of step (b) is an alkali metal zinc ate; and
wherein the aqueous solution of step (b) additionally comprises an amine compound.
15 . A process according to claim 14 , wherein the alkali metal zincate is selected from the group consisting of sodium zincate and potassium zincate.
16 . A process according to claim 14 , wherein the alkali metal zincate is present in the aqueous solution of step (b) at a concentration of between about 2 and about 30 g/l.
17 . A process according to claim 16 , wherein the alkali metal zincate is present in the aqueous solution of step (b) at a concentration of between about 8 and about 12 g/l.
18 . A process for plating upon a zinc die-cast article, said process comprising:
(a) cleaning said article;
(b) electroplating said article in an aqueous alkaline solution comprising (i) zinc ions, (ii) alloy metal ions, and (iii) counter ions, by making said article a negative cathode in said solution to produce a zinc-nickel alloy coating thereon; and
(c) electroplating said article with a metal selected from the group consisting of copper, nickel, chromium, tin, and alloys of the foregoing,
wherein said aqueous alkaline solution has a pH in the range of about 4.5 to about 7.0.
19 . A process according to claim 18 , wherein the pH of the aqueous solution in step (b) is between about 5.0 to about 5.5.
20 . A process according to claim 18 wherein the concentration of zinc ions in the aqueous solution of step (b) is from about 10 to about 100 g/l.
21 . A process according to claim 1 wherein the concentration of alloy ions in the aqueous solution of step (b) is from about 10 to about 100 g/l.