Weak anisotropic high strength and toughness magnesium alloy sheet forming die and method

Abstract

The application discloses a weak anisotropy high-strength and high-toughness magnesium alloy plate forming die and method, and belongs to the field of metal plastic deformation process and plate forming technology. The weak anisotropy high-strength and high-toughness magnesium alloy plate forming die comprises a split die, a deformation cavity is arranged in the split die, the deformation cavity comprises a direct extrusion deformation zone and a corner extrusion deformation zone, a funnel-shaped necking portion is arranged at the bottom of the direct extrusion deformation zone, the bottom of the necking portion is connected with the top of the corner extrusion deformation zone, and a downward protruding portion is arranged at the bottom of the corner extrusion deformation zone. The direct extrusion deformation zone, the corner extrusion deformation zone, the necking portion and the protruding portion are symmetrically arranged along the vertical central axis of the split die. The width of the corner extrusion deformation zone is greater than that of the direct extrusion deformation zone, so that a corner extrusion structure is formed. The material is subjected to the combined effect of three-directional compressive stress and shearing stress during deformation, the grain refinement effect and the uniform breaking of the second phase are more obvious, and the comprehensive mechanical properties of the alloy are further improved.

Description

Technical Field

[0001] This invention belongs to the field of metal plastic deformation technology and sheet metal forming technology, and relates to a mold and method for forming weakly anisotropic high-strength and high-toughness magnesium alloy sheets. Background Technology

[0002] Magnesium alloys are currently the lightest structural metals used in engineering applications, widely applied in aerospace, defense, transportation, and electronics. The ability of magnesium alloys to improve strength and toughness through plastic deformation is widely recognized by researchers. Magnesium alloy sheets are crucial components in aerospace, military, automotive, and high-speed rail equipment. Currently, they are mainly manufactured using forging, extrusion, and rolling processes, which are characterized by mature technology and relatively low equipment requirements. However, their low cumulative deformation and strong deformation anisotropy limit their use in high-end equipment structural components, necessitating the development of new processing methods and technical solutions.

[0003] Large plastic deformation, with its multiple deformations and high cumulative strain, has attracted close attention and extensive research from scientists, and is considered the most effective method for obtaining high-strength and high-toughness magnesium alloys. Currently, processes such as equal-diameter angular extrusion (ECAP), high-pressure torsion (HPT), and cumulative rolling (ARB) have been studied for the preparation of high-strength and high-toughness fine-grained / ultra-fine-grained magnesium alloys. Li, Garces, and others used ECAP to prepare rare-earth magnesium alloys with strengths exceeding 360 MPa; Sun et al. used high-pressure torsion to prepare nanocrystalline magnesium alloys, exhibiting superplasticity; Luo Xuan prepared nanostructured Mg-Gd alloy plates through a four-pass ARB process, whose microstructure mainly consists of 119 nm ultrafine grains and 142 nm layered nanotwins. However, limitations such as high equipment requirements and small sample sizes hinder their widespread industrial application.

[0004] Therefore, there is an urgent need to develop a new processing method to produce large-size, weakly anisotropic, high-strength and high-toughness magnesium alloy sheets to meet industrial application requirements. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and proposes a forming mold and method for weakly anisotropic high-strength and tough magnesium alloy sheets, based on a cumulative positive extrusion-bidirectional corner extrusion process, to solve the problems existing in the above-mentioned background technology.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: A molding die for forming low-anisotropic high-strength and high-toughness magnesium alloy sheets includes an upper die structure and a lower die structure. The lower die structure includes a segmented die with a deformation cavity. The deformation cavity includes a positive extrusion deformation zone and a corner extrusion deformation zone. The positive extrusion deformation zone is located directly above the corner extrusion deformation zone. The bottom of the positive extrusion deformation zone has a funnel-shaped constriction, the bottom of which connects to the top of the corner extrusion deformation zone. The bottom of the corner extrusion deformation zone has a downward-facing protrusion. The positive extrusion deformation zone, the corner extrusion deformation zone, the constriction, and the protrusion are all symmetrically arranged along the vertical central axis of the segmented die. The positive extrusion deformation zone and the corner extrusion deformation zone are perpendicular. The width of the corner extrusion deformation zone is greater than the width of the positive extrusion deformation zone, forming a corner extrusion structure.

[0007] Preferably, the lower mold structure also includes a stress ring, and the segmented die includes two die units with the same structure. The two die units are assembled relative to each other and installed in the stress ring.

[0008] Even better, the bottom of the segmented die is provided with a lower template.

[0009] Preferably, the upper mold structure includes a forming upper template, a punch fixing plate, and a punch; the forming upper template is connected to the top of the punch, and the punch fixing plate is fixed at the connection between the forming upper template and the punch; the size of the punch is adapted to the positive extrusion deformation zone.

[0010] Preferably, the positive extrusion deformation zone has a vertical columnar structure, and the corner extrusion deformation zone has a horizontal columnar structure.

[0011] A method for forming a weakly anisotropic high-strength and high-toughness magnesium alloy sheet, comprising the following steps, using the aforementioned weakly anisotropic high-strength and high-toughness magnesium alloy sheet forming mold: Magnesium alloy billets are placed into the positive extrusion deformation zone. The press drives the upper die structure downward until it contacts the upper surface of the billet. The press applies pressure, causing the punch at the bottom of the upper die structure to press the billet sequentially into the funnel-shaped constriction and corner extrusion deformation zones along the positive extrusion deformation zone to obtain magnesium alloy sheets. The magnesium alloy sheets are cut into equal parts and then placed back into the positive extrusion deformation zone for a second deformation to obtain magnesium alloy sheets in a stacked state. They are then cut and extruded again, and this process is repeated to complete multiple deformations to obtain weakly anisotropic high-strength and tough magnesium alloy sheets.

[0012] Preferably, the width D of the magnesium alloy billet and the thickness d of the billet after the first deformation have a dimensional relationship of d = (1 / n)D.

[0013] Preferably, a lubricant is uniformly applied inside the deformable cavity for lubrication; the lubricant is a mixture of graphite and machine oil in a mass ratio of 1:1.5.

[0014] Preferably, the magnesium alloy billet is first homogenized, water-quenched and preheated in sequence, and then placed in the positive extrusion deformation zone for pressing and forming.

[0015] Preferably, the punch pressing speed is 2-5 mm / s.

[0016] The beneficial effects of this invention compared to the prior art are as follows: (1) Compared with the existing equal diameter angular extrusion materials, which are mainly subjected to shearing during deformation, the method of the present invention makes the material subjected to the combined effect of triaxial compressive stress and shear stress during deformation, resulting in more obvious grain refinement and uniform fragmentation of the second phase, which is conducive to further improving the comprehensive mechanical properties of the alloy.

[0017] (2) Compared with the alloy sheets obtained by deformation processes such as rolling and cumulative rolling, the alloy sheets have obvious basal texture, resulting in strong anisotropy. The method of the present invention can realize a multi-pass cumulative deformation process, and the corner extrusion deformation process can effectively weaken the basal texture of the extrusion ED and enhance the deformation uniformity of the alloy sheet in all directions.

[0018] (3) Compared with the traditional extrusion process, the method of the present invention incorporates corner extrusion deformation and can perform multi-pass deformation, thus providing higher cumulative strain, which allows the alloy microstructure to be fully refined and enables the uniform preparation of bimetallic laminated materials.

[0019] (4) This invention combines the advantages of positive extrusion and bidirectional corner extrusion deformation, so that the material is subjected to the combined effect of triaxial compressive stress and shear stress during deformation. At the same time, the design of the "protruding" part in the corner cavity allows the material to flow into the structure after positive extrusion to undergo upsetting and extrusion deformation process, further increasing the material strain, obtaining fine grain structure, and improving the overall performance of the material. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the molding die assembly structure of the present invention; Figure 2 This is a front view of the lower mold structure of the present invention; Figure 3 This is a left view of the lower mold structure of the present invention; Figure 4 This is a top view of the lower mold structure of the present invention; Figure 5 This is a schematic diagram of the deformable cavity of the present invention; Figure 6 This is a schematic flowchart of the molding method of the present invention; Figure 7 These are schematic diagrams of two deformation paths, A and B. Figure 8This is the microstructure of the Mg-9Gd-4Y-2Zn-0.5Zr alloy in Example 2 of this invention; Figure 9 This is the deformation texture of the Mg-9Gd-4Y-2Zn-0.5Zr alloy in Example 2 of this invention.

[0021] Numbering on the map: 1-Forming upper template, 2-Punch fixing plate, 3-Punch, 4-Segmented die, 5-Stress ring, 6-Die fixing plate, 7-Deformation cavity, 8-Magnesium alloy billet, 71-Positive extrusion deformation zone, 72-Corner extrusion deformation zone, 73-Narrowing, 74-Protrusion. Detailed Implementation

[0022] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0023] Example 1 like Figures 1-5 As shown, this embodiment proposes a weakly anisotropic high-strength and tough magnesium alloy sheet forming mold, which includes an upper mold structure composed of a forming upper template 1, a punch fixing plate 2 and a punch 3, and a lower mold structure composed of a split die 4, a stress ring 5 and a die fixing plate 6. The split die 4 is divided into left and right parts, which are inserted into the stress ring 5 when assembled, and the stress ring 5 is fixed on the die fixing plate 6. The segmented die 4 contains a deformation cavity 7, which includes a positive extrusion deformation zone 71 and a corner extrusion deformation zone 72. The positive extrusion deformation zone 71 is located directly above the corner extrusion deformation zone 72. The bottom of the positive extrusion deformation zone 71 has a funnel-shaped constriction 73, the bottom of which is connected to the top of the corner extrusion deformation zone 72. The bottom of the corner extrusion deformation zone 72 has a downward-facing protrusion 74. The positive extrusion deformation zone 71, the corner extrusion deformation zone 72, the constriction 73, and the protrusion 74 are all symmetrically arranged along the vertical central axis of the segmented die 4. The positive extrusion deformation zone 71 and the corner extrusion deformation zone 72 are perpendicular to each other. The positive extrusion deformation zone 71 is a vertical columnar structure, and the corner extrusion deformation zone 72 is a horizontal columnar structure. The width of the corner extrusion deformation zone 72 is greater than the width of the positive extrusion deformation zone 71, forming a corner extrusion structure.

[0024] The deformation cavity 7 is located inside the segmented die 4. Under the pressure of the punch 3, the magnesium alloy billet 8 flows into the deformation cavity 7 to complete the plastic deformation process. After undergoing positive extrusion deformation, the magnesium alloy billet 8 first flows through the necking 73 into the protrusion 74 at the bottom of the corner extrusion deformation zone 72, and then enters the bidirectional corner extrusion deformation cavities on both sides of the corner extrusion deformation zone 72. During the entire deformation process, the magnesium alloy billet 8 is subjected to multiple complex stresses such as upsetting, drawing, and shearing, achieving a combined effect of triaxial compressive stress and shear stress, so that the magnesium alloy billet 8 is fully and uniformly deformed.

[0025] In this embodiment, the feed area size of the positive extrusion deformation zone 71 is 200mm×100mm×100mm, the positive extrusion ratio is 4, the output size of the corner extrusion deformation zone 72 is 50mm×100mm×300mm, and the size of the protrusion 74 is 10mm×40mm×100mm.

[0026] Example 2 This embodiment proposes a method for forming weakly anisotropic high-strength and tough magnesium alloy sheets, which uses the forming mold described in Example 1 for forming and pressing, and specifically includes the following steps: Mg-9Gd-4Y-2Zn-0.5Zr alloy was used as the magnesium alloy billet 8, with dimensions of 100mm×100mm×100mm. First, the alloy underwent homogenization treatment at 520℃ for 16 hours, followed by water quenching at 70℃. The homogenized alloy was then preheated to 450℃ and held for 2 hours. The forming mold was heated to 420℃ and fully preheated for 4 hours. Heating was performed using a resistance furnace, employing induction heating combined with heat preservation and supplementary heat supply.

[0027] After heating, the upper forming plate 1 of the mold forming die is fixed on the Tianduan 630000kN press, and machine oil and graphite are evenly applied to the deformation cavity 7 for lubrication (the mixing ratio of graphite and machine oil is 1:1.5 by mass). The billet is placed into the positive extrusion deformation zone 71, and the press drives the punch 3 to move downward until it contacts the upper surface of the magnesium alloy billet 8. The press applies pressure to keep the punch 3 at a pressing speed of about 3mm / s, and the magnesium alloy billet 8 enters the positive extrusion deformation zone 71, the necking 73, the protrusion 74, and the corner extrusion deformation zone 72 in sequence under the extrusion pressure to obtain the corresponding extruded magnesium alloy sheet.

[0028] The magnesium alloy sheet is surface-machined and cut into four equal parts. These parts are then placed back into the positive extrusion deformation zone 71 for a second deformation pass, resulting in a stacked magnesium alloy sheet. The above process can be found in [reference needed]. Figure 6 As shown. When placing it, you can use either horizontal or vertical placement methods. Please refer to [link / reference]. Figure 7 The structure of path A and path B is shown.

[0029] By repeating this process, four to five deformation passes can be completed to obtain magnesium alloy sheets with finer grain sizes and more pronounced texture reduction.

[0030] The metallographic structure of the first-pass plate obtained in this embodiment is as follows: Figure 8 As shown, the recrystallization texture is as follows Figure 9 As shown, the average grain size of the alloy after deformation is refined from 138 μm to 37 μm, and the basal texture intensity is 1.7 MRD.

[0031] This invention combines the advantages of direct extrusion and bidirectional corner extrusion deformation, subjecting the material to a combined effect of triaxial compressive stress and shear stress during deformation. Meanwhile, the design of the protrusion 74 in the corner extrusion deformation zone 72 allows the material to flow into the structure after direct extrusion to undergo upsetting and extrusion deformation processes, further increasing the material strain, obtaining a fine-grained structure, and improving the overall performance of the material.

[0032] The method of this invention can also be used to prepare aluminum alloys and magnesium / aluminum laminated materials.

[0033] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the present invention, and all of these should be considered to fall within the scope of patent protection determined by the submitted claims.

Claims

1. A method for forming a weakly anisotropic high-strength and high-toughness magnesium alloy sheet, characterized in that, The forming mold is used for processing. The forming mold includes an upper mold structure and a lower mold structure. The lower mold structure includes a segmented die (4). A deformation cavity (7) is provided inside the segmented die (4). The deformation cavity (7) includes a positive extrusion deformation area (71) and a corner extrusion deformation area (72). The positive extrusion deformation area (71) is located directly above the corner extrusion deformation area (72). A funnel-shaped constriction (73) is provided at the bottom of the positive extrusion deformation area (71). The bottom of the constriction (73) is connected to the top of the corner extrusion deformation area (72). A downward protrusion (74) is provided at the bottom of the corner extrusion deformation area (72). The positive extrusion deformation area (71), the corner extrusion deformation area (72), the constriction (73), and the protrusion (74) are all symmetrically arranged along the vertical central axis of the segmented die (4). The positive extrusion deformation area (71) and the corner extrusion deformation area (72) are symmetrically arranged along the vertical central axis of the segmented die (4). The corner extrusion deformation zone (72) is perpendicular to each other, and the width of the corner extrusion deformation zone (72) is greater than the width of the normal extrusion deformation zone (71), forming a corner extrusion structure; the normal extrusion deformation zone (71) is a vertical column structure, and the corner extrusion deformation zone (72) is a horizontal column structure; the corner extrusion deformation zone (72) includes bidirectional corner extrusion deformation cavities located on the left and right sides of the protrusion (74), and the outlet of the constriction (73) is vertically opposite to the protrusion (74), so that the billet entering from the normal extrusion deformation zone enters the area where the protrusion (74) is located first after passing through the constriction (73), and then flows to the bidirectional corner extrusion deformation cavities on the left and right sides of the protrusion (74); the lower die structure also includes a stress ring (5), and the split die (4) includes two die units with the same structure. The two die units are assembled relative to each other and installed in the stress ring (5); And includes the following steps: Magnesium alloy billet (8) is placed into the positive extrusion deformation zone (71). The press drives the upper die structure to move downward until it contacts the upper surface of the billet. The press applies pressure so that the punch (3) at the bottom of the upper die structure presses the billet into the funnel-shaped constriction zone (73) and the corner extrusion deformation zone (72) along the positive extrusion deformation zone (71) to obtain magnesium alloy sheet. The magnesium alloy sheet is cut into equal parts and then placed back into the positive extrusion deformation zone (71) for two-pass deformation to obtain a stacked magnesium alloy sheet. It is then cut and extruded again, and so on to complete multiple-pass deformation to obtain a weakly anisotropic high-strength and tough magnesium alloy sheet.

2. The method for forming a weakly anisotropic high-strength and high-toughness magnesium alloy sheet according to claim 1, characterized in that, The bottom of the segmented die (4) is provided with a die fixing plate (6).

3. The method for forming a weakly anisotropic high-strength and high-toughness magnesium alloy sheet according to claim 1, characterized in that, The upper mold structure consists of a forming upper template (1), a punch fixing plate (2) and a punch (3); the forming upper template (1) is connected to the top of the punch (3), and the punch fixing plate (2) is fixed at the connection between the forming upper template (1) and the punch (3); the size of the punch (3) is adapted to the positive extrusion deformation zone (71).

4. The method for forming a weakly anisotropic high-strength and high-toughness magnesium alloy sheet according to claim 1, characterized in that, The width D of the magnesium alloy billet (8) and the thickness d of the billet after the first deformation have a dimensional relationship of d = (1 / n)D.

5. The method for forming a weakly anisotropic high-strength and high-toughness magnesium alloy sheet according to claim 1, characterized in that, Lubricant is evenly applied inside the deformable cavity (7) for lubrication; the lubricant is a mixture of graphite and machine oil with a mass ratio of 1:1.

5.

6. The method for forming a weakly anisotropic high-strength and high-toughness magnesium alloy sheet according to claim 1, characterized in that, First, the magnesium alloy billet (8) is homogenized, water-quenched and preheated in sequence, and then placed in the positive extrusion deformation zone (71) for pressing and forming.

7. The method for forming a weakly anisotropic high-strength and high-toughness magnesium alloy sheet according to claim 1, characterized in that, The pressing speed of the punch (3) is 2-5 mm / s.

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