JP7780323B2 - Aluminum alloy foil - Google Patents

Description

This invention relates to aluminum alloy foil that can be used as packaging material, etc.

Aluminum alloy foils used as packaging materials for food products, lithium-ion batteries, etc. are required to have high formability because they are subjected to large deformations during press forming and other processes.
Traditionally, pure aluminum and Al-Fe alloys such as JIS A8079 and 8021 have been used for aluminum foil packaging. Elongation is an important parameter for forming. For aluminum alloy foil to have high elongation and formability, fine uniformity of crystal grains and random texture are important, but to achieve these, it is necessary to suppress the coarsening of intermetallic compounds that are formed during casting.
For example, Patent Document 1 attempts to control the number density of intermetallic compounds to refine the crystal grain size after final annealing.
Furthermore, since the aluminum alloy foil is not deformed in one direction but is often subjected to so-called stretch forming, high elongation is required not only in the direction parallel to the rolling direction, which is generally used as the elongation value of the material, but also in each direction such as 45° and 90°.
In addition, even if a material has high elongation in stretch forming, if strong forming processing is applied locally, coarse intermetallic compounds present in the aluminum foil become the starting point of cracks. Therefore, it is required to suppress coarse intermetallic compounds.

Japanese Patent Application Laid-Open No. 2005-163097

Conventional technology controls the amount of Fe and Si added to suppress the formation of coarse Al-Fe intermetallic compounds during casting, but reducing the amount of added elements can easily reduce the density of the intermetallic compounds, which can reduce the rate of discontinuous recrystallization nucleated by intermetallic compounds. When the rate of discontinuous recrystallization decreases, the rate of continuous recrystallization increases, making it more likely that coarse crystal grains with poor anisotropy will be formed, resulting in reduced elongation and formability. Furthermore, when the amount of Fe added is high, there is a risk that coarse intermetallic compounds will form, depending on the cooling rate during casting.

The present invention was made against the background of the above circumstances, and one of its objectives is to provide an aluminum alloy foil that has high formability by suppressing the size of intermetallic compounds while maintaining the density of the intermetallic compounds, while adding the same amount of Fe as conventional Al-Fe alloys.

That is, a first embodiment of the aluminum alloy foil of the present invention has a composition containing Fe: 0.8% by mass or more and 4.0% by mass or less, Si: 0.2% by mass or less, a rare earth element : 0.2 % by mass or more and 1.0% by mass or less, and the balance being Al and inevitable impurities,
The intermetallic compound has an average diameter (circle equivalent diameter) particle size of 0.48 to 1.0 μm and a dispersion density of 2.0×10 5 ^to 5.0×10 ⁵ particles/mm ² .

A second aspect of the aluminum alloy foil invention is characterized in that, in the aluminum alloy foil invention of the above aspect, the elongation at angles of 0°, 45°, and 90° relative to the rolling direction is 15% or more.

The following explains the provisions of this invention.

Fe: 0.8% by mass or more and 4.0% by mass or less. Fe crystallizes as an Al-Fe intermetallic compound during casting, and if the size is appropriate, it serves as a recrystallization site during annealing, thereby refining the recrystallized grains. If the content is less than 0.8% by mass, the distribution density of the intermetallic compounds is low, the refining effect is low, and the final crystal grain size distribution becomes non-uniform. If the content exceeds 4.0% by mass, the effect of refining the crystal grains saturates or decreases, and the size of the Al-Fe intermetallic compounds formed during casting becomes very large, resulting in poor elongation, forming position, and rollability of the foil. A particularly preferred range is 1.2% by mass or more at the lower limit and 2.5% by mass or less at the upper limit.

Si: 0.2% 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 0.2% by mass or less.

Rare earth elements: 0.01% by mass or more and 1.0% by mass or more. Rare earth elements such as Y, La, Ce, Pr, Nd, and Sm preferentially form intermetallic compounds with Fe in Al-Fe alloys, suppressing the formation of coarse Al-Fe intermetallic compounds during casting and cooling. This can prevent the coarse crystals from reducing elongation and formability, as well as the uniformity of the recrystallized grain size distribution after final annealing. Ce and La are particularly effective. The amount of rare earth element added suitable for achieving this effect is 0.01% by mass or more and 1.0% by mass or less. Less than 0.01% by mass is insufficient, while more than 1.0% by mass results in the rare earth element remaining in the aluminum without being completely dissolved during casting. The rare earth element may be incorporated into the aluminum alloy using misch metal.

- Elongation of 15% or more at 0°, 45°, and 90° angles relative to the rolling direction Aluminum alloy foil used in packaging materials is subjected to three-dimensional deformation during press forming. Therefore, elongation is required in various directions, not just the rolling direction. If the elongation in any direction is less than 15%, that direction becomes rate-limiting and formability decreases. To maintain formability, it is desirable for the elongation to be 15% or more in all directions relative to the rolling direction.

As explained above, the present invention makes it possible to obtain high elongation properties while maintaining formability.

FIG. 1 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.

A method for producing an aluminum alloy foil according to one embodiment of the present invention will be described.
An aluminum alloy ingot was produced by adjusting the composition to contain 0.8% by mass or more and 4.0% by mass or less of Fe, 0.2% by mass or less of Si, 0.01% by mass or more and 1.0% by mass or less of rare earth elements, and the balance consisting of Al and inevitable impurities. The method for producing the ingot is not particularly limited, and can be carried out by a conventional method such as semi-continuous casting. The obtained ingot is subjected to a homogenization treatment, for example, by holding it at 450 to 600°C for 6 hours or more.

The homogenization treatment here aims to eliminate microsegregation within the ingot and adjust the distribution of intermetallic compounds, making it extremely important for achieving a fine, uniform grain structure. During homogenization, temperatures below 450°C are undesirable because they require a very long time to eliminate microsegregation within the ingot, and the distribution of intermetallic compounds is not optimal. Temperatures above 600°C also cause crystallization to grow, reducing the density of coarse intermetallic compounds that serve as nucleation sites for recrystallization, leading to coarse grain size. Furthermore, to achieve the desired texture during intermediate annealing and final annealing, it is necessary to precipitate as much Fe as possible. At temperatures above 600°C, a small amount of Fe redissolves, so temperatures below 600°C are desirable to minimize the amount of dissolved Fe. The time required for homogenization varies depending on the temperature, but a minimum of six hours is required at any temperature. A temperature of less than six hours may result in insufficient elimination of microsegregation and Fe precipitation.

After the homogenization treatment, hot rolling is performed, and the rolling finish temperature is set to, for example, 230°C or higher and lower than 300°C. Then, cold rolling is performed, and intermediate annealing can be performed during the cold rolling. In the intermediate annealing, the temperature can be set to 300°C to 400°C, and the intermediate annealing time is preferably 3 hours or higher and less than 10 hours. If the annealing time is less than 3 hours, the material may not be softened sufficiently if the annealing temperature is low, and long-term annealing of 10 hours or higher is not economically preferable.
The cold rolling after the intermediate annealing corresponds to the final cold rolling, and the final cold rolling reduction can be 91% or more. The foil thickness is not particularly limited, but can be, for example, 10 μm to 40 μm. The final annealing is performed under conditions equivalent to a batch process at 250 to 350°C for 10 hours or more.
The foil is completely softened by final annealing. If the temperature is less than 250°C or the holding time is less than 10 hours, softening may be insufficient, while if the temperature exceeds 350°C, problems such as deformation of the foil and reduced economic efficiency may occur. From the viewpoint of economic efficiency, the upper limit of the holding time is preferably less than 24 hours.

In the aluminum alloy foil, it is desirable that the dispersion of the intermetallic compounds satisfies the following requirements.
The intermetallic compound has an average diameter (circle equivalent diameter) particle size of 0.3 to 1.0 μm and a dispersion density of 8.0×10 ⁴ to 5.0×10 ⁵ particles/mm ² .
The presence of intermetallic compounds with the above average diameter and dispersion density can more reliably achieve high elongation in the foil. An average particle size of less than 0.3 μm may inhibit recrystallization of the foil, thereby reducing its properties. An average particle size of 1.0 μm or more may cause cracks to form during foil molding. A density of less than 8.0 × 10 ⁴ particles/mm ² results in fewer nucleation sites for recrystallization, resulting in non-uniform crystal grains. A density of 5.0 × 10 ⁵ particles/mm ² or more results in too many compounds, resulting in increased strength and reduced elongation. Therefore, it is desirable to keep the average diameter and density of the intermetallic compounds within the above ranges.

The particle size and density can be measured by degreasing and cleaning the surface of the aluminum alloy foil, then electrolytically etching it with an aqueous solution of perchloric acid and ethanol, taking a photograph at 2000x magnification with a scanning electron microscope, and analyzing and calculating the size and density of the intermetallic compounds using image analysis software.

The resulting aluminum alloy foil has excellent elongation properties, with elongation of 15% or more in directions at 0°, 45°, and 90° to the rolling direction.

The resulting aluminum alloy foil can be deformed by press molding or other methods, and is suitable for use as packaging for food products and lithium-ion batteries. However, the uses of the aluminum alloy foil of the present invention are not limited to those described above, and it can be used for any suitable purpose.

Aluminum alloy ingots with the composition shown in Table 1 (the balance being Al and unavoidable impurities) were produced using a semi-continuous casting method. The resulting ingots were then homogenized at 520°C for 8 hours, hot rolled at a finishing temperature of 280-300°C, cold rolled to a thickness of 2.5 mm, and then subjected to intermediate annealing at 360°C for 3 hours. After cold rolling again, final batch annealing at 270°C for 10 hours was performed to produce aluminum alloy foil. The foil thickness was 40 μm.

The following measurements and evaluations were performed on the obtained aluminum alloy foil, and the results are shown in Table 1.

Elongation Elongation was measured by a tensile test in accordance with JIS Z2241, in which a JIS No. 5 test piece was taken from the sample and measured using a universal tensile tester (manufactured by Shimadzu Corporation) at a tensile speed of 2 mm/s.

Intermetallic Compounds The intermetallic compounds in the matrix were determined by degreasing and cleaning the surface of the aluminum alloy foil, followed by electrolytic etching with an aqueous solution of a mixture of perchloric acid and ethanol, taking a photograph at 2000 times magnification with a scanning electron microscope, and analyzing and calculating the size and density of the intermetallic compounds using image analysis software (product name: Image J).

- Limit forming height The forming height was evaluated in a square tube forming test. The test was performed using a universal sheet forming tester (Model 142/20 manufactured by ERICHSEN) and was performed by forming an aluminum foil having a thickness of 40 μm and the shape shown in FIG. 1 using a square 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 (forming speed) scale set to 1, and mineral oil was applied as a lubricant to one side of the aluminum foil (the surface where the punch hits). The punch rising from the bottom of the device hits the aluminum foil and forms the aluminum foil. The maximum punch rise height that could be formed without cracks or pinholes when formed three times consecutively was defined as the limit forming height (mm) of the material. The punch height was changed at 0.5 mm intervals. Here, a protrusion height of 5.0 mm or more was deemed to have good formability and was judged as ◯, a protrusion height of 7.5 mm or more was judged as particularly good as ⊚, and a protrusion height of less than 5.0 mm was judged as x.

As shown in the table, the examples of the present invention have a larger formed height and superior formability than the comparative examples. Furthermore, in example Nos. 3 to 8, the elongation at 0°, 45°, and 90° angles relative to the rolling direction is all 15% or more. Furthermore, comparative examples Nos. 9 to 13, which have compositions outside the range of the present invention, have a small formed height and inferior formability.

Claims (2)

Fe: 0.8% by mass or more and 4.0% by mass or less, Si: 0.2% by mass or less, rare earth elements: 0.2 % by mass or more and 1.0% by mass or less, and the balance being Al and inevitable impurities;
An aluminum alloy foil in which the average diameter (circle equivalent diameter) particle size of the intermetallic compound is 0.48 to 1.0 μm and the dispersion density is 2.0×10 ⁵ to 5.0×10 ⁵ particles/mm ² . The aluminum alloy foil according to claim 1, characterized in that the elongation at angles of 0°, 45°, and 90° relative to the rolling direction is 15% or more.