Method for improving creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance

Abstract

The present invention provides a method for improving the creep aging forming performance of aluminum-lithium alloy components with electric pulse assistance. This forming method controls the component to be formed to perform creep aging forming according to a preset process using an autoclave and an electric pulse generator. The component to be formed includes an aluminum-lithium alloy sheet, multiple first electrodes, and multiple second electrodes, each of which is connected to the positive and negative electrodes of the electric pulse generator, respectively. The angle between the current direction of the pulse current applied by the electric pulse generator and the rolling direction of the aluminum-lithium alloy sheet is 30° to 60°. The preset process improves on the conventional creep aging forming process. During the first preset duration of creep aging and the third preset duration of creep aging, the electric pulse generator applies a pulse current to assist in creep aging forming of the aluminum-lithium alloy sheet. This forming method ensures a good elongation while increasing the creep amount corresponding to the two opportunities for increased creep deformation.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal component forming, and in particular relates to a method for improving the creep aging forming performance of aluminum-lithium alloy components with the assistance of electric pulses. Background Art

[0002] Complex thin-walled components of aluminum-lithium alloys are widely used in aviation, aerospace, high-speed rail, automobiles and other fields. Their precise forming is extremely important for subsequent equipment parts assembly, aerodynamic shape and service performance.

[0003] Existing technology primarily uses aluminum-lithium alloy rolled plate as raw material to form aluminum-lithium alloy components through a creep aging forming process. This advanced sheet metal processing technology, which leverages the metal's creep, stress relaxation, and aging-strengthening properties, is suitable for the high-performance, precision forming of complex metal components. It primarily involves three stages: component loading and bending, creep aging, and unloading and rebound. Specifically, the sheet is secured to the mold surface of a forming die and heated by an autoclave's heating system, maintaining the sheet at the creep aging temperature for a specified period of time to complete the creep aging forming process. However, this method suffers from low forming efficiency and low creep strength.

[0004] To address this technical problem, CN117025937A discloses a laser shock method for improving the collaborative manufacturing capability of creep deformation properties in thin-walled aluminum-lithium alloys. The method comprises: solutionizing an aluminum-lithium alloy sheet, followed by water quenching and aging; marking an area with a radius of 10-20 cm, with the intersection of the maximum transverse and longitudinal dimensions of the sheet as the center, as the location where the component has the maximum creep; cleaning the marked area, then applying a constraining layer and an energy absorption layer, and then subjecting it to laser shock; cold rolling the sheet, followed by thinning the non-laser-shocked side to obtain the target thickness of the aluminum-lithium alloy sheet; wire cutting the aluminum-lithium alloy sheet according to the unfolded view of the target forming surface to obtain the final aluminum-lithium alloy sheet to be formed; placing the aluminum-lithium alloy sheet to be formed on a forming die, and then subjecting it to creep aging. The present invention effectively improves the local creep of thin-walled aluminum-lithium alloy components through local laser shock, while also increasing local toughness, inhibiting the appearance and propagation of cracks, and preventing cracking. Due to the high cost of the laser shock equipment itself, the experimental process also requires high experimental protection costs, making the entire experimental process relatively complex.

[0005] CN112981284A: This invention relates to a method for preparing a stress-aged high-strength aluminum-lithium alloy, belonging to the field of aluminum-lithium alloy heat treatment technology. The aluminum-lithium alloy prepared by conventional methods is first solution treated at 500°C to 530°C for 0.5 to 5 hours, then tensile deformed by 4% to 10% along the rolling direction. Finally, it is aged at 155°C to 225°C and 160 MPa to 220 MPa for 7 to 14 hours, followed by air cooling to obtain the stress-aged high-strength aluminum-lithium alloy. The method of the present invention achieves comprehensive regulation of the type, quantity, and size distribution of precipitated phases in the aluminum-lithium alloy by controlling the pre-deformation amount, the stress field during heat treatment, and the temperature field distribution to achieve optimal values, thereby significantly improving the yield strength and elongation of the aluminum-lithium alloy. Furthermore, this method effectively shortens the heat treatment time of the aluminum-lithium alloy, thereby effectively improving production efficiency and saving energy consumption. This invention only improves performance. After initial forming, the deformation resistance during subsequent forming is relatively high, which is not conducive to forming.

[0006] CN106917058B: A room-temperature forming method for 2198 aluminum-lithium alloy sheet. The method comprises the following steps: 1) solution treatment, placing the sheet in a heating furnace and controlling the holding time; 2) quenching treatment, rapidly transferring the solutionized sheet into low-temperature water, strictly controlling the transfer time to ensure thorough quenching of the entire sheet; 3) room-temperature forming, rapidly removing the sheet from the water and completing leveling and forming of the sheet in a short period of time; 4) natural aging, allowing the sheet to rest for 3 to 9 days; 5) artificial aging, placing the part in a heating furnace and holding it for a predetermined period of time; 6) removing the part, performing trimming and surface treatment, to obtain 2198 aluminum-lithium alloy sheet parts. By performing room-temperature forming on the 2198 aluminum-lithium alloy sheet before aging treatment, the present invention combines plastic forming with the necessary pre-deformation before aging, avoiding the difficulty of the poor plasticity of the 2198 aluminum-lithium alloy and increasing the strength of the parts. This effectively reduces processing costs and improves the geometric accuracy of the parts, thus possessing the potential for large-scale industrial production. This method inevitably produces large residual stress during the third step of room temperature forming. The residual stress will be released during the subsequent natural aging and artificial aging processes. The residual stress release process will inevitably lead to a significant decrease in the initial forming accuracy of the material. Summary of the Invention

[0007] The purpose of the present invention is to assist the creep aging forming of aluminum-lithium alloy sheets through two-stage pulse current, and the current direction of the pulse current has a certain angle θ (30°≤θ≤60°) with the rolling direction of the aluminum-lithium alloy sheet, so as to increase the creep amount of the aluminum-lithium alloy sheet and ensure better mechanical properties, thereby promoting better shape-property coordinated manufacturing of aluminum-lithium alloy components.

[0008] To achieve the above-mentioned object, the present invention provides a method for improving the creep aging forming performance of an aluminum-lithium alloy component with the assistance of electric pulses. The method controls a workpiece to be formed to perform creep aging forming according to a preset process through an autoclave and an electric pulse generator. The workpiece to be formed includes an aluminum-lithium alloy sheet, and a plurality of first electrodes and a plurality of second electrodes respectively installed at opposite ends of the aluminum-lithium alloy sheet. The aluminum-lithium alloy sheet is a rolled sheet. The plurality of first electrodes and the plurality of second electrodes are evenly distributed, and the plurality of first electrodes and the plurality of second electrodes are respectively connected to the positive electrode and the negative electrode of the electric pulse generator. The angle between the current direction of the pulse current applied by the electric pulse generator and the rolling direction of the aluminum-lithium alloy sheet is θ, and 30°≤θ≤60°. The preset process includes:

[0009] At room temperature, vacuuming the sealed cavity between the workpiece to be formed and the mold panel of the forming mold so that the workpiece to be formed approaches the mold panel and the edge of the workpiece to be formed is in contact with the mold panel;

[0010] Starting the heating system of the autoclave to heat the workpiece to be formed to a preset target temperature and then keeping it warm;

[0011] Starting the pressurizing system of the autoclave to load the component to be formed, so that the component to be formed completely fits the mold panel, and maintaining the pressure;

[0012] While starting the pressurization system of the autoclave, the electric pulse generator is turned on to apply a primary pulse current, and the electric pulse generator is kept powered on for a first preset time, so that the workpiece to be formed undergoes primary creep aging forming, wherein the first preset time is 0.75 to 1.25 hours;

[0013] At the end of the first preset time, the electric pulse generating device is turned off, and the heating system and the pressurizing system of the autoclave are used to keep the workpiece to be formed at a temperature and pressure for a second preset time, so that the workpiece to be formed undergoes secondary creep aging forming;

[0014] At the end of the second preset time, the electric pulse generator is turned on to apply a secondary pulse current, and the electric pulse generator is kept powered on for a third preset time, so that the workpiece to be formed undergoes three-stage creep aging forming, wherein the third preset time is 0.75 to 1.25 hours;

[0015] At the end of the third preset time, the autoclave and the electric pulse generator are closed to unload and rebound the workpiece to be formed, thereby obtaining the aluminum-lithium alloy component.

[0016] In a specific embodiment, θ is 45°.

[0017] In a specific embodiment, the first preset duration is the same as the third preset duration.

[0018] In a specific implementation, the first preset duration and the third preset duration are both 1 hour.

[0019] In a specific implementation, the sum of the first preset time length, the second preset time length, and the third preset time length is 10 to 20 hours.

[0020] In a specific embodiment, the target temperature is 160-180°C.

[0021] In a specific embodiment, the electric pulse parameters of the first-level pulse current include: a pulse frequency of 250-350 Hz, a pulse current density of 8-15 A / mm 2 , the duty cycle is 15-25%; the electric pulse parameters of the secondary pulse current include: pulse frequency of 250-350Hz, pulse current density of 8-15A / mm 2 , with a duty cycle of 15-25%.

[0022] In a specific embodiment, the electric pulse parameters of the primary pulse current are the same as the electric pulse parameters of the secondary pulse current.

[0023] In a specific embodiment, the maximum temperature of the primary creep aging forming and the maximum temperature of the tertiary creep aging forming are both lower than the corresponding maximum creep aging temperature of the aluminum-lithium alloy material.

[0024] In a specific embodiment, the aluminum-lithium alloy component is a melon-shaped component or a thin-walled metal component.

[0025] The beneficial effects of the present invention include at least:

[0026] 1. The method provided by the present invention for improving the creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance, controls the component to be formed to perform creep aging forming according to a preset process through an autoclave and an electric pulse generator. The preset process improves the conventional creep aging forming process. During the first preset time at the beginning of creep aging and the third preset time at the end of creep aging, a pulse current is applied by the electric pulse generator to assist the creep aging forming of the aluminum-lithium alloy sheet. The creep strain experimental data show that the greater the angle θ between the current direction of the pulse current and the rolling direction of the aluminum-lithium alloy sheet, the greater the creep strain. However, the creep amount of the primary / tertiary creep aging deformation corresponding to θ of 90° is greater than that of the primary / tertiary creep aging deformation corresponding to θ of 45°. The creep amount of θ is not improved much, while the creep amount of the primary / tertiary creep aging deformation corresponding to θ of 45° is much improved compared with the creep amount of the primary / tertiary creep aging deformation corresponding to θ of 0°, that is, as the angle θ increases, the increase in the creep amount decreases; at the same time, the mechanical property data show that the mechanical properties corresponding to θ of 90° are poor, while the mechanical properties corresponding to θ of 45° are slightly worse than those corresponding to θ of 0°, that is, the elongation is slightly worse, but a small loss of elongation can obtain a larger deformation; in this way, the current direction of the pulse current is made to have a certain angle θ (30°≤θ≤60°) with the rolling direction of the aluminum-lithium alloy sheet, so that better mechanical properties are obtained while obtaining a larger deformation than θ of 0°.

[0027] Second, the creep aging forming provided by the present invention is divided into three stages, and pulse current is applied in the first stage (the first stage creep aging duration is 0.75h to 1.25h) and the third stage (the third stage creep aging duration is 0.75h to 1.25h) to assist the autoclave creep aging forming. On the one hand, the electron wind effect of the pulse current increases the atomic diffusion capacity, reduces the resistance to dislocation movement, and reduces the barrier difference between the deformation activation energy and the precipitation activation energy, thereby accelerating the aging precipitation process and increasing the nucleation rate of the precipitated phase, thereby greatly improving the creep amount and forming efficiency of the aluminum-lithium alloy. On the other hand, the two pulse current-assisted forming processes provide two opportunities to increase creep deformation. Moreover, because the pulse current is applied simultaneously for a period of time at the beginning and end of the creep aging, good elongation can also be ensured.

[0028] 3. The preset process of creep aging forming of aluminum-lithium alloy components provided by the present invention is to pass a pulse current while loading and bending. On the one hand, the non-thermal effect of the electric pulse can reduce the flow stress of the aluminum-lithium alloy, making it easier for the component to be formed to fit the mold panel; on the other hand, the electroplastic effect of the pulse current can effectively avoid the occurrence of buckling instability due to the large deformation resistance.

[0029] Fourth, the secondary pulse current assists the creep aging forming process, which accelerates the aging precipitation process and increases the nucleation rate of the precipitate phase, improves the forming efficiency and reduces the processing cost.

[0030] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic structural diagram of a component to be formed being installed on a forming die according to an embodiment of the present invention;

[0032] Figure 2 A flow chart of the steps of the preset process in the method for improving the creep aging forming performance of aluminum-lithium alloy components with electric pulse assistance provided by the present invention;

[0033] Figure 3 Creep strain diagrams of conventional creep aging process and electric pulse assisted creep aging process provided by Example 1 of the present invention;

[0034] Figure 4 Creep strain diagram corresponding to the angles of 0°, 45°, and 90° between the current direction of the pulse current and the rolling direction of the aluminum-lithium alloy sheet;

[0035] Figure 5 The temperature curve of the component to be formed during the first hour of power-on is shown when the angles between the pulse current direction and the rolling direction of the aluminum-lithium alloy sheet are 0°, 45°, and 90°;

[0036] Figure 6 The tensile curves corresponding to the conventional creep aging process are shown in Figure 2 when the angles of the pulse current direction to the rolling direction of the aluminum-lithium alloy sheet are 0°, 45°, and 90°. DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention in detail with reference to the accompanying drawings. However, the present invention can be defined and covered by various different implementations according to the claims.

[0038] See also Figure 1 and Figure 2The present invention provides a creep aging forming method for an aluminum-lithium alloy component. The forming method controls a component to be formed 200 to perform creep aging forming according to a preset process through an autoclave and an electric pulse generating device. The component to be formed 200 includes an aluminum-lithium alloy sheet 210, and a plurality of first electrodes 220 and a plurality of second electrodes 230 respectively installed at opposite ends of the aluminum-lithium alloy sheet 210. The plurality of first electrodes 220 and the plurality of second electrodes 230 are evenly distributed, and the plurality of first electrodes 220 and the plurality of second electrodes 230 are respectively connected to the positive electrode and the negative electrode of the electric pulse generating device.

[0039] When the plurality of first electrodes 220 are positive electrodes, the plurality of second electrodes 230 are negative electrodes; when the plurality of first electrodes 220 are negative electrodes, the plurality of second electrodes 230 are positive electrodes.

[0040] It can be understood that the number of the first electrodes and the number of the second electrodes are the same.

[0041] In the present invention, the plurality of first electrodes 220 and the plurality of second electrodes 230 are all copper electrodes.

[0042] In the present invention, the plurality of first electrodes 220 and the plurality of second electrodes 230 are respectively connected to the positive electrode and the negative electrode of the electric pulse generating device through a plurality of wires.

[0043] In the present invention, the aluminum-lithium alloy sheet 210 is a rectangular rolled plate, and a plurality of first electrodes 220 and a plurality of second electrodes 230 are respectively installed at both ends of the width direction of the aluminum-lithium alloy sheet 210. The angle between the current direction of the pulse current applied by the electric pulse generating device and the rolling direction of the aluminum-lithium alloy sheet 210 is θ, and 30°≤θ≤60°.

[0044] The preset process includes:

[0045] Step S10 , at room temperature, by evacuating the sealed cavity between the component to be formed 200 and the mold panel 110 of the forming mold 100 , the component to be formed 200 is moved closer to the mold panel 110 and the edge of the component to be formed 200 is attached to the mold panel 110 .

[0046] The forming mold 100 includes a support mechanism 120 and a mold panel 110 fixed on the top of the support mechanism 120. In the present invention, the forming mold 100 is a forming mold provided by the prior art, and the present invention does not make any improvements.

[0047] In the present invention, the techniques for forming a sealed cavity between the component to be formed 200 and the mold panel 110 of the forming mold 100 are all prior art and are not improved upon by the present invention. Specifically, the component to be formed 200 is completely covered with breathable felt, at least one layer of sealant is applied to the edge of the forming mold 100, and a vacuum bag is attached to the sealant so that the vacuum bag and the mold panel together form a sealed cavity.

[0048] It can be understood that when the sealed cavity is formed, the plurality of first electrodes and the second electrodes all extend out of the vacuum bag to facilitate connection with the electric pulse generating device.

[0049] In step S10 , a vacuum of 0.1 MPa is drawn into the sealed cavity, and the component to be formed 200 and the mold panel 110 are connected.

[0050] Step S20: starting the heating system of the autoclave to heat the component to be formed to a preset target temperature and then keeping the temperature constant.

[0051] The target temperature is associated with the creep aging forming temperature of the aluminum-lithium alloy and the pulse current generated by the electric pulse generating device.

[0052] In this step, the preset target temperature is 160°C to 180°C.

[0053] Step S30: Start the pressurizing system of the autoclave to load the component to be formed, so that the component to be formed completely fits the mold panel, and maintain the pressure.

[0054] In this step, the loading pressure is 160 MPa to 220 MPa.

[0055] Step S40: while starting the pressurization system of the autoclave, turn on the electric pulse generator to apply a primary pulse current, and keep the electric pulse generator powered on for a first preset time, so that the component to be formed undergoes primary creep aging forming, wherein the first preset time is 0.75 to 1.25 hours.

[0056] When a pulse current is applied while loading, on the one hand, the non-thermal effect of the electric pulse can reduce the flow stress of the aluminum-lithium alloy, making it easier for the component to be formed to fit the mold panel; on the other hand, the electroplastic effect brought about by the pulse current can effectively avoid the buckling instability caused by the large deformation resistance.

[0057] When the first preset time is less than 0.75h, the pulse current has little effect on increasing the creep strain. When the first preset time is greater than 1.25h, such as 1.5h, it may have an adverse effect on the formability of the component.

[0058] Preferably, the first preset duration is 1 hour.

[0059] Preferably, the maximum temperature of the primary creep aging forming is lower than the corresponding maximum creep aging temperature of the aluminum-lithium alloy material.

[0060] In the present invention, the maximum creep aging temperature corresponding to the aluminum-lithium alloy material is 200°C, that is, the maximum temperature of the primary creep aging forming is less than 200°C.

[0061] Preferably, the electric pulse parameters of the first-level pulse current are: pulse frequency of 250Hz to 350Hz, pulse current density of 8 to 15A / mm 2 , the duty cycle is 15~25%.

[0062] More preferably, the electric pulse parameters of the first-level pulse current are as follows: the pulse frequency is 300 Hz, the pulse current density is 10 / mm 2 , with a duty cycle of 20%.

[0063] The above electric pulse parameters are used to assist heating of the component to be formed, so that the maximum temperature of creep aging forming will not exceed 200° C., thereby avoiding degradation of material performance.

[0064] Step S50: turning off the electric pulse generator at the end of the first preset time, and keeping the heating system and the pressurizing system of the autoclave working for a second preset time, so that the component to be formed undergoes secondary creep aging forming.

[0065] In the present invention, the second preset time is associated with the creep aging time corresponding to the aluminum-lithium alloy material.

[0066] Step S60: At the end of the second preset time, the electric pulse generating device is turned on to apply a secondary pulse current, and the electric pulse generating device is kept powered on for a third preset time, so that the component to be formed undergoes three-stage creep aging forming, wherein the third preset time is 0.75 to 1.25 hours.

[0067] Preferably, the maximum temperature of the three-stage creep aging forming is lower than the corresponding maximum creep aging temperature of the aluminum-lithium alloy material.

[0068] In the present invention, the maximum creep aging temperature corresponding to the aluminum-lithium alloy material is 200°C.

[0069] Preferably, the third preset duration is the same as the first preset duration.

[0070] Passing a pulse current for the initial first preset time to perform primary creep aging forming can greatly increase the creep amount, but it has a certain impact on the elongation of the formed component. Passing a pulse current for the final third preset time to perform three-stage creep aging forming, although it has little effect on the deformation (the "little impact" here refers to the amount of deformation increased relative to the initial first preset time when the pulse current is passed), it is very helpful to improve the elongation of the formed component. Therefore, by passing a pulse current for both the initial first preset time and the final third preset time, the defect of the deterioration of the elongation of the primary creep aging forming can be improved through the three-stage creep aging forming, so that the damage to the elongation of the final aluminum-lithium alloy component is reduced. At the same time, two opportunities to increase creep deformation are obtained, thereby increasing the total creep amount.

[0071] Preferably, the third preset duration is 1 hour.

[0072] Preferably, the sum of the first preset time length, the second preset time length and the third preset time length is 10 to 20 hours.

[0073] In the present invention, 10 to 20 hours can be understood as the total creep aging deformation time of the creep aging forming of the aluminum-lithium alloy component provided by the present invention, and this time is associated with the preset target temperature, that is, the creep aging forming temperature.

[0074] Preferably, the electric pulse parameters of the secondary pulse current are as follows: the pulse frequency is 250Hz to 350Hz, the pulse current density is 8 to 15A / mm 2 , the duty cycle is 15~25%.

[0075] More preferably, the electric pulse parameters of the secondary pulse current are as follows: the pulse frequency is 300 Hz, the pulse current density is 10 A / mm 2 , with a duty cycle of 20%.

[0076] By using the above electric pulse parameters to assist in heating the component to be formed, the maximum temperature of creep aging forming will not exceed 200° C., thereby avoiding degradation of material properties.

[0077] In the present invention, the autoclave's heating system maintains a constant temperature and the pressurizing system maintains a constant pressure throughout the creep aging process. The pulse current during creep aging is used to assist the autoclave in creep aging. Specifically, primary creep aging involves both the autoclave and the electric pulse generator operating simultaneously; secondary creep aging involves only the autoclave operating; and tertiary creep aging involves both the autoclave and the electric pulse generator operating simultaneously.

[0078] In the present invention, the overall creep aging forming process is divided into three stages. Pulse current is used to assist the forming process in the first and third stages, providing two opportunities to increase creep deformation without affecting the mechanical properties of the aluminum-lithium alloy component. If pulse current were used throughout the entire creep aging forming process, while creep would be increased, the mechanical properties of the resulting aluminum-lithium alloy component would be significantly poor. Therefore, the present invention requires careful control of the pulse current application time in the first and third stages to achieve both increased creep and maintained mechanical properties.

[0079] Step S70: closing the autoclave and the electric pulse generator at the end of the third preset time, so that the component to be formed is unloaded and rebounded to obtain the aluminum-lithium alloy component.

[0080] Preferably, the aluminum-lithium alloy component is a thin-walled metal component.

[0081] Example 1

[0082] Please refer to Figures 1 to 6 , the aluminum-lithium alloy component creep aging forming method provided by the present invention is used to form thin-walled metal components.

[0083] The specific steps include:

[0084] Step 1: Provide an aluminum-lithium alloy sheet 210, and install a plurality of first electrodes 220 and a plurality of second electrodes 230 at both ends of the aluminum-lithium alloy sheet 210 to form a component 200 to be formed, wherein the aluminum-lithium alloy sheet 210 is a rectangular rolled sheet with a rolling direction of Figure 1 In the length direction of the aluminum-lithium alloy sheet 210 shown, multiple first electrodes 220 and multiple second electrodes 230 are evenly arranged along the width direction of the aluminum-lithium alloy sheet, so that the angle θ between the current direction when current is passed through the first electrode 220 and the multiple second electrodes 230 and the rolling direction of the aluminum-lithium alloy sheet 210 is 45°.

[0085] In this embodiment, the aluminum-lithium alloy sheet material is 2195 aluminum-lithium alloy.

[0086] In this embodiment, the first electrode and the second electrode are both copper electrodes.

[0087] Step 2: Provide an autoclave, an electric pulse generator, and a plurality of wires, wherein the plurality of wires are used to connect the first electrode, the second electrode, and the electric pulse generator.

[0088] Step 3: Provide a forming mold 100, breathable felt, a vacuum bag, a vacuum tube, and high-temperature adhesive, wherein the forming mold includes a support mechanism and a mold panel fixed on the top of the support mechanism.

[0089] It should be noted that, in this embodiment, there is no sequential order among step one, step two, and step three.

[0090] Step 4: Install the component to be formed on the mold panel 110, and seal the gap between the component to be formed 200 and the mold panel 110 to form a sealed cavity between the component to be formed and the mold panel.

[0091] It should be noted that sealing the component to be formed and the mold panel to form a sealed cavity is an existing technology. Breathable felt, vacuum bags, vacuum tubes and high-temperature glue are sealing materials, and the present invention has not made any improvements. It can be understood that since the first electrode and the second electrode need to be connected to the electric pulse generating device, the first electrode and the second electrode both extend out of the vacuum bag.

[0092] Step 5: Place the forming mold and the component to be formed in an autoclave as a whole, and connect the multiple first electrodes and the multiple second electrodes to the positive electrode and the negative electrode of the electric pulse generating device through wires.

[0093] Step 6: Control the component to be formed to undergo creep aging forming according to a preset process through the autoclave and the electric pulse generator. The preset process includes:

[0094] Step (1): at room temperature, vacuuming the sealed cavity between the component to be formed and the mold panel of the forming mold, so that the component to be formed is moved closer to the mold panel and the edge of the component to be formed is in contact with the mold panel.

[0095] In this step, a vacuum of 0.1 MPa is drawn into the sealed cavity to connect the component to be formed and the mold panel.

[0096] Step (2): starting the heating system of the autoclave to heat the component to be formed to a preset target temperature and then keeping it warm.

[0097] In this step, the preset target temperature is 160°C.

[0098] Step (3): start the pressurizing system of the autoclave to load the component to be formed, so that the component to be formed completely fits the mold panel, and maintains the pressure.

[0099] In this step, the loading pressure was 160 MPa.

[0100] Step (4): while starting the pressurization system of the autoclave, turn on the electric pulse generator to apply a first-level pulse current, and keep the electric pulse generator powered on for a first preset time, so that the component to be formed undergoes first-level creep aging forming, wherein the first preset time is 1 hour.

[0101] In this step, the electric pulse parameters of the first-level pulse current are as follows: pulse frequency is 300Hz, pulse current density is 10A / mm 2 , with a duty cycle of 20%.

[0102] By using the above electric pulse parameters to assist in heating the component to be formed, the maximum temperature of the primary creep aging forming will not exceed 200° C., thereby avoiding degradation of the material performance.

[0103] Step (5) turns off the electric pulse generating device at the end of the first preset time, and keeps the heating system and the pressurizing system of the autoclave working for the second preset time, so that the component to be formed undergoes secondary creep aging forming.

[0104] In this step, the second preset time length is 18 hours.

[0105] Step (6): At the end of the second preset time, the electric pulse generator is turned on to apply a secondary pulse current, and the electric pulse generator is kept powered on for a third preset time, so that the component to be formed undergoes three-stage creep aging forming, wherein the third preset time is 1 hour.

[0106] In this step, the electric pulse parameters of the secondary pulse current are as follows: pulse frequency is 300 Hz, pulse current density is 10 A / mm 2 , with a duty cycle of 20%.

[0107] By using the above electric pulse parameters to assist in heating the component to be formed, the maximum temperature of the three-stage creep aging forming will not exceed 200° C., thereby avoiding degradation of the material performance.

[0108] Step (7): at the end of the third preset time, the autoclave and the electric pulse generator are closed to allow the component to be unloaded and rebound to obtain an aluminum-lithium alloy component.

[0109] See also Figure 3 , Figure 3 The creep strain diagrams of conventional creep aging forming and electric pulse assisted creep aging forming provided in Example 1 of the present invention are shown in FIG. Figure 3 It can be seen that after the electric pulse is applied, the creep strain is significantly increased after the first 1 hour and the last 1 hour, respectively. Among them, the promoting effect on creep strain in the first 1 hour is particularly obvious; and the total creep strain is also significantly greater than the total creep strain of conventional creep aging.

[0110] See also Figure 4 , Figure 4 The creep strain diagram corresponding to the angles of 0°, 45° and 90° between the current direction of the pulse current and the rolling direction of the aluminum-lithium alloy sheet is shown in Figure 2. Figure 4It can be seen that the greater the angle θ between the current direction of the pulse current and the rolling direction of the aluminum-lithium alloy sheet, the greater the creep strain. However, the creep amount of the primary / tertiary creep aging deformation corresponding to θ of 90° is not much higher than that of the primary / tertiary creep aging deformation corresponding to θ of 45°. The creep amount of the primary / tertiary creep aging deformation corresponding to θ of 45° is much higher than that of the primary / tertiary creep aging deformation corresponding to θ of 0°. That is, as the angle increases, the increase in the creep amount decreases.

[0111] See also Figure 5 , Figure 5 The temperature curve of the component to be formed in the first hour of power-on is shown in the figure when the angles of the pulse current direction and the rolling direction of the aluminum-lithium alloy sheet are 0°, 45° and 90°. Figure 5 It can be seen that the temperature of θ 0° and θ 45° is relatively similar, but the temperature of θ 90° increases more, which means that under the same parameter pulse current, the more crystal defects are encountered when flowing through the 90-degree direction, the more obvious the local Joule heating effect is. Figure 4 It is known that although the temperature change at θ of 45° is not obvious compared with the temperature change at θ of 0°, the creep amount of the corresponding primary / tertiary creep aging deformation increases significantly.

[0112] See also Figure 6 , Figure 6 The tensile curves corresponding to the conventional creep aging process are shown in the figure when the angles between the pulse current direction and the rolling direction of the aluminum-lithium alloy sheet are 0°, 45° and 90°. Figure 6 It can be seen that the mechanical properties corresponding to θ of 0° are essentially the same as those obtained with conventional creep aging, while the mechanical properties corresponding to θ of 90° are relatively poor. The mechanical properties corresponding to θ of 45° are slightly worse than those corresponding to θ of 0°, i.e., the elongation is slightly lower. It should be noted that in the present invention, the mechanical properties obtained with conventional creep aging are used to determine whether the mechanical properties at different angles are good or bad.

[0113] Combine Figures 4 to 6It is known that although the creep amount of primary / tertiary creep aging deformation corresponding to θ of 90° is the largest, its mechanical properties are very poor. However, the creep amount of primary / tertiary creep aging deformation corresponding to θ of 45° is significantly improved compared to the creep amount of primary / tertiary creep aging deformation corresponding to θ of 0°, and the mechanical properties corresponding to θ of 45° are only slightly worse than those corresponding to θ of 0°, with a slight loss of elongation, while a larger deformation can be achieved. The present invention sets the angle between the current direction of the pulse current and the rolling direction of the aluminum-lithium alloy sheet to 30° to 60°. The increase in the creep amount of secondary pulse current assisted aging forming relative to the creep amount of conventional creep aging deformation is much greater than the increase in the creep amount of secondary pulse current aging forming relative to conventional creep aging deformation when θ is 0°, and the mechanical properties are better.

[0114] The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for improving creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance, characterized in that: The method controls a component to be formed to perform creep aging forming according to a preset process by using an autoclave and an electric pulse generator. The component to be formed includes an aluminum-lithium alloy sheet, and a plurality of first electrodes and a plurality of second electrodes respectively installed at opposite ends of the aluminum-lithium alloy sheet. The aluminum-lithium alloy sheet is a rolled sheet. The plurality of first electrodes and the plurality of second electrodes are evenly distributed, and the plurality of first electrodes and the plurality of second electrodes are respectively connected to the positive electrode and the negative electrode of the electric pulse generator. The angle between the current direction of the pulse current applied by the electric pulse generator and the rolling direction of the aluminum-lithium alloy sheet is θ, and 30°≤θ≤60°. The preset process includes: At room temperature, vacuuming the sealed cavity between the component to be formed and the mold panel of the forming mold, so that the component to be formed is moved closer to the mold panel and the edge of the component to be formed is in contact with the mold panel; Starting the heating system of the autoclave to heat the component to be formed to a preset target temperature and then keeping it warm; Starting the pressurizing system of the autoclave to load the component to be formed, so that the component to be formed completely fits the mold panel, and maintaining the pressure; While starting the pressurization system of the autoclave, the electric pulse generator is turned on to apply a primary pulse current, and the electric pulse generator is kept powered on for a first preset time, so that the component to be formed undergoes primary creep aging forming, wherein the first preset time is 0.75 to 1.25 hours; At the end of the first preset time, the electric pulse generating device is turned off, and the heating system and the pressurizing system of the autoclave are used to keep the component to be formed at a temperature and pressure for a second preset time, so that the component to be formed undergoes secondary creep aging forming; At the end of the second preset time, the electric pulse generator is turned on to apply a secondary pulse current, and the electric pulse generator is kept on for a third preset time, so that the component to be formed undergoes three-stage creep aging forming, wherein the third preset time is 0.75 to 1.25 hours; At the end of the third preset time, the autoclave and the electric pulse generator are closed to unload and rebound the component to be formed, thereby obtaining the aluminum-lithium alloy component.

2. The method for improving creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance according to claim 1, characterized in that: θ is 45°.

3. The method for improving creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance according to claim 1, characterized in that: The first preset time length and the third preset time length are the same.

4. The method for improving creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance according to claim 3, characterized in that: The first preset time length and the third preset time length are both 1 hour.

5. The method for improving creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance according to claim 3 or 4, characterized in that: The sum of the first preset time length, the second preset time length and the third preset time length is 10 to 20 hours.

6. The method for improving creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance according to claim 1, characterized in that: The target temperature is 160-180°C.

7. The method for improving creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance according to claim 6, characterized in that: The electric pulse parameters of the first-level pulse current include: pulse frequency of 250-350 Hz, pulse current density of 8-15 A / mm 2 , the duty cycle is 15-25%; the electric pulse parameters of the secondary pulse current include: pulse frequency is 250-350Hz, pulse current density is 8-15A / mm 2 , the duty cycle is 15-25%.

8. The method for improving creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance according to claim 7, characterized in that: The electric pulse parameters of the primary pulse current are the same as the electric pulse parameters of the secondary pulse current.

9. The method for improving creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance according to claim 8, characterized in that: The maximum temperature of the first-stage creep aging forming and the maximum temperature of the third-stage creep aging forming are both lower than the corresponding maximum creep aging temperature of the aluminum-lithium alloy material.

10. The method for improving creep aging forming performance of aluminum-lithium alloy components by electric pulse assistance according to claim 1, characterized in that: The aluminum-lithium alloy component is a thin-walled metal component.

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