Hypoeutectic magnesium alloy with low melting point and high toughness and preparation method thereof
By scientifically formulating Mg-Zn alloy and combining heat treatment and extrusion processes, low-melting and tough sub-eutectic magnesium alloys are prepared, which solves the problem that existing alloys cannot have both low melting point and high mechanical properties, and achieves appropriate melting point reduction and mechanical properties improvement, meeting the dynamic weight reduction needs of aerospace equipment.
Patent Information
- Application Number
- CN202510412055.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-02
- Publication Date
- 2025-06-20
AI Technical Summary
The existing high alloy content eutectic alloys cannot have both low melting point and high mechanical properties, and cannot meet the dynamic weight reduction needs of aerospace equipment.
By scientifically and reasonably preparing the Mg-Zn binary alloy, combining heat treatment and extrusion processes, the microstructure structure of the alloy is optimized, and a low-melting high-strength tough sub-eutectic magnesium alloy with a melting point of no more than 340℃ is prepared.
The alloy has achieved a balance between low melting point and high mechanical properties, with the melting point lowered to below 340℃, the tensile strength and tensile yield strength significantly improved, and the elongation rate has also reached 16.8%, meeting the lightweight and dynamic weight reduction requirements in the aerospace field.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of metal materials, and particularly to a hypoeutectic magnesium alloy with low melting point and high strength and toughness and a preparation method thereof. Background Art
[0002] Magnesium alloys have excellent properties such as low density, high specific strength and high specific stiffness, and have broad application prospects in the fields of the automotive industry, aerospace, etc. Lightweighting can reduce fuel or power consumption and improve the performance of the endurance mileage of high-speed aircraft. The low density characteristic of magnesium alloys can achieve component lightweighting. If the heat generated by friction during flight is used to melt and ablate parts, so that the components that have completed their service functions are separated from the equipment, the component mass can be further reduced. However, the melting point of conventional magnesium alloys is relatively high, which limits their application in the aerospace field.
[0003] Generating eutectic phases with low melting points through alloying is an effective method to reduce the melting point of magnesium alloys. For example, Pan, F et al. studied the formation mechanism of eutectic phases in Mg-Al-Ca ternary alloys and verified the role of Ca elements in reducing the melting point and improving the casting performance; Liu, C et al. discussed the effect of Sn elements on reducing the melting point of magnesium alloys and designed a low melting point Mg-Sn-Ca alloy system through eutectic reactions. Mg-Zn series alloys are an important class of commercial magnesium alloys, but there are few reports on preparing low melting point Mg-Zn alloys using eutectic phases. This is because in Mg-Zn alloys near the eutectic point, although the melting point can be effectively reduced by forming eutectic phases, the Zn content is too high, resulting in a relatively large density of the alloy, and a large number of eutectic structures and shrinkage cavities and other defects are generated, seriously reducing the mechanical properties of magnesium alloys, especially the plastic forming performance of the alloy deteriorates significantly and it cannot be processed and formed; moreover, due to the galvanic cell reaction formed by the potential difference between the eutectic phase and the matrix phase, the corrosion of magnesium is aggravated, reducing the corrosion resistance of magnesium alloys. Therefore, there are still challenges in the optimization of traditional magnesium alloys at present. How to ensure high plasticity and strength while reducing the melting point of binary Mg-Zn alloys is an urgent problem to be solved. Summary of the Invention
[0004] Aiming at the deficiencies of the above-mentioned prior art, the technical problem to be solved by the present invention is: how to provide a hypoeutectic magnesium alloy with low melting point and high strength and toughness and a preparation method thereof, to solve the problem that existing eutectic alloys with high alloy content cannot have both low melting point and high mechanical properties and cannot meet the requirements of dynamic weight reduction of aerospace equipment.
[0005] To solve the above technical problems, the present invention adopts the following technical solutions: A low-melting-point high-strength and tough hypoeutectic magnesium alloy, comprising the following components in mass percentage: Zn 6.5-13.4 wt.%, and the balance is Mg and inevitable impurities; the melting point of the magnesium alloy is not higher than 340 °C. Specifically, the melting point of the magnesium alloy is 310-340 °C. It is found that the maximum solid solubility of Zn in the magnesium alloy is 6.2 wt%, and the Zn content at the eutectic point is 52 wt%. If the Zn content in the Mg-Zn binary alloy is too high, the density of the alloy is relatively large, and eutectic structure and porosity shrinkage cavities will be generated, seriously reducing the mechanical properties of the magnesium alloy, especially the plasticity reduction is the most prominent. If the Zn content in the Mg-Zn binary alloy is lower than its maximum solid solubility point in Mg, mainly solid solution is formed and the melting point of the magnesium alloy cannot be effectively reduced. When the Zn content in the Mg-Zn binary alloy is 6.5-13.4 wt.%, the alloy at room temperature is mainly composed of HCP and MgZn phases. According to the phase diagram calculation: when the temperature exceeds 325 °C, all the MgZn phases are transformed into low-melting-point Mg5Zn2 phases, and when the temperature rises to 339 °C, the low-melting-point Mg5Zn2 phases begin to melt, and liquid phase appears in the alloy, thus achieving low melting point.
[0006] Another object of the present invention also lies in providing a preparation method of the above low-melting-point high-strength and tough hypoeutectic magnesium alloy, comprising the following steps:
[0007] 1) Using pure magnesium ingots and pure zinc as raw materials for component batching, and then obtaining a magnesium alloy ingot through melting and casting;
[0008] 2) Sequentially performing homogenization treatment and hot extrusion treatment on the magnesium alloy ingot obtained in step 1), and then the low-melting-point high-strength and tough hypoeutectic magnesium alloy is obtained.
[0009] Preferably, the melting is to polish, weigh and batch pure magnesium and pure zinc, 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, and then add the preheated pure zinc and keep it at 680 °C for 10-15 min to obtain a melt.
[0010] Preferably, the protective atmosphere is a mixed gas formed by CO2 and SF6 in a volume ratio of 99:1.
[0011] Preferably, the casting is to inject the melt into a preheated metal mold, cool it to room temperature, and demold it to obtain a magnesium alloy ingot.
[0012] Preferably, the homogenization treatment is to keep it at 300-335 °C for 8-15 h. In this way, by regulating the temperature of the homogenization treatment, the internal structure of the alloy is improved, the casting stress is eliminated, the extrusion performance is improved, and further the alloy performance is improved.
[0013] Preferably, during the hot extrusion process, 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 the grains, make the structure more uniform and dense, and further improve the alloy properties.
[0014] Another object of the present invention also lies in providing an application of the above-mentioned magnesium alloy or the magnesium alloy prepared by the above method in the field of aerospace.
[0015] Compared with the prior art, the present invention has the following beneficial effects:
[0016] 1. The magnesium alloy provided by the present invention is obtained through a scientific and reasonable formula design of Mg-Zn binary alloy elements, combined with heat treatment and extrusion processes, optimizing the microstructure and properties of the alloy to obtain a hypoeutectic Mg-Zn alloy. Compared with eutectic alloys, the number of eutectic phases and shrinkage cavity defects in the alloy of the present invention is greatly reduced, but there are still a certain number of eutectic phases. On the one hand, it reduces the tissue defects and corrosion problems brought by the eutectic phase; on the other hand, while achieving a low melting point of the alloy, it also improves the strength and plasticity of the alloy. The magnesium alloy obtained by the present invention is tested for room temperature mechanical properties, its melting point can be reduced to below 340°C, the tensile strength is 307 MPa, the tensile yield strength is 208 MPa, and the elongation is 16.8%, which is superior to conventional magnesium alloys on the market. It not only ensures the characteristics of a low melting point, but also has high strength and plasticity, can meet the lightweight requirements of magnesium alloys in the fields of aerospace and other fields, and achieves the goal of dynamically reducing weight of aerospace equipment at a lower temperature.
[0017] 2. The present invention proposes a design idea of hypoeutectic alloy, and by applying the method of alloying, a hypoeutectic Mg-Zn alloy with a melting point in the range of 310-340°C is prepared, which is an excellent low melting point, high strength and tough magnesium alloy material. Moreover, the preparation process flow of the present invention is simple, the production time is short, and the equipment used, such as melting furnaces, hot extrusion machines, etc., are all conventional general equipment. The alloy does not contain rare earth elements, the cost is low, which is conducive to large-scale industrial production, and can help the wide application of magnesium alloys in the fields of aerospace and other fields. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 It is the SEM diagram of the magnesium alloy prepared by the present invention.
[0019] Figure 2 It is the DSC curve diagram of the extruded magnesium alloy prepared by the present invention.
[0020] Figure 3 It is the room temperature tensile stress-strain curve of the extruded magnesium alloy prepared by the present invention.
[0021] Figure 4Column chart of the room temperature mechanical properties of the extruded magnesium alloy prepared according to the present invention. Detailed implementation manners
[0022] The present invention will be further described in detail below in conjunction with embodiments.
[0023] I. Preparation method of a hypoeutectic magnesium alloy with low melting point and high strength and toughness
[0024] Embodiment 1: The following steps are adopted in this embodiment:
[0025] (1) Batching: The content of Zn element is 7.0 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.%) and pure zinc (99.99 wt.%).
[0026] (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 (with a ratio of 99:1). After melting, sequentially put the preheated pure zinc, and keep it at 680 °C for 10 - 15 min to form a magnesium alloy melt.
[0027] (3) Pouring: Stir the magnesium alloy melt obtained in step (2) for 3 min, keep it at 680 °C for 15 min under a protective atmosphere of a mixed gas of CO2 and SF6 (with a ratio of 99:1), remove the slag on the surface of the melt, and then 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.
[0028] (4) Heat treatment: Put the ingot obtained in step (3) into a heat treatment furnace, keep it at 330 °C for 10 h, and then air-cool it to room temperature.
[0029] (5) Extrusion: Preheat the magnesium alloy ingot after heat treatment in step (4) at 280 °C for 30 min, and then place it in an extrusion die. At a deformation temperature of 270 - 290 °C, extrude it into a Φ20 mm bar with an extrusion ratio of 18:1, and air-cool it to room temperature to obtain the extruded magnesium alloy.
[0030] Embodiment 2: The following steps are adopted in this embodiment:
[0031] (1) Batching: The content of Zn element is 10.0 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.%) and pure zinc (99.99 wt.%).
[0032] (2) Melting: Put the weighed raw materials into the heat treatment furnace for preheating at 200 °C for 10 - 20 min respectively. Then put the preheated pure magnesium into the resistance furnace and heat it to 740 - 750 °C under the protective atmosphere of the mixed gas of CO2 and SF6 (with a ratio of 99:1). After melting, successively put the preheated pure zinc, keep it at 680 °C for 10 - 15 min to form a magnesium alloy melt.
[0033] (3) Pouring: Stir the magnesium alloy melt obtained in step (2) for 3 min, keep it at 680 °C for 15 min under the protective atmosphere of the mixed gas of CO2 and SF6 (with a ratio of 99:1) for static setting. After removing the slag on the surface of the melt, pour the alloy melt into the metal mold preheated at 250 °C, cool it to room temperature, and cut a Φ80 mm × 50 mm ingot by machining after demolding.
[0034] (4) Heat treatment: Put the ingot obtained in step (3) into the heat treatment furnace, keep it at 330 °C for 10 h, and then air-cool it to room temperature.
[0035] (5) Extrusion: Preheat the magnesium alloy ingot after heat treatment in step (4) at 280 °C for 30 min, then put it into the 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 extruded magnesium alloy.
[0036] Example 3: The following steps are adopted in this example:
[0037] (1) Batching: The content of Zn element is 13.0 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, weigh them for use, and the raw materials used are high-purity magnesium (99.99 wt.%) and pure zinc (99.99 wt.%).
[0038] (2) Melting: Put the weighed raw materials into the heat treatment furnace for preheating at 200 °C for 10 - 20 min respectively. Then put the preheated pure magnesium into the resistance furnace and heat it to 740 - 750 °C under the protective atmosphere of the mixed gas of CO2 and SF6 (with a ratio of 99:1). After melting, successively put the preheated pure zinc, keep it at 680 °C for 10 - 15 min to form a magnesium alloy melt.
[0039] (3) Pouring: Stir the magnesium alloy melt obtained in step (2) for 3 min, keep it at 680 °C for 15 min under the protective atmosphere of the mixed gas of CO2 and SF6 (with a ratio of 99:1) for static setting. After removing the slag on the surface of the melt, pour the alloy melt into the metal mold preheated at 250 °C, cool it to room temperature, and cut a Φ80 mm × 50 mm ingot by machining after demolding.
[0040] (4) Heat treatment: The ingot obtained in step (3) is placed in a heat treatment furnace and kept at 330 °C for 10 h, and then air-cooled to room temperature.
[0041] (5) Extrusion: The magnesium alloy ingot after heat treatment in step (4) is preheated at 280 °C for 30 min, and then placed in an extrusion die. At a deformation temperature of 270 - 290 °C, it is extruded into a rod with a diameter of Φ20 mm at an extrusion ratio of 18:1, and then air-cooled to room temperature, thus obtaining the extruded magnesium alloy.
[0042] II. Performance verification
[0043] 1. The morphologies of the as-cast, solution-treated, and extruded magnesium alloys prepared in Examples 1 - 3 are observed under a scanning microscope respectively, and the results are as Figure 1 shown.
[0044] It can be seen from Figure 1 that the lamellar secondary phase in the alloy is a eutectic phase composed of α-Mg and MgZn phases, and the secondary phase is uniformly dispersed in the matrix. With the increase of Zn content, the content of the secondary phase in the alloy also increases, gradually developing from an island-like shape to a continuous network structure, and no obvious shrinkage pores and other defects are observed in the alloy. The secondary phase in the extruded magnesium alloy is broken and evenly distributed in the matrix in a streamline shape, enhancing the dispersion strengthening effect, and dynamic recrystallization occurs, forming fine and uniform equiaxed grains, thereby improving the mechanical properties of the alloy through fine grain strengthening and secondary phase strengthening. When the temperature rises, all the MgZn phases are transformed into low-melting-point Mg5Zn2 phases. When reaching the low melting point of the Mg5Zn2 phase, the Mg5Zn2 phase begins to melt, resulting in a rapid loss of the grain boundary bonding force. Even if the matrix phase does not melt, the overall alloy has lost its structural strength due to grain boundary weakening, thus achieving the goal of dynamic weight reduction in the aerospace field at a lower temperature.
[0045] 2. The extruded magnesium alloys prepared in Examples 1 - 3 are subjected to differential scanning calorimetry measurement. The test gas atmosphere is helium, the heating range is RT - 550 °C, and the rate is 10 °C / min. The results are as Figure 2 shown.
[0046] It can be seen from Figure 2It can be seen that during the heating process, the left inflection point of the first endothermic peak corresponding to the curve means that the liquid phase begins to precipitate from the solid alloy, and the corresponding temperature range is 339°C to 340°C, which is the melting point. The right inflection point of the second endothermic peak is when the alloy is completely transformed into a liquid, and the corresponding temperature range is 620°C to 650°C. Moreover, as the Zn content increases, the liquidus line of the alloy gradually decreases, and the solidus line remains basically unchanged. During the cooling process, the right inflection point of the first exothermic peak is when the alloy begins to solidify, and the corresponding temperature range is 606°C to 621°C. The left inflection point of the second exothermic peak means that the alloy is completely solidified, and the corresponding temperature range is 307°C to 317°C. During the cooling process, the phase transformation of the material usually requires a degree of supercooling to occur, so the temperature of the exothermic peak in the cooling curve is lower than that of the corresponding endothermic peak in the heating process. Taking the average value of the solidus temperatures in the heating and cooling curves as the melting point, it is obtained that: the melting point of the magnesium alloy prepared in Example 1 is 329°C, the melting point of the magnesium alloy prepared in Example 2 is 328°C, and the melting point of the magnesium alloy prepared in Example 3 is 326°C. It can be seen that compared with conventional magnesium alloys, the melting point of the magnesium alloy of the present invention is reduced by about 250°C, showing significant effects.
[0047] 3. The extruded magnesium alloys prepared in Examples 1 to 3 were subjected to tensile tests at room temperature. The tensile specimens were in the dimensions within the national standard range. The gauge length of the tensile bar was 25 mm, the diameter was 5 mm, and the preloading rate was 2 mm / min. The results are as Figure 3 and Figure 4 shown.
[0048] It can be seen from the figure that as the Zn content increases, the yield strength and tensile strength of the extruded magnesium alloy prepared by the present invention gradually increase, and the plasticity gradually decreases. Among them, the yield strength can reach up to 208 MPa at most, the tensile strength can reach 307 MPa, and the plasticity can reach 16.8%. It shows that too high or too low Zn content in the Mg-Zn binary alloy seriously reduces the mechanical properties of the magnesium alloy, especially the plasticity. The extruded magnesium alloy prepared by the present invention through scientific and reasonable formula design has good plasticity, and both the yield strength and tensile strength are at a relatively high level, having good comprehensive mechanical properties.
[0049] In summary, the magnesium alloy prepared by the present invention has good strength and plasticity, effectively reduces the melting point of the magnesium alloy Mg-Zn, making it not higher than 340°C, and can contribute to the dynamic weight reduction of aerospace equipment.
[0050] The above are only the preferred embodiments of the present invention and do not limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.
Claims
1. A low melting point, high strength and toughness hypoeutectic magnesium alloy, characterized in that: The invention comprises the following components in percentage by weight: 6.5-13.4 wt.% of Zn, and the balance of Mg and inevitable impurities; the melting point of the magnesium alloy is not higher than 340°C.
2. The low melting point, high strength and toughness hypoeutectic magnesium alloy according to claim 1, characterized in that: The melting point of the magnesium alloy is 310-340°C.
3. A method for preparing a low melting point, high strength and toughness hypoeutectic magnesium alloy as claimed in claim 1 or 2, characterized in that: The following steps are involved: 1) Using pure magnesium ingot and pure zinc 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 high strength and toughness hypoeutectic magnesium alloy.
4. The method for preparing the low melting point high strength and toughness hypoeutectic magnesium alloy according to claim 3, characterized in that: The smelting is to grind and weigh pure magnesium and pure zinc and then preheat them, then heat the preheated pure magnesium ingot to 740-750° C. in a protective atmosphere, melt them to obtain a magnesium melt, then add the preheated pure zinc, keep the temperature at 680° C. for 10-15 minutes, and obtain a melt.
5. The method for preparing the low melting point high strength and toughness hypoeutectic magnesium alloy according to claim 4, characterized in that: The protective atmosphere is a mixed gas of CO2 and SF6 in a volume ratio of 99:
1.
6. The method for preparing the low melting point high strength and toughness hypoeutectic magnesium alloy according to claim 3, characterized in that: The casting is to inject the melt into a preheated metal mold, cool it to room temperature, and then demould to obtain a magnesium alloy ingot.
7. The method for preparing the low melting point high strength and toughness hypoeutectic magnesium alloy according to claim 3, characterized in that: The homogenization treatment is carried out at 300-335° C. for 8-15 hours.
8. The method for preparing the low melting point high strength and toughness hypoeutectic magnesium alloy according to claim 3, characterized in that: The temperature during the hot extrusion treatment is 270-290° C., and the extrusion ratio is 15:1-18:
1.
9. Use of the magnesium alloy according to any one of claims 1 to 2 or the magnesium alloy prepared by the method according to any one of claims 3 to 8 in the field of aerospace.