A copper alloy aluminum composite material, a preparation method and application thereof

Abstract

This invention discloses a copper-aluminum composite material, which has a layered composite structure comprising, from top to bottom: a copper alloy layer, wherein the copper alloy layer is made of Cu-Ni-Si alloy; a copper-aluminum interface layer; and an aluminum layer; wherein the copper-aluminum interface layer is a transition layer formed by atomic diffusion, comprising a first diffusion layer adjacent to the copper alloy layer and a second diffusion layer adjacent to the aluminum layer, the first diffusion layer having a thickness of 137-152 nm, and the second diffusion layer having a thickness of 432-459 nm. This composite material exhibits excellent resistance to thermal stress fatigue and can be widely used in automotive wiring harness connection materials, meeting the welding requirements of aluminum wires to aluminum components in low-voltage wiring harnesses, thus achieving a balance between electrochemical safety, process compatibility, and cost-effectiveness at the system level. This invention also provides a method for preparing this copper-aluminum composite material and its application in wiring harness terminals.

Description

Technical Field

[0001] This invention belongs to the field of copper-based composite material technology, specifically relating to a copper alloy aluminum composite material, its preparation method, and its application. Background Technology

[0002] As the automotive industry accelerates its evolution towards electrification, lightweighting, and low cost, systemic requirements are being placed on the conductivity, reliability, and cost control of wiring harness connection materials. Currently, low-voltage wiring harness connections commonly use pure copper terminals, which offer excellent conductivity. However, the industry's high dependence on imported copper resources and its volatile prices have prompted the industry to actively promote a "copper-saving with aluminum" strategy. However, directly replacing copper with aluminum at terminal connections faces significant challenges: high risk of electrochemical corrosion, aluminum creep leading to loose connections, and the difference in thermal expansion coefficients between copper and aluminum affecting long-term reliability. These factors restrict the large-scale application of aluminum-for-copper technology in the low-voltage wiring harness field.

[0003] Copper-aluminum composite terminal technology offers a breakthrough solution to the aforementioned bottlenecks through localized material optimization and structural innovation. This approach retains a copper layer at the connector contact area to ensure reliable electrical connections, while employing copper-aluminum composite materials in the wire harness crimping area to achieve welding between the aluminum wire and the aluminum components. This approach balances electrochemical safety, process compatibility, and cost-effectiveness at the system level. Currently, this direction is considered a key component for achieving safe "aluminum wire-copper connector" connections in automotive low-voltage wiring harnesses.

[0004] However, most existing copper-aluminum composite strips use pure copper (such as C11000) as the copper layer substrate, and their strengthening mainly relies on work hardening. Under actual service conditions, especially after experiencing harsh thermal cycling, the pure copper matrix is ​​prone to recovery and recrystallization, resulting in the loss of its initial work hardening effect and a significant decrease in strength. At the same time, an excessively thick brittle intermetallic compound layer is easily formed at the copper-aluminum interface, which cracks at the interface due to the mismatch in thermal expansion coefficients under cyclic thermal stress. Ultimately, this leads to unsatisfactory bending performance of the composite strip, making it difficult to meet the long-term reliability requirements of automotive wiring harness connectors.

[0005] Patent application CN117199845A discloses a copper-aluminum composite material for terminals and its preparation method, relating to the field of electrical connections. The copper-aluminum composite material for terminals includes an aluminum connecting part and a copper connecting part, with the aluminum connecting part embedded in the copper connecting part. A diffusion layer is disposed between the aluminum and copper connecting parts; the diffusion layer is formed by the interdiffusion of atoms in the aluminum and copper connecting parts. The copper-aluminum composite material exhibits good electrical conductivity and corrosion resistance, and shows good connection strength after welding with aluminum or aluminum alloy wires. However, the diffusion heat treatment temperature in this patent application is too high, resulting in an excessively thick copper-aluminum intermetallic compound layer, which affects the electrical conductivity and resistance to thermal stress fatigue.

[0006] Patent application CN121290860A discloses an aluminum-copper composite strip and its preparation method. The strip comprises a copper alloy layer, an aluminum layer, and an intermetallic compound layer. The aluminum layer is embedded within the copper alloy layer, and the intermetallic compound layer is located between the copper alloy layer and the aluminum layer. The copper alloy layer is a precipitation-strengthened copper-nickel alloy with an average particle size of ≤20nm for the second phase particles. The intermetallic compound layer consists of a stacked first diffusion layer and a second diffusion layer. The first diffusion layer contains Cu9Al4 intermetallic compound, and the second diffusion layer contains CuAl2 intermetallic compound. The thickness of the second diffusion layer is ≤2μm. The preparation method of this strip includes the following process: grooving → surface cleaning → composite rolling → intermediate annealing → cold rolling → pre-forming annealing → slitting → packaging. This strip achieves a good balance of strength, conductivity, thermal stress relaxation resistance, and bending performance, making it suitable for applications requiring high comprehensive material performance, such as automotive wiring harness connection terminals. However, the thickness of the oxide layer between copper and aluminum in this aluminum-copper composite strip is relatively thick, that is, the brittle phase is too thick, which leads to insufficient resistance to thermal stress fatigue and makes it difficult to meet the long-term reliability requirements of automotive wiring harness connectors.

[0007] Therefore, developing a copper-aluminum composite material with excellent resistance to thermal stress fatigue has become an urgent technical problem to be solved in this field. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a copper alloy-aluminum composite material. This composite material exhibits excellent resistance to thermal stress fatigue and can be widely used in automotive wiring harness connection materials. It meets the welding requirements for aluminum wires and aluminum components in the low-voltage wiring harness field, thereby balancing electrochemical safety, process compatibility, and cost-effectiveness at the system level.

[0009] This invention provides a copper alloy-aluminum composite material, which has a layered composite structure and comprises, from top to bottom: A copper alloy layer, wherein the material of the copper alloy layer is a Cu-Ni-Si alloy; Copper-aluminum interface layer; and Aluminum layer; The copper-aluminum interface layer is a transition layer formed by atomic diffusion, which includes a first diffusion layer adjacent to the copper alloy layer and a second diffusion layer adjacent to the aluminum layer. The thickness of the first diffusion layer is 137-152 nm, and the thickness of the second diffusion layer is 432-459 nm.

[0010] Since the copper alloy layer provided by this invention is a copper-rich Cu-Ni-Si alloy with a high copper content, the diffusion annealing temperature provided by this invention can achieve mutual atomic diffusion between copper and aluminum at a relatively low level, forming a continuous copper-aluminum interface layer to strengthen the interface bonding. More importantly, due to the low diffusion annealing temperature, the thickness of the hard and brittle first and second diffusion layers is relatively thin, which reduces the risk of cracking along the brittle interface under stress, minimizes the risk of overheating accelerating compound growth, reduces the risk of small interface stress caused by mismatch in thermal expansion coefficients, and is less prone to thermal stress fatigue cracking.

[0011] More preferably, the thickness of the first diffusion layer is 145-152 nm, and the thickness of the second diffusion layer is 441-459 nm.

[0012] Preferably, the dislocation density of the copper alloy-aluminum composite material is 3.1~5.8×10⁻⁶. 14 m -2 .

[0013] Since the copper alloy provided by this invention is a Cu-Ni-Si alloy, an appropriate amount of second-phase particles can be precipitated after aging annealing. After cold rolling, the precipitated second-phase particles effectively pin the large number of dislocations introduced by cold working, resulting in a high dislocation density in the copper alloy aluminum composite material provided by this invention, which in turn greatly improves the strength and conductivity of the alloy. Furthermore, since the precipitated phase provided by this invention still maintains a stable pinning effect at high temperatures, the copper alloy aluminum composite material provided by this invention has resistance to thermal stress fatigue.

[0014] Preferably, the microstructure of the copper alloy layer includes second-phase particles with a particle size of 24-41 nm and a distribution density of 7.4 × 10⁻⁶. 6 ~10.2×10 6 pcs / mm 2 .

[0015] This invention effectively pins dislocations by controlling the particle size and distribution density of the second phase particles, thereby significantly improving the strength of the alloy. At the same time, its precipitation process purifies the matrix, which helps to improve conductivity.

[0016] More preferably, the microstructure of the copper alloy layer includes second-phase particles with a particle size of 36-41 nm and a distribution density of 9.5 × 10⁻⁶. 6 ~10.2×10 6 pcs / mm 2 .

[0017] Preferably, the Cu-Ni-Si alloy is a C70260 copper alloy, a C70250 copper alloy, a C70252 copper alloy, a C64700 copper alloy, a C19010 copper alloy, or a C19015 copper alloy.

[0018] The copper alloys provided by this invention are all copper-rich alloys. Due to the high copper content, Cu and Al can diffuse at a relatively low diffusion heat treatment temperature to form a continuous and thin copper-aluminum interface layer. At the same time, due to the appropriate amount of Ni and Si content, it is possible to form second-phase particles of suitable size.

[0019] The C70260 copper alloy provided by this invention has the following component contents: Ni content is 1.0~3.0 wt%, Si content is 0.2~0.7 wt%, and the balance is Cu. The composition of C70250 copper alloy is as follows: Ni content is 2.2~4.2 wt%, Si content is 0.25~1.2 wt%, and the balance is Cu; The composition of C70252 copper alloy is as follows: Ni content is 3.0~4.2 wt%, Si content is 0.4~1.2 wt%, Mn content is 0.11~0.2 wt%, and the balance is Cu.

[0020] Preferably, the aluminum layer is made of 1060 series aluminum, 1070 series aluminum, 1100 series aluminum, 3003 series aluminum or 8011 series aluminum.

[0021] Preferably, the total thickness of the copper alloy aluminum composite material is 0.295~0.305mm and the width is 22.80~22.90mm, and the method limits the copper alloy aluminum composite material to strip.

[0022] Preferably, the copper alloy-aluminum composite material has a tensile strength of 555~685 MPa, a yield strength of 523~625 MPa, and a conductivity of 37.4~47.6% IACS.

[0023] Preferably, under bending conditions of 90° (R / t=1.0) and 180° (R / t=2.0), the composite strip has a smooth surface without wrinkles after bending along the Good Way direction, and the initial bending performance is qualified.

[0024] Preferably, the composite strip remains qualified after 100 cycles of thermal shock testing at -40℃ / 30min and +150℃ / 30min.

[0025] The copper-aluminum alloy composite material provided by this invention exhibits excellent thermal stress fatigue resistance because the dispersed nano-precipitates remain stable at 150°C, continuously pinning dislocations and effectively resisting stress relaxation. The continuous and thin intermetallic compound layer formed at the interface experiences less interfacial stress due to the mismatch in thermal expansion coefficients under cyclic thermal stress, thus making it less prone to thermal stress fatigue cracking.

[0026] On the other hand, the present invention also provides a method for preparing the copper alloy-aluminum composite material, comprising: (1) Grooving is performed on the surface of the aged annealed Cu-Ni-Si alloy; (2) Clean the Cu-Ni-Si alloy and aluminum layer with grooves, and place the aluminum layer into the groove to form a composite; (3) The composite is subjected to composite rolling, diffusion annealing, second cold rolling and tension straightening in sequence to obtain copper alloy aluminum composite material, wherein the diffusion annealing temperature is 300-450℃.

[0027] Since the Cu-Ni-Si alloy provided by this invention is a copper-rich alloy, the diffusion annealing temperature can be relatively low due to the large amount of copper in the copper-aluminum diffusion reaction. Therefore, this invention can appropriately lower the diffusion annealing temperature, ensuring the formation of a continuous and relatively thin copper-aluminum oxide (brittle phase) after diffusion, thus ensuring a good bond between the copper alloy layer and the aluminum layer, and avoiding the brittle phase being too thick and affecting the thermal stress fatigue resistance.

[0028] This invention obtains an aged annealed Cu-Ni-Si alloy before slotting, where Ni2Si second-phase particles precipitate first. These Ni2Si second-phase particles pin the numerous dislocations formed during the second cold rolling and composite rolling processes, forming dislocation loops that significantly enhance the alloy's strength. Furthermore, this process essentially purifies the matrix material, ensuring good conductivity. In contrast, if aging annealing is performed after the aluminum layer is embedded, the aluminum layer will become excessively softened or even melted, which is detrimental to its composite with the copper alloy layer. This invention eliminates residual stress through diffusion annealing and tension straightening, minimizing dislocation elimination. Through the synergistic effect of these factors, the copper alloy-aluminum composite material provided by this invention exhibits a high dislocation density, resulting in high strength.

[0029] In the preparation process provided by the present invention, composite rolling is performed directly after cleaning the Cu-Ni-Si alloy and aluminum layer. This composite rolling is cold rolling, which reduces the formation of new oxides and is beneficial to the interfacial bonding between the aluminum and copper alloy layers.

[0030] Preferably, the total processing rate of the composite rolling is 50-80%.

[0031] This invention controls the total processing rate of composite rolling, causing the aluminum layer to undergo plastic deformation first. Then, under extrusion pressure, the aluminum layer is embedded in the groove of the copper alloy layer, and the residual oxide film on the surface of copper and aluminum is broken to expose fresh metal and achieve composite. As rolling proceeds, the copper alloy layer and aluminum layer deform together. Under pressure, the fresh metal surfaces come into close contact, forming a physical bond and a weak metallic bond, thereby achieving a good interfacial composite effect.

[0032] Preferably, diffusion annealing is performed in an Ar or H2 / Ar atmosphere at a temperature of 300-450°C for 0.5-1 h.

[0033] This invention controls diffusion annealing in an Ar or H2 / Ar atmosphere to prevent oxidation of the strip surface. Simultaneously, by controlling the diffusion annealing time and temperature, atoms at the copper / aluminum interface diffuse into each other, forming atomic bonds and generating Cu9Al4 (copper-rich phase near the copper alloy side) and CuAl2 (aluminum-rich phase near the aluminum side) intermetallic compounds, thereby strengthening the interfacial bonding. Furthermore, annealing also eliminates residual stress introduced by composite rolling and controls the strip shape. If the diffusion temperature is too low, insufficient atomic movement leads to ineffective metallurgical bonding at the interface, relying only on weak mechanical connections. This under-diffused interface contains numerous microscopic voids, making the strip prone to copper-aluminum delamination during bending or stamping. It also causes localized overheating due to increased contact and thermal resistance, affecting electrical conductivity. Simultaneously, the loose interface easily absorbs moisture, leading to corrosion, and subsequent ultrasonic welding failure due to weak bonding, severely impacting product yield. Conversely, if the diffusion temperature is too high, the copper-aluminum reaction is too vigorous, generating an excessively thick, hard, and brittle intermetallic compound layer. This not only makes the strip extremely prone to cracking along the brittle interface when under stress, but also hinders electron flow due to its high resistivity, causing overheating under high current and accelerating compound growth, forming a vicious cycle; in addition, the mismatch of thermal expansion coefficients will generate thermal stress fatigue during temperature changes, reduce long-term reliability, and ultimately lead to part breakage or delamination during stamping or welding, significantly increasing finished product losses.

[0034] Preferably, diffusion annealing is performed online in an Ar or H2 / Ar atmosphere, with a holding time of 0.5-1 h and a cooling rate of 40-80 °C / min. Compared to offline annealing, online annealing enables continuous production, ensuring uniform heating of the strip in its unfolded state, more precise and stable temperature control, and effectively avoiding the problems of large temperature differences between the inner and outer rings and uneven interface diffusion that exist in offline coil annealing. It can promote the full diffusion of copper-aluminum interface to form a uniform and reliable metallurgical bond, while inhibiting the excessive growth of brittle intermetallic compounds, ensuring the interfacial bonding strength and material plasticity.

[0035] Preferably, the total processing rate of the second cold rolling is 50-80%.

[0036] This invention, by controlling the total processing rate of the second cold rolling, further refines the grain size of the copper alloy layer and increases the dislocation density, thereby introducing more fine-grain strengthening and work hardening, further improving the overall strength of the composite strip, especially the aluminum layer. Aluminum softens after annealing, and cold rolling can further strengthen it. In addition, it can crush brittle intermetallic compounds at the interface, thereby improving the coordinated deformation capability of the copper alloy layer and aluminum layer at the interface. Simultaneously, it can reduce the thickness to the finished product thickness and correct the sheet shape.

[0037] Preferably, the process parameters for tension straightening are: an applied tension of 300~600 MPa and a plastic elongation of 0.5~1.5%.

[0038] This invention eliminates residual stress and plate defects (such as wavy edges and bends) inside the strip by applying tension. While eliminating residual stress, it does not affect the dislocation density and maintains the strength of the copper alloy aluminum material.

[0039] Preferably, edge trimming is performed before tension straightening to remove microcracks and burrs on the strip edge caused by uneven rolling deformation, ensuring that the strip edge is neat and conforms to the target strip width.

[0040] Preferably, mirror polishing is performed after tension straightening. The specific steps of mirror polishing include: rough polishing using an 8-10 μm diamond suspension, a polishing pressure of 20-25 N, a polishing speed of 120-150 r / min, and a target surface roughness (Ra) < 0.4 μm; fine polishing using a 2-4 μm diamond suspension, a polishing pressure of 15-20 N, a polishing speed of 120-150 r / min, and a target surface roughness (Ra) < 0.1 μm; and final mirror polishing using 0.04-0.06 μm colloidal silica, a polishing pressure of 10-15 N, a polishing speed of 100-120 r / min, and a target surface roughness (Ra) ≤ 0.05 μm, thereby obtaining a scratch-free and deformation-free surface.

[0041] Preferably, the preparation process of the Cu-Ni-Si alloy in the age-annealed state includes: semi-continuous casting → hot rolling → milling → first cold rolling → age-annealing.

[0042] Preferably, the process parameters for the semi-continuous casting are as follows: the raw materials are batched and smelted according to the mass percentage of each component of the Cu-Ni-Si alloy, the raw materials are electrolytic copper, pure Ni, pure Si and / or pure Mn, the smelting temperature is 1350~1450℃, and the casting temperature is 1200~1300℃.

[0043] Preferably, the hot rolling temperature is 850~950℃, the processing rate is 85~95%, and the temperature is maintained at the hot rolling temperature for 4~6 hours before hot rolling.

[0044] This invention achieves homogenization annealing of ingots and eliminates dendritic segregation by controlling the hot rolling temperature, processing rate, and holding time. Hot rolling can eliminate casting defects, break up the as-cast structure, and achieve initial thinning. Dynamic recrystallization occurs during hot rolling, refining the grains, improving the material's processing plasticity, and preparing it for subsequent cold rolling.

[0045] Preferably, the processing rate of the first cold rolling is 70-85%. This invention, by controlling the processing rate, introduces a large number of dislocations through cold deformation, significantly improving the material strength. Simultaneously, the deformation energy storage provides the driving force for the subsequent aging precipitation of the second phase. Cold rolling rolls the material to the target thickness, also preparing it for subsequent composite processes.

[0046] Preferably, the aging annealing temperature is 500~580℃, and the time is 6~8h. This invention, by controlling the aging annealing temperature and holding time, causes Ni and Si atoms in the supersaturated solid solution to precipitate as Ni₂Si second-phase particles. These nanoscale second-phase particles pin dislocations, significantly improving the alloy's strength and conductivity (matrix purification).

[0047] Preferably, before grooving the surface of the aged annealed Cu-Ni-Si alloy, the aged annealed Cu-Ni-Si alloy is slit. The purpose is to longitudinally cut the wide material into narrow strips of the required width, so as to provide dimensionally accurate blanks for subsequent inlay and composite.

[0048] On the other hand, the present invention also provides the application of the copper alloy aluminum composite material in wire harness terminals.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention forms a continuous, relatively thin first diffusion layer and a second diffusion layer between the copper alloy layer and the aluminum layer, which enhances the interfacial bonding between the copper alloy layer and the aluminum layer. At the same time, because the first diffusion layer and the second diffusion layer, i.e. the brittle layer, are relatively thin, the risk of cracking along the brittle interface under stress is reduced, so that the copper alloy aluminum composite material provided by the present invention has excellent resistance to thermal stress fatigue. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the structure of the C70250 / 1060 composite strip prepared in Example 2 of the present invention, including a cross-sectional metallographic image and a cross-sectional SEM image. Figure 1 (a) in the diagram is a structural schematic. Figure 1 Image (b) is a cross-sectional metallographic image. Figure 1 (c) in the image is a cross-sectional SEM image; Figure 2The images shown are cross-sectional SEM images and EDS-mapping elemental diagrams of the C70250 / 1060 composite strip obtained in Example 2 of this invention, as well as SEM images detailing the thickness of the Al layer and the intermetallic compound at the Cu / Al interface. Figure 2 (a) in the image is a cross-sectional SEM image. Figure 2 (b) in the diagram is the EDS-mapping element diagram. Figure 2 (c) in the image shows the EDS-mapping elemental map and the SEM image showing the thickness details of the Al layer and the intermetallic compound at the Cu / Al interface. Detailed Implementation

[0051] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, 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. The present invention provides three embodiments.

[0052] Example 1 C70260 / 1060 composite tape (1) C70260 alloy ingots were obtained by batching, smelting, and semi-continuous casting using electrolytic copper, pure Ni, and pure Si as raw materials. The smelting temperature was 1400℃ and the casting temperature was 1250℃. The Ni content was 1.66 wt%, the Si content was 0.41 wt%, and the balance was Cu.

[0053] (2) After sawing the head and tail, hot roll to 15 mm at 900℃, with a processing rate of 92%. Before hot rolling, keep warm at the hot rolling temperature for 4 hours to achieve the effect of homogenization annealing of the ingot and eliminate dendrite segregation. (3) After milling, the surface is cold rolled to 3 mm for the first time.

[0054] (4) 580℃ / 6h aging annealing precipitates Ni2Si second phase in Cu matrix, which greatly improves the strength and conductivity of alloy.

[0055] (5) Cut the strip longitudinally into narrow strips with a width of 35mm.

[0056] (6) Grooves are cut on the surface of C7026 alloy strip, and then alkaline washing, acid washing and brushing are performed on it and the 1060 aluminum layer to be laminated to remove oil, dust and oxide film from the surface.

[0057] (7) At room temperature, the C7026 alloy layer with embedded groove and the 1060 aluminum layer are composite rolled with a processing rate of 70%.

[0058] (8) Perform diffusion annealing at 350℃ / 1h in an Ar atmosphere to allow atoms at the copper / aluminum interface to diffuse into each other and form atomic bonds, thereby strengthening the interface bonding.

[0059] (9) The strip was cold-rolled a second time to 0.3 mm, with a processing rate of 66.7%. Then, the micro-cracks and burrs caused by uneven rolling deformation at the edge of the strip were removed. The final strip width was 22.9 mm, the aluminum layer width was 5 mm, and the aluminum layer was 6 mm away from one side of the overall composite strip.

[0060] (10) Perform tension straightening with a tension of 500 MPa and a plastic elongation of 1% to eliminate residual stress and plate defects inside the strip.

[0061] (11) Perform mirror polishing. First, rough polishing is performed using a 9 μm diamond suspension at a polishing pressure of 25 N and a polishing speed of 140 r / min, with a target surface roughness (Ra) < 0.4 μm. Fine polishing is performed using a 3 μm diamond suspension at a polishing pressure of 20 N and a polishing speed of 120 r / min, with a target surface roughness (Ra) < 0.1 μm. Finally, mirror polishing is performed using 0.05 μm colloidal silica at a polishing pressure of 15 N and a polishing speed of 100 r / min, with a target surface roughness (Ra) ≤ 0.05 μm, thereby obtaining a scratch-free and deformation-free surface.

[0062] Example 2 C70250 / 1060 composite tape The only difference from Example 1 is that in step (1) of this Example 2, C70250 alloy ingots are obtained by semi-continuous casting. The Ni content is 2.92 wt%, the Si content is 0.54 wt%, and the balance is Cu; the tension for tension straightening in step (10) is 520 MPa.

[0063] Example 3 C70252 / 1060 composite tape The only difference from Example 1 is that in step (1) of this Example 3, C70252 alloy ingots are obtained by semi-continuous casting. The Ni content is 3.78 wt%, the Si content is 0.85 wt%, the Mn content is 0.15 wt%, and the balance is Cu; the tension of tension straightening in step (10) is 540 MPa.

[0064] Example 4 C70250 / 1060 composite tape The difference from Example 2 is that in this Example 4, step (4) is aging annealing at 500℃ for 6 hours; the processing rate of composite rolling in step (7) is 60%; in step (9), the second cold rolling is performed to 0.3mm with a processing rate of 75%; and the tension of tension straightening in step (10) is 560MPa.

[0065] Example 5 The difference from Example 3 is that the diffusion annealing in Example 5 is online annealing, the annealing time is 0.5h, and the cooling rate is 50℃ / min.

[0066] Example 6 The difference between this embodiment and Embodiment 3 is that the diffusion annealing temperature is 330°C.

[0067] Comparative Example 1 C11000 / 1060 composite tape (1) C11000 ingots were obtained by semi-continuous casting using electrolytic copper as raw material. The melting temperature was 1200℃ and the casting temperature was 1150℃. (2) After sawing the head and tail, hot roll to 15 mm at 900℃, with a processing rate of 92%. Before hot rolling, keep warm at the hot rolling temperature for 2 hours. (3) After milling, cold roll to 3 mm; (4) Cut the strip longitudinally into narrow strips with a width of 35mm; (5) Grooving is performed on the surface of C11000 strip, and then alkaline washing, acid washing and brushing are performed on it and the 1060 aluminum layer to be laminated to remove oil, dust and oxide film from the surface. (6) At room temperature, the C1000 copper layer and 1060 aluminum layer with embedded grooves are composite rolled with a processing rate of 70%.

[0068] (7) Perform diffusion annealing at 350℃ / 1h in an Ar atmosphere to allow atoms at the copper / aluminum interface to diffuse into each other and form atomic bonds, thereby strengthening the interfacial bonding; (8) Cold rolled to 0.3 mm, with a processing rate of 66.7%. Then, the micro-cracks and burrs caused by uneven rolling deformation at the edge of the strip were removed. The final strip width was 22.9 mm, the aluminum layer width was 5 mm, and the aluminum layer was 6 mm away from one side of the overall composite strip.

[0069] (9) Perform tension straightening with a tension of 350 MPa and a plastic elongation of 1% to eliminate residual stress and plate defects inside the strip.

[0070] (10) Perform mirror polishing. First, rough polishing is performed using a 9 μm diamond suspension at a polishing pressure of 25 N and a polishing speed of 140 r / min, with a target surface roughness (Ra) < 0.4 μm. Fine polishing is performed using a 3 μm diamond suspension at a polishing pressure of 20 N and a polishing speed of 120 r / min, with a target surface roughness (Ra) < 0.1 μm. Finally, mirror polishing is performed using 0.05 μm colloidal silica at a polishing pressure of 15 N and a polishing speed of 100 r / min, with a target surface roughness (Ra) ≤ 0.05 μm, thereby obtaining a scratch-free and deformation-free surface.

[0071] Comparative Example 2 H65 / 1060 composite tape Compared to Example 1, the copper alloy layer is made of H65 brass, and the specific preparation process is as follows: (1) H65 brass ingots were obtained by batching, smelting, and semi-continuous casting using electrolytic copper and pure zinc as raw materials. The smelting temperature was 1080℃ and the casting temperature was 1000℃. The Zn content was 35 wt%, with the balance being Cu.

[0072] (2) After sawing off the head and tail, hot roll to 15 mm at 720℃, with a processing rate of 92%. Keep warm at the hot rolling temperature for 1 hour before hot rolling; (3) After milling, the surface is cold rolled to 3 mm for the first time.

[0073] (4) Perform recrystallization annealing at 450℃ for 2 hours.

[0074] (5) Cut the strip longitudinally into narrow strips with a width of 35mm.

[0075] (6) Grooves are cut on the surface of H65 brass strip, and then alkaline washing, acid washing and brushing are performed on it and the 1060 aluminum layer to be laminated to remove oil, dust and oxide film from the surface.

[0076] (7) At room temperature, the H65 brass layer with embedded groove and the 1060 aluminum layer are composite rolled with a processing rate of 70%.

[0077] (8) Perform diffusion annealing at 350℃ / 1h in an Ar atmosphere to allow atoms at the copper / aluminum interface to diffuse into each other and form atomic bonds, thereby strengthening the interface bonding.

[0078] (9) The strip was cold-rolled a second time to 0.3 mm, with a processing rate of 66.7%. Then, the micro-cracks and burrs caused by uneven rolling deformation at the edge of the strip were removed. The final strip width was 22.9 mm, the aluminum layer width was 5 mm, and the aluminum layer was 6 mm away from one side of the overall composite strip.

[0079] (10) Perform tension straightening with a tension of 500 MPa and a plastic elongation of 1% to eliminate residual stress and plate defects inside the strip.

[0080] (11) Mirror polishing was performed. First, rough polishing was performed using a 9 μm diamond suspension at a polishing pressure of 25 N and a polishing speed of 140 r / min, resulting in a target surface roughness (Ra) < 0.4 μm. Fine polishing was performed using a 3 μm diamond suspension at a polishing pressure of 20 N and a polishing speed of 120 r / min, resulting in a target surface roughness (Ra) < 0.1 μm. Finally, mirror polishing was performed using 0.05 μm colloidal silica at a polishing pressure of 15 N and a polishing speed of 100 r / min, resulting in a target surface roughness (Ra) ≤ 0.05 μm, thus obtaining a scratch-free and deformation-free surface. The copper alloy layer provided in Comparative Example 2 is brass, which has poor bonding performance with the aluminum layer, poor mechanical properties, poor bending properties, poor resistance to thermal stress fatigue, and poor electrical conductivity.

[0081] Comparative Example 3 Compared to Example 3, the diffusion annealing temperature was 480°C. The diffusion annealing temperature provided in this comparative example is too high, the thickness of the first and second diffusion layers is too thick, the aluminum-copper interface layer is brittle, and the mechanical properties, bending resistance, and thermal stress fatigue resistance are poor.

[0082] Comparative Example 4 Compared to Example 3, the diffusion annealing temperature was 250°C. The diffusion annealing temperature provided in this comparative example is too low, the thickness of the first and second diffusion layers is too thin, the interpenetration between aluminum and copper is insufficient, delamination is easy, and the mechanical properties and resistance to thermal stress fatigue are poor.

[0083] Comparative Example 5 Compared to Example 3, tension straightening was replaced with pre-forming annealing at a temperature of 300°C for 2 hours. Because pre-forming annealing was used, more dislocations were eliminated, and the brittle phase grew, resulting in excessively thick first and second diffusion layers. Consequently, the thermal stress fatigue resistance was poor.

[0084] Comparative Example 6 Compared to Example 3, the Cu-Ni-Si alloy was directly grooved on the surface. The second phase was not fully precipitated, affecting electrical conductivity, mechanical properties, and resistance to thermal stress fatigue.

[0085] Table 1 shows the dimensional information of the composite strips obtained in Examples 1-6 and Comparative Examples 1-6 of the present invention, specifically including the width, thickness, and relative position of the copper alloy layer and the aluminum layer. The data in the table shows that the actual specifications of each finished product basically match the design values, indicating that the process parameters of each step in the present invention are reasonably designed and controllable.

[0086] Table 2 summarizes the microstructural characteristics of the aforementioned composite strips, mainly including the size and distribution density of the second-phase particles, and the thickness of the Cu9Al4 and CuAl2 intermetallic compound layers at the copper / aluminum interface. Data shows that the dislocation density in Examples 1-6 ranges from 3.1 to 5.8 × 10⁻⁶. 14 m -2 Within this range, the size of the Ni₂Si second phase is in the range of 24–41 nm, and the distribution density reaches 7.4 × 10⁻⁶. 6 ~11.0×10 6 pcs / mm 2 These nanoscale precipitates effectively pin dislocations, thus significantly improving alloy strength; simultaneously, their precipitation process purifies the matrix, contributing to increased conductivity. Regarding the interface structure, the thicknesses of the Cu9Al4 and CuAl2 layers are controlled between 137–152 nm and 432–459 nm, respectively. This continuous and moderately thick intermetallic compound layer not only enhances the bonding strength of the copper / aluminum interface but also prevents a decline in thermal stress fatigue resistance due to excessive interface brittleness.

[0087] Table 3 presents the mechanical and electrical properties of the composite strips of Examples 1-6 and Comparative Examples 1-6 of the present invention, covering indicators such as hardness, tensile strength, yield strength, elongation, and conductivity. Compared with Comparative Example 1, which uses C11000 pure copper, Example 1 uses C70260 age-hardening copper alloy as the base material, resulting in a significant improvement in the strength of its composite strip. Examples 2 and 3 further utilize C70250 alloy and C70252 alloy, respectively. Due to their higher Ni and Si content, the solid solution strengthening effect is more significant, and the precipitation driving force of the second phase is stronger, thus further improving the strength compared to Example 1. Example 4 enhances the strengthening effect by reducing the aging annealing temperature and controlling the moderate coarsening of the precipitated phase, while increasing the cold working rate of the final pass to increase the work hardening effect. Therefore, its strength is further improved based on Example 2. Examples 5 and 6 change the annealing method to online annealing and optimize the annealing temperature based on Example 3, respectively, and the results show further improvement in mechanical properties.

[0088] Table 4 shows the bending performance test results of each composite strip. Under bending conditions of 90° (R / t=1.0) and 180° (R / t=2.0), the composite strips in Examples 1-6 all showed smooth surfaces without wrinkles after bending along the Good Way direction, and their initial bending performance was qualified. However, after 100 cycles of thermal shock testing at -40℃ / 30min and +150℃ / 30min, the composite strips in Comparative Examples 1-6 showed bending failure, while the composite strips in Examples 1-6 remained qualified. Analysis revealed that the main reason for the failure of the composite strips in the comparative examples was the low strength of the copper matrix, which underwent recovery and recrystallization under repeated thermal shock, resulting in the loss of its initial work hardening effect and a significant decrease in strength. In contrast, the C70260 / 1060, C70250 / 1060, and C70252 / 1060 composite bands in the embodiments benefit from the age-strengthening mechanism. The dispersed nano-precipitates remain stable at 150°C, continuously pinning dislocations and effectively resisting stress relaxation, thus endowing the material with excellent thermal stress fatigue resistance. Furthermore, compared to C11000 / 1060, the brittle intermetallic compound layer formed at the interface of the C70260 / 1060, C70250 / 1060, and C70252 / 1060 composite bands is thinner, resulting in lower interfacial stress due to the mismatch in thermal expansion coefficients under cyclic thermal stress, thus making them less prone to thermal stress fatigue cracking.

[0089] Figure 1 Images (a), (b), and (c) in the figure are schematic diagrams of the C70250 / 1060 composite strip prepared in Example 2, along with cross-sectional metallographic images and cross-sectional SEM images, respectively. It can be seen that after composite rolling and subsequent deformation, the Al layer has a trapezoidal shape in cross-section, and the Cu / Al interface is well bonded.

[0090] Figure 2 Images (a), (b), and (c) in the figure show cross-sectional SEM images and EDS-mapping elemental maps of the C70250 / 1060 composite strip prepared in Example 2, as well as SEM images detailing the thickness of the Al layer and the intermetallic compound at the Cu / Al interface. It can be seen that the composite Al layer, after deformation, has a thickness of approximately 32 μm. At the Cu / Al interface, there are two intermetallic compounds with different chemical compositions: CuAl2 near the Al layer has a thickness of approximately 455 nm, and Cu9Al4 near the Cu layer has a thickness of approximately 148 nm.

[0091] Table 1 Dimensional information of composite strip Table 2 Microstructure information of composite strips Table 3 Mechanical and electrical properties of composite strips Table 4. Bending performance (Good Way) of composite strip

Claims

1. A copper alloy-aluminum composite material, characterized in that, It has a layered composite structure, which includes, from top to bottom: A copper alloy layer, wherein the material of the copper alloy layer is a Cu-Ni-Si alloy; Copper-aluminum interface layer; and Aluminum layer; The copper-aluminum interface layer is a transition layer formed by atomic diffusion, which includes a first diffusion layer adjacent to the copper alloy layer and a second diffusion layer adjacent to the aluminum layer. The thickness of the first diffusion layer is 137-152 nm, and the thickness of the second diffusion layer is 432-459 nm.

2. The copper alloy-aluminum composite material according to claim 1, characterized in that, The dislocation density of the copper alloy aluminum composite material is 3.1-5.8×10 14 m -2 .

3. The copper alloy-aluminum composite material according to claim 1, characterized in that, The microstructure of the copper alloy layer includes second-phase particles with a particle size of 24-41 nm and a distribution density of 7.4 × 10⁻⁶. 6 ~10.2×10 6 pcs / mm 2 .

4. The copper alloy-aluminum composite material according to claim 1, characterized in that, The Cu-Ni-Si alloy is C70260 copper alloy, C70250 copper alloy, C70252 copper alloy, C64700 copper alloy, C19010 copper alloy or C19015 copper alloy.

5. The copper alloy-aluminum composite material according to claim 1, characterized in that, The aluminum layer is made of 1060 series aluminum, 1070 series aluminum, 1100 series aluminum, 3003 series aluminum or 8011 series aluminum.

6. The copper alloy-aluminum composite material according to claim 1, characterized in that, The total thickness of the copper alloy-aluminum composite material is 0.295~0.305mm, and the width is 22.80~22.90mm.

7. A method for preparing a copper alloy-aluminum composite material according to any one of claims 1-6, characterized in that, include: (1) Grooving is performed on the surface of the aged annealed Cu-Ni-Si alloy; (2) Clean the Cu-Ni-Si alloy and aluminum layer with grooves, and place the aluminum layer into the groove to form a composite; (3) The composite is subjected to composite rolling, diffusion annealing, second cold rolling and tension straightening in sequence to obtain copper alloy aluminum composite material, wherein the diffusion annealing temperature is 300-450℃.

8. The method for preparing the copper alloy-aluminum composite material according to claim 7, characterized in that, The total processing rate of the composite rolling is 50-80%.

9. The method for preparing the copper alloy-aluminum composite material according to claim 7, characterized in that, Diffusion annealing is performed in an Ar or H2 / Ar atmosphere using an online annealing method, with a holding time of 0.5-1 h and a cooling rate of 40-80 °C / min.

10. The application of a copper alloy-aluminum composite material according to any one of claims 1-6 in a wire harness terminal.

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