Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Reexamination Certificate
2001-12-13
2004-10-05
Zimmerman, John J. (Department: 1775)
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
C148S432000, C148S679000, C148S684000, C148S685000
Reexamination Certificate
active
06800151
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of modifying strength- and conductivity-related properties of high-strength, high-conductivity Cu—Ag alloy plate, and method of producing high-strength, high-conductivity Cu—Ag alloy plate.
BACKGROUND ART
Development of high-strength, high-conductivity materials has been urged for, e.g., IC lead frames and conductive materials of magnet for superstrong magnetic field. These electroconductive materials are required to have various properties, e.g., sufficient strength even under a high electromagnetic force produced by the magnetic field of high strength in which it is placed, and generate less heat due to the resistance even in the presence of large current. As the electric/electronic industries advances recently, these trends become prominent.
A Cu—Ag alloy is commonly used as an electroconductive material. However, it is difficult for the conventional Cu—Ag alloy to have sufficiently high strength and conductivity simultaneously, because ensuring of the conductivity and ensuring of the strength are not compatible with each other: increasing Ag content to improve strength decreases conductivity, and increasing Cu content to secure sufficient conductivity decreases strength. Therefore, the conventional alloy must keep Ag content at a very low level of about 0.3 to 0.5% by atom to secure conductivity, resulting in sacrifice of the strength.
Among Cu—Ag alloy materials recently developed in this context, a high-strength, high-conductivity Cu—Ag alloy is produced by a method disclosed in Japanese Patent No. 2,104,108. The Cu—Ag alloy is produced through subjecting the alloy ingot containing Ag at 4 to 32% by atom, and Cu as the balance to casting, rapidly quenching, cold rolling, and annealing at 300 to 500° C. for 0.5 to 5 hours in a vacuum or inert atmosphere, then repeating the cold rolling and annealing steps at least twice. Since the Cu—Ag alloy has a crystal structure with the Cu/Ag eutectic crystal phase distributed uniformly and finely, and with the primary Cu and eutectic crystal phases stretched in filament, and it has an advantage of very high strength while keeping high conductivity. It is assumed to be a promising material for the above purposes. This method employing cold rolling as the cold treatment step has been used to produce the high-strength, high-conductivity Cu—Ag alloy plate.
The above-described high-strength, high-conductivity Cu—Ag alloy material is provided with the properties of high strength and conductivity by undergoing cold rolling and annealing twice or more for each treatment. It is normally treated further by finish rolling to have a desired thickness in the last stage before it becomes the final commercial product.
Its properties of conductivity and strength depend on processing history. More specifically, its properties, depends on reduction ratio at each of the cold rolling steps effected twice or more before finish rolling and reduction ratio at the finish rolling step. Therefore, its properties are defined uniquely processing history. Usually, requirement of the properties for the commercial product varies to some extent, depending on its purposes; strength taking precedence over conductivity for a product, and conductivity taking precedence over strength for another product. It is therefore necessary, when two or more types of products having different property requirements are to be produced, to treat the work at different reduction ratio for each product type.
Changing reduction ratio for different property requirements depending on production requirement is not desirable viewed from production efficiency. Since the material is produced by undergoing a relatively large number of production steps, such as undergoing annealing and cold rolling twice or more for each, variation of reduction ratio for each product provides large influence on the production efficiency. Moreover, the special materials, like the high-strength, high-conductivity Cu—Ag alloy plate of the present invention, are not necessarily produced massively. When a manufacturer runs the production in low production efficiency because of requirement of diversified product types produced in a small quantity, the manufacturer inevitably increases the product prices.
The present invention is developed, in the context described above. It is an object of the present invention to provide a method of modifying properties for the high-strength, high-conductivity Cu—Ag alloy plate produced by the above-described steps, which allows to produce the product with two or more required properties at any reduction ratio, i.e., without changing processing history or reduction ratio for each property requirement. It is another object of the present invention to provide a method of producing high-strength, high-conductivity Cu—Ag alloy plate, based on the same method of modifying properties.
DISCLOSURE OF THE INVENTION
The inventor of the present invention found, after having extensively studied to solve the above problems, that annealing of the finish-rolled plate changes its properties with respect to conductivity and strength. The inventor further found that the changed properties as a result of annealing show a certain tendency that increasing annealing temperature decreases strength and increases conductivity, irrespective of reduction ratio. The inventor investigated the trends of the properties changed by the annealing for the plates prepared at varying reduction ratios, and considered that the desired product could be produced by annealing the plate produced at a certain reduction ratio at varying temperature levels to modify its properties, reaching the present invention.
The present invention provides a method of modifying conductivity- or strength-related properties of a Cu—Ag alloy plate, prepared by the steps of:
(a) casting and rapidly quenching an alloy ingot composed of 4 to 32% by atom of Ag and Cu accounting for the balance,
(b) cold rolling, then annealing the ingot at 300 to 500° C. for 0.5 to 5 hours under a vacuum, or in an inert gas, reducing gas or mixture of inert and reducing gas atmosphere,
(c) repeating the above step (b) once or more, and
(d) cold rolling as the finish rolling to provide a desired thickness of the plate,
wherein the plate rolled at any reduction ratio in the steps (b) to (d) is heated at different temperature levels, and strength and conductivity of the plate after the annealing are measured for each annealing temperature so as to establish the conductivity-annealing temperature curve and strength-annealing temperature curve as the correlations between annealing temperature and strength and between annealing temperature and conductivity, then, an optimum annealing temperature required to provide a desired conductivity or strength is determined by extrapolating the above-described conductivity-annealing temperature curve or strength-annealing temperature curve at the desired conductivity or strength, and the plate prepared at any reduction ratio is annealed at the optimum annealing temperature.
The method of the present invention for modifying the properties of the Cu—Ag alloy plate is described more specifically. FIGS.
1
(
a
) and
1
(
b
) show the properties of the high-strength, high-conductivity Cu—Ag alloy plate, prepared at a certain reduction ratio and annealing temperature, changing with annealing temperature; FIG.
1
(
a
) for conductivity and FIG.
1
(
b
) for strength, both of the annealed alloy plate. Strictly speaking, shape of each curve is considered to vary with the treatment history the plate has undergone. However, there is a general trend that increasing annealing temperature decreases strength and increases conductivity, as shown in FIG.
1
.
The method of the present invention allows to find the optimum annealing temperature by obtaining the conductivity-annealing temperature curve or strength-annealing temperature curve for the plate prepared at any reduction ratio, and on the basis of the both curves, extrapolating the both curves at a desired conductivity or strength o
Rothwell Figg Ernst & Manbeck P.C.
Tanaka Kikinzoku Kogyo K.K.
Zimmerman John J.
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