Isothermal extrusion method for aluminum alloy thin-wall profile with complex section

Abstract

The invention discloses an isothermal extrusion method for an aluminum alloy thin-wall profile with a complex section, and belongs to the technical field of profile forming. The method comprises the steps that (1) different parts of a blank are preheated, and the preheating heat preservation time of each part is 1 h; (2) the preheated blank is subjected to extrusion forming, and the aluminum alloy profile is obtained; according to the method, different parts of the blank are preheated, and it is guaranteed that isothermal extrusion of the blank is truly achieved, so that the aluminum alloy profile obtained through extrusion has uniform and stable mechanical properties, and meanwhile serious defects are avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of profile forming and relates to an isothermal extrusion method for a thin-walled aluminum alloy profile with a complex cross-section. Background Art

[0002] Extrusion molding technology is a method of forming a plastic material through a die by forcefully extruding it. For aluminum alloy profiles with complex cross-sections, due to the differences in the structures of different parts, different extrusion parameters need to be used for different parts of the billet during the extrusion molding process. Usually, the billet is extruded by controlling the extrusion speed and the extrusion rod stroke to obtain aluminum alloy profiles with irregular structures. The extrusion speed and the extrusion rod stroke directly affect the temperature of the billet during the billet extrusion process (such as Figure 4 As shown in the figure, therefore, whether it is forward extrusion or reverse extrusion, the temperature of the billet and the temperature of the die outlet will be inconsistent in the actual production process. Due to the irregular change of deformation temperature during the extrusion process, the actual temperature of different parts of the metal material at the die outlet will fluctuate greatly. The temperature difference between different parts of the metal material at the die outlet will cause uneven structure and performance of the profile section, and even cause more serious defects such as distortion and cracks.

[0003] Therefore, it is necessary to provide an isothermal extrusion method for thin-walled aluminum alloy profiles with complex cross-sections to reduce or eliminate the impact of the extrusion process on the temperature change of the billet, so that the temperature of different parts of the metal material is more uniform when it is extruded, so that the final extruded profile has a uniform structure and stable and uniform mechanical properties, while avoiding serious defects such as distortion and cracks in the profile. Summary of the invention

[0004] In order to overcome the problems in the background technology, the present invention preheats different parts of the billet according to specific calculation results before extrusion, so that the billet can truly achieve isothermal extrusion, so that the microstructure of the extruded profile is more uniform, and its mechanical properties are more uniform and stable, and the risk of serious defects such as distortion and cracks in the profile during the extrusion process is reduced or avoided.

[0005] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0006] The isothermal extrusion method comprises the following steps:

[0007] (1) The cylindrical bar is divided into three parts: head, middle and tail according to its axial direction. Different parts of the cylindrical bar are preheated respectively. The preheating and holding time of each part is 1 hour. The preheating temperature is calculated and determined by the following formula:

[0008] Where ΔT is the temperature gradient in °C; T F is the isothermal extrusion temperature, unit: °C; v0 is the initial extrusion velocity, unit: mm / s; Q is the deformation activation energy, unit: J / mol; R=8.341 is the gas constant, unit: J / (mol·K).

[0009] By controlling the various parameters in the formula, the temperature gradient of the billet (cylindrical bar) during the extrusion process can be adjusted according to different extrusion conditions and the specific characteristics of the aluminum alloy. Specifically, the temperature gradient ΔT in the formula reflects the difference between the actual extrusion speed v and the reference speed v0 and the result of the nonlinear effect of the speed, so that the heating process can be optimized to ensure that the temperature distribution of the billet remains consistent throughout the extrusion process. The temperature change simulation of the heating process, feeding process and extrusion process is combined with the heat formula to calculate the gradient heating temperature ΔT, maintain the constant temperature state of the mold, and ensure that the temperature distribution of the billet is uniform during extrusion; in order to control the thermal balance of the entire extrusion process.

[0010] T1=T F -ΔT, T2 = T F -2ΔT, T3=T F -3ΔT, where T3 is the preheating temperature of the head of the cylindrical bar, in °C; T2 is the preheating temperature of the middle of the cylindrical bar, in °C; T1 is the preheating temperature of the tail of the cylindrical bar, in °C.

[0011] During the extrusion process, the aluminum alloy billet passes through the extrusion barrel, and there is a deformation thermal effect. About 5% of the work done by the extrusion rod is stored in the metal lattice in the form of distortion energy, and the rest is converted into heat and conducted into the extrusion barrel to heat the aluminum alloy billet, causing its temperature to rise gradually. In order to ensure that the temperature of the aluminum alloy billet is the same during extrusion deformation, it is necessary to design a formula between the temperature gradient and the extrusion speed, put the billet into a medium-frequency induction heating furnace for gradient heating, and then control the temperature of the mold so that the billet can achieve the effect of isothermal extrusion when it passes through the die working belt, and finally obtain a finished product with uniform and consistent organizational properties.

[0012] Deformation heat effect: When extruding aluminum alloy, extrusion temperature and extrusion speed are two main parameters in the extrusion process. The temperature of the plastic deformation zone depends on the billet heating temperature, deformation heat and the heat absorbed by the surrounding materials. The greater the extrusion speed or the metal flow rate, the smaller the heat absorbed by the surrounding materials, and the higher the temperature of the plastic deformation zone, and vice versa. Under a certain deformation level, either selecting a suitable heating temperature or selecting a suitable deformation rate can keep the temperature of the plastic deformation zone within the required range. When the deformation rate is slow, the heating temperature must be increased. When the deformation rate is large, the heating temperature must be reduced. Therefore, reasonable control of the temperature change trend can obtain higher extrusion molding efficiency. In order to achieve isothermal extrusion during the extrusion process, the head, middle and tail of the billet are preheated before extrusion to form a temperature gradient to compensate for the uneven temperature rise at different positions caused by the generation of extrusion heat.

[0013] The medium frequency induction furnace realizes gradient heating of the billet. By adjusting the induction intensity in different areas, the billet is heated to different temperature ranges, and finally the temperature is consistent at the extrusion outlet, thereby realizing isothermal extrusion. In specific operation, by gradually increasing or adjusting the heating power, the temperature of the billet increases gradually from the head to the back. During isothermal forming, the mold and the billet should be kept within a constant temperature range throughout the forming process to ensure the overall temperature balance during profile extrusion and effectively reduce extrusion defects caused by temperature differences.

[0014] This process can effectively avoid material defects caused by temperature differences and enable the aluminum alloy profile to maintain optimal mechanical properties and microstructure during the extrusion process, ultimately ensuring the high quality of the molded products.

[0015] The above-mentioned isothermal control process ensures that the temperature of the metal in the deformation zone near the die hole remains constant or basically constant throughout the extrusion process, and the metal deformation resistance and the uniformity of the metal flow are maintained as much as possible, so that the pressure of the die hole remains unchanged or basically unchanged, thereby obtaining a higher extrusion speed. At the same time, the shape and dimensional accuracy of the extruded profile, and the uniformity of the structure and performance along the cross-section and length directions are also improved, and the obtained profile has a uniform structure.

[0016] (2) The preheated cylindrical rod is extruded to obtain an aluminum alloy profile.

[0017] Preferably, the axial lengths of the head, middle and tail of the cylindrical rod are determined according to the finite element simulation temperature field, wherein, when the axial length L of the cylindrical rod is less than 500 mm, the ratio of the axial lengths of the head, middle and tail is head: middle: tail = 2:6:2; when the axial length L of the cylindrical rod is 500 mm < L < 2000 mm, the ratio of the axial lengths of the head, middle and tail is head: middle: tail = 3:4:3; when the axial length L of the cylindrical rod is greater than 2000 mm, the ratio of the axial lengths of the head, middle and tail is head: middle: tail = 1:1:1. Finite element simulation and finite element analysis are methods of simulating real physical systems using mathematical approximation. Using simple and interacting elements, a real system with infinite unknowns can be approximated with a finite number of unknowns.

[0018] Preferably, the initial extrusion speed v0 is determined according to a particle swarm optimization algorithm, and the initial extrusion speed v0 = 3 mm / s or 5 mm / s or 7 mm / s. The particle swarm optimization algorithm is an evolutionary computing technology proposed by Dr. Eberhart and Dr. Kennedy in 1995.

[0019] Preferably, the isothermal extrusion temperature T F , the deformation activation energy Q is determined based on the finite element simulation results.

[0020] Beneficial effects of the present invention:

[0021] 1. The present invention obtains the preheating temperature during the billet extrusion molding process by calculation, thereby preheating different parts of the billet to compensate for the irregular extrusion heat change caused by the difference in extrusion parameters during the billet extrusion process, thereby truly realizing isothermal extrusion, so that when the metal material is extruded, the temperature of different parts is relatively uniform, and the mechanical properties of the final extruded aluminum alloy profile are uniform and stable, and the quality is higher.

[0022] 2. In the process of calculating the preheating temperature, the present invention combines multiple extrusion process parameters such as extrusion temperature, extrusion speed, deformation activation energy and the characteristics of the metal material itself, so that the calculation result is more reliable and is conducive to truly realizing isothermal extrusion.

[0023] 3. The process flow of the present invention is short and the production cost is low. The prepared profile has uniform grain size and stable and consistent mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of preheating of the present invention.

[0025] Figure 2 This is a physical picture of the aluminum alloy extruded profile in Example 3 of the present invention.

[0026] Figure 3is a microstructure diagram of the aluminum alloy profile in Example 3 of the present invention, wherein (a)-(f) correspond to Figure 2 1-6 edges in the middle.

[0027] Figure 4 This is a graph showing the effect of extrusion speed and extrusion rod stroke on billet temperature. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the described contents.

[0029] In the embodiments of the present invention, cylindrical aluminum alloy bars are used as blanks, and the aluminum alloy components are conventional components. The cylindrical bars are obtained through conventional casting processes or directly purchased. In the embodiments of the present invention, 6082 aluminum alloy is specifically selected, and the casting process is as follows: according to the addition amount of each component of the 6082 alloy, various raw materials are matched, and the matched raw materials are added into the smelting furnace for melting according to the process requirements, and after degassing and slag removal and refining, the slag and gas in the melt are effectively removed, and the smelted aluminum liquid passes through a deep well casting system and is cooled and cast into cylindrical bars. According to the diameter and length of the bar, it is cast into various specifications to adapt to the subsequent extrusion process.

[0030] Example 1

[0031] In this embodiment, the aluminum alloy profile is extruded by the following method:

[0032] (1) First, the initial extrusion speed v0 = 3 mm / s and the isothermal extrusion temperature T are determined according to the particle swarm optimization algorithm and finite element simulation. F =540℃, deformation activation energy Q=150000 J / mol.

[0033] (2) According to the formula And the formula T1 = T F -ΔT, T2 = T F -2ΔT, T3=T F -3ΔT is calculated to obtain a temperature gradient of ΔT = 15°C, T1 = 525°C, T2 = 510°C, and T3 = 495°C. Then, the corresponding parts of the cylindrical bar are heated according to the preheating temperature, and each part is kept warm for 1 hour.

[0034] (3) After the preheating is completed, the extrusion equipment is set according to the extrusion parameters determined in step (1) through a conventional extrusion process, and then the cylindrical rod is extruded to obtain an aluminum alloy profile.

[0035] The aluminum alloy profile in this embodiment has the same structure as that in Embodiment 3. Figure 2The structure of the aluminum alloy profile in this embodiment is shown in FIG. 6 . The performance of the six edges of the aluminum alloy profile obtained in this embodiment is tested, and the results are shown in Table 1.

[0036] Table 1

[0037] edge 1 2 3 4 5 6 Stress / MPa 155.2 155.8 156 156.2 155.5 155 strain / % 25.3 25.6 26. 26.2 25.5 25.1 Strength / HV 50 55 52.2 52 56.1 52.2

[0038] It can be seen from Table 1 that in this embodiment, the mechanical properties of the six edges of the aluminum alloy profile have little difference, which means that the mechanical properties of the aluminum alloy profile extruded by the method of the present invention are relatively uniform.

[0039] Example 2

[0040] This embodiment adopts the same method as embodiment 1 to obtain an aluminum alloy profile by extrusion molding, except that: in this embodiment, the initial extrusion speed v0 = 5 mm / s, and the calculated temperature gradient ΔT = 17.5°C, T1 = 522.5°C, T2 = 505°C, and T3 = 487.5°C.

[0041] The aluminum alloy profile in this embodiment has the same structure as that in Embodiment 3. Figure 2 The structure of the aluminum alloy profile in this embodiment is shown in FIG. 6 . The performance of the six edges of the aluminum alloy profile obtained in this embodiment is tested, and the results are shown in Table 2.

[0042] Table 2

[0043] edge 1 2 3 4 5 6 Stress / MPa 161 160.4 156 163 162.3 161.7 strain / % 25.5 26.6 26.1 25.8 26.5 26.4 Strength / HV 61.1 63.2 62.3 64.1 66.1 63.4

[0044] It can be seen from Table 2 that in this embodiment, the mechanical properties of the six edges of the aluminum alloy profile have little difference, which means that the mechanical properties of the aluminum alloy profile extruded by the method of the present invention are relatively uniform.

[0045] Example 3

[0046] This embodiment adopts the same method as embodiment 1 to extrude and form an aluminum alloy profile, except that: in this embodiment, the initial extrusion speed v0 = 7 mm / s, and the calculated temperature gradient ΔT = 20°C, T1 = 520°C, T2 = 500°C, and T3 = 480°C.

[0047] The aluminum alloy profile in this embodiment is as follows Figure 2 As shown in Table 3, the performance test was performed on the six edges of the aluminum alloy profile obtained in this embodiment, and the results are shown in Table 3. The microstructure of the aluminum alloy profile obtained in this embodiment was observed, and the results are shown in Table 3. Figure 3 shown.

[0048] Table 3

[0049] edge 1 2 3 4 5 6 Stress / MPa 171.3 170.5 173 171.4 172.1 171.6 strain / % 26.8 25.3 25.2 26.4 25.1 25.3 Strength / HV 60.4 64.1 65.2 65.7 62.6 60.5

[0050] pass Figure 2 It can be seen that the surface of the aluminum alloy profile in this embodiment is relatively smooth, without obvious defects such as cracks.

[0051] It can be seen from Table 3 that the mechanical properties of the six edges of the aluminum alloy profile in this embodiment have little difference, which indicates that the mechanical properties of the aluminum alloy profile extruded by the method of the present invention are relatively uniform.

[0052] pass Figure 3 It can be seen that the grains of the six edges of the aluminum alloy profile are small and evenly distributed, the grain size is about 5-10 μm, and the grain size is uniform and round, indicating that the aluminum alloy profile extruded by the method of the present invention has a uniform microstructure.

[0053] In summary, the method of the present invention can better achieve isothermal extrusion, so that the aluminum alloy profile has relatively uniform and stable mechanical properties and uniform microstructure, while avoiding serious defects in the extrusion process of the aluminum alloy profile.

[0054] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. An isothermal extrusion method for thin-walled aluminum alloy profiles with complex cross-sections, characterized in that: The isothermal extrusion method comprises the following steps: (1) The cylindrical bar is divided into three parts: head, middle and tail according to its axial direction. Different parts of the cylindrical bar are preheated respectively. The preheating and holding time of each part is 1 hour. The preheating temperature is calculated and determined by the following formula: Where ΔT is the temperature gradient in °C; T F is the isothermal extrusion temperature, unit ℃; v0 is the initial extrusion velocity, unit mm / s; Q is the deformation activation energy, unit J / mol; R = 8.341, is the gas constant, unit J / (mol·K); T1=T F -ΔT, T2 = T F -2ΔT, T3=T F -3ΔT, where T3 is the preheating temperature of the head of the cylindrical bar, in °C; T2 is the preheating temperature of the middle of the cylindrical bar, in °C; T1 is the preheating temperature of the tail of the cylindrical bar, in °C; (2) The preheated cylindrical rod is extruded to obtain an aluminum alloy profile.

2. The isothermal extrusion method according to claim 1, characterized in that: The axial lengths of the head, middle and tail of the cylindrical rod are determined according to the finite element simulation temperature field, wherein, when the axial length L of the cylindrical rod is less than 500 mm, the ratio of the axial lengths of the head, middle and tail is head: middle: tail = 2:6:2; when the axial length of the cylindrical rod is 500 mm < L < 2000 mm, the ratio of the axial lengths of the head, middle and tail is head: middle: tail = 3:4:3; when the axial length L of the cylindrical rod is greater than 2000 mm, the ratio of the axial lengths of the head, middle and tail is head: middle: tail = 1:1:

1.

3. The isothermal extrusion method according to claim 1, characterized in that: The initial extrusion speed v0 is determined according to a particle swarm optimization algorithm, and the initial extrusion speed v0 = 3 mm / s or 5 mm / s or 7 mm / s.

4. The isothermal extrusion method according to claim 1, characterized in that: The isothermal extrusion temperature T F , the deformation activation energy Q is determined based on the finite element simulation results.

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