JP2011214036A - Cu-Zn ALLOY STRIP FOR TAB MATERIAL FOR CONNECTING CELLS - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Cu-Zn alloy suitable for a battery connection tab material having good repeated bendability and weldability.
SOLUTION: Cu-Zn used for a charging battery tab containing 2 to 12% by mass of Zn, the balance being copper and inevitable impurities, and having a twin boundary frequency of 40 to 70% Alloy strip. This alloy strip may further contain 0.1 to 0.8% by mass of Sn, the aspect ratio of crystal grain size in the rolling parallel direction and the perpendicular direction may be 0.3 to 0.7, Ni, You may contain 0.005-0.5 mass% of at least 1 type or more in total among Mg, Fe, P, Al, and Ag. A Cu—Zn alloy Sn-plated alloy strip obtained by subjecting the Cu—Zn alloy to 0.3 to 2 μm of Sn plating is also provided.
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Description

  The present invention relates to a Cu—Zn alloy strip used for 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 electrical resistance to ensure connection. In order to accommodate a plurality of batteries having tabs welded to the electrodes in a compact case, the tabs are subjected to severe bending. Therefore, the material used for the tab is required to have good weldability and repeated bendability with the electrode.

  When connecting a tab with a stainless steel plate or mild steel plate using a series-type resistance welder, if the conductivity is too high, excessive current flows through the tab and leads to melting. In particular, a copper alloy having a low electrical conductivity has been used. However, in response to the recent rise in nickel prices, there is a movement to change the metal material from conventional nickel to a copper alloy for cost reduction. An example of a copper alloy suitable as a tab material is a Cu—Ni—Sn alloy. However, the weldability and repeated bendability of the Cu—Ni—Sn alloy are not sufficient, and improvement has been desired.

  The present invention is directed to a Cu—Zn-based alloy suitable for a battery connection tab material having good repeated bendability and weldability.

The present invention is a Cu-Zn-based alloy suitable for a battery tab material satisfying good repeated bendability and weldability by adjusting the manufacturing process and adjusting the aspect ratio of crystal grain size and the twin boundary frequency. Specifically, it is as follows.
(1) A charging battery tab characterized in that it contains 2 to 12% by mass of Zn, and the balance is a copper alloy composed of copper and inevitable impurities, and has a twin boundary frequency of 40 to 70%. Cu-Zn alloy strip used.
(2) The Cu—Zn alloy strip according to (1), further containing 0.1 to 0.8% by mass of Sn.
(3) The Cu—Zn alloy strip according to (1) or (2), wherein the aspect ratio of the crystal grain size in the rolling parallel direction and the perpendicular direction is 0.3 to 0.7.
(4) The Cu—Zn according to any one of (1) to (3), further containing 0.005 to 0.5 mass% in total of at least one of Ni, Mg, Fe, P, Al, and Ag. Alloy strip.
(5) A Cu—Zn alloy Sn-plated alloy strip obtained by subjecting the Cu—Zn alloy according to any one of (1) to (4) to Sn plating of 0.3 to 2 μm.
The Cu—Zn-based alloy of the present invention has good repeated bendability and weldability and is suitable as a battery tab material.

It is the schematic which shows the aspect ratio of a crystal grain diameter.

(Cu-Zn alloy strip)
(A) Zn Concentration The alloy of the present invention is a copper alloy containing 2 to 12% by mass (hereinafter expressed as%), preferably 3 to 10% Zn, with the balance being copper and inevitable impurities. If the Zn content is less than 2%, the strength required for the tab becomes insufficient. Moreover, since the electrical conductivity becomes too high, the tab is melted at the time of welding, or the current is difficult to flow through the stainless steel plate or the mild steel plate on the electrode side, so that the weldability is deteriorated. If Zn exceeds 12%, the component of the oxide film formed on the surface becomes Zn-rich and the weldability deteriorates.
(B) Sn concentration Sn has an effect of promoting work hardening during rolling and contributes to an increase in strength. Therefore, the alloy of the present invention may further contain 0.1 to 0.8%, preferably 0.2 to 0.6% of Sn. If Sn is less than 0.1%, the desired effect cannot be obtained, and if Sn exceeds 0.8%, the electrical conductivity decreases.
(C) Additive elements other than those described above The alloy of the present invention contains at least one of Ni, Mg, Fe, P, Al and Ag for the purpose of improving the strength, heat resistance, stress relaxation resistance, etc. of the alloy. A total of 0.005 to 0.5% can be added. If the total amount is less than 0.005%, desired properties cannot be obtained. If the total amount exceeds 0.5%, desired properties can be obtained, but conductivity and bending workability are deteriorated.

(D) Twin boundary frequency When the twin boundary frequency is less than 40%, repeated bendability deteriorates. Since it is industrially difficult to adjust the twin boundary frequency to exceed 70% in the component system of the present invention, the upper limit is set to 70%.
The twin boundary refers to the boundary between two crystals in a twin relationship, and the two crystals are mirror-symmetrical with respect to this boundary. According to the corresponding grain boundary theory, the twin boundary corresponds to the grain boundary of Σ3. Since twin boundaries have good atomic alignment between the boundaries, non-uniform deformation is unlikely to occur near the boundaries, and cracks and wrinkles based on the vicinity of the boundaries are less likely to occur during bending deformation.
The twin boundary frequency refers to the ratio of twin boundaries in all boundaries including the grain boundaries and twin boundaries. The generation frequency of twins is related to the stacking fault energy. The lower the stacking fault energy, the higher the twin boundary frequency.
The composition of the present invention has a small amount of Zn in order to satisfy weldability and conductivity as compared with brass (Cu 65%, Zn 35%). Since the stacking fault energy becomes higher as the Zn content decreases, the twin boundary frequency becomes lower than that of brass, and it is difficult to obtain a high twin boundary frequency exceeding 40% in a normal process. In order to increase the twin boundary frequency in the alloy of the present invention, the inventor conducted an intensive investigation on the relationship between the manufacturing process and the twin boundary frequency, and as a result, the conditions of the cold rolling performed before the final annealing are important. It turned out to be. In rolling, the material is repeatedly passed (passed) between a pair of rolls, and finished to a target plate thickness. In this series of passes, in the last pass and the pass before the last pass, the finishing degree per one pass is increased and the finishing speed is increased, and then the final annealing is performed under appropriate conditions. And found that a high twinning boundary frequency exceeding 40% can be obtained.

  Here, as a method for obtaining the twin boundary frequency, for example, there is an EBSP (Electron Backscattering Pattern) method using FESEM (Field Emission Scanning Electron Microscope). This method is a method of analyzing crystal orientation based on a backscattered electron diffraction pattern (Kikuchi pattern) generated when an electron beam is obliquely applied to a sample surface. After analyzing the crystal orientation by this method, the orientation difference between adjacent crystal orientations can be obtained, and the ratio of the random grain boundaries and the corresponding grain boundaries (grain boundary character distribution) can be determined. Since the twin boundary corresponds to a Σ3-corresponding grain boundary, the twin boundary frequency is calculated by (total length of corresponding grain boundary Σ3) / (total length of crystal grain boundary) × 100. The crystal grain boundary means a boundary where the orientation difference between adjacent crystal grains is 15 ° or more, and does not include a small-angle grain boundary or a sub-grain boundary.

(E) Aspect ratio of crystal grain size In the present invention, in order to further improve repeated bendability, as a result of research on the metal structure and repeat bendability, the metal structure after final annealing is controlled to uniform equiaxed grains. It became clear that repeated bendability was improved by doing. Since the final product is cold-rolled by 30 to 60%, the aspect ratio b / a and d / c of the crystal grain size in the rolling parallel direction and the perpendicular direction in the final product can be improved in order to improve the repeated bendability. Is preferably controlled to 0.3 to 0.7. More preferably, b / a is 0.3 to 0.5, and d / c is 0.5 to 0.7. FIG. 1 is a schematic diagram of crystal grains observed in a sample cross section.
When the aspect ratio b / a and / or d / c of the crystal grain size in the direction parallel to and perpendicular to the rolling is less than 0.3 or more than 0.7, the strain is locally concentrated during repeated bending, and the shear band Are formed, and the repeated bendability deteriorates.
Since the composition of the alloy strip of the present invention has a smaller amount of Zn than brass, the metal structure after recrystallization tends to be mixed grains. In addition, when recrystallization is completed in a halfway pass during hot rolling, coarse crystal grains that extend in the rolling direction remain, which hinders equalization of the metal structure. Therefore, in order to obtain uniform equiaxed grains at the time of final annealing, the end temperature of hot rolling is controlled and the metal structure is equiaxed by dynamic recrystallization by rolling at an appropriate working degree, and then multiple times. It is necessary to repeat rolling and annealing.
The average crystal grain size of the present invention is preferably 12 μm or less, more preferably 7 μm or less.

(Characteristic)
When the tensile strength (JISZ2241) of the alloy strip of the present invention is usually 420 MPa or more, preferably 450 MPa or more, more preferably 500 MPa or more, it can be suitably used as a tab material.
The electrical conductivity (JISH0505) of the alloy strip of the present invention can be suitably used as a tab material when it is 70% IACS or less, more preferably 60% IACS or less. If it exceeds 70% IACS, melting damage occurs during resistance welding, or a sufficient current does not flow through the metal plate on the electrode side, resulting in poor weldability.
The repeated bendability of the alloy strip of the present invention is preferably 3.0 times or more, and more preferably 3.2 times or more, as a tab material.

The thickness of the alloy strip of the present invention is not particularly limited, but is preferably 0.03 to 1.00 mm, more preferably 0.12 to 0.6 mm, for example, 0.15 mm. Satisfies strength and weldability as battery connection tab material.
The alloy strip of the present invention can be subjected to Sn plating of 0.3 to 2 μm to form a Cu—Zn-based alloy Sn-plated alloy strip. The Sn plating method can be performed by a conventional method, and the weldability is improved by applying Sn plating of about 0.3 to 2 μm.

(Production method)
The manufacturing process of the Cu-Zn alloy strip of the present invention is basically the same as that of a normal alloy strip, and after multiple casting, homogenization annealing and hot rolling, face cutting, multiple cold rolling, Manufactured by repeated annealing.
However, in order to manufacture the alloy strip of the present invention, it is necessary to control the manufacturing conditions so that the twin boundary frequency is within the range of the present invention.
The average working degree of the final pass of the cold rolling before the final annealing and the pass immediately before the final pass is suitably 32 to 40%, and the rolling speed is suitably 220 to 350 mpm. When the degree of work is lower than the above range or the rolling speed is slow, the twin boundary frequency becomes low and the repeated bendability deteriorates. When the degree of work is high or the rolling speed is high, the edge cracks (edge cracks) occur at the edge of the material, and the productivity is significantly reduced, for example, the material breaks during rolling.
As conditions for the final annealing, a temperature of 660 to 760 ° C. and an annealing time of 5 to 20 s are appropriate. When the temperature is lower than the above-mentioned range or the time is short, the final annealing is insufficient, so the twin boundary frequency is lowered and the repeated bendability is deteriorated. When the final annealing temperature is high or the time is long, the crystal grains are significantly coarsened, the twin boundary frequency is lowered, and the repeated bendability is deteriorated.
Repeatability can be further improved by adjusting the following manufacturing conditions.
The end temperature of hot rolling is preferably 600 to 750 ° C., and the final workability is preferably 30 to 55%. If these are out of the range, the aspect ratio is out of the preferred range in the present invention, and the repeated bendability deteriorates.
The intermediate annealing temperature is preferably 680 to 780 ° C. for 5 to 20 seconds. If the annealing condition is outside the above range, the aspect ratio is outside the preferable range in the present invention, and the repeated bendability deteriorates.

The measurement conditions performed in the examples are as follows.
[Twinning Boundary Frequency] Each copper alloy plate was measured by an EBSP (Electron Backscattering Pattern) method using FESEM (Field Emission Scanning Electron Microscope).
[Aspect Ratio] For each copper alloy plate, the crystal grain size of the cross section parallel to the rolling direction and the cross section perpendicular to the rolling direction was measured and calculated according to the cutting method of JISH0501. In the cross section parallel to the rolling direction shown in FIG. 1, the crystal grain size is measured in two directions, a direction parallel to the rolling surface and a direction perpendicular to the rolling surface. The measured value in the perpendicular direction was taken as the minor axis b. In the cross section perpendicular to the rolling direction, the crystal grain size is measured in two directions, a direction parallel to the rolling direction and a direction perpendicular to the rolling direction, and the measured value in the parallel direction is taken as the major axis c and the direction perpendicular to the rolling direction. The measured value was taken as the minor axis d.
[Repeated bendability] Four final product 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 direction perpendicular to the longitudinal direction of the test piece is set. The bending axis was 180 ° bending and then bending 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.

[Weldability] A 0.3 mm mild steel plate and a copper alloy were spot welded at two points with a pressurizing force of 30 N, a welding current of 3.5 kA, and a welding time of 10 msec using a series spot welder. A tensile test was carried out with a precision load measuring machine manufactured by Aiko Engineering, and the welding strength was measured. If the weld strength was 35N or more, the weldability was judged as good, and if the weld strength was less than 35N, it was evaluated as poor.
[Tensile strength] Each copper alloy plate was subjected to a tensile test in a direction parallel to the rolling direction, and determined according to JISZ2241.
[Conductivity] For each copper alloy plate,% IACS was calculated from the volume resistivity determined by the four-terminal method using a double bridge device in accordance with JISH0505.

Example 1
After electrolytic copper was melted in a high frequency induction furnace and the surface of the molten metal was coated with charcoal, an alloy element was added to adjust the molten metal to a desired composition. Casting is performed at a casting temperature of 1200 ° C, and the obtained ingot is heated at 850 ° C for 3 hours, and then rolled to a plate thickness of 8 mm so that the degree of processing in the final pass of hot rolling is 35%. The end temperature was adjusted to 650 ° C. or higher. The oxidized scale formed on the surface was removed by chamfering. Then, it is processed to a plate thickness of 1.5 mm by cold rolling, subjected to intermediate annealing at 700 ° C. for 12 seconds, and in cold rolling to 0.35 mm, the final pass and the pass before the final pass The average working degree was adjusted to 35%, and the rolling speed of both the final pass and the pass before the final pass was 250 m / min. After this cold rolling, final annealing was performed at 680 ° C. for 10 seconds, and the copper alloy plate after the final annealing was cold-rolled to finish a 0.15 mm plate. Intermediate annealing and final annealing were performed in a continuous line in an ammonia decomposition gas atmosphere. Table 1 shows the test results.

(Example 2)
After melting electrolytic copper in a high-frequency induction furnace and coating the surface of the molten metal with charcoal, adjust the components by adding Zn and Sn into the molten metal so that the composition is 8.0% Zn, 0.30% Sn and Cu. Then, casting was performed at a casting temperature of 1200 ° C. The obtained ingot was heated at 900 ° C. for 3 hours and then hot-rolled to produce a copper alloy plate having a plate thickness of 8 mm, and the oxide scale generated on the surface was removed by chamfering. Then, after cold-rolling to a plate thickness of 1.5 mm and performing intermediate annealing, cold rolling was performed to a plate thickness of 0.25 mm. Further, final annealing was performed, and the copper alloy plate after the final annealing was cold-rolled to finish a 0.15 mm plate. Intermediate annealing and final annealing were performed using a continuous line in an ammonia decomposition gas atmosphere. Table 2 shows the conditions for hot rolling and intermediate annealing, conditions for cold rolling before final annealing (average working degree and rolling speed of the last pass and pass one before the final pass), final annealing conditions and test results. .

  Since Invention Examples 1 to 19 in Table 1 are within the scope of the present invention, they were alloy strips having good repeated bendability and weldability and sufficient strength. Inventive Example 20 has good repeated bendability and weldability because the amount of Sn added was relatively small, but the strength was lower than Inventive Examples 1-19. Inventive example 21 has a relatively large amount of Sn, and thus the conductivity is lower than in inventive examples 1-19. On the other hand, Comparative Example 22 had a small amount of Zn and was inferior in repeated bending and reduced in strength as compared with the inventive examples. In Comparative Example 23, the amount of Zn was large and the repetitive bendability was good, but the surface oxide film became Zn-rich, so that the weldability was deteriorated and the conductivity was also lowered.

Since Invention Examples 24-38 in Table 2 are within the scope of the present invention, they were alloy strips having good repeated bendability and weldability and sufficient strength.
Invention Example 32 has a low hot rolling end temperature, Invention Examples 33 and 34 have a low or high hot rolling final workability, Invention Examples 35 and 36 have a low or high intermediate annealing temperature, and Invention Examples 37 and 38. Is too short or too long for recrystallization annealing in intermediate annealing. Therefore, in these invention examples, the aspect ratio is out of the preferred range, and the repeated bendability is inferior to that of Invention Examples 24-31.
In Comparative Example 39, the average degree of work in the final pass of the cold rolling after the intermediate annealing and the pass before the final pass is low, and in the Comparative Example 41, the average pass is one from the final pass of the cold rolling after the intermediate annealing and the final pass. The twin boundary frequency is low because the rolling speed of the previous pass is slow. In Comparative Example 40, the average degree of work in the final pass of the cold rolling after the intermediate annealing and the pass before the final pass is too high, and in the comparative example 42, the average passability is 1 in the final pass of the cold rolling after the intermediate annealing and the final pass. Since the rolling speed of the previous pass was too high, an edge crack occurred at the edge of the material, and the material broke during the final rolling. In Comparative Examples 43 and 44, the final annealing temperature was low or high. In Comparative Examples 45 and 46, the final annealing time was short or long. Therefore, the twin boundary frequency was low, and the aspect ratio was outside the preferable specified range. For this reason, those that did not break in these comparative examples were inferior in repeatability to the invention examples.

Claims (5)

  Cu used in a battery tab for charging, characterized in that it contains 2 to 12% by mass of Zn, and the balance is a copper alloy composed of copper and inevitable impurities, and the twin boundary frequency is 40 to 70% -Zn alloy strip.   Furthermore, the Cu-Zn type alloy strip of Claim 1 containing 0.1-0.8 mass% Sn.   The Cu-Zn alloy strip according to claim 1 or 2, wherein the aspect ratio of the grain size in the rolling parallel direction and the perpendicular direction is 0.3 to 0.7.   The Cu-Zn alloy strip according to any one of claims 1 to 3, further comprising 0.005 to 0.5 mass% in total of at least one of Ni, Mg, Fe, P, Al, and Ag. .   A Cu-Zn alloy Sn-plated alloy strip obtained by subjecting the Cu-Zn alloy according to any one of claims 1 to 4 to Sn plating of 0.3 to 2 µm.

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