Metal treatment – Stock – Copper base
Reexamination Certificate
1999-05-04
2001-06-26
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Copper base
C148S544000, C148S685000, C420S473000
Reexamination Certificate
active
06251199
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to copper base alloys having particular application as connectors or lead frames in electronics. The alloy of this invention comprises a precipitation hardenable nickel-silicon-tin copper alloy to which iron is added within certain limits. The alloy provides improved resistance to cracking or fracture during localized plastic deformation, a fine grain size and improved resistance to grain growth at elevated temperatures. The alloy also provides an excellent combination of properties including bend formability, high strength, stampability and improved resistance to stress relaxation at elevated temperatures.
2. Description of Related Art
One copper alloy used to manufacture electrical connector or leadframe electronic components is designated by the Copper Development Association (CDA, New York, N.Y.) as copper alloy C70250. Copper alloy C70250 has the nominal composition, by weight, of 2.2%-4.2% nickel, 0.25%-1.2% silicon, 0.05%-0.30% magnesium, 0.2% max iron, 1.0% max zinc, 0.1% max manganese, 0.05% max lead and the balance copper and unavoidable impurities. Further details concerning alloys of this type can be found in U.S. Pat. Nos. 4,594,221 and 4,728,372 to Caron et al. Both of which are incorporated by reference in their entireties herein.
United States patents that disclose copper alloys containing nickel, silicon, tin and iron, include U.S. Pat. Nos. 4,971,758 to Suzuki et al., 5,024,814 to Futatasuka et al. and 5,508,001 to Suzuki et al. All of which are incorporated by reference in their entireties herein. U.S. Pat. No. 5,846,346 discloses a copper alloy containing nickel, silicon, tin and an optional addition of iron.
While copper alloys containing nickel, silicon, tin and iron within certain limits are known, there remains a need for a copper alloy with an improved resistance to cracking or fracture during localized plastic deformation, a fine grain size and improved resistance to grain growth at elevated temperatures while maintaining an excellent combination of properties including bend formability, high strength, stampability and improved resistance to stress relaxation at elevated temperatures.
SUMMARY OF THE INVENTION
The design of electrical/electronic connectors, particularly for use in the automotive industry, has become much more complex and miniaturized. This has imposed increasingly higher formability demands on the copper alloys from which they are made. For example, box type connectors include transitions from the box type socket to the wire crimp portion wherein the copper alloy is subjected to localized plastic deformation due to a combination of bending and stretching. Typical prior art measures of tensile elongation and minimum bend radius have surprisingly been found to inadequately predict the performance of copper alloys when subjected to such localized plastic deformation. As a result, copper alloys which have excellent tensile elongation and bend formability as measured by the minimum bend radius, have failed in such applications due to a propensity for cracking under such localized plastic deformation.
In accordance with this invention, applicants have developed a local ductility index which enables one to predict whether a copper alloy will be suitable for applications which will require localized plastic deformation of the alloy. It has surprisingly been found that a precipitation hardenable nickel-silicon-tin copper alloy to which iron is added within certain limits provides such improved resistance to cracking or fracture during localized plastic deformation. The alloy of this invention also has a fine grain size and improved resistance to grain growth at elevated processing temperatures. The alloy also provides an excellent combination of properties including excellent bend formability, high strength, excellent stampability and improved resistance to stress relaxation at elevated temperatures. The alloy preferably provides an improved solution anneal processing window and a more stable response to age annealing at finished strip thickness.
In accordance with this invention a copper alloy is provided having improved resistance to cracking due to localized plastic deformation. The alloy consists essentially of: from 0.7 to 3.5 weight percent nickel; from 0.2 to 1 weight percent silicon; from 0.05 to 1 weight percent tin; from 0.26 to 1 weight percent iron; and the balance copper and unavoidable impurities. The copper alloy has a local ductility index of greater than 0.7 and a tensile elongation exceeding 5%.
In a preferred embodiment of this invention, nickel is from 1.2 to 2.8 weight percent, silicon is from 0.3 to 0.7 weight percent, tin is from 0.2 to 0.6 weight percent, iron is from 0.28 to 0.7 weight percent and the alloy further includes an effective amount of manganese for improving hot workability up to 0.15 weight percent. In a more preferred embodiment of this invention, nickel is from 1.5 to 2.5 weight percent, silicon is from 0.35 to 0.55 weight percent, tin is from 0.3 to 0.5 weight percent, iron is from 0.3 to 0.5 weight percent and manganese is from 0.02 to 0.1 weight percent.
In accordance with an alternative embodiment of this invention cobalt may be substituted, in whole or in part, on a 1:1 basis by weight for iron to improve resistance to grain growth at elevated temperatures and improved aging response.
The copper alloys of this invention generally possess a yield strength of from 60 to 100 ksi, an electrical conductivity of greater than or equal to 35% IACS, stress relaxation resistance at 150° centigrade of at least 80% longitudinal stress remaining after 3000 hours exposure and excellent bend formability. The alloys of this invention are particularly useful in electrical or electronic connector applications, although they may be used in any application where their unique combination of properties make them suitable, such as without limitation, lead frames, or other electronic uses.
An electrical connector formed from the copper alloy of this invention also forms part of this invention.
The process for making the alloy of this invention also forms a part of the invention. The critical minimum amount of iron used in the alloys of the present invention avoids cracking problems during hot working as the temperature of the strip falls during succeeding hot rolling passes. This results in a significant improvement in hot workability for the alloys of this invention and provides a broad processing window, which increases productivity by increasing the manufacturing yield from the hot working operation.
Accordingly it is an aim of the present invention to provide an improved copper base alloy and the process for making it, which will provide an alloy having increased resistance to cracking during localized plastic deformation.
It is a further aim of this invention to provide a precipitation hardenable nickel-silicon-tin copper alloy to which iron is added within certain limits.
It is a still further aim of this invention, in accordance with a preferred embodiment thereof, to provide an alloy which has an excellent combination of properties including, fine grain size, excellent bend formability, high strength, excellent stampability and improved resistance to stress relaxation at elevated temperatures.
It is a still further aim of this invention, in accordance with a preferred embodiment thereof, to provide an alloy with a large solution anneal processing window and a more stable response to age annealing at finish gauge.
The above stated objects, features and advantages will become more apparent from the specification and drawings that follow.
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patent: 4591484 (1986-05-01), Miyafuji et al.
patent: 4594221 (1986-06-01), Caron et al.
patent: 46
Breedis John F.
Mandigo Frank N.
Ip Sikyin
Olin Corporation
Rosenblatt Gregory S.
Wiggin & Dana
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