Low-cost vacuum melting magnesium-lithium alloy and high-purity melting and casting method thereof

Abstract

The invention discloses a low-cost vacuum melting magnesium-lithium alloy and a high-purity melting and casting method thereof, and belongs to the technical field of alloy melting and casting. The method comprises the steps of material preparation quality inspection, vacuum furnace preheating and air exhaust, argon introduction, stirring and slag fishing after medium-frequency segmented melting of a melt, standing, pouring of the melt into a mold with a pouring gate and a slag removal ladle (a ceramic filter screen is arranged in the mold, and a circulating water cooling disc is arranged below the mold), cooling demolding, machining, oxide skin removal and the like. By optimizing technological parameters and structural design, the problems that in the prior art, magnesium-lithium alloy is uneven in component, many in inclusions, low in availability rate of cast ingots and the like are solved, and the obtained alloy cast ingots are uniform in structure, high in purity and stable in performance; the method effectively solves the problems of non-uniform components, more inclusions, low utilization rate, serious burning loss of a riser shrinkage cavity and the like in the process of vacuum melting of the magnesium-lithium alloy, is simple in process, convenient to operate and controllable in cost, and meets the requirements of the fields of aerospace, 3C electronics, weapon industry and the like on ultra-light high-strength materials.

Description

Technical Field

[0001] This invention relates to the field of alloy casting technology, and in particular to a low-cost vacuum melting method for magnesium-lithium alloys and a high-purity melting and casting method thereof. Background Technology

[0002] Magnesium alloys possess advantages such as low density, high specific strength, and good machinability. However, their HCP (hexagonal close-packed) structure, with a c / a ratio of approximately 1.62 and only three slip systems, results in poor room temperature deformation capacity. Conventional extrusion or rolling deformation easily forms a strong basal texture within magnesium alloy sheets, leading to significant anisotropy. Adding lithium to magnesium alloys can reduce the c / a ratio, increasing the number of non-basal slip systems, weakening the basal texture, reducing anisotropy, and improving room temperature deformation capacity. Furthermore, magnesium-lithium alloys have the lowest density among existing alloy systems, only 2 / 3 to 3 / 4 the density of general magnesium alloys, and 1 / 3 to 1 / 2 lighter than most aluminum alloys; therefore, magnesium-lithium alloys are also known as ultralight alloys. They also possess excellent plasticity and toughness, high specific strength, high specific stiffness, and good formability, showing broad application prospects in military, aerospace, weapons industry, and 3C (computer, smart wearable, and communication) industries.

[0003] However, the industrial application of magnesium-lithium alloys is subject to many limitations: on the one hand, the smelting process for large-volume, high-quality magnesium-lithium alloys is complex, and melt purification technology is lacking; on the other hand, the alloy itself has defects such as poor heat resistance, low absolute strength, and poor corrosion resistance. During the casting process of magnesium-lithium alloys, their composition and ingot structure are greatly affected by the smelting process. If the ingot quality is substandard, the strength of the structural components obtained through subsequent plastic deformation will be difficult to meet standards. Furthermore, alloying elements are easily burned off during the magnesium-lithium alloy smelting and casting process, which may lead to fires or explosions in severe cases. Therefore, covering agents or inert gases are usually required to protect the melt.

[0004] In existing preparation technologies, the blending-doping method suffers from problems such as uneven lithium mixing, difficulty in controlling composition, and severe loss of other alloying elements. While the mainstream vacuum melting method can avoid oxidation loss to some extent, it still has drawbacks such as uneven microstructure, numerous internal inclusions, and low ingot utilization, which seriously affect the mechanical properties and subsequent plastic deformation of the alloy. Therefore, developing a novel, low-cost, and high-purity magnesium-lithium alloy casting method to overcome the shortcomings of existing technologies is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a low-cost vacuum melting method for magnesium-lithium alloys and its high-purity casting method. By optimizing process parameters, improving slag removal and casting structure, and strengthening melt purification and solidification control, a magnesium-lithium alloy ingot with uniform microstructure, high purity, and high availability is obtained. At the same time, production costs are reduced and product quality stability is improved, thereby solving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides a low-cost vacuum melting and casting method for high-purity magnesium-lithium alloys, comprising the following steps: 1) Material preparation: Select pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloy, magnesium-calcium master alloy, and magnesium-yttrium master alloy as raw materials, and conduct quality inspection on them; 2) Loading: Load the inspected and qualified raw materials into the vacuum melting furnace; 3) Preheating and vacuuming: Preheat the vacuum melting furnace, then evacuate it and introduce argon gas; 4) Melting and slag removal: Start the medium frequency power supply to heat the metal in stages until it melts, then reduce the power and stir the melt, and then remove the slag from bottom to top; 5) Settling and casting: After slag removal, let the mixture stand, turn off the medium frequency power supply, and pour the melt into a casting mold with a runner and slag removal bag. A circulating water cooling plate is set under the mold. 6) Cooling and demolding: Turn off the vacuum system and demold after the furnace has cooled down; 7) Post-processing: Machining removes the riser and surface oxide scale to obtain magnesium-lithium alloy ingots.

[0007] Preferably, in step 3), the preheating heating power is 5-8KW; the vacuum level is 5×10⁻⁶. -2 Pa, then argon gas was introduced until the pressure inside the furnace reached 0.05 MPa.

[0008] Preferably, in step 4), the initial power of the segmented heating is 5kW, and it is increased by 5kW every 5 minutes until the metal is completely melted.

[0009] Preferably, in step 4), the stirring temperature is 680-750℃ and the stirring time is 3-6 minutes.

[0010] Preferably, in step 5), the pouring temperature is 720-750℃ and the pouring time is 30s.

[0011] Preferably, in step 5), the inner diameter of the casting mold is 90-200mm and the height is 200-600mm, and a ceramic filter screen is placed in the casting mold.

[0012] Preferably, in step 6), the cooling time is 1-1.5 hours.

[0013] The present invention also provides a low-cost vacuum-melted magnesium-lithium alloy obtained by the above-mentioned melting and casting method.

[0014] Preferably, the chemical element composition of the magnesium-lithium alloy, by mass fraction, includes: Li: 1-20 wt.%, Zn: 0.1-4 wt.%, Ca: 0-3 wt.%, Y: 0.1-5 wt.%, with the remainder being magnesium and unavoidable impurities, the total impurity content being ≤0.3%.

[0015] Preferably, the chemical element composition of the magnesium-lithium alloy, by mass fraction, includes: Li: 5-15 wt.%, Zn: 0.1-3 wt.%, Ca: 0-2 wt.%, Y: 0.1-4 wt.%, with the remainder being magnesium and unavoidable impurities, the total impurity content being ≤0.3%.

[0016] At present, the smelting process of high-purity magnesium-lithium alloy is of unparalleled importance. By strictly controlling the purity and particle size of raw materials, creating a high-vacuum argon atmosphere, and using a new type of low-cost vacuum slag removal device for magnesium-lithium alloy smelting, inclusions of different sizes are removed from the alloy melt from bottom to top. During this process, the pouring temperature and pouring time (speed) must be strictly controlled. At the same time, a ceramic filter screen is placed during the pouring process to filter out smaller inclusions. The pouring mold is also designed with runners and slag removal bags to further obtain a relatively pure alloy melt. After the alloy melt is cooled with the furnace for 1-1.5 hours to a safe temperature, the furnace door is opened for demolding. Then, the riser and surface oxide scale are machined with a wire EDM machine to finally obtain a magnesium-lithium alloy ingot with uniform microstructure, high purity, and high yield, thereby improving product quality stability and greatly reducing production costs.

[0017] Therefore, the low-cost vacuum melting method for magnesium-lithium alloys and its high-purity casting method provided by this invention have at least the following advantages compared with the prior art: (1) The present invention uses a vacuum induction melting furnace, with visual control of the heating process power, strict control of the high vacuum argon atmosphere, and strict control of the holding time, which greatly reduces the burn-off rate of the alloy and improves the stability of the magnesium-lithium alloy.

[0018] (2) The present invention removes large inclusions from the alloy melt from bottom to top, and at the same time, a ceramic filter screen is placed during the casting process to filter small inclusions, which greatly improves the purity of the alloy melt, significantly reduces the content of inclusions of different sizes inside the ingot, and thus improves the mechanical properties of the alloy.

[0019] (3) The present invention uses a casting mold containing a gating system and a slag removal bag, which greatly increases the fluidity of the alloy melt and further improves the purity of the alloy melt.

[0020] (4) The present invention uses a circulating water cooling plate for water cooling and solidification, which greatly increases the solidification rate during the casting process, avoids the generation of shrinkage cavities and porosity in the ingot, and greatly improves the uniformity of the alloy structure.

[0021] (5) The process of this invention is simple, easy to operate, low in cost, and the magnesium-lithium alloy ingots obtained have a high utilization rate.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 Metallographic structure and X-ray flaw detection images of the magnesium-lithium alloy ingot prepared in Example 1; wherein, (a) is the metallographic structure at different scales, and (b) is the X-ray flaw detection image; Figure 2 Metallographic structure and X-ray flaw detection images of the magnesium-lithium alloy ingot prepared in Example 2; wherein, (a) is the metallographic structure at different scales, and (b) is the X-ray flaw detection image; Figure 3 Metallographic structure and X-ray flaw detection images of the magnesium-lithium alloy ingot prepared in Comparative Example 1; where (a) is the metallographic structure at different scales and (b) is the X-ray flaw detection image. Figure 4 Metallographic structure and X-ray flaw detection images of the magnesium-lithium alloy ingot prepared in Comparative Example 2; where (a) is the metallographic structure at different scales and (b) is the X-ray flaw detection image. Figure 5 Metallographic structure and X-ray flaw detection images of the magnesium-lithium alloy ingot prepared in Comparative Example 3; where (a) is the metallographic structure at different scales and (b) is the X-ray flaw detection image. Figure 6 The metallographic structure and X-ray flaw detection images of the magnesium-lithium alloy ingot prepared in Comparative Example 4 are shown. Among them, (a) is the metallographic structure at different scales, and (b) is the X-ray flaw detection image. Detailed Implementation

[0024] This invention provides a low-cost vacuum melting and casting method for high-purity magnesium-lithium alloys, comprising the following steps: 1) Material preparation: Based on the required magnesium-lithium alloy composition, select pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloys, magnesium-calcium master alloys, and magnesium-yttrium master alloys as raw materials. Conduct quality inspections on the raw materials to ensure that their purity, particle size, and other indicators meet the process requirements.

[0025] 2) Loading: The raw materials that have passed inspection and been weighed and prepared in proportion in step 1) are loaded into the vacuum melting furnace according to the type and shape of the raw materials, and the loading method is adjusted according to the process requirements.

[0026] 3) Preheating and Vacuuming: Set the preheating power to 5-8KW to preheat the vacuum melting furnace to remove moisture that is difficult to remove from the furnace and raw materials; open the low-altitude valve, start the vacuum pump when the vacuum degree is ≤1000Pa, open the pre-evacuation valve when the vacuum degree reaches 40Pa, and start heating the diffusion pump; close the low-altitude valve when the vacuum degree is ≤5Pa and the diffusion pump oil temperature is ≥260℃; then open the high-vacuum valve to perform high-vacuum evacuation, so that the vacuum degree in the furnace reaches 5×10 -2 Pa, further remove gases and impurities from the furnace; turn off the vacuum gauge, open the argon control valve, and purge argon into the furnace until the vacuum pressure gauge shows 0.05 MPa, then stop purging to create a high-vacuum argon protective atmosphere.

[0027] 4) Melting and Slag Removal: Under the high vacuum argon gas conditions in step 3), start the medium frequency power supply with an initial power of 5KW. Adjust the power every 5 minutes according to the melting process requirements, increasing the power by 5KW each time, until the metal is completely melted. Observe the changes in the metal inside the furnace during this period. If severe volatilization occurs (such as smoke inside the furnace that cannot be observed), appropriately reduce the input power of the medium frequency power supply to reduce volatilization. After the raw materials are melted, turn the medium frequency power supply to the minimum and slowly stir the liquid metal at a temperature of 680℃-750℃ for 3-6 minutes. Then, use a slag removal device to remove slag from the alloy melt from bottom to top, removing larger inclusions.

[0028] 5) Settling and casting: Let the alloy melt after slag removal in step 4) stand for 8-12 minutes; turn off the medium frequency power supply, and pour the liquid alloy into the casting mold containing the runner and slag removal bag at a temperature of 720℃-750℃ by controlling the tilting of the melting furnace. The casting time is controlled to be 30 seconds; place a circulating water cooling plate under the casting mold, and observe and operate through the viewing window during the casting process to ensure that the casting process is smooth and avoid defects such as porosity and inclusions.

[0029] 6) Cooling and demolding: After the alloy melt is poured, shut down the vacuum system, gradually restore the furnace pressure, and stop the cooling water supply; wait for the alloy melt to cool with the furnace for 1-1.5 hours. After cooling to a safe temperature, open the furnace door to demold the ingot, remove it from the mold and mark it.

[0030] 7) Post-processing: The ingots after demolding in step 6) are machined to remove the risers and surface oxide scale, and finally a homogeneous magnesium-lithium alloy ingot with high usability is obtained.

[0031] In this invention, based on the requirements of the ingot size for the subsequent deformation processing, the casting mold is selected with an inner diameter of 90-200mm and a height of 200-600mm, and a crucible with a suitable volume that can melt 10-60Kg is placed in the vacuum induction heating furnace.

[0032] In this invention, the chemical element composition of the obtained magnesium-lithium alloy, by mass fraction, includes: Li: 1-20 wt.%, Zn: 0.1-4 wt.%, Ca: 0-3 wt.%, Y: 0.1-5 wt.%, with the remainder being magnesium and unavoidable impurities, and the total impurity content ≤ 0.3%; preferably, the chemical element composition is: Li: 5-15 wt.%, Zn: 0.1-3 wt.%, Ca: 0-2 wt.%, Y: 0.1-4 wt.%, with the remainder being magnesium and unavoidable impurities, and the total impurity content ≤ 0.3%.

[0033] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the protection scope of the present invention.

[0034] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0035] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0036] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that this is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range. Unless otherwise stated, all percentages, parts, ratios, etc., herein are by weight. Unless otherwise specified, the reagents, instruments, and equipment used in this invention are those commonly used by those skilled in the art, and the testing standards all use national or international standards commonly used in the field, which will not be further elaborated here.

[0037] Example 1 This embodiment provides a novel, low-cost vacuum melting method for high-purity casting of magnesium-lithium alloys. Based on the ingot size requirements for subsequent deformation processing, a casting mold with an inner diameter of 90mm and a height of 300mm, equipped with a gating system and a slag removal bag, is selected. A ceramic filter screen is placed in the casting mold. Simultaneously, a crucible with a suitable volume capable of melting 30kg is placed in a vacuum induction heating furnace. The resulting magnesium-lithium alloy has the following composition by mass fraction: Li: 9wt.%, Zn: 3wt.%, Ca: 0.4wt.%, Y: 0.4wt.%, with the remainder being magnesium and unavoidable impurities, the total impurity content being ≤0.3%.

[0038] The casting method specifically includes the following steps: 1) Based on the materials to be prepared, select pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloys, magnesium-calcium master alloys, and magnesium-yttrium master alloys as raw materials, and conduct quality inspections to ensure that their purity meets the requirements. Among them, the purity of magnesium ingots is ≥99.95% and the purity of pure zinc ingots is ≥99.99%.

[0039] 2) Load the qualified and weighed raw materials from step 1) into the vacuum melting furnace according to the process requirements. The loading method can be adjusted according to the type and shape of the raw materials.

[0040] 3) After loading the raw materials prepared in step 2) into the vacuum melting furnace, set the preheating power to 7KW to preheat the furnace, ensuring that moisture that is difficult to remove during vacuuming can be driven away or removed. Open the low-altitude valve, start the vacuum pump when the vacuum degree reaches 1000Pa, open the pre-evacuation valve when the vacuum degree reaches 40Pa, and start heating the diffusion pump. When the vacuum degree reaches 5Pa and the diffusion pump oil temperature reaches 260℃, close the low-altitude valve. Then open the high-vacuum valve to perform high-vacuum evacuation, making the vacuum degree reach 5×10 -2 Pa, further remove gases and impurities from the furnace. Close the vacuum gauge, open the argon control valve, and purge argon into the furnace until the vacuum pressure gauge shows 0.05 MPa, then stop purging.

[0041] 4) Under the high vacuum argon atmosphere of step 3), start the medium-frequency power supply with an initial power of 5KW. Adjust the power every 5 minutes, increasing by 5KW each time, according to the melting process requirements, until the metal melts. Observe the changes in the metal inside the furnace during this period, noting any significant volatilization. If a smoke-like substance appears inside the furnace and cannot be observed, appropriately reduce the input power of the medium-frequency power supply to reduce volatilization. After the raw materials are completely melted, reduce the medium-frequency power supply to its minimum setting. Stir the molten metal at 720℃ for 5 minutes, and use a slag removal device to remove slag from the prepared alloy melt from bottom to top.

[0042] 5) After removing the slag in step 4), let the alloy melt stand for 10 minutes, turn off the medium frequency power supply, control the tilting of the melting furnace, set the pouring temperature to 740℃, control the pouring time (speed) to 30s, and pour the liquid alloy into the pouring mold containing the runner and slag removal bag. Place a circulating water cooling plate under the pouring mold, and observe the pouring process through the viewing window to ensure a smooth pouring process and avoid defects.

[0043] 6) After the alloy melt in step 5) is poured, shut down the vacuum system and gradually restore the ambient pressure. Stop the cooling water supply and wait for the alloy melt to cool with the furnace for 1.5 hours until it reaches a safe temperature. Open the furnace door to demold the material, remove it from the mold, and mark the ingot.

[0044] 7) The riser and surface oxide scale of the material after demolding in step 6) are machined off, and finally a homogenized magnesium-lithium alloy ingot with high usability is obtained.

[0045] Example 2 This embodiment provides a novel, low-cost vacuum melting method for high-purity casting of magnesium-lithium alloys. Based on the ingot size requirements for subsequent deformation processing, a casting mold with an inner diameter of 90mm and a height of 300mm, equipped with a gating system and a slag removal bag, is selected. A ceramic filter screen is placed in the casting mold. Simultaneously, a crucible with a suitable volume capable of melting 30kg is placed in a vacuum induction heating furnace. The resulting magnesium-lithium alloy has the following composition by mass fraction: Li: 12wt.%, Zn: 3wt.%, Y: 2wt.%, with the remainder being magnesium and unavoidable impurities, the total impurity content being ≤0.3%.

[0046] The casting method specifically includes the following steps: 1) Based on the materials to be prepared, select pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloys, and magnesium-yttrium master alloys as raw materials, and conduct quality inspections to ensure that their purity meets the requirements. Among them, the purity of magnesium ingots is ≥99.95% and the purity of pure zinc ingots is ≥99.99%.

[0047] 2) Load the qualified and weighed raw materials from step 1) into the vacuum melting furnace according to the process requirements. The loading method can be adjusted according to the type and shape of the raw materials.

[0048] 3) After loading the raw materials prepared in step 2) into the vacuum melting furnace, set the preheating power to 7KW to preheat the furnace, ensuring that moisture that is difficult to remove during vacuuming can be driven away or removed. Open the low-altitude valve, start the vacuum pump when the vacuum degree reaches 1000Pa, open the pre-evacuation valve when the vacuum degree reaches 40Pa, and start heating the diffusion pump. When the vacuum degree reaches 5Pa and the diffusion pump oil temperature reaches 260℃, close the low-altitude valve. Then open the high-vacuum valve to perform high-vacuum evacuation, making the vacuum degree reach 5×10-2 Pa, further remove gases and impurities from the furnace. Close the vacuum gauge, open the argon control valve, and purge argon into the furnace until the vacuum pressure gauge shows 0.05 MPa, then stop purging.

[0049] 4) Under the high vacuum argon atmosphere of step 3), start the medium-frequency power supply with an initial power of 5KW. Adjust the power every 5 minutes, increasing by 5KW each time, according to the melting process requirements, until the metal melts. Observe the changes in the metal inside the furnace during this period, noting any significant volatilization. If a smoke-like substance appears inside the furnace and cannot be observed, appropriately reduce the input power of the medium-frequency power supply to reduce volatilization. After the raw materials are completely melted, reduce the medium-frequency power supply to its minimum setting. Stir the molten metal at 730℃ for 5 minutes, and use a slag removal device to remove slag from the prepared alloy melt from bottom to top.

[0050] 5) After removing the slag in step 4), let the alloy melt stand for 12 minutes, turn off the medium frequency power supply, control the tilting of the melting furnace, set the pouring temperature to 720℃, control the pouring time (speed) to 30s, and pour the liquid alloy into the pouring mold containing the runner and slag removal bag. Place a circulating water cooling plate under the pouring mold, and observe the pouring process through the viewing window to ensure a smooth pouring process and avoid defects.

[0051] 6) After the alloy melt in step 5) is poured, shut down the vacuum system and gradually restore the ambient pressure. Stop the cooling water supply and wait for the alloy melt to cool with the furnace for 1.5 hours until it reaches a safe temperature. Open the furnace door to demold the material, remove it from the mold, and mark the ingot.

[0052] 7) The riser and surface oxide scale of the material after demolding in step 6) are machined off, and finally a homogenized magnesium-lithium alloy ingot with high usability is obtained.

[0053] The microstructure of the magnesium-lithium alloy ingots prepared in the above embodiments was analyzed using metallographic microscopy and X-ray flaw detection. Note: Red boxes indicate areas where inclusions were detected, and green boxes indicate areas where internal shrinkage porosity, shrinkage cavities, etc., were detected.

[0054] The metallographic structure and X-ray flaw detection results of the low-cost, high-purity magnesium-lithium alloy ingots prepared in Examples 1 and 2 using a high-vacuum argon atmosphere, slag removal, slag removal mold, and water cooling process are as follows: Figure 1 and Figure 2As shown in the figure, the high-purity casting method of this invention results in a uniform distribution of the second phase in the metallographic structure and a significant reduction in inclusions as indicated by X-ray flaw detection. This demonstrates the need for effective slag removal to eliminate larger inclusions and purify the alloy melt. The design, incorporating a gating system and a slag removal bag, further removes smaller inclusions during the alloy melt's flow, increasing its fluidity and purity. Furthermore, the addition of water cooling further enhances the core feeding effect, significantly increasing the solidification rate during casting and preventing shrinkage cavities and porosity in the ingot. This greatly improves the uniformity of the alloy's microstructure. This significantly increases the utilization rate of magnesium-lithium alloy ingots, reduces production costs, and provides a reliable casting process for manufacturing low-cost, high-purity magnesium-lithium alloy ingots.

[0055] Comparative Example 1 This comparative example relates to a vacuum melting and casting method for magnesium-lithium alloys. The composition of the resulting magnesium-lithium alloy is the same as that in Example 1, except that the vacuum degree in step 3) of the melting and casting process is 5 × 10⁻⁶. -1 Pa, excluding the slag removal process in step 4), the remaining process steps are the same as in Example 1, and will not be repeated here.

[0056] The metallographic structure and X-ray flaw detection results of the magnesium-lithium alloy ingot prepared in this comparative example are as follows: Figure 3 As shown. From Example 1 Figure 1 Compared with Comparative Example 1 Figure 3 In comparison, the inclusions shown by X-ray flaw detection were significantly reduced. This is likely due to the absence of a high vacuum and a slag removal process to remove larger inclusions from the alloy melt from the bottom up. This suggests that in vacuum induction melting of magnesium-lithium alloys, the alloy melt needs to be in a high vacuum argon atmosphere and requires effective slag removal to remove larger inclusions in order to purify the alloy melt.

[0057] Comparative Example 2 This comparative example relates to a vacuum melting and casting method for magnesium-lithium alloy. The composition of the magnesium-lithium alloy obtained is the same as that in Example 1. The difference is that no circulating water cooling plate is placed under the casting mold, that is, no water cooling process is included, and the casting mold is a straight cylinder mold without ceramic filter screen. The remaining process steps are the same as those in Example 1, and will not be repeated here.

[0058] The metallographic structure and X-ray flaw detection results of the magnesium-lithium alloy ingot prepared in this comparative example are as follows: Figure 4 As shown. From Example 1 Figure 1 Compared with Comparative Example 2 Figure 4The comparison shows that the inclusions detected by X-ray flaw detection were further reduced. This is likely due to the absence of a slag removal mold. The design of the mold, which includes a gating system and a slag removal bag, further removes smaller inclusions during the flow of the alloy melt, increasing its fluidity and purity. This effect cannot be achieved by adding a ceramic filter to a straight-tube mold. Furthermore, the addition of water cooling further enhances the core feeding effect through X-ray flaw detection, significantly increasing the solidification rate during casting and preventing shrinkage cavities and porosity in the ingot. This greatly improves the uniformity of the alloy's microstructure. Therefore, this demonstrates that in vacuum induction melting of magnesium-lithium alloys, the effective use of a slag removal mold and water cooling can reduce inclusions and prevent microscopic defects such as shrinkage cavities and porosity in the ingot, thus purifying the alloy melt.

[0059] Comparative Example 3 This comparative example relates to a vacuum melting and casting method for magnesium-lithium alloys. The composition of the resulting magnesium-lithium alloy is the same as that in Example 2, except that the vacuum degree in step 3) of the melting and casting process is 5 × 10⁻⁶. -1 Pa, excluding the slag removal process in step 4), the remaining process steps are the same as in Example 2, and will not be repeated here.

[0060] The metallographic structure and X-ray flaw detection results of the magnesium-lithium alloy ingot prepared in this comparative example are as follows: Figure 5 As shown, from Example 2 Figure 2 Compared with Comparative Example 3 Figure 5 The comparison shows that the inclusions detected by X-ray flaw detection were significantly reduced. This is likely due to the absence of a high-vacuum argon atmosphere and a slag removal process to remove larger inclusions from the alloy melt from the bottom up. This indicates that in vacuum induction melting of magnesium-lithium alloys, a high-vacuum argon atmosphere and effective slag removal are necessary to purify the alloy melt.

[0061] Comparative Example 4 This comparative example relates to a vacuum melting and casting method for magnesium-lithium alloy. The composition of the magnesium-lithium alloy obtained is the same as that in Example 2. The difference is that no circulating water cooling plate is placed under the casting mold, that is, no water cooling process is included, and the casting mold is a straight cylinder mold without ceramic filter screen. The remaining process steps are the same as those in Example 2, and will not be repeated here.

[0062] The metallographic structure and X-ray flaw detection results of the magnesium-lithium alloy ingot prepared in this comparative example are as follows: Figure 6 As shown. From Example 2 Figure 2 Compared with Comparative Example 4 Figure 6The comparison shows that the inclusions detected by X-ray flaw detection were further reduced. This is likely due to the absence of a slag removal mold. The design of the mold, which includes a gating system and a slag removal bag, further removes smaller inclusions during the flow of the alloy melt, increasing its fluidity and purity. This effect cannot be achieved by adding a ceramic filter to a straight-tube mold. Furthermore, the addition of water cooling further enhances the core feeding effect through X-ray flaw detection, significantly increasing the solidification rate during casting and preventing shrinkage cavities and porosity in the ingot. This greatly improves the uniformity of the alloy's microstructure. Therefore, this demonstrates that in vacuum induction melting of magnesium-lithium alloys, the effective use of a slag removal mold and water cooling can reduce inclusions and prevent microscopic defects such as shrinkage cavities and porosity in the ingot, thus purifying the alloy melt.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A low-cost vacuum melting and high-purity casting method for magnesium-lithium alloys, characterized in that, Includes the following steps: 1) Material preparation: Select pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloy, magnesium-calcium master alloy, and magnesium-yttrium master alloy as raw materials, and conduct quality inspection on them; 2) Loading: Load the inspected and qualified raw materials into the vacuum melting furnace; 3) Preheating and vacuuming: Preheat the vacuum melting furnace, then evacuate it and introduce argon gas; 4) Melting and slag removal: Start the medium frequency power supply to heat the metal in stages until it melts, then reduce the power and stir the melt, and then remove the slag from bottom to top; 5) Settling and casting: After slag removal, let the mixture stand, turn off the medium frequency power supply, and pour the melt into a casting mold with a runner and slag removal bag. A circulating water cooling plate is set under the mold. 6) Cooling and demolding: Turn off the vacuum system and demold after the furnace has cooled down; 7) Post-processing: Machining removes the riser and surface oxide scale to obtain magnesium-lithium alloy ingots.

2. The low-cost vacuum melting and high-purity casting method for magnesium-lithium alloy according to claim 1, characterized in that: In step 3), the preheating power is 5-8KW; the vacuum is evacuated to a degree of 5×10⁻⁶. -2 Pa, then argon gas was introduced until the pressure inside the furnace reached 0.05 MPa.

3. The low-cost vacuum melting and high-purity casting method for magnesium-lithium alloy according to claim 1, characterized in that: In step 4), the initial power of the segmented heating is 5kW, and it is increased by 5kW every 5 minutes until the metal is completely melted.

4. The low-cost vacuum melting and high-purity casting method for magnesium-lithium alloy according to claim 1, characterized in that: In step 4), the stirring temperature is 680-750℃ and the stirring time is 3-6 minutes.

5. The low-cost vacuum melting and high-purity casting method for magnesium-lithium alloy according to claim 1, characterized in that: In step 5), the pouring temperature is 720-750℃ and the pouring time is 30s.

6. The low-cost vacuum melting and high-purity casting method for magnesium-lithium alloy according to claim 1, characterized in that: In step 5), the inner diameter of the casting mold is 90-200mm and the height is 200-600mm. A ceramic filter screen is placed in the casting mold.

7. The low-cost vacuum melting and high-purity casting method for magnesium-lithium alloy according to claim 1, characterized in that: In step 6), the cooling time is 1-1.5 hours.

8. A low-cost vacuum-melted magnesium-lithium alloy, characterized in that: The magnesium-lithium alloy is obtained by any one of the casting methods according to claims 1-7.

9. The low-cost vacuum-melted magnesium-lithium alloy according to claim 8, characterized in that: The chemical element composition of the magnesium-lithium alloy, by mass fraction, includes: Li: 1-20 wt.%, Zn: 0.1-4 wt.%, Ca: 0-3 wt.%, Y: 0.1-5 wt.%, with the remainder being magnesium and unavoidable impurities, the total content of which is ≤0.3%.

10. A low-cost vacuum-melted magnesium-lithium alloy according to claim 9, characterized in that: The chemical element composition of the magnesium-lithium alloy, by mass fraction, includes: Li: 5-15 wt.%, Zn: 0.1-3 wt.%, Ca: 0-2 wt.%, Y: 0.1-4 wt.%, with the remainder being magnesium and unavoidable impurities, the total content of which is ≤0.3%.

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