A forging method for a high-strength and low-toughness 7-series aluminum alloy and its application

Abstract

The present invention discloses a forging method for a high-strength and low-anisotropic 7-series aluminum alloy and its application. The method preheats the alloy ingot to 440-480°C, adjusts it to 330-350°C for multi-directional forging, and obtains a primary forging; the primary forging is sequentially annealed and multi-directionally forged, and air-cooled to room temperature. The method can improve the degree of recrystallization of the alloy and obtain a strong and tough grain structure with a large number of large deformed grains and recrystallized fine grains, thereby improving the rheological properties of the central part of the forging, while preventing excessive high-directional deformation energy storage from causing uneven segregation of the crystalline phase and reducing the thickness direction performance, thereby improving the anisotropic uniformity of the thick plate, improving the comprehensive performance, and reducing the directional sensitivity of the forging. Based on the forging method provided by the present invention, the thick-section aluminum alloy material with a thickness of ≥50 mm is processed in a targeted manner, which can effectively eliminate the anisotropy of the material and reduce the directional sensitivity of the forging as a whole, especially the surface and core directional sensitivity in the T direction.

Description

Technical Field

[0001] The present invention relates to an aluminum alloy forging method, in particular to a forging method of a high-strength and low-anisotropic 7-series aluminum alloy and an application thereof, belonging to the field of metal material processing. Background Art

[0002] 7 series alloys are widely used in civil and military industries, especially in aerospace and transportation. In order to better meet industrial needs, large-section aluminum alloy forgings often need to be processed as a whole to obtain large and complex workpieces. However, the 7 series aluminum alloy forgings in the existing technology have strong directional sensitivity and a large anisotropy index, which limits the advantages of longitudinal and lateral performance in the design and restricts the improvement of comprehensive weight reduction benefits.

[0003] A Chinese patent (CN 113441665A) discloses a forging method and application of a low-directionally sensitive 7xxx series aluminum alloy. It uses a combination of medium-temperature forging and differential temperature forging (hot forging in that patent is a comparative example, and the main body of the patent is a combination of medium-temperature forging and differential temperature forging) to enable the alloy to obtain a large number of fine grains in the high direction and improve the rheological properties of the center part of the forging, improve the isotropic uniformity of the thick plate, and reduce the directional sensitivity of the forging. However, this technology also has some defects, that is, under the medium size limit of 50mm-100mm, isothermal hot forging cannot provide sufficient core deformation, and composite forging and differential temperature forging will introduce excessive deformation energy storage, resulting in excessive precipitation and abnormal growth of the high-directional crystalline phase during the heat treatment stage, and the grains are deformed into a flat shape, which greatly reduces the high-directional elongation and toughness. Summary of the Invention

[0004] To address the problems of the prior art, the first objective of the present invention is to provide a forging method for a high-strength, low-anisotropic 7-series aluminum alloy. This method utilizes a staged forging process. During the primary forging process, due to the relatively low temperature, the material accumulates a large amount of deformation energy. Recovery recrystallization occurs during the annealing and holding process. The annealing time is strictly controlled to control the recrystallized crystals to fine grains, thereby increasing the fine-grained structure content. A secondary forging process at a higher temperature is then performed to induce dynamic recrystallization, releasing the accumulated deformation energy. This controls the accumulation of the material's own deformation energy, thereby producing aluminum alloy forgings with excellent anisotropic uniformity.

[0005] A second objective of the present invention is to provide an application of a forging method for a high-strength, low-anisotropy 7-series aluminum alloy for forging thick aluminum alloy materials with thicknesses ≥50 mm. This forging method, specifically targeting thick aluminum alloy materials, effectively eliminates anisotropy caused by excessive deformation energy storage and insufficient recrystallization during the forging process, thereby reducing the overall directional sensitivity of the forging, particularly in the T-direction.

[0006] To achieve the above technical objectives, the present invention provides a forging method for a high-strength and low-anisotropic 7-series aluminum alloy, characterized in that it comprises: preheating an alloy ingot to A°C, adjusting it to B°C and performing multi-directional forging to obtain a primary forging; subjecting the primary forging to annealing treatment and multi-directional forging in sequence, and air-cooling it to room temperature to obtain a forging; the value of A is 440-480°C, and the value of B is 330-350°C; the multi-directional forging process comprises sequentially upsetting each side of the alloy ingot, and performing stretching between upsetting different sides of the alloy ingot; the unidirectional deformation amount of each upsetting and stretching process is ≤30%; the volume of the alloy ingot is ≥1dm 3 , the length in each direction is ≥50mm; and the temperature difference between the surface and the core of the alloy ingot during the multi-directional forging process is ≤25°C.

[0007] The forging method provided by the present invention, by strictly controlling the process parameters of the two-stage forging, especially the temperature and deformation parameters, effectively reduces the anisotropy of the material while improving the comprehensive mechanical properties of the material, and is particularly suitable for aluminum alloy materials with large thick sections.

[0008] As a preferred solution, the unidirectional deformation amount in each upsetting and stretching process is 30%.

[0009] As a preferred solution, the deformation amount in the forging direction during each multi-directional forging process is ≤30%. Further preferably, the deformation amount in the forging direction during each multi-directional forging process is 30%.

[0010] As a preferred solution, the preheating process of the alloy ingot is: heating to A℃ at 5-10℃ / min, keeping warm for 0.5-1h, and the alloy ingot is heated to 1dm 3 As a benchmark, the holding time will be extended by 1 min for every 10% increase in volume.

[0011] As a preferred solution, the alloy ingot is kept at B℃ for 0.5 to 1h. 3 As a benchmark, the holding time will be extended by 1 min for every 10% increase in volume.

[0012] The values ​​of A and B in the present invention must be strictly implemented in accordance with the above requirements. This is because when the deformation temperature is lower than the recrystallization temperature, dynamic recrystallization is suppressed, the recovery effect is strong, and a large amount of deformation energy storage is introduced into the forging at this stage, which facilitates the generation of fine-grained recrystallized structure in the subsequent intermediate annealing process.

[0013] As a preferred solution, the annealing conditions of the alloy ingot are: keeping the temperature at 440-480°C for 0.5-1h, and the alloy ingot is 1dm 3As a benchmark, the holding time is extended by 1 minute for every 10% increase in volume. The temperature and holding time must be strictly controlled during the annealing process. During the annealing process, the deformation energy stored in the material is initially released, and a large number of recrystallized fine crystals are nucleated. In a relatively short period of time, the recrystallization does not fully grow, thus forming a fine-grained structure evenly dispersed within the material.

[0014] As a preferred solution, the temperature difference between the surface and the core of the alloy ingot during the multi-directional forging process is 20°C.

[0015] When the obtained single forging is subjected to multiple forgings again, its temperature is the same as the temperature during annealing and is higher than the recrystallization temperature. At this time, dynamic recrystallization is the dominant mechanism, and recrystallized fine grains continue to be generated. The degree of deformation in the core is low, and the introduction of deformation storage energy is not as good as that of composite forging. In addition, the grain boundary energy is high, which induces recrystallization to form at the grain boundary and the coarse crystal phase at the grain boundary, and the grain boundary phase is used as the germination site. In addition, by strictly controlling the temperature difference between the surface and the core of the alloy ingot during forging, the deformation energy can be effectively prevented from accumulating again, and the abnormal growth of the crystal phase in the L direction can be suppressed, thereby further reducing the directional sensitivity of the material.

[0016] As a preferred solution, it also includes heat treatment and aging treatment of the product.

[0017] As a preferred solution, the heat treatment conditions are: temperature of 460-480°C, holding time of 0.5-1h, the alloy ingot is 1dm 3 As a benchmark, for every 1% increase in volume, the holding time will be extended by 1 minute.

[0018] As a preferred solution, the aging treatment conditions are: keeping the temperature at 110-130°C for 4-10 hours, then raising the temperature to 150-170°C and keeping the temperature for 8-12 hours, and the alloy ingot is 1dm 3 The aging treatment adopted in the present invention is T74 aging treatment, which can introduce strengthening dispersed precipitation phase and effectively improve the strength of the alloy.

[0019] As a preferred solution, when the alloy ingot is 7085 aluminum alloy, the product is obtained after aging treatment;

[0020] The difference in tensile strength between any two of the three directions of L, LS and ST of the product is less than or equal to 15 MPa;

[0021] The difference in yield strength between any two of the three directions of L, LS and ST of the product is less than or equal to 20 MPa;

[0022] The difference in elongation between any two directions of the product in the three directions of L, LS and ST is less than or equal to 3%.

[0023] As a preferred solution, when the alloy ingot is 7085 aluminum alloy, the product is obtained after aging treatment;

[0024] The difference in tensile strength between the surface and the core of the product in any direction is less than or equal to 20 MPa;

[0025] The difference in yield strength between the surface and the core of the product in any direction is less than or equal to 15 MPa;

[0026] The difference in elongation between the surface and core of the product in any direction is less than or equal to 3%.

[0027] The present invention also provides an application of a forging method for a high-strength, low-anisotropic creep-resistant 7-series aluminum alloy, which is used for forging aluminum alloy materials with large thick sections and a thickness of ≥50 mm.

[0028] For forgings of different specifications and sizes, the conditions of differential temperature forging are often different. Even if the forgings with a thickness of just 100mm and those with a thickness of more than 200mm have the same composition, the microstructure and properties of the forgings obtained by using the same differential temperature forging process will be very different. In addition, it is difficult to control the surface temperature of the forgings by differential temperature forging. In some cases, cooling the surface of the forging by differential temperature forging will also cause the temperature of the core of the forging to drop at the same time. Once the temperature of the core of the forging is too low, the high-axis deformation energy storage during the forging process will increase significantly. Excessive deformation energy storage will lead to an increase in the degree of recrystallization and abnormal precipitation and growth of secondary phases in the high direction. At the same time, the high-axis grains are deformed into a flat shape, which greatly reduces the high-axis toughness and elongation of the forgings.

[0029] During the forging process, the present invention utilizes a method of first warm forging and then hot forging, resulting in a more uniform microstructure and all-directional properties of the forged parts. This method also provides the advantages of recrystallized microstructure and releases stored deformation energy. Furthermore, after hot forging, the present invention maintains a final forging temperature above B°C and air cools the forged parts, preventing excessive recrystallization during subsequent processing that could degrade the surface material's properties. Failure to adhere to the present process sequence can negatively impact the performance differences of the final product in all directions.

[0030] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are:

[0031] 1) In the forging method provided by the present invention, a segmented forging process is adopted. During the primary forging process, due to the low temperature, the material accumulates a large amount of deformation energy. Recovery recrystallization occurs during the annealing and heat preservation process. The annealing time is strictly controlled to control the recrystallized crystals to be fine grains, thereby increasing the fine grain content of the material. After the secondary forging at a higher temperature, the accumulated deformation energy of the material is released and dynamic recrystallization occurs, which greatly reduces the deformation energy of the material itself, thereby obtaining aluminum alloy forgings with excellent isotropic uniformity.

[0032] 2) In the forging method provided by the present invention, by controlling the unidirectional deformation in the upsetting and drawing in the multi-directional forging process and utilizing the "three upsetting and two drawing" process, the deformation in the L direction of the large thick cross-section aluminum alloy material is quantitatively controlled, which not only reduces the internal stress of the material as a whole, but also effectively improves the mechanical properties of the material such as tensile strength and yield strength.

[0033] 3) In the technical solution provided by the present invention, the process combination is simple and easy to implement industrially. Through the combined process of medium-temperature forging and hot forging, the problem of excessive growth of crystalline phase and excessive deformation of grains in the T-direction center caused by high deformation energy storage and T-direction deformation degree in differential temperature forging of aluminum alloy forgings is effectively overcome, thereby achieving an improvement in comprehensive mechanical properties of more than 10%. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the forging process in Example 1 of the present invention;

[0035] Figure 2 This is a radial sampling diagram of the product obtained in Example 1 of the present invention;

[0036] Figure 3 This is a high-level sampling diagram of the product obtained in Example 2 of the present invention. DETAILED DESCRIPTION

[0037] The following comparative examples and embodiments are intended to further illustrate the present invention rather than to limit the present invention.

[0038] The room temperature tensile test is carried out according to the national standard GB / T228-2002 to produce relevant standard tensile specimens.

[0039] Example 1

[0040] The blank is a 100x100x100mm 7085 aluminum alloy. The blank is heated to 460°C, held for 1 hour, then lowered to 340°C and held for 0.5 hour. Multi-directional forging is performed at 340°C, with a single upsetting and drawing process resulting in a 30% unidirectional deformation. After forging, the L-axis is forged from 100mm to 70mm to produce a primary forging. The forging is then heated to 460°C, held for 0.5 hour, and multi-directional forging is performed at 460°C, with a 20°C temperature difference between the surface and core temperatures. A single upsetting and drawing process results in a 30% unidirectional deformation. After forging, the T-axis is forged from 70mm to 50mm. The blank is then air-cooled to produce the final product.

[0041] Comparative Example 1

[0042] The blank is a 7085 aluminum alloy with a size of 100x100x100mm. The blank is heated to 460℃, kept at this temperature for 1 hour, and then open forged at 460℃. After forging, the T-axis is forged from 100mm to 50mm, and then air-cooled.

[0043] Comparative Example 2

[0044] The blank is a 100x100x100mm 7085 aluminum alloy. The blank is heated to 460°C, held for 1 hour, then lowered to 340°C and held for 0.5 hour. Free forging is performed at 340°C. After forging, the L-axis is forged from 100mm to 70mm. The forging is then heated to 460°C, held for 0.5 hour, and free forged at 460°C. After forging, the T-axis is forged from 70mm to 50mm. Coolant is sprayed on the upper and lower surfaces during the 460°C free forging process until the surface temperature reaches 380°C. Air cooling is performed after forging.

[0045] The final plate size after treatment in the comparative example and the example was 150 x 110 x 50 mm. The materials prepared in the comparative example and the example were heat treated to a T74 temper at 470°C for 2 hours, followed by water quenching. Table 1 shows a comparison of the properties of the materials prepared using the conventional forging process and the inventive process in three directions and at the surface and core.

[0046] Table 1 Comparison of performance in various directions between comparative examples and examples

[0047]

[0048] It can be seen from the data in Table 1 that the surface layer of the forging provided in Example 1 of the present invention has a mean square deviation of 8.8 in tensile strength, 9.9 in yield strength, and 0.67% in elongation; the surface layer of the forging provided in Comparative Example 1 has a mean square deviation of 15.7 in tensile strength, 14.7 in yield strength, and 1.96% in elongation; the surface layer of the forging provided in Comparative Example 2 has a mean square deviation of 18.8 in tensile strength, 23.3 in yield strength, and 1.96% in elongation.

[0049] Compared with Comparative Example 1, Example 1 provided by the present invention can effectively inhibit dynamic recrystallization, introduce a certain amount of deformation energy storage, improve the work hardening effect, and through recrystallization in the crystalline phase and grain boundary nucleation during annealing, the fracture mode is transformed from intergranular fracture to transgranular fracture, thereby improving toughness. Its high centripetal elongation is increased by 23.2%, and the average elongation in all directions is increased by 20.1%. Compared with Comparative Example 2, the deformation energy storage introduced by Example 1 is lower, which can effectively inhibit the abnormal growth of the high centripetal phase and reduce the proportion of the crystalline phase. Moreover, due to the strict control of the temperature difference between the surface and the core of the material, the deformation degree of the core is controlled, the formation of a flat grain structure in the high centripetal portion is prevented, and the toughness and elongation are improved. The elongation in the high centripetal portion is increased by 82.1% compared with Comparative Example 2, and the average elongation in all directions is increased by 23.4%. At the same time, the tensile strength is basically the same, with a loss of less than 3%. The three-dimensional grain structure tends to be consistent, and the performance in all directions is uniform, forming a pattern of mixed and spaced distribution of large and small grains, achieving a balance of performance strengthening and toughness.

Claims

1. A forging method for a high-strength and low-anisotropic 7-series aluminum alloy, characterized in that: include: The alloy ingot is preheated to A°C, adjusted to B°C and multi-directional forged to obtain a primary forging; the primary forging is sequentially annealed and multi-directional forged, and air-cooled to room temperature; the value of A is 440-480°C, and the value of B is 330-350°C; the multi-directional forging process is to sequentially upset each side of the alloy ingot, and stretch the alloy ingot between upsetting different sides; the unidirectional deformation of each upsetting and stretching process is ≤30%; the volume of the alloy ingot is ≥1dm 3 , the length in each direction is ≥50mm; the temperature difference between the surface and the core of the alloy ingot during the multi-directional forging process is ≤25°C; when the obtained single forging is subjected to multiple forgings again, its temperature is the same as the temperature during annealing and is higher than the recrystallization temperature; The forging method further includes heat treatment and aging treatment of the product. The heat treatment conditions are: temperature of 460-480°C, holding time of 0.5-1 hour; the aging treatment conditions are: holding at 110-130°C for 4-10 hours, then heating to 150-170°C, holding for 8-12 hours.

2. The forging method of a high-strength and low-toughness 7-series aluminum alloy according to claim 1, characterized in that: The preheating process of the alloy ingot is: heating to A℃ at 5~10℃ / min, keeping warm for 0.5~1h, and heating the alloy ingot to 1dm 3 As a benchmark, for every 10% increase in volume, the insulation time will be extended by 1 minute.

3. The forging method of a high-strength and low-toughness 7-series aluminum alloy according to claim 1, characterized in that: The alloy ingot is kept at B℃ for 0.5~1h. 3 As a benchmark, for every 10% increase in volume, the insulation time will be extended by 1 minute.

4. The forging method of a high-strength and low-toughness 7-series aluminum alloy according to claim 1, characterized in that: The annealing conditions of the alloy ingot are: keeping the temperature at 440-480°C for 0.5-1h, 3 As a benchmark, for every 10% increase in volume, the insulation time will be extended by 1 minute.

5. The forging method of a high-strength and low-toughness 7-series aluminum alloy according to claim 1, characterized in that: During the multi-directional forging process, the temperature difference between the surface and the core of the alloy ingot is 20°C.

6. The forging method of a high-strength and low-toughness 7-series aluminum alloy according to claim 1, characterized in that: When the alloy ingot is 7085 aluminum alloy, the product is obtained after aging treatment; The difference in tensile strength between any two of the three directions of L, LS and ST of the product is less than or equal to 15 MPa; The difference in yield strength between any two of the three directions of L, LS and ST of the product is less than or equal to 20 MPa; The difference in elongation of the product in any two directions of L, LS and ST is less than or equal to 3%.

7. The forging method of a high-strength and low-toughness 7-series aluminum alloy according to claim 6, characterized in that: The difference in tensile strength between the surface and the core of the product in any direction is less than or equal to 20 MPa; The difference in yield strength between the surface and the core of the product in any direction is less than or equal to 15 MPa; The difference in elongation between the surface and core of the product in any direction is less than or equal to 3%.

8. An application of a forging method for a high-strength and low-anisotropic 7-series aluminum alloy according to any one of claims 1 to 7, characterized in that: Used for forging aluminum alloy materials with thickness ≥50mm.

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