A precision forging process for aluminum-lithium alloys

Abstract

The application is a kind of aluminum lithium alloy precision forging process, which comprises the following steps: (1) open forging; (2) blank making; (3) pre-forging; (4) final forging; (5) solid solution and quenching; (6) precision die forging; (7) aging, wherein the open forging is divided into three steps: the first step: high temperature forging, the blank heating temperature T1 = 350-420 DEG C, the forging ratio is not less than 4; the second step: medium temperature forging, the blank heating temperature T2 = 190-280 DEG C, the forging ratio is not less than 4; the third step: high temperature forging, the blank heating temperature T3 = 440-460 DEG C, the forging ratio is not less than 5, after the process parameters of the forging, pre-forging, final forging, solid solution and quenching heat treatment, precision die forging and artificial aging, the precision forgings are made, which have the characteristics of high size precision, small machining amount and excellent performance. The application is suitable for the production of forgings in the fields of aerospace, nuclear industry, transportation, sports goods, weapons and the like.

Description

Technical Field

[0001] This invention relates to a precision forging process for aluminum-lithium alloys, belonging to the field of metal materials engineering. Background Technology

[0002] Al-Cu-Li-X series aluminum-lithium alloys containing the basic alloying elements Cu and Li are gradually gaining widespread application in the aerospace manufacturing field due to their excellent comprehensive properties of strength, toughness, fatigue resistance, and corrosion resistance. Significant progress has been made in the development of aluminum-lithium alloy metallurgical technology in recent years. The metallurgical development trend of aluminum alloys is towards high purity, high alloying, and micro-alloying, thereby achieving excellent comprehensive properties. High-performance new aluminum-lithium alloys in the Al-Cu-Li-X series, such as 2198, 2196, 2297, 2397, 2099, 2060, and 2050, have already been applied in aerospace. The urgent need for structural weight reduction in aircraft design necessitates the development of large-scale, high-performance materials to meet the needs of integral manufacturing of large parts. The development of aluminum-lithium alloy materials with high modulus, high strength, high toughness, and high hardenability can replace high-strength and high-toughness aluminum alloys such as 7050 and 7085 to meet the needs of aerospace manufacturing development. However, the unit cost of aluminum-lithium alloy materials is more than four times that of ordinary aluminum alloys such as 7050 and 7085. Traditional aluminum alloy thick plates and forgings keep the application cost of aluminum-lithium alloys high, thus limiting the large-scale application of aluminum-lithium alloys in aerospace. There is an urgent need to develop new technologies to reduce the application cost of aluminum-lithium alloy materials.

[0003] In recent years, research results on aluminum-lithium alloys have mostly focused on casting, new alloy design, and hot working technology. The core content of these research results is mainly material modification, while preparation methods for aluminum-lithium alloy die forging technology are rarely reported. Summary of the Invention

[0004] This invention addresses the aforementioned limitations of existing technologies by providing a precision forging process for aluminum-lithium alloys. Its aim is to significantly reduce the application cost of aluminum-lithium alloys while ensuring the uniformity and superior overall performance of aluminum-lithium alloy products. Specifically, precision forgings of aluminum-lithium alloys produced using the precision forging process described in this invention exhibit a room temperature tensile strength exceeding 530 MPa, a yield strength exceeding 480 MPa, an elongation exceeding 7%, and a LT-direction KⅠc exceeding 32 MPa1 / 2.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This precision forging process for aluminum-lithium alloys is designed for Al-Cu-Li-X series alloy products. The steps of this process are as follows:

[0007] Step 1: Forging the billet

[0008] The process of forming Al-Cu-Li-X alloy ingots into forged billets with deformable structures is carried out in three steps:

[0009] First step: High-temperature forging: Heat the alloy ingot to T1 = 350℃~420℃, forge it, and the forging ratio is not less than 4;

[0010] Second step: Medium temperature forging: Heat the alloy ingot to T2 = 190℃~280℃, forge it, and the forging ratio is not less than 4;

[0011] Third step: High temperature forging: Heat the alloy ingot to T3 = 440℃~460℃, forge it, and the forging ratio is not less than 5;

[0012] Step 2: Blank preparation

[0013] The forging billet obtained in step one is processed into a forging billet according to the design requirements by machining or forging. During this process, the initial forging temperature is 440℃, the final forging temperature is not lower than 350℃, and the die temperature is not lower than 350℃.

[0014] Step 3: Pre-forging

[0015] The forging billet is placed in the mold to complete the pre-forging according to the design requirements. During this process, the initial forging temperature Tpreforging_initial = 440℃, the final forging temperature is not lower than 350℃, and the mold temperature Tmold satisfies the following: 0.95Tpreforging_initial ≤ Tpreforging_mold ≤ 1.05Tpreforging_initial.

[0016] Step 4: Intermediate Forging

[0017] After pre-forging, the billet is placed in the die to complete intermediate forging according to the design requirements. During this process, the initial forging temperature Tintermediate_forging_initial = 440℃, the final forging temperature is not lower than 350℃, and the die temperature Tfinal_forging_die satisfies the following:

[0018] 0.95T intermediate forging starter ≤ T final forging die ≤ 1.05T intermediate forging starter;

[0019] Step 5: Solution treatment and quenching

[0020] After intermediate forging, the billet is heated to 500℃~540℃ for solution treatment, and then quenched.

[0021] Step Six: Final Forging

[0022] Under room temperature conditions, the forging billet after intermediate forging is forged in a die to the final size required by the product design, and the product forging is obtained.

[0023] Step 7: Artificially age the product forgings to obtain optimal overall performance.

[0024] The aging temperature is between 135℃ and 165℃, and the aging time is between 12 and 60 hours.

[0025] In practice, the chemical composition and weight percentage of the Al-Cu-Li-X alloy are as follows: Cu 2.0–4.2%, Li 0.6–2.2%, Zr 0.04–0.20%, with the balance being Al. In addition, it contains less than 1% of 0–4 of the elements Ag, Mg, Mn, and Zn.

[0026] In practice, the forgings targeted by the technical solution of this invention are multi-H-shaped cross-section combination structures for aircraft beams and frames. The dimensions of each part of the forging are inconsistent, with the upper and lower edge strips having a thickness of 12mm, the rib strips having a thickness of 10mm, the rib strips having a height of 21mm, and the web plates having thicknesses of 4mm and 8mm. The dimensional tolerance requirement is ±0.2mm.

[0027] During implementation, the relationship between the heating temperature in the second step of step one and the heating temperature in the third step is: T2 = 0.45 ~ 0.65T3.

[0028] In practice, the molds used for pre-forging, final forging and precision forging consist of two symmetrical parts, the upper part including the upper mold base (1), the upper mold mating plate (2) and the upper mold (3), and the lower part including the lower mold base (7), the lower mold mating plate (6) and the lower mold (5). A pad (4) is provided between the upper mold base (1) and the lower mold base (7) in conjunction with the upper mold mating plate (2) and the lower mold mating plate (6) to control the opening and closing gap of the upper mold base (1) and the lower mold base (7).

[0029] During implementation, the compression deformation of the final forging in step six is ​​2% to 4%.

[0030] During implementation, the transfer time for quenching after solution treatment in step five shall not exceed 30 seconds, and the temperature of the quenching medium shall not exceed 60℃.

[0031] In practice, the final forging in step six is ​​completed at room temperature and within 4 hours after solution treatment and quenching in step five.

[0032] The features and beneficial effects of the technical solution of this invention are as follows:

[0033] I. Of the seven steps described in the technical solution of this invention, the initial forging in step one is divided into three steps, the functions and effects of which are as follows: the high-temperature forging in the first step ensures that the material obtains sufficient forging process performance; the medium-temperature forging in the second step ensures that the material has sufficient intergranular energy storage, enabling recrystallization; and the high-temperature forging in the third step ensures that recrystallization occurs during the heating process in the third step, and obtains a tough texture through high-temperature forging with sufficient deformation. The sequence and combination of these three steps can significantly improve the forming performance and microstructure of the initial billet, laying a good foundation for improving the comprehensive performance and performance uniformity of the forgings.

[0034] II. The technical solution of this invention enables the machining of a precision forging with a multi-H-shaped cross-section composite structure. This product is used as a main structural component in aircraft beams and frames, such as... Figure 3 , 4 As shown, most of the surface area of ​​this product part is unmachined, requiring high control over the forging process. Uneven stress distribution during the forging process can lead to deformation in subsequent processes. The fabrication of multi-H-shaped cross-section forgings is more difficult than that of conventional Π-shaped or T-shaped cross-section forgings, easily resulting in large dimensional deviations and performance defects. Multi-H-shaped forgings integrate the complex structure of the part, reducing the number of parts, eliminating redundant weight from connecting parts, and removing connection defects and processes, thereby effectively improving weapon performance, increasing manufacturing efficiency, reducing assembly costs, and simplifying maintenance. Currently, such parts are mostly manufactured using subtractive manufacturing methods, machined from thick plates or free forgings. However, this invention uses precision die forging for integral forming, with only the upper and lower "H"-shaped surfaces machined, resulting in less machining and improving the utilization rate of expensive aluminum-lithium alloy materials while reducing raw material and overall manufacturing costs. Therefore, the Al-Cu-Li-X alloy used in this invention has a density of 2.71 g / cm³, lower than the density of the traditional 7050 alloy (2.83 g / cm³), giving the product superior overall strength and toughness, as well as a lighter weight. Replacing traditional 7050 aluminum alloy thick plates or free forgings with this alloy can generate significant weight reduction and economic benefits. This invention increases the utilization rate of expensive aluminum-lithium alloy materials from less than 10% to over 70%, reduces raw material and overall manufacturing costs by over 50%, and improves parts manufacturing efficiency by over 5 times. Replacing traditional 7050 aluminum alloy thick plates or free forgings with Al-Cu-Li-X series aluminum-lithium alloy precision forgings reduces costs by over 20%.

[0035] Furthermore, in the process steps, the final forging described in step six of the technical solution of this invention is the last step in forming the product. This step adopts precision die forging to ensure the dimensional requirements of the final product. In addition, the forming in this step is completed at room temperature, which can significantly reduce the residual stress generated in the solution quenching step in step five, avoid deformation of the die forging in subsequent processes due to residual stress and additional straightening processes, further ensure the dimensional accuracy of the workpiece, improve the quality of parts, increase manufacturing efficiency and reduce manufacturing costs. At the same time, step six can also cause a large number of dislocations to germinate and multiply in the aluminum matrix, providing a large number of nucleation sites for the precipitation of strengthening phases in the aging stage, accelerating the aging response process, and promoting the precipitation and dispersion of a large number of strengthening phases.

[0036] In the process steps, steps five and seven are the heat treatment methods of the present invention for regulating the strength and toughness of forgings. The solution quenching treatment in step five allows excess phases such as Cu and Li in the high Cu content Al-Cu-Li-X alloy to fully dissolve back into the aluminum matrix, forming a double supersaturated state of solute supersaturation and vacancy supersaturation, which prepares the microstructure for the aging stage. The aging treatment in step seven allows solute atoms such as Cu and Li in the forging microstructure to diffuse and precipitate strengthening phases such as Al2CuLi and Al2Cu, which greatly improves the strength of the workpiece.

[0037] Third, the mold in this invention has significant advantages over conventional forging fixtures. Conventional forging fixtures have gaps between the upper and lower dies, resulting in incomplete closure and thus open-die forging. This structure makes it impossible to precisely and stably control the deformation during forging, leading to excessive or insufficient deformation in various parts of complex "H"-shaped forgings, such as flanges, ribs, and webs. This can result in low dimensional accuracy, uneven residual stress reduction, and unstable performance. However, the mold of this invention, by adding a backing plate, ensures the stability of the Δh dimension during forging and the overall height of the fixture after forging, thus avoiding the dimensional instability caused by the instability of Δh in open-die forging. The mold of this invention ensures dimensional stability for each forging while maintaining dimensional accuracy. When used in conjunction with adjustable upper and lower die fitting plates, the upper and lower dies are closed, which is a closed die forging. This structure allows for precise and stable control of the amount of deformation during forging, resulting in high dimensional accuracy and uniform and qualified performance of the forged parts. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the forging process in the present invention, wherein: the billet is uplifted longitudinally as shown in the diagram, and then drawn back to the original size;

[0039] Figure 2 This is a schematic diagram of the mold structure used in the process of this invention;

[0040] Figure 3This is a schematic diagram of a forging product with a multi-"H" cross-section combination structure, for which the process of this invention is applied.

[0041] Figure 4 This is a three-dimensional schematic diagram of a forging product with a multi-H-shaped cross-section combination structure, which is the target of the process of this invention.

[0042] Figure 5 Photographs of forging products with multiple "H"-shaped cross-section composite structures for which the process of this invention is applied. Detailed Implementation

[0043] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0044] In this embodiment, an alloy ingot with a size of 70×80×210mm was taken from an Al-Cu-Li-X series aluminum-lithium alloy ingot with a size of 400×1300×2000mm. The composition is shown in Table 1. The alloy ingot has undergone homogenization annealing treatment.

[0045] Table 1 Chemical composition of Al-Cu-Li-X series aluminum-lithium alloys

[0046]

[0047] The process steps for manufacturing a precision forging with a multi-H-shaped cross-section composite structure using the process of this invention are as follows:

[0048] The structure, shape, and dimensions of this type of precision forging with a multi-H-shaped cross-section combination are as follows: Figure 3-5 As shown;

[0049] 1. Forging of billet

[0050] A 70×80×210mm Al-Cu-Li-X series aluminum-lithium alloy forging billet was forged in three steps, each step being carried out according to... Figure 1 The forging process parameters are shown in Table 2.

[0051] Table 2. Forging Process Parameters

[0052]

[0053]

[0054] 2. Blank preparation

[0055] The blank with dimensions of 70×80×210mm was forged to 32×63×583mm, and then machined into a forging blank of 27×58×520mm. The forging process parameters were: initial forging temperature of 440℃, final forging temperature of not less than 350℃, and die temperature of not less than 350℃.

[0056] 3. Pre-forging

[0057] The forging billet is placed in the pre-forging mold to complete the pre-forging. The size of the pre-forging part is controlled by the pad plate 4 to ensure the amount of deformation that needs to continue to deform during intermediate forging. The pre-forging process parameters are: initial forging temperature T_initial = 440℃, final forging temperature not lower than 350℃, and mold temperature 420℃.

[0058] 4. Intermediate forging

[0059] The pre-forged billet is placed into the final forging die to complete the intermediate forging. The intermediate forging should conform to the final forging drawing. The size of the final forging is controlled by the shim plate 4 to ensure that the deformation amount of 2% to 4% is required to continue to deform during the final forging. The intermediate forging process parameters are: initial forging temperature T_initial = 440℃, final forging temperature not lower than 350℃, and die temperature 420℃.

[0060] 5. Solution treatment and quenching

[0061] The forging billet that has completed intermediate forging is heated to 500℃~540℃ for high-temperature solution treatment, and then quenched after solution treatment. The transfer time is not more than 30 seconds and the temperature of the quenching medium is not more than 60℃.

[0062] 6. Final forging

[0063] The quenched forging billet is placed in the die and precision forging is completed at room temperature. The size of the forging is controlled by the pad plate 4, the upper die fitting plate 2 and the lower die fitting plate 6. The final forging is completed at room temperature within 4 hours after solution treatment and quenching to obtain the product forging.

[0064] 7. Timeliness

[0065] The product forgings are subjected to artificial aging to obtain the best comprehensive performance. The artificial aging process parameters are: aging temperature between 135℃ and 165℃, and aging time between 12 and 60 hours.

[0066] The mold used in the above steps consists of two symmetrical parts, the upper part including the upper mold base (1), the upper mold fitting plate (2) and the upper mold (3), and the lower part including the lower mold base (7), the lower mold fitting plate (6) and the lower mold (5). A pad (4) is provided between the upper mold base (1) and the lower mold base (7) to control the opening and closing gap between the upper mold base (1) and the lower mold base (7).

[0067] Implementation results:

[0068] The room temperature tensile and fracture toughness properties of the product forgings are shown in Tables 3 and 4. The product forgings exhibit excellent fatigue performance; in the L direction, with R = 0.06, 115 Hz, and Kt = 1 specimen, the axial loading fatigue limit after 107 cycles is 320 MPa, an improvement of approximately 25% compared to 7050 alloy forgings. The room temperature tensile testing method for this forging follows GB / T 228.1 "Metallic Materials - Tensile Testing - Part 1: Room Temperature Test Method," the fracture toughness testing method follows HB 5487 "Metallic Materials - Plane Strain Fracture Toughness KIC Test Method," and the room temperature axial loading fatigue testing method follows HB 5287 "Metallic Materials - Axial Loading Fatigue Test Method." Table 4 shows that the dimensional inspection results of the product forgings demonstrate high dimensional accuracy. This product forging can be used for parts in aerospace, nuclear industry, transportation, sporting goods, and weaponry.

[0069] Table 3 Properties of Forgings

[0070]

[0071] Table 4. Dimensional Inspection Results of Forgings

[0072]

[0073]

Claims

1. A precision forging process for an aluminum-lithium alloy, characterized by: This process is for Al-Cu-Li-X alloys, and the steps are as follows: Step 1: Forging the billet The process of forming Al-Cu-Li-X alloy ingots into forged billets with deformable structures is carried out in three steps: First step: High temperature forging: Heat the alloy ingot to T1=350℃~420℃, forge it, and the forging ratio is not less than 4; Second step: Medium temperature forging: Heat the alloy ingot to T2=190℃~280℃, forge it, and the forging ratio is not less than 4; Third step: High temperature forging: Heat the alloy ingot to T3=440℃~460℃, forge it, and the forging ratio is not less than 5; Step 2: Blank preparation The forging billet obtained in step one is processed into a forging billet according to the design requirements by machining or forging. During this process, the initial forging temperature is 440℃, the final forging temperature is not lower than 350℃, and the die temperature is not lower than 350℃. Step 3: Pre-forging The forging billet is placed in the mold to complete the pre-forging according to the design requirements. During this process, the initial forging temperature Tpre-forging_initial = 440℃, the final forging temperature is not lower than 350℃, and the mold temperature Tpre-forging_mold meets the following condition: 0.95Tpre-forging_initial ≤ Tpre-forging_mold ≤ 1.05Tpre-forging_initial. Step 4: Intermediate Forging After pre-forging, the billet is placed in the die to complete intermediate forging according to the design requirements. During this process, the initial forging temperature Tintermediate_forging_initial = 440℃, the final forging temperature is not lower than 350℃, and the die temperature Tfinal_forging_die meets the following requirements: 0.95T intermediate forging starter ≤ T final forging die ≤ 1.05 T intermediate forging starter; Step 5: Solution treatment and quenching After intermediate forging, the billet is heated to 500℃~540℃ for solution treatment, and then quenched. Step Six: Final Forging Under room temperature conditions, the forging billet after solution treatment and quenching is forged in a mold according to the product design requirements to obtain the product forging; Step 7: Artificially age the product forgings to obtain optimal overall performance. The aging temperature is between 135℃ and 165℃, and the aging time is between 12 and 60 hours.

2. The aluminum-lithium alloy precision forging process of claim 1, wherein: The chemical composition and weight percentage of the Al-Cu-Li-X alloy are as follows: Cu 2.0-4.2%, Li 0.6-2.2%, Zr 0.04-0.20%, with the balance being Al.

3. The aluminum-lithium alloy precision forging process of claim 1, wherein: The forgings are multi-H-shaped cross-section composite structures used for aircraft beams and frames. The dimensions of each part of the forging are inconsistent. The thickness of the upper and lower edge strips is 12mm, the thickness of the rib strips is 10mm, the height of the rib strips is 21mm, and the thickness of the web is 4mm and 8mm. The dimensional tolerance requirement is ±0.2mm.

4. The aluminum-lithium alloy precision forging process of claim 1, wherein: The relationship between the heating temperature of the second step and the heating temperature of the third step in step one is: T2 = 0.45 ~ 0.65T3.

5. The aluminum-lithium alloy precision forging process of claim 1, wherein: The molds used for pre-forging, intermediate forging and final forging consist of two symmetrical parts. The upper part includes an upper mold base (1), an upper mold mating plate (2) and an upper mold (3). The lower part includes a lower mold base (7), a lower mold mating plate (6) and a lower mold (5). A pad (4) is provided between the upper mold base (1) and the lower mold base (7) in conjunction with the upper mold mating plate (2) and the lower mold mating plate (6) to control the opening and closing gap between the upper mold base (1) and the lower mold base (7).

6. The aluminum-lithium alloy precision forging process of claim 1, wherein: The final forging in step six has a compression deformation of 2% to 4%.

7. The aluminum-lithium alloy precision forging process of claim 1, wherein: The transfer time after completing the solution treatment in step five is not more than 30 seconds, and the quenching medium temperature is not higher than 60℃.

8. The aluminum-lithium alloy precision forging process of claim 1, wherein: The final forging in step six is completed at room temperature, and is performed within 4 hours after completing the solution treatment and quenching in step five.

Images