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

Abstract

The invention discloses a low-melting-point high-strength magnesium alloy and a preparation method thereof. The magnesium alloy comprises, by mass, 19.5-20.4% of Ga, 24.5-25.4% of Sn and the balance Mg and inevitable impurities, and the content of the impurities is smaller than or equal to 0.04%. The melting point of the magnesium alloy is not higher than 440 DEG C. Through scientific and reasonable formula design of alloy elements Ga and Sn, the content of the alloy elements Ga and Sn exceeds the maximum solid solubility of the alloy elements Ga and Sn in Mg, and a large amount of second phases Mg5Ga2 and Mg2Sn with low melting points are separated out. A room-temperature mechanical property test shows that the melting point of the magnesium alloy can be reduced to 431 DEG C, the compressive strength reaches up to 714 MPa, the compressive yield strength reaches up to 433 MPa, the compression ratio is 18.8%, and the magnesium alloy is an excellent low-melting-point high-strength magnesium alloy material and can be widely applied to dynamic weight reduction of aerospace equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and particularly to a low-melting-point and high-strength magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium alloys have the advantages of low density, high specific strength, good heat dissipation, etc., and have high application value in the aerospace field. Lightweight is of great significance for improving the key service performance of high-speed aircraft (such as long range and high speed). In addition to the lightweight of the components themselves, dynamic weight reduction also has an important impact on improving the key performance during the flight of high-speed aircraft. By using the heat generated by friction during flight, parts are melted and ablated, so that the components that have completed their service functions are separated from the equipment, thereby achieving the goal of dynamic weight reduction. However, conventional magnesium alloys have relatively high melting points and cannot meet the requirements of aerospace equipment for dynamic weight reduction. Therefore, in order to develop low-melting-point alloys for dynamic weight reduction and boost the dynamic weight reduction of aerospace equipment, it is of great significance to research and prepare low-melting-point and high-strength magnesium alloys.

[0003] Currently, the core of preparing low-melting-point alloys is to select main metal elements with relatively low melting points and form a eutectic system through combination. For example, the invention patent CN115592295A discloses an Al-Mg alloy welding wire with low melting point and good wettability and a preparation method thereof. The raw material components of the aluminum-magnesium alloy welding wire are as follows: by mass percentage, Mg 4.0 - 4.5%, Zn 0.1 - 2.0%, Cr 0.1 - 0.15%, Mn 0.1 - 0.40%, Si 0.2 - 0.4%, Ti 0.10 - 0.45%, Sc 0.05 - 0.21%, and transition metal 0.05 - 2.0%, and the balance is aluminum, and the melting point of the obtained alloy is about 630°C. The invention patent CN106825979B discloses a low-melting-point Sn-Zn-Bi-Mg series lead-free solder and a preparation method thereof. The solder has alloy components including trace elements such as low content of zinc, bismuth, magnesium, etc., and the balance is tin. Although the above methods reduce the melting point of the alloy to a certain extent, the magnesium content is low, which does not meet the requirements of the aviation field for lightweight structural materials, and the reduction of the melting point is limited and cannot meet the requirements of aerospace equipment for dynamic weight reduction.

[0004] In view of this, with the rapid development of the aviation field, in order to assist the dynamic weight reduction of aerospace equipment, it has become an urgent need in the industry to not only improve the mechanical properties of the lightweight structural material magnesium alloy but also improve the low melting point of the magnesium alloy. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned existing technologies, the technical problem to be solved by the present invention is: how to provide a low-melting-point and high-strength magnesium alloy and its preparation method, to solve the problem that the existing magnesium alloys do not have both low melting point and high strength and other properties, and cannot meet the requirements of dynamic weight reduction of aerospace equipment.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions: A low-melting-point and high-strength magnesium alloy, comprising the following components in mass percentage: Ga 19.5 - 20.4 wt.%, Sn 24.5 - 25.4 wt.%, the balance being Mg and unavoidable impurities, and the impurity content ≤ 0.04 wt.%; the melting point of the magnesium alloy is not higher than 440 °C, specifically, the melting point of the magnesium alloy is 410 - 440 °C. Since Ga and Sn have relatively high solid solubilities in Mg, up to 8.4 wt% and 14.48 wt% respectively. It has been found that when the contents of Ga and Sn exceed their maximum solid solubilities in Mg, a large amount of low-melting-point second phases will precipitate, rather than mainly forming solid solutions, thus reducing the melting point of the alloy; therefore, by adding relatively high contents of Ga and Sn to Mg to prepare Mg-20Ga-25Sn alloy, the large amount of precipitated low-melting-point phases of Mg5Ga2 and Mg2Sn can significantly reduce the melting point of the magnesium alloy, reducing the melting point of the magnesium alloy to about 430 °C.

[0007] Another object of the present invention also lies in providing a preparation method of the above low-melting-point and high-strength magnesium alloy, comprising the following steps:

[0008] 1) Using pure magnesium ingots, pure tin and pure gallium as raw materials for component batching, and then obtaining a magnesium alloy ingot through melting and casting;

[0009] 2) Sequentially performing homogenization treatment and hot extrusion treatment on the magnesium alloy ingot obtained in step 1), and then the low-melting-point and high-strength magnesium alloy is obtained.

[0010] Preferably, the melting is to polish, weigh and batch pure magnesium, pure tin and pure gallium, then preheat them, and then heat the preheated pure magnesium ingot to 740 - 750 °C under a protective atmosphere to melt it into a magnesium melt. After the pure magnesium is melted, the temperature is lowered to 650 - 680 °C, and then the preheated pure tin and pure gallium are added, and kept warm for 10 - 15 min to obtain a melt. In this way, sufficient protective atmosphere is introduced during the melting process to reduce the oxidation and burning loss of the metal, and the burning loss of the alloy is considered during the melting batching and the alloy burning loss rate is added for batching to make up for the burned part so that the composition of the melted alloy is accurate.

[0011] Preferably, the protective atmosphere is a mixed gas formed by CO2 and SF6 in a volume ratio of 99:1.

[0012] Preferably, the casting is carried out by keeping the melt at 680 °C for 15 min under a protective atmosphere, then injecting it into a preheated metal mold, cooling it to room temperature, and demolding to obtain a magnesium alloy ingot.

[0013] Preferably, the homogenization treatment is carried out at 280 - 400 °C for 10 - 15 h. In this way, by controlling the temperature of the homogenization treatment, the internal structure of the alloy is improved, the casting stress is eliminated, and the extrusion performance is enhanced, thereby improving the alloy properties.

[0014] Preferably, during the hot extrusion treatment, the temperature is 270 - 290 °C and the extrusion ratio is 15:1 - 18:1. In this way, by controlling the deformation conditions during extrusion, it helps to eliminate casting defects, refine grains, make the structure more uniform and dense, and further improve the alloy properties. If the extrusion temperature is too low, the extrusion force will increase, increasing the equipment load, and the dynamic recrystallization will be insufficient, the grain refinement effect will be limited, and it is easy to form a deformed structure, resulting in cracking of the alloy and an increase in material brittleness. If the extrusion temperature is too high, cracks will appear in the extrusion rod, and the grain growth phenomenon is obvious at too high a temperature, and the structure tends to coarsen, thus reducing the mechanical properties of the alloy.

[0015] Another object of the present invention also lies in providing the application of the above magnesium alloy or the magnesium alloy prepared by the above method in the field of aerospace.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The low-melting-point and high-strength magnesium alloy of the present invention is designed with a scientific and reasonable formula of Ga and Sn alloying elements, so that the contents of the alloying elements Ga and Sn exceed their maximum solid solubility in Mg, and a large amount of low-melting-point second phases Mg5Ga2 and Mg2Sn are precipitated, rather than mainly existing in a solid solution form, which can significantly reduce the melting point of the magnesium alloy. By combining casting, heat treatment and extrusion processes, the internal structure of the alloy is improved, the casting stress and defects are eliminated, the grains are refined, and the structure becomes more uniform and dense, thereby improving the alloy properties. The magnesium alloy obtained by the present invention is tested for its mechanical properties at room temperature. The melting point of this magnesium alloy can be reduced to 431 °C, the compressive strength is as high as 714 MPa, the compressive yield strength is as high as 433 MPa, and the compression ratio is 18.8%. It is an excellent low-melting-point and high-strength magnesium alloy material, and at the same time provides a new research direction for the research on preparing high-performance magnesium alloys, with good application prospects.

[0018] 2. The preparation process of the present invention is simple, the production time is short, the equipment used, such as melting furnaces and hot extruders, are conventional general-purpose equipment, the alloy does not contain rare earth elements, the cost is low, and it is conducive to industrial large-scale production. Through the combination of material design and process control, an alloy with a low melting point and high strength has been developed, which can help the application of magnesium alloys in dynamic weight reduction of aerospace equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 1 is a phase ratio diagram of the magnesium alloy of the embodiment.

[0020] Figure 2 Phase ratio diagram of magnesium alloy of comparative example.

[0021] Figure 3 The DSC curve of the cast magnesium alloy prepared in the present invention is shown in FIG.

[0022] Figure 4 The room temperature mechanical properties of the extruded magnesium alloy prepared by the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with embodiments.

[0024] 1. A method for preparing a low melting point and high strength magnesium alloy

[0025] Embodiment 1: This embodiment adopts the following steps:

[0026] (1) Ingredients: The Ga element content is 20.0wt.%, the Sn element content is 25.0wt.%, and the rest is Mg and inevitable impurity elements. The materials are prepared according to the above ingredients and the raw materials are polished to have a metallic luster and weighed for use. The raw materials used are high-purity magnesium (99.99wt.%), pure tin (99.99wt.%) and pure gallium (99.99wt.%).

[0027] (2) Melting: The weighed raw materials are placed in a heat treatment furnace and preheated at 200°C for 10 to 20 minutes. The preheated pure magnesium is then placed in a resistance furnace and heated to 740 to 750°C in a protective atmosphere of a mixture of CO2 and SF6 (ratio 99:1). After melting, the temperature is lowered to 650 to 680°C and the preheated pure tin and pure gallium are placed in turn. The temperature is kept at this temperature for 10 to 15 minutes to form a magnesium alloy melt.

[0028] (3) Pouring: Stir the magnesium alloy melt obtained in step (2) for 3 min, keep it warm and static at 680 °C for 15 min under a mixed gas of protective atmosphere CO2 and SF6 (with a ratio of 99:1). After removing the slag on the surface of the melt, pour the alloy melt into a metal mold preheated to 250 °C, cool it to room temperature, and cut a Φ80 mm × 50 mm ingot by machining after demolding.

[0029] (4) Heat treatment: Put the ingot obtained in step (3) into a heat treatment furnace, keep it warm at 280 °C for 12 h, and then air-cool it to room temperature.

[0030] (5) Extrusion: Preheat the magnesium alloy ingot after heat treatment in step (4) at 280 °C 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 °C with an extrusion ratio of 18:1, and air-cool it to room temperature to obtain the deformed magnesium alloy.

[0031] Example 2: The following steps are adopted in this example:

[0032] (1) Batching: The content of Ga element is 20.0 wt.%, the content of Sn element is 25.0 wt.%, and the rest are Mg and inevitable impurity elements. Prepare materials according to the above composition, polish the raw materials to a metallic luster and then weigh them for use. The raw materials used are high-purity magnesium (99.99 wt.%), pure tin (99.99 wt.%) and pure gallium (99.99 wt.%).

[0033] (2) Melting: Put the weighed raw materials into a heat treatment furnace and preheat them at 200 °C for 10 - 20 min respectively. Then put the preheated pure magnesium into an electric resistance furnace, heat it to 740 - 750 °C under a mixed gas of protective atmosphere CO2 and SF6 (with a ratio of 99:1). After melting, lower the temperature to 650 - 680 °C and then put the preheated pure tin and pure gallium in turn, and keep it warm for 10 - 15 min to form a magnesium alloy melt.

[0034] (3) Pouring: Stir the magnesium alloy melt obtained in step (2) for 3 min, keep it warm and static at 680 °C for 15 min under a mixed gas of protective atmosphere CO2 and SF6 (with a ratio of 99:1). After removing the slag on the surface of the melt, pour the alloy melt into a metal mold preheated to 250 °C, cool it to room temperature, and cut a Φ80 mm × 50 mm ingot by machining after demolding.

[0035] (4) Heat treatment: Put the ingot obtained in step (3) into a heat treatment furnace, keep it warm at 320 °C for 12 h, and then air-cool it to room temperature.

[0036] (5) Extrusion: The magnesium alloy ingot after heat treatment in step (4) is preheated at 280 °C for 30 min, then placed in an extrusion die, and extruded into a Φ20 mm bar at a deformation temperature of 270 - 290 °C with an extrusion ratio of 18:1, and air-cooled to room temperature to obtain the deformed magnesium alloy.

[0037] Example 3: The following steps are adopted in this example:

[0038] (1) Batching: The content of Ga element is 20.0 wt.%, the content of Sn element is 25.0 wt.%, and the rest are Mg and inevitable impurity elements. Prepare the materials according to the above composition, polish the raw materials to a metallic luster, and then weigh them for use. The raw materials used are high-purity magnesium (99.99 wt.%), pure tin (99.99 wt.%), and pure gallium (99.99 wt.%).

[0039] (2) Melting: The weighed raw materials are preheated in a heat treatment furnace at 200 °C for 10 - 20 min respectively, then the preheated pure magnesium is put into an electric resistance furnace, heated to 740 - 750 °C under a protective atmosphere of a mixed gas of CO2 and SF6 (with a ratio of 99:1). After melting, the temperature is lowered to 650 - 680 °C, and then the preheated pure tin and pure gallium are put in successively, and kept warm for 10 - 15 min to form a magnesium alloy melt.

[0040] (3) Pouring: Stir the magnesium alloy melt obtained in step (2) for 3 min, keep it warm and static at 680 °C for 15 min under a protective atmosphere of a mixed gas of CO2 and SF6 (with a ratio of 99:1). After removing the slag on the surface of the melt, pour the alloy melt into a metal mold preheated at 250 °C, cool it to room temperature, and cut a Φ80 mm × 50 mm ingot by machining after demolding.

[0041] (4) Heat treatment: Put the ingot obtained in step (3) into a heat treatment furnace, keep it warm at 360 °C for 12 h, and then air-cool it to room temperature.

[0042] (5) Extrusion: The magnesium alloy ingot after heat treatment in step (4) is preheated at 280 °C for 30 min, then placed in an extrusion die, and extruded into a Φ20 mm bar at a deformation temperature of 270 - 290 °C with an extrusion ratio of 18:1, and air-cooled to room temperature to obtain the deformed magnesium alloy.

[0043] Example 4: The following steps are adopted in this example:

[0044] (1) Ingredients: The content of Ga element is 20.0 wt.%, the content of Sn element is 25.0 wt.%, and the rest are Mg and inevitable impurity elements. Prepare materials according to the above composition, polish the raw materials to a metallic luster, and then weigh them for use. The raw materials used are high-purity magnesium (99.99 wt.%), pure tin (99.99 wt.%), and pure gallium (99.99 wt.%).

[0045] (2) Melting: Put the weighed raw materials into a heat treatment furnace and preheat them at 200 °C for 10 - 20 min. Then put the preheated pure magnesium into an electric resistance furnace, heat it to 740 - 750 °C under a protective atmosphere of a mixed gas of CO2 and SF6 (the ratio is 99:1). After melting, lower the temperature to 650 - 680 °C, and then sequentially put in the preheated pure tin and pure gallium, and keep it warm for 10 - 15 min to form a magnesium alloy melt.

[0046] (3) Pouring: Stir the magnesium alloy melt obtained in step (2) for 3 min, keep it warm and static at 680 °C for 15 min under a protective atmosphere of a mixed gas of CO2 and SF6 (the ratio is 99:1). After removing the slag on the surface of the melt, pour the alloy melt into a metal mold preheated at 250 °C, cool it to room temperature, and cut a Φ80 mm × 50 mm ingot by machining after demolding.

[0047] (4) Heat treatment: Put the ingot obtained in step (3) into a heat treatment furnace, keep it warm at 400 °C for 12 h, and then air-cool it to room temperature.

[0048] (5) Extrusion: Preheat the magnesium alloy ingot after heat treatment in step (4) at 280 °C 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 °C with an extrusion ratio of 18:1, and air-cool it to room temperature to obtain a deformed magnesium alloy.

[0049] Comparative example: In this comparative example, for the alloy Mg-3Ga-5Sn, the content of Ga element is 3 wt.%, the content of Sn element is 5 wt.%, and the rest are Mg and inevitable impurity elements; other steps are the same as in Example 1.

[0050] II. Performance verification

[0051] 1. Calculate the phase ratio diagrams of the magnesium alloys in the examples and comparative examples, and the results are as Figure 1 and Figure 2 shown.

[0052] From Figure 1It can be seen that for the alloy Mg-20Ga-25Sn of the embodiment, the volume fractions of the Mg5Ga2 phase and the Mg2Sn phase exceed 50% at room temperature. When the temperature exceeds 415 °C, the low-melting-point second phase begins to melt, and a liquid phase starts to precipitate in the alloy. When the temperature reaches 550 °C, the alloy completely melts into a liquid phase. For the alloy Mg-3Ga-5Sn of the comparative example, due to the low contents of Sn and Ga elements, the content of the formed second phase is small, about 1% of the total volume. When the temperature reaches above 550 °C, a liquid phase gradually precipitates, and the melting point of the alloy is relatively high. It completely transforms into a liquid when the temperature exceeds 630 °C( Figure 2 ). This is because in the alloy of the comparative example, Sn and Ga elements mainly exist in the form of solid solution, and the amount existing in the form of the low-melting-point second phase is extremely small, and its melting point is still close to that of pure Mg. Compared with the comparative example, through precise regulation of the contents of Sn and Ga elements in the present invention, its melting point is reduced from 550 °C to about 410 °C.

[0053] 2. The as-cast magnesium alloys prepared in Examples 1 to 4 were subjected to differential scanning calorimetry measurement. The test gas atmosphere was helium, the heating range was RT to 550 °C, and the rate was 10 °C / min. The results are as Figure 3 shown.

[0054] From Figure 3 it can be seen that the left inflection point of the endothermic peak in the curve means that the alloy starts to transform from solid to liquid, and the corresponding temperature of 431 °C is the melting point. The right inflection point is when the alloy completely transforms into a liquid, and the corresponding temperature is 503 °C. It shows that the melting point of the magnesium alloy prepared in the present invention is significantly reduced, and the difference from the calculation result of the phase ratio diagram is not large.

[0055] 3. The extruded magnesium alloys prepared in Examples 1 to 4 were subjected to room temperature mechanical property tests. Compression specimens with dimensions of Φ8 and h12 were used, and the preloading rate was 1 mm / min. The results are as Figure 4 shown.

[0056] From Figure 4 it can be seen that the mechanical properties of the magnesium alloy prepared in the present invention change non-linearly with the homogenization treatment temperature. As the heat treatment temperature increases, the mechanical properties of the magnesium alloy first gradually increase and then decrease. When the homogenization treatment temperature is 360 °C, the alloy has the best performance. Its compressive yield strength can reach 433 MPa, the ultimate compressive strength can reach 714 MPa, and the compression ratio reaches 18.8%, which is better than conventional magnesium alloys on the market. It shows that the magnesium alloy prepared in the present invention has certain improvements in strength and plasticity while ensuring a low melting point, and can contribute to the dynamic weight reduction of aerospace equipment.

[0057] The above are only the preferred embodiments of the present invention, and the present invention is not limited thereto. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A low melting point high strength magnesium alloy, characterized in that: The magnesium alloy comprises the following components in percentage by weight: Ga 19.5-20.4wt.%, Sn 24.5-25.4wt.%, the remainder being Mg and inevitable impurities, and the impurity content is ≤0.04wt.%; the melting point of the magnesium alloy is not higher than 440°C.

2. A method for preparing a low melting point high strength magnesium alloy as claimed in claim 1, characterized in that: The following steps are involved: 1) Using pure magnesium ingot, pure tin and pure gallium as raw materials for component preparation, and then obtaining magnesium alloy ingot by smelting and casting; 2) The magnesium alloy ingot obtained in step 1) is subjected to homogenization treatment and hot extrusion treatment in sequence to obtain the low melting point and high strength magnesium alloy.

3. The method for preparing a low melting point high strength magnesium alloy according to claim 2, characterized in that: The smelting process comprises the following steps: grinding, weighing and mixing pure magnesium, pure tin and pure gallium, and then preheating the preheated pure magnesium ingot, heating the preheated pure magnesium ingot to 740-750° C. in a protective atmosphere, melting the preheated pure tin and pure gallium to obtain a magnesium melt, and then lowering the temperature to 650-680° C., adding the preheated pure tin and pure gallium, and keeping the temperature for 10-15 minutes to obtain a melt.

4. The method for preparing a low melting point high strength magnesium alloy according to claim 3, characterized in that: The protective atmosphere is a mixed gas of CO2 and SF6 in a volume ratio of 99:

1.

5. The method for preparing a low melting point high strength magnesium alloy according to claim 2, characterized in that: The casting is to wait for the melt to stand at 680° C. for 15 minutes under a protective atmosphere, inject it into a preheated metal mold, cool it to room temperature, and demold it to obtain a magnesium alloy ingot.

6. The method for preparing a low melting point high strength magnesium alloy according to claim 2, characterized in that: The homogenization treatment is carried out at 280-400° C. for 10-15 hours.

7. The method for preparing a low melting point high strength magnesium alloy according to claim 2, characterized in that: The temperature during the hot extrusion treatment is 270-290° C., and the extrusion ratio is 15:1-18:

1.

8. Use of the magnesium alloy according to claim 1 or the magnesium alloy prepared by the method according to any one of claims 2 to 7 in the field of aerospace.

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