CROSS REFERENCE OF RELATED APPLICATIONS

The present application is a US national stage of a PCT international application, Serial no. PCT/KR2020/002654, filed on Feb. 25, 2020, which claims the priority of Korean patent application No. 10-2019-0090805, filed with KIPO of Republic of Korea on Jul. 26, 2019, the entire content of these applications are incorporated into the present application by reference herein.

TECHNICAL FIELD

The present disclosure relates to a method of producing a copper alloy sheet material having excellent strength, conductivity and bending formability, and a copper alloy sheet material produced therefrom.

BACKGROUND ART

Recently, components (electronic components) constituting electronic devices have been gradually downsized and refined. Accordingly, characteristics required for a sheet material used for the components are diversified. Characteristics required for a connector among the electronic components are strength, conductivity, bending formability, etc. Copper is mainly used as a material that satisfies these characteristics. However, pure copper has low strength. Thus, various types of copper alloys containing one or greater elements to increase the strength are advantageously used.

Hardening methods commonly used to increase strength of alloys including the copper alloy include solid solution hardening, work hardening, and precipitation hardening, etc. The solid solution hardening allows an alloy element to be formed solid solution in a matrix to lower purity of a matrix to rapidly decrease conductivity. The work hardening tends to increase density of dislocations in the matrix to decrease the conductivity. The precipitation hardening may increase the purity of the matrix via the nucleation and growth mechanism of precipitates and at the same time effectively contribute to hardening. As a typical precipitation hardened copper alloy, a copper (Cu)-nickel (Ni)-silicon (Si)-based (so-called, Corson-based) alloy has excellent bending formability and thus is often used for a component with high workability such as a connector.

However, in recent years, as the electronic component has been further miniaturized, thinning of the copper alloy sheet material has been demanded. In order to overcome increase in electrical resistance and decrease in load carrying capacity due to the thinning, it is necessary to improve strength and conductivity. Further, in order to improve the strength, an amount of nickel (Ni) should be increased. However, when the nickel addition amount exceeds 2.6% by weight, it is difficult to avoid formation of coarse particles having a precipitate size exceeding 3 μm. Since the coarse particles act as a crack initiator during bending and deteriorate the bending formability, it is difficult to achieve both of the required properties of the strength and the bending formability at the same time in the existing Colson-based alloy.

Conventionally, in order to solve this problem, a method is proposed in which cobalt (Co) or chromium (Cr) is added alone or in combination to the Colson-based alloy, and then, solid solution heat treatment is executed, and, then, one or two times additional heat treatments are carried out, and then a last cold rolling is performed, thereby improving strength and conductivity of the alloy.

Specifically, Japanese Patent No. 6385383 intends to improve properties by adding nickel (Ni), silicon (Si), cobalt (Co), and chromium (Cr) in a copper alloy sheet material. However, this approach may not simultaneously achieve conductivity of 55.0% IACS or higher, and strength of 720 MPa or higher as 0.2% proof stress.

Further, Japanese Patent No. 5647703 discloses that a total content of nickel (Ni) and cobalt (Co) exceeded 3.0% by mass, and the 0.2% proof stress exhibits excellent strength of 980 MPa or greater. However, formation of coarse particles having a size exceeding 3 μm is not completely suppressed, and thus the bending formability is deteriorated. Further, there is a limit that conductivity of an obtained copper alloy sheet material could not reach 45% IACS.

Further, in the above documents, a process mechanism for facilitating cobalt (Co) precipitation during the production process has not been clearly identified. Further, after performing long-term or multiple precipitation heat treatments, finish rolling is performed. Thus, solid solubility of the alloy element in the copper matrix is rapidly reduced, and thus there is a limit in achieving both of high strength and excellent conductivity at the same time in the finish rolling.

DISCLOSURE

Technical Problem

A purpose of the present disclosure is to provide a method of producing a copper (Cu)-nickel (Ni)-cobalt (Co)-silicon (Si)-chromium (Cr) alloy sheet material having excellent strength and conductivity using thermal-mechanical two-stages precipitation, and to provide a copper alloy sheet material produced therefrom.

Technical Solutions

According to the present disclosure, there is proposed a method of producing a copper alloy sheet material, wherein the copper alloy sheet material contains: nickel (Ni) 0.5 to 1.5% by weight; cobalt (Co) 0.3 to 1.5% by weight; silicon (Si) 0.35 to 0.8% by weight; chromium (Cr) 0.05 to 0.5% by weight; a balance amount of copper (Cu); and inevitable impurities, wherein the method comprises: melting and casting the component elements (Ni, Co, Si, Cr, and Cu) to form an ingot; hot-rolling the ingot at 950 to 1040° C.; cooling the hot-rolled product; cold-rolling the cooled product at a cold reduction rate of 70% or higher to form a copper alloy sheet material; performing solid solution heat treatment of the sheet material at 800 to 1040° C. for 20 to 60 seconds; and performing thermal-mechanical double aging of the solid solution heat treated sheet material, wherein the thermal-mechanical double aging includes: performing first precipitation of the solid solution heat treated sheet material at 550 to 700° C. for 20 to 60 seconds; cold-rolling the first precipitated sheet material at a cold reduction rate of 10 to 50%; and performing second precipitation of the cold rolled sheet material at 300 to 550° C. for 1 to 24 hours.

A sum of contents of nickel (Ni) and cobalt (Co) meets a following relationship: 1.5≤Ni+Co≤2.6, and a ratio between contents of nickel (Ni) and cobalt (Co) satisfies a following relationship: 0.8≤Ni/Co≤1.3.

Contents of nickel (Ni), cobalt (Co), silicon (Si) and chromium (Cr) satisfies a following relationship: 3.5≤(Ni+Co)/(Si−Cr/3)≤4.5.

The copper alloy sheet material further contains at least one selected from a group consisting of manganese (Mn) 0.01 to 0.2% by weight, phosphorus (P) 0.01 to 0.2% by weight, magnesium (Mg) 0.01 to 0.2% by weight, tin (Sn) 0.01 to 0.2% by weight, zinc (Zn) 0.01 to 0.5% by weight, and zirconium (Zr) 0.01 to 0.1% by weight.

According to the present disclosure, there is proposed a copper alloy sheet material produced using the method defined above, wherein the copper alloy sheet material has a microstructure containing an α mother phase and intermetallic compound precipitates, wherein the intermetallic compound precipitates has an average diameter of 3 μm or smaller.

0.2% proof stress of the copper alloy sheet material measured in a direction parallel to a rolling direction thereof is in a range of 720 MPa to 820 MPa, wherein conductivity of the copper alloy sheet material is in a range of 55% IACS to 60% IACS, wherein a 90° bending formability in a direction parallel to a rolling direction and a direction perpendicular to a rolling direction of the copper alloy sheet material is R/t=0.

Advantageous Effects

The production method of the copper alloy sheet material proposed from the present disclosure may produce the copper alloy sheet material having excellent strength and conductivity and excellent bending formability.

