A new energy automobile power battery shell uses small processing rate high crystal grain level aluminum alloy strip and its preparation method

Abstract

The application discloses a new energy automobile power battery shell small processing rate high grain level aluminum alloy strip and a preparation method thereof, and relates to the aluminum alloy processing technical field. The preparation process flow is: smelting and casting, ingot treatment, homogenization heat treatment, hot continuous rolling, cold rolling and annealing and finished product treatment; wherein, the final rolling temperature of the hot continuous rolling is less than or equal to 280 DEG C; the total processing rate of the cold rolling is less than or equal to 65%, the cold rolling pass is 2 times, and the processing rate of the first pass cold rolling is 45-50%. The application realizes the preparation of the aluminum alloy strip with high grain level (G is greater than or equal to 4.5), tensile strength of 145-156 MPa, earing rate of 2.3-3.0%, excellent deep drawing performance, good surface quality and no color difference under the premise of the great reduction of the processing rate through the synergistic optimization of the reduction of the hot rolling final rolling temperature, the reduction of the cold rolling pass and the reduction of the cold rolling processing rate, meets the harsh requirements of manufacturing the power battery shell, improves the production efficiency and reduces the cost.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy processing technology, and in particular to a high-grain-level aluminum alloy strip with low processing rate for use in power battery casings of new energy vehicles and its preparation method. Background Technology

[0002] Developing new energy vehicles is an important strategy for addressing climate change and promoting green development. As a core component of new energy vehicles, the casing material of the power battery needs to be lightweight, highly safe, and possess excellent formability and weldability. Aluminum alloys, due to their low density, corrosion resistance, ease of processing and forming, and good electrical and thermal conductivity, have become an ideal material for power battery casings.

[0003] Currently, power battery casings mainly use 3-series aluminum alloys such as 3003. To meet the stringent requirements of large deformation and numerous passes in the stamping process of battery casings, the material must possess excellent deep-drawing performance, one of the indicators being a high grain size index (G value). Traditional production processes, in order to obtain a high grain size (requiring G≥4), generally employ a large total cold rolling rate (≥75%) and multiple cold rolling passes (usually 3 passes). This "high processing rate, multiple passes" model has significant drawbacks: First, it has high energy consumption, as the numerous rolling passes directly lead to high electricity consumption; second, the production process is long and inefficient, and multiple rolling passes easily lead to an increase in aluminum powder on the strip surface, often requiring additional cleaning processes, which not only increases water and chemical consumption and environmental pressure but may also introduce surface defects.

[0004] While existing technologies employ methods to improve performance through composition optimization and complex heat treatment—such as adjusting the Mn / Fe ratio and controlling the size and distribution of second-phase compounds—or using a casting-rolling process combined with multi-step annealing and cold rolling to save costs, none of these fundamentally address the reliance on high cold rolling rates. Other technologies balance texture by increasing hot rolling rates, controlling the final rolling temperature (typically 330-350℃), and using annealing processes; however, the high final rolling temperature fails to fully utilize the microstructure control regulated by hot rolling to create conditions for subsequent low-deformation processing. Therefore, developing a new process that can significantly reduce cold rolling rates, simplify production processes, and achieve energy savings while ensuring or even improving the deep-drawing performance of materials has become a pressing technical challenge in this field.

[0005] In recent years, the research and development of aluminum alloy strips for power battery casings of new energy vehicles has mainly focused on composition optimization, process innovation, and performance improvement, forming the following mainstream technical routes: The traditional process optimization route based on hot rolling is currently the most mature and widely used technical route. It produces high-performance products through semi-continuous casting, two-stage homogenization heat treatment, hot continuous rolling (final rolling temperature 330-350℃), and multi-pass cold rolling. For example, patent CN114653904A discloses an aluminum alloy preparation method that, through precise composition control (Si 0.17-0.28%, Fe 0.45-0.58%, Mn 1.05-1.25%), two-stage heat treatment (600-610℃ and 530-540℃), and a cold rolling process including intermediate cleaning and complete recrystallization annealing, ultimately obtains excellent products with tensile strength of 145-156MPa and earing rate of 2.3-3.0%. Patent CN201910825885 also employs a similar process of hot rolling (final rolling temperature 320-360℃) combined with cold rolling and intermediate annealing, with the final cold rolling rate controlled at 20-30% to achieve the target performance. The advantage of this route is stable process and reliable performance, but it generally suffers from drawbacks such as long process and high energy consumption.

[0006] Cost reduction and efficiency improvement based on the casting and rolling process: To overcome the problems of long cycle and high cost of hot rolling, some technologies have shifted to the development of casting and rolling methods. The casting and rolling process combines casting and hot rolling in one step, which can significantly shorten the process and reduce costs. However, the strip produced by casting and rolling has challenges such as high inclusion content, uneven grain size, and poor deep-drawing performance. To address these challenges, related patents have optimized the composition design, such as adding rare earth elements as modifiers and reconstructing the annealing-cold rolling process. For example, moving the homogenization annealing to after the initial cold rolling and using two-step annealing and cold rolling can improve the uniformity of microstructure and performance. For instance, patent CN121061097A adopts a casting and rolling path, controlling the second-phase compound by adjusting the Mn / Fe ratio (1.2~2.0) and the casting and rolling process, aiming to achieve uniform grain size and meet performance standards. The core innovation of this route lies in the innovation of the production process, but the performance, especially high consistency, still lags behind the traditional hot rolling method, and the technical control is more difficult.

[0007] Special alloy routes based on extreme process and composition design: A few patents explore achieving high strength and high corrosion resistance through extremely complex compositional designs, such as adding multiple rare earth elements, using special proportions, or extreme heat treatment processes, such as cryogenic treatment and multi-stage solution aging. For example, some patents add rare earth elements such as erbium and gadolinium to alloys, combined with complex cooling solution aging treatments, including cryogenic treatment and oil baths, aiming to refine grains, reduce stress, and improve performance. These technologies are typically complex and costly, focusing more on solving specific extreme performance requirements rather than large-scale, low-cost manufacturing for the mainstream market of power battery casings.

[0008] Microstructure control based on rolling process innovation: Some patents innovate from the rolling process itself to directly regulate the microstructure. For example, patent CN114226459A proposes a "segmented rolling" strategy in the hot roughing stage: the first segment uses high speed and large reduction rate (>30%) to fully break down the grains; the second segment uses extremely low speed rolling to provide sufficient time for dynamic recrystallization, thereby achieving fine grain strengthening during the hot rolling stage and improving the material's formability and strength. This approach directly controls recrystallization behavior during deformation through the precise design of rolling parameters, representing a deep innovation at the process mechanism level.

[0009] Currently, power battery casings mainly use 3-series aluminum alloys such as 3003. To meet the stringent requirements of large deformation and numerous passes in the stamping process of battery casings, the material must possess excellent deep-drawing performance, one of the indicators being a high grain size index (G value). Traditional production processes, in order to obtain a high grain size (requiring G≥4), generally employ a large total cold rolling rate (≥75%) and multiple cold rolling passes (usually 3 passes). This "high processing rate, multiple passes" model has significant drawbacks: First, it has high energy consumption, as the numerous rolling passes directly lead to high electricity consumption; second, the production process is long and inefficient, and multiple rolling passes easily lead to an increase in aluminum powder on the strip surface, often requiring additional cleaning processes, which not only increases water and chemical consumption and environmental pressure but may also introduce surface defects. Summary of the Invention

[0010] To address the above shortcomings, this invention provides a high-grain-level aluminum alloy strip with low processing ratio for new energy vehicle power battery casings and its preparation method, overcoming the defects of high energy consumption, long process, and high cost in existing production processes for aluminum alloy strips used in power battery casings. The specific technical solution is as follows: A method for preparing high-grain-level aluminum alloy strip with low processing rate for power battery casing of new energy vehicles, the process flow includes: raw material melting and casting, ingot treatment, homogenization heat treatment, hot rolling, cold rolling and annealing and finished product treatment, wherein the hot rolling is to perform hot rolling on the heat-treated ingot to obtain a hot-rolled billet with a thickness of 2.8-5.0mm, and the final rolling temperature of the hot rolling is ≤280℃; The cold rolling and annealing process involves two cold rolling passes on the hot-rolled billet, with a total processing rate of ≤65%. The first cold rolling pass has a processing rate of 45-50%, rolling the billet to an intermediate thickness. Subsequently, the intermediate billet is cleaned and fully recrystallized and annealed. Finally, the second cold rolling pass is performed to achieve a target thickness of 1.0-2.0 mm.

[0011] Furthermore, the raw material smelting and casting are designed according to the composition of 3003 alloy, and after smelting, refining, online degassing and slag removal, ingots are prepared by a semi-continuous casting method.

[0012] Furthermore, the ingot processing involves sawing and milling the ingot to remove surface defects.

[0013] Furthermore, the homogenization heat treatment is performed on the milled ingot to homogenize it.

[0014] Furthermore, the finished product processing involves longitudinally slitting the cold-rolled aluminum coil to obtain aluminum alloy strips of the required width.

[0015] The present invention also provides an aluminum alloy strip prepared by the above preparation method.

[0016] Furthermore, the aluminum alloy strip has a grain size index G≥4.5, a tensile strength of 145-156MPa, a low ear-making rate of 2.3-3.0%, excellent deep-drawing performance, good surface quality, and no color difference, meeting the stringent requirements for manufacturing power battery casings.

[0017] The present invention also provides applications of the above-mentioned aluminum alloy strip, which can be used as the shell of power batteries for new energy vehicles, and can also be extended to the explosion-proof sheet, tab and connecting piece of battery pack.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention achieves significant reductions in processing efficiency by synergistically optimizing hot rolling final temperature, cold rolling passes, and cold rolling rate. Specifically, it reduces the hot continuous rolling final temperature from the conventional 330-350℃ to ≤280℃, decreases the cold rolling passes from 3 to 2, and reduces the total cold rolling rate from the traditional ≥75% to ≤65%. This allows for the production of aluminum alloy strips with high grain size, excellent deep-drawing performance, superior mechanical properties, and surface quality, while still maintaining a high processing rate. This improves production efficiency, reduces costs, and aligns with national strategies for green manufacturing and energy conservation and emission reduction. The aluminum alloy strips produced using this method have a grain size index G≥4.5, a tensile strength of 145-156MPa, a low earing rate of 2.3-3.0%, excellent deep-drawing performance, good surface quality, and no color difference, meeting the stringent requirements for manufacturing power battery casings.

[0019] 2. This invention significantly reduces the final rolling temperature of hot continuous rolling to ≤280℃, which is much lower than the conventional 330-350℃. This low-temperature final rolling process helps to obtain a billet structure with higher dislocation density and more favorable energy distribution, creating unique initial conditions for sufficient recrystallization to occur even with a smaller amount of cold rolling deformation.

[0020] 3. This invention involves two-pass cold rolling of hot-rolled billets, with a total processing rate of ≤65%. The first pass of cold rolling uses a large processing rate of 45-50% to roll the billet to an intermediate thickness. This large single-pass deformation can efficiently accumulate high-density deformation energy in the material while reducing the total processing rate. Subsequently, the intermediate billet is cleaned and fully recrystallized and annealed. Finally, the second pass of cold rolling is performed to the target thickness, which can obtain an aluminum alloy with a grain size index G≥4.5.

[0021] 4. This invention reduces the number of cold rolling passes from 3 to 2, and the total cold rolling processing rate from the traditional ≥75% to ≤65%, thus simplifying the process and eliminating the cleaning process before slitting. This directly leads to a significant reduction in the consumption of electricity, water resources and chemicals, thereby improving production efficiency and reducing production costs. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The image shows the metallographic microstructure of the aluminum alloy prepared in Example 1; the average grain intercept is about 58 μm, and the grain level index G reaches 5.0. Figure 2 The image shows the metallographic microstructure of the aluminum alloy prepared in Example 2; the average grain intercept is about 50 μm, and the grain size index G reaches 5.3. Figure 3 The image shows the metallographic microstructure of the aluminum alloy prepared in Example 3; the average grain intercept is about 56 μm, and the grain level index G reaches 4.8. Figure 4 The metallographic microstructure of the aluminum alloy prepared in Comparative Example 1 is shown in the image. The average grain intercept is about 78 μm, and the grain size index G reaches 4.3. Detailed Implementation

[0024] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0025] Example 1 This embodiment describes a method for preparing high-grain-level aluminum alloy strip with low processing rate for power battery casings in new energy vehicles. The process flow includes: melting → casting → sawing → milling → homogenization heat treatment → heating → hot rolling → cold rolling (one pass) → cleaning → annealing → cold rolling (one pass) → slitting → packaging. Specifically: S1. Raw material smelting and casting: The raw materials are batched according to the 3003 alloy composition design. After smelting, ingots are prepared using a semi-continuous casting method.

[0026] S2. Ingot processing: Sawing and milling the ingots to remove surface defects.

[0027] S3. Homogenization heat treatment: Homogenization heat treatment is performed on the milled ingot.

[0028] S4. Hot continuous rolling: The heated ingot is hot continuously rolled at a final rolling temperature of 280℃ to obtain a hot-rolled billet with a thickness of 2.0mm.

[0029] S5, Cold Rolling, Cleaning and Annealing: The hot-rolled billet is cold rolled in two passes. The first pass uses a large processing rate of 45% to roll the billet to the intermediate thickness. Then, the intermediate billet is cleaned and fully recrystallized and annealed. The second pass is then cold rolled to the target thickness of 1.0 mm to obtain fine grains. The total processing rate is 65%.

[0030] S6. Finished product processing: The cold-rolled aluminum coil is longitudinally sheared to obtain aluminum alloy strip with a width of 250mm.

[0031] Example 2 This embodiment describes a method for preparing high-grain-level aluminum alloy strip with low processing rate for power battery casings in new energy vehicles. The process flow includes: melting → casting → sawing → milling → homogenization → heating → hot rolling → cold rolling (one pass) → cleaning → annealing → cold rolling (one pass) → slitting → packaging. Specifically: S1. Raw material smelting and casting: The raw materials are batched according to the 3003 alloy composition design. After smelting, refining, and online degassing and slag removal, ingots are prepared using a semi-continuous casting method.

[0032] S2. Ingot processing: Sawing and milling the ingots to remove surface defects.

[0033] S3. Homogenization heat treatment: Homogenization heat treatment is performed on the milled ingot.

[0034] S4. Hot continuous rolling: The heated ingot is hot continuously rolled at a final rolling temperature of 275℃ to obtain a hot-rolled billet with a thickness of 4.0mm.

[0035] S5, Cold Rolling, Cleaning and Annealing: The hot-rolled billet is cold rolled in two passes. The first pass uses a large processing rate of 50% to roll the billet to the intermediate thickness. Then, the intermediate billet is cleaned and fully recrystallized and annealed. The second pass is then cold rolled to the target thickness of 1.5 mm to obtain fine grains. The total processing rate is 62.5%.

[0036] S6. Finished product processing: The cold-rolled aluminum coil is longitudinally sheared to obtain aluminum alloy strip with a width of 500mm.

[0037] Example 3 This embodiment describes a method for preparing high-grain-level aluminum alloy strip with low processing rate for power battery casings in new energy vehicles. The process flow includes: melting → casting → sawing → milling → homogenization → heating → hot rolling → cold rolling (one pass) → cleaning → annealing → cold rolling (one pass) → slitting → packaging. Specifically: S1. Raw material smelting and casting: The raw materials are batched according to the 3003 alloy composition design. After smelting, refining, and online degassing and slag removal, ingots are prepared using a semi-continuous casting method.

[0038] S2. Ingot processing: Sawing and milling the ingots to remove surface defects.

[0039] S3. Homogenization heat treatment: Homogenization heat treatment is performed on the milled ingot.

[0040] S4. Hot continuous rolling: The ingot after heat treatment is hot continuously rolled. The final rolling temperature of the hot continuous rolling is 270℃, and a hot rolled billet with a thickness of 5.0mm is obtained.

[0041] S5, Cold Rolling, Cleaning and Annealing: The hot-rolled billet is cold rolled in two passes. The first pass uses a large processing rate of 48% to roll the billet to the intermediate thickness. Then, the intermediate billet is cleaned and fully recrystallized and annealed. The second pass is then cold rolled to the target thickness of 2mm to obtain fine grains. The total processing rate is 60%.

[0042] S6. Finished product processing: The cold-rolled aluminum coil is longitudinally sheared to obtain aluminum alloy strip with a width of 900mm.

[0043] Comparative Example 1: This comparative example uses conventional processes to prepare aluminum alloy strip. The specific process flow is as follows: melting → casting → sawing → milling → homogenization → heating → hot rolling → cold rolling (two passes) → cleaning → annealing → cold rolling (one pass) → cleaning → slitting → packaging. The steps of melting, casting, sawing, milling, homogenization, slitting, and packaging are all the same as in Example 1. However, the final rolling temperature of the hot continuous rolling (heating → hot rolling) is set at 350℃, the total cold rolling processing rate is 75%, and the number of cold rolling passes is 3.

[0044] Performance testing: The grain size index, tensile strength, and ear-making rate of the aluminum alloy strips prepared in Examples 1, 2, 3, and Comparative Example 1 were tested respectively, and the results are shown in Table 1. The grain size index was tested according to the average grain size calculation method in GB / T 3246.1-2024; the tensile strength was tested according to the method in GB / T 228.1-2021; and the ear-making rate was tested according to the method in GB / T 24183-2021.

[0045] Table 1 Properties of aluminum alloys in each group The table above shows that, compared with existing technologies, the aluminum alloy strip produced by the method of this invention has a grain size index G≥4.5, a tensile strength of 145-156MPa, a low ear-making rate of 2.3-3.0%, excellent deep-drawing performance, good surface quality, and no color difference, fully meeting the stringent requirements for manufacturing power battery casings. This material can not only be used for battery casings but also extended to components such as explosion-proof sheets, electrode tabs, and connecting pieces in battery packs. Simultaneously, this invention reduces the number of cold rolling passes from 3 to 2, and the total cold rolling processing rate from the traditional ≥75% to ≤65%, simplifying the process and eliminating the cleaning step before slitting. This directly leads to a significant reduction in energy, water, and chemical consumption, improving production efficiency, and lowering production costs, making it suitable for widespread application.

[0046] Figures 1 to 3 Metallographic microstructures of aluminum alloys prepared in Examples 1, 2, and 3 are shown. The figures show that the average grain intercept of Example 1 is about 58 μm, the grain level index G reaches 5.0, and the microstructure is uniform and fine; the average grain intercept of Example 2 is about 50 μm, the grain level index G reaches 5.3, and the microstructure is even finer and more uniform; the average grain intercept of Example 3 is about 56 μm, the grain level index G reaches 4.8, the microstructure is slightly coarser, and the grain size has increased. Figure 4 The image shows the metallographic microstructure of the aluminum alloy prepared in Comparative Example 1. The average grain intercept is about 78 μm and the grain level index G reaches 4.3. The microstructure is coarser than that of Examples 1, 2 and 3.

[0047] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a high-grain-level aluminum alloy strip with low processing rate for use in power battery casings of new energy vehicles, the process flow of which includes: Raw material smelting and casting, ingot processing, homogenization heat treatment, hot continuous rolling, cold rolling and annealing, and finished product processing, characterized in that, The hot rolling process involves hot rolling a heated ingot to obtain a hot-rolled billet with a thickness of 2.8-5.0 mm. The final rolling temperature of the hot rolling process is ≤280℃. The cold rolling and annealing process involves two cold rolling passes on the hot-rolled billet, with a total processing rate of ≤65%. The first cold rolling pass has a processing rate of 45-50%, rolling the billet to an intermediate thickness. Subsequently, the intermediate billet is cleaned and fully recrystallized and annealed. Finally, the second cold rolling pass is performed to achieve a target thickness of 1.0-2.0 mm.

2. The method for preparing a high-grain-level aluminum alloy strip with low processing rate for a power battery casing of a new energy vehicle according to claim 1, characterized in that, The raw material smelting and casting process involves batching materials according to the 3003 alloy composition, followed by smelting, refining, and online degassing and slag removal, and then preparing ingots using a semi-continuous casting method.

3. The method for preparing a high-grain-level aluminum alloy strip with low processing rate for a power battery casing of a new energy vehicle according to claim 1, characterized in that, The ingot processing involves sawing and milling the ingot to remove surface defects.

4. The method for preparing a high-grain-level aluminum alloy strip with low processing rate for a power battery casing of a new energy vehicle according to claim 1, characterized in that, The homogenization heat treatment is a process performed on the milled ingot to achieve homogenization.

5. The method for preparing a high-grain-level aluminum alloy strip with low processing rate for a power battery casing of a new energy vehicle according to claim 1, characterized in that, The finished product processing involves longitudinally slitting the cold-rolled aluminum coil into strips to obtain aluminum alloy strips of the required width.

6. An aluminum alloy strip prepared by the preparation method according to any one of claims 1 to 5.

7. The aluminum alloy strip according to claim 6, characterized in that, The aluminum alloy strip has a grain size index G≥4.5, a tensile strength of 145-156MPa, and an ear-forming rate as low as 2.3-3.0%, meeting the stringent requirements for manufacturing power battery casings.

8. An application of the aluminum alloy strip as described in claim 6, characterized in that: The aluminum alloy strip can be used for the casing of power batteries for new energy vehicles, and can also be extended to the explosion-proof sheet, tabs and connecting pieces of battery packs.

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