Device and method for preparing weak texture fine-grained magnesium alloy by continuous variable channel torsional extrusion

Abstract

The present invention belongs to the technical field of light alloy plastic forming, and specifically relates to a device and method for preparing high-performance magnesium alloy billets by variable channel continuous torsion extrusion. Through the device and its processing method, the magnesium alloy billet undergoes continuous torsion deformation during the processing process, achieving grain refinement while weakening the texture, improving the room temperature mechanical properties of the magnesium alloy, and expanding the application range of the magnesium alloy. The present invention forms an extrusion channel through a concave die assembly, and the interior of the extrusion channel is composed of a fixed area I, a torsion area II and a fixed area III from top to bottom. The torsion area II continuously twists and extrude the magnesium alloy billet entering this area during the forming process of the magnesium alloy billet, and finally the magnesium alloy billet is shaped by the fixed area III. This scheme makes the grain refinement effect of the magnesium alloy material more significant, the base surface texture is weakened to a large extent, and the obtained fine-grained magnesium alloy material has a uniform structure, and the strength and toughness are greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of light alloy plastic forming, and in particular relates to a device and a method for preparing a high-performance magnesium alloy billet by variable-channel continuous torsional extrusion. Background Art

[0002] As the lightest metal structural material, magnesium alloy has the advantages of high specific strength and specific stiffness, good vibration damping, excellent electromagnetic shielding performance, good machinability and hot forming, and easy recycling. It has broad application prospects in aerospace, medical and military fields. However, the crystal structure of most magnesium alloys is a close-packed hexagonal structure, and there are only three slip systems that can be activated at room temperature, which cannot meet the Von-Misese criterion required for plastic deformation. Therefore, the room temperature mechanical properties of magnesium alloys are poor. In addition, magnesium alloys prepared by traditional extrusion methods often have strong basal textures, which leads to very obvious anisotropy of magnesium alloy materials, limiting their application range. Refining grains can significantly improve the strength of magnesium alloys, and weakening basal textures can improve their plasticity. Therefore, various processing technologies have been widely developed, such as equal channel angular extrusion and high-pressure torsion. However, the existing technology has certain disadvantages, such as discontinuous processing, low efficiency, and small sample size, which to a certain extent limits its application. How to obtain a continuous large-size fine-grained weak-textured high-performance magnesium alloy material processing technology method is a problem that needs to be solved urgently to expand the application range of magnesium alloys. Summary of the invention

[0003] The present invention aims to solve the above problems and invents a device and a process method for preparing weak texture fine-grained magnesium alloy by continuous variable channel torsion extrusion. Through the device and its processing method, the magnesium alloy billet undergoes continuous torsion deformation during the processing process, achieving grain refinement and texture weakening, improving the room temperature mechanical properties of the magnesium alloy, and expanding the application range of the magnesium alloy.

[0004] The present invention is implemented through the following technical scheme: a device for preparing weak texture fine-grained magnesium alloy by continuous torsion extrusion, comprising a vertical hydraulic press, the vertical hydraulic press comprising a hydraulic press top seat, a pressure motor, an extrusion punch telescopic pressure head, an extrusion punch mold, a column, a working platform and a hydraulic press base, through holes are opened in the centers of the working platform and the hydraulic press base, two of the columns vertically support the hydraulic press top seat above the working platform, the hydraulic press top seat spans above the columns, the pressure motor is installed on the hydraulic press top seat, the extrusion punch telescopic pressure head is installed at the active end of the pressure motor and is located below the hydraulic press top seat, and the extrusion punch mold is vertically installed below the extrusion punch telescopic pressure head;

[0005] A working platform and a telescopic device are fixed on the base of the hydraulic press, a die fixing frame and a pad located in the middle of the die fixing frame and having a central opening are fixed on the working platform, a die assembly is fixed on the pad and between the die fixing frames, and the die assembly includes an upper die, a middle die and a lower die arranged from top to bottom; the bottom surface of the upper die and the top surface of the lower die are both provided with protruding annular bosses, the top surface and the bottom surface of the middle die are both provided with annular grooves, the annular bosses and the annular grooves are matched to fix the middle die, and the middle die is allowed to rotate freely without displacement; a heating channel for the flow of organic heat carrier is provided in the upper die, the middle die and the lower die; extrusion channels that are interconnected are opened from top to bottom in the upper die, the middle die and the lower die, and the parts of the pad, the working platform and the base of the hydraulic press that are opposite to the discharge port of the extrusion channel are also penetrated from top to bottom as leakage holes;

[0006] The outside of the middle die is gear-shaped, and the telescopic device includes a pair of telescopic brackets located on the left and right sides of the die fixing frame, a driving device, and left and right telescopic rods horizontally installed on the telescopic brackets; the left and right telescopic rods are tangent to the middle die, are serrated and can be freely telescopic, and are meshed with the gears on the outside of the middle die, and the two telescopic rods move in opposite directions at the same time parallel to the direction of the telescopic rods themselves, driving the gears to rotate the middle die; a multi-layer spring device is fixed from top to bottom on the inner wall of the extrusion channel inside the middle die, and each layer of the spring device includes a plurality of springs arranged around the extrusion channel inside the middle die, and a high-temperature rubber pad and a hemispherical die extrusion head are connected to one end of the spring facing the center of the middle die, and the high-temperature rubber pad is rectangular, and the rectangular high-temperature rubber pad is connected to the hemispherical die extrusion head as a fixed whole, forming a torsion area II in the extrusion channel of the middle die.

[0007] The hemispherical die extrusion heads have different radii and are arranged irregularly and freely in the channel. The side length of the rectangular module below is the same as the diameter of the hemispherical module. As the extrusion process proceeds, the middle die rotates slightly, and the springs and modules in the channel can freely stretch and retract, changing the shape of the channel and forming an irregular channel.

[0008] The telescopic rod drives the gear to make the middle mold rotate slightly in the counterclockwise or clockwise direction. The rotation angle of the middle die does not exceed 15°, and the rotation speed is v1. When the telescopic rod moves away from the middle die, the middle die rotates in the clockwise direction, and the channel shape can be changed to twist the channel in the counterclockwise or clockwise direction; when the telescopic rod moves toward the middle die, the middle die rotates in the counterclockwise direction, and the channel shape can be changed to twist the channel in the clockwise or counterclockwise direction, such as Figure 3 As shown. The billet undergoes torsion deformation during the extrusion process, and the spring device freely expands and contracts. The width and bending angle of each part of the channel are different, forming Figure 6The deformation state of the billet shown in the figure shows that the billets Ⅰ, Ⅱ, Ⅲ, Ⅳ, and Ⅴ have different widths and different torsion angles. The flow rates of different parts of the billet are different, which introduces a large amount of shear deformation, deflects the c-axis of the magnesium alloy grains, and then refines the grains and weakens the basal surface texture. The torsion area Ⅱ is continuously twisted and squeezed during the forming process of the magnesium alloy billet, resulting in severe plastic deformation to refine the grains and weaken the basal surface texture.

[0009] Furthermore, the sizes of the hemispherical die extrusion heads at the top of the spring in the channel are inconsistent, r<R, and modules of different sizes can be arranged irregularly, such as the radius of the hemispherical module on the left side of the torsion channel is larger than the radius of the hemispherical module on the right side, and the large and small diameter hemispherical die extrusion heads are arranged alternately in the torsion channel, etc. Figure 5 As shown in the figure, during the torsional extrusion process, the die extrusion heads are of different sizes and arranged irregularly, and the flow velocities of different parts in the torsional channel are different. The flow velocity through the arc of radius r is v3, and the flow velocity through the arc of radius R is v4, v3>v4, so that the billet is subjected to the shear force in the torsional extrusion channel and undergoes continuous shear deformation, forcing the magnesium alloy grains to deflect along the c-axis, thereby refining the grains and weakening the basal texture.

[0010] Furthermore, the torsion extrusion space includes a fixed area I, a torsion area II and a fixed area III from top to bottom. The torsion area II continuously twists and extrude the magnesium alloy billet entering this area during the forming process of the magnesium alloy billet, resulting in severe plastic deformation to refine the grains, and finally the fixed area III shapes the magnesium alloy billet.

[0011] Furthermore, the upper, middle and lower three-part die, extrusion punch mold and telescopic rod are all made of 4Cr5MoSiV1 hot working die steel, and the surface roughness of the upper, middle and lower three-part die and extrusion punch mold is Ra0.16~0.4μm.

[0012] Furthermore, the temperature of the organic heat carrier introduced into the concave mold is 250-500°C.

[0013] Furthermore, the lower die can be replaced as needed to produce high-performance magnesium alloy bars, profiles, blocks, tubes, etc. of different shapes.

[0014] The present invention also discloses a process for preparing a weakly textured fine-grained magnesium alloy by continuous torsion extrusion, wherein the supporting facilities include an oil tank controller and an oil temperature machine for providing hot oil for a heating channel of a die assembly, a telescopic device controller for controlling a telescopic device, a heating furnace and a heating furnace controller for heating a magnesium alloy billet, a pressure motor controller for controlling a pressure motor, and an electrical control cabinet integrating various controllers; the extrusion channels inside the upper die, the middle die, and the lower die are respectively used as a fixed area I, a torsion area II, and a fixed area III; the process method comprises the following steps: S1, pretreatment of the magnesium alloy billet:

[0015] S1-1. The surface of the magnesium alloy billet is polished with 600-mesh sandpaper to remove oil stains, and then polished with 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence until the surface of the magnesium alloy billet is smooth;

[0016] S1-2, prepare an ultrasonic cleaning solution by mixing acetone and anhydrous ethanol in a volume ratio of 3:2, and mix and stir evenly in a cleaning tank;

[0017] S1-3, immersing the magnesium alloy blank prepared in step S1-1 into the cleaning solution prepared in step S1-2, placing the cleaning tank on an ultrasonic cleaning machine to ultrasonically clean the magnesium alloy blank for 30 to 60 minutes, taking out the magnesium alloy blank and cleaning it with anhydrous ethanol, and finally drying it with cold air from a hair dryer;

[0018] S1-4, applying graphite oil solution on the surface of the magnesium alloy blank prepared in step S1-3 for subsequent use;

[0019] S2. Preheating of magnesium alloy billet: operate the vacuum atmosphere heating furnace controller to start the vacuum atmosphere heating furnace, and set the heating temperature to 400-500°C. After the heating furnace temperature reaches the set temperature, put the magnesium alloy billet into the heating furnace and keep it warm for 2-4 hours.

[0020] S3. Lubrication, assembly and preheating of continuous torsion extrusion dies:

[0021] S3-1, Lubrication: Wipe all mold surfaces clean, and apply graphite oil solution to the contact surfaces between the upper die and the middle die, the contact surfaces between the middle die and the lower die, the contact surfaces of each part of the middle die, and the surfaces of all parts that constitute the extrusion channel;

[0022] S3-2, assembly: first, fix the lower die on the working platform, then fix the parts of the middle die in turn, and finally fix the upper die, so that the axes of the upper die, the middle die and the lower die coincide with each other; fix the telescopic device, so that the serrated telescopic rod meshes with the gear of the middle die; control the extrusion punch mold on the top seat of the hydraulic press to insert downward into the upper die, and do not touch the upper die, so as to ensure that the axis of the extrusion punch mold 14 coincides with the axis of the straight wall area of ​​the upper die, and the position of the discharge port is aligned with the leakage hole set through the working platform and the pad;

[0023] S3-3, preheating: the oil temperature machine controller turns on three oil temperature machines, sets the temperature of the hot oil entering the upper die to 250-500°C, the temperature of the hot oil entering the middle die to 250-500°C, and the temperature of the hot oil entering the lower die 19 to 250-500°C, and keeps the temperature for 2-4 hours after reaching the set temperature;

[0024] S4, continuous differential extrusion forming:

[0025] S4-1. Control the top seat of the vertical hydraulic press to withdraw the extrusion punch die, put the magnesium alloy billet into the extrusion channel and make it contact with the upper die, control the extrusion punch die to move downward for extrusion, and the extrusion speed is 10~200mm / min. During the extrusion process, control the three oil temperature machines to always ensure that the temperature of the hot oil entering the upper die is 250~500℃, the temperature of the hot oil entering the middle die is 250~500℃, and the temperature of the hot oil entering the lower die is 250~500℃. The magnesium alloy billet passes through the fixed area I, the torsion area II and the fixed area III from top to bottom in the extrusion channel, and is finally extruded from the leakage hole to obtain a high-performance fine-grained magnesium alloy material;

[0026] It also includes steps S4-2 and S4-3:

[0027] S4-2, after the continuous differential extrusion forming is completed, perform the following steps a or b:

[0028] a. If it is necessary to continue to prepare high-performance fine-grained magnesium alloy materials: first, turn off the oil temperature machine, control the top seat of the vertical hydraulic press to withdraw the extrusion punch die until it is large enough to place the next magnesium alloy billet; then, saw off the high-performance fine-grained magnesium alloy material obtained by extrusion in step S4-1 from the leakage hole; finally, restore the telescopic device and the middle die to the initial assembly position, place the next magnesium alloy billet, turn on the oil temperature machine and repeat step S4-1 to perform continuous torsion extrusion forming, until all magnesium alloy billets are continuously torsion extruded and formed, and then execute step b;

[0029] b. If it is not necessary to continue to obtain high-performance fine-grained magnesium alloy, turn off the oil temperature machine, control the top seat of the vertical hydraulic press to withdraw the extrusion punch die, wait for the die and the billet to cool to room temperature, remove the die from the vertical hydraulic press, saw off the high-performance fine-grained magnesium alloy obtained by extrusion from the leakage hole, take out the unformed magnesium alloy billet in the channel, and seal the die for subsequent use;

[0030] S4-3. Take out the high-performance fine-grained magnesium alloy material obtained in step S4-2, polish its surface with sandpaper, then clean it with the ultrasonic cleaning solution prepared in step S1-2, finally clean it twice with anhydrous ethanol, and blow dry it with a hair dryer to obtain a high-performance fine-grained magnesium alloy product.

[0031] Compared with the prior art, the invention has the following beneficial effects:

[0032] 1. The variable channel continuous twisting extrusion of magnesium alloy billets makes the grain refinement effect of magnesium alloy materials more significant, the base surface texture is weakened to a large extent, and the obtained fine-grained magnesium alloy material has uniform structure and greatly improved strength and toughness.

[0033] 2. Block structure, users can change modules according to needs to prepare different fine-grained magnesium alloy bars, profiles, blocks, tubes, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the main structure of the mold of the present invention;

[0035] Figure 2 This is a schematic diagram of the main structure of the channel of the mold of the present invention;

[0036] Figure 3 for Figure 1 A schematic diagram of the top view of the structure of the intermediate mold and the telescopic device;

[0037] Figure 4 It is the front view and side view of the spring component in the torsion extrusion channel;

[0038] Figure 5 A top view of the free arrangement channel for some spring components;

[0039] Figure 6 Schematic diagram of the shape of the billet in the torsional extrusion channel under some different shapes.

[0040] In the figure: 1-display screen; 2-indicator light; 3-start button; 4-oil tank controller; 5-heating furnace controller; 6-connecting wires; 7-electrical control cabinet; 8-pressure motor controller; 9-telescopic device controller; 10-stop button; 11-pressure motor; 12-hydraulic press top seat; 13-extrusion punch telescopic pressure head; 14-extrusion punch mold; 15-upper die; 16-die fixing frame; 17-middle die; 18-telescopic device; 19-lower die; 20-pad; 21-magnesium alloy billet; 22-column; 23-working platform; 24-heating channel; 25-hydraulic press base; 26-spring device; 27-high temperature rubber pad; 28-mold extrusion head. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0042] A device for preparing a weak texture fine-grained magnesium alloy by continuous torsion extrusion, comprising a vertical hydraulic press, wherein the vertical hydraulic press comprises a hydraulic press top seat 12, a pressure motor 11, an extrusion punch telescopic pressure head 13, an extrusion punch mold 14, a column 22, a working platform 23 and a hydraulic press base 25, through holes are opened in the centers of the working platform 23 and the hydraulic press base 25, two of the columns 22 vertically support the hydraulic press top seat 12 above the working platform 23, the hydraulic press top seat 12 spans above the columns 22, the pressure motor 11 is installed on the hydraulic press top seat 12, the extrusion punch telescopic pressure head 13 is installed at the active end of the pressure motor 11 and is located below the hydraulic press top seat 12, and the extrusion punch mold 14 is vertically installed below the extrusion punch telescopic pressure head 13;

[0043] The hydraulic press base 25 is fixed with a working platform 23 and a telescopic device 18, the working platform 23 is fixed with a die fixing frame 16 and a pad 20 located in the middle of the die fixing frame 16 and having a central opening, a die assembly is fixed on the pad 20 and between the die fixing frames 16, and the die assembly includes an upper die 15, a middle die 17 and a lower die 19 arranged from top to bottom; the bottom surface of the upper die 15 and the top surface of the lower die are both provided with a protruding annular boss, and the top and bottom surfaces of the middle die 17 are both provided with an annular groove, and the annular boss cooperates with the annular groove to fix the middle die 17 and enable the middle die 17 to rotate freely without displacement. The upper die 15, the middle die 17 and the lower die 19 are all provided with a heating channel 24 for the flow of organic heat carrier. The upper die 15, the middle die 17 and the lower die 19 are provided with mutually interpenetrating extrusion channels from top to bottom, and the backing plate 20, the working platform 23 and the hydraulic press base 25 are also penetrated from top to bottom as leakage holes at the parts opposite to the discharge port of the extrusion channels.

[0044] Furthermore, the outside of the middle die 17 is gear-shaped, and the telescopic device 18 includes telescopic brackets located on the left and right sides of the die fixing frame 16, a driving device, and left and right telescopic rods installed horizontally on the telescopic brackets; the left and right telescopic rods are tangent to the middle die 17, are sawtooth-shaped and can be freely telescopic, and mesh with the gears on the outside of the middle die 17, and the two telescopic rods move in opposite directions at the same time parallel to the direction of the telescopic rods themselves, driving the gears to rotate the middle die 17. A multi-layer spring device 26 is fixed from top to bottom around the extrusion channel inside the middle die 17, and each layer of the spring device 26 includes a plurality of springs arranged around the extrusion channel inside the middle die 17. The end of the spring facing the center of the middle die 17 is connected to a high-temperature rubber pad and a hemispherical die extrusion head, the die is hemispherical, the high-temperature rubber pad is rectangular, and the rectangular and hemispherical modules are connected as a fixed whole to form a torsion area II. The hemispherical die extrusion heads have different radii and are arranged irregularly and freely in the channel. The side length of the rectangular module below is the same as the diameter of the hemispherical die extrusion head. As the extrusion process proceeds, the middle die rotates slightly, and the springs and modules in the channel can freely stretch and retract, changing the shape of the channel and forming an irregular channel.

[0045] Furthermore, the serrated telescopic rod is meshed with the gear of the middle die 17, and the telescopic device 18 is controlled by the electrical control cabinet through the telescopic device controller 9. The two telescopic rods move in opposite directions at the same time parallel to the direction of the telescopic rod itself, and the movement speed is v2. The telescopic rod drives the gear to make the middle mold rotate slightly in the counterclockwise or clockwise direction. The rotation angle of the middle die does not exceed 15°, and the rotation speed is v1. When the telescopic rod moves away from the middle die 17, the middle die 17 rotates in the clockwise direction, and the shape of the channel can be changed to a twisted channel in the counterclockwise or clockwise direction; when the telescopic rod moves toward the middle die, the middle die rotates in the counterclockwise direction, and the shape of the channel can be changed to a twisted channel in the clockwise or counterclockwise direction, such as Figure 3 The magnesium alloy blank 21 undergoes torsional deformation during the extrusion process, and the spring device freely expands and contracts, and the width and bending angle of each part of the channel are different, forming a Figure 6 In the deformation state of the billet shown, billets I, II, III, IV, and V have different widths and different torsion angles. The flow rates of different parts of the magnesium alloy billet 21 are different, which introduces a large amount of shear deformation, deflects the c-axis of the magnesium alloy grains, and then refines the grains and weakens the base surface texture. The torsion area II is continuously twisted and squeezed during the forming process of the magnesium alloy billet, resulting in severe plastic deformation to refine the grains and weaken the base surface texture.

[0046] Furthermore, the sizes of the hemispherical die extrusion heads at the top of the spring in the channel are inconsistent, r<R, and modules of different sizes can be arranged irregularly, such as the radius of the hemispherical die extrusion head on the left side of the torsion channel is larger than the radius of the hemispherical die extrusion head on the right side, and the large and small diameter hemispherical modules are arranged alternately in the torsion channel, etc. Figure 5 As shown in the figure, during the torsional extrusion process, the die extrusion heads are of different sizes and arranged irregularly, and the flow velocities of different parts in the torsional channel are different. The flow velocity through the arc of radius r is v3, and the flow velocity through the arc of radius R is v4, v3>v4, so that the billet is subjected to the shear force in the torsional extrusion channel and undergoes continuous shear deformation, forcing the magnesium alloy grains to deflect along the c-axis, thereby refining the grains and weakening the basal texture.

[0047] Furthermore, the torsion extrusion space includes a fixed area I, a torsion area II and a fixed area III from top to bottom. The torsion area II continuously twists and extrude the magnesium alloy billet 21 entering the area during the forming process of the magnesium alloy billet 21, and finally the fixed area III shapes the magnesium alloy billet 21.

[0048] Furthermore, the upper, middle and lower three-part die, extrusion punch mold and telescopic rod are all made of 4Cr5MoSiV1 hot working die steel, and the surface roughness of the upper, middle and lower three-part die and extrusion punch mold is Ra0.16~0.4μm.

[0049] Furthermore, the temperature of the organic heat carrier introduced into the concave mold is 250-500°C.

[0050] Furthermore, the serrated telescopic rod is meshed with the gear of the middle die 17, and the telescopic device 18 is controlled by the control cabinet. The two telescopic rods move in opposite directions at the same time in parallel to the direction of the telescopic rod itself, and the movement speed is v2. The telescopic rod 18 drives the gear to make the middle die 17 rotate slightly in the counterclockwise or clockwise direction. The rotation angle of the middle die 17 does not exceed 15°, and the rotation speed is v1. During the extrusion process, the channel spring device 26 inside the middle die 17 can arbitrarily change the channel shape to form an irregular continuous torsion extrusion channel. The hemispherical modules at the top of the spring in the channel are inconsistent in size, r<R, and modules of different sizes can be arranged irregularly. During the torsional extrusion process, the magnesium alloy billet 21 has different flow velocities in different parts under the action of modules of different sizes. The flow velocity through the arc of radius r is v3, and the flow velocity through the arc of radius R is v4, v3>v4, so that the magnesium alloy billet 21 is subjected to the shear force and undergoes continuous shear deformation, forcing the c-axis of the magnesium alloy grains to deflect, thereby refining the grains and weakening the basal texture.

[0051] Furthermore, the lower die can be replaced as needed to produce high-performance magnesium alloy bars, profiles, blocks, tubes, etc. of different shapes.

[0052] In this specific embodiment, before continuous torsion extrusion deformation is performed to prepare high-performance magnesium alloy, the materials and chemical reagents required for the preparation process are first selected:

[0053] 1. Magnesium alloy blank 21;

[0054] 2. Sandpaper, solid;

[0055] 3. Graphite oil solution, viscous liquid;

[0056] 4. Anhydrous ethanol, liquid, purity 99.5%;

[0057] 5. Acetone, liquid, purity 99%.

[0058] A method for preparing a weakly textured fine-grained magnesium alloy by continuous torsion extrusion in the above manner comprises the following steps:

[0059] S1. Pretreatment of magnesium alloy billet 21:

[0060] S1-1, the surface of the magnesium alloy blank 21 is polished with 600-mesh sandpaper to remove oil stains, and then polished with 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence until the surface of the magnesium alloy blank 21 is smooth;

[0061] S1-2. Prepare an ultrasonic cleaning solution by mixing acetone and anhydrous ethanol in a volume ratio of 3:2, and mix and stir evenly in a cleaning tank.

[0062] S1-3, immersing the magnesium alloy blank 21 prepared in step S1-1 into the cleaning solution prepared in step S1-2, placing the cleaning tank on an ultrasonic cleaning machine to ultrasonically clean the magnesium alloy blank 21 for 30 to 60 minutes, taking out the magnesium alloy blank 21 and cleaning it with anhydrous ethanol, and finally drying it with cold air from a hair dryer;

[0063] S1-4, applying graphite oil solution to the surface of the magnesium alloy blank 21 prepared in step S1-3 for subsequent use;

[0064] S2, preheating the magnesium alloy blank 21: operate the heating furnace controller 5 to start the vacuum atmosphere heating furnace, preset the heating temperature to 400-500° C., after the heating furnace temperature reaches the set temperature, put the magnesium alloy blank 21 into the heating furnace and keep it warm for 2-4 hours;

[0065] S3. Lubrication, assembly and preheating of continuous torsion extrusion dies:

[0066] S3-1, Lubrication: Wipe all mold surfaces clean, and apply graphite oil solution to the contact surfaces between the upper die 15 and the middle die 17, the contact surfaces between the middle die 17 and the lower die 19, the contact surfaces of each part of the middle die 17, and the surfaces of all parts constituting the extrusion channel;

[0067] S3-2, assembly: First, fix the lower die 19 on the working platform 23, then fix the parts of the middle die 17 in turn, and finally fix the upper die 15, so that the axes of the upper die 15, the middle die 17 and the lower die 19 coincide with each other; fix the telescopic device, so that the serrated telescopic rod is meshed with the gear of the middle die; control the extrusion punch mold 14 of the hydraulic press top seat 12 to be inserted downward into the upper die 15, and do not touch the upper die 15, so as to ensure that the axis of the extrusion punch mold 14 coincides with the axis of the straight wall area of ​​the upper die 15, and the position of the discharge port is aligned with the leakage hole set through the working platform 23 and the pad 20;

[0068] S3-3, preheating: the oil tank controller 4 turns on three oil temperature machines, sets the temperature of the hot oil entering the upper die 15 to 250-500°C, the temperature of the hot oil entering the middle die 17 to 250-500°C, and the temperature of the hot oil entering the lower die 19 to 250-500°C, and keeps the temperature for 2-4 hours after reaching the set temperature;

[0069] S4, continuous differential extrusion forming:

[0070] S4-1, control the extrusion punch retractable pressure head 13 to withdraw the extrusion punch die 14 from the upper die 15, put the magnesium alloy billet 21 into the extrusion channel and make it contact with the upper die 15, control the extrusion punch die 14 to move downward for extrusion, the extrusion speed is 10~200mm / min, during the extrusion process, control the three oil temperature machines to always ensure that the temperature of the hot oil entering the upper die 15 is 250~500℃, the temperature of the hot oil entering the middle die 17 is 250~500℃, and the temperature of the hot oil entering the lower die 19 is 250~500℃, the magnesium alloy billet 21 passes through the fixed area I, the torsion area II and the fixed area III from top to bottom in the extrusion channel, and is finally extruded from the leakage hole to obtain a high-performance fine-grained magnesium alloy rod;

[0071] S4-2, after the continuous differential extrusion forming is completed, perform the following steps a or b:

[0072] a. If it is necessary to continue to prepare high-performance fine-grained magnesium alloy materials: first, turn off the oil temperature machine, control the extrusion punch telescopic pressure head 13 to withdraw from the extrusion punch die 14 until it is large enough to place the next magnesium alloy billet 21; then, saw off the high-performance fine-grained magnesium alloy material obtained by extrusion in step S4-1 from the leakage hole; finally, restore the telescopic device 18, the middle die 17 and its spring device 26 to the initial assembly position, place the next magnesium alloy billet 21, turn on the oil temperature machine and repeat step S4-1 to perform continuous torsion extrusion forming, until all magnesium alloy billets 21 are continuously torsion extruded and formed, and then execute step b;

[0073] b. If it is not necessary to continue to obtain high-performance fine-grained magnesium alloy material, turn off the oil temperature machine, control the extrusion punch telescopic pressure head 13 to withdraw from the extrusion punch die 14, wait for the die and the billet to cool to room temperature, remove the die from the vertical hydraulic press, saw off the high-performance fine-grained magnesium alloy material obtained by extrusion from the leakage hole, take out the unformed magnesium alloy billet 21 in the channel, and seal the die for subsequent use;

[0074] S4-3. Take out the high-performance fine-grained magnesium alloy material obtained in step S4-2, polish its surface with sandpaper, then clean it with the ultrasonic cleaning solution prepared in step S1-2, finally clean it twice with anhydrous ethanol, and blow dry it with a hair dryer to obtain a high-performance fine-grained magnesium alloy material product. Specific embodiments

[0075] The supporting facilities of the present invention include an oil tank controller 4 and an oil temperature machine for providing hot oil to the heating channel 24 of the die assembly, a telescopic device controller 9 for controlling the telescopic device, a heating furnace and a heating furnace controller 5 for heating the magnesium alloy billet 21, a pressure motor controller 8 for controlling the pressure motor 11, and an electrical control cabinet 7 integrating various controllers; the electrical control cabinet and the vertical hydraulic press are connected by wires.

[0076] A processing technology and method for preparing a weak texture fine-grained magnesium alloy by continuous torsion extrusion, comprising the following steps:

[0077] (1) Install the extrusion device on the vertical hydraulic extruder, install it firmly, ensure the positions and connections of each part are correct, and operate in sequence;

[0078] (2) The outer surface of the AZ31 magnesium alloy bar blank was polished with 600-grit sandpaper to remove oil stains, and then polished with 1000, 1200, and 2500-grit sandpaper in sequence to ensure that the surface was clean and smooth; the polished magnesium alloy bar blank was placed in a mixture of acetone and anhydrous ethanol in a volume ratio of 3:2 for ultrasonic cleaning for 30 minutes, and then cleaned with alcohol and dried with a hair dryer;

[0079] (3) Start the vacuum atmosphere heating furnace to preheat the magnesium alloy bar blank, the preset temperature is 400°C, and when the preset temperature is reached, continue to place the magnesium alloy bar blank in the heating furnace for 2 hours;

[0080] (4) Apply high-temperature graphite oil solution to the surface of the magnesium alloy block bar billet for lubrication, fix the lower die 19 on the working platform 23, then fix the middle die 17, and finally fix the upper die 15, so that the axes of the upper die 15, the middle die 17 and the lower die 19 coincide; fix the telescopic rod device, and the serrated telescopic rod is meshed with the gear of the middle die;

[0081] (5) Turn on the oil temperature machine heating device to heat the extrusion die cavities I, II, and III. The heating temperature is preset to 400°C. After reaching the preset temperature, continue to keep warm for 2 hours;

[0082] (6) The preheated magnesium alloy bar blank is placed in the die cavity I, and the extrusion punch die 14 is extended into the die cavity I to contact the magnesium alloy bar blank, and the discharge port is aligned with the leakage hole set through the working platform 23 and the pad 20; the concave die, the extrusion punch and the telescopic rod in the present invention are all made of 4Cr5MoSiV1 hot working die steel, and the surface of the extrusion die cavity and the extrusion punch die is smooth, with a roughness of Ra0.16μm;

[0083] (7) Turn on the pressure motor and set the pressure to 400MPa. At the same time, turn on the telescopic device 18. The vertical hydraulic press beam drives the extrusion punch mold 14 to move downward at the same time to extrude the magnesium alloy billet 21 placed in the extrusion cavity Ⅰ. The billet undergoes shear deformation in the corner area of ​​the extrusion cavity Ⅰ. When the billet passes through the central cavity Ⅱ, the spring device in the cavity freely expands and contracts, forming an irregular continuous torsion channel. At the same time, the telescopic device 18 drives the middle die to rotate slightly, and the cavity wall exerts a torsional force on the billet. The billet passing through cavity Ⅱ continues to undergo torsional deformation. At the same time, the extrusion punch mold 14 continuously applies pressure to extrude the billet. When the magnesium alloy billet 21 passes through cavity Ⅲ, it undergoes shear deformation in the corner area and is squeezed and thinned. The lower die 19 adjusts the billet shape to form a rod with a diameter of 20mm, realizing the variable channel torsional extrusion process of the magnesium alloy rod.

[0084] (8) Take out the magnesium alloy rod, polish its surface with sandpaper, and then place it in a mixture of acetone and anhydrous ethanol with a volume ratio of 3:2 for ultrasonic cleaning. Finally, clean it with alcohol and blow dry it with cold air from a hair dryer.

[0085] Conclusion: Through the variable channel torsional extrusion processing method of the present invention, the average grain size of the magnesium alloy billet is greatly reduced compared with conventional magnesium alloys, from the original 20.83 μm to 1.32 μm, the texture strength is reduced from 25.48 to 6.33, the texture strength is significantly reduced, and the comprehensive mechanical properties of the magnesium alloy are significantly improved, which can meet the current market demand for high-performance magnesium alloys.

[0086] Materials and chemical reagents used: magnesium alloy profile: AZ31 magnesium alloy block billet; sandpaper: SiC, 600 mesh, 2 sheets; 1000 mesh, 2 sheets; 1200 mesh, 2 sheets; 2500 mesh, 2 sheets; high temperature graphite oil solution: C, 500g; anhydrous ethanol: CH3CH2OH, 1200ml; acetone: C3H6O, 800ml.

[0087] The principle of obtaining the weak base texture magnesium alloy material through the above steps of the present invention is described in detail below in conjunction with the accompanying drawings:

[0088] like Figure 1 The figure shows the main structure of the mold in the present invention; before the blank is placed in the blank, the blank needs to be heated to a specified temperature in a vacuum atmosphere heating furnace and a high-temperature graphite oil solution is evenly applied on the surface for lubrication. The concave die, extrusion punch and telescopic rod are all made of 4Cr5MoSiV1 hot working die steel. The inner surface of the cavity is smooth with a roughness of Ra0.16~0.4μm. A heating device is provided outside the cavity. The heating temperature can be set to quickly heat up the cavity. When the blank is processed, the cavity is heated to a specified temperature through the heating device.

[0089] like Figure 2 As shown, it is a schematic diagram of the main structure of the channel of the mold of the present invention; during the extrusion process, when the magnesium alloy billet 21 passes through the corner area of ​​the die cavity I, shear deformation occurs, the base surface texture is weakened, and the grains are refined; when the magnesium alloy billet 21 passes through the die cavity II, the size of the hemispherical die extrusion head 28 at the top of the spring in the channel is inconsistent, r<R, and modules of different sizes are arranged irregularly, and finally various irregular channels with different torsion angles and different widths are formed; under the action of modules of different sizes, the flow velocity of each part is different, the flow velocity through the arc of radius r is v3, and the flow velocity through the arc of radius R is v4, v3>v4, and the width and bending angle of each part of the channel are different, so that the billet is subjected to the action of shear force and undergoes continuous shear deformation, forcing the magnesium alloy grains to deflect along the c-axis, thereby refining the grains and weakening the base surface texture; in addition, when the magnesium alloy billet 21 passes through the die cavity III, shear deformation occurs in the corner area, weakening the base surface texture and refining the grains.

[0090] like Figure 3 As shown, Figure 1 Schematic diagram of the top view of the structure of the middle die and the telescopic device; during the torsional extrusion process of the billet, an irregular torsional channel is formed inside the middle die 17, and at the same time, the external telescopic device 18 drives the middle die 17 to make a small rotation, and the cavity wall exerts a torsional force on the billet, and the billet passing through the center cavity II continuously produces torsional deformation.

[0091] like Figure 4 As shown, it is the front view and side view of the spring component in the torsion extrusion channel;

[0092] like Figure 5 As shown, it is a top view of a free arrangement channel of some spring components;

[0093] like Figure 6 As shown, it is a schematic diagram of the shape of the blank in the torsional extrusion channel under some different shapes.

[0094] During the entire process of variable-channel continuous torsional extrusion shear deformation, the magnesium alloy billet continuously accumulates deformation through multiple deformations, introducing large strain, forcing the c-axis deflection of the magnesium alloy grains, refining the metal grains, obtaining ultrafine-grained metal, weakening the basal texture, and improving the mechanical properties of the magnesium alloy.

[0095] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A device for preparing weak texture fine-grained magnesium alloy by continuous torsion extrusion, comprising a vertical hydraulic press, characterized in that: The vertical hydraulic press comprises a hydraulic press top seat (12), a pressure motor (11), an extrusion punch telescopic pressure head (13), an extrusion punch mold (14), a column (22), a working platform (23) and a hydraulic press base (25); a through hole is opened in the center of the working platform (23) and the hydraulic press base (25); two columns (22) vertically support the hydraulic press top seat (12) above the working platform (23); the hydraulic press top seat (12) spans above the columns (22); the pressure motor (11) is mounted on the hydraulic press top seat (12); the extrusion punch telescopic pressure head (13) is mounted at the movable end of the pressure motor (11) and is located below the hydraulic press top seat (12); and the extrusion punch mold (14) is vertically mounted below the extrusion punch telescopic pressure head (13); A working platform (23) and a telescopic device (18) are fixed on the hydraulic press base (25); a die fixing frame (16) and a pad (20) located in the middle of the die fixing frame (16) and having a central opening are fixed on the working platform (23); a die assembly is fixed on the pad (20) and between the die fixing frame (16); the die assembly comprises an upper die (15), a middle die (17) and a lower die (19) arranged from top to bottom; the bottom surface of the upper die (15) and the top surface of the lower die (19) are both provided with a protruding annular boss, and the middle die (17) is provided with a protruding annular boss. The top surface and the bottom surface are both provided with an annular groove, and the annular boss cooperates with the annular groove to fix the middle die (17) and enable the middle die (17) to rotate freely without deviation; the upper die (15), the middle die (17) and the lower die (19) are all provided with a heating channel (24) for the flow of organic heat carrier; the upper die (15), the middle die (17) and the lower die (19) are provided with extrusion channels that are interconnected from top to bottom, and the portions of the pad (20), the working platform (23) and the hydraulic press base (25) that are opposite to the extrusion channel outlet are also penetrated from top to bottom as leakage holes; The exterior of the middle die (17) is gear-shaped. The telescopic device (18) comprises a pair of telescopic brackets located on the left and right sides of the die fixing frame (16), a driving device, and left and right telescopic rods horizontally mounted on the telescopic brackets. The left and right telescopic rods are tangent to the middle die (17). The left and right telescopic rods are sawtooth-shaped and can be freely telescopic. The left and right telescopic rods are meshed with gears on the exterior of the middle die (17). The two telescopic rods move in opposite directions at the same time in parallel with the direction of the telescopic rods themselves, driving the gears to rotate the middle die (17). The inner wall circumference of the extrusion channel inside the middle die (17) is from top to bottom. A multi-layer spring device (26) is fixed at the bottom, each layer of the spring device (26) includes a plurality of springs arranged around the circumference of the internal extrusion channel of the middle die (17), one end of the spring facing the center of the middle die (17) is connected to a high-temperature rubber pad (27) and a hemispherical die extrusion head (28), the high-temperature rubber pad (27) is rectangular, and the rectangular high-temperature rubber pad (27) and the hemispherical die extrusion head (28) are connected to form a fixed whole; the extrusion channels inside the upper die (15), the middle die (17) and the lower die (19) serve as a fixed area I, a torsion area II and a fixed area III, respectively.

2. The device for preparing weak texture fine-grained magnesium alloy by continuous torsional extrusion according to claim 1, characterized in that: The middle and lower part of the extrusion channel in the upper die (15) is a closed structure, forming a corner area; the middle and upper part of the extrusion channel in the lower die (19) is a closed structure, forming a corner area.

3. The device for preparing weak texture fine-grained magnesium alloy by continuous torsional extrusion according to claim 1 or 2, characterized in that: The die extrusion heads (28) have different radii and are arranged irregularly and freely in the channel.

4. The device for preparing weak texture fine-grained magnesium alloy by continuous torsional extrusion according to claim 1 or 2, characterized in that: The radius of the die extrusion head (28) is divided into R and r, R>r, the radius of the left die extrusion head (28) in the torsion zone II is larger than the radius of the right die extrusion head (28); or the large and small diameter die extrusion heads (28) are arranged alternately in the torsion channel.

5. The device for preparing weak texture fine-grained magnesium alloy by continuous torsional extrusion according to claim 1 or 2, characterized in that: The inner wall of the middle die (17) is also installed with a rectangular high-temperature rubber pad, and the spring is installed on the inner wall of the middle die through the high-temperature rubber pad.

6. The device for preparing weak texture fine-grained magnesium alloy by continuous torsion extrusion according to claim 1 or 2, characterized in that: The die assembly, the extrusion punch die (14) and the telescopic rod are all made of 4Cr5MoSiV1 hot working die steel. The inner wall of the extrusion channel and the extrusion punch die (14) have smooth surfaces with a roughness of Ra0.16μm.

7. A method for preparing a weakly textured fine-grained magnesium alloy by continuous torsional extrusion, the supporting facilities comprising an oil temperature machine and an oil tank controller (4) for providing hot oil to a heating channel (24) of a die assembly, a telescopic device controller (9) for controlling a telescopic device, a vacuum atmosphere heating furnace and a heating furnace controller (5) for heating a magnesium alloy billet (21), a pressure motor controller (8) for controlling a pressure motor (11), and an electrical control cabinet (7) integrating the above controllers; the extrusion channels inside the upper die (15), the middle die (17), and the lower die (19) are respectively used as a fixed area I, a torsional area II, and a fixed area III; characterized in that: The method comprises the following steps: S1, pretreatment of magnesium alloy blank: S1-1, the surface of the magnesium alloy blank (21) is polished with 600-mesh sandpaper to remove oil stains, and then polished with 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence until the surface of the magnesium alloy blank is smooth; S1-2, prepare an ultrasonic cleaning solution by mixing acetone and anhydrous ethanol in a volume ratio of 3:2, and mix and stir evenly in a cleaning tank; S1-3, immersing the magnesium alloy blank (21) prepared in step S1-1 into the cleaning solution prepared in step S1-2, placing the cleaning tank on an ultrasonic cleaning machine to ultrasonically clean the magnesium alloy blank for 30 to 60 minutes, taking out the magnesium alloy blank and cleaning it with anhydrous ethanol, and finally drying it with cold air from a hair dryer; S1-4, applying a graphite oil solution to the surface of the magnesium alloy blank (21) prepared in step S1-3 for subsequent use; S2, preheating the magnesium alloy billet: operate the heating furnace controller (5) to start the vacuum atmosphere heating furnace, and preset the heating temperature to 400-500° C. After the temperature of the vacuum atmosphere heating furnace reaches the set temperature, place the magnesium alloy billet (21) into the vacuum atmosphere heating furnace and keep it warm for 2-4 hours; S3. Lubrication, assembly and preheating of continuous torsion extrusion dies: S3-1, Lubrication: Wipe all mold surfaces clean, and apply graphite oil solution to the contact surfaces between the upper die (15) and the middle die (17), the contact surfaces between the middle die (17) and the lower die (19), the contact surfaces of the various parts of the middle die (17), and the surfaces of all parts constituting the extrusion channel; S3-2, assembly: first, fix the lower die (19) on the working platform (23), then fix the parts of the middle die (17) in turn, and finally fix the upper die (15), so that the axes of the upper die (15), the middle die (17) and the lower die (19) coincide with each other; fix the telescopic device (18), so that the serrated telescopic rod meshes with the gear of the middle die (17); control the extrusion punch mold (14) of the hydraulic press top seat (12) to insert downward into the upper die (15), and do not touch the upper die (15), so that the axis of the extrusion punch mold (14) coincides with the axis of the straight wall area of ​​the upper die (15), and the position of the discharge port is aligned with the leakage hole set through the working platform (23) and the pad (20); S3-3, preheating: turn on the three oil temperature machines, set the temperature of the hot oil entering the upper die (15) to 250-500°C, the temperature of the hot oil entering the middle die (17) to 250-500°C, and the temperature of the hot oil entering the lower die (19) to 250-500°C. After reaching the set temperature, keep the temperature for 2-4 hours; S4, continuous differential extrusion forming: S4-1. By controlling the pressure motor (11) installed on the top seat (12) of the hydraulic press, the extrusion punch die (14) is withdrawn from the extrusion channel, the magnesium alloy billet (21) is placed in the extrusion channel and brought into contact with the upper die (15), and the extrusion punch die (14) is controlled to move downward for extrusion, with an extrusion speed of 10-200 mm / min. During the extrusion process, the three oil temperature controllers are controlled to always ensure that the temperature of the hot oil introduced into the upper die (15) is 250-500°C, the temperature of the hot oil introduced into the middle die (17) is 250-500°C, and the temperature of the hot oil introduced into the lower die (19) is 250-500°C. The magnesium alloy billet (21) passes through the fixed area I, the torsion area II and the fixed area III from top to bottom in the extrusion channel, and is finally extruded from the leakage hole to obtain a high-performance fine-grained magnesium alloy material.

8. The method for preparing a weakly textured fine-grained magnesium alloy by continuous torsional extrusion according to claim 7, characterized in that: It also includes steps S4-2 and S4-3: S4-2, after the continuous differential extrusion forming is completed, perform the following steps a or b: a. If it is necessary to continue to prepare the high-performance fine-grained magnesium alloy material: first, turn off the oil temperature machine, and control the pressure motor (11) installed on the top seat (12) of the hydraulic press to withdraw the extrusion punch die (14) from the extrusion channel until it is large enough to accommodate the next magnesium alloy billet (21); then, saw off the high-performance fine-grained magnesium alloy material obtained by extrusion in step S4-1 from the leakage hole; finally, restore the telescopic device (18) and the middle die (17) to the initial assembly position, place the next magnesium alloy billet (21), turn on the oil temperature machine and repeat step S4-1 to perform continuous twisting extrusion forming, until all magnesium alloy billets (21) are continuously twisted and extruded. After that, perform step b; b. If it is not necessary to continue to obtain high-performance fine-grained magnesium alloy, the oil temperature machine is turned off, and the extrusion punch die (14) is withdrawn from the extrusion channel by controlling the pressure motor (11) installed on the top seat (12) of the hydraulic press. After the die and the billet are cooled to room temperature, the die is removed from the vertical hydraulic press, the high-performance fine-grained magnesium alloy obtained by extrusion is sawed off from the leakage hole, the unformed magnesium alloy billet (21) in the channel is taken out, and the die is sealed for subsequent use; S4-3. Take out the high-performance fine-grained magnesium alloy material obtained in step S4-2, polish its surface with sandpaper, then clean it with the ultrasonic cleaning solution prepared in step S1-2, finally clean it twice with anhydrous ethanol, and blow dry it with a hair dryer to obtain a high-performance fine-grained magnesium alloy product.

Images