Low-melting-point high-strength hypoeutectic magnesium alloy and preparation method thereof

Abstract

The invention discloses a low-melting-point high-strength hypoeutectic magnesium alloy and a preparation method thereof. The magnesium alloy comprises the following components in percentage by mass: 12.0-14.0% of Zn; 0 to 0.8 percent of Ca; 0.3 to 0.8 percent of Zr; the balance is Mg and inevitable impurities; the content of Ca is not 0, and the melting point of the magnesium alloy is not higher than 340 DEG C. By accurately controlling the addition amount of Ca and the ratio of Ca to Zn and assisting with the grain refinement effect of Zr, formation of a fine and dispersively-distributed second phase is successfully promoted in the alloy, the elongation of the obtained magnesium alloy is kept above 8%, and the elongation of the magnesium alloy is greatly improved while the basic requirement of engineering application for plasticity is met. The yield strength and the tensile strength of the Mg-Zn alloy are greatly and synchronously improved at the room temperature and the high temperature, the inherent defect that the absolute strength of a traditional low-melting-point Mg-Zn alloy is insufficient is effectively overcome, finally, ideal combination of low melting point, high strength and good plasticity is achieved, and the urgent requirement for high-performance sacrificial structural parts in the fields of aerospace and the like is met.

Description

Technical Field

[0001] This invention relates to the field of metallic materials technology, and in particular to a low-melting-point, high-strength hypoeutectic magnesium alloy and its preparation method. Background Technology

[0002] Magnesium alloys possess significant potential for lightweighting equipment due to their low density, high specific strength, and excellent thermal conductivity. Particularly in the aerospace field, their low density allows for weight reduction, effectively improving aircraft range and performance. Furthermore, if the heat generated by friction during flight can be used to melt and ablate components that have completed their service life (such as fairings and auxiliary supports), causing them to detach from the main body, dynamic weight reduction during flight can be achieved, resulting in significant performance gains. However, conventional magnesium alloys (such as the AZ and AM series) generally have high melting points, making it difficult to achieve this "controlled ablation" function. Therefore, developing novel magnesium alloys with low melting points has become an important research direction in this field.

[0003] Obtaining a low-melting-point eutectic structure through alloying design is an effective way to reduce the melting point of magnesium alloys. Among these, Mg-Zn binary alloys have attracted much attention due to their low eutectic temperature (approximately 339°C) and are considered ideal low-melting-point matrix systems. In existing technologies, researchers have successfully obtained magnesium alloys with low melting points and certain plasticity by controlling the composition near the Mg-Zn binary eutectic point or by designing hypoeutectic compositions combined with hot deformation processes. For example, publicly disclosed hypoeutectic Mg-Zn alloys, by controlling the Zn content and combining it with extrusion processes, achieve lower melting initiation temperatures and good plasticity, making it possible to form complex components. However, these Mg-Zn alloy schemes targeting low melting points and plasticity generally suffer from a significant performance bottleneck: their absolute strength, especially yield strength and tensile strength, remains at a medium or low level. Although their toughness is acceptable, the insufficient strength severely limits their application in structural components with slightly higher load-bearing requirements. More importantly, during flight, friction generates heat, causing components to reach high temperatures. Therefore, these components must maintain their structural integrity and load-bearing capacity under the high temperatures generated by aerodynamic friction. This means that materials must possess good high-temperature strength well below their melting and ablation temperatures to meet the application requirements of the alloy before melting; otherwise, components may fail prematurely due to their inability to withstand the load. However, conventional low-melting-point Mg-Zn alloys typically exhibit significant strength degradation at high temperatures, making them unsuitable for this task. Therefore, excellent high-temperature strength is a prerequisite and guarantee for achieving controlled ablation functionality.

[0004] To improve the strength of Mg-Zn alloys, those skilled in the art typically consider two approaches: increasing the Zn content or adding a third alloying element. However, both of these traditional strengthening methods face significant challenges in low-melting-point Mg-Zn systems. First, while increasing the Zn content can enhance strength through solid solution strengthening and increasing the amount of the second phase, once the Zn content exceeds the hypoeutectic window, it leads to the formation of a large amount of continuous, hard, and brittle network eutectic structure. Although this improves strength, it causes a sharp deterioration in alloy plasticity, resulting in an imbalance between strength and toughness, making it unsuitable for applications requiring both sufficient plasticity and high strength. Second, adding traditional high-efficiency strengthening elements, such as rare earth elements (Y, Gd, etc.), while significantly improving alloy strength, introduces two new problems: first, rare earth elements are expensive, hindering large-scale applications; second, the addition of most rare earth elements significantly increases the solidus and liquidus temperatures of the alloy, contradicting the initial design goal of "low melting point."

[0005] Calcium (Ca), as a low-cost alloying element that effectively refines the grain size of magnesium alloys, offers the possibility of low-cost strengthening. However, its introduction into the low-melting-point Mg-Zn system presents a thorny contradiction: improper addition or poor content control can easily lead to the formation of coarse, network-like or skeletal brittle intermetallic compounds (such as the Ca2Mg6Zn3 phase) with Mg and Zn. The continuous distribution of this brittle phase at grain boundaries often results in a catastrophic decrease in alloy plasticity while providing limited strength gains, leading to the "brittleness upon addition" dilemma and failing to achieve a synergistic effect of strengthening and toughening. Therefore, improving both the mechanical properties of lightweight structural magnesium alloys and their low melting point remains a challenge in the industry. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a low melting point high strength hypoeutectic magnesium alloy and its preparation method, so as to solve the problem that hypoeutectic Mg-Zn alloy is difficult to balance between low melting point and excellent room temperature / high temperature strength, thereby meeting the dynamic weight reduction requirements of aerospace equipment.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a low-melting-point, high-strength hypoeutectic magnesium alloy, comprising the following components by mass percentage: Zn 12.0~14.0%; Ca 0~0.8%; Zr 0.3~0.8%; the balance being Mg and unavoidable impurities; the melting point of the magnesium alloy is not higher than 340℃.

[0008] Thus, the Zn content is controlled within the hypoeutectic range of 12.0–14.0%. Utilizing the characteristic that a higher Zn content exceeds its solid solubility in Mg to form a low-melting-point eutectic phase, a basic low-melting-point framework is provided for the alloy. Based on this, the Ca content is precisely controlled. On the one hand, its grain-refining and second-phase strengthening potential is utilized; on the other hand, its content is limited to avoid the drastic deterioration of plasticity caused by the formation of coarse and brittle phases (such as Ca2Mg6Zn3) due to excessive Ca. The addition of Zr mainly leverages its excellent grain-refining effect in magnesium alloys, laying the foundation for obtaining a uniform and fine recrystallized structure in subsequent hot deformation processes. Through the synergistic addition of Ca and Zr, and the synergistic effect of the components and their proportions, while maintaining the alloy's low-melting-point characteristics, the initial strengthening modification of the binary Mg-Zn alloy is achieved, improving the microstructure and enhancing strength at room temperature and high temperatures.

[0009] Preferably, the magnesium alloy comprises the following components by mass percentage: Zn 12.5~13.5%; Ca 0.3~0.6%; Zr 0.49~0.66%; with the balance being Mg and unavoidable impurities.

[0010] Preferably, the magnesium alloy has a melting point of 330~340℃.

[0011] Preferably, the high strength of the magnesium alloy includes its yield strength, tensile strength, and elongation at room temperature and / or at a high temperature of 100~200℃. Preferably, the magnesium alloy has a yield strength of not less than 235 MPa, a tensile strength of not less than 329 MPa, and an elongation of not less than 8% at room temperature; and a yield strength of not less than 230 MPa, a tensile strength of not less than 279 MPa, and an elongation of not less than 9% at 100℃.

[0012] Another object of the present invention is to provide a method for preparing the above-mentioned low-melting-point, high-strength hypoeutectic magnesium alloy, comprising the following steps:

[0013] 1) Pure magnesium, pure zinc, Mg-Ca master alloy and Mg-Zr master alloy are used as raw materials for composition and feeding. Then, they are smelted and cast under a protective atmosphere. The resulting alloy melt is poured into a mold and cooled to obtain an ingot.

[0014] 2) The ingot obtained in step 1) is subjected to homogenization annealing at 300~340℃, held at that temperature for 8~15h and then air-cooled to room temperature.

[0015] 3) After preheating the ingot after homogenization treatment in step 2), hot extrusion is carried out at a temperature of 270~290℃ to obtain the low melting point high strength hypoeutectic magnesium alloy.

[0016] Thus, homogenization primarily involves dissolving the non-equilibrium eutectic phase and promoting the homogenization of solute atom diffusion, preparing a uniform microstructure for subsequent deformation. Temperature selection must avoid excessive melting of low-melting-point phases. Hot extrusion further refines the microstructure and densifies the material through large plastic deformation, breaking down and dispersing the coarse second phase into fine, dispersed particles, forming a strong and toughened deformation texture. Temperature selection is designed to accommodate the alloy's low melting point characteristics and prevent overheating. This method, highly synergistic with alloy composition design, systematically solves problems that may arise during the preparation of low-melting-point, Ca-containing alloys, such as compositional segregation, coarse microstructure, precipitation of coarse brittle phases, and processing cracking.

[0017] Preferably, the weight percentage of Ca in the Mg-Ca master alloy is 20-30%, and the weight percentage of Zr in the Mg-Zr master alloy is 25-35%.

[0018] Preferably, the protective atmosphere is a mixture of CO2 and SF6 in a volume ratio of 99:1. This provides oxidation and combustion protection for the magnesium alloy during smelting and casting, reduces elemental oxidation and burn-off during smelting, and minimizes inclusions in the melt, ensuring the purity and accuracy of the alloy melt's chemical composition.

[0019] Preferably, the melting temperature is 680~750℃ and the casting temperature is 670~690℃.

[0020] Preferably, the preheating involves holding the ingot at 270-290°C for 30-90 minutes; the extrusion ratio during the hot extrusion treatment is 15:1-18:1. This higher extrusion ratio effectively breaks down the as-cast and homogenized microstructure, significantly refines the grains, promotes dynamic recrystallization, and allows for a more dispersed distribution of the second-phase particles, thereby simultaneously improving the alloy's strength and plasticity.

[0021] Another objective of this invention is to provide the application of the aforementioned magnesium alloy in the aerospace field. In aerospace, this alloy is particularly suitable for manufacturing lightweight structural components or non-load-bearing components with "controlled ablation" or "sacrifice" functional requirements, and must possess good high-temperature strength below the melting ablation temperature to ensure the alloy maintains its structural integrity and load-bearing capacity before melting. Examples include fairings, supports, or canopies that can be self-melted and removed by aerodynamic heating after a specific flight phase. This fully utilizes its low melting point to achieve dynamic weight reduction, and its high specific strength meets the structural load-bearing requirements of this phase, addressing the urgent need in this field for materials that combine lightweight, low melting point, certain load-bearing capacity, and reliable detachment functionality.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. Based on hypoeutectic Mg-Zn alloys, this invention, through precise control of the amount of Ca added and its ratio with Zn, coupled with the grain-refining effect of Zr, successfully promotes the formation of a fine, dispersed second phase in the alloy, reduces the formation of continuous network eutectic phases, and controls the content of high-temperature resistant and coarse brittle phases (such as Ca2Mg6Zn3). This allows the inexpensive Ca element to fully exert its potential for grain refinement and second-phase strengthening, while avoiding the catastrophic decrease in plasticity caused by brittle phases, achieving a "toughening" effect rather than a "brittleness-strengthening" effect. While ensuring that the alloy's melting point is below 340℃, the absolute strength of the alloy is significantly improved. Compared with typical hypoeutectic Mg-13Zn binary alloys, the magnesium alloy obtained by this invention maintains an elongation of over 8%, meets the basic requirements for plasticity in engineering applications, and achieves a significant simultaneous increase in yield strength and tensile strength at room temperature and high temperature. This effectively overcomes the inherent disadvantage of insufficient absolute strength in traditional low-melting-point Mg-Zn alloys and successfully avoids the risk of embrittlement, especially caused by the addition of Ca. Ultimately, it achieves an ideal combination of low melting point, high strength at room temperature and high temperature, and good plasticity, to meet the urgent needs of aerospace and other fields for high-performance sacrificial structural components.

[0024] 2. The preparation process of this invention is simple and the production time is short. The equipment used, such as melting furnaces and hot extrusion presses, are all conventional and general-purpose equipment. The alloy does not contain rare earth elements, resulting in low cost and facilitating large-scale industrial production. Through ingenious composition design and process control, the invention systematically solves the long-standing technical problems in the field of low-melting-point magnesium alloys, such as "low strength," "brittleness after calcium addition," and "difficulty in achieving both strength and plasticity." It yields a novel magnesium alloy material with excellent comprehensive performance (low melting point, high strength, and good toughness), controllable cost, and stable process. This material can facilitate the application of magnesium alloys in dynamic weight reduction in aerospace equipment and meets the economic requirements for large-scale material applications in aerospace and other fields, making it highly valuable for application. Attached Figure Description

[0025] Figure 1 This is a DSC curve of the deformed magnesium alloy prepared according to the present invention.

[0026] Figure 2 This is a SEM image of the deformed magnesium alloy prepared according to the present invention.

[0027] Figure 3 This is the EBSD image of the deformed magnesium alloy prepared according to the present invention.

[0028] Figure 4 The room temperature tensile stress-strain curve of the deformed magnesium alloy prepared in this invention is shown.

[0029] Figure 5 This is a bar chart showing the room temperature mechanical properties of the deformed magnesium alloy prepared according to the present invention.

[0030] Figure 6 The high-temperature tensile stress-strain curve of the deformed magnesium alloy prepared in this invention is shown.

[0031] Figure 7 This is a bar chart showing the high-temperature mechanical properties of the deformed magnesium alloy prepared according to the present invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the embodiments.

[0033] I. A method for preparing a low-melting-point, high-strength magnesium alloy

[0034] Example 1: This example uses the following steps:

[0035] 1) Ingredients: The Zn element content is 13.16 wt.%, the Ca element content is 0.27 wt.%, the Zr element content is 0.55 wt.%, and the remainder is Mg and unavoidable impurity elements. Prepare the raw materials according to the above composition, polish the raw materials to a metallic luster, weigh them and set them aside for use. The raw materials used are high-purity magnesium (99.99 wt.%), pure zinc (99.99 wt.%), Mg-25 wt.%Ca master alloy and Mg-30 wt.%Zr master alloy.

[0036] 2) Melting: The weighed raw materials are placed into a heat treatment furnace and preheated at 200℃ for 10-20 minutes. Then, the preheated pure magnesium is placed into a resistance furnace and heated to 740-750℃ under a protective atmosphere of CO2 and SF6 mixed gas (ratio of 99:1). After melting, the preheated pure zinc is added and held at 680℃ for 10-15 minutes. The preheated Mg-25wt.%Ca master alloy and Mg-30wt.%Zr master alloy are added in sequence and held at 680℃ for 10-15 minutes to form an alloy melt.

[0037] 3) Casting: Stir the magnesium alloy melt obtained in step 2) for 3 min, keep it at 680℃ for 15 min under a protective atmosphere of CO2 and SF6 mixed gas (ratio of 99:1), remove the slag on the surface of the melt, pour the alloy melt into a metal mold preheated to 250℃, cool to room temperature, demold, and cut Φ80mm×50mm ingots by machining.

[0038] 4) Heat treatment: Place the ingot obtained in step 3) into a heat treatment furnace and keep it at 320~340℃ for 10 h, then air cool to room temperature.

[0039] 5) Extrusion: The magnesium alloy ingot after heat treatment in step 4) is preheated at 270-290℃ for 30 min, and then placed in an extrusion die. It is extruded into a Φ20 mm bar at a deformation temperature of 270-290℃ and an extrusion ratio of 18:1. It is then air-cooled to room temperature to obtain a deformed magnesium alloy.

[0040] Example 2: This example uses the following steps:

[0041] 1) Ingredients: Zn content is 13.06 wt.%, Ca content is 0.59 wt.%, Zr content is 0.66 wt.%, and the remainder is Mg and unavoidable impurity elements. Prepare the raw materials according to the above composition, polish them to a metallic luster, and weigh them for use. The raw materials used are high-purity magnesium (99.99 wt.%), pure zinc (99.99 wt.%), Mg-25 wt.%Ca master alloy and Mg-30 wt.%Zr master alloy.

[0042] 2) Melting: The weighed raw materials are placed into a heat treatment furnace and preheated at 200℃ for 10-20 minutes. Then, the preheated pure magnesium is placed into a resistance furnace and heated to 740-750℃ under a protective atmosphere of CO2 and SF6 mixed gas (ratio of 99:1). After melting, the preheated pure zinc is added and held at 680℃ for 10-15 minutes. The preheated Mg-25wt.%Ca master alloy and Mg-30wt.%Zr master alloy are added in sequence and held at 680℃ for 10-15 minutes to form an alloy melt.

[0043] 3) Casting: Stir the magnesium alloy melt obtained in step 2) for 3 min, keep it at 680℃ for 15 min under a protective atmosphere of CO2 and SF6 mixed gas (ratio of 99:1), remove the slag on the surface of the melt, pour the alloy melt into a metal mold preheated to 250℃, cool to room temperature, demold, and cut Φ80mm×50mm ingots by machining.

[0044] 4) Heat treatment: Place the ingot obtained in step 3) into a heat treatment furnace and keep it at 320~340℃ for 10 h, then air cool to room temperature.

[0045] 5) Extrusion: The magnesium alloy ingot after heat treatment in step 4) is preheated at 270-290℃ for 30 min, and then placed in an extrusion die. It is extruded into a Φ20 mm bar at a deformation temperature of 270-290℃ and an extrusion ratio of 18:1. It is then air-cooled to room temperature to obtain a deformed magnesium alloy.

[0046] Comparative Example 1: This comparative example adopts the following steps:

[0047] 1) A Mg-Zn hypoeutectic magnesium alloy material, wherein the Zn element content is 12.53 wt.%, the remainder is Mg and unavoidable impurity elements, the raw materials are prepared according to the above composition and the raw materials are polished to a metallic luster and weighed for use. The raw materials used are high-purity magnesium (99.99 wt.%) and pure zinc (99.99 wt.%).

[0048] 2) Place the weighed raw materials into a heat treatment furnace and preheat at 200℃ for 10-20 minutes. Then, put the preheated pure magnesium into a resistance furnace and heat it to 740-750℃ under a protective atmosphere of CO2 and SF6 mixed gas (ratio of 99:1). After melting, put in the preheated pure zinc and hold at 680℃ for 10-15 minutes to form an alloy melt.

[0049] 3) Stir the magnesium alloy melt obtained in step (2) for 3 min, keep it at 680℃ for 10~15 min under a protective atmosphere of CO2 and SF6 mixed gas (ratio of 99:1), remove the slag on the surface of the melt, pour the alloy melt into a metal mold preheated to 250℃, cool to room temperature, demold, and cut Φ80mm×50mm ingots by machining.

[0050] 4) Place the ingot obtained in step (3) into a heat treatment furnace and keep it at 320~340℃ for 10 h, then air cool it to room temperature.

[0051] 5) Place the magnesium alloy ingot after heat treatment in step (4) at 270~290℃ for 30 min, then place it in an extrusion die and extrude it into a Φ20 mm bar at a deformation temperature of 270~290℃ with an extrusion ratio of 18:1. Air cool it to room temperature to obtain deformed magnesium alloy.

[0052] Comparative Example 2: This comparative example adopts the following steps:

[0053] 1) Ingredients: Zn content is 13.22 wt.%, Ca content is 0 wt.%, Zr content is 0.51 wt.%, and the remainder is Mg and unavoidable impurity elements. Prepare the raw materials according to the above composition, polish them to a metallic luster, and weigh them for use. The raw materials used are high-purity magnesium (99.99 wt.%), pure zinc (99.99 wt.%), Mg-25 wt.%Ca master alloy and Mg-30 wt.%Zr master alloy.

[0054] 2) Melting: The weighed raw materials are placed into a heat treatment furnace and preheated at 200℃ for 10-20 minutes. Then, the preheated pure magnesium is placed into a resistance furnace and heated to 740-750℃ under a protective atmosphere of CO2 and SF6 mixed gas (ratio of 99:1). After melting, the preheated pure zinc is added and held at 680℃ for 10-15 minutes. The preheated Mg-25wt.%Ca master alloy and Mg-30wt.%Zr master alloy are added in sequence and held at 680℃ for 10-15 minutes to form an alloy melt.

[0055] 3) Casting: Stir the magnesium alloy melt obtained in step 2) for 3 min, keep it at 680℃ for 15 min under a protective atmosphere of CO2 and SF6 mixed gas (ratio of 99:1), remove the slag on the surface of the melt, pour the alloy melt into a metal mold preheated to 250℃, cool to room temperature, demold, and cut Φ80mm×50mm ingots by machining.

[0056] 4) Heat treatment: Place the ingot obtained in step 3) into a heat treatment furnace and keep it at 320~340℃ for 10 h, then air cool to room temperature.

[0057] 5) Extrusion: The magnesium alloy ingot after heat treatment in step 4) is preheated at 270-290℃ for 30 min, and then placed in an extrusion die. It is extruded into a Φ20 mm bar at a deformation temperature of 270-290℃ and an extrusion ratio of 18:1. It is then air-cooled to room temperature to obtain a deformed magnesium alloy.

[0058] Comparative Example 3: This comparative example adopts the following steps:

[0059] 1) Ingredients: Zn content is 13.15 wt.%, Ca content is 0.98 wt.%, Zr content is 0.54 wt.%, and the remainder is Mg and unavoidable impurity elements. Prepare the raw materials according to the above composition, polish them to a metallic luster, and weigh them for use. The raw materials used are high-purity magnesium (99.99 wt.%), pure zinc (99.99 wt.%), Mg-25 wt.%Ca master alloy and Mg-30 wt.%Zr master alloy.

[0060] 2) Melting: The weighed raw materials are placed into a heat treatment furnace and preheated at 200℃ for 10-20 minutes. Then, the preheated pure magnesium is placed into a resistance furnace and heated to 740-750℃ under a protective atmosphere of CO2 and SF6 mixed gas (ratio of 99:1). After melting, the preheated pure zinc is added and held at 680℃ for 10-15 minutes. The preheated Mg-25wt.%Ca master alloy and Mg-30wt.%Zr master alloy are added in sequence and held at 680℃ for 10-15 minutes to form an alloy melt.

[0061] 3) Casting: Stir the magnesium alloy melt obtained in step 2) for 3 min, keep it at 680℃ for 15 min under a protective atmosphere of CO2 and SF6 mixed gas (ratio of 99:1), remove the slag on the surface of the melt, pour the alloy melt into a metal mold preheated to 250℃, cool to room temperature, demold, and cut Φ80mm×50mm ingots by machining.

[0062] 4) Heat treatment: Place the ingot obtained in step 3) into a heat treatment furnace and keep it at 320~340℃ for 10 h, then air cool to room temperature.

[0063] 5) Extrusion: The magnesium alloy ingot after heat treatment in step 4) is preheated at 270-290℃ for 30 min, and then placed in an extrusion die. It is extruded into a Φ20 mm bar at a deformation temperature of 270-290℃ and an extrusion ratio of 18:1. It is then air-cooled to room temperature to obtain a deformed magnesium alloy.

[0064] II. Performance Verification

[0065] 1. Differential scanning calorimetry (DSC) was performed on the deformed magnesium alloys of Examples 1-2 and Comparative Examples 1-3. The test gas atmosphere was helium, the heating range was RT to 650℃, the cooling range was 650℃ to 100℃, and the rate was 10℃ / min. Results Figure 1 As shown. By statistically analyzing the inflection points of the endothermic and exothermic peaks in the DSC curves of the alloy during heating and cooling processes, the solidus and liquidus temperatures of the alloy were determined. During heating, the inflection point to the left of the first endothermic peak on the curve indicates the beginning of liquid phase precipitation from the solid alloy; this temperature corresponds to the solidus temperature and is the melting point. The inflection point to the right of the second endothermic peak indicates the complete transformation of the alloy into a liquid, corresponding to the liquidus temperature. During cooling, the inflection point to the right of the first exothermic peak on the curve indicates the beginning of liquid metal crystallization; this temperature corresponds to the liquidus temperature. The inflection point to the left of the second exothermic peak indicates the completion of alloy crystallization; this temperature corresponds to the solidus temperature. Therefore, the melting point of the alloy is taken as the average of the solidus temperatures during the heating and cooling processes. Similarly, the liquidus temperature is taken as the average of the liquidus temperatures during the heating and cooling processes, as shown in the figure. Figure 1 As shown in Table 1.

[0066] Table 1

[0067]

[0068] from Figure 1 As can be seen from Table 1, compared with Comparative Example 1, the melting points of Examples 1-2 and Comparative Examples 2-3 did not change much and were all less than 340°C, indicating that the Zr and Ca elements added to the hypoeutectic Mg-Zn alloy had little effect on the solidus temperature of the alloy.

[0069] 2. The microstructures of the deformed magnesium alloys from Examples 1-2 and Comparative Examples 1-3 were observed under scanning electron microscopy and electron backscatter diffraction, respectively. The results are as follows: Figure 2 and Figure 3 As shown.

[0070] As can be seen from the figure, compared with Comparative Example 1, the alloys prepared in Examples 1-2 and Comparative Examples 1-2 have fine second phases dispersed in the matrix. The proportion of second phases in the alloys increases significantly after the addition of Ca and Zr. The second phases pinning and hindering dislocation movement improve the room temperature and high temperature strength of the alloys. Figure 2 Simultaneously, the fine second phase pins the grain boundaries, thereby refining the grains. The addition of Zr significantly refines the grains, and the grain size further decreases with increasing Ca content, achieving the goal of grain refinement and strengthening, thus improving the alloy's strength. Figure 3 However, as the Ca content in the magnesium alloy system increases, the amount of brittle phase Ca2Mg6Zn3 produced in the alloy also increases, leading to a deterioration in the alloy's plasticity at room temperature. Figure 2 ).

[0071] 3. The deformed magnesium alloys prepared in Examples 1-2 and Comparative Examples 1-3 were subjected to tensile tests at room temperature. The tensile specimens were within the national standard range, with a gauge length of 25 mm and a diameter of 5 mm. The preloading rate was 2 mm / min. The results are as follows: Figure 4 and Figure 5 As shown.

[0072] from Figure 4 and Figure 5 As can be seen, compared with Comparative Example 1, the addition of Zr and Ca significantly improves the room temperature yield strength and tensile strength of the alloy. With increasing Ca content, the room temperature yield strength and tensile strength of the alloy show an upward trend, reaching a maximum of 250 MPa and 342 MPa, respectively. However, when the Ca content reaches 1.0 wt.%, the alloy's plasticity deteriorates rapidly, with an elongation of only 3.7%. This is because the extrusion process breaks down the originally coarse network-like second phase into blocky or granular forms, thereby strengthening the alloy and increasing its strength. However, when the Ca content is too high, it leads to an increase in the number and volume of the second phase, causing a sharp deterioration in the alloy's plasticity.

[0073] 5. The deformed magnesium alloys prepared in Examples 1-2 and Comparative Examples 1-3 were subjected to tensile tests at high temperatures of 100℃ and 200℃, respectively. The tensile specimens were of dimensions within the national standard range, with a gauge length of 25 mm and a diameter of 5 mm. The preloading rate was 2 mm / min. The results are as follows: Figure 6 and Figure 7 As shown.

[0074] from Figure 6 and Figure 7 As can be seen, the high-temperature strength of different magnesium alloys decreases to varying degrees compared to their room temperature strength. Compared to Comparative Examples 1 and 2, the alloys of Examples 1 and 2 show significantly improved strength at 100℃, with high-temperature yield strength and tensile strength reaching 247 MPa and 321 MPa, respectively. When the temperature rises to 200℃, the high-temperature yield strength and tensile strength of the alloys of Examples 1 and 2 reach 170 MPa and 192 MPa, respectively. This indicates that the addition of certain amounts of Ca and Zr can significantly improve the high-temperature mechanical properties of the alloys. This is because the fine, high-temperature resistant Ca2Mg6Zn3 phase, although sacrificing some of the alloy's plasticity, can exist stably at high temperatures and pin grain boundaries, hindering grain boundary sliding and thus improving the mechanical properties at high temperatures. Therefore, Comparative Example 3 has the best yield strength and tensile strength, but with a greater sacrifice of plasticity, resulting in overall mechanical properties that cannot meet the requirements of high-performance sacrificial structural components in aerospace and other fields.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low melting point high strength hypoeutectic magnesium alloy, characterized by, The magnesium alloy comprises the following components in mass percentage: Zn 12.0-14.0%; Ca 0-0.8%; Zr 0.3-0.8%; the balance being Mg and inevitable impurities; and the content of Ca is not 0, and the melting point of the magnesium alloy is not higher than 340 DEG C.

2. The low melting high strength hypoeutectic magnesium alloy according to claim 1, characterized in that, The magnesium alloy comprises the following components in mass percentage: Zn 12.5-13.5%; Ca 0.3-0.6%; Zr 0.49-0.66%; the balance being Mg and inevitable impurities.

3. The low melting high strength hypoeutectic magnesium alloy according to claim 1, characterized in that, The melting point of the magnesium alloy is 330-340 DEG C.

4. The low melting high strength hypoeutectic magnesium alloy according to claim 1, characterized in that, The high strength of the magnesium alloy includes yield strength, tensile strength and elongation at room temperature and high temperature, and the high temperature is 100-200 DEG C.

5. A method of producing a low melting point high strength hypoeutectic magnesium alloy according to any one of claims 1 to 4, characterized by, The method comprises the following steps: 1) pure magnesium, pure zinc, Mg-Ca intermediate alloy and Mg-Zr intermediate alloy are used as raw materials to allocate components, then melting and casting are carried out under a protective atmosphere, and the obtained alloy melt is poured into a mold to obtain a cast ingot after cooling; 2) the cast ingot obtained in step 1) is subjected to homogenization annealing at 300-340 DEG C, and is cooled to room temperature after heat preservation for 8-15 h; 3) the cast ingot after homogenization treatment in step 2) is preheated, and hot extrusion is carried out at a temperature of 270-290 DEG C, so that the low-melting-point high-strength hypoeutectic magnesium alloy is obtained.

6. The method of claim 5, wherein the low melting point high strength hypoeutectic magnesium alloy is prepared by the steps of: preparing a magnesium alloy ingot by mixing and melting magnesium, manganese, zinc, and rare earth elements; and performing homogenization treatment on the magnesium alloy ingot. The weight percentage of Ca in the Mg-Ca intermediate alloy is 20-30%, and the weight percentage of Zr in the Mg-Zr intermediate alloy is 25-35%.

7. The method of claim 5, wherein the low melting point high strength hypoeutectic magnesium alloy is prepared by the steps of: preparing a magnesium alloy ingot by mixing and melting magnesium, manganese, zinc, calcium, strontium, and rare earth elements; and performing homogenization treatment on the magnesium alloy ingot. The protective atmosphere is a mixed gas formed by CO2 and SF6 in a volume ratio of 99:

1.

8. The method of claim 5, wherein the low melting point high strength hypoeutectic magnesium alloy is prepared by the steps of: preparing a magnesium alloy ingot by mixing and melting magnesium, manganese, zinc, and rare earth elements; and performing homogenization treatment on the magnesium alloy ingot. The temperature of the melting is 680-750 DEG C, and the temperature of the casting is 670-690 DEG C.

9. The method of claim 5, wherein the low melting point high strength hypoeutectic magnesium alloy is prepared by the steps of: preparing a magnesium alloy ingot by mixing and melting magnesium, manganese, zinc, calcium, strontium, and rare earth elements; and performing homogenization treatment on the magnesium alloy ingot. The preheating is heat preservation of the cast ingot at 270-290 DEG C for 30-90 min; and the extrusion ratio during the hot extrusion treatment is 15:1-18:

1.

10. Application of the magnesium alloy in aerospace field as claimed in any one of claims 1-4 or prepared by the method as claimed in any one of claims 6-9.

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