A copper-clad carbon alloy aluminum-based enameled wire and its preparation method

Abstract

This invention relates to the field of enameled wire technology, and more particularly to a copper-clad carbon alloy aluminum-based enameled wire and its preparation method, comprising: firstly, mixing aluminum alloy powder with carbon nanotubes and graphene, and preparing an aluminum-based core wire through ball milling, vacuum hot pressing, extrusion, and drawing; after pretreatment of the core wire surface, sequentially performing chemical nickel plating and electroplating copper to obtain a wire with a gradient transition layer; then coating it with copper strip; and obtaining a copper-clad aluminum conductor through interfacial diffusion, drawing, and annealing treatment; further synthesizing a copolymer, compounding modified hydroxyapatite nanorods and additives to prepare an insulating varnish, coating it, and baking it through multi-stage temperature control to obtain the finished enameled wire. This invention effectively improves the defects of traditional aluminum-based enameled wires, such as weak mechanical properties, easy interface delamination, poor insulation and thermal conductivity, and insufficient thermal shock resistance, through carbon component dispersion to strengthen the matrix, constructing a nickel-copper gradient composite interface, and synergistic optimization of the hybrid modified insulation system.

Description

Technical Field

[0001] This invention relates to the field of enameled wire technology, and in particular to a copper-clad carbon alloy aluminum-based enameled wire and its preparation method. Background Technology

[0002] Enameled wire is a core winding material for electrical equipment such as motors, transformers, new energy power controls, and precision electronic components. Its conductivity, mechanical properties, heat resistance, insulation properties, and environmental stability directly determine the operating efficiency, service life, and safety and reliability of electrical equipment. Currently, the mainstream enameled wires on the market are mainly divided into three categories: pure copper enameled wire, pure aluminum enameled wire, and conventional copper-clad aluminum enameled wire. Among them, pure copper enameled wire has the advantages of high conductivity, good ductility, excellent welding performance, and stable mechanical strength, and has long dominated the high-end enameled wire market. However, the high price and density of copper lead to high production costs and heavy finished products, significantly increasing the overall weight and manufacturing cost of electrical equipment, which does not conform to the industry trend of lightweight and low-cost development. Pure aluminum enameled wire has a good cost advantage due to its low raw material cost, low density, and significant weight reduction effect. However, pure aluminum substrate has inherent performance defects. Its conductivity is much lower than that of copper, and its temperature rise is higher when energized, which can easily reduce the service life of equipment. At the same time, aluminum substrate has poor tensile strength and bending resistance, and is prone to tensile deformation and wire breakage during winding. In addition, a dense oxide film is easily formed on the aluminum surface, resulting in poor welding reliability, unstable contact resistance, and rapid aging rate under high temperature and humidity conditions, which greatly limits its application in high-end heavy-duty and long-term continuous operation conditions.

[0003] To optimize the substrate performance of aluminum-based enameled wires, the research and application of carbon-modified aluminum-based composite materials have gradually emerged in the existing technology. By doping carbon components into the aluminum substrate, the high strength, high thermal conductivity, and high stability of carbon materials are utilized to improve the defects of low mechanical strength and poor thermal stability of pure aluminum substrates, thereby enhancing the overall performance of aluminum-based conductors to a certain extent. For example, the invention patent with patent publication number CN111834044A discloses an aluminum-coated carbon steel wire, its preparation method, and the conductor. The method involves drawing carbon steel wire rod into carbon steel wire, and then sequentially passing it through isothermal treatment, aluminum coating, stretching, and online heating aging treatment to obtain the aluminum-coated carbon steel wire. This method improves the matching of the elongation at break between the aluminum-coated carbon steel wire and the conductor unit or optical fiber unit through online aging treatment, ensuring that the aluminum-coated carbon steel wire in the formed conductor does not break before the conductor unit, thereby improving the tensile and compressive strength of the conductor and extending its service life.

[0004] However, the poor uniformity of carbon fiber integration with the aluminum matrix leads to component agglomeration and interface defects, resulting in uneven stress distribution within the substrate and poor overall conductivity and mechanical stability of the wire. Furthermore, carbon fiber modification alone cannot effectively address the core issues of poor surface welding performance and weak interface oxidation resistance in aluminum-based conductors; surface conductivity and connection reliability still cannot meet the standards of pure copper enameled wire. Simultaneously, the composite interface stability between the copper layer and the carbon alloy aluminum core is poor, making it prone to interface failure and performance degradation under long-term high temperature, humidity, and alternating load conditions. Moreover, the compatibility between the insulation layer and the modified substrate is insufficient, making it difficult to achieve long-term protective effects with high insulation, high heat resistance, and high adhesion. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention provides a copper-clad carbon alloy aluminum-based enameled wire and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing copper-clad carbon alloy aluminum-based enameled wire includes the following steps: S1. After mixing aluminum alloy powder with carbon nanotubes and graphene, aluminum-based core wires are obtained by ball milling, vacuum hot pressing, extrusion and drawing. S2. The aluminum-based core wire is pretreated by chemical nickel plating and electroplating copper plating to obtain a gradient transition layer wire. S3. T2 copper strip is wrapped around the surface of the gradient transition layer wire, and interface diffusion treatment, drawing and annealing are performed to obtain copper-clad aluminum conductor. S4. Synthesize 2-vinylnaphthalene-itaconic acid monobutyl ester copolymer, add modified hydroxyapatite nanorods and additives to obtain insulating varnish; S5. Apply insulating varnish to the surface of the copper-clad aluminum conductor and bake it under multiple temperature-controlled conditions to obtain the enameled wire.

[0007] Further, in step S1, the aluminum alloy powder is selected from at least one of 6061 aluminum alloy, 6063 aluminum alloy, 1060 aluminum alloy, and 5052 aluminum alloy.

[0008] The carbon nanotubes selected have a diameter of 5-30 nm and a length of 5-50 μm; the graphene has a thickness of 0.5-5 nm and a sheet diameter of 2-20 μm.

[0009] The mass ratio of aluminum alloy powder, carbon nanotubes and graphene is (97-98.5):(0.8-2.0):(0.5-1.0).

[0010] In addition, ball milling includes: placing the mixture under inert gas protection for planetary ball milling, controlling the ball-to-material ratio to be (8-12):1, the rotation speed to be 280-320 rpm, and the ball milling time to be 3-5 h, to obtain composite aluminum alloy powder.

[0011] The temperature for vacuum hot pressing is 590-610℃, the pressure is 35-45MPa, and the holding time is 1.5-2h.

[0012] The extrusion temperature is 420-440℃, and the diameter of the extruded aluminum rod is 8-12mm.

[0013] The drawing process involves two intermediate annealing processes at a temperature of 360-370℃ and a holding time of 1-1.5h, resulting in a final aluminum core wire diameter of 1.8-2.2mm.

[0014] Further, in step S2, the surface pretreatment specifically involves: immersing the aluminum-based core wire sequentially in acetone and anhydrous ethanol for ultrasonic cleaning for 10-15 minutes each, then immersing it in a 5-10 wt% NaOH solution for alkaline washing for 20-40 seconds at room temperature, rinsing it with deionized water until neutral, then immersing it in a 10-15 wt% HNO3 solution for acid washing for 10-20 seconds, and finally rinsing it with deionized water and drying it at 110-130°C.

[0015] Electroless nickel plating involves immersing pretreated aluminum-based core wires in an alkaline electroless nickel plating solution, adjusting the pH value to 8.5-9.0 with ammonia, and plating at 85-90℃ for 10-20 minutes.

[0016] Copper electroplating involves transferring the nickel-plated core wire into an acidic copper sulfate plating solution for stepped current electroplating, controlling the initial current density of the electroplating to be 1.2-1.8 A / dm³. 2 It decreases linearly with time to 0.4-0.6 A / dm. 2 The electroplating time is 8-12 minutes.

[0017] The alkaline electroless nickel plating solution consists of: nickel sulfate 20-30 g / L, sodium hypophosphite 25-35 g / L, sodium citrate 10-20 g / L, and ammonium chloride 25-35 g / L.

[0018] The composition of the acidic copper sulfate plating solution is: 140-160 g / L copper sulfate, 45-55 g / L sulfuric acid, and 40-60 mg / L chloride ions.

[0019] Furthermore, in step S3, the thickness of the T2 copper strip is 0.4-0.6 mm, and it is subjected to degreasing, pickling and drying treatments in sequence before coating.

[0020] The coating process parameters are: extrusion temperature 390-410℃, extrusion ratio 10-15, and extrusion speed 0.8-1.2m / min.

[0021] The interface diffusion treatment is carried out under nitrogen or argon protection at a temperature of 460-470℃ for 15-25 minutes.

[0022] Drawing consists of three sequential processes: rough drawing, intermediate drawing, and fine drawing. The rough drawing temperature is 330-340℃, with a deformation rate of 15-20% per pass; the intermediate drawing temperature is 300-310℃, with a deformation rate of 10-15% per pass; and the fine drawing temperature is 220-230℃, with a deformation rate of 6-10% per pass.

[0023] Annealing is carried out in a protective atmosphere of ammonia decomposition, at a temperature of 350-360℃, for a holding time of 3-4 hours, and then cooled in the furnace to below 150℃ before being removed from the furnace.

[0024] Further, in step S4, the step of synthesizing the 2-vinylnaphthalene-itaconic acid monobutyl copolymer includes: Under nitrogen protection, 2-vinylnaphthalene, itaconic acid monobutyl ester and itaconic anhydride are mixed in a mass ratio of (55-65):(30-40):(3-7), dissolved in N-methylpyrrolidone, and benzoyl peroxide is added as an initiator at 1-2% of the total monomer mass. The mixture is reacted at 70-90℃ for 4-6 hours to obtain a copolymer solution with a solid content of 40-50%.

[0025] The modified hydroxyapatite nanorods have a diameter of 20-30 nm and a length of 100-200 nm. Their surface is grafted with γ-methacryloyloxypropyltrimethoxysilane, i.e., silane coupling agent KH570.

[0026] The preparation method of the insulating varnish includes: adding 5-10 parts of modified hydroxyapatite nanorods to 100 parts of copolymer solution, stirring at high speed of 2500-3500 rpm for 20-40 min, then ultrasonically dispersing for 15-25 min, then adding 2-5 parts of trimethylolpropane triacrylate crosslinking agent, 0.5-1.0 parts of di-tert-butyl peroxide initiator and 0.2-0.5 parts of leveling agent, stirring and mixing evenly, and adjusting the solid content to 33-37% with xylene.

[0027] Furthermore, in step S5, the coating is done using a mold coating method, with a total of 5-7 coats applied, and each coat is baked independently after application.

[0028] Multi-stage temperature-controlled baking adopts five-zone temperature control, which are set sequentially along the production line as follows: inlet zone temperature 160-180℃, pre-curing zone temperature 270-290℃, first main curing zone temperature 350-370℃, second main curing zone temperature 390-410℃, and outlet zone temperature 230-250℃.

[0029] The linear speed is controlled at 25-30 m / min to ensure that each coat of paint film completes solvent evaporation and cross-linking curing during the baking process.

[0030] After coating, the wire is forced to cool to room temperature and then wound up to obtain the finished enameled wire. The total thickness of the enameled wire is 0.025-0.035 mm.

[0031] According to another aspect of the present invention, a copper-clad carbon alloy aluminum-based enameled wire prepared by the above-described method is provided, comprising, from the inside out: A carbon alloy aluminum-based conductor core, which consists of an aluminum alloy matrix and carbon nanotubes and graphene reinforcement phases dispersed therein; A nickel-copper gradient transition layer is disposed on the surface of the conductor core, with a thickness of 13-16 μm, wherein the side closer to the conductor core is a nickel-rich layer and the side farther from the conductor core is a copper-rich layer; The copper cladding layer, covering the transition layer, has a thickness of 0.05-0.15mm and is formed by continuous extrusion and diffusion treatment of T2 copper strip. The interface between the copper layer and the aluminum core is in a metallurgical bonding state. An insulating varnish layer, coated on the outside of the copper cladding layer, has a thickness of 0.025-0.035 mm and is composed of a 2-vinylnaphthalene-itaconic acid monobutyl copolymer matrix and a modified hydroxyapatite nanorod reinforcing phase uniformly dispersed therein.

[0032] The beneficial effects of this invention are: 1. The copper-clad carbon alloy aluminum-based enameled wire prepared by this invention has a four-level micro-layer structure with a gradient distribution from the inside to the outside, mainly including a carbon-based reinforced aluminum core layer, a nickel-copper gradient transition layer, a copper-aluminum metallurgical composite conductive surface layer, and an organic-inorganic hybrid insulating layer. This invention achieves comprehensive optimization of the overall performance by directionally controlling the microstructure and interfacial bonding state of each layer through a layered and controllable preparation process, combined with the synergistic effect of physicochemical and structural chemistry. This improves many technical problems of traditional enameled wires, such as high self-weight and cost, insufficient mechanical and thermal stability of the substrate, poor reliability of the composite interface, and imbalance of insulation and protection performance.

[0033] 2. This invention employs a combination of powder ball milling, vacuum hot pressing, gradient plastic processing, and segmented annealing to prepare a carbon alloy aluminum-based core layer. This allows carbon nanotubes and graphene to be uniformly dispersed within the aluminum alloy matrix, forming a dense and stable three-dimensional covalent reinforcement network. This effectively improves the problems of component agglomeration, numerous internal defects, and uneven stress distribution in traditional carbon-modified aluminum-based materials. This microstructure refines the aluminum matrix grains, pins grain boundaries, and alleviates high-temperature lattice slip. While retaining the advantages of aluminum alloys—lightweight, low-cost, and highly conductive—it effectively enhances the mechanical strength and high-temperature creep resistance of the substrate, addressing the shortcomings of pure aluminum wire, such as low strength, easy deformation during processing, and significant temperature rise during high-temperature operation. Furthermore, this invention utilizes a nickel-copper gradient plating and high-temperature interface diffusion process to construct a continuously transitioning metallic bonding interface between the aluminum matrix and the copper layer. This alleviates interfacial thermal stress during thermal cycling, inhibits the formation of brittle copper-aluminum intermetallic compounds, and improves the bonding stability and anti-aging ability of the multilayer metal composite interface. The dense copper metallurgical structure on the surface optimizes the conductivity and welding reliability of the wire, compensating for the weak oxidation resistance and insufficient connection stability of aluminum-based materials. This allows the conductivity and assembly performance of aluminum-based composite wires to approach that of pure copper enameled wires. Combined with gradient drawing and protective atmosphere annealing, the conductor's microstructure is homogenized, residual processing stress and lattice distortion are eliminated, ensuring the wire's conductivity uniformity and long-term mechanical stability.

[0034] 3. The 2-vinylnaphthalene-itaconic acid monobutyl copolymer modified hybrid insulating layer prepared by this invention effectively improves the problems of mismatch between thermal conductivity and insulation performance, poor high-temperature adhesion, and weak corona aging resistance of traditional enameled wire insulation layers. The copolymer resin, through the complementary structure of rigid aromatic rings and flexible alkyl chains, balances the thermal stability and mechanical flexibility of the insulating layer. The active functional groups on the resin side chains can form stable chemical reactions with the copper conductor surface, improving the interfacial bonding performance between the insulating layer and the metal substrate, and reducing the risk of varnish cracking and peeling under high-temperature aging conditions. The silane covalently grafted hydroxyapatite inorganic phase can form a stable cross-linked network with the organic resin matrix, improving the problems of poor compatibility and easy agglomeration of inorganic fillers and resin matrix. It constructs a uniform thermal conductivity pathway within the insulating layer, improving the overall heat dissipation capacity of the varnish film while ensuring insulation performance, thus alleviating the drawback of the mutual constraint between thermal conductivity and insulation performance in traditional insulating materials. Meanwhile, the dense organic-inorganic cross-linked network can optimize the space charge distribution and weaken the partial discharge effect, which helps to improve the insulation layer's resistance to corona aging and high-temperature service stability. Moreover, this hybrid structure has good compatibility with the modified copper-clad aluminum conductor substrate and can maintain a stable insulation protection effect for a long time. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the following examples and comparative examples, 2-vinylnaphthalene (CAS No.: 827-54-3), itaconic acid monobutyl ester (CAS No.: 6439-57-2), and itaconic anhydride (CAS No.: 2170-03-8) were all analytical grade with a purity ≥98.0%; benzoyl peroxide (CAS No.: 94-36-0) was analytical grade with a purity ≥98.5%; hydroxyapatite nanorods were industrial high-purity grade with a purity ≥98.0%; and γ-methacryloyloxypropyltrimethoxysilane (KH570) was... Analytical grade, purity ≥98.0%; nickel sulfate (CAS No.: 7786-81-4), sodium hypophosphite (CAS No.: 7681-53-0), sodium citrate (CAS No.: 68-04-2), ammonium chloride (CAS No.: 12125-02-7), copper sulfate (CAS No.: 7758-98-7), concentrated sulfuric acid, sodium hydroxide (CAS No.: 1310-73-2), nitric acid (CAS No.: 7697-37-2), and ammonia were all analytical grade, purity ≥98.5%.

[0037] Example 1 This embodiment provides a method for preparing copper-clad carbon alloy aluminum-based enameled wire, including the following steps: S1. Weigh 985g of 1060 aluminum alloy powder, 8g of carbon nanotubes, and 5g of graphene. The carbon nanotubes have a diameter of 5nm and a length of 5μm, and the graphene has a thickness of 0.5nm and a sheet diameter of 2μm. Mix them evenly. Place the mixture under argon protection and perform planetary ball milling, controlling the ball-to-powder ratio at 8:1, the rotation speed at 280rpm, and the milling time at 3h to obtain composite aluminum alloy powder. Vacuum hot pressing the composite powder at 590℃ and 35MPa for 1.5h, followed by extrusion at 420℃ to obtain aluminum rods with a diameter of 8mm. The aluminum rods are drawn in multiple passes, with two intermediate annealing processes performed at 360℃ for 1h, finally obtaining aluminum-based core wires with a diameter of 1.8mm.

[0038] S2. Surface pretreatment of the aluminum-based core wire: The wire is ultrasonically cleaned sequentially with 500 mL of acetone and 500 mL of anhydrous ethanol for 10 min each. It is then placed in 500 mL of 5 wt% NaOH solution for 20 s at room temperature, rinsed with deionized water until neutral, and then acid-washed in 500 mL of 10 wt% HNO3 solution for 10 s. After rinsing with deionized water, it is dried at 110℃. The pretreated core wire is then immersed in 1 L of alkaline electroless nickel plating solution containing 20 g nickel sulfate, 25 g sodium hypophosphite, 10 g sodium citrate, and 25 g ammonium chloride. The pH of the plating solution is adjusted to 8.5 with ammonia water, and plating is performed at 85℃ for 10 min. Subsequently, the core wire is transferred to 1 L of acidic copper sulfate plating solution containing 140 g copper sulfate, 45 g sulfuric acid, and 40 mg chloride ions. A stepped current electroplating method is used, with an initial current density of 1.2 A / dm³. 2 It decreases linearly to 0.4 A / dm 2 Electroplating was performed continuously for 8 minutes to obtain a gradient transition layer wire.

[0039] S3. Select 0.4mm thick T2 copper strip, after degreasing, pickling, and drying, and coat it onto the surface of the gradient transition layer wire under the conditions of 390℃, extrusion ratio 10, and extrusion speed 0.8m / min. Perform interface diffusion at 460℃ for 15min under nitrogen protection, followed by rough drawing, intermediate drawing, and fine drawing processes sequentially. The rough drawing temperature is 330℃ with a single-pass deformation rate of 15%, the intermediate drawing temperature is 300℃ with a single-pass deformation rate of 10%, and the fine drawing temperature is 220℃ with a single-pass deformation rate of 6%. Finally, anneal at 350℃ for 3h in an ammonia decomposition protective atmosphere, furnace-cooled to below 150℃, and removed from the furnace to obtain the copper-clad aluminum conductor.

[0040] S4. Under nitrogen protection, weigh 55g of 2-vinylnaphthalene, 30g of itaconic acid monobutyl ester, and 3g of itaconic anhydride. Mix them and dissolve them in 200mL of N-methylpyrrolidone solvent. Add 0.88g of benzoyl peroxide initiator and stir at 70℃ for 4h to obtain a copolymer solution with a solid content of 40%. Weigh 5g of KH570 modified hydroxyapatite nanorods (20nm in diameter and 100nm in length) and add them to 100g of the above copolymer solution. Stir at 2500rpm for 20min and then ultrasonically disperse for 15min. Then add 2g of trimethylolpropane triacrylate, 0.5g of di-tert-butyl peroxide, and 0.2g of BYK-333 leveling agent. Continue stirring and mixing until homogeneous. Adjust the solid content of the varnish to 33% using xylene solvent to obtain a uniform and stable insulating varnish.

[0041] S5. Insulating varnish is applied to the surface of the copper-clad aluminum conductor using a mold coating method, with a total of five coats. Each coat is baked and cured independently. A five-zone continuous oven temperature control process is employed: 160℃ in the inlet zone, 270℃ in the pre-curing zone, 350℃ in the first main curing zone, 390℃ in the second main curing zone, and 230℃ in the outlet zone. The production line speed is stably controlled at 25m / min. After all coatings and curing are complete, the wire is forced to cool to room temperature and then wound up to obtain a finished enameled wire with a varnish film thickness of 0.025mm.

[0042] Example 2 This embodiment provides a method for preparing copper-clad carbon alloy aluminum-based enameled wire, including the following steps: S1. Weigh 980g of 6061 aluminum alloy powder, 14g of carbon nanotubes, and 8g of graphene. The carbon nanotubes have a diameter of 15nm and a length of 25μm, and the graphene has a thickness of 2nm and a sheet diameter of 10μm. Mix them evenly. Place the mixture under argon protection and perform planetary ball milling, controlling the ball-to-powder ratio at 10:1, the rotation speed at 300rpm, and the milling time at 4h to obtain composite aluminum alloy powder. Vacuum hot pressing the composite powder at 600℃ and 40MPa for 1.8h, followed by extrusion at 430℃ to obtain aluminum rods with a diameter of 10mm. The aluminum rods are drawn in multiple passes, with two intermediate annealing processes performed at 365℃ for 1.2h, finally obtaining aluminum-based core wires with a diameter of 2.0mm.

[0043] S2. Surface pretreatment of the aluminum-based core wire: The wire was ultrasonically cleaned sequentially with 500 mL of acetone and 500 mL of anhydrous ethanol for 12 min each. It was then placed in 500 mL of 8 wt% NaOH solution for 30 s at room temperature, rinsed with deionized water until neutral, and then acid-washed in 500 mL of 12 wt% HNO3 solution for 15 s. After rinsing with deionized water, it was dried at 120℃. The pretreated core wire was then immersed in 1 L of alkaline electroless nickel plating solution containing 25 g nickel sulfate, 30 g sodium hypophosphite, 15 g sodium citrate, and 30 g ammonium chloride. The pH of the plating solution was adjusted to 8.8 with ammonia water, and plating was performed at 88℃ for 15 min. Subsequently, the core wire was transferred to 1 L of acidic copper sulfate plating solution containing 150 g copper sulfate, 50 g sulfuric acid, and 50 mg chloride ions. A stepped current electroplating method was used, with an initial current density of 1.5 A / dm³. 2 It decreases linearly to 0.5 A / dm 2 Electroplating was performed continuously for 10 minutes to obtain a gradient transition layer wire.

[0044] S3. Select 0.5mm thick T2 copper strip, after degreasing, pickling, and drying, and coat it onto the surface of the gradient transition layer wire under the conditions of 400℃, extrusion ratio 12, and extrusion speed 1.0m / min. Perform interface diffusion at 465℃ for 20min under nitrogen protection, followed by rough drawing, intermediate drawing, and fine drawing processes sequentially. The rough drawing temperature is 335℃ with a single-pass deformation rate of 18%, the intermediate drawing temperature is 305℃ with a single-pass deformation rate of 12%, and the fine drawing temperature is 225℃ with a single-pass deformation rate of 8%. Finally, anneal at 355℃ for 3.5h in an ammonia decomposition protective atmosphere, furnace-cooled to below 150℃, and removed from the furnace to obtain a copper-clad aluminum conductor.

[0045] S4. Under nitrogen protection, weigh 60g of 2-vinylnaphthalene, 35g of itaconic acid monobutyl ester, and 5g of itaconic anhydride, mix them, and dissolve them in 200mL of N-methylpyrrolidone solvent. Add 1.5g of benzoyl peroxide initiator, and stir at 80℃ for 5h to obtain a copolymer solution with a solid content of 45%. Weigh 7g of KH570 modified hydroxyapatite nanorods (25nm in diameter and 150nm in length), add them to 100g of the above copolymer solution, stir at 3000rpm for 30min, and then ultrasonically disperse for 20min. Subsequently, add 3g of trimethylolpropane triacrylate, 0.7g of di-tert-butyl peroxide, and 0.3g of BYK-333 leveling agent, and continue stirring to mix evenly. Adjust the solid content of the varnish to 35% using xylene solvent to obtain a uniform and stable insulating varnish.

[0046] S5. The insulating varnish is applied to the surface of the copper-clad aluminum conductor using a mold coating method, with a total of six coats applied. Each coat is baked and cured independently. A five-zone continuous oven temperature control process is employed: 170℃ in the inlet zone, 280℃ in the pre-curing zone, 360℃ in the first main curing zone, 400℃ in the second main curing zone, and 240℃ in the outlet zone. The production line speed is stably controlled at 28 m / min. After all coatings and curing are complete, the wire is forced to cool to room temperature and then wound up to obtain a finished enameled wire with a varnish film thickness of 0.03 mm.

[0047] Example 3 This embodiment provides a method for preparing copper-clad carbon alloy aluminum-based enameled wire, including the following steps: S1. Weigh 970g of 5052 aluminum alloy powder, 20g of carbon nanotubes, and 10g of graphene. The carbon nanotubes have a diameter of 30nm and a length of 50μm, and the graphene has a thickness of 5nm and a sheet diameter of 20μm. Mix them evenly. Place the mixture under argon protection and perform planetary ball milling, controlling the ball-to-powder ratio at 12:1, the rotation speed at 320rpm, and the milling time at 5h to obtain composite aluminum alloy powder. Vacuum hot pressing the composite powder at 610℃ and 45MPa for 2h, followed by extrusion at 440℃ to obtain aluminum rods with a diameter of 12mm. The aluminum rods are drawn in multiple passes, with two intermediate annealing processes performed at 370℃ for 1.5h, finally obtaining aluminum-based core wires with a diameter of 2.2mm.

[0048] S2. Surface pretreatment of the aluminum-based core wire: The wire is ultrasonically cleaned sequentially with 500 mL of acetone and 500 mL of anhydrous ethanol for 15 min each. It is then placed in 500 mL of 10 wt% NaOH solution for 40 s at room temperature, rinsed with deionized water until neutral, and then acid-washed in 500 mL of 15 wt% HNO3 solution for 20 s. After rinsing with deionized water, it is dried at 130℃. The pretreated core wire is then immersed in 1 L of alkaline electroless nickel plating solution containing 30 g nickel sulfate, 35 g sodium hypophosphite, 20 g sodium citrate, and 35 g ammonium chloride. The pH of the plating solution is adjusted to 9.0 with ammonia water, and plating is performed at a constant temperature of 90℃ for 20 min. The core wire was then transferred to a 1L acidic copper sulfate plating solution containing 160g copper sulfate, 55g sulfuric acid, and 60mg chloride ions. A stepped current plating method was used, with an initial current density of 1.8A / dm², which was linearly reduced to 0.6A / dm² and continuously plating for 12 minutes to obtain a gradient transition layer wire.

[0049] S3. Select 0.6mm thick T2 copper strip, after degreasing, pickling, and drying, and coat it onto the surface of the gradient transition layer wire under the conditions of 410℃, extrusion ratio 15, and extrusion speed 1.2m / min. Perform interface diffusion at 470℃ for 25min under argon protection, followed by rough drawing, intermediate drawing, and fine drawing processes sequentially. The rough drawing temperature is 340℃ with a single-pass deformation rate of 20%, the intermediate drawing temperature is 310℃ with a single-pass deformation rate of 15%, and the fine drawing temperature is 230℃ with a single-pass deformation rate of 10%. Finally, anneal at 360℃ for 4 hours in an ammonia decomposition protective atmosphere, and furnace cool to below 150℃ to obtain the copper-clad aluminum conductor.

[0050] S4. Under nitrogen protection, weigh 65g of 2-vinylnaphthalene, 40g of itaconic acid monobutyl ester, and 7g of itaconic anhydride. Mix them and dissolve them in 200mL of N-methylpyrrolidone solvent. Add 2.24g of benzoyl peroxide initiator and stir at 90℃ for 6 hours to obtain a copolymer solution with a solid content of 50%. Weigh 10g of KH570 modified hydroxyapatite nanorods (30nm in diameter and 200nm in length) and add them to 100g of the above copolymer solution. Stir at 3500rpm for 40 minutes and then ultrasonically disperse for 25 minutes. Subsequently, add 5g of trimethylolpropane triacrylate, 1.0g of di-tert-butyl peroxide, and 0.5g of BYK-333 leveling agent. Continue stirring and mixing until homogeneous. Adjust the solid content of the varnish to 37% using xylene solvent to obtain a uniform and stable insulating varnish.

[0051] S5. The insulating varnish is applied to the surface of the copper-clad aluminum conductor using a mold coating method, with a total of 7 coats, each independently baked and cured. A five-zone continuous oven temperature control process is employed: 180℃ in the inlet zone, 290℃ in the pre-curing zone, 370℃ in the first main curing zone, 410℃ in the second main curing zone, and 250℃ in the outlet zone. The production line speed is stably controlled at 30m / min. After all coatings and curing are complete, the wire is forced to cool to room temperature and then wound up to obtain a finished enameled wire with a varnish film thickness of 0.035mm.

[0052] Comparative Example 1 The process parameters and preparation steps of this comparative example are basically the same as those of Example 2. The difference is that carbon nanotubes and graphene carbon reinforcement components are not added in step S1. Only 6061 aluminum alloy powder is used as the matrix raw material. The rest of the preparation process and parameters are exactly the same, and pure aluminum alloy enameled wire is obtained.

[0053] Comparative Example 2 The process parameters and preparation steps of this comparative example are basically the same as those of Example 2. The difference is that the chemical nickel plating and gradient copper plating steps in step S2 are omitted. After the surface pretreatment of the aluminum core wire is completed, the copper strip is directly coated and formed. No nickel-copper gradient transition layer is set. The rest of the preparation process and parameters are exactly the same.

[0054] Comparative Example 3 The process parameters and preparation steps of this comparative example are basically the same as those of Example 2. The difference is that in step S4, the original hydroxyapatite nanorods that have not been modified by KH570 silane grafting are directly used to replace the modified hydroxyapatite nanorods. The rest of the preparation process and parameters are exactly the same.

[0055] Comparative Example 4 The process parameters and preparation steps of this comparative example are basically the same as those of Example 2. The difference is that the 2-vinylnaphthalene-itaconic acid monobutyl ester copolymer system is not added in step S4, and conventional acrylic insulating resin is used instead of the self-made copolymer solution of this invention. The ratio of other additives, dispersion process and coating and curing parameters are exactly the same.

[0056] To verify the comprehensive performance of the copper-clad carbon alloy aluminum-based enameled wire prepared according to the present invention, the enameled wires prepared in Examples 1, 2, and 3 of the present invention, as well as Comparative Examples 1, 2, 3, and 4, were used as test samples. For each group of samples, 200mm long, regular wires were cut, and five parallel samples were set up in each group. After removing surface dust and impurities, all samples were placed in a dry environment at room temperature for 24 hours to complete the pretreatment.

[0057] (a) Conductor mechanical property testing Referring to GB / T 4074.2-2024 "Test Methods for Winding Wires - Part 2: Dimensions and Mechanical Properties", each group of enameled wire specimens was individually fixed between the upper and lower clamps of an electronic universal testing machine, ensuring that the specimens were clamped upright, without radial offset, and without pre-tension residual stress. The effective gauge length of the specimens was set to 100 mm. The testing machine was set to a constant tensile rate of 20 mm / min, and the specimens were stretched uniformly until fracture under a standard test environment of ambient temperature and pressure (temperature 23℃±2℃, relative humidity 50%±5%). The tensile strength and elongation at break of each individual specimen were collected. Parallel tests were performed on all five specimens in each group sequentially.

[0058] (II) Testing of paint film adhesion and high-temperature thermal shock performance Referring to GB / T 4074.4-2024 "Test Methods for Winding Wires - Part 4: Adhesion, Flexibility and Thermal Shock" and GB / T 6109.1-2025 "Enamelled Round Winding Wires - Part 1: General Provisions", the standard cross-cut adhesion test was used to test the adhesion of each group of samples at room temperature. A special cross-cutting tool was used to uniformly cut 1mm × 1mm grids on the enamel film surface, penetrating the enamel film layer to the surface of the metal conductor. After cleaning debris from the grid area, the cracking, peeling, and detachment of the enamel film on each group of samples were visually observed and recorded. After completing the room temperature adhesion test, all samples were placed in an enamelled wire thermal shock test chamber. The test temperature was set to 200℃ ± 2℃, and the samples were kept at this temperature for 30 minutes before being removed and allowed to cool naturally to room temperature. This constituted a single thermal shock cycle, and 20 cycles were continuously performed. Throughout the test, the temperature of the test chamber was kept uniform and no airflow was blown directly onto the samples. After the test, the integrity of the metal composite interface and the surface paint film of each group of samples was observed one by one, and the defects such as delamination, cracking and peeling of the samples were recorded.

[0059] (III) Insulation and electrical performance testing Referring to GB / T 1410-2006 "Test Methods for Volume Resistivity and Surface Resistivity of Solid Insulating Materials" and GB / T4074.5-2024 "Test Methods for Winding Wires Part 5: Electrical Properties", under standard test conditions of normal temperature and pressure, each group of enameled wire samples was connected to the test circuit of a high-resistivity meter and allowed to stand for 5 minutes to eliminate surface electrostatic interference. The equipment was then started to test the volume resistivity of the insulation layer of each group of samples. Each group of samples was tested three times, and the average value was calculated after removing abnormal data. Subsequently, the power frequency breakdown voltage tester was replaced, and the samples were stably clamped between the test electrodes. A uniform step voltage increase method was used to carry out the breakdown test, with the voltage increase rate set to 500V / s. The power frequency breakdown voltage value when the insulation varnish of each group of samples failed was recorded. After all samples were tested, the average breakdown voltage of each group was calculated.

[0060] (iv) Testing the thermal conductivity of the insulation layer Referring to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method", the hot-wire thermal conductivity tester was preheated for 30 minutes. After the equipment baseline and temperature parameters were completely stable, and the temperature measurement accuracy was calibrated to ±0.01 W / (m·K), each group of enameled wire samples was placed flat on the testing station, ensuring that the outer surface of the sample was completely in contact with the test probe, without gaps, offsets, or extrusion deformation. The testing environment was kept windless, with constant temperature and humidity. The automatic testing program of the equipment was started, and the testing time for a single sample was set to 10 minutes. The equipment automatically collected the thermal conductivity data of the insulation layer. Each group of samples was tested three times, and the average value of the valid data was calculated.

[0061] The results are shown in Table 1: Table 1. Experimental results of different embodiments and comparative examples As shown in Table 1, the copper-clad carbon alloy aluminum-based enameled wires prepared in Examples 1-3 have better overall tensile strength, elongation at break, power frequency breakdown voltage, volume resistivity, and thermal conductivity of the insulation layer than the comparative sample. Furthermore, after 20 cycles of high-temperature thermal shock at 200℃, no cracking, delamination, or peeling defects were observed. This indicates that the enameled wires prepared by this invention possess excellent mechanical structural stability, electrical insulation reliability, thermal conductivity and heat dissipation performance, and resistance to high-temperature alternating current. This invention employs a multi-level structural design, utilizing carbon nanoparticles to disperse and reinforce an aluminum matrix, a nickel-copper gradient interface transition, silane-modified inorganic hybrid fillers, and aromatic copolymer resin film formation. Through the grain refinement and grain boundary pinning effects of carbon nanotubes and graphene, the inherent mechanical defects of the aluminum alloy matrix are compensated, enhancing the conductor's load-bearing capacity and resistance to deformation. The nickel-copper gradient transition structure eliminates the brittle phase of the copper-aluminum composite and mitigates thermal cycling stress, ensuring the stability of the multi-layer metal interface. Silane grafting modification improves the interfacial compatibility between the inorganic filler and the organic resin, constructing a dense cross-linked network and continuous thermal conductivity pathways within the insulating layer. Simultaneously, relying on the rigid-flexible complementary copolymer resin molecular structure, the heat resistance, adhesion, and insulation shielding capability of the coating film are significantly improved. The synergistic effect of these multiple structures achieves simultaneous optimization of the mechanical, electrical, thermal conductivity, and heat resistance properties of the enameled wire.

[0062] Comparative Example 1, which omitted carbon nanotubes and graphene as carbon reinforcement components, showed a significant decrease in tensile strength and elongation at break, and exhibited slight microcracks after high-temperature thermal shock. This is because without the introduction of carbon reinforcement phases, the aluminum alloy matrix lacks grain refinement and defect repair mechanisms, resulting in numerous lattice defects and pores within the matrix. Under stress, crack propagation is easily generated, and lattice slip is significant under high-temperature conditions, leading to a decrease in structural stability and ultimately a significant deterioration in mechanical and thermal properties.

[0063] Comparative Example 2, which did not have a nickel-copper gradient transition layer and instead used a direct composite of copper and aluminum, showed a slight decrease in mechanical and insulation properties. After thermal shock testing, localized delamination at the interface and micro-cracks at the paint film edges appeared. This is because copper and aluminum have significantly different coefficients of thermal expansion. Direct composite bonding easily leads to the formation of brittle intermetallic compounds during high-temperature preparation and thermal cycling, resulting in weak interfacial bonding strength. This makes it unable to buffer the thermal stress generated by temperature alternation, easily causing interfacial delamination and paint film cracking, thus reducing the overall service stability of the wire.

[0064] Comparative Example 3 used unmodified hydroxyapatite nanofiller. The sample showed a significant decrease in power frequency breakdown voltage, volume resistivity, and thermal conductivity, and localized micro-cracks appeared in the coating film after thermal shock. This is because the unmodified hydroxyapatite has poor interfacial compatibility with the organic copolymer resin matrix, and the filler is prone to agglomeration and accumulation, resulting in a large number of micropores and structural defects inside the insulating coating film. This damages the film's density and reduces its insulation shielding performance. At the same time, the agglomeration of filler cannot form a continuous thermal conduction path, significantly weakening the heat dissipation capacity of the insulation layer. Furthermore, the defect sites are prone to becoming stress concentration points, which can easily induce coating film cracking and failure under high-temperature alternating conditions.

[0065] Comparative Example 4, which used conventional acrylic resin instead of the self-made 2-vinylnaphthalene-itaconic acid monobutyl copolymer resin, exhibited the worst overall performance, with multiple micro-cracks in the coating film and a significant decrease in adhesion. Conventional acrylic resin has weak molecular chain rigidity and poor thermal stability, making it prone to molecular chain thermal degradation and thermal shrinkage deformation under high-temperature environments. It also lacks sufficient adhesion to the metal conductor interface and cannot withstand high-temperature thermal shock and electric field aging, leading to the destruction of the insulating coating film's integrity. Ultimately, this results in a comprehensive decline in electrical insulation performance, heat resistance, and structural stability.

[0066] In summary, this invention effectively solves the defects of traditional aluminum-based enameled wires, such as weak mechanical properties, easy delamination of metal interfaces, poor insulation and thermal conductivity, and insufficient thermal shock resistance, by dispersing carbon nanotubes and graphene to strengthen the aluminum matrix, constructing a nickel-copper gradient transition composite interface, using silane-modified hydroxyapatite hybrid modification insulation system, and combining it with self-made 2-vinylnaphthalene-itaconic acid monobutyl copolymer resin for film formation.

[0067] In the description of this specification, the reference to terms such as "example," "various examples," etc., means that a specific feature, structure, material, or characteristic described in connection with that example or preparation is included in at least one example or preparation of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same example or preparation. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more examples or preparations.

[0068] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a copper-coated carbon alloy aluminum-based enameled wire, characterized by, Includes the following steps: S1. After mixing aluminum alloy powder with carbon nanotubes and graphene, aluminum-based core wires are obtained by ball milling, vacuum hot pressing, extrusion and drawing. S2. The aluminum-based core wire is pretreated by chemical nickel plating and electroplating copper plating to obtain a gradient transition layer wire. S3. Copper strip is wrapped around the surface of the gradient transition layer wire, and interface diffusion treatment, drawing, and annealing are performed to obtain copper-clad aluminum conductor. S4. Synthesize 2-vinylnaphthalene-itaconic acid monobutyl ester copolymer, add modified hydroxyapatite nanorods and additives to obtain insulating varnish; S5. Apply insulating varnish to the surface of the copper-clad aluminum conductor and bake it under multiple temperature-controlled conditions to obtain the enameled wire.

2. The production method according to claim 1, characterized by, In step S1, the aluminum alloy powder is selected from at least one of 6061 aluminum alloy, 6063 aluminum alloy, 1060 aluminum alloy, and 5052 aluminum alloy. The carbon nanotubes are selected with a diameter of 5-30 nm and a length of 5-50 μm; the graphene has a thickness of 0.5-5 nm and a sheet diameter of 2-20 μm. The mass ratio of aluminum alloy powder, carbon nanotubes and graphene is (97-98.5):(0.8-2.0):(0.5-1.0).

3. The preparation method according to claim 1, characterized in that, In step S1, the temperature of vacuum hot pressing is 590-610℃, the pressure is 35-45MPa, and the holding time is 1.5-2h. The extrusion temperature is 420-440℃, and the diameter of the extruded aluminum rod is 8-12mm. The drawing process involves two intermediate annealing processes at a temperature of 360-370℃ and a holding time of 1-1.5h, resulting in a final aluminum core wire diameter of 1.8-2.2mm.

4. The method of claim 1, wherein, In step S2, electroless nickel plating includes immersing the pretreated aluminum-based core wire in an alkaline electroless nickel plating solution, adjusting the pH value to 8.5-9.0 with ammonia water, and plating at 85-90℃ for 10-20 minutes. Copper electroplating involves transferring the nickel-plated core wire into an acidic copper sulfate plating solution for stepped current electroplating, controlling the initial current density of the electroplating to be 1.2-1.8 A / dm³. 2 The electroplating time is 8-12 minutes.

5. The preparation method according to claim 4, characterized in that, The composition of the alkaline electroless nickel plating solution is: nickel sulfate 20-30 g / L, sodium hypophosphite 25-35 g / L, sodium citrate 10-20 g / L, and ammonium chloride 25-35 g / L; The composition of the acidic copper sulfate plating solution is: 140-160 g / L copper sulfate, 45-55 g / L sulfuric acid, and 40-60 mg / L chloride ions.

6. The method of claim 1, wherein, In step S3, the interface diffusion treatment is carried out under nitrogen or argon protection, the treatment temperature is 460-470℃, and the holding time is 15-25min. Drawing involves sequential roughing, intermediate drawing, and fine drawing processes: roughing temperature is 330-340℃, with a deformation rate of 15-20% per pass; intermediate drawing temperature is 300-310℃, with a deformation rate of 10-15% per pass; and fine drawing temperature is 220-230℃, with a deformation rate of 6-10% per pass. Annealing is carried out in a protective atmosphere of ammonia decomposition, at a temperature of 350-360℃, for a holding time of 3-4 hours, and then cooled in the furnace to below 150℃ before being removed from the furnace.

7. The preparation method according to claim 1, characterized in that, Step S4, the step of synthesizing the 2-vinylnaphthalene-itaconic acid monobutyl copolymer includes: Under nitrogen protection, 2-vinylnaphthalene, monobutyl itaconic acid and itaconic anhydride were mixed in a mass ratio of (55-65):(30-40):(3-7), dissolved in N-methylpyrrolidone, and benzoyl peroxide was added as an initiator at 1-2% of the total mass of monomers. The mixture was reacted at 70-90℃ for 4-6 hours to obtain a copolymer solution. The modified hydroxyapatite nanorods have a diameter of 20-30 nm and a length of 100-200 nm, and their surface is modified with γ-methacryloyloxypropyltrimethoxysilane.

8. The method of claim 1, wherein, In step S4, the preparation method of the insulating varnish includes: adding 5-10 parts of modified hydroxyapatite nanorods to 100 parts of copolymer solution, stirring at high speed of 2500-3500 rpm for 20-40 min, then ultrasonically dispersing for 15-25 min, then adding 2-5 parts of trimethylolpropane triacrylate crosslinking agent, 0.5-1.0 parts of di-tert-butyl peroxide initiator and 0.2-0.5 parts of leveling agent, stirring and mixing evenly, and adjusting the solid content to 33-37% with xylene.

9. The method of claim 1, wherein, In step S5, the coating is done using a mold coating method, with a total of 5-7 coats applied, and each coat is baked independently after application. Multi-stage temperature-controlled baking adopts five-zone temperature control, which are set sequentially along the production line as follows: inlet zone temperature 160-180℃, pre-curing zone temperature 270-290℃, first main curing zone temperature 350-370℃, second main curing zone temperature 390-410℃, and outlet zone temperature 230-250℃.

10. A copper-clad carbon alloy aluminum-based enameled wire prepared by the preparation method according to any one of claims 1-9.

Images