Rolling process for improving electric conduction and heat conduction performance of aluminum foil for power battery

Abstract

The invention relates to the technical field of metal material processing, and discloses a rolling process for improving electric conduction and heat conduction performance of an aluminum foil for a power battery, which comprises the following steps: monitoring an acoustic emission signal generated by plastic deformation of the aluminum foil in real time when the aluminum foil is subjected to last-pass rolling; when a characteristic transition peak indicating dynamic recrystallization nucleation is monitored, a pulsed magnetic field is synchronously applied in the rolling direction of the aluminum foil, and then the rolled aluminum foil is rapidly cooled on line. The invention further discloses an integrated rolling system for realizing the process. According to the technical scheme, the oriented physical field is applied in the critical stage of dynamic recrystallization, so that the finally obtained aluminum foil forms a crystal texture with high preferred orientation in the rolling direction, the resistivity in the direction is directionally reduced, and the heat conductivity is improved. According to the integrated process, rolling and microstructure regulation and control are combined, independent off-line annealing treatment is not needed, the production period is shortened, and the energy consumption of unit products is reduced.

Description

Technical Field

[0001] This invention relates to the field of metal material processing technology, specifically a rolling process for improving the electrical and thermal conductivity of aluminum foil used in power batteries. Background Technology

[0002] Aluminum foil is used as the positive electrode current collector material in power lithium-ion batteries due to its conductivity, lightweight, and cost-effectiveness. This application scenario places continuous demands on the conductivity and thermal conductivity of aluminum foil to support the high-rate charge and discharge capabilities of the battery and to facilitate internal thermal management of the cell.

[0003] In existing technologies, the manufacturing process of aluminum foil for this purpose typically involves a multi-pass cold rolling process and a separate offline heat treatment process. During cold rolling, the aluminum undergoes intense plastic deformation to reach the desired thickness. However, this process accumulates a large number of crystal defects such as dislocations and vacancies, as well as significant processing stress within the material, leading to increased hardness and decreased ductility and conductivity. To eliminate these adverse effects, the rolled aluminum foil rolls require a separate finished product annealing treatment. This annealing process holds the aluminum foil at a specific temperature for several hours to induce internal recovery and recrystallization, thereby eliminating internal stress, reducing defect density, and restoring the material's ductility and conductivity.

[0004] However, this process route, which separates rolling and annealing, has inherent technical limitations. First, the two-step process is lengthy, requiring the transfer and storage of intermediate products, reducing production continuity and efficiency. Simultaneously, the prolonged operation of large annealing furnaces results in significant energy consumption. More critically, in traditional annealing, the nucleation and growth of recrystallized crystal nuclei are spontaneous and random processes, leading to a final aluminum foil microstructure composed of equiaxed grains with varying orientations. This random crystal orientation results in isotropic macroscopic physical properties of the aluminum foil, meaning its electrical and thermal conductivity is essentially consistent in all directions. For the specific application of battery current collectors, current and heat are primarily transported along the planar direction of the foil. The isotropic material properties are not optimized for this application requirement, and the randomly distributed grain boundaries become scattering sources for electron and phonon transport, limiting their transport efficiency along critical paths. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a rolling process for improving the electrical and thermal conductivity of aluminum foil used in power batteries. This process solves the problems of low production efficiency and high energy consumption caused by the inclusion of separate rolling and offline annealing processes in the manufacturing of aluminum foil for power batteries, and the inability of the final product to achieve optimal electrical and thermal conductivity in the critical transmission direction due to the random orientation of micro-grains.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a rolling process for improving the electrical and thermal conductivity of aluminum foil for power batteries, comprising the following steps: S1: Provide aluminum alloy blanks; S2: The aluminum alloy billet is cold rolled in the intermediate stage to obtain the intermediate billet; S3: Perform the final rolling pass on the intermediate billet; S4: During the final rolling process, monitor the acoustic emission signals generated inside the aluminum foil due to plastic deformation in real time; S5: When a preset characteristic transition peak is detected in the acoustic emission signal, a pulsed magnetic field is simultaneously applied in the rolling direction of the aluminum foil; S6: The aluminum foil is rapidly cooled by an online forced air cooling device.

[0007] The technical mechanism of this invention lies in the following: During the final high-speed rolling process with a large reduction rate, the aluminum foil generates processing heat and accumulates a large amount of strain energy due to intense plastic deformation, providing thermodynamic and kinetic conditions for dynamic recrystallization. Acoustic emission signals are a direct external characterization of the microscopic behaviors of dislocation movement and grain boundary slip within the material; their characteristic transition peaks indicate that the dynamic recrystallization nuclei are in the critical stage of large-scale nucleation. By capturing this critical stage and simultaneously applying a pulsed magnetic field, this invention utilizes the magnetization anisotropy of aluminum crystals to apply a preferred orientation torque to the newly formed nuclei in a high-mobility state, thereby inducing them to align along the magnetic field direction. The subsequent rapid cooling step suppresses further grain growth and orientation changes, stably preserving this preferred orientation texture in the final aluminum foil product.

[0008] In S3, the rolling speed of the final pass is 600–1500 m / min, and the single-pass reduction rate is over 90%.

[0009] In S5, the peak magnetic induction intensity of the pulsed magnetic field is 1.0–5.0 T, and the pulse duration is 10–500 μs.

[0010] The preset characteristic transition peak refers to a sudden signal peak in which the root mean square value of the acoustic emission signal has an amplitude that exceeds 1.5–3.0 times the dynamic baseline.

[0011] The root mean square value of the acoustic emission signal is calculated and compared by an FPGA-based real-time signal acquisition and processing card with a time window of 100μs.

[0012] In S5, the total delay time from the detection of the characteristic transition peak to the pulsed magnetic field strength reaching its peak value is controlled within 10 μs.

[0013] In S4, the acoustic emission signal is monitored by a piezoelectric acoustic emission sensor with a response frequency range of 100kHz–2.0MHz.

[0014] The aluminum alloy billet is made of high-purity aluminum alloy, wherein the mass percentage of aluminum is not less than 99.70%.

[0015] In S6, rapid cooling reduces the surface temperature of the aluminum foil to below 100°C within 1-2 seconds.

[0016] Once the process is completed in S6, no separate offline finished product annealing is required.

[0017] This invention provides a rolling process for improving the electrical and thermal conductivity of aluminum foil used in power batteries. It offers the following advantages: 1. This invention utilizes acoustic emission signals to synchronously trigger a pulsed magnetic field during the final rolling pass, enabling in-situ dynamic recrystallization and texture control. This is combined with a subsequent online rapid cooling step to solidify the microstructure. This integrated series of online processing steps eliminates the need for a separate, time-consuming offline annealing process, significantly simplifying the overall production flow, shortening the product manufacturing cycle, and reducing the equipment footprint and energy consumption associated with large annealing furnaces.

[0018] 2. This invention can actively construct a crystal texture with a specific advantageous orientation within aluminum foil. The mechanism lies in the fact that, during the critical stage of dynamic recrystallization nucleation identified by acoustic emission signals, a pulsed magnetic field applied along the rolling direction exerts a directional torque on the newly formed crystal nuclei. This results in the final aluminum foil having highly aligned internal grains macroscopically along the rolling direction—the primary direction of current and heat flow during battery operation—forming low-scattering electron and phonon transport channels, thereby achieving a lower resistivity and higher thermal conductivity in this direction compared to traditional randomly textured aluminum foil.

[0019] 3. By eliminating the traditional long-duration offline annealing process, this invention fundamentally avoids microstructural defects such as abnormal grain growth that may result from uneven temperature control or excessively long holding times during annealing. Furthermore, the rapid online cooling immediately following the texture control step quickly stabilizes the optimized, fine, and uniformly oriented grain structure, suppressing disordered evolution of the microstructure during cooling and ensuring highly consistent microstructure and performance across the entire roll length and width of the finished aluminum foil. Detailed Implementation

[0020] Example: Example 1 This embodiment provides a rolling process for improving the electrical and thermal conductivity of aluminum foil used in power batteries, including the following steps: Billet preparation: High-purity aluminum alloy ingots were selected, with the following chemical composition: aluminum content 99.75 wt%, silicon content 0.15 wt%, iron content 0.18 wt%, and other impurities meeting the standards. The aluminum ingots were melted and refined at 720℃, and then prepared into aluminum alloy billets with a thickness of 8.0 mm through a casting and rolling mill.

[0021] Intermediate cold rolling: The aluminum alloy billet is cold rolled in multiple passes to prepare an intermediate billet with a thickness of 0.20 mm.

[0022] Final pass synchronous dynamic texture control rolling: An intermediate billet with a thickness of 0.20 mm is fed into the final foil mill with an integrated synchronous control system. The rolling speed is set to 1000 m / min, the target finished product thickness is 12.0 μm, and the single-pass reduction rate is 94%.

[0023] During the rolling process, the acoustic emission monitoring system monitors the signal in real time. When a sudden signal peak with an amplitude exceeding 2.2 times the dynamic baseline is detected in the root mean square value of the acoustic emission signal, the synchronous control system immediately triggers the pulse electromagnetic system.

[0024] A pulsed electromagnetic system applies a pulsed magnetic field in the aluminum foil rolling direction, with a peak magnetic induction intensity of 3.0 T and a pulse duration of 250 μs. The total delay time from the detected signal peak to the magnetic field intensity reaching its peak is 5 μs.

[0025] Online cooling and finished product handling: The aluminum foil after the final rolling process is immediately passed through an online forced air cooling device, which reduces its surface temperature to below 100°C within 1.5 seconds.

[0026] The cooled aluminum foil is then wound up. The finished aluminum foil obtained in this embodiment does not require offline annealing.

[0027] Example 2 This embodiment provides a rolling process for improving the electrical and thermal conductivity of aluminum foil used in power batteries, including the following steps: Billet preparation: High-purity aluminum alloy ingots were selected, with the following chemical composition: aluminum content 99.70 wt%, silicon content 0.20 wt%, iron content 0.25 wt%, and other impurities meeting the standards. The aluminum ingots were melted and refined at 690℃, and then processed into aluminum alloy billets with a thickness of 6.0 mm using a casting and rolling mill.

[0028] Intermediate cold rolling: The aluminum alloy billet is cold rolled in multiple passes to prepare an intermediate billet with a thickness of 0.10 mm.

[0029] Final pass synchronous dynamic texture control rolling: An intermediate billet with a thickness of 0.10 mm is fed into the final foil mill with an integrated synchronous control system. The rolling speed is set to 600 m / min, the target finished product thickness is 8.0 μm, and the single-pass reduction rate is 92%.

[0030] During the rolling process, the acoustic emission monitoring system monitors the signal in real time. When a sudden signal peak with an amplitude exceeding 1.5 times the dynamic baseline is detected in the root mean square value of the acoustic emission signal, the synchronous control system immediately triggers the pulse electromagnetic system.

[0031] A pulsed electromagnetic system applies a pulsed magnetic field in the aluminum foil rolling direction, with a peak magnetic induction intensity of 1.0 T and a pulse duration of 10 μs. The total delay time from the detected signal peak to the magnetic field intensity reaching its peak is 10 μs.

[0032] Online cooling and finished product handling: The aluminum foil after the final rolling process is immediately passed through an online forced air cooling device, which reduces its surface temperature to below 100°C within 2 seconds.

[0033] The cooled aluminum foil is then wound up. The finished aluminum foil obtained in this embodiment does not require offline annealing.

[0034] Example 3 This embodiment provides a rolling process for improving the electrical and thermal conductivity of aluminum foil used in power batteries, including the following steps: Billet preparation: High-purity aluminum alloy ingots were selected, with the following chemical composition: aluminum content 99.85 wt%, silicon content 0.08 wt%, iron content 0.10 wt%, and other impurities meeting the standards. The aluminum ingots were melted and refined at 740℃, and then processed into aluminum alloy billets with a thickness of 10.0 mm using a casting and rolling mill.

[0035] Intermediate cold rolling: The aluminum alloy billet is cold rolled in multiple passes to prepare an intermediate billet with a thickness of 0.30 mm.

[0036] Final pass synchronous dynamic texture control rolling: An intermediate billet with a thickness of 0.30 mm is fed into the final foil mill with an integrated synchronous control system. The rolling speed is set to 1500 m / min, the target finished product thickness is 15.0 μm, and the single-pass reduction rate is 95%.

[0037] During the rolling process, the acoustic emission monitoring system monitors the signal in real time. When a sudden signal peak with an amplitude exceeding 3.0 times the dynamic baseline is detected in the root mean square value of the acoustic emission signal, the synchronous control system immediately triggers the pulse electromagnetic system.

[0038] A pulsed electromagnetic system applies a pulsed magnetic field in the aluminum foil rolling direction, with a peak magnetic induction intensity of 5.0 T and a pulse duration of 500 μs. The total delay time from the detected signal peak to the magnetic field intensity reaching its peak is 1 μs.

[0039] Online cooling and finished product handling: The aluminum foil after the final rolling process is immediately passed through an online forced air cooling device, which reduces its surface temperature to below 100°C within 1 second.

[0040] The cooled aluminum foil is then wound up. The finished aluminum foil obtained in this embodiment does not require offline annealing.

[0041] Comparative Example Comparative Example 1: Compared with Example 1, the difference is that no pulsed magnetic field is applied in the final pass synchronous dynamic texture control rolling step, while the rest are the same.

[0042] Comparative Example 2: Compared with Example 1, the difference is that the final rolling process adopts conventional cold rolling process, without acoustic emission signal monitoring and pulse magnetic field application, and after rolling, the obtained aluminum foil is subjected to independent offline finished product annealing treatment. The annealing process parameters are: annealing temperature 320°C, holding time 4 hours, and the rest are the same.

[0043] Comparative Example 3: Compared with Example 2, the difference is that no pulsed magnetic field is applied in the final pass synchronous dynamic texture control rolling step, while the rest are the same.

[0044] Comparative Example 4: Compared with Example 2, the difference is that in the final pass synchronous dynamic texture control rolling step, acoustic emission signal monitoring and synchronous triggering are not performed. Instead, during the entire final pass rolling, a pulsed magnetic field with the same parameters as in Example 2 is continuously applied at a fixed frequency of 1 kHz. All other parameters are the same.

[0045] Comparative Example 5: Compared with Example 3, the difference is that no pulsed magnetic field is applied in the final pass synchronous dynamic texture control rolling step, while the rest are the same.

[0046] Comparative Example 6: Compared with Example 3, the difference is that the final rolling process adopts conventional cold rolling process, without acoustic emission signal monitoring and pulse magnetic field application, and after rolling, the obtained aluminum foil is subjected to independent offline finished product annealing treatment. The annealing process parameters are: annealing temperature 350°C, holding time 2 hours, and the rest are the same.

[0047] Test Example 1: Comparative Test of Electrical Conductivity Experimental steps To determine and compare the electrical conductivity of the aluminum foil samples obtained in each example and the comparative example, the following steps were performed: Sample preparation: Samples measuring 50 mm × 10 mm were cut from the center width of each batch of aluminum foil rolls prepared in Examples 1-3 and Comparative Examples 1-6. For each batch, 5 samples were prepared along the rolling direction and 5 samples in the transverse direction perpendicular to the rolling direction.

[0048] Thickness measurement: Using a micrometer with an accuracy of 0.1 μm, the thickness of each sample was measured at 5 different locations, and the average value was calculated as the thickness (t) of the sample.

[0049] Resistivity Test: The sample was tested using an ST-2258C four-probe tester. The sample was placed on the insulation test platform. The probes of the four probes were positioned in the center of the sample. For samples in the RD direction, the linear alignment of the four probes was parallel to the length of the sample. For samples in the TD direction, the linear alignment of the four probes was parallel to the length of the sample. The constant DC current applied by the tester was set to 100.0 mA. The test was started, and the voltage (V) measured by the instrument was recorded. Each sample was measured three times, and the average voltage value was recorded. The resistivity (ρ) was calculated using the formula ρ=(V / I)×t×C, where C is the probe correction factor calibrated by the instrument.

[0050] Data processing: The resistivity values ​​measured from 5 samples in the same direction for each batch are averaged to obtain the final resistivity of that batch of samples in that direction.

[0051] The experimental data are shown in Table 1. Table 1: Test results of electrical conductivity of aluminum foil samples Experimental Results Analysis The test data in Table 1 show that the aluminum foil samples prepared by the processes of Examples 1, 2, and 3 exhibit significantly lower resistivity in the rolling direction (RD) than in the transverse direction (TD), demonstrating anisotropic characteristics. In contrast, the samples prepared by the processes of Comparative Examples 1-3 and 5-6 show essentially the same resistivity values ​​in both the RD and TD directions, without exhibiting significant anisotropy. This result reflects that the process steps included in this technical solution can directionally reduce the resistivity of the aluminum foil in the rolling direction.

[0052] The mechanism behind this directional performance change lies in a key step introduced during the final rolling pass. At the critical stage where intense plastic deformation induces dynamic recrystallization within the material, a pulsed magnetic field applied along the rolling direction exerts an effective preferred orientation torque on the newly formed, highly active nuclei in the aluminum crystals. This torque induces the nuclei to align and grow along the magnetic field direction (i.e., the rolling direction), ultimately forming a dominant texture along the rolling direction on a macroscopic scale. This highly ordered microstructure reduces grain boundary scattering encountered by electrons during transport along the rolling direction, thereby lowering the resistivity in that direction. In contrast, the samples in the comparative examples without the applied pulsed magnetic field (such as Comparative Examples 1, 3, and 5) lack this directional torque, resulting in a spontaneous and disordered dynamic recrystallization process, ultimately forming randomly oriented equiaxed grains, thus exhibiting isotropic electrical conductivity.

[0053] Comparing the data from Example 2 and Comparative Example 4 further confirms the necessity of synchronous triggering of the acoustic emission signal. Comparative Example 4, which continuously applied a pulsed magnetic field throughout the rolling process, showed a decrease in resistivity along the RD direction, but the reduction was less significant than that of Example 2, which employed synchronous triggering. This demonstrates that precisely limiting the application window of the pulsed magnetic field to the instant of large-scale dynamic recrystallization nucleation indicated by the acoustic emission signal allows external energy to act more effectively on the nucleus orientation control process, thereby achieving a more significant texture optimization effect and improved orientation performance.

[0054] Test Example 2: Microtexture Analysis Experimental steps To determine and compare the microtexture of the aluminum foil samples obtained in each example and the comparative example, the following steps were performed: Sample preparation: 10 mm × 10 mm samples were cut from each batch of aluminum foil prepared in Examples 1-3 and Comparative Examples 1-6. The samples were embedded in conductive resin, exposing the rolled surface (RD-TD plane) for observation.

[0055] Mechanical grinding and polishing: The surface of the mounted sample was successively ground using silicon carbide sandpaper with grits of 400, 800, 1200, and 2000 mesh. Subsequently, it was finely polished using diamond polishing paste with a particle size of 3μm and 1μm.

[0056] Final polishing: To eliminate the residual stress layer on the surface, the sample was finally polished using a vibratory polishing machine. The polishing solution was a suspension containing silica particles with a particle size of 50 nm, and the polishing time was 45 minutes.

[0057] EBSD Data Acquisition: The prepared sample was placed in a field emission scanning electron microscope equipped with an electron backscatter diffraction (EBSD) detector. The microscope's accelerating voltage was set to 20 kV and the working distance to 18 mm. The sample stage was tilted at 70° to achieve geometric focusing of the electron beam and the EBSD detector. A 100 μm × 100 μm area was selected in the central region of each sample for scanning, with a scan step size of 0.2 μm.

[0058] Data Processing: The acquired Kikuchi diffraction patterns were calibrated and analyzed using dedicated EBSD data analysis software to generate orientation imaging (OIM). The average grain size of each sample was calculated using the software. {111} pole figures were calculated and generated to quantitatively analyze the intensity of the main texture components along the rolling direction (RD), with the intensity expressed in "multiple random distribution" (mrd).

[0059] The experimental data are shown in Table 2. Table 2: Microstructure Analysis Results of Aluminum Foil Samples Experimental Results Analysis The test data in Table 2 reveal the influence of different processes on the final microstructure of the aluminum foil. The samples prepared using processes 1, 2, and 3 all exhibited significantly high main texture strength in the rolling direction, while the texture strength values ​​of all comparative samples remained at a low level. Furthermore, the data show that the example samples and some comparative samples (Comparative Examples 1, 3, 4, and 5) achieved fine grain sizes, while the comparative samples processed using conventional annealing (Comparative Examples 2 and 6) exhibited coarse grains.

[0060] These differences in microstructure stem directly from the physical processes in the final rolling pass. The core of this technical solution lies in using acoustic emission signals to identify the precise time window for large-scale nucleation during dynamic recrystallization, and simultaneously applying a directional pulsed magnetic field at this moment. Due to the anisotropic magnetization of aluminum crystals, this magnetic field can exert a torque on the newly formed, high-mobility nuclei, causing their specific crystal orientation to be parallel to the magnetic field direction. Therefore, the orientation of the nuclei is no longer random, but is induced to preferentially align along the rolling direction and is fixed by the subsequent rapid cooling step, ultimately forming a strong texture along the rolling direction in the finished aluminum foil. Comparative Examples 1, 3, and 5, although also undergoing a dynamic recrystallization process, lack the intervention of this directional physical field of a magnetic field, resulting in isotropic nuclei orientations and thus failing to form an effective preferential texture.

[0061] The comparison between Comparative Example 4 and Example 2 further confirms the decisive role of synchronous control. Comparative Example 4, which continuously applied a pulsed magnetic field throughout the rolling process, also produced a certain texture-inducing effect, but its main texture intensity (4.8 mrd) was far lower than that of Example 2 (9.4 mrd). This indicates that precisely concentrating energy input in the critical stage of dynamic recrystallization nucleation is more efficient at controlling crystal orientation than continuously applying energy in the non-critical stage. This comparative result demonstrates that the synchronous triggering mechanism based on acoustic emission signals is a key technical step in constructing highly ordered microstructures.

[0062] Test Example 3: Thermal Conductivity Comparison Test Experimental steps To determine and compare the thermal conductivity of the aluminum foil samples obtained in each example and the comparative example, the following steps were performed: Sample preparation: Rectangular specimens with dimensions of 25.4 mm × 5 mm were cut from each batch of aluminum foil rolls prepared in Examples 1-3 and Comparative Examples 1-6 for in-plane thermal conductivity testing. For each batch, three specimens were prepared along the rolling direction (RD) and three in the transverse direction perpendicular to the rolling direction (TD).

[0063] Surface treatment: To ensure effective absorption of laser energy and uniform emission of thermal radiation during the test, a graphite coating with a thickness of about 5 μm was applied to both sides of all samples using a spraying method.

[0064] Parameter measurements: The specific heat capacity (Cp) of each batch of samples was measured using a differential scanning calorimeter (DSC). The density of each batch of samples was measured using the Archimedes method.

[0065] Thermal diffusivity test: A laser flare thermal analyzer (LFA) was used, equipped with an in-plane test sample holder. The prepared sample was placed in the sample holder and then placed in the test chamber, which was purged with argon gas as a protective atmosphere. The test temperature was set to 25°C. The test program was started, and a pulsed laser beam irradiated one end of the sample. An infrared detector located at the other end of the sample recorded the surface temperature change curve over time. Based on the temperature response curve, the instrument's built-in software calculated the thermal diffusivity (α) of the sample using the Parker model.

[0066] Thermal conductivity calculation and data processing: The thermal conductivity (λ) of each sample is calculated according to the formula λ=α×ρdensity×Cp. The thermal conductivity values ​​measured from three samples in the same direction for each batch are averaged to obtain the final thermal conductivity of the batch of samples in that direction.

[0067] The experimental data are shown in Table 3. Table 3: Test results of thermal conductivity of aluminum foil samples Experimental Results Analysis The test data in Table 3 show that the aluminum foil samples prepared using the processes of Examples 1, 2, and 3 all exhibit higher thermal conductivity values ​​in the rolling direction (RD) than in the transverse direction (TD), demonstrating clear thermal anisotropy. In contrast, the samples of Comparative Examples 1-3 and 5-6 show no systematic difference in thermal conductivity values ​​in the RD and TD directions. Furthermore, the absolute value of the thermal conductivity of the Example samples in the RD direction is higher than that of all comparative example samples in any direction. This phenomenon is consistent with the conductivity anisotropy observed in Test Example 1.

[0068] Heat transfer in metallic materials primarily occurs through two types of charge carriers: free electrons and lattice vibrations (phonons). Grain boundaries are one of the main scattering sources hindering the free movement of these charge carriers. In this technical solution, during the final rolling pass, a pulsed magnetic field is applied simultaneously during the dynamic recrystallization nucleation stage. Utilizing the magnetization anisotropy of aluminum crystals, this induces the preferential alignment of newly formed nuclei along the rolling direction. The strong texture created by this process results in grain boundaries along the rolling direction being predominantly small-angle grain boundaries with high lattice matching, significantly reducing the scattering probability of electrons and phonons during transmission along this direction and forming a low-thermal-resistance conduction path. In contrast, the comparative samples, lacking magnetic field orientation induction (e.g., Comparative Examples 1, 3, 5) or undergoing conventional high-temperature annealing (e.g., Comparative Examples 2, 6), exhibit random grain orientations, leading to equal scattering of heat in all directions, resulting in isotropic thermal conductivity.

[0069] Comparing the test results of Example 2 and Comparative Example 4 reveals the technical effect of the synchronous control step. Comparative Example 4, which continuously applied a pulsed magnetic field throughout the rolling process, exhibited a higher thermal conductivity in the RD direction (215.7 W / (m·K)) than Comparative Example 3 (204.3 W / (m·K)) without a magnetic field, but lower than Example 2 (221.8 W / (m·K)) which used an acoustic emission signal to synchronously trigger the magnetic field. This difference indicates that precisely applying magnetic field energy within the specific time window for large-scale dynamic recrystallization nucleation determined by the acoustic emission signal is more effective in constructing ordered microstructures than continuously or imprecisely applying energy throughout the entire process. This confirms a direct physical correlation between the timing accuracy of the process and the directional thermal conductivity of the final material.

[0070] Test Example 4: Mechanical Property Test Experimental steps To determine and compare the macroscopic mechanical properties of the aluminum foil samples obtained in each example and the comparative example, the following steps were performed: Sample preparation: Dumbbell-shaped tensile specimens were cut along the rolling direction (RD) from each batch of aluminum foil rolls prepared in Examples 1-3 and Comparative Examples 1-6. The gauge length of the specimen was 12.5 mm wide and 50 mm long. Five valid specimens were prepared from each batch.

[0071] Parameter measurement: Using a micrometer with an accuracy of 0.1 μm, the width and thickness of the gauge length of each sample were measured. Each parameter was measured 3 times and the average value was taken to calculate the original cross-sectional area (A0) of the sample.

[0072] Tensile test: The test was conducted using an electronic universal testing machine equipped with a 1kN load cell. The specimen was clamped at both ends in the machine's fixtures, ensuring the long axis of the specimen was aligned with the tensile axis. The tensile rate of the testing machine was set to 2 mm / min. The test was started, and the machine applied a constant load to the specimen until it fractured. Load (F) and displacement (ΔL) data were recorded simultaneously.

[0073] Data Processing: The maximum load (Fmax) is read from the load-displacement curve. The tensile strength (σb) of the material is calculated using the formula σb = Fmax / A0. The two parts of the fractured specimen are closely aligned, and the gauge length (Lu) is measured. The elongation at break (δ) of the material is calculated using the formula δ = [(Lu - L0) / L0] × 100%, where L0 is the original gauge length. The tensile strength and elongation at break measured from the five specimens in each batch are averaged to obtain the final mechanical property index for that batch of samples.

[0074] The experimental data are shown in Table 4. Table 4: Test Results of Mechanical Properties of Aluminum Foil Samples Experimental Results Analysis Table 4 shows the test data, revealing the influence of different processes on the mechanical properties of aluminum foil. The samples prepared using processes in Examples 1, 2, and 3 exhibited tensile strengths ranging from 139 to 155 MPa and elongation after fracture ranging from 4.1% to 5.3%. The samples in Comparative Examples 2 and 6 (after conventional annealing) showed a combination of low strength (below 95 MPa) and high elongation (above 18%). In contrast, the samples in Comparative Examples 1, 3, and 5 (rolled without any heat treatment or magnetic field treatment) showed a combination of high strength (above 180 MPa) and low elongation (below 1.5%).

[0075] The mechanical properties of a sample are directly determined by its final microstructure. In this technical solution, dynamic recrystallization is induced online during the final rolling pass, followed by a magnetic field and rapid cooling. The resulting microstructure consists of fine, recrystallized equiaxed grains, as shown in the data from Test Example 2. According to the Hall-Page relation, fine grains mean more grain boundaries per unit volume. These grain boundaries effectively hinder dislocation movement, thus giving the material higher strength. Simultaneously, because the microstructure has undergone recrystallization, the significant work hardening accumulated during rolling is eliminated, thus the material retains a certain degree of plastic deformation capacity, i.e., exhibiting a certain elongation after fracture.

[0076] In contrast, the traditional offline annealing process used in Comparative Examples 2 and 6, with its prolonged high-temperature treatment, resulted in significant grain growth and the formation of a coarse-grained structure. The coarse grains reduce the resistance to dislocation movement, macroscopically manifesting as lower yield strength and tensile strength, but fully recovering plastic deformation capacity, resulting in very high elongation after fracture. In contrast, the samples in Comparative Examples 1, 3, and 5 exhibit a typical rolled microstructure, filled with high-density dislocations and deformation bands, indicating severe work hardening. This structure significantly hinders subsequent plastic deformation, resulting in the highest tensile strength but almost complete loss of plasticity and extremely low elongation after fracture. This technical solution, through online microstructure control, achieves a microstructure composed of fine recrystallized grains—different from the two traditional states—within a single process, thus enabling the final product to achieve a specific combination of strength and elongation.

[0077] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A rolling process for improving the electrical and thermal conductivity of aluminum foil used in power batteries, characterized in that, Includes the following steps: S1: Provide aluminum alloy blanks; S2: The aluminum alloy billet is subjected to intermediate cold rolling to obtain an intermediate billet; S3: Perform the final rolling pass on the intermediate billet; S4: During the final rolling process, the acoustic emission signal generated inside the aluminum foil due to plastic deformation is monitored in real time; S5: When a preset characteristic transition peak is detected in the acoustic emission signal, a pulsed magnetic field is simultaneously applied in the rolling direction of the aluminum foil; S6: The aluminum foil is rapidly cooled by an online forced air cooling device.

2. The process according to claim 1, characterized in that, In S3, the rolling speed of the final rolling pass is 600–1500 m / min, and the single-pass reduction rate is above 90%.

3. The process according to claim 1, characterized in that, In S5, the peak magnetic induction intensity of the pulsed magnetic field is 1.0–5.0T, and the pulse duration is 10–500μs.

4. The process according to claim 1, characterized in that, The preset characteristic transition peak refers to a sudden signal peak in which the root mean square value of the acoustic emission signal has an amplitude exceeding 1.5–3.0 times the dynamic baseline.

5. The process according to claim 4, characterized in that, The root mean square value of the acoustic emission signal is calculated and compared by an FPGA-based real-time signal acquisition and processing card with a time window of 100μs.

6. The process according to claim 1, characterized in that, In S5, the total delay time from the detection of the characteristic transition peak to the pulse magnetic field strength reaching its peak value is controlled within 10 μs.

7. The process according to claim 1, characterized in that, In S4, the acoustic emission signal is monitored by a piezoelectric acoustic emission sensor with a response frequency range of 100kHz–2.0MHz.

8. The process according to claim 1, characterized in that, The aluminum alloy billet is made of high-purity aluminum alloy, wherein the mass percentage content of aluminum is not less than 99.70%.

9. The process according to claim 1, characterized in that, In S6, the rapid cooling is to reduce the surface temperature of the aluminum foil to below 100°C within 1-2 seconds.

10. The process according to claim 1, characterized in that, After the process is completed in step S6, no separate offline finished product annealing process is required.

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