Aluminum alloy plate for battery shell and preparation method of aluminum alloy plate

Abstract

The invention relates to the technical field of aluminum alloy, and discloses an aluminum alloy plate for a battery shell and a preparation method thereof, and the preparation method comprises the following steps: S1, sequentially putting electrolytic aluminum liquid, an aluminum ingot and an alloy additive into a smelting furnace; s2, adding an Al10Ti alloy when the molten aluminum is transferred into a heat preservation furnace from a smelting furnace; carrying out refining and primary degassing operation; a refiner needs to be added before entering the degassing box; continuously casting and rolling to obtain a thick blank; s3, carrying out cold rolling on the cast-rolled blank prepared in the step S2, and carrying out an annealing process; s4, after the annealing treatment is completed, performing cold rolling for three times; carrying out intermediate annealing treatment on the aluminum strip; and S5, after cold rolling, the aluminum strip is subjected to withdrawal and straightening, cleaning and longitudinal cutting, and a finished product is obtained. According to the technical scheme, the grain size of the aluminum alloy plate for the battery shell produced in a cast rolling mode is basically consistent with that of an aluminum alloy plate produced through a hot rolling process, meanwhile, the problems of low elongation, poor deep drawability and the like are solved, meanwhile, good structure uniformity and uniform second-phase compound distribution are ensured, and compared with hot rolling process production, the production efficiency is improved, and the production cost is reduced. And the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloys, and more specifically, to an aluminum alloy sheet for battery cases and a preparation method thereof. Background Art

[0002] In recent years, the global and Chinese new energy vehicle markets have both shown a continuous growth trend. New energy vehicles have many advantages compared to traditional fuel vehicles, which are mainly reflected in aspects such as environmental protection, energy conservation, economy, and technological innovation. In particular, the application of lightweight aluminum alloy materials further reduces the weight of the whole vehicle and improves the endurance. As the power source of new energy vehicles, the battery pack is one of the important components of new energy vehicles, and the battery case plays an important protective role for the battery pack and even the whole vehicle, which is the key to new energy vehicles. With the increase in battery pack capacity and the requirement for lifespan, higher requirements are also put forward for the performance of the battery case. Especially under the conditions of reducing the thickness of the battery case and increasing the volume, it is necessary to ensure indicators such as the mechanical properties, ear formation rate, and Erichsen value of the material. 3003 aluminum alloy is widely used in battery case products for new energy vehicles due to its strong corrosion resistance, excellent processing performance, and good welding performance.

[0003] Currently, the main method for supplying billets for battery case sheet and strip is hot rolling. However, the hot rolling process requires multiple processes such as melting and casting, surface milling, sawing, heat treatment, hot rolling, and cold rolling, resulting in disadvantages such as long time consumption and high cost. As a production method with small investment, high efficiency, and low cost, there are mainly the following problems when used to produce battery case sheet and strip: (1) The grain size of the battery case sheet produced by cold rolling the cast-rolled sheet is much larger than that of the battery case sheet product produced by hot rolling for blooming; (2) The elongation of the battery case sheet produced by using the cast-rolled sheet is low and the ear formation rate is too high, which cannot meet the requirements of the battery case sheet product; (3) The tissue uniformity of the cast-rolled sheet is poor, there are a large number of second-phase compounds, and Mn segregation is likely to occur.

[0004] For example, the invention patent CN 115247239A relates to an aluminum alloy strip for power battery cases and a production method thereof. This patent reduces the content and size of inclusions in the aluminum liquid by adopting reasonable composition design and adding a certain amount of rare earth as a modifying agent, and realizes the uniformity of grain size through two-step annealing and cold rolling. At the same time, an aluminum alloy for power battery cases with high strength, good deep drawing property, and low cost is obtained. However, this patent only relates to the production of O-state battery case finished products, and does not involve the H14-state power battery cases with a large consumption in GB / T 33824-2017 "Aluminum and Aluminum Alloy Sheets and Strips for New Energy Power Battery Cases and Covers". At the same time, this patent adds some rare earth elements, which will further increase the production cost.

[0005] For example, the invention patent CN111074110A provides a production method of aluminum and aluminum alloy strip for new energy power battery cases, including the preparation of aluminum alloy melt, continuous casting and rolling, homogenization annealing, cold rolling, and finished product annealing, etc. It can be used to produce products in O, H12, and H14 states, and the products have high strength and yield ratio. However, the patent still uses the hot rolling method for production, resulting in relatively high production costs.

[0006] For example, the invention patent CN114438372A discloses a rapid cast-rolled aluminum alloy strip for battery cases and its preparation method. The composition and mass percentage of this invention are as follows: Mn: 1.00 - 1.25%, Fe: 0.40 - 0.60%, Si: 0.20 - 0.40%, Cu: 0.05 - 0.1%, Ti: 0.05 - 0.10%, other impurities ≤ 0.05% individually, and the total impurity content ≤ 0.10%. At the same time, the patent stipulates that the composition satisfies the conditions of Fe / Si ≥ 1.80 and Fe + Mn < 1.85% according to the metal mass ratio. The strip production process of this invention includes processes such as melting and casting, cast rolling, cold rolling, homogenization annealing, online annealing, and finishing. However, the rolled finished products in this patent only focus on the tensile strength and earring rate, and do not mention the elongation after fracture and Erichsen value in GB / T 33824-2017 "Aluminum and Aluminum Alloy Sheets and Strips for New Energy Power Battery Cases and Covers". At the same time, only the metallographic diagram after homogenization is analyzed in the patent, but the grain size of the strip finished products is not concerned. Meanwhile, it does not provide direct comparison data with the traditional hot rolling method to prove the superiority of the new process. Although the tensile strength and earring rate are mentioned, there is not enough data provided to comprehensively evaluate the performance of the material. In this patent document, homogenization treatment and online annealing treatment are mentioned, and these heat treatment steps are crucial for improving the microstructure and macroscopic properties of the alloy. However, it does not elaborate on the specific effects of these heat treatment steps on the alloy microstructure, such as grain size, phase distribution, and the nature of the precipitated phases. In this patent document, it is emphasized to improve the overall uniformity of the strip through online continuous annealing treatment. However, no specific data or test results are provided to prove the consistency and uniformity of the products among different batches. In this patent document, it is mentioned to reduce production costs by simplifying the process and increasing the finished product rate. However, no detailed cost analysis or economic benefit comparison with the existing technology is provided to prove its market competitiveness.

[0007] Given that the process for preparing aluminum foil blanks by the hot rolling method is cumbersome and costly, while the cast rolling method has the advantages of simple process, low cost, and high production efficiency, the industry is committed to researching the replacement of the hot rolling method with the cast rolling method to produce aluminum-plastic film aluminum foil blanks. Nevertheless, the blanks prepared by the current cast rolling method still face several technical challenges:

[0008] First, the improper ratio of Fe+Mn elements fails to form a large number of dispersed second-phase particles during the casting and rolling process, affecting the grain refinement. In addition, due to the rapid cooling rate of the cast-rolled sheet, alloying elements are mainly solid-solved in the matrix, making the intermetallic compounds too fine to serve as effective recrystallization nucleation sites. This results in coarse grain structure after recrystallization, thereby affecting the surface quality and formability of the product.

[0009] Second, high temperature may cause overburning of the Al5TiB grain refiner, losing its nucleation ability, resulting in grain coarsening and affecting the plasticity and mechanical properties of the alloy.

[0010] Third, in the traditional rolling and heat treatment processes, there may be a lack of control over the grain size uniformity. Unreasonable rolling passes and reduction distribution, as well as inappropriate annealing treatment, lead to uneven grain fragmentation and elongation, affecting the overall properties of the material.

[0011] Fourth, during the heat treatment of traditional aluminum alloy sheets, there may be insufficient control over grain refinement and second-phase distribution caused by single-temperature annealing, as well as segregation problems of Mn elements. These problems result in insufficient strength and ductility of the material, too high earring rate during deep drawing forming, increasing production costs and reducing material utilization efficiency. Summary of the Invention

[0012] Technical problems to be solved by the present invention:

[0013] By adjusting the alloy composition, reasonably distributing the rolling passes and reduction per pass, and adopting the heat treatment processes of double-stage homogenization annealing and low-temperature intermediate annealing, to solve the problems of low elongation and poor deep drawability existing in the production by the casting and rolling method in the prior art.

[0014] The purpose of the present invention is to provide a method suitable for producing aluminum alloy sheets for battery cases by the casting and rolling method.

[0015] Technical solutions adopted by the present invention:

[0016] For the aluminum alloy sheet for battery case provided by the present invention, the analysis of the 1.2-mm aluminum alloy sheet for battery case shows that by adjusting the alloy composition, reasonably distributing the rolling passes and reduction per pass, and adopting the heat treatment processes of double-stage homogenization annealing and low-temperature intermediate annealing, the grain size of the aluminum alloy sheet for battery case produced by the casting and rolling method is basically the same as that produced by the hot rolling process. At the same time, problems such as low elongation and poor deep drawability are solved, and good tissue uniformity and uniform distribution of second-phase compounds are ensured. Compared with the production by the hot rolling process, the production efficiency is improved and the production cost is reduced.

[0017] First, the present invention provides a preparation method for an aluminum alloy sheet for battery case, comprising the following steps:

[0018] S1 Pour a certain proportion of electrolytic aluminum liquid, aluminum ingots, and various alloy additives into the melting furnace successively as required. Adjust the temperature to an appropriate level to ensure full melting and uniform mixing at high temperature. In addition, powder spraying and slag skimming treatments are also required to remove impurities and oxide films in the molten metal and to remove the floating slag to prevent the mixing of impurities;

[0019] S2 Transfer the aluminum liquid from the melting furnace to the holding furnace. Add Al10Ti master alloy during the transfer process and control the Ti content in the furnace. Refine and preliminarily degas the aluminum liquid in the holding furnace, and keep the temperature of the aluminum liquid within an appropriate range. Add Al5TiB grain refiner before entering the degassing box, and finally control the Ti content to 0.01 - 0.03%. Pass an inert gas into the degassing box and introduce it into the aluminum liquid through a specific rotor to form a large number of tiny bubbles. During the rising process of the bubbles, hydrogen and other impurities are adsorbed and carried to the liquid surface. The filter box is equipped with a filter plate, which has a microporous structure with different mesh numbers. The impurities in the aluminum liquid are removed through mechanical blocking and adsorption effects. The temperature of the filter box is 700 - 730 °C. One of the functions of the front box is to keep the aluminum liquid in a stable state. Next, the aluminum liquid is continuously and rapidly cast-rolled into cast-rolled billets through a rolling mill.

[0020] S3 Send the cast-rolled billet obtained in S2 to a cold rolling mill for cold rolling once, and then put it into a high-temperature annealing furnace. Adopt a high-temperature two-stage homogenization annealing process to make the temperature of the billet in the annealing furnace reach the first-stage temperature of 420 - 460 °C and keep it warm for 12 - 16 h; then continue to raise the temperature of the annealing furnace to make the temperature in the annealing furnace reach the second-stage temperature of 560 - 580 °C and keep it warm for 10 - 12 h;

[0021] S4 After the two-stage homogenization annealing treatment, perform three more cold rollings on the cold rolling mill. Clean the guide rollers during the cold rolling process and use rolling oil to prevent indentation and adhesion damage. Subsequently, the aluminum strip undergoes intermediate annealing treatment;

[0022] S5 After the aluminum strip undergoes intermediate annealing treatment and is cold rolled to 1.2 mm, it undergoes tension leveling, cleaning, slitting, and surface inspection to meet the quality standards, and then is slit according to specifications. The qualified products are stored in the warehouse for standby.

[0023] According to some preferred embodiments, in S2, the titanium content is up to 0.01 - 0.03%.

[0024] According to some preferred embodiments, in S2, the grain refiner is Al5TiB grain refiner, the addition amount is 1.0 - 2.5 kg / t of molten aluminum, the addition temperature is 700 - 730 °C; the temperature of the molten aluminum in the degassing box is 700 - 730 °C. In the casting and rolling process, precise temperature control is a key factor to ensure product quality. Specifically, the temperature needs to be controlled within a specific range to ensure the metal fluidity and tissue uniformity during the casting and rolling process. Specifically in this technical solution, if the temperature is less than 700 °C, the minimum temperature requirement for casting cannot be met, which may lead to defects such as segregation and streaks during the casting and rolling process. These defects will seriously affect the microstructure and macroscopic properties of the material. If the temperature is greater than 730 °C, it will not only cause waste of energy but also may cause overburning. Overburning means that the metal stays at a high temperature for too long, resulting in coarsening of the grains, which will reduce the plasticity and toughness of the material and affect the further processing performance of the material. In addition, overburning may also lead to non-compliance of the grain size. When the temperature is around 715 °C, the metal fluidity and tissue uniformity during the casting and rolling process can be ensured, preventing the occurrence of segregation and overburning. This requires strict temperature monitoring and adjustment measures to be implemented in the casting and rolling process to ensure the consistency and reliability of product quality and performance.

[0025] According to some preferred embodiments, in S2, the thickness of the casting and rolling blank is 6.0 - 9.0 mm.

[0026] According to some preferred embodiments, cold rolling is carried out to 5.0 mm for the first time.

[0027] According to some preferred embodiments, in S3, the process parameters of homogenization annealing are: (1) 420 - 460 °C, 12 - 16 h; (2) 560 - 580 °C, 10 - 12 h. Specifically, in this technical solution, during homogenization annealing, a two-stage homogenization annealing treatment is adopted. This process can make the distribution of the second phase in the surface layer and the core of the aluminum alloy sheet more uniform. Due to the difference in the amount of deformation between the surface layer and the core, the two-stage homogenization annealing treatment can effectively regulate this difference and promote the uniform precipitation of the second phase particles in the sheet. At the same time, it can also better control the size and quantity of the second phase particles. In the range of 420 - 460 °C, heterogeneous nucleation dominates, which helps to form finer second phase particles; while in the stage of 560 - 580 °C, it can promote the growth and Ostwald ripening of the second phase particles, thereby optimizing the size distribution of the particles. In addition, the two-stage homogenization annealing treatment can also reduce the tissue inhomogeneity between the surface layer and the core caused by different deformation amounts, thereby improving the overall performance of the sheet.

[0028] According to some preferred embodiments, in S4, the pass distribution is 3.6 mm, 2.0 mm, and 1.6 mm. The design of the pass distribution needs to comprehensively consider the performance parameters of the rolling mill equipment, the theoretically processing efficiency, the subsequent process requirements, and the overall production efficiency. In this technical solution, the advantages of the pass distribution of 3.6 mm, 2.0 mm, and 1.6 mm are that, on the premise of ensuring that the load-bearing capacity of the equipment is not damaged, this pass distribution and the reduction per pass can effectively promote the fragmentation of grains and their elongation along the rolling direction during cold rolling. This process is accompanied by significant lattice distortion, thus laying a foundation for subsequent microstructure refinement and property improvement.

[0029] According to some preferred embodiments, in S4, the process parameters of the intermediate annealing are: 420 - 460 °C / 4 h. In the temperature range of 420 - 460 °C, the atomic activity of the Mn element increases, which is beneficial to its precipitation from the aluminum matrix to form second-phase particles. These second-phase particles can serve as the cores for secondary recrystallization of grains, promoting grain refinement. By controlling this temperature range, the solid solution and precipitation behavior of the Mn element can be regulated, optimizing the microstructure of the material, thereby improving the comprehensive properties of the material, such as strength, toughness, corrosion resistance, and workability, etc.

[0030] Second, the present invention provides an aluminum alloy sheet for battery cases obtained by the preparation method mentioned above.

[0031] According to some preferred embodiments, by weight percentage, the components are: Si 0.1 - 0.4%, Fe 0.3 - 0.5%, Mn 0.8 - 1.2%, Cu 0.05 - 0.15%, Zn ≤ 0.05%, Ti 0.01 - 0.03%, and the balance is Al and inevitable impurities.

[0032] The beneficial effects achieved by the present invention are as follows:

[0033] First, design a new alloy by adjusting the contents of Si, Fe, Mn, and Cu elements. By increasing the content of the Mn element to 0.8 - 1.2%, the area fraction of the primary phase is increased, achieving the purpose of refining the grain size. By increasing the ratio of Fe + Mn elements to 1.1 - 1.7%, a large number of dispersed second-phase particles are ensured to form during the casting and rolling process, serving as recrystallization nucleation sites (PSN particles), achieving the purpose of refining the grains.

[0034] Second, by adding Al10Ti master alloy into the melting furnace, the Ti content in the furnace is 0.005 - 0.01%, and adding Al5TiB grain refiner before entering the degassing box. The addition amount of the grain refiner is 1.0 - 2.5 kg / t of aluminum melt, so as to reduce the grain size. Adding Al5TiB at this stage can avoid the overburn phenomenon caused by high temperature compared with adding it in the melting furnace, thus ensuring the effectiveness of the grain refiner. In the melting furnace, due to the high temperature, after adding Al5TiB, it may lose its nucleation ability due to overburn, resulting in grain coarsening, and may also lead to a decrease in the plasticity and mechanical properties of the alloy. The temperature before entering the degassing box is relatively appropriate. The Al5TiB grain refiner releases TiB2 and Al3Ti particles in the aluminum melt. TiB2 exists stably in the aluminum melt due to its high melting point and acts as a heterogeneous nucleation site. Among them, Al3Ti particles dissolve during the solidification process of the aluminum melt, releasing free Ti atoms. These Ti atoms form compositional supercooling on the surface of TiB2, promoting the nucleation activity of the particles. The stable 2D-compound layer formed on the surface of TiB2 is the key to ensuring that these particles can effectively act as heterogeneous nucleation sites. After adding the Al5TiB grain refiner into the aluminum melt, the TiB2 particles and Al3Ti particles act together. The dissolution of Al3Ti particles provides excess Ti atoms, which form a concentration gradient on the surface of TiB2 particles, promoting the regeneration of TiAl3, and finally promoting the nucleation of α-Al through the peritectic reaction (L + TiAl3 → α-Al), thus effectively refining the grains. Refining the grains is of great significance for improving the mechanical properties and corrosion resistance of the alloy, because fine grains can provide more grain boundaries, thus hindering the propagation of cracks and improving the strength of the material.

[0035] Third, by reasonably allocating the rolling passes and the reduction per pass, the grains are broken and elongated during the cold rolling process, and the crystal lattice is distorted. At the same time, homogenizing annealing and intermediate annealing treatments are carried out under the conditions of 5.0 mm and 1.6 mm thickness respectively to achieve recovery and recrystallization under heat treatment conditions and improve the uniformity of the grain size.

[0036] Fourth, by combining the double-stage homogenization annealing process with the low-temperature intermediate annealing process, the double-stage homogenization annealing process is 420 - 460 °C / 12 - 16 h + 560 - 580 °C / 10 - 12 h, and the intermediate annealing process is 420 - 460 °C / 4 h. After the double-stage homogenization annealing treatment, the supersaturated solid solubility of the sheet is reduced, and a large number of coarse second-phase compounds are formed, effectively reducing the precipitation of dispersed phases during the subsequent intermediate annealing process, which is beneficial to particle-induced recrystallization nucleation (PSN mechanism). Combining with the intermediate annealing process of 420 - 460 °C / 4 h, the problem of Mn element segregation is solved, and at the same time, the grain size is reduced, and the problems of low elongation and high earing rate are solved. The existing heat treatment of aluminum alloys usually involves a single-temperature annealing process, lacking precise control over grain refinement and second-phase distribution. Traditional single-stage homogenization annealing methods may not be able to effectively reduce the grain size and form coarse second-phase compounds, which may lead to insufficient strength and ductility of the material. During traditional casting and rolling and annealing processes, the segregation of Mn element is a common problem, which will lead to non-uniformity of material properties and affect the plasticity and toughness of the material. When traditional aluminum alloy materials are used in deep drawing forming, the problem of high earing rate may occur, which will increase production costs and reduce the utilization efficiency of the material.

[0037] During the double-stage extreme homogenization annealing treatment process, at the low-temperature stage (420 - 460 °C), the precipitation phase is more likely to nucleate and grow on the existing second phase, which helps to obtain fine and uniformly distributed second-phase particles. The purpose of the low-temperature stage is to slow down the diffusion rate of Mn element and reduce the growth of second-phase particles, so as to maintain the fineness and uniformity of particle size.

[0038] The main function of the high-temperature stage (560 - 580 °C) is to promote the diffusion of Mn element and the coarsening of second-phase particles. High temperature enables solute atoms to enrich at the interface of primary phases, resulting in the growth of primary phases. At the same time, the Ostwald ripening effect will also cause the growth of large-sized stable eutectic phases, and the dissolution of small-sized or unstable phases will also promote the continuous growth of large-sized second phases. This stage is mainly to promote the nucleation and growth of second phases and adjust the solid solubility of Mn element.

[0039] Through this double-stage homogenization annealing treatment process with low temperature followed by high temperature, the quantity, size of second phases on the surface layer and core of aluminum alloy sheets and the content of dissolved Mn element can be regulated, ultimately controlling the quality of aluminum alloy sheets, obtaining fine and uniform grain structures, and improving the mechanical properties and processing properties of materials. Description of the Drawings

[0040] Figure 1 SEM image of the aluminum alloy sheet prepared in Example 3.

[0041] Figure 2SEM image of the aluminum alloy sheet prepared in Comparative Example 1.

[0042] Figure 3 SEM image of the aluminum alloy sheet prepared in Comparative Example 11.

[0043] Figure 4 Metallographic image of the aluminum alloy sheet prepared in Example 1.

[0044] Figure 5 Metallographic image of the aluminum alloy sheet prepared in Comparative Example 13. Detailed implementation manners

[0045] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained by purchasing in the market.

[0046] The process route of the present invention is as follows:

[0047] Melting (powder spraying, slag skimming) → converter → heat preservation (refining, degassing) → addition of Al5TiB grain refiner → degassing → filtration → forehearth → casting and rolling → cold rolling I → two-stage homogenization annealing treatment → cold rolling II → cold rolling III → cold rolling IV → intermediate annealing treatment → cold rolling V → trimming → inspection.

[0048] Example 1

[0049] A preparation method of an aluminum alloy sheet for a battery case, comprising the following steps:

[0050] S1 The components and mass percentages of the aluminum alloy sheet are as follows: Si 0.1 - 0.4%, Fe 0.3 - 0.5%, Mn 0.8 - 1.2%, Cu 0.05 - 0.15%, Zn ≤ 0.05%, Ti 0.01 - 0.03%, and the balance is Al and inevitable impurities. Appropriate electrolytic aluminum liquid, aluminum ingots and various alloy additives are successively put into a melting furnace for melting to reach the specified mass percentage, and powder spraying and slag skimming treatments are carried out.

[0051] S2. Transfer the molten aluminum from the melting furnace to the holding furnace. During the transfer process, add the Al10Ti master alloy and control the Ti content in the furnace. The Ti content is 0.005 - 0.01%. Refine and initially degas the molten aluminum in the holding furnace, and keep the temperature of the molten aluminum within the range of 710 - 740 °C. Add the Al5TiB grain refiner before entering the degassing box, with the addition temperature of 700 - 730 °C, and finally control the Ti content at 0.01 - 0.03%. Pass inert gas into the degassing box and introduce it into the molten aluminum through a specific rotor to form a large number of tiny bubbles. During the rising process of the bubbles, hydrogen and other impurities are adsorbed and carried to float out of the liquid surface together. The temperature of the degassing box is 700 - 730 °C. The filter box is equipped with filter plates, and the filter plates have microporous structures with different mesh numbers. Remove the impurities in the molten aluminum through mechanical blocking and adsorption. The temperature of the filter box is 700 - 730 °C. One of the functions of the front box is to keep the molten aluminum in a stable state. Next, the molten aluminum is continuously and rapidly cast-rolled into a cast-rolled billet with a thickness of 6.0 - 9.0 mm through a rolling mill.

[0052] S3. Feed the cast-rolled billet into a cold rolling mill and cold roll it to 5.0 mm. Then enter the annealing furnace and adopt a high-temperature double-stage homogenization annealing process. The temperature of the billet after the first cold rolling in the annealing furnace reaches the first-stage temperature of 420 - 460 °C and is kept warm for 12 - 16 h. Then, continue to raise the temperature of the annealing furnace so that the temperature in the high-temperature annealing furnace reaches the second-stage temperature of 560 - 580 °C and is kept warm for 10 - 12 h.

[0053] S4. Cold roll on the cold rolling mill with the pass distribution of 3.6 mm, 2.0 mm, and 1.6 mm. During the cold rolling process, it is necessary to clean the guide rollers and use rolling oil for lubrication and cooling to prevent surface defects such as indentations or adhesion damage on the aluminum coil. Next, feed it into the annealing furnace for intermediate annealing treatment. The annealing temperature is 420 - 460 °C and the time is 4 h.

[0054] S5. After cold rolling to 1.2 mm on the cold rolling mill, the aluminum coil needs to go through tension leveling, cleaning, and slitting. During tension leveling, it is necessary to thoroughly clean the guide rollers to avoid surface defects. It is also necessary to adjust the elongation rate to avoid shape problems. During cleaning, control the water temperature, water pressure, and speed to prevent oil stains. Check for surface defects to ensure that the aluminum strip after slitting meets the surface quality standard and is slit into the required width. After passing the inspection, store it in the warehouse for subsequent processing.

[0055] In the above, the addition amounts of various elements in Examples 1 - 6 are shown in Table 1, and the operating process parameters are shown in Tables 2 - 3.

[0056] Comparative Examples 1 - 14

[0057] The differences between Comparative Examples 1 - 14 and the examples lie in that the addition amounts of various elements are different, as shown in Table 1 specifically, and the grain refinement process, rolling process, and heat treatment process parameters are different, as shown in Tables 2 - 3 specifically.

[0058] Table 1 Chemical Composition Table of Examples and Comparative Examples (Example - E, Comparative Example - D)

[0059] Number Si (wt%) Fe (wt%) Mn (wt%) Cu (wt%) Zn (wt%) Ti (wt%) Range value 0.1～0.4 0.3-0.5 0.8～1.2 0.05-0.15 ≤0.05 0.01～0.03 E1 0.1 0.3 0.8 0.05 0.03 0.02 E2 0.15 0.4 1 0.05 0.03 0.03 E3 0.2 0.5 1.2 0.10 0.03 0.03 E4 0.3 0.4 1 0.05 0.03 0.03 E5 0.3 0.5 1.2 0.15 0.03 0.03 E6 0.4 0.5 1.2 0.15 0.03 0.03 D1 0.05 0.4 0.9 0.05 0.03 0.02 D2 0.2 0.1 0.8 0.05 0.03 0.03 D3 0.3 0.4 0.6 0.15 0.03 0.02 D4 0.3 0.5 1 0.3 0.03 0.02 D5 0.3 0.7 1 0.15 0.03 0.01 D6 0.05 0.7 0.9 0.05 0.03 0.02 D7 0.5 0.2 1 0.05 0.03 0.02 D8 0.2 0.3 1.3 0.05 0.03 0.02 D9 0.05 0.3 1.3 0.05 0.03 0.02 D10 0.5 0.5 0.7 0.10 0.03 0.03 D11 0.05 0.4 1.0 0.3 0.03 0.03 D12 0.3 0.2 1.3 0.15 0.03 0.03 D13 0.4 0.7 0.7 0.15 0.03 0.03 D14 0.2 0.2 0.8 0.3 0.03 0.03

[0060]

[0061]

[0062] In Table 3, the homogenization annealing process is referred to as the homogenization annealing process, and the parameters of homogenization annealing processes 1 - 6 are shown in Table 4; the intermediate annealing process is referred to as the intermediate annealing process, and the intermediate annealing process is shown in Table 4.

[0063] Table 4 Heat Treatment Process Parameter Table of Examples and Comparative Examples

[0064] Number Heat treatment process Uniform annealing process 1 420°C / 12h + 560°C / 12h Uniform annealing process 2 450°C / 14h + 560°C / 10h Uniform annealing process 3 460°C / 12h + 570°C / 10h Uniform annealing process 4 460°C / 16h + 580°C / 12h Uniform annealing process 5 560℃ / 12h Uniform annealing process 6 580℃ / 12h Intermediate annealing process 1 420℃ / 4h Intermediate annealing process 2 460℃ / 4h Intermediate annealing process 3 380℃ / 5h Intermediate annealing process 4 500℃ / 5h

[0065] Test Example

[0066] Taking the aluminum alloy sheets obtained from Examples 1 - 6 and Comparative Examples 1 - 14 as samples, tests were carried out.

[0067] Figure 1 SEM image of the aluminum alloy sheet prepared for Example 3.

[0068] Figure 2 SEM image of the aluminum alloy sheet prepared for Comparative Example 1.

[0069] Figure 3 SEM image of the aluminum alloy sheet prepared for Comparative Example 11.

[0070] Figure 4 Metallographic image of the aluminum alloy sheet prepared for Example 1.

[0071] Figure 5 Metallographic image of the aluminum alloy sheet prepared for Comparative Example 13.

[0072] The standard referred to for the determination of tensile strength is GB / T 3880.1 - 2023 "Aluminum and Aluminum Alloy Sheets and Strips for General Industrial Use - Part 1: General Requirements"; the standard referred to for the determination of elongation is GB / T 16865 - 2023 "Specimens and Methods for Tensile Testing of Wrought Aluminum, Magnesium and Their Alloys"; the standard referred to for the determination of earing rate is GB / T 5125 - 2008 "Test Method for Drawing Cups of Non - Ferrous Metals".

[0073] The test results of performance parameters are shown in Table 5.

[0074] Table 5 Performance Test Result Table

[0075] Number Tensile strength / Mpa Elongation / % Earing rate % E1 153 9.8 4.6 E2 153.7 9.7 4.67 E3 154 9.6 4.73 E4 155 9.5 4.8 E5 155.4 9.3 4.6 E6 156 9.2 4.5 D1 158 7.8 4.2 D2 152 9.4 4.8 D3 140 10.2 5.1 D4 153 8.8 5.3 D5 156 7.3 4.6 D6 152 7.1 4.5 D7 154 7.2 4.4 D8 155 7.4 4.3 D9 153 7.3 4.25 D10 156 7.1 4.2 D11 158 7.0 4.1 D12 157 6.9 4 D13 160 6.8 3.9 D14 140 5.6 4.7

[0076] It can be seen from the measurement results in Table 1 that the anisotropy difference of the aluminum alloy strip prepared in this embodiment is small. For example, in Example 1, the strip has a tensile strength of 153 MPa, an earing rate of 4.6%, and an elongation of 9.8%.

[0077] The above examples prove that by precisely controlling the contents of Si, Fe, Mn and Cu, the ratio of Fe+Mn elements is increased to 1.7%, which successfully promotes the generation of second phase compounds with a size greater than 2 μm. Figure 1 ) shows that the second phase compounds are well distributed evenly, and the number of second phase compounds with sizes exceeding 2 μm is relatively large. Figure 2 ) observed that the size of the second phase compounds was larger, but the number was relatively small, and the number of nucleation cores during recrystallization was relatively small. Figure 3 ) in the microstructure, although the number of second phase particles is relatively abundant, the size of most second phase compounds is less than 1um, so it is difficult for them to become recrystallization nucleation points (PSN points) and cannot serve as effective nucleation cores to promote grain refinement. Figure 4 ), a large number of second phase compounds with a size greater than 2 μm successfully formed nucleation cores, which promoted grain refinement. In addition, by implementing a two-stage homogenization annealing treatment, a significant reduction in grain size was further achieved. In D13 ( Figure 5 ), due to the single-stage heat treatment process, the formation of a large number of second phase compounds with a size exceeding 2um was not effectively promoted. This resulted in a lack of sufficient nucleation cores, and thus the grain size could not be refined.

Claims

1. A method for preparing an aluminum alloy sheet for a battery shell, characterized in that: The steps include: S1 puts a certain proportion of electrolytic aluminum liquid, aluminum ingots and various alloy additives into the smelting furnace in turn; When the S2 aluminum liquid is transferred from the smelting furnace to the holding furnace, Al10Ti master alloy is added to control the titanium content; the aluminum liquid in the holding furnace is kept at an appropriate temperature for refining and initial degassing operations; before entering the degassing box, a refiner is added to adjust the titanium content to 0.01-0.03%; after the aluminum liquid in the front box is stable, continuous casting and rolling are performed to obtain thick billets; S3 sends the cast-rolled billet obtained in S2 to a cold rolling mill for cold rolling once, and then puts it into a high-temperature annealing furnace, using a two-stage homogenization annealing process; After the S4 double-stage homogenization annealing treatment is completed, the aluminum strip is cold-rolled three times on the cold rolling mill; then, the aluminum strip undergoes intermediate annealing treatment; After intermediate annealing, the aluminum strip of S5 is cold rolled to 1.2 mm, straightened, cleaned, and slit to obtain the finished product.

2. The method for preparing the aluminum alloy sheet for battery shell according to claim 1, characterized in that: In S2, the titanium content is 0.01-0.03%.

3. The method for preparing the aluminum alloy sheet for battery shell according to claim 1, characterized in that: In S2, the refiner is Al5TiB refiner, the addition amount is 1.0-2.5 kg / t aluminum liquid, the addition temperature is 700-730°C; the aluminum liquid temperature in the degassing box is 700-730°C.

4. The method for preparing an aluminum alloy sheet for a battery shell according to claim 1, characterized in that: In S2, the thickness of the cast billet is 6.0-9.0 mm.

5. The method for preparing the aluminum alloy sheet for battery shell according to claim 1, characterized in that: In S3, cold rolling is performed once to 5.0 mm.

6. The method for preparing the aluminum alloy sheet for battery shell according to any one of claims 1 to 5, characterized in that: In S3, the process parameters of homogenization annealing are: (1) 420-460°C, 12-16h; (2) 560-580°C, 10-12h.

7. The method for preparing an aluminum alloy sheet for a battery case according to any one of claims 1 to 5, characterized in that: In S4, the passes are 3.6mm, 2.0mm, and 1.6mm.

8. The method for preparing the aluminum alloy sheet for battery shell according to any one of claims 1 to 5, characterized in that: In S4, the process parameters of the intermediate annealing are: 420-460°C / 4h.

9. An aluminum alloy plate for battery shell obtained by the preparation method according to any one of claims 1 to 8.

10. The aluminum alloy plate material for battery case according to claim 9, characterized in that: The component elements are calculated by weight percentage: Si 0.1-0.4%, Fe 0.3-0.5%, Mn 0.8-1.2%, Cu0.05-0.15%, Zn≤0.05%, Ti0.01-0.03%, and the balance is Al and inevitable impurities.

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