A rare earth magnesium alloy, its preparation method and application

Abstract

This invention provides a rare-earth magnesium alloy, its preparation method, and its application. The rare-earth magnesium alloy comprises, by weight percentage: Gd 9.0~11.0 wt.%, Y 0.8~2.0 wt.%, Zn 0.3~0.6 wt.%, Zr 0.3~0.5 wt.%, Ca 0.05~0.1 wt.%, Ag 0.05~0.2 wt.%, Sc 0.02~0.1 wt.%, with the balance being Mg and unavoidable impurity elements; wherein the weight ratio of Gd to Y is (5~14):1, and the sum of the weights of Gd and Y is 10~12 wt.%. This invention, by controlling the content of alloying elements, obtains a high-strength, high-toughness, and heat-resistant rare-earth magnesium alloy material, which can balance strength and plasticity at both room temperature and high temperature. It can be used for semi-solid injection molding, meeting the application requirements of lightweight magnesium alloys and their components for low-altitude aircraft.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy technology, and more specifically, to a rare earth magnesium alloy, its preparation method, and its application. Background Technology

[0002] In recent years, the emerging low-altitude economy has shown a booming development trend, with electric vertical takeoff and landing (eVTOL) aircraft and drones experiencing explosive growth due to their efficient and convenient transportation attributes and diverse application scenarios. To achieve higher payload and longer endurance, lightweighting has become one of the core indicators for the development of advanced low-altitude aircraft. However, aircraft face harsh operating conditions during service: on the one hand, the area around the power system is prone to high-temperature environments; on the other hand, rapid ascent and descent, complex airflow, and other factors cause the aircraft to endure high-frequency alternating loads and instantaneous impacts. Against this backdrop, key components (such as motor housings) must simultaneously possess high heat resistance (ensuring mechanical performance stability at high temperatures) and excellent fatigue resistance (coping with lifespan degradation under cyclic loads) to achieve the reliability and safety goals of the aircraft.

[0003] Magnesium alloys, as the lightest metallic structural materials currently available, are ideal for meeting the weight reduction requirements of low-altitude aircraft. However, conventional magnesium alloys (such as the AZ and AM series) have inherent defects such as insufficient high-temperature strength and toughness, making it difficult to meet the safety requirements of high reliability and long service life for key components such as motor housings of aerospace vehicles. Therefore, it is necessary to develop rare earth magnesium alloy materials with higher strength and toughness to meet the demand for high-performance lightweight magnesium alloy materials in low-altitude aircraft.

[0004] Semi-solid injection molding technology is an emerging advanced molding process for magnesium alloy parts in recent years. With its advantages of low cost, high efficiency, low energy consumption, high material utilization, and ability to fabricate complex thin-walled structures, it has demonstrated significant application value in the manufacturing of magnesium alloy parts in the automotive and 3C electronics industries. However, limited by the upper temperature limit of existing semi-solid injection molding equipment (typically ≤610℃), this technology is currently mainly applicable to AZ and AM series magnesium alloys with lower melting points and medium strength. It still faces technical bottlenecks in the injection molding of high-strength, high-toughness, and high-melting-point rare-earth magnesium alloys. Therefore, addressing the urgent need for high-strength, high-toughness, and heat-resistant magnesium alloy parts in emerging low-altitude economic vehicles, developing high-strength, high-toughness, and heat-resistant magnesium alloy materials and breaking through key semi-solid injection molding technologies has become one of the core research directions for promoting the lightweight and high-performance development of low-altitude economic equipment, possessing significant engineering application value and market prospects. Summary of the Invention

[0005] The main objective of this invention is to provide a rare earth magnesium alloy, its preparation method and application, in order to solve the problem that rare earth magnesium alloys in the prior art are difficult to balance strength and plasticity at both room temperature and high temperature.

[0006] To achieve the above objectives, according to one aspect of the present invention, a rare earth magnesium alloy is provided, comprising, by weight percentage: Gd 9.0~11.0 wt.%, Y 0.8~2.0 wt.%, Zn 0.3~0.6 wt.%, Zr 0.3~0.5 wt.%, Ca 0.05~0.1 wt.%, Ag 0.05~0.2 wt.%, Sc 0.02~0.1 wt.%, with the balance being Mg and unavoidable impurity elements, the total content of impurity elements being ≤0.1%; wherein the weight ratio of Gd to Y is (5~14):1, and the sum of the weights of Gd and Y is 10~12 wt.%.

[0007] Furthermore, by weight percentage, the rare earth magnesium alloy comprises: Gd 9.5~10.5wt.%, Y 0.8~1.5wt.%, Zn 0.35~0.55wt.%, Zr 0.35~0.45wt.%, Ca 0.05~0.1wt.%, Ag 0.05~0.19wt.%, Sc 0.02~0.1wt.%, with the balance being Mg and unavoidable impurity elements.

[0008] Furthermore, the weight ratio of the sum of Gd and Y to Ca is (117~218):1; and / or the weight ratio of Ca to Ag is 0.1~0.28 wt.%; and / or the weight ratio of Zn to Ag is (2.5~8.5):1.

[0009] Furthermore, the melting temperature range of the rare earth magnesium alloy is 620~640℃; and / or the β' phase size of the rare earth magnesium alloy is 20~80nm.

[0010] According to another aspect of the present invention, a method for preparing the rare earth magnesium alloy described above is provided, comprising the following steps: Step S1, mixing and casting raw materials according to the alloy composition to obtain a magnesium alloy ingot; the raw materials include pure magnesium, pure zinc, pure silver, magnesium-calcium master alloy and magnesium-based rare earth master alloy, wherein the magnesium-based rare earth master alloy includes magnesium-gadolinium master alloy, magnesium-yttrium master alloy, magnesium-zirconium master alloy and magnesium-scandium master alloy; Step S2, performing a solution treatment on the magnesium alloy ingot to obtain a solution-treated magnesium alloy; Step S3, performing an aging treatment on the solution-treated magnesium alloy to obtain a rare earth magnesium alloy.

[0011] Further, in step S1, the mixed casting includes: Step S11, adding pure magnesium and heating to 690~710℃ to melt the pure magnesium; after the melt temperature reaches 740~760℃, sequentially adding magnesium-gadolinium master alloy, magnesium-yttrium master alloy, magnesium-calcium master alloy, magnesium-scandium master alloy, and pure zinc to melt, obtaining a first melt; Step S12, subjecting the first melt to a first ultrasonic homogenization treatment; after the melt temperature reaches 770~790℃, adding magnesium-zirconium master alloy and pure silver to melt, obtaining a second melt; Step S13, subjecting the second melt to a second ultrasonic homogenization treatment, then sequentially refining, slag removal, heat preservation, cooling and settling, and then casting, obtaining... The casting process involves casting magnesium alloy ingots; preferably, the atmosphere for mixed casting is a mixture of CO2 and SF6, with a volume ratio of CO2 to SF6 of (99.6~99.8):(0.2~0.4); and / or the mixed casting also uses a chloride flux, which includes one or more of magnesium chloride, calcium chloride, potassium chloride, sodium chloride, and barium chloride; and / or independently, the ultrasonic frequency of the first ultrasonic homogenization treatment and the second ultrasonic homogenization treatment is 20~22kHz, and the ultrasonic treatment time is 5~10min; and / or the holding time after slag removal is 8~10min, and the cooling and settling includes cooling to 710~730℃ and holding for 8~12min.

[0012] Further, in step S2, the solution treatment includes: under a first inert atmosphere, the magnesium alloy ingot is sequentially subjected to a rapid solution heating section and a slow solution heating section, followed by water quenching to obtain a solution-treated magnesium alloy; the heating rate of the rapid solution heating section is greater than the heating rate of the slow solution heating section; preferably, the heating rate of the rapid solution heating section is 12~18℃ / min, the temperature is 440~460℃, and the holding time is 5~10min; and / or the heating rate of the slow solution heating section is 3~8℃ / min, the temperature is 480~500℃, and the holding time is 8~12h.

[0013] Further, in step S3, the aging treatment includes: under a second inert atmosphere, the solid solution magnesium alloy is subjected to a rapid aging heating section and a slow aging heating section in sequence, and then air-cooled to obtain a rare earth magnesium alloy; the heating rate of the rapid aging heating section is greater than the heating rate of the slow aging heating section; preferably, the heating rate of the rapid aging heating section is 12~18℃ / min, the temperature is 170~190℃, and the holding time is 5~10min; and / or the heating rate of the slow aging heating section is 3~8℃ / min, the temperature is 200~220℃, and the holding time is 12~48h.

[0014] According to another aspect of the present invention, a semi-solid injection molding method for magnesium alloy workpieces is provided, wherein the rare earth magnesium alloy ingot described above is processed into solid magnesium particles, and then injection molded using a semi-solid injection molding machine to obtain magnesium alloy workpieces; the semi-solid injection molding machine includes a screw, the surface of which is coated with a tungsten-based alloy.

[0015] Furthermore, the solid magnesium particles have a length of 3~6mm, a width of 0.5~1mm, and a thickness of 0.5~1mm; and / or the screw has an operating temperature of 640~660℃ and a rotation speed of 120~180r / min.

[0016] By applying the technical solution of this invention, the significant "solid solution plasticizing" and "precipitation strengthening" effects of Gd element on magnesium alloys, and the inhibitory effect of Y element on the high-temperature coarsening of Mg-Gd nano-precipitates, the strength, toughness, and heat resistance of magnesium alloys are improved through the grain-refining strengthening effect of Zr and Ca elements. Furthermore, Sc and a small amount of Ag are added to further enhance the strength and plasticity of the magnesium alloy, and an appropriate amount of Zn element is added to reduce the viscosity of the magnesium alloy melt and improve its filling properties. This invention, by controlling the content of alloying elements, yields a high-strength, high-toughness, and heat-resistant rare-earth magnesium alloy material that balances strength and plasticity at both room temperature and high temperature. It can be used for semi-solid injection molding, meeting the application requirements of lightweight magnesium alloys and their components for low-altitude aircraft. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1 A photograph of the nano-precipitated phase (β' phase) in a rare earth magnesium alloy according to Example 1 of the present invention is shown;

[0019] Figure 2 Solid magnesium particles processed from a rare earth magnesium alloy according to Embodiment 8 of the present invention are shown. Detailed Implementation

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] Unless otherwise specified, "inert atmosphere" in this invention refers to argon atmosphere.

[0022] As described in the background section of this invention, existing technologies suffer from the problem that rare earth magnesium alloys cannot simultaneously achieve both strength and ductility at room temperature and high temperatures. To address this issue, in a typical embodiment of this invention, a rare earth magnesium alloy is provided, comprising, by weight percentage: Gd 9.0~11.0 wt.%, Y 0.8~2.0 wt.%, Zn 0.3~0.6 wt.%, Zr 0.3~0.5 wt.%, Ca 0.05~0.1 wt.%, Ag 0.05~0.2 wt.%, Sc 0.02~0.1 wt.%, with the balance being Mg and unavoidable impurity elements, the total impurity element content ≤0.1%; wherein the weight ratio of Gd to Y is (5~14):1, and the sum of the weights of Gd and Y is 10~12 wt.%.

[0023] Rare earth elements such as Gd, Y, and Sc can enhance the strength and toughness of magnesium alloys through "solid solution plasticization" and "precipitation strengthening" mechanisms. Gd is the main strengthening and toughening element. Compared with Y, Gd has a higher effect on age-hardening precipitation strengthening and "solid solution plasticization". Y can inhibit the coarsening tendency of Mg-Gd nano-precipitates at high temperatures. However, excessive Y addition will reduce the effect of Gd on improving the plasticity of magnesium alloys and make the alloy embrittled. Insufficient Y addition will cause Mg-Gd nano-precipitates to coarsen easily during high-temperature aging, resulting in a decrease in the strength of magnesium alloys. Therefore, the addition of Gd and Y should be controlled in a coordinated manner. Zn can reduce the viscosity of magnesium alloy melts and improve the fluidity and filling properties of liquid and semi-solid melts, but excessive addition can cause thermal cracking of the material. Zr and Ca are both effective grain refiners for magnesium alloys, which can improve the plasticity and strength of magnesium alloys. At the same time, grain refinement helps to promote the formation of spheroidal crystals in semi-solid slurries, which helps to improve the fluidity and filling properties of semi-solid melts. The addition of Sc and Ag can improve the plasticity of magnesium alloys and enhance the precipitation strengthening effect of rare earth magnesium alloys, which is beneficial to promoting the strengthening and toughening of magnesium alloys.

[0024] This invention, by controlling the content of alloying elements and further coordinating with heat treatment processes, yields a high-strength, high-toughness, and heat-resistant rare-earth magnesium alloy material. At room temperature (20-30℃), the tensile strength reaches 320-380 MPa, the yield strength reaches 210-260 MPa, and the elongation reaches 12-18%. At 200℃, the tensile strength reaches 280-330 MPa, the yield strength reaches 180-220 MPa, and the elongation reaches 20-26%. This achieves a balance between strength and plasticity at both room and high temperatures. When used in semi-solid injection molding, the resulting semi-solid melt exhibits good fluidity and filling properties, meeting the application requirements of lightweight magnesium alloys and their components for low-altitude aircraft.

[0025] To further improve the strength, toughness, heat resistance, and fatigue resistance of rare earth magnesium alloys, and to better balance their strength and plasticity at both room temperature and high temperature, in a preferred embodiment, the rare earth magnesium alloy comprises, by weight percentage: Gd 9.5~10.5wt.%, Y 0.8~1.5wt.%, Zn 0.35~0.55wt.%, Zr 0.35~0.45wt.%, Ca 0.05~0.1wt.%, Ag 0.05~0.19wt.%, Sc 0.02~0.1wt.%, with the balance being Mg and unavoidable impurity elements.

[0026] In a preferred embodiment, the weight ratio of the sum of Gd and Y to Ca is (117~218):1; and / or the weight ratio of Ca to Ag is 0.1~0.28 wt.%; and / or the weight ratio of Zn to Ag is (2.5~8.5):1. Under these conditions, the contents of Ca, Ag, and Zn are all within the range of complete solid solution, and large-size second phases are less likely to precipitate at grain boundaries during aging. At the same time, it can promote the formation of appropriately sized nano-precipitates (β' phase) in the matrix, which is beneficial for the alloy to obtain excellent mechanical strength and plasticity simultaneously.

[0027] In a preferred embodiment, the melting temperature range of the rare-earth magnesium alloy is 620~640℃; and / or the β' phase size of the rare-earth magnesium alloy is 20~80nm. The β' phase is a nano-precipitate composed of Mg and various rare-earth elements and non-rare-earth elements. Under the above conditions, the nano-precipitate can effectively pin dislocations while allowing dislocations to move under certain conditions, thereby improving the alloy strength while maintaining good plasticity. This synergistic effect enables the alloy to achieve an excellent match between mechanical strength and plasticity within a specific composition range.

[0028] In another typical embodiment of the present invention, a method for preparing the rare earth magnesium alloy described above is also provided, comprising the following steps: Step S1, mixing and casting raw materials according to the alloy composition to obtain a magnesium alloy ingot; the raw materials include pure magnesium, pure zinc, pure silver, magnesium-calcium master alloy and magnesium-based rare earth master alloy, the magnesium-based rare earth master alloy including magnesium-gadolinium master alloy, magnesium-yttrium master alloy, magnesium-zirconium master alloy and magnesium-scandium master alloy; Step S2, performing a solution treatment on the magnesium alloy ingot to obtain a solution-treated magnesium alloy; Step S3, performing an aging treatment on the solution-treated magnesium alloy to obtain a rare earth magnesium alloy.

[0029] Specifically, the raw materials are first mixed and cast according to the alloy composition to obtain a magnesium alloy ingot. Then, the magnesium alloy ingot undergoes solution treatment. During this process, because the amounts of Gd, Y, Zn, Zr, Ca, Ag, and Sc added are within the range where the magnesium matrix can be completely dissolved, the large-sized blocky second phases (mainly rare-earth-rich phases) formed at the grain boundaries due to non-equilibrium solidification in the cast magnesium alloy matrix gradually decompose and disappear during solution treatment, resulting in a solution-treated magnesium alloy. After solution treatment, the mechanical strength of the rare-earth magnesium alloy decreases slightly, but its plasticity is significantly improved. Finally, the solution-treated magnesium alloy undergoes aging treatment. During this process, the alloying elements dissolved in the matrix, because their content exceeds the limiting solid solubility in the magnesium matrix at the aging temperature, gradually precipitate from the solution-supersaturated magnesium alloy matrix in the form of nanoscale second phases, thus obtaining an aged rare-earth magnesium alloy. After aging treatment, the plasticity of the rare-earth magnesium alloy decreases slightly, but its mechanical strength is significantly improved, thus achieving a balance between strength and plasticity at both room temperature and high temperature.

[0030] Preferably, the calcium content in the magnesium-calcium master alloy is 8-12% by weight, and the rare earth content in the magnesium-based rare earth master alloy is 25-35% by weight, facilitating element content control. The above preparation method is simple and easy to operate. Through composition and heat treatment process design, cast rare earth magnesium alloys can possess both excellent room temperature / high temperature strength and ductility.

[0031] In Gd-Y-Zn-Zr alloys, the formation of blocky Gd-Y phases and acicular Zn-Zr phases during solution treatment is unavoidable, negatively impacting the alloy's mechanical properties. By employing optimized solution treatment and aging processes, the influence of these phases on the mechanical properties of magnesium alloys can be reduced, achieving a synergistic improvement in the strength and ductility of rare-earth magnesium alloys. Furthermore, by synergistically controlling the amount of alloying elements added and the heat treatment process, it is beneficial to prepare high-strength, high-toughness, and heat-resistant rare-earth magnesium alloys. Solution treatment also helps improve the compositional uniformity of the magnesium alloy semi-solid slurry and the microstructure uniformity of the castings during subsequent semi-solid injection molding.

[0032] In a preferred embodiment, step S1, the mixed casting includes: step S11, adding pure magnesium and heating to 690~710℃ to melt the pure magnesium; after the melt temperature reaches 740~760℃, adding magnesium gadolinium master alloy, magnesium yttrium master alloy, magnesium calcium master alloy, magnesium scandium master alloy and pure zinc in sequence to melt, to obtain a first melt; step S12, subjecting the first melt to a first ultrasonic homogenization treatment; after the melt temperature reaches 770~790℃, adding magnesium zirconium master alloy and pure silver to melt, to obtain a second melt; step S13, subjecting the second melt to a second ultrasonic homogenization treatment, then refining, removing slag, holding at a constant temperature, cooling and allowing to stand before casting, to obtain a magnesium alloy ingot. Preferably, the atmosphere for mixed casting is a mixture of CO2 and SF6, with a volume ratio of CO2 to SF6 of 99.6~99.8:(0.2~0.4); and / or the mixed casting also uses a chloride flux, which includes one or more of magnesium chloride, calcium chloride, potassium chloride, sodium chloride, and barium chloride; and / or independently, the ultrasonic frequency of the first ultrasonic homogenization treatment and the second ultrasonic homogenization treatment is 20~22kHz, and the ultrasonic treatment time is 5~10min; and / or the holding time after slag removal is 8~10min, and the cooling and settling includes cooling to 710~730℃ and holding for 8~12min.

[0033] Before melting and casting, the raw materials, tools, and molds can be cleaned and baked at 160-200℃ for 25-35 minutes to reduce the introduction of impurities during the magnesium alloy melting process. To improve material purity, an additional 0.5-1.0 kg of raw material can be added before melting and casting. During the melt casting process, continuous CO2+SF6 gas protection is preferred to reduce oxide inclusions in the ingot.

[0034] First, pure magnesium is melted under a CO2+SF6 atmosphere and chloride flux protection. Then, magnesium gadolinium master alloy, magnesium yttrium master alloy, magnesium calcium master alloy, magnesium scandium master alloy, and pure zinc are added sequentially. After the master alloys and pure zinc are completely melted, the melt is subjected to ultrasonic homogenization treatment, which can be done by inserting an ultrasonic amplitude transformer into the melt. Finally, magnesium zirconium master alloy and pure silver are added. After the magnesium zirconium master alloy and pure silver are melted, another ultrasonic homogenization treatment is performed. Then, the mixture is refined, slag is removed, and the temperature is maintained. Finally, it is cooled and allowed to stand before casting. At the end of the casting process, a feeding action can be performed to further reduce internal defects in the magnesium alloy ingot and obtain a high-quality magnesium alloy ingot.

[0035] To further reduce magnesium alloy oxidation, it is preferable to carry out the solution treatment under an inert atmosphere. The inert atmosphere can be prepared by evacuating the heat treatment furnace to a vacuum degree of -0.05 to -0.1 MPa, purging it with argon to a pressure of 0.01 to 0.03 MPa, and repeating this process 2 to 3 times.

[0036] In a preferred embodiment, step S2, the solution treatment includes: under a first inert atmosphere, sequentially subjecting a magnesium alloy ingot to a rapid solution heating section and a slow solution heating section, followed by water quenching, to obtain a solution-treated magnesium alloy; the heating rate of the rapid solution heating section is greater than the heating rate of the slow solution heating section; preferably, the heating rate of the rapid solution heating section is 12~18℃ / min, the temperature is 440~460℃, and the holding time is 5~10min; and / or the heating rate of the slow solution heating section is 3~8℃ / min, the temperature is 480~500℃, and the holding time is 8~12h. The water temperature for water quenching is 80~90℃.

[0037] In a preferred embodiment, step S3, the aging treatment includes: under a second inert atmosphere, sequentially subjecting the solution-treated magnesium alloy to a rapid aging heating section and a slow aging heating section, followed by air cooling, to obtain a rare-earth magnesium alloy; the heating rate of the rapid aging heating section is greater than the heating rate of the slow aging heating section; preferably, the heating rate of the rapid aging heating section is 12~18℃ / min, the temperature is 170~190℃, and the holding time is 5~10min; and / or the heating rate of the slow aging heating section is 3~8℃ / min, the temperature is 200~220℃, and the holding time is 12~48h. The inert atmosphere can be prepared with reference to the solution treatment method.

[0038] The aforementioned two-stage solution heating and / or aging heating treatments are beneficial for shortening heating time while improving the accuracy and stability of the alloy solution temperature and / or aging temperature. The rapid solution heating stage, due to its fast heating rate, helps shorten the overall solution treatment time. A short holding period after rapidly reaching a certain temperature promotes uniform temperature distribution within the furnace, improving the heat uniformity of the heat-treated sample. The slow solution heating stage, due to its slower heating rate, helps avoid overheating after reaching the set temperature, which could negatively impact the solution heat treatment process. It also promotes uniform heating and temperature rise of the sample. The same principle applies to the rapid and slow aging heating stages of the aging process. These conditions further improve the solution and aging effects, refine the alloy microstructure, and thus improve the strength and toughness of the magnesium alloy at room temperature and high temperatures.

[0039] In another typical embodiment of the present invention, a semi-solid injection molding method for magnesium alloy workpieces is also provided. The rare-earth magnesium alloy ingot described above is processed into solid magnesium particles, which are then injection molded using a semi-solid injection molding machine to obtain the magnesium alloy workpiece. The semi-solid injection molding machine includes a screw, the surface of which is coated with a tungsten-based alloy. By using the magnesium alloy of the present invention and increasing the operating temperature of the screw by adding a high-temperature resistant tungsten-based alloy coating to the surface of the key component (screw) of the semi-solid injection molding machine, semi-solid injection molding of rare-earth magnesium alloys can be achieved, meeting the application requirements of low-altitude aircraft for lightweight, high-strength, tough, and heat-resistant magnesium alloys and their components. Since many high-temperature resistant tungsten-based alloys can be used, no specific composition is limited.

[0040] Rare earth magnesium alloy ingots (cast ingots or alloys after aging treatment) are mechanically cut into solid magnesium alloy particles, which are then fed into the barrel of a semi-solid injection molding machine equipped with a high-temperature coated and reinforced screw. The magnesium particles gradually melt under the shearing action of the screw device and the heating action of the heating device in the barrel, transforming from solid particles into a semi-solid slurry composed of a mixture of partially spherical solid particles and liquid melt. When the semi-solid slurry is stored at a set amount at the front end of the screw, the screw stops rotating and the semi-solid slurry is injected. The semi-solid slurry is injected from the barrel into the mold, and after cooling, it forms a workpiece.

[0041] The typical temperature range for preparing the semi-solid slurry of the high-strength, high-toughness, and heat-resistant magnesium alloy particles of the present invention is about 640~660℃. By adding a high-temperature resistant coating (high-temperature resistant tungsten-based alloy) to the surface of the screw of the semi-solid injection molding machine, the working temperature of the screw can reach above 650℃, realizing the semi-solid injection molding of high-melting-point rare earth magnesium alloy.

[0042] For similar reasons, in a preferred embodiment, the solid magnesium particles have a length of 3-6 mm, a width of 0.5-1 mm, and a thickness of 0.5-1 mm; and / or the screw has an operating temperature of 640-660°C and a rotation speed of 120-180 r / min.

[0043] Typical, but not limiting, rare earth magnesium alloys, by weight percentage, include: Gd 9.0 wt.%, 9.2 wt.%, 9.5 wt.%, 9.8 wt.%, 10.0 wt.%, 10.2 wt.%, 10.5 wt.%, 10.8 wt.%, 11.0 wt.%, or any two of these values; Y 0.8 wt.%, 1.0 wt.%, 1.2 wt.%, 1.5 wt.%, 1.8 wt.%, 2.0 wt.%, or any two of these values; Zn 0.3 wt.%, 0.35 wt.%, 0.4 wt.%, 0.45 wt.%, 0.5 wt.%, 0.55 wt.%, 0.6 wt.%, or any two of these values; and Zr 0.3 wt.%, 0.32 wt.%, 0.35 wt.%, 0.38 wt.%, 0.4 wt.%. wt.%, 0.42 wt.%, 0.45 wt.%, 0.48 wt.%, 0.5 wt.%, or any two of these values; Ca 0.05 wt.%, 0.06 wt.%, 0.07 wt.%, 0.08 wt.%, 0.09 wt.%, 0.1 wt.%, or any two of these values; Ag 0.05 wt.%, 0.08 wt.%, 0.1 wt.%, 0.12 wt.%, 0.15 wt.%, 0.18 wt.%, 0.19 wt.%, 0.2 wt.%, or any two of these values; Sc 0.02 wt.%, 0.04 wt.%, 0.05 wt.%, 0.06 wt.%, 0.08 wt.%, 0.1 wt.%, or any two of these values; the balance being Mg and unavoidable impurity elements.

[0044] Typical, but not limiting, weight ratios of Gd to Y are 5:1, 6:1, 8:1, 10:1, 12:1, 14:1, or any two of these ratios; the sum of the weights of Gd and Y is 10 wt.%, 10.5 wt.%, 11 wt.%, 11.5 wt.%, 12 wt.%, or any two of these ratios.

[0045] Typical, but not limiting, weight ratios of the sum of Gd and Y to Ca are 117:1, 120:1, 140:1, 150:1, 160:1, 180:1, 200:1, 218:1, or any two of these values; weight ratios of Ca and Ag are 0.1 wt.%, 0.12 wt.%, 0.15 wt.%, 0.18 wt.%, 0.2 wt.%, 0.22 wt.%, 0.25 wt.%, 0.26 wt.%, 0.28 wt.%, or any two of these values; and weight ratios of Zn and Ag are 2.5:1, 3.5:1, 4.5:1, 5.5:1, 6.5:1, 7.5:1, 8.5:1, or any two of these values.

[0046] Typical, but not limiting, melting temperature ranges for rare earth magnesium alloys are 620℃, 625℃, 630℃, 635℃, 640℃ or any two of these values; β' phase sizes for rare earth magnesium alloys are 20nm, 40nm, 50nm, 60nm, 80nm or any two of these values.

[0047] Typical, but not limiting, heating rates for the rapid solution heating section are 12℃ / min, 14℃ / min, 15℃ / min, 16℃ / min, 18℃ / min, or any two of these values; temperatures are 440℃, 445℃, 450℃, 455℃, 460℃, or any two of these values; and holding times are 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, or any two of these values. For the slow solution heating section, heating rates are 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, or any two of these values; temperatures are 480℃, 485℃, 490℃, 495℃, 500℃, or any two of these values; and holding times are 8h, 9h, 10h, 11h, 12h, or any two of these values.

[0048] Typical, but not limiting, heating rates for the rapid aging stage are 12℃ / min, 14℃ / min, 15℃ / min, 16℃ / min, 18℃ / min, or any two of these values; temperatures are 170℃, 175℃, 180℃, 185℃, 190℃, or any two of these values; and holding times are 5 min, 6 min, 8 min, 9 min, 10 min, or any two of these values. For the slow aging stage, heating rates are 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 8℃ / min, or any two of these values; temperatures are 200℃, 205℃, 210℃, 215℃, 220℃, or any two of these values; and holding times are 12 h, 18 h, 24 h, 32 h, 36 h, 42 h, 48 h, or any two of these values.

[0049] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0050] Example 1

[0051] The composition of rare earth magnesium alloys is shown in Table 1, and the preparation method is as follows:

[0052] Step S1, Alloy Casting: Weigh the raw materials according to the composition ratio and burn-off amount, including pure magnesium, pure zinc, pure silver, magnesium-calcium master alloy (calcium content 10%), and magnesium-based rare earth master alloy (corresponding rare earth element content 30%). The magnesium-based rare earth master alloys include magnesium-gadolinium master alloy, magnesium-yttrium master alloy, magnesium-zirconium master alloy, and magnesium-scandium master alloy. Bake the raw materials, operating tools, and casting molds at 180℃ for 30 minutes.

[0053] Step S11: Place pure magnesium in a crucible and put it into a pit-type resistance furnace and heat it up with the furnace. When the furnace temperature reaches 500°C, introduce CO2+SF6 (volume ratio of 99.7:0.3) protective gas and cover it with a layer of chloride protective flux. Continue to heat up to 700°C to completely melt the magnesium ingot. After the magnesium alloy melt heats up to 750°C, add raw materials other than magnesium zirconium master alloy and pure silver. After complete melting, the first melt is obtained.

[0054] Step S12: The first melt is subjected to ultrasonic homogenization treatment at a frequency of 20 kHz for 5 min; the melt is heated to 780°C, and magnesium-zirconium master alloy and pure silver are added. After the magnesium-zirconium master alloy and pure silver melt, the second melt is obtained.

[0055] Step S13: The second melt is subjected to ultrasonic homogenization treatment at a frequency of 20 kHz for 10 min; then it is refined, slag is removed, and the temperature is maintained for 10 minutes; the magnesium alloy melt is cooled to 720℃ and allowed to stand for 10 minutes before being cast into a magnesium alloy mold.

[0056] Step S2, solution treatment: Place the magnesium alloy ingot in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process twice, then stop purging and start heating. First, heat the ingot to 450℃ at 15℃ / min and hold for 8min, then heat it to 480℃ at 5℃ / min and hold for 8h. Finally, quench the ingot in hot water at 80℃ to obtain a solution-treated magnesium alloy.

[0057] Step S3, aging treatment: Place the solution-treated magnesium alloy in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process twice, then stop purging and start heating. First, heat the alloy to 180℃ at a rate of 15℃ / min and hold for 8 minutes. Then, heat the alloy to 200℃ at a rate of 5℃ / min and hold for 24 hours. Remove the alloy and air cool it to obtain the rare earth magnesium alloy.

[0058] Example 2

[0059] The difference from Example 1 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0060] In step S13, the ultrasound duration is 5 minutes.

[0061] Example 3

[0062] The difference from Example 2 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0063] In step S2, solution treatment: At room temperature, the magnesium alloy ingot is placed in a muffle furnace, the container is evacuated to a vacuum degree of -0.1MPa, and argon is purged to a pressure of 0.01MPa. This process is repeated twice. Then, the purging is stopped and the temperature is raised. The temperature is first raised to 450℃ at 15℃ / min and held for 8min. Then, the temperature is raised to 490℃ at 5℃ / min and held for 8h. Finally, the ingot is quenched in hot water at 80℃ to obtain a solution-treated magnesium alloy.

[0064] Example 4

[0065] The difference from Example 2 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0066] In step S2, solution treatment: At room temperature, the magnesium alloy ingot is placed in a muffle furnace, the container is evacuated to a vacuum degree of -0.1MPa, and argon is purged to a pressure of 0.01MPa. This process is repeated twice. Then, the purging is stopped and the temperature is raised. The temperature is first raised to 450℃ at 15℃ / min and held for 8min. Then, the temperature is raised to 500℃ at 5℃ / min and held for 8h. Finally, the alloy is quenched in hot water at 80℃ to obtain a solution-treated magnesium alloy.

[0067] Example 5

[0068] The difference from Example 2 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0069] Step S2, solution treatment: Place the magnesium alloy ingot in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process twice, then stop purging and start heating. First, heat the ingot to 450℃ at 15℃ / min and hold for 8min, then heat it to 500℃ at 5℃ / min and hold for 8h. Finally, quench the ingot in hot water at 80℃ to obtain a solution-treated magnesium alloy.

[0070] Step S3, aging treatment: Place the solution-treated magnesium alloy in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process twice, then stop purging and start heating. First, heat the alloy to 180℃ at 15℃ / min and hold for 8 minutes, then heat it to 210℃ at 5℃ / min and hold for 24 hours. Remove the alloy and air cool it to obtain the rare earth magnesium alloy.

[0071] Example 6

[0072] The difference from Example 2 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0073] Step S2, solution treatment: Place the magnesium alloy ingot in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process twice, then stop purging and start heating. First, heat the ingot to 450℃ at 15℃ / min and hold for 8min, then heat it to 500℃ at 5℃ / min and hold for 8h. Finally, quench the ingot in hot water at 80℃ to obtain a solution-treated magnesium alloy.

[0074] Step S3, aging treatment: Place the solution-treated magnesium alloy in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process twice, then stop purging and start heating. First, heat the alloy to 180℃ at 15℃ / min and hold for 8 minutes, then heat it to 220℃ at 5℃ / min and hold for 24 hours. Remove the alloy and air cool it to obtain the rare earth magnesium alloy.

[0075] Example 7

[0076] The difference from Example 2 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0077] In step S2, solution treatment: At room temperature, the magnesium alloy ingot is placed in a muffle furnace, the container is evacuated to a vacuum degree of -0.1MPa, and argon is purged to a pressure of 0.01MPa. This process is repeated twice. Then, the purging is stopped and the temperature is raised. The temperature is first raised to 450℃ at 15℃ / min and held for 8min. Then, the temperature is raised to 500℃ at 5℃ / min and held for 8h. Finally, the alloy is quenched in hot water at 80℃ to obtain a solution-treated magnesium alloy.

[0078] Examples 8 to 10

[0079] The difference from Example 2 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0080] In step S2, solution treatment: At room temperature, the magnesium alloy ingot is placed in a muffle furnace, the container is evacuated to a vacuum degree of -0.1MPa, and argon is purged to a pressure of 0.01MPa. This process is repeated twice. Then, the purging is stopped and the temperature is raised. The temperature is first raised to 450℃ at 15℃ / min and held for 8min. Then, the temperature is raised to 500℃ at 5℃ / min and held for 8h. Finally, the alloy is quenched in hot water at 80℃ to obtain a solution-treated magnesium alloy.

[0081] Example 11

[0082] The difference from Example 2 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0083] Step S2, solution treatment: Place the magnesium alloy ingot in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process twice, then stop purging and start heating. First, heat the ingot to 450℃ at 15℃ / min and hold for 8min, then heat it to 480℃ at 5℃ / min and hold for 12h. Finally, quench the ingot in hot water at 90℃ to obtain a solution-treated magnesium alloy.

[0084] Step S3, aging treatment: Place the solution-treated magnesium alloy in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process twice, then stop purging and start heating. First, heat the alloy to 180℃ at a rate of 15℃ / min and hold for 8 minutes. Then, heat the alloy to 200℃ at a rate of 5℃ / min and hold for 12 hours. Remove the alloy and air cool it to obtain the rare earth magnesium alloy.

[0085] Example 12

[0086] The difference from Example 2 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0087] Step S2, solution treatment: Place the magnesium alloy ingot in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process twice, then stop purging and start heating. First, heat the ingot to 450℃ at 15℃ / min and hold for 8 min, then heat it to 480℃ at 5℃ / min and hold for 10 h. Finally, quench the ingot in hot water at 90℃ to obtain a solution-treated magnesium alloy.

[0088] Step S3, Aging treatment: Place the solution-treated magnesium alloy in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process twice, then stop purging and start heating. First, heat the alloy to 180℃ at a rate of 15℃ / min and hold for 8 minutes. Then, heat the alloy to 210℃ at a rate of 5℃ / min and hold for 48 hours. Remove the alloy and air cool it to obtain the rare earth magnesium alloy.

[0089] Example 13

[0090] The composition of the rare earth magnesium alloy is the same as in Example 2, and the preparation method is as follows:

[0091] Step S1, Alloy Casting: Weigh the raw materials according to the composition ratio and burn-off amount, including pure magnesium, pure zinc, pure silver, magnesium-calcium master alloy (calcium content 10%), and magnesium-based rare earth master alloy (corresponding rare earth element content 30%). The magnesium-based rare earth master alloys include magnesium-gadolinium master alloy, magnesium-yttrium master alloy, magnesium-zirconium master alloy, and magnesium-scandium master alloy. Bake the raw materials, operating tools, and casting molds at 180℃ for 30 minutes.

[0092] Step S11: Place pure magnesium in a crucible and put it into a pit-type resistance furnace and heat it up with the furnace. When the furnace temperature reaches 500°C, introduce CO2+SF6 (volume ratio of 99.6:0.4) protective gas and cover it with a layer of chloride protective flux. Continue to heat up to 690°C to completely melt the magnesium ingot. After the magnesium alloy melt heats up to 740°C, add raw materials other than magnesium zirconium master alloy and pure silver. After complete melting, the first melt is obtained.

[0093] Step S12: The first melt is subjected to ultrasonic homogenization treatment at a frequency of 22 kHz for 10 min; the melt is heated to 770°C, and magnesium-zirconium master alloy and pure silver are added. After the magnesium-zirconium master alloy and pure silver melt, the second melt is obtained.

[0094] Step S13: The second melt is subjected to ultrasonic homogenization treatment at a frequency of 22 kHz for 10 min; then it is refined, slag is removed, and the temperature is maintained for 8 minutes; the magnesium alloy melt is cooled to 710℃ and allowed to stand for 12 min before being cast into a magnesium alloy mold.

[0095] Step S2, solution treatment: Place the magnesium alloy ingot in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.08MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process 3 times, then stop purging and start heating. First, heat the ingot to 440℃ at 12℃ / min and hold for 10min, then heat it to 480℃ at 3℃ / min and hold for 12h. Finally, quench the ingot in hot water at 80℃ to obtain a solution-treated magnesium alloy.

[0096] Step S3, aging treatment: Place the solution-treated magnesium alloy in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.08MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process 3 times, then stop purging and start heating. First, heat the alloy to 170℃ at 12℃ / min and hold for 10min, then heat it to 200℃ at 3℃ / min and hold for 48h. Remove the alloy and air cool it to obtain the rare earth magnesium alloy.

[0097] Example 14

[0098] The composition of the rare earth magnesium alloy is the same as in Example 2, and the preparation method is as follows:

[0099] Step S1, Alloy Casting: Weigh the raw materials according to the composition ratio and burn-off amount, including pure magnesium, pure zinc, pure silver, magnesium-calcium master alloy (calcium content 10%), and magnesium-based rare earth master alloy (corresponding rare earth element content 30%). The magnesium-based rare earth master alloys include magnesium-gadolinium master alloy, magnesium-yttrium master alloy, magnesium-zirconium master alloy, and magnesium-scandium master alloy. Bake the raw materials, operating tools, and casting molds at 180℃ for 30 minutes.

[0100] Step S11: Place pure magnesium in a crucible and put it into a pit-type resistance furnace and heat it up with the furnace. When the furnace temperature reaches 500°C, introduce CO2+SF6 (volume ratio of 99.8:0.2) protective gas and cover it with a layer of chloride protective flux. Continue to heat up to 710°C to completely melt the magnesium ingot. After the magnesium alloy melt heats up to 760°C, add raw materials other than magnesium zirconium master alloy and pure silver. After complete melting, the first melt is obtained.

[0101] Step S12: The first melt is subjected to ultrasonic homogenization treatment at a frequency of 22 kHz for 5 min; the melt is heated to 790°C, and magnesium-zirconium master alloy and pure silver are added. After the magnesium-zirconium master alloy and pure silver melt, the second melt is obtained.

[0102] Step S13: The second melt is subjected to ultrasonic homogenization treatment at a frequency of 22 kHz for 5 minutes; then it is refined, slag is removed, and the temperature is maintained for 10 minutes; the magnesium alloy melt is cooled to 730°C and allowed to stand for 8 minutes before being cast into a magnesium alloy mold.

[0103] Step S2, solution treatment: Place the magnesium alloy ingot in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.03MPa. Repeat this process twice, then stop purging and start heating. First, heat the ingot to 460℃ at 18℃ / min and hold for 5min, then heat it to 500℃ at 8℃ / min and hold for 8h. Finally, quench the ingot in hot water at 90℃ to obtain a solution-treated magnesium alloy.

[0104] Step S3, aging treatment: Place the solution-treated magnesium alloy in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.03MPa. Repeat this process twice, then stop purging and start heating. First, heat the alloy to 190℃ at 18℃ / min and hold for 5 min, then heat it to 220℃ at 8℃ / min and hold for 12 h. Remove the alloy and air cool it to obtain the rare earth magnesium alloy.

[0105] Comparative Examples 1 to 2

[0106] The difference from Example 2 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0107] Comparative Example 3

[0108] The difference from Example 2 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0109] Step S3, Aging treatment: Place the solution-treated magnesium alloy in a muffle furnace at room temperature, evacuate the container to a vacuum degree of -0.1MPa, and purge with argon to a pressure of 0.01MPa. Repeat this process twice, then stop purging and start heating. First, heat the alloy to 180℃ at a rate of 15℃ / min and hold for 8 minutes. Then, heat the alloy to 240℃ at a rate of 5℃ / min and hold for 24 hours. Remove the alloy and air cool it to obtain the rare earth magnesium alloy.

[0110] Comparative Example 4

[0111] The difference from Example 2 is that the rare earth magnesium alloy has a different composition, as detailed in Table 1.

[0112] Performance testing:

[0113] Tensile strength, yield strength, and elongation: Tested according to GB / T 228.1-2021 and GB / T 228.2-2015. The rare earth magnesium alloys prepared in the above examples and comparative examples were processed into bar-shaped tensile samples of national standard dimensions, and their tensile strength, yield strength, and elongation at room temperature and 200℃ were tested. The results are shown in Table 2.

[0114] Semi-solid injection molding experiment: The rare earth magnesium alloy obtained in Example 8 was subjected to a semi-solid injection molding experiment. Phase diagram calculations combined with DSC testing showed that the alloy's melting point was approximately 630℃, exceeding the operating temperature range of a conventional semi-solid injection molding machine. The rare earth magnesium alloy from Example 8 was processed into magnesium particles, and then injection molded in an injection molding machine equipped with a high-temperature resistant reinforced screw. The heating temperatures of the magnesium alloy in the barrel were set to 630℃, 640℃, and 650℃, the screw speed was set to 130 r / min, and the mold temperature was set to 250℃. The injection molding results are shown in Table 3.

[0115]

[0116]

[0117]

[0118] As shown in Table 3, the semi-solid injection molding method of the present invention, using a semi-solid injection molding machine equipped with a high-temperature resistant coating reinforced screw, can meet the requirements for semi-solid injection molding of high-melting-point rare earth magnesium alloy samples at 650°C.

[0119] Photograph of the β' phase in the rare earth magnesium alloy of Example 1 is shown below. Figure 1 As can be seen, the precipitated phase is nanoscale, with high density and uniform distribution. Solid magnesium particles processed from the rare-earth magnesium alloy in Example 8 are shown... Figure 2 .

[0120] As can be seen, due to the high Y content and Gd / Y < 5 in Comparative Example 1, the Mg-RE nano-precipitates in the matrix are not sufficiently coarsened after solid solution and aging, and have a high number density. During the deformation of the magnesium alloy, the nano-precipitates have a strong pinning effect on dislocations, which easily leads to stress concentration and material fracture, thus significantly reducing tensile strength and elongation.

[0121] In Comparative Example 2, due to Gd+Y>12wt.%, the number density of Mg-RE nano-precipitates in the matrix of the alloy is relatively high after solid solution and aging. During the deformation of the magnesium alloy, the pinning effect of the nano-precipitates on dislocations is strong, which easily leads to stress concentration and material fracture, resulting in a significant reduction in the tensile strength and elongation of the alloy.

[0122] In Comparative Example 3, due to the Zn content > 0.6 wt.% and the aging treatment temperature > 220℃, a large amount of Gd and Y elements in the alloy matrix were consumed and combined with Zn elements to form LPSO phase (long ordered / short ordered phase) with weak strengthening ability. This resulted in a decrease in the precipitation density of the nano Mg-RE reinforcing phase, and the precipitation phase coarsened under high temperature aging conditions, leading to a significant decrease in the tensile strength and yield strength of the alloy.

[0123] In Comparative Example 4, due to the Ca content being >0.1 wt.%, the higher Ca content increases the tendency of Ca to segregate at grain boundaries, reduces the grain boundary bonding strength, and makes grain boundaries the preferred path for crack initiation and propagation, thereby increasing the tendency for intergranular fracture and significantly reducing the tensile strength and elongation of the alloy.

[0124] As can be seen from the above, compared with the comparative example, the embodiments of the present invention synergistically regulate the significant "solid solution plasticizing" and "precipitation strengthening" effects of Gd element on magnesium alloys, as well as the inhibitory effect of Y element on the high-temperature coarsening of Mg-Gd nano-precipitates. Simultaneously, the strength, toughness, and heat resistance of magnesium alloys are improved through the grain-refining strengthening effect of Zr and Ca elements. Furthermore, the addition of Sc and a small amount of Ag further enhances the strength and plasticity of magnesium alloys, while the addition of an appropriate amount of Zn element reduces the viscosity of the magnesium alloy melt and improves its filling properties. By controlling the content of alloying elements, the present invention obtains a high-strength, high-toughness, and heat-resistant rare-earth magnesium alloy material that balances strength and plasticity at both room temperature and high temperature. It can be used for semi-solid injection molding, meeting the application requirements of lightweight magnesium alloys and their components for low-altitude aircraft.

[0125] Furthermore, it can be seen that the overall effect is better when all process parameters are within the preferred range of the present invention.

[0126] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A rare earth magnesium alloy, characterized in that, The composition, by weight percentage, includes: Gd 9.0~11.0 wt.%, Y 0.8~2.0 wt.%, Zn 0.3~0.6 wt.%, Zr 0.3~0.5 wt.%, Ca 0.05~0.1 wt.%, Ag 0.05~0.19 wt.%, Sc 0.02~0.1 wt.%, with the balance being Mg and unavoidable impurity elements, the total impurity element content being ≤0.1%; wherein, the weight ratio of Gd to Y is (5~13.5):1, and the sum of the weights of Gd and Y is 10~12. The weight percentage of Ca and Ag is 0.1~0.28 wt.%; the melting temperature range of the rare earth magnesium alloy is 620~640℃; the weight ratio of the sum of Gd and Y to Ca is (117~218):1; the weight ratio of Zn to Ag is (2.5~8.5):

1.

2. The rare earth magnesium alloy according to claim 1, characterized in that, The rare earth magnesium alloy comprises, by weight percentage: Gd 9.5~10.5wt.%, Y 0.8~1.5wt.%, Zn 0.35~0.55wt.%, Zr 0.35~0.45wt.%, Ca 0.05~0.1wt.%, Ag 0.05~0.19wt.%, Sc 0.02~0.1wt.%, with the balance being Mg and unavoidable impurity elements.

3. The rare earth magnesium alloy according to claim 1 or 2, characterized in that, The β' phase size of the rare earth magnesium alloy is 20~80 nm.

4. The method for preparing the rare earth magnesium alloy according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step S1: Mix and melt the raw materials according to the alloy composition to obtain a magnesium alloy ingot; the raw materials include pure magnesium, pure zinc, pure silver, magnesium-calcium master alloy and magnesium-based rare earth master alloy, the magnesium-based rare earth master alloy includes magnesium-gadolinium master alloy, magnesium-yttrium master alloy, magnesium-zirconium master alloy and magnesium-scandium master alloy. Step S2: The magnesium alloy ingot is subjected to solution treatment to obtain a solution-treated magnesium alloy. Step S3: The solid solution magnesium alloy is subjected to aging treatment to obtain the rare earth magnesium alloy.

5. The method for preparing rare earth magnesium alloy according to claim 4, characterized in that, In step S1, the mixed casting includes: Step S11: Add pure magnesium and heat to 690~710℃ to melt the pure magnesium. After the melt temperature reaches 740~760℃, add the magnesium-gadolinium master alloy, the magnesium-yttrium master alloy, the magnesium-calcium master alloy, the magnesium-scandium master alloy and pure zinc in sequence to melt and obtain the first melt. Step S12: The first melt is subjected to a first ultrasonic homogenization treatment. After the melt temperature reaches 770~790℃, the magnesium-zirconium master alloy and pure silver are added and melted to obtain the second melt. Step S13: The second melt is subjected to a second ultrasonic homogenization treatment, and then refined, slag removed and kept at a constant temperature. After cooling and standing, it is cast to obtain the magnesium alloy ingot. The atmosphere for the mixed casting is a mixture of CO2 and SF6, with a volume ratio of CO2 to SF6 of (99.6~99.8):(0.2~0.4); and / or The mixed casting also uses a chloride flux, which includes one or more of magnesium chloride, calcium chloride, potassium chloride, sodium chloride, and barium chloride; and / or Independently, the ultrasonic frequency of the first ultrasonic homogenization treatment and the second ultrasonic homogenization treatment are 20~22kHz, and the ultrasonic treatment time is 5~10min; and / or The heat preservation time after slag removal is 8-10 minutes, and the cooling and settling includes cooling to 710-730℃ and keeping it at that temperature for 8-12 minutes.

6. The method for preparing rare earth magnesium alloy according to claim 4, characterized in that, In step S2, the solution treatment includes: under a first inert atmosphere, the magnesium alloy ingot is subjected to a rapid solution heating section and a slow solution heating section in sequence, and then water quenched to obtain the solution-treated magnesium alloy; the heating rate of the rapid solution heating section is greater than the heating rate of the slow solution heating section.

7. The method for preparing rare earth magnesium alloy according to claim 6, characterized in that, The rapid heating section of the solution treatment process has a heating rate of 12~18℃ / min, a temperature of 440~460℃, and a holding time of 5~10min; and / or the slow heating section of the solution treatment process has a heating rate of 3~8℃ / min, a temperature of 480~500℃, and a holding time of 8~12h.

8. The method for preparing rare earth magnesium alloy according to claim 4, characterized in that, In step S3, the aging treatment includes: under a second inert atmosphere, the solid solution magnesium alloy is subjected to a rapid aging heating section and a slow aging heating section in sequence, and then air-cooled to obtain the rare earth magnesium alloy; the heating rate of the rapid aging heating section is greater than the heating rate of the slow aging heating section.

9. The method for preparing rare earth magnesium alloy according to claim 8, characterized in that, The rapid aging heating section has a heating rate of 12~18℃ / min, a temperature of 170~190℃, and a holding time of 5~10min; and / or the slow aging heating section has a heating rate of 3~8℃ / min, a temperature of 200~220℃, and a holding time of 12~48h.

10. A semi-solid injection molding method for magnesium alloy workpieces, characterized in that, The rare earth magnesium alloy ingot of any one of claims 1 to 3 is processed into solid magnesium particles, and then injection molded using a semi-solid injection molding machine to obtain a magnesium alloy workpiece; the semi-solid injection molding machine includes a screw, the surface of which is coated with a tungsten-based alloy.

11. The semi-solid injection molding method according to claim 10, characterized in that, The solid magnesium particles have a length of 3-6 mm, a width of 0.5-1 mm, and a thickness of 0.5-1 mm; and / or The screw operates at a temperature of 640~660℃ and a rotational speed of 120~180 r / min.

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