High formability 3-series aluminum alloy sheet and method of making

Abstract

This invention discloses a high-formability 3-series aluminum alloy sheet and its preparation method, belonging to the field of aluminum alloy material technology. This aluminum alloy is Mg-free and contains, by mass percentage: Mn 1.0%-1.5%, Fe 0.3%-0.6%, Si 0.15%-0.35%, and Cu 0.05%-0.10%, with an Fe / Si mass ratio ≤ 2:1. The preparation method employs gradient casting, hot rolling, three-stage asynchronous cold rolling, two-stage rapid annealing, and chromium-free passivation and micro-arc oxidation surface treatment. This invention utilizes the quaternary synergistic strengthening of Mn-Fe-Si-Cu to suppress acicular brittle phases, improve deep-drawing formability and anodized surface uniformity, while reducing recycling energy consumption and production costs. The resulting sheet has a tensile strength ≥ 140 MPa, elongation ≥ 9.0%, and cupping value ≥ 7.0 mm, making it particularly suitable for deep-drawing applications such as high-end cosmetic packaging shells and consumer electronics casings.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy material technology, specifically relating to a highly formable 3-series aluminum alloy sheet suitable for deep drawing applications such as cosmetic packaging shells and consumer electronics casings, and its preparation method. Background Technology

[0002] With the cosmetics industry's surging demand for lightweight, aesthetically pleasing, and recyclable packaging materials, aluminum alloy sheets with a thickness of 0.4-0.6mm have become the preferred material for the outer shells of high-end cosmetic tubes, cushion compacts, and serum bottles. 3-series aluminum alloys (Al-Mn series) are widely used due to their good corrosion resistance, weldability, and moderate strength.

[0003] In the existing technology, domestic and foreign patent technologies involving aluminum alloy sheets for cosmetic packaging mainly present the following technical routes:

[0004] Prior art 1, CN113874535A / WO2020239276A1, discloses a rolled aluminum-based alloy product for cosmetic packaging, with the following composition: Mn 1.0–1.5%, Mg 0.2–0.6%, Si 0.2–0.6%, Fe 0.1–0.7%, and Cu 0.05–0.3%, requiring the Al(Fe,Mn)Si phase to account for at least 50%. The technical feature of this patent is the forced introduction of Mg (0.2–0.6%) to improve strength through solid solution strengthening. However, the addition of Mg leads to the following problems: firstly, it increases the alloy density and cost; secondly, the energy consumption for recycling and smelting 5-series aluminum is 18% higher than that for 3-series aluminum; and thirdly, the presence of Mg reduces the surface uniformity after anodizing, which is detrimental to the high-end appearance requirements of cosmetic packaging.

[0005] Prior art 2, CN107299262A, discloses a 3XXX series aluminum alloy with high Si content, comprising Si 0.62–0.78%, Fe 0.51–0.61%, Cu 0.10–0.16%, Mn 1.07–1.33%, and Mg 1.09–1.22%. This patent also relies on a high Mg content (above 1.0%) for strengthening, and the Si content is significantly high (above 0.62%), which leads to the precipitation of coarse eutectic silicon phase, impairing deep-drawing performance. Furthermore, this patent does not address the precise control of the Fe / Si ratio.

[0006] Prior art 3, CN201811015307A, discloses an aluminum alloy for cosmetics, characterized by extremely low alloying (Si≤0.12%, Fe≤0.25%, Cu≤0.05%, Mn≤0.05%), with a tensile strength of only 100–130 MPa, an elongation of only 4%–5%, and insufficient cupping value, making it difficult to meet the forming requirements of complex deep-drawing shells;

[0007] Prior art 4, US20160265095A1, discloses a 3000 series aluminum alloy sheet for automobile bodies. Although it has high strength and high flexibility, its application scenario is automobile body panels rather than cosmetic packaging. It has not been specifically optimized for surface gloss and deep drawing performance under ultra-thin (≤0.5mm) conditions.

[0008] In summary, the existing technology currently has the following shortcomings:

[0009] The current technology relies heavily on Mg for strengthening: the patents of existing technologies 1 and 2 both introduce Mg (0.2–1.22%), which increases recycling costs and surface treatment difficulty, and the deep drawing performance of Mg-based alloys is unstable in ultra-thin states;

[0010] Fe / Si ratio control is lacking: Except for a few patents, most existing technologies do not precisely constrain the Fe / Si ratio, resulting in the precipitation of needle-like β-AlFeSi phase, which impairs formability;

[0011] The Cu content range is too wide or too high: In the existing technology, the Cu content is 0.05-0.30%, and an upper limit that is too high can easily lead to intergranular corrosion.

[0012] Insufficient coupling between composition and process: Existing patents are mostly isolated composition designs, and do not systematically and collaboratively optimize composition control with process parameters such as asynchronous cold rolling and two-stage annealing.

[0013] Therefore, there is an urgent need to develop a highly formable 3-series aluminum alloy sheet with no Mg addition, precise control of the Fe / Si ratio, and trace Cu addition to solve the above-mentioned technical problems. Summary of the Invention

[0014] The purpose of this invention is to provide a high-formability 3-series aluminum alloy sheet and its preparation method. It achieves a balance between high strength and high elongation through Mn-Fe-Si-Cu quaternary synergistic strengthening, and eliminates the alloy system design and preparation process that requires the addition of Mg. This solves the technical problems of existing 3-series aluminum alloys, such as high recycling costs due to Mg dependence, difficulty in surface treatment, brittle phase precipitation caused by uncontrolled Fe / Si ratio, easy cracking in deep drawing, and increased corrosion risk due to improper Cu content. At the same time, it reduces the dependence on imported materials.

[0015] To achieve the above objectives, the present invention provides the following technical solution:

[0016] A high-formability 3-series aluminum alloy sheet, by weight percentage, is composed of the following components:

[0017] Mn: 1.0%-1.5%; Fe: 0.3%-0.6%; Si: 0.15%-0.35%; Cu: 0.05%-0.10%; balance is Al and unavoidable impurities; the aluminum alloy does not contain Mg; and the Fe / Si mass ratio is ≤2:1.

[0018] Furthermore, the Mn content is 1.15%-1.25%; the Fe / Si mass ratio is 1.7:1-1.9:1.

[0019] Furthermore, the Cu content is 0.075%-0.085%.

[0020] Furthermore, the aluminum alloy sheet has a thickness of 0.4-0.6 mm; tensile strength ≥140 MPa, elongation ≥9.0%, and cupping value ≥7.0 mm.

[0021] A method for preparing a high-formability 3-series aluminum alloy sheet includes the following steps:

[0022] S1 melting: electromagnetic stirring melting, online composition control by spectroscopy, casting ingots with Mn gradient distribution along the rolling direction;

[0023] S2 hot rolling: final rolling temperature 290℃-310℃, rolling speed 5-15m / s; dynamic recrystallization completion ≥95%, grain size 45-65μm;

[0024] S3 cold rolling: adopts three-stage asynchronous cold rolling, with a total reduction rate of ≥80% and a tension difference of 10%-20% between the intermediate rolling stage;

[0025] S4 Annealing: Two-stage annealing is adopted, with the temperature increased to 270℃-290℃ at 80-120℃ / min and held for 3-5 hours, resulting in a recrystallization rate of ≥85%;

[0026] S5 Surface Treatment: Chromium-free passivation followed by micro-arc oxidation.

[0027] Furthermore, S1, electromagnetic frequency 10-40Hz, current 100-500A; online monitoring of composition fluctuations by spectrometer ±0.02%; casting into gradient ingots: Mn content gradually changes from 1.10% to 1.50% along the rolling direction.

[0028] Furthermore, S2, final rolling temperature 300℃, rolling speed 10m / s, and grain size after crystallization 55μm.

[0029] Furthermore, S3, three-stage asynchronous rolling: the roughing stage rolls from 5.0 to 1.2 mm with a rolling force of 3500 kN; the intermediate rolling stage rolls from 1.2 to 0.6 mm with a tension difference of 15%; the finishing stage rolls from 0.6 to 0.48 mm with a work roll crown of 0.005 mm.

[0030] Furthermore, S4 is kept at a temperature in a nitrogen-hydrogen mixed atmosphere and recrystallized.

[0031] Furthermore, in the S5 chromium-free passivation process, the passivation system was: sodium molybdate 10g / L, GPTMS 4%, pH 3.8, temperature 40℃, immersion for 2min, and passivation film thickness 220nm; in the micro-arc oxidation process, the electrical parameters were 400V / 800Hz, duty cycle 15%, the electrolyte was a silicate system, and the Al2O3 ceramic layer thickness was 5μm.

[0032] Furthermore, the size of the needle-like β-AlFeSi phase in the finished aluminum alloy is ≤2μm, and the spherical α-Al(Fe,Mn)Si phase accounts for more than 80% of the total precipitated phase; after sulfuric acid anodizing treatment, the surface has no color difference or dark stripes, and the gloss uniformity ΔE is ≤0.5.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: The high formability 3-series aluminum alloy sheet and its preparation method have the following advantages:

[0034] 1. High formability: elongation of 9.2% (about 1.5% higher than traditional 3-series aluminum alloys), cupping value ≥7.0mm, r value ≥0.75, stamping qualification rate increased from 40% to over 65%, meeting 90% of the needs of conventional cosmetic shells;

[0035] 2. Strength requirements: Tensile strength ≥ 140 MPa, with fracture toughness increased by 20%;

[0036] 3. Grain refinement: The grain size of the hot-rolled plate is refined to 55–60 μm, the Al6Mn phase size is ≤2 μm, the acicular β phase is suppressed, and the spherical α phase accounts for more than 80%;

[0037] 4. Green and low-cost: The absence of Mg reduces the energy consumption of recycling and smelting by 18% compared to 5-series aluminum alloys, increases the smelting and casting yield to 88%, and reduces the cost per ton by approximately 20% compared to 5-series aluminum alloys;

[0038] 5. Breaking through patent barriers: The combination strategy of Mg-free + precise Fe / Si ratio + narrow range Cu in this invention forms a clear compositional differentiation from existing patents, realizing independent intellectual property rights. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] A high-formability 3-series aluminum alloy sheet, by weight percentage, is composed of the following components:

[0041] Mn: 1.0%-1.5%; Fe: 0.3%-0.6%; Si: 0.15%-0.35%; Cu: 0.05%-0.10%; balance is Al and unavoidable impurities; the aluminum alloy does not contain Mg; and the Fe / Si mass ratio is ≤2:1.

[0042] Example 1 (Preferred Solution, Overall Performance)

[0043] A high-formability 3-series aluminum alloy sheet, by weight percentage, is composed of the following components:

[0044] Mn: 1.20%; Fe: 0.45%; Si: 0.25%; Cu: 0.08%; Fe / Si = 1.8:1; balance is Al and unavoidable impurities.

[0045] The method for preparing the above-mentioned high formability 3-series aluminum alloy sheet includes the following steps:

[0046] S1 Smelting: A 100-ton smelting furnace was used. The raw materials were A00 pure aluminum ingots, Al-Mn 10%, Al-Fe 10%, Al-Si 20%, and Al-Cu 50% master alloy. The temperature was raised to 740±5℃ for melting. After slag removal, argon gas was introduced for refining for 15 minutes to remove gas and impurities. The electromagnetic stirring parameters were: frequency 20Hz and current 300A to ensure uniform composition. The composition was monitored online by a spectrometer, and the fluctuation was controlled within ±0.02%. The ingots were cast into gradient ingots with the Mn content gradually changing from 1.10% to 1.30% along the rolling direction. The ingot size was 420mm×1200mm×5000mm.

[0047] S2 hot rolling: Hold at 600℃ for 8 hours, furnace cool to 450℃ and exit the furnace; hot rolling start temperature 440℃, finishing rolling temperature 305℃, rolling speed 10m / s, 5 passes to roll to 5.0mm thick hot rolled coil; dynamic recrystallization completion 95%, grain size 55μm, Al6Mn phase size ≤2μm;

[0048] S3 Cold Rolling: Roughing: 5.0mm→1.2mm, rolling force 3500kN, roll diameter difference 30mm, asynchronous ratio 1.05; Intermediate Rolling: 1.2mm→0.6mm, front and rear tension difference 15%, sheet shape control warpage ≤3I; Finishing Rolling: 0.6mm→0.48mm, work roll crown 0.005mm, ensuring same sheet difference ≤0.003mm; total reduction rate 85%;

[0049] S4 annealing: Nitrogen-hydrogen mixed atmosphere (N2:H2=95:5), rapidly heated to 280℃ at 100℃ / min, held for 4h; recrystallization rate 88%, uniform grains with no abnormal growth.

[0050] S5 surface treatment: 10g / L sodium molybdate + 4% GPTMS, pH=3.8, temperature 40℃, immersion for 2min, passivation film thickness 220nm; micro-arc oxidation: 400V / 800Hz, duty cycle 15%, electrolyte is silicate system, Al2O3 ceramic layer thickness 5μm.

[0051] Samples were selected for performance testing. Performance test results:

[0052] Tensile strength: 148 MPa;

[0053] Yield strength: 122 MPa;

[0054] Elongation: 9.2%;

[0055] Cupping value: 7.0 mm;

[0056] Plastic strain ratio r: 0.75;

[0057] Salt spray test for 48 hours: white rust area ≤ 0.5%;

[0058] Stamping pass rate: 65% (Φ30mm cylindrical shell, height-to-diameter ratio 0.8);

[0059] Anodized surface uniformity: After sulfuric acid anodizing, the surface has no color difference or dark stripes, and the gloss uniformity ΔE=0.42 (ΔE≤0.5).

[0060] Example 2 (Low Fe, High Si type, suitable for higher surface gloss requirements)

[0061] A high-formability 3-series aluminum alloy sheet, by weight percentage, is composed of the following components:

[0062] Mn: 1.15%; Fe: 0.30%; Si: 0.35%; Cu: 0.07%; Mg: 0.00%; Fe / Si = 0.86:1; balance is Al and unavoidable impurities.

[0063] The method for preparing the above-mentioned high formability 3-series aluminum alloy sheet includes:

[0064] Melting temperature 735℃, argon refining for 12 min; gradient ingot Mn fluctuation 1.05%-1.25%; hot rolling final rolling temperature 300℃, rolling speed 9m / s, hot rolling thickness 5.0mm; three-stage asynchronous cold rolling to 0.45mm, total reduction rate 86%, intermediate rolling tension difference 12%; two-stage annealing: heating from 90℃ / min to 275℃, holding for 4.5h; passivation + micro-arc oxidation same as in Example 1.

[0065] Samples were selected for performance testing. Performance test results:

[0066] Tensile strength: 142 MPa;

[0067] Elongation: 9.5%;

[0068] Cupping value: 7.2 mm;

[0069] r-value: 0.78;

[0070] After 48 hours of salt spray treatment, the area of ​​white rust is ≤0.3%.

[0071] Stamping pass rate: 68%;

[0072] Anodizing ΔE=0.38 results in a brighter surface, making it suitable for high-gloss cosmetic cases.

[0073] Example 3 (High Fe, Low Si type, adapted to higher strength requirements)

[0074] A high-formability 3-series aluminum alloy sheet, by weight percentage, is composed of the following components:

[0075] Mn: 1.25%; Fe: 0.60%; Si: 0.30%; Cu: 0.10%; Mg: 0.00%; Fe / Si = 2.0:1; balance is Al and unavoidable impurities.

[0076] The preparation method of the above-mentioned high formability 3-series aluminum alloy sheet includes: melting temperature 745℃, refining for 18 min; gradient ingot Mn fluctuation of 1.15%-1.35%; hot rolling final rolling temperature of 310℃, rolling speed of 11 m / s; asynchronous cold rolling to 0.50 mm, total reduction rate of 84%, intermediate rolling tension difference of 18%; two-stage annealing: heating at 110℃ / min to 290℃, holding for 3.5 h; surface treatment is the same as in Example 1.

[0077] Samples were selected for performance testing. Performance test results:

[0078] Tensile strength: 155 MPa;

[0079] Elongation: 9.0%;

[0080] Cupping value: 6.9 mm;

[0081] r-value: 0.72;

[0082] After 48 hours of salt spray treatment, the area of ​​white rust is ≤0.6%.

[0083] The stamping pass rate is 62%; suitable for thick-walled cosmetic housings and consumer electronics casings that require higher structural strength.

[0084] Comparative Example 1 (containing Mg)

[0085] A 3-series aluminum alloy sheet, by mass percentage, is composed of the following components: Mn 1.2%, Mg 0.4%, Si 0.3%, Fe 0.4%, Cu 0.10%, Fe / Si = 1.33, with no Fe / Si ratio constraint. The preparation process is the same as in Example 1.

[0086] Performance test results: tensile strength 152 MPa (comparable to the present invention), elongation 7.8% (1.4% lower than the present invention), stamping pass rate 54%, slight color difference and streaks appeared on the surface after anodizing. The test results verify the effect of the Mg-free design on improving surface quality and formability. In addition, the energy consumption of recycling and smelting of Mg-containing alloys is about 18% higher than that of the present invention.

[0087] Comparative Example 2 (Fe / Si>2:1)

[0088] A 3-series aluminum alloy sheet, by mass percentage, is composed of the following components: Mn 1.20%, Fe 0.70%, Si 0.20% (Fe / Si=3.5), Cu 0.08%, and no Mg. The preparation process is the same as in Example 1.

[0089] Performance test results: The amount of needle-like β-AlFeSi phase in the microstructure increased (size > 5 μm), the elongation decreased to 6.8%, the burr height at the stamping edge was 20 μm, and the sealing performance was unqualified. The test results verified the necessity of the Fe / Si ratio ≤ 2:1 constraint condition.

[0090] Comparative Example 3 (Cu level is too high)

[0091] A 3-series aluminum alloy sheet, by mass percentage, is composed of the following components: Mn 1.20%, Fe 0.45%, Si 0.25%, Cu 0.25% (high), and no Mg. The preparation process is the same as in Example 1.

[0092] Performance test results: Cu segregation at grain boundaries intensified, and the tendency for intergranular corrosion increased significantly. After 72 hours of neutral salt spray testing, obvious intergranular corrosion spots appeared, with an area ratio >2%, while in Example 1 of this invention, corrosion spots were <0.3% under the same conditions. The test results verified the synergistic effect of adding 0.05-0.10% Cu.

[0093] Comparative Example 4 (without Cu)

[0094] A 3-series aluminum alloy sheet, by mass percentage, is composed of the following components: Mn 1.20%, Fe 0.45%, Si 0.25%; free of Cu and Mg. The preparation process is the same as in Example 1.

[0095] Performance test results: recrystallization temperature 305℃, elongation after annealing 7.7%, fracture toughness decreased by 20% compared to Example 1, and stamping pass rate 52%. The test results of Comparative Examples 3 and 4 verified the synergistic effect of adding 0.05-0.10% Cu.

[0096] Comparative analysis of this application with existing patents:

[0097] 1. Eliminate the addition of Mg to achieve green and low-cost production.

[0098] Existing technologies all force the addition of 0.2–1.22% Mg to improve strength. This invention achieves mechanical properties of tensile strength ≥140MPa and elongation ≥9.2% without relying on Mg by precisely controlling the Fe / Si ratio and adding trace amounts of Cu. This avoids the increased energy consumption of recycling and smelting (18% higher than the 3-series) and the problem of uneven anodized surface caused by Mg.

[0099] Second: Precise control of the Fe / Si ratio ≤ 2:1 suppresses acicular brittle phase.

[0100] Existing patents generally do not constrain the Fe / Si ratio (CN113874535A specifies a Fe / Si ratio range of 0.17–3.5, which lacks sufficient control precision). This invention is the first to explicitly propose a Fe / Si ratio constraint of ≤2:1 in 3-series aluminum alloys used in cosmetic packaging. Thermodynamic calculations show that this ratio can effectively suppress the formation of needle-like β-AlFeSi phases (phase size ≤2μm), promote the precipitation of spherical α-Al(Fe,Mn)Si phases (accounting for over 80%), and improve the deep-drawing r-value to above 0.8. While the latest patent CN120945241A proposes Fe / Si ratio control (0.08–0.28), it targets 6-series aluminum alloys containing 0.8–1.2% Mg, applied in the semiconductor equipment field, which is completely different from the Mg-free 3-series system technology of this invention.

[0101] 3. Precise control of trace Cu addition (0.05–0.10%)

[0102] Existing patents have excessively wide ranges for Cu content (CN113874535A: 0.05–0.30%, CN107299262A: 0.10–0.16%), with the upper limit being too high, which can easily lead to intergranular corrosion. This invention strictly limits the Cu content to a narrow range of 0.05–0.10%, utilizing its grain boundary segregation effect to reduce the recrystallization temperature by 15℃ (from 305℃ to 290℃), achieving an 8% saving in annealing energy consumption. Simultaneously, TEM observation confirms that Cu forms 5-10nm nanoscale segregations at the grain boundaries, avoiding the corrosion risk caused by excessive Cu.

[0103] 4. Deep Synergy Between Ingredients and Processes

[0104] Existing patents mostly focus on isolated composition design. This invention systematically couples composition control with process parameters: gradient ingot casting technology (Mn content gradually changes ±0.2% along the rolling direction) compensates for elemental losses during rolling; three-stage asynchronous cold rolling (roughing / intermediate rolling / finishing, with a tension difference of 15% between the front and rear) combined with two-stage rapid annealing (heating rate of 100℃ / min) forms a closed-loop optimization of "composition → microstructure → properties". Existing asynchronous rolling patent (CN106903166A) only focuses on warpage control and does not involve the synergistic optimization of composition design and asynchronous rolling.

[0105] The present invention is systematically compared with the prior art, and the comparison results are shown in Table 1.

[0106] Comparison elements CN113874535A CN107299262A CN201811015307A This invention Alloy system Al-Mn-Mg-Si-Fe-Cu Al-Mn-Mg-Si-Fe-Cu-Zn Al-Mg-Ti (Very Low Alloying) Al-Mn-Fe-Si-Cu (without Mg) Mg content 0.2-0.6% 1.09-1.22% 0.05-0.2% 0% (No additives) Fe / Si ratio constraint none none none ≤2:1 (Precise control) Cu content 0.05-0.30% (wide range) 0.10-0.16% ≤0.05% 0.05-0.10% (narrow range) Si content 0.2-0.6% 0.62-0.78% (Slightly high) ≤0.12% 0.15-0.35% (moderate) Strengthening mechanism Mg solid solution strengthening Mg solid solution + Si precipitation Ultra-low alloying Fe / Si ratio regulation + Cu grain boundary segregation Application areas Cosmetic Packaging General Motors 3XXX series High-gloss appearance of cosmetics Cosmetic deep-drawing casing + consumer electronics Process collaboration Conventional hot rolling + cold rolling conventional process conventional process Gradient casting + asynchronous cold rolling + rapid annealing

[0107] Table 1

[0108] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A high-formability 3-series aluminum alloy sheet, characterized in that, It consists of the following components by mass percentage: Mn: 1.0%-1.5%; Fe: 0.3%-0.6%; Si: 0.15%-0.35%; Cu: 0.05%-0.10%; balance is Al and unavoidable impurities; the aluminum alloy does not contain Mg; and the Fe / Si mass ratio is ≤2:

1.

2. The high formability 3-series aluminum alloy sheet according to claim 1, characterized in that, The Mn content is 1.15%-1.25%; the Fe / Si mass ratio is 1.7:1-1.9:

1.

3. The high formability 3-series aluminum alloy sheet according to claim 1, characterized in that, The Cu content is 0.075%-0.085%.

4. The high formability 3-series aluminum alloy sheet according to claim 1, characterized in that, The aluminum alloy sheet has a thickness of 0.4-0.6 mm; tensile strength ≥140 MPa, elongation ≥9.0%, and cupping value ≥7.0 mm.

5. A method for preparing a high-formability 3-series aluminum alloy sheet according to any one of claims 1-4, characterized in that, Includes the following steps: S1 melting: electromagnetic stirring melting, online composition control by spectroscopy, casting ingots with Mn gradient distribution along the rolling direction; S2 hot rolling: final rolling temperature 290℃-310℃, rolling speed 5-15m / s; dynamic recrystallization completion ≥95%, grain size 45-65μm; S3 cold rolling: adopts three-stage asynchronous cold rolling, with a total reduction rate of ≥80% and a tension difference of 10%-20% between the intermediate rolling stage; S4 Annealing: Two-stage annealing is adopted, with the temperature increased to 270℃-290℃ at 80-120℃ / min and held for 3-5 hours, resulting in a recrystallization rate of ≥85%; S5 Surface Treatment: Chromium-free passivation followed by micro-arc oxidation.

6. The method for preparing a high-formability 3-series aluminum alloy sheet according to claim 5, characterized in that, S1, electromagnetic frequency 10-40Hz, current 100-500A; online monitoring of composition fluctuations by spectrometer ±0.02%; cast into gradient ingots: Mn content gradually changes from 1.10% to 1.50% along the rolling direction.

7. The method for preparing a high-formability 3-series aluminum alloy sheet according to claim 5, characterized in that, S2, final rolling temperature 300℃, rolling speed 10m / s, grain size after crystallization 55μm.

8. The method for preparing a high-formability 3-series aluminum alloy sheet according to claim 5, characterized in that, S3. Three-stage asynchronous rolling: the roughing stage rolls from 5.0 to 1.2 mm with a rolling force of 3500 kN; the intermediate rolling stage rolls from 1.2 to 0.6 mm with a tension difference of 15%; the finishing stage rolls from 0.6 to 0.48 mm with a work roll crown of 0.005 mm.

9. The method for preparing a high-formability 3-series aluminum alloy sheet according to claim 5, characterized in that... S5. During the chromium-free passivation process, the passivation system was: sodium molybdate 10g / L, GPTMS 4%, pH 3.8, temperature 40℃, immersion for 2min, and passivation film thickness 220nm. During the micro-arc oxidation process, the electrical parameters were 400V / 800Hz, duty cycle 15%, electrolyte was silicate system, and Al2O3 ceramic layer thickness was 5μm.

10. The method for preparing a high-formability 3-series aluminum alloy sheet according to claim 5, characterized in that, In finished aluminum alloy products, the size of the needle-like β-AlFeSi phase is ≤2μm, and the spherical α-Al(Fe,Mn)Si phase accounts for more than 80% of the total precipitated phase; after sulfuric acid anodizing treatment, the surface has no color difference or dark stripes, and the gloss uniformity ΔE is ≤0.5.