Preparation method of high-strength and high-plasticity product heat-resistant aluminum-lithium alloy and aluminum-lithium alloy

Abstract

This application relates to the technical field of aluminum alloy materials, and discloses a preparation method of a high-strength and high-plasticity heat-resistant aluminum-lithium alloy and an aluminum-lithium alloy. A preparation method of a high-strength and high-plasticity heat-resistant aluminum-lithium alloy includes the following steps: The ingot comprises: 1.8 - 2.5% of Cu, 0.8 - 1.2% of Li, 0.1 - 0.5% of Mg, 0.1 - 0.2% of Sc, 0.05 - 0.15% of Zr, other impurity elements ≤ 0.1%, and the balance is Al. The ingot is subjected to homogenization treatment; the ingot is subjected to preliminary hot rolling, medium-temperature solution treatment, first aging treatment, medium-temperature hot rolling, high-temperature solution treatment, cold pre-deformation, and second aging treatment to obtain the aluminum-lithium alloy. This application reduces the brittle primary phase in the matrix, refines the grain size, increases the grain boundary density, and improves the heat-resistant plasticity of the alloy; inhibits the coarsening of the T1 phase and improves the heat-resistant strength of the alloy; finally enables the alloy to have good heat-resistant strength and plasticity product.

Description

Technical Field

[0001] This application relates to the technical field of aluminum alloy materials. Specifically, it relates to a preparation method of a high-strength and high-plasticity heat-resistant aluminum-lithium alloy and an aluminum-lithium alloy. Background Art

[0002] Due to the requirements of energy conservation and equipment lightweighting, the research and development of lightweight structural materials have become increasingly important. Among them, aluminum-lithium alloys have the advantages of low density, high strength, and high elastic modulus, and are now widely used in the aerospace field. The current third-generation aluminum-lithium alloys are mainly used in structural components with service temperatures below 150 °C, such as the front, middle, and rear fuselage, floor beams, seat slides, boundary beams, and cabin floors of aircraft. Such usage limitations are attributed to the insufficient strength of the third-generation aluminum-lithium alloys in high-temperature environments (above 175 °C), mainly because the thermal coarsening of the strengthening phase Al2CuLi-T1 phase leads to a rapid decay of its strength at high temperatures. However, the fuselage skin, tail fins, load-bearing frames near the engine, etc. of supersonic aircraft have put forward harsh requirements for the long-term service performance at 250 °C. Therefore, the development of heat-resistant aluminum-lithium alloys is of great significance for further promoting the lightweighting of aerospace equipment.

[0003] At present, the research and development of heat-resistant aluminum-lithium alloys are in the initial stage. The general idea is to add transition metal elements and rare earth elements to form a large number of high-melting-point compounds in the aluminum matrix to improve the high-temperature strength of the aluminum-lithium alloy. For example, adding Fe element forms Al3Fe phase, adding Mn, Zr, Sc, and Er elements forms Al6Mn, Al 20 Cu2Mn3, Al8Cu4Sc phase, and Al3(Sc, Zr, Er) phase, adding Ce forms Al8Cu4Ce phase, etc. Although these methods improve the heat resistance of aluminum-lithium alloys by introducing high-melting-point compounds, they ignore the damage to the plasticity of aluminum-lithium alloys after thermal exposure caused by these brittle phases. Moreover, compared with conventional aluminum alloys, aluminum-lithium alloys are more prone to brittle fracture after thermal exposure, mainly because Li element will segregate at grain boundaries during the thermal exposure process, reducing the atomic bonding force between grain boundaries.

[0004] The heat resistance design of structural components not only considers high strength to counteract the deformation caused by external forces, but high plasticity is also indispensable, which can greatly improve the service safety of structural components. If there is only heat-resistant strength but lack of heat-resistant plasticity, once the force exceeds a certain limit, brittle fracture is very likely to occur, which will undoubtedly bring catastrophic consequences to flight missions. Therefore, it is of great significance to develop heat-resistant aluminum-lithium alloys that can maintain high strength, high plasticity, and high strength-plasticity product after thermal exposure. Summary of the Invention

[0005] The purpose of this application is to provide a preparation method of a high-strength and high-plasticity heat-resistant aluminum-lithium alloy and an aluminum-lithium alloy, which can maintain high strength-plasticity product, high plasticity, and high strength after thermal exposure.

[0006] To achieve the above object, the present application provides the following technical solutions:

[0007] A preparation method of a high-strength and high-plasticity heat-resistant aluminum-lithium alloy, comprising the following steps:

[0008] Step 1: According to the alloy composition, batching and melting are carried out, and casting is performed to obtain an ingot. By mass percentage, the ingot includes: Cu 1.8 - 2.5%, Li 0.8 - 1.2%, Mg 0.1 - 0.5%, Sc 0.1 - 0.2%, Zr 0.05 - 0.15%, other impurity elements ≤ 0.1%, and the balance is Al. The ingot is subjected to two-stage homogenization treatment, and then the ingot is peeled to obtain a peeled ingot;

[0009] Step 2: The peeled ingot is subjected to preliminary hot rolling at 450 - 470 °C. After the hot rolling is completed, the hot-rolled billet is oil-cooled and quenched to room temperature within 15 s to complete the medium-temperature solution treatment;

[0010] Step 3: The rolled billet after the medium-temperature solution treatment is subjected to the first aging treatment;

[0011] Step 4: The rolled billet after the first aging treatment is heated to 220 - 250 °C for heat preservation, and medium-temperature hot rolling is carried out at 220 - 250 °C;

[0012] Step 5: High-temperature solution treatment is carried out, and the temperature of the high-temperature solution treatment is 7 - 12 °C lower than the melting point of the aluminum-lithium alloy;

[0013] Step 6: 3 - 6% cold drawing pre-deformation is carried out, and then the second aging treatment is carried out to obtain the aluminum-lithium alloy.

[0014] Further, in the two-stage homogenization treatment, the temperature of the first-stage homogenization treatment is 400 - 420 °C, and the heat preservation time is 12 - 24 hours. The temperature of the second-stage homogenization treatment is 450 - 500 °C, and the heat preservation time is 15 - 30 hours.

[0015] Further, before the preliminary hot rolling is carried out, the ingot is preheated at 450 - 470 °C for 3 - 10 hours.

[0016] Further, the reduction of the hot rolling is 20 - 40%, and the number of rolling passes is 2 - 4 times.

[0017] Further, the temperature of the first aging treatment is 100 - 120 °C, and the treatment time is 15 - 20 hours.

[0018] Further, the heat preservation time in Step 4 is 1 - 3 hours.

[0019] Furthermore, the reduction ratio of medium-temperature hot rolling is 40 - 60%, and the number of rolling passes is 4 - 7 times.

[0020] Furthermore, the time of high-temperature solution treatment is 1 - 1.5 hours.

[0021] Furthermore, the temperature of the second aging treatment is 150 - 165 °C, and the treatment time is 15 - 25 hours.

[0022] A high-strength and high-ductility heat-resistant aluminum-lithium alloy, which is the aluminum-lithium alloy obtained according to the preparation method of any of the above high-strength and high-ductility heat-resistant aluminum-lithium alloys. After a long-term thermal exposure test at 250 °C for 100 h, its tensile strength is not less than 346 MPa, the elongation is not less than 15.6%, and the product of strength and ductility is not less than 5397.6 MPa%.

[0023] This application has the following advantages:

[0024] (1) Through a reasonable Cu, Sc, Zr composition ratio in this application, combined with a high-temperature solution treatment process where the solution temperature is only 7 - 12 °C lower than the melting point, brittle phases such as Al8Cu4Sc phase, primary Al3Sc, Al3Zr, Al3(Sc,Zr) phase in the matrix can be basically dissolved, which is beneficial to heat resistance and plasticity.

[0025] (2) After the dissolution of the above brittle phases, Sc and Zr elements enter the aluminum matrix and exist in a solid solution form. These slow-diffusion elements can inhibit the diffusion of Cu elements, improve the coarsening resistance of the nano-T1 phase, and are beneficial to heat resistance strength.

[0026] (3) The addition of Sc and Zr elements, combined with the hot working process of "preliminary hot rolling - medium-temperature solution - aging treatment - warm rolling", can maximally inhibit the recovery and recrystallization of dislocations during the hot working process, increase the distortion energy, refine the grain size of the alloy after high-temperature solution treatment, and at the same time retain a large number of sub-boundaries, increase the grain boundary density, and can dilute the grain boundary damage caused by the grain boundary segregation of Li elements, which is beneficial to heat resistance and plasticity.

[0027] (4) Through the above collaborative design of "alloy composition - hot working process - high-temperature solution treatment process", the heat-resistant aluminum-lithium alloy of this application, after a long-term thermal exposure test at 250 °C for 100 h, has a tensile strength of not less than 346 MPa, an elongation of not less than 15.6%, and a product of strength and ductility of not less than 5397.6 MPa%. Currently, for commercial aluminum-lithium alloys 8090 and 2090 alloys, after a long-term thermal exposure test at 250 °C for 100 h, the products of strength and ductility are approximately 2856 MPa% and 2960 MPa% respectively. It can be seen that the advantages of this application are obvious. Description of the Drawings

[0028] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the accompanying drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a TEM photograph of the precipitation phase constructed in the matrix after "preliminary hot rolling - medium temperature solution treatment - aging treatment" for Example 1.

[0030] Figure 2 It is SEM photographs of Example 1, Example 2, Comparative Example 2, and Comparative Example 4 after high-temperature solution treatment. Among them, Figure 2 (a) is the SEM photograph of the aluminum-lithium alloy of Example 1 after high-temperature solution treatment; 2(b) is the SEM photograph of the aluminum-lithium alloy of Example 2 after high-temperature solution treatment; Figure 2 (c) is the SEM photograph of the aluminum-lithium alloy of Comparative Example 2 after solution treatment; Figure 2 (d) is the SEM photograph of the aluminum-lithium alloy of Comparative Example 4 after high-temperature treatment.

[0031] Figure 3 It is the inverse pole figure (IPF figure) and grain boundary distribution map of Example 1, Comparative Example 1 - 3 after high-temperature solution treatment. Among them, Figure 3 (a1) is the IPF figure of the aluminum-lithium alloy of Example 1 after high-temperature solution treatment; Figure 3 (a2) is the grain boundary distribution map of the aluminum-lithium alloy of Example 1 after high-temperature solution treatment; Figure 3 (b1) is the IPF figure of the aluminum-lithium alloy of Comparative Example 1 after thermal exposure test; Figure 3 (b2) is the grain boundary distribution map of the aluminum-lithium alloy of Comparative Example 1 after high-temperature solution treatment; Figure 3 (c1) is the IPF figure of the aluminum-lithium alloy of Comparative Example 2 after high-temperature solution treatment; Figure 3 (c2) is the grain boundary distribution map of the aluminum-lithium alloy of Comparative Example 2 after high-temperature solution treatment; Figure 3 (d1) is the IPF figure of the aluminum-lithium alloy of Comparative Example 3 after high-temperature solution treatment; Figure 3 (d2) is the grain boundary distribution map of the aluminum-lithium alloy of Comparative Example 3 after high-temperature solution treatment.

[0032] Figure 4 It is a TEM photograph of the sub-grain boundary of Example 1 after long-term thermal exposure test.

[0033] Figure 5 It is TEM photographs of the matrix precipitation phases of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 4 after long-term thermal exposure test. Among them, Figure 5(a) TEM micrograph of the matrix precipitation phase of the Al-Li alloy in Example 1 after thermal exposure test; Figure 5 (b) TEM micrograph of the matrix precipitation phase of the Al-Li alloy in Comparative Example 1 after thermal exposure test; Figure 5 (c) TEM micrograph of the precipitation phase of the matrix of the Al-Li alloy in Comparative Example 2 after thermal exposure test; Figure 5 (d) TEM micrograph of the matrix precipitation phase of the Al-Li alloy in Comparative Example 4 after thermal exposure test.

[0034] Figure 6 Fracture surface photos of Example 1 and Comparative Examples 1-3 after long-term thermal exposure test, where Figure 6 (a) Fracture surface photo of the Al-Li alloy in Example 1 after tensile test; Figure 6 (b) is Figure 6 (a) Local enlarged view of the marked area; Figure 6 (c) Fracture surface photo of the Al-Li alloy in Comparative Example 1 after tensile test; Figure 6 (d) Fracture surface photo of the Al-Li alloy in Comparative Example 2 after tensile test; Figure 6 (e) Fracture surface photo of the Al-Li alloy in Comparative Example 3 after tensile test. Detailed implementation manners

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. The following embodiments are merely examples for clearly illustrating the technical solutions of the present application and do not limit the present application.

[0036] A preparation method of a high-strength and high-ductility heat-resistant Al-Li alloy includes the following steps:

[0037] Step 1: According to the alloy composition, batching and melting are carried out, and ingots are obtained by casting. By mass percentage, the ingots include: Cu 1.8 - 2.5%, Li 0.8 - 1.2%, Mg 0.1 - 0.5%, Sc 0.1 - 0.2%, Zr 0.05 - 0.15%, other impurity elements ≤ 0.1%, and the balance is Al. After adding Sc and Zr elements, secondary L12 phases of Al3Sc, Al3Zr, and Al3(Sc,Zr) can be generated during the two-stage homogenization process, which plays a role in inhibiting dislocation recovery and recrystallization during the subsequent hot rolling process. If the content of Cu, Sc, or Zr elements is too high, a large number of insoluble primary Al8Cu4Sc phases, primary Al3Sc, Al3Zr, and Al3(Sc,Zr) phases will be formed, and these brittle phases will seriously endanger the plasticity of the alloy. After the components of this application are subjected to high-temperature solution treatment at a temperature only 7 - 12°C lower than the melting point, the brittle intermediate phases can be basically dissolved. The ingots are subjected to two-stage homogenization treatment. The temperature of the first-stage homogenization treatment is 400 - 420°C, and the holding time is 12 - 24 hours. The temperature of the second-stage homogenization treatment is 450 - 500°C, and the holding time is 15 - 30 hours. Then the ingots are peeled to obtain peeled ingots.

[0038] Step 2: The ingots are preheated at 450 - 470°C for 3 - 10 hours, and then preliminarily hot-rolled at 450 - 470°C. The reduction of hot rolling is 20 - 40%, and the number of rolling passes is 2 - 4. After hot rolling, the hot-rolled billets are oil-cooled and quenched to room temperature within 15 s to complete the medium-temperature solution treatment. Preliminary hot rolling can close the defects of the ingots, improve the quality of the ingots, and lay a foundation for subsequent medium-temperature rolling; oil-cooling quenching after hot rolling can play the role of medium-temperature solution.

[0039] Step 3: The rolled billets after medium-temperature solution treatment are subjected to the first aging treatment at a temperature of 100 - 120°C for 15 - 20 hours. This step can construct nano-aged phase Al2CuLi-T1 phase in the aluminum matrix.

[0040] Step 4: The rolled billets after the first aging treatment are heated to 220 - 250°C for holding, and the holding time is 1 - 3 hours. Medium-temperature hot rolling is carried out at 220 - 250°C, the reduction is 40 - 60%, and the number of rolling passes is 4 - 7. During medium-temperature hot rolling, the nano-T1 phase will further intensify the dislocation pile-up, hinder the slip and climb of dislocations, and cooperate with the L12 phase formed during the homogenization process to inhibit dislocation recovery and recrystallization, increase the deformation distortion energy, improve the nucleation driving force of subsequent high-temperature solution treatment, and refine the grain size. Medium-temperature rolling can improve the deformation ability of the rolled billets and reduce the risk of cracking compared with cold rolling; compared with hot rolling, it can weaken the thermal movement of dislocations, reduce dislocation annihilation, and is also beneficial to storing distortion energy.

[0041] Step 5: Perform solution heat treatment at a high temperature. The temperature of the solution heat treatment is relatively high, only 7 - 12 °C lower than the melting point of the Al - Li alloy. The melting point of the alloy can be measured by differential thermal analysis or calculated by thermal simulation software. Solution heat treatment at a temperature 7 - 12 °C lower than the melting point of the alloy can basically dissolve the primary brittle phase and dissolve as much Sc and Zr elements as possible. These slow - diffusion elements will reduce the diffusion rate of Cu elements and increase the coarsening resistance of the T1 phase, thereby improving the heat - resistant strength of the alloy. The solution temperature of the Al - Li alloy is usually selected to be 30 - 50 °C lower than the melting point to avoid grain coarsening and reduce the plasticity of the alloy. After the composite addition of Sc and Zr elements, the secondary L12 phase formed during the homogenization process can pin the grain boundary migration during the solution heat treatment at high temperature, inhibit grain growth, and finally ensure that the grain size of the alloy is less than 15 μm and a large number of sub - grain boundaries can be retained, increasing the grain boundary density.

[0042] Step 6: Perform cold drawing pre - deformation of 3 - 6%, and then perform the second aging treatment at a temperature of 150 - 165 °C for 15 - 25 hours to obtain the Al - Li alloy.

[0043] Example 1

[0044] A preparation method of a high - strength and high - ductility heat - resistant Al - Li alloy, comprising the following steps:

[0045] Step 1: Melt pure aluminum, pure lithium, pure magnesium, scandium - containing aluminum master alloy, and zirconium - containing aluminum master alloy under argon atmosphere and cast them into ingots. By mass percentage, the ingots include: Cu 2.4%, Li 1.0%, Mg 0.4%, Sc 0.19%, Zr 0.13%, other impurity elements 0.1%, and the balance is Al. Perform two - stage homogenization treatment on the ingots. The first - stage homogenization treatment is carried out at 400 °C for 12 hours, and the second - stage homogenization treatment is carried out at 450 °C for 15 hours. After the homogenization treatment, perform peeling treatment on the ingots to obtain peeled ingots.

[0046] Step 2: Pre - heat the peeled ingots at 450 °C for 5 hours, then perform hot rolling on the ingots at 450 °C with a reduction of 40% and 3 rolling passes. After hot rolling is completed, oil - quench the hot - rolled billet to room temperature within 15 s.

[0047] Step 3: Put the quenched rolled billet into an aging furnace at 120 °C for the first aging treatment for 15 hours to obtain a billet.

[0048] Step 4: Heat the billet to 250 °C and hold for 2 hours. Perform medium - temperature hot rolling at 250 °C with a reduction of 50% and 4 rolling passes.

[0049] Step 4: Use ThermoCalc software to calculate that the melting point of the alloy is 572 °C. After solution treatment at 563 °C for 1.5 hours, a solution-treated sample is obtained.

[0050] Step 5: Subject the solution-treated sample to 5% cold drawing pre-deformation, and then perform aging treatment at 165 °C for 25 hours to obtain an Al-Li alloy.

[0051] Perform long-term thermal exposure testing on the Al-Li alloy of this example. Specifically: After thermal exposure of the sample at 250 °C for 100 h, perform room-temperature tensile property testing. The mechanical properties of the sample are shown in Table 1.

[0052] Perform microstructure characterization on the Al-Li alloy of this example. The data of the grain size, grain boundary density after high-temperature solution treatment, and the size of the T1 phase after thermal exposure testing are shown in Table 1.

[0053] The TEM micrograph of the precipitation phase constructed in the matrix after the Al-Li alloy of this example undergoes "preliminary hot rolling - medium-temperature solution treatment - aging treatment" is as Figure 1 shown. The SEM micrograph of the Al-Li alloy of this example after high-temperature solution treatment is as Figure 2 (a). The IPF diagram and grain boundary distribution diagram of the Al-Li alloy of this example after high-temperature solution treatment are as Figure 3 (a1, a2). The TEM micrograph at the sub-grain boundary after long-term thermal exposure testing of this example is as Figure 4 shown. The TEM micrograph of the matrix precipitation phase of the Al-Li alloy of this example after thermal exposure testing is as Figure 5 (a). The fracture surface micrograph of the Al-Li alloy of this example after tensile testing is as Figure 6 (a, b).

[0054] Example 2

[0055] A preparation method of a high-strength and high-ductility heat-resistant Al-Li alloy, comprising the following steps:

[0056] Step 1: Melt pure aluminum, pure lithium, pure magnesium, aluminum scandium master alloy, and aluminum zirconium master alloy under argon conditions, and cast and mold to obtain an ingot. By mass percentage, the ingot includes: Cu 1.9%, Li 1.0%, Mg 0.3%, Sc 0.12%, Zr 0.08%, other impurity elements are 0.1%, and the balance is Al. Perform two-stage homogenization treatment on the ingot. The first-stage homogenization treatment is carried out at 420 °C for 15 hours, and the second-stage homogenization treatment is carried out at 460 °C for 18 hours. After homogenization treatment, perform peeling treatment on the ingot to obtain a peeled ingot.

[0057] Step 2: Preheat the peeled ingot at 460°C for 3 hours, then perform hot rolling on the ingot at 460°C with a reduction of 30% and 3 rolling passes. After hot rolling is completed, oil-cool the hot-rolled billet to room temperature within 15 s to complete medium-temperature solution treatment.

[0058] Step 3: Put the quenched rolled billet into an aging furnace at 110°C for the first aging treatment for 15 hours to obtain a billet.

[0059] Step 4: Heat the billet to 230°C and hold for 2 hours. Perform medium-temperature hot rolling at 230°C with a reduction of 55% and 5 rolling passes.

[0060] Step 5: Use ThermoCalc software to calculate that the melting point of the alloy is 588°C. Perform high-temperature solution treatment on it at 578°C for 1.5 hours to obtain a solution sample.

[0061] Step 6: Perform 6% cold drawing pre-deformation on the solution sample, and then perform aging treatment at 160°C for 25 hours to obtain an Al-Li alloy.

[0062] Perform long-term thermal exposure test on the Al-Li alloy of this example. Specifically: after the sample is thermally exposed at 250°C for 100 h, perform room-temperature tensile property test. The mechanical properties of the sample are shown in Table 1.

[0063] Perform microstructure characterization on the Al-Li alloy of this example. The data of the grain size, grain boundary density after high-temperature solution treatment and the size of T1 phase after thermal exposure test are shown in Table 1.

[0064] The SEM photograph of the Al-Li alloy of this example after high-temperature solution treatment is as Figure 2 (b) shown.

[0065] Comparative Example 1

[0066] An Al-Li alloy Al-2.5Cu-1.1Li-0.38Mg without adding Sc and Zr elements.

[0067] Adopt conventional hot working and heat treatment processes, including the following preparation steps: (1) Melting under argon protection and casting with a metal mold to obtain an ingot. (2) Homogenize the ingot at 400°C for 17 hours, then homogenize it at 470°C for 22 hours, and then peel the ingot. (3) Preheat the ingot at 460°C for 3 hours, and then perform hot rolling with a reduction of 90% at 430°C with 6 rolling passes. (4) Solutionize the rolled sample at 510°C for 1 hour. (5) Perform 5% cold drawing pre-deformation on the solution sample, and then age it at 165°C for 20 hours.

[0068] The aluminum-lithium alloy of this comparative example was subjected to long-term thermal exposure tests. Specifically: after the samples were thermally exposed at 250 °C for 100 h, room-temperature tensile property tests were carried out. The mechanical properties of the samples are shown in Table 1.

[0069] Microstructure characterization was carried out on the aluminum-lithium alloy of this comparative example. The data of the grain size, grain boundary density after high-temperature solution treatment, and the size of the T1 phase after thermal exposure tests are shown in Table 1.

[0070] The IPF diagram and grain boundary distribution diagram of the aluminum-lithium alloy of this comparative example after thermal exposure tests are as shown in Figure 3 (b1, b2). The TEM micrographs of the matrix precipitation phases of the aluminum-lithium alloy of this comparative example after thermal exposure tests are as shown in Figure 5 (b). The fracture surface micrographs of the aluminum-lithium alloy of this comparative example after tensile tests are as shown in Figure 6 (c).

[0071] Comparative Example 2

[0072] The material of this comparative example is Al-2.3Cu-0.9Li-0.4Mg-0.17Sc-0.12Zr, but conventional hot working and heat treatment processes are adopted. The preparation steps include: (1) melting under argon protection and casting with a conventional metal mold to obtain an ingot. (2) The ingot was homogenized at 420 °C for 15 hours, then homogenized at 460 °C for 18 hours, and then the ingot was peeled to obtain a peeled ingot. (3) The peeled ingot was preheated at 460 °C for 3 hours, and then hot rolled at 460 °C with a reduction of 90%, and the number of rolling passes was 6 passes. (4) The rolled samples were solution treated at 525 °C for 1.5 hours. (5) The solution-treated samples were pre-deformed by 4% cold drawing and then aged at 160 °C for 25 hours.

[0073] The aluminum-lithium alloy of this comparative example was subjected to long-term thermal exposure tests. Specifically: after the samples were thermally exposed at 250 °C for 100 h, room-temperature tensile property tests were carried out. The mechanical properties of the samples are shown in Table 1.

[0074] Microstructure characterization was carried out on the aluminum-lithium alloy of this comparative example. The data of the grain size, grain boundary density after high-temperature solution treatment, and the size of the T1 phase after thermal exposure tests are shown in Table 1.

[0075] The SEM micrographs of the aluminum-lithium alloy of this comparative example after solution treatment are as shown in Figure 2 (c). The IPF diagram and grain boundary diagram of the aluminum-lithium alloy of this comparative example after high-temperature solution treatment are as shown in Figure 3 (c1, c2). The TEM micrographs of the precipitation phases in the matrix of the aluminum-lithium alloy of this comparative example after thermal exposure tests are as shown in Figure 5 (c). The fracture surface micrographs of the aluminum-lithium alloy of this comparative example after tensile tests are as shown in Figure 6 (d).

[0076] Comparative Example 3

[0077] The material of this comparative example is Al-2.4Cu-1Li-0.4Mg-0.15Sc, without adding Zr element. It adopts the hot working process of "preliminary hot rolling - solution treatment at medium temperature - aging treatment - medium temperature rolling" and the solution treatment process at high temperature 10°C below the melting point, including the following preparation steps: (1) Melting under argon protection and casting ingots with conventional metal molds. (2) Homogenizing the ingots at 420°C for 15 hours, then homogenizing at 460°C for 18 hours, and then skiving the ingots to obtain skived ingots. (3) Preheating the ingots at 460°C for 3 hours, and then performing hot rolling with a reduction of 30% at 460°C, with 3 rolling passes. After hot rolling is completed, the hot-rolled billet is oil quenched to room temperature within 15 s to complete the solution treatment at medium temperature. (4) Putting the rolled billet into an aging furnace at 120°C for 15 hours for aging treatment. (5) Preheating the aged rolled billet at 250°C for 2 hours, and then performing medium temperature rolling with a reduction of 50% at 250°C, with 5 rolling passes. (6) Using ThermoCalc software to calculate that the melting point of the alloy is 575°C, and solution treating the rolled sample at 565°C for 1.5 hours. (7) Subjecting the solution-treated sample to 5% cold tensile deformation, and then aging at 155°C for 25 hours.

[0078] The aluminum-lithium alloy of this comparative example was subjected to long-term thermal exposure test. Specifically: After the sample was thermally exposed at 250°C for 100 h, room temperature tensile property test was carried out. The mechanical properties of the sample are shown in Table 1.

[0079] Microstructure characterization was carried out on the aluminum-lithium alloy of this comparative example. The data of grain size, grain boundary density after high temperature solution treatment and T1 phase size after thermal exposure test are shown in Table 1.

[0080] The IPF diagram and grain boundary diagram of the aluminum-lithium alloy of this comparative example after high temperature solution treatment are as Figure 3 (d1, d2) shown. The fracture surface photograph of the aluminum-lithium alloy of this comparative example after tensile test is as Figure 6 (e) shown.

[0081] Comparative Example 4

[0082] The material of this comparative example is Al-3.5Cu-1Li-0.3Mg-0.28Sc-0.21Zr. The hot working process of "preliminary hot rolling - solution treatment at medium temperature - aging treatment - medium temperature rolling" and the solution treatment process at a high temperature 10°C below the melting point are adopted, including the following preparation steps: (1) Melting under argon protection and casting ingots with a conventional metal mold. (2) Homogenizing the ingots at 420°C for 17 hours, then homogenizing at 460°C for 23 hours, and then skimming the ingots to obtain skinned ingots. (3) Preheating the skinned ingots at 460°C for 5 hours, then performing hot rolling with a reduction of 30% at 460°C, and the number of rolling passes is 3. After the last hot rolling pass is completed, the hot rolled billet is oil quenched to room temperature within 15 s to complete the solution treatment at medium temperature. (4) Putting the quenched rolled piece into an aging furnace at 110°C for 15 hours for aging treatment. (5) Preheating the rolled piece after aging at 250°C for 2 hours, and then performing medium temperature rolling with a reduction of 40% at 250°C, and the number of rolling passes is 4. (6) Using ThermoCalc software to calculate that the melting point of the alloy is 550°C, and solution treating the rolled sample at 542°C for 1 hour. (7) Subjecting the solution treated sample to 6% cold drawing deformation, and then aging at 165°C for 22 hours.

[0083] The long-term thermal exposure test was carried out on the aluminum-lithium alloy of this comparative example. Specifically: after the sample was thermally exposed at 250°C for 100 h, the tensile properties at room temperature were tested. The mechanical properties of the sample are shown in Table 1.

[0084] Microstructure characterization was carried out on the aluminum-lithium alloy of this comparative example. The data of the grain size, grain boundary density after high-temperature solution treatment and the size of the T1 phase after thermal exposure test are shown in Table 1.

[0085] The SEM photograph of the aluminum-lithium alloy of this comparative example after high-temperature treatment is as Figure 2 (d) shown. The TEM photograph of the matrix precipitation phase of the aluminum-lithium alloy of this comparative example after thermal exposure test is as Figure 5 (d) shown.

[0086] Table 1

[0087]

[0088] Combined with the measured data in Table 1, it can be seen that after the long-term thermal exposure test at 250°C for 100 hours, Examples 1 and 2 have better strength, plasticity and strength-plasticity product compared with the alloys of Comparative Examples 1-4. This is because the T1 phase in the alloy of the example has better coarsening resistance, smaller grain size and higher grain boundary density. Combined with Figure 1 it can be known that "preliminary hot rolling - solution treatment at medium temperature - aging treatment" can construct dense nano-sized T1 phases in the matrix, with an average size of 18 nm. Combined with Figure 2It can be seen from (a,b) that through reasonable design of the Cu, Sc, and Zr components and a solution treatment process at a high temperature only 7-12 °C below the melting point, the brittle phases in the matrix can be basically dissolved. Combining with Figure 4 It can be seen that after thermal exposure, the grain boundary precipitation phases can precipitate by aggregating at the sub-grain boundaries. Since the grain boundary density of the examples is very high, it can dilute the damage to the grain boundaries caused by the grain boundary precipitation phases and the segregation of Li elements. Combining with Figure 6 It can be seen from (a,b) that the fracture surface of the example shows the characteristics of ductile fracture, and dense and fine dimples can be seen from the local enlarged view.

[0089] The comparison between Comparative Example 1 and Examples 1 and 2 demonstrates the improvement of the alloy's heat-resistant strength, heat-resistant plasticity, and strength-ductility product by the composition design and hot working and heat treatment processes of the examples. Combining with Figure 3 It can be seen from (b1,b2) that the larger grain size and lower grain boundary density lead to the low elongation of this comparative example. Combining with Figure 5 It can be seen from (b) that the severely coarsened T1 phase results in the lower tensile strength of this comparative example. Combining with Figure 6 It can be seen from (c) that the fracture surface of this comparative example shows the characteristics of standard brittle intergranular fracture. Generally speaking, compared with Example 1, the strength-ductility product of this comparative example is about 67.2% lower.

[0090] The comparison between Comparative Example 2 and Examples 1 and 2 shows that the composition design of the examples needs to be combined with hot working and heat treatment processes to achieve better results. Combining with Figure 2 It can be seen from (c) that when the solution treatment temperature at high temperature is not high enough, some brittle intermediate phases will remain in the matrix, damaging the plasticity; combining with Figure 3 It can be seen from (c) that when the hot working process of "preliminary hot rolling - solution treatment at medium temperature - aging treatment - hot rolling at medium temperature" is not used, the grain size after solution treatment will be significantly larger than that of the examples, and the grain boundary density is lower than that of the examples, which will also lead to a decrease in plasticity. Combining with Figure 6 It can be seen from (d) that the brittle fracture characteristics are also relatively obvious in the fracture surface of this comparative example. In addition, combining with Figure 2 (c) and Figure 5 (c) It can be seen that the undissolved brittle phases will waste a part of Sc and Zr elements, weakening the inhibition effect on the coarsening of the T1 phase, which reduces the heat-resistant strength of this comparative example. Generally speaking, compared with Example 1, the strength-ductility product of this comparative example is about 39.2% lower.

[0091] The comparison between Comparative Example 3 and Examples 1 and 2 shows that only by adding Sc and Zr elements in combination can better results be achieved. Combining with Figure 3 It can be seen from (d1,d2) that when only Sc element is added, the grain size of this comparative example is larger and there are very few remaining sub-grain boundaries. This makes the grain boundary density of this comparative example decrease by 33.6% and the elongation decrease by about 24.7% compared with Example 1. Combining with Figure 6As can be seen from (e), the fracture surface of this comparative example exhibits obvious characteristics of brittle fracture.

[0092] The comparison between Comparative Example 4 and Examples 1 and 2 shows that the elements Cu, Sc, and Zr need to be added according to the requirements of the examples to achieve better effects. Combining Figure 2 As can be seen from (d), excessive contents of Cu, Sc, and Zr generate a large number of brittle phases in the alloy matrix. Even after high-temperature solution treatment, these brittle phases cannot be dissolved, seriously damaging the plasticity of the alloy. Compared with Example 1, the elongation of this comparative example is reduced by approximately 49.4%.

[0093] It should be noted that any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this application by those of ordinary skill in the art to which this technology pertains shall be included within the protection scope of this application.

Claims

1. A method for preparing a high-strength and high-plasticity heat-resistant aluminum-lithium alloy, characterized in that: The following steps are involved: Step 1: smelting the ingredients according to the alloy composition, casting and forming an ingot, wherein the ingot includes, by mass percentage, Cu 1.8-2.5%, Li 0.8-1.2%, Mg 0.1-0.5%, Sc 0.1-0.2%, Zr 0.05-0.15%, other impurity elements ≤0.1%, and the balance is Al, performing a two-stage homogenization treatment on the ingot, and then performing a peeling treatment on the ingot to obtain a peeled ingot; Step 2, the peeled ingot is preliminarily hot rolled at 450-470° C., the reduction of the hot rolling is 20-40%, the number of rolling passes is 2-4 times, after the hot rolling is completed, the hot rolled billet is oil-quenched to room temperature within 15 seconds to complete the medium-temperature solution treatment; Step 3, performing a first aging treatment on the rolled slab after the medium-temperature solution treatment, wherein the temperature of the first aging treatment is 100-120° C. and the treatment time is 15-20 hours; Step 4, heating the rolled billet after the first aging treatment to 220-250° C. for insulation, and performing medium-temperature hot rolling at 220-250° C., wherein the reduction of the medium-temperature hot rolling is 40-60%, and the number of rolling passes is 4-7 times; Step 5, performing high temperature solution treatment, wherein the temperature of the high temperature solution treatment is 7-12°C lower than the melting point of the aluminum-lithium alloy; Step six, performing 3-6% cold stretching pre-deformation, and then performing a second aging treatment to obtain the aluminum-lithium alloy.

2. The method for preparing a high-strength and high-ductility heat-resistant aluminum-lithium alloy according to claim 1, characterized in that: In the two-stage homogenization treatment, the temperature of the first stage homogenization treatment is 400~420℃, the insulation time is 12~24 hours, and the temperature of the second stage homogenization treatment is 450~500℃, the insulation time is 15~30 hours.

3. The method for preparing a high-strength-plasticity heat-resistant aluminum-lithium alloy according to claim 1, characterized in that: Before the initial hot rolling, the ingot is preheated at 450-470°C for 3-10 hours.

4. The method for preparing a high-strength and high-ductility heat-resistant aluminum-lithium alloy according to claim 1, characterized in that: The insulation time of step 4 is 1 to 3 hours.

5. The method for preparing a high-strength-ductility-heat-resistant aluminum-lithium alloy according to claim 1, characterized in that: The time of high temperature solution treatment is 1 to 1.5 hours.

6. The method for preparing a high-strength-plasticity heat-resistant aluminum-lithium alloy according to claim 1, characterized in that: The temperature of the second aging treatment is 150~165℃, and the treatment time is 15~25 hours.

7. A high-strength, high-plasticity, heat-resistant aluminum-lithium alloy, characterized in that: It is the aluminum-lithium alloy obtained according to the preparation method of the high-strength-plasticity heat-resistant aluminum-lithium alloy according to any one of claims 1 to 6. After a long-term heat exposure test at 250°C for 100 hours, its tensile strength is not less than 346MPa, its elongation is not less than 15.6%, and its strength-plasticity product is not less than 5397.6MPa%.

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