Device and process method for preparing high-performance fine-grained and weak-texture magnesium alloy by multi-directional dynamic torsion extrusion

Abstract

The present invention belongs to the technical field of light metal plastic forming, and specifically relates to a device and a process method for preparing a high-performance fine-grained and weak texture magnesium alloy by multi-directional dynamic torsion extrusion. In the present invention, dynamic torsion extrusion of different traveling speeds and different torsion angular velocities is respectively carried out on a magnesium alloy blank by dynamic torsion extrusion rods on the left and right sides. At the same time, a threaded punch also drives the blank to twist forward, forcing the c-axis of the magnesium alloy blank to deflect and refining the grains. At the same time, asymmetric grooves exist in the front parts of the dynamic torsion extrusion rods on the left and right sides, intensifying the plastic deformation of the magnesium alloy blank, weakening the texture and refining the grains. At the same time, the torsion directions of the dynamic torsion extrusion rods on the left and right sides and the upper threaded punch are opposite on the left side and the same on the right side at the contact point, making the frictional forces on both sides different, intensifying the deformation of the magnesium alloy and achieving the purpose of weakening the texture and refining the grains. Finally, through the extrusion zone, the blank is further extruded to obtain a magnesium alloy bar with a desired uniform structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of light metal plastic forming, and particularly relates to a device and a process method for preparing a high-performance fine-grained and weak-texture magnesium alloy by multi-directional dynamic torsion extrusion. Background Art

[0002] Magnesium alloy is the structural material with the lowest density among current metals, and has advantages such as high specific strength and specific stiffness, good hot formability, and easy recyclability. Therefore, it occupies an important position in fields such as automobiles, 3C, aerospace, and military, and is even known as the "green energy material in the 21st century". However, the crystal structure of magnesium alloy is hexagonal close-packed, and only two slip systems are easy to activate at room temperature, which is less than the five independent slip systems required for polycrystalline deformation. As a result, it is difficult to plastically process magnesium alloy at room temperature, and the macroscopic manifestation is poor mechanical properties at room temperature. In addition, due to the large difference in the critical shear stress between the basal plane and non-basal plane slips of magnesium alloy, it is not easy to initiate non-basal plane slips during low-temperature deformation, resulting in a preferred orientation of grains in the deformed material to form a strong basal texture, which is not conducive to subsequent deformation and limits the application of magnesium alloy in various fields. Grain refinement can significantly improve the mechanical properties of metal materials, and the same is true for magnesium alloys. Severe plastic deformation techniques have been proven to be able to effectively refine the grains of magnesium alloys, such as high-pressure torsion (HPT), multi-directional forging (MDF), equal-channel angular pressing (ECAP), and torsion extrusion (TE), which can extremely refine the grains and even obtain ultrafine-grained structures. However, torsional deformation is generally more complex, with high requirements for die processing and equipment, and it needs to withstand large pressures. The degree of material torsion is low, which greatly limits the realization of large-scale continuous preparation.

[0003] Therefore, it is very important to invent an effective device and method for weakening the deformation texture and refining the grains of magnesium alloy to expand the application range of magnesium alloy. Summary of the Invention

[0004] The present invention aims to solve the above problems and provides a device and a process method for preparing a high-performance fine-grained and weak-texture magnesium alloy by multi-directional dynamic torsion extrusion. Through this device and its processing method, the magnesium alloy blank undergoes continuous severe torsional extrusion deformation during the processing, causing the c-axis of the magnesium alloy to deflect, thereby realizing texture weakening and grain refinement, improving the mechanical properties of the magnesium alloy at room temperature, and expanding the application range of the magnesium alloy.

[0005] The present invention is realized through the following technical solutions: A device for preparing a high-performance fine-grained and weak-texture magnesium alloy by multi-directional dynamic torsion extrusion, including a vertical extrusion press, an upper torsion extrusion die, a left torsion extrusion die, a right torsion extrusion die, an external die holder, and a power device, wherein:

[0006] The vertical extruder includes a movable crossbeam, two columns, and a working platform; the two columns are vertically arranged above the working platform, the movable crossbeam spans above the columns and can move up and down along the columns;

[0007] The upper torsion extrusion die includes a threaded punch fixing plate, a first bearing, a threaded punch, and a first threaded pipe. The threaded punch fixing plate is installed below the movable crossbeam. The first bearing is axially installed vertically below the threaded punch fixing plate and is assembled with the threaded punch. A first threaded pipe meshing with the threaded punch is sleeved on the threaded punch, and the first threaded pipe is fixed to the column on the right side of the extruder through a fourth support rod;

[0008] The left torsion extrusion die includes a left torsion extrusion rod, a second threaded pipe, a universal ball, a connecting rod, and a wheel disc; the wheel disc is rotatably supported on the left column through a first support rod. The left end of the connecting rod is hinged to the edge of the wheel disc and rotates with the wheel disc. The right end of the connecting rod is connected to the universal ball. The universal ball is installed at the top of the left torsion extrusion rod. The second threaded pipe is fixed to the left column through a second support rod. The upper half of the left torsion extrusion rod is a threaded rod paired with the second threaded pipe, and the cross-sectional area of the lower half gradually decreases and is provided with a left groove. The wheel disc is driven to rotate by a first motor, thereby driving the connecting rod to rotate, and the connecting rod drives the left torsion extrusion rod to twist and advance in cooperation with the threaded pipe;

[0009] The right torsion extrusion die includes a right torsion extrusion rod, a second bearing, a positioning sleeve, a power sleeve, and a threaded rod; the right torsion extrusion die is fixed to the column on the right side of the extruder through a third support rod. The threaded rod penetrates through the positioning sleeve, the power sleeve, and the inside of the torsion extrusion rod. The positioning sleeve is fixed in position on the threaded rod through a bearing, and the threaded rod can rotate freely. The power sleeve is embedded inside the positioning sleeve and is circumferentially fixed to the positioning sleeve through a groove on the edge and moves up and down limited by the length of the positioning sleeve. The threaded rod is threadedly connected to the power sleeve. A second bearing is installed inside the power sleeve and is matched with the right torsion extrusion rod. The upper half of the right torsion extrusion rod is hollow, and the inner surface is provided with protrusions parallel to its axis. The surface of the threaded rod is provided with grooves parallel to its axis. The protrusions of the right torsion extrusion rod are fitted with the grooves of the threaded rod. The lower half of the right torsion extrusion rod is a solid rod with a gradually decreasing cross-sectional area and is provided with a right groove. The right groove and the left groove of the left torsion extrusion rod are partially asymmetric;

[0010] The external die carrier is arranged on a fixed backing plate above the working platform and includes a front module and a rear module; the front module and the rear module are fixed by bolts, and an extrusion space is formed inside the rear module. The extrusion space includes a vertical middle channel and left and right channels which are inclined and communicate with the bottom of the middle channel on the left and right sides of the rear module; leakage holes which communicate with the middle channel and have an inner diameter smaller than that of the middle channel are formed in the working platform and the backing plate; a threaded punch extends downward into the middle channel, and the left and right torsion extrusion rods extend into the left and right channels respectively; the middle channel, the left and right channels together with the leakage holes form a torsion extrusion channel; heating channels for the flow of organic heat carriers are arranged inside both the front module and the rear module;

[0011] The power mechanism is a first motor and a second motor (both motors capable of rotating bidirectionally) for driving the left and right torsion extrusion dies; the first motor drives a disc to rotate, and the second motor drives a threaded rod to rotate.

[0012] The torsion extrusion channel is successively a torsion pushing area, a dynamic torsion extrusion area and an extrusion area from top to bottom. In the torsion pushing area, the magnesium alloy blank continuously twists and advances driven by the threaded punch, reaches the dynamic torsion extrusion area, and is subjected to dynamic torsion extrusion with different advancing speeds and different torsion angular velocities by the dynamic torsion extrusion rods on the left and right sides respectively. At the same time, the threaded punch also drives the blank to twist and advance, forcing the c-axis of the magnesium alloy blank to deflect and refining the grains. At the same time, asymmetric grooves exist at the front ends of the left and right torsion extrusion rods, intensifying the plastic deformation of the magnesium alloy blank, weakening the texture and refining the grains. At the same time, the torsion directions of the left and right torsion extrusion rods and the upper threaded punch are opposite on the left side at the contact point and the same on the right side, making the frictional forces on both sides different, further intensifying the deformation of the magnesium alloy and achieving the purpose of refining the grains. Finally, through the extrusion area, the magnesium alloy blank becomes the required high-performance magnesium alloy bar. This device can realize the preparation of high-performance fine-grained and weak-texture magnesium alloy through multi-directional dynamic torsion extrusion deformation.

[0013] Further, the materials of the front module, the rear module, the left torsion extrusion rod, the right torsion extrusion rod and the threaded punch are all 4Cr5MoSiV1 hot work die steel.

[0014] Further, the surface roughness of the left torsion extrusion rod is Ra0.08 - 0.16 μm, the surface roughness of the right torsion extrusion rod is Ra0.16 - 0.4 μm, and the surface roughness of the torsion extrusion channel of the rear module is Ra0.4 - 0.8 μm. The asymmetry in the roughness between the torsion extrusion channel and the left and right torsion extrusion rods forms a difference in the frictional force generated during the extrusion process and the blank, further promoting the differential flow of the blank and generating shear extrusion deformation to weaken its basal texture.

[0015] Further, when the preparation of the magnesium alloy bar is completed, the vertical extrusion press moves upward, controlling the reverse rotation of the threaded punch to withdraw from the channel, and the torsion extrusion rods on the left and right sides also withdraw from the channels on the left and right sides through motor control, preparing for the next bar extrusion.

[0016] A process method for preparing a high-performance fine-grained and weak texture magnesium alloy bar by multi-directional dynamic torsion extrusion, comprising the following steps:

[0017] S1. Pretreatment of the magnesium alloy blank:

[0018] S1-1. Process the magnesium alloy blank into a cylindrical magnesium alloy bar, and polish the surface of the magnesium alloy bar with 600-mesh sandpaper to remove oil stains, and then polish it with 800-mesh, 1000-mesh, and 1200-mesh sandpapers in sequence until the surface of the magnesium alloy bar is smooth;

[0019] S1-2. Mix acetone and absolute ethanol in a volume ratio of 3:2 in a cleaning tank and stir evenly to prepare a cleaning solution;

[0020] S1-3. Immerse the magnesium alloy bar prepared in step S1-1 into the cleaning solution prepared in step S1-2, place the cleaning tank on an ultrasonic cleaner to ultrasonically clean the magnesium alloy bar for 60 min, then take out the magnesium alloy bar and clean it with absolute ethanol, and finally dry it with a hair dryer;

[0021] S1-4. Apply a graphite oil solution to the surface of the magnesium alloy bar prepared in step S1-3 for later use;

[0022] S2. Preheating of the magnesium alloy bar: Set the heating temperature of the vacuum atmosphere heating furnace to 450 °C. After the furnace temperature of the heating furnace reaches the set temperature, put the magnesium alloy bar into the heating furnace and keep it warm for 3 h;

[0023] S3. Lubrication, assembly and preheating of the dynamic torsion extrusion deformation device:

[0024] S3-1. Lubrication: Apply a graphite oil solution to the surface of the threaded punch, the surface of the left torsion extrusion rod, the surface of the right torsion extrusion rod, the power sleeve, the contact part between the positioning sleeve and the second bearing and the right torsion extrusion rod, and the inner surface of the torsion extrusion channel;

[0025] S3-2. Assembly:

[0026] First, install and fix the backing plate on the working platform of the vertical extrusion press. Install the rear module and the front module together with four bolts and fix them on the backing plate. Then, assemble and insert the left torsion extrusion rod into the left channel of the rear module and cooperate it with the second threaded pipe. The upper part of the left torsion extrusion rod is connected to the connecting rod and the wheel disc through a universal ball. Next, penetrate the threaded rod in the right torsion extrusion die into the positioning sleeve, the power sleeve and the inside of the right torsion extrusion rod. Install the power sleeve and the right torsion extrusion rod, and circumferentially fix the positioning sleeve and the power sleeve so that the power sleeve moves up and down along the edge of the positioning sleeve. The power sleeve cooperates with the second bearing and the torsion extrusion rod. Then, assemble and insert the right torsion extrusion rod into the right channel, and align the position of the discharge port with the leakage hole penetrating the working platform and the backing plate.

[0027] S3-3. Preheating: Control the temperature of the medium in the heating channel to be 300-500 °C. After reaching the set temperature, keep it warm for 2-4 h for subsequent use.

[0028] S4. Multi-directional dynamic torsion extrusion forming: The middle channel, the left and right channels together with the leakage hole jointly form a torsion extrusion channel; the torsion extrusion channel includes three regions: the torsion pushing region I, the dynamic torsion extrusion region II, and the extrusion region III arranged from top to bottom.

[0029] S4-1. Withdraw the threaded punch from the torsion extrusion channel, fill the magnesium alloy billet in the torsion pushing region I, and then push the threaded punch into the torsion extrusion channel. Operate the vertical extrusion press to push the threaded punch downward, driving the magnesium alloy billet to rotate and move downward. When the magnesium alloy billet reaches the dynamic torsion extrusion region II, the first motor on the left drives the wheel disc to rotate, the wheel disc drives the connecting rod to rotate, and then pushes the left torsion extrusion rod to torsionally extrude the blank forward. The second motor on the right drives the threaded rod to rotate, driving the power sleeve to move forward, and at the same time driving the right torsion extrusion rod to rotate and move forward, and extruding the magnesium alloy billet. During this process, as the threaded punch at the top drives the magnesium alloy billet to twist, the magnesium alloy billet realizes a spiral forward movement during the asymmetric spiral extrusion process on the left and right, causing the c-axis of the magnesium alloy billet to deflect, weakening the texture and further refining the grains. When the billet reaches the extrusion region III, the billet is further extruded to obtain the desired magnesium alloy bar with uniform structure. During the torsion extrusion forming process, control the temperature of the medium in the heating channel to be 300-500 °C.

[0030] S4-2. Take out the magnesium alloy bar prepared in step S4-1, polish its surface with sandpaper, then clean the magnesium alloy bar 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 and weak-texture high-performance magnesium alloy bar that can be directly put into use.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1. The torsional extrusion channel provides severe helical torsional deformation and dynamic recrystallization, effectively weakening the basal texture of the magnesium alloy and improving the mechanical properties of the magnesium alloy.

[0033] 2. The extrusion speeds of the left and right torsional extrusion rods and the angular velocity of torsion can both be adjusted. There are small asymmetric grooves on them. At the same time, the torsion directions of the left and right torsional extrusion rods and the upper threaded punch can be adjusted, making the frictional forces on both sides at the contact different, enabling the blank to further achieve helical extrusion deformation and making the grain refinement effect of the magnesium alloy bar more significant. Description of the Drawings

[0034] Figure 1 It is the front view structural schematic diagram of the mold of the present invention;

[0035] Figure 2 It is the top view of the external mold frame of the channel of the mold of the present invention;

[0036] Figure 3 is Figure 1 the front view and top view of the upper threaded punch in

[0037] Figure 4 is Figure 1 the detailed view of the crank - connecting rod part of the left - hand torsional extrusion die in

[0038] Figure 5 is Figure 1 the detailed view of the driving part of the right - hand torsional extrusion die in

[0039] Figure 6 is the detailed view of the left and right torsional extrusion rods;

[0040] Figure 7 is the schematic diagram of the torsional extrusion channel;

[0041] Figure 8 is the schematic diagram of the blank shape in the torsional extrusion channel.

[0042] In the figure: 1 - movable crossbeam; 2 - threaded punch fixing plate; 3 - column; 4 - first bearing; 5 - threaded punch; 6 - first threaded pipe; 7 - first support rod; 8 - wheel disc; 9 - connecting rod; 10 - first motor; 11 - universal ball; 12 - second support rod; 13 - second threaded pipe; 14 - left torsion extrusion rod; 15 - front module; 16 - right torsion extrusion rod; 17 - threaded rod; 18 - power sleeve; 19 - second bearing; 20 - positioning sleeve; 21 - third support rod; 22 - second motor; 23 - fourth support rod; 24 - central console; 25 - oil temperature machine controller; 26 - movable crossbeam controller; 27 - vacuum atmosphere heating furnace controller; 28 - wire; 29 - stop button; 30 - start button; 31 - emergency stop button; 32 - display screen; 33 - heating channel; 34 - cross-shaped protrusion; 35 - left groove; 36 - right groove; 37 - working platform; 38 - backing plate; 39 - bolt; 40 - magnesium alloy billet; 41 - rear module.

[0043] Ⅰ - Torsion pushing area; Ⅱ - Dynamic torsion extrusion area; Ⅲ - Extrusion area. Specific implementation mode

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0045] A device for preparing high-performance fine-grained and weakly textured magnesium alloy by multi-directional dynamic torsion extrusion includes a vertical extruder, an upper torsion extrusion die, a left torsion extrusion die, a right torsion extrusion die, an external die holder and a power device, wherein:

[0046] The vertical extruder includes a movable crossbeam 1, columns 3 and a working platform 37. The two columns 3 are vertically arranged above the working platform 37, and the movable crossbeam 1 spans above the columns 3 and can move up and down along the columns 3;

[0047] The upper torsion extrusion die includes a threaded punch fixing plate 2, a first bearing 4, a threaded punch 5, and a first threaded pipe 6; the threaded punch fixing plate 2 is arranged below the movable crossbeam 1, the first bearing 4 is installed below the threaded punch fixing plate 2 and is assembled with the threaded punch 5, the first threaded pipe 6 meshing with the threaded punch 5 is sleeved on the threaded punch 5, the first threaded pipe 6 is fixed to the column 3 on the right side of the extruder through the fourth support rod 23, and a cross-shaped protrusion 34 is arranged at the front end of the threaded punch 5, and the front angle thereof is θ3 for fixing the blank;

[0048] The left torsion extrusion die includes a left torsion extrusion rod 14, a second threaded pipe 13, a universal ball 11, a connecting rod 9, and a wheel disc 8. The wheel disc 8 is rotatably supported on the left column 3 by a first support rod 7. The left end of the connecting rod 9 is hinged to the edge of the wheel disc 8 and rotates with the wheel disc 8. The right end of the connecting rod 9 is connected to the universal ball 11, and the other end of the universal ball 11 is connected to the left torsion extrusion rod 14. The second threaded pipe 13 is fixed to the left column 3 by a second support rod 12. The upper half of the left torsion extrusion rod 14 is a threaded rod that mates with the second threaded pipe 13, and the cross-sectional area of the lower half gradually decreases and is provided with an asymmetric left groove 35. The wheel disc 8 is driven to rotate by a first motor 10, thereby driving the connecting rod 9 to rotate. The connecting rod 9 drives the torsion extrusion rod 14 to twist and advance in cooperation with the threaded pipe 13;

[0049] The right torsion extrusion die includes a right torsion extrusion rod 16, a second bearing 19, a positioning sleeve 20, a power sleeve 18, and a threaded rod 17. The entire die is fixed to the column 3 on the right side of the extruder by a third support rod 21 (the positioning sleeve 20 is connected to the third support rod 21). The threaded rod 17 passes through the inside of the positioning sleeve 20, the power sleeve 18, and the right torsion extrusion rod 16. The positioning sleeve 20 is fixed in position on the threaded rod 17 through a bearing, and the threaded rod 17 can rotate freely. The power sleeve 18 is embedded inside the positioning sleeve 20 and is circumferentially fixed to the positioning sleeve 20 by means of a groove on the edge and moves up and down limited by the length of the positioning sleeve 20. The threaded rod 17 is threadedly connected to the power sleeve 18. A second bearing 19 is installed inside the power sleeve 18 and cooperates with the right torsion extrusion rod 16 (the right torsion extrusion rod 16 is connected to the inner ring of the second bearing). The upper half of the right torsion extrusion rod 16 is hollow, and the inner surface is provided with protrusions parallel to its axis. The surface of the threaded rod 17 is provided with grooves parallel to its axis (through the threads). The protrusions of the right torsion extrusion rod 16 are engaged with the grooves of the threaded rod 17 (the right torsion extrusion rod 16 can be driven by the power sleeve 18 to move forward or backward and rotate synchronously with the threaded rod at the same time). The lower half of the right torsion extrusion rod 16 is a solid rod with a gradually decreasing cross-sectional area and is provided with a right groove 36, and its groove part and the left groove 35 part of the left torsion extrusion rod are asymmetric;

[0050] The external mold base is arranged on the fixed backing plate 38 above the working platform 37 and includes a front module 15 and a rear module 41. The front module 15 and the rear module 41 are fixed by four bolts 39. An extrusion space is formed inside the rear module 41. The extrusion space includes a vertical middle channel and left and right channels which are inclined and communicate with the bottom of the middle channel on the left and right sides of the rear module 41. Leakage holes which are communicated with the middle channel and have an inner diameter smaller than that of the middle channel are formed in the working platform 37 and the backing plate 38. The threaded punch 5 extends into the middle channel from top to bottom, and the left and right torsion extrusion rods extend into the left and right channels respectively. The middle channel, the left and right channels together with the leakage holes jointly form a torsion extrusion channel. Moreover, heating channels 33 for the flow of the organic heat carrier are arranged inside both the front module 15 and the rear module 41.

[0051] The power mechanism is a first motor 10 and a second motor 22 for driving the left and right torsion extrusion dies. The motors are both bidirectional motors.

[0052] Further, the torsion extrusion channel sequentially includes a torsion pushing area Ⅰ from top to bottom, a dynamic torsion extrusion area Ⅱ and an extrusion area Ⅲ. In the torsion pushing area Ⅰ, the magnesium alloy bar 40 continuously twists and advances driven by the threaded punch 5. The advancing speed of the threaded punch 5 is V3, and the torsion angular velocity is ω3. When reaching the dynamic torsion extrusion area Ⅱ, dynamic torsion extrusion with different advancing speeds and different torsion angular velocities is respectively performed by the dynamic torsion extrusion rods on the left and right sides. The first motor on the left side drives the disc to rotate, and its rotation angular velocity is ω4, which causes the left torsion extrusion rod to advance and rotate forward. The advancing speed of the left torsion extrusion rod is V1, and the torsion angular velocity is ω1. The threaded rod in the right torsion extrusion die rotates driven by the second motor, and the rotation angular velocity of the threaded rod is ω5, which drives the advancing speed of the right torsion extrusion rod to be V2, and the torsion angular velocity is ω2, and V1≠V2≠V3, ω1≠ω2≠ω3, further increasing the asymmetric deformation, forcing the c-axis of the magnesium alloy blank to deflect and refining the grains. At the same time, asymmetric left grooves 35 and right grooves 36 exist at the front ends of the left and right torsion extrusion rods. The inner radius of the left groove at the front end of the left torsion extrusion rod is r1, and the inner radius of the right groove at the front end of the right torsion extrusion rod is r2. The two are asymmetric, r1≠r2. The angles between the two torsion extrusion rods and the rear module are θ1 and θ2 respectively. At the same time, the torsion directions of the left and right torsion extrusion rods and the upper threaded punch are opposite on the left side and the same on the right side at the contact point, so that the frictional forces on both sides are different, further intensifying the plastic deformation of the magnesium alloy blank, weakening the texture and refining the grains. Finally, through the extrusion area Ⅲ, the magnesium alloy blank reaches the required high-performance magnesium alloy bar. This device can realize the preparation of fine-grained and weak-texture magnesium alloy through multi-directional dynamic torsion extrusion deformation.

[0053] Further, the materials of the front module 15, the rear module 41, the left torsion extrusion rod 14, the right torsion extrusion rod 16, and the threaded punch 5 are all 4Cr5MoSiV1 hot work die steel.

[0054] Further, the surface roughness of the left torsion extrusion rod 14 is Ra0.08 - 0.16 μm, the surface roughness of the right torsion extrusion rod 16 is Ra0.16 - 0.4 μm, and the surface roughness of the torsion extrusion channel of the rear module is Ra0.4 - 0.8 μm. The roughness of the torsion extrusion channel and the left and right torsion extrusion rods forms an asymmetric distribution, creating a difference in the frictional force generated during the extrusion process and the blank, further promoting the differential flow of the blank and generating shear extrusion deformation to weaken its basal texture.

[0055] In this specific embodiment, before performing reciprocating torsion extrusion deformation to prepare the fine-grained and weak-texture magnesium alloy, the materials and chemical reagents required for the preparation process are first selected:

[0056] 1. Magnesium alloy bar blank: A cylindrical blank, made of AZ31 material, containing 96% magnesium, 3% aluminum, and 1% zinc;

[0057] 2. Sandpaper: Solid solid;

[0058] 3. Graphite oil solution: Viscous liquid;

[0059] 4. Absolute ethanol: Liquid liquid, with a purity of 99.5%;

[0060] 5. Acetone: Liquid liquid, with a purity of 99%.

[0061] A method for preparing a high-performance fine-grained and weak-texture magnesium alloy bar by multi-directional dynamic torsion extrusion includes the following steps:

[0062] S1. Pretreatment of the magnesium alloy bar blank:

[0063] S1-1. Process the magnesium alloy bar blank into a cylindrical magnesium alloy bar 40, and polish the surface of the magnesium alloy bar 40 with 600-mesh sandpaper to remove oil stains, and then polish it with 800-mesh, 1000-mesh, and 1200-mesh sandpapers in sequence until the surface of the magnesium alloy bar 40 is smooth;

[0064] S1-2. Mix acetone and absolute ethanol in a volume ratio of 3:2 in a cleaning tank and stir evenly to prepare a cleaning solution;

[0065] S1-3. Immerse the magnesium alloy bar 40 prepared in step S1-1 into the cleaning solution prepared in step S1-2, place the cleaning tank on an ultrasonic cleaner to ultrasonically clean the magnesium alloy bar 40 for 60 minutes, then take out the magnesium alloy bar 40 and clean it with absolute ethanol, and finally dry it with a hair dryer;

[0066] S1-4. Apply a graphite oil solution to the surface of the magnesium alloy bar 40 prepared in step S1-3 for later use.

[0067] S2. Preheat the magnesium alloy bar 40: Set the heating temperature of the vacuum atmosphere heating furnace to 450 °C. After the furnace temperature reaches the set temperature, place the magnesium alloy bar 40 into the heating furnace and keep it warm for 3 h.

[0068] S3. Lubrication, assembly, and preheating of the dynamic torsional extrusion forming device:

[0069] S3-1. Lubrication: Apply a graphite oil solution to the surface of the threaded punch 5, the surface of the left torsional extrusion rod 14, the surface of the right torsional extrusion rod 16, the power sleeve 18, the positioning sleeve 20, the contact part between the second bearing 19 and the right torsional extrusion rod 16, and the inner surfaces of the torsional extrusion channels I, II, and III.

[0070] S3-2. Assembly:

[0071] First, install and fix the backing plate 38 on the working platform 37 of the vertical extrusion machine. Install the rear module 41 and the front module 15 together with four bolts 39 and fix them on the backing plate 38. Then, assemble and insert the left torsional extrusion rod 14 into the left channel of the rear module 41 and cooperate with the second threaded pipe 13. The upper part of the left torsional extrusion rod 14 is connected to the connecting rod 9 and the wheel disc 8 through the universal ball 11. Then, pass the threaded rod 17 in the right torsional extrusion die through the inside of the positioning sleeve 20, the power sleeve 18, and the right torsional extrusion rod 16. The power sleeve 18 is installed together with the right torsional extrusion rod 16, and the positioning sleeve 20 is circumferentially fixed to the power sleeve 18 so that the power sleeve 18 moves up and down along the edge of the positioning sleeve 20. The power sleeve 18 cooperates with the second bearing 19 and the right torsional extrusion rod 16. Then, assemble and insert the right torsional extrusion rod 16 into the right channel, and align the position of the discharge port with the leakage hole passing through the working platform and the backing plate.

[0072] S3-3. Preheating: Control the medium temperature of the heating channel 33 to be 300 - 500 °C. After reaching the set temperature, keep it warm for 2 - 4 h for later use.

[0073] S4. Multi-directional dynamic torsional extrusion forming: The middle channel, the left and right channels together with the leakage hole jointly form the torsional extrusion channel; the torsional extrusion space includes three regions: the torsional pushing region I, the dynamic torsional extrusion region II, and the extrusion region III arranged from top to bottom.

[0074] S4-1. Withdraw the threaded punch 5 from the channel, fill the magnesium alloy billet 40 in the torsion propulsion zone I, and then push the threaded punch 5 into the channel. Operate the vertical extrusion press, push the threaded punch 5 downward, drive the magnesium alloy billet 40 to rotate and move downward. When the magnesium alloy billet 40 reaches the dynamic torsion extrusion zone II, the first motor 10 on the left drives the wheel disc 8 to rotate, the wheel disc 8 drives the connecting rod 9 to rotate, and then pushes the left torsion extrusion rod 14 to twist and extrude the blank forward. The second motor 22 on the right drives the threaded rod to rotate, drives the power sleeve 18 to move forward, and at the same time drives the right torsion extrusion rod 16 to rotate and move forward, and extrudes the magnesium alloy billet 40. During this process, as the threaded punch 5 at the top drives the magnesium alloy billet 40 to twist, the magnesium alloy billet 40 realizes a helical advance during the asymmetric spiral extrusion process on the left and right, deflects the c-axis of the magnesium alloy billet, weakens the texture and grains to achieve further refinement. When the magnesium alloy billet 40 reaches the extrusion zone III, the blank is further extruded to obtain the required magnesium alloy bar with uniform structure. During the torsion extrusion forming process, control the temperature of the heating wire to be 300 - 500 °C;

[0075] S4-2. Take out the magnesium alloy bar prepared in step S4-1, polish its surface with sandpaper, then clean the magnesium alloy bar 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-texture high-performance magnesium alloy bar that can be directly put into use. Specific embodiment

[0076] An apparatus and process method for preparing a fine-grained weak-texture magnesium alloy bar by multi-directional dynamic torsion extrusion, adopting the following steps:

[0077] (1) Install the upper torsion extrusion die and the external die holder on the vertical extrusion press, install the torsion extrusion dies on the left and right sides into the channels on the left and right sides, install firmly, and the connection relationship of each part position should be correct, and operate in sequence;

[0078] (2) Polish the outer surface of the AZ31 magnesium alloy bar blank with 600-mesh sandpaper to remove oil stains, and then polish it with 1000, 1200, and 2500-mesh sandpapers in sequence to ensure the surface is clean and smooth. Place the polished magnesium alloy bar blank in a mixed solution of acetone and anhydrous ethanol with a volume ratio of 3:2 for ultrasonic cleaning for 30 minutes, then clean it with alcohol and dry it with a hair dryer;

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

[0080] (4) Turn on the torsional extrusion die cavity heating device to heat regions I and II of the torsional extrusion channel. The preset heating temperature is 400 °C, and keep the temperature for 3 h after reaching the preset temperature;

[0081] (5) Lubricate the surface of the magnesium alloy bar blank with a high-temperature graphite oil solution. The outer dimensions of the left torsional extrusion rod 14 and the right torsional extrusion rod 16 are the same, but the dimensions of the left groove 35 and the right groove 36 inside are different. Place the preheated magnesium alloy bar blank into the torsional extrusion die cavity I. The threaded punch 5 extends into the torsional pushing region I, and inserts the cross-shaped protrusion 34 on its surface into the magnesium alloy bar blank to fix them together as a whole.

[0082] (6) In the present invention, the materials of the front module 15, the rear module 41, the left torsional extrusion rod 14, the right torsional extrusion rod 16 and the threaded punch 5 are all 4Cr5MoSiV1 hot work die steel. The surface roughness of the left torsional extrusion rod 14 is Ra0.08 - 0.16 μm, the surface roughness of the right torsional extrusion rod 16 is Ra0.16 - 0.4 μm, and the surface roughness of the torsional extrusion channels I, II, and III of the rear module is Ra0.4 - 0.8 μm.

[0083] (7) Turn on the motor of the vertical extruder, set the pressure to 400 MPa, and turn on the motors on both the left and right sides at the same time. The vertical extruder pushes the threaded punch forward and rotates downward, with an angular velocity of ω3 = 0.05 r / s and a traveling speed of V3 = 50 mm / min. Under the action of the left motor, drive the wheel disk to rotate, with a rotational angular velocity of ω4 = 0.1 r / s. The wheel disk drives the connecting rod and then drives the left torsional extrusion rod to twist and advance. The traveling speed of the left torsional extrusion rod is V1 = 60 mm / min, and the torsional angular velocity is ω1 = 0.1 r / s. The threaded rod in the right torsional extrusion die rotates driven by the second motor, with a rotational angular velocity of ω5 = 0.15 r / s, driving the traveling speed of the right torsional extrusion rod to be V2 = 70 mm / min and the torsional angular velocity to be ω2 = 0.15 r / s, further increasing the asymmetric deformation, forcing the c-axis of the magnesium alloy blank to deflect and refining the grains. At the same time, there are asymmetric left grooves 35 and right grooves 36 at the front ends of both the left and right torsional extrusion rods. The inner radius of the left groove at the front end of the left torsional extrusion rod is r1 = 3 mm, and the inner radius of the right groove at the front end of the right torsional extrusion rod is r2 = 5 mm. The angles between the two torsional extrusion rods and the rear module are θ1 and θ2 respectively. In this experiment, θ1 = 45° and θ2 = 50° are set, and it further intensifies the plastic deformation of the magnesium alloy blank, weakens the texture and refines the grains. Finally, through the extrusion zone III, the spiral blank is further extruded to reach the required size of the magnesium alloy bar, realizing the processing process of the magnesium alloy bar.

[0084] (8) Take out the magnesium alloy bar, polish its surface with sandpaper, then place it in a mixed solution of acetone and absolute ethanol with a volume ratio of 3:2 for ultrasonic cleaning, and finally clean it with alcohol and blow it dry with a hair dryer at room temperature.

[0085] Conclusion: Through the device and process method for preparing fine-grained and weak-textured magnesium alloy bars by multi-directional dynamic torsion extrusion of the present invention, the average grain size of the magnesium alloy billet is greatly reduced compared with that of the conventional magnesium alloy, from the original 35 μm to 2.55 μm. The basal texture is effectively weakened compared with the initial magnesium alloy bar, and the mechanical properties of the magnesium alloy are effectively improved.

[0086] Materials and chemical reagents used: AZ31 magnesium alloy bulk billet with a diameter d = 50 mm; sandpaper: SiC, 600 mesh, 2 pieces; 1000 mesh, 2 pieces; 1200 mesh, 2 pieces; 2500 mesh, 2 pieces; high-temperature graphite oil solution: C, 500 g; absolute ethanol: CH3CH2OH, 1200 ml; acetone: C3H6O, 800 ml.

[0087] The principle of obtaining the fine-grained and weak-textured magnesium alloy by the present invention is described in detail below with reference to the accompanying drawings:

[0088] 1) Size parameters of the torsion extrusion rods: The torsion extrusion rods on the left and right sides are first different in the angle between the rod and the external die holder, that is , and secondly, their angular velocities and traveling speeds are also different from those of the thread punch, that is, V1≠V2≠V3, ω1≠ω2≠ω3. The minimum inner diameters of the grooves on the left and right sides are also different, r1≠r2.

[0089] 2) Dynamic torsion extrusion process: The magnesium alloy billet is extruded downward by the thread punch. When it reaches the dynamic torsion extrusion zone II, it is dynamically helically extruded by the torsion extrusion rods on the left and right sides respectively. The torsion extrusion rods on the left and right sides have different downward speeds and torsion speeds during torsion extrusion. In addition, the groove parts are asymmetric, and the torsion directions of the torsion extrusion rods on the left and right sides and the upper thread punch are different at the contact points respectively, making the frictional forces on both sides different, further intensifying the deformation of the magnesium alloy and achieving the purpose of grain refinement. The magnesium alloy billet is subjected to asymmetric dynamic helical extrusion, and the billet changes from a rod shape to an asymmetric spiral shape. The c-axis of the billet grains deflects, weakening its basal texture and refining the grains. Finally, through the extrusion zone III, the deformed billet is further extruded into a bar, further weakening the basal texture and refining the grains.

[0090] 3) Poor surface roughness: The torsional directions of the torsional extrusion rods on the left and right sides and the upper threaded punch are opposite on the left side and the same on the right side at the contact point, resulting in different frictional forces on both sides. At the same time, among the parts constituting the extrusion channel, the surface roughness of the left torsional extrusion rod 14 is Ra0.08 - 0.16 μm, the surface roughness of the right torsional extrusion rod 16 is Ra0.16 - 0.4 μm, and the surface roughness of the torsional extrusion channels I, II, and III of the rear module is Ra0.4 - 0.8 μm. These surface roughness differences will directly lead to differences in the friction coefficients between the corresponding surfaces and the surface of the magnesium alloy blank, causing uneven flow velocities of the magnesium alloy blank near these surfaces during the deformation process. Based on the dimensional parameters of the torsional extrusion rod and the dynamic torsional extrusion process, this further deflects the c-axis of the grains of the magnesium alloy blank, further weakening the basal texture of the magnesium alloy blank and refining the grains.

[0091] Through the above three principles, finally, the magnesium alloy blank undergoes a large amount of shear extrusion deformation to obtain a high-performance magnesium alloy rod with a weak basal texture.

[0092] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claimed rights.

Claims

1. An apparatus for preparing a high-performance fine-grained and weak-texture magnesium alloy by multi-directional dynamic torsion extrusion, characterized in that It includes a vertical extruder, an upper torsion extrusion die, a left torsion extrusion die, a right torsion extrusion die, an external die holder and a power device, wherein: The vertical extruder includes a movable crossbeam (1), two columns (3) and a working platform (37); the two columns (3) are vertically arranged above the working platform (37), and the movable crossbeam (1) spans above the columns (3) and can move up and down along the columns (3); The upper torsion extrusion die includes a threaded punch fixing plate (2), a first bearing (4), a threaded punch (5), and a first threaded pipe (6). The threaded punch fixing plate (2) is installed below the movable crossbeam (1). The first bearing (4) is axially vertically installed below the threaded punch fixing plate (2) and is assembled with the threaded punch (5). The threaded punch (5) is sleeved with a first threaded pipe (6) meshing with it. The first threaded pipe (6) is fixed to the column (3) on the right side of the extruder through a fourth support rod (23); The left torsion extrusion die includes a left torsion extrusion rod (14), a second threaded pipe (13), a universal ball (11), a connecting rod (9) and a disc (8); wherein the disc (8) is rotatably supported on the left column (3) through a first support rod (7). The left end of the connecting rod (9) is hinged to the edge of the disc (8) and rotates with the disc (8). The right end of the connecting rod (9) is connected to the universal ball (11). The universal ball (11) is installed at the top of the left torsion extrusion rod (14). The second threaded pipe (13) is fixed to the left column (3) through a second support rod (12). The upper half of the left torsion extrusion rod (14) is a threaded rod paired with the second threaded pipe (13), and the cross-sectional area of the lower half gradually becomes smaller and is provided with an asymmetric left groove (35); The right torsion extrusion die includes a right torsion extrusion rod (16), a second bearing (19), a positioning sleeve (20), a power sleeve (18) and a threaded rod (17); the right torsion extrusion die is fixed to the column (3) on the right side of the extruder through a third support rod (21), wherein the threaded rod (17) passes through the inside of the positioning sleeve (20), the power sleeve (18) and the right torsion extrusion rod (16). The positioning sleeve (20) is fixed on the threaded rod (17) through a bearing and the threaded rod (17) can rotate freely. The power sleeve (18) is embedded inside the positioning sleeve (20) and is circumferentially fixed to the positioning sleeve (20) by slitting at the edge, and moves up and down limited by the length of the positioning sleeve (20). The threaded rod (17) is threadedly connected with the power sleeve (18). A second bearing (19) is installed inside the power sleeve (18), and the second bearing (19) cooperates with the right torsion extrusion rod (16). The upper half of the right torsion extrusion rod (16) is hollow, and a protruding part parallel to its axis is provided on the inner surface. A groove parallel to its axis is provided on the surface of the threaded rod (17). The protruding part of the right torsion extrusion rod (16) is fitted with the groove of the threaded rod (17). The lower half of the right torsion extrusion rod (16) is a solid rod with a gradually decreasing cross-sectional area and a right groove (36) opened, and the right groove (36) and the left groove (35) of the left torsion extrusion rod are partially asymmetric; The external die holder is arranged on a backing plate (38) fixed above a working platform (37) and includes a front module (15) and a rear module (41); the front module (15) and the rear module (41) are fixed by bolts (39). An extrusion space is opened inside the rear module (41). The extrusion space includes a vertical middle channel and left and right channels which are inclined and communicate with the bottom of the middle channel and are opened on the left and right sides of the rear module (41). Leakage holes which are communicated with the middle channel and have an inner diameter smaller than that of the middle channel are opened on the working platform (37) and the backing plate (38). The threaded punch (5) extends into the middle channel from top to bottom, and the left and right torsion extrusion rods respectively extend into the left and right channels; the middle channel, the left and right channels together with the leakage holes jointly form a torsion extrusion channel; heating channels (33) for the flow of organic heat carriers are arranged inside both the front module (15) and the rear module (41); The power device is a first motor (10) and a second motor (22) for driving the left and right torsion extrusion dies; wherein the first motor (10) drives the disc (8) to rotate, and the second motor (22) drives the threaded rod (17) to rotate.

2. The apparatus for preparing a high-performance fine-grained and weak-texture magnesium alloy by multi-directional dynamic torsion extrusion according to claim 1, characterized in that The rotation directions of the left and right torsion extrusion rods are opposite.

3. The apparatus for preparing a high-performance fine-grained and weak-texture magnesium alloy by multi-directional dynamic torsion extrusion according to claim 1, characterized in that A cross-shaped protrusion (34) is provided at the front end of the threaded punch (5).

4. The apparatus for preparing a high-performance fine-grained and weak-texture magnesium alloy by multi-directional dynamic torsion extrusion according to claim 1, characterized in that The materials of the front module (15), the rear module (41), the left torsion extrusion rod (14), the right torsion extrusion rod (16) and the threaded punch (5) are all 4Cr5MoSiV1 hot work die steel.

5. The apparatus for preparing a high-performance fine-grained and weak-texture magnesium alloy by multi-directional dynamic torsion extrusion according to claim 1, characterized in that The surface roughness of the left torsion extrusion rod (14) is Ra0.08 - 0.16 μm, the surface roughness of the right torsion extrusion rod (16) is Ra0.16 - 0.4 μm, and the surface roughness of the post-module extrusion space is Ra0.4 - 0.8 μm.

6. A process for preparing a high-performance fine-grained and weak-texture magnesium alloy bar by multi-directional dynamic torsion extrusion, which is realized by using the apparatus for preparing a high-performance fine-grained and weak-texture magnesium alloy by multi-directional dynamic torsion extrusion according to claim 1, characterized in that It includes the following steps: S1. Pretreatment of the magnesium alloy bar blank: S1-1. Process the magnesium alloy bar blank into a cylindrical magnesium alloy bar (40), and polish the surface of the magnesium alloy bar with 600-mesh sandpaper to remove oil stains, and then polish it with 800-mesh, 1000-mesh, and 1200-mesh sandpapers in sequence until the surface of the magnesium alloy bar (40) is smooth; S1-2. Mix acetone and absolute ethanol in a volume ratio of 3:2 in a cleaning tank and stir evenly to prepare a cleaning solution; S1-3. Immerse the magnesium alloy bar (40) prepared in step S1-1 into the cleaning solution prepared in step S1-2, place the cleaning tank on an ultrasonic cleaner to ultrasonically clean the magnesium alloy bar (40) for 60 min, then take out the magnesium alloy bar (40) and clean it with absolute ethanol, and finally dry it with a hair dryer; S1-4. Apply a graphite oil solution to the surface of the magnesium alloy bar (40) prepared in step S1-3 for later use; S2. Preheat the magnesium alloy bar (40): Set the heating temperature of the vacuum atmosphere heating furnace to 450 °C. After the furnace temperature of the heating furnace reaches the set temperature, put the magnesium alloy bar (40) into the heating furnace and keep it warm for 3 h; S3. Lubrication, assembly and preheating of the dynamic torsion extrusion deformation device: S3-1. Lubrication: Apply a graphite oil solution to the surface of the threaded punch (5), the surface of the left torsion extrusion rod (14), the surface of the right torsion extrusion rod (16), the power sleeve (18), the contact part between the positioning sleeve (20) and the second bearing (19) and the right torsion extrusion rod (16), and the inner surface of the torsion extrusion channel; S3-2. Assembly: First, install and fix the backing plate (38) on the working platform (37) of the vertical extrusion press, install the post-module (41) and the front-module (15) together with four bolts (39) and fix them on the backing plate (38). Then, assemble and insert the left torsion extrusion rod (14) into the left channel of the post-module (41) and cooperate with the second threaded pipe (13). The upper part of the left torsion extrusion rod (14) is connected to the connecting rod (9) and the wheel disc (8) through a universal ball (11). Then, penetrate the threaded rod (17) in the right torsion extrusion die into the positioning sleeve (20), the power sleeve (18) and the right torsion extrusion rod (16). Install the power sleeve (18) and the right torsion extrusion rod (16), and circumferentially fix the positioning sleeve (20) and the power sleeve (18) so that the power sleeve (18) moves up and down along the edge of the positioning sleeve (20). The power sleeve (18) cooperates with the second bearing (19) and the right torsion extrusion rod (16). Then, assemble and insert the right torsion extrusion rod (16) into the right channel, and align the position of the discharge port with the leakage hole penetrating the working platform (37) and the backing plate (38); S3-3. Preheating: Control the temperature of the medium in the heating channel (33) to 300 - 500 °C, keep it at the set temperature for 2 - 4 h for subsequent use. S4. Multi-directional dynamic torsion extrusion forming: The middle channel, the left and right channels together with the leakage hole form a torsion extrusion channel; the torsion extrusion channel includes three regions: torsion pushing region I, dynamic torsion extrusion region II, and extrusion region III arranged from top to bottom. S4-1. Withdraw the threaded punch (5) from the torsion extrusion channel, fill the magnesium alloy billet (40) in the torsion pushing region I, and then push the threaded punch (5) into the torsion extrusion channel. Operate the vertical extrusion machine, push the threaded punch (5) downward to drive the magnesium alloy billet (40) to rotate and move downward. When the magnesium alloy billet (40) reaches the dynamic torsion extrusion region II, the first motor (10) on the left drives the wheel disc (8) to rotate, the wheel disc (8) drives the connecting rod (9) to rotate, and further pushes the left torsion extrusion rod (14) to torsionally extrude the blank forward. The second motor (22) on the right drives the threaded rod (17) to rotate, drives the power sleeve (18) to move forward, and at the same time drives the right torsion extrusion rod (16) to rotate and move forward, and extrudes the magnesium alloy billet (40). During this process, as the threaded punch (5) at the top drives the magnesium alloy billet (40) to twist, the magnesium alloy billet (40) realizes spiral advancement during the asymmetric spiral extrusion on the left and right, deflects the c-axis of the magnesium alloy blank, weakens the texture and grains to achieve further refinement. When the magnesium alloy billet (40) reaches the extrusion region III, the blank is further extruded to obtain the magnesium alloy bar with the required uniform structure. During the torsion extrusion forming process, control the temperature of the medium in the heating channel (33) to 300 - 500 °C. S4-2. Take out the magnesium alloy bar prepared in step S4-1, polish its surface with sandpaper, then clean the magnesium alloy bar 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 and weak-texture high-performance magnesium alloy bar that can be directly put into use.

7. A process for preparing a high-performance fine-grained and weak texture magnesium alloy bar by multi-directional dynamic torsion extrusion according to claim 6, characterized in that, In the torsion pushing region I, the magnesium alloy billet (40) continuously twists and advances driven by the threaded punch (5). The advancing speed of the threaded punch is V3, and the torsional angular velocity is ω3. When it reaches the dynamic torsion extrusion region II, dynamic torsion extrusion with different advancing speeds and different torsional angular velocities is carried out by the torsion extrusion rods on the left and right sides respectively. The first motor (10) on the left drives the wheel disc to rotate, with a rotational angular velocity of ω4, promoting the left torsion extrusion rod (14) to move forward and rotate. The advancing speed of the left torsion extrusion rod (14) is V1, and the torsional angular velocity is ω1. The threaded rod (17) in the right torsion extrusion die rotates driven by the second motor (22), with a rotational angular velocity of ω5, driving the advancing speed of the right torsion extrusion rod (16) to be V2, and the torsional angular velocity to be ω2, and V1 ≠ V2 ≠ V3, ω1 ≠ ω2 ≠ ω3.

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