Isothermal extrusion method for thin-walled aluminum alloy profiles with complex cross-sections

Abstract

The present invention discloses a method for isothermal extrusion of thin-walled aluminum alloy profiles with complex cross-sections, belonging to the technical field of profile forming. The method comprises: (1) preheating different parts of a blank, with each part being preheated and held at a temperature for 1 hour; and (2) extruding the preheated blank to obtain an aluminum alloy profile. By preheating different parts of the blank, the method ensures that the blank is truly isothermally extruded, thereby ensuring that the extruded aluminum alloy profile has uniform and stable mechanical properties while avoiding the occurrence of serious defects.

Description

Technical Field

[0001] The invention belongs to the technical field of profile forming, and relates to an isothermal extrusion method for aluminum alloy thin-walled profiles with complex cross-sections. 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, since the structures of different parts are different, 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 extrusion process (such as Figure 4 As shown in Figure 1, in both forward and reverse extrusion, inconsistencies between the billet temperature and the die exit temperature occur during actual production. Because the deformation temperature fluctuates irregularly during extrusion, the actual temperature of the metal material at the die exit fluctuates significantly. Temperature differences between different parts of the metal material at the die exit can cause uneven microstructure and properties across the profile, and even lead to serious defects such as distortion and cracking.

[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 during extrusion, 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 through 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 separately. The preheating and holding time of each part is 1 hour. The preheating temperature is 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, as well as the result of the nonlinear effect of the speed, thereby optimizing the heating process and ensuring 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; and T1 is the preheating temperature of the tail of the cylindrical bar, in °C.

[0011] During the extrusion process, the aluminum alloy billet experiences deformation and thermal effects as it passes through the extrusion barrel. Approximately 5% of the work performed by the extrusion rod is stored in the metal lattice as distortion energy, while the remainder is converted into heat and conducted into the extrusion barrel, heating the aluminum alloy billet and causing a gradient temperature rise. To ensure consistent temperatures during extrusion deformation, a formula must be developed to determine the relationship between the temperature gradient and the extrusion speed. The billet is then placed in a medium-frequency induction heating furnace for gradient heating. The die is then temperature-controlled to achieve isothermal extrusion as the billet passes through the die working zone, resulting in a finished product with uniform microstructure and properties.

[0012] Deformation Heat Effect: When extruding aluminum alloys, extrusion temperature and extrusion speed are two key parameters in the extrusion process. The temperature of the plastic deformation zone is determined by the billet heating temperature, deformation heat, and the amount of heat absorbed by the surrounding material. The higher the extrusion speed or metal flow rate, the less heat absorbed by the surrounding material, and the higher the temperature of the plastic deformation zone, and vice versa. At a given deformation level, either selecting an appropriate heating temperature or an appropriate deformation rate can maintain 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 high, the heating temperature must be reduced. Therefore, effectively controlling the temperature gradient can achieve higher extrusion efficiency. To achieve isothermal extrusion, the billet's head, middle, and tail are preheated before extrusion to create a temperature gradient. This compensates for the uneven temperature rise at different locations caused by extrusion heat generation.

[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 must be kept within a constant temperature range throughout the forming process to ensure that the overall temperature of the profile is balanced during extrusion, effectively reducing 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 formed 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 metal flow uniformity 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 based on a finite element simulation of the temperature field. 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; and 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 utilize mathematical approximations to simulate real physical systems. Using simple, interacting elements, a real system with an infinite number of unknowns can be approximated using 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 variation caused by differences in extrusion parameters during the billet extrusion process, thereby truly realizing isothermal extrusion. 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, resulting in higher quality.

[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 results are more reliable and conducive to truly achieving 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 This 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 the 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 diagram showing the influence of extrusion speed and extrusion rod stroke on billet temperature. DETAILED DESCRIPTION

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

[0029] In the embodiments of the present invention, cylindrical aluminum alloy bars are used as billets. The aluminum alloy composition is conventional, and the cylindrical bars are obtained through conventional casting processes or directly purchased. Specifically, 6082 aluminum alloy is used in the embodiments of the present invention. The casting process is as follows: Based on the addition amount of each component of the 6082 alloy, various raw materials are matched and added to the melting furnace according to the process requirements. The matched raw materials are then melted and refined through degassing and deslagging to effectively remove the impurities and gases in the melt. The molten aluminum liquid is then passed through a deep well casting system and cooled and cast into cylindrical bars. The bars are cast into various specifications based on their diameter and length to accommodate the subsequent extrusion process.

[0030] Example 1

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

[0032] (1) First, the initial extrusion speed v0 = 3 mm / s and the isothermal extrusion temperature T are determined based on 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 The temperature gradient calculated by -3ΔT is 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 preheating, the extrusion equipment is set according to the extrusion parameters determined in step (1) through a conventional extrusion process, and then the cylindrical bar is extruded to obtain an aluminum alloy profile.

[0035] The aluminum alloy profile in this embodiment has the same structure as that in Example 3. Figure 2The structure of the aluminum alloy profile in this embodiment is shown in FIG. 6 . The performance test was conducted on the six edges of the aluminum alloy profile obtained in this embodiment, 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] As can be seen from Table 1, in this embodiment, the mechanical properties of the six edges of the aluminum alloy profile have relatively small differences, indicating 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 extrusion molding method as that of Example 1 to obtain an aluminum alloy profile, 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 Example 3. Figure 2 The structure of the aluminum alloy profile in this embodiment is shown in FIG. 6 . The performance test was conducted on the six edges of the aluminum alloy profile obtained in this embodiment, 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] As can be seen from Table 2, in this embodiment, the mechanical properties of the six edges of the aluminum alloy profile have little difference, indicating 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 Example 1 to extrude and form the 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 carried out on the six edges of the aluminum alloy profile obtained in this embodiment, and the results were shown in Table 3. The microstructure of the aluminum alloy profile obtained in this embodiment was observed, and the results were 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] As can be seen from Table 3, the mechanical properties of the six edges of the aluminum alloy profile in this embodiment have little difference, which shows 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, with a grain size of about 5-10 μm and good grain size uniformity and roundness, 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 and are not limiting. 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 by: 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 separately. The preheating and holding time of each part is 1 hour. The preheating temperature is determined by the following formula: 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); T1=T F -ΔT, T2=T F -2ΔT, T3=T F -3ΔT, where T3 is the preheating temperature of the cylindrical bar head, in °C; T2 is the preheating temperature of the cylindrical bar middle, in °C; T1 is the preheating temperature of the cylindrical bar tail, 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, wherein: 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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