Copper / graphene composite wire with high thermal conductivity and low temperature rise as well as preparation method and application of copper / graphene composite wire

Abstract

The invention discloses a copper / graphene composite wire with high thermal conductivity and low temperature rise as well as a preparation method and application of the copper / graphene composite wire, the copper / graphene composite wire comprises the following components in percentage by mass: 99.50-99.98% of Cu and 0.02-0.5% of graphene; copper matrix crystal grains of the copper / graphene composite wire are isometric crystals, the size of the crystal grains is 5-30 microns, and graphene is distributed at a crystal boundary. The copper / graphene composite wire has high heat-conducting property and low temperature rise.

Description

Technical Field

[0001] The present invention belongs to the technical field of copper / graphene composite materials, and particularly relates to a copper / graphene composite wire with high thermal conductivity and low temperature rise, and a preparation method and application thereof. Background Art

[0002] With the rapid development of new energy, electronic appliances and other fields, higher requirements are put forward for conductive materials, which not only need to have excellent electrical conductivity, but also need to have good thermal conductivity, lightweight and other characteristics. Traditional copper wires have limited thermal conductivity and are prone to high temperature rise under high current density, affecting the performance and service life of devices. Graphene, as a new type of two-dimensional material, has excellent electrical conductivity, thermal conductivity, mechanical strength and other characteristics, and is considered an ideal material for improving the performance of copper wires. Combining graphene with copper can significantly improve the thermal conductivity of copper wires, reduce the temperature rise, improve the mechanical strength, and at the same time maintain excellent electrical conductivity.

[0003] The invention patent application with the publication number of CN118910457A discloses a copper / graphene composite material, a preparation method and an application thereof. The preparation method includes: chemically vapor depositing graphene on the surface of a mixed powder of copper powder and nano-magnesium oxide; obtaining a copper / graphene / nano-magnesium oxide composite powder, removing the nano-magnesium oxide in the composite powder to obtain a copper / graphene composite powder; then performing vacuum hot pressing sintering to obtain a copper / graphene composite green body; melting and stirring copper materials and the copper / graphene composite green body, performing vacuum continuous casting, drawing and annealing. Through chemically vapor depositing graphene and combining with vacuum hot pressing sintering and vacuum continuous casting processes, the invention patent realizes the coordination of the structural integrity and uniform dispersion of graphene in the composite material, greatly improves the bonding strength between graphene and the copper matrix, improves the strength and electrical conductivity of the composite material, and makes it have broad application prospects in high-temperature service scenarios. However, for the preparation method disclosed in this patent application, the uniformity of graphene distribution is poor, and the thermal conductivity and low temperature rise performance need to be further improved.

[0004] The invention patent application with the publication number CN107245590A discloses a copper-graphene composite material and a preparation method thereof. The preparation method at least includes the following steps: (1) Mix graphene and an appropriate amount of copper to form spherical bodies with a diameter of 0.5 to 1 cm; (2) Place the copper material in a vacuum device, preheat the vacuum device and evacuate it to 10-4 to 10-3 Pa; the graphene accounts for 0.1 to 5% of the total mass of graphene and copper; (3) Fill in a protective gas to 500 to 1000 Pa; heat the vacuum device until the copper material melts, put the spherical bodies into the molten copper liquid, stir, and immediately pour the copper liquid into a mold after the spherical bodies melt, and cool it to room temperature in a protective gas atmosphere to obtain a copper-graphene composite material ingot. The distribution of graphene in the ingot prepared by the method disclosed in this patent application can be further improved.

[0005] At present, there have been some research reports on copper / graphene composite materials, but most of them focus on bulk materials or thin film materials prepared by methods such as powder metallurgy and electrochemical deposition, which are difficult to meet the requirements of new energy, electronic and electrical fields for wire materials. In addition, problems such as the interfacial bonding strength and the uniform dispersion of graphene in the existing copper / graphene composite materials still need to be further solved.

[0006] The present invention aims to provide a copper / graphene composite wire with high conductivity, high thermal conductivity and low temperature rise, solve the problems of insufficient performance of traditional copper wires and limitations of existing preparation methods of copper / graphene composite materials, and meet the requirements of new energy, electronic and electrical fields for high-performance wire materials. Summary of the Invention

[0007] The present invention provides a copper / graphene composite wire with high thermal conductivity and low temperature rise, which has high thermal conductivity performance and low temperature rise.

[0008] The present invention provides a copper / graphene composite wire with high thermal conductivity and low temperature rise. By mass percentage, the components of the copper / graphene composite wire include Cu: 99.50 - 99.98%, graphene: 0.02 - 0.5%;

[0009] The copper matrix grains of the copper / graphene composite wire are equiaxed grains with a grain size of 5 - 30 μm, and graphene is distributed at the grain boundaries.

[0010] Preferably, the graphene in the copper / graphene composite wire structure is in a connected network-like structure. As a fast transmission channel for electrons and heat, it realizes excellent electrical conductivity, heat dissipation and temperature rise performance.

[0011] Preferably, the conductivity of the copper / graphene composite material is 100.3 - 102.5% IACS, and the thermal conductivity is 457 - 481 W·m -1 ·K -1, the temperature rise under a current density of 18 - 20 A / mm 2 is reduced by 14.7 - 18.3% compared with pure copper.

[0012] The present invention also provides a method for preparing the copper / graphene composite wire with high thermal conductivity and low temperature rise, comprising:

[0013] (1) subjecting copper powder and graphene to acoustic resonance mixing to obtain copper / graphene mixed powder;

[0014] (2) subjecting the copper / graphene mixed powder to vacuum hot pressing and sintering to obtain a copper / graphene composite preform;

[0015] (3) vacuum melting oxygen-free copper material and the copper / graphene composite preform, stirring, casting through a water-cooled copper mold, and subjecting the obtained casting blank to cold rolling, continuous extrusion, and finishing drawing to obtain the copper / graphene composite wire.

[0016] The present invention uses a continuous extrusion process to continuously hot extrude the casting blank to form equiaxed grains. At the same time, due to the pinning effect of graphene at the grain boundaries, the grain size becomes finer. Since fine equiaxed grains are obtained and graphene is uniformly distributed at the grain boundaries, it is more conducive to the formation of a connected three-dimensional network structure, accelerating the migration of electrons and the conduction of heat energy, so that the obtained composite wire has significantly improved electrical conductivity, thermal conductivity, and temperature rise performance under large current.

[0017] The present invention uses the continuous high-pressure effect of continuous extrusion to eliminate casting defects such as completely closed pores and porosity, making the material have a higher density and improving the conductivity.

[0018] Preferably, the extrusion deformation temperature of the continuous extrusion is 400 - 500 °C, and the extrusion speed is 10 - 30 m / min.

[0019] The present invention controls the extrusion deformation temperature to make the copper / graphene composite material reach the dynamic recrystallization temperature, reducing the deformation resistance and avoiding overheating oxidation at the same time. By controlling the extrusion speed, rapid cooling can inhibit grain growth, thereby forming fine equiaxed grains with a grain size of 5 - 30 μm.

[0020] Under the condition of reasonably regulating the extrusion deformation temperature and extrusion speed, as a high-strength nano-reinforcement, graphene can improve the comprehensive performance of copper-based composites through the following synergistic mechanisms:

[0021] (1) Graphene inhibits abnormal grain growth by pinning grain boundary migration, promotes uniform nucleation during dynamic recrystallization, thereby refining the grains of the copper matrix, significantly improving the high-temperature deformation ability of the material, and reducing the work hardening effect at the same time.

[0022] (2) Under the action of thermal-mechanical coupling, graphene and the copper matrix form a strong interface bond through chemical bonding and mechanical interlocking, which effectively transfers loads and inhibits interface debonding, allowing the composite material to maintain structural integrity during deformation.

[0023] (3) Graphene forms a three-dimensional continuous network between copper grains, which has high intrinsic electrical conductivity (~106S / m) and high thermal conductivity (~5000W·m -1 ·K -1 ) can significantly improve the electrical conductivity of the composite material, and reduce the temperature gradient in the processing area by quickly conducting deformation heat, thereby reducing the structural inhomogeneity caused by local overheating.

[0024] (4) The weak van der Waals force between graphene layers gives it self-lubricating properties, which can reduce the friction coefficient between the copper substrate and the die during the extrusion process, promote the uniformity of material flow, and thus reduce the probability of defects such as cracks and pores.

[0025] The present invention controls the extrusion deformation temperature to avoid excessive softening of the copper matrix leading to coarsening of dynamic recrystallization grains, interface oxidation to form a CuO insulating layer, hindering electron / phonon transmission, and reducing electrical / thermal conductivity. It can also avoid insufficient plastic deformation of the copper matrix, causing work hardening, and causing accelerated mold wear rate.

[0026] The present invention controls the extrusion speed to avoid the adiabatic shear effect causing the local temperature to rise instantaneously by 100-150°C, inducing abnormal grain growth, and causing the destruction of the graphene network topological structure, affecting the conductivity. If the extrusion speed is too slow, the processing cycle is extended and the economy is reduced.

[0027] Further preferably, the extrusion deformation temperature of the continuous extrusion is 400-450° C., and the extrusion speed is 10-20 m / min.

[0028] Preferably, the extrusion pressure of the continuous extrusion is 30-50 MPa, and the extrusion wheel speed is 5-10 rpm. The present invention controls the strain rate by controlling the extrusion pressure and the extrusion wheel speed to avoid inducing shear bands as much as possible.

[0029] Preferably, the processing rate of the cold rolling is 70-84%. By controlling the processing rate of the cold rolling, the ingot structure is broken before continuous extrusion, which is more conducive to continuous extrusion to form fine and uniform equiaxed crystals.

[0030] Further preferably, the as-cast round ingot is obtained by casting, and the as-cast round ingot is milled to Remove surface defects, cold rolled to Subsequently, it is continuously extruded to 2-2.1 mm x 3.2-3.3 mm.

[0031] Preferably, after continuous extrusion, alcohol cooling is adopted to inhibit grain growth and prevent oxidation of the wire surface.

[0032] Preferably, in step (1), the particle size of the copper powder is less than 50 μm, the diameter of graphene is < 6 μm, the number of layers is < 5 layers, the specific surface area is 80 - 120 m 2 / g, and the content of graphene in the copper powder is 0.1 - 1%.

[0033] Preferably, in step (1), the conditions for acoustic resonance mixing are: acceleration is 80 - 100 g (1 g ≈ 9.8 m / s 2 ), the vibration frequency is 40 - 100 Hz, the vibration intensity is 30 - 60%, and the mixing time is 5 - 10 min. The present invention adopts the acoustic resonance mixing technology to promote the movement of copper powder and graphene powder by using a low-frequency and high-intensity sound field to promote uniform mixing.

[0034] Preferably, in step (2), the temperature of the vacuum hot pressing sintering is 900 - 1000 °C, the time is 2 - 3 h, the pressure is 20 - 40 MPa, and the vacuum degree is 10 -3 ~10 -1 Pa. By controlling the parameters of the vacuum hot pressing sintering, a better pre-bonding state is formed between graphene and copper, thereby inhibiting the floating of graphene during the subsequent melting process.

[0035] Preferably, in step (3), the mass ratio of the copper / graphene composite green compact to the copper material is 1:1 - 24.

[0036] Preferably, in step (3), by adjusting the ratio of the copper / graphene composite green compact and the copper material, the content of graphene in the obtained copper / graphene composite material is 0.01 - 0.5 wt.%.

[0037] The present invention can control the distribution density of graphene by controlling the content of graphene in the copper / graphene composite green compact and the ratio of oxygen-free copper material and copper / graphene composite green compact during the vacuum melting casting process, and use a water-cooled copper mold for casting to rapidly cool the melt, inhibit the agglomeration and floating of graphene, and make it evenly dispersed in the copper matrix.

[0038] Preferably, in step (3), the vacuum degree of the vacuum melting is 10 -2 ~10 -1 Pa, the protective atmosphere is Ar, and the melting temperature is 1200 - 1250 °C.

[0039] Preferably, in step (3), after the copper material and the copper / graphene composite billet are completely melted, electromagnetic stirring is started. The frequency of the electromagnetic stirring is 20 - 80 Hz, and the current is 200 - 400 A. In the vacuum melting process of the present invention, electromagnetic stirring is adopted to uniformly mix the copper material and the copper / graphene composite billet after melting, so as to realize the uniform dispersion of graphene in the copper matrix.

[0040] Preferably, in step (3), after the melt temperature drops to 1120 - 1180 °C, it is poured into a water-cooled copper mold for casting, so that the melt is rapidly cooled, suppressing the agglomeration and floating of graphene, and making it uniformly dispersed in the copper matrix.

[0041] On the other hand, the present invention also provides the application of the copper / graphene composite wire in the fields of new energy, electronic appliances, etc. as a high thermal conductivity and low temperature rise material. The copper / graphene composite wire with high thermal conductivity and low temperature rise of the present invention can be applied to key components in service scenarios such as new energy drive motors, so as to improve its heat dissipation performance, efficiency and endurance.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] Since the copper matrix grains provided by the present invention are equiaxed grains with fine grains, the grain boundaries are more uniformly distributed in the copper matrix provided by the present invention. And since the present invention also provides an appropriate amount of graphene distributed at the grain boundaries, graphene can be uniformly distributed in the copper / graphene composite wire, forming a path, accelerating the migration of electrons and the conduction of heat energy, so that the copper / graphene composite wire has high thermal conductivity.

[0044] The present invention continuously extrudes the cast billet. While converting the casting structure into equiaxed grains, it also synergistically uses the pinning effect of graphene already in the casting structure on the grain boundaries, making the obtained equiaxed grains uniformly distributed and finer. Since graphene is distributed at the grain boundaries and the grains are equiaxed fine grains, graphene can be uniformly distributed in the matrix, forming a connected three-dimensional network structure, realizing good heat dissipation and low temperature rise. Description of the Drawings

[0045] Figure 1 is the metallographic picture of the copper / graphene composite wire prepared in Example 1;

[0046] Figure 2 is the metallographic picture of the copper / graphene composite wire prepared in Comparative Example 2;

[0047] Figure 3 is the metallographic picture of the copper / graphene composite wire prepared in Comparative Example 3;

[0048] Figure 4Raman spectrogram of the copper / graphene composite wire prepared in Example 2;

[0049] Figure 5 Optical photograph of the graphene extracted after complete corrosion of the copper / graphene composite wire prepared in Example 2( Figure 5 a) and SEM image( Figure 5 b);

[0050] Figure 6 SEM image of the copper / graphene composite wire prepared in Example 3, showing that the graphene is uniformly distributed at the grain boundaries in a three-dimensional network structure. Detailed implementation manners

[0051] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention. The present invention provides 3 embodiments and 1 comparative example. It can be understood that in some embodiments, inevitable impurities will be obtained, and the mass percentage content of the inevitable impurities is <0.005%.

[0052] Example 1

[0053] Prepare a copper / graphene composite material with a graphene content of 0.02 wt.%, which specifically includes the following steps:

[0054] (1) Use an acoustic resonance mixing device to uniformly mix copper powder with a particle size less than 70 μm and graphene powder with a diameter <6 μm and a number of layers <5 layers. The content of graphene in the copper powder is 0.5%. The acceleration of acoustic resonance mixing is 85 g (1 g≈9.8 m / s 2 ), the vibration frequency is 60 Hz, the vibration intensity is 50%, and the mixing time is 10 min;

[0055] (2) Load the copper / graphene mixed powder into a graphite mold of a hot press, and perform vacuum hot pressing and sintering at 1000 °C for 2 h, with a pressure of 30 MPa and a vacuum degree of 10 -3 Pa. After furnace cooling, mill the surface to obtain a copper / graphene composite preform for use;

[0056] (3) Add 2.4 kg of oxygen-free copper material to the crucible of a vacuum melting furnace, and evacuate to 10 -2After introducing Ar at 10 Pa, the temperature was then raised to 1230 °C to melt the oxygen-free copper material. After the oxygen-free copper material was completely melted, 0.1 kg of copper / graphene composite green billet (the mass ratio of the copper / graphene composite green billet to the copper material was 1:24) was added, and then electromagnetic stirring was carried out at a stirring frequency of 60 Hz and a stirring current of 250 A. Subsequently, the heating was turned off. When the melt temperature dropped to 1120 °C, it was poured into a water-cooled copper mold for casting;

[0057] (4) The as-cast ingot was milled to to remove surface defects and cold-rolled to Subsequently, it was continuously extruded to 2.1 mm × 3.3 mm. The working temperature of the die was 300 °C, the extrusion deformation temperature was 450 °C, and alcohol cooling was used at the outlet to inhibit grain growth and prevent oxidation of the flat wire surface. The extrusion pressure was 40 MPa. The rotation speed of the extrusion wheel was 10 rpm. The extrusion speed was 20 m / min. Finally, it was further finish-drawn to 2 mm × 3.2 mm at a drawing speed of 15 m / min.

[0058] Example 2

[0059] To prepare a copper / graphene composite material with a graphene content of 0.1 wt.%, the specific steps are as follows:

[0060] (1) A sound resonance mixing device was used to uniformly mix copper powder with a particle size less than 70 μm and graphene powder with a diameter < 6 μm and a number of layers < 5 layers. The content of graphene in the copper powder was 1%. The acceleration of sound resonance mixing was 85 g (1 g ≈ 9.8 m / s 2 ), the vibration frequency was 60 Hz, the vibration intensity was 50%, and the mixing time was 10 min;

[0061] (2) The copper / graphene mixed powder was loaded into a graphite mold of a hot press and vacuum hot-pressed and sintered at 1000 °C for 2 h, with a pressure of 30 MPa and a vacuum degree of 10 -3 Pa. After furnace cooling, it was milled to obtain a copper / graphene composite green billet for use;

[0062] (3) 1.8 kg of oxygen-free copper material was added to the crucible of a vacuum melting furnace, and the vacuum was pumped to 10 -2 Pa, then Ar was introduced. Subsequently, the temperature was raised to 1230 °C to melt the oxygen-free copper material. After the oxygen-free copper material was completely melted, 0.2 kg of copper / graphene composite green billet (the mass ratio of the copper / graphene composite green billet to the copper material was 1:9) was added, and then electromagnetic stirring was carried out at a stirring frequency of 60 Hz and a stirring current of 250 A. Subsequently, the heating was turned off. When the melt temperature dropped to 1120 °C, it was poured into a water-cooled copper mold for casting;

[0063] (4) The as-cast ingot was milled to Remove surface defects and cold roll to Subsequently, continuously extrude to 2.1 mm × 3.3 mm. The working temperature of the die is 300 °C, the extrusion deformation temperature is 450 °C, and alcohol cooling is used at the outlet to inhibit grain growth and prevent oxidation of the flat wire surface. The extrusion pressure is 40 MPa. The rotational speed of the extrusion wheel is 10 rpm. The extrusion speed is 20 m / min. Finally, further finish draw to 2 mm × 3.2 mm, and the drawing speed is 15 m / min.

[0064] Example 3

[0065] Prepare a copper / graphene composite material with a graphene content of 0.5 wt.%, which specifically includes the following steps:

[0066] (1) Use an acoustic resonance mixing device to uniformly mix copper powder with a particle size less than 70 μm and graphene powder with a diameter < 6 μm and a number of layers < 5 layers. The content of graphene in the copper powder is 1%. The acceleration of acoustic resonance mixing is 85 g (1 g ≈ 9.8 m / s 2 ), the vibration frequency is 60 Hz, the vibration intensity is 50%, and the mixing time is 10 min;

[0067] (2) Load the copper / graphene mixed powder into a graphite mold of a hot press, and perform vacuum hot press sintering at 1000 °C for 2 h, with a pressure of 30 MPa and a vacuum degree of 10 -3 Pa. After furnace cooling, mill the surface to obtain a copper / graphene composite preform for use;

[0068] (3) Add 1.2 kg of oxygen-free copper material to the crucible of a vacuum melting furnace, evacuate to 10 -2 Pa and then introduce Ar, and then heat up to 1230 °C to melt the oxygen-free copper material. After the oxygen-free copper material is completely melted, add 1.2 kg of copper / graphene composite preform (the mass ratio of the copper / graphene composite preform to the copper material is 1:1), and then perform electromagnetic stirring, with a stirring frequency of 60 Hz and a stirring current of 250 A. Subsequently, turn off the heating. When the melt temperature drops to 1120 °C, pour it into a water-cooled copper mold for casting;

[0069] (4) Mill the surface of the as-cast ingot to Remove surface defects and cold roll to Subsequently, continuously extrude to 2.1 mm × 3.3 mm. The working temperature of the die is 300 °C, the extrusion deformation temperature is 450 °C, and alcohol cooling is used at the outlet to inhibit grain growth and prevent oxidation of the flat wire surface. The extrusion pressure is 40 MPa. The rotational speed of the extrusion wheel is 10 rpm. The extrusion speed is 20 m / min. Finally, further finish draw to 2 mm × 3.2 mm, and the drawing speed is 15 m / min.

[0070] Comparative Example 1

[0071] A pure copper material with a graphene content of 0 wt.% was prepared by the same vacuum melting and casting process as a comparative sample, which specifically included the following steps:

[0072] (1) Add 2 kg of oxygen-free copper material into the crucible of the vacuum melting furnace, evacuate to 10 -2 Pa and then introduce Ar. Subsequently, heat up to 1230 °C to melt the oxygen-free copper material. After the oxygen-free copper material is completely melted, turn off the heating. When the melt temperature drops to 1120 °C, pour it into the water-cooled copper mold for casting;

[0073] (2) Milling the as-cast ingot to to remove surface defects, and cold rolling to Subsequently, continuously extrude to 2.1 mm × 3.3 mm. The working temperature of the die is 300 °C, the extrusion deformation temperature is 450 °C, and the outlet is cooled with alcohol to inhibit grain growth and prevent surface oxidation of the flat wire. The extrusion pressure is 40 MPa. The rotation speed of the extrusion wheel is 10 rpm. The extrusion speed is 20 m / min. Finally, further finish drawing to 2 mm × 3.2 mm, and the drawing speed is 15 m / min.

[0074] Comparative Example 2

[0075] Prepare a copper / graphene composite material with a graphene content of 0.02 wt.%, which specifically includes the following steps:

[0076] (1) Use an acoustic resonance mixing device to uniformly mix copper powder with a particle size less than 70 μm and graphene powder with a diameter < 6 μm and a number of layers < 5 layers. The content of graphene in the copper powder is 0.5%. The acceleration of acoustic resonance mixing is 85 g (1 g ≈ 9.8 m / s 2 ), the vibration frequency is 60 Hz, the vibration intensity is 50%, and the mixing time is 10 min;

[0077] (2) Load the copper / graphene mixed powder into the graphite mold of the hot press, and vacuum hot press and sinter at 1000 °C for 2 h, with a pressure of 30 MPa and a vacuum degree of 10 -3 Pa. After furnace cooling, mill the surface to obtain a copper / graphene composite preform for use;

[0078] (3) Add 2.4 kg of oxygen-free copper material into the crucible of the vacuum melting furnace, evacuate to 10 -2After introducing Ar at [[Pa]], the temperature was then raised to 1230 °C to melt the oxygen-free copper material. After the oxygen-free copper material was completely melted, 0.1 kg of copper / graphene composite preform (the mass ratio of the copper / graphene composite preform to the copper material was 1:24) was added, and then electromagnetic stirring was carried out. The stirring frequency was 60 Hz and the stirring current was 250 A. Subsequently, the heating was turned off. When the melt temperature dropped to 1120 °C, it was poured into a water-cooled copper mold for casting;

[0079] (4) Milling the as-cast ingot to removing surface defects, cold rolling to Subsequently, continuous extrusion was carried out to 2.1 mm × 3.3 mm. The working temperature of the die was 300 °C, the extrusion deformation temperature was 450 °C, and the outlet was cooled with alcohol to inhibit grain growth and prevent oxidation of the flat wire surface. The extrusion pressure was 40 MPa. The rotational speed of the extrusion wheel was 10 rpm. The extrusion speed was 35 m / min. Finally, further finishing drawing was carried out to 2 mm × 3.2 mm, and the drawing speed was 15 m / min.

[0080] Comparative Example 3

[0081] To prepare a copper / graphene composite material with a graphene content of 0.02 wt.%, the specific steps are as follows:

[0082] (1) Using an acoustic resonance mixing device to uniformly mix copper powder with a particle size less than 70 μm and graphene powder with a diameter < 6 μm and a number of layers < 5 layers. The content of graphene in the copper powder was 0.5%. The acceleration of acoustic resonance mixing was 85 g (1 g ≈ 9.8 m / s 2 ), the vibration frequency was 60 Hz, the vibration intensity was 50%, and the mixing time was 10 min;

[0083] (2) Loading the copper / graphene mixed powder into a graphite mold of a hot press, vacuum hot pressing and sintering at 1000 °C for 2 h, the pressure was 30 MPa, and the vacuum degree was 10 -3 Pa, and after furnace cooling, milling was carried out to obtain a copper / graphene composite preform for use;

[0084] (3) Adding 2.4 kg of oxygen-free copper material to the crucible of a vacuum melting furnace, evacuating to 10 -2 Pa and then introducing Ar. Subsequently, the temperature was raised to 1230 °C to melt the oxygen-free copper material. After the oxygen-free copper material was completely melted, 0.1 kg of copper / graphene composite preform (the mass ratio of the copper / graphene composite preform to the copper material was 1:24) was added, and then electromagnetic stirring was carried out. The stirring frequency was 60 Hz and the stirring current was 250 A. Subsequently, the heating was turned off. When the melt temperature dropped to 1120 °C, it was poured into a water-cooled copper mold for casting;

[0085] (4) Milling the as-cast ingot to Remove surface defects and cold roll to Subsequently, continuously extrude to 2.1 mm × 3.3 mm. The working temperature of the die is 500 °C, the extrusion deformation temperature is 650 °C, and alcohol cooling is used at the outlet to inhibit grain growth and prevent surface oxidation of the flat wire. The extrusion pressure is 40 MPa. The rotational speed of the extrusion wheel is 10 rpm. The extrusion speed is 20 m / min. Finally, further finish draw to 2 mm × 3.2 mm, and the drawing speed is 15 m / min.

[0086] Figure 1 The metallographic pictures of the copper / graphene composite flat wire in Example 1 are shown, showing that after continuous extrusion, its structure is all equiaxed grains, the grain crushing effect is ideal, and the grain size is about 5 - 30 μm.

[0087] Figure 2 The metallographic pictures of the copper / graphene composite flat wire in Comparative Example 2 are shown, showing that when the extrusion speed is increased to 35 m / min, the adiabatic shear effect causes the local temperature to instantaneously increase by 100 - 150 °C, resulting in abnormal growth of local grains.

[0088] Figure 3 The metallographic pictures of the copper / graphene composite flat wire in Comparative Example 3 are shown, showing that when the extrusion deformation temperature is increased to 650 °C, the excessive softening of the copper matrix leads to significant coarsening of the dynamically recrystallized grains.

[0089] Figure 4 The Raman spectrum of the copper / graphene composite flat wire in Example 2 is shown. It can be seen that although there is a strong background peak of copper, three characteristic peaks of graphene (D peak, G peak, and 2D peak) appear at 1350 cm -1 , 1580 cm -1 and 2700 cm -1 respectively. Among them, the D peak representing the number of graphene defects is very weak, and the intensity ratio (I D / I G ) of the D peak and the G peak is 0.855, indicating that the quality of graphene in the composite flat wire of the present invention is relatively high. Using concentrated nitric acid to completely corrode the copper matrix of the copper / graphene composite flat wire in Example 2 and filtering by suction to obtain the extraction product, its optical photo and SEM image are shown in Figure 5 (a) and (b) respectively, and lamellar graphene can be seen.

[0090] Figure 4 And Figure 5 The results together confirm that through the preparation process of the present invention, high-quality graphene is successfully introduced into the copper matrix, and the copper / graphene composite flat wire is obtained by combining processing deformation.

[0091] Figure 6SEM image of the copper / graphene composite flat wire in Example 3. It can be seen that graphene is uniformly distributed at the grain boundaries of copper grains, presenting a connected network structure.

[0092] Table 1 shows the graphene content, conductivity, thermal conductivity, and temperature rise performance data of the copper / graphene composite flat wire and pure copper materials in Examples 1-3 and Comparative Examples 1-3. Compared with Comparative Example 1, in Examples 1-3, copper powder with uniformly dispersed graphene was obtained through the acoustic resonance mixing technique. Subsequently, a copper / graphene composite billet was obtained by vacuum hot pressing sintering, and a copper / graphene composite material with uniformly dispersed graphene was obtained by vacuum melting and water-cooled copper mold casting. Then, through cold rolling, continuous extrusion, and finishing drawing, a copper / graphene composite flat wire with excellent electrical conductivity, thermal conductivity, and temperature rise performance was obtained. Compared with Example 1, in Comparative Example 2, the adiabatic shear effect caused by too fast extrusion speed induced abnormal grain growth and led to the destruction of the graphene network topological structure, affecting the electrical and thermal conductivity. In Comparative Example 3, due to too high extrusion deformation temperature, an insulating layer was generated by interface oxidation, hindering electron / phonon transmission and reducing the electrical and thermal conductivity.

[0093] Table 1 Conductivity, thermal conductivity, and temperature rise performance data of copper / graphene composite flat wire and pure copper flat wire

[0094]

Claims

1. A copper / graphene composite wire with high thermal conductivity and low temperature rise, characterized in that: In terms of mass percentage, the components of the copper / graphene composite wire include Cu: 99.50-99.98%, graphene: 0.02-0.5%; The copper matrix grains of the copper / graphene composite wire are equiaxed grains with a grain size of 5-30 μm, and the graphene is distributed at the grain boundaries.

2. The copper / graphene composite wire with high thermal conductivity and low temperature rise according to claim 1, characterized in that: The graphene presents a connected network structure in the copper / graphene composite wire tissue.

3. The copper / graphene composite wire with high thermal conductivity and low temperature rise according to claim 1, characterized in that: The electrical conductivity of the copper / graphene composite material is 100.3-102.5% IACS and the thermal conductivity is 457-481 W·m -1 ·K -1 , current density is 18-20A / mm 2 The temperature rise under the condition is reduced by 14.7-18.3% compared with pure copper.

4. A method for preparing a copper / graphene composite wire with high thermal conductivity and low temperature rise according to any one of claims 1 to 3, characterized in that: include: (1) mixing copper powder and graphene by acoustic resonance to obtain copper / graphene mixed powder; (2) performing vacuum hot pressing sintering on the copper / graphene mixed powder to obtain a copper / graphene composite preform; (3) The oxygen-free copper material and the copper / graphene composite blank are vacuum melted, stirred, and cast through a water-cooled copper mold. The cast blank is cold rolled, continuously extruded, and finely drawn to obtain the copper / graphene composite wire.

5. The method for preparing the copper / graphene composite wire with high thermal conductivity and low temperature rise according to claim 4, characterized in that: The extrusion deformation temperature of the continuous extrusion is 400-500° C., and the extrusion speed is 10-30 m / min.

6. The method for preparing the copper / graphene composite wire with high thermal conductivity and low temperature rise according to claim 5, characterized in that: The extrusion deformation temperature of the continuous extrusion is 400-450° C., and the extrusion speed is 10-20 m / min.

7. The method for preparing the copper / graphene composite wire with high thermal conductivity and low temperature rise according to claim 4, characterized in that: The extrusion pressure of the continuous extrusion is 30-50 MPa, and the extrusion wheel speed is 5-10 rpm.

8. The method for preparing the copper / graphene composite wire with high thermal conductivity and low temperature rise according to claim 4, characterized in that: The processing rate of the cold rolling is 70-84%.

9. The method for preparing the copper / graphene composite wire with high thermal conductivity and low temperature rise according to claim 4, characterized in that: In step (2), the vacuum hot pressing sintering is carried out at a temperature of 900 to 1000° C., for a time of 2 to 3 hours, at a pressure of 20 to 40 MPa, and at a vacuum degree of 10-3 to 10-1 Pa.

10. Application of the copper / graphene composite wire according to any one of claims 1 to 3 as a high thermal conductivity and low temperature rise material in new energy and electronic appliances.

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