Short-process preparation method of magnesium alloy with high yield ratio and high plasticity

Abstract

The invention belongs to the technical field of magnesium alloy material processing and manufacturing, and particularly relates to a short-process preparation method of a high-yield-ratio and high-plasticity magnesium alloy, which is characterized by specifically comprising the following steps: 1) preparation of semi-solid slurry: pouring a magnesium alloy melt into a steel cylindrical crucible, and eccentrically rotating to obtain the semi-solid slurry with the solid fraction of 70-80%; (2) plastic deformation is conducted, specifically, the semi-solid slurry is subjected to low-temperature extrusion shear deformation, and a magnesium alloy bar is obtained; and (3) water-cooling quenching is conducted, specifically, the magnesium alloy bar is subjected to quenching treatment in cold water. By means of the steps, the magnesium alloy material can have a double-peak structure grain structure with coarse grains and fine grains mixed, and a non-basal texture forming an angle of 34-47 degrees with the extrusion axial direction is formed in the structure. According to the method, semi-solid pulping, plastic deformation and water-cooling quenching are combined, homogenization heat treatment of a blank before traditional extrusion is not needed, and the magnesium alloy with the high yield-tensile ratio and high plasticity is prepared in a short process, low energy consumption and low cost.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy material processing and manufacturing technology, and particularly relates to a short-process preparation method for magnesium alloys with high yield strength ratio and high plasticity. Background Art

[0002] Magnesium alloys possess advantages such as low density, high specific strength, good damping performance, and easy recycling, making them widely used in aerospace and defense fields. However, magnesium alloys have a hexagonal close-packed (HCP) crystal structure, resulting in a limited number of open slip systems at room temperature, leading to poor plastic processing capabilities. Furthermore, compared to other metals such as steel and aluminum, magnesium alloys have lower strength. To further enhance the application of magnesium alloys as structural components, it is necessary to improve their strength and plasticity.

[0003] Current methods for improving the strength and ductility of alloys mainly involve adding rare earth elements and combining this with complex processes: one is to form a high-alloy system, which includes increasing the amount of alloying elements or adding rare earth elements; the other is to employ complex processing techniques, including high-temperature, long-term heating and multi-pass extrusion and shearing processes. This leads to increased production costs, more complex manufacturing processes, and higher energy consumption.

[0004] Current research mainly focuses on improving the synergistic enhancement of room-temperature strength and ductility of magnesium alloys by using large plastic deformation and the addition of rare earth elements to improve grain refinement and construct bimodal grain structures. Chinese patent CN117551951A discloses a method for preparing high-strength, high-ductility magnesium alloys. Li Rongguang et al. found that by extruding WE43 magnesium alloy under relatively low temperature and relatively small extrusion ratio conditions, this method yields a mixed-grain structure composed of fine recrystallized equiaxed grains and non-recrystallized elongated grains, achieving a yield strength of 325 MPa and an elongation of 10.2%. However, this method has limitations: the homogenization process is time-consuming, the addition of rare earth elements increases costs, and the process is complex and energy-intensive. Therefore, developing high-strength, high-ductility magnesium alloys while reducing alloy costs, simplifying processes, and achieving short processes and low energy consumption remains a key technical challenge. Summary of the Invention

[0005] The purpose of this invention is to provide a short-process preparation method for magnesium alloys with high yield strength ratio and high plasticity, overcoming the shortcomings of the prior art. By combining a semi-solid rotary slurry process with an extrusion shearing process, and then adding water-cooled quenching, a magnesium alloy with high yield strength ratio and high plasticity can be prepared with a short process flow, saving process costs and simplifying the production process.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A short-process preparation method for magnesium alloys with high yield strength ratio and high ductility specifically includes the following steps:

[0008] 1) Semi-solid slurry preparation: Magnesium alloy melt at 700-720℃ is poured into a steel cylindrical crucible coated with a release agent, and the crucible is eccentrically rotated according to a semi-solid rotary slurry preparation process to obtain a semi-solid slurry with a solid content of 70%-80%; 2) Plastic deformation: The semi-solid slurry obtained in step 1) is subjected to low-temperature extrusion shear deformation. The extrusion shear die temperature is 180-230℃, the extrusion speed is 20-30mm / min, and the extrusion ratio is 10-20:1 to obtain magnesium alloy rods; 3) Water quenching: The magnesium alloy rods obtained in step 2) are quenched in cold water at 5-15℃ to obtain a magnesium alloy material with high yield strength ratio and high plasticity. This material has a bimodal grain structure with coarse and fine grains. At the same time, a non-basal plane texture with an angle of 34-47° to the extrusion axis is formed in the alloy.

[0009] Furthermore, the eccentricity of the eccentric rotation is 8 cm.

[0010] Furthermore, the magnesium alloy is a ZM21 alloy, and its chemical composition by mass percentage is: Zn 1.65-1.92%, Mn 0.91-0.95%, total impurity content ≤0.08%, and the balance is Mg.

[0011] Furthermore, the semi-solid rotary pulping process parameters are as follows: crucible temperature is 280-320℃, rotation time is 80-100s, and rotation speed is 180-200r / min.

[0012] Furthermore, the high yield strength and high plasticity magnesium alloy material has a room temperature tensile strength of 282-291 MPa, a yield strength of 258-277 MPa, a yield strength ratio of 0.91-0.95, and an elongation of 24-26%.

[0013] Furthermore, in step 1), the semi-solid slurry temperature is measured by an infrared thermometer. When the slurry temperature drops to the temperature corresponding to a melt solidity of 70%-80%, it is obtained.

[0014] Furthermore, in step 2), the low-temperature extrusion shear deformation occurs during the extrusion process, where the shear direction is always at 90° to the extrusion direction.

[0015] Furthermore, in step 2), the low-temperature extrusion shear deformation causes the texture direction to deviate significantly from the extrusion axis, with the 0001 axis deviating from the extrusion direction by an angle of 34-47°.

[0016] Furthermore, the bimodal grain structure is a combination of deformed grains and recrystallized grains, obtained by restricting the growth of recrystallized grains during deformation, with fine grains ≤5μm accounting for 74%-93%.

[0017] Furthermore, the release agent is a boron nitride release agent or a zinc oxide release agent.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1) This invention combines a semi-solid rotary pulping process with an extrusion shearing process, eliminating the need for the homogenization heat treatment of the billet required before traditional extrusion. This significantly shortens the alloy preparation cycle and eliminates the need for subsequent processing and heat treatment. The magnesium alloy obtained using this process exhibits a significant improvement in strength and plasticity, achieving a short-process, low-energy-consumption, and low-cost preparation of magnesium alloys with high yield strength ratio and high plasticity, and realizing a synergistic improvement in the strength and plasticity of magnesium alloys.

[0020] 2) After being prepared and processed by the method of this invention, the magnesium alloy has a bimodal grain structure with coarse and fine grains, wherein the proportion of fine grains (≤5μm) is 74%-93%; at the same time, the non-basal texture formed in the alloy at 34-47° with the extrusion axis can provide strong grain boundary strengthening and dislocation strengthening; the low proportion of coarse grains is conducive to dislocation slip and dislocation storage during plastic deformation, which significantly improves the work hardening ability and plastic deformation ability of the material;

[0021] 3) A non-basal plane texture with an angle of 34-47° to the extrusion axis is formed in the alloy microstructure. This non-basal plane texture effectively enhances the synergistic effect of the multi-slip system during room temperature stretching, promotes multi-slip activation, and improves room temperature plasticity.

[0022] 4) This invention can effectively save material preparation time, and can produce comprehensive mechanical properties comparable to rare earth magnesium alloys using rare earth-free and low-cost ZM21 magnesium alloy. The resulting alloy rod has a room temperature tensile strength of 291MPa, a yield strength of 277MPa, a yield ratio of 0.95, and an elongation of 24%. This invention achieves significant technical effects while saving raw material costs and simplifying the production process. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the semi-solid pulping platform structure of the present invention;

[0024] Figure 2 These are the electron backscatter diffraction (EBSD) microstructure characterization results of the ZM21 alloy prepared in Example 1 of this invention, where (a) is the inverse pole figure, (b) is the pole figure, (c) is the texture intensity diagram, (d) is the grain size distribution diagram, and (e) is the statistical diagram of the angle between the grain 0001 axis and the extrusion direction.

[0025] Figure 3 This is a diagram showing the room temperature tensile mechanical properties of the ZM21 alloy prepared in Example 1 of this invention.

[0026] Wherein: 1-Pulping platform, 2-Rotating tray, 3-Center of rotating tray, 4-Semi-solid pulping mold, 5-Center of semi-solid mold, 6-Eccentricity (distance between the center of rotating tray and the center of semi-solid mold). DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the specific embodiments used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the specific embodiments described below are some embodiments of the present invention. For those skilled in the art, other specific embodiments can be obtained based on these specific embodiments without creative effort.

[0029] The components of the embodiments of the invention described and shown in the specific embodiments herein can be arranged and designed in countless different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the specific embodiments is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0030] The following examples 1-3 are in Figure 1 The process is carried out on the semi-solid pulping platform shown. The rotating tray 2 is on the pulping platform 1, with the center 3 of the rotating tray. The semi-solid pulping mold 4 rotates eccentrically around the center 5 of the semi-solid mold. The eccentricity 6 (the distance between the center of the rotating tray and the center of the semi-solid mold) is 8cm.

[0031] Example 1

[0032] A short-process preparation method for magnesium alloys with high yield strength ratio and high ductility specifically includes the following steps:

[0033] 1) Semi-solid slurry preparation: Magnesium alloy melt at 700℃ was poured into a steel cylindrical crucible (65mm in diameter) coated with a release agent, and the crucible was eccentrically rotated according to a semi-solid rotary slurry preparation process to obtain a semi-solid slurry with a solid content of 80%; the magnesium alloy was ZM21 alloy, namely Mg-2Zn-1Mn alloy, and its chemical composition by mass percentage was: Zn 1.92%, Mn 0.91%, impurity content ≤0.08%, and the balance being Mg; the semi-solid rotary slurry preparation process parameters were: crucible temperature 300℃, rotation time 100s, and rotation speed 190r / min;

[0034] 2) Plastic deformation: The semi-solid slurry obtained in step 1) is subjected to low-temperature extrusion shear deformation. The extrusion shear die is 200°C, the extrusion speed is 20 mm / min, and the extrusion ratio is 12:1 to obtain magnesium alloy rods.

[0035] 3) Water quenching: The magnesium alloy rods obtained in step 2) are quenched in cold water at 10°C to obtain a magnesium alloy material with high yield strength ratio and high plasticity. This material has a bimodal grain structure with coarse and fine grains, of which fine grains (≤5μm) account for 89% of the total. At the same time, a non-basal texture with a 34° angle to the extrusion axis is formed in the alloy. The room temperature tensile strength of the alloy rods can reach 291MPa, the yield strength is 277MPa, the yield strength ratio is 0.95, and the elongation is 24%.

[0036] Example 2

[0037] A short-process preparation method for magnesium alloys with high yield strength ratio and high ductility specifically includes the following steps:

[0038] 1) Semi-solid slurry preparation: Magnesium alloy melt at 720℃ was poured into a steel cylindrical crucible (65mm in diameter) coated with a release agent, and the crucible was eccentrically rotated according to a semi-solid rotary slurry preparation process to obtain a semi-solid slurry with a solid content of 70%; the magnesium alloy was ZM21 alloy, namely Mg-2Zn-1Mn alloy, and its chemical composition by mass percentage was: Zn 1.65%, Mn 0.93%, impurity content ≤0.08%, and the balance being Mg; the semi-solid rotary slurry preparation process parameters were: crucible temperature 280℃, rotation time 80s, and rotation speed 180r / min;

[0039] 2) Plastic deformation: The semi-solid slurry obtained in step 1) is subjected to low-temperature extrusion shear deformation. The extrusion shear die is 200°C, the extrusion speed is 20 mm / min, and the extrusion ratio is 10:1 to obtain magnesium alloy rods.

[0040] 3) Water quenching: The magnesium alloy rods obtained in step 2) are quenched in cold water at 5°C to obtain a magnesium alloy material with high yield strength ratio and high plasticity. This material has a bimodal grain structure with coarse and fine grains, of which fine grains (≤5μm) account for 74% of the total. At the same time, a non-basal plane texture is formed in the alloy at 47° to the extrusion axis. The room temperature tensile strength of the alloy rods can reach 282MPa, the yield strength is 258MPa, the yield strength ratio is 0.91, and the elongation is 26%.

[0041] Example 3

[0042] A short-process preparation method for magnesium alloys with high yield strength ratio and high ductility specifically includes the following steps:

[0043] 1) Semi-solid slurry preparation: Magnesium alloy melt at 700-720℃ is poured into a steel cylindrical crucible (65mm in diameter) coated with a release agent. The crucible is then eccentrically rotated using a semi-solid rotary slurry preparation process to obtain a semi-solid slurry with a solid content of 75%. The magnesium alloy is ZM21 alloy, i.e., Mg-2Zn-1Mn alloy, and its chemical composition by mass percentage is: Zn 1.83%, Mn 0.91%, impurity content ≤0.08%, and the balance is Mg. The semi-solid rotary slurry preparation process parameters are: crucible temperature 320℃, rotation time 100s, and rotation speed 200r / min.

[0044] 2) Plastic deformation: The semi-solid slurry obtained in step 1) is subjected to low-temperature extrusion shear deformation. The extrusion shear die is 200°C, the extrusion speed is 20 mm / min, and the extrusion ratio is 20:1 to obtain magnesium alloy rods.

[0045] 3) Water quenching: The magnesium alloy rods obtained in step 2) are quenched in cold water at 15°C to obtain a magnesium alloy material with high yield strength ratio and high plasticity. This material has a bimodal grain structure with coarse and fine grains, of which fine grains (≤5μm) account for 93% of the total. At the same time, a non-basal texture with a 43° angle to the extrusion axis is formed in the alloy. The room temperature tensile strength of the alloy rods can reach 287MPa, the yield strength is 268MPa, the yield strength ratio is 0.93, and the elongation is 25%.

[0046] Comparative Example 1

[0047] In their article "Microstructure, mechanical behavior and low-temperature superplasticity of ECAP-processed ZM21 magnesium alloy," published in the *Journal of Alloys and Compounds*, Volume 638, pp. 267-276, Ehsan Mostaed et al. disclosed a method for preparing a high-strength, high-ductility commercial ZM21 alloy: A 10mm diameter, 100mm long bar-shaped commercial ZM21 magnesium alloy (composition by mass: Zn 1.78%, Mn 0.89%, balance Mg) was subjected to four ECAP processes at 200°C, with each pass involving a 110° rotation and an extrusion speed of 30mm / min. The resulting alloy exhibited a yield strength of 212 MPa, an elongation of 24%, and an average fine grain size of 0.7 μm.

[0048] Comparative Example 2

[0049] In their article "Effect of extrusion ratio on the microstructure and mechanical properties of AZ31 magnesium alloy," published in Volume 182, pp. 281-285 of the *Journal of Materials Research and Technology*, Yongjun Chen et al. disclosed a high-strength, high-ductility commercial AZ31 magnesium alloy (Al: 3.091%, Zn: 1.023%, Mn: 0.421% by mass). The alloy underwent reverse extrusion experiments at 250°C, with an extrusion ratio of 24:1 and an extrusion speed of 20 mm / min. The resulting alloy exhibited a yield strength of 233 MPa and an elongation of 17.9%.

[0050] Comparative Example 3

[0051] In their article "Effect of addition of small amounts of samarium on microstructural evolution and mechanics," published in Volume 9, pp. 133-141 of the *Journal of Materials Research and Technology*, Tian Tian Zhang et al. disclosed a high-strength, high-ductility magnesium alloy (chemical composition, by mass percentage: Zn 5.49%, Zr 0.745%, balance Mg). An extrusion experiment was conducted at 400℃ with an extrusion ratio of 20:1 and an extrusion speed of 1.6 cm / s. The resulting alloy exhibited a yield strength of 246 MPa and an elongation of 16.9%.

[0052] Compared with existing magnesium alloy products with large plastic deformation, this invention combines a semi-solid rotary slurry process with an extrusion shearing process to achieve mechanical properties comparable to those of large plastic deformation, and achieves a synergistic improvement in strength and plasticity. Simultaneously, it saves production costs and simplifies the process. Comparing this invention with Comparative Example 1, the yield strength obtained by this invention is superior to that of Comparative Example 1. Furthermore, the alloy composition used in this invention is similar to that of Comparative Example 2 and Comparative Example 3. Comparing this invention with Comparative Example 2 and Comparative Example 3, the yield strength and elongation obtained by this invention are both higher than those of the comparative examples. In summary, this invention achieves significantly better results than existing technologies while simplifying the process, thus saving production costs and achieving a shorter process flow. It also simultaneously improves the strength and plasticity of the magnesium alloy. The comprehensive mechanical properties of the alloy bars are: a maximum room temperature tensile strength of 291 MPa, a maximum yield strength of 277 MPa, a yield-to-tensile ratio of 0.95, and an elongation of 24%.

[0053] In summary, this invention eliminates the lengthy preparation process of traditional extrusion requiring homogenization heat treatment, significantly shortening the alloy preparation cycle and eliminating the need for subsequent processing and heat treatment. The magnesium alloy obtained using this process exhibits a marked improvement in strength and ductility. The non-basal texture prepared by this method effectively enhances the synergistic effect of multi-slip systems during room temperature stretching, promoting multi-slip activation and avoiding the poor ductility of magnesium alloys due to limitations imposed by finite slip systems. Simultaneously, the obtained high-density dislocations and non-basal texture synergistically improve the alloy's strength and ductility, and compared to large plastic deformation, only one deformation is required to achieve the desired effect. This is particularly suitable for magnesium alloy structural components requiring high yield strength ratio and high ductility, such as in aerospace and automotive lightweighting applications. Furthermore, the high yield strength ratio and high ductility of the material significantly improve the service safety of the magnesium alloy. This provides new guidance for the development of high-reliability magnesium alloys and broadens their industrial application scope.

[0054] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A short-process preparation method for magnesium alloys with high yield strength ratio and high ductility, characterized in that, Specifically, the steps include the following: 1) Semi-solid slurry preparation: Magnesium alloy melt at 700-720℃ is poured into a steel cylindrical crucible coated with a release agent, and the crucible is eccentrically rotated according to the semi-solid rotary slurry preparation process to obtain a semi-solid slurry with a solid phase of 70%-80%. 2) Plastic deformation: The semi-solid slurry obtained in step 1) is subjected to low-temperature extrusion shear deformation. The temperature of the extrusion shear die is 180-230℃, the extrusion speed is 20-30mm / min, and the extrusion ratio is 10-20:1 to obtain magnesium alloy rods. 3) Water quenching: The magnesium alloy rods obtained in step 2) are quenched in cold water at 5-15℃ to obtain a magnesium alloy material with high yield strength ratio and high plasticity. The material has a bimodal grain structure with coarse and fine grains. At the same time, a non-basal texture with an angle of 34-47° to the extrusion axis is formed in the alloy.

2. The short-process preparation method for a high yield strength ratio and high ductility magnesium alloy according to claim 1, characterized in that, The eccentricity of the eccentric rotation is 8 cm.

3. The short-process preparation method for a high yield strength ratio and high ductility magnesium alloy according to claim 1, characterized in that, The magnesium alloy is a ZM21 alloy, and its chemical composition by mass percentage is: Zn 1.65-1.92%, Mn 0.91-0.95%, total impurity content ≤0.08%, and the balance is Mg.

4. The short-process preparation method for a high yield strength ratio and high ductility magnesium alloy according to claim 1, characterized in that, The semi-solid rotary pulping process parameters are as follows: crucible temperature is 280-320℃, rotation time is 80-100s, and rotation speed is 180-200r / min.

5. The short-process preparation method for a high yield strength ratio and high ductility magnesium alloy according to claim 1, characterized in that, The high yield strength and high plasticity magnesium alloy material has a room temperature tensile strength of 282-291 MPa, a yield strength of 258-277 MPa, a yield strength ratio of 0.91-0.95, and an elongation of 24-26%.

6. The short-process preparation method for a high yield strength ratio and high ductility magnesium alloy according to claim 1, characterized in that, The semi-solid slurry in step 1) is obtained by measuring the temperature of the semi-solid slurry with an infrared thermometer. When the slurry temperature drops to the temperature corresponding to a melt solidity of 70%-80%, it is ready.

7. The short-process preparation method for a high yield strength ratio and high ductility magnesium alloy according to claim 1, characterized in that, In step 2), the low-temperature extrusion shear deformation occurs during the extrusion process, where the shear direction is always at 90° to the extrusion direction.

8. The short-process preparation method for a high yield strength ratio and high ductility magnesium alloy according to claim 1, characterized in that, In step 2), the low-temperature extrusion shear deformation causes the texture direction to deviate significantly from the extrusion axis, with the 0001 axis deviating from the extrusion direction by an angle of 34-47°.

9. The short-process preparation method for a high yield strength ratio and high ductility magnesium alloy according to claim 1, characterized in that, The bimodal grain structure is a combination of deformed grains and recrystallized grains, obtained by restricting the growth of recrystallized grains during deformation, with the proportion of fine grains ≤5μm ranging from 74% to 93%.

10. The short-process preparation method for a high yield strength ratio and high ductility magnesium alloy according to claim 1, characterized in that, The release agent is either boron nitride or zinc oxide.

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