Device and method for preparing fine-grain magnesium alloy pipe

Abstract

The invention aims to provide a device and a method for preparing a fine-grain magnesium alloy pipe, and belongs to the technical field of light metal plastic forming. Differential torsion and continuous shear deformation are generated in the machining process of a magnesium alloy pipe blank, grain refinement and texture weakening are achieved while the torsion direction of the blank is not changed, and the yield of the fine-grain magnesium alloy pipe is improved. Room-temperature mechanical properties of magnesium alloy pipes are improved, and the magnesium alloy application range is widened. By means of the method, the grain refining effect of the magnesium alloy pipe is more remarkable, the basal texture is weakened to a large extent, the obtained fine-grain magnesium alloy pipe is uniform in structure, and the obdurability is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of light metal plastic forming, and in particular relates to a device and a method for preparing a fine-grained magnesium alloy pipe. Background Art

[0002] Magnesium alloy is an alloy composed of magnesium and other elements. The more significant advantages of magnesium alloy over other alloys are low density, high specific strength, large elastic modulus, good shock absorption, and strong ability to withstand impact loads. Therefore, it is widely used in aviation, aerospace, transportation, chemical industry, rocket and other industrial sectors, and its development prospects are excellent. However, an obvious defect of magnesium alloy is that its plasticity and mechanical properties at room temperature are poor, which seriously restricts the development of magnesium alloy. The reason is that the crystal structure of magnesium is a close-packed hexagonal structure. At room temperature, only two basal slip systems are activated, while non-basal slip systems can generally only be activated near grain boundaries with severe stress concentration, which is far from the 5 or more independent slip systems of the Von-Mises criterion. This is the main reason for the poor plasticity of magnesium alloy. At the same time, the limited slip system of magnesium alloy leads to the easy formation of strong basal texture after plastic deformation. The strong basal texture further limits the plastic deformation of magnesium alloy. Therefore, how to solve the poor processing performance of magnesium alloy is the main problem faced at this stage.

[0003] It has been proven that severe plastic deformation can effectively refine the grains of magnesium alloys and weaken the texture. The specific deformation modes include shear deformation, torsion deformation, and composite deformation. The effect of fine grain strengthening is achieved by refining the grains of magnesium alloys, so that the strength, plasticity, and comprehensive mechanical properties of magnesium alloys are significantly enhanced. Common technologies include high pressure torsion (HPT), multi-directional forging (MDF), equal channel angular extrusion (ECAP), rotary extrusion (TE), etc. However, the existing technologies have technical drawbacks and defects for magnesium alloy tubes, such as discontinuous processing and low efficiency. Therefore, inventing a processing technology method for refining grains and weakening texture to obtain high-performance fine-grained magnesium alloy tubes is a problem that needs to be solved urgently to expand the application range of magnesium alloys. Summary of the invention

[0004] In view of the above problems, the object of the present invention is to provide a device and method for preparing fine-grained magnesium alloy tubes. Through the device and method, the magnesium alloy tube blank undergoes reciprocating differential torsion and continuous shear deformation during the processing process, and the torsion direction of the blank is not changed while the grain refinement and texture weakening are achieved, thereby improving the room temperature mechanical properties of the magnesium alloy tube and expanding the application range of magnesium alloys.

[0005] To achieve the above object, the present invention adopts the following technical solution: A device for preparing fine-grained magnesium alloy tubes, comprising a horizontal extruder, the horizontal extruder comprising an operating box, two sides of the operating box are respectively provided with left and right pressure motors, the top ends of the left and right pressure motors are respectively connected with left and right extrusion telescopic chambers through left and right transmission belts; A fixing frame is provided at the top of the operation box, a motor is provided on one side of the fixing frame, a transmission rod is connected to the output end of the motor, the other end of the transmission rod is connected to the fixing frame, an elliptical gear is connected to the transmission rod, the teeth of the elliptical gear are half, an elliptical die is meshed at the bottom of the elliptical gear, an extrusion channel is provided at the center of the elliptical die, and a core shaft is provided in the extrusion channel; The two ends of the extrusion channel are respectively provided with a left punch and a right punch, and the left punch and the right punch are respectively connected with the left extrusion telescopic cavity and the right extrusion telescopic cavity through a left extrusion rod and a right extrusion rod.

[0006] Furthermore, a display screen is provided on one side surface of the operation box, and a power switch, a heating sleeve switch, and left and right extrusion rod switches are provided in sequence on the other side of the operation box, and indicator lights are respectively connected to the power switch, the heating sleeve switch, and the left and right extrusion rod switches.

[0007] Furthermore, bases are provided at the bottoms of the operation box and the left and right pressure motors, respectively, and the left and right squeezing rod switches of the operation box are electrically connected to the left and right pressure motors.

[0008] Furthermore, a torsional shearing channel is provided at the central edge of the elliptical die. The torsional shearing channel is arc-shaped, with one end having an angle of 126° with the horizontal line and the other end having an angle of 140° with the horizontal line.

[0009] Furthermore, a heating sleeve is provided on the outer side of the elliptical die.

[0010] A method for preparing a fine-grained magnesium alloy tube comprises the following steps: S1. Pretreatment of magnesium alloy tube blanks; S2, preheating magnesium alloy tube blank; S3. The device is lubricated with graphite oil solution. After assembly, the temperature is set to 300-500℃ through the heating jacket. After reaching the set temperature, keep it warm for 2-4 hours. S4, reciprocating differential torsional shear extrusion molding.

[0011] Furthermore, the pretreatment of the magnesium alloy tube blank comprises the following steps: S1-1, processing the magnesium alloy tube blank into an outer diameter of D and a wall thickness of t, and grinding the surface of the magnesium alloy tube 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 tube 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 a cleaning solution; S1-3, immerse the magnesium alloy tube blank into the cleaning solution, place the cleaning tank on an ultrasonic cleaning machine to ultrasonically clean the magnesium alloy tube for 30 to 60 minutes, then take out the magnesium alloy tube blank and clean it with anhydrous ethanol, and finally blow dry it with a hair dryer; S1-4. Apply graphite oil solution to the surface of the cleaned magnesium alloy tube blank for use.

[0012] Furthermore, the magnesium alloy tube blank preheating step is as follows: the heating temperature of the vacuum atmosphere heating furnace is set to 300-500° C., and after the temperature of the heating furnace reaches the set temperature, the magnesium alloy tube blank is placed in the heating furnace and kept warm for 2-4 hours.

[0013] Furthermore, the reciprocating differential torsional shear extrusion molding comprises the following steps: S4-1. Withdraw the left punch from the elliptical die to fill the magnesium alloy tube blank inside the elliptical die, and push the left punch back into the magnesium alloy tube blank inside the elliptical die; start the left extrusion rod to drive the left punch to move rightward at a speed of 100-300 mm / min, and the left extrusion rod extrudes the magnesium alloy tube blank to move rightward into the torsional shear channel inside the elliptical die, and extrudes the shear angle from left to right at 126° to perform shear deformation, so that the magnesium alloy tube blank undergoes large plastic deformation; at the same time, the motor drives the elliptical gear to rotate at a constant angular speed of 0.01-1 r / s, and the elliptical die meshes with the elliptical gear and rotates at an angular speed that varies from 0.01-1 r / s, so that the magnesium alloy tube blank inside the elliptical die undergoes torsional deformation at different linear speeds; S4-2. Keep the position of the magnesium alloy tube billet unchanged after torsion deformation. When the elliptical gear rotates at an angle of π / 2, start the right extrusion rod to drive the right punch to move left at a speed of 100-300 mm / min. When the right punch contacts the magnesium alloy tube billet in the torsion shear channel, start extrusion from right to left. The extrusion shear angle from right to left is 140° for shear deformation. The extrusion shear angle is reciprocated. This process causes large plastic deformation of the magnesium alloy tube billet, which refines the magnesium alloy grains. When the elliptical gear rotates at an angle of π, the extrusion process from right to left ends, the pure severe plastic shear deformation ends, and the magnesium alloy tube blank begins the next stage of differential torsional shear deformation; during the reciprocating differential torsional shear extrusion forming process, the temperature of the heating sleeve is controlled to be 300~500℃; S4-3, the left punch and the right punch extrude the magnesium alloy tube blank to make it reciprocate in the torsional shear channel formed by the elliptical die and the mandrel, so that the grains of each section of the magnesium alloy tube blank are refined; when the reciprocating motion is ≥20 times and the internal die is in the initial position, the stop button is pressed to complete the reciprocating differential torsional shear extrusion of the magnesium alloy tube blank; S4-4. Take out the magnesium alloy tube blank, polish its surface with sandpaper, then clean the magnesium alloy tube blank with cleaning liquid, finally clean it twice with anhydrous ethanol, and blow dry it with a hair dryer to obtain a fine-grained weak-textured magnesium alloy tube that can be directly put into use.

[0014] The beneficial effects of the present invention are as follows: 1. Through the meshing of elliptical gears, the elliptical die rotates at a variable speed, causing the tube metal to rotate differentially, thereby generating differential torsional deformation, causing the tube grains to deflect along the corresponding torsional direction, and the strong base surface texture is weakened. This drastic plastic deformation refines the grains and improves the mechanical properties of the magnesium alloy tube.

[0015] 2. During the reciprocating differential torsional shear extrusion process, the elliptical gear meshes with the elliptical die at a rotation angle of π / 2, so that the tube undergoes differential torsional shear deformation in the extrusion process from left to right, and pure shear deformation in the extrusion process from right to left. The reciprocating motion does not change the direction of torsional deformation. At the same time, the different shear angles of the reciprocating motion lead to different metal flow speeds, making the shear deformation of the magnesium alloy tube more comprehensive and uniform, and the grain refinement and texture weakening effects are more significant. When the number of reciprocating differential torsional shear extrusion n≥20, the magnesium alloy tube structure obtained is more uniform. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the device of the present invention; Figure 2 for Figure 1 Schematic diagram of the internal torsional shear extrusion channel; Figure 3 It is a schematic diagram of the front view structure of the elliptical gear of the present invention; Figure 4 It is a schematic side view of the structure of the elliptical gear of the present invention; Figure 5 It is a schematic diagram of the main structure of the elliptical concave mold of the present invention; Figure 6 It is a side view structural schematic diagram of the elliptical concave mold of the present invention; Figure 7 It is a schematic diagram of the meshing of the elliptical gear and the elliptical concave die of the present invention; Figure 8 It is the main view of the magnesium alloy tube blank in the torsional shear deformation state; Fig. 9It is a side view of the magnesium alloy tube blank in the torsional shear deformation state; Among them: 1-operation box; 2-display screen; 3-indicator light; 4-power switch; 5-heating sleeve switch; 6-left extrusion rod switch; 7-right extrusion rod switch; 8-base; 9-left connecting wire; 10-right connecting wire; 11-left pressure motor base; 12-right pressure motor base; 13-left pressure motor; 14-right pressure motor; 15-left pressure motor drive belt; 16-right pressure motor drive belt; 17-left extrusion telescopic chamber; 18-right extrusion telescopic chamber; 19-left extrusion rod; 20-left punch; 21-left fixed bracket; 22-upper fixed bracket; 23-mandrel; 24-blank; 25-elliptical die; 26-elliptical gear; 27-drive rod; 28-motor; 29-right punch; 30-right fixed bracket; 31-heating sleeve; 32-right extrusion rod; 33-torsion deformation channel I (extrusion cavity I); 34-shear deformation channel II (extrusion cavity II); 35-shear deformation channel III (extrusion cavity III). DETAILED DESCRIPTION

[0017] The present invention will be further described with reference to the accompanying drawings.

[0018] As shown in the figure, a device for preparing fine-grained magnesium alloy tubes includes a horizontal extruder, wherein the horizontal extruder includes an operating box 1, and a left pressure motor 13 and a right pressure motor 14 are respectively provided on both sides of the operating box 1, and the top ends of the left pressure motor 13 and the right pressure motor 14 are respectively connected to a left extrusion telescopic chamber 17 and a right extrusion telescopic chamber 18 through a left pressure motor transmission belt 15 and a right pressure motor transmission belt 16; The top of the operation box 1 is provided with a fixed frame, and a motor 28 is provided on one side of the fixed frame. The output end of the motor 28 is connected to a transmission rod 27, and the other end of the transmission rod 27 is connected to the fixed frame. The transmission rod 27 is connected to an elliptical gear 26, and the teeth of the elliptical gear 26 are half. The bottom of the elliptical gear 26 is meshed with an elliptical die 25. When the elliptical gear 26 rotates, the elliptical die 25 meshed with it is driven to rotate. Since the rotation of the elliptical gear 26 is consistent with the motor 28, its angular velocity remains unchanged, and the elliptical die 25 meshed with it will produce different linear speeds due to the shape characteristics of the ellipse itself, and then produce different speeds of rotation. An extrusion channel is provided at the center of the elliptical die 25, and a mandrel 23 is provided in the extrusion channel; the elliptical die 25 rotates at a non-uniform speed, and the mandrel 23 remains stationary, which causes the pipe blank in the middle to rotate at different speeds in the radial direction. This radial speed difference causes the pipe blank to deform asynchronously and then produce torsional deformation. The rotation of the elliptical die 25 will cause the pipe blank to deform synchronously.

[0019] The teeth of the elliptical gear 26 are half, and the elliptical die 25 does not rotate during the return stroke, and the pipe blank does not rotate either.

[0020] The fixing frame includes a left fixing bracket 21, a right fixing bracket 30 and an upper fixing bracket 22. One end of the left fixing bracket 21 and the right fixing bracket 30 are respectively connected to the operation box 1, and both ends of the upper fixing bracket 22 are respectively connected to the left fixing bracket 21 and the right fixing bracket 30.

[0021] A left punch 20 and a right punch 29 are respectively disposed at both ends of the extrusion channel. The left punch 20 and the right punch 29 are respectively connected to the left extrusion telescopic cavity 17 and the right extrusion telescopic cavity 18 through the left extrusion rod 19 and the right extrusion rod 32.

[0022] Furthermore, a display screen 2 is provided on one side surface of the operation box, and a power switch 4, a heating sleeve switch 5, a left extrusion rod switch 6 and a right extrusion rod switch 7 are provided in sequence on the other side of the operation box 1. Indicator lights 3 are respectively connected to the power switch 4, the heating sleeve switch 5, the left extrusion rod switch 6 and the right extrusion rod switch 7.

[0023] Furthermore, the bottom of the operating box 1, the left pressure motor 13 and the right pressure motor 14 are respectively provided with a base 8, a left pressure motor base 11 and a right pressure motor base 12, and the left squeezing rod switch 6 and the right squeezing rod switch 7 of the operating box 1 are respectively electrically connected to the left pressure motor 13 and the right pressure motor 14.

[0024] Furthermore, a torsional shear channel is provided at the center of the elliptical die 25, and the angle between one end of the torsional shear channel and the horizontal line is 126°, and the angle between the other end and the horizontal line is 140°. When the tube blank passes through this channel, shear deformation will occur, and the shear deformation generated at the inlet end and the outlet end due to the inconsistency of their angles is also different. Therefore, the elliptical die 25 is driven to rotate by the motor 28, and at the same time, the left punch 20 and the right punch 29 reciprocate to extrude in this torsional shear channel to achieve torsional shear deformation.

[0025] During the reciprocating extrusion process between the left punch 20 and the right punch 29, the tube blank undergoes reciprocating shearing motion. Affected by the shape of the mandrel, the shearing deformation occurs at a shearing angle of 126° from left to right and at a shearing angle of 140° from right to left. The reciprocating extrusion shearing angles are different.

[0026] The motor 28 drives the elliptical gear 26 to rotate at a constant angular speed (0.01~1 r / s), and the elliptical die 25 meshes with the elliptical gear 26 and rotates at a variable angular speed (0.01~1 r / s), so that the blank inside the elliptical die 25 rotates at different linear speeds v 1Torsion deformation occurs. The elliptical gear 26 is a half gear design, so during the extrusion process from left to right, the elliptical gear 26 meshes with the elliptical die 25 to rotate, and the blank undergoes differential torsion deformation. During the extrusion process from right to left, the elliptical gear 26 does not contact the elliptical die 25, and the elliptical die 25 performs pure shear extrusion at this time, and reciprocating extrusion does not change the torsion direction.

[0027] The left extrusion rod 19, the right extrusion rod 32, the left punch 20, the right punch 29, the elliptical gear 26, the elliptical die 25, and the core shaft 23 are all made of hot working die steel 4Cr5MoSiV1, and the surface roughness is Ra0.16~0.4μm.

[0028] Furthermore, a heating jacket is provided on the outer side of the elliptical die 25 .

[0029] A method for preparing a fine-grained magnesium alloy tube comprises the following steps: S1. Pretreatment of magnesium alloy tube blanks: S1-1. Process the magnesium alloy tube blank into an outer diameter of D and a wall thickness of t, and polish the surface with 600-mesh sandpaper to remove oil stains, and then polish with 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence until the surface of the magnesium alloy tube blank 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 a cleaning solution; S1-3, immersing the magnesium alloy tube 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 tube blank for 30 to 60 minutes, then taking out the magnesium alloy tube blank 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 tube blank prepared in step S1-3, and leaving it for use in the next step; S2. Preheating of magnesium alloy tube blanks: Set the heating temperature of the vacuum atmosphere heating furnace to 300-500°C. After the heating furnace temperature reaches the set temperature, place the magnesium alloy tube blanks into the heating furnace and keep them warm for 2-4 hours. S3. Lubrication, assembly and preheating of reciprocating torsion shearing and extrusion deformation device: S3-1, Lubrication: Wipe all mold surfaces clean, and apply graphite oil solution to all meshing surfaces of gears, inner surfaces of cavity filling molds, and surfaces of all molds constituting the extrusion channel; S3-2, assembly; S3-3, preheating: operate the heating jacket controller to control the heating jacket temperature to 300~500℃, keep it warm for 2~4 hours after reaching the set temperature, and reserve it for later use; S4, reciprocating differential torsional shear extrusion forming: S4-1, withdraw the left punch 20 from the elliptical die 25, so that the magnesium alloy tube blank is filled in the elliptical die 25, and push the left punch 20 back into the magnesium alloy tube blank in the elliptical die 25; operate the left extrusion rod switch 6, so that the left extrusion rod 19 drives the left punch 20 to move rightward, and the moving speed is (100~300mm / min). The left extrusion rod 19 extrude the magnesium alloy tube blank to move rightward into the torsional shear channel in the elliptical die 25. Affected by the shape of the mandrel 23, the extrusion shear angle is 126° from left to right to perform shear deformation, so that the magnesium alloy tube blank undergoes large plastic deformation. This asymmetric deformation caused by the radial asymmetric flow of the metal belongs to shear deformation. The shear deformation refines the grains while causing the c-axis of the grains to deflect along the extrusion direction, further causing the strong base surface texture orientation to change along the shear direction and transform into a weak base surface texture, thereby achieving the weakening of the magnesium alloy tube texture; at the same time, the motor drives the elliptical gear at a constant angular velocity (0.01~1 r / s), the elliptical die 25 meshes with the elliptical gear 26 and rotates at a variable angular velocity (0.01~1 r / s), so that the blank inside the elliptical die 25 rotates at different linear velocities v 1 Torsion deformation occurs. Due to the thin wall thickness of the tube and the phenomenon of heating and softening, the metal on the outside of the magnesium alloy tube blank will be twisted, causing the magnesium alloy tube blank to be torsionally deformed, and the metal in the rest of the part will not be twisted, so that the metal fillet sheared by the elliptical die 25 and the mandrel 23 is inconsistent each time, and further causes the blank to produce different radial asymmetric flow and deformation each time it passes through the torsion shear channel, and further causes the magnesium alloy tube blank to produce different torsion and shear asymmetric deformation in the radial direction during each deformation, and further makes the overall torsion and shear deformation of the magnesium alloy tube blank more comprehensive and uniform, so that the shear deformation of each part of the magnesium alloy tube blank is more comprehensive and uniform, the grains are more uniformly refined, the texture is weakened, and the overall performance of the magnesium alloy tube is improved; S4-2. Keep the position of the magnesium alloy tube blank unchanged after torsional deformation. When the elliptical gear 26 rotates at an angle of π / 2, operate the right extrusion rod switch 7 to make the right extrusion rod 32 drive the right punch 29 to move leftward at a speed of (100-300 mm / min). When the right punch 29 contacts the magnesium alloy tube blank in the torsional shear channel, it starts to extrude from right to left. Affected by the shape of the mandrel 23, the shearing angle from right to left is 140° for shear deformation. The reciprocating extrusion shearing angle causes large plastic deformation of the magnesium alloy tube blank and refines the magnesium alloy grains. The elliptical gear 26 is designed as a half gear. During the extrusion process from left to right, the elliptical gear 26 meshes with the elliptical die 25 to rotate. At this time, the blank undergoes differential torsional deformation. During the extrusion process from right to left, the elliptical gear 26 meshes with the elliptical die 25 to rotate. 5 is not in contact, and pure shear extrusion is performed at this time, and the torsion direction of the billet after the previous extrusion process is not changed; at this time, the billet flows in the cavity in a radially asymmetric manner, which further makes the thickness of the billet at each radial position at the shear fillet different. The asymmetric deformation caused by the radial asymmetric flow of the tube billet belongs to shear deformation. The shear deformation refines the grains while causing the c-axis of the grains to deflect along the extrusion direction, further changing the orientation of the strong base surface texture along the shear direction and turning it into a weak base surface texture, thereby weakening the texture of the magnesium alloy tube; when the elliptical gear 26 rotates at an angle of π, the extrusion process from right to left ends, the pure severe plastic shear deformation ends, and the billet is about to start the next stage of differential torsion shear deformation; in the reciprocating differential torsion shear extrusion forming process, the heating jacket controller is operated to control the heating jacket temperature to 300~500℃; S4-3, operate the left extrusion rod switch 6 and the right extrusion rod switch 7 to control the left punch 20 and the right punch 29 to extrude the magnesium alloy tube blank so that it reciprocates in the torsional shear channel formed by the elliptical die 25 and the mandrel 23, so that the grains of each section of the magnesium alloy tube are refined; after reciprocating for n times (n≥20 times) and the internal mold is in the initial position, press the stop button to complete the reciprocating differential torsional shear extrusion of the magnesium alloy tube; S4-4. Take out the magnesium alloy tube obtained in step S4-3, polish its surface with sandpaper, then clean the magnesium alloy tube with the cleaning solution prepared in step S1-2, finally clean it twice with anhydrous ethanol, and dry it with a hair dryer to obtain a fine-grained weak-textured magnesium alloy tube that can be directly put into use.

[0030] Example A device and process for preparing fine-grained magnesium alloy pipes by reciprocating differential torsional shear extrusion, comprising the following steps: S1. The outer surface of the AZ31 magnesium alloy tube blank was polished with 600-mesh sandpaper to remove oil stains, and then polished with 1000, 1200, and 2500-mesh sandpaper in sequence to ensure that the surface was clean and smooth; the polished magnesium alloy tube 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; S2, start the vacuum atmosphere heating furnace to preheat the magnesium alloy tube blank, the preset temperature is 400° C. When the preset temperature is reached, continue to place the magnesium alloy tube blank in the heating furnace for 3 hours; S3, assembling the installation device; S4, turn on the external heating device of the extrusion die cavity to heat the torsional shear deformation channel, the heating temperature is preset to 400°C, and after reaching the preset temperature, continue to keep warm for 3 hours; S5. Withdraw the left punch 20 from the elliptical die 25 to fill the magnesium alloy tube blank inside the elliptical die 25, and push the left punch 20 back into the magnesium alloy tube blank inside the elliptical die 25; operate the left extrusion rod switch 6, so that the left extrusion rod 19 drives the left punch 20 to move rightward, and the moving speed is 200mm / min. The left extrusion rod 19 extrude the magnesium alloy tube blank to move rightward into the torsional shear channel in the elliptical die 25. Affected by the shape of the mandrel 23, the extrusion shear angle is 126° from left to right for shear deformation, so that the magnesium alloy tube blank undergoes large plastic deformation. The materials of the accessories used are all hot working die steel 4Cr5MoSiV1, and the surface roughness is Ra0.16μm.

[0031] S6, at the same time, the motor 28 drives the elliptical gear 26 to rotate at a constant angular velocity of 0.5 r / s, and the elliptical die 25 meshes with the elliptical gear 26 and rotates at a variable angular velocity, so that the blank inside the elliptical die 25 rotates at different linear velocities v 1 Torsional deformation occurs; S7. Keep the position of the magnesium alloy tube blank unchanged after torsional deformation. When the elliptical gear 26 rotates at an angle of π / 2, operate the right extrusion rod switch 7 to make the right extrusion rod 32 drive the right punch 29 to move leftward at a speed of 200 mm / min. When the right punch 29 contacts the magnesium alloy tube blank in the torsional shear channel, it starts to extrude from right to left. Affected by the shape of the mandrel, the shearing angle from right to left is 140° for shear deformation. The reciprocating extrusion shearing angle causes large plastic deformation of the magnesium alloy tube blank and refines the grains of the magnesium alloy. The elliptical gear 26 is designed as a half gear. During the extrusion process from left to right, the elliptical gear 26 meshes with the elliptical die 25 to rotate. At this time, the blank undergoes differential torsional deformation. During the extrusion process from right to left, the elliptical gear 26 and the elliptical die 25 do not mesh. Contact, pure shear extrusion is performed at this time, and the torsion direction of the billet after the previous extrusion process is not changed; at this time, the billet flows in the cavity in a radially asymmetric manner, which further makes the thickness of the billet at each radial position at the shear fillet different. The asymmetric deformation caused by the radial asymmetric flow of the tube billet belongs to shear deformation. The shear deformation refines the grains while causing the c-axis of the grains to deflect along the extrusion direction, further changing the orientation of the strong base surface texture along the shear direction and turning it into a weak base surface texture, thereby weakening the texture of the magnesium alloy tube; when the elliptical gear rotates at an angle of π, the extrusion process from right to left ends, the pure severe plastic shear deformation ends, and the billet is about to start the next stage of differential torsion shear deformation; during the reciprocating differential torsion shear extrusion forming process, the heating jacket controller is operated to control the heating jacket temperature to 400°C; S8, operate the left extrusion lever switch 6 and the right extrusion lever switch 7 to control the left punch 20 and the right punch 29 to extrude the magnesium alloy tube blank so that it reciprocates in the torsional shear channel formed by the elliptical die 25 and the mandrel 23, so that the grains of each section of the magnesium alloy tube are refined; after 25 reciprocating movements and the internal mold is in the initial position, press the stop button to complete the reciprocating differential torsional shear extrusion of the magnesium alloy tube; S9. Take out the magnesium alloy tube, polish its surface with sandpaper, then place it in a mixture of acetone and anhydrous ethanol in 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.

[0032] Conclusion: Through the device and process method of the present invention for preparing high-performance fine-grained weak-textured magnesium alloy tubes by reciprocating differential torsional shear extrusion, the average grain size of the magnesium alloy tube is greatly reduced compared with conventional magnesium alloy tubes, from the original 33μm to 1.52μm, and the basal texture is transformed from a strong basal texture to a deflected weak basal texture, and the texture is effectively weakened compared with the initial magnesium alloy bar.

[0033] Materials and chemical reagents used: AZ31 magnesium alloy tube blank, with an outer diameter of D = 24 mm and a wall thickness of t = 2 mm; sandpaper: SiC, 600 mesh, 2 sheets; 1000 mesh, 2 sheets; 1200 mesh, 2 sheets; 2500 mesh, 2 sheets; high temperature graphite oil solution: C, 500 g; anhydrous ethanol: CH 3 CH 2 OH, 1200ml; Acetone: C 3 H 6 O, 800ml.

Claims

1. A device for preparing fine-grained magnesium alloy tubes, characterized in that: It comprises a horizontal extruder, the horizontal extruder comprising an operating box (1), the operating box (1) having left and right pressure motors respectively disposed on both sides, the top ends of the left and right pressure motors respectively connected to left and right extrusion telescopic chambers via left and right transmission belts; A fixing frame is provided at the top of the operation box (1), a motor (28) is provided on one side of the fixing frame, an output end of the motor (28) is connected to a transmission rod (27), the other end of the transmission rod (27) is connected to the fixing frame, an elliptical gear (26) is connected to the transmission rod (27), the teeth of the elliptical gear (26) are half, an elliptical die (25) is meshed at the bottom of the elliptical gear (26), an extrusion channel is provided at the center of the elliptical die (25), and a core shaft (23) is provided in the extrusion channel; The two ends of the extrusion channel are respectively provided with a left punch and a right punch, and the left punch and the right punch are respectively connected with the left extrusion telescopic cavity and the right extrusion telescopic cavity through a left extrusion rod and a right extrusion rod.

2. The device for preparing fine-grained magnesium alloy tube according to claim 1, characterized in that: A display screen (2) is provided on one side surface of the operation box (1), and a power switch (4), a heating sleeve switch (5), and left and right squeeze rod switches are provided in sequence on the other side of the operation box (1). Indicator lights (3) are connected to the power switch (4), the heating sleeve switch (5), and the left and right squeeze rod switches, respectively.

3. The device for preparing fine-grained magnesium alloy tube according to claim 2, characterized in that: The operating box (1) and the bottoms of the left and right pressure motors are respectively provided with bases, and the left and right squeezing rod switches of the operating box (1) are respectively electrically connected to the left and right pressure motors.

4. The device for preparing fine-grained magnesium alloy tube according to claim 1, characterized in that: A torsion shearing channel is provided at the central edge of the elliptical concave die (25); the torsion shearing channel is arc-shaped, with one end having an angle of 126° with the horizontal line and the other end having an angle of 140° with the horizontal line.

5. The device for preparing fine-grained magnesium alloy tube according to claim 1, characterized in that: A heating sleeve is provided on the outer side of the elliptical concave mold (25).

6. A method for preparing fine-grained magnesium alloy tubes using the device according to claim 1, characterized in that: The steps include: S1. Pretreatment of magnesium alloy tube blanks; S2, preheating of magnesium alloy tube blank; S3. The device is lubricated with graphite oil solution. After assembly, the temperature is set to 300-500℃ through the heating jacket. After reaching the set temperature, keep it warm for 2-4 hours. S4, reciprocating differential torsional shear extrusion molding.

7. The method for preparing a fine-grained magnesium alloy tube according to claim 6, characterized in that: The pretreatment of the magnesium alloy tube blank comprises the following steps: S1-1, processing the magnesium alloy tube blank into an outer diameter of D and a wall thickness of t, and grinding the surface of the magnesium alloy tube 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 tube 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 a cleaning solution; S1-3, immerse the magnesium alloy tube blank into the cleaning solution, place the cleaning tank on an ultrasonic cleaning machine to ultrasonically clean the magnesium alloy tube for 30 to 60 minutes, then take out the magnesium alloy tube blank and clean it with anhydrous ethanol, and finally blow dry it with a hair dryer; S1-4. Apply graphite oil solution to the surface of the cleaned magnesium alloy tube blank for use.

8. The method for preparing a fine-grained magnesium alloy tube according to claim 6, characterized in that: The magnesium alloy tube blank preheating steps are as follows: the heating temperature of the vacuum atmosphere heating furnace is set to 300-500° C. After the heating furnace temperature reaches the set temperature, the magnesium alloy tube blank is placed in the heating furnace and kept warm for 2-4 hours.

9. The method for preparing a fine-grained magnesium alloy tube according to claim 6, characterized in that: The reciprocating differential torsional shearing extrusion molding comprises the following steps: S4-1, withdraw the left punch (20) from the elliptical die (25), so that the magnesium alloy tube blank is filled in the elliptical die (25), and push the left punch (20) back into the magnesium alloy tube blank in the elliptical die (25); start the left extrusion rod (19) to drive the left punch (20) to move rightward at a speed of 100~300mm / min, and the left extrusion rod (19) extrude the magnesium alloy tube blank to move rightward into the torsional shear channel in the elliptical die (25), and perform shear deformation from left to right at an extrusion shear angle of 126°, so that the magnesium alloy tube blank undergoes large plastic deformation; at the same time, the motor (28) drives the elliptical gear (26) to rotate at a constant angular velocity of 0.01~1 r / s, and the elliptical die (25) meshes with the elliptical gear (26) and rotates at an angular velocity that varies from 0.01~1 r / s, so that the magnesium alloy tube blank in the elliptical die (25) undergoes torsional deformation at different linear velocities; S4-2, keeping the position of the magnesium alloy tube billet unchanged after torsion deformation, when the elliptical gear (26) rotates at an angle of π / 2, starting the right extrusion rod (32) to drive the right punch (29) to move leftward at a speed of 100-300 mm / min, and when the right punch (29) contacts the magnesium alloy tube billet in the torsion shear channel, starting extrusion from right to left; The extrusion shearing angle is 140° from right to left for shear deformation, and the extrusion shearing angle is reciprocated. This process causes large plastic deformation of the magnesium alloy tube billet and refines the magnesium alloy grains; When the elliptical gear rotates at an angle of π, the extrusion process from right to left ends, the pure severe plastic shear deformation ends, and the magnesium alloy tube blank begins the next stage of differential torsional shear deformation; during the reciprocating differential torsional shear extrusion forming process, the temperature of the heating sleeve is controlled to be 300~500℃; S4-3, the left punch (20) and the right punch (29) extrude the magnesium alloy tube billet so that it reciprocates in the torsional shear channel formed by the elliptical die (25) and the mandrel (23), so that the grains of each section of the magnesium alloy tube billet are refined; when the reciprocating motion is performed ≥20 times and the internal die is in the initial position, the stop button is pressed to complete the reciprocating differential torsional shear extrusion of the magnesium alloy tube billet; S4-4. Take out the magnesium alloy tube blank, polish its surface with sandpaper, then clean the magnesium alloy tube blank with cleaning liquid, finally clean it twice with anhydrous ethanol, and blow dry it with a hair dryer to obtain a fine-grained weak-textured magnesium alloy tube that can be directly put into use.

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