Aluminum-lithium alloy heat treatment method and ribbed cylindrical shell

Abstract

The invention belongs to the technical field of aerospace material preparation, and particularly relates to an aluminum-lithium alloy heat treatment method and a ribbed cylindrical shell, the aluminum-lithium alloy is heated to 400-440 DEG C in a segmented mode, heat preservation is conducted, then the aluminum-lithium alloy is placed at 500-510 DEG C, heat preservation is conducted, and the aluminum-lithium alloy is cooled to the room temperature; during segmented heating, the heating rate of the aluminum-lithium alloy is controlled to be not larger than 1 DEG C / min, segmented heating is at least divided into three segments, heat preservation is conducted after each time of heating is completed, the interval temperature difference of the heat preservation temperature of each segment is 50-70 DEG C, and the heat preservation temperature after the first time of heating is 230-250 DEG C; the grain size is remarkably reduced, and meanwhile the product strength and the ductility are improved.

Description

Technical Field

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

[0002] With the development of the aerospace industry, new challenges have been posed to the service indicators of aerospace carrier components. There is an urgent need to improve the performance of the barrel shell components of the new generation of aerospace carrier rockets to enhance the structural integrity and carrying capacity.

[0003] As the main structure of the carrier rocket, the barrel shell bears loads such as the torsion, axial compression, and shear of the rocket body, accounting for about 54% - 67% of the total dry weight of the rocket. By adopting advanced forming manufacturing technology and combining high-strength Al-Cu-Li alloy, the component performance can be significantly improved, the structural weight can be reduced, and the carrying capacity of the rocket can be enhanced.

[0004] Fine grain strengthening is a method that can effectively improve the strength and plasticity of materials. By deforming to refine the grain size of components, the number and area of grain boundaries in the material can be increased, and the overall deformation can be coordinated to improve the strength and plasticity of components. Therefore, it is particularly important to prepare fine grain structures through deformation and heat treatment processes. However, in order to further improve the performance of Al-Cu-Li alloy components, solution treatment is often required to form a supersaturated solid solution required for precipitation strengthening. However, under the action of stored energy of forming dislocations, the alloy undergoes a relatively high degree of static recrystallization at high temperatures, and the grains are easily grown, thus limiting the performance of components.

[0005] Existing patents CN115896652B, CN108034909B, and CN111057975B have already introduced in detail the methods for obtaining fine grains through deformation means. Comparatively, the deformation involved in the existing technology is plate rolling, and the focus is on regulating the deformation process. However, the method for maintaining fine grains in the solution stage of the integral barrel shell components in forming manufacturing needs to be studied and solved urgently. Summary of the Invention

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

[0007] An embodiment of the present invention provides a heat treatment method for aluminum-lithium alloy, which heats the aluminum-lithium alloy in segments to 400 - 440 °C, holds the temperature, and then places it at 500 - 510 °C (by means of transfer, with a fast heating rate, the heating rate is greater than 100 °C / min, generally greater than 200 °C / min), holds the temperature, and cools to room temperature; During the stepwise heating, the heating rate of the aluminum-lithium alloy is controlled not to exceed 1 °C / min. The stepwise heating is divided into at least three stages, and heat preservation is carried out after each heating. The temperature difference between the heat preservation temperatures of each stage is 50-70 °C, and the heat preservation temperature after the first heating is 230-250 °C.

[0008] Preferably, the first heating is from room temperature to 240 °C.

[0009] Preferably, the temperature difference between the heat preservation temperatures of each stage is 60 °C.

[0010] Preferably, the stepwise heating is divided into four stages.

[0011] Preferably, during the stepwise heating, the heat preservation time after heating is 7-9 h.

[0012] Preferably, the aluminum-lithium alloy is stepwise heated to 420 °C, heat-preserved, then placed at 505 °C, heat-preserved for 1 h, and water-quenched and cooled to room temperature.

[0013] Preferably, it is placed at 500-510 °C, heat-preserved, and after cooling to room temperature, aging treatment is carried out.

[0014] Preferably, the aging treatment is heat preservation at 160 °C for 65 h.

[0015] Preferably, the aluminum-lithium alloy is a ribbed barrel shell obtained by rotary extrusion hot deformation.

[0016] An embodiment of the present invention provides a ribbed barrel shell obtained by using the above-mentioned heat treatment method of aluminum-lithium alloy.

[0017] The beneficial effect of the present invention is that deformation is one of the main means to obtain fine grains at present. However, during the plastic deformation process, in addition to the work consumed during deformation, a part of the energy is stored in the form of elastic strain and increasing defects such as alloy crystal dislocations and vacancies. Moreover, the lower the forming temperature and the greater the deformation amount, the higher the stored energy. Overall forming and manufacturing the barrel shell and generating fine grains in the form of point-by-point high pressure often require a large deformation amount, which leads to a relatively high stored energy in the deformed barrel shell. Therefore, obvious static recrystallization will occur in the barrel shell component during high-temperature solution treatment. Under the catalysis of inhomogeneous strain and stored energy, abnormal grain growth will also occur in the grains.

[0018] The present invention provides a method for effectively suppressing abnormal grain growth in deformed components during high-temperature heat treatment, and proposes a multi-step double-heating-rate annealing treatment process. Through a step-by-step multi-step medium and low-temperature annealing process, the driving force of static recrystallization is reduced under the action of the temperature field, the formation of coarse grains is suppressed, and the barrel shell component is allowed to maintain the fine grains during forming.

[0019] The present invention designs a multi-stage recovery annealing followed by rapid solution treatment process, which eliminates the stored energy of thermal deformation during the step-by-step recovery annealing of the ribbed cylindrical shell obtained by rotary extrusion and heat forming, making the stored energy of the ribbed cylindrical shell tend to be uniform. Subsequently, according to the rapid high-temperature solution treatment, the non-uniform growth of grains is further inhibited. It effectively improves the thermal stability of the grain structure of the rotary extrusion cylindrical shell, inhibits recrystallization and the formation of coarse grains during the high-temperature solution stage, and provides excellent conditions for improving the strength and plasticity of aluminum-lithium alloy components and reducing anisotropy.

[0020] The experimental results of the present invention show that after the multi-stage recovery annealing treatment of the aluminum-lithium alloy cylindrical shell using the heat treatment method provided by the present invention, the average grain size of the cylindrical shell is only 20 μm, while the average grain size of the untreated alloy is as high as 1500 μm. For the cylindrical shell not treated by this process, the yield strength of the final T6 is 499 MPa, the tensile strength is 545 MPa, and the elongation is 9.5%. After being treated by this process method, the yield strength and tensile strength of the cylindrical shell component are increased to 525 Mpa and 580 MPa respectively, and the elongation is increased to 12.2%.

[0021] Other heat treatment processes, such as two-stage heating heat treatment, or heat treatment with rapid heating + slow heating to the solution temperature, or slow heating heat treatment, or slow heating heat treatment, although they can all improve the strength and elongation to a certain extent, but compared with the conventional heat treatment methods, the present invention has a greater improvement in strength and elongation and a smaller grain size. The process method of the present invention can more effectively inhibit the formation of coarse grains and improve the service performance of aluminum-lithium alloy components. Brief Description of the Drawings

[0022] Figure 1 It is a physical diagram of the ribbed cylindrical shell before heat treatment of the present invention.

[0023] Figure 2 It is a grain structure diagram of the ribbed cylindrical shell before heat treatment of the present invention.

[0024] Figure 3 It is a grain structure diagram obtained after heat treatment of Comparative Example 1 of the present invention.

[0025] Figure 4 It is a grain structure diagram obtained after heat treatment of Comparative Example 2 of the present invention.

[0026] Figure 5 It is a grain structure diagram obtained after heat treatment of Comparative Example 3 of the present invention.

[0027] Figure 6 It is a grain structure diagram obtained after heat treatment of Comparative Example 4 of the present invention.

[0028] Figure 7 It is a grain structure diagram obtained after heat treatment of Comparative Example 5 of the present invention.

[0029] Figure 8 This is the grain structure diagram obtained after heat treatment in Example 1 of the present invention. Detailed implementation manners

[0030] The present invention will be further described in detail below with specific examples. Example 1

[0031] The alloy grade used in the example of the present invention is 2195 alloy, and the mass percentages of chemical components are 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.

[0032] The object of this example is a ribbed cylinder shell obtained by spin extrusion. The forming temperature is 420 °C, and the dimensions of the cylinder shell are inner diameter φ = 315 mm, wall thickness t = 3 mm, and length d = 300 mm.

[0033] The ribbed cylinder shell is heat-treated, and the heat treatment process is as follows: 1) Heat from room temperature to 240 °C at a heating rate of 1 °C / min and hold for 8 h; 2) Heat from 240 °C to 300 °C at a heating rate of 1 °C / min and hold for 8 h; 3) Heat from 300 °C to 360 °C at a heating rate of 1 °C / min and hold for 8 h; 4) Heat from 360 °C to 420 °C at a heating rate of 1 °C / min and hold for 8 h; 5) Place the ribbed cylinder shell after being treated in 1) - 4) in a heating furnace at 505 °C (the heating furnace is first heated to 505 °C, and then the ribbed cylinder shell is put into the heating furnace. In this way, for a ribbed cylinder shell with a thickness of about 3 mm, it only takes 1 minute to be heated through, which is equivalent to a heating rate of 480 °C / min), hold for 1 h, and then water quench to room temperature to form a supersaturated solid solution.

[0034] 6) Perform aging treatment on the heat-treated ribbed cylinder shell at 160 °C for 65 h.

[0035] Comparative Example 1 Do not perform any annealing treatment on the ribbed cylinder shell. Directly heat it to 505 °C at a slow heating rate of 1 °C / min, then hold at 505 °C for 1 h, and then water quench to room temperature to form a supersaturated solid solution; then perform aging treatment on the ribbed cylinder shell at 160 °C for 65 h.

[0036] Comparative Example 2 The ribbed cylindrical shell was annealed at 240°C and 420°C for 8 hours respectively, 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. That is, the heat treatment process is as follows: 1) Heat from room temperature to 240°C at a heating rate of 1°C / min and hold for 8 hours; 2) Heat from 240°C to 420°C at a heating rate of 1°C / min and hold for 8 hours.

[0037] The subsequent steps are the same as steps 5)-6) of Example 1.

[0038] Comparative Example 3 The ribbed cylindrical shell was annealed at 240°C, 300°C, 360°C and 420°C for 8 hours respectively, with rapid heating treatment, and then solution treatment at 505°C / 1h was carried out at a slow heating rate of 1°C / min. That is, the heat treatment process is as follows: 1) Heat from room temperature to 240°C at a heating rate of ≥100°C / min and hold for 8 hours; 2) Heat from 240°C to 300°C at a heating rate of ≥100°C / min and hold for 8 hours; 3) Heat from 300°C to 360°C at a heating rate of ≥100°C / min and hold for 8 hours; 4) Heat from 360°C to 420°C at a heating rate of ≥100°C / min and hold for 8 hours; The heating method adopted above is to directly place the ribbed cylindrical shell in a heating furnace at the target temperature. For example, in step 1), heating from room temperature to 240°C is to directly place the ribbed cylindrical shell at room temperature in a 240°C heating furnace, directly heated at the target temperature, and 3mm aluminum alloy material can be thermally penetrated unilaterally in 1 minute. Therefore, the time required for the ribbed cylindrical shell to reach 240°C from room temperature is within 1 minute, and the heating rate is not less than 100°C / min.

[0039] 5) Heat the ribbed cylindrical shell after being treated in 1)-4) from 420°C to 505°C at a heating rate of 1°C / min, hold for 1 hour, and then water quench to room temperature to form a supersaturated solid solution.

[0040] 6) Carry out aging treatment on the heat-treated ribbed cylindrical shell at 160°C for 65 hours.

[0041] Comparative Example 4 The ribbed cylindrical shell was annealed at 240°C, 300°C, 360°C and 420°C for 8 hours respectively, and then solution treatment at 505°C / 1h was carried out, all at a slow heating rate of 1°C / min. The heat treatment process is as follows: 1) Heat from room temperature to 240°C at a heating rate of 1°C / min and hold for 8 hours; 2) Heat from 240 °C to 300 °C at a heating rate of 1 °C / min and hold for 8 h; 3) Heat from 300 °C to 360 °C at a heating rate of 1 °C / min and hold for 8 h; 4) Heat from 360 °C to 420 °C at a heating rate of 1 °C / min and hold for 8 h; 5) Heat the ribbed cylinder shell after being treated in 1) - 4) from 420 °C to 505 °C at a heating rate of 1 °C / min, hold for 1 h, and then water quench to room temperature to form a supersaturated solid solution.

[0042] 6) Perform aging treatment on the heat - treated ribbed cylinder shell at 160 °C for 65 h.

[0043] Comparative Example 5 The ribbed cylinder shell is annealed at 240 °C, 300 °C, 360 °C and 420 °C for 8 h respectively, with a fast heating rate of 20 °C / min, and then quickly heated to 505 °C for 1 h of solution treatment. The specific heat treatment process is as follows: 1) Heat from room temperature to 240 °C at a heating rate of 20 °C / min and hold for 8 h; 2) Heat from 240 °C to 300 °C at a heating rate of 20 °C / min and hold for 8 h; 3) Heat from 300 °C to 360 °C at a heating rate of 20 °C / min and hold for 8 h; 4) Heat from 360 °C to 420 °C at a heating rate of 20 °C / min and hold for 8 h; 5) Place the ribbed cylinder shell after being treated in 1) - 4) in a heating furnace at 505 °C (directly transfer it into a heating furnace at 505 °C), hold for 1 h, and then water quench to room temperature to form a supersaturated solid solution.

[0044] 6) Perform aging treatment on the heat - treated ribbed cylinder shell at 160 °C for 65 h.

[0045] The materials and forming processes used in all Comparative Examples 1 - 5 and Example 1 are the same. Compare the differences in grain structures and mechanical properties as Figure 2-8 shown in Table 1.

[0046] Figure 3-7 The grain size of each comparative example is shown. It can be seen that its average grain size is larger. The grain size of Example 1 is significantly smaller than that of each comparative example.

[0047] Table 1 Differences in grain structures and mechanical properties

[0048] As can be seen from Table 1, the crystal grains of Example 1 are significantly lower than those of each comparative example, and the products of Example 1 have obvious improvements in tensile strength, yield strength and elongation rate.

[0049] Those of ordinary skill in the art should understand that the discussion of any above embodiments is only exemplary and is not intended to imply that the protection scope of this application is limited to these examples; under the idea of this application, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other variations in different aspects of one or more embodiments in this application as described above, and they are not provided in detail for the sake of brevity.

[0050] One or more embodiments of this application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of this application shall be included in the protection scope 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, then placed at 500-510°C, kept warm, 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. After each heating is completed, the temperature is kept warm. The temperature difference of 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, characterized in that: 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 the temperature is raised in stages, the heat preservation time after the temperature rise 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 for 1 h, 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, characterized in that: 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 extrusion.

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

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