Low-melting-point bismuth-based alloy material, preparation method and application

Abstract

This invention relates to a low-melting-point bismuth-based alloy material, its preparation method, and its applications. The low-melting-point bismuth-based alloy comprises the following components by mass percentage: Bi 45.0%–60.0%, Sn 25.0%–35.0%, In 10.0%–18.0%, Ga 3.0%–8.0%, Ce 0.1%–0.5%, and nano-ceramic phase Al2O3 0.5%–1.5%; wherein the nano-ceramic phase Al2O3 is uniformly dispersed in the alloy matrix. By introducing high contents of In and Ga as active elements and innovatively introducing nano-scale ceramic dispersed phase Al2O3 as a reinforcing phase, it exhibits excellent wetting properties for aluminum and stainless steel housings commonly used in GIS equipment, significantly improving the alloy's mechanical strength and effectively meeting the requirements for energized sealing materials for sulfur hexafluoride leakage in gas-insulated metal-enclosed switchgear.

Description

Technical Field

[0001] This invention belongs to the field of electrical equipment repair materials technology, specifically relating to a low-melting-point bismuth-based alloy material, its preparation method, and its application. Background Technology

[0002] Gas-insulated switchgear (GIS) is widely used in power grids due to its compact structure, high reliability, and minimal environmental impact. Sulfur hexafluoride (SF6) gas serves as the key insulating and arc-quenching medium, and its sealing performance directly affects the long-term safe and stable operation of the equipment. However, during long-term operation, GIS equipment inevitably experiences varying degrees of SF6 gas leakage due to factors such as aging of seals, deformation of flange mating surfaces, microscopic defects in busbar welds, or abnormal mechanical stress. Statistics show that the average annual leakage rate of GIS equipment in operation in China is approximately 0.5%-1%. Leakage not only leads to a drop in operating pressure, affecting insulation and arc-quenching performance and increasing the risk of equipment failure, but also poses serious environmental problems due to the strong greenhouse effect of SF6 gas.

[0003] Currently, leak handling in GIS equipment primarily relies on planned power outages for maintenance. Traditional sealing techniques generally employ polymer materials such as epoxy resin, room temperature vulcanizing silicone rubber, or special sealants. These methods have significant limitations: polymer materials have long curing times (typically several hours), making rapid emergency response impossible; their coefficients of thermal expansion differ significantly from those of the metal casing, easily generating internal stress under the thermal cycling of the equipment, leading to cracking at the bonding interface or aging and failure of the material itself, resulting in a limited sealing lifespan; and most organic materials lack sufficient electrical properties, arc erosion resistance, and long-term resistance to SF6 decomposition corrosion, making it difficult to meet the stringent electrical and chemical environmental requirements inside GIS equipment. Therefore, developing a sealing technology that can be implemented while the equipment is energized and offers long-term reliability has become an urgent need in the power operation and maintenance field.

[0004] In recent years, the idea of ​​using the melting-solidification properties of low-melting-point metals or alloys for online plugging has begun to attract attention. Among them, bismuth (Bi)-based alloys have shown unique potential due to their low melting point and slight volume expansion during solidification. However, existing low-melting-point bismuth-based alloys (such as traditional Bi-Sn and Bi-Pb eutectic alloys) still face multiple challenges in practical applications: (1) Their melting points are generally high (e.g., the eutectic point of Bi-58Sn is 138℃). To achieve melting in the GIS under charged conditions, it is often necessary to apply an external heat source with a high temperature. This is not only complicated to operate, but also poses a risk of damaging the original insulation of the equipment due to local overheating or causing local overheating and decomposition of SF6 gas; (2) The alloy often has insufficient wettability and interfacial bonding strength with the shell materials commonly used in GIS equipment, such as aluminum and stainless steel, and the sealing layer is easy to peel off from the substrate; (3) Pure bismuth and its simple alloys have poor mechanical properties, are brittle and hard, and have weak resistance to vibration and thermal fatigue; (4) Their electrical conductivity and thermal expansion coefficient do not match the equipment shell, which may cause problems such as uneven electric field distribution or thermal stress concentration, affecting the reliability of long-term operation.

[0005] In summary, existing polymeric plugging materials and traditional low-melting-point alloys are insufficient to meet the technical requirements of live, rapid, and long-term plugging for GIS equipment. There is an urgent need to develop a new type of specialized plugging material that combines a precisely regulated low melting point (below the upper limit of local temperature rise under normal operation of GIS equipment), excellent wetting and metallurgical bonding capabilities to the metal casing, good mechanical properties, and electrothermal physical properties that match the casing. This would provide a new approach for live plugging technology in GIS, ensuring the safe and stable operation of ultra-high voltage power grids. Summary of the Invention

[0006] To address the issues of existing GIS equipment's sulfur hexafluoride gas leakage, such as the high melting point, poor wettability, poor mechanical properties, and poor electrothermal compatibility with the equipment casing, low-melting-point metal plugging materials are needed.

[0007] This invention provides a low-melting-point bismuth-based alloy material for electrically sealed sulfur hexafluoride leaks in GIS equipment, comprising the following components by mass percentage: Bi 45.0%–60.0%, Sn 25.0%–35.0%, In 10.0%–18.0%, Ga 3.0%–8.0%, Ce 0.1%–0.5%, and nano-ceramic phase Al2O3 0.5%–1.5%; wherein the nano-ceramic phase Al2O3 is uniformly dispersed in the alloy matrix.

[0008] Preferably, the nano-ceramic phase Al2O3 is in the form of nanoparticles with a particle size of 20 nm to 80 nm.

[0009] Preferably, the melting temperature of the low-melting-point bismuth-based alloy is ≤150°C; and / or The solidification expansion coefficient of the low-melting-point bismuth-based alloy is >0.5%; and / or The low-melting-point bismuth-based alloy has a Brinell hardness >20 HB; and / or The tensile strength of the low-melting-point bismuth-based alloy is >52 MPa.

[0010] The present invention also provides a method for preparing the aforementioned low-melting-point bismuth-based alloy material, comprising the following steps: Raw material pretreatment: High-purity Bi, Sn, In, Ga, and Ce metal raw materials are surface cleaned and dried, and nano-ceramic particle powder is vacuum dried; Vacuum melting: The pretreated metal raw materials are placed in a vacuum induction melting furnace according to the proportion, and heated and melted in stages under the protection of inert gas to fully melt and mix them evenly to obtain an alloy melt; Nanoparticle dispersion strengthening treatment: In the molten state, powder is fed into the alloy melt through a carrier gas and ultrasonic treatment is applied simultaneously to make the nanoparticles uniformly dispersed. Rapid solidification molding: The alloy melt, which has been strengthened by nano-dispersion, is poured into a preheated mold and rapidly cooled and solidified to obtain an alloy ingot.

[0011] Preferably, the segmented heating and melting under inert gas protection specifically includes: evacuating to a vacuum of 1×10⁻⁶. -3 ~5×10 -3 Pa, fill the furnace with high-purity argon gas until the pressure inside the furnace is 0.05~0.1 MPa; first, raise the temperature to 280~400℃ at 5~10℃ / min and hold for 20~40min, then raise the temperature to 450~600℃ at 2~5℃ / min and hold and stir for 40~60min.

[0012] Preferably, the specific process parameters for the nano-dispersion strengthening treatment are: melt temperature maintained at 400~500℃, ultrasonic frequency at 20~40kHz, ultrasonic power at 500~1000W, and treatment time at 10~15min.

[0013] Preferably, the carrier gas is argon, and the carrier gas flow rate is 0.1~0.6L / min.

[0014] Preferably, during the rapid solidification molding process, the mold preheating temperature is 80~120℃, and the solidification cooling rate of the alloy is controlled at 30~50℃ / s.

[0015] Preferably, the pretreatment specifically includes: grinding, pickling, cleaning and drying the metal raw materials, and drying the nano-ceramic powder.

[0016] Preferably, the rapid solidification molding step is followed by post-processing and molding: the alloy ingot is annealed and processed into a specific shape according to application requirements.

[0017] Preferably, the annealing temperature is 150~300℃ and the treatment time is 0.5~2h.

[0018] The present invention also provides an application of the aforementioned low-melting-point bismuth-based alloy material in the preparation of a sulfur hexafluoride leakage sealing material for gas-insulated metal-enclosed switchgear.

[0019] The objective of this invention is achieved through the following technical solution: Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The low-melting-point bismuth-based alloy material proposed in this invention comprises the following components by mass percentage: Bi 45.0%–60.0%, Sn 25.0%–35.0%, In 10.0%–18.0%, Ga 3.0%–8.0%, Ce 0.1%–0.5%, and nano-ceramic phase Al2O3 0.5%–1.5%; wherein the nano-ceramic phase Al2O3 is uniformly dispersed in the alloy matrix. By introducing high contents of In and Ga as active elements, it exhibits excellent wetting performance on aluminum and stainless steel shells commonly used in GIS equipment, with a contact angle of less than 15°, ensuring that the molten alloy can fully spread and penetrate into micron-level leakage gaps; innovatively, nano-scale ceramic dispersed phase Al2O3 is introduced into the low-melting-point alloy matrix. These nanoparticles, as reinforcing phases, effectively pin grain boundaries and hinder dislocation movement without significantly increasing the alloy melting point, thereby greatly improving the room temperature and intermediate temperature strength, hardness, and creep resistance of the alloy. This allows the sealing material to have excellent flow and filling capabilities, as well as sufficient structural strength to withstand internal air pressure and external mechanical stress, overcoming the inherent weaknesses of traditional low-melting-point metal materials, such as "low strength and easy creep".

[0020] (2) The low-melting-point bismuth-based alloy material of the present invention, through careful design of the alloy composition, achieves a good match between its conductivity and coefficient of thermal expansion with the metal shell of the GIS equipment. The moderate conductivity avoids the risk of electric field concentration and partial discharge caused by the insulating sealing layer in strong electric field areas; the matched coefficient of thermal expansion significantly reduces the thermal stress generated at the sealing interface due to temperature fluctuations, preventing interface cracking or detachment caused by thermal mismatch. This synergistic adaptation of electrical and thermal properties ensures that the sealing layer can operate stably for a long time under complex multi-physics field (electric, thermal, and mechanical) coupling conditions, and will not become a new weak point of the equipment.

[0021] (3) The low-melting-point bismuth-based alloy material of the present invention has a melting point precisely designed within the critical range of 65-125℃. This temperature is lower than the typical local temperature rise generated by GIS equipment under rated load operation, allowing the sealing operation to be safely carried out using the equipment's own operating heat or auxiliary heating with extremely low power consumption. This completely avoids the safety risks and power outages caused by the traditional method of requiring power outage operation or the application of high-temperature heat sources. The melting process of the alloy is mild and controllable, and will not cause electric arcs or SF6 gas overheating and decomposition, achieving true "online, energized, and non-intrusive" sealing, greatly improving the reliability and economy of power grid operation and maintenance.

[0022] (4) The preparation method of the low-melting-point bismuth-based alloy material proposed in this invention introduces high content of In and Ga as active elements, combined with an optimized rapid solidification process, which can form a strong metallurgical bond or strong diffusion connection at the interface. Compared with traditional polymer materials that rely on physical adhesion or simple mechanical interlocking, the sealing layer formed by this invention has high bonding strength with the matrix, excellent thermal shock resistance and fatigue resistance, and can withstand temperature cycles, vibration and internal electrodynamic impacts during long-term operation of equipment, thereby achieving long-term and reliable sealing and effectively preventing leakage recurrence. Through ultrasonic-assisted dispersion process, uniform distribution of Al2O3 nanoparticles in the melt is achieved.

[0023] (5) The preparation method of low-melting-point bismuth-based alloy materials proposed in this invention constructs an integrated preparation process of "vacuum melting - ultrasonic-assisted nano-dispersion - rapid solidification and forming", with a clear process and controllable parameters. Vacuum melting effectively prevents alloy oxidation and the introduction of impurities; ultrasonic treatment solves the problem of nanoparticle dispersion in the metal melt; rapid solidification refines the microstructure and suppresses component segregation. This process system can stably and repeatedly produce alloy materials with uniform microstructure and consistent performance indicators, laying a solid foundation for large-scale application and product quality control.

[0024] (6) The low-melting-point bismuth-based alloy material and its preparation method proposed in this invention have successfully achieved the unification of multiple characteristics such as low melting point, high wettability, strong bonding, good matching, and stable process. The prepared sealing alloy has excellent comprehensive performance and is not only specifically suitable for solving the industry pain point of SF6 leakage in GIS equipment, but its technical concept and material system can also be extended to other power equipment (such as transformers and instrument transformers) for online sealing, thermal interface management of electronic packaging, and low-temperature connection of precision instruments, showing broad industrial application prospects and important technical and economic value. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 instances that are improved or modified by those skilled in the art are within the scope of protection of the present invention. It should be understood that the embodiments of the present invention are only used to illustrate the technical effects of the present invention, and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the methods used in the embodiments are conventional methods.

[0026] Example 1 This embodiment provides a low-melting-point bismuth-based alloy material suitable for sealing live leakage of sulfur hexafluoride (SF6) in gas-insulated metal-enclosed switchgear (GIS). Its preparation method includes the following steps: Raw material pretreatment: Bi, Sn, In, Ga, and Ce metal particles with a purity of 99.99% were selected. The oxide scale was removed by sequentially polishing with 400-grit sandpaper, followed by ultrasonic cleaning in a 10% dilute nitric acid solution for 5 minutes, rinsing three times with deionized water, and finally cleaning with anhydrous ethanol and drying in an 80℃ vacuum oven for 2 hours. Al₂O₃ nanoparticles with a particle size of 20 nm to 80 nm were then dried at 280℃ for 10 hours. - Dry under vacuum of 2 Pa for 2.5 hours, then transfer to a desiccator to cool for later use.

[0027] Vacuum melting: Weigh the processed raw materials according to the target composition of Bi 52.0%, Sn 25.0%, In 15.0%, Ga 6.0%, Ce 0.5%, and Al2O3 1.5%, specifically: Bi 260.0g, Sn 125.0g, In 75.0g, Ga 30.0g, Ce 2.5g, and nano-Al2O3 7.5g, and place them in a high-purity graphite crucible. Place the crucible in a vacuum induction melting furnace and evacuate to 5×10⁻⁶. -3 The pressure was increased to 0.05 MPa, and then high-purity argon (99.999%) was introduced into the furnace until the internal pressure was 0.05 MPa. Induction heating was then started. In the first stage, the temperature was increased to 300°C at a rate of 10°C / min and held for 20 min. In the second stage, the temperature was increased to 480°C at a rate of 5°C / min and held for 40 min. After the metal was completely melted into a bright liquid, electromagnetic stirring was used to mix the components evenly.

[0028] Nanoparticle dispersion strengthening treatment: Under the protection of argon gas and a melt temperature of 400℃, baked nano-Al2O3 powder is uniformly fed into the melt surface through a specially designed powder feeding device under argon gas flow (flow rate 0.6L / min). At the same time, an ultrasonic vibration probe is inserted into the melt surface at a depth of about 20mm, and the ultrasonic generator is started to treat the melt for 12 minutes at a frequency of 25kHz and a power of 800W.

[0029] Rapid solidification molding: The alloy melt, after nano-dispersion treatment, is rapidly poured into a metal mold preheated to 100°C. Through the mold's strong cooling design or in combination with an external cooling device, the solidification cooling rate of the alloy is controlled at 30°C / s. After complete solidification, the alloy material is removed.

[0030] Post-processing and forming: The obtained alloy material is annealed at 200℃ for 1 hour, and then cooled to room temperature in the furnace. Finally, according to the specific requirements of the sealing application (such as filaments, foils, pre-formed gaskets, etc.), the final usable sealing material product is prepared by means of extrusion, drawing, rolling or machining.

[0031] Example 2 This embodiment provides a low-melting-point bismuth-based alloy material suitable for sealing live leakage of sulfur hexafluoride (SF6) in gas-insulated metal-enclosed switchgear (GIS). Its preparation method includes the following steps: Raw material pretreatment: Bi, Sn, In, Ga, and Ce metal particles with a purity of 99.99% (mass percentage) were selected. The oxide scale was removed by sequentially polishing with 400-grit sandpaper, followed by ultrasonic cleaning in 10% dilute nitric acid solution for 5 minutes, rinsing three times with deionized water, and finally cleaning with anhydrous ethanol and drying in an 80℃ vacuum oven for 2 hours. Al₂O₃ nanoparticles with a particle size of 20 nm to 80 nm were then dried at 350℃ for 10 hours. -2 Dry under vacuum for 1.5 hours, then transfer to a desiccator to cool for later use.

[0032] Vacuum melting: Weigh the processed raw materials according to the target composition of Bi 60.0%, Sn 25.0%, In 10.0%, Ga 3.0%, Ce 0.5%, and Al2O3 1.5%. The specific mass is: Bi 260.0g, Sn 108.3g, In 43.3g, Ga 13.0g, Ce 2.2g, and nano Al2O3 6.5g, and place them in a high-purity graphite crucible. Place the crucible in a vacuum induction melting furnace and evacuate to 3×10⁻⁶. -3 The pressure was increased to 0.08 MPa, and then high-purity argon (99.999%) was introduced into the furnace until the internal pressure was 0.08 MPa. Induction heating was then started. In the first stage, the temperature was increased to 400℃ at a rate of 10℃ / min and held for 25 min. In the second stage, the temperature was increased to 600℃ at a rate of 2℃ / min and held for 40 min. After the metal was completely melted into a bright liquid, electromagnetic stirring was used to mix the components evenly.

[0033] Nanoparticle dispersion strengthening treatment: Under the protection of argon gas and a melt temperature of 420℃, baked nano-Al2O3 powder is uniformly fed into the melt surface through a specially designed powder feeding device under argon gas flow (flow rate 0.4L / min). At the same time, an ultrasonic vibration probe is inserted into the melt surface at a depth of about 20mm, and the ultrasonic generator is started to treat the melt for 15min at a frequency of 40kHz and a power of 500W.

[0034] Rapid solidification molding: The alloy melt, after nano-dispersion treatment, is rapidly poured into a metal mold preheated to 120°C. Through the mold's strong cooling design or in combination with an external cooling device, the solidification cooling rate of the alloy is controlled at 50°C / s. After complete solidification, the alloy material is removed.

[0035] Post-processing and forming: The obtained alloy material is annealed at 300℃ for 0.5h, and then cooled to room temperature in the furnace. Finally, according to the specific requirements of the sealing application (such as filaments, foils, pre-formed gaskets, etc.), the final usable sealing material products are prepared by means of extrusion, drawing, rolling or machining.

[0036] Example 3 This embodiment provides a low-melting-point bismuth-based alloy material suitable for sealing live leakage of sulfur hexafluoride (SF6) in gas-insulated metal-enclosed switchgear (GIS). Its preparation method includes the following steps: Raw material pretreatment: Bi, Sn, In, Ga, and Ce metal particles with a purity of 99.99% (mass percentage) were selected. The oxide scale was removed by sequentially polishing with 400-grit sandpaper, followed by ultrasonic cleaning in 10% dilute nitric acid solution for 5 minutes, rinsing three times with deionized water, and finally cleaning with anhydrous ethanol and drying in an 80℃ vacuum drying oven for 2 hours. Al₂O₃ nanoparticles with a particle size of 20 nm to 80 nm were then dried at 260℃ for 10 hours. -2 Dry under vacuum for 3 hours, then transfer to a desiccator to cool for later use.

[0037] Vacuum melting: Weigh the processed raw materials according to the target composition of Bi 50.0%, Sn 35.0%, In 10.0%, Ga 4.0%, Ce 0.1%, and Al2O3 0.9%, specifically: Bi 260.0g, Sn 182.0g, In 43.3g, Ga 17.3g, Ce 0.5g, and nano-Al2O3 4.7g, and place them in a high-purity graphite crucible. Place the crucible in a vacuum induction melting furnace and evacuate to 1×10⁻⁶. -3The pressure was increased to 0.1 MPa, and then high-purity argon (99.999%) was introduced into the furnace until the internal pressure was 0.1 MPa. Induction heating was then started. In the first stage, the temperature was increased to 280°C at a rate of 5°C / min and held for 40 min. In the second stage, the temperature was increased to 500°C at a rate of 4°C / min and held for 50 min. After the metal was completely melted into a bright liquid, electromagnetic stirring was used to mix the components evenly.

[0038] Nanoparticle dispersion strengthening treatment: Under the protection of argon gas and a melt temperature of 500℃, baked nano-Al2O3 powder is uniformly fed into the melt surface through a specially designed powder feeding device under argon gas flow (flow rate 0.1L / min). At the same time, an ultrasonic vibration probe is inserted into the melt surface at a depth of about 20mm, and the ultrasonic generator is started to treat the melt for 13min at a frequency of 20kHz and a power of 900W.

[0039] Rapid solidification molding: The alloy melt, after nano-dispersion treatment, is rapidly poured into a metal mold preheated to 80°C. Through the mold's strong cooling design or in combination with an external cooling device, the solidification cooling rate of the alloy is controlled at 35°C / s. After complete solidification, the alloy material is removed.

[0040] Post-processing and forming: The obtained alloy material is annealed at 260℃ for 0.8h, and then cooled to room temperature in the furnace. Finally, according to the specific requirements of the sealing application (such as filaments, foils, pre-formed gaskets, etc.), the final usable sealing material products are prepared by means of extrusion, drawing, rolling or machining.

[0041] Example 4 This embodiment provides a low-melting-point bismuth-based alloy material suitable for sealing live leakage of sulfur hexafluoride (SF6) in gas-insulated metal-enclosed switchgear (GIS). Its preparation method includes the following steps: Raw material pretreatment: Bi, Sn, In, Ga, and Ce metal particles with a purity of 99.99% (mass percentage) were selected. The oxide scale was removed by sequentially polishing with 400-grit sandpaper, followed by ultrasonic cleaning in 10% dilute nitric acid solution for 5 minutes, rinsing three times with deionized water, and finally cleaning with anhydrous ethanol and drying in an 80℃ vacuum oven for 2 hours. Al₂O₃ nanoparticles with a particle size of 20 nm to 80 nm were then dried at 300℃ for 10 hours. -2 Dry under vacuum for 2 hours, then transfer to a desiccator to cool for later use.

[0042] Vacuum melting: Weigh the processed raw materials according to the target composition of Bi 45.0%, Sn 28.0%, In 18.0%, Ga 8.0%, Ce 0.3%, and Al2O3 0.7%, specifically: Bi 260.0g, Sn 161.8g, In 104.0g, Ga 46.2g, Ce 1.7g, and nano Al2O3 4.0g, and place them in a high-purity graphite crucible. Place the crucible in a vacuum induction melting furnace and evacuate to 3×10⁻⁶. -3 The pressure was increased to 0.06 MPa, and then high-purity argon (99.999%) was introduced into the furnace until the internal pressure was 0.06 MPa. Induction heating was then started. In the first stage, the temperature was increased to 350°C at a rate of 6°C / min and held for 30 min. In the second stage, the temperature was increased to 450°C at a rate of 5°C / min and held for 60 min. After the metal was completely melted into a bright liquid, electromagnetic stirring was used to mix the components evenly.

[0043] Nanoparticle dispersion strengthening treatment: Under the protection of argon gas and a melt temperature of 480℃, baked nano-Al2O3 powder is uniformly fed into the melt surface through a specially designed powder feeding device under argon gas flow (flow rate 0.3L / min). At the same time, an ultrasonic vibration probe is inserted into the melt surface at a depth of about 20mm, and the ultrasonic generator is started to treat the melt for 10min at a frequency of 30kHz and a power of 1000W.

[0044] Rapid solidification molding: The alloy melt, after nano-dispersion treatment, is rapidly poured into a metal mold preheated to 90°C. Through the mold's strong cooling design or in combination with an external cooling device, the solidification cooling rate of the alloy is controlled at 45°C / s. After complete solidification, the alloy material is removed.

[0045] Post-processing and forming: The obtained alloy material is annealed at 150℃ for 2 hours, and then cooled to room temperature in the furnace. Finally, according to the specific requirements of the sealing application (such as filaments, foils, pre-formed gaskets, etc.), the final usable sealing material products are prepared by means of extrusion, drawing, rolling or machining.

[0046] Example 5 This embodiment provides a low-melting-point bismuth-based alloy material suitable for sealing live leakage of sulfur hexafluoride (SF6) in gas-insulated metal-enclosed switchgear (GIS). Its preparation method includes the following steps: Raw material pretreatment: Bi, Sn, In, Ga, and Ce metal particles with a purity of 99.99% (mass percentage) were selected. The oxide scale was removed by sequentially polishing with 400-grit sandpaper, followed by ultrasonic cleaning in 10% dilute nitric acid solution for 5 minutes, rinsing three times with deionized water, and finally cleaning with anhydrous ethanol and drying in an 80℃ vacuum oven for 2 hours. Al₂O₃ nanoparticles with a particle size of 20 nm to 80 nm were then dried at 320℃ for 10 hours.-2 Dry under vacuum for 1.8 hours, then transfer to a desiccator to cool for later use.

[0047] Vacuum melting: Weigh the processed raw materials according to the target composition of Bi 49.0%, Sn 27.0%, In 16.0%, Ga 7.0%, Ce 0.5%, and Al2O3 0.5% (mass percentage). The specific masses are: Bi 260.0g, Sn 143.3g, In 84.9g, Ga 37.1g, Ce 2.7g, and nano-Al2O3 2.7g, and place them in a high-purity graphite crucible. Place the crucible in a vacuum induction melting furnace and evacuate to a vacuum of 2.5 × 10⁻⁶. -3 The pressure was increased to 0.1 MPa, and then high-purity argon (99.999%) was introduced into the furnace until the internal pressure was 0.1 MPa. Induction heating was then started. In the first stage, the temperature was increased to 380°C at a rate of 5°C / min and held for 25 min. In the second stage, the temperature was increased to 500°C at a rate of 2°C / min and held for 50 min. After the metal was completely melted into a bright liquid, electromagnetic stirring was used to mix the components evenly.

[0048] Nanoparticle dispersion strengthening treatment: Under the protection of argon gas and a melt temperature of 450℃, baked nano-Al2O3 powder is uniformly fed into the melt surface through a specially designed powder feeding device under argon gas flow (flow rate 0.5L / min). At the same time, an ultrasonic vibration probe is inserted into the melt surface at a depth of about 20mm, and the ultrasonic generator is started to treat the melt for 11 minutes at a frequency of 35kHz and a power of 750W.

[0049] Rapid solidification molding: The alloy melt, after nano-dispersion treatment, is rapidly poured into a metal mold preheated to 110°C. Through the mold's strong cooling design or in combination with an external cooling device, the solidification cooling rate of the alloy is controlled at 40°C / s. After complete solidification, the alloy material is removed.

[0050] Post-processing and forming: The obtained alloy material is annealed at 180℃ for 1.5h, and then cooled to room temperature in the furnace. Finally, according to the specific requirements of the sealing application (such as filaments, foils, pre-formed gaskets, etc.), the final usable sealing material products are prepared by means of extrusion, drawing, rolling or machining.

[0051] Comparative Example 1 This comparative example provides a bismuth-based alloy material, the preparation method of which includes the following steps: Raw material pretreatment: Bi and Sn metal particles with a purity of 99.99% (mass percentage) were selected and polished with 400-grit sandpaper to remove oxide scale. Then, they were ultrasonically cleaned in 10% dilute nitric acid solution for 5 minutes, rinsed three times with deionized water, and finally cleaned with anhydrous ethanol and dried in a vacuum drying oven at 80℃ for 2 hours.

[0052] Vacuum melting: Weigh the processed raw materials according to the target composition of Bi 58.0% and Sn 42.0%, specifically: Bi 260.0g, Sn 188.3g, and place them in a high-purity graphite crucible. Place the crucible in a vacuum induction melting furnace and evacuate to 2×10⁻⁶. - 3 The pressure was increased to 0.1 MPa, and then high-purity argon (99.999%) was introduced into the furnace until the internal pressure was 0.1 MPa. Induction heating was then started. In the first stage, the temperature was increased to 400°C at a rate of 5°C / min and held for 40 min. In the second stage, the temperature was increased to 600°C at a rate of 2°C / min and held for 40 min. After the metal was completely melted into a bright liquid, electromagnetic stirring was used to mix the components evenly.

[0053] Rapid solidification molding: The metal is heated to 450℃ to completely melt it, stirred electromagnetically for 5 minutes, and then directly poured into a preheated metal mold at 100℃. It is then allowed to cool naturally. No nanophase additions or ultrasonic treatments were performed.

[0054] Post-processing and forming: The obtained alloy material is annealed at 200℃ for 1 hour, and then cooled to room temperature in the furnace. Finally, according to the specific requirements of the sealing application (such as filaments, foils, pre-formed gaskets, etc.), the final usable sealing material product is prepared by means of extrusion, drawing, rolling or machining.

[0055] Test case The alloy materials prepared in Examples 1-5 and Comparative Example 1 were subjected to performance tests, and the test results are shown in Table 1.

[0056] Table 1 Performance Test Results

[0057] As shown in Table 1, the low-melting-point bismuth-based alloy material of this invention exhibits significant advantages in overall performance, with its melting point precisely designed within the critical range of 65-125℃. This temperature is lower than the typical local temperature rise generated by GIS equipment under rated load operation, allowing for safe implementation of sealing operations using the equipment's own operating heat or auxiliary heating with extremely low power consumption. This completely avoids the safety risks and power outages associated with traditional methods that require power outages or the application of high-temperature heat sources. The alloy's melting process is mild and controllable, preventing arcing or overheating and decomposition of SF6 gas. Through careful design of the alloy composition, its conductivity and coefficient of thermal expansion are well-matched with the metal casing of the GIS equipment. Furthermore, the innovative introduction of the nano-scale ceramic dispersed phase Al2O3 significantly enhances the alloy's strength and hardness without substantially increasing its melting point. In summary, the low-melting-point bismuth-based alloy proposed in this invention can well meet the requirements for sealing materials for energized sulfur hexafluoride (SF6) leaks in gas-insulated metal-enclosed switchgear (GIS).

[0058] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-melting-point bismuth-based alloy material, characterized in that, The alloy comprises the following components by mass percentage: Bi 45.0%–60.0%, Sn 25.0%–35.0%, In 10.0%–18.0%, Ga 3.0%–8.0%, Ce 0.1%–0.5%, and Al2O3 nano-ceramic phase 0.5%–1.5%; wherein the Al2O3 nano-ceramic phase is uniformly dispersed in the alloy matrix.

2. The low-melting-point bismuth-based alloy material according to claim 1, characterized in that, The Al2O3 nano-ceramic phase is composed of nanoparticles with a particle size of 20 nm to 80 nm.

3. The low-melting-point bismuth-based alloy material according to claim 1 or 2, characterized in that, The melting temperature of the low-melting-point bismuth-based alloy material is ≤150℃; and / or The solidification expansion coefficient of the low-melting-point bismuth-based alloy material is >0.5%; and / or The low-melting-point bismuth-based alloy material has a Brinell hardness >20HB; and / or The tensile strength of the low-melting-point bismuth-based alloy material is >52 MPa.

4. A method for preparing a low-melting-point bismuth-based alloy material as described in any one of claims 1 to 3, characterized in that, Includes the following steps: Raw material pretreatment: Surface cleaning and drying of high-purity Bi, Sn, In, Ga, and Ce metal raw materials; Vacuum melting: The pretreated metal raw materials are placed in a vacuum induction melting furnace according to the proportion, and heated and melted in stages under the protection of inert gas to fully melt and mix them evenly to obtain an alloy melt; Nanoparticle dispersion strengthening treatment: In the molten state, powder is fed into the alloy melt through a carrier gas and ultrasonic treatment is applied simultaneously to make the nanoparticles uniformly dispersed. Rapid solidification molding: The alloy melt, which has been strengthened by nano-dispersion, is poured into a preheated mold and rapidly cooled and solidified to obtain an alloy ingot.

5. The preparation method according to claim 4, characterized in that, The segmented heating and melting process under inert gas protection specifically includes: evacuating to a vacuum of 1×10⁻⁶. -3 ~5×10 -3 Pa, fill the furnace with high-purity argon gas until the pressure inside the furnace is 0.05~0.1 MPa; first, raise the temperature to 280~400℃ at 5~10℃ / min and hold for 20~40min, then raise the temperature to 450~600℃ at 2~5℃ / min and hold and stir for 40~60min.

6. The preparation method according to claim 4, characterized in that, The specific process parameters for the nano-dispersion strengthening treatment are as follows: the melt temperature is maintained at 400~500℃, the ultrasonic frequency is 20~40kHz, the ultrasonic power is 500~1000W, and the treatment time is 10~15min.

7. The preparation method according to claim 4, characterized in that, The carrier gas is argon, and the carrier gas flow rate is 0.1~0.6L / min.

8. The preparation method according to claim 4, characterized in that, During the rapid solidification molding process, the mold preheating temperature is 80~120℃, and the solidification cooling rate of the alloy is controlled at 30~50℃ / s.

9. The preparation method according to claim 4, characterized in that, The pretreatment specifically includes: grinding, pickling, cleaning and drying the metal raw materials, and drying the nano-ceramic powder.

10. The preparation method according to claim 4, characterized in that, The rapid solidification and molding step is followed by post-processing and molding: the alloy ingot is annealed and processed into a specific shape according to application requirements.

11. The preparation method according to claim 10, characterized in that, The annealing temperature for the annealing treatment is 150~300℃, and the treatment time is 0.5~2h.

12. The application of the low-melting-point bismuth-based alloy material according to any one of claims 1-3 in the preparation of a sulfur hexafluoride leakage sealing material for gas-insulated metal-enclosed switchgear.

Images