JP2016041835A - Aluminum alloy foil and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy foil having high strength, high elongation and high conductivity and a production method therefor.SOLUTION: There is provided the aluminum alloy foil which has a composition containing, by mass%, Fe:over 1.0% to less than 1.8%, Cu:0.01% or less and Si:0.15% or less and the balance Al with inevitable impurities, and has an Fe solid solution amount of 400 ppm or more, a tensile strength of 250 MPa or more and an elongation of 3% or more. The high strength and high elongation of the aluminum alloy foil is achieved by continuously casting and rolling an aluminum alloy molten metal having the above composition to a sheet material having a thickness of 3 to 20 mm at a cooling speed of 300°C/sec. or more and cold rolling the sheet material to an aluminum alloy foil having a thickness of 10 to 20 μm without heat treating the sheet material thereby preventing reduction of solid solution amount of Fe and dispersing an intermetallic compound finely.SELECTED DRAWING: None

Description

  The present invention relates to an aluminum alloy foil that can be used for a lithium ion secondary battery electrode current collector and the like, and a method for producing the same.

  Aluminum alloy foil used for packaging materials for batteries such as lithium ion secondary batteries is unwound from a foil coil by a battery maker, and an active material is applied to the foil surface, followed by drying and pressure bonding to produce an electrode. Yes. This electrode (positive electrode / negative electrode) is wound through a separator and stored in a battery case. At this time, if the strength or elongation of the foil is low, the risk of breakage at the time of electrode production or at the time of winding the electrode increases, so it is desirable that these two physical properties be as high as possible. If the conductivity of the foil itself is low, there is a possibility that a problem such as a decrease in battery characteristics due to an increase in internal resistance of the battery or a decrease in safety due to heat generation of the battery may occur. In particular, in recent years, the current collector foil of consumer batteries has been remarkably thinned, and the demand for high conductivity has increased. That is, an aluminum alloy foil that simultaneously satisfies high strength, high rollability, and high conductivity is desired.

  Further, Fe is generally cited as an alloy element that contributes little to the decrease in conductivity, but although Fe can improve the strength by solid solution, its solubility in Al is extremely small. In addition, it is difficult to dissolve Fe in a supersaturated state by direct casting casting.

  In Cited Document 1, an aluminum alloy plate containing four elements of Fe, Si, Cu, and Ti is formed by continuous casting, and cold rolling and foil rolling are sequentially performed without performing heat treatment on the aluminum alloy plate. By doing so, a technique that enables forced dissolution of Fe and dispersion of a fine metal compound has been proposed. In Cited Document 1, it is said that the strength after the drying process is high, the aluminum alloy foil is not easily deformed even during pressing, and the active material can be prevented from being peeled off or broken at the time of slitting.

International Publication No. 2013/018165

  However, in the technique described in the cited document 1, Cu effective for increasing the strength of the foil is positively contained. Naturally, as the amount of solid solution increases, the conductivity of the material is lowered, and the coarse intermetallic Compounds and the like are easily generated, and the rollability is lowered. Therefore, the means proposed in the cited document 1 has not yet achieved high strength, high rollability and high conductivity.

  This invention is made | formed based on the said situation, and it aims at providing the aluminum alloy foil which has high intensity | strength, high elongation, and high electroconductivity, and its manufacturing method.

  That is, among the aluminum alloy foils of the present invention, the first present invention is in mass%, Fe: more than 1.0% to less than 1.8%, Cu: 0.01% or less, Si: 0.15% It has the following composition, the balance is composed of Al and inevitable impurities, the Fe solid solution amount is 400 ppm or more, the tensile strength is 250 MPa or more, and the elongation is 3% or more.

  The aluminum alloy foil of the second aspect of the present invention is characterized in that, in the first aspect of the present invention, the aluminum alloy foil is for a secondary battery electrode current collector.

  The manufacturing method of the aluminum alloy foil of the third aspect of the present invention includes, in mass%, Fe: more than 1.0%, less than 1.8%, Cu: 0.01% or less, Si: 0.15% or less. The molten aluminum alloy having a composition composed of Al and inevitable impurities is continuously cast and rolled into a plate material having a thickness of 3 to 20 mm at a cooling rate of 300 ° C./second or more, and the plate material is heated without being heat-treated. It is characterized by cold rolling to a 10-20 μm aluminum alloy foil.

  In the method for producing an aluminum alloy foil of the fourth invention, in the third invention, the aluminum alloy foil has an Fe solid solution amount of 400 ppm or more, a tensile strength of 250 MPa or more, and an elongation of 3% or more. It is characterized by.

  The composition and production conditions in the present invention will be described below. In addition, all the following component content is shown by the mass%.

Fe: more than 1.0% to less than 1.8% By containing Fe, the strength and elongation of the foil are improved and the recrystallized grains are refined. If it is 1.0% or less, sufficient strength and elongation cannot be obtained, and if it is 1.8% or more, a coarse intermetallic compound of Al-Fe or Al-Fe-Si is produced during casting, and breakage or Perforations and the like occur, resulting in a decrease in rollability and elongation characteristics. Therefore, the Fe content is set to more than 1.0% and less than 1.8%. For the same reason, the Fe content is desirably 1.2% or more, and desirably 1.6% or less.

Cu: 0.01% or less While Cu has the effect of improving the strength of the foil, the rolling properties such as edge cracks during rolling are extremely deteriorated, and the conductivity of the material is lowered as the amount of solid solution increases. Therefore, when emphasizing rollability, it is treated as an inevitable impurity. Although the content is not extremely restricted, if the content exceeds 0.01%, the elongation characteristic is lowered, so the upper limit is made 0.01%. For the same reason, the upper limit of the Cu content is preferably 0.008%. In the case where strength is more important than rollability, the Cu content is preferably 0.001% or more.

Si: 0.15% or less Strength is improved by containing Si, but the effect is not high compared to Cu. Si is inherently an impurity element and is desirably not contained. Since Si forms a metal compound with Fe, if Si is contained excessively, precipitation of Fe increases with Si, and strength and elongation decrease. Therefore, when Si contains as an impurity, the fall of elongation and the solid solution amount fall of Fe can be prevented by making it 0.15% or less. For the same reason, the upper limit of the Si content is preferably 0.1%.

Fe solid solution amount 400 ppm or more High strength can be achieved by solid solution of Fe 400 ppm or more. When the Fe solid volume is less than 400 ppm, sufficient strength cannot be obtained.

When the tensile strength is 250 MPa or more and the elongation is 3% or more. When the tensile strength is less than 250 MPa and the elongation is less than 3%, the foil is unwound from the coil, the active material is applied to the surface, pressed, and dried during the electrode manufacturing process. There is a risk of breaking. Therefore, the tensile strength is 250 MPa or more and the elongation is 3% or more.

Continuous casting cooling rate of 300 ° C / second or more By setting the Fe content to over 1.0% and the cooling rate to 300 ° C / second or more, Fe is dissolved in supersaturation at 400 ppm or more in the Al matrix, and is an intermetallic compound. Can be distributed sufficiently finely and at high density, and high strength can be achieved by solid solution strengthening and dispersion strengthening. When the cooling rate is less than 300 ° C./sec, the solid solution amount of Fe is reduced, and the intermetallic compound is coarsened, resulting in a decrease in rollability and strength.

Continuous casting thickness 3-20mm
By setting the thickness to 3 to 20 mm, a sufficient cooling rate and cold rolling rate can be ensured during casting, and high strength and high elongation can be achieved. If the thickness is 3 mm or less, the cold rolling rate is insufficient, and the strength cannot be ensured. If the thickness exceeds 20 mm, the cooling rate at the time of casting is lowered and the amount of Fe solid solution is reduced, so that it is difficult to obtain high strength.

The distribution density of the intermetallic compound having an equivalent circle diameter of 0.1 to 1.0 μm is 6.0 × 10 ⁵ pieces / mm ² or more. The ND-RD cut surface of the aluminum alloy foil is observed with an SEM, and the intermetallic compound Size and distribution density were determined. As the distribution density of the intermetallic compound having an equivalent circle diameter of 0.1 to 1.0 μm that contributes to dispersion strengthening is higher, the strength is improved. However, even if the density is too high, deformation resistance increases due to dispersion strengthening, which may make foil rolling difficult. The upper limit is 10 ⁶ pieces / mm ² .

No heat treatment is performed. Fe is solid-dissolved in supersaturation at the time of casting, and a high-strength and high-elongation foil is obtained by maintaining the state in which the intermetallic compound is finely dispersed until the final foil. When high-temperature annealing is performed during cold rolling, the solid solution amount of Fe is reduced, the intermetallic compound is coarsened, and the distribution density is also reduced, so that the strength of the foil is greatly reduced. In addition, regarding recovery annealing at 200 ° C. or lower for the purpose of improving rollability, there is no problem regardless of where it is added during the rolling process or after the rolling process.

Final thickness 10-20μm
When the thickness of the aluminum alloy foil is less than 10 μm, battery characteristics may be deteriorated due to an increase in electrical resistance. In addition, it is difficult to produce an aluminum foil having a thickness of less than 10 μm by rolling, and there is a risk that a process may be added. When the thickness of the aluminum alloy foil exceeds 20 μm, the number of aluminum alloy foils that can be wound in the battery is reduced, and there is a concern that the battery capacity may be reduced.

As described above, according to the present invention, the following three effects can be obtained.
(1) By regulating the content of Cu and Si and containing a predetermined amount of Fe, it is possible to prevent a decrease in the solid solution amount of Fe, finely disperse the intermetallic compound, and realize high strength and high elongation. .
(2) Casting Al-Fe alloy by quenching, obtaining high-strength and high-elongation foil by dissolving Fe in a supersaturated state in Al matrix and finely dispersing intermetallic compounds in high density. Can do.
(3) By performing only cold rolling without performing heat treatment, the amount of Fe solid solution and the dispersion state of the intermetallic compound can be maintained up to the final product.
Therefore, according to the present invention, an aluminum alloy foil having high strength, high elongation, and high conductivity can be obtained.

Hereinafter, an embodiment of the present invention will be described.
The aluminum alloy used as the material of the aluminum alloy foil includes the component range of the present invention, Fe: more than 1.0% to less than 1.8%, Cu: 0.01% or less, Si: 0.15% or less The remaining portion is prepared so as to obtain a composition composed of Al and inevitable impurities, and is subjected to a continuous casting rolling method (CC method). In continuous casting and rolling, the molten alloy is cooled at a cooling rate of 300 ° C./second or more to obtain an aluminum alloy sheet having a thickness of 3 to 20 mm.
In addition, as a continuous casting rolling method, a twin roll method, a belt method, etc. can be selected suitably, However As this invention, the method of a continuous casting rolling method is not limited to a specific thing.

  The aluminum alloy sheet is made into an aluminum alloy foil having a final thickness of 10 to 20 μm by cold rolling. Heat treatment such as intermediate annealing and homogenization is not performed before, during, or during the cold rolling. Note that recovery annealing at 200 ° C. or lower for the purpose of improving rolling properties can be performed during the rolling process or after the rolling process. The recovery annealing described here is performed in order to improve rollability while suppressing a decrease in strength, and it is important that the temperature is not higher than the recrystallization temperature. When normal intermediate annealing performed at a temperature higher than the recrystallization temperature is performed, a foil having a target property cannot be obtained due to strength reduction or Fe precipitation.

In the aluminum alloy foil of the present invention, the Fe solid solution amount is not less than a predetermined value, the intermetallic compound is finely dispersed, and high strength, high elongation, and high conductivity can be satisfied at the same time.
The aluminum alloy foil of the present invention can be used for a secondary battery electrode current collector, and can be suitably used particularly for a lithium ion secondary battery. The electrode current collector can be used for both the positive electrode and the negative electrode, but is mainly used for the positive electrode.

Examples of the present invention will be described below in comparison with comparative examples.
An aluminum alloy having the composition shown in Table 1 (the balance being Al and inevitable impurities) is melted, and the plate material is continuously cast and rolled by a twin roll type continuous casting and rolling method.
The molten alloy was cast by continuous casting and rolling at a cooling rate shown in Table 1 to obtain an aluminum alloy sheet having a thickness of 5 mm. The cooling rate is about 600 to 700 ° C./second.
Except for Comparative Example 12, all the aluminum alloy sheets were made into an aluminum alloy foil having a thickness of 12 μm by cold rolling without heat treatment. In Comparative Example 12, the aluminum alloy sheet was 1 mm thick and 360 ° C. × 3 hours in the middle of cold rolling. Intermediate annealing was performed, and then final cold rolling was performed to obtain an aluminum alloy foil having a thickness of 12 μm.
In Comparative Example 13, an aluminum alloy having the composition shown in Table 1 (the balance being Al and inevitable impurities) was cast by semi-continuous casting, and the resulting ingot was subjected to a homogenization treatment at 490 ° C. for 6 hours. An aluminum alloy hot plate material having a thickness of 7 mm was obtained by hot rolling. The aluminum alloy hot plate material was cold rolled to form an aluminum alloy foil having a thickness of 12 μm.

  Tensile tests were performed on the specimens made of each aluminum alloy foil to evaluate tensile strength and elongation. In accordance with JIS Z2241, the tensile test was performed by collecting a JIS No. 5 test piece from the sample and using a universal tensile tester (manufactured by Shimadzu Corporation) at a pulling speed of 2 mm / s.

  The Fe solid solution amount was evaluated for each sample material. The amount of Fe solid solution was measured by the phenol dissolution filtrate method. This is a method in which an aluminum alloy foil as a test material is dissolved in a heated phenol solution, an intermetallic compound is removed by filtration, and Fe in the filtrate is quantified by ICP emission analysis.

  The conductivity was measured by the double bridge method in the atmosphere at 25 ° C. In addition, when using an aluminum alloy foil as a collector of a lithium ion secondary battery, the electrical conductivity is preferably 50% IACS or more. When it is less than 50%, there is a concern that the battery capacity may be reduced during charge / discharge at a high rate.

  The ND-RD cut surface of the aluminum alloy foil was observed with an SEM, and the size and distribution density of the intermetallic compound were evaluated.

  For the evaluation of the rollability, in the final rolling process aiming at a width of 1200 mm and a thickness of 12 μm, the presence or absence of defects such as thickness failure, breakage, shape failure, winding slippage, hole opening, wrinkle, etc. was evaluated. If none of the problems occurred, it was rated as “Good”. When any defect occurred, the product was not rated as a product or was extremely problematic in production.

  The evaluation of the breakage was a final rolling process aiming at a width of 1200 mm and a thickness of 12 μm, where the foil could be rolled without breaking. Those that were judged to be difficult to continue rolling due to breakage exceeding 3 times or being too hard were evaluated as x. ○ is preferable, but if it is Δ or more (with a final pass of about 10000 m within 3 breaks), there is no problem in production.

  As is apparent from Table 1, Examples 1 to 6 have a tensile strength of 250 MPa or more and an elongation of 3% or more. In Comparative Examples 7, 8, 12, and 13, the tensile strength was 238 MPa or less. In Comparative Example 9, perforation and breakage occurred. In Comparative Examples 10 and 11, wrinkles and breakage occurred, and the fracture occurred before reaching the thickness of 12 μm in the final rolling process, so the mechanical properties could not be measured. Therefore, it turned out that Examples 1-6 have high intensity | strength and high elongation compared with Comparative Examples 7-13.

Claims (4)

  In mass%, Fe: more than 1.0% to less than 1.8%, Cu: 0.01% or less, Si: 0.15% or less, the balance is composed of Al and inevitable impurities, An aluminum alloy foil characterized by having an Fe solid solution amount of 400 ppm or more, a tensile strength of 250 MPa or more, and an elongation of 3% or more.   The aluminum alloy foil according to claim 1, wherein the aluminum alloy foil is for a secondary battery electrode current collector.   Aluminum alloy containing, by mass%, Fe: more than 1.0% to less than 1.8%, Cu: 0.01% or less, Si: 0.15% or less, and the balance consisting of Al and inevitable impurities The molten metal is continuously cast and rolled to a plate material having a thickness of 3 to 20 mm at a cooling rate of 300 ° C./second or more, and the plate material is cold-rolled to an aluminum alloy foil having a thickness of 10 to 20 μm without performing heat treatment. A method for producing a featured aluminum alloy foil.   The method for producing an aluminum alloy foil according to claim 3, wherein the aluminum alloy foil has an Fe solid solution amount of 400 ppm or more, a tensile strength of 250 MPa or more, and an elongation of 3% or more.