JP6431314B2 - Method for producing aluminum alloy foil - Google Patents

Description

  The present invention relates to a method for producing an aluminum alloy foil.

  An aluminum alloy foil used for a packaging material for a battery such as a lithium ion secondary battery is greatly deformed by press molding or the like. For this reason, a material having a large elongation has been demanded in the past, and in recent years, thinning of the foil has been progressing in the battery packaging field.

Conventionally, a technique has been proposed for improving the rollability without reducing the strength of the foil by performing low-temperature heat treatment under appropriate conditions and thickness during the manufacturing process for a foil for a battery current collector with high strength and thin thickness. ing.
For example, the cited document 1 proposes a technique for suppressing generation of wrinkles and cracks by performing heat treatment for 24 to 72 hours at 40 to 65 ° C. during foil rolling, and performing 7 μm finish rolling immediately after the heat treatment. . Further, in the cited document 2, a technique for improving the rollability by maintaining the finish temperature of the cold rolling at 100 to 180 ° C. is proposed for the Al—Fe based alloy material.

  In Cited Document 3, with respect to the Al—Fe-based alloy material, Si, Cu, and Mn are sufficiently precipitated to maintain high conductivity, thereby suppressing thin foil pinholes. The technique which precipitates Si and improves rolling property by performing intermediate annealing of this is proposed. In Cited Document 4, when producing a hard electrode foil, after foil rolling, the foil is held at 45 to 120 ° C. for 1 hour or longer in order to eliminate the distortion of the foil. Techniques for suppressing coating unevenness during coating have been proposed.

Japanese Patent No. 2810249 Japanese Patent Laid-Open No. 11-217656 Japanese Patent Laid-Open No. 4-41645 Japanese Patent No. 4971277

  By the way, in recent years, battery manufacturers unwind a foil coil and apply an active material to the surface of the foil, then dry and press-fit electrodes. This electrode (positive electrode / negative electrode) is wound through a separator and stored in a battery case. At this time, if the strength and elongation of the foil are low, the risk of breakage during the production of the electrode or during the winding of the electrode increases. Since the thickness of the current collector foil is as thin as about 15 μm or less, a high-strength foil that can avoid the above-described breakage has very poor rolling properties and low productivity. In particular, when the strength is 190 MPa or more and the thickness is 15 μm or less, it is extremely difficult to obtain a target thickness and shape (shape).

In order to solve such a problem, the techniques described in the cited documents 1 and 3 improve the rollability by performing a heat treatment in the middle of rolling, but have not yet achieved high strength. Moreover, although the technique described in the cited document 2 improves rolling properties by adjusting the finishing temperature, the improvement effect is not sufficient. In the technique described in the cited document 4, the heat treatment after rolling can improve the distortion of the foil without reducing the strength, but does not effectively improve the rollability.
That is, with the techniques disclosed in the cited documents 1 to 4, it is difficult to satisfy high strength and rollability at the same time.

  The present invention has been made based on the above circumstances, and provides a method for producing an aluminum alloy foil that improves rolling properties while maintaining high strength by performing low-temperature heat treatment under appropriate conditions during the production process. The purpose is to do.

Here, the aluminum alloy foil has a high rolling rate and, for example, draws a work hardening curve as shown in FIG. Dislocations are introduced into the material at a very high density in the high-pressure ratio region of thin foils, and dislocations introduced during processing and hardening due to interaction are parallel to softening due to coalescence annihilation between dislocations and removal from the material surface. However, the increase in strength becomes extremely slow. It has been found from knowledge that, when rolling in this equilibrium region, defective thickness, cracks, wrinkles, etc. are likely to occur even if the strength is not so high. We thought that this decrease in rollability was not caused by a stagnation in strength, but was simply caused by the strength (hardness) of the foil. When rolling is completed before it occurs, the result is that defects during rolling are greatly improved. That is, the dislocation density of the material is rearranged by the low-temperature heat treatment, and the dislocation density is lowered, so that work hardening does not stagnate even in the high pressure lower rate region. Like conventional intermediate annealing, a curve like B can be drawn even at high temperature heat treatment above the recrystallization temperature exceeding 300 ° C. However, the decrease in strength and the decrease in elongation due to the coarsening of the crystal grains of the foil It is difficult to obtain a material having both strength and elongation.
The advantages of low-temperature heat treatment are summarized as follows: (1) There is almost no decrease in strength by ensuring a sufficient final cold rolling rate. (2) Since recrystallization does not occur, the crystal grain size of the final product does not become coarse. It can be said that the elongation does not decrease and (3) the rolling property is improved. Therefore, it was found that the rollability was improved while maintaining the strength by performing the low temperature heat treatment, and the present invention was completed.

That is, in the manufacturing method of an aluminum alloy foil of the present invention, a first aspect of the present invention, the tensile strength of 190MPa or more, elongation of 2.5% or more, a process for producing an aluminum alloy foil having the final thickness 6～15Myuemu, JIS A cold rolling step of rolling an aluminum alloy material having any one composition of A1000 series, JIS A3000 series, and JIS A8000 series to the final thickness at a final cold rolling rate of 96% or more, and the cold rolling process In the middle, a heat treatment step of heating the aluminum alloy material at 100 to 250 ° C. for 2 hours or more is performed, and in the heat treatment step, the 0% of the aluminum alloy material is 0.2% proof stress immediately before the heat treatment step. .2% proof stress is reduced by 4.0 to 9.0%.

The method for producing an aluminum alloy foil according to the second aspect of the present invention is characterized in that, in the first aspect of the present invention , a rolling rate after the heat treatment step is 99.6% or less .

The method for producing an aluminum alloy foil according to a third aspect of the present invention is the method according to the first or second aspect , wherein the aluminum alloy material is coiled in the heat treatment step, and the heating temperature in the heat treatment step is the coil temperature. It is based on the temperature of the innermost peripheral part of the said aluminum alloy material wound.

  Below, the manufacturing conditions etc. which are prescribed | regulated by this invention are demonstrated.

  The aluminum alloy material of the present invention is not limited to a specific one, but any one of JIS A1000 series, JIS A3000 series, and JIS A8000 series can be mentioned as a suitable one.

Cold rolling step In the cold rolling step, the aluminum alloy material is rolled to a final thickness at a final cold rolling rate of 96% or more.
In general, foils for electrode current collectors are commercialized at a high cold working rate. Although it differs depending on the alloy, the stagnation of work hardening during rolling appears at least in the high-pressure ratio region where the cold rolling rate is 96% or more. The rollability improvement according to the present invention is considered to have great significance in the case of producing a high-strength thin foil in such a high pressure reduction rate region. The final cold rolling rate shown here is not the rolling reduction rate from the low-temperature heat treatment to the final thickness. If intermediate annealing is not performed, it indicates the rolling rate of cold rolling in general and reaches the final thickness after hot rolling. When performing, the rolling rate from after intermediate annealing to final thickness is shown.

Low-temperature heat treatment The aluminum alloy material is heated at 100 to 250 ° C. for 2 hours or more during the cold rolling process.
This heating reduces the 0.2% proof stress by 4.0-9.0% against the 0.2% proof strength of the aluminum alloy material immediately before the heat treatment step.
The optimum heat treatment conditions are different depending on the heat treatment such as alloy or homogenization treatment, so the optimum heat treatment conditions cannot be defined by temperature and time.
It is desirable that the heat treatment temperature be based on the temperature of the innermost peripheral portion of the coiled aluminum alloy material, in which the temperature rise is most delayed when the coiled aluminum alloy material is heated. As a result, the desired effect can be reliably obtained for all aluminum alloy materials.

  When the decrease in 0.2% proof stress during heat treatment is less than 4.0%, the stagnation of work hardening in the high pressure under-rate region cannot be sufficiently relaxed, and the effect of improving the rollability becomes low. On the other hand, in the heat treatment in the region where the 0.2% yield strength drop is over 9.0%, the target strength is not reached depending on the alloy. In addition, in the case of high-temperature heat treatment in which the proof stress changes by more than 9.0% and 0.2%, the mechanical properties of the material change greatly due to slight fluctuations in temperature and heat treatment time. There is a high risk of variations in physical properties.

  If the heat treatment time is less than 2 hours, the recovery of the material does not proceed sufficiently and there is a risk that the physical properties of the coil may vary. Therefore, the minimum holding time is 2 hours. Furthermore, if the temperature range is maintained, there is no upper limit on the processing time, but the effect of improving the rolling property is not particularly improved even if it is performed for a long time. In consideration of productivity, the upper limit is preferably 20 hours. In order to obtain optimum heat treatment conditions for each material, it is desirable to measure the annealing softening curve of the material in advance.

  It is desirable that the low temperature heat treatment is applied at a lower stage of the manufacture, that is, with a plate thickness of 99.6% or less of the final thickness. Even if it is loaded when the plate thickness of the upper process is thick, there is a sufficient effect, but particularly in the case of a high-strength foil such as JIS A 3003 alloy, the rolling property is further improved by loading in the lower process. The lower limit of the rolling rate is not particularly specified. However, in manufacturing, it is necessary to secure a certain rolling rate per pass, so in practice, the lower limit is about 20%. However, among the 8000 series alloys, particularly in the case of Al-Fe series alloys such as 8021 and 8079, work softening may occur in the rolling after the low-temperature heat treatment, and the strength may be lowered or not sufficiently improved. Therefore, it is desirable to secure a rolling rate of 30% or more with respect to the final thickness.

When tensile strength is 190 MPa or more and elongation is 2.5% or more, when the strength of the aluminum alloy foil as the electrode current collector is 190 MPa and elongation is less than 2.5%, the foil is unwound from the coil, and an active material is applied to the surface. There is a risk that the foil may break during the electrode manufacturing process for pressing and drying. Furthermore, if the tensile strength is less than 190 MPa, there are few problems during rolling, and the significance of application of the present invention is small.

Thickness 6-15μm
Assuming an electrode current collector, the strength is insufficient when the thickness is less than 6 μm. If it exceeds 15 μm, the ratio of the positive electrode current collector to the volume inside the battery increases, and the battery capacity decreases. Further, when it exceeds 15 μm, there is little problem in rolling properties, and the significance of application of the present invention is small.

  As described above, according to the present invention, an aluminum alloy foil that simultaneously satisfies high strength and rollability can be obtained.

It is a graph which shows the relationship between the material thickness of aluminum alloy material, and tensile strength in rolling by low-temperature heat processing, and normal rolling.

Hereinafter, an embodiment of the present invention will be described.
As the aluminum alloy used as the material of the aluminum alloy foil, any one of JIS A1000 alloy, JIS A3000 alloy, and JIS A8000 alloy can be preferably used.
For an ingot of aluminum alloy, for example, a homogenization treatment can be performed under conditions of a temperature of 450 to 600 ° C. and a holding time of 3 to 7 hours.

A rolled aluminum alloy material is obtained by performing hot rolling on an ingot of the aluminum alloy that has been subjected to the homogenization treatment or has not been subjected to the homogenization treatment.
Cold rolling is performed on the hot-rolled aluminum alloy material to obtain an aluminum alloy foil having a final thickness of 6 to 15 μm.
In the middle of the cold rolling, intermediate annealing can be performed on the aluminum alloy material. There are two types of intermediate annealing methods: batch annealing (Bach Annealing, BACH) in which coils are placed in a furnace and held for a certain period of time, and annealing in which materials are rapidly heated and rapidly cooled by a continuous annealing line (Continuous Annealing Line, CAL). It has been known. The conditions of the intermediate annealing are, for example, 3 to 10 hours at 300 to 400 ° C. for batch annealing, and a heating rate: 50 to 250 ° C./second, heating temperature: 400 to 520 ° C., holding time: none or 5 seconds for CAL annealing. Hereinafter, the cooling rate is 50 to 200 ° C./second. The intermediate annealing can be performed twice or more.
If intermediate annealing is not performed, after hot rolling, the cold rolling rate until the final thickness is obtained by cold rolling, and if intermediate annealing is performed, the cold rolling rate from the intermediate annealing to the final thickness is determined as the final cold rolling rate. 96% or more.
The final thickness in hot rolling is determined from the final thickness and the final cold rolling rate.

  During the cold rolling, the aluminum alloy material is subjected to low temperature heat treatment at 100 to 250 ° C. for 2 hours or more. The low-temperature heat treatment can be performed in a batch furnace with an aluminum alloy material coiled. In addition, the coil is put into the furnace, and a temperature measuring instrument such as a thermocouple is set at least on the innermost circumference of the outermost and innermost circumferences of the coil, so that the temperature rise is most delayed during heating. It is desirable to perform low temperature heat treatment based on the temperature of the inner periphery.

The low-temperature heat treatment is not particularly limited as long as it is in the middle of cold rolling, but the low-temperature heat treatment is carried out with a sheet thickness within 99.6% of the final thickness of the aluminum alloy material. It is desirable to do.
By the low-temperature heat treatment, the 0.2% yield strength can be reduced by 4.0 to 9.0% with respect to the 0.2% yield strength of the aluminum alloy material immediately before the low-temperature heat treatment.
The obtained aluminum alloy foil has a tensile strength of 190 MPa or more and an elongation of 2.5% or more.

  The aluminum alloy shown in Table 1 (the balance being Al and inevitable impurities) was subjected to a homogenization treatment at a temperature of 560 ° C. and a holding time of 6 hours. Then, by hot rolling, a 7 mm aluminum alloy hot-rolled sheet was produced, and after cold rolling the aluminum alloy hot-rolled sheet, 1085 alloy was not subjected to intermediate annealing, 3003 alloy was 0.7 mm, and 8021 alloy was Intermediate annealing was performed at 2.5 mm under the conditions described later. When the plate thickness reached the value shown in Table 2, low temperature heat treatment was performed to produce an aluminum alloy foil.

  The intermediate annealing was all carried out in a continuous annealing line (CAL) under the conditions of a heating rate: 120 ° C./second, a heating temperature: 500 ° C., a holding time: 0 seconds, and a cooling rate: 100 ° C./second.

The low-temperature heat treatment at 100 to 250 ° C. for 2 hours or more is conducted according to Comparative Example No. Except for 8, 9, 11, and 14, Example No. 1-7, Comparative Example No. This was performed for 10, 12, and 13. In Comparative Example 9, have line heat treatment of 80 ° × 4 hours, Comparative Example No. No. 14 was heat-treated at 280 ° C. for 3 hours . Example No. In the low-temperature heat treatment of 1 to 7, the 0.2% proof stress of the material decreased by 4.1 to 7.6% before and after the heat treatment. In Comparative Examples 9, 10, and 12-14, the 0.2% yield strength of the material decreased by 2.4%, 12.1%, 2.2%, 4.2%, and 27.8% before and after the heat treatment, respectively. .

The final product was used as a specimen of an aluminum alloy foil having a width of 1200 mm and a final thickness of 12 μm.
Example No. 1-7, Comparative Example No. Tensile tests were performed on 8 to 14 specimens to evaluate elongation. The tensile test was based on JIS Z2241 and a JIS No. 5 test piece was taken from the sample and tested with a universal tensile tester (manufactured by Shimadzu Corporation) at a pulling speed of 2 mm / s.
It went on condition of.
The 0.2% proof stress value was measured before and after the low-temperature heat treatment, and the decrease rate of the 0.2% proof stress value before and after the heat treatment was calculated.

For the evaluation of the rollability, the presence or absence of thickness failure, breakage, shape failure, winding slip, hole opening, etc. was evaluated in the final rolling pass when obtaining the test material. When none occurred, it was marked as “Good”.
The evaluation of the breakage was that the roll could be rolled without breaking in the final pass. ○ If breakage of 3 times or less per coil (about 10000 m) occurred △ For more than 3 breaks or too hard Those that were judged to be difficult to continue rolling were marked as x. ○ is preferable, but if it is Δ or more (with a final pass of about 10000 m within 3 breaks), there is no problem in production.

As is apparent from Table 2, Example No. 1 was subjected to low-temperature heat treatment so that the 0.2% proof stress of the material was reduced by 4.0 to 9.0% before and after the heat treatment. 1-7 are comparative example No.1. Compared with 8-14, the tensile strength was 190 MPa or more and the elongation was 2.5% or more.
Comparative Example No. in which the 0.2% proof stress of the material decreased by 2.4% before and after the low-temperature heat treatment. In No. 9, shape failure occurred during the final rolling process. Comparative example No. which did not perform low-temperature heat treatment Nos. 8 and 11 were broken or perforated during the final rolling process. Comparative Example No. in which the 0.2% yield strength of the material decreased by 12.1% before and after the low-temperature heat treatment. No. 10 had a tensile strength after final rolling of 190 MPa or less and an elongation of 2.5% or less. Comparative Example No. in which the 0.2% proof stress of the material decreased by 2.2% before and after the low temperature heat treatment. No. 12, winding slippage occurred during the final rolling process.
Therefore, aluminum that satisfies both high strength and rollability at the same time without causing breakage in the test material subjected to low-temperature heat treatment so that the 0.2% proof stress of the material is reduced by 4.0 to 9.0% before and after heat treatment. An alloy foil was obtained.
In the present embodiment, only the final product thickness of 12 μm is shown. However, the final thickness can be arbitrarily selected within the range of 6 to 15 μm as defined in the present application, and the above-mentioned case is different even when the final thickness is different in the range. The same effect on strength characteristics and rollability can be obtained by low-temperature heat treatment.

Claims (3)

In a method for producing an aluminum alloy foil having a tensile strength of 190 MPa or more, an elongation of 2.5% or more, and a final thickness of 6 to 15 μm,
A cold rolling step of rolling an aluminum alloy material having any one composition of JIS A1000 series, JIS A3000 series, JIS A8000 series to the final thickness at a final cold rolling rate of 96% or more, and the cold rolling In the middle of the process, a heat treatment step of heating the aluminum alloy material at 100 to 250 ° C. for 2 hours or more is performed. In the heat treatment step, the 0.2% proof stress of the aluminum alloy material immediately before the heat treatment step is A method for producing an aluminum alloy foil, wherein the 0.2% proof stress is reduced by 4.0 to 9.0%. The method for producing an aluminum alloy foil according to claim 1 , wherein a rolling rate after the heat treatment step is 99.6% or less . The heat treatment and the aluminum alloy material is coiled in the process, the heating temperature in the heat treatment step according to claim 1 or, characterized in that based on the temperature of the innermost portion of the being coiled said aluminum alloy material 2. A method for producing an aluminum alloy foil according to 2 .

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