A method for preparing a high-density copper-chromium contact and the copper-chromium contact itself.

Abstract

This application discloses a method for preparing a high-density copper-chromium contact and the copper-chromium contact itself. The method includes: weighing copper powder and chromium powder according to a ratio, controlling the mass fraction of chromium powder to be 39% to 51%, and mixing the powders by ball milling to obtain a modified mixed powder; loading the modified mixed powder into a mold, molding it, holding the pressure for a period of time, and then releasing the pressure to obtain a copper-chromium blank with a density of 92% to 95%; placing a pure copper sheet on top of the copper-chromium blank, and then subjecting the copper-chromium blank and the pure copper sheet to sand embedding treatment; sintering the sand-embedded copper-chromium blank and the pure copper sheet to obtain a copper-chromium sintered blank; and machining the copper-chromium sintered blank by turning and milling to obtain a high-density copper-chromium contact. This application adopts a vacuum buried sand liquid phase sintering process, which effectively solves the technical problems of high difficulty and low density of copper-chromium contacts with chromium content of less than 50% prepared by the existing metallurgical melting and infiltration method. The density of the finished copper-chromium contact is ≥99%, which can be adapted to various contacts such as CuCr40, CuCr45 and CuCr50.

Description

Technical Field

[0001] This application relates to the field of electrical contact technology, and in particular to a method for preparing a high-density copper-chromium contact and the copper-chromium contact itself. Background Technology

[0002] In existing power facilities operating at voltage levels of 40.5kV-12kV, vacuum switches occupy a dominant position, and the contact material, as a key material in vacuum switches, directly affects their application range. Copper-chromium contacts, due to their excellent breaking capacity, good withstand voltage characteristics, good resistance to arc erosion, and resistance to welding, have been widely used in vacuum switches.

[0003] Currently, copper-chromium contacts are mainly prepared using powder metallurgy melting and infiltration. First, a porous and interconnected chromium skeleton is obtained by molding chromium powder and vacuum sintering. Molten high-purity copper liquid is then fully infiltrated into the pores of the chromium skeleton by capillary action. Densification melting and infiltration are completed by heat preservation and pressure holding. After cooling, copper-chromium contacts with a density of ≥95% are obtained through finishing and processing.

[0004] Although the metallurgical melting method can produce copper-chromium contacts with a density of ≥95%, this method is suitable for the preparation of copper-chromium contacts with a relatively high chromium content (above 50%). For copper-chromium contacts with a chromium content of less than 50%, it is difficult to prepare them using the melting process. At the same time, the quality of copper-chromium contacts with a density of ≥99% is difficult to guarantee. Summary of the Invention

[0005] The main objective of this application is to provide a method for preparing high-density copper-chromium contacts and a copper-chromium contact, aiming to solve the technical problems of difficulty in preparing copper-chromium contacts with a chromium content of less than 50% and low density of copper-chromium contacts by metallurgical infiltration.

[0006] To achieve the above objectives, this application provides a method for preparing a high-density copper-chromium contact, comprising the following steps: Weigh out copper powder and chromium powder according to the ratio, control the mass fraction of chromium powder to be 39% to 51%, and mix them by ball milling to obtain modified mixed powder. The modified mixed powder is loaded into a mold and molded. After holding the pressure for a period of time, the pressure is released to obtain a copper-chromium blank with a density of 92% to 95%. A pure copper sheet is placed on top of the copper-chromium blank, and then the copper-chromium blank and the pure copper sheet are subjected to sand embedding treatment together. The copper-chromium blank after sand embedding treatment is sintered with the pure copper sheet. The temperature is increased by gradient heating during the sintering process and cooled after sintering to obtain the copper-chromium sintered blank. The copper-chromium sintered billet is machined into shape by turning and milling to obtain the high-density copper-chromium contact.

[0007] Optionally, the method of mixing powder by ball milling is as follows: the ball-to-material ratio of a single tank is controlled to be 1:1 to 1:1.3, the ball milling time is 8h to 10h, stainless steel balls are used as the grinding medium, and the sharp corners of chromium particles are blunted and the surface activity and flowability of chromium powder are improved during the ball milling process.

[0008] Optionally, the modified mixed powder contains 0.3‰ to 0.5‰ carbon black.

[0009] Optionally, the inner wall of the mold cavity is sprayed with a release agent; the number of vibrations of the mandrel during the compression molding process is controlled to be 10 to 15 times; the pressure holding time is 0.1s to 0.3s, and the pressure release time is 1s to 1.5s.

[0010] Optionally, the size of the pure copper sheet is adapted to the size of the copper-chromium billet, the sand used in the sand embedding treatment is alumina sand, the particle size of the alumina sand is controlled between 20 mesh and 100 mesh, and a layer of alumina sand is laid at the bottom of the copper-chromium billet.

[0011] Optionally, during the sintering process, the vacuum level is controlled to be ≤1×10⁻⁶. -1 Pa, the gradient heating rate is 3℃ / min~5℃ / min, the final firing temperature is controlled at 1150℃~1380℃, and the holding time is 1h~2h.

[0012] Optionally, the method for cooling down after sintering is as follows: after sintering, the furnace is cooled down, and when the furnace temperature drops to 500°C, the fan is turned on to accelerate the cooling.

[0013] Optionally, the density of the prepared copper-chromium sintered billet is ≥99%.

[0014] In addition, to achieve the above objectives, this application also provides a copper-chromium contact, which is prepared by the above-described method.

[0015] Optionally, the copper-chromium contact is a CuCr40 contact, a CuCr45 contact, or a CuCr50 contact; The copper-chromium contact has a density of ≥99% and is suitable for vacuum switches with voltage levels of 12kV to 40.5kV.

[0016] The beneficial effects that this application can achieve are as follows: 1. Precise proportioning and mixing to overcome the bottleneck in the preparation of low-chromium grades: This application limits the proportion of chromium powder to a wide range of 39% to 51% by mass, which is suitable for the preparation of low-chromium copper-chromium contacts such as CuCr40 and CuCr45. It overcomes the shortcomings of traditional metallurgical melting and infiltration methods, such as poor adaptability to low-chromium proportions, high molding difficulty, and difficulty in controlling composition. By combining ball milling and powder mixing, the copper-chromium powder is uniformly mixed. From the source of raw material proportioning and mixing, the stable and controllable preparation of low-chromium copper-chromium contacts is achieved, which solves the core problems of compositional segregation, unstable performance, and high difficulty in mass production of low-chromium copper-chromium contacts in traditional processes.

[0017] 2. Precise molding lays the foundation for high density: This application uses controllable molding and a matching exclusive pressure holding and decompression process to precisely prepare 92% to 95% medium-high density copper-chromium blanks. This ensures the structural strength and integrity of the copper-chromium blanks while retaining uniform micro-porosity. This allows for smooth gas discharge and full molten copper wetting and filling during subsequent sintering, completely improving the defects of disordered pore structure and low upper limit of sintering density in traditional copper-chromium blanks. This solves the technical problem of low density in finished copper-chromium contact products from the molding process.

[0018] 3. This application, by adding a pure copper sheet to the top of the copper-chromium blank and combining it with full-area sand embedding treatment, can effectively compensate for the evaporation loss of copper components during vacuum high-temperature sintering, accurately stabilize the composition system of low-chromium copper-chromium alloy, and avoid compositional imbalance and performance degradation of low-chromium contacts due to copper loss; at the same time, the sand embedding structure can constrain the deformation of the blank, achieve uniform heat transfer, and eliminate the problems of blank dispersion, warping, and local porosity during sintering, further ensuring the forming quality and microstructure uniformity of low-chromium copper-chromium contacts.

[0019] 4. This application adopts a gradient heating mode in the sintering stage, which can achieve uniform heating of the green blank, stable gas precipitation, and slow release of thermal stress, avoiding defects such as bulging, microcracks, and residual pores caused by rapid heating. It allows the copper phase to be fully liquid-phase wetted and fills the micropores, achieving a dense metallurgical bond between the copper and chromium phases, and significantly improving the overall density of the copper-chromium sintered blank. It completely solves the problems of low density and many internal defects of copper-chromium contacts in traditional processes from the core sintering process. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation method of the high-density copper-chromium contact in the embodiments of this application; Figure 2 This is a schematic diagram of the buried sand liquid phase sintering charging in the embodiments of this application; Figure 3 This is an electron microscope image of the metallographic structure of the CuCr40 contact in Example 1 of this application; Figure 4 This is an electron microscope image of the metallographic structure of the CuCr45 contact in Example 2 of this application; Figure 5Electron micrograph of the metallographic structure of the CuCr50 contact in Example 3 of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0022] Reference Figure 1 This application provides a method for preparing a high-density copper-chromium contact, comprising the following steps: S1. Weigh copper powder and chromium powder according to the ratio, control the mass fraction of chromium powder to be 39% to 51%, and mix them by ball milling to obtain modified mixed powder.

[0023] S2. The modified mixed powder is loaded into the mold and molded. After holding the pressure for a period of time, the pressure is released to obtain a copper-chromium blank with a density of 92% to 95%.

[0024] S3. Place a pure copper sheet on top of the copper-chromium blank, and then perform sand embedding treatment on the copper-chromium blank and the pure copper sheet together.

[0025] S4. The copper-chromium blank after sand embedding treatment is sintered with pure copper sheets. The temperature is increased by gradient during the sintering process, and then cooled after sintering to obtain the copper-chromium sintered blank.

[0026] S5. The copper-chromium sintered billet is machined into shape by turning and milling to obtain a high-density copper-chromium contact.

[0027] Specifically, step S1 controls the chromium powder mass fraction between 39% and 51% by limiting the ratio of copper powder to chromium powder, matching the performance ratio requirements of copper-chromium contacts used in mainstream medium and high voltage switches. This is combined with a physical modification method of ball milling to prepare the mixed powder. From the perspective of powder metallurgy forming principles, precise component ratios can ensure the stability of the finished contact's composition from the source, avoiding the defects of component segregation and large performance fluctuations in traditional processes. The ball milling process can mechanically activate the powder particles, passivate the sharp corners of the chromium powder particles, improve powder flowability, and break up the agglomeration of powder particles, achieving uniform mixing of copper and chromium powders. This lays the foundation for the uniformity of the subsequent cold-pressed blank and the stability of the interface bonding during the sintering process, ensuring from the raw material level that the subsequent finished product is free from component segregation and uneven structure.

[0028] Step S2 employs a compression molding process, precisely controlling the molding pressure, holding pressure, and depressurization parameters to prepare a copper-chromium blank with a density of 92%–95%. Analysis of the compatibility principle between copper-chromium blank forming and sintering indicates that this density range represents a highly dense pre-formed state. This ensures sufficient structural strength for the copper-chromium blank, preventing damage and deformation during transport and sand embedding, while retaining a small amount of uniform porosity. This provides channels for gas expulsion and trace copper infiltration during subsequent vacuum liquid phase sintering, preventing blistering and porosity defects caused by residual gas in closed pores within the copper-chromium blank after sintering. Simultaneously, the segmented holding and depressurization control effectively counteracts the elastic after-effects of powder molding, preventing expansion and cracking of the copper-chromium blank after demolding, ensuring the overall structural integrity of the copper-chromium blank, and providing a qualified copper-chromium blank foundation for subsequent near-net-shape forming processing.

[0029] Step S3 employs a composite pretreatment method of stacking pure copper sheets on top of the copper-chromium billet and embedding sand throughout, which is the core pretreatment process adapted to vacuum liquid phase sintering in this application. Analysis of the characteristics of the vacuum sintering environment reveals that copper components are highly susceptible to evaporation and melting under high-temperature conditions, leading to component loss and morphological distortion in the finished product. The pure copper sheets on top can provide trace amounts of copper replenishment during the sintering melting stage, compensating for high-temperature copper evaporation losses, accurately controlling the component ratio of the finished product, and simultaneously enabling copper resource recycling and reuse. The external sand-embedded structure provides comprehensive shaping and constraint for the copper-chromium billet, limiting the flow and deformation of the molten copper, completely solving the problems of billet collapse and dimensional deviations in unconstrained sintering. Simultaneously, the sand-embedded medium creates a uniform heat transfer and buffering environment, ensuring uniform heating of the copper-chromium billet and guaranteeing simultaneous densification during subsequent sintering.

[0030] Step S4 employs a sintering process involving gradient heating, precise heat preservation, and controlled cooling under vacuum conditions. This is the core process for achieving high density and high performance in copper-chromium contacts. From the perspective of liquid-phase sintering mechanisms, the gradient heating mode allows the internal temperature of the copper-chromium billet to rise at a uniform rate, avoiding the problems of bulging and cracking caused by excessive temperature differences between the inside and outside of the billet and rapid expansion of internal gases due to rapid heating. This ensures that the internal gases of the copper-chromium billet are slowly and fully discharged, reducing the oxygen and nitrogen impurity content of the finished product. The heat preservation process within a constant temperature range allows the copper phase to fully melt and uniformly wet the chromium phase skeleton, achieving a tight bond at the copper-chromium interface. Relying on the capillary filling effect of the liquid phase, the internal porosity of the billet is completely eliminated. Combined with the staged forced cooling process, the alloy microstructure can be stabilized, and the agglomeration and coarsening of chromium phase particles can be inhibited. Ultimately, a copper-chromium sintered billet with a uniform structure and extremely high density is obtained, fundamentally solving the technical pain points of insufficient density and uneven structure in traditional sintering.

[0031] Step S5 employs a milling and turning process to precision-machine the sintered billet, adapting to the finished product preparation requirements of high-density sintered billets. From the perspective of product forming and precision control, the copper-chromium sintered billet prepared by the aforementioned process is a high-density, high-precision near-net-shape blank. The billet has a regular shape, uniform internal structure, and no deformation or cracking defects, eliminating the need for large-mass cutting and significantly improving raw material utilization. Sequential milling and turning can precisely adjust the shape, dimensions, and end-face accuracy according to the structural dimensional requirements of the contact product, avoiding dimensional deviations and surface damage problems that are prone to occur in one-time machining. While fully preserving the excellent mechanical and electrical properties of the copper-chromium sintered billet, it produces finished copper-chromium contacts with high dimensional accuracy, regular structure, and strong service stability, meeting the precision assembly and long-term service requirements of high-voltage vacuum switches.

[0032] In other embodiments, in step S1, the method of mixing powder by ball milling can be: controlling the ball-to-material ratio of a single tank to be 1:1 to 1:1.3, and the ball milling time to be 8h to 10h. Stainless steel balls can be used as the grinding medium. During the ball milling process, the sharp corners of chromium particles are blunted, and the surface activity and flowability of chromium powder are improved.

[0033] In this embodiment, the ball milling and powder mixing process in step S1 can use stainless steel balls as the dedicated grinding medium, limiting the ball-to-material ratio per tank to 1:1 to 1:1.3 and the ball milling time to 8 to 10 hours, to achieve refined mechanical modification of the copper-chromium mixed powder. Controlling the ball-to-material ratio within this range ensures a moderate frequency of contact between the grinding medium and the powder material. This avoids insufficient grinding impact force, inadequate powder modification, and particle agglomeration due to an excessively small ball-to-material ratio, while also preventing over-grinding, disordered particle size gradient, and increased fine powder, which could negatively impact subsequent pressing and molding performance. The controllable ball milling time of 8 to 10 hours is the optimal modification range. Too short a time will result in incomplete blunting of chromium particle sharpness, low powder activation, and poor copper-chromium mixing uniformity; too long a time can easily lead to powder work hardening and surface activity decay, thus reducing the bonding performance of the sintering interface. Leveraging the high strength, high hardness, and impurity-free properties of stainless steel balls, the ball milling process effectively blunts the sharp edges of high-hardness chromium particles through continuous high-frequency impact, kneading, and shearing, eliminating the microscopic bridging effect that easily occurs in chromium particles and significantly improving the overall flowability and packing uniformity of the powder. At the same time, mechanical force activates the powder surface, enhancing the surface activity of chromium powder and strengthening the interfacial wetting ability and bonding strength of the copper and chromium phases during subsequent sintering. This addresses the problems of uneven powder mixing, forming pore defects, and segregation of sintered structure in traditional processes from the perspective of powder microstructure, providing a high-quality powder raw material foundation for the preparation of highly uniform and high-density copper-chromium contacts.

[0034] In other embodiments, in step S1, 0.3‰ to 0.5‰ of carbon black is added to the modified mixed powder.

[0035] In this embodiment, carbon black is added to the modified mixed powder prepared in step S1 at a concentration of 0.3‰ to 0.5‰ of the total powder mass. This is a key auxiliary process for optimizing powder purity and sintering quality. Copper and chromium powders readily adsorb oxygen, water vapor, and various gaseous impurities during storage and ball milling. Simultaneously, an oxide film easily forms on the powder surface. If directly pressed and sintered, oxide inclusions and residual gases will form micropores, inclusions, and loose defects inside the green body, significantly reducing the contact density and electrical and mechanical properties. This embodiment precisely limits the amount of carbon black added to 0.3‰ to 0.5‰. This trace amount of doping can undergo a thermal carbon reduction reaction under the high-temperature environment of vacuum liquid-phase sintering. The carbon black can fully react with oxides, adsorbed oxygen, and combined oxygen on the powder surface, reducing the metal oxides to a pure metal phase. Simultaneously, gaseous products are generated and discharged with the vacuum system, achieving efficient degassing and deoxygenation of the green body throughout the process. This significantly reduces the oxygen and nitrogen impurity content inside the copper-chromium contacts from the source, purifying the copper-chromium two-phase interface. When the carbon black addition is less than 0.3‰, the reduction and deoxygenation dosage is insufficient, failing to completely eliminate oxidized inclusions in the powder, resulting in limited degassing effect. When the addition is greater than 0.5‰, the excess carbon black cannot react completely, and the residual carbon phase will remain inside the sintered blank, forming non-metallic inclusion defects, disrupting the continuity of the copper-chromium matrix, and reducing the conductivity and arc erosion resistance of the copper-chromium contacts. Trace carbon black doping within this parameter range can fully utilize the thermal carbon reduction purification effect, ensuring high powder purity and high interface cleanliness, while also avoiding excess impurity residues, further optimizing the sintering densification effect, and improving the uniformity of the metallographic structure and service stability of the copper-chromium contacts.

[0036] In other embodiments, in step S2, the inner wall of the mold cavity is sprayed with a release agent, and the number of vibrations of the mandrel during the compression molding process is controlled to be 10 to 15 times, the pressure holding time is 0.1s to 0.3s, and the pressure release time is 1s to 1.5s.

[0037] This embodiment implements multi-parameter refined control of the cold pressing process in step S2. By spraying a release agent onto the inner wall of the mold, limiting the number of mandrel vibrations to 10-15 times, and matching the holding pressure time to 0.1-0.3 seconds and the pressure release time to 1-1.5 seconds, near-net-shape forming of copper-chromium blanks with high uniformity, high integrity, and high dimensional accuracy is achieved. The uniform spraying of the release agent onto the inner wall of the mold cavity forms a uniform insulating lubricating layer, effectively reducing the frictional resistance between the mixed powder and the mold cavity wall. This significantly reduces adhesion, chipping, and roughening during demolding, protecting the precision mold structure, extending its service life, and ensuring a smooth surface and complete contour of the blank after demolding, avoiding defects such as missing corners, chipping, and surface cracks caused by demolding damage. The preferred release agent is a powder metallurgy-specific release agent that is high-temperature residue-free, low-volatility, non-carburizing, and does not react with copper-chromium powder, such as water-soluble graphite release agents, boron nitride release agents, and water-soluble polymer release agents.

[0038] During the molding process, the number of vibrations of the mandrel is controlled to be 10 to 15 times. The micro-vibration can promote the secondary flow and rearrangement of the powder inside the mold, eliminate local bridging, voids and uneven filling problems, make the powder density in each area of ​​the mold cavity more consistent, ensure the overall density of the molded blank is uniform, and avoid problems such as uneven local shrinkage, warping deformation and microstructure differences caused by density differences in the subsequent sintering process.

[0039] The precise pressure holding setting of 0.1s to 0.3s allows for the tight packing and positioning of powder particles under stable pressure, enabling sufficient plastic deformation of the powder and tight particle interlocking. This results in a stable 92% to 95% optimal green body density, while avoiding stress accumulation and excessive internal residual stress caused by excessively long pressure holding. Combined with a slow, controllable pressure release method of 1s to 1.5s, the internal compressive stress of the copper-chromium green body is released slowly and evenly, effectively offsetting the inherent elastic aftereffect of powder pressing and preventing defects such as rapid springback, delamination, cracking, and volume expansion caused by instantaneous pressure release.

[0040] This embodiment optimizes the entire process of demolding, material distribution, pressure holding, and pressure release by coupling parameters. This ensures that the copper-chromium billet has a complete structure, uniform density, and extremely low internal stress from the source of forming, providing a reliable billet foundation for subsequent sand sintering to achieve deformation-free, highly dense, and highly uniform forming.

[0041] In other embodiments, in step S3, the size of the pure copper sheet is adapted to the size of the copper-chromium billet, the sand used for the sand embedding treatment is alumina sand, the particle size of the alumina sand is controlled between 20 mesh and 100 mesh, and a layer of alumina sand is laid on the bottom of the copper-chromium billet.

[0042] like Figure 2 As shown, this embodiment refines the pre-treatment structure and filler parameters for sand embedding in step S3. Pure copper sheets with dimensions compatible with the copper-chromium blank are used in conjunction with 20-100 mesh alumina sand to complete the overall sand embedding and encapsulation. An alumina sand pad is pre-laid on the graphite crucible at the bottom of the copper-chromium blank, forming a standardized sand embedding structure with bottom sand support, a centered blank, a compatible top sheet, and full coverage. This further improves the forming stability and compositional uniformity of vacuum liquid phase sintering. The matching size of the pure copper sheets with the copper-chromium blank ensures that the copper addition range completely covers the effective working surface of the copper-chromium blank during the sintering and melting stage, achieving uniform micro-copper infiltration throughout the entire area. This avoids compositional inconsistencies caused by excessive or insufficient copper addition in certain areas due to copper sheet sizes that are too large or too small. This significantly improves the batch-to-batch consistency of chromium content, density, and hardness performance of the finished product. Simultaneously, the matching size structure reduces the ineffective loss of excess copper material and improves the copper sheet recycling rate.

[0043] In this embodiment, 20-100 mesh alumina sand is selected as the burial medium. This material is resistant to high temperature, does not decompose or soften under high temperature vacuum, and does not react with copper or chromium metals. It has extremely strong chemical inertness, which can completely avoid the introduction of impurities during sintering. At the same time, alumina sand in this particle size range has both reasonable packing gap and support strength. When the particle size is greater than 20 mesh, the gap between the sand bodies is too large and the support is loose, which cannot effectively restrain the flow of molten copper and easily causes the billet to collapse and deform. When the particle size is less than 100 mesh, the sand body is too fine and has poor air permeability, which makes it difficult for the gas inside the copper-chromium billet to escape, which easily causes bulging and porosity defects. A separate alumina sand pad is laid at the bottom to completely isolate the copper-chromium blank, preventing it from directly contacting the bottom surface of the graphite crucible. This prevents uneven heat transfer due to localized overheating at high temperatures, which can lead to inconsistent sintering shrinkage of the blank's bottom surface, sticking to the crucible, rough bottom surface, and localized copper deficiency. Combined with the sand-covered structure covering the entire perimeter and top, the blank is placed in a uniform, stable, and inert isothermal sintering environment. This comprehensively restricts the flow of molten copper and inhibits high-temperature evaporation of copper, ultimately ensuring that the sintered blank has a regular shape, high dimensional accuracy, uniform metallographic structure, and no localized porosity defects.

[0044] In other embodiments, during step S4, the vacuum level is controlled to be ≤1×10⁻⁶ during the sintering process. -1 Pa, the gradient heating rate is 3℃ / min~5℃ / min, the final firing temperature is controlled at 1150℃~1380℃, and the holding time is 1h~2h.

[0045] Specifically, this embodiment precisely defines the core process parameters for the vacuum buried sand liquid phase sintering process in step S4, by controlling the sintering vacuum degree to ≤1×10 -1 The process involves using a gradient heating rate of 3℃ / min to 5℃ / min, a final firing temperature of 1150℃ to 1380℃, and a holding time of 1h to 2h to achieve liquid-phase sintering of copper-chromium blanks with low impurities, no defects, high density, and uniform microstructure. This is the core process guarantee for the preparation of high-density, high-performance contacts.

[0046] The vacuum level is controlled at 1×10⁻⁶. -1 At Pa and below, air, water vapor and residual impurity gases in the furnace can be removed to the greatest extent, effectively suppressing the secondary oxidation and nitriding reaction of copper and chromium powders at high temperatures, significantly reducing the oxygen and nitrogen gas inclusion content in the finished product, ensuring the cleanliness of the copper-chromium two-phase interface, and providing a high-purity vacuum environment for full liquid phase wetting and densification sintering. If the vacuum is insufficient, the residual gas in the furnace will aggravate oxidation defects at high temperatures, resulting in increased porosity, decreased density and conductivity of the billet.

[0047] Using a gradient heating rate of 3℃ / min to 5℃ / min is within the uniform heating range suitable for the structure of copper-chromium billets. If the heating rate is too high, a huge temperature difference will form between the inside and outside of the copper-chromium billet, and the internal gas will expand rapidly and cannot escape smoothly, causing defects such as bubbling, delamination and microcracks in the billet. If the heating rate is too low, the production efficiency will be low and the powder will easily be oxidized and carbonized for a long time at low temperature, which will affect the sintering quality. This rate range can ensure that the temperature of the copper-chromium billet rises synchronously, the gas is released steadily and the thermal stress is released gradually.

[0048] The final firing temperature is strictly limited to 1150℃~1380℃, which can precisely match the metallurgical characteristics of copper phase melting and chromium phase maintaining a stable skeleton. When the temperature is below 1150℃, the copper liquid melts insufficiently and the liquid phase has poor fluidity, which cannot effectively fill the micropores of the chromium skeleton, making it difficult to break through the sintering density. When the temperature is above 1380℃, the copper liquid will boil excessively and the amount of evaporation will surge. At the same time, it will cause high-temperature coarsening of chromium particles, grain boundary erosion, and loose skeleton, which will seriously damage the metallographic structure and mechanical properties.

[0049] The holding time is controlled at 1h to 2h to ensure that the copper liquid fully wets the surface of the chromium particles and completes the filling of the pores throughout the entire area through capillary action, so as to achieve the overall synchronous densification of the copper-chromium blank. If the holding time is too short, it will lead to insufficient local wetting and pore residue, while if the holding time is too long, it will aggravate the copper evaporation loss and the erosion defects at the chromium phase boundary.

[0050] This embodiment achieves precise control of multiple parameters, including vacuum degree, heating rate, sintering temperature, and holding time, by optimizing the sintering behavior of the copper-chromium composite phase from the perspectives of sintering kinetics and thermodynamics. This completely solves the problems of insufficient density, high impurities, uneven microstructure, and large performance fluctuations in traditional liquid phase sintering, and stably obtains high-performance copper-chromium sintered billets with a density of ≥99%, uniform metallographic structure, and very few defects.

[0051] In other embodiments, in step S4, the method for cooling down after sintering is as follows: after sintering, the furnace is cooled down, and when the furnace temperature drops to 500°C, the fan is turned on to accelerate the cooling.

[0052] Specifically, this embodiment implements refined control over the cooling process after sintering in step S4. A segmented cooling strategy is adopted, combining high-temperature slow cooling with furnace cooling and 500℃ critical forced air cooling. After sintering and holding, the furnace first cools naturally. Once the furnace temperature drops to 500℃, the fan is activated to accelerate cooling. This approach ensures the copper-chromium sintered billet is crack-free and structurally stable, while also considering product metallographic quality and production efficiency, avoiding the drawbacks of traditional one-time rapid cooling or slow cooling throughout the process. During the high-temperature stage after sintering, the copper and chromium phases inside the billet are not yet fully solidified, and the metallographic structure is in an unstable remodeling state. Direct forced rapid cooling would cause a drastic increase in the temperature difference between the inside and outside of the sintered billet, inducing significant residual thermal stress. This leads to hidden microcracks, delamination, and warping deformation in the billet. Simultaneously, it easily causes interfacial peeling and loosening of the structure due to the inconsistent shrinkage coefficients of the copper and chromium phases, severely reducing the mechanical properties and density of the contacts.

[0053] This embodiment employs a high-temperature section with slow furnace cooling, allowing the temperature of the copper-chromium sintered billet to decrease uniformly. This enables the internal liquid copper phase to gradually solidify and the chromium phase skeleton structure to stabilize and form. It fully releases the internal thermal stress generated during sintering, ensuring a tight copper-chromium interface, a stable microstructure, and eliminating thermal stress defects. Once the furnace temperature drops to the critical temperature of 500℃, the copper-chromium alloy microstructure is essentially completely solidified, and the crystal structure and phase distribution no longer undergo significant phase transitions or deformations. At this point, the fan is activated to forcibly accelerate cooling. This avoids damaging the already formed uniform microstructure, preventing cracking and deformation, and significantly shortening the cooling cycle, thus improving batch production efficiency. This segmented cooling mode, by precisely dividing the phase transition-sensitive temperature zone and the safe cooling temperature zone, achieves controllable microstructure, stress, and efficiency, further ensuring high dimensional stability, uniform microstructure, and absence of internal stress defects in the finished copper-chromium contacts, improving batch performance consistency and service reliability.

[0054] In other embodiments, the density of the copper-chromium sintered billet prepared in step S5 is ≥99%.

[0055] Specifically, this embodiment precisely defines the performance of the copper-chromium sintered billet before processing in step S5. The copper-chromium sintered billet obtained by the entire process of this application has a density of ≥99%, which is the core performance characteristic that distinguishes this application from traditional copper-chromium contact preparation processes. It is also the key foundation for ensuring the electrical, mechanical, and arc-resistant performance of the contact. Density, as a core indicator of powder metallurgy contact materials, directly determines the internal porosity, matrix continuity, and interface bonding state of the material. Copper-chromium billets prepared by traditional powder metallurgy sintering and conventional liquid phase sintering processes generally have a large number of interconnected pores, closed micropores, and loose defects, with a density usually below 98%. Pores easily become arc erosion concentration sites, stress concentration sites, and conductivity isolation sites, which can easily cause copper-chromium contacts to fail during high-voltage breaking processes, such as severe arc initiation, welding, wear and detachment, and unstable conductivity.

[0056] This application achieves a complete process coupling optimization through front-end refined ball milling modification, trace carbon black deoxygenation purification, uniform and dense green billet forming, sand embedding to prevent dispersion and shaping, vacuum low-impurity sintering, gradient temperature densification, and segmented temperature control to stabilize the microstructure. This thoroughly eliminates interconnected pores, microscopic porosity, and void defects within the green billet, allowing the copper liquid phase to fully fill all microscopic gaps in the chromium skeleton, achieving a tight interlocking of the copper and chromium phases and a fully dense metallurgical bond. This enables the copper-chromium sintered green billet to stably achieve an ultra-high density of 99% or higher, ensuring the continuity and integrity of the copper-chromium matrix, minimal internal defects, and uniform microstructure. It significantly reduces gas inclusions and porosity, substantially improving the overall electrical and thermal conductivity, hardness, and structural stability of the contacts, while effectively enhancing the contacts' resistance to arc erosion, welding, and fatigue service.

[0057] This application also provides a copper-chromium contact prepared by the above-described method.

[0058] Specifically, this embodiment provides a copper-chromium contact prepared by the aforementioned high-density copper-chromium contact preparation method. This copper-chromium contact is prepared using the aforementioned vacuum buried sand liquid-phase sintering integrated process. It differs from copper-chromium contacts prepared by traditional melt infiltration and ordinary sintering methods in terms of material microstructure, internal purity, macroscopic properties, and structural stability. It belongs to a new type of electrical contact material characterized by high uniformity, low impurities, high density, and high service stability. The copper-chromium contact has no obvious porosity, voids, microcracks, or oxide inclusions. The chromium phase particles are uniformly distributed in the copper phase matrix, without local agglomeration, segregation, or coarsening. The two-phase interface is tightly bonded with high metallurgical bonding quality, and the matrix is ​​continuous and intact. Compared to traditional copper-chromium contacts, copper-chromium contacts significantly reduce the content of harmful oxygen and nitrogen gas impurities through the synergistic effect of carbon black thermal carbon reduction for oxygen removal and high-vacuum sintering environment, resulting in a significant improvement in material purity. Simultaneously, relying on embedded sand shaping to prevent spillage, gradient heating for densification, and segmented stress release temperature control technology, the product exhibits extremely low internal residual stress, excellent dimensional consistency, and a regular structure, free from sintering deformation, warping, and edge collapse defects. This copper-chromium contact can stably achieve an ultra-high overall density of ≥99%, while also possessing excellent electrical and thermal conductivity, moderate structural hardness, and superior resistance to arc erosion and welding. It can be adapted to various mainstream grades such as CuCr40, CuCr45, and CuCr50, comprehensively covering vacuum switch applications at voltage levels from 12kV to 40.5kV. Meanwhile, this product is manufactured using a near-net-shape forming process, which results in high blank forming precision, small machining allowance, high material utilization, and small batch performance dispersion. It can meet the domestic supporting needs of large-capacity, miniaturized, highly reliable, and long-life power equipment, and has extremely strong engineering application value and advantages in mass industrialization.

[0059] Example 1 This embodiment provides a method for preparing a high-density CuCr40 contact, including the following steps: S1. Ball Milling and Powder Mixing: Copper and chromium powders are selected according to the specified ratio, with the chromium powder mass fraction controlled at 39% and the remainder being copper powder. Carbon black, accounting for 0.4‰ of the total powder mass, is also added. Stainless steel balls are used as the grinding medium, with a ball-to-powder ratio of 1:1.2. The entire process is sealed and ball-milled for 9 hours. During ball milling, the continuous impact, shearing, and kneading action of the stainless steel balls effectively blunts the sharp corners of the chromium particles, improves powder flowability, and eliminates the microscopic bridging phenomenon of chromium particles. Simultaneously, the uniform doping of carbon black provides a stable carbon source for subsequent sintering hot carbon reduction and deoxygenation, achieving a highly uniform mixture of copper and chromium powders to obtain a modified mixed powder with high activity, high purity, and uniform flowability.

[0060] S2. Cold Pressing: A robotic arm, in conjunction with a spray gun, evenly sprays a high-temperature resistant, residue-free release agent (water-soluble graphite release agent) onto the inner wall of the mold cavity, forming a uniform lubricating and insulating layer. Modified mixed powder is then evenly loaded into the mold cavity, with the mandrel vibrating 12 times to ensure secondary rearrangement and uniform filling of the powder within the cavity, eliminating local voids and uneven density defects. A press is used for uniform-speed molding, controlling the holding time to 0.2s and the depressurization time to 1.2s. This precise pressure regime suppresses elastic after-effect cracking, ultimately yielding a CuCr40 green blank with a density of 93.63%. The green blank has an intact overall structure, without missing corners, cracks, or uneven density.

[0061] S3. Pre-treatment with buried sand: Select 20-mesh alumina sand that has undergone high-temperature vacuum sintering and degassing treatment, and evenly lay a layer of alumina sand at the bottom of the graphite crucible as the bottom support layer; place the prepared CuCr40 blank stably in the center of the bottom sand; then select wire-cut pure copper sheets that match the outer diameter and size of the CuCr40 blank and attach them to the top of the CuCr40 blank; finally, use alumina sand to completely bury and cover the four sides, sides and top of the CuCr40 blank, so that the whole is in a fully enclosed alumina sand constraint environment, and achieve the pre-treatment effect of shaping and preventing flow, inhibiting copper evaporation and uniform heat transfer.

[0062] S4. Vacuum-embedded sand liquid-phase sintering: Place the graphite crucible with the embedded sand charge into a vacuum sintering furnace, close the furnace body, and evacuate to ensure the vacuum level inside the furnace is stable at ≤1×10⁻⁶. -1Pa. A gradient heating method was adopted, with a uniform heating rate of 4℃ / min. The final firing temperature was set at 1250℃, and the temperature was held at this temperature for 1.5 hours. Gradient heating ensured that the internal and external temperatures of the CuCr40 billet rose synchronously, allowing for stable gas release and preventing bulging and microcracks. Precise holding ensured complete melting of the copper phase, uniform infiltration of the chromium skeleton by the liquid phase, and capillary filling of all micropores, completing the densification sintering. After holding, heating was stopped, and a high-temperature slow cooling mode was used to release residual thermal stress from sintering. When the furnace temperature dropped to the critical phase transformation temperature of 500℃, the fan was turned on to forcefully accelerate cooling, shorten the cooling cycle, stabilize the metallographic structure, and obtain a CuCr40 sintered billet that was free of deformation and porosity, and highly dense.

[0063] S5. Finished Product Processing: The sintered CuCr40 blank is processed by turning and milling in sequence. According to the structural and dimensional requirements of the contact product, the blank is precision turned and milled step by step to adjust the external dimensions and assembly end face, remove a small amount of process allowance, and obtain a high-density CuCr40 contact product with high dimensional accuracy, good surface quality and regular structure while fully preserving the excellent sintered structure and performance.

[0064] The performance of the prepared high-density CuCr40 contact product was tested. The metallographic structure of the CuCr40 contact product is as follows: Figure 3 As shown, the test results of other indicators are as follows: oxygen content is 340ppm, nitrogen content is 16ppm, chromium content is 39.92%, hardness is 88.5HBW, density is 8.09g / cm³, density is ≥99%, and the chromium phase in the metallographic structure is diffusely and uniformly distributed without agglomeration, segregation, or porosity defects.

[0065] Example 2 This embodiment provides a method for preparing a high-density CuCr45 contact, including the following steps: S1. Ball Milling and Powder Mixing: Copper and chromium powders are selected according to the specified ratio, with the chromium powder mass fraction controlled at 45% and the remainder being copper powder. Carbon black, accounting for 0.35‰ of the total powder mass, is also added. Stainless steel balls are used as the grinding medium, with a ball-to-powder ratio of 1:1.2. The entire process is sealed and ball-milled for 8.5 hours. During ball milling, the continuous impact, shearing, and kneading action of the stainless steel balls effectively blunts the sharp corners of the chromium particles, improves powder flowability, and eliminates the microscopic bridging phenomenon of chromium particles. Simultaneously, the uniform doping of carbon black provides a stable carbon source for subsequent sintering hot carbon reduction and deoxygenation, achieving a highly uniform mixture of copper and chromium powders to obtain a modified mixed powder with high activity, high purity, and uniform flowability.

[0066] S2. Cold pressing: The mold inner wall is uniformly sprayed with release agent (same as in Example 1). After filling with powder, the mandrel is vibrated 12 times to ensure uniform material distribution. The molding process is carried out with pressure holding for 0.2s and pressure release for 1.2s to precisely control the release of molding stress. A complete CuCr45 green blank with a density of 93.68% is prepared. The CuCr45 green blank has a smooth surface, no scratches, no cracks, and excellent overall density consistency.

[0067] S3. Pre-treatment with buried sand: A layer of 60-mesh alumina sand that has been degassed by high-temperature vacuum sintering is evenly laid at the bottom of the graphite crucible as the bottom support layer; the prepared CuCr45 blank is placed stably in the center of the bottom sand; then wire-cut pure copper sheets that match the outer diameter and size of the CuCr45 blank are selected and attached to the top of the CuCr45 blank; finally, alumina sand is used to completely bury and cover the four sides, sides and top of the CuCr45 blank.

[0068] S4. Vacuum-embedded sand liquid-phase sintering: Place the graphite crucible with the embedded sand charge into a vacuum sintering furnace, close the furnace body, and evacuate to ensure the vacuum level inside the furnace is stable at ≤1×10⁻⁶. -1 Pa. A gradient heating method was adopted, with a uniform heating rate of 4℃ / min. The final firing temperature was set at 1300℃, and the temperature was held at this temperature for 1.5 hours. Gradient heating ensured that the internal and external temperatures of the CuCr45 billet rose synchronously, allowing for stable gas release and preventing bulging and microcracks. Precise holding ensured complete melting of the copper phase, uniform infiltration of the chromium skeleton by the liquid phase, and capillary filling of all micropores, completing the densification sintering. After holding, heating was stopped, and a high-temperature slow cooling mode was used to release residual thermal stress from sintering. When the furnace temperature dropped to the critical phase transformation temperature of 500℃, the fan was turned on to forcefully accelerate cooling, shorten the cooling cycle, stabilize the metallographic structure, and obtain a highly dense CuCr45 sintered billet without deformation or porosity.

[0069] S5. Finished Product Processing: The sintered CuCr45 blank is processed by turning and milling in sequence. According to the structural and dimensional requirements of the contact product, the blank is precision turned and milled step by step to adjust the external dimensions and assembly end face, remove a small amount of process allowance, and obtain a high-density CuCr45 contact product with high dimensional accuracy, good surface quality and regular structure while fully preserving the excellent sintered structure and performance.

[0070] The performance of the prepared high-density CuCr45 contact product was tested. The metallographic structure of the CuCr45 contact product is as follows: Figure 4 As shown, the test results for other indicators are as follows: oxygen content is 380ppm, nitrogen content is 16ppm, chromium content is 46.67%, hardness is 88.9HBW, density is 8.01g / cm³, density is ≥99%, metallographic structure is uniform, porosity is minimal, and performance stability is excellent.

[0071] Example 3 This embodiment provides a method for preparing a high-density CuCr50 contact, including the following steps: S1. Ball Milling and Powder Mixing: Select copper powder and chromium powder according to the specified ratio, controlling the chromium powder mass fraction to 51%, with the remainder being copper powder, and add 0.5‰ carbon black of the total powder mass; use stainless steel ball milling with a ball-to-powder ratio of 1:1.2, and ball milling time of 10 hours. Through long-term and moderate ball milling, the sharp edges of high-chromium particles are fully passivated, the powder activity and mixing uniformity are improved, and the highest proportion of carbon black is used to meet the deoxygenation requirements of high-chromium powder, ensuring high purity and high activity of the powder.

[0072] S2. Cold Pressing: A robotic arm, in conjunction with a spray gun, evenly sprays a high-temperature resistant, residue-free release agent (water-soluble graphite release agent) onto the inner wall of the mold cavity, forming a uniform lubricating and insulating layer. Modified mixed powder is then evenly loaded into the mold cavity, with the mandrel vibrating 12 times to ensure secondary rearrangement and uniform filling of the powder within the cavity, eliminating local voids and uneven density defects. A press is used for uniform-speed molding, controlling the holding time at 0.2s and the depressurization time at 1.2s. This precise pressure regime suppresses elastic after-effect cracking, ultimately yielding a CuCr50 green blank with a density of 94.99%. The green blank has an intact overall structure, without missing corners, cracks, or uneven density.

[0073] S3. Pre-treatment with buried sand: A layer of 100-mesh alumina sand that has been degassed by high-temperature vacuum sintering is evenly laid at the bottom of the graphite crucible as the bottom support layer; the prepared CuCr50 blank is placed stably in the center of the bottom sand; then wire-cut pure copper sheets that match the outer diameter and size of the CuCr50 blank are selected and attached to the top of the CuCr45 blank; finally, alumina sand is used to completely bury and cover the four sides, sides and top of the CuCr50 blank.

[0074] S4. Vacuum-embedded sand liquid-phase sintering: Place the graphite crucible with the embedded sand charge into a vacuum sintering furnace, close the furnace body, and evacuate to ensure the vacuum level inside the furnace is stable at ≤1×10⁻⁶. -1 Pa. A gradient heating method was adopted, with a uniform heating rate of 4℃ / min. The final firing temperature was set at 1350℃, and the temperature was held at this temperature for 2 hours. Gradient heating ensured that the internal and external temperatures of the CuCr50 billet rose synchronously, allowing for stable gas release and preventing bulging and microcracks. Precise holding ensured complete melting of the copper phase, uniform infiltration of the chromium skeleton by the liquid phase, and capillary filling of all micropores, completing the densification sintering. After holding, heating was stopped, and a high-temperature slow cooling mode was used to release residual thermal stress from sintering. When the furnace temperature dropped to the critical phase transformation temperature of 500℃, the fan was turned on to forcefully accelerate cooling, shorten the cooling cycle, stabilize the metallographic structure, and obtain a CuCr50 sintered billet that was free of deformation and porosity, and highly dense.

[0075] S5. Finished Product Processing: The sintered CuCr50 sintered billet is processed by turning and milling in sequence. According to the structural and dimensional requirements of the contact product, it is precision turned and milled step by step to adjust the external dimensions and assembly end face, remove a small amount of process allowance, and obtain a high-density CuCr50 contact finished product with high dimensional accuracy, good surface quality and regular structure while fully preserving the excellent sintered structure and performance.

[0076] The performance of the prepared high-density CuCr45 contact product was tested, and the metallographic structure of the CuCr50 contact product was as follows: Figure 3 As shown, the test results for other indicators are as follows: oxygen content is 470ppm, nitrogen content is 24ppm, chromium content is 49.27%, hardness is 92.0HBW, density is 7.96g / cm³, density is ≥99%, the metallographic structure is dense and continuous, and there are no obvious defects.

[0077] Compare with Example 1 This comparative example is completely identical to Example 1 in terms of process parameters, raw material ratio, molding parameters, and sintering regime, except that no carbon black is added during the ball milling and powder mixing process. The specific process is as follows: chromium powder mass fraction 39%, balance copper powder, no carbon black doping; ball-to-material ratio 1:1.2, ball milling for 9 hours; cold pressing molding, vibration frequency, and pressure holding and releasing parameters are completely consistent; the embedded sand structure, pure copper sheet arrangement, and alumina sand particle size are completely consistent; vacuum degree, heating rate, sintering temperature, holding time, and cooling regime are all consistent with Example 1.

[0078] The test results showed that, due to the absence of carbon black, thermal carbon reduction and deoxygenation could not be achieved during the sintering process. The oxide film and adsorbed gas on the powder surface could not be effectively removed, resulting in a significant increase in the oxygen and nitrogen impurity content of the finished product. Trace amounts of oxide inclusions and closed pores were present inside the green body, and the sintering density decreased to 97.2%. Local oxidation sites and loose areas were present in the metallographic structure, and the electrical conductivity and arc erosion resistance were significantly lower than those in Example 1. This demonstrates that trace carbon black doping plays an important role in purifying the interface, reducing gaseous impurities, and improving density.

[0079] Compare with Example 2 This comparative example is based on Example 1. All raw material parameters, ball milling, forming, sintering and cooling processes are exactly the same. The only difference is that in step S3 sand pretreatment, pure copper sheets are not placed on the top of the blank, and only alumina sand is used to directly bury the copper-chromium blank.

[0080] The test results showed that the copper components lacked copper replenishment during the vacuum high-temperature sintering process, and the high-temperature evaporation loss of copper under vacuum conditions could not be compensated, resulting in low copper content and excessive chromium content in the finished product, and deviation of the composition ratio. The surface of the billet showed local chromium porosity and increased surface porosity, and the overall density decreased to 97.8%. The finished product had uneven hardness and poor batch composition consistency. At the same time, copper recycling could not be achieved, and the material utilization rate was reduced. This proves that the top-mounted pure copper sheet plays a key technical role in stabilizing the composition, compensating for copper loss, and improving the uniformity of the structure.

[0081] Compare with Example 3 This comparative example is based on Example 1, with the same raw materials, powder mixing, molding, and sand embedding structure. The difference lies in the sintering temperature control: the 4℃ / min gradient heating is cancelled, and a direct rapid heating to 1250℃ is adopted; at the same time, the 500℃ segmented forced cooling strategy is cancelled, and the entire process is directly air-cooled after sintering and heat preservation without a high-temperature slow cooling process.

[0082] The test results showed that rapid heating caused a huge temperature difference between the inside and outside of the blank, resulting in insufficient instantaneous expansion and precipitation of internal gases, leading to micro-bulges, micropores, and a small number of micro-cracks in the blank. Rapid cooling throughout the process caused huge residual thermal stress in the sintered blank, mismatched shrinkage of the copper and chromium phases, loose interface bonding, and localized delamination and slight warping deformation. The finished product had a density of only 96.5%, with many internal defects, large residual stress, significant fluctuations in mechanical and electrical properties, and a substantial decrease in product service stability. This proves that the segmented temperature control system of the present invention, which involves gradient heating and exhaust, slow cooling at high temperature to relieve stress, and forced acceleration and cooling at low temperature, is the core key to achieving a high-density, low-defect, and low-stress finished product.

[0083] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for preparing a high-density copper-chromium contact, characterized in that, Includes the following steps: Weigh out copper powder and chromium powder according to the ratio, control the mass fraction of chromium powder to be 39% to 51%, and mix them by ball milling to obtain modified mixed powder. The modified mixed powder is loaded into a mold and molded. After holding the pressure for a period of time, the pressure is released to obtain a copper-chromium blank with a density of 92% to 95%. A pure copper sheet is placed on top of the copper-chromium blank, and then the copper-chromium blank and the pure copper sheet are subjected to sand embedding treatment together. The copper-chromium blank after sand embedding treatment is sintered with the pure copper sheet. The temperature is increased by gradient heating during the sintering process and cooled after sintering to obtain the copper-chromium sintered blank. The copper-chromium sintered billet is machined into shape by turning and milling to obtain the high-density copper-chromium contact.

2. The preparation method according to claim 1, characterized in that, The method of mixing powder by ball milling is as follows: the ball-to-material ratio of a single tank is controlled at 1:1 to 1:1.3, the ball milling time is 8h to 10h, stainless steel balls are used as the grinding medium, and the sharp corners of chromium particles are blunted and the surface activity and flowability of chromium powder are improved during the ball milling process.

3. The preparation method according to claim 1, characterized in that, The modified mixed powder contains 0.3‰ to 0.5‰ carbon black.

4. The preparation method according to claim 1, characterized in that, The inner wall of the mold cavity is coated with a release agent; the number of vibrations of the mandrel during the molding process is controlled to be 10 to 15 times; the pressure holding time is 0.1s to 0.3s, and the pressure release time is 1s to 1.5s.

5. The preparation method according to claim 1, characterized in that, The size of the pure copper sheet is adapted to the size of the copper-chromium billet. The sand used in the sand embedding process is alumina sand, and the particle size of the alumina sand is controlled between 20 mesh and 100 mesh. A layer of alumina sand is laid on the bottom of the copper-chromium billet.

6. The preparation method according to any one of claims 1 to 5, characterized in that, During the sintering process, the vacuum level is controlled to be ≤1×10⁻⁶. -1 Pa, the gradient heating rate is 3℃ / min~5℃ / min, the final firing temperature is controlled at 1150℃~1380℃, and the holding time is 1h~2h.

7. The preparation method according to claim 6, characterized in that, The method for cooling down after sintering is as follows: after sintering, the furnace is cooled down. When the furnace temperature drops to 500°C, the fan is turned on to accelerate the cooling.

8. The preparation method according to claim 6, characterized in that, The density of the prepared copper-chromium sintered billet is ≥99%.

9. A copper-chromium contact, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. The copper-chromium contact according to claim 9, characterized in that, The copper-chromium contact is a CuCr40 contact, a CuCr45 contact, or a CuCr50 contact; The copper-chromium contact has a density of ≥99% and is suitable for vacuum switches with voltage levels of 12kV to 40.5kV.

Images