Novel Cyanide-Free Electroplating Process for Zinc and Zinc Alloy Die-Cast Components

Abstract

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.