A low-cost high-quality aluminum-lithium alloy preparation method

Abstract

The application relates to the technical field of aluminum-lithium alloy processing, and particularly discloses a low-cost high-quality aluminum-lithium alloy preparation method, which comprises the following steps: concentrating aluminum alloy raw materials without lithium to carry out smelting, then refining and degassing to obtain a base aluminum alloy melt; maintaining and heat-insulating the base aluminum alloy melt; introducing inert gas into a transition cabin and a sealed cabin to keep the sealed cabin and the transition cabin in a micro-positive pressure state and keep the pressure in the sealed cabin higher than that in the transition cabin; placing the base aluminum alloy melt in a tundish, then transferring the tundish into the transition cabin, closing an outer cabin door, and introducing inert gas into the transition cabin; opening an inner cabin door, closing the inner cabin door after transferring the tundish into the sealed cabin, adding pure lithium raw materials into the base aluminum alloy melt, and stirring the pure lithium raw materials uniformly; and then pressure casting to obtain an aluminum-lithium alloy pressure casting part. The application can effectively avoid oxidation of lithium elements, guarantee high cleanliness and component accuracy of the melt, reduce production cost, and is suitable for popularization and application.

Description

Technical Field

[0001] This invention relates to the field of aluminum-lithium alloy processing technology, and specifically to a low-cost, high-quality aluminum-lithium alloy preparation method. Background Technology

[0002] Due to their excellent properties of low density, high specific strength, and specific stiffness, aluminum-lithium alloys have become key materials for achieving structural lightweighting in aerospace, military, and high-end civilian fields. Die casting, with its high efficiency, high precision, and ability to form complex thin-walled components near-net-shape, is considered one of the processes for expanding the application of aluminum-lithium alloys in mass production. However, during the melting, holding, and die casting filling processes of aluminum-lithium alloys, the melt is highly susceptible to interfacial reactions with oxygen, nitrogen, and water vapor in the furnace atmosphere, leading to a series of problems. For example, the preferential oxidation of lithium results in severe loss of alloying elements, not only reducing the lithium yield but also causing the actual composition of the melt to deviate from the nominal design composition, making it difficult to ensure the consistency of alloy performance. In addition, the oxide film and inclusions generated by the reaction remain in the matrix after the casting solidifies, significantly disrupting the continuity of the alloy and deteriorating its mechanical properties and corrosion resistance. Furthermore, the hydrogen absorption behavior accompanying the reaction, under rapid solidification conditions, easily forms dispersed micropores and pinhole defects, severely reducing the density and service reliability of the casting.

[0003] Among existing methods, the most mature aluminum-lithium alloy preparation method is casting. This technology can produce aluminum-lithium alloy ingots with uniform composition and low defect levels. However, the limitation of this technology is that its output form is only primary processed blanks such as round or flat ingots. Its fundamental purpose is to provide raw materials for subsequent plastic deformation processes such as extrusion, forging, and rolling, and it cannot directly achieve precision forming of parts. In other words, this type of technology has not solved the problems of oxidation resistance and densification of aluminum-lithium alloys in near-net-shape forming processes such as die casting. Current aluminum-lithium alloy casting methods employ flux coating combined with localized inert gas protection, or vacuum melting environment for melt treatment, followed by gravity casting or low-pressure casting. These methods suffer from incomplete protection, large fluctuations in melt quality, easy introduction of non-metallic inclusions by the flux, and cumbersome operating procedures. Other methods, such as vacuum die casting, which attempts to complete filling and solidification in an oxygen-free environment, face challenges including huge investment in vacuum die casting equipment, extremely high mold sealing requirements, expensive maintenance, and long cycle times, making it difficult to meet the demands of continuous, efficient, and low-cost industrial production. Therefore, although cast aluminum-lithium alloys have shown performance potential in laboratory or small-batch pilot production, their large-scale industrial application is slow due to the aforementioned technological bottlenecks.

[0004] In summary, there is an urgent need to develop a new method for die-casting aluminum-lithium alloys that can effectively suppress the oxidation reaction of lithium elements throughout the die-casting process, ensure high purity and compositional accuracy of the melt, while also considering production costs and being suitable for continuous production. This will better meet actual production needs. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a method for preparing aluminum-lithium alloys that can effectively avoid lithium oxidation, ensure high purity and accurate composition of the melt, and reduce production costs.

[0006] The technical problem solved by this invention is achieved by the following technical solution: A low-cost, high-quality aluminum-lithium alloy preparation method is carried out in a forming system. The forming system includes an intermediate ladle, a transition chamber and a sealed chamber arranged adjacent to each other. The transition chamber is provided with an outer door and an inner door, and the transition chamber is connected to the interior of the sealed chamber through the inner door. A die-casting machine is provided in the sealed chamber, and a lithium addition port is provided on the sealed chamber. Includes the following steps: Preparation of the base aluminum alloy melt: lithium-free aluminum alloy raw materials are concentrated and melted, and then refined and degassed to obtain the base aluminum alloy melt; the base aluminum alloy melt is kept at a constant temperature; Atmosphere replacement and transfer: Inert gas is introduced into the transition chamber and the sealed chamber to maintain a slight positive pressure in both chambers, with the pressure in the sealed chamber being greater than that in the transition chamber; the base aluminum alloy melt is placed in the tundish, and then the tundish is transferred to the transition chamber. The outer hatch is closed, and inert gas is introduced into the transition chamber. Feeding and die casting: Open the inner door, transfer the intermediate ladle to the sealed chamber and close the inner door. Add pure lithium raw material to the base aluminum alloy melt in the intermediate ladle through the lithium filling port and stir evenly. Then transfer it to the die casting machine for die casting to obtain aluminum-lithium alloy die castings.

[0007] Furthermore, in the preparation step of the base aluminum alloy melt, the centralized smelting is carried out in an atmospheric environment, while the refining and degassing are carried out in a holding furnace.

[0008] Furthermore, in the step of preparing the base aluminum alloy melt, the base aluminum alloy melt is maintained at 770~800℃.

[0009] Furthermore, using the external atmospheric pressure as a reference, the positive pressure difference in the transition chamber is 100Pa~300Pa, and the positive pressure difference in the sealed chamber is 200Pa~500Pa, with the positive pressure difference in the sealed chamber always being greater than that in the transition chamber. This process control is extremely critical. If the pressure in the transition chamber and sealed chamber is too low, external air will enter during the atmosphere replacement and transfer process; if the pressure is too high, it will be wasteful, and excessive pressure will lead to instability in the production system. Furthermore, in the atmosphere replacement and transfer step, after closing the outer hatch, inert gas is introduced into the transition chamber to reduce the oxygen content to below 1000 ppm.

[0010] Furthermore, in the feeding and die-casting step, the feeding temperature of the pure lithium raw material is 700~740℃.

[0011] Furthermore, in the feeding and die-casting step, after feeding is completed, an electromagnetic stirring rod is used, with a stirring frequency of 1.2~2Hz and a stirring time of 10~20min.

[0012] Furthermore, in the feeding and die-casting steps, the positive pressure difference inside the sealed chamber is maintained at 200Pa~500Pa, based on the atmospheric pressure outside the chamber.

[0013] Furthermore, the forming system also includes a conveying assembly for conveying the intermediate ladle and die-cast products. The conveying assembly includes a track and a transfer vehicle mounted on the track.

[0014] An aluminum-lithium alloy die-casting part, prepared using the method described above, exhibits a compressive strength greater than 450 MPa, an elongation greater than 10%, a hydrogen content less than 0.2 μg / g, and a slag content less than 0.2 mm². 2 / kg.

[0015] Beneficial Effects: The low-cost, high-quality aluminum-lithium alloy preparation method of this invention utilizes the original temperature of the base aluminum alloy melt and the low melting point of lithium. Combined with other processes, it achieves uniform alloying without reheating and remelting. Furthermore, the lithium-containing melt is prepared under a fully inert gas protective atmosphere, eliminating the need for a covering agent and avoiding the introduction of new impurities, oxide inclusions, and hydrogen absorption. This effectively solves the bottleneck problems of complex operation and interference between protection and slag removal processes in existing local inert gas protection and solvent protection processes, as well as insufficient protection. The oxidation problems of easily oxidized and easily absorbed hydrogen in lithium-containing melts in traditional processes are also effectively solved. The simplified process significantly improves the mechanical properties of the final aluminum-lithium alloy castings and significantly reduces the hydrogen and slag content.

[0016] Furthermore, this invention employs a sealed chamber with overall inert gas protection. After gas replacement is completed before production, only a small amount of inert gas is needed for subsequent adjustment and maintenance. Compared with traditional processes that require continuous supply of protective gas, this process can achieve low-cost continuous production.

[0017] The aluminum-lithium alloy die-casting parts prepared by this invention have a compressive strength greater than 450 MPa, an elongation greater than 10%, a hydrogen content less than 0.2 ug / g, and a slag content less than 0.2 mm. 2 / kg, with high melt purity, accurate product composition, and excellent overall performance. Attached Figure Description

[0018] Figure 1 This is a top view of the forming system in this invention.

[0019] Figure 2 This is a side view of the forming system in this invention.

[0020] The components are: 1. Intermediate tank; 2. Transition chamber; 3. Sealed chamber; 4. Die-casting machine; 5. Outer door; 6. Inner door; 7. Transfer vehicle; 8. Mixing mechanism; 9. Track; 10. Robotic arm; 11. First air outlet; 12. First air filling port; 13. Lithium filling port; 14. Second air outlet; 15. Second air filling port. Detailed Implementation

[0021] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0022] Example 1

[0023] like Figure 1 and Figure 2 As shown, the forming system used in this invention includes an intermediate ladle 1, a transition chamber 2, and a sealed chamber 3. The intermediate ladle 1 is used to contain the molten aluminum alloy matrix and the mixture after adding pure lithium to the molten aluminum alloy matrix. The intermediate ladle 1 is an open container made of refractory material and is movable. The transition chamber 2 is located on the side wall of the sealed chamber 3. The transition chamber 2 is equipped with an outer door 5 and an inner door 6. The transition chamber 2 has independent first air inlet 12, first air outlet 11, and first oxygen content detection port (not shown in the figure). The transition chamber 2 communicates with the interior of the sealed chamber 3 through the inner door 6. The sealed chamber 3 also has independent second air inlet 15, second air outlet 14, and second oxygen content detection port (not shown in the figure). The sealed chamber 3 also has a lithium addition port 13. A die-casting machine 4 and a stirring mechanism 8 are installed inside the sealed chamber 3. The stirring mechanism is preferably an electromagnetic stirring mechanism 8.

[0024] In a preferred embodiment, the electromagnetic stirring mechanism 8 is fixed to the wall of the sealed chamber 3, and both the electromagnetic stirring mechanism 8 and the lithium filling port 13 are located close to the electromagnetic stirring station on the worktable.

[0025] The forming system also includes a conveying assembly for conveying the intermediate ladle 1 and the die-cast products. The conveying assembly includes a track 9 and a transfer car 7 set on the track 9. The track 9 is laid from the melting zone and connects to the transition chamber 2. The transition chamber 2 and the sealed chamber 3 are also equipped with connecting tracks 9.

[0026] In a preferred embodiment, a robotic arm 10 is also included: the robotic arm 10 is arranged inside the sealed chamber 3 and is used for loading, gripping and removing die-cast parts.

[0027] In a preferred embodiment, a rotating platform can be provided at the location where a track change is required to ensure the variable track operation of the transfer vehicle 7. These designs can be made according to existing technology and are not the focus of this invention, so they will not be described in detail here.

[0028] Example 2

[0029] A low-cost, high-quality aluminum-lithium alloy preparation method, carried out in the forming system described in Example 1, includes the following steps: Preparation of the base aluminum alloy melt: A conventional melting furnace was used to centrally melt lithium-free aluminum alloy raw materials. The lithium-free aluminum alloy raw materials were designed to contain all elements except lithium in the target composition of the aluminum-lithium alloy casting product. Then, refining and degassing were carried out in a holding furnace to obtain a homogeneous and pure base aluminum alloy melt. The alloy composition of this melt was designed as 3.5% Cu, 0.6% Mg, 0.5% Ni, 0.12% Zr, with the balance being Al. The temperature in the holding furnace was controlled at 780℃.

[0030] Atmosphere replacement and transfer: Open the inner hatch, close the outer hatch, and introduce argon gas into the transition chamber and the sealed chamber until the oxygen content in the transition chamber and the sealed chamber is 180 Ppm. Then close the inner hatch and continue to moderately ventilate into the sealed chamber to maintain a slight positive pressure of 300 Pa in the sealed chamber and a slight positive pressure of 150 Pa in the transition chamber.

[0031] The base aluminum alloy melt is in a liquid state. The base aluminum alloy melt is poured into the intermediate ladle, the outer hatch is opened, and the transfer vehicle transports the intermediate ladle along the track to the transition chamber. Then the outer hatch is closed, and the oxygen content inside the transition chamber is monitored in real time to control the oxygen content to be below 1000ppm.

[0032] Feeding and Die Casting: The inner hatch is opened, and the transfer vehicle moves the intermediate ladle along the track to the sealed chamber. The inner hatch is then closed, and the material is precisely conveyed to the electromagnetic stirring station. Electromagnetic stirring devices are installed on both sides of the chamber wall corresponding to this station, and a lithium-adding port is located on the upper chamber wall. A predetermined amount of pure lithium raw material is added to the base aluminum alloy melt in the intermediate ladle through the lithium-adding port. In this embodiment, the amount of pure lithium raw material added accounts for 1.2% of the mass of the product to be processed, and the feeding temperature of the pure lithium raw material is 720℃. After feeding, the electromagnetic stirring is activated at a frequency of 1.5Hz for 15 minutes. Then, the transfer vehicle transports the intermediate ladle along the track from the electromagnetic stirring station to the loading position of the die casting machine.

[0033] The die-casting machine is started, and the molten aluminum-lithium alloy is die-cast into shape in a sealed chamber filled with argon gas to obtain an aluminum-lithium alloy die-cast part. In this embodiment, the die-casting adopts a conventional die-casting process, without the need for special die-casting processes such as vacuum die-casting.

[0034] Example 3

[0035] A low-cost, high-quality aluminum-lithium alloy preparation method, carried out in the forming system described in Example 1, includes the following steps: Preparation of the matrix aluminum alloy melt: A lithium-free aluminum alloy raw material was centrally melted in a conventional melting furnace, followed by refining and degassing in a holding furnace to obtain a homogeneous and pure matrix aluminum alloy melt. The alloy composition of this melt was designed as 3.5% Cu, 0.6% Mg, 0.5% Ni, 0.12% Zr, with the balance being Al. The temperature in the holding furnace was controlled at 770℃.

[0036] Atmosphere replacement and transfer: Open the inner hatch, close the outer hatch, and introduce argon gas into the transition chamber and the sealed chamber until the oxygen content in the transition chamber and the sealed chamber is 190 ppm. Then close the inner hatch and continue to moderately ventilate into the sealed chamber to maintain a slight positive pressure of 250 Pa in the sealed chamber and a slight positive pressure of 100 Pa in the transition chamber.

[0037] The base aluminum alloy melt is in a liquid state. The base aluminum alloy melt is poured into the intermediate ladle, the outer hatch is opened, and the transfer vehicle transports the intermediate ladle along the track to the transition chamber. Then the outer hatch is closed, and the oxygen content inside the transition chamber is monitored in real time to control the oxygen content to be below 1000ppm.

[0038] Feeding and Die Casting: The inner hatch is opened, and the transfer vehicle moves the intermediate ladle along the track to the sealed chamber, then closes the inner hatch and precisely delivers it to the electromagnetic stirring station. Electromagnetic stirring devices are installed on both sides of the chamber wall corresponding to this station, and a lithium-adding port is located on the upper chamber wall. A predetermined amount of pure lithium raw material is added to the base aluminum alloy melt in the intermediate ladle through the lithium-adding port. In this embodiment, the amount of pure lithium raw material added accounts for 1.2% of the mass of the aluminum-lithium alloy die-cast part to be obtained, and the feeding temperature of the pure lithium raw material is 710℃. After feeding, the electromagnetic stirring is activated at a frequency of 1.5Hz for 15 minutes. Then, the transfer vehicle transports the intermediate ladle along the track from the electromagnetic stirring station to the loading position of the die-casting machine.

[0039] The die-casting machine is started, and the molten aluminum-lithium alloy is die-cast into shape in a sealed chamber filled with argon gas to obtain an aluminum-lithium alloy die-cast part. In this embodiment, the die-casting adopts a conventional die-casting process, without the need for special die-casting processes such as vacuum die-casting.

[0040] Compare with Example 1 In this comparative example, a conventional die-casting process is used, including the following steps: alloy melting, refining, and degassing are performed in a furnace with a protective atmosphere to obtain a homogeneous and pure aluminum-lithium alloy melt. The alloy composition of this melt is designed to be 3.5% Cu, 0.6% Mg, 0.5% Ni, 0.12% Zr, with the balance being Al. The melt temperature is controlled at 720℃. The die-casting machine is started to die-cast the aluminum-lithium alloy melt into shape, obtaining an aluminum-lithium alloy die-cast part. In this comparative example, the die-casting uses a conventional die-casting process. Compare with Example 2 In this comparative example, pure lithium raw material is added to the base aluminum alloy melt in a local gas protection environment, and then processed together with the intermediate ladle in the transition chamber and the sealed chamber.

[0041] Compare with Example 3 In this comparative example, during the atmosphere replacement and transfer steps, the transition chamber remained open, and the processing was carried out directly in a sealed chamber.

[0042] Compare with Example 4 In this comparative example, the pressure settings in the transition chamber and the sealed chamber were improper; specifically, the pressure in the transition chamber was 50 Pa and the pressure in the sealed chamber was 100 Pa.

[0043] The aluminum-lithium alloy die castings prepared in Examples 2-3 and Comparative Examples 1-4 were tested. The tensile strength and elongation were tested according to GB / T 228.1-2021, "Metallic materials, tensile testing - Part 1: Room temperature test method", and the hydrogen content and slag content were tested according to GB / T 32186-2015, "Methods for testing the purity of aluminum and aluminum alloy ingots". The results are shown in Table 1.

[0044] Table 1 Performance Test Results Statistics

[0045] As shown in Table 1, compared with the conventional method of Comparative Example 1, the mechanical properties of the product prepared by the present invention are significantly improved, while the hydrogen content and slag content are greatly reduced. Furthermore, as shown in Comparative Examples 2-4, the addition of pure lithium raw material, the design of the transition chamber, and the control of overall process conditions all have a crucial impact on the final product in the present invention.

[0046] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method of producing a low cost high quality aluminum lithium alloy, characterized by, The process is carried out in a forming system, which includes an intermediate ladle, a transition chamber and a sealed chamber arranged adjacent to each other. The transition chamber is provided with an outer door and an inner door, and the transition chamber communicates with the interior of the sealed chamber through the inner door. A die-casting machine is provided in the sealed chamber, and a lithium filling port is provided on the sealed chamber. Includes the following steps: Preparation of the base aluminum alloy melt: lithium-free aluminum alloy raw materials are concentrated and melted, and then refined and degassed to obtain the base aluminum alloy melt; the base aluminum alloy melt is kept at a constant temperature; Atmosphere replacement and transfer: Inert gas is introduced into the transition chamber and the sealed chamber to maintain a slight positive pressure in both chambers, with the pressure in the sealed chamber being greater than that in the transition chamber; the base aluminum alloy melt is placed in the tundish, and then the tundish is transferred to the transition chamber. The outer hatch is closed, and inert gas is introduced into the transition chamber. Feeding and die casting: Open the inner door, transfer the intermediate ladle to the sealed chamber and close the inner door. Add pure lithium raw material to the base aluminum alloy melt in the intermediate ladle through the lithium filling port and stir evenly. Then transfer it to the die casting machine for die casting to obtain aluminum-lithium alloy die castings.

2. The method of claim 1, wherein the low cost high quality aluminum lithium alloy is produced by the steps of: In the preparation steps of the base aluminum alloy melt, the centralized melting is carried out in an atmospheric environment, while the refining and degassing are carried out in a holding furnace. ​ 3. The method for preparing low-cost, high-quality aluminum-lithium alloy according to claim 1, characterized in that, In the preparation step of the base aluminum alloy melt, the base aluminum alloy melt is maintained at 770~800℃.

4. The method of claim 1, wherein the low cost high quality aluminum lithium alloy is produced by the steps of: In the atmosphere replacement and transfer steps, with the external atmospheric pressure as the reference, the positive pressure difference in the transition chamber is 100Pa~300Pa, and the positive pressure difference in the sealed chamber is 200Pa~500Pa, and the positive pressure difference in the sealed chamber is always greater than the positive pressure difference in the transition chamber. ​ 5. The method of claim 1, wherein the low cost high quality aluminum lithium alloy is produced by the steps of: During the atmosphere replacement and transfer process, after closing the outer hatch, inert gas is introduced into the transition chamber to reduce the oxygen content to below 1000 ppm. ​ 6. The method of claim 1, wherein the low cost high quality aluminum lithium alloy is produced by the steps of: In the feeding and die-casting process, the feeding temperature of the pure lithium raw material is 700~740℃.

7. The method of claim 1, wherein the low cost high quality aluminum lithium alloy is produced by the steps of: In the feeding and die-casting process, after feeding is completed, an electromagnetic stirring rod is used with a stirring frequency of 1.2~2Hz and a stirring time of 10~20min. ​ 8. The method of claim 1, wherein the low cost high quality aluminum lithium alloy is produced by the steps of: During the feeding and die-casting process, the positive pressure difference inside the sealed chamber is maintained at 200Pa~500Pa, with the atmospheric pressure outside the chamber as the reference. ​ 9. The method for preparing low-cost, high-quality aluminum-lithium alloy according to claim 1, characterized in that, The forming system also includes a conveying assembly for conveying the intermediate ladle and die-cast products. The conveying assembly includes a track and a transfer vehicle mounted on the track.

10. An aluminum-lithium alloy die casting, characterized by, The aluminum-lithium alloy die casting has a compressive strength greater than 450 MPa, an elongation greater than 10%, a hydrogen content less than 0.2 ug / g, and a slag content less than 0.2 mm / kg. 2 / kg.

Images