Forming method for thin-walled aluminum-lithium alloy parts

Abstract

The application discloses a forming method of an aluminum-lithium alloy thin-walled part, which comprises the following steps: S1, quenching the aluminum-lithium alloy plate after solid solution treatment; S2, performing low-temperature pre-drawing forming treatment on the aluminum-lithium alloy plate at a temperature of-180 to-196 DEG C, wherein the low-temperature pre-drawing forming amount is 60% to 80% of the total drawing forming amount, and a pre-formed component is obtained; S3, performing medium-temperature drawing forming treatment on the pre-formed component at a temperature of 200 to 350 DEG C, wherein the drawing forming amount is the total drawing forming amount, and a formed component is obtained; and S4, performing aging treatment on the formed component, and an aluminum-lithium alloy thin-walled part is obtained. The application can meet the forming requirement of the aluminum-lithium alloy component with a complex shape, the material inside the formed component is uniform nanometer scale precipitated phase and low-density deformed structure, and the component has excellent mechanical properties and fatigue properties.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy forming and manufacturing technology, and in particular to a method for forming thin-walled aluminum-lithium alloy parts. Background Technology

[0002] Lithium is the lightest metallic element. Adding 1% lithium to traditional aluminum alloys can reduce density by 3% and increase elastic modulus by 6%. At the same time, aluminum-lithium alloys have excellent resistance to fatigue cracking and corrosion, making them one of the most promising materials for thin-walled aircraft parts.

[0003] With increasingly fierce aerospace competition, high reliability, long service life, and good aerodynamic performance are required for thin-walled aircraft components. This has led to the emergence of a number of complex-shaped structural components. These components are characterized by large depth, numerous local features, and complex curvature, requiring materials with excellent plasticity to prevent cracking during forming. Simultaneously, aluminum-lithium alloy components require the suppression of defect formation during forming to achieve high strength, plasticity, fatigue resistance, and corrosion resistance. However, compared to traditional aluminum alloys such as 2024 and 6061, aluminum-lithium alloys have poorer plasticity. This is because the addition of lithium leads to the formation of various second phases in aluminum-lithium alloys. Taking 2060 aluminum-lithium alloy as an example, it contains T1-Al2CuLi, δˊ-Al3Li, T2-Al6CuLi3, θˊ-Al2Cu, βˊ-Al3Zr, and Al... 20 More than 10 second phases, such as Cu2Mn3, significantly hinder dislocation movement during plastic deformation, resulting in high strength but poor plasticity in aluminum-lithium alloys. These phases are prone to cracking during forming, leading to reduced performance. Currently, 2060 aluminum-lithium alloys are mainly used for simple-shaped components and are difficult to form for complex shapes.

[0004] Chinese Patent Publication No. CN 111940585 B discloses a method for performance control in the ultra-low temperature forming process of high-strength aluminum alloy thin shells. It describes forming under ultra-low temperature conditions. Although this method can improve the formability of the component, a lot of deformation structure accumulates inside during the forming process, which will reduce the plasticity of the component. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for forming thin-walled aluminum-lithium alloy parts that prevents cracking and has good mechanical properties.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for forming thin-walled aluminum-lithium alloy parts includes the following steps:

[0008] S1. The solution-treated aluminum-lithium alloy sheet is then quenched.

[0009] S2. The aluminum-lithium alloy sheet is subjected to low-temperature pre-drawing forming at a temperature of -180 to -196°C. The low-temperature pre-drawing forming amount is 60% to 80% of the total drawing forming amount, to obtain a pre-formed component.

[0010] S3. The preformed component is subjected to medium-temperature deep drawing at a temperature of 200-350℃. The deep drawing amount is the total deep drawing amount, and the formed component is obtained.

[0011] S4. The formed component is subjected to aging treatment to obtain a thin-walled aluminum-lithium alloy component.

[0012] As a further improvement to the above technical solution:

[0013] In step S2, during the low-temperature pre-drawing forming process, the aluminum-lithium alloy sheet is located in the forming mold. The forming mold includes a punch, a die, and a blank holder. The die and punch are correspondingly arranged to form forming cavities. The blank holder is located outside the punch and is used to press the two ends of the aluminum-lithium alloy sheet. The aluminum-lithium alloy sheet is placed between the die and the blank holder.

[0014] Step S2 includes the following steps:

[0015] A1. First, coat the surface of the aluminum-lithium alloy sheet with a low-temperature lubricant, and then apply pressure to both ends of the aluminum-lithium alloy sheet using a pressure ring.

[0016] A2. Cool the aluminum-lithium alloy sheet to -180 to -196°C using a low-temperature cooling medium and hold for 5 to 10 minutes.

[0017] A3. Move the punch at a speed of 10-20 mm / s until the punch travels to the preset travel. The preset travel is the travel of the aluminum-lithium alloy sheet at a low temperature pre-drawing forming amount of 60%-80% of the total drawing forming amount, to obtain the pre-formed component.

[0018] In step A2, the cryogenic cooling medium is liquid nitrogen or cryogenic CO2.

[0019] In step A1, the pressure applied by the pressure ring to both ends of the aluminum-lithium alloy sheet is 0.7 to 1.5 MPa.

[0020] Step S3 includes the following steps:

[0021] B1. Heat the preformed component and the forming mold to 200-350℃ at a heating rate of 500-1000℃ / h, and hold for 5-15 minutes.

[0022] B2. Move the punch at a speed of 5-15 mm / s until the punch and die are closed. Let it stand for 3-5 minutes, then reset the punch and pressure ring to obtain the formed component.

[0023] In step S1, the solution treatment includes the following steps: heating the aluminum-lithium alloy plate to 500-540°C at a heating rate of 100-150°C / h, and holding it at that temperature for 1-2 hours.

[0024] In step S1, the quenching process includes the following steps: transferring the aluminum-lithium alloy plate to room temperature water for cooling for 2-5 minutes.

[0025] In step S1, the aluminum-lithium alloy sheet is immersed in water perpendicularly along the rolling direction of the sheet.

[0026] In step S4, during the aging process, the preformed component is heated to 160-170°C at a heating rate of 100-200°C / h, held at that temperature for 25-40h, and then cooled at room temperature.

[0027] Compared with the prior art, the advantages of the present invention are as follows:

[0028] This invention discloses a method for forming thin-walled aluminum-lithium alloy parts, comprising solution treatment, quenching treatment, low-temperature pre-drawing forming treatment, medium-temperature deep drawing forming treatment, and aging treatment. This method significantly improves the formability of aluminum-lithium alloy sheets. Solution treatment dissolves the second phase in the aluminum-lithium alloy into the aluminum matrix, suppressing localized deformation caused by the second phase during forming. The solution treatment and quenching treatment induce a supersaturated solid solution in the aluminum-lithium alloy. The introduction of an ultra-low temperature energy field (-180 to -196°C) during pre-drawing forms suppresses the precipitation of nano-precipitates, significantly enhancing the work hardening ability of the aluminum-lithium alloy and promoting material... The material is deformed uniformly. In the later stage of deformation, medium-temperature deep drawing (200-350℃) allows the deformed structures (such as dislocations and subgrain boundaries) formed during the low-temperature pre-deep drawing process to fully recover, reducing the crystal defect density. Even if the deformed structures formed at ultra-low temperatures undergo dynamic recovery, the material softens, further improving the formability of the component. Aging treatment induces uniform precipitation of nano-precipitates. This method can meet the forming requirements of complex-shaped aluminum-lithium alloy components. After forming, the interior of the material consists of uniform nano-scale precipitates and low-density deformed structures, which enables the component to have excellent mechanical properties and fatigue performance. Attached Figure Description

[0029] Figure 1 This is a simplified structural diagram of the mold of the present invention.

[0030] Figure 2 The thickness distribution of the components after forming in Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention is shown.

[0031] Figure 3 The locations for sampling the tensile specimens after forming the components of Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention are shown.

[0032] Figure 4The mechanical properties of the components after forming in Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention are shown.

[0033] Figure 5 This is a flowchart of the present invention.

[0034] The labels in the diagram represent: 1. Forming mold; 11. Punch; 12. Die; 13. Pressure ring; 2. Slab; 21. Flange; 22. Side wall; 23. Bottom; 3. Insulation box; 31. Nozzle; 32. Heating element; 33. Controller. Detailed Implementation

[0035] The present invention will be further described in detail below. Unless otherwise specified, the instruments or materials used in the present invention are commercially available.

[0036] like Figure 5 As shown, the present invention provides a method for forming thin-walled aluminum-lithium alloy parts, comprising solution treatment, quenching treatment, ultra-low temperature pre-drawing, medium temperature deep drawing, and artificial aging treatment, including the following steps:

[0037] S1. The aluminum-lithium alloy sheet after solution treatment is quenched. Solution treatment and quenching of aluminum alloy materials are to dissolve the second phase in the material into the aluminum matrix to obtain a supersaturated solid solution, reduce the obstruction effect of the second phase on dislocations during subsequent pre-drawing forming, suppress excessive plastic forming of the component, and thus improve the formability of the sheet.

[0038] S2. The aluminum-lithium alloy sheet is subjected to low-temperature pre-drawing forming at a temperature of -180 to -196°C. The low-temperature pre-drawing forming amount is 60% to 80% of the total drawing forming amount, and a pre-formed component is obtained. The purpose of pre-drawing forming under ultra-low temperature conditions is to improve the work hardening ability of the material, achieve uniform forming of the sheet, and suppress cracking during the forming process of complex-shaped components.

[0039] S3. The pre-formed component is subjected to medium-temperature deep drawing at a temperature of 200–350°C, with the deep drawing amount being the total deep drawing amount, to obtain the formed component. Medium-temperature deep drawing is used to restore the deformed structure accumulated during the ultra-low temperature pre-drawing process and further improve the formability of the component. If the medium-temperature deep drawing temperature exceeds this temperature range, the aluminum alloy structure will recrystallize, and the properties will decrease sharply.

[0040] S4. The formed component is subjected to aging treatment to obtain a thin-walled aluminum-lithium alloy part. This is done to allow the nano-reinforcing phases such as T1, δˊ, θˊ, and S in the aluminum-lithium alloy to be fully released, thereby improving the mechanical properties, fatigue properties, and corrosion resistance of the component.

[0041] Example 1

[0042] This embodiment describes a method for forming thin-walled aluminum-lithium alloy parts, including the following steps:

[0043] (1) Solution treatment

[0044] Take a 2060 aluminum-lithium alloy slab 2 (length × width × thickness: 380 × 100 × 2 mm) and place it in a resistance furnace for heating. Eight thermocouples are evenly arranged on the rectangular slab to monitor the slab temperature. The resistance furnace heating program is set as follows: heating from room temperature (25℃) to 525℃ takes 240 minutes (heating rate is 125℃ / h), and holding at the target temperature for 60 minutes after reaching the target temperature. To prevent the slab 2 from deforming during the heating process, heat-resistant bricks are used to support the middle part of the slab 2.

[0045] (2) Quenching treatment

[0046] After the slab 2 has been kept at a temperature for 60 minutes, it is quickly transferred to room temperature water using a clamp for quenching. To prevent deformation of the slab 2 during the quenching process, the slab 2 is placed vertically into the water along its length (the rolling direction of the sheet) during the quenching process. After being kept in the water for 5 minutes, it is taken out.

[0047] After being removed, it needs to be quickly transferred to a double-acting press for forming to prevent the slab 2 from being left at room temperature for too long and causing natural aging. If it cannot be formed in a short time, the solution-quenched slab 2 needs to be placed in a low-temperature chamber for storage. The temperature of the low-temperature chamber needs to be below -20℃.

[0048] (3) Ultra-low temperature deep drawing

[0049] Transfer the quenched slab 2 as follows: Figure 1 Inside the heat preservation box 3 shown, the blank 2 is placed in the forming mold 1. The forming mold 1 includes a punch 11, a die 12 and a pressure ring 13. The die 12 and the punch 11 are respectively arranged to form forming cavities. The pressure ring 13 is located outside the punch 11 and is used to press the two ends of the blank 2. The blank 2 is placed between the die 12 and the pressure ring 13.

[0050] The heat preservation box 2 is equipped with a nozzle 31, which is connected to an external low-temperature medium source and is located near the area of ​​the slab 2 that is prone to cracking.

[0051] The insulation box 2 also includes a heating element 32 and a controller 33. The heating element 32 is located inside the box, and the controller 33 is located outside the box. The controller 33 is electrically connected to both the nozzle 31 and the heating element 32, and is used to control the heating element 32 and the nozzle 31. In this embodiment, the heating element 32 is also located near the area of ​​the slab 2 that is prone to cracking, and is located below the nozzle 31.

[0052] Low-temperature deep drawing includes the following steps:

[0053] 1) Spray a layer of titanium-based lubricant evenly on the surface of the slab 2, use nuts to pre-tighten the blank holder 13, apply a blank holder force of 1.5MPa to the slab 2, and press the two ends of the slab 2.

[0054] 2) Arrange low-temperature thermocouples on the surface of slab 2, open the liquid nitrogen flow control valve, cool the crack-prone area of ​​slab 2 to -180℃, and hold it at the target temperature for 5 minutes after reaching the target temperature;

[0055] 3) Control the punch 11 to move downward at 12mm / s. Stop moving after the blank 2 reaches a deep drawing depth of 80mm to obtain a pre-formed component.

[0056] In this invention, the low-temperature pre-drawing amount is 60% to 80% of the total drawing amount. In this embodiment, the low-temperature pre-drawing amount is 80% of the total drawing amount. If the deformation amount is less than 60%, local thinning is likely to occur during subsequent hot deformation. If the deformation amount is greater than 80%, cracking is likely to occur.

[0057] In this embodiment, liquid nitrogen is used to cool the slab 2. Liquid helium or low-temperature CO2 gas can also be used for cooling. Optionally, in order to improve the forming efficiency of the slab 2 and save costs, only the crack-prone areas of the slab 2 can be sprayed for cooling, while other areas are still formed at room temperature or low temperature. This treatment is because the cracking areas of complex-shaped components are relatively fixed, while the deformation of other areas is small, and the requirements for material plasticity are low.

[0058] (4) Medium-temperature deep drawing

[0059] 1) Heat the preformed component and forming mold 1 from room temperature (25℃) to 250℃ for 20 min (heating rate is 675℃ / h) and hold for 10 min; subject the preformed component to medium-temperature heating treatment. After reaching the target temperature in step 1), the holding time shall not exceed 15 min to prevent the precipitation of the second phase and reduce the formability of the material.

[0060] 2) Control the punch 11 to move downward at 12 mm / s. After the punch 11, blank 2 and die 12 are fully fitted, hold for 5 minutes, return the punch 11 to the initial position, remove the pressure ring 13, and obtain the formed component.

[0061] When the punch 11, blank 2, and die 12 are fully fitted together, the deep drawing depth of blank 2 reaches 100mm, which is the total forming amount.

[0062] The temperature of the medium-temperature deep drawing step in this invention is 200-350°C. If the temperature exceeds this range, the aluminum alloy structure will recrystallize and its properties will drop sharply.

[0063] (5) Artificial aging treatment

[0064] The formed component was transferred to an aging furnace for artificial aging treatment at 177℃. The heating and holding procedures were as follows: heating from room temperature (25℃) to 160℃ took 60 minutes (heating rate 135℃ / h), and holding at the target temperature for 30 hours to obtain the desired result. Figure 3 The aluminum-lithium alloy thin-walled component shown includes a flange portion 21, a side wall portion 22, and a bottom portion 23 connected in sequence.

[0065] Comparative Example 1

[0066] The forming method of the aluminum-lithium alloy thin-walled part in this comparative example is roughly the same as that in Example 1, except that the intermediate temperature stretching forming in step (4) is not included.

[0067] Comparative Example 2

[0068] The forming method of the aluminum-lithium alloy thin-walled part in this comparative example is roughly the same as that in Example 1, except that step (3) of ultra-low temperature stretching is not included.

[0069] Depend on Figure 2 ( Figure 2 As shown in sections A, B, and C (flange 21, sidewall 22, and bottom 23, respectively), the forming method of Embodiment 1 of this invention can achieve the forming of 2060 aluminum-lithium alloy components. No cracking was observed in the sample after the deep drawing depth reached 90 mm. However, the component formed under ultra-low temperature conditions exhibited significant local thinning (Comparative Example 1), and cracking was observed in the sidewall 22. Although the medium-temperature stretch forming in Comparative Example 2 could achieve component forming, significant thinning still occurred in the sidewall 22.

[0070] Depend on Figure 4 It can be seen that the components formed by the forming method of the present invention have good strength and plasticity. Although Comparative Example 1 has high strength, it has low plasticity, while Comparative Example 2 has low strength but good plasticity.

[0071] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, should fall within the protection scope of the present invention.

Claims

1. A method for forming thin-walled aluminum-lithium alloy parts, characterized in that: Includes the following steps: S1. The aluminum-lithium alloy plate after solution treatment is quenched. S2. The aluminum-lithium alloy sheet is subjected to low-temperature pre-drawing forming at a temperature of -180 to -196°C. The low-temperature pre-drawing forming amount is 60% to 80% of the total drawing forming amount, to obtain a pre-formed component. S3. The preformed component is subjected to medium-temperature deep drawing at a temperature of 200-350℃. The deep drawing amount is the total deep drawing amount, and the formed component is obtained. S4. The formed component is subjected to aging treatment to obtain a thin-walled aluminum-lithium alloy component.

2. The method for forming thin-walled aluminum-lithium alloy parts according to claim 1, characterized in that: In step S2, during the low-temperature pre-drawing forming process, the aluminum-lithium alloy sheet is located in the forming mold (1). The forming mold (1) includes a punch (11), a die (12), and a pressure ring (13). The die (12) and the punch (11) are respectively arranged to form forming cavities. The pressure ring (13) is located outside the punch (11) and is used to press the two ends of the aluminum-lithium alloy sheet. The aluminum-lithium alloy sheet is placed between the die (12) and the pressure ring (13).

3. The method for forming thin-walled aluminum-lithium alloy parts according to claim 2, characterized in that: Step S2 includes the following steps: A1. First, coat the surface of the aluminum-lithium alloy plate with a low-temperature lubricant, and then apply pressure to both ends of the aluminum-lithium alloy plate using a pressure ring (13). A2. Cool the aluminum-lithium alloy sheet to -180 to -196°C using a low-temperature cooling medium and hold for 5 to 10 minutes. A3. Move the punch (11) at a speed of 10-20 mm / s until the punch (11) reaches the preset stroke. The preset stroke is the stroke of the aluminum-lithium alloy sheet at low temperature pre-drawing forming amount of 60%-80% of the total drawing forming amount, to obtain the pre-formed component.

4. The method for forming thin-walled aluminum-lithium alloy parts according to claim 3, characterized in that: In step A2, the cryogenic cooling medium is liquid nitrogen or cryogenic CO2.

5. The method for forming thin-walled aluminum-lithium alloy parts according to claim 3, characterized in that: In step A1, the pressure applied by the pressure ring (13) to both ends of the aluminum-lithium alloy plate is 0.7 to 1.5 MPa.

6. The method for forming thin-walled aluminum-lithium alloy parts according to claim 3, characterized in that: Step S3 includes the following steps: B1. Heat the preformed component and forming mold (1) to 200-350℃ at a heating rate of 500-1000℃ / h and hold for 5-15 minutes. B2. Move the punch (11) at a speed of 5-15 mm / s until the punch (11) and the die (12) are closed. Let it stand for 3-5 minutes, then reset the punch (11) and the pressure ring (13) to obtain the formed component.

7. The method for forming thin-walled aluminum-lithium alloy parts according to any one of claims 1 to 6, characterized in that: In step S1, the solution treatment includes the following steps: heating the aluminum-lithium alloy plate to 500-540°C at a heating rate of 100-150°C / h, and holding it at that temperature for 1-2 hours.

8. The method for forming thin-walled aluminum-lithium alloy parts according to any one of claims 1 to 6, characterized in that: In step S1, the quenching process includes the following steps: transferring the aluminum-lithium alloy plate to room temperature water for cooling for 2-5 minutes.

9. The method for forming thin-walled aluminum-lithium alloy parts according to claim 8, characterized in that: In step S1, the aluminum-lithium alloy sheet is immersed in water perpendicularly along the rolling direction of the sheet.

10. The method for forming thin-walled aluminum-lithium alloy parts according to any one of claims 1 to 6, characterized in that: In step S4, during the aging process, the preformed component is heated to 160-170°C at a heating rate of 100-200°C / h, held at that temperature for 25-40h, and then cooled at room temperature.

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