Electroforming method and part or layer obtained via the method

Abstract

The invention concerns an electroformed gold alloy part, characterized in that the gold alloy is made up of 88 to 94% by weight of gold, x % by weight of copper and/or silver, and 2x % by weight of zinc, x being comprised between 2 and 4.

1 - 17 . (canceled) 
   
   
       18 . A method of electroforming a layer of a gold alloy, consisting in:
 dipping a metal substrate into an alkaline electrolytic bath containing an anode, said bath containing at least mainly gold salts, in the form of potassium gold cyanide, copper salts in the form of copper cyanide, zinc salts in the form of zinc oxide, sodium cyanide, sodium hydroxide, ethylenediamino tetra-acetic acid and a surfactant, said substrate forming a cathode,   electroforming said layer by creating a voltage between the anode and the cathode to deposit metallic ions on the surface of the substrate,   interrupting the voltage once the desired thickness of the electroplated layer is obtained in order to generate a layer containing 88 to 94% by weight of gold.   
   
   
       19 . The method according to  claim 18  wherein the bath contains 7 to 15 g.l −1  gold in the form of potassium gold cyanide. 
   
   
       20 . The method according to  claim 18  wherein the bath contains 1.5 to 5 g.l −1  zinc in the form of zinc oxide. 
   
   
       21 . The method according to  claim 18 , wherein the bath contains 1.5 to 3 g.l −1  copper in the form of copper cyanide. 
   
   
       22 . The method according to  claim 18 , wherein the copper in the form of copper cyanide of the bath is replaced by silver in the form of silver oxide. 
   
   
       23 . The method according to  claim 18 , wherein the voltage is varied during the step of electroforming said layer in order to obtain the gold deposition in the phase α 
   
   
       24 . The method according to  claim 23 , wherein the voltage is decreased in the final phase of the electroforming step to increase the concentration of gold in the superficial zone of the deposited layer. 
   
   
       25 . The method according to  claim 18 , wherein the electroforming step is followed by a thermal anneal process, the temperature of which is comprised between 300° and 700° C. for a duration of at least 30 minutes. 
   
   
       26 . The method according to  claim 25 , wherein the thermal anneal process temperature does not exceed the liquefaction temperature of said gold alloy in order to avoid a gold deposition in several phases. 
   
   
       27 . The method according to  claim 25 , wherein the thermal anneal step is followed by a rapid cooling. 
   
   
       28 . The method according to  claim 27 , wherein the cooling step is made in a reducing atmosphere in order to reduce the zinc oxide. 
   
   
       29 . The method according to  claim 18 , wherein the surfactant is a butyl or nonyl phenolpolyglycol phosphatide ester. 
   
   
       30 . The method according to  claim 18 , wherein the electroforming is performed at a temperature of between 40° and 80° C. and preferably between 60 and 75° C. 
   
   
       31 . A electroformed part made of gold alloy obtained with the method according to  claim 18 , wherein the gold alloy is made up of 88 to 94% by weight of gold, x % by weight of copper and/or silver, and 2x % by weight of zinc, x being comprised between 2 and 4. 
   
   
       32 . The electroformed part according to  claim 31 , wherein the alloy is made up of 88% by weight of gold, 8% by weight of zinc and 4% by weight of copper. 
   
   
       33 . The electroformed part according to  claim 31 , wherein the alloy layer has a thickness of several hundreds of microns. 
   
   
       34 . The electroformed part according to  claim 31 , wherein the gold in said alloy is essentially formed of phase α gold.