EP2695957B1

EP2695957B1 - Copper alloy sheet

Info

Publication number: EP2695957B1
Application number: EP13005148.5A
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: 2018-11-28
Anticipated expiration: 2028-07-24
Also published as: EP2695958A2; EP2695958B1; US20110223056A1; EP2184371A4; EP2695956A3; EP2695956A2; KR20100031138A; EP2695957A3; CN101743333A; EP2695958A3; KR101227315B1; EP2184371A1; EP2184371B1; EP2695957A2; EP2695956B1; WO2009019990A1

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, 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. 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. EP 1 612 285 A1 discloses a Cu-Ni-Sn-P based alloy containing Ni, Sn, P and also at least one or more elements selected from a group consisting of Zn, Si, Fe, Co, Mg, Ti, Cr, Zr and A1 in a total amount of 0.01-30 wt.% with the remainder being Cu and unavoidable impurities, where the x-ray diffraction intensity ratio of the surface S_ND is specified. 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. JP 2001 262297 A also discloses a Cu-Ni-Sn-P based alloy comprising 0.2 to 3.0 mass% of Ni, 2.0 mass% or less of Sn, 0.005 to 2.0 mass% of P with the remainder being copper and inevitable impurities. JP 2000 256814 A discloses a Cu-Ni-Sn-P based alloy comprising 0.2 to 3.0 mass% of Ni, 0.5 to 2.0 mass% of Sn, 0.01 to 1.0 mass% of P with the remainder being copper and inevitable impurities. JP 2001 262255 A discloses a Cu-Ni-Sn-P based alloy comprising 0.2 to 3.0 mass% of Ni, 2.0 mass% or less of Sn, 0.005 to 2.0 mass% of P with the remainder being copper and inevitable impurities.
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
Also, although the usage or alloy system is utterly different, in other copper alloys such as Cu-Fe-P-based copper alloy sheet for use as a lead frame, a technique of controlling the chemical components, for example, adding a small amount of Pb, Ca or the like or dispersing a compound working out to a starting point of fracture, or a technique of controlling a grain size, has been heretofore generally employed as the means for enhancing the press punchability. However, when such a technique is intended to be applied to a Cu-Ni-Sn-P-based copper alloy, there may arise a problem that the control itself is difficult or other properties are deteriorated or that the production cost in turn rises.
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 which not only satisfies the properties required for a terminal or connector, such as stress relaxation resistance characteristic, but also is excellent in the press punchability.
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 press punchability (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 less, with the balance being copper, wherein a value obtained by dividing a half-value breadth of a X-ray diffraction intensity peak from {200} plane in the sheet surface by a height of the peak is 1.0 × 10^-4 or more, , 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 dislocation density of the Cu-Ni-Sn-P-based copper alloy sheet texture is controlled. More specifically, the dislocation density of the Cu-Ni-Sn-P-based copper alloy sheet texture is increased, whereby the press punchability is enhanced. According to the knowledge of the present inventors, as for the dislocation density, the amount of dislocations introduced can be controlled by the rolling conditions of the Cu-Ni-Sn-P-based copper alloy and at the same time, this control of the dislocation density has a great effect of enhancing the press punchability.
In the embodiment of the present invention, it is not intended to control the crystal orientation texture such as accumulation ratio of a specific orientation (crystal orientation) by specifying the X-ray diffraction intensity from a specific crystal orientation in a sheet surface of a Cu-Fe-P-based copper alloy or the like, which is attempted, for example, in JP-A-2000-328158 , JP-A-2002-339028 , JP-A-2000-328157 and JP-A-2006-63431 . In a copper alloy originally having random orientations, there is a large limitation in increasing only the accumulation ratio of a specific orientation. This applies also to the case of controlling the texture such as accumulation ratio of a specific orientation (crystal orientation) described, for example, in JP-A-2000-328158 , JP-A-2002-339028 , JP-A-2000-328157 and JP-A-2006-63431 . In other words, the conventional control of the texture has a large limitation in terms of the effect of enhancing the press punchability, not only in a Cu-Fe-P-based copper alloy sheet but also in a Cu-Ni-Sn-P-based copper alloy sheet.
The dislocation density which is controlled in the embodiment of the present invention is an extremely microscopic issue and it is very difficult to directly observe or quantify the dislocation density introduced into the Cu-Ni-Sn-P-based copper alloy sheet texture. However, according to the knowledge of the present inventors, the dislocation density introduced into the Cu-Ni-Sn-P-based copper alloy sheet texture is fairly well correlated to the half-value breadth of the X-ray diffraction intensity peak, particularly, the value obtained by dividing the half-value breadth by the height of the X-ray diffraction intensity peak.
In this case, the dislocation density is correlated equally to any X-ray diffraction intensity peak. However, the X-ray diffraction intensity peak from {200} plane in the sheet surface, specified in the embodiment of the present invention, is not large (high) as the X-ray diffraction intensity peak which should divide the half-value breadth, in comparison with X-ray diffraction intensities from other planes, and because of a relatively fair half-value breadth, the value obtained by dividing the half-value breadth of the X-ray diffraction intensity peak by the height is highly reliable. Accordingly, in the embodiment of the present invention, the dislocation density is indirectly but exactly and reproducibly specified and quantified by the X-ray diffraction intensity peak from {200} plane in the sheet surface.
In this way, in the embodiment of the present invention, the amount of dislocation density is specified by the half-value breadth of the X-ray diffraction intensity peak from {200} plane in the sheet surface, which is closely correlated to the amount of dislocation density, to enhance the press punchability and satisfy the press punchability required for the Cu-Ni-Sn-P-based copper alloy sheet.

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.
Fig. 3 shows a schematic view showing the half-value breadth of the X-ray diffraction intensity peak.
Fig. 4 shows explanatory views showing the measuring method of a shear plane ratio.

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.

(Half-Value Breadth)

In the embodiment of the present invention, for enhancing the press punchability, the copper alloy sheet is specified to have a dislocation density in not less than a given amount such that the value obtained by dividing the half-value breadth of the X-ray diffraction intensity peak from {200} plane in the Cu-Ni-Sn-P-based copper alloy sheet surface by the peak height is 1.0 × 10^-4 or more. By this construction, the stress relaxation resistance characteristic and press punchability of the Cu-Ni-Sn-P-based copper alloy sheet can be enhanced.
If the value obtained by dividing the half-value breadth of the X-ray diffraction intensity peak by the peak height is less than 1.0 × 10^-4, the dislocation density introduced into the sheet is reduced, making a little difference from the conventional Cu-Ni-Sn-P-based with a small dislocation density, and the stress relaxation resistance characteristic and press punchability are decreased or not enhanced.
As is well known, the half-value breadth is defined as a width (β) of the X-ray diffraction intensity peak at the position half (height: H/2) the X-ray diffraction intensity peak (height: H) shown in a schematic view of Fig. 3 where the ordinate indicates the X-ray diffraction intensity and the abscissa indicates the angle (2θ).
Incidentally, the half-value breadth of the X-ray diffraction intensity peak is usually used for determining or quantifying the crystallinity or non-crystallinity of metal surface, the crystallite size or the lattice strain. On the other hand, in the embodiment of the present invention, as described above, the dislocation density that cannot be directly observed or quantified is specified using the value (β/H) obtained by dividing the half-value breadth β of the X-ray diffraction intensity peak from {200} plane in the sheet surface, which is fairly well correlated to the dislocation density, by the peak height H.
As for the X-ray diffraction intensity peak of the Cu-Ni-Sn-P-based copper alloy sheet surface, the half-value breadth (β) or peak height (H) of the X-ray diffraction intensity peak from other {220} plane is largest. However, when the height of the X-ray diffraction intensity peak is large (high), the peak height which divides the half-value breadth is also large and this is disadvantageous in that the value obtained by dividing the half-value breadth of the X-ray diffraction intensity peak by the peak height becomes too small and many errors occur in the value itself, giving rise to poor reproducibility. For this reason, in the embodiment of the present invention, the X-ray diffraction intensity peak from {200} plane, ensuring that the value obtained by dividing the half-value breadth of the X-ray diffraction intensity peak by the peak height is large (the peak height is not large and the half-value breadth is fairly large), is employed.
Accordingly, in the embodiment of the present invention, the issue is absolutely the introduced state of dislocation intensity into the sheet and it is not intended to control the accumulation ratio in texture, the grain size on sheet surface or the rolled texture by the above-described X-ray diffraction intensity peak from a specific crystal plane in the sheet surface. In other words, the introduced state of dislocation intensity into the sheet cannot be specified or controlled by this X-ray diffraction intensity peak from a specific crystal plane in the sheet surface or the control of the accumulation ratio in texture, the grain size on sheet surface or the rolled texture.

(Introduction of Dislocation Density)

In order to introduce a dislocation density such that the value obtained by dividing the half-value breadth of the X-ray diffraction intensity peak from {200} plane in the Cu-Ni-Sn-P-based copper alloy sheet surface by the peak height is 1.0 × 10^-4 or more, as described later, the strain amount introduced in the final cold rolling is increased. That is, in the final cold rolling, a technique such as use of a small-size roll having a roll diameter of less than 80 mmφ or setting of the rolling reduction (cold rolling ratio) per pass to 20% or more is selected and used, or these techniques are used in combination.

(Burr Height)

In the embodiment of the present invention, the press punchability is exactly evaluated by the "burr height" generated in a press punching test of punching a circular round hole in a copper alloy sheet according to Japan Copper and Brass Association Technical Standards JCBA T310 "Shear Test Method of Copper and Copper Alloy Thin Sheet Materials". When the burr height is 5 µm or less, the press punchability of the Cu-Ni-Sn-P-based copper alloy sheet can be rated as good.
At this time, in order to impart reproducibility to the measurement of a shear plane ratio in the press punching test, test conditions enabling assurance of the reproducibility in the above-described press punching test are specifically specified. That is, in the press punching test, a punching press shown in Fig. 4(a) is used, and a copper alloy sheet (test specimen, material to be worked) held on the top of a die having a circular round hole, which is supported by a die holder, is punched from the upper side to the down side by a 10 mmφ punch. The clearance with the punch is set to 3%, and the copper alloy sheet is fixed to the die top from the upper part by a platelike stopper. A lubricating oil, UNIPRESS PA5, produced by Nisseki Mitsubishi is used. The construction material of the punch and die is SKS-3, the die cutter length is 5 mm, and the punching die taper is 0°.
Fig. 4(b) shows the side cross-section of the punched hole generated in the copper alloy sheet by the punching above. The side cross-section of the punched hole is observed through a scanning microscope, and the "burr height" (height of burr or flash: µm) projecting downward in the peripheral part at the bottom of the punched hole is measured. At this time, as for the "burr height" per one punched hole, values at 4 points created by 90° dividing the circumference of the circular punched hole are averaged and furthermore, by punching 6 sheets (6 pieces) for each copper alloy sheet, an average of these sheets is taken as the "burr height" (µm). In Fig. 4(b), t is the thickness of the copper alloy sheet, a is the shear plane of the punched hole, b is a fracture plane of punched hole, and c is a shear droop generated in the peripheral part at the top of the punched hole.

(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% including the indication in the claims. The alloy elements of the copper alloy according to the embodiment of the present invention are described below by referring to the reasons of incorporation (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. If the Ni content is less than 0.1%, even by an optimal production method, the absolute amount of a fine Ni compound of 0.1 µm or less or of Ni contained as a solid solution becomes insufficient. 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, stress relaxation resistance characteristic and press punchability, and these are described below. Also, in order to introduce a dislocation density in not less than a given amount with respect to the half-value breadth of the X-ray diffraction intensity peak, which is specified in the embodiment of the present invention, it is necessary to control the conditions in the final cold rolling as described later.
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.

(Final Cold Rolling)

In order to introduce a dislocation density in not less than a given amount such that the value obtained by dividing the half-value breadth of the X-ray diffraction intensity peak from {200} plane in the copper alloy sheet surface by the peak height is 1.0 × 10^-4 or more, the strain amount introduced in the final cold rolling is increased. That is, after setting the roll length (roll width) in the final cold rolling to 500 mm or more, a technique such as use of a small-size roll having a roll diameter of less than 80 mmφ or setting of the minimum rolling reduction (cold rolling ratio, working ratio) per pass to 20% or more is selected and used, or these techniques are used in combination.
If the roll diameter in the final cold rolling is too small, if the minimum rolling reduction per pass is too small or if the roll length is too short, there is a high possibility that the dislocation density introduced into the copper alloy sheet is insufficient. As a result, the value obtained by dividing the half-value breadth of the X-ray diffraction intensity peak from {200} plane in the sheet surface by the peak height becomes less than 1.0 × 10^-4, making little difference from the conventional copper alloy sheet with a small dislocation density, and the stress relaxation resistance characteristic and press punchability are decreased or not enhanced.
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, minimum rolling reduction per pass, and maximum rolling reduction.

(Final Annealing)

In the finish annealing, 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.
The strain relief annealing or stabilizing annealing after the final finish cold rolling is preferably performed under the conditions of a substantial temperature of 250 to 450°C × 20 to 40 seconds. By this annealing, the strain introduced in the final finish rolling can be removed. At the same time, softening of the material does not occur and reduction in the strength can be suppressed.

Examples

Working examples according to the embodiment of the present invention are described below. Copper alloy thin sheets varied in the half-value breadth (dislocation density) of the X-ray diffraction intensity peak from {200} plane in the sheet surface were produced by changing the roll diameter and minimum rolling reduction per pass in 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, shear plane ratio 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 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 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 roll diameter (mm) and minimum rolling reduction (%) per pass in this final cold rolling are shown in Table 1. Incidentally, a roll having the same roll diameter was used in all of 4 passes of the final cold rolling. Also, even though the roll diameter was changed, the roll length was set constant at 500 mm in common. After the final cold rolling, low-temperature strain relief annealing was performed under the conditions of substantial temperature of 400°C × 20 seconds to obtain a copper alloy thin sheet having a thickness of 0.25 mm.
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, shear plane ratio and stress relaxation resistance characteristic. The results obtained are shown in Table 2.

(Measurement of Half-Value Breadth)

An X-ray diffraction pattern of the copper alloy sheet sample was obtained by a normal X-ray diffraction method 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. From this pattern, the half-value breadth of the X-ray diffraction intensity-peak from {200} plane in the sheet surface was determined by the method described above. The measurement was performed at two portions and an average of the values obtained was used as the half-value breadth.

(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.

(Measurement of Burr Height)

The burr height of the copper alloy sheet sample was measured under the above-described test conditions. The sample was rated A when the burr height was 5 µm or less, rated B when the burr height was from 5 to 10 µm, and rated C when the burr height exceeded 10 µm.

(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 to the rolling direction 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.
As apparent from Table 2, in Inventive Examples 64 to 72 using a copper alloy within the composition range of the embodiment of the present invention in Table 1 (alloy Nos. 49 to 56), the copper alloy sheets are produced within preferred conditions of the production method such as roll diameter and minimum rolling reduction per pass in final cold rolling. Accordingly, in Inventive Examples of Table 2, the copper alloy sheet has a dislocation density such that the value obtained by dividing the half-value breadth of the X-ray diffraction intensity peak from {200} plane in the sheet surface by the peak height is 1.0 × 10^-4 or more.
In addition, it is presumed that in Inventive Examples, since the composition range is appropriate and the copper alloy sheet is 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 64 to 72 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 and further have, as mechanical properties, a 0.2%-proof stress of 500 MPa or more and excellent press punchability. That is, the copper alloy sheets of Inventive Examples are assured of high electrical conductivity and strength and excellent particularly in the press punchability and stress relaxation resistance characteristic, revealing that the copper alloy sheet satisfies all of these properties at the same time.
In Inventive Example 67 of Table 2 (alloy No. 51 of Table 1), the Ni content is the lower limit of 0.1%; in Inventive Example 68 (alloy No. 52 of Table 1), the Ni content is the upper limit of 3.0%; in Inventive Example 69 (alloy No. 53 of Table 1), the Sn content is the lower limit of 0.01%; in Inventive Example 70 (alloy No. 54 of Table 1), the Sn content is the upper limit of 3.0%; in Inventive Example 71 (alloy No. 55 of Table 1), the P content is the lower limit of 0.01%; and in Inventive Example 72 (alloy No. 56 of Table 1), the P content is the upper limit of 0.3%.
Also, in Inventive Example 65 where the production conditions such as roll diameter and minimum rolling reduction per pass in final cold rolling are on the lower limit side, the stress relaxation resistance characteristic and strength are relative lower than in Inventive Example 64.
In Comparative Examples 75 to 79 of Table 2, the copper alloy sheets are produced within preferred conditions of the production method such as roll diameter and minimum rolling reduction per pass in final cold rolling. Accordingly, in Comparative Examples 75 to 79, the copper alloy sheet has a dislocation density such that the value obtained by dividing the half-value breadth of the X-ray diffraction intensity peak from {200} plane in the sheet surface by the peak height is 1.0 × 10^-4 or more. Nevertheless, in these Comparative Examples, due to use of alloy Nos. 59 to 63 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 press punchability is significantly inferior to Inventive Examples.
In Comparative Example 75 of Table 2, the Ni content deviates below the lower limit (alloy No. 59 of Table 1), as a result, the strength and stress relaxation resistance characteristic are low and the press punchability is also poor due to low strength. In Comparative Example 76, the Ni content deviates above the upper limit (alloy No. 60 of Table 1) and therefore, the balance between strength and electrical conductivity is low.
In Comparative Example 77, the Sn content deviates below the lower limit (alloy No. 61 of Table 1), as a result, the strength is too low and the press punchability is also poor. In the copper alloy of Comparative Example 78, the Sn content deviates above the upper limit (alloy No. 62 of Table 1) and therefore, the electrical conductivity is low.
In Comparative Example 79, the P content deviates below the lower limit (alloy No. 63 of Table 1) and therefore, the strength, stress relaxation resistance characteristic and press punchability are low. In Comparative Example 80, the P content deviates above the upper limit (alloy No. 64 of Table 1) and therefore, cracking occurred during hot rolling, failing in characterization.
In Comparative Examples 81 and 82 of Table 2, a copper alloy within the composition range of the embodiment of the present invention in Table 1 is used (alloy Nos. 49 and 50) and other production conditions are also within the preferred range, similarly to Inventive Examples. Nevertheless, only the conditions of the final cold rolling are out of the preferred range. In Comparative Example 81, the minimum rolling reduction (%) per pass of the final cold rolling is too small, and in Comparative Example 82, the roll diameter (mm) of the final cold rolling is too large and the minimum rolling reduction (%) per pass is too small.
As a result, in Comparative Examples 81 and 82, the value obtained by dividing the half-value breadth of the X-ray diffraction intensity peak from {200} plane in the sheet surface by the peak height is less than 1.0 × 10^-4 and the dislocation density is too small. In turn, in these Comparative Examples, the press punchability is significantly poor as compared with Inventive Examples. Furthermore, the strength and stress relaxation resistance characteristic are also lower than in 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 press punchability and being excellent in other properties required for a terminal or a connector, such as strength and stress relaxation resistance characteristic, 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	49	0.7	1.2	0.05	0.02	0.05	-	-	-	-	-
	50	1.2	0.7	0.07	0.02	-	-	0.01	-	-	-
	51	0.1	1.2	0.05	0.02	0.05	-	-	-	-	-
	52	3.0	1.2	0.05	0.02	-	0.01	-	-	-	-
	53	0.7	0.01	0.05	0.02	0.05	-	-	0.01	-	-
	54	0.5	3.0	0.04	0.02	-	-	0.01	-	-	-
	55	1.2	0.7	0.01	0.02	-	-	-	0.01	-	-
	56	1.2	0.7	0.3	0.02	-	0.01	-	-	-	-
Comparative Example	59	0.04	1.2	0.05	0:02	0.05	0.01	-	-	-	-
	60	3.2	1.0	0.05	0.02	-	-	0.01	-	-	-
	61	0.7	-	0.05	0.02	0.05	-	-	-	-	-
	62	0.7	3.2	0.05	0.02	-	0.01	-	0.01	-	-
	63	0.7	1.2	0.004	0.02	0.05	-	-	-	-	-
	64	0.7	1.2	0.35	0.02	-	-	-	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		Texture of Copper Alloy Sheet	Properties of Copper Alloy Sheet
Class	No.	Alloy No. of Table 1	Roll Diameter (mm)	Minimum Rolling Reduction (%/1 pass)	Half-Value Breadth of X-Ray Diffraction (200) Plane Intensity Peak/Peak Height (× 10^-4)	Electrical Conductivity (%IACS)	Tensile Strength (MPa)	0.2%-Proof Stress (MPa)	Stress Relaxation Ratio (%)	Press Punchability
Inventive Example	64	49	60	30	1.6	35	595	575	7	A
	65	49	70	20	1.2	36	570	555	9	A
	66	50	60	20	1.2	37	565	545	8	A
	67	51	70	20	1.1	40	540	525	9	A
	68	52	60	20	1.5	34	585	570	7	A
	69	53	60	20	1.1	44	520	505	9	A
	70	54	50	40	2.0	30	640	620	7	A
	71	55	60	20	1.2	43	520	505	9	A
	72	56	50	40	1.6	32	620	600	8	A
Comparative Example	75	59	60	20	1.1	39	505	485	11	B
	76	60	50	20	1.4	30	570	555	7	A
	77	61	60	20	1.2	43	490	470	9	B
	78	62	60	30	1.7	25	640	620	7	A
	79	63	60	20	1.0	41	500	480	11	B
	80	64	-	-	-	-	-	-	-	-
	81	49	60	10	0.90	36	545	530	11	C
	82	50	100	10	0.71	38	530	515	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 press punchability and being excellent also in other properties required for a terminal or a connector, such as strength and stress relaxation resistance characteristic, 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 a value obtained by dividing a half-value breadth of a X-ray diffraction intensity peak from {200} plane in the sheet surface by a height of the peak is 1.0 × 10^-4 or more, and wherein the copper alloy sheet has, as terminal/connector properties, an electrical conductivity of 30% IACS or more.