Method for preparing gradient nanometer structure in as-cast aluminum-lithium alloy through friction stir processing and product

Abstract

The invention provides a method for preparing a gradient nanometer structure in an as-cast aluminum-lithium alloy through friction stir processing and a product, and belongs to the technical field of aluminum-lithium alloy gradient structure preparation. The method comprises the following steps: carrying out bipolar homogenization treatment and solid solution pretreatment on an as-cast aluminum-lithium alloy plate, carrying out friction stir processing treatment, and carrying out aging treatment on the plate subjected to friction stir processing treatment to obtain the as-cast aluminum-lithium alloy with a gradient nanometer structure. Through a series of steps of bipolar homogenization treatment, solid solution pretreatment, stirring friction processing with a specific path, aging treatment and the like, the aluminum-lithium alloy with a gradient structure from surface nanocrystals to ultra-fine crystals to core coarse crystals can be prepared, and the strength and plasticity of the aluminum-lithium alloy are effectively improved. The method is simple in process, low in energy consumption, free of pollution and suitable for gradient strengthening and lightweight manufacturing of aerospace large-size aluminum-lithium alloy structural parts.

Description

Technical Field

[0001] This invention belongs to the field of aluminum-lithium alloy gradient structure preparation technology, and particularly relates to a method and product for preparing gradient nanostructures in cast aluminum-lithium alloys by friction stir processing. Background Technology

[0002] Aluminum-lithium alloys have become the preferred material for large aerospace structural components due to their low density, high specific strength, and good damage resistance. However, aluminum-lithium alloys prepared by conventional casting have low strength and plasticity due to their coarse grain size. This as-cast structure requires large deformation processes, such as extrusion and rolling, combined with recrystallization annealing, to improve its mechanical properties, such as strength and plasticity. Consequently, aluminum-lithium alloys used in the as-cast state exhibit relatively low strength and plasticity.

[0003] For as-cast aluminum-lithium alloys, it is difficult to improve their strength without significant overall deformation. Existing technologies for processing as-cast aluminum-lithium alloy sheets often neglect the impact of dendritic segregation defects on material properties and fail to perform effective pretreatment before processing. During processing, traditional methods cannot achieve precise control and uniform refinement of the surface microstructure, making it difficult to meet the demands of modern industry for high-performance aluminum-lithium alloy materials. This invention, based on in-depth research and analysis of these problems, proposes a novel method for preparing gradient nanostructures, providing new ideas and approaches for the processing and application of aluminum-lithium alloy materials. Summary of the Invention

[0004] To address the technical problems of dendritic segregation defects in existing cast aluminum-lithium alloy plates, which lead to poor material properties, and the inability of traditional processing methods to effectively achieve uniform and refined surface microstructure, performance improvement, and full coverage of the processing area, this invention proposes a method and product for preparing gradient nanostructures in cast aluminum-lithium alloys using friction stir processing.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention proposes a method for preparing gradient nanostructures in cast aluminum-lithium alloys by friction stir processing. The method involves subjecting the cast aluminum-lithium alloy sheet to bipolar homogenization treatment and solution pretreatment, followed by friction stir processing, and then aging treatment to obtain a cast aluminum-lithium alloy with gradient nanostructures.

[0007] The chemical composition of the cast aluminum-lithium alloy plate, by mass percentage, is: Cu 3.7-4.3%, Li 0.8-1.2%, Mg 0.25-0.8%, Ag 0.25-0.6%, Zr 0.08-0.16%, with the balance being Al and trace impurities.

[0008] Beneficial effects:

[0009] Friction stir processing (FSP) is commonly used for welding alloy materials. This welding is achieved through plastic deformation of the material at the weld joint. Specifically, the contact between the friction stir head and the alloy generates intense plastic deformation and dynamic recrystallization (DXR) effects, refining the original coarse grains to the micrometer size. This invention employs a friction stir processing (FSP) method on the surface of a casting to prepare a gradient nanostructure. Due to the dynamic recrystallization that occurs during the friction stir process, this gradient nanostructure can refine coarse grains to nanometer and submicrometer sizes. This refined structure often exhibits high strength and ductility. Furthermore, further aging heat treatment of this gradient nanostructure can balance strength and toughness. The gradient structure material, through the synergistic effect of surface ultrafine grain strengthening and core coarse grain toughening, can significantly improve overall mechanical properties while reducing crack susceptibility.

[0010] Furthermore, the friction stir processing adopts a Z-shaped path processing method, starting from one corner of the cast aluminum-lithium alloy plate, moving at a constant speed along the length of the plate to the end point, and then the stirring head moves along the width direction by a distance equivalent to the diameter of the stirring needle to perform the next processing. Subsequently, the stirring head moves in the opposite direction along the length of the plate to the end point, and the above steps are repeated so that the friction stir processing area covers the entire surface of the plate.

[0011] During friction stir processing, the cast aluminum-lithium alloy sheet at the stirring position undergoes plastic flow, generating a large amount of heat. Under the influence of thermo-mechanical coupling, dislocation multiplication and redistribution occur, inducing the formation of subgrains. These subgrains, accompanied by thermo-mechanical coupling, transform into recrystallized nano- and submicron grains. Since the deformation is greatest and recrystallization is most significant at the stirring shoulder, the surface grain size is the smallest, with an average grain size of only 300 nm. Near the needle tip, due to smaller deformation and lower temperature, recrystallization is less complete, resulting in larger grain sizes, with an average grain size of 700 nm. Therefore, a gradient structure with increasing grain size is formed from the stirring needle shoulder to the needle tip to the unstirred area.

[0012] Furthermore, in the next processing pass, the new processing area overlaps with the processing area of ​​the previous pass, and the width of the overlapping area is at least 10% of the diameter of the stirring needle, to ensure continuous coverage of the processing area and uniformity of material properties.

[0013] Furthermore, the stirring head used in the friction stir processing is a threaded cylindrical stirring needle with a diameter of 3-6 mm. The stirring head rotation speed is 600-2000 r / min, the feed rate is 50-200 mm / min, the shoulder depressor is 0.1-0.5 mm, the shoulder diameter is 8-32 mm, and the pressure is 8-25 kN. Single-pass gradual friction stir processing induces intense plastic deformation and dynamic recrystallization in the material, refining the surface grain size and forming a gradient nanostructure from surface nanocrystals to ultrafine crystals to coarse grains in the core. By controlling the stirring head's path, pass spacing, and heat input, a gradient distribution of grain size along the thickness direction is achieved.

[0014] Furthermore, the material of the stirring head is selected from one or more of martensitic stainless steel, medium carbon steel, high carbon steel, tool steel, and high-temperature alloys.

[0015] Furthermore, the formula for calculating the heat input of the friction stir processing is as follows:

[0016]

[0017] In the formula, q E k represents the heat input. m Here, is a constant coefficient, n represents the stirring head rotation speed, and v represents the feed rate. By changing the stirring head rotation speed n and the feed rate v, the thickness of the anti-gradient structure can be quantitatively controlled.

[0018] Friction stir processing involves temperature input, which is a process in which heat and force act on the material simultaneously. This process induces the recrystallization of coarse grains on the surface.

[0019] Furthermore, the bipolar homogenization process involves holding the material at 440°C for 16 hours, followed by holding it at 480°C for 20 hours.

[0020] Furthermore, the solution pretreatment temperature is 500℃-530℃, and the holding time is 1-2 hours.

[0021] Furthermore, the aging treatment temperature is 165℃-190℃, and the holding time is 6-35h. After aging, a large number of lamellar T1 phases are generated in the nanocrystals, and the number of precipitated phases increases with the increase of aging time and aging temperature.

[0022] This invention also proposes a cast aluminum-lithium alloy with a gradient nanostructure, which is prepared according to the above method.

[0023] Furthermore, the gradient nanostructure is a mixed-crystal heterostructure gradient structure with a grain size of 300 micrometers in the original structure, and a grain size of only 300 nanometers after surface stirring and friction, and a grain size of 300 nanometers to 700 nanometers to 30 micrometers near the surface.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] (1) The present invention can prepare an aluminum-lithium alloy with a gradient structure from surface nanocrystals to ultrafine crystals to core coarse crystals by a series of steps such as bipolar homogenization treatment, solid solution pretreatment, stirring friction processing along a specific path and aging treatment. Compared with the cast aluminum-lithium alloy in the aged state, the yield strength is increased from 500MPa to 550MPa and the elongation is increased from 7% to 15%, which is more than 8%. This shows that the method of the present invention simultaneously improves the strength and plasticity of the cast aluminum-lithium alloy.

[0026] (2) The present invention employs friction stir processing, which avoids melting and solidification defects, is environmentally friendly, and can achieve the formation of surface gradient nanocrystals in an aluminum-lithium alloy in a single processing step. The surface grain size is refined from 300 μm in the original as-cast state to 300 nm at the outermost layer, with the degree of grain size refinement decreasing from the surface to the core. Due to the gradient structure, the prepared as-cast aluminum-lithium alloy with gradient nanostructure can significantly improve the surface strength and hardness while maintaining the core toughness, exhibiting excellent fatigue and fracture performance. The method of the present invention is applicable to the mechanical property modification of large-size, complex-shaped as-cast aluminum-lithium alloy components, meeting the requirements of lightweighting and high performance in aerospace. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 This is a schematic diagram of the processing path for friction stirring processing according to an embodiment of the present invention;

[0029] Figure 2 This is a diagram showing the depth of the deformed layer of the cast aluminum-lithium alloy obtained by step (3) of friction stirring processing in Embodiment 1 of the present invention.

[0030] Figure 3 This is a schematic diagram of the surface structure of the cast aluminum-lithium alloy obtained by step (3) friction stirring processing in Embodiment 1 of the present invention;

[0031] Figure 4 This is a schematic diagram of the transition layer structure of the cast aluminum-lithium alloy obtained by step (3) friction stirring processing in Embodiment 1 of the present invention;

[0032] Figure 5 This is a schematic diagram of the structure of the cast aluminum-lithium alloy core obtained by step (3) friction stirring processing in Embodiment 1 of the present invention;

[0033] Figure 6This is a statistical diagram of the surface grain size of the cast aluminum-lithium alloy obtained by step (3) of friction stirring processing in Example 1 of the present invention;

[0034] Figure 7 The surface precipitates of the cast aluminum-lithium alloy obtained after aging treatment in step (4) in this embodiment of the invention are shown in the figure. Here, a is the nanocrystal observed under a transmission electron microscope, b is the precipitate observed in the nanocrystal, and c is the precipitate in the nanocrystal determined to be the T1 phase by high resolution and diffraction spots.

[0035] Figure 8 The mechanical property test results are for the casting-aged specimen of Comparative Example 1 and the casting-aged specimen treated with friction stir in Example 1. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] This invention proposes a method for preparing gradient nanostructures in cast aluminum-lithium alloys by friction stir processing. The method involves subjecting the cast aluminum-lithium alloy sheet to bipolar homogenization treatment and solution pretreatment, followed by friction stir processing, and then aging treatment to obtain a cast aluminum-lithium alloy with gradient nanostructures.

[0042] The chemical composition of the cast aluminum-lithium alloy sheet, by mass percentage, is: Cu 3.7-4.3%, Li 0.8-1.2%, Mg 0.25-0.8%, Ag 0.25-0.6%, Zr 0.08-0.16%, with the balance being Al and trace impurities.

[0043] In a preferred embodiment of the present invention, the thickness of the cast aluminum-lithium alloy sheet used is 3-7 mm.

[0044] In a preferred embodiment of the present invention, a schematic diagram of the processing path for friction stirring is shown below. Figure 1 The process employs a zigzag path, starting from one corner of the cast aluminum-lithium alloy sheet (point A), and moving at a constant speed along the length of the sheet (positive X-axis) to the endpoint (point B). The stirring head then moves along the width (Y-axis) a distance equivalent to the diameter of the stirring needle to perform the next processing pass. Subsequently, the stirring head moves along the length of the sheet in the opposite direction (negative X-axis) to the endpoint, and the above steps are repeated to ensure that the friction stirring processing area covers the entire surface of the sheet.

[0045] In a preferred embodiment of the present invention, during the next processing pass, the new processing area overlaps with the processing area of ​​the previous pass, and the width of the overlapping area is at least 10% of the diameter of the stirring needle, so as to ensure continuous coverage of the processing area and uniformity of material properties.

[0046] In a preferred embodiment of the present invention, the stirring head for friction stirring processing is a threaded cylindrical stirring needle with a diameter of 3-6 mm, a rotational speed of 600-2000 r / min, a feed speed of 50-200 mm / min, a shoulder pressing amount of 0.1-0.5 mm, a shoulder diameter of 8-32 mm, and a pressure of 8-25 KN.

[0047] In a preferred embodiment of the present invention, the material of the stirring head is selected from one or more of martensitic stainless steel, medium carbon steel, high carbon steel, tool steel and high temperature alloy.

[0048] In a preferred embodiment of the present invention, the formula for calculating the heat input of friction stir processing is as follows:

[0049]

[0050] In the formula, q E k represents the heat input.m Here, is a constant coefficient, n represents the stirring head rotation speed, and v represents the feed rate. By changing the stirring head rotation speed n and the feed rate v, the thickness of the anti-gradient structure can be quantitatively controlled.

[0051] Friction stir processing involves temperature input, which is a process in which heat and force act on the material simultaneously. This process induces the recrystallization of coarse grains on the surface.

[0052] In a preferred embodiment of the present invention, the bipolar homogenization treatment involves holding the material at 440°C for 16 hours, followed by holding it at 480°C for 20 hours.

[0053] In a preferred embodiment of the present invention, the solution pretreatment temperature is 500℃-530℃, and the holding time is 1-2h.

[0054] In a preferred embodiment of the present invention, the aging treatment temperature is 165℃-190℃, and the holding time is 6-35h. After aging, a large number of lamellar T1 phases are generated in the nanocrystals, and the number of precipitated phases increases with the increase of aging time and aging temperature.

[0055] This invention also proposes a cast aluminum-lithium alloy with a gradient nanostructure, which is prepared according to the above method.

[0056] In a preferred embodiment of the present invention, the original grain size is 300 micrometers, while after the stirring friction processing of the present invention, the grain size is only 300 nm, and the grain size near the surface is a mixed crystal heterogeneous gradient structure of 300 nm to 700 nm to 30 μm.

[0057] In a preferred embodiment of the present invention, bipolar homogenization treatment, solution pretreatment, and aging treatment are all conventional techniques in the art. The bipolar homogenization treatment, solution pretreatment, and aging treatment are all performed in a muffle furnace, and the friction stir processing is performed on the worktable of a friction stir welding machine.

[0058] Patent CN 118893299 A discloses a method for preparing anti-gradient structure metal sheets based on friction stir welding. The difference between this invention and that patent is that the patent uses friction stir to coarsen grains, while this invention uses friction stir recrystallization to refine the originally coarse cast-rolled grains (average grain size 300 μm). Furthermore, the aluminum alloy involved in the patent did not undergo aging heat treatment, nor did it mention the impact of the anti-gradient structure on mechanical properties. In this invention, through gradient structure design and subsequent aging heat treatment, the strength and plasticity of cast-aged aluminum-lithium alloys can be simultaneously improved. Typically, refining the grains of aluminum-lithium alloys to the nanoscale using other processing methods increases strength but decreases plasticity. However, the gradient nanostructure prepared using the method of this invention improves both the strength and plasticity of the aluminum-lithium alloy.

[0059] The technical solution of the present invention will be further illustrated by the following embodiments.

[0060] Example 1

[0061] A method for preparing gradient nanostructures in cast aluminum-lithium alloys by friction stir processing includes the following steps:

[0062] (1) A 2195 aluminum-lithium alloy casting plate with a thickness of 3mm and a size of 200mm×100mm was placed in a muffle furnace for bipolar homogenization treatment to eliminate defects such as dendrite segregation. The bipolar homogenization treatment was specifically carried out at 440℃ for 16h and then at 480℃ for 20h. The chemical composition of the 2195 aluminum-lithium alloy T8 plate by mass percentage is: Cu 3.87%, Li 0.96%, Mg 0.47%, Ag 0.37%, Zr 0.13%, with the balance being Al and trace impurities.

[0063] (2) The 2195 aluminum-lithium alloy plate after step (1) was placed in a muffle furnace for solution pretreatment. The holding temperature was 510℃ and the holding time was 1.5h. Then, a solution pretreated sample was obtained.

[0064] (3) The obtained solution-treated sample is clamped on the worktable of the friction stir welding machine for friction stir processing. Ensure that the plate is flat and firmly fixed. A zigzag path processing method is adopted. Starting from one corner of the cast aluminum-lithium alloy plate (point A), the plate moves at a constant speed along the length direction (positive X-axis) to the end point (point B). The stirring head moves along the width direction (Y-axis) by a distance equivalent to the diameter of the stirring needle to perform the next processing pass. Then the stirring head moves along the length of the plate in the opposite direction (negative X-axis) to the end point. The above steps are repeated so that the friction stir processing area covers the entire surface of the plate. The overlap area between the first and second passes is 1 mm to ensure continuous coverage of the processing area and uniformity of material properties. The stirring head for friction stir processing is a threaded cylindrical stirring needle with a diameter of 6 mm. The stirring head rotation speed is 600 r / min, the feed speed is 150 mm / min, the shoulder pressure is 0.5 mm, the stirring head shoulder diameter is 8-32 mm, and the pressure is 22 KN.

[0065] (4) The sample obtained in step (3) is placed in a muffle furnace for aging treatment. The aging temperature is 170℃ and the holding time is 32h. After the treatment, a cast aluminum-lithium alloy with gradient nanostructure is obtained.

[0066] The image showing the depth of the deformed layer of the cast aluminum-lithium alloy obtained by step (3) friction stirring processing in this embodiment of the invention is shown below. Figure 2The structural schematic diagrams of the surface layer, transition layer, and core are shown below. Figure 3 , Figure 4 and Figure 5 See the surface grain size statistics chart. Figure 6 It can be seen that after the stirring friction processing in step (3), the depth of the deformed layer of the cast aluminum-lithium alloy is 817.7 μm, the surface grain size is 0.3 μm, and the core grain size is greater than 300 μm. This indicates that the grain size of the original structure is 300 μm, while after the stirring friction processing of the present invention, the grain size is only 300 nm, and the grain size near the surface is a mixed crystal heterogeneous gradient structure of 300 nm to 700 nm to 30 μm.

[0067] The surface precipitates of the as-cast aluminum-lithium alloy obtained after the aging treatment in step (4) in this embodiment of the invention are shown below. Figure 7 In the diagram, a represents the nanocrystals observed under a transmission electron microscope, b represents the precipitated phase observed within the nanocrystals, and c represents the T1 phase identified in the nanocrystals through high-resolution diffraction and spot analysis. It can be seen that a composite nanostructure consisting of nanocrystals and a large amount of T1 precipitated phase within the nanocrystals can be obtained on the surface through solution treatment, stirring and friction treatment, and subsequent aging treatment.

[0068] Comparative Example 1

[0069] A method for preparing a cast-aged alloy, the same as in Example 1, except that step (3) is omitted, and specifically includes the following steps:

[0070] (1) A 2195 aluminum-lithium alloy casting plate with a thickness of 7 mm and a size of 200 mm × 100 mm was placed in a muffle furnace for bipolar homogenization treatment to eliminate defects such as dendrite segregation. The bipolar homogenization treatment was specifically carried out at 440℃ for 16 h and then at 480℃ for 20 h. The chemical composition of the 2195 aluminum-lithium alloy plate by mass percentage was: Cu 3.87%, Li 0.96%, Mg 0.47%, Ag 0.37%, Zr 0.13%, with the balance being Al and trace impurities.

[0071] (2) The 2195 aluminum-lithium alloy plate after step (1) was placed in a muffle furnace for solution pretreatment. The holding temperature was 530℃ and the holding time was 1h. Then, a solution pretreated sample was obtained.

[0072] (3) The sample obtained in step (2) is placed in a muffle furnace for aging treatment. The aging temperature is 190℃ and the holding time is 6h. After the treatment, the cast aged alloy is obtained.

[0073] The mechanical property test results of the cast aged alloy of Comparative Example 1 and the cast friction stir treated specimen (cast aluminum-lithium alloy) of Example 1 are shown in the figure. Figure 8As can be seen, compared with the traditional solution aging treatment in Comparative Example 1, when casting + surface stirring and friction treatment + aging is used, the stirring and friction treatment in Example 1 can obtain a gradient microstructure compared with the traditional treatment method. This gradient microstructure increases both the strength and plasticity of the aluminum-lithium alloy. Compared with the cast-aged aluminum-lithium alloy, the yield strength increases from 500 MPa to 550 MPa, and the elongation increases from 7% to 15%, an increase of more than 8%, indicating that the method of the present invention simultaneously improves the strength and plasticity of the cast aluminum-lithium alloy.

[0074] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing gradient nanostructures in cast aluminum-lithium alloys by friction stir processing, characterized in that, After bipolar homogenization and solution pretreatment, the as-cast aluminum-lithium alloy sheet is subjected to friction stirring. Then, the as-cast aluminum-lithium alloy with gradient nanostructure is subjected to aging treatment. The chemical composition of the cast aluminum-lithium alloy plate, by mass percentage, is: Cu 3.7-4.3%, Li 0.8-1.2%, Mg 0.25-0.8%, Ag 0.25-0.6%, Zr 0.08-0.16%, with the balance being Al and trace impurities.

2. The method for preparing gradient nanostructures in cast aluminum-lithium alloys by friction stir processing according to claim 1, characterized in that, The friction stir processing adopts a Z-shaped path processing method. Starting from one corner of the cast aluminum-lithium alloy plate, it moves at a constant speed along the length of the plate to the end point. The stirring head moves a distance equivalent to the diameter of the stirring needle along the width direction to perform the next processing. Then the stirring head moves in the opposite direction along the length of the plate to the end point. The above steps are repeated so that the friction stir processing area covers the entire surface of the plate.

3. The method for preparing gradient nanostructures in cast aluminum-lithium alloys by friction stir processing according to claim 2, characterized in that, In the next processing pass, the new processing area overlaps with the processing area of ​​the previous pass, and the width of the overlapping area is at least 10% of the diameter of the stirring needle.

4. The method for preparing gradient nanostructures in cast aluminum-lithium alloys by friction stir processing according to claim 2, characterized in that, The stirring head for friction stirring processing is a threaded cylindrical stirring needle with a diameter of 3-6 mm, a rotational speed of 600-2000 r / min, a feed speed of 50-200 mm / min, a shoulder pressing amount of 0.1-0.5 mm, a shoulder diameter of 8-32 mm, and a pressure of 8-25 KN.

5. The method for preparing gradient nanostructures in cast aluminum-lithium alloys by friction stir processing according to claim 1, characterized in that, The bipolar homogenization process involves holding the material at 440°C for 16 hours, followed by holding it at 480°C for 20 hours.

6. The method for preparing gradient nanostructures in cast aluminum-lithium alloys by friction stir processing according to claim 1, characterized in that, The solution pretreatment temperature is 500℃-530℃, and the holding time is 1-2h.

7. The method for preparing gradient nanostructures in cast aluminum-lithium alloys by friction stirring according to claim 1, characterized in that, The aging treatment temperature is 165℃-190℃, and the holding time is 6-35h.

8. A cast aluminum-lithium alloy with a gradient nanostructure, characterized in that, Prepared by the method according to any one of claims 1-7.

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