JP7736893B2 - Aluminum alloy foil and its manufacturing method - Google Patents

Description

The present invention relates to aluminum alloy foil and a method for producing the same.

Aluminum alloy foil used in packaging for food products, lithium-ion batteries, etc. is required to have high elongation because it is subjected to large deformation during press forming and other processes.

For example, Patent Document 1 below discloses a method for producing a foil made of an aluminum alloy containing 0.7 to 2.0% Fe as a method for producing an aluminum foil with excellent formability. The technology described in Patent Document 1 describes a technology in which after hot rolling, the foil product is subjected to intensive processing at a processing rate of 97% or more without intermediate annealing during the cold rolling process, and then finish annealing is performed at 300 to 450 ° C.
Furthermore, Patent Document 2 below describes an aluminum alloy soft foil containing 0.7 to 1.4 mass % of Fe, in which the average crystal grain size of crystal grains having a tilt angle of more than 5° is 3.5 μm or less. Patent Document 2 describes a technology for producing a soft foil exhibiting excellent strength by homogenizing an ingot at 400 to 500°C, hot rolling it with a hot rolling finish temperature of 300°C or higher, cold rolling it without intermediate annealing, and final annealing it at 220 to 275°C.

Japanese Patent Application Publication No. 2-080541 JP 2017-160509 A

When producing this type of aluminum alloy foil for packaging, an ingot is obtained by casting a molten alloy having a required composition, and the ingot is subjected to a homogenization treatment, followed by hot rolling and cold rolling, and then final annealing to obtain a packaging material having the desired mechanical properties.
In view of the above-mentioned background, the present inventors have been conducting research and development into aluminum alloy foils suitable as packaging materials for battery exterior foils and the like, with regard to packaging materials manufactured through such processes.

Based on this research, the present inventors believe that in order to obtain an aluminum alloy foil with high formability, it is important to be able to suppress surface roughness during deformation.
Furthermore, as a result of the inventor's research into aluminum alloy foil for packaging, it was found that the ratio of the area rate of Cu orientation to the area rate of Cube orientation in the crystal grain structure of the packaging material is important in terms of surface roughness during deformation.

The inventors therefore aimed to provide aluminum alloy foil for packaging that can improve productivity and has excellent formability by reviewing the manufacturing method and examining the crystal structure of the foil.

"1" The aluminum alloy foil of this embodiment is an aluminum alloy foil made of an aluminum alloy having a composition containing 0.8% by mass or more and 2.0% by mass or less of Fe, 0.2% by mass or less of Si, with the remainder being Al and unavoidable impurities, characterized in that the aluminum alloy foil has a 0.2% proof stress of 45 MPa or more, an elongation of 15% or more, a ratio of the area ratio of Cu orientation to the area ratio of Cube orientation in the area ratios of each orientation on the surface (Cu orientation/Cube orientation) of 3 or more, an average crystal grain size of crystal grains surrounded by an orientation difference of 5° or more on the surface of 3.5 μm or less, a ratio of crystal grain boundary lengths in the same field of view on the surface obtained by performing crystal orientation analysis by an EBSD method satisfies the following formula (1) , and a maximum tensile strength of 85 MPa or more in a tensile test in a 45° direction relative to the rolling direction .
Length of the grain boundary of the crystal grain with misorientation of 2° or more and less than 15° / Length of the grain boundary of the crystal grain with misorientation of 15° or more > 0.5... (1)

[2] In the aluminum alloy foil according to [1] of the present embodiment, instead of the formula (1), it is preferable that the ratio of grain boundary lengths in the same field of view obtained by performing crystal orientation analysis on the surface by the EBSD method satisfies the following formula (2):
0.52≦grain boundary length of crystal grains with orientation difference of 2° or more and less than 15°/grain boundary length of crystal grains with orientation difference of 15° or more≦0.88...(2) Formula "3" In the aluminum alloy foil according to "1" or "2" of this embodiment, it is preferable that the surface roughness (Ra ₂₅ - Ra ₀ ), which is the difference between the initial surface roughness Ra ₀ and the surface roughness Ra ₂₅ at a strain of 25% in a tensile test, is 0.30 μm or less.

"4" The aluminum alloy foil of this embodiment is an aluminum alloy foil made of an aluminum alloy having a composition containing 0.8% by mass or more and 2.0% by mass or less of Fe, 0.2% by mass or less of Si, the balance being Al and unavoidable impurities, characterized in that the aluminum alloy foil has a 0.2% yield strength of 45 MPa or more, an elongation of 15% or more, a ratio of the area ratio of Cu orientation to the area ratio of Cube orientation in the area ratios of each orientation on the surface (Cu orientation/Cube orientation) of 3 or more, an average crystal grain size of crystal grains surrounded by an orientation difference of 5° or more on the surface of 3.5 μm or less, a surface roughness (Ra ₂₅ -Ra ₀ ) which is the difference between the initial surface roughness Ra ₀ and the surface roughness Ra ₂₅ at a strain of 25% in a tensile test of 0.30 μm or less , and a maximum tensile strength of 85 MPa or more in a tensile test at 45° to the rolling direction .
[5] In the aluminum alloy foil according to [4] of this embodiment, the surface roughness (Ra ₂₅ -Ra ₀ ) is preferably 0.17 μm or more and 0.29 μm or less.

"6" A method for producing an aluminum alloy foil according to this embodiment is a method for producing an aluminum alloy foil made of an aluminum alloy having a composition containing 0.8% by mass or more and 2.0% by mass or less of Fe, 0.2% by mass or less of Si, the balance being Al and unavoidable impurities, the method being characterized in that the aluminum alloy foil has a 0.2% proof stress of 45 MPa or more, an elongation of 15% or more, a ratio of the area ratio of Cu orientation to the area ratio of Cube orientation in the area ratios of each orientation on the surface (Cu orientation/Cube orientation) of 3 or more, an average grain size of crystal grains surrounded by an orientation difference of 5° or more on the surface of 3.5 μm or less, a ratio of grain boundary lengths in the same field of view on the surface obtained by performing crystal orientation analysis by an EBSD method satisfies the following formula (1), and a maximum tensile strength of 85 MPa or more in a tensile test in a 45° direction relative to the rolling direction ,
The aluminum alloy ingot having the above composition is subjected to a homogenization treatment in which the ingot is heated and held at 480 to 540°C for 8 hours or more, followed by cooling, and then hot-rolled to a finishing temperature of 240 to 300°C, and then cold-rolled to a rolling ratio of 98% or more, followed by foil rolling without intermediate annealing, and finally annealed by heating to 220 to 350°C for 30 minutes to 20 hours.
Length of the grain boundary of the crystal grain with misorientation of 2° or more and less than 15° / Length of the grain boundary of the crystal grain with misorientation of 15° or more > 0.5... (1)

[7] In the method for producing an aluminum alloy foil according to [6] of this embodiment, it is preferable to produce an aluminum alloy foil in which the ratio of grain boundary lengths in the same field of view, obtained by performing crystal orientation analysis on the surface by an EBSD method, satisfies the following formula (2) instead of the formula (1):
0.52≦grain boundary length of crystal grains with orientation difference of 2° or more and less than 15°/grain boundary length of crystal grains with orientation difference of 15° or more≦0.88...(2) Equation "8" In the method for producing an aluminum alloy foil according to "6" or "7" according to this embodiment, it is preferable that the method for producing an aluminum alloy foil is characterized in that the surface roughness (Ra ₂₅ −Ra ₀ ), which is the difference between the initial surface roughness Ra ₀ and the surface roughness Ra ₂₅ at a strain of 25% in a tensile test, is 0.30 μm or less.

"9" A method for producing an aluminum alloy foil according to this embodiment is an aluminum alloy foil made of an aluminum alloy having a composition containing 0.8% by mass or more and 2.0% by mass or less of Fe, 0.2% by mass or less of Si, and the balance being Al and unavoidable impurities, wherein the aluminum alloy foil has a 0.2% proof stress of 45 MPa or more, an elongation of 15% or more, a ratio of the area ratio of Cu orientation to the area ratio of Cube orientation in the area ratios of each orientation on the surface (Cu orientation/Cube orientation) of 3 or more, an average crystal grain size of crystal grains surrounded by an orientation difference of 5° or more on the surface of 3.5 μm or less, and a surface roughness (Ra ₂₅ -Ra _{0 )} which is the difference between an initial surface roughness Ra ₀ and a surface roughness Ra ₂₅ at a strain of 25% in a tensile test. ) is 0.30 μm or less, and the maximum tensile strength is 85 MPa or more in a tensile test in a 45° direction relative to the rolling direction , and the method for producing an aluminum alloy foil is characterized in that an ingot of an aluminum alloy having the above composition is subjected to a homogenization treatment in which it is heated and held at 480 to 540°C for 8 hours or more and then cooled, and then hot-rolled to a finishing temperature of 240 to 300°C, and then cold-rolled to a rolling ratio of 98% or more, followed by foil rolling without intermediate annealing, and then final annealing in which it is heated to 220 to 350°C for 30 minutes to 20 hours.

[10] In the method for producing an aluminum alloy foil according to this embodiment, it is preferable to produce an aluminum alloy foil having the surface roughness (Ra ₂₅ -Ra ₀ ) of 0.17 μm or more and 0.29 μm or less.
[11] In the method for producing an aluminum alloy foil according to any one of [6], [7], [9], and [10] according to the present embodiment, it is preferable that the homogenization treatment is carried out under conditions of heating and holding at 480 to 540°C for 8 hours or more and 16 hours or less, followed by cooling.
[12] In the method for producing an aluminum alloy foil according to [8] according to this embodiment, the homogenization treatment is preferably carried out under conditions of heating and holding at 480 to 540°C for 8 hours or more and 16 hours or less, followed by cooling.

The aluminum alloy foil of the present invention can provide aluminum alloy foil with high formability.

1 is a plan view showing a first embodiment of an aluminum alloy foil according to the present invention. FIG. FIG. 2 is a diagram showing the planar shape of a square punch used in a limit forming height test in an example of the present invention.

An example of an embodiment of the present invention will be described in detail below with reference to the accompanying drawings. Note that the drawings used in the following description may show enlarged portions of key features for ease of understanding.

FIG. 1 is a plan view showing one 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 hot rolling, cold rolling, and foil rolling of an ingot obtained by a casting method, and is depicted in FIG. 1 as a strip-like body having a constant width and with its length oriented left and right.
The rolling direction of this aluminum alloy foil 1 is the left-right direction (length direction of the strip-shaped foil) shown in Fig. 1, and for convenience, the direction at 0° to the rolling direction means the left-right direction in Fig. 1, the direction at 45° to the rolling direction means the direction of the arrow labeled 45° in Fig. 1, and the direction at 90° to the rolling direction means the direction of the arrow labeled 90° in Fig. 1. In other words, the direction at 90° to the rolling direction in the aluminum alloy foil 1 means the width direction of the strip-shaped aluminum alloy foil 1 (the vertical direction on the paper surface of Fig. 1).

The aluminum alloy foil 1 shown in FIG. 1 is formed to a thickness of, for example, about 0.01 mm to 0.2 mm. The thickness of the aluminum alloy foil 1 may be a typical thickness used for foil. For example, it is formed to a thickness of about 0.04 mm (40 μm). In this specification, when "to" is used to indicate a range by specifying upper and lower limits, the range includes the upper and lower limits unless otherwise specified. Therefore, 0.01 mm to 0.2 mm means 0.01 mm or more and 0.2 mm or less.
The aluminum alloy foil 1 is made of an aluminum alloy having a composition containing, for example, 0.8 mass % to 2.0 mass % Fe, 0.2 mass % or less Si, and the remainder being Al and unavoidable impurities.

As an example, this aluminum alloy foil 1 has a maximum tensile strength of 85 MPa or more, a 0.2% yield strength of 45 MPa or more, and an elongation of 15% or more in a tensile test in a direction at an angle of 45° to the rolling direction, and the ratio of the area ratio of the Cu orientation to the area ratio of the Cube orientation in the area ratios of each orientation on the surface (Cu orientation/Cube orientation) is 3 or more.
In the aluminum alloy foil 1, it is preferable that the average crystal grain size surrounded by an orientation difference of 5° or more is 4 μm or less. In the aluminum alloy foil 1, it is preferable that the surface roughness (Ra ₂₅ −Ra ₀ ), which is the difference between the initial surface roughness Ra ₀ and the surface roughness Ra ₂₅ at a strain of 25% in a tensile test, is 0.30 μm or less. Details of the surface roughness measurement will be explained in the examples below.

In addition, in the aluminum alloy foil 1, it is preferable that the ratio of grain boundary lengths in the same field of view obtained by performing crystal orientation analysis by the EBSD method satisfies the following formula (1).
Grain boundary length of crystal grains with orientation misorientation of 2° or more and less than 15° / Grain boundary length of crystal grains with orientation misorientation of 15° or more > 0.5 (1) Furthermore, it is preferable that the aluminum alloy foil 1 has an elongation of 10% or more in both the 0° direction and the 90° direction relative to the rolling direction.

The reasons for limiting the composition, properties, and structure of the aluminum alloy constituting the aluminum alloy foil 1 will be explained below.
Fe: 0.8% by mass or more and 2.0% by mass or less Fe crystallizes as an Al-Fe intermetallic compound during casting, and when the size of these compounds is appropriate, they become recrystallization sites during annealing, and have the effect of refining the recrystallized grains.
If the Fe content is less than 0.8% by mass, the distribution density of intermetallic compounds will be low, the effect of refining crystal grains will be reduced, the final recrystallized grains will be coarse, and the grain boundary density of crystal grains with an orientation misorientation of 2° or more and less than 15° will be low. If the Fe content exceeds 2.0% by mass, the effect of refining crystal grains will saturate or decrease, and further, the size of the Al-Fe intermetallic compounds generated during casting will become very large, reducing the elongation, formability, and productivity of the foil. A particularly preferred range for the Fe content is 1.2% by mass or more and 1.8% by mass or less.
Si: 0.20% by mass or less Si forms intermetallic compounds with Fe, but excessive addition of Si leads to coarsening of the compound size and a decrease in distribution density. If the content exceeds the upper limit, there is a concern that coarse crystals will cause a decrease in elongation and formability, and further that the uniformity of the recrystallized grain size distribution after final annealing will decrease. For these reasons, the Si content is set to 0.20% by mass or less. For the same reasons, it is more preferable to set the upper limit of the Si content to 0.04% by mass.

The remainder of the components constituting the aluminum alloy foil of the present invention consists of Al and inevitable impurities. These inevitable impurities refer to elements that are inevitably mixed in during the production of the aluminum alloy foil. These inevitable impurities may be contained to a degree that does not affect the properties of the aluminum alloy foil of the present invention. Examples of these inevitable impurities include elements such as magnesium (Mg), chromium (Cr), manganese (Mn), copper (Cu), zinc (Zn), titanium (Ti), vanadium (V), gallium (Ga), nickel (Ni), boron (B), and zirconium (Zr). One or more of these may be contained in an amount of 500 ppm by mass or less each.

- "In a tensile test at a 45° angle to the rolling direction, the maximum tensile strength is 85 MPa or more, the 0.2% yield strength is 45 MPa or more, and the elongation is 15% or more."
Aluminum alloy foils used in packaging materials are subjected to three-dimensional deformation during press forming, and therefore are required to have good mechanical properties not only in the rolling direction but also in various directions.
The inventors have found that mechanical properties in the 45° direction relative to the rolling direction are particularly important during press forming. Regarding the maximum tensile strength and 0.2% yield strength, in order to maintain the shape during forming and ensure strength after forming, it is preferable that the maximum tensile strength be 85 MPa or more and the 0.2% yield strength be 45 MPa. While there are no particular upper limits, if the maximum tensile strength and 0.2% yield strength are too high, handling during forming becomes difficult, so more preferably the maximum tensile strength be 130 MPa or less and the 0.2% yield strength be 85 MPa or less. Elongation is most correlated with formability, and it has been confirmed that in this product, a high elongation value in the 45° direction, in particular, results in good formability. It is preferable that the elongation in the 45° direction relative to the rolling direction be 15% or more, and most preferably 20% or more.

"Azimuth area ratio"
In the aluminum alloy foil 1, the ratio of the area ratio of Cu orientation to Cube orientation (Cu orientation area ratio/Cube orientation area ratio) is preferably 3 or more. The (Cu orientation area ratio/Cube orientation area ratio) can be, for example, 5.0 or more and 31 or less.
After electrolytically polishing the foil surface, crystal orientation analysis can be performed using a scanning electron microscope (SEM)-EBSD to calculate the area ratio of each orientation. TSL Solutions' OIM Analysis can be used for the analysis. Deviation from the ideal orientation is limited to 15°. From the obtained area ratio, the ratio of the area ratio of the Cu orientation to the Cube orientation (Cu orientation area ratio/Cube orientation area ratio) can be calculated. The ideal orientation of each orientation is shown below. Details of the method for calculating the orientation area ratio will be described in detail in the Examples.
In the aluminum alloy foil of this embodiment, aligning the crystal orientation in the same direction can suppress surface roughness and improve formability. The inventors have found that, in the alloy foil of this embodiment, the Cu orientation and the Cube orientation are the main crystal orientations, and that it is important to align the crystal orientation to the Cu orientation. Furthermore, even if the proportion of the Cu orientation increases, if the Cube orientation is present in large amounts, surface roughness is likely to occur, which is a factor that deteriorates formability.
Therefore, it was decided to index it by the ratio of the area ratio of Cu orientation to Cube orientation. As a result of the investigation, it was confirmed that the ratio of the area ratio of Cu orientation to Cube orientation (Cu orientation area ratio/Cube orientation area ratio) is preferably 3 or more, and more preferably 5 or more. If it is less than 3, even if the crystal grains are fine, the surface of the aluminum alloy foil is likely to become rough, and the limit forming height is reduced, resulting in a decrease in formability.
Cu orientation {112}<111>
Cube orientation {001}<100>
This ideal direction is expressed as a direction that includes all equivalent directions.

When the aluminum alloy foil of this embodiment is plastically deformed, surface roughness (irregularities) occurs on the material surface. The surface roughness is considered to be unevenness in thickness, and by suppressing this, it is possible to prevent a decrease in the limit forming height.
The inventors have found that the surface roughness (Ra ₂₅ - Ra 0 ), which is the difference between the surface roughness Ra ₀ at the initial stage before plastic deformation and the surface roughness Ra ₂₅ at 25% strain in a tensile test, is important for the three-dimensional deformation that occurs when the material is used as a packaging material. The surface roughness (Ra ₂₅ - _{Ra 0} ) is preferably 0.30 μm or less, and more preferably 0.25 μm or less. If the surface roughness (Ra ₂₅ - Ra ₀ ) exceeds 0.30 μm, the limit forming height decreases.

- "The average grain size of grains surrounded by an orientation difference of 5° or more is 4.0 μm or less."
The fine grains of soft aluminum foil can suppress the roughness of the foil surface when deformed, and high elongation and high formability can be expected. One of the factors that affect this surface roughness is the grain size. In order to achieve high elongation characteristics and the high formability associated with it, it is desirable that the average grain size of crystal grains surrounded by grain boundaries with an orientation difference of 5° or more is 4.0 μm or less. The inventors have also found that when the average grain size exceeds 4.0 μm, surface roughness during forming becomes significant, and control of the grain structure is also important for suppressing surface roughness.
In the aluminum alloy foil 1, the average crystal grain size is preferably 4.0 μm or less, and more preferably 3.5 μm or less. In electron backscatter diffraction (EBSD), a grain boundary map can be obtained by analyzing the crystal orientation per unit area, depicting crystal grains with an orientation difference of 5° or more. Details of the method for calculating the average crystal grain size will be described in the examples.

Length of grain boundary (LAGB) of crystal grains with misorientation of 2° or more and less than 15° / Length of grain boundary (HAGB) of crystal grains with misorientation of 15° or more > 0.5
In order to suppress the surface roughness of the aluminum alloy foil, it is considered important that the density of crystal grains having a misorientation of 2° or more and less than 15° is high on the surface of the aluminum alloy foil. Therefore, it is preferable to satisfy the relationship of the grain boundary length (LAGB) of crystal grains having a misorientation of 2° or more and less than 15°/the grain boundary length (HAGB) of crystal grains having a misorientation of 15° or more>0.5 as expressed by equation (1).
If the relationship is such that the grain boundary length of crystal grains with a misorientation of 2° or more but less than 15°/the grain boundary length of crystal grains with a misorientation of 15° or more is ≦0.5, the foil surface will become rough, the limit forming height will be lowered, etc., resulting in reduced formability. More preferably, the grain boundary length of crystal grains with a misorientation of 2° or more but less than 15° (LAGB)/the grain boundary length of crystal grains with a misorientation of 15° or more (HAGB) is >0.6.

"Method of manufacturing aluminum alloy foil"
1, a molten aluminum alloy satisfying the above-mentioned composition is prepared, and an aluminum alloy ingot is obtained by a casting method using this molten aluminum alloy. Next, this aluminum alloy ingot is subjected to a homogenization treatment, and processed to a target thickness by hot rolling, cold rolling, and foil rolling, and finally annealed to obtain the aluminum alloy foil 1.

Homogenization treatment: Holding at 480-540°C for 6 hours or more It is desirable to perform homogenization treatment on the obtained ingot by holding at 480-540°C for 6 hours or more. At temperatures below 480°C, there is little Fe precipitation and the growth of intermetallic compounds is insufficient. On the other hand, at temperatures above 540°C, the growth of intermetallic compounds is significant, and the density of fine intermetallic compounds with particle diameters of 0.1 μm or more and less than 1 μm is significantly reduced. For this reason, it is more preferable to select a temperature range of 500-540°C, for example.
In order to precipitate fine intermetallic compounds at a high density in such homogenization treatment at around 500°C, a long heat treatment time is required, and a minimum of 6 hours is required. If the treatment time is less than 6 hours, precipitation is insufficient, and the density of the fine intermetallic compounds may decrease. There is no particular upper limit to the homogenization treatment time, but from the viewpoint of production costs, it is desirable that the treatment time be 16 hours or less.

Hot rolling: finishing temperature of 240°C or higher and lower than 300°C In hot rolling, it is desirable to set the finishing temperature to less than 300°C to suppress recrystallization. By setting the hot rolling finishing temperature to less than 300°C, the hot-rolled sheet will have a uniform fibrous structure. If the hot-rolling finishing temperature is 300°C or higher, recrystallization will occur in part of the hot-rolled sheet, resulting in a structure in which fibrous structure and recrystallized structure are mixed, and there is a risk that the recrystallized grain size will become non-uniform during final annealing. If hot rolling is finished at less than 240°C, the temperature during hot rolling will also be extremely low, which may make cracks more likely to occur on the sides of the rolled sheet and significantly reduce productivity. Therefore, the finishing temperature of hot rolling is preferably in the range of 240°C or higher and lower than 300°C.
There are no particular restrictions on the finished thickness, but it is preferably 3.0 mm or more in order to reduce the final cold rolling reduction ratio.

Final cold rolling ratio: 98% or more The higher the cold rolling ratio from hot rolling to the final foil thickness, the greater the amount of strain accumulated in the material, resulting in finer recrystallized grains after final annealing.
By performing the cold rolling a required number of times at a required processing rate and performing foil rolling, an aluminum alloy foil 1 having a thickness of about 10 μm to 0.2 mm, for example, a thickness of 40 μm, can be obtained.
When cold rolling is performed the required number of times, it is preferable to perform final foil rolling without intermediate annealing, and then perform final annealing.
Furthermore, when final annealing is performed after cold rolling, the final annealing conditions are preferably such that the steel sheet is heated to 220° C. to 350° C. for about 30 minutes to 20 hours, and then slowly cooled.

The obtained aluminum alloy foil 1 contains a predetermined amount of Fe, which affects the texture of the aluminum alloy and contributes to refinement of the crystal grain size. Although the aluminum alloy contains 0.8 to 2.0 mass % of Fe, by performing foil rolling as final cold rolling without intermediate annealing in the final stage of cold rolling and then final annealing, the aluminum alloy has good elongation even with an Fe content within the above range.
The aluminum alloy used here may contain about 0.2 mass % or less of Si in addition to Fe. Even if the aluminum alloy foil 1 of this embodiment contains Si in the above range, an aluminum alloy foil that can achieve the purpose can be obtained.

By the manufacturing method described above, it is possible to obtain an aluminum alloy foil 1 having a maximum tensile strength of 85 MPa or more, a 0.2% yield strength of 45 MPa or more, and an elongation of 15% or more in a tensile test in a direction at 45° to the rolling direction, and having a ratio of the area ratio of Cu orientation to the area ratio of Cube orientation in the area ratios of each orientation on the surface (Cu orientation/Cube orientation) of 3 or more.
The aluminum alloy foil 1 described above is suitable for food packaging or for formed packaging materials for lithium ion batteries, and can provide an aluminum alloy foil suitable for applications requiring large deformation by press forming or applications requiring high elongation and formability. Furthermore, since it can be produced without intermediate annealing after cold rolling, an aluminum alloy foil 1 with excellent productivity can be obtained.

Ingots of aluminum alloys having the compositions shown in Tables 1 and 2 (the balance being Al and other unavoidable impurities) were produced by semi-continuous casting. The resulting ingots were then subjected to homogenization treatment, hot rolling, cold rolling, and final annealing under the production conditions shown in Tables 1 and 2 (homogenization treatment conditions, hot rolling finish temperature, hot rolling finish thickness, cold rolling finish foil thickness), to produce aluminum alloy foils.
The final annealing conditions were 300°C x 20 hours. The final thicknesses of the aluminum alloy foils were the thicknesses (foil thicknesses) shown in Tables 1 and 2. For samples that underwent intermediate annealing, intermediate annealing was performed under conditions of 360°C x 3 hours. In Tables 1 and 2, examples that were not subjected to intermediate annealing are marked with an X in the intermediate annealing column, and examples that were subjected to intermediate annealing are marked with an O.

The obtained aluminum alloy foil was subjected to the following measurements and evaluations.
Tensile strength (MPa), elongation (%)
All of the measurements were performed by a tensile test, which conformed to JIS Z2241, and involved punching JIS No. 5 test pieces (using Super Dumbbell (registered trademark) manufactured by Dumbbell Co., Ltd.) from aluminum alloy foil samples so that the elongation in the 45° direction relative to the rolling direction could be measured, and the tensile test was performed using a universal tensile tester (AGS-X 10 kN manufactured by Shimadzu Corporation) at a pulling rate of 2 mm/min.
The elongation percentage was calculated as follows. First, before the test, two lines were marked at the longitudinal center of the test piece in the direction perpendicular to the test piece, spaced 50 mm apart (the gauge length). After the test, the fracture surfaces of the aluminum alloy foils were butted together to measure the distance between the marks, and the gauge length (50 mm) was subtracted from the distance to obtain the elongation amount (mm), which was then divided by the gauge length (50 mm) to obtain the elongation percentage (%).

Prior to crystal orientation analysis, the foil surface was subjected to mirror finishing by electrolytic polishing using a solution of perchloric acid:ethanol = 1:4 (volume ratio) at a voltage of 20 V for 5 seconds.
After electrolytic polishing of the foil surface, crystal orientation analysis was performed using a scanning electron microscope (SEM)-EBSD, and the area ratio of each orientation was calculated. A FE-SEM (JSM-7900F manufactured by JEOL Ltd.) was used as the SEM, and TSL Solutions' OIM Analysis (Ver. 8.0) was used for the analysis. Deviation from the ideal orientation was limited to 15°.

The measurement conditions were as follows: observation magnification: 900 times, acceleration voltage: 15 kV, sample tilt angle: 70°, step size: 0.3 μm.
The observation area was a total area of 50,000 ^μm or more, obtained by connecting images measured at 900x magnification. CI (Confidence Index) values of 0.1 or less were excluded, and a minimum grain size [points] of 2 and anti-grains of 2 were adopted.

(Azimuth analysis)
The area ratio of each orientation was calculated using the Crystal Orientation function. The tolerance was set to less than 15°, and the Orientation Euler Angles and Orientation {hk(i)l}<uv(t)w> of each orientation were defined as shown in Table 3 below to obtain the area ratio. From the obtained area ratios, the ratio of the area ratios (Cu orientation area ratio/Cube orientation area ratio) was calculated.

Surface Roughness In this example, the plastic working was carried out by a tensile test. The tensile test was carried out in the same manner as in the elongation measurement in the previous section, using a JIS No. 5 test piece and applying tensile strain using the universal tensile tester.
The surface roughness of the test material was measured based on JIS B0601:2001. The actual measurements were performed using a confocal laser microscope (Keyence Corporation, VK-X100) and analyzed using an analysis application (Keyence Corporation, VK-H1XA). The observation magnification was 500x, the field of view size was 1000 x 500 μm, and the measurement points were the center of the width and length of the JIS No. 5 test piece.
The data scanned by the laser microscope was subjected to noise removal and tilt correction processing before measuring the surface roughness. For noise removal, the noise detection level was set to "Normal," and for tilt correction, the correction method was selected to be "Surface tilt correction (profile)." The surface roughness parameter was calculated based on JIS B0601:2001, using the arithmetic mean roughness of the surface roughness.
First, the surface texture of the test piece before the test is observed with a confocal laser microscope, and this is designated as _R0 . Then, a tensile test is performed. The test is stopped midway when the strain during plastic deformation reaches 25%, and the surface texture (surface roughness measurement) is performed again on the test piece after plastic deformation at the same location as before the test, and this is designated as _R25 . For the same test piece measured using the above procedure, the value of ( _R25 - _R0 ) is calculated using _R0 and _R25 . At least n=5 tests are performed for the same level, and the average value excluding the maximum and minimum values is used as the calculated value of surface roughness.

Average crystal grain size After electrolytic polishing of the foil surface, crystal orientation analysis was performed using SEM-EBSD, and crystal grains surrounded by grain boundaries with an inclination angle of more than 5° were analyzed using the Number method (number average crystal grain size) under the following conditions to calculate the average crystal grain size. Details of the analysis conditions are as follows.
Grain Tolerance Angle: 5°
Minimum Grain Size[points]: 2 Anti Grains: 2
Minimum Confidence Index: 0
Multiple rows required: All OFF
Apply partition before calculation：OFF
Include grains at edges of scan in statistics：OFF
The average crystal grain size measured by the Number method is the diameter of a circle calculated by dividing the measurement area by the number of crystal grains. The measurement conditions were the same as in the case of the orientation area ratio described above, with an observation magnification of 900 times and a total area of 50,000 ^μm2 .

LAGB length/HAGB length After electrolytic polishing of the foil surface, crystal orientation analysis was performed using SEM-EBSD to observe high-angle grain boundaries (HAGBs) with an orientation misorientation of 15° or more between crystal grains and low-angle grain boundaries (LAGBs) with an orientation misorientation of 2° to 15°. Three fields of view with a field size of 45 x 90 μm were measured at a magnification of 900x, and the lengths of the HAGBs and LAGBs within the field of view were determined, and the ratio was calculated. The measurement conditions were the same as in the case of the orientation area ratio described above: observation magnification: 900x, total area: 50,000 ^μm2 .
In EBSD, by specifying boundaries in Grain-MAP, it is possible to perform analysis on grain boundaries with any misorientation. Note that grain boundaries with a misorientation of less than 2° may contain noise, so they were excluded from the calculation. In this application, the analysis was performed by specifying a minimum of 2° - a maximum of 15° for misorientations of 2° or more but less than 15° (=LAGB), and a minimum of 15° (- a maximum of 90°) for misorientations of 15° or more (=HAGB), and the grain boundary length obtained by the analysis was used to calculate LAGB/HAGB.

The forming height limit was evaluated in a square tube forming test. The test was performed using a universal sheet metal forming tester (Model 142/20 manufactured by ERICHSEN) and a square punch 2 (side length D = 37 mm, corner chamfer diameter R = 4.5 mm) with a 40 μm thick aluminum foil, as shown in Figure 2. The test conditions were a wrinkle suppression force of 10 kN, a punch rise speed (forming speed) scale of 1, and mineral oil as a lubricant applied to one side of the foil (the side that contacts the punch).
The maximum punch height (mm) at which the aluminum alloy foil could be formed without cracks or pinholes after three consecutive presses was defined as the limiting press height of the aluminum alloy foil. The punch height was varied in 0.1 mm increments.
In this example, samples with a formed height of 11.0 mm or more were designated as excellent products and were indicated with the symbol A, samples with a formed height of 10.0 mm or more but less than 11.0 mm were designated as acceptable products and were indicated with the symbol B, and samples with a formed height of less than 10.0 mm were designated as unacceptable products and were indicated with the symbol C.

Using the alloy compositions shown in Tables 1 and 2 and the manufacturing conditions shown in Tables 1 and 2, Examples No. 1 to 22 and Comparative Examples No. 23 to 31 were prepared. All of the Examples are examples that satisfy the desired compositions or manufacturing conditions described above. All of the Comparative Examples are examples that do not satisfy either the desired compositions or manufacturing conditions described above.
For Samples No. 1 to 31, the tensile strength (MPa) in the 0°, 45°, and 90° directions is shown in Tables 1 and 2. Furthermore, the yield strength (MPa) in the 0°, 45°, and 90° directions, the elongation (%) in the 0°, 45°, and 90° directions, the Cu orientation area ratio, the Cube orientation area ratio, the area ratio ratio (Cu orientation area ratio/Cube orientation area ratio), the average crystal grain size (μm), the surface roughness (ΔRa ₂₅ - ΔRa ₀ : μm), the (LAGB length/HAGB length), and the limit forming height (mm) were determined. The measurement results and evaluations are shown in Tables 4 and 5.

As shown in the results shown in Tables 1, 2, 4, and 5, the aluminum alloy foils were made of aluminum alloys containing 0.8% by mass or more and 2.0% by mass or less of Fe, 0.2% by mass or less of Si, with the balance being Al and inevitable impurities. In a tensile test at 45° to the rolling direction, the maximum tensile strength was 85 MPa or more, the 0.2% proof stress was 45 MPa or more, and the elongation was 15% or more. In addition, the ratio of the area ratio of the Cu orientation to the area ratio of the Cube orientation in the area ratios of each orientation on the surface (Cu/Cube) was 3 or more. Samples No. 1 to 22 (Examples) had small surface roughness and were excellent in limit forming height.
Furthermore, the samples of these examples have a sufficiently small average crystal grain size of 4 μm or less, and a sufficiently small surface roughness (Ra ₂₅ −Ra ₀ ) of 0.30 μm or less.

The Fe content of the example samples is 0.82% or more and 1.96% or less, and the Si content is 0.03% or more and 0.19% or less. The foil thickness of the example samples is 25 μm or more and 80 μm or less. The maximum tensile strength of the example samples in a tensile test at a 45° angle to the rolling direction is 86 MPa or more and 101 MPa or less. The 0.2% yield strength of the example samples in a 45° angle to the rolling direction is 48 MPa or more and 74 MPa or less. The Cu orientation/Cube orientation value of the example samples is 5.8 or more and 30.8 or less. The average crystal grain size of the example samples is 2.53 μm or more and 3.42 μm or less. The surface roughness of the example samples is 0.17 μm or more and 0.29 μm or less. The LAGB/HAGB value of the example samples is 0.52 or more and 0.88 or less. The limit forming height for the example samples is between 10.1 mm and 12.5 mm.

In contrast to these Examples, Samples No. 23 and No. 24 had Fe contents outside the above range, but compared to the Example Samples, they had lower tensile strength, lower proof stress, and lower elongation in the same direction. They also tended to have greater surface roughness and a lower limit forming height.
Samples No. 25 and No. 26 had Si contents outside the above range, but compared with the Example samples, they had lower tensile strength, lower proof stress, and lower elongation in the same direction. In addition, the limit forming height was also lower.
Samples No. 27, 28, and 29 were samples that underwent intermediate annealing, but had lower tensile strength, lower proof stress, and lower elongation in the same direction than the Example Samples. Furthermore, compared to the Example Samples, Samples No. 27 to 29 had larger average crystal grain size, greater surface roughness, smaller (LAGB/HAGB) values, and lower limit forming heights.

Sample No. 30 was a sample in which the homogenization temperature was higher than the desired range, and it had low yield strength, an average crystal grain size slightly larger than that of the example samples, slightly larger surface roughness, and a worsened limit forming height.
Sample No. 31 was a sample in which the homogenization temperature was lower than the desired range, but the average crystal grain size was slightly larger than that of the example samples, the surface roughness was slightly larger, and the limit forming height was worse than that of the example samples.

1...Aluminum alloy foil, 2...Punch.

Claims (12)

An aluminum alloy foil made of an aluminum alloy containing 0.8% by mass or more and 2.0% by mass or less of Fe, 0.2% by mass or less of Si, with the remainder being Al and unavoidable impurities, the aluminum alloy foil having a 0.2% yield strength of 45 MPa or more and an elongation of 15% or more, and a ratio of an area ratio of Cu orientation to an area ratio of Cube orientation (Cu orientation/Cube orientation) in the area ratios of each orientation on the surface being 3 or more,
On the surface, the average grain size of grains surrounded by an orientation difference of 5° or more is 3.5 μm or less,
The ratio of grain boundary lengths in the same field of view, obtained by performing crystal orientation analysis on the surface using an EBSD method, satisfies the following formula (1) :
An aluminum alloy foil characterized in that the maximum tensile strength is 85 MPa or more in a tensile test in a direction at an angle of 45° to the rolling direction .
Length of the grain boundary of the crystal grain with misorientation of 2° or more and less than 15° / Length of the grain boundary of the crystal grain with misorientation of 15° or more > 0.5... (1) The aluminum alloy foil according to claim 1, characterized in that, instead of the formula (1), the ratio of grain boundary lengths in the same field of view obtained by performing crystal orientation analysis on the surface by an EBSD method satisfies the following formula (2):
0.52≦grain boundary length of crystal grains with misorientation of 2° or more and less than 15°/grain boundary length of crystal grains with misorientation of 15° or more≦0.88 (2) 3. The aluminum alloy foil according to claim 1, wherein the surface roughness (Ra ₂₅ -Ra ₀ ), which is the difference between the initial surface roughness Ra ₀ and the surface roughness Ra ₂₅ at 25% strain in a tensile test, is 0.30 μm or less. An aluminum alloy foil made of an aluminum alloy containing 0.8% by mass or more and 2.0% by mass or less of Fe, 0.2% by mass or less of Si, with the remainder being Al and unavoidable impurities, the aluminum alloy foil having a 0.2% yield strength of 45 MPa or more and an elongation of 15% or more, and a ratio of an area ratio of Cu orientation to an area ratio of Cube orientation (Cu orientation/Cube orientation) in the area ratios of each orientation on the surface being 3 or more,
On the surface, the average grain size of grains surrounded by an orientation difference of 5° or more is 3.5 μm or less,
The surface roughness (Ra ₂₅ -Ra ₀ ), which is the difference between the initial surface roughness Ra ₀ and the surface roughness Ra ₂₅ at a strain of 25% in a tensile test , is 0.30 μm or less;
An aluminum alloy foil characterized in that the maximum tensile strength is 85 MPa or more in a tensile test in a direction at an angle of 45° to the rolling direction . The aluminum alloy foil according to claim 4, wherein the surface roughness (Ra ₂₅ - Ra ₀ ) is 0.17 μm or more and 0.29 μm or less. a method for producing an aluminum alloy foil, the aluminum alloy foil comprising an aluminum alloy containing 0.8% by mass or more and 2.0% by mass or less of Fe, 0.2% by mass or less of Si, the balance being Al and unavoidable impurities; a 0.2% proof stress of 45 MPa or more, an elongation of 15% or more, a ratio of an area ratio of Cu orientation to an area ratio of Cube orientation in the area ratios of each orientation on the surface (Cu orientation/Cube orientation) of 3 or more, an average grain size of crystal grains surrounded by an orientation difference of 5° or more on the surface of 3.5 μm or less, a ratio of grain boundary lengths in the same field of view on the surface obtained by performing crystal orientation analysis by an EBSD method satisfies the following formula (1), and a maximum tensile strength of 85 MPa or more in a tensile test in a 45° direction relative to the rolling direction ,
A method for producing an aluminum alloy foil, comprising: subjecting an ingot of an aluminum alloy having the above composition to a homogenization treatment in which the ingot is heated and held at 480 to 540°C for 8 hours or more, followed by cooling; subjecting the ingot to hot rolling to a finishing temperature of 240 to 300°C; subjecting the ingot to cold rolling at a rolling reduction of 98% or more; and then subjecting the ingot to foil rolling without intermediate annealing; and subjecting the ingot to final annealing in which the ingot is heated to 220 to 350°C for 30 minutes to 20 hours.
Length of the grain boundary of the crystal grain with misorientation of 2° or more and less than 15° / Length of the grain boundary of the crystal grain with misorientation of 15° or more > 0.5... (1) The method for producing aluminum alloy foil according to claim 6, characterized in that, instead of formula (1), the ratio of grain boundary lengths within the same field of view obtained by performing crystal orientation analysis on the surface using the EBSD method satisfies the following formula (2): 0.52≦grain boundary length of grains with a misorientation of 2° or more but less than 15°/grain boundary length of grains with a misorientation of 15° or more≦0.88...formula (2) 8. The method for producing an aluminum alloy foil according to claim 6, wherein the surface roughness (Ra ₂₅ - Ra ₀ ), which is the difference between the initial surface roughness Ra ₀ and the surface roughness Ra ₂₅ at 25% strain in a tensile test, is 0.30 μm or less. a method for producing an aluminum alloy foil, the aluminum alloy foil comprising an aluminum alloy containing 0.8% by mass or more and 2.0% by mass or less of Fe, 0.2% by mass or less of Si, the balance being Al and unavoidable impurities; a 0.2% proof stress of 45 MPa or more, an elongation of 15% or more, a ratio of the area ratio of Cu orientation to the area ratio of Cube orientation in the area ratios of each orientation on the surface (Cu orientation/Cube orientation) of 3 or more, an average crystal grain size of crystal grains surrounded by an orientation difference of 5° or more on the surface of 3.5 μm or less, a surface roughness (Ra ₂₅ −Ra ₀ ) which is the difference between an initial surface roughness Ra ₀ and a surface roughness Ra ₂₅ at a strain of 25% in a tensile test of 0.30 μm or less, and a maximum tensile strength of 85 MPa or more in a tensile test at 45° to the rolling direction ;
A method for producing an aluminum alloy foil, comprising: subjecting an ingot of an aluminum alloy having the above composition to a homogenization treatment in which the ingot is heated and held at 480 to 540°C for 8 hours or more, followed by cooling; subjecting the ingot to hot rolling to a finishing temperature of 240 to 300°C; subjecting the ingot to cold rolling at a rolling reduction of 98% or more; and then subjecting the ingot to foil rolling without intermediate annealing; and subjecting the ingot to final annealing in which the ingot is heated to 220 to 350°C for 30 minutes to 20 hours. The method for producing an aluminum alloy foil according to claim 9, wherein the aluminum alloy foil has a surface roughness (Ra ₂₅ -Ra ₀ ) of 0.17 μm or more and 0.29 μm or less. The method for producing aluminum alloy foil according to any one of claims 6, 7, 9, and 10, characterized in that the homogenization treatment is carried out by heating and holding the foil at 480 to 540°C for 8 to 16 hours, followed by cooling. The method for producing aluminum alloy foil described in claim 8, characterized in that the homogenization treatment is carried out by heating and holding the foil at 480 to 540°C for 8 to 16 hours, followed by cooling.