Device and method for preparing magnesium alloy sheet by three-way variable-camber differential shear extrusion

Abstract

The application belongs to the technical field of light metal plastic forming, and particularly relates to a device and method for preparing high-performance fine-grain magnesium alloy sheet through three-way variable-camber differential shear extrusion. The device comprises a vertical extruder, an external die frame, a female die, a male die and a power device. The male die slides to the middle with the downward extrusion of the left and right extrusion punches, resulting in continuous change of the channel in the dynamic differential deformation zone, and the deformation degree of the magnesium alloy blank on the left and right sides also changes, so that the magnesium alloy is subjected to dynamic extrusion force in three directions at the same time, and the magnesium alloy basal plane texture is weakened. The dynamic differential deformation channel can continuously change the flow speed of the magnesium alloy on the left and right sides in the front and back directions during the extrusion process, so that the blank further realizes differential extrusion deformation; the shear deformation of the magnesium alloy on the left and right sides and the front and back sides is different during the extrusion process, so that the magnesium alloy deforms unevenly, the deformation degree of each part is greatly different, and the basal plane texture is weakened.

Description

Technical Field

[0001] This invention belongs to the field of light metal plastic forming technology, specifically relating to an apparatus and method for preparing high-performance fine-grained magnesium alloy sheets by three-dimensional variable arc surface differential shear extrusion. Background Technology

[0002] Magnesium alloys are the least dense structural materials among metals, possessing advantages such as high specific strength and specific stiffness, good hot formability, and easy recyclability. Therefore, they occupy an important position in the automotive, 3C, aerospace, and military industries, and are hailed as "green energy materials of the 21st century." However, the close-packed hexagonal crystal structure of magnesium alloys means that only two slip systems are easily activated at room temperature, fewer than the five independent slip systems required for polycrystalline deformation. This leads to difficulties in plastic processing of magnesium alloys at room temperature, resulting in poor room-temperature mechanical properties. Furthermore, magnesium alloy sheets produced by traditional rolling and extrusion processes often exhibit strong basal texture, leading to significant anisotropy and further limiting their applications. Therefore, improving the room-temperature mechanical properties of magnesium alloy sheets is one of the urgent problems to be solved. Grain refinement can significantly improve the strength of magnesium alloys, while weakening basal texture can improve their plasticity. Therefore, various processing technologies have been widely developed, such as high-pressure torsion (HPT), multi-directional forging (MDF), and equal channel angular extrusion (ECAP). However, existing technologies have certain drawbacks, such as discontinuous processing, low efficiency, and a single extrusion channel, which limits their application to some extent. Therefore, how to obtain a new, continuous production method for processing weak-surface textured magnesium alloy sheets is an urgent problem to be solved. Summary of the Invention

[0003] This invention aims to solve the above-mentioned problems by providing a three-dimensional variable-arc differential shearing and extrusion processing apparatus and method for preparing fine-grained, weak-texture magnesium alloy sheets. Through this apparatus and processing method, the magnesium alloy billet undergoes continuous differential shearing and extrusion deformation during processing, achieving grain refinement while weakening the basal surface texture, improving the room-temperature mechanical properties of the magnesium alloy sheet, and thus expanding the application range of magnesium alloys.

[0004] The apparatus for preparing magnesium alloy sheets by three-dimensional variable arc surface differential shear extrusion as described in this invention is achieved through the following technical solution: it includes a vertical extruder, an external die frame, a concave die, a convex die, and a power unit.

[0005] The vertical extrusion press includes a base, a column fixed on the base, and a top seat fixed on the top of the column; a power unit is installed at the center of the top seat, and an extrusion telescopic head is installed at the bottom of the power unit. A main pressure block and a pair of auxiliary pressure blocks are fixed at the end of the extrusion telescopic head. An extrusion punch is fixed at the bottom of the main pressure block, and an extrusion punch is fixed at the bottom of each of the auxiliary pressure blocks. The working surface of the extrusion punch is an inclined surface, and a worktable is fixed at the center of the base.

[0006] The external mold frame includes a die fixing frame mounted on the workbench. The die fixing frames on the left and right sides have through holes. The inner walls of the die fixing frames on the front and rear sides are provided with heating sleeves. Die pads are placed inside the heating sleeves and on the workbench. The die mold is placed inside the heating sleeves and the bottom of the die mold is fixed to the die pads. The punch mold is placed inside the die mold.

[0007] The upper part of the die cavity has equidistant cylindrical extrusion channels into which the extrusion punch can extend. The middle part has a rectangular cavity that extends horizontally through which the punch can extend. The rectangular cavity extends horizontally and corresponds to the through holes of the die cavity fixing frame on the left and right sides. The bottom surface of the rectangular cavity has a shear deformation channel facing downwards. The equidistant cylindrical extrusion channels, the rectangular cavity, and the shear deformation channel are connected vertically to form the die cavity. The upper part of the rectangular cavity has two axially symmetrical arc-shaped grooves on the front and rear sides. The arc-shaped grooves gradually change from a circular arc to a horizontal straight line from top to bottom. The arc-shaped grooves and the rectangular cavity are connected vertically. The top surface and the vertical surface of the cavity are connected with rounded corners. The bottom surface of the cuboid cavity is provided with at least one sliding positioning groove on each of the left and right sides. The left and right sides of the shear deformation channel transition from the vertical edge running front and back to the middle along the lower arc edge. The two arc edges on the front side, one of which is recessed towards the middle in the horizontal direction, and the other is recessed towards the middle in both the horizontal direction and the front and back horizontal direction. The two arc edges on the rear side of the shear deformation channel are symmetrical with the two arc edges on the front side relative to the mold cavity axis, so that the horizontal cross section of the shear deformation channel gradually changes from a rectangle to a parallelogram from top to bottom.

[0008] The punch mold consists of two punches axially symmetrical about the mold cavity. Both punches are slidably positioned in sliding positioning grooves via positioning blocks at their bottoms. The opposing sides of the two punches serve as the working surface. From top to bottom, the working surface of the punch gradually changes from an outwardly convex arc to an inwardly convex arc, forming a portion of a horizontal circle of equidistant cylindrical extrusion channels, and finally becomes a vertical edge running front to back. The outwardly convex arc and the inwardly convex arc together form an outwardly convex arc surface, and the inwardly convex arc together with the horizontal line form an inwardly convex arc surface. The outwardly convex arc surface connects to the top surface of the punch mold with a rounded corner, and simultaneously connects to the inwardly convex arc surface with a rounded corner. The rounded corners gradually change from an outward convex shape to an inward convex shape from front to back. At the same time, the outward convex arc of the punch working surface and the arc above the arc groove of the die form a complete circle corresponding to the equidistant cylindrical extrusion channel. The inward convex arc and the horizontal straight line below the arc groove of the die are on the same horizontal plane. The bottom of the two punch working surfaces are in contact with the bottom surface of the cuboid cavity. The left and right sides of the punch are respectively corresponding to an extrusion punch and are inclined surfaces with the same inclination angle as the extrusion punch. The worktable and the base are provided with through holes that communicate with the bottom of the shear deformation channel.

[0009] The extrusion punch, the two punches, and the die cavity together form a relatively axially symmetrical extrusion channel. From top to bottom, the extrusion channel consists of the extrusion pushing zone I, the dynamic differential deformation zone II, and the shear extrusion deformation zone III.

[0010] In operation, the extrusion die and extrusion punch move downwards simultaneously under the action of the extrusion telescopic pressure head. This causes the magnesium alloy bar in the extrusion pushing zone to continuously advance downwards to the dynamic differential deformation zone. The upper part of the dynamic differential deformation zone consists of two concave die arc grooves and two convex arc surfaces of the left and right punches. Due to the different curvatures of the convex arc surfaces and arc grooves, the flow velocity of the magnesium alloy bar differs on different arc surfaces of this zone, resulting in differential shear deformation during extrusion. This induces the c-axis of the grains to deflect, weakening the basal texture. The lower part of the dynamic differential deformation zone consists of two vertical surfaces of the cuboid cavity of the concave die and two convex arc surfaces of the left and right punches. The two convex arc surfaces gradually become vertical, causing the flow velocity of the magnesium alloy bar on both sides to continuously change in the front-to-back direction. Simultaneously, the punches slide towards the center within the sliding positioning groove using positioning blocks as the extrusion punches on both sides press downwards. The continuous variation in deformation on the left and right sides of the magnesium alloy bar further induces differential shear deformation, refining the grain structure and weakening the basal texture. Within this channel, the horizontal cross-section of the magnesium alloy bar gradually changes from a circle to a quadrilateral composed of two curved edges on the left and right and two horizontal edges on the front and back. Finally, the curved edges on the left and right of the quadrilateral gradually straighten towards the center, becoming a rectangle, ultimately transforming the magnesium alloy bar into a magnesium alloy block. Then, when the magnesium alloy block is extruded into the shear extrusion deformation zone, it undergoes differential deformation and shear deformation in the left and right directions through the action of the curved surfaces on both sides of the channel. Simultaneously, the front and back sides of the channel gradually change from vertical to inclined surfaces, causing the right rear end and left front end of the magnesium alloy block to be subjected to forward and backward shear deformation, respectively. The combined effect of these two factors causes the c-axis of the magnesium alloy grains to tilt again, further weakening the basal texture and intensifying the deformation of the magnesium alloy. Finally, it is extruded through a hole, resulting in a fine-grained, weakly textured magnesium alloy sheet. This device enables the preparation of fine-grained, weakly textured magnesium alloy sheets through differential shearing and extrusion on a three-dimensional variable arc surface.

[0011] Furthermore, the extrusion punch, extrusion die, and die are all made of 4Cr5MoSiV1 hot work die steel.

[0012] Furthermore, the surface roughness of the working surface of the extrusion punch is Ra 0.08~0.16μm, the surface roughness of the working surface of the extrusion punch is Ra 0.04~0.08μm, the surface roughness of the working surface of the die is Ra 0.4~0.8μm, the surface roughness of the working surface of the punch is Ra 0.16~0.4μm, and the surface roughness of the left and right inclined surfaces of the punch is Ra 0.04~0.08μm. The inconsistent roughness of the die and punch in the extrusion channel creates a difference in the frictional force generated between the extrusion process and the billet, further promoting differential flow of the billet and generating shear extrusion deformation to weaken its base surface texture.

[0013] The present invention discloses a method for preparing magnesium alloy sheets by three-dimensional variable arc surface differential shear extrusion, comprising the following steps:

[0014] S1. Pretreatment of magnesium alloy blocks and bars:

[0015] S1-1. Use 600-grit sandpaper to polish the surface of the magnesium alloy bar to remove oil stains, and then use 800-grit, 1000-grit, and 1200-grit sandpaper in sequence until the surface of the magnesium alloy bar is smooth.

[0016] 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.

[0017] 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 and ultrasonically clean the magnesium alloy bar for 60 minutes, then take out the magnesium alloy billet and clean it with anhydrous ethanol, and finally dry it with a hair dryer.

[0018] S1-4. Coat the surface of the magnesium alloy rod prepared in step S1-3 with graphite oil solution for later use.

[0019] S2. Preheating of magnesium alloy bars: Set the heating temperature of the vacuum atmosphere heating furnace to 450℃. After the furnace temperature reaches the set temperature, put the magnesium alloy bars into the heating furnace and keep them warm for 3 hours.

[0020] S3. Lubrication, assembly, and preheating of the three-dimensional variable arc surface differential shear extrusion forming device:

[0021] S3-1, Lubrication: Apply graphite oil solution to the surfaces of the die cavity, arc groove and sliding positioning groove, punch surface and extrusion punch working surface;

[0022] S3-2, Assembly:

[0023] First, install and fix the die pad block on the worktable of the vertical extruder. Then, fix a front die on the die pad block. Next, fix the punch in the positioning area of ​​the sliding positioning groove of the die using a positioning block. Then, assemble the positioning area of ​​the sliding positioning groove of the rear die with the positioning block of the punch and fix it on the die pad block. Finally, the punch is assembled in the cuboid cavity of the die. Then, install the heating sleeve on the inner surface of the die fixing frame on the front and rear sides. Finally, fix the die fixing frame on the worktable with bolts. The die fixing frame with through holes is fixed on the left and right sides to ensure that the punch can slide in the left and right directions. Control the extrusion punch to move down and be placed in the top cavity of the die cavity to ensure that the extrusion punch and the die cavity are in close vertical contact.

[0024] S3-3. Preheating: Control the temperature of the heating jacket 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.

[0025] S4. Three-dimensional variable arc surface differential shear extrusion deformation forming: The extrusion punch, the die, and the punch together form the extrusion channel; the extrusion channel includes three areas arranged from top to bottom: the extrusion pushing zone I, the dynamic differential deformation zone II, and the shear extrusion deformation zone III.

[0026] S4-1. Withdraw the extrusion punch from the channel, allowing the magnesium alloy bar to fill the extrusion pushing zone I. Then, push the extrusion punch back into the channel. Operate the vertical extruder; the extrusion punch and extrusion plunger move downwards simultaneously under the action of the extrusion telescopic pressure head, causing the magnesium alloy bar in extrusion pushing zone I to continuously advance downwards to the dynamic differential deformation zone II. The upper part of the channel in dynamic differential deformation zone II consists of two front and rear arc-shaped grooves and two convex arc surfaces of the left and right punches. Due to the different degrees of curvature of the convex arc surfaces and the arc-shaped grooves, the magnesium alloy bar... The material flows at different velocities on different arc surfaces of the channel, resulting in differential shear deformation during extrusion. This induces c-axis deflection in the grains, weakening the basal texture. The lower part of the dynamic differential deformation zone II consists of the vertical surfaces of two concave dies and the inner convex arc surfaces of two convex dies. The two inner convex arc surfaces gradually become vertical, causing the flow velocity of the magnesium alloy bar to continuously change in the front-to-back direction. Simultaneously, the convex dies slide towards the center in the sliding positioning groove using positioning blocks as the extrusion punches on both sides press downwards, causing the magnesium alloy... The deformation degree of the bar stock continues to change on the left and right sides, which will further induce differential shear deformation in the magnesium alloy, refining the grain structure and weakening the basal texture. Within the dynamic differential deformation channel, the horizontal cross-section of the magnesium alloy bar stock gradually changes from a circle to a quadrilateral composed of two curved edges on the left and right sides and two horizontal edges on the front and back. Finally, the two curved edges of the quadrilateral gradually straighten towards the center, becoming a rectangle, and the magnesium alloy bar stock eventually becomes a magnesium alloy block. Then, when the magnesium alloy block is compressed into shear compression deformation zone III, the curved surfaces on both sides of the shear deformation channel... The magnesium alloy block continuously undergoes differential deformation and shear deformation in the left and right directions. At the same time, the front and rear sides of the shear deformation channel gradually change from vertical to inclined surfaces, causing the right rear end and left front end of the magnesium alloy block to be subjected to forward and backward shear deformation, respectively. Ultimately, the horizontal cross-section of the magnesium alloy block in the shear deformation channel gradually changes from a rectangle to a parallelogram from top to bottom. The combined effect of these two factors causes the c-axis of the magnesium alloy grains to tilt again, thereby further weakening the basal texture and intensifying the deformation of the magnesium alloy. Finally, it is extruded through the hole, resulting in a fine-grained, weakly textured magnesium alloy sheet.

[0027] S4-2. Take out the magnesium alloy sheet obtained in step S4-1, polish its surface with sandpaper, clean the magnesium alloy sheet 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 sheet that can be put into use directly.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. This invention has significant advantages over the prior art. As the extrusion punches on both sides extrude downwards, the punch slides towards the center, causing the channel in the dynamic differential deformation zone to change continuously. The degree of deformation of the magnesium alloy billet on the left and right sides also changes accordingly, so that the magnesium alloy is subjected to dynamic extrusion forces in three directions at the same time, thereby weakening the texture of the magnesium alloy base surface and improving the mechanical properties of the magnesium alloy.

[0030] 2. The variable arc surface and dynamic variable channel enable the flow velocity of the magnesium alloy on both sides to continuously change in the front and back directions during the extrusion process, so that the billet can further achieve differential extrusion deformation, and the grain refinement effect of magnesium alloy rod is more significant.

[0031] 3. During the extrusion process, magnesium alloys experience different shear deformations on the left and right sides and the front and back sides, resulting in uneven deformation and large differences in the degree of deformation at different locations, which weakens the base texture. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the main structure of the mold of the present invention;

[0033] Figure 2 This is a side view of the mold structure of the present invention;

[0034] Figure 3 This is a three-dimensional schematic diagram of the mold of the present invention;

[0035] Figure 4 This is a schematic diagram of the front view structure of the concave mold of the present invention;

[0036] Figure 5 This is a side view of the concave mold of the present invention.

[0037] Figure 6 for Figure 4 A top view of the inner rectangular cavity;

[0038] Figure 7 This is a schematic diagram of the extrusion channel of the present invention;

[0039] Figure 8 for Figure 7 Top view of the extrusion channel;

[0040] Figure 9This is a diagram showing the changes in the extrusion channel during the extrusion process of the present invention;

[0041] Figure 10 This is a schematic diagram of the shape of the billet inside the extrusion channel;

[0042] In the diagram: 1-Electrical control box; 2-Wire; 3-Base; 4-Top seat; 5-Column; 6-Pressure motor; 7-Extrusion telescopic head; 8-Main pressure block; 9-Extrusion punch; 10-Secondary pressure block; 11-Extrusion punch; 12-Die die; 13-Punch die; 14-Die pad; 15-Die fixing frame; 16-Heating jacket; 17-Bolt; 18-Workbench; 19-Display screen; 20-Start button; 21-Stop button; 22-Emergency stop button; 23-Heating jacket controller; 24-Pressure motor controller; 25-Telescopic device controller; 26-Equidistant cylindrical extrusion channel; 27-Cuboid cavity; 28-Arc groove; 29-Sliding positioning groove; 30-Shear deformation channel; 31-Positioning block; 32-Dynamic differential deformation channel;

[0043] 12-1-Front die, 12-2-Rear die, 13-1-Left punch, 13-2-Right punch; 29-1-Opening area, 29-2-Positioning area, 29-3-Sliding area;

[0044] Ⅰ-Extrusion pushing zone; Ⅱ-Dynamic differential deformation zone; Ⅲ-Shear extrusion deformation zone. Detailed Implementation

[0045] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0046] In the description of this invention, it should be understood that the terms "center," "middle," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the purpose of simplifying the description of this invention and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0047] This invention provides an apparatus for preparing fine-grained, weakly textured magnesium alloy sheets by three-dimensional variable-arc differential shear extrusion, comprising a vertical extruder, an external die frame, a concave die, a convex die, and a power unit, wherein:

[0048] like Figure 1 , 9As shown, the vertical extrusion press includes a base 3, a column 5 fixed on the base 3, and a top seat 4 fixed on the top of the column 5; a pressure motor 6 is installed at the center of the top seat 4, and an extrusion telescopic head 7 is installed at the bottom of the pressure motor 6. A main pressure block 8 and a secondary pressure block 10 are fixed at the end of the extrusion telescopic head 7. An extrusion punch 9 is fixed at the bottom of the main pressure block 8, and an extrusion punch 11 is fixed at the bottom of the secondary pressure block 10. The inner working surface of the extrusion punch 11 is an inclined surface with an inclination angle θ1 of 7°-10° and a height H5 of 65-85mm. A worktable 18 is fixed at the center of the base 3.

[0049] like Figure 2 As shown, the external mold frame includes a die fixing frame 15 mounted on the worktable 18. The die fixing frames 15 on the left and right sides have through holes with a width (left-right direction) W1 of 22-42mm and a height H1 of 86-106mm. Heating sleeves 16 are provided on the inner walls of the die fixing frames 15 on the front and rear sides. Die pads 14 are placed inside the heating sleeves 16 and on the worktable 18. The die mold 12 is placed inside the heating sleeves 16 and the bottom of the die mold 12 is fixed to the die pads 14. The punch mold 13 is placed inside the die mold 12 and passes through the through hole.

[0050] like Figure 3 , 4As shown in Figures 5 and 8, the die cavity 12 consists of two axially symmetrical concave dies 12-1 and 12-2. The upper part of the die cavity 12 is provided with equidistant cylindrical extrusion channels 26 into which the extrusion punch 9 can extend. The diameter d1 of the equidistant cylindrical extrusion channels is 70-90mm and the height H2 is 54-74mm. The middle part is provided with a rectangular parallelepiped cavity 27 through which the punch 13 can extend. The width W1 of the rectangular parallelepiped cavity 27 is 22-42mm and the height H1 is 86-106mm. The rectangular parallelepiped cavity 27 extends through the left and right side through holes of the die cavity fixing frame 15. The upper front and rear sides of the rectangular parallelepiped cavity 27 are provided with two arcs axially symmetrical with respect to the die cavity. The surface groove 28 gradually changes from a circular arc to a horizontal straight line from top to bottom. The circular arc is part of the horizontal circle of the extrusion channel, and the line connecting the left and right endpoints of the arc is horizontal, with a distance L1 of 12-20mm from the horizontal line at the center of the mold cavity. The horizontal straight line of the arc groove 28 is 43-53mm from the bottom height H3 of the cuboid cavity. The vertical width W2 of the left endpoint from the left endpoint of the arc is 26-34mm, and the radius R1 of the arc between the two endpoints is 50-70mm. The vertical width W3 of the right endpoint of the horizontal line from the right endpoint of the arc is 10-16mm, and the radius R2 of the arc between the two endpoints is 120-140mm. The arc groove intersects with the top surface and vertical surface of the cavity. All joints are rounded, with radii r2 of 6-10mm and r1 of 1-5mm. The bottom surface of the cuboid cavity 27 has four sliding positioning grooves 29 with a height H4 of 6-10mm. Each sliding positioning groove 29 is divided into three areas: an opening area 29-1 with a length (front-back direction) L3 of 6-10mm and a width W3 of 14-18mm; a positioning area 29-2 with a length L2 of 6-10mm and a width W3 of 14-18mm; and a sliding area 29-3 with a length L2 of 6-10mm and a width W4 of 6-10mm. The cuboid cavity 27 extends horizontally, corresponding to the through holes of the left and right mold fixing frames 15. The lower end of the mold die 12 has a shearing deformation channel 3. 0. The left and right sides of the shear deformation channel 30 transition from the vertical edges running front and back to the middle along the arc edges. The two arc edges on the front side of the shear deformation channel 30, one of which is recessed in the middle by W5 for 60-70mm in the horizontal direction, and the other is recessed in the middle by W5 for 7-11mm in the horizontal direction on the left and right sides, and also recessed in the middle by L4 for 1-3mm in the horizontal direction on the front and back sides. The two arc edges on the rear side of the shear deformation channel 30 are symmetrical with respect to the cavity axis with respect to the two arc edges on the front side. Finally, the horizontal cross section of the shear deformation channel 30 gradually changes from a rectangle with a length L5 of 28-36mm and a width W7 of 18-22mm from top to bottom into a parallelogram with a length L6 of 29-31mm and a width W6 of 1-3mm.

[0051] like Figure 6 , 7As shown in Figure 8, the punch mold 13 consists of two axially symmetrical punches, a left punch 13-1 and a right punch 13-2. The punch's working surface gradually changes from a convex arc (part of the horizontal circle of the extrusion channel) to an inward convex arc (radius R3 of 30-50mm) from top to bottom, and finally to a vertical edge with a length L5 of 28-36mm running forward and backward. The convex arc and the inward convex arc together form the convex arc surface. The front arc radius R4 of the convex arc is 120-140mm, and the rear arc radius R5 is 50-70mm. The inward convex arc and the vertical edge together form the inward convex arc surface. The front arc radius R6 of the inward convex arc is 80-90mm, and the rear arc radius R7 is 240-260mm. The convex arc surface is connected to the top surface of the punch mold 13 by a rounded corner with a radius r2 of 6-10mm, and simultaneously connected to the inward convex arc surface. The rounded corners connect the two parts. The rounded corners smoothly transition from an outward convex shape with a radius r3 of 3-7mm to an inward convex shape with a radius r4 of 3-7mm from front to back. At the same time, the outward convex arc of the working surface of the punch mold 13 and the arc above the arc groove 28 of the die mold together form a complete circle corresponding to the cylindrical extrusion channel. The inward convex arc and the horizontal straight line below the arc groove 28 of the die mold are on the same horizontal plane. The bottom of the working surface of the punch mold 13 and the two vertical sides (i.e. the left and right sides of the rectangle) of the entrance to the shear deformation channel in the lower part of the die mold 12 are parallel to each other on the same horizontal plane. The bottom of the punch mold 13 is provided with four positioning blocks 31. The positioning blocks 31 fit into the positioning area 29-2 in the sliding positioning groove 29. The left and right sides of the punch mold 13 are inclined surfaces with the same inclination angle θ1 as the extrusion punch 11 and a height H6 of 86-106mm.

[0052] Combination Figure 4 , 6 As shown in Figure 7, the punch mold 13 is first fixed in the positioning area 29-2 of the sliding positioning groove 29 of the front die 12-1 by the positioning block 31. Then, the sliding positioning groove 29 of the rear die 12-2 is assembled with the positioning block 31 of the punch mold, so that the punch mold 13 is finally assembled in the cuboid cavity 27 of the die mold 12. The punch mold 13 and the die mold 12 together form a differential shearing channel. At the same time, the left and right inclined surfaces of the punch mold 13 match the inclined surfaces of the extrusion punch 11. The extrusion punch 11 can push the punch mold downward to slide towards the middle, from the positioning area 29-2 to the sliding area 29-3, so that the original differential shearing channel becomes a dynamic differential deformation channel 32.

[0053] The power unit is a pressure motor 6 that drives the extrusion punch 9 and the extrusion punch 11.

[0054] Furthermore, the extrusion channel is a relatively axially symmetrical channel, consisting of an extrusion pushing zone I, a dynamic differential deformation zone II, and a shearing extrusion deformation zone III from top to bottom. First, the extrusion punch 9 and the extrusion plunger 11 move downwards simultaneously under the action of the extrusion telescopic head 7, causing the magnesium alloy bar in the extrusion pushing zone I to continuously advance downwards to the dynamic differential deformation zone II. The upper part of the channel in the dynamic differential deformation zone II is composed of the arc grooves 28 of the two concave dies and the convex arc surfaces of the two convex dies 13. Due to the different curvatures of the convex arc surfaces and the arc grooves 28, the flow velocity of the magnesium alloy bar differs on different arc surfaces of this channel, resulting in differential shearing deformation during the extrusion process. This induces the c-axis of the grains to deflect, weakening the basal texture. The dynamic differential deformation zone II... The lower part consists of two vertical surfaces of front and rear concave dies 12 and two inner convex arc surfaces of left and right convex dies 13. The two inner convex arc surfaces gradually become vertical, causing the flow velocity of the magnesium alloy bar to continuously change in the front-to-back direction on both sides. At the same time, as the extrusion punches 11 on both sides extrude downwards, the convex dies 13 slide towards the center in the sliding positioning groove 29 using the positioning block 31, causing the deformation degree of the magnesium alloy bar to continuously change on both sides. This will further induce differential shear deformation in the magnesium alloy, further refining the grain structure and weakening the basal texture. The magnesium alloy bar is in the dynamic differential deformation channel 32. The horizontal cross-section gradually transforms from a circle with a diameter d1 of 70-90mm at top to bottom into a quadrilateral composed of two arc edges with radii R3 of 30-50mm on the left and right sides and two horizontal sides with a width W8 of 26-32mm at the front and back. Finally, the two arc edges of the quadrilateral gradually straighten towards the center, becoming a rectangle with a length L5 of 28-36mm and a width W9 of 3-6mm. Ultimately, the magnesium alloy bar is transformed into a magnesium alloy block. Then, when the magnesium alloy block is extruded into the shear extrusion deformation zone III, through the action of the arc surfaces on both sides of the shear extrusion channel 30, the magnesium alloy block continuously undergoes differential deformation and shear deformation in the left and right directions. Simultaneously, the front and rear sides of the shear deformation channel 30 gradually change from vertical to inclined surfaces, causing the right rear end and left front end of the magnesium alloy block to undergo forward and backward shear deformation, respectively. Ultimately, the horizontal cross-section of the magnesium alloy block within the shear deformation channel 30 gradually changes from a rectangle with a length L5 of 28-36 mm and a width W9 of 3-6 mm to a parallelogram with a length L6 of 29-31 mm and a width W6 of 1-3 mm. The combined effect of these two factors causes the c-axis of the magnesium alloy grains to tilt again, further weakening the basal texture and intensifying the deformation of the magnesium alloy. Finally, the grains are extruded through a through-hole, resulting in a fine-grained, weakly textured magnesium alloy sheet. This device can achieve the preparation of fine-grained, weakly textured magnesium alloy sheets through triaxial variable-arc differential shear extrusion deformation.

[0055] Furthermore, the extrusion punch 9, extrusion punch 11, die 12 and punch 13 are all made of 4Cr5MoSiV1 hot work die steel.

[0056] Furthermore, the surface roughness of the working surface of the extrusion punch 9 is Ra 0.08~0.16μm, the surface roughness of the working surface of the extrusion punch 10 is Ra 0.04~0.08μm, the surface roughness of the working surface of the die 12 is Ra 0.4~0.8μm, the surface roughness of the working surface of the punch 13 is Ra 0.16~0.4μm, and the surface roughness of the left and right inclined surfaces of the punch 13 is Ra 0.04~0.08μm. The inconsistent roughness of the die and punch in the extrusion channel creates a difference in the frictional force generated between the extrusion process and the billet, further promoting differential flow of the billet and generating shear extrusion deformation to weaken its base surface texture.

[0057] In this specific embodiment, before preparing fine-grained, weakly textured magnesium alloy plates by triaxial variable arc surface differential shear extrusion deformation, the materials and chemical reagents required for the preparation process are carefully selected:

[0058] 1. Magnesium alloy billet: round bar stock, material selected is AZ31, containing 96% magnesium, 3% aluminum and 1% zinc;

[0059] 2. Sandpaper: Solid.

[0060] 3. Graphite oil solution: a viscous liquid;

[0061] 4. Anhydrous ethanol: Liquid, purity 99.5%;

[0062] 5. Acetone: Liquid, 99% purity.

[0063] A method for preparing fine-grained, weakly textured magnesium alloy sheets by three-dimensional variable-arc surface differential shear extrusion deformation includes the following steps:

[0064] S1. Pretreatment of magnesium alloy blocks and bars:

[0065] S1-1. Use 600-grit sandpaper to polish the surface of the magnesium alloy bar to remove oil stains, and then use 800-grit, 1000-grit, and 1200-grit sandpaper in sequence until the surface of the magnesium alloy bar is smooth.

[0066] 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.

[0067] S1-3. Immerse the magnesium alloy rod prepared in step S1-1 into the cleaning solution prepared in step S1-2, place the cleaning tank on an ultrasonic cleaner and ultrasonically clean the magnesium alloy rod for 60 minutes, then take out the magnesium alloy rod and clean it with anhydrous ethanol, and finally dry it with a hair dryer.

[0068] S1-4. Coat the surface of the magnesium alloy rod prepared in step S1-3 with graphite oil solution for later use.

[0069] S2. Preheating of magnesium alloy bars: Set the heating temperature of the vacuum atmosphere heating furnace to 450℃. After the furnace temperature reaches the set temperature, put the magnesium alloy bars into the heating furnace and keep them warm for 3 hours.

[0070] S3. Lubrication, assembly, and preheating of the three-dimensional variable arc surface differential shear extrusion forming device:

[0071] S3-1, Lubrication: Apply graphite oil solution to the surface of the cavity of the concave mold 12, the surface of the arc groove 28 and the sliding positioning groove 29, the surface of the punch 13, and the working surface of the extrusion punch 11.

[0072] S3-2, Assembly:

[0073] First, the die pad 14 is installed and fixed on the worktable 18 in the middle of the vertical extruder. Then, a front die 12-1 is fixed on the die pad 14. Next, the punch 13 is fixed in the positioning area 29-2 of the sliding positioning groove 29 of the die 12-1 by the positioning block 31. Then, the positioning area 29-2 of the sliding positioning groove 29 of the rear die 12-2 is assembled with the positioning block 31 of the punch 13 and fixed on the die pad 14. Finally, the punch 13 is assembled on the die 12-1. Inside the rectangular cavity 27 of 2, the heating sleeve 16 is installed on the inner surface of the die fixing frame 15 on the front and rear sides. Finally, the die fixing frame 15 is fixed to the worktable 18 with bolts 17. The die fixing frame 15 with through holes is fixed on the left and right sides to ensure that the punch mold 13 can slide in the left and right directions, control the extrusion punch mold 9 to descend and be placed in the top cavity of the die mold 12, so as to ensure that the extrusion punch mold 9 and the die mold 12 are in close vertical contact.

[0074] S3-3. Preheating: Control the temperature of heating jacket 16 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.

[0075] S4. Three-dimensional variable arc surface differential shear extrusion deformation forming: Extrusion punch 9, die 12 and punch 13 together form an extrusion channel; the extrusion channel includes three areas arranged from top to bottom: extrusion pushing area I, dynamic differential deformation area II and shear extrusion deformation area III.

[0076] S4-1. The extrusion punch 9 is withdrawn from the channel, allowing the magnesium alloy bar to fill the extrusion pushing zone I. Then, the extrusion punch 9 is pushed back into the channel. The vertical extruder is operated, and the extrusion punch 9 and extrusion plunger 11 move downwards simultaneously under the action of the extrusion telescopic head 7. This causes the magnesium alloy bar in extrusion pushing zone I to continuously advance downwards to the dynamic differential deformation zone II. The upper part of the channel in dynamic differential deformation zone II is composed of the arc-shaped grooves 28 of the front and rear concave dies and the convex arc surfaces of the left and right punches 13. Due to the different degrees of curvature of the convex arc surfaces and the arc-shaped grooves 28, the flow speed of the magnesium alloy bar differs on different arc surfaces of this channel. During the extrusion process, differential shear deformation occurs, inducing the c-axis of the grains to deflect and weakening the basal texture. The lower part of the dynamic differential deformation zone II consists of the vertical surfaces of two concave dies 12 and the inner convex arc surfaces of two convex dies 13. The two inner convex arc surfaces gradually become vertical, causing the flow velocity of the magnesium alloy bar on both sides to continuously change in the front-back direction. At the same time, as the extrusion punches 11 on both sides extrude downwards, the convex dies 13 slide towards the center in the sliding positioning groove 29 using the positioning block 31, causing the degree of deformation of the magnesium alloy bar on both sides to continuously change, which will further induce differential shear deformation on the magnesium alloy bar, and the grain structure will be refined again. The texture of the base surface is weakened again. Within the dynamic differential deformation channel 32, the horizontal cross-section of the magnesium alloy bar gradually changes from a circle with a diameter d1 of 70-90mm to a quadrilateral composed of two arc edges with radii R3 of 30-50mm on the left and right sides and two horizontal sides with a width W8 of 26-32mm on the front and back. Finally, the two arc edges of the quadrilateral gradually straighten towards the center, becoming a rectangle with a length L5 of 28-36mm and a width W9 of 3-6mm. Ultimately, the magnesium alloy bar first transforms into a magnesium alloy block. Then, when the magnesium alloy block is compressed into the shear compression deformation zone III, through the action of the arc surfaces on both sides of the shear deformation channel 30, the magnesium alloy block continuously undergoes... Differential deformation and lateral shear deformation, with the shear deformation channel 30 gradually changing from a vertical plane to an inclined plane, cause the right rear end and left front end of the magnesium alloy block to be subjected to forward and backward shear deformation respectively. Ultimately, the horizontal cross-section of the magnesium alloy block within the shear deformation channel 30 gradually changes from a rectangle with a length L5 of 28-36 mm and a width W9 of 3-6 mm to a parallelogram with a length L6 of 29-31 mm and a width W6 of 1-3 mm from top to bottom. The combined effect of these two factors causes the c-axis of the magnesium alloy grains to tilt again, further weakening the basal texture and intensifying the deformation of the magnesium alloy. Finally, it is extruded through a through-hole, obtaining a fine-grained, weakly textured magnesium alloy sheet. This device can realize the preparation of fine-grained, weakly textured magnesium alloy sheets through three-dimensional variable-arc surface differential shear extrusion deformation. During the extrusion forming process, the heating jacket temperature is controlled at 300~500℃.

[0077] S4-2. Take out the magnesium alloy sheet obtained in step S4-1, polish its surface with sandpaper, clean the magnesium alloy sheet 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 sheet that can be put into use directly.

[0078] A specific embodiment of the apparatus and process for preparing fine-grained, weakly textured magnesium alloy plates by three-dimensional variable arc surface differential shear extrusion deformation includes the following steps:

[0079] (1) Install the upper extrusion die and the external die frame on the vertical extruder. The connection relationship of each part must be correct, and the operation should be carried out in sequence.

[0080] (2) Polish the outer surface of the AZ31 magnesium alloy bar with 600 grit sandpaper to remove oil stains, and then polish it with 1000, 1200 and 2500 grit sandpaper in sequence to ensure that the surface is clean and smooth; place the polished magnesium alloy bar in a mixture 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;

[0081] (3) Turn on the vacuum atmosphere heating furnace to preheat the magnesium alloy bar. The preset temperature is 400℃. When the preset temperature is reached, continue to keep the magnesium alloy bar in the heating furnace for 3 hours.

[0082] (4) Turn on the extrusion mold cavity heating device to heat the extrusion mold cavity I, II and III areas. The heating temperature is preset to 400℃. After reaching the preset temperature, continue to keep it warm for 3 hours.

[0083] (5) Remove the extrusion punch 9 from the equidistant cylindrical extrusion channel 26, apply high-temperature graphite oil solution to the surface of the magnesium alloy bar for lubrication, so that the magnesium alloy bar fills the extrusion pushing area I, and then push the extrusion punch 9 into the equidistant cylindrical extrusion channel 26.

[0084] (6) In this invention, the surface roughness of the working surface of the extrusion punch 9 is Ra0.08~0.16μm, the surface roughness of the working surface of the extrusion punch 11 is Ra0.04~0.08μm, the surface roughness of the working surface of the die 12 is Ra0.4~0.8μm, the surface roughness of the working surface of the punch 13 is Ra0.16~0.4μm, and the surface roughness of the left and right inclined surfaces of the punch 13 is Ra0.04~0.08μm.

[0085] (7) Turn on the motor of the vertical extruder, set the pressure to 400MPa, and turn on the motor at the same time. The vertical extruder pushes the extrusion punch 9 and the extrusion punch 11 downwards at a speed of V1=40mm / min; at the same time, the inner working surface of the extrusion punch 11 is an inclined surface with an inclination angle θ1 of 7° and a height H5 of 75mm; the diameter d1 of the equidistant cylindrical extrusion channel is set to 80mm, and the channel height H2 is set to 64mm; the width W1 of the cuboid cavity 27 is set to 32mm, and the height H1 is set to 96mm; the line connecting the top arc end of the inner arc groove 28 of the cuboid cavity 27 is a horizontal line and the distance L1 from the center horizontal line is set to 16mm; the distance H3 from the horizontal line of the arc groove 28 to the bottom of the cuboid cavity 27 is set to 48mm, and the left The vertical width W2 of the distance from the left endpoint of the arc is set to 29mm, and the arc radius R1 between the two endpoints is set to 60mm. The vertical width W3 of the distance from the right endpoint of the horizontal line to the right endpoint of the arc is set to 13mm, and the arc radius R2 between the two endpoints is set to 130mm. The fillet radii r2 and r1 at the intersection of the arc groove with the top surface of the cavity and the vertical surface are set to 8mm and 3mm respectively. The height H4 of the sliding positioning groove 29 is set to 8mm. The length L3 of the opening area 29-1 is set to 8mm, and the width W3 is set to 16mm. The length L2 of the positioning area 29-2 is set to 8mm, and the width W3 is set to 16mm. The length L2 of the sliding area 29-3 is set to 8mm. mm, width W4 is set to 8mm; the two arc edges on the front side of the shear deformation channel 30, one is recessed in the middle in the horizontal direction with W5 set to 9mm, the other is recessed in the middle in both the horizontal direction with W5 set to 9mm and in the middle in the vertical direction with L4 set to 2mm, the two arc edges on the rear side of the shear deformation channel 30 are symmetrical with respect to the axial direction of the cavity, so that the horizontal cross section of the shear deformation channel 30 gradually changes from a rectangle with length L5 of 32mm and width W7 of 20.8mm from top to bottom into a parallelogram with length L6 of 30mm and width W6 of 2mm; the radius of the arc of the inner convex arc of the punch mold 13 is 40mm, the punch mold 13 acts The vertical side length L5 of the front and back direction of the surface is set to 32mm; the front arc radius R4 of the outer convex arc is set to 130mm, the rear arc radius R5 is set to 60mm, the front arc radius R6 of the inner convex arc is set to 85mm, and the rear arc radius R7 is set to 250mm. The outer convex arc surface is connected to the top surface of the punch mold 13 with a fillet radius r2 of 8mm, and is also connected to the inner convex arc surface with a fillet radius. The fillet is smoothly transitioned from the outer convex shape with a fillet radius r3 of 5mm to the inner convex shape with a fillet radius r4 of 5mm from front to back; the left and right sides of the punch mold 13 are set as inclined surfaces with the same inclination angle θ1 as the extrusion punch 11 and a height H6 of 96mm.As the magnesium alloy bar advances downwards to the dynamic differential deformation zone II, the varying degrees of curvature between the convex arc surface and the arc groove 28 in the upper part of the zone cause different flow velocities of the magnesium alloy bar on different arc surfaces within this zone. This results in differential shear deformation during extrusion, inducing grain c-axis deflection and weakening the basal texture. In the lower part of the dynamic differential deformation zone II, the gradual verticalization of the two inner convex arc surfaces causes the flow velocity of the magnesium alloy bar on both sides to continuously change in the front-to-back direction. Simultaneously, the punch... 13. As the extrusion punches 11 on both sides extrude downwards, the positioning block 31 slides towards the center in the sliding positioning groove 29, causing the deformation degree of the magnesium alloy bar to continuously change on the left and right sides. This further induces differential shear deformation in the magnesium alloy, refining the grain structure and weakening the basal texture. Within the dynamic differential deformation channel 32, the horizontal cross-section of the magnesium alloy bar gradually changes from top to bottom from a circle with a diameter d1 of 70-90 mm to two arc edges with a radius R3 of 30-50 mm on the left and right sides and two arc edges with a width W8 of 2 mm on the front and back. The quadrilateral, composed of horizontal sides of 6-32mm, gradually straightens towards the center on the left and right sides, becoming a rectangle with a length L5 of 28-36mm and a width W9 of 3-6mm. The magnesium alloy bar is then transformed into a magnesium alloy block. Next, when the magnesium alloy block is extruded into the shear deformation zone III, it undergoes differential deformation and lateral shear deformation through the arc surfaces on both sides of the shear deformation channel 30. Simultaneously, the front and rear sides of the shear deformation channel 30 gradually change from vertical to inclined surfaces, causing the right rear end and left... The front end is subjected to forward and backward shear deformation, ultimately causing the horizontal cross-section of the magnesium alloy block within the shear deformation channel 30 to gradually change from a rectangle with a length L5 of 28-36 mm and a width W9 of 3-6 mm from top to bottom into a parallelogram with a length (front-back direction) L6 of 29-31 mm and a width (left-right direction) W6 of 1-3 mm. The combined effect of these two changes causes the c-axis of the magnesium alloy grains to tilt again, further weakening the basal texture and intensifying the deformation of the magnesium alloy. Finally, it is extruded through a through hole, resulting in a fine-grained, weakly textured magnesium alloy sheet.

[0086] Conclusion: The apparatus and process for preparing fine-grained, weakly textured magnesium alloy rods by three-dimensional variable arc surface differential shear extrusion according to the present invention significantly reduces the average grain size of the magnesium alloy sheet compared to conventional magnesium alloys, from the original 45.6 μm to 3.2 μm. The basal texture is effectively weakened compared to the initial magnesium alloy rod material, and the mechanical properties of the magnesium alloy are effectively improved.

[0087] Materials and chemical reagents used: AZ31 magnesium alloy rod with a diameter d=80mm and a diameter height H=64mm; sandpaper: SiC, 600 mesh, 2 sheets; 1000 mesh, 2 sheets; 1200 mesh, 2 sheets; 2500 mesh, 2 sheets; high-temperature graphite oil solution: C, 500g; anhydrous ethanol: CH3CH2OH, 1200ml; acetone: C3H6O, 800ml. The principle of obtaining fine-grained, weakly textured magnesium alloy rods through the above steps is described in detail below with reference to the accompanying drawings:

[0088] 1) Dimensional parameters of the extrusion channel: The radii of the arcs on the front and back sides of the convex surface in the extrusion channel are different from those on the inner convex surface, i.e., R4≠R6; R5≠R7. At the same time, the radii of the arcs on the front sides of the convex and inner convex surfaces are different from those on the back sides, i.e., R4≠R5; R6≠R7. This causes the flow velocity of the magnesium alloy to change continuously in the vertical and front-back directions during the extrusion process, resulting in differential shear deformation of the material. This causes the c-axis of the magnesium alloy bar grains to deflect, weakening the basal texture of the magnesium alloy and refining the grains.

[0089] 2) Variable arc surface dynamic variable channel extrusion process: The vertical extruder pushes the extrusion punch and extrusion plunger downwards simultaneously. The magnesium alloy bar is continuously advanced under the extrusion of the extrusion punch and reaches the dynamic differential deformation zone II. At the same time, the extrusion punch slides towards the middle as the extrusion plungers on both sides extrude downwards, so that the magnesium alloy bar is subjected to triaxial stress at the same time. When the extrusion punch slides downwards and fills the extrusion pushing zone I, the punch positioning block slides from the positioning zone and fills the sliding zone. This causes the channel in the dynamic differential deformation zone II to change continuously during one extrusion process, so that the billet can further achieve differential extrusion deformation, and the grain refinement effect of the magnesium alloy bar is more significant.

[0090] Based on the above two principles, the magnesium alloy bar undergoes extensive differential shearing and extrusion deformation to obtain a fine-grained, weak-matrix textured magnesium alloy sheet.

[0091] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An apparatus for preparing magnesium alloy sheets by three-dimensional variable arc surface differential shearing and extrusion, characterized in that, Includes a vertical extruder, an external die set, a die cavity (12), a punch die (13), and a power unit: The vertical extrusion press includes a base (3), a column (5) fixed on the base (3), and a top seat (4) fixed on the top of the column (5); a power unit is installed at the center of the top seat (4), and an extrusion telescopic head (7) is installed at the bottom of the power unit. A main pressure block (8) and a pair of auxiliary pressure blocks (10) are fixed at the end of the extrusion telescopic head (7). An extrusion punch (9) is fixed at the bottom of the main pressure block (8), and an extrusion punch (11) is fixed at the bottom of each of the auxiliary pressure blocks (10). The working surface of the extrusion punch (11) is an inclined surface. A worktable (18) is fixed at the center of the base (3). The external mold frame includes a die fixing frame (15) installed on the workbench (18). The die fixing frames (15) on the left and right sides are provided with through holes. The inner walls of the die fixing frames (15) on the front and rear sides are provided with heating sleeves (16). Die pads (14) are placed inside the heating sleeves (16) and on the workbench (18). The die mold (12) is placed inside the heating sleeves (16) and the bottom of the die mold (12) is fixed to the die pads (14). The punch mold (13) is placed inside the die mold (12). The upper part of the die cavity (12) is provided with equidistant cylindrical extrusion channels (26) into which the extrusion punch (9) can extend. The middle part is provided with a rectangular cavity (27) that extends from left to right into which the punch (13) can extend. The rectangular cavity (27) extends from left to right and corresponds to the through holes of the die cavity fixing frame (15) on the left and right sides. The bottom surface of the rectangular cavity (27) is provided with a shear deformation channel (30). The equidistant cylindrical extrusion channels (26), the rectangular cavity (27) and the shear deformation channel (30) extend from top to bottom to form the die cavity (12). The upper front and rear sides of the rectangular cavity (27) are provided with two arc-shaped grooves (28) that are axially symmetrical to the die cavity. The arc-shaped grooves (28) gradually change from top to bottom. The arc becomes a horizontal straight line. The arc groove (28) and the top and vertical surfaces of the cuboid cavity (27) are connected with rounded corners. At least one sliding positioning groove (29) is provided on each of the left and right sides of the bottom surface of the cuboid cavity (27). The left and right sides of the shear deformation channel (30) transition from the vertical edge running front and back to the middle along the lower arc edge. The two front arc edges, one of which shrinks towards the middle in the horizontal direction, and the other shrinks towards the middle in both the horizontal direction and the front and back horizontal direction. The two rear arc edges of the shear deformation channel (30) are symmetrical with the two front arc edges relative to the mold cavity axis, so that the horizontal cross section of the shear deformation channel (30) gradually changes from a rectangle to a parallelogram from top to bottom. The punch mold (13) consists of two punches axially symmetrical about the cavity. Both punches are slidably limited in the sliding positioning groove (29) by the positioning block (31) at their bottom. The opposite side of the two punches serves as the working surface. The working surface of the punch gradually changes from an outward convex arc to an inward convex arc from a part of the horizontal circle of the equidistant cylindrical extrusion channel (26) from top to bottom, and finally becomes a vertical edge running front to back. The outward convex arc and the inward convex arc together form an outward convex arc surface, and the inward convex arc and the vertical edge together form an inward convex arc surface. The outward convex arc surface is connected to the top surface of the punch mold (13) with rounded corners, and at the same time connected to the inward convex arc surface with rounded corners. The rounded corners run from front to back. The outer convex shape gradually becomes the inner convex shape; at the same time, the outer convex arc of the punch working surface and the arc above the arc groove (28) of the die (12) together form a complete circle corresponding to the equidistant cylindrical extrusion channel (26), the inner convex arc and the horizontal straight line below the arc groove (28) of the die are on the same horizontal plane, the bottom of the two punch working surfaces are in contact with the bottom surface of the cuboid cavity (27), the left and right sides of the punch (13) are respectively corresponding to an extrusion punch (11) and are inclined surfaces with the same inclination angle as the extrusion punch (11); the worktable (18) and the base (3) are provided with through holes that communicate with the bottom of the shear deformation channel (30); The extrusion punch (9), the two punches and the die cavity (12) together form a relatively axially symmetrical extrusion channel. The extrusion channel consists of the extrusion pushing zone I, the dynamic differential deformation zone II and the shear extrusion deformation zone III from top to bottom.

2. The apparatus for preparing magnesium alloy sheets by three-dimensional variable arc surface differential shearing and extrusion as described in claim 1, characterized in that, The inner working surface of the extrusion punch (11) is an inclined surface with an inclination angle θ1 of 7°-10° and a height H5 of 65-85mm; The through hole width W1 of the left and right side die fixing frame (15) is 22-42mm and the height H1 is 86-106mm; The die (12) consists of two axially symmetrical front dies (12-1) and rear dies (12-2) with respect to the cavities. The equidistant cylindrical extrusion channels (26) have a diameter d1 of 70-90 mm and a height H2 of 54-74 mm. The cuboid cavity (27) has a width W1 of 22-42 mm and a height H1 of 86-106 mm. The arc-shaped groove (28) gradually changes from a circular arc to a horizontal straight line from top to bottom, wherein the circular arc is the equidistant cylindrical extrusion channel. The channel (26) is part of a horizontal circle, and the line connecting the two ends of the arc is a horizontal line on the left and right sides. The distance L1 between the horizontal line of the center of the extrusion channel is 12-20mm. The horizontal line at the bottom of the arc groove (28) is 43-53mm from the bottom height H3 of the cuboid cavity (27). The distance W2 between the left end point and the left end point of the arc is 26-34mm in the vertical direction. The radius R1 of the arc between the two ends is 50-70mm. The distance between the right end point of the horizontal line and the right end point of the arc is 50-70mm. The vertical width W3 of the endpoint is 10-16mm, and the radius of the arc between the two endpoints R2 is 120-140mm. The arc groove (28) and the top and vertical surfaces of the cuboid cavity (27) are connected with rounded corners, with rounded corner radii of r2 being 6-10mm and r1 being 1-5mm respectively. The two arc edges on the front side of the shear deformation channel (30) are one recessed towards the middle in the left and right horizontal direction by W5 for 60-70mm, and the other is along the left and right horizontal direction. The horizontal direction is recessed towards the center by W5 for 7-11mm, and the horizontal direction is also recessed towards the center by L4 for 1-3mm. The two arc edges on the rear side of the shear deformation channel (30) are symmetrical with the two arc edges on the front side relative to the cavity axis. Finally, the horizontal section of the shear deformation channel (30) gradually changes from a rectangle with a length of L5 of 28-36mm and a width of W7 of 18-22mm to a parallelogram with a length of L6 of 29-31mm and a width of W6 of 1-3mm from top to bottom.

3. The apparatus for preparing magnesium alloy sheets by three-dimensional variable arc surface differential shearing and extrusion as described in claim 2, characterized in that, The punch mold (13) consists of two axially symmetrical punches, a left punch (13-1) and a right punch (13-2), which are relatively symmetrical about the mold cavity. The working surface of the punch gradually changes from top to bottom from a part of the horizontal circle of the equidistant cylindrical extrusion channel (26) to an inward convex arc with a radius of 30-50 mm, and finally to a vertical edge with a length of 28-36 mm. The radius of the arc on the front side of the outward convex arc is 120-140 mm. The radius of the rear arc R5 is 50-70mm, the radius of the front arc R6 of the inner convex arc is 80-90mm, and the radius of the rear arc R7 is 240-260mm. The outer convex arc surface is connected to the top surface of the punch mold (13) with a fillet radius r2 of 6-10mm, and is also connected to the inner convex arc surface with a fillet radius. The fillet is smoothly transitioned from the outer convex shape with a fillet radius r3 of 3-7mm to the inner convex shape with a fillet radius r4 of 3-7mm from front to back.

4. The apparatus for preparing magnesium alloy sheets by three-dimensional variable arc surface differential shearing and extrusion as described in claim 3, characterized in that, The bottom surface of the cuboid cavity (27) is provided with four sliding positioning grooves (29) with a height H4 of 6-10mm. The sliding positioning grooves (29) are divided into three areas: an opening area (29-1) with a length L3 of 6-10mm and a width W3 of 14-18mm, a positioning area (29-2) with a length L2 of 6-10mm and a width W3 of 14-18mm, and a sliding area (29-3) with a length L2 of 6-10mm and a width W4 of 6-10mm. The bottom of the punch mold (13) is provided with four positioning blocks (31). The positioning blocks (31) fit into the positioning area (29-2) in the sliding positioning groove (29). The left and right sides of the punch mold (13) are inclined surfaces with a height H6 of 86-106mm, which are the same as the inclination angle θ1 of the extrusion punch (11). The punch (13) is first fixed in the positioning area (29-2) of the sliding positioning groove (29) of a front die (12-1) by the positioning block (31). Then the sliding positioning groove (29) of the rear die (12-2) is assembled with the positioning block (31) of the punch (13), so that the punch (13) is finally assembled in the cuboid cavity (27) of the die (12). The punch (13) and the die (12) together form a differential shearing channel. At the same time, the left and right inclined surfaces of the punch (13) are matched with the inclined surfaces of a pair of extrusion punches (11). The extrusion punches (11) can push the punch downward to slide towards the middle, from the positioning area (29-2) to the sliding area (29-3), so that the original differential shearing channel becomes a dynamic differential deformation channel (32).

5. The apparatus for preparing magnesium alloy sheets by three-dimensional variable arc surface differential shearing and extrusion as described in any one of claims 1-4, characterized in that, The extrusion punch (9), extrusion punch (11), die (12) and punch (13) are all made of 4Cr5MoSiV1 hot work die steel.

6. The apparatus for preparing magnesium alloy sheets by three-dimensional variable arc surface differential shearing and extrusion as described in any one of claims 1-4, characterized in that, The surface roughness of the working surface of the extrusion punch (9) is Ra0.08~0.16μm, the surface roughness of the working surface of the extrusion punch (11) is Ra0.04~0.08μm, the surface roughness of the working surface of the die (12) is Ra0.4~0.8μm, the surface roughness of the working surface of the punch (13) is Ra0.16~0.4μm, and the surface roughness of the left and right inclined surfaces of the punch (13) is Ra0.04~0.08μm.

7. The apparatus for preparing magnesium alloy sheets by three-dimensional variable arc surface differential shearing and extrusion as described in any one of claims 1-4, characterized in that, The power unit is a pressure motor (6) that drives the extrusion die and the extrusion punch.

8. A method for preparing magnesium alloy sheets by three-dimensional variable arc surface differential shear extrusion, characterized in that, Includes the following steps: S1. Pretreatment of magnesium alloy bars: S1-1. Use 600-grit sandpaper to polish the surface of the magnesium alloy bar to remove oil stains, and then use 800-grit, 1000-grit, and 1200-grit sandpaper in sequence until the surface of the magnesium alloy bar is 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 rod prepared in step S1-1 into the cleaning solution prepared in step S1-2, place the cleaning tank on an ultrasonic cleaner and ultrasonically clean the magnesium alloy rod for 60 minutes, then take out the magnesium alloy rod and clean it with anhydrous ethanol, and finally dry it with a hair dryer. S1-4. Coat the surface of the magnesium alloy rod prepared in step S1-3 with graphite oil solution for later use. S2. Preheating of magnesium alloy bars: Set the heating temperature of the vacuum atmosphere heating furnace to 450℃. After the furnace temperature reaches the set temperature, put the magnesium alloy bars into the heating furnace and keep them warm for 3 hours. S3. Lubrication, assembly, and preheating of the three-dimensional variable arc surface differential shear extrusion forming device: S3-1, Lubrication: Apply graphite oil solution to the surface of the cavity and arc groove (28) and sliding positioning groove (29) of the concave mold (12), the surface of the punch (13), and the working surface of the extrusion punch (11); S3-2, Assembly: First, the die pad (14) is installed and fixed on the worktable (18) of the vertical extruder. Then, a front die (12-1) is fixed on the die pad (14). Next, the punch (13) is fixed in the positioning area (29-2) of the sliding positioning groove (29) of the front die (12-1) by the positioning block (31). Then, the positioning area (29-2) of the sliding positioning groove (29) of the rear die (12-2) is assembled with the positioning block (31) of the punch (13) and fixed on the die pad (14). Finally, the punch (13) is assembled on the die pad. Inside the cuboid cavity (27) of the mold (12), the heating sleeve (16) is installed on the inner surface of the die fixing frame (15) on the front and rear sides. Finally, the die fixing frame (15) is fixed on the worktable (18) by bolts (17). The die fixing frame (15) with through holes is fixed on the left and right sides to ensure that the punch mold (13) can slide in the left and right directions. The extrusion punch mold (9) is controlled to move down and placed in the top cavity of the die mold (12) to ensure that the extrusion punch mold (9) and the die mold (12) are in close vertical contact. S3-3, Preheating: Control the temperature of the heating jacket (16) 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. Three-dimensional variable arc surface differential shear extrusion deformation forming: The extrusion punch (9), the die (12) and the punch (13) together form the extrusion channel; the extrusion channel includes three areas arranged from top to bottom: the extrusion pushing area I, the dynamic differential deformation area II and the shear extrusion deformation area III; S4-1. Remove the extrusion punch (9) from the channel, allowing the magnesium alloy bar to fill the extrusion pushing zone I. Then, push the extrusion punch (9) back into the channel. Operate the vertical extruder. The extrusion punch (9) and the extrusion punch (11) move downwards simultaneously under the action of the extrusion telescopic head (7), causing the magnesium alloy bar in the extrusion pushing zone I to continuously move downwards to the dynamic differential deformation zone II. The upper part of the channel in the dynamic differential deformation zone II is composed of two front and rear arc grooves (28) and two convex arc surfaces of the left and right punches (13). Due to the bending of the convex arc surfaces and the arc grooves (28) Different degrees of flow velocity of magnesium alloy bars on different arc surfaces of the channel result in different flow velocities, leading to differential shear deformation during extrusion, which induces the c-axis of the grains to deflect and weakens the basal texture. The lower part of the dynamic differential deformation zone II consists of the vertical surfaces of two concave dies (12) and the inner convex arc surfaces of two convex dies (13). The two inner convex arc surfaces gradually become vertical, causing the flow velocity of magnesium alloy bars on the left and right sides to continuously change in the front-back direction. At the same time, the convex dies (13) are pressed downward by the extrusion punches (11) on the left and right sides, thereby utilizing the positioning block (31) in the sliding position. Sliding towards the center in the slot (29), the magnesium alloy bar undergoes continuous deformation on the left and right sides, further generating differential shear deformation on the magnesium alloy. The grain structure is refined again, and the basal texture is weakened again. In the dynamic differential deformation channel (32), the horizontal cross-section of the magnesium alloy bar gradually changes from a circle to a quadrilateral composed of two arc edges on the left and right sides and two horizontal edges on the front and back. Finally, the two arc edges on the left and right sides of the quadrilateral gradually straighten towards the center to become a rectangle, and the magnesium alloy bar eventually becomes a magnesium alloy block. Then, when the magnesium alloy block is squeezed into the shear extrusion deformation zone III, it passes through the shear deformation channel ( 30) Due to the effect of the two curved surfaces, the magnesium alloy block continuously undergoes differential deformation and shear deformation in the left and right directions. At the same time, the front and rear sides of the shear deformation channel (30) gradually change from vertical to inclined, so that the right rear end and left front end of the magnesium alloy block are subjected to forward and backward shear deformation respectively. Finally, the horizontal section of the magnesium alloy block in the shear deformation channel (30) gradually changes from a rectangle to a parallelogram from top to bottom. The combined effect of the two causes the c-axis of the magnesium alloy grains to tilt again, thereby further weakening the base texture and aggravating the deformation of the magnesium alloy. Finally, it is extruded through the hole to obtain a fine-grained weak-textured magnesium alloy plate. S4-2. Take out the magnesium alloy sheet obtained in step S4-1, polish its surface with sandpaper, clean the magnesium alloy sheet 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 sheet that can be put into use directly.

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