Preparation process of bismuth-graphene copper composite wire

Abstract

This invention belongs to the field of conductive metal composite material processing technology, and specifically to a bismuth-graphene copper composite wire preparation process, which includes the following steps in sequence: S1, raw material preparation; S2, sandwich feeding and composite; S3, inert atmosphere anchoring and temperature-controlled cooling; S4, multi-pass cold drawing forming. This invention abandons the overall high-temperature sintering and annealing scheme above 400℃, only locally heating to 275℃ for a short time during the rolling process to melt a trace amount of bismuth in the sandwich layer; the molten bismuth only fills the microscopic pits on the copper foil surface, without forming a continuous bismuth film that blocks current conduction; after the bismuth solidifies under a pressurized argon atmosphere through gradient cooling, stable discrete mechanically positioned anchoring nodes are formed at the interface of the two-layer copper foil, fundamentally solving the defects of interlayer delamination and arc impact peeling in traditional rolled composite wires. The entire process avoids high-temperature damage to graphene, completely preserving the continuous conductive path of graphene. The finished product achieves a conductivity of 98.5% IACS at 20℃, with conductivity performance close to that of pure copper.

Description

Technical Field

[0001] This invention relates to the field of conductive metal composite material processing technology, specifically a bismuth-graphene copper composite wire preparation process. Background Technology

[0002] Graphene-modified copper conductors, thanks to graphene's excellent conductivity and wear resistance, are widely used in new energy cables, motor windings, and arc contact conductors. Currently, the mainstream manufacturing processes for graphene-copper composite conductors fall into three categories: powder metallurgy composite method, electroplating coating method, and traditional copper foil roll forming composite process. Each of these processes has inherent drawbacks that are difficult to overcome. Powder metallurgy and electroplating coating processes: Graphene sheets have poor dispersion uniformity, are prone to agglomeration and stacking, have many interlayer interface gaps, generate serious heat under high current conditions, and are prone to interlayer delamination after the wire is stressed. Traditional single-layer copper foil roll forming process: It relies solely on mechanical extrusion to bond the copper foil interface without a dedicated interface anchoring structure. After repeated bending and exposure to electric arc impact, the wire is prone to interlayer delamination failure. If high-temperature annealing above 400℃ is used to improve the interface bonding strength, the high temperature will destroy the continuous conductive network of graphene, significantly reducing the conductivity of the wire. The conventional sandwich roll forming fabric design is not perfect, and the powder spreading process is prone to displacement and overflow, resulting in poor performance consistency of mass-produced wire rods; when the composite billet is heated as a whole, the temperature difference between the inner and outer layers is large, and the interface anchoring effect is uneven. Traditional large-deformation cold drawing process requires an intermediate tempering process to eliminate work hardening, making the entire process lengthy. Furthermore, the high temperature of tempering can damage the conductive pathways of graphene again.

[0003] The existing flat plate hot-pressing layered process has a large difference in the ratio of bismuth powder to graphene, and the material gap parameters are completely independent of this solution, making it unusable. The traditional prefabricated flat plate re-rolling process is prone to direct bonding of bare copper foil surfaces, resulting in significant delamination failure problems after long-term use.

[0004] In summary, the existing copper foil roll forming composite process cannot simultaneously meet the four core requirements of interlayer bonding strength, high conductivity, good mass production stability, and simplified processing steps. Therefore, there is an urgent need to develop a bismuth-graphene copper composite wire preparation process. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a process for preparing bismuth-graphene copper composite wires, which solves the problems mentioned in the background section.

[0006] To achieve the above objectives, the present invention specifically adopts the following technical solution: A process for fabricating a bismuth-graphene copper composite wire includes the following steps: S1. Raw material preparation: Select high-purity copper foil with the surface oxide layer removed as the upper and lower composite skeleton; mix spherical bismuth powder with 1 to 2 layers of few-layer graphene powder at a mass ratio of 1:1, control the total amount of powder added, so that the mass ratio of graphene in the final finished wire is 0.3% to 0.4%; the powder is mixed at low speed in a closed environment throughout the process, and the mixing process is isolated from water vapor and air oxidation to avoid the powder absorbing moisture, oxidizing and agglomerating; S2, Sandwich Feeding Composite: Two layers of high-purity copper foil are synchronously fed towards each other to form a sealed sandwich gap. Bismuth powder and graphene mixed powder are evenly spread into the gap between the two copper foil layers. The gap is equipped with a baffle structure to prevent the powder from spilling out. The powder completely isolates the two copper foil layers to prevent the bare copper from being directly bonded. The copper foil and sandwich powder are synchronously fed into the roller gap for rolling and pressing to complete the initial pre-compacting composite between the layers. S3. Inert Atmosphere Anchoring and Temperature Controlled Cooling: High-purity argon gas is continuously introduced into the sandwich roll forming cavity to create an inert protective atmosphere and control the low-oxygen environment within the cavity. The cavity maintains a basic constant temperature of 210–260°C. When the sandwich material passes through the roll gap, the temperature briefly rises to 275°C, melting only trace amounts of bismuth within the sandwich. The molten bismuth only wets and fills the microscopic pits on the surface of the copper foil, without forming a continuous bismuth film that blocks conductivity. After the molten bismuth has completed its wetting and filling, it is gradually cooled to the range of 130–200°C under argon protection and pressure to suppress the rebound and opening of the copper foil. After the bismuth has completely cooled and solidified, a stable mechanical locking and anchoring structure is formed at the interface of the two copper foil layers. S4. Multi-stage cold drawing forming: After anchoring and cooling, the sandwich composite plate is first rolled and compacted gradually, and then continuously cold-drawn and reduced in diameter through multiple hard alloy drawing dies; no tempering stress relief process is set up throughout the process, and the radial compressive stress generated by the plastic deformation of the wire drawing is used to further compact the bismuth interlocking interface and strengthen the interlayer bonding force; conventional specification wires are directly cold-drawn to the target wire diameter; when preparing fine specification wires, copper tubes can be wrapped around the composite blank before deep drawing. Copper tube wrapping is an optional optimization process and not a necessary step in the process.

[0007] Furthermore, the oxidation removal process of the high-purity copper foil in S1 includes acid washing, water washing, ultrasonic cleaning with organic solvents, and drying with inert protective gas; the powder is vacuum dried to remove water before mixing, the powder mixing environment is under low humidity control, the exposure time of the powder is strictly limited, and air and water vapor are completely isolated throughout the process.

[0008] Furthermore, the argon gas used in S3 is high-purity argon gas, and the oxygen content in the interlayer cavity is strictly controlled; after the molten bismuth is anchored, it is slowly cooled under pressure in an argon atmosphere until the bismuth is completely solidified to form an interlayer locking structure.

[0009] Furthermore, the total cross-sectional shrinkage rate of the S4 cold-drawn wire is ≥96%; after the wire drawing process is completed, the surface lubricating medium is removed by cleaning, and the wire is dried with inert gas and then wound up to obtain the finished composite wire.

[0010] Furthermore, the bismuth-graphene copper composite wire prepared by this process can achieve a conductivity of 98.5% IACS at 20℃, and the interlayer shear strength is increased by 42% compared with ordinary pure copper wound wire, while the arc reciprocating wear and ablation amount is reduced by 37%.

[0011] Compared with the prior art, the present invention provides a process for preparing bismuth-graphene copper composite wires, which has the following beneficial effects: Low-temperature trace bismuth in-situ mechanical anchoring simultaneously solves the problems of interlayer delamination and conductivity attenuation. This invention abandons the overall high-temperature sintering and annealing process above 400°C, instead only briefly heating to 275°C in a localized area during the rolling process to melt a trace amount of bismuth. The molten bismuth only fills the microscopic pits on the copper foil surface, without forming a continuous bismuth film that blocks current conduction. After the bismuth solidifies under a pressurized argon atmosphere through gradient cooling, it forms stable, discrete mechanically anchored nodes at the interface of the double-layer copper foil, fundamentally solving the defects of interlayer delamination and arc-induced peeling in traditional rolled composite conductors. The entire process avoids high-temperature damage to graphene, fully preserving the continuous conductive pathway of graphene. The finished product achieves a conductivity of 98.5% IACS at 20°C, with conductivity performance approaching that of pure copper.

[0012] The double-layer copper foil opposing roll-press sandwich fabric structure ensures uniform and controllable powder spreading, resulting in high mass production stability. The core of this invention employs a double-layer copper foil opposing-facing conveying and pressing sandwich structure. The powder is completely confined within the sealed gap formed by the two layers of copper foil, and a matching baffle structure prevents lateral powder spillage, completely avoiding direct contact with the bare copper surface. Graphene is uniformly dispersed at the interlayer interface, and the roller pressing pre-compacts and simultaneously degassing, resulting in minimal performance fluctuations in single batches and entire rolls of wire, and excellent consistency in mass production. This process is compatible with copper wire skeleton spiral winding as an alternative mass production route, requiring only a change in the material feeding mechanism; the core processes of anchoring and wire drawing remain unchanged, thus broadening the process's adaptability.

[0013] The entire process is protected by high-purity argon inert gas, effectively preventing raw material oxidation and failure. From copper foil pretreatment and powder mixing to interlayer anchoring and cooling, high-purity argon gas is introduced throughout the entire process to isolate air and moisture, strictly control the oxygen content in the cavity, and effectively inhibit bismuth powder oxidation and graphene moisture absorption and agglomeration. The low-oxygen inert environment throughout the roll forming process ensures the cleanliness of the interlayer interface, the stable forming quality of the anchoring structure, and significantly reduces the dispersion of the mechanical and electrical properties of the finished product.

[0014] Integrated multi-stage cold drawing without intermediate tempering simplifies the process and enhances the interfacial bonding strength. The bismuth-anchored composite sheet does not require intermediate tempering to relieve stress and can be directly slit, rolled, and then subjected to continuous cold drawing with large deformation. The soft bismuth phase and graphene work synergistically to reduce friction, and the billet can withstand a total area reduction rate of ≥96%. The radial compressive stress generated by the plastic deformation during wire drawing further compacts the bismuth anchoring interface, doubly enhancing the interlayer bonding force. The interlayer shear strength of the finished product is 42% higher than that of ordinary pure copper rolled wire, and the arc reciprocating wear and erosion is reduced by 37%. At the same time, the tempering process is eliminated, shortening the processing time of the entire production line and reducing production energy consumption.

[0015] Flexible post-processing, adaptable to large-scale continuous mass production of multi-specification wires. Double-layer copper foil roll forming is a continuous production line. After the composite plate is formed, it can be slit and lightly drawn and shaped as needed. When preparing fine-gauge wires, copper tubes can be wrapped around the blank and then deeply drawn. The copper tube is only an optional process to optimize the appearance of the wire and does not affect the core conductivity and anchoring performance. The finished products can be adapted to the mass production of multiple categories of products such as new energy wire harnesses, high-power motor windings, plate, conventional wires, and ultra-fine wires. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the fabrication process of a bismuth-graphene copper composite wire according to the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example: Continuous roll forming of double-layer copper foil like Figure 1 As shown in the process flow diagram, this embodiment discloses a process for preparing bismuth-graphene copper composite wires, which specifically includes the following steps: S1. Raw material preparation: High-purity electrolytic copper foil is selected as the upper and lower composite skeleton. A complete process of pickling, deionized water countercurrent rinsing, organic solvent ultrasonic cleaning, and high-purity inert nitrogen blowing is adopted to thoroughly remove the oxide layer on the surface of the copper foil. Spherical bismuth powder and 1-2 layers of few-layer graphene powder are selected and mixed in a 1:1 mass ratio. After the powder is dried in a vacuum oven to remove moisture, it is transferred to a closed mixing equipment for low-speed stirring and compounding. Argon gas is continuously introduced into the mixing chamber to isolate air. The workshop environment is kept at low humidity and the time for the powder to be stored in the open is strictly limited. The total amount of powder applied is controlled to keep the graphene mass ratio of the finished wire stable at 0.3% to 0.4%. After mixing, the powder is transported to the material placement station through a closed pipeline.

[0019] S2, Sandwich Feeding Composite: Two layers of copper foil are synchronously and continuously conveyed towards each other, converging at the front end to form a sealed sandwich gap; a matching quantitative synchronous feeding mechanism continuously and evenly feeds the bismuth-graphene mixed powder into the gap between the two layers of copper foil, and elastic baffle structures are configured on both sides of the gap to prevent the powder from overflowing laterally; the powder completely separates the two layers of copper foil, preventing direct bonding of bare copper surfaces; the double-layer copper foil carrying the powder is synchronously conveyed to the heated roller gap, and light pre-compacted and degassed by roller pressing to achieve preliminary interlayer composite.

[0020] S3. In-situ anchoring and temperature-controlled cooling in an inert atmosphere: High-purity argon gas is introduced into the sandwich roll forming cavity throughout the process to create an inert protective atmosphere and strictly control the oxygen content in the cavity; the cavity maintains a basic constant temperature range of 210-260℃, and the sandwich composite strip is instantly heated to 275℃ when passing through the heated roll gap, melting only trace amounts of bismuth inside the sandwich; the molten bismuth liquid only wets and fills the micro-pits on the surface of the copper foil, and does not form a continuous bismuth film that blocks conductivity; After the composite strip leaves the heated roll gap, it is continuously protected by argon gas and kept under roll pressure. It is then gradually cooled to the range of 130-200℃, and the copper foil is suppressed from springing open by the pressure constraint. It is then continuously cooled until the bismuth in the interlayer is completely solidified. After the bismuth is solidified, it forms continuously distributed mechanical positioning and anchoring nodes at the interface of the two copper foil layers, thus obtaining an integrated bismuth-graphene copper composite plate.

[0021] S4. Multi-pass cold drawing forming: The long composite plate after anchoring and cooling is cut into narrow composite strips. The narrow strips are first rolled and compacted by a gradual forming mold, and then sent into a multi-pass cemented carbide drawing mold for continuous cold drawing and diameter reduction. No tempering stress relief process is added to the entire drawing process. The radial compressive stress generated by the plastic deformation of the drawing further compacts the bismuth interposition interface, doubly improving the interlayer bonding strength and completely preserving the continuous conductive path of graphene. Standard specification wires can be directly cold-drawn to the target outer diameter; if fine specification wires are required, copper tubes can be wrapped around the rolled blank before deep drawing. The outer copper tube is only used to optimize the surface smoothness of the wire and is an optional optimization step, not a necessary process to achieve the core performance of this invention. After drawing, the surface lubricant is removed by ultrasonic cleaning with water, and the wire is dried with inert protective gas and then wound up to obtain the finished bismuth-graphene copper composite wire.

[0022] In this embodiment, after bismuth melts and cools, it forms discrete locking nodes that lock the interface of the two copper foil layers. The graphene is completely confined and sealed inside the interlayer gap, and will not slip or fail. The overall tensile load of the wire is borne by the copper foil skeleton, and bismuth only serves as an interface anchoring structure. The brittleness of bismuth itself will not cause the wire to break as a whole.

[0023] The finished product is tested according to national standards for conductivity, mechanical properties and arc wear resistance. The conductivity at room temperature of 20℃ can reach 98.5% IACS, the interlaminar shear strength is 42% higher than that of conventional pure copper composite plates, and the arc reciprocating wear ablation is reduced by 37%.

[0024] Additional notes: In addition to the core double-layer copper foil rolling route in this embodiment, this process can be adapted to the spiral winding sandwich forming of copper wire skeleton as an alternative mass production route. The overall anchoring and wire drawing process logic is the same as the rolling scheme. Only the sandwich material feeding mechanism is adapted to the winding dynamic gap structure. This alternative route is not the core disclosed protection scheme of this invention. The detailed equipment parameters are proprietary processes.

[0025] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. 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 process for preparing bismuth-graphene copper composite wires, characterized in that, The process includes the following steps in sequence: S1. Raw material preparation: Select high-purity copper foil with the surface oxide layer removed as the upper and lower composite skeleton; mix spherical bismuth powder with 1 to 2 layers of few-layer graphene powder at a mass ratio of 1:1, control the total amount of powder added, so that the mass ratio of graphene in the final finished wire is 0.3% to 0.4%; the powder is mixed at low speed in a closed environment throughout the process, and the mixing process is isolated from water vapor and air oxidation to avoid the powder absorbing moisture, oxidizing and agglomerating; S2, Sandwich Feeding Composite: Two layers of high-purity copper foil are synchronously fed towards each other to form a sealed sandwich gap. Bismuth powder and graphene mixed powder are evenly spread into the gap between the two copper foil layers. The gap is equipped with a baffle structure to prevent the powder from spilling out. The powder completely isolates the two copper foil layers to prevent the bare copper from being directly bonded. The copper foil and sandwich powder are synchronously fed into the roller gap for rolling and pressing to complete the initial pre-compacting composite between the layers. S3. Inert Atmosphere Anchoring and Temperature Controlled Cooling: High-purity argon gas is continuously introduced into the sandwich roll forming cavity to create an inert protective atmosphere and control the low-oxygen environment within the cavity. The cavity maintains a basic constant temperature of 210–260°C. When the sandwich material passes through the roll gap, the temperature briefly rises to 275°C, melting only trace amounts of bismuth within the sandwich. The molten bismuth only wets and fills the microscopic pits on the surface of the copper foil, without forming a continuous bismuth film that blocks conductivity. After the molten bismuth has completed its wetting and filling, it is gradually cooled to the range of 130–200°C under argon protection and pressure to suppress the rebound and opening of the copper foil. After the bismuth has completely cooled and solidified, a stable mechanical locking and anchoring structure is formed at the interface of the two copper foil layers. S4. Multi-stage cold drawing forming: After anchoring and cooling, the sandwich composite plate is first rolled and compacted gradually, and then continuously cold-drawn and reduced in diameter through multiple hard alloy drawing dies; no tempering stress relief process is set up throughout the process, and the radial compressive stress generated by the plastic deformation of the wire drawing is used to further compact the bismuth interlocking interface and strengthen the interlayer bonding force; conventional specification wires are directly cold-drawn to the target wire diameter; when preparing fine specification wires, copper tubes can be wrapped around the composite blank before deep drawing. Copper tube wrapping is an optional optimization process and not a necessary step in the process.

2. The fabrication process of a bismuth-graphene copper composite wire according to claim 1, characterized in that: The oxidation removal process of the high-purity copper foil in S1 includes acid washing, water washing, ultrasonic cleaning with organic solvents, and drying with inert protective gas. Before mixing, the powder is vacuum dried to remove water. The powder mixing environment is under low humidity control, and the exposure time of the powder is strictly limited. Air and water vapor are completely isolated throughout the process.

3. The fabrication process of a bismuth-graphene copper composite wire according to claim 1, characterized in that: The argon gas used in S3 is high-purity argon gas, and the oxygen content in the interlayer cavity is strictly controlled. After the molten bismuth is anchored, it is slowly cooled under pressure in an argon atmosphere until the bismuth is completely solidified to form an interlayer locking structure.

4. The fabrication process of a bismuth-graphene copper composite wire according to claim 1, characterized in that: The total cross-sectional shrinkage rate of the S4 cold-drawn wire is ≥96%; after the wire drawing process is completed, the surface lubricating medium is removed by cleaning, and the wire is dried with inert gas and then wound up to obtain the finished composite wire.

5. The fabrication process of a bismuth-graphene copper composite wire according to claim 1, characterized in that: The bismuth-graphene copper composite wire prepared by this process can achieve a conductivity of 98.5% IACS at 20℃, and the interlayer shear strength is increased by 42% compared with ordinary pure copper wound wire, while the arc reciprocating wear and ablation amount is reduced by 37%.

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