Metal alloy manufacturing

Abstract

Silver alloys containing copper and germanium e.g. about 1 wt % Ge and of very low copper content e.g. about 0.8 wt % Cu can be precipitation hardened to 65 HV or above, whereas alloys of similar copper content and not containing germanium remain soft. In an embodiment, a silver alloy comprises 92.5-97 wt % Ag, 1-4.5 wt % Cu, 0.4-4 wt % Zn, 0.8-1.5 wt % Ge, 0 to 0.2 wt % Si, In or Sn and 0-0.2 wt % Mn, the balance being boron as grain refiner, incidental ingredients and impurities. The said alloy preferably comprises boron as grain refiner added as a boron hydride, e.g. sodium borohydride. A further group of alloys comprises a ternary alloy of silver, copper and germanium containing from more than 93.5 wt % to 95.5 wt % Ag, from 0.5 to 3 wt % Ge and the remainder, apart from incidental ingredients (if any), impurities and grain refiner, copper, the grain refiner being sodium borohydride or another boron hydride. Silicon-containing casting grain that gives rise to bright as-cast products is also disclosed. In a further embodiment, a zinc-containing silver alloy resistant to tarnish under severe conditions e.g. exposure to human sweat or French dressing comprises 1-5 wt % Zn, 0.7-3 wt % Cu, 0.1-3 wt % Ge, 0-0.3 wt % Mn, 0-0.25 wt % Si, B in an amount effective for grain refinement, up to 0.5 wt % incidental ingredients, the balance being Ag in an amount of 92.5-96 wt %, and impurities. A preferred manufacturing method giving an alloy with favourable physical properties involves melting together the ingredients, and incorporating boron by dispersing into molten silver alloy to foirn the whole or a precursor pait of said alloy a compound selecting fiom alkyl boron compounds, boron hydrides, boron halides, boron-containing metal hydrides, boron-containing metal halides and mixtures thereof The alloy is particularly suitable for castings which may be hardened in an oven e.g. at about 300° C. for 30-45 min.

1 . A silver alloy including at least 93.5 wt % Ag, 0.5-4.6 wt % Cu, 0.1-3 wt % Ge and B in an amount effective for grain refinement, and optionally Mn, Si and/or one or more incidental ingredients selected from the group consisting of Al, Ba, Be, Cd, Co, Cr, Er, Ga, In, Mg, Ni, Pb, Pd, Pt, Si, Sn, Ti, V, Y, and Yb, said alloy being precipitation hardened to a hardness of 65 VH or above.  
     
     
         2 . The alloy of  claim 1 , wherein Ge is 0.8-1.5 wt %.  
     
     
         3 . The alloy of  claim 1 , wherein Ge is 0.9-1.2 wt %.  
     
     
         4 . The alloy of  claim 2 , wherein Cu is 0.7-3 wt %.  
     
     
         5 . The alloy of  claim 2 , wherein Cu is 0.7-2 wt %.  
     
     
         6 . The alloy of  claim 4 , which has been precipitation hardened to 70 VH or above.  
     
     
         7 . The alloy of  claim 4 , which has been precipitation hardened to 75 VH or above.  
     
     
         8 . The alloy of  claim 1 , having a content of 1-3 wt % Zn for reducing or preventing pitting or sagging on heating the alloy.  
     
     
         9 . The alloy of  claim 1 , having a content of 1-3 wt % Zn for reducing or preventing pitting or sagging on heating the alloy and to for increasing annealed hardness.  
     
     
         10 . The alloy of  claim 1  having a content of 0.8-3 wt % of 1-3 wt % Zn to for reducing or preventing pitting or sagging on heating the alloy and up to 0.2 wt % of Sn, In or Si or a mixture thereof for reducing or preventing zinc oxide formation on heating the alloy.  
     
     
         11 . A process for making a finished or semi-finished article of silver alloy, said process comprising the steps of: 
 providing a silver alloy containing silver in an amount of at least 77 wt %, copper in an amount of 0.5-5.5 wt %, an amount of germanium that is at least 0.5 wt % and is effective to reduce tarnishing and/or firestain and boron in an amount effective for grain refinement;    making or processing the finished or semi-finished article of the alloy by heating at least to an annealing temperature;    cooling the article gradually, without an abrupt cooling step, so that cooling to ambient temperature takes more than 10 seconds; and    reheating the article to effect precipitation hardening thereof.    
     
     
         12 . The process of  claim 11 , wherein the boron is incorporated using a compound selecting from alkyl boron compounds, boron hydrides, boron halides, boron-containing metal hydrides, boron-containing metal halides and mixtures thereof.  
     
     
         13 . The process of  claim 11 , wherein precipitation hardening is at 180-350° C.  
     
     
         14 . A precipitation-hardenable silver alloy comprising 96-97.3 wt % Ag, 1-1.55 wt % Ge, balance copper and optionally zinc, and boron as grain refiner.  
     
     
         15 . The alloy of  claim 14 , comprising 01.-0.7 wt % Zn.  
     
     
         16 . The alloy of  claim 14  comprising 0.3-0.5 wt % Zn.  
     
     
         17 . The alloy of claim  24 , comprising about 97-97.3 wt % Ag, about 1.2 wt % Ge, balance copper and boron as grain refiner.  
     
     
         18 . The alloy of  claim 17 , precipitation hardened to a hardness of at least 75 HV.