A method for manufacturing a round edge copper-aluminum composite power bar

Abstract

The application discloses a preparation method of a round-edge copper-aluminum composite power strip and belongs to the technical field of copper-aluminum composite material preparation. The method comprises the following steps: raw material pretreatment, aluminum liquid smelting, solid-liquid hot melting casting and rolling compounding, cold rolling forming, annealing treatment, length cutting, round-edge drawing, electroplating treatment and inspection and packaging. The application adopts the solid-liquid hot melting casting and rolling method, directly compounding the aluminum liquid with the solid copper strip, omits the semi-solid cooling step, improves the production efficiency by more than 30%, reduces the energy consumption by 25-30%, realizes the continuous and stable production of the 6-12-meter long-size products through the synergistic effect of the cold rolling, annealing and round-edge drawing, the straightness error of the products is less than or equal to 0.5 mm / m, the sharp-end discharge risk is eliminated with the round corner radius R1.5-R3.0 mm, the product interface bonding strength is greater than or equal to 20 N / mm, the conductivity is greater than or equal to 60% IACS, and the cost is reduced by 40-50% compared with the pure copper power strip. The application is suitable for industrial scenes such as power transmission and electrical equipment connection, and has the advantages of high efficiency, energy saving, stable product performance and the like.

Description

Technical Field

[0001] This invention relates to the field of copper-aluminum composite material preparation technology, specifically to a method for preparing a round-edged copper-aluminum composite power bus. Background Technology

[0002] Copper-aluminum composite power buses, combining the high conductivity of copper with the lightweight and low-cost advantages of aluminum, have been widely used in power systems and electrical equipment. Existing manufacturing technologies mainly include explosive bonding, hot rolling bonding, and semi-solid casting-rolling bonding, but these methods have several technical drawbacks. First, explosive bonding processes are inefficient and costly, and struggle to achieve continuous production of products longer than 6 meters. Second, traditional hot-rolling bonding requires heating both copper and aluminum bimetals to high temperatures, resulting in high energy consumption and easy interface oxidation, leading to insufficient bonding strength (typically below 20 N / mm) and delamination during use. Third, existing semi-solid casting and rolling processes involve cooling the molten aluminum to a semi-solid state, resulting in significant energy waste. Furthermore, the products often have right-angled edges, increasing the risk of tip discharge during installation and use. Additionally, there is a lack of specific rounded edge forming and long-dimensional stability control processes.

[0003] Therefore, there is an urgent need to develop a method for preparing long-sized round-edge copper-aluminum composite power buses that is efficient, energy-saving, and has stable product performance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a round-edged copper-aluminum composite power busbar, so as to solve the problems of high energy consumption, low production efficiency, insufficient product bonding strength, difficulty in forming long dimensions, and unreasonable edge structure in the existing technology.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: This invention utilizes a solid-liquid hot-melt casting and rolling method to achieve copper-aluminum composite bonding, combined with processes such as cold rolling, annealing, slitting, drawing, electroplating, and packaging. The specific steps are as follows: Step 1: Raw material pretreatment: Select industrial aluminum ingots with a purity of ≥99.7% and remove surface oxide scale and impurities; select copper strips with a thickness of 0.8-4.0mm and a purity of ≥99.9%, and after alkaline washing and degreasing (sodium hydroxide solution concentration 5-8%, temperature 50-60℃, treatment time 3-5min), use a grinding brush to polish the surface to remove the oxide layer, and then preheat to 230-400℃ under nitrogen protection to increase the surface activation energy of the copper strip.

[0006] Step 2, Aluminum molten metal smelting: The pretreated aluminum ingots are put into the smelting furnace and heated to 660-760℃. The temperature is held for 15-20 minutes for refining and degassing to remove hydrogen and impurities from the aluminum molten metal, resulting in pure aluminum molten metal. Then it is transferred to the holding furnace.

[0007] Step 3: Solid-liquid hot-melt casting and rolling composite: The preheated copper strip is continuously fed into a twin-roll casting mill, while the refined aluminum liquid is uniformly poured through the casting nozzle. The copper strip is inserted into the surface of the aluminum liquid in the rolls. The casting and rolling temperature is controlled at 620-750℃, the rolling speed at 0.3-2.0m / s, the rolling pressure at 1000-2000t, and the tension at 1-5t. Metallurgical bonding between the aluminum liquid and the solid copper strip is achieved in an oxygen-free environment, and copper-aluminum composite plate and strip billets are continuously prepared. The billet thickness is 4.5-15mm, of which the copper layer accounts for 10-30%.

[0008] Step 4, Cold Rolling: The composite billet is fed into a cold rolling mill and subjected to multiple cold rolling passes at a temperature of 20-100℃. The total reduction rate is controlled at 30-70%, and the reduction rate of each pass does not exceed 35%. Finally, it is rolled into a composite strip with a thickness of 1.0-8.0mm to ensure the dimensional accuracy of the product and the tightness of the interface bonding.

[0009] Step 5, Annealing: Place the cold-rolled composite strip into an annealing furnace and heat it to 200-350℃ under nitrogen protection. Hold it at that temperature for 2-8 hours, and then cool it to room temperature with the furnace to eliminate cold rolling stress, balance the mechanical and electrical properties of the product, and prevent cracking during subsequent processing.

[0010] Step 6, Slitting to Length: According to the product specifications, use a CNC slitting machine to slit the annealed composite strip into strips with a width of 20-200mm, and cut them to standard lengths of 6 meters, 9 meters or 12 meters, with the cutting tolerance controlled within ±5mm.

[0011] Step 7, Rounding the edges: The slit strips are fed into a special drawing die, and the edges of the strips are rounded through a progressive drawing process, so that the radius of the rounded corners reaches R1.5-R3.0mm, eliminating right-angled sharp points. At the same time, the straightening machine further improves the straightness and dimensional accuracy of the product.

[0012] Step 8: Electroplating treatment: Electroplating is performed on the surface of the rounded-edge formed power busbar. Nickel, tin or silver is selected as the electroplating layer, and the thickness of the electroplating layer is 5-15μm to improve the corrosion resistance and electrical contact performance of the product. After electroplating, the busbar is cleaned and dried.

[0013] Step 9: Inspection and Packaging: After electroplating, the product is tested for appearance, dimensions, mechanical properties, and conductivity to ensure that the product surface is free of oxidation and scratches, the interface bonding strength is ≥20N / mm, the conductivity is ≥60% IACS, and it meets the requirements of GB / T 32468-2025 standard. After passing the test, the product is individually packaged with moisture-proof packaging materials, and the product specifications, length, and production date are marked.

[0014] The present invention has the following beneficial effects: This invention employs a solid-liquid hot melt casting and rolling method, which enables the direct metallurgical bonding of molten aluminum and solid copper strip in an oxygen-free environment. This eliminates the intermediate step of cooling molten aluminum to a semi-solid state in the traditional semi-solid process. This significantly shortens the production cycle and reduces energy consumption, while effectively avoiding interface oxidation and the introduction of inclusions. As a result, the quality of interface bonding is greatly improved, and the industry problem of easy delamination failure of copper-aluminum composite products during use is completely solved. Based on this, through the coordinated control of cold rolling and annealing processes, the balance between the mechanical and electrical properties of the product is ensured while eliminating work hardening and residual stress. Furthermore, by combining precision slitting, progressive drawing and rounding of the edges, and multi-roll straightening, consistent forming of the rounded corner structure of products ranging from 6 meters to 12 meters in length and precise control of straightness are achieved. This eliminates the electric field concentration effect at right-angled tips to ensure safe high-voltage use and guarantees the fitting accuracy when multiple power busbars are installed side by side. With the addition of surface electroplating, the corrosion resistance and contact reliability of the product are further enhanced. Ultimately, a continuous manufacturing scheme for long-size rounded-edge copper-aluminum composite power busbars has been formed, which is highly efficient, energy-saving, and has excellent comprehensive performance, with good industrial application prospects and economic benefits. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the process flow for the preparation method of the present invention.

[0016] Figure 2 This is a schematic diagram of the solid-liquid hot melting casting and rolling composite process of the present invention. Detailed Implementation

[0017] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0018] Example 1 Preparation target: A round-edged copper-aluminum composite power busbar with a length of 6 meters, a width of 50 mm, and a thickness of 3 mm.

[0019] Raw material pretreatment: Industrial pure aluminum ingots with a purity ≥99.7% are selected and mechanically ground to remove surface oxide scale and oil stains, ensuring a clean surface. T2 industrial pure copper strips with a thickness of 1.0 mm and a purity ≥99.9% are selected and immersed in a 5% sodium hydroxide solution for alkaline washing and degreasing. The alkaline solution temperature is controlled at 55℃ for 4 minutes to remove rolling oil and natural oxide film from the copper strip surface. Immediately after alkaline washing, the strip is rinsed thoroughly with deionized water, and then mechanically ground on both sides using a stainless steel grinding brush to remove residual oxide layers, resulting in a uniform metallic luster. The ground copper strip is then continuously passed through a preheating furnace under a nitrogen protective atmosphere. The preheating temperature is set at 280℃ for 3 minutes to increase the surface activation energy of the copper strip, providing favorable conditions for subsequent metallurgical bonding.

[0020] Aluminum molten metal smelting: Pretreated aluminum ingots are placed into a medium-frequency induction melting furnace, and high-purity argon gas is introduced as a protective atmosphere to prevent hydrogen absorption and oxidation of the aluminum molten metal. The furnace is heated to 680℃ at a heating rate of ≥5℃ / min. After the aluminum ingots are completely melted, they are held at this temperature for 18 minutes for refining and degassing. Simultaneously, nitrogen gas is introduced using a rotary jet method, and an appropriate amount of hexachloroethane refining agent is added to effectively remove dissolved hydrogen and non-metallic inclusions from the aluminum molten metal. After refining, the furnace is allowed to stand for 10 minutes to allow inclusions to float or settle, resulting in high-purity aluminum molten metal. The aluminum molten metal is then transferred to a holding furnace for later use, with the holding temperature maintained at 680±10℃.

[0021] Solid-liquid hot-melt casting-rolling composite: Preheated copper strip is continuously traction-fed into the nozzle area of ​​a twin-roll horizontal casting mill. Simultaneously, pure molten aluminum from a holding furnace is uniformly poured through a flow channel and nozzle into the molten pool formed between two rotating rolls, allowing the copper strip to penetrate the surface of the molten aluminum and come into contact with it. The casting-rolling zone temperature is controlled at 700℃, the rolling speed at 0.6 m / s, the rolling pressure dynamically adjusted within the range of 1000–2000 t, and the tension controlled between 1–5 t. The entire casting-rolling process is carried out within a nitrogen-sealed hood, with the oxygen content controlled below 50 ppm. Under the combined action of high temperature and rolling pressure, atomic interdiffusion occurs at the interface between the molten aluminum and the solid copper strip, forming a reliable metallurgical bonding layer. A copper-aluminum composite strip billet with a thickness of 10.0 mm is continuously cast and rolled, with a copper layer thickness of 1.0 mm (10%) and a billet width of 52 mm (with allowance for subsequent slitting). The strip is straight and has no obvious oxide color on the surface.

[0022] Cold rolling: The composite billet obtained from casting and rolling is fed into a four-high reversible cold rolling mill at room temperature (20–80℃) for multi-pass cold rolling. A four-pass rolling process is adopted, with reduction rates set at 25%, 20%, 15%, and 10% for each pass, resulting in a cumulative total reduction rate of 70%. The billet is ultimately rolled into a composite strip with a thickness of 3.0 mm. Online leveling and tension adjustment are performed after each pass to ensure uniform strip thickness and width dimensional deviation controlled within ±0.1 mm. Emulsion cooling and lubrication are used during cold rolling, and the rolling temperature is maintained below 80℃ to prevent excessive growth of interfacial compounds due to temperature rise.

[0023] Annealing treatment: The cold-rolled composite strip is neatly loaded into a box-type annealing furnace. High-purity nitrogen (purity ≥99.99%) is continuously introduced into the furnace as a protective atmosphere, with the flow rate controlled at 0.5 m³ / s. 3The furnace is heated to 300°C at a rate of 3°C / min, held for 5 hours, and then the power is cut off to allow the furnace to cool naturally to room temperature (cooling rate approximately 1°C / min). This annealing process effectively eliminates work hardening and residual stress generated during cold rolling, while controlling the thickness of brittle intermetallic compounds (such as Al2Cu and Al4Cu9) dispersed at the copper-aluminum interface to within 200 nm. This optimizes the overall mechanical and electrical properties of the composite strip while ensuring interfacial bonding strength.

[0024] Slitting to Length: A CNC slitting machine is used to slit the annealed composite strip into strips with a width of 50mm along the length direction, with the slitting accuracy controlled within ±0.2mm. Then, a fixed-length shearing machine is used to cut the strips into standard sections with a length of 6 meters, with the cutting tolerance controlled within ±3mm, and the cut ends are flat and burr-free.

[0025] Edge Rounding: The slit strips of fixed length are fed into a dedicated drawing die system, which consists of an inlet guide section, a progressive deformation section, and an outlet finishing section. A traction machine pulls the strip at a speed of 0.5 m / min, guiding it through each section of the die sequentially. Under the progressive extrusion action, the edges gradually form a rounded corner structure, ultimately achieving a rounded corner radius of R2.0 mm. Immediately after drawing, the strip undergoes online straightening using a three-roll straightener. The gap between the straightening rollers is dynamically adjusted according to the product thickness to ensure a straightness error ≤0.3 mm / m, meeting the requirements for long-length installations.

[0026] Electroplating: The rounded-edge power busbar is immersed in an electroplating bath for surface tin plating. A sulfate tin plating system is used, with a current density of 2A / dm³. 2 The electroplating time was 15 minutes, and the coating thickness was controlled at 10 μm. During the electroplating process, a circulating filtration system was used to keep the plating solution clean, while gentle stirring was applied to evenly distribute the current. After electroplating, the surface underwent three stages of countercurrent rinsing and hot air drying to ensure a clean, bright surface free of residual plating solution and moisture.

[0027] Inspection and Packaging: Each finished product undergoes individual inspection: Visual inspection and magnification are used to ensure the surface is free of scratches, oxidation spots, and electroplating defects; dimensional inspection uses micrometers and vernier calipers to measure thickness, width, and length; interface bonding strength is tested using the peel test, with a measured value of 30 N / mm; conductivity is determined using the double bridge method, with a result of 85% IACS. All indicators meet the requirements of GB / T 32468-2025 standard. After passing inspection, each product is individually wrapped in a moisture-proof polyethylene film, then placed in a custom-made cardboard box with a desiccant inside. The outer box is labeled with the product specifications (50mm × 3mm × 6mm), copper layer thickness, production batch, and production date, and then stored for shipment.

[0028] Example 2 Preparation target: A round-edged copper-aluminum composite power busbar with a length of 12 meters, a width of 100 mm, and a thickness of 6 mm.

[0029] Raw material pretreatment: 99.8% pure industrial aluminum ingots were selected, and the surface oxide scale was removed; 2.0mm thick copper strips with 99.9% purity were selected. Alkali washing was performed using a 6% sodium hydroxide solution at 60℃ for 5 minutes. After alkaline washing, the strips were polished with a grinding brush, and then preheated to 350℃ under nitrogen protection for 5 minutes to ensure uniform temperature and sufficient surface activation energy.

[0030] Aluminum molten metal smelting: Aluminum ingots are placed into a smelting furnace and heated to 720°C under argon protection, held at that temperature for 20 minutes, while simultaneously employing a bottom-blowing argon refining process with an argon flow rate of 0.8 Nm³. 3 / h, effectively removes hydrogen and inclusions from the molten aluminum. After refining, it is allowed to stand for 15 minutes to obtain pure molten aluminum, which is then transferred to a holding furnace and the holding temperature is controlled at 720±5℃.

[0031] Solid-liquid hot-melt casting-rolling composite: Preheated copper strip and molten aluminum are simultaneously fed into a twin-roll casting mill. The casting temperature is set to 720℃, the rolling speed is adjusted to 1.0 m / s, the rolling pressure is set to 1500t, and the tension is controlled at 3t. An oxygen-free environment is maintained using a nitrogen + argon mixed gas (oxygen content ≤30ppm). Continuous casting and rolling produces a composite billet with a thickness of 12.0 mm, a copper layer thickness of 20% (i.e., a copper layer thickness of 2.4 mm), a billet width of 102 mm (leaving a 2 mm allowance), and a smooth surface free of bubbles and cracks.

[0032] Cold rolling: Under room temperature conditions, a 5-pass cold rolling process is employed, with reduction rates of 18%, 15%, 10%, 7%, and 5% for each pass, resulting in a cumulative total reduction rate of 50% and a final rolled thickness of 6.0 mm. After each pass, intermediate edge trimming is performed to eliminate micro-cracks at the edges and ensure the quality of subsequent processes. Oil-based lubrication is used during cold rolling, and the surface roughness of the rolls, Ra, is ≤0.4 μm, ensuring the surface quality of the strip.

[0033] Annealing treatment: Under a nitrogen protective atmosphere, the temperature is increased to 300℃ at a rate of 2.5℃ / min, held at that temperature for 6 hours, and then cooled to room temperature in the furnace. This annealing process allows for sufficient recovery and partial recrystallization of the cold-rolled structure, eliminating anisotropy, while stabilizing the thickness of the interfacial diffusion layer at 150–250 nm, ensuring an excellent match between mechanical and electrical properties.

[0034] Slitting to Length: A high-precision slitting machine is used to cut the material into strips with a width of 100mm, with a width tolerance of ±0.3mm. Then, hydraulic cutting is used to cut the strips to 12-meter lengths, with a cutting tolerance of ±5mm and an end face perpendicularity deviation of ≤0.5°.

[0035] Edge rounding: The strip edge is machined into a radius of 2.5mm using a progressive drawing die at a drawing speed of 0.3m / min to control deformation and temperature rise. The strip is then straightened using a five-roll straightener, ensuring a straightness error of ≤0.4mm / m.

[0036] Electroplating: A Watt-type nickel plating system was used for electroplating at a current density of 3 A / dm³. 2 The electroplating time was 20 minutes, and the coating thickness was controlled at 12 μm. After electroplating, the coating was washed with hot water, passedivated (passivation solution was 0.5 g / L chromic anhydride, temperature 40℃, immersion for 30 seconds), and dried to improve the corrosion resistance of the coating.

[0037] Packaging and inspection: Tested according to the same standards, the interface bonding strength was measured at 28 N / mm, and the conductivity was 82% IACS, all of which passed. The packaging used was a moisture-proof cardboard box sealed with plastic film, and the dimensions (100mm × 6mm × 12m) and relevant information were clearly marked.

[0038] Example 3 Preparation target: A round-edged copper-aluminum composite power busbar with a length of 9 meters, a width of 80 mm, and a thickness of 4 mm.

[0039] Raw material pretreatment: 99.7% pure aluminum ingots were selected; 1.5mm thick, 99.9% pure copper strips were selected. Alkali washing conditions: sodium hydroxide concentration 7%, temperature 50℃, time 3min. After polishing, nitrogen protection was applied and preheated to 300℃ for 4min.

[0040] Aluminum molten metal smelting: Aluminum ingots are heated to 700℃ under argon protection and held at that temperature for 15 minutes. Refining is performed using a nitrogen rotary jet method (300 rpm, flow rate 0.6 Nm³). 3 ( / h), after refining, let stand for 8 minutes, then transfer to a heat preservation furnace for later use, with a heat preservation temperature of 700±5℃.

[0041] Solid-liquid hot-melt casting-rolling composite: casting and rolling temperature 680℃, rolling speed 0.8m / s, rolling pressure 1200t, tension 2t, oxygen-free environment (oxygen content ≤40ppm). Continuous casting and rolling yields a composite billet with a thickness of 8.0mm, a copper layer thickness of 25% (copper layer thickness 2.0mm), and a billet width of 82mm.

[0042] Cold rolling: Four-pass cold rolling is used, with reduction rates of 20%, 15%, 10%, and 5% for each pass, resulting in a total reduction rate of 50% and a final rolled thickness of 4.0 mm. Compressed air is used to blow away the surface after each pass to prevent rolling oil residue from affecting subsequent annealing.

[0043] Annealing treatment: Under nitrogen protection, the temperature is increased to 250°C at a rate of 4°C / min, held for 4 hours, and then cooled to room temperature in the furnace. This mild annealing process eliminates stress while maximizing the preservation of the fine-grained strengthening effect formed by cold rolling, giving the product both high strength and good plasticity.

[0044] Slitting to fixed length: slitting width 80mm, accuracy ±0.25mm, fixed length cutting 9 meters, tolerance ±4mm, burr-free cut.

[0045] Drawing rounded edge: The die corner radius is designed to be R1.8mm, the drawing speed is 0.6m / min, and the straightness error after straightening by the straightening machine is ≤0.35mm / m.

[0046] Electroplating treatment: cyanide silver plating process (silver content 30g / L), current density 1.5A / dm³ 2 The electroplating time is 12 minutes, and the silver plating layer thickness is controlled at 8μm. After plating, the surface is successively washed, acid-washed and neutralized, washed with pure water, and dried, resulting in a bright silver-white surface.

[0047] Packaging inspection: The measured interface bonding strength was 32 N / mm, the conductivity was 87% IACS, and the appearance and dimensions were all qualified. The packaging method was the same as in Example 1, with the specifications (80mm×4mm×9m) and production information marked on it.

[0048] Comparative Example 1 (Semi-solid casting and rolling method) Preparation target: a copper-aluminum composite power busbar with a length of 6 meters, a width of 50 mm, and a thickness of 3 mm (same specifications as in Example 1).

[0049] Process differences: This comparative example uses the traditional semi-solid casting and rolling method, which adds a cooling step to semi-solid state after aluminum melt is smelted. After the temperature of aluminum melt drops to 590-620℃ (the aluminum melt is in a semi-solid slurry state), it is then cast and rolled together with preheated copper strip. The remaining processes (cold rolling, annealing, slitting, drawing and rounding edges, electroplating, inspection and packaging) are consistent with Example 1.

[0050] The specific steps are as follows: Raw material pretreatment is the same as in Example 1; after refining and degassing the molten aluminum at 680℃, the molten aluminum is transferred to a holding furnace and naturally cooled to 600℃ (this cooling process takes approximately 25 minutes), causing primary α-Al solid particles to precipitate in the molten aluminum, forming a semi-solid slurry; then, the semi-solid aluminum slurry is cast through a nozzle into a casting and rolling mill to be combined with preheated copper strip. The casting and rolling temperature is controlled at 620℃, the rolling speed is 0.6 m / s, and the rolling pressure is 1500 t. Subsequent cold rolling, annealing, slitting, edge drawing, electroplating, and inspection and packaging processes are exactly the same as in Example 1.

[0051] Comparative Example 2 (without annealing) Preparation target: a copper-aluminum composite power busbar with a length of 6 meters, a width of 50 mm, and a thickness of 3 mm (same specifications as in Example 1).

[0052] Process differences: In this comparative example, no annealing treatment is performed after cold rolling. The remaining processes (raw material pretreatment, aluminum melt smelting, solid-liquid hot melt casting and rolling composite, cold rolling, slitting, drawing and rounding edges, electroplating, inspection and packaging) are consistent with those in Example 1. After cold rolling, the material directly enters the slitting and length setting process, and the "annealing treatment" step is omitted. The parameters for slitting and subsequent processes are exactly the same as those in Example 1.

[0053] Comparative Example 3 (Right-legged structure) Preparation target: a copper-aluminum composite power busbar with right-angled sides, 6 meters long, 50 mm wide, and 3 mm thick (same specifications as in Example 1).

[0054] Process differences: In this comparative example, after slitting to a fixed length, no drawing and rounding treatment is performed, that is, the right-angled edge structure is retained and directly enters the electroplating process. The remaining processes (raw material pretreatment, aluminum liquid smelting, solid-liquid hot melting casting and rolling composite, cold rolling, annealing, slitting, electroplating, inspection and packaging) are consistent with those in Example 1.

[0055] Comparative Example 4 (without straightening treatment) Preparation target: a round-edged copper-aluminum composite power busbar with a length of 6 meters, a width of 50 mm, and a thickness of 3 mm (same specifications as in Example 1).

[0056] Process differences: In this comparative example, no straightening treatment is performed after drawing the rounded edge. The remaining processes (raw material pretreatment, aluminum melt smelting, solid-liquid hot melting casting and rolling composite, cold rolling, annealing, slitting, drawing the rounded edge, electroplating, inspection and packaging) are consistent with those in Example 1.

[0057] Performance testing and comparison The copper-aluminum composite power bus products prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to system performance testing. The testing methods are as follows: Interface bonding strength: The peel test (GB / T 32468-2025 Appendix A) is used. One end of the product is clamped in a universal testing machine, and the copper layer and aluminum layer are peeled off along the interface. The peel force divided by the sample width is the bonding strength. The average value of 5 samples in each group is taken.

[0058] Conductivity: The volume resistivity was determined by the double bridge method (GB / T 3048.2) under constant temperature conditions of 20℃ and converted to the International Standard for Annealed Copper (IACS) percentage. The average value of 3 samples in each group was taken.

[0059] Straightness error: Place the 6m / 9m / 12m finished products horizontally on the testing platform, and measure the offset between the side of the product and the platform baseline every 500mm along the length direction. Take the maximum offset and divide it by the corresponding measurement length. Take the maximum value for each group of 3 products.

[0060] Edge fillet radius: The edge fillet radius of the product is measured using a contour projector or R-gauge, and the average value is taken for each group of 10 measurements.

[0061] Interfacial compound layer thickness: After the product cross-section is inlaid, ground and polished, the interfacial diffusion layer is observed using a scanning electron microscope (SEM) in backscattered electron mode. The total thickness of the Al2Cu and Al4Cu9 compound layers is measured, and the average value is taken for each group of 10 fields of view.

[0062] Interface integration strength comparison Table 1 Comparison of interface bonding strength between each embodiment and the comparative example Statistical analysis: The average bonding strength of the three embodiments was 30.0 N / mm, with a standard deviation of 2.0 N / mm, which is much higher than the standard requirement of 20 N / mm, exceeding it by 40% to 60%. This indicates that the method of the present invention has high stability and significant advantages in terms of interface bonding quality.

[0063] Example 2 (12m long, 6mm thick) showed a slightly lower bonding strength than the other two groups. The reason for this was that the product was thicker and the total cold rolling reduction was only 50% (Example 1 and the three-part ratio were 70% and 50%, respectively). The amount of plastic deformation at the interface was relatively small, and the degree of atomic diffusion activation was slightly lower, resulting in a decrease in bonding strength of about 6.7%. However, it was still as high as 28 N / mm, which fully met the requirements for use.

[0064] The bonding strength of Comparative Example 1 (semi-solid method) was only 15 N / mm, which was 50% lower than that of Example 1 and did not meet the standard requirements. The fundamental reason is that the presence of solid particles in the semi-solid aluminum paste hinders the full wetting of the aluminum liquid and copper strip and atomic interdiffusion. In addition, the paste is prone to forming an oxide film during transportation and mixing into the interface, resulting in serious deterioration of the bonding quality.

[0065] Comparative Example 2 (without annealing) showed a bond strength of 22 N / mm, which barely met the lower limit of the standard, but was 26.7% lower than Example 1. This indicates that if the residual stress from cold rolling is not fully released through annealing, the tensile stress in the interface region will weaken the atomic bonding force and affect the effective performance of the bond strength.

[0066] Annealing and straightening processes have no significant impact on the interfacial bonding strength (comparative examples three and four are basically the same as example one), further indicating that the key processes affecting the bonding strength are concentrated in the solid-liquid composite stage and the subsequent cold rolling deformation control.

[0067] Comparison of electrical conductivity Table 2. Comparison of conductivity between each embodiment and the comparative example Statistical analysis: The average conductivity of the three embodiments was 84.7% IACS, with a standard deviation of 2.5% IACS, exceeding the standard requirement (≥60% IACS) by 36.7% to 45.0%, demonstrating excellent conductivity.

[0068] Example 3 (25% copper layer) exhibited the highest conductivity (87% IACS), followed by Example 1 (10% copper layer) (85% IACS), while Example 2 (20% copper layer) showed a slightly lower conductivity (82% IACS). The conductivity is not strictly positively correlated with the copper layer percentage, indicating that conductivity is the result of the coupling of multiple factors, including the copper layer ratio, the thickness of the interfacial compound layer, grain size, and dislocation density.

[0069] Comparative Example 1 (semi-solid method) has a conductivity of only 73% IACS, which is 14.1% lower than that of Example 1. The direct reason for the decrease in conductivity is that the thicker Al2Cu and Al4Cu9 compound layers (300-500nm) at the interface increase the interfacial resistance. At the same time, the residual oxide film and gas inclusions in the semi-solid slurry also increase the probability of electron scattering.

[0070] Comparative Example 2 (without annealing) had a conductivity of 78% IACS, which was 8.2% lower than that of Example 1. Analysis suggests that the unannealed composite strip after cold rolling contains numerous dislocations and lattice distortions, increasing electron scattering centers and reducing the mean free path of electrons, thus weakening conductivity. Annealing significantly reduced the dislocation density and restored the integrity of the lattice, thereby restoring conductivity to normal levels.

[0071] Comparison of dimensional accuracy and geometric quality Table 3 Comparison of dimensional accuracy and geometric quality between various embodiments and comparative examples Statistical analysis: The straightness error of Examples 1 to 3 was consistently controlled within the range of 0.3 to 0.4 mm / m, far exceeding the standard requirement (≤0.5 mm / m), with a yield rate of 100%. This demonstrates that the combined cold rolling + annealing + straightening process of the present invention has a significant effect on the straightness control of long-dimension products.

[0072] Comparative Example 2 (unannealed) showed a straightness error of 0.7–1.0 mm / m, exceeding the standard rate of 40%–100%. The mechanism of its geometric instability lies in the redistribution of residual stress introduced by cold rolling during slitting and drawing. When the stress exceeds the material's yield strength, the strip warps. This is especially pronounced for 6-meter strips with extremely high aspect ratios (length to thickness ratio reaching 2000:1), where the bending deformation caused by residual stress exhibits an amplified effect.

[0073] Comparative Example 4 (without straightening) shows a straightness error ≥1.5mm / m, exceeding the standard by 200%. This indicates that even after annealing to eliminate most of the residual stress, the drawing process itself will still introduce uneven deformation. Strips that have not been straightened cannot meet the installation accuracy requirements.

[0074] Regarding the fillet radius, the R1.8~R2.5mm distribution range of Examples 1 to 3 meets the design target (R1.5~R3.0mm), indicating that the drawing die design is reasonable and the process is stable. Although the right-angled side structure (R≈0.1mm) of Comparative Example 3 has no problem in terms of dimensional accuracy, it does not meet the safety structure requirements.

[0075] Comparison of Interface Microstructure and Security Table 4 Comparison of interface compound layer thickness and safety between each embodiment and the comparative example Statistical analysis: In Examples 1 to 3, the thickness of the interfacial compound layer was controlled within the range of 200–250 nm, which is within the ideal range. A compound layer that is too thin (<100 nm) indicates insufficient metallurgical reaction and inadequate bonding strength; a compound layer that is too thick (>500 nm) increases the proportion of brittle phase, reduces interfacial toughness, and makes the surface prone to brittle fracture upon impact. 200–250 nm is the optimal range for balancing bonding strength and interfacial toughness.

[0076] Comparative Example 1 (semi-solid method) showed a compound layer thickness of 300–500 nm, more than 50% thicker than Example 1. This is because the presence of solid particles in the semi-solid slurry prolonged the interdiffusion path between aluminum and copper atoms at the interface, while simultaneously forming an uneven diffusion layer at the interface, resulting in localized concentrated compound growth. Furthermore, the oxide film entrained in the semi-solid slurry became an interfacial impurity, significantly reducing long-term reliability.

[0077] The risk of tip discharge is "high" only relative to Example 3 (right-angled edge). The radius of curvature at the right-angled edge is extremely small (≈R0.1mm). According to electric field simulation calculations, the electric field concentration factor at the tip can reach 3 to 5 times the normal value at a 10kV operating voltage, reducing the corona initiation voltage threshold by approximately 60%. This makes it more prone to discharge accidents in humid and hot environments. The rounded corner structure with R1.8 to R2.5mm in Examples 1 to 3 can control the electric field concentration factor below 1.2 times, significantly improving safety.

[0078] V. Production Efficiency and Energy Consumption Analysis Table 5. Comparison of production efficiency and energy consumption between each embodiment and comparative example. Statistical analysis: The production efficiency of Examples 1 to 3 is basically the same. Among them, Example 1 (6m specification) has the highest efficiency (100%) due to its shorter length and fewer passes, while Example 2 (12m specification) has a slightly lower efficiency (95%) due to the slightly longer time spent on processes such as slitting and straightening. The difference is within a reasonable range.

[0079] Comparative Example 1 (semi-solid method) suffers from a significant decrease in production efficiency due to the added settling step of cooling molten aluminum to a semi-solid state (approximately 25 minutes per furnace), reaching only 75% of that of Example 1. Furthermore, the cooling process increases energy consumption, resulting in a 35% increase in overall cost compared to Example 1. In industrial production scenarios with high capacity demands, this gap will be further amplified.

[0080] Comparative Example 2 (without annealing) performed best in both efficiency and energy consumption (efficiency 105%, energy consumption 92%), but the product straightness was unqualified. It was an unbalanced solution of "trading quality for efficiency", which is not advisable.

[0081] Comparative Example 3 (right-angled edge) eliminates the process of drawing rounded edges, which improves efficiency, but sacrifices safety in use, and is also unacceptable.

[0082] VI. Overall Pass Rate and Performance Compliance Statistics Table 6. Overall pass rate statistics for each embodiment and comparative example Statistical analysis: The overall pass rate of the three embodiments was 100%, and all test indicators were passed on the first attempt, which fully demonstrates the process stability, repeatability and reliability of the method of the present invention.

[0083] All four comparative examples had at least one key indicator failing to meet the standard due to defects in their respective processes, resulting in an overall pass rate of 0%. This highlights the "barrel effect" of constraints between processes—the absence of any process or improper parameters can lead to the scrapping of the entire product.

[0084] The non-conforming items of each comparative example are distributed as follows: Comparative Example 1 (bonding strength), Comparative Example 2 (straightness), Comparative Example 3 (edge ​​structure), and Comparative Example 4 (straightness), involving multiple dimensions such as mechanical properties, geometric accuracy, and safety structure, which shows that each step in the "nine-step full-process" process chain designed in this invention has its irreplaceable functional positioning.

[0085] Overall Conclusion Based on the test data and statistical analysis from the above six dimensions, the following conclusions can be drawn: The process advantages are statistically significant: the three examples all far exceed the standard requirements in three core indicators: interfacial bonding strength (mean 30.0±2.0 N / mm), conductivity (mean 84.7±2.5% IACS), and straightness (mean ≤0.35±0.05mm / m), and the batch consistency is high (relative deviation <10%), proving that the method of the present invention has good industrial reproducibility.

[0086] The solid-liquid hot melt casting and rolling method is the determining factor of the bonding strength: the bonding strength of Comparative Example 1 (semi-solid method) is 50% lower than the average of the examples (15 N / mm vs 30 N / mm), and the difference is significant (p<0.01), which proves that direct aluminum liquid composite has an essential advantage over semi-solid composite in terms of interfacial metallurgical bonding quality.

[0087] Annealing and straightening are the dual guarantees of geometric accuracy for long-dimensional products: if annealing (Comparative Example 2) or straightening (Comparative Example 4) is missing alone, the straightness exceeds the standard by 0.7~1.0mm / m and ≥1.5mm / m respectively, while the synergistic effect of the two can stably control the straightness at ≤0.4mm / m, indicating that neither can be missing.

[0088] Rounded edges are a necessary condition for safe use of high voltage: the electric field concentration effect of right-angled edges cannot be compensated for by other processes. Therefore, Comparative Example 3 is deemed unqualified, indicating that in high-voltage power application scenarios, rounded edge processing is a "safety-necessary process" rather than an "optional optimization process".

[0089] End-to-end collaboration is a sufficient condition for product quality to meet standards: only when all nine steps are executed completely and parameters are precisely controlled can the product simultaneously meet the standards in all five assessment dimensions (combining strength, conductivity, straightness, rounded edge structure, and interface quality). Omission or simplification of any step will cause at least one key indicator to fail, and the overall pass rate will drop to 0%.

[0090] In summary, this invention, through the coordinated process control of "solid-liquid hot-melt casting and rolling, cold rolling, annealing, drawing and rounding edges, and straightening," successfully achieves efficient, energy-saving, and high-quality continuous production of standard 6-meter to 12-meter long rounded-edge copper-aluminum composite power buses. The overall pass rate of the three embodiments reached 100%, and the core performance indicators significantly exceeded the requirements of the GB / T 32468-2025 standard, providing a highly reliable and cost-effective copper-aluminum composite conductive material solution for the fields of power transmission and electrical equipment connection.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a round-edged copper-aluminum composite power busbar, characterized in that, Includes the following steps: Raw material pretreatment: Remove surface oxide scale and impurities from industrial aluminum ingots; The copper strip is degreased by alkaline washing, polished to remove the oxide layer, and preheated under a protective atmosphere; Aluminum molten metal smelting: Pretreated aluminum ingots are heated and smelted, then refined and degassed to obtain aluminum molten metal; Solid-liquid hot melt casting and rolling composite: The preheated copper strip is continuously fed into a twin-roll casting mill, while the refined aluminum liquid is cast into the rolls through the casting nozzle. The metallurgical combination of aluminum liquid and solid copper strip is achieved in an oxygen-free environment to prepare copper-aluminum composite plate and strip billet. Cold rolling forming: The composite billet is fed into a cold rolling mill for multiple cold rolling passes to obtain composite sheet and strip; Annealing: The cold-rolled composite strip is heated and held at a temperature under a protective atmosphere, and then cooled. Slitting to standard length: The annealed composite board strip is slit into strips and cut to standard length. Drawing and rounding the edges: The slit strips are fed into the drawing die for edge rounding, so that the edges form a rounded corner structure, and straightening is performed at the same time; Electroplating treatment: The electric busbars with rounded edges are electroplated, and then cleaned and dried. Inspection and Packaging: The product is inspected and packaged after passing the inspection.

2. The method for preparing a round-edged copper-aluminum composite power bus according to claim 1, characterized in that, In the raw material pretreatment step: the industrial aluminum ingot has a purity of ≥99.7%; the copper strip has a thickness of 0.8-4.0 mm and a purity of ≥99.9%; the alkaline washing uses a 5-8% sodium hydroxide solution and is treated at 50-60℃ for 3-5 minutes; the preheating temperature is 230-400℃.

3. The method for preparing a round-edged copper-aluminum composite power bus according to claim 1, characterized in that, In the aluminum molten metal smelting step: the aluminum ingot is heated to 660-760℃ and held for 15-20 minutes for refining and degassing.

4. The method for preparing a round-edged copper-aluminum composite power bus according to claim 1, characterized in that, In the solid-liquid hot melt casting and rolling composite step: the casting and rolling temperature is 620-750℃, the rolling speed is 0.3-2.0m / s, the rolling pressure is 1000-2000t, and the tension is 1-5t; the thickness of the resulting composite billet is 4.5-15mm, of which the copper layer accounts for 10-30%.

5. The method for preparing a round-edged copper-aluminum composite power bus according to claim 1, characterized in that, In the cold rolling forming step: the cold rolling temperature is 20-100℃, the total reduction rate is 30-70%, the reduction rate per pass does not exceed 35%, and the final rolling thickness is 1.0-8.0mm.

6. The method for preparing a round-edged copper-aluminum composite power bus according to claim 1, characterized in that, In the annealing process: the furnace is heated to 200-350°C under nitrogen protection, held for 2-8 hours, and then cooled to room temperature in the furnace.

7. The method for preparing a round-edged copper-aluminum composite power bus according to claim 1, characterized in that, In the slitting and length-fixing step: the slitting width is 20-200mm, the fixed length is 6 meters, 9 meters or 12 meters, and the cutting tolerance is controlled within ±5mm.

8. The method for preparing a round-edged copper-aluminum composite power bus according to claim 1, characterized in that, In the step of drawing rounded edges: the radius of the edge rounded corners is made to reach R1.5-R3.0mm through a progressive drawing process.

9. The method for preparing a round-edged copper-aluminum composite power bus according to claim 1, characterized in that, In the electroplating process, the electroplating layer is made of nickel, tin or silver, and the thickness of the electroplating layer is 5-15 μm.

10. The method for preparing a round-edged copper-aluminum composite power bus according to claim 1, characterized in that, After passing inspection, the product's interface bonding strength is ≥20N / mm, and its conductivity is ≥60% IACS.

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