Low-temperature sectional annealing synergistic strengthening process for 5052-H34 state

Abstract

The invention discloses a low-temperature sectional annealing synergistic strengthening process for a 5052-H34 state, belongs to the technical field of aluminum alloy heat treatment, and aims to solve the technical problem that the strength and the electric conductivity of a 5052 aluminum alloy strip for a soft package battery are difficult to obtain at the same time. The process comprises two core steps: firstly, preserving heat of a cold-rolled 5052 aluminum alloy strip at 175-185 DEG C for 0.8-1.2 hours to complete low-temperature pre-annealing, cooling to room temperature, heating to 225-235 DEG C at a heating rate of less than or equal to 50 DEG C / hour, preserving heat for 1.8-2.2 hours to perform precise recrystallization, and finally cooling to 100 DEG C or below at a rate of less than or equal to 30 DEG C / hour. The microstructure is optimized by precisely regulating and controlling the thermal history, so that the product forms a fine grain structure island and high dislocation density matrix composite structure, the tensile strength reaches 260-290 MPa, the electric conductivity is larger than or equal to 35% IACS, the grain size is ASTM10-12 level, the method is particularly suitable for soft package battery tabs or structural part aluminum foils with the thickness smaller than or equal to 0.5 mm, the process is simple, industrialization is easy, and the performance comprehensively exceeds that of a traditional process.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy heat treatment technology, specifically to a low-temperature segmented annealing synergistic strengthening process for preparing the 5052-H34 state of a soft-pack battery backsheet. Background Technology

[0002] In the production of pouch batteries, 5052-H34 temper aluminum alloy strip is often used as a key component such as the battery backsheet and tabs due to its excellent basic properties. Its synergistic performance in terms of strength and conductivity directly affects the overall performance and lifespan of the battery. However, existing heat treatment processes for this material have many shortcomings, making it difficult to meet the industry's demand for a synergistic improvement in both strength and conductivity.

[0003] Existing heat treatment processes for 5052 alloy mostly focus on improving the material's plasticity (such as the O state) or treating the as-cast structure. These processes typically use high treatment temperatures (≥300℃). However, high-temperature treatment can lead to excessive loss of the work hardening effect required for the battery foil, making it impossible for the material to meet the strength standards required for the H34 state, and thus failing to meet the structural strength requirements of key components in pouch batteries.

[0004] Furthermore, although some technologies propose the idea of ​​segmented annealing, the core steps (such as the cooling process accompanied by physical tumbling) and the ultimate goal (stress relief and hardness reduction) of these technologies are fundamentally different from the core requirement of this invention to achieve a synergistic improvement in strength and conductivity, and cannot provide an effective solution to the problem of synergistic strength and conductivity of 5052-H34 aluminum foil.

[0005] Therefore, developing a 5052-H34 foil material specifically for batteries, and an annealing process that can precisely balance recrystallization and dislocation retention to synergistically improve strength and conductivity, has become an urgent need for the current industry development. Summary of the Invention

[0006] The purpose of this invention is to provide a low-temperature segmented annealing synergistic strengthening process for preparing the backsheet of a pouch cell in the 5052-H34 state, which optimizes the microstructure and achieves synergistic improvement in strength and conductivity by precisely controlling the thermal process.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A low-temperature segmented annealing synergistic strengthening process for 5052-H34 state includes: performing a first low-temperature stage annealing on the cold-rolled strip; and then heating it to a second temperature at a heating rate of ≤50℃ / hour and holding it at that temperature.

[0009] Furthermore, a low-temperature segmented annealing synergistic strengthening process for the 5052-H34 state includes the following steps:

[0010] S1: Low-temperature pre-annealing stage: Place the cold-rolled 5052 aluminum alloy strip in an annealing furnace and hold it at a temperature range of 175-185℃ for 0.8-1.2 hours. After the holding period, air cool or furnace cool to room temperature.

[0011] S2: Precision recrystallization stage: Transfer the strip treated in S1 to a protective atmosphere annealing furnace, heat it to 225-235℃ at a heating rate of no more than 50℃ / hour, and hold it at this temperature for 1.8-2.2 hours. After holding, control the cooling rate to no more than 30℃ / hour to cool the strip to below 100℃.

[0012] Furthermore, in S1, the temperature is maintained at 180°C for 1.0 hour.

[0013] Furthermore, in S1 or S2, the protective gas is nitrogen, and the oxygen content in the annealing furnace is controlled at ≤50ppm.

[0014] Furthermore, in S2, the temperature is increased to 230°C at a heating rate of 35-45°C / hour, and held at that temperature for 2.0 hours.

[0015] Furthermore, in S2, the cooling rate is controlled at 20-25℃ / hour to cool the strip to below 100℃.

[0016] Furthermore, the method is applicable to the preparation of aluminum foil for tabs or structural components of pouch batteries with a thickness ≤0.5mm.

[0017] Furthermore, the 5052-H34 aluminum alloy strip prepared by the above-mentioned low-temperature segmented annealing method has a tensile strength of 260-290 MPa, a conductivity ≥35% IACS, and a grain size of ASTM 10-12.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This system and method for high-value preservation, utilization, and harmless treatment of waste aluminum has the following advantages:

[0019] 1. This invention innovatively designs a synergistic control process path of low-temperature preparation + medium-temperature fixation, which is different from the simple high-temperature annealing or complex physical-assisted annealing methods in the prior art.

[0020] 2. In this invention, the first stage of low-temperature pre-annealing at 175-185℃ can gently adjust the dislocation structure, creating the best "soil" for uniform nucleation in the second stage; the second stage of precise isothermal recrystallization at 225-235℃ can "fix" the degree of recrystallization of the material at a partial recrystallization window, achieving an organic unity of fine grain strengthening and conductivity improvement, fundamentally breaking the "seesaw" effect of mutual constraint between strength and conductivity in traditional processes.

[0021] 3. This invention uses precise process parameters as the "control handle" for performance, including pre-annealing temperature (175-185℃), recrystallization temperature (225-235℃), heating rate (≤50℃ / h), and cooling rate (≤30℃ / h). These parameters were determined through repeated experiments and optimizations, ensuring a high and uniform recrystallization nucleation rate, which is a decisive process window for achieving breakthroughs in material performance.

[0022] 4. Through the process of this invention, a composite microstructure is formed within the material, in which "fine-grained islands" are uniformly distributed in a "high dislocation density matrix." The fine-grained islands effectively enhance the material's strength, while the high dislocation density matrix serves as an excellent conductive channel; their synergistic effect achieves a simultaneous improvement in both strength and conductivity. Actual testing shows that the 5052-H34 state battery aluminum foil produced using this invention's process comprehensively surpasses the performance indicators of products produced using traditional processes, fully demonstrating the effectiveness and superiority of this invention's technical solution.

[0023] 5. The process of this invention requires no additional complex equipment or auxiliary means; it can be achieved simply by optimizing the process parameters of existing annealing furnaces. The production process is simple, highly controllable, and easy to promote on a large scale in industrial applications. The process is applicable to aluminum foil for tabs or structural components of pouch batteries with a thickness ≤0.5mm, which can meet the urgent need of the pouch battery industry for high-performance aluminum alloy strips, and has a very broad application prospect. Detailed Implementation

[0024] 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.

[0025] A low-temperature segmented annealing synergistic strengthening process for 5052-H34 state includes the following steps:

[0026] S1: Low-temperature pre-annealing stage: Place the cold-rolled 5052 aluminum alloy strip in an annealing furnace and hold it at a temperature range of 175-185℃ for 0.8-1.2 hours. After the holding period, air cool or furnace cool to room temperature.

[0027] S2: Precision recrystallization stage: Transfer the strip treated in S1 to a protective atmosphere annealing furnace, heat it to 225-235℃ at a heating rate of no more than 50℃ / hour, and hold it at this temperature for 1.8-2.2 hours. After holding, control the cooling rate to no more than 30℃ / hour to cool the strip to below 100℃.

[0028] Example 1: Production of 0.3mm thick 5052-H34 state battery aluminum foil

[0029] (1) Material preparation: Select 5052 aluminum alloy coils that have been cold rolled to a thickness of 0.3mm through seven passes as raw materials to be processed. The width of the coil is 1200mm. Flatten it and load it into the continuous annealing furnace to ensure that the coil is in uniform contact with the guide rollers in the furnace and avoid uneven heating in some areas.

[0030] (2) Low-temperature pre-annealing stage: High-purity nitrogen (purity ≥99.99%) is introduced into the annealing furnace to continuously replace the air in the furnace for 30 minutes to ensure that the initial oxygen content in the furnace is ≤100ppm; then the furnace temperature is raised to 180℃ at a heating rate of 50℃ / h and held at this temperature for 1 hour. During the holding process, the temperature fluctuation in the furnace is monitored in real time to control the temperature difference ≤±2℃. After this stage, the strip is cooled to room temperature by furnace cooling. After stress testing, the internal stress of the strip is released by 78% compared with that after cold rolling, and the dislocation structure is uniformly distributed.

[0031] (3) Precise recrystallization stage: Maintain the nitrogen protective atmosphere in the furnace, continue to raise the furnace temperature to 230℃ at a heating rate of 50℃ / h, and precisely hold the temperature for 2 hours; during the holding process, monitor the oxygen content in the furnace in real time through an online oxygen content analyzer, and strictly control the oxygen content in the furnace to ≤50ppm to avoid oxidation of the strip surface;

[0032] (4) Cooling and unloading: After the heat preservation is completed, the furnace temperature is reduced to 80°C at a cooling rate of 25°C / h. Then, nitrogen supply is stopped, the furnace door is opened and the strip is taken out after natural cooling to room temperature, thus completing the entire annealing process.

[0033] Effect verification: The treated strip was subjected to comprehensive testing, and the results are as follows:

[0034] Metallographic examination (using an AxioObserver Z1 metallographic microscope): Grain size meets ASTM 11 standard, average grain size is 1.2 μm, and uniformity deviation is ≤15%;

[0035] EBSD analysis (using ZEISG GeminiSEM equipped with an EBSD detector): the proportion of small-angle grain boundaries (2-15°) decreased to 30%, while the proportion of large-angle grain boundaries increased to 70%, indicating a dense microstructure;

[0036] Mechanical property testing (using an Instron 5969 universal testing machine, tensile rate 5 mm / min): tensile strength 278 MPa, yield strength 265 MPa, elongation 9%;

[0037] Conductivity test (using SigmaTest 2.0 conductivity meter): conductivity reached 36.2% IACS;

[0038] Example 2: Production of 0.2mm thick 5052-H34 state tab aluminum foil

[0039] (1) Material preparation: Select 5052 aluminum alloy coils that have been cold rolled to a thickness of 0.2mm in eight passes. The coil width is 800mm. Load them into a batch-type protective atmosphere annealing furnace.

[0040] (2) Low temperature pre-annealing stage: After nitrogen is introduced to replace the air, the temperature is raised to 175℃ at a rate of 45℃ / h, held for 0.8 hours, and then air-cooled to room temperature (cooling time is about 40 minutes).

[0041] (3) Precision recrystallization stage: Heat to 225℃ at a heating rate of 40℃ / h, hold for 1.8 hours, and control the oxygen content in the furnace to ≤45ppm;

[0042] (4) Cooling and unloading: After the heat preservation is completed, the temperature is reduced to 75°C at a cooling rate of 20°C / h and then unloaded from the furnace for cooling.

[0043] Performance verification: Grain size: ASTM grade 12 (average grain size 1.0 μm); tensile strength: 272 MPa, yield strength 250 MPa, elongation 8.5%; electrical conductivity: 35.8% IACS.

[0044] Example 3: Production of 0.5mm thick aluminum foil for 5052-H34 state battery backsheet

[0045] (1) Material preparation: Select 5052 aluminum alloy coils that have been cold rolled to a thickness of 0.5mm in six passes, with a coil width of 1500mm, and load them into a continuous annealing furnace;

[0046] (2) Low-temperature pre-annealing stage: After nitrogen is introduced to replace the air, the temperature is raised to 185°C at a rate of 50°C / h, held for 1.2 hours, and then cooled to room temperature with the furnace;

[0047] (3) Precise recrystallization stage: Heat to 235℃ at a heating rate of 50℃ / h, hold for 2.2 hours, and control the oxygen content in the furnace to ≤48ppm;

[0048] (4) Cooling and unloading: After the heat preservation is completed, the temperature is reduced to 90℃ at a cooling rate of 30℃ / h and then unloaded and cooled.

[0049] Performance verification: Grain size: ASTM grade 10 (average grain size 1.5μm); Tensile strength: 283MPa, yield strength 272MPa, elongation 9.5%; Electrical conductivity: 35.8%IACS; Bending performance: No cracks were found in the 180° bending test (bending radius = material thickness), meeting the strength requirements of the back plate structure.

[0050] Example 4: Production of 0.4mm thick 5052-H34 temper structural aluminum foil

[0051] (1) Material preparation: Select 5052 aluminum alloy coils that have been cold rolled to a thickness of 0.4mm in seven passes, with a coil width of 1000mm, and load them into a batch annealing furnace;

[0052] (2) Low-temperature pre-annealing stage: After nitrogen is introduced to replace the air, the temperature is raised to 182℃ at a rate of 48℃ / h, held for 1.0 hour, and then air-cooled to room temperature;

[0053] (3) Precision recrystallization stage: Heat to 232℃ at a heating rate of 45℃ / h, hold for 2.0 hours, and control the oxygen content in the furnace to ≤42ppm;

[0054] (4) Cooling and unloading: After the heat preservation is completed, the temperature is reduced to 85°C at a cooling rate of 28°C / h and then unloaded and cooled.

[0055] Performance verification: Grain size: ASTM grade 11; Tensile strength: 275 MPa, yield strength: 260 MPa, elongation: 9.2%; Electrical conductivity: 36.0% IACS; Corrosion resistance: No obvious corrosion points were observed in the neutral salt spray test (5% NaCl solution, continuous spraying for 48 hours), and the corrosion resistance performance is superior to products made by traditional processes.

[0056] Comparative experiment: Traditional single-stage annealing process (control group)

[0057] A 0.3mm thick 5052 aluminum alloy coil was treated using a commonly used single-stage high-temperature annealing process. The process parameters were: 320℃ for 3 hours, followed by natural cooling. The post-treatment test results were: tensile strength 235MPa, conductivity 33.2% IACS, grain size ASTM grade 8, and elongation 12%. Compared to Example 1 of this invention, the tensile strength is 15.5% lower, the conductivity is 8.3% lower, and the grain size is coarser, failing to meet the strength requirements of the H34 temper.

[0058] The four embodiments described above employed different combinations of process parameters within the range of this invention, covering a target thickness range of 0.2-0.5 mm. All were controlled through processes such as nitrogen protection, precise temperature control, and limited-rate heating and cooling. The resulting 5052-H34 aluminum alloy strips all met the core performance indicators of tensile strength 260-290 MPa, conductivity ≥35% IACS, and grain size ASTM 10-12. Furthermore, auxiliary indicators such as surface quality, corrosion resistance, and bending performance were superior to products produced using traditional processes. This fully demonstrates that the low-temperature segmented annealing process of this invention has excellent parameter adaptability and product versatility, enabling flexible adjustment of process parameters according to the different thicknesses and applications of aluminum foil for soft-pack batteries, stably achieving synergistic enhancement of strength and conductivity.

[0059] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A low-temperature segmented annealing synergistic strengthening process for 5052-H34 state, characterized in that, include: The cold-rolled strip is subjected to a first low-temperature annealing stage; then heated to a second temperature at a heating rate of ≤50℃ / hour and held at that temperature.

2. The low-temperature segmented annealing synergistic strengthening process for 5052-H34 state according to claim 1, characterized in that, Includes the following steps: S1: Low-temperature pre-annealing stage: Place the cold-rolled 5052 aluminum alloy strip in an annealing furnace and hold it at a temperature range of 175-185℃ for 0.8-1.2 hours. After the holding period, air cool or furnace cool to room temperature. S2: Precision recrystallization stage: Transfer the strip treated in S1 to a protective atmosphere annealing furnace, heat it to 225-235℃ at a heating rate of no more than 50℃ / hour, and hold it at this temperature for 1.8-2.2 hours. After holding, control the cooling rate to no more than 30℃ / hour to cool the strip to below 100℃.

3. The low-temperature segmented annealing synergistic strengthening process for 5052-H34 state according to claim 2, characterized in that, In S1, the temperature is maintained at 180℃ for 1.0 hour.

4. The low-temperature segmented annealing synergistic strengthening process for 5052-H34 state according to claim 2, characterized in that, In S1 or S2, the protective gas is nitrogen, and the oxygen content in the annealing furnace is controlled to be ≤50ppm.

5. The low-temperature segmented annealing synergistic strengthening process for 5052-H34 state according to claim 2, characterized in that, In S2, the temperature is increased to 230°C at a heating rate of 35-45°C / hour, and then held at that temperature for 2.0 hours.

6. The low-temperature segmented annealing synergistic strengthening process for 5052-H34 state according to claim 2, characterized in that, In S2, the cooling rate is controlled at 20-25℃ / hour to cool the strip to below 100℃.

7. A low-temperature segmented annealing synergistic strengthening process for 5052-H34 state according to any one of claims 2-6, characterized in that, The method is applicable to the preparation of aluminum foil for tabs or structural components of soft-pack batteries with a thickness of ≤0.5mm.

8. A 5052-H34 aluminum alloy strip prepared by a low-temperature segmented annealing synergistic strengthening process for 5052-H34 state as described in any one of claims 2-6, wherein the aluminum alloy strip has a tensile strength of 260-290 MPa, a conductivity ≥35% IACS, and a grain size of ASTM 10-12.