EP2695956B1

EP2695956B1 - Copper alloy sheet

Info

Publication number: EP2695956B1
Application number: EP13005147.7A
Authority: EP
Inventors: Yasuhiro Aruga; Daisuke Hashimoto; Koya Nomura
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2007-08-07
Filing date: 2008-07-24
Publication date: 2018-12-19
Anticipated expiration: 2028-07-24
Also published as: EP2184371A1; KR101227315B1; EP2695956A2; KR20100031138A; EP2695957B1; EP2184371A4; EP2695957A2; WO2009019990A1; EP2695957A3; CN101743333A; US20110223056A1; EP2695958B1; EP2184371B1; EP2695958A3; EP2695956A3; EP2695958A2

Description

The present invention relates to a cold rolled copper alloy sheet. More specifically, the present invention relates to a copper alloy sheet having properties suitable for a connection component such as automotive terminal or connector.
A connection component such as automotive terminal or connector recently requires a performance enough to ensure reliability in a high-temperature environment such as engine room. One of most important properties for the reliability in a high-temperature environment is a contact-fitting force maintaining characteristic, that is, a stress relaxation resistance characteristic.
Fig. 2 shows a structure of a box-type connector (female terminal 3) representative of a connection component such as automotive terminal or connector. Fig. 2(a) is an elevational view and Fig. 2(b) is a cross-sectional view. In Fig. 2, the female terminal 3 has a pressing strip 5 cantilever-supported in an upper holder part 4 and when a male terminal (tab) 6 is inserted into the holder, the pressing strip 5 is elastically deformed and the male terminal (tab) 6 is fixed by the reaction force. Incidentally, in Fig. 2, 7 is a wire connecting part and 8 is an anchoring tongue strip.
As shown in Fig. 2, in the case where a stationary displacement is given to a spring-shaped component composed of a copper alloy sheet and a male terminal (tab) 6 is fitted at a spring-shaped contact part (pressing strip) 5, if the connector is kept standing in a high-temperature environment such as engine room, the contact-fitting force is lost with the lapse of time. Accordingly, the stress relaxation resistance characteristic is such a resistance characteristic against high temperatures as not allowing great reduction in the contact-fitting force of the spring-shaped component composed of a copper alloy sheet even when the connection component is kept standing in a high-temperature environment.
In the SAEJ (the Society of Automotive Engineers of Japan) Standards JASO-C400, as regards the stress relaxation resistance characteristic, the stress relaxation ratio after holding under the conditions of 150°C × 1,000 hr is specified to be 15% or less. Figs. 1(a) and (b) each shows a tester for the stress relaxation resistance characteristic according to this standard. Using this tester, a test specimen 1 cut out into a strip shape is fixed at one end to a rigid test board 2, warped by lifting another end in a cantilever manner (d: warpage size), kept standing at a predetermined temperature for a predetermined time, and then unloaded at room temperature, and the warpage size after unloading (permanent distortion) is determined as δ. Here, the stress relaxation ratio (RS) is represented by RS = (δ/d) × 100.
However, the stress relaxation ratio of a copper alloy sheet has anisotropy and takes a different value according to the direction in which the longitudinal direction of the test specimen runs with respect to the rolling direction of the copper alloy sheet. In this respect, the connection component such as automotive terminal or connector must have a stress relaxation ratio of 15% or less in the direction used as a spring, that is, in either one direction parallel or orthogonal to the rolling direction of the sheet.
As for the copper alloy excellent in the stress relaxation resistance characteristic, a Cu-Ni-Si-based alloy, a Cu-Ti-based alloy, a Cu-Be-based alloy and the like have been heretofore widely known, but in recent years, a Cu-Ni-Sn-P-based alloy having a relatively small additive element content has been used. This Cu-Ni-Sn-P-based alloy allows for ingot making in a shaft furnace which is a large-scale melting furnace with the opening being widely opened to the atmosphere, and because of its high productivity, a great cost down can be achieved.
Also, various techniques for enhancing the stress relaxation resistance characteristic of the Cu-Ni-Sn-P-based alloy itself have been conventionally proposed. For example, Patent Documents 1 and 2 disclose a technique of uniformly and finely dispersing an Ni-P intermetallic compound in a Cu-Ni-Sn-P-based alloy matrix to enhance the electrical conductivity and at the same time, enhance the stress relaxation resistance characteristic and the like, and Patent Documents 2 and 3 disclose a technique of decreasing the P content of a Cu-Ni-Sn-P-based alloy to obtain a solid solution-type copper alloy reduced in the precipitation of an Ni-P compound. Furthermore, Patent Documents 4 and 5 disclose a technique of specifying the substantial temperature and holding time in finish annealing at the production of a Cu-Ni-Sn-P-based alloy sheet to enhance the electrical conductivity and at the same time, enhance the stress relaxation resistance characteristic and the like.

Patent Document 1: Japanese Patent No. 2,844,120
Patent Document 2: Japanese Patent No. 3,871,064
Patent Document 3: JP-A-11-293367 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")
Patent Document 4: JP-A-2002-294368
Patent Document 5: JP-A-2006-213999

Further, JP 2006-083465 A discloses a copper alloy sheet which contains, by mass%, 0.01 to 3.0% Fe and 0.01 to 0.3% P having a texture that the orientation distribution density of Brass orientation is 20 or less, and a sum of the orientation distribution density of the Brass orientation, S orientation and Copper orientation is 10 to 50%, measured by X-ray diffraction method.
However, mechanical properties of these conventional Cu-Ni-Sn-P-based alloys enhanced in the stress relaxation resistance characteristic are such that, for example, when the 0.2%-proof stress is about 500 MPa, the elongation is only less than 10%, and the elongation is low for the strength. Also, as for the terminal/connector properties, while a stress relaxation ratio of 15% or less is achieved in the direction parallel to the rolling direction, the electrical conductivity is as low as less than 35% IACS.
Heretofore, however, press forming such as bending of a Cu-Ni-Sn-P-based alloy sheet which becomes a raw material of the connection component such as automotive terminal or connector is mostly performed under working conditions in a relatively low-speed deformation region where the sheet is less subject to a large strain rate. As a result, even when elongation of the conventional Cu-Ni-Sn-P-based alloy is low as described above, generation of various shaping defects such as cracking can be suppressed by virtue of, for example, mild or devised working conditions and there are not caused many troubles in the working into a terminal or a connector.
Meanwhile, the stress relaxation ratio of a rolled copper alloy sheet (obtained by rolling) has anisotropy and takes a different value according to the direction in which the longitudinal direction of the female terminal 3 in Fig. 2 runs with respect to the rolling direction of the raw material copper alloy sheet. The same applies to the measurement of the stress relaxation ratio, and the measured stress relaxation ratio takes a different value according to the direction in which the longitudinal direction of a test specimen runs with respect to the rolling direction of the raw material copper alloy sheet. Accordingly, the stress relaxation ratio is liable to be low in the orthogonal direction than in the parallel direction with respect to the rolling direction of the copper alloy sheet.
In this respect, at the time of press working a raw material copper alloy sheet to produce a female terminal 3 in Fig. 2, blanking is sometimes performed such that the longitudinal direction of the female terminal 3 (the longitudinal direction of the pressing strip 5) runs in the direction orthogonal to the rolling direction. A high stress relaxation resistance characteristic is usually required for the bending (elastic deformation) in the length direction of the pressing strip 5. Accordingly, when blanking is performed to allow for running in the direction orthogonal to the rolling direction, it is required to have a high stress relaxation resistance characteristic not in the parallel direction but in the orthogonal direction with respect to the rolling direction of the copper alloy sheet.
In this respect, when the stress relaxation ratio is high in the direction orthogonal to the rolling direction as well as in the direction parallel to the rolling direction, even when the blanking is performed in either one direction of parallel direction and orthogonal direction with respect to the rolling direction, the stress relaxation resistance characteristic as a terminal or connector can be satisfied irrespective of the blanking direction of the raw material copper alloy sheet.
On the other hand, the conventional Cu-Ni-Sn-P-based copper alloy enhanced in the stress relaxation resistance characteristic is not excellent in bendability or press punchability. The working of a copper alloy sheet into a terminal or connector sometimes involves a severe bending work such as contact bending or 90° bending after notching or a stamping work such as press punching of the sheet, and bendability high enough to withstand such a working or excellent press punchability is becoming required.
However, like conventional Cu-Ni-Sn-P-based alloy enhanced in the stress relaxation resistance characteristic, when the strength is increased, for example, to a 0.2%-proof stress of 500 MPa or more by adding a solid solution strengthening element or increasing the working ratio of cold rolling, deterioration of bendability is inevitably incurred and it is quite difficult to satisfy both of required strength and bendability.
In the field of Cu-Fe-P-based copper alloy sheet, many proposals have been made to enhance the press punchability or bendability by taking note of the sheet texture (see, JP-A-2000-328158 , JP-A-2002-339028 , JP-A-2000-328157 and JP-A-2006-63431 ). In these techniques, the press punchability is enhanced mainly by controlling the accumulation degree of crystal orientation of the copper alloy sheet.
However, in a Cu-Ni-Sn-P-based copper alloy sheet greatly differing in the alloy system or properties from the Cu-Fe-P system, there have not heretofore been made many proposals on this technique of enhancing the press punchability. The reason therefor is presumed because necessity for or usage requiring enhancement of press punchability of the Cu-Ni-Sn-P-based copper alloy sheet has not conventionally been so pressing.
In view of these points, an object of the present invention is to provide a Cu-Ni-Sn-P-based copper alloy sheet satisfying, as a terminal or connector, the requisite properties such as stress relaxation resistance characteristic and bendability.
In order to achieve the object of the present invention, the gist of the copper alloy sheet excellent in the stress relaxation resistance characteristic and bendability (hereinafter sometimes referred to as an embodiment of the present invention) is a cold rolled copper alloy sheet with a 0.2%-proof stress of 500 MPa or more consisting of, in terms of mass%, 0.3 to 3.0% of Ni, 0.01 to 3.0% of Sn and 0.01 to 0.3% of P, and optionally at least one member selected from the group consisting of, in terms of mass%, 0.3% or less of Fe, 0.05% or less of Zn, 0.1% or less of Mn, 0.1% or less of Si and 0.3% or less of Mg, optionally at least one member selected from the group consisting of Ca, Zr, Ag, Cr, Cd, Be, Ti, Co, Au and Pt, in a total amount of 1.0 mass% or less, and optionally at least one member selected from the group consisting of Hf, Th, Li, Na, K, Sr, Pd, W, S, C, Nb, Al, V, Y, Mo, Pb, In, Ga, Ge, As, Sb, Bi, Te, B and Misch metal, in a total amount of 0.1 mass% or less, with the balance being copper, wherein the copper alloy sheet has a texture in which a distribution density of Brass orientation is 40% or less and a sum of distribution densities of Brass orientation, S orientation and Copper orientation is 30 to 90%, measured by a crystal orientation analysis method using an electron backscatter diffraction pattern (EBSP) through a field emission scanning electron microscope (FESEM), and wherein the copper alloy sheet has, as terminal/connector properties, an electrical conductivity of 30% IACS or more.
In the case of a normal copper alloy sheet, mainly the following Cube orientation, Goss orientation, Brass orientation (hereinafter sometimes referred to as B orientation), Copper orientation (hereinafter sometimes referred to as Cu orientation), S orientation and the like form a texture, and crystal planes corresponding to these orientations are present.

The formation of this texture differs according to the working or heat-treatment method even in the same crystal system. The texture of a sheet material obtained by rolling is indicated by the rolling plane and rolling direction. The rolling plane is expressed by {ABC}, and the rolling direction is expressed by <DEF>. Based on these expressions, each orientation is expressed as follows.

Cube orientation	{001}<100>
Goss orientation	{011}<100>
Rotated-Goss orientation	{011}<011>
Brass orientation (B orientation)	{011}<211>
Copper orientation (Cu orientation)	{112}<111>
	(or D orientation {4 4 11}<11 11 8>)
S orientation	{123}<634>
B/G orientation	{011}<511>
B/S orientation	{168}<211>
P orientation	{011}<111>

As described above, the texture of a normal copper alloy sheet is composed of a fairly large number of orientation factors and when the constituent ratio of these factors is varied, the plastic anisotropy of the sheet material changes. In the case of a Cu-Ni-Sn-P-based copper alloy sheet, the properties such as stress relaxation resistance characteristic and bendability are greatly changed.
According to the knowledge of the present inventors, for enhancing the bendability of a Cu-Ni-Sn-P-based copper alloy sheet while maintaining the high strength, the distribution density of Brass orientation (B orientation) needs to be reduced. In addition, for achieving a good balance between high density and bendability, the sum of distribution densities of B orientation, S orientation and Cu orientation also needs to be controlled to a specific range.
Although the alloy system differs, there is conventionally a case, for example, where, in a Cu-Fe-P-based copper alloy sheet, the orientation density of Cube orientation [hereinafter sometimes referred to as D(Cube)] is controlled to an appropriate range with an attempt to enhance and stabilize the bendability. However, according to the knowledge of the present inventors, such control of the Cube orientation cannot enhance the bendability particularly of a high-strength Cu-Ni-Sn-P-based copper alloy sheet with a 0.2%-proof stress of 500 MPa or more, which is enhanced in the stress relaxation resistance characteristic.
In a high-strength Cu-Ni-Sn-P-based copper alloy sheet with a 0.2%-proof stress of 500 MPa or more, out of the texture above, particularly the distribution density of B orientation and further the distribution densities of B orientation, S orientation and Cu orientation have great effect on the strength. As the distribution densities of B orientation, S orientation and Cu orientation are larger, the rolled texture is developed and the strength is higher.
However, on the other hand, as the distribution density of B orientation is larger or the sum of distribution densities of B orientation, S orientation and Cu orientation is larger, conversely, the stress relaxation resistance characteristic or bendability decreases. In contrast, as the distribution density of B orientation is smaller or the sum of distribution densities of B orientation, S orientation and Cu orientation is smaller, the crystal orientations become random and the stress relaxation resistance characteristic or bendability is enhanced.
That is, in a high-strength Cu-Ni-Sn-P-based copper alloy sheet with a 0.2%-proof stress of 500 MPa or more, for enhancing the stress relaxation resistance characteristic and bendability while maintaining the high strength, it is effective to reduce the distribution density of B orientation and simultaneously control the sum of distribution densities of B orientation, S orientation and Cu orientation to a specific range.

Fig. 1 shows cross-sectional views for explaining the stress relaxation resistance test of a copper alloy sheet.
Fig. 2 shows cross-sectional views showing the structure of a box-type connector.

Description of Reference Numerals and Signs

1: test specimen
2: test board
3: box-type connector (female terminal)
4: upper holder part
5: pressing strip
6: male terminal
7: wire connecting part
8: anchoring tongue strip

The present invention is described in detail below. In the context of the present invention, all percentages defined by the mass are the same as those defined by the weight, respectively.

(Measurement of Orientation Distribution Density)

In the embodiment of the present invention, the distribution density of B orientation and the sum of distribution densities of B orientation, S orientation and Cu orientation are measured by a crystal orientation analysis method using an electron backscatter diffraction pattern EBSP through a field emission scanning electron microscope FESEM.
In specifying the orientation density of each of these orientations, the orientation density is measured by a crystal orientation analysis method using EBSP, because for enhancing the stress relaxation resistance characteristic or bendability while maintaining high strength, this is affected by the texture (aggregate texture) in a more microscopic region of the sheet (sheet surface). In the crystal orientation analysis method using EBSP, the texture in a microscopic region can be quantified.
On the other hand, in the X-ray diffraction (e.g., X-ray diffraction intensity) generally employed for specifying or measuring the texture, a texture (aggregate texture) in a relatively macroscopic region is measured as compared with the crystal orientation analysis method using EBSP. Accordingly, the texture (aggregate texture) in a microscopic region cannot be measured accurately.
In the crystal orientation analysis method using an electron backscatter diffraction pattern EBSP, the crystal orientation is analyzed based on the electron backscatter diffraction pattern (Kikuchi pattern) generated when an electron beam is obliquely applied to the sample surface. This method is also known as a high-resolution crystal orientation analysis (FESEM/EBSP) method for the analysis of crystal orientation of a diamond thin film, a copper alloy or the like. A case of performing the crystal orientation analysis of a copper alloy by this method similarly to the embodiment of the present invention is disclosed, for example, in JP-A-2005-29857 and 2005-139501 .
As for the procedure of analysis by this crystal orientation analysis method, first, a measurement region of a material to be measured is usually partitioned into hexagonal regions or the like, and the partitioned regions each is determined for a Kikuchi pattern from the reflected electron of an electron beam injected into the sample surface. At this time, an electron beam is two-dimensionally scanned on the sample surface and the crystal orientation is measured at predetermined pitch intervals, whereby the orientation distribution in the sample surface can be measured.
Next, the obtained Kikuchi pattern is analyzed to determine the crystal orientation at the electron beam incident position. That is, the obtained Kikuchi pattern is compared with a known crystal structure data, and the crystal orientation at the measurement point is determined. The crystal orientation at a measurement point adjacent to the measurement point above is determined in the same manner, and those where the orientation difference between crystals adjacent to each other is within ± 15° (slippage within ± 10° from the crystal plane) are taken (regarded) as belonging to the same crystal plane.
More specifically, a test specimen for the observation of texture is sampled from the produced copper alloy sheet and after mechanical polishing and buff polishing, the surface is regulated by electrolytic polishing. With respect to the thus-obtained test specimen, whether or not the orientation of each grain is the objective orientation (within 10° from the ideal orientation) is judged using, for example, FESEM manufactured by JEOL Ltd. and the EBSP measurement/analysis system OIM (Orientation Imaging Macrograph) manufactured by TSL and using an analysis software (software name: "OIM Analysis") for the system, and the orientation density in the measured view is determined.
The range of measured view is a fine (microscopic) region of about 500 µm × 500 µm and is an extremely fine region as compared with the measuring range of X-ray diffraction. Accordingly, the orientation density of the texture in a more microscopic region of the sheet, which affects the stress relaxation resistance characteristic or bendability, can be measured in greater detail with higher precision as described above than in the measurement of orientation density by the X-ray diffraction.
Incidentally, since the orientation distribution is changed in the sheet thickness direction, it is preferred to measure the orientation distribution density at arbitrary several points in the sheet thickness direction and average the values obtained. However, the connection component such as automotive terminal or connector is a thin sheet having a thickness of about 0.1 to 0.3 mm and therefore, the value measured with the sheet thickness may be directly evaluated.

(Significance of Orientation Distribution Density)

In the embodiment of the present invention, for enhancing the stress relaxation resistance characteristic or bendability while maintaining high strength in a high-strength Cu-Ni-Sn-P-based copper alloy sheet with a 0.2%-proof stress of 500 MPa or more, as described above, the distribution density of B orientation is reduced and at the same time, the sum of distribution densities of B orientation, S orientation and Cu orientation is controlled to a specific range.
Accordingly, in the embodiment of the present invention, the texture of the copper alloy sheet is specified such that the distribution density of B orientation is 40% or less and the sum of distribution densities of B orientation, S orientation and Cu orientation is 30 to 90%.
If the distribution density of B orientation exceeds 40% or the sum of distribution densities of B orientation, S orientation and Cu orientation exceeds 90%, as described in Examples later, the bendability cannot be enhanced with the above-described high strength.
On the other hand, in order to set the sum of distribution densities of B orientation, S orientation and Cu orientation to be less than 30%, this requires reducing the work-hardened amount in the cold rolling. Accordingly, if the sum of distribution densities of B orientation, S orientation and Cu orientation is less than 30%, as described in Examples later, the bendability may be enhanced but high strength cannot be achieved and the strength required in usage as a terminal or connector becomes insufficient.
As regards the Cu-Ni-Sn-P-based copper alloy sheet, in a normal sheet made to have high strength by increasing the work-hardened amount in the heavy working of cold rolling, excessive development of the rolled texture inevitably results and therefore, the distribution density of B orientation is necessarily liable to become large and exceed 40%. Incidentally, this development of the rolled texture also affects other orientation densities such as Cube orientation. However, particularly, in the region of a high-strength Cu-Ni-Sn-P-based copper alloy sheet with a 0.2%-proof stress of 500 MPa or more, the effect of development of Cu orientation, B orientation and S orientation on the bendability is by far higher than the effect of other orientations such as Cube orientation.

(Copper Alloy Component Composition)

The component composition of the copper alloy according to the embodiment of the present invention is described below. In the embodiment of the present invention, as a premise, the component composition of the copper alloy is, as described above, a Cu-Ni-Sn-P-based alloy allowing for ingot making in a shaft furnace and because of its high productivity, enabling a great cost down.
In order to obtain a copper alloy that is responsive to the high-efficiency highspeed press forming process for producing a connection component such as automotive terminal or connector and satisfies the properties required for a connection component such as automotive terminal or connector and also that is excellent in the strength, stress relaxation resistance characteristic, electrical conductivity and bendability, the copper alloy fundamentally comprises 0.3 to 3.0% of Ni, 0.01 to 3.0% of Sn, and 0.01 to 0.3% of P, with the balance being copper and inevitable impurities. The % indicative of the content of each element means mass%. The alloy elements of the copper alloy are described below by referring to the reasons of addition or restraint.

(Ni)

Ni is an element necessary for enhancing the strength or stress relaxation resistance characteristic by being present as a solid solution in the copper alloy matrix or forming a fine precipitate or compound with other alloy elements such as P. An Ni content of less than 0.1% causes, even by an optimal production method, shortage in the absolute amount of a fine Ni compound of 0.1 µm or less or of Ni contained as a solid solution. Accordingly, a content of 0.1% or more is necessary for effectively bringing out those effects of Ni.
However, if Ni is excessively contained to exceed 3.0%, a compound such as oxide, crystallized product or precipitate of Ni is coarsened or a coarse Ni compound increases, as a result, the amount of a fine Ni compound or the amount of Ni contained as a solid solution rather decreases. The coarsened Ni compound becomes a starting point of fracture and leads to reduction in the strength or bendability. Accordingly, the Ni content is specified to be 0.3 to 3.0%, preferably 0.3 to 2.0%.

(Sn)

Sn is contained as a solid solution in the copper alloy matrix and thereby enhances the strength. Also, Sn contained as a solid solution suppresses the softening due to recrystallization during annealing. If the Sn content is less than 0.01%, the amount of Sn is too small and the strength cannot be enhanced, whereas if the Sn content exceeds 3.0%, not only the electrical conductivity is significantly decreased but also Sn contained as a solid solution is segregated in the grain boundary to reduce the strength or bendability. Accordingly, the Sn content is specified to be 0.01 to 3.0%, preferably 0.1 to 2.0%.

(P)

P is an element necessary for enhancing the strength or stress relaxation resistance characteristic by forming a fine precipitate with Ni. Also, P acts as a deoxidizing agent. A content of less than 0.01% causes shortage in the P-based fine precipitate particle and therefore, a content of 0.01% or more is necessary. However, if this element is excessively contained to exceed 0.3%, an Ni-P intermetallic compound precipitated particle is coarsened, which leads to reduction not only in the strength or stress relaxation resistance characteristic but also in the hot workability. Accordingly, the P content is specified to be 0.01 to 0.3%, preferably 0.02 to 0.2%.

(Fe, Zn, Mn, Si and Mg)

Fe, Zn, Mn, Si and Mg are impurities that readily intermix from a molten raw material such as scrap. These elements each produces an effect when contained but generally decreases the electrical conductivity. Also, if the content is increased, ingot making in a shaft furnace becomes difficult. Accordingly, in the case of obtaining a high electrical conductivity, the contents are specified to be 0.3% or less of Fe, 0.05% or less of Zn, 0.1% or less of Mn, 0.1% or less of Si and 0.3% or less of Mg. In other words, the contents lower than these upper limits are allowable in the embodiment of the present invention.
Fe elevates the recrystallization temperature of the copper alloy, similarly to Sn. However, if its content exceeds 0.5%, the electrical conductivity decreases. The content is 0.3% or less.
Zn prevents separation of tin plating. However, if its content exceeds 1%, the electrical conductivity decreases and a high electrical conductivity cannot be obtained. Also, in the case of ingot making in a shaft furnace, the content is 0.05% or less. In the temperature region (from about 150 to 180°C) where the alloy sheet is used as an automotive terminal, the effect of preventing separation of tin plating can be obtained even with a content of 0.05% or less.
Mn and Si have an effect as a deoxidizing agent. However, if the content thereof exceeds 0.1%, the electrical conductivity decreases and a high electrical conductivity cannot be obtained. In the case of ingot making in a shaft furnace, the contents are preferably 0.001% or less of Mn and 0.002% or less of Si.
Mg has an activity of enhancing the stress relaxation resistance characteristic. However, if its content exceeds 0.3%, the electrical conductivity decreases and a high electrical conductivity cannot be obtained. In the case of ingot making in a shaft furnace, the content is preferably 0.001% or less.

(Ca, Zr, Ag, Cr, Cd, Be, Ti, Co, Au and Pt)

The copper alloy according to the embodiment of the present invention is allowed to further contain at least one member selected from the group consisting of Ca, Zr, Ag, Cr, Cd, Be, Ti, Co, Au and Pt in an amount of 1.0% or less as a total amount of these elements. These elements have an activity of preventing coarsening of the grain but, if the amount of these elements exceeds 1.0% in total, the electrical conductivity decreases and a high electrical conductivity cannot be obtained. Also, ingot making in a shaft furnace becomes difficult.
In addition, Hf, Th, Li, Na, K, Sr, Pd, W, S, C, Nb, Al, V, Y, Mo, Pb, In, Ga, Ge, As, Sb, Bi, Te, B and Misch metal are also impurities, and the amount of these elements is limited to 0.1% or less in total.

(Production Method of Copper Alloy Sheet)

The production method of the copper alloy sheet according to the embodiment of the present invention is described below. In producing the copper alloy sheet according to the embodiment of the present invention, the production method itself may be an ordinary method except for the conditions in the finish annealing step. That is, a molten copper alloy after adjusting the component composition is subjected to casting, ingot scalping, soaking and hot rolling and then repeatedly to cold rolling and annealing, whereby a final (product) sheet is obtained. However, preferred production conditions are present for allowing the copper alloy sheet according to the embodiment of the present invention to obtain necessary properties such as strength, stress relaxation resistance characteristic and bendability, and these are described below. Also, in order to compose the texture of the copper alloy sheet according to the embodiment of the present invention, as described later, it is necessary to perform final cold rolling and subsequent final low-temperature annealing in combination and control the conditions in each of these steps.
In casting the above-described copper alloy composition according to the embodiment of the present invention, high-productivity ingot making in a shaft furnace which is a large-scale melting furnace is possible. However, the time required is preferably as short as possible, such that the time required from the completion of addition of alloy elements to the initiation of casting in the copper alloy melting furnace is within 1,200 seconds and further, the time required from the extraction of ingot out of the ingot heating furnace to the completion of hot rolling is within 1,200 seconds.
By virtue of shortening the time from the completion of addition of alloy elements to the initiation of casting in the copper alloy melting furnace and shortening the time from the extraction of ingot out of the ingot heating furnace to the completion of hot rolling, generation of a coarse Ni compound can be suppressed and at the same time, the amount of a fine Ni compound or the amount of Ni contained as a solid solution can be ensured. As a result, the copper alloy sheet can be assured of the electrical conductivity, stress relaxation resistance characteristic and strength.
Incidentally, even when it is intended to control the amount of a fine Ni compound or the amount of Ni contained as a solid solution mainly by the cold rolling conditions or annealing conditions in the later stage, the absolute amount of a fine Ni compound or of Ni contained as a solid solution already becomes small in the previous steps until the completion of hot rolling. Furthermore, in the case where the amount of a coarse Ni compound produced in the previous steps above is large, a fine product precipitated in the cold rolling and annealing steps is trapped by the coarse product and the amount of a fine product independently present in the matrix is more and more reduced. Accordingly, despite the large amount of Ni added, sufficiently high strength and excellent stress relaxation resistance characteristic may not be obtained.
Hot rolling may be performed in an ordinary manner. The inlet-side temperature of hot rolling is approximately from 600 to 1,000°C, and the finishing temperature is approximately from 600 to 850°C. After the hot rolling, water cooling or standing to cool is performed.
Thereafter, cold rolling and annealing are repeatedly performed to obtain a copper alloy sheet having a product sheet thickness. The annealing and cold rolling may be repeated according to the final (product) sheet thickness. In the cold rolling, the working ratio is selected so that a working ratio of approximately from 30 to 80% can be obtained in the final finish rolling. In the middle of the cold rolling, intermediate recrystallization annealing may be appropriately interposed.
As for the finish annealing temperature, the finish annealing is preferably performed at a maximum peak temperature of 500 to 800°C in terms of the substantial temperature of the sheet, and the holding time in this temperature range is preferably from 10 to 60 seconds.

(Final Cold Rolling)

In order to obtain a high-strength Cu-Ni-Sn-P-based copper alloy sheet with a 0.2%-proof stress of 500 MPa or more, also in the embodiment of the present invention, increase in the work-hardened amount (dense accumulation of introduced dislocations by the Orowan mechanism) by the heavy working of final cold rolling is effected. However, for allowing the texture of the copper alloy sheet to satisfy the conditions that the distribution density of B orientation is 40% or less and the sum of distribution densities of B orientation, S orientation and Cu orientation is from 30 to 90% and preventing the rolled texture from excessively developing outside of the ranges above, the cold rolling ratio (rolling reduction) per pass of the final cold rolling needs to be controlled.
Namely, the cold rolling ratio per pass of the final cold rolling is specified to be from 10 to 50%. As for the number of passes in the final cold rolling, the rolling is preferably performed usually in 3 or 4 passes while avoiding an excessively small or large number of passes.
With this normal number of passes, if the cold rolling ratio per pass of the final cold rolling exceeds 50%, there is a high possibility that the distribution density of B orientation exceeds 40% or the sum of distribution densities of B orientation, S orientation and Cu orientation becomes large to exceed 90%, though this may vary depending on the component composition of the copper alloy or the past production history or production conditions.
On the other hand, if the cold rolling ratio per pass of the final cold rolling is less than 10%, the sum of distribution densities of B orientation, S orientation and Cu orientation is liable to be less than 30% and the work-hardened amount in the cold rolling has a high possibility of becoming insufficient. In turn, it is likely impossible to satisfy the above-described high strength or enhance the stress relaxation resistance characteristic or bendability.

(Final Annealing)

Based on the knowledge above, the final annealing is performed in a continuous heat-treating furnace, whereby the texture specified in the embodiment of the present invention can be composed and the stress relaxation resistance characteristic and bendability can be enhanced while maintaining the high strength. That is, in the continuous heat-treating furnace, the tension imposed on the sheet when passing can be controlled and in turn, the texture of the copper alloy sheet can be controlled to a rolled texture where the distribution density of B orientation is 40% or less and the sum of distribution densities of B orientation, S orientation and Cu orientation is from 30 to 90%. The tension imposed on the sheet when passing in the continuous heat-treating furnace greatly affects the distribution density of Brass orientation (B orientation).
In order to obtain the texture specified in the embodiment of the present invention, the tension imposed on the copper alloy sheet when passing during final annealing in the continuous heat-treating furnace is controlled in the range of 0.1 to 8 kgf/mm². If the tension on passing of the sheet is out of this range, there is a high possibility that the texture specified in the embodiment of the present invention is not composed.
The temperature of the final annealing in the continuous heat-treating furnace is preferably from 100 to 400°C. If the annealing temperature is a temperature condition of less than 100°C, this is the same as not performing the low-temperature annealing and the texture/properties of the copper alloy sheet have a high possibility of scarcely changing from the state after the final cold rolling. Conversely, if the annealing is performed at an annealing temperature exceeding 400°C, this incurs recrystallization, excessive occurrence of a rearrangement or recovery phenomenon of dislocations or coarsening of the precipitate and therefore, the texture specified in the embodiment of the present invention may not be composed. Also, the strength is highly likely to decrease.

Examples

Working examples according to the embodiment of the present invention are described below. Copper alloy thin sheets varied in the texture with respect to a distribution density of Brass orientation and a sum of distribution densities of Brass orientation, S orientation and Copper orientation, were produced by
controlling the cold rolling ratio (rolling reduction) per pass at the final cold rolling and the tension imposed on the copper alloy sheet when passing at the final annealing in a continuous heat-treating furnace. These copper alloy thin sheets each was evaluated for various properties such as electrical conductivity, tensile strength, 0.2%-proof stress, stress relaxation resistance characteristic and bendability.
More specifically, a copper alloy having a chemical component composition shown in Table 1 (the balance of the composition excluding the element amounts shown is Cu) was melted in a coreless furnace and then subjected to ingot making by a semicontinuous casting method (cold solidification rate of casting: 2°C/sec) to obtain an ingot of 70 mm (thickness) × 200 mm (width) × 500 mm (length). The obtained ingots were rolled in common under the following conditions to produce a copper alloy thin sheet. After the surface of each ingot was scalped and heated, the ingot was heated at 960°C in a heating furnace and immediately hot-rolled at a hot rolling finishing temperature of 750°C into a 16 mm-thick sheet, and the sheet was quenched in water from a temperature of 650°C or more.
In this process, the time required from the completion of addition of alloy elements to the initiation of casting in the melting furnace was set to 1,200 seconds or less commonly among respective Examples, and the time required from the extraction out of the heating furnace to the completion of hot rolling was set to 1,200 seconds or less commonly among respective Examples.
After the removal of oxide scales, the sheet was subjected to cold rolling, continuous finish annealing, cold rolling and strain relief annealing in this order to produce a copper alloy thin sheet. That is, the sheet after primary cold rolling (rough cold rolling, intermediate cold rolling) was scalped. Finish annealing of the sheet was performed in an annealing furnace at the maximum peak temperature of 600°C in terms of the substantial temperature of the sheet by holding the sheet at this temperature for 60 seconds.
After the finish annealing, final cold rolling was performed. The cold rolling ratio (rolling reduction) in this final cold rolling was controlled to the values shown in Table 2. Incidentally, a roll having the same roll diameter (60 mm) and roll length (500 mm) was used in all of 4 passes of the final cold rolling.
After the final cold rolling, low-temperature annealing was performed in a continuous annealing furnace by making constant the substantial temperature (maximum peak temperature) at 350°C and varying the tension imposed on the copper alloy sheet when passing to obtain a 0.25 mm-thick copper alloy thin sheet.
In all of the copper alloys shown in Table 1, the balance of the composition excluding the element amounts shown is Cu, and the content of elements of Group A, that is, Ca, Zr, Ag, Cr, Cd, Be, Ti, Co, Au and Pt, as other impurity elements was 1.0 mass% or less in total of these elements.
Also, the content of elements of Group B, that is, Hf, Th, Li, Na, K, Sr, Pd, W, S, Si, C, Nb, Al, V, Y, Mo, Pb, In, Ga, Ge, As, Sb, Bi, Te, B and Misch metal, was 0.1 mass% or less in total of these elements.
In each of Examples, a sample was cut out from the obtained copper alloy sheet, and the sample was evaluated for various properties such as electrical conductivity, tensile strength, 0.2%-proof stress, stress relaxation resistance characteristic and bendability. The results obtained are shown in Table 2.

(Measurement of Texture)

A test specimen for the observation of texture was sampled from the obtained copper alloy sheet and after mechanical polishing and buff polishing, the surface was regulated by electrolytic polishing. Measurement of each of the obtained test specimens by the above-described method was performed at intervals of 1 µm with respect to a region of 500 µm × 500 µm. The measurement and analysis were performed, as described above, by using FESEM manufactured by JEOL Ltd. and the EBSP measurement/analysis system manufactured by TSL and using an analysis software for the system, whereby the distribution density of B orientation and the sum of distribution densities of B orientation, S orientation and Cu orientation were determined.

(Tensile Test)

A test specimen was sampled from the copper alloy thin sheet and machined to produce a JIS No. 5 tensile test specimen such that the longitudinal direction of the test specimen runs in the direction orthogonal to the rolling direction of the sheet material. This test specimen was measured for mechanical properties including elongation under the conditions of room temperature, a test speed of 10.0 mm/min and GL = 50 mm by a universal tester Model 5882 manufactured by Instron Corp. Incidentally, the proof stress is tensile strength corresponding to a permanent elongation of 0.2%.

(Measurement of Electrical Conductivity)

A sample was extracted from the copper alloy thin sheet and measured for the electrical conductivity. In measuring the electrical conductivity of the copper alloy sheet sample, the sheet was worked into a strip-like test specimen of 10 mm (width) × 300 mm (length) by milling and measured for the electrical resistance by a double bridge-type resistance measuring apparatus according to the measuring method of electrical conductivity of nonferrous metal materials specified in JIS-H0505, and the electrical conductivity was calculated according to the average cross-sectional area method.

(Stress Relaxation Characteristic)

The copper alloy thin sheet was evaluated for the stress relaxation resistance characteristic in the orthogonal direction involving severer stress relaxation than in the parallel direction, with respect to the rolling direction by measuring the stress relaxation ratio in this direction. In the stress relaxation ratio measuring test below, a sample where the stress relaxation ratio in the direction orthogonal is less than 10% is judged as passed in terms of the stress relaxation resistance characteristic.
More specifically, in the measurement of the stress relaxation ratio, a test specimen was sampled from the copper alloy thin sheet and measured using the cantilever system shown in Fig. 1. A 10 mm-wide strip-like specimen 1 (with the length direction running in the direction orthogonal to the rolling direction of the sheet material) was cut out and fixed at one end to a rigid test board 2, and deflection in a size of d (= 10 mm) was given to the portion in a span length L of the specimen 1. At this time, L was determined such that a surface stress corresponding to 80% of the proof stress of the material was loaded on the material. After holding in an oven at 120°C for 3,000 hours, the specimen was taken out, and the permanent distortion δ after removing the deflection d was determined. The stress relaxation ratio (RS) was calculated according to the formula: RS = (δ/d) × 100.

(Evaluation Test of Bendability)

The bending test of the copper alloy sheet sample was performed according to Japan Copper and Brass Association Technical Standards. The sheet material was cut into a size of 10 mm (width) × 30 mm (length) and while applying bending in Bad Way (where bending axis is parallel to the rolling direction), the presence or absence of cracking in the bent part was observed through an optical microscope at a magnification of 50. At this time, the bending was performed under the conditions such that the ratio R/t of the minimum bend radius R to the sheet thickness t (0.25 mm) of the copper alloy sheet is as small as possible and becomes almost 0. The bendability was rated A when cracking was not observed, rated B when fine cracking was generated, and rated C when relatively large cracking was generated. Usually, a smaller R/t is rated as excellent bendability.
As apparent from Table 2, in Inventive Examples 44 to 53 using a copper alloy within the composition range of the embodiment of the present invention in Table 1 (alloy Nos. 33 to 40), the copper alloy sheets are produced also within preferred conditions of the production method, such as cold rolling ratio (rolling reduction) per pass at the final cold rolling and the tension imposed on the copper alloy sheet when passing at the final annealing in a continuous heat-treating furnace. Accordingly, in Inventive Examples of Table 2, as the texture of the Cu-Ni-Sn-P-based copper alloy sheet, the distribution density of B orientation is 40% or less and at the same time, the sum of distribution densities of B orientation, S orientation and Cu orientation is from 30 to 90%.
In addition, it is presumed that in Inventive Examples, since the composition range is appropriate and the copper alloy sheet is produced within the above-described preferred conditions, production of a coarse Ni compound such as oxide, crystallized product or precipitate of Ni is suppressed and the amount of a fine Ni compound or the like or the amount of Ni contained as a solid solution can be ensured.
As a result, the copper alloy sheets of Inventive Examples 44 to 53 of Table 2 have, as terminal/connector properties, an electrical conductivity of 30% IACS or more and a stress relaxation ratio of less than 10% in the orthogonal direction involving severer stress relaxation, with respect to the rolling direction. In Inventive Examples, the bendability is excellent. Moreover, the copper alloy sheets of Inventive Examples further have, as mechanical properties, a 0.2%-proof stress of 500 MPa or more. That is, the copper alloy sheets of Inventive Examples are assured of high electrical conductivity and strength and excellent particularly in the stress relaxation resistance characteristic and bendability, revealing that the copper alloy sheet satisfies all of these properties at the same time.
In Inventive Example 49 of Table 2 (alloy No. 36 of Table 1), the Ni content is the upper limit of 3.0%; in Inventive Example 50 (alloy No. 37 of Table 1), the Sn content is the lower limit of 0.01%; in Inventive Example 51 (alloy No. 38 of Table 1), the Sn content is the upper limit of 3.0%; in Inventive Example 52 (alloy No. 39 of Table 1), the P content is the lower limit of 0.01%; and in Inventive Example 53 (alloy No. 40 of Table 1), the P content is the upper limit of 0.3%.
Also, in Inventive Example 45 where the production conditions such as cold rolling ratio per pass at the final cold rolling and the tension imposed on the copper alloy sheet when passing at the final annealing in a continuous heat-treating furnace are on the lower limit side, the stress relaxation resistance characteristic and strength are relatively lower than those in Inventive Example 44.
In Comparative Examples 56 to 61 of Table 2, the copper alloy sheets are produced within preferred conditions of the production method such as rolling speed in final cold rolling and sheet passage rate in final annealing. Accordingly, in Comparative Examples 56 to 61, the Cu-Ni-Sn-P-based copper alloy sheet has the texture specified in the embodiment of the present invention. Nevertheless, in these Comparative Examples, due to use of alloy Nos. 43 to 48 of Table 1 which are a copper alloy out of the composition range of the embodiment of the present invention, any one of the electrical conductivity, strength, stress relaxation resistance characteristic and bendability is significantly inferior to Inventive Examples.
In Comparative Example 56 of Table 2, the Ni content deviates below the lower limit (alloy No. 43 of Table 1) and therefore, the strength and stress relaxation resistance characteristic are low. In Comparative Example 57, the Ni content deviates above the upper limit (alloy No. 44 of Table 1) and therefore, the balance between strength and electrical conductivity or the bendability is low.
In Comparative Example 58, the Sn content deviates below the lower limit (alloy No. 45 of Table 1) and therefore, the strength is excessively low. In the copper alloy of Comparative Example 59, the Sn content deviates above the upper limit (alloy No. 46 of Table 1) and therefore, the electrical conductivity and bendability are low.
In Comparative Example 60, the P content deviates below the lower limit (alloy No. 47 of Table 1) and therefore, the strength and stress relaxation resistance characteristic are low. In Comparative Example 61, the P content deviates above the upper limit (alloy No. 48 of Table 1) and therefore, cracking occurred during hot rolling, failing in characterization.
In Comparative Examples 62 and 63 of Table 2, a copper alloy within the composition range of the embodiment of the present invention in Table 1 is used (alloy Nos. 33 and 34) and other production conditions are also within the preferred range, similarly to Inventive Examples. Nevertheless, the cold rolling ratio (rolling reduction) per pass at the final cold rolling or the tension imposed on the copper alloy sheet when passing at the final annealing in a continuous heat-treating furnace are out of the preferred range. In Comparative Example 62, the tension imposed on the sheet at the final annealing is substantially not present and is too small, and in Comparative Example 63, the cold rolling ratio per pass at the final cold rolling is too small and at the same time, the tension imposed on the sheet at the final annealing is too large.
As a result, in Comparative Examples 62 and 63, the texture of the Cu-Ni-Sn-P-based copper alloy sheet deviates from the texture specified in the embodiment of the present invention. Accordingly, in these Comparative Examples, the stress relaxation resistance characteristic in the direction orthogonal to the rolling direction is extremely inferior to Inventive Examples. Furthermore, the bendability is significantly poor as compared with Inventive Examples.

These results reinforce the meanings of the component composition and texture of the copper alloy in the embodiment of the present invention for obtaining a Cu-Ni-Sn-P-based alloy sheet satisfying the stress relaxation resistance characteristic in the direction orthogonal to the rolling direction and being excellent in the bendability and also in other properties required for a terminal or a connector, and further the meaning of the preferred production conditions for obtaining the texture.

Table 1

Class	No.	Chemical Component Composition of Copper Alloy Sheet (balance: Cu)
Class	No.	Ni	Sn	P	Fe	Zn	Mn	Si	Mg	Element Group A, #	Element Group B, #
Inventive Example	33	0.8	1.0	0.07	0.02	0.03	-	-	-	-	-
	34	1.0	0.9	0.06	0.02	-	-	0.01	0.01	-	-
	36	3.0	1.0	0.07	0.02	0.03	-	-	-	-	-
	37	1.0	0.01	0.06	0.02	-	0.01	-	0.01	-	-
	38	0.6	3.0	0.04	0.02	-	0.01	-	-	-	-
	39	1.0	0.8	0.01	0.02	-	0.01	-	0.01	-	-
	40	1.0	0.8	0.3	0.02	-	0.01	-	-	-	-
Comparative Example	43	0.04	1.0	0.07	0.02	0.03	-	-	-	-	-
	44	3.2	1.0	0.07	0.02	0.03	0.01	-	-	-	-
	45	0.8	-	0.07	0.02	0.03	-	0.01	-	-	-
	46	0.8	3.2	0.07	0.02	0.03	-	-	0.01	-	-
	47	0.8	1.0	0.004	0.02	0.03	-	-	0.01	-	-
	48	0.8	1.0	0.35	0.02	0.03	0.01	-	-	-	-

* "-" indicates that the content is below the detection limit.
* Other Element Group A: the total content of Ca, Zr, Ag, Cr, Cd, Be, Ti, Co, Au and Pt.
* Other Element Group B: the total content of Hf, Th, Li, Na, K, Sr, Pd, W, S, C, Nb, Al, V, Y, Mo, Pb, In, Ga, Ge, As, Sb, Bi, Te, B and Misch metal.

Table 2

Class	No.	Alloy No. of Table 1	Final Cold Rolling, Cold Rolling Ratio (%)	Final Continuous Annealing, Sheet Passage Tension (kgf/mm²)	Texture of Copper Alloy Sheet		Properties of Copper Alloy Sheet
Class	No.	Alloy No. of Table 1	Final Cold Rolling, Cold Rolling Ratio (%)	Final Continuous Annealing, Sheet Passage Tension (kgf/mm²)	B Orientation Density (%)	B+S+Cu Orientation Density (%)	Electrical Conductivity (%IACS)	Tensile Strength (MPa)	0.2%-Proof Stress (MPa)	Stress Relaxation Ratio (%)	Bendability (R/t)
Inventive Example	44	33	30	4	29	67	36	565	540	7	A
	45	33	10	0.5	14	33	37	535	520	9	A
	46	33	50	3	32	74	35	570	550	8	A
	47	34	20	4	24	56	38	535	520	8	A
	49	36	30	2	20	45	34	570	555	7	A
	50	37	30	7	37	84	45	520	500	8	A
	51	38	20	2	18	41	30	625	605	8	A
	52	39	40	2	23	51	43	515	500	9	A
	53	40	30	1	17	37	32	600	580	9	A
Comparative Example	56	43	40	2	35	77	40	505	490	11	A
	57	44	30	3	40	85	33	550	530	7	C
	58	45	10	5	29	62	46	485	465	9	A
	59	46	30	1	15	31	27	635	615	8	C
	60	47	20	2	23	50	43	495	480	11	A
	61	48	-	-	-	-	-	-	-	-	-
	62	33	10	none	10	24	37	530	515	11	B
	63	34	5	10	44	95	38	540	520	12	C

As described in the foregoing pages, according to the embodiment of the present invention, a Cu-Ni-Sn-P-based alloy sheet satisfying the stress relaxation resistance characteristic in the direction orthogonal to rolling and being excellent in bendability and also in other properties required for a terminal or a connector, can be provided.
Accordingly, the present invention is suitable particularly for a connection component such as automotive terminal or connector.

Claims

A cold rolled copper alloy sheet with a 0.2%-proof stress of 500 MPa or more consisting of, in terms of mass%, 0.3 to 3.0% of Ni, 0.01 to 3.0% of Sn and 0.01 to 0.3% of P, and optionally at least one member selected from the group consisting of, in terms of mass%, 0.3% or less of Fe, 0.05% or less of Zn, 0.1% or less of Mn, 0.1% or less of Si and 0.3% or less of Mg, optionally at least one member selected from the group consisting of Ca, Zr, Ag, Cr, Cd, Be, Ti, Co, Au and Pt, in a total amount of 1.0 mass% or less, and optionally at least one member selected from the group consisting of Hf, Th, Li, Na, K, Sr, Pd, W, S, C, Nb, Al, V, Y, Mo, Pb, In, Ga, Ge, As, Sb, Bi, Te, B and Misch metal, in a total amount of 0.1 mass% or less, with the balance being copper, wherein the copper alloy sheet has a texture in which a distribution density of Brass orientation is 40% or less and a sum of distribution densities of Brass orientation, S orientation and Copper orientation is 30 to 90%, measured by a crystal orientation analysis method using an electron backscatter diffraction pattern (EBSP) through a field emission scanning electron microscope (FESEM), and wherein the copper alloy sheet has, as terminal/connector properties, an electrical conductivity of 30% IACS or more.