A copper core aluminum clad composite wire and a preparation method thereof

Abstract

This invention provides a copper-core aluminum-clad composite wire and its preparation method, belonging to the field of metal composite wire preparation technology. The invention constructs a composite alloy interface between the copper core and the aluminum cladding layer, synergistically reinforced by functionalized carbon nanotubes. An acid-treated carbon nanotube, nickel powder as the bonding agent, and selenium powder with refined grains are made into a slurry and coated onto the copper core. Then, hydrostatic extrusion achieves a tight composite with the aluminum tube. In subsequent drawing and annealing processes, high temperature drives the in-situ reaction of nickel and aluminum to generate intermetallic compounds, while the carbon nanotubes form a relatively stable bond with them, thereby improving interface strength and inhibiting cracking. Finally, a copper-core aluminum-clad composite wire with good interfacial bonding, mechanical properties, and electrical conductivity is obtained.

Description

Technical Field

[0001] This invention belongs to the field of metal composite wire preparation technology, and relates to a copper core aluminum clad composite wire and its preparation method. Background Technology

[0002] Copper-aluminum composite wires combine the high electrical and thermal conductivity of copper with the low density and good surface compatibility of aluminum, making them valuable for applications in precision conductors and composite fine wires. The fabrication of existing copper-aluminum composite wires typically involves composite blank construction, extrusion bonding, and multi-pass drawing processes. The forming quality and final performance largely depend on the bonding state of the copper / aluminum interface.

[0003] However, copper and aluminum are dissimilar metals with significantly different physical properties and deformation behaviors. During the extrusion of composite billets and subsequent large-deformation drawing processes, problems such as insufficient interface adhesion, incoordination of interlayer plastic deformation, embrittlement of the intermetallic compound layer, and delamination or cracking during drawing are prone to occur. These problems are particularly pronounced when composite wires are processed towards smaller diameters, severely affecting the continuous processing stability, yield, and overall performance of the composite wires.

[0004] In existing technologies, while mechanical bonding alone can achieve a certain degree of interlayer adhesion, the interfacial bonding strength is insufficient. Conversely, relying on thermal diffusion to form a metallurgical bond easily leads to the formation of a thick and brittle intermetallic compound layer at the interface, making the composite wire more susceptible to interfacial damage during subsequent drawing and annealing processes. Therefore, how to construct a copper-aluminum composite interface suitable for continuous processing of hydrostatic extrusion-drawing-annealing, improve the ability to process composite billets into smaller diameters, and balance the mechanical and electrical properties of the wire are key technical issues in the manufacturing of high-quality copper-based composite wires. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a copper-core aluminum-clad composite wire and its preparation method, thereby solving the issues of interface embrittlement, insufficient stability during fine-diameter processing, and poor interlayer bonding performance in existing copper-aluminum composite wires during hydrostatic extrusion and multi-pass drawing. The present invention constructs a composite interface reinforced with functionalized carbon nanotubes between the copper core and the aluminum cladding layer. A composite slurry containing acid-activated carbon nanotubes, nickel powder as the bonding agent, and selenium powder as a grain refiner is prepared and coated onto the surface of the copper core. Hydrostatic extrusion then achieves a seamless and tight bond with the aluminum cladding layer. During subsequent drawing and annealing processes, high temperature drives the reaction between nickel and aluminum to form an intermetallic compound transition layer. Simultaneously, the active functional groups on the surface enable the carbon nanotubes to form a relatively stable bond with this newly formed interface. These carbon nanotubes effectively suppress interfacial cracking through mechanisms such as crack bridging during tensile deformation, and refine grains through pinning effect during annealing. This transforms the potentially brittle interface into a strong, stable, and co-deformable composite functional interface, improving the interfacial stability and fine-diameter forming capability of the composite billet during subsequent hot drawing, cold drawing, and annealing processes, ultimately achieving the preparation of high-performance copper-core aluminum-clad composite wires.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a copper-core aluminum-clad composite wire, the method comprising:

[0008] S1: Carbon nanotubes are placed in a mixed acid and stirred, washed, and dried to obtain pretreated carbon nanotubes. Carbonyl nickel powder, nano selenium powder and pretreated carbon nanotubes are mixed and ground to obtain a mixed powder. An N-methylpyrrolidone solution of polyvinylpyrrolidone is prepared. The mixed powder is added to the N-methylpyrrolidone solution of polyvinylpyrrolidone and wet ball milled to obtain a composite slurry.

[0009] S2: The composite slurry is coated on the surface of the copper rod and dried to obtain a surface-coated copper rod. The rod is then inserted into an aluminum tube to obtain a pre-treated composite billet. The billet is then subjected to argon arc welding to seal the ends and hydrostatic extrusion to obtain a composite billet.

[0010] S3: After preheating the composite billet, it is placed on a wire drawing machine for hot drawing to obtain the first billet. After cooling, it is cold drawn to obtain the second billet. Vacuum calcination and annealing are performed to obtain the third billet. After multiple fine stretching and annealing, copper core aluminum clad composite wire is obtained.

[0011] As a preferred technical solution of the present invention, in step S1, the volume ratio of sulfuric acid to nitric acid in the mixed acid is 3:1.

[0012] In some alternative embodiments, the carbon nanotubes are treated in mixed acid at a temperature of 65-75°C, for example, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 72°C, 73°C, 74°C or 75°C, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0013] In some alternative embodiments, the carbon nanotubes are treated in the mixed acid for 2-3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, but are not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0014] In some optional embodiments, the mass-to-volume ratio of the carbon nanotubes to the mixed acid is 1 g: (50-70) mL, for example, it can be 1 g: 50 mL, 1 g: 52 mL, 1 g: 54 mL, 1 g: 56 mL, 1 g: 58 mL, 1 g: 60 mL, 1 g: 62 mL, 1 g: 64 mL, 1 g: 66 mL, 1 g: 68 mL or 1 g: 70 mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0015] In some optional embodiments, the mass ratio of the carbonyl nickel powder, nano-selenium powder, and pretreated carbon nanotubes is 40:54:(1-5), for example, it can be 40:54:1.0, 40:54:1.4, 40:54:1.8, 40:54:2.2, 40:54:2.6, 40:54:3.0, 40:54:3.4, 40:54:3.8, 40:54:4.2, 40:54:4.6, or 40:54:5.0, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0016] In some optional embodiments, the mass-to-volume ratio of polyvinylpyrrolidone to N-methylpyrrolidone is (1-2) g:(30-40) mL, for example, it can be 1.0 g:30 mL, 1.1 g:31 mL, 1.2 g:32 mL, 1.3 g:33 mL, 1.4 g:34 mL, 1.5 g:35 mL, 1.6 g:36 mL, 1.7 g:37 mL, 1.8 g:38 mL, 1.9 g:39 mL or 2.0 g:40 mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0017] In some optional embodiments, the solid-liquid mass ratio of the mixed powder to the N-methylpyrrolidone solution of polyvinylpyrrolidone is 1:(5-6), for example, it can be 1:5.0, 1:5.1, 1:5.2, 1:5.3, 1:5.4, 1:5.5, 1:5.6, 1:5.7, 1:5.8, 1:5.9 or 1:6.0, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0018] In some optional embodiments, the wet ball milling time is 4-6 hours, for example, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours, or 6.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0019] As a preferred technical solution of the present invention, in step S2, the temperature at which the composite slurry is dried after being coated on the surface of the copper rod is 60-80°C, for example, it can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] In some optional embodiments, the drying time of the composite slurry after being coated on the surface of the copper rod is 1-2 hours, for example, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0021] In some alternative embodiments, the copper rod has a diameter of Φ3mm.

[0022] In some alternative embodiments, the inner diameter of the aluminum tube is Φ3.2mm.

[0023] In some optional embodiments, the thickness of the slurry coating on the surface of the copper rod is 30-40 μm, for example, it can be 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm or 40 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0024] As a preferred technical solution of the present invention, in step S3, the preheating temperature of the composite billet is 300-400℃, for example, it can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃ or 400℃, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0025] In some optional embodiments, the preheating time of the composite billet is 15-25 min, for example, it can be 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min or 25 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0026] The diameter of the first blank is Φ1.5mm.

[0027] In some alternative embodiments, the diameter of the second blank is Φ0.8-1mm, for example, it can be Φ0.80mm, Φ0.82mm, Φ0.84mm, Φ0.86mm, Φ0.88mm, Φ0.90mm, Φ0.92mm, Φ0.94mm, Φ0.96mm, Φ0.98mm or Φ1.00mm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0028] In some optional embodiments, the heating rate of the second billet vacuum calcination annealing is 8-12℃ / min, for example, it can be 8.0℃ / min, 8.4℃ / min, 8.8℃ / min, 9.2℃ / min, 9.6℃ / min, 10.0℃ / min, 10.4℃ / min, 10.8℃ / min, 11.2℃ / min, 11.6℃ / min or 12.0℃ / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0029] In some optional embodiments, the vacuum calcination annealing temperature of the second billet is 280-380°C, for example, it can be 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C or 380°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0030] In some optional embodiments, the vacuum calcination and annealing time of the second billet is 40-60 min, for example, it can be 40 min, 42 min, 44 min, 46 min, 48 min, 50 min, 52 min, 54 min, 56 min, 58 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0031] In some optional embodiments, the single-section compression rate during multiple fine stretching of the third billet is 60-70%, for example, it can be 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69% or 70%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0032] Once the single-section compression ratio is reached, an annealing process is performed.

[0033] In some optional embodiments, the diameter of the copper core aluminum-clad composite wire is Φ0.3-0.5mm, for example, it can be Φ0.3mm, Φ0.32mm, Φ0.34mm, Φ0.36mm, Φ0.38mm, Φ0.4mm, Φ0.42mm, Φ0.44mm, Φ0.46mm, Φ0.48mm or Φ0.50mm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0034] Secondly, the present invention provides a copper core aluminum clad composite wire, which is prepared according to the preparation method described above.

[0035] This application constructs a composite alloy bonding interface with optimized structure and performance, synergistically reinforced by carbon nanotubes, between a copper core and an aluminum cladding layer. First, the carbon nanotubes are subjected to mixed acid treatment, introducing active functional groups such as carboxyl and hydroxyl groups onto their surface through strong oxidation. This not only overcomes the agglomeration of carbon nanotubes caused by van der Waals forces, enabling uniform and stable dispersion in subsequent N-methylpyrrolidone solvents using polyvinylpyrrolidone dispersant, but more importantly, it endows the carbon nanotubes with the ability to chemically react with the metal matrix. Carbonyl nickel powder in the composite slurry forms the main body of the transition layer, designed to react with aluminum to generate nickel-aluminum intermetallic compounds, thus acting as a diffusion barrier and bonding bridge. Nano-selenium powder acts as an interface modifier, reacting with the metal at high temperatures to form fine selenides, refining the intermetallic compound grains and improving interfacial properties. Through wet ball milling, these components are uniformly mixed to form a stable precursor slurry with good coatability.

[0036] A slurry is coated onto the surface of a copper rod and dried, forming a solid composite powder layer through the bonding effect of polyvinylpyrrolidone. This layer is then inserted into an aluminum tube and sealed by argon arc welding and hydrostatic extrusion. The hydrostatic extrusion utilizes immense hydrostatic pressure, which helps eliminate gaps between the copper rod coating and the inner wall of the aluminum tube, ensuring a tight bond between the three. Simultaneously, it introduces numerous crystal defects at the interface, providing a driving force and diffusion channels for subsequent solid-phase diffusion reactions.

[0037] During the subsequent preheating and hot drawing processes, the high temperature activated interfacial atomic diffusion, causing aluminum and nickel to react and form an in-situ nickel-aluminum intermetallic compound layer. At this point, the pre-functionalized carbon nanotubes play a crucial role; their surface active functional groups chemically react with the newly formed intermetallic compound matrix, forming a relatively stable bond that anchors them within the interfacial layer. This interfacial bonding is a prerequisite for effective load transfer. A cold drawing-annealing cycle is then performed to optimize the interface and finally shape the material. Each large-deformation cold drawing results in severe work hardening, while vacuum annealing not only restores the material's plasticity through recrystallization but also regulates the interface. In the annealing thermal environment, carbon nanotubes inhibit intermetallic compound grain growth, maintaining a fine-grained structure in the interfacial layer and thus improving its strength and toughness. More importantly, during repeated intense tensile deformation, these anchored and uniformly distributed carbon nanotubes bear the main stress at the interface and effectively suppress the initiation and propagation of microcracks in the brittle intermetallic compound layer through mechanisms such as crack bridging and deflection. This multifunctional synergy transforms a potentially brittle and weak link into a strong, stable, and co-deformable nanocomposite interface with the copper-aluminum matrix, thereby helping to obtain high-performance copper-core aluminum-clad composite wires.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] By introducing a nickel-selenium-carbon nanotube composite intermediate layer between the copper core and the aluminum cladding layer, and combining it with a hydrostatic extrusion process, the adhesion and interfacial bonding between the copper rod, the interface layer and the aluminum tube can be improved, which is beneficial to obtaining a composite billet with continuous structure and uniform interface.

[0040] The constructed composite interface can suppress interface cracking and embrittlement during subsequent hot drawing, cold drawing and annealing processes, improve the synergistic deformation ability of copper and aluminum dissimilar metals during large deformation processing, thereby improving the processing stability and yield of composite wire in the process of drawing thinner diameter.

[0041] The toughening effect of carbon nanotubes combined with the refining effect of nano-selenium is beneficial to optimizing the microstructure of the interface layer, so that the resulting composite wire has good tensile strength, elongation and conductivity, and is suitable for manufacturing high-quality copper-based composite wires. Detailed Implementation

[0042] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The embodiments described herein are specific implementations of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limiting the implementation of the present invention or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include technical solutions that employ any obvious substitutions and modifications made to the embodiments described herein.

[0043] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone further purification or processing.

[0044] Example 1

[0045] This embodiment provides a copper-core aluminum-clad composite wire and its preparation method. The preparation method of the copper-core aluminum-clad composite wire specifically includes the following steps:

[0046] S1: Carbon nanotubes are placed in a mixed acid and stirred at 65°C for 2.8 h. After washing and drying, pretreated carbon nanotubes are obtained. The volume ratio of sulfuric acid to nitric acid in the mixed acid is 3:1, and the mass-volume ratio of carbon nanotubes to the mixed acid is 1 g:50 mL. Carbonyl nickel powder, nano selenium powder, and pretreated carbon nanotubes are mixed and ground at a mass ratio of 40:54:1 to obtain a mixed powder. A polyvinylpyrrolidone (PVP) N-methylpyrrolidone solution is prepared, wherein the mass-volume ratio of PPVP to N-methylpyrrolidone is 1 g:30 mL. The mixed powder is added to the PPVP N-methylpyrrolidone solution and wet ball-milled for 5 h to obtain a composite slurry. The solid-liquid mass ratio of the mixed powder to the PPVP N-methylpyrrolidone solution is 1:6.

[0047] S2: The composite slurry is coated on the surface of a copper rod with a diameter of Φ3mm and dried at 75℃ for 1.4h to obtain a surface-coated copper rod, wherein the thickness of the slurry coating on the surface of the copper rod is 34µm; it is inserted into an aluminum tube with an inner diameter of Φ3.2mm to obtain a pre-treated composite billet, which is then subjected to argon arc welding end sealing treatment and hydrostatic extrusion to obtain a composite billet;

[0048] S3: The composite billet is preheated at 380℃ for 22 minutes and then hot-drawn on a wire drawing machine to obtain a first billet with a diameter of Φ1.5mm; after cooling to 30℃, it is cold-drawn to obtain a second billet with a diameter of Φ0.95mm; then vacuum calcination and annealing are performed to obtain a third billet, wherein the heating rate of vacuum calcination and annealing is 10℃ / min, the calcination temperature is 350℃, and the time is 50min; after multiple fine stretching-annealing, the single cross-sectional compression ratio is 65%. After the single cross-sectional compression ratio is reached, an annealing treatment is performed to finally obtain a copper core aluminum clad composite wire with a diameter of Φ0.4mm.

[0049] Example 2

[0050] This embodiment provides a copper-core aluminum-clad composite wire and its preparation method. The preparation method of the copper-core aluminum-clad composite wire specifically includes the following steps:

[0051] S1: Carbon nanotubes were placed in a mixed acid and stirred at 75°C for 2.4 h. After washing and drying, pretreated carbon nanotubes were obtained. The volume ratio of sulfuric acid to nitric acid in the mixed acid was 3:1, and the mass-volume ratio of carbon nanotubes to the mixed acid was 1 g:70 mL. Carbonyl nickel powder, nano selenium powder, and pretreated carbon nanotubes were mixed and ground at a mass ratio of 40:54:5 to obtain a mixed powder. An N-methylpyrrolidone solution of polyvinylpyrrolidone was prepared, wherein the mass-volume ratio of polyvinylpyrrolidone to N-methylpyrrolidone was 2 g:40 mL. The mixed powder was added to the N-methylpyrrolidone solution of polyvinylpyrrolidone and wet ball milled for 4 h to obtain a composite slurry. The solid-liquid mass ratio of the mixed powder to the N-methylpyrrolidone solution of polyvinylpyrrolidone was 1:5.3.

[0052] S2: The composite slurry is coated on the surface of a copper rod with a diameter of Φ3mm and dried at 60℃ for 1h to obtain a surface-coated copper rod, wherein the thickness of the slurry coating on the surface of the copper rod is 30µm; it is inserted into an aluminum tube with an inner diameter of Φ3.2mm to obtain a pre-treated composite billet, which is then subjected to argon arc welding end sealing treatment and hydrostatic extrusion to obtain a composite billet;

[0053] S3: The composite billet is preheated at 300℃ for 15 minutes and then hot-drawn on a wire drawing machine to obtain a first billet with a diameter of Φ1.5mm; after cooling to 40℃, it is cold-drawn to obtain a second billet with a diameter of Φ0.80mm; then vacuum calcination and annealing are performed to obtain a third billet, wherein the heating rate of vacuum calcination and annealing is 8℃ / min, the calcination temperature is 280℃, and the time is 60min; after multiple fine stretching-annealing, the single cross-sectional compression rate is 60%, and after the single cross-sectional compression rate is reached, an annealing treatment is performed to finally obtain a copper core aluminum clad composite wire with a diameter of Φ0.3mm.

[0054] Example 3

[0055] This embodiment provides a copper-core aluminum-clad composite wire and its preparation method. The preparation method of the copper-core aluminum-clad composite wire specifically includes the following steps:

[0056] S1: Carbon nanotubes are placed in a mixed acid and stirred at 70°C for 3 hours. After washing and drying, pretreated carbon nanotubes are obtained. The volume ratio of sulfuric acid to nitric acid in the mixed acid is 3:1, and the mass-volume ratio of carbon nanotubes to the mixed acid is 1 g:58 mL. Carbonyl nickel powder, nano selenium powder, and pretreated carbon nanotubes are mixed and ground at a mass ratio of 40:54:3 to obtain a mixed powder. An N-methylpyrrolidone solution of polyvinylpyrrolidone is prepared, wherein the mass-volume ratio of polyvinylpyrrolidone to N-methylpyrrolidone is 1.8 g:38 mL. The mixed powder is added to the N-methylpyrrolidone solution of polyvinylpyrrolidone and wet ball milled for 6 hours to obtain a composite slurry. The solid-liquid mass ratio of the mixed powder to the N-methylpyrrolidone solution of polyvinylpyrrolidone is 1:5.

[0057] S2: The composite slurry is coated on the surface of a copper rod with a diameter of Φ3mm and dried at 80℃ for 1.8h to obtain a surface-coated copper rod, wherein the thickness of the slurry coating on the surface of the copper rod is 40µm; it is inserted into an aluminum tube with an inner diameter of Φ3.2mm to obtain a pre-treated composite billet, which is then subjected to argon arc welding end sealing treatment and hydrostatic extrusion to obtain a composite billet;

[0058] S3: The composite billet is preheated at 350℃ for 25 minutes and then hot-drawn on a wire drawing machine to obtain a first billet with a diameter of Φ1.5mm; after cooling to 20℃, it is cold-drawn to obtain a second billet with a diameter of Φ1.00mm; then vacuum calcination and annealing are performed to obtain a third billet, wherein the heating rate of vacuum calcination and annealing is 12℃ / min, the calcination temperature is 380℃, and the time is 40 minutes; after multiple fine stretching-annealing, the single cross-sectional compression rate is 70%. After the single cross-sectional compression rate is reached, an annealing treatment is performed to finally obtain a copper core aluminum clad composite wire with a diameter of Φ0.44mm.

[0059] Example 4

[0060] This embodiment provides a copper-core aluminum-clad composite wire and its preparation method. The preparation method of the copper-core aluminum-clad composite wire specifically includes the following steps:

[0061] S1: Carbon nanotubes were placed in a mixed acid and stirred at 68°C for 2 hours. After washing and drying, pretreated carbon nanotubes were obtained. The volume ratio of sulfuric acid to nitric acid in the mixed acid was 3:1, and the mass-volume ratio of carbon nanotubes to the mixed acid was 1 g:65 mL. Carbonyl nickel powder, nano selenium powder, and pretreated carbon nanotubes were mixed and ground at a mass ratio of 40:54:2 to obtain a mixed powder. An N-methylpyrrolidone solution of polyvinylpyrrolidone was prepared, wherein the mass-volume ratio of polyvinylpyrrolidone to N-methylpyrrolidone was 1.5 g:35 mL. The mixed powder was added to the N-methylpyrrolidone solution of polyvinylpyrrolidone and wet ball milled for 5.5 hours to obtain a composite slurry. The solid-liquid mass ratio of the mixed powder to the N-methylpyrrolidone solution of polyvinylpyrrolidone was 1:5.8.

[0062] S2: The composite slurry is coated on the surface of a copper rod with a diameter of Φ3mm and dried at 70℃ for 2h to obtain a surface-coated copper rod, wherein the thickness of the slurry coating on the surface of the copper rod is 37µm; it is inserted into an aluminum tube with an inner diameter of Φ3.2mm to obtain a pre-treated composite billet, which is then subjected to argon arc welding end sealing treatment and hydrostatic extrusion to obtain a composite billet;

[0063] S3: The composite billet is preheated at 400℃ for 20 minutes and then hot-drawn on a wire drawing machine to obtain a first billet with a diameter of Φ1.5mm; after cooling to 50℃, it is cold-drawn to obtain a second billet with a diameter of Φ0.90mm; then vacuum calcination and annealing are performed to obtain a third billet, wherein the heating rate of vacuum calcination and annealing is 9℃ / min, the calcination temperature is 320℃, and the time is 55min; after multiple fine stretching-annealing, the single cross-sectional compression ratio is 68%. After the single cross-sectional compression ratio is reached, an annealing treatment is performed to finally obtain a copper core aluminum clad composite wire with a diameter of Φ0.5mm.

[0064] Comparative Example 1

[0065] This comparative example provides a copper-core aluminum-clad composite wire. The difference from Example 1 is that no pretreated carbon nanotubes are added in S1, while the other operation steps and process parameters are exactly the same as in Example 1.

[0066] Comparative Example 2

[0067] This comparative example provides a copper-core aluminum-clad composite wire. The difference from Example 1 is that in S1, the carbon nanotubes are not placed in the mixed acid for treatment. Other operating steps and process parameters are exactly the same as in Example 1.

[0068] Comparative Example 3

[0069] This comparative example provides a copper core aluminum-clad composite wire. The difference from Example 1 is that no nano selenium powder is added in S1, while the other operating steps and process parameters are exactly the same as in Example 1.

[0070] The performance of the copper core aluminum-clad composite wires of Examples 1-4 and Comparative Examples 1-3 was tested, and the specific process is as follows:

[0071] The tensile strength and elongation of the test samples were determined according to GB / T 228.1-2021.

[0072] The resistivity of the sample was tested according to ASTM B193;

[0073] The test results are shown in Table 1.

[0074] Table 1 Performance test results of copper core aluminum-clad composite wires in Examples 1-4 and Comparative Examples 1-3

[0075]

[0076] The test results from Example 1 and Comparative Example 1 show that without the toughening phase of carbon nanotubes, the interface layer becomes a pure Ni-Se-Al intermetallic compound layer, which is inherently brittle. During tensile deformation, this intermetallic compound layer cannot deform in tandem with the copper core and aluminum foil, and microcracks will initiate even with minimal strain. Without the "crack bridging" and "deflection" effects of carbon nanotubes, these cracks will propagate rapidly, leading to premature brittle fracture of the entire wire along the interface, resulting in decreased tensile strength and elongation. Due to the collapse of mechanical properties, a large number of microcracks and defects will be generated at the interface during the tensile process. These physically discontinuous structures form new and stronger electron scattering centers, hindering effective current conduction and increasing resistivity.

[0077] The test results from Example 1 and Comparative Example 2 show that without acid treatment, the original carbon nanotubes are prone to agglomeration, forming large stress concentration points in the interface layer, which accelerates crack initiation. The inert carbon nanotube surface and the matrix exhibit only weak physical adsorption. When the interface is subjected to stress, the load cannot be effectively transferred to the carbon nanotubes, and cracks bypass these "ineffective" reinforcements, leading to a loss of toughening effect; a decrease in tensile strength and elongation; and the carbon nanotube agglomerates and the tiny gaps between them and the matrix due to poor bonding, forming numerous electron scattering centers. This chaotic microstructure hinders current flow, resulting in increased resistivity.

[0078] The test results from Example 1 and Comparative Example 3 show that without the addition of nano-selenium powder, the absence of fine selenide particles acting as "grain boundary pinning" during annealing makes grain growth easier. Coarse grains lead to increased brittleness and decreased toughness in the material. Although carbon nanotubes still play a major toughening role at the interface, the matrix they reinforce becomes brittle, resulting in a decrease in overall tensile strength and elongation. The metal selenide phase formed after heat treatment of nano-selenium is a semiconductor or poor conductor, constituting additional electron scattering centers. Removing the selenium powder is equivalent to reducing the "impurity phase" at the interface, making the conductive channels more "pure" in composition, which helps reduce resistivity. On the other hand, the lack of selenium powder leads to coarsening of intermetallic compound grains, but theoretically, grain coarsening reduces the number of grain boundaries per unit volume, thereby weakening electron scattering caused by grain boundaries. The combined effect of these two effects means that removing the selenium powder does not lead to a deterioration in resistivity; the change in resistivity is minimal.

[0079] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a copper-core aluminum-clad composite wire, characterized in that, The preparation method includes: S1: Carbon nanotubes are placed in a mixed acid and stirred, washed, and dried to obtain pretreated carbon nanotubes. Carbonyl nickel powder, nano selenium powder and pretreated carbon nanotubes are mixed and ground to obtain a mixed powder. An N-methylpyrrolidone solution of polyvinylpyrrolidone is prepared. The mixed powder is added to the N-methylpyrrolidone solution of polyvinylpyrrolidone and wet ball milled to obtain a composite slurry. S2: The composite slurry is coated on the surface of the copper rod and dried to obtain a surface-coated copper rod. The rod is then inserted into an aluminum tube to obtain a pre-treated composite billet. The billet is then subjected to argon arc welding to seal the ends and hydrostatic extrusion to obtain a composite billet. S3: After preheating the composite billet, it is placed on a wire drawing machine for hot drawing to obtain the first billet. After cooling, it is cold drawn to obtain the second billet. Vacuum calcination and annealing are performed to obtain the third billet. After multiple fine stretching and annealing, copper core aluminum clad composite wire is obtained.

2. The method for preparing a copper-core aluminum-clad composite wire according to claim 1, characterized in that, In S1: The volume ratio of sulfuric acid to nitric acid in the mixed acid is 3:1; The mass-to-volume ratio of the carbon nanotubes to the mixed acid is 1 g: (50-70) mL.

3. The method for preparing a copper-core aluminum-clad composite wire according to claim 1, characterized in that, In S1: the mass ratio of the carbonyl nickel powder, nano selenium powder and pretreated carbon nanotubes is 40:54:(1-5).

4. The method for preparing a copper-core aluminum-clad composite wire according to claim 1, characterized in that, In S1: The mass-to-volume ratio of polyvinylpyrrolidone to N-methylpyrrolidone is (1-2)g:(30-40)mL; The solid-liquid mass ratio of the mixed powder to the N-methylpyrrolidone solution of polyvinylpyrrolidone is 1:(5-6).

5. The method for preparing a copper-core aluminum-clad composite wire according to claim 1, characterized in that, In S2: The diameter of the copper rod is Φ3mm; The inner diameter of the aluminum tube is Φ3.2mm; The thickness of the slurry coating on the surface of the copper rod is 30-40 μm.

6. The method for preparing a copper-core aluminum-clad composite wire according to claim 1, characterized in that, In S3: The preheating temperature of the composite billet is 300-400℃; The preheating time for the composite billet is 15-25 minutes.

7. The method for preparing a copper-core aluminum-clad composite wire according to claim 1, characterized in that, In S3: The diameter of the first blank is Φ1.5mm; The diameter of the second blank is Φ0.8-1mm.

8. The method for preparing a copper-core aluminum-clad composite wire according to claim 1, characterized in that, In S3: The single-section compression rate of the third billet during multiple fine stretching operations is 60-70%. After the single-section compression ratio is reached, an annealing process is performed. The diameter of the copper core aluminum clad composite wire is Φ0.3-0.5mm.

9. A copper-core aluminum-clad composite wire prepared by the preparation method according to any one of claims 1-8.

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