JP5927615B2 - Aluminum alloy foil for lithium battery exterior and its manufacturing method - Google Patents

Description

  The present invention relates to an aluminum alloy foil for a lithium battery exterior used for an exterior of a lithium battery and a method for producing the same.

  In recent years, lithium ion secondary batteries and lithium ion polymer batteries have a large power capacity, are light, and have a long service life. Therefore, they have been put to practical use as batteries for portable electronic devices and electric vehicles, or research and development have been promoted. ing.

  As an exterior container of such a lithium battery, an aluminum foil laminated with a resin film has been attracting attention and being put into practical use because it has merits such as light weight, thinness, and flexibility.

  Conventionally known materials for aluminum foil include 1N30 for industrial pure aluminum, and 8021 alloy and 8079 alloy containing Fe and Si. Patent documents 1-3 are known as prior art which examined aluminum alloy foil for exteriors, such as a lithium battery.

  Patent Document 1 relates to a laminated material for a secondary battery container in which a resin film and an aluminum foil or the like are laminated. As a material for the aluminum foil, an aluminum alloy containing 1% by weight or more of Mn, Fe or Si is disclosed from the viewpoint of improving stiffness (rigidity), and a typical example thereof is an 8021 alloy.

  Patent Document 2 relates to a packaging material for an electronic component case in which a resin film and an aluminum foil are laminated. As the material of the aluminum foil, 8021 alloy and 8079 alloy are disclosed from the viewpoint of ease of press forming.

  Patent Document 3 relates to an aluminum laminate material for battery packaging in which a polypropylene layer and an aluminum foil or the like are laminated. As an aluminum foil material, an aluminum alloy containing Fe of 1.2 to 1.7% by weight, Si of 0.2% by weight or less, and Mn of 0.1% by weight or less is disclosed from the viewpoint of mechanical strength. ing.

JP 2003-288865 A JP 2002-187233 A JP 2005-56729 A

  When using an aluminum foil for the exterior of a lithium battery, it is molded so that a recess is formed in the center of the aluminum foil, and an electrode, an electrolyte, a separator, etc. are accommodated in the recess and sealed with an aluminum foil or the like. A manufacturing method has been developed. In such cases, the recess is usually a legislature or a cuboid.

  When such a manufacturing method is adopted, the aluminum foil is molded while being pulled in the vertical and horizontal biaxial directions. Therefore, the aluminum foil is required to be suitable for such a molding method and excellent in the square tube formability as referred to in the present invention.

  In the case of 1N30, 8021 alloy and 8079 alloy, when considering from the viewpoint of square tube formability, the elongation is low, and when forming a recess having a depth, breakage and cracks occur, and the material with sufficient square tube formability is not used. Not found out.

  This invention is made | formed in view of said situation, The subject is providing the aluminum alloy foil for lithium battery exteriors excellent in square tube moldability. Moreover, it is providing the manufacturing method of the aluminum alloy foil for lithium battery exterior excellent in square tube moldability.

  Therefore, in order to develop an aluminum alloy foil excellent in square tube formability, investigations were made from both aspects of the aluminum alloy composition and the manufacturing method of the aluminum alloy foil. The inventors have found that the above problems can be solved by controlling the grain size of the grains to a predetermined size or less and managing the elongation within a predetermined range, and have reached the present invention.

  That is, the aluminum alloy foil for lithium battery exterior of the present invention contains Fe: 1.2-1.7 mass%, Si: 0.04-0.08 mass%, Cu: 0.2 mass% or less, Mn: Aluminum alloy foil that is controlled to 0.2% by mass or less, the balance is made of aluminum and inevitable impurities, and Cu and Mn are made of an aluminum alloy with a total content of 0.05% by mass or more The average grain size of the crystal grains is 7 μm or less, and the elongation in the 0 °, 45 °, and 90 ° directions is 20% or more.

  According to the said structure, it can prevent that a crystal grain coarsens and a moldability falls by containing a predetermined amount of Cu and / or Mn. Further, since the average grain size of the crystal grains is small and the elongation is high, the material has excellent moldability.

  Moreover, it is preferable that the elongation in the 0 °, 45 °, and 90 ° directions of the aluminum alloy foil for lithium battery exterior of the present invention is 30% or more. By having high elongation, it becomes possible to produce a molded article having a deeper recess.

  Furthermore, it is preferable that the aluminum alloy foil for a lithium battery exterior of the present invention has a yield ratio of 0 °, 45 °, and 90 ° in any of 0.5 or less. By having a low yield ratio, the material is further excellent in moldability.

The method for producing an aluminum alloy foil for lithium battery exterior according to the present invention comprises a heat treatment step in which an aluminum alloy ingot having the above composition is subjected to a heat treatment at a temperature of 450 to 550 ° C. for 1 hour or longer, and the end of hot finish rolling. A hot rolling step in which hot rolling is performed under conditions where the temperature is 250 ° C. or higher and lower than 350 ° C., a first cold rolling step in which cold rolling is performed at a cold work rate of 80% or higher, and 400 ° C. or higher and lower than 500 ° C. An intermediate annealing step in which an intermediate annealing is performed at a temperature of 2, a second cold rolling step in which a cold rolling with a cold work rate of 90 % or more is performed, and an annealing that is held at a temperature of 300 ° C. or higher and lower than 400 ° C. for 1 hour or longer is performed. An annealing process is performed in this order.

  According to the manufacturing method of the said structure, it can recrystallize uniformly from the aluminum alloy which has the said composition, can aim at the improvement of elongation, and can manufacture the aluminum alloy foil for lithium battery exteriors which has the said characteristic. It becomes possible.

  The aluminum alloy foil for lithium battery exterior of this invention is excellent in square tube moldability, maintaining mechanical strength, such as tensile strength. Moreover, the manufacturing method of the aluminum alloy foil for lithium battery exterior of this invention can manufacture the aluminum alloy foil for lithium battery exterior excellent in square tube moldability.

It is a flowchart which shows the manufacturing process S of the aluminum alloy foil for lithium battery exterior of this embodiment. It is a perspective view which shows the external appearance of the jig used for a square tube shaping | molding test. It is sectional drawing which shows the procedure of the test method of a square tube molding test. It is a perspective view of the sample shape | molded by the square tube shaping | molding test. It is an image of the scanning electron microscope which shows the specific example of the measuring method of a crystal grain diameter.

  Hereinafter, the aluminum alloy foil for lithium battery exterior of this invention and its manufacturing method are demonstrated based on specific embodiment.

  In the present invention, the lithium battery is a battery using lithium as a battery material, and includes a lithium primary battery and a lithium secondary battery. The present invention is not particularly limited to any type of lithium battery. The present invention can be applied to various types of lithium batteries such as lithium ion secondary batteries, lithium ion polymer batteries, manganese dioxide lithium batteries, and graphite fluoride lithium batteries. Further, the present invention can be applied to a capacitor or a capacitor having a function similar to that of a battery.

  The aluminum alloy foil for lithium battery exterior of the present invention generally has a thickness of 200 μm or less. In the present invention, an aluminum foil having a thickness of 10 to 150 μm is preferable and an aluminum foil having a thickness of 30 to 50 μm is more preferable from the viewpoints of practical strength, moldability, and handleability.

  The composition of the aluminum alloy constituting the aluminum alloy foil for lithium battery exterior of the present invention contains Fe: 1.2 to 1.7% by mass, Si: 0.04 to 0.08% by mass, and Cu: 0.00. 2 mass% or less, Mn: Restricted to 0.2 mass% or less, the balance is made of Al and inevitable impurities, and the total content of Cu and Mn is 0.05 mass% or more.

In particular, when annealing at a relatively high temperature in the manufacturing method described later, it is characterized by containing a predetermined amount of Cu and / or Mn in order to prevent crystal grains from coarsening and formability from decreasing It is. Moreover, in order to improve the castability at the time of manufacture, it is characterized by containing a predetermined amount of Si.
Each element constituting the aluminum alloy of the present invention and its content will be described below.

(Fe: 1.2-1.7% by mass)
Fe is an element added for improving the tensile strength by solid solution strengthening and refining the crystal grains, and can suppress the coarsening of the crystal grains even when the annealing temperature is increased. The content of Fe needs to be 1.2 to 1.7% by mass, and preferably 1.3 to 1.6% by mass. If the Fe content is less than 1.2% by mass, these effects cannot be obtained sufficiently. On the other hand, when it exceeds 1.7 mass%, a crystallized substance (intermetallic compound) will coarsen and the rolling property and square tube moldability of foil will fall.

(Si: 0.04-0.08 mass%)
Si is an element that contributes to improvement of castability as a foil. The Si content needs to be 0.04 to 0.08% by mass, and preferably 0.05 to 0.07% by mass. If the Si content is less than 0.04% by mass, it is not possible to reduce hot water leakage during ingot formation. On the other hand, if the Si content exceeds 0.08% by mass, the crystallized product (intermetallic compound) becomes coarse, which becomes a stress concentration point at the time of molding processing, becomes a starting point of cracks, and suppresses the generation of cracks. I can't.

(Cu: 0.2% by mass or less)
Cu is an element added to increase tensile strength by solid solution strengthening and prevent coarsening of crystal grains. The Cu content must be 0.2% by mass or less, and preferably 0.15% by mass or less. If it exceeds 0.2% by mass, it is solid-solved in the matrix and the elongation is reduced, so that the square tube formability is lowered.

(Mn: 0.2% by mass or less)
Mn is an element added to increase tensile strength and prevent coarsening of crystal grains. The Mn content needs to be 0.2% by mass or less, and preferably 0.1% by mass or less. If it exceeds 0.2 mass%, an Al—Fe—Mn coarse intermetallic compound is likely to be generated, and cracks and cracks are likely to occur starting from the coarse intermetallic compound.

  Furthermore, Cu and Mn are required to have a total content of Cu and Mn of 0.05% by mass or more in order to prevent coarsening of crystal grains. The total content of Cu and Mn should just be 0.05 mass% or more, Comprising: There is no restriction | limiting in particular in the relative ratio of both. For example, the Cu content may be 0.05 to 0.2% by mass, the Mn content may be less than 0.05% by mass, and conversely, the Mn content may be 0.05 to The content of Cu may be 0.2% by mass and less than 0.05% by mass. At this time, either one of Mn and Cu may be 0% by mass.

(Ti-B)
In order to refine the ingot structure, Ti and B may be added. That is, an ingot refining agent having a ratio of Ti: B = 5: 1 or 5: 0.2 may be added to the molten metal in the form of a waffle or a rod. The inclusion of is acceptable.

(Inevitable impurities)
As unavoidable impurities, elements such as Mg, Cr, Zn, Sn, Ni, Zr, C, In, Na, Ca, V, Bi, Sr and the like can be assumed, but all of them do not impair the characteristics of the present invention. It is permissible to contain. Specifically, the elements of these inevitable impurities are allowed if the content of each individual element is 0.02% by mass or less and the total content is 0.05% by mass or less.

  Next, the crystal structure and characteristics required for the aluminum alloy foil composed of the aluminum alloy will be described below.

(Average grain size)
When the crystal grains in the aluminum alloy foil are large, the stress concentration in the crystal grains increases during tensile deformation, and it is difficult to achieve high elongation at room temperature. Therefore, in order to have excellent square tube formability, the average grain size of the crystal grains of the aluminum alloy foil needs to be 7 μm or less. More preferably, it is 6 μm or less.

  In order to control the average grain size of the crystal grains to 7 μm or less, it is necessary to have the above-described specific composition as the alloy composition. Furthermore, it is necessary to adopt specific manufacturing steps and manufacturing conditions described later for the manufacturing method. That is, by controlling both the alloy composition and the manufacturing conditions within a specific range, an aluminum alloy foil having an average grain size of 7 μm or less can be obtained.

Here, the measuring method of the average particle diameter of the crystal grain of aluminum foil is demonstrated.
First, using a scanning electron microscope (SEM), a sample surface of an aluminum foil is photographed at an observation magnification of 1,000 times. The orientation difference between adjacent crystal grains is 15 on the OSL (Orientation Imaging Microscopy, TM) software manufactured by TSL based on the data obtained by analyzing the orientation by the EBSD method at a measurement interval of 0.10 μm from the obtained crystal structure image. A crystal grain surrounded by a crystal grain boundary within ± ° is drawn as one crystal grain region. Next, 10 grid lines each having a length of 100 μm are drawn on the image at 10 μm intervals. With each line segment having a length of 100 μm, the number of crystal grains completely cut is counted for each line segment. Thereafter, the average value of the number of crystal grains in each of the 10 vertical and horizontal line segments is obtained. By dividing 100 μm by the average value of the number of crystal grains, the average grain diameter of the crystal grains can be obtained.

  As a general rule, the average grain size of crystal grains is measured at the center of the prepared sample. In addition, the surface of the sample is polished in advance before measurement and used for measurement. In the polishing, the processed layer on the surface is removed by a chemical polishing method such as ion milling after mechanical polishing.

(Elongation)
In order to perform forming, the aluminum alloy foil is required to have high elongation in all directions. Therefore, specifically, the elongation in the 0 °, 45 °, and 90 ° directions needs to be 20% or more. Here, 0 °, 45 ° and 90 ° indicate angles with respect to the rolling direction, 0 ° is the same direction as the rolling direction, 90 ° is a direction perpendicular to the rolling direction, and 45 ° is rolling. The direction is 45 ° to the direction.

  In particular, in the case of square tube formability, since the outermost corner of the molded body recess is greatly stretched in the 45 ° direction, the elongation in the 45 ° direction is higher than the elongation in the 0 ° and 90 ° directions. Is preferred. Specifically, the elongation in the 0 ° and 90 ° directions is preferably 20% or more, and the elongation in the 45 ° direction is preferably 30% or more. Furthermore, it is more preferable that the elongation in the 0 °, 45 °, and 90 ° directions is 30% or more.

  Elongation, the following tensile strength and proof stress are a strip shape of 15 mm width × about 200 mm length so that the tensile direction is 0 °, 45 ° and 90 ° respectively with the rolling direction from the center in the width direction of the aluminum foil sample. The test piece is cut out and the distance between the chucks of 100 mm is used as the distance between the gauge points in accordance with LIS AT5 of the Light Metal Association standard.

(Tensile strength)
The aluminum alloy foil of the present invention is required to be excellent in handleability and difficult to break due to tensile stress in all directions during molding. Therefore, it is preferable that the tensile strength in the 0 °, 45 ° and 90 ° directions is 90 MPa or more. Moreover, it is more preferable that the tensile strength in the 0 °, 45 °, and 90 ° directions is 100 MPa or more.

(Strength)
Yield strength is 0.2% proof stress and is a stress value at 0.2% permanent elongation.
The aluminum alloy foil of the present invention preferably has a proof stress in the directions of 0 °, 45 ° and 90 ° of 35 MPa or more from the viewpoint of shape stability and moldability. Moreover, it is more preferable that the proof stress in the 0 °, 45 °, and 90 ° directions is 45 MPa or more.

(Yield ratio)
Yield ratio is 0.2% yield strength divided by tensile strength. In the present invention, when an aluminum foil is formed, the moldability is excellent when the difference in strength from the start of deformation until the occurrence of constriction is large. Therefore, the aluminum alloy foil of the present invention preferably has a yield ratio in the 0 °, 45 °, and 90 ° directions that is 0.5 or less. Moreover, it is more preferable that the yield ratios in the 0 °, 45 °, and 90 ° directions are all 0.48 or less. In order to reduce the yield ratio, it is preferable to have an alloy composition that is easy to work harden and a solid solution precipitation state.

Next, the manufacturing method of the aluminum alloy foil for lithium battery exterior of this invention is demonstrated.
The method for producing an aluminum alloy foil for lithium battery exterior according to the present invention comprises a heat treatment step in which an aluminum alloy ingot having the above composition is subjected to a heat treatment at a temperature of 450 to 550 ° C. for 1 hour or longer, and the end of hot finish rolling. A hot rolling step in which hot rolling is performed under conditions where the temperature is 250 ° C. or higher and lower than 350 ° C., a first cold rolling step in which cold rolling is performed at a cold work rate of 80% or higher, and 400 ° C. or higher and lower than 500 ° C. An intermediate annealing step in which an intermediate annealing is performed at a temperature of 2, a second cold rolling step in which a cold rolling with a cold work rate of 85% or more is performed, and an annealing to be held at a temperature of 300 ° C. or higher and lower than 400 ° C. for 1 hour or longer. An annealing process is performed in this order.

  In the production method of the present invention, in the second cold rolling step after the intermediate annealing step, a relatively high cold rolling with a cold work rate of 85% or more is performed, and in the annealing step, 300 ° C. or higher and lower than 400 ° C. It is characterized by annealing at a relatively high temperature. In particular, after improving the workability by performing intermediate annealing, cold working is performed at a high processing rate of 85% or more, and then sufficient annealing is performed to uniformly recrystallize and soften in all directions. It has a great feature in improving the elongation.

FIG. 1 is a flowchart showing a manufacturing process S of the lithium alloy exterior aluminum alloy foil of the present embodiment.
In the method for producing an aluminum alloy foil for lithium battery exterior of the present invention, steps other than those described below may be further added. Further, processes and conditions other than those specifically described below can be produced by a conventional method. Below, the conditions of each process are demonstrated.

(Casting process S1)
The casting process S1 is a process for producing an aluminum alloy ingot by melting and casting an aluminum alloy for a lithium battery exterior. In the casting step S1, an ingot having a predetermined shape is produced from a molten metal in which an aluminum alloy having the above composition is melted. The method for melting and casting the aluminum alloy is not particularly limited, and a conventionally known method may be used. For example, it can be melted using a vacuum induction furnace and cast using a continuous casting method or a semi-continuous casting method.

(Chamfering process)
After the casting step S1, before the next heat treatment step S2, it is preferable to chamfer the ingot in order to remove the surface film formed during casting and the segregation thereunder.

(Heat treatment step S2)
The heat treatment step S2 is a step of subjecting the aluminum alloy ingot having the above composition to a heat treatment (homogenization heat treatment) for 1 hour or more at a temperature of 450 to 550 ° C. The heat treatment temperature is more preferably 460 to 520 ° C. If the heat treatment temperature is less than 450 ° C., the ingot structure is not sufficiently homogenized. In addition, the hot workability is reduced. On the other hand, when it exceeds 550 degreeC, a fine intermetallic compound will coarsen during heating, a crystal grain will coarsen, and elongation will fall. In addition, the amount of solid solution is increased, and the rollability is lowered. Moreover, in order to acquire the said effect, heat processing time needs to be 1 hour or more. On the other hand, since the effect is saturated when it exceeds 24 hours, the heat treatment time is preferably 1 to 24 hours, and more preferably 3 to 8 hours from the viewpoint of production efficiency. Further, the heat treatment step S2 is not limited to once, and can be performed twice or more as necessary.

(Hot rolling process S3)
The hot rolling step S3 is a step of performing hot rolling after the heat treatment step S2 under the condition that the end temperature of the hot finish rolling is 250 ° C. or higher and lower than 350 ° C. The end temperature of hot finish rolling is more preferably 290 to 340 ° C. When the finishing temperature of hot finish rolling is less than 250 ° C., the rollability of the material is lowered, and the rolling itself becomes difficult or the thickness control becomes difficult. On the other hand, at 350 ° C. or higher, since a coarse recrystallized structure is formed by hot rolling, a predetermined crystal grain size cannot be obtained after temper annealing.

(First cold rolling step S4)
The cold working step S4 is a step of performing cold working (cold rolling) with a cold working rate of 80% or more after the hot rolling step S3. After the hot rolling step S3, the cold working is performed once or a plurality of times to obtain a desired final plate thickness. However, if the cold work rate is less than 80%, the crystal grains become coarse after temper annealing. In addition, since a cold work rate is so preferable that it is high, there is no upper limit in particular.

(Intermediate annealing step S5)
The intermediate annealing step S5 is a step of performing the intermediate annealing after the first cold rolling step S4. In the first cold rolling step S4, the cold-rolled material is cured and the workability is lowered, so that the workability is recovered and the next second cold rolling step S6 is performed with a high cold work rate. This is done to allow cold rolling. The intermediate annealing temperature needs to be a temperature of 400 ° C. or higher and lower than 500 ° C., and more preferably 400 to 450 ° C. If it is less than 400 ° C., a sufficient tissue recovery effect cannot be obtained. On the other hand, if it is 500 ° C. or higher, coarse recrystallized grains are generated after annealing, and cracks are generated starting from this. In addition, the intermediate annealing time is preferably 2 to 6 hours from the viewpoint of suppressing grain coarsening.

(Second cold rolling step S6)
The second cold rolling step S6 is a step of performing cold rolling with a cold work rate of 85% or more after the intermediate annealing step S5. It is performed to improve the tensile strength, reduce the thickness of the plate, and improve the surface. Furthermore, it is performed in order to increase the elongation by performing cold working at a high working rate of 85% or more and then recrystallizing in the next annealing step S7. If the cold work rate is less than 85%, an aluminum alloy foil having sufficient elongation cannot be obtained. The cold work rate is preferably 90% or more.

(Annealing step S7)
The annealing step S7 is a step of performing annealing for 1 hour or more at a temperature of 300 ° C. or higher and lower than 400 ° C. after the second cold rolling step. The annealing temperature is more preferably 300 to 350 ° C. This step is performed in order to recrystallize uniformly and sufficiently to generate fine crystal grains, thereby increasing elongation in all directions and imparting excellent rectangular tube formability. If the annealing temperature is less than 300 ° C., uniform recrystallization does not proceed sufficiently and elongation cannot be obtained. On the other hand, if it is 400 ° C. or higher, coarse recrystallized grains are generated after annealing, and cracks are generated starting from this. Further, the refinement of crystal grains is not promoted. In order to acquire the said effect, annealing time needs to be 1 hour or more. On the other hand, since the effect is saturated when it exceeds 70 hours, the heat treatment time is preferably 1 to 70 hours in terms of production efficiency. More preferably, it is 35 to 60 hours.

  The aluminum alloy foil obtained through the manufacturing step S having the above steps can have excellent square tube formability as an aluminum alloy for a lithium battery exterior.

  When polymerized rolling is used as a process for producing an aluminum foil, an aluminum foil having both a glossy bright surface and a matte mat surface is produced. In the present invention, there is no particular limitation on bringing either the bright surface or the mat surface to the front side of the lithium battery exterior.

  Actually, when the aluminum alloy foil for lithium battery exterior of the present invention is used as an exterior material for a lithium battery, a resin film is laminated on the surface of the aluminum foil or a resin is coated. Known methods can be applied to the resin sheet laminating method and resin coating method.

  Next, this invention is demonstrated based on an Example. In addition, this invention is not limited to the Example shown below.

Example 1
An aluminum alloy having the composition shown in Table 1 was melted and cast to form an ingot, and the ingot was subjected to face cutting, followed by heat treatment at 480 ° C. for 4 hours. The ingot subjected to the heat treatment was hot-rolled by controlling the finish temperature of hot finish rolling to be 330 ° C. to obtain a hot-rolled sheet having a thickness of 2.8 mm. Furthermore, the 1st cold rolling was given with the cold work rate of about 84.5%, and the intermediate annealing for 4 hours was given at 420 degreeC. Next, second cold rolling was performed at a cold working rate of about 90.5%, and annealing was performed at 320 ° C. for 35 hours to obtain an aluminum alloy foil for lithium battery exterior.

(Examples 2-7, Comparative Examples 1-9)
Production was performed under the same conditions as in Example 1 except that the composition of the aluminum alloy, the processing rate in the second cold rolling process, and the annealing conditions were changed to the conditions described in Table 1, and Examples 2 to 7 and Comparison The aluminum alloy foil for lithium battery exterior of Examples 1-9 was obtained. However, in Comparative Example 6, since the Si content was low, a hot water leak occurred and a cast product could not be obtained.

  In the examples and comparative examples, the evaluation conditions of the composition and properties of the obtained aluminum alloy foil are as follows.

[Alloy composition]
The alloy composition was measured using an emission analyzer OES-1014 manufactured by Shimadzu Corporation. The measurement site of the product is not particularly limited as long as measurement is possible.

[Average grain size]
Based on the measurement method described above, the average grain size of the crystal grains of the sample was measured.
The average grain size of the crystal grains was measured at three locations at different locations in the central portion of the manufactured sample, and obtained as an average value. Further, the surface of the sample was mechanically polished before measurement, and the processed layer on the surface was removed by a chemical polishing method of ion milling, and then subjected to measurement.

  FIG. 5 is a scanning electron microscope image showing a specific example of the method for measuring the crystal grain size. FIG. 5 (a) shows an inverted pole figure based on data subjected to orientation analysis by the EBSD method. FIG. 5 (b) shows a case where a crystal grain surrounded by a crystal grain boundary whose orientation difference between adjacent crystal grains is 15 ° or less is drawn as one crystal grain region on the analysis software in Example 6. 10 grid lines each having a length of 100 μm are drawn at 10 μm intervals in the vertical and horizontal directions. It shows that the average crystal grain size is 5.3 μm. FIG. 5C is a graph in which crystal grains and lattices surrounded by crystal grain boundaries are drawn in Comparative Example 2 as in FIG. 5B. It shows that the average crystal grain size is 9.9 μm.

[Tensile test]
Tensile strength, elongation, and proof stress were performed under the following conditions. A strip-shaped test piece of 15 mm width × about 200 mm length is cut out from the center in the width direction of the sample so that the tensile direction is 0 °, 45 °, and 90 ° with the rolling direction, respectively. A tensile test was carried out in accordance with the Light Metal Association standard LIS AT5, with a chuck distance of 100 mm. Elongation was calculated from the displacement of the crosshead. The number of tests was 5 times per sample. The values of tensile strength and elongation were average values of 3 times excluding the maximum and minimum values out of 5 times.

[Square tube forming test method]
A sample for evaluation having a size of 100 mm × 100 mm was cut out from the sample, and the test relating to the square tube formability described below was performed. In this example, evaluation was performed using an aluminum foil having a thickness of 40 μm. In addition, as a test apparatus, the apparatus for Eriksen test of JIS Z 2247 can be diverted.

FIG. 2 is a perspective view showing an appearance of the jig 1 used in the square tube forming test.
The die 2 has a regular quadrangular prism cavity corresponding to a female die at the center. This cavity has a side of 40.25 mm, and a punch 4 having a side of 40 mm has a clearance of 0.125 mm on one side. The lower corner of the die 2 has a roundness with R of 3 mm.

  The die 2 is placed on the sample stage 3 and can be fixed (fixing tool is not shown). The sample table 3 also has a cavity at the center, and the punch 4 can be inserted into the cavity at the center of the die 2 from below with a predetermined length. The punch 4 has a quadrangular prism shape and corresponds to a male mold. The length of one side of the punch 4 is 40 mm, and the corner of the shoulder of the punch 4 has a roundness with R of 4.5 mm.

3A to 3F are cross-sectional views showing the procedure of the test method for the square tube forming test. It is shown as a cross-sectional view at the AA position in FIG.
FIG. 3A shows the positional relationship between the sample table 3 and the punch 4. In FIG. 3 (b), the sample 5 is placed on the inner bottom of the sample table 3. At this time, the sample 5 is placed so that the bright surface is on the lower side (the punch 4 side). In addition, a water-soluble plastic working oil No. 700 manufactured by Castrol Co., Ltd. is previously applied as a lubricant to the bright surface (on the punch 4 side) of the sample 5.

  In FIG. 3C, the die 2 is placed on the sample 5 in the sample table 3 and fixed.

  In FIG. 3D, the punch 4 is pushed up from below the fixed sample 5. At this time, the pushing speed of the punch 4 was set to 17 mm / min.

  In FIG. 3 (e), the upper edge of the punch 4 is pushed up to a position where it rises by a predetermined distance with respect to the upper surface of the inner bottom portion of the sample stage 3, that is, the position of the original lower surface of the sample 5. Immediately thereafter, the punch 4 is lowered to the initial position. At this time, the predetermined distance is a specific numerical value with an interval of 0.1 mm from less than 4.0 mm to about 7.0 mm.

  In FIG. 3 (f), the molded specimen 5 can be removed from the sample table 3 by removing the die 2 from the sample table 3.

  3A to 3F are repeated while exchanging the sample 5 for a new one and changing the distance for pushing up the punch 4 by 0.1 mm. That is, while changing the distance by which the punch 4 is raised in increments of 0.1 mm, the sample 5 is replaced, the center part of the sample 5 is pushed up, the molding operation is repeated, and various molded products having different push-up distances are obtained. obtain.

  FIG. 4 is a perspective view of the sample 5 formed in the square tube forming test. The bright surface of the sample 5 is on the lower side, and the molded product has a rectangular convex portion at the center.

  The molded sample 5 is observed to visually determine whether or not a crack has occurred in the molded part, and the maximum push-up distance at which no crack is generated is defined as a limit molding height (mm).

  The evaluation results of Examples 1 to 7 and Comparative Examples 1 to 9 are shown in Table 1. In the alloy composition of Table 1, the composition indicated by “-” indicates that it is below the detection limit of the analyzer. Moreover, among the numerical values shown in Table 1, the numerical value underlined indicates that the numerical value is out of the numerical range of the claims.

  Examples 1 to 7 have the alloy composition according to claim 1 and are manufactured under the manufacturing conditions according to claim 4, and all of them are excellent square tubes having a limit forming height of 5 mm or more. It had moldability.

  In Comparative Example 1, in the aluminum alloy composition, the Fe content was high, neither Cu nor Mn was contained, the elongation was low at less than 20%, and the square tube formability was poor. In Comparative Example 2, the Fe content is low, the Si content is high, and neither Cu nor Mn is contained, but the crystal grain size is as large as 9.9 μm, and the elongation and tensile strength are inferior. It was a thing.

  In Comparative Example 3, the aluminum alloy composition contained neither Cu nor Mn, the crystal grain size was as large as 7.3 μm, the elongation was low, and the square tube formability was poor. Comparative Examples 4 and 5 each had a high Cu and Mn content, both of which had low elongation, a high yield ratio, and poor square tube formability.

  In Comparative Examples 7 and 8, in the annealing process, the annealing temperature is low or the annealing time is short, but the recrystallization does not proceed sufficiently, the elongation is low, the yield ratio is high, and the square tube formability is high. Was inferior. In Comparative Example 9, in the second cold rolling step, the cold working rate was as low as 84.0%, but the crystal grain size was high, the elongation was low, and the square tube formability was inferior. It was.

S Production process of aluminum alloy foil for lithium battery exterior of this embodiment S1 Casting process S2 Heat treatment process S3 Hot rolling process S4 First cold rolling process S5 Intermediate annealing process S6 Second cold rolling process S7 Annealing process 1 Square tube forming Jig used for testing 2 Die 3 Sample stand 4 Punch 5 Sample (Aluminum alloy foil)

Claims (4)

Fe: 1.2-1.7% by mass, Si: 0.04-0.08% by mass, Cu: 0.2% by mass or less, Mn: 0.2% by mass or less, the balance being The aluminum alloy foil is made of an aluminum alloy composed of Al and inevitable impurities, and the total content of Cu and Mn is 0.05% by mass or more,
The average grain size of the crystal grains is 7 μm or less,
An aluminum alloy foil for an exterior of a lithium battery, wherein the elongation in the 0 °, 45 °, and 90 ° directions is 20% or more.   The aluminum alloy foil for a lithium battery exterior according to claim 1, wherein the elongation in the directions of 0 °, 45 °, and 90 ° is 30% or more.   The aluminum alloy foil for a lithium battery exterior according to claim 1 or 2, wherein the yield ratio in the 0 °, 45 °, and 90 ° directions is 0.5 or less. It is a manufacturing method of the aluminum alloy foil for lithium battery exterior given in any 1 paragraph of Claims 1-3,
A heat treatment step of subjecting the aluminum alloy ingot having the above composition to a heat treatment at a temperature of 450 to 550 ° C. for 1 hour or more;
A hot rolling step in which hot rolling is performed under conditions where the finish temperature of hot finish rolling is 250 ° C. or higher and lower than 350 ° C .;
A first cold rolling step of performing cold rolling with a cold working rate of 80% or more;
An intermediate annealing step in which intermediate annealing is performed at a temperature of 400 ° C or higher and lower than 500 ° C;
A second cold rolling step for performing cold rolling with a cold working rate of 90 % or more;
And an annealing step of performing annealing at a temperature of 300 ° C. or higher and lower than 400 ° C. for 1 hour or longer in this order.