High-toughness large-specification aluminum alloy thick plate and preparation method thereof

Abstract

The invention belongs to the technical field of aluminum alloy materials, and relates to a high-toughness large-specification aluminum alloy thick plate and a preparation method thereof. The aluminum alloy thick plate has the characteristics of large specification, high toughness and high strength, the strength and toughness of the aluminum alloy thick plate in three directions have the characteristic of low anisotropy, and the aluminum alloy thick plate also has the characteristic of low inter-batch variation coefficient. By designing and controlling the alloy component range of the thick aluminum alloy plate, the component fluctuation of the thick aluminum alloy plate at different parts is greatly reduced, the thick aluminum alloy plate with the uniform alloy internal structure is obtained, and the variation coefficient between batches of the thick aluminum alloy plates is reduced. And meanwhile, the process steps of fusion casting, multi-stage homogenization, large-strain rolling, solid solution quenching, two-stage aging heat treatment and the like are matched, so that the obtained large-specification aluminum alloy thick plate has the characteristics of high toughness, high strength, low anisotropy and good inter-batch stability.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy material technology, and relates to a high-toughness, large-size aluminum alloy thick plate and its preparation method. Background Technology

[0002] 7000 series aluminum alloys are the main structural material for aircraft, primarily used in critical load-bearing components such as the main load-bearing beams and joints of the aircraft fuselage. To meet the overall manufacturing requirements of these main load-bearing components, large-size aluminum alloy plates are required. With advancements in materials technology, aircraft design has shifted from initial static strength design to damage tolerance design, placing higher demands on the toughness of the main structural materials. Due to the rolling process, aluminum alloy plates undergo varying degrees of deformation in different directions, inevitably resulting in higher longitudinal and transverse properties and lower vertical properties. During flight, aircraft experience complex stresses and alternating loads, requiring more uniform mechanical properties across the main structural materials to prevent overall structural failure due to lower performance in one direction. Furthermore, for large-size aluminum alloy plates used in aircraft main load-bearing structures, high overall performance is no longer the sole control objective. To meet aircraft safety and airworthiness requirements for both military and civilian aircraft, aluminum alloy plates must also exhibit better batch-to-batch strength stability while maintaining high overall performance. Summary of the Invention

[0003] Research has found that the main aluminum alloy plates used for aircraft main load-bearing frame beams are currently 7050-T7451 plates, with a maximum thickness of 203mm, allowing for the integral manufacturing of the main load-bearing frame beams; however, their strength is relatively low, with a tensile strength of approximately 500MPa, which limits their application. Taking the 7050-T7451 plate, which is widely used in the 76-102mm thickness range, as an example, its fracture toughness in the LT direction is 28MPa·m. 1 / 2 The fracture toughness in the TL direction is 25 MPa·m. 1 / 2 The fracture toughness in the SL direction is 23 MPa·m. 1 / 2 To achieve structural weight reduction, 7A55-T7751 aluminum alloy thick plates with a strength of 600 MPa have been developed. However, due to the inherent trade-offs between strength and toughness, and strength and hardenability in aluminum alloys, the maximum thickness of 7A55-T7751 aluminum alloy thick plates can only reach 38 mm while ensuring the overall performance of the aluminum alloy thick plates. This thickness is insufficient for the integral manufacturing of the main load-bearing frame beams. Furthermore, the LT fracture toughness of 7A55-T7751 aluminum alloy thick plates is 23 MPa·m. 1 / 2 However, it also cannot meet the long service life requirements of the main load-bearing frame beam.

[0004] To overcome the shortcomings of existing technologies, this invention provides a high-toughness, large-size aluminum alloy thick plate and its preparation method. By designing the types and composition ranges of alloying elements, and combining this invention with specific process steps (including casting, multi-stage homogenization annealing, high-strain rolling, solution quenching, pre-stretching, and two-stage aging), this invention effectively controls the microstructure of the aluminum alloy thick plate in different directions. The resulting aluminum alloy thick plate exhibits characteristics such as large dimensions (especially large thickness), high toughness, high strength, low anisotropy (specifically, low anisotropy in strength and toughness in three directions), and good batch stability. In particular, by designing and precisely controlling the types and composition ranges of alloying elements, this invention significantly reduces compositional fluctuations in different parts of the aluminum alloy thick plate. This significantly reduces batch-to-batch performance differences, resulting in aluminum alloy thick plates with good batch stability.

[0005] The objective of this invention is achieved through the following technical solution: A method for preparing a high-toughness, large-size aluminum alloy thick plate, the method comprising the following steps: 1) Aluminum ingots, magnesium ingots, zinc ingots, aluminum-copper master alloy, aluminum-zirconium master alloy, and aluminum-manganese master alloy are mixed and melted to prepare an aluminum alloy melt; the alloy composition of the aluminum alloy thick plate, by weight percentage, includes the following components: Zn: 6.8%-7.9%, Mg: 1.8%-2.2%, Cu: 1.5%-1.8%, Zr: 0.08%-0.15%, Mn: 0.05%-0.25%, Cr≤0.04%, Ti≤0.06%, Fe≤0.10%, Si≤0.08%, and the total amount of other impurities is <0.05%, with the balance being aluminum; 2) The aluminum alloy melt from step 1) is refined, slag removed, degassed, and filtered; 3) Cast the aluminum alloy melt processed in step 2). During casting, add an online grain refiner to refine the grains. The temperature of adding the online grain refiner is controlled at 720℃-730℃. The time from adding the online grain refiner to the start of solidification of the aluminum alloy melt is controlled at 15-25 minutes. During the solidification of the aluminum alloy melt, monitor the temperature gradient on the surface of the aluminum alloy ingot in real time within the range of 5-15℃ / cm. At the same time, ensure that the solidification front of the aluminum alloy melt is stable at 20-30mm below the crystallizer outlet to prepare a large-size aluminum alloy ingot. 4) Perform multi-stage homogenization annealing on the large-size aluminum alloy ingots from step 3). 5) The large-size aluminum alloy ingot after the multi-stage homogenization annealing treatment in step 4) is milled and then rolled. The initial rolling temperature is 385℃-400℃, the total number of rolling passes does not exceed 15, the intermediate rolling stage adopts 2-5 consecutive passes of large strain rolling, the single pass reduction in the large strain rolling process is 40-55mm, and the final rolling temperature is not lower than 350℃ to prepare aluminum alloy thick plate. 6) Perform solution quenching treatment on the rolled aluminum alloy thick plate from step 5). 7) Perform pre-stretching treatment on the aluminum alloy thick plate after solution quenching in step 6). 8) The aluminum alloy thick plate after the pre-stretching treatment in step 7) is subjected to a two-stage aging treatment to prepare a high-toughness large-size aluminum alloy thick plate.

[0006] According to an embodiment of the present invention, in step 1), the alloy composition of the aluminum alloy thick plate, by weight percentage, includes the following components: Zn: 6.8%-7.9%, Mg: 1.8%-2.2%, Cu: 1.5%-1.8%, Zr: 0.08%-0.15%, Mn: 0.05%-0.25%, Cr≤0.04%, Ti≤0.06%, Fe≤0.10%, Si≤0.08%, with the total amount of other impurities <0.05%, and the balance being aluminum. Studies have found that when the alloy composition of the aluminum alloy melt is within the above range and the preparation process of the present invention is used, the uniform dispersion of the alloy composition and precipitated phases in the prepared aluminum alloy thick plate can be guaranteed, thereby obtaining an aluminum alloy thick plate with high toughness, high strength, low anisotropy, and good batch stability (low coefficient of variation between batches). Furthermore, when selecting alloy compositions that meet the above weight percentage requirements, the aluminum alloy melt will form a low-melting-point MgZn2 phase during the homogenization process. This low-melting-point MgZn2 phase can dissolve rapidly, preventing abnormal grain growth within the aluminum alloy thick plate. This is beneficial for obtaining aluminum alloy thick plates with low anisotropy and low batch-to-batch strength variation coefficients. During the homogenization process, the aluminum alloy melt will disperse and precipitate an Al6Mn phase. The Al6Mn phase can pin grain boundaries, inhibiting recrystallization of aluminum alloy grains. During hot deformation, it weakens the deformation texture strength and increases the recrystallization texture strength, reducing the anisotropy of the alloy's mechanical properties. In addition, the dispersed fine Al6Mn phase can change the alloy's fracture mode from intergranular fracture to transgranular ductile fracture, improving the alloy's elongation and fracture toughness, which is beneficial for obtaining aluminum alloy thick plates with high toughness and low anisotropy.

[0007] According to an embodiment of the present invention, in step 1), the alloy composition of the aluminum alloy thick plate includes Zn: 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, or 7.9% by weight percentage.

[0008] According to an embodiment of the present invention, in step 1), the alloy composition of the aluminum alloy plate, by weight percentage, includes Mg: 1.8%, 1.9%, 2.0%, 2.1% or 2.2%.

[0009] According to an embodiment of the present invention, in step 1), the alloy composition of the aluminum alloy plate includes Cu: 1.5%, 1.6%, 1.7% or 1.8% by weight percentage.

[0010] According to an embodiment of the present invention, in step 1), the alloy composition of the aluminum alloy thick plate includes Zr as a percentage by weight: 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, or 0.15%.

[0011] According to an embodiment of the present invention, in step 1), the alloy composition of the aluminum alloy thick plate, by weight percentage, includes Mn: 0.05%, 0.06%, 0.08%, 0.10%, 0.12%, 0.15%, 0.16%, 0.18%, 0.20%, 0.22%, 0.24%, or 0.25%.

[0012] According to an embodiment of the present invention, in step (1), the purity of the aluminum ingot is ≥99.99%. The purity of the magnesium ingot is ≥99.99%. The purity of the zinc ingot is ≥99.99%. The aluminum-copper master alloy is, for example, an Al-20Cu master alloy or an Al-30Cu master alloy, wherein the purity of the Al-Cu master alloy is ≥99%, and the purity of the Al-Cu master alloy refers to the sum of the contents of Al and Cu elements in the master alloy. The Al-Mn master alloy is, for example, an Al-10Mn master alloy or an Al-20Mn master alloy, wherein the purity of the Al-Mn master alloy is ≥99%, and the purity of the Al-Mn master alloy refers to the sum of the contents of Al and Mn elements in the master alloy. The Al-Zr master alloy is, for example, an Al-5Zr master alloy, an Al-6Zr master alloy, or an Al-10Zr master alloy, and the purity of the Al-Zr master alloy is ≥99%. The purity of the Al-Zr master alloy refers to the sum of the contents of Al and Zr elements in the master alloy.

[0013] According to an embodiment of the present invention, in step 1), aluminum ingots, zinc ingots, aluminum-copper master alloys, aluminum-zirconium master alloys and aluminum-manganese master alloys are mixed and heated to 760℃-790℃ and held for smelting for 10-30 minutes. Then, the temperature is lowered to 720℃-730℃ and magnesium ingots are added. The mixture is then held for smelting for another 10-30 minutes.

[0014] According to an embodiment of the present invention, in step 2), the refining, slag removal, degassing and filtration processes are achieved by the cooperation of a settling furnace, a slag skimmer, an online degassing device and a filtration device; for example, refining is carried out in a settling furnace, the slag skimmer is used to remove oxide inclusions at the top of the settling furnace, an online degassing device is set at the bottom of the settling furnace for degassing, and a filtration device is used to filter the aluminum alloy melt.

[0015] According to an embodiment of the present invention, in step 2), high-purity argon gas is used as the refining medium. The purity of the high-purity argon gas is not less than 99.999%, and the flow rate of the high-purity argon gas is 600-1200 L / h, for example, 600 L / h, 700 L / h, 800 L / h, 900 L / h, 1000 L / h, 1100 L / h, or 1200 L / h. The introduction time of the high-purity argon gas is 10-15 min. By introducing high-purity argon gas into the aluminum alloy melt, the aluminum alloy melt can be refined. When the flow rate of the high-purity argon gas is >1200 L / h or the introduction time of the high-purity argon gas is >15 min, it will cause the refining bubbles to spread and merge, thereby affecting the degassing efficiency and effect, which in turn affects the refining effect and makes it impossible to obtain a high-quality aluminum alloy melt. When the flow rate of the high-purity argon gas is less than 600 L / h or the introduction time of the high-purity argon gas is less than 10 min, the refining is incomplete, resulting in an insignificant refining effect and an inability to obtain high-quality aluminum alloy melt.

[0016] According to an embodiment of the present invention, in step 2), a dual-rotor online degassing device is used to degas the aluminum alloy melt. The rotational speed of the N1 rotor in the dual-rotor online degassing device is 450-550 rpm, and the argon flow rate is 4.5-5.5 m³ / s. 3 In the dual-rotor online degassing unit, the N2 rotor rotates at 300-350 rpm, and the argon flow rate is 3.0-3.2 m³ / h. 3 / h. By selecting the above-mentioned dual-rotor online degassing process, hydrogen dissolved in the aluminum alloy melt can be effectively removed, reducing the hydrogen content in the aluminum alloy melt to an extremely low level (less than 0.08 μg / g), which is beneficial for obtaining high-quality aluminum alloy melt.

[0017] According to an embodiment of the present invention, in step 2), a two-stage plate filter with a pressure of 30 PPI + 50 PPI is used to filter the aluminum alloy melt. Compared to a single-stage plate filter with a pressure of 60 PPI, the two-stage plate filter with a pressure of 30 PPI + 50 PPI of the present invention can effectively filter out the tiny solid inclusions in the aluminum alloy melt, which is beneficial for obtaining high-quality aluminum alloy melt.

[0018] According to an embodiment of the present invention, in step 2), it was found that by refining, slag removal, degassing, and filtering the aluminum alloy melt using the above-mentioned method, the hydrogen content in the aluminum alloy melt can be significantly reduced to below 0.08 μg / g. It can also significantly reduce the presence of micro solid inclusions in the aluminum alloy melt. By reducing the hydrogen content and micro solid inclusions in the aluminum alloy melt, the adverse effects on the toughness and fatigue performance of the aluminum alloy thick plate are eliminated. At the same time, the strength and toughness differences of the aluminum alloy thick plate in the three directions are significantly reduced, thereby obtaining aluminum alloy thick plates with low anisotropy and low batch-to-batch coefficient of variation.

[0019] According to an embodiment of the present invention, in step 3), the online grain refiner is an Al-Ti-C master alloy, and the Al-Ti-C master alloy is in the form of wire with a diameter of 4 mm-6 mm. The composition of the Al-Ti-C master alloy is, for example, AlTi5C. 0.18 AlTi3C 0.15 Or AlTi5C 1.2 .

[0020] According to an embodiment of the present invention, in step 3), the amount of the online grain refiner added is 0.01-0.015% of the total mass of the aluminum alloy melt, for example, 0.01%, 0.011%, 0.012%, 0.013%, 0.014% or 0.015%.

[0021] According to an embodiment of the present invention, in step 3), the temperature at which the online grain refiner is added is controlled between 720°C and 730°C, for example, 720°C, 721°C, 722°C, 723°C, 724°C, 725°C, 726°C, 727°C, 728°C, 729°C, or 730°C. Adding the online grain refiner within this temperature range allows it to melt rapidly and mix uniformly with the aluminum alloy melt. Furthermore, it enables the online grain refiner to quickly form effective nucleation cores, preventing grain growth and resulting in a fine and uniform grain structure, thus fully utilizing the grain refinement effect. The addition of the online grain refiner also allows for adjustments to the microstructure of the aluminum alloy, resulting in a more uniform internal microstructure distribution, which is beneficial for obtaining thick aluminum alloy plates with high toughness, high strength, low anisotropy, and low batch-to-batch variation coefficient.

[0022] According to an embodiment of the present invention, in step 3), the time from the addition of the online grain refiner to the start of solidification and crystallization of the aluminum alloy melt is controlled within 15-25 minutes, for example, 15 minutes, 16 minutes, 18 minutes, 20 minutes, 22 minutes, 24 minutes, or 25 minutes. Within this time range, it is possible to ensure that the online grain refiner quickly forms an effective nucleation core, and to effectively prevent the metal around the nucleus from continuing to diffuse into the nucleus, thus slowing down the growth rate of the nucleus and avoiding the formation of coarse grains inside the aluminum alloy melt due to excessive time. This is more conducive to obtaining aluminum alloy thick plates with uniform internal structure, thereby ensuring that the obtained aluminum alloy thick plates have high toughness and high strength, as well as low anisotropy and low batch-to-batch variation coefficient.

[0023] According to an embodiment of the present invention, in step 3), the temperature gradient on the surface of the aluminum alloy ingot is monitored in real time during the solidification and crystallization process of the aluminum alloy melt. The temperature gradient on the surface of the aluminum alloy ingot is controlled within 5-15℃ / cm by controlling the casting process, such as 5℃ / cm, 6℃ / cm, 7℃ / cm, 8℃ / cm, 9℃ / cm, 10℃ / cm, 11℃ / cm, 12℃ / cm, 13℃ / cm, 14℃ / cm, or 15℃ / cm. Under this temperature gradient, the casting speed and cooling intensity are well matched, resulting in a stable solidification process. The force is released, preventing thermal cracking; under this temperature gradient, the liquid phase of the solute will not flow long distances between dendrites, resulting in a more uniform ingot composition, which is beneficial for obtaining aluminum alloy thick plates with more uniform microstructure and properties; under this temperature gradient, the solidification front can advance smoothly, avoiding isolated solidification of local areas and the formation of microporous structures due to untimely feeding; in summary, by controlling the temperature gradient on the surface of aluminum alloy ingots, the uniform distribution of the internal microstructure of the alloy can be regulated, resulting in aluminum alloy thick plates with high toughness, high strength, low anisotropy, and low batch-to-batch variation coefficient.

[0024] According to an embodiment of the present invention, in step 3), the temperature gradient can be monitored by an infrared thermal imager.

[0025] According to an embodiment of the present invention, in step 3), due to the different solubilities of alloying elements (such as Mg and Cu) in the liquid and solid phases of the aluminum alloy, some solute atoms tend to accumulate at the solidification front and cannot fully diffuse into the liquid metal. This results in intragranular segregation or regional segregation at the grain boundaries or center of the ingot, leading to uneven composition of the ingot and affecting the uniform distribution of the internal structure of the alloy. This problem can be effectively solved by stabilizing the solidification front position of the aluminum alloy melt at 20-30 mm below the crystallizer outlet, thereby obtaining a thick aluminum alloy plate with a uniform internal structure, thus ensuring that the prepared thick aluminum alloy plate has the characteristics of low anisotropy and low batch-to-batch variation coefficient. Furthermore, when the solidification front of the aluminum alloy melt is stabilized at 20-30mm below the crystallizer outlet (e.g., 22cm, 25cm, or 28cm), it can effectively prevent concentrated shrinkage cavities or scattered looseness from forming inside the aluminum alloy ingot due to insufficient replenishment of the aluminum alloy melt during solidification, thus reducing the density of the aluminum alloy ingot. It can also prevent tensile stress between the solid shell and liquid metal caused by sudden changes in local solidification rate inside the aluminum alloy ingot due to an unstable solidification front position, which could lead to the appearance of hot cracks on the surface or inside the aluminum alloy ingot.

[0026] According to an embodiment of the present invention, in step 3), the casting temperature is 700-725℃, for example, 700℃, 705℃, 710℃, 715℃, 720℃, or 725℃; the casting speed is 45-50 mm / min, for example, 45 mm / min, 46 mm / min, 48 mm / min, 49 mm / min, or 50 mm / min; the casting water pressure is 0.02-0.04 MPa, for example, 0.02 MPa, 0.025 MPa, 0.03 MPa, 0.035 MPa, or 0.04 MPa; and the casting water flow rate is 22 m³ / min. 3 / h-30m 3 / h, for example, 22m 3 / h、23m 3 / h、24m 3 / h, 25m 3 / h、26m 3 / h、27m 3 / h、28m 3 / h、29m 3 / h or 30m 3 / h.

[0027] According to an embodiment of the present invention, in step 3), by using the above-described casting method, the temperature gradient on the surface of the aluminum alloy ingot can be effectively controlled; the role of the online grain refiner can also be fully utilized to ensure the formation of uniform and fine equiaxed crystals in the internal structure of the alloy, avoiding the formation of coarse columnar crystals in the alloy, which would reduce the strength, toughness, and processing plasticity of the aluminum alloy ingot; the grain size of the internal structure of the alloy can also be controlled at level 1-2, with a microporous size <100μm, avoiding the acquisition of aluminum alloy ingots with defects such as pores, inclusions, and cracks, which would adversely affect the toughness and fatigue performance of the aluminum alloy thick plate; the reduction in grain size and microporous size, and the improvement in the uniformity of the internal structure of the alloy, can also significantly improve the strength, toughness, and uniformity of strength and toughness in the three directions of the aluminum alloy thick plate, which is beneficial to obtaining aluminum alloy thick plates with low anisotropy and low batch-to-batch variation coefficient. In summary, by selecting the above casting process, aluminum alloy ingots with uniform composition, dense structure, and free from defects such as porosity, inclusions, cracks, and coarse second phases can be obtained, thereby ensuring the preparation of aluminum alloy thick plates with high strength, high toughness, low anisotropy, and low batch-to-batch variation coefficient.

[0028] According to an embodiment of the present invention, in step 3), the large-size aluminum alloy ingot is a flat ingot with a thickness of 420 mm or more, for example, a flat ingot with a thickness of 520 mm; exemplarily, it is an aluminum alloy flat ingot with dimensions of 520 mm × 1620 mm × 5000 mm. The selection of a large-size aluminum alloy ingot ensures both the dimensional requirements of the aluminum alloy thick plate and sufficient processing deformation to fully break down the coarse grains inside the ingot and compact any possible micro-porosity, thereby obtaining an aluminum alloy thick plate with high internal structural uniformity. This ensures that an aluminum alloy thick plate with large size, high toughness, and high strength can be prepared; furthermore, it ensures that the strength and fracture toughness of the aluminum alloy thick plate have low anisotropy in the three directions, reducing the batch-to-batch variation coefficient of the aluminum alloy thick plate.

[0029] According to an embodiment of the present invention, in step 4), the multi-stage homogenization annealing process includes the following steps: holding at 398-400℃ for 10-36 hours to perform the first-stage homogenization annealing process; then raising the temperature to 465℃-470℃ and holding at this temperature for 24-36 hours to perform the second-stage homogenization annealing process; and continuing to raise the temperature to 475℃-477℃ and holding at this temperature for 12-36 hours to perform the third-stage homogenization annealing process.

[0030] For example, a first-stage homogenization annealing treatment is performed by holding the temperature at 398-400°C for 10-36 hours (e.g., 12 hours, 15 hours, 18 hours, 24 hours, 28 hours, 30 hours, or 36 hours); then the temperature is raised to 465-470°C (e.g., 465°C, 466°C, 467°C, 468°C, 469°C, or 470°C) and held at this temperature for 24-36 hours (e.g., 24 hours, 28 hours, 30 hours, or 36 hours) for a second-stage homogenization annealing treatment; and then the temperature is raised further to 475-477°C (e.g., 475°C, 476°C, or 477°C) and held at this temperature for 12-36 hours (e.g., 12 hours, 15 hours, 18 hours, 24 hours, 28 hours, 30 hours, or 36 hours) for a third-stage homogenization annealing treatment.

[0031] According to an embodiment of the present invention, in step 4), the first-stage homogenization annealing treatment can disperse and precipitate Al3Zr and Al6Mn phases in the aluminum alloy ingot. The precipitated Al3Zr and Al6Mn phases can pin grain boundaries and inhibit the recrystallization of aluminum alloy grains. The second-stage homogenization annealing treatment is carried out at a temperature of 465℃-470℃, which can effectively dissolve the low-melting-point phases in the aluminum alloy ingot. At the same time, it can further diffuse the alloying elements (such as Cu, Mg, etc.) enriched in the aluminum alloy ingot, so as to homogenize the chemical composition of the entire aluminum alloy ingot and avoid the performance fluctuation caused by compositional segregation during subsequent processing or heat treatment due to compositional inhomogeneity, thus making it impossible to obtain aluminum alloy thick plates with low anisotropy and low batch-to-batch variation coefficient. The third-stage homogenization annealing treatment can further dissolve the residual phases in the aluminum alloy ingot and eliminate the coarse and unbalanced second phase inside the aluminum alloy ingot, which is beneficial to obtaining aluminum alloy thick plates with low anisotropy and low batch-to-batch variation coefficient.

[0032] According to an embodiment of the present invention, in step 5), the rolling temperature is 385°C-400°C, for example, 385°C, 390°C, 395°C or 400°C.

[0033] According to an embodiment of the present invention, in step 5), the rolling direction is along the length of the billet.

[0034] According to an embodiment of the present invention, in step 5), the total deformation of the rolling process is 60%-70%, for example, 60%, 62%, 65%, 68%, or 70%. Meeting this total deformation (60%-70%) can effectively break down the coarse grain structure inside the aluminum alloy ingot and compact the small, loose structure, resulting in better microstructure consistency from the surface to the core of the aluminum alloy thick plate. This is beneficial for obtaining aluminum alloy thick plates with low anisotropy and low batch-to-batch variation. It also avoids the problem of insufficient deformation (total deformation <60%) leading to a loose core structure, which would prevent the production of high-strength and high-toughness aluminum alloy thick plates. The selection of the total deformation also ensures the production of aluminum alloy thick plates, especially those with a thickness of 102-203 mm.

[0035] According to an embodiment of the present invention, in step 5), the initial rolling stage employs 3-8 consecutive passes (e.g., 3, 4, 5, 6, 7, or 8 passes) of low-strain rolling, and the single-pass reduction during the low-strain rolling process at the initial rolling stage is 10-20 mm (e.g., 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, or 20 mm).

[0036] According to an embodiment of the present invention, in step 5), the intermediate rolling stage adopts 2-5 consecutive passes (such as 2 passes, 3 passes, 4 passes or 5 passes) of high-strain rolling, and the single-pass reduction in the high-strain rolling process of the intermediate rolling stage is 40-55mm (such as 40mm, 43mm, 45mm, 50mm or 55mm).

[0037] According to an embodiment of the present invention, in step 5), the rolling termination stage uses 3-5 consecutive passes (such as 3 passes, 4 passes or 5 passes) of small strain rolling to the required plate thickness. The single pass reduction in the small strain rolling process at the rolling termination stage is 10-15mm (such as 10mm, 11mm, 12mm, 13mm, 14mm or 15mm).

[0038] According to an embodiment of the present invention, in step 5), by controlling the initial rolling temperature within the range of 380℃-400℃, the deformation energy storage of large-size aluminum alloy ingots can be well controlled, the recrystallization of the alloy structure within the aluminum alloy ingot can be suppressed, and more subgrain structures can be retained. The rolling process of the present invention employs a combined rolling process of small-strain rolling-large-strain rolling-small-strain rolling. By selecting different strain rolling processes at different rolling stages, the coarse grains within the microstructure are broken down to the greatest extent, and a more complex dislocation structure is generated. The large-strain rolling process can effectively… By addressing metallurgical defects and controlling the proportion of subgrains, the toughness and fatigue life of thick aluminum alloy plates can be effectively improved while maintaining a relatively small total deformation (total deformation during the large-strain rolling stage). Simultaneously, the uniformity of the alloy microstructure distribution can be enhanced, ensuring the production of thick aluminum alloy plates with low anisotropy and low batch-to-batch variation coefficients. In particular, the effective combination of small-strain rolling and large-strain rolling can significantly improve the toughness and fatigue life of thick aluminum alloy plates, thereby obtaining large-size thick aluminum alloy plates that combine high strength, high toughness, high fatigue life, low anisotropy, and low batch-to-batch variation coefficients.

[0039] According to an embodiment of the present invention, in step 6), the solution quenching treatment is carried out by holding at a temperature of 475℃-482℃ for 4-8.5 hours, and after the holding is completed, the solution is removed from the furnace and quenched. The quenching transfer time is ≤15s, and the quenching water temperature is room temperature.

[0040] For example, the solution quenching treatment is performed by holding the solution at a temperature of 475℃-482℃ (such as 475℃, 478℃, 480℃ or 482℃) for 4-8.5 hours. Specifically, the holding time can be determined by the thickness of the aluminum alloy plate. For example, aluminum alloy plates with a thickness of 76-89mm are held for 4 hours, aluminum alloy plates with a thickness of 89-102mm are held for 4.5 hours, and for aluminum alloy plates with a thickness of 102mm or more, the holding time is increased by 0.5 hours for every 12.7mm increase in thickness. The quenching transfer time is ≤15s.

[0041] According to an embodiment of the present invention, in step 6), during the solution quenching process, a large number of complex dislocation structures formed during rolling are eliminated, and newly formed strain-free fine equiaxed crystals become new nucleation sites in the deformed structure, gradually growing and replacing all the deformed structure, thereby obtaining a thick aluminum alloy plate with uniform microstructure, grains refined to the micro-nano level, and high toughness and high strength. At the same time, the uniformity of the internal microstructure of the alloy can also ensure that the prepared aluminum alloy thick plate has the characteristics of low anisotropy and low batch-to-batch variation coefficient.

[0042] According to an embodiment of the present invention, in step 7), the stretching amount of the pre-stretching treatment is 1.5-3%, for example, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.8% or 3%; the pre-stretching treatment can fully eliminate the residual stress of the aluminum alloy thick plate.

[0043] According to an embodiment of the present invention, in step 8), the two-stage aging treatment is performed by holding at 117℃-123℃ for 12-24 hours for the first stage of aging heat treatment, followed by heating in the furnace to 154℃-160℃ and holding for 7-16 hours for the second stage of aging heat treatment, and then air cooling to room temperature after being removed from the furnace.

[0044] The present invention also provides aluminum alloy thick plates prepared by the above method.

[0045] According to an embodiment of the present invention, the aluminum alloy thick plate is a high-toughness, large-size aluminum alloy thick plate.

[0046] According to an embodiment of the present invention, the thickness of the aluminum alloy plate is ≥76mm, preferably 76-203mm, more preferably 102-203mm, for example 76mm, 80mm, 85mm, 90mm, 95mm, 100mm, 102mm, 105mm, 110mm, 120mm, 130mm, 140mm, 150mm, 160mm, 170mm, 180mm, 190mm, 200mm or 203mm.

[0047] According to an embodiment of the present invention, the width of the aluminum alloy thick plate is ≥1200mm.

[0048] According to an embodiment of the present invention, the length of the aluminum alloy thick plate is ≥10000mm.

[0049] According to an embodiment of the present invention, the aluminum alloy thick plate satisfies at least one of the following conditions: (1) The tensile strength in the L direction reaches 530 MPa or more, the tensile strength in the LT direction reaches 530 MPa or more, and the tensile strength in the ST direction reaches 510 MPa or more; (2) The yield strength in the L direction reaches 490 MPa or more, the yield strength in the LT direction reaches 490 MPa or more, and the yield strength in the ST direction reaches 480 MPa or more; (3) The elongation rate in the L direction reaches more than 10%, the elongation rate in the LT direction reaches more than 9%, and the elongation rate in the ST direction reaches more than 7%; (4) The fracture toughness in the LT direction reaches 35 MPa·m 1 / 2 The fracture toughness in the TL direction reaches 33 MPa·m. 1 / 2 The fracture toughness in the SL direction reaches 32 MPa·m.1 / 2 above; (5) Under R=0.1 and 241MPa stress, the average fatigue life reaches more than 180,000 cycles.

[0050] According to an embodiment of the present invention, the aluminum alloy thick plate satisfies that the coefficient of variation of tensile strength Cv between batches reaches less than 2.0%, and the number of batches is not less than 20, preferably more than 30, such as more than 40, more than 50, more than 100, more than 150, or more than 200.

[0051] According to an embodiment of the present invention, the aluminum alloy thick plate satisfies that the yield strength variation coefficient Cv between batches reaches less than 2.0%, and the number of batches is not less than 20, preferably more than 30, such as more than 40, more than 50, more than 100, more than 150, or more than 200.

[0052] In this invention, the coefficient of variation (C) V The Coefficient of Variation (SD) is used to characterize the degree of dispersion of the strength (tensile strength or yield strength) of aluminum alloy thick plates between different batches; the calculation formula is: Standard Deviation (SD) / Average × 100%.

[0053] According to an embodiment of the present invention, the aluminum alloy thick plate satisfies that the difference in strength (tensile strength or yield strength) in the three directions (L direction, LT direction and ST direction) does not exceed 5%.

[0054] According to an embodiment of the present invention, the aluminum alloy thick plate satisfies that the difference in fracture toughness in three directions (LT direction, TL direction and SL direction) does not exceed 10%.

[0055] The beneficial effects of this invention are: This invention provides a high-toughness, large-size aluminum alloy thick plate and its preparation method. The aluminum alloy thick plate is characterized by its large size, high toughness, and high strength. It exhibits low anisotropy in both strength and toughness in three directions, and also has a low batch-to-batch coefficient of variation. This invention, by designing and controlling the alloy composition range of the aluminum alloy thick plate, significantly reduces compositional fluctuations in different parts of the plate, resulting in an aluminum alloy thick plate with a uniform internal structure and lowering the batch-to-batch coefficient of variation. Simultaneously, the invention incorporates the processes of melting and casting, multi-stage homogenization, high-strain rolling, solution quenching, and double-stage aging heat treatment, resulting in a large-size aluminum alloy thick plate with high toughness, high strength, low anisotropy, and good batch-to-batch stability. Detailed Implementation

[0056] The preparation method of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0057] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0058] The following examples use pure aluminum ingots with a purity of 99.95% or higher, magnesium ingots with a purity of 99.5% or higher, zinc ingots with a purity of 99.9% or higher, Al-50Cu aluminum-copper master alloy, Al-10Zr aluminum-zirconium master alloy, and Al-20Mn aluminum-manganese master alloy.

[0059] Example 1 (1) Ingredients: The ingredients are prepared according to the following weight percentages: Zn: 7.2%, Mg: 2.0%, Cu: 1.6%, Zr: 0.12%, Mn: 0.25%.

[0060] (2) Smelting: Add aluminum ingots, zinc ingots, aluminum-copper master alloy, aluminum-zirconium master alloy, and aluminum-manganese master alloy to the smelting furnace, raise the temperature and control the smelting temperature to 770°C, and after the alloy raw materials melt, lower the temperature to 725°C and add magnesium ingots, and continue to keep the temperature and smelt for 20 minutes.

[0061] (3) Refining: High-purity argon is used as the refining medium to refine the aluminum alloy melt in the settling furnace. The purity of the argon is not less than 99.999%, the argon flow rate is 800 L / h, and the flow time is 10 min. Oxide inclusions on the top of the settling furnace are removed using a slag skimmer. A dual-rotor online degassing device is used to degas the aluminum alloy melt in the settling furnace. The N1 rotor in the dual-rotor online degassing device rotates at 500 rpm, and the argon flow rate is 5 m³ / h. 3 The N2 rotor in the dual-rotor online degassing unit rotates at 350 rpm, and the argon flow rate is 3.0 m³ / h. 3 / h. A two-stage ceramic filter plate of 30PPI+50PPI was used to filter the aluminum alloy melt after online degassing. The alloy element composition of the prepared aluminum alloy melt was analyzed, with Fe: 0.08% and Si: 0.06%.

[0062] (4) Casting: During casting, an online grain refiner, Al-Ti-C wire, is added to the aluminum alloy melt to refine the grains. The addition temperature of the Al-Ti-C wire is controlled at 725℃, and the time from the addition of the Al-Ti-C wire to the start of solidification of the aluminum alloy melt is controlled at 20min. The amount of Al-Ti-C wire added accounts for 0.01% of the total mass of the aluminum alloy melt. The casting temperature is 720℃, the casting speed is 48mm / min, the casting water pressure is 0.03MPa, and the casting water flow rate is 25m³ / min. 3 / h, during the solidification and crystallization process of the aluminum alloy melt, the surface temperature gradient of the aluminum alloy ingot is monitored in real time to be 10℃ / cm, and the solidification front of the aluminum alloy melt is kept stable at 25mm below the crystallizer outlet. In this way, aluminum alloy flat ingots with specifications of 520 mm×1620 mm×5000 mm are prepared.

[0063] (5) Three-stage homogenization annealing: The cast aluminum alloy ingot is subjected to three-stage homogenization annealing treatment. The first stage homogenization annealing is held at 400℃ for 24 hours, the second stage homogenization annealing is held at 468℃ for 36 hours, and the third stage homogenization annealing is held at 477℃ for 24 hours.

[0064] (6) Rolling: The aluminum alloy ingot after homogenization annealing is milled to obtain an ingot with a size of 500 mm × 1600 mm. The ingot is rolled along its length. The initial rolling temperature is 395℃. The number of rolling passes and the amount of deformation are as follows: 500mm→490mm→470mm→450mm→430mm→410mm→360mm→310mm→265mm→220mm→205mm→190mm→175mm→160mm, with a final rolling temperature not lower than 350℃.

[0065] (7) Solution quenching: The aluminum alloy thick plate obtained after rolling is solution quenched using a solution quenching process of 478℃ / 7h. The quenching transfer time is <10s, and the plate is quenched to room temperature.

[0066] (8) Pre-stretching: The aluminum alloy sheet after solution quenching is pre-stretched by 2%.

[0067] (9) Two-stage aging treatment: The pre-stretched aluminum alloy sheet is subjected to two-stage aging treatment. Specifically, it is held at 120°C for 20 hours for the first stage of aging heat treatment, and then heated to 157°C in the furnace for 12 hours for the second stage of aging heat treatment. After being taken out of the furnace, it is air-cooled to room temperature.

[0068] Comparative Example 1 The other operations of Comparative Example 1 are the same as those of Example 1, except that step (1) is performed as follows: (1) Batching: The following weight percentages are used for batching: Zn: 6.5%, Mg: 2.5%, Cu: 2.2%, Zr: 0.12%. The alloy element composition of the aluminum alloy melt prepared after refining in step (3) is tested, wherein Fe: 0.10% and Si: 0.08%.

[0069] Comparative Example 2 The other operations in Comparative Example 2 are the same as in Example 1, except that step (3) is performed as follows: (3) Refining: High-purity argon is used as the refining medium to refine the aluminum alloy melt in the settling furnace. The purity of the argon is not less than 99.99%, the argon flow rate is 1500 L / h, and the flow time is 10 min. A dual-rotor online degassing device is used to degas the aluminum alloy melt in the settling furnace. The N1 rotor in the dual-rotor online degassing device rotates at 300 rpm, and the argon flow rate is 4 m³ / h. 3 The N2 rotor in the dual-rotor online degassing unit rotates at 250 rpm, and the argon flow rate is 2.5 m³ / h. 3 / h. A single-stage ceramic filter plate with a 60PPI is used to filter the aluminum alloy melt after online degassing.

[0070] Comparative Example 3 The other operations of Comparative Example 3 are the same as those of Example 1, except that step (4) is performed as follows: (4) Casting: During casting, an online grain refiner, Al-Ti-B wire, is added to the aluminum alloy melt to refine the grains. The addition temperature of the Al-Ti-B wire is controlled at 710℃, and the time from the addition of the Al-Ti-B wire to the start of solidification of the aluminum alloy melt is controlled at 30 min. The amount of Al-Ti-B wire added accounts for 0.01% of the total mass of the aluminum alloy melt. The casting temperature is 720℃, the casting speed is 48 mm / min, the casting water pressure is 0.03 MPa, and the casting water flow rate is 25 m³ / min. 3 / h, during the solidification and crystallization process of the aluminum alloy melt, the surface temperature gradient of the aluminum alloy ingot is monitored in real time to be 10℃ / cm, and the solidification front of the aluminum alloy melt is kept stable at 25mm below the crystallizer outlet. In this way, aluminum alloy flat ingots with specifications of 520 mm×1620 mm×5000 mm are prepared.

[0071] Comparative Example 4 The other operations in Comparative Example 4 are the same as in Example 1, except that step (4) is performed as follows: (4) Casting: During casting, an online grain refiner, Al-Ti-C wire, is added to the aluminum alloy melt to refine the grains. The addition temperature of the Al-Ti-C wire is controlled at 725℃, and the time from the addition of the Al-Ti-C wire to the start of solidification of the aluminum alloy melt is controlled at 20min. The amount of Al-Ti-C wire added accounts for 0.01% of the total mass of the aluminum alloy melt. The casting temperature is 740℃, the casting speed is 55mm / min, the casting water pressure is 0.01MPa, and the casting water flow rate is 32m³ / min. 3 / h, during the solidification and crystallization process of the aluminum alloy melt, the surface temperature gradient of the aluminum alloy ingot was monitored in real time and was 20℃ / cm. The solidification front of the aluminum alloy melt was stabilized at 35mm below the crystallizer outlet, and an aluminum alloy flat ingot with a specification of 520 mm×1620 mm×5000 mm was prepared.

[0072] Comparative Example 5 The other operations of Comparative Example 5 are the same as those of Example 1, except that step (6) is performed as follows: (6) Rolling: The aluminum alloy ingot after homogenization annealing is milled to obtain an ingot with a size of 500 mm × 1600 mm. The ingot is rolled along its length. The initial rolling temperature is 420℃. The number of rolling passes and the amount of deformation are as follows: 500mm→490mm→470mm→450mm→430mm→410mm→390mm→370mm→340mm→310mm→280mm→250mm→230mm→210mm→190mm→170mm→160mm, with a final rolling temperature not lower than 350℃.

[0073] Comparative Example 6 The other operations of Comparative Example 6 are the same as those of Example 1, except that step (6) is performed as follows: (6) Rolling: The aluminum alloy ingot after homogenization annealing is milled to obtain an ingot with a size of 500 mm × 1600 mm. The ingot is rolled along its length. The initial rolling temperature is 420℃. The number of rolling passes and the amount of deformation are as follows: 500mm→490mm→480mm→470mm→460mm→450mm→430mm→410mm→390mm→370mm→350mm→330mm→310mm→265mm→220mm→175mm→170mm→165mm→160mm, with a final rolling temperature not lower than 350℃.

[0074] The performance of the aluminum alloy thick plates prepared in the above embodiments and comparative examples was tested, and the results are shown in Tables 1 to 3.

[0075] Table 1. Performance Comparison of Aluminum Alloy Thick Plates in Examples and Comparative Examples

[0076] Table 2. Performance differences of aluminum alloy thick plates in different directions in the examples and comparative examples.

[0077] Table 3. Batch stability statistics of aluminum alloy thick plates in the examples and comparative examples.

[0078] Comparative Example 1 uses the same process as Example 1, but the alloy composition of Comparative Example 1 is different from that of Example 1. Compared with Example 1, the alloy composition dispersion of the aluminum alloy thick plate obtained in Comparative Example 1 is increased, resulting in higher anisotropy of the aluminum alloy thick plate and increased strength variation coefficient between different batches. That is, the difference in strength and fracture toughness between the three directions of the thick plate is large, and the batch stability is reduced.

[0079] Comparative Example 2 uses the same process as Example 1, but the alloy in Comparative Example 2 is refined with ordinary argon gas and the argon gas flow rate is relatively large; online degassing with dual rotors is used, but the rotor speed and argon gas flow rate are relatively low; a single-stage ceramic filter plate is used to filter the melt; the above parameters and operations result in limited degassing efficiency of the aluminum alloy melt, resulting in high hydrogen content and slag content in the aluminum alloy thick plate, and large fluctuations in hydrogen content and slag content between batches, leading to high anisotropy, low fracture toughness, low fatigue performance, and reduced batch stability of the aluminum alloy thick plate. Comparative Example 3 uses the same process as Example 1, but the alloy in Comparative Example 3 uses Al-Ti-B wire to refine the grains. B and Zr form hard and brittle intermetallic compound particles such as ZrB2. These particles affect the toughness and fatigue performance of the aluminum alloy thick plate. They also affect the uniformity of the alloy structure, resulting in lower room temperature tensile strength, lower fracture toughness, lower fatigue performance, and reduced batch stability of the aluminum alloy thick plate.

[0080] Comparative Example 4 follows the same process as Example 1, but the solidification front of the aluminum alloy melt in Comparative Example 4 is stably located 35 mm below the crystallizer outlet. At the same time, the casting temperature of the aluminum alloy is too high, the casting speed is too fast, and the casting pressure is too low. It is impossible to effectively control the temperature gradient on the surface of the aluminum alloy ingot during the solidification and crystallization process of the aluminum alloy melt. This results in a coarse internal structure, severe component segregation, and severe microporousness in the aluminum alloy ingot, which affects the mechanical properties, fracture toughness, and batch stability of the aluminum alloy thick plate. Consequently, the aluminum alloy thick plate has low room temperature tensile strength, low fracture toughness, low fatigue performance, and reduced batch stability.

[0081] Comparative Examples 5-6 follow the same process as Example 1, but the alloys in Comparative Examples 5-6 are rolled using a multi-pass uniform deformation rolling process. Due to insufficient deformation per pass, metallurgical defects such as internal microporousness in the aluminum alloy thick plates are not properly welded, resulting in significant performance differences in the aluminum alloy thick plates in the three directions. The room temperature tensile strength, fracture toughness, and fatigue performance are low, and batch stability is reduced.

[0082] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-toughness, large-size aluminum alloy thick plate, the method comprising the following steps: 1) Aluminum ingots, magnesium ingots, zinc ingots, aluminum-copper master alloy, aluminum-zirconium master alloy, and aluminum-manganese master alloy are mixed and melted to prepare an aluminum alloy melt; the alloy composition of the aluminum alloy thick plate, by weight percentage, includes the following components: Zn: 6.8%-7.9%, Mg: 1.8%-2.2%, Cu: 1.5%-1.8%, Zr: 0.08%-0.15%, Mn: 0.05%-0.25%, Cr≤0.04%, Ti≤0.06%, Fe≤0.10%, Si≤0.08%, and the total amount of other impurities is <0.05%, with the balance being aluminum; 2) The aluminum alloy melt from step 1) is refined, slag removed, degassed, and filtered; 3) Cast the aluminum alloy melt processed in step 2). During casting, add an online grain refiner to refine the grains. The temperature of adding the online grain refiner is controlled at 720℃-730℃. The time from adding the online grain refiner to the start of solidification of the aluminum alloy melt is controlled at 15-25 minutes. During the solidification of the aluminum alloy melt, monitor the temperature gradient on the surface of the aluminum alloy ingot in real time within the range of 5-15℃ / cm. At the same time, ensure that the solidification front of the aluminum alloy melt is stable at 20-30mm below the crystallizer outlet to prepare a large-size aluminum alloy ingot. 4) Perform multi-stage homogenization annealing on the large-size aluminum alloy ingots from step 3). 5) The large-size aluminum alloy ingot after the multi-stage homogenization annealing treatment in step 4) is milled and then rolled. The initial rolling temperature is 385℃-400℃, the total number of rolling passes does not exceed 15, the intermediate rolling stage adopts 2-5 consecutive passes of large strain rolling, the single pass reduction in the large strain rolling process is 40-55mm, and the final rolling temperature is not lower than 350℃ to prepare aluminum alloy thick plate. 6) Perform solution quenching treatment on the rolled aluminum alloy thick plate from step 5). 7) Perform pre-stretching treatment on the aluminum alloy thick plate after solution quenching in step 6). 8) Perform a two-stage aging treatment on the aluminum alloy thick plate after the pre-stretching treatment in step 7) to prepare a high-toughness, large-size aluminum alloy thick plate; the thickness of the aluminum alloy thick plate is ≥76mm.

2. The preparation method according to claim 1, wherein, In step 1), aluminum ingots, zinc ingots, aluminum-copper master alloys, aluminum-zirconium master alloys and aluminum-manganese master alloys are mixed and heated to 760℃-790℃ and smelted for 10-30 minutes. Then, the temperature is lowered to 720℃-730℃ and magnesium ingots are added. The mixture is then kept at the same temperature and smelted for another 10-30 minutes.

3. The preparation method according to claim 1, wherein, In step 2), high-purity argon is used as the refining medium. The purity of the high-purity argon is not less than 99.999%, the flow rate of the high-purity argon is 600-1200 L / h, and the introduction time of the high-purity argon is 10-15 min. And / or, in step 2), a dual-rotor online degassing device is used to degas the aluminum alloy melt. The rotational speed of the N1 rotor in the dual-rotor online degassing device is 450-550 rpm, and the argon flow rate is 4.5-5.5 m³ / s. 3 In the dual-rotor online degassing unit, the N2 rotor rotates at 300-350 rpm, and the argon flow rate is 3.0-3.2 m³ / h. 3 / h; And / or, in step 2), a two-stage plate filter device with a 30PPI+50PPI is used to filter the aluminum alloy melt.

4. The preparation method according to claim 1, wherein, In step 3), the online grain refiner is an Al-Ti-C master alloy, and the Al-Ti-C master alloy is in the form of wire. And / or, in step 3), the amount of the online grain refiner added is 0.01-0.015% of the total mass of the aluminum alloy melt.

5. The preparation method according to claim 1, wherein, In step 3), the casting temperature is 700-725℃; the casting speed is 45-50 mm / min; the casting water pressure is 0.02-0.04 MPa; and the casting water flow rate is 22 m³ / min. 3 / h-30m 3 / h; And / or, in step 3), the large-size aluminum alloy ingot is a flat ingot with a thickness of 420mm or more.

6. The preparation method according to claim 1, wherein, In step 5), the initial rolling temperature is 385℃-400℃; And / or, in step 5), the total deformation of the rolling process is 60%-70%; And / or, in step 5), the initial rolling stage uses 3-8 consecutive passes of low-strain rolling, with a single pass reduction of 10-20 mm during the initial low-strain rolling process; the intermediate rolling stage uses 2-5 consecutive passes of high-strain rolling, with a single pass reduction of 40-55 mm during the intermediate high-strain rolling process; and the final rolling stage uses 3-5 consecutive passes of low-strain rolling to the required plate thickness, with a single pass reduction of 10-15 mm during the final low-strain rolling process.

7. The preparation method according to claim 1, wherein, In step 4), the multi-stage homogenization annealing process includes the following steps: holding at 398-400℃ for 10-36 hours for the first stage of homogenization annealing; then raising the temperature to 465℃-470℃ and holding at this temperature for 24-36 hours for the second stage of homogenization annealing; and continuing to raise the temperature to 475℃-477℃ and holding at this temperature for 12-36 hours for the third stage of homogenization annealing. And / or, in step 6), the solution quenching treatment is carried out at a temperature of 475℃-482℃ for 4-8.5 hours, and after the heat treatment is completed, the furnace is removed for quenching, the quenching transfer time is ≤15s, and the quenching water temperature is room temperature. And / or, in step 7), the stretching amount of the pre-stretching treatment is 1.5-3%; And / or, in step 8), the two-stage aging treatment is performed by holding at 117℃-123℃ for 12-24 hours for the first stage of aging heat treatment, followed by heating in the furnace to 154℃-160℃ and holding for 7-16 hours for the second stage of aging heat treatment, and then air cooling to room temperature after being removed from the furnace.

8. The aluminum alloy thick plate prepared by the method according to any one of claims 1-7.

9. The aluminum alloy thick plate according to claim 8, wherein, The aluminum alloy thick plate satisfies at least one of the following conditions: (1) The tensile strength in the L direction reaches 530 MPa or more, the tensile strength in the LT direction reaches 530 MPa or more, and the tensile strength in the ST direction reaches 510 MPa or more; (2) The yield strength in the L direction reaches 490 MPa or more, the yield strength in the LT direction reaches 490 MPa or more, and the yield strength in the ST direction reaches 480 MPa or more; (3) The elongation rate in the L direction reaches more than 10%, the elongation rate in the LT direction reaches more than 9%, and the elongation rate in the ST direction reaches more than 7%; (4) The fracture toughness in the LT direction reaches 35 MPa·m 1 / 2 The fracture toughness in the TL direction reaches 33 MPa·m. 1 / 2 The fracture toughness in the SL direction reaches 32 MPa·m. 1 / 2 above; (5) Under R=0.1 and 241MPa stress, the average fatigue life reaches more than 180,000 cycles.

10. The aluminum alloy thick plate according to claim 8, wherein, The aluminum alloy thick plate meets the requirement that the coefficient of variation of tensile strength Cv between batches is less than 2.0%, and the number of batches is not less than 20. And / or, the aluminum alloy thick plate satisfies that the yield strength variation coefficient Cv between batches reaches less than 2.0%, and the number of batches is not less than 20; And / or, the aluminum alloy plate satisfies that the strength difference in the L, LT and ST directions does not exceed 5%; And / or, the aluminum alloy thick plate satisfies that the difference in fracture toughness in the LT, TL and SL directions does not exceed 10%.

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