Metal treatment – Stock – Copper base
Reexamination Certificate
2000-05-09
2001-07-24
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Copper base
C420S473000
Reexamination Certificate
active
06264764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention generally relates to copper base alloys having utility in electrical applications and to a process for making the copper base alloys.
2. Description of Prior Art
Electronic components, including connectors, form the basis of information technology, especially in computers. One of the most important considerations in any connector design is to optimize performance at the lowest cost. As computer prices continue to decline, there is a need in the computer industry for, inter alia, alternative materials to those presently used as electrical components that possess the desirable properties of high electrical and thermal conductivity, high yield and tensile strengths, and that are cost effective.
Copper alloys are typically used as connectors and in other electrical and thermal applications because of their generally superior corrosion resistance, high electrical and thermal conductivity, and good bearing and wear qualities. Copper alloys also are useful for their good cold or hot-working properties and machinability.
Copper is alloyed with other metals primarily to increase tensile strength of the alloy. However, electrical and thermal conductivities, corrosion resistance, formability and color of the alloy are strongly affected by alloying copper with other elements. For example, when alloying elements are present in significant concentrations or when low concentrations of deoxidized elements are present, they tend to decrease electrical and thermal conductivity of a copper alloy.
The addition of beryllium to copper results in a significant age hardening response, making these copper alloys one of the few non-ferrous materials that can reach 200 ksi tensile strength. Beryllium copper alloys, however, are very expensive, are limited in their forming ability, and often require extra heat treatment after preparation, further adding to the cost.
Phosphor bronze copper alloys have high strengths, excellent forming properties, and are widely used in the electronic and telecommunications industries. However, the addition of high amounts of tin increases the cost of these alloys.
Copper alloys that include small quantities of tin and zinc provide many desirable properties. One tin brass alloy, commercially available as C42500 (as specified in the ASM Handbook), has a composition of 87%-90% copper, 1.5%-3.0% of tin, a maximum of 0.05% of iron, and a maximum of 0.35% phosphorous, the balance being zinc. The ASM Handbook specifies that the copper alloy designated as C42500 has a nominal electrical conductivity of 28% International Annealed Copper Standard (IACS). This is the traditional way of comparing the conductivity of other metals and copper alloys with high conductivity copper where “pure” copper is assigned a conductivity value of 100% ICAS at 20 degrees Celsius. C42500 also has a yield strength, dependent on temper, of between 45 ksi and 92 ksi. This alloy is used for many electrical applications, such as electrical switch springs, terminals, connectors, and fuse clips. However, its yield strength is lower than desired (i.e., approximately 22 ksi at 40% reduction) for electrical applications.
U.S. Pat. No. 5,853,505 to Brauer et al (“the Brauer '505 patent”) describes a tin brass alloy that has been annealed twice at a temperature between about 400 degrees Celsius and 600 degrees Celsius to a grain size of 0.002 mm and contains from 1% to 4% by weight of tin, from 0.8% to 4.0% by weight of iron, up to 0.4% by weight of phosphorous, and the balance being copper.
According to the Brauer '505 patent, when a tin content less than 1.5% is used, the copper alloy lacks adequate strength and resistance to stress relaxation for spring application. The Brauer '505 patent also specifies that the addition of zinc to the alloy would be expected to provide a moderate increase in strength with some decrease in electrical conductivity.
Example 2 in the Bauer '505 patent describes a copper alloy containing 10.4% by weight of zinc, 1.8% by weight of iron, 0.04% by weight of phosphorous, between 1.8% and 4.0% by weight of tin, the balance being copper. An embodiment of the tin brass alloy containing the composition of example 2 in the Brauer '505 patent is commercially available from Olin Corporation as C663. The C663 alloy is available from Olin Corporation with compositions containing from 1.4% to 2.4% by weight of iron, from 1.5% to 3.0% by weight of tin, from 84.5% to 87.5% by weight of copper, up to 0.35% by weight of phosphorous, and the balance being zinc.
Olin Corporation specifies that C663 possesses, depending on the temper, a yield strength of 100 ksi and a tensile strength between 95 ksi and 110 ksi for spring temper, a yield strength of 104 ksi and a tensile strength between 100 ksi and 114 ksi for extra spring temper, and a yield strength of 105 ksi (min) and a tensile strength of 105 ksi (min) for super spring temper. Olin Corporation also specifies that these alloys have an electrical conductivity of 25% ICAS, as annealed. However, these alloys are undesirable because of their high copper content resulting in a higher cost.
There exists a need for a cost effective alternative to existing copper alloys that will still possess high electrical conductivity, high tensile strength, and high yield strength.
SUMMARY OF THE INVENTION
Copper alloys have been discovered that provide higher tensile and yield strengths and a higher electrical conductivity than prior art copper alloys, but which reduce the amounts of copper in the alloy, and a process for making same. More particularly, copper alloys have been discovered having tensile strengths greater than 110 ksi and less than 130 ksi, yield strengths greater than 100 and less than 120 ksi and electrical conductivity greater than 25% ICAS and less than 35% ICAS, as annealed.
In one aspect, the present invention is directed to a copper alloy consisting essentially of 13% to 15% by weight of zinc, 0.7% to 0.9% by weight of tin, 0.7% to 0.9% by weight of iron, the balance being copper.
In another aspect, the present invention is directed to a process for making the copper alloy that employs only one annealing step at a temperature between 400° C. and 600° C. The process comprises the steps of:
casting a copper alloy consisting essentially of 13% to 15% by weight of zinc, 0.7% to 0.9% by weight of tin, 0.7% to 0.9% by weight of iron, the balance being copper;
hot rolling the cast copper alloy at a temperature between 800° C. and 950° C. to reduce its thickness to 80% to 95% of the original thickness of the copper alloy;
annealing the reduced copper alloy for a time period between about three and about eight hours at a temperature between about 450° C. and 575° C.;
roll reducing the annealed copper alloy to produce a second reduction of thickness of up to 70% in the copper alloy; and
relief annealing the twice reduced copper alloy for a time period between about three and about eight hours at a temperature between 200° C. and 280° C.
In an alternate embodiment, the process of making the copper alloy is carried out in the absence of a hot rolling step. The process comprises:
vertical upward casting a copper alloy consisting essentially of 13% to 15% by weight of zinc, 0.7% to 0.9% by weight of tin, 0.7% to 0.9% by weight of iron and the balance being copper;
rolling the vertical upward casting copper alloy to reduce its thickness at least around 60% of the original thickness of the copper alloy;
annealing the reduced copper alloy for a time period between three and eight hours at a temperature between about 450° C. and about 575° C;
cold rolling the annealed copper alloy to reduce its thickness up to 70%; and, thereafter, relief annealing the cold rolled copper alloy for a time period between about three and about eight hours at a temperature between about 200° C. to 280° C.
REFERENCES:
patent: 5429794 (1995-07-01), Kamf et al.
patent: 5853505 (1998-12-01), Brauer et al.
patent: 5893953 (1999-04-01), Bhargava
patent: 5916386 (1999-06-01), Bhargava
paten
Finney M. Parker
Kamf Anders Claes
Ip Sikyin
Morgan & Finnegan, L.L
Outokumpu Oyj
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