A plasma melt refining method

Abstract

This invention belongs to the field of metal and alloy refining technology, specifically disclosing a plasma melt refining method. The plasma melt refining method provided by this invention includes the following steps: heating and melting the alloy components, stirring to obtain a melt; using a gas delivery device to deliver argon gas to the reaction chamber of a plasma torch, replacing the air therein; applying voltage to the cathode and anode in the plasma torch to ionize the argon gas into plasma, the resulting plasma jet passing through a temperature control device; the temperature-controlled plasma jet being introduced into the melt through a conduit, and moving the conduit to allow the plasma jet to act on various parts of the melt. The plasma melt refining method provided by this invention can solve the problem of difficult removal of impurity atoms during the melting process of metals and their alloys, achieving deep dehydrogenation of the melt, efficient removal of trace harmful elements, and interface modification of non-metallic inclusions, providing a new technical path for melt purification and microstructure control.

Description

Technical Field

[0001] This invention relates to the field of metal and alloy refining technology, and in particular to a plasma melt refining method. Background Technology

[0002] In the field of high-end metal materials and equipment manufacturing, melt purity is a key factor determining the upper limit of material performance and an important guarantee for ensuring the continuous operation of equipment under extreme conditions. During the smelting of metals and their alloys, melt purification and impurity removal have always been key technical challenges restricting the improvement of material performance. Currently used refining methods, such as inert gas flotation, mainly rely on the physical adsorption of bubbles to remove hydrogen and non-metallic inclusions. However, they have limited effectiveness in removing impurities such as alkali metals dissolved in the melt and are prone to secondary oxidation and compositional fluctuations due to gas agitation. With the increasing demands for the performance of materials such as aluminum alloys and high-temperature alloys in aerospace, high-end equipment, and other fields, the industry urgently needs to develop new melt refining technologies that offer higher efficiency, better purity, and stronger process controllability.

[0003] Plasma technology, with its extremely high energy density and rich content of active particles, is widely used in materials processing, semiconductor manufacturing, environmental protection, and other fields for etching, deposition, cleaning, or surface modification of materials. Plasma, as the fourth state of matter, is composed of ionized gas and contains high-energy components such as electrons, ions, excited-state atoms, and photons. When reactive or inert gases are excited into a plasma state, their behavior changes from passive physical isolation to active energy intervention, forming a reactive medium system with both thermodynamic and chemical reactivity. However, traditional high-temperature thermal plasma still suffers from limited impurity removal in melt refining and difficulty in avoiding the oxidation and loss of alloying elements, thus its effective application in melt refining has not yet been realized.

[0004] Therefore, there is an urgent need to develop new plasma melt refining technologies to solve the problem of removing impurity atoms during the smelting process of metals and their alloys. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a plasma melt refining method. The melt refining method of this invention can solve the key problem of the difficulty in completely purifying and removing impurities from metals and their alloys during the smelting process.

[0006] This invention provides a plasma melt refining method, comprising the following steps:

[0007] S1. Add the alloy components to pure aluminum melt, heat to melt, and stir to obtain aluminum alloy melt;

[0008] S2. Use a gas delivery device to deliver argon gas with a volume fraction ≥98% to the reaction chamber of the plasma torch to replace the air in it;

[0009] S3. Apply voltage to the cathode and anode inside the plasma torch to ionize argon gas into plasma. The plasma jet formed is then passed through a temperature control device to reduce the temperature of the plasma jet to 10-80°C higher than the temperature of the melt.

[0010] S4. The temperature-controlled plasma jet is introduced into the melt through a conduit. The conduit is moved to allow the plasma jet to act on various parts of the melt.

[0011] According to specific embodiments of the present invention, the plasma melt refining method provided by the present invention can solve the problem of the difficulty in removing impurity atoms during the melting process of metals and their alloys. Based on the synergistic effect of multiple physical fields and chemical processes, it achieves overall purification of the melt from the inside out, and has outstanding effects in removing deep inclusions and dissolved gases. The present invention can carry a large number of high-energy electrons and active reactive groups generated by plasma excitation under conditions close to the melt temperature. With the help of the physicochemical synergistic mechanism under non-equilibrium state, it can achieve deep dehydrogenation of the melt, efficient removal of trace harmful elements, and interface modification of non-metallic inclusions, thereby providing a new technical path for melt purification and microstructure control.

[0012] According to some embodiments of the present invention, the alloy is an aluminum alloy, wherein the weight fraction of aluminum in the aluminum alloy is ≥80%.

[0013] According to some embodiments of the present invention, in step S1, the melt temperature is maintained at 720~750°C.

[0014] This invention explores and discovers that by controlling the plasma jet temperature to be slightly higher than the melt temperature, it is possible to ensure good refining performance of the plasma jet while avoiding overheating of the aluminum melt due to the high temperature of the plasma. Overheating of the melt not only leads to the rupture of the surface Al2O3 film, exacerbating the oxidation and hydrogen absorption of the Al matrix, but also causes the loss of alloying elements such as Zn and Mg, and introduces more impurity elements due to the corrosion of the crucible / furnace lining by the molten aluminum. This invention effectively avoids the occurrence of melt overheating by precisely controlling the temperature of the jet when it enters the melt.

[0015] According to some embodiments of the present invention, after the melt is obtained by stirring, the temperature is maintained and the mixture is allowed to stand for 4 to 6 minutes.

[0016] According to some embodiments of the present invention, in step S2, the argon gas with a volume fraction ≥98% further contains chlorine gas, and the chlorine gas accounts for 0.5% to 2% of the total gas volume.

[0017] This invention has discovered that adding a small amount of chlorine gas as an active gas to argon can dissociate it into atomic or ionic states in plasma. Chlorine reacts directly with atomic hydrogen [H] dissolved in molten aluminum to generate hydrogen chloride gas ([Cl] + [H] → HCl ↑); it preferentially reacts with more reactive alkali metals to generate chloride scum ([Na] + [Cl] → NaCl); and the AlCl3 gas generated from aluminum precipitates at the interface between alumina inclusions and molten aluminum ([Al] + 3[Cl] → AlCl3 ↑), creating a "gas wedge" effect that mechanically peels off the oxide film, causing it to detach from the melt and float upwards with the argon flow. The above reactivity is exponentially enhanced, thus achieving more efficient and thorough removal of melt impurities and microstructure modification.

[0018] According to some embodiments of the present invention, in step S2, the inlet pressure of the gas delivered by the gas delivery device is 0.1~0.6MPa, and the flow rate is 0.2~4m³. 3 / h.

[0019] According to some preferred embodiments of the present invention, the inlet pressure of the gas delivered by the gas delivery device is 0.3~0.4MPa, and the flow rate is 1~3.5m³. 3 / h.

[0020] This invention avoids excessive thermal shock to the melt by precisely controlling the temperature, flow rate and position of the plasma jet, effectively reducing metal oxidation loss and shortening the refining cycle.

[0021] According to some embodiments of the present invention, in step S3, the plasma torch adopts a DC or non-transfer arc plasma excitation mode, the power of the plasma torch is 5kW~100kW, and the applied voltage is 30~80V.

[0022] According to some embodiments of the present invention, in step S3, the temperature control device precisely adjusts the temperature by regulating the flow rate of cooling water or other cooling media.

[0023] According to some embodiments of the present invention, in step S4, the plasma refining time is 5 to 10 minutes for every 150 to 300 kg of melt.

[0024] According to some embodiments of the present invention, the plasma melt refining method further includes the following steps: letting the melt refined in step S4 stand for 3-5 minutes, removing slag, and then casting it into shape to obtain a high-purity alloy casting.

[0025] The beneficial effects of this invention are:

[0026] 1) Enhanced physical refining effect: This invention utilizes the significant cavitation effect and shock wave action accompanying the plasma beam injection into the melt to efficiently break and disperse oxide inclusions (such as Al2O3) in the melt, promote the collision and aggregation of fine particles and accelerate their flotation and separation; the high temperature and high activity environment of the plasma zone can deeply decompose hydrogen-containing compounds (such as AlH3), while the strong stirring effect of the plasma jet on the melt shortens the diffusion path of hydrogen and significantly increases its migration rate to the surface, thus making the hydrogen removal efficiency and the depth of action superior to the traditional bubble flotation process;

[0027] 2) Chemical refining and microstructure control: The high energy density (high temperature, high energy particles) environment of argon plasma utilized in this invention can significantly reduce the activation energy of the reaction, effectively stimulating and promoting chemical reactions inside the melt. For example, without the addition of chlorine gas, the plasma may still cause trace amounts of residual chloride salts (such as MgCl2 from the flux) or active hydrogen [H] and oxygen [O] produced by the decomposition of surface water vapor in the aluminum melt to react with alkali metal elements, thereby improving their removal efficiency. In this invention, trace amounts of active gas (such as Cl2) can be further doped into the argon plasma. The active gas can be dissociated into atomic or ionic states in the plasma, and the reactivity is exponentially enhanced, thereby achieving more efficient and thorough impurity removal and microstructure modification treatment.

[0028] 3) The temperature control device and moving mechanism constructed in this invention enable the plasma heat source to have concentrated energy and flexible control, achieving precise control of the molten pool temperature and superheat, effectively avoiding grain coarsening and melt gas absorption caused by overall overheating; the synergistic effect of multiple physical fields and chemical processes achieved by the present invention can purify the melt from the inside out, with significant advantages in removing deep inclusions and dissolved gases; taking high-purity, high-strength aluminum alloys commonly used in the aerospace field (such as 6061 and 7055) as an example, the refining process of this invention can further reduce the hydrogen content of the melt, improve cleanliness and optimize the uniformity of microstructure, thereby breaking through the material performance limits and improving its batch consistency and service reliability.

[0029] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0031] Figure 1 This is a schematic diagram of the process flow of the plasma melt refining method according to an embodiment of the present invention;

[0032] Figure 2This is a schematic diagram of the overall structure of the plasma refining apparatus used in an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram illustrating the plasma degassing and impurity removal effect of the present invention on the purification of the melt. Detailed Implementation

[0034] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0035] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0036] Example 1

[0037] This embodiment provides a plasma melt refining method for preparing high-purity aluminum alloys.

[0038] The process flow diagram of this embodiment is as follows: Figure 1 As shown, the plasma melt refining system used is as follows: Figure 2 As shown, its core components include a plasma generator, a gas source and distribution system, a plasma temperature control system, a plasma delivery conduit, a plasma torch moving / rotating mechanism, and a plasma refining molten pool. A schematic diagram illustrating the hydrogen removal and impurity removal mechanism and melt purification effect generated after the argon plasma jet enters the molten aluminum in this embodiment is shown below. Figure 3 As shown.

[0039] The Al-Zn-Mg-Cu-Zr-Sc aluminum alloy composition in this embodiment is as follows by weight percentage: Zn 10.5%, Mg 2.5%, Cu 1.0%, Zr 0.1%, Sc 0.1%, with the balance being Al.

[0040] The specific steps for plasma melt refining are as follows:

[0041] 1) Using 99.9% pure Al ingots, pure Zn ingots, pure Mg ingots, and Al-50wt%Cu, Al-10wt%Zr and Al-2wt%Sc master alloys, the components are added to the medium frequency induction furnace in sequence according to the above aluminum alloy composition weight percentages. The temperature is raised to 730℃. After the raw materials melt, mechanical stirring is applied to make them uniformly mixed. Then the melt is allowed to stand at this temperature for 5 minutes.

[0042] 2) Start the plasma torch cooling water system and plasma temperature control device. The cooling water flow rate can be dynamically adjusted according to the actual temperature of the plasma torch. The pressure range of the cooling water system is controlled at 0.3~0.5MPa, and the water flow rate is maintained at 8~9L / min.

[0043] 3) Start the gas supply device to deliver argon gas with a purity ≥99% from the storage cylinder to the plasma torch via the delivery pipeline. The atmosphere is purified by continuously introducing argon gas to replace the residual air in the reaction chamber. The argon gas inlet pressure is controlled within the range of 0.3~0.5MPa, and the gas flow rate is 3m³ / h. 3 / h;

[0044] 4) After the gas in the reaction chamber has been replaced, start the plasma torch power supply, set the working current to 400A and the working voltage to 50V, and ionize the argon gas into plasma.

[0045] 5) The high-temperature, high-speed plasma jet migrates downwards and passes through a temperature control device, which reduces the temperature of the plasma jet to 780°C. The cooling water pressure of the temperature control device is controlled within the range of 0.3~0.5MPa, and the water flow rate is maintained at 8~9L / min.

[0046] 6) The plasma jet, after passing through the temperature control device, is directly introduced into the melt through the delivery conduit. Then, the moving / rotating mechanism is activated to refine various parts of the melt. For a 200kg alloy melt, the refining process using argon plasma takes about 7 minutes.

[0047] 7) The Al-Zn-Mg-Cu-Zr-Sc alloy melt, after being refined by plasma, was allowed to stand for 4 minutes, and after slag removal, it was poured into the furnace to form high-purity aluminum alloy castings.

[0048] Example 2

[0049] This embodiment provides a plasma melt refining method for preparing high-purity aluminum alloys.

[0050] The Al-Mg-Si-Cu-Cr aluminum alloy composition of this embodiment is as follows by weight percentage: Mg 1.2%, Si 0.8%, Cu 0.3%, Cr 0.1%, with the balance being Al. It is prepared using 99.9% pure Al ingots, pure Mg ingots, and Al-50wt%Cu, Al-10wt%Si, and Al-2wt%Cr master alloys.

[0051] The specific steps of plasma melt refining in this embodiment are the same as those in Embodiment 1.

[0052] High-purity Al-Mg-Si-Cu-Cr aluminum alloy castings were finally obtained.

[0053] Example 3

[0054] This embodiment provides a plasma melt refining method for preparing high-purity aluminum alloys.

[0055] This embodiment uses aluminum alloy melt with the same composition ratio as in Embodiment 1. The specific steps for plasma melt refining are as follows:

[0056] 1) Using 99.9% pure Al ingots, pure Zn ingots, pure Mg ingots, and Al-50wt%Cu, Al-10wt%Zr and Al-2wt%Sc master alloys, the components are added to the medium frequency induction furnace in sequence according to the weight percentage of the aluminum alloy composition. The temperature is raised to 730℃. After the raw materials melt, mechanical stirring is applied to make them evenly mixed. Then the melt is allowed to stand at this temperature for 5 minutes.

[0057] 2) Start the plasma torch cooling water system and plasma temperature control device. The cooling water flow rate can be dynamically adjusted according to the actual temperature of the plasma torch. The pressure range of the cooling water system is controlled at 0.3~0.5MPa, and the water flow rate is maintained at 8~9L / min.

[0058] 3) Start the gas supply device to mix argon gas (≥99% purity) with chlorine gas at a volume ratio of 99:1, and transport it to the plasma torch through the delivery pipeline. The atmosphere is purified by continuously introducing argon gas to replace the residual air in the reaction chamber. The argon gas inlet pressure is controlled within the range of 0.3~0.5MPa, and the gas flow rate is 3m³ / h. 3 / h;

[0059] 4) After the gas in the reaction chamber has been replaced, start the plasma power supply, set the working current to 400A and the working voltage to 50V, and ionize the mixed gas into plasma.

[0060] 5) The high-temperature, high-speed plasma jet migrates downwards and passes through a temperature control device, which reduces the temperature of the plasma jet to 780°C. The cooling water pressure of the temperature control device is controlled within the range of 0.3~0.5MPa, and the water flow rate is maintained at 8~9L / min.

[0061] 6) The plasma jet, after passing through the temperature control device, is directly introduced into the melt through the delivery conduit. Then, the moving / rotating mechanism is activated to refine various parts of the melt. For a 200kg alloy melt, the refining process using argon plasma takes about 7 minutes.

[0062] 7) The Al-Zn-Mg-Cu-Zr-Sc alloy melt, after being refined by plasma, was allowed to stand for 4 minutes, and after slag removal, it was poured into the furnace to form high-purity aluminum alloy castings.

[0063] Comparative Example 1

[0064] This comparative example provides an argon melt refining method for preparing high-purity aluminum alloys.

[0065] This comparative example uses the same aluminum alloy melt as in Example 1. The gas supply device is activated, and argon gas with a purity ≥99% is introduced from the gas storage cylinder into the alloy melt via a delivery pipeline. The argon gas directly contacts the melt to achieve dehydrogenation and impurity removal refining. The argon gas inlet pressure is controlled within the range of 0.3~0.5 MPa, and the gas flow rate is 3 m³ / s. 3 / h; Start the moving / rotating mechanism to refine each part of the melt. For a 200 kg alloy melt, use argon to refine for about 7 minutes; Let the argon-refined liquid phase Al-Zn-Mg-Cu-Zr-Sc alloy stand for 4 minutes, remove the slag, and then pour it into the furnace to form an aluminum alloy casting.

[0066] Comparative Example 2

[0067] This comparative example provides a plasma melt refining method for preparing high-purity aluminum alloys.

[0068] This comparative example uses aluminum alloy melt with the same composition ratio as in Example 1. The specific steps for plasma melt refining are as follows:

[0069] 1) Using 99.9% pure Al ingots, pure Zn ingots, pure Mg ingots, and Al-50wt%Cu, Al-10wt%Zr and Al-2wt%Sc master alloys, the components are added to the medium frequency induction furnace in sequence according to the weight percentage of the aluminum alloy composition. The temperature is raised to 730℃. After the raw materials melt, mechanical stirring is applied to make them evenly mixed. Then the melt is allowed to stand at this temperature for 5 minutes.

[0070] 2) Start the plasma torch cooling water system and plasma temperature control device. The cooling water flow rate can be dynamically adjusted according to the actual temperature of the plasma torch. The pressure range of the cooling water system is controlled at 0.3~0.5MPa, and the water flow rate is maintained at 8~9L / min.

[0071] 3) Start the gas supply device to deliver argon gas with a purity ≥99% from the storage cylinder to the plasma torch via the delivery pipeline. The atmosphere is purified by continuously introducing argon gas to replace the residual air in the reaction chamber. The argon gas inlet pressure is controlled within the range of 0.3~0.5MPa, and the gas flow rate is 3m³ / h. 3 / h;

[0072] 4) After the gas in the reaction chamber has been replaced, start the plasma power supply, set the working current to 400A and the working voltage to 50V, and ionize the argon gas into plasma.

[0073] 5) The high-temperature, high-speed plasma jet migrates downwards and passes through a temperature control device, which reduces the temperature of the plasma jet to 1200℃. The cooling water pressure of the temperature control device is controlled within the range of 0.2~0.4MPa, and the water flow rate is maintained at 5~7L / min.

[0074] 6) The plasma jet, after passing through the temperature control device, is directly introduced into the melt through the delivery conduit. Then, the moving / rotating mechanism is activated to refine various parts of the melt. For a 200kg alloy melt, the refining process using argon plasma takes about 7 minutes.

[0075] 7) The Al-Zn-Mg-Cu-Zr-Sc alloy melt, after being refined by plasma, was allowed to stand for 4 minutes, and after slag removal, it was poured into the furnace to form high-purity aluminum alloy castings.

[0076] Performance testing:

[0077] The hydrogen content and slag content of the aluminum alloy melts and their as-cast microstructures prepared in Examples 1, 2, and 3 and Comparative Examples 1 and 2 were tested according to GB / T 32186-2015 "Test Method for Purity of Aluminum and Aluminum Alloy Ingots". The test results of hydrogen content in liquid state, online slag analysis (LIMCA), and offline slag analysis (PoDFA) are shown in Table 1.

[0078]

[0079] As shown in Table 1 above, the hydrogen and slag contents in the melt significantly decreased after using the plasma refining method of the present invention, reaching the Class I purity standard in GB / T 32186-2015. In the plasma melt refining method of Example 3, a trace amount of Cl2 is doped into the argon plasma as an active gas. Cl2 can be dissociated into atomic or ionic states in the plasma, further significantly enhancing the reactivity. This results in more efficient and thorough impurity removal and microstructure modification treatment, leading to a product with significantly better microstructure purity.

[0080] Comparative Example 1, using a conventional argon refining method, showed significantly worse dehydrogenation and impurity removal effects compared to the argon plasma refining method in Example 1. In Comparative Example 2, a high-temperature plasma jet was used to refine the melt; however, the excessively high temperature led to overheating and accelerated oxidation of the aluminum melt, increasing the inclusion content and making it difficult to achieve more comprehensive dehydrogenation and impurity removal.

[0081] In summary, the plasma refining method provided by this invention has significant advantages in removing hydrogen and impurities from the melt, resulting in outstanding melt purification. Furthermore, the method requires only a small amount of additional electricity to significantly improve melt purity, making it a highly efficient and economical melt refining method.

[0082] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A plasma melt refining method, characterized in that, Includes the following steps: S1. Add the alloy components to pure aluminum melt, heat to melt, and stir to obtain aluminum alloy melt; S2. Use a gas delivery device to deliver argon gas with a volume fraction ≥98% to the reaction chamber of the plasma torch to replace the air in it; S3. Apply voltage to the cathode and anode inside the plasma torch to ionize argon gas into plasma. The plasma jet formed is then passed through a temperature control device to reduce the temperature of the plasma jet to 10-80°C higher than the temperature of the melt. S4. The temperature-controlled plasma jet is introduced into the melt through a conduit. The conduit is moved to allow the plasma jet to act on various parts of the melt.

2. The plasma melt refining method according to claim 1, characterized in that, The alloy is an aluminum alloy, and the weight fraction of aluminum in the aluminum alloy is ≥80%.

3. The plasma melt refining method according to claim 1, characterized in that, In step S1, the melt temperature is maintained at 720~750℃.

4. The plasma melt refining method according to claim 1, characterized in that, In step S2, the argon gas with a volume fraction ≥98% also contains chlorine gas, and the chlorine gas accounts for 0.5%~2% of the total gas volume.

5. The plasma melt refining method according to claim 1, characterized in that, In step S2, the inlet pressure of the gas delivered by the gas delivery device is 0.1~0.6MPa, and the flow rate is 0.2~4m³ / s. 3 / h.

6. The plasma melt refining method according to claim 1, characterized in that, In step S3, the plasma torch adopts a DC, non-transfer arc plasma excitation mode, and the power of the plasma torch is 5kW~100kW; the applied voltage is 30~80V.

7. The plasma melt refining method according to claim 1, characterized in that, In step S3, the temperature control device precisely adjusts the temperature by regulating the flow rate of cooling water or other cooling media.

8. The plasma melt refining method according to claim 1, characterized in that, In step S4, the plasma refining time is 5 to 10 minutes for every 150 to 300 kg of melt.

9. The plasma melt refining method according to claim 1, characterized in that, It also includes the following steps: After refining the melt in step S4, let it stand for 3-5 minutes, remove the slag, and then pour it into the furnace to form a high-purity alloy casting.

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