Graphene copper composite material for transmission under high current density and preparation method of graphene copper composite material

Abstract

The invention relates to the technical field of copper material processing and manufacturing, in particular to a graphene copper composite material for transmission under high current density and a preparation method thereof.The method comprises the steps that cold isostatic pressing treatment is conducted on copper powder for in-situ growth of graphene, and a compressed blank is obtained; sintering the compressed blank to obtain a sintered blank; carrying out extrusion treatment on the sintered blank to obtain an extruded blank; the extrusion blank is subjected to a drawing process and annealing treatment, and the graphene copper composite material is obtained; the temperature rise of the obtained graphene copper composite material is at least 10% lower than that of oxygen-free copper under the large current density, the high-temperature conductivity is 3%-7% higher than that of TU0 oxygen-free copper, the temperature coefficient of resistance (TCR) is at least 3%-11% lower than that of pure copper, the heat conductivity coefficient reaches at least 440 W / (m.K), the conductivity is at least 105% IACS, the tensile strength is larger than or equal to 350 MPa, and the softening temperature is larger than or equal to 300 DEG C.

Description

Technical Field

[0001] This application relates to the field of copper material processing and manufacturing technology, specifically to graphene-copper composite materials for transmission under high current density and their preparation methods. Background Technology

[0002] In modern electronics and electrical engineering, high-current-density and high-temperature current transmission scenarios are becoming increasingly common, such as the power battery systems of new energy vehicles, high-voltage direct current transmission equipment, and power modules of high-power servers. Traditional copper conductors, due to their inherent limitations in conductivity and thermal conductivity, struggle to meet the demands of high-current-density and high-temperature current transmission. When current flows through, the Joule heat generated by the resistance of the copper conductor is significant, causing the temperature to rise. This not only reduces transmission efficiency but may also lead to safety hazards such as insulation aging and equipment failure. Furthermore, heat accumulation can increase the resistivity of the copper conductor, creating a vicious cycle.

[0003] To improve the performance of copper conductors, incorporating graphene into a copper matrix to form a composite material has become a research hotspot. Graphene possesses excellent electrical and thermal properties, with a theoretical conductivity as high as 10⁻⁶. 6 With a thermal conductivity of up to 5300 W / (m·K), graphene-copper composite wires are ideal reinforcements. However, existing graphene-copper composite wires still face numerous challenges in preparation and performance. On one hand, during preparation, insufficient interfacial bonding strength between graphene and the copper matrix leads to agglomeration, severely hindering electron and phonon conduction and limiting the performance improvement of the composite material. On the other hand, traditional preparation processes struggle to precisely control the dispersion state of graphene and the microstructure of the composite wire, resulting in large fluctuations in electrical and thermal conductivity, failing to consistently meet the stringent requirements of current transmission under high current density and high-temperature conditions. Furthermore, some preparation methods are complex and costly, hindering large-scale industrial production. Therefore, there is an urgent need to develop a graphene-copper composite wire and its preparation method that can effectively solve these problems, achieve high electrical and thermal conductivity, and be suitable for industrial production. Summary of the Invention

[0004] This application provides a graphene-copper composite material and its preparation method for current transmission under high current density or high temperature conditions. By rationally controlling process parameters such as cold isostatic pressing, sintering, hot extrusion, and continuous drawing, the interface between graphene and copper is optimized, and the oxygen content and grain size are precisely controlled. This produces graphene-copper wires with high thermal and electrical conductivity, low temperature rise under high current conditions, and good electrical and mechanical properties in high-temperature environments, thus meeting the needs of high-end fields for conductive materials.

[0005] The first aspect of this application provides a method for preparing a graphene-copper composite material for transmission at high current densities, comprising:

[0006] Copper powder from which graphene is grown in situ is subjected to cold isostatic pressing to obtain a compressed billet.

[0007] The compressed billet is sintered to obtain a sintered billet;

[0008] The sintered billet is extruded to obtain an extruded billet;

[0009] The extruded billet is subjected to a drawing process and annealing to obtain a graphene copper composite material;

[0010] The graphene in the copper powder from which the in-situ graphene is grown has a carbon content of 100–500 ppm, an oxygen content of <350 ppm, and a Raman characteristic peak I. G / I Cu >0.85, Raman characteristic peak I 2D / I Cu <1.0.

[0011] Preferably, the step of cold isostatic pressing the copper powder from which graphene is grown in situ to obtain a compressed blank includes:

[0012] A pressure of 20–100 MPa is applied to the copper powder from which graphene is grown in situ for 20–60 minutes to obtain a compressed blank with a density of <70%.

[0013] Preferably, the compressed billet is sintered to obtain a sintered billet comprising:

[0014] The compressed billet is subjected to a low-temperature deoxygenation stage and a high-temperature pore-closing stage to obtain a sintered billet with an oxygen content of <100ppm.

[0015] Preferably, the low-temperature deoxygenation stage is held at 300–400°C for 60–90 minutes; the high-temperature pore-closing stage is held at 850–880°C for 120–150 minutes; and the cavity pressure during sintering is 1 × 10⁻² to 1 × 10⁻². -3 Pa.

[0016] Preferably, the extrusion process employs a combination of hot extrusion and continuous extrusion, with the hot extrusion temperature controlled at 600–700°C and the extrusion ratio at 10:1–40:1; the continuous extrusion speed is 5–25 mm / s.

[0017] Preferably, the wire drawing deformation is controlled at 10% to 25% in the drawing process, and annealing is performed after 3 to 5 drawing passes.

[0018] Preferably, online annealing is used, with an online annealing temperature of 400–500℃ and an annealing time of 30–60 seconds.

[0019] Preferably, annealing is performed using a bell-shaped furnace, followed by surface impurity removal; the surface impurity removal includes:

[0020] The material obtained after drawing and annealing is placed in a vacuum of ≤1×10⁻⁶. -3 Under an environment of Pa and a temperature of 200℃~400℃ for 60~600min, while a protective gas with a flow rate of 2~5L / min is passed through to remove impurities from the material surface, the oxygen content of the obtained graphene copper composite material is <80ppm.

[0021] The protective gas is one of nitrogen, hydrogen, or argon.

[0022] The second aspect of this application provides a graphene-copper composite material for transmission under high current density prepared according to the above method. The graphene-copper composite material has a temperature rise at high current density that is at least 10% lower than that of oxygen-free copper, a high-temperature conductivity that is 3% to 7% higher than that of TOO oxygen-free copper, and a temperature coefficient of resistance (TCR) that is at least 3-11% lower than that of pure copper.

[0023] Preferably, the graphene-copper composite material has a thermal conductivity of at least 440 W / (m·K), an electrical conductivity of at least 105% IACS, a tensile strength of ≥350 MPa, and a softening temperature of ≥300℃.

[0024] The principle of this application is as follows:

[0025] The core principle of this application lies in the synergistic control of the graphene-copper interface state, oxygen impurity concentration, and grain evolution behavior through multi-stage processes. First, copper powder for in-situ graphene growth is selected as the raw material (specific surface area 0.1-0.5 μm²). 2 / g, carbon content 100–500ppm), its Raman characteristics I G / I Cu The presence of a >0.85 ohm and the absence of a 2D peak indicates a strong interfacial coupling between graphene and the copper matrix, laying the structural foundation for a highly conductive / thermally conductive pathway. Secondly, an innovative "low-temperature deoxygenation-high-temperature pore-closure" sintering mechanism is employed: holding at a low temperature of 300–400℃ for 60–90 minutes to bond 10 -2 A high vacuum environment (Pa) promotes the escape of oxygen atoms from the grain boundaries; holding at a high temperature of 850–880℃ for 120–150 minutes achieves pore closure and simultaneously inhibits copper grain coarsening. Finally, plastic deformation driven by hot extrusion (600–700℃ / extrusion ratio 10:1–40:1) and continuous extrusion (roller speed 5–25 mm / s) drives the graphene to oriented alignment, followed by segmented drawing (deformation amount 10–25%) and customized annealing (bell furnace nitrogen-hydrogen atmosphere) to eliminate work hardening, ultimately yielding a high-performance graphene-copper composite material.

[0026] The technical effects achieved by the above-mentioned technical solution in this application are as follows:

[0027] This application successfully prepared a high-performance graphene-copper composite material by precisely controlling the core parameters of in-situ grown graphene-copper powder (such as carbon content, oxygen content, and specific Raman characteristic peaks) and combining them with optimized sintering, extrusion, and drawing processes. Its most significant beneficial effect is reflected in 180 A / mm². 2 The temperature rise is 10% lower than that of oxygen-free copper, directly improving motor efficiency and service life; the thermal conductivity exceeds 460W / (m·K) and its high-temperature thermal conductivity surpasses that of pure copper, meeting the requirements of demanding heat dissipation scenarios; the combination of reduced high-frequency AC impedance and 105% IACS high conductivity supports the stable operation of high-power electrical systems; and with a softening temperature of ≥300℃, it breaks through the high-temperature application limit of pure copper, promoting the large-scale replacement of this material in emerging fields such as aerospace thermal management and high-temperature electrical connections, expanding the technological boundaries of copper-based composite materials. Attached Figure Description

[0028] The accompanying drawings are provided to further illustrate the present application and form part of the specification. They are used together with the embodiments of the present application to explain the application and do not constitute a limitation thereof. In the drawings:

[0029] Figure 1 A flowchart illustrating a method for preparing a graphene-copper composite material for high current density transmission, provided for some embodiments of this application.

[0030] Figure 2 The graph shows the high-current temperature rise test results of graphene-copper composite materials provided in some embodiments of this application.

[0031] Figure 3 The resistivity changes of graphene-copper composite materials and oxygen-free copper at different temperatures are shown in some embodiments of this application.

[0032] Figure 4 A comparison graph showing the change in thermal conductivity of graphene-copper composite material and oxygen-free copper at different temperatures, provided in some embodiments of this application. Detailed Implementation

[0033] In the following description, only certain exemplary embodiments are depicted simply. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of this application. Therefore, the drawings and description are considered exemplary in nature and not restrictive.

[0034] Unless otherwise defined herein, scientific and technical terms used in conjunction with this application will have the meanings commonly understood by one of ordinary skill in the art. Furthermore, unless the context otherwise requires, singular terms shall include plural forms, and plural terms shall include singular forms. More specifically, as used in this specification and the appended claims, unless the context explicitly indicates otherwise, the singular forms “a,” “an,” and “the” include plural indicators. In this application, unless otherwise stated, the use of “or” means “and / or.” Furthermore, the use of the term “comprising” and other forms such as “including” and “containing” is not limiting. Moreover, the scope provided in the specification and the appended claims includes all values ​​between endpoints. Preferred embodiments of this application are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this application.

[0035] Figure 1 A flowchart illustrating a method for preparing a graphene-copper composite material for high current density transmission, provided for some embodiments of this application.

[0036] like Figure 1 As shown, the first aspect of this application provides a method for preparing graphene-copper composite materials for transmission at high current densities, comprising:

[0037] S1. Electrolytic copper powder, which is used to grow graphene in situ by chemical vapor deposition, is used as raw material and subjected to cold isostatic pressing to obtain compressed billet.

[0038] S2. Sinter the compressed billet to obtain a sintered billet;

[0039] S3. Extrusion process the sintered billet to obtain an extruded billet;

[0040] S4. The extruded blank is subjected to a drawing process to obtain a graphene copper composite material.

[0041] In some embodiments, the copper powder used for in-situ graphene growth must meet the following key indicators:

[0042] The specific surface area of ​​the copper powder is strictly controlled within the range of 0.1–0.5 m². 2 / g, which has a dendritic microstructure, and the larger the specific surface area, the more graphene will grow.

[0043] Preferably, electrolytic copper powder is used, which has a well-developed dendritic structure and a large specific surface area, thus enabling the deposition of more graphene.

[0044] Copper powder has a particle size of 5 to 75 micrometers. If the particle size is larger than 75 micrometers, the amount of graphene that will be grown later will be insufficient, and a continuous graphene network cannot be formed after processing. If the particle size is smaller than 5 micrometers, the more active the surface atoms are, the easier it is to oxidize and agglomerate into large particles during processing, which makes it difficult to grow graphene and cannot be processed into qualified products.

[0045] The loose packing density is between 0.7 and 2.0 g / mL, reflecting its porous dendritic structure; the micron-sized particle size and loose packing density are matched to avoid high pressure damage to the graphene structure during cold isostatic pressing, while providing a uniform preform for subsequent molding processes.

[0046] The carbon content of graphene in graphene copper powder is 100-500 ppm. When the carbon content is less than 100 ppm, the graphene network will be severely damaged during processing due to the high affinity of oxygen for carbon (the activation energy of carbon oxidation reaction is lower than that of copper oxidation), making it impossible to form a continuous conductive / thermal pathway. When the carbon content is higher than 500 ppm, the excessive graphene will destroy the continuity of the copper matrix, resulting in weakened interfacial bonding and a sharp increase in the work hardening index. This manifests as an increased wire breakage rate during drawing, making it impossible to prepare continuous fine wires, or even completely losing processability due to the brittleness of the material.

[0047] The oxygen content of graphene in graphene-copper powder is less than 350 ppm. Oxygen can form brittle compounds (such as cuprous oxide) with copper, which can cause microcracks during subsequent high-temperature processing (hot extrusion / drawing), thus damaging the interfacial bonding between graphene and copper. Furthermore, oxygen can also form carbon-oxygen bonds with carbon. Both the oxygen-containing functional groups in carbon-oxygen bonds and cuprous oxide have very low electrical conductivity, affecting the movement of electrons between graphene and copper, thereby severely impacting electrical and thermal conductivity.

[0048] The Raman spectral characteristics of graphene copper powder must satisfy I G / I Cu >0.85, Raman characteristic peak I 2D / I Cu <1.0.

[0049] Among them, I G The peak value of the G peak and the I peak value in the Raman spectrum of copper graphene powder. 2D The peak value of the 2D peak in the Raman spectrum of copper graphene powder, I Cu The peak value of the fluorescence peak in the Raman spectrum representing graphene copper powder.

[0050] The height of the G peak in a Raman spectrum indicates the strength of the symmetric vibration of the C-C bonds in the material. When the G peak is higher than the fluorescence peak of copper, it means that there is more carbon related to graphene in the material, which is beneficial to the electrical and thermal conductivity of the final product.

[0051] Raman characteristic peak I2D / I Cu A value <1.0 indicates that graphene has low defect characteristics and a good interface, preventing graphene from lifting off the copper atom surface. This forms the structural basis for the high electrical and thermal conductivity of subsequent graphene-copper composites. The principle is that the 2D peak of graphene originates from the out-of-plane vibration mode of carbon atoms. When graphene forms a strong interfacial coupling with the copper matrix, the constraint effect of copper atoms will significantly suppress its out-of-plane vibration, meaning the 2D peak is not obvious. Conversely, if a significant 2D peak can be detected, it indicates that the interface has been damaged (graphene is suspended due to oxidation and exfoliation) or that oxidation of the copper matrix has caused graphene to detach from the contact.

[0052] In some embodiments, the graphene copper powder used for in-situ graphene growth is specifically the CP300 from Suzhou Shengguang Materials Co., Ltd.

[0053] In some embodiments, for copper powder used for in-situ graphene growth, this application employs a cold isostatic pressing process to pre-treat the billet. The pressure in the cold isostatic pressing process is set to 50-200 MPa, and the time is controlled to be 20-60 min.

[0054] If the pressure is less than 50 MPa, the powder particles can only achieve "weak contact stacking," and the porosity cannot be effectively reduced, resulting in a low relative density of the billet. Under this condition, during hot extrusion, the bonding force between powder particles is insufficient, and the billet is prone to delamination / cracking due to high temperature and pressure. In the subsequent drawing process, the low density of the billet leads to "weak graphene-copper interface bonding," and the drawing breakage rate increases sharply.

[0055] If the pressure is greater than 200 MPa, on the one hand, overpressure can easily lead to mold deformation and seal failure, and introduce air impurities that cause the billet to oxidize (a CuO layer is formed on the surface of the copper powder, which hinders the metallurgical bonding during hot extrusion); on the other hand, under excessive pressure, the shear stress between graphene copper powder particles increases dramatically, which can cause the graphene sheets to "fold and break", weakening its strengthening and toughening effect on the copper matrix; in addition, excessive pressure will also make the billet relatively dense, which will cause the resistance to subsequent hot extrusion deformation to increase exponentially, easily causing surface cracks and internal residual stress concentration in the extruded billet, and the breakage rate will actually increase during drawing.

[0056] If the holding time is less than 20 minutes, the powder particles only undergo "short-range rearrangement," and a large number of "bridging pores" (i.e., unstable support structures formed between particles due to rapid extrusion) exist inside the billet. Under this condition, during hot extrusion, the bridging pores collapse under high pressure, resulting in large fluctuations in the density of the extruded billet, and poor consistency in the high-frequency electrical properties (AC resistance) of the subsequently formed graphene-copper composite material. During the drawing process, the "stress concentration zone" caused by the collapse of pores becomes a crack source, which greatly increases the dispersion of copper wire strength, resulting in insufficient strength of the subsequently formed graphene-copper composite material.

[0057] If the pressure holding time exceeds 60 minutes, production efficiency will be reduced.

[0058] In some embodiments, in-situ grown graphene copper powder that meets specific requirements is sintered, and the cavity pressure during sintering is 1×10⁻² to 1×10⁻². -3 Pa, the sintering process is divided into a low-temperature deoxygenation stage and a high-temperature closed-cell stage, in order to obtain sintered billets with an oxygen content of <100ppm.

[0059] During the low-temperature deoxygenation stage, the cold isostatically pressed billet is placed in a vacuum sintering furnace, and the cavity pressure is reduced to 1×10⁻⁶. -2 A high-vacuum environment at the Pa level creates the physical conditions for efficient removal of oxygen impurities. During this stage, the temperature is precisely controlled within the 300–400℃ range and maintained for 60–90 minutes. Utilizing the decomposition kinetics of oxides on the copper powder surface at low temperatures, oxygen atoms escape from the copper matrix and graphene interface, thereby reducing the overall oxygen content of the material to below 100ppm, thus mitigating the risk of oxygen damaging electrical / thermal conductive pathways at the source.

[0060] After entering the high-temperature pore-closure stage, the temperature is gradually increased to 850–880℃ and held at this temperature for 120–150 minutes. This temperature window design has two significances: firstly, the high temperature activates the diffusion ability of copper atoms, driving the formation of dense metallurgical bonds between powder particles, achieving pore closure and grain boundary migration; secondly, it precisely avoids the melting point of copper (900℃) while simultaneously inhibiting abnormal copper grain growth. During this process, the activation of the pore-closure mechanism effectively isolates secondary intrusion of external oxygen, while the continuous high-vacuum environment further eliminates residual gaseous oxygen molecules, laying the foundation for the stability of the material's microstructure.

[0061] The maximum sintering temperature is limited to 880℃. Exceeding this threshold will cause localized melting of the copper matrix, disrupting the interfacial coupling of the in-situ grown graphene, and inducing grain coarsening, resulting in graphene enrichment at grain boundaries and even structural damage. By controlling temperature and time in a coordinated manner, not only are the above risks avoided, but the graphene network is also kept uniformly distributed in the copper matrix, providing structurally intact sintered blanks for subsequent processing.

[0062] The technical advantages of this sintering process are as follows: First, the oxygen content is strictly controlled to within 100 ppm, significantly reducing the probability of the formation of the brittle cuprous oxide phase and ensuring the free transport of electrons at the graphene-copper interface. Second, through the grain boundary pinning effect of graphene, the composite material achieves controlled grain size growth during sintering, thereby retaining the work hardening potential. In other words, the fine-grained structure provides dislocation storage space for subsequent deformation, avoiding the deterioration of mechanical properties, i.e., inhibiting the decrease in strength / plasticity caused by grain coarsening. Third, the phased combination of low-temperature deoxidation and high-temperature pore closing achieves densification while realizing deep deoxidation, so that the billet has both low oxygen impurity concentration and high structural integrity, providing an ideal precursor for subsequent extrusion and drawing processes.

[0063] In some embodiments, the sintered billet needs to undergo a combined hot extrusion and continuous extrusion process to achieve material densification and interface optimization.

[0064] During the hot extrusion stage, the temperature is strictly controlled within the range of 600–650℃. This temperature range ensures that the copper matrix is ​​in a state of high plastic deformation while avoiding excessive temperature that could cause coarsening of copper grains or damage to the graphene structure. At the same time, an extrusion ratio of 10:1–40:1 is used to drive the copper grains to extend along the extrusion direction through appropriate deformation, forcing the graphene sheets to align and embed into the copper matrix, laying the structural foundation for the subsequent formation of a continuous thermally / electrically conductive network.

[0065] Subsequently, a continuous extrusion process is employed, with dynamic processing conditions set at a wheel groove speed of 5–25 mm / s, enabling secondary densification of the material under high-pressure shearing. Too low a speed prolongs the high-temperature exposure time, leading to abnormal grain growth; too high a speed causes uneven deformation, generating internal residual stress. Under these optimized parameters, the intense plastic flow generated by continuous extrusion effectively eliminates micropores in the sintered billet, while simultaneously strengthening the metallurgical bond between graphene and copper through a mechanical-thermal synergistic effect.

[0066] The technical advantages of this composite extrusion process are as follows: First, the appropriate extrusion ratio (10:1–40:1) during the hot extrusion stage complements the high-speed shearing of continuous extrusion, thereby increasing the relative density of the material and significantly reducing the scattering effect of pores on electron / phonon transmission. Second, during the dynamic extrusion process, the graphene sheets achieve preferential orientation within the copper matrix, constructing efficient three-dimensional thermal / electrical conduction pathways and improving the interfacial bonding strength. Third, precise temperature control maintains the work hardening potential of the copper matrix while avoiding the performance degradation caused by high-temperature agglomeration of graphene, providing a highly intact extrusion blank precursor for subsequent drawing processes, ultimately improving the thermal conductivity, electrical conductivity, and tensile strength of the composite material.

[0067] In some embodiments, the degree of plastic deformation and processing rhythm must be strictly controlled during continuous drawing, limiting the deformation per pass to 10%–25%, and annealing is performed promptly after 3–5 passes. This segmented processing strategy effectively balances material work hardening and structural integrity: moderate deformation avoids microcracks caused by excessive work hardening, while staged annealing eliminates internal residual stress through dynamic recrystallization, preventing the risk of wire breakage. Crucially, this design avoids the problem of excessive grain refinement caused by traditional continuous large deformation, providing structural protection for maintaining the material's electrical and thermal conductivity.

[0068] The annealing process offers two optimized pathways: bell-furnace annealing and online annealing. Bell-furnace annealing employs precise atmosphere control. First, the furnace atmosphere is replaced 3–5 times with a nitrogen-hydrogen mixture (8-10:1 volume ratio) to thoroughly remove residual oxygen. Then, the furnace is heated to 400–500°C at a controlled heating rate of 10–15°C / min and held for 60–90 minutes. The advantage of this progressive heat treatment is that the nitrogen-hydrogen mixture can reduce cuprous oxide on the copper substrate surface at high temperatures, while sufficient holding time ensures complete grain boundary migration, achieving synergistic control of deep deoxygenation and grain size.

[0069] The technical advantages of this composite process are as follows: First, a strict oxygen control system (atmosphere (nitrogen, hydrogen, argon) replacement + vacuum deoxygenation before pore closing) ensures that the oxygen content of the finished product is stably reduced to below 100 ppm, significantly weakening the impact of oxygen impurities on electron scattering and laying the foundation for high conductivity. Second, the precise matching of annealing temperature and time eliminates processing stress and avoids conductivity decay caused by excessive grain refinement, allowing the material to maintain high strength and excellent ductility. Third, the synergistic strategy of segmented drawing and differentiated annealing ensures that the graphene-reinforced phase is oriented in the copper matrix while maintaining continuous production without interruption, ultimately achieving a breakthrough in the overall performance of the product and meeting the application requirements of demanding scenarios such as motor windings.

[0070] The graphene-copper composite material can be prepared into industrial standard products (such as 30mm copper rods, 8mm copper bars, and copper wires with diameters of 0.2mm to 2.0mm) through the drawing process, which can be seamlessly integrated with the current copper processing industry.

[0071] In some embodiments, surface impurity removal is performed on the finished product to further deoxidize it, resulting in a graphene-copper composite material with an oxygen content of <80ppm. Specifically, a differentiated temperature-time control strategy is implemented based on the wire diameter. For fine-diameter products (e.g., diameter ≤0.5mm), a lower processing temperature of 200℃ is selected and maintained for a short period of 60 minutes. This utilizes a gentle thermal activation effect to promote the separation of surface-adsorbed impurities from oxygen atoms, achieving surface impurity removal and preliminary deoxidation. For coarse-diameter products (e.g., diameter ≥2mm), a high-temperature treatment of 400℃ combined with a long-time treatment of 600 minutes is used. Through deep thermal penetration, not only are subsurface inclusions eliminated, but internal oxygen atoms are also promoted to diffuse to the surface and be removed. Under these conditions, surface impurities (organic residues, cuprous oxide (Cu2O)) can be effectively removed; surface roughness can be improved, and contact resistance can be reduced; and oxygen segregation at grain boundaries can be eliminated, repairing lattice distortion caused by pulling.

[0072] In fact, fine-diameter products have unique advantages in the deoxidation process due to their larger specific surface area. A larger specific surface area means a greater contact area between a unit mass of material and the external environment (such as vacuum, reducing gases, etc.), making it easier for the deoxidation medium (such as the pressure difference in a vacuum environment, the protective effect of inert gases, etc.) to interact with oxygen atoms on the material surface and inside. In this embodiment, the triple protection mechanism implemented simultaneously in the sealed chamber fully considers this characteristic. First, the vacuum level is raised to an ultra-high vacuum environment of ≤1×10⁻³ Pa, and oxygen molecules adsorbed on the material surface are forcibly removed through physical suction. Due to the large specific surface area of ​​fine-diameter products, oxygen molecules adsorbed on their surface can be removed more quickly. Subsequently, a protective gas with a flow rate of 2-5 L / min is continuously introduced as a protective medium, forming a dynamic gas barrier layer on the material surface. For fine-diameter products, this gas barrier layer can more tightly encapsulate the material, further blocking the intrusion of oxygen atoms. This combined process, through the synergistic effect of vacuum deoxygenation and inert gas covering, completely blocks the secondary oxidation path of the copper substrate under high temperature conditions. Compared with coarse wire diameter products, fine wire diameter products show a more significant reduction in the amount of cuprous oxide generated on the surface under this process, thus achieving a more efficient deoxidation effect.

[0073] The protective gas is one of nitrogen, hydrogen, or argon.

[0074] The second aspect of this application provides a graphene-copper composite material for current transmission under high current density or high temperature conditions, prepared by the method described above. This graphene-copper composite material is used in motors with high current density (30 A / mm²) applications. 2 Its temperature rise is at least 10% lower than that of oxygen-free copper, its high-temperature conductivity is 3% to 7% higher than that of TU0 oxygen-free copper, and its temperature coefficient of resistance (TCR) is at least 3-11% lower than that of pure copper.

[0075] Furthermore, the thermal conductivity reaches at least 440 W / (m·K), the electrical conductivity is at least 105% IACS, the tensile strength is ≥350 MPa, and the softening temperature is ≥300℃.

[0076] Furthermore, graphene-copper composite materials have high strength and high softening temperature, making them suitable for use in high-temperature environments.

[0077] The present application is further illustrated by the following embodiments.

[0078] Example 1

[0079] The graphene copper powder used in this embodiment is Suzhou Shengguang's CP300, with a specific surface area of ​​0.2 m². 2 / g, particle size -325 mesh (<45 micrometers), density 1.6g / mL, carbon content 256ppm, graphene characteristic peak I G / I Cu It is 0.858.

[0080] The graphene copper powder was subjected to cold isostatic pressing, with the cold isostatic pressing pressure maintained at around 60 MPa and the holding time being 30 min.

[0081] The cold isostatically pressed billet is placed in a vacuum sintering furnace, and the chamber pressure is reduced to 1×10⁻⁶. -2 Pa precisely controls the temperature within the 400℃ range and maintains it for 60 minutes. Then, the temperature is raised to 880℃ and held for 150 minutes.

[0082] The sintered billet is subjected to hot extrusion treatment, with the temperature strictly controlled within the range of 650℃ and an extrusion ratio of 10:1. Then, a continuous extrusion process is connected, and the wheel groove speed is set to 20mm / s.

[0083] During continuous drawing, the degree of plastic deformation and processing rhythm must be strictly controlled, the deformation amount of a single drawing pass is limited to within 30%, and bell furnace annealing is carried out in time after 3 passes.

[0084] During bell furnace annealing, the furnace atmosphere is first replaced three times with a mixed gas with a nitrogen-hydrogen volume ratio of 10:1 to completely remove the residual oxygen environment; then, it is heated to 400℃ at a controlled heating rate of 15℃ / min and held for 90 minutes.

[0085] After drawing and annealing, a 12mm copper rod is obtained. The final surface impurity removal process involves ultrasonic cleaning at a frequency of 40kHz for 10 minutes, which effectively removes impurities from the copper rod surface. This is done under a vacuum degree <10 -3 Pa, without introducing gas, heat to 400℃ at a heating rate of 10℃ / min, and hold for 120min.

[0086] Example 2

[0087] The graphene copper powder used in this embodiment is Suzhou Shengguang's CP300, with a specific surface area of ​​0.2 m². 2 / g, particle size -325 mesh (<45 micrometers), density 1.6g / mL, carbon content 306ppm, graphene characteristic peak I G / I Cu It is 9.027.

[0088] The graphene copper powder was subjected to cold isostatic pressing, with the cold isostatic pressing pressure maintained at around 100 MPa and the holding time being 20 min.

[0089] The cold isostatically pressed billet is placed in a vacuum sintering furnace, and the chamber pressure is reduced to 1×10⁻⁶. -2 Pa precisely controls the temperature within the 400℃ range and maintains it for 90 minutes. Then, the temperature is raised to 865℃ and held for 120 minutes.

[0090] The sintered billet is subjected to hot extrusion treatment, with the temperature strictly controlled within the range of 600℃. An extrusion ratio of 8:1 is adopted, followed by a continuous extrusion process, with the wheel groove speed set at 15mm / s.

[0091] During continuous drawing, the degree of plastic deformation and processing rhythm must be strictly controlled, the deformation of a single drawing pass must be limited to within 25%, and bell furnace annealing should be carried out in time after 5 passes.

[0092] During bell-shaped furnace annealing, the furnace atmosphere is first purged three times with argon to thoroughly remove any residual oxygen. Then, the furnace is heated to 200°C at a rate of 5°C / min, with argon gas introduced at a rate of 3L / min and held at that temperature for 60 minutes. Afterward, the furnace is heated to 450°C at a rate of 10°C / min, without any gas flow.

[0093] After drawing and annealing, a 4.7mm wire is obtained. A gradient heating process is used, with the wire temperature at 10... -3 Under vacuum conditions, holding at 200℃ for 60 min and introducing argon at 5 L / min can remove adsorbed oxygen and residual organic matter from the surface. Then, the temperature is increased to 500℃ at a rate of 10℃ / min, held for 90 min, and 5% H2 + 95% Ar2 is introduced at 3 L / min to effectively reduce Cu2O. Finally, the temperature is increased to 700℃ and held for 120 min to promote the migration of oxygen at the grain boundaries, thereby achieving a highly efficient deoxygenation effect in the finished product.

[0094] Example 3

[0095] The graphene copper powder used in this embodiment is Suzhou Shengguang's CP300, with a specific surface area of ​​0.2 m². 2 / g, particle size -325 mesh (<45 micrometers), density 1.6g / mL, carbon content 177ppm, graphene characteristic peak I G / I Cu It is 0.894.

[0096] The graphene copper powder was subjected to cold isostatic pressing, with the cold isostatic pressing pressure maintained at around 80 MPa and the holding time being 30 min.

[0097] The cold isostatically pressed billet is placed in a vacuum sintering furnace, and the chamber pressure is reduced to 1×10⁻⁶. -2 Pa precisely controls the temperature within the 300℃ range and maintains it for 120 minutes. Then, the temperature is raised to 850℃ and held for 150 minutes.

[0098] The sintered billet is subjected to hot extrusion treatment, with the temperature strictly controlled within the range of 630℃. An extrusion ratio of 8:1 is adopted, followed by a continuous extrusion process, with the wheel groove speed set at 20mm / s.

[0099] During continuous drawing, the degree of plastic deformation and processing rhythm must be strictly controlled, and the deformation amount of a single drawing pass must be limited to within 35%. After three passes, the wire should be annealed in a bell furnace in a timely manner.

[0100] During bell furnace annealing, the temperature is raised to 500°C at a controlled heating rate of 15°C / min and held for 60 minutes.

[0101] After drawing and annealing, an 8mm copper wire is obtained, which is then processed at 10... -3 Under vacuum conditions, the temperature was increased at 10℃ / min and held at 600℃ for 360 min, while 5% H2 + 95% N2 was introduced at a rate of 5 L / min. This effectively improved work hardening during the drawing process, eliminated oxygen segregation at grain boundaries, and repaired lattice distortion caused by drawing.

[0102] Figure 2 The graph shows the high current density temperature rise test results of the graphene-copper composite material provided in some embodiments of this application. Figure 2 The horizontal axis is "30A / mm" 2 The graph shows the energizing time (s) under current density conditions, with the vertical axis representing "temperature (°C)". This compares the temperature rise characteristics of oxygen-free copper and the graphene copper wire of this application. The results show that under the same high-temperature and current conditions, the temperature rise of the graphene copper wire is significantly lower than that of oxygen-free copper, directly verifying the advantage of this product in terms of current-temperature rise under high-temperature conditions.

[0103] Figure 3 The graph shows the resistivity changes of graphene-copper composite materials and oxygen-free copper at different temperatures, as provided in some embodiments of this application. Figure 3As shown, at the same temperature, the resistance of graphene copper wire is always lower than that of oxygen-free copper wire, which directly verifies that this product has better resistance characteristics in high-temperature environments and is suitable for high-temperature conductive applications.

[0104] Figure 4 This is a comparison graph showing the change in thermal conductivity of graphene-copper composite materials and oxygen-free copper at different temperatures, provided in some embodiments of this application. Figure 4 As shown, compared with pure copper, the graphene copper obtained in this application has better performance in terms of thermal conductivity and temperature stability, and is suitable for scenarios with high thermal conductivity requirements and variable temperature environments.

[0105] Table 1 shows a comparison of the temperature rise of graphene-copper composite materials provided in some embodiments of this application under different current densities. As shown in Table 1, the higher the current, the more prominent the temperature rise advantage of graphene-copper.

[0106] Low electrical density (10A / mm) 2 The difference is only 0.35%, which is minimal (the material generates little heat under low load, making it difficult to demonstrate its temperature control capability).

[0107] Medium power density (15A / mm) 2 ): Reduced by 1.76%, the advantages began to emerge (load increased, the thermal conductivity and resistance characteristics of graphene copper gradually came into play).

[0108] High electrical density (20A / mm) 2 The difference increased dramatically by 15.14% (under high load, graphene copper has a much better heat dissipation and heat decay resistance than oxygen-free copper, and the temperature control effect is obvious).

[0109] High electrical density (25A / mm) 2 ): Reduced by 7.56% (although the magnitude is less than 20A / mm) 2 However, under extreme heat generation conditions with high electrical density, a significant temperature rise occurred within 5 minutes, yet the voltage still dropped by 7.56%, demonstrating the material's heat resistance potential.

[0110] Table 1

[0111]

[0112] Table 2 is a comparison chart of the properties of graphene copper composite material and oxygen-free copper (oxygen content below 3 ppm) provided in some embodiments of this application.

[0113] As shown in Table 2, the graphene-copper composite material prepared in this application has the following advantages compared with oxygen-free copper:

[0114] Electrical performance: Higher carrier concentration (1.33 × 10²³ 1 / cm²) 3 >8.47×1022 1 / cm 3It has strong theoretical conductivity potential; its AC impedance at 100kHz is only 40% of that of oxygen-free copper, and its high-frequency conductivity loss is low.

[0115] Thermal properties: Higher thermal conductivity (480W / (m·K)>380W / (m·K)), with better heat dissipation and thermal conductivity.

[0116] Environmental stability: When heated to 200℃, the oxidation resistance time is longer (80s>30s), and the high-temperature oxidation resistance is good.

[0117] Overall performance: By leveraging the synergistic effect of graphene and copper, it is expected to improve properties such as conductivity while maintaining mechanical properties. In some scenarios (such as motors), power density may be improved, and low-cost, large-scale production can be achieved through technological optimization.

[0118] Table 2

[0119] oxygen-free copper Graphene copper unit illustrate Graphene content 0 100 ppm Carbon and sulfur analyzer oxygen content <3 30 ppm Oxygen, nitrogen and hydrogen analyzer carrier concentration <![CDATA[8.47×10 22 ]]> <![CDATA[1.33×10 23 ]]> <![CDATA[1 / cm 3 ]]> Hall effect method thermal conductivity 380 440 W / (m·K) Netzsch 467, Flash Method DC resistance 102 >105 %IACS 8mm copper rod, four-end method test AC impedance 100 40 ％ 10kHz, 4.6mm Antioxidant time 30 70 s Heating at 200 degrees

[0120] Finally, it should be noted that the above descriptions are merely preferred embodiments of this application and are not intended to limit this application. Although this application 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 this application should be included within the protection scope of this application.

Claims

1. A method for preparing graphene-copper composite materials for transmission under high current density, characterized in that, include: Copper powder from which graphene is grown in situ is subjected to cold isostatic pressing to obtain a compressed billet. The compressed billet is sintered to obtain a sintered billet; The sintered billet is extruded to obtain an extruded billet; The extruded billet is subjected to a drawing process and annealing to obtain a graphene copper composite material; The graphene on the copper powder in which the graphene is grown in situ has a carbon content of 100-500 ppm, an oxygen content of <350 ppm, a Raman characteristic peak IG / ICu>0.85, and a Raman characteristic peak I2D / ICu<1.

0.

2. The method for preparing graphene-copper composite material for high current density transmission according to claim 1, characterized in that, The process of cold isostatically pressing copper powder to obtain compressed blanks by in-situ growing graphene includes: A pressure of 20–100 MPa is applied to the copper powder from which graphene is grown in situ for 20–60 minutes to obtain a compressed blank with a density of <70%.

3. The method for preparing graphene-copper composite material for high current density transmission according to claim 1, characterized in that, The compressed billet is sintered to obtain a sintered billet comprising: The compressed billet is subjected to a low-temperature deoxygenation stage and a high-temperature pore-closing stage to obtain a sintered billet with an oxygen content of <100ppm.

4. The method for preparing graphene-copper composite material for high current density transmission according to claim 3, characterized in that, The low-temperature deoxygenation stage is held at 300–400℃ for 60–90 minutes; the high-temperature pore-closing stage is held at 850–880℃ for 120–150 minutes; and the cavity pressure during sintering is 1×10⁻² to 1×10⁻². -3 Pa.

5. The method for preparing graphene-copper composite material for high current density transmission according to claim 1, characterized in that, The extrusion process employs a combination of hot extrusion and continuous extrusion. The hot extrusion temperature is controlled at 600–700°C, and the extrusion ratio is 10:1–40:

1. The continuous extrusion speed is 5–25 mm / s.

6. The method for preparing graphene-copper composite material for high current density transmission according to claim 1, characterized in that, The drawing process controls the wire deformation to be between 10% and 25%, and annealing is performed after 3 to 5 drawing passes.

7. The method for preparing graphene-copper composite material for high current density transmission according to claim 6, characterized in that, Online annealing is used, with an online annealing temperature of 400–500℃ and an annealing time of 30–60 seconds.

8. The method for preparing graphene-copper composite material for high current density transmission according to claim 1, characterized in that, Annealing is performed using a bell-shaped furnace, followed by surface impurity removal. The surface impurity removal process includes: The material obtained after drawing and annealing is placed in a vacuum of ≤1×10⁻⁶. -3 Under an environment of Pa and a temperature of 200℃~400℃ for 60~600min, while a protective gas with a flow rate of 2~5L / min is passed through to remove impurities from the material surface, the oxygen content of the obtained graphene copper composite material is <80ppm. The protective gas is one of nitrogen, hydrogen, or argon.

9. The graphene-copper composite material prepared by the method for preparing graphene-copper composite material for high current density transmission according to any one of claims 1 to 8, characterized in that, The graphene-copper composite material has a temperature rise that is at least 10% lower than that of oxygen-free copper under high current density, a high-temperature conductivity that is 3% to 7% higher than that of TU0 oxygen-free copper, and a temperature coefficient of resistance that is 3-11% lower than that of pure copper.

10. The graphene-copper composite material according to claim 9, characterized in that, The graphene-copper composite material has a thermal conductivity of at least 440 W / (m·K), an electrical conductivity of at least 105% IACS, a tensile strength of ≥350 MPa, and a softening temperature of ≥300℃.

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