KR20120130343A - Cu-zn alloy strip for tab material for connecting cells - Google Patents

Abstract

2 ? It is a copper alloy containing 12 mass% Zn and remainder consists of copper and an unavoidable impurity, and has a twin boundary frequency of 40? The Cu-Zn-based alloy bath having 70% has good cyclic bendability and weldability, and is suitable for a battery connection tab material for charging. This alloy bath is additionally 0.1? You may contain 0.8 mass% Sn, and the aspect ratio of the crystal grain diameter of a rolling parallel direction and a right angle direction is 0.3? 0.7 may be sufficient, and 0.005-in total at least 1 sort (s) or more of Ni, Mg, Fe, P, Al, and Ag further; You may contain 0.5 mass%. 0.3 to the Cu-Zn-based alloy; Also provided is a Cu-Zn-based alloy Sn-plated alloy bath with 2 µm Sn plating.

Description

Cu-ZN-based alloy bath for battery connection tab material {CU-ZN ALLOY STRIP FOR TAB MATERIAL FOR CONNECTING CELLS}

This invention relates to the Cu-Zn type alloy bath used for a battery connection tab material.

Rechargeable batteries, such as a nickel card battery and a lithium battery, are used for portable electronic devices, such as a video camera. In addition, demand for electric vehicles and hybrid vehicles has increased in response to recent environmental load reduction movements, and development of on-vehicle lithium ion secondary batteries is also in progress. These rechargeable batteries are used by electrically connecting a plurality of single-structure batteries in a state in which they are close to each other in order to secure a necessary electric capacity. The metal parts used for the connection of the battery are called current collector tabs or tabs, and are often welded to the electrode of the battery by resistance welding using heat generation by electrical resistance in order to ensure connection. In order to accommodate a plurality of batteries in which the tabs are welded to the electrodes in a compact case, the tabs are subjected to severe bending. Therefore, the material used for a tab requires favorable weldability and repeatable bendability with an electrode.

When connecting a tap with a stainless steel plate or a mild steel plate using a series resistance welding machine, if the electrical conductivity is too high, excessive current flows to the tap and leads to melting. Therefore, conventional taps have relatively low conductivity. Copper alloys were used. However, in order to reduce the cost by accommodating the recent high price of nickel, there is a movement to change the metal material from the conventional nickel to the copper alloy. Cu-Ni-Sn type alloy is mentioned as a copper alloy suitable as a tab material. However, the weldability and cyclic bending property of Cu-Ni-Sn type alloy were not enough, and improvement was desired.

This invention aims at the Cu-Zn type alloy suitable for the battery connection tab material which has favorable repeat bending property and weldability.

This invention provides the Cu-Zn type alloy suitable for the battery tab material which satisfy | filled favorable cyclic bending property and weldability by adjusting a manufacturing process and adjusting the aspect ratio of a crystal grain diameter, and a twinning boundary frequency. Specifically, same.

(1) 2? It is a copper alloy containing 12 mass% Zn and remainder consists of copper and an unavoidable impurity, and has a twin boundary frequency of 40? It is 70%, Cu-Zn type alloy bath used for the rechargeable battery tab.

(2) additionally 0.1? The Cu-Zn system alloy bath as described in (1) containing 0.8 mass% Sn.

(3) The aspect ratio of the crystal grain diameter in the rolling parallel direction and the perpendicular direction is 0.3? The Cu-Zn system alloy bath as described in 0.7 phosphorus (1) or (2).

(4) Furthermore, in total, at least one or more of Ni, Mg, Fe, P, Al, and Ag is 0.005? (1) containing 0.5 mass%? Cu-Zn type alloy bath in any one of (3).

(5) above (1)? 0.3 to Cu-Zn-based alloy according to any of (4). Cu-Zn-based alloy Sn-plated alloy bath with 2 µm Sn plating.

The Cu-Zn alloy of the present invention has good repeatability and weldability and is suitable as a tab material for batteries.

1 is a schematic diagram showing the aspect ratio of the crystal grain size.

(Cu-Zn-based alloy bath)

(A) Zn concentration

The alloy of the present invention is 2? 12 mass% (represented by% below), Preferably it is 3? It is a copper alloy containing 10% of Zn and remainder consisting of copper and an unavoidable impurity. If Zn is less than 2%, the strength required as the tap is insufficient. In addition, the conductivity is excessively high, so that the tab is melted at the time of welding, and the current does not flow easily through the stainless steel plate or the mild steel plate on the electrode side, so that the weldability is deteriorated. When Zn exceeds 12%, the components of the oxide film formed on the surface become Zn rich and the weldability deteriorates.

(B) Sn concentration

Sn has the effect | action which accelerates work hardening at the time of rolling, and contributes to a raise of strength. Therefore, the alloy of the present invention is further 0.1? 0.8%, preferably 0.2? You may contain 0.6% Sn. If Sn is less than 0.1%, a desired effect is not obtained, and if Sn exceeds 0.8%, electrical conductivity will fall.

(C) Additional elements other than the above

In the alloy of the present invention, at least one of Ni, Mg, Fe, P, Al, and Ag is added in an amount of 0.005? To the purpose of improving the strength, heat resistance, stress relaxation resistance, etc. 0.5% can be added. If the total amount is less than 0.005%, the desired characteristics are not obtained. If the total amount exceeds 0.5%, the desired characteristics are obtained, but the conductivity and the bending workability are lowered.

(D) twin boundary frequency

When the twin boundary frequency is less than 40%, the repeatable bendability deteriorates. Since it is industrially difficult to adjust so that the twinning frequency may exceed 70% in the component system of this invention, the upper limit was 70%.

The twin boundary refers to the boundary of two crystals in twin relationship, and the two crystals are in mirror-symmetrical relationship. According to the corresponding grain boundary theory, the twin boundary is equivalent to the grain boundary of? 3. Because of the good match between atoms in the twin boundary, the heterogeneous deformation hardly occurs in the vicinity of the boundary, and during bending deformation, cracks and wrinkles originating near the boundary do not easily occur.

The twin boundary frequency means the ratio of the twin boundary in the whole boundary which combined the crystal boundary and twin boundary. The occurrence frequency of twins is related to the stacking defect energy, and the lower the stacking defect energy, the higher the twin boundary frequency.

Since the composition of this invention satisfies weldability and electroconductivity compared with brass (Cu65%, Zn35%), there is little Zn amount. Since the stacking defect energy increases with the decrease in the amount of Zn, the twin boundary frequency is lower than that of brass, and it is difficult to obtain a high twin boundary frequency of more than 40% in a conventional process. As a result of earnestly examining the relationship between the manufacturing process and the twin boundary frequency in the alloy of the present invention, the inventors found that the conditions of the cold rolling carried out before the final annealing are important. In rolling, a material is repeatedly passed (passed) between a pair of rolls, and it finishes to the target plate | board thickness. In this series of passes, in one pass before the last pass and the last pass, finish rolling is performed by increasing the workability per pass and increasing the rolling speed, and then performing final annealing under suitable conditions. It was found that a high twin boundary frequency exceeding 40% was obtained.

Here, as a method of calculating the twin boundary frequency, there is an EBSP (Electron Backscattering Pattern) method by FESEM (Field Emission Scanning Electron Microscope). This method is a method of analyzing the crystal orientation based on the backscattered electron diffraction pattern (kikuchi pattern) generated when the sample surface is irradiated with the electron beam obliquely. After analyzing the crystal orientation by this method, the orientation difference between adjacent crystal grains can be calculated | required and the ratio of a random grain boundary and each corresponding grain boundary (grain boundary distribution) can be determined. Since the twin boundary corresponds to the Σ3 corresponding grain boundary, the twin boundary frequency is calculated as (sum total of the length of the corresponding grain boundary Σ3) / (sum total of the length of the crystal grain boundary) × 100. In addition, a crystal grain boundary refers to the boundary which the orientation difference between adjacent crystal grains becomes 15 degrees or more, and does not contain an incineration grain boundary or a subgrain boundary.

(E) Aspect ratio of crystal grain size

In the present invention, in order to further improve the repeat bendability, as a result of research on the metal structure and the repeat bendability, it was found that the repeat bendability is improved by controlling the metal structure after the final annealing to uniform equiaxed particles. The final product has 30? Since 60% of cold rolling is performed, in order to improve the repeatability, the aspect ratios b / a and d / c of the crystal grain diameters in the rolling parallel direction and the right angle direction in the final product are 0.3? It is preferable to control to 0.7. More preferably, b / a is 0.3? 0.5 and d / c is 0.5? 0.7. 1 is a schematic diagram of crystal grains observed in a sample cross section.

If the aspect ratios b / a and / or d / c of the grain size in the rolling parallel direction and the perpendicular direction are less than 0.3 or more than 0.7, the strain is locally concentrated at the time of repeated bending, and the shear zone is formed to deteriorate the repeatable bending property. .

Since the composition of the alloy bath of the present invention has a smaller Zn amount than that of brass, the metal structure after recrystallization tends to be mixed. Moreover, when recrystallization is complete | finished in the pass | pass at the time of hot rolling, the coarse crystal grain extended | stretched in the rolling direction will remain, and the equalization of metal structure will be inhibited. Therefore, in order to obtain uniform equiaxed particles at the time of final annealing, it is necessary to control the end temperature of hot rolling, and to roll to an appropriate degree of work to equiax the metal structure by dynamic recrystallization, and then to repeat rolling and annealing a plurality of times. have.

The average crystal grain diameter of this invention becomes like this. Preferably it is 12 micrometers or less, More preferably, it is 7 micrometers or less.

(characteristic)

The tensile strength (JIS Z 2241) of the alloy bath of the present invention can be suitably used as a tab material if it is usually 420 MPa or more, preferably 450 MPa or more, and more preferably 500 MPa or more.

The electrical conductivity (JIS H 0505) of the alloy bath of this invention can be used suitably as a tab material as it is 70% IACS or less, More preferably, it is 60% IACS or less. If it exceeds 70% IACS, melt loss will arise at the time of resistance welding, or sufficient electric current will not flow to the metal plate of an electrode side, and weldability will fall.

The repeatable bendability of the alloy bath of the present invention is preferably 3.0 times or more, more preferably 3.2 times or more, and is preferable as the tab material.

Although the thickness of the alloy bath of this invention is not specifically limited, Preferably it is 0.03? 1.00 mm, more preferably 0.12? It is 0.6 mm and is 0.15 mm, for example, and if it is this thickness, it will satisfy | fill the strength and weldability as a tab material for battery connection.

The alloy bath of the present invention is 0.3? Sn plating of 2 micrometers is given and it can be set as Cu-Zn type alloy Sn plating alloy bath. The Sn plating method can be carried out by a conventional method, 0.3? Weldability becomes more favorable by performing Sn plating about 2 micrometers.

(Manufacturing method)

The manufacturing process of the Cu-Zn type alloy bath of this invention is basically the same as a normal alloy bath, and is produced by repeating a plurality of cold rolling and annealing after melt casting, homogenization annealing, hot rolling, and surface roughening.

However, in order to manufacture the alloy bath of this invention, it is necessary to control manufacturing conditions so that it may become the twinning boundary frequency of the range of this invention.

The average workability of the final pass of cold rolling before the final annealing and the pass one before the last pass is 32? 40%, the rolling speed is 220? 350 mpm is appropriate. If the workability is lower than the above-mentioned range or the rolling speed is slow, the twin boundary frequency is lowered and the cyclic bendability deteriorates. If the workability is high or the rolling speed is high, manufacturability is remarkably deteriorated, such as edge cracks (edge cracks) occur at the edges of the material and the material breaks during rolling.

As a condition of final annealing, the temperature is 660? 760 ° C., annealing time 5? 20 s is appropriate. If the temperature is lower or the time is shorter than the above-mentioned range, since the final annealing is insufficient, the twin boundary frequency is lowered and the repetitive bendability is degraded. When the final annealing temperature is high or the time is long, remarkable coarsening of the crystal grains occurs, the frequency of twin boundaries decreases, and the cyclic bendability deteriorates.

By adjusting the following manufacturing conditions, repeatable bendability can be improved further.

The end temperature of hot rolling is preferably 600? 750 degreeC, and final processability becomes like this. 55%. If they are out of range, an aspect ratio will become out of a range preferable in this invention, and cyclic bending property will deteriorate.

The intermediate annealing temperature is preferably 680? 5 at 780 ℃? If it is 20 second and annealing conditions are out of the range mentioned above, an aspect ratio will become out of the range preferable in this invention, and cyclic bending property will deteriorate.

Example

The measurement conditions performed in the Example are as follows.

[Twine Boundary Frequency] Each copper alloy plate was measured by an EBSP (Electron Backscattering Pattern) method by FESEM (Field Emission Scanning Electron Microscope).

[Aspect Ratio] For each copper alloy sheet, the grain sizes of the cross section parallel to the rolling direction and the cross section perpendicular to the rolling direction were measured and calculated according to the JIS H 0501 cutting method. In the cross section parallel to the rolling direction shown in FIG. 1, the crystal grain diameters are respectively measured in two directions parallel to the rolling surface and in a direction perpendicular to the rolling surface, and the measured value in the parallel direction is determined by the long diameter a and the right angle direction. The measured value was made into the short diameter b. In the cross section perpendicular to the rolling direction, the crystal grain diameter is measured in two directions, respectively, in a direction parallel to the rolling direction and a direction perpendicular to the rolling direction, and the measured value in the parallel direction is determined by the long diameter c and the measured value in the perpendicular direction. d was set.

[Repeat bendability] Four final product test pieces having a thickness of 0.15 mm, a width of 10 mm, and a length of 40 mm were produced so that the longitudinal direction thereof was parallel to the rolling direction, and the bending direction was set at 180 degrees in the direction perpendicular to the longitudinal direction of the test piece. ° After bending, remove the bend. This was repeated once and repeated bending was performed until the sample broke, and the average number of breaks (repetitive bending) of four samples was obtained.

[Welding] The spot welded a 0.3 mm mild steel sheet and a copper alloy at two points with a pressing force of 30 N, a welding current of 3.5 mA, and a welding time of 10 msec. Tensile tests were performed with an Aiko Engineering Precision Load Meter to measure weld strength. When weld strength was 35 N or more, weldability was judged to be favorable (circle), and when weld strength was less than 35 N, it evaluated as defect x.

Tensile strength About each copper alloy plate, the tensile test was done in the direction parallel to a rolling direction, and it calculated | required based on JISZ22241.

[Conductivity] The% IACS was calculated from the volume resistivity obtained by the four-terminal method using the double bridge device in accordance with JIS H 0505 for each copper alloy plate.

(Example 1)

The electric copper was dissolved in a high frequency induction furnace, the surface of the molten metal was charcoal coated, and then an alloying element was added to adjust the molten metal to a desired composition. After heating the ingot obtained by casting at injection temperature 1200 degreeC for 3 hours at 850 degreeC, it rolls to 8 mm of plate | board thickness so that the workability of the final pass of hot rolling may be 35%, and the hot rolling finish temperature is It adjusted to 650 degreeC or more. Oxidation scale generated on the surface was removed by face. Thereafter, by cold rolling, the sheet thickness is processed to 1.5 mm, the intermediate annealing is carried out at 700 ° C for 12 seconds, and in cold rolling to 0.35 mm, the average workability of the final pass and one pass before the final pass is obtained. It adjusted so that the rolling speed of 35%, a final pass, and the pass before one of the last pass may be 250 m / min. After this cold rolling, the final annealing was performed at 680 ° C for 10 seconds, and the copper alloy plate after the final annealing was cold rolled to finish with a 0.15 mm plate. Intermediate annealing and final annealing were carried out in a continuous line in an ammonia decomposition gas atmosphere. Table 1 shows the test results.

(Example 2)

After dissolving the electric copper in a high frequency induction furnace and charcoal coating the surface of the molten metal, Zn and Sn were added to the molten metal so as to have a composition of 8.0% Zn, 0.30% Sn and Cu, and the components were adjusted. Was carried out. After heating the obtained ingot at 900 degreeC for 3 hours, it hot-rolled and manufactured the copper alloy plate of 8 mm of plate | board thickness, and removed the oxidation scale produced | generated on the surface by surface-cutting. Then, it cold-rolled and processed to plate | board thickness 1.5mm, and after performing intermediate annealing, cold-rolled to plate | board thickness 0.25mm. Furthermore, final annealing was performed, and the copper alloy plate after final annealing was cold rolled, and it was finished by the board of 0.15 mm. Intermediate annealing and final annealing were carried out using a continuous line in an ammonia decomposition gas atmosphere. Table 2 shows the conditions of hot rolling and intermediate annealing, the conditions of cold rolling before final annealing (average workability and rolling speed of one pass before the final pass and the final pass), final annealing conditions and the test results.

Inventive Example 1 in Table 1? Since 19 was in the scope of the present invention, it was an alloy bath having good cyclic bendability and weldability and sufficient strength. Inventive Example 20 has good repeatability and weldability because the amount of Sn added is relatively small. The strength was lower than that of 19. Inventive Example 21 has a relatively large amount of Sn. The conductivity was lowered compared with 19. On the other hand, in Comparative Example 22, the amount of Zn was small, the cyclic bendability was inferior to that of the Invention Example, and the strength was also reduced. In Comparative Example 23, the amount of Zn was large and the repeatability was good. However, since the surface oxide film became Zn rich, the weldability was deteriorated and the conductivity was also lowered.

Inventive Example 24 in Table 2? Since 38 was in the scope of the present invention, it was an alloy bath having good cyclic bendability and weldability and sufficient strength.

Inventive Example 32 has a low end temperature of hot rolling, Inventive Examples 33 and 34 have a low or high final workability, and Inventive Examples 35 and 36 have a low or high intermediate annealing temperature, Inventive examples 37 and 38 The recrystallization annealing time in the intermediate annealing is short or too long. Therefore, in these invention examples, the aspect ratio is outside the preferred range, and the repeatability is inventive example 24? Fell compared to 31.

Comparative example 39 has a low average workability of the final pass of the cold rolling after the intermediate annealing and one pass before the final pass, and the comparative example 41 has a rolling speed of the final pass of the cold rolling after the intermediate annealing and one pass before the final pass. Because of the slow frequency of twin boundaries. Comparative Example 40 had an average workability of one pass before the final pass and the final pass of cold rolling after intermediate annealing, and Comparative Example 42 rolled one pass before the final pass and final pass of cold rolling after intermediate annealing. Due to the excessively high speed, an edge crack occurred at the edge of the material, and the material broke during the final rolling. Comparative Examples 43 and 44 had a low or high final annealing temperature, and Comparative Examples 45 and 46 had a low twinning frequency because of their short or long final annealing time, and the aspect ratio was also outside the preferred range. For this reason, the thing which was not broken in these comparative examples was inferior in repeatability to the invention example.

Claims (6)

2 ? It is a copper alloy containing 12 mass% Zn and remainder consists of copper and an unavoidable impurity, and has a twin boundary frequency of 40? It is 70%, Cu-Zn type alloy bath used for the rechargeable battery tab. The method of claim 1,
Additionally 0.1? Cu-Zn type alloy bath containing 0.8 mass% Sn. The method of claim 1,
The aspect ratio of the crystal grain diameter in the rolling parallel direction and the perpendicular direction is 0.3? Cu-Zn based alloy bath with 0.7. The method according to any one of claims 1 to 3,
Furthermore, in total, at least one or more of Ni, Mg, Fe, P, Al, and Ag is 0.005? Cu-Zn type alloy bath containing 0.5 mass%. 0.3 to Cu-Zn-based alloy according to any one of claims 1 to 3. Cu-Zn-based alloy Sn-plated alloy bath with 2 µm Sn plating. 0.3 to Cu-Zn-based alloy according to claim 4 Cu-Zn-based alloy Sn-plated alloy bath with 2 µm Sn plating.

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