Composite strips, their preparation methods and applications

Abstract

This application relates to composite strips, their preparation methods, and applications. The composite strip of this application includes a first copper layer and an aluminum layer; the first copper layer covers the surface of the aluminum layer; the thickness ratio of the first copper layer to the aluminum layer is 1:(2~10); the thickness of the first copper layer is less than or equal to 25 μm.

Description

Technical Field

[0001] This application relates to the field of composite materials technology, and in particular to composite strips, their preparation methods, and applications. Background Technology

[0002] Copper-aluminum-copper layered composite materials combine the excellent electrical and thermal conductivity, corrosion resistance, and weldability of copper with the lightweight and low-cost advantages of aluminum, making them widely used in electronics, lithium battery connectors, automotive wiring harnesses, and heat dissipation devices. With the miniaturization and lightweighting of devices, the thickness of the copper layer in composite strips needs to be increasingly reduced to further decrease weight and cost. However, copper and aluminum have significantly different plastic deformation capabilities at room temperature. During multi-pass cold rolling thinning, the aluminum layer flows easily, while the ultra-thin copper layer becomes brittle due to rapid work hardening. Under interfacial shear stress, microcracks easily initiate at weak points such as impurity points and uneven areas. These cracks tend to propagate and connect during subsequent rolling, leading to the exposure of the aluminum matrix and the formation of aluminum leakage points. Therefore, obtaining composite strips with a copper layer thickness of no more than 25 μm and without aluminum leakage remains a technical challenge in the industry. Summary of the Invention

[0003] Therefore, it is necessary to provide composite strips, their preparation methods, and applications. This application enables the production of copper-aluminum composite strips with ultra-thin copper layers, while also preventing aluminum leakage during the preparation of the composite strips.

[0004] In a first aspect, this application provides a composite strip comprising a first copper layer and an aluminum layer; the first copper layer covers the surface of the aluminum layer; the thickness ratio of the first copper layer to the aluminum layer is 1:(2~10); the thickness of the first copper layer is less than or equal to 25μm.

[0005] In some embodiments, a second copper layer is also included, the aluminum layer having a first surface and a second surface disposed opposite to each other along its thickness direction, the first surface being covered by the first copper layer and the second surface being covered by the second copper layer; the thickness of the second copper layer is less than or equal to 25 μm.

[0006] In some embodiments, the thickness ratio of the first copper layer to the second copper layer is 1:(0.5~2).

[0007] In some embodiments, the first copper layer and the second copper layer are brass, and the thickness of the first copper layer and the second copper layer is 15μm to 25μm.

[0008] In some embodiments, both the first copper layer and the second copper layer are made of pure copper, and the thickness of the first copper layer and the second copper layer is 10μm to 20μm.

[0009] Secondly, this application provides a method for preparing a composite strip, comprising the following steps:

[0010] The first copper material and the aluminum material are stacked and then subjected to first rolling and diffusion annealing in sequence. The temperature of the first rolling is 400℃~500℃ and the deformation of the first rolling is 40%~50%. The temperature of the diffusion annealing is 380℃~460℃ and the diffusion annealing time is 2min~30min to obtain the composite material.

[0011] The composite material is subjected to a second rolling process, wherein the second rolling is an electromagnetic induction heating temperature precision rolling process, the temperature of the second rolling is 250℃~350℃, and the second rolling includes:

[0012] The composite material is subjected to one or two first sub-rolling passes to achieve a first preset thickness for the first copper material, with each first sub-rolling pass having a deformation of 20% to 35%.

[0013] The composite material after the first sub-rolling is subjected to multiple passes of second sub-rolling, with the deformation amount of each second sub-rolling decreasing sequentially, and the deformation amount of each second sub-rolling being less than 20%, so that the first copper material reaches a second preset thickness, which is less than or equal to 25 μm.

[0014] In some embodiments, a first copper material, an aluminum material, and a second copper material are stacked sequentially and subjected to the first rolling and the diffusion annealing in sequence; the first sub-rolling causes the first copper material and the second copper material to reach a first preset thickness; the second sub-rolling causes the first copper material and the second copper material to reach a second preset thickness.

[0015] In some embodiments, the first copper material and the second copper material are brass, and the second preset thickness is 15μm~25μm.

[0016] In some embodiments, the first copper material and the second copper material are copper, and the second preset thickness is 10μm~20μm.

[0017] In some embodiments, the ratio of the first preset thickness to the second preset thickness is 1:(1.1~1.3).

[0018] In some embodiments, the second rolling process further includes: annealing the second rolled composite material at a temperature of 320°C to 420°C for 1 min to 10 min.

[0019] In some embodiments, the process includes, before sequentially stacking the first copper material, the aluminum material, and the second copper material, the following:

[0020] The mating surfaces of the first copper material, the aluminum material, and the second copper material are roughened to achieve a surface roughness Ra of 1 μm to 6 μm.

[0021] In some embodiments, the mating surfaces of the first copper material, the aluminum material, and the second copper material are roughened using a wire brush and abrasive putty; the wire diameter of the wire brush is 0.08mm~0.12mm; the abrasive putty includes a plastic matrix and silicon carbide abrasive.

[0022] In some embodiments, before the second rolling of the composite material, the process further includes: performing rough rolling and intermediate annealing on the composite material in sequence; the intermediate annealing temperature is 400℃~450℃, and the intermediate annealing holding time is 5min~20min.

[0023] Thirdly, this application provides an LED bracket comprising the composite strip described in any one of the above-mentioned methods, or the composite strip prepared by the method described in any one of the above-mentioned methods.

[0024] The composite strip in this application embodiment, by reasonably allocating the thickness ratio of the aluminum layer and the copper layer, not only ensures the core functional requirements of the aluminum layer, but also ensures that the outer copper layer has sufficient coverage and structural strength, providing a basic structural guarantee to avoid aluminum leakage. At the same time, it precisely controls the finished thickness of the single layer of outer copper, reducing the amount of copper used and controlling production costs while ensuring that the copper layer is intact and undamaged, thus eliminating aluminum leakage defects caused by the copper layer being too thin or damaged.

[0025] In the method for preparing the composite strip according to this application embodiment, the temperature of the first rolling is 400℃~500℃, and the deformation amount of the first rolling is 40%~50%. At this temperature, the deformation resistance of the material is reduced, allowing copper and aluminum to interlock in a softer state. At the same time, the appropriate deformation amount ensures sufficient initial bonding strength and significantly reduces dislocation pile-up and micro-stress concentration caused by excessive deformation, creating a low-stress interface starting point for subsequent processing. Meanwhile, the diffusion annealing temperature is 380℃~460℃, and the time is 2min~30min. Annealing at this temperature allows the brass to fully recrystallize and restore its plasticity. More importantly, at the copper-aluminum interface, atoms diffuse to form a thin and continuous intermetallic compound transition layer. If this transition layer is too thick, it will be brittle. Through the temperature and time control of this application, a dense diffusion layer with a thickness of nanometer to micrometer can be formed to connect the two metals, greatly improving the interfacial bonding strength and shear resistance, making the interface less prone to separation during subsequent deformation. Furthermore, electromagnetic induction heating is used for warm precision rolling at 250℃~350℃. When the copper layer is still relatively thick, one or two large deformation passes are used, utilizing the plasticity brought about by the increased temperature to further strengthen the interface under higher stress. When the copper layer approaches the target ultra-thin thickness, the rolling mode is switched to multi-pass, small deformation. Each small deformation pass allows sufficient time for the copper and aluminum layers to flow in coordination, dispersing the interfacial shear stress and avoiding concentrated stress that could trigger cracks at local weak points in the copper layer. Maintaining the temperature keeps the copper layer in a good plastic state, making it less prone to brittleness. In other words, the composite strip preparation method of this application can overcome the problem of surface aluminum leakage when preparing composite strips with ultra-thin copper layers in traditional methods, and thus can prepare composite strips with a copper layer thickness of less than or equal to 25μm. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the surface aluminum leakage that occurs during the preparation of traditional ultrathin copper-aluminum-copper layered composite materials.

[0027] Figure 2 This is a cross-sectional schematic diagram showing aluminum leakage on the surface during the preparation of traditional ultrathin copper-aluminum-copper layered composite materials.

[0028] Figure 3 This is a schematic diagram of the structure of the composite strip provided in one embodiment of this application;

[0029] Figure 4 This is a schematic cross-sectional view of the composite strip prepared in Example 1 of this application;

[0030] Figure 5 This is a schematic diagram of the surface of the composite strip prepared in Example 1 of this application;

[0031] Figure 6This is a schematic cross-sectional view of the composite strip prepared in Example 2 of this application;

[0032] Figure 7 This is a schematic diagram of the surface of the composite strip prepared in Example 2 of this application.

[0033] Explanation of reference numerals in the attached figures:

[0034] 10 - Aluminum layer; 20 - First copper layer; 30 - Second copper layer. Detailed Implementation

[0035] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0037] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0039] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0040] Reference Figure 1 and Figure 2 As shown, Figure 1 and Figure 2 The images show a surface schematic and a cross-sectional schematic of aluminum leakage that occurs during the preparation of traditional ultrathin copper-aluminum-copper layered composite materials. The inventors discovered that when preparing composite strips with relatively thin copper layers using traditional composite strip preparation methods, the significant difference in plastic deformation capabilities between copper and aluminum at room temperature easily leads to cracks in the copper layer during rolling, exposing the aluminum matrix in the middle. This phenomenon is particularly pronounced when the copper layer thickness is reduced to below 30 μm.

[0041] Therefore, refer to Figure 3 As shown, one embodiment of this application provides a composite strip including a first copper layer 20 and an aluminum layer 10; the first copper layer 20 covers the surface of the aluminum layer 10; the thickness ratio of the first copper layer 20 to the aluminum layer 10 is 1:(2~10); the thickness of the first copper layer 20 is less than or equal to 25μm.

[0042] The composite strip in this embodiment of the application, by reasonably allocating the thickness ratio of the aluminum layer 10 and the first copper layer 20, not only ensures the core functional requirements of the aluminum layer 10, but also ensures that the outer copper layer has sufficient coverage and structural strength, providing a basic structural guarantee to avoid aluminum leakage. At the same time, it precisely controls the finished thickness of the single layer of outer copper, reducing the amount of copper used and controlling production costs, while ensuring that the copper layer is intact and undamaged, and eliminating aluminum leakage defects caused by the copper layer being too thin or damaged.

[0043] In some embodiments, a second copper layer 30 is also included, wherein the aluminum layer 10 has a first surface and a second surface disposed opposite to each other along its thickness direction, the first surface being covered by the first copper layer 20 and the second surface being covered by the second copper layer 30; the thickness of the second copper layer 30 is less than or equal to 25 μm.

[0044] In some embodiments, the thickness ratio of the first copper layer 20 to the second copper layer 30 is 1:(0.5~2).

[0045] It should be noted that the thickness ratio of the first copper layer 20, the aluminum layer 10, and the second copper layer 30 is 1:(2~10):(0.5~2), and the thicknesses of both the first copper layer 20 and the second copper layer 30 are less than or equal to 25μm, indicating a mutual matching and complementarity in process constraints. These two sets of parameters represent a strong binding relationship between process objectives and structural assurance, with mutual constraints and coordinated adaptation to the rolling process.

[0046] Copper layer thickness less than or equal to 25μm is used to reduce copper usage and control production costs. However, this process has inherent drawbacks: when the copper layer thickness is less than 30μm, due to the difference in plastic deformation capabilities between copper and aluminum, it is prone to cracking and exposing the aluminum substrate (aluminum leakage) during rolling. Simply limiting the copper layer thickness to ≤25μm cannot solve the cracking and aluminum leakage problem; a suitable thickness ratio is necessary to provide structural support. A thickness ratio of 1:(2~10):(0.5~2) provides structural stability for the ultra-thin copper layer rolling process and is crucial for its feasibility. The aluminum layer accounts for 2~10 parts: as the core support layer of the composite strip, it provides sufficient rigidity and plasticity matching for the surface thin copper layer, offsetting the deformation differences between copper and aluminum and reducing the risk of cracking during rolling and forming. The second copper layer comprises 0.5 to 2 parts: This avoids excessively thin copper layers, ensuring the coverage and structural strength of the surface copper layer and structurally preventing aluminum leakage. The total proportion of the copper layer should not exceed 3 parts, and the proportion of the aluminum layer should not be less than 2 parts. This ensures that an excessively high proportion of copper layer does not negate the cost reduction effect, and that an excessively thin aluminum layer does not compromise the core functions of lightweighting and thermal conductivity. These two sets of parameters do not exist in isolation but work together to achieve a comprehensive technical effect of preventing aluminum leakage, reducing costs, maintaining performance, and resisting molding, forming a logical closed loop of structural proportion → process adaptation → performance compliance. This ensures that during the stamping, bending, and baking processes in LED bracket fabrication, the copper layer is less prone to peeling and cracking, and the aluminum layer is not exposed. This is the molding performance advantage brought about by the synergy of the two sets of parameters.

[0047] When the thickness ratio of the first copper layer 20 to the aluminum layer 10 is too large, that is, when the thickness of the copper layer accounts for a large proportion, the cost-saving effect is not significant. When the thickness ratio of the first copper layer 20 to the aluminum layer 10 is too small, that is, when the thickness of the copper layer is too thin, the copper layer will be too thin when the overall thickness of the composite strip is thin, thereby increasing the risk of aluminum leakage.

[0048] Optionally, the thickness ratio of the first copper layer 20 to the aluminum layer 10 is 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, or the thickness ratio of the first copper layer 20 to the aluminum layer 10 can be within the range of any two of the above thickness ratios.

[0049] Optionally, the thickness ratio of the first copper layer 20 and the second copper layer 30 is 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8 or 1:2, or the thickness ratio of the first copper layer 20 and the second copper layer 30 may be within the range of any two of the above thickness ratios.

[0050] In some embodiments, the first copper layer 20 and the second copper layer 30 are brass, and the thickness of the first copper layer 20 and the second copper layer 30 is 15μm to 25μm.

[0051] Optionally, the thickness of the first copper layer 20 is 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm or 25μm, or the thickness of the first copper layer 20 may be within any two of the above thicknesses.

[0052] Optionally, the thickness of the second copper layer 30 is 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm or 25μm, or the thickness of the second copper layer 30 may be within any two of the above thicknesses.

[0053] In some embodiments, the first copper layer 20 and the second copper layer 30 are both copper, and the thickness of the first copper layer 20 and the second copper layer 30 is 10μm~20μm.

[0054] Optionally, the thickness of the first copper layer 20 is 10μm, 12μm, 14μm, 16μm, 18μm or 20μm, or the thickness of the first copper layer 20 may be within any two of the above thicknesses.

[0055] Optionally, the thickness of the second copper layer 30 is 10μm, 12μm, 14μm, 16μm, 18μm or 20μm, or the thickness of the second copper layer 30 may be within any two of the above thicknesses.

[0056] In some embodiments, the composite strip is prepared by the following composite strip preparation method:

[0057] The first copper material and aluminum material are stacked and then subjected to first rolling and diffusion annealing in sequence. The temperature of the first rolling is 400℃~500℃ and the deformation of the first rolling is 40%~50%. The temperature of the diffusion annealing is 380℃~460℃ and the diffusion annealing time is 2min~30min to obtain the composite material.

[0058] The composite material undergoes a second rolling process, which is an electromagnetic induction heating temperature finishing roll. The temperature of the second rolling process is 250℃~350℃, and the second rolling process includes:

[0059] The composite material is subjected to one or two first sub-rolling passes to achieve the first preset thickness of the copper material, with the deformation amount of each first sub-rolling pass being 20% ​​to 35%.

[0060] The composite material after the first sub-rolling is subjected to multiple passes of second sub-rolling, with the deformation amount of each second sub-rolling decreasing sequentially, and the deformation amount of each second sub-rolling being less than 20%, so that the first copper material reaches the second preset thickness, which is less than or equal to 25μm.

[0061] It is understandable that deformation refers to the change in thickness. For example, if the total thickness of the sheet before the first rolling is a, and the total thickness of the sheet after the first rolling is b, then the deformation of the first rolling is (ab) / a.

[0062] The composite strip of this application, by rationally allocating the thickness ratio of the aluminum layer 10 and the copper layer, ensures both the core functional requirements of the aluminum layer 10 and sufficient coverage and structural strength of the outer copper layer, providing a basic structural guarantee to avoid aluminum leakage. Simultaneously, it precisely controls the finished thickness of the outer copper layer, reducing copper usage and controlling production costs while ensuring the copper layer remains intact and undamaged, eliminating aluminum leakage defects caused by an excessively thin or damaged copper layer. Furthermore, this application abandons the traditional all-cold rolling process and introduces an electromagnetic induction heating temperature precision rolling process. Through active temperature field control, it achieves precise adjustment of the copper layer's plasticity. Addressing the significant difference in plasticity between copper and aluminum, it utilizes electromagnetic induction heating technology to precisely control the rolling temperature, optimizing the plastic state of the copper layer. This allows the copper-aluminum bimetallic layer to achieve good plasticity matching during rolling, enabling coordinated deformation and preventing copper layer cracking and aluminum layer 10 overflow caused by plasticity mismatch, further eliminating aluminum leakage defects.

[0063] Another embodiment of this application provides a method for preparing a composite strip, comprising the following steps:

[0064] The first copper material and aluminum material are stacked and then subjected to first rolling and diffusion annealing in sequence. The temperature of the first rolling is 400℃~500℃ and the deformation of the first rolling is 40%~50%. The temperature of the diffusion annealing is 380℃~460℃ and the diffusion annealing time is 2min~30min to obtain the composite material.

[0065] The composite material undergoes a second rolling process, which is an electromagnetic induction heating temperature finishing roll. The temperature of the second rolling process is 250℃~350℃, and the second rolling process includes:

[0066] The composite material is subjected to one or two first sub-rolling passes to achieve the first preset thickness of the copper material, with the deformation amount of each first sub-rolling pass being 20% ​​to 35%.

[0067] The composite material after the first sub-rolling is subjected to multiple passes of second sub-rolling, with the deformation amount of each second sub-rolling decreasing sequentially, and the deformation amount of each second sub-rolling being less than 20%, so that the first copper material reaches the second preset thickness, which is less than or equal to 25μm.

[0068] In the method for preparing the composite strip according to this application embodiment, the temperature of the first rolling is 400℃~500℃, and the deformation amount of the first rolling is 40%~50%. At this temperature, the deformation resistance of the material is reduced, allowing copper and aluminum to interlock in a softer state. At the same time, the appropriate deformation amount ensures sufficient initial bonding strength and significantly reduces dislocation pile-up and micro-stress concentration caused by excessive deformation, creating a low-stress interface starting point for subsequent processing. Meanwhile, the diffusion annealing temperature is 380℃~460℃, and the time is 2min~30min. Annealing at this temperature allows the brass to fully recrystallize and restore its plasticity. More importantly, at the copper-aluminum interface, atoms diffuse to form a thin and continuous intermetallic compound transition layer. If this transition layer is too thick, it will be brittle. Through the temperature and time control of this application, a dense diffusion layer with a thickness of nanometer to micrometer can be formed to connect the two metals, greatly improving the interfacial bonding strength and shear resistance, making the interface less prone to separation during subsequent deformation. Furthermore, electromagnetic induction heating is used for warm precision rolling at 250℃~350℃. When the copper layer is still relatively thick, one or two large deformation passes are used, utilizing the plasticity brought about by the increased temperature to further strengthen the interface under higher stress. When the copper layer approaches the target ultra-thin thickness, the rolling mode is switched to multi-pass, small deformation. Each small deformation pass allows the copper and aluminum layers 10 seconds for coordinated flow, dispersing the interfacial shear stress and avoiding concentrated stress at local weak points in the copper layer that could trigger cracks. Maintaining the temperature keeps the copper layer in a good plastic state, making it less prone to brittleness. In other words, the composite strip preparation method of this application can overcome the problem of surface aluminum leakage when preparing composite strips with ultra-thin copper layers in traditional methods, and thus can prepare composite strips with a copper layer thickness of less than or equal to 25μm.

[0069] Optionally, the temperature of the first rolling process is 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, or 500°C, or the temperature of the first rolling process may be within the range of any two of the above temperatures.

[0070] Optionally, the deformation amount of the first rolling is 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%, or the deformation amount of the first rolling can be within the range of any two of the above deformation amounts.

[0071] Optionally, the diffusion annealing temperature is 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, or 460°C, or the diffusion annealing temperature may be within any two of the above temperatures.

[0072] Optionally, the diffusion annealing time can be 2 min, 2 min, 10 min, 15 min, 20 min, 25 min, or 30 min, or the diffusion annealing time can be within any two of the above times.

[0073] Optionally, the temperature of the second rolling process is 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, or 350°C, or the temperature of the second rolling process may be within the range of any two of the above temperatures.

[0074] Optionally, the deformation amount of each first sub-roll is 20%, 22%, 25%, 28%, 30%, 32% or 35%, or the deformation amount of each first sub-roll can be within the range of any two of the above deformation amounts.

[0075] Optionally, the deformation amount of each second sub-roll is 0.1% to 20%. More preferably, the deformation amount of each second sub-roll is 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18% or 20%. Alternatively, the deformation amount of each second sub-roll can be within the range of any two of the above deformation amounts.

[0076] It is understood that all annealing steps in this application are performed in a protective gas atmosphere. For example, they are performed in a nitrogen or argon atmosphere.

[0077] In some embodiments, a first copper material, an aluminum material, and a second copper material are stacked sequentially and subjected to a first rolling and diffusion annealing in sequence; the first sub-rolling makes the first copper material and the second copper material reach a first preset thickness; the second sub-rolling makes the first copper material and the second copper material reach a second preset thickness.

[0078] In some embodiments, the ratio of the first preset thickness to the second preset thickness is 1:(1.1~1.3).

[0079] Optionally, the ratio of the first preset thickness to the second preset thickness is 1:1.1, 1:1.12, 1:1.15, 1:1.18, 1:1.2, 1:1.22, 1:1.25, 1:1.28 or 1:1.3, or the ratio of the first preset thickness to the second preset thickness may be within the range of any two of the above ratios.

[0080] In some embodiments, the first and second copper materials are brass, and the second preset thickness is 15μm to 25μm.

[0081] Optionally, the second preset thickness is 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm or 25μm, or the second preset thickness may be within the range of any two of the above thicknesses.

[0082] In some embodiments, the first and second copper materials are copper, and the second preset thickness is 10μm to 20μm.

[0083] Optionally, the second preset thickness is 10μm, 12μm, 14μm, 16μm, 18μm or 20μm, or the second preset thickness may be within the range of any two of the above thicknesses.

[0084] In some embodiments, the second rolling process further includes: annealing the second rolled composite material at a temperature of 320°C to 420°C for 1 min to 10 min.

[0085] Optionally, the annealing temperature of the finished product is 320°C, 340°C, 360°C, 380°C, 400°C or 420°C, or the annealing temperature of the finished product can be within the range of any two of the above temperatures.

[0086] Optionally, the annealing time of the finished product is 1 min, 2 min, 4 min, 5 min, 6 min, 8 min or 10 min, or the annealing time of the finished product can be within any two of the above times.

[0087] In some embodiments, the process includes, before sequentially stacking the first copper material, the aluminum material, and the second copper material, the following:

[0088] The mating surfaces of the first copper material, aluminum material, and second copper material are roughened to achieve a surface roughness Ra of 1μm to 6μm.

[0089] In some embodiments, the mating surfaces of the first copper material, the aluminum material, and the second copper material are roughened using a wire brush and abrasive putty; the wire diameter of the wire brush is 0.08mm~0.12mm; the abrasive putty includes a plastic matrix and silicon carbide abrasive.

[0090] Using an ultra-fine steel wire brush with a wire diameter of 0.08mm~0.12mm combined with an abrasive brush to roughen the bonding surfaces of the first copper, aluminum, and second copper materials results in a more uniform and delicate surface. This replaces the traditional coarse steel wire brush, creating fine, uniform, and shallow scratches on the surface. This increases the bonding surface area, promotes mechanical interlocking, and avoids the formation of excessively deep grooves that could easily become crack initiations.

[0091] Optionally, the roughness Ra of the mating surface is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or 6 μm, or the roughness Ra of the mating surface may be within the range of any two of the above roughnesses.

[0092] Optionally, the wire diameter of the wire brush is 0.08mm, 0.09mm, 0.1mm, 0.11mm or 0.12mm, or the wire diameter can be within any two of the above ranges.

[0093] In some embodiments, before the second rolling of the composite material, the process further includes: rough rolling and intermediate annealing of the composite material in sequence; the intermediate annealing temperature is 400°C to 450°C, and the intermediate annealing holding time is 5 min to 20 min.

[0094] Optionally, the intermediate annealing temperature is 400°C, 410°C, 420°C, 430°C, 440°C, or 450°C, or the intermediate annealing temperature can be within any two of the above temperatures.

[0095] Optionally, the holding time for intermediate annealing is 5 min, 8 min, 10 min, 12 min, 15 min, 18 min or 20 min, or the holding time for intermediate annealing can be within any two of the above times.

[0096] In some embodiments, intermediate annealing is performed in a nitrogen and / or argon atmosphere.

[0097] Compared with traditional technologies, this application can achieve the following technical effects:

[0098] (1) It can achieve a breakthrough in product performance, pushing the lower limit of copper layer thickness that can be stably mass-produced to nearly 10μm for red copper and nearly 15μm for brass, with an aluminum leakage defect rate close to zero. This expands the application range of composite materials in ultra-thin and miniaturized devices, and achieves the goal of cost reduction and copper saving with aluminum.

[0099] (2) A systematic solution is proposed: The preparation method of the composite strip in this application is not a single process improvement, but a complete anti-cracking technology system from interface creation to deformation synergy is constructed. There is a significant synergistic enhancement effect between each step, such as fine hairization to reduce stress source, warm composite to reduce initial stress, diffusion annealing to enhance interface, and warm precision rolling to synergistically deform, which together solve the problem of coordinated deformation of ultrathin copper layers.

[0100] (3) Balancing quality and efficiency: While ensuring an ultra-high yield, this application reduces work hardening and rolling force through warm rolling, thus saving energy. The diffusion annealing process effectively inhibits the excessive growth of brittle intermetallic compounds while ensuring bonding strength.

[0101] (4) Synergistic control of interface microstructure: Through a combination of fine and uniform texturing, mild and stable composite and fully diffusion annealing, an ideal initial interface with no major stress concentration, sufficient metallurgical bonding and able to withstand severe subsequent deformation is constructed.

[0102] (5) Active management of deformation process: abandoning the whole process of cold rolling, introducing electromagnetic induction heating temperature precision rolling process, actively controlling the plasticity of copper layer through temperature field, so that copper layer and aluminum layer 10 are in harmony in terms of softness and hardness during rolling process, and achieving coordinated deformation.

[0103] (6) The technology is quantifiable and controllable: All key process parameters, such as texturing Ra, warm composite temperature and deformation amount, annealing regime, warm finishing temperature and deformation amount per pass, are clear and quantifiable, making it easy to achieve precise control and automation in production, and have industrialization promotion value.

[0104] The following are specific examples:

[0105] Example 1

[0106] The composite strip prepared in Example 1 is: H68 brass (25μm) - 3003 aluminum alloy (200μm) - H68 brass (25μm) composite strip.

[0107] Raw materials: H68-O state brass strip, initial thickness 0.5mm; 3003-O state aluminum strip, initial thickness 2.0mm. Target total thickness 0.25mm, layer thickness ratio 1:8:1.

[0108] Preparation method of composite strip:

[0109] (1) Texturing: Using a steel wire brush with a wire diameter of 0.1 mm, the surface roughness of the copper and aluminum strips after texturing is Ra=3.5μm.

[0110] (2) Warm rolling composite: The billet is heated to 480°C and rolled in one pass to a total thickness of 1.25 mm with a deformation of 50%.

[0111] (3) Diffusion annealing: Hold at 380℃ for 13 min under nitrogen atmosphere.

[0112] (4) Rough rolling and intermediate annealing: cold rolling to 0.45 mm, intermediate annealing, and holding at 420℃ for 12 min in a nitrogen atmosphere.

[0113] (5) Warm finishing rolling:

[0114] First pass: Electromagnetic induction heating to 320℃, rolled to 0.35mm, deformation 22%;

[0115] Second to fifth passes: Maintain 250℃~300℃ and roll to the following thicknesses in sequence: 0.29mm, 17% deformation, 0.26mm, 10% deformation, 0.252mm, 3% deformation, 0.250mm, and 0.8% deformation.

[0116] Reference Figure 4 , Figure 5 As shown, in Example 1, after cleaning, annealing, straightening, and passivation, the thickness of the brass monolayer is approximately 25 μm. No aluminum leakage points were observed by the naked eye and under a microscope.

[0117] Example 2

[0118] The composite strip prepared in Example 2 is: T2 copper (12μm)-1060 aluminum (96μm)-T2 copper (12μm) composite strip.

[0119] Preparation method of composite strip:

[0120] The preparation method of the composite strip in Example 2 is roughly the same as that in Example 1. The main parameters are adjusted as follows: the temperature of warm rolling composite is 420°C, the diffusion annealing temperature is 360°C, the time is 15 min, and the warm finishing rolling adopts more small deformation passes, rolling from 0.3 mm to 0.12 mm in 8 passes.

[0121] Reference Figure 6 , Figure 7 As shown, in Example 2, the final copper layer thickness in the finished product is approximately 12 μm, with no aluminum leakage.

[0122] Example 3

[0123] The composite strip prepared in Example 3 is: H70 brass (20μm) - 5052 aluminum alloy (120μm) - H70 brass (20μm) composite strip.

[0124] Raw materials: H70-O brass strip, initial thickness 0.3mm; 5052-O aluminum strip, initial thickness 1.2mm. Target total thickness 0.16mm, layer thickness ratio 1:6:1.

[0125] Preparation method of composite strip:

[0126] (1) Roughening: Use a steel wire brush with a wire diameter of 0.08 mm. After roughening, the surface roughness Ra = 2.0 μm.

[0127] (2) Warm rolling composite: The billet is heated to 450°C and rolled in one pass to a total thickness of 0.75 mm with a deformation of 50%.

[0128] (3) Diffusion annealing: Hold at 400℃ for 8 minutes under an argon atmosphere.

[0129] (4) Rough rolling and intermediate annealing: Rough rolling and intermediate annealing: Cold rolling to 0.30 mm, intermediate annealing, and holding at 400℃ for 20 min in a nitrogen atmosphere.

[0130] (5) Warm finishing rolling:

[0131] The material is heated to 250-320℃ by electromagnetic induction and then rolled. Rolling process: 0.30mm → 0.24mm (deformation 20%) → 0.20mm (deformation 17%) → 0.18mm (deformation 10%) → 0.165mm (deformation 8.3%) → 0.160mm (deformation 3.0%).

[0132] In Example 3, the thickness of the brass single layer in the finished product is about 20 μm. Visual inspection showed no aluminum leakage in the entire roll. Further testing with a helium mass spectrometer revealed good interface sealing and no visible aluminum leakage points on the surface. Metallographic microscopy revealed no cracks on the copper layer surface and good interface bonding.

[0133] Comparative Example 1

[0134] The preparation target is the same as in Example 1 (H68 brass 25μm / layer).

[0135] The preparation method of the composite strip in Comparative Example 1 is roughly the same as that in Example 1. The main parameters are adjusted as follows: a traditional steel wire brush with a wire diameter of 0.30 mm is used for texturing. After texturing, the surface roughness Ra>8μm, and the grooves are deep and uneven.

[0136] Results: When the strip was warm-rolled to a thickness of approximately 0.3 mm (corresponding to a copper layer thickness of ~30 μm), sporadic bright white dot-like aluminum leaks began to appear on the surface. The density of aluminum leaks in the finished product reached 5-8 per square meter. Metallographic analysis showed that the aluminum leaks all originated from the bottom of the coarse roughened grooves and expanded into cracks under rolling stress. This proves that even with subsequent process optimization, the rough initial interface remains a weak point.

[0137] Comparative Example 2

[0138] The preparation target is the same as in Example 2 (T2 copper 12μm / layer).

[0139] The preparation method of the composite strip in Comparative Example 2 is roughly the same as that in Example 2, with the main parameters adjusted as follows: traditional large deformation room temperature composite is adopted: the billet is not heated, the deformation of one rolling pass is 65%, and only simple low temperature stress relief annealing (250°C, 1 hour) is performed.

[0140] Results: Localized interfacial cracking occurred during the rough rolling stage. In the finish rolling stage, when the copper layer reached approximately 20 μm, large-area, strip-shaped aluminum leakage distributed along the rolling direction appeared. Interfacial bond strength tests showed severe delamination after bending and fracture.

[0141] Analysis: Large deformation at room temperature resulted in significant residual stress at the interface; the lack of sufficient diffusion annealing meant the interface was only mechanically engaged, failing to form a strong metallurgical bond. During subsequent deformation, the interface preferentially separated, leading to tearing of the copper layer.

[0142] Comparative Example 3

[0143] The preparation target is the same as in Example 3 (H70 brass 20μm / layer).

[0144] The preparation method of the composite strip in Comparative Example 3 is roughly the same as that in Example 3, with the main parameters adjusted as follows: the finishing rolling stage is changed to full-process room temperature cold rolling, and the conventional large-pass deformation strategy is adopted: 0.30mm → 0.22mm (deformation amount 27%) → 0.17mm (deformation amount 23%) → 0.16mm (deformation amount 6%).

[0145] result:

[0146] Microcracks appeared at the edge of the strip after the second finishing pass (0.22mm). The surface of the finished product had a large number of small, dense aluminum leakage points, which were distributed in a star-like pattern, with a density of more than 20 aluminum leakage points per square meter.

[0147] Microscopic analysis revealed obvious transverse microcracks in the brass layer, through which the aluminum layer 10 was extruded. This is because brass undergoes severe work hardening at room temperature, resulting in poor plasticity. The stress generated by multiple deformations cannot be released through coordinated deformation, directly leading to cracking of the brittle, ultra-thin copper layer.

[0148] Comparative Example 4

[0149] The composite material and its preparation method in Comparative Example 4 are basically the same as those in Example 1, except that the layer thickness ratio is 1:1:1.

[0150] In Comparative Example 4, the aluminum layer 10 has a small thickness in the composite material, which does not provide an advantage in saving costs.

[0151] Comparative Example 5

[0152] The composite material and its preparation method in Comparative Example 5 are basically the same as those in Example 1, except that the layer thickness ratio is 1:15:1.

[0153] In Comparative Example 5, the copper layer accounts for too small a proportion of the composite material thickness, meaning the copper layer is too thin. This results in poor copper-aluminum co-deformation capability, leading to a higher risk of aluminum leakage when preparing composite materials with a relatively thin overall thickness, making it difficult to control the aluminum leakage problem.

[0154] Comparative Example 6

[0155] The composite material and its preparation method in Comparative Example 6 are basically the same as those in Example 1, except that the layer thickness ratio is 1:6:0.25.

[0156] In Comparative Example 6, one of the copper layers was too thin, which could easily lead to aluminum leakage. At the same time, asymmetric rolling increases the rolling difficulty, makes the plate shape uncontrollable, and can easily cause problems such as plate warping, affecting subsequent stamping and other processes.

[0157] Comparative Example 7

[0158] The composite material and its preparation method in Comparative Example 7 are basically the same as those in Example 1, except that the layer thickness ratio is 1:6:3.

[0159] In Comparative Example 7, an excessively thick copper layer increases the cost of the composite material, negating its cost advantage. Furthermore, asymmetric rolling increases rolling difficulty, makes the sheet shape uncontrollable, and easily leads to problems such as sheet warping, affecting subsequent stamping and other processes.

[0160] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0161] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A composite strip comprising a first copper layer and an aluminum layer; the first copper layer covering the surface of the aluminum layer; the thickness ratio of the first copper layer to the aluminum layer being 1:(2~10); the thickness of the first copper layer being less than or equal to 25 μm.

2. The composite strip according to claim 1, wherein, It also includes a second copper layer, wherein the aluminum layer has a first surface and a second surface disposed opposite to each other along its thickness direction, the first surface being covered by the first copper layer and the second surface being covered by the second copper layer; the thickness of the second copper layer is less than or equal to 25 μm.

3. The composite strip according to claim 2, wherein, The thickness ratio of the first copper layer to the second copper layer is 1:(0.5~2).

4. The composite strip according to claim 3, wherein, The first copper layer and the second copper layer are made of brass, and the thickness of the first copper layer and the second copper layer is 15μm~25μm.

5. The composite strip according to claim 3, wherein, Both the first copper layer and the second copper layer are made of pure copper, and the thickness of the first copper layer and the second copper layer is 10μm~20μm.

6. A method for preparing a composite strip, comprising the following steps: The first copper material and the aluminum material are stacked and then subjected to first rolling and diffusion annealing in sequence. The temperature of the first rolling is 400℃~500℃ and the deformation of the first rolling is 40%~50%. The temperature of the diffusion annealing is 380℃~460℃ and the diffusion annealing time is 2min~30min to obtain the composite material. The composite material is subjected to a second rolling process, wherein the second rolling is an electromagnetic induction heating temperature precision rolling process, the temperature of the second rolling is 250℃~350℃, and the second rolling includes: The composite material is subjected to one or two first sub-rolling passes to achieve a first preset thickness for the first copper material, with each first sub-rolling pass having a deformation of 20% to 35%. The composite material after the first sub-rolling is subjected to multiple passes of second sub-rolling, with the deformation amount of each second sub-rolling decreasing sequentially, and the deformation amount of each second sub-rolling being less than 20%, so that the first copper material reaches a second preset thickness, which is less than or equal to 25 μm.

7. The method for preparing the composite strip according to claim 6, wherein, The first copper material, aluminum material, and second copper material are stacked in sequence and subjected to the first rolling and diffusion annealing in sequence; the first sub-rolling makes the first copper material and the second copper material reach a first preset thickness; the second sub-rolling makes the first copper material and the second copper material reach a second preset thickness.

8. The method for preparing the composite strip according to claim 7, wherein, The first copper material and the second copper material are brass, and the second preset thickness is 15μm~25μm.

9. The method for preparing the composite strip according to claim 7, wherein, The first copper material and the second copper material are both copper, and the second preset thickness is 10μm~20μm.

10. The method for preparing the composite strip according to any one of claims 6 to 9, wherein, The ratio of the first preset thickness to the second preset thickness is 1:(1.1~1.3).

11. The method for preparing the composite strip according to any one of claims 6 to 10, wherein, The process after the second rolling includes: annealing the composite material after the second rolling, wherein the annealing temperature is 320℃~420℃ and the time is 1min~10min.

12. The method for preparing the composite strip according to any one of claims 7 to 11, wherein, Before the first copper material, aluminum material, and second copper material are stacked in sequence, the following steps are also included: The mating surfaces of the first copper material, the aluminum material, and the second copper material are roughened to achieve a surface roughness Ra of 1 μm to 6 μm.

13. The method for preparing the composite strip according to claim 12, wherein, The bonding surfaces of the first copper material, the aluminum material, and the second copper material are roughened using a wire brush and abrasive putty; the wire diameter of the wire brush is 0.08mm~0.12mm; the abrasive putty includes a plastic matrix and silicon carbide abrasive.

14. The method for preparing the composite strip according to any one of claims 6 to 13, wherein, Before the second rolling of the composite material, the process further includes: performing rough rolling and intermediate annealing on the composite material in sequence; the intermediate annealing temperature is 400℃~450℃, and the intermediate annealing holding time is 5min~20min.

15. An LED bracket comprising the composite strip according to any one of claims 1 to 5, or the composite strip prepared by the method of preparing the composite strip according to any one of claims 6 to 14.

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