High-toughness large-size aluminum alloy thick plate and method for manufacturing the same

Abstract

The application belongs to the technical field of aluminum alloy materials, and relates to a high-toughness large-size aluminum alloy thick plate and a preparation method thereof.The aluminum alloy thick plate has the characteristics of large size, high toughness and high strength, the strength and toughness of the aluminum alloy thick plate in three directions have the characteristics of low anisotropy, and the aluminum alloy thick plate also has the characteristics of low batch-to-batch variation coefficient.The application controls the alloy composition range of the aluminum alloy thick plate, greatly reduces the composition fluctuation of the aluminum alloy thick plate at different positions, obtains the aluminum alloy thick plate with uniform internal alloy organization, and reduces the batch-to-batch variation coefficient of the aluminum alloy thick plate.Meanwhile, the application is matched with the process steps of melting and casting, multi-stage homogenization, large-strain rolling, solid solution quenching, double-stage aging heat treatment and the like, so that the obtained large-size aluminum alloy thick plate has the characteristics of high toughness, high strength, low anisotropy and good batch-to-batch stability.

Description

TECHNICAL FIELD

[0001] The application 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. BACKGROUND

[0002] 7000 series aluminum alloy is a main body structure material of an airplane, and is mainly used in important main load-bearing parts such as a main load-bearing frame beam and a joint of the airplane. In order to meet the demand of integral manufacturing of the main load-bearing parts of the airplane, a large-specification requirement is put forward for the aluminum alloy thick plate. With the development of material technology, the airplane design has been changed from the first static strength design to damage tolerance design, and higher requirements are put forward for the toughness of the main body structure material. The aluminum alloy thick plate inevitably has higher longitudinal and transverse performance and lower high-direction performance due to the use of rolling deformation. During the flight of the airplane, complex stress and alternating load are borne, and more uniform requirements are put forward for the mechanical properties of the main body structure material in different directions, so as to avoid the failure of the overall structure material due to the lower performance in a certain direction. In addition, for the large-specification aluminum alloy thick plate for the main load-bearing structure of the airplane, the high comprehensive performance is not a single control target, and in order to meet the requirements of the safety of the airplane and the airworthiness of the military and civilian airplanes, the aluminum alloy thick plate is required to have better stability of the strength performance between batches on the premise of the high comprehensive performance. SUMMARY

[0003] It is found through research that the aluminum alloy thick plate for the main load-bearing frame beam of the airplane at present is mainly 7050-T7451 thick plate, the maximum thickness of which can reach 203 mm, and the integral manufacturing of the main load-bearing frame beam can be realized. However, the strength of the 7050-T7451 thick plate is low, and the tensile strength is about 500 MPa, which limits the application thereof. Taking the 7050-T7451 thick plate with a larger amount of thickness in the range of 76-102 mm as an example, the L-T direction fracture toughness is 28 MPa·m 1 / 2 , the T-L direction fracture toughness is 25 MPa·m 1 / 2 , and the S-L direction fracture toughness is 23 MPa·m 1 / 2 . In order to realize the weight reduction of the structure, the 7A55-T7751 aluminum alloy thick plate with a strength of 600 MPa has been developed at present, but due to the contradiction between the strength and the toughness and the strength and the hardenability of the aluminum alloy, the maximum thickness of the 7A55-T7751 aluminum alloy thick plate can only reach 38 mm on the premise of ensuring the comprehensive performance of the aluminum alloy thick plate, and the thickness of the thick plate of this specification cannot realize the integral manufacturing of the main load-bearing frame beam. At the same time, the L-T direction fracture toughness of the 7A55-T7751 aluminum alloy thick plate is 23 MPa·m 1 / 2 , and the 7A55-T7751 aluminum alloy thick plate cannot meet the use requirement of the long service life of the main load-bearing frame beam.

[0004] To improve the deficiencies of the prior art, the present application provides a high-toughness large-size aluminum alloy thick plate and a preparation method thereof. The present application can effectively control the microstructure of the aluminum alloy thick plate in different directions by designing the types and composition ranges of alloying elements and combining with specific process steps (including melting and casting, multi-stage homogenization annealing treatment, large-strain rolling, solid solution quenching treatment, pre-stretching treatment and two-stage aging treatment). The obtained aluminum alloy thick plate has the characteristics of large size (especially large thickness), high toughness, high strength, low anisotropy (especially the strength and toughness of the aluminum alloy thick plate in three directions have low anisotropy), and good batch stability. In particular, by designing and accurately controlling the types and composition ranges of alloying elements, the composition fluctuation of the aluminum alloy thick plate at different positions is greatly reduced, which can significantly reduce the performance difference between batches of the aluminum alloy thick plate, and obtain an aluminum alloy thick plate with good batch stability.

[0005] The object of the present application is achieved by the following technical solution:

[0006] A preparation method of a high-toughness large-size aluminum alloy thick plate, the method comprising the following steps:

[0007] 1) mixing aluminum ingots, magnesium ingots, zinc ingots, aluminum copper intermediate alloy, aluminum zirconium intermediate alloy and aluminum manganese intermediate alloy, heating and melting to prepare an aluminum alloy melt; the alloy composition of the aluminum alloy thick plate comprises the following components in terms of weight percentage: 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%, total amount of impurities <0.05%, and the balance being aluminum;

[0008] 2) refining, skimming, degassing and filtering the aluminum alloy melt of step 1);

[0009] 3) casting the aluminum alloy melt treated in step 2), adding an online grain refiner to refine the grains, the addition temperature of the online grain refiner being controlled at 720-730°C, the time from the addition of the online grain refiner to the start of solidification and crystallization of the aluminum alloy melt being controlled at 15-25 min, the temperature gradient of the surface of the aluminum alloy ingot being monitored in real time during the solidification and crystallization of the aluminum alloy melt to be within 5-15°C / cm, and the solidification front of the aluminum alloy melt being ensured to be stably located at 20-30 mm below the outlet of the crystallizer, to prepare a large-size aluminum alloy ingot;

[0010] 4) performing multi-stage homogenization annealing treatment on the large-size aluminum alloy ingot of step 3);

[0011] 5) milling the large-size aluminum alloy ingot after the multi-stage homogenization annealing treatment of step 4), and then rolling, the rolling starting temperature is 385-400℃, the total pass of rolling is not more than 15 passes, large strain rolling is adopted in the middle stage of rolling for 2-5 passes, the single pass reduction of the large strain rolling is 40-55mm, the final rolling temperature is not less than 350℃, and the aluminum alloy plate is prepared;

[0012] 6) solid solution quenching treatment is conducted on the aluminum alloy plate after rolling of step 5);

[0013] 7) pre-stretching treatment is conducted on the aluminum alloy plate after the solid solution quenching treatment of step 6);

[0014] 8) double-stage aging treatment is conducted on the aluminum alloy plate after the pre-stretching treatment of step 7), and the high-toughness large-size aluminum alloy plate is prepared.

[0015] According to the embodiment of the present application, in step 1), the alloy composition of the aluminum alloy plate includes the following components in percentage by weight: 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%, the total amount of the rest impurities is <0.05%, and the rest is aluminum. It is found that when the alloy composition of the aluminum alloy melt is within the above range and the preparation process of the present application is adopted, the alloy composition and the uniform dispersion of precipitated phase of the prepared aluminum alloy plate can be ensured, thereby obtaining the aluminum alloy plate with high toughness, high strength, low anisotropy and good batch stability (low batch variation coefficient). Further, when the alloy composition satisfying the above percentage by weight is selected, the low-melting-point MgZn2 phase will be formed in the homogenization process of the aluminum alloy melt, the low-melting-point MgZn2 phase can be quickly dissolved, and the grain size in the aluminum alloy plate is prevented from abnormally growing, which is beneficial to obtaining the aluminum alloy plate with low anisotropy and low strength variation coefficient between batches. The Al6Mn phase will be dispersedly precipitated in the homogenization process of the aluminum alloy melt, the Al6Mn phase can pin the grain boundary, inhibit the recrystallization of the aluminum alloy grain, weaken the deformation texture intensity in the process of thermal deformation, increase the recrystallization texture intensity, and reduce the anisotropy of the mechanical properties of the alloy. In addition, the dispersed fine Al6Mn phase can change the fracture mode of the alloy from intergranular fracture to transgranular ductile fracture, improve the elongation and fracture toughness of the alloy, and is beneficial to obtaining the aluminum alloy plate with high toughness and low anisotropy.

[0016] According to an embodiment of the present application, in step 1), the alloying components of the aluminum alloy thick plate include, in percentage by weight, 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%.

[0017] According to an embodiment of the present application, in step 1), the alloying components of the aluminum alloy thick plate include, in percentage by weight, Mg: 1.8%, 1.9%, 2.0%, 2.1% or 2.2%.

[0018] According to an embodiment of the present application, in step 1), the alloying components of the aluminum alloy thick plate include, in percentage by weight, Cu: 1.5%, 1.6%, 1.7% or 1.8%.

[0019] According to an embodiment of the present application, in step 1), the alloying components of the aluminum alloy thick plate include, in percentage by weight, Zr: 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14% or 0.15%.

[0020] According to an embodiment of the present application, in step 1), the alloying components of the aluminum alloy thick plate include, in percentage by weight, 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%.

[0021] According to an embodiment of the present application, 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 Al-Cu intermediate alloy is, for example, an Al-20Cu intermediate alloy or an Al-30Cu intermediate alloy, and the purity of the Al-Cu intermediate alloy is ≥99%, which refers to the sum of the content of Al element and Cu element in the intermediate alloy. The Al-Mn intermediate alloy is, for example, an Al-10Mn intermediate alloy or an Al-20Mn intermediate alloy, and the purity of the Al-Mn intermediate alloy is ≥99%, which refers to the sum of the content of Al element and Mn element in the intermediate alloy. The Al-Zr intermediate alloy is, for example, an Al-5Zr intermediate alloy, an Al-6Zr intermediate alloy or an Al-10Zr intermediate alloy, and the purity of the Al-Zr intermediate alloy is ≥99%, which refers to the sum of the content of Al element and Zr element in the intermediate alloy.

[0022] According to the embodiment of the present application, in step 1), the aluminum ingot, zinc ingot, aluminum copper intermediate alloy, aluminum zirconium intermediate alloy and aluminum manganese intermediate alloy are mixed and heated to 760-790℃ for 10-30min, and then the magnesium ingot is added and heated for another 10-30min.

[0023] According to the embodiment of the present application, in step 2), the refining, slagging, degassing and filtering are achieved by the cooperation of the static furnace, slagging ladle, online degassing device and filtering device. For example, the refining is performed in the static furnace, the slag and oxidation on the top of the static furnace are removed by the slagging ladle, the online degassing device is arranged at the bottom of the static furnace for degassing, and the filtering device is used for filtering the aluminum alloy melt.

[0024] According to the embodiment of the present application, 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%, the flow rate of the high-purity argon gas is 600-1200L / h, for example, 600L / h, 700L / h, 800L / h, 900L / h, 1000L / h, 1100L / h or 1200L / h, and the time of the high-purity argon gas is 10-15min. By introducing the high-purity argon gas into the aluminum alloy melt, the refining of the aluminum alloy melt can be achieved. When the flow rate of the high-purity argon gas is greater than 1200L / h or the time of the high-purity argon gas is greater than 15min, the bubble diameter of the refining gas will spread and merge, which will affect the degassing efficiency and effect, and thus the refining effect will be affected, and high-quality aluminum alloy melt cannot be obtained. When the flow rate of the high-purity argon gas is less than 600L / h or the time of the high-purity argon gas is less than 10min, the refining is not complete, the refining effect is not obvious, and high-quality aluminum alloy melt cannot be obtained.

[0025] According to the embodiment of the present application, in step 2), the double-rotor online degassing device is used for degassing the aluminum alloy melt, the rotation speed of the N1 rotor in the double-rotor online degassing device is 450-550rpm, the argon gas flow rate is 4.5-5.5m 3 / h, the rotation speed of the N2 rotor in the double-rotor online degassing device is 300-350rpm, and the argon gas flow rate is 3.0-3.2m 3 / h. By selecting the above double-rotor online degassing process, the hydrogen dissolved in the aluminum alloy melt can be effectively removed, and the hydrogen content in the aluminum alloy melt can be reduced to a very low level (less than 0.08μg / g), which is beneficial to obtain high-quality aluminum alloy melt.

[0026] According to the embodiment of the present application, in step 2), the aluminum alloy melt is filtered by using a double-stage plate filter device with 30PPI+50PPI. Compared with the single-stage plate filter device with 60PPI, the double-stage plate filter device with 30PPI+50PPI of the present application can sufficiently filter out the tiny solid inclusions in the aluminum alloy melt, which is beneficial to obtain the aluminum alloy melt with high quality.

[0027] According to the embodiment of the present application, in step 2), it is found that by using the above-mentioned method to refine, remove slag, degas and filter the aluminum alloy melt, the hydrogen content in the aluminum alloy melt can be significantly reduced to below 0.08 μg / g, and the tiny solid inclusions in the aluminum alloy melt can also be significantly reduced. By reducing the hydrogen content and the tiny solid inclusions in the aluminum alloy melt, the adverse effects of the aluminum alloy thick plate on toughness and fatigue performance can be reduced, and the strength and toughness difference of the aluminum alloy thick plate in three directions can also be significantly reduced, thereby obtaining the aluminum alloy thick plate with low anisotropy and low batch-to-batch variation coefficient.

[0028] According to the embodiment of the present application, in step 3), the online grain refiner is Al-Ti-C intermediate alloy, the specification of the Al-Ti-C intermediate alloy is wire, and the diameter of the wire is 4 mm-6 mm. The composition of the Al-Ti-C intermediate alloy is, for example, AlTi5C 0.18 , AlTi3C 0.15 or AlTi5C 1.2 .

[0029] According to the embodiment of the present application, in step 3), the addition amount of the online grain refiner 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%.

[0030] According to the embodiment of the present application, in step 3), the addition temperature of the online grain refiner is controlled at 720℃-730℃, for example, 720℃, 721℃, 722℃, 723℃, 724℃, 725℃, 726℃, 727℃, 728℃, 729℃ or 730℃. Within this temperature range, the online grain refiner can be quickly melted and uniformly mixed with the aluminum alloy melt, and on the other hand, the online grain refiner can quickly form effective nucleation cores to prevent grain growth, obtain fine and uniform grain structure, and fully play the role of grain refinement. By adding the online grain refiner, the aluminum alloy structure can also be adjusted, which can make the internal structure of the aluminum alloy more uniform, and is beneficial to obtain the aluminum alloy thick plate with high toughness, high strength, low anisotropy and low batch-to-batch variation coefficient.

[0031] According to the embodiment of the present application, in step 3), the time from the addition of the on-line grain refiner to the start of solidification of the aluminum alloy melt is controlled to be 15-25 min, for example, 15 min, 16 min, 18 min, 20 min, 22 min, 24 min or 25 min; within this time range, the on-line grain refiner can quickly form effective nucleation cores, and can effectively prevent the metal around the crystal nucleus from continuing to diffuse into the crystal nucleus, slow down the growth rate of the crystal nucleus, avoid the formation of coarse grains in the aluminum alloy melt due to too long time, and be more conducive to obtaining an aluminum alloy thick plate with uniform distribution of internal organization, thereby ensuring that the obtained aluminum alloy thick plate has high toughness, high strength, low anisotropy and low batch-to-batch variation coefficient.

[0032] According to the embodiment of the present application, in step 3), the temperature gradient of the aluminum alloy ingot surface is monitored in real time during the solidification of the aluminum alloy melt, and the temperature gradient of the aluminum alloy ingot surface is controlled to be 5-15 ℃ / cm, 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 by controlling the casting process; at this temperature gradient, the casting speed and cooling intensity are well matched, the solidification process is stable, the stress is released, and thermal cracking is prevented; at this temperature gradient, the liquid phase of the solute does not flow long distances between dendrites, the composition of the ingot is more uniform, and it is conducive to obtaining an aluminum alloy thick plate with more uniform organization and performance; at this temperature gradient, the solidification front can smoothly advance, avoid local areas from being isolated and solidified, and cause the formation of microporosity due to insufficient feeding; in summary, by controlling the temperature gradient of the aluminum alloy ingot surface, the uniform distribution of the internal organization of the alloy can be regulated, and an aluminum alloy thick plate with high toughness, high strength, low anisotropy and low batch-to-batch variation coefficient can be obtained.

[0033] According to the embodiment of the present application, in step 3), the temperature gradient can be monitored by an infrared thermal imager.

[0034] According to the embodiment of the present application, in step 3), due to the different solubility of alloying elements (such as Mg, Cu) in the aluminum alloy in the liquid-solid two-phase, part of the solute atoms are prone to enrich at the solidification front, and cannot fully diffuse into the liquid metal, eventually forming intragranular segregation or regional segregation at the grain boundary or center of the ingot, resulting in uneven composition of the ingot, and further affecting the uniform distribution of the internal structure of the alloy; when the solidification front position of the aluminum alloy melt is stabilized at 20-30 mm below the crystallizer outlet, this problem can be well solved, and an aluminum alloy thick plate with uniform internal structure of the alloy is obtained, thereby ensuring that the prepared aluminum alloy thick plate has the characteristics of low anisotropy and low batch-to-batch variation coefficient. In addition, when the solidification front position of the aluminum alloy melt is stabilized at 20-30 mm (such as 22 cm, 25 cm or 28 cm) below the crystallizer outlet, it can also effectively avoid the formation of concentrated shrinkage holes or dispersed loose in the aluminum alloy ingot due to the delayed replenishment of the aluminum alloy melt during solidification after solidification shrinkage, thereby reducing the density of the aluminum alloy ingot; it can also avoid the occurrence of thermal cracks on the surface or inside of the aluminum alloy ingot caused by the tensile stress between the solid shell and the liquid metal due to the sudden change of the local solidification speed in the aluminum alloy ingot.

[0035] According to the embodiment of the present application, in step 3), the temperature of the casting is 700-725℃, for example, 700℃, 705℃, 710℃, 715℃, 720℃ or 725℃; the speed of the casting is 45-50 mm / min, for example, 45 mm / min, 46 mm / min, 48 mm / min, 49 mm / min or 50 mm / min; the water pressure of the casting is 0.02-0.04 MPa, for example, 0.02 MPa, 0.025 MPa, 0.03 MPa, 0.035 MPa or 0.04 MPa; the water flow rate of the casting is 22 m 3 / h-30 m 3 / h, for example, 22 m 3 / h, 23 m 3 / h, 24 m 3 / h, 25 m 3 / h, 26 m 3 / h, 27 m 3 / h, 28 m 3 / h, 29 m 3 / h or 30 m 3 / h.

[0036] According to the embodiment of the present application, in step 3), by adopting the above casting method, the temperature gradient of the surface of the aluminum alloy ingot can be effectively controlled; the effect of the on-line grain refiner can be fully played, the uniform and fine equiaxed grains in the internal structure of the alloy can be ensured, the coarse columnar grains in the internal structure of the alloy can be avoided, and the strength, toughness and processing plasticity of the aluminum alloy ingot can be reduced; the grain size of the internal structure of the alloy can be controlled to be 1-2 grade, and the size of the microporosity is less than 100 μm, so that the aluminum alloy ingot with defects such as pores, inclusions and cracks in the internal structure can be avoided, and the toughness and fatigue performance of the aluminum alloy thick plate can be adversely affected; the reduction of the grain size and the size of the microporosity and the improvement of the uniformity of the internal structure of the alloy can significantly improve the strength, toughness and uniformity of the strength and toughness in three directions of the aluminum alloy thick plate, and are beneficial to obtaining the aluminum alloy thick plate with low anisotropy and low batch-to-batch variation coefficient. In summary, by selecting the above casting process, the aluminum alloy ingot with uniform composition, dense structure and without defects such as pores, inclusions, cracks and coarse second phase can be obtained, so that the aluminum alloy thick plate with high strength, high toughness, low anisotropy and low batch-to-batch variation coefficient can be prepared.

[0037] According to the embodiment of the present application, 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; and exemplarily, the aluminum alloy flat ingot with a size of 520 mm x 1620 mm x 5000 mm. The selection of the large-size aluminum alloy ingot can not only ensure the size requirement of the aluminum alloy thick plate, but also ensure that the aluminum alloy ingot has sufficient processing deformation, fully breaks the coarse grains in the internal structure of the aluminum alloy ingot, compacts the possible microporosity, obtains the aluminum alloy thick plate with high internal structure uniformity, and ensures that the aluminum alloy thick plate with large size, high toughness and high strength characteristics can be prepared; and the strength and fracture toughness of the aluminum alloy thick plate in three directions have the characteristics of low anisotropy, and the batch-to-batch variation coefficient of the aluminum alloy thick plate is reduced.

[0038] According to the embodiment of the present application, in step 4), the multi-stage homogenization annealing treatment comprises the following steps: performing first-stage homogenization annealing treatment at a temperature of 398-400 ℃ for 10-36 hours; then increasing the temperature to 465-470 ℃, and performing second-stage homogenization annealing treatment at this temperature for 24-36 hours; and continuously increasing the temperature to 475-477 ℃, and performing third-stage homogenization annealing treatment at this temperature for 12-36 hours.

[0039] Exemplarily, the first-stage homogenization annealing treatment is performed at a temperature of 398-400 ℃ for 10-36 hours (such as 12 hours, 15 hours, 18 hours, 24 hours, 28 hours, 30 hours or 36 hours), then the temperature is raised to 465-470 ℃ (such as 465 ℃, 466 ℃, 467 ℃, 468 ℃, 469 ℃ or 470 ℃) and the second-stage homogenization annealing treatment is performed at this temperature for 24-36 hours (such as 24 hours, 28 hours, 30 hours or 36 hours), and then the temperature is continuously raised to 475-477 ℃ (such as 475 ℃, 476 ℃ or 477 ℃) and the third-stage homogenization annealing treatment is performed at this temperature for 12-36 hours (such as 12 hours, 15 hours, 18 hours, 24 hours, 28 hours, 30 hours or 36 hours).

[0040] According to the embodiments of the present application, in step 4), the first-stage homogenization annealing treatment can diffuse Al3Zr phase and Al6Mn phase in the aluminum alloy ingot, and the precipitated Al3Zr phase and Al6Mn phase can pin the grain boundaries and inhibit the recrystallization of the aluminum alloy grains; the second-stage homogenization annealing treatment is performed at a temperature of 465-470 ℃, which can effectively dissolve the low-melting-point phases in the aluminum alloy ingot, and further diffuse the alloying elements (such as Cu and Mg) enriched in the aluminum alloy ingot, so as to homogenize the chemical composition of the entire aluminum alloy ingot and avoid the composition segregation to cause the performance fluctuation due to the non-uniform composition during subsequent processing or heat treatment, and thus the aluminum alloy thick plate with low anisotropy and low batch-to-batch variation coefficient cannot be obtained; the third-stage homogenization annealing treatment can further dissolve the residual phases in the aluminum alloy ingot and eliminate the coarse and unbalanced second phases in the aluminum alloy ingot, which is beneficial to obtain the aluminum alloy thick plate with low anisotropy and low batch-to-batch variation coefficient.

[0041] According to the embodiments of the present application, in step 5), the opening rolling temperature is 385-400 ℃, for example, 385 ℃, 390 ℃, 395 ℃ or 400 ℃.

[0042] According to the embodiments of the present application, in step 5), the rolling direction is along the length direction of the blank.

[0043] According to an embodiment of the present application, in step 5), the total deformation amount of rolling is 60-70%, for example, 60%, 62%, 65%, 68% or 70%. When the total deformation amount of rolling (60-70%) is met, the coarse grain structure inside the aluminum alloy ingot can be fully broken, and the small loose structure can be compacted, so that the consistency of the structure of the aluminum alloy plate from the surface to the core is better, which is beneficial to obtain the aluminum alloy plate with low anisotropy and low batch-to-batch variation coefficient, and can also avoid the loose core structure due to insufficient deformation (total deformation amount of rolling < 60%) to obtain the aluminum alloy plate with high strength and high toughness. The selection of the total deformation amount of rolling can also ensure that the aluminum alloy plate, especially the aluminum alloy plate with a thickness specification of 102-203 mm, is prepared.

[0044] According to an embodiment of the present application, in step 5), the small strain rolling is used in the starting stage of rolling for 3-8 passes (for example, 3 passes, 4 passes, 5 passes, 6 passes, 7 passes or 8 passes) in succession, and the single pass reduction amount in the small strain rolling process in the starting stage of rolling is 10-20 mm (for example, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm or 20 mm).

[0045] According to an embodiment of the present application, in step 5), the large strain rolling is used in the intermediate stage of rolling for 2-5 passes (for example, 2 passes, 3 passes, 4 passes or 5 passes) in succession, and the single pass reduction amount in the large strain rolling process in the intermediate stage of rolling is 40-55 mm (for example, 40 mm, 43 mm, 45 mm, 50 mm or 55 mm).

[0046] According to an embodiment of the present application, in step 5), the small strain rolling is used in the ending stage of rolling for 3-5 passes (for example, 3 passes, 4 passes or 5 passes) in succession to the required plate thickness, and the single pass reduction amount in the small strain rolling process in the ending stage of rolling is 10-15 mm (for example, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm or 15 mm).

[0047] According to the embodiment of the present application, in step 5), the deformation energy storage of the large-size aluminum alloy ingot can be well controlled by controlling the roughing temperature in the temperature range of 380-400°C, the recrystallization of the alloy structure in the aluminum alloy ingot is inhibited, and more subgrain structures are retained; in the rolling process of the present application, the combined rolling process of small-strain rolling-large-strain rolling-small-strain rolling is adopted, by selecting different strain rolling processes in different rolling stages, the coarse grains inside the structure are broken to the greatest extent, and more complex dislocation structures are generated, wherein the large-strain rolling process can well bridge the metallurgical defects, control the proportion of subgrains, and effectively improve the toughness and fatigue life of the aluminum alloy plate while keeping a small total deformation (the total deformation in the large-strain rolling stage), and at the same time, the uniformity of the alloy structure distribution is also improved, so as to ensure that the aluminum alloy plate has low anisotropy and low batch-to-batch variation coefficient; in particular, the small-strain rolling and the large-strain rolling are effectively matched, which can more significantly improve the toughness and fatigue life of the aluminum alloy plate, so as to obtain the large-size aluminum alloy plate with high strength, high toughness, high fatigue life, low anisotropy and low batch-to-batch variation coefficient.

[0048] According to the embodiment of the present application, in step 6), the solution quenching treatment is carried out at a temperature of 475-482°C for 4-8.5 hours, after the holding is completed, the furnace is discharged and quenched, the quenching transfer time is ≤15s, and the quenching water temperature is room temperature.

[0049] Exemplarily, the solution quenching treatment is carried out at a temperature of 475-482°C (such as 475°C, 478°C, 480°C or 482°C) for 4-8.5 hours, and specifically, the holding time can be determined according to the thickness of the aluminum alloy plate, for example, the aluminum alloy plate with a thickness of 76-89 mm is held for 4 hours, the aluminum alloy plate with a thickness of 89-102 mm is held for 4.5 hours, and the aluminum alloy plate with a thickness of more than 102 mm, the holding time is increased by 0.5 hours based on 4.5 hours for each increase of 12.7 mm in thickness; the quenching transfer time is ≤15s.

[0050] According to the embodiment of the present application, in step 6), in the solution quenching treatment process, a large amount of complex dislocation structures formed in the rolling process are eliminated, the newly generated strain-free fine equiaxed grains become new nucleation sites in the deformed structure, and gradually grow and replace all the deformed structure, so as to obtain the aluminum alloy plate with high toughness and high strength, and the uniformity of the alloy internal structure can also ensure that the prepared aluminum alloy plate has the characteristics of low anisotropy and low batch-to-batch variation coefficient.

[0051] According to an embodiment of the present application, 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 sufficiently eliminate the residual stress of the aluminum alloy thick plate.

[0052] According to an embodiment of the present application, in step 8), the two-stage aging treatment is a first-stage aging heat treatment at 117-123℃ for 12-24 hours, followed by a second-stage aging heat treatment at 154-160℃ for 7-16 hours by furnace temperature rising, and air cooling to room temperature after furnace discharge.

[0053] The present application also provides an aluminum alloy thick plate prepared by the above method.

[0054] According to an embodiment of the present application, the aluminum alloy thick plate is a high-toughness, large-size aluminum alloy thick plate.

[0055] According to an embodiment of the present application, the thickness of the aluminum alloy thick 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.

[0056] According to an embodiment of the present application, the width of the aluminum alloy thick plate is ≥1200mm.

[0057] According to an embodiment of the present application, the length of the aluminum alloy thick plate is ≥10000mm.

[0058] According to an embodiment of the present application, the aluminum alloy thick plate satisfies at least one of the following conditions:

[0059] (1) the tensile strength of L direction is ≥530MPa, the tensile strength of LT direction is ≥530MPa, and the tensile strength of ST direction is ≥510MPa;

[0060] (2) the yield strength of L direction is ≥490MPa, the yield strength of LT direction is ≥490MPa, and the yield strength of ST direction is ≥480MPa;

[0061] (3) the elongation of L direction is ≥10%, the elongation of LT direction is ≥9%, and the elongation of ST direction is ≥7%;

[0062] (4) the fracture toughness of L-T direction is ≥35MPa·m 1 / 2The fracture toughness of the S-L direction reaches 32 MPa·m above. 1 / 2 The fracture toughness of the S-L direction reaches 32 MPa·m above. 1 / 2 above;

[0063] (5) R=0.1, the average fatigue life reaches 180000 cycles above under the stress of 241 MPa.

[0064] According to the embodiment of the present application, the aluminum alloy thick plate satisfies that the coefficient of variation Cv of tensile strength between batches reaches 2.0% below, and the number of batches is not less than 20 batches, preferably more than 30 batches, such as more than 40 batches, more than 50 batches, more than 100 batches, more than 150 batches or more than 200 batches.

[0065] According to the embodiment of the present application, the aluminum alloy thick plate satisfies that the coefficient of variation Cv of yield strength between batches reaches 2.0% below, and the number of batches is not less than 20 batches, preferably more than 30 batches, such as more than 40 batches, more than 50 batches, more than 100 batches, more than 150 batches or more than 200 batches.

[0066] In the present application, the coefficient of variation (C V , Coefficient of Variation) is used to represent the discrete degree of the strength (tensile strength or yield strength) of the aluminum alloy thick plate between different batches; the calculation formula is: standard deviation (SD, Standard Deviation) / average value × 100%.

[0067] According to the embodiment of the present application, the aluminum alloy thick plate satisfies that the difference of the strength (tensile strength or yield strength) in three directions (L direction, LT direction and ST direction) is not more than 5%.

[0068] According to the embodiment of the present application, the aluminum alloy thick plate satisfies that the difference of the fracture toughness in three directions (L-T direction, T-L direction and S-L direction) is not more than 10%.

[0069] The beneficial effects of the present application are:

[0070] The application provides a high-toughness large-size aluminum alloy thick plate and a preparation method thereof. The aluminum alloy thick plate has the characteristics of large size, high toughness and high strength, the strength and toughness of the aluminum alloy thick plate in three directions have the characteristics of low anisotropy, and the aluminum alloy thick plate also has the characteristics of low batch-to-batch variation coefficient. The application controls the alloy composition range of the aluminum alloy thick plate, so that the composition fluctuation of the aluminum alloy thick plate at different positions is greatly reduced, the aluminum alloy thick plate with uniform internal alloy organization is obtained, and the batch-to-batch variation coefficient of the aluminum alloy thick plate is reduced. Meanwhile, the process steps such as melting, multi-stage homogenization, large-strain rolling, solid solution quenching and double-stage aging heat treatment of the application are matched, so that the obtained large-size aluminum alloy thick plate has the characteristics of high toughness, high strength, low anisotropy and good batch-to-batch stability. DETAILED DESCRIPTION

[0071] The preparation method of the application will be further described in detail below in combination with specific examples. It should be understood that the following examples are only illustratively described and explained, and should not be interpreted as limiting the scope of protection of the application. Any technology realized based on the above description of the application is covered within the scope of protection intended by the application.

[0072] In the following examples, the experimental methods are conventional methods unless otherwise specified; the reagents, materials and the like used in the following examples can be obtained from commercial channels unless otherwise specified.

[0073] In the following examples, pure aluminum ingots with a purity of 99.95% or above, magnesium ingots with a purity of 99.5% or above, zinc ingots with a purity of 99.9% or above, Al-50Cu aluminum copper intermediate alloy, Al-10Zr aluminum zirconium intermediate alloy and Al-20Mn aluminum manganese intermediate alloy are used.

[0074] Example 1

[0075] (1) Proportioning: proportioning according to the following weight percentage: Zn: 7.2%, Mg: 2.0%, Cu: 1.6%, Zr: 0.12%, Mn: 0.25%.

[0076] (2) Melting: aluminum ingots, zinc ingots, aluminum copper intermediate alloy, aluminum zirconium intermediate alloy and aluminum manganese intermediate alloy are added to a melting furnace, the temperature is raised and the melting temperature is controlled at 770℃, the magnesium ingot is added after the alloy raw materials are melted and the temperature is lowered to 725℃, and the melting is continued for 20 min.

[0077] 3 / h, the rotation speed of N2 rotor in the double-rotor on-line degassing device is 350 rpm, and the flow rate of argon is 3.0 m 3 / h. A double-stage ceramic filter plate of 30PPI+50PPI is used to filter the aluminum alloy melt after on-line degassing. The alloy element composition of the prepared aluminum alloy melt is detected, in which Fe: 0.08%, Si: 0.06%.

[0078] (4) Casting: On-line grain refiner Al-Ti-C wire is added to the aluminum alloy melt during casting to refine the grains, the addition temperature of Al-Ti-C wire is controlled at 725℃, the time from the addition of Al-Ti-C wire to the start of solidification and crystallization of the aluminum alloy melt is controlled at 20 min, and the addition amount of Al-Ti-C wire 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 water pressure during casting is 0.03 MPa, the water flow rate during casting is 25 m 3 / h, the surface temperature gradient of the aluminum alloy ingot during solidification and crystallization is 10℃ / cm, and the solidification front position of the aluminum alloy melt is ensured to be stable at 25 mm below the crystallizer outlet, thereby preparing an aluminum alloy flat ingot with a size of 520 mm×1620 mm×5000 mm.

[0079] (5) Three-stage homogenization annealing: The cast aluminum alloy ingot after casting is subjected to three-stage homogenization annealing treatment, wherein the first-stage homogenization annealing is at 400℃ for 24 hours, the second-stage homogenization annealing is at 468℃ for 36 hours, and the third-stage homogenization annealing is at 477℃ for 24 hours.

[0080] (6) Rolling: The aluminum alloy ingot after homogenization annealing treatment is milled to obtain an ingot with a size of 500 mm×1600 mm, and rolling is performed along the length direction of the billet, the opening rolling temperature is 395℃, and the rolling passes and deformation amounts are as follows:

[0081] 500 mm→490 mm→470 mm→450 mm→430 mm→410 mm→360 mm→310 mm→265 mm→220 mm→205 mm→190 mm→175 mm→160 mm, and the final rolling temperature is not lower than 350℃.​

[0082] (7) Solution quenching: the solution quenching treatment was performed on the rolled aluminum alloy thick plate by using a solution quenching process of 478℃ / 7h, the quenching transfer time was <10s, and the quenching was to room temperature.

[0083] (8) Pre-stretching: the pre-stretching treatment was performed on the solution quenched aluminum alloy plate, and the stretching amount was 2%.

[0084] (9) Two-stage aging treatment: the two-stage aging treatment was performed on the pre-stretched aluminum alloy plate, specifically, the first stage aging heat treatment was performed at 120℃ for 20 hours, then the furnace was heated to 157℃ for the second stage aging heat treatment for 12 hours, and the furnace was discharged and air cooled to room temperature.

[0085] Comparative Example 1

[0086] The other operations of Comparative Example 1 were the same as those of Example 1, except that step (1) was performed as follows:

[0087] (1) Blending: blending was performed according to the following weight percentages: Zn: 6.5%, Mg: 2.5%, Cu: 2.2%, Zr: 0.12%. The alloy element composition of the aluminum alloy melt prepared after the refining of step (3) was detected, in which Fe: 0.10%, Si: 0.08%.

[0088] Comparative Example 2

[0089] The other operations of Comparative Example 2 were the same as those of Example 1, except that step (3) was performed as follows:

[0090] (3) Refining: the aluminum alloy melt in the static furnace was refined by using high-purity argon as the refining medium, the purity of the argon was not less than 99.99%, the flow rate of the argon was 1500L / h, and the flow time was 10min. The aluminum alloy melt in the static furnace was degassed by using a double-rotor online degassing device, the rotation speed of N1 rotor in the double-rotor online degassing device was 300rpm, the flow rate of the argon was 4m 3 / h, and the rotation speed of N2 rotor in the double-rotor online degassing device was 250rpm, the flow rate of the argon was 2.5m 3 / h. The online degassed aluminum alloy melt was filtered by using a single-stage ceramic filter plate with 60PPI.

[0091] Comparative Example 3

[0092] The other operations of Comparative Example 3 were the same as those of Example 1, except that step (4) was performed as follows:

[0093] (4) Casting: On-line grain refiner Al-Ti-B wire was added to the aluminum alloy melt to refine the grains during casting, the addition temperature of Al-Ti-B wire was controlled at 710℃, the time from the addition of Al-Ti-B wire to the start of solidification and crystallization of the aluminum alloy melt was controlled at 30 min, the addition amount of Al-Ti-B wire was 0.01% of the total mass of the aluminum alloy melt; the casting temperature was 720℃, the casting speed was 48 mm / min, the water pressure for casting was 0.03 MPa, the water flow rate for casting was 25 m 3 / h, the surface temperature gradient of the aluminum alloy ingot was monitored in real time during the solidification and crystallization of the aluminum alloy melt, which was 10℃ / cm, and the solidification front position of the aluminum alloy melt was ensured to be stable at 25 mm below the crystallizer outlet, thereby obtaining an aluminum alloy flat ingot with a size of 520 mm x 1620 mm x 5000 mm.

[0094] Comparative Example 4

[0095] Comparative Example 4 was operated in the same way as Example 1, except that step (4) was performed as follows:

[0096] (4) Casting: On-line grain refiner Al-Ti-C wire was added to the aluminum alloy melt to refine the grains during casting, the addition temperature of Al-Ti-C wire was controlled at 725℃, the time from the addition of Al-Ti-C wire to the start of solidification and crystallization of the aluminum alloy melt was controlled at 20 min, the addition amount of Al-Ti-C wire was 0.01% of the total mass of the aluminum alloy melt; the casting temperature was 740℃, the casting speed was 55 mm / min, the water pressure for casting was 0.01 MPa, the water flow rate for casting was 32 m 3 / h, the surface temperature gradient of the aluminum alloy ingot was monitored in real time during the solidification and crystallization of the aluminum alloy melt, which was 20℃ / cm, and the solidification front position of the aluminum alloy melt was ensured to be stable at 35 mm below the crystallizer outlet, thereby obtaining an aluminum alloy flat ingot with a size of 520 mm x 1620 mm x 5000 mm.

[0097] Comparative Example 5

[0098] Comparative Example 5 was operated in the same way as Example 1, except that step (6) was performed as follows:

[0099] (6) Rolling: The aluminum alloy ingot after homogenization annealing treatment was milled to obtain an ingot with a size of 500 mm x 1600 mm, and rolling was performed along the length direction of the billet, the rolling temperature was 420℃, and the rolling pass and deformation amount were as follows:

[0100] 500mm→490mm→470mm→450mm→430mm→410mm→390mm→370mm→340mm→310mm→280mm→250mm→230mm→210mm→190mm→170mm→160mm, the final rolling temperature is not lower than 350℃.

[0101] Comparative Example 6

[0102] Comparative Example 6 is operated as Example 1 except that step (6) is performed as follows:

[0103] (6) Rolling: the aluminum alloy ingot after homogenization annealing treatment is milled to obtain an ingot with a size of 500 mm x 1600 mm, and rolling is performed along the length direction of the ingot, and the temperature for starting rolling is 420℃, and the rolling passes and deformation are as follows:

[0104] 500mm→490mm→480mm→470mm→460mm→450mm→430mm→410mm→390mm→370mm→350mm→330mm→310mm→265mm→220mm→175mm→170mm→165mm→160mm, the final rolling temperature is not lower than 350℃.

[0105] The aluminum alloy thick plates prepared in the above examples and comparative examples are tested for performance, and the results are shown in Tables 1 to 3.

[0106] Table 1 Comparison of performance of aluminum alloy thick plates of examples and comparative examples

[0107]

[0108] Table 2 Difference in performance of aluminum alloy thick plates of examples and comparative examples in different directions

[0109]

[0110] Table 3 Statistical results of batch stability of aluminum alloy thick plates of examples and comparative examples

[0111]

[0112] Comparative Example 1 has 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 prepared by Comparative Example 1 increases, resulting in higher anisotropy of the aluminum alloy thick plate, larger strength variation coefficient between batches, i.e. larger difference in strength and fracture toughness between the three directions of the thick plate, and lower batch stability.

[0113] The comparative example 2 has the same process as the example 1, but the alloy of the comparative example 2 is refined by common argon, and the argon flow is larger; the on-line degassing is performed by double rotors, but the rotor speed and the argon flow are lower; the melt is filtered by single-stage ceramic filter plate; the above parameters and operations result in limited degassing efficiency of the aluminum alloy melt, so that the hydrogen content and the slag content in the aluminum alloy thick plate are higher, the hydrogen content and the slag content fluctuate greatly between batches, and the anisotropy of the aluminum alloy thick plate is higher, the fracture toughness is lower, the fatigue performance is lower, and the batch stability is reduced.

[0114] The comparative example 3 has the same process as the example 1, but the alloy of the comparative example 3 is refined by Al-Ti-B wires, and B and Zr form hard and brittle intermetallic compound particles such as ZrB2, which affect the toughness and fatigue performance of the aluminum alloy thick plate; and also affect the uniformity of the alloy organization, so that the room temperature tensile strength, the fracture toughness and the fatigue performance of the aluminum alloy thick plate are lower, and the batch stability is reduced.

[0115] The comparative example 4 has the same process as the example 1, but the solidification front position of the aluminum alloy melt of the comparative example 4 is stabilized at 35 mm below the outlet of the crystallizer, and 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 lower, so that the surface temperature gradient of the aluminum alloy during the solidification and crystallization of the aluminum alloy melt cannot be effectively controlled, the internal organization of the aluminum alloy ingot is coarse, the composition segregation is serious, and the microporosity is serious, which affects the mechanical properties, the fracture toughness and the batch stability of the aluminum alloy thick plate, so that the room temperature tensile strength, the fracture toughness and the fatigue performance of the aluminum alloy thick plate are lower, and the batch stability is reduced.

[0116] The comparative examples 5-6 have the same process as the example 1, but the alloys of the comparative examples 5-6 are rolled by multi-pass uniform deformation process, and due to insufficient deformation amount, the internal metallurgical defects such as microporosity of the aluminum alloy thick plate are not welded enough, the performance of the aluminum alloy thick plate in three directions is greatly different, the room temperature tensile strength, the fracture toughness and the fatigue performance are lower, and the batch stability is reduced.

[0117] The above describes the embodiments of the present application. However, the present application is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a high-toughness large-size aluminum alloy thick plate, the method comprising the following steps: 1) mixing aluminum ingots, magnesium ingots, zinc ingots, aluminum copper intermediate alloy, aluminum zirconium intermediate alloy and aluminum manganese intermediate alloy, heating and melting to prepare an aluminum alloy melt; the alloy composition of the aluminum alloy thick plate comprises the following components in percentage by weight: 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%, total amount of impurities <0.05%, and the balance being aluminum; 2) refining, skimming, degassing and filtering the aluminum alloy melt of step 1); 3) casting the aluminum alloy melt treated in step 2), adding an online grain refiner to refine the grains, the temperature for adding the online grain refiner being controlled at 720-730°C, the time from adding the online grain refiner to the start of solidification and crystallization of the aluminum alloy melt being controlled at 15-25 min, the temperature gradient of the surface of the aluminum alloy ingot being monitored in real time during the solidification and crystallization of the aluminum alloy melt to be within 5-15°C / cm, and the solidification front of the aluminum alloy melt being ensured to be stably located at 20-30 mm below the outlet of the crystallizer, to prepare a large-size aluminum alloy ingot; 4) subjecting the large-size aluminum alloy ingot of step 3) to multi-stage homogenization annealing treatment; 5) subjecting the large-size aluminum alloy ingot of step 4) to milling processing after the multi-stage homogenization annealing treatment, and then to rolling, the starting temperature being 385-400°C, the total pass number of rolling being not more than 15, large strain rolling being adopted for 2-5 consecutive passes in the middle stage of rolling, the single-pass reduction amount during the large strain rolling being 40-55 mm, and the final rolling temperature being not lower than 350°C, to prepare an aluminum alloy thick plate; 6) subjecting the rolled aluminum alloy thick plate of step 5) to solid solution quenching treatment; 7) subjecting the aluminum alloy thick plate of step 6) to pre-stretching treatment after the solid solution quenching treatment; 8) subjecting the aluminum alloy thick plate of step 7) to double-stage aging treatment after the pre-stretching treatment, to prepare a high-toughness large-size aluminum alloy thick plate; the thickness of the aluminum alloy thick plate is≥76 mm; In step 3), the large-size aluminum alloy ingot is a flat ingot with a thickness≥420 mm; In step 5), small strain rolling is adopted for 3-8 consecutive passes at the starting stage of rolling, the single-pass reduction amount during the small strain rolling at the starting stage of rolling being 10-20 mm; large strain rolling is adopted for 2-5 consecutive passes at the middle stage of rolling, the single-pass reduction amount during the large strain rolling at the middle stage of rolling being 40-55 mm; and small strain rolling is adopted for 3-5 consecutive passes at the ending stage of rolling to the required plate thickness, the single-pass reduction amount during the small strain rolling at the ending stage of rolling being 10-15 mm.

2. The production method according to claim 1, wherein In step 1), the aluminum ingot, zinc ingot, aluminum copper intermediate alloy, aluminum zirconium intermediate alloy and aluminum manganese intermediate alloy are mixed and heated to 760-790℃ for 10-30 minutes, and then the magnesium ingot is added after the temperature is lowered to 720-730℃, and the melting is continued for 10-30 minutes.

3. The production method according to claim 1, wherein 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%, the flow rate of the high-purity argon gas is 600-1200L / h, and the high-purity argon gas is introduced for 10-15 minutes. And / or, in step 2), the aluminum alloy melt is treated by a double-rotor on-line degassing device, the rotating speed of N1 rotor in the double-rotor on-line degassing device is 450-550 rpm, the argon flow rate is 4.5-5.5 m 3 / h, the rotating speed of N2 rotor in the double-rotor on-line degassing device is 300-350 rpm, and the argon flow rate is 3.0-3.2 m 3 / h. In step 2), a double-stage plate filter device with 30PPI+50PPI is used to filter the aluminum alloy melt.

4. The production method according to claim 1, wherein In step 3), the online grain refiner is Al-Ti-C intermediate alloy, and the specification of the Al-Ti-C intermediate alloy is wire material. In step 3), the addition amount of the online grain refiner is 0.01-0.015% of the total mass of the aluminum alloy melt.

5. The production method according to claim 1, wherein In step 3), the temperature of the casting is 700-725°C; the speed of the casting is 45-50 mm / min; the water pressure of the casting is 0.02-0.04 MPa; the water flow of the casting is 22 m 3 / h-30 m 3 / h.

6. The production method according to claim 1, wherein In step 5), the rolling temperature is 385-400℃. In step 5), the total deformation amount of the rolling is 60-70%.

7. The production method according to claim 1, wherein In step 4), the multi-stage homogenization annealing treatment includes the following steps: first-stage homogenization annealing treatment at 398-400℃ for 10-36 hours; then heating to 465-470℃ and holding for 24-36 hours at this temperature for second-stage homogenization annealing treatment; and then heating to 475-477℃ and holding for 12-36 hours at this temperature for third-stage homogenization annealing treatment. In step 6), the solution quenching treatment is solution treatment at 475-482℃ for 4-8.5 hours, and then the furnace is taken out for quenching after the holding, the quenching transfer time is ≤15s, and the quenching water temperature is room temperature. In step 7), the stretching amount of the pre-stretching treatment is 1.5-3%. In step 8), the two-stage aging treatment is first-stage aging heat treatment at 117-123℃ for 12-24 hours, and then second-stage aging heat treatment at 154-160℃ for 7-16 hours after the furnace is heated up, and the furnace is taken out for air cooling to room temperature.

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

9. The aluminum alloy plate of claim 8, wherein, The aluminum alloy thick plate meets at least one of the following conditions: (1) the tensile strength in L direction is above 530MPa, the tensile strength in LT direction is above 530MPa, and the tensile strength in ST direction is above 510MPa; (2) the yield strength in L direction is above 490MPa, the yield strength in LT direction is above 490MPa, and the yield strength in ST direction is above 480MPa; (3) the elongation in L direction is above 10%, the elongation in LT direction is above 9%, and the elongation in ST direction is above 7%; (4) L-T direction fracture toughness reached 35 MPa-m 1 / 2 Above, T-L direction fracture toughness reached 33 MPa-m 1 / 2 Above, S-L direction fracture toughness reached 32 MPa-m 1 / 2 Above; (5) the fatigue life average under 241MPa stress is above 180000 cycles.

10. The aluminum alloy plate of claim 8, wherein, The aluminum alloy thick plate meets the condition that the coefficient of variation Cv of the tensile strength between batches is below 2.0%, and the number of batches is not less than 20 batches. And / or, the aluminum alloy thick plate satisfies that the coefficient of variation Cv of yield strength between batches reaches 2.0% or less, and the number of batches is not less than 20 batches; And / or, the aluminum alloy thick plate satisfies that the difference of strength in L direction, LT direction and ST direction is not more than 5%; And / or, the aluminum alloy thick plate satisfies that the difference of fracture toughness in L-T direction, T-L direction and S-L direction is not more than 10%.

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