Copper Tin Nickel Phosphorus Alloys With Improved Strength and Formability and Method of Making Same

Abstract

A new copper-based alloy is described along with a processing method to make a strip that can be used for various automotive interconnects. The alloy process combination yields a material with high strength and electrical conductivity with excellent formability. The combination of properties result from a Cu—Sn—Ni—P alloy with optional Mg additions and thermal-mechanical processing to make an alloy with a conductivity of 40% IACS, yield strength of 80 KSI, bend formability of 1t/1t minimum, and stress relaxation of 65% at 150° C. after 1000 hours. Processing can be modified to increase formability at the expense of yield strength. Improvements to conductivity come from changes in chemistry as well as processing. The new chemistry-process optimization results in a low cost alloy of Cu—Sn—Ni—P—Mg.

1 . A copper base alloy comprising between about 1% and about 2% Sn; between about 0.3% and about 1% Ni; between about 0.05% and about 0.15% P, and at least one of up to about 0.20% Mg and between about 0.1 and about 0.4% Fe, the balance being copper. 
     
     
         2 . The copper base alloy according to  claim 1  containing Mg but no Fe. 
     
     
         3 . The copper base alloy according to  claim 1  containing Fe but no Mg. 
     
     
         4 . The copper base alloy according to  claim 1  containing both Mg and Fe. 
     
     
         5 . The copper base alloy according to  claim 1  containing up to about 0.06% Mg. 
     
     
         6 . The copper base alloy according to  claim 1  processed to have a yield strength of at least about 77 ksi, while maintaining bend formability (90° GW/BW) of 1.0/1.0. 
     
     
         7 . The copper base alloy according to  claim 6  wherein the alloy is processes to have a conductivity of at least about 37% IACS. 
     
     
         8 . The copper base alloy according to  claim 6  wherein the alloy is processed to have a conductivity of at least about 40% IACS 
     
     
         9 . The copper base alloy according to  claim 1  wherein the Ni:P ratio is less than about 9. 
     
     
         10 . The copper alloy according to  claim 1  wherein the (Ni+Mg):P ratio is between about 4 and about 8.5. 
     
     
         11 . The copper base alloy according to  claim 1  wherein the Sn is between about 1.2% and about 1.5%, the Ni is between about 0.5% and 0.7%, and the P is between about 0.09% and about 0.13%. 
     
     
         12 . The copper base alloy according to  claim 11  wherein the Ni:P ratio is less than about 9. 
     
     
         13 . The copper alloy according to  claim 11  wherein the (Ni+Mg):P ratio is between about 4 and about 8.5. 
     
     
         14 . The copper base alloy according to  claim 11  processed to have a yield strength of at least about 77 ksi, while maintaining bend formability (90° GW/BW) of 1.0/1.0. 
     
     
         15 . The copper base alloy according to  claim 14  wherein the alloy is process to have a conductivity of at least about 37% IACS. 
     
     
         16 . The copper base alloy according to  claim 14  wherein the alloy is process to have a conductivity of at least about 40% IACS. 
     
     
         17 . A copper base alloy comprising between about 1.2% and about 1.5% Sn; between about 0.5% and about 0.7% Ni; between about 0.09% and about 0.13% P, and at least one of up to about 0.20% Mg and between about 0.1 and about 0.4% Fe, the balance being copper, the alloy processed to have a yield strength of at least about 77 ksi, and an electrical conductivity of at least about 37% IACS. 
     
     
         18 . The copper base alloy according to  claim 17  wherein the alloy is processed to have a conductivity of at least about 40% IACS. 
     
     
         19 . The copper base alloy according to  claim 17  processed to have a bend formability (90° GW/BW) of 1.0/1.0. 
     
     
         20 . The copper alloy according to  claim 11  wherein the (Ni+Mg):P ratio is between about 4 and about 8.5. 
     
     
         21 . A method of processing a copper base alloy comprising between about 1% and about 2% Sn; between about 0.03% and about 1% Ni; between about 0.05% and about 0.15% P, and at least one of up to about 0.20% Mg and between about 0.1 and about 0.4% Fe, the method comprising:
 casting the alloy;   hot rolling the alloy at about 850 to about 1000° C.;   subjecting the alloy to at least one cold rolling and annealing to substantially recrystalize the alloy;   cold rolling the alloy to the desired thickness and mechanical strength; and   subjecting the alloy to a thermal stress relief treatment, to provide an alloy with a yield strength of at least about 77 ksi and an electrical conductivity of at least about 37% IACS.   
     
     
         22 . The method according to  claim 21  wherein there are at least three cold rollings and annealings. 
     
     
         23 . The method according to  claim 22  wherein the at least three cold rollings and annealings comprise:
 a first cold rolling up to about a 75% reduction followed by annealing between about 450 and about 600° C. for 1 to 48 hours;   a second cold rolling up to about a 60% reduction followed by annealing at about 425 and about 600° C. for 1 to 48 hours; and   a third cold rolling up to about a 50% reduction followed by an annealing at between about 400 and about 550° C. for 1 to 48 hours.   
     
     
         24 . The method according to  claim 22  wherein one of the annealings comprises a step anneal. 
     
     
         25 . The method according to  claim 24  wherein the step anneal comprises a first anneal at between about 400 and about 500° C. followed by a second anneal at between about 300 and about 400° C.