Extrusion die and manufacturing method of equiaxed magnesium alloy rod

Abstract

The present invention discloses an extrusion die and a manufacturing method for a magnesium alloy bar. The extrusion die comprises: a lower die (1), an upper die (2), an inner extrusion barrel (3), an outer extrusion barrel (4), a heating ring (6) and a thermocouple (8); the inner extrusion barrel (3) is nested inside the outer extrusion barrel (4); a heating ring (6) is provided inside or outside the outer extrusion barrel (4); the thermocouple (8) is inserted into a hole communicating between the outer extrusion barrel (4) and the inner extrusion barrel (3); the inner extrusion barrel (3) is a hollow structure that passes through from top to bottom; the upper die (2) is installed in the hollow structure of the inner extrusion barrel (3) from the top of the inner extrusion barrel (3); and the lower die (1) is installed in the hollow structure of the inner extrusion barrel (3) from the bottom of the inner extrusion barrel (3). The extrusion die can efficiently and quickly manufacture ultrafine equiaxed magnesium alloy bars, greatly improving their strength and plasticity.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal plastic forming, and in particular relates to an extrusion die and a manufacturing method for an equiaxed crystal magnesium alloy bar. Background Art

[0002] As the lightweighting trend accelerates, magnesium alloys are gaining increasing attention. Magnesium alloys offer numerous advantages, including low density, light weight, excellent electrical and thermal conductivity, high impact toughness, and superior electromagnetic shielding properties. They are hailed as "the most promising green engineering material of the 21st century." Magnesium alloy profiles are widely used in aviation, aerospace, automotive manufacturing, electronics, and other fields.

[0003] Furthermore, magnesium alloys possess excellent biocompatibility, with density and elastic modulus similar to those of human bone. They are also fully degradable within the human body, making them suitable for biomedical applications. Due to the unique structure of HCP, magnesium alloys only have three active slip systems at room temperature, resulting in poor plastic deformation and significant processing difficulties. However, at temperatures above 225°C, the conical and prismatic slip systems of magnesium alloys can be activated, improving their plastic deformation capacity. Therefore, hot extrusion is currently the primary method for producing magnesium alloy profiles.

[0004] Currently, the main methods for processing and manufacturing magnesium alloy bars include semi-continuous casting, conventional forward extrusion, equal-angle forward extrusion, reciprocating extrusion, and high-pressure torsion. Southwest University's patent, "A Processing Method for Magnesium Alloy Bars" (Application Number: 201510029162.2, Publication Number: CN104498848A, Publication Date: April 8, 2015), discloses a method for producing magnesium alloy bars by torsional plastic deformation of a magnesium alloy bar blank and controlling the trimming amount in combination with a heat treatment process. Henan University of Science and Technology's patent, "A High-Gadolinium Rare Earth Magnesium Alloy Bar and Its Preparation Method" (Application Number: 202110699449.1, Publication Number: CN113444903A, Publication Date: September 28, 2021), discloses a method for controlling the alloy through alloying and heat treatment processes, and then achieving large plastic deformation of magnesium alloy bars through equal-angle forward extrusion.

[0005] Although the above method can achieve grain refinement to a certain extent, the degree of refinement each time is less than half of the original grain. If ultra-fine-grained magnesium alloy rods are to be obtained, multiple extrusion passes are required. The process is too complicated, the production cycle is long, and the structure is uneven, which has certain limitations in the production of high-performance magnesium alloy rods.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] In response to the problems and / or shortcomings of the prior art, the present invention aims to provide an extrusion die for magnesium alloy bars. This extrusion die utilizes variable-angle extrusion and effective welding to efficiently and quickly produce ultrafine equiaxed magnesium alloy bars, significantly improving the strength and plasticity of the magnesium alloy bars and effectively expanding the application and use of magnesium alloys.

[0008] The present invention provides a magnesium alloy bar extrusion die, which comprises: a lower die (1), an upper die (2), an inner extrusion cylinder (3), an outer extrusion cylinder (4), a heating ring (6) and a thermocouple (8);

[0009] in,

[0010] The inner extrusion cylinder (3) is nested inside the outer extrusion cylinder (4);

[0011] A heating ring (6) is provided inside or outside the outer extrusion cylinder (4);

[0012] The thermocouple (8) is inserted into a hole communicating between the outer extrusion cylinder (4) and the inner extrusion cylinder (3);

[0013] The inner extrusion cylinder (3) is a hollow structure that penetrates from top to bottom;

[0014] The upper mold (2) is installed in the hollow structure of the inner extrusion cylinder (3) from the top of the inner extrusion cylinder (3);

[0015] The lower mold (1) is installed in the hollow structure of the inner extrusion cylinder (3) from the bottom of the inner extrusion cylinder (3).

[0016] Further,

[0017] In any of the above technical solutions (magnesium alloy bar extrusion die), the upper die (2) is an inverted truncated cone structure, or the upper die (2) is an inverted truncated cone structure with a cylinder on the top;

[0018] The top of the upper mold (2) is provided with 3 to 30 (for example, 3, 6, 9, 12, 15, 18, 21, 24, etc.) circular holes (201) with equal diameters; the bottom of the upper mold (2) is provided with semicircular holes (202), each semicircular hole (202) is connected to a corresponding circular hole (201), and the diameter of the semicircular hole (202) is equal to the diameter of the circular hole (201).

[0019] Further,

[0020] In any of the above technical solutions (magnesium alloy bar extrusion die), the circular holes (201) are arranged to be evenly distributed.

[0021] Further,

[0022] In any of the above technical solutions (magnesium alloy bar extrusion dies), the lower die (1) is installed in the hollow structure of the inner extrusion barrel (3) from the bottom of the inner extrusion barrel (3) via a threaded structure.

[0023] Further,

[0024] In any of the above technical solutions (magnesium alloy bar extrusion die),

[0025] The upper portion of the lower mold (1) is provided with a hollow inverted truncated cone structure (101);

[0026] The inverted truncated cone structure of the upper mold (2) and the hollow inverted truncated cone structure (101) of the lower mold (1) have the same cone angle, preferably the cone angle is 90° to 150° (for example, 90°, 120°, 135°, 150°, etc.);

[0027] A welding chamber (102) is provided in the middle of the lower mold (1) and is connected to the bottom of the inverted truncated cone structure (101);

[0028] The lower portion of the lower mold (1) is provided with an extrusion port (103) which is in communication with the bottom of the welding chamber (102).

[0029] Further,

[0030] In any of the above technical solutions (magnesium alloy bar extrusion die), the inner diameter of the extrusion port (103) is larger than the inner diameter of the welding chamber (102); preferably, the inner diameter of the extrusion port (103) is 3 mm to 5 mm larger than the inner diameter of the welding chamber (102).

[0031] The present invention also provides a method for manufacturing a magnesium alloy bar, which comprises the following steps:

[0032] ①. Place the magnesium alloy bar extrusion die described in any one of the above on the extruder workbench, place the magnesium alloy billet with the skin removed into the inner extrusion cylinder (3), place the extrusion rod (5) into the inner extrusion cylinder (3) to contact the magnesium alloy billet, and apply a pre-pressure of 2 to 5 MPa under the action of the extruder;

[0033] ②, heating the extrusion die and the magnesium alloy billet to 250-450° C. through a heating ring (6), and monitoring the temperature of the extrusion die with a thermocouple (8);

[0034] ③. When the temperature of the extrusion die is heated to the required temperature, the temperature is kept for 5 to 15 minutes, and then extrusion is started. Under the action of the extruder, the extrusion rod (5) pushes the magnesium alloy billet to first pass through the circular hole (201) of the upper die (2), flow out through the semicircular hole (202), enter the welding chamber (102) of the lower die (1) for welding, and finally extrude through the extrusion port (103) to obtain a magnesium alloy rod.

[0035] Further,

[0036] In any of the above technical solutions (method for manufacturing magnesium alloy rods), the magnesium alloy rods are AZ31 magnesium alloy rods, AZ91 magnesium alloy rods, ZK61 magnesium alloy rods or ZM5 magnesium alloy rods.

[0037] Further,

[0038] In any of the above technical solutions (method for manufacturing magnesium alloy rods), in step ②, the heating rate is 10-20° C. / min.

[0039] Further,

[0040] In any of the above technical solutions (method for manufacturing magnesium alloy bars), the movement rate of the extrusion rod (5) is 1 to 8 m / min.

[0041] During the extrusion process, the magnesium alloy billet flows through the 1 / 2 section variable diameter angle extrusion, and is subjected to severe shear deformation and large plastic deformation, and is upset in the welding chamber to obtain severe large plastic deformation. At this time, the grain structure of the extruded material is sheared, broken, flowed and turned into fine ultrafine equiaxed crystals (submicron and nanocrystalline structures).

[0042] The beneficial effects of the present invention specifically include the following aspects:

[0043] (1) The present invention improves the magnesium alloy bar extrusion die, adopts variable-angle extrusion to achieve multi-channel variable-angle extrusion, and effectively welds in the welding chambers of the upper die and the lower die to extrude the magnesium alloy bar into a bar;

[0044] (2) During the extrusion process, the magnesium alloy is under triaxial stress, and a large cumulative strain and deformation can be obtained through a single extrusion, thereby obtaining a magnesium alloy rod with ultrafine equiaxed grains, which greatly improves the strength and plasticity of the magnesium alloy rod, simplifies the process, and reduces production costs;

[0045] (3) The magnesium alloy bar extrusion die of the present invention is not only suitable for the plastic deformation of magnesium alloys, but also suitable for the plastic deformation and production of various alloys such as aluminum alloys, copper alloys, titanium alloys, and stainless steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of the structure of the magnesium alloy bar extrusion die of the present invention;

[0047] Figure 2 Schematic diagram of the three-dimensional structure of the upper mold of the present invention;

[0048] Figure 3 It is a schematic cross-sectional structural diagram of the upper mold of the present invention;

[0049] Figure 4 It is a schematic cross-sectional structural diagram of the lower mold of the present invention;

[0050] In the figure, 1-lower mold, 2-upper mold, 3-inner extrusion cylinder, 4-outer extrusion cylinder, 5-extrusion rod, 6-heating ring, 7-magnesium alloy billet, 8-thermocouple, 101-hollow inverted frustum structure, 102-welding chamber, 103-extrusion port, 201-circular hole, 202-semicircular hole. DETAILED DESCRIPTION

[0051] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention is further described in detail below by way of examples, but it does not mean that the scope of protection of the present invention is limited to the scope of the examples. Based on the examples in this application, other similar embodiments obtained by those of ordinary skill in the art without making creative efforts should fall within the scope of protection of this application.

[0052] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the present invention.

[0053] Unless otherwise expressly specified or limited, the terms "connected," "connect," "installed," and "disposed" should be understood broadly; for example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0054] In the present invention, if no specific conditions are specified, conventional conditions or conditions recommended by the manufacturer shall be followed.

[0055] Regarding the definitions of terms used in the present invention, unless otherwise stated, the initial definitions provided for the terms in this document apply to the terms throughout the text; for terms not specifically defined herein, the meanings that can be given to them by those skilled in the art should be given based on the disclosure content and / or context.

[0056] Example 1

[0057] like Figures 1 to 4 As shown, the magnesium alloy bar extrusion die of the present invention comprises: a lower die 1, an upper die 2, an inner extrusion cylinder 3, an outer extrusion cylinder 4, a heating ring 6 and a thermocouple 8;

[0058] in,

[0059] The inner extrusion cylinder 3 is nested inside the outer extrusion cylinder 4;

[0060] A heating ring 6 is provided inside or outside the outer extrusion cylinder 4;

[0061] The thermocouple 8 is inserted into the hole connecting the outer extrusion cylinder 4 and the inner extrusion cylinder 3;

[0062] The inner extrusion cylinder 3 is a hollow structure that passes through from top to bottom;

[0063] The upper mold 2 is installed in the hollow structure of the inner extrusion cylinder 3 from the top of the inner extrusion cylinder 3;

[0064] The upper mold 2 is an inverted truncated cone structure, or the upper mold 2 is an inverted truncated cone structure with a cylinder on the top;

[0065] The top of the upper mold 2 is provided with 3 to 30 circular holes 201 of equal diameter, preferably the circular holes 201 are arranged to be evenly distributed;

[0066] The bottom of the upper mold 2 is provided with semicircular holes 202, each of which is connected to a corresponding circular hole 201. The diameter of the semicircular hole 202 is equal to the diameter of the circular hole 201, which can achieve 1 / 2 cross-section variable diameter angular extrusion;

[0067] The lower mold 1 is installed in the hollow structure of the inner extrusion cylinder 3 from the bottom of the inner extrusion cylinder 3. Preferably, the lower mold 1 is installed in the hollow structure of the inner extrusion cylinder 3 from the bottom of the inner extrusion cylinder 3 through a threaded structure.

[0068] The upper portion of the lower mold 1 is provided with a hollow inverted truncated cone structure 101;

[0069] The inverted truncated cone structure of the upper mold 2 and the hollow inverted truncated cone structure 101 of the lower mold 1 have the same cone angle, and the two can fit tightly together. Preferably, the cone angle is 90° to 150°.

[0070] The middle part of the lower mold 1 is provided with a welding chamber 102 which is connected to the bottom of the inverted truncated cone structure 101;

[0071] The lower portion of the lower mold 1 is provided with an extrusion port 103 which is connected to the bottom of the welding chamber 102;

[0072] The inner diameter of the extrusion port 103 is slightly larger than the inner diameter of the welding chamber 102 . For example, the inner diameter of the extrusion port 103 is 3 mm to 5 mm larger than the inner diameter of the welding chamber 102 .

[0073] The working process is as follows:

[0074] (1) Assembly: The inner extrusion cylinder 3 is nested inside the outer extrusion cylinder 4, the lower die 1 is installed in the hollow structure of the inner extrusion cylinder 3 from the bottom of the inner extrusion cylinder 3, the upper die 2 is installed in the hollow structure of the inner extrusion cylinder 3 from the top of the inner extrusion cylinder 3, the outer extrusion cylinder 4 is installed with a heating ring 6, and the thermocouple 8 is inserted into the hole connecting the outer extrusion cylinder 4 and the inner extrusion cylinder 3 to obtain an assembled magnesium alloy bar extrusion die;

[0075] (2) Place the assembled magnesium alloy bar extrusion die on the extruder workbench, place the magnesium alloy billet 7 with the skin removed into the inner extrusion cylinder 3, place the extrusion rod 5 into the inner extrusion cylinder 3 to contact the magnesium alloy billet 7, and apply a pre-pressure of 2 to 5 MPa under the action of the extruder;

[0076] (3) The extrusion die and magnesium alloy billet 7 are heated to 250-450°C by the heating ring 6, and the temperature of the extrusion die is monitored by the thermocouple 8;

[0077] (4) When the temperature of the extrusion die is heated to the required temperature, it is kept warm for 5 to 15 minutes and then extrusion is started. Under the action of the extruder, the extrusion rod 5 pushes the magnesium alloy billet 7 through the circular hole 201 of the upper die 2, flows out through the semicircular hole 202, enters the welding chamber 102 of the lower die 1 for welding, and finally is extruded through the extrusion port 103, thereby realizing the extrusion production of equiaxed crystal magnesium alloy bars.

[0078] Example 2

[0079] A method for manufacturing an AZ31 magnesium alloy bar comprises the following steps:

[0080] (1) Assemble the magnesium alloy bar extrusion die in the same manner as in Example 1;

[0081] (2) Place the assembled magnesium alloy bar extrusion die on the extruder workbench, place the magnesium alloy billet with the skin removed into the inner extrusion cylinder 3, place the extrusion rod 5 into the inner extrusion cylinder 3 to contact the magnesium alloy billet, and apply a pre-pressure of 2 MPa under the action of the extruder;

[0082] (3) The extrusion die and magnesium alloy billet are heated to 250°C by the heating ring 6, and the temperature of the extrusion die is monitored by the thermocouple 8;

[0083] (4) When the extrusion die is heated to the desired temperature, it is kept warm for 5 minutes before extrusion begins. Under the action of the extruder, the extrusion rod 5 pushes the magnesium alloy billet through the circular hole 201 of the upper die 2, flows out through the semicircular hole 202, enters the welding chamber 102 of the lower die 1 for welding, and finally extrudes through the extrusion port 103, thereby achieving the extrusion production of equiaxed magnesium alloy bars. During the extrusion process, the movement rate of the extrusion rod is 1 m / min.

[0084] In this embodiment, 30 circular holes 201 of equal diameter are evenly distributed on the upper mold 2. The inverted frustum of the upper mold 2 and the hollow inverted frustum of the lower mold 1 have the same cone angle of 150°, and the two can fit tightly together. The results show that the magnesium alloy rods produced have good surface quality, precise dimensions, uniform, dense and defect-free structure, a grain size of about 500nm, a tensile strength of 336MPa, and an elongation of 18%.

[0085] Example 3

[0086] A method for manufacturing an AZ91 magnesium alloy bar comprises the following steps:

[0087] (1) Assemble the magnesium alloy bar extrusion die in the same manner as in Example 1;

[0088] (2) Place the assembled magnesium alloy bar extrusion die on the extruder workbench, place the magnesium alloy billet with the skin removed into the inner extrusion cylinder 3, place the extrusion rod 5 into the inner extrusion cylinder 3 to contact the magnesium alloy billet, and apply a pre-pressure of 4 MPa under the action of the extruder;

[0089] (3) The extrusion die and magnesium alloy billet are heated to 450°C by the heating ring 6, and the temperature of the extrusion die is monitored by the thermocouple 8;

[0090] (4) When the extrusion die is heated to the desired temperature, it is kept warm for 8 minutes before extrusion begins. Under the action of the extruder, the extrusion rod 5 pushes the magnesium alloy billet through the circular hole 201 of the upper die 2, flows out through the semicircular hole 202, enters the welding chamber 102 of the lower die 1 for welding, and finally extrudes through the extrusion port 103, completing the extrusion production of the equiaxed magnesium alloy bar. During the extrusion process, the movement rate of the extrusion rod is 1.5 m / min.

[0091] In this embodiment, three circular holes 201 of equal diameter are evenly distributed on the upper mold 2. The inverted frustum structure of the upper mold 2 and the hollow inverted frustum structure 101 of the lower mold 1 have the same cone angle, which is 90°, and the two can fit tightly together. The results show that the magnesium alloy rod produced has good surface quality, precise size, uniform, dense and defect-free structure, a grain size of about 305nm, a tensile strength of 286MPa, and an elongation of 16.4%.

[0092] Example 4

[0093] A method for manufacturing a ZK61 magnesium alloy bar comprises the following steps:

[0094] (1) Assemble the magnesium alloy bar extrusion die in the same manner as in Example 1;

[0095] (2) Place the assembled magnesium alloy bar extrusion die on the extruder workbench, place the magnesium alloy billet with the skin removed into the inner extrusion cylinder 3, place the extrusion rod 5 into the inner extrusion cylinder 3 to contact the magnesium alloy billet, and apply a pre-pressure of 3 MPa under the action of the extruder;

[0096] (3) The extrusion die and magnesium alloy billet are heated to 330°C by the heating ring 6, and the temperature of the extrusion die is monitored by the thermocouple 8;

[0097] (4) When the extrusion die is heated to the desired temperature, it is kept warm for 12 minutes before extrusion begins. Under the action of the extruder, the extrusion rod 5 pushes the magnesium alloy billet through the circular hole 201 of the upper die 2, out through the semicircular hole 202, into the welding chamber 102 of the lower die 1 for welding, and finally extruded through the extrusion port 103, thereby achieving the extrusion production of equiaxed magnesium alloy bars. During the extrusion process, the movement rate of the extrusion rod is 2.5 m / min.

[0098] In this embodiment, nine circular holes 201 of equal diameter are evenly distributed on the upper mold 2. The inverted frustum of the upper mold 2 and the hollow inverted frustum of the lower mold 1 have the same cone angle of 120°, and the two can fit tightly together. The results show that the magnesium alloy rods produced have good surface quality, precise dimensions, uniform, dense and defect-free structure, a grain size of approximately 412 nm, a tensile strength of 368 MPa, and an elongation of 24.5%.

[0099] Example 5

[0100] A method for manufacturing an AZ31 magnesium alloy bar comprises the following steps:

[0101] (1) Assemble the magnesium alloy bar extrusion die in the same manner as in Example 1;

[0102] (2) Place the assembled magnesium alloy bar extrusion die on the extruder workbench, place the magnesium alloy billet with the skin removed into the inner extrusion cylinder 3, place the extrusion rod 5 into the inner extrusion cylinder 3 to contact the magnesium alloy billet, and apply a pre-pressure of 5 MPa under the action of the extruder;

[0103] (3) The extrusion die and magnesium alloy billet are heated to 350°C by the heating ring 6, and the temperature of the extrusion die is monitored by the thermocouple 8;

[0104] (4) When the extrusion die is heated to the desired temperature, it is kept warm for 10 minutes before extrusion begins. Under the action of the extruder, the extrusion rod 5 pushes the magnesium alloy billet through the circular hole 201 of the upper die 2, flows out through the semicircular hole 202, enters the welding chamber 102 of the lower die 1 for welding, and finally extrudes through the extrusion port 103, thereby achieving the extrusion production of equiaxed magnesium alloy bars. During the extrusion process, the movement rate of the extrusion rod is 5 m / min.

[0105] In this embodiment, 12 circular holes 201 of equal diameter are evenly distributed on the upper mold 2. The inverted frustum of the upper mold 2 and the hollow inverted frustum of the lower mold 1 have the same cone angle of 135°, and the two can fit tightly together. The results show that the magnesium alloy rod produced has good surface quality, precise size, uniform, dense and defect-free structure, a grain size of about 352nm, a tensile strength of 357MPa, and an elongation of 17.2%.

[0106] Example 6

[0107] A method for manufacturing a ZM5 magnesium alloy bar comprises the following steps:

[0108] (1) Assemble the magnesium alloy bar extrusion die in the same manner as in Example 1;

[0109] (2) Place the assembled magnesium alloy bar extrusion die on the extruder workbench, place the magnesium alloy billet with the skin removed into the inner extrusion cylinder 3, place the extrusion rod 5 into the inner extrusion cylinder 3 to contact the magnesium alloy billet, and apply a pre-pressure of 3 MPa under the action of the extruder;

[0110] (3) The extrusion die and magnesium alloy billet are heated to 400°C by the heating ring 6, and the temperature of the extrusion die is monitored by the thermocouple 8;

[0111] (4) When the extrusion die is heated to the desired temperature, it is kept warm for 15 minutes before extrusion begins. Under the action of the extruder, the extrusion rod 5 pushes the magnesium alloy billet through the circular hole 201 of the upper die 2, flows out through the semicircular hole 202, enters the welding chamber 102 of the lower die 1 for welding, and finally extrudes through the extrusion port 103, thereby achieving the extrusion production of equiaxed magnesium alloy bars. During the extrusion process, the movement rate of the extrusion rod is 3 m / min.

[0112] In this embodiment, six circular holes 201 of equal diameter are evenly distributed on the upper mold 2. The inverted frustum of the upper mold 2 and the hollow inverted frustum of the lower mold 1 have the same cone angle of 120°, and the two can fit tightly together. The results show that the magnesium alloy rod produced has good surface quality, precise size, uniform, dense and defect-free structure, a grain size of about 415nm, a tensile strength of 429MPa, and an elongation of 14.4%.

[0113] It should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A magnesium alloy bar extrusion die, characterized in that: It includes: A lower mold (1), an upper mold (2), an inner extrusion cylinder (3), an outer extrusion cylinder (4), a heating ring (6) and a thermocouple (8); in, The inner extrusion cylinder (3) is nested inside the outer extrusion cylinder (4); A heating ring (6) is provided inside or outside the outer extrusion cylinder (4); The thermocouple (8) is inserted into a hole communicating between the outer extrusion cylinder (4) and the inner extrusion cylinder (3); The inner extrusion cylinder (3) is a hollow structure that penetrates from top to bottom; The upper mold (2) is installed in the hollow structure of the inner extrusion cylinder (3) from the top of the inner extrusion cylinder (3); The lower mold (1) is installed in the hollow structure of the inner extrusion cylinder (3) from the bottom of the inner extrusion cylinder (3); The upper mold (2) is an inverted truncated cone structure, or the upper mold (2) is an inverted truncated cone structure with a cylinder on the top; The top of the upper mold (2) is provided with 3 to 30 circular holes (201) of equal diameter; the bottom of the upper mold (2) is provided with semicircular holes (202), each of which is connected to a corresponding circular hole (201), and the diameter of the semicircular hole (202) is equal to the diameter of the circular hole (201); The upper portion of the lower mold (1) is provided with a hollow inverted truncated cone structure (101); The inverted truncated cone structure of the upper mold (2) and the hollow inverted truncated cone structure (101) of the lower mold (1) have the same cone angle, and the cone angle is 90° to 150°; A welding chamber (102) is provided in the middle of the lower mold (1) and is connected to the bottom of the inverted truncated cone structure (101); The lower portion of the lower mold (1) is provided with an extrusion port (103) that is in communication with the bottom of the welding chamber (102); The inner diameter of the extrusion port (103) is larger than the inner diameter of the welding chamber (102); the inner diameter of the extrusion port (103) is 3 mm to 5 mm larger than the inner diameter of the welding chamber (102).

2. The magnesium alloy bar extrusion die according to claim 1, characterized in that: The circular holes (201) are arranged to be evenly distributed.

3. The magnesium alloy bar extrusion die according to any one of claims 1 to 2, characterized in that: The lower mold (1) is installed in the hollow structure of the inner extrusion cylinder (3) from the bottom of the inner extrusion cylinder (3) through a threaded structure.

4. A method for manufacturing a magnesium alloy bar, characterized in that: It includes the following steps: ①. Place the magnesium alloy bar extrusion die according to any one of claims 1 to 3 on the workbench of the extruder, place the magnesium alloy billet with the skin removed into the inner extrusion cylinder (3), place the extrusion rod (5) into the inner extrusion cylinder (3) to contact the magnesium alloy billet, and apply a pre-pressure of 2 to 5 MPa under the action of the extruder; ②, heating the extrusion die and the magnesium alloy billet to 250-450°C through the heating ring (6), and monitoring the temperature of the extrusion die with the thermocouple (8); ③. When the temperature of the extrusion die is heated to the required temperature, it is kept warm for 5 to 15 minutes and then extrusion is started. Under the action of the extruder, the extrusion rod (5) pushes the magnesium alloy billet to first pass through the circular hole (201) of the upper die (2), flow out through the semicircular hole (202), enter the welding chamber (102) of the lower die (1) for welding, and finally extrude through the extrusion port (103) to obtain a magnesium alloy rod.

5. The method for manufacturing a magnesium alloy bar according to claim 4, wherein: The magnesium alloy rod is AZ31 magnesium alloy rod, AZ91 magnesium alloy rod, ZK61 magnesium alloy rod or ZM5 magnesium alloy rod.

6. The method for manufacturing a magnesium alloy bar according to claim 4, wherein: In step ②, the heating rate is 10-20°C / min.

7. The method for manufacturing a magnesium alloy bar according to claim 4, wherein: The movement speed of the extrusion rod (5) is 1 to 8 m / min.

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