Aluminum alloy foil and method for manufacturing the same

Abstract

This aluminum alloy foil (1) is formed of an aluminum alloy which has a composition that contains 1.2% by mass to 2.5% by mass of Fe and 0.5% by mass or less of other elements including at least Si, with the balance being made up of Al and unavoidable impurities. With respect to this aluminum alloy foil, all of the elongation in the 0° direction, the elongation in the 45° direction and the elongation in the 90° direction with respect to the rolling direction are 20% or more; and if L ( / µm) is the length of grain boundaries having a misorientation of 2° or more per unit area of 1 µm2, and S (µm) is the average grain size of crystal grains surrounded by grain boundaries having a misorientation of 15° or more as determined by an electron backscattered diffraction method, formula (1) is satisfied.　Formula (1): L × S ≤ 15

Description

[Technical Field]

[0001] The present invention relates to aluminum alloy foil and a method for producing the same. This application claims priority based on Japanese Patent Application No. 2022-140851, filed in Japan on September 5, 2022, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] Aluminum alloy foil used in packaging for food products and lithium-ion batteries is formed by press molding and other processes that subject it to significant deformation, and therefore requires high elongation. For aluminum alloy foil to possess both high elongation and good formability, fine and uniform crystal grains, as well as random texture, are considered important.

[0003] For example, Patent Document 1 discloses an aluminum alloy foil with excellent formability, containing Fe and Mg, and with a Si content restricted to 0.10% or less. Furthermore, Patent Document 2 discloses an aluminum alloy foil containing Fe and Si, with the upper limit of Cu and Mn content restricted to 0.2%, and the size of the crystal grains restricted. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 3-191042 [Patent Document 2] Japanese Patent Publication No. 2014-65956 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In light of the aforementioned background, the inventors are conducting research and development on aluminum alloy foil suitable for use as outer foil for lithium-ion batteries. When the inventors considered aluminum alloy foil for packaging materials, they found that elongation is often achieved not by deforming the aluminum alloy foil in one direction, but by a process known as stretch molding. Therefore, high elongation is required not only in the direction parallel to the rolling direction, which is commonly used for the elongation value of materials, but also in directions such as 45° and 90° relative to the rolling direction. Furthermore, in recent years, there has been a trend towards thinner packaging materials, particularly in the battery packaging sector.

[0006] However, the aluminum alloy foil described in Patent Document 1 has a problem in that it does not have sufficient uniformity of elongation in each direction, making it difficult to achieve uniform deformation in processes such as stretch molding. Furthermore, while the aluminum alloy foil described in Patent Document 2 shows sufficient elongation, it also shows an example where Cu and Mn are added in amounts of 0.2% or less to refine the crystal grains. However, even trace amounts of these elements can lead to a decrease in rollability and an increased risk of fracture during rolling due to edge crack formation, raising concerns about reduced productivity. In addition, in aluminum alloy materials containing nearly 1.5% Fe, even a small amount of Mn can cause coarsening of Al-Fe-Mn precipitates. Therefore, if the foil is thin, there is a concern that this increases the risk of fracture during rolling or hole formation during forming.

[0007] The present invention aims to provide an aluminum alloy foil that has good processability and high formability. [Means for solving the problem]

[0008] The inventors conducted a more detailed structural analysis of aluminum alloy foil for packaging materials, and based on that knowledge, fundamentally revised the manufacturing method of the alloy. This led to the development of a technology that can provide the desired aluminum alloy foil, and thus to the present invention. (1) An aluminum alloy foil according to one aspect of the present invention contains Fe: 1.2% by mass or more and 2.5% by mass or less It contains, and of the elements Si, Mg, Cu, Mn, Zn, and Ti, it contains at least Si, and the total content of Si combined with any of the other elements from Si, Mg, Cu, Mn, Zn, and Ti is 0.5% by mass or less.This aluminum alloy foil is made of an aluminum alloy having a composition in which the remainder is Al and unavoidable impurities, and the elongation in the 0° direction, 45° direction, and 90° direction with respect to the rolling direction is all 20% or more, and the area measured by electron backscattered diffraction (EBSD) is 1 μm. 2 The following equation (1) is satisfied when L ( / μm) is the grain boundary length with an orientation difference of 2° or more at a given point, and S (μm) is the average grain size of the crystal grains surrounded by grain boundaries with an orientation difference of 15° or more. L×S≦15 …(1) formula

[0009] (2) In the aluminum alloy foil described in (1) above, it is preferable that the average crystal grain size is less than 20 μm. (3) In the aluminum alloy foil described in (1) or (2) above, the average particle size (equivalent circle diameter) of the intermetallic compounds dispersed inside the foil is 0.50 to 0.80 μm, and the dispersion density is 150,000 to 320,000 particles / mm 2 It is preferable that the number density range is within this range.

[0010] (4) A method for manufacturing aluminum alloy foil according to one aspect of the present invention comprises the steps of pouring molten aluminum alloy from a nozzle provided in a tundish into a conveying and cooling device, cooling it to continuously cast a cast sheet, and cold rolling the cast sheet to manufacture aluminum alloy foil, wherein the aluminum alloy is Fe: 1.2% by mass or more and 2.5% by mass or less It contains, and of the elements Si, Mg, Cu, Mn, Zn, and Ti, it contains at least Si, and the total content of Si combined with any of the other elements from Si, Mg, Cu, Mn, Zn, and Ti is 0.5% by mass or less. The composition consists of Al and unavoidable impurities, and in the continuous casting process, the cooling rate of the molten metal is set to 50-500°C / second, and in this process, the elongation in the 0° direction, 45° direction, and 90° direction relative to the rolling direction is all 20% or more, and the area measured by electron backscatter diffraction is 1 μm 2 The present invention is characterized by obtaining an aluminum alloy foil that satisfies the following equation (1) when the grain boundary length with an orientation difference of 2° or more at a given point is L ( / μm), and the average grain size of the crystal grains surrounded by grain boundaries with an orientation difference of 15° or more is S (μm). L×S≦15 …(1) formula

[0011] (5) In the method for producing an aluminum alloy foil according to (4) above, in the produced aluminum alloy foil, it is preferable that the average crystal grain diameter is less than 20 μm. (6) In the method for producing an aluminum alloy foil according to (4) or (5) above, in the produced aluminum alloy foil, the average particle diameter (equivalent circle diameter) of the intermetallic compound dispersed inside the foil is 0.50 to 0.80 μm, and the dispersion density is 150,000 to 320,000 particles / mm 2 and it is preferable that the number density is in the range. [Effect of the Invention]

[0012] According to one aspect of the present invention, it is possible to provide an aluminum alloy foil having good workability and high formability. [Brief Description of the Drawings]

[0013] [Figure 1] FIG. 1 is a plan view showing a first embodiment of an aluminum alloy foil according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing an example of a continuous casting apparatus for producing a casting slab (slab) that is the basis of the aluminum alloy foil according to the present invention. [Embodiments for Carrying Out the Invention]

[0014] Hereinafter, an example of an embodiment of the present invention will be described in detail based on the accompanying drawings. In the drawings used in the following description, for the sake of clarity of the features, parts that are characteristic may be shown enlarged for convenience.

[0015] FIG. 1 is a plan view showing an embodiment of an aluminum alloy foil according to the present invention. The aluminum alloy foil 1 shown in FIG. 1 is a foil obtained by obtaining a casting slab by a continuous casting method described later and cold-rolling this casting slab, and is depicted as a strip having a certain width and the longitudinal direction facing left and right in FIG. 1. The rolling direction of this aluminum alloy foil 1 is the left-right direction shown in Figure 1 (the length direction of the strip-shaped foil 1). For convenience, the direction at 0° to the rolling direction means the left-right direction in Figure 1, the direction at 45° to the rolling direction means the direction of the arrow labeled 45° in Figure 1, and the direction at 90° to the rolling direction means the direction of the arrow labeled 90° in Figure 1. In other words, the direction at 90° to the rolling direction in aluminum alloy foil 1 means the width direction of the strip-shaped aluminum alloy foil 1 (the vertical direction on the paper in Figure 1).

[0016] The aluminum alloy foil 1 shown in Figure 1 is formed to have a thickness of, for example, about 0.1 μm to 0.2 mm. The thickness of the aluminum alloy foil 1 can be any thickness that is typical for foils. This aluminum alloy foil 1, as an example, is made of an aluminum alloy having a composition in which Fe: 1.2% to 2.5% by mass, other elements including at least Si totaling 0.5% by mass or less, and the remainder being Al and unavoidable impurities. Furthermore, as an example, aluminum alloy foil 1 has an elongation of 20% or more in the 0° direction, the 45° direction, and the 90° direction with respect to the rolling direction, and an average grain size of less than 20 μm.

[0017] The following explains the reasons for limiting the composition, properties, and structure of the aluminum alloy constituting aluminum alloy foil 1. ·Fe: 1.2 mass% or more and 2.5 mass% or less Fe crystallizes as Al-Fe intermetallic compounds during casting, and if the size of these compounds is suitable, they act as recrystallization sites during annealing, resulting in the refinement of the recrystallized grains. If the Fe content is less than 1.2 mass%, the distribution density of the intermetallic compounds decreases, reducing the grain refinement effect and resulting in a non-uniform final grain distribution. If the Fe content exceeds 2.5 mass%, the grain refinement effect saturates or decreases, and the size of the Al-Fe intermetallic compounds generated during casting becomes very large, reducing the elongation, formability, and rollability of the alloy foil. The particularly preferable Fe content range is 1.4 mass% to 1.8 mass%.

[0018] • Other elements containing at least Si (elements other than Fe): 0.5% by mass or less Si forms Al-Fe-Si intermetallic compounds with Fe, but adding other elements containing Si in excess can lead to coarser compound size and reduced distribution density. If the content of other elements containing Si exceeds the upper limit, there is a concern that coarser crystals will reduce elongation and formability, and furthermore, that the uniformity of the recrystallized grain size distribution will decrease after final annealing. For these reasons, the total content of other elements containing Si should be set at 0.5 mass% or less. For the same reasons, it is desirable to set the upper limit of Si content at 0.4 mass%. In addition to Si, other elements that can be contained in the aluminum alloy include Mg, Cu, Mn, Zn, and Ti. The total content of these elements, including Si, is preferably 0.5% by mass or less. If the total content of these elements, including Si, exceeds 0.5% by mass, the desired elongation cannot be obtained. While there is no particular lower limit to the total content of other elements, including at least Si, it is preferably 0.04% or more.

[0019] • The elongation in the 0° direction, the 45° direction, and the 90° direction relative to the rolling direction are all 20% or more. The aluminum alloy foil 1 used in packaging is subjected to three-dimensional deformation by press molding. Therefore, it is required to have good elongation not only in the rolling direction but also in various directions. If the elongation in any of the above directions is less than 20%, the elongation in that direction becomes the rate-limiting factor, and the formability of the aluminum alloy foil 1 decreases. In order to maintain the formability of the aluminum alloy foil 1, it is necessary that the elongation is 20% or more in all directions relative to the rolling direction. In this embodiment, as an example of having excellent elongation in all directions, it is intended that the elongation in the 0° direction, the 45° direction, and the 90° direction relative to the rolling direction are excellent. In the aluminum alloy foil 1, it is more preferable that the elongation in the 0° direction, the 45° direction, and the 90° direction with respect to the rolling direction are all 25% or more. The upper limits of the elongation in the 0° direction, the 45° direction, and the 90° direction with respect to the rolling direction are not particularly limited, but are preferably 40% or less.

[0020] • The average crystal grain size of the foil is less than 20 μm. In the aluminum alloy foil 1 of this embodiment, the roughness of the foil surface when deformed can be suppressed by refining its crystal grains. Therefore, high elongation and consequently high formability can be expected. If the average crystal grain size of the foil is 20 μm or more, the crystal grains are coarse, which makes the foil surface prone to roughness during molding, leading to a decrease in formability. The lower limit of the average crystal grain size is not particularly limited, but 6 μm or more is preferred.

[0021] • Area measured by EBSD method: 1 μm 2 Let L ( / μm) be the grain boundary length with an orientation difference of 2° or more, and let S (μm) be the average grain size of the crystal grains surrounded by grain boundaries with an orientation difference of 15° or more. Then, L × S ≤ 15 …(1) is satisfied. In Al-Fe alloys, continuous recrystallization preferentially occurs after annealing following rolling, resulting in a high density of grain boundaries in the annealed microstructure. A high number of grain boundaries with orientation differences of 2° or more can easily lead to stress concentration during forming, reducing formability. On the other hand, grains surrounded by grain boundaries with orientation differences of 15° or more are considered to contribute significantly to formability and therefore need to be fine. Considering these balances, an area of ​​1 μm is desirable. 2 It is necessary that the grain boundary length with an orientation difference of 2° or more per unit area, and the average grain size of the crystal grains surrounded by grain boundaries with an orientation difference of 15° or more, satisfy equation (1). Preferably, the relationship is L × S ≤ 10. Note that a grain boundary with an azimuth difference of 2° or more refers to a grain boundary with an azimuth difference of 2° to 180°, and a grain boundary with an azimuth difference of 15° or more refers to a grain boundary with an azimuth difference of 15° to 180°.

[0022] The average particle size (equivalent circle diameter) of the intermetallic compound is 0.50 to 0.80 μm, and the dispersion density is 150,000 to 320,000 particles / mm³.2 This is the number density range. In this embodiment, the intermetallic compounds are mainly Al-Fe-based or Al-Fe-Si-based intermetallic compounds dispersed in the metal structure. Other examples include Al-Mg-Si intermetallic compounds, Al-Fe-Mn intermetallic compounds, and Al-Mn intermetallic compounds. The average particle size of intermetallic compounds is 0.50 to 0.80 μm, and the dispersion number density is 150,000 to 320,000 particles / mm³. 2 A certain degree is desirable. If the grain size of intermetallic compounds is too small or the dispersion number density is too low, they do not contribute to grain refinement, and good formability cannot be obtained. Conversely, if the grain size of intermetallic compounds is large, especially if coarse intermetallic compounds are present, they tend to become the starting point for cracks during forming, thus hindering formability. Also, if the dispersion number density of intermetallic compounds is too high, work hardening during forming becomes greater, and stress concentration is more likely to occur, which also hinders formability.

[0023] "Method for manufacturing aluminum alloy foil" To manufacture the aluminum alloy foil 1 shown in Figure 1, a molten aluminum alloy satisfying the above-mentioned composition is prepared, and an aluminum alloy cast sheet is obtained by continuous casting using this molten aluminum alloy. Next, the aluminum alloy foil 1 can be obtained by cold rolling this cast aluminum alloy sheet to the desired thickness.

[0024] Figure 2 shows an example of a continuous casting apparatus suitable for the process of manufacturing aluminum alloy foil 1. The continuous casting apparatus A shown in Figure 2 includes a tundish 3 for storing molten alloy M of the target composition, a refractory nozzle 5 mounted horizontally on the side wall 3A of the tundish 3, and an upper roll (conveying and cooling device) 6 and a lower roll (conveying and cooling device) 7 positioned at the tip of the nozzle 5. A trough 8 for supplying molten alloy M is provided above the tundish 3. A supply pipe 9 is provided below the trough 8, allowing molten alloy M to be supplied to the tundish 3 via the supply pipe 9.

[0025] In Figure 2, the upper roll 6 and lower roll 7 are shown in a simplified manner. These rolls have a double-layered structure with a roll core and a roll shell. A flow path for a cooling medium (not shown) is formed between the roll core and the roll shell, allowing each roll to be cooled from the inside. In Figure 2, only a portion of the roll shell is shown with a break line, and the details of each roll are omitted.

[0026] Since molten alloy M can be supplied (pouring) from the tip of nozzle 5 between the upper roll 6 and the lower roll 7, an aluminum alloy cast plate, indicated by reference numeral 10 in Figure 2, can be cast by rotating the upper roll 6 and the lower roll 7 while supplying the molten alloy M. By supplying molten alloy from the trough 8 to the tundish 3 to adjust the amount of molten alloy in the tundish 3, and continuously supplying the molten aluminum alloy from the tundish 3 through the nozzle 5 to the rolls 6 and 7, aluminum alloy cast plates 10 can be continuously cast.

[0027] The continuous casting apparatus A shown in Figure 2 can be used to manufacture aluminum alloy cast plates 10 by setting the cooling rate to approximately 50 to 500°C / second. The thickness of these cast plates 10 can be approximately 4 mm to 10 mm, for example, about 7 mm. By adopting a cooling rate within this range, it becomes easier to create a microstructure in the aluminum alloy foil 1 described later that satisfies the aforementioned equation L × S ≤ 15 …(1). It is preferable to subject the obtained aluminum alloy cast plate 10 to a homogenization treatment. The homogenization treatment can be carried out at 550°C to 620°C for several hours, for example, at 595°C for 8 hours. The duration of the homogenization treatment is preferably 1 to 12 hours.

[0028] Once an aluminum alloy cast sheet 10 is manufactured, an aluminum alloy foil 1 with a thickness of approximately 10 μm to 0.2 mm, for example, 40 μm, can be obtained by performing cold rolling at the required rate for the required number of times. The rate of processing per pass of cold rolling (rolling rate) is preferably 40% or more, and the total rate of processing is preferably 60% or more. It is preferable to perform cold rolling multiple times, with intermediate annealing between cold rolling cycles. For intermediate annealing, it is preferable to heat at 200°C to 400°C for several tens of minutes to several hours. For example, it is preferable to heat at 360°C for about 3 hours, followed by slow cooling. Furthermore, it is preferable to perform a final annealing after cold rolling. In the final annealing, it is desirable to heat at 220°C to 350°C for about 30 minutes to 10 hours, and then cool slowly.

[0029] By continuously casting to produce a cast sheet at the cooling rate described above, and by cold rolling the obtained cast sheet and performing cold rolling and final annealing under the conditions described above, an aluminum alloy foil 1 that satisfies equation (1) can be obtained. The resulting aluminum alloy foil 1 contains a predetermined amount of Fe, which influences the texture of the aluminum alloy and contributes to the refinement of the grain size. Although the aluminum alloy contains 1.2 to 2.5 mass% Fe, casting it into a sheet using a continuous casting method results in good elongation even with Fe content within the above range. Furthermore, the aluminum alloy used here may contain, in addition to Fe, other elements, including at least Si, in an amount of approximately 0.5% by mass or less. Even if the aluminum alloy foil 1 of this embodiment contains other elements such as Si in the amount described above, an aluminum alloy foil that can achieve the objective can be obtained.

[0030] By the manufacturing method described above, an aluminum alloy foil 1 can be obtained in which the elongation in the 0° direction, the 45° direction, and the 90° direction with respect to the rolling direction are all 20% or more, the average grain size is less than 20 μm, and the above equation (1) is satisfied. The aluminum alloy foil 1 described above is suitable for food packaging or as a molded packaging material for lithium-ion batteries, and provides an aluminum alloy foil suitable for applications where large deformation is applied by press molding, and where high elongation and formability are required.

[0031] It should be noted that the continuous casting apparatus used to manufacture the aluminum alloy foil 1 according to this embodiment is not limited to the twin-roll type shown in Figure 2. Other methods and apparatuses for continuous casting of aluminum alloys are also known, such as the Hunter method, Lauener Caster I (Alusuisse Caster I), Davey McKee Twin-roll sheet caster, and Twin belt caster, and any of these may be used. [Examples]

[0032] Aluminum alloy molten metal was prepared to have alloy compositions No. 1 to 46 as shown in Tables 1 and 2. Using the twin-roll type continuous casting apparatus shown in Figure 2, 7 mm thick aluminum alloy cast plates were manufactured under the cooling rates of 4 to 483 °C / sec shown in Tables 1 and 2. The obtained aluminum alloy cast plates were rolled and placed in a heating furnace, where they were subjected to a homogenization treatment by heating at temperatures of 540 to 620 °C for 8 hours as shown in Table 3. Next, the aluminum alloy foil was subjected to cold rolling and intermediate annealing by heating at a temperature of 200-400°C for 3 hours as shown in Table 3. Here, intermediate annealing was performed on a cold-rolled sheet with a thickness of 0.7 mm. As a result, an aluminum alloy foil with the desired thickness of 40 μm was obtained. The obtained aluminum alloy foil was then subjected to final annealing by heating at a temperature of 220-350°C for 8 hours as shown in Table 3, followed by slow cooling, to obtain the final product. Table 3 shows the temperature and time for homogenization, intermediate annealing, and final annealing for manufacturing processes A through I.

[0033] • Measurement of elongation Elongation was measured by conducting tensile tests in accordance with JIS Z2241. JIS No. 5 test specimens were taken from each sample (foil thickness 40 μm) to measure elongation in directions of 0°, 45°, and 90° relative to the rolling direction. The tests were performed on a universal tensile testing machine (Shimadzu AGS-X 10kN) at a tensile speed of 2 mm / min. The elongation rate is calculated as follows. First, before the test, two lines were marked at an interval of 50 mm, which is the gauge length, in the direction perpendicular to the test piece at the longitudinal center of the test piece. After the test, the fracture surfaces of the aluminum alloy foil were joined together, the distance between the marks was measured, and the elongation amount (mm) obtained by subtracting the gauge length (50 mm) from it was divided by the gauge length (50 mm) to obtain the elongation rate (%). Regarding the elongation rate, for the obtained aluminum alloy foil, specimen pieces were taken and measured for the elongation in the 0° direction with respect to the rolling direction, the elongation in the 45° direction with respect to the rolling direction, and the elongation in the 90° direction with respect to the rolling direction.

[0034] · Measurement of average crystal grain size As a pretreatment, the surface of the aluminum alloy foil was mirror-finished by electrolytic polishing. Specifically, electrolytic polishing was performed at a voltage of 20 V for 5 seconds using a solution containing perchloric acid and ethanol at a volume ratio of perchloric acid:ethanol = 1:4. Next, the measurement and analysis of the crystal orientation were performed with a crystal orientation measuring device (SEM (Scanning Electron Microscope) - EBSD) under the following conditions. (Conditions of the electron microscope) Observation magnification: 1000 times Acceleration voltage: 15 kV Sample tilt angle: 70° Step Size: 0.3 μm (Conditions of the EBSD detector) Analysis software: OIM Analysis (Ver.8.0) from TSL Solutions Area: Images measured at 1000 times magnification were connected to a total area of 50000 μm 2 The above was analyzed. CI value (Confidence Index): Measurement points with a CI value of 0.1 or less were excluded. Minimum Grain Size (points): 2 Anti Grains: 2 (Measurement and calculation conditions of average crystal grain size) Grain Tolerance Angle: 15° Minimum Grain Size (points): 2 Anti-grains: 2 Minimum Confidence Index: 0.1 Multiple rows required: All were turned OFF. Apply partition before control: OFF. Include grains at edges of scan in statistics: OFF. Grain boundaries with an orientation difference of 15° or more between crystal grains were defined as HAGBs (high-angle grain boundaries), and the size of the crystal grains enclosed by HAGBs was measured. Images measured at 1000x magnification were stitched together to obtain a total area of ​​50,000 μm². 2 Based on the above analysis, the average grain size was calculated. The EBSD Area method (Average by Area Fraction Method) was used to calculate the average grain size. TSL Solutions' OIM Analysis (Ver. 8.0) was used for the analysis. In detail, crystal grains enclosed by HAGBs were identified. Here, crystal grains whose outlines intersected the observation field of view were excluded (edge ​​grain excluded in analysis). The area of ​​a crystal grain was calculated from the number of measurement points within that crystal grain. The value obtained by multiplying the area fraction occupied by a single crystal grain within the observation field of view by the area of ​​that crystal grain was calculated. The average area of ​​the crystal grains was calculated by summing the values ​​obtained by multiplying the area fractions of all observed crystal grains by their areas (area method). The average crystal grain size was calculated by determining the diameter of a circle with the same area as the average area of ​​the crystal grains (equivalent circular area diameter).

[0035] L×SValue In a grain map obtained by EBSD (Electron Microscopy) by setting an orientation difference between crystal grains that constitute grain boundaries, the set grain boundaries can be analyzed. The grain boundary length L of grain boundaries with an orientation difference of 2° or more within the field of view was analyzed, with a minimum of 2° (maximum of 180°) set for the orientation difference between crystal grains. The measurement conditions for grain boundary length L (electron microscope conditions, EBSD detector conditions, measurement area) were the same as those for measuring the average grain size, except that a boundary with an orientation difference of 2° or more between crystal grains was defined as a grain boundary. The obtained metallographic structure was observed using EBSD, with an area of ​​1 μm. 2 The value of L × S was calculated when the grain boundary length with an orientation difference of 2° or more at a given point was defined as L ( / μm), and the average grain size of the crystal grains surrounded by grain boundaries with an orientation difference of 15° or more was defined as S (μm). The grain boundary length L is given by the unit area (1 μm). 2 This is the grain boundary length (μm) per unit area, also called grain boundary density, and its unit is μm / μm. 2 = / μm. The average grain size S is a value measured using the same method as the average crystal grain size measurement method described above.

[0036] • Measurement of average particle size and dispersion density of intermetallic compounds The average particle size and dispersion density of intermetallic compounds were measured by observing the cross-section (RD-ND plane) obtained by cutting aluminum alloy foil perpendicular to the rolling direction (RD) under the following conditions. (Measurement conditions for average particle size and dispersion density of intermetallic compounds) Measurement surface: RD-ND cross section Cutting method: CP (Cross-section polisher) Observation method: Backscattered electron images (compositional images) were observed using SEM. Observation magnification: 2000x Observation area: Images are stitched together to cover a total area of ​​40,000 μm². 2 The above observations were made. Image analysis software: ImageJ Size of Analyzed Particles: Projection area is 0.5 μm 2 The above particles Circularity of Analyzed Particles:0.00~1.00 The aluminum alloy foil was cut using a cross-section polisher (CP). A backscattered electron image (compositional image) of the cross-section was captured using a scanning electron microscope (SEM) at 2000x magnification, and the captured images were stitched together to create a total area of ​​40,000 μm². 2 The above images were obtained. Using the obtained images, the average particle size and dispersion density of the intermetallic compounds were analyzed. As an example, the image analysis software ImageJ was used to analyze the average particle size and dispersion density of the intermetallic compounds, specifically the density of the number of particles (particles / mm³) within the field of view. 2 The average particle size (μm) was calculated based on the equivalent diameter of the circle. Under the above conditions, the particle number density and average particle size were calculated within the observation field, regardless of the particle shape, assuming a projected area of ​​0.5 μm. 2 The calculation was performed considering all of the above particles. In detail, considering the effects of sagging during cutting, 10% of the thickness was removed from each surface of the aluminum alloy foil (cropping), and images of the central part of the thickness in the cross-section of the aluminum alloy foil were used for analysis. The Threshold value was set to a value in the range of 100 to 130, and the images were binarized. The area of ​​each intermetallic compound particle was measured. The average area was calculated by dividing the sum of the areas of the intermetallic compounds by the number of intermetallic compounds. The diameter of a circle with the same area as the average area of ​​the intermetallic compounds (equivalent circular area diameter) was calculated as the average particle size.

[0037] • Molding limit height (limit molding height) The molding height was evaluated using a rectangular tube molding test. The test was conducted using a universal thin sheet molding tester (ERICHSEN Model 142 / 20), and involved molding a 40 μm thick aluminum foil with the shape shown in Figure 1 using a rectangular punch (side length L=37 mm, corner chamfer diameter R=4.5 mm). The test conditions were: wrinkle suppression force of 10 kN, punch rise speed (molding speed) scale set to 1, and mineral oil applied as a lubricant to one side of the aluminum foil (the side that the punch strikes). The punch rising from the bottom of the device struck the aluminum foil, molding it. The maximum punch rise height at which molding was achieved without cracks or pinholes after three consecutive moldings was defined as the limit molding height (mm) for that material. The punch height was varied in 0.5 mm increments. Here, a protrusion height (limit molding height) of 7.0 mm or more is judged as good moldability and is indicated with "B". A protrusion height (limit molding height) of 9.5 mm or more is judged as excellent moldability and is indicated with "A". A protrusion height (limit molding height) of less than 7.0 mm is judged as poor moldability and is indicated with "C".

[0038] Using alloys with one of the compositions shown in Tables 1 and 2, and employing one of the manufacturing processes shown in A to I of Table 3, examples No. 1 to 33 and comparative examples No. 34 to 46 shown in Tables 1 and 2 were prepared. All examples satisfy the desired composition or manufacturing conditions described above. All comparative examples do not satisfy either the desired composition or manufacturing conditions described above. For Examples No. 1 to 33 and Comparative Examples No. 34 to 46, the elongation in the 0° direction, elongation in the 45° direction, elongation in the 90° direction, average grain size, grain boundary density, intermetallic compound density, average grain size of intermetallic compounds, and forming limit height were measured, and the measurement results and evaluation results are shown in Tables 4 and 5 below. Note that the units for the content of each element listed in Tables 1 and 2 are in mass percent, and the remainder consisted of Al and unavoidable impurities.

[0039] [Table 1]

[0040] [Table 2]

[0041] [Table 3]

[0042] [Table 4]

[0043] [Table 5]

[0044] As shown in Tables 4 and 5, the aluminum alloy foil is made of an aluminum alloy having a composition containing Fe: 1.2% to 2.5% by mass, other elements including at least Si: 0.5% by mass or less, and the remainder being Al and unavoidable impurities, and is measured by EBSD over an area of ​​1 μm. 2 When L ( / μm) is the grain boundary length with an orientation difference of 2° or more at a given point, and S (μm) is the average grain size of the crystal grains surrounded by grain boundaries with an orientation difference of 15° or more, aluminum alloy foils that satisfy the equation L × S ≤ 15…(1) exhibited excellent properties. For example, the elongation in the 0° direction, the 45° direction, and the 90° direction were all 20%, the value of L × S was 15 or less, the limit height for forming was 7 mm or more, and the average crystal grain size was less than 20 μm. Specifically, in Examples No. 1 to 33 shown in Tables 4 and 5, the average crystal grain size was in the range of 8.5 to 19.3 μm, and the elongation in the 0° direction, 45° direction, and 90° direction showed excellent values ​​of 20 to 35%, with the moldable limit height being 7.0 mm or higher in all cases. In addition, the L×S values ​​of all the samples in the examples were 5.36 to 14.77.

[0045] Compared to these examples, sample No. 34, which had a slower cooling rate during casting, showed good elongation, but its L×S value exceeded 15, resulting in a lower limit height for molding compared to the examples. Sample No. 36, which also had a slower cooling rate during casting, showed elongation in the 0° and 90° directions of less than 20%, and its L×S value exceeded 15, resulting in a lower limit height for molding compared to the examples. Samples No. 35 and 37, which had lower homogenization temperatures, showed elongation in the 0°, 45°, and 90° directions of less than 20%, resulting in a lower limit height for molding compared to the examples. Samples No. 38 and 39, which had low Fe content, had an L×S value exceeding 15, and any of the elongations in the 0° direction, 45° direction, or 90° direction were less than 20%, resulting in a lower molding limit height than the examples. Samples No. 40 and 41, which had high Fe content, also had any of the elongations in the 0° direction, 45° direction, or 90° direction less than 20%, resulting in a lower molding limit height than the examples.

[0046] In samples No. 42-46, one of Si, Mg, Cu, Mn, or Zn was added in an amount of 0.5 mass% or more, and the total amount of all additive elements except Fe, including other additive elements, exceeded 0.5 mass%. In these samples, the elongation in the 0° direction, the 45° direction, or the 90° direction was less than 20%, and even when the elongation was 20% or more, the L×S value exceeded 15, resulting in a lower molding limit height than that of the examples. [Industrial applicability]

[0047] The aluminum alloy foil of this embodiment is suitably applied as packaging material for food and lithium-ion batteries. [Explanation of Symbols]

[0048] 1...Aluminum alloy foil, A...Continuous casting apparatus, 3...Tundish, 5...Nozzle, 6...Upper roll (conveying and cooling device), 7...Lower roll (conveying and cooling device), 8...Tunnel, 10...Aluminum alloy cast plate.

Claims

1. This aluminum alloy foil is made of an aluminum alloy having a composition of 1.2% to 2.5% by mass of Fe, containing at least Si from among Si, Mg, Cu, Mn, Zn, and Ti, and the total content of Si combined with any other element from among Si, Mg, Cu, Mn, Zn, and Ti being 0.5% by mass or less, with the remainder being Al and unavoidable impurities, and exhibiting elongation of 20% or more in the 0° direction, 45° direction, and 90° direction relative to the rolling direction, with an area of ​​1 μm measured by electron beam backscatter diffraction. ２ An aluminum alloy foil characterized in that it satisfies the following equation (1) when the grain boundary length with an orientation difference of 2° or more at a given point is L ( / μm), and the average grain size of the crystal grains surrounded by grain boundaries with an orientation difference of 15° or more is S (μm). L×S≦15…(1) formula

2. The aluminum alloy foil according to claim 1, characterized in that the average crystal grain size is less than 20 μm.

3. The average particle size (equivalent circle diameter) of the intermetallic compounds dispersed within the foil is 0.50 to 0.80 μm, and the dispersion density is 150,000 to 320,000 particles / mm³. ２ The aluminum alloy foil according to claim 1 or 2, characterized in that it is within the number density range.

4. When continuously casting cast aluminum alloy plates by pouring molten aluminum alloy containing Fe: 1.2% to 2.5% by mass, containing at least Si from among Si, Mg, Cu, Mn, Zn, and Ti, and having a total content of Si and any other element from among Si, Mg, Cu, Mn, Zn, and Ti of 0.5% by mass or less, with the remainder being Al and unavoidable impurities, from a nozzle provided in a tundish into a transport and cooling means, the cooling rate of the molten metal is set to 50 to 500°C / second to cast the cast plates, and these cast plates are cold-rolled to produce aluminum alloy foil, the elongation in the 0° direction, 45° direction, and 90° direction relative to the rolling direction are all 20% or more, and the area due to backscattered electron diffraction is 1 μm. ２ A method for producing aluminum alloy foil, characterized by obtaining aluminum alloy foil that satisfies the following equation (1) when the grain boundary length with an orientation difference of 2° or more at a given point is L ( / μm) and the average grain size of the crystal grains surrounded by grain boundaries with an orientation difference of 15° or more is S (μm). L×S≦15…(1) formula

5. A method for producing aluminum alloy foil according to claim 4, characterized in that the average crystal grain size is less than 20 μm.

6. The average particle size (equivalent circle diameter) of the intermetallic compounds dispersed within the foil is 0.50 to 0.80 μm, and the dispersion density is 150,000 to 320,000 particles / mm³. ２ A method for manufacturing aluminum alloy foil according to claim 4 or 5, characterized in that the number density range is within that range.

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