An ultra-low-speed pressure-cast aluminum alloy battery module end plate and a heat treatment method thereof

Abstract

This invention discloses an ultra-low speed die-cast aluminum alloy battery module end plate and its heat treatment method. Based on the existing alloy A356.2, this invention optimizes the alloy composition by increasing the Mg content and adding trace amounts of Zr. The optimized alloy composition is melted and then die-cast at ultra-low speed to form the end plate. It is then subjected to low-temperature solution treatment at 450-500℃ for 4-12 hours, followed by quenching, and high-temperature aging treatment at 180-230℃ for 2-8 hours, thus optimizing the heat treatment process of the end plate. Through the comprehensive optimization of low-temperature solution treatment, high-temperature aging, and chemical composition, this invention significantly reduces the scrap rate caused by deformation and blistering after heat treatment while maintaining and improving the mechanical properties of existing products.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment and material alloying technology, and more specifically, relates to an ultra-low speed die-cast aluminum alloy battery module end plate and its heat treatment method. Background Technology

[0002] End plates are a crucial component in battery modules for new energy vehicles and energy storage industries, requiring high performance. They must maintain high strength and toughness while ensuring dimensional stability, good thermal conductivity, and excellent weldability. A356.2 aluminum alloy, due to its high comprehensive mechanical properties, heat-treatable characteristics, and good casting performance, has become the mainstream choice for end plates. To reduce porosity and increase material density, ultra-low-speed die casting is typically used, followed by heat treatment for strengthening. To achieve high strength and toughness, a combination of high-temperature solution treatment and low-temperature artificial aging is generally employed. The solution treatment temperature is typically in the range of 520-545℃, followed by artificial aging at 130-155℃, which promotes the precipitation of fine and dispersed Mg2Si phases, thereby strengthening the material.

[0003] However, existing high-temperature solution treatment processes have several problems. First, high-temperature solution treatment approaches the solidus of the material, leading to severe softening and increasing the risk of thermal stress during quenching. This can cause end plate deformation, resulting in a large number of scrapped and reworked products. Second, even in ultra-low-speed die casting, porosity is unavoidable. During high-temperature solution treatment, these pores expand and blister, leading to further scrap and rework. Furthermore, high-temperature solution treatment can also cause problems such as easy burning of the furnace walls and various components.

[0004] Although the industry has explored low-temperature solution treatment, the mismatch between chemical composition and aging process often results in the mechanical properties of products after low-temperature solution treatment failing to meet the requirements of industrial applications. In addition, the diffusion rate of various alloy atoms in low-temperature solution treatment is relatively slow, which generally requires a long time and reduces production efficiency. As a result, the entire industry still generally adopts high-temperature solution treatment.

[0005] Therefore, it is necessary to develop a low-temperature solution treatment process for aluminum alloy end plates that can take into account both mechanical properties and process advantages, in order to meet the higher requirements of the battery module industry for end plate performance and quality. Summary of the Invention

[0006] The purpose of this invention is to provide an ultra-low speed die-cast aluminum alloy battery module end plate and its heat treatment method. Based on low-temperature solution treatment, a high-temperature over-aging process is introduced, and the chemical composition of A356.2 alloy is optimized to match the new heat treatment process. This greatly reduces heat treatment deformation and blistering, while also improving mechanical properties and elongation.

[0007] To achieve the above objectives, the technical solution adopted by the present invention includes:

[0008] This invention first provides an ultra-low speed die-cast aluminum alloy battery module end plate, which is made of ultra-low speed die-cast aluminum alloy. The chemical composition of the ultra-low speed die-cast aluminum alloy, by mass percentage, includes: Si 6.5-7.5%, Fe<0.15%, Mg 0.45-0.55%, Sr 0.010-0.025%, Zr 0.08-0.35%, Mn <0.10%, Ni<0.02%, Zn<0.02%, Pb<0.01%, Sn<0.01%, Ti<0.01%, Ca<0.003%, with the balance being Al and unavoidable impurities.

[0009] Preferably, the chemical composition of the ultra-low speed die casting aluminum alloy, by mass percentage, includes: Si 6.5-7.5%, Fe <0.15%, Mg 0.45-0.55%, Sr 0.010-0.025%, Zr 0.14-0.3%, Mn <0.10%, Ni <0.02%, Zn <0.02%, Pb <0.01%, Sn <0.01%, Ti <0.01%, Ca <0.003%, with the balance being Al and unavoidable impurities.

[0010] The present invention also provides a heat treatment method for the end plate of the ultra-low speed die-cast aluminum alloy battery module, comprising the following steps:

[0011] The end plate to be treated is placed in a heat treatment device for low-temperature solution heat treatment, which is held at a first temperature range for a first time. The end plate after solution heat treatment is then quenched in water for a second time within a second temperature range. After quenching, the end plate is removed. The end plate is then aged in a third temperature range for a third time.

[0012] Optionally, the first temperature range is 450-500℃, and the first time is 4-12h. Preferably, the temperature is maintained at 480℃ for 8h.

[0013] Optionally, after the low-temperature solution heat treatment, the end plate is quickly immersed in water for 20 seconds.

[0014] Optionally, the second temperature range is 60-90℃, and the second time is 5-20 min. Preferably, quenching is performed at 75℃ for 15 min.

[0015] Optionally, the third temperature range is 180-230℃, and the third time is 2-8 hours. Preferably, the temperature is maintained at 200℃ for 4 hours.

[0016] Optionally, the end plate to be processed is prepared by the following steps:

[0017] a. Add alloy ingots and recycled materials to a furnace for smelting, remove slag in the furnace at a temperature range of 760-800℃ to form molten metal, and pour the molten metal into a transfer bag;

[0018] b. Add Mg, Zr, and Sr elements to the transfer bag by means of single metal or intermediate alloy to adjust the chemical composition, and then carry out degassing and slag removal treatment in the transfer bag.

[0019] c. Pour the molten metal into a holding furnace for ultra-low speed die casting to form an ultra-low speed die casting blank, and remove the gating system and slag from the end plate blank to obtain the end plate to be processed.

[0020] Optionally, Zr is added to the transport package in the form of an Al-10%Zr master alloy, Mg is added in the form of pure Mg or an Al-Mg master alloy, and Sr is added in the form of Al-10%Sr. Mg is mainly added to improve the strength of the alloy. The addition of Sr is to modify the eutectic Si and change its morphology. By adding Zr, the grain size of the aluminum alloy is refined and the secondary dendrite spacing of the material is increased, thereby improving the overall mechanical properties of the alloy.

[0021] Optionally, the preparation method of the end plate to be processed further includes, after degassing and slag removal of the molten metal in the transfer bag, performing a vacuum density test on the molten metal, wherein the test is performed at 700-740℃ and the vacuum density is greater than 2.65 g / cm³. 3 This ensures that the cleanliness and gas content of the molten aluminum meet the requirements.

[0022] The battery module end plates obtained by the above heat treatment process have an average tensile strength of over 285 MPa, an average yield strength of over 185 MPa, and an elongation of over 8%, and can even reach 10%.

[0023] The technical principles and beneficial effects of this invention are as follows:

[0024] This invention provides an optimized A356.2 ultra-low-speed die-casting aluminum alloy, mainly by increasing the Mg content and adding a small amount of Zr, eliminating the use of Ti alloy, and replacing the conventional Al-5Ti-1B master alloy with Al-10%Zr as a grain refiner. The higher Mg content is designed to adapt to low-temperature solution treatment and high-temperature aging processes. Even under low-temperature solution treatment conditions, sufficient Mg can still be dissolved in the α-Al matrix, thereby achieving effective solid solution strengthening. In addition to refining the grains, the addition of Zr can reduce the size of the secondary dendrite spacing during casting. The reduction in the secondary dendrite spacing reduces the migration distance of Mg and Si during solution heat treatment, improving the efficiency of solid solution treatment. This ensures the effectiveness of solid solution treatment at low temperatures, thereby improving the overall mechanical properties of the material, especially the elongation, and compensating for the potential decrease in elongation due to the increased Mg content. In the optimized alloy, the main strengthening phase is the Mg2Si phase. The atomic sizes of Mg and Si are not much different from those of Al atoms, and their diffusion rates are very fast during the solid solution process, which objectively provides conditions for low-temperature solid solution.

[0025] This invention effectively solves the problems of deformation and surface blistering that easily occur in aluminum alloy end plates during heat treatment through a low-temperature solution heat treatment process. Combined with high-temperature over-aging, it can impart superior comprehensive mechanical properties to the alloy. Even at higher Mg contents, the elongation can still be maintained at a high level.

[0026] In summary, this invention, by optimizing the alloy chemical composition and heat treatment process, further improves the elongation while ensuring material strength, achieving a good match in mechanical properties. Furthermore, this invention also reduces end-plate heat treatment defects, improves product quality, and extends the lifespan of heat treatment equipment, demonstrating significant industrial application value. Attached Figure Description

[0027] Figure 1 This is a schematic diagram showing the locations for grain size detection and secondary dendrite spacing detection.

[0028] Figure 2 X-ray imaging for casting inspection.

[0029] Figure 3 Metallographic images were used to optimize the grain size of Alloy II.

[0030] Figure 4 Metallographic images were obtained to optimize the secondary dendrite spacing of alloy II. Detailed Implementation

[0031] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to specific examples and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0032] This invention provides an ultra-low speed die-cast aluminum alloy battery module end plate and its heat treatment method. The method includes steps such as metal smelting, ultra-low speed die casting, solution aging treatment, and post-treatment. In a preferred embodiment, the preparation of the ultra-low speed die-cast aluminum alloy includes the following steps:

[0033] a. Add the alloy ingots and recycled materials to the furnace for smelting, remove slag in the furnace, and pour the molten metal into the transfer bag after the preset temperature is reached.

[0034] The amount of alloy ingots and recycled materials added is proportioned according to the chemical composition requirements of the end plate. During the slag removal in the furnace, powder spraying and refining are carried out every 4 hours for 15 minutes. After the powder spraying and refining is completed, the slag is removed until the surface of the molten metal is completely bright and there is no more floating oxide slag.

[0035] Preferably, the preset temperature of the molten metal is 760-800℃.

[0036] b. The final chemical composition is adjusted during the transfer process, mainly by adding Mg, Sr, and Zr. Mg is primarily added to improve the alloy's strength. Sr is added to temper the eutectic Si, altering its morphology. Zr is added to refine the aluminum alloy grains and increase the secondary dendrite spacing of the cast material, thereby improving the alloy's overall mechanical properties.

[0037] Mg is added in the form of pure Mg blocks; Sr is added in the form of Al-10%Sr master alloy; similarly, Zr is added in the form of Al-10%Zr master alloy. Only after these additions can degassing be performed, so that Mg, Sr and Zr elements can be fully dissolved and mixed in the molten metal.

[0038] After adding various alloying elements, a special aluminum alloy slag remover is also needed for slag removal. Approximately 0.1% of the slag remover by weight of the molten metal is sprinkled onto the surface of the molten metal, followed by degassing. Degassing is performed by introducing nitrogen into a rotary degasser. After degassing, the mixture is allowed to stand for about 10 minutes. This degassing and slag removal process not only effectively removes hydrogen from the molten metal but also removes oxide inclusions, slag, and other non-metallic inclusions.

[0039] After degassing and slag removal, the molten metal inside the transfer package undergoes density testing. The required vacuum density value is greater than 2.65 g / cm³. 3The temperature of the molten metal after degassing in the transfer bag is 700-740℃.

[0040] c. Pour the molten metal into the holding furnace for ultra-low speed die casting to cast the end plate blank. After casting, cut off the gating system and slag bag from the end plate blank.

[0041] d. Perform the above-mentioned low-temperature solution treatment + optimized aging heat treatment process on the end plate blank to ensure that the end plate meets the mechanical performance requirements; specifically including the following steps:

[0042] The end plate to be treated is placed in a heat treatment apparatus and subjected to low-temperature solution heat treatment at 450-500℃ for 4-12 hours. After solution heat treatment, the end plate is quickly immersed in water for quenching. To ensure rapid immersion, the end plate, along with the heat treatment rack, is simultaneously submerged in water, facilitating easy removal. The end plate is immersed in water within 20 seconds; the initial water temperature is controlled at 75℃, and the end plate is removed after 15 minutes of immersion. After draining, the end plate undergoes aging treatment at 180-230℃ for 2-8 hours. In a preferred embodiment, the aging treatment temperature is 200℃ for 4 hours.

[0043] e. The end plates are then sandblasted, drilled, and machined sequentially.

[0044] This invention utilizes a low-temperature solution heat treatment process, along with optimization of the chemical composition and aging process, to significantly reduce deformation and blistering during the end plate heat treatment process, while maintaining the end plate strength and achieving a high elongation rate.

[0045] To achieve low-temperature solution treatment, the proportions of the aluminum alloy itself, which is the target for low-temperature solution treatment, are also very important. This invention describes an ultra-low-speed die-casting aluminum alloy optimized based on the A356.2 alloy. The end plate to be treated is made of an ultra-low-speed die-casting aluminum alloy, which, by mass percentage of chemical composition, comprises: Si 6.5-7.5%; Fe <0.15%; Mg 0.40-0.55%; Sr 0.010-0.025%; Zr 0.08-0.3%; Mn <0.10%; Ni <0.02%; Zn <0.02%; Pb <0.01%; Sn <0.01%; Ti <0.01%; Ca <0.003%, with the balance being Al.

[0046] In optimizing the chemical composition of the alloy, the Mg content in the A356.2 alloy was increased, while a small amount of Zr was added. The increased Mg content ensured sufficient Mg to dissolve into the Al dendrites even under low-temperature solution treatment. The addition of a small amount of Zr not only refined the grains but also reduced the secondary dendrite spacing after casting, thus improving elongation while maintaining strength and offsetting the effect of increased Mg on reduced elongation. Subsequent high-temperature over-aging further improved elongation. Therefore, the combined optimization of low-temperature solution treatment, chemical composition, and aging process not only reduces heat treatment deformation and blistering but also improves the overall mechanical properties of the material.

[0047] Example 1

[0048] Ultra-low speed die-casting aluminum alloy composition design: Based on chemical composition by mass percentage, the composition includes: Si 7%; Fe < 0.15%; Mg 0.5%; Sr 0.02%; Zr (0.08, 0.15, 0.3)%; Mn < 0.10%; Ni < 0.02%; Zn < 0.02%; Pb < 0.01%; Sn < 0.01%; Ti < 0.01%; Ca < 0.003%, with the balance being Al. The values ​​for Si, Mg, Sr, and Zr are the design median values. Six different compositions were verified, and the specific composition is based on the actual composition, as shown in Table 1. Considering that Ti and Zr are both grain-refining elements and interact to affect the refining effect, only one grain refiner was added to the alloy. Chemical composition testing was conducted in a holding furnace.

[0049] After the alloy is melted, degassed, allowed to stand, and its chemical composition is adjusted, the molten alloy is poured into a holding furnace for ultra-low speed die casting to cast the end plate blank. After casting, the end plate blank is cut off to remove the gating and slag bag to obtain the end plate to be processed.

[0050] Table 1 Alloy Chemical Composition / wt%

[0051]

[0052] To ensure the accuracy of the comparison, all products were die-cast using the same mold, with all casting parameters maintained identically throughout the process. Each group consisted of 100 die-cast products. All endplate products underwent visual inspection and 100% X-ray inspection for internal defects. Additionally, two samples from each product with different chemical compositions were selected for grain size and secondary dendrite spacing testing. The testing locations are as follows: Figure 1As shown in the red box. The X-ray inspection standard is rated according to ASTM E155, "Standard Reference Radiography for the Inspection of Aluminum and Magnesium Alloy Castings." The internal quality requirements for endplate products are very high, exceeding Level 2. Grain size is observed under a metallographic microscope using polarized light and measured using the intercept method. Secondary dendrite spacing is measured by selecting five larger dendrites within a field of view and taking the average value. The average X-ray grade, grain size, and secondary dendrite spacing values ​​for various alloys are shown in Table 2.

[0053] The results showed that all cast products met the appearance requirements, with no obvious defects such as cold shuts, porosity, or shrinkage cavities. X-Ray values ​​were also within the acceptable range. This indicates that the addition of Mg and Zr did not significantly change the die-casting performance of the alloy. Furthermore, the grain sizes of different products were relatively similar, suggesting that the grain refinement effects of Zr and Ti were not significantly different. However, the secondary dendrite spacing in the Zr-added products was significantly reduced compared to the original alloy, and this reduction became less pronounced with increasing Zr content. The reduction in secondary dendrites shortens the diffusion distance of elements such as Si and Mg during solid solution treatment, thus creating conditions for low-temperature solid solution treatment.

[0054] Table 2. Values ​​of X-Ray grade, grain size, and secondary dendrite spacing for different alloys

[0055]

[0056] Example 2

[0057] After the end plate blanks of optimized alloy II and A356.2 were cast, the gating system and slag bag were sawn off. The A356.2 end plates underwent the original heat treatment process of 540℃ x 6h + 150℃ x 4h. The optimized alloy II end plates underwent two heat treatment processes: 540℃ x 6h + 150℃ x 4h (original heat treatment process) and 480℃ x 8h + 200℃ x 4h (new heat treatment process). All times were holding times. After aging, sandblasting was performed, followed by machining of the assembly surfaces according to the drawings. The specific process is as follows:

[0058] Solution treatment: The two alloys were subjected to solution treatment at different temperatures: high-temperature solution treatment at 540℃ for 6 hours and low-temperature solution treatment at 480℃ for 8 hours. The lower solution temperature was used with a longer treatment time to ensure that the strengthening phase could dissolve in the matrix.

[0059] Quenching: Water temperature 75℃, immersion time 18s, stay in water for 15min to achieve sufficient cooling, and then aging.

[0060] Aging: For two alloys with different chemical compositions, the aging processes are 150℃ for 4 hours and 200℃ for 4 hours respectively.

[0061] Sandblasting: Removes ash spots and burrs from the surface after heat treatment, improving surface quality.

[0062] Machining: Machining the assembly surfaces according to customer requirements.

[0063] Then, deformation, bubbling, and mechanical property tests were conducted on the products that had completed all processes. The specific test results are as follows.

[0064] 1. Deformation and Bubbling Inspection: Deformation and bubbling inspections were conducted on the products in three groups. Deformation inspection mainly focused on the flatness of the end plates, while bubbling was measured by the number of bubbles appearing on each end plate after heat treatment. Twenty products were selected from each process group for inspection. Specific inspection results are shown in Table 3.

[0065] Table 3. Statistics on Deformation and Bubbling Data of End Plate Products after Heat Treatment

[0066]

[0067] As can be seen from the three sets of data in Table 3, after heat treatment, the product deformation and blistering numbers are not significantly correlated with the material or aging temperature, but are highly correlated with the solution temperature. At lower solution temperatures, the deformation and blistering of the end plates are significantly improved. This is mainly because lower solution temperature greatly reduces the thermal deformation of the product during high-temperature solution treatment and reduces the thermal stress during quenching. The reduction in the number of blisters also indicates that at lower solution temperatures, the expansion of residual bubbles in the product is correspondingly reduced, thus reducing blistering. In conclusion, the new heat treatment process significantly reduces the product scrap rate.

[0068] 2. Mechanical Property Testing: Mechanical property testing was conducted on the three groups of products. The testing location was the gate position of the end plate, as required by the drawings. Ten products were selected from each group for tensile mechanical property testing. The tensile standard was based on GB / T 228.1-2021 "Metallic materials – Tensile testing – Part 1: Test at room temperature". Specific data are shown in Table 4.

[0069] Table 4 Mechanical property data of end plate products after heat treatment

[0070]

[0071] As can be seen from the mechanical property data in Table 4, after alloy optimization, under the same heat treatment regime as A356.2, the tensile strength, yield strength, and elongation of the alloy were significantly improved. This is mainly due to the addition of more Mg in the optimized alloy, resulting in a greater introduction of the strengthening phase Mg2Si. Simultaneously, the addition of Zr not only refined the grains but also reduced the secondary dendrite spacing, thus maintaining high elongation while strengthening the alloy. Comparing different heat treatment regimes for the optimized alloy, the tensile strength, yield strength, and elongation of the material under the 480℃×8h+200℃×4h regime were significantly improved compared to the original 540℃×6h+150℃×4h heat treatment regime. This indicates that the new material is more suitable for the low-temperature solution treatment followed by high-temperature aging process. This is mainly due to the increased amount of the strengthening phase Mg2Si, which provides sufficient precipitation even at low temperatures. Simultaneously, the reduced secondary dendrite spacing leads to a shorter diffusion distance. After over-aging at higher temperatures, the precipitated phase aggregates and grows, significantly improving elongation while maintaining strength.

[0072] Example 3

[0073] This embodiment, based on the optimized composition of Alloy II, investigates the effects of different heat treatment regimes on the mechanical properties of the end plates. Groups 6 and 7 use data from Example 2, while the other groups consist of 5 products for each heat treatment, and the mechanical properties are the average of the 5 products. Specific parameters and results are shown in Table 5.

[0074] Table 5. Mechanical properties of end plate products after different heat treatments

[0075]

[0076] As shown in Table 5, under the same aging process of 200℃×4h, the mechanical properties gradually decrease with decreasing solution temperature. This indicates that at lower temperatures, atomic diffusion slows down, resulting in ineffective solution treatment. Under the same 480℃×8h solution treatment process, 200℃×4h is also optimal. Too low an aging temperature will not achieve the required mechanical properties, while too high an aging temperature, such as 230℃×4h, leads to excessive over-aging; although elongation increases, strength decreases significantly. The performance of the 500℃×6h solution treatment process in Group 5 and the process in Group 6 is not significantly different. However, considering that higher solution temperatures increase the risk of deformation and blistering, the process in Group 6 is the best overall.

[0077] Example 4

[0078] This embodiment examines the mechanical properties of optimized alloys with different alloy compositions under the optimal heat treatment regime. Five products from optimized alloys I and III were selected for heat treatment, and the mechanical properties are the average of the five products. Specific results are shown in Table 6.

[0079] Table 6 Mechanical property data of end plate products after heat treatment (480℃×8h+200℃×4h)

[0080]

[0081] As shown in Table 6, optimized alloys II and III are slightly better than optimized alloy I, but the difference is not significant, depending on the amount of Zr added. Considering factors such as alloy cost, the median Zr content for the preferred alloys is approximately 0.15%.

[0082] This invention solves the deformation problem of end plates after heat treatment through a low-temperature solution heat treatment process. Simultaneously, the blistering problem on the end plate surface is effectively suppressed due to the lower solution temperature. The lower solution temperature also reduces the damage to the furnace caused by high-temperature solution treatment. In summary, through the combined optimization of materials, solution treatment, and aging processes, not only is the scrap rate of end plate products significantly reduced, but the overall mechanical properties of the products are also significantly improved.

[0083] Unless otherwise specified, all raw materials used in the above embodiments are commercially available materials commonly used in the art, and all process steps not specifically described are conventional process steps used in the art. The above descriptions are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An ultra-low speed die-cast aluminum alloy battery module end plate, characterized in that, Made from ultra-low speed die-cast aluminum alloy, the chemical composition of which, by mass percentage, includes: Si 6.5-7.5%, Fe <0.15%, Mg 0.45-0.55%, Sr 0.010-0.025%, Zr 0.08-0.35%, Mn <0.10%, Ni <0.02%, Zn <0.02%, Pb <0.01%, Sn <0.01%, Ti <0.01%, Ca <0.003%, with the balance being Al and unavoidable impurities.

2. The ultra-low speed die-cast aluminum alloy battery module end plate according to claim 1, characterized in that, The chemical composition of the ultra-low speed die-cast aluminum alloy, by mass percentage, includes: Si 6.5-7.5%, Fe <0.15%, Mg 0.45-0.55%, Sr 0.010-0.025%, Zr 0.14-0.3%, Mn <0.10%, Ni <0.02%, Zn <0.02%, Pb <0.01%, Sn <0.01%, Ti <0.01%, Ca <0.003%, with the balance being Al and unavoidable impurities.

3. The heat treatment method for the end plate of the ultra-low speed die-cast aluminum alloy battery module as described in claim 1 or 2, characterized in that, Includes the following steps: The end plate to be processed is subjected to low-temperature solution heat treatment, which is to hold at 450-500℃ for 4-12 hours. The end plate after solution heat treatment is quenched at 60-90℃ for 5-20 minutes. The quenched end plate is subjected to high-temperature aging treatment, which is to hold at 180-230℃ for 2-8 hours.

4. The heat treatment method for the end plate of the ultra-low speed die-cast aluminum alloy battery module as described in claim 3, characterized in that, The low-temperature solution heat treatment is performed at a temperature of 480°C for 8 hours.

5. The heat treatment method for the end plate of the ultra-low speed die-cast aluminum alloy battery module as described in claim 3, characterized in that, The quenching is carried out in water with an initial water temperature of 75°C and a quenching time of 15 minutes.

6. The heat treatment method for the end plate of the ultra-low speed die-cast aluminum alloy battery module as described in claim 3, characterized in that, The high-temperature aging treatment is performed at a temperature of 200°C for 4 hours.

7. The heat treatment method for the end plate of the ultra-low speed die-cast aluminum alloy battery module as described in claim 3, characterized in that, The end plate to be processed is prepared by the following steps: a. Add alloy ingots and recycled materials to a furnace for smelting, remove slag in the furnace at a temperature range of 760-800℃ to form molten metal, and pour the molten metal into a transfer bag; b. Add Mg, Zr, and Sr elements to the transfer bag by means of single metal or intermediate alloy to adjust the chemical composition, and then carry out degassing and slag removal treatment in the transfer bag. c. Pour the molten metal into the holding furnace for ultra-low speed casting, then perform ultra-low speed die casting of the end plate blank, and remove the gate and slag from the end plate blank to obtain the end plate to be processed.

8. The heat treatment method for the end plate of the ultra-low speed die-cast aluminum alloy battery module as described in claim 7, characterized in that, Zr was added to the transshipment package in the form of an Al-10%Zr master alloy, Mg was added in the form of pure Mg or Al-Mg master alloy, and Sr was added in the form of Al-10%Sr.

9. The heat treatment method for the end plate of the ultra-low speed die-cast aluminum alloy battery module as described in claim 7, characterized in that, This also includes, after degassing and slag removal from the molten metal inside the transfer package, performing a vacuum density test on the molten metal. The test is conducted at 700-740℃ to ensure that the vacuum density requirement is greater than 2.65 g / cm³. 3 above.

10. The heat treatment method for the end plate of the ultra-low speed die-cast aluminum alloy battery module as described in claim 7, characterized in that, The battery module end plate obtained by the method has an average tensile strength of over 285 MPa, an average yield strength of over 185 MPa, and an elongation of over 8%.

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