A method for preparing large-size, high-performance aerospace aluminum alloy thick plates

Abstract

A method for preparing large-format, high-performance aerospace aluminum alloy thick plates belongs to the field of aluminum alloy sheet manufacturing technology. The method includes proportionally proportioning aluminum alloy raw materials and sequentially performing melting, heat preservation, degassing and filtration, casting in a low-crystallizer, homogenization, machining, preheating, hot rolling, two-stage solution quenching, stretching, flaw detection, secondary aging, and stress testing to obtain large-format, high-performance aerospace aluminum alloy thick plates. This invention, through the design of high-performance aerospace aluminum alloy compositions and research on Zn, Cu, Mg, and Sc, reveals the influence trends of Zn, Mg, Cu, and Sc compositions on the microstructure of aerospace aluminum alloy thick plates, developing a technology for preparing large-format, high-performance aerospace aluminum alloy thick plates and achieving industrial-scale mass production.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal processing technology, specifically to a method for preparing large-size, high-performance aerospace aluminum alloy thick plates. Background Technology

[0002] Large-format, high-performance aerospace aluminum alloy plates are high-strength aluminum alloy materials, and their industrial manufacturing is technically challenging, mainly due to the following aspects: High alloying degree, high tendency to casting cracks, and high casting difficulty; the tendency of alloying elements such as Zn, Cu, and Mg to segregate poses difficulties in controlling the composition and microstructure uniformity of the ingot and reducing the slag content; high comprehensive performance requirements for the material, including strength, toughness, and corrosion resistance, which are often inversely related, requiring reasonable process control to achieve a good balance of comprehensive performance; furthermore, during the manufacturing process of ultra-thick high-performance aerospace aluminum alloy plates, uneven plastic deformation and quenching cooling processes will create residual stress in the plate, and poor residual stress reduction will cause deformation during subsequent machining of components. In summary, the production of ultra-thick high-performance aerospace aluminum alloy plates places high demands on the technologies of melting and casting, rolling, solution quenching, and aging. Summary of the Invention

[0003] To address the aforementioned challenges, this invention provides a method for preparing large-scale, high-performance aerospace aluminum alloy thick plates. Through research on high-performance aerospace aluminum alloy composition design, high-quality ingot casting technology, large-scale plate rolling technology, precision heat treatment technology, and residual stress assessment and reduction technology, this invention develops a method for preparing large-scale, high-performance aerospace aluminum alloy thick plates and achieves industrial-scale mass production.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows: A large-size, high-performance aerospace aluminum alloy thick plate, with a thickness of 150~220mm, and the alloy composition by weight percentage includes the following alloying elements: 6.02~11.27% Zn, 1.69~2.25% Mg, 1.66~2.35% Cu, 0.11~0.16% Zr, 0.10~0.12% Fe, unavoidable impurities, and aluminum.

[0005] A method for preparing large-size, high-performance aerospace aluminum alloy thick plates with a thickness of 150~220mm includes the following steps: S1. Composition design and ingredient formulation: Alloy elements are proportioned according to weight percentage; S2, Smelting: The aluminum ingots and intermediate alloys of S1 are put into a dry smelting furnace and completely melted and mixed evenly to obtain an aluminum alloy melt. The melt temperature is controlled within the range of 780~800℃. S3, Degassing and Filtration: The aluminum alloy melt from S2 is first refined and degassed in a holding furnace, and then refined and degassed again in the casting trough. After degassing, the hydrogen content is controlled within the range of ≤0.10ml / 100gAl. Finally, it is filtered through a ceramic filter screen. S4. Casting: The aluminum alloy melt after S3 treatment is cast through a short crystallizer, and the aluminum alloy flat ingot is finally obtained by controlling the cooling water temperature, water flow rate and casting temperature. S5. Homogenization heat treatment: The S4 aluminum alloy flat ingot is homogenized by heating and holding at a temperature of 450~460℃ in the homogenization furnace for 41 hours. S6. Machining: After cooling the S5 aluminum alloy flat ingot, cut off the head and tail and mill the surface to cut it into a casting; S7, Preheating, Rolling, Trimming: Before rolling, the S6 ingot is preheated. After preheating, it is rolled in several passes on a hot rolling mill to obtain a thick aluminum alloy plate. It is then lubricated with emulsion and trimmed after rolling. S8. Quenching: The S7 aluminum alloy thick plate is first subjected to a two-stage solution treatment, and then quenched. S9. Tensile testing and flaw detection: The S8 aluminum alloy thick plate is subjected to tensile testing and flaw detection. S10, Aging: Aging is performed on the S9 aluminum alloy thick plate; S11, stress testing, sawing of finished products.

[0006] The alloying elements, by weight percentage, are: 10.41~11.27% Zn, 1.73~1.77% Mg, 1.71~1.80% Cu, 0.13~0.14% Zr, 0.11% Fe, with the remainder being aluminum and unavoidable impurities. The resulting thick plate has the following properties: a hardness value of 187~191.5 HV at a distance of 3 mm from the quenched end face, and a hardness value of 166.5~168 HV at a distance of 120 mm.

[0007] The alloying elements, by weight percentage, are: 6.02~6.55% Zn, 2.25% Mg, 2.20~2.35% Cu, 0.12% Zr, 0.10~0.11% Fe, with the remainder being aluminum and unavoidable impurities. The resulting thick plate exhibits the following properties: a hardness retention value of 89~93% at 120mm from the quenched end face; and a stress corrosion sensitivity factor of I. SSRT The range is 2.04% to 5.83%.

[0008] The alloying elements, by weight percentage, are: 8.21% Zn, 1.70% Mg, 1.66% Cu, 0.16% Zr, 0.21% Sc, 0.12% Fe, with the remainder being aluminum and unavoidable impurities. The resulting thick plate has the following properties: tensile strength in air of 580 MPa and elongation of 19.7%; tensile strength in a 3.5% NaCl solution of 560 MPa and elongation of 19.2%.

[0009] in: In step S2, the melt temperature is controlled within the range of 780~800℃, the furnace gas temperature is controlled within the range of 1100±50℃ during the heating stage and 900±50℃ during the holding stage, and the aluminum melt temperature uniformity is ≤±3℃. The smelting furnace mainly melts solid raw materials into a liquid melt, and after the temperature is adjusted appropriately, it is transferred to a holding furnace. Simultaneously, slag generated during the smelting process is removed using a slag remover to ensure the purity of the melt.

[0010] In step S3, the material temperature in the holding furnace is controlled within the range of 760~780℃, the furnace gas temperature is controlled within the range of 830±50℃, and the holding time is 1.5h. In the refining and degassing process in the flow channel, a mixed gas of argon and chlorine is used by rotary jetting to remove hydrogen and inclusions by causing bubbles to float. The argon flow rate is controlled within the range of 1~2m³. 3 The rotor speed is controlled within a range of 500–600 r / min, and the hydrogen content after online degassing during casting is controlled within a range of ≤0.10 ml / 100 g Al. The holding furnace mainly focuses on refining, degassing, and composition adjustment to provide qualified melt for casting. Electromagnetic stirrers are also used during melting and holding to agitate the melt during production, ensuring uniform composition and temperature. The electromagnetic stirrer can operate back and forth between the melting furnace and the holding furnace to ensure the melt quality of both furnaces. Argon and chlorine gases can remove alkali metals, hydrogen, slag, etc., to the maximum extent.

[0011] Other functions of electromagnetic stirrers: (1) Non-contact stirring, which does not contaminate the aluminum melt; (2) Accelerates the melting rate of the smelting furnace, reduces the generation of oxide slag, thereby reducing the number of furnace cleanings and extending the service life of the furnace; (3) Stirring when the furnace door is closed, preventing heat dissipation, reducing production time and greatly improving productivity; (4) Get rid of the scraper used for manual stirring, reducing the labor intensity of workers.

[0012] Step S4: The casting crystallizer thickness is 120mm, the casting temperature control range is 740~760℃, the cooling tower water temperature control range is 10~40℃, the casting speed control range is 20~30mm / min, and the cooling water flow rate control range is 50~60m³ / min. 3The water pressure is controlled within the range of 0.08~0.15 MPa, and the wire feeder speed is controlled within the range of 30±10 cm / min. A short crystallizer is used for casting, and cooling is accelerated by controlling the cooling water temperature, water flow rate, and casting temperature. This results in a shallower and flatter casting cavity, reducing ingot component segregation and improving the uniformity of ingot composition and microstructure. The casting process is fixed into a menu; production is initiated from the menu during casting, thus avoiding human input errors, improving quality stability, and ensuring traceability.

[0013] By controlling the refining process and casting process in a multi-stage linkage, the goal of reducing gas slag content, minimizing component segregation, and improving the uniformity of ingot structure can be achieved.

[0014] Step S5 involves controlling the temperature of the homogenizing furnace within the range of 450~460℃ and holding it at that temperature for 41 hours. The homogenizing furnace heats the ingot to a specific temperature and holds it there, allowing the unbalanced metastable structure from the casting process to gradually stabilize. Homogenization annealing eliminates intragranular segregation and promotes the dissolution and diffusion of soluble intermetallic compounds and strengthening phases. The entire homogenizing process is fully automated; the heating rate, holding temperature, and holding time require no manual intervention, and the temperature profile can be viewed at any time.

[0015] The heating temperature control range for step S7 preheating is 400~450℃, and the heating time is 4~8h; the hot rolling mill adopts asynchronous rolling process for 9 passes, and the thickness range of the rolled aviation aluminum alloy thick plate is 152~203mm, the initial rolling temperature is 400~450℃, and the final rolling temperature is 350℃. Before the hot rolling mill is rolled, the surface needs to be wiped with aviation kerosene. The main purposes are: (1) to remove surface oil or impurities. Aviation kerosene has good solubility and volatility, and can effectively remove grease, dust or other contaminants from the metal surface, providing a clean surface for subsequent rolling. (2) to prevent high-temperature oxidation of the ingot surface. During the preheating stage, the metal surface is easy to react with oxygen in the air to generate oxide scale. Aviation kerosene can form a thin oil film on the surface, which can isolate oxygen to a certain extent and slow down the oxidation process. (3) to improve lubrication conditions. In the early stage of hot rolling, aviation kerosene can be used as a temporary lubricant to reduce the friction between the roll and the metal billet, reduce the rolling force, and improve the surface quality.

[0016] Step S8 involves a two-stage solution treatment at temperatures of 465℃ + 475℃, with the first stage lasting 2.5~3 hours and the second stage lasting 2.5~3 hours. The quenching method is water quenching. After solution quenching, the plate needs to undergo a quenching uniformity test, which involves testing the conductivity of the entire solution-quenched plate. The test step size is every 500mm in the length direction and every 100mm in the width direction.

[0017] The purpose of solution treatment is primarily to fully dissolve solute atoms into the matrix, facilitating a highly supersaturated solid solution after quenching. Simultaneously, it controls the recrystallization structure, preventing coarse recrystallization and laying the foundation for aging-controlled alloy properties. The first stage of solution treatment (465℃) aims to dissolve the η phase into the matrix without causing the plate to burn. After sufficient η phase dissolution, the solution temperature is increased to 475℃ for the second stage. The purpose of the second stage is to fully dissolve the high-temperature S phase into the matrix. This two-stage solution treatment ensures that the plate does not burn while achieving a more complete and efficient dissolution of the strengthening phase.

[0018] The comparison of the microstructure of the plates in Example 2 below after single-stage and double-stage solution treatment shows that after single-stage solution treatment at 465℃, most of the T(AlZnMgCu) phase dissolved into the matrix, while a small amount of S(Al2MgCu) phase and Fe and Si-containing impurity phases remained in the matrix. However, after double-stage solution treatment, almost all of the T(AlZnMgCu) and S(Al2MgCu) phases dissolved into the matrix, leaving only insoluble Fe and Si-rich impurity phases in the microstructure.

[0019] The stretching amount in step S9 is 1.5%~2.5%. The purpose of stretching is to straighten the sheet material, eliminate residual stress, improve dimensional stability, improve flatness and surface quality, and enhance processing performance.

[0020] Step S10: The first-stage aging temperature is 121℃, and the first-stage aging time is 6 hours; the second-stage aging temperature is 163℃, and the second-stage aging time is 16~26 hours.

[0021] The purpose of aging is to achieve a good balance between the strength, toughness, and corrosion resistance of the sheet material to obtain optimal overall performance. The primary purpose of the first-stage aging is to act as a pre-nucleation agent, generating numerous GP zones in the matrix, providing a nucleation basis for the precipitation of strengthening phases during the second-stage aging. The first-stage aging time is set at 6 hours, while the second-stage aging time has the greatest impact on the sheet material's performance and is closely related to the sheet thickness.

[0022] After simulating the ultrasonic sound field using CIVA software in step S11, the final scanning process selected is as follows: ① A water-immersion phased array ultrasonic linear array probe with a frequency of 10MHz was used. ② Plot TCG gain compensation curves using a set of Φ1.2 mm flat-bottomed holes with a sound path of 3.2 mm to 146.1 mm manufactured according to ASTM E 127 standard; ③ Two virtual probes are used for parallel sequential excitation. The excitation mode of the virtual probes is selected to excite 14 crystals at a time, and the electronic scanning step is set to 3 crystals, so as to ensure that the -6dB effective sound beam coverage between the sequentially excited virtual probes reaches 100%; ④ Scanning speed 100mm / s; ⑤ The scanning mechanical step is 170mm.

[0023] Advantages of this invention: 1. This invention, by optimizing the composition of Zn, Mg, Cu, and Sc in the alloying elements, prepares three types of aerospace-grade aluminum alloy thick plates with excellent properties; these plates respectively possess high hardness values, low quenching sensitivity, and low stress corrosion sensitivity factor I. SSRT It has the advantages of low tensile strength and high elongation. The influence trends of Zn, Mg, Cu, and Sc composition on the microstructure of thick aerospace aluminum alloy plates were also revealed.

[0024] 2. The aerospace aluminum alloy thick plate prepared by this invention solves the problems of small size, mismatched comprehensive performance, uneven microstructure and properties, and failure to form large-scale production of domestic aerospace aluminum alloy plates, and meets the urgent needs of major national projects in aerospace and other fields for high-end aluminum alloy materials.

[0025] 3. The large-size, high-performance aluminum alloy thick plate successfully developed by this invention serves my country's major aviation strategic projects. The annual demand is considerable, and it has a very broad application prospect. The product has high added value and will generate huge economic and social benefits. Attached Figure Description

[0026] Figure 1 This is a flowchart of the aluminum alloy thick plate manufacturing process of the present invention; Figure 2 Cooling curves of alloy #1 at different positions away from the quenched end face; Figure 3 Quenching rate curves for plates with different alloy contents and different quenching end face distances are shown; among them, Figure 3 Figure (a) shows the quenching rate curves of plates with different quenching end face distances for alloys #1, #2, and #3; Figure 3 Figure (b) shows the quenching rate curves of plates with different quenching end face distances for alloys #1, #4, and #5; Figure 3 Figure (c) shows the quenching rate curves of plates with different quenching end face distances for alloys #1 and #6; Figure 4 The curves show the hardness variation of plates with different alloy contents and different quenching end face distances; among them, Figure 4 Figure (a) shows the hardness variation curves of plates with different quenching end face distances for alloys #1, #2, and #3; Figure 4Figure (b) shows the hardness variation curves of plates with different quenching end face distances for alloys #1, #4, and #5; Figure 4 Figure (c) shows the hardness variation curves of plates with different quenching end face distances for alloys #1 and #6. Figure 5 Hardness curves were retained for plates with different alloy contents and different quenching end face distances; among them, Figure 5 Figure (a) shows the hardness retention curves of plates with different quenching end face distances for alloys #1, #2, and #3; Figure 5 Figure (b) shows the hardness retention curves of plates with different quenching end face distances for alloys #1, #4, and #5; Figure 5 Figure (c) shows the hardness retention curves of plates with different quenching end face distances for alloys #1 and #6. Figure 6 OM photographs of alloy plate #1 at distances of 3mm and 120mm from the quenched end face; among them, Figure 6 Figure (a) is an OM photograph taken at a distance of 3 mm from the quenched end face; Figure 6 Figure (b) is an OM photograph taken at a distance of 120mm from the quenched end face; Figure 7 OM photographs of 6# alloy sheet at 3mm and 120mm; among them Figure 7 Figure (a) is an OM photograph taken at a distance of 3 mm from the quenched end face; Figure 7 Figure (b) is an OM photograph taken at a distance of 120mm from the quenched end face; Figure 8 SEM images of alloy plates #1, #2, and #3 taken at a distance of 3mm from the quenched end faces; among them, Figure 8 Figure (a) is a SEM image taken at a distance of 3 mm from the quenched end face of alloy plate #1. Figure 8 Figure (b) is a SEM image taken at a distance of 3 mm from the quenched end face of alloy plate #2; Figure 8 Figure (c) is a SEM image of the quenched end face of alloy plate #3, located 3 mm away. Figure 9 SEM images of the quenched end faces of alloy plates #4 and #5, taken at a distance of 3mm: Figure 9 Figure (a) is a SEM image taken at a distance of 3 mm from the quenched end face of alloy plate #4; Figure 9 Figure (b) is a SEM image taken at a distance of 3 mm from the quenched end face of alloy plate #5; Figure 10 SEM image of a quenched end face of No. 6 alloy plate at a distance of 3mm from the end face; Figure 11 High-magnification metallographic image of the quenched end face of No. 6 alloy plate at a distance of 120 mm from the end face; Figure 12SEM images of alloy plates #1, #2, and #3 at a distance of 120mm from the quenched end faces; among them, Figure 12 Figure (a) is a SEM image of the quenched end face of alloy plate #1 at a distance of 120mm; Figure 12 Figure (b) is a SEM image of the quenched end face of alloy plate #2 at a distance of 120mm; Figure 12 Figure (c) is a SEM image of the quenched end face of alloy plate #3 at a distance of 120mm; Figure 13 SEM images of the quenched end faces of alloy plates #4 and #5 at a distance of 120 mm; among them, Figure 13 Figure (a) is a SEM image of the quenched end face of alloy plate #4 at a distance of 120 mm; Figure 13 Figure (b) is a SEM image of the quenched end face of alloy plate #5 at a distance of 120 mm; Figure 14 SEM image of alloy #6 at 120mm; Figure 15 The SSRT curves of alloys 1-6# with different alloy contents under peak aging conditions in air and 3.5% NaCl solution are shown. Figure 16 Fracture morphology images of alloys #1 and #3 subjected to SSRT in air and 3.5% NaCl solution; among them, Figure 16 Figure (a) in the image is a photograph of the fracture morphology of alloy #1 after SSRT in air; Figure 16 Figure (b) is a photograph of the fracture morphology of alloy #3 after SSRT in air; Figure 16 Figure (c) in the middle and Figure 16 Figure (d) is a photograph of the fracture morphology of alloy #1 after SSRT in 3.5% NaCl solution; Figure 16 Figure (e) in the middle and Figure 16 Figure (f) in the figure is a photograph of the fracture morphology of alloy #3 after SSRT in 3.5% NaCl solution; Figure 17 Fracture morphology images of alloys #4 and #5 subjected to SSRT in air and 3.5% NaCl solution; among them, Figure 17 Figure (a) is a photograph of the fracture morphology of alloy #4 after SSRT in air; Figure 17 Figure (b) is a photograph of the fracture morphology of alloy #5 after SSRT in air; Figure 17 Figure (c) in the middle and Figure 17 Figure (d) in the image is a photograph of the fracture morphology of alloy #4 after SSRT in 3.5% NaCl solution; Figure 17 Figure (e) in the middle and Figure 17Figure (f) in the figure is a photograph of the fracture morphology of alloy #5 after SSRT in 3.5% NaCl solution; Figure 18 TEM images and EDS analysis diagrams of the grain boundaries of alloys #4 and #5 are shown; among them, Figure 18 Figure (a) shows the grain boundary TEM image and EDS analysis diagram of alloy #4; Figure 18 Figure (b) shows the grain boundary TEM image and EDS analysis diagram of alloy #5; Figure 19 The images show the fracture morphology of alloy #6 after SSRT in air and 3.5% NaCl solution; among them, Figure 19 Figure (a) in the image is a photograph of the fracture morphology of alloy #6 after SSRT in air; Figure 19 Figure (b) in the middle and Figure 19 Figure (c) is a photograph of the fracture morphology of alloy #6 after SSRT in 3.5% NaCl solution; Figure 20 Photos of OM alloys #1 and #6; among them, Figure 20 Figure (a) in the image is a photograph of alloy OM #1; Figure 20 Figure (b) is a photograph of alloy OM #6. Detailed Implementation

[0027] Example 1

[0028] The method for preparing a 150mm thick pre-stretched aluminum alloy plate includes the following steps: S1. Composition Design and Ingredients: The alloying elements by weight percentage are: 10.41~11.27% Zn, 1.73~1.77% Mg, 1.71~1.80% Cu, 0.13~0.14% Zr, 0.11% Fe, with the remainder being aluminum and unavoidable impurities; S2, Smelting: The aluminum ingots and intermediate alloys of S1 are put into a dry smelting furnace and completely melted and mixed evenly to obtain an aluminum alloy solution; S3, Degassing and Filtration: The aluminum alloy solution from S2 is transferred to a holding furnace for first-stage refining and degassing. During casting, it is further refined and degassed in the casting tank. After degassing, the hydrogen content is controlled within the range of ≤0.10ml / 100gAl. Finally, it is filtered through a ceramic filter screen. S4. Casting: The aluminum alloy solution after S3 treatment is cast through a short crystallizer, and the aluminum alloy flat ingot is finally obtained by controlling the cooling water temperature, water flow rate and casting temperature. S5. Homogenization heat treatment: The S4 aluminum alloy flat ingot is homogenized by heating and holding at a temperature of 450~460℃ in the homogenization furnace for 41 hours. S6. Machining: After cooling the S5 aluminum alloy flat ingot, cut off the head and tail and mill the surface to cut it into a casting; S7, Preheating, Rolling, Trimming: Before rolling, the S6 ingot is preheated. After preheating, it is rolled in several passes on a hot rolling mill to obtain a thick aluminum alloy plate. It is then lubricated with emulsion and trimmed after rolling. S8. Quenching: The S7 aluminum alloy thick plate is first subjected to a two-stage solution treatment, and then quenched. S9. Tensile testing and flaw detection: The S8 aluminum alloy thick plate is subjected to tensile testing and flaw detection. S10, Aging: Aging is performed on the S9 aluminum alloy thick plate; S11, Stress Assessment: Non-destructive testing is performed on the aluminum alloy thick plate after S10 aging; S12. After passing the stress test, saw the finished product, inspect it, package it, and ship it.

[0029] During the smelting process in step S2, the melt temperature is controlled within the range of 780~800℃; the furnace gas temperature is controlled within the range of 1100±50℃ during the heating stage and 900±50℃ during the holding stage; and the aluminum liquid temperature uniformity is ≤±3℃.

[0030] In step S3, the material temperature in the holding furnace is controlled within the range of 760~780℃, the furnace gas temperature is controlled within the range of 830±50℃, and the holding time is 1.5h. In the refining and degassing process in the flow channel, a mixed gas of argon and chlorine is used by rotary jetting to remove hydrogen and inclusions by allowing bubbles to float. The argon flow rate is controlled within the range of 1~2m³. 3 / h, the rotor speed control range is 500~600r / min, and the hydrogen content control range after online degassing during casting is ≤0.10ml / 100gAl.

[0031] Step S4: The casting crystallizer thickness is 120mm, the casting temperature control range is 740~760℃, the cooling tower water temperature control range is 10~40℃, the casting speed control range is 20~30mm / min, and the cooling water flow rate control range is 50~60m³ / min. 3 / h, water pressure control range is 0.08~0.15Mpa, and wire feeder speed control range is 30±10cm / min.

[0032] The heating temperature control range for the preheating in step S7 is 400~450℃, and the heating time is 4~8h. The hot rolling mill adopts an asynchronous rolling process to roll 9 passes. The thickness range of the rolled aerospace aluminum alloy plate is 152~203mm. The initial rolling temperature is 400~450℃, and the final rolling temperature is 350℃.

[0033] The temperature for the two-stage solution treatment in step S8 is 465℃ + 475℃, the first-stage solution treatment time is 2.5~3h, and the second-stage solution treatment time is 2.5~3h.

[0034] In step S10, the first-stage aging temperature is 121℃ and the first-stage aging time is 6 hours; the second-stage aging temperature is 163℃ and the second-stage aging time is 16~26 hours.

[0035] Example 2

[0036] The difference from Example 1 is that the alloying elements by weight percentage are: 6.02~6.55% Zn, 2.25% Mg, 2.20~2.35% Cu, 0.12% Zr, 0.10~0.11% Fe, with the remainder being aluminum and unavoidable impurities; Example 3

[0037] The difference from Example 1 is that the alloying elements by weight percentage are: 8.21% Zn, 1.70% Mg, 1.66% Cu, 0.16% Zr, 0.21% Sc, 0.12% Fe, with the remainder being aluminum and unavoidable impurities; Six aerospace aluminum alloy thick plate alloy compositions were designed. Alloy 1 is based on the 7085 alloy; Alloys 2 and 3 are high-zinc alloys obtained by increasing the Zn content on the basis of Alloy 1; Alloys 4 and 5 are low-copper and high-copper alloys obtained by adjusting the Zn, Mg, and Cu contents on the basis of 7050 alloy; Alloy 6 is a scandium-containing alloy obtained by adding Sc to Alloy 1.

[0038] Table 1. Main alloy composition data (wt%) for #1 to #6

[0039] Note: The remainder consists of aluminum ingots and unavoidable impurities.

[0040] The following are the data from the study on the quenching sensitivity and stress corrosion resistance of alloys 1-6: (1) Study on quenching sensitivity: Effect of Zn, Cu and Sc content on quenching sensitivity of 7xxx series aluminum alloys As attached Figure 2 As shown, during the end-quenching experiment, the alloy temperature drops rapidly above 150℃, and slowly between 150-50℃. The alloy temperature drops fastest at 3 mm from the quenching end face and slowest at 120 mm from the quenching end face (hereinafter, 3 mm from the quenching end face will be referred to as 3 mm, and 120 mm from the quenching end face will be referred to as 120 mm). The cooling curves of alloys 2-6# at different locations show a similar trend to alloy 1#.

[0041] From the appendix Figure 3It can be seen that: (1) The quenching rate of the alloy decreases with the increase of distance from the quenching end face. Within 45 mm from the quenching end face, the quenching rate of the alloy decreases rapidly, while when the distance is greater than 45 mm, the quenching rate of the alloy decreases slowly. (2) The quenching rate of the alloy decreases with the increase of Zn and Cu content. Alloy #3 has the highest Zn content, and Alloy #5 has the highest Cu content, and both have the lowest quenching rate at their respective positions. However, the effect of Cu on the quenching rate of the alloy is less than that of Zn. (3) Comparing the quenching rate curves of alloys with and without Sc, it can be seen that adding Sc will reduce the quenching rate of the alloy far from the quenching end.

[0042] From the appendix Figure 4 It can be seen that: (1) The hardness value of the alloy decreases with the increase of distance from the quenched end face. The hardness value of alloy #1 is the lowest at 3mm, which is 183HV; the hardness value of alloy #3 is the highest at 3mm, which is 191.5HV. The hardness values ​​of alloys #1 and #6 are the lowest at 120mm, which is 165HV; the hardness value of alloy #4 is the highest at 120mm, which is 173HV. (2) The hardness value of the alloy depends on the Zn content of the alloying element. Compared with alloy #1, the hardness values ​​of alloys #2 and #3 are higher than those of alloy #1 at the corresponding positions.

[0043] Referring to the definition of hardenability of steel, the distance corresponding to a 10% decrease in the alloy's hardness value relative to the quenched end after peak aging treatment is defined as the critical hardenability depth of the alloy. A larger hardenability depth indicates a lower quenching sensitivity of the alloy. The formula for defining Hardness Retention Values ​​(HRV) is as follows: HRV = HVi / HV3 × 100% Where: HV3 is the hardness value at a distance of 3 mm from the quenched end face; HVi is the hardness value at a distance of i mm from the quenched end face (i=3, 10, 20...120).

[0044] From the appendix Figure 5 It can be seen that the hardened layer depths of alloys 1#, 2# and 3# are approximately 120mm, 110mm and 100mm respectively; the hardened layer depth of alloy 4# is much greater than 120mm; and the hardened layer depths of alloys 5# and 6# are approximately 60mm. (1) The hardened layer depth of the alloy decreases with the increase of Zn content, indicating that increasing Zn content will increase the quenching sensitivity of the alloy. (2) The hardened layer depth of the alloy decreases with the increase of Cu content, indicating that increasing Cu content will increase the quenching sensitivity of the alloy, and the effect of alloying element Cu on the quenching sensitivity of the alloy is greater than that of alloying element Zn. (3) Adding 0.21wt% Sc will increase the quenching sensitivity of the alloy.

[0045] From the appendix Figure 6It can be seen that the grain size and morphology of alloy #1 at 3mm and 120mm are similar, both being coarse recrystallized grains with an average grain size of approximately 200μm. The metallographic structures of alloys #2 and #3 at 3mm and 120mm exhibit similar characteristics.

[0046] From the appendix Figure 7 It can be seen that the grain size and morphology of alloy #6 are quite different from those of alloy #1. The grains of alloy #6 are slender grains along the rolling direction. The grain size and morphology at 3mm and 120mm are similar, with an average width and length of approximately 30μm and 220μm, respectively.

[0047] From the appendix Figure 8 It can be seen that alloy #1 contains irregular, coarse secondary phases. EDS analysis of the secondary phase indicated by the black arrow in the figure shows that this phase is rich in Cu and Fe elements, and is an Al7Cu2Fe phase. Furthermore, two secondary phases with different contrasts were observed. The brighter contrasting secondary phase is located in the center of the darker contrasting secondary phase. EDS analysis revealed that the darker contrasting phase is an Al3Fe phase containing 4 at% Cu, while the brighter contrasting phase is an Al7Cu2Fe phase. Figure 8 (a) indicates that the Al7Cu2Fe phase is formed after the Al3(Fe,Cu) phase, evolving from the Al3(Fe,Cu) phase during high-temperature heat treatment. The alloy contains approximately 0.11 wt% Fe. Fe atoms have very low solubility in the aluminum matrix, making the Fe-containing phase a poorly soluble phase in aluminum alloys. The second phase at 3 mm in alloys #2 and #3 is also the Al7Cu2Fe phase. The size, morphology, and density of the second phase are similar to those in alloy #1, with a size of approximately 5-20 μm. Figure 8 (b) and Figure 8 (c)).

[0048] From the appendix Figure 9 It can be seen that adjusting the Cu content has little effect on the grain size and morphology at the quenched end and away from the quenched end of the alloy. The second phase at 3 mm in both alloys #4 and #5 is the Al7Cu2Fe phase. The size and morphology of the second phase are similar to those of alloy #1. The density of the second phase in alloy #5 is greater than that in alloy #4, indicating that increasing the Cu content promotes the formation of coarse Al7Cu2Fe phase.

[0049] From the appendix Figure 10 It can be seen that the 6# alloy with added Sc not only has an irregularly shaped Al7Cu2Fe phase at 3mm, but also a rhomboid second phase, which, according to EDS analysis, is a nascent Al3(Sc,Zr) particle.

[0050] From the appendix Figure 11It can be seen that the rhombic particles are primary Al3(Sc,Zr). There are a large number of subgrain boundaries inside the grains of this sample, which indicates that the alloying element Sc can effectively inhibit the recrystallization of the alloy.

[0051] From the appendix Figure 12 It can be seen that, in addition to the Al7Cu2Fe phase, there is a second phase with brighter contrast and a chain-like distribution at 120 mm in alloy #1. EDS analysis of the second phase indicated by the black arrow in the figure shows that this phase contains Zn, Mg, and Cu elements, and is a T(AlZnMgCu) phase. Figure 12 (a)). The second phase at 120 mm in both alloys #2 and #3 is Al7Cu2Fe and T phase, with the atomic ratio of the T phase close to 1:1:1:1. The size and morphology of the second phase are similar to those in alloy #1, with a size of approximately 5-20 μm. Compared to the density of the second phase at 3 mm, the density of the Al7Cu2Fe phase at 120 mm is similar, while the density of the T phase is greater than that of the Al7Cu2Fe phase. The density of the second phase at 120 mm in alloy #3 is greater than that in alloy #2. Figure 12 (b) and Figure 12 (c) indicates that in the low quenching rate region, increasing the Zn content will promote the formation of the T phase.

[0052] From the appendix Figure 13 It can be seen that the second phase at 120mm in alloys #4 and #5 are both Al7Cu2Fe and T phase. The size and morphology of the second phase are similar to those of alloy #1. The density of the T phase in alloy #5 is greater than that in alloy #4, indicating that in the low quenching rate region, increasing the Zn and Cu content will promote the formation of the T phase.

[0053] From the appendix Figure 14 It can be seen that: at 120mm, alloy #6 only has Al7Cu2Fe phase and primary Al3(Sc,Zr) particles, and no T phase was observed.

[0054] (2) Study on stress corrosion performance: Effect of Zn, Cu and Sc content on stress corrosion performance of 7xxx series aluminum alloys From the appendix Figure 15(a) It can be seen that in air, with the increase of Zn content, the strength of the alloy increases and the elongation decreases; the maximum tensile strength of alloy #1 is 520 MPa, and the elongation is 19.8%; the maximum tensile strengths of alloys #2 and #3 are 582 MPa and 589 MPa, respectively, which are 11.92% and 13.27% higher than alloy #1; the elongation of alloys #2 and #3 is 16.7% and 11.7%, respectively, which are 15.65% and 40.91% lower than alloy #1. In 3.5% NaCl solution, with the increase of Zn content, the strength of the alloy increases and the elongation decreases; the maximum tensile strength of alloy #1 is 505 MPa, and the elongation is 17.5%. The maximum tensile strengths of alloys #2 and #3 are 550 MPa and 552 MPa, respectively, representing increases of 8.91% and 9.31% compared to alloy #1. The elongations of alloys #2 and #3 are 15% and 9%, respectively, representing decreases of 14.29% and 48.57% compared to alloy #1. In a 3.5% NaCl solution, both the strength and elongation of the alloys are lower than in air. The maximum tensile strengths of alloys #1, #2, and #3 decrease by 2.88%, 5.5%, and 6.28%, respectively. The elongations of alloys #1, #2, and #3 decrease by 11.62%, 10.18%, and 23.08%, respectively.

[0055] From the appendix Figure 15 (b) It can be seen that in air, the strength of both high-copper and low-copper alloys increases, while the elongation decreases. The maximum tensile strengths of alloys #4 and #5 are 554 MPa and 579 MPa, respectively, which are 6.54% and 11.35% higher than that of alloy #1. The elongation of alloys #4 and #5 is 12% and 17.7%, respectively, which are 39.39% and 10.61% lower than that of alloy #1. In 3.5% NaCl solution, the strength of both high-copper and low-copper alloys increases, while the elongation decreases. The maximum tensile strengths of alloys #4 and #5 are 525 MPa and 574 MPa, respectively, which are 3.96% and 13.66% higher than that of alloy #1. The elongation of alloys #4 and #5 is 11.3% and 16.3%, respectively, which are 35.43% and 6.86% lower than that of alloy #1. In a 3.5% NaCl solution, the strength and elongation of the alloys were lower than those in air. The maximum tensile strength of alloys #4 and #5 decreased by 5.23% and 0.86%, respectively. The elongation of alloys #4 and #5 decreased by 5.83% and 7.91%, respectively.

[0056] From the appendix Figure 15(c) It can be seen that: In air, the addition of Sc increases the strength and decreases the elongation of the alloy; the maximum tensile strength of alloy #6 is 580 MPa, an increase of 11.54% compared to alloy #1; the elongation of this alloy is 19.7%, a decrease of 0.51% compared to alloy #1. In 3.5% NaCl solution, the addition of Sc increases the strength and decreases the elongation of the alloy; the maximum tensile strength of alloy #6 is 560 MPa, an increase of 10.89% compared to alloy #1; the elongation of this alloy is 19.2%, a decrease of 9.71% compared to alloy #1. In 3.5% NaCl solution, both the strength and elongation of the alloy are lower than in air; the maximum tensile strength of alloy #6 decreases by 3.45%, and the elongation decreases by 2.54%.

[0057] From the appendix Figure 16 It can be seen that the fracture morphology of alloy #1 is characterized by numerous equiaxed dimples, belonging to the dimple-type transgranular fracture mode, thus alloy #1 has a higher elongation. The fracture morphology of alloy #3 is mainly characterized by numerous dimples, with the intergranular fracture resembling rock candy within the red box, belonging to a mixed fracture mode of dimple-type transgranular fracture and intergranular fracture, thus alloy #3 has a lower elongation than alloy #1. Figure 16 (a) and Figure 16 (b)).

[0058] The alloy exhibits typical stress corrosion cracking after SSRT in a 3.5% NaCl solution. Figure 16 (c)- Figure 16 (f)). The red arrow points to a typical localized intergranular crack generated under stress corrosion conditions, with a length of approximately 500 μm. Figure 16 (c)). The red arrow points to a slender intergranular crack. Figure 16 (d) The fracture morphology of alloy #1 consists of numerous dimples and some intergranular cracks. Therefore, the tensile strength and elongation of alloy #1 in 3.5% NaCl solution are lower than those in air, exhibiting stress corrosion cracking. Compared to alloy #1, the fracture cracks of alloy #3 are wider and deeper, almost penetrating the entire fracture surface. Figure 16 (e)). The red arrow points to the corrosion products accumulated on the alloy fracture surface, exhibiting obvious stress corrosion characteristics. Figure 16 (f) Therefore, the stress corrosion susceptibility of alloy #3 is higher than that of alloy #1, and the I of alloy #3 is higher. SSRT Greater than 1# alloy.

[0059] The effect of the width of the non-precipitated zone on stress corrosion susceptibility remains uncertain. Some studies suggest that the non-precipitated zone increases the stress corrosion susceptibility of the alloy, while others suggest that the width of the non-precipitated zone has no significant impact on stress corrosion susceptibility. However, comprehensive performance analysis suggests that a narrower non-precipitated zone is better. Anodic dissolution theory and hydrogen embrittlement theory are commonly used theories to explain the stress corrosion cracking mechanism of Al-Zn-Mg-Cu alloys. Grain boundary precipitates with higher Zn and Mg content are more susceptible to corrosion. The electrode potentials of the matrix, MgZn2, and non-precipitated zone in aluminum alloys are -0.68 V, -0.86 V, and -0.57 V, respectively. The MgZn2 phase acts as the anode in the corrosion microcell. Under tensile stress, the grain boundary precipitates tend to form anodic corrosion channels along the grain boundaries and preferentially dissolve.

[0060] Related studies have shown that under constant stress, there is a certain negative linear relationship between the concentration of Zn in the solid solution and the logarithm of the failure time. When hydrogen generated in the corrosive environment accumulates to a certain concentration, it diffuses and accumulates at the Mg segregation grain boundaries, causing stress concentration, leading to intergranular cracking and increasing the anodic dissolution rate. The electronegativity difference between Mg atoms and H atoms at the grain boundaries is greater than that between Al atoms and H atoms. Mg in the grain boundaries increases the amount of hydrogen absorbed, thereby accelerating its diffusion and increasing the solubility of hydrogen in the grain boundaries, leading to grain boundary embrittlement and accelerating the propagation of stress corrosion cracks. Therefore, the stress corrosion susceptibility of alloy #3 is higher than that of alloy #1, and the ISSRT of alloy #3 is greater than that of alloy #1.

[0061] From the appendix Figure 17 It can be seen that the fracture surface of alloy #4 includes shallow dimples and quasi-cleavage planes, belonging to a mixed fracture mode of dimple-type transgranular fracture and intergranular fracture. Therefore, alloy #4 has a lower elongation. The fracture surface morphology of alloy #5 has a large number of dimples, belonging to the dimple-type transgranular fracture mode. Therefore, the elongation of alloy #5 is significantly higher than that of alloy #4. Figure 17 (a) and Figure 17 (b)).

[0062] The alloy exhibits typical stress corrosion cracking after SSRT in a 3.5% NaCl solution. Figure 17 (c)- Figure 17 (f)). The red arrow points to a typical wide and deep crack generated by intergranular fracture under stress corrosion conditions, with the crack almost penetrating the entire fracture surface. Figure 17 (c)). In the high-magnification photograph, the red arrow points to stress corrosion products, which exhibit obvious stress corrosion characteristics. Figure 17 (d) The fracture morphology of alloy #4 is a flat quasi-cleavage plane, large cracks and a small number of dimples. Therefore, in 3.5% NaCl solution, the tensile strength and elongation of alloy #4 are lower than those in air, and it exhibits stress corrosion cracking.

[0063] The fracture cracks of alloy #5 are numerous and short. Figure 17 (e) This is because increasing the Cu content leads to the formation of more coarse Al7Cu2Fe phases. Related studies have shown that under stress corrosion conditions, the electrode potential of the Al7Cu2Fe phase differs from that of the matrix, promoting the initiation of stress corrosion cracks. In the high-magnification photograph, the red arrow points to intergranular fracture. The fracture surface of alloy #5 includes dimples and quasi-cleavage planes. Figure 17 (f) Therefore, in a 3.5% NaCl solution, the tensile strength and elongation of alloy #5 are lower than those in air, exhibiting stress corrosion cracking.

[0064] From the appendix Figure 18 It is known that the precipitates on the grain boundaries of the alloy are continuously distributed. With the increase of Zn and Cu content, the size of the grain boundary precipitates and the width of the non-precipitated zone increase, and the Cu content of the grain boundary precipitates increases. Related studies show that the Cu content in the grain boundary precipitates depends on the Cu content in the alloy. High Cu content in the grain boundary precipitates can effectively reduce the potential difference with the matrix and reduce the anodic and cathodic reaction rates at the crack tip. Therefore, a higher Cu content is beneficial to improving the stress corrosion resistance of the alloy. When the Cu content in 7xxx series aluminum alloys is increased from 0 to 2.1 wt%, the crack propagation rate gradually decreases. This is because increasing the Cu content can change the electrochemical activity of the grain boundary precipitates, reducing the crack propagation rate by two orders of magnitude. When the grain boundary precipitates are larger than the critical size (20 nm) for hydrogen formation, the large-sized grain boundary precipitates have a "hydrogen capture" effect, reducing the lattice hydrogen concentration, delaying crack initiation, and reducing the stress corrosion susceptibility of the alloy. The average size of the grain boundary precipitates in alloy #4 is approximately 10 nm, while that in alloy #5 is approximately 40 nm. Therefore, alloy #5 exhibits greater resistance to stress corrosion than alloy #4. The Ig of alloy #5 is... SSRT Less than 1# alloy.

[0065] From the appendix Figure 19 It can be seen that the fracture morphology of alloy #6 is characterized by numerous equiaxed dimples, which are large and deep. Figure 19 (a) belongs to the dimple-type transgranular fracture mode, so alloy #6 has a high elongation. Figure 19 (b) shows the fracture morphology of the alloy after SSRT in 3.5% NaCl solution. The red arrows indicate fine intergranular cracks, approximately 200 μm in length. The fracture morphology shows numerous equiaxed dimples and a very small amount of corrosion products. Figure 19 (c) Therefore, alloy #6 still maintains a high elongation in 3.5% NaCl solution. Compared to alloy #1, alloy #6 has lower stress corrosion susceptibility. The I of alloy #6 SSRT Less than 1# alloy.

[0066] From the appendix Figure 20 It is evident that alloy #1 underwent significant recrystallization, retaining a very small amount of fibrous structure parallel to the rolling direction in the matrix, while alloy #6 is mainly composed of slender fibrous structures. Related research indicates that adding Sc to aluminum alloys significantly increases the recrystallization temperature. Coherent nano-Al3Sc particles strongly pin grain boundary movement, inhibiting recrystallization. The Al3(Sc,Zr) particles formed by the combined addition of Sc and Zr significantly improve the recrystallization resistance and strength of 7xxx series aluminum alloys. Therefore, the tensile strength of alloy #6 is significantly higher than that of alloy #1. Furthermore, the trace element Sc has a significant grain-refining effect. Grain refinement reduces planar slip and forms a more uniform slip mode. A uniform slip mode effectively reduces dislocation movement and further reduces hydrogen transport to grain boundaries, reducing intergranular fracture and lowering stress corrosion sensitivity. Therefore, alloy #6 has lower stress corrosion sensitivity than alloy #1.

[0067] According to HB 7235-95, the stress corrosion susceptibility factor (I) is calculated. SSRT The stress corrosion resistance of an alloy is measured by the following formula: In the formula, and The tensile strength and elongation of the alloy sample in 3.5% NaCl solution are respectively. and Table 1 shows the tensile strength and elongation of the alloy samples in air. Table 2 shows the SSRT results of the six alloys at peak aging state in air and 3.5% NaCl solution. SSRT The smaller the value, the better the alloy's resistance to stress corrosion.

[0068] Table 2. SSRT results of six alloys at peak aging state in air and 3.5% NaCl solution.

[0069] Table 2 shows that the I of alloys #1, #2, and #3... SSRT The concentrations were 4.75%, 6.87%, and 8.55% respectively, indicating that increasing the Zn content reduces the stress corrosion resistance of the Al-Zn-Mg-Cu alloy. The I content of alloys #4 and #5... SSRT The values ​​were 5.83% and 2.04% respectively, indicating that increasing the Cu content improves the stress corrosion resistance of the Al-Zn-Mg-Cu alloy. The I content of alloy #6... SSRT The value was 3.85%, indicating that adding Sc element improves the stress corrosion resistance of Al-Zn-Mg-Cu alloy.

[0070] summary: Based on 7085 and 7050, three novel high-hardness, low-quench-sensitivity 7xxx series aluminum alloys were developed by adjusting the Zn, Cu, and Sc compositions. The influence of alloy composition on the grain size and microstructure (composition, distribution, size, and morphology of the second phase) of thick 7xxx series aluminum alloy plates was elucidated. The strengthening mechanism, quench-sensitivity, and stress corrosion mechanism of the novel 7xxx series aluminum alloys were clarified. Specific conclusions are as follows: (1) Increasing the Zn content and the Zn / Mg ratio can improve the overall hardness of 7xxx series aluminum alloy thick plates. However, increasing the Zn content reduces the cooling rate of the core of the thick plate during end quenching and leads to the precipitation of high-density coarse η phase, which in turn consumes too many Mg solute atoms and inhibits the formation of nano phases during aging. Therefore, increasing the Zn content reduces the hardened layer depth of 7xxx series aluminum alloy thick plates. Increasing the Zn content to 11% based on 7085 reduces the hardened layer depth of the alloy from 120 mm to 100 mm.

[0071] (2) Reducing the Cu content can improve the overall hardness of 7xxx series aluminum alloy thick plates. The low Cu content reduces the density of coarse T phase in the core region of 7xxx series aluminum alloy thick plates, thereby retaining a large number of Zn and Mg solute atoms and promoting the precipitation of nano phases, ultimately increasing the hardenability depth of the alloy. Based on the 7050 alloy, reducing the Cu content to 1.2% can increase the hardenability depth to over 120 mm.

[0072] (3) The addition of microalloying element Sc can refine the alloy grains and improve its fine grain strengthening effect. However, high-density grain boundaries promote the precipitation of coarse η phase under low cooling rate conditions, thereby reducing the hardenability depth of the alloy. Adding 0.21% Sc by mass to 7085 can reduce its hardenability depth to 60 mm.

[0073] (4) Increasing the Zn content and decreasing the Cu content while keeping the Mg content constant helps to obtain 7xxx series aluminum alloy thick plates with both high hardness and low quenching sensitivity.

[0074] (5) Increasing the Cu content and adding Sc can improve the stress corrosion resistance of 7xxx series aluminum alloys. However, increasing the Zn content will weaken the stress corrosion resistance of 7xxx series aluminum alloys. Grain size, grain boundary precipitate size / composition / distribution, and width of the non-precipitate zone can all affect the corrosion path of the alloy, and thus affect its stress corrosion resistance.

Claims

1. A method for preparing large-size, high-performance aerospace aluminum alloy thick plates, with a plate thickness of 150~220mm, characterized in that, Includes the following steps: S1. Composition design and ingredient formulation: The alloy composition is formulated by weight percentage, including the following alloying elements: 6.02~11.27% Zn, 1.69~2.25% Mg, 1.66~2.35% Cu, 0.11~0.16% Zr, 0.10~0.12% Fe, unavoidable impurities and aluminum; S2, Smelting: The aluminum ingots and intermediate alloys of S1 are put into a dry smelting furnace and completely melted and mixed evenly to obtain an aluminum alloy melt. The melt temperature is controlled within the range of 780~800℃. S3, Degassing and Filtration: The aluminum alloy melt from S2 is first refined and degassed in a holding furnace, and then refined and degassed again in the casting trough. After degassing, the hydrogen content is controlled within the range of ≤0.10ml / 100gAl. Finally, it is filtered through a ceramic filter screen. S4. Casting: The aluminum alloy melt after S3 treatment is cast through a short crystallizer, and the aluminum alloy flat ingot is finally obtained by controlling the cooling water temperature, water flow rate and casting temperature. S5. Homogenization heat treatment: The S4 aluminum alloy flat ingot is homogenized and heated and held at the same temperature. The temperature of the homogenization furnace is controlled within the range of 450~460℃ and held for 41 hours. S6. Machining: After cooling the S5 aluminum alloy flat ingot, cut off the head and tail and mill the surface to cut it into a casting; S7, Preheating, Rolling, Trimming: Before rolling, the S6 ingot is preheated. After preheating, it is rolled in several passes on a hot rolling mill to obtain a thick aluminum alloy plate. It is then lubricated with emulsion and trimmed after rolling. S8. Quenching: The S7 aluminum alloy thick plate is first subjected to a two-stage solution treatment. The first stage solution temperature is 465℃, the second stage solution temperature is 475℃, the first stage solution time is 2.5~3h, and the second stage solution time is 2.5~3h. Then, it is water-cooled spray quenching. S9. Tensile testing and flaw detection: The S8 aluminum alloy thick plate is subjected to tensile testing and flaw detection. S10, Aging: Aging is performed on the S9 aluminum alloy thick plate; S11, stress testing, sawing of finished products.

2. The method for preparing large-size, high-performance aerospace aluminum alloy thick plates according to claim 1, characterized in that, The alloying elements, by weight percentage, are: 10.41~11.27% Zn, 1.73~1.77% Mg, 1.71~1.80% Cu, 0.13~0.14% Zr, 0.11% Fe, with the remainder being aluminum and unavoidable impurities; the resulting thick plate has the following properties: a hardness value of 187~191.5 HV at a distance of 3 mm from the quenched end face, and a hardness value of 166.5~168 HV at a distance of 120 mm.

3. The method for preparing large-size, high-performance aerospace aluminum alloy thick plates according to claim 1, characterized in that, The alloying elements, by weight percentage, are: 6.02~6.55% Zn, 2.25% Mg, 2.20~2.35% Cu, 0.12% Zr, 0.10~0.11% Fe, with the remainder being aluminum and unavoidable impurities. The resulting thick plate exhibits the following properties: a hardness retention of 89~93% at 120 mm from the quenched end face; and a stress corrosion sensitivity factor. I SSRT The range is 2.04% to 5.83%.

4. The method for preparing large-size, high-performance aerospace aluminum alloy thick plates according to claim 1, characterized in that, The alloying elements, by weight percentage, are: 8.21% Zn, 1.70% Mg, 1.66% Cu, 0.16% Zr, 0.21% Sc, 0.12% Fe, with the remainder being aluminum and unavoidable impurities. The resulting thick plate has the following properties: tensile strength in air of 580 MPa and elongation of 19.7%; tensile strength in a 3.5% NaCl solution of 560 MPa and elongation of 19.2%.

5. The method for preparing large-size, high-performance aerospace aluminum alloy thick plates according to claim 1, characterized in that, The melt temperature control range of the holding furnace in step S3 is 760~780℃, and the holding time is 1.5h.

6. The method for preparing large-size, high-performance aerospace aluminum alloy thick plates according to claim 1, characterized in that, In step S4, the casting temperature is controlled within the range of 740~760℃, the casting speed is controlled within the range of 20~30mm / min, and the cooling water flow rate is controlled within the range of 50~60m³. 3 / h.

7. The method for preparing large-size, high-performance aerospace aluminum alloy thick plates according to claim 1, characterized in that, The heating temperature control range for the preheating in step S7 is 400~450℃, and the heating time is 4~8h. The hot rolling mill adopts an asynchronous rolling process to roll 9 passes. The thickness range of the rolled aerospace aluminum alloy plate is 152~203mm. The initial rolling temperature is 400~450℃, and the final rolling temperature is 350℃.

8. The method for preparing large-size, high-performance aerospace aluminum alloy thick plates according to claim 1, characterized in that, The aging process in step S10 is a two-stage aging process. The first-stage aging temperature is 121℃ and the first-stage aging time is 6 hours. The second-stage aging temperature is 163℃ and the second-stage aging time is 16~26 hours.

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