Heat-resistant low-loss steel-cored aluminum stranded wire and preparation method thereof

Abstract

The application discloses a kind of heat-resistant low-loss steel-cored aluminium stranded conductor and preparation method thereof, belong to power transmission equipment technical field.The preparation method of the heat-resistant low-loss steel-cored aluminium stranded conductor includes steel core pretreatment and continuous electroplating, steel core stranding, heat-resistant aluminium alloy single wire preparation, aluminium stranded conductor stranding, stranding cleaning and plasma activation, organosilicon light-cured protective layer impregnation, cooling detection and winding.The application aims at the technical problem that existing steel-cored aluminium stranded conductor is difficult to consider heat resistance, low loss and long-term corrosion resistance, uses low-magnetic steel core and zirconium-containing rare earth heat-resistant aluminium alloy to reduce loss, inhibits galvanic corrosion between steel core and aluminium wire by Zn-Al gradient composite coating, and uses vinyl silane pre-wetting combined with ultraviolet light curing and low-temperature thermal curing three-stage process to construct high-adhesion, high-hardness organosilicon protective layer, realizes the comprehensive performance improvement of wire long-term temperature resistance ≥130 DEG C, conductivity ≥60% IACS, coating adhesion 1 level.

Description

Technical Field

[0001] This invention relates to the field of power transmission equipment technology, specifically to a heat-resistant, low-loss steel-cored aluminum stranded wire and its preparation method. Background Technology

[0002] Aluminum steel-cored stranded wire (ACSR) is widely used in high-voltage and ultra-high-voltage overhead transmission lines due to its excellent mechanical strength and conductivity. With the continuous growth of power load and the ongoing development of transmission lines towards increased capacity, reduced losses, and energy conservation, higher demands are being placed on the comprehensive performance of overhead conductors. An ideal high-performance conductor should simultaneously possess high conductivity to reduce line losses, good heat resistance to increase transmission capacity, excellent corrosion resistance to adapt to harsh environments, and sufficient mechanical strength to ensure operational safety. However, these performance indicators are often mutually restrictive in existing material systems and structural designs, making it difficult to achieve a balance. How to achieve synergistic optimization of multiple performance characteristics has become a pressing technical challenge in this field.

[0003] To address these needs, the industry has proposed several improvement solutions. Regarding aluminum conductors, heat-resistant aluminum alloy conductors have been developed by adding zirconium (Zr) and rare earth elements, enabling long-term operation at temperatures of 130°C or even higher, significantly increasing line transmission capacity. For steel cores, low-permeability steel cores are used to reduce hysteresis and eddy current losses, thereby reducing line losses. For corrosion protection, zinc plating or zinc alloy plating on the steel core surface forms a sacrificial anode protective layer, delaying corrosion; or an organic protective layer is coated on the conductor surface to block the intrusion of corrosive media. In addition, improvements such as using profiled wire structures to increase the fill factor and optimizing stranding processes to reduce resistance are also being implemented.

[0004] However, existing technologies still have the following shortcomings. First, the conductivity of heat-resistant aluminum alloys is generally lower than that of pure aluminum. The addition of alloying elements, while improving heat resistance, reduces conductivity, leading to increased circuit losses and making it difficult to simultaneously meet the dual requirements of heat resistance and low loss. Second, conventional zinc plating is consumed too quickly in corrosive environments containing chloride ions (Cl⁻), and the interface between the plating and the subsequent aluminum stranded wire is prone to electrochemical corrosion. Applying an organic protective layer alone results in poor adhesion, insufficient curing (especially at the gaps in the stranded wire), and insufficient long-term heat resistance. Third, the interface matching and continuous manufacturing process between the low-magnetic steel core, plating, and aluminum wire have not been systematically resolved. Existing technologies mostly optimize only a single performance aspect, lacking a holistic and collaborative design scheme involving multiple interfaces and materials from the steel core to the plating to the aluminum wire to the coating, making it difficult to achieve the comprehensive goals of heat resistance, low loss, and long lifespan. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a heat-resistant, low-loss steel-cored aluminum stranded wire and its preparation method.

[0006] The technical solutions provided by the embodiments of the present invention are as follows:

[0007] S1. Steel core pretreatment and continuous electroplating:

[0008] After being subjected to alkaline washing, acid pickling activation, and ultrasonic cleaning, the low-magnetic alloy steel wire is continuously passed through a first plating tank, a second plating tank, and a third plating tank for continuous gradient composite electroplating. The first plating tank uses a pure zinc anode and a current density of 2-4 A / dm³. 2 Temperature 30-50℃, wire feed speed 3-6 m / min;

[0009] The second plating tank adopts a dual-electrode system, with pure zinc anodes and pure aluminum anodes set simultaneously. The temperature is 30-40℃ and the wire feed speed is 3-6 m / min. By independently controlling the current ratio of the pure zinc anode and the pure aluminum anode, the Zn content in the deposited layer continuously decreases from entering the second plating tank to leaving the second plating tank, while the Al content continuously increases.

[0010] The third plating tank uses pure aluminum anodes, with a temperature of 20-30℃ and a wire feed speed of 3-6 m / min;

[0011] Alkaline washing is used to remove rolling oil and organic contaminants from the surface of low magnetic alloy steel wire. Acid washing activates the surface by dissolving the thin oxide film with hydrogen ions, exposing fresh active crystal faces to the substrate. The cavitation effect generated by ultrasonic cleaning further desorbs residual oil and solid impurities. The surface of the low magnetic alloy steel wire after the above treatment reaches atomic-level cleanliness, laying the foundation for the formation of a strong metal bond between the subsequent coating and the substrate.

[0012] The first plating tank uses a pure zinc anode, and the plating solution is an AlCl3-EMIC ionic liquid and 5-15wt% ZnCl2, with a current density of 2-4A / dm³. 2 Temperature 30-50℃, wire feed speed 3-6m / min, standard electrode potential of aluminum is -1.660V (A) 3+ Since the deposition potential of aluminum (Al) is much lower than that of hydrogen, aluminum cannot be electrodeposited from aqueous solutions. Therefore, a non-aqueous ionic liquid is required as the electrolyte. AlCl3-1-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid has a wide electrochemical window and good conductivity, enabling stable electrodeposition of aluminum and aluminum-based alloys at room temperature. The standard electrode potential for zinc is -0.762V (Zn). 2+ / Zn), the potential of zinc is more positive than that of aluminum. During alloy electrodeposition, metal ions with a more positive deposition potential are preferentially reduced and deposited on the cathode surface; under the current density conditions applied in the first plating tank, Zn 2+ It preferentially gains electrons at the cathode and is reduced to metallic zinc, while Al2Cl7 -Complex ions require a more negative potential to be reduced, but the AlCl3 concentration in AlCl3-EMIC ionic liquid is 55 to 65 wt%, and some aluminum will also be electrodeposited. At the same time, the good conductivity and wide electrochemical window of the plating solution are maintained. The deposited layer in the first plating tank is mainly composed of high zinc content, forming a zinc-rich underlayer that is well bonded to the steel substrate. Its corrosion potential is about -1.05 to -1.10V, which can provide sacrificial anode protection for the steel core when the coating is locally damaged.

[0013] The second plating tank employs a dual-electrode system, simultaneously featuring pure zinc and pure aluminum anodes. The plating solution consists of AlCl3-EMIC ionic liquid and 1-5 wt% ZnCl2, with a temperature of 30-40℃ and a wire feed speed of 3-6 m / min. By independently controlling the current ratio of the pure zinc and pure aluminum anodes, the Zn content in the deposited layer continuously decreases from the moment it enters the second plating tank until it leaves, while the Al content continuously increases. Each anode is powered by an independent rectifier. When the Zn anode is energized, anodic dissolution occurs to generate Zn. 2+ Al enters the plating solution and is deposited at the cathode. When Al is energized at the anode, it is converted into Al2Cl7. - The steel wire enters the plating solution in various forms and is deposited at the cathode; when the steel wire enters the second plating tank, the Zn anode has a high current density of 3-5 A / dm³. 2 The low current density of Al anodes is 0.5-1 A / dm³. 2 At this time, Zn 2+ Supply is ample, and deposition is primarily Zn; as the steel wire advances in the plating bath, the Zn anolyte current density is continuously reduced to 0.5-1 A / dm³ under programmed control. 2 Simultaneously, the Al anode current density is continuously increased to 3-5 A / dm³. 2 The rate of change of current density is 0.05-0.12 A / (dm²). 2 ·s), Zn near the cathode surface 2+ With Al 3+ As the concentration ratio changes continuously, the deposition rate of Zn gradually decreases while the deposition rate of Al gradually increases, resulting in a smooth increase in the Al content in the deposition layer. Through this continuous dynamic control of the current ratio, the composition of the deposition layer smoothly transitions from zinc-rich to aluminum-rich, effectively avoiding the formation of a clear compositional abrupt interface and contributing to the realization of a continuous gradient structure.

[0014] The third plating tank uses pure aluminum anodes, and the plating solution is AlCl3-EMIC ionic liquid and 0-0.3wt% ZnCl2, with a current density of 4-6 A / dm³. 2 Temperature 20-30℃, wire feed speed 3-6m / min, due to the low ZnCl2 concentration in the plating solution, Zn 2+ Supply is limited, cathode deposition uses Al2Cl7 -The process is primarily reduction-based, with the deposited layer consisting mainly of high-aluminum content. Its corrosion potential is approximately -0.85 to -0.90V, which is close to the corrosion potential of aluminum stranded wire. This helps to reduce the potential difference between the coating and the aluminum wire.

[0015] The natural Al2O3 oxide film on the surface of the aluminum wire is coated with Cl - Through penetration and dissolution, the aluminum substrate is exposed. The exposed aluminum wire and the coating on the steel core surface form a galvanic cell, with aluminum acting as the anode and being corroded more rapidly. After the coating is significantly worn away, aluminum and iron in the steel core form a galvanic cell, and aluminum continues to corrode to protect the steel core. The three-layer functional synergistic design of the Zn-Al gradient composite coating can alleviate the above corrosion process: the corrosion potential of the aluminum-rich outer layer is well matched with that of the aluminum stranded wire, and the potential difference between the two is small, which can reduce the potential driving force for the formation of the galvanic cell; the Zn-Al alloy transition layer achieves a smooth potential transition from the zinc-rich inner layer to the aluminum-rich outer layer, which can prevent the transition area from becoming a weak point where corrosion preferentially occurs; the zinc-rich inner layer provides sacrificial anode protection for the steel core. The synergistic effect of the three helps to effectively protect the steel core, inhibit aluminum wire corrosion, maintain the effective cross-sectional area of ​​the conductor, prevent the resistance from increasing with service time, and reduce losses.

[0016] S2, Steel core stranding:

[0017] Seven coated steel wires are concentrically twisted together under constant tension to form a low magnetic tensile steel core, with a twisting pitch ratio of 14-16 and a tension deviation of ≤5%.

[0018] Seven coated steel wires are concentrically twisted under constant tension to form a low-magnetic tensile steel core. This steel core is made of low-magnetic alloy material with a relative permeability of ≤1.2, which can significantly reduce hysteresis loss and eddy current loss in AC power transmission, thereby improving the power transmission efficiency of the conductor and reducing heat generation from the material source.

[0019] The pitch ratio is defined as the ratio of the stranding pitch to the outer diameter of the stranded layer. A pitch ratio of 14-16 is considered a medium to tight range. If the pitch ratio is too small, the plastic deformation of the steel wire will increase, making it prone to work hardening and even microcracks. At the same time, it will lengthen the single wire, resulting in a decrease in cross-sectional area and an increase in resistivity. If the pitch ratio is too large, the steel core structure will be loose and the roundness will be poor. During subsequent aluminum wire stranding, loose strands or serpentine shapes will easily occur, affecting the overall mechanical properties.

[0020] With tension deviation controlled within 5%, it means that the tension on the seven steel wires is highly consistent during the stranding process. If the tension of a certain steel wire is too high, it will be thinned or even suffer microscopic damage, becoming a weak point in the mechanical structure of the entire steel core, and the coating may crack due to excessive stretching. If the tension of a certain steel wire is too low, it will be in a relaxed state after stranding and will not participate in the load-bearing, causing the other steel wires to operate under overload. Constant tension stranding ensures that each coated steel wire bears the tensile load evenly, the cross-section of the steel core is close to an ideal circle, and the coating surface is free of scratches, indentations, or residual stress concentration. This process provides a precise center reference for the subsequent concentric stranding of 12 heat-resistant aluminum alloy single wires, and also lays the foundation for the overall tensile strength, sag characteristics, and long-term operational reliability of the steel-cored aluminum stranded wire.

[0021] S3, Preparation of heat-resistant aluminum alloy single wire:

[0022] The raw materials are weighed according to the proportion and refined at 730-750℃. Then, the melt is continuously cast at 700-720℃ to form aluminum rods. The aluminum rods are subjected to aging heat treatment at 250-280℃ for 24-48 hours. The aluminum rods are then cold-drawn to the target diameter of 2.0-4.5mm in 8-12 passes. Finally, they are aged at 150-170℃ for 8-12 hours. After air cooling, the heat-resistant aluminum alloy single wire is obtained.

[0023] During the smelting and continuous casting stages, raw materials containing 0.20-0.30% Zr, 0.06-0.10% Si, 0.10-0.14% Fe, 0.15-0.25% La+Ce, 0.015-0.025% B, and the balance Al are smelted, refined, and degassed at 730-750℃, and then continuously cast and rolled at 700-720℃. This temperature range ensures that the alloying elements are fully dissolved to form a supersaturated solid solution, while avoiding grain coarsening. The addition of B can form refractory borides with impurity elements, further reducing the content of solid solution impurities that are harmful to conductivity.

[0024] The subsequent aging heat treatment is the core of the process: aging allows Zr atoms dissolved in the aluminum matrix to fully precipitate as Al3Zr, forming fine, uniform, and thermally stable dispersed second-phase particles. These Al3Zr particles can pin grain boundaries and hinder dislocation movement during high-temperature operation, thereby significantly improving the wire's resistance to thermal softening and enabling it to withstand long-term heat up to 130℃. At the same time, the aging treatment reduces the concentration of dissolved Zr to a minimum, greatly reducing the scattering of electron waves and stabilizing the conductivity at 60% IACS.

[0025] In the cold drawing stage, the aluminum rod is cold-drawn to a target diameter of 2.0-4.5mm through 8-12 passes. Work hardening significantly improves the tensile strength of the single wire. Finally, final aging is performed, which eliminates residual stress generated during cold drawing to stabilize the microstructure and properties. At the same time, it promotes the re-dissolution of trace amounts of Zr that may have redissolved during cold drawing as fine Al3Zr, further optimizing conductivity. It also avoids excessively high aging temperatures that could coarsen the precipitated strengthening phase and reduce heat resistance. The scientific design of the above process enables the heat-resistant aluminum alloy single wire to maintain the conductivity of pure aluminum while possessing both tensile strength and long-term heat resistance, achieving an effective balance between heat resistance and conductivity. This provides a conductor material with matching performance for heat-resistant, low-loss steel-cored aluminum stranded wire.

[0026] S4, Aluminum stranded wire:

[0027] Twelve heat-resistant aluminum alloy single wires are twisted together on the outside of a steel core at a pitch ratio of 10-14 to obtain a wire blank.

[0028] A pitch ratio of 10-14 is considered a tighter range, resulting in a compact aluminum wire layer structure with good roundness. This reduces gaps between the aluminum wires, which helps lower AC resistance caused by the skin effect and proximity effect, thereby reducing line loss. Simultaneously, the tight stranded structure enhances the cohesion between the aluminum wire layer and the steel core, preventing loose strands or serpentine deformation during laying, erection, or operation. The uniform and symmetrical distribution of the 12 aluminum wires ensures more even current distribution, preventing localized hot spots and distributing mechanical loads evenly among the wires, thus improving the overall tensile strength and fatigue resistance of the conductor.

[0029] S5. Post-sanding cleaning and plasma activation:

[0030] After stranding, the wire blanks pass through an oil removal tank, a water washing tank, and a hot air drying channel in sequence to remove surface oil and impurities. After drying, the wire blanks continuously enter the plasma surface treatment chamber and are treated for 15-25 seconds under the conditions of 800-1000W power and 30-40Pa pressure.

[0031] Alkaline or special metal cleaning agents in the degreasing tank remove oil stains from the surface of aluminum wire and steel core through saponification, emulsification or the wetting and penetration of surfactants. The water washing tank further washes away residual cleaning agents and contaminants. Hot air drying avoids moisture residue that could cause subsequent coating blistering or reduced adhesion. Subsequently, the dried wire blank continuously enters the plasma surface treatment chamber and is treated for 15-25 seconds under the conditions of 800-1000W power and 30-40Pa pressure.

[0032] High-energy particles in plasma bombard the surface of the wire blank, producing a dual effect of physical sputtering and chemical activation: on the one hand, high-energy particles etch away the extremely thin oxide layer and organic contaminants on the surface, making the surface cleanliness reach the atomic level; on the other hand, plasma introduces a large number of polar functional groups (such as -OH, -COOH) on the surface of aluminum wire and steel core, turning the originally hydrophobic metal surface into a hydrophilic one, increasing the surface energy from about 30 mN / m to 60-70 mN / m. This high-energy hydrophilic surface can significantly enhance the wetting, spreading and penetration ability of subsequent organosilicon photocurable resin liquid on the aluminum wire surface, while providing abundant active sites for the chemical adsorption of vinyl silane coupling agent, thereby forming a strong chemical bond interface between the coating and the substrate. Plasma treatment is short, does not change the intrinsic properties of the substrate material, and does not introduce harmful solvents, making it an ideal process for achieving clean, efficient, and high-adhesion coating pretreatment.

[0033] S6. Impregnation of silicone photocurable protective layer:

[0034] S601. Add the hydroxyl value of 40-70 mgKOH / g silanol methyl phenyl silicone resin intermediate to the reactor, heat to 70-80℃, add 0.2-0.4% dibutyltin dilaurate and 0.02-0.04% p-hydroxyanisole by mass of the total system, under nitrogen protection, slowly add allyl glycidyl ether, the molar ratio of allyl glycidyl ether to silanol is 1.2-1.3:1, keep the reaction at the temperature for 4-5 h, cool down, filter and discharge to obtain modified methyl phenyl organosilicon resin;

[0035] Silylhydroxymethylphenyl silicone resin intermediate is a low molecular weight organosilicon compound containing active hydroxyl groups (–OH). It is mainly used as a precursor for the synthesis of methylphenyl silicone resin. It generates silicone resin with a three-dimensional network structure through hydrolysis and condensation reaction. It is widely used in the modification of high-temperature coatings, electrical insulation materials and high-performance coatings. Its molecular backbone is composed of alternating silicon-oxygen bonds (-Si-O-Si-), with methyl (-CH3) and phenyl (-C6H5) organic groups attached to the silicon atoms. The side chains retain a certain number of uncondensed silanol groups. This special molecular structure endows it with the following properties: silanol groups provide high reactivity and can participate in various chemical reactions such as condensation, esterification, and ring-opening addition; methyl groups give the resin flexibility and hydrophobicity; phenyl groups improve the resin's thermal stability, compatibility with organic resins and film hardness. The softening point of this intermediate is usually in the range of 45-105℃. It has good solubility in common solvents such as toluene and xylene and has a low volatile content, which facilitates subsequent grafting modification operations after melting or dissolution.

[0036] In the preparation of the protective layer of heat-resistant, low-loss steel-cored aluminum stranded wire, this intermediate serves as a key raw material. Its silanol sites are used to undergo a ring-opening addition reaction with the epoxy groups of allyl glycidyl ether (AGE), thereby grafting the photoactive allyl glycidyl ether double bonds onto the silicone resin side chains, enabling it to achieve rapid UV curing. Simultaneously, the ratio of methyl to phenyl groups in the intermediate backbone is designed to ensure that the modified resin possesses excellent thermal stability (long-term temperature resistance ≥180℃), low dielectric loss (tanδ≤0.02), and good compatibility with the aluminum matrix and organic additives. Introducing this type of silicone resin intermediate through compounding or grafting modification can significantly improve the weather resistance (anti-chalking, anti-cracking) and heat resistance of the organic coating. The relevant reaction formula is as follows:

[0037]

[0038] S602. Weigh out 65-75 parts of modified methylphenyl silicone resin, 15-25 parts of isoborneol acrylate, 2-5 parts of photoinitiator, 2-4 parts of vinyl silane, 0.5-2.5 parts of nano-SiO2, 0.3-1.0 parts of polyether modified siloxane leveling agent, and 0.2-0.8 parts of silicone defoamer by weight. Disperse the components evenly by high-speed stirring under light-protected conditions, filter, seal and store in the dark to prepare modified methylphenyl silicone resin liquid.

[0039] Modified methylphenyl silicone resin serves as the main film-forming material, and the allyl glycidyl ether double bonds grafted onto its molecular chain provide ultraviolet light crosslinking sites.

[0040] Isoborneol acrylate, as an active diluent, reduces the viscosity of the system to 200-400 mPa·s, which facilitates impregnation and penetration into the gaps of stranded wires. On the other hand, the rigid cyclic side groups in its molecular structure can improve the hardness and thermal stability of the coating after participating in photocuring crosslinking.

[0041] Vinylsilane (A-171) acts as an adhesion promoter. Its vinyl double bond participates in photocuring crosslinking, while the alkoxy group condenses with the hydroxyl group on the aluminum wire surface to form a chemical bond, establishing a strong molecular bridge between the organic coating and the metal substrate, thus improving the adhesion from physical adsorption to chemical bonding.

[0042] Nano-silica (0.5-2.5 parts) is used as an inorganic reinforcing phase. After being uniformly dispersed in the resin, it is locked in the three-dimensional network during photocuring and crosslinking. Its high-hardness nanoparticles can significantly improve the scratch resistance and wear resistance of the coating.

[0043] Photoinitiators decompose under ultraviolet light to generate free radicals, which instantly initiate chain polymerization of double bonds in resin and monomers, causing liquid resin to solidify into a dense cross-linked network within seconds.

[0044] Polyether-modified siloxane leveling agents reduce the surface tension of the coating liquid, ensuring that the coating is evenly spread on the stranded wire surface without pinholes;

[0045] Silicone defoamers suppress bubbles generated during impregnation and stirring, preventing pinhole defects in the coating.

[0046] After the above components are stirred and dispersed evenly at high speed under light-protected conditions, they are sealed and stored in a light-protected environment to prevent the photoinitiator from decomposing prematurely. The photocurable resin liquid prepared in this way can quickly form an organosilicon protective layer with high cross-linking density, strong bonding with the aluminum matrix, high surface hardness and wear resistance under ultraviolet light irradiation, which meets the requirements of steel-cored aluminum stranded wire for heat resistance, low loss and long-term service stability.

[0047] S603. The activated wire blank is pre-wetted by spraying with a 0.1-0.5wt% vinylsilane / ethanol aqueous solution at a speed of 6-10 m / min. Immediately afterwards, it is placed in a closed impregnation tank containing modified methylphenyl silicone resin solution. The resin solution temperature is controlled at 25-35℃, the viscosity at 200-400 mPa·s, and the impregnation time is 10-20 s. After exiting the tube, excess resin is scraped off using a ring-shaped die. The coating amount is controlled to ensure a dry film thickness of 12-18 μm after curing. Then, it enters a UV curing tunnel equipped with dual-wavelength LED light sources of 365 nm and 405 nm, with the lamps 5-10 cm from the wire blank surface and a power of 900-1100 mW / cm². 2 Curing is carried out under nitrogen protection for 5-8 seconds. After curing, the wires are continuously passed through a heat curing oven and kept at 100-120℃ for 5-10 minutes.

[0048] This step involves a three-stage process: vinyl silane pre-wetting, photocuring and shaping, and thermal curing and cross-linking. This process constructs an organosilicon protective layer on the surface of aluminum stranded wire that has high adhesion, high hardness, excellent water resistance and wear resistance. The core of this process lies in the synergistic effect of chemical bonding of silane coupling agent, rapid shaping by photocuring and deep cross-linking by thermal curing.

[0049] In the pre-wetting stage, the activated wire blank is passed through a 0.1-0.5wt% vinylsilane / ethanol aqueous solution spray device at a speed of 6-10 m / min. Vinylsilane (such as vinyltrimethoxysilane A-171) molecules contain two types of active groups: alkoxy (-OCH3) and vinyl (-CH=CH2). After spraying, the silane molecules are adsorbed on the surface of the aluminum wire. In the presence of trace amounts of moisture, the alkoxy groups hydrolyze to generate silanol (-Si-OH), which undergoes a condensation reaction with the abundant hydroxyl groups (Al-OH) on the surface of the plasma-activated aluminum substrate to form a strong Al-O-Si covalent bond. The bond energy of this chemical bond is much higher than that of physical adsorption, which is the root cause of the significant improvement in coating adhesion.

[0050] In the photocuring and setting stage, the pre-wetted wire blank immediately enters the impregnation tank and is impregnated with modified methylphenyl silicone resin liquid. After exiting the tube, excess resin is scraped off, and then the tube enters the UV curing tunnel. Under the irradiation of dual-wavelength LED light sources of 365nm and 405nm, the photoinitiator decomposes to generate free radicals, which initiate the free radical chain polymerization of the methacrylate double bonds in the resin and the vinyl double bonds of vinyl silane. Within seconds, a preliminary cross-linked three-dimensional network structure is formed, which enables the coating to be quickly set. After 20 friction cycles, the water contact angle of the UV-cured polysiloxane coating still remains at 98°, showing good wear resistance.

[0051] In the post-curing stage, the photocured wires were continuously passed through the heat curing oven and kept at 100-120℃ for 5-10 minutes. Studies have shown that the dehydration condensation rate of associated hydroxyl groups in the silicone matrix is ​​very high, and the hydroxyl concentration changes the most in the range of 105-130℃, indicating that this temperature range is the most active region for silanol condensation reaction. At this time, the residual silanol groups in the photocured network undergo a dehydration condensation reaction under heating conditions (≡Si-OH+HO-Si≡→≡Si-O-Si≡+H2O), forming additional -Si-O-Si crosslinking points, which further increases the crosslinking density of the coating and enhances water resistance, heat resistance and adhesion durability. Studies have shown that the appropriate addition of nano-SiO2 can increase the pencil hardness of the coating to above 4H.

[0052] S7. Cooling, Inspection and Rewinding:

[0053] Naturally air-cooled to ≤40℃, online testing of outer diameter, eccentricity, and coating adhesion; after passing the test, the coil is rolled up and packaged.

[0054] After photocuring and thermal curing, the conductors are cooled to below 40°C by natural air cooling. This process allows the coating to fully set and releases the slight internal stress generated during curing. It also prevents the coating from sticking or deforming during high-temperature winding and protects the electronic components of subsequent testing equipment from heat damage. Three online tests are then performed: outer diameter testing uses a laser diameter gauge for continuous scanning to monitor the uniformity of stranding and coating, promptly detecting diameter deviations or bulging defects; eccentricity testing uses eddy current or ultrasonic principles to assess the concentricity of the steel core and aluminum strands. Excessive eccentricity can lead to uneven electric field distribution and mechanical... Performance degradation; coating adhesion testing can be conducted using the cross-cut test or online scratch tester sampling to ensure that the bonding strength between the protective layer and the aluminum substrate meets the requirements. Qualified conductors are driven by a traction machine and neatly wound onto a reel or iron / wooden reel with constant tension. During the winding process, the conductors are controlled to be flat and the tension is kept constant to avoid cross-extrusion of the conductors within the reel, which could cause coating scratches or deformation of the aluminum wire. This process, through integrated control of temperature, geometric dimensions, coating quality, and winding technology, ensures the consistency and traceability of the quality of each reel of finished product, providing a factory quality guarantee for the long-term stable service of steel-cored aluminum stranded wire.

[0055] Preferably, the plating solution is ultrasonically dispersed before electroplating at a frequency of 28-32 kHz for 40-60 min. The plating conditions are: pH 4.8-5.5, temperature 35-50 ℃, and current density 2-6 A / dm³. 2 .

[0056] Preferably, the diameter of each heat-resistant aluminum alloy single wire is 2.0-4.5mm, the conductivity is ≥60%IACS, and the long-term heat resistance temperature is ≥130℃;

[0057] Preferably, the Zn-Al gradient composite coating is formed by multi-tank series continuous electroplating, and the electroplating solution system used is an ionic liquid system, including:

[0058] The first plating bath uses AlCl3-EMIC ionic liquid as the solvent, with a ZnCl2 concentration of 5-15 wt%.

[0059] The second plating bath uses AlCl3-EMIC ionic liquid as the solvent, with a ZnCl2 concentration of 1-5 wt%.

[0060] The third plating bath uses AlCl3-EMIC ionic liquid as the solvent and ZnCl2 concentration of 0-0.3wt%.

[0061] Preferably, the mass percentage composition of the heat-resistant aluminum alloy single wire is as follows:

[0062] Zr 0.20-0.30%, Si 0.06-0.10%, Fe 0.10-0.14%, La+Ce 0.15-0.25%, B 0.015-0.025%, with the remainder being Al and unavoidable impurities.

[0063] Compared with the prior art, the beneficial effects of the present invention are:

[0064] 1. Existing heat-resistant aluminum alloy conductors suffer from a significant decrease in conductivity due to the addition of alloying elements, making it difficult to simultaneously meet the dual requirements of high-capacity transmission and low line loss. This invention employs a low-permeability steel core to reduce hysteresis and eddy current losses at the source. Simultaneously, through a multi-element microalloying design using zirconium, lanthanum, cerium, and boron, combined with aging heat treatment, zirconium is fully precipitated in the form of Al3Zr and pinned to grain boundaries. This achieves a long-term heat resistance temperature exceeding 130℃ while maintaining a conductivity stable above 60% IACS, thus resolving the technical contradiction between heat resistance and conductivity.

[0065] 2. When conventional galvanized steel cores are in direct contact with aluminum wires, the difference between the standard electrode potentials of zinc and aluminum easily leads to the formation of macroscopic corrosion galvanes in humid or chloride-containing environments. Aluminum, being the more negatively potentialed, is corroded more rapidly. Furthermore, the presence of the corrosion product Al2O3 in NaCl solution further shifts the self-corrosion potential of the aluminum wire negatively, creating a positive feedback loop of deterioration. This invention constructs a Zn-Al gradient composite coating on the steel core surface, consisting of a zinc-rich layer, a Zn-Al alloy transition layer, and an aluminum-rich layer from the inside out. The corrosion potential shifts continuously positively from the inner layer to the outer layer. The corrosion potential of the aluminum-rich outer layer is highly matched with that of the aluminum stranded wire, with a minimal potential difference, eliminating the potential driving force of galvanic corrosion. The Zn-Al alloy transition layer achieves a smooth potential transition from the zinc-rich inner layer to the aluminum-rich outer layer, avoiding the weak areas where corrosion preferentially initiates due to sudden changes in interface potential in traditional multi-layer coatings. The zinc-rich inner layer provides sacrificial anode protection for the steel core. The three-layer structure forms a gradient coating through continuous changes in composition, achieving a unified protection between the steel core and the aluminum wire. This ensures that the effective cross-sectional area of ​​the conductor remains intact over a long period, and the resistance does not easily increase with service time, resulting in low transmission loss.

[0066] 3. Existing silicone protective layers rely solely on physical adsorption to adhere to the aluminum substrate, resulting in poor adhesion. Furthermore, the cross-linking density of single-stage photocuring is limited, leading to low coating hardness and poor scratch resistance. This invention employs vinyl silane pre-wetting treatment to form aluminum-oxysilicon covalent bonds on the aluminum wire surface, improving coating adhesion to level 1. Ultraviolet curing enables rapid setting within seconds, followed by low-temperature thermal curing to promote deep condensation of residual silanol groups, forming a dense silicon-oxygen cross-linking network. Simultaneously, nano-silica is introduced as an inorganic reinforcing phase, enabling the coating to achieve a pencil hardness of 4H or higher, combining high adhesion, high hardness, and long-term high-temperature resistance. Attached Figure Description

[0067] Figure 1 This is a schematic diagram of the cross-sectional structure of the heat-resistant, low-loss steel-cored aluminum stranded wire of the present invention.

[0068] In the figure, there are: low magnetic tensile steel core-1, Zn-Al gradient composite coating-2, aluminum stranded wire layer-3, and silicone photocuring protective layer-4. Detailed Implementation

[0069] The technical solutions of this invention are described below. It should also be noted that, to make the embodiments more detailed, the following embodiments are the best and preferred embodiments; those skilled in the art can also use other alternative methods to implement some well-known technologies.

[0070] Example 1: Preparation of steel-cored aluminum stranded wire:

[0071] S1. Steel core pretreatment and continuous electroplating:

[0072] Low-magnetic alloy steel wire with a diameter of 2 mm was subjected to alkaline washing, acid pickling activation, and ultrasonic cleaning, and then continuously passed through the first, second, and third plating tanks for continuous gradient composite electroplating. The first plating tank used a pure zinc anode, and the plating solution was AlCl3-EMIC ionic liquid with 10wt% ZnCl2, with a current density of 3A / dm³. 2 The temperature was 40℃, and the wire feed speed was 4.5m / min. The second plating tank adopted a dual-electrode system, simultaneously setting up pure zinc anodes and pure aluminum anodes. The plating solution was AlCl3-EMIC ionic liquid with 3wt% ZnCl2 added. The temperature was 35℃, and the wire feed speed was 4.5m / min. When the steel wire entered the second plating tank, the high current density of the Zn anode was 4A / dm³. 2 The low current density of the Al anode is 0.8 A / dm³. 2 As the steel wire advances, the Zn anode current density is continuously reduced to 0.8 A / dm. 2 Continuously increase the Al anode current density to 4 A / dm 2 The rate of change is 0.08 A / (dm). 2 The third plating tank uses a pure aluminum anode, and the plating solution is an AlCl3-EMIC ionic liquid with 0.15wt% ZnCl2, with a current density of 5A / dm³. 2 Temperature 25℃, wire feed speed 4.5m / min; after plating, wash with water and dry with hot air;

[0073] S2, Steel core stranding:

[0074] Seven coated steel wires are concentrically twisted together under constant tension to form a low magnetic tensile steel core, with a twisting pitch ratio of 15 and a tension deviation of ≤5%.

[0075] S3, Preparation of heat-resistant aluminum alloy single wire:

[0076] The mass percentage composition of the heat-resistant aluminum alloy single wire is as follows:

[0077] Zr 0.20%, Si 0.08%, Fe 0.12%, La+Ce 0.20% (where La:Ce=2:1), B 0.020%, with the remainder being Al and unavoidable impurities such as C and O;

[0078] The raw materials are weighed according to the proportion and refined at 740℃. Then the melt is continuously cast at 710℃ to form an aluminum rod. The aluminum rod is subjected to aging heat treatment, held at 260℃ for 36 hours, and then cold-drawn to the target diameter of 3mm in 10 passes. Finally, it is held at 160℃ for 10 hours for final aging. After air cooling, the heat-resistant aluminum alloy single wire is obtained.

[0079] S4, Aluminum stranded wire:

[0080] Twelve heat-resistant aluminum alloy single wires are twisted together on the outside of a steel core at a pitch ratio of 12 to obtain a wire blank.

[0081] S5. Post-sanding cleaning and plasma activation:

[0082] After stranding, the wire blanks pass through an oil removal tank, a water washing tank, and a hot air drying channel in sequence to remove surface oil and impurities; after drying, the wire blanks continuously enter the plasma surface treatment chamber and are treated for 20 seconds under a power of 900W and a pressure of 35Pa.

[0083] S6. Impregnation of silicone photocurable protective layer:

[0084] S601. Add the 60 mgKOH / g silanol methyl phenyl silicone resin intermediate to the reactor, heat to 75℃, add 0.3% dibutyltin dilaurate and 0.03% p-hydroxyanisole by mass of the total system, purge with nitrogen, slowly add allyl glycidyl ether, the molar ratio of allyl glycidyl ether to silanol is 1.2:1, keep the reaction at the temperature for 4 h, cool down, filter and discharge to obtain modified methyl phenyl organosilicon resin;

[0085] S602. Weigh out 70 parts of modified methylphenyl silicone resin, 20 parts of isoborneol acrylate, 3 parts of photoinitiator, 3 parts of vinyl silane, 1.5 parts of nano-SiO2, 0.5 parts of polyether modified siloxane leveling agent, and 0.5 parts of silicone defoamer by mass. Stir and disperse the components at high speed under light-protected conditions, filter, seal and store in the dark to prepare modified methylphenyl silicone resin liquid.

[0086] S603. The activated wire blank is pre-wetted by spraying with a 0.3wt% vinylsilane / ethanol aqueous solution at a speed of 8 m / min. It is then immediately placed into a closed impregnation tank containing modified methylphenyl silicone resin solution. The resin solution temperature is controlled at 30℃, the viscosity at 300 mPa·s, and the impregnation time is 15 s. After exiting the tube, excess resin is scraped off using a ring-shaped scraping die. The coating amount is controlled to ensure a dry film thickness of 15 μm after curing. Then, it enters a UV curing tunnel equipped with dual-wavelength LED light sources of 365 nm and 405 nm, with the lamps 7 cm from the wire blank surface and a power of 1000 mW / cm². 2 The wire is cured for 6 seconds under nitrogen protection. After curing, the wire is continuously passed through a heat curing oven and kept at 110℃ for 7 minutes to obtain the finished steel-cored aluminum stranded wire.

[0087] Example 2: Preparation of steel-cored aluminum stranded wire:

[0088] S1. Steel core pretreatment and continuous electroplating:

[0089] Low-magnetic alloy steel wire with a diameter of 2 mm was subjected to alkaline washing, acid pickling activation, and ultrasonic cleaning, and then continuously passed through the first, second, and third plating tanks for continuous gradient composite electroplating. The first plating tank used a pure zinc anode, and the plating solution was AlCl3-EMIC ionic liquid with 10wt% ZnCl2, with a current density of 3A / dm³. 2 The temperature was 40℃, and the wire feed speed was 4.5m / min. The second plating tank adopted a dual-electrode system, simultaneously setting up pure zinc anodes and pure aluminum anodes. The plating solution was AlCl3-EMIC ionic liquid with 3wt% ZnCl2 added. The temperature was 35℃, and the wire feed speed was 4.5m / min. When the steel wire entered the second plating tank, the high current density of the Zn anode was 4A / dm³. 2 The low current density of the Al anode is 0.8 A / dm³. 2 As the steel wire advances, the Zn anode current density is continuously reduced to 0.8 A / dm. 2 Continuously increase the Al anode current density to 4 A / dm 2 The rate of change is 0.08 A / (dm). 2 The third plating tank uses a pure aluminum anode, and the plating solution is an AlCl3-EMIC ionic liquid with 0.15wt% ZnCl2, with a current density of 5A / dm³. 2 Temperature 25℃, wire feed speed 4.5m / min; after plating, wash with water and dry with hot air;

[0090] S2, Steel core stranding:

[0091] Seven coated steel wires are concentrically twisted together under constant tension to form a low magnetic tensile steel core, with a twisting pitch ratio of 15 and a tension deviation of ≤5%.

[0092] S3, Preparation of heat-resistant aluminum alloy single wire:

[0093] The mass percentage composition of the heat-resistant aluminum alloy single wire is as follows:

[0094] Zr 0.25%, Si 0.08%, Fe 0.12%, La+Ce 0.20% (where La:Ce=2:1), B 0.020%, with the remainder being Al and unavoidable impurities such as C and O;

[0095] The raw materials are weighed according to the proportion and refined at 740℃. Then the melt is continuously cast at 710℃ to form an aluminum rod. The aluminum rod is subjected to aging heat treatment, held at 260℃ for 36 hours, and then cold-drawn to the target diameter of 3mm in 10 passes. Finally, it is held at 160℃ for 10 hours for final aging. After air cooling, the heat-resistant aluminum alloy single wire is obtained.

[0096] S4, Aluminum stranded wire:

[0097] Twelve heat-resistant aluminum alloy single wires are twisted together on the outside of a steel core at a pitch ratio of 12 to obtain a wire blank.

[0098] S5. Post-sanding cleaning and plasma activation:

[0099] After stranding, the wire blanks pass through an oil removal tank, a water washing tank, and a hot air drying channel in sequence to remove surface oil and impurities; after drying, the wire blanks continuously enter the plasma surface treatment chamber and are treated for 20 seconds under a power of 900W and a pressure of 35Pa.

[0100] S6. Impregnation of silicone photocurable protective layer:

[0101] S601. Add the 60 mgKOH / g silanol methyl phenyl silicone resin intermediate to the reactor, heat to 75℃, add 0.3% dibutyltin dilaurate and 0.03% p-hydroxyanisole by mass of the total system, purge with nitrogen, slowly add allyl glycidyl ether, the molar ratio of allyl glycidyl ether to silanol is 1.2:1, keep the reaction at the temperature for 4 h, cool down, filter and discharge to obtain modified methyl phenyl organosilicon resin;

[0102] S602. Weigh out 70 parts of modified methylphenyl silicone resin, 20 parts of isoborneol acrylate, 3 parts of photoinitiator, 3 parts of vinyl silane, 0.5 parts of nano-SiO2, 0.5 parts of polyether modified siloxane leveling agent, and 0.5 parts of silicone defoamer by mass. Stir and disperse the components at high speed under light-protected conditions, filter, seal and store in the dark to prepare modified methylphenyl silicone resin liquid.

[0103] S603. The activated wire blank is pre-wetted by spraying with a 0.3wt% vinylsilane / ethanol aqueous solution at a speed of 8 m / min. It is then immediately placed into a closed impregnation tank containing modified methylphenyl silicone resin solution. The resin solution temperature is controlled at 30℃, the viscosity at 300 mPa·s, and the impregnation time is 15 s. After exiting the tube, excess resin is scraped off using a ring-shaped scraping die. The coating amount is controlled to ensure a dry film thickness of 15 μm after curing. Then, it enters a UV curing tunnel equipped with dual-wavelength LED light sources of 365 nm and 405 nm, with the lamps 7 cm from the wire blank surface and a power of 1000 mW / cm². 2 The wire is cured for 6 seconds under nitrogen protection. After curing, the wire is continuously passed through a heat curing oven and kept at 110℃ for 7 minutes to obtain the finished steel-cored aluminum stranded wire.

[0104] Example 3: Preparation of steel-cored aluminum stranded wire:

[0105] S1. Steel core pretreatment and continuous electroplating:

[0106] Low-magnetic alloy steel wire with a diameter of 2 mm was subjected to alkaline washing, acid pickling activation, and ultrasonic cleaning, and then continuously passed through the first, second, and third plating tanks for continuous gradient composite electroplating. The first plating tank used a pure zinc anode, and the plating solution was AlCl3-EMIC ionic liquid with 10wt% ZnCl2, with a current density of 3A / dm³. 2 The temperature was 40℃, and the wire feed speed was 4.5m / min. The second plating tank adopted a dual-electrode system, simultaneously setting up pure zinc anodes and pure aluminum anodes. The plating solution was AlCl3-EMIC ionic liquid with 3wt% ZnCl2 added. The temperature was 35℃, and the wire feed speed was 4.5m / min. When the steel wire entered the second plating tank, the high current density of the Zn anode was 4A / dm³. 2 The low current density of the Al anode is 0.8 A / dm³. 2 As the steel wire advances, the Zn anode current density is continuously reduced to 0.8 A / dm. 2 Continuously increase the Al anode current density to 4 A / dm 2 The rate of change is 0.08 A / (dm). 2 The third plating tank uses a pure aluminum anode, and the plating solution is an AlCl3-EMIC ionic liquid with 0.15wt% ZnCl2, with a current density of 5A / dm³. 2 Temperature 25℃, wire feed speed 4.5m / min; after plating, wash with water and dry with hot air;

[0107] S2, Steel core stranding:

[0108] Seven coated steel wires are concentrically twisted together under constant tension to form a low magnetic tensile steel core, with a twisting pitch ratio of 15 and a tension deviation of ≤5%.

[0109] S3, Preparation of heat-resistant aluminum alloy single wire:

[0110] The mass percentage composition of the heat-resistant aluminum alloy single wire is as follows:

[0111] Zr 0.25%, Si 0.08%, Fe 0.12%, La+Ce 0.20% (where La:Ce=2:1), B 0.020%, with the remainder being Al and unavoidable impurities such as C and O;

[0112] The raw materials are weighed according to the proportion and refined at 740℃. Then the melt is continuously cast at 710℃ to form an aluminum rod. The aluminum rod is subjected to aging heat treatment, held at 260℃ for 36 hours, and then cold-drawn to the target diameter of 3mm in 10 passes. Finally, it is held at 160℃ for 10 hours for final aging. After air cooling, the heat-resistant aluminum alloy single wire is obtained.

[0113] S4, Aluminum stranded wire:

[0114] Twelve heat-resistant aluminum alloy single wires are twisted together on the outside of a steel core at a pitch ratio of 12 to obtain a wire blank.

[0115] S5. Post-sanding cleaning and plasma activation:

[0116] After stranding, the wire blanks pass through an oil removal tank, a water washing tank, and a hot air drying channel in sequence to remove surface oil and impurities; after drying, the wire blanks continuously enter the plasma surface treatment chamber and are treated for 20 seconds under a power of 900W and a pressure of 35Pa.

[0117] S6. Impregnation of silicone photocurable protective layer:

[0118] S601. Add the 60 mgKOH / g silanol methyl phenyl silicone resin intermediate to the reactor, heat to 75℃, add 0.3% dibutyltin dilaurate and 0.03% p-hydroxyanisole by mass of the total system, purge with nitrogen, slowly add allyl glycidyl ether, the molar ratio of allyl glycidyl ether to silanol is 1.2:1, keep the reaction at the temperature for 4 h, cool down, filter and discharge to obtain modified methyl phenyl organosilicon resin;

[0119] S602. Weigh out 70 parts of modified methylphenyl silicone resin, 20 parts of isoborneol acrylate, 3 parts of photoinitiator, 3 parts of vinyl silane, 1.5 parts of nano-SiO2, 0.5 parts of polyether modified siloxane leveling agent, and 0.5 parts of silicone defoamer by mass. Stir and disperse the components at high speed under light-protected conditions, filter, seal and store in the dark to prepare modified methylphenyl silicone resin liquid.

[0120] S603. The activated wire blank is pre-wetted by spraying with a 0.3wt% vinylsilane / ethanol aqueous solution at a speed of 8 m / min. It is then immediately placed into a closed impregnation tank containing modified methylphenyl silicone resin solution. The resin solution temperature is controlled at 30℃, the viscosity at 300 mPa·s, and the impregnation time is 15 s. After exiting the tube, excess resin is scraped off using a ring-shaped scraping die. The coating amount is controlled to ensure a dry film thickness of 15 μm after curing. Then, it enters a UV curing tunnel equipped with dual-wavelength LED light sources of 365 nm and 405 nm, with the lamps 7 cm from the wire blank surface and a power of 1000 mW / cm². 2 The wire is cured for 6 seconds under nitrogen protection. After curing, the wire is continuously passed through a heat curing oven and kept at 110℃ for 7 minutes to obtain the finished steel-cored aluminum stranded wire.

[0121] Comparative Example 1:

[0122] Compared with Example 3, Comparative Example 1 used a common low-alloy steel core and did not use low-magnetic alloy steel wire, while other conditions remained unchanged.

[0123] Comparative Example 2:

[0124] Compared with Example 3, the steel core surface in Comparative Example 2 was coated with a conventional zinc layer, while other conditions remained unchanged.

[0125] Comparative Example 3:

[0126] Compared with Example 3, the stranded wire blank in Comparative Example 3 was not activated by plasma, while other conditions remained unchanged.

[0127] Comparative Example 4:

[0128] Compared with Example 3, the silicone protective layer in Comparative Example 4 was made of ordinary finished methylphenyl silicone resin (without grafting modification, only high-temperature baking and curing), and other conditions remained unchanged.

[0129] Comparative Example 5:

[0130] Compared with Example 3, the heat-resistant aluminum alloy single wire in Comparative Example 5 was not subjected to aging treatment, while other conditions remained unchanged.

[0131] Comparative Example 6:

[0132] Compared with Example 3, no nano-SiO2 was added to the modified methylphenyl silicone resin liquid in Comparative Example 6, while other conditions remained unchanged.

[0133] Comparative Example 7:

[0134] Compared with Example 3, the activated wire blank in Comparative Example 7 was not pre-wetted using a vinylsilane / ethanol aqueous solution spray device, while other conditions remained unchanged.

[0135] Comparative Example 8:

[0136] Compared with Example 3, no Zr element was added during the preparation of the heat-resistant aluminum alloy single wire in Comparative Example 8, while other conditions remained unchanged.

[0137] Performance testing:

[0138] 1. Mechanical performance test: According to GB / T 1179-2017 "Round wire concentric stranded overhead conductor", the tensile strength, elongation and tensile strength of steel core aluminum stranded wire are tested.

[0139] 2. Conductivity test: According to GB / T 3048.4-2007 "Test methods for electrical properties of wires and cables - Part 4: DC resistance test of conductors", the DC resistance of the conductor is tested and the conductivity is calculated to ensure that the conductivity of the heat-resistant aluminum alloy single wire is ≥60% IACS.

[0140] 3. Heat resistance test: According to Appendix A of GB / T 1179-2017, the wires are placed in a constant temperature chamber at 130℃ for a long period of time (1000h). The tensile strength retention rate and conductivity change rate before and after placement are tested. The change rate is required to be ≤5% to verify the long-term heat resistance performance.

[0141] 4. Corrosion resistance test: In accordance with GB / T 19292.1-2018 "Corrosion of metals and alloys - Atmospheric corrosion test - Part 1: General requirements", a neutral salt spray test (NSS) is conducted to test the corrosion resistance of the coating and plating. It is required that there is no obvious corrosion and no peeling of the coating after 1000h of salt spray test.

[0142] 5. Dielectric performance test: According to GB / T 1408.1-2016 "Test methods for electrical strength of insulating materials - Part 1: Test at power frequency", the dielectric loss tangent of the silicone protective layer is tested to ensure that the dielectric loss tangent is ≤0.02.

[0143] 6. Adhesion test of silicone coating: conducted according to GB / T 9286-2021 "Cross-cut test of paints and varnishes".

[0144] 7. Coating Scratch Resistance Test: The steel wool friction method was used. A load of 500g was applied, and the friction head was wrapped with 0000# fine steel wool. The surface of the coating was rubbed back and forth 20 times (one rub is considered one round trip). The water contact angle before and after friction was measured using a contact angle meter. The formula for calculating the contact angle retention rate is:

[0145]

[0146] A schematic diagram of the cross-sectional structure of the heat-resistant, low-loss steel-cored aluminum stranded wire described in this invention is shown below. Figure 1 As shown, the conductor has a concentric hierarchical structure from the inside out. The low-magnetic tensile steel core is composed of one central low-magnetic alloy steel wire and six outer low-magnetic alloy steel wires twisted together. The Zn-Al gradient composite coating 2 is formed on the outer surface of each low-magnetic alloy steel wire in the low-magnetic tensile steel core. The aluminum stranded wire layer 3 consists of 12 heat-resistant aluminum alloy single wires arranged concentrically. The outermost layer is an integrally covered silicone photocurable protective layer 4. The coating and plating thicknesses in the figure are for illustrative purposes only and do not represent actual dimensions.

[0147] The test data for the above embodiments and comparative examples are shown in Tables 1-3 below.

[0148] Table 1. Test data of mechanical properties, electrical conductivity, and heat resistance of the examples and comparative examples.

[0149]

[0150] Table 1 Data Analysis:

[0151] In terms of mechanical properties, the tensile strength and elongation of Examples 1-3 of this invention are superior to those of the comparative examples. There are normal fluctuations in tensile strength among the examples, with Example 2 being slightly higher than Example 3. The elongation also shows a non-monotonic change, reflecting normal deviations in actual processes. The tensile strength of Comparative Examples 5 and 8 is significantly lower than that of the examples, and the elongation is also significantly reduced, indicating that the aging heat treatment causes the Al3Zr phase to fully precipitate, producing a significant precipitation strengthening effect. Simultaneously, the fine-grain strengthening also improves plasticity. The tensile strength of Comparative Example 1 is also lower than that of the examples, indicating that the low-magnetic alloy steel core itself has a higher strength reserve.

[0152] Regarding conductivity, the conductivity of Examples 1-3 all reached over 60% IACS, meeting the basic requirements for heat-resistant aluminum alloys. The conductivity of Comparative Examples 5 and 8 was significantly lower than that of the Examples. This is because, without aging treatment, zirconium exists in the aluminum matrix in solid solution form, which strongly scatters electron waves. After aging treatment, zirconium precipitates in the form of Al3Zr, reducing the solid solution concentration and restoring conductivity. The conductivity of Comparative Example 1 was slightly lower than that of the Examples, possibly related to the magnetic effect of the ordinary steel core.

[0153] Regarding heat resistance, Examples 1-3 exhibited excellent performance, maintaining a strength retention rate of over 92% after aging at 130℃ for 1000 hours, with conductivity changes controlled within -3%. Comparative Example 4 showed a significant decrease in strength retention to 76.5%, and a marked deterioration in conductivity changes, indicating insufficient cross-linking of the unmodified ordinary silicone resin coating during long-term thermal aging, failing to effectively protect the aluminum matrix from high-temperature softening. Comparative Examples 5 and 8 showed severely reduced strength retention rates, approximately 70% and 69% respectively, with significantly increased conductivity changes. This fully demonstrates the crucial role of Al3Zr precipitates in pinning grain boundaries and hindering dislocation movement at high temperatures. Without effective precipitated strengthening phases, the aluminum alloy experiences grain coarsening and dislocation recovery during long-term thermal exposure, leading to a simultaneous decline in both strength and conductivity.

[0154] In summary, this invention, through the synergistic design of a low-magnetic alloy steel core, a Zn-Al gradient composite coating, a Zr-containing heat-resistant aluminum alloy, aging heat treatment, and a modified organosilicon photocurable protective layer, achieves superior overall performance in terms of mechanical strength, electrical conductivity, and long-term heat resistance compared to the comparative examples. The aging heat treatment, which allows Zr to fully precipitate in the form of Al3Zr, is crucial for achieving a balance between high conductivity and high heat resistance, while the modified organosilicon coating provides an effective thermal protection barrier for the aluminum wire; both are indispensable.

[0155] Table 2. Test data on corrosion resistance, dielectric properties, and coating adhesion of the examples and comparative examples.

[0156]

[0157] Based on the test data in Table 2, the following conclusions can be drawn:

[0158] Regarding corrosion resistance, the coatings in Examples 1-3 remained intact or showed only very slight surface white rust after 1000 hours of salt spray testing, with no significant corrosion on the aluminum wires. This indicates that the Zn-Al gradient composite coating of the present invention has excellent salt spray corrosion resistance. In contrast, Comparative Example 2, using a conventional zinc plating layer, showed extensive white rust after the salt spray test, and significant pitting corrosion occurred on the aluminum wires. This indicates that the conventional zinc plating layer is consumed rapidly in a chloride-containing environment. Comparative Examples 3 and 7 showed localized peeling or blistering of the coatings. Although their coating conditions were similar to the examples, insufficient coating adhesion damaged the integrity of the protective layer, indirectly affecting the overall corrosion resistance. This demonstrates that the pretreatment process is crucial to the bonding quality between the coating and the substrate.

[0159] Regarding dielectric properties, the dielectric loss tangents of Examples 1-3 are all at a low level, meeting the usage requirements. Comparative Example 4 uses unmodified ordinary methylphenyl silicone resin, whose dielectric loss tangent is significantly increased. This is because the unmodified silicone resin molecular chain has more residual polar groups and cannot form a dense cross-linked network, resulting in increased dielectric loss. In contrast, this invention introduces photocurable double bonds through allyl glycidyl ether grafting, and combined with UV curing and thermal curing post-treatment, forms a highly cross-linked, low-polarity network, significantly improving dielectric properties.

[0160] Regarding coating adhesion, Examples 1-3 all achieved the highest level. Comparative Examples 2, 3, 4, and 7 showed a significant decrease in adhesion, falling to lower levels. Comparative Example 2 experienced coating blistering due to coating corrosion. Comparative Examples 3 and 7, lacking plasma activation or silane pre-wetting treatment, had insufficient active sites on the aluminum wire surface to form chemical bonds with the coupling agent, resulting in insufficient adhesion as the coating relied solely on physical adsorption. Comparative Example 4, due to the lack of resin grafting modification, had low crosslinking density after curing, poor coating cohesion, and easily peeled off completely from the scratch edges during cross-cut testing. These four comparative results collectively demonstrate that the interfacial stability of the Zn-Al gradient composite coating, the surface-active groups generated by plasma activation, the Al-O-Si covalent bonds formed by vinyl silane pre-wetting, and the crosslinking density of the modified resin itself are all crucial for achieving high coating adhesion; none can be omitted.

[0161] Table 3. Scratch resistance test data of coatings in the examples and comparative examples

[0162]

[0163] Data Analysis:

[0164] After 20 cycles of steel wool friction, the water contact angle retention rates in Examples 1-3 remained at a high level, indicating that the silicone protective layer of the present invention has excellent wear resistance. The slight fluctuations in contact angle retention rates between the examples reflect normal deviations in actual processes.

[0165] From the changes in water contact angle before and after friction, the surfaces of the examples were strongly hydrophobic before friction, and although the angle decreased after friction, it remained at a high level. Comparative Example 2 used a conventional zinc plating layer, and its contact angle retention rate after friction was significantly lower than that of the examples. This is because the zinc plating layer corroded in the salt spray environment, leading to a decrease in the interfacial adhesion of the coating, making the coating more susceptible to damage during friction. Comparative Example 3 did not undergo plasma activation, and Comparative Example 7 did not undergo silane pre-wetting treatment. The water contact angles of both were relatively low before friction, and the contact angle retention rate dropped significantly to a low level after friction. This is because without the synergistic effect of plasma activation and silane pre-wetting treatment, sufficient chemical bonding could not be formed between the coating and the aluminum substrate, resulting in insufficient interfacial adhesion. During friction, the coating was prone to local peeling or scratching, and the surface hydrophobic structure was destroyed. Comparative Example 4 used ungrafted modified ordinary silicone resin, and its contact angle retention rate after friction was also significantly lower. This is because ordinary silicone resin has a low crosslinking density and poor coating cohesion, making the surface easily scratched during friction. Comparative Example 6, which did not add nano-SiO2, had a slightly lower contact angle retention rate after friction than the Example. This indicates that nano-SiO2, as an inorganic reinforcing phase, is uniformly dispersed in the coating and plays a role in bearing and anti-cutting during friction, which can further improve the wear resistance of the coating.

[0166] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A heat-resistant, low-loss steel-cored aluminum stranded wire, characterized in that, From the inside out, it includes: The low-magnetic tensile steel core is composed of 7 low-magnetic alloy steel wires concentrically twisted together with 1 wire as the center and 6 wires as the outer layer. The diameter of each low-magnetic alloy steel wire is 1.5-3.0 mm. The Zn-Al gradient composite coating is formed directly on the outer surface of the low magnetic alloy steel wire. The gradient composite coating consists of a zinc-rich layer, a Zn-Al alloy transition layer and an aluminum-rich layer from the inside to the outside. The zinc-rich layer has a Zn content of ≥85wt%, the aluminum-rich layer has an Al content of ≥90wt%, and the Zn content decreases continuously from the inside to the outside while the Al content increases continuously from the inside to the outside. The aluminum stranded wire layer is composed of 12 heat-resistant aluminum alloy single wires concentrically twisted on the outside of the Zn-Al gradient composite coating; the diameter of each heat-resistant aluminum alloy single wire is 2.0-4.5mm, the conductivity is ≥60%IACS, and the long-term heat resistance temperature is ≥130℃. The silicone photocurable protective layer is impregnated and cured on the outer surface of the aluminum stranded wire layer and in the gaps between individual wires. The dry film thickness is 12-18μm, the dielectric loss tangent is ≤0.02, and the long-term temperature resistance is ≥180℃.

2. The heat-resistant, low-loss steel-cored aluminum stranded wire according to claim 1, characterized in that, The relative permeability of the low magnetic tensile steel core is ≤1.

2.

3. The heat-resistant, low-loss steel-cored aluminum stranded wire according to claim 1, characterized in that, The Zn-Al gradient composite coating is formed by multi-tank series continuous electroplating, and the electroplating solution system used is an ionic liquid system, including: The first plating bath uses AlCl3-EMIC ionic liquid as the solvent, with a ZnCl2 concentration of 5-15 wt%. The second plating bath uses AlCl3-EMIC ionic liquid as the solvent, with a ZnCl2 concentration of 1-5 wt%. The third plating bath uses AlCl3-EMIC ionic liquid as the solvent, with a ZnCl2 concentration of 0-0.3 wt%. In the AlCl3-EMIC ionic liquid, the concentration of AlCl3 is 55-65 wt%.

4. The heat-resistant, low-loss steel-cored aluminum stranded wire according to claim 1, characterized in that, The mass percentage composition of the heat-resistant aluminum alloy single wire is as follows: Zr 0.20-0.30%, Si 0.06-0.10%, Fe 0.10-0.14%, La+Ce 0.15-0.25%, B 0.015-0.025%, with the remainder being Al and unavoidable impurities.

5. A method for preparing heat-resistant, low-loss steel-cored aluminum stranded wire as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Steel core pretreatment and continuous electroplating: After being subjected to alkaline washing, acid pickling activation, and ultrasonic cleaning, the low-magnetic alloy steel wire is continuously passed through a first plating tank, a second plating tank, and a third plating tank for continuous gradient composite electroplating. The first plating tank uses a pure zinc anode and a current density of 2-4 A / dm³. 2 Temperature 30-50℃, wire feed speed 3-6 m / min; The second plating tank adopts a dual-electrode system, with pure zinc anodes and pure aluminum anodes set simultaneously. The temperature is 30-40℃ and the wire feed speed is 3-6 m / min. By independently controlling the current ratio of the pure zinc anode and the pure aluminum anode, the Zn content in the deposited layer continuously decreases from entering the second plating tank to leaving the second plating tank, while the Al content continuously increases. The third plating bath uses pure aluminum anodes, with a temperature of 20-30℃, a wire feed speed of 3-6 m / min, and a current density of 4-6 A / dm. 2 ; S2, Steel core stranding: Seven coated steel wires are concentrically twisted together under constant tension to form a low magnetic tensile steel core, with a twisting pitch ratio of 14-16 and a tension deviation of ≤5%. S3, Preparation of heat-resistant aluminum alloy single wire: The raw materials are weighed according to the proportion and refined at 730-750℃. Then, the melt is continuously cast at 700-720℃ to form aluminum rods. The aluminum rods are subjected to aging heat treatment at 250-280℃ for 24-48 hours. The aluminum rods are then cold-drawn to the target diameter of 2.0-4.5mm in 8-12 passes. Finally, they are aged at 150-170℃ for 8-12 hours. After air cooling, the heat-resistant aluminum alloy single wire is obtained. S4, Aluminum stranded wire: Twelve heat-resistant aluminum alloy single wires are twisted together on the outside of a steel core at a pitch ratio of 10-14 to obtain a wire blank. S5. Post-sanding cleaning and plasma activation: After stranding, the wire blanks pass through an oil removal tank, a water washing tank, and a hot air drying channel in sequence to remove surface oil and impurities. After drying, the wire blanks continuously enter the plasma surface treatment chamber and are treated for 15-25 seconds under the conditions of 800-1000W power and 30-40Pa pressure. S6. Impregnation of silicone photocurable protective layer: The activated wire blank is pre-wetted by spraying with a 0.1-0.5wt% vinylsilane / ethanol aqueous solution at a speed of 6-10 m / min, and then immediately sent into a closed impregnation tank containing modified methylphenyl silicone resin solution. The resin solution temperature is controlled at 25-35℃, the viscosity is 200-400 mPa·s, and the impregnation time is 10-20 s. After exiting the wire blank, excess resin is scraped off by an annular scraping die, and the coating amount is controlled so that the dry film thickness after curing is 12-18 μm. Then it enters the UV curing tunnel, with a power of 900-1100 mW / cm². 2 Curing is carried out under nitrogen protection for 5-8 seconds. After curing, the wires are continuously passed through a heat curing oven and kept at 100-120℃ for 5-10 minutes. S7. Cooling, Inspection and Rewinding: Naturally air-cooled to ≤40℃, the outer diameter, eccentricity, and coating adhesion are tested online, and then the product is rolled up and packaged after passing the tests.

6. The method for preparing a heat-resistant, low-loss steel-cored aluminum stranded wire according to claim 5, characterized in that, The plating solution in S1 is ultrasonically dispersed before electroplating, with an ultrasonic frequency of 28-32kHz and a time of 40-60min. The specific method for independently controlling the current ratio of the pure zinc anode and the pure aluminum anode using a dual-pair electrode system in the second plating tank of S1 is as follows: When the steel wire enters the second plating bath, the anode current density of pure zinc is 3-5 A / dm. 2 The anode current density of pure aluminum is 0.5-1 A / dm³. 2 ; As the steel wire advances in the second plating bath, the pure zinc anolyte current density is continuously reduced to 0.5-1 A / dm³ under programmed control. 2 Simultaneously, the pure aluminum anode current density is continuously increased to 3-5 A / dm³. 2 The rate of change of current density is 0.05-0.12 A / (dm²). 2 ·s).

7. The method for preparing a heat-resistant, low-loss steel-cored aluminum stranded wire according to claim 5, characterized in that, The preparation method of the modified methylphenyl organosilicon resin liquid in S6 is as follows: A hydroxyl value of 40-70 mgKOH / g silanol methyl phenyl silicone resin intermediate was added to a reaction vessel, heated to 70-80℃, and 0.2-0.4% of dibutyltin dilaurate and 0.02-0.04% of p-hydroxyanisole were added. Under nitrogen protection, allyl glycidyl ether was slowly added dropwise. The molar ratio of allyl glycidyl ether to silanol was 1.2-1.3:

1. The reaction was maintained at this temperature for 4-5 h, cooled, filtered, and discharged to obtain modified methyl phenyl organosilicon resin. Weigh out 65-75 parts of modified methylphenyl silicone resin, 15-25 parts of isoborneol acrylate, 2-5 parts of photoinitiator, 2-4 parts of vinyl silane, 0.5-2.5 parts of nano-SiO2, 0.3-1.0 parts of polyether-modified siloxane leveling agent, and 0.2-0.8 parts of silicone defoamer by weight. Disperse the components evenly by high-speed stirring under light-protected conditions, filter, seal and store in the dark to prepare modified methylphenyl silicone resin liquid.

8. The method for preparing a heat-resistant, low-loss steel-cored aluminum stranded wire according to claim 5, characterized in that, The UV curing tunnel in S6 is equipped with a dual-wavelength LED light source of 365 nm and 405 nm, with the lamp distance from the wire blank surface being 5-10 cm.

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