Method for reducing quenching residual stress of aluminum alloy landing gear forgings and landing gear forgings
Patent Information
- Application Number
- CN202610959361.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-30
- Publication Date
- 2026-09-25
AI Technical Summary
但对于起落架，锻件在热处理之前机加了多处热处理工艺槽和工艺通孔，机加工处的圆角以及锻件中心位置为中空结构，如采用冷变形（冷压）工序进行消除残余应力，极易在冷变形过程中产生开裂，导致产品报废，因此该锻件不具备冷变形工艺操作性
1.本申请通过优化淬火工艺参数组合即可有效降低淬火后残余应力，避免了冷变形带来的开裂风险；无需投入额外模具，显著降低了生产成本和开发周期。
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Figure CN122811667A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of aluminum alloy heat treatment technology, specifically relating to a method for reducing residual stress during quenching of aluminum alloy landing gear forgings and the landing gear forgings themselves. Background Technology
[0002] For large-scale, complex-structure forgings, especially critical load-bearing components in aerospace such as landing gear, the residual stress generated during quenching is a particularly prominent issue. Landing gears are made of aluminum alloy and are characterized by large dimensions, irregular asymmetry, and high ribs. Due to the large size, complex structure, and significant variations in cross-sectional thickness of the forgings, uneven plastic deformation occurs between different parts during the quenching and cooling process, generating substantial residual stress. If this stress is not effectively controlled, it will lead to excessive deformation during subsequent machining and may even result in product scrap.
[0003] Currently, the industry commonly uses cold deformation (cold pressing) to reduce residual stress in complex forgings after quenching. However, for landing gear, the forgings have multiple heat treatment process grooves and through holes machined before heat treatment. The rounded corners at the machined areas and the center of the forging are hollow structures. If cold deformation (cold pressing) is used to eliminate residual stress, cracking is very likely to occur during the cold deformation process, leading to product scrap. Therefore, this forging is not suitable for cold deformation.
[0004] Therefore, for forgings whose residual stress cannot be reduced by cold pressing, how to reduce quenching residual stress is a problem that needs to be solved by those skilled in the art. Summary of the Invention
[0005] The purpose of this invention is to provide a method for reducing the residual stress after quenching of aluminum alloy landing gear forgings, which effectively reduces the residual stress after quenching and makes it uniformly distributed without the need for a cold deformation process.
[0006] The objective of this invention is achieved through the following technical solution: a method for reducing residual stress during quenching of aluminum alloy landing gear forgings is provided, comprising the following steps: S1. Establish a three-dimensional finite element model of the forging; S2. Set multiple sets of quenching process parameter combinations. The quenching process parameters shall include at least the diameter of the heat treatment process hole and the entry posture of the forging when it enters the quenching medium. S3. Based on the three-dimensional finite element model, the quenching process of forgings under each combination of quenching process parameters is simulated to obtain the residual stress distribution data of each group of forgings after quenching, and the target quenching process parameter combination is selected from multiple combinations of quenching process parameters. S4. Quench the forgings using the target quenching process parameter combination.
[0007] Preferably, the heat treatment process holes include at least a first hole and a second hole with unequal diameters; the entry posture includes at least: the forging with the large end facing down into the quenching medium, the forging with the large end facing up into the quenching medium, and the forging horizontally into the quenching medium.
[0008] Preferably, step S3 further includes the following steps: S31. Simulate the quenching process of heat treatment process holes with different apertures under the same entry posture to obtain the residual stress distribution data of each group of forgings after quenching and obtain the target heat treatment process hole. S32. Using the same target heat treatment process hole diameter, simulate the quenching process under different entry postures to obtain residual stress distribution data of each group of forgings after quenching and obtain the target entry posture.
[0009] Preferably, step S4 includes the following steps: S41. Select multiple feature points on the surface of the quenched forging and measure the actual residual stress value at each feature point; S42. Compare and verify the actual residual stress value with the simulated residual stress value at the corresponding position in step S3.
[0010] Preferably, the quenching medium is water.
[0011] Another aspect of the present invention provides an aluminum alloy landing gear forging, employing the method described in this application.
[0012] Preferably, the diameter of the heat treatment process hole is 110 mm. Because of the adoption of the above technical solution, the present invention has the following advantages: 1. This application can effectively reduce residual stress after quenching by optimizing the combination of quenching process parameters, thus avoiding the risk of cracking caused by cold deformation; no additional molds are required, which significantly reduces production costs and development cycle.
[0013] 2. Through simulation and screening, the target quenching process parameter combination was determined, achieving simultaneous optimization of the absolute value and distribution uniformity of residual stress. Attached Figure Description
[0014] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly introduced below. In all the drawings, the elements or parts are not necessarily drawn to scale.
[0015] Figure 1 This is a schematic diagram of an aluminum alloy landing gear forging according to the present invention; Figure 2 A schematic diagram of the heat treatment process holes for an aluminum alloy landing gear forging. Figure 3This is a schematic diagram of the overall stress in Scheme 5; Figure 4 This is a schematic diagram of the stress on the symmetry plane of scheme 5; Figure 5 This is a low-magnification diagram of the stress at the location in Scheme 5; Figure 6 This is a schematic diagram of the overall stress in Scheme 2; Figure 7 This is a schematic diagram of the stress on the symmetry plane of Scheme 2; Figure 8 This is a low-magnification diagram of the stress at the location in Scheme 2.
[0016] Figure 9 This is a schematic diagram of the overall stress in Scheme 4; Figure 10 This is a schematic diagram of the stress on the symmetry plane of scheme 4; Figure 11 This is a low-magnification diagram of the stress at the location in Scheme 4.
[0017] Figure 12 This is a schematic diagram of the overall stress in Scheme 6; Figure 13 This is a schematic diagram of the stress on the symmetry plane of Scheme 6; Figure 14 This is a low-magnification diagram of the stress at the location in Scheme 6; Figure 15 This is a schematic diagram of the overall stress in Scheme 7; Figure 16 This is a schematic diagram of the stress on the symmetry plane of Scheme 7; Figure 17 This is a low-magnification diagram of the stress at the location in Scheme 7; Figure 18 A schematic diagram of the locations of eight feature points for forgings or forging simulation. Detailed Implementation
[0018] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings.
[0019] Please see Figure 1 and Figure 2 A method for reducing residual stress in aluminum alloy landing gear forgings after quenching includes the following steps: S1. Establishing a three-dimensional finite element model of the forging; S2. Setting multiple sets of quenching process parameter combinations, wherein the quenching process parameters include at least the diameter of the heat treatment process holes and the entry posture of the forging when entering the quenching medium. S3. Based on a three-dimensional finite element model, the quenching process of forgings under each combination of quenching process parameters is simulated to obtain residual stress distribution data after quenching for each group of forgings. The target quenching process parameter combination is then selected from multiple combinations. S4. The forgings are quenched using the target quenching process parameter combination. Specifically, the residual stress distribution data includes residual stress values and residual stress distribution states. Based on the residual stress distribution data, the target quenching process parameter combination is selected from multiple combinations of quenching process parameters. In this embodiment, the aluminum alloy landing gear forging is made of 7050 aluminum alloy. It is a large-sized, irregularly shaped, asymmetrical, high-ribbed die forging with a maximum envelope size of 1600×1100×400mm. It is irregularly shaped and asymmetrical with high ribs. Before heat treatment, multiple machined fillets and through holes were added to the forging at various locations. During cold deformation at room temperature, the machined fillets and the center of the forging are hollow, making them highly susceptible to cracking during cold deformation, leading to product scrap. Therefore, cold deformation is not feasible for this forging. A three-dimensional finite element model is constructed based on the forging's structure. Adjustable heat treatment process holes are preset. These holes are machined before heat treatment, and their diameter is one of the variable parameters for subsequent simulation. The entry posture into the quenching medium refers to the forging's orientation and direction of movement at the moment it enters the quenching medium. This determines which part of the forging contacts the quenching medium first and which part contacts it later. Finite element simulation was performed using dedicated simulation software (Deform); residual stress was verified by X-ray diffraction.
[0020] This application uses the entry posture into the quenching medium and the size of the heat treatment process hole as variables, while other factors, including the immersion rate, quenching medium temperature, and forging transfer time, are set as constants. Increasing the size of the heat treatment process hole reduces the effective heat treatment thickness of the forging, shortens the heat transfer path between the core and surface, and reduces the temperature gradient during quenching, thereby reducing thermal stress. Different entry postures select the thickest section of the forging, prioritizing its entry into the quenching medium to ensure more thorough cooling. This compensates for uneven cooling rates caused by differences in section thickness and avoids asymmetrical stress distribution caused by differences in entry time between the upper and lower surfaces when horizontally entering the quenching medium. This allows for simultaneous optimization of the absolute value and uniformity of residual stress without the need for cold deformation processes.
[0021] Furthermore, the heat treatment process holes include at least a first hole and a second hole with unequal diameters; the entry posture includes at least: the forging with its larger end facing down into the quenching medium, the forging with its larger end facing up into the quenching medium, and the forging horizontally into the quenching medium. Specifically, the larger end refers to the end of the forging with the larger cross-sectional area along its length, and the smaller end refers to the end with the smaller cross-sectional area. Entering the quenching medium with the larger end facing down means that the end with the larger cross-sectional area of the forging enters the quenching medium first, and entering the quenching medium with the larger end facing up means that the end with the smaller cross-sectional area of the forging enters the quenching medium first. Preferably, the quenching medium is water.
[0022] Furthermore, step S3 includes the following steps: S31 simulates the quenching process for heat treatment process holes of different diameters under the same entry posture to obtain residual stress distribution data after quenching for each group of forgings, and obtains the target heat treatment process hole; S32 simulates the quenching process under different entry postures with the same target heat treatment process hole diameter to obtain residual stress distribution data after quenching for each group of forgings, and obtains the target entry posture. Specifically, the residual stress is related to the diameter of the heat treatment process holes in the forging structure. Increasing the diameter of the process hole reduces the heat treatment thickness, shortens the path of heat conduction from the inside of the forging to the surface during quenching, reduces the difference in cooling rate between the inside and the surface of the forging, and reduces the overall residual stress and makes it more uniformly distributed when other parameters are the same; however, increasing the hole diameter will affect the final wall thickness, machining allowance, and structural strength of the forging. Therefore, in the design of this application, the hole diameter should be as large as possible while ensuring the final wall thickness and structural strength of the forging. The combination scheme of multiple quenching process parameters is as follows: Option 1: The heat treatment process hole is Φ115mm, and the entry posture is horizontal when entering the quenching medium; Option 2, Φ110mm, enters the quenching medium horizontally; Option 3, Φ105mm, enters the quenching medium horizontally; Option 4, Φ95mm, enters the quenching medium horizontally; Option 5, Φ80mm, enters the quenching medium horizontally; In each scheme, except for the entry posture and aperture size, all other factors (such as ingot batch, billet preparation process, die forging process, heat treatment regime, equipment, entry speed into quenching medium, quenching medium temperature, forging transfer time, etc.) are set to the same values to ensure the validity of the simulation results comparison. Please refer to the stress diagrams of the forgings in the quenched state for each scheme. Figures 3 to 11 .
[0023] Table 1 compares the overall stress of different aperture designs under the same quenching medium entry posture (horizontal immersion in water): As shown in Table 1, the diameter of the hole decreases significantly from Φ95mm to Φ105mm (a decrease of 17.1%). The increase in hole diameter has a critical breakthrough effect on the improvement of residual stress uniformity. The improvement of residual stress narrows from Φ105mm to Φ115mm. This range can be considered as the optimal range. Considering the subsequent machining allowance requirements, and on the premise of ensuring the final wall thickness of the forging, Φ110mm is selected as the optimal hole diameter, which is the hole diameter of the target heat treatment process hole.
[0024] For the same heat treatment process, different entry attitudes into the quenching medium are selected, as follows: Option 2, Φ110mm, enters the quenching medium horizontally; Option 6, Φ110mm, enters the quenching medium with the larger end facing upwards; Option 7, Φ110mm, enters the quenching medium with the larger end facing down; Please refer to the stress diagrams of the forgings in the quenched state for Schemes 6 and 7. Figures 12 to 17 .
[0025] Table 2 compares the stress under different entry posture schemes for the target heat treatment process holes: This invention addresses 7050 aluminum alloy landing gear forgings characterized by large size, asymmetry, and hollow holes. Their residual stress field exhibits a non-uniform three-dimensional distribution, necessitating evaluation from the perspectives of overall stress, symmetry plane stress, and low-magnification location stress. Overall stress represents the macroscopic deformation trend of the forging; symmetry plane stress (central hole axial stress) represents the cracking risk at structural abrupt changes; and low-magnification location stress represents the dimensional stability after final machining. Only by simultaneously comparing the stress values and standard deviations across these three dimensions can the quality of the quenching process be comprehensively and thoroughly evaluated.
[0026] As shown in Table 2, under the target heat treatment process hole, the larger end is the thickest section of the forging, and it is preferentially immersed in water to obtain more sufficient cooling. This compensates for the uneven cooling rate caused by the difference in cross-sectional thickness and avoids the asymmetrical stress distribution caused by the difference in immersion time between the upper and lower surfaces when immersing in water horizontally. The optimal posture for entering the quenching medium with the larger end facing down is obtained. By obtaining the target entry posture, the combination of target quenching process parameters can be obtained.
[0027] This application achieves simultaneous optimization of the absolute value and distribution uniformity of residual stress through a combination of target quenching process parameters, ultimately reducing the residual stress of forgings from -219~208MPa to -135~101MPa and the stress variance from 38.1 to 31.5.
[0028] Furthermore, S4 also includes the following steps: S41: Select multiple feature points on the surface of the quenched forging and measure the actual residual stress value at each feature point; S42: Compare and verify the actual residual stress value with the simulated residual stress value at the corresponding position in step S3. Specifically, in order to verify the accuracy of the simulation results, eight feature points with the same positions as the actual object are obtained on the three-dimensional finite element model. This embodiment uses the same batch of ingots, the same billet-making process, the same die forging process, the same heat treatment regime, and the same equipment. Eight feature points were selected on the surface of the two experimental forgings of Scheme 5 and Scheme 7, as shown in the attached figure. Figure 18 Surface residual stress tests were conducted in the quenched state. The axial direction along the middle major axis of the main landing gear was marked as L.
[0029] Table 3 Comparison of surface internal stress of forgings in quenched state with simulated data (MPa) in Scheme 5 Table 4 Comparison of surface internal stress of forgings in quenched state with simulated data (MPa) for Scheme 7 The present invention also provides a landing gear forging, prepared by the method of this application. Specifically, the diameter of the heat treatment process hole in the landing gear forging is 110 mm.
[0030] This invention analyzes the distribution of internal stress in the quenched state of forgings and the influence of different schemes on the magnitude of internal stress by simulating different machining schemes (hole size in heat treatment process) and the attitude of forgings in the quenching medium. The invention selects a quenching scheme with more uniform internal stress distribution and smaller stress value.
[0031] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the scope of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for reducing residual stress during quenching of aluminum alloy landing gear forgings, characterized in that, Includes the following steps: S1. Establish a three-dimensional finite element model of the forging; S2. Set multiple sets of quenching process parameter combinations. The quenching process parameters shall include at least the diameter of the heat treatment process hole and the entry posture of the forging when it enters the quenching medium. S3. Based on the three-dimensional finite element model, the quenching process of forgings under each combination of quenching process parameters is simulated to obtain the residual stress distribution data of each group of forgings after quenching, and the target quenching process parameter combination is selected from multiple combinations of quenching process parameters. S4. Quench the forgings using the target quenching process parameter combination.
2. The method according to claim 1, characterized in that, The heat treatment process holes include at least a first hole and a second hole with unequal diameters; the entry posture includes at least: the forging with the large end facing down entering the quenching medium, the forging with the large end facing up entering the quenching medium, and the forging horizontally entering the quenching medium.
3. The method according to claim 1 or 2, characterized in that, S3 includes the following steps: S31. Simulate the quenching process of heat treatment process holes with different diameters under the same entry posture, obtain the residual stress distribution data of each group of forgings after quenching, and obtain the target heat treatment process hole. S32. Using the same target heat treatment process hole diameter, simulate the quenching process under different entry postures to obtain residual stress distribution data of each group of forgings after quenching, and obtain the target entry posture.
4. The method according to claim 1 or 2, characterized in that, Step S4 includes the following steps: S41. Select multiple feature points on the surface of the quenched forging and measure the actual residual stress value at each feature point; S42. Compare and verify the actual residual stress value with the simulated residual stress value at the corresponding position in step S3.
5. The method according to claim 3, characterized in that, Step S4 includes the following steps: S41. Select multiple feature points on the surface of the quenched forging and measure the actual residual stress value at each feature point; S42. Compare and verify the actual residual stress value with the simulated residual stress value at the corresponding position in step S3.
6. The method according to claim 1, 2, or 5, characterized in that, The quenching medium is water.
7. A landing gear forging, characterized in that, The method comprising any one of claims 1 to 6 is employed.
8. The landing gear forging according to claim 7, wherein the diameter of the heat treatment process hole is 110 mm.