Aluminum-lithium alloy heat treatment method and ribbed cylindrical shell

Abstract

The present invention belongs to the technical field of aerospace material preparation, and specifically relates to a heat treatment method for an aluminum-lithium alloy and a ribbed cylindrical shell. The aluminum-lithium alloy is heated in stages to 400-440°C, maintained at this temperature, then placed at 500-510°C, maintained at this temperature, and cooled to room temperature. During the staged heating, the heating rate of the aluminum-lithium alloy is controlled to be no more than 1°C / min. The staged heating is divided into at least three stages, and the temperature is maintained after each heating is completed. The temperature difference between the insulation temperatures of each stage is 50-70°C, and the insulation temperature after the first heating is 230-250°C. The present invention significantly reduces grain size while improving product strength and elongation.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerospace material preparation, and in particular relates to an aluminum-lithium alloy heat treatment method and a ribbed cylindrical shell. Background Art

[0002] With the development of the aerospace industry, new challenges have been posed to the various service indicators of space launch vehicle components. There is an urgent need to improve the performance of the shell components of the new generation of space launch vehicles in order to enhance the structural integrity and carrying capacity.

[0003] The shell, the primary structure of a launch vehicle, bears loads such as torsion, axial compression, and shear, and accounts for approximately 54%-67% of the rocket's dry weight. Using advanced forming and manufacturing techniques, combined with a high-strength Al-Cu-Li alloy, significantly improves component performance, reduces structural weight, and enhances the rocket's carrying capacity.

[0004] Grain refinement strengthening is an effective method to improve the strength and plasticity of materials. Refining the grain size of components through deformation can increase the number and area of grain boundaries in the material, coordinate the overall deformation and thus improve the strength and plasticity of the component. Therefore, it is particularly important to prepare fine-grained structure through deformation and heat treatment processes. However, in order to further improve the performance of Al-Cu-Li alloy components, it is often necessary to perform solution treatment on the components to form the supersaturated solid solution required for precipitation strengthening. However, under the action of the energy storage of forming dislocations, the alloy undergoes a high degree of static recrystallization at high temperature, and the grains are easily grown, thereby limiting the performance of the component.

[0005] Existing patents CN115896652B, CN108034909B, and CN111057975B have detailed methods for achieving fine grains through deformation. In comparison, existing technologies involve plate rolling, focusing on controlling the deformation process. However, maintaining fine grains during the solution stage of formed, integral cylindrical shell components requires urgent research and development. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an aluminum-lithium alloy heat treatment method and a ribbed cylindrical shell, which can significantly reduce the grain size and improve the product strength and elongation.

[0007] An embodiment of the present invention provides a heat treatment method for an aluminum-lithium alloy, comprising heating the aluminum-lithium alloy in stages to 400-440°C, holding the temperature, then placing the alloy at 500-510°C (performed by transfer, with a fast heating rate of greater than 100°C / min, generally greater than 200°C / min), holding the temperature, and cooling the alloy to room temperature.

[0008] During the segmented heating, the heating rate of the aluminum-lithium alloy is controlled to be no more than 1°C / min. The segmented heating is divided into at least three sections. After each heating is completed, the temperature is kept warm. The temperature difference between each insulation temperature is 50-70°C. The insulation temperature after the first heating is 230-250°C.

[0009] Preferably, the first heating is from room temperature to 240°C.

[0010] Preferably, the temperature difference between each insulation temperature section is 60°C.

[0011] Preferably, the staged heating is divided into four stages.

[0012] Preferably, when heating in stages, the holding time after heating is completed is 7-9 hours.

[0013] Preferably, the aluminum-lithium alloy is heated to 420° C. in stages, kept warm, then placed at 505° C., kept warm for 1 hour, and cooled to room temperature by water quenching.

[0014] Preferably, the material is placed at 500-510° C., kept warm, cooled to room temperature, and then subjected to aging treatment.

[0015] Preferably, the aging treatment is carried out at 160° C. for 65 hours.

[0016] Preferably, the aluminum-lithium alloy is a ribbed cylindrical shell obtained by hot deformation through extrusion.

[0017] An embodiment of the present invention provides a ribbed cylindrical shell, which is obtained by adopting the aluminum-lithium alloy heat treatment method.

[0018] The beneficial effects of the present invention are that deformation is currently one of the main means of obtaining fine grains. However, in the plastic deformation process, in addition to the work consumed during deformation, a portion of energy is stored in the form of elastic strain and increased defects such as dislocations and vacancies in the alloy crystals, and the lower the forming temperature, the greater the deformation amount, and the higher the stored energy. Integrally forming the cylindrical shell and producing fine grains in a point-by-point high-pressure form often requires a large deformation amount, which has led to a relatively high energy storage accumulated in the deformed cylindrical shell. Therefore, the cylindrical shell component will undergo obvious static recrystallization during high-temperature solution treatment. Under the catalysis of uneven strain and stored energy, the grains will also grow abnormally.

[0019] This invention provides a method for effectively suppressing abnormal grain growth during high-temperature heat treatment of deformed components. It proposes a multi-step, dual-heating-rate annealing process. Through this multi-step, medium- and low-temperature annealing process, the static recrystallization dynamics are reduced under the influence of the temperature field, suppressing the formation of coarse grains and maintaining the fine grains of the cylindrical shell component during forming.

[0020] This invention utilizes a multi-stage recovery annealing followed by a rapid solution treatment process. This process eliminates the stored energy of thermal deformation during the step-by-step recovery annealing process, resulting in a uniform energy storage pattern within the ribbed cylindrical shell. Subsequent rapid high-temperature solution treatment further suppresses uneven grain growth. This effectively enhances the thermal stability of the extruded cylindrical shell's grain structure, inhibiting recrystallization and the formation of coarse grains during the high-temperature solution stage. This provides excellent conditions for increasing the strength and ductility of aluminum-lithium alloy components and reducing anisotropy.

[0021] Experimental results show that after multi-stage recovery annealing of aluminum-lithium alloy cylindrical shells using the heat treatment method provided by this invention, the average grain size of the cylindrical shells is only 20μm, while the average grain size of the untreated alloy is as high as 1500μm. The cylindrical shells without this process have a final T6 yield strength of 499MPa, a tensile strength of 545MPa, and an elongation of 9.5%. After treatment with this process, the yield strength and tensile strength of the cylindrical shell components increased to 525MPa and 580MPa, respectively, and the elongation increased to 12.2%.

[0022] While other heat treatment processes, such as two-stage heating, rapid heating followed by slow heating to solution temperature, or slow heating, can improve strength and elongation to a certain extent, the present invention achieves greater strength and elongation improvements and smaller grain sizes compared to conventional heat treatment methods. The process of the present invention can significantly suppress the formation of coarse grains, improving the service performance of aluminum-lithium alloy components. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a real picture of the ribbed cylinder shell of the present invention before heat treatment.

[0024] Figure 2 This is the grain structure diagram of the ribbed cylinder shell before heat treatment of the present invention.

[0025] Figure 3 This is the grain structure diagram obtained after heat treatment of Comparative Example 1 of the present invention.

[0026] Figure 4 This is the grain structure diagram obtained after heat treatment of Comparative Example 2 of the present invention.

[0027] Figure 5 This is the grain structure diagram obtained after heat treatment of Comparative Example 3 of the present invention.

[0028] Figure 6 This is the grain structure diagram obtained after heat treatment of Comparative Example 4 of the present invention.

[0029] Figure 7 This is the grain structure diagram obtained after heat treatment of Comparative Example 5 of the present invention.

[0030] Figure 8 This is the grain structure diagram obtained after heat treatment of Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to specific examples. Example 1

[0032] The alloy grade used in the embodiment of the present invention is 2195 alloy, and the chemical composition by mass percentage is Fe<0.07%, Cu: 4.10%, Li: 1.10%, Mn: 0.20%, Zn: 0.2%, Mg: 0.40%, Zr: 0.11%, Ag: 0.40%, and the rest is Al.

[0033] The object of this embodiment is a ribbed cylindrical shell obtained by rotary extrusion, the forming temperature is 420°C, the dimensions of the cylindrical shell are inner diameter φ=315mm, wall thickness t=3mm, and length d=300mm.

[0034] The ribbed shell is heat treated, and the heat treatment process is as follows:

[0035] 1) Heating from room temperature to 240°C at a rate of 1°C / min and holding for 8 hours;

[0036] 2) Heating from 240°C to 300°C at a rate of 1°C / min and holding for 8 hours;

[0037] 3) Heating from 300°C to 360°C at a rate of 1°C / min and holding for 8 hours;

[0038] 4) Heating from 360°C to 420°C at a rate of 1°C / min and holding for 8 hours;

[0039] 5) Place the ribbed shell after treatments 1) to 4) in a 505°C heating furnace (the furnace is first heated to 505°C, and then the ribbed shell is placed in the heating furnace. In this way, a ribbed shell with a thickness of about 3 mm can be heated through in just 1 minute, equivalent to a heating rate of 480°C / min), hold the heat for 1 hour, and then water quench to room temperature to form a supersaturated solid solution.

[0040] 6) The heat-treated ribbed shell is aged at 160°C for 65 hours.

[0041] Comparative Example 1

[0042] The ribbed shell was not subjected to any annealing treatment. It was directly heated to 505°C at a slow heating rate of 1°C / min, then kept at 505°C for 1 hour, and then water quenched to room temperature to form a supersaturated solid solution; the ribbed shell was then aged at 160°C for 65 hours.

[0043] Comparative Example 2

[0044] The ribbed shell was annealed at 240°C and 420°C for 8 hours, with a slow heating rate of 1°C / min, and then rapidly heated to 505°C (directly placed in a heating furnace at 505°C) for 1 hour of solution treatment. The heat treatment process is as follows:

[0045] 1) Heating from room temperature to 240°C at a rate of 1°C / min and holding for 8 hours;

[0046] 2) Heat from 240°C to 420°C at a rate of 1°C / min and hold for 8 h.

[0047] The subsequent steps are the same as steps 5)-6) of Example 1.

[0048] Comparative Example 3

[0049] The ribbed shell was annealed at 240℃, 300℃, 360℃ and 420℃ for 8 hours, rapidly heated, and then solution treated at 505℃ for 1 hour at a slow heating rate of 1℃ / min. The heat treatment process is as follows:

[0050] 1) Heating from room temperature to 240°C at a rate of ≥100°C / min, and holding for 8 hours;

[0051] 2) Heating from 240℃ to 300℃, heating rate ≥ 100℃ / min, keeping warm for 8h;

[0052] 3) Heating from 300°C to 360°C at a rate of ≥100°C / min, and holding for 8 hours;

[0053] 4) Heat from 360°C to 420°C at a rate of ≥100°C / min and hold for 8 hours;

[0054] The above-mentioned heating methods are all to directly place the ribbed cylinder shell in a heating furnace at the target temperature. For example, in step 1), the temperature is raised from room temperature to 240°C by directly placing the ribbed cylinder shell at room temperature in a 240°C heating furnace. Directly heated at the target temperature, 3mm aluminum alloy material can be heated through on one side in 1 minute. Therefore, the time required for the ribbed cylinder shell to rise from room temperature to 240°C is within 1 minute, and the heating rate is not less than 100°C / min.

[0055] 5) The ribbed shell after treatments 1) to 4) was heated from 420°C to 505°C at a heating rate of 1°C / min, kept at that temperature for 1 h, and then quenched in water to room temperature to form a supersaturated solid solution.

[0056] 6) The heat-treated ribbed shell is aged at 160°C for 65 hours.

[0057] Comparative Example 4

[0058] The ribbed shell was annealed at 240℃, 300℃, 360℃ and 420℃ for 8 hours, and then solution treated at 505℃ for 1 hour, all with a slow heating rate of 1℃ / min. The heat treatment process is as follows:

[0059] 1) Heating from room temperature to 240°C at a rate of 1°C / min and holding for 8 hours;

[0060] 2) Heating from 240°C to 300°C at a rate of 1°C / min and holding for 8 hours;

[0061] 3) Heating from 300°C to 360°C at a rate of 1°C / min and holding for 8 hours;

[0062] 4) Heating from 360°C to 420°C at a rate of 1°C / min and holding for 8 hours;

[0063] 5) The ribbed shell after treatments 1) to 4) was heated from 420°C to 505°C at a heating rate of 1°C / min, kept at that temperature for 1 h, and then quenched in water to room temperature to form a supersaturated solid solution.

[0064] 6) The heat-treated ribbed shell is aged at 160°C for 65 hours.

[0065] Comparative Example 5

[0066] The ribbed shell was annealed at 240℃, 300℃, 360℃ and 420℃ for 8 hours, with a rapid heating rate of 20℃ / min, and then rapidly heated to 505℃ for 1 hour for solution treatment. The specific heat treatment process is as follows:

[0067] 1) Heating from room temperature to 240°C at a rate of 20°C / min and holding for 8 hours;

[0068] 2) Heating from 240°C to 300°C at a rate of 20°C / min and holding for 8 hours;

[0069] 3) Heating from 300°C to 360°C at a rate of 20°C / min and holding for 8 hours;

[0070] 4) Heating from 360°C to 420°C at a rate of 20°C / min and holding for 8 hours;

[0071] 5) Place the ribbed shell after treatments 1) to 4) in a 505°C heating furnace (directly transfer into a 505°C heating furnace), keep warm for 1 hour, and then water quench to room temperature to form a supersaturated solid solution.

[0072] 6) The heat-treated ribbed shell is aged at 160°C for 65 hours.

[0073] The materials and forming processes used in all comparative examples 1-5 are the same as those in Example 1. The differences in grain structure and mechanical properties are shown in the figure below. Figure 2-8 and as shown in Table 1.

[0074] Figure 3-7 The grain size of each comparative example is shown in FIG. 1 , and it can be seen that the average grain size is larger. The grain size of Example 1 is significantly smaller than the grain size of each comparative example.

[0075] Table 1 Differences in microstructure and mechanical properties of various grains

[0076]

[0077] It can be seen from Table 1 that the grain size of Example 1 is significantly smaller than that of the comparative examples, and the product of Example 1 has significant improvements in tensile strength, yield strength and elongation.

[0078] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of protection of the present application is limited to these examples. In line with the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0079] The one or more embodiments of this application are intended to encompass 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 of this application should be included in the scope of protection of this application.

Claims

1. A method for heat treatment of aluminum-lithium alloy, characterized in that: The aluminum-lithium alloy is heated to 400-440°C in stages, kept warm, and then placed at 500-510°C, wherein the placing at 500-510°C is performed by transfer, with a heating rate greater than 100°C / min, kept warm, and cooled to room temperature; During the segmented heating, the heating rate of the aluminum-lithium alloy is controlled to be no more than 1°C / min. The segmented heating is divided into at least three sections. After each heating is completed, the temperature is kept warm. The temperature difference between each insulation temperature is 50-70°C. The insulation temperature after the first heating is 230-250°C.

2. The aluminum-lithium alloy heat treatment method according to claim 1, wherein: The first heating is from room temperature to 240°C.

3. The aluminum-lithium alloy heat treatment method according to claim 1 or 2, characterized in that: The temperature difference between each insulation temperature section is 60℃.

4. The aluminum-lithium alloy heat treatment method according to claim 1 or 2, characterized in that: The staged heating is divided into four stages.

5. The aluminum-lithium alloy heat treatment method according to claim 1 or 2, characterized in that: When heating in stages, the holding time after heating is completed is 7-9 hours.

6. The aluminum-lithium alloy heat treatment method according to claim 1 or 2, characterized in that: The aluminum-lithium alloy was heated to 420°C in stages, kept warm, then placed at 505°C, kept warm for 1 hour, and cooled to room temperature by water quenching.

7. The aluminum-lithium alloy heat treatment method according to claim 1 or 2, characterized in that: Place at 500-510℃, keep warm, cool to room temperature, and then carry out aging treatment.

8. The aluminum-lithium alloy heat treatment method according to claim 7, wherein: The aging treatment is carried out at 160° C. for 65 hours.

9. The aluminum-lithium alloy heat treatment method according to claim 1 or 2, characterized in that: The aluminum-lithium alloy is a ribbed cylindrical shell obtained by hot deformation through rotary extrusion.

10. A ribbed cylindrical shell, characterized in that: The aluminum-lithium alloy is obtained by the aluminum-lithium alloy heat treatment method according to any one of claims 1 to 9.

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