Device for preparing fine-grain weak-texture magnesium alloy through multi-conical-surface differential twisting and extruding and machining method

Abstract

The invention discloses a device for preparing a fine-grain weak-texture magnesium alloy through multi-conical-surface differential twisting and extruding and a machining method, and belongs to the field of magnesium alloy machining. The device comprises a vertical hydraulic machine, a multi-conical-surface module differential twisting and extruding forming die and a hypoid gear transmission device. Asymmetric conical surfaces are distributed in the multi-conical-surface module differential twisting and extruding forming die, and the radiuses of different positions of each conical surface are different, so that the contact areas of magnesium alloy blanks at all parts of the module are different, and then the flowing speeds of different parts of the blanks are different; the magnesium alloy blank is subjected to different degrees of extrusion force of the conical surface of the module in the machining process, and meanwhile, shearing force is urgently generated in an extrusion channel when a gear train rotates, so that extrusion shearing deformation is generated, and the c-axis of the magnesium alloy is forced to deflect along the conical surface of the module and the transmission direction; texture weakening and grain refinement are achieved, the mechanical property of the magnesium alloy is improved, and the application range is widened.

Description

Technical Field

[0001] The present invention relates to an extrusion device and a processing method for improving the mechanical properties of a magnesium alloy by extrusion deformation, in particular to a device and a processing method for preparing a fine-grained weak-textured magnesium alloy by multi-cone differential twisting extrusion. Background Art

[0002] Magnesium alloy is the lightest metal structural material at present. It has the advantages of high specific strength and specific stiffness, excellent machining performance, and easy recycling. Therefore, it is widely used in automobiles, 3C, aerospace, national defense and military industries, and is known as the "green energy material of the 21st century". However, due to the close-packed hexagonal crystal structure of magnesium alloy, only two slip systems are easy to activate at room temperature, and the five independent slip systems required for polycrystalline plastic deformation cannot be achieved; the grains in the material after deformation have a preferred orientation to form a strong surface-based texture, which is not conducive to subsequent deformation. Magnesium alloys are difficult to plastically process at room temperature, which limits the application of magnesium alloys in various fields. Grain refinement can significantly improve the mechanical properties of magnesium alloys, and severe plastic deformation techniques (such as high pressure torsion (HPT), equal channel angular pressing (ECAP), etc.) have been proven to effectively refine magnesium alloy grains. The adjustable texture strength of magnesium alloys is of great practical significance for improving the performance of magnesium alloys. Changing the deformation path is an effective method to weaken the texture of magnesium alloys. Commonly used methods include large plastic deformation methods such as ECAP and asymmetric extrusion. Therefore, it is very important to invent an effective device and method for weakening the deformation texture and refining the grains of magnesium alloys in order to expand the application range of magnesium alloys. Summary of the invention

[0003] The present invention aims to solve the above problems and provides a device and processing method for preparing fine-grained weak-textured magnesium alloy by multi-cone torsional extrusion. Through the device and processing method, the magnesium alloy billet is subjected to different degrees of extrusion pressure from the module cone surface during the processing, and at the same time, the extrusion channel is forced to generate shear force when the gear train rotates, thereby generating extrusion shear deformation, forcing the c-axis of the magnesium alloy to deflect along the module cone surface and the transmission direction, achieving weakened texture and grain refinement, improving the mechanical properties of the magnesium alloy, and expanding the scope of application.

[0004] The present invention is achieved through the following technical solutions: A device for preparing fine-grained weak-textured magnesium alloy by multi-cone differential extrusion, comprising a vertical hydraulic press, a multi-cone module differential extrusion forming die and a hypoid gear transmission device, wherein: The vertical hydraulic press comprises a hydraulic press top seat, a pressure motor, an extrusion punch telescopic pressure head, an extrusion punch, a column, a working platform and a hydraulic press base; the hydraulic press top seat is supported by the column, a pressure motor is installed above it, the movable end of the pressure motor faces downward and passes through the hydraulic press top seat, the extrusion punch telescopic pressure head is installed at the movable end of the pressure motor; the extrusion punch is installed below the extrusion punch telescopic pressure head; A working platform is fixed above the hydraulic press base, a lower pad and a die fixing frame surrounding the lower pad are fixed on the working platform, and an upper pad is installed on the top of the die fixing frame; the multi-cone module differential extrusion forming die is located between the die fixing frame, the upper pad and the lower pad, and a sleeve is also provided on the outer ring of the multi-cone module differential extrusion forming die; a groove serving as a slide rail is provided on the upper surface of the lower pad and the lower surface of the upper pad; a through hole matching the extrusion punch is provided on the top of the upper pad, and mutually interpenetrating through holes are provided in the center of the lower pad, the working platform and the hydraulic press base as a material leakage hole; The multi-cone module differential twisting and extrusion forming mold is provided with an extrusion channel that runs through from top to bottom. The upper and lower surfaces of the multi-cone module differential twisting and extrusion forming mold are provided with arc-shaped bosses as sliders, and the arc-shaped bosses cooperate with the grooves on the surfaces of the lower pad and the upper pad to ensure the movement trajectory of the multi-cone module differential twisting and extrusion forming mold; the multi-cone module differential twisting and extrusion forming mold is provided with grooves at the middle positions of the left and right ends, and threaded holes are provided in the grooves. The threaded holes are used to fix the large gear of the quasi-hyperbolic gear transmission device, and the grooves are used to accommodate the small gear and the large gear of the quasi-hyperbolic gear transmission device to realize continuous twisting of the multi-cone module differential twisting and extrusion forming mold; the upper pad and the multi-cone module differential twisting and extrusion forming mold are provided with heating channels for connecting to external circulation pipelines; in the quasi-double-sided gear transmission device, the large gear is fixed to the threaded hole of the multi-cone module differential twisting and extrusion forming mold by bolt connection, and the small gear is connected to the motor through a transmission shaft to realize rotation; The extrusion channel is composed of torsion zone I, variable cross-section torsion zone II, and extrusion zone III from top to bottom; the cross-section of the upper port of the extrusion channel is rectangular and extends downward to form an entrance section, and four asymmetric conical surfaces protruding toward the inner side of the extrusion channel are distributed below the entrance section, and each conical surface has different radii at different positions, and each conical surface is connected to two adjacent rectangular sides. The four conical surfaces are connected in sequence and then surround the four rectangular sides, but the first conical surface is not connected to the fourth conical surface, and an unconnected section is left on a rectangular side; the minimum radius end of the first conical surface is connected to the minimum radius end of the second conical surface, the maximum radius of the second conical surface is connected to the minimum radius end of the third conical surface, and the maximum half of the third conical surface is connected to the minimum radius end of the third conical surface. The diameter is connected to the minimum radius end of the fourth conical surface, and the extrusion channel from the entrance section to the bottom of the maximum radius of the conical surface constitutes a torsion zone I; the four conical surfaces and the five lower ends of the unconnected sections are transitioned through the arc section, and then vertically extended downward for a certain distance to form five vertical sections, and a plurality of asymmetric conical surfaces or frustums protrude toward the inner side of the extrusion channel below the five vertical sections, and the extrusion channel is transitioned into an extrusion zone III with a rectangular cross-section, and the bottom outlet of the extrusion zone III is connected with the through hole of the lower pad; the area of ​​the extrusion zone III is smaller than the entrance section, and there is a deviation between the center of the extrusion zone III and the entrance section, and the extrusion zone III is deflected by a certain angle relative to the entrance section; the extrusion channel between the torsion zone I and the extrusion zone III serves as a variable cross-section torsion zone II.

[0005] Furthermore, the multi-cone module differential twisting extrusion forming die is composed of four modules with similar shapes; the module is composed of a long strip segment and a short straight segment vertically connected to one end of the long strip segment; the four modules are spliced ​​inwardly with the side without the short straight segment to form a multi-cone module differential twisting extrusion forming die; The generatrix radii of the four conical surfaces are R1, R2, R3, and R4 respectively, and the centers of the four generatrixes are respectively located at the four vertices O1, O2, O3, and O4 of the modules at the diagonals of the two rectangular sides connected by each conical surface, and the four generatrixes are respectively rotated around the central axis perpendicular to the inner wall of the mold cavity and passing through the center of the maximum radius of the conical surface to form a conical surface; the maximum radii of the four conical surfaces are R5, R6, R7, and R8 respectively, and the radius of the transition fillet of the arc segment is R9; the four conical surfaces respectively extend downward by different distances L 13 , L 14 , L 15 , L 16 , the unconnected segment extends downward L 16 The distance from the sum of the corresponding radii R8; the perpendicular lines between the five endpoints of the four conical surfaces and the four rectangular sides of the extrusion area III are used as the five radii R 10 , R 11 , R 12 , R 13 , R 14The inner wall of the extrusion channel on both sides of the five radii transitions downward to the four rectangular sides of the extrusion zone III through a conical surface or a frustum surface, R 10 , R 11 , R 12 , R 13 , R 14 As the maximum radius of the corresponding cone or frustum.

[0006] Furthermore, the multi-cone module differential extrusion forming die, the large gear, small gear, extrusion punch telescopic pressure head and extrusion punch in the hypoid gear transmission device are all made of 4Cr5MoSiV1 hot working die steel; their surface roughness reaches Ra0.16~0.4μm.

[0007] The quasi-hyperbolic gear transmission device, the large gear is fixed on the multi-cone module differential torsion extrusion forming die through a boss and bolt connection, the small gear is connected to the transmission shaft (the transmission shaft extends from the hole opened on the sleeve), and the transmission shaft is controlled by the motor to rotate, driving the small gear and the end face large gear meshing with it. Therefore, during the extrusion process, the multi-cone module differential torsion extrusion forming die rotates to control the torsion deformation of the square billet. In the torsion zone, the magnesium alloy billet is torsion-advanced under the push of the telescopic pressure head of the extrusion punch and the rotation of the quasi-hyperbolic gear. During the forward process, the billet is extruded by the extrusion punch and the multi-cone module differential torsion extrusion forming die is torsion-advanced, the billet is plastically deformed, and the grain is refined; when it reaches the variable cross-section torsion zone, the multi-cone module differential torsion extrusion forming die is torsioned through the quasi-hyperbolic gear transmission device, and the internal extrusion channel of the multi-cone module differential torsion extrusion forming die changes the cross-sectional shape with multiple conical surface profiles of different sizes. While the extrusion punch pushes the billet forward, the multi-cone module differential torsion extrusion die is driven by the hypoid gear transmission device to twist; during the torsion process of the multi-cone module differential torsion extrusion die, the magnesium alloy billet is squeezed by the extrusion punch and the module, and the magnesium alloy billet undergoes more intense plastic deformation, and the c-axis of the billet grain rotates in the Y direction, weakening the texture. At the same time, the multi-cone module differential torsion extrusion die has asymmetric conical surfaces distributed inside, and the radius of each conical surface at different positions is different, so that the contact area of ​​the magnesium alloy billet at each part of the module is different, which leads to different flow speeds at different parts of the billet and different friction resistance. The differential flow of the magnesium alloy billet gradually changes the cross-sectional shape into a curved polygon. Along with the torsion deformation caused by the rotation of the module, the billet undergoes strong plastic deformation, and the c-axis deflects significantly in the Y and Z directions, achieving the purpose of weakening the texture. Finally, through the extrusion zone, the magnesium alloy billet achieves the required fine-grained weak texture. The device can prepare fine-grained weak-textured magnesium alloy through multi-cone torsion extrusion deformation.

[0008] The hypoid gear transmission mechanism drives the multi-cone module mold to twist to a maximum angle of 0-90°, and the intensity of the twisting of the magnesium alloy billet is controlled by adjusting the speed of the pinion. The sleeve is provided with corresponding long holes to facilitate the connection of the external flexible pipeline with the heating channel without affecting the limited angle rotation of the mold.

[0009] Furthermore, when the extrusion preparation of the magnesium alloy bar is completed, the top seat of the vertical hydraulic press is controlled to withdraw the extrusion punch die until it is large enough to place the next magnesium alloy billet, so as to prepare for the next bar extrusion.

[0010] A processing method for preparing fine-grained weak-textured magnesium alloy by multi-cone differential extrusion comprises the following steps: S1. Pretreatment of magnesium alloy billet: S1-1, processing the magnesium alloy billet into a magnesium alloy square bar, grinding the surface of the magnesium alloy square bar with 600-mesh sandpaper to remove oil stains, and then grinding with 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence until the surface of the magnesium alloy billet is smooth; S1-2, mixing acetone and anhydrous ethanol in a volume ratio of 3:2 in a cleaning tank and stirring evenly to prepare an ultrasonic cleaning solution; S1-3, immersing the magnesium alloy square bar 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 square bar for 60 minutes, then taking out the magnesium alloy square bar and cleaning it with anhydrous ethanol, and finally drying it with a hair dryer; S1-4, applying graphite oil solution on the surface of the magnesium alloy square rod prepared in step S1-3, and leaving it for use in the next step; S2. Preheating of magnesium alloy square bars: Set the heating temperature of the vacuum atmosphere heating furnace to 450°C. After the heating furnace temperature reaches the set temperature, place the magnesium alloy square bars into the heating furnace and keep them warm for 3 hours. S3, lubrication, assembly and preheating of multi-cone module differential extrusion forming die; S3-1, lubrication: smear the upper and lower surfaces of the multi-cone module differential extrusion forming die, the arc boss surface and the upper pad 15, the lower pad surface, the groove and all the parts that constitute the extrusion channel with graphite oil solution; S3-2, assembly: first fix the lower pad on the working platform, and the sleeve on the lower pad; then fix the four modules of the multi-cone module differential extrusion forming mold to the large gear in the quasi-hyperbolic gear transmission device through bolts, and place the assembled multi-cone module differential extrusion forming mold on the lower pad, and the arc boss below the multi-cone module differential extrusion forming mold matches the groove of the lower pad; fix the pinion and the transmission shaft in the quasi-hyperbolic gear transmission device, and the pinion meshes with the large gear on the mold, and install the upper pad, and the groove of the upper pad matches the upper arc boss of the multi-cone module differential extrusion forming mold; control the extrusion punch of the hydraulic press top seat to insert downward into the through hole of the upper pad without contacting the upper pad, to ensure that the axis of the extrusion punch coincides with the axis of the upper pad, and the leakage hole set at the extrusion zone III position through the working platform is aligned with the pad; S3-3, preheating: the oil temperature machine controller turns on the oil temperature machine, sets the temperature of the hot oil entering the upper pad and the multi-cone module differential extrusion forming die to 350-500°C, and keeps the temperature for 2-4 hours after reaching the set temperature; S4, multi-cone differential extrusion forming: S4-1. Control the pressure motor to withdraw the extrusion punch from the extrusion channel, put the magnesium alloy square bar into the extrusion channel and make it contact with the upper pad and the upper part of the multi-cone module differential extrusion forming die, control the extrusion punch to move downward for extrusion, and the extrusion speed is 10~200mm / min. During the extrusion process, control the oil temperature machine to always ensure that the hot oil temperature entering the upper pad and the multi-cone module differential extrusion forming die is 350~500℃. The magnesium alloy square bar passes through the torsion zone I, the variable cross-section torsion zone II and the extrusion zone 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; S4-2, after the multi-cone differential speed twisting extrusion forming, perform the following steps a or b: a. When extruding the second magnesium alloy square bar: first, turn off the oil temperature machine, control the vertical hydraulic press to withdraw the extrusion punch until it is large enough to place the next magnesium alloy square bar; then, saw off the fine-grained weak-textured magnesium alloy material obtained by extrusion in step S4-1 from the leakage hole; after placing the next magnesium alloy square bar, turn on the oil temperature machine and repeat step S4-1 to perform variable-section differential extrusion until all magnesium alloy billets are differentially extruded and step b is performed; b. After the extrusion of the magnesium alloy billet is completed, the oil temperature machine is turned off, and the vertical hydraulic press is controlled to withdraw the extrusion punch from the multi-cone module differential twisting and extrusion forming die. After the multi-cone module differential twisting and extrusion forming die and the magnesium alloy billet are cooled to room temperature, the multi-cone module differential twisting and extrusion forming die is disassembled from the vertical hydraulic press, the fine-grained weak-textured magnesium alloy obtained by extrusion is sawed off from the leakage hole, the unformed magnesium alloy square bar in the channel is taken out, and the mold is sealed for subsequent use; S4-3. Take out the fine-grained weak-textured magnesium alloy rod 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 fine-grained weak-textured magnesium alloy rod that can be directly put into use.

[0011] When using the device and processing method of the present invention to prepare magnesium alloy square bars by differential extrusion, due to the synergistic effect of a. the reliable mechanical transmission effect of the quasi-hyperbolic gear transmission system and b. the asymmetric conical surface structure of the internal multi-conical module differential extrusion forming die, the grain refinement effect of the obtained fine-grained magnesium alloy square bar is more obvious than that of the magnesium alloy square bar obtained by the traditional process method.

[0012] Compared with the prior art, the present invention has the following beneficial effects: 1. The extrusion channel provides severe differential shear deformation, torsional deformation and dynamic recrystallization, effectively weakening the basal texture of magnesium alloy and improving the mechanical properties of magnesium alloy; 2. The speed of the hypoid gear transmission mechanism is adjustable, which can control the torsion speed of the billet, and the extrusion channel realizes variable cross-section with a conical surface profile, so that the flow speed of the magnesium alloy billet is different when it contacts different parts of different conical surfaces, so that the billet can further realize differential spiral extrusion deformation, making the grain refinement and texture weakening effect of the magnesium alloy bar more significant. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the main structure of the device of the present invention; Figure 2 This is one of the oblique cross-sectional schematic diagrams of the channel of the mold of the present invention; Figure 3 The second oblique cross-sectional diagram of the channel of the mold of the present invention; Figure 4 It is a top view of the continuous torsion and extrusion deformation die of the multi-conical module; Figure 5 It is the axonometric view of the continuous torsion extrusion deformation die of the multi-cone module; Figure 6 for Figure 1 Schematic diagram of the arc-shaped boss (slider) of the middle mold and the groove (slide rail) of the pad; Figure 7 for Figure 1 Schematic diagram of the groove (slide rail) of the middle and lower pad; Figure 8 for Figure 7 A side sectional view of Fig. 9 for Figure 1 One of the details of the hypoid gear meshing; Fig.10 for Figure 1 Detailed drawing of the meshing of hypoid gears (part 2); Fig.11 It is one of the schematic diagrams of the deformed blank shape; Fig.12 This is the second schematic diagram of the deformed blank shape; Fig.13 This is the second schematic diagram of the deformed blank shape.

[0014] In the figure: 1-display screen; 2-indicator light; 3-start button; 4-fuel tank controller; 5-heating furnace controller; 6-electrical control cabinet; 7-pressure motor controller; 8-hypoid gear transmission system controller; 9-stop button; 10-connecting wire; 11-pressure motor; 12-hydraulic press top seat; 13-extrusion punch telescopic pressure head; 14-extrusion punch; 15-upper pad; 16-die fixing frame; 17-small gear; 18-large gear; 19-multi-cone module differential twisting extrusion forming die; 20-transmission shaft; 21-lower pad; 22-magnesium alloy square bar; 23-sleeve; 24-column; 25-working platform; 26-hydraulic press base; 27-heating channel; 28-bolt; Ⅰ-torsion zone; Ⅱ-variable cross-section torsion zone; Ⅲ-extrusion zone. DETAILED DESCRIPTION

[0015] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0016] A device for preparing fine-grained weak-textured magnesium alloy by multi-cone differential extrusion, comprising a vertical hydraulic press, a multi-cone module differential extrusion forming die 19, and a hypoid gear transmission device, 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 14, a column 24, a working platform 25 and a hydraulic press base 26. Through holes are provided in the centers of the working platform 25 and the hydraulic press base 26. The hydraulic press top seat 12 is supported by the column 24, and the pressure motor 11 is installed above it. The extrusion punch telescopic pressure head 13 below is installed at the movable end of the pressure motor 11; the extrusion punch 14 is installed below the extrusion punch telescopic pressure head 13; The working platform 25 and the hypoid gear transmission device, the die fixing frame 16 and the lower pad 21 with a through hole in the center are fixed on the hydraulic press base 26 in sequence, and the multi-cone module differential extrusion forming die 19 is fixed on the lower pad 21.

[0017] The internal deformation channel of the multi-cone module differential extrusion forming die 19 is a conical profile. The magnesium alloy square bar 22 is extruded by the conical module for the first time to undergo plastic deformation, and the cross section gradually changes into a curved polygon. It is extruded and deformed by the conical module for the second time to obtain a small square bar. The conical module enables the blank to obtain different flow speeds and undergo shear deformation. A sleeve 23 is arranged outside the multi-cone module to assist the die fixing frame 16 in positioning the multi-cone module differential extrusion forming die 19. The multi-cone module differential twisting and extruding forming die 19 is composed of four modules with similar shapes. Each movable block has an arc-shaped boss (i.e., a slider) on the upper and lower surfaces. The boss (slider) cooperates with the grooves (slide rails) on the surface of the lower pad 21 and the upper pad 15 to ensure the movement trajectory of the multi-cone module differential twisting and extruding forming die 19; threaded holes and grooves are opened at the middle positions of the left and right ends of the four modules. The threaded holes are used to fix the large gear 18 of the quasi-hyperbolic gear, and the grooves are used to accommodate the small gear 17 of the quasi-hyperbolic gear, so as to realize the continuous twisting of the multi-cone module differential twisting and extruding forming die; The quasi-double-sided gear transmission device, the large gear 18 is connected and fixed to the multi-cone module differential extrusion forming die 19 through a boss and a bolt 28, and the small gear 17 is connected to the transmission shaft 20. The transmission shaft 20 is controlled to rotate by a motor to drive the small gear 17 and the large gear 18 meshing therewith. Therefore, during the extrusion process, the multi-cone module differential extrusion forming die 19 rotates to control the torsional deformation of the magnesium alloy square bar 22; Furthermore, the extrusion channel is divided into torsion zone I, variable cross-section torsion zone II, and extrusion zone III from top to bottom. In torsion zone I, the magnesium alloy square bar 22 is twisted and advanced under the push of the telescopic ram 13 of the extrusion punch and the rotation of the hypoid gear. During the advancement process, the rotation speed of the small gear 17 is ω1, the linear speed is v1, the angular velocity of the large gear 18 and the multi-cone module differential torsion extrusion forming die 19 is ω2, and the linear speed is v2; the billet is extruded by the extrusion punch 14 and twisted by the multi-cone module differential torsion extrusion forming die 19, and gradually rotates at a speed of ω2. With the accumulation of plastic deformation of the billet, the grains are refined; when it reaches the variable cross-section torsion zone II, the multi-cone module differential torsion extrusion forming die 19 is twisted by the hypoid gear transmission device, and the internal channel of the multi-cone module differential torsion extrusion forming die 19 changes the cross-sectional shape with multiple conical surface contours of different sizes. While the extrusion punch telescopic ram 13 pushes the magnesium alloy square bar 22 forward, the multi-cone module differential twisting extrusion forming die is twisted under the drive of the quasi-hyperbolic gear transmission device; during the twisting process of the multi-cone module differential twisting extrusion forming die 19, the magnesium alloy square bar 22 is squeezed by the extrusion punch 14 and the module, and the magnesium alloy square bar 22 undergoes more severe plastic deformation, and the c-axis of the billet grain deflects in Y and Z, weakening the texture. At the same time, the multi-cone module differential twisting extrusion forming die 19 is internally distributed with asymmetric conical surfaces (maximum radii are R5, R6, R7, and R8, respectively), and the radii at different positions of each conical surface are different, so that the contact area of ​​the magnesium alloy square bar 22 at each part of the module is different, which leads to different flow velocities at different parts of the billet and different friction resistance. The magnesium alloy billet's differential flow gradually changes the cross-sectional shape into a curved polygon. The radii of the four curves in the curved polygon are R1, R2, R3, and R4, respectively. Accompanied by the torsional deformation caused by the rotation of the module, the billet undergoes strong plastic deformation, and the c-axis undergoes significant deflection, achieving the purpose of weakening the texture and refining the grains. Finally, through the extrusion zone III, the magnesium alloy billet achieves the desired fine-grained weak texture. The device can prepare fine-grained weak-textured magnesium alloys through multi-conical torsional extrusion deformation.

[0018] Furthermore, the multi-cone module differential extrusion forming die 19, the large gear 18 in the hypoid gear, the small gear 17, the extrusion punch telescopic pressure head 13, and the extrusion punch 14 are all made of 4Cr5MoSiV1 hot working die steel. Their surface roughness reaches Ra0.16~0.4μm. The hypoid gear transmission mechanism drives the multi-cone module differential extrusion forming die 19 to twist to a maximum angle of 0~90°, and the intensity of the twisting of the magnesium alloy billet is controlled by adjusting the speed of the small gear.

[0019] Furthermore, when the extrusion preparation of the magnesium alloy square bar 22 is completed, the pressure motor is controlled to withdraw the extrusion punch 14 from the extrusion channel until it is large enough to place the next magnesium alloy billet, so as to prepare for the next bar extrusion.

[0020] In this specific implementation, before performing multi-cone differential extrusion to prepare fine-grained magnesium alloy rods, the materials and chemical reagents required for the preparation process are first selected: 1. Magnesium alloy billet, square billet, the material is AZ31, containing 96% magnesium, 3% aluminum and 1% zinc; 2. Sandpaper, solid; 3. Graphite oil solution, viscous liquid; 4. Anhydrous ethanol, liquid, purity 99.5%; 5. Acetone, liquid, purity 99%.

[0021] A method for preparing fine-grained magnesium alloy rods by multi-cone differential extrusion in the above manner comprises the following steps: S1. Pretreatment of magnesium alloy billet: S1-1, processing the magnesium alloy billet into a square bar, grinding the surface of the magnesium alloy square bar 22 with 600-mesh sandpaper to remove oil stains, and then grinding with 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence until the surface of the magnesium alloy square bar 22 is smooth; S1-2. Mix acetone and anhydrous ethanol in a volume ratio of 3:2 in a cleaning tank and stir evenly to prepare an ultrasonic cleaning solution.

[0022] S1-3, immersing the magnesium alloy square bar 22 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 bar for 60 minutes, then taking out the magnesium alloy square bar 22 and cleaning it with anhydrous ethanol, and finally drying it with a hair dryer; S1-4, applying graphite oil solution on the surface of the magnesium alloy square bar 22 prepared in step S1-3, and leaving it for use in the next step; S2. Preheating the magnesium alloy square bar 22: setting the heating temperature of the vacuum atmosphere heating furnace to 450° C., after the heating furnace temperature reaches the set temperature, placing the magnesium alloy square bar into the heating furnace and keeping it warm for 3 hours; S3, lubrication, assembly and preheating of multi-cone differential extrusion die; S3-1, lubrication: smear the upper and lower surfaces of the multi-cone module differential extrusion forming die 19, the surface of the arc boss (slider), the surface of the upper pad 15, the surface of the lower pad 21, the groove (slide rail) and the surfaces of all parts constituting the extrusion channel with graphite oil solution; S3-2, assembly: first fix the lower pad 21 on the working platform, and the sleeve 23 on the lower pad 21; then connect and fix the four modules of the multi-cone module differential extrusion forming mold to the large gear 18 in the hypoid gear through bolts 28 respectively, and place the assembled multi-cone module differential extrusion forming mold 19 on the lower pad 21, and the arc boss (slider) under the multi-cone module differential extrusion forming mold 19 matches the groove (slide rail) of the lower pad 21; fix the small gear 18 in the hypoid gear The gear 17 is meshed with the transmission shaft 20, and the pinion 17 is meshed with the end face gear 18 on the mold. The upper pad 15 is installed, and the groove (slide rail) of the upper pad 15 is matched with the upper arc boss (slider) of the multi-cone module differential extrusion forming die 19; the extrusion punch 14 of the hydraulic press top seat 12 is controlled to be inserted downward into the through hole of the upper pad 15 without contacting the upper pad 15, ensuring that the axis of the extrusion punch 14 coincides with the axis of the upper pad 15, and the discharge port position penetrates the working platform 25 and is aligned with the leakage hole set in the pad 21; S3-3, preheating: the oil temperature machine controller turns on the oil temperature machine, sets the temperature of the hot oil entering the upper pad and the multi-cone module mold to 350-500°C, and keeps warm for 2-4 hours after reaching the set temperature; S4, multi-cone differential extrusion forming: S4-1, control the pressure motor to make the extrusion punch 14 withdraw from the extrusion channel, put the magnesium alloy square bar 22 into the extrusion channel and make it contact with the upper pad 15 and the upper part of the multi-cone module differential twisting extrusion forming die 19, control the extrusion punch 14 to move downward for extrusion, and the extrusion speed is 10~200mm / min. During the extrusion process, control the oil temperature machine to always ensure that the hot oil temperature entering the upper pad 15 and the multi-cone module differential twisting extrusion forming die 19 is 350~500℃. The magnesium alloy square bar 22 passes through the torsion zone I, the variable cross-section torsion zone II and the extrusion zone 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; S4-2, after the multi-cone differential speed twisting extrusion forming, perform the following steps a or b: a. When extruding the second magnesium alloy billet: first, turn off the oil temperature machine, control the pressure motor to make the extrusion punch 14 withdraw from the extrusion channel until it is large enough to place the next magnesium alloy billet; then, saw off the fine-grained weak-textured magnesium alloy material obtained by extrusion in step S4-1 from the leakage hole; after placing the next magnesium alloy billet, turn on the oil temperature machine and repeat step S4-1 to perform variable-section differential extrusion until all magnesium alloy billets are subjected to differential extrusion and then execute step b; b. After the extrusion of the magnesium alloy billet is completed, the oil temperature machine is turned off, and the pressure motor is controlled to withdraw the extrusion punch from the extrusion channel. After the die and the billet are cooled to room temperature, the die is removed from the vertical hydraulic press, the fine-grained weak-textured magnesium alloy obtained by extrusion is sawed off from the leakage hole, the unformed magnesium alloy billet in the channel is taken out, and the die is sealed for subsequent use; S4-3. Take out the fine-grained weak-textured magnesium alloy rod 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 fine-grained weak-textured magnesium alloy rod that can be directly put into use. Specific embodiments

[0023] The supporting facilities of the present invention include an oil tank controller 4 for providing hot oil to the heating channel 27 of the die assembly, a hypoid gear transmission system controller 8 for controlling the hypoid gear transmission mechanism, a heating furnace and a heating furnace controller 5 for heating the magnesium alloy square bar 22, a pressure motor controller 7 for controlling the pressure motor 11, and an electrical control cabinet 6 integrating various controllers; the electrical control cabinet and the vertical hydraulic press are connected by wires.

[0024] A processing method for preparing weak texture fine grain weak texture magnesium alloy rod by multi-cone differential extrusion, comprising the following steps: (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; (2) The outer surface of the AZ31 magnesium alloy square bar 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; (3) Start the vacuum atmosphere heating furnace to preheat the magnesium alloy square bar, the preset temperature is 400°C, and when the preset temperature is reached, continue to place the magnesium alloy square bar in the heating furnace for 3 hours; (4) Apply high-temperature graphite oil solution to the surface of the magnesium alloy square bar 22 for lubrication, fix the lower pad 21 on the working platform 25, then fix the multi-cone module differential extrusion forming die 19, and finally fix the upper pad 15. The axes of the upper pad 15, the multi-cone module die 19 and the lower pad 21 coincide with each other; fix the hypoid gear system, and the pinion 17 meshes with the large gear 18; (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; (6) The preheated magnesium alloy bar blank is placed in the torsion zone I, and the extrusion punch 14 is extended into the torsion zone I and contacts the magnesium alloy square bar 22, and the discharge port is aligned with the leakage hole set through the working platform 25 and the lower pad 21; the multi-cone module differential extrusion forming die 19, the large gear 18 in the hypoid gear, the small gear 17, the extrusion punch telescopic pressure head 13, and the extrusion punch 14 of the present invention are all made of 4Cr5MoSiV1 hot working die steel, and the extrusion die cavity and the extrusion punch surface are smooth, with a roughness of Ra0.16μm; (7) Turn on the pressure motor and set the pressure to 400 MPa. At the same time, turn on the hypoid gear transmission device. The vertical hydraulic press beam drives the extrusion punch 14 to move downward at the same time to extrude the magnesium alloy square bar 22 placed in the torsion zone I. The angular velocity of the multi-cone module differential extrusion forming die is ω2=0.002r / s, and the linear speed is 120mm / min. The billet undergoes torsion deformation in the torsion zone I, the c-axis deflects, and the grains begin to refine. When the billet passes through the variable cross-section torsion zone II, accompanied by the multi-cone module, the billet is deformed and the c-axis is deflected. The torsion of the module differential torsion extrusion forming die 19 and the contour characteristics of the conical surface inside the die are as follows: the radius of the conical surface is R5=105mm, R6=60mm, R7=50mm, R4=80mm, the radius of each curve of the curve polygon is R1=400mm, R2=300mm, R3=550mm, R4=200mm, and the radius of the transition fillet of the conical surface R9 is 20mm; the wall of the extrusion channel exerts torsion and shear force on the blank, and the blank passing through the variable cross-section torsion zone II continuously produces torsion shear deformation. At the same time, the extrusion punch 14 continuously applies pressure to extrude the blank. When the magnesium alloy square bar 22 passes through the extrusion zone III, torsion deformation occurs and it is squeezed and thinned. The lower pad 21 adjusts the shape of the blank to form a square bar with a side length of 150mm, realizing the multi-cone differential torsion extrusion process of the magnesium alloy square bar 22; (8) Take out the extruded 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.

[0025] Conclusion: Through the device and process method of the present invention for preparing fine-grained weak-textured magnesium alloy rods by multi-conical differential extrusion, the average grain size of the magnesium alloy billet is significantly reduced compared with conventional magnesium alloys, from the original 32μm to 2.63μm, the basal surface texture is effectively weakened compared with the initial magnesium alloy rod, and the mechanical properties of the magnesium alloy are effectively improved.

[0026] Materials and chemical reagents used: AZ31 magnesium alloy block billet, with side length a=400mm; 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.

[0027] 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: like Figure 1 The figure shows the main structure of the mold in the present invention; before the blank is placed, 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 multi-cone module differential extrusion forming die, the upper pad, the large gear and the small gear of the hypoid gear transmission device are all made of 4Cr5MoSiV1 hot working die steel. The inner surface of the mold cavity is smooth with a roughness of Ra0.16~0.4μm. A heating device is provided outside the mold cavity. The heating temperature can be set to quickly heat up the mold cavity. When the blank is processed, the mold cavity is heated to a specified temperature by the heating device.

[0028] like Figure 2 , 3 As shown, it is a schematic diagram of the main structure of the channel of the die of the present invention; during the extrusion process, when the magnesium alloy square bar 22 passes through the torsion zone I of the extrusion channel, torsion deformation occurs (the torsion length is L 12 ), refine the grains; when the magnesium alloy square bar 22 passes through the variable cross-section torsion zone II, the extrusion channel begins to undergo continuous shear torsion deformation with a conical surface (the cone generatrix has radii R1, R2, R3, and R4, respectively, and the maximum radii of the conical surface are R5, R6, R7, and R8, respectively, and R9 is the transition fillet radius). Due to the different radii of the conical surface at different positions, the contact area between each part of the billet and the extrusion channel is different, so there is obvious differential deformation during the deformation process. The magnesium alloy square bar 22 gradually becomes a bar with a curved polygonal cross section, which is convenient for changing the cross section of the bar. A transition zone is set: Due to the different maximum radii of the conical surface, the length of the transition zone is also different, which are L 13 , L 14 , L 15 , L 16 ; Then the conical surface (maximum radius is R 10 , R 11 , R 12 , R 13 , R 14) undergoes continuous differential shear torsion extrusion deformation, and the magnesium alloy square bar becomes a square bar with a side length of L5. With the accumulation of plastic deformation, the c-axis of the magnesium alloy grain deflects along the Y and Z directions, thereby weakening the basal texture. When the magnesium alloy square bar 22 passes through the extrusion zone III, torsion deformation occurs in the extrusion zone III (the torsion length is L 17 , L 18 , L 19 , L 20 , L 21 ), weakening the basal texture and refining the grains.

[0029] like Figure 4 As shown in the figure, it is a top view of the mold of the present invention. The basic dimensions of the conical surface movable block are length L1, width L2, L3, L4, height L 10 ; The sizes of irregular protrusions inside the active block are L6, L7, L8, and L9, corresponding to Figure 2 , 3 R5, R6, R7, R8, the deflection angle of the upper and lower rectangular openings of the mold is ψ1. Figure 2 , Figure 3 , Figure 4 , the upper and lower sliders of the mold are R 15 , R 16 , L 23 .like Figure 5 As shown, it is an oblique isometric view of the mold of the present invention; Figure 6 , 7 8, which is a diagram showing the matching of the mold and the backing plate slider rail of the present invention, the width and depth of the rail are both L 25 The outer diameter of the slide rail is D1, the inner diameter is D2, and the diameter of the leakage hole of the pad is D3. Figure 4 It can be seen that the centers of R1, R2, R3, and R4 are O1, O2, O3, and O4 respectively, and the radius is R 10 , R 11 , R 12 , R 13 , R 14 The centers of the circles are O 10 , O 11 , O 12 , O 13 , O 14; These five centers are the intersection points of the five endpoints of the four upper conical surfaces and the perpendicular lines of the four rectangular sides of the nearest extrusion zone III. Multiple conical surfaces or frustums are formed with these five centers to realize the transition from the variable cross-section torsion zone II to the extrusion zone III. These conical surfaces or frustums basically have the four sides of the extrusion zone as the central axis. The generatrix radii of the four conical surfaces are R1, R2, R3, and R4 respectively. The centers of the four conical surfaces are respectively located at the four vertices O1, O2, O3, and O4 of the modules at the diagonals of the two rectangular sides connected by each conical surface. The centers O1, O2, O3, and O4 are located on the diagonal lines of the rectangles with the four generatrixes, which are respectively rotated around the central axis perpendicular to the inner wall of the mold cavity and passing through the center of the maximum radius of the conical surface to form a conical surface. For example, the conical surface with the generatrix R1 rotates around the central axis perpendicular to the radius R5. The four central axes are the four rectangular sides at the bottom of the top entrance section of the extrusion channel (or the projections coincide).

[0030] like Fig. 9 , 10 As shown, it is the transmission diagram of the quasi-hyperbolic gear and the mold of the present invention, the large gear 18 is fixed to the multi-cone module differential torsion extrusion forming mold 19 by bolts 28, the small gear 17 is meshed with the large gear 18, and the small gear 17 drives the multi-cone module differential torsion extrusion forming mold 19 to rotate under the rotation of the transmission shaft 20. The rotation speed of the small gear 17 is ω1, and the linear velocity is v1. The angular velocity of the large gear 18 and the multi-cone module mold 19 is ω2, and the linear velocity is v2, so that the blank undergoes torsional deformation.

[0031] During the entire process of variable-channel continuous torsional extrusion differential 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.

[0032] 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 fine-grained weak-textured magnesium alloy by multi-cone differential extrusion, characterized in that: It comprises a vertical hydraulic press, a multi-cone module differential extrusion forming die (19) and a hypoid gear transmission device, 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 (14), a column (24), a working platform (25) and a hydraulic press base (26); the hydraulic press top seat (12) is supported by the column (24), the pressure motor (11) is installed above the hydraulic press top seat (12), the movable end of the pressure motor (11) faces downward and passes through the hydraulic press top seat (12), the extrusion punch telescopic pressure head (12) is installed on the movable end of the pressure motor (11); the extrusion punch 14 is installed below the extrusion punch telescopic pressure head (13); A working platform (25) is fixed above the hydraulic press base (26), a lower pad (21) and a die fixing frame (16) surrounding the lower pad (21) are fixed on the working platform (25), and an upper pad (15) is installed on the top of the die fixing frame (16); the multi-cone module differential twisting extrusion forming die (19) is located between the die fixing frame (16), the upper pad (15) and the lower pad (21), and a sleeve (23) is also provided on the outer ring of the multi-cone module differential twisting extrusion forming die (19); a groove serving as a slide rail is provided on the upper surface of the lower pad (21) and the lower surface of the upper pad (15); a through hole matching the extrusion punch (14) is provided on the top of the upper pad (15), and mutually interpenetrating through holes are provided in the center of the lower pad (21), the working platform (25) and the hydraulic press base (26) as a material leakage hole; The multi-cone module differential twisting and extruding forming die (19) is provided with an extrusion channel extending upward and downward therein. The upper and lower surfaces of the multi-cone module differential twisting and extruding forming die (19) are both provided with arc-shaped bosses serving as sliders. The arc-shaped bosses cooperate with the grooves on the surfaces of the lower pad (21) and the upper pad (15) to ensure the movement trajectory of the multi-cone module differential twisting and extruding forming die (19). The multi-cone module differential twisting and extruding forming die (19) is provided with grooves at the middle positions of the left and right ends of the multi-cone module differential twisting and extruding forming die (19). The grooves are provided with threaded holes, which are used to fix the large gear (18) of the hypoid gear transmission device. The groove is used to accommodate the pinion (17) and the large gear (18) of the hypoid gear transmission device, so as to realize continuous twisting of the multi-cone module differential twisting and extruding forming die (19); the upper pad (15) and the multi-cone module differential twisting and extruding forming die (19) are both provided with a heating channel (27) for connecting to an external circulation pipeline; in the hypoid gear transmission device, the large gear (18) is connected and fixed to the threaded hole of the multi-cone module differential twisting and extruding forming die (19) by bolts (28), and the pinion (17) is connected to the motor through a transmission shaft (20) to realize rotation; The extrusion channel is composed of torsion zone I, variable cross-section torsion zone II, and extrusion zone III from top to bottom; the cross-section of the upper port of the extrusion channel is rectangular and extends downward to form an entrance section, and four asymmetric conical surfaces protruding toward the inner side of the extrusion channel are distributed below the entrance section, and each conical surface has different radii at different positions, and each conical surface is connected to two adjacent rectangular sides. The four conical surfaces are connected in sequence and then surround the four rectangular sides, but the first conical surface is not connected to the fourth conical surface, and an unconnected section is left on a rectangular side; the minimum radius end of the first conical surface is connected to the minimum radius end of the second conical surface, the maximum radius of the second conical surface is connected to the minimum radius end of the third conical surface, and the maximum radius of the third conical surface is connected to the fourth conical surface. The extrusion channel is connected to the minimum radius end of the conical surface, and the extrusion channel from the entrance section to the bottom of the maximum radius of the conical surface constitutes a torsion zone I; the four conical surfaces and the five lower ends of the unconnected sections are all transitioned through the arc section, and then vertically extend downward for a certain distance to form five vertical sections and extend to the same horizontal height. The lower parts of the five vertical sections respectively protrude multiple asymmetric conical surfaces or truncated cones toward the inner side of the extrusion channel, and the extrusion channel is transitioned into an extrusion zone III with a rectangular cross-section, and the bottom outlet of the extrusion zone III is connected with the through hole of the lower pad (21); the area of ​​the extrusion zone III is smaller than the entrance section, the extrusion zone III is offset from the center of the entrance section, and the extrusion zone III is deflected by a certain angle relative to the entrance section; the extrusion channel between the torsion zone I and the extrusion zone III serves as a variable cross-section torsion zone II.

2. The device for preparing fine-grained weak-textured magnesium alloy by multi-cone differential extrusion as claimed in claim 1, characterized in that: The multi-cone module differential twisting and extruding forming die (19) is composed of four modules with similar shapes; the modules are composed of a long strip segment and a short straight segment vertically connected to one end of the long strip segment; the four modules are spliced ​​inwardly with the side without the short straight segment facing inward to form the multi-cone module differential twisting and extruding forming die (19); The generatrix radii of the four conical surfaces are R1, R2, R3, and R4 respectively, and the centers of the four generatrixes are respectively located at the four vertices O1, O2, O3, and O4 of the modules at the diagonals of the two rectangular sides connected by each conical surface, and the four generatrixes are respectively rotated around the central axis perpendicular to the inner wall of the mold cavity and passing through the center of the maximum radius of the conical surface to form a conical surface; the maximum radii of the four conical surfaces are R5, R6, R7, and R8 respectively, and the radius of the arc segment transition fillet is R9; The four cones extend downward by different distances L. 13 , L 14 , L 15 , L 16 , the unconnected segment extends downward L 16 The distance from the sum of the corresponding radii R8; the perpendicular lines between the five endpoints of the four conical surfaces and the four rectangular sides of the extrusion area III are used as the five radii R 10 , R 11 , R 12 , R 13 , R 14 The inner wall of the extrusion channel on both sides of the five radii transitions downward to the four rectangular sides of the extrusion zone III through a conical surface or a frustum surface, R 10 , R 11 , R 12 , R 13 , R 14 As the maximum radius of the corresponding cone or frustum.

3. The device for preparing fine-grained weak-textured magnesium alloy by multi-cone differential extrusion as claimed in claim 2, characterized in that: The multi-cone module differential extrusion forming die (19), the large gear (18) in the hypoid gear transmission device, the small gear (17), the extrusion punch telescopic pressure head (13), and the extrusion punch (14) are all made of 4Cr5MoSiV1 hot working die steel; their surface roughness reaches Ra0.16~0.4μm.

4. A method for preparing a fine-grained weak-textured magnesium alloy by multi-cone differential extrusion, which is implemented by using the device for preparing a fine-grained weak-textured magnesium alloy by multi-cone differential extrusion according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Pretreatment of magnesium alloy billet: S1-1, processing the magnesium alloy billet into a magnesium alloy square bar (22), grinding the surface of the magnesium alloy square bar (22) with 600-mesh sandpaper to remove oil stains, and then grinding with 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence until the surface of the magnesium alloy billet is smooth; S1-2, mixing acetone and anhydrous ethanol in a volume ratio of 3:2 in a cleaning tank and stirring evenly to prepare an ultrasonic cleaning solution; S1-3, immersing the magnesium alloy square bar (22) 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 square bar (22) for 60 minutes, then taking out the magnesium alloy square bar (22) and cleaning it with anhydrous ethanol, and finally drying it with a hair dryer; S1-4, applying a graphite oil solution to the surface of the magnesium alloy square rod (22) prepared in step S1-3, and leaving it for use in the next step; S2. Preheating the magnesium alloy square bar (22): setting the heating temperature of the vacuum atmosphere heating furnace to 450° C. After the heating furnace temperature reaches the set temperature, the magnesium alloy square bar (22) is placed in the heating furnace and kept warm for 3 hours; S3, lubrication, assembly and preheating of the multi-cone module differential extrusion forming die (19); S3-1, lubrication: smear the upper and lower surfaces of the multi-cone module differential extrusion forming die (19), the surface of the arc boss, the surface of the upper pad (15), the surface of the lower pad (21), the grooves, and the surfaces of all parts constituting the extrusion channel with a graphite oil solution; S3-2, assembly: first, fix the lower pad (21) on the working platform (25), and fix the sleeve (23) on the lower pad (21); then, respectively connect and fix the four modules of the multi-cone module differential twisting and extruding forming die (19) to the large gear (18) in the quasi-hypoid gear transmission device through bolts (28), and place the assembled multi-cone module differential twisting and extruding forming die (19) on the lower pad (21), and the arc-shaped boss below the multi-cone module differential twisting and extruding forming die (19) matches with the groove of the lower pad (21); fix the quasi-hypoid gear transmission device The pinion (17) is meshed with the transmission shaft (20), and the pinion (17) is meshed with the large gear (18) on the die, and the upper pad (15) is installed, and the groove of the upper pad (15) is matched with the upper arc-shaped boss of the multi-cone module differential twisting extrusion forming die (19); the extrusion punch (14) of the hydraulic press top seat (12) is controlled to be inserted downward into the through hole of the upper pad (15) without contacting the upper pad (15), so as to ensure that the axis of the extrusion punch (14) coincides with the axis of the upper pad (15), and the leakage hole set on the lower pad (21) is aligned with the working platform (25) at the position of the extrusion zone III; S3-3, preheating: the oil temperature machine controller turns on the oil temperature machine, sets the temperature of the hot oil entering the upper pad (15) and the multi-cone module differential extrusion forming die (19) to 350-500°C, and keeps the temperature for 2-4 hours after reaching the set temperature; S4, multi-cone differential extrusion forming: S4-1, controlling the pressure motor (11) to withdraw the extrusion punch (14) from the extrusion channel, placing the magnesium alloy square bar (22) into the extrusion channel and making it contact with the upper pad (15) and the upper part of the multi-cone module differential twisting extrusion forming die (19), controlling the extrusion punch (14) to move downward for extrusion, and the extrusion speed is 10-200 mm / min. During the extrusion process, controlling the oil temperature machine to always ensure that the temperature of the hot oil entering the upper pad (15) and the multi-cone module differential twisting extrusion forming die (19) is 350-500° C., and the magnesium alloy square bar (22) passes through the torsion zone I, the variable cross-section torsion zone II and the extrusion zone 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; S4-2, after the multi-cone differential speed twisting extrusion forming, perform the following steps a or b: a. When extruding the second magnesium alloy square bar (22): first, turn off the oil temperature machine, control the vertical hydraulic press to withdraw the extrusion punch (14) until it is large enough to accommodate the next magnesium alloy square bar (22); then, saw off the fine-grained weak-textured magnesium alloy material obtained by extrusion in step S4-1 from the leakage hole; after placing the next magnesium alloy square bar (22), turn on the oil temperature machine and repeat step S4-1 to perform variable-section differential extrusion until all magnesium alloy billets are differentially extruded and step b is performed; b. After the extrusion of the magnesium alloy billet is completed, the oil temperature controller is turned off, and the vertical hydraulic press is controlled to withdraw the extrusion punch (14) from the multi-cone module differential twisting extrusion forming die (19). After the multi-cone module differential twisting extrusion forming die (19) and the magnesium alloy billet are cooled to room temperature, the multi-cone module differential twisting extrusion forming die (19) is removed from the vertical hydraulic press, the fine-grained weak-textured magnesium alloy obtained by extrusion is sawed off from the leakage hole, the unformed magnesium alloy square bar (22) in the channel is taken out, and the die is sealed for subsequent use; S4-3. Take out the fine-grained weak-textured magnesium alloy rod 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 fine-grained weak-textured magnesium alloy rod that can be directly put into use.

5. The processing method for preparing fine-grained weak-textured magnesium alloy by multi-cone differential extrusion as claimed in claim 4, characterized in that: The raw materials used for processing are as follows: Magnesium alloy billet, square billet, material selected is AZ31, containing 96% magnesium, 3% aluminum and 1% zinc; Sandpaper, solid solid; Graphite oil solution, viscous liquid; Anhydrous ethanol, liquid, purity 99.5%; Acetone, liquid, purity 99%.

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