Aluminum alloy strip for explosion-proof valve of battery cover and preparation method of aluminum alloy strip

Abstract

The invention belongs to the technical field of aluminum alloy, and discloses an aluminum alloy strip for an explosion-proof valve of a battery cover, which comprises the following components in percentage by weight: 1.0%-1.8% of Fe, 0.2%-0.6% of Mn, 0.05%-0.25% of Si, 0.005%-0.1% of Ti, 0.05%-0.25% of Cr, 0.05%-0.25% of Zr and the balance of Al and inevitable impurities. According to the technical scheme, by optimizing and adjusting alloy components and controlling the machining process, the average grain size of a finished product is controlled within 12 microns, the maximum size of metal compounds is controlled within 20 microns, and the number of intermetallic compounds is controlled within 22000-38000 / mm < 2 >. Through component optimization and processing technology control, the tensile strength is 100-116 MPa, the ductility is larger than or equal to 38%, and the bursting pressure stability after welding is within the range of + / -0.08 MPa.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum alloy strips, and particularly relates to an aluminum alloy strip for a battery cover explosion-proof valve and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are mainly used in fields such as power energy and 3C electronic products. With the continuous development of fields such as new energy electric vehicles and 3C electronic products, the market for lithium-ion batteries is gradually growing. The explosion-proof valve needs to release the internal pressure in case of accidental events such as damage accidents and increased internal pressure in the battery container, so an explosion-proof valve component is designed on the battery cover. The explosion-proof valve must work reliably and be able to automatically break when the internal pressure in the container exceeds the specified pressure to achieve the safety protection effect.

[0003] The explosion-proof valve is required to have excellent mechanical properties, formability, welding performance, and stable bursting pressure. Among them, the stability of the bursting pressure of the explosion-proof valve is crucial. At present, the stability of the bursting pressure of aluminum alloy explosion-proof valves after welding in the market is within the range of ±0.2 MPa. The explosion-proof valve on the battery cover plate is an important component of the battery, and improving the stability of the bursting pressure of the explosion-proof valve is one of the important development directions for improving the safety of the battery. Summary of the Invention

[0004] Since there are problems such as insufficient welding in the laser welding of Al-Mn series aluminum alloys, and the Al-Mg series aluminum alloys soften too quickly after welding, it is difficult to ensure the stability of the bursting pressure. Aluminum alloys based on the Al-Fe series have excellent forming performance and excellent laser welding performance, but their strength is slightly lower than that of Al-Mn series aluminum alloys.

[0005] Therefore, in the design of the alloy composition of the present invention, a certain amount of Fe and Mn are added to increase the strength of the alloy. At the same time, the processing process is combined to avoid the generation of coarse phases, and the harm of laser welding caused by impurity elements is also avoided. In addition, an appropriate amount of Zr and Cr are added in the composition design to enhance the effect of suppressing welding rupture. Then, a suitable homogenization heat treatment process is combined to promote the formation of nano-sized intermetallic compounds of Al3Zr and AlMn(Fe)SiCr. Both of these intermetallic compounds are beneficial to refine the recrystallization annealing grains during the finished product annealing of the sheet, thereby ensuring the uniform formability of each part of the explosion-proof valve and improving the stability of the bursting pressure of the explosion-proof valve.

[0006] The present invention is realized by adopting the following technical solutions:

[0007] To achieve the above object, the present invention provides an aluminum alloy strip for the explosion-proof valve of a battery cover. The composition of the aluminum alloy strip is as follows by mass percentage: Fe 1.0% - 1.8%, Mn 0.2% - 0.6%, Si 0.05% - 0.25%, Ti 0.005% - 0.1%, Cr 0.05 - 0.25%, Zr 0.05 - 0.25%, and the balance is Al and inevitable impurities.

[0008] The present invention also provides a preparation method for the aluminum alloy strip for the explosion-proof valve of a battery cover, comprising the following steps:

[0009] S1. Mix each component according to the composition ratio of the aluminum alloy strip for the explosion-proof valve of a battery cover, and then prepare an ingot using semi-continuous casting equipment;

[0010] Fe and Mn can increase the strength of the aluminum alloy strip. At the same time, combined with the processing technology, the generation of coarse phases can be avoided, and the hazards such as poor laser welding caused by impurity elements can also be avoided. In addition, an appropriate amount of Zr and Cr is added in the composition design to enhance the effect of suppressing welding rupture. Then, combined with a suitable homogenization heat treatment process, Zr and Cr are promoted to form Al3Zr intermetallic compounds and AlMn(Fe)SiCr intermetallic compounds with nano-sized particles. Both of these intermetallic compounds are beneficial to refine the grains during the recrystallization annealing of the finished sheet.

[0011] S2. Homogenization heat treatment;

[0012] Before hot rolling, the ingot is subjected to single-stage or multi-stage homogenization treatment. It is kept at a high temperature for a certain time to eliminate composition segregation, promote the continuous dissolution and spheroidization of coarse solidification phases, and avoid the appearance of coarse intermetallic compound phases. At a low temperature, it is kept for a period of time or in the slow heating / cooling stage to promote the formation of a large proportion of Al3Zr intermetallic compounds and AlMn(Fe)SiCr intermetallic compounds with nano-sized particles by Zr and Cr;

[0013] S3. Hot rough rolling and hot finish rolling;

[0014] The hot rolling thickness is controlled to be <10 mm, and the final rolling temperature is controlled at 220°C - 380°C. Considering the total cold rolling reduction rate, it promotes the fragmentation of coarse intermetallic compound phases and the welding of micro-porosities in the original ingot, and finally achieves the obtaining of fine grains and fine intermetallic compound phases;

[0015] S4. Cold rolling;

[0016] The total cold rolling processing rate ≥ 60% to ensure sufficient deformation energy storage before the finished product annealing, which is beneficial to obtaining fine recrystallized grains;

[0017] S5. Finished product annealing;

[0018] To obtain a recrystallized grain structure, especially fine recrystallized grains, if the temperature is too high, the probability of grain coarsening increases. The annealing temperature is controlled at 300 - 400 °C, and the holding time is determined according to the temperature - reaching technical characteristics and temperature - control technical characteristics of the annealing industrial furnace. The annealing time is 0.5 min - 5 h.

[0019] Furthermore, in the step S2, the homogenization heat treatment method includes one of the following:

[0020] The first method: Heat at a heating rate of 1 - 100 °C / h to 550 - 600 °C and hold for 2 - 10 h.

[0021] The second method: First, heat at a heating rate of 1 - 100 °C / h to 550 - 600 °C and hold for 2 - 10 h; then cool at a cooling rate of 10 - 100 °C / h to 450 - 550 °C and hold for 0.1 - 8 h.

[0022] The third method: First, heat at a heating rate of 10 - 100 °C / h to 450 - 550 °C and hold for 0.1 - 8 h; then heat at a heating rate of 30 - 100 °C / h to 550 - 600 °C and hold for 2 - 10 h.

[0023] Furthermore, in the step S4, there are two cold - rolling processes: direct cold - rolling and multi - stage cold - rolling.

[0024] Direct cold - rolling: That is, directly cold - roll the hot - rolled plate to 0.5 - 1.0 mm, and the cold - rolling rate is >90%.

[0025] Multi - stage cold - rolling includes primary cold - rolling, intermediate annealing, and secondary cold - rolling.

[0026] Furthermore, the process of the intermediate annealing is: Anneal at a temperature of 300 - 450 °C, take it out after holding for 1 - 5 h, and cool to room temperature.

[0027] Furthermore, in the step S4, the cold - rolling thickness is controlled at 0.2 - 1.0 mm, the processing rate of each pass in the cold - rolling process is controlled at 10% - 60%, and the total processing rate ≥60%.

[0028] Furthermore, the process of the finished - product annealing in the step S5 is: Anneal at a temperature of 300 - 400 °C, take it out after holding for 1 - 5 h, and cool to room temperature.

[0029] Furthermore, the process of the finished - product annealing in the step S5 is: Anneal at a temperature of 300 - 400 °C, take it out after holding for 0.5 - 25 min, and cool to room temperature.

[0030] Further, for the finished aluminum alloy strip prepared by annealing in step S5: the average grain size is controlled within 12 μm, the maximum size of metal compounds is controlled within 20 μm, and the number of intermetallic compounds is controlled at 22,000 - 38,000 per mm 2 .

[0031] Further, for the finished aluminum alloy strip prepared by annealing in step S5: the tensile strength is 100 - 116 MPa, the elongation is ≥ 38%, and the burst pressure after welding is within the range of ±0.08 MPa.

[0032] Beneficial effects:

[0033] At present, the stability of the burst pressure of aluminum alloy explosion-proof valves in the market after welding is within the range of ±0.2 MPa. In view of the actual demand for improving the stability of the burst pressure, the formability of the explosion-proof valve, especially the forming uniformity, is improved from the principle of grain refinement. For the aluminum alloy material of the present invention, alloying elements Zr and Cr that can promote grain refinement are comprehensively considered in the alloy composition design. At the same time, a corresponding homogenization heat treatment process is provided to promote the elimination of composition segregation and phase transformation, so as to obtain a maximum size of metal compounds controlled within 20 μm and the number of intermetallic compounds controlled at 22,000 - 38,000 per mm 2 , which ensures the prerequisite for recrystallization grain refinement. Combined with a specific primary / secondary cold rolling process or a direct cold rolling process and a specific finished product annealing process, the average grain size of the finished strip is effectively obtained within 12 μm, and the stability of the burst pressure after welding is within the range of ±0.08 MPa.

[0034] Compared with the original aluminum alloy strip for the explosion-proof valve of the battery cover, the present invention realizes the improvement of the stability of the burst pressure of the material without significantly increasing the process steps and without affecting the material strength and welding performance, thus improving the safety of the product.

[0035] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, based on the study of the following text, will be obvious to those skilled in the art or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a flowchart of a preparation method of an aluminum alloy strip for an explosion-proof valve of a battery cover according to the present invention;

[0037] Figure 2 is a grain structure diagram of the aluminum alloy strip prepared in Example 1;

[0038] Figure 3Grain structure diagram of the aluminum alloy strip prepared in Example 2;

[0039] Figure 4 Grain structure diagram of the aluminum alloy strip prepared in Example 3;

[0040] Figure 5 Grain structure diagram of the aluminum alloy strip prepared in Comparative Example 1. Detailed implementation manners

[0041] To make the technical solutions, advantages and objectives of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of this application.

[0042] The present invention provides an aluminum alloy strip for a battery cover explosion-proof valve. The composition of the aluminum alloy strip is as follows by mass percentage: Fe 1.0% - 1.8%, Mn 0.2% - 0.6%, Si 0.05% - 0.25%, Ti 0.005% - 0.1%, Cr 0.05 - 0.25%, Zr 0.05 - 0.25%, and the balance is Al and inevitable impurities.

[0043] As Figure 1 shown, the present invention also provides a preparation method for an aluminum alloy strip for a battery cover explosion-proof valve, including the following steps:

[0044] S1. Mix each component according to the composition ratio of the aluminum alloy strip for the battery cover explosion-proof valve, and then prepare an ingot using semi-continuous casting equipment;

[0045] S2. Homogenization heat treatment;

[0046] The method of homogenization heat treatment includes one of the following:

[0047] The first one: Heat at a heating rate of 1 - 100 °C / h to 550 - 600 °C and hold for 2 - 10 h;

[0048] The second one: First heat at a heating rate of 1 - 100 °C / h to 550 °C - 600 °C and hold for 2 - 10 h; then cool at a cooling rate of 10 - 100 °C / h to 450 - 550 °C and hold for 0.1 - 8 h;

[0049] The third one: First heat at a heating rate of 10 - 100 °C / h to 450 - 550 °C and hold for 0.1 - 8 h; then heat at a heating rate of 30 - 100 °C / h to 550 °C - 600 °C and hold for 2 - 10 h.

[0050] S3. Hot rough rolling and hot finish rolling;

[0051] The hot rolling thickness is controlled within <10 mm, and the finish rolling temperature is controlled at 220°C to 380°C;

[0052] S4. Cold rolling;

[0053] The cold rolling thickness is controlled at 0.2 - 1.0 mm. During cold rolling, the processing rate for each pass is controlled at 10% - 60%, and the total processing rate ≥ 60%.

[0054] There are two cold rolling processes: direct cold rolling and multi - stage cold rolling;

[0055] Direct cold rolling: That is, directly cold - roll the hot finish - rolled sheet to 0.5 - 1.0 mm, and the cold rolling rate is >90%;

[0056] Multi - stage cold rolling includes primary cold rolling, intermediate annealing, and secondary cold rolling;

[0057] Among them, the process of intermediate annealing is: anneal at a temperature of 300 - 450°C, take it out after heat preservation for 1 - 5 h, and cool it to room temperature.

[0058] S5. Final annealing;

[0059] The process of final annealing is: anneal at a temperature of 300 - 400°C, take it out after heat preservation for 0.5 min - 5 h, and cool it to room temperature;

[0060] The finished product of aluminum alloy strip prepared by annealing in step S5: The average grain size is controlled within 12 μm, the maximum size of metal compounds is controlled within 20 μm, and the number of intermetallic compounds is controlled at 22000 - 38000 per mm 2 ;

[0061] The finished product of aluminum alloy strip prepared by annealing in step S5: The tensile strength is 100 - 116 MPa, the elongation rate ≥ 38%, and the bursting pressure after welding is within the range of ±0.08 MPa.

[0062] Example 1

[0063] S1. Melting is carried out according to the alloy element composition ratio, and an ingot is prepared by using semi - continuous casting equipment;

[0064] Among them, the composition ratio of the aluminum alloy strip for the explosion - proof valve of the battery cover in this example is: Fe 1.33%, Mn 0.44%, Si 0.1%, Ti 0.021%, Cr 0.05%, Zr 0.08%, and the balance is Al and unavoidable impurities.

[0065] S2. Homogenization heat treatment: The ingot is subjected to homogenization heat treatment. First, it is heated to 600 °C at a rate of 50 °C / h and held for 10 h, and then cooled to 500 °C at a cooling rate of 50 °C / h and held for 3 h.

[0066] S3. Hot rolling: The ingot after homogenization heat treatment is directly subjected to hot rough rolling and rolled to 36 mm. The finishing temperature of hot rough rolling is 420 °C; then the hot rolled plate is subjected to hot finish rolling and rolled to 7 mm. The finishing temperature of hot finish rolling is 300 °C.

[0067] S4. Cold rolling;

[0068] Primary cold rolling: The hot rolled plate is cold rolled to 1.5 mm, and the cold rolling rate > 70%;

[0069] Intermediate annealing: The plate after primary cold rolling is subjected to intermediate annealing. The annealing temperature is 360 °C, and the annealing holding time is 5 h;

[0070] Secondary cold rolling: The plate after intermediate annealing is subjected to secondary cold rolling and rolled to 0.5 mm, and the cold rolling rate is 66%.

[0071] S5. Final annealing: The annealing temperature is 380 °C. After holding for 25 min, it is taken out and cooled to room temperature.

[0072] Finally, the finished strip is obtained, with a tensile strength of 108 MPa, an elongation rate of 39%, an average grain size of 11.4 μm, the maximum size of metal compounds of 17.8 μm, and the number of intermetallic compounds of 26,000 - 30,000 per mm 2 . It can complete the stamping forming of the battery explosion-proof valve and the laser welding with the cover plate, and the stability of the bursting pressure after welding is within the range of ±0.07 MPa.

[0073] The grain structure of the aluminum alloy strip prepared in this example is as Figure 2 shown. It can be seen from Figure 2 that the grain structure of the aluminum alloy strip prepared in this example is fine and uniform.

[0074] Example 2

[0075] S1. Melting is carried out according to the alloy element composition ratio, and an ingot is prepared by using semi-continuous casting equipment;

[0076] Among them, the composition ratio of the aluminum alloy strip for the battery cover explosion-proof valve in this example is: Fe 1.35%, Mn 0.47%, Si 0.1%, Ti 0.025%, Zr 0.06%, and the balance is Al and inevitable impurities. S2. Homogenization heat treatment: The ingot is subjected to homogenization heat treatment. First, it is heated to 600 °C at a heating rate of 10 °C / h and held for 9 h.

[0077] S3. Hot rolling: The ingot after homogenization heat treatment is directly subjected to hot rough rolling until it reaches 34 mm, and the final rolling temperature of hot rough rolling is 420 °C; then the hot-rolled plate is subjected to hot finish rolling until it reaches 7 mm, and the final rolling temperature of hot finish rolling is 280 °C.

[0078] S4. Direct cold rolling: The hot-finished rolled plate is cold-rolled until it reaches 0.5 mm, and the cold rolling rate is >90%.

[0079] S5. Finished product annealing: The annealing temperature is 380 °C. After holding for 4 h, it is taken out and cooled to room temperature.

[0080] Finally, the finished strip is obtained, with a tensile strength of 113 MPa, an elongation rate of 40%, an average grain size of 9.8 μm, the maximum size of metal compounds of 18.9 μm, and the number of intermetallic compounds of 24,000 - 28,000 per mm 2 . It can complete the stamping forming of the battery explosion-proof valve and the laser welding with the cover plate, and the stability of the burst pressure after welding is within the range of ±0.08 MPa.

[0081] The grain structure of the aluminum alloy strip prepared in this example is as Figure 3 shown. It can be seen from Figure 3 that the grain structure of the aluminum alloy strip prepared in this example is fine and uniform.

[0082] Example 3

[0083] S1. Melting is carried out according to the alloy element composition ratio, and an ingot is prepared by using semi-continuous casting equipment;

[0084] Among them, the composition ratio of the aluminum alloy strip for the battery cover explosion-proof valve in this example is: Fe 1.64%, Mn 0.42%, Si 0.1%, Ti 0.023%, Cr 0.08%, Zr 0.06%, and the balance is Al and inevitable impurities.

[0085] S2. Homogenization heat treatment: The ingot is subjected to homogenization heat treatment. First, it is heated to 550 °C at a heating rate of 10 °C / h and held for 8 h, and then it is heated to 600 °C at a heating rate of 50 °C / h and held for 8 h.

[0086] S3. Hot rolling: The ingot after homogenization heat treatment is directly subjected to hot rough rolling until it reaches 35 mm, and the final rolling temperature of hot rough rolling is 400 °C; then the hot-rolled plate is subjected to hot finish rolling until it reaches 7 mm, and the final rolling temperature of hot finish rolling is 280 °C.

[0087] S4. Direct cold rolling: The hot-finished rolled plate is cold-rolled until it reaches 0.5 mm, and the cold rolling rate is >80%.

[0088] S5. Final annealing of the finished product: The annealing temperature is 400 °C. After holding for 20 minutes, it is taken out and cooled to room temperature. Finally, the finished strip is obtained, with a tensile strength of 110 MPa, an elongation rate of 40%, an average grain size of 10.3 μm, a maximum size of metal compounds of 19.1 μm, and the number of intermetallic compounds being 26,000 - 29,000 per mm 2 . It can complete the stamping and forming of the battery explosion-proof valve and the laser welding with the cover plate. The stability of the burst pressure after welding is within the range of ±0.06 MPa.

[0089] The grain structure of the aluminum alloy strip prepared in this embodiment is as Figure 4 shown. It can be seen from Figure 4 that the grain structure of the aluminum alloy strip prepared in this embodiment is fine and uniform.

[0090] Example 4

[0091] S1. Melting is carried out according to the alloy element composition ratio, and an ingot is prepared using a semi-continuous casting device;

[0092] Among them, the composition ratio of the aluminum alloy strip for the battery cover explosion-proof valve in this embodiment is: Fe 1.42%, Mn 0.51%, Si 0.09%, Ti 0.031%, Cr 0.08%, Zr 0.057%, and the balance is Al and unavoidable impurities.

[0093] S2. Homogenization heat treatment: The ingot is subjected to homogenization heat treatment. First, it is heated to 550 °C at a heating rate of 50 °C / h and held for 6 hours, and then it is heated to 600 °C at a heating rate of 50 °C / h and held for 10 hours.

[0094] S3. Hot rolling: The ingot after homogenization heat treatment is directly subjected to hot rough rolling until it reaches 36 mm, and the final rolling temperature of hot rough rolling is 400 °C; then the hot rough rolled plate is subjected to hot finish rolling until it reaches 7 mm, and the final rolling temperature of hot finish rolling is 320 °C.

[0095] S4. Cold rolling;

[0096] First cold rolling: The hot finish rolled plate is cold rolled until it reaches 2.5 mm, and the cold rolling rate is >50%;

[0097] Intermediate annealing: The plate after the first cold rolling is subjected to intermediate annealing, with an annealing temperature of 340 °C and an annealing holding time of 4 hours;

[0098] Second cold rolling: The plate after intermediate annealing is cold rolled until it reaches 0.5 mm, and the cold rolling rate is 80%.

[0099] S5. Annealing of the cold rolled finished product: The annealing temperature is 380 °C. After holding for 15 minutes, it is taken out and cooled to room temperature.

[0100] Finally, a finished strip is obtained, with a tensile strength of 111 MPa, an elongation rate of 40%, an average grain size of 10.6 μm, a maximum size of metal compounds of 18.3 μm, and the number of intermetallic compounds being 30,000 - 32,000 per mm 2 It can complete the stamping and forming of the battery explosion-proof valve and the laser welding with the cover plate, and the stability of the bursting pressure after welding is within the range of ±0.07 MPa.

[0101] Comparative Example 1

[0102] S1. Melting is carried out according to the alloy element composition ratio, and an ingot is prepared using a semi-continuous casting device;

[0103] Among them, the composition ratio of the aluminum alloy strip for the battery cover explosion-proof valve in this embodiment is: Fe 1.42%, Mn 0.44%, Si 0.1%, Ti 0.02%, and the balance is Al and unavoidable impurities.

[0104] S2. Homogenization heat treatment: The ingot is subjected to homogenization heat treatment, heated in the furnace to 600 °C, and held for 10 h.

[0105] S3. Hot rolling: The ingot after homogenization heat treatment is directly subjected to hot rough rolling, rolled to 36 mm, and the final rolling temperature of hot rough rolling is 420 °C; then the hot-rolled plate is subjected to hot finish rolling, rolled to 8 mm, and the final rolling temperature of hot finish rolling is 320 °C.

[0106] S4. Cold rolling;

[0107] Primary cold rolling: The hot-rolled plate is cold-rolled to 1.5 mm, and the cold rolling rate is >70%;

[0108] Intermediate annealing: The plate after primary cold rolling is subjected to intermediate annealing, the annealing temperature is 360 °C, and the annealing holding time is 5 h;

[0109] Secondary cold rolling: The plate after intermediate annealing is subjected to secondary cold rolling, rolled to 0.5 mm, and the cold rolling rate is 66%.

[0110] S5. Finish annealing: The annealing temperature is 380 °C, taken out after holding for 5 h, and cooled to room temperature.

[0111] Finally, a finished strip is obtained, with a tensile strength of 102 MPa, an elongation rate of 38%, an average grain size of 19.4 μm, which can complete the stamping and forming of the battery explosion-proof valve and the laser welding with the cover plate, and the stability of the bursting pressure after welding is within the range of ±0.18 MPa.

[0112] The grain structure of the aluminum alloy strip prepared in this comparative example is as Figure 5 shown, and it can be seen through Figure 5 that the grain structure of the aluminum alloy strip prepared in this comparative example is relatively large and the uniformity is poor.

[0113] Comparative Example 2

[0114] S1. Melting is carried out according to the alloy element composition ratio, and an ingot is prepared by using a semi-continuous casting device;

[0115] Among them, the composition ratio of the aluminum alloy strip for the explosion-proof valve of the battery cover in this embodiment is: Fe 1.63%, Mn 0.26%, Si 0.12%, Ti 0.06%, and the balance is Al and unavoidable impurities.

[0116] S2. Homogenization heat treatment: The ingot is subjected to homogenization heat treatment, heated in the furnace to 600 °C and held for 8 h.

[0117] S3. Hot rolling: The ingot after homogenization heat treatment is directly subjected to hot rough rolling until it is rolled to 32 mm, and the final rolling temperature of hot rough rolling is 420 °C; then the hot-rolled rough plate is subjected to hot finish rolling until it is rolled to 8 mm, and the final rolling temperature of hot finish rolling is 340 °C.

[0118] S4. Cold rolling;

[0119] Primary cold rolling: The hot-rolled finish plate is cold-rolled until it is rolled to 1.2 mm, and the cold rolling rate is >70%;

[0120] Intermediate annealing: The plate after primary cold rolling is subjected to intermediate annealing, the annealing temperature is 380 °C, and the annealing holding time is 4 h;

[0121] Secondary cold rolling: The plate after intermediate annealing is subjected to secondary cold rolling until it is rolled to 0.5 mm, and the cold rolling rate is 58%.

[0122] S5. Finish annealing: The annealing temperature is 340 °C, and it is taken out after holding for 5 h and cooled to room temperature.

[0123] Finally, a finished strip is obtained, its tensile strength is 100 MPa, the elongation rate is 38%, the average grain size is 18.9 μm, and it can complete the stamping forming of the battery explosion-proof valve and the laser welding with the cover plate, and the stability of the burst pressure after welding is within the range of ±0.2 MPa.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered within the protection scope of the present invention.

Claims

1. An aluminum alloy strip for an explosion-proof valve of a battery cover, characterized in that: The composition of the aluminum alloy strip is by mass percentage: Fe 1.0% - 1.8%, Mn 0.2% - 0.6%, Si 0.05% - 0.25%, Ti 0.005% - 0.1%, Cr 0.05 - 0.25%, Zr 0.05 - 0.25%, and the balance is Al and inevitable impurities.

2. A preparation method of an aluminum alloy strip for an explosion-proof valve of a battery cover as described in claim 1, characterized in that, It includes the following steps: S1. Mix each component according to the composition ratio of the aluminum alloy strip for the explosion-proof valve of the battery cover, and then prepare an ingot with a semi-continuous casting device; S2. Homogenization heat treatment; S3. Hot rough rolling and hot finish rolling; The hot rolling thickness is controlled within <10 mm, and the final rolling temperature is controlled at 220°C - 380°C; S4. Cold rolling; The total cold rolling reduction rate ≥ 60%; S5. Finish annealing.

3. The preparation method of an aluminum alloy strip for an explosion-proof valve of a battery cover according to claim 2, wherein, In the step S2, the method of homogenization heat treatment includes one of the following; The first: Heat up at a heating rate of 1 - 100°C / h to 550 - 600°C and hold for 2 - 10 h; The second: First heat up at a heating rate of 1 - 100°C / h to 550°C - 600°C and hold for 2 - 10 h; then cool down at a cooling rate of 10 - 100°C / h to 450 - 550°C and hold for 0.1 - 8 h; The third: First heat up at a heating rate of 10 - 100°C / h to 450 - 550°C and hold for 0.1 - 8 h; then heat up at a heating rate of 30 - 100°C / h to 550°C - 600°C and hold for 2 - 10 h.

4. The preparation method of an aluminum alloy strip for an explosion-proof valve of a battery cover according to claim 3, characterized in that, In the step S4, there are two cold rolling processes: direct cold rolling and multi-stage cold rolling; Direct cold rolling: That is, directly cold roll the hot finish rolled plate to 0.5 - 1.0 mm, and the cold rolling rate is >90%; Multi-stage cold rolling includes primary cold rolling, intermediate annealing, and secondary cold rolling.

5. The preparation method of an aluminum alloy strip for an explosion-proof valve of a battery cover according to claim 4, characterized in that, The process of the intermediate annealing is: Anneal at a temperature of 300 - 450°C, take it out after holding for 1 - 5 h, and cool to room temperature.

6. The preparation method of an aluminum alloy strip for an explosion-proof valve of a battery cover according to claim 5, characterized in that, In the step S4, the cold rolling thickness is controlled at 0.2 - 1.0 mm, and the reduction rate of each pass in the cold rolling process is controlled at 10% - 60%, and the total reduction rate ≥ 60%.

7. The preparation method of an aluminum alloy strip for an explosion-proof valve of a battery cover according to claim 6, characterized in that, The process of the finish annealing in the step S5 is: Anneal at a temperature of 300 - 400°C, take it out after holding for 1 - 5 h, and cool to room temperature.

8. The preparation method of an aluminum alloy strip for an explosion-proof valve of a battery cover according to claim 7, characterized in that, The process of the finish annealing in the step S5 is: Anneal at a temperature of 300 - 400°C, take it out after holding for 0.5 - 25 min, and cool to room temperature.

9. The preparation method of an aluminum alloy strip for an explosion-proof valve of a battery cover according to claim 8, wherein, The finished aluminum alloy strip prepared by annealing in step S5: the average grain size is controlled within 12 μm, the maximum size of the metal compound is controlled within 20 μm, and the number of intermetallic compounds is controlled within 22,000 - 38,000 / mm 2 .

10. The preparation method of an aluminum alloy strip for an explosion-proof valve of a battery cover according to claim 8, characterized in that, The finished product of the aluminum alloy strip prepared by the annealing in the step S5: The tensile strength is 100 - 116 MPa, the elongation rate ≥ 38%, and the bursting pressure after welding is within the range of ±0.08 MPa.

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