Process for Electroless Deposition on Magnesium Using a Nickel Hydrate Plating Bath

Abstract

A plating process using an electroless plating bath formed from a single component solution used to effect nickel or nickel alloy plating on magnesium. The plating solution is provided with a nickel hydrate compound as a source of plating ions, a sodium hydrate compound and ammonium hydroxide. The bath solution is heated to a temperature of 50° C. or more, and the substrate is immersed therein for upto ten minutes to allow for formation of the heating layer.

We claim: 
     
         1 . A process for electroless plating a plating metal on a magnesium or magnesium alloy substrate comprising,
 preparing a plating bath solution having a pH of at least 9, the bath solution comprising:
 7 to 15 g/L of a nickel hydrate compound; 
 15 to 25 g/L sodium hydrate compound; 
 10 to 50 g/L of ammonium hydroxide; and 
 optionally sodium hydroxide in an amount upto 3 g/L; 
 heating the bath solution to a temperature of at least 50° C.; and 
 immersing the substrate to be plated in the heated solution. 
   
     
     
         2 . The process as claimed in  claim 1 , wherein the nickel hydrate compound is selected from the group consisting of nickel acetate tetrahydrate, nickel sulfate hexahydrate and nickel sulfamate tetrahydrate. 
     
     
         3 . The process as claimed in  claim 1 , wherein the sodium hydrate compound comprises at least one selected from the group consisting of sodium citrate tribasic dehydrate and sodium hypophosphite hydrate. 
     
     
         4 . The process as claimed in  claim 1 , wherein the bath solution comprises ammonium hydroxide in an amount of between about 10 to about 50 g/L. 
     
     
         5 . The process as claimed in  claim 4 , wherein the bath solution comprises sodium hydroxide in an amount of 0.1 to 1.5 g/L. 
     
     
         6 . The process as claimed in  claim 2 , wherein the bath solution has a pH of between 11 and 14, and comprises between about 12 to 40 g/L ammonium hydroxide. 
     
     
         7 . The process as claimed in  claim 6 , wherein the substrate comprises a magnesium alloy substrate. 
     
     
         8 . The process as claimed in  claim 1 , wherein the solution is heated to a temperature of from about 60° C. to about 85° C. 
     
     
         9 . The process as claimed in  claim 1 , wherein the solution further includes 3 to 7 g/L zinc sulfate heptahydrate, and which preferably maintained at a level below 60% (cut) of the Ni present in the bath. 
     
     
         10 . The process as claimed in  claim 9 , wherein the nickel hydrate compound comprises 4 to 7 g/L nickel sulfate hexahydrate. 
     
     
         11 . A method for the electroless plating of nickel or a nickel alloy on a magnesium or magnesium alloy substrate, said method comprising:
 preparing a plating bath solution having a pH of between 10.5 and 14, the bath solution being substantially free of chloride salts and comprising:   6 to 13 g/L of a nickel hydrate compound, the nickel hydrate compound being selected from one or more of the group consisting of nickel acetate tetrahydrate, nickel sulfate hexahydrate and nickel sulfamate tetrahydrate;   17 to 24 g/L sodium hydrate compound, the sodium hydrate compound comprising at least one of sodium citrate tribasic dihydrate and sodium hypophosphite hydrate;   13 to 38 g/L of ammonium hydroxide and/or sodium hydroxide;   heating the bath solution to a temperature of at least 50° C.; and   immersing the substrate in the heated solution.   
     
     
         12 . The method as claimed in  claim 11 , wherein the bath solution comprises ammonium hydroxide in an amount of between about 10 to about 40 g/L. 
     
     
         13 . The method as claimed in  claim 11 , wherein the bath solution comprises sodium hydroxide in an amount of upto 3 g/L and preferably 0.1 to 1.5 g/L. 
     
     
         14 . The method as claimed in  claim 13 , wherein the bath solution comprises between about 12 to 40 g/L ammonium hydroxide. 
     
     
         15 . The method as claimed in  claim 11 , wherein the substrate comprises a AZ91D magnesium alloy. 
     
     
         16 . The method as claimed in  claim 11 , wherein the solution is heated to a temperature of from about 68° C. to about 74° C. 
     
     
         17 . The method as claimed in  claim 11 , wherein the solution further includes 3 to 7 g/L zinc sulfate heptahydrate which is maintained at a level below 60% cut of the nickel in the bath. 
     
     
         18 . The method as claimed in  claim 17 , wherein the nickel hydrate compound comprises 4 to 7 g/L nickel sulfate hexahydrate. 
     
     
         19 . The method as claimed in  claim 11 , wherein said sodium hydrate compound comprises sodium citrate tribasic dihydrate in an amount selected to maintain nickel in solution, and further wherein said plating bath comprises sodium hypophosphite in an amount selected to reduce nickel ions to metal at the surface of the substrate.