Profile extrusion container for realizing gradient differential temperature of magnesium alloy round ingot blank and optimized heating method

Abstract

The invention discloses a profile extrusion container capable of achieving gradient differential temperature of a magnesium alloy round ingot blank and an optimized heating method, and relates to the field of magnesium alloy machining forming, the profile extrusion container comprises an inner layer, a middle layer, an outer layer, an induction heating coil, a ceramic curing sleeve and a cooling water circulation channel, and the optimized heating method specifically comprises the steps that a constant-temperature blank is repeatedly extruded; obtaining a target blank heating temperature and an extrusion rod speed set value; extrusion is conducted according to the target blank heating temperature and the extrusion rod speed set value, and distribution data of the average section temperature # imgabs0 # of the outlet profile along with the stroke x of the outlet profile are obtained through calculation; according to an extrusion outlet temperature optimization model, the actual heating temperature of the blank in each axial length range is solved by combining a metal volume invariant principle; axial temperature gradient control is carried out on a blank through partition heating of the extrusion container, and isothermal rapid extrusion is achieved. According to the method, the problems that a large amount of friction heat and plastic deformation heat are easily generated during extrusion production of the ultra-long profile, and the consistency of the structure and the performance of the extruded profile in the length direction is reduced are solved, guidance can be provided for isothermal controllability in the rapid extrusion process of the magnesium alloy profile, and the forming quality and the production efficiency of the magnesium alloy profile can be effectively improved.

Description

Technical Field

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

[0002] With the rapid development of modern industry, promoting the sustainable development of lightweight components has become an important issue in the world today. Magnesium alloys have the characteristics of light weight, high specific strength, good impact resistance, wear resistance and excellent thermal conductivity. Their extruded profiles are widely used in rail transportation, aerospace, national defense and military fields. However, due to the poor plastic fluidity of magnesium alloys, they are not easy to form, and face challenges in obtaining ideal organization and controlling profile quality. Although many achievements have been made in theoretical and experimental research on the extrusion production of ultra-long profiles, there are still many key problems to be solved in actual production, especially because the plastic deformation of magnesium alloys has strong strain, speed and temperature sensitivity. With the increase of extrusion speed and extrusion stroke, a large amount of friction heat and plastic deformation heat are easily generated. With the continuation of the extrusion process, a large degree of plastic deformation heat accumulation and conduction will be caused, which will further cause the coarsening and unevenness of the deformed grains, the mechanical properties will decrease, and the consistency of the organization and performance of the extruded profile in the length direction will be reduced. Therefore, it is particularly important to achieve isothermal control of the rapid extrusion process of the profile to obtain ideal profile performance. Summary of the invention

[0003] In view of the problem that a large amount of friction heat and plastic deformation heat are generated during the rapid extrusion of magnesium alloys, the present invention provides a profile extrusion barrel and an optimized heating method for realizing gradient temperature difference of magnesium alloy round ingots. The outlet temperature of the extruded profile is detected by experiment, combined with the extrusion outlet temperature optimization model, and the axial temperature gradient of the billet is controlled by zone heating of the extrusion barrel to realize isothermal rapid extrusion. This method is suitable for the actual operation of the project and can realize the rapid isothermal extrusion process of magnesium alloys.

[0004] The present invention provides a profile extrusion cylinder and an optimized heating method for realizing a gradient temperature difference of a magnesium alloy round ingot, comprising the following steps: Step 1: Determine the alloy system of the raw materials, and calculate the extrusion ratio according to the geometric size parameters of the extrusion splitter die and the ingot; then, determine the heating temperature of the billet in the extrusion barrel and the speed range of the extrusion rod according to the alloy system and the extrusion ratio, wherein, when the extrusion ratio of the ZA series magnesium alloy is 10-60, the temperature is 350-430°C and the speed is 0.5-3mm / s; when the extrusion ratio of the ZK series alloy is 30-70, the temperature is 300-400°C and the speed is 1-3mm / s; when the extrusion ratio of the AZ series alloy is 40-80, the temperature is 350-400°C and the speed is 1.5-3.5mm / s; Step 2: Place the billet into the extrusion barrel, adjust the frequency of the induced current in each heating zone to heat the billet at a constant temperature, and keep it warm for 1-2 hours; then, within the temperature and speed range determined in step 1, adjust the billet heating temperature and the extrusion rod speed in order to repeat the test extrusion, first try the combination of the lowest temperature and the highest extrusion speed for test extrusion, if the profile forming quality is poor, first try to increase the heating temperature while keeping the extrusion speed unchanged, if the highest heating temperature is still not ideal, then consider reducing the extrusion speed to ensure both production quality and efficiency, so as to obtain the target billet heating temperature and extrusion rod speed setting value; Step 3: Extrusion is performed according to the target billet heating temperature and the extrusion rod speed setting value. During the process, a temperature measuring point is set at the die outlet. The positions of the temperature measuring points are evenly arranged according to the profile cross-sectional shape, and include shape mutation points. The number of temperature measuring points is greater than 8; a high-sensitivity contact thermocouple is fixed at each temperature measuring point to obtain the temperature change data of different temperature measuring points over time during the extrusion process; then, the average temperature of the outlet profile cross section is calculated. The distribution data of the exit profile travel x is plotted to show the variation curve of the average temperature, where the average temperature of the cross section is Calculated, where n is the number of temperature measurement points, is the temperature at the i-th node; Step 4: According to With the curve extension characteristics of x, taking the inflection point of the average temperature curve near the profile head as the reference, every 10℃ temperature change amplitude along the x direction is divided into a characteristic interval, and the starting point of each characteristic area is The end point is ,in is the i-th feature area, As the starting point, as the end point; then according to the principle of constant metal volume, use Calculate and determine the axial position of the original blank corresponding to each characteristic area ,in is the temperature range of the billet in the i-th section, , is the distance from the billet head; finally, the model is optimized according to the extrusion outlet temperature , inversely calculate the actual heating temperature of the blank in each axial length range, where: is the average temperature increase of the outlet profile, is the extrusion rod speed, is the decrease value of the corresponding axial temperature of the blank; Step 5: Adjust the frequency of the induced current in each zone of the extrusion sleeve, control the heating intensity of each length range of the billet, and perform extrusion after a gradient temperature difference state is formed in the axial direction, so as to finally realize the isothermal rapid extrusion preparation of magnesium alloy profiles. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 It is a schematic diagram of the extrusion cylinder structure; In the figure: 1. Inner layer 2. Middle layer 3. Outer layer 4. Induction heating coil 5. Ceramic curing sleeve 6. Cooling water circulation channel; Figure 2 Schematic diagram of the extrusion process; In the figure: 1. extrusion rod 2. extrusion cylinder 3. extrusion die 4. contact thermocouple 5. extrusion profile 6. blank; Figure 3 The distribution diagram of the temperature measurement points for the export profiles; Figure 4 Schematic diagram of the extrusion outlet temperature optimization model. DETAILED DESCRIPTION

[0006] The present invention discloses a profile extrusion barrel and an optimized heating method for achieving gradient temperature difference of magnesium alloy round ingots. The embodiments described below are only part of the embodiments of the method and should not be interpreted as limiting the scope of the method.

[0007] Taking a magnesium alloy AZ31 round ingot with a specification of ∅300×2000mm as an example, its chemical composition is shown in Table 1 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. Step 1: According to the geometrical dimension parameters of the extrusion splitter die and the ingot, the extrusion ratio is calculated to be 40, the temperature is 350-400°C, and the extrusion rod speed is 1.5-3.5 mm / s; Step 2: Place the billet into the extrusion barrel, adjust the frequency of the induced current in each heating zone for constant temperature heating, and keep it warm 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 order to repeat the extrusion test to ensure that the surface quality and microstructure of the finished export profile are good, and finally obtain the target billet heating temperature of 355°C and the extrusion rod speed setting value of 2mm / s; Step 3: Extrusion is performed according to the target billet heating temperature and the extrusion rod speed setting value. During the process, 9 temperature measuring points are set at the die outlet, and high-sensitivity contact thermocouples are fixed at each temperature measuring point to obtain the temperature change data of different temperature measuring points over time during the extrusion process; then, the average temperature of the outlet profile section is calculated. With the distribution data of the exit profile stroke x, a curve of the average temperature change is plotted; Step 4: According to With the curve extension characteristics of x, taking the inflection point (4000, 380) of the average temperature curve near the head of the profile as the benchmark, every 10℃ temperature change amplitude along the x direction is divided into a characteristic interval, and 4 characteristic intervals are obtained: (4000, 8000), (8000, 16000), (16000, 68000), (68000, 80000). According to the principle of constant volume, using The axial positions of the original blank corresponding to each characteristic zone are calculated and determined (100, 200), (200, 400), (400, 1700), (1700, 2000). Finally, the model is optimized according to the extrusion outlet temperature. , and inversely calculate the actual heating temperature of the blank in each axial length range (355, 350), (350, 345), (345, 340), (340, 335); Step 5: Adjust the frequency of the induced current in each zone of the extrusion sleeve, control the heating intensity of each length range of the billet, and perform extrusion after a gradient temperature difference state is formed in the axial direction, so as to finally realize the isothermal rapid extrusion preparation of magnesium alloy profiles.

Claims

1. A profile extrusion cylinder for realizing gradient temperature difference of magnesium alloy round ingot, comprising an inner layer, a middle layer, an outer layer, an induction heating coil, a ceramic curing sleeve, and a cooling water circulation channel, characterized in that: The inner layer, middle layer and outer layer are made of H13 steel, and the circumferential compressive stress of the inner extrusion cylinder is increased by interference fit between the layers; λ heating zones are divided along the length direction of the extrusion cylinder, where λ≥8, and the induction heating coil is evenly arranged on the outer wall of the outer layer of each heating zone to form a heating component, and an independent heating function control is performed; ceramics are poured outside the spiral part of the induction heating coil to form a ceramic curing sleeve, which is a hollow structure and is coaxially arranged with the induction heating coil; a cooling water circulation channel is formed through 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 heat conduction of the ceramic curing sleeve.

2. A method for optimizing heating of magnesium alloy round ingots by using the zoned heating function of the extrusion barrel according to claim 1, characterized in that: The steps include: Step 1: Determine the alloy system of the raw materials, and calculate the extrusion ratio according to the geometric size parameters of the extrusion splitter die and the ingot; then, determine the heating temperature of the billet in the extrusion barrel and the speed range of the extrusion rod according to the alloy system and the extrusion ratio, wherein, when the extrusion ratio of the ZA series magnesium alloy is 10-60, the temperature is 350-430°C and the speed is 0.5-3mm / s; when the extrusion ratio of the ZK series alloy is 30-70, the temperature is 300-400°C and the speed is 1-3mm / s; when the extrusion ratio of the AZ series alloy is 40-80, the temperature is 350-400°C and the speed is 1.5-3.5mm / s; Step 2: placing the billet into the extrusion barrel of claim 1, adjusting the frequency of the induced current in each heating zone to heat the billet at a constant temperature, and keeping it warm for 1-2 hours; then, within the temperature and speed range determined in step 1, orderly adjusting the billet heating temperature and the extrusion rod speed to repeat the test extrusion to ensure that the surface quality and microstructure of the finished export profile are good, thereby obtaining the target billet heating temperature and extrusion rod speed setting values; Step 3: Extrusion is performed according to the target billet heating temperature and the extrusion rod speed setting value. During the process, multiple temperature measuring points are set at the die outlet, and high-sensitivity contact thermocouples are fixed at each temperature measuring point to obtain the temperature change data of different temperature measuring points over time during the extrusion process; then, the average temperature of the outlet profile section is calculated. The distribution data of the exit profile travel x is plotted to show the variation curve of the average temperature, where the average temperature of the cross section is Calculated, where n is the number of temperature measurement points, is the temperature at the i-th node; Step 4: According to With the curve extension characteristics of x, taking the inflection point of the average temperature curve near the profile head as the reference, every 10℃ temperature change amplitude along the x direction is divided into a characteristic interval, and the starting point of each characteristic area is The end point is ,in is the i-th feature area, As the starting point, As the end point; then according to the principle of constant metal volume, the axial position of the original blank corresponding to each characteristic area is calculated and determined ,in is the temperature range of the billet in the i-th section, , is the distance from the billet head; finally, according to the extrusion outlet temperature optimization model, the actual heating temperature of the billet in each axial length range is inversely calculated; Step 5: Adjust the frequency of the induced current in each zone of the extrusion sleeve, control the heating intensity of each length range of the billet, and perform extrusion after a gradient temperature difference state is formed in the axial direction, so as to finally realize the isothermal rapid extrusion preparation of magnesium alloy profiles.

3. The method for optimizing heating of magnesium alloy round ingots to achieve gradient temperature difference according to claim 2, characterized in that: The step 2 orderly adjusts the billet heating temperature and the extrusion outlet speed, including the following process: within the heating temperature and extrusion speed range specified in step 1 of claim 2, first try the combination of the lowest temperature and the highest extrusion speed for trial extrusion; if the profile forming quality is poor, first try to increase the heating temperature while keeping the extrusion speed unchanged; if reaching the highest heating temperature is still not ideal, then consider reducing the extrusion speed to ensure both production quality and efficiency.

4. The method for optimizing heating of magnesium alloy round ingots to achieve gradient temperature difference according to claim 2, characterized in that: The positions of the temperature measuring points in step 3 are evenly arranged according to the contour of the cross-sectional shape of the profile, and include shape mutation points, and the number of temperature measuring points is greater than 8.

5. The method for optimizing heating of magnesium alloy round ingots to achieve gradient temperature difference according to claim 2, characterized in that: The axial position of the original blank corresponding to each characteristic area in step 4 according to Determine; the extrusion outlet temperature optimization model is , where is the average temperature increase of the outlet profile, is the extrusion rod speed, is the decrease value corresponding to the axial temperature of the billet.

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