Aluminum alloy pipe forming method and device

Abstract

The invention relates to an aluminum alloy pipe forming method and device, belongs to the technical field of metal material forming, and solves the problem that in the prior art, the transverse performance, the longitudinal performance and the high performance of a 7 * * * ultrahigh-strength wrought aluminum alloy pipe are large in difference. According to the pipe forming method, a heated ingot blank is freely forged, and then a special near-isothermal backward extrusion forming device is adopted for carrying out near-isothermal backward extrusion forming on a heated pre-forged blank. By accurately controlling the total forging deformation amount, the extrusion forming temperature and the like, the grain morphology and the recrystallization integral number of the pipe are controlled, the cooperation of a deformation structure and a recrystallization structure is fully exerted, the transverse, longitudinal and high three-direction performance of the pipe is approximately isotropic, and the cracking risk of the pipe is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of metal material forming, and in particular to an aluminum alloy pipe forming method and a device thereof. Background Art

[0002] In the fields of aerospace, shipbuilding, etc., the requirements for aluminum alloy pipes for shells of large-size, high-performance equipment are becoming increasingly stringent. In particular, 7××× series ultra-high-strength deformed aluminum alloys are widely used due to their excellent mechanical properties.

[0003] 7××× series aluminum alloys have good specific strength and heat treatability. The high strength of these alloys mainly comes from their complex microstructures, including various precipitation phases and textures. However, these complex microstructures may also lead to significant differences in the alloy's transverse, longitudinal and high-altitude properties, resulting in deformation tolerances and even cracking during machining, increasing the difficulty and cost of machining.

[0004] The traditional near-isothermal reverse extrusion forming device for aluminum alloy pipes is a horizontal extruder with a die. The aluminum alloy billet is placed in the hopper of the extruder in a heated state and extruded through high pressure and the die. However, this type of extrusion requires a large extrusion force, which is unevenly distributed in the die, resulting in uneven metal flow, which can easily lead to uneven grain orientation and distribution inside the material, resulting in large differences in performance in the horizontal, vertical and high directions.

[0005] In order to solve the above problems, the commonly used methods are free forging round bars and then machining holes, or other methods such as powder metallurgy, etc. However, most of these methods are complicated, not only with a long production cycle, but also with high production costs and low material utilization. Summary of the invention

[0006] In view of the above analysis, the embodiments of the present invention are intended to provide an aluminum alloy tube forming method and device thereof, so as to solve at least one of the following problems: (1) During the existing 7××× series aluminum alloy tube forming process, the tube has relatively large differences in transverse, longitudinal and height properties; (2) The existing 7××× series aluminum alloy tube near-isothermal reverse extrusion forming device is difficult to meet the requirements of high precision and high performance.

[0007] On the one hand, an embodiment of the present invention provides a 7××× series aluminum alloy tube forming method, comprising the following steps:

[0008] S1, heating of aluminum alloy ingot and flat die;

[0009] S2, free forging the heated ingot to form a pre-forged billet;

[0010] S3, heating the pre-forged billet and the near-isothermal reverse extrusion forming device respectively;

[0011] S4, placing the heated pre-forged billet into a near-isothermal reverse extrusion forming device for near-isothermal reverse extrusion forming.

[0012] Furthermore, in S2, the total free forging deformation is 6 to 10.

[0013] Furthermore, in S1, the aluminum alloy ingot is heated to a temperature T 锭坯 : 350℃~440℃, flat die heating temperature T 平模 : 300℃~450℃.

[0014] Furthermore, in S3, the pre-forged billet heating temperature T 预锻坯 The heating temperature of the near-isothermal reverse extrusion forming device is 200-300°C. 装置 T 预锻坯 ±20℃.

[0015] Furthermore, the near-isothermal reverse extrusion forming device includes an extrusion rod, an extrusion punch, a heating and heat preservation device, a concave die, and an ejector rod;

[0016] The extrusion punch is fixed at the lower end of the extrusion rod, and the extrusion punch extrudes the pre-forged billet through the movement of the extrusion rod; the die is fixed at the bottom of the near-isothermal reverse extrusion forming device, opposite to the ejector rod, to form a closed forming cavity, providing a forming space for the pre-forged billet; the inner shape of the forming cavity matches the cross-sectional shape of the aluminum alloy pipe to be formed; the heating and heat preservation device surrounds the die to control the temperature; the ejector rod is used to support the pre-forged billet during the forming process and to eject the finished product from the die after the forming is completed.

[0017] Furthermore, in S2, the height h of the pre-forged blank formed after free forging is 预锻坯 =h 凹模 - (50~70) mm, diameter of pre-forged billet d 预锻坯 =d 凹模 -(5~15)mm; where h 凹模 is the die forming height, d 凹模 The inner diameter of the die.

[0018] Furthermore, in S4, the forming speed S of the near-isothermal reverse extrusion forming is 2 to 6 mm / s, and the forming pressure margin is not less than 15 mm.

[0019] Furthermore, in S4, when performing near-isothermal reverse extrusion forming, the heating and insulation device is first started to heat the die. When the temperature is reached, the hydraulic press connected to the extrusion rod is turned on to push the extrusion rod downward. The extrusion punch moves downward with the movement of the extrusion rod, exerting pressure on the pre-forged billet, forcing the pre-forged billet to flow along the inner wall of the die to the open end of the die. When the pre-forged billet reaches the desired shape and size, the hydraulic press is turned off, the extrusion punch stops moving, and the forming process is completed; thereafter, the pressure direction of the hydraulic press is changed to push the ejector rod upward to eject the formed metal part from the die.

[0020] Further, in S4, when performing near-isothermal reverse extrusion forming, the heating temperature of the heating and heat preservation device is T=T 预锻坯 ±20℃, where T 预锻坯 Heating temperature for pre-forging.

[0021] On the other hand, an embodiment of the present invention provides a 7××× series aluminum alloy pipe near-isothermal reverse extrusion forming device, which can be used for the above-mentioned forming method, and the near-isothermal reverse extrusion forming device includes an extrusion rod, an extrusion punch, a heating and heat preservation device, a die, and an ejector rod;

[0022] The extrusion punch is fixed at the lower end of the extrusion rod, and the extrusion punch extrudes the pre-forged billet through the movement of the extrusion rod;

[0023] The female die is fixed at the bottom of the near-isothermal reverse extrusion forming device, opposite to the ejector rod, to form a closed forming cavity, providing a forming space for the pre-forged billet; the inner cavity shape of the forming cavity matches the cross-sectional shape of the aluminum alloy pipe to be formed;

[0024] The heating and heat-insulating device surrounds the die to control the temperature; the ejector rod is used to support the pre-forged billet during the forming process and to eject the finished product from the die after the forming is completed.

[0025] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0026] 1) The traditional aluminum alloy pipe forming method is to directly put the ingot into the extruder in a heated state for extrusion forming. For 7××× series aluminum alloy pipes, the performance in the three directions of transverse, longitudinal and height is quite different. The aluminum alloy pipe forming method of the present invention does not directly perform extrusion forming, but performs free forging on it, and then adopts a special near-isothermal reverse extrusion forming device to perform near-isothermal reverse extrusion forming. By accurately controlling the deformation temperature and deformation amount during free forging and near-isothermal reverse extrusion forming, the grain morphology and recrystallization volume fraction of the pipe are controlled, so that the transverse, longitudinal and height performance of the pipe are nearly isotropic, reducing the risk of pipe cracking.

[0027] 2) The existing near-isothermal reverse extrusion forming device for 7××× series aluminum alloy pipes is difficult to meet the requirements of high precision and high performance. The near-isothermal reverse extrusion forming device of the present invention is a reverse extrusion forming device on a vertical hydraulic press. It has an innovative structural design and an optimized metal flow direction. Compared with the traditional horizontal extruder, it is more compact and easy to operate. The metal flow is consistent with the direction of gravity, which reduces friction and improves product quality. Reverse extrusion reduces the extrusion force, allows the use of larger ingots, achieves uniform deformation, and reduces stress concentration and waste. The insulation device ensures uniform heating of the pre-forged billet and improves forming accuracy. The extrusion rod and punch act directly on the pre-forged billet to improve efficiency. The design of the die and ejector rod adapts to reverse extrusion forming and simplifies operation. These improvements meet the requirements of high precision and high performance while saving energy and improving production efficiency.

[0028] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings are only for the purpose of illustrating specific embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0030] Figure 1 It is a schematic diagram of the near-isothermal reverse extrusion forming device of the aluminum alloy pipe of the present invention;

[0031] Figure 2 for Figure 1 Schematic diagram of key dimensions of the concave die;

[0032] Figure 3 for Figure 1 Schematic diagram of the key dimensions of the extrusion punch.

[0033] Reference numerals:

[0034] 1-extrusion rod; 2-extrusion punch; 3-heating and heat preservation device; 4-die; 5-ejector rod; 6-pre-forged billet. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0036] In one aspect, the present invention discloses a 7××× series aluminum alloy tube forming method, comprising the following steps:

[0037] S1, heating of aluminum alloy ingot and flat die;

[0038] S2, free forging the heated ingot to form a pre-forged billet;

[0039] S3, heating the pre-forged billet and the near-isothermal reverse extrusion forming device respectively;

[0040] S4, placing the heated pre-forged billet into a near-isothermal reverse extrusion forming device for near-isothermal reverse extrusion forming.

[0041] Furthermore, the method is applicable to 7××× series ultra-high strength deformed aluminum alloy materials, the outer diameter range of the pipe can reach Ф300mm~Ф1000mm, such as 300mm, 400mm, 500mm, 600mm, 700mm, 800mm, 900mm, 1000mm, and the wall thickness can reach 30mm~70mm, such as 30mm, 40mm, 50mm, 60mm, 70mm.

[0042] It should be noted that the traditional aluminum alloy tube forming method is to put the ingot into the extruder directly in a heated state to extrude it into an aluminum alloy tube with a certain shape and wall thickness. However, this method, during the extrusion process, due to the large extrusion force and uneven metal flow, can easily lead to uneven grain orientation and distribution inside the material, resulting in large differences in transverse, longitudinal and height performance.

[0043] In order to solve this problem, the present invention does not directly extrude the heated aluminum alloy ingot, but performs free forging on it, and then adopts a special near-isothermal reverse extrusion forming device to perform near-isothermal reverse extrusion forming, so that the transverse, longitudinal and height properties of the tube are nearly isotropic.

[0044] Furthermore, the near isothermal reverse extrusion forming device is as follows Figure 1 As shown, it includes an extrusion rod, an extrusion punch, a heating and heat preservation device, a die, and an ejector rod;

[0045] The extrusion punch is fixed at the lower end of the extrusion rod, and the extrusion punch extrudes the pre-forged billet through the movement of the extrusion rod; the die is fixed at the bottom of the near-isothermal reverse extrusion forming device, opposite to the ejector rod, to form a closed forming cavity, providing a forming space for the pre-forged billet; the inner shape of the forming cavity matches the cross-sectional shape of the aluminum alloy pipe to be formed; the heating and heat preservation device surrounds the die to control the temperature; the ejector rod is used to support the pre-forged billet during the forming process and to eject the finished product from the die after the forming is completed.

[0046] Further, in S2, the free forging mainly includes the following three steps:

[0047] (1) Upsetting: The ingots heated at 350-440°C, such as 350°C, 370°C, 390°C, 400°C, 410°C, 420°C, 430°C, and 440°C, are upset to increase the cross-section of the ingots and prepare for the subsequent drawing step. The holding time of the ingots can be set to 1.5 to 2 times the minimum thickness of the aluminum alloy ingots. The upsetting step helps to break the original cast structure, promote grain refinement, and lay the foundation for obtaining a uniform microstructure.

[0048] (2) Reversing drawing: The ingot is stretched along the axial direction. This step can further refine the grains, improve the uniformity of the material, and reduce the anisotropy of the material. Generally, the drawing ratio is controlled to be no less than 2, such as 2, 3, 4, 5, 6, and 7.

[0049] (3) Upsetting and shaping to size: After the previous step of reversing and stretching to a size close to the final size, upsetting and shaping are performed again to meet the design requirements. This step requires precise control of the final size and shape of the upsetting and shaping to ensure that the final size and shape of the forging meet the requirements.

[0050] The above forging can be free forging, and the number of upsetting and reversing drawing is not limited, and can be two upsetting and one drawing, two upsetting and two drawing, three upsetting and two drawing, etc., and due to the different sizes of the ingots, the deformation amount of each step of forging can be different.

[0051] However, in order to ensure uniform deformation and avoid residual cast structure, the total deformation of free forging needs to be controlled within 6 to 10, such as 6, 7, 8, 9, and 10.

[0052] Finally, the height of the pre-forged billet h 预锻坯 =h 凹模 - (50~70) mm, diameter of pre-forged billet d 预锻坯 =d 凹模 -(5~15)mm; where h 凹模 is the die forming height, d 凹模 The inner diameter of the die.

[0053] Specifically, the height is 50 to 70 mm lower than the forming height of the die, such as 50 mm, 55 mm, 60 mm, 65 mm, and 70 mm, which provides sufficient space for the metal during the extrusion process, ensuring that the metal can flow evenly and completely fill the die, reducing voids and defects; the diameter is 5 to 15 mm less than the inner diameter of the die, such as 5 mm, 8 mm, 10 mm, 12 mm, and 15 mm, which provides space for the expansion of the metal during the extrusion process, helps the metal to flow evenly in the die, and controls the inner diameter of the extruded part.

[0054] Free forging effectively breaks the grain orientation in the original material through intense plastic deformation and recrystallization process, crushes the grains, and makes the grains more evenly distributed in the material, which helps to improve the performance of the material.

[0055] After free forging, the performance of the material is optimized, and it can still maintain sufficient plasticity and deformation capacity at a lower temperature, and can be reverse extruded at a lower temperature, providing strong support for the subsequent near-isothermal reverse extrusion at a lower temperature.

[0056] Furthermore, in S1, the aluminum alloy ingot is heated to a temperature T 锭坯 : 350℃~440℃, such as 350℃, 370℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, flat die heating temperature T 平模 : 300℃~450℃, such as 300℃, 320℃, 350℃, 370℃, 390℃, 400℃, 430℃, 450℃.

[0057] Furthermore, in S3, the pre-forged billet heating temperature T 预锻坯 The heating temperature T of the near-isothermal reverse extrusion forming device is 200-300°C, such as 200°C, 220°C, 250°C, 280°C, 300°C. 装置 T 预锻坯 ±20℃.

[0058] Specifically, for 7××× series aluminum alloy, the conventional extrusion forming temperature is 400-440°C, which can ensure that the aluminum alloy has good plasticity and deformation ability during the extrusion process. However, the present invention adopts reverse extrusion forming at a lower temperature. 预锻坯 It is 200~300℃.

[0059] When forming at a lower temperature, the material does not recover or recovers only a small amount after plastic deformation, and the distortion energy is greater. In this case, when the material is solution heated, driven by both distortion energy and heating, more deformed grains reach the driving force for recrystallization and recrystallize, so that a large number of recrystallized grains are embedded in the middle of the deformed structure, and the recrystallization volume fraction is increased by about 20%. In this way, the strength of the material is guaranteed and the anisotropy of the material properties is reduced.

[0060] Specifically, the temperature matching between the near-isothermal reverse extrusion forming device and the aluminum alloy ingot helps to reduce thermal stress and thermal shock. When the temperature difference between the two is too large, it may cause uneven deformation of the material and increase the risk of cracks and defects. In order to ensure temperature matching during the forming process and ensure the consistency of material properties. The near-isothermal reverse extrusion forming device is heated to the temperature T 装置 Set to T 锭坯 ±20℃.

[0061] Furthermore, in S4, the forming speed S is 2 to 6 mm / s, such as 2 mm / s, 3 mm / s, 4 mm / s, 5 mm / s, and 6 mm / s, and the forming pressure margin is not less than 15 mm, such as 15 mm, 18 mm, and 20 mm.

[0062] Specifically, aluminum alloy has good fluidity after heating, but too fast forming speed can easily lead to uneven material flow and defects. The slower forming speed (2-6 mm / s) of the present invention can ensure that the material has enough time to flow and fill during the extrusion process, thereby obtaining a better forming effect. The forming pressure margin is not less than 15 mm, which can ensure that the material has enough space to fill during the extrusion process to avoid voids and defects.

[0063] Further, in S4, when performing near-isothermal reverse extrusion, the heated pre-forged billet is placed above the bottom of the die, such as Figure 1 As shown in the middle left figure, the heating and heat preservation device is started to heat the die. When the die reaches the appropriate temperature, the hydraulic press connected to the extrusion rod is turned on to push the extrusion rod downward. The extrusion punch moves downward with the movement of the extrusion rod and directly contacts the pre-forged billet, exerting pressure on the pre-forged billet, forcing the pre-forged billet to flow along the inner wall of the die to the open end of the die. This process is called reverse extrusion. When the pre-forged billet reaches the desired shape and size, the hydraulic press is turned off, the extrusion punch stops moving, and the forming process is completed.

[0064] The final pre-forged billet is Figure 1 As shown in the middle right figure, the outer diameter of the tube is gradually formed by the inner wall of the die, and the inner diameter of the tube is gradually formed by the extrusion punch.

[0065] Then change the pressure direction of the hydraulic press, push the ejector rod upward, eject the formed metal part from the die, take out the metal part, and then carry out necessary inspection and subsequent processing, such as cooling and trimming.

[0066] Furthermore, when performing near-isothermal reverse extrusion, the heating temperature of the heating and heat preservation device is T = T 预锻坯 ±20℃, and the heating temperature T of the previous near-isothermal reverse extrusion forming device 装置 Consistent.

[0067] On the other hand, the present invention discloses a near-isothermal reverse extrusion forming device for 7××× series aluminum alloy pipes, which can be used in the forming method described above, that is, the device mentioned in the above forming method.

[0068] Specifically, it includes an extrusion rod, an extrusion punch, a heating and heat preservation device, a die, and an ejector rod; the extrusion punch is fixed at the lower end of the extrusion rod; the die is fixed at the bottom of the near-isothermal reverse extrusion forming device, opposite to the ejector rod, to form a closed forming cavity; the heating and heat preservation device surrounds the die.

[0069] Furthermore, the taper of the bottom surface of the extrusion punch is 冲头 = 1°~5°, such as 1°, 2°, 3°, 4°, 5°. The existence of taper helps the metal to better fill the mold cavity during the extrusion process and reduce the generation of cavities and cracks. A smaller taper of 1°~5° can reduce the friction between the metal and the punch when it flows, reduce the extrusion force, and help the metal flow more evenly to the outlet of the mold, thereby reducing the defects of the extruded parts.

[0070] Furthermore, the extrusion punch forms a rounded corner R 冲头 = R3~R8, such as R3, R4, R5, R6, R7, R8. Larger fillets can reduce stress concentration during metal flow and reduce the risk of rupture of extruded parts. 冲头 =R3~R8 helps to obtain better surface quality of extruded parts and reduce surface defects.

[0071] Furthermore, the heating and heat preservation device adopts a wrap-around electric heating tube heating and a K-type thermocouple temperature control.

[0072] Furthermore, the taper of the die forming wall surface is 凹模 The taper of the die forming wall is 0.5°~1°, such as 0.5°, 0.6°, 0.7°, 0.8°, 0.9°, 1°. The taper of the die forming wall refers to the slope of the inner wall of the die from the bottom to the top. The taper helps the metal to flow smoothly on the inner wall of the die, reducing flow resistance and friction. A smaller taper of 0.5°~1° can reduce the adhesion of metal on the inner wall of the die, reduce the draft force, and reduce the surface damage of the extruded part.

[0073] Furthermore, the near-isothermal reverse extrusion forming device is a vertical structure. Compared with the traditional horizontal extruder, the vertical structure is more compact, occupies less space, and is easy to operate and maintain. The metal flow direction is consistent with the gravity direction, which helps to reduce the friction and distortion of the metal during the forming process, and the flow is smoother, which helps to obtain a more uniform microstructure and reduce the performance difference of the material in different directions. In contrast, the metal flow direction in the horizontal extruder is perpendicular to the gravity direction, which easily leads to uneven metal flow and affects product quality.

[0074] Furthermore, the near-isothermal reverse extrusion forming device is reverse extrusion forming. Compared with the forward extrusion forming, the metal flow direction is opposite to the movement direction of the extrusion punch, the extrusion force and friction are reduced, the stress concentration is reduced, the metal flow is more uniform, and it is helpful to reduce the performance difference of the material in different directions. A larger ingot can be used, and the outer diameter range of the tube can reach Ф300mm~Ф1000mm, such as 300mm, 400mm, 500mm, 600mm, 700mm, 800mm, 900mm, 1000mm. The deformation of the metal is more uniform, and the waste such as the residual pressure is also significantly reduced.

[0075] Furthermore, the near-isothermal reverse extrusion forming device is added with a heat preservation device. This design can heat the pre-forged billet more evenly, ensure more precise temperature control during the forming process, and avoid differences in material properties caused by uneven temperature.

[0076] In addition, the configuration of the extrusion rod and the extrusion punch allows the extrusion force to act directly on the pre-forged billet, improving the forming efficiency. The design of the die can be more complex to meet the special requirements of reverse extrusion forming. The design of the ejector rod can push the formed tube out of the die after the extrusion is completed, which is convenient for subsequent operations.

[0077] In summary, the structural design of these devices helps to reduce the performance differences of materials in different directions. When using the device for near-isothermal reverse extrusion forming, the performance differences in the transverse, longitudinal and height directions of the pipe can be reduced, the quality of the product can be improved, and high precision and high performance requirements can be met.

[0078] Compared with the prior art, the aluminum alloy pipe forming method provided in this embodiment does not directly perform extrusion forming, but performs free forging on it, and then adopts the special near-isothermal reverse extrusion forming device of the present invention to perform reverse extrusion forming (the device can optimize metal flow and uniform deformation through compact design, precise temperature control, complex die design and convenient ejection function, thereby realizing efficient production of high-precision and high-performance aluminum alloy pipes), during which the total forging deformation, extrusion forming temperature, etc. are precisely controlled to control the grain morphology and recrystallization volume fraction of the pipe, so as to make the transverse, longitudinal and high-height properties of the pipe nearly isotropic, thereby reducing the risk of pipe cracking.

[0079] Through experiments, the transverse, longitudinal and high R p0.2 and R m The average absolute deviation of the performance is only 4-10 and 5-6 respectively. The performance differences in the transverse, longitudinal and height directions of the tube are small, which can meet the high-precision and high-performance requirements of aluminum alloy tubes for shells and has broad application prospects.

[0080] The present invention is further described below with reference to the specification using examples, but the examples are only used for the present invention and are not intended to limit the present invention.

[0081] Example 1

[0082] A nearly isothermal reverse extrusion forming device for an aluminum alloy pipe comprises an extrusion rod, an extrusion punch, a heating and heat-insulating device, a die, and an ejector rod; the extrusion punch is fixed at the lower end of the extrusion rod, and the extrusion of the pre-forged billet is achieved by moving the extrusion rod; the die is fixed at the bottom of the nearly isothermal reverse extrusion forming device, opposite to the ejector rod, to form a closed forming cavity; the heating and heat-insulating device surrounds the die to control the temperature.

[0083] Extrusion punch forming bottom taper α 冲头 =2°. Extrusion punch forming radius R 冲头 = R5. Heating and insulation device The heating and insulation form is a surrounding electric heating tube heating, K-type thermocouple temperature control. Concave die forming height h 凹模 =660mm, forming inner diameter d 凹模 =445mm, forming wall taper α 凹模 =1°.

[0084] Example 2

[0085] A near-isothermal reverse extrusion forming device for an aluminum alloy pipe, which differs from the first embodiment only in that the taper of the bottom surface of the extrusion punch is α 冲头 =3°. Extrusion punch forming radius R 冲头 =R5. Die forming height h 凹模 =670mm, forming inner diameter d 凹模 =560mm, forming wall taper α 凹模 =0.5°.

[0086] Example 3

[0087] A near-isothermal reverse extrusion forming device for an aluminum alloy pipe, which differs from the first embodiment only in that the taper of the bottom surface of the extrusion punch is α 冲头 =5°. Extrusion punch forming radius R 冲头 = R8. Concave die forming height h 凹模 =750mm, forming inner diameter d 凹模 =900mm, forming wall taper α 凹模 =0.8°.

[0088] Example 4

[0089] A 7A99 aluminum alloy tube with an outer diameter of 445 mm and a wall thickness of 40 mm is formed by using the near-isothermal reverse extrusion forming device of Example 1, comprising the following steps:

[0090] Step 1: Heating of ingot and mold. Heat the aluminum alloy ingot to 380℃. At the same time, heat the flat mold to 400℃.

[0091] Step 2: Free forging. The initial ingot size is diameter d 锭坯 =350mm, height h 锭坯 =930mm. Free forging is performed, first upsetting to a height of 350mm, with a deformation of 2.6. Then the length is changed to 930mm, and the deformation is again 2.6. Finally, the pre-forged blank is upset and shaped to an outer diameter d = 435mm and a height h 预锻坯 =600mm, deformation 1.5. The total deformation is 6.7.

[0092] Step 3: Heating of the pre-forged billet and the near-isothermal reverse extrusion forming device. Heat the pre-forged billet to 250°C. At the same time, heat the near-isothermal reverse extrusion forming device to 270°C;

[0093] Step 4: Near-isothermal reverse extrusion. Place the heated pre-forged billet in the die of the near-isothermal reverse extrusion forming device of Example 1. Apply pressure to the pre-forged billet through the extrusion rod and the extrusion punch, so that it is formed into the desired tube shape in the die. Place the heated pre-forged billet in the die of the near-isothermal reverse extrusion forming device of Example 1. Apply pressure to the pre-forged billet through the extrusion rod and the extrusion punch, so that it is formed into the desired tube shape in the die. Perform the forming at a forming speed of 3mm / s to ensure the stability of the forming process and the quality of the product. Ensure that the forming pressure margin is not less than 15mm to ensure the forming quality. During the forming process, a heating and heat preservation device surrounds the die to keep the temperature in the forming cavity stable.

[0094] Example 4-1

[0095] The only difference from Example 4 is that in step 2, the total deformation amount of free forging is 9.

[0096] Example 4-2

[0097] The only difference from Example 4 is that in step 3, the pre-forged billet is heated to 290°C. At the same time, the nearly isothermal reverse extrusion forming device is heated to 300°C.

[0098] Example 4-3

[0099] The only difference from Example 4 is that in step 4, the near-isothermal reverse extrusion forming speed is 5 mm / s.

[0100] Example 5

[0101] A 7A85 aluminum alloy tube with an outer diameter of 560 mm and a wall thickness of 55 mm is formed by using the near-isothermal reverse extrusion forming device of Example 2, comprising the following steps:

[0102] Step 1: Heating of ingot and mold. Heat the aluminum alloy ingot to 400℃. At the same time, heat the flat mold to 400℃;

[0103] Step 2: Free forging. Ingot diameter d 锭坯 =400mm, height h 锭坯 =1180mm, free forging two upsets and one pull, upsetting to height 400mm, deformation 2.9---reversing pull to length 1100mm, deformation 2.7---upsetting and shaping to outer diameter d 预锻坯 =550mm height h 预锻坯 =620mm, deformation 1.7, total deformation 7.3.

[0104] Step 3: Heating of the pre-forged billet and the near-isothermal reverse extrusion forming device. Heat the pre-forged billet to 290°C. At the same time, heat the near-isothermal reverse extrusion forming device to 300°C;

[0105] Step 4: Near-isothermal reverse extrusion forming. The difference from step 4 of embodiment 5 is that the near-isothermal reverse extrusion forming device of embodiment 2 is used for the forming process, and the forming process is performed at a forming speed of 4 mm / s.

[0106] Example 5-1

[0107] The only difference from Example 5 is that in step 2, the total deformation amount of free forging is 9.

[0108] Example 5-2

[0109] The only difference from Example 5 is that in step 3, the pre-forged billet is heated to 250°C. At the same time, the nearly isothermal reverse extrusion forming device is heated to 270°C.

[0110] Example 5-3

[0111] The only difference from Example 5 is that in step 4, the near-isothermal reverse extrusion forming speed is 5 mm / s.

[0112] Example 6

[0113] A 7075 aluminum alloy tube with an outer diameter of 900 mm and a wall thickness of 65 mm is formed by using the near-isothermal reverse extrusion forming device of Example 3, comprising the following steps:

[0114] Step 1: Heating of ingot and mold. Heat the aluminum alloy ingot to 440℃. At the same time, heat the flat mold to 450℃;

[0115] Step 2: Free forging. Ingot diameter d 锭坯 =600mm, height h 锭坯=1500mm, free forging two upsets and one pull, upsetting to height 600mm, deformation 2.5---reversing pull to length 1500mm, deformation 2.5---upsetting and shaping to outer diameter d 预锻坯 =880mm height h 预锻坯 =695mm, deformation 2.1, total deformation 7.1.

[0116] Step 3: Heating of the pre-forged billet and the near-isothermal reverse extrusion forming device. Heat the pre-forged billet to 200°C. At the same time, heat the near-isothermal reverse extrusion forming device to 220°C;

[0117] Step 4: Near-isothermal reverse extrusion forming. The difference from step 4 of embodiment 5 is that the near-isothermal reverse extrusion forming device of embodiment 3 is used for the forming, and the forming is performed at a forming speed of 6 mm / s.

[0118] Example 6-1

[0119] The only difference from Example 6 is that in step 2, the total deformation amount of free forging is 6.

[0120] Example 6-2

[0121] The only difference from Example 6 is that in step 3, the pre-forged billet is heated to 250°C. At the same time, the nearly isothermal reverse extrusion forming device is heated to 270°C.

[0122] Example 6-3

[0123] The only difference from Example 6 is that in step 4, the near-isothermal reverse extrusion forming speed is 4 mm / s.

[0124] Comparative Example 1

[0125] A method for forming an aluminum alloy tube, which differs from Example 4 only in that the free forging in step 2 is missing.

[0126] Comparative Example 2

[0127] A method for forming an aluminum alloy tube, which differs from Example 4 only in that, in step 3, the heating temperature of the pre-forged billet is relatively high at 450°C, and the heating temperature of the near-isothermal reverse extrusion forming device is 470°C.

[0128] Comparative Example 3

[0129] A method for forming an aluminum alloy tube, which differs from Example 4 only in that step 4 uses a conventional horizontal extruder near-isothermal reverse extrusion forming device for extrusion forming.

[0130] Comparative Example 4

[0131] A method for forming an aluminum alloy tube, which differs from Example 4 only in that, in step 4, the near-isothermal extrusion forming speed is too fast to 10 mm / s.

[0132] Performance Characterization

[0133] The room temperature tensile properties of the pipes prepared in Examples 4-6 and Comparative Examples 1-4 are shown in Table 1. The deviation in the table refers to the average absolute deviation in the three directions of Z (longitudinal), H (transverse), and G (height), which can represent the performance differences in the three directions of transverse, longitudinal, and height to a certain extent.

[0134] Example 4-6 Horizontal and vertical height R p0.2 and R m The deviations are 4 to 9 and 4 to 6 respectively; the R p0.2 and R m The deviations are 10-16 and 15-23 respectively; Examples 4-6 are higher in R in the horizontal and vertical directions than Comparative Examples 1-4. p0.2 and R m The above deviation is much smaller, which indicates that the performance differences of the pipes prepared by the method of the present invention in the transverse, longitudinal and height directions are relatively small.

[0135] Comparative Examples 1-4 are all comparative examples of Example 4. Comparative Example 1 finally had insufficient deformation, and the as-cast structure remained. p0.2 , R m The performance of A is low; Comparative Example 2 is over-burned due to the high forming temperature, R p0.2 , R m The performance of the comparative example 3 is relatively low because the traditional extrusion deformation organization is mainly composed of fibrous grains, the longitudinal performance of the material is relatively high, while the transverse performance and high performance are relatively low, especially in the elongation A. p0.2 Deviation up to 16, R m The deviation of A is as high as 23, and the deviation of A is as high as 3, which is mainly attributed to the low recrystallization volume fraction in the extrusion deformation structure, resulting in obvious anisotropy; Comparative Example 4 finally produced problems such as bending, punch holding, and inability to be removed due to the fast forming speed and uneven material flow, and R p0.2 , R m The performance of A is relatively low. This shows that the aluminum alloy tube forming method of the present invention has certain advantages.

[0136] Microscopic observation revealed that the recrystallization volume fraction of Example 1 was 38%, while the recrystallization volume fraction of Comparative Example 3 was only 18%. The method of the present invention increases the recrystallization volume fraction by about 20% compared with the traditional method, which helps to reduce the anisotropy of material properties.

[0137] Table 1

[0138]

[0139]

[0140]

[0141]

[0142]

[0143] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A 7××× series aluminum alloy tube forming method, characterized in that: The following steps are involved: S1, heating of aluminum alloy ingot and flat die; S2, free forging the heated ingot to form a pre-forged billet; S3, heating the pre-forged billet and the near-isothermal reverse extrusion forming device respectively; S4, placing the heated pre-forged billet into a near-isothermal reverse extrusion forming device for near-isothermal reverse extrusion forming.

2. The forming method according to claim 1, characterized in that: In S2, the total free forging deformation is 6 to 10.

3. The forming method according to claim 1, characterized in that: In S1, the aluminum alloy ingot heating temperature T 锭坯 : 350℃~440℃, flat die heating temperature T 平模 : 300℃~450℃.

4. The forming method according to claim 1, characterized in that: In S3, the pre-forging billet is heated to the temperature T 预锻坯 The heating temperature of the near-isothermal reverse extrusion forming device is 200-300°C. 装置 T 预锻坯 ±20℃.

5. The forming method according to claim 1, characterized in that: The near-isothermal reverse extrusion forming device comprises an extrusion rod, an extrusion punch, a heating and heat-insulating device, a concave die, and an ejector rod; The extrusion punch is fixed at the lower end of the extrusion rod, and the extrusion punch extrudes the pre-forged billet through the movement of the extrusion rod; the die is fixed at the bottom of the near-isothermal reverse extrusion forming device, opposite to the ejector rod, to form a closed forming cavity, providing a forming space for the pre-forged billet; The inner shape of the forming cavity matches the cross-sectional shape of the aluminum alloy pipe to be formed; the heating and heat-insulating device surrounds the die to control the temperature; the ejector rod is used to support the pre-forged billet during the forming process and to eject the finished product from the die after the forming is completed.

6. The forming method according to claim 5, characterized in that: In S2, the height h of the pre-forged billet after free forging 预锻坯 =h 凹模 - (50~70) mm, diameter of pre-forged billet d 预锻坯 =d 凹模 -(5~15)mm; where h 凹模 is the die forming height, d 凹模 The inner diameter of the die.

7. The forming method according to claim 1, characterized in that: In S4, the forming speed S of the near-isothermal reverse extrusion forming is 2 to 6 mm / s, and the forming pressure margin is not less than 15 mm.

8. The forming method according to claim 7, characterized in that: In S4, when performing near-isothermal reverse extrusion forming, the heating and insulation device is first started to heat the die. When the temperature is reached, the hydraulic press connected to the extrusion rod is turned on to push the extrusion rod downward. The extrusion punch moves downward with the movement of the extrusion rod, exerting pressure on the pre-forged billet, forcing the pre-forged billet to flow along the inner wall of the die toward the open end of the die. When the pre-forged billet reaches the desired shape and size, the hydraulic press is turned off, the extrusion punch stops moving, and the forming process is completed; then the pressure direction of the hydraulic press is changed to push the ejector rod upward to eject the formed metal part from the die.

9. The forming method according to claim 8, characterized in that: In S4, when the near-isothermal reverse extrusion forming is performed, the heating temperature of the heating and heat preservation device is T = T 预锻坯 ±20℃, where T 预锻坯 Heating temperature for pre-forging.

10. A 7××× series aluminum alloy pipe near-isothermal reverse extrusion forming device, characterized in that: It can be used in the forming method according to any one of claims 1 to 8, wherein the near-isothermal reverse extrusion forming device comprises an extrusion rod, an extrusion punch, a heating and heat-insulating device, a concave die, and an ejector rod; The extrusion punch is fixed at the lower end of the extrusion rod, and the extrusion punch extrudes the pre-forged billet through the movement of the extrusion rod; The concave die is fixed at the bottom of the near-isothermal reverse extrusion forming device, opposite to the ejector rod, to form a closed forming cavity, providing a forming space for the pre-forged billet; The inner cavity shape of the forming cavity matches the cross-sectional shape of the aluminum alloy pipe to be formed; The heating and heat-insulating device surrounds the die to control the temperature; the ejector rod is used to support the pre-forged billet during the forming process and to eject the finished product from the die after the forming is completed.

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