Copper alloys for use as connector materials having high resistance to stress corrosion cracking and a process for producing the same

Abstract

The improved copper alloy suitable for use as a connector material contains 17-32 wt % of Zn, 0.1-4.5 wt % of Sn and 0.01-2.0 wt % of Si, with Zn and Sn satisfying the relation 54≦3X+Y≦100 where X is the amount in wt % of Zn added and Y is the amount in wt % of Sn added. Rolled material of the alloy can be produced by a process comprising the steps of melting a copper alloy of the composition specified above, cooling the melt over a temperature range from the liquidus line to 600° C. at a rate of at least 50° C./min, and subsequently hot rolling the resulting ingot at an elevated temperature of 900° C. or below.

What is claimed is:  
     
         1 . A copper alloy for use as a connector material having high resistance to stress corrosion cracking that contains 17-32 wt % Zn, Sn and Si, with the balance being copper and incidental impurities, and which has resistance to stress corrosion cracking such that its stress cracking life in a 3% NH 3  atmosphere is at least five times as long as the value for class 1 brass.  
     
     
         2 . A copper alloy for use as a connector material having high resistance to stress corrosion cracking that contains 17-32 wt % Zn, Sn and Si, with the balance being copper and incidental impurities, which has resistance to stress corrosion cracking such that its stress cracking life in a 3% NH 3  atmosphere is at least five times as long as the value for class 1 brass, and which has a 0.2 wt % yield strength of at least 600 N/mm 2 , a tensile strength of at least 650 N/mm 2 , an electrical conductivity of at least 20 % IACS, a Young's modulus of no more than 120 kN/mm 2  and a percent stress relaxation of no more than 20%, each in rolling direction.  
     
     
         3 . The copper alloy according to  claim 1  or  2 , which consists essentially of 17-32 wt % Zn, 0.1-41.5 wt % Sn and 0.01-2.0 wt % Si, with the balance being copper and incidental impurities, provided that Zn and Sn satisfy the following relation (1):  
       54≦3 X+Y≦ 100  (1)  
       where X is the amount in wt % of Zn added and Y is the amount in wt % of Sn added.  
     
     
         4 . A copper alloy for use as a connector material having high resistance to stress corrosion craking that contain 17-32 wt % Zn, 0.1-4.5 wt % Sn and 0.01-2.0 wt % Si, with the balance being copper and incidental impurities, provided that Zn and Sn satisfy the following relation (1):  
       54≦3 X+Y≦ 100  (1)  
       where X is the amount in wt % of Zn added and Y is the amount in wt % of Sn added, which has resistance to stress corrosion cracking such that its stress cracking life in a 3% NH 3  atmosphere is at least five times as long as the value for class 1 brass, and which has a 0.2 wt % yield strength of at least 600 N/mm 2 , a tensile strength of at least 650 N/mm 2 , an electrical conductivity of at least 20% IACS, a Young's modulus of no more than 120 kN/mm 2  and a percent stress relaxation of no more than 20% in the direction where said alloy was wrought whereas it has a 0.2% yield strength of at least 650 N/mm 2 , a tensile strength of at least 700 N/mm 2  and a Young's modulus of no more than 130 kN/mm 2  in a direction perpendicular to said first direction.  
     
     
         5 . The copper alloy according to  claim 1  or  claim 2 , which further contains at least one element selected from the group consisting of 0.01-3 wt % Fe, 0.01-5 wt % Ni, 0.01-3 wt % Co, 0.01-3 wt % Ti, 0.01-2 wt % Mg, 0.01-2 wt % Zr, 0.01-1 wt % Ca, 0.01-10 w % Mn, 0.01-3 wt % Cd, 0.01-5 wt % Al, 0.01-3 wt % Pb, 0.01-3 wt % Bi, 0.01-3 wt % Be, 0.01-1 wt % Te, 0.01-3 wt % Y, 0.01-3 wt % La, 0.01-3 wt % Cr, 0.01-3 wt % Ce, 0.01-5wt % Au, 0.01-5 wt % Ag and 0.005-0.5 wt % P, with the sum of the contents of said elements being 0.01-5 wt %, provided that S is present in an amount of up to 30 ppm.  
     
     
         6 . The copper alloy according to  claim 3 , which further contains at least one element selected from the group consisting of 0.01-3 wt % Fe, 0.01-5 wt % Ni, 0.01-3 wt % Co, 0.01-3 wt % Ti, 0.01-2 wt % Mg, 0.01-2 wt % Zr, 0.01-1 wt % Ca, 0.01-10 w % Mn, 0.01-3 wt % Cd, 0.01-5 wt % Al, 0.01-3 wt % Pb, 0.01-3 wt % Bi, 0.01-3 wt % Be, 0.01-1 wt % Te, 0.01-3 wt % Y, 0.01-3 wt % La, 0.01-3 wt % Cr, 0.01-3 wt % Ce, 0.01-5 wt % Au, 0.01-5 wt % Ag and 0.005-0.5 wt % P, with the sum of the contents of said elements being 0.01-5 wt %, provided that S is present in an amount of up to 30 ppm.  
     
     
         7 . The copper alloy according to  claim 4 , which further contains at least one element selected from the group consisting of 0.01-3 wt % Fe, 0.01-5 wt % Ni, 0.01-3 wt % Co, 0.01-3 wt % Ti, 0.01-2 wt % Mg, 0.01-2 wt % Zr, 0.01-1 wt % Ca, 0.01-10 w % Mn, 0.01-3 wt % Cd, 0.01-5 wt % Al, 0.01-3 wt % Pb, 0.01-3 wt % Bi, 0.01-3 wt % Be, 0.01-1 wt % Te, 0.01-3 wt % Y, 0.01-3 wt % La, 0.01-3 wt % Cr, 0.01-3 wt % Ce, 0.01-5 wt % Au, 0.01-5 wt % Ag and 0.005-0.5 wt % P, with the sum of the contents of said elements being 0.01-5 wt %, provided that S is present in an amount of up to 30 ppm.  
     
     
         8 . A process for producing a copper alloy for use as a connector material having high resistance to stress corrosion cracking which comprises the steps of: 
 melting a copper alloy that contains 17-32 wt % Zn, Sn and Si, with the balance being copper and incidental impurities;    cooling the melt over a temperature range from the liquidus line to 600° C. at a rate of at least 50° C./min; and    subsequently hot rolling the resulting ingot at an elevated temperature of 900° C. or below.    
     
     
         9 . The process according to  claim 8 , wherein said copper alloy to be melted consists essentially of 17-32 wt % Zn, 0.1-4.5 wt % Sn and 0.01-2.0 wt % Si, with the balance being copper and incidental impurities, provided that Zn and Sn satisfy the following relation (1),:  
       54≦3 X+Y≦ 100  (1)  
       where X is the amount in wt % of Zn added and Y is the amount in wt % of Sn added.  
     
     
         10 . A process for producing a copper alloy for use as a connector material having high resistance to stress corrosion cracking which comprises the steps of: 
 melting an alloy that contains 17-32 wt % Zn, 0.1-4.5 wt % Sn and 0.01-2.0 wt % Si, with the balance being copper and incidental impurities, provided that Zn and Sn satisfy the following relation (1),:    54≦3 X+Y≦ 100  (1)    where X is the amount in wt % of Z added and Y is the amount in wt % of Sn added;    cooling the melt over a temperature range from the liquidus line to 600° C. at a rate of a,: least 50° C./min;    subsequently hot rolling the resulting ingot at an elevated temperature of 900° C. or below; and    repeating the process of cold rolling and annealing in a temperature range of 300-650° C. until the as-annealed rolled material has a crystal grain size of no more than 10 μm.    
     
     
         11 . A process for producing a copper alloy for use as a connector material having high resistance to stress corrosion cracking which comprises the steps of: 
 melting an alloy that contains 17-32 wt % Zn, 0.1-4.5 wt % Sn and 0.01-2.0 wt % Si, with the balance being Cu and incidental impurities, provided that 2n and Sn satisfy the following relation (l):    54≦3 X+Y≦ 100  (1)    where X is the amount in wt % of Zn added and Y is the amount in wt % of Sn added;    cooling the melt over a temperature range from the liquidus line to 600° C. at a rate of at least 50° C./min;    subsequently hot rolling the resulting ingot at an elevated temperature of 900° C. or below;    repeating the process of cold rolling and annealing in a temperature range of 300 -650° C. until the as-annealed rolled material has a crystal grain size of no more than 10 μm; and    further performing rolling for a reduction ratio of at least 30% and low-temperature annealing at 450° C. or below so that the rolled material has a stress corrosion cracking property such that the corrosion cracking life in a 3% NH 3  atmosphere is at least five times as long as the value for class 1 brass, and that it has a 0.2% yield strength of at least 600 N/mm 2 , a tensile strength of at least 650 N/mm 2 , a Young's modulus of no more than 120 kN/mm 2 , an electrical conductivity of at least 20% IACS and a percent stress relaxation of no more than 20% in the direction where said alloy was wrought whereas the alloyed material has a 0.2% yield strength of at least 650N/mm 2 , a tensile strength of at least 700 N/mm 2  and a Young's modulus of no more than 130 kN/mm 2  in a direction perpendicular to said first direction.    
     
     
         12 . The process according to  claim 8 , wherein said copper alloy to be melted further contains at: least one element selected from the group consisting of 0.01-3 wt % Fe, 0.01-5 wt % Ni, 0.01-3 wt % Co, 0.01-3 wt % Ti, 0.01-2 wt % Mg, 0.01-2 wt % Zr, 0.01-1 wt % Ca, 0.01-10 w% Mn, 0.01-3 wt % Cd, 0.01-5 wt % Al, 0.01-3 wt % Pb, 0.01-3 wt % Bi, 0.01-3 wt % Be, 0.01-1 wt % Te, 0.01-3 wt % Y, 0.01-3 wt % La, 0.01-3 wt % Cr, 0.01-3 wt % Ce, 0.01-5 wt % Au, 0.01-5 wt % Ag and 0.005-0.5 wt % P, with the sum of the contents of said elements being 0.01-5 wt %, provided that S is present in an amount of up to 30 ppm.  
     
     
         13 . The process according to  claim 9 , wherein said copper alloy to be melted further contains at least one element selected from the group consisting of 0.01-3 wt % Fe, 0.01-5 wt % Ni, 0.01-3 wt % Co, 0.01-3 wt % Ti, 0.01-2 wt % Mg, 0.01-2 wt % Zr, 0.01-1 wt % Ca, 0.01- 10 w % Mn, 0.01-3 wt % Cd, 0.01-5 wt % Al, 0.01-3 wt % Pb, 0.01-3 wt % Bi, 0.01-3 wt % Be, 0.01-1 wt % Te, 0.01-3 wt % Y, 0.01-3 wt % La, 0.01-3 wt % Cr, 0.01-3 wt % Ce, 0.01-5 wt % Au, 0.01-5 wt % Ag and 0.005-0.5 wt % P, with the sum of the contents of said elements being 0.01-5 wt %, provided that S is present in an amount of up to 30 ppm.  
     
     
         14 . The process according to  claim 10  or  claim 11 , wherein said copper alloy to be melted further contains at least one element selected from the group consisting of 0.01-3 wt % Fe, 0.01-5 wt % Ni, 0.01-3 wt % Co, 0.01-3 wt % Ti, 0.01- 2 wt % Mg, 0.01-2 wt % Zr, 0.01- 1wt % Ca, 0.01- 10 w % Mn, 0.01-3 wt % Cd, 0.01-5 wt % Al, 0.01-3 wt % Pb, 0.01-3 wt % Bi, 0.01-3 wt % Be, 0.01-1 wt % Te, 0.01-3 wt % Y, 0.01-3 wt % La, 0.01-3 wt % Cr, 0.01-3 wt % Ce, 0.01-5 wt % Au, 0.01-5 wt % Ag and 0.005-0.5 wt % P, with the sum of the contents of said elements being 0.01-5 wt %, provided that S is present in an amount of up to 30 ppm.