A method for producing a low residual stress aluminum alloy forging

Abstract

The application belongs to the technical field of aluminum alloy material preparation, and particularly relates to a preparation method of low-residual-stress aluminum alloy forgings, which comprises the following steps: sequentially performing homogenization heat treatment, multi-directional free forging, graded solid solution, composite stress relief treatment and aging treatment on aluminum alloy ingots to obtain low-residual-stress aluminum alloy forgings; the homogenization heat treatment is at least two gradient homogenization heat treatments; the graded solid solution is at least two grades of solid solution; the composite stress relief treatment comprises sequentially performing deep cooling treatment and cold-heat cycle treatment on the aluminum alloy ingots after the graded solid solution, the temperature of the deep cooling treatment is-190 to-170 DEG C, and the single cycle of the cold-heat cycle treatment is 110 to 120 DEG C heat preservation followed by heat preservation at-80 to-70 DEG C; the application effectively reduces residual stress while maintaining the mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy material preparation technology, specifically relating to a method for preparing low residual stress aluminum alloy forgings. Background Technology

[0002] 7-series aluminum alloys possess high strength, high toughness, and excellent corrosion resistance, making them indispensable key structural materials in aerospace, shipbuilding, and weaponry. Aluminum alloy forgings are widely used in modern high-end weaponry, and the demand for high-performance aluminum alloy forgings in the weapons industry and aerospace sector is increasingly urgent. Typical applications include tank armor plates, missile structural components, and load-bearing structural components such as aircraft upper and lower wing panels, stringers, bulkheads, wing spars, and fuselage frames. The level of manufacturing capabilities for high-performance aluminum alloy forgings is of great significance to national economic development and the upgrading of military weaponry.

[0003] In traditional manufacturing processes, 7-series aluminum alloy forgings require solution hardening to achieve the desired mechanical properties. However, due to the high degree of alloying in this series, rapid quenching is necessary to ensure sufficient dissolution of the alloying elements, resulting in significant residual stress within the forgings. The presence of residual stress reduces the material's fatigue performance and resistance to stress corrosion, thereby affecting the service safety and lifespan of the components.

[0004] Existing 7075 free forging processes generally employ conventional unidirectional drawing, single-stage homogenization, rapid water quenching, and conventional T6 aging processes, which mainly have the following technical defects: 1) Conventional ingots have a single homogenization temperature, resulting in severe dendrite segregation and difficulty in fully dissolving the coarse second phase into the matrix, which easily leads to local stress concentration during forging. 2) Traditional free forging often adopts unidirectional large deformation forging, resulting in uneven metal flow, large internal stress gradient of forging, and high difference between core tensile stress and surface compressive stress. 3) The cooling rate of ordinary water quenching is too fast, the temperature difference between the inside and outside of the forging is large, and the residual stress of quenching generally reaches 200-320MPa, resulting in serious deformation and warping during subsequent machining. 4) Conventional single-stage aging easily leads to stress recovery, obvious microstructure and texture, large anisotropy of forgings, and poor dimensional stability.

[0005] In summary, the existing 7075 free forging process generally suffers from problems such as high residual stress, uneven stress distribution, large processing deformation, and poor batch stability, making it difficult to meet the requirements of high-end equipment for low stress, high dimensional accuracy, and long service life of large-section free forgings. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing aluminum alloy forgings with low residual stress, which effectively reduces residual stress while maintaining their mechanical properties.

[0007] This invention provides a method for preparing low residual stress aluminum alloy forgings, which involves sequentially subjecting aluminum alloy ingots to homogenization heat treatment, multi-directional free forging, graded solution treatment, composite stress relief treatment, and aging treatment to obtain low residual stress aluminum alloy forgings. The homogenization heat treatment is at least a two-gradient homogenization heat treatment, and the graded solution treatment is at least a two-stage solution treatment; The composite stress relief treatment involves sequentially subjecting the graded solution-treated aluminum alloy ingot to cryogenic treatment and thermal cycling treatment. The cryogenic treatment temperature is -190 to -170°C, and each cycle of the thermal cycling treatment consists of holding at 110 to 120°C followed by holding at -80 to -70°C.

[0008] Preferably, the number of cold and hot cycle treatments is 1 to 2.

[0009] Preferably, the cryogenic treatment time is 1 to 2 hours, and in a single cycle of the thermal cycling treatment, the holding time at 110 to 120°C is 1 to 2 hours, and the holding time at -80 to -70°C is 1 to 2 hours.

[0010] Preferably, the homogenization heat treatment is a two-gradient homogenization heat treatment, specifically: after the aluminum alloy ingot is held at 280-320℃, it is heated to 450-465℃ and held.

[0011] Preferably, the aluminum alloy ingot is held at 280–320℃ for 4–8 hours and at 450–465℃ for 18–24 hours, with a heating rate of 3–5℃ / min.

[0012] Preferably, the multi-directional free forging is a three-directional alternating upsetting-drawing multi-directional free forging, with an initial forging temperature of 450-470℃ and a final forging temperature of not less than 380℃; during the forging process, the single-pass reduction rate is controlled at 15-22%, and the deformation rate is 5-8mm / s; when the billet temperature drops to the final forging temperature, it is reheated in the furnace, and between each forging pass, the billet is kept warm in a furnace at 350-380℃ before continuing the next forging pass.

[0013] Preferably, the graded solution solution is a two-stage solution solution, with the temperature of the first-stage solution solution being 410–420°C and the temperature of the second-stage solution solution solution being 470–485°C.

[0014] Preferably, the aging treatment is a two-stage aging treatment, with the temperature of the first stage aging treatment being 70-90℃ and the temperature of the second stage aging treatment being 120-140℃.

[0015] Preferably, after aging treatment, the process also includes room temperature cold pressing shaping, with a total deformation under pressure of 2-3% and a single pressure holding time of 30-60 seconds.

[0016] Preferably, the aluminum alloy is a 7-series aluminum alloy, more preferably a 7075 aluminum alloy or a 7050 aluminum alloy.

[0017] The beneficial effects of this invention are that, through the coordinated control of the entire process of gradient homogenization, multi-directional free forging, graded solution treatment, composite stress relief treatment and aging treatment, the residual stress of forgings is reduced to 10.3-11.7 MPa, which significantly reduces residual stress compared with existing conventional processes.

[0018] The present invention exhibits low residual stress during quenching without loss of mechanical properties. The stepped heating and graded solution treatment reduces the internal and external temperature difference during quenching of the forging, thereby lowering instantaneous thermal and structural stresses. Within 2 hours after quenching, utilizing the high plasticity window of the supersaturated solid solution, ultra-low temperature cryogenic treatment is performed before the precipitated phase pins dislocations, followed by high-low temperature thermal cycling. This thoroughly releases the root stress through lattice microplastic slip. The high-temperature range of 110–120°C balances stress release without coarsening the precipitated phase or losing strength, while the low-temperature range of -70–-80°C effectively shrinks and relaxes lattice distortion, avoids introducing additional cold stress, and maintains controllable costs.

[0019] This invention exhibits excellent overall performance and good batch stability. The 7075 forgings prepared by this invention have a hardness of 168-170 HV, a tensile strength of over 490 MPa, a yield strength of over 402 MPa, and an elongation of over 12.5%. While significantly reducing residual stress, it maintains a good balance between high strength and high plasticity. Furthermore, the performance of each embodiment shows small fluctuations and good batch stability, which can meet the requirements of high-end equipment for low stress, high dimensional accuracy, and long service life of large-section free forgings. Attached Figure Description

[0020] Figure 1 This is a microstructure diagram of the product from Example 1. Detailed Implementation

[0021] Example 1 A method for preparing a 7075 forging with low residual stress includes the following steps: (1) Ingot pretreatment 7075 aluminum alloy ingots were selected as raw materials, and the ingots underwent a two-stage gradient homogenization heat treatment: first, the ingots were heated to 300℃ at a heating rate of 3℃ / min and held for 6 hours; then, they were heated to 460℃ at a heating rate of 3℃ / min and held for 22 hours. After the holding period, the ingots were removed from the furnace and cooled to obtain the pretreated ingots.

[0022] (2) Multidirectional free forging The pretreated ingot was subjected to three-dimensional alternating upsetting-drawing multi-directional free forging. Specific process parameters were: initial forging temperature 450℃, final forging temperature not lower than 380℃; single-pass reduction rate controlled at 15% and deformation rate at 5mm / s during forging; when the billet temperature dropped to the final forging temperature, it was reheated in the furnace, and the billet was held at 350℃ for 1 hour between forging passes before continuing with the next forging pass. After forging, it was air-cooled to obtain the forged blank.

[0023] (3) Graded solid solution The forging blanks are subjected to step-by-step solution treatment: first, the forgings are heated to 420℃ and held for 3 hours; then the temperature is increased to 470℃ and held for 4 hours; after the holding is completed, the forgings are quickly transferred into a water tank for water quenching.

[0024] (4) Composite stress relief treatment Within 2 hours after quenching, the forging is subjected to a combined stress relief treatment of ultra-low temperature cryogenic treatment and high-low temperature thermal cycling: first, the forging is placed in a -180℃ environment and kept at that temperature for 1 hour for ultra-low temperature cryogenic treatment; after cryogenic treatment, high-low temperature thermal cycling is performed. Each cycle is as follows: the forging is moved into a 120℃ furnace and kept at that temperature for 2 hours, and then moved into a -80℃ environment and kept at that temperature for 1 hour; the above thermal cycling is performed twice.

[0025] (5) Low stress aging Forgings that have undergone composite stress relief treatment are subjected to a two-stage heating and aging process: first, they are heated to 80℃ and held for 8 hours for primary aging; then, they are heated to 130℃ and held for 12 hours for secondary aging; after the holding period, the forgings are cooled to room temperature with the furnace.

[0026] (6) Room temperature cold pressing shaping The aged forgings were subjected to multiple small-deformation step-by-step cold pressing at room temperature: the total reduction deformation was 2%, applied in 3 stages, with each stage reducing the deformation by about one-third of the total deformation, and holding the pressure for 40 seconds after each stage to the set deformation amount. The resulting low residual stress 7075 aluminum alloy forging was obtained after cold pressing.

[0027] Example 2 The difference between Example 2 and Example 1 is that step (1) is different. Step (1) of Example 2 is as follows: 7075 aluminum alloy ingots were selected as raw materials, and the ingots underwent a two-stage gradient homogenization heat treatment: first, the ingots were heated to 320℃ at a heating rate of 4℃ / min and held for 4 hours; then, they were heated to 450℃ at a heating rate of 4℃ / min and held for 24 hours. After the holding period, the ingots were removed from the furnace and cooled to obtain the pretreated ingots.

[0028] Everything else is the same as in Example 1.

[0029] Example 3 The difference between Example 3 and Example 1 is that step (4) is different. Step (4) in Example 3 is as follows: Within 2 hours after quenching, the forging is subjected to a combined stress relief treatment of ultra-low temperature cryogenic treatment and high-low temperature thermal cycling: first, the forging is placed in a -170℃ environment for 2 hours for ultra-low temperature cryogenic treatment; after the cryogenic treatment, high-low temperature thermal cycling is performed. Each cycle is as follows: the forging is moved into a 115℃ furnace for 2 hours and then moved into a -75℃ environment for 1 hour; the above thermal cycling is performed twice.

[0030] Everything else is the same as in Example 1.

[0031] Example 4 The difference between Example 4 and Example 1 is that step (4) is different. Step (4) of Example 4 is as follows: Within 2 hours after quenching, the forging is subjected to a combined stress relief treatment of ultra-low temperature cryogenic treatment and high-low temperature thermal cycling: first, the forging is placed in a -190℃ environment and kept at temperature for 1 hour for ultra-low temperature cryogenic treatment; after the cryogenic treatment, high-low temperature thermal cycling is performed. Each cycle is as follows: the forging is moved into a 110℃ furnace and kept at temperature for 2 hours, and then moved into a -80℃ environment and kept at temperature for 1 hour; the above thermal cycling is performed twice.

[0032] Everything else is the same as in Example 1.

[0033] Comparative Example 1 Compared with Example 1, Comparative Example 1 differs in that step (1) is different. Step (1) of Comparative Example 1 is as follows: 7075 aluminum alloy ingots were selected as raw materials, and the ingots underwent homogenization heat treatment: the ingots were heated to 460℃ at a heating rate of 5℃ / min and held at that temperature for 24 hours. After the holding period, the ingots were removed from the furnace and cooled to obtain pretreated ingots.

[0034] Everything else is the same as in Example 1.

[0035] Comparative Example 2 Compared with Example 2, the difference lies in step (3). Step (3) of Comparative Example 2 is different: Solution treatment of forging blanks: Heat the forging to 470℃ and hold for 6 hours; after holding, quickly transfer the forging into a water tank for water quenching.

[0036] Comparative Example 3 Compared with Example 1, Comparative Example 3 differs in that step (4) is different. Step (4) of Comparative Example 3 is as follows: Within 2 hours after quenching, the forging is subjected to a combined stress relief treatment of ultra-low temperature cryogenic treatment and high-low temperature thermal cycling: first, the forging is placed in a -180℃ environment and kept at that temperature for 1 hour for ultra-low temperature cryogenic treatment; after the cryogenic treatment, high-low temperature thermal cycling is performed. Each cycle is as follows: the forging is moved into a 90℃ furnace and kept at that temperature for 2 hours, and then moved into a -80℃ environment and kept at that temperature for 1 hour; the above thermal cycling is performed twice.

[0037] Everything else is the same as in Example 1.

[0038] Comparative Example 4 Compared with Example 1, Comparative Example 4 differs in that step (4) is different. Step (4) of Comparative Example 4 is as follows: Within 2 hours after quenching, the forgings are subjected to a combined stress relief treatment of ultra-low temperature cryogenic treatment and high-low temperature thermal cycling: first, the forgings are placed in a -180℃ environment and kept at temperature for 1 hour for ultra-low temperature cryogenic treatment; after the cryogenic treatment, high-low temperature thermal cycling is performed. Each cycle is as follows: the forgings are moved into a 160℃ furnace and kept at temperature for 2 hours, and then moved into a -80℃ environment and kept at temperature for 1 hour; the above thermal cycling is performed twice.

[0039] Everything else is the same as in Example 1.

[0040] Comparative Example 5 Compared with Example 1, Comparative Example 5 differs in that step (4) is different. Step (4) of Comparative Example 5 is as follows: Within 2 hours after quenching, the forging is subjected to a combined stress relief treatment of ultra-low temperature cryogenic treatment and high-low temperature thermal cycling: first, the forging is placed in a -180℃ environment and kept at that temperature for 1 hour for ultra-low temperature cryogenic treatment; after cryogenic treatment, high-low temperature thermal cycling is performed. Each cycle is as follows: the forging is moved into a 120℃ furnace and kept at that temperature for 2 hours, and then moved into a -196℃ environment and kept at that temperature for 1 hour; the above thermal cycling is performed twice.

[0041] Everything else is the same as in Example 1.

[0042] Comparative Example 6 Compared with Example 1, Comparative Example 6 differs in that step (4) is different. Step (4) of Comparative Example 6 is as follows: Within 2 hours after quenching, the forging is subjected to a combined stress relief treatment of ultra-low temperature cryogenic treatment and high-low temperature thermal cycling: first, the forging is placed in a -180℃ environment and kept at that temperature for 1 hour for ultra-low temperature cryogenic treatment; after the cryogenic treatment, high-low temperature thermal cycling is performed. Each cycle is as follows: the forging is moved into a 120℃ furnace and kept at that temperature for 2 hours, and then moved into a -40℃ environment and kept at that temperature for 1 hour; the above thermal cycling is performed twice.

[0043] Everything else is the same as in Example 1.

[0044] Comparative Example 7 Compared with Example 1, Comparative Example 7 differs in that step (4) is different. Step (4) of Comparative Example 7 is as follows: Within 2 hours after quenching, the forging is subjected to a combined stress relief treatment of ultra-low temperature cryogenic treatment and high-low temperature thermal cycling: first, the forging is placed in a -180℃ environment and kept at that temperature for 1 hour for ultra-low temperature cryogenic treatment; after the cryogenic treatment, high-low temperature thermal cycling is performed. Each cycle is as follows: the forging is moved to a -80℃ environment and kept at that temperature for 1 hour, and then moved to a 120℃ environment and kept at that temperature for 2 hours; the above thermal cycling is performed twice.

[0045] Everything else is the same as in Example 1.

[0046] Comparative Example 8 Compared with Example 1, Comparative Example 8 differs in that step (4) is different. Step (4) of Comparative Example 8 is as follows: Within 2 hours after quenching, the forging is subjected to a combined stress relief treatment of high and low temperature thermal cycling and ultra-low temperature cryogenic treatment: First, the forging is subjected to high and low temperature thermal cycling. A single cycle is as follows: the forging is moved into a furnace at 120℃ and held for 2 hours, and then moved into an environment at -80℃ and held for 1 hour. The above thermal cycling is performed twice. After the holding is completed, the forging is placed in an environment at -180℃ and held for 1 hour for ultra-low temperature cryogenic treatment.

[0047] Everything else is the same as in Example 1.

[0048] Performance testing and data analysis The aluminum alloy bars prepared in Examples 1-4 and Comparative Examples 1-8 were subjected to tests for hardness, tensile strength, yield strength, elongation and residual stress, as shown in Table 1.

[0049] Table 1 - Properties of 7-series aluminum alloy forgings prepared under different cases

[0050] As can be seen from Table 1: 1) The 7075 forgings prepared in Examples 1-4 have a hardness of 168-173 HV, a tensile strength of 490-495 MPa, a yield strength of 402-409 MPa, an elongation of 12%-14%, and a residual stress of only 10.3-11.9 MPa. When the process parameters vary within the range, the mechanical properties of each example show minimal fluctuation, and the residual stress remains consistently below 12 MPa. This indicates that the preparation method of the present invention can stably control the residual stress at an extremely low level while ensuring high strength and high plasticity of the forgings, exhibiting a wide process window and good batch stability.

[0051] 2) Comparative Example 1 used a traditional single-stage homogenization heat treatment instead of the two-stage gradient homogenization of the present invention. The hardness of the forging decreased to 149 HV, the tensile strength decreased to 475 MPa, and the residual stress increased to 72.9 MPa, approximately 6 to 7 times that of the example. This indicates that single-temperature homogenization cannot sufficiently eliminate dendrite segregation and coarse second phases. The forging stress concentration caused by compositional inhomogeneity directly leads to a significant increase in residual stress and a decrease in mechanical properties, demonstrating that two-stage gradient homogenization is an important prerequisite for reducing residual stress in forgings.

[0052] The ingot structure of this invention is uniform, and the forging stress source is weakened. The two-stage gradient homogenization heat treatment, which combines low-temperature holding and high-temperature homogenization, can effectively eliminate dendritic segregation in the ingot compared to the traditional single high-temperature homogenization. This promotes the full dissolution and breakup of coarse and brittle second phases, weakens the forging stress concentration caused by compositional inhomogeneity, and lays the microstructure foundation for subsequent low-stress forging.

[0053] 3) In Comparative Example 2, a single-stage 470℃ solution treatment was used instead of the multi-stage solution treatment of the present invention. The residual stress of the forging increased to 95.4 MPa, and the elongation dropped sharply to 6%. This shows that the multi-stage solution treatment with stepped heating can effectively reduce the internal and external temperature difference during quenching of the forging, and reduce the instantaneous thermal stress and structural stress during quenching; while the single-stage high-temperature solution treatment has a large temperature difference and concentrated thermal stress, and cannot avoid high residual stress while sacrificing the plasticity of the forging.

[0054] 4) In Comparative Examples 3 and 4, the high-temperature section temperature in the thermal cycling was adjusted to 90℃ and 160℃, respectively. When the high-temperature section temperature was too low (90℃), stress release was insufficient, with residual stress reaching 101.3 MPa and elongation only 7.5%. When the high-temperature section temperature was too high (160℃), although the residual stress decreased somewhat (35.1 MPa), the excessively high temperature led to premature aging and coarsening of precipitates, causing the forging hardness to plummet to 114 HV, and the tensile strength and yield strength to drop to 406 MPa and 315 MPa, respectively, resulting in severe strength loss. Therefore, the holding temperature in the high-temperature section needs to be strictly controlled between 110 and 120℃ to balance stress release and strength maintenance.

[0055] 5) Comparative Examples 5 and 6 adjusted the low-temperature section temperature in the thermal cycling to -196℃ and -40℃, respectively. When the low-temperature section temperature was too low (-196℃), excessive thermal shrinkage introduced new cold stress inside the forging, causing the residual stress to rise to 115.2 MPa and the elongation to drop to 6%; when the low-temperature section temperature was too high ( At 40℃, the shrinkage was insufficient to fully relax the lattice distortion, and the residual stress remained as high as 81.52 MPa. It is evident that when the holding temperature in the low-temperature section is controlled between -70℃ and -80℃, the lattice can fully shrink and relax the distortion without introducing additional cold stress, resulting in the best stress relief effect.

[0056] 6) In Comparative Example 7, the order of thermal cycling was reversed (first -80℃ then 120℃), resulting in a decrease in the hardness of the forging to 141HV, a decrease in tensile strength and yield strength to 430MPa and 364MPa respectively, and an increase in residual stress to 106.8MPa. In Comparative Example 8, the ultra-low temperature cryogenic treatment was performed later (first thermal cycling, then cryogenic treatment), resulting in a residual stress as high as 124.8MPa, the highest value among all cases. This indicates that the treatment sequence of "cryogenic treatment beforehand + high temperature before low temperature" is the key to achieving low residual stress in this invention: within 2 hours after quenching, the supersaturated solid solution is in a high plasticity window period. At this time, deep cryogenic treatment can completely release the root stress through lattice microplastic slip before the precipitated phase pins dislocations. If the order is reversed or deep cryogenic treatment is performed later, not only will premature aging lead to a decrease in strength, but new cold stress will also be introduced, rendering the stress relief effect ineffective.

[0057] In summary, the comparison results between Examples 1-4 and the comparative examples show that the temperature ranges (high temperature range 110-120℃, low temperature range -70--80℃) and processing sequence (pre-cryogenic treatment, high temperature followed by low temperature treatment) of the two-stage gradient homogenization, graded solution treatment, and composite stress relief treatment in this invention constitute an inseparable synergistic whole. Any deviation from the scope defined by this invention will lead to a significant increase in residual stress and / or a significant deterioration in mechanical properties. Only by adopting the complete process route of this invention can the residual stress be stably controlled below 12MPa while maintaining the high strength and high plasticity of 7075 forgings.

[0058] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0059] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A method for preparing low residual stress aluminum alloy forgings, characterized in that, The aluminum alloy is a 7-series aluminum alloy. The aluminum alloy ingot is subjected to homogenization heat treatment, multi-directional free forging, graded solution treatment, composite stress relief treatment and aging treatment in sequence to obtain low residual stress aluminum alloy forgings. The homogenization heat treatment is at least a two-gradient homogenization heat treatment, and the graded solution treatment is at least a two-stage solution treatment; The composite stress relief treatment involves sequentially subjecting the graded solution-treated aluminum alloy ingot to cryogenic treatment and thermal cycling treatment. The cryogenic treatment temperature is -190 to -170°C, and each cycle of the thermal cycling treatment consists of holding at 110 to 120°C followed by holding at -80 to -70°C.

2. The preparation method according to claim 1, characterized in that, The hot and cold cycle treatment is performed 1 to 2 times.

3. The preparation method according to claim 1, characterized in that, The cryogenic treatment time is 1 to 2 hours. In a single cycle of the cryogenic cycle treatment, the holding time at 110 to 120°C is 1 to 2 hours, and the holding time at -80 to -70°C is 1 to 2 hours.

4. The preparation method according to claim 1, characterized in that, The homogenization heat treatment is a two-gradient homogenization heat treatment. Specifically, the aluminum alloy ingot is held at 280-320℃, and then heated to 450-465℃ and held.

5. The preparation method according to claim 4, characterized in that, The aluminum alloy ingot is held at 280–320℃ for 4–8 hours and at 450–465℃ for 18–24 hours, with a heating rate of 3–5℃ / min.

6. The preparation method according to any one of claims 1-5, characterized in that, The multi-directional free forging is a three-directional alternating upsetting-drawing multi-directional free forging, with an initial forging temperature of 450-470℃ and a final forging temperature of not less than 380℃. During the forging process, the single-pass reduction rate is controlled at 15-22%, and the deformation rate is 5-8 mm / s. When the billet temperature drops to the final forging temperature, it is reheated in the furnace. Between each forging pass, the billet is kept warm in a furnace at 350-380℃ before continuing the next forging pass.

7. The preparation method according to any one of claims 1-5, characterized in that, The graded solution is a two-stage solution, with the first stage solution temperature being 410–420℃ and the second stage solution temperature being 470–485℃.

8. The preparation method according to any one of claims 1-5, characterized in that, The aging process is a two-stage aging process, with the first stage aging process at a temperature of 70–90°C and the second stage aging process at a temperature of 120–140°C.

9. The preparation method according to any one of claims 1-5, characterized in that, After aging treatment, room temperature cold pressing shaping is also included, with a total deformation of 2-3% and a single holding time of 30-60 seconds.

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