Cyanide-free pre-treating solution for electroplating copper coating layer on zinc alloy surface and a pre-treating method thereof

Abstract

A pre-treating solution for electroplating zinc alloy surface contains copper ions, hydroxyl ions, a complexing agent and an additive, wherein the additive is selected from sodium phosphate, sodium hypophosphite, phosphoric acid and dissolvable salts of phosphoric acid. The zinc alloy is dipped in the pre-treating solution and electroplated with a copper coating layer. Then, the zinc alloy is further dipped in a copper sulfate solution for thickening the copper coating layer and lastly coated with an anti-corrosion metal layer. Thereby, zinc alloy has excellent anti-corrosion and anti-wearing efficiency and varnish appearance. Moreover, the pre-treating solution contains no cyanide and thus is low toxic and safe to operator during electroplating and to environment after discharging.

1 . A cyanide-free pre-treating solution for zinc alloy surface, the pre-treating solution comprising an aqua solution added with copper ions, hydroxyl ions, a complexing agent and an additive, wherein the additive is selected from the group consisting of sodium phosphate, sodium hypophosphite, phosphoric acid and dissolvable salts derivative from phosphoric acid or hypophosphite acid. 
     
     
         2 . The pre-treating solution as claimed in  claim 1 , wherein the additive is 1 to 50 g/L in concentration. 
     
     
         3 . The pre-treating solution as claimed in  claim 1 , wherein the hydroxyl ions are obtained from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide and dissolvable salts of alkaline. 
     
     
         4 . The pre-treating solution as claimed in  claim 1 , wherein the hydroxyl ions are 5 to 30 g/L in concentration. 
     
     
         5 . The pre-treating solution as claimed in  claim 1 , wherein the complexing agent is selected from the group consisting of potassium sodium tartrate, potassium tartrate, sodium tartrate, tartaric acid, and dissolvable salts derivative from tartaric acid. 
     
     
         6 . The pre-treating solution as claimed in  claim 5 , wherein the complexing agent is 10 to 150 g/L in concentration. 
     
     
         7 . The pre-treating solution as claimed in  claim 1 , wherein the copper ions are obtained from the group consisting of copper chloride, copper sulfate, copper pyrophosphate and hydrates of foregoing motioned salts. 
     
     
         8 . The pre-treating solution as claimed in  claim 7 , wherein the copper ions are 3 to 50 g/L in concentration. 
     
     
         9 . A pre-treating method for zinc alloy surface comprising steps of:
 (a) degreasing: a prepared workpiece made of zinc alloy is degreased with a degreasing agent to remove oil and dirt from surface of the prepared workpiece;   (b) washing: the prepared workpiece is washed to remove the degreasing agent and to keep the surface of the prepared workpiece clean;   (c) copper electroplating: the prepared workpiece is dipped into the pre-treating solution with auxiliary electrodes and electroplated to obtain a copper coating layer by applying a fixed current from an additional power supplier; and   (d) drying: the pre-treating solution residual on the prepared workpiece is removed from the surface of the workpiece to make the surface dry rapidly.   
     
     
         10 . The pre-treating method as claimed in  claim 9  further comprising a washing step after (c) step of copper electroplating. 
     
     
         11 . The pre-treating method as claimed in  claim 9 , wherein the fixed current provided by the additional power supplier has a range from 0.002 to 0.02 ampere per square decimeter. 
     
     
         12 . The pre-treating method as claimed in  claim 9 , wherein the auxiliary electrodes are made of material selected from the group comprising titanium core coated with platinum, titanium, platinum, graphite and stainless steel. 
     
     
         13 . The pre-treating method as claimed in  claim 9 , wherein surface temperature of the prepared workpiece in (c) step of copper electroplating is 10 to 90° C. 
     
     
         14 . The pre-treating method as claimed in  claim 9 , wherein the workpiece is further treated with another copper electroplating process and a nickel coating process after the step of drying. 
     
     
         15 . The pre-treating method as claimed in  claim 10 , wherein, wherein the pre-treating solution comprises an aqua solution added with copper ions, hydroxyl ions, a complexing agent and an additive;
 wherein the additive is selected from the group consisting of sodium phosphate, sodium hypophosphite, phosphoric acid and dissolvable salts derivative from phosphoric acid or hypophosphite acid.