Low-vacuum melting manufacturing method for high-quality cast aluminum alloy

Abstract

The invention discloses a low-vacuum smelting manufacturing method for a high-quality cast aluminum alloy. The low-vacuum smelting manufacturing method comprises the following steps that S1, lithium-free molten aluminum is smelted in a low-vacuum smelting furnace; s2, inert gas is blown into the lithium-free aluminum liquid, lithium is added into the lithium-free aluminum liquid, and aluminum-lithium melt is formed through smelting; s3, the aluminum-lithium melt continues to be smelted under the low-vacuum ultrasonic vibration condition, and the aluminum-lithium melt is refined; and S4, a furnace cover of the smelting furnace is opened, after slag on the surface of the melt is removed, the aluminum-lithium melt is poured into a mold for casting, and the aluminum-lithium alloy is formed after cooling. According to the low-vacuum smelting manufacturing method for the high-quality cast aluminum alloy, hydrogenation oxidation reaction in the smelting process of the aluminum-lithium alloy and burning loss of lithium in the air environment can be avoided, the utilization rate of the lithium element is increased, and the defects of air holes, composition segregation and the like of the aluminum-lithium alloy are overcome.

Description

Technical Field

[0001] The invention relates to a low-vacuum melting and manufacturing method for high-quality cast aluminum alloy, belonging to the technical field of metallurgy and casting of metal materials. Background Art

[0002] Aluminum-lithium alloy is an aluminum alloy material with very low density, and is an ideal material for weapons, equipment, and aerospace. However, lithium has active chemical properties and is very easy to react with oxygen, water vapor, and nitrogen in the air. Therefore, smelting and processing aluminum-lithium alloy in the atmosphere will cause a large amount of lithium burning and severe air absorption, making the alloy castings unable to achieve the designed mechanical properties and increasing material costs. Therefore, conventional aluminum alloy smelting methods are no longer suitable for the preparation of aluminum-lithium alloys. Aluminum-lithium alloys with high lithium content are currently mostly added with lithium elements or smelted under the dual protection of high vacuum, inert gas + covering agent.

[0003] For high vacuum melting and casting, the equipment for melting lithium-containing alloys needs to pump the furnace to a high vacuum and high sealing state, so that the melting, lithium addition, melt treatment and pouring processes are all completed in a high vacuum and high sealing environment. However, only a few casting processes can adapt to high vacuum and closed melting environments, such as gravity investment casting, gravity gypsum casting, etc., while efficient and clean casting processes are difficult to apply to high vacuum environments, such as high pressure die casting, extrusion casting and other processes. In addition, the whole process is cumbersome to operate, the equipment is complex and the cost is high. It is not suitable for the preparation of complex structure precision castings and is not conducive to industrial promotion. When melting aluminum-lithium alloys in an atmospheric environment, even if double protection of inert gas and covering agent is used, the protection effect of the melt is greatly weakened compared to vacuum conditions, and defects such as pores and component segregation will appear in the alloy, which is not conducive to the preparation of high-quality aluminum-lithium alloys.

[0004] Ultrasonic treatment of melts has been proven to have good grain refinement, degassing and slag removal effects. This technology has been widely used in the industrial production of aluminum alloys such as aluminum silicon and aluminum copper. However, conventional melt ultrasonic equipment can only perform ultrasonic treatment in an open atmospheric environment, so it is not suitable for ultrasonic treatment of alloy melts containing active elements, such as lithium-containing aluminum alloys. Therefore, how to provide an industrial-oriented high-quality aluminum-lithium alloy low-vacuum melting method is an urgent problem that technicians in this field need to solve.

[0005] The patent application publication number CN105483403A discloses an aluminum alloy smelting method, which comprises the following steps: smelting Al into liquid Al under a protective gas environment, and then adding ferric oxide thereto, so that the hydrogen molecules formed in the Al liquid react with the ferric oxide to reduce the iron ion valence and the hydrogen content; after a certain period of heat preservation treatment, spray granulation treatment is performed, so that the molten aluminum alloy is precipitated in a particle state, so that some non-metallic impurities are volatilized in a gaseous form during the spray granulation process, and the impurity content in the Al liquid is reduced; and then ultrasonic cleaning treatment in acetone-ethanol is performed to clean the impurities on the surface of the aluminum alloy particles and avoid the reaction of the aluminum alloy with elements in the air; and then smelting, refining, casting, high-temperature cerium salt conversion liquid immersion, medium-temperature oxygen-carbon-sulfur co-penetration liquid treatment, and low-temperature phosphating liquid treatment are performed to change the structure of the aluminum alloy, reduce the impurity content in the aluminum alloy, and improve the quality of the aluminum alloy. However, the invention still has deficiencies in avoiding hydrogenation and oxidation reactions during the smelting process, as well as defects such as lithium burning, pores, and component segregation in an air environment. Summary of the invention

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: to provide a low vacuum melting method for high-quality cast aluminum alloy, comprising the following steps: S1. Smelting lithium-free aluminum liquid in a low vacuum smelting furnace, wherein a mechanical vacuum pump is used to extract air in the resistance heating furnace body of the smelting furnace through a copper tube of a cooling plate until a specified low vacuum state is reached in the furnace body, and a cooling water channel is provided on the resistance furnace body, and the sealing of the sealing ring and the furnace cover is ensured; S2, blowing inert gas into the lithium-free aluminum liquid and adding lithium into the lithium-free aluminum liquid to form an aluminum-lithium melt, wherein the blowing and lithium adding method uses argon gas to blow lithium particles in the charging hopper into the melt below the liquid surface, ensuring that the metallic lithium is always under the protection of the inert gas and melts below the melt surface, thereby avoiding lithium burning in an air environment; S3. Continue to melt the aluminum-lithium melt under low vacuum ultrasonic vibration conditions to refine the aluminum-lithium melt, wherein the ultrasonic treatment method includes using an horn and an ultrasonic transducer, the ultrasonic transducer and the horn are connected to the quartz glass furnace cover through a vacuum bellows, the quartz glass furnace cover is fixed to the resistance heating furnace through a locking clamp, the sealing ring keeps the quartz glass furnace cover and the resistance heating furnace well sealed, the horn head is inserted into the melt in the crucible, and the entire ultrasonic process is carried out under a preset vacuum degree; S4. Open the cover of the smelting furnace, remove the slag on the surface of the melt, pour the aluminum-lithium melt into a mold for casting, and form an aluminum-lithium alloy after cooling.

[0007] Preferably, in step S1, the mechanical vacuum pump of the smelting furnace extracts the gas in the smelting furnace cavity through the copper tube of the cooling plate, the cooling water cools the furnace cover through the cooling water inlet and outlet in turn, the stainless steel furnace cover is connected to the resistance heating furnace body through a hinge locking clamp, the air blowing and feeding pipe is fixed to the stainless steel furnace cover through a ball head, and the air blowing and feeding pipe extends into the smelting furnace cavity to add material to the crucible in the smelting furnace cavity for refining.

[0008] Preferably, in step S1, the mechanical vacuum pump is turned on to extract the air in the furnace chamber of the smelting furnace so that the air pressure in the furnace chamber of the smelting furnace reaches 5-10Pa, and argon gas is filled into the furnace chamber of the smelting furnace. The argon gas pressure is controlled at 60-80kPa, and the smelting temperature is 720~750℃.

[0009] Preferably, the upper end of the hopper of the smelting furnace is connected to the argon bottle, the lower end of the hopper is connected to the upper end of the blowing feeding tube, the lower end of the blowing feeding tube is immersed in the molten aluminum in the crucible, and the lithium particles are placed in the hopper and enter the molten aluminum in the crucible through the blowing feeding tube.

[0010] Preferably, the particle size of the lithium particles is 1-5 mm, the inert gas is high-purity argon, the lower end of the blowing and feeding pipe (7) is immersed in the bottom of the aluminum liquid, and when adding lithium, mechanical vibration is applied to the hopper (13) so that the lithium particles are blown into the aluminum liquid along with the argon gas.

[0011] Preferably, in step S2, the temperature of the aluminum liquid is lowered to 610-650°C before adding lithium to prevent serious overburning and hydrogen absorption oxidation of the Li element due to excessive temperature, and then the temperature is raised to 650-720°C.

[0012] Preferably, in step S3, an ultrasonic vibration device is used to treat the aluminum-lithium melt, and the ultrasonic transducer and the amplitude transformer in the ultrasonic vibration device are connected to the quartz glass furnace cover through a vacuum bellows. The vacuum bellows is a retractable metal tube. The quartz glass furnace cover is made of transparent, high-temperature resistant quartz glass. The amplitude transformer can move up and down with the vacuum bellows, and the ultrasonic transducer is connected to the ultrasonic controller through a cable.

[0013] Preferably, in step S3, the ultrasonic temperature is 650-700°C, and semi-solid or liquid ultrasonic refining treatment can be performed. The ultrasonic frequency, power and time can be matched according to the amount of aluminum liquid in industrial production. In some embodiments, the ultrasonic frequency is 0-30kHz, the ultrasonic power is 0-2000w, and the ultrasonic time is 1-3min.

[0014] Preferably, in step S4, the casting temperature during casting is 650-700°C.

[0015] The beneficial effects of the present invention are as follows: (1) The present invention adopts an inert gas-assisted low vacuum melting technology to prepare lithium-free aluminum liquid, which is different from the traditional non-vacuum melting and long-time rotary degassing refining technology of aluminum alloy. While greatly reducing the gas content in the lithium-free aluminum liquid, the operation is simpler and more efficient, providing high-quality lithium-free aluminum liquid for subsequent addition of pure lithium particles; (2) Based on the existing technology, the present invention optimizes the order of adding pure lithium particles and temperature control during the smelting process. A matching air blowing feeding device is used to use inert gas to add pure lithium particles to the bottom of the aluminum liquid through the air blowing feeding pipe. Different from the current method of wrapping lithium particles with aluminum foil and pressing them into the aluminum liquid during non-vacuum smelting, the entire lithium particle adding process does not contact the air, which greatly reduces the burn-out rate of the lithium element. At the same time, before adding lithium particles, the temperature of the aluminum liquid is lowered to the semi-solid range to avoid serious overburning and hydrogen absorption oxidation of the Li element due to excessively high temperature. In addition, the air blowing feeding device can be used not only to add lithium particles, but also to add second phase reinforcement particles to prepare aluminum-lithium based composite materials; (3) In view of the deficiency that conventional ultrasonic equipment can only perform ultrasonic refining of melt in an open atmospheric environment, the present invention integrates ultrasonic vibration with low vacuum melting technology, and the ultrasonic refining process is as short as 1-3 minutes, which is expected to reduce the original gas content and slag inclusions in the melt, improve the homogeneity of the melt, and avoid the problem of secondary hydrogen absorption and oxidation during ultrasonic refining. This is different from traditional refining methods such as inert gas rotary injection or environmentally friendly refining agents, thereby providing a fast and efficient refining method for high-quality aluminum-lithium alloy melts; (4) The low vacuum melting-inert gas blowing and lithium-ultrasonic refining integrated technology provided by the present invention has the advantages of convenient operation, high integration and good aluminum liquid quality. Compared with the high vacuum melting and casting method, this technology overcomes the shortcomings of the existing high vacuum melting process that it is impossible to perform refining treatments such as degassing and slag removal, and at the same time avoids the limitation that high vacuum melting equipment can only be gravity cast under vacuum. In particular, the high-quality aluminum-lithium alloy melt obtained by the present invention can be applied to new forming methods such as die casting and extrusion casting, thereby promoting industrial production. In addition, compared with the double protection melting method of inert gas plus covering agent under non-vacuum conditions, the present invention can avoid the contact between the melt and the air as much as possible, thereby greatly reducing the problems of hydrogen absorption and oxidation burning, and solves the defects such as shrinkage cavities, shrinkage, and component segregation, thereby obtaining a higher quality aluminum-lithium alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. 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 work, among which: Figures 1 to 32 is a schematic diagram of the structure of a melting furnace in an embodiment of the method for manufacturing high-quality cast aluminum alloy by low vacuum melting according to the present invention; Figure 4 is a microstructure diagram of a water-quenched sample of an aluminum-lithium alloy melt obtained by low vacuum smelting in Example 1 of the present invention; Figure 5 It is a microstructure diagram of a water-quenched sample of an aluminum-lithium alloy melt obtained by conventional non-vacuum melting in the prior art of the present invention.

[0017] In the figure: 1-mechanical vacuum pump; 2-cooling water tank; 3-cooling plate copper tube; 4-argon gas bottle; 5-gas pipe; 6-cooling water inlet and outlet; 7-air blowing and feeding pipe; 8-stainless steel furnace cover; 9-sealing ring; 10-hinge locking clamp; 11-crucible; 12-resistance heating furnace body; 13-feeding hopper; 14-ultrasonic transducer; 15-vacuum bellows; 16-quartz glass furnace cover; 17-amplifier; 18-ultrasonic controller. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] A method for manufacturing high-quality cast aluminum alloy by low vacuum melting, comprising the following steps: Example 1: Reference Figures 1 to 5 The low vacuum melting method for manufacturing high-quality cast aluminum alloy of the present invention has no special restrictions on the composition of the cast aluminum-lithium alloy. In this embodiment, the alloy composition of the cast aluminum-lithium alloy is as follows: 3% Li, 2% Cu, and the balance is Al in percentage by mass.

[0020] The specific preparation method is: S101: prepare high-purity aluminum, aluminum-copper intermediate alloy and high-purity lithium particles required for Al-3Li-2Cu (wt.%) alloy according to the configuration quality; put pure aluminum and aluminum-copper intermediate alloy blocks into crucible 11, turn on the mechanical vacuum pump 1 to extract the air in the furnace chamber to make the pressure in the furnace chamber reach 5-10Pa, then introduce high-purity argon gas to clean the residual oxygen and nitrogen in the furnace, and finally control the argon gas pressure in the furnace to 60-80kPa, turn on the resistance heating furnace to heat the crucible 11 in the furnace body, and smelt the pure aluminum and aluminum-copper intermediate alloy blocks at a smelting temperature of 720-750°C to obtain lithium-free aluminum liquid; S102: High-purity lithium particles are loaded into the feeding hopper 13, and the mechanical vacuum pump 1 is turned on to extract the air in the feeding hopper 13 to 5-10Pa and introduce high-purity argon gas to prevent the lithium particles from being oxidized. The feeding hopper 13 is connected to the air blowing and feeding pipe, and high-purity argon gas is introduced to remove the air in the pipeline; when the temperature of the aluminum liquid drops to 650°C, the tip of the lower end of the air blowing and feeding pipe 7 is immersed in the bottom of the aluminum liquid, and the argon gas flow rate is adjusted to 20ml / min. At the same time, mechanical vibration is applied to the feeding hopper 13, and the lithium particles are blown into the bottom of the aluminum liquid with the argon gas. After the lithium addition is completed, the aluminum liquid is heated to 690-700°C; the entire process of adding metallic lithium does not contact with air, thereby avoiding oxidation and burning of aluminum-lithium liquid, thereby improving the utilization rate of lithium elements; S103: Open the stainless steel furnace cover 8, install the quartz glass furnace cover 16, the ultrasonic transducer 14 and the horn 17 on the resistance heating furnace body 12, and press them on the resistance heating furnace body through the hinge locking fixture 10, turn on the mechanical vacuum pump 1, pump the air pressure in the furnace to 5-10Pa, adjust and control the melt temperature to 700°C, compress the vacuum bellows 15 to lower the ultrasonic horn 17, immerse the head of the horn 17 in the melt, turn on the ultrasound through the ultrasonic controller 18, the melt temperature during the ultrasound process is 690°C-700°C, the ultrasound time is 3min, and the ultrasound power is 2000W; S104: After the ultrasonic refining is completed, the melt temperature is controlled at 700°C, the crucible 11 is taken out, the molten metal is poured into a mold, and a high-quality cast aluminum-lithium alloy sample or part is obtained by extrusion casting or die casting. The microstructure of the alloy sample is as follows: Figure 4 shown.

[0021] Embodiment 2: The low vacuum melting method for manufacturing high-quality cast aluminum alloy of the present invention has no special restrictions on the composition of the cast aluminum-lithium alloy. In this embodiment, the alloy composition of the cast aluminum-lithium alloy is as follows by mass percentage: 2% Li, 2% Cu, and the balance is Al.

[0022] The specific preparation method is: S101: prepare high-purity aluminum, aluminum-copper master alloy and high-purity lithium particles required for Al-2Li-2Cu (wt.%) alloy according to the configuration quality; put pure aluminum and aluminum-copper master alloy blocks into crucible 11, turn on the mechanical vacuum pump 1 to extract the air in the furnace chamber to 5-10Pa, then introduce high-purity argon gas to clean the residual oxygen and nitrogen in the furnace, and finally control the argon gas pressure in the furnace to 60-80kPa, turn on the resistance heating furnace to heat the crucible 11 in the furnace body, and the melting temperature is 720-750℃ to obtain lithium-free aluminum liquid; S102: High-purity lithium particles are loaded into the feeding hopper 13, and the mechanical vacuum pump 1 is turned on to extract the air in the hopper to 5-10Pa and introduce high-purity argon gas to prevent the lithium particles from being oxidized. The feeding hopper 13 is connected to the air blowing and feeding pipe 7, and high-purity argon gas is introduced to remove the air in the pipeline; when the temperature of the aluminum liquid drops to 630°C, the lower end tip of the air blowing and feeding pipe 7 is immersed in the bottom of the aluminum liquid, and the argon gas flow rate is adjusted to 20ml / min. At the same time, mechanical vibration is applied to the feeding hopper 13, and the lithium particles are blown into the bottom of the aluminum liquid with the argon gas. After the lithium is added, the temperature rises to 650-660°C; the entire process of adding metallic lithium does not contact with air, thereby avoiding the oxidation of aluminum-lithium liquid and improving the utilization rate of lithium elements; S103: Open the stainless steel furnace cover 8, install the quartz glass furnace cover 16, ultrasonic transducer 14 and horn 17 on the resistance heating furnace body 12, and press them on the furnace body through the hinge locking fixture 10, turn on the mechanical vacuum pump 1, pump the air pressure in the furnace to 5-10Pa, adjust and control the melt temperature to 660°C, compress the vacuum bellows 15 to lower the ultrasonic horn 17, immerse the head of the horn 17 in the melt, turn on the ultrasound through the ultrasonic controller 18, the melt temperature during the ultrasound process is 650°C-660°C, the ultrasound time is 1min, and the ultrasound power is 1500W; S104: After the ultrasonic refining is completed, the melt temperature is controlled at 650° C., the crucible 11 is taken out, the molten metal is poured into a mold, and a high-quality cast aluminum-lithium alloy sample or part is obtained by extrusion casting or die casting.

[0023] The low-vacuum melting and manufacturing method of high-quality cast aluminum alloy of the present invention can avoid the hydrogenation oxidation reaction in the aluminum-lithium alloy melting process and the burning loss of lithium in the air environment, improve the utilization rate of the lithium element, and overcome the defects of the aluminum-lithium alloy such as pores and component segregation.

[0024] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for manufacturing high-quality cast aluminum alloy by low vacuum melting, characterized in that: The steps include: S1. Melting lithium-free aluminum liquid in a low vacuum melting furnace; S2, blowing inert gas into the lithium-free aluminum liquid and adding lithium into the lithium-free aluminum liquid to smelt and form an aluminum-lithium melt; S3, continuing to melt the aluminum-lithium melt under low vacuum ultrasonic vibration conditions to refine the aluminum-lithium melt; S4, opening the furnace cover of the smelting furnace, removing the slag on the surface of the melt, pouring the aluminum-lithium melt into a mold for casting, and forming an aluminum-lithium alloy after cooling; In step S1, the mechanical vacuum pump (1) of the smelting furnace extracts gas in the smelting furnace cavity through the cooling plate copper tube (3), cooling water cools the furnace cover through the cooling water inlet and outlet (6) in turn, the stainless steel furnace cover (8) is connected to the resistance heating furnace body (12) through the hinge locking clamp (10), the air blowing and feeding pipe (7) is fixed to the stainless steel furnace cover (8) through the ball head, and the air blowing and feeding pipe (7) extends into the smelting furnace cavity to feed the crucible (11) in the smelting furnace cavity for refining; In step S1, the mechanical vacuum pump (1) is turned on to extract air from the furnace chamber of the smelting furnace so that the pressure in the furnace chamber of the smelting furnace reaches 5-10 Pa, and argon gas is filled into the furnace chamber of the smelting furnace. The argon gas pressure is controlled at 60-80 kPa, and the smelting temperature is 720-750°C; In step S2, the upper end of the hopper (13) of the smelting furnace is connected to the argon gas bottle (4), the lower end of the hopper (13) is connected to the upper end of the blowing feeding pipe (7), the lower end of the blowing feeding pipe (7) is immersed in the aluminum liquid in the crucible (11), and the lithium particles are placed in the hopper (13) and enter the aluminum liquid in the crucible (11) through the blowing feeding pipe (7).

2. The method for manufacturing high-quality cast aluminum alloy by low vacuum melting according to claim 1, characterized in that: In step S2, the particle size of the lithium particles is 1-5 mm, the inert gas is high-purity argon, the lower end of the blowing and feeding pipe (7) is immersed in the bottom of the aluminum liquid, and when lithium is added, mechanical vibration is applied to the hopper (13) so that the lithium particles are blown into the aluminum liquid along with the argon gas.

3. The method for manufacturing high-quality cast aluminum alloy by low vacuum melting according to claim 2, characterized in that: In step S2, the temperature of the aluminum liquid is lowered to 610-650°C before adding lithium, and then the temperature is raised to 650-720°C.

4. The method for manufacturing high-quality cast aluminum alloy by low vacuum melting according to claim 1, characterized in that: In step S3, an ultrasonic vibration device is used to treat the aluminum-lithium melt. The ultrasonic transducer (14) and the horn (17) in the ultrasonic vibration device are connected to the quartz glass furnace cover (16) through a vacuum bellows (15). The vacuum bellows (15) is a retractable metal tube. The quartz glass furnace cover (16) is made of transparent, high-temperature resistant quartz glass. The horn (17) can move up and down with the vacuum bellows (15). The ultrasonic transducer (14) is connected to the ultrasonic controller (18) through a cable.

5. The method for manufacturing high-quality cast aluminum alloy by low vacuum melting according to claim 4, characterized in that: In step S3, the ultrasonic temperature is 650-700°C, the ultrasonic frequency is 0-30kHz, the ultrasonic power is 0-2000w, and the ultrasonic time is 1-3min.

6. The method for manufacturing high-quality cast aluminum alloy by low vacuum melting according to claim 1, characterized in that: In step S4, the casting temperature during casting is 650-700°C.

Images