An aluminum alloy strip for a power battery cover plate and a method of manufacturing the same

Abstract

The application belongs to the technical field of aluminum-based materials, and particularly relates to an aluminum alloy strip for a power battery cover plate and a preparation method thereof. The aluminum alloy strip preparation method provided by the application successfully realizes 'free homogenization treatment' and 'free intermediate annealing' through unique component design and accurate synergistic control of key process parameters, so that the production energy consumption and cost are greatly reduced while the excellent performance of the product is ensured, and the processing efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of aluminum-based materials technology, specifically relating to an aluminum alloy strip for power battery cover plates and its preparation method. Background Technology

[0002] With the global energy structure shifting towards cleaner and lower-carbon energy, the new energy vehicle industry has experienced explosive growth. As the "heart" of new energy vehicles, the performance, safety, and cost of power batteries directly determine the vehicle's range, reliability, and market competitiveness. The power battery casing, as a key structural component protecting the battery core, isolating it from the external environment, and ensuring a secure seal, requires extremely stringent material performance. It not only needs excellent strength, formability, and corrosion resistance to ensure structural integrity and long service life under complex operating conditions, but also must possess good electrical and thermal conductivity, as well as laser welding performance, to meet the demands of battery charge and discharge management and efficient production assembly. Among numerous materials, 3003 aluminum alloy, due to its good processing performance, moderate strength, and excellent corrosion resistance, has long been considered one of the ideal candidate materials for battery casings.

[0003] The traditional manufacturing process for 3003 aluminum alloy cover plates typically follows a classic and complex workflow: casting → homogenization treatment → hot rolling → cold rolling → intermediate annealing → cold rolling → finished product annealing, etc. Among these, "homogenization treatment" and "intermediate annealing" are two crucial steps, but they are also where energy consumption and time costs are primarily concentrated.

[0004] First, during the casting process, due to non-equilibrium solidification, severe dendritic segregation and a large amount of coarse, brittle second phases (such as iron- and manganese-rich intermetallic compounds) are generated inside the ingot. These inhomogeneous structures significantly reduce the material's plasticity, toughness, and subsequent processing properties. Therefore, a long-term (usually 10–24 hours) high-temperature (typically above 580°C) "homogenization treatment" is necessary to ensure uniform element diffusion and dissolve the soluble brittle eutectic phase, thereby improving the material's processing characteristics. This process is extremely energy-intensive, consuming a large portion of the entire production cycle, and is one of the bottlenecks restricting production efficiency and cost reduction.

[0005] Secondly, during cold rolling deformation, a large number of dislocations accumulate within the material, resulting in significant work hardening. This leads to an increase in strength and hardness, while plasticity and toughness decrease sharply. Once work hardening reaches a certain level, without softening treatment, the material cannot continue rolling deformation and may even crack. Therefore, an "intermediate annealing" process must be inserted between traditional multi-pass cold rolling. This process eliminates work hardening and restores the material's plasticity through recrystallization, preparing it for subsequent cold rolling. However, intermediate annealing is also a high-energy-consuming process, increasing production steps and extending the production cycle. It may also introduce quality control problems such as surface oxidation and grain coarsening.

[0006] While the aforementioned traditional processes can produce qualified battery casing materials, their inherent high energy consumption, long production cycles, and high costs are becoming increasingly prominent, making them difficult to meet the urgent needs of the new energy vehicle industry for cost reduction and efficiency improvement. To overcome this technological bottleneck, the industry has undertaken numerous explorations. One mainstream technical approach is to try optimizing the alloy composition, for example, by adding trace amounts of transition elements such as manganese (Mn), chromium (Cr), and zirconium (Zr), utilizing the dispersed nanoscale intermetallic compound particles (Al6Mn, Al12Mn, etc.) formed to generate dispersion strengthening and substructure strengthening, while simultaneously suppressing recrystallization and refining the grains. However, simply adjusting the composition is often insufficient to completely eliminate the homogenization process, because if the brittle phase is not fully dissolved, it will directly lead to hot-rolling cracking or substandard finished product performance. On the other hand, if intermediate annealing is to be eliminated, the microstructure evolution and work hardening state of the material must be precisely controlled throughout the entire processing flow to ensure that it can still maintain sufficient plasticity to meet the final performance requirements after undergoing a sufficiently large total deformation. This places extremely high demands on the coordinated matching of composition design and process control (especially hot rolling final rolling temperature and cold rolling processing rate).

[0007] In existing technologies, hot rolling finishing temperature and cold rolling processing rate are usually set within a fixed range based on experience, lacking a dynamic and precise correlation with specific alloy compositions. This "static" process control mode cannot adapt to the slight fluctuations in composition between different heats, making it difficult to consistently control the material state within the optimal window. When the composition is too high, it may lead to excessively high finishing temperature or insufficient cold processing rate, failing to effectively suppress recrystallization and resulting in substandard strength. Conversely, when the composition is too low, it may lead to excessively low finishing temperature or excessive cold processing rate, resulting in excessive work hardening, depletion of plasticity reserves, and the risk of strip breakage, ultimately necessitating intermediate annealing.

[0008] Therefore, developing a new type of aluminum alloy strip that can completely eliminate the high-energy-consuming homogenization and intermediate annealing processes while ensuring stable and excellent product performance, as well as its efficient preparation method, has become a key technical problem that urgently needs to be solved in the field of new energy vehicle materials. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide an aluminum alloy strip for power battery cover plates and its preparation method.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A method for preparing aluminum alloy strip for power battery cover plates includes the following steps:

[0012] S1. Batching and Smelting: Prepare raw materials according to the following mass percentage ratios: Si: 0.15%~0.25%, Fe: 0.4%~0.6%, Cu: 0.09%~0.13%, Mn: 1.03%~1.15%, Cr: 0.05%~0.25%, Zr: 0.03%~0.15%, Mg≤0.015%, Zn≤0.018%, Ti: 0.02%~0.03%, other impurity elements total ≤0.15%, balance Al;

[0013] The above raw materials are smelted, refined, degassed and slag removed, and then semi-continuously cast to obtain aluminum alloy flat ingots.

[0014] S2. Heat treatment: After the flat ingot is sawn and milled, it is heated to 490~550℃ and held for 3~24 hours for heat treatment.

[0015] S3. Hot rolling: After heating, the product is hot rolled. The final rolling temperature T of the hot finishing rolling is determined by the following formula:

[0016] T = 290 + 30×[Mn] + 20×[Cr] + 35×[Zr] - 8×[Zr]²;

[0017] Wherein, [Mn], [Cr], and [Zr] represent the numerical part of the mass percentage content of manganese, chromium, and zirconium elements (pure numbers after removing the percentage sign), and the unit of the hot finishing rolling temperature T is ℃;

[0018] S4. Cold rolling: After the hot-rolled strip is cooled, it is rolled to the finished thickness on a cold rolling mill;

[0019] S5. Clean the cold-rolled strip on the rewinding machine;

[0020] S6. After cleaning, the strip is cut into predetermined finished widths by a slitting machine to obtain the aluminum alloy strip.

[0021] Furthermore, in step S2, the temperature for heating the flat ingot is 520–540°C, and the holding time is 3 hours.

[0022] Furthermore, in S3, the hot-rolled thickness is 2.5–3.0 mm.

[0023] Furthermore, the cold rolling cold working rate R in S4 is determined by the following formula:

[0024] R = 25 - 2×[Mn] - 3×[Cr] - 4×[Zr] - 0.03×(T - 325);

[0025] Where: R is the cold rolling cold working rate, in %; [Mn], [Cr], and [Zr] are the numerical parts of the mass percentage content of the corresponding elements (pure numbers after removing the percentage sign); T is the hot finishing rolling temperature, in ℃.

[0026] Furthermore, in step S4, the roughness of the cold rolling work roll is 0.25–0.35 μm, and the rolling speed is 150–300 m / min.

[0027] This invention provides an aluminum alloy strip, which is prepared by the above method.

[0028] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0029] The aluminum alloy strip preparation method provided by this invention, through unique composition design and precise synergistic control of key process parameters, successfully achieves "no homogenization treatment" and "no intermediate annealing", thereby significantly reducing production energy consumption and costs and improving processing efficiency while ensuring excellent product performance.

[0030] First, by optimizing the ratio of elements such as Mn, Cr, and Zr, and combining it with a specific heat treatment process (holding at 520~540℃ for 3 hours), the brittle eutectic phase in the ingot is fully dissolved. At the same time, by utilizing the synergistic effect of these elements, the recrystallization process is effectively suppressed, the grain structure is refined, and the homogenization process, which is time-consuming and energy-intensive in the traditional process, is successfully replaced.

[0031] Secondly, the core innovation of this invention lies in establishing a dynamic calculation formula for the hot finishing rolling temperature T and the cold rolling cold working rate R. This formula dynamically correlates the alloy composition with key process parameters. By precisely controlling the finishing rolling temperature, the material is in the optimal processing state immediately after hot rolling. Then, the optimal cold working rate is calculated to perform one-time cold rolling, avoiding the intermediate annealing step required in traditional processes to prevent work hardening.

[0032] Ultimately, the aluminum alloy strip prepared by this invention not only has a uniform structure and stable performance (tensile strength 147~162MPa, yield strength 131~149MPa, elongation 8%~12%), fully meeting the stringent requirements of new energy battery casing covers, but also significantly shortens the process flow, increases production efficiency by about 20%~30%, and reduces overall production costs by about 15%~25%, giving it extremely high market competitiveness and industrial application value. Attached Figure Description

[0033] Figure 1 This is a metallographic image of the aluminum alloy strip produced in Example 1. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] An aluminum alloy strip for use as a cover plate for a power battery and its preparation method are disclosed. The aluminum alloy strip comprises, by mass percentage: Si 0.20%, Fe 0.50%, Cu 0.11%, Mn 1.09%, Cr 0.15%, Zr 0.09%, Mg 0.010%, Zn 0.015%, Ti 0.025%, other impurity elements totaling 0.12%, with the balance being Al.

[0037] Its preparation method includes the following steps:

[0038] S1. Melting and casting: The above-mentioned ingredients are prepared, and after melting, refining, degassing and slag removal, aluminum alloy flat ingots are semi-continuously cast.

[0039] S2. Heat treatment: After the flat ingot is sawn and milled, it is heated to 530℃ and held for 3 hours.

[0040] S3. Hot Rolling: After heating, the material is hot rolled, with a hot finishing thickness of 2.7 mm. The final hot finishing temperature T is calculated according to the formula: T = 290 + 30×[Mn] + 20×[Cr] + 35×[Zr] - 8×[Zr]² = 290 + 30×1.09 + 20×0.15 + 35×0.09 - 8×(0.09)² = 290 + 32.7 + 3.0 + 3.15 - 0.065 ≈ 329℃.

[0041] S4. Cold Rolling: After the hot-rolled strip is cooled, it is rolled on a cold rolling mill to a finished thickness of 2.0 mm. The cold working rate R is calculated according to the formula: R = 25 - 2×[Mn] - 3×[Cr] - 4×[Zr] - 0.03×(T - 325) = 25 - 2×1.09 - 3×0.15 - 4×0.09 - 0.03×(329 - 325) = 25 - 2.18 - 0.45 - 0.36 - 0.12 = 21.89%. The surface roughness of the cold rolling work rolls is 0.30 μm, and the rolling speed is 250 m / min.

[0042] S5. Cleaning: Clean the cold-rolled strip on a rewinding machine.

[0043] S6. Slitting: The cleaned strip is slitting into predetermined finished widths using a slitting machine to obtain the aluminum alloy strip.

[0044] The aluminum alloy strip (2.0 mm thick) produced by this method has the following properties: tensile strength of 154 MPa, yield strength of 142 MPa, elongation of 9.8%, and surface hardness of HV49. The production cycle for this strip is 7 days, with a yield rate of 80%, and production costs are reduced by approximately 18%.

[0045] Figure 1 This is a metallographic image of the aluminum alloy strip produced in Example 1. Figure 1 As can be seen, the aluminum alloy strip exhibits a fine and uniform grain structure with no obvious coarse second phase or segregation. The grain size distribution is consistent, and no abnormally large grains are observed, indicating that the composition design and heat treatment process of this invention effectively suppresses the recrystallization process, achieving a uniform and refined microstructure. Furthermore, no obvious pores, cracks, or other defects are observed in the figure, indicating that the material possesses good density and processing performance, providing a reliable microstructural basis for its excellent mechanical properties.

[0046] Example 2

[0047] An aluminum alloy strip for use as a cover plate for a power battery and its preparation method are disclosed. The aluminum alloy strip comprises, by mass percentage: Si 0.15%, Fe 0.40%, Cu 0.09%, Mn 1.03%, Cr 0.05%, Zr 0.03%, Mg 0.008%, Zn 0.010%, Ti 0.020%, other impurity elements totaling 0.10%, with the balance being Al.

[0048] Its preparation method includes the following steps:

[0049] S1. Melting and casting: The above-mentioned ingredients are prepared, and after melting, refining, degassing and slag removal, aluminum alloy flat ingots are semi-continuously cast.

[0050] S2. Heat treatment: After the flat ingot is sawn and milled, it is heated to 520℃ and held for 3 hours.

[0051] S3. Hot Rolling: After heating, the material is hot rolled, with a hot finishing thickness of 2.5 mm. The final hot finishing temperature T is calculated according to the formula: T = 290 + 30×[Mn] + 20×[Cr] + 35×[Zr] - 8×[Zr]² = 290 + 30×1.03 + 20×0.05 + 35×0.03 - 8×(0.03)² = 290 + 30.9 + 1.0 + 1.05 - 0.007 ≈ 323℃.

[0052] S4. Cold Rolling: After the hot-rolled strip is cooled, it is rolled on a cold rolling mill to a finished thickness of 2.0 mm. The cold working rate R is calculated according to the formula: R = 25 - 2×[Mn] - 3×[Cr] - 4×[Zr] - 0.03×(T - 325) = 25 - 2×1.03 - 3×0.05 - 4×0.03 - 0.03×(323 - 325) = 25 - 2.06 - 0.15 - 0.12 + 0.06 = 22.73%. The surface roughness of the cold rolling work rolls is 0.25 μm, and the rolling speed is 150 m / min.

[0053] S5. Cleaning: Clean the cold-rolled strip on a rewinding machine.

[0054] S6. Slitting: The cleaned strip is slitting into predetermined finished widths using a slitting machine to obtain the aluminum alloy strip.

[0055] The aluminum alloy strip (2.0 mm thick) produced by this method has the following properties: tensile strength of 147 MPa, yield strength of 131 MPa, elongation of 11.6%, and surface hardness of HV46. The production cycle for this strip is 8 days, with a yield rate of 78%, and production costs are reduced by approximately 20%.

[0056] Example 3

[0057] An aluminum alloy strip for use as a cover plate for a power battery and its preparation method are disclosed. The aluminum alloy strip comprises, by mass percentage: Si 0.25%, Fe 0.60%, Cu 0.13%, Mn 1.15%, Cr 0.25%, Zr 0.15%, Mg 0.015%, Zn 0.018%, Ti 0.030%, other impurity elements totaling 0.15%, with the balance being Al.

[0058] Its preparation method includes the following steps:

[0059] S1. Melting and casting: The above-mentioned ingredients are prepared, and after melting, refining, degassing and slag removal, aluminum alloy flat ingots are semi-continuously cast.

[0060] S2. Heat treatment: After the flat ingot is sawn and milled, it is heated to 540℃ and held for 3 hours.

[0061] S3. Hot Rolling: After heating, the material is hot rolled, with a hot finishing thickness of 3.0 mm. The final hot finishing temperature T is calculated according to the formula: T = 290 + 30×[Mn] + 20×[Cr] + 35×[Zr] - 8×[Zr]² = 290 + 30×1.15 + 20×0.25 + 35×0.15 - 8×(0.15)² = 290 + 34.5 + 5.0 + 5.25 - 0.18 ≈ 335℃.

[0062] S4. Cold Rolling: After the hot-rolled strip is cooled, it is rolled on a cold rolling mill to a finished thickness of 2.0 mm. The cold working rate R is calculated according to the formula: R = 25 - 2×[Mn] - 3×[Cr] - 4×[Zr] - 0.03×(T - 325) = 25 - 2×1.15 - 3×0.25 - 4×0.15 - 0.03×(335 - 325) = 25 - 2.3 - 0.75 - 0.6 - 0.3 = 21.05%. The surface roughness of the cold rolling work rolls is 0.35 μm, and the rolling speed is 300 m / min.

[0063] S5. Cleaning: Clean the cold-rolled strip on a rewinding machine.

[0064] S6. Slitting: The cleaned strip is slitting into predetermined finished widths using a slitting machine to obtain the aluminum alloy strip.

[0065] The aluminum alloy strip (2.0 mm thick) produced by this method has the following properties: tensile strength of 162 MPa, yield strength of 149 MPa, elongation of 8.4%, and surface hardness of HV52. The production cycle for this strip is 6 days, with a yield rate of 82%, and production costs are reduced by approximately 15%.

[0066] Example 4

[0067] An aluminum alloy strip for use as a cover plate for a power battery and its preparation method are disclosed. The aluminum alloy strip comprises, by mass percentage: Si 0.18%, Fe 0.45%, Cu 0.10%, Mn 1.06%, Cr 0.10%, Zr 0.06%, Mg 0.012%, Zn 0.014%, Ti 0.022%, other impurity elements totaling 0.11%, with the balance being Al.

[0068] Its preparation method includes the following steps:

[0069] S1. Melting and casting: The above-mentioned ingredients are prepared, and after melting, refining, degassing and slag removal, aluminum alloy flat ingots are semi-continuously cast.

[0070] S2. Heat treatment: After the flat ingot is sawn and milled, it is heated to 490℃ and kept at that temperature for 24 hours.

[0071] S3. Hot Rolling: After heating, the material is hot rolled, with a hot finishing thickness of 2.6 mm. The final hot finishing temperature T is calculated according to the formula: T = 290 + 30×[Mn] + 20×[Cr] + 35×[Zr] - 8×[Zr]² = 290 + 30×1.06 + 20×0.10 + 35×0.06 - 8×(0.06)² = 290 + 31.8 + 2.0 + 2.1 - 0.029 ≈ 326℃.

[0072] S4. Cold Rolling: After the hot-rolled strip is cooled, it is rolled on a cold rolling mill to a finished thickness of 2.0 mm. The cold working rate R is calculated according to the formula: R = 25 - 2×[Mn] - 3×[Cr] - 4×[Zr] - 0.03×(T - 325) = 25 - 2×1.06 - 3×0.10 - 4×0.06 - 0.03×(326 - 325) = 25 - 2.12 - 0.30 - 0.24 - 0.03 = 22.31%. The surface roughness of the cold rolling work rolls is 0.28 μm, and the rolling speed is 180 m / min.

[0073] S5. Cleaning: Clean the cold-rolled strip on a rewinding machine.

[0074] S6. Slitting: The cleaned strip is slitting into predetermined finished widths using a slitting machine to obtain the aluminum alloy strip.

[0075] The aluminum alloy strip (2.0 mm thick) produced by this method has the following properties: tensile strength of 152 MPa, yield strength of 135 MPa, elongation of 10.7%, and surface hardness of HV48. The production cycle for this strip is 7.5 days, with a yield rate of 79%, and production costs are reduced by approximately 19%.

[0076] Example 5

[0077] An aluminum alloy strip for use as a cover plate for a power battery and its preparation method are disclosed. The aluminum alloy strip comprises, by mass percentage: Si 0.22%, Fe 0.55%, Cu 0.12%, Mn 1.12%, Cr 0.20%, Zr 0.12%, Mg 0.014%, Zn 0.016%, Ti 0.028%, other impurity elements totaling 0.14%, with the balance being Al.

[0078] Its preparation method includes the following steps:

[0079] S1. Melting and casting: The above-mentioned ingredients are prepared, and after melting, refining, degassing and slag removal, aluminum alloy flat ingots are semi-continuously cast.

[0080] S2. Heat treatment: After the flat ingot is sawn and milled, it is heated to 550℃ and held for 5 hours.

[0081] S3. Hot Rolling: After heating, the material is hot rolled, with a hot finishing thickness of 2.8 mm. The final hot finishing temperature T is calculated according to the formula: T = 290 + 30×[Mn] + 20×[Cr] + 35×[Zr] - 8×[Zr]² = 290 + 30×1.12 + 20×0.20 + 35×0.12 - 8×(0.12)² = 290 + 33.6 + 4.0 + 4.2 - 0.115 ≈ 332℃.

[0082] S4. Cold Rolling: After the hot-rolled strip is cooled, it is rolled on a cold rolling mill to a finished thickness of 2.0 mm. The cold working rate R is calculated according to the formula: R = 25 - 2×[Mn] - 3×[Cr] - 4×[Zr] - 0.03×(T - 325) = 25 - 2×1.12 - 3×0.20 - 4×0.12 - 0.03×(332 - 325) = 25 - 2.24 - 0.60 - 0.48 - 0.21 = 21.47%. The surface roughness of the cold rolling work rolls is 0.32 μm, and the rolling speed is 280 m / min.

[0083] S5. Cleaning: Clean the cold-rolled strip on a rewinding machine.

[0084] S6. Slitting: The cleaned strip is slitting into predetermined finished widths using a slitting machine to obtain the aluminum alloy strip.

[0085] The aluminum alloy strip (2.0 mm thick) produced by this method has the following properties: tensile strength of 158 MPa, yield strength of 146 MPa, elongation of 9.2%, and surface hardness of HV51. The production cycle for this strip is 6.5 days, with a yield rate of 81%, and production costs are reduced by approximately 17%.

[0086] To illustrate the technical effects of the present invention, the inventors have provided the following comparative examples:

[0087] Comparative Example 1

[0088] Comparative Example 1 has the same alloy composition as Example 1, except that it adopts a conventional processing route, including homogenization treatment and intermediate annealing.

[0089] Specifically as follows:

[0090] The aluminum alloy strip is composed of the following components by mass percentage: Si 0.20%, Fe 0.50%, Cu 0.11%, Mn 1.09%, Cr 0.15%, Zr 0.09%, Mg 0.010%, Zn 0.015%, Ti 0.025%, other impurity elements totaling 0.12%, with the balance being Al.

[0091] Its preparation method includes the following steps:

[0092] S1, casting: Same as in Example 1.

[0093] S2. Homogenization treatment: After the flat ingots are sawn and milled, they undergo traditional homogenization treatment: heated to 600℃ and held for 8 hours, then slowly cooled.

[0094] S3. Hot Rolling: The homogenized flat ingot is reheated to 530℃ and held for 3 hours, then hot rolled. The hot-rolled thickness is 2.7mm, but the final rolling temperature is not controlled by the formula, but is set empirically to 300℃ (a common temperature, but not optimized for this composition).

[0095] S4, Cold Rolled: Cold rolled to a thickness of 2.0 mm, with a cold working rate of 22%. (Calculations were not performed using formula R.)

[0096] S5. Intermediate Annealing: After cold rolling, intermediate annealing is performed at a temperature of 450℃ for 2 hours.

[0097] S6, Light Cold Rolling (Quenching and Tempering): After intermediate annealing, a light cold rolling process is performed with a processing rate of about 5% to adjust the mechanical properties;

[0098] S7. Cleaning and cutting: Same as in Example 1.

[0099] Results and Analysis:

[0100] Results: The obtained strip exhibits the following properties: tensile strength 149 MPa, yield strength 136 MPa, and elongation 9.6%. These properties are similar to those of the product in Example 1 of this invention.

[0101] Comparative analysis of processes:

[0102] 1. Process complexity: This comparative example includes two additional, energy-intensive heat treatment processes: "homogenization" and "intermediate annealing".

[0103] 2. Production cycle: Due to the addition of two long heat treatment processes, the total production cycle is as long as 12 days, which is much longer than the 7 days in Example 1.

[0104] 3. Production costs: Energy consumption increases significantly, equipment occupancy time is longer, and the yield rate decreases slightly due to the increase in processes (approximately 77%). The production cost is about 25% higher than that of Example 1.

[0105] Conclusion: This comparative example demonstrates that if the core formula of this invention is not used to optimize and control the final rolling temperature of hot finishing, traditional homogenization treatment and intermediate annealing must be relied upon to ensure the processability and final performance of the material, resulting in a long production cycle and high costs.

[0106] Comparative Example 2

[0107] Comparative Example 2 has the same alloy composition as Example 1, except that the hot rolling and cold rolling process parameters in Comparative Example 2 were not calculated according to the formula in Example 1, and the homogenization treatment was omitted.

[0108] Specifically as follows:

[0109] The aluminum alloy strip is composed of the following components by mass percentage: Si 0.20%, Fe 0.50%, Cu 0.11%, Mn 1.09%, Cr 0.15%, Zr 0.09%, Mg 0.010%, Zn 0.015%, Ti 0.025%, other impurity elements totaling 0.12%, with the balance being Al.

[0110] Preparation steps:

[0111] S1. Melting and casting: Same as in Example 1;

[0112] S2. Heat treatment: Same as in Example 1, heat to 530℃ and hold for 3 hours. (Attempt to avoid uniform heating)

[0113] S3, Hot Rolling: After heating, the product is hot rolled and the hot finishing thickness is 2.7mm. However, the final rolling temperature was set too low (280℃) and was not calculated according to the formula.

[0114] S4. Cold rolling: An attempt was made to cold roll the hot-rolled strip to a finished thickness of 2.0 mm in one go. The cold working rate was relatively high, at 25%, and was not calculated according to the formula R.

[0115] Problem: During cold rolling, the strip was found to be abnormally hard, the rolling force increased sharply, and the strip shape was poor after rolling, with huge internal stress. Sampling tests of the cold-rolled strip showed tensile strength >180MPa and elongation <5%, which failed to meet subsequent processing requirements.

[0116] S5. Forced intermediate annealing: To solve the above problems, it is necessary to add an intermediate annealing process (400℃ for 3 hours) to soften the material.

[0117] S6. Cleaning and Slitting

[0118] Results and Analysis:

[0119] Results: The final product properties of the strip prepared in Comparative Example 2 were: tensile strength 151 MPa, yield strength 137 MPa, and elongation 9.1%. Although the performance met the standards, the process failed.

[0120] Comparative analysis of processes:

[0121] 1. Attempt to eliminate the need for homogenization: Successful. This demonstrates that the heating regime in S2 of this invention can replace homogenization.

[0122] 2. Attempt to skip intermediate annealing: Failed. Due to the excessively low final rolling temperature of the hot finishing mill and the excessively high cold working rate, the material underwent excessive work hardening, necessitating additional intermediate annealing.

[0123] Production cycle and cost: Due to the addition of an unplanned intermediate annealing, the production cycle was extended to 10 days, and the cost was about 15% higher than that of Example 1.

[0124] Conclusion: This comparative example demonstrates that only by precisely controlling the hot finishing rolling temperature T and the cold working rate R using the formula of this invention can we ensure that the material does not harden excessively after cold rolling while eliminating the need for homogenization, thereby truly achieving short-process production without intermediate annealing.

[0125] Comparative Example 3

[0126] Comparative Example 3 has the same alloy composition as Example 1, but differs in that: Comparative Example 3 does not use the formula of the present invention to control the core parameters. In order to achieve the elimination of homogenization and intermediate annealing, the hot finishing rolling temperature is aggressively increased and the cold working rate is reduced.

[0127] Specifically as follows:

[0128] The aluminum alloy strip is composed of the following components by mass percentage: Si 0.20%, Fe 0.50%, Cu 0.11%, Mn 1.09%, Cr 0.15%, Zr 0.09%, Mg 0.010%, Zn 0.015%, Ti 0.025%, other impurity elements totaling 0.12%, with the balance being Al.

[0129] Preparation steps:

[0130] S1. Melting and casting: Same as in Example 1;

[0131] S2. Heating treatment: Same as in Example 1; (No need for uniform heating)

[0132] S3, Hot Rolled: The thickness of the hot finishing roll is 2.7mm, and the final rolling temperature is set too high (380℃) and is not calculated according to the formula.

[0133] S4. Cold rolling: Cold rolled to a finished thickness of 2.0 mm in one pass. The cold working rate is low, at 18%, and was not calculated according to formula R; (attempt to avoid intermediate rework).

[0134] S5. Cleaning and cutting.

[0135] Results and Analysis:

[0136] Properties of the produced strip:

[0137] Tensile strength: 133 MPa (lower than the lower limit of Examples 1-5); Yield strength: 127 MPa (lower than the lower limit of Examples 1-5); Elongation: 13.6% (meets the standard, but the strength is insufficient); Surface hardness: HV43 (lower than the HV46-52 range of Examples 1-5).

[0138] Performance Analysis: Due to excessively high hot finishing rolling temperature, the solid solution elements were not fully extracted, resulting in an overly soft matrix. Furthermore, insufficient cold working rate prevented adequate work hardening, leading to a final product with significantly lower strength (tensile and yield strength) and hardness than the standard. This material cannot meet the strength and rigidity requirements for battery casing covers and is therefore a substandard product.

[0139] Conclusion: This comparative example demonstrates that blindly omitting the heat treatment process without scientifically and precisely controlling the key process parameters (T and R) will not produce products with qualified performance.

[0140] In summary, this invention, through its unique calculation formula, links the composition and process, ensuring that even with a short process that eliminates the need for homogenization and intermediate cooling, it can still stably obtain finished products with excellent comprehensive mechanical properties.

[0141] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.

Claims

1. A method for preparing aluminum alloy strip for power battery cover plates, characterized in that, Includes the following steps: S1. Batching and Smelting: Prepare raw materials according to the following mass percentage ratios: Si: 0.15%~0.25%, Fe: 0.4%~0.6%, Cu: 0.09%~0.13%, Mn: 1.03%~1.15%, Cr: 0.05%~0.25%, Zr: 0.03%~0.15%, Mg≤0.015%, Zn≤0.018%, Ti: 0.02%~0.03%, other impurity elements total ≤0.15%, balance Al; The above raw materials are smelted, refined, degassed and slag removed, and then semi-continuously cast to obtain aluminum alloy flat ingots. S2. Heat treatment: After the flat ingot is sawn and milled, it is heated to 490~550℃ and held for 3~24 hours for heat treatment. S3. Hot rolling: After heating, the product is hot rolled. The final rolling temperature T of the hot finishing rolling is determined by the following formula: T=290+30×[Mn]+20×[Cr]+35×[Zr]-8×[Zr]²; Wherein, [Mn], [Cr], and [Zr] represent the numerical part of the mass percentage content of manganese, chromium, and zirconium, respectively, and the unit of the hot finishing rolling temperature T is ℃; S4. Cold rolling: After the hot-rolled strip is cooled, it is rolled to the finished thickness on a cold rolling mill; the cold rolling cold working rate R in S4 is determined by the following formula: R=25-2×[Mn]-3×[Cr]-4×[Zr]-0.03×(T-325); Where: R is the cold rolling cold working rate, in %; [Mn], [Cr], and [Zr] are the numerical parts of the mass percentage content of the corresponding elements; T is the hot finishing rolling temperature, in ℃. The surface roughness of the cold rolling work roll is 0.25–0.35 μm, and the rolling speed is 150–300 m / min; S5. Clean the cold-rolled strip on the rewinding machine; S6. After cleaning, the strip is cut into predetermined finished widths by a slitting machine to obtain the aluminum alloy strip.

2. The preparation method according to claim 1, characterized in that, In step S2, the temperature for heating the flat ingot is 520–540°C, and the holding time is 3 hours.

3. The preparation method according to claim 1, characterized in that, In S3, the hot-rolled thickness is 2.5–3.0 mm.

4. An aluminum alloy strip, characterized in that, Prepared by the method described in any one of claims 1-3.

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