Aluminum alloy foil with high resistivity and preparation method thereof

Abstract

The present invention provides an aluminum alloy foil with high resistivity and a preparation method thereof. The components of the aluminum alloy foil include: Mn: 1.7-1.9%, Cr: 0.2-0.5%, Ti: 0.1-0.3%, Fe: 0.1-0.2%, Si: 0.5-1.5%, and the balance is Al and inevitable impurities; the preparation method includes: mixing, smelting, refining, heat preservation, and casting and rolling with specific parameters of the raw materials in sequence to obtain a cast-rolled plate, and then cold rolling and annealing in sequence, controlling the single-pass deformation of the cold rolling to be ≤30%, and foil rolling the obtained heat-treated plate with a single-pass deformation of ≤25% to obtain the aluminum alloy foil. The present invention increases the solid solubility of the elements by adding a specific proportion of metal elements, adopts a casting and rolling process with specific parameters, and combines a single-pass small cold rolling and foil rolling deformation to reduce the number of heat treatments, so as to obtain an aluminum alloy foil with high resistivity and good wettability, which is suitable for resistance heating elements.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy foil and processing thereof, and in particular to an aluminum alloy foil with high resistivity and a preparation method thereof. Background Art

[0002] As the core component of new energy vehicles, power batteries have a decisive influence on vehicle performance. Temperature is one of the key factors affecting the performance of lithium batteries, and the ideal operating temperature range is 15 to 40°C. The working principle of lithium-ion batteries is based on the movement of lithium ions in liquid electrolytes and their deintercalation in positive and negative electrode materials. Under low temperature conditions, the lithium intercalation reaction rate of the active material on the electrode surface slows down, and the lithium ion concentration inside the active material decreases, which will cause the battery's equilibrium potential to drop, the internal resistance to increase, and the discharge capacity to decrease. Under extremely low temperature conditions, the electrolyte may even freeze, causing the battery to be unable to discharge, seriously affecting the power output and range of electric vehicles. In extremely cold environments, the safety of battery use may also be threatened.

[0003] To overcome these problems, new energy vehicles use battery temperature control technology to keep the battery within the optimal operating temperature range. This usually involves installing temperature control equipment in the battery pack, and the core of the temperature control equipment is the heating element. Currently, common heating elements include variable resistance heating elements and constant resistance heating elements, the latter of which are usually heating films composed of metal heating wires.

[0004] Traditional metal heating wires are usually made of steel foil, but this material needs to be processed by chemical etching, which is not only cumbersome but also pollutes the environment. In addition, steel foil has a high hardness and is not suitable for die-cutting. If aluminum foil is used instead, physical cutting can be used, which is not only efficient but also environmentally friendly. However, the resistivity of conventional aluminum alloy foil on the market is about 3.5μΩ·cm, which is far from the resistivity of metal wire required for resistance heating elements (at least 7μΩ·cm).

[0005] Therefore, in order to meet the demand for resistive heating elements, it is necessary to develop aluminum foil products with higher resistivity to improve the performance of heating elements, thereby improving the battery performance and safety of new energy vehicles in low temperature environments. Summary of the invention

[0006] The main purpose of the present invention is to provide an aluminum alloy foil with high resistivity and a preparation method thereof, so as to solve the problem in the prior art that the aluminum foil has low resistivity and cannot be used for metal heating wires of battery packs.

[0007] In order to achieve the above object, according to one aspect of the present invention, a method for preparing an aluminum alloy foil with high resistivity is provided, wherein the resistivity of the aluminum alloy foil is 8-12 μΩ·cm, and the components of the aluminum alloy foil include, by weight percentage, Mn: 1.7-1.9%, Cr: 0.2-0.5%, Ti: 0.1-0.3%, Fe: 0.1-0.2%, Si: 0.5-1.5%, the total amount of unavoidable impurities is ≤0.2%, and the balance is Al; the preparation method comprises the following steps: step S1, according to the aluminum The composition ratio of the alloy foil is that the raw materials are mixed, smelted, refined, heat-insulated and cast-rolled in sequence to obtain a cast-rolled plate; wherein the casting and rolling temperature is 730-780°C, the casting and rolling speed is 600-850 mm / min, the cooling rate is 100-200°C / h, and the thickness of the cast-rolled plate is 6-8 mm; step S2, cold rolling and annealing the cast-rolled plate in sequence, the deformation amount of a single cold rolling is ≤30%, and a heat-treated plate is obtained; step S3, foil rolling the heat-treated plate, the deformation amount of a single foil rolling is ≤25%, and an aluminum alloy foil is obtained.

[0008] Furthermore, in step S1, the smelting temperature is 800-850°C; and / or, the number of refining is 2-3 times, the temperature of a single refining is 770-800°C, and the standing time is 20-30 min; and / or, the insulation temperature is 750-790°C, and the time is 2-5 h.

[0009] Furthermore, in step S2, the annealing temperature is 200-290°C, the heating rate is 40-70°C / h, and the holding time is 1-5h.

[0010] Furthermore, in step S2, the thickness of the heat-treated plate is 0.2-0.5 mm.

[0011] Furthermore, in step S3, the thickness of the aluminum alloy foil is 0.04-0.06 mm.

[0012] Furthermore, step S3 also includes a step of high-temperature degreasing after foil rolling; preferably, the temperature of high-temperature degreasing is 100-200° C., the heating rate is 10-70° C. / h, and the insulation time is 10-200h.

[0013] Furthermore, in terms of weight percentage, the sum of the weight percentages of Cr, Ti and Fe in the composition is ≤0.6%.

[0014] Furthermore, in terms of weight percentage, the sum of the weight percentages of Cr, Ti and Mn in the composition is 1.9-2.5%; and / or the sum of the weight percentages of Cr, Ti, Fe and Mn is 2.2-2.5%.

[0015] Furthermore, the alloy phase of the aluminum alloy foil includes an AlFeMnSi(CrTi) phase, the area percentage of the AlFeMnSi(CrTi) phase in the matrix of the aluminum alloy foil is 0.3-3%, and the size is ≤1um; and / or the hardness of the aluminum alloy foil is ≥70HV, and / or the wetting tension is ≥40 dynes.

[0016] According to another aspect of the present invention, there is provided an aluminum alloy foil with high resistivity, which is obtained using the above preparation method.

[0017] The present invention significantly improves the resistivity of aluminum alloy foil through the design of specific alloy components and the optimization of the process flow. The precise ratio of elements such as Mn, Cr, Ti, Fe, Si, etc., combined with the high cooling rate of the casting and rolling process, effectively increases the content of solid solution elements and enhances the resistance characteristics. Casting and rolling parameter control, such as temperature, speed and cooling rate, ensures the uniformity and stability of the material structure. The single-pass small deformation strategy of cold rolling and foil rolling, combined with annealing treatment, avoids excessive work hardening and reduces the number of heat treatments, thereby inhibiting the precipitation of effective elements and maintaining the high resistivity of the foil. The method of the present invention not only effectively solves the problem of insufficient resistivity of traditional aluminum alloy foil, but also ensures the processing performance and surface quality of the material.

[0018] When the high-resistivity aluminum alloy foil of the present invention is used as the metal heating wire in the battery pack heating element, it can meet the resistivity requirements of the metal heating wire and has good wetting properties. When used for processing and manufacturing battery packs and heating elements, it can be effectively combined with other components, thereby facilitating the manufacture of battery packs and heating elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0020] Figure 1 The SEM image of the microstructure of the aluminum alloy foil of Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0022] As described in the background of the present invention, there is a problem in the prior art that the resistivity of aluminum foil is low and thus it cannot be used for the metal heating wire of the battery pack. In order to solve the above problem, in a typical embodiment of the present invention, a method for preparing an aluminum alloy foil is provided. The resistivity of the aluminum alloy foil is 8 to 12 μΩ·cm. The components of the aluminum alloy foil include, by weight percentage: Mn: 1.7 to 1.9%, Cr: 0.2 to 0.5%, Ti: 0.1 to 0.3%, Fe: 0.1 to 0.2%, Si: 0.5 to 1.5%, the total amount of unavoidable impurities is ≤ 0.2%, and the balance is Al; the preparation method comprises the following steps: Step S1, according to the aluminum The composition ratio of the alloy foil is that the raw materials are mixed, smelted, refined, heat-insulated and cast-rolled in sequence to obtain a cast-rolled plate; wherein the casting and rolling temperature is 730-780°C, the casting and rolling speed is 600-850 mm / min, the cooling rate is 100-200°C / h, and the thickness of the cast-rolled plate is 6-8 mm; step S2, cold rolling and annealing the cast-rolled plate in sequence, the deformation amount of a single cold rolling is ≤30%, and a heat-treated plate is obtained; step S3, foil rolling the heat-treated plate, the deformation amount of a single foil rolling is ≤25%, and an aluminum alloy foil is obtained.

[0023] In the raw materials of the aluminum alloy foil of the present application, Mn, Cr and Ti are specially added because the inventor unexpectedly found in a large number of experiments that the addition of Mn, Cr and Ti can form a solid solution, and the solid solubility of the element has a direct effect on the resistivity. When the content of Mn is 1.7-1.9%, the content of Cr is 0.2-0.5%, and the content of Ti is 0.1-0.3%, the solid solubility of these three elements in the matrix is ​​high, which can significantly improve the resistivity of the alloy.

[0024] It should be noted that in the present application, the Ti element is not used as a refiner, but is added as an alloying element. Its main purpose is to reduce the precipitation of Ti to form the Al3Ti second phase. On the one hand, it can reduce the refinement effect of the Ti element, and on the other hand, it can increase the solid solubility of the Ti element, thereby increasing the resistivity of the alloy.

[0025] In addition, the foil raw material of the present application also includes Fe, and the addition of Fe is beneficial to improving the resistivity of the finished aluminum foil.

[0026] However, the inventors found during the experiment that when the content of any one or more elements among Mn, Cr, Ti and Fe is too high, a coarse second phase AlFeMn (CrTi) phase is easily formed, which is easy to become a hard point and cause the strip to break during the foil rolling process, and may even lead to the inability to produce continuously or a low yield. If its content is too low, it may cause the resistivity of the finished aluminum foil to decrease. After a large number of experimental studies, the inventors optimized the content of the above components and limited the content of Mn, Cr, Ti and Fe to the above specific range. The aluminum foil under the above conditions has a high resistivity and a high yield, which can meet the resistivity requirements of the metal heating wire.

[0027] Moreover, Si element is also added in the present application. The addition of Si can effectively improve the fluidity of the alloy, effectively inhibit the insufficient shrinkage of the alloy and cause a large number of loose and shrinkage defects in the cast plate, thereby reducing the pinhole defects of the finished aluminum foil. However, if the Si content is too high, it may increase the number and size of the second phase, thereby inducing the risk of breaking the aluminum foil during the production process. If its content is too low, it may cause the alloy to have poor fluidity, easily increase the risk of looseness and shrinkage, and further may affect the strength, processability and yield of the foil. Therefore, the present application limits the Si content to the above-mentioned specific range.

[0028] In addition, in the preparation method of the present application, the raw materials with the above-mentioned composition ratio are first mixed, smelted, refined, and heat-insulated to fully melt the elements and effectively remove the gas and impurities in the melt. It should be noted that in the raw materials of the present application, the Ti element is mixed with other components and added together, rather than added separately. This operation is because the Ti element in the present application is not used as a refiner, but as an alloying element. Its main purpose is to reduce the precipitation of the second phase of Al3Ti formed by Ti and Al. On the one hand, it can reduce the refinement effect of the Ti element and avoid the occurrence of fine grain strengthening leading to excessive hardness; on the other hand, it can increase the solid solubility of the Ti element, thereby increasing the resistivity of the alloy.

[0029] The melt is then cast and rolled to obtain a cast-rolled plate. Compared with other casting processes, on the one hand, the cooling rate of cast-rolling is fast, which can make each element fully dissolved, thus helping to improve the resistivity of the alloy. On the other hand, the cast-rolling process can mass-produce foils with high production efficiency. After a large number of experiments, the inventors have obtained cast-rolling process parameters suitable for the specific composition alloy of this application. The casting temperature is 730-780°C, the casting speed is 600-850mm / min, the cooling water temperature is 20-40°C, the cooling rate of cast-rolling is 100-200°C / h, and the thickness of the cast-rolled plate is 6-8mm; the casting method is a double-roll casting method.

[0030] Under the above conditions, the solid solubility of each element in the alloy is high, which is conducive to improving the resistivity of the alloy. Moreover, the internal stress and cracks on the surface of the foil are small, which is conducive to improving the hardness and wettability of the alloy. However, if the temperature of the casting is too low, it will cause the cast-rolled plate to break, resulting in a large amount of looseness inside the foil. If the temperature is too high, it will cause the cooling rate to be too slow, which will easily make the resistivity fail to meet the requirements, and will also cause a large number of pore defects inside the cast-rolled plate. If the speed of the casting is too slow, the resistivity may not meet the index requirements. If the casting speed is too fast, it is easy to cause the cast-rolled plate to break. In addition, if the cooling water temperature is too low, the cooling rate may be too fast, resulting in a broken belt problem. If the cooling water temperature is too high, the cooling rate may be too slow. If the cooling rate of the casting is too low, the solid solubility of the effective elements may be reduced, resulting in the resistivity failing to meet the index requirements. If the cooling rate of the casting is too high, the production efficiency and yield rate may be reduced, and the problem of uneven organization may occur. In addition, the current production equipment conditions limit the further improvement of the cooling rate.

[0031] Next, the cast-rolled plate is cold-rolled and annealed in sequence to obtain a heat-treated plate. It should be noted that in the prior art, intermediate annealing is usually performed during the cold rolling process. The inventor of the present application, in consideration of reducing the amount of effective element precipitation during the cold rolling process, specifically limits annealing to after cold rolling to increase the resistivity of the foil. It should be noted that in step S2, the deformation of a single pass of cold rolling is ≤30%. If the deformation of a single pass of cold rolling is too large, severe work hardening will occur, resulting in increased difficulty when continuing to roll, and long-term and multiple heat treatments are required to soften the material. However, the heat treatment process may cause the precipitation of effective elements, which reduces the resistivity of the foil. In order to avoid this situation, the present application specifically controls the deformation of a single pass of foil rolling within a specific range to reduce work hardening, thereby effectively reducing the number of heat treatment softening, preventing the precipitation of effective elements, and thus significantly improving the resistivity of the finished product.

[0032] Finally, the heat-treated plate is foil rolled to obtain an aluminum alloy foil of a specific size and a smooth surface. Based on similar reasons, in order to inhibit the precipitation of effective elements, the present application also specifically limits the deformation of the foil rolling to ≤ 25% per pass, so as to reduce the number of softening times during heat treatment and improve the resistivity of the finished product.

[0033] The present invention significantly improves the resistivity of aluminum alloy foil through the design of specific alloy components and the optimization of the process flow. The precise ratio of elements such as Mn, Cr, Ti, Fe, Si, etc., combined with the high cooling rate of the casting and rolling process, effectively increases the content of solid solution elements and enhances the resistance characteristics. Casting and rolling parameter control, such as temperature, speed and cooling rate, ensures the uniformity and stability of the material structure. The single-pass small deformation strategy of cold rolling and foil rolling, combined with annealing treatment, avoids excessive work hardening and reduces the number of heat treatments, thereby inhibiting the precipitation of effective elements and maintaining the high resistivity of the foil (such as 8 to 12 μΩ·cm).

[0034] In addition, the preparation method of the present application can make the aluminum alloy foil of specific composition have suitable hardness. When used for processing and manufacturing heating elements of products such as battery packs, physical cutting can be adopted, which has low processing difficulty, high production efficiency and environmental protection. On the other hand, the preparation method of the present application can make the aluminum alloy foil have good wetting properties. When used for processing and manufacturing battery packs and heating elements, it can be effectively combined with other components, which is convenient for the production of battery packs and heating elements.

[0035] In a preferred embodiment, in step S1, the melting temperature is 800-850°C, preferably, the melting time is 1-5h; and / or, the number of refining is 2-3 times, the temperature of a single refining is 770-800°C, and the standing time is 20-30min; and / or, the insulation temperature is 750-790°C, and the time is 2-5h. Under the above conditions, the alloy components can be melted more fully, the phase change is more complete, the resistivity of the alloy is higher, the hardness is more suitable, and the wettability is better.

[0036] In order to further effectively inhibit the precipitation of effective elements and further improve the resistivity of aluminum foil, in a preferred embodiment, the annealing temperature is 200-290° C., the heating rate is 40-70° C. / h, and the holding time is 1-5 h.

[0037] The inventors have particularly considered that if the thickness of the plate is too thin during annealing, the resistivity may drop too quickly; and annealing under thicker plate conditions may lead to an increase in the number of annealing times. In order to make the alloy have both higher resistivity and fewer annealing times, in a preferred embodiment, the thickness of the heat-treated plate is 0.2 to 0.5 mm.

[0038] In a preferred embodiment, the thickness of the aluminum alloy foil is 0.04-0.06 mm.

[0039] On the basis of not losing the high resistivity of the aluminum foil, in order to obtain good surface wettability of the foil, in a preferred embodiment, step S3 also includes a step of high-temperature degreasing after the foil is rolled. Preferably, the temperature of the high-temperature degreasing is 100-200°C, the heating rate is 10-70°C / h, and the insulation time is 10-200h. In a preferred embodiment, step S3 also includes a step of cleaning and degreasing after the foil is rolled. The cleaning and degreasing includes the steps of cleaning, rinsing and drying in sequence; preferably, an alkaline solution with a pH of 7-8 is used for cleaning and degreasing; preferably, water is used for rinsing; preferably, the drying temperature is 100-120°C and the time is 30-120s. Under the above conditions, the cost of degreasing is lower, the efficiency is higher, the uniformity of the foil is better, the wetting performance of the foil surface can be quickly improved, and the subsequent processing and use of the foil is convenient.

[0040] In order to further increase the solid solubility of Mn, Cr and Ti, inhibit the formation of coarse phases, and thus further improve the resistivity of the alloy, in a preferred embodiment, the sum of the weight percentages of Cr, Ti and Fe in the composition is ≤0.6%.

[0041] Based on similar reasons, in a preferred embodiment, in the composition, the sum of the weight percentages of Cr, Ti and Mn is 1.9-2.5%; and / or the sum of the weight percentages of Cr, Ti, Fe and Mn is 2.2-2.5%.

[0042] As mentioned above, the present application optimizes the element ratio and preparation process of the aluminum alloy foil so that each element can be effectively dissolved, thereby improving the resistivity of the alloy and reducing pinhole defects. In addition, the aluminum alloy foil of the present application with a specific composition also has suitable hardness and wettability. Specifically, in a preferred embodiment, the alloy phase of the aluminum alloy foil includes an AlFeMnSi (CrTi) phase, and the area percentage of the AlFeMnSi (CrTi) phase in the matrix of the aluminum alloy foil is 0.3 to 3%, and the size is ≤1um; and / or, the hardness of the aluminum alloy foil is ≥70HV, and / or, the wetting tension is ≥40 dynes, and / or, the maximum size of the pinholes in the aluminum alloy foil is <0.2mm, and the pinhole rate is <1 hole / m 2 The alloy prepared by the preparation method of the present application has high resistivity, avoids the band breaking phenomenon caused by excessive and large AlFeMnSi (CrTi) as hard points, and has appropriate hardness, good strength and machinability.

[0043] In another typical embodiment of the present invention, a high resistivity aluminum alloy foil is provided, which is obtained by the above preparation method. As mentioned above, by optimizing the element ratio and preparation process of the aluminum alloy foil, the resistivity of the aluminum alloy foil is effectively improved, and the wettability is good and the surface quality is high.

[0044] It should be noted that due to the particularity of the alloy field and the limitations of existing testing and characterization methods, it is difficult to conduct a comprehensive quantitative characterization of the complex microstructure of the aluminum alloy foil obtained above, but experiments show that the aluminum alloy foil obtained in this application has higher comprehensive mechanical properties.

[0045] In another typical embodiment of the present invention, a material for a metal heating wire is also provided, using the above-mentioned high-resistivity aluminum alloy foil. As mentioned above, the present application effectively improves the resistivity of the aluminum alloy foil by optimizing the element ratio and preparation process of the aluminum alloy foil. When the high-resistivity aluminum alloy foil of the present invention is used as the metal heating wire in the battery pack heating element, the resistivity requirements of the metal heating wire can be met. In addition, the preparation method of the present application enables the aluminum alloy foil to have a suitable hardness, reduces the processing difficulty of the heating wire, improves the production efficiency, and is more environmentally friendly. On the other hand, the preparation method of the present application enables the aluminum alloy foil to have good wetting properties, so that the heating wire can be effectively combined with other components.

[0046] Typically but not limiting, the composition of the aluminum alloy foil, by weight percentage, is 1.7%, 1.8%, 1.9% Mn or a range consisting of any two of them; 0.2%, 0.3%, 0.4%, 0.5% Cr or a range consisting of any two of them; 0.1%, 0.2%, 0.3% Ti or a range consisting of any two of them; 0.1%, 0.2% Fe or a range consisting of any two of them; 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% Si or a range consisting of any two of them, other unavoidable impurity elements ≤ 0.2%, and the balance is Al.

[0047] Typically but not limitatively, the casting temperature is 730°C, 740°C, 750°C, 760°C, 770°C, 780°C or a range consisting of any two of them, the casting speed is 600mm / min, 650mm / min, 700mm / min, 750mm / min, 800mm / min, 850mm / min or a range consisting of any two of them, the cooling rate is 100°C / h, 150°C / h, 200°C / h or a range consisting of any two of them, and the thickness of the cast plate is 6mm, 7mm, 8mm or a range consisting of any two of them.

[0048] Typically but not limiting, in step S2, the deformation amount of a single cold rolling pass is 10%, 15%, 20%, 25%, 30% or a range consisting of any two of them.

[0049] Typically but not limiting, in step S3, the deformation amount of a single pass of foil rolling is 10%, 15%, 20%, 25% or a range consisting of any two of them.

[0050] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0051] Example 1

[0052] The composition ratio of the aluminum alloy foil is shown in Table 1.

[0053] Step S1, according to the composition ratio of the aluminum alloy foil, the raw materials are put into the melting furnace together, mixed for 2.5 hours at a melting temperature of 825°C, and then refined twice, with a single refining temperature of 770°C and a standing time of 25 minutes. Then, the melt is transferred to a holding furnace, kept at 760°C for 3.5 hours, and then cast by a twin-roll casting method, with a casting temperature of 730°C, a casting speed of 650mm / min, a cooling water temperature of 30°C, a casting cooling rate of 150°C / h, and a cast plate thickness of 8mm;

[0054] Step S2, cold rolling the cast plate, with a deformation of 20% in each cold rolling pass, and then annealing at a temperature of 290° C., a heating rate of 70° C. / h, and a holding time of 1 h to obtain a heat-treated plate with a thickness of 0.5 mm;

[0055] Step S3, using a foil rolling mill to perform foil rolling on the heat-treated plate, the deformation amount of each foil rolling is 20%, and the thickness of the obtained aluminum foil is 0.04 mm;

[0056] Step S4, placing the aluminum foil in an annealing furnace for high-temperature degreasing treatment, the temperature is 100° C., the heating rate is 70° C. / h, and the insulation time is 20 h; obtaining an aluminum alloy foil.

[0057] The SEM image of the microstructure of the aluminum alloy foil obtained is shown in Figure 1 , and use it as a metal heating wire to make batteries.

[0058] Example 2

[0059] The composition ratio of the aluminum alloy foil is the same as that of Example 1.

[0060] Step S1, according to the composition ratio of the aluminum alloy foil, the raw materials are put into the melting furnace together, mixed for 2.5 hours at a melting temperature of 825°C, and then refined twice, with a single refining temperature of 770°C and a standing time of 25 minutes. Then, the melt is transferred to a holding furnace, kept at 760°C for 3.5 hours, and then cast by a twin-roll casting method, with a casting temperature of 730°C, a casting speed of 650mm / min, a cooling water temperature of 30°C, a casting cooling rate of 150°C / h, and a cast plate thickness of 8mm;

[0061] Step S2, cold rolling the cast plate, with a deformation of 20% in each cold rolling pass, and then annealing at a temperature of 290° C., a heating rate of 70° C. / h, and a holding time of 1 h to obtain a heat-treated plate with a thickness of 0.5 mm;

[0062] Step S3, using a foil rolling mill to perform foil rolling on the heat-treated plate, the deformation amount of each foil rolling is 20%, and the thickness of the obtained aluminum foil is 0.04 mm;

[0063] Step S4, using an alkaline solution (sodium carbonate solution) with a pH of 7 to clean the aluminum foil, rinsing it with water, and then drying it at a temperature of 100° C. for 90 seconds to obtain an aluminum alloy foil, which is used as a metal heating wire for making batteries.

[0064] Examples 3 to 6

[0065] The only difference from Example 1 is:

[0066] The composition ratios of aluminum alloy foil are different, and the specific ratios are shown in Table 1.

[0067] Example 7

[0068] The only difference from Example 1 is:

[0069] Step S1, according to the composition ratio of the aluminum alloy foil, the raw materials are put into a smelting furnace, mixed at a smelting temperature of 800°C for 5 hours, and then refined twice, with a single refining temperature of 800°C and a standing time of 30 minutes. Next, the melt is transferred to a holding furnace, kept at 750°C for 5 hours, and then cast by a twin-roll casting method, with a casting temperature of 730°C, a casting speed of 600mm / min, a cooling water temperature of 40°C, a casting cooling rate of 100°C / h, and a cast plate thickness of 7mm.

[0070] Example 8

[0071] The only difference from Example 1 is:

[0072] Step S1, according to the composition ratio of the aluminum alloy foil, the raw materials are put into a smelting furnace, mixed for 1 hour at a smelting temperature of 850°C, and then refined for 3 times, with a single refining temperature of 770°C and a standing time of 20 minutes. Next, the melt is transferred to a holding furnace, kept at 790°C for 2 hours, and then cast by a twin-roll casting method, with a casting temperature of 780°C, a casting speed of 850mm / min, a cooling water temperature of 25°C, a casting cooling rate of 200°C / h, and a cast plate having a thickness of 6mm.

[0073] Example 9

[0074] The only difference from Example 1 is:

[0075] Step S2, cold rolling the cast plate, with a deformation of 30% in each cold rolling pass, and then annealing at a temperature of 200°C, a heating rate of 40°C / h, and a holding time of 5h to obtain a heat-treated plate.

[0076] Example 10

[0077] The only difference from Example 1 is:

[0078] Step S2, cold rolling the cast plate, with a deformation of 15% in each cold rolling pass, and then annealing at a temperature of 290°C, a heating rate of 70°C / h, and a holding time of 1h to obtain a heat-treated plate.

[0079] Embodiment 11

[0080] The only difference from Example 1 is:

[0081] Step S3, using a foil rolling mill to perform foil rolling on the heat-treated plate, and the deformation amount of each foil rolling is 10%.

[0082] Example 12

[0083] The only difference from Example 1 is:

[0084] Step S3, using a foil rolling mill to perform foil rolling on the heat-treated plate, and the deformation amount of each foil rolling is 25%.

[0085] Embodiment 13

[0086] The only difference from Example 1 is:

[0087] Step S4, placing the aluminum foil in an annealing furnace for high-temperature degreasing treatment, the temperature is 100° C., the heating rate is 10° C. / h, and the insulation time is 200 h; obtaining an aluminum alloy foil.

[0088] Embodiment 14

[0089] The only difference from Example 1 is:

[0090] Step S4, placing the aluminum foil in an annealing furnace for high-temperature degreasing treatment, the temperature is 200° C., the heating rate is 70° C. / h, and the insulation time is 10 hours; and an aluminum alloy foil is obtained.

[0091] Embodiment 15

[0092] The composition ratio of the aluminum alloy foil is the same as that of Example 1.

[0093] Step S1, according to the composition ratio of the aluminum alloy foil, the raw materials are put into the melting furnace together, mixed for 2.5 hours at a melting temperature of 825°C, and then refined twice, with a single refining temperature of 770°C and a standing time of 25 minutes. Then, the melt is transferred to a holding furnace, kept at 760°C for 3.5 hours, and then cast by a twin-roll casting method, with a casting temperature of 730°C, a casting speed of 650mm / min, a cooling water temperature of 30°C, a casting cooling rate of 150°C / h, and a cast plate thickness of 8mm;

[0094] Step S2, cold rolling the cast plate, with a deformation of 20% in each cold rolling pass, and then annealing at a temperature of 290° C., a heating rate of 70° C. / h, and a holding time of 1 h to obtain a heat-treated plate with a thickness of 0.5 mm;

[0095] Step S3, using a foil rolling mill to perform foil rolling on the heat-treated plate, the deformation amount of each foil rolling is 20%, and the thickness of the obtained aluminum foil is 0.04 mm;

[0096] Step S4, first use an alkaline solution to clean the aluminum foil, rinse it with water, and then dry it at a temperature of 100° C. for 120 seconds to obtain an aluminum alloy foil.

[0097] Example 16

[0098] The composition ratio of the aluminum alloy foil is the same as that of Example 1.

[0099] Step S1, according to the composition ratio of the aluminum alloy foil, the raw materials are put into the melting furnace together, mixed for 2.5 hours at a melting temperature of 825°C, and then refined twice, with a single refining temperature of 770°C and a standing time of 25 minutes. Then, the melt is transferred to a holding furnace, kept at 760°C for 3.5 hours, and then cast by a twin-roll casting method, with a casting temperature of 730°C, a casting speed of 650mm / min, a cooling water temperature of 30°C, a casting cooling rate of 150°C / h, and a cast plate thickness of 8mm;

[0100] Step S2, cold rolling the cast plate, with a deformation of 20% in each cold rolling pass, and then annealing at a temperature of 290° C., a heating rate of 70° C. / h, and a holding time of 1 h to obtain a heat-treated plate with a thickness of 0.5 mm;

[0101] Step S3, using a foil rolling mill to perform foil rolling on the heat-treated plate, the deformation amount of each foil rolling is 20%, and the thickness of the obtained aluminum foil is 0.04 mm;

[0102] Step S4, firstly clean the aluminum foil with an alkaline solution, rinse it with water, and then dry it at a temperature of 120° C. for 30 seconds to obtain an aluminum alloy foil.

[0103] Comparative Example 1

[0104] The only difference from Example 1 is:

[0105] Step S2, cold rolling the cast plate, with the deformation amount of each cold rolling being 35%.

[0106] Comparative Example 2

[0107] The only difference from Example 1 is:

[0108] Step S3, using a foil rolling mill to perform foil rolling on the heat-treated plate, and the deformation amount of each foil rolling is 30%.

[0109] Comparative Example 3

[0110] The only difference from Example 1 is:

[0111] Step S1, the casting temperature is 650°C, the casting speed is 500mm / min, and the cooling rate is 50°C / h.

[0112] Comparative Example 4

[0113] The only difference from Example 1 is:

[0114] Step S1, the casting temperature is 850°C, the casting speed is 900 mm / min, and the cooling rate is 250°C / h.

[0115] The test results of the microstructure characteristics and performance parameters of the aluminum alloy foils prepared in the above embodiments and comparative examples are shown in Table 2.

[0116] Test method:

[0117] The maximum size and area ratio test of the second phase: the test shall be carried out in accordance with GB / T 15749-2008.

[0118] Resistivity test: At room temperature of 20±5℃, use a four-probe resistance tester to measure the resistance of the aluminum foil sample.

[0119] Hardness test: At room temperature, a micro Vickers hardness tester was used to test the hardness of the aluminum foil sample in accordance with GB / T4340.1.

[0120] Maximum pinhole size and pinhole rate test: Tested in accordance with GB / T 22638.2-2016 and GB / T 3198-2020.

[0121] Table 1

[0122]

[0123]

[0124] Table 2

[0125]

[0126]

[0127] It can be seen from the above that, compared with the comparative example, the embodiments of the present invention significantly improve the resistivity of aluminum alloy foil through the design of specific alloy components and the optimized process flow. The precise ratio of elements such as Mn, Cr, Ti, Fe, Si, combined with the high cooling rate of the casting and rolling process, effectively increases the content of solid solution elements and enhances the resistance characteristics. Casting and rolling parameter control, such as temperature, speed and cooling rate, ensures the uniformity and stability of the material structure. The single-pass small deformation strategy of cold rolling and foil rolling, combined with appropriate annealing treatment, avoids excessive work hardening and reduces the number of heat treatments, thereby inhibiting the precipitation of effective elements and maintaining the high resistivity of the foil. The method of the present invention not only effectively solves the problem of insufficient resistivity of traditional aluminum alloy foil, but also ensures the processing performance and surface quality of the material.

[0128] When the high-resistivity aluminum alloy foil of the present invention is used as the metal heating wire in the battery pack heating element, it can meet the resistivity requirements of the metal heating wire and has good wetting properties. When used for processing and manufacturing battery packs and heating elements, it can be effectively combined with other components, thereby facilitating the manufacture of battery packs and heating elements.

[0129] In addition, it can be seen that when each process parameter is within the preferred range of the present invention, the comprehensive effect of the alloy is better.

[0130] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a high resistivity aluminum alloy foil, characterized in that: The resistivity of the aluminum alloy foil is 8-12 μΩ·cm. The components of the aluminum alloy foil include, by weight percentage, 1.7-1.9% Mn, 0.2-0.5% Cr, 0.1-0.3% Ti, 0.1-0.2% Fe, 0.5-1.5% Si, the total amount of inevitable impurities is ≤0.2%, and the balance is Al. The preparation method comprises the following steps: Step S1, according to the composition ratio of the aluminum alloy foil, the raw materials are mixed, smelted, refined, heat-insulated, and cast-rolled in sequence to obtain a cast-rolled plate; wherein the casting temperature is 730-780° C., the casting speed is 600-850 mm / min, the cooling rate is 100-200° C. / h, and the thickness of the cast-rolled plate is 6-8 mm; Step S2, cold rolling and annealing the cast-rolled plate in sequence, wherein the deformation of a single pass of the cold rolling is ≤30%, to obtain a heat-treated plate; Step S3, foil rolling the heat-treated plate, wherein the deformation amount of a single pass of the foil rolling is ≤25%, to obtain the aluminum alloy foil.

2. The preparation method according to claim 1, characterized in that: In the step S1, The smelting temperature is 800-850°C; and / or, The refining is performed 2 to 3 times, the refining temperature is 770 to 800° C., and the standing time is 20 to 30 minutes; and / or, The temperature of the insulation is 750-790° C., and the time is 2-5 hours.

3. The preparation method according to claim 1 or 2, characterized in that: In the step S2, The annealing temperature is 200-290° C., the heating rate is 40-70° C. / h, and the heat preservation time is 1-5h.

4. The preparation method according to any one of claims 1 to 3, characterized in that In the step S2, The thickness of the heat-treated plate is 0.2-0.5 mm.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In the step S3, The thickness of the aluminum alloy foil is 0.04-0.06 mm.

6. The preparation method according to any one of claims 1 to 5, characterized in that The step S3 also includes the step of performing high temperature degreasing after the foil rolling; Preferably, the temperature of the high-temperature oil removal is 100-200° C., the heating rate is 10-70° C. / h, and the insulation time is 10-200 h.

7. The preparation method according to any one of claims 1 to 6, characterized in that In terms of weight percentage, among the above ingredients, The sum of the weight percentages of Cr, Ti and Fe is ≤0.6%.

8. The preparation method according to any one of claims 1 to 7, characterized in that In terms of weight percentage, among the above ingredients, The sum of the weight percentages of Cr, Ti and Mn is 1.9-2.5%; and / or, The sum of the weight percentages of Cr, Ti, Fe and Mn is 2.2-2.5%.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The alloy phase of the aluminum alloy foil comprises an AlFeMnSi(CrTi) phase, the area percentage of the AlFeMnSi(CrTi) phase in the matrix of the aluminum alloy foil is 0.3-3%, and the size is ≤1 um; and / or, The aluminum alloy foil has a hardness of ≥70 HV, and / or a wetting tension of ≥40 dynes.

10. A high resistivity aluminum alloy foil, characterized in that: The method according to any one of claims 1 to 9 is used to obtain the

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