Vacuum arc-extinguishing chamber composite conductive rod special brazing filler metal and preparation process thereof

Abstract

This invention discloses a special brazing filler metal for vacuum interrupter composite conductive rods and its preparation process. The chemical composition, by mass percentage, is: Mn 38.0–39.0%, Ni 8.0–9.5%, Si 0.2–0.5%, with the balance being Cu. The copper-based brazing filler metal foil is prepared through a process of batching, smelting and protection, casting, hot rolling, cold rolling and annealing, and final product treatment. This copper-based brazing filler metal is designed for the service conditions of vacuum interrupter composite conductive rods, with a brazed joint interface bonding strength ≥220 MPa and an airtightness ≥4 × 10⁻⁶. ‑11 Pa·m 3 / s; Optimize the alloy element ratio to achieve synergistic effect of solid solution strengthening and wetting improvement, with no volatile harmful elements; The brazing filler metal is compatible with a brazing temperature window of 880~950℃, which can obtain high-quality welds with strong interface bonding, few defects and controllable thermal stress, suitable for mass production, and improve the long-term operational reliability and life of the copper-clad stainless steel conductive rod of the vacuum interrupter.

Description

Technical Field

[0001] This invention relates to the field of brazing technology, and in particular to a special brazing filler metal for a composite conductive rod in a vacuum interrupter and its preparation process. Background Technology

[0002] Vacuum interrupters are critical breaking components in medium- and high-voltage power systems. Their conductive rods typically employ a copper-clad stainless steel composite structure to balance high conductivity with high structural strength. The significant differences in the physicochemical properties (such as coefficients of thermal expansion, thermal conductivity, and crystal structure) between copper and stainless steel present a long-standing technical challenge in achieving a high-strength, airtight, and reliable metallurgical connection between them. Brazing is the primary process for achieving such dissimilar metal connections, and the performance of the brazing filler metal directly determines the quality of the joint.

[0003] In the prior art, the solders used for this type of connection mostly use conventional silver-based, copper-based, or nickel-based solders, which have the following limitations: 1. General-purpose silver-copper brazing filler metals (such as the BAg series) have a relatively moderate melting point and acceptable wettability, but insufficient high-temperature strength and poor creep resistance. Under long-term working temperature and electrodynamic action in the vacuum interrupter, the joints are prone to loosening. In addition, some elements have high vapor pressure, which may contaminate the ultra-high vacuum environment inside the interrupter.

[0004] 2. Although standard nickel-based brazing filler metals (such as the BNi series) have excellent high-temperature strength, their brazing temperature is usually too high (often above 1000℃), which aggravates the huge thermal stress caused by the difference in thermal expansion coefficients between copper and stainless steel, which can easily cause workpiece deformation or weld cracking, and requires extremely stringent process control.

[0005] 3. Ordinary copper-based brazing filler metals (such as pure copper or Cu-P series) have poor wettability on stainless steel and weak brazing seam forming ability. In addition, some copper-based brazing filler metals have too high melting points or contain volatile elements, making them unsuitable for the high cleanliness requirements of vacuum interrupters.

[0006] Furthermore, existing brazing filler metal formulations are not designed for the specific operating conditions of the conductive rod in the vacuum interrupter (such as high vacuum, current carrying, and resistance to thermal cycling and electrodynamic shock), making it difficult to achieve the best balance between joint strength, conductivity, thermal stability, and vacuum compatibility.

[0007] Therefore, developing a special brazing filler metal and its supporting manufacturing process specifically for composite conductive rods in vacuum interrupters that can systematically solve the above problems is of great significance for improving the overall performance, reliability and service life of vacuum interrupters. Summary of the Invention

[0008] Purpose of the invention: In view of the above problems, one purpose of the present invention is to provide a special brazing filler metal for composite conductive rods of vacuum interrupters, which is particularly suitable for high-strength, high-airtightness, and high-stability connections of dissimilar metals such as copper and stainless steel. Another purpose of the present invention is to provide a preparation process for the special brazing filler metal.

[0009] Technical solution: A special brazing filler metal for composite conductive rods in vacuum interrupters, with the following chemical composition by mass percentage: Mn 38.0-39.0%, Ni 8.0-9.5%, Si 0.2-0.5%, and the balance being Cu.

[0010] Furthermore, the mass ratio of Mn to Ni is 4:1 to 4.9:1.

[0011] Furthermore, the liquidus temperature of the special brazing filler metal is 890–930°C, and the solidus temperature is 840–870°C.

[0012] Furthermore, the special solder is in the form of foil strip with a nominal thickness of 0.03 to 0.08 mm and a width of 5 to 50 mm.

[0013] This invention relates to a special brazing filler metal optimized for vacuum interrupter conditions. The copper-based brazing filler metal system, composed of Cu, Mn, Ni, and Si, possesses unique comprehensive properties: a moderate melting point, good wettability to both copper and stainless steel, high joint strength, and excellent resistance to high-temperature oxidation and vacuum stability. This enables high-quality, high-reliability vacuum brazing connections for copper-stainless steel composite conductive rods. Through the synergistic effect of solid solution strengthening and improved wetting, the use of volatile harmful elements such as Cd, Zn, and Pb is avoided, ensuring a clean vacuum environment.

[0014] A process for preparing the above-mentioned brazing filler metal for the composite conductive rod of the vacuum interrupter includes the following steps: Step S1, Ingredient preparation: Select electrolytic copper, electrolytic manganese, electrolytic nickel and silicon copper intermediate alloy raw materials with a purity ≥99.95% according to the chemical composition of the special brazing filler metal, and mix them evenly to obtain the mixture; Step S2, Melting Protection: Place the mixture in a medium-frequency induction furnace and heat it to 1200-1280℃ under an argon protective atmosphere for melting. After the mixture has completely melted, refine it for 5-15 minutes. Step S3, Casting: Pour the molten alloy into a water-cooled copper mold to obtain an ingot; Step S4, hot rolling: Heat the ingot to 850-900℃ and hold for 2-3 hours, then perform multiple hot rolling passes, with a final rolling temperature of not less than 750℃, to obtain a hot-rolled strip with a thickness of 3-6mm. Step S5, Cold rolling and annealing: The hot-rolled strip is cold rolled in multiple passes, with a deformation of 15-25% per pass. After each 2-3 cold rolling passes, intermediate annealing is carried out at 600-650℃ and held for 1-2 hours. Step S6, Finished product processing: The strip cold-rolled to the nominal thickness is finished and slit, and then stress-relieved annealed at 450-500℃ for 0.5-1h to obtain the finished copper-based brazing foil strip.

[0015] Furthermore, the silicon-copper master alloy raw material is CuSi20.

[0016] Furthermore, multi-pass hot rolling involves 5 to 12 passes, while multi-pass cold rolling involves 4 to 9 passes.

[0017] The key to the preparation process of this invention lies in refining the as-cast microstructure through rapid cooling and obtaining foil strips with accurate dimensions, smooth surfaces, and uniform mechanical properties through precisely controlled rolling and annealing processes.

[0018] Beneficial effects: The present invention has the following advantages: 1. Highly Targeted and Superior Performance: The copper-based brazing filler metal is designed specifically for the service conditions of composite conductive rods in vacuum interrupters. It has a moderate melting point, with a brazing temperature between 880 and 950℃. The filler metal exhibits excellent wettability with copper and stainless steel base materials and has low vacuum vapor pressure, meeting the requirements for high strength and high airtightness of the joint. The interfacial bonding strength of the brazed joint is ≥220MPa, and the airtightness is ≥4×10⁻⁶. -11 Pa·m 3 / s; 2. The special brazing filler metal has a scientifically and rationally designed composition: By optimizing the alloy element ratio, it achieves a synergistic effect of solid solution strengthening and wetting improvement, and contains no volatile harmful elements, ensuring a clean vacuum environment; 3. High adaptability to manufacturing process: The special brazing filler metal is compatible with the brazing temperature window of 880~950℃, making process control simpler, reducing thermal stress, and suitable for large-scale production; 4. Stable and reliable preparation process: The proposed preparation process route is mature and controllable, which can effectively ensure the uniformity of the solder composition, the density of the structure, and the dimensional accuracy and surface quality of the product. 5. Improve product reliability: Vacuum brazing using this special brazing filler metal can produce high-quality welds with strong interface bonding, few defects, and controllable thermal stress, significantly improving the long-term operational reliability and lifespan of the copper-clad stainless steel conductive rod in the vacuum interrupter. Attached Figure Description

[0019] Figure 1 The image shows the microstructure of the copper-based solder foil obtained in Example 1. Figure 2 The image shows the microstructure of the interface of a copper-stainless steel joint brazed using the copper-based filler metal prepared in Example 1. Detailed Implementation

[0020] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0021] A special brazing filler metal for composite conductive rods in vacuum interrupters has the following chemical composition by mass percentage: Mn 38.0–39.0%, Ni 8.0–9.5%, Si 0.2–0.5%, with the balance being Cu. The preferred mass ratio of Mn to Ni is 4:1 to 4.9:1. The liquidus temperature of the special brazing filler metal is 890–930℃, and the solidus temperature is 840–870℃. The product form of the special brazing filler metal is foil strip with a nominal thickness of 0.03–0.08 mm and a width of 5–50 mm.

[0022] A process for preparing a special brazing filler metal for a composite conductive rod in a vacuum interrupter includes the following steps S1 to S6.

[0023] Step S1, Ingredient Preparation: According to the chemical composition of the special brazing filler metal, select electrolytic copper, electrolytic manganese, electrolytic nickel and silicon copper master alloy raw materials (e.g., CuSi2O) with a purity ≥99.95%, and mix them evenly to obtain the mixture; Step S2, Melting Protection: Place the mixture in a medium-frequency induction furnace and heat it to 1200-1280℃ under an argon protective atmosphere for melting. After the mixture has completely melted, refine it for 5-15 minutes. Step S3, Casting: Pour the molten alloy into a water-cooled copper mold to obtain an ingot; Step S4, Hot rolling: Heat the ingot to 850-900℃ and hold for 2-3 hours, then perform multiple hot rolling passes. The final rolling temperature is not lower than 750℃ to obtain a hot-rolled strip with a thickness of 3-6mm. The multiple hot rolling passes are 5-12 passes. Step S5, Cold Rolling and Annealing: The hot-rolled strip is subjected to multiple cold rolling passes, with a deformation of 15-25% per pass. After each 2-3 cold rolling passes, intermediate annealing is carried out at 600-650℃ for 1-2 hours. The multiple cold rolling passes are 4-9 passes. Step S6, Finished product processing: The strip cold-rolled to the nominal thickness is finished and slit, and then stress-relieved annealed at 450-500℃ for 0.5-1h to obtain the finished copper-based brazing foil strip.

[0024] The present invention has the following advantages: 1. Highly Targeted and Superior Performance: The copper-based brazing filler metal is designed specifically for the service conditions of composite conductive rods in vacuum interrupters. It has a moderate melting point, with a brazing temperature between 880 and 950℃. The filler metal exhibits excellent wettability with copper and stainless steel base materials and has low vacuum vapor pressure, meeting the requirements for high strength and high airtightness of the joint. The interfacial bonding strength of the brazed joint is ≥220MPa, and the airtightness is ≥4×10⁻⁶. -11Pa·m 3 / s; 2. The special brazing filler metal has a scientifically and rationally designed composition: By optimizing the alloy element ratio, it achieves a synergistic effect of solid solution strengthening and wetting improvement, and contains no volatile harmful elements, ensuring a clean vacuum environment; 3. High adaptability to manufacturing process: The special brazing filler metal is compatible with the brazing temperature window of 880~950℃, making process control simpler, reducing thermal stress, and suitable for large-scale production; 4. Stable and reliable preparation process: The proposed preparation process route is mature and controllable, which can effectively ensure the uniformity of the solder composition, the density of the structure, and the dimensional accuracy and surface quality of the product. 5. Improve product reliability: Vacuum brazing using this special brazing filler metal can produce high-quality welds with strong interface bonding, few defects, and controllable thermal stress, significantly improving the long-term operational reliability and lifespan of the copper-clad stainless steel conductive rod in the vacuum interrupter.

[0025] Example 1

[0026] This invention relates to a special brazing filler metal for composite conductive rods in vacuum interrupters and its preparation process: Step S1, Ingredients: Weigh electrolytic copper, electrolytic manganese, electrolytic nickel and Cu-10%Si master alloy, calculate and weigh according to the following mass percentages: Mn 38.5%, Ni 8.5%, Si 0.35%, balance Cu, and mix evenly to obtain a mixture.

[0027] Step S2, Melting Protection: Place the mixture in a graphite crucible of a medium-frequency induction furnace, introduce high-purity argon gas as a protective atmosphere, heat to 1230℃ for melting, and refine for 10 minutes after the mixture has completely melted.

[0028] Step S3, Casting: The molten alloy is quickly poured into a flat copper mold cooled by circulating water to obtain an ingot with a thickness of about 20mm.

[0029] Step S4, Hot Rolling: After milling the surface of the ingot, heat it to 870℃ and hold it for 2.5 hours. Then, roll it through multiple passes on a hot rolling mill to obtain a hot-rolled strip with a thickness of 5mm. The final rolling temperature is about 780℃.

[0030] Step S5, Cold Rolling and Annealing: The hot-rolled strip is cold-rolled in multiple passes to achieve a target thickness of 0.05 mm. The deformation per pass is approximately 20%, and intermediate annealing is performed at 620°C between every two passes, held for 1.2 hours under argon protection.

[0031] Step S6, Finished Product Processing: The cold-rolled strip to the target thickness is finished and slit, then stress-relieved annealed at 480℃ for 40 minutes to obtain a copper-based solder foil strip with a width of 20mm and a smooth surface. Figure 1The image shows its microstructure. Tests indicate that its liquidus temperature is approximately 930℃ and its solidus temperature is approximately 850℃.

[0032] The copper-based brazing filler metal prepared in Example 1 was used for brazing the composite conductive rod of the vacuum interrupter. The composite conductive rod includes a 316L stainless steel core rod (18 mm in diameter and 350 mm in length) and an oxygen-free copper outer layer (56 mm in initial outer diameter and 20 mm in inner diameter). The brazing process was vacuum brazing at a temperature of 910°C for 25 min.

[0033] The performance of the brazed conductive rod was tested, and the test results are as follows: (1) Mechanical properties of brazed joint: The tensile strength of the brazed joint is 225 MPa, and the fracture occurs in the oxygen-free copper base material; (2) Interface structure: The brazing layer is continuous and dense, with a thickness of 30μm, and there are no cracks or pores at the interface with the copper and stainless steel base materials. Figure 2 Microscopic morphology of the interface of the brazed copper-stainless steel joint. (3) Air tightness: Helium mass spectrometry leak detection test showed that the air tightness was 4.2 × 10⁻⁶. -11 Pa·m 3 / s; (4) Straightness: The straightness tolerance over a length of 350mm is 0.05mm; (5) Corrosion resistance: After 1000 hours of neutral salt spray corrosion test, there was no corrosion leakage at the joint.

[0034] Comparative Example 1 A nickel-based solder and its preparation process: Step P1, Ingredients: Weigh electrolytic nickel plate, metallic chromium block, pure iron block, ferrosilicon alloy (Si mass percentage 75%), ferroboron alloy (B mass percentage 20%), and high-purity graphite powder. Calculate and weigh according to the following mass percentages: Cr 7.2%, Si 4.5%, B 2.8%, Fe 3.0%, C 0.04%, balance Ni. Mechanically mix evenly to obtain a mixture.

[0035] Step P2, Vacuum Melting: The mixture is placed into the corundum crucible of the vacuum induction melting furnace, and a vacuum of 3.0 × 10⁻⁶ is drawn. - 2 Pa, slowly heat to 1520℃ for melting, hold for 2 hours, and perform electromagnetic stirring 3 times during the process to ensure uniform composition. Then remove slag and let stand for 15 minutes.

[0036] Step P3, casting: Pour the molten material into a cylindrical steel mold preheated to 350°C, and air cool it to room temperature to obtain an ingot with a diameter of 80mm.

[0037] Step P4, hot rolling: The ingot is rolled into a strip, heated to 800℃ and held for 1.5 hours, and then rolled into a 5mm hot-rolled strip on a rolling mill.

[0038] Step P5, Cold Rolling and Annealing: The rolled strip is subjected to multiple cold rolling passes, gradually rolling it to a foil strip with a thickness of 0.04 mm. The deformation amount of each cold rolling pass is about 15%, and an intermediate annealing is performed at 850℃ between every two rolling passes, held at that temperature for 45 min, under hydrogen protection.

[0039] Step P6, Finished Product Annealing: Place the shaped foil strip into a vacuum annealing furnace, maintaining a vacuum level of 2.0 × 10⁻⁶. -3 Pa was heated to 620°C at a rate of 5°C / min, held for 1.5 hours, and then cooled to room temperature in the furnace to obtain a bright nickel-based solder foil strip.

[0040] The nickel-based brazing filler metal prepared in Comparative Example 1 was used for brazing the composite conductive rod of the vacuum interrupter. The composite conductive rod includes a 316L stainless steel core rod (diameter 18mm, length 350mm) and an oxygen-free copper outer layer (initial outer diameter 56mm, inner hole 20mm). The brazing process adopted vacuum brazing, the brazing temperature was 1050℃, and the holding time was 60min.

[0041] The performance of the brazed conductive rod was tested, and the test results are as follows: (1) Mechanical properties of brazed joint: tensile strength of brazed joint is 235 MPa; (2) Air tightness: 3.5 × 10 -11 Pa·m 3 / s; (3) Straightness: The straightness tolerance over a length of 350mm is 0.06mm.

[0042] As can be seen from the comparison between Example 1 and Comparative Example 1, the copper-based special brazing filler metal of the present invention has a reasonable composition design and a stable and reliable preparation process. The composite conductive rod after brazing exhibits excellent performance in terms of mechanical properties, electrical conductivity, airtightness, and dimensional accuracy, and fully meets the requirements for use in vacuum interrupters.

Claims

1. A special brazing filler metal for a composite conductive rod in a vacuum interrupter, characterized in that: Its chemical composition by mass percentage is: Mn 38.0-39.0%, Ni 8.0-9.5%, Si 0.2-0.5%, with the balance being Cu.

2. The brazing filler metal for a composite conductive rod in a vacuum interrupter according to claim 1, characterized in that: The mass ratio of Mn to Ni is 4:1 to 4.9:

1.

3. The special brazing filler metal for a composite conductive rod in a vacuum interrupter according to claim 1, characterized in that: The liquidus temperature of the special brazing filler metal is 890–930℃, and the solidus temperature is 840–870℃.

4. The brazing filler metal for a composite conductive rod in a vacuum interrupter according to claim 1, characterized in that: The special solder is in the form of foil strip, with a nominal thickness of 0.03 to 0.08 mm and a width of 5 to 50 mm.

5. A process for preparing the special brazing filler metal for the composite conductive rod of the vacuum interrupter according to any one of claims 1 to 4, characterized in that... Includes the following steps: Step S1, Ingredient preparation: Select electrolytic copper, electrolytic manganese, electrolytic nickel and silicon copper intermediate alloy raw materials with a purity ≥99.95% according to the chemical composition of the special brazing filler metal, and mix them evenly to obtain the mixture; Step S2, Melting Protection: Place the mixture in a medium-frequency induction furnace and heat it to 1200-1280℃ under an argon protective atmosphere for melting. After the mixture has completely melted, refine it for 5-15 minutes. Step S3, Casting: Pour the molten alloy into a water-cooled copper mold to obtain an ingot; Step S4, hot rolling: Heat the ingot to 850-900℃ and hold for 2-3 hours, then perform multiple hot rolling passes, with a final rolling temperature of not less than 750℃, to obtain a hot-rolled strip with a thickness of 3-6mm. Step S5, Cold rolling and annealing: The hot-rolled strip is cold rolled in multiple passes, with a deformation of 15-25% per pass. After each 2-3 cold rolling passes, intermediate annealing is carried out at 600-650℃ and held for 1-2 hours. Step S6, Finished product processing: The strip cold-rolled to the nominal thickness is finished and slit, and then stress-relieved annealed at 450-500℃ for 0.5-1h to obtain the finished copper-based brazing foil strip.

6. The preparation process according to claim 1, characterized in that: The raw material for the silicon-copper master alloy is CuSi2O.

7. The preparation process according to claim 1, characterized in that: Multi-pass hot rolling has 5 to 12 passes, while multi-pass cold rolling has 4 to 9 passes.

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