A method for preparing a high-rare earth content Mg-rare earth alloy with uniform composition

Abstract

The application discloses a preparation method of high-rare earth content Mg-rare earth alloy with uniform components, and belongs to the field of preparation of Mg-rare earth alloy. The application provides a simple preparation method of high-rare earth content Mg-rare earth alloy with uniform components. The method is as follows: magnesium particles and rare earth metals are cut into strips, then the pure magnesium particles and the strip-shaped rare earth are alternately placed in a graphite crucible in a layer-by-layer mode, sealed in a quartz tube, smelted by a box-type resistance furnace or inducted heating, and post-processed. The Mg-rare earth alloy synthesized by the method is composed of alpha and beta dual phases, mainly beta single phase, and a small amount of alpha phase, has uniform components, and has good mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of Mg-rare earth alloy preparation; specifically, it relates to a method for preparing a Mg-rare earth alloy with uniform composition and high rare earth content. Background Technology

[0002] Magnesium alloys are the lightest metallic structural materials currently used in practical applications, with a density generally below 2.0 g / cm³. 3 Magnesium alloys possess advantages such as high specific strength, high specific stiffness, good vibration absorption, and good electromagnetic shielding, making them potential lightweight structural materials for aerospace applications. The application of magnesium alloys in the aerospace industry can not only bring significant weight reduction benefits and improve fuel efficiency, but also enhance maneuverability, transport capacity, and reduce costs. Furthermore, due to their good biocompatibility, biodegradability, and superior osteogenic properties, they also have great application prospects in the biomedical field. However, traditional magnesium alloys, due to their hexagonal close-packed (hcp) structure, i.e., the α phase, exhibit high plastic anisotropy and poor plastic deformation capacity at room temperature. This poor plastic deformation capacity limits the application of magnesium alloys. Therefore, to improve their strength, researchers have used methods such as deformation strengthening, solid solution strengthening, dispersion strengthening, and grain refinement strengthening. However, due to the inherent defects of the hcp structure, these strengthening methods have limited effectiveness in improving the strength of magnesium alloys. To improve their strength and fundamentally solve the problem of poor plasticity in magnesium alloys, it is hoped that a body-centered cubic (bcc) structure, i.e., the β phase structure, can be introduced. Magnesium-scandium alloys are the only Mg-rare earth alloys with a bcc structure in a relatively high temperature range, and Mg-Sc alloys exhibit shape memory effect and superelasticity within a certain composition range. They are the only lightweight magnesium-based shape memory alloys discovered to date.

[0003] However, due to its relatively reactive chemical properties, magnesium readily reacts with oxygen in the liquid state, resulting in oxidative combustion. Therefore, flux or gas protection is required during the smelting and casting of magnesium alloys. Currently, SF6 is the primary protective gas used, but SF6 gas at high temperatures can produce toxic gases such as SO2 and SF4, and even the highly toxic gas S2F. 10This process causes environmental pollution and can only last for a few minutes, requiring a continuous supply during smelting. Furthermore, both Mg and Sc have relatively high melting points: Mg melts at approximately 650°C and boils at 1090°C, while Sc melts at approximately 1541°C. If the conventional method of raising the temperature above the melting points of each element is used to smelt Mg-Sc alloys, the temperature will exceed the boiling point of Mg when Sc reaches its melting point, posing a potential hazard. Moreover, high-Sc content Mg-Sc alloys prepared in laboratories using pure magnesium and pure scandium exhibit highly uneven composition within the same ingot, deviating significantly from the nominal composition. Even minute variations in composition can significantly affect the alloy's properties. Alternatively, high-Sc content Mg-Sc alloys can be prepared using commercial master alloys; however, commercially available high-Sc content Mg-Sc master alloys are expensive and unsuitable for small-scale laboratory research, resulting in high costs.

[0004] Therefore, it is of great significance to find a simple way to prepare Mg-rare earth alloys with uniform composition and high rare earth content in the laboratory. Summary of the Invention

[0005] This invention addresses the problems of uneven composition, high cost, complex anti-oxidation process, and environmentally unfriendly effects of existing laboratory methods for preparing high rare earth content Mg-rare earth alloys. It proposes a smelting method that uses environmentally friendly protective gases and can easily produce high rare earth content Mg-rare earth alloys with uniform composition.

[0006] To solve the above-mentioned technical problems, the present invention provides a method for preparing a Mg-rare earth alloy with uniform composition and high rare earth content, specifically comprising the following steps: Step 1: Pre-treat magnesium particles with a purity of 99%-99.99% by acid washing. Cut rare earth particles with a purity of 99%-99.99% into strip-like shapes with a length of 1mm-6mm, a width of 1mm-3mm, and a thickness of 0.3mm-1.5mm. Clean them with anhydrous ethanol using ultrasound and then blow them dry. Step 2: Then, place a layer of pure magnesium particles and a layer of strip-shaped rare earth elements alternately in the graphite crucible. The bottom and top layers are made of pure magnesium particles. Then, place the graphite lid on top of the graphite crucible, put it in the quartz tube, and seal it. Step 3, box-type resistance furnace melting: Then place it in the box-type resistance furnace, and preheat it at 543K-573K for 30min-60min, raise the temperature to 1223K, hold it for 90min-120min, and then remove it and air cool it. Step 4: Then grind away the graphite powder on the surface, ultrasonically clean with acetone, take it out and dry it with cold air, place it in a graphite crucible, put it into a new quartz tube, seal the quartz tube, place it in a box-type resistance furnace, heat it to 873K, hold it for 24 hours, and after the holding time is over, take it out and quench it. Step 5: Then grind away the graphite powder on the surface, ultrasonically clean with acetone, take it out and dry it with cold air, place it in a graphite crucible, then put it into a new quartz tube, seal the quartz tube, place it in a box-type resistance furnace, heat it to 963K, hold it for 30min-45min, after the holding time is over, take it out and quench it with ice water.

[0007] Another technical solution of the present invention uses induction heating to replace box-type resistance furnace melting. Step three can also be performed as follows: heating is performed using an induction coil. A sealed quartz tube is clamped on the induction heating device, and the graphite crucible containing the metal raw material inside the quartz tube is placed between the two uppermost coils of the induction coil. Then, melting is performed with a power of 294W~304W for 100s~130s. The power is then turned off and the furnace is air-cooled.

[0008] Further specifying, in step one, the rare earth element is Y, Sc, or Gd, and the atomic percentage of rare earth elements in the alloy is 19% to 21%.

[0009] Further specifying, in step one, the magnesium particles are spherical with a diameter of 3mm-6mm.

[0010] Further specifying, in step one, the pickling is done by cleaning with dilute hydrochloric acid of 1.8%-1.9% concentration for 30s-45s to remove surface oxides, followed by ultrasonic cleaning with anhydrous ethanol for 10min-15min, and then drying with cold air.

[0011] Further specifying, in step three, the heat preservation and preheating shall be carried out in the following steps: the furnace temperature shall be raised to 543K-573K, and then the sealed quartz tube shall be placed in the furnace.

[0012] To further specify, in step three, the quartz tube is placed at an angle of 60° to 90°.

[0013] Further specifying, the heating rate in step three is 3K / min~5K / min.

[0014] Further specifying, different sizes of quartz tubes are selected according to the size of the graphite crucible / alloy ingot, and the quartz tube encapsulation method is carried out according to the following steps: Step 1: Take a quartz tube with an inner diameter of 20mm~25mm and a length of 30cm with holes at both ends, immerse it in a 5%~10% dilute nitric acid solution, ultrasonically clean it for 20min~30min, let it stand and soak for 12h~24h, take out the quartz tube, wash it with distilled water, and dry it at 353K for 3h~12h. Step 2: Seal one end of the quartz glass tube with an oxyacetylene flame, and then place the covered graphite crucible containing the metal raw material into the quartz glass tube. Step 3: Then insert a quartz glass tube with an inner diameter of 4mm~6mm, a wall thickness of 1mm~1.5mm, and a length of 15cm~20cm into the open end of a quartz glass tube with an inner diameter of 20mm~25mm, 2~3cm away. Heat the open end of the 20mm~25mm inner diameter glass tube with an oxyacetylene flame to reduce the opening, so that the two quartz glass tubes become one. Step 4: Apply 3cm to 4cm of vacuum grease to the surface of an open quartz tube with an inner diameter of 4mm to 6mm, insert it into a rubber hose connected to a vacuum system, and use a retaining ring to fix it in place to prevent air leakage. Step 5: Turn on the vacuum system and evacuate for 25-35 minutes until the vacuum level inside the quartz glass tube stabilizes at 10. -4 Below Pa, then backfill with 0.05MPa~0.1MPa of 99.999% (volume) high-purity argon gas, repeat the gas washing 3~4 times, and finally backfill with 0.01MPa~0.02MPa of 99.999% (volume) high-purity argon gas; Step 6: Then use an oxyacetylene flame to aim at the middle of the quartz glass tube with an inner diameter of 4-6 mm until the quartz glass tube is completely softened and melted, thus completing the seal.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) Compared with the environmentally harmful protective gases such as SF6 and CO2 mainly used in the existing magnesium alloy smelting process, the protective gas used in the magnesium-rare earth alloy smelting process of the present invention is high-purity argon, which is a non-environmentally harmful gas. Moreover, it does not need to be continuously replenished during the smelting process. It is only necessary to refill a certain amount of high-purity argon into a sealed quartz tube once before smelting. The anti-oxidation process is simple and easy to operate.

[0016] (2) The experimental apparatus / instruments used in this invention, namely the box-type resistance furnace and the induction heating device, are low in cost, simple to operate, and have a low risk factor. The alloy composition can be adjusted according to actual research needs, and the Mg-rare earth alloy that can be smelted can be used as an intermediate alloy to smelt multi-element alloys.

[0017] (3) The drawback of this invention is that, since magnesium reacts with the quartz tube at high temperatures, the metal raw material needs to be placed in a graphite crucible for melting during the smelting process. This may result in graphite contamination on the surface of the smelted magnesium alloy ingot, affecting the composition and properties of the alloy. In addition, the melting of the metal raw material during high-temperature smelting will generate a certain amount of magnesium vapor, which will cause the pressure inside the sealed tube to rise and react with the inner wall of the quartz tube, potentially causing the quartz tube to rupture. Therefore, the tube needs to be resealed before each remelting. Although the number of times the tube is sealed is more cumbersome than the existing method of continuously introducing protective gas in the magnesium alloy smelting process, the sealed quartz tube with protective gas greatly reduces the possibility of oxidation, because the existing magnesium alloy smelting environment is basically in the open air, and even if protective gas is continuously introduced, oxidation is easy to occur during the casting process. The graphite that may be mixed on the surface of the magnesium alloy can be removed by wire cutting from the surface of the smelted alloy ingot.

[0018] The method of this invention is applicable to all solid solution Mg-rare earth alloys, mainly including Mg-Y and Mg-Gd. The Mg-rare earth alloys synthesized by the method of this invention consist of α and β dual phases, mainly β single phase, with a small amount of α phase present. The composition is uniform and they have good mechanical properties.

[0019] To further understand the features and technical content of this invention, please refer to the following detailed description and accompanying drawings. However, the accompanying drawings are for reference and illustration only and are not intended to limit the invention. Attached Figure Description

[0020] Figure 1 (a) in the figure shows the macroscopic morphology of the cast Mg-Sc alloy melted in a box-type resistance furnace; Figure 1 (b) is the XRD pattern of the as-cast Mg-Sc alloy melted in a box-type resistance furnace. Figure 1 Image (c) shows the electron backscattering pattern and energy diffraction spectrum analysis of the as-cast Mg-Sc alloy melted in a box-type resistance furnace. Figure 2 (a) is the XRD pattern of the Mg-Sc alloy after solution heat treatment by melting in a box-type resistance furnace; Figure 2 (b) is a metallographic diagram of the Mg-Sc alloy after solution heat treatment in a box-type resistance furnace. Figure 2 (c) is the compressive stress-strain curve of the Mg-Sc alloy after solution heat treatment in a box-type electric resistance furnace; Figure 3 Image (a) shows the macroscopic morphology of the induction-melted cast Mg-Sc alloy; Figure 3In (b) are an electron backscatter diffraction pattern and energy dispersive spectroscopy analysis of an as-cast Mg-Sc alloy obtained by induction melting; Figure 4(a) is an XRD pattern of the Mg-Sc alloy after solution heat treatment obtained by induction melting, Figure 4(b) is a metallographic image of the Mg-Sc alloy after solution heat treatment obtained by induction melting; Figure 4(c) is a compressive stress-strain curve of the Mg-Sc alloy after solution heat treatment obtained by induction melting; Figure 5 is a schematic diagram of a quartz tube. Detailed Description of Embodiments

[0021] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0022] Example 1: In this example, the melting method for Mg-20.5at%Sc alloy adopts a box-type resistance furnace to melt and prepare alloy ingots, comprising the following steps: 1) Pretreatment of metal raw materials. High-purity metals are used as raw materials. Spherical-like pure magnesium particles with an average diameter of 5 mm (mass purity of 99.99%) are cleaned with dilute hydrochloric acid with a mass concentration of 1.9% for 30 s to remove surface oxides, then ultrasonically cleaned with anhydrous ethanol for 10 minutes, taken out and dried by a cold air blower. Then, bulk pure scandium (mass purity of 99.99%) is cut into strip-like pieces with a length of 5 mm, a width of 2 mm and a thickness of 1 mm by pliers, then placed in a beaker filled with anhydrous ethanol, ultrasonically cleaned for 20 minutes, taken out and dried by a cold air blower. The compositions of each element in the Mg-Sc alloy are designed, and according to the required atomic ratio x:y of magnesium and scandium (81<x<79, 19<y<21, x+y=100), an analytical balance of model G324A is used to weigh magnesium particles and scandium pieces of corresponding mass as raw materials.

[0023] 2) Quartz Tube Sealing. Weigh the magnesium and scandium raw materials and place them in a cylindrical, covered graphite crucible with an inner diameter of 14 mm and a height of 30 mm. When placing the raw materials, alternate between layers of pure magnesium granules and pure scandium, with pure magnesium granules at the bottom and top layers of the crucible. Take a quartz glass tube with an inner diameter of 20 mm and a length of 30 cm (with holes at both ends) and immerse it in a 10% dilute nitric acid solution. Ultrasonically clean it for 20 minutes. Remove the dilute nitric acid and the quartz glass tube from the ultrasonic cleaner and let it stand for 24 hours. After soaking, rinse with distilled water and place in a drying oven at 353 K for 12 hours. Seal one end of the quartz glass tube using an oxyacetylene flame, and then place the covered graphite crucible containing the metal raw materials inside the quartz glass tube. Then, a quartz glass tube with an inner diameter of 6mm, a wall thickness of 1.5mm, and a length of 15cm (open at both ends) is inserted 2cm into the open end of a quartz glass tube with an inner diameter of 20mm. The open end of the 20mm inner diameter tube is heated with an oxyacetylene flame to reduce the diameter, making the two quartz glass tubes a single unit. A 3cm layer of vacuum grease is applied to the surface of the 6mm inner diameter open quartz tube, and it is inserted into a rubber hose connected to a vacuum system, secured with a retaining ring to prevent air leakage. The vacuum system is turned on, and a vacuum is drawn until the vacuum level inside the quartz glass tube stabilizes at 10. -4 Below Pa, then refill with 0.05 MPa of 99.999% (volume) high-purity argon gas, repeating the purging process three times. Finally, refill with 0.01 MPa of 99.999% (volume) high-purity argon gas. Using an oxyacetylene flame, aim at the middle of the 6 mm inner diameter quartz glass tube (4 cm from the connection point with the 20 mm inner diameter quartz glass tube) until the quartz glass tube completely softens and melts. A schematic diagram of the quartz tube is shown below. Figure 5 As shown.

[0024] 3) Preparation of alloy ingots by melting in a box-type resistance furnace: The melting point of the corresponding alloy composition is determined according to the Mg-Sc binary alloy phase diagram. In this invention, the melting point of the Mg-20.5at%Sc alloy is approximately 1193K. Since it is a static solution process, the actual heating temperature needs to be 303~323K higher than the melting point of the alloy for sufficient solution. Therefore, the melting temperature of this invention is selected as 1223K. The sealed quartz tube is placed in the box-type resistance furnace and preheated at 573K for 30 minutes (the quartz tube can be placed in the furnace at room temperature and then heated to the preheating temperature with the furnace, or the furnace temperature can be preheated to the preheating temperature before placing the sealed quartz tube in the furnace). Then, the furnace temperature is increased to 1223K and held for 90 minutes. Then, it is removed and air-cooled. During air cooling, in order to ensure the shape of the ingot, it needs to be tilted at 60°. The heating rate of the resistance furnace is 5K / min. To prevent graphite powder from the graphite crucible from contaminating the alloy during the smelting process, the graphite powder adhering to the surface of the alloy ingot needs to be polished off with 120# metallographic sandpaper before each remelting, followed by ultrasonic cleaning with acetone. To prevent the high pressure inside the sealed quartz tube from causing it to rupture, the tube needs to be resealed after each remelting, as described in step 2).

[0025] 4) Alloy homogenization and single-phase solution treatment. The smelted alloy ingot is polished with 120# metallographic sandpaper to remove surface graphite powder, then ultrasonically cleaned with acetone for 5 minutes to remove surface oil and debris. After removal, it is dried with a cold air blower. The cleaned alloy ingot is placed in a graphite crucible, then placed in a quartz glass tube for sealing (as in step 2). The sealed quartz tube is then placed in a box-type resistance furnace. During heat treatment, the furnace temperature is first raised to the heat treatment temperature of 873K, then the sealed quartz tube is placed in the furnace for heat treatment for 24 hours. After heat treatment, it is removed and quenched. To obtain the single-phase β phase, the homogenized alloy is polished with 120# metallographic sandpaper to remove the oxide scale generated during quenching, then ultrasonically cleaned with acetone for 10 minutes to remove surface oil and debris. After removal, it is dried with a cold air blower. The cleaned alloy ingot is placed in a graphite crucible, then placed in a quartz glass tube for sealing (as in step 2). Then, the sealed quartz tube is placed in a box-type resistance furnace. During the heat treatment process, the furnace temperature is first raised to the heat treatment temperature of 963K, and then the sealed quartz tube is placed in the furnace for heat treatment for 45 minutes. After the heat treatment is completed, it is quenched with ice water.

[0026] Macroscopic morphology of as-cast Mg-Sc alloy ingots prepared by box-type resistance furnace heating is shown in the figure. Figure 1As shown in (a), the test result obtained by inductively coupled plasma-atomic emission spectrometry (ICP-AES) shows that its composition is Mg-32.3wt%Sc, that is, Mg-20.5at%Sc; backscattered electron imaging shows that the as-prepared alloy consists of acicular gray phases and white phases at room temperature. EDS results show that the composition of the white phase is Mg-23.92at%Sc, and the composition of the gray phase is Mg-18.05at%Sc. The Sc content of the white phase is higher than that of the gray phase, indicating that the gray phase and the white phase are α phase and β phase respectively. XRD also shows that the as-cast alloy consists of two phases at room temperature.

[0027] The microstructure and compressive mechanical properties of the Mg-Sc alloy after solution treatment are shown in Figure 2 , the results show that the solution-treated alloy is mainly composed of β single phase with a small amount of α phase at room temperature, which may be formed during quenching. The alloy has equiaxed grains with a size of 50-200 μm. The compressive stress-strain curve shows that the yield strength of the alloy is about 200MPa, and the alloy has good mechanical properties.

[0028] Example 2: In this example, the smelting method of Mg-20.5at%Sc alloy adopts induction heating smelting to prepare alloy ingots, comprising the following steps: 1) Pretreatment of metal raw materials. The raw materials are high-purity metals. Spherical-like pure magnesium particles with an average diameter of 5 mm (mass purity of 99.99%) are cleaned with dilute hydrochloric acid with a mass concentration of 1.9% for 30 s to remove surface oxides, then cleaned ultrasonically with absolute ethanol for 10 minutes, taken out and blown dry with a cold air blower. Then bulk pure scandium (mass purity of 99.99%) is cut into strips with a length of 5 mm, a width of 2 mm and a thickness of 1 mm with pliers, then placed in a beaker filled with absolute ethanol, ultrasonically cleaned for 20 minutes, taken out and blown dry with a cold air blower. The composition of each element in the Mg-Sc alloy is designed. According to the required atomic ratio of magnesium to scandium x:y (81<x<79, 19<y<21, x+y=100), a G324A analytical balance is used to weigh the corresponding mass of raw material magnesium particles and scandium strips.

[0029] 2) Quartz Tube Sealing. Weigh the magnesium and scandium raw materials and place them in a cylindrical, covered graphite crucible with an inner diameter of 14 mm and a height of 30 mm. When placing the raw materials, alternate between layers of pure magnesium granules and pure scandium, with pure magnesium granules at the bottom and top layers of the crucible. Take a quartz glass tube with an inner diameter of 20 mm and a length of 30 cm (with holes at both ends) and immerse it in a 10% dilute nitric acid solution. Ultrasonically clean it for 20 minutes. Remove the dilute nitric acid and the quartz glass tube from the ultrasonic cleaner and let it stand for 24 hours. After soaking, rinse with distilled water and place in a drying oven at 353 K for 12 hours. Seal one end of the quartz glass tube using an oxyacetylene flame, and then place the covered graphite crucible containing the metal raw materials inside the quartz glass tube. Then, a quartz glass tube with an inner diameter of 6mm, a wall thickness of 1.5mm, and a length of 15cm (open at both ends) is inserted 2cm into the open end of a quartz glass tube with an inner diameter of 20mm. The open end of the 20mm inner diameter tube is heated with an oxyacetylene flame to reduce the diameter, making the two quartz glass tubes a single unit. A 3cm layer of vacuum grease is applied to the surface of the 6mm inner diameter open quartz tube, and it is inserted into a rubber hose connected to a vacuum system, secured with a retaining ring to prevent air leakage. The vacuum system is turned on, and a vacuum is drawn until the vacuum level inside the quartz glass tube stabilizes at 10. -4 Below Pa, then refill with 0.05 MPa of 99.999% (volume) high-purity argon gas, repeating the purging process three times. Finally, refill with 0.01 MPa of 99.999% (volume) high-purity argon gas. Using an oxyacetylene flame, aim at the middle of the 6 mm inner diameter quartz glass tube (4 cm from the connection point with the 20 mm inner diameter quartz glass tube) until the quartz glass tube completely softens and melts. A schematic diagram of the quartz tube is shown below. Figure 5 As shown.

[0030] 3) Induction heating melting for alloy ingot preparation: A sealed quartz tube is clamped onto a self-made induction heating device, with the graphite crucible containing the metal raw material placed between the top two coils of the induction coil. Melting is then performed at 304W for 100 seconds, followed by power shutdown and air cooling. Due to the rapid temperature rise and short melting time during induction melting, four remelting processes are required to ensure the uniformity of the alloy composition. To prevent graphite powder from the graphite crucible from contaminating the alloy during melting, the graphite powder adhering to the surface of the alloy ingot must be removed with 120# metallographic sandpaper before each remelting, followed by ultrasonic cleaning with acetone. To prevent rupture due to excessive pressure inside the sealed quartz tube, the tube must be resealed after each remelting, as described in step 2).

[0031] 4) Alloy homogenization and single-phase solution treatment. The smelted alloy ingot is polished with 120# metallographic sandpaper to remove surface graphite powder, then ultrasonically cleaned with acetone for 5 minutes to remove surface oil and debris. After removal, it is dried with a cold air blower. The cleaned alloy ingot is placed in a graphite crucible, then placed in a quartz glass tube for sealing (as in step 2). The sealed quartz tube is then placed in a box-type resistance furnace. During heat treatment, the furnace temperature is first raised to the heat treatment temperature of 873K, then the sealed quartz tube is placed in the furnace for heat treatment for 24 hours. After heat treatment, it is removed and quenched. To obtain the single-phase β phase, the homogenized alloy is polished with 120# metallographic sandpaper to remove the oxide scale generated during quenching, then ultrasonically cleaned with acetone for 10 minutes to remove surface oil and debris. After removal, it is dried with a cold air blower. The cleaned alloy ingot is placed in a graphite crucible, then placed in a quartz glass tube for sealing (as in step 2). Then, the sealed quartz tube is placed in a box-type resistance furnace. During the heat treatment process, the furnace temperature is first raised to the heat treatment temperature of 963K, and then the sealed quartz tube is placed in the furnace for heat treatment for 45 minutes. After the heat treatment is completed, it is quenched with ice water.

[0032] Macroscopic morphology of the as-cast Mg-Sc alloy ingot prepared by induction heating melting is shown in the figure below. Figure 3 As shown in (a), the electron probe microanalyzer (EMPA) showed that the average composition of the alloy was Mg-19.5at%Sc; backscattered electron microscopy showed that the as-cast alloy at room temperature was also composed of needle-like gray and white phases, with the white phase composition being Mg-25.18at%Sc and the gray phase composition being Mg-18.87at%Sc. The as-cast alloy at room temperature was also composed of α and β dual phases. The microstructure and compressive mechanical properties of the Mg-Sc alloy after solution treatment are shown in Figures 4(a), 4(b), and 4(c). The results show that the alloy after solution treatment is mainly composed of a β single phase at room temperature, with a small amount of α phase present, which may have been formed during quenching. The alloy has equiaxed grains with a grain size of approximately 50 μm and uniform distribution; the yield strength of the alloy is approximately 250 MPa, exhibiting good mechanical properties.

Claims

1. A method for preparing a Mg-rare earth alloy with uniform composition and high rare earth content, characterized in that, The preparation method is carried out according to the following steps: Step 1: Pre-treat magnesium particles with a purity of 99%-99.99% by acid washing. Cut rare earth particles with a purity of 99%-99.99% into strip-like shapes with a length of 1mm-6mm, a width of 1mm-3mm, and a thickness of 0.3mm-1.5mm. Clean them with anhydrous ethanol using ultrasound and then blow them dry. Step 2: Then, place a layer of pure magnesium particles and a layer of strip-shaped rare earth elements alternately in the graphite crucible. The bottom and top layers are made of pure magnesium particles. Then, place the graphite lid on top of the graphite crucible, put it in the quartz tube, and seal it. Step 3: Then place it in a box-type resistance furnace, preheat at 543K-573K for 30-60 minutes, raise the temperature to 1223K, hold for 90-120 minutes, and then remove and air cool; specifically including: Heating is performed using induction coils. A sealed quartz tube is clamped on an induction heating device, with the graphite crucible containing the metal raw material inside the quartz tube placed between the top two coils of the induction coil. Melting is then carried out at a power of 294W~304W for 100s~130s. The power is then turned off and the mixture is air-cooled. Step 4: Then grind away the graphite powder on the surface, ultrasonically clean with acetone, take it out and dry it with cold air, place it in a graphite crucible, put it into a new quartz tube, seal the quartz tube, place it in a box-type resistance furnace, heat it to 873K, hold it for 24 hours, and after the holding time is over, take it out and quench it. Step 5: Then grind away the graphite powder on the surface, ultrasonically clean with acetone, take it out and dry it with cold air, place it in a graphite crucible, then put it into a new quartz tube, seal the quartz tube, place it in a box-type resistance furnace, heat it to 963K, hold it for 30min-45min, after the holding time is over, take it out and quench it with ice water. The quartz tube encapsulation method is carried out according to the following steps: Step 1: Take a quartz tube with an inner diameter of 20mm~25mm and a length of 30cm with holes at both ends, immerse it in a 5%~10% dilute nitric acid solution, ultrasonically clean it for 20min~30min, let it stand and soak for 12h~24h, take out the quartz tube, wash it with distilled water, and dry it at 353K for 3h~12h. Step 2: Seal one end of the quartz glass tube with an oxyacetylene flame, and then place the covered graphite crucible containing the metal raw material into the quartz glass tube. Step 3: Then insert a quartz glass tube with an inner diameter of 4mm~6mm, a wall thickness of 1mm~1.5mm, and a length of 15cm~20cm into the open end of a quartz glass tube with an inner diameter of 20mm~25mm, 2~3cm away. Heat the open end of the 20mm~25mm inner diameter glass tube with an oxyacetylene flame to reduce the opening, so that the two quartz glass tubes become one. Step 4: Apply 3cm to 4cm of vacuum grease to the surface of an open quartz tube with an inner diameter of 4mm to 6mm, insert it into a rubber hose connected to a vacuum system, and use a retaining ring to fix it in place to prevent air leakage. Step 5: Turn on the vacuum system and evacuate for 25-35 minutes until the vacuum level inside the quartz glass tube stabilizes at 10. -4 Below Pa, then backfill with 0.05MPa~0.1MPa of 99.999% (volume) high-purity argon gas, repeat the gas washing 3~4 times, and finally backfill with 0.01MPa~0.02MPa of 99.999% (volume) high-purity argon gas; Step 6: Then use an oxyacetylene flame to aim at the middle of the quartz glass tube with an inner diameter of 4-6 mm until the quartz glass tube is completely softened and melted, thus completing the seal.

2. The preparation method according to claim 1, characterized in that, In step one, the rare earth element is Y, Sc, or Gd, and the atomic percentage of rare earth elements in the alloy is 19% to 21%.

3. The preparation method according to claim 1, characterized in that, In step one, the magnesium particles are spherical with a diameter of 3mm-6mm.

4. The preparation method according to claim 1, characterized in that, In step one, pickling is done by cleaning with 1.8%-1.9% dilute hydrochloric acid for 30-45 seconds to remove surface oxides, followed by ultrasonic cleaning with alcohol for 10-15 minutes, and then drying with cold air.

5. The preparation method according to claim 1 or 2, characterized in that, In step three, the heat preservation and preheating are carried out as follows: raise the furnace temperature to 543K-573K, and then place the sealed quartz tube in the furnace.

6. The preparation method according to claim 1, characterized in that, In step three, the quartz tube is placed at an angle of 60° to 90°.

7. The preparation method according to claim 1, characterized in that, In step three, the heating rate is 3K / min~5K / min.

Images