A low-cost and high-efficiency smelting method of high-homogenized magnesium-lithium alloy

Abstract

The application belongs to the technical field of non-ferrous metallurgy, and particularly relates to a low-cost and high-efficiency smelting method for high-homogenization magnesium-lithium alloy, which comprises the following steps: preparing a closed crucible with a proper volume according to the size requirement of the cast ingot for later processing, selecting a seamless steel pipe, welding the bottom of the steel pipe first, adding raw materials, welding the top of the steel pipe and reserving a vacuum interface, pressure welding the reserved vacuum interface after vacuumizing; placing the closed crucible into an industrial electric furnace, heating to fully melt and mix the metal in the crucible; after smelting is completed, taking out the sealed crucible from the electric furnace and vertically placing it into a water cooling tank; uniformly treating the completely cooled crucible first, then removing the steel skin on the surface by machining, and taking out the cast ingot of the magnesium-lithium alloy. The method effectively solves the problems of high burning loss rate, high cost and low efficiency in the traditional vacuum induction smelting process of the magnesium-lithium alloy, and has the advantages of precise alloy component control and uniform distribution of solute elements.

Description

A low-cost and high-efficiency smelting method for highly homogeneous magnesium-lithium alloys Technical Field

[0001] This invention belongs to the field of non-ferrous metal metallurgy technology, specifically relating to a low-cost and high-efficiency smelting method for highly homogenized magnesium-lithium alloys. Background Technology

[0002] Magnesium-lithium alloys are currently the lightest metallic structural materials (1.25–1.65 g / cm³). 3 Magnesium-lithium alloys (Mg-Li) are 1 / 4 to 1 / 3 lighter than ordinary magnesium alloys and 1 / 3 to 1 / 2 lighter than aluminum alloys, possessing enormous development potential in lightweighting and energy-saving emission reduction industries. Interestingly, the addition of Li reduces the c / a axis ratio of the Mg lattice, and when its content exceeds 5.7% (unless otherwise specified, % represents mass fraction), a transformation occurs from a close-packed hexagonal (hcp) structure to a body-centered cubic (bcc) structure, effectively improving the alloy's plastic deformation capacity. Simultaneously, Mg-Li alloys possess advantages such as high specific strength, excellent damping performance, and good electromagnetic shielding performance, making them one of the most ideal structural materials in aerospace, weaponry, and the 3C industry. Currently, my country has successfully applied Mg-Li alloys in the aerospace field, partially replacing relatively heavy structural materials and significantly reducing the mass of satellites and spacecraft. Taking aerospace satellites as an example, the application of Mg-Li alloys can achieve a weight reduction of approximately 40%, significantly increasing the satellite's payload capacity and thus generating substantial economic benefits.

[0003] Magnesium-lithium alloys, primarily composed of highly reactive metals Mg and Li, are more challenging to prepare than other alloys. Severe loss of alloying elements is common during the smelting process, and in extreme cases, fires or explosions can occur. Therefore, covering agents or inert gases are typically used to protect the melt. Previous studies have primarily employed methods such as the melting-doping method, vacuum melting, and molten salt electrolysis. The melting-doping method involves mixing various single metals or intermediate alloys in air, followed by casting to obtain the as-cast alloy. Covering agents (LiCl and LiF) are added during melting for protection, the mold's height-to-diameter ratio is maximized, and the casting process must be conducted under argon protection. This method is fast and convenient, but the resulting magnesium-lithium alloys often suffer from severe lithium segregation, uneven mixing, difficulty in controlling composition, and severe loss of alloying elements. Vacuum melting, on the other hand, utilizes electromagnetic induction to generate eddy currents within a metal conductor to heat and melt the metal material under vacuum conditions. Vacuum melting facilitates temperature and pressure control and avoids oxidation and combustion of metals during the melting process. It also allows for vacuum stirring of the melt, resulting in a more uniform and controllable alloy composition. However, vacuum melting also suffers from significant loss of alloying elements due to burn-off, and the method is cumbersome and requires sophisticated equipment. Molten salt electrolysis can directly prepare magnesium-lithium alloys using salts as raw materials, eliminating the need for separate preparation processes for Mg and Li, and significantly reducing the alloy electrolysis temperature. However, it requires strict control of electrolysis process parameters, and the separation and refining of the alloy product from the salt are complex.

[0004] Currently, the mainstream method for smelting magnesium-lithium alloys is vacuum induction melting technology. However, the process of "loading the furnace, vacuuming, melting, casting, cooling, and cleaning" is cumbersome and the casting volume per furnace is very limited (<20 kg / furnace). Therefore, it is necessary to provide a low-cost and high-efficiency smelting method for highly homogeneous magnesium-lithium alloys. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems in traditional technologies and provide a low-cost, high-efficiency smelting method for highly homogeneous magnesium-lithium alloys. The preparation of high-quality magnesium-lithium alloy ingots can be completed in just three steps: "sealed crucible preparation - furnace smelting - water cooling and solidification". The entire process does not require complex processes and is safe, reliable and low-cost: the sealed crucible preparation only uses seamless steel pipes and electric arc welding, which can reduce costs; the smelting process can be carried out in a general industrial electric furnace, which can greatly improve production efficiency; and the introduction of water cooling into the magnesium-lithium alloy casting process during solidification can suppress the diffusion of solute elements and reduce solute segregation.

[0006] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0007] This invention provides a low-cost, high-efficiency smelting method for highly homogenized magnesium-lithium alloys, comprising the following steps:

[0008] 1) Prepare a sealed crucible of suitable volume according to the requirements of the ingot size in the later processing. Select a seamless steel pipe with an inner diameter of 50-500mm and a length of 300-800mm. First, weld the bottom of the steel pipe together, then add pure magnesium, pure lithium, pure aluminum, and pure zinc raw materials. Next, weld the top of the steel pipe together and reserve a vacuum port. Use a vacuum pump to evacuate the vacuum inside the crucible to 1×10⁻⁶. -2 Below Pa, the reserved vacuum interface is then pressure welded.

[0009] 2) Place the sealed crucible into an industrial electric furnace and heat it to 650-750°C at a rate of 2-15°C / min, and hold it at that temperature for 1-3 hours to allow the metal inside the crucible to fully melt and mix.

[0010] 3) After melting is complete, remove the sealed crucible from the electric furnace and place it vertically into the water-cooling tank;

[0011] 4) After the crucible has been completely cooled, it is first homogenized, and then the steel scale on the surface is removed by machining to take out the magnesium-lithium alloy ingot.

[0012] Further, in step 1), the raw materials of pure magnesium, pure lithium, pure aluminum and pure zinc are configured according to the composition of the magnesium-lithium alloy, and the mass percentage of the magnesium-lithium alloy is: Li 3-16%, Al 1-6%, Zn 1-4%, and the remainder is Mg.

[0013] Furthermore, in step 1), the ultimate vacuum of the vacuum pump cannot reach 1×10⁻⁶. -2 At Pa, the crucible is purged with argon gas at least three times to reduce the oxygen content inside.

[0014] Furthermore, in step 2), the industrial electric furnace is one of the following: pit furnace, box furnace, or bogie furnace.

[0015] Furthermore, in step 2), the method for fully melting and mixing the metal is the upside-down method. Specifically, the crucible is turned over in the furnace during the melting process to increase the probability of solute mixing. It needs to be turned over 2 to 5 times during the melting process.

[0016] Furthermore, in step 2), the method for fully melting and mixing the metal is the rolling method. Specifically, the crucible is taken out of the electric furnace and rolled back and forth on the ground during the melting process to promote the mixing of the solute. This rolling is only required once during the melting process.

[0017] Furthermore, in step 3), the water level in the water-cooling tank must be higher than the height of the crucible to ensure that the crucible is completely submerged, thereby increasing the solidification rate of the melt.

[0018] Furthermore, in step 4), the homogenization process is 300-400℃, the holding time is 1-8h, and the cooling method is furnace cooling or air cooling.

[0019] The beneficial effects of this invention are:

[0020] 1. This invention uses a closed crucible for melting, which eliminates the need for strict control of the melting temperature, greatly reducing the burn-off rate of the magnesium-lithium alloy and improving the stability of the magnesium-lithium alloy ratio.

[0021] 2. This invention uses water-cooled solidification, which greatly increases the solidification rate of magnesium-lithium alloy, avoids shrinkage cavities and solute element segregation in ingots, and improves product quality through homogenized microstructure.

[0022] 3. This invention features a simple process, convenient operation, high production efficiency, and extremely low cost. It eliminates the need for expensive vacuum melting equipment, and operators can perform high-efficiency, large-scale production without any metallurgical training.

[0023] Of course, any product implementing this invention does not necessarily need to achieve all of the above advantages at the same time. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 is a schematic diagram of the process flow of the smelting method of the present invention;

[0026] Figure 2 is a morphology diagram of the magnesium-lithium alloy of the present invention;

[0027] Wherein, a-lathe removal of crucible, b-macromorphology of ingot;

[0028] Figure 3 is a photograph of the microstructure of the magnesium-lithium alloy in Example 1 of the present invention;

[0029] Wherein, a-low magnification metallographic image, b-high magnification metallographic image, c-scanned photograph;

[0030] Figure 4 is a photograph of the microstructure of the magnesium-lithium alloy in Example 2 of the present invention;

[0031] Wherein, a-low magnification metallographic image, b-high magnification metallographic image, c-scanned photograph;

[0032] Figure 5 is a photograph of the microstructure of the magnesium-lithium alloy in Example 3 of the present invention;

[0033] Wherein, a-metallographic photograph, b-scanned photograph. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] A low-cost, high-efficiency smelting method for highly homogeneous magnesium-lithium alloy ingots is illustrated in Figure 1. Three representative magnesium-lithium alloys are selected for example: a single-phase α-Mg LAZ532 alloy, a dual-phase α-Mg+β-Li LAZ832 alloy, and a single-phase β-Li LAZ1132 alloy. The macroscopic morphology of the sealed crucible and ingot during smelting is shown in Figure 2. Specific embodiments are as follows:

[0036] Example 1

[0037] LAZ532 alloy was prepared using the smelting process of this invention. The alloy composition by mass percentage includes the following components: Li 4.0%, Al 3.0%, Zn 2.0%, and the balance Mg. The raw materials were selected as pure Mg, pure Li, pure Zn, and pure Al. After being cleaned with alcohol, they were placed in a crucible, which was then welded and sealed. A vacuum was then drawn up to 1 × 10⁻⁶ using a mechanical pump and a diffusion pump. -2 Below Pa, close the vacuum valve of the crucible. Then place the crucible in the electric furnace, setting the heating rate to 5℃ / min until the temperature reaches 750℃ and hold for 2 hours. During this period, remove the crucible from the furnace at 1.5 hours, roll it back and forth on the ground for 2 minutes, and then put it back into the furnace to continue holding for 0.5 hours. Then turn off the power to the electric furnace, remove the crucible, and vertically and quickly immerse it in cooling water until it is completely cooled. Place the cooled crucible in another electric furnace for homogenization annealing at 350℃ for 8 hours. After annealing, turn off the power and air cool to room temperature. Finally, remove the surface steel sleeve using a lathe and take out the smelted magnesium-lithium alloy ingot.

[0038] The actual and nominal composition of the LAZ532 magnesium-lithium alloy ingot obtained in this embodiment, as measured by inductively coupled plasma optical emission spectrometry (ICP), are shown in Table 1.

[0039] Table 1 Comparison of Nominal Composition and Actual Composition of LAZ532 Alloy Batching Material with Ingot Measured Composition

[0040] LAZ532LiAlZnMg Nominal composition 5.0 3.0 2.0 Balance Actual composition 4.9 2.8 1.8 Balance surface

[0041] Furthermore, the microstructure of the LAZ532 magnesium-lithium alloy ingot, including its metallographic structure and scanning electron micrograph, is shown in Figure 3. It can be observed that the alloy prepared by the process in this embodiment exhibits precise control over smelting and batching, and a homogeneous microstructure.

[0042] Example 2

[0043] LAZ832 alloy was prepared using the smelting process described in this example. The alloy composition by mass percentage included the following components: Li 8.0%, Al 3.0%, Zn 2.0%, and the balance Mg. Pure Mg, pure Li, pure Zn, and pure Al were selected as raw materials. After being cleaned with alcohol, they were placed in a crucible, which was then welded shut. A vacuum was then drawn, and the vacuum level was increased to 1 × 10⁻⁶ using a mechanical pump and a diffusion pump. -2 Below Pa, close the vacuum valve of the crucible. Then place the crucible in the electric furnace, set the heating rate to 5℃ / min, until the temperature reaches 730℃ and hold for 2 hours. During this period, remove the crucible from the electric furnace at 1.5 hours, roll it back and forth on the ground for 2 minutes, and then put it back into the electric furnace to continue holding for 0.5 hours. Then turn off the power to the electric furnace, remove the crucible, and vertically and quickly immerse it in cooling water until the crucible is completely cooled. Place the cooled crucible in another electric furnace for homogenization annealing at 350℃ for 8 hours. After annealing, turn off the power and air cool to room temperature. Finally, remove the surface steel sleeve using a lathe and take out the smelted magnesium-lithium alloy ingot.

[0044] The actual and nominal composition of the LAZ832 magnesium-lithium alloy ingot obtained in this embodiment, as measured by inductively coupled plasma optical emission spectrometry (ICP), are shown in Table 2.

[0045] Table 2 Comparison of Nominal Composition and Actual Composition of LAZ832 Alloy Batching Material with Ingot Measured Composition

[0046] LAZ832LiAlZnMg Nominal composition 8.0 3.0 2.0 Balance Actual composition 8.2 3.1 2.1 Balance surface

[0047] Furthermore, the microstructure of the LAZ832 magnesium-lithium alloy ingot, including its metallographic structure and scanning electron micrographs, is shown in Figure 4. It can be observed that the alloy prepared by the process in this embodiment exhibits precise control over smelting and batching, and a homogeneous microstructure.

[0048] Example 3

[0049] The LAZ1132 alloy was prepared using the smelting process described in this embodiment. The alloy composition by mass percentage includes the following components: Li 11.0%, Al 3.0%, Zn 2.0%, and the balance Mg. Pure Mg, pure Li, pure Zn, and pure Al were selected as raw materials. After being cleaned with alcohol, they were placed in a crucible, which was then welded and sealed. A vacuum was then drawn up to 1 × 10⁻⁶ using a mechanical pump and a diffusion pump. -2Below Pa, close the vacuum valve of the crucible. Then place the crucible in the electric furnace, set the heating rate to 5℃ / min, until the temperature reaches 700℃ and hold for 2 hours. During this period, remove the crucible from the furnace at 1.5 hours, roll it back and forth on the ground for 2 minutes, and then put it back into the furnace to continue holding for 0.5 hours. Then turn off the power to the electric furnace, remove the crucible, and vertically and quickly immerse it in cooling water until the crucible is completely cooled. Place the cooled crucible in another electric furnace for homogenization annealing at 300℃ for 12 hours. After annealing, turn off the power and air cool to room temperature. Finally, remove the surface steel sleeve using a lathe and take out the smelted magnesium-lithium alloy ingot.

[0050] The actual and nominal composition of the LAZ1132 magnesium-lithium alloy ingot obtained in this embodiment, as measured by inductively coupled plasma optical emission spectrometry (ICP), are shown in Table 3.

[0051] Table 3 Comparison of nominal composition and actual composition of LAZ1132 alloy feedstock with ingot casting

[0052] LAZ1132LiAlZnMg Nominal composition 11.0 3.0 2.0 Balance Actual composition 11.2 3.0 1.9 Balance surface

[0053] Furthermore, the microstructure of the LAZ1132 magnesium-lithium alloy ingot, including its metallographic structure and scanning electron micrographs, is shown in Figure 5. It can be observed that the alloy prepared by the process in this embodiment exhibits precise control over smelting and batching, and a homogeneous microstructure.

[0054] The process parameters and magnesium-lithium alloy compositions described in this invention are not limited to the specific processes selected in the embodiments; the same effects can be achieved within the range of process parameters and alloy compositions. The above embodiments are merely examples to clearly illustrate this invention and are not intended to limit the implementation. Those skilled in the art can make other variations based on the above description, and it is neither necessary nor possible to exhaustively list all embodiments here. However, any variations derived therefrom are still within the scope of protection of this invention.

[0055] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A low-cost, high-efficiency smelting method for highly homogeneous magnesium-lithium alloys, characterized in that, The process includes the following steps: 1) Prepare a sealed crucible with a suitable volume according to the requirements of the ingot size for later processing. Select a seamless steel pipe with an inner diameter of 50-500mm and a length of 300-800mm. First, weld the bottom of the steel pipe together, then add pure magnesium, pure lithium, pure aluminum, and pure zinc raw materials. Next, weld the top of the steel pipe together and reserve a vacuum port. Use a vacuum pump to evacuate the vacuum inside the crucible to 1×10⁻⁶. -2 1) After the pressure is below Pa, the reserved vacuum interface is pressure welded; 2) The sealed crucible is placed in the industrial electric furnace and heated to 650-750℃ at a rate of 2-15℃ / min, and kept at the temperature for 1-3 hours to allow the metal in the crucible to fully melt and mix; 3) After the melting is completed, the sealed crucible is taken out of the electric furnace and placed vertically in the water cooling tank; 4) The completely cooled crucible is first homogenized, and then the steel scale on the surface is removed by machining, and the magnesium-lithium alloy ingot is taken out.

2. The low-cost and high-efficiency smelting method for highly homogeneous magnesium-lithium alloys according to claim 1, characterized in that, In step 1), pure magnesium, pure lithium, pure aluminum and pure zinc raw materials are configured according to the composition of magnesium-lithium alloy. The mass percentage of the magnesium-lithium alloy is: Li 3-16%, Al 1-6%, Zn 1-4%, and the remainder is Mg.

3. The low-cost, high-efficiency smelting method for highly homogeneous magnesium-lithium alloys according to claim 1, characterized in that, In step 1), the ultimate vacuum of the vacuum pump cannot reach 1×10⁻⁶. -2 At Pa, the crucible is purged with argon gas at least three times to reduce the oxygen content inside.

4. The low-cost and high-efficiency smelting method for highly homogeneous magnesium-lithium alloys according to claim 1, characterized in that, In step 2), the industrial electric furnace is one of the following: pit furnace, box furnace, or bogie furnace.

5. The low-cost, high-efficiency smelting method for highly homogeneous magnesium-lithium alloys according to claim 1, characterized in that, In step 2), the method for fully melting and mixing the metal is the upside-down method. Specifically, the crucible is turned over in the furnace during the melting process to increase the probability of solute mixing. It needs to be turned over 2 to 5 times during the melting process.

6. The low-cost, high-efficiency smelting method for highly homogeneous magnesium-lithium alloys according to claim 1, characterized in that, In step 2), the method for fully melting and mixing the metal is the rolling method. Specifically, the crucible is taken out of the electric furnace and rolled back and forth on the ground during the melting process to promote the mixing of the solute. This rolling is only required once during the melting process.

7. The low-cost and high-efficiency smelting method for highly homogeneous magnesium-lithium alloys according to claim 1, characterized in that, In step 3), the water level in the water-cooling tank must be higher than the height of the crucible to ensure that the crucible is completely submerged, thereby increasing the solidification rate of the melt.

8. The low-cost and high-efficiency smelting method for highly homogeneous magnesium-lithium alloys according to claim 1, characterized in that, In step 4), the homogenization process is 300-400℃, the holding time is 1-8h, and the cooling method is furnace cooling or air cooling.

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