Aluminum-copper composite strip and preparation method thereof

Abstract

The invention discloses an aluminum-copper composite strip and a preparation method thereof, the strip comprises a copper alloy layer, an aluminum material layer and an intermetallic compound layer, the aluminum material layer is embedded in the copper alloy layer, the intermetallic compound layer is located between the copper alloy layer and the aluminum material layer, the copper alloy layer is a precipitation strengthening type copper-nickel alloy, and the intermetallic compound layer is an aluminum alloy layer. The average particle size of second-phase particles in the copper alloy layer is smaller than or equal to 20 nm, the intermetallic compound layer is composed of a first diffusion layer and a second diffusion layer which are stacked, the first diffusion layer contains a Cu9Al4 intermetallic compound, the second diffusion layer contains a CuAl2 intermetallic compound, and the thickness of the second diffusion layer is smaller than or equal to 2 microns. The preparation method of the strip comprises the technological processes of grooving, surface cleaning, composite rolling, intermediate annealing, cold rolling, annealing before forming, splitting and packaging. The strip achieves good matching of strength, conductivity, heat stress relaxation resistance and bending performance, and is suitable for occasions with high requirements for comprehensive performance of materials, such as automobile wire harness connecting terminals and the like.

Description

Technical Field

[0001] This invention belongs to the field of copper alloys, and specifically relates to an aluminum-copper composite strip and its preparation method. Background Technology

[0002] The terminal materials used in automotive wiring harness connections require high standards for bonding strength, thermal stability, and chemical stability to ensure proper functioning during subsequent manufacturing processes or in environments with temperature variations. Copper, with its excellent electrical and thermal conductivity, is the preferred material for terminal manufacturing. Aluminum, on the other hand, offers advantages such as light weight, corrosion resistance, and low cost. With the increasing demand for lightweight automotive wiring harnesses, aluminum or aluminum alloys are gradually replacing copper or copper alloys in some conductors. However, corrosion is a potential problem at the connection between aluminum conductors and copper terminals. The contact between dissimilar metals can cause corrosion, leading to significant aluminum dissolution. This corrosion issue has long hindered the aluminumization of wiring harnesses.

[0003] Aluminum-copper composites combine the high strength, excellent electrical conductivity, good thermal conductivity, and wear resistance of copper with the advantages of aluminum, such as lightweight, corrosion resistance, ease of processing, and economy. Furthermore, aluminum-copper composites can meet the requirements for mating copper and aluminum materials, solving the challenge of welding dissimilar metals. However, aluminum-copper composites are prone to separation at the interface during long-term use in environments with varying temperatures. Additionally, due to the potential difference between copper and aluminum, direct connection can easily lead to electrochemical corrosion. During bending and deformation, the aluminum-copper transition layer is prone to cracking, affecting the reliability and stability of the connection between the wire harness and the terminal.

[0004] Currently, the main production methods for aluminum-copper composite materials include solid-solid composite methods (such as rolling composite methods) and solid-liquid composite methods (such as casting-rolling composite methods). However, aluminum-copper composite materials prepared by existing production methods are prone to forming brittle and hard intermetallic compounds at the composite interface. This not only reduces the mechanical properties of the material but also results in a thicker composite layer, affecting the overall performance of the material. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an aluminum-copper composite strip and its preparation method, which achieves a good match between strength, conductivity, heat stress relaxation resistance and bending performance, avoiding failure during application, and is suitable for occasions with high requirements for the comprehensive performance of materials, such as automotive wiring harness connection terminals.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: an aluminum-copper composite strip, comprising a copper alloy layer, an aluminum material layer, and an intermetallic compound layer, wherein the aluminum material layer is embedded in the copper alloy layer, and the intermetallic compound layer is located between the copper alloy layer and the aluminum material layer. The copper alloy layer is a precipitation-strengthened copper-nickel alloy, and the average particle size of the second phase particles in the copper alloy layer is ≤20nm. The intermetallic compound layer is composed of a stacked first diffusion layer and a second diffusion layer. The first diffusion layer is connected to the copper alloy layer, and the second diffusion layer is connected to the aluminum 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.

[0007] This invention embeds an aluminum layer within a copper alloy layer, replacing a portion of the copper alloy with the aluminum layer to meet the requirements for mating and welding two metal materials, copper and aluminum. Between the copper alloy layer and the aluminum layer lies an intermetallic compound layer consisting of a first diffusion layer and a second diffusion layer, wherein the first diffusion layer contains Cu9Al4 intermetallic compound and the second diffusion layer contains CuAl2 intermetallic compound. These layers form a strong metallurgical bond, enhancing the bonding strength of the composite strip interface.

[0008] The copper alloy layer in the aluminum-copper composite strip of this invention is a precipitation-strengthened copper-nickel alloy, and the average particle size of the second phase particles in the copper alloy layer is ≤20nm. The precipitation-strengthened copper-nickel alloy can be selected from alloy series such as Cu-Ni-Si, Cu-Ni-P, and Cu-Ni-Co-Si, for example, C70250, C19000, C19005, C19010, C19025, and C70318.

[0009] The presence of second-phase particles in the copper alloy layer serves two purposes. Firstly, these particles synergistically strengthen the alloy, enhancing its strength. Secondly, during recrystallization, they pin grain boundaries, refining the average grain size of the copper alloy layer and improving bending workability and resistance to stress corrosion cracking. However, excessively large second-phase particles in the copper alloy layer can cause localized stress concentration, leading to deterioration of the strip's high-temperature performance and adversely affecting its resistance to thermal stress relaxation. Therefore, the size and distribution of the second-phase particles are closely related to the strip's properties. This invention controls the average particle size of the second-phase particles to be ≤20 nm. Preferably, the number density of second-phase particles with a particle size of 5–15 nm in the copper alloy layer is 3 × 10⁻⁶. 7 pcs / mm 2The finer and more dispersed the precipitated phase distribution, the better the alloy's strength, conductivity, and high-temperature performance. When the second-phase particles in the copper alloy layer are uniformly dispersed, the alloy can simultaneously possess high strength, high conductivity, good bending performance, and excellent heat resistance. Furthermore, the microstructure distribution in the copper alloy layer also reflects the bonding performance of the aluminum-copper composite strip interface to a certain extent. The finer and more dispersed the precipitated phase distribution, the more beneficial it is to the composite of the copper alloy layer and the aluminum layer, and the better the bonding stability between the two. Therefore, to ensure that the aluminum-copper composite strip achieves its overall performance goals while possessing good interfacial bonding, this invention controls the number density of the second-phase particles in the copper alloy layer to 3 × 10⁻⁶. 7 pcs / mm 2 above.

[0010] The thickness of the second diffusion layer in the intermetallic compound layer is ≤2μm, and the second diffusion layer contains CuAl2 intermetallic compound. During the forming process of aluminum-copper composite strip, copper and aluminum atoms react to form intermetallic compounds. CuAl2 is the first phase to form, which has high strength but almost no plasticity, and its coefficient of thermal expansion differs significantly from that of the copper alloy layer and the aluminum layer. Therefore, it becomes the main area where cracks first occur and propagate, seriously affecting the interfacial strength, processing performance, and thermophysical properties of the composite strip. Thus, controlling the thickness of the second diffusion layer is crucial to the performance of the composite strip. This invention controls the thickness of the second diffusion layer to ≤2μm. On the one hand, this helps improve the mechanical properties and interfacial bonding strength of the composite strip; on the other hand, it helps reduce the release of thermal stress in the intermetallic compound layer, further improving the overall thermal stability of the composite strip.

[0011] Preferably, a third diffusion layer is formed between the first diffusion layer and the second diffusion layer, and the third diffusion layer contains CuAl intermetallic compounds. As the first and second diffusion layers grow, the third diffusion layer nucleates and precipitates between them. The formation of the third diffusion layer promotes the stabilization of the microstructure in the intermetallic compound layer, thereby inhibiting the formation of brittle compounds caused by temperature changes and further improving the heat resistance and bending performance of the composite strip.

[0012] Preferably, the total thickness of the aluminum-copper composite strip is 0.1–0.8 mm, and the thickness of the aluminum layer accounts for 5–40% of the total thickness of the aluminum-copper composite strip. In the aluminum-copper composite strip of the present invention, the thermal conductivity of the copper alloy layer and the aluminum layer differs, with the copper alloy layer exhibiting superior thermal conductivity compared to the aluminum layer. If the aluminum layer is too thick, the thermal stress relaxation resistance of the composite strip will decrease; if the aluminum layer is too thin, it is easily damaged during the welding or crimping process in subsequent wire harness fabrication, leading to direct connection between the wire harness and the copper alloy layer, causing electrochemical corrosion, thereby reducing the reliability and stability of the connection. Therefore, the present invention controls the thickness of the aluminum layer to account for 5–40% of the total thickness of the aluminum-copper composite strip. Furthermore, the present invention controls the total thickness of the aluminum-copper composite strip to be 0.1–0.8 mm, and this extremely thin composite strip within this thickness range can meet the requirements of automotive lightweighting.

[0013] Preferably, along the thickness direction of the intermetallic compound layer, from the first diffusion layer to the second diffusion layer, the Al concentration within the intermetallic compound layer forms a gradient concentration of 10–75 wt% / μm. The intermetallic compound layer of the composite strip of the present invention exhibits a continuous change in Al concentration, increasing from the first diffusion layer to the second diffusion layer. SEM-EDS line scan analysis shows that along the thickness direction of the intermetallic compound layer, from the first diffusion layer to the second diffusion layer, the Al concentration forms a gradient concentration of 10–75 wt% / μm. The aluminum-copper composite strip of the present invention has an intermetallic compound layer formed by atomic diffusion at the composite interface between the copper alloy layer and the aluminum layer. If the Al gradient concentration in the intermetallic compound layer is too high, the interfacial bonding strength of the composite strip will be insufficient; if the Al gradient concentration in the intermetallic compound layer is too low, excessive brittle and hard intermetallic compounds are easily formed, causing interfacial delamination during heating or deformation, thereby reducing the thermal stress relaxation resistance and bending performance of the composite strip, failing to meet the requirements for terminal use. By forming an intermetallic compound layer with an Al concentration gradient of 10–75 wt% / μm, the Al content variation within the intermetallic compound layer tends to be stable, avoiding significant abrupt changes in composition and resulting in a more continuous and uniform elemental distribution. This gentle concentration gradient can effectively absorb thermal stress caused by temperature changes, suppressing crack formation and propagation in the intermetallic compound layer, thereby improving the interfacial bonding strength, heat resistance, and overall bending performance of the composite strip. More preferably, along the thickness direction of the intermetallic compound layer, from the first diffusion layer to the second diffusion layer, the Al concentration within the intermetallic compound layer forms a gradient concentration of 20–60 wt% / μm.

[0014] Preferably, the Al concentration within the copper alloy layer, along its thickness direction, at a distance of 10 μm from the interface between the copper alloy layer and the first diffusion layer, is no higher than 0.05 wt%. Excluding the intermetallic compound layer, Al exists in a solid solution form within the surface layer of the copper alloy layer on the side closest to the intermetallic compound layer. If the Al content in this surface layer is too high, segregation is likely to occur at grain boundaries, leading to a decrease in the alloy's ductility, cold working properties, impact characteristics, and high-temperature performance. By controlling the Al concentration at 10 μm from the interface between the copper alloy layer and the first diffusion layer to below 0.05 wt%, segregation can be suppressed. If the Al concentration at 10 μm from the interface between the copper alloy layer and the first diffusion layer exceeds 0.05 wt%, the uniformity of the copper alloy layer's composition and microstructure will decrease, thereby reducing the overall ductility, cold working properties, impact characteristics, and high-temperature performance of the composite strip. Furthermore, during subsequent long-term high-temperature service, brittle compounds are prone to form in this region, affecting interfacial bonding and performance reliability. Therefore, the present invention controls the Al concentration at a distance of 10 μm from the interface between the copper alloy layer and the first diffusion layer to be no higher than 0.05 wt%.

[0015] Preferably, the aluminum layer is a 1-series, 3-series, 6-series, or 8-series aluminum alloy. These aluminum alloys possess excellent thermal conductivity, enabling them to achieve good thermal performance matching with the copper alloy layer. This helps reduce internal stress in the composite strip caused by differences in thermal expansion, thereby improving its resistance to thermal stress relaxation.

[0016] Preferably, the copper alloy layer has a conductivity of 40% IACS or higher, a yield strength of 500 MPa or higher, and a thermal stress relaxation rate of ≥70% after exposure at 130°C for 1000 hours; the side curvature of the aluminum-copper composite strip is less than 3 mm / m, the 90° bend R / t at the interface between the aluminum layer and the copper alloy layer on one side of the width direction is ≤1, and the 90° bend R / t at the long centerline of the surface of the aluminum layer is ≤1, which can meet the requirements for terminal materials for automotive wiring harness connections.

[0017] The process flow for preparing the aforementioned aluminum-copper composite strip includes: grooving → surface cleaning → composite rolling → intermediate annealing → cold rolling → pre-forming annealing → slitting → packaging. The composite rolling includes hot rolling, with a final rolling temperature >350℃, a total processing rate of 40-90%, and a cooling rate ≥30℃ / s after hot rolling. The specific process is as follows:

[0018] Grooving: Using precipitation-strengthened copper-nickel alloy plate and aluminum strip as raw materials for copper alloy layer and aluminum material layer respectively, grooves are cut in the precipitation-strengthened copper-nickel alloy plate to obtain a precipitation-strengthened copper-nickel alloy plate with embedded grooves.

[0019] Surface cleaning: In order to maintain good bonding strength between the copper alloy layer and the aluminum layer, the precipitation-strengthened copper-nickel alloy plate and aluminum strip with embedded grooves are cleaned. Then, the aluminum strip is embedded in the embedded groove of the precipitation-strengthened copper-nickel alloy plate to obtain the semi-finished aluminum-copper composite strip.

[0020] Composite rolling: This involves hot rolling of aluminum-copper composite strip semi-finished products. The initial rolling temperature is 400–550℃, the final rolling temperature is >350℃, the total processing rate is 40–90%, and the cooling rate after hot rolling is ≥30℃ / s. In the initial stage of hot rolling, the aluminum layer undergoes plastic deformation first. Then, the aluminum and copper alloy layers are pressed together under pressure, achieving surface-to-surface composite bonding. As hot rolling progresses, copper and aluminum atoms diffuse into each other, bonding at the interface through atomic bonds to form CuAl2, Cu9Al4, and CuAl intermetallic compounds sequentially. If the initial rolling temperature is too low, the bonding between the copper alloy layer and the aluminum layer will be insufficient. If the initial rolling temperature is higher than 550℃, more brittle compounds will be generated at the interface. The increased total amount of brittle compounds leads to reduced interfacial bonding strength and increased thermal stress sensitivity. Simultaneously, it causes the second-phase particles in the copper alloy layer to coarsen, making it difficult to simultaneously guarantee the alloy's high yield strength, good bending workability, and excellent resistance to thermal stress relaxation. During hot rolling, as the total reduction rate increases, the difference in reduction rate between the copper alloy layer and the aluminum layer gradually decreases, which is beneficial for the co-deformation of both, improves the interfacial composite rate, achieves a good composite effect, and also facilitates the full precipitation of second-phase particles. Therefore, this invention controls the total processing rate of hot rolling to be 40-90%. To further promote the full, fine, and dispersed precipitation of second-phase particles in the copper alloy layer, this invention controls the final rolling temperature of hot rolling to be >350℃, and the cooling rate after hot rolling to be ≥30℃ / s.

[0021] Intermediate annealing: The annealing temperature for intermediate annealing is 350–550℃, and the holding time is 5–60 min. The purpose of intermediate annealing is to eliminate work hardening and residual stress in the strip after composite rolling, restore its plasticity, and promote the formation of a fine-grained structure in the interfacial reaction layer to improve the interfacial bonding strength.

[0022] Cold rolling: The cold rolling rate is 20-40%, and the rolling speed is no more than 30 cm / s. Cold rolling the composite strip at a rate of 20-40% can reduce the grain size of the second-phase particles in the copper alloy layer, promote the further precipitation of the second-phase particles, and also cause the intermetallic compound layer to crush and fracture, thereby enhancing the coordinated deformation ability at the interface. If the cold rolling rate is less than 20%, the refinement of the second-phase particles will be insufficient; if the cold rolling rate is too high, the copper alloy layer and the aluminum layer cannot be coordinated and extended, and the interface is prone to mutual rubbing, leading to a decrease in interfacial bonding strength and the appearance of serrated cracks at the edges, affecting the forming quality of the strip.

[0023] Preferably, the above-mentioned intermediate annealing → cold rolling process can be carried out in multiple cycles as needed. More preferably, multiple precision rolling is carried out before pre-forming annealing to obtain the required composite strip thickness, and the rolling reduction rate of each pass is controlled to be below 15%.

[0024] Pre-forming annealing: The annealing temperature for pre-forming annealing is 300–400℃, the holding time is 30–90 min, and the cooling rate after holding is 5–60℃ / min. The purpose of pre-forming annealing is to regulate the final microstructure of the intermetallic compound layer and the copper alloy layer. By pre-forming annealing the composite strip, the interdiffusion of copper and aluminum atoms is accelerated, promoting the formation of an intermetallic compound layer with a suitable concentration gradient, improving the bonding strength of the interface, and ensuring a stable bond between the copper alloy layer and the aluminum layer. In addition, pre-forming annealing of the composite strip can effectively eliminate residual stress generated by rolling, thereby improving the high-temperature heat resistance, strength, and electrical conductivity of the composite strip. Preferably, in order to control the oxygen content at the interface of the composite strip, pre-forming annealing is preferably carried out under the protection of an inert gas or reducing atmosphere.

[0025] Controlling the rolling parameters of each pass alone has a limited impact on the microstructure of aluminum-copper composite strip. Only through the synergistic coordination of process parameters can the microstructure of the composite strip be optimized to the maximum extent, resulting in aluminum-copper composite strip with high interfacial bonding strength and excellent comprehensive performance, and achieving a good match between its strength, conductivity, thermal stress relaxation resistance and bending performance.

[0026] Compared with the prior art, the present invention has the following advantages: By controlling the microstructure of the copper alloy layer and the intermetallic compound layer in the aluminum-copper composite strip, the present invention achieves a good match between strength, conductivity, thermal stress relaxation performance and bending performance, resulting in excellent comprehensive performance. The conductivity of the copper alloy layer is above 40% IACS, the yield strength is above 500MPa, and the thermal stress relaxation rate after exposure at 130℃ for 1000h is ≥70%. The side curvature of the aluminum-copper composite strip is below 3mm / m, the 90° bend R / t at the interface between the aluminum layer and the copper alloy layer on one side of the width direction is ≤1, and the 90° bend R / t at the long centerline of the surface of the aluminum layer is ≤1. It is suitable for applications such as automotive wiring harness connection terminals where the comprehensive performance of materials is required. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the cross-section of the aluminum-copper composite strip sample prepared in Example 1, perpendicular to the rolling direction.

[0028] Figure 2 for Figure 1 Enlarged view of point A in the middle;

[0029] Figure 3 This is an electron microscope image of a cross-section perpendicular to the rolling direction of the aluminum-copper composite strip sample prepared in Example 1. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0031] Using precipitation-reinforced copper-nickel alloy plates and aluminum strips as raw materials for the copper alloy layer and aluminum layer respectively, aluminum-copper composite strips were prepared using the materials and process parameters of Examples 1-3 and Comparative Examples 1-3 in Table 1. The strips were then processed into aluminum-copper composite strip samples with a thickness of 0.3 mm. The process flow for preparing the aluminum-copper composite strips includes: grooving → surface cleaning → composite rolling → intermediate annealing → cold rolling → pre-forming annealing → slitting → packaging, as detailed below:

[0032] Grooving: Grooving is performed in the precipitation-strengthened copper-nickel alloy plate to obtain a precipitation-strengthened copper-nickel alloy plate with embedded grooves;

[0033] Surface cleaning: The precipitation-strengthened copper-nickel alloy plate and aluminum strip with embedded grooves are cleaned, and then the aluminum strip is embedded in the embedded groove of the precipitation-strengthened copper-nickel alloy plate to obtain the semi-finished aluminum-copper composite strip.

[0034] Composite rolling: The semi-finished aluminum-copper composite strip is composite rolled by hot rolling. The initial rolling temperature is 400-550℃, the final rolling temperature is >350℃, the total processing rate of hot rolling is 40-90%, and the cooling rate after hot rolling is ≥30℃ / s.

[0035] Intermediate annealing: The annealing temperature for intermediate annealing is 350–550℃, and the holding time is 5–60 min;

[0036] Cold rolling: The processing rate of cold rolling is 20-40%, and the rolling speed is not greater than 30cm / s;

[0037] Pre-forming annealing: The annealing temperature for pre-forming annealing is 300-400℃, the holding time is 30-90min, and the cooling rate after holding is 5-60℃ / min.

[0038] For the aluminum-copper composite strip samples of Examples 1-3 and Comparative Examples 1-3, the characteristics were evaluated under the following conditions. Specifically, the copper alloy layer without the aluminum composite layer was cut from the aluminum-copper composite strip sample, and tests were performed on conductivity, yield strength, and resistance to thermal stress relaxation. Side bending and bending performance were also tested. The test results are shown in Tables 2 and 3. A schematic diagram of the cross-section perpendicular to the rolling direction of the aluminum-copper composite strip sample prepared in Example 1 is shown below. Figure 1 See electron microscope images Figure 3 . Figures 1-3In the diagram, 1 is a copper alloy layer, 2 is an aluminum layer, 3 is an intermetallic compound layer, 31 is the first diffusion layer, 32 is the second diffusion layer, 33 is the third diffusion layer, and 34 is the surface layer of the copper alloy layer 1 closest to the intermetallic compound layer 3. Figure 1 As shown, the aluminum-copper composite strip includes a copper alloy layer 1, an aluminum layer 2, and an intermetallic compound layer 3. The aluminum layer 2 is embedded in the copper alloy layer 1, and the intermetallic compound layer 3 is located between the copper alloy layer 1 and the aluminum layer 2. The copper alloy layer 1 is a precipitation-strengthened copper-nickel alloy. The intermetallic compound layer 3 is composed of a first diffusion layer 31, a second diffusion layer 32, and a third diffusion layer 33 stacked together. The first diffusion layer 31 is connected to the copper alloy layer 1, and the second diffusion layer 32 is connected to the aluminum layer 2. The first diffusion layer 31 contains Cu9Al4 intermetallic compound, and the second diffusion layer 32 contains CuAl2 intermetallic compound.

[0039] Microstructure observation: A cross-section of the composite strip perpendicular to the rolling direction was selected. The microstructure of the copper alloy layer and the intermetallic compound layer in the width direction was observed under scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron probe microanalysis. TEM was used to observe and statistically analyze the size of the second-phase particles in the copper alloy layer. SEM was used to observe the microstructure and thickness of the aluminum-copper composite strip. SEM equipped with an energy dispersive spectroscopy (EDS) instrument was used to perform energy dispersive spectroscopy analysis on the intermetallic compound layer in the width direction of the composite strip to obtain the mass fraction variation curve of Al elemental composition. The Al concentration gradient was calculated by fitting the data. The distribution of the Al concentration gradient in the intermetallic compound layer and the resulting interface products were analyzed. The thickness of the second diffusion layer was measured at three locations within the same field of view, and the average value was taken as the thickness of the second diffusion layer. Electron probe microanalysis was used to measure and analyze the Al concentration at a distance of 10 μm from the interface between the copper alloy layer and the first diffusion layer along the thickness direction of the copper alloy layer, according to GB / T 15074-2025 General Rules for Electron Probe Quantitative Analysis.

[0040] Conductivity: Conductivity was tested in accordance with GB / T 32971-2016 "Eddy Current Test Method for Conductivity of Copper and Copper Alloys".

[0041] Yield strength: The yield strength was tested on an electronic universal mechanical performance testing machine in accordance with GB / T 228.1-2024 Metallic materials, tensile testing - Part 1: Test method at room temperature.

[0042] Thermal stress relaxation performance: Samples of copper alloy strips were taken along the rolling direction, with each sample being a 10mm wide strip. One end of the strip was then fixed to a test fixture, and a stress was applied to the other end, causing the strip to bend and form a cantilever beam. The stress on the cantilever beam can be calculated using the following formula: 6Etδ / L 2Where E is the Young's modulus of elasticity of the copper alloy strip, t is the thickness of the copper alloy strip, δ is the deflection of the copper alloy strip, and L is the length of the cantilever beam. The magnitude of the applied stress can be changed by altering the deflection and fixing other parameters. The test stress is 80% of the yield strength. After holding the load in an oven at 130℃ for 1000 hours, the applied stress is removed. At this point, the cantilever beam will undergo permanent bending. The bending height divided by the initial deflection is the thermal stress relaxation rate, expressed as a percentage. (100% - thermal stress relaxation rate) is the thermal stress relaxation rate of the material, expressed as a percentage.

[0043] Side curvature: The side curvature test shall be conducted in accordance with the 6.5 side curvature test of GB / T 26303.3-2010 Copper and Copper Alloy Processed Materials - Dimensional Inspection Method - Part 3: Sheet and Strip Materials. Take a strip with a length greater than 1000mm, place it flat on the inspection platform, place a 1000mm long straight ruler against the side of the strip, and use another straight ruler to measure the maximum distance between the side of the strip and the side of the straight ruler.

[0044] Bending performance: In accordance with GB / T 232-2024 Metallic Materials Bending Test Method, a 90° bending test in the Bad Way direction was conducted at the interface between the aluminum layer and the copper alloy layer on one side of the width direction and at the long centerline of the aluminum layer surface. The bending performance was expressed as the minimum bending radius / plate thickness (R / t) that did not produce surface cracks. R / t≤1 was judged as qualified, and otherwise, it was judged as unqualified.

[0045] As shown in Tables 2 and 3, this invention achieves a good balance of strength, conductivity, thermal stress relaxation resistance, and bending performance by controlling the microstructure of the copper alloy layer and the intermetallic compound layer in the aluminum-copper composite strip. Its comprehensive performance is excellent; the conductivity of the copper alloy layer is above 40% IACS, the yield strength is above 500 MPa, and the thermal stress relaxation rate after exposure at 130℃ for 1000 hours is ≥70%. The side curvature of this aluminum-copper composite strip is below 3 mm / m, and the interface between the aluminum layer and the copper alloy layer on one side of the width direction (i.e.,...) Figure 1 The straight line indicated by the arrow at point B in the diagram is affected by the viewing angle shown. Figure 1 For a 90° bend (shown as a point in the image), R / t ≤ 1, at the long centerline of the aluminum layer surface (i.e., Figure 1 The straight line indicated by the arrow at point C in the diagram is affected by the viewing angle shown. Figure 1 The 90° bend R / t≤1 (shown as a point in the image) can meet the application requirements of automotive wiring harness connection terminals and other occasions with high requirements for the comprehensive performance of materials.

[0046] In Comparative Example 1, the copper alloy layer is T2 pure copper. The microstructure of the copper alloy layer does not contain second-phase particles. The thickness of the second diffusion layer, the thickness ratio of the aluminum layer, and the gradient concentration of Al in the intermetallic compound layer in the composite strip all exceed the design range of this invention. The yield strength, side curvature, the interface between the aluminum layer and the copper alloy layer on one side of the width direction, and the 90° bending performance at the long centerline of the surface of the aluminum layer do not meet the requirements.

[0047] Compared with the preparation method of Example 1, the preparation method of Comparative Example 2 is different in that the final rolling temperature of Comparative Example 2 is too low. The size of the second phase particles and the distribution density of fine second phase particles in the prepared composite strip sample are significantly different from those of Example 1. The thickness of the second diffusion layer and the thickness of the surface layer on the side of the copper alloy layer near the intermetallic compound layer exceed the design range of this invention. Its conductivity, yield strength, thermal stress relaxation performance, side curvature, and 90° bending performance at the interface between the aluminum layer and the copper alloy layer in the width direction do not meet the requirements.

[0048] Compared with the preparation method of Example 1, the preparation method of Comparative Example 3 is different in that the pre-annealing temperature of Comparative Example 3 is too high. The distribution density of fine second phase particles in the prepared composite strip sample is significantly different from that of Example 1. The thickness of its second diffusion layer and the thickness of the surface layer on the side of the copper alloy layer near the intermetallic compound layer exceed the design range of this invention. The conductivity, strength, thermal stress relaxation performance, side curvature, the interface between the aluminum layer and the copper alloy layer on one side of the width direction, and the 90° bending performance at the long centerline of the surface of the aluminum layer do not meet the requirements.

[0049] Table 1. Composite strip materials and key process parameters of the examples and comparative examples.

[0050] Table 2. Microstructure of composite strips in the examples and comparative examples.

[0051]

[0052] Table 3 Performance of composite strips in the examples and comparative examples

[0053]

Claims

1. An aluminum-copper composite strip, characterized in that, The aluminum-copper composite strip comprises a copper alloy layer, an aluminum material layer, and an intermetallic compound layer. The aluminum material layer is embedded in the copper alloy layer, and the intermetallic compound layer is located between the copper alloy layer and the aluminum material layer. The copper alloy layer is a precipitation-strengthened copper-nickel alloy, and the average particle size of the second phase particles in the copper alloy layer is ≤20nm. The intermetallic compound layer consists of a stacked first diffusion layer and a second diffusion layer. The first diffusion layer is connected to the copper alloy layer, and the second diffusion layer is connected to the aluminum 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.

2. The aluminum-copper composite strip according to claim 1, characterized in that, A third diffusion layer is formed between the first diffusion layer and the second diffusion layer, and the third diffusion layer contains a CuAl intermetallic compound.

3. The aluminum-copper composite strip according to claim 1, characterized in that, The number density of second-phase particles with a particle size of 5–15 nm in the copper alloy layer is 3 × 10⁻⁶. 7 pcs / mm 2 above.

4. The aluminum-copper composite strip according to claim 1, characterized in that, The total thickness of the aluminum-copper composite strip is 0.1 to 0.8 mm, and the thickness of the aluminum layer accounts for 5 to 40% of the total thickness of the aluminum-copper composite strip.

5. The aluminum-copper composite strip according to claim 1, characterized in that, Along the thickness direction of the intermetallic compound layer, from the first diffusion layer to the second diffusion layer, the Al concentration in the intermetallic compound layer forms a gradient concentration of 10 to 75 wt% / μm.

6. The aluminum-copper composite strip according to claim 1, characterized in that, Within the copper alloy layer, the Al concentration at a distance of 10 μm from the interface between the copper alloy layer and the first diffusion layer along the thickness direction of the copper alloy layer is no higher than 0.05 wt%.

7. The aluminum-copper composite strip according to claim 1, characterized in that, The aluminum layer is made of 1-series aluminum alloy, 3-series aluminum alloy, 6-series aluminum alloy, or 8-series aluminum alloy.

8. The aluminum-copper composite strip according to claim 1, characterized in that, The copper alloy layer has a conductivity of ≥40% IACS, a yield strength of ≥500MPa, and a thermal stress relaxation rate ≥70% after exposure at 130℃ for 1000h; the side curvature of the aluminum-copper composite strip is ≤3mm / m, the 90° bend R / t at the interface between the aluminum layer and the copper alloy layer on one side of the width direction is ≤1, and the 90° bend R / t at the long centerline of the surface of the aluminum layer is ≤1.

9. A method for preparing the aluminum-copper composite strip according to any one of claims 1 to 8, characterized in that, The process flow of this preparation method includes: grooving → surface cleaning → composite rolling → intermediate annealing → cold rolling → pre-forming annealing → slitting → packaging. The composite rolling includes hot rolling, the final rolling temperature of the hot rolling is >350℃, the total processing rate of the hot rolling is 40-90%, and the cooling rate after the hot rolling is ≥30℃ / s.

10. The method for preparing the aluminum-copper composite strip according to claim 9, characterized in that, The annealing temperature for pre-annealing is 300-400℃, the holding time is 30-90 min, and the cooling rate after holding is 5-60℃ / min.

11. The method for preparing the aluminum-copper composite strip according to claim 9, characterized in that, The cold rolling process has a processing rate of 20% to 40%.

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