Low-voltage aluminum conductor and preparation method thereof

Abstract

The present invention relates to the technical field of metal wires, and in particular to a low-voltage aluminum wire and a preparation method thereof. The wire has a cross-sectional area of ​​35 square millimeters and comprises an aluminum alloy conductor and an insulating layer. The aluminum alloy conductor has a chemical composition comprising 0.7-0.9% magnesium, 0.4-0.6% silicon, 0.15-0.25% copper, 0.08-0.12% zirconium, 0.05-0.09% scandium, 0.03-0.07% silver, 0.01-0.03% erbium, 0.02-0.04% vanadium, and the remainder being aluminum. The microstructure of the low-voltage aluminum wire is gradient distributed, with ultrafine grains in the center, nano-precipitated phases in the transition region, and a surface layer having a synergistic reinforcement structure of high-density dislocations and nano-precipitated phases. The insulating layer is a double-layer composite structure, with an inner layer being a cross-linked polyethylene modified layer and an outer layer being an ethylene-tetrafluoroethylene copolymer modified layer. The electrical conductivity is increased to above 58% IACS, and the tensile strength is increased to above 280 MPa.

Description

Technical Field

[0001] The present invention relates to the field of metal conductor technology, particularly to low-voltage aluminum conductors and methods for their preparation. More specifically, the present invention provides a gradient-reinforced nanocomposite high-conductivity aluminum alloy conductor with high strength, high conductivity, excellent corrosion resistance, and stable connection. This conductor is particularly suitable for the high-performance requirements of conductors with a cross-sectional area of ​​35 square millimeters in new energy vehicles. Background Art

[0002] Currently, commonly used automotive aluminum wires on the market primarily include pure aluminum, 5000 series aluminum alloy, and 6000 series aluminum alloy. Pure aluminum offers good conductivity but low strength; 5000 series aluminum alloy offers improved strength but significantly reduced conductivity; and while 6000 series aluminum alloy offers a balance between conductivity and strength, it still suffers from issues like poor fatigue resistance and insufficient connection stability.

[0003] Chinese patent CN114015906B discloses a "nanoceramic composite 6201 aluminum alloy, ultrasonic-assisted low-temperature synthesis method, and use thereof." This solution uses TiB2 nanoparticles to reinforce 6201 aluminum alloy and is prepared through ultrasonic-assisted low-temperature synthesis, which improves the alloy's strength and conductivity to a certain extent. However, this solution has the following shortcomings: first, it only uses TiB2 as a single strengthening phase, failing to achieve multi-component synergistic strengthening; second, it fails to form a gradient microstructure, resulting in uneven performance distribution; third, it lacks surface protection measures, resulting in poor corrosion resistance; and fourth, the insulation layer design is simple, making it difficult to meet the requirements of complex working conditions.

[0004] Patent US20190111478A1 discloses the self-dispersion and self-stabilization of nanostructures in molten metals, and improves the strength of the alloy by adding a small amount of rare elements. However, this solution is mainly aimed at applications in the aerospace field, has a high cost, and the improvement in conductivity is limited, making it difficult to meet the cost-effectiveness requirements of new energy vehicles.

[0005] Therefore, there is an urgent need to develop a low-voltage aluminum wire that has high strength, high conductivity, excellent corrosion resistance and connection stability to meet the comprehensive performance requirements of new energy vehicles for wires with a cross-sectional area of ​​35 square millimeters. Summary of the Invention

[0006] The purpose of the present invention is to provide a low-voltage aluminum wire and a preparation method thereof, so as to overcome the technical problems of low strength, poor conductivity, insufficient corrosion resistance and unstable connection of aluminum wires in the prior art, and provide a low-voltage aluminum wire solution with excellent performance for new energy vehicles.

[0007] To achieve the above object, the present invention provides a low-voltage aluminum conductor, the cross-sectional area of ​​the conductor being 35 square millimeters, comprising an aluminum alloy conductor and an insulating layer, wherein the chemical composition of the aluminum alloy conductor is as follows by weight: magnesium 0.7-0.9%, silicon 0.4-0.6%, copper 0.15-0.25%, zirconium 0.08-0.12%, scandium 0.05-0.09%, silver 0.03-0.07%, erbium 0.01-0.03%, vanadium 0.02-0.04%, iron not more than 0.15%, manganese The content of tantalum is not more than 0.05%, titanium is not more than 0.03%, other elements are not more than 0.03% each, the total is not more than 0.10%, and the balance is aluminum; the aluminum alloy conductor has a gradient microstructure from the center to the surface, including an ultrafine grain structure in the central area, a gradient distribution of nano-precipitated phases in the transition area, and a high-density dislocation strengthening layer and a nano-precipitated phase synergistic strengthening structure in the surface area; the insulating layer adopts a double-layer composite insulating structure, including an inner cross-linked polyethylene modified insulating layer and an outer ethylene-tetrafluoroethylene copolymer modified insulating layer.

[0008] Preferably, in the gradient microstructure, the grain size in the central region is 1-3 μm, and the dislocation density in the surface region is 10 14 -10 15 The dislocation density in the central area is 10 per square meter. 12 -10 13 per square meter; the nano-precipitated phase includes a needle-like β "phase, 5-10 nanometers in length and 2-3 nanometers in diameter; a plate-like Q' phase, 15-25 nanometers in diameter and 3-5 nanometers in thickness; and a spherical Al3 (Sc, Zr) phase, 8-15 nanometers in diameter.

[0009] Furthermore, the inner cross-linked polyethylene modified insulation layer is composed of the following components: 92.5-93.5 weight percent of low-density polyethylene, 2.0-2.5 weight percent of cross-linking agent, 4.0-4.5 weight percent of nano-alumina, 0.3-0.5 weight percent of antioxidant, 0.2-0.3 weight percent of ultraviolet absorber, and 0.2-0.4 weight percent of lubricant; the average particle size of the nano-alumina is 30±5 nanometers; the thickness of the inner cross-linked polyethylene modified insulation layer is 0.9±0.05 mm.

[0010] Preferably, the outer ethylene-tetrafluoroethylene copolymer modified insulation layer is composed of the following components: 93-95 weight percent of ethylene-tetrafluoroethylene copolymer, 3.0-3.5 weight percent of nano-silicon dioxide, 0.5-0.8 weight percent of antioxidant, 0.8-1.2 weight percent of heat stabilizer, 0.3-0.5 weight percent of processing aid, and 0.2-0.4 weight percent of lubricant; the average particle size of the nano-silicon dioxide is 20±3 nanometers; the thickness of the outer ethylene-tetrafluoroethylene copolymer modified insulation layer is 0.5±0.05 mm.

[0011] In one embodiment of the present invention, the surface of the aluminum alloy conductor is provided with a nano-ceramic composite coating, which is composed of aluminum oxide-titania-silicon dioxide nano-composite ceramic with a molar ratio of 3:1:1, a particle size of 15-30 nanometers, and a coating thickness of 1.0±0.1 micrometers; the surface of the nano-ceramic composite coating is provided with a fluorosilane modified layer, which is formed by triethoxy 3,3,3-trifluoropropylsilane and has a thickness of 120-150 nanometers.

[0012] The present invention also provides a method for preparing the above-mentioned low-voltage aluminum conductor, comprising the following steps:

[0013] (1) Alloy melting and casting: Industrial pure aluminum and various master alloys are vacuum induction melted in a predetermined ratio, the melt temperature is controlled at 740±10℃, ultrasonic assisted stirring is performed, and then continuous casting is performed at 690±5℃ to obtain ingots with a diameter of 100±2 mm;

[0014] (2) Homogenization treatment: keep the ingot at 520±5℃ for 14±0.5 hours for homogenization treatment;

[0015] (3) Multi-step hot extrusion: the homogenized ingot was extruded for the first time at 490±5℃ with an extrusion ratio of 6.0:1, then annealed at 400±5℃ for 1.5±0.2 hours, and then extruded for the second time at 450±5℃ with an extrusion ratio of 4.0:1 to obtain a rod with a diameter of 20±0.5 mm;

[0016] (4) Gradient cold drawing: The bar is subjected to multi-stage cold drawing, including a first-stage drawing deformation of 22-24%, a second-stage drawing deformation of 17-19%, a third-stage drawing deformation of 12-14%, and a final stage drawing deformation of 6-7%. Intermediate annealing treatment is performed between each stage to finally obtain a single wire with a diameter of 14.0 ± 0.1 mm. 25 wires are then stranded to obtain a wire with a cross-sectional area of ​​35 ± 0.5 square mm.

[0017] (5) Surface treatment: The stranded conductors were subjected to pulse electrolytic polishing, and then a nano-ceramic composite coating was prepared by combining the sol-gel method with electrostatic spraying, sintered at 450±5℃ for 25±3 minutes, and then subjected to fluorosilane modification.

[0018] (6) Heat treatment: The surface treated conductor is subjected to a multi-stage aging treatment, including pre-aging at 150±3℃ for 4.0±0.5 hours, main aging at 180±3℃ for 9.0±0.5 hours, post-aging at 120±3℃ for 18.0±1.0 hours, and then stress relief treatment at 200±3℃ for 2.5±0.2 hours;

[0019] (7) Preparation of insulation layer: First, an inner cross-linked polyethylene modified insulation layer is extruded and cross-linked by electron beam irradiation, and then an outer ethylene-tetrafluoroethylene copolymer modified insulation layer is extruded to obtain a low-voltage aluminum conductor.

[0020] In one embodiment of the present invention, the alloy smelting and casting in step (1) specifically includes:

[0021] Preheat the crucible to 500±10℃, keep it warm for 2 hours, then heat it to 1000±20℃ and keep it warm for 1 hour. After cooling to room temperature, apply a magnesium borate coating with a thickness of 0.1-0.2 mm.

[0022] Melt the high-purity aluminum ingot at 500±10℃. After the aluminum ingot is completely melted, heat it to 650±10℃. Add the master alloys in the order of aluminum-copper alloy, aluminum-silicon alloy, and aluminum-magnesium alloy. Stir for 5-8 minutes after adding each alloy.

[0023] Raise the temperature to 720±10℃, add aluminum-zirconium alloy and aluminum-vanadium alloy, and stir for 10-15 minutes;

[0024] Raise the temperature to 750±10℃, add aluminum-scandium alloy, aluminum-erbium alloy and aluminum-silver alloy, and stir for 15-20 minutes;

[0025] Add refining agent in an amount of 0.2 weight percent of the total metal weight and stir for 15±2 minutes;

[0026] High-purity argon is introduced for gas refining at 740±10°C, with a flow rate of 2-3 L / min for 20-25 minutes;

[0027] Perform three ultrasonic treatments at a frequency of 20.5 ± 0.5 kHz and a power of 1100 ± 50 W for 3-5 minutes each, with manual stirring for 1-2 minutes between treatments;

[0028] Continuous casting is carried out at 690±5°C, the cooling water temperature is 20±2°C, the cooling water flow rate is 15-20 liters / minute, and the ingot is demoulded when it is cooled to no more than 100°C.

[0029] In one embodiment of the present invention, the gradient cold drawing in step (4) specifically includes:

[0030] The first stage of drawing: the starting diameter is 20±0.5 mm, the ending diameter is 17.5±0.2 mm, and it is completed in 4 passes. The deformation of each pass is 5.0-6.5%, the drawing speed is 0.6-0.7 m / s, and after drawing, intermediate annealing is carried out at 300±5℃ for 40±5 minutes;

[0031] The second stage of drawing: the starting diameter is 17.5±0.2 mm, the ending diameter is 15.8±0.2 mm, and it is completed in 3 passes. The deformation of each pass is 4.5-6.0%, the drawing speed is 0.9-1.1 m / s, and after drawing, intermediate annealing is carried out at 290±5℃ for 35±5 minutes;

[0032] The third stage of drawing: the starting diameter is 15.8±0.2 mm, the ending diameter is 14.5±0.2 mm, and it is completed in 3 passes. The deformation of a single pass is 3.5-5.0%, the drawing speed is 1.3-1.4 m / s, and after drawing, intermediate annealing is carried out at 280±5℃ for 30±5 minutes;

[0033] Final stage drawing: starting diameter is 14.5±0.2 mm, ending diameter is 14.0±0.1 mm, completed in 2 passes, deformation of single pass is 3.0-4.0%, and drawing speed is 1.7-1.9 m / s;

[0034] Wire twisting: 25 single wires are twisted at a twisting pitch of 140-160 mm, with a twisting tension of 20-25 Newtons per wire and a twisting speed of 25-30 m / min, ultimately obtaining a wire with a cross-sectional area of ​​35±0.5 mm2.

[0035] In one embodiment of the present invention, the surface treatment in step (5) specifically includes:

[0036] Pulse electropolishing: A mixed solution of phosphoric acid, sulfuric acid, and water in a volume ratio of 6:3:1 was used as the electrolyte. The electrolyte temperature was 25±2°C, the current density was 25±2 mA / cm2, the pulse frequency was 75±5 Hz, and the processing time was 50±5 seconds.

[0037] Preparation of nano-ceramic composite coating:

[0038] (a) Sol-gel precursor preparation: To a mixture of 85 ± 2 mL of anhydrous ethanol, 10 ± 0.5 mL of deionized water, and 5 ± 0.3 mL of glacial acetic acid, 15.3 ± 0.2 g of aluminum n-butyl ester, 5.6 ± 0.1 g of tetrabutyl titanate, and 3.4 ± 0.1 g of tetraethoxysilane were added in sequence and aged at 40 ± 2 °C for 24 ± 1 h.

[0039] (b) Electrostatic spraying: spray gun voltage is 60±5 kV, the distance between the spray gun and the workpiece is 200±10 mm, the workpiece preheating temperature is 60±5℃, and spray 3-4 circles;

[0040] (c) Sintering: a three-stage heating program was used: from room temperature to 200±10°C at a heating rate of 1.5±0.2°C / min, and holding for 60±5 minutes; from 200±10°C to 350±10°C at a heating rate of 2.0±0.2°C / min, and holding for 45±5 minutes; from 350±10°C to 450±5°C at a heating rate of 1.0±0.2°C / min, and holding for 25±3 minutes;

[0041] Fluorosilane modification: Prepare a solvent using anhydrous ethanol and deionized water in a volume ratio of 95:5, add triethoxy 3,3,3-trifluoropropylsilane to a concentration of 0.8±0.1 weight percent, adjust the pH value to 4.0±0.2, and hydrolyze for 3.0±0.5 hours before immersion treatment for 6±1 minutes. Curing should be carried out at 150±3°C for 35±3 minutes.

[0042] In one embodiment of the present invention, the preparation of the insulating layer in step (7) specifically includes:

[0043] Preparation of inner cross-linked polyethylene modified insulation layer:

[0044] (a) Surface modification of nano-alumina: Surface modification of nano-alumina was performed using γ-aminopropyltriethoxysilane at a dosage of 3-5 weight percent of the weight of the nano-alumina, and stirring was performed at 60±5°C for 4.0±0.5 hours.

[0045] (b) Inner layer material mixing: 92.5-93.5 weight percent of low-density polyethylene, 2.0-2.5 weight percent of diisopropylbenzene peroxide, 4.0-4.5 weight percent of modified nano-alumina, 0.3-0.5 weight percent of antioxidant, 0.2-0.3 weight percent of ultraviolet absorber, and 0.2-0.4 weight percent of lubricant are uniformly mixed;

[0046] (c) Inner layer extrusion: using a twin-screw extruder, the temperature zones from the feed port to the die are 140±5°C, 160±5°C, 175±5°C, 190±5°C, 200±5°C, and 205±5°C, and the extrusion speed is 15-20 m / min;

[0047] (d) Irradiation cross-linking: using an electron beam accelerator with an accelerating voltage of 1.5-2.0 MeV and a total irradiation dose of 60 ± 5 kGy, completed in 2-3 times;

[0048] Preparation of outer ethylene-tetrafluoroethylene copolymer modified insulation layer:

[0049] (a) Nano-silica surface modification: The nano-silica was surface modified using hexadecyltrimethoxysilane at a dosage of 4-6 weight percent of the weight of the nano-silica, and stirred at 110±5°C for 6.0±0.5 hours;

[0050] (b) outer layer material mixing: 93-95 weight percent of ethylene-tetrafluoroethylene copolymer, 3.0-3.5 weight percent of modified nano-silica, 0.5-0.8 weight percent of antioxidant, 0.8-1.2 weight percent of thermal stabilizer, 0.3-0.5 weight percent of processing aid, and 0.2-0.4 weight percent of lubricant are uniformly mixed;

[0051] (c) Outer layer extrusion: using a single-screw extruder, the temperature zones from the feed port to the die are 230±5°C, 250±5°C, 270±5°C, 280±5°C, and 290±5°C, the extrusion speed is 10-15 m / min, and the water bath cooling temperature is 45±2°C.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] 1. This invention utilizes a multi-element microalloying design, adding conventional elements such as Mg, Si, and Cu to the aluminum matrix, creating a synergistic effect with rare elements such as Sc, Zr, Ag, Er, and V. This creates multi-type and multi-scale nano-precipitates, achieving a balance of high strength and high conductivity. This results in increased conductivity to over 58% IACS and tensile strength to over 280 MPa, far superior to conventional aluminum conductors.

[0054] 2. The gradient microstructure designed in this invention creates structural layers with different functions within and on the surface of the conductor: the central region is dominated by an ultrafine grain structure, ensuring excellent conductivity; the surface region is primarily strengthened by a high density of dislocations and synergistic reinforcement of nano-precipitates, providing excellent mechanical properties; and the gradient distribution of nano-precipitates in the transition region achieves a smooth transition in performance. This gradient structure enables the conductor to exhibit excellent mechanical properties under complex stress conditions such as bending and torsion, and increases its bending life by approximately 2 times.

[0055] 3. The nano-ceramic composite coating and fluorosilane-modified surface treatment technology employed in this invention form a highly effective dual protective barrier, significantly enhancing the corrosion and oxidation resistance of the conductor. Salt spray testing has demonstrated an approximately 300% improvement in corrosion resistance, effectively extending the conductor's service life.

[0056] 4. The double-layer composite insulation structure designed by the present invention adopts cross-linked polyethylene modified with nano-alumina as the inner layer and ethylene-tetrafluoroethylene copolymer modified with nano-silica as the outer layer, which synergistically provide excellent electrical insulation, temperature resistance and mechanical protection. The operating temperature range is extended to -40°C to 150°C, adapting to extreme environmental conditions.

[0057] 5. The preparation process of the present invention innovatively combines advanced technologies such as vacuum induction melting, ultrasonic-assisted stirring, multi-step hot extrusion, and gradient cold drawing to achieve precise preparation of nanocomposites and precise control of their microstructure, making product performance more stable and reliable while maintaining the feasibility and applicability of the process.

[0058] Overall, the low-voltage aluminum conductor provided by the present invention not only meets the electrical performance requirements of new energy vehicles for conductors with a cross-sectional area of ​​35 square millimeters, but also significantly improves mechanical properties, corrosion resistance, and connection stability, significantly extends service life, and reduces maintenance costs, thus having important engineering application value. DETAILED DESCRIPTION

[0059] Below in conjunction with specific embodiment, the present invention is described in further detail.Should be appreciated that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.In addition, should be appreciated that after reading the present invention, those skilled in the art can make corresponding changes or modifications according to the teachings of the present invention, and these changes or modifications still fall within protection scope of the present invention.

[0060] 1. Preparation and Characterization of Raw Materials

[0061] 1. High-purity aluminum ingots: purity ≥99.95%, A00 grade aluminum ingots produced by Shanghai Nonferrous Metals (Group) Co., Ltd.

[0062] 2. Master alloy:

[0063] Al-25wt.%Mg master alloy: purity ≥99.9%, product of Northeast Light Alloy Co., Ltd.;

[0064] Al-50wt.%Si master alloy: purity ≥99.9%, product of YUYAN Rare Earth New Materials Co., Ltd.;

[0065] Al-33wt.%Cu master alloy: purity ≥99.9%, product of Kunshan Aluminum Co., Ltd.;

[0066] Al-5wt.%Zr master alloy: purity ≥99.9%, product of Yongjie New Materials Co., Ltd.;

[0067] Al-2wt.%Sc master alloy: purity ≥99.9%, product of YUYAN Rare Earth New Materials Co., Ltd.;

[0068] Al-50wt.%Ag master alloy: purity ≥99.9%, product of Guiyan Platinum Co., Ltd.;

[0069] Al-4wt.%Er master alloy: purity ≥99.9%, product of YUYAN Rare Earth New Materials Co., Ltd.;

[0070] Al-10wt.%V master alloy: purity ≥99.9%, product of Yongjie New Materials Co., Ltd.

[0071] 3. Insulation layer material:

[0072] Low-density polyethylene (LDPE): melt index 1.8-2.2 g / 10min, DOWLEX2045 product of The Dow Chemical Company, USA;

[0073] Cross-linking agent (diisopropylbenzene peroxide, DCP): purity ≥98%, Akzo Nobel Perkadox BC-40B product;

[0074] Ethylene tetrafluoroethylene copolymer (ETFE): melt index 8-12 g / 10min, Tefzel HT-2183 product from DuPont, USA;

[0075] Nano-alumina (Al2O3): average particle size 30±5 nm, purity ≥99.9%, Puralox SCFa-140 product from Alderman Company;

[0076] Nano-silicon dioxide (SiO2): average particle size 20±3 nm, purity ≥99.9%, Aerosil 200 product of Evonik Industries, Germany;

[0077] Antioxidant: Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), purity ≥98%, BASF Irganox 1010 product;

[0078] UV absorber: Methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl) propionic acid, purity ≥98%, BASF Tinuvin 1130 product;

[0079] Heat stabilizer: barium sulfate, purity ≥98%, product of Guangdong Guanghua Technology Co., Ltd.

[0080] Lubricant: calcium stearate, purity ≥97%.

[0081] 4.Surface treatment materials:

[0082] Aluminum n-butyl ester (Al(OC4H9)3): purity ≥98%, product of Alfa Aesar;

[0083] Tetrabutyl titanate (Ti(OC4H9)4): purity ≥98%, product of Alfa Aesar;

[0084] Tetraethoxysilane (Si(OC2H5)4): purity ≥98%, product of Alfa Aesar;

[0085] Triethoxy 3,3,3-trifluoropropylsilane ((CH3CH2O)3Si(CH2)2CF3): purity ≥97%, product of Gelest;

[0086] γ-Aminopropyltriethoxysilane (KH550): purity ≥98%, Dow Corning Z-6011 product;

[0087] Hexadecyltrimethoxysilane (KH-31): Purity ≥96%, Shin-Etsu Chemical KBM-3016 product.

[0088] 2. Example Example 1

[0089] A low-voltage aluminum conductor is prepared in the following specific steps:

[0090] (1) Alloy melting and casting: First, pre-treat the high-purity alumina crucible by preheating it at 500°C for 2 hours, heating it to 1000°C and holding it for 1 hour for drying. After cooling it to room temperature, apply a magnesium borate coating with a thickness of 0.15 mm. Melt the high-purity aluminum ingot (accounting for 82 weight percent of the total ingredients) at 500°C. After the aluminum ingot is completely melted, heat it to 650°C. Add the intermediate alloys in the order of Al-33wt.%Cu alloy, Al-50wt.%Si alloy, and Al-25wt.%Mg alloy. Stir for 6 minutes after adding each alloy. Raise the temperature to 720°C, add Al-5wt.%Zr alloy and Al-10wt.%V alloy, and stir for 12 minutes. Raise the temperature to 750°C, add Al-2wt.%Sc alloy, Al-4wt.%Er alloy, and Al-50wt.%Ag alloy, and stir for 18 minutes. A refining agent (a mixture of high-purity AlF3 and KCl, in a weight ratio of 3:1) was added at a rate of 0.2 weight percent based on the total metal weight, and stirring was carried out for 15 minutes. Gas refining was carried out at 740°C with high-purity argon gas at a flow rate of 2.5 liters / minute for 22 minutes. This was followed by three ultrasonic treatments at a frequency of 20.5 kHz, a power of 1100 watts, and a temperature of 730°C, each for 3 minutes, with manual stirring for 1 minute between treatments. Finally, continuous casting was carried out at 690°C with a cooling water temperature of 20°C and a cooling water flow rate of 18 liters / minute to produce an ingot with a diameter of 100 mm. The ingot was demolded when it cooled below 100°C.

[0091] The final aluminum alloy conductor's chemical composition (by weight percentage) is: magnesium 0.7%, silicon 0.4%, copper 0.15%, zirconium 0.08%, scandium 0.05%, silver 0.03%, erbium 0.01%, vanadium 0.02%, iron 0.10%, manganese 0.03%, titanium 0.01%, other elements totaling 0.05%, and the balance being aluminum. Impurity elements are strictly controlled to standards: Fe ≤ 0.15 wt%; Mn ≤ 0.05 wt%; Ti ≤ 0.03 wt%; Cr ≤ 0.02 wt%; Ni ≤ 0.02 wt%; Zn ≤ 0.03 wt%; and other elements individually ≤ 0.01 wt% and in total ≤ 0.10 wt%.

[0092] (2) Homogenization: The ingot was placed in a micro-oxygen environment heat treatment furnace and heated to 520°C at a heating rate of 50°C / hour and held at this temperature for 14 hours. The ingot was cooled to 300°C at a rate of 25°C / hour using furnace cooling, and then air-cooled to room temperature. The ingot after homogenization treatment was surface treated by mechanical turning to remove the surface layer to a depth of 1.8 mm and then polished with sandpaper.

[0093] (3) Multi-step hot extrusion: The homogenized ingot was cut into short bars with a length of 200 mm and preheated at 490°C for 3.5 hours in a micro-oxygen argon atmosphere (oxygen content ≤ 100 ppm). The preheating rate of the preheating furnace was 80°C / hour. The first extrusion temperature was 490°C, the extrusion ratio was 6.0:1, the extrusion speed was 2.8 mm / s, the extrusion pressure was 400 MPa, the extrusion die material was H13 die steel (hardness HRC 50), the extrusion die preheating temperature was 450°C, the lubricant was a mixture of molybdenum disulfide and graphite powder (weight ratio 1:1), and the coating thickness was 0.4 mm. The extruded bar had a diameter of 40 mm.

[0094] Intermediate annealing treatment: the bar is kept at 400℃ for 1.5 hours in a micro-oxygen argon atmosphere (oxygen content ≤ 100 ppm), cooled to 200℃ by furnace cooling, and then air-cooled to room temperature.

[0095] Second extrusion: The annealed bars were preheated at 450°C for 2.5 hours. The extrusion temperature was 450°C, the extrusion ratio was 4.0:1, the extrusion speed was 1.8 mm / s, the extrusion pressure was 440 MPa, the die was preheated to 420°C, and the lubricant was the same as for the first extrusion. The extruded bars had a diameter of 20 mm. After extrusion, they were immediately water-quenched at 20°C for 2 seconds. Straightening was then performed, the gap between the rolls was adjusted to 19.5 mm, and the surface was cleaned.

[0096] (4) Gradient cold drawing: Before the first stage of drawing, a calcium-based soap lubricant (containing 22 weight percent calcium oxide, 43 weight percent fatty acid, and 12 weight percent paraffin) was applied to the surface of the rod. The coating thickness was 0.15 mm, and a pointed tip was made with a taper angle of 16°. The first stage of drawing had a starting diameter of 20 mm and an ending diameter of 17.5 mm. It was completed in 4 passes, with a single pass deformation of 5.5% and a total deformation of 23%. The drawing speed was 0.65 m / s. The drawing die material was nano-cemented carbide (93 weight percent WC, 7 weight percent Co, and an average grain size of approximately 180 nm). The die preheating temperature was 80°C, and the die taper angle was 13°. After the first stage of drawing, intermediate annealing was performed at 300°C for 40 minutes in a micro-oxygen argon atmosphere (oxygen content ≤ 100 ppm), and then air-cooled to room temperature.

[0097] The second stage drawing process starts at a diameter of 17.5 mm and ends at a diameter of 15.8 mm. This process is completed in three passes, with a deformation of 5.0% per pass and a total deformation of 18%. The drawing speed is 1.0 m / s, and the die taper angle is 11°. After the second stage drawing, an intermediate annealing is performed at 290°C, held for 35 minutes, and then air-cooled to room temperature.

[0098] The third stage drawing process starts at a diameter of 15.8 mm and ends at a diameter of 14.5 mm. This process is completed in three passes, with a deformation of 4.0% per pass and a total deformation of 13%. The drawing speed is 1.35 m / s, and the die taper angle is 9°. After the third stage drawing, an intermediate annealing is performed at 280°C, held for 30 minutes, and then air-cooled to room temperature.

[0099] The final stage of drawing has a starting diameter of 14.5 mm and an ending diameter of 14.0 mm. It is completed in two passes, with a single-pass deformation of 3.5% and a total deformation of 6.5%. The drawing speed is 1.8 m / s and the die cone angle is 7°.

[0100] Conductor twisting: 25 single conductors are twisted at a twisting pitch of 150 mm, with a twisting tension of 22 Newtons per conductor and a twisting speed of 28 m / min, ultimately obtaining a conductor with a cross-sectional area of ​​35 mm2.

[0101] (5) Surface treatment: Pulse electropolishing treatment uses a mixed solution of phosphoric acid, sulfuric acid, and water in a volume ratio of 6:3:1 as the electrolyte, the electrolyte temperature is 25°C, the current density is 25 mA / cm2, the pulse frequency is 75 Hz, and the treatment time is 50 seconds.

[0102] Preparation of the nano-ceramic composite coating: First, a precursor was prepared using a sol-gel method. To a mixture of 85 ml of anhydrous ethanol, 10 ml of deionized water, and 5 ml of glacial acetic acid, 15.3 g of aluminum n-butyl ester, 5.6 g of tetrabutyl titanate, and 3.4 g of tetraethoxysilane were added, sequentially. The mixture was aged at 40°C for 24 hours. Then, an electrostatic spraying process was used with a spray gun voltage of 60 kV, a spray gun-to-workpiece distance of 200 mm, and a preheated workpiece temperature of 60°C for three spray cycles. Finally, a three-stage sintering process was performed: from room temperature to 200°C at a ramp rate of 1.5°C / min, with a hold time of 60 minutes; from 200°C to 350°C at a ramp rate of 2.0°C / min, with a hold time of 45 minutes; and from 350°C to 450°C at a ramp rate of 1.0°C / min, with a hold time of 25 minutes. A nano-ceramic composite coating with a thickness of 1.0 μm was obtained.

[0103] Fluorosilane modification treatment: A solvent was prepared using anhydrous ethanol and deionized water in a volume ratio of 95:5, triethoxy 3,3,3-trifluoropropylsilane was added to a concentration of 0.8 weight percent, the pH value was adjusted to 4.0, and after hydrolysis for 3.0 hours, an immersion treatment was performed for 6 minutes, and the film was cured at 150°C for 35 minutes to obtain a fluorosilane-modified layer with a thickness of 130 nm.

[0104] (6) Heat treatment: The surface treated wires are subjected to multi-stage aging treatment. Pre-aging treatment is carried out at 150°C for 4.0 hours, with a heating rate of 5°C / min, and air cooling to room temperature. Main aging treatment is carried out at 180°C for 9.0 hours, with a heating rate of 3°C / min, and air cooling to room temperature. Post-aging treatment is carried out at 120°C for 18.0 hours, with a heating rate of 2°C / min, furnace cooling to 80°C, and air cooling to room temperature. Finally, stress relief treatment is carried out at 200°C, with a heating rate of 2°C / min, and slow furnace cooling to 100°C at a rate of 8°C / hour, and then natural cooling to room temperature.

[0105] (7) Preparation of the insulating layer: First, the surface of the nano-alumina was modified using γ-aminopropyltriethoxysilane. The amount of modifier was 4% by weight of the nano-alumina. The mixture was stirred at 60°C for 4 hours. The inner layer material formula was as follows: 93% by weight of low-density polyethylene, 2.2% by weight of diisopropylbenzene peroxide, 4.2% by weight of modified nano-alumina, 0.4% by weight of antioxidant, 0.25% by weight of ultraviolet absorber, and 0.3% by weight of lubricant. A twin-screw extruder was used. The temperature zones from the feed port to the die were 140°C, 160°C, 175°C, 190°C, 200°C, and 205°C, respectively. The screw speed was 45 rpm, the extrusion speed was 18 m / min, and the inner layer thickness was 0.9 mm. Subsequently, an electron beam accelerator was used for irradiation cross-linking with an acceleration voltage of 1.8 MeV and a total irradiation dose of 60 kGy, which was completed in three times.

[0106] Outer Layer Material Preparation: Nanosilica was surface-modified using hexadecyltrimethoxysilane at a modifier dosage of 5% by weight of the nanosilica. The mixture was stirred at 110°C for 6 hours. The outer layer material formulation was as follows: 94% by weight of ethylene-tetrafluoroethylene copolymer, 3.2% by weight of modified nanosilica, 0.6% by weight of antioxidant, 1% by weight of thermal stabilizer, 0.4% by weight of processing aid, and 0.3% by weight of lubricant. A single-screw extruder was used, with the temperature zones from feed port to die head being 230°C, 250°C, 270°C, 280°C, and 290°C, respectively. The screw speed was 35 rpm, the extrusion speed was 12 m / min, the outer layer thickness was 0.5 mm, and the water bath cooling temperature was 45°C.

[0107] The aluminum alloy conductor has a gradient microstructure from the center to the surface, including an ultrafine grain structure in the center region, a gradient distributed nano-precipitated phase in the transition region, and a high-density dislocation strengthening layer in the surface region and a synergistic strengthening structure of the nano-precipitated phase;

[0108] In the gradient microstructure, the grain size in the central region is 1-3 microns, and the dislocation density in the surface region is 10 14 -10 15 The dislocation density in the central area is 10 per square meter. 12 -10 13 per square meter; the nano-precipitated phase includes a needle-like β "phase, 5-10 nanometers in length and 2-3 nanometers in diameter; a plate-like Q' phase, 15-25 nanometers in diameter and 3-5 nanometers in thickness; and a spherical Al3 (Sc, Zr) phase, 8-15 nanometers in diameter. Example 2

[0109] A low-voltage aluminum conductor was prepared using a method similar to that of Example 1, except that the chemical composition of the aluminum alloy conductor was as follows: 0.9% magnesium, 0.6% silicon, 0.25% copper, 0.12% zirconium, 0.09% scandium, 0.07% silver, 0.03% erbium, 0.04% vanadium, 0.12% iron, 0.04% manganese, 0.02% titanium, 0.08% other elements in total, and the balance being aluminum.

[0110] Ultrasonic treatment was conducted at a frequency of 21.0 kHz and a power of 1150 W for four minutes per treatment. The homogenization temperature was 525°C for 13.5 hours. The first extrusion temperature was 495°C at a speed of 2.5 mm / s. The second extrusion temperature was 455°C at a speed of 1.5 mm / s.

[0111] During the gradient cold drawing process, the first stage of the drawing deformation was 24%, the second stage of the drawing deformation was 19%, the third stage of the drawing deformation was 14%, and the final stage of the drawing deformation was 7%. During the surface treatment, the electrolytic polishing current density was 27 mA / cm² and the treatment time was 45 seconds. The nano-ceramic composite coating was sintered at a temperature of 455°C and held at this temperature for 23 minutes.

[0112] The inner cross-linked polyethylene modified insulation layer is formulated as follows: 92.5 weight percent low-density polyethylene, 2.5 weight percent diisopropylbenzene peroxide, 4.5 weight percent modified nano-alumina, 0.3 weight percent antioxidant, 0.2 weight percent UV absorber, and 0.2 weight percent lubricant. The outer ethylene-tetrafluoroethylene copolymer modified insulation layer is formulated as follows: 93.0 weight percent ethylene-tetrafluoroethylene copolymer, 3.5 weight percent modified nano-silica, 0.8 weight percent antioxidant, 1.2 weight percent heat stabilizer, 0.5 weight percent processing aid, and 0.4 weight percent lubricant. Example 3

[0113] A low-voltage aluminum conductor was prepared using a method similar to that of Example 1, except that the chemical composition of the aluminum alloy conductor was as follows: 0.8% magnesium, 0.5% silicon, 0.2% copper, 0.1% zirconium, 0.07% scandium, 0.05% silver, 0.02% erbium, 0.03% vanadium, 0.08% iron, 0.03% manganese, 0.02% titanium, 0.06% other elements in total, and the balance being aluminum.

[0114] During the alloy smelting process, the refining agent dosage was 0.18 weight percent of the total metal weight, the gas refining flow rate was 2.8 liters / minute, and the refining time was 24 minutes. The homogenization temperature was 520°C and the holding time was 14.5 hours. The die preheat temperature for the first extrusion was 445°C, and the second extrusion die preheat temperature was 415°C.

[0115] During the gradient cold drawing process, the intermediate annealing temperature after the first stage of drawing was 295°C, and the temperature was kept at this temperature for 38 minutes; the intermediate annealing temperature after the second stage of drawing was 285°C, and the temperature was kept at this temperature for 33 minutes; and the intermediate annealing temperature after the third stage of drawing was 275°C, and the temperature was kept at this temperature for 28 minutes.

[0116] During the preparation of the nano-ceramic composite coating, the spray gun voltage was 58 kV, the distance between the spray gun and the workpiece was 210 mm, and four spray revolutions were performed. During the fluorosilane modification treatment, the concentration of triethoxy 3,3,3-trifluoropropylsilane was 0.9 weight percent, the hydrolysis time was 3.5 hours, and the immersion time was 6.5 minutes.

[0117] During the heat treatment process, the pre-aging temperature is 148°C and the holding time is 4.2 hours; the main aging temperature is 178°C and the holding time is 9.2 hours; the post-aging temperature is 122°C and the holding time is 18.5 hours; the stress relief treatment temperature is 198°C and the holding time is 2.6 hours. Example 4

[0118] A low-voltage aluminum conductor was prepared using a method similar to that of Example 1, except that the chemical composition of the aluminum alloy conductor was as follows: magnesium 0.85%, silicon 0.55%, copper 0.22%, zirconium 0.11%, scandium 0.08%, silver 0.06%, erbium 0.025%, vanadium 0.035%, iron 0.06%, manganese 0.02%, titanium 0.015%, other elements totaling 0.04%, and the balance being aluminum.

[0119] The homogenization temperature was 515°C for 13.8 hours. The first extrusion ratio was 5.8:1, and the second extrusion ratio was 3.8:1. The final stage of the gradient cold drawing process had a drawing speed of 1.9 m / s.

[0120] During the preparation of the nano-ceramic composite coating, the aging temperature was 38°C and the aging time was 23 hours. During the fluorosilane modification treatment, the curing temperature was 148°C and the curing time was 38 minutes. During the multi-stage aging treatment, the pre-aging heating rate was 4.5°C / minute, the main aging heating rate was 2.8°C / minute, and the post-aging heating rate was 1.8°C / minute.

[0121] The inner cross-linked polyethylene modified insulation layer is 0.85 mm thick and is irradiated and cross-linked in two steps. The outer ethylene-tetrafluoroethylene copolymer modified insulation layer is 0.55 mm thick. Example 5

[0122] A low-voltage aluminum conductor was prepared using a method similar to that of Example 1, except that the chemical composition of the aluminum alloy conductor was as follows: magnesium 0.75%, silicon 0.45%, copper 0.18%, zirconium 0.09%, scandium 0.06%, silver 0.04%, erbium 0.015%, vanadium 0.025%, iron 0.14%, manganese 0.04%, titanium 0.025%, other elements totaling 0.07%, and the balance being aluminum.

[0123] After homogenization, the ingots were cut into 200 mm long bars with a 20 mm x 20 mm square cross-section. The first extrusion temperature was 485°C and the extrusion pressure was 380 MPa. The second extrusion temperature was 445°C and the extrusion pressure was 420 MPa. During the gradient cold drawing process, the deformation per pass was 6.0% in the first stage, 5.5% in the second stage, 4.5% in the third stage, and 3.2% in the final stage.

[0124] During the preparation of the nano-ceramic composite coating, the sintering environment was a low-oxygen argon atmosphere (oxygen content ≤ 80 ppm). The inner cross-linked polyethylene modified insulation layer was extruded at a speed of 16 meters per minute, while the outer ethylene-tetrafluoroethylene copolymer modified insulation layer was extruded at a speed of 10 meters per minute. Example 6

[0125] A low-voltage aluminum conductor was prepared using a method similar to that of Example 1, except that the surface treatment steps were adjusted to: first, preparation of a nano-ceramic composite coating, followed by fluorosilane modification, and finally, a multi-stage aging treatment. During the preparation of the nano-ceramic composite coating, 0.5 g of citric acid was added to the precursor solution as a stabilizer. Prior to the fluorosilane modification, the nano-ceramic coating was treated with UV-ozone for 10 minutes to enhance surface activity.

[0126] During the preparation of the inner cross-linked polyethylene modified insulation layer, 0.2 weight percent of a silane coupling agent (vinyltrimethoxysilane) was added to the mixture to enhance the interfacial bonding between the nanoalumina and the polyethylene matrix. During the preparation of the outer ethylene-tetrafluoroethylene copolymer modified insulation layer, a water bath-air cooling system was used, initially cooling the insulation in a water bath for 3 meters, followed by air cooling for 2 meters. Example 7

[0127] A low-voltage aluminum conductor was prepared using a method similar to that of Example 1, except that the chemical composition of the aluminum alloy conductor was as follows: 0.78% magnesium, 0.48% silicon, 0.19% copper, 0.095% zirconium, 0.065% scandium, 0.045% silver, 0.018% erbium, 0.028% vanadium, 0.09% iron, 0.035% manganese, 0.022% titanium, 0.05% other elements in total, and the balance being aluminum.

[0128] During the alloy melting and casting process, ultrasonic treatment was performed in pulse mode, with an on-time of 2 minutes and an off-time of 30 seconds, repeated three times. Homogenization was performed using a two-stage heating program: first, heating to 450°C at a rate of 40°C / hour and holding for 2 hours, then heating to 520°C at a rate of 30°C / hour and holding for 12 hours.

[0129] During the multi-step hot extrusion process, an annealing step is added between the first and second extrusions at 380°C for one hour. During the gradient cold drawing process, the inside of the drawing die is coated with a 5-micron-thick nanodiamond film to reduce the coefficient of friction.

[0130] During the heat treatment process, an intermediate cooling step is added between the main aging and post-aging stages. The temperature is cooled to room temperature at a rate of 20°C per hour and held for 2 hours before the post-aging stage is performed. An intermediate treatment step is added between the inner cross-linked polyethylene modified insulation layer and the outer ethylene-tetrafluoroethylene copolymer modified insulation layer. This treatment uses plasma surface activation at a power of 200 watts for 30 seconds to enhance the bonding strength between the two layers. Example 8

[0131] A low-voltage aluminum conductor was prepared using a method similar to that of Example 1, with the following differences: the nano-alumina and low-density polyethylene in the inner cross-linked polyethylene modified insulation layer were first pre-blended and melt-blended at 170°C for 10 minutes at a shear rate of 60 rpm. The mixture was then cooled and pelletized, mixed with the other components, and extruded. The nano-silica in the outer ethylene-tetrafluoroethylene copolymer modified insulation layer was synthesized in situ by directly synthesizing nano-silica particles in the ethylene-tetrafluoroethylene copolymer melt at a reaction temperature of 260°C for 15 minutes.

[0132] The multi-stage aging treatment uses a cyclic aging method. Between the pre-aging and main aging, a rapid cooling to 50°C is performed, which is held for 30 minutes before the main aging treatment. Between the main aging and post-aging, a rapid cooling to 40°C is performed, which is held for 40 minutes before the post-aging treatment. This cyclic aging method can produce more fine precipitates, further improving the strength and conductivity of the material.

[0133] Comparative Example 1

[0134] A low-voltage aluminum conductor was prepared using a method similar to that of Example 1, except that the rare elements scandium, silver, and erbium were not added. The chemical composition of the aluminum alloy conductor was as follows: magnesium 0.7%, silicon 0.4%, copper 0.15%, zirconium 0.08%, vanadium 0.02%, iron 0.10%, manganese 0.03%, titanium 0.01%, and other elements totaling 0.05%, with the balance being aluminum. Other process parameters during the preparation process were the same as those of Example 1.

[0135] Comparative Example 2

[0136] A low-voltage aluminum conductor was prepared using a method similar to that used in Example 1, except that a single-stage aging treatment at 180°C for 8 hours was performed instead of a multi-stage aging treatment. The chemical composition of the aluminum alloy conductor was the same as in Example 1. Other process parameters during the preparation process were the same as in Example 1.

[0137] Comparative Example 3

[0138] A low-voltage aluminum conductor was prepared using a method similar to that used in Example 1, except that the surface nano-ceramic composite coating and fluorosilane modification were omitted. Instead, heat treatment was performed directly after surface electrolytic polishing. The chemical composition of the aluminum alloy conductor was the same as in Example 1. Other process parameters during the preparation process were the same as in Example 1.

[0139] Comparative Example 4

[0140] A low-voltage aluminum conductor was prepared using a method similar to that of Example 1, except that the insulation layer was a single-layer structure using only unmodified cross-linked polyethylene (XLPE) as the insulating material, with a thickness of 1.4 mm. The chemical composition of the aluminum alloy conductor was the same as that of Example 1. All other process parameters during the preparation process were the same as those of Example 1.

[0141] Comparative Example 5

[0142] The low-voltage aluminum conductor is made from conventional 6201 aluminum alloy. The chemical composition of the aluminum alloy conductor is as follows: 0.6% magnesium, 0.7% silicon, 0.20% iron, 0.05% manganese, 0.10% copper, 0.05% zinc, 0.02% titanium, 0.10% other elements, and the balance being aluminum. The production process utilizes conventional smelting, casting, extrusion, and drawing techniques, omitting ultrasonic-assisted stirring and gradient cold drawing. The insulation layer is a single-layer polyethylene structure with a thickness of 1.4 mm.

[0143] 3. Performance Testing and Result Analysis

[0144] To evaluate the comprehensive performance of the low-voltage aluminum conductor of the present invention, a series of performance tests were conducted on samples of all embodiments and comparative examples, including electrical conductivity, mechanical properties, corrosion resistance, connection reliability, and temperature adaptability.

[0145] 1. Conductivity test

[0146] The conductivity of the samples was tested using the eddy current method according to ASTM B193. Test conditions: 60 kHz frequency, 20 ± 0.5°C temperature. Five points were measured for each sample, and the average value was taken. The test results are shown in Table 1.

[0147] Table 1 Conductivity test results

[0148]

[0149] As can be seen from Table 1, the electrical conductivity of the low-voltage aluminum conductors of the present invention is consistently above 56.8% IACS, with Example 5 achieving 60.1% IACS, significantly exceeding Comparative Examples 1 and 5. This is primarily due to the rare element Ag significantly enhancing the conductivity of the aluminum alloy in the multi-element microalloying design employed in the present invention. Furthermore, the gradient microstructure design creates an ultrafine grain structure in the conductor's center, reducing electron scattering and further enhancing conductivity. Furthermore, the multi-stage aging treatment optimizes the size and distribution of precipitated phases, reducing electron scattering and also playing a significant role in enhancing conductivity.

[0150] 2. Mechanical properties test

[0151] The tensile strength, yield strength, and elongation of the samples were tested using an electronic universal testing machine according to ASTM E8. The test conditions were: a tensile rate of 2 ± 0.2 mm / min, an ambient temperature of 23 ± 2°C, and a relative humidity of 50 ± 5%. Three samples were tested under each condition, and the average value was calculated. The test results are shown in Table 2.

[0152] Table 2 Mechanical properties test results

[0153]

[0154] As can be seen from Table 2, the tensile strength of the low-voltage aluminum conductors of the present invention is consistently above 280 MPa, with Example 2 reaching 305 MPa, significantly higher than Comparative Examples 1 and 5. This is primarily due to the multi-element microalloying design employed in the present invention, particularly the strong dispersion strengthening effect exerted by the nano-precipitates formed by rare elements such as Sc, Zr, and Er on the aluminum alloy matrix. Furthermore, the gradient cold drawing process forms a high-density dislocation-strengthened layer in the conductor surface region, further enhancing the material's strength. Furthermore, bending life test results demonstrate that the low-voltage aluminum conductors of the present invention exhibit excellent fatigue performance, primarily due to the synergistic strengthening structure of the high-density dislocations and nano-precipitates in the surface region, which effectively inhibits the initiation and propagation of fatigue cracks.

[0155] 3. Corrosion resistance test

[0156] Salt spray corrosion testing was conducted according to ASTM B117. Test conditions: 5 ± 0.5% NaCl solution, pH 6.5-7.2, temperature 35 ± 2°C, and test duration 500 hours. After the test, surface corrosion was observed and conductivity changes were measured. The test results are shown in Table 3.

[0157] Table 3 Corrosion resistance test results

[0158]

[0159] Note: Surface corrosion grade is assessed according to ASTM B537-70, with grade 0 indicating no obvious corrosion and grade 4 indicating severe corrosion.

[0160] As can be seen from Table 3, the low-voltage aluminum conductors of the present invention exhibit excellent corrosion resistance. In particular, the samples of Examples 3-8 showed essentially no corrosion, with conductivity reduction rates all below 1%. This is primarily due to the dual protective barrier formed by the nano-ceramic composite coating and fluorosilane-modified surface treatment, which effectively blocks contact between the corrosive medium and the aluminum alloy substrate. In comparison, Comparative Example 3, which did not undergo surface treatment, and Comparative Example 5, using a conventional aluminum alloy, exhibited significant corrosion, with conductivity reduction rates reaching 3.8% and 5.2%, respectively. This result fully demonstrates the remarkable effectiveness of the surface treatment technology proposed in the present invention in improving the corrosion resistance of aluminum conductors.

[0161] 4. Connection reliability test

[0162] Connection reliability was tested according to the SAE J1654 standard. Test conditions: Tin-plated copper crimp terminals were used, employing a hexagonal crimping process. Temperature cycling tests (-40±2°C to +125±2°C, 1000 cycles) were performed, and contact resistance changes and pull-off force were measured. The test results are shown in Table 4.

[0163] Table 4 Connection reliability test results

[0164]

[0165] As can be seen from Table 4, the low-voltage aluminum conductors of the present invention exhibit excellent connection reliability, with contact resistance change rates below 3.5% and pull-off force to fracture force ratios above 92%. This is primarily due to the surface nano-ceramic composite coating and fluorosilane modification treatment, which improves surface hardness and lubricity, reducing wear and oxidation on the contact surface. In particular, the contact resistance of Example 6 is only 0.30 mΩ, far lower than that of the comparative example sample, which is of great significance for reducing heat generation and power loss at the connection. In comparison, the contact resistance change rates of Comparative Example 3, which did not undergo surface treatment, and Comparative Example 5, which used a conventional aluminum alloy, reached 9.6% and 12.1%, respectively, demonstrating poor connection stability.

[0166] 5. Temperature adaptability test

[0167] The samples were tested for performance stability at different temperatures, including a low-temperature bend test (bending 180° at -40±2°C) and a high-temperature load test (applying rated current at 150±2°C for 1000 hours). The test results are shown in Table 5.

[0168] Table 5 Temperature adaptability test results

[0169]

[0170] As can be seen from Table 5, the low-voltage aluminum conductor of the present invention exhibits excellent temperature adaptability. After the bending test at a low temperature of -40°C, no cracks appeared in the insulation layer; after 1000 hours of high-temperature loading at 150°C, the decrease rates of conductivity and tensile strength were relatively low, especially in Example 6, where the decrease rate of conductivity was only 1.3%, and the decrease rate of tensile strength was only 4.8%. This is mainly due to the thermally stable precipitation phases formed by rare elements such as Er and Sc in the multi-element microalloying design adopted by the present invention, and the excellent temperature resistance provided by the double-layer composite insulation structure. In comparison, the insulation layer of Comparative Example 5 showed obvious cracks after the low-temperature bending test, and the decrease rate of conductivity after high-temperature loading reached 8.5%, and the decrease rate of tensile strength reached 18.7%, showing poor temperature adaptability.

[0171] Through various performance tests and analyses of the low-voltage aluminum conductor and its preparation method of the present invention, the following conclusions can be drawn:

[0172] 1. The multi-element microalloying design proposed in this invention, through the synergistic effect of conventional elements such as Mg, Si, and Cu with rare elements such as Sc, Zr, Ag, Er, and V, forms multi-type and multi-scale nano-precipitates, effectively achieving a balance between high strength and high conductivity. Specifically, Example 2 achieved a tensile strength of 305 MPa, and Example 5 achieved a conductivity of 60.1% IACS, with overall performance far superior to conventional aluminum conductors.

[0173] 2. The gradient microstructure designed in this invention creates structural layers with different functions inside and on the surface of the wire, synergistically improving the wire's overall performance. In particular, in the bending life test, Example 5 achieved 5,400 cycles, more than double that of Comparative Example 5, demonstrating excellent fatigue resistance.

[0174] 3. The nano-ceramic composite coating and fluorosilane-modified surface treatment technology employed in this invention form a highly effective dual protective barrier, significantly improving the corrosion resistance and connection stability of the wires. In salt spray testing, the conductivity drop rates of Examples 5-7 were all below 0.8%, significantly lower than the 3.8% in Comparative Example 3 and the 5.2% in Comparative Example 5.

[0175] 4. The double-layer composite insulation structure designed in this invention provides excellent electrical insulation, temperature resistance, and mechanical protection. In temperature adaptability testing, all example samples showed no cracks in the insulation layer after bending at -40°C, and showed minimal performance degradation after 1000 hours of high-temperature loading at 150°C.

[0176] 5. The preparation process of the present invention comprehensively utilizes advanced technologies such as vacuum induction melting, ultrasonic-assisted stirring, multi-step hot extrusion, and gradient cold drawing to achieve precise preparation of nanocomposites and precise control of their microstructure, making product performance more stable and reliable.

[0177] The low-voltage aluminum wire provided by the present invention not only meets the electrical performance requirements of new energy vehicles for wires with a cross-sectional area of ​​35 square millimeters, but also greatly improves the mechanical properties, corrosion resistance and connection stability, significantly extends the service life, reduces maintenance costs, and has broad application prospects.

Claims

1. A low-voltage aluminum conductor, characterized in that: The cross-sectional area of ​​the wire is 35 square millimeters, and it includes an aluminum alloy conductor and an insulating layer, wherein: The chemical composition of the aluminum alloy conductor is as follows by weight: magnesium 0.7-0.9%, silicon 0.4-0.6%, copper 0.15-0.25%, zirconium 0.08-0.12%, scandium 0.05-0.09%, silver 0.03-0.07%, erbium 0.01-0.03%, vanadium 0.02-0.04%, iron not more than 0.15%, manganese not more than 0.05%, titanium not more than 0.03%, other elements each not more than 0.03%, total not more than 0.10%, the balance being aluminum; The aluminum alloy conductor has a gradient microstructure from the center to the surface, including an ultrafine grain structure in the center region, a gradient distributed nano-precipitated phase in the transition region, and a high-density dislocation strengthening layer in the surface region and a synergistic strengthening structure of the nano-precipitated phase; The insulating layer adopts a double-layer composite insulating structure, comprising an inner cross-linked polyethylene modified insulating layer and an outer ethylene-tetrafluoroethylene copolymer modified insulating layer.

2. The low-voltage aluminum conductor according to claim 1, characterized in that: In the gradient microstructure, the grain size in the central region is 1-3 microns, and the dislocation density in the surface region is 10 14 -10 15 The dislocation density in the central area is 10 per square meter. 12 -10 13 per square meter; the nano-precipitated phase includes a needle-like β "phase, 5-10 nanometers in length and 2-3 nanometers in diameter; a plate-like Q' phase, 15-25 nanometers in diameter and 3-5 nanometers in thickness; and a spherical Al3 (Sc, Zr) phase, 8-15 nanometers in diameter.

3. The low-voltage aluminum conductor according to claim 1, characterized in that: The inner cross-linked polyethylene modified insulation layer is composed of the following components: 92.5-93.5 weight percent of low-density polyethylene, 2.0-2.5 weight percent of cross-linking agent, 4.0-4.5 weight percent of nano-alumina, 0.3-0.5 weight percent of antioxidant, 0.2-0.3 weight percent of ultraviolet absorber, and 0.2-0.4 weight percent of lubricant; the average particle size of the nano-alumina is 30±5 nanometers; the thickness of the inner cross-linked polyethylene modified insulation layer is 0.9±0.05 mm.

4. The low-voltage aluminum conductor according to claim 1, characterized in that: The outer ethylene-tetrafluoroethylene copolymer modified insulation layer is composed of the following components: 93-95 weight percent of ethylene-tetrafluoroethylene copolymer, 3.0-3.5 weight percent of nano-silicon dioxide, 0.5-0.8 weight percent of antioxidant, 0.8-1.2 weight percent of heat stabilizer, 0.3-0.5 weight percent of processing aid, and 0.2-0.4 weight percent of lubricant; the average particle size of the nano-silicon dioxide is 20±3 nanometers; the thickness of the outer ethylene-tetrafluoroethylene copolymer modified insulation layer is 0.5±0.05 mm.

5. The low-voltage aluminum conductor according to any one of claims 1 to 4, characterized in that: The surface of the aluminum alloy conductor is provided with a nano-ceramic composite coating, which is composed of aluminum oxide-titania-silicon dioxide nano-composite ceramics with a molar ratio of 3:1:1, a particle size of 15-30 nanometers, and a coating thickness of 1.0±0.1 micrometers; the surface of the nano-ceramic composite coating is provided with a fluorosilane modified layer, which is formed by triethoxy 3,3,3-trifluoropropylsilane and has a thickness of 120-150 nanometers.

6. A method for preparing the low-voltage aluminum conductor according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Alloy melting and casting: Industrial pure aluminum and various master alloys are vacuum induction melted in a predetermined ratio, the melt temperature is controlled at 740±10℃, ultrasonic assisted stirring is performed, and then continuous casting is performed at 690±5℃ to obtain ingots with a diameter of 100±2 mm; (2) Homogenization treatment: keep the ingot at 520±5℃ for 14±0.5 hours for homogenization treatment; (3) Multi-step hot extrusion: the homogenized ingot was extruded for the first time at 490±5℃ with an extrusion ratio of 6.0:1, then annealed at 400±5℃ for 1.5±0.2 hours, and then extruded for the second time at 450±5℃ with an extrusion ratio of 4.0:1 to obtain a rod with a diameter of 20±0.5 mm; (4) Gradient cold drawing: The bar is subjected to multi-stage cold drawing, including a first-stage drawing deformation of 22-24%, a second-stage drawing deformation of 17-19%, a third-stage drawing deformation of 12-14%, and a final stage drawing deformation of 6-7%. Intermediate annealing treatment is performed between each stage to finally obtain a single wire with a diameter of 14.0 ± 0.1 mm. 25 wires are then stranded to obtain a wire with a cross-sectional area of ​​35 ± 0.5 square mm. (5) Surface treatment: The stranded conductors were subjected to pulse electrolytic polishing, and then a nano-ceramic composite coating was prepared by combining the sol-gel method with electrostatic spraying, sintered at 450±5℃ for 25±3 minutes, and then subjected to fluorosilane modification. (6) Heat treatment: The surface treated conductor is subjected to a multi-stage aging treatment, including pre-aging at 150±3℃ for 4.0±0.5 hours, main aging at 180±3℃ for 9.0±0.5 hours, post-aging at 120±3℃ for 18.0±1.0 hours, and then stress relief treatment at 200±3℃ for 2.5±0.2 hours; (7) Preparation of insulation layer: First, an inner cross-linked polyethylene modified insulation layer is extruded and cross-linked by electron beam irradiation, and then an outer ethylene-tetrafluoroethylene copolymer modified insulation layer is extruded to obtain a low-voltage aluminum conductor.

7. The method according to claim 6, characterized in that The alloy smelting and casting in step (1) specifically include: Preheat the crucible to 500±10℃, keep it warm for 2 hours, then heat it to 1000±20℃ and keep it warm for 1 hour. After cooling to room temperature, apply a magnesium borate coating with a thickness of 0.1-0.2 mm. Melt the high-purity aluminum ingot at 500±10℃. After the aluminum ingot is completely melted, heat it to 650±10℃. Add the master alloys in the order of aluminum-copper alloy, aluminum-silicon alloy, and aluminum-magnesium alloy. Stir for 5-8 minutes after adding each alloy. Raise the temperature to 720±10℃, add aluminum-zirconium alloy and aluminum-vanadium alloy, and stir for 10-15 minutes; Raise the temperature to 750±10℃, add aluminum-scandium alloy, aluminum-erbium alloy and aluminum-silver alloy, and stir for 15-20 minutes; Add refining agent in an amount of 0.2 weight percent of the total metal weight and stir for 15±2 minutes; High-purity argon is introduced for gas refining at 740±10°C, with a flow rate of 2-3 L / min for 20-25 minutes; Perform three ultrasonic treatments at a frequency of 20.5 ± 0.5 kHz and a power of 1100 ± 50 W for 3-5 minutes each, with manual stirring for 1-2 minutes between treatments; Continuous casting is carried out at 690±5°C, the cooling water temperature is 20±2°C, the cooling water flow rate is 15-20 liters / minute, and the ingot is demoulded when it is cooled to no more than 100°C.

8. The method according to claim 6, characterized in that The gradient cold drawing in step (4) specifically includes: The first stage of drawing: the starting diameter is 20±0.5 mm, the ending diameter is 17.5±0.2 mm, and it is completed in 4 passes. The deformation of each pass is 5.0-6.5%, the drawing speed is 0.6-0.7 m / s, and after drawing, intermediate annealing is carried out at 300±5℃ for 40±5 minutes; The second stage of drawing: the starting diameter is 17.5±0.2 mm, the ending diameter is 15.8±0.2 mm, and it is completed in 3 passes. The deformation of each pass is 4.5-6.0%, the drawing speed is 0.9-1.1 m / s, and after drawing, intermediate annealing is carried out at 290±5℃ for 35±5 minutes; The third stage of drawing: the starting diameter is 15.8±0.2 mm, the ending diameter is 14.5±0.2 mm, and it is completed in 3 passes. The deformation of a single pass is 3.5-5.0%, the drawing speed is 1.3-1.4 m / s, and after drawing, intermediate annealing is carried out at 280±5℃ for 30±5 minutes; Final stage drawing: starting diameter is 14.5±0.2 mm, ending diameter is 14.0±0.1 mm, completed in 2 passes, deformation of single pass is 3.0-4.0%, and drawing speed is 1.7-1.9 m / s; Wire twisting: 25 single wires are twisted at a twisting pitch of 140-160 mm, with a twisting tension of 20-25 Newtons per wire and a twisting speed of 25-30 m / min, ultimately obtaining a wire with a cross-sectional area of ​​35±0.5 mm2.

9. The method according to claim 6, characterized in that The surface treatment in step (5) specifically includes: Pulse electropolishing: A mixed solution of phosphoric acid, sulfuric acid, and water in a volume ratio of 6:3:1 was used as the electrolyte. The electrolyte temperature was 25±2°C, the current density was 25±2 mA / cm2, the pulse frequency was 75±5 Hz, and the processing time was 50±5 seconds. Preparation of nano-ceramic composite coating: (a) Sol-gel precursor preparation: To a mixture of 85 ± 2 mL of anhydrous ethanol, 10 ± 0.5 mL of deionized water, and 5 ± 0.3 mL of glacial acetic acid, 15.3 ± 0.2 g of aluminum n-butyl ester, 5.6 ± 0.1 g of tetrabutyl titanate, and 3.4 ± 0.1 g of tetraethoxysilane were added in sequence and aged at 40 ± 2 °C for 24 ± 1 h. (b) Electrostatic spraying: spray gun voltage is 60±5 kV, the distance between the spray gun and the workpiece is 200±10 mm, the workpiece preheating temperature is 60±5℃, and spray 3-4 circles; (c) Sintering: a three-stage heating program was used: from room temperature to 200±10°C at a heating rate of 1.5±0.2°C / min, and holding for 60±5 minutes; from 200±10°C to 350±10°C at a heating rate of 2.0±0.2°C / min, and holding for 45±5 minutes; from 350±10°C to 450±5°C at a heating rate of 1.0±0.2°C / min, and holding for 25±3 minutes; Fluorosilane modification: Prepare a solvent using anhydrous ethanol and deionized water in a volume ratio of 95:5, add triethoxy 3,3,3-trifluoropropylsilane to a concentration of 0.8±0.1 weight percent, adjust the pH value to 4.0±0.2, and hydrolyze for 3.0±0.5 hours before immersion treatment for 6±1 minutes. Curing should be carried out at 150±3°C for 35±3 minutes.

10. The method according to claim 6, characterized in that The preparation of the insulating layer in step (7) specifically includes: Preparation of inner cross-linked polyethylene modified insulation layer: (a) Surface modification of nano-alumina: Surface modification of nano-alumina was performed using γ-aminopropyltriethoxysilane at a dosage of 3-5 weight percent of the weight of the nano-alumina, and stirring was performed at 60±5°C for 4.0±0.5 hours. (b) Inner layer material mixing: 92.5-93.5 weight percent of low-density polyethylene, 2.0-2.5 weight percent of diisopropylbenzene peroxide, 4.0-4.5 weight percent of modified nano-alumina, 0.3-0.5 weight percent of antioxidant, 0.2-0.3 weight percent of ultraviolet absorber, and 0.2-0.4 weight percent of lubricant are uniformly mixed; (c) Inner layer extrusion: using a twin-screw extruder, the temperature zones from the feed port to the die are 140±5°C, 160±5°C, 175±5°C, 190±5°C, 200±5°C, and 205±5°C, and the extrusion speed is 15-20 m / min; (d) Irradiation cross-linking: using an electron beam accelerator with an accelerating voltage of 1.5-2.0 MeV and a total irradiation dose of 60 ± 5 kGy, completed in 2-3 times; Preparation of outer ethylene-tetrafluoroethylene copolymer modified insulation layer: (a) Nano-silica surface modification: The nano-silica was surface modified using hexadecyltrimethoxysilane at a dosage of 4-6 weight percent of the weight of the nano-silica, and stirred at 110±5°C for 6.0±0.5 hours; (b) outer layer material mixing: 93-95 weight percent of ethylene-tetrafluoroethylene copolymer, 3.0-3.5 weight percent of modified nano-silica, 0.5-0.8 weight percent of antioxidant, 0.8-1.2 weight percent of thermal stabilizer, 0.3-0.5 weight percent of processing aid, and 0.2-0.4 weight percent of lubricant are uniformly mixed; (c) Outer layer extrusion: using a single-screw extruder, the temperature zones from the feed port to the die are 230±5°C, 250±5°C, 270±5°C, 280±5°C, and 290±5°C, the extrusion speed is 10-15 m / min, and the water bath cooling temperature is 45±2°C.

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