EP2695958B1

EP2695958B1 - Copper alloy sheet

Info

Publication number: EP2695958B1
Application number: EP13005149.3A
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: 2018-12-26
Anticipated expiration: 2028-07-24
Also published as: US20110223056A1; CN101743333A; EP2184371B1; EP2695957B1; EP2695958A3; KR101227315B1; EP2695958A2; EP2695956A3; EP2695957A2; EP2184371A4; EP2695956B1; KR20100031138A; EP2184371A1; EP2695956A2; WO2009019990A1; EP2695957A3

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, US 2002/108685 A1 discloses a copper-base alloy having improved punching properties on press that contains a total of 0.01-30 wt % of at least one element selected from the group consisting of Sn, Ni, P, Zn, Si, Fe, Co, Mg, Ti, Cr, Zr and Al, with the balance being Cu and incidental impurities, and which has a surface X-ray diffraction intensity ratio S_D of at least 10 [S_ND=I{220}/I{200}; I{220} is the X-ray diffraction intensity of {220} and I{200} is the X-ray diffraction intensity of {200}]. EP 1 630 239 A1 discloses a copper alloy wherein the integrated intensity ratio I{200}/I{111} found by X-ray diffraction of a rolled surface is 1.5 or less. EP 1 801 249 A1 discloses a Cu-Ni-Sn-P based alloy comprising 0.1 to 3.0% of Ni, 0.1 to 3.0% of Sn, and 0.01 to 0.3% of P in mass percent respectively, and the remainder being copper and inevitable impurities, wherein in a radial distribution function around a Ni atom according to a XAFS analysis method, a first peak position is within a range of 2.16 to 2.35 Å, the position indicating a distance between a Ni atom in Cu and an atom nearest to the Ni atom. WO 2006/132317 A1 discloses a Cu-Ni-Sn-P based alloy comprising 0.1 to 3.0 mass% of Ni, 0.01 to 3.0 mass% of Sn, 0.01 to 0.3 mass% of P with the remainder being copper and inevitable impurities. JP 2006 342389 A discloses a copper alloy sheet having a composition which is composed of 0.4 to 1.6% of Ni, 0.4 to 1.6% of Sn, 0.027 to 0.15 of P and 0.005 to 0.15% of Fe in mass percent respectively, and the remainder being copper and inevitable impurities, wherein the ratio of the Ni content and P content is < 1.5, wherein the copper alloy sheet has a structure in which precipitates of an Ni-P intermetallic compound are dispersed in the matrix phase of the copper alloy and the precipitates have a diameter of ≤ 60 nm, and ≥ 20 pieces of the precipitates having a diameter of 5 to 60 nm are observed in the region of a visual field of 500 nm × 500 nm.
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.
In view of this point, an object of the present invention is to provide a Cu-Ni-Sn-P-based copper alloy sheet with an excellent stress relaxation resistance characteristic, which satisfies, as a terminal or connector, a high stress relaxation ratio in the direction orthogonal to the rolling direction as well as in the direction parallel to the rolling direction.
In order to achieve the object of the present invention, the gist of the copper alloy sheet with excellent stress relaxation resistance characteristic (hereinafter sometimes referred to as an embodiment of the present invention) is a cold rolled copper alloy sheet consisting of, in terms of mass%, 0.1 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 lesswith the balance being copper, wherein the copper alloy sheet has a ratio I(200)/I(220) of a X-ray diffraction intensity I(200) from (200) plane in the sheet surface to a X-ray diffraction intensity I(220) from (220) plane in the sheet surface of 0.25 or less, has an average grain size of 5.0 µm or less, and wherein the copper alloy sheet has, as terminal/connector properties, an electrical conductivity of 30% IACS or more.
In the embodiment of the present invention, the X-ray diffraction intensity ratio I(200)/I(220) is specified so as to suppress the development of Cube orientation of the Cu-Ni-Sn-P-based copper alloy sheet and develop a specific crystal orientation except for the Cube orientation. In combination with this, the average grain size is specified to be fine as 5.0 µm or less. By virtue of these constructions, in the embodiment of the present invention, anisotropy in specific directions such as parallel direction or orthogonal direction with respect to the rolling direction is reduced, whereby the stress relaxation resistance characteristic in the direction orthogonal to the rolling direction is enhanced and at the same time, the difference in the stress relaxation resistance characteristic between the parallel direction and the orthogonal direction with respect to the rolling direction is made small.
Contrary to the embodiment of the present invention, if the Cube orientation is developed, if the development of a specific crystal orientation except for the Cube orientation is suppressed or if the average grain size is coarsened, anisotropy in a specific direction such as parallel direction with respect to the rolling direction is intensified in any case and the stress relaxation resistance characteristic in the orthogonal direction is rather not enhanced. Also, the difference in the stress relaxation resistance characteristic between the parallel direction and the orthogonal direction with respect to the rolling direction cannot be made small and anisotropy (difference in the stress relaxation resistance characteristic) between these two directions becomes large.

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.

(X-Ray Diffraction Intensity Ratio)

The X-ray diffraction intensity ratio in the embodiment of the present invention is determined as follows. The X-ray diffraction intensity I(200) from (200) plane as the Cube orientation in the sheet surface and the X-ray diffraction intensity I(220) from (220) plane as the orientation except for the Cube orientation are measured using a normal X-ray diffraction method, and the ratio of these X-ray diffraction intensities (X-ray diffraction peak ratio), I(200)/I(220) can be determined from these.
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 and the stress relaxation resistance characteristic are changed. Out of these factors, the orientation density of Cube orientation [hereinafter sometimes referred to as D(Cube)] and a specific crystal orientation density other than that are controlled to appropriate ranges, whereby the anisotropy in a specific direction such as parallel direction or orthogonal direction with respect to the rolling direction is reduced.
That is, the development of Cube orientation is suppressed and the development of a specific crystal orientation other than Cube orientation is intensified. By this control, the stress relaxation resistance characteristic in the direction orthogonal to the rolling direction is enhanced, and the difference in the stress relaxation resistance characteristic between the parallel direction and the orthogonal direction with respect to the rolling direction is made small. Furthermore, even if 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 is high in the direction orthogonal to the rolling direction as well as in the direction parallel to the rolling direction, so that 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.
Accordingly, in the embodiment of the present invention, the ratio I(200)/I(220) of the X-ray diffraction intensity I(200) from (200) plane as Cube orientation in the sheet surface to the X-ray diffraction intensity I(220) from (220) plane as an orientation other than Cube orientation is specified as 0.25 or less, preferably 0.20 or less.
If the ratio I(200)/I(220) exceeds 0.25, the Cube orientation is developed and the development of a specific crystal orientation other than Cube orientation is suppressed. Also, anisotropy in a specific direction such as parallel direction with respect to the rolling direction is intensified and the stress relaxation resistance characteristic in the orthogonal direction is rather not enhanced. Furthermore, the difference in the stress relaxation resistance characteristic between the parallel direction and the orthogonal direction with respect to the rolling direction cannot be made small and anisotropy (difference in the stress relaxation resistance characteristic) between these two directions becomes large.

(Average grain size)

In the embodiment of the present invention, the control of the texture of the Cu-Ni-Sn-P-based copper alloy sheet is combined with the control for decreasing the average grain size to reduce the anisotropy in a specific direction such as parallel direction or orthogonal direction with respect to the rolling direction, whereby the stress relaxation resistance characteristic in the direction orthogonal to the rolling direction is enhanced and at the same time, the difference in the stress relaxation resistance characteristic between the parallel direction and the orthogonal direction with respect to the rolling direction is made small.
Accordingly, in the embodiment of the present invention, the average grain size is made fine as 5.0 µm or less. If the average grain size is coarsened to exceed 5.0 µm, despite the above-described control of the texture, anisotropy in a specific direction such as parallel direction with respect to the rolling direction is intensified and the stress relaxation resistance characteristic in the orthogonal direction is rather not enhanced. Furthermore, the difference in the stress relaxation resistance characteristic between the parallel direction and the orthogonal direction with respect to the rolling direction cannot be made small and anisotropy (difference in the stress relaxation resistance characteristic) between these two directions becomes large.
The average grain size can be measured in the process of measuring the distribution density of a specific orientation by a crystal orientation analysis method using FESEM/EBSP. That is, in this crystal orientation analysis method, 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 (specific orientation mapping) 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 ± 10° (slippage within ±10° from the crystal plane) are taken (regarded) as belonging to the same crystal plane. In the case where the orientation difference of two crystals exceeds ± 10°, the space therebetween (for example, the side at which two hexagons are contacted) is taken as a grain boundary. In this way, the distribution of grain boundaries in the sample surface is determined.
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, the average grain size of grains can be measured by 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. The range of measured view is set to, for example, a region of about 500 µm × 500 µm and after measuring the test specimen at an appropriate number of portions, the values are averaged.

(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 and electrical conductivity, the copper alloy fundamentally comprises 0.1 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 0.1 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 in terms of 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 and stress relaxation resistance characteristic, 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 the final cold rolling, the rolling speed is set large and is 200 m/min or more. In combination with this, as described later, final annealing at a low temperature is performed. By increasing the rolling speed in the final cold rolling, the strain rate introduced into the Cu-Ni-Sn-P-based copper alloy is increased and this allows a crystal orientation other than Cube orientation to readily develop and suppresses the development of Cube orientation, so that anisotropy of the stress relaxation resistance characteristic can be reduced. Also, randomization of the crystal orientation is accelerated and since a group of the same orientation grains (grains close in the crystal orientation come adjacent to each other and form a group) is reduced, the grain size of individual grain also becomes fine. Accordingly, the X-ray diffraction intensity ratio I(200)/I(220) in the surface of the Cu-Ni-Sn-P-based copper alloy sheet can be made to be 0.25 or less, and a fine average grain size of 5.0 µm or less can be obtained. As a result, the stress relaxation resistance characteristic in the direction orthogonal to the rolling direction can be enhanced and the difference from the stress relaxation ratio in the direction parallel to the rolling direction can also be made small.
If the rolling speed in the final cold rolling is too small and is less than 200 m/min, the strain rate is small and in the Cu-Ni-Sn-P-based copper alloy sheet like the embodiment of the present invention, the development of a crystal orientation other than Cube orientation is suppressed or a group of the same orientation grains is readily formed, giving rise to an increase in the grain size of individual grains. Therefore, the X-ray diffraction intensity ratio I(200)/I(220) cannot be made to be 0.25 or less and the average grain size is also readily coarsened to exceed 5.0 µm.
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. Also, the rolling reduction per pass need not exceed 50% and each rolling reduction per pass is determined by taking into consideration the original sheet thickness, final sheet thickness after cold rolling, number of passes, and maximum rolling reduction.

(Final Annealing)

In the production of the copper alloy according to the embodiment of the present invention, final annealing at a low temperature is performed in a continuous heat-treating furnace after the final cold rolling. In the continuous annealing step using a continuous heat-treating furnace, low-temperature annealing can be performed in a short time at a maximum peak temperature of 100 to 400°C by controlling the sheet passage rate of the sheet passing through the furnace. In this respect, when the sheet passage rate is set to be from 10 to 100 m/min at the above-described maximum peak temperature of 100 to 400°C, the development of Cube orientation of the Cu-Ni-Sn-P-based copper alloy sheet is suppressed, whereas the development of a specific crystal orientation other than Cube orientation is intensified, so that anisotropy can be reduced. Also, the growth of a grain can be suppressed. Accordingly, the X-ray diffraction intensity I(200)/I(220) in the surface of the Cu-Ni-Sn-P-based copper alloy sheet can be made to be 0.25 or less and a fine average grain size of 5.0 µm or less can be obtained. As a result, the stress relaxation resistance characteristic in the direction orthogonal to the rolling direction can be enhanced and the difference from the stress relaxation ratio in the direction parallel to the rolling direction can also be made small.
If the sheet passage rate exceeds 100 m/min, an abrupt temperature change of the sheet occurs from room temperature to the maximum peak temperature of 100 to 400°C and therefore, the residual strain amount remaining in the sheet after passing the furnace is increased, allowing easy occurrence of a rearrangement or recovery phenomenon of dislocations. That is, the stress relaxation resistance characteristic decreases in both the orthogonal direction and the parallel direction with respect to the rolling direction. On the other hand, if the sheet passage rate is less than 10 m/min, not only the processing time in the above-described maximum peak temperature range of 100 to 400°C is too long but also because of a small temperature rise or drop rate, in the Cu-Ni-Sn-P-based copper alloy sheet like the embodiment of the present invention, the development of a crystal orientation other than Cube orientation is particularly suppressed and the growth of a grain is accelerated. Consequently, anisotropy of the stress relaxation resistance characteristic is intensified and the X-ray diffraction intensity ratio I(200)/I(220) cannot be made to be 0.25 or less, as a result, the average grain size is readily coarsened to exceed 5.0 µm.
Also, if the annealing temperature is less than 100°C or the above-described low-temperature annealing is not performed, there is a high possibility that the texture/properties of the copper alloy sheet are scarcely changed from the state after the final cold rolling. On the contrary, if the annealing temperature exceeds 400°C, this incurs recrystallization, excessive occurrence of a rearrangement or recovery phenomenon of dislocations or coarsening of the precipitate and therefore, 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 X-ray diffraction intensity ratio I(200)/I(220) by controlling the rolling speed in the final cold rolling and the sheet passage rate and annealing temperature at the low-temperature final annealing in a continuous heat-treating furnace after the final cold rolling. These copper alloy thin sheets each was evaluated for various properties such as electrical conductivity, tensile strength, 0.2%-proof stress and stress relaxation resistance characteristic.
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 produce an ingot of 70 mm (thickness) × 200 mm (width) × 500 mm (length). The obtained ingots were rolled in common under the following conditions to obtain 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 at a rolling reduction of 60% was performed. The rolling speed in this final cold rolling was controlled. 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, and the rolling reduction per pass was also made the same at 30%.
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 sheet passage rate as shown in Table 2 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 and stress relaxation resistance characteristic. The results obtained are shown in Table 2.

(Measurement of Texture)

With respect to the copper alloy sheet sample, the X-ray diffraction intensity I(200) from (200) plane in the sheet surface and the X-ray diffraction intensity I(220) from (220) plane were measured under the conditions of a tube voltage of 40 kV, a tube current of 200 mA, a scan rate of 2°/min, a sampling width of 0.02° and a measurement range (2θ) of 30 to 115° by using an X-ray diffraction analyzer (Model: RINT 1500) manufactured by Rigaku Corporation and using Co as the target, and the X-ray diffraction intensity ratio I(200)/I(220) was determined. The measurement was performed at two portions and an average of the values obtained was used as I(200)/I(220).

(Measurement of Average grain size)

The average grain size was measured by a crystal orientation analysis method using FESEM/EBSP described above. The measured portion of the test specimen was in common arbitrary 5 portions, the measured values as the average particle grain size of these 5 portions were averaged, and the obtained value was used for the average crystal grin size.

(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 each of the parallel direction and 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 these directions. In the stress relaxation ratio measuring test below, a sample where the stress relaxation ratio is less than 10% in both the parallel direction and the orthogonal direction with respect to the rolling direction and the difference in the stress relaxation ratio between the parallel direction and the orthogonal direction is within 3% 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.
As apparent from Table 2, in Inventive Examples 25 to 33 using a copper alloy within the composition range of the embodiment of the present invention in Table 1 (alloy Nos. 17 to 24), 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 Inventive Examples of Table 2, the X-ray diffraction intensity ratio I(200)/I(220) in the surface of the Cu-Ni-Sn-P-based copper alloy sheet is 0.25 or less. Also, the average grain size was as fine as 5.0 µm or less.
In addition, it is presumed that since the copper alloy sheets of Inventive Examples have a composition in an appropriate range and are 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 25 to 33 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. The difference in the stress relaxation ratio between the orthogonal direction and the parallel direction with respect to the rolling direction is also as small as approximately from about 2 to 3%. Moreover, the copper alloy sheet further has, 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, revealing that the copper alloy sheet satisfies all of these properties at the same time.
In Inventive Example 28 of Table 2 (alloy No. 19 of Table 1), the Ni content is the lower limit of 0.1%; in Inventive Example 29 (alloy No. 20 of Table 1), the Ni content is the upper limit of 3.0%; in Inventive Example 30 (alloy No. 21 of Table 1), the Sn content is the lower limit of 0.01%; in Inventive Example 31 (alloy No. 22 of Table 1), the Sn content is the upper limit of 3.0%; in Inventive Example 32 (alloy No. 23 of Table 1), the P content is the lower limit of 0.01%; and in Inventive Example 33 (alloy No. 24 of Table 1), the P content is the upper limit of 0.3%.
Also, in Inventive Example 26 of Table 2 where the production conditions such as rolling speed in final cold rolling and sheet passage rate in final annealing are on the lower limit side, the stress relaxation resistance characteristic and strength are relatively lower than those in Inventive Example 25.
In Comparative Examples 36 to 40 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 36 to 40, the copper alloy sheet has anisotropy that the X-ray diffraction intensity ratio I(200)/I(220) in the surface of the Cu-Ni-Sn-P-based copper alloy sheet is 0.25 or less. Nevertheless, in these Comparative Examples, due to use of alloy Nos. 27 to 32 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 and stress relaxation resistance characteristic is significantly inferior to Inventive Examples.
In Comparative Example 36 of Table 2, the Ni content deviates below the lower limit (alloy No. 27 of Table 1) and therefore, the strength and stress relaxation resistance characteristic are low. In Comparative Example 37, the Ni content deviates above the upper limit (alloy No. 28 of Table 1) and therefore, the balance between strength and electrical conductivity is low.
In Comparative Example 38, the Sn content deviates below the lower limit (alloy No. 29 of Table 1) and therefore, the strength and stress relaxation resistance characteristic are excessively low. In the copper alloy of Comparative Example 39, the Sn content deviates above the upper limit (alloy No. 30 of Table 1) and therefore, the electrical conductivity is low.
In Comparative Example 40, the P content deviates below the lower limit (alloy No. 31 of Table 1) and therefore, the strength and stress relaxation resistance characteristic are low. In Comparative Example 41, the P content deviates above the upper limit (alloy No. 32 of Table 1) and therefore, cracking occurred during hot rolling, failing in characterization.
In Comparative Examples 42 and 43 of Table 2, a copper alloy within the composition range of the embodiment of the present invention in Table 1 is used (alloy Nos. 17 and 18) and other production conditions are also within the preferred range, similarly to Inventive Examples. Nevertheless, the rolling speed in final cold rolling or the sheet passage rate in final annealing are out of the preferred range. In Comparative Example 42, the rolling speed in final cold rolling is too slow, and in Comparative Example 43, the rolling speed in final cold rolling is too low and at the same time, the sheet passage rate in final annealing is too slow.
As a result, in Comparative Examples 42 and 43, the X-ray diffraction intensity ratio I(200)/I(220) in the surface of the Cu-Ni-Sn-P-based copper alloy sheet exceeds 0.25. Also, the average grain size is coarsened to exceed 5.0 µm. 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 difference between the stress relaxation ratio in the direction orthogonal to the rolling direction and the stress relaxation ratio in the direction parallel to the rolling direction is large. In addition, the strength is low 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, creating not so much difference from the stress relaxation resistance characteristic in the direction parallel to the rolling direction, and being excellent 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	17	0.9	1.1	0.08	0.02	0.04	-	-	-	-	-
	18	1.1	0.7	0.06	0.02	0.01	-	-	0.01	-	-
	19	0.1	1.0	0.08	0.02	0.03	0.01	-	0.01	-	-
	20	3.0	1.0	0.08	0.02	0.03	-	0.01	-	-	-
	21	0.9	0.01	0.08	0.02	-	-	0.01	-	-	-
	22	0.6	3.0	0.04	0.02	-	0.01	-	-	-	-
	23	1.1	0.7	0.01	0.02	0.04	-	-	0.01	-	-
	24	1.1	0.7	0.3	0.02	-	-	0.01	-	-	-
Comparative Example	27	0.04	1.0	0.08	0.02	-	-	-	0.01	-	-
	28	3.2	1.0	0.08	0.02	0.04	0.01	-	-	-	-
	29	0.9	-	0.08	0.02	0.04	0.01	-	-	-	-
	30	0.9	3.2	0.08	0.02	0.04	-	0.01	-	-	-
	31	0.9	1.0	0.004	0.02	0.03	0.01	0.01	-	-	-
	32	0.9	1.0	0.35	0.02	-	0.01	-	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, Rolling Speed (m/min)	Final Continuous Annealing, Sheet Passage Rate (m/min)	Properties of Copper Alloy Sheet
					Texture		Electrical Conductivity (%IACS)	Tensile Strength (MPa)	0.2%-Proof Stress (MPa)	Stress Relaxation Ratio
					X-Ray Diffraction Intensity Ratio I(200)/I(220)	Average grain size (µm)	Electrical Conductivity (%IACS)	Tensile Strength (MPa)	0.2%-Proof Stress (MPa)	Orthogonal Direction (%)	Parallel Direction (%)	Difference (%)
Inventive Example	25	17	300	500	0.17	3.0	35	590	570	7	5	2
	26	17	200	100	0.24	4.5	37	550	535	9	7	2
	27	18	300	30	0.19	4.9	38	555	540	8	6	2
	28	19	200	50	0.20	3.5	41	540	520	9	6	3
	29	20	300	30	0.16	4.2	34	595	580	8	5	3
	30	21	250	70	0.21	3.6	44	530	510	9	7	2
	31	22	300	30	0.18	3.2	31	640	620	8	6	2
	32	23	300	70	0.22	3.5	42	535	515	9	7	2
	33	24	250	30	0.20	4.0	33	625	605	9	6	3
Comparative Example	36	27	200	30	0.22	3.9	41	510	490	12	8	4
	37	28	300	30	0.19	4.2	32	580	560	9	6	3
	38	29	200	30	0.23	3.8	45	490	475	10	7	3
	39	30	300	10	0.20	3.1	28	615	595	9	7	2
	40	31	200	50	0.24	3.7	43	505	485	11	7	4
	41	32	-	-	-	-	-	-	-	-	-	-
	42	17	100	50	0.27	5.4	35	560	540	12	7	5
	43	18	100	5	0.29	6.8	38	540	520	13	8	5

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 the rolling direction, creating not so much difference from the stress relaxation resistance characteristic in the direction parallel to the rolling direction, and being excellent 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 consisting of, in terms of mass%, 0.1 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 ratio I(200)/I(220) of a X-ray diffraction intensity I(200) from (200) plane in the sheet surface to a X-ray diffraction intensity I(220) from (220) plane in the sheet surface of 0.25 or less, has an average grain size of 5.0 µm or less, and wherein the copper alloy sheet has, as terminal/connector properties, an electrical conductivity of 30% IACS or more.