Method for producing high-strength and high-toughness ultra-thin aluminum foil for power battery by casting and rolling 8006 alloy

Abstract

This invention discloses a method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries using cast-rolled 8006 alloy, belonging to the field of aluminum alloy material technology. The method uses 20%–30% by mass of remelted aluminum ingots and 70%–80% by mass of 8021 alloy cast-rolled coil scrap as raw materials. Ceramic aluminum seed crystals are added, and the alloy composition is adjusted to Si 0.2%–0.3%, Fe 1.2%–1.4%, Cu 0.05%–0.07%, Mn 0.3%–0.5%, Mg≤0.02%, Zn≤0.05%, Ti 0.01%–0.02%, with the balance being Al. After melting, adding aluminum-titanium-carbon and aluminum-titanium-boron grain refiners, degassing, two-stage filtration, and tubular filtration, the aluminum foil is cast using an electromagnetic casting crystallizer, followed by high-temperature recrystallization annealing, cold rolling, longitudinal shearing, foil rolling, inspection, and packaging to obtain the finished aluminum foil. The aluminum foil prepared by this invention has a thickness of 0.008 mm, a tensile strength ≥310 MPa, a yield strength ≥280 MPa, and an elongation ≥4.0%, and has the advantages of high strength, high elongation, low pinhole rate, and low oil content.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy material technology, specifically relating to a method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries using cast and rolled 8006 alloy. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage power stations, and the consumer electronics industry, lithium-ion batteries are facing increasingly higher requirements for energy density, cycle life, fast charging performance, and safety. Aluminum foil, as a core material for the positive electrode current collector in lithium-ion batteries, directly affects the battery's charge / discharge efficiency, rate performance, and long-term reliability due to its mechanical properties, conductivity, surface quality, and structural stability.

[0003] Currently, aluminum foil for lithium-ion batteries is mainly made from 1-series aluminum alloys such as 1060 and 1070, produced through hot rolling or cast-rolling-cold rolling-foil rolling processes. Although 1-series pure aluminum has high conductivity, its strength is relatively low, with a tensile strength in the H18 state typically only 180MPa to 210MPa. During ultra-thinning and high-speed coating processes, 1-series pure aluminum foil is prone to problems such as strip breakage, tensile deformation, and poor sheet shape, making it difficult to meet the requirements of power batteries and energy storage batteries for high stiffness and high resistance to deformation.

[0004] In recent years, some companies have attempted to use 8021 alloy to produce aluminum foil for lithium-ion batteries. Although 8021 alloy has improved strength compared to 1-series aluminum alloys, its thermal stability is poor, and its creep resistance under high-temperature conditions is insufficient. It is prone to cracking, burrs, and even breakage during the folding process, which limits its application in high-end power batteries and pouch batteries. Furthermore, 8021 alloy is prone to developing coarse second phases during casting and rolling, and its poor microstructure uniformity leads to a higher number of pinholes, thus affecting the consistency and lifespan of the battery foil.

[0005] 8006 alloy belongs to the Al-Fe-Si-Mn aluminum alloy system and features high strength, excellent thermal stability, and balanced corrosion resistance. It is less prone to softening at high temperatures, exhibits stronger resistance to deformation, and has superior elongation, making it ideal for producing ultra-thin, high-strength, and high-toughness battery aluminum foil. However, no company has yet conducted research on producing 8006 alloy battery foil using a casting-rolling process. Therefore, developing a method for stably producing high-strength, high-toughness, ultra-thin 8006 alloy battery foil using a casting-rolling process to meet the comprehensive requirements of lithium-ion battery current collectors for high strength, ultra-thinness, low defects, and high heat resistance has become a pressing technical problem in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy. The method involves producing 8006 alloy billets by casting and rolling, followed by high-temperature recrystallization annealing, cold rolling, edge trimming, and foil rolling to obtain ultra-thin aluminum foil products. The mechanical properties of the finished products are superior to those of 1-series aluminum alloys and 8021 alloy products, and can fully meet the needs of customers.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy includes the following steps: Step S1, Smelting: By mass percentage, 20%–30% of remelting aluminum ingots and 70%–80% of 8021 alloy casting coil scrap are melted. Ceramic aluminum seed crystals are added to each furnace, followed by aluminum-iron alloy, quick-dissolving silicon, manganese agent, copper agent, and titanium agent to adjust the alloy composition so that the final billet is 8006 aluminum alloy with the mass percentage of each element satisfying: Si 0.2%–0.3%, Fe 1.2%–1.4%, Cu 0.05%–0.07%, Mn 0.3%–0.5%, Mg≤0.02%, Zn≤0.05%, Ti 0.01%–0.02%, with the balance being Al. After refining, the melt is poured into a holding furnace and the temperature of the melt in the holding furnace is controlled at 735–745℃. Step S2, Online Melt Processing: At the inlet of the degassing box, add aluminum-titanium-carbon grain refiner and aluminum-titanium-boron grain refiner to the melt flowing out of the holding furnace, and then perform degassing, two-stage filtration and tubular filter box filtration. Step S3, Casting: The filtered melt enters the front box equipped with an electromagnetic casting crystallizer. The melt enters the casting nozzle through the aluminum supply port. The melt flowing out of the casting nozzle is cast and cooled between two counter-rotating rollers to form a billet. Step S4, High-temperature recrystallization annealing: The cast-rolled coil made after the billet is rolled up is annealed. The annealing process is to hold the metal at a temperature of 460-490℃ for 4-6 hours. Step S5, Cold Rolling: The annealed cast-rolled coil is naturally cooled to below 45°C and rolled sequentially to thicknesses of 4.0mm, 2.4mm, 1.4mm, 0.85mm, 0.5mm, and 0.3mm. The first five passes are rolled by a cold rolling mill, and the last pass is rolled by a cold intermediate mill. The roughness of the work rolls of the cold rolling mill is 0.4-0.45μm, and the roughness of the work rolls of the cold intermediate mill is 0.23-0.28μm. Step S6, Longitudinal shearing: Cool the cold-rolled coil obtained after cold rolling to below 45°C, and shear the edges at a speed of ≤150m / min. The strip does not contact the guide plate during the shearing process. Step S7, Foil Rolling: The trimmed cold-rolled coil is rolled sequentially to thicknesses of 0.17mm, 0.096mm, 0.054mm, 0.033mm, 0.02mm, 0.012mm, and 0.008mm. The first five passes are rolled on an aluminum foil roughing mill, and the last two passes are rolled on an aluminum foil finishing mill. The roughness of the work rolls on the aluminum foil roughing mill is 0.18-0.22μm, and the roughness of the work rolls on the aluminum foil finishing mill is 0.13-0.17μm. The rolling oil used in the aluminum foil roughing mill contains 3%-5% alcohol, 3%-5% ester, and [amount missing]% acid. The rolling oil has a weight ratio of 0.2%-0.5%, with the remainder being 80# light white oil. This rolling oil is filtered through a two-stage filter with pore sizes of 20μm and 10μm, respectively. The rolling oil used in the aluminum foil finishing mill contains 0.5%-1% alcohol, 5%-7% ester, and 0.5%-0.8% acid by weight, with the remainder being mixed base oil. This rolling oil is filtered through a three-stage filter with pore sizes of 20μm, 10μm, and 3μm, respectively. The mixed base oil is a mixture of 70# light white oil and 80# light white oil in a 1:1 weight ratio. Step S8, Inspection and Packaging: After the finished product is rolled off the machine, it is inspected and packaged after passing the inspection.

[0008] Further, in step S1, the amount of ceramic aluminum seed crystal added is 50 kg per furnace, and the furnace is simmered for 20 minutes. The ceramic aluminum seed crystal is a naturally cast block with a width not exceeding 50 mm, a thickness not exceeding 20 mm, and a weight not exceeding 3 kg per block. In step S1, the mass percentage of iron in the aluminum-iron alloy is 3% to 4%.

[0009] Further, in step S1, after adding ceramic aluminum seed crystals and simmering the furnace for 20 minutes, the electromagnetic stirrer is turned on, and high-purity argon is used for a pre-refining process to achieve degassing, slag removal, and localized uniform stirring of the melt in the furnace. The melt in the furnace is then heated again using a natural gas torch to raise the temperature to 735-750℃. Then, aluminum-iron alloy, quick-dissolving silicon, manganese agent, copper agent, and titanium agent are added to the furnace to adjust the alloy composition. After the alloy composition is found to be qualified, argon and granular refining agent are used for refining. After refining, the electromagnetic stirrer is turned off and the melt is allowed to stand for more than 15 minutes. The slag on the surface of the melt is skimmed off, and the melt is allowed to stand for another 30 minutes before being poured into the holding furnace. Within 5 minutes after pouring the melt into the holding furnace, the granular refining agent is used again for refining. After refining, the slag on the surface of the melt is skimmed off, and the electric heater in the holding furnace is turned on to control the temperature of the melt in the holding furnace at 735-745℃.

[0010] Furthermore, in step S2, the aluminum-titanium-carbon grain refiner and the aluminum-titanium-boron grain refiner are added in a 1:1 ratio, and the addition temperature is above 725°C.

[0011] Furthermore, in step S2, degassing is performed using a rotor speed of 400±10 r / min and a high-purity argon flow rate of 50±5 L / min; the first-stage filter plate of the dual-stage filtration system has an accuracy of 50 ppi and the second-stage filter plate has an accuracy of 60 ppi; the tubular filter box uses 22 filter tubes in a group, the melt temperature is 715-725℃, and the liquid level difference between the inlet and outlet of the tubular filter box is no more than 30 mm.

[0012] Further, in step S3, the melt temperature in the front chamber is 688-691℃, and the hydrogen content is 0.08-0.11mL / (100g•Al); the power supply frequency of the electromagnetic casting crystallizer is 80-100kHz, the magnetic induction intensity is 0.1-0.5T, and the excitation power is 200-250kW; the aluminum supply port of the casting nozzle is more than 40mm higher than the bottom of the front chamber; the thickness of the cast billet is 6.5-7.0mm, and the casting speed is 800-850m / min.

[0013] Further, in step S5, the rolling oil used in the cold rolling mill contains, by mass percentage, 4%-6% alcohol, 1%-2% ester, 0.5%-1.0% acid, with the balance being a mixed base oil; the rolling oil used in the intermediate cold rolling mill contains, by mass percentage, 5%-7% alcohol, 1%-2% ester, 1.0%-1.5% acid, with the balance being a mixed base oil. The mixed base oil is composed of 70# light white oil and 80# light white oil mixed in a weight ratio of 1:1.

[0014] Further, in step S8, the qualified finished aluminum foil meets the following indicators: pinholes with a diameter exceeding 150μm are not allowed; the number of pinholes with a diameter less than 150μm in a single 36,000m roll of aluminum foil does not exceed 650; the aluminum foil surface is free of roller marks, blistering, vibration marks, and color difference; tensile strength ≥310MPa, yield strength ≥280MPa, elongation ≥4.0%; deviation between transverse and longitudinal tensile strength ≤2MPa, deviation between transverse and longitudinal yield strength ≤2MPa, deviation between transverse and longitudinal elongation ≤0.5%; dyne value ≥33; oil content per square meter of aluminum foil ≤10mg; edge collapse ≤3mm; thickness fluctuation ≤2.5%.

[0015] Beneficial effects of the present invention (1) Within the standard alloy composition range of 8006 alloy in GB / T 3190-2020 "Chemical Composition of Wrought Aluminum and Aluminum Alloys", this invention selects an optimized composition range, namely Si 0.2%~0.3%, Fe 1.2%~1.4%, Cu 0.05%~0.07%, and Mn 0.3%~0.5%. This composition range belongs to a customized 8006 series alloy with high Fe, medium Si, low Mn, and low Cu. Among them, the Fe content of 1.2% to 1.4% can promote the formation of a large number of fine and dispersed (Fe,Mn)Al6 intermetallic compounds, achieving dispersion strengthening and significantly improving tensile strength, yield strength and high-temperature softening resistance; the Si content of 0.2% to 0.3% can promote the formation of fine AlFeSi second phase, and controlling it within 0.3% can avoid the formation of coarse needle-like Al-Si phase, thereby ensuring high toughness and elongation and preventing strip breakage during ultra-thin rolling; the Mn content of 0.3% to 0.5% can promote the formation of (Fe,Mn)Al6 spherical dispersed phase, significantly improving the brittleness of the material; the Cu content of 0.05% to 0.07% can achieve weak solid solution strengthening, improve grain boundary strength, and slightly improve strength without sacrificing conductivity and corrosion resistance. By rationally combining the above alloy components, a synergistic effect of high Fe strengthening, medium Si plasticizing, low Mn stabilizing microstructure, and micro Cu strength enhancement is achieved. High strength, good toughness, ultra-thin and easy-to-roll, and excellent corrosion resistance aluminum foil for power batteries can be stably prepared by casting and rolling.

[0016] (2) In the smelting step, 50 kg of ceramic aluminum seed crystals are uniformly added to each furnace. As a high-density heterogeneous crystal nucleus, the ceramic aluminum seed crystals can promote the formation of uniform and fine equiaxed crystals during casting and solidification, eliminate columnar crystals and compositional segregation, suppress unfavorable casting and rolling texture, significantly reduce the anisotropy of the material, and thus improve the consistency of the transverse and longitudinal properties of the finished aluminum foil.

[0017] (3) The present invention uses an electromagnetic casting crystallizer for casting, which can promote the formation of fine equiaxed crystals, reduce the dendrite spacing to 30-50 μm, effectively suppress compositional segregation, avoid the generation of coarse Al3Fe brittle phases, and reduce the problems of strip breakage and pinholes during aluminum foil rolling. At the same time, the electromagnetic force can drive inclusions and slag to float and be removed, improve the purity of the melt, make the grain boundaries more stable, more resistant to electrolyte corrosion, and extend the cycle life.

[0018] (4) This invention uses a combination of aluminum-titanium-carbon grain refiner and aluminum-titanium-boron grain refiner. The TiC phase in the aluminum-titanium-carbon grain refiner has good high-temperature stability, is not prone to agglomeration, and is not prone to failure. The TiB2 phase in the aluminum-titanium-boron grain refiner has a high nucleation rate and a strong refining effect. The combined use of the two can break up and spheroidize the second phase, reduce component segregation and banded structure, and make the grains in the coarse grain region of the core of the cast and rolled billet finer and more uniform. The refining efficiency is significantly better than using aluminum-titanium-boron grain refiner or aluminum-titanium-carbon grain refiner alone.

[0019] (5) In this invention, the remaining amount of rolling oil used in the aluminum foil roughing mill is 80# light white oil; the remaining amount of rolling oil used in the aluminum foil finishing mill, cold rolling mill, and cold intermediate mill is mixed base oil, which is a mixture of 70# light white oil and 80# light white oil in a weight ratio of 1:1. 70# light white oil has low viscosity, good fluidity, and fast cooling speed, while 80# light white oil has slightly higher viscosity but better oil film strength and better lubrication effect. By selecting different base oils or mixed base oils at different rolling stages, the viscosity can be precisely controlled, taking into account the characteristics of no oil film breakage and good flushing and cooling effect during high-speed rolling, thus achieving the excellent effect of high hysteresis value and low oil content on the aluminum foil surface.

[0020] (6) In this invention, the rolling oil used in the aluminum foil roughing mill is filtered by a two-stage filter, using filter elements with pore sizes of 20μm and 10μm respectively; the rolling oil used in the aluminum foil finishing mill is filtered by a three-stage filter, using filter elements with pore sizes of 20μm, 10μm and 3μm respectively. Through multi-stage filtration, solid particulate impurities such as aluminum powder, rust flakes from pipes, and oxide flakes from sealing rings in the rolling oil can be effectively intercepted, reducing the probability and risk of foreign objects being pressed into the aluminum foil, and significantly improving the pinhole control level of the aluminum foil. In addition, the reduction of solid particulate impurities in the rolling oil can avoid nozzle blockage and uneven spraying, ensuring the stability of cooling and lubrication, and making the surface quality, plate quality and surface aluminum powder content of the finished aluminum foil product more excellent.

[0021] (7) This invention uses 70%–80% of 8021 alloy cast-rolled coil scrap and a low-iron content aluminum-iron alloy with an iron mass percentage of 3%–4% to formulate 8006 alloy. Since the composition of 8021 alloy cast-rolled coil scrap is similar to that of 8006 alloy matrix, there is no need to add a large proportion of aluminum-iron alloy during melting and mixing. The added low-iron content aluminum-iron alloy dissolves evenly and has no local iron enrichment areas. According to this scheme, the 1.2%–1.4% Fe content can ensure that intragranular segregation, layered segregation, and edge enrichment are significantly reduced during the casting and rolling process, and the composition uniformity of the cast plate is higher. In addition, the 8021 alloy cast-rolled coil scrap and the low-iron content aluminum-iron alloy have already undergone one alloying. During the secondary alloying in the melting and mixing, this method of mixing will make the alloying more thorough. After casting and rolling, the problems of oxide inclusions, iron-rich agglomeration, segregation nodules and other issues in the internal structure are greatly reduced, which facilitates the control of pinholes in the subsequent aluminum foil products.

[0022] (8) The battery foil product with a thickness of 0.008 mm prepared by the method of the present invention has a tensile strength ≥310 MPa, a yield strength ≥280 MPa, and an elongation ≥4.0%. The finished product has high strength, is not easily stretched or deformed during coating, and can withstand higher rolling pressure during rolling, making the electrode sheet more compact and improving the ion transport efficiency of the finished battery product, supporting fast charging and discharging; the finished product has good toughness, is not easily cracked or brittle when bent or wound in an arc, and can meet the harsh working conditions such as large cylindrical winding and long cell stretching; the finished product is thin, and more active material can be coated in the same volume of cell, improving the energy density of the battery. The method of the present invention achieves the effects of thinner, safer, higher yield, longer cycle life and higher energy density, and is the ideal material choice for current high-end batteries. Detailed Implementation

[0023] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the scope of protection of the present invention is not limited to the following embodiments.

[0024] This invention selects an optimized composition range within the standard alloy composition range of 8006 alloy in GB / T 3190-2020 "Chemical Composition of Wrought Aluminum and Aluminum Alloys", namely, Si 0.2%–0.3%, Fe 1.2%–1.4%, Cu 0.05%–0.07%, Mn 0.3%–0.5%, Mg≤0.02%, Zn≤0.05%, Ti 0.01%–0.02%, with the balance being Al. This composition range belongs to a customized 8006 series alloy with high Fe, medium Si, low Mn, and low Cu. The design principles of the above components are as follows: 1.2% to 1.4% Fe content can promote the formation of a large number of fine and dispersed (Fe,Mn)Al6 intermetallic compounds, achieving dispersion strengthening and significantly improving tensile strength, yield strength and high-temperature softening resistance; 0.2% to 0.3% Si content can promote the formation of fine AlFeSi second phase, and controlling it within 0.3% can avoid the formation of coarse needle-like Al-Si phase, thereby ensuring high toughness and elongation and preventing strip breakage during ultra-thin rolling; 0.3% to 0.5% Mn content can promote the formation of (Fe,Mn)Al6 spherical dispersed phase, significantly improving the brittleness of the material; 0.05% to 0.07% Cu content can achieve weak solid solution strengthening, improve grain boundary strength, and slightly improve strength without sacrificing conductivity and corrosion resistance.

[0025] The manufacturing process of battery foil is described below: Step S1, Smelting: By mass percentage, add 20%–30% of remelting aluminum ingots and 70%–80% of 8021 alloy cast-rolled coil scrap to the smelting furnace; use a natural gas torch to heat and melt the solid material; uniformly add 50 kg of ceramic aluminum seed crystals to each furnace and let it simmer for 20 minutes; turn on the electromagnetic stirrer and perform a pre-refining operation using high-purity argon; heat again using a natural gas torch to raise the temperature of the melt in the smelting furnace to 735–750°C; add iron by mass percentage to the smelting furnace. The alloy composition is adjusted by adding 3%–4% aluminum-iron alloy, quick-dissolving silicon, manganese, copper, and titanium. After the alloy composition is tested and found to be qualified, it is refined using argon and granular refining agents. After refining, the electromagnetic stirring is turned off and the melt is allowed to stand for more than 15 minutes. The slag on the surface of the melt is skimmed off, and after standing for another 30 minutes, the melt is poured into a holding furnace. Within 5 minutes after pouring into the furnace, it is refined again using granular refining agents. After refining, the slag on the surface of the melt is skimmed off, and the electric heater in the holding furnace is turned on to control the temperature of the melt in the holding furnace at 735-745℃. In the above operation, 70%–80% high proportion of 8021 alloy cast-rolled coil scrap is used as raw material. The reason is that the matrix composition of 8021 alloy is similar to that of 8006 alloy, which can reduce the amount of additives such as aluminum-iron alloy. At the same time, the 8021 alloy cast-rolled coil scrap has already undergone one alloying, and the alloying is more thorough during the second alloying, which is beneficial to improving the uniformity of the billet composition. The ceramic aluminum seed crystal used in this invention is a TiB2 / Al seed crystal, which, as a high-density heterogeneous nucleus, can promote the formation of uniform and fine equiaxed crystals during casting and solidification, eliminate columnar crystals and compositional segregation, suppress unfavorable casting and rolling textures, and significantly reduce the anisotropy of the material. The ceramic aluminum seed crystal is made from naturally cast blocks with a width not exceeding 50 mm, a thickness not exceeding 20 mm, and a weight not exceeding 3 kg, which facilitates uniform dispersion in the melt. The granular refining agent used in this invention can be a sodium-free granular refining agent, such as a refining agent composed of magnesium chloride, potassium chloride, sodium fluoroaluminate, etc., mixed in a certain proportion, or a commercially available aluminum alloy-specific granular refining agent can be used. The granular refining agent is sprayed into the melt under the action of argon carrier gas, which can adsorb oxide inclusions in the melt and carry them to the melt surface, thereby purifying the melt. This invention uses a low-iron-content aluminum-iron alloy with an iron mass percentage of 3% to 4% to adjust the iron content. The reason is that the low-iron-content aluminum-iron alloy is conducive to the uniform dissolution of iron in the melt, avoiding local iron enrichment, thereby reducing intragranular segregation, layered segregation and edge enrichment problems during the casting and rolling process. Step S2, Online Melt Treatment: The melt in the holding furnace flows out through the outlet; at the inlet of the degassing box, aluminum-titanium-carbon grain refiner and aluminum-titanium-boron grain refiner are added to the outflowing melt in a 1:1 ratio, with the addition point temperature controlled above 725℃; the melt with added grain refiner enters the degassing box and is degassed at a rotor speed of 400±10 r / min and a high-purity argon flow rate of 50±5 L / min; the degassed melt then passes through a double-stage filtration system with a primary filter plate accuracy of 50 ppi and a secondary filter plate accuracy of 60 ppi, and then enters a tubular filter box using 22 filter tubes, controlling the melt temperature at 715-725℃, and ensuring the liquid level difference between the inlet and outlet of the tubular filter box is no greater than 30 mm. The combined use of aluminum-titanium-carbon grain refiner and aluminum-titanium-boron grain refiner is crucial in the above operation. The TiB2 phase in aluminum-titanium-boron grain refiners exhibits high nucleation rate and strong grain refinement effect, while the TiC phase in aluminum-titanium-carbon grain refiners demonstrates good high-temperature stability, is less prone to agglomeration, and is less susceptible to failure. The combined use of these two phases achieves superior grain refinement, resulting in finer and more uniform grains in the coarse-grained core region of the cast-rolled billet. During the degassing process, a high-speed rotating silicon nitride rotor disperses high-purity argon gas into microbubbles. As these bubbles rise within the melt, they adsorb hydrogen and inclusions, carrying them to the melt surface. Multi-stage filtration effectively removes both large and small inclusions from the melt, further improving its purity and laying the foundation for producing aluminum foil with low pinhole rates. Step S3, Casting: The filtered melt enters the front chamber equipped with an electromagnetic casting crystallizer. The temperature of the melt in the front chamber is controlled at 688-691℃, and the hydrogen content is 0.08-0.11mL / (100g•Al). The melt enters the casting nozzle through the aluminum supply port, which is more than 40mm higher than the bottom of the front chamber. The melt flowing out of the casting nozzle is cast and cooled between two counter-rotating rolls to form a billet. The casting and rolling zone is controlled at 50-55mm, the billet thickness is 6.5-7.0mm, and the casting and rolling speed is 800-850m / min. The power supply frequency of the electromagnetic casting crystallizer is 80-100kHz, the magnetic induction intensity is 0.1-0.5T, and the excitation power is 200-250kW. Electromagnetic casting crystallizers utilize electromagnetic fields applied to the solidification front to promote the formation of fine equiaxed crystals, reducing dendrite spacing to 30–50 μm, effectively suppressing compositional segregation, and preventing the formation of coarse Al3Fe brittle phases. The hydrogen content in the front chamber is controlled at 0.08–0.11 mL / (100 g•Al), a lower hydrogen content significantly reducing porosity defects in the cast billet. The aluminum feed nozzle is positioned at least 40 mm higher than the bottom of the front chamber; this design helps ensure the stability of melt flow and avoids turbulent slag entrapment. Step S4, High-Temperature Recrystallization Annealing: The cast-rolled coils made from the cast billet are then transferred to an annealing furnace for annealing. The annealing process involves holding the metal at 460-490℃ for 4-6 hours, with the furnace gas temperature not exceeding 550℃. High-temperature recrystallization annealing eliminates the internal stress generated during casting and rolling, allowing for complete recrystallization of the microstructure, refining the grains, and improving the material's plasticity. Simultaneously, during annealing, dispersed phases such as (Fe,Mn)Al6 are fully precipitated and uniformly distributed, providing a uniformly structured and plastically sound billet for subsequent cold rolling and foil rolling. Step S5, Cold Rolling: The annealed cast-rolled coil is naturally cooled to below 45°C and then transferred to a cold rolling mill for rolling. The rolling passes are 4.0mm, 2.4mm, 1.4mm, 0.85mm, 0.5mm, and 0.3mm respectively. The first five passes are rolled by a cold rolling mill, and the last pass is rolled by a cold intermediate mill. The surface roughness of the work rolls of the cold rolling mill is 0.4-0.45μm, and the rolling oil used contains 4%-6% alcohol by mass and 4% ester by mass. The percentage of alcohol is 1%-2%, the mass percentage of acid is 0.5%-1.0%, and the balance is mixed base oil; the roughness of the work rolls in the cold intermediate rolling mill is 0.23-0.28μm, and the mass percentage of alcohol in the rolling oil is 5%-7%, the mass percentage of ester is 1%-2%, the mass percentage of acid is 1.0%-1.5%, and the balance is mixed base oil; the mixed base oil is composed of 70# light white oil and 80# light white oil mixed in a 1:1 weight ratio. A reasonable reduction distribution per pass can ensure the stability of the rolling process and the quality of the sheet shape. Different work roll roughnesses and rolling oil formulations are used in different rolling stages to adapt to the different requirements for friction lubrication and surface quality at different thicknesses; Step S6, Longitudinal shearing: Cool the cold-rolled coil obtained after cold rolling to below 45°C, and shear the edges at a speed of ≤150m / min. The strip does not contact the guide plate during the shearing process. Step S7, Foil Rolling: The trimmed cold-rolled coil is transferred to a foil rolling mill for rolling. The rolling passes are 0.17mm, 0.096mm, 0.054mm, 0.033mm, 0.02mm, 0.012mm, and 0.008mm respectively. The first five passes are rolled on an aluminum foil roughing mill, and the last two passes are rolled on an aluminum foil finishing mill. The roughness of the work rolls of the aluminum foil roughing mill is 0.18-0.22μm. The rolling oil used contains 3%-5% alcohol, 3%-5% ester, and 0.2%-0.5% acid by mass, with the balance being 80# light white oil. The rolling oil is filtered through a two-stage filter with pore sizes of 20μm and 10μm, respectively. The work roll roughness of the aluminum foil finishing mill is 0.13-0.17μm. The rolling oil contains 0.5%-1% alcohol, 5%-7% ester, and 0.5%-0.8% acid by mass, with the remainder being a mixed base oil. This rolling oil is also filtered through a three-stage filter with pore sizes of 20μm, 10μm, and 3μm, respectively. The mixed base oil is a 1:1 mixture of 70# light white oil and 80# light white oil by weight. The use of different work roll roughnesses, rolling oil additive formulations, and filtration precision in the aluminum foil roughing and finishing mills is to balance the requirements of lubrication, cooling, surface quality, and cleanliness during high-speed rolling. In particular, the blended base oils used in the finishing and cold rolling stages can precisely control viscosity, balancing oil film strength and cooling effect, achieving excellent results with high viscosity and low oil content on the aluminum foil surface. Multi-stage filtration can effectively intercept solid particulate impurities such as aluminum powder, rust flakes from pipes, and oxide flakes from sealing rings in the rolling oil, reducing the probability and risk of foreign objects being pressed into the aluminum foil; Step S8, Inspection and Packaging: After the finished product is rolled off the mill, it is inspected and packaged. The finished aluminum foil must meet the following quality indicators: pinholes with a diameter exceeding 150μm are not allowed; the number of pinholes with a diameter less than 150μm in a single 36,000m roll of aluminum foil shall not exceed 650; the aluminum foil surface shall be free of roller marks, bulging, vibration marks, and color difference; tensile strength ≥310MPa, yield strength ≥280MPa, elongation ≥4.0%; deviation between transverse and longitudinal tensile strength ≤2MPa, deviation between transverse and longitudinal yield strength ≤2MPa, deviation between transverse and longitudinal elongation ≤0.5%; dyne value ≥33; oil content per square meter of aluminum foil ≤10mg; edge collapse ≤3mm; thickness fluctuation ≤2.5%.

[0026] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Example 1

[0027] This embodiment provides a method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy, including the following steps: Step S1, Smelting: Add 20.5% (by mass) of remelting aluminum ingots and 79.5% (by mass) of 8021 alloy cast-rolled coil scrap to the smelting furnace. Heat using a natural gas torch. After 4.5 hours, the solid material in the furnace melts and levels. Add 50 kg of ceramic aluminum seed crystals evenly to each batch of the smelting furnace and let it simmer for 20 minutes. Turn on the electromagnetic stirring and perform a pre-refining operation using high-purity argon. Heat the melt in the smelting furnace again using a natural gas torch to raise the temperature to 743°C. Add the melt to the smelting furnace... Add 3.5% by weight of aluminum-iron alloy, quick-dissolving silicon, manganese agent, copper agent, and titanium agent to adjust the alloy composition; after the alloy composition is tested and found to be qualified, refine it with argon and granular refining agent. After refining, turn off the electromagnetic stirring and let it stand for 16 minutes. Remove the slag from the surface of the melt and let it stand for 30 minutes before pouring the melt into the holding furnace; after pouring the melt into the furnace, refine it with granular refining agent for 3 minutes. After refining, remove the slag from the surface of the melt and turn on the electric heater in the holding furnace to control the temperature of the melt in the holding furnace at 744℃. Step S2, Online Melt Processing: The melt in the holding furnace flows out through the flow port; at the inlet of the degassing box, add one aluminum-titanium-carbon grain refiner and one aluminum-titanium-boron grain refiner rod to the outflowing melt, with an addition ratio of 1:1, and the temperature at the rod addition point is 729℃; the melt with added grain refiner enters the degassing box, where a silicon nitride rotor is circulated with high-purity argon gas at a rotor speed of 398 r / min and a high-purity argon gas flow rate of 48 L / min; after online degassing, the melt enters a two-stage filtration box, with a first-stage filter plate accuracy of 50 ppi and a second-stage filter plate accuracy of 60 ppi; the melt after two-stage filtration enters a tubular filter box, which uses 22 filter tubes, with a melt temperature of 718℃ and a liquid level difference of 25 mm between the inlet and outlet of the tubular filter box; the melt after thorough filtration in the tubular filter box enters the front box through the flow channel; Step S3, Casting: The melt temperature in the front box is 689℃, the hydrogen content in the front box is 0.085mL / (100g•Al), and an electromagnetic casting crystallizer is installed in the front box. The power frequency of the electromagnetic casting crystallizer is 88kHz, the magnetic induction intensity is 0.35T, and the excitation power is 230kW. The melt in the front box enters the casting nozzle through the aluminum supply port. The aluminum supply port of the casting nozzle is 50mm higher than the bottom of the front box. The melt flowing out of the casting nozzle is cast and cooled between two counter-rotating rolls to form a billet. The casting and rolling zone is 52mm, the billet thickness is 6.5mm, the casting and rolling speed is 820m / min, and the middle of the rolls is cooled by circulating water. The billet is coiled into a coil by a coiling device. Step S4, High-temperature recrystallization annealing: The cast-rolled coil obtained in step S3 is rolled into a steel strip and transferred to an annealing furnace. A temperature measuring hole with a diameter of 8 mm and a depth of 95 mm is drilled close to the core of the cast-rolled coil. A temperature measuring thermocouple is inserted into the temperature measuring hole. The cast-rolled coil is loaded into a box-type annealing furnace in batches of 4 coils per furnace for annealing. The annealing process is to hold the metal at 485℃ for 5 hours. The furnace gas temperature of the annealing furnace is 540℃. Step S5, Cold Rolling: After annealing, the cast-rolled coil is naturally cooled to 42°C and then transferred to a cold rolling mill for rolling. The rolling passes are 4.0mm, 2.4mm, 1.4mm, 0.85mm, 0.5mm, and 0.3mm respectively. The first five passes are rolled by a cold rolling mill, and the last pass is rolled by a cold intermediate mill. The roughness of the work rolls of the cold rolling mill is 0.42μm. The mass percentage of alcohol in the rolling oil is 4.85%, the mass percentage of ester is 1.25%, the mass percentage of acid is 0.63%, and the balance is a mixed base oil. The roughness of the work rolls of the cold intermediate mill is 0.24μm. The mass percentage of alcohol in the rolling oil is 5.96%, the mass percentage of ester is 1.35%, the mass percentage of acid is 1.42%, and the balance is a mixed base oil. The mixed base oil is composed of 70# light white oil and 80# light white oil mixed in a weight ratio of 1:1. Step S6, Longitudinal shearing: Cool the cold-rolled coil obtained in step S5 to 34°C, and then cut the edge on a longitudinal shearing machine at a speed of 122 m / min. During the cutting process, the strip does not come into contact with the guide plate and no scratches occur. Step S7, Foil Rolling: The cold-rolled coil after edge trimming is transferred to a foil rolling mill for rolling. The rolling passes are 0.17mm, 0.096mm, 0.054mm, 0.033mm, 0.02mm, 0.012mm, and 0.008mm respectively. The first five passes are rolled on an aluminum foil roughing mill, and the last two passes are rolled on an aluminum foil finishing mill. The rolling oil used in the aluminum foil roughing mill contains 3.85% alcohol, 4.22% ester, and 0.31% acid by mass, with the balance being 80# light white oil. The rolling oil used in the aluminum foil roughing mill is filtered through a two-stage filter. The core filter pore sizes are 20μm and 10μm, respectively; the rolling oil used in the aluminum foil finishing mill contains 0.67% alcohol, 6.12% ester, and 0.62% acid by mass, with the balance being mixed base oil. The rolling oil used in the aluminum foil finishing mill is filtered through a three-stage filter with filter core pore sizes of 20μm, 10μm, and 3μm, respectively. The mixed base oil is composed of 70# light white oil and 80# light white oil mixed in a 1:1 weight ratio. The roughness of the work rolls in the aluminum foil roughing mill is 0.19μm, and the roughness of the work rolls in the aluminum foil finishing mill is 0.14μm. Step S8, Inspection and Packaging: After the finished product is rolled off the mill, the inspection results are as follows: there are no pinholes with a diameter exceeding 150μm, and 587 pinholes with a diameter less than 150μm are found in a single 36,000m roll of aluminum foil; the aluminum foil surface is free of roller marks, bulging, vibration marks, and color difference; the transverse tensile strength is 318MPa, the transverse yield strength is 291MPa, and the transverse elongation is 4.1%; the longitudinal tensile strength is 317MPa, the longitudinal yield strength is 292MPa, and the longitudinal elongation is 4.3%; the dyne value of the aluminum foil surface is 33; the oil content per square meter of aluminum foil is 8.52mg; the edge collapse is 2.9mm, and the thickness fluctuation is 2.2%; after passing the inspection, the product is packaged according to the packaging requirements. Example 2

[0028] This embodiment provides a method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy, including the following steps: Step S1, Smelting: Add 28.3% (by mass) of remelting aluminum ingots and 71.7% (by mass) of 8021 alloy cast-rolled coil scrap to the smelting furnace. Heat using a natural gas torch. After 5.25 hours, the solid material in the furnace melts and levels. Add 50 kg of ceramic aluminum seed crystals evenly to each batch of the smelting furnace and let it simmer for 20 minutes. Turn on the electromagnetic stirring and perform a pre-refining operation using high-purity argon. Heat the melt in the smelting furnace again using a natural gas torch to raise the temperature to 748°C. Add the melt to the smelting furnace... Add 3.2% (by weight) of aluminum-iron alloy, quick-dissolving silicon, manganese, copper, and titanium to adjust the alloy composition. After the alloy composition is found to be qualified, refine it using argon and granular refining agent. After refining, turn off the electromagnetic stirring and let it stand for 17 minutes. Remove the slag from the surface of the melt and let it stand for 30 minutes before pouring the melt into the holding furnace. After pouring the melt into the furnace, refine it with granular refining agent for 4 minutes. After refining, remove the slag from the surface of the melt and turn on the electric heater in the holding furnace to control the temperature of the melt in the holding furnace at 739℃. Step S2, Online Melt Processing: The melt in the holding furnace flows out through the flow port; at the inlet of the degassing box, add one aluminum-titanium-carbon grain refiner and one aluminum-titanium-boron grain refiner rod to the outflowing melt, with an addition ratio of 1:1, and the temperature at the rod addition point is 727℃; the melt with added grain refiners enters the degassing box, where a silicon nitride rotor is circulated with high-purity argon gas at a rotor speed of 402 r / min and a high-purity argon gas flow rate of 52 L / min; after online degassing, the melt enters a two-stage filtration box, with a first-stage filter plate accuracy of 50 ppi and a second-stage filter plate accuracy of 60 ppi; the melt after two-stage filtration enters a tubular filter box, which uses 22 filter tubes, with the melt temperature inside the box at 722℃ and a liquid level difference of 23 mm between the inlet and outlet of the tubular filter box; the melt after being fully filtered by the tubular filter box enters the front box through the flow channel; Step S3, Casting: The melt temperature in the front box is 690℃, the hydrogen content in the front box is 0.091mL / (100g•Al), and an electromagnetic casting crystallizer is configured in the front box. The power frequency of the electromagnetic casting crystallizer is 94kHz, the magnetic induction intensity is 0.42T, and the excitation power is 240kW. The melt in the front box enters the casting nozzle through the aluminum supply port. The aluminum supply port of the casting nozzle is 45mm higher than the bottom of the front box. The melt flowing out of the casting nozzle is cast and cooled between two counter-rotating rolls to form a billet. The casting and rolling zone is 54mm, the billet thickness is 6.7mm, the casting and rolling speed is 840m / min, and the middle of the rolls is cooled by circulating water. The billet is coiled into a coil by a coiling device. Step S4, High-temperature recrystallization annealing: The cast-rolled coil obtained in step S3 is rolled into a steel strip and transferred to an annealing furnace. A temperature measuring hole with a diameter of 8 mm and a depth of 102 mm is drilled close to the core of the cast-rolled coil. A temperature measuring thermocouple is inserted into the temperature measuring hole. The cast-rolled coil is loaded into a box-type annealing furnace in batches of 4 coils per furnace for annealing. The annealing process is to hold the metal at 480℃ for 6 hours. The furnace gas temperature of the annealing furnace is 545℃. Step S5, Cold Rolling: After annealing, the cast-rolled coil is naturally cooled to 42°C and then transferred to a cold rolling mill for rolling. The rolling passes are 4.0mm, 2.4mm, 1.4mm, 0.85mm, 0.5mm, and 0.3mm respectively. The first five passes are rolled by a cold rolling mill, and the last pass is rolled by a cold intermediate mill. The roughness of the work rolls of the cold rolling mill is 0.44μm, and the mass percentage of alcohol, ester, and acid in the rolling oil is 4.74%, 1.56%, and 0.86%, with the balance being a mixed base oil. The roughness of the work rolls of the cold intermediate mill is 0.27μm, and the mass percentage of alcohol, ester, and acid in the rolling oil is 6.12%, 1.76%, and 1.21%, with the balance being a mixed base oil. The mixed base oil is composed of 70# light white oil and 80# light white oil mixed in a weight ratio of 1:1. Step S6, Longitudinal shearing: The cold-rolled coil obtained in step S5 is cooled to 41°C and then sheared on a slitting machine at a speed of 136 m / min. During the shearing process, the strip does not come into contact with the guide plate and no scratches are produced. Step S7, Foil Rolling: The cold-rolled coil after edge trimming is transferred to a foil rolling mill for rolling. The rolling passes are 0.17mm, 0.096mm, 0.054mm, 0.033mm, 0.02mm, 0.012mm, and 0.008mm respectively. The first five passes are rolled on an aluminum foil roughing mill, and the last two passes are rolled on an aluminum foil finishing mill. The mass percentage of alcohol in the aluminum foil roughing mill is 4.13%, the mass percentage of ester is 3.85%, the mass percentage of acid is 0.42%, and the balance is 80# light white oil. The rolling oil used in the aluminum foil roughing mill is filtered through a two-stage filter. The filter pore sizes are 20μm and 10μm, respectively; the rolling oil used in the aluminum foil finishing mill contains 0.75% alcohol, 5.96% ester, and 0.74% acid by mass, with the balance being a mixed base oil. The rolling oil used in the aluminum foil finishing mill is filtered through a three-stage filter with filter element pore sizes of 20μm, 10μm, and 3μm, respectively; the mixed base oil is composed of 70# light white oil and 80# light white oil mixed in a weight ratio of 1:1; the roughness of the work rolls in the aluminum foil roughing mill is 0.21μm, and the roughness of the work rolls in the aluminum foil finishing mill is 0.16μm; Step S8, Inspection and Packaging: After the finished product is rolled off the mill, the inspection results are as follows: there are no pinholes with a diameter exceeding 150μm, and 612 pinholes with a diameter less than 150μm are found in a single 36,000m roll of aluminum foil; the aluminum foil surface is free of roller marks, bulging, vibration marks, and color difference; the transverse tensile strength is 321MPa, the transverse yield strength is 302MPa, and the transverse elongation is 4.0%; the longitudinal tensile strength is 321MPa, the longitudinal yield strength is 302MPa, and the longitudinal elongation is 4.2%; the dyne value of the aluminum foil surface is 33; the oil content per square meter of aluminum foil is 7.23mg; the edge collapse is 1.9mm, and the thickness fluctuation is 2.1%; after passing the inspection, the product is packaged according to the packaging requirements.

[0029] Comparative Example 1 The difference between this comparative example and Example 1 is that ceramic aluminum seeds are not added in step S1.

[0030] The aluminum foil produced in this comparative example has a transverse tensile strength of 315 MPa, a transverse yield strength of 290 MPa, a transverse elongation of 4.1%, a longitudinal tensile strength of 309 MPa, a longitudinal yield strength of 285 MPa, and a longitudinal elongation of 3.3%.

[0031] Comparative Example 2 The difference between this comparative example and Example 1 is that: in step S2, aluminum-titanium-carbon grain refiner is not used, but aluminum-titanium-boron grain refiner is used entirely.

[0032] The aluminum foil produced in this comparative model is prone to white streaks and stripes on the surface, causing the entire roll of aluminum foil to be scrapped.

[0033] Comparative Example 3 The difference between this comparative example and Example 1 is that in step S7, neither the rolling oil used in the aluminum foil roughing mill nor the rolling oil used in the aluminum foil finishing mill is filtered.

[0034] The maximum pinhole diameter of the aluminum foil produced in this comparative example reached 452μm, and the number of pinholes with a diameter of less than 150μm in a single 36,000m roll of aluminum foil reached 1,562.

[0035] Comparative Example 4 The difference between this comparative example and Example 1 is that in step S7, the mass percentage of alcohol in the rolling oil used in the aluminum foil finishing mill is 0.75%, the mass percentage of ester is 5.96%, the mass percentage of acid is 0.74%, and the balance is 80# light white oil.

[0036] The finished aluminum foil produced in this comparative example has an oil content of 23mg per square meter.

[0037] Comparative Example 5 The difference between this comparative example and Example 1 is that in step S7, the mass percentage of alcohol in the rolling oil used in the aluminum foil finishing mill is 0.75%, the mass percentage of ester is 5.96%, the mass percentage of acid is 0.74%, and the balance is 70# light white oil.

[0038] The aluminum foil produced in this comparative example had severe oil mist during rolling. The oil mist condensed in the fume hood and dripped onto the surface of the aluminum foil, causing the entire roll of aluminum foil to be scrapped.

[0039] The aluminum foils obtained in Examples 1 and 2 all exhibit excellent comprehensive properties. Example 1 shows a tensile strength of 317-318 MPa, a yield strength of 291-292 MPa, and an elongation of 4.1%-4.3%, with minimal deviations in transverse and longitudinal properties, a low number of pinholes (587 / 36000m), low oil content (8.52mg oil per square meter of aluminum foil), and good control over edge collapse and thickness fluctuations. Example 2's properties are comparable to Example 1, further verifying the stability of the method of this invention. In contrast, Comparative Example 1 shows a significant decrease in longitudinal elongation to 3.3%, with increased anisotropy; Comparative Example 2 shows severe surface white streaks; Comparative Example 3 (without a filter) shows a dramatic increase in the number of pinholes to 1562, including large-sized pinholes; Comparative Example 4 shows an increase in oil content to 23mg per square meter of aluminum foil; and Comparative Example 5 shows severe oil mist, leading to the scrapping of the entire roll. The above comparative examples fully demonstrate the importance of the synergistic effect of key steps such as the addition of ceramic aluminum seed crystals, composite grain refiners, multi-stage filtration, and rolling oil formulation in this invention.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy, characterized in that, Includes the following steps: Step S1, Smelting: By mass percentage, 20%–30% of remelting aluminum ingots and 70%–80% of 8021 alloy cast-rolled coil scrap are melted. Ceramic aluminum seed crystals are added to each furnace of the smelting furnace, followed by aluminum-iron alloy, quick-dissolving silicon, manganese agent, copper agent, and titanium agent to adjust the alloy composition so that the final billet is 8006 aluminum alloy, with the mass percentage of each element satisfying Si 0.2%–0.3%, Fe 1.2%–1.4%, Cu 0.05%–0.07%, Mn 0.3%–0.5%, Mg≤0.02%, Zn≤0.05%, Ti0.01%–0.02%, and the balance being Al. After refining, the melt is poured into a holding furnace. Step S2, Online Melt Processing: At the inlet of the degassing box, add aluminum-titanium-carbon grain refiner and aluminum-titanium-boron grain refiner to the melt flowing out of the holding furnace, and then perform degassing, two-stage filtration and tubular filter box filtration. Step S3, Casting: The filtered melt enters the front box equipped with an electromagnetic casting crystallizer. The melt enters the casting nozzle through the aluminum supply port. The melt flowing out of the casting nozzle is cast and cooled between two counter-rotating rollers to form a billet. Step S4, High-temperature recrystallization annealing: The cast-rolled coil made after the billet is rolled up is annealed. The annealing process is 460-490℃ followed by holding at 4-6h. Step S5, Cold Rolling: The annealed cast-rolled coil is naturally cooled to below 45°C and rolled sequentially to thicknesses of 4.0mm, 2.4mm, 1.4mm, 0.85mm, 0.5mm, and 0.3mm. The first five passes are rolled by a cold rolling mill, and the last pass is rolled by a cold intermediate mill. The roughness of the work rolls of the cold rolling mill is 0.4-0.45μm, and the roughness of the work rolls of the cold intermediate mill is 0.23-0.28μm. Step S6, Longitudinal shearing: Cool the cold-rolled coil obtained after cold rolling to below 45°C, and shear the edges at a speed of ≤150m / min. The strip does not contact the guide plate during the shearing process. Step S7, Foil Rolling: The trimmed cold-rolled coil is rolled sequentially to thicknesses of 0.17mm, 0.096mm, 0.054mm, 0.033mm, 0.02mm, 0.012mm, and 0.008mm. The first five passes are rolled on an aluminum foil roughing mill, and the last two passes are rolled on an aluminum foil finishing mill. The roughness of the work rolls on the aluminum foil roughing mill is 0.18-0.22μm, and the roughness of the work rolls on the aluminum foil finishing mill is 0.13-0.17μm. The rolling oil used in the aluminum foil roughing mill contains 3%-5% alcohol, 3%-5% ester, and [amount missing]% acid. The rolling oil has a weight ratio of 0.2%-0.5%, with the remainder being 80# light white oil. This rolling oil is filtered through a two-stage filter with pore sizes of 20μm and 10μm, respectively. The rolling oil used in the aluminum foil finishing mill contains 0.5%-1% alcohol, 5%-7% ester, and 0.5%-0.8% acid by weight, with the remainder being mixed base oil. This rolling oil is filtered through a three-stage filter with pore sizes of 20μm, 10μm, and 3μm, respectively. The mixed base oil is a mixture of 70# light white oil and 80# light white oil in a 1:1 weight ratio. Step S8, Inspection and Packaging: After the finished product is rolled off the machine, it is inspected and packaged after passing the inspection.

2. The method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy according to claim 1, characterized in that, In step S1, the amount of ceramic aluminum seed crystal added is 50 kg per furnace, and the furnace is simmered for 20 minutes. The ceramic aluminum seed crystal is a naturally cast block with a width not exceeding 50 mm, a thickness not exceeding 20 mm, and a weight not exceeding 3 kg per block. In step S1, the mass percentage of iron in the aluminum-iron alloy is 3% to 4%.

3. The method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy according to claim 1, characterized in that, In step S1, after adding ceramic aluminum seed crystals and simmering the furnace for 20 minutes, the electromagnetic stirrer is turned on, and high-purity argon is used for a pre-refining process to achieve degassing, slag removal, and localized uniform stirring of the melt in the furnace. The melt in the furnace is then heated again using a natural gas torch to raise the temperature to 735-750℃. Then, aluminum-iron alloy, quick-dissolving silicon, manganese agent, copper agent, and titanium agent are added to the furnace to adjust the alloy composition. After the alloy composition is found to be qualified, argon and granular refining agent are used for refining. After refining, the electromagnetic stirrer is turned off and the melt is allowed to stand for more than 15 minutes. The slag on the surface of the melt is skimmed off, and the melt is allowed to stand for another 30 minutes before being poured into the holding furnace. Within 5 minutes after pouring the melt into the holding furnace, the granular refining agent is used again for refining. After refining, the slag on the surface of the melt is skimmed off, and the electric heater in the holding furnace is turned on to control the temperature of the melt in the holding furnace at 735-745℃.

4. The method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy according to claim 1, characterized in that, In step S2, the aluminum-titanium-carbon grain refiner and the aluminum-titanium-boron grain refiner are added in a 1:1 ratio, and the addition temperature is above 725°C.

5. The method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy according to claim 1, characterized in that, In step S2, the degassing process uses a rotor speed of 400±10 r / min and a high-purity argon flow rate of 50±5 L / min; the first-stage filter plate of the dual-stage filtration system has an accuracy of 50 ppi and the second-stage filter plate has an accuracy of 60 ppi; the tubular filter box uses 22 filter tubes, the melt temperature is 715-725℃, and the liquid level difference between the inlet and outlet of the tubular filter box is no more than 30 mm.

6. The method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy according to claim 1, characterized in that, In step S3, the melt temperature in the front chamber is 688–691°C, and the hydrogen content is 0.08–0.11 mL / (100g·Al); the power supply frequency of the electromagnetic casting crystallizer is 80–100 kHz, the magnetic induction intensity is 0.1–0.5 T, and the excitation power is 200–250 kW; the aluminum supply port of the casting nozzle is more than 40 mm higher than the bottom of the front chamber; the billet thickness is 6.5–7.0 mm, and the casting speed is 800–850 m / min.

7. The method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy according to claim 1, characterized in that, In step S5, the rolling oil used in the cold rolling mill contains, by mass percentage, 4%-6% alcohol, 1%-2% ester, 0.5%-1.0% acid, with the balance being a mixed base oil; the rolling oil used in the intermediate cold rolling mill contains, by mass percentage, 5%-7% alcohol, 1%-2% ester, 1.0%-1.5% acid, with the balance being a mixed base oil. The mixed base oil is composed of 70# light white oil and 80# light white oil mixed in a weight ratio of 1:

1.

8. The method for preparing high-strength, high-toughness, ultra-thin aluminum foil for power batteries by casting and rolling 8006 alloy according to claim 1, characterized in that, In step S8, the qualified finished aluminum foil must meet the following indicators: pinholes with a diameter exceeding 150μm are not allowed; the number of pinholes with a diameter less than 150μm in a single 36,000m roll of aluminum foil shall not exceed 650; the aluminum foil surface shall be free of roller marks, blistering, vibration marks, and color difference; tensile strength ≥310MPa, yield strength ≥280MPa, elongation ≥4.0%; deviation between transverse and longitudinal tensile strength ≤2MPa, deviation between transverse and longitudinal yield strength ≤2MPa, deviation between transverse and longitudinal elongation ≤0.5%; dyne value ≥33; oil content per square meter of aluminum foil ≤10mg; edge collapse ≤3mm; thickness fluctuation ≤2.5%.