JP2013204109A - Cu-Zn-Sn BASED COPPER ALLOY STRIP - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Cu-Zn-Sn based copper alloy strip having satisfactory repeated bendability and fatigue resistance.SOLUTION: A Cu-Zn-Sn based copper alloy strip includes, by mass, 2.0 to 12.0% Zn and 0.1 to 1.0% Sn, and the balance copper with inevitable impurities, and, in the surface, provided that X-ray diffraction intensity from the {200} face is defined as I{200}, the X-ray diffraction intensity from the {311} face is defined as I{311}, and the X-ray diffraction intensity from the {220} face is defined as I{220}, and also, provided that the X-ray diffraction intensities from the (200), (220) and (311) faces of a pure copper powder standard sample are defined as I{200}, I{220} and I{311}, respectively, 2.5≤[I{220}/I{220}]≤3.5, 2.2≤[I{200}/I{200}+I{311}/I{311}] and also 1.5≤I{311}/I{200} are satisfied.

Description

  The present invention relates to a copper alloy strip suitably used for applications requiring repeated bendability such as a battery connection tab material.

A rechargeable battery such as a nickel cadmium battery or a lithium battery is used for a portable electronic device such as a video camera. In addition, demand for electric vehicles and hybrid vehicles has increased in response to the recent trend of reducing environmental impact, and the development of in-vehicle lithium-ion secondary batteries is also progressing. These rechargeable batteries are used by electrically connecting a plurality of single-structure batteries in a state of being close to each other in order to ensure a necessary electric capacity. Metal parts used for battery connection are called current collecting tabs or tabs, and are often welded to battery electrodes by resistance welding using heat generated by electric resistance in order to achieve reliable connection (Patent Documents). 1).
In order to house a plurality of batteries in which the tabs are welded to the electrodes in a compact manner, the tabs are subjected to severe bending. Therefore, the material used for the tab is required to have good weldability with the electrode and repeated bendability.

  When connecting a stainless steel plate or mild steel plate constituting an electrode and a tab using a series resistance welding machine, if the conductivity of the tab is too high, an excessive current flows through the tab, resulting in melting damage. For this reason, nickel or a copper alloy having a relatively low conductivity has been used for the conventional tab.

Patent Publication 2004-134197

However, in response to the recent rise in nickel prices, there is a move to change the tab material from nickel to copper alloy to reduce costs. A copper alloy suitable as a tab material includes a Cu—Ni—Sn alloy, but the Cu—Ni—Sn alloy has insufficient weldability and repeated bendability, and improvement of these characteristics has been desired. .
Accordingly, an object of the present invention is to provide a Cu—Zn—Sn based copper alloy strip having good repeated bendability and fatigue resistance.

The present inventor has found that good repeatability and strength can be achieved by reducing the ratio of {220} plane and increasing the ratio of {200} plane and {311} plane.
The Cu—Zn—Sn-based copper alloy strip of the present invention contains 2.0 to 12.0% by mass of Zn and 0.1 to 1.0% by mass of Sn, with the balance being copper and inevitable impurities. , The X-ray diffraction intensity from the {200} plane on the surface is I {200}, the X-ray diffraction intensity from the {311} plane is I {311}, and the X-ray diffraction intensity from the {220} plane is I { 220}, and the X-resolved diffraction intensities from the (200), (220), (311) planes of the pure copper powder standard sample were I ₀ {200}, I ₀ {220}, I ₀ {311}, respectively. Then, 2.5 ≦ [I {220} / I ₀ {220}] ≦ 3.5, 2.2 ≦ [I {200} / I ₀ {200} + I {311} / I ₀ {311}] And 1.5 ≦ I {311} / I {200}.

Furthermore, it is preferable to contain 0.005-0.8 mass% in total of 1 or more types chosen from the group of Ni, Mg, Fe, P, Mn, and Cr.
The crystal grain size determined by the cutting method is preferably 15 μm or less.
It is preferable to have a reflow Sn plating layer on the surface.

  According to the present invention, a Cu—Zn—Sn based copper alloy strip having good repeated bendability and fatigue resistance can be obtained.

It is a figure which shows the state which carried out resistance welding of the tab piece using the alloy strip of this invention with the electrode of a single battery. It is a figure which shows the method of a UN-proof test (fatigue test).

Hereinafter, the Cu—Zn—Sn based copper alloy strip according to the embodiment of the present invention will be described. In the present invention, “%” means “% by mass” unless otherwise specified.
As shown in FIG. 1, the copper alloy strip of the present invention is cut into, for example, a strip-shaped tab piece 10 and connected (welded) to the electrode 20a of the unit cell 20 by resistance welding. In FIG. 1, electrodes having different polarities of the individual batteries 20 are electrically connected by a tab piece 10 and connected in series.

First, the reasons for limiting the composition of the copper alloy strip will be described.
(Zn)
The Zn content is set to 2.0 to 12.0 mass%, preferably 2.0 to 9.0 mass%. If the Zn content is less than 2.0%, the strength required for the tab will be insufficient, the electrical conductivity will be too high, and the tab will melt during welding, or current will flow through the stainless steel plate or mild steel plate on the electrode side. Since it becomes difficult, weldability deteriorates. If Zn exceeds 12.0%, not only does Zn vaporize during welding, the material becomes brittle and weldability deteriorates, but also the conductivity becomes low and it is difficult to achieve high performance of the battery.
(Sn)
The Sn content is 0.1 to 1.0% by mass, preferably 0.1 to 0.5% by mass. If Sn is less than 0.1%, sufficient strength cannot be obtained. When Sn exceeds 1.0%, the electrical conductivity decreases.
(Additive elements other than the above)
For the purpose of improving the strength, heat resistance, stress relaxation resistance, etc. of the alloy, the above alloy strip further contains at least 0.005 in total selected from the group consisting of Ni, Mg, Fe, P, Mn, and Cr. It can contain -0.8 mass%. If the total amount of these elements is less than 0.005%, the desired characteristics cannot be obtained. If the total amount exceeds 0.8%, the desired characteristics can be obtained, but the conductivity and bending workability deteriorate.

Next, the rules for the texture of the copper alloy strip will be described. As a result of investigating and analyzing the relationship between the degree of integration of each crystal plane and repeated bendability when the Cu—Zn—Sn based copper alloy strip is produced under various conditions, the following knowledge has been obtained. It was.
First, Cu—Zn—Sn-based copper alloy strips are usually manufactured by repeating cold rolling and annealing several times (usually about twice) after hot rolling and chamfering, and finally finish rolling. The repeated bendability is best at the final annealing, and the repeatability decreases with an increase in the degree of finish cold rolling. On the other hand, the strength of the copper alloy strip is improved with an increase in the degree of finish cold rolling.
Therefore, in order to achieve both good repeatability and strength, it is necessary not to make the degree of finish cold rolling too high. And since I (220) increases and I (200) and I (311) decrease with the increase in the finish rolling work degree, the ratio of {220} plane is reduced as follows, and { The ratio of the 200} plane and the {311} plane is increased. The degree of finish rolling is preferably 15 to 50%.
Further, when the temperature rising rate during annealing is increased, more {311} planes, which are correct grains, are grown compared to {200} planes, and distortion in the alloy strip is reduced, so that repeated bendability and fatigue resistance are increased. Improved characteristics.
In addition, if the strength (tensile strength) of the Cu—Zn—Sn-based copper alloy strip is controlled to the texture as described above and passes the UN resistance test described later, the tensile strength is 320 MPa or more. no problem. In particular, 400 MPa or more is preferable.

That is, the X-ray diffraction intensity from the {200} plane on the surface is I {200}, the X-ray diffraction intensity from the {311} plane is I {311}, and the X-ray diffraction intensity from the {220} plane is I {220}, and X solution diffraction intensities from the (200), (220), (311) planes of the pure copper powder standard sample are I ₀ {200}, I ₀ {220}, I ₀ {311}, respectively. When
The Cu—Zn—Sn based copper alloy strip of the present invention has 2.5 ≦ [I {220} / I ₀ {220}] ≦ 3.5, 2.2 ≦ [I {200} / I ₀ {200}. The texture is controlled to satisfy + I {311} / I ₀ {311}] and 1.5 ≦ I {311} / I {200}.

When [I {220} / I ₀ {220}] is less than 2.5, the workability of finish cold rolling is not sufficient, and the strength of the copper alloy strip is lowered. When [I {220} / I ₀ {220}] exceeds 3.5, the workability of finish cold rolling becomes too high, and the repeated bendability decreases.
When [I {200} / I ₀ {200} + I {311} / I ₀ {311}] is less than 2.2, the degree of finish cold rolling becomes too high, and repeated bendability is increased. descend. In addition, the upper limit of [I {200} / I ₀ {200} + I {311} / I ₀ {311}] is, for example, about 4.0 due to manufacturing.

  In addition, as described above, in order to produce a Cu-Zn-Sn-based copper alloy strip, after hot rolling and chamfering, cold rolling and annealing are repeated several times. , The {311} plane that is sized is grown more than the {200} plane, the strain in the alloy strip is reduced, and the repeated bendability and fatigue resistance are further improved. If 1.5 ≦ I {311} / I {200}, the ratio of {311} planes in the texture is sufficiently large, which is preferable. In order to satisfy 1.5 ≦ I {311} / I {200}, the temperature rising rate during annealing is preferably set to 20 ° C./sec or more, for example. Conventionally, the temperature increase rate during annealing is usually 5 to 15 ° C./sec.

The thickness of the Cu—Zn—Sn copper alloy strip of the present invention is not particularly limited, but if it is 0.4 mm or less, the weight can be reduced when it is used for battery tabs and the like, and the repeated bendability is further increased. Since it improves, it is preferable.
In addition, a reflow Sn plating layer having a thickness of 5 μm or less may be provided on one side or both sides of the Cu—Zn—Sn copper alloy strip of the present invention. For the reflow Sn plating layer, the surface of the Cu—Zn—Sn-based copper alloy strip is subjected to a known electric Sn plating, or the above-mentioned electric Sn plating is applied on a 0.1 to 1.0 μm Cu base plating. Thereafter, it can be formed by a reflow process that maintains the melting temperature of Sn or higher. Even when a reflow treatment with a thickness of 5 μm or less is performed, the degree of texture accumulation (I {220}, etc.) and repeated bendability of the copper alloy strip described above do not change.

The Cu—Zn—Sn-based copper alloy strip of the present invention is usually manufactured by repeatedly rolling cold rolling and annealing several times (usually about twice) after hot rolling and chamfering, and finally finish rolling. Can do. The repeat bendability is best at the final annealing, and the repeat bendability decreases as the workability of finish cold rolling increases.
Furthermore, as described above, in order to satisfy 1.5 ≦ I {311} / I {200}, the temperature increase rate during annealing is preferably set to 20 ° C./sec or more. The upper limit of the rate of temperature increase during annealing is not particularly specified, but is, for example, about 35 ° C./sec.
In addition, it is preferable that the temperature at the time of completion | finish of hot rolling shall be 600-750 degreeC, for example.
Moreover, it is preferable that the highest temperature of the material at the time of annealing described above after hot rolling is 900 ° C. or less. When the maximum temperature of the material during annealing exceeds 900 ° C., the crystal grain size obtained by the cutting method exceeds 15 μm, and I {311} / I {200} is less than 1.5, resulting in poor repeatability. There is a case.

Samples of Examples and Comparative Examples were prepared as follows.
Using copper as a raw material, a copper alloy having the composition shown in Table 1 was melted using an atmospheric melting furnace and cast into an ingot. This ingot was hot-rolled to a plate thickness of 10 mm at 600 to 750 ° C., then face chamfered, cold rolling and annealing were repeated a plurality of times, and finally finished rolling was performed. Example 16 is a plate after finish rolling. Samples were manufactured with a thickness of 0.4 mm, and a thickness of 0.15 mm after finish rolling. The furnace temperature during annealing was set to 650 to 1000 ° C., and the annealing time was set to 15 to 110 seconds. When slowing the rate of temperature rise during annealing, the furnace temperature was lowered and the annealing time was lengthened. On the other hand, when increasing the heating rate during annealing, the furnace temperature was increased and the annealing time was shortened. In addition, when the sample was put into the furnace, a K thermocouple was brought into contact with the sample, and the highest temperature of the material during annealing was measured.
The total workability of cold rolling was 98%, and the workability of finish rolling and the rate of temperature increase during annealing were as shown in Table 1.

Furthermore, for Example 17, both sides of the obtained sample were subjected to pretreatment, Cu base plating (thickness 0.5 μm), and Sn plating (thickness 1.5 μm) in this order by the following method. Next, the Sn plating layer was reflowed.
Pretreatment: The sample was pickled with a 10% by mass sulfuric acid-1% by mass hydrogen peroxide solution to remove the surface oxide film. Electrolytic degreasing was performed using a sample as a cathode in an alkaline aqueous solution (current density: 7.5 A / dm ² , degreasing agent: sodium hydroxide 10 g / L, sodium carbonate 30 g / L, sodium metasilicate 7 g / L, remaining water, Temperature: 80 ° C., time 60 seconds). Next, it pickled using 10 mass% sulfuric acid aqueous solution.
Cu plating; bath composition: sulfuric acid 60 g / L, copper sulfate 200 g / L, remaining water, plating bath temperature: 25 ° C., current density: 5.0 A / dm ²
Sn plating; bath composition: sulfuric acid first tin 40 g / L, sulfuric acid 60 g / L, cresol sulfonic acid 40 g / L, gelatin 2 g / L, β-naphthol 1 g / L, remaining water, plating bath temperature: 20 ° C., current density : 1.5 A / dm ²
Measurement of Cu plating thickness and Sn plating thickness; plating electrolysis time (in the case of electrolysis time of 2 minutes, the thickness of the Cu layer before reflow treatment was 0.8 μm, and the thickness of the Sn layer was about 1 μm).
Reflow treatment: The sample after Sn plating was inserted into a heating furnace adjusted to 400 ° C. and the atmosphere gas to nitrogen (oxygen 1 vol% or less) for 5 to 30 seconds and cooled with water.

<X-ray diffraction intensity>
The X-ray diffraction intensity I of the {200}, {311}, and {220} planes of the surface of the obtained sample was measured. For the measurement, RINT 2500 made by Rigaku was used, the X-ray irradiation conditions were a Co tube, tube voltage 25 KV, tube current 20 mA. Similarly, {200} of the pure copper powder standard sample, {311}, the X-ray diffraction intensity _{I 0} of the surface were measured.
<Crystal grain size>
The crystal grain size of the rolled parallel section was determined by the cutting method specified in JIS-H0501.
<Tensile strength (TS)>
The tensile strength (TS) in a direction parallel to the rolling direction was measured by a tensile tester according to JIS-Z2241. Table 1 shows values obtained by averaging the tensile strengths measured in the direction parallel to the rolling direction.

<UN resistance test (fatigue resistance)>
A UN resistance test was conducted by the method shown in FIG. 2 to evaluate fatigue resistance. The UN resistance test is a type of fatigue test. After the unit cells 20 are arranged in three rows (in series) × two steps (in parallel) and the sample (tab piece) 10 is welded to the electrode 20a as shown in FIG. The outermost tab piece 10 is soldered 32 to the circuit board 30. The circuit board 30 is connected to the connector 40, and the whole is accommodated in the case 50. The case 50 has an amplitude of 0.8 mm in the X direction (the direction in which the unit cells 20 are connected in series), the Y direction (the direction in which the unit cells 20 are connected in parallel), and the Z direction (the direction perpendicular to the XY direction). Vibration frequency: 7.0 to 200 Hz, sweep time: 7.5 min × 12 cycles (total 90 min). The vibration direction is only one of the X, Y, and Z directions, and the vibration frequency is not simultaneously vibrated in a plurality of directions. The vibration frequency is proportional to time, and the vibration frequency is increased or decreased within the above range.
Thus, the test was conducted and evaluated according to the following criteria. If evaluation is (circle), it is good.
○: No tab break or crack after test ×: Tab break or crack after test

<Repeatability>
Four test pieces having a thickness of 0.15 mm, a width of 10 mm, and a length of 40 mm are prepared so that the longitudinal direction is parallel to the rolling direction, and the test piece is bent 180 ° with the direction perpendicular to the longitudinal direction of the test piece as the bending axis. After performing, it was bent back. This was taken as one time and repeated bending until the sample broke, and the average number of times of breaking (repeating bending) of four samples was determined. Evaluation was made according to the following criteria. If the evaluation is で あ れ ば to △, there is no practical problem.
A: The number of repeated bending exceeds 3 times
○: The number of repeated bending is 2 times or more and less than 3 times
Δ: The number of repeated bendings is 2 ×: The number of repeated bendings is less than 2

  The obtained results are shown in Table 1.

As is apparent from Table 1, 2.5 ≦ [I {220} / I ₀ {220}] ≦ 3.5, 2.2 ≦ [I {200} / I ₀ {200} + I {311} / In each example satisfying I ₀ {311} and 1.5 ≦ I {311} / I {200}, both fatigue resistance and repeated bendability were excellent.

On the other hand, in the case of Comparative Examples 1, 5, and 6 in which the degree of finish cold rolling exceeds 50%, [I {200} / I ₀ {200} + I {311} / I ₀ {311}] is 2 Less than 2 and the bendability repeatedly decreased.
In Comparative Examples 2 and 3 in which the temperature rising rate during annealing was less than 20 ° C./sec, I {311} / I {200} was less than 1.5, and the fatigue resistance was deteriorated.
In the case of Comparative Example 4 where the finish cold rolling was not performed and in the case of Comparative Example 7 where the degree of finish cold rolling was less than 15%, [I {220} / I ₀ {220}] was 2.5. The fatigue resistance was inferior.
In the case of Comparative Example 8 where the rate of temperature increase during annealing is less than 20 ° C./sec and the degree of finish cold rolling is less than 15%, I {311} / I {200} is less than 1.5, [I {220} / I ₀ {220}] was less than 2.5, and both fatigue resistance and repeated bendability were inferior.
In the case of Comparative Example 9 in which the maximum temperature of the material during annealing exceeded 900 ° C., the crystal grain size after finish rolling was larger than 15 μm, and I {311} / I {200} was less than 1.5. The repeated bendability was poor.

10 Tab piece 20 Single battery 20a Electrode

The present inventor has found that good repeatability and strength can be achieved by reducing the ratio of {220} plane and increasing the ratio of {200} plane and {311} plane.
The Cu—Zn—Sn-based copper alloy strip of the present invention contains 2.0 to 12.0% by mass of Zn and 0.1 to 1.0% by mass of Sn, with the balance being copper and inevitable impurities. The crystal grain size determined by the cutting method is 15 μm or less, the X-ray diffraction intensity from the {200} plane on the surface is I {200}, and the X-ray diffraction intensity from the {311} plane is I {311} X-ray diffraction intensity from the {220} plane is I {220}, and X solution diffraction intensity from the (200), (220), (311) plane of the pure copper powder standard sample is I ₀ {200}, respectively. , I ₀ {220}, I ₀ {311}, 2.5 ≦ [I {220} / I ₀ {220}] ≦ 3.5, 2.2 ≦ [I {200} / I ₀ { 200} + I {311} / I ₀ {311}] and 1.5 ≦ I {311} / I {200}.

Furthermore, it is preferable to contain 0.005-0.8 mass% in total of 1 or more types chosen from the group of Ni, Mg, Fe, P, Mn, and Cr .
It is preferable to have a reflow Sn plating layer on the surface.

Claims (4)

Containing 2.0-12.0 mass% Zn, 0.1-1.0 mass% Sn, the balance consisting of copper and inevitable impurities,
The X-ray diffraction intensity from the {200} plane on the surface is I {200}, the X-ray diffraction intensity from the {311} plane is I {311}, and the X-ray diffraction intensity from the {220} plane is I {220 } And the X-resolved diffraction intensities from the (200), (220), (311) planes of the pure copper powder standard sample are I ₀ {200}, I ₀ {220}, I ₀ {311}, respectively. ,
2.5 ≦ [I {220} / I ₀ {220}] ≦ 3.5, 2.2 ≦ [I {200} / I ₀ {200} + I {311} / I ₀ {311}] and 1 Cu—Zn—Sn based copper alloy strip satisfying 5 ≦ I {311} / I {200}. The Cu-Zn-Sn based copper alloy strip according to claim 1, further comprising 0.005 to 0.8 mass% in total of at least one selected from the group consisting of Ni, Mg, Fe, P, Mn and Cr. The Cu-Zn-Sn-based copper alloy strip according to claim 1 or 2, wherein the crystal grain size determined by a cutting method is 15 µm or less. The Cu—Zn—Sn-based copper alloy strip according to claim 1, which has a reflow Sn plating layer on a surface thereof.