Device and method for preparing fine-grained magnesium alloy pipe by multi-edge reverse roller rolling-twisting-extrusion composite

Abstract

The present application belongs to the technical field of light metal plastic processing and mechanical property increasing, and particularly relates to a device and method for preparing fine-grained magnesium alloy pipe by multi-edge reverse roller rolling-twisting-extrusion composite. The device comprises a power device, a reciprocating extrusion device, a differential speed rotating extrusion device, a horizontal extruder, an extrusion die and a bracket. The left extrusion channel, the differential speed rotating extrusion channel and the right extrusion channel jointly form a reciprocating rotating differential speed extrusion channel. In the present application, the differential speed rotating extrusion channel makes the C-axis of the magnesium alloy deflect, effectively weakens the basal plane texture of the magnesium alloy, refines the grains and improves the mechanical properties of the magnesium alloy; the thickness of the extrusion channel has a decreasing trend; after entering the inlet, the pipe is subjected to the pressure between the gradually thinned extrusion channel walls, and at the same time, under the action of the inner and outer rotating extrusion cylinders, the pipe is subjected to the shearing force along the radial direction, and the size of the shearing force can be controlled by adjusting the friction coefficient of the outer wall of the extrusion cylinder. The grain texture weakening effect of the magnesium alloy rod is more remarkable.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of light metal plastic processing and increasing mechanical properties, and particularly relates to a device and method for preparing fine-grained magnesium alloy pipe by multi-edge reverse roller rolling-twisting-extrusion. BACKGROUND

[0002] In recent years, magnesium and magnesium alloys have been widely concerned due to their unique and excellent comprehensive mechanical properties, and are currently the lightest metal structural materials. Due to the excellent performance characteristics of magnesium and magnesium alloys, such as low density, light weight, excellent electrical and thermal conductivity, high specific strength and specific stiffness, good electromagnetic shielding performance, excellent machining performance, in addition, magnesium and magnesium alloys are easy to recycle, so they have excellent application prospects and have been widely used in military, aerospace and digital electronic products. At the same time, high-performance magnesium alloy thin-walled pipes, as a kind of hollow profile, are widely used in the fields of national defense and transportation, and are an important magnesium alloy structural part, which can replace aluminum alloy and other metal thin-walled parts to achieve the effect of weight reduction and energy saving. However, due to the crystal structure defects of magnesium and magnesium alloys, such as: magnesium is a close-packed hexagonal structure, has few independent slip systems that can be started, is difficult to deform, and has poor room temperature mechanical properties; in addition, magnesium is a lively metal, is easy to react and oxidize, and has poor corrosion resistance, which greatly limits the popularization and application of magnesium and magnesium alloys. Therefore, only the production and processing of magnesium alloy materials with good comprehensive mechanical properties can broaden their application range.

[0003] According to the current research status, in order to improve the comprehensive mechanical properties of magnesium alloys, two ways are mainly used, which are alloying and grain refinement. Alloying refers to adding one or more elements to the common magnesium alloy through melting, so as to improve the strength and hardness of the magnesium alloy. However, due to the need to add alloying elements or rare earth elements in the alloying melting process, the cost is high. Severe plastic deformation is a main way of grain refinement, which can overcome the shortcomings of traditional processing methods, refine the grain size of the material to sub-micron or even nanometer, and obtain excellent comprehensive mechanical properties. Common severe plastic deformation methods include equal channel angular extrusion, high pressure torsion and accumulative roll bonding, etc. These severe plastic deformation methods have their own characteristics. Equal channel angular extrusion is the most widely used method at present, the shape and size of the sample do not change before and after extrusion, and the sample can be repeatedly extruded to accumulate a large amount of plastic deformation, but the single extrusion deformation is small; high pressure torsion can prepare thin sheet samples with smaller grain size, but the sample size is small and the organization is not uniform. In summary, many severe plastic deformation methods have many technical problems and deficiencies. Therefore, it is very important to invent an effective device and method for weakening the deformation texture of magnesium alloy and refining the grain, which can expand the application range of magnesium alloy. SUMMARY

[0004] The purpose of the present application is to provide a device and method for preparing fine-grain magnesium alloy pipe by multi-edge reverse roller rolling and twist extrusion, aiming at the situation of the background art. Through the device and its processing method, the magnesium alloy pipe blank enters the deformation extrusion channel at the feeding port, and the inner and outer walls of the pipe are subjected to radial friction force from the inner and outer cylindrical rollers. Under the action of the radial friction force, the magnesium alloy pipe deforms unevenly in the radial direction, and the c-axis of the magnesium alloy deflects along the radial force direction and undergoes severe plastic deformation. Thus, the texture is weakened and the grain is refined, the room temperature mechanical properties of the magnesium alloy pipe are improved, and the application range of the magnesium alloy pipe is expanded.

[0005] The present application is implemented by the following technical scheme: a device for preparing fine-grain magnesium alloy pipe by multi-edge reverse roller rolling and twist extrusion, comprising a power device, a reciprocating extrusion device, a differential speed rotating extrusion device, a horizontal extruder, an extrusion die and a support;

[0006] The reciprocating extrusion device comprises a left pressure motor and a right pressure motor located on the left and right sides of the horizontal extruder respectively. The left pressure motor is connected with a left extrusion telescopic cavity through a left pressure motor conveying belt, and the right pressure motor is connected with a right extrusion telescopic cavity through a right pressure motor conveying belt. The left and right extrusion telescopic cavities are respectively provided with left and right extrusion telescopic cavity connecting rods arranged oppositely. The left and right extrusion telescopic cavity connecting rods are respectively connected with left and right extrusion telescopic cavity connecting rods.

[0007] The support comprises a left fixed support and a right fixed support arranged above the horizontal extruder. The extrusion die comprises a left fixed extrusion convex die, a fixed extrusion concave die and a right fixed extrusion convex die fixedly arranged between the left and right fixed supports. The fixed extrusion concave die has a cavity inside. The left and right fixed extrusion convex dies are respectively fixedly installed on the left and right sides of the fixed extrusion concave die cavity. An annular cavity is formed between the outer periphery of the left fixed extrusion convex die and the inner wall of the fixed extrusion concave die, and between the outer periphery of the right fixed extrusion convex die and the inner wall of the fixed extrusion concave die. Ring-shaped openings are formed on the left and right fixed supports at positions corresponding to the annular cavities. The left and right extrusion telescopic pressure rings can respectively extend into the two annular cavities through the ring-shaped openings. A heating jacket is sleeved on the outer periphery of the fixed extrusion concave die.

[0008] The differential rotation extrusion device comprises upper and lower outer rotating extrusion cylinders, an inner rotating extrusion cylinder, upper and lower outer rotating extrusion cylinder transmission shafts, left and right inner rotating extrusion cylinder transmission shafts, and a differential rotation extrusion channel; the upper and lower outer rotating extrusion cylinders have the same structure and an unequal diameter structure; the upper and lower outer rotating extrusion cylinders are arranged in a top-to-bottom manner and have opposite head-to-tail directions; the upper and lower outer rotating extrusion cylinders are supported by the upper and lower outer rotating extrusion cylinder transmission shafts between the left and right fixed supports and in the cavity between the left and right fixed extrusion punches; the upper and lower outer rotating extrusion cylinders are spaced apart; the two outer rotating extrusion cylinder transmission shafts are located above and below the left and right fixed extrusion punches; the right side of the left fixed extrusion punch extends to the left and enters the space between the left sides of the upper and lower outer rotating extrusion cylinders; the left side of the right fixed extrusion punch extends to the right and enters the space between the right sides of the upper and lower outer rotating extrusion cylinders; the left fixed extrusion punch and the left fixed extrusion table have an axle cavity and are rotatably connected with the left inner rotating extrusion cylinder transmission shaft; the right fixed extrusion punch and the right fixed extrusion table have an axle cavity and are rotatably connected with the right inner rotating extrusion cylinder transmission shaft; the inner rotating extrusion cylinder is located in the middle part of the space between the upper and lower outer rotating extrusion cylinders; the left and right ends of the inner rotating extrusion cylinder extend into the axle cavities of the left and right fixed extrusion tables and are supported by the bearings arranged in the left and right fixed extrusion tables; the left and right ends of the inner rotating extrusion cylinder are connected with the half ball gears after passing through the bearings; the left and right ends of the inner rotating extrusion cylinder are connected with the half ball gears; the upper and lower outer rotating extrusion cylinders have an unequal diameter structure and are matched with the inner wall of the fixed extrusion die; the outer diameters of the left and right fixed extrusion tables have an unequal diameter structure; the inner rotating extrusion cylinder is axially inclined and its outer wall deviates from the horizontal plane; the outer wall of the corresponding part of the upper and lower outer rotating extrusion cylinders deviates from the horizontal plane at an angle greater than that of the outer wall of the inner rotating extrusion cylinder; the differential rotation extrusion channel is formed between the inner rotating extrusion cylinder and the outer walls of the upper and lower outer rotating extrusion cylinders and the inner wall of the fixed extrusion die; the left unequal diameter channel is formed between the left fixed extrusion table, the outer walls of the upper and lower outer rotating extrusion cylinders, and the inner wall of the fixed extrusion die; the right unequal diameter channel is formed between the right fixed extrusion table, the outer walls of the upper and lower outer rotating extrusion cylinders, and the inner wall of the fixed extrusion die; the left extrusion channel is formed by the left unequal diameter channel and the left annular cavity; the right extrusion channel is formed by the right unequal diameter channel and the right annular cavity; the left extrusion channel, the differential rotation extrusion channel, and the right extrusion channel jointly form the reciprocating rotation differential extrusion channel; the diameters of the left and right ends of the inner rotating extrusion cylinder are smaller than that of the middle part.

[0009] The power device comprises a first outer cylinder motor, a second outer cylinder motor and an inner cylinder motor located in the center of the extrusion telescopic cavity, one end of the transmission shaft of the upper and lower outer rotating extrusion cylinders is extended out of the support and connected with the first outer cylinder motor and the second outer cylinder motor respectively, and the inner rotating extrusion cylinder transmission shaft is extended out of the support and the hollow extrusion telescopic cavity connecting rod and connected with the inner cylinder motor.

[0010] The inner and outer rotating extrusion cylinders are driven by the power device to rotate in opposite directions along the transmission shaft, so that the magnesium alloy pipe in the cavity is subjected to radial shear force and shear deformation.

[0011] The outer wall of the outer rotating extrusion cylinder deviates from the horizontal plane at an angle greater than that of the outer wall of the inner rotating extrusion cylinder, so that the thickness of the differential speed rotating extrusion channel changes and gradually thins.

[0012] The reciprocating rotation differential speed extrusion channel is composed of a left extrusion channel composed of a feeding area, a fixed extrusion punch and a fixed extrusion die, a differential speed rotating extrusion channel composed of an outer rotating extrusion cylinder and an inner rotating extrusion cylinder, a right extrusion channel composed of a fixed extrusion punch and a fixed extrusion die, and a discharging area. The magnesium alloy billet is pushed by the left and right extrusion rings to make reciprocating motion, and the diameter of the magnesium alloy pipe changes continuously and the thickness decreases during the reciprocating motion.

[0013] Further, the fixed extrusion die, the left fixed extrusion punch, the right fixed extrusion punch, the left fixed extrusion cylinder, the right fixed extrusion cylinder, the upper outer rotating extrusion cylinder, the lower outer rotating extrusion cylinder and the inner rotating extrusion cylinder are all made of 4Cr5MoSiV1 hot work die steel; the surface roughness of the fixed extrusion die, the left fixed extrusion punch and the right fixed extrusion punch is Ra0.08~0.16μm, the surface roughness of the inner rotating extrusion cylinder is Ra0.16~0.4μm, and the surface roughness of the upper and lower outer rotating extrusion cylinders is Ra0.4~0.8μm. The difference between the surface roughness of the magnesium alloy pipe and the roughness of the inner rotating extrusion cylinder and the outer rotating extrusion cylinder forms an asymmetric distribution, so that the difference between the friction generated during the extrusion process and the inner and outer walls of the pipe billet is further promoted to make the billet flow at different speeds and shear deformation, shear extrusion deformation occurs, the c-axis of the magnesium alloy pipe grain deflects along the radial direction, the effect of weakening the basal texture is produced, and the mechanical properties of the magnesium alloy are improved.

[0014] A method for preparing fine-grained magnesium alloy pipe by multi-edge reverse roller twisting and extrusion compounding, comprising the following steps:

[0015] S1, magnesium alloy billet pretreatment:

[0016] S1-1, the magnesium alloy blank is processed into a magnesium alloy pipe, and the surface of the magnesium alloy pipe is polished with 600 mesh sandpaper to remove oil stains, and then polished with 800 mesh, 1000 mesh and 1200 mesh sandpaper in sequence until the inner and outer surfaces of the magnesium alloy pipe are smooth;

[0017] S1-2, acetone and anhydrous ethanol are mixed in a cleaning tank at a volume ratio of 3:2, and then stirred uniformly to prepare a cleaning solution;

[0018] S1-3, the magnesium alloy pipe prepared in step S1-1 is immersed in the cleaning solution prepared in step S1-2, the cleaning tank is placed on the ultrasonic cleaner, and the magnesium alloy pipe is ultrasonically cleaned for 60 min, then the magnesium alloy pipe is taken out and cleaned with anhydrous ethanol, and finally dried with a hair dryer;

[0019] S1-4, the surface of the magnesium alloy pipe prepared in step S1-3 is smeared with a graphite oil solution, which is used later;

[0020] S2, magnesium alloy pipe preheating: set the heating temperature of the vacuum atmosphere heating furnace to 350-450℃, after the furnace temperature of the heating furnace reaches the set temperature, put the magnesium alloy pipe into the heating furnace, and keep the temperature for 12-48h;

[0021] S3, lubrication, assembly and preheating of the differential speed rotary extrusion device:

[0022] S3-1, lubrication: apply graphite oil solution to the surface of the outer rotating extrusion cylinder transmission shaft, the contact surface of the hemispherical gear, the inner rotating extrusion cylinder, the outer surface of the upper and lower outer rotating extrusion cylinders, the left and right extrusion expansion cavity connecting rods, and the inner surface of the reciprocating differential speed rotary extrusion channel;

[0023] S3-2, assembly:

[0024] Install left and right fixed supports on the horizontal extruder, assemble the upper and lower outer rotating extrusion cylinders with the fixed extrusion concave die, place the upper and lower outer rotating extrusion cylinders in the fixed extrusion concave die, and gap fit between the outer rotating extrusion cylinder and the inner wall of the fixed extrusion concave die; connect the inner rotating extrusion cylinder with the left and right inner rotating extrusion cylinder transmission shafts through the hemispherical gear, and assemble with the left and right fixed extrusion convex dies, tightly connect the inner rotating extrusion cylinder with the left and right inner rotating extrusion cylinder transmission shafts; assemble the left and right fixed extrusion convex dies and the fixed extrusion concave die between the left and right fixed supports, and tightly connect them; connect the installed upper and lower outer rotating extrusion cylinder transmission shafts and the inner rotating extrusion cylinder transmission shafts with the power device; connect the left and right extrusion compression rings with the left and right extrusion expansion cavities respectively, and match the left and right extrusion compression rings with the left and right extrusion channels;

[0025] S3-3, preheating: control the temperature of the heating jacket to be 300~500℃, and keep the temperature for 2~4 hours after reaching the set temperature, and wait for the next step;

[0026] S4, rotary differential speed extrusion forming: the fixed extrusion concave die, the left and right fixed extrusion convex dies, the upper and lower outer rotary extrusion cylinders and the inner extrusion cylinder form a reciprocating rotary differential speed extrusion channel; the reciprocating rotary differential speed extrusion channel includes three regions of a left extrusion channel, a rotary differential speed extrusion channel and a right extrusion channel;

[0027] S4-1, the magnesium alloy pipe is placed at the left extrusion channel inlet, then the left and right extrusion rings are fixed, the power device is started, and the upper and lower outer rotary extrusion cylinders and the inner rotary extrusion cylinder rotate in the opposite directions under the driving of the transmission shaft; the left pressure motor is started, and the magnesium alloy pipe passes through the left extrusion channel, the differential speed rotary extrusion channel and the right extrusion channel in turn under the action of the left extrusion ring, the channel walls on both sides of the differential speed rotary extrusion channel have different angles with the horizontal direction, the extrusion channel is gradually thinned, the diameters of both sides of the inner rotary extrusion cylinder are smaller than that of the middle part, and the diameter of the magnesium alloy pipe increases first and then decreases after entering the extrusion channel to restore the original pipe diameter; in the rotary differential speed extrusion channel part, the magnesium alloy pipe is rotated and extruded under the driving of the friction force, because the friction coefficients of the outer walls of the upper and lower outer rotary extrusion cylinders and the inner rotary extrusion cylinder are different, therefore, when the magnesium alloy pipe passes through the differential speed rotary extrusion channel, the inner and outer walls receive opposite and different radial friction forces, and shear deformation occurs; when the magnesium alloy pipe completes the left extrusion, the magnesium alloy pipe reaches the right extrusion channel, the left pressure motor is turned off, the right pressure motor is turned on, and the magnesium alloy pipe moves to the left and passes through the differential speed rotary extrusion channel again under the action of the right extrusion ring, and the reciprocation is repeated, after several reciprocation cycles, the right pressure motor and the right extrusion ring 29 are removed, and the fine-grained magnesium alloy pipe is removed from the material withdrawal port;

[0028] S4-2, the magnesium alloy pipe prepared in step S4-1 is taken out, the surface thereof is polished with sandpaper, then the magnesium alloy pipe is cleaned with the cleaning solution prepared in step S1-2, finally, the magnesium alloy pipe is cleaned with anhydrous ethanol again, and is dried with a hair dryer, so that the fine-grained and weak-textured magnesium alloy pipe capable of being directly used is prepared.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] 1. The differential speed rotary extrusion channel makes the C-axis of the magnesium alloy deflect, effectively weakens the basal plane texture of the magnesium alloy, refines the grains and improves the mechanical properties of the magnesium alloy;

[0031] 2. The thickness of the extrusion channel has a tendency to decrease, after entering the inlet, the pipe is subjected to the pressure between the gradually thinned extrusion channel wall, while under the action of the inner and outer rotating extrusion cylinder, the pipe is subjected to the shear force along the radial direction, the size of the shear force can be controlled by adjusting the friction coefficient of the outer wall of the extrusion cylinder. The weakening effect of magnesium alloy rod grain texture is more significant. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The reciprocating differential speed extrusion processing state diagram of the fine grain weak texture magnesium alloy pipe of the present application;

[0033] Figure 2 It is a cross section schematic diagram of the extrusion channel;

[0034] Figure 3 It is a profile schematic diagram of the fixed extrusion die and the corresponding part of the outer rotating extrusion cylinder;

[0035] Figure 4 It is a top view of the inner rotating extrusion cylinder and the transmission shaft connection;

[0036] Figure 5 It is a cross section view of the inner rotating extrusion cylinder and the transmission shaft connection;

[0037] As shown in the figure, the list of reference signs is as follows:

[0038] 1 - indicator light, 2 - heating sleeve switch, 3 - power switch, 4 - left extrusion expansion ring switch, 5 - left extrusion expansion ring switch, 6 - horizontal extruder base, 7 - display screen, 8 - horizontal extruder, 9 - left connecting wire, 10 - left pressure motor base, 11 - left pressure motor, 12 - left pressure motor transmission belt, 13 - left inner rotating extrusion cylinder transmission shaft, 14 - left extrusion expansion cavity, 15 - left extrusion expansion cavity connecting rod, 16 - left fixed extrusion punch, 17 - left extrusion pressure ring, 18 - left extrusion channel, 19 - left fixed support, 20 - heating sleeve, 21 - upper outer rotating extrusion cylinder transmission shaft, 22 - left fixed extrusion cylinder, 23 - upper outer rotating extrusion cylinder, 24 - fixed extrusion die, 25 - inner rotating extrusion cylinder, 26 - right fixed extrusion cylinder, 27 - right extrusion channel, 28 - right fixed support, 29 - right extrusion pressure ring, 30 - right extrusion expansion cavity connecting rod, 31 - first outer cylinder motor, 32 - right extrusion expansion cavity, 33 - right inner rotating extrusion cylinder transmission shaft, 34 - right fixed extrusion punch, 35 - hemispherical gear, 36 - magnesium alloy pipe, 37 - lower outer rotating extrusion cylinder transmission shaft, 38 - right pressure motor, 39 - lower outer rotating extrusion cylinder, 40 - left connecting wire, 41 - motor connecting wire, 42 - motor controller, 43 - display, 44 - indicator light, 45 - motor power switch, 46 - right pressure motor transmission belt. DETAILED DESCRIPTION

[0039] The application will be further described in detail below with reference to the accompanying drawings and examples.

[0040] The device for preparing fine-grain magnesium alloy pipe by multi-edge reverse roller twisting and extrusion composite includes a power device, a reciprocating extrusion device, a differential speed rotating extrusion device, a horizontal extruder 8, an extrusion die and a support;

[0041] The reciprocating extrusion device includes a left pressure motor 11 and a right pressure motor 38 respectively arranged on the left and right sides of the horizontal extruder 8, the left pressure motor 11 is connected with a left extrusion telescopic cavity 14 through a left pressure motor transmission belt 12, the right pressure motor 38 is connected with a right extrusion telescopic cavity 32 through a right pressure motor transmission belt 46, the left and right extrusion telescopic cavities are respectively installed with left and right extrusion telescopic cavity connecting rods 15 and 30 arranged oppositely, and the left and right extrusion telescopic cavity connecting rods 15 and 30 are respectively connected with left and right extrusion pressure rings 17 and 29;

[0042] The support includes a left fixed support 19 and a right fixed support 28 arranged above the horizontal extruder 8, and the extrusion die includes a left fixed extrusion convex die 16, a fixed extrusion concave die 24 and a right fixed extrusion convex die 34 fixedly arranged between the left and right fixed supports; the fixed extrusion concave die 24 is internally provided with a cavity, the left and right fixed extrusion convex dies 16 and 34 are respectively fixedly installed on the left and right sides of the cavity of the fixed extrusion concave die 24; annular cavities are respectively formed between the outer periphery of the left fixed extrusion convex die 16 and the inner wall of the fixed extrusion concave die 24 and between the outer periphery of the right fixed extrusion convex die 34 and the inner wall of the fixed extrusion concave die 24, annular openings are respectively arranged on the left and right fixed supports and correspond to the annular cavities, the left and right extrusion pressure rings 17 and 29 can respectively extend into the two annular cavities through the annular openings, and a heating sleeve 20 is sleeved on the outer periphery of the fixed extrusion concave die 24;

[0043] The differential rotation extrusion device comprises upper outer rotation extrusion cylinders 23, lower outer rotation extrusion cylinders 39, inner rotation extrusion cylinders 25, upper and lower outer rotation extrusion cylinder transmission shafts 21 and 37, left inner rotation extrusion cylinder transmission shafts 13 and right inner rotation extrusion cylinder transmission shafts 33; the upper and lower outer rotation extrusion cylinders are identical in structure, have unequal diameters in external contour, are arranged in upper and lower positions and have opposite head-to-tail directions during installation; each of the upper and lower outer rotation extrusion cylinders is supported by one outer rotation extrusion cylinder transmission shaft between left and right fixed supports and in a cavity between left and right fixed extrusion punches, and a space is left between the upper and lower outer rotation extrusion cylinders; the two outer rotation extrusion cylinder transmission shafts are respectively located above and below the left and right fixed extrusion punches, the right side of the left fixed extrusion punch 16 extends out of the left fixed extrusion cylinder 22 and into the space between the left sides of the upper and lower outer rotation extrusion cylinders, and the left side of the right fixed extrusion punch 34 extends out of the right fixed extrusion cylinder 26 and into the space between the right sides of the upper and lower outer rotation extrusion cylinders; the left fixed extrusion punch 16 and the left fixed extrusion cylinder 22 are provided with shaft cavities and rotatably installed with the left inner rotation extrusion cylinder transmission shaft 13, and the right fixed extrusion punch 34 and the right fixed extrusion cylinder 26 are provided with shaft cavities and rotatably installed with the right inner rotation extrusion cylinder transmission shaft 33; the inner rotation extrusion cylinder 25 is located in the middle of the space between the upper and lower outer rotation extrusion cylinders, the left and right ends of the inner rotation extrusion cylinder 25 extend into the shaft cavities of the left and right fixed extrusion cylinders and are supported by bearings arranged in the left and right fixed extrusion cylinders, and the left and right ends of the inner rotation extrusion cylinder 25 are connected with half ball gears 35 after passing through the bearings; the front ends of the left and right inner rotation extrusion cylinder transmission shafts are respectively installed with half ball gears 35 engaged with the left and right ends of the inner rotation extrusion cylinder 25; the upper and lower outer rotation extrusion cylinders and the inner rotation extrusion cylinder 25 are gap-fitted with the inner wall of the fixed extrusion punch 24; the outer diameters of the left and right fixed extrusion cylinders are of unequal diameters in structure, the inner rotation extrusion cylinder 25 is axially inclined and its outer wall deviates from the horizontal plane, the outer walls of the corresponding parts of the upper and lower outer rotation extrusion cylinders and the inner rotation extrusion cylinder 25 deviate from the horizontal plane at an angle greater than that of the outer wall of the inner rotation extrusion cylinder 25; the inner rotation extrusion cylinder 25, the outer walls of the upper and lower outer rotation extrusion cylinders 23 and 39 and the inner wall of the fixed extrusion punch 24 form a differential rotation extrusion channel, the outer wall of the left fixed extrusion cylinder 22 and the outer walls of the upper and lower outer rotation extrusion cylinders and the inner wall of the fixed extrusion punch 24 form a left unequal diameter channel connecting the left annular cavity and the differential rotation extrusion channel, and the outer wall of the right fixed extrusion cylinder 26 and the outer walls of the upper and lower outer rotation extrusion cylinders and the inner wall of the fixed extrusion punch 24 form a right unequal diameter channel connecting the right annular cavity and the differential rotation extrusion channel; the left unequal diameter channel and the left annular cavity form a left extrusion channel 18, and the right unequal diameter channel and the right annular cavity form a right extrusion channel 27; the left extrusion channel 18, the differential rotation extrusion channel and the right extrusion channel 27 jointly form a reciprocating rotation differential extrusion channel.The inner rotating extrusion cylinder 25 has a smaller diameter than the middle part, and the upper and lower outer rotating extrusion cylinders 23 and 39 have different friction coefficients with the outer wall of the inner rotating extrusion cylinder 25.

[0044] The power device comprises a first outer cylinder motor 31, a second outer cylinder motor, and an inner cylinder motor located in the center of the extrusion telescopic cavity. One end of the transmission shaft of the upper and lower outer rotating extrusion cylinders extends out of the support and is connected with the first outer cylinder motor 31 and the second outer cylinder motor, respectively. The transmission shaft of the inner rotating extrusion cylinder extends out of the support and the hollow extrusion telescopic cavity connecting rod and is connected with the inner cylinder motor.

[0045] The left and right extrusion telescopic cavities are connected with the left and right telescopic compression rings to realize the reciprocating movement of the pipe in the deformation cavity.

[0046] The inner rotating extrusion cylinder 25 is rotated by the inner rotating extrusion cylinder transmission shaft, and the upper and lower outer rotating extrusion cylinders 23 and 39 are rotated in opposite directions by the transmission device along the upper and lower outer rotating extrusion cylinder transmission shafts 21 and 37, so that the magnesium alloy pipe 36 in the cavity is subjected to radial shear force and shear deformation.

[0047] The outer wall of the upper and lower outer rotating extrusion cylinders 23 and 39 deviates from the horizontal plane at an angle greater than that of the outer wall of the inner rotating extrusion cylinder 25, so that the thickness of the differential rotating extrusion channel changes and gradually thins.

[0048] The upper and lower outer rotating extrusion cylinders 23 and 39 are arranged in the fixed extrusion concave die 24, and the upper and lower outer rotating extrusion cylinders 23 and 39 are gap-jointed with the fixed extrusion concave die 24. The left and right inner rotating extrusion cylinder transmission shafts 13 and 33 are arranged in the fixed extrusion convex die 34, and the left and right inner rotating extrusion cylinder transmission shafts 13 and 33 are respectively gap-jointed with the left and right fixed extrusion convex dies 13 and 34.

[0049] The reciprocating rotating differential extrusion channel comprises, from left to right, a feeding area, a left extrusion channel 18 composed of the left fixed extrusion convex die 16 and the fixed extrusion concave die 24, a differential rotating extrusion channel composed of the upper and lower outer rotating extrusion cylinders 23 and 39 and the inner rotating extrusion cylinder 25, a right extrusion channel 27 composed of the right fixed extrusion convex die 34 and the fixed extrusion concave die 24, and a discharging area. The magnesium alloy pipe 36 reciprocates under the push of the left and right extrusion compression rings 17 and 29. The diameter of the magnesium alloy pipe 36 changes continuously and the thickness decreases during the reciprocating movement.

[0050] Further, the outer diameter of the upper outer rotating extrusion cylinder 23 is divided into three parts from left to right, which are the expanding diameter section, the reducing diameter section and the horizontal section, and the outer diameter of the lower outer rotating extrusion cylinder 39 is divided into three parts from right to left, which are the expanding diameter section, the reducing diameter section and the horizontal section, and correspond to the horizontal section, the reducing diameter section and the expanding diameter section of the upper outer rotating extrusion cylinder 23 respectively; the bottom of the left fixed extrusion frustum 22 is consistent with the horizontal section of the lower outer rotating extrusion cylinder 39, and the top is consistent with the expanding diameter section of the upper outer rotating extrusion cylinder 23; the bottom of the right fixed extrusion frustum 26 is consistent with the expanding diameter section of the lower outer rotating extrusion cylinder 39, and the top is consistent with the horizontal section of the upper outer rotating extrusion cylinder 23.

[0051] Further, the fixed extrusion concave die 24, the left fixed extrusion convex die 16, the right fixed extrusion convex die 34, the left fixed extrusion frustum 22, the right fixed extrusion frustum 26, the upper outer rotating extrusion cylinder 23, the lower outer rotating extrusion cylinder 39 and the inner rotating extrusion cylinder 25 are all made of 4Cr5MoSiV1 hot work die steel; the surface roughness of the fixed extrusion concave die 24, the left fixed extrusion convex die 16 and the right fixed extrusion convex die 34 is Ra0.08~0.16μm, the surface roughness of the inner rotating extrusion cylinder 25 is Ra0.16~0.4μm, and the surface roughness of the upper and lower outer rotating extrusion cylinders is Ra0.4~0.8μm.

[0052] The difference between the surface roughness of the magnesium alloy pipe 36 and the surface roughness of the inner rotating extrusion cylinder 25, the upper and lower outer rotating extrusion cylinders 23 and 39 forms an asymmetric distribution, so that the difference between the friction generated in the extrusion process and the inner and outer walls of the pipe blank is further promoted to make the magnesium alloy pipe 36 flow at different speeds and generate shear deformation, so as to weaken the basal plane texture.

[0053] In the specific embodiment, before the reciprocating torsion extrusion deformation is performed to prepare the fine-grained and weak-textured magnesium alloy, the materials and chemical reagents required in the preparation process are first selected: magnesium alloy bar, acetone, anhydrous ethanol, high-temperature graphite powder, machine oil and sandpaper, and the preparation amounts are as follows: millimeter, milliliter, gram and pascal are used as the measurement units.

[0054] Magnesium alloy pipe: AZ31, φ10mm×100mm, thickness 3mm;

[0055] Acetone: C3H6O, 1000ml;

[0056] Anhydrous ethanol: CH3CH2OH, 2000ml;

[0057] High-temperature graphite powder: C, 600g;

[0058] Machine oil: SN 0W-40, 1500ml; sandpaper: SiC, 800 mesh, 3 pieces; 2400 mesh, 4 pieces;

[0059] A method for preparing fine-grained magnesium alloy pipe by multi-edge reverse roller twist extrusion composite, comprising the following steps:

[0060] S1, magnesium alloy blank pretreatment:

[0061] S1-1, the magnesium alloy blank is processed into a magnesium alloy pipe 36, and the surface of the magnesium alloy pipe 36 is polished with 600 mesh sandpaper to remove oil stains, and then polished with 800 mesh, 1000 mesh and 1200 mesh sandpaper in turn until the inner and outer surfaces of the magnesium alloy pipe are smooth;

[0062] S1-2, after mixing acetone and anhydrous ethanol in a cleaning tank at a volume ratio of 3:2, stirring uniformly to prepare a cleaning solution;

[0063] S1-3, the magnesium alloy pipe 36 prepared in step S1-1 is immersed in the cleaning solution prepared in step S1-2, the cleaning tank is placed on the ultrasonic cleaner for ultrasonic cleaning of the magnesium alloy pipe for 60 min, then the magnesium alloy pipe 36 is taken out and cleaned with anhydrous ethanol, and finally dried with a hair dryer;

[0064] S1-4, the surface of the magnesium alloy pipe 36 prepared in step S1-3 is smeared with a graphite oil solution, which is used later;

[0065] S2, magnesium alloy pipe preheating: set the heating temperature of the vacuum atmosphere heating furnace to 350~450℃, after the furnace temperature of the heating furnace reaches the set temperature, put the magnesium alloy pipe 36 into the heating furnace, and keep the temperature for 12~48h;

[0066] S3, lubrication, assembly and preheating of the differential speed rotating extrusion device:

[0067] S3-1, lubrication: the surfaces of the upper and lower outer rotating extrusion cylinders transmission shafts 21, 37, the contact parts of the hemispherical gears 35, the inner rotating extrusion cylinder 25, the upper outer rotating extrusion cylinder 23, the lower outer rotating extrusion cylinder 39, the left and right extrusion telescopic cavity connecting rods 15, 30, and the inner surface of the differential speed rotating extrusion channel are smeared with a graphite oil solution;

[0068] S3-2, assembly:

[0069] The horizontal extruding machine 8 is installed with left and right fixed supports 19, 28, and the upper and lower outer rotating extruding cylinders 23, 39 are assembled with the fixed extruding concave die 24. The upper and lower outer rotating extruding cylinders 23, 39 are placed in the fixed extruding concave die 24, and the outer rotating extruding cylinder is gap-fitted with the inner wall of the fixed extruding concave die 24. The inner rotating extruding cylinder 25 is connected with the left and right inner rotating extruding cylinder transmission shafts 13, 33 through the half-ball gear 35, and then assembled with the left and right fixed extruding convex dies 16, 34. The inner rotating extruding cylinder 25 and the left and right inner rotating extruding cylinder transmission shafts 13, 33 are tightly connected in the left and right fixed extruding convex dies 16, 34. The left and right fixed extruding convex dies 16, 34 and the fixed extruding concave die 24 are assembled between the left fixed support 19 and the right fixed support 28, and are tightly connected. The assembled upper and lower outer rotating extruding cylinder transmission shafts 21 are connected with the power device. The left and right extruding pressure rings 17, 29 are connected with the left and right extruding telescopic cavities 14, 32 respectively, and the left and right extruding pressure rings 17, 29 are matched with the left and right extruding channels 18, 27.

[0070] S3-3, preheating: control the temperature of the heating jacket 20 to be 300-500℃, and keep the temperature for 2-4 hours after reaching the set temperature, and wait for use in the next step;

[0071] S4, rotating differential speed extrusion forming: the fixed extruding concave die 24, the left and right fixed extruding convex dies 16, 34, the upper and lower outer rotating extruding cylinders 23, 39 and the inner rotating extruding cylinder 25 form a reciprocating rotating differential speed extruding channel. The reciprocating rotating differential speed extruding channel includes three regions of the left extruding channel 18, the rotating differential speed extruding channel and the right extruding channel 27.

[0072] S4-1, the magnesium alloy pipe 36 is placed at the left extrusion channel 18 inlet, then the left and right extrusion rings 17, 29 are fixed, the power device is started, and the upper and lower outer rotating extrusion cylinders 23, 39 and the inner rotating extrusion cylinder 25 rotate in the opposite direction under the driving of the transmission shaft; the left pressure motor 11 is started, the magnesium alloy pipe 36 passes through the left extrusion channel 18, the differential speed rotating extrusion channel and the right extrusion channel 27 in turn under the action of the left extrusion ring 17, the channel walls on both sides of the differential speed rotating extrusion channel are different from the horizontal direction, the extrusion channel is gradually thinned, the diameters of both sides of the inner rotating extrusion cylinder 25 are smaller than that of the middle part, and the diameter of the magnesium alloy pipe 36 becomes larger and then smaller after entering the extrusion channel to restore the original pipe diameter; in the rotating differential speed extrusion channel part, the magnesium alloy pipe 36 starts to rotate and extrude under the driving of the friction force, because the friction coefficients of the outer walls of the upper and lower outer rotating extrusion cylinders 23, 39 and the inner rotating extrusion cylinder 25 are different, therefore, when the magnesium alloy pipe 36 passes through the differential speed rotating extrusion channel, the inner and outer walls are subjected to opposite and different radial friction forces, and shear deformation occurs; when the magnesium alloy pipe 36 completes the left extrusion, the magnesium alloy pipe reaches the right extrusion channel 27, the left pressure motor 11 is turned off, the right pressure motor 38 is turned on, and the magnesium alloy pipe 36 moves to the left and passes through the differential speed rotating extrusion channel again under the action of the right extrusion ring 29, so as to reciprocate, after several reciprocation cycles, the right pressure motor 38 and the right extrusion ring 29 are removed, and the fine-grained magnesium alloy pipe is removed from the material outlet;

[0073] S4-2, the magnesium alloy pipe 36 prepared in step S4-1 is taken out, the surface thereof is polished with sandpaper, then the magnesium alloy pipe is cleaned with the cleaning solution prepared in step S1-2, finally, the magnesium alloy pipe is cleaned with anhydrous ethanol for the second time, and is dried with a hair dryer, so that the fine-grained and weak-textured magnesium alloy pipe which can be directly used is prepared.

[0074] Further details are as follows: Figure 2In the embodiment, the thickness of the top inlet of the left unequal-diameter channel is t1; the thickness of the top inlet of the differential-rotation extrusion channel is t2, the thickness of the middle section of the top of the differential-rotation extrusion channel is t3, and the thickness of the outlet of the differential-rotation extrusion channel is t4; the thickness of the bottom inlet of the left unequal-diameter channel is t5; the thickness of the bottom inlet of the differential-rotation extrusion channel is t6, the thickness of the middle section of the bottom of the differential-rotation extrusion channel is t7, and the thickness of the outlet of the differential-rotation extrusion channel is t8; the thicknesses have the following relationships: t1>t2>t3>t4, t5>t6>t7>t8; the thickness of the region between the top and the bottom of the inlet of the left unequal-diameter channel is between t1 and t5, the thickness of the region between the top and the bottom of the inlet of the differential-rotation extrusion channel is between t2 and t6, the thickness of the region between the top and the bottom of the middle section of the differential-rotation extrusion channel is between t3 and t7, and the thickness of the region between the top and the bottom of the outlet of the differential-rotation extrusion channel is between t4 and t8; the thicknesses between the inlet and the outlet of the left unequal-diameter channel change linearly from t1 and t5 to t2 and t4; the thicknesses from the inlet to the middle section of the differential-rotation extrusion channel change linearly from t2 and t6 to t3 and t7, and the thicknesses from the middle section to the outlet of the differential-rotation extrusion channel change linearly from t3 and t7 to t4 and t8.

[0075] The angle between the outer wall of the upper outer rotating extrusion cylinder 23 at the top inlet of the left unequal-diameter channel and the horizontal plane is θ1, and the angle between the outer wall of the left fixed extrusion circular platform 22 and the horizontal plane is θ2; the angle between the outer wall of the upper outer rotating extrusion cylinder 23 at the top inlet of the differential-rotation extrusion channel and the horizontal plane is θ3, the angle between the outer wall of the inner rotating extrusion cylinder 25 at the top inlet of the differential-rotation extrusion channel and the horizontal plane is θ4, the angle between the outer wall of the upper outer rotating extrusion cylinder 23 at the middle section of the top of the differential-rotation extrusion channel and the horizontal plane is θ5, the angle between the outer wall of the inner rotating extrusion cylinder 25 at the middle section of the top of the differential-rotation extrusion channel and the horizontal plane is θ6, the angle between the outer wall of the left fixed extrusion circular platform 22 at the bottom of the left unequal-diameter channel and the horizontal plane is θ7, the angle between the outer wall of the lower outer rotating extrusion cylinder 39 at the bottom of the left unequal-diameter channel and the horizontal plane is θ8, the angle between the outer wall of the lower outer rotating extrusion cylinder 39 at the bottom inlet of the differential-rotation extrusion channel and the horizontal plane is θ9, the angle between the outer wall of the inner rotating extrusion cylinder 25 at the bottom inlet of the differential-rotation extrusion channel and the horizontal plane is θ 10 , the angle between the outer wall of the lower outer rotating extrusion cylinder 39 at the middle section of the bottom of the differential-rotation extrusion channel and the horizontal plane is θ 11 , and the angle between the outer wall of the inner rotating extrusion cylinder 25 at the middle section of the bottom of the differential-rotation extrusion channel and the horizontal plane is θ 12 The above angles have the following relationships: θ1>θ2, θ4>θ3, θ5>θ6, θ8>θ7, θ9>θ 10 , θ 11 >θ 12 . Specific embodiments

[0076] A method for preparing fine-grained magnesium alloy pipe by multi-edge reverse roller twisting and extrusion composite, which comprises the following steps: (1) firmly installing power device, reciprocating extrusion device, differential speed rotating extrusion device, horizontal extruder, semi-spherical transmission device (semi-spherical gear), base and support, and correctly connecting positions in sequence and operating in sequence;

[0077] (2) polishing the outer surface of AZ31 magnesium alloy pipe blank with 600-mesh sandpaper, removing oil stains, and then polishing with 1000-mesh, 1200-mesh and 2500-mesh sandpaper in sequence to ensure that the surface is clean and smooth; placing the polished magnesium alloy block material in a mixed solution of acetone and anhydrous ethanol with a volume ratio of 3:2 for ultrasonic cleaning for 30 min, and then cleaning with alcohol and drying with a hair dryer;

[0078] (3) preheating the magnesium alloy pipe blank in a vacuum atmosphere heating furnace, with a preset temperature of 400 DEG C, and continuing to place the magnesium alloy pipe blank in the heating furnace for 3 h when the predetermined temperature is reached;

[0079] (4) heating the pipe, with a preset heating temperature of 400 DEG C, and continuing to heat for 3 h after the preset temperature is reached; (5) lubricating the magnesium alloy pipe with high-temperature graphite oil solution on the inner and outer surfaces, with the diameter of the pipe being consistent with the diameter of the feeding port. The pipe is placed in the feeding port in a regular manner.

[0080] (6) the surface roughness of the fixed extrusion concave die 24, the left and right fixed extrusion convex dies 16 and 34 is Ra 0.08-0.16 μm, the surface roughness of the inner rotating extrusion cylinder 25 is Ra 0.16-0.4 μm, and the surface roughness of the upper and lower outer rotating extrusion cylinders 23 and 39 is Ra 0.4-0.8 μm. The materials of the fixed extrusion concave die, the fixed extrusion convex die, the outer rotating extrusion cylinder and the inner rotating extrusion cylinder are all 4Cr5MoSiV1 hot work die steel.

[0081] (7) starting the motor, setting the pressure to 400 MPa, and simultaneously starting the left and right presses and the motors, the motors driving the inner and outer rotating extrusion cylinders to rotate, the magnesium alloy pipe passing through the deformation channel under the action of compression pressure ring, and sequentially passing through the left extrusion channel, the differential speed rotating extrusion channel and the right extrusion channel, the inner and outer walls of the pipe in the differential speed rotating extrusion channel being subjected to opposite direction shearing force, forcing the c-axis of the magnesium alloy blank to deflect and refine the grains, further intensifying the plastic deformation of the magnesium alloy blank, weakening the texture and refining the grains, reciprocating extrusion multiple times, and finally passing through the discharge area, under the combined action of the fixed extrusion convex die, the fixed extrusion concave die and the extrusion cylinder, realizing the processing of the magnesium alloy pipe.

[0082] (8) Take out the magnesium alloy pipe, polish its surface using sandpaper, then place it in a mixed liquid with a volume ratio of acetone and anhydrous ethanol of 3:2 for ultrasonic cleaning, finally clean it with alcohol and dry it with a cold air blower. Conclusion: By the method for preparing fine-grained magnesium alloy pipe material through multi-edge reverse roller twisting and extrusion compounding of the application, the average grain size of the magnesium alloy pipe blank is greatly reduced compared with conventional magnesium alloy, the basal plane texture and the initial magnesium alloy pipe are effectively weakened, and the mechanical properties of the magnesium alloy are effectively improved. The materials and chemical reagents used are: AZ31 magnesium alloy block blank, with a diameter d=50mm; sandpaper: SiC, 600 mesh, 2 pieces; 1000 mesh, 2 pieces; 1200 mesh, 2 pieces; 2500 mesh, 2 pieces; high-temperature graphite oil solution: C, 500g; anhydrous ethanol: CH3CH2OH, 1200ml; acetone: C3H6O, 800ml.

[0083] The principle of obtaining fine-grained weak-textured magnesium alloy by the above steps of the application is described in detail below with reference to the accompanying drawings:1) Figure 2 As shown, the feeding speed of the feeding port is v, the angular velocity of the driving shaft of the outer rotating extrusion cylinder is ω 1， The rotating angular velocity of the driving shaft of the inner rotating extrusion cylinder is ω2, the rotating angular velocity of the inner rotating extrusion cylinder is ω3, ω1≠ω3, the included angle between the outer wall of the extrusion channel and the horizontal direction is θ1>θ2, θ4>θ3, θ5>θ6, θ8>θ7, θ9>θ 10 , θ 11 >θ 12 . The channel thickness t1>t2>t3>t4, t5>t6>t7>t8.

[0084] 2) differential speed rotating extrusion process: open the left extrusion pressure ring, and extrude the magnesium alloy pipe blank pre-placed in the cavity of the extrusion die. The magnesium alloy pipe blank enters the irregular shear extrusion channel from the left extrusion channel under the action of the left extrusion pressure ring. The diameter of the magnesium alloy pipe blank gradually increases and then gradually decreases to the initial size with the shape of the inner die, and the wall thickness changes continuously. Under the action of the shear force generated by the differential rotation of the intermediate inner rotating extrusion cylinder and the upper and lower outer rotating extrusion cylinder in opposite directions, the flow rate of the blank is different, multiple shear deformations occur, the grain structure is refined, and the c-axis of the grain is inclined to weaken the basal plane texture; when the left extrusion pressure ring completely enters the left extrusion channel of the extrusion die, the left extrusion telescopic pressure ring stops advancing; open the right extrusion telescopic pressure ring, and extrude the magnesium alloy pipe blank placed in the cavity of the extrusion die. The magnesium alloy pipe blank enters the irregular differential speed rotating extrusion channel from the right extrusion channel under the action of the right extrusion pressure ring. The diameter of the magnesium alloy pipe blank gradually increases and then gradually decreases to the initial state with the shape of the inner die, and the wall thickness changes continuously. Under the differential speed reverse extrusion action of the inner and outer extrusion cylinders, multiple shear deformations occur again, the grain structure is continuously refined, and the basal plane texture is continuously weakened. The cycle is repeated to obtain high-performance ultra-fine-grained magnesium alloy pipe.

[0085] Through the above principles, the magnesium alloy pipe blank finally undergoes a large amount of shear extrusion deformation to obtain a weak basal plane texture high-performance magnesium alloy pipe.

[0086] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements easily thought of by those skilled in the art within the technical scope disclosed by the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. An apparatus for preparing fine-grained magnesium alloy tubing using a multi-sided reverse roll-to-extrusion composite process, characterized in that, Includes power unit, reciprocating extrusion unit, differential rotary extrusion unit, horizontal extrusion press (8), extrusion die and support; The reciprocating extrusion device includes a left pressure motor (11) and a right pressure motor (38) located on the left and right sides of the horizontal extruder (8). The left pressure motor (11) is connected to the left extrusion telescopic cavity (14) via the left pressure motor conveyor belt (12), and the right pressure motor (38) is connected to the right extrusion telescopic cavity (32) via the right pressure motor conveyor belt (46). The left and right extrusion telescopic cavities are respectively equipped with a left extrusion telescopic cavity connecting rod (15) and a right extrusion telescopic cavity connecting rod (30) arranged in opposite directions. The left extrusion telescopic cavity connecting rod (15) and the right extrusion telescopic cavity connecting rod (30) are respectively connected to a left extrusion pressure ring (17) and a right extrusion pressure ring (29). The support includes a left fixed support (19) and a right fixed support (28) located above the horizontal extruder (8). The extrusion die includes a left fixed extrusion punch (16), a fixed extrusion die (24), and a right fixed extrusion punch (34) fixedly located between the left and right fixed supports. The fixed extrusion die (24) has a cavity inside. The left fixed extrusion punch (16) and the right fixed extrusion punch (34) are respectively fixedly installed on the left and right sides of the cavity of the fixed extrusion die (24). Annular cavities are formed between the outer periphery of the left fixed extrusion punch (16) and the inner wall of the fixed extrusion die (24), and between the outer periphery of the right fixed extrusion punch (34) and the inner wall of the fixed extrusion die (24). Annular openings are opened on the left and right fixed supports at positions corresponding to the annular cavities. The left extrusion ring (17) and the right extrusion ring (29) can extend into the two annular cavities through the annular openings respectively. A heating sleeve (20) is fitted around the outer periphery of the fixed extrusion die (24). The differential rotary extrusion device includes an upper outer rotary extrusion cylinder (23), a lower outer rotary extrusion cylinder (39), an inner rotary extrusion cylinder (25), upper and lower outer rotary extrusion cylinder drive shafts, a left inner rotary extrusion cylinder drive shaft (13), and a right inner rotary extrusion cylinder drive shaft (33). The upper and lower outer rotary extrusion cylinders have the same structure, and their outer contours are of unequal diameter. They are arranged vertically and horizontally with opposite orientations when installed. The upper and lower outer rotating extrusion cylinders are supported by upper and lower outer rotating extrusion cylinder drive shafts between the left and right fixed supports and located in the cavity between the left and right fixed extrusion punches, with a gap between the upper and lower outer rotating extrusion cylinders; the two outer rotating extrusion cylinder drive shafts are located above and below the left and right fixed extrusion punches, respectively; the left fixed extrusion punch (16) extends to the right from the right side to extend out the left fixed extrusion platform (22) and into the gap between the left sides of the upper and lower outer rotating extrusion cylinders, and the right fixed extrusion punch (34) extends to the left from the left side to extend out the right fixed extrusion platform (26) and into the gap between the right sides of the upper and lower outer rotating extrusion cylinders, with openings in the left fixed extrusion punch (16) and the left fixed extrusion platform (22). A left inner rotating extrusion cylinder drive shaft (13) is rotatably mounted in the shaft cavity. A right fixed extrusion punch (34) and a right fixed extrusion platform (26) have shaft cavities in which a right inner rotating extrusion cylinder drive shaft (33) is rotatably mounted. The inner rotating extrusion cylinder (25) is located in the middle of the interval between the upper and lower outer rotating extrusion cylinders. The left and right ends of the inner rotating extrusion cylinder (25) extend into the shaft cavities of the left and right fixed extrusion platforms respectively and are supported by bearings provided in the left and right fixed extrusion platforms. The left and right ends of the inner rotating extrusion cylinder (25) are connected to hemispherical gears (35) after passing through the bearings. The front ends of the left and right inner rotating extrusion cylinder drive shafts are respectively equipped with gears that mesh with the left and right ends of the inner rotating extrusion cylinder (25). The hemispherical gear (35); the outer contours of the upper and lower outer rotating extrusion cylinders and the inner rotating extrusion cylinder (25) are clearance-fitted with the inner wall of the fixed extrusion die (24); the outer diameters of the left and right fixed extrusion pedestals are of unequal diameter, the inner rotating extrusion cylinder (25) is axially inclined and its outer wall is deviated from the horizontal plane, the outer wall of the corresponding part of the upper and lower outer rotating extrusion cylinders and the inner rotating extrusion cylinder (25) deviates from the horizontal plane at an angle greater than the angle of the outer wall of the inner rotating extrusion cylinder (25) deviating from the horizontal plane; the inner rotating extrusion cylinder (25) and the outer walls of the upper and lower outer rotating extrusion cylinders and the inner wall of the fixed extrusion die (24) form a differential rotation extrusion channel, the outer wall of the left fixed extrusion pedestal (22) and the upper and lower outer rotating extrusion cylinders are clearance-fitted with the inner wall of the fixed extrusion die (24); The outer wall of the pressing cylinder and the inner wall of the fixed extrusion die (24) form a left unequal diameter channel connecting the left annular cavity and the differential rotation extrusion channel. The outer wall of the right fixed extrusion frustum (26) and the outer walls of the upper and lower outer rotating extrusion cylinders and the inner wall of the fixed extrusion die (24) form a right unequal diameter channel connecting the right annular cavity and the differential rotation extrusion channel. The left unequal diameter channel and the left annular cavity form a left extrusion channel (18), and the right unequal diameter channel and the right annular cavity form a right extrusion channel (27). The left extrusion channel (18), the differential rotation extrusion channel, and the right extrusion channel (27) together form a reciprocating rotation differential extrusion channel. The diameters on both sides of the inner rotating extrusion cylinder (25) are smaller than the diameter of the middle part. The power unit includes a first outer cylindrical motor (31), a second outer cylindrical motor, and an inner cylindrical motor located at the center of an extrusion and telescopic cavity. One end of the upper and lower outer rotating extrusion cylinder drive shafts extends out of the bracket and is connected to the first outer cylindrical motor (31) and the second outer cylindrical motor, respectively. An inner rotating extrusion cylinder drive shaft extends out of the bracket and the hollow extrusion and telescopic cavity connecting rod and is connected to the inner cylindrical motor.

2. The apparatus for preparing fine-grained magnesium alloy tubing by multi-sided reverse roll forming and twisting as described in claim 1, characterized in that, The outer diameter of the upper outer rotating extrusion cylinder (23) is divided into three parts from left to right: an expanding section, a contracting section, and a horizontal section. The outer diameter of the lower outer rotating extrusion cylinder (39) is divided into three parts from right to left: an expanding section, a contracting section, and a horizontal section, which correspond to the horizontal section, contracting section, and expanding section of the upper outer rotating extrusion cylinder (23), respectively. The bottom of the left fixed extrusion cylinder (22) is aligned with the horizontal section of the lower outer rotating extrusion cylinder (39), and the top is aligned with the expanding section of the upper outer rotating extrusion cylinder (23). The bottom of the right fixed extrusion cylinder (26) is aligned with the expanding section of the lower outer rotating extrusion cylinder (39), and the top is aligned with the horizontal section of the upper outer rotating extrusion cylinder (23).

3. The apparatus for preparing fine-grained magnesium alloy tubing by multi-sided reverse roll forming and twisting as described in claim 2, characterized in that, The thickness at the top inlet of the left unequal diameter channel is t1; the thickness at the top inlet of the differential rotary extrusion channel is t2, the thickness in the middle section of the top of the channel is t3, and the thickness at the top outlet of the channel is t4; the thickness at the bottom inlet of the left unequal diameter channel is t5; the thickness at the bottom inlet of the differential rotary extrusion channel is t6, the thickness in the middle section of the bottom of the channel is t7, and the thickness at the bottom outlet of the channel is t8; the thicknesses have the following relationship: t1 > t2 > t3 > t4, t5 > t6 > t7 > t8; the thickness value of the region between the top and bottom of the left unequal diameter channel inlet is between t1 and t5, and the thickness value of the region between the top and bottom of the differential rotary extrusion channel inlet is... The thickness values ​​of the region are between t2 and t6; the thickness values ​​of the region between the top and bottom of the middle section of the differential rotary extrusion channel are between t3 and t7; the thickness values ​​of the region between the top and bottom of the outlet of the differential rotary extrusion channel are between t4 and t8; the thickness between the inlet and outlet of the left unequal diameter channel shows a linear trend from t1 and t5 to t2 and t4; the thickness from the inlet to the middle section of the differential rotary extrusion channel shows a linear trend from t2 and t6 to t3 and t7; the thickness from the middle section to the outlet of the differential rotary extrusion channel shows a linear trend from t3 and t7 to t4 and t8. The angle between the outer wall of the upper outer rotating extrusion cylinder (23) at the top entrance of the left unequal diameter channel and the horizontal plane is θ1, and the angle between the left fixed extrusion frustum (22) and the horizontal plane is θ2; the angle between the outer wall of the upper outer rotating extrusion cylinder (23) at the top entrance of the differential rotation extrusion channel and the horizontal plane is θ3, the angle between the outer wall of the inner rotating extrusion cylinder (25) at the top entrance of the differential rotation extrusion channel and the horizontal plane is θ4, and the angle between the outer wall of the upper outer rotating extrusion cylinder (23) at the middle section of the top of the differential rotation extrusion channel and the horizontal plane is θ5. The outer wall of the inner rotating extrusion cylinder (25) at the top middle section of the high-speed rotating extrusion channel makes an angle of θ6 with the horizontal plane; the outer wall of the left fixed extrusion frustum (22) at the bottom of the left unequal diameter channel makes an angle of θ7 with the horizontal plane; the outer wall of the lower outer rotating extrusion cylinder (39) at the bottom of the left unequal diameter channel makes an angle of θ8 with the horizontal plane; the outer wall of the lower outer rotating extrusion cylinder (39) at the bottom inlet of the differential rotating extrusion channel makes an angle of θ9 with the horizontal plane; and the outer wall of the inner rotating extrusion cylinder (25) at the bottom inlet of the differential rotating extrusion channel makes an angle of θ9 with the horizontal plane. 10 The outer wall of the lower outer rotating extrusion cylinder (39) at the bottom middle section of the differential rotating extrusion channel makes an angle θ with the horizontal plane. 11 The outer wall of the inner rotating extrusion cylinder (25) at the bottom middle section of the differential rotating extrusion channel makes an angle θ with the horizontal plane. 12 The included angles mentioned above have the following relationships: θ1 > θ2, θ4 > θ3, θ5 > θ6, θ8 > θ7, θ9 > θ6. 10 θ 11 >θ 12 .

4. The apparatus for preparing fine-grained magnesium alloy tubing by multi-sided reverse roll forming and twisting as described in any one of claims 1-3, characterized in that, The fixed extrusion die (24), left fixed extrusion punch (16), right fixed extrusion punch (34), left fixed extrusion frustum (22), right fixed extrusion frustum (26), upper outer rotating extrusion cylinder (23), lower outer rotating extrusion cylinder (39), and inner rotating extrusion cylinder (25) are all made of 4Cr5MoSiV1 hot work die steel. The surface roughness of the fixed extrusion die (24), left fixed extrusion punch (16), and right fixed extrusion punch (34) is Ra0.08~0.16μm, the surface roughness of the inner rotating extrusion cylinder (25) is Ra0.16~0.4μm, and the surface roughness of the upper and lower outer rotating extrusion cylinders is Ra0.4~0.8μm.

5. A method for preparing fine-grained magnesium alloy tubing using a multi-sided reverse roll-to-extrusion composite process, comprising the apparatus for preparing fine-grained magnesium alloy tubing using a multi-sided reverse roll-to-extrusion composite process as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Pretreatment of magnesium alloy billet: S1-1. Process the magnesium alloy billet into magnesium alloy tubes (36), and polish the surface of the magnesium alloy tubes (36) with 600-grit sandpaper to remove oil stains. Then polish with 800-grit, 1000-grit, and 1200-grit sandpaper in sequence until the inside and outside of the magnesium alloy tubes are smooth. S1-2. Mix acetone and anhydrous ethanol in a cleaning tank at a volume ratio of 3:2 and stir until homogeneous to prepare a cleaning solution. S1-3. Immerse the magnesium alloy pipe (36) prepared in step S1-1 into the cleaning solution prepared in step S1-2, place the cleaning tank on the ultrasonic cleaner and ultrasonically clean the magnesium alloy pipe (36) for 60 minutes, then take out the magnesium alloy pipe (36) and clean it with anhydrous ethanol, and finally dry it with a hair dryer. S1-4. Coat the surface of the magnesium alloy tube (36) prepared in step S1-3 with graphite oil solution for later use. S2. Preheating of magnesium alloy pipe: Set the heating temperature of the vacuum atmosphere heating furnace to 350~450℃. After the furnace temperature reaches the set temperature, put the magnesium alloy pipe (36) into the heating furnace and keep it warm for 12~48h. S3. Lubrication, assembly, and preheating of the differential rotary extrusion device: S3-1, Lubrication: Apply graphite oil solution to the surfaces of the upper and lower outer rotating extrusion cylinder drive shafts, the contact point of the hemispherical gear (35), the inner rotating extrusion cylinder (25), the outer surfaces of the upper outer rotating extrusion cylinder (23) and the lower outer rotating extrusion cylinder (39), the surfaces of the left extrusion telescopic cavity connecting rod (15), the right extrusion telescopic cavity connecting rod (30), and the inner surface of the differential rotating extrusion channel; S3-2, Assembly: Left and right fixed supports are installed on the horizontal extruder (8). The upper and lower outer rotating extrusion cylinders are assembled with the fixed extrusion die (24). The upper and lower outer rotating extrusion cylinders are placed inside the fixed extrusion die (24). The outer rotating extrusion cylinders are fitted with the inner wall of the fixed extrusion die (24) with a clearance fit. The inner rotating extrusion cylinder (25) is connected to the drive shafts of the left and right inner rotating extrusion cylinders through a hemispherical gear (35) and then assembled with the left and right fixed extrusion punches. The inner rotating extrusion cylinder (25) and the drive shafts of the left and right inner rotating extrusion cylinders are placed inside the left and right fixed extrusion punches and tightly connected. The left and right fixed extrusion punches and the fixed extrusion die (24) are assembled between the left fixed support (19) and the right fixed support (28) and tightly connected. The upper and lower outer rotating extrusion cylinder drive shafts after installation are connected to the power unit. The left and right extrusion rings are connected to the left and right extrusion telescopic cavities respectively and the left and right extrusion rings are fitted with the left and right extrusion channels. S3-3, Preheating: Control the temperature of the heating jacket (20) to 300~500℃, and keep it warm for 2~4 hours after reaching the set temperature, so that it can be used in the next step; S4, Rotary differential extrusion forming: Fixed extrusion die (24), left and right fixed extrusion punches, upper and lower outer rotating extrusion cylinders and inner rotating extrusion cylinder (25) form a reciprocating rotary differential extrusion channel; the reciprocating rotary differential extrusion channel includes three areas: left extrusion channel (18), rotary differential extrusion channel and right extrusion channel (27); S4-1. Place the magnesium alloy tube (36) at the inlet of the left extrusion channel (18), then fix the left and right extrusion rings, start the power device, and make the upper and lower outer rotating extrusion cylinders and the inner rotating extrusion cylinder (25) rotate in the opposite direction under the drive of the transmission shaft; start the left pressure motor (11), and the magnesium alloy tube (36) passes through the left extrusion channel (18), the differential rotating extrusion channel, and the right extrusion channel (27) in sequence under the action of the left extrusion ring (17). The angle between the channel walls on both sides of the differential rotating extrusion channel and the horizontal direction is different, and the extrusion channel gradually thins. The diameters on both sides of the inner rotating extrusion cylinder (25) are smaller than the diameter of the middle part. After the magnesium alloy tube (36) enters the extrusion channel, the tube diameter first increases and then decreases to restore the original tube diameter; in the rotating differential extrusion channel section In the first stage, the magnesium alloy tube (36) is rotated and extruded under the influence of friction. Since the friction coefficients of the outer walls of the upper and lower outer rotating extrusion cylinders and the inner rotating extrusion cylinder (25) are different, the inner and outer walls of the magnesium alloy tube (36) are subjected to opposite radial friction forces of different magnitudes when passing through the differential rotating extrusion channel, resulting in shear deformation. When the magnesium alloy tube (36) completes the left extrusion and reaches the right extrusion channel (27), the left pressure motor (11) is turned off and the right pressure motor (38) is turned on. Under the action of the right extrusion ring (29), the magnesium alloy tube (36) moves to the left and passes through the differential rotating extrusion channel again. This process is repeated. After several cycles, the right pressure motor (38) and the right extrusion ring (29) are removed, and the fine-grained magnesium alloy tube is removed from the discharge port. S4-2. Take out the magnesium alloy tube (36) obtained in step S4-1, polish its surface with sandpaper, clean the magnesium alloy tube with the cleaning solution prepared in step S1-2, clean it a second time with anhydrous ethanol, and dry it with a hair dryer to obtain a fine-grained weak-textured magnesium alloy tube that can be put into use directly.

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