Method and apparatus for forming aluminum alloy tube

Abstract

The present application relates to a kind of aluminum alloy pipe forming method and its device, belong to metal material forming technical field, solve the problem that the transverse, vertical, high three-way performance of 7 × × × series super high strength deformed aluminum alloy pipe in prior art is greatly different.The pipe forming method of the present application, after heating, ingot is carried out free forging, and then special near isothermal backward extrusion forming device is used to the near isothermal backward extrusion forming of pre-forged blank after heating.By precisely controlling the total deformation of forging, extrusion forming temperature and the like, the grain morphology and recrystallization volume fraction of pipe are controlled, the synergy of deformed structure and recrystallized structure is fully played, the transverse, vertical, high three-way performance of pipe is close to isotropy, and the risk of pipe cracking is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal material forming, in particular to an aluminum alloy pipe forming method and device. BACKGROUND

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

[0003] 7xxx series aluminum alloys have good specific strength and heat treatability. The high strength of these alloys mainly comes from their complex microstructure, including various precipitates and textures. However, these complex microstructures can also lead to significant differences in transverse, longitudinal, and high-directional properties, resulting in deformation overruns or even cracking during machining, increasing the difficulty and cost of processing.

[0004] Traditional near-isothermal backward extrusion forming devices for aluminum alloy pipes are horizontal extrusion machines combined with molds. The aluminum alloy billets are placed in the hopper of the extrusion machine in a heated state and are extruded into a pipe shape by high pressure and the mold. However, this extrusion requires a large extrusion force, and the extrusion force is unevenly distributed in the mold, leading to uneven metal flow and causing uneven grain orientation and distribution within the material, resulting in large differences in transverse, longitudinal, and high-directional properties.

[0005] To solve the above problems, the current common methods are free forging of round bars and then machining of hole-drawing, or other methods such as powder metallurgy, etc. However, these methods are mostly complex in process, not only long in production cycle, but also high in production cost and low in material utilization rate. SUMMARY

[0006] In view of the above analysis, the embodiments of the present application aim to provide an aluminum alloy pipe forming method and device to at least solve one of the following problems: (1) the existing 7xxx series aluminum alloy pipe forming process has large differences in transverse, longitudinal, and high-directional properties; (2) the existing near-isothermal backward extrusion forming device for 7xxx series aluminum alloy pipes cannot meet the requirements of high precision and high performance.

[0007] In one aspect, the embodiments of the present application provide a 7xxx series aluminum alloy pipe forming method, comprising the following steps:

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

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

[0010] S3, heating of the pre-forged billet and a near-isothermal backward extrusion forming device;

[0011] S4, the heated pre-forging blank is put into a near isothermal backward extrusion forming device to perform near isothermal backward extrusion forming.

[0012] Further, in S2, the total deformation of the free forging is 6-10.

[0013] Further, in S1, the heating temperature T of the aluminum alloy ingot blank is 350-440 DEG C, and the heating temperature T of the flat die is 300-450 DEG C. 锭坯 平模

[0014] Further, in S3, the heating temperature T of the pre-forging blank is 200-300 DEG C, and the heating temperature T of the near isothermal backward extrusion forming device is T ± 20 DEG C. 预锻坯 装置 预锻坯

[0015] Further, the near isothermal backward extrusion forming device comprises an extrusion rod, an extrusion punch, a heating and holding device, a female die, and an ejection rod.

[0016] The extrusion punch is fixed at the lower end of the extrusion rod and extrudes the pre-forging blank by moving the extrusion rod. The female die is fixed at the bottom of the near isothermal backward extrusion forming device and is opposite to the ejection rod, forming a closed forming cavity to provide forming space for the pre-forging blank. The inner cavity shape of the forming cavity matches the cross-sectional shape of the aluminum alloy pipe to be formed. The heating and holding device surrounds the female die to control the temperature. The ejection rod is used to support the pre-forging blank during forming and to eject the finished product from the female die after forming.

[0017] Further, in S2, the height h of the pre-forging blank formed after free forging is h - (50-70) mm, and the diameter d of the pre-forging blank is d - (5-15) mm; wherein h is the forming height of the female die, and d is the forming inner diameter of the female die. 预锻坯 凹模 预锻坯 凹模 凹模 凹模

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

[0019] ​​​​​​​​​​​Further, in S4, when the near-isothermal backward extrusion forming is performed, first, the heating and holding device is started to heat the concave die, when the temperature reaches, the hydraulic machine connected with the extrusion rod is opened to push the extrusion rod to move downward, the extrusion punch moves downward with the movement of the extrusion rod to apply pressure to the pre-forged blank to force the pre-forged blank to flow along the inner wall of the concave die to the opening end of the concave die, when the pre-forged blank reaches the required shape and size, the hydraulic machine is closed and the extrusion punch stops moving, and the forming process is completed; then the pressure direction of the hydraulic machine is changed to push the ejector rod to move upward to eject the formed metal piece from the concave die.

[0020] Further, in S4, when the near-isothermal backward extrusion forming is performed, the heating temperature T of the heating and holding device is T 预锻坯 ±20℃, wherein T 预锻坯 is the pre-forged blank heating temperature.

[0021] On the other hand, the embodiment of the present application provides a near-isothermal backward extrusion forming device for 7××× series aluminum alloy pipe, which can be used in the forming method described above, and the near-isothermal backward extrusion forming device comprises an extrusion rod, an extrusion punch, a heating and holding device, a concave die, and an ejector rod.

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

[0023] The concave die is fixed at the bottom of the near-isothermal backward extrusion forming device and opposite to the ejector rod to form a closed forming cavity to provide forming space for the pre-forged blank; 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 holding device surrounds the concave die to control the temperature; and the ejector rod is used to support the pre-forged blank during the forming process and to eject the finished product from the concave die after the forming is completed.

[0025] Compared with the prior art, the present application 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 blank into the extruder for extrusion forming in a heated state, and for 7××× series aluminum alloy pipe, the transverse, longitudinal and high performance differences are large. The aluminum alloy pipe forming method of the present application does not directly perform extrusion forming, but performs free forging, and then performs near-isothermal backward extrusion forming by using a special near-isothermal backward extrusion forming device. By accurately controlling the deformation temperature and deformation amount in the free forging and near-isothermal backward extrusion forming process, the grain morphology and recrystallization volume fraction of the pipe are controlled, the transverse, longitudinal and high performance of the pipe is close to isotropy, and the pipe cracking risk is reduced.

[0027] 2) The existing 7xxx series aluminum alloy pipe near-isothermal backward extrusion forming device is difficult to meet the requirements of high precision and high performance. The near-isothermal backward extrusion forming device is backward extrusion forming on a vertical hydraulic machine, has innovative structural design and optimized metal flow direction, is more compact and convenient to operate compared with a traditional horizontal extrusion machine. The metal flow is consistent with the direction of gravity, reduces friction, and improves product quality. Backward extrusion forming reduces extrusion pressure, allows the use of larger ingots, realizes uniform deformation, reduces stress concentration and waste. The heat preservation device ensures uniform heating of the pre-forged blank, improves forming precision. The extrusion rod and punch directly act on the pre-forged blank, improving efficiency, and the die and ejector rod are designed to adapt to backward extrusion forming, simplifying operation. These improvements meet the requirements of high precision and high performance, while saving energy and improving production efficiency.

[0028] In the present application, the above technical solutions can be combined with each other to realize more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification, or will be understood by implementing the present application. The purpose and other advantages of the present application can be realized and obtained through the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0029] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

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

[0031] Figure 2 Figure 2 is a schematic diagram of the key dimensions of the die of the present application; Figure 1

[0032] Figure 3 is a schematic diagram of the key dimensions of the extrusion punch of the present application. Figure 3 Figure 1 Figure 4 is a schematic diagram of the key dimensions of the extrusion punch of the present application.

[0033] Reference signs:

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

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

[0036] In one aspect, the present application discloses a 7xxx series aluminum alloy pipe forming method, comprising the following steps: ​

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

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

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

[0040] S4, placing the heated pre-forged blank into the near-isothermal counter extrusion forming device to perform near-isothermal counter extrusion forming.

[0041] Further, the method is suitable for 7xxx series ultra-high strength deformed aluminum alloy material, and the outer diameter 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 pipe forming method is to directly put the ingot in the heated state into the extruder for extrusion forming to become an aluminum alloy pipe with a certain shape and wall thickness. However, this method, in the extrusion process, due to the large extrusion force and the uneven flow of metal, is easy to cause the uneven grain orientation and distribution inside the material, thereby causing large differences in transverse, longitudinal and high performance.

[0043] In order to solve this problem, the aluminum alloy ingot after heating is not directly extruded, but is subjected to free forging, and then a special near-isothermal counter extrusion forming device is used for near-isothermal counter extrusion forming, so that the transverse, longitudinal and high performance of the pipe is close to isotropy.

[0044] Further, the near-isothermal counter extrusion forming device, as shown in Figure 1 includes an extrusion rod, an extrusion punch, a heating and holding device, a concave die, and an ejection rod;

[0045] The extrusion punch is fixed at the lower end of the extrusion rod, and the extrusion of the extrusion punch on the pre-forged blank is realized by the movement of the extrusion rod; the concave die is fixed at the bottom of the near-isothermal counter extrusion forming device and opposite to the ejection rod, forming a closed forming cavity to provide forming space for the pre-forged blank; the inner cavity shape of the forming cavity matches the cross-sectional shape of the aluminum alloy pipe to be formed; the heating and holding device surrounds the concave die for temperature control; the ejection rod is used to support the pre-forged blank during forming and to eject the finished product from the concave die after forming.

[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. This step of upsetting helps to break the original cast structure, promote grain refinement, and lay the foundation for obtaining a uniform microstructure.

[0048] (2) Reversing drawing: Lengthen the ingot 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. It 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 in 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 d of pre-forged billet 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 is formed.

[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 lower 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 flow evenly in the die, and controls the inner diameter of the extruded part.

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

[0055] After the free forging, the performance of the material is optimized, and the material still has sufficient plasticity and deformation ability at a lower temperature, and can be subjected to backward extrusion forming at a lower temperature, which provides strong support for subsequent near-isothermal backward extrusion forming at a lower temperature.

[0056] Further, in S1, the heating temperature T of the aluminum alloy ingot blank 锭坯 : 350-440℃, such as 350℃, 370℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, the flat die heating temperature T 平模 : 300-450℃, such as 300℃, 320℃, 350℃, 370℃, 390℃, 400℃, 430℃, 450℃.

[0057] Further, in S3, the pre-forging blank heating temperature T 预锻坯 is 200-300℃, such as 200℃, 220℃, 250℃, 280℃, 300℃, and the near-isothermal backward extrusion forming device heating temperature T 装置 is T 预锻坯 ±20℃.

[0058] Specifically, for 7××× series aluminum alloy, the traditional extrusion forming temperature is 400-440℃, which can ensure that the aluminum alloy has good plasticity and deformation ability during extrusion. However, the present application adopts backward extrusion forming at a lower temperature T 预锻坯 of 200-300℃.

[0059] At a lower temperature, the material has little or no recovery after plastic deformation, and the distortion energy is greater. In this case, when the material is subjected to solid solution heating, more deformed grains reach the driving force for recrystallization under the double driving of distortion energy and heating, and recrystallization occurs, so that a large number of recrystallized grains are embedded in the deformed structure, and the volume fraction of recrystallized grains increases by about 20%. In this way, the strength of the material is ensured, and the anisotropy of the material performance is reduced.

[0060] Specifically, the temperature matching between the near-isothermal backward extrusion forming device and the aluminum alloy ingot blank 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 the temperature matching during forming and ensure the consistency of the material performance, the near-isothermal backward extrusion forming device heating temperature T 装置 is set to T 锭坯 ±20℃.

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

[0062] Specifically, the aluminum alloy has good fluidity after heating, but too fast forming speed is easy to cause uneven material flow and produce defects. The slower forming speed (2-6 mm / s) of the present application can ensure that the material has enough time to flow and fill during extrusion, thereby obtaining better forming effect. The forming pressure surplus of not less than 15 mm can ensure that the material has enough space to fill during extrusion, avoiding the production of voids and defects.

[0063] Further, in S4, when near-isothermal backward extrusion forming is performed, the heated pre-forging blank is placed above the bottom of the concave die, such as Figure 1 as shown in the left drawing of FIG. 4, the heating and holding device is started, the concave die is heated, when the concave die reaches the appropriate temperature, the hydraulic machine connected with the extrusion rod is opened, the extrusion rod is pushed to move downward, the extrusion punch moves downward with the movement of the extrusion rod, directly contacts the pre-forging blank, and applies pressure to the pre-forging blank, forcing the pre-forging blank to flow along the inner wall of the concave die to the open end of the concave die. This process is called backward extrusion. When the pre-forging blank reaches the required shape and size, the hydraulic machine is closed, the extrusion punch stops moving, and the forming process is completed.

[0064] The final pre-forging blank is shown in the right drawing of FIG. 4, which is gradually formed into the outer diameter of the pipe through the inner wall of the concave die, and gradually formed into the inner diameter of the pipe through the extrusion punch. Figure 1

[0065] After that, the direction of the hydraulic machine pressure is changed, the ejector rod is pushed to move upward, the formed metal piece is ejected from the concave die, the metal piece is taken out, and necessary inspection and subsequent processing, such as cooling, trimming, etc. are performed.

[0066] Further, when near-isothermal backward extrusion forming is performed, the heating temperature T of the heating and holding device is T 预锻坯 ±20℃, which is consistent with the heating temperature T 装置 of the previous near-isothermal backward extrusion forming device.

[0067] On the other hand, the present application discloses a near-isothermal backward extrusion forming device for 7××× series aluminum alloy pipe, which can be used in the above forming method, i.e. the device mentioned in the above forming method.

[0068] ​Specifically comprising an extrusion rod, an extrusion punch, a heating and heat preservation device, a concave die, an ejection rod; the extrusion punch is fixed at the lower end of the extrusion rod; the concave die is fixed at the bottom of the near-isothermal backward extrusion forming device, opposite to the ejection rod, forming a closed forming cavity; the heating and heat preservation device surrounds the concave die.

[0069] Further, the extrusion punch forming bottom surface taper α 冲头 = 1° ~ 5°, such as 1°, 2°, 3°, 4°, 5°. The existence of taper helps the metal to fill the cavity of the die better in the extrusion process, reducing the generation of voids and cracks. The smaller taper of 1° ~ 5° can reduce the friction of the metal flowing with the punch, reduce the extrusion force, and help the metal flow more uniformly to the outlet of the die, thereby reducing the defects of the extruded part.

[0070] Further, the extrusion punch forming fillet R 冲头 = R3 ~ R8, such as R3, R4, R5, R6, R7, R8. Larger fillet can reduce stress concentration when the metal flows, reducing the risk of breaking the extruded part. 冲头 = R3 ~ R8 helps to obtain better surface quality of the extruded part and reduce surface defects.

[0071] Further, the heating and heat preservation device of the heating and heat preservation type is a surrounding electric heating pipe heating, and a K-type thermocouple is used for temperature control.

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

[0073] Further, the near-isothermal backward 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. Moreover, the metal flow direction is consistent with the direction of gravity, which helps to reduce the friction and distortion of the metal during the forming process, and the flow is more smooth, which helps to obtain 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 direction of gravity, which easily leads to uneven metal flow and affects the product quality.

[0074] Further, the near-isothermal backward extrusion forming device is backward extrusion forming, compared with 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, which helps to reduce the performance difference of the material in different directions, a larger ingot can be used, and the outer diameter of the pipe 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 excess pressure is also significantly reduced.

[0075] Further, the near-isothermal backward extrusion forming device increases the heat preservation device, which can more uniformly heat the pre-forged blank, ensure more accurate temperature control during forming, and avoid performance differences of the material caused by uneven temperature.

[0076] In addition, the configuration of the extrusion rod and the extrusion punch makes the extrusion force directly act on the pre-forged blank, improving the forming efficiency. The design of the concave die can be more complex to meet the special requirements of backward extrusion forming. The design of the ejector rod can push the formed pipe out of the die after extrusion is completed, facilitating subsequent operation.

[0077] In summary, the structural design of these devices helps to reduce the performance difference of the material in different directions, and when near-isothermal backward extrusion forming is performed with the aid of the device, the transverse, longitudinal, and high performance differences of the pipe can be reduced, the quality of the product can be improved, and the high-precision and high-performance requirements can be met.

[0078] Compared with the prior art, the aluminum alloy pipe forming method provided by the embodiment does not directly perform extrusion forming, but performs free forging, and then performs backward extrusion forming by using the special near-isothermal backward extrusion forming device (the device can optimize metal flow and uniform deformation through compact design, precise temperature control, complex die design, and convenient ejection function, etc., to realize efficient production of high-precision and high-performance aluminum alloy pipes), and the total deformation amount during forging, the extrusion forming temperature, etc. are accurately controlled to control the grain morphology and recrystallization volume fraction of the pipe, so that the transverse, longitudinal, and high performance of the pipe is close to isotropy, and the risk of pipe cracking is reduced.

[0079] Through experiments, the transverse, longitudinal, and high R p0.2 and R m performance average absolute deviation is only 4-10 and 5-6, respectively, the transverse, longitudinal, and high performance difference of the pipe is small, which can meet the high-precision and high-performance use requirements of the aluminum alloy pipe for the shell, and has broad application prospects.

[0080] The embodiments of the present application will be further described in conjunction with the description of the present application, but the embodiments are only used to illustrate the present application and not to limit the present application.

[0081] Example 1

[0082] A near isothermal backward extrusion forming device for aluminum alloy pipe, comprising an extrusion rod, an extrusion punch, a heating and holding device, a female die, and an ejection rod; the extrusion punch is fixed at the lower end of the extrusion rod, and the extrusion of the pre-forging blank is realized by the movement of the extrusion rod; the female die is fixed at the bottom of the near isothermal backward extrusion forming device and is opposite to the ejection rod, forming a closed forming cavity; the heating and holding device is wrapped around the female die to control the temperature.

[0083] The forming bottom taper of the extrusion punch is α 冲头 = 2°. The forming fillet of the extrusion punch is R 冲头 = R5. The heating and holding form of the heating and holding device is a ring-shaped electric heating tube, and the temperature is controlled by a K-type thermocouple. The forming height of the female die is h 凹模 = 660 mm, the forming inner diameter is d 凹模 = 445 mm, the forming wall taper is α 凹模 = 1°.

[0084] Example 2

[0085] A near isothermal backward extrusion forming device for aluminum alloy pipe, and the difference from Example 1 is only that the forming bottom taper of the extrusion punch is α 冲头 = 3°. The forming fillet of the extrusion punch is R 冲头 = R5. The forming height of the female die is h 凹模 = 670 mm, the forming inner diameter is d 凹模 = 560 mm, the forming wall taper is α 凹模 = 0.5°.

[0086] Example 3

[0087] A near isothermal backward extrusion forming device for aluminum alloy pipe, and the difference from Example 1 is only that the forming bottom taper of the extrusion punch is α 冲头 = 5°. The forming fillet of the extrusion punch is R 冲头 = R8. The forming height of the female die is h 凹模 = 750 mm, the forming inner diameter is d 凹模 = 900 mm, the forming wall taper is α 凹模 = 0.8°.

[0088] Example 4

[0089] A 7A99 aluminum alloy pipe with an outer diameter of Ф445 mm and a wall thickness of 40 mm, and the forming method is carried out by means of the near isothermal backward extrusion forming device of Example 1, comprising the following steps:

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

[0091] Step 2: free forging. The initial ingot size is diameter d 锭坯 = 350 mm, height h 锭坯 = 930 mm. Free forging is performed, first upsetting to height 350 mm, deformation 2.6. Then reversing to length 930 mm, again deformation 2.6. Finally, upsetting to finish to outer diameter dpreform = 435 mm, height h 预锻坯 = 600 mm, deformation 1.5. The total deformation is 6.7.

[0092] Step 3: heating of the preform and the near-isothermal reverse extrusion forming device. The preform is heated to 250°C. At the same time, the near-isothermal reverse extrusion forming device is heated to 270°C;

[0093] Step 4: near-isothermal reverse extrusion forming. The heated preform is placed in the female die of the near-isothermal reverse extrusion forming device of Example 1. Pressure is applied to the preform by the extrusion rod and the extrusion punch to form it into the desired shape of the tube in the female die. The heated preform is placed in the female die of the near-isothermal reverse extrusion forming device of Example 1. Pressure is applied to the preform by the extrusion rod and the extrusion punch to form it into the desired shape of the tube in the female die. Forming is performed at a forming speed of 3 mm / s to ensure stability of the forming process and product quality. The forming pressure margin is ensured to be not less than 15 mm to ensure forming quality. During the forming process, the heating and holding device is wrapped around the female die to maintain stable temperature in the forming cavity.

[0094] Example 4-1

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

[0096] Example 4-2

[0097] The difference from Example 4 is only in Step 3, the preform is heated to 290°C. At the same time, the near-isothermal reverse extrusion forming device is heated to 300°C.

[0098] Example 4-3

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

[0100] Example 5

[0101] A 7A85 aluminum alloy tube with outer diameter Ф560 mm and wall thickness 55 mm is formed by means of the near-isothermal reverse extrusion forming device of Example 2, including the following steps:

[0102] Step 1: Heating of the ingot and the die. The aluminum alloy ingot is heated to 400°C. At the same time, the flat die is heated to 400°C;

[0103] Step 2: Free forging. The ingot diameter d 锭坯 = 400 mm, the height h 锭坯 = 1180 mm, two upsetting and drawing, upsetting to the height of 400 mm, the deformation of 2.9 - reversing drawing to the length of 1100 mm, the deformation of 2.7 - upsetting to the outer diameter d 预锻坯 = 550 mm, the height h 预锻坯 = 620 mm, the deformation of 1.7, the total deformation of 7.3.

[0104] Step 3: Heating of the pre-forged blank and the near-isothermal backward extrusion forming device. The pre-forged blank is heated to 290°C. At the same time, the near-isothermal backward extrusion forming device is heated to 300°C;

[0105] Step 4: Near-isothermal backward extrusion forming. The difference from Step 4 of Example 5 is that it is performed with the near-isothermal backward extrusion forming device of Example 2, and the forming is performed at a forming speed of 4 mm / s.

[0106] Example 5-1

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

[0108] Example 5-2

[0109] The difference from Example 5 is only in Step 3, where the pre-forged blank is heated to 250°C. At the same time, the near-isothermal backward extrusion forming device is heated to 270°C.

[0110] Example 5-3

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

[0112] Example 6

[0113] A 7075 aluminum alloy pipe with an outer diameter of Ф900 mm and a wall thickness of 65 mm, the forming method of which is performed with the near-isothermal backward extrusion forming device of Example 3, includes the following steps:

[0114] Step 1: Heating of the ingot and the die. The aluminum alloy ingot is heated to 440°C. At the same time, the flat die is heated to 450°C;

[0115] Step 2: Free forging. The ingot diameter d 锭坯 = 600 mm, the height h 锭坯= 1500 mm, free forging two-up one drawing, upsetting to height 600 mm, deformation 2.5 - reversing drawing to length 1500 mm, deformation 2.5 - upsetting to shape to outer diameter d 预锻坯 = 880 mm height h 预锻坯 = 695 mm, deformation 2.1, total deformation 7.1.

[0116] Step 3: Heating of the preform and the near isothermal backward extrusion forming device. The preform is heated to 200°C. At the same time, the near isothermal backward extrusion forming device is heated to 220°C.

[0117] Step 4: Near isothermal backward extrusion forming. The difference from Step 4 of Example 5 is that it is performed by means of the near isothermal backward extrusion forming device of Example 3, and the forming is performed at a forming speed of 6 mm / s.

[0118] Example 6-1

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

[0120] Example 6-2

[0121] The difference from Example 6 is only in Step 3, where the preform is heated to 250°C. At the same time, the near isothermal backward extrusion forming device is heated to 270°C.

[0122] Example 6-3

[0123] The difference from Example 6 is only in Step 4, where the near isothermal backward extrusion forming speed is 4 mm / s.

[0124] Comparative Example 1

[0125] An aluminum alloy pipe forming method, and the difference from Example 4 is only that the free forging of Step 2 is absent.

[0126] Comparative Example 2

[0127] An aluminum alloy pipe forming method, and the difference from Example 4 is only that Step 3: the preform heating temperature is higher, at 450°C, and the near isothermal backward extrusion forming device heating temperature is 470°C.

[0128] Comparative Example 3

[0129] An aluminum alloy pipe forming method, and the difference from Example 4 is only that Step 4 is performed by means of a conventional horizontal extruder near isothermal backward extrusion forming device.

[0130] Comparative Example 4

[0131] The aluminum alloy pipe forming method of Example 4 is only different from the method in that the speed of the near-isothermal extrusion forming in step 4 is too fast, 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, wherein the deviation refers to the average absolute deviation in the Z (lengthwise), H (widthwise) and G (heightwise) directions, which can represent the performance difference in the three directions to some extent.

[0134] The R p0.2 and R m of the pipes prepared in Examples 4-6 are 4-9 and 4-6 respectively; the R p0.2 and R m of the pipes prepared in Comparative Examples 1-4 are 10-16 and 15-23 respectively; the R p0.2 and R m of the pipes prepared in Examples 4-6 are much smaller than those of Comparative Examples 1-4, which indicates that the pipes prepared by the method of the present application have smaller performance difference in the three directions.

[0135] Comparative Examples 1-4 are all comparative examples of Example 4. Comparative Example 1 has insufficient deformation amount, residual as-cast structure, and low R p0.2 , R m and A; Comparative Example 2 has excessively high forming temperature, overburning, and low R p0.2 , R m and A; Comparative Example 3 has fiber-like grains in the traditional extrusion deformation structure, higher longitudinal performance, and lower widthwise and heightwise performance, especially in the elongation A; the R p0.2 , R m and A of the pipes prepared in Comparative Example 3 have high deviations of 16, 23 and 3 respectively, which is mainly due to the low recrystallization volume fraction in the extrusion deformation structure, resulting in obvious anisotropy; Comparative Example 4 has fast forming speed, uneven material flow, bending, seizing the punch, and other problems, and low R p0.2 , R m and A. It is indicated that the aluminum alloy pipe forming method of the present application has certain advantages.

[0136] Microscopic observation shows that the recrystallization volume fraction of Example 1 is 38%, and that of Comparative Example 3 is only 18%. The recrystallization volume fraction of the method of the present application is increased by about 20% compared with the traditional method, which helps to reduce the anisotropy of the material performance.

[0137] Table 1

[0138]

[0139]

[0140]

[0141]

[0142]

[0143] The above description is merely that of the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any change or substitution easily conceived by those skilled in the art within the technical range disclosed by the present application should be encompassed within the protection scope of the present application.

Claims

1. A method of forming a 7xxx-series aluminum alloy tube, characterized by, It comprises the following steps: S1, an aluminum alloy ingot and flat die heating; the aluminum alloy ingot heating temperature T 锭坯 : 350℃~440℃, the flat die heating temperature T 平模 : 300℃~450℃; S2, the heated ingot is subjected to free forging to form a pre-forged blank; the total deformation of the free forging is 6-10; the height h of the pre-forged blank formed after the free forging 预锻坯 = 凹模 - (50-70) mm, the diameter d of the pre-forged blank 预锻坯 = 凹模 - (5-15) mm; wherein h 凹模 is the concave die forming height, d 凹模 is the concave die forming inner diameter; S3, heating the pre-forging blank and the near-isothermal backward extrusion forming device respectively; the pre-forging blank heating temperature T 预锻坯 is 200-300℃, the near-isothermal backward extrusion forming device heating temperature T 装置 is T 预锻坯 ±20℃; S4, the heated pre-forging blank is put into the near isothermal backward extrusion forming device to perform near isothermal backward extrusion forming; the forming speed S of the near isothermal backward extrusion forming is 2-6 mm / s, and the forming pressure surplus is not less than 15 mm.

2. The forming method of claim 1, wherein In S2, the total deformation of the free forging is 7-9.

3. The forming method of claim 1 wherein, In S1, the aluminum alloy ingot is heated at a temperature T 锭坯 : 370°C to 420°C, and the flat die is heated at a temperature T 平模 : 350°C to 400°C.

4. The forming method of claim 1 wherein, In S3, the preform heating temperature T 预锻坯 is 220 to 280°C.

5. The forming method of claim 1 wherein, The near isothermal backward extrusion forming device comprises an extrusion rod, an extrusion punch, a heating and holding device, a female die and an ejection rod; The extrusion punch is fixed at the lower end of the extrusion rod, and the extrusion of the extrusion punch on the pre-forging blank is realized by the movement of the extrusion rod; the female die is fixed at the bottom of the near isothermal backward extrusion forming device and is opposite to the ejection rod, forming a closed forming cavity to provide forming space for the pre-forging blank; The inner cavity shape of the forming cavity matches the cross-sectional shape of the aluminum alloy pipe to be formed; the heating and holding device surrounds the female die to control the temperature; and the ejection rod is used to support the pre-forging blank during the forming process and to eject the finished product from the female die after the forming is completed.

6. The forming method of claim 5, wherein, S2, the height h of the preform after the free forging 预锻坯 = h 凹模 - (55-65) mm, the diameter d of the preform 预锻坯 = d 凹模 - (8-12) mm; wherein h 凹模 is the height of the female die forming, d 凹模 is the inner diameter of the female die forming.

7. The forming method of claim 1 wherein, In S4, the forming speed S of the near isothermal backward extrusion forming is 3-5 mm / s, and the forming pressure surplus is not less than 18 mm.

8. The forming method of claim 1 wherein, In S4, when the near isothermal backward extrusion forming is performed, the heating and holding device is first started to heat the female die, and when the temperature reaches a certain value, the hydraulic machine connected with the extrusion rod is opened to push the extrusion rod to move downward, and the extrusion punch moves downward along with the movement of the extrusion rod to apply pressure on the pre-forging blank, forcing the pre-forging blank to flow along the inner wall of the female die to the open end of the female die; when the pre-forging blank reaches the required shape and size, the hydraulic machine is closed, and the extrusion punch stops moving, and the forming process is completed; then the pressure direction of the hydraulic machine is changed to push the ejection rod to move upward to eject the formed metal piece from the female die.

9. The forming method of claim 8, wherein, In S4, when near-isothermal backward extrusion forming is performed, the heating temperature T=T 预锻坯 ±20℃ of the heating and holding device, wherein T 预锻坯 is the heating temperature of the pre-forged blank.

10. A device for near isothermal backward extrusion forming of 7xxx series aluminum alloy tubular product, characterized by, The near isothermal backward extrusion forming device can be used in the forming method of any one of claims 1-8; The extrusion punch is fixed at the lower end of the extrusion rod, and the extrusion of the extrusion punch on the pre-forging blank is realized by the movement of the extrusion rod; The female die is fixed at the bottom of the near isothermal backward extrusion forming device and is opposite to the ejection rod, forming a closed forming cavity to provide forming space for the pre-forging blank; The inner cavity shape of the forming cavity matches the cross-sectional shape of the aluminum alloy pipe to be formed; The heating and holding device surrounds the female die to control the temperature; and the ejection rod is used to support the pre-forging blank during the forming process and to eject the finished product from the female die after the forming is completed.

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