Copper alloy having improved stress relaxation resistance

• US 20020044881A1
• Filed: 06/12/2001
• Published: 04/18/2002
• Est. Priority Date: 06/26/2000
• Status: Active Grant

• Current Assignee: Wieland Rolled Products North America, LLC
• Original Assignee: OLIN Corporation
• Inventors: Brauer, Dennis R., Robinson, Peter W., Breedis, John F.
• Granted Patent: US 6,632,300 B2
• Time in Patent Office: Days
• US Class Current: 420/496
• CPC Class Codes: C22C 9/00 Alloys based on copper
• CPC Class Codes: C22F 1/08 of copper or alloys based thereon

Abstract

A copper alloy having improved stress relaxation resistance is formed from a copper base alloy that consists, by weight, essentially of 1.8%-3.0% iron, 0.01%-1.0% zinc, 0.001 %-0.25% phosphorus, 0.1 %-0.35% magnesium and the balance is copper and unavoidable impurities. When compared to other copper base alloys that include iron, zinc and phosphorous, the disclosed alloy has improved resistance to stress relaxation. In addition, directionality of stress relaxation resistance (where stress relaxation resistance is typically poorer in a transverse strip direction relative to a longitudinal strip direction for a copper alloy that is strengthened by cold rolling) is reduced to being nearly equivalent, regardless of strip direction. The alloy is particularly useful for electronic applications, such as being formed into an electrical connectors.

Claims

1. A copper alloy having improved stress relaxation resistance, said copper alloy consisting essentially of:

from 1.8 to 3.0 weight percent iron;

from 0.01 to 1.0 weight percent zinc;

from 0.001 to 0.25 weight percent phosphorous;

from greater than 0.1 to 0.35 weight percent magnesium; and

the balance copper and unavoidable impurities.

2. The copper alloy of claim 1 wherein said iron content is, by weight, from 2.0% to 2.7%.

3. The copper alloy of claim 2 wherein said magnesium content is, by weight, from 0.11% to 0.30%.

4. The copper alloy of claim 3 wherein said zinc content is, by weight, from 0.01 % to 0.50%.

5. The copper alloy of claim 4 wherein said alloy has a resistance to stress relaxation that is approximately equivalent in a direction transverse to a rolling direction and in a direction longitudinal to said rolling direction.

6. The copper alloy of claim 4 wherein at least a portion of said iron is replaced with cobalt on a 1:

1, by weight, basis.

7. An electrical connector formed from the copper alloy of claim 5.

8. A metal foil formed from the copper alloy of claim 5.

9. A wire formed from the copper alloy of claim 5.

10. A copper alloy having improved stress relaxation resistance, said copper alloy consisting essentially of:

from 2.1 to 2.6 weight percent iron;

from 0.05 to 0.25 weight percent zinc;

from 0.01 to 0.09 weight percent phosphorous;

from greater than 0.12 to 0.25 weight percent magnesium; and

the balance copper and unavoidable impurities.

11. The copper alloy of claim 10 wherein said alloy has a resistance to stress relaxation that is approximately equivalent in a direction transverse to a rolling direction and in a direction longitudinal to said rolling direction.

12. The copper alloy of claim 10 wherein at least a portion of said iron is replaced with cobalt on a 1:

1, by weight, basis.

13. An electrical connector formed from the copper alloy of claim 11.

14. A metal foil formed from the copper alloy of claim 11.

15. A wire formed from the copper alloy of claim 11.

17. The process of claim 16 wherein during said annealing step (d) said temperature is from 500°

C. to 600°

C. and said time is in excess of one hour.

18. The process of claim 17 wherein during said annealing step (d) said temperature is from 550°

C. to 580°

C. and said time is from 5 hours to 10 hours.

19. The process of claim 17 wherein during said annealing step (f) said temperature is from 425°

C. to 550°

C. and said time is in excess of one hour.

20. The process of claim 19 wherein during said annealing step (f) said temperature is from 475°

C. to 525°

C. and said time is from 6 hours to 10 hours.

21. The process of claim 19 further including a relief anneal step (h) following step (g), said relief anneal step being at a temperature of from 200°

C. to 425°

C. for a time of from 30 seconds to 5 hours.

22. The process of claim 21 wherein said relief anneal step is at a temperature of from 250°

C. and 400°

C. for a time of from 1 minute to 5 hours.

23. The process of claim 21 wherein said step (e) reduction in thickness is up to 70%.

24. The process of claim 19 wherein a difference, Δ

, between said intermediate gauge and said final gauge is selected to achieve a desired temper.

25. The process of claim 24 wherein Δ

is between 5% and 75% in thickness.

26. The process of claim 25 wherein Δ

is between 10% and 60% in thickness.

27. The process of claim 26 including the step of forming said copper base alloy strip at final gauge into an electrical spring contact.

28. The process of claim 27 wherein said electrical spring contact is oriented along an axis transverse to a rolling direction of said copper alloy strip.

29. The process of claim 19 wherein said step (e) reduction in thickness is up to 70%.

30. The process of claim 29 wherein a difference, Δ

, between said intermediate gauge and said final gauge is selected to achieve a desired temper.

31. The process of claim 30 wherein Δ

is between 5% and 75% in thickness.

32. The process of claim 31 wherein Δ

is between 10% and 60% in thickness.

33. The process of claim 32 including the step of forming said relief annealed copper base alloy strip at final gauge into an electrical spring contact.

34. The process of claim 33 wherein said electrical spring contact is oriented along an axis transverse to a rolling direction of said copper alloy strip.

16. A process for making a copper alloy that has improved resistance to stress relaxation comprising the steps of:

(a) casting a copper base alloy ingot having a composition, by weight of, from 1.8 to 3.0 percent iron, from 0.01 to 1.0 percent zinc, from 0.001 to 0.25 percent phosphorous, from 0.1 to 0.35 percent magnesium and the balance copper and unavoidable impurities;

(b) hot rolling said copper base alloy ingot to a slab;

(c) cold working said copper base alloy slab forming a copper alloy strip;

(d) annealing said copper alloy strip at a temperature and for a time effective to precipitate both an iron phase and an iron phosphide phase;

(e) cold working said copper alloy strip for a reduction in thickness, thereby forming a copper alloy strip having an intermediate thickness;

(f) annealing said copper alloy strip having an intermediate gauge at a temperature and for a time effective to precipitate said iron phase;

(g) cold working said copper base alloy strip to a desired final gauge.