Method for superplastic forming of complex thin-walled components from rolled aluminum-lithium alloy

Abstract

The application provides a rolling state aluminum-lithium alloy complex thin-walled component superplastic forming method, which comprises the following steps: heating a forming die to a target temperature T; placing an aluminum-lithium alloy sheet into the forming die, heating to the target temperature T and keeping for a period of time; increasing the air pressure in the forming die, and air-pressure expanding the aluminum-lithium alloy sheet to form a thin-walled component, wherein the air-pressure expansion comprises the following stages: a first stage: loading the pressure in the forming die to P1 at a certain air pressure loading rate; a second stage: keeping the target temperature T and the pressure P1 unchanged, and keeping for a period of time; a third stage: loading the pressure in the forming die to P2 at a certain air pressure loading rate; a fourth stage: keeping the pressure P2 unchanged, and keeping for a period of time; and taking out the thin-walled component and air cooling to room temperature. The superplastic forming method provided by the application has the advantages of low production cost, high forming efficiency, small grain size after forming and low cavitation degree.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of superplastic forming, and more particularly to a method for superplastic forming of a rolled aluminum-lithium alloy complex thin-walled component. BACKGROUND

[0002] Aluminum-lithium alloy has the characteristics of low density, high specific strength, high elastic modulus, and large specific stiffness, and is an ideal lightweight structural material in the field of aerospace. However, aluminum-lithium alloy has poor room temperature plasticity, large notch sensitivity, and large springback, and it is difficult to realize the overall forming of complex structures. Superplastic forming is a method of forming by utilizing the superplasticity (elongation greater than 100%) of materials under specific temperature and strain rate conditions. This method can realize the overall forming of aluminum-lithium alloy complex thin-walled components, but the traditional superplastic forming conditions are relatively harsh:

[0003] (1) First, the superplastic sheet material requires fine-grained structure, and the grain size is usually less than 10 μm. The fine-grained structure of aluminum-lithium alloy needs to be obtained by salt bath annealing, which increases the manufacturing difficulty and cost of the sheet material;

[0004] (2) The superplastic forming temperature is high, usually at 450-520℃. The superplastic forming speed of aluminum-lithium alloy is slow, and the pressurization rate is usually 0.01-0.04 MPa / min. The forming process usually takes 1.5-2 hours, resulting in low forming efficiency. Moreover, long-term exposure of the material to high temperature can cause grain coarsening and performance degradation;

[0005] (3) For high rib (rib height greater than 40 mm) complex thin-walled components, the deformation is uneven and the degree of cavitation is intensified, resulting in local severe thinning or even rupture.

[0006] For example, the use of 2A97 aluminum-lithium alloy fine-grained sheet material (grain size <10 μm) to superplastically form high-rib complex thin-walled components results in a large wall thickness reduction, with local thinning reaching more than 40%, which cannot meet the load-bearing requirements of the component. Moreover, the superplastic fine-grained sheet material of aluminum-lithium alloy has a serious degree of cavitation after superplastic forming, which affects the performance of the formed component. In addition, the superplastic forming rate of the superplastic fine-grained sheet material of aluminum-lithium alloy is slow (the pressurization rate of gas pressure expansion is 0.01-0.04 MPa / min), the forming temperature is high (450-520℃), and the part is exposed to high temperature for a long time (the forming time needs 1.5-2 hours), which causes the grains to coarsen and the degree of cavitation to intensify after forming. This not only affects the quality and performance of the formed part, but also results in low forming efficiency. Furthermore, the manufacturing cost of the superplastic fine-grained sheet material of aluminum-lithium alloy is high. In order to obtain fine-grained structure, recrystallization annealing is also required. SUMMARY

[0007] (I) Technical problems to be solved

[0008] The technical problems to be solved by the present application are that the plate manufacturing is difficult, the cost is high, the forming efficiency is low, the grain size is coarse after forming, and the hollow degree is increased.

[0009] (II) Technical solutions

[0010] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0011] A rolling state aluminum lithium alloy complex thin-walled component superplastic forming method is provided, comprising the following steps:

[0012] The forming die is heated to a target temperature T, wherein T is 300-420℃;

[0013] The aluminum lithium alloy sheet is placed into the forming die, heated to the target temperature T and kept for 2-5min;

[0014] The air pressure in the forming die is increased, and the aluminum lithium alloy sheet is subjected to air pressure bulging to form a thin-walled component, the air pressure bulging comprising the following stages:

[0015] First stage: the pressure in the forming die is loaded to P1 at a pressure loading rate of 0.1-0.8MPa / min, wherein P1 is 0.5-1.5MPa;

[0016] Second stage: the target temperature T and the pressure P1 are kept unchanged, and kept for 2-5min;

[0017] Third stage: the pressure in the forming die is loaded to P2 at a pressure loading rate of 0.02-0.08MPa / min, wherein P2 is 1.0-3.0MPa;

[0018] Fourth stage: the pressure P2 is kept unchanged, and kept for 2-10min;

[0019] The thin-walled component is taken out and air-cooled to room temperature.

[0020] Preferably, the superplastic forming method further comprises:

[0021] The wall thickness distribution of the thin-walled component is measured using a thickness gauge;

[0022] The deformed zone structure of the thin-walled component after forming is observed using a metallographic microscope and electron backscatter diffraction.

[0023] Preferably, the total forming time of the thin-walled component formed by the superplastic forming method is 10-30min.

[0024] Preferably, the maximum thinning rate of the thin-walled component formed by the superplastic forming method is less than 30%.

[0025] Preferably, the thin-walled component made by the superplastic forming method has a void area fraction of less than 2%.

[0026] Preferably, the thin-walled component made by the superplastic forming method has an average grain size of 2-5 μm.

[0027] Preferably, the thin-walled component made by the superplastic forming method has a rib height of not less than 40 mm.

[0028] (III) Beneficial Effects

[0029] The above technical solutions of the present application have at least the following advantages:

[0030] 1. The superplastic forming method provided by the present application directly uses a rolled aluminum-lithium alloy sheet for superplastic forming, and the sheet does not need to be subjected to recrystallization annealing, thereby reducing the manufacturing cost of the material.

[0031] 2. The superplastic forming method provided by the present application obtains a small grain size (0.5-3 μm) in the dynamic recrystallization during the deformation process, further reduces the temperature of the third-stage superplastic forming, improves the forming efficiency, and the forming temperature of the aluminum-lithium alloy sheet is 300-420 ℃ (reduced by 100-150 ℃ compared with the conventional superplastic forming), and the forming time only needs to be 10-30 min, which is shorter than the conventional superplastic forming (forming time of 1.5-3 h), thereby shortening the exposure time of the aluminum-lithium alloy sheet at high temperature.

[0032] 3. The present application can realize the overall forming of a high-rib complex thin-walled component, and the uniformity of the wall thickness of the thin-walled component after forming is improved, and the maximum thinning amount of the thin-walled component is controlled to be within 30%.

[0033] 4. The material organization of the thin-walled component after forming is small, and the average grain size is only 3-5 μm, thereby avoiding the problem of performance deterioration caused by grain growth and coarsening in the conventional fine-grained sheet superplastic forming process.

[0034] 5. The thin-walled component after forming does not have problems such as aggregation and cross-linking of cavities, and the degree of cavitation is low, thereby further improving the forming quality and performance of the thin-walled component. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0036] Figure 1 is the pressurization fold line diagram of the air pressure bulging provided by the embodiments of the present application.

[0037] Figure 2 is a structural schematic diagram of a thin-walled component provided by an embodiment of the present application.

[0038] Figure 3 is a wall thickness distribution diagram of a maximum deformation zone of a thin-walled component provided by an embodiment of the present application.

[0039] Figure 4 is a metallographic structure diagram of an aluminum-lithium alloy sheet provided by an embodiment of the present application.

[0040] Figure 5 is a metallographic structure diagram of a B region in the middle provided by an embodiment of the present application. Figure 2

[0041] Figure 6 is a comparison diagram of a forming result of prior art and the present application provided by an embodiment of the present application. DETAILED DESCRIPTION

[0042] In order to make the technical problems to be solved by the present application, technical solutions and beneficial effects clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not intended to limit the present application.

[0043] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected or indirectly connected to the other element.

[0044] It should be understood that the terms "length", "width", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application, and are not intended to indicate that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0045] In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating relative importance or indicating the number of technical features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited. The specific implementation of the present application will be described in more detail below in combination with specific embodiments:

[0046] The embodiment of the present application provides a rolling state aluminum-lithium alloy complex thin-walled component superplastic forming method, comprising the following steps:

[0047] ​The forming die is heated to a target temperature T, wherein T is 300-420°C; the target temperature T can be set according to the characteristics of different materials, since the 2A97 aluminum-lithium alloy sheet with a thickness of 1.0-3.0 mm is selected in the embodiment, the temperature range of the target temperature T is preferably 300-420°C. The shape of the cavity of the forming die is designed according to the specific shape of the thin-walled component, and the metallographic structure of the 2A97 aluminum-lithium alloy sheet is as shown in Figure 4

[0048] The aluminum-lithium alloy sheet is placed into the forming die, heated to the target temperature T and kept for 2-5 min; specifically, the aluminum-lithium alloy sheet and the forming die are heated to the set temperature, and the plasticity of the aluminum-lithium alloy sheet is obviously improved in the hot state, so that the aluminum-lithium alloy sheet is pressurized and expanded by using high-pressure gas.

[0049] The air pressure in the forming die is increased to perform air pressure expansion on the aluminum-lithium alloy sheet to form a thin-walled component. In the high-pressure gas expansion forming, high-pressure gas is rapidly filled into the cavity through the air filling holes locally arranged on the forming die, and the aluminum-lithium alloy sheet is deformed by the high-pressure gas. The air pressure expansion includes the following stages (as shown in the line graph of Figure 1 , wherein the abscissa of the line graph is time, in min; and the ordinate of the line graph is air pressure, in MPa):

[0050] The first stage (0-t1 shown in Figure 1 ): the pressure in the forming die is loaded to P1 at an air pressure loading rate of 0.1-0.8 MPa / min, wherein P1 is 0.5-1.5 MPa; the air pressure loading rate in this stage is relatively fast, and the purpose is to make the aluminum-lithium alloy sheet realize dynamic recrystallization through rapid deformation, to refine the grains in the deformation process through dynamic recrystallization, and to obtain fine-grained structure.

[0051] The second stage (t1-t2 shown in Figure 1 ): the target temperature T and the pressure P1 are kept unchanged, and the pressure is kept for 2-5 min; in this stage, equiaxed fine-grained structure can be obtained, and the average grain size is 0.5-3 μm.

[0052] The third stage (t2-t3 shown in Figure 1 ): the pressure in the forming die is loaded to P2 at an air pressure loading rate of 0.02-0.08 MPa / min, wherein P2 is 1.0-3.0 MPa; the deformation rate in this stage is slow, and the deformation in this stage is mainly grain boundary sliding, and the slow deformation rate is beneficial to improve the deformation uniformity.

[0053] The fourth stage (t3-t4 shown in Figure 1 ): the pressure P2 is kept unchanged, and the pressure is kept for 2-10 min;​

[0054] The thin-walled component is taken out and air-cooled to room temperature.

[0055] As one of the optional embodiments of the present embodiment, the superplastic forming method further comprises:

[0056] The thickness distribution of the thin-walled component is measured using a thickness gauge; the measurement shows that the maximum wall thickness reduction of the formed thin-walled component is 20-30%.

[0057] The deformed zone structure of the thin-walled component after forming is observed using a metallographic microscope and electron backscatter diffraction. As shown in Figure 5 the average grain size of the formed thin-walled component is less than 5 μm, and there are few cavities in the material, and no large-size aggregated cavities appear.

[0058] As one of the optional embodiments of the present embodiment, the total forming time of the thin-walled component formed by the superplastic forming method is 10-30 min.

[0059] As one of the optional embodiments of the present embodiment, the maximum reduction rate of the thin-walled component formed by the superplastic forming method is less than 30%.

[0060] As one of the optional embodiments of the present embodiment, the cavity area fraction of the thin-walled component formed by the superplastic forming method is less than 2%.

[0061] As one of the optional embodiments of the present embodiment, the average grain size of the thin-walled component formed by the superplastic forming method is 2-5 μm.

[0062] As one of the optional embodiments of the present embodiment, the rib height of the thin-walled component formed by the superplastic forming method is 40 mm.

[0063] The following is a specific embodiment provided in the present application:

[0064] A 2A97 aluminum-lithium alloy sheet with a thickness of 1.4 mm is cut using a shearing machine, and the sheet size is 500*650 mm. The forming die is loaded into a hot press and heated to a target temperature of 360°C. When the die temperature rises to 360°C, the furnace door of the hot press is opened to load the 2A97 aluminum-lithium alloy sheet. The air pressure is added through the die vent hole of the upper die, and the pressure loading rate is 0.4 MPa / min. The pressure reaches 0.8 MPa after 2 min, and the pressure is maintained for 5 min at this pressure. Then, the pressure is increased to 1.2 MPa at a rate of 0.05 MPa / min for 8 min, and the pressure is maintained for 5 min at 1.2 MPa. After the pressure maintaining is completed, the air inlet valve of the hot press is closed and the heating is stopped. The thin-walled component is taken out and air-cooled, and then pickled. The entire forming time of the thin-walled component is only 20 min. The formed thin-walled component is shown in Figure 2As shown, the rib height of the thin-walled component is 40 mm (i.e. the distance between the lowest and the highest of the thin-walled component), Figure 3 the wall thickness distribution at the maximum deformation position of the thin-walled component, Figure 2 As shown, the thinnest wall thickness of the thin-walled component is 1.03 mm, and the maximum thinning rate is 26.4%, Figure 5 the metallographic structure diagram of the thin-walled component after forming (at the B region), Figure 2 As shown, the thinnest wall thickness of the thin-walled component is 1.03 mm, and the maximum thinning rate is 26.4%,

[0065] As shown, compared with the conventional superplastic forming technology in the prior art, the superplastic forming method provided by the present application has the following advantages (for comparison, the same thickness of raw material is used to make a thin-walled component with the same shape and size): Figure 6 Firstly, the conventional superplastic forming technology needs to use fine-grained sheet material with a grain size of less than 10 μm as raw material, while the present application can directly use the rolled sheet material as raw material without recrystallization annealing, thereby reducing the manufacturing cost of the raw material.

[0066] Secondly, the fine-grained 2A97 aluminum-lithium alloy sheet material used in the conventional superplastic forming technology needs to be formed at a temperature of 450℃-520℃, while the forming temperature of the rolled 2A97 aluminum-lithium alloy provided by the present application is 300℃-420℃ (lower than the former by 100-150℃), thereby reducing the forming temperature and saving energy consumption.

[0067] Thirdly, the forming time required by the conventional superplastic forming technology is 1.5-2 h, while the forming time of the superplastic forming method provided by the present application is 10-30 min, thereby shortening the exposure time of the sheet material at high temperature and avoiding the problems of grain coarsening and performance degradation caused by long-term exposure of the material at high temperature.

[0068] Fourthly, the maximum thinning rate of the conventional superplastic forming technology is greater than 38%, while the maximum thinning rate of the superplastic forming method provided by the present application is less than 30%, thereby improving the uniformity of the wall thickness of the thin-walled component after forming and avoiding the problem of severe local thinning, so as to meet the load bearing requirements of the thin-walled component.

[0069] Fifthly, the void area fraction of the conventional superplastic forming technology is 8-10%, while the void area fraction of the superplastic forming method provided by the present application is less than 2%, so that the thin-walled component made by the superplastic forming method provided by the present application has a low degree of cavitation, and no problems such as aggregation and cross-linking of cavities are found in the thin-walled component after forming, thereby further improving the forming quality and performance of the thin-walled component.

[0070]

[0071] ​Sixth, the average grain size of the thin-walled component formed by the traditional superplastic forming technology is 15-30 mu m, and the average grain size of the thin-walled component formed by the superplastic forming method provided by the application is 2-5 mu m, the material structure is uniform, fine and high in material strength.

[0072] The above merely provides the preferred embodiments of the application, but should not be used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method of superplastic forming of a complex thin-walled component from a rolled aluminum-lithium alloy, characterized in that The method comprises the following steps: heating a forming die to a target temperature T, wherein T is 300-420℃; placing an aluminum-lithium alloy sheet into the forming die, heating to the target temperature T and holding for 2-5 min; the aluminum-lithium alloy sheet is a 2A97 aluminum-lithium alloy sheet with a thickness of 1.0-3.0 mm; increasing the air pressure in the forming die to perform air-pressure bulging on the aluminum-lithium alloy sheet to form a thin-walled component, the air-pressure bulging comprising the following stages: first stage: loading the pressure in the forming die to P1 at a pressure loading rate of 0.1-0.8 MPa / min, wherein P1 is 0.5-1.5 MPa; second stage: keeping the target temperature T and the pressure P1 unchanged and holding for 2-5 min; third stage: loading the pressure in the forming die to P2 at a pressure loading rate of 0.02-0.08 MPa / min, wherein P2 is 1.0-3.0 MPa; fourth stage: keeping the pressure P2 unchanged and holding for 2-10 min; taking out the thin-walled component and air-cooling to room temperature.

2. The superplastic forming method for complex thin-walled components of rolled aluminum-lithium alloy as described in claim 1, characterized in that, The superplastic forming method further comprises: measuring the wall thickness distribution of the thin-walled component using a thickness gauge; observing the deformed zone structure of the thin-walled component after forming using a metallographic microscope and electron backscatter diffraction.

3. The superplastic forming method for complex thin-walled components of rolled aluminum-lithium alloy as described in claim 1, characterized in that, The total forming time of the thin-walled component formed by the superplastic forming method is 10-30 min.

4. The superplastic forming method for complex thin-walled components of rolled aluminum-lithium alloy as described in claim 1, characterized in that, The maximum thinning rate of the thin-walled component formed by the superplastic forming method is less than 30%.

5. The superplastic forming method for complex thin-walled components of rolled aluminum-lithium alloy as described in claim 1, characterized in that, The void area fraction of the thin-walled component formed by the superplastic forming method is less than 2%.

6. The method of claim 1, wherein the complex thin-walled component is a complex thin-walled component of a rolled aluminum-lithium alloy. The average grain size of the thin-walled component formed by the superplastic forming method is 2-5 μm.

7. The as-rolled aluminum-lithium alloy complex thin-walled component superplastic forming process of claim 1 wherein, The rib height of the thin-walled component formed by the superplastic forming method is not less than 40 mm.

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