A high-rare earth element content magnesium alloy bar with strength and plastic tensile-compressive isotropy and a preparation method thereof

Abstract

The application discloses a preparation method of a high-rare earth element content magnesium alloy rod with strength and plastic tensile-compressive isotropy. According to the designed magnesium alloy component allocation ratio, each component is weighed, and magnesium, magnesium gadolinium intermediate alloy, magnesium yttrium intermediate alloy, silver, magnesium zirconium intermediate alloy and magnesium neodymium intermediate alloy are sequentially subjected to smelting and casting under SF6 protection atmosphere to obtain a cast ingot. The cast ingot is subjected to homogenization treatment and continuous extrusion to obtain the magnesium alloy rod. The alloy rod prepared by the method has a room temperature tensile yield strength of 288 MPa and a room temperature compressive yield strength of 266 MPa, and the elongation after fracture can reach 19.0% and 18.2% respectively, and the alloy rod has good tensile-compressive isotropy.

Description

Technical Field

[0001] This invention relates to a magnesium alloy with high rare earth content, and more particularly to a magnesium alloy bar with high rare earth element content and isotropic tensile and compressive strength and plasticity, and its preparation method, belonging to the field of metal material preparation. Background Technology

[0002] Magnesium alloys are hailed as the lightest metallic structural materials, playing an irreplaceable role in weight reduction for automobiles, 3C products, and aerospace equipment. Magnesium alloys with added rare earth elements have even higher high-temperature strength.

[0003] Chinese invention patent application "A Heat Treatment Method for Heat-Resistant Cast Magnesium Alloy Material" (CN201811041410.5) describes a method for heat treatment of Mg-10.5Gd-2.5Y-1.5Nd-0.1Zn-0.5Zr alloy. In one example, the alloy exhibits a room temperature tensile strength of 365 MPa and an elongation of 4.5%, while at 300°C, the tensile strength is 225 MPa and the elongation is 18%. However, due to the close-packed hexagonal structure of magnesium alloys, twins open to coordinate dislocation slip. The effects of tension and compression on twins differ at room temperature, resulting in a significant asymmetry in the strength and plasticity of magnesium alloys under tensile and compressive conditions. As a lightweight structural material, only the worst performance under tension or compression can be selected as the standard for use, which limits the application of magnesium alloys.

[0004] Chinese invention patent application CN202311425543.3 discloses a processing method for eliminating tensile-compressive asymmetry in magnesium alloys. This patent reduces the tensile-compressive asymmetry of magnesium alloys by preparing ultrafine grains through rapid solidification. Chinese invention patent application CN201310552197.5 discloses a processing method for improving the tensile-compressive asymmetry of magnesium alloys. This patent obtains magnesium alloys with significantly improved strength and tensile-compressive asymmetry through torsion. However, the above patents only focus on the tensile-compressive symmetry of magnesium alloy strength and do not investigate the difference in elongation after tensile and compressive fracture. Summary of the Invention

[0005] To address the severe asymmetry between strength and plastic tensile / compressive properties in magnesium alloys, this invention designs deformed rare-earth magnesium alloy rods with added Gd, Y, Zr, Ag, and Nd elements. This alloy can meet the requirements for lightweight magnesium alloy structural materials in aerospace, automotive, and other fields.

[0006] The second objective of this invention is to provide a method for preparing magnesium alloy bars with high rare earth element content that exhibits both strength and plasticity in tensile and compressive stresses. By using slow hot extrusion, sufficient dynamic recrystallization time is provided for the alloy, thereby reducing the severe tensile and compressive asymmetry of the magnesium alloy.

[0007] To achieve the above-mentioned technical objectives, this invention provides a method for preparing magnesium alloy rods with high rare earth element content that exhibit both strength and plasticity in tensile and compressive stresses. The method involves weighing each component according to a designed magnesium alloy composition ratio, and sequentially melting and casting magnesium, gadolinium magnesium master alloy, yttrium magnesium master alloy, silver, zirconium magnesium master alloy, and neodymium magnesium master alloy under an SF6 protective atmosphere to obtain an ingot. The ingot is then homogenized and continuously extruded to obtain the magnesium alloy rod.

[0008] The magnesium alloy rod is composed of the following components by mass percentage: Gd: 10-12%, Y: 1-2%, Zr: 0.01-0.5%, Ag: 0.01-0.5%, Nd: 0.01-0.5%, and the total mass content of rare earth elements is ≥12%; impurity elements Al≤0.01%, Fe≤0.04%, Mn≤0.02%, the total content of impurity elements does not exceed 0.1%, and the remainder is Mg. More preferably, the composition is Gd: 11.5-12%, Y: 1-1.7%, Zr: 0.01-0.37%, Ag: 0.01-0.5%, Nd: 0.01-0.39%, and the total mass content of rare earth elements is ≥12%; impurity elements Al≤0.01%, Fe≤0.04%, Mn≤0.02%, the total content of impurity elements does not exceed 0.1%, and the remainder is Mg. Within a further optimized range of alloy compositions, the prepared magnesium alloy rods exhibit optimal tensile-compressive isomorphism, as well as high plasticity and strength.

[0009] The key to the technical solution of this invention lies in the combination of compositional design and preparation method. Specifically, by adding Gd and Y elements to magnesium alloys, the mechanical properties of magnesium alloys can be improved, while the basal texture (0001 basal plane) after extrusion deformation is weakened, reducing anisotropy and tensile-compressive asymmetry. Ag and Zr elements can refine the alloy grains during the casting stage, and the addition of trace amounts of Nd elements can improve the mechanical properties of magnesium alloys during the casting stage. Furthermore, the synergistic addition of rare earth elements Gd, Y, and Nd can improve the room temperature strength of magnesium alloys. In addition, the composition needs to be combined with the control of process parameters in this invention. The preparation method of this invention mainly uses slow hot extrusion to provide sufficient dynamic recrystallization time for the alloy. At the same time, by introducing shear stress during the extrusion process, the dislocation density inside the grains can be increased, causing changes in grain orientation, thereby breaking the basal texture in the magnesium alloy.

[0010] The inventors discovered that using SF6 as a protective atmosphere during the preparation process can effectively prevent the oxidation of magnesium alloys during smelting. SF6 can form a dense protective film on the surface of the magnesium alloy, mainly composed of MgO and MgF2. These films can effectively isolate oxygen from contact with the magnesium alloy, thereby slowing down or preventing the oxidation of magnesium.

[0011] Meanwhile, in this invention, the amount of each metal element used also needs to be controlled, especially the amount of Zr, Ag and Nd. If the amount of these three elements is too high, it will cause a serious decrease in the elongation of the magnesium alloy.

[0012] As a preferred embodiment, the purity of the magnesium and silver is greater than 99.9%.

[0013] As a preferred embodiment, during the smelting process, magnesium is first added and the temperature is raised to 770-800°C, then magnesium-gadolinium master alloy, magnesium-yttrium master alloy and silver are added. After they are completely melted, magnesium-zirconium master alloy and magnesium-neodymium master alloy are added and kept at the temperature for 30-40 minutes, and then refined at 750-760°C.

[0014] As a preferred embodiment, the melting process is followed by a standing period of 30–40 minutes before casting; the casting speed is 2–10 cm / min. This invention, by allowing the melt to stand for a period after melting, can effectively remove gases from the melt, improve the microstructure and macroscopic properties of the magnesium alloy, and reduce porosity and micro-permeability in the casting. As a preferred embodiment, the homogenization treatment conditions are as follows: first, heat to 300–320℃ and hold for 10–12 hours, then heat to 480–500℃ and continue holding for 10–12 hours, followed immediately by water quenching.

[0015] As a preferred embodiment, the continuous extrusion conditions are: a temperature of 400–450°C, a holding time of 20–30 min, a continuous extrusion ratio greater than 10, an extrusion speed of 0.1–0.2 m / s, and immediate water quenching after continuous extrusion. Within the alloy composition and dosage range of this invention, increasing the extrusion ratio can further refine the alloy grains and improve mechanical properties; while slow extrusion is beneficial for sufficient dynamic recrystallization during the extrusion process, resulting in a uniform microstructure without distortion. Simultaneously, the extrusion temperature affects the rate of dynamic recrystallization of the alloy; appropriately increasing the extrusion temperature is beneficial for dynamic recrystallization. Further preferred is an extrusion ratio of 16–20:1 and a temperature of 420–450°C; even more preferred is an extrusion ratio of 20:1. Within further preferred ranges, the ratio of tensile-compressive-elongation yield strength of the alloy is 1.08–1.12, and the ratio of tensile-compressive elongation after fracture is 1.04–1.29.

[0016] This invention also provides a high-rare-earth element content magnesium alloy rod with isotropic strength and plasticity in tensile and compressive forces, obtained by the above-described preparation method. The magnesium alloy rod obtained through the preparation method and composition design of this invention, in addition to being a Mg5Gd precipitate-strengthened alloy, also contains Mg... 24 Precipitated phases such as Y5 and Mg3Ag can also effectively strengthen alloys.

[0017] As a preferred embodiment, the high rare earth element content magnesium alloy rod of the present invention has a grain size of 2.4–3.2 μm. The magnesium alloy rod obtained by the preparation method of the present invention has a fine grain size and a narrow distribution range. The fine grains can effectively hinder the movement of dislocations and promote grain boundary slip as a mechanism for plastic deformation, thus bringing a dual improvement in strength and plasticity to the magnesium alloy.

[0018] As a preferred embodiment, the ratio of tensile-compressive-elongation yield strength is 0.91 to 1.12, and the ratio of tensile-compressive elongation after fracture is 1.04 to 1.29.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The alloy of the present invention has a maximum tensile-compression-elongation yield strength ratio of 1.08 at room temperature and a maximum tensile-compression elongation ratio of 1.04.

[0021] (2) In this invention, the basal texture is reduced through continuous extrusion. Continuous extrusion introduces shear stress during the extrusion process, which can break the basal texture (0001 basal plane) in the magnesium alloy. During the extrusion process, the material undergoes severe plastic deformation, which leads to an increase in dislocation density within the grains and a change in grain orientation, thereby weakening the dominance of the basal texture. In addition, the material undergoes complete dynamic recrystallization during long-term extrusion, which helps to refine the grains and further weaken the basal texture, thereby increasing the plasticity, strength, and deformation degree of the magnesium alloy and solving the problem of severe tension-compression asymmetry in magnesium alloys.

[0022] (3) In this invention, by continuously extruding and adding Zr, Ag and trace Nd elements to the alloy, a large number of recrystallized grains can be introduced into the alloy, with an average grain size of about 2.4 μm, which significantly improves the mechanical properties of the alloy. Attached Figure Description

[0023] Figure 1 This is a typical scanning electron microscope image after homogenization processing according to the present invention.

[0024] Figure 2 The EBSD results are for the alloy in Example 1 of this invention.

[0025] Figure 3 This is a grain size distribution diagram of the alloy in Example 1 of the present invention.

[0026] Figure 4 The stress-strain curves for room temperature tensile and compressive stresses of the alloy in Example 1 of this invention are shown.

[0027] Figure 5 These are photographs of the room temperature tensile and compressive fracture surfaces of the alloy in Example 1 of this invention.

[0028] Figure 6 The room temperature tensile and compressive stress-strain curves of the alloy in Example 2 are shown. Detailed Implementation

[0029] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0031] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods.

[0032] Example 1

[0033] (1)Alloy composition

[0034] The alloy composition (mass fraction) is: Gd: 11.5%, Y: 1.7%, Zr: 0.37%, Ag: 0.5%, Nd: 0.39%, impurity elements Al≤0.01%, Fe≤0.04%, Mn≤0.02%, and the remainder is Mg.

[0035] (2) Alloy casting

[0036] The weighed alloy was placed in a drying oven at 150℃. Pure magnesium was then added, followed by heating to approximately 770℃. Mg-30Gd, Mg-30Y, and pure silver were then added and allowed to melt completely. Mg-20Zr and Mg-20Nd were added, and the mixture was held at this temperature for 30 minutes. After refining, the alloy was allowed to stand for 30 minutes before being poured into a steel mold. The entire melting process was carried out under an SF6 protective atmosphere, with a casting speed of 10 cm / min. The alloy composition met the above requirements.

[0037] (3) Alloy homogenization treatment

[0038] The above-mentioned ingots were placed in a resistance furnace and heated to 320°C and held for 12 hours. Then, the temperature was raised to 500°C and held for 12 hours before water quenching.

[0039] (4) Continuous extrusion of alloys

[0040] The resistance furnace was heated to 450℃. After the temperature stabilized for 30 minutes, the homogenized and annealed alloy was placed in the resistance furnace and held for 20 minutes. Then, extrusion was started at a speed of 0.1 m / s and an extrusion ratio of 20:1. After extrusion, the alloy was immediately water-cooled and quenched to obtain the alloy.

[0041] (5) Mechanical properties

[0042] After homogenization and extrusion at 450℃ (20:1), the alloy in this example exhibits a tensile yield strength of 288 MPa and an elongation after fracture of 19.0% at room temperature, and a compressive yield strength of 266 MPa and an elongation after fracture of 18.2% at room temperature. The tensile-compressive yield strength ratio is 1.08, and the tensile-compressive elongation after fracture ratio is 1.04.

[0043] The EBSD results of the alloy prepared in Example 1 are shown in [Figure 1]. Figure 2 The EBSD inverse pole figure shows that the alloy contains a large number of dynamically recrystallized grains, without elongated deformed grains. The pole figure also shows that the alloy did not exhibit strong basal texture after extrusion. The grain size distribution diagram of the alloy prepared in Example 1 is shown below. Figure 3 As shown in the figure, the average grain size of the alloy prepared by the present invention is 2.4 μm, the grains are fine, and the grain distribution range of the alloy is narrow.

[0044] Example 2

[0045] (1)Alloy composition

[0046] The alloy composition (mass fraction) is: Gd: 11.5%, Y: 1.7%, Zr: 0.37%, Ag: 0.5%, Nd: 0.39%, impurity elements Al≤0.01%, Fe≤0.04%, Mn≤0.02%, and the remainder is Mg.

[0047] (2) Alloy casting

[0048] The weighed alloy was placed in a drying oven at 150℃. Pure magnesium was then added, followed by heating to approximately 770℃. Mg-30Gd, Mg-30Y, and pure silver were then added and allowed to melt completely. Mg-20Zr and Mg-20Nd were added, and the mixture was held at this temperature for 30 minutes. After refining, the alloy was allowed to stand for 30 minutes before being poured into a steel mold. The entire melting process was carried out under an SF6 protective atmosphere, with a casting speed of 10 cm / min. The alloy composition met the above requirements.

[0049] (3) Alloy homogenization treatment

[0050] The above-mentioned ingots were placed in a resistance furnace and heated to 320°C and held for 12 hours. Then, the temperature was raised to 500°C and held for 12 hours before water quenching.

[0051] (4) Continuous extrusion of alloys

[0052] The resistance furnace was heated to 450℃. After the temperature stabilized for 30 minutes, the homogenized and annealed alloy was placed in the resistance furnace and held for 20 minutes. Then, extrusion was started at a speed of 0.1 m / s and an extrusion ratio of 16:1. After extrusion, the alloy was immediately water-cooled and quenched to obtain the alloy.

[0053] (5) Mechanical properties

[0054] After homogenization and extrusion at 450℃ (16:1), the alloy in this example exhibits a tensile yield strength of 284 MPa and an elongation after fracture of 17.3% at room temperature, and a compressive yield strength of 260 MPa and an elongation after fracture of 13.8% at room temperature. The tensile-compressive yield strength ratio is 1.09, and the tensile-compressive elongation after fracture ratio is 1.25.

[0055] Example 3

[0056] (1)Alloy composition

[0057] The alloy composition (mass fraction) is: Gd: 11.5%, Y: 1.7%, Zr: 0.37%, Ag: 0.5%, Nd: 0.39%, impurity elements Al≤0.01%, Fe≤0.04%, Mn≤0.02%, and the remainder is Mg.

[0058] (2) Alloy casting

[0059] The weighed alloy was placed in a drying oven at 150℃. Pure magnesium was then added, followed by heating to approximately 770℃. Mg-30Gd, Mg-30Y, and pure silver were then added and allowed to melt completely. Mg-20Zr and Mg-20Nd were added, and the mixture was held at this temperature for 30 minutes. After refining, the alloy was allowed to stand for 30 minutes before being poured into a steel mold. The entire melting process was carried out under an SF6 protective atmosphere, with a casting speed of 10 cm / min. The alloy composition met the above requirements.

[0060] (3) Alloy homogenization treatment

[0061] The above-mentioned ingots were placed in a resistance furnace and heated to 320°C and held for 12 hours. Then, the temperature was raised to 500°C and held for 12 hours before water quenching.

[0062] (4) Continuous extrusion of alloys

[0063] The resistance furnace was heated to 450℃. After the temperature stabilized for 30 minutes, the homogenized and annealed alloy was placed in the resistance furnace and held for 20 minutes. Then, extrusion was started at a speed of 0.1 m / s and an extrusion ratio of 10:1. After extrusion, the alloy was immediately water-cooled and quenched to obtain the alloy.

[0064] (5) Mechanical properties

[0065] After homogenization and extrusion at 450℃ (10:1), the alloy in this example exhibits a tensile yield strength of 240 MPa and an elongation after fracture of 12.6% at room temperature, and a compressive yield strength of 213 MPa and an elongation after fracture of 9.8% at room temperature. The tensile-compressive yield strength ratio is 1.12, and the tensile-compressive elongation after fracture ratio is 1.29.

[0066] Example 4

[0067] (1)Alloy composition

[0068] The alloy composition (mass fraction) is: Gd: 11.5%, Y: 1.7%, Zr: 0.37%, Ag: 0.5%, Nd: 0.39%, impurity elements Al≤0.01%, Fe≤0.04%, Mn≤0.02%, and the remainder is Mg.

[0069] (2) Alloy casting

[0070] The weighed alloy was placed in a drying oven at 150℃. Pure magnesium was then added, followed by heating to approximately 770℃. Mg-30Gd, Mg-30Y, and pure silver were added, and after complete melting, Mg-20Zr and Mg-20Nd were added. The mixture was held at this temperature for 30 minutes, then refined at 750℃. After refining, it was allowed to stand for 30 minutes before being poured into a steel mold. The entire melting process was carried out under an SF6 protective atmosphere, with a casting speed of 10 cm / min. The alloy composition met the above requirements.

[0071] (3) Alloy homogenization treatment

[0072] The above-mentioned ingots were placed in a resistance furnace and heated to 320°C and held for 12 hours. Then, the temperature was raised to 500°C and held for 12 hours before water quenching.

[0073] (4) Continuous extrusion of alloys

[0074] The resistance furnace was heated to 400℃. After the temperature stabilized for 30 minutes, the homogenized and annealed alloy was placed in the resistance furnace and held for 20 minutes. Then, extrusion was started at a speed of 0.1 m / s and an extrusion ratio of 20:1. After extrusion, the alloy was immediately water-cooled and quenched to obtain the alloy.

[0075] (5) Mechanical properties

[0076] After homogenization and extrusion at 400℃ (10:1), the alloy in this example exhibits a tensile yield strength of 262 MPa and an elongation after fracture of 17.6% at room temperature, and a compressive yield strength of 288 MPa and an elongation after fracture of 13.9% at room temperature. The tensile-compressive yield strength ratio is 0.91, and the tensile-compressive elongation after fracture ratio is 1.27.

[0077] Example 5

[0078] (1)Alloy composition

[0079] The alloy composition (mass fraction) is: Gd: 10.5%, Y: 1.8%, Zr: 0.45%, Ag: 0.5%, Nd: 0.41%, impurity elements Al≤0.01%, Fe≤0.04%, Mn≤0.02%, and the remainder is Mg.

[0080] (2) Alloy casting

[0081] The weighed alloy was placed in a drying oven at 150℃. Pure magnesium was then added, followed by heating to approximately 770℃. Mg-30Gd, Mg-30Y, and pure silver were then added and allowed to melt completely. Mg-20Zr and Mg-20Nd were added, and the mixture was held at this temperature for 30 minutes. After refining, the alloy was allowed to stand for 30 minutes before being poured into a steel mold. The entire melting process was carried out under an SF6 protective atmosphere, with a casting speed of 10 cm / min. The alloy composition met the above requirements.

[0082] (3) Alloy homogenization treatment

[0083] The above-mentioned ingots were placed in a resistance furnace and heated to 320°C and held for 12 hours. Then, the temperature was raised to 500°C and held for 12 hours before water quenching.

[0084] (4) Continuous extrusion of alloys

[0085] The resistance furnace was heated to 450℃. After the temperature stabilized for 30 minutes, the homogenized and annealed alloy was placed in the resistance furnace and held for 20 minutes. Then, extrusion was started at a speed of 0.2 m / s and an extrusion ratio of 20:1. After extrusion, the alloy was immediately water-cooled and quenched to obtain the alloy.

[0086] (5) Mechanical properties

[0087] After homogenization and extrusion at 450℃ (20:1), the alloy in this example exhibits a tensile yield strength of 253 MPa and an elongation after fracture of 16.3% at room temperature, and a compressive yield strength of 213 MPa and an elongation after fracture of 9.9% at room temperature. The tensile-compressive yield strength ratio is 1.19, and the tensile-compressive elongation after fracture ratio is 1.65.

[0088] Example 6

[0089] (1)Alloy composition

[0090] The alloy composition (mass fraction) is as follows: Gd: 10.5%, Y: 1.8%, Zr: 0.45%, Ag: 0.5%, Nd: 0.41%, impurity elements Al≤0.01%, Fe≤0.04%, Mn≤0.02%, and the remainder is Mg.

[0091] (2) Alloy casting

[0092] The weighed alloy was placed in a drying oven at 150℃. Pure magnesium was then added, followed by heating to approximately 770℃. Mg-30Gd, Mg-30Y, and pure silver were then added and allowed to melt completely. Mg-20Zr and Mg-20Nd were added, and the mixture was held at this temperature for 30 minutes before refining at 750℃. After refining, the mixture was allowed to stand for 40 minutes before being poured into a steel mold. The entire melting process was carried out under an SF6 protective atmosphere, with a casting speed of 10 cm / min. The alloy composition met the above requirements.

[0093] (3) Alloy homogenization treatment

[0094] The above-mentioned ingots were placed in a resistance furnace and heated to 320°C and held for 12 hours. Then, the temperature was raised to 500°C and held for 12 hours before water quenching.

[0095] (4) Continuous extrusion of alloys

[0096] The resistance furnace was heated to 400℃. After the temperature stabilized for 30 minutes, the homogenized and annealed alloy was placed in the resistance furnace and held for 20 minutes. Then, extrusion was started at a speed of 0.1 m / s and an extrusion ratio of 20:1. After extrusion, the alloy was immediately water-quenched.

[0097] (5) Mechanical properties

[0098] After homogenization and extrusion at 400℃ (20:1), the alloy in this example exhibits a tensile yield strength of 238 MPa and an elongation after fracture of 13.3% at room temperature, and a compressive yield strength of 256 MPa and an elongation after fracture of 10.6% at room temperature. The tensile-compressive yield strength ratio is 0.92, and the tensile-compressive elongation after fracture ratio is 1.25.

[0099] Comparative Example 1

[0100] The only difference between this comparative example and Example 1 is that the mass fraction of Gd in the magnesium alloy is replaced with 8.5%, while the other components, preparation steps and conditions are the same, resulting in an alloy.

[0101] Comparative Example 2

[0102] The only difference between this comparative example and Example 1 is that the extrusion speed is increased to 0.5 m / s, while the other components, steps and conditions are the same, resulting in an alloy.

[0103] The mechanical properties of the alloys prepared in Examples 1-6 and Comparative Examples 1-2 are shown in Table 1.

[0104] Table 1

[0105]

[0106] Note: The test data in Table 1 are from tests conducted at room temperature.

[0107] As shown in Table 1, when the alloy composition remains constant in Examples 1-3, increasing the extrusion ratio further refines the alloy grains, leading to increased strength and ductility in the magnesium alloy. The extrusion ratio has a particularly significant impact on the tensile-compressive elongation-to-fracture ratio of the ductility. Comparing the data from Examples 1 and 4, when the alloy composition remains constant, decreasing the extrusion temperature slows down the dynamic recrystallization rate of the alloy, resulting in an increased tensile-compressive elongation-to-fracture ratio in the magnesium alloy. Comparing the data from Examples 5 and 1, when the amounts of Gd, Y, Zr, and Nd in the alloy change, and the extrusion speed increases, both the strength and ductility of the magnesium alloy decrease, especially the tensile-compressive symmetry of the ductility. Comparing the data from Comparative Example 1 and Example 1, when the Gd content in the alloy decreases, the overall performance of the magnesium alloy significantly decreases. Comparing the data from Comparative Example 2 and Example 1, increasing the extrusion speed has no significant effect on the tensile-compressive symmetry of the alloy's strength, but it significantly reduces the tensile-compressive symmetry of the alloy's ductility.

Claims

1. A method of producing a high rare earth element content magnesium alloy rod material that is strong and plastic in both tension and compression, characterized by: According to the designed magnesium alloy component distribution ratio, each component is weighed, and magnesium, magnesium gadolinium intermediate alloy, magnesium yttrium intermediate alloy, silver, magnesium zirconium intermediate alloy and magnesium neodymium intermediate alloy are sequentially melted and cast under SF6 protection atmosphere to obtain an ingot; the ingot is subjected to homogenization treatment and continuous extrusion to break the 0001 basal plane texture, thereby obtaining a magnesium alloy rod; The magnesium alloy rod is composed of the following components in terms of mass percentage: Gd: 10-12%, Y: 1-2%, Zr: 0.01-0.5%, Ag: 0.01-0.5%, Nd: 0.01-0.5%, and the total mass content of rare earth elements is ≥12%; impurity elements Al≤0.01%, Fe≤0.04%, Mn≤0.02%, the total content of impurity elements is not more than 0.1%, and the rest is Mg; The continuous extrusion conditions are: temperature is 400-450℃, holding for 20-30min, continuous extrusion ratio is greater than 10, extrusion speed is 0.1-0.2m / s, and water quenching is performed immediately after continuous extrusion.

2. The method of producing a high rare earth element content magnesium alloy bar having strength and plasticity symmetrical in tension and compression according to claim 1, characterized by: The purity of the magnesium and silver is greater than 99.9%.

3. A method of producing a high rare earth element content magnesium alloy rod material having strength and plastic tensile and compressive isotropy according to claim 2, characterized by: In the melting process, magnesium is first added and heated to 770-800℃, then magnesium gadolinium intermediate alloy, magnesium yttrium intermediate alloy and silver are added, after complete melting, magnesium zirconium intermediate alloy and magnesium neodymium intermediate alloy are added, holding for 30-40min, and refining is performed at 750-760℃.

4. The method of producing a high rare earth element content magnesium alloy bar having strength and plasticity symmetrical in tension and compression according to any one of claims 1 to 3, characterized in that: The ingot is cast after holding for 30-40min after melting; the down-drawing speed of the casting is 2-10cm / min.

5. The method of producing a high rare earth element content magnesium alloy bar having strength and plasticity symmetrical in tension and compression according to claim 4, characterized in that: The homogenization treatment conditions are: first heated to 300-320℃ and holding for 10-12h, then heated to 480-500℃ and holding for 10-12h, and then immediately water quenched.

6. A high rare earth element content magnesium alloy rod material having strength and plasticity equal in tension and compression, characterized by: Obtained by the preparation method of any one of claims 1-5.

7. The high rare earth element content magnesium alloy rod of strength and plasticity equal in tension and compression according to claim 6, characterized in that: The tensile-compressive yield strength ratio is 0.91-1.12, the tensile-compressive elongation ratio after fracture is 1.04-1.29, and the grain size is 2.4-3.2μm.

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