A profile extrusion cylinder for achieving gradient temperature difference of magnesium alloy round ingot and optimized heating method

Abstract

This invention discloses a profile extrusion cylinder and optimized heating method for achieving gradient differential temperature in magnesium alloy round ingots, relating to the field of magnesium alloy processing and forming. The cylinder includes an inner layer, middle layer, outer layer, induction heating coil, ceramic curing sleeve, and cooling water circulation channel. The optimized heating method specifically includes obtaining the target billet heating temperature and extrusion rod speed setpoints by repeatedly extruding a constant-temperature billet; performing extrusion based on the target billet heating temperature and extrusion rod speed setpoints, and calculating the distribution data of the average temperature of the exit profile cross-section as a function of the exit profile stroke x; determining the actual heating temperature of the billet in each axial length range based on an optimized extrusion exit temperature model and the principle of constant metal volume; and controlling the axial temperature gradient of the billet using zoned heating within the extrusion cylinder to achieve isothermal rapid extrusion. This method solves the problem of excessive frictional heat and plastic deformation heat generated during the extrusion production of ultra-long profiles, reducing the consistency of the microstructure and properties of the extruded profiles along the length direction. It provides guidance for achieving isothermal controllability in the rapid extrusion process of magnesium alloy profiles and can effectively improve the forming quality and production efficiency of magnesium alloy profiles.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy processing and forming, and specifically relates to a profile extrusion cylinder for realizing gradient differential temperature of magnesium alloy round ingot billets and an optimized heating method. Background Technology

[0002] With the rapid development of modern industry, promoting the sustainable development of lightweight components has become an important issue worldwide. Magnesium alloys are characterized by their light weight, high specific strength, good impact and wear resistance, and excellent thermal conductivity. Their extruded profiles are widely used in rail transportation, aerospace, and national defense. However, due to the poor plasticity of magnesium alloys, they are not easy to form, posing challenges in obtaining ideal microstructures and controlling profile quality. Although significant achievements have been made in theoretical and experimental research on the extrusion production of ultra-long profiles, many key issues still need to be addressed for practical production. In particular, because the plastic deformation of magnesium alloys is highly sensitive to strain, speed, and temperature, as the extrusion speed and stroke increase, a large amount of frictional heat and plastic deformation heat are easily generated. With the continuous extrusion process, a significant amount of plastic deformation heat accumulates and is conducted, further causing coarsening and inhomogeneity of deformed grains, a decrease in mechanical properties, and a reduction in the consistency of the microstructure and properties of the extruded profile along its length. Therefore, achieving isothermal control of the rapid extrusion process is crucial for obtaining ideal profile performance. Summary of the Invention

[0003] To address the issue of significant frictional and plastic deformation heat generated during rapid extrusion of magnesium alloys, this invention provides a profile extrusion cylinder and optimized heating method for achieving gradient temperature differential in magnesium alloy round billets. By experimentally detecting the extruded profile exit temperature and combining it with an optimized extrusion exit temperature model, the axial temperature gradient of the billet is controlled through zoned heating of the extrusion cylinder, achieving isothermal rapid extrusion. This method is applicable to practical engineering operations and can realize rapid isothermal extrusion processes for magnesium alloys.

[0004] This invention provides a profile extrusion cylinder for achieving gradient temperature difference in magnesium alloy round ingots and an optimized heating method, comprising the following steps:

[0005] Step 1: Determine the alloy system of the raw material and calculate the extrusion ratio based on the geometric parameters of the extrusion die and the billet. Then, based on the alloy system and the extrusion ratio, determine the range of billet heating temperature and extrusion bar speed in the extrusion cylinder. Specifically, for ZA series magnesium alloys with an extrusion ratio of 10-60, the temperature is 350-430℃ and the speed is 0.5-3mm / s; for ZK series alloys with an extrusion ratio of 30-70, the temperature is 300-400℃ and the speed is 1-3mm / s; for AZ series alloys with an extrusion ratio of 40-80, the temperature is 350-400℃ and the speed is 1.5-3.5mm / s.

[0006] Step 2: Place the billet into the extrusion cylinder, adjust the frequency of the induced current in each heating zone to heat the billet at a constant temperature, and hold it at that temperature for 1-2 hours; then, within the temperature and speed range determined in Step 1, systematically adjust the billet heating temperature and the extrusion bar speed to perform repeated trial extrusions. First, try the combination of the lowest temperature and the highest extrusion speed for trial extrusion. If the profile forming quality is poor, try increasing the heating temperature while keeping the extrusion speed constant. If reaching the highest heating temperature is still not ideal, then consider reducing the extrusion speed to ensure both production quality and efficiency, thereby obtaining the target billet heating temperature and extrusion bar speed settings.

[0007] Step 3: Extrusion is performed based on the target billet heating temperature and extrusion bar speed settings. During the process, temperature measuring points are set at the die exit. The positions of the temperature measuring points are evenly distributed according to the contour of the profile cross-section, including points where the shape changes abruptly, and the number of temperature measuring points is greater than 8. High-sensitivity contact thermocouples are fixed at each temperature measuring point to obtain temperature change data of different temperature measuring points over time during the extrusion process. Then, the average temperature of the profile cross-section at the exit is calculated. Plot the average temperature variation curve based on the distribution data of the export profile stroke x, where the cross-sectional average temperature is obtained by... The calculation yields the result, where n is the number of temperature measurement points. Let be the temperature at the i-th node;

[0008] Step Four: According to The curve extension characteristic along x is defined by taking the inflection point of the average temperature curve near the profile head as the reference, and dividing the temperature change amplitude along the x direction into a characteristic interval every 10℃. The starting point of each characteristic interval is... The endpoint is ,in For the i-th feature region, Starting point The endpoint is determined by the principle of constant metal volume; then, based on this principle, the following is used... Calculate and determine the axial position of the original billet corresponding to each feature region. ,in For the i-th temperature range of the billet, , This refers to the distance from the head of the billet; finally, the optimization model is based on the extrusion exit temperature. The actual heating temperature of the billet for each axial length range is then calculated using the formula. This represents the average temperature increase of exported profiles. For the extrusion rod speed, This corresponds to the decrease in the axial temperature of the billet;

[0009] Step 5: Adjust the frequency of the induced current in each zone of the extrusion sleeve, control the heating intensity of the billet in each length range, and extrude after forming a gradient temperature difference state in the axial direction, so as to finally achieve isothermal rapid extrusion preparation of magnesium alloy profiles. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the extrusion cylinder structure;

[0011] In the diagram: 1. Inner layer 2. Middle layer 3. Outer layer 4. Induction heating coil 5. Ceramic curing sleeve 6. Cooling water circulation channel;

[0012] Figure 2 This is a schematic diagram of the extrusion process;

[0013] In the diagram: 1. Extrusion bar; 2. Extrusion cylinder; 3. Extrusion die; 4. Contact thermocouple; 5. Extruded profile; 6. Billet.

[0014] Figure 3 A distribution diagram of temperature measurement points for exported profiles;

[0015] Figure 4 A schematic diagram of the optimization model for extrusion outlet temperature. Detailed Implementation

[0016] This invention discloses a profile extrusion cylinder for achieving gradient differential temperature of magnesium alloy round ingot billets and an optimized heating method. The embodiments described below are only some embodiments of this method and should not be construed as limiting the scope of this method.

[0017] A magnesium alloy AZ31 round ingot with dimensions of ∅300×2000mm was used as an example, and its chemical composition is shown in Table 1.

[0018] Table 1 Chemical composition of AZ31 magnesium alloy (wt, %) Al Zn Mn Si Fe Cu Ni Mg 2.85 0.88 0.36 0.1 0.003 0.01 0.005 Bal.

[0019] Step 1: Calculate the extrusion ratio as 40, the temperature as 350-400℃, and the extrusion bar speed as 1.5-3.5mm / s based on the geometric parameters of the extrusion sprue and the billet.

[0020] Step 2: Place the billet into the extrusion cylinder, adjust the frequency of the induced current in each heating zone for constant temperature heating, and keep it at that temperature for 1-2 hours; within the temperature and extrusion rod speed range determined in Step 1, adjust the billet heating temperature and extrusion rod speed in an orderly manner to repeat the trial extrusion, ensuring that the surface quality and microstructure of the finished profile are good, and finally obtain the target billet heating temperature of 355℃ and the set value of extrusion rod speed of 2mm / s;

[0021] Step 3: Extrusion is performed based on the target billet heating temperature and extrusion bar speed settings. During the process, nine temperature measuring points are set at the die exit, and high-sensitivity contact thermocouples are fixed at each measuring point to obtain temperature change data of different measuring points over time during the extrusion process; then, the average temperature of the exit profile section is calculated. Plot the curve of the average temperature variation based on the distribution data of the export profile stroke x;

[0022] Step Four: According to As the curve extends along x, taking the inflection point of the average temperature curve near the profile head (4000, 380) as a reference, the temperature change amplitude along the x direction is divided into characteristic intervals of every 10℃, resulting in four characteristic intervals: (4000, 8000), (8000, 16000), (16000, 68000), and (68000, 80000). Based on the principle of constant volume, using... The axial positions of the original billet corresponding to each feature zone were calculated and determined as (100, 200), (200, 400), (400, 1700), and (1700, 2000). Finally, the extrusion exit temperature optimization model was used. Then, calculate the actual heating temperatures of the billet for each axial length range: (355, 350), (350, 345), (345, 340), (340, 335).

[0023] Step 5: Adjust the frequency of the induced current in each zone of the extrusion sleeve, control the heating intensity of the billet in each length range, and extrude after forming a gradient temperature difference state in the axial direction, so as to finally achieve isothermal rapid extrusion preparation of magnesium alloy profiles.

Claims

1. An optimized heating method for achieving gradient differential temperature in magnesium alloy round ingots, achieved through the zoned heating function of an extrusion cylinder. The extrusion cylinder includes an inner layer, a middle layer, an outer layer, an induction heating coil, a ceramic curing sleeve, and a cooling water circulation channel. The inner, middle, and outer layers are made of H13 steel. The extrusion cylinder is divided into λ heating zones along its length, where λ ≥ 8. The induction heating coil is evenly arranged on the outer wall of the outer layer of each heating zone to form a heating assembly, and its heating function is independently controlled. Ceramic is cast outside the spiral portion of the induction heating coil to form a ceramic curing sleeve. The ceramic curing sleeve has a hollow structure and is coaxially arranged with the induction heating coil. A cooling water circulation channel is formed between the outer wall of the outer layer and the inner wall of the ceramic curing sleeve, and the induction heating coil is cooled by the thermal conductivity of the ceramic curing sleeve. The method is characterized by... Includes the following steps: Step 1: Determine the alloy system of the raw material and calculate the extrusion ratio based on the geometric parameters of the extrusion die and the billet. Then, based on the alloy system and the extrusion ratio, determine the range of billet heating temperature and extrusion bar speed in the extrusion cylinder. Specifically, for ZA series magnesium alloys with an extrusion ratio of 10-60, the temperature is 350-430℃ and the speed is 0.5-3mm / s; for ZK series alloys with an extrusion ratio of 30-70, the temperature is 300-400℃ and the speed is 1-3mm / s; for AZ series alloys with an extrusion ratio of 40-80, the temperature is 350-400℃ and the speed is 1.5-3.5mm / s. Step 2: Place the billet into the extrusion cylinder, adjust the frequency of the induced current in each heating zone to heat the billet at a constant temperature, and keep it at that temperature for 1-2 hours; then, within the temperature and speed range determined in Step 1, adjust the billet heating temperature and extrusion bar speed in an orderly manner to perform repeated trial extrusions to ensure that the surface quality and microstructure of the finished profile are good, thereby obtaining the target billet heating temperature and extrusion bar speed settings. Step 3: Extrusion is performed based on the target billet heating temperature and extrusion bar speed settings. During the process, multiple temperature measuring points are set at the die exit, and high-sensitivity contact thermocouples are fixed at each measuring point to obtain temperature change data of different measuring points over time during the extrusion process; then, the average temperature T of the exit profile section is calculated. a Plot the average temperature variation curve based on the distribution data of the export profile stroke x, where the cross-sectional average temperature is obtained by... The calculation yields the result, where n is the number of temperature measurement points, and T is the temperature reading. i Let be the temperature at the i-th node; Step 4: Based on T a As the curve extends along x, taking the inflection point of the average temperature curve near the profile head as a reference, the temperature change amplitude along the x direction is divided into a characteristic interval every 10℃, with the starting point of each characteristic interval being A. i (x0), endpoint is A i (x1), where A i Let x0 be the starting point and x1 be the ending point of the i-th feature region; then, based on the principle of constant metal volume, calculate and determine the axial position (a) of the original billet corresponding to each feature region. i (l0),a i (l1)), where a i Let be the i-th temperature range of the billet, and l0 and l1 be the distances from the billet head; finally, based on the extrusion exit temperature optimization model ΔT... a = (1.45v-2.38)ΔT0 to calculate the actual heating temperature of the billet for each length range along the axial direction, where ΔT a ΔT0 represents the average temperature increase of the exported profile, v represents the extrusion bar speed, and ΔT0 represents the corresponding decrease in the axial temperature of the billet. Step 5: Adjust the frequency of the induced current in each heating zone of the extrusion cylinder to control the heating intensity of the billet in each length range. After forming a gradient temperature difference state in the axial direction, extrusion is carried out to finally achieve isothermal rapid extrusion preparation of magnesium alloy profiles.

2. The optimized heating method for achieving gradient temperature difference in magnesium alloy round ingots according to claim 1, characterized in that, Step two involves systematically adjusting the billet heating temperature and extrusion exit speed, including the following process: Within the heating temperature and extrusion speed range specified in step one, first try a combination of the lowest temperature and the highest extrusion speed for trial extrusion. If the profile forming quality is poor, first try increasing the heating temperature while keeping the extrusion speed constant. If reaching the highest heating temperature is still not ideal, then consider reducing the extrusion speed to ensure both production quality and efficiency.

3. The optimized heating method for achieving gradient temperature difference in magnesium alloy round ingots according to claim 1, characterized in that, In step three, the temperature measurement points are evenly distributed according to the outline of the profile cross-section shape, including points where the shape changes abruptly, and the number of temperature measurement points is greater than 8.

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