A production method of high-flexibility high-conductivity copper-coated steel wire for automobile signal wire harness

Abstract

This invention discloses a method for producing high-flexibility, high-conductivity copper-clad steel wire for automotive signal harnesses. The steel core wire rod undergoes mechanical stripping, straightening, and bright annealing pretreatment under a nitrogen-hydrogen protective atmosphere; the copper strip undergoes degreasing, pickling, and passivation pretreatment. The steel core is activated in a vacuum chamber by argon plasma at a pressure of 10-18 Pa, a power of 300-500 W, a time of 12-30 s, and a p×t ratio of 5500-9000, while a 0.1-0.5 μm copper-based transition layer is deposited in the same chamber. Subsequently, the copper strip is continuously coated and formed by high-frequency induction welding at 400-600 kHz. It then undergoes multiple drawing passes and segmented heat treatments of intermediate / finished annealing, followed by electrolytic cleaning and passivation before winding. The resulting wire exhibits excellent conductivity, flexibility, and interfacial bonding properties, with a conductivity ≥40% IACS. Its repeated bending and corrosion resistance meet automotive service requirements.

Description

Technical Field

[0001] This invention relates to the field of copper-clad steel wire technology, and in particular to a method for producing a highly flexible and highly conductive copper-clad steel wire for automotive signal harnesses. Background Technology

[0002] With the rapid development of automotive electrification, intelligence, and connectivity technologies, the electronic and electrical architecture of vehicles is gradually evolving from distributed to centralized and networked structures. Various electronic and electrical systems, such as onboard control systems, sensor systems, communication systems, and vehicle network systems, place increasingly stringent requirements on the signal transmission stability, electromagnetic interference resistance, and long-term service reliability of wiring harnesses. Automotive signal wiring harnesses typically need to be laid within confined vehicle body cavities and cable trays, and endure the combined effects of driving vibrations, repeated bending, temperature shocks, and multiple environmental stresses such as humidity, salt spray, and corrosive gases throughout the vehicle's entire lifespan. Therefore, the conductor materials used for signal transmission not only need to possess low resistivity and stable electrical connection characteristics to ensure signal integrity, but also need to have good flexibility, fatigue resistance, and corrosion resistance to meet the long-term usage requirements under complex service environments.

[0003] Currently, automotive signal harness conductors are mostly made of pure copper or copper alloys, which offer excellent conductivity and mature manufacturing processes. However, they still have limitations in terms of lightweight design, strength enhancement, and cost control. In some applications requiring structural support or tensile strength, using only pure copper conductors may lead to problems such as tensile deformation and insufficient dimensional stability after end crimping, thus affecting assembly process consistency and long-term connection reliability. To balance conductivity and mechanical properties, the industry has gradually developed a technical solution using copper-clad steel wire as the conductor or reinforcing core of the signal harness. The steel core provides high strength and elastic support, while the outer copper layer provides conductivity, corrosion resistance, and solderability, thereby achieving a certain degree of optimized balance in overall performance.

[0004] However, copper-clad steel wire still faces technical challenges in the actual manufacturing process, particularly in terms of interface bonding quality control and ensuring processing stability. On one hand, steel surfaces are prone to oxide scale formation and the adsorption of oil and other contaminants during processing and storage. Furthermore, steel and copper exhibit significant differences in physicochemical properties and plastic deformation behavior. If interface cleaning is incomplete or the transition layer is poorly controlled, the composite interface may rely primarily on mechanical bonding rather than forming a stable and robust metallurgical bond. This can lead to defects such as interface peeling, flaking, and microcrack propagation during subsequent drawing, repeated bending, or terminal crimping, resulting in fluctuations in conductivity and even product failure. On the other hand, while continuous production methods involving copper strip cladding and welding offer high efficiency, factors such as the forming stability of the weld lap joint, microstructural changes caused by welding heat input, and the coordinated deformation of the copper layer and steel core during drawing all significantly impact the flexibility and conductivity of the finished product. If the drawing deformation amount and annealing process are not properly matched, a contradiction may arise between sufficient softening of the copper layer and maintenance of the steel core strength, thereby affecting the wire's resistance to bending fatigue and its service life.

[0005] In addition, in order to improve the bonding strength and corrosion resistance of the copper-steel interface, existing technologies also include wet processes such as electroplating and chemical plating to pre-form a copper plating layer or transition layer on the surface of the steel core. However, such processes often have problems such as long process flow, difficulty in uniform coating thickness and control of interface inclusions, and are accompanied by wastewater treatment and environmental protection pressures containing heavy metal pollutants such as copper, nickel and chromium, making it difficult to meet the requirements of green manufacturing and sustainable development.

[0006] Therefore, how to achieve efficient cleaning and activation of the steel core surface and controllable deposition of the transition layer while ensuring continuous production efficiency, so as to obtain copper-clad steel wire for automotive signal harnesses with strong interface bonding, stable weld formation, good drawing performance, and high flexibility and high conductivity, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the technical problems in the existing copper-clad steel wire manufacturing process, such as weak interface bonding, poor weld formation stability, and difficulty in balancing flexibility and conductivity, this invention provides a method for producing high-flexibility, high-conductivity copper-clad steel wire for automotive signal harnesses. This method organically combines processes such as mechanical peeling and bright annealing pretreatment of the steel core surface, vacuum plasma activation and physical vapor deposition of a copper-based transition layer, high-frequency induction welding cladding, and multi-pass drawing combined with segmented annealing. This achieves metallurgical-grade bonding of the copper-steel interface and coordinated optimization of microstructure and properties. The resulting copper-clad steel wire exhibits excellent flexibility, high conductivity, good resistance to bending fatigue, and corrosion resistance, meeting the long-term use requirements of automotive signal harnesses in complex service environments.

[0008] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: A method for producing highly flexible and highly conductive copper-clad steel wire for automotive signal harnesses includes the following steps: S1. The steel core wire rod is subjected to mechanical peeling to remove oxide scale, straightening, and then bright annealing pretreatment under a protective atmosphere. Mechanical peeling effectively removes the oxide scale and rust layer formed on the surface of the steel core wire rod during rolling, transportation, and storage. Straightening ensures good straightness and surface consistency of the steel core, laying the foundation for subsequent vacuum processing and cladding. Bright annealing pretreatment is carried out under a nitrogen-hydrogen mixed protective atmosphere. This eliminates work hardening and residual stress generated during the previous processing, softens the microstructure to improve subsequent plastic processing performance, and prevents secondary oxidation of the steel core surface during annealing, ensuring surface cleanliness and activity.

[0009] Further, the steel core wire rod in S1 is a medium-carbon steel wire rod with a carbon content of 0.25%-0.60% and a diameter of φ5.0-8.0mm. Medium-carbon steel wire rod is chosen as the core material because it possesses both moderate strength and ductility, and after appropriate heat treatment, it can achieve good comprehensive mechanical properties. The carbon content within the aforementioned range ensures that the finished wire has sufficient tensile strength and elastic support capacity, without causing a significant decrease in ductility or difficulties in drawing due to excessive carbon content. Bright annealing is carried out in a nitrogen-hydrogen mixed protective atmosphere, where the nitrogen gas fraction is 90%-95%, the hydrogen gas fraction is 5%-10%, the annealing temperature is 700-750℃, the holding time is 3-5h, and the cooling rate is 40-60℃ / h. This annealing process allows for sufficient recrystallization of the steel core structure, obtaining a uniform and fine ferrite and pearlite structure. Simultaneously, the cooling rate is controlled to avoid uneven microstructure caused by excessively rapid cooling or grain coarsening caused by excessively slow cooling.

[0010] S2. Electrolytic copper is processed into copper strips and subjected to degreasing, pickling, and passivation pretreatment. After electrolytic copper is rolled into copper strips of a specified thickness, its surface may have residual rolling oil, oxide film, and other contaminants. Degreasing removes surface oil, pickling removes surface oxide film and activates the surface, and passivation forms a dense protective film on the surface of the copper strip to prevent oxidation and discoloration during storage and subsequent processing. At the same time, this passivation film can decompose and volatilize during welding without affecting the welding quality.

[0011] Furthermore, in step S2, the electrolytic copper has a purity ≥99.95%, and the copper strip thickness is 0.5-1.2 mm. High-purity electrolytic copper ensures excellent conductivity in the finished copper-clad steel wire. The copper strip thickness within the aforementioned range ensures sufficient thickness of the copper layer after cladding to meet conductivity and corrosion resistance requirements, while also facilitating the bending and cladding operation of the forming mold. Pickling uses a 5%-10% dilute sulfuric acid solution at a temperature of 40-50℃ for 30-60 seconds. Appropriately increasing the pickling temperature can accelerate the dissolution and removal of the oxide film, but excessively high temperatures may lead to excessive corrosion of the copper strip surface or accelerated acid mist volatilization. The above pickling process parameters ensure the cleaning effect while avoiding damage to the copper strip substrate.

[0012] S3. The pretreated steel core is then subjected to plasma activation treatment and copper-based transition layer deposition treatment sequentially. Plasma activation treatment is one of the key process steps of this invention. It uses high-energy plasma to bombard the surface of the steel core, further removing residual oxides, adsorbed gases, and organic contaminants. Simultaneously, it induces a certain degree of microscopic roughening and atomic-level activation on the steel core surface, significantly improving surface energy and chemical activity, creating favorable conditions for the subsequent firm adhesion of the copper-based transition layer. The process pressure of the plasma activation treatment is controlled at 10-18 Pa, the plasma power p is 300-500 W, and the treatment time is 12-30 s. Furthermore, the product of power p and treatment time t satisfies 5500 ≤ p × t ≤ 9000. The above parameter ranges have been systematically optimized: if the process pressure is too low, the plasma density will be insufficient and the activation efficiency will be reduced; if the pressure is too high, the mean free path of the ions will be shortened and the bombardment energy will decrease. The product of power and time represents the total energy input of the plasma activation process. If this product value is too small, the activation will be insufficient; if it is too large, it may lead to excessive etching of the steel core surface or local overheating. Therefore, controlling it within the above range can achieve the best activation effect.

[0013] Furthermore, in step S3, before plasma activation, the vacuum chamber is evacuated to a base pressure of 0.01 Pa - 0.1 Pa, and argon gas with a flow rate of 20-100 sccm is introduced for plasma activation. The product of plasma power p and processing time t satisfies 6000 ≤ p × t ≤ 8000. Evacuating the vacuum chamber to a lower base pressure effectively removes reactive gases such as oxygen and water vapor from the chamber, avoiding side reactions such as oxidation or nitriding on the steel core surface during plasma activation. Using inert argon gas as the working gas, its plasma mainly activates the surface through physical sputtering, without introducing impurity elements or forming compound layers on the steel core surface. Further optimization ensures that the product of power and time is within the range of 6000-8000, achieving optimal interfacial bonding while ensuring sufficient activation.

[0014] The copper-based transition layer deposition process employs physical vapor deposition to deposit a copper-based transition layer on the surface of the steel core. The introduction of the copper-based transition layer is another key technical measure for achieving a robust interfacial bond in this invention. This transition layer acts as a bridge between the steel core and the outer copper strip: on the one hand, the transition layer forms an atomically tight bond with the plasma-activated steel core surface; on the other hand, atomic diffusion and recrystallization occur between the transition layer and the outer copper strip during welding heat and subsequent drawing deformation, forming a metallurgical bonding interface, thereby significantly improving the bonding strength and stability of the copper-steel composite interface.

[0015] Furthermore, the copper-based transition layer deposition process in S3 is performed in the same vacuum chamber after plasma activation. A copper-based transition layer with a thickness of 0.1-0.5 μm is deposited on the steel core surface using either magnetron sputtering or arc ion plating. Continuously completing the activation and deposition processes in the same vacuum chamber avoids surface recontamination or oxidation of the steel core during the transition between the two processes, maximizing the cleanliness and activity of the activated surface. When using magnetron sputtering, the sputtering power is 1.5-3 kW, the deposition time is 60-120 s, and the working pressure is 0.3-0.8 Pa. This process offers a moderate deposition rate, good film uniformity, and high density. When using arc ion plating, the arc current is 60-100 A, the deposition time is 30-60 s, and the working pressure is 0.1-0.5 Pa. This process offers a faster deposition rate, higher ion energy, and stronger film-substrate adhesion. The thickness of the transition layer is controlled within the range of 0.1-0.5μm. This thickness can effectively play the role of interfacial bridging of the transition layer, and will not affect the coordinated deformation of subsequent coating and drawing processes due to excessive thickness of the transition layer.

[0016] S4. The steel core and copper strip treated in S3 are simultaneously fed into the cladding mold for continuous cladding. High-frequency induction welding is used to weld the copper strip overlap seam, with a welding frequency of 400-600kHz. High-frequency induction welding has advantages such as concentrated heating, small heat-affected zone, and fast welding speed. It can bring the metal at the copper strip overlap seam to a molten or plastic state in a very short time and achieve metallurgical connection under the action of upsetting force. The welding frequency is selected in the range of 400-600kHz. At this frequency, the skin effect is significant, and the welding current is mainly concentrated in the extremely thin surface layer near the copper strip overlap surface. This can achieve rapid local heating while reducing the thermal impact on the copper strip matrix and steel core, which is beneficial to maintaining the material's microstructure and properties.

[0017] Furthermore, in step S4, the copper strip is guided by a forming mold to bend longitudinally and wrap around the outer periphery of the steel core to form a tubular structure. The bonding gap between the inner surface of the copper strip and the outer surface of the steel core is ≤0.02mm. Strict control of the bonding gap ensures close contact between the copper strip and the steel core, reducing porosity and gap defects at the interface. This facilitates atomic diffusion and interface fusion between the copper-based transition layer and the copper strip during subsequent drawing and annealing processes. The welding current is 800-1200A, and the welding speed is 15-40m / min. The welding current and welding speed need to be matched to ensure sufficient heat input at the lap joint for reliable welding, while avoiding excessive heat input that could lead to overheating of the weld zone, grain coarsening, or welding defects.

[0018] S5. The welded composite wire blank is subjected to multiple consecutive drawing passes. The drawing process gradually reduces the diameter of the composite wire blank to the target size. At the same time, during the drawing deformation process, the copper layer and the steel core produce coordinated plastic flow, which further promotes the mechanical interlocking and diffusion bonding of the interface and improves the interfacial bonding strength.

[0019] Furthermore, in S5, the number of drawing passes is 9-18, and the deformation amount per pass is 15%-25%. The deformation amount per pass in this invention refers to the reduction rate of the outer diameter of the wire between adjacent passes. , , in , These represent the outer diameters of the wire before and after each drawing pass. Reasonable pass allocation and deformation control are crucial for ensuring smooth drawing operations: insufficient deformation results in too many passes and low production efficiency; excessive deformation leads to excessively high deformation resistance per pass, potentially causing defects such as wire breakage, surface scratches, or interface cracking. Polycrystalline diamond dies are used, as these dies possess extremely high hardness and wear resistance, ensuring the dimensional accuracy and surface finish of the die holes, thereby obtaining finished wires with excellent surface quality and high dimensional accuracy. The lubricant uses a 6%-10% water-based wire drawing emulsion, which is one or more combinations of mineral oil-based water-based wire drawing emulsion, synthetic ester-based water-based wire drawing emulsion, and semi-synthetic water-based wire drawing emulsion, preferably a synthetic ester-based water-based wire drawing emulsion. This emulsion has both cooling and lubrication functions, which can effectively reduce the drawing friction coefficient, remove deformation heat, prevent wire surface oxidation and die overheating and wear. Under the premise of satisfying the lubrication and cooling effects, the water-based wire drawing emulsion can be replaced by an equivalent system without affecting the core effect of the invention.

[0020] S6. The drawn wire undergoes segmented annealing, including intermediate annealing and finished product annealing. The intermediate annealing temperature is 450-550℃, and the finished product annealing temperature is 350-450℃. Segmented annealing is an important process measure in this invention to achieve a coordinated balance between high flexibility and high conductivity. Intermediate annealing is performed during the drawing process. Its main purpose is to eliminate the work hardening accumulated from the previous drawing deformation, restore the plasticity of the copper layer and the steel core, and ensure smooth subsequent drawing. The intermediate annealing temperature is appropriately higher to allow the copper layer to fully recrystallize and soften. Finished product annealing is performed after drawing to the target diameter. Its temperature is lower than the intermediate annealing temperature. The purpose is to eliminate the processing stress of the finished wire, restore the flexibility of the copper layer, and maintain a certain processing strengthening effect on the steel core, thereby obtaining an ideal microstructure where the copper layer is soft and the steel core has moderate strength.

[0021] Furthermore, in step S6, intermediate annealing is performed when the cumulative deformation reaches 60%-70%, with a holding time of 1-2 hours. The timing of intermediate annealing is set when the cumulative deformation reaches this range because the work hardening of the material is significant at this deformation level, and continued drawing may lead to wire breakage or interface defects. Intermediate annealing at this point effectively restores the material's workability. After drawing to the target diameter, finished product annealing is performed, with a holding time of 2-3 hours and a cooling rate of 25-35℃ / h. The longer holding time in finished product annealing ensures sufficient uniform heating of the wire core, while a slower cooling rate achieves a uniform and stable microstructure and reduces thermal stress. All annealing processes are carried out in a nitrogen-hydrogen mixed protective atmosphere, with nitrogen comprising 90%-95% and hydrogen comprising 5%-10%. Nitrogen provides inert protection to prevent oxidation of the wire surface, while hydrogen, with its reducing properties, further removes residual oxides and maintains a glossy surface.

[0022] S7. After electrolytic cleaning and passivation treatment, the wire is wound up to obtain a high-flexibility, high-conductivity copper-clad steel wire for automotive signal harnesses. Electrolytic cleaning removes residual lubricant, oxides, and other contaminants formed on the wire surface during drawing and annealing, restoring the surface to a clean state. Passivation treatment forms a dense protective film on the wire surface, improving its corrosion resistance and discoloration resistance, extending its shelf life, and facilitating subsequent processing such as insulation layer coating.

[0023] Furthermore, the electrolytic cleaning in step S7 uses a 1%-3% sodium carbonate solution with a current density of 5-10 A / dm³. 2The cleaning time is 30-60 seconds. Sodium carbonate solution is weakly alkaline, effectively emulsifying and decomposing surface oil stains while being non-corrosive to the copper layer. Appropriate current density allows the bubbles generated during electrolysis to peel off surface contaminants, further enhancing the cleaning effect. Passivation treatment uses trivalent chromium passivation solution or chromium-free passivation solution at a temperature of 20-40℃ for 15-30 seconds. The trivalent chromium passivation solution is a conversion passivation solution with trivalent chromium salts as the main film-forming component, wherein the trivalent chromium salt is one or more combinations of chromium sulfate, chromium nitrate, and chromium chloride, preferably chromium sulfate. The chromium-free passivation solution is one or more combinations of zirconium salt system chromium-free passivation solution, titanium salt system chromium-free passivation solution, silane system chromium-free passivation solution, and rare earth salt system chromium-free passivation solution, preferably zirconium salt system chromium-free passivation solution. The above passivation solution types are commonly used systems in the field, and their formulations can be adjusted within a conventional range to obtain a stable passivation film layer without affecting the core process route and interface bonding mechanism of this invention.

[0024] The present invention also provides a copper-clad steel wire for automotive signal harnesses with high flexibility and high conductivity prepared by the above method. The copper-clad steel wire is composed of a steel core, a copper-based transition layer and an outer copper layer, and has the characteristics of strong interface bonding and excellent structural properties.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention employs a steel core pretreatment process that combines mechanical peeling with bright annealing, which effectively removes the oxide scale and contaminant layer on the surface of the steel core. At the same time, it eliminates work hardening and obtains a uniformly softened microstructure, providing a high-quality core material with high surface cleanliness and good plasticity for subsequent vacuum processing and overmolding.

[0026] 2. This invention innovatively employs a dry surface treatment process combining vacuum plasma activation and physical vapor deposition of a copper-based transition layer, replacing traditional electroplating or chemical plating wet processes. Plasma activation cleans and activates the steel core surface at the atomic scale, significantly increasing surface energy. The copper-based transition layer is deposited in situ on the activated surface, forming an atomically tight bond with the steel core. During subsequent welding and drawing processes, it further fuses with the outer copper strip to form a metallurgical interface, significantly improving the bonding strength and stability of the copper-steel interface and effectively reducing the risk of interface delamination. Simultaneously, this dry process has a short flow rate, high controllability, and avoids the problem of heavy metal-containing wastewater discharge generated by wet electroplating processes, making it environmentally friendly.

[0027] 3. This invention employs high-frequency induction welding to weld the lap joints of copper strips. The welding frequency is preferably within the range of 400-600kHz. Utilizing the skin effect, rapid localized heating is achieved, resulting in a small heat-affected zone and stable weld quality, meeting the requirements of high-speed continuous production. Simultaneously, by strictly controlling the bonding gap between the copper strip and the steel core, as well as the welding process parameters, the interface quality and geometric accuracy of the composite wire rod are guaranteed.

[0028] 4. This invention employs a segmented annealing process to heat-treat the drawn wire. The intermediate annealing temperature is higher to fully eliminate work hardening and restore work plasticity, while the finished annealing temperature is lower to soften the copper layer while maintaining appropriate work strengthening of the steel core. This annealing process achieves a harmonious balance between the high flexibility of the copper layer and the appropriate strength of the steel core, resulting in finished wires that possess both excellent resistance to bending fatigue and good mechanical strength.

[0029] 5. The various process steps of this invention are interconnected and coordinated, forming a complete continuous production process route with high production efficiency and stable product quality. The resulting high-flexibility, high-conductivity copper-clad steel wire for automotive signal harnesses possesses excellent conductivity, good flexibility and fatigue resistance, a strong copper-steel interface bond, and stable corrosion resistance. It can meet the usage requirements of automotive signal harnesses under harsh service conditions such as installation in confined spaces, long-term vibration and bending, and complex environmental corrosion, and has good application prospects and promotion value. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0031] This embodiment provides a method for producing copper-clad steel wire for high-flexibility and high-conductivity automotive signal harnesses, including the following steps: S1. Steel core pretreatment: Medium carbon steel wire rod with a carbon content of 0.42% and a diameter of φ6.5mm is selected as the core material. The steel core wire rod is mechanically peeled to remove oxide scale and straightened. Then, it is subjected to bright annealing pretreatment in a nitrogen-hydrogen mixed protective atmosphere. The annealing temperature is 725℃, the holding time is 4h, and the cooling rate is 50℃ / h.

[0032] S2. Copper strip pretreatment: Electrolytic copper with a purity of 99.97% is selected and rolled into a copper strip with a thickness of 0.85mm. The copper strip is then subjected to degreasing, pickling, and passivation pretreatment in sequence. The pickling uses an 8% dilute sulfuric acid solution at a temperature of 45℃ for 45 seconds.

[0033] S3. Steel Core Surface Treatment: The pretreated steel core is placed in a vacuum chamber for plasma activation and copper-based transition layer deposition. First, the vacuum chamber is evacuated to a base pressure of 0.05 Pa, and argon gas at a flow rate of 60 sccm is introduced for plasma activation. The process pressure is controlled at 14 Pa, the plasma power p is 400 W, and the treatment time is 18 s. The product of power and treatment time, p×t, is 7200. After activation, a copper-based transition layer is deposited on the steel core surface using magnetron sputtering in the same vacuum chamber. The sputtering power is 2.2 kW, the deposition time is 90 s, the working pressure is 0.5 Pa, and the resulting copper-based transition layer thickness is 0.3 μm.

[0034] S4. Coating and Welding Forming: The steel core treated in S3 and the copper strip are simultaneously fed into the coating mold for continuous coating. The copper strip is guided by the forming mold to gradually bend longitudinally and wrap around the outer periphery of the steel core to form a tubular structure. The bonding gap between the inner surface of the copper strip and the outer surface of the steel core is controlled within 0.01mm. High-frequency induction welding is used to weld the copper strip overlap seam, with a welding frequency of 500kHz, a welding current of 1000A, and a welding speed of 28m / min.

[0035] S5. Multi-pass drawing: The welded composite wire blank is continuously drawn in 12 passes, with the deformation amount of each pass controlled within the range of 20%-22%. Polycrystalline diamond molds are used, and the lubricant is a synthetic ester-based water-based wire drawing emulsion with a concentration of 8%.

[0036] S6. Segmented Annealing: When the cumulative deformation reaches 65%, intermediate annealing is performed at a temperature of 500℃ for 1.5 hours. After drawing to the target diameter φ0.5mm, finished product annealing is performed at a temperature of 400℃ for 2.5 hours and a cooling rate of 30℃ / h. All annealing processes are carried out under a nitrogen-hydrogen mixed protective atmosphere, with nitrogen comprising 93% and hydrogen comprising 7%.

[0037] S7. Post-treatment: The wire is sequentially subjected to electrolytic cleaning and passivation treatment before being wound up. Electrolytic cleaning uses a 2% sodium carbonate solution at a current density of 8 A / dm³. 2 The cleaning time was 45 seconds. The passivation treatment used a trivalent chromium passivation solution with chromium sulfate as the main film-forming component, at a temperature of 30°C and a treatment time of 22 seconds, to obtain a finished product of copper-clad steel wire for automotive signal harnesses with high flexibility and high conductivity. Example 2

[0038] This embodiment provides a method for producing copper-clad steel wire for high-flexibility and high-conductivity automotive signal harnesses, including the following steps: S1. Steel core pretreatment: Medium carbon steel wire rod with a carbon content of 0.28% and a diameter of φ5.0mm is selected as the core material. The steel core wire rod is mechanically peeled to remove oxide scale and straightened. Then, it is subjected to bright annealing pretreatment in a nitrogen-hydrogen mixed protective atmosphere. The annealing temperature is 700℃, the holding time is 5h, and the cooling rate is 40℃ / h.

[0039] S2. Copper strip pretreatment: Electrolytic copper with a purity of 99.95% is selected and rolled into a copper strip with a thickness of 0.5 mm. The copper strip is then subjected to degreasing, pickling, and passivation pretreatment in sequence. The pickling uses a 5% dilute sulfuric acid solution at a temperature of 40℃ for 60 seconds.

[0040] S3. Steel Core Surface Treatment: The pretreated steel core is placed in a vacuum chamber for plasma activation and copper-based transition layer deposition. First, the vacuum chamber is evacuated to a base pressure of 0.1 Pa, and argon gas at a flow rate of 20 sccm is introduced for plasma activation. The process pressure is controlled at 10 Pa, the plasma power p is 300 W, the treatment time is 20 s, and the product of power and treatment time p×t is 6000. After activation, a copper-based transition layer is deposited on the steel core surface using magnetron sputtering in the same vacuum chamber. The sputtering power is 1.5 kW, the deposition time is 120 s, the working pressure is 0.3 Pa, and the resulting copper-based transition layer thickness is 0.1 μm.

[0041] S4. Coating and Welding Forming: The steel core treated in S3 and the copper strip are simultaneously fed into the coating mold for continuous coating. The copper strip is guided by the forming mold to gradually bend longitudinally and wrap around the outer periphery of the steel core to form a tubular structure. The bonding gap between the inner surface of the copper strip and the outer surface of the steel core is controlled within 0.02mm. High-frequency induction welding is used to weld the copper strip overlap seam, with a welding frequency of 400kHz, a welding current of 800A, and a welding speed of 15m / min.

[0042] S5. Multi-pass drawing: The welded composite wire blank is continuously drawn in 9 passes, with the deformation amount of each pass controlled within the range of 22%-25%. Polycrystalline diamond molds are used, and 6% synthetic ester-based water-based wire drawing emulsion is used for lubrication.

[0043] S6. Segmented Annealing: When the cumulative deformation reaches 60%, intermediate annealing is performed at a temperature of 450℃ for 2 hours. After drawing to the target diameter φ0.5mm, finished product annealing is performed at a temperature of 350℃ for 3 hours, with a cooling rate of 25℃ / h. All annealing processes are carried out under a nitrogen-hydrogen mixed protective atmosphere, with nitrogen comprising 95% and hydrogen comprising 5%.

[0044] S7. Post-treatment: The wire is sequentially subjected to electrolytic cleaning and passivation treatment before being wound up. Electrolytic cleaning uses a 1% sodium carbonate solution at a current density of 5 A / dm³. 2 The cleaning time was 60 seconds. The passivation treatment used a chromium-free passivation solution based on a zirconium salt system, at a temperature of 20°C, for a treatment time of 30 seconds, to obtain a finished product of highly flexible and highly conductive copper-clad steel wire for automotive signal harnesses. Example 3

[0045] This embodiment provides a method for producing copper-clad steel wire for high-flexibility and high-conductivity automotive signal harnesses, including the following steps: S1. Steel core pretreatment: Medium carbon steel wire rod with a carbon content of 0.58% and a diameter of φ8.0mm is selected as the core material. The steel core wire rod is mechanically peeled to remove oxide scale and straightened. Then, it is subjected to bright annealing pretreatment in a nitrogen-hydrogen mixed protective atmosphere. The annealing temperature is 750℃, the holding time is 3h, and the cooling rate is 60℃ / h.

[0046] S2. Copper strip pretreatment: Electrolytic copper with a purity of 99.98% is selected and rolled into a copper strip with a thickness of 1.2mm. The copper strip is then subjected to degreasing, pickling, and passivation pretreatment in sequence. The pickling uses a 10% dilute sulfuric acid solution at a temperature of 50℃ for 30 seconds.

[0047] S3. Steel Core Surface Treatment: The pretreated steel core is placed in a vacuum chamber for plasma activation and copper-based transition layer deposition. First, the vacuum chamber is evacuated to a base pressure of 0.01 Pa, and argon gas at a flow rate of 100 sccm is introduced for plasma activation. The process pressure is controlled at 18 Pa, the plasma power p is 500 W, the treatment time is 16 s, and the product of power and treatment time p×t is 8000. After activation, a copper-based transition layer is deposited on the steel core surface using an arc ion plating process in the same vacuum chamber. The arc current is 80 A, the deposition time is 45 s, the working pressure is 0.3 Pa, and the thickness of the resulting copper-based transition layer is 0.5 μm.

[0048] S4. Coating and Welding Forming: The steel core treated in S3 and the copper strip are simultaneously fed into the coating mold for continuous coating. The copper strip is guided by the forming mold to gradually bend longitudinally and wrap around the outer periphery of the steel core to form a tubular structure. The bonding gap between the inner surface of the copper strip and the outer surface of the steel core is controlled within 0.015mm. High-frequency induction welding is used to weld the copper strip overlap seam, with a welding frequency of 600kHz, a welding current of 1200A, and a welding speed of 40m / min.

[0049] S5. Multi-pass drawing: The welded composite wire blank is continuously drawn in 18 passes, with the deformation amount of each pass controlled within the range of 15%-17%. Polycrystalline diamond molds are used, and 10% synthetic ester-based water-based wire drawing emulsion is used for lubrication.

[0050] S6. Segmented Annealing: When the cumulative deformation reaches 70%, intermediate annealing is performed at a temperature of 550℃ for 1 hour. After drawing to the target diameter φ0.5mm, finished product annealing is performed at a temperature of 450℃ for 2 hours, with a cooling rate of 35℃ / h. All annealing processes are carried out under a nitrogen-hydrogen mixed protective atmosphere, with nitrogen comprising 90% and hydrogen comprising 10%.

[0051] S7. Post-treatment: The wire is sequentially subjected to electrolytic cleaning and passivation treatment before being wound up. Electrolytic cleaning uses a 3% sodium carbonate solution at a current density of 10 A / dm³. 2 The cleaning time is 30 seconds. The passivation treatment uses a trivalent chromium passivation solution with chromium sulfate as the main film-forming component, at a temperature of 40°C and a treatment time of 15 seconds, to obtain a finished product of copper-clad steel wire for automotive signal harnesses with high flexibility and high conductivity. Example 4

[0052] This embodiment is used to verify the effect of arc ion plating process in depositing a copper-based transition layer. The difference from Example 1 is that in step S3, arc ion plating is used instead of magnetron sputtering for the copper-based transition layer deposition: the arc current is 80A, the deposition time is 45s, the working gas pressure is 0.3Pa, and the thickness of the resulting copper-based transition layer is 0.35μm. This thickness is slightly higher than that of the magnetron sputtering process in Example 1 (0.3μm), due to the higher ionization rate and deposition rate of the arc ion plating process. The remaining process parameters are the same as in Example 1. Comparative Example 1

[0053] This comparative example is basically the same as Example 1, except that the plasma activation treatment is omitted in step S3, and only the copper-based transition layer deposition treatment is performed. The remaining process parameters are the same as in Example 1. Comparative Example 2

[0054] This comparative example is basically the same as Example 1, except that the copper-based transition layer deposition process is omitted in step S3, and the process proceeds directly to step S4 for encapsulation welding after only plasma activation treatment. The remaining process parameters are the same as in Example 1. Comparative Example 3

[0055] This comparative example is basically the same as Example 1, except that: in step S3, the plasma activation power p is 350W, the processing time is 12s, and the product of power and processing time p×t is 4200, which is lower than the range of 5500-9000 required by this invention. The remaining process parameters are the same as in Example 1. Comparative Example 4

[0056] This comparative example is basically the same as Example 1, except that intermediate annealing is omitted in step S6. That is, intermediate annealing is not performed during the drawing process, but only after drawing to the target diameter φ0.5mm. The finished product annealing temperature is 400℃, the holding time is 2.5h, the cooling rate is 30℃ / h, and the annealing atmosphere is the same as in Example 1. The remaining process parameters are the same as in Example 1. Comparative Example 5

[0057] This comparative example is basically the same as Example 1, except that the welding frequency in step S4 is 200kHz, which is lower than the 400-600kHz range required by this invention. The remaining process parameters are the same as in Example 1. Comparative Example 6

[0058] This comparative example is basically the same as Example 1, except that: in step S3, the plasma activation power p is 500W, the processing time is 20s, and the product of power and processing time p×t is 10000, which is higher than the range of 5500-9000 required by this invention. The remaining process parameters are the same as in Example 1. Performance testing

[0059] The copper-clad steel wire products (all with a diameter of φ0.5mm) obtained in the examples and comparative examples were subjected to performance tests. The test items and methods are as follows: 1. Conductivity test: The test shall be conducted in accordance with GB / T 3048.2-2007 "Test methods for electrical properties of wires and cables - Part 2: Test for resistivity of metallic materials", and the percentage of conductivity shall be calculated based on the International Standard for Annealed Copper (IACS).

[0060] 2. Tensile strength and elongation test: The tensile test was carried out in accordance with GB / T 4909.3-2009 "Test methods for bare wires - Part 3: Tensile test". The gauge length of the specimen was 200 mm and the tensile speed was 50 mm / min. The maximum load at the time of fracture was recorded to calculate the tensile strength, and the gauge length elongation after fracture was recorded to calculate the elongation.

[0061] 3. Repeated bending test: Perform repeated bending test according to GB / T 4909.5-2009 "Bare wire test method Part 5: Bending test repeated bending". The bending radius is 5 times the wire diameter and the bending angle is 90°. Record the number of bends before breakage.

[0062] 4. Interface Bond Strength Test: The shear strength of the copper-steel interface is determined using the axial push-pull method. A 50mm long wire sample is taken, and the outer copper layer is chemically removed axially at one end to expose the steel core for clamping. Copper removal is performed using a 5%-15% (w / w) dilute nitric acid solution at 20-30℃ for 30-120 seconds, ending when the copper layer is completely removed and there is no obvious corrosion / pitting on the steel core surface. The sample is then washed with water and neutralized with a 1%-3% sodium carbonate solution for 30 seconds, followed by further washing and drying. During testing, the exposed steel core is clamped in the tensile testing machine grips, and the outer copper layer is restrained by a peeling die (or limiting sleeve). The axial width of the peeling die is the effective shear length. , The value range is 0.5-2.0 mm, and the inner diameter of the peeling mold is ( +0.01-0.03)mm, where The diameter of the interface between the copper layer and the steel core is equal to the diameter of the steel core. Measure at least three points along the axial direction on the steel core section after copper stripping, and take the average value. Apply an axial tensile force of 2 mm / min and record the maximum load when relative slippage occurs between the copper layer and the steel core. The interfacial shear strength is calculated using the following formula: ; In the formula: The interfacial shear strength is denoted as MPa. The maximum load is (N). The diameter of the interface is in mm. The effective shear length (mm) is used. Each group of samples should contain no fewer than 5 specimens, and the arithmetic mean is taken as the test result.

[0063] 5. Salt spray corrosion test: A neutral salt spray test shall be conducted in accordance with GB / T 10125-2021 "Chemical Atmosphere Corrosion Test - Salt Spray Test" for 96 hours. The corrosion status of the sample surface shall be observed and rated. The salt spray test rating shall be conducted in accordance with GB / T 6461-2002 "Rating of Specimens and Test Pieces of Metals and Other Inorganic Coatings on Metal Substrates After Corrosion Test". Level 10 is no corrosion, and the higher the level, the better the corrosion resistance. Test Results

[0064] Table 1. Performance test results of the examples and comparative examples: .

[0065] Test Result Analysis As can be seen from the test data in Table 1, Examples 1-4 all achieved excellent overall performance. Among them, Example 1 showed the best performance in terms of conductivity (42.5% IACS), elongation (18.5%), number of repeated bends (58 times), and interfacial shear strength (125 MPa). Example 4 only replaced the copper-based transition layer deposition with arc ion plating instead of magnetron sputtering (the rest was the same as Example 1). Its interfacial shear strength (123 MPa) and number of repeated bends (56 times) were close to those of Example 1, indicating that arc ion plating can also obtain a copper-based transition layer with good adhesion, and the deposition process is replaceable. Comparative Examples 1 and 2 omitted plasma activation or transition layer deposition, respectively. Their conductivity remained at 42.0% and 41.8% IACS, but their interfacial shear strength was only 68 MPa and 45 MPa, the number of repeated bends decreased to 32 and 25 times, and the salt spray rating decreased to level 7 and level 6, respectively. This indicates that the synergy between activation and transition layer is the key to achieving strong interfacial bonding and inhibiting interfacial peeling / crevice corrosion. The interfacial shear strengths of Comparative Example 3 (p×t=4200) and Comparative Example 6 (p×t=10000) were 85MPa and 92MPa, respectively, and the number of repeated bending cycles were 40 and 45, respectively. Both were inferior to the Example Group, indicating that both too low and too high activation energy are detrimental, thus verifying the rationality of 5500≤p×t≤9000.

[0066] In Comparative Example 4, omitting intermediate annealing resulted in a tensile strength of 825 MPa, a decrease in elongation to 6.5%, a reduction in the number of repeated bending cycles to 12, and a decrease in interfacial shear strength to 108 MPa, exhibiting characteristics of severe work hardening and damage accumulation. This demonstrates that intermediate annealing is crucial for restoring plasticity, improving flexibility, and enhancing fatigue life. In Comparative Example 5, with a welding frequency of 200 kHz, the tensile strength decreased to 612 MPa, the number of repeated bending cycles (38) and interfacial shear strength (108 MPa) decreased, and the salt spray rating dropped to level 8. This indicates that excessively low welding frequency leads to deeper heat-affected zones, worsening of weld microstructure and defects, thereby weakening mechanical, fatigue, and corrosion resistance properties. In summary, this invention achieves a unified balance of high flexibility, high electrical conductivity, and robust interfacial bonding through synergistic activation and transition layer treatment, p×t window control, 400-600 kHz high-frequency welding, and segmented heat treatment involving intermediate / finished annealing.

[0067] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing copper-clad steel wire for automotive signal harnesses with high flexibility and high conductivity, characterized in that, Includes the following steps: S1. The steel core wire rod is mechanically peeled to remove oxide scale, straightened, and then pre-treated with bright annealing under a protective atmosphere. S2. Electrolytic copper is processed into copper strips and subjected to degreasing, pickling and passivation pretreatment; S3. The pretreated steel core is subjected to plasma activation treatment and copper-based transition layer deposition treatment in sequence; wherein the process pressure of plasma activation treatment is controlled at 10-18 Pa, the plasma power p is 300-500 W, the treatment time is 12-30 s, and the product of power p and treatment time t satisfies 5500≤p×t≤9000; the copper-based transition layer deposition treatment uses physical vapor deposition process to deposit a copper-based transition layer on the surface of the steel core. S4. The steel core and copper strip treated in S3 are simultaneously fed into the cladding mold for continuous cladding, and the copper strip overlap seam is welded and formed by high-frequency induction welding at a frequency of 400-600kHz. S5. Perform multiple continuous drawing passes on the welded composite wire blank; S6. Perform segmented annealing on the drawn wire, including intermediate annealing and finished product annealing. The intermediate annealing temperature is 450-550℃, and the finished product annealing temperature is 350-450℃. S7. The wire is sequentially electrolytically cleaned and passivated before being wound up to obtain a highly flexible and highly conductive copper-clad steel wire for automotive signal harnesses.

2. The method according to claim 1, characterized in that, The steel core wire rod in S1 is a medium carbon steel wire rod with a carbon content of 0.25%-0.60% and a diameter of φ5.0-8.0mm. Bright annealing is carried out in a nitrogen-hydrogen mixed protective atmosphere, with an annealing temperature of 700-750℃, a holding time of 3-5h, and a cooling rate of 40-60℃ / h.

3. The method according to claim 1, characterized in that, The electrolytic copper in S2 has a purity of ≥99.95% and a copper strip thickness of 0.5-1.2 mm; the pickling is performed using a 5%-10% dilute sulfuric acid solution at a temperature of 40-50℃ for 30-60 seconds.

4. The method according to claim 1, characterized in that, Before plasma activation treatment in S3, the vacuum chamber is evacuated to a base pressure of 0.01Pa-0.1Pa, and argon gas with a flow rate of 20-100 sccm is introduced for plasma activation. The product of plasma power p and treatment time t satisfies 6000≤p×t≤8000.

5. The method according to claim 1, characterized in that, The copper-based transition layer deposition process in S3 is carried out in the same vacuum chamber after plasma activation treatment. A copper-based transition layer with a thickness of 0.1-0.5 μm is deposited on the steel core surface using either magnetron sputtering or arc ion plating. When using magnetron sputtering, the sputtering power is 1.5-3 kW, the deposition time is 60-120 s, and the working pressure is 0.3-0.8 Pa. When using arc ion plating, the arc current is 60-100 A, the deposition time is 30-60 s, and the working pressure is 0.1-0.5 Pa.

6. The method according to claim 1, characterized in that, In S4, the copper strip is guided by the forming mold to bend longitudinally and wrap around the outer periphery of the steel core to form a tubular structure. The bonding gap between the inner surface of the copper strip and the outer surface of the steel core is ≤0.02mm. The welding current is 800-1200A and the welding speed is 15-40m / min.

7. The method according to claim 1, characterized in that, The S5 process involves 9-18 drawing passes, with each pass exhibiting a deformation of 15%-25%. Polycrystalline diamond molds are used, and a 6%-10% water-based wire drawing emulsion is employed for lubrication.

8. The method according to claim 1, characterized in that, In step S6, intermediate annealing is performed when the cumulative deformation reaches 60%-70%, with a holding time of 1-2 hours; after drawing to the target diameter, finished product annealing is performed, with a holding time of 2-3 hours and a cooling rate of 25-35℃ / h; the annealing process is carried out in a nitrogen-hydrogen mixed protective atmosphere, in which the nitrogen gas fraction is 90%-95% and the hydrogen gas fraction is 5%-10%.

9. The method according to claim 1, characterized in that, The electrolytic cleaning in S7 uses a 1%-3% sodium carbonate solution with a current density of 5-10 A / dm³. 2 The cleaning time is 30-60 seconds; the passivation treatment uses trivalent chromium passivation solution or chromium-free passivation solution, at a temperature of 20-40℃, and a treatment time of 15-30 seconds.

10. A copper-clad steel wire for automotive signal harnesses with high flexibility and high conductivity prepared by the method described in any one of claims 1-9, wherein the copper-clad steel wire is composed of a steel core, a copper-based transition layer and an outer copper layer.