Preparation method of ultra-high-strength, low-pinhole and corrosion-resistant ultra-thin battery aluminum foil

Abstract

The invention discloses a preparation method of ultra-high-strength, low-pinhole and corrosion-resistant ultrathin battery aluminum foil, which comprises the following steps: firstly, smelting industrial waste aluminum and industrial pure aluminum ingots in proportion, adding alloy elements to treat into an aluminum melt which contains 0.050-0.080% of Cr element after the industrial waste aluminum and the industrial pure aluminum ingots are completely smelted, then casting the aluminum melt into an aluminum alloy plate ingot, and then sawing and milling the plate ingot to obtain the ultra-high-strength, low-pinhole and corrosion-resistant ultrathin battery aluminum foil. The method comprises the following steps: firstly, carrying out heat preservation for 2-4 hours at the material temperature of 600-620 DEG C, then reducing the material temperature to 520-550 DEG C, carrying out heat preservation for 3-6 hours, carrying out homogenizing annealing, rolling an aluminum alloy plate ingot into an aluminum coil with the thickness of 0.5-0.2 mm, and finally, carrying out foil rolling on the aluminum coil to obtain an aluminum foil coil. The two-stage homogenizing annealing is matched with diffusion and precipitation of the Cr element in the Al matrix, the microstructure of the Al matrix is optimized, and the tensile strength and the ductility are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery aluminum foil production, and in particular to a method for preparing ultra-thin battery aluminum foil with ultra-high strength, low pinhole properties and corrosion resistance. Background Art

[0002] Lithium-ion batteries have developed rapidly in the new energy vehicle market in recent years due to their advantages such as high energy density, low self-discharge, no memory effect, long cycle life and environmental protection, driving the rapid growth of the lithium-ion battery market. Battery aluminum foil is an important component of lithium batteries.

[0003] In order to meet the power market's demand for high energy density and fast charging and discharging, the production of aluminum foil must reduce its thickness while increasing its tensile strength and elongation, while ensuring low pinhole rate and good corrosion resistance. High tensile strength allows the battery to withstand a higher positive electrode material density, thereby increasing the battery's energy density; appropriate elongation and low pinhole rate help improve the quality of battery electrodes, reduce the chance of tape breakage during the production process, and increase the yield of finished products.

[0004] However, there is a contradiction between the thinning thickness of aluminum foil and its strength and toughness. The toughness of aluminum foil is related to its microstructure, which is affected by the alloy composition and processing conditions. The production process of battery aluminum foil is complex and technically difficult, so there are high barriers in the industry.

[0005] With the world's increasing emphasis on clean energy, the demand for new energy vehicles and energy storage systems has grown rapidly, driving the development of the lithium-ion battery industry. Aluminum foil, as the current collector of the battery's positive electrode, needs to have high strength, high elongation and low pinhole rate to reduce defects in production.

[0006] At present, the tensile strength of battery aluminum foil is generally required to reach 180 MPa, but with technological advancements, many users hope that the strength can reach above 200 MPa, or even 270 MPa, and the elongation should not be less than 2% while maintaining the purity of aluminum. However, the tensile strength and elongation of existing aluminum foil are generally low, and there are also problems such as many pinholes and easy corrosion by electrolyte. These will affect the production efficiency of the battery, increase production costs, and may affect the service life and safety of the battery.

[0007] This gave rise to this case. Summary of the Invention The purpose of the present invention is to provide a method for preparing ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil, and the technical problem to be solved is to provide a method for preparing battery aluminum foil that can produce high tensile strength and high elongation.

[0008] To achieve the above objectives, the present invention provides a method for preparing ultra-thin battery aluminum foil with ultra-high strength, low pinholes and corrosion resistance, comprising the following steps: S1: Smelting and alloying treatment: adding industrial aluminum scrap and industrial pure aluminum ingots in a certain proportion into a smelting furnace, smelting at a temperature of 680°C to 760°C, adding alloying elements after all the raw materials are melted, and obtaining an aluminum melt. The aluminum melt includes the following alloying elements by mass percentage: Si: 0.060~0.150%, Fe: 0.40~0.80%, Cu: 0.050~0.080%, Ti: 0.012~0.020%, Cr: 0.050~0.080%, Al≥99.00%, and the individual content of other impurity elements ≤0.03%, the total amount ≤0.1%; S2: Casting: Casting the aluminum melt obtained in step S1 into aluminum alloy plate ingots; S3: Homogenization annealing: The milled aluminum alloy plate ingot is placed in a heating furnace for two-stage homogenization annealing. In the two-stage homogenization annealing, the material temperature is first kept at 600-620°C for 2-4 hours, and then the plate ingot temperature is reduced to 520-550°C and kept at this temperature for 3-6 hours. S4: rolling: rolling the aluminum alloy ingot into an aluminum coil with a thickness of 0.2 to 0.5 mm; S5: Foil rolling: The aluminum coil obtained in step S4 is rolled into an aluminum foil coil through 4 to 5 passes.

[0009] Furthermore, the Cr element added in step S1 is added in the form of an Al-Cr master alloy, and the content of the Cr element in the Al-Cr master alloy is ≤5%.

[0010] Furthermore, in step S1, the smelting temperature is 740-760°C.

[0011] Furthermore, in step S2, a grain refiner is added during casting. The grain refiner is AlTiB, and the addition amount of AlTiB is 1.5-1.8 kg / T.

[0012] Furthermore, in step S4, rolling includes hot rolling and cold rolling; First, the aluminum alloy ingot is hot rolled 20 times to obtain an aluminum coil with a thickness of 2.5 to 3.0 mm; After the aluminum coil cools down, it is cold rolled three times to a thickness of 0.2-0.5 mm, and the cold rolling reduction is controlled at more than 2 mm.

[0013] Furthermore, the hot rolling start temperature is ≥450°C.

[0014] Furthermore, hot rolling includes hot rough rolling and hot finish rolling; First, the aluminum alloy plate ingot is hot-rough rolled 17 times to a thickness of 25mm, and then hot-finished rolled 3 times to hot-roll the 25mm thick plate ingot to 2.5-3.0mm. After hot rolling, the final rolling temperature of the aluminum coil is controlled at 360-380℃.

[0015] Furthermore, the reduction in each pass of cold rolling is as follows: the first pass is from 2.5-3.0 mm to 0.8-1.5 mm, the second pass is from 0.8-1.5 mm to 0.3-0.6 mm, and the third pass is from 0.3-0.6 mm to 0.20-0.28 mm.

[0016] Furthermore, in step S5, the deformation amount of each pass is 40-50%, the rolling speed is 600-1200 mm / min, the temperature of the rolling oil added during rolling is 40-60° C., and the rolling force is 2000-4000 N.

[0017] Furthermore, in step S1, the industrial aluminum scrap is the aluminum scrap generated during the production process of steps S1 to S5, and the proportion of the industrial aluminum scrap is 0 to 35%, and the rest is pure aluminum ingots.

[0018] After adopting the above scheme, the beneficial effect of the present invention is that: industrial waste aluminum generated in various processes of aluminum processing plants is utilized as a resource and combined with industrial pure aluminum ingots to form aluminum melt for alloying. During the alloying process, Cr is dissolved in the Al matrix as a solute atom, which can produce a solid solution strengthening effect on the alloy. The Cr content is controlled within the range of 0.050-0.080%, which can enable the Cr element to react with the Al matrix to produce a large number of fine and dispersed intermetallic compounds. During the solidification process of the alloy melt, the Cr element acts as a heterogeneous nucleation point, providing more fulcrums for metal solidification, refining the cast structure of the alloy, and making the alloy grain size uniform and fine. Secondly, in the first stage of the homogenization annealing process, the temperature is first raised to 600-620℃ and kept for 2-4 hours to fully dissolve the second phase, promote the diffusion of Cr elements, and form a fine mass phase. Then, in the second stage, the temperature is lowered to 520-550℃ and kept for 3-6 hours to evenly distribute the Cr precipitation phase, inhibit the growth of recrystallized grains, obtain a uniform fine-grained structure, better cooperate with the diffusion and precipitation of Cr elements in the matrix, increase the matrix recrystallization temperature, prevent the growth of grains, refine the grains, and play a role in fine grain strengthening in the subsequent hot deformation process. In addition, the Cr element will produce dispersed Al7Cr compounds during the homogenization annealing of the ingot. These dispersed phases have high density and high thermal stability. They will pin dislocations and grain boundaries during heat treatment and hot deformation, play a role in dispersion strengthening, and promote the transformation of the needle-shaped β-AlFeSi phase to the spherical α-AlFeSi phase. The amount of AlFeSi increases during the transformation process. During the deformation process, it can hinder dislocation slip with dispersed phases such as Al7Cr, further enhance dispersion strengthening, and significantly inhibit the recrystallized grain size, with the dual effects of grain refinement and dispersion strengthening. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 1 is the metallographic diagram of the as-cast structure of each embodiment and comparative example.

[0020] Figure 2 2 are the second phase distribution diagrams after hot rolling deformation of various embodiments and comparative examples.

[0021] Figure 3 This is the metallographic diagram of Example 1 after hot rolling deformation.

[0022] Figure 4 This is the metallographic diagram of Example 2 after hot rolling deformation.

[0023] Figure 5 This is the metallographic diagram of comparative example 1 after hot rolling deformation.

[0024] Figure 6 The figures are pinhole images of the finished aluminum foils of various embodiments and comparative examples. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] The present invention provides a method for preparing an ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil, comprising the following steps: S1: Smelting and alloying treatment: adding industrial aluminum scrap and industrial pure aluminum ingots in a certain proportion into a smelting furnace, smelting at a temperature of 680°C to 760°C, adding alloying elements after all the raw materials are melted, and obtaining an aluminum melt. The aluminum melt includes the following alloying elements by mass percentage: Si: 0.060-0.150%, Fe: 0.40-0.80%, Cu: 0.050-0.080%, Ti: 0.012-0.020%, Cr: 0.050-0.080%, Al ≥ 99.00%, and other impurity elements with a single content ≤ 0.03% and a total content ≤ 0.1%. During the process of adding alloying elements, stirring, refining, slagging, sampling, analysis and fine-tuning are carried out. Preferably, the Cr element is added in the form of an Al-Cr master alloy, and the Cr content in the Al-Cr master alloy is ≤ 5%; S2: Casting: The aluminum melt obtained in step S1 is cast into an aluminum alloy ingot, and the cast aluminum alloy ingot is sawn and milled, with 10-15 mm of each side of the aluminum alloy ingot being milled off. In addition, a grain refiner is added during the casting, wherein the grain refiner is AlTiB, and the addition amount of AlTiB is 1.5-1.8 kg / t; S3: Homogenization annealing: The aluminum alloy plate ingot after milling is placed in a heating furnace for two-stage homogenization annealing treatment, first keeping the material temperature at 600-620°C for 2-4 hours, then reducing the plate ingot temperature to 520-550°C and keeping it at this temperature for 3-6 hours; S4: Rolling: Rolling the aluminum alloy ingot into an aluminum coil with a thickness of 0.2-0.5 mm. Specifically, the rolling includes hot rolling and cold rolling. The aluminum alloy ingot is first hot rolled 20 times to obtain an aluminum coil with a thickness of 2.5-3.0 mm. The temperature of the aluminum coil is controlled at 220-300° C. After the aluminum coil is cooled, the aluminum coil is cold rolled 3 times to a thickness of 0.2-0.5 mm. The cold rolling reduction is controlled to be more than 2 mm. S5: Foil rolling: The aluminum coil obtained in step S4 is rolled into an aluminum foil coil with a thickness of 9 μm through 4 to 5 passes, wherein the deformation of each pass is 40 to 50%, the rolling speed is 600 to 1200 mm / min, the temperature of the rolling oil added during rolling is 40 to 60°C, the rolling force is 2000 to 4000 N, and the hardness of the aluminum coil in the last pass is relatively high. The pressure of the ironing roller needs to be increased by 20-30 MPa to ensure flatness and surface quality; then the finished aluminum foil coil is trimmed, and the pinhole condition of the aluminum foil coil is observed using a pinhole meter. Finally, the finished aluminum foil coil is thinly sheared, packaged and put into storage.

[0027] Preferably, in step S1, the melting temperature is 740-760° C., so that the Cr element can be better fused and diffused in the aluminum melt, and an electromagnetic stirrer is also included to stir the Cr element more evenly.

[0028] Furthermore, in step S4, the starting temperature of hot rolling is ≥450°C to ensure that the material temperature of the final aluminum coil is maintained at 360-380°C. Preferably, the starting temperature is 450-500°C.

[0029] Preferably, hot rolling includes hot rough rolling and hot finish rolling. The aluminum alloy slab is first rough rolled 17 times to a thickness of 25 mm, and then hot finish rolled 3 times to hot roll the 25 mm thick slab to 2.5-3.0 mm. The final rolling temperature of the hot rolled coil is controlled at 360-380°C.

[0030] Preferably, the reduction in each pass of cold rolling is: from 2.5 to 3.0 mm to 0.8 to 1.5 mm in the first pass, from 0.8 to 1.5 mm to 0.3 to 0.6 mm in the second pass, and from 0.3 to 0.6 mm to 0.20 to 0.28 mm in the third pass.

[0031] Industrial aluminum scrap is aluminum scrap generated during the production process of steps S1 to S5, and the proportion of industrial aluminum scrap is 0 to 35%, and the rest is pure aluminum ingots.

[0032] Table 1 is a comparison table of trace element contents added in the present invention and the prior art;

[0033] Table 2 is a comparison table of the homogenization annealing temperature and the finished product temperature of the hot rolling process of the present invention and the prior art;

[0034] It can be seen from Tables 1 and 2 that the existing solution does not add Cr elements, and during the homogenization annealing process, the temperature of the hot-rolled coil is not controlled, and the annealing temperatures of the two stages are relatively low.

[0035] The present invention systematically designs alloy components, increases the content of the trace element Cr, and regulates multiple microalloying components so that the content of the Cr element is controlled within a certain range. The Cr element can be combined with an Al matrix to form dispersed phases such as Al7Cr, and promotes the transformation of a needle-shaped β-AlFeSi phase into a spherical α-AlFeSi phase. At the same time, the annealing temperature is controlled to be higher than the annealing temperature of the existing solution, thereby promoting the diffusion capacity of atoms. Under the coordinated action of the two, the morphology and size of the iron-rich and silicon-rich phases are changed, and the casting grain size is synergistically refined, thereby ensuring the comprehensive properties of the aluminum foil such as high strength, low pinhole rate, and corrosion resistance. In addition, the transformation of the second phase structure is conducive to the rolling of ultra-thin aluminum foil.

[0036] The following is further described by specific examples: Example 1 A method for preparing ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil comprises the following steps: S1: Smelting and alloying treatment, adding the industrial aluminum scrap and industrial pure aluminum ingots into a smelting furnace in a certain proportion, with the industrial aluminum scrap accounting for 8.27% and the rest being pure aluminum ingots; smelting at a temperature of 680°C to 760°C, adding various alloying elements after all are melted, and obtaining the aluminum melt through stirring, refining, slagging, sampling, analysis and fine-tuning. The aluminum melt contains the following alloying elements by mass percentage: Si: 0.06705%, Fe: 0.64524%, Cu: 0.05202%, Ti: 0.01761%, Cr: 0.06722%, Al: 99.10253%, and the rest are impurities; S2: Casting, sawing, and milling: The aluminum melt from step 1 is transferred to a holding furnace for standing, slag removal, degassing, and filtration before being cast into aluminum alloy ingots. The casting is performed using Wagstaff's patented "low-level direct condensation technology." During casting, the casting level is lowered by 2 to 3 mm from the original casting level. The low casting level can make the grain structure more uniform. The grain refiner is added at a rate of 1.6 kg / T. The cast aluminum alloy ingots are sawn and milled 10 mm on each of the upper and lower surfaces. S3: Homogenization annealing: The aluminum alloy ingot after milling in step 2 is placed in a heating furnace and kept at 630°C for 2 hours, then cooled to 550°C and kept at this temperature for 5 hours for homogenization heat treatment. The hot rolling start temperature is 484°C. S4: Rolling: The aluminum alloy ingot after homogenization annealing in step 3 is subjected to 17 passes of hot rough rolling to a thickness of 25 mm, and then to 3 passes of hot finish rolling to a thickness of 2.49 mm of the aluminum sheet strip. The final rolling temperature is 369°C. After the aluminum coil is cooled, it is cold rolled for 3 passes to a thickness of 0.28 mm, with a total reduction of more than 2 mm. S5: Foil rolling: The aluminum coil after cold rolling in step 4 is rolled through 4 to 5 passes to finally be made into a battery aluminum foil with a thickness of 9 μm.

[0037] Example 2 A method for preparing ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil comprises the following steps: S1: Smelting and alloying treatment, adding the industrial aluminum scrap and industrial pure aluminum ingots into a smelting furnace in a certain proportion, with the industrial aluminum scrap accounting for 13.56% and the rest being pure aluminum ingots; smelting at a temperature of 680°C to 760°C, adding various alloying elements after all are melted, and obtaining the aluminum melt through stirring, refining, slagging, sampling, analysis and fine-tuning. The aluminum melt contains the following alloying elements by mass percentage: 0.06379%, Fe: 0.56743%, Cu: 0.04762%, Ti: 0.01897%, Cr: 0.06252%, Al: 99.15496%, and the rest are impurities; S2: Casting, sawing, and milling: The aluminum melt from step 1 is transferred to a holding furnace for standing, slag removal, degassing, and filtration before being cast into aluminum alloy ingots. Wagstaff's patented "low-level direct condensation technology" is used for casting. During casting, the casting level is lowered by 2 to 3 mm from the original casting level. The low casting level can make the grain structure more uniform. The grain refiner is added at a rate of 1.7 kg / T. The cast aluminum alloy ingots are sawn and milled 10 mm on each of the upper and lower surfaces. S3: Homogenization annealing: The aluminum alloy ingot after milling in step 2 is placed in a heating furnace and kept at 630°C for 2 hours, then cooled to 550°C and kept at this temperature for 5 hours for homogenization heat treatment. The hot rolling start temperature is 493°C. S4: Rolling: The aluminum alloy ingot after homogenization annealing in step 3 is subjected to 17 passes of hot rough rolling to a thickness of 25 mm, and then to 3 passes of hot finish rolling to a thickness of 2.52 mm for the aluminum sheet strip. The final rolling temperature is 375°C. After the aluminum coil is cooled, it is cold rolled for 3 passes to a thickness of 0.28 mm, with a total reduction of more than 2 mm. S5: Foil rolling: The aluminum coil after cold rolling in step 4 is rolled through 4 to 5 passes to finally be made into a battery aluminum foil with a thickness of 9 μm.

[0038] Comparative Example 1 A method for preparing ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil comprises the following steps: S1: smelting and alloying treatment, adding the industrial aluminum scrap and industrial pure aluminum ingots into a smelting furnace in a certain proportion, with the industrial aluminum scrap accounting for 15.72% and the rest being pure aluminum ingots; smelting is performed at a temperature of 680°C to 740°C, and various alloying elements are added after all are melted. The aluminum melt is obtained by stirring, refining, slagging, sampling, analysis and fine-tuning. The aluminum melt contains the following alloying elements by mass percentage: Si: 0.07021%, Fe: 0.62742%, Cu: 0.04089%, Ti: 0.01757%, Cr: 0.00674%, Al: 99.13759%, and the rest are impurities.

[0039] S2: Casting, sawing, and milling: The aluminum melt from step 1 is transferred to a holding furnace for standing, slag removal, degassing, and filtration before being cast into aluminum alloy ingots. The casting is performed using Wagstaff's patented "low-level direct condensation technology." During casting, the casting level is lowered by 2 to 3 mm from the original casting level. The low casting level can make the grain structure more uniform. The grain refiner is added at a rate of 1.6 kg / T. The cast aluminum alloy ingots are sawn and milled 10 mm on each of the upper and lower surfaces. S3: Homogenization annealing: The aluminum alloy ingot after milling in step 2 is placed in a heating furnace and kept at 600°C for 2 hours, then cooled to 520°C and kept at this temperature for 5 hours for homogenization heat treatment. The hot rolling start temperature is 492°C. S4: Rolling: The aluminum alloy ingot after homogenization annealing in step 3 is subjected to 17 passes of hot rough rolling to a thickness of 25 mm, and then to 3 passes of hot finish rolling to a thickness of 2.52 mm of the aluminum sheet strip. The final rolling temperature is 382°C. After the aluminum coil is cooled, it is cold rolled 3 times to a thickness of 0.28 mm. The total reduction is controlled to be above 2 mm.

[0040] S5: Foil rolling: The aluminum coil after cold rolling in step 4 is rolled through 4 to 5 passes to finally be made into a battery aluminum foil with a thickness of 9 μm.

[0041] By comparison, it can be seen that the difference between the embodiments and the comparative examples mainly lies in the different Cr contents. A4 samples of the aluminum foil produced in each embodiment and the comparative example were taken to measure the mechanical properties. The mechanical properties were measured in accordance with the standard "GB∕T 22638.11-2023 Aluminum Foil Test Method Part 11: Test of Mechanical Properties".

[0042] Table 3 is a comparison table of the composition and mechanical properties of each embodiment and comparative example;

[0043] As can be seen from Table 3, when the elongation of Example 1 and Example 2 is maintained above 2%, the tensile strength of Example 1 is 294.96 MPa, and the tensile strength of Example 2 is 290.11 MPa, which has obvious mechanical performance advantages compared with Comparative Example 1.

[0044] Focus on combining Figure 1-6 To illustrate the microstructural changes of each embodiment and the microstructural changes of the comparative example.

[0045] from Figure 1 It can be seen that the as-cast structures of Example 1 and Example 2 are finer and more uniform than those of Comparative Example 1. Figure 2 Further explanation: the average size of the second phase in Example 1 is 0.9 μm, the average size of the second phase in Example 2 is 0.93 μm, and the average size of the second phase in Comparative Example 1 is 1.37 μm. This is because the content of Cr added in Example 1 is controlled within 0.050-0.080%, which is much higher than that in Comparative Example 1. This allows the Cr element to react with the Al matrix to produce a large number of fine second phases. These second phases act as heterogeneous nucleation points during the solidification of the alloy melt, providing more fulcrums for metal solidification, refining the cast structure of the alloy, making the alloy grain size very uniform and fine, and improving the uniformity of the structure. In addition, the Cr element will produce dispersed Al7Cr compounds during the homogenization annealing of the ingot. These dispersed phases have high density and high thermal stability. During heat treatment and hot deformation, they will pin dislocations and grain boundaries, inhibit grain growth, enhance the dispersion strengthening effect, and thus improve the tensile strength of the aluminum alloy in the example.

[0046] Secondly, some uneven structures may be generated during the casting process, such as segregation and supersaturated solid solution. The present invention adopts a two-stage annealing process to better eliminate the unevenness. Specifically, the annealing temperature in the first stage is increased to 600-620°C and kept warm for 2-4 hours. The higher temperature promotes the diffusion of Cr elements, eliminates segregation, and accelerates the precipitation of the second phase; the temperature is lowered to 520-550°C in the second stage and kept warm for 3-6 hours. The cooling stabilizes the precipitated phase and avoids grain coarsening. At the same time, the matrix recrystallization temperature is increased to prevent grain growth during subsequent hot rolling. This process not only optimizes the uniformity of the structure, but also enhances the strength of the aluminum foil.

[0047] Focus on combination Figure 3 and Figure 4 As shown in FIG, the hot-rolled grains in the embodiment have been recrystallized but not grown, which inhibits further grain coarsening, maintains fine grains, and effectively releases hot rolling stress and eliminates deformation stress. Figure 5 As shown, the grains in the comparative example are relatively coarse.

[0048] The addition of Cr not only refines the grains, but also inhibits grain boundary migration through the pinning effect of Al7Cr phase, ensuring the stability of grain size after recrystallization and improving the strength and formability of aluminum foil. Cr also promotes the transformation of β-AlFeSi phase to spherical α-AlFeSi phase, making the size of the second phase in the matrix smaller and more evenly distributed. These changes also reduce the problems of pinholes and holes caused by the second phase during the rolling process of ultra-thin battery aluminum foil. Figure 6 As shown, it can also improve the stress corrosion resistance of aluminum foil.

[0049] By optimizing the Cr element content and the two-stage homogenization annealing process, the present invention enables the embodiment to achieve a finer and more uniform cast structure, stable dispersion strengthening, such as Al7Cr phase, improved strength and recrystallization temperature, fine recrystallized grains after hot rolling, stress release and coarsening inhibition, reduced rolling defects such as pinholes and holes, and improved aluminum foil processing performance.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the design of this case. Any equivalent changes made based on the key design of this case shall fall within the scope of protection of this case.

Claims

1. A method for preparing ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil, characterized by: The following steps are involved: S1: Smelting and alloying treatment: adding industrial aluminum scrap and industrial pure aluminum ingots in a certain proportion into a smelting furnace, smelting at a temperature of 680°C to 760°C, adding alloying elements after all the raw materials are melted, and obtaining an aluminum melt. The aluminum melt includes the following alloying elements by mass percentage: Si: 0.060~0.150%, Fe: 0.40~0.80%, Cu: 0.050~0.080%, Ti: 0.012~0.020%, Cr: 0.050~0.080%, Al≥99.00%, and the individual content of other impurity elements ≤0.03%, the total amount ≤0.1%; S2: Casting: Casting the aluminum melt obtained in step S1 into aluminum alloy plate ingots; S3: Homogenization annealing: The milled aluminum alloy plate ingot is placed in a heating furnace for two-stage homogenization annealing. In the two-stage homogenization annealing, the material temperature is first kept at 600-620°C for 2-4 hours, and then the plate ingot temperature is reduced to 520-550°C and kept at this temperature for 3-6 hours. S4: rolling: rolling the aluminum alloy ingot into an aluminum coil with a thickness of 0.2 to 0.5 mm; S5: Foil rolling: The aluminum coil obtained in step S4 is rolled into an aluminum foil coil through 4 to 5 passes.

2. The method for preparing the ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil according to claim 1, characterized in that: The Cr element added in step S1 is added in the form of an Al-Cr master alloy, and the content of the Cr element in the Al-Cr master alloy is ≤5%.

3. The method for preparing the ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil according to claim 1, characterized in that: In the step S1, the melting temperature is 740-760°C.

4. The method for preparing the ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil according to claim 1, characterized in that: In step S2, a grain refiner is added during casting. The grain refiner is AlTiB, and the addition amount of AlTiB is 1.5-1.8 kg / T.

5. The method for preparing a lithium battery connector with high conductivity and high surface quality according to claim 1, wherein: In step S4, rolling includes hot rolling and cold rolling; First, the aluminum alloy ingot is hot rolled 20 times to obtain an aluminum coil with a thickness of 2.5 to 3.0 mm; After the aluminum coil cools down, it is cold rolled three times to a thickness of 0.2-0.5 mm, and the cold rolling reduction is controlled at more than 2 mm.

6. The method for preparing the ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil according to claim 5, characterized in that: The hot rolling start temperature is ≥450°C.

7. The method for preparing the ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil according to claim 5, characterized in that: The hot rolling includes hot rough rolling and hot finish rolling; First, the aluminum alloy plate ingot is hot-rough rolled 17 times to a thickness of 25mm, and then hot-finished rolled 3 times to hot-roll the 25mm thick plate ingot to 2.5-3.0mm. After hot rolling, the final rolling temperature of the aluminum coil is controlled at 360-380℃.

8. The method for preparing the ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil according to claim 5, characterized in that: The reduction amount of each cold rolling pass is: the first pass is from 2.5-3.0 mm to 0.8-1.5 mm, the second pass is from 0.8-1.5 mm to 0.3-0.6 mm, and the third pass is from 0.3-0.6 mm to 0.20-0.28 mm.

9. The method for preparing the ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil according to claim 1, characterized in that: In step S5, the deformation amount of each pass is 40-50%, the rolling speed is 600-1200 mm / min, the temperature of the rolling oil added during rolling is 40-60° C., and the rolling force is 2000-4000 N.

10. The method for preparing the ultra-high-strength, low-pinhole, corrosion-resistant ultra-thin battery aluminum foil according to claim 1, characterized in that: In step S1, the industrial aluminum scrap is the aluminum scrap generated during the production process of steps S1 to S5, and the proportion of the industrial aluminum scrap is 0 to 35%, and the rest is pure aluminum ingots.

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