Process for Making Finished or Semi-Finished Articles of Silver Alloy Comprising Copper and Germanium

Abstract

A process is provided for making a finished or semi-finished article of silver alloy, said process comprising steps of: providing a silver alloy containing silver in an amount of at least 77 wt %, copper and an amount of germanium that is at least 0.5 wt % and is effective to reduce tarnishing and/or firestain; making or processing the finished or semi-finished article of the alloy by heating at least to an annealing temperature; and gradually air cooling the article from the temperature at which it is made or processed to develop a Vickers hardness of more than 70.

1 - 26 . (canceled)  
     
     
         27 . A process for making a finished or semi-finished article of silver alloy, said process comprising the steps of: 
 (i) providing a silver alloy containing silver in an amount of at least 77 wt %, copper and an amount of germanium that is at least 0.5 wt % and is effective to reduce tarnishing and/or firestain;    (ii) making or processing the finished or semi-finished article of the alloy by heating at least to an annealing temperature;    (iii) cooling the article gradually, without an abrupt cooling step, so that cooling to ambient temperature takes more than 10 seconds; and    (iv) reheating the article to effect precipitation hardening thereof.    
     
     
         28 . The process of  claim 27 , wherein the article is of a ternary alloy of silver, copper and germanium.  
     
     
         29 . The process of  claim 27 , wherein the article is of a ternary alloy that consists, apart from impurities, of 92.5-98 wt % silver, 0.5-3 wt % germanium, and 1-7.2 wt % copper together with 1-40 ppm boron as grain refiner.  
     
     
         30 . The process of  claim 27 , wherein the article is of a ternary alloy of 92.5-92.7 wt % Ag, 6.1-6.3 wt % Cu, about 1.2 wt % Ge and 1-15 ppm boron as grain refiner.  
     
     
         31 . The process of  claim 27 , wherein the article is of a ternary alloy of 96-97.3 wt % Ag, 1-1.55 wt % Ge, balance copper and boron as grain refiner.  
     
     
         32 . The process of  claim 27 , wherein the article is a quaternary alloy of silver, copper, zinc and germanium.  
     
     
         33 . The process of  claim 27 , wherein annealing is during brazing the article in a furnace, and subsequent air cooling.  
     
     
         34 . The process of  claim 33 , wherein the alloy is annealed or brazed by heating in a furnace at 600-680° C.  
     
     
         35 . The process of  claim 33 , wherein the alloy is annealed or brazed by heating in a furnace at 600-660° C.  
     
     
         36 . The process of  claim 33 , wherein the alloy is brazed using a solder which comprises (a) 56% silver, 22% copper, 17% zinc, and 5% tin or (b) 58 wt % Ag, 2 wt % Ge, 2.5 wt % Sn, 14.5 wt % Zn 0.1 wt % Si, 0.14 wt % B, and the balance Cu.  
     
     
         37 . The process of  claim 33 , wherein annealing and/or brazing is carried out at a temperature of from 600-650° C.  
     
     
         38 . The process of  claim 27 , wherein the article is investment cast and air-cooled.  
     
     
         39 . The process of  claim 27 , wherein the article is of jewellery or giftware.  
     
     
         40 . The process of  claim 27 , wherein reheating is at 180-350° C.  
     
     
         41 . The process of  claim 27 , wherein reheating is at 200-300° C.  
     
     
         42 . A precipitation-hardenable silver alloy comprising 96-97.3 wt % Ag, 1-1.55 wt % Ge, balance copper and boron as grain refiner.  
     
     
         43 . The alloy of  claim 42 , containing about 97.3 wt % Cu, about 1 wt % Ge, balance copper and boron as grain refiner.  
     
     
         44 . The alloy of  claim 42 , precipitation hardened to a hardness of at least 93 HV.