A large-sized, multi-interface silver-copper composite strip and its preparation method

Abstract

The present invention belongs to the technical field of melt materials for fuses, and particularly relates to a large-size and multi-interface silver-copper composite strip and a preparation method thereof. In the preparation method of the large-size and multi-interface silver-copper composite strip of the present invention, a plurality of blind hole grooves are processed on an oxygen-free copper plate, and silver bars are impregnated with a brazing filler metal liquid containing carbon nanotubes and then embedded in the blind hole grooves coated with a brazing flux at high temperature, thereby realizing the dip brazing connection of a plurality of silver bars and oxygen-free copper. Then, the silver-copper composite strip is obtained by cutting. The above preparation method of the present invention truly realizes the integrated preparation of the large-size and multi-interface silver-copper composite strip. The number of silver bars and the bandwidth in the composite strip are no longer limited by pressure, and there is no need for multi-pass rolling. The method is simple and efficient. The interface bonding strength of the prepared composite strip is high, the resistivity is moderate, and the comprehensive quality is excellent, having a wide application prospect in the field of melt materials for large-voltage DC circuits.

Description

Technical Field

[0001] The invention belongs to the technical field of melt materials for fuses, and in particular relates to a large-size, multi-interface silver-copper composite strip and a preparation method thereof. Background Art

[0002] Silver-copper composite strip is a composite metal material that is firmly bonded along the contact surface of silver and copper. At present, as a substitute for pure silver strip, silver-copper composite strip not only maintains the fast-fusing characteristics of the original pure silver strip, but also saves the material cost of precious metal silver. It is an ideal material to replace pure silver fusing and has been widely used in low-voltage electrical appliances and fuses. For example, the Chinese patents with announcement numbers CN109585235B, CN216928470U, CN209454299U, and CN207602503U all use silver-copper composite strips to replace pure silver strips, thereby achieving good application effects.

[0003] In recent years, with the sustained and rapid development of high-end equipment manufacturing industries such as high-speed trains, new energy vehicles, and photovoltaic inverters in my country, higher requirements have been placed on fuse materials. Taking new energy vehicles as an example, with the increase in battery life and the promotion of fast charging technology, the safety issues of high-voltage DC circuits have become increasingly prominent, so higher requirements have been placed on the fusing sensitivity of silver-copper composite tapes. Large-size (total width ≥ 120mm) and multi-interface (number of silver strips ≥ 6) silver-copper composite tapes have become a technically inevitable choice because they can better meet the application requirements of high-voltage DC circuit fusing materials.

[0004] However, in the prior art, the integrated precision forming technology of large-sized, multi-interface silver-copper composite belts is difficult to achieve. This is because, when using traditional hot pressing diffusion composite, due to the large number of silver-copper interfaces and the transmission of diffusion pressure layer by layer, the load transfer caused by the change in the silver-copper contact area is prone to inconsistency, resulting in excessive deformation between silver and copper or even "crushing" of the silver material, or the problem of inability to effectively achieve precise diffusion composite of silver and copper when under-pressured. When the traditional mechanical inlay method is used for composite, due to the excessive number of silver-copper composite interfaces in the large-sized, multi-interface silver-copper composite belt, multiple interface dislocations are prone to occur during the composite process, and the contact area changes, making it difficult to accurately composite. If the current overlapping method is used for forming, such as two 72mm wide silver-copper composite belts are overlapped by resistance welding to form a 140mm wide composite belt melt, it still has the problem of being unable to be formed in an integrated manner.

[0005] Therefore, developing a silver-copper composite tape and a preparation method thereof to achieve integrated molding of large-size, multi-interface, high-quality silver-copper composite tapes has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] The first object of the present invention is to provide a method for preparing a large-size and multi-interface silver-copper composite strip, which can realize the integrated forming of the large-size and multi-interface silver-copper composite strip, and the forming process is not limited by pressure and does not require multi-pass rolling. At the same time, the composite strength of the silver-copper interface of the prepared composite strip is high, and the resistivity is moderate, which is suitable for industrial applications.

[0007] The second object of the present invention is to provide a large-size and multi-interface silver-copper composite strip, which has a high composite strength at the silver-copper interface and a moderate resistivity, and is suitable for use as a fusing material for large-voltage DC circuits.

[0008] In order to achieve the above object, the technical solution adopted for the method for preparing a large-size and multi-interface silver-copper composite strip of the present invention is as follows:

[0009] A method for preparing a large-size and multi-interface silver-copper composite strip includes the following steps:

[0010] (1) Uniformly cut a preset number of blind hole grooves along the length direction of the oxygen-free copper plate, and brush a brazing flux on the inner wall of the blind hole grooves;

[0011] Take pure silver strips equal in number and matching in size with the blind hole grooves, and heat-treat the pure silver strips and the oxygen-free copper plate after brushing the brazing flux;

[0012] Melt a BAg72Cu alloy block into a metal liquid, add carbon nanotubes to the metal liquid and mix evenly to obtain a mixed liquid;

[0013] (2) Immerse the heated pure silver strips obtained in step (1) into the mixed liquid, and then sequentially embed the pure silver strips into the blind hole grooves of the heated oxygen-free copper plate, and cool to obtain a silver-copper composite strip preform;

[0014] (3) Cut the silver-copper composite strip preform to obtain a large-size and multi-interface silver-copper composite strip finished product.

[0015] For the method for preparing a large-size and multi-interface silver-copper composite strip provided by the present invention, a plurality of uniformly distributed blind hole grooves are wire-cut along the length direction of the oxygen-free copper plate, the surface of the pure silver strip is impregnated with a BAg72Cu brazing filler metal liquid containing carbon nanotubes, and is sequentially embedded into the high-temperature blind hole grooves coated with silver brazing flux, so that the pure silver strip and the blind hole grooves are connected by dip brazing. Finally, by cutting, a composite strip with a certain thickness is continuously cut, thereby obtaining a large-size, multi-interface and high-quality silver-copper composite strip.

[0016] The present invention does not limit the preset number of the blind hole grooves, which can be selected according to the use requirements. To prepare a large-size composite strip, preferably, in step (1), the preset number ≥ 6.

[0017] In step (1) of the present invention, the thickness of the selected oxygen-free copper plate determines the number of finished silver-copper composite strips with large size and multiple interfaces finally obtained, and the size of the blind hole groove determines the size of the silver strip in the composite strip. Both of them can be selected according to the preparation requirements and usage requirements, and the present invention does not make special limitations.

[0018] In step (1), a brazing flux is used to wet the blind hole groove to achieve the tight bonding of the pure silver strip and the oxygen-free copper plate. Preferably, the type of the brazing flux is any one of FB102, FB103, FB104, and FB302.

[0019] The dimensional fit clearance between the pure silver strip and the blind hole groove is equivalent to the brazing clearance, which has a certain influence on the bonding strength of the silver-copper interface. Preferably, in step (1), the dimensional fit clearance between the pure silver strip and the blind hole groove is 0.05 - 0.2 mm.

[0020] Furthermore, in step (1), the temperature of the heat treatment is 780 - 850 °C, and the time of the heat treatment is 25 - 40 min.

[0021] For the selection of the material of the molten metal, it is necessary to consider both the cost, electrical conductivity, melting point, and dip brazing performance of the composite strip. The present invention uses a BAg72Cu alloy block as the interface material, which belongs to a eutectic alloy. It not only has a moderate price, but also has a low melting point, good dip soldering operability, and good electrical conductivity, becoming the optimal solder selection. As a further preferred solution, in step (1), the temperature for melting the BAg72Cu alloy block into the molten metal is 780 - 800 °C.

[0022] Compared with pure silver, the resistivity of the BAg72Cu material is relatively large, and its electrical conductivity is somewhat lacking. The present invention adds carbon nanotubes to make its electrical conductivity equivalent to that of silver, and further increases the bonding strength of the brazing seam. Preferably, in step (1), the addition amount of the carbon nanotubes is 0.03 - 0.06% of the mass of the molten metal, and more preferably 0.05%.

[0023] Preferably, in step (2), the immersion is to completely immerse the pure silver strip into the molten metal, and the immersion time is 8 - 10 s.

[0024] Furthermore, in step (2), after cooling, it further includes the steps of mechanically removing the excess brazing flux and the excess oxygen-free copper.

[0025] In step (3), the cutting is for the thickness cutting of the silver-copper composite strip preform. After the silver-copper composite strip preform is prepared in the present invention, rolling is not required, and the silver-copper composite strip with the required thickness can be obtained only by cutting. Preferably, in step (3), the cutting is performed by using a picosecond laser; the output power of the picosecond laser is 3-5 W, the focused light plate is 4-6 μm, and the moving speed is 400-600 mm / s.

[0026] The technical solution adopted for the large-size, multi-interface silver-copper composite strip provided by the present invention is as follows:

[0027] The large-size, multi-interface silver-copper composite strip is prepared by using the preparation method as described above. The silver-copper composite strip is mainly formed by arranging pure silver bars and oxygen-free copper bars in sequence along the width direction; a BAg72Cu material layer is formed at the interface between the pure silver bar and the oxygen-free copper bar; the number of the oxygen-free copper bars is 1 more than the number of the pure silver bars, and the outermost side of the silver-copper composite strip is an oxygen-free copper bar.

[0028] In the large-size, multi-interface silver-copper composite strip of the present invention, no special limitation is made on the width of the silver bar and the width of the oxygen-free copper bar. Since different circuits need to carry different currents, the width requirements for silver bars and copper bars are different. Therefore, the widths of the silver bar and the oxygen-free copper bar are ultimately limited by the requirements of each user factory and can be customized according to the factory requirements.

[0029] As a further preferred solution, the width of the silver-copper composite strip ≥ 120 mm, and the number of pure silver bars in the silver-copper composite strip ≥ 6; the lengths and thicknesses of the oxygen-free copper bars and the pure silver bars in the silver-copper composite strip are equal; the thickness of the silver-copper composite strip is 0.1-0.3 mm.

[0030] More preferably, the width of the silver-copper composite strip ≥ 200 mm, and the number of pure silver bars in the silver-copper composite strip ≥ 10.

[0031] Compared with the prior art, the beneficial effects of the present invention mainly lie in:

[0032] (1) At present, traditional methods for preparing large-size, multi-interface silver-copper composite strips, such as hot pressing diffusion composite method, mechanical inlay method, and lap joint method, cannot achieve the integrated and precise composite of large-size, multi-interface silver-copper composite strips.

[0033] The preparation method of the composite strip of the present invention is as follows: First, a plurality of blind hole grooves are processed on an oxygen-free copper plate. After impregnating a silver strip with a brazing filler metal liquid containing carbon nanotubes, it is embedded in the blind hole grooves coated with a brazing flux at high temperature, thereby realizing the dip brazing connection of a plurality of silver strips and oxygen-free copper. Finally, the successful preparation of the composite strip is achieved through a simple cutting process. By adopting the above preparation process, the present invention can make the number of silver strips and the bandwidth in the composite strip not limited by pressure. The number of composite silver strips can exceed 6, and the width can be ≥ 120 mm, truly realizing the integrated preparation of large-size and multi-interface silver-copper composite strips, reducing the complexity of the process operation, and ensuring the composite quality.

[0034] (2) The brazing filler metal liquid used in the present invention contains carbon nanotubes. On the one hand, it can compensate for the loss of the conductivity of the brazing seam caused by the lack of silver content in the brazing filler metal and enhance the conductivity of the silver-copper dip brazing seam. On the other hand, the carbon nanotubes can play an effective supporting skeleton role by being embedded in the brazing seam, thereby enhancing the bonding strength of the silver-copper interface.

[0035] (3) The preparation method of the silver-copper composite strip of the present invention provides a new preparation idea and preparation approach for the integrated preparation of large-size and multi-interface silver-copper composite strips. This method does not require multi-pass rolling, is simple, has high efficiency, and the interface bonding strength of the prepared composite strip is as high as 166 - 170 MPa, and the resistivity is only (1.85 - 1.88) × 10 -8 Ω·m, with excellent comprehensive quality, and has broad application prospects in the field of preparing melt materials for large-voltage DC circuits. Description of the Drawings

[0036] Figure 1 It is a schematic cross-sectional view of cutting blind hole grooves on an oxygen-free copper plate in step (1) during the preparation of the silver-copper composite strip of the present invention;

[0037] Figure 2 It is a schematic structural view of the pre-finished product of the silver-copper composite strip obtained in step (2) (left figure) and the finished product of the silver-copper composite strip obtained in step (3) (right figure) during the preparation of the silver-copper composite strip of the present invention;

[0038] Figure 3 It is an external view of a silver-copper composite strip obtained by traditional hot pressing and diffusion compounding;

[0039] Figure 4 It is an external view of a silver-copper composite strip obtained by traditional mechanical inlaying method compounding;

[0040] Figure 5 It is an external view of a silver-copper composite strip obtained by compounding with the preparation method of Example 1 of the present invention;

[0041] Among them, Figures 1-2 in: 1 - blind hole groove, 2 - oxygen-free copper plate, 3 - pure silver strip, 4 - oxygen-free copper strip. Detailed implementation manners

[0042] The technical solutions of the present invention will be further described below in conjunction with specific implementation manners. However, those skilled in the art should understand that the following embodiments are only used to illustrate the present invention and should not be regarded as a limitation to the present invention. The specific conditions not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, unless otherwise specified, are all conventional products obtained through commercial channels.

[0043] Among them, in the following embodiments, the oxygen content of the oxygen-free copper is not more than 0.003%, the total impurity content is not more than 0.05%, and the purity of the copper is greater than 99.95%; the Ag content in the pure silver is 99.99%, the Pb content is not more than 0.01%, the Pd content is not more than 0.01%, and the total impurity content is not more than 0.1%. The BAg72Cu alloy block is a silver-copper binary eutectic material. In terms of mass percentage, the main chemical components are: Ag 72±1%, and the balance is copper; the diameter of the carbon nanotubes is 10-20 nm, and the length is 6-10 μm.

[0044] Among them, in the following embodiments, when preparing a large-size and multi-interface silver-copper composite strip, the schematic cross-sectional view of the blind hole groove cut on the oxygen-free copper plate in step (1) is as Figure 1 shown. Figure 1 In, along the length direction of the oxygen-free copper plate 2, the blind hole grooves 1 are evenly cut, thereby obtaining several uniformly distributed blind hole grooves.

[0045] In the following embodiments, when preparing the silver-copper composite strip, the schematic structural views of the silver-copper composite strip preform obtained in step (2) and the silver-copper composite strip finished product obtained in step (3) are as Figure 2 shown. Among them, Figure 2 The left figure is the silver-copper composite strip preform, Figure 2 The right figure is the silver-copper composite strip finished product. The silver-copper composite strip preform obtained in step (2) is already the preform obtained after cutting off the excess solder and the excess oxygen-free copper layer. It is formed by arranging pure silver strips 3 and oxygen-free copper strips 4 evenly and alternately. After the thickness cutting in step (3), the silver-copper composite strip finished product formed by arranging the pure silver strips 3 and the oxygen-free copper strips 4 in sequence can be obtained.

[0046] Embodiment 1

[0047] The large-sized, multi-interface silver-copper composite strip of this embodiment is composed of pure silver strips and oxygen-free copper strips arranged in sequence along the width direction; the number of pure silver strips in the silver-copper composite strip is 10, the number of oxygen-free copper strips is 11, and the outermost side of the composite strip is an oxygen-free copper strip. A BAg72Cu material layer is formed at the interface between the pure silver strip and the oxygen-free copper strip. The width of the silver-copper composite strip is 200 mm and the thickness is 0.1 mm; the lengths and thicknesses of the oxygen-free copper strips and pure silver strips in the silver-copper composite strip are equal. The width of the pure silver strip is 4.6 mm, and the width of the oxygen-free copper strip is 14 mm.

[0048] The preparation method of the large-sized, multi-interface silver-copper composite strip of this embodiment includes the following steps:

[0049] (1) Cut out 10 evenly distributed blind hole grooves along the length direction of the oxygen-free copper plate. The length of the blind hole grooves almost runs through the length direction, and a little machining allowance is left at both ends. Then, brush a layer of silver brazing flux QJ102 on the inner wall of the blind hole grooves;

[0050] Take 10 pure silver strips with a dimensional fit clearance of 0.05 - 0.2 mm with the blind hole grooves, and place the pure silver strips and the oxygen-free copper plate after brushing the brazing flux together in a box-type resistance furnace for heat treatment; the heat treatment temperature is 780 - 850 °C, and the time is 25 min;

[0051] Separately, place the BAg72Cu eutectic alloy block in a graphite crucible, induction heat it to 780 - 800 °C to melt it into a metal liquid, and then stir and add 0.05% of carbon nanotubes into the metal liquid to mix evenly to obtain a mixed liquid for standby;

[0052] (2) Immerse the heated pure silver strips obtained in step (1) completely into the mixed liquid obtained in step (1) for 8 s. After taking them out, embed the pure silver strips into the blind hole grooves of the heated oxygen-free copper plate, cool, and mechanically remove the excess brazing material and the excess oxygen-free copper layer to obtain a silver-copper composite strip preform;

[0053] (3) Place the silver-copper composite strip preform on a femtosecond laser cutting machine. The laser is a femtosecond laser with a wavelength of 355 nm, the output power is 4 W, the focused spot is 5 μm, and the moving speed is 500 mm / s. Continuously cut it into a 0.1 mm thick composite strip, and that's it.

[0054] Example 2

[0055] The large-sized, multi-interface silver-copper composite strip of this embodiment is composed of pure silver strips and oxygen-free copper strips arranged in sequence along the width direction; the number of pure silver strips in the silver-copper composite strip is 11, the number of oxygen-free copper strips is 12, and the outermost side of the composite strip is an oxygen-free copper strip. A BAg72Cu material layer is formed at the interface between the pure silver strip and the oxygen-free copper strip. The width of the silver-copper composite strip is 220 mm and the thickness is 0.2 mm; the lengths and thicknesses of the oxygen-free copper strips and pure silver strips in the silver-copper composite strip are equal, the width of the silver strip is 5 mm, and the width of the oxygen-free copper strip is 13.75 mm.

[0056] The preparation method of the large-sized, multi-interface silver-copper composite strip of this embodiment is basically the same as that of Embodiment 1, and the difference between the two is that: the size and quantity parameters of the raw materials for preparing the silver-copper composite strip are set according to Embodiment 2; meanwhile, in step (1), the temperature of the heat treatment is 800 - 820 °C and the time is 30 min.

[0057] Embodiment 3

[0058] The large-sized, multi-interface silver-copper composite strip of this embodiment is composed of pure silver strips and oxygen-free copper strips arranged in sequence along the width direction; the number of pure silver strips in the silver-copper composite strip is 12, the number of oxygen-free copper strips is 13, and the outermost side of the composite strip is an oxygen-free copper strip. A BAg72Cu material layer is formed at the interface between the pure silver strip and the oxygen-free copper strip. The width of the silver-copper composite strip is 240 mm and the thickness is 0.3 mm; the lengths and thicknesses of the oxygen-free copper strips and pure silver strips in the silver-copper composite strip are equal, the width of the silver strip is 7 mm, and the width of the oxygen-free copper strip is 12 mm.

[0059] The preparation method of the large-sized, multi-interface silver-copper composite strip of this embodiment is basically the same as that of Embodiment 1, and the difference between the two is that: the size and quantity parameters of the raw materials for preparing the silver-copper composite strip are set according to Embodiment 3; in step (1), the temperature of the heat treatment is 820 - 850 °C and the time is 35 min.

[0060] Embodiment 4

[0061] The large-sized, multi-interface silver-copper composite strip of this embodiment is composed of pure silver strips and oxygen-free copper strips arranged in sequence along the width direction; the number of pure silver strips in the silver-copper composite strip is 13, the number of oxygen-free copper strips is 14, and the outermost side of the composite strip is an oxygen-free copper strip. A BAg72Cu material layer is formed at the interface between the pure silver strip and the oxygen-free copper strip. The width of the silver-copper composite strip is 250 mm and the thickness is 0.1 mm; the lengths and thicknesses of the oxygen-free copper strips and pure silver strips in the silver-copper composite strip are equal, the width of the silver strip is 5.3 mm, and the width of the oxygen-free copper strip is 13 mm.

[0062] The preparation method of the large-sized and multi-interface silver-copper composite strip in this embodiment is basically the same as that in Embodiment 1, and the difference between the two is that: the size and quantity parameters of the raw materials for preparing the silver-copper composite strip are set according to Embodiment 4; in step (1), the temperature of the heat treatment is 800 - 820 °C, and the time is 40 min.

[0063] Embodiment 5

[0064] The large-sized and multi-interface silver-copper composite strip in this embodiment is composed of pure silver strips and oxygen-free copper strips arranged in sequence along the width direction; the number of pure silver strips in the silver-copper composite strip is 15, the number of oxygen-free copper strips is 16, and the outermost side of the composite strip is an oxygen-free copper strip. A BAg72Cu material layer is formed at the interface between the pure silver strip and the oxygen-free copper strip. The width of the silver-copper composite strip is 280 mm, and the thickness is 0.2 mm; the lengths and thicknesses of the oxygen-free copper strips and pure silver strips in the silver-copper composite strip are equal, the width of the silver strip is 4 mm, and the width of the oxygen-free copper strip is 13.75 mm.

[0065] The preparation method of the large-sized and multi-interface silver-copper composite strip in this embodiment is basically the same as that in Embodiment 1, and the difference between the two is that: the size and quantity parameters of the raw materials for preparing the silver-copper composite strip are set according to Embodiment 5; in step (1), the temperature of the heat treatment is 820 - 850 °C, and the time is 40 min.

[0066] Comparative Example 1

[0067] The silver-copper composite strip provided in Comparative Example 1 has the same material composition and size as those in Embodiment 1, that is, it is composed of pure silver strips and oxygen-free copper strips arranged in sequence along the width direction; the number of pure silver strips in the silver-copper composite strip is 10, the number of oxygen-free copper strips is 11, and the outermost side of the composite strip is an oxygen-free copper strip. A BAg72Cu material layer is formed at the interface between the pure silver strip and the oxygen-free copper strip. The width of the silver-copper composite strip is 200 mm, and the thickness is 0.1 mm; the lengths and thicknesses of the oxygen-free copper strips and pure silver strips in the silver-copper composite strip are equal, the width of the pure silver strip is 4.6 mm, and the width of the oxygen-free copper strip is 14 mm.

[0068] The preparation method of the silver-copper composite strip in Comparative Example 1 is basically the same as that in Embodiment 1, and the difference between the two is that: when preparing the mixed solution in step (1), carbon nanotubes are not added, and the remaining steps and parameters are the same.

[0069] Comparative Example 2

[0070] The silver-copper composite strip provided in Comparative Example 2 has the same material composition and dimensions as those in Example 1, that is, it is composed of pure silver strips and oxygen-free copper strips arranged in sequence along the width direction; the number of pure silver strips in the silver-copper composite strip is 10, the number of oxygen-free copper strips is 11, and the outermost side of the composite strip is an oxygen-free copper strip. A BAg72Cu material layer is formed at the interface between the pure silver strip and the oxygen-free copper strip. The width of the silver-copper composite strip is 200 mm, and the thickness is 0.1 mm; the lengths and thicknesses of the oxygen-free copper strips and pure silver strips in the silver-copper composite strip are equal, the width of the pure silver strip is 4.6 mm, and the width of the oxygen-free copper strip is 14 mm.

[0071] The preparation method of the silver-copper composite strip in Comparative Example 2 is basically the same as that in Example 1. The difference between the two is that in step (1) when preparing the mixed solution, the carbon nanotubes are replaced with 0.05% of nano graphite powder, and the remaining steps and parameters are the same.

[0072] Comparative Example 3

[0073] The silver-copper composite strip provided in Comparative Example 3 has the same material composition and dimensions as those in Example 1, that is, it is composed of pure silver strips and oxygen-free copper strips arranged in sequence along the width direction; the number of pure silver strips in the silver-copper composite strip is 10, the number of oxygen-free copper strips is 11, and the outermost side of the composite strip is an oxygen-free copper strip. A BAg72Cu material layer is formed at the interface between the pure silver strip and the oxygen-free copper strip. The width of the silver-copper composite strip is 200 mm, and the thickness is 0.1 mm; the lengths and thicknesses of the oxygen-free copper strips and pure silver strips in the silver-copper composite strip are equal, the width of the pure silver strip is 4.6 mm, and the width of the oxygen-free copper strip is 14 mm.

[0074] The preparation method of the silver-copper composite strip in Comparative Example 3 is basically the same as that in Example 1. The difference between the two is that in step (1) when preparing the mixed solution, the carbon nanotubes are replaced with 0.05% of nano cubic boron nitride, and the remaining steps and parameters are the same.

[0075] Comparative Example 4

[0076] The silver-copper composite strip provided in Comparative Example 4 has the same material composition and dimensions as those in Example 1, that is, it is composed of pure silver strips and oxygen-free copper strips arranged in sequence along the width direction; the number of pure silver strips in the silver-copper composite strip is 10, the number of oxygen-free copper strips is 11, and the outermost side of the composite strip is an oxygen-free copper strip. A BAg72Cu material layer is formed at the interface between the pure silver strip and the oxygen-free copper strip. The width of the silver-copper composite strip is 200 mm, and the thickness is 0.1 mm; the lengths and thicknesses of the oxygen-free copper strips and pure silver strips in the silver-copper composite strip are equal, the width of the pure silver strip is 4.6 mm, and the width of the oxygen-free copper strip is 14 mm.

[0077] The preparation method of the silver-copper composite strip in Comparative Example 4 is basically the same as that in Example 1. The difference between the two is that the clearance between the pure silver strip used in step (1) and the size of the blind hole groove is 0.5 - 1 mm.

[0078] Comparative Example 5

[0079] The silver-copper composite belt provided in Comparative Example 5 has the same material composition and size as Example 1, that is, it is composed of pure silver strips and oxygen-free copper strips arranged in sequence along the width direction; the number of pure silver strips in the silver-copper composite belt is 10, the number of oxygen-free copper strips is 11, and the outermost side of the composite belt is an oxygen-free copper strip, and a BAg72Cu material layer is formed at the interface between the pure silver strip and the oxygen-free copper strip. The width of the silver-copper composite belt is 200mm and the thickness is 0.1mm; the length and thickness of the oxygen-free copper strip and the pure silver strip in the silver-copper composite belt are equal, the width of the pure silver strip is 4.6mm, and the width of the oxygen-free copper strip is 14mm.

[0080] The preparation method of the silver-copper composite strip of comparative example 5 is basically the same as the preparation method of embodiment 1, except that the pure silver strip used in step (1) has a clearance of 0.01 to 0.04 mm with the size of the blind hole groove.

[0081] Test Example 1

[0082] This test example investigates the preparation method of the silver-copper composite belt in Example 1 of the present invention, and the differences between the traditional hot pressing diffusion composite and mechanical inlay composite methods. Three silver-copper composite belts of the same specifications are prepared by these three methods. Then the appearance morphology of the three silver-copper composite belts is compared. The results are as follows: Figures 3-5 shown.

[0083] Figure 3 This is the appearance of the silver-copper composite tape obtained by traditional hot pressing diffusion composite. Figure 3 It can be seen that in traditional hot pressing diffusion composite, if a multi-interface silver-copper composite belt is to be prepared, multiple silver strips and copper strips need to be composited at the interface. Due to the large number of silver-copper interfaces, the pressure of the diffusion pressure head is transmitted layer by layer, which is prone to inconsistent load transmission caused by changes in the silver-copper contact area, resulting in excessive or insufficient pressure between silver and copper. When the pressure is too high and "overpressure" occurs, the deformation will be too large or even the silver material will be "crushed" (see Figure 3 Left figure); insufficient pressure, that is, underpressure, cannot effectively achieve precise diffusion and recombination of silver and copper (see Figure 3 right).

[0084] Figure 4 This is the appearance of the silver-copper composite strip obtained by the traditional mechanical inlay method. Figure 4 It can be seen that when the traditional mechanical inlay method is used for compounding, if a silver-copper composite belt with multiple interfaces is to be prepared, multiple silver bars and copper bars need to be compounded. Due to the large number of composite interfaces, multiple interfaces are prone to misalignment during the composite process, which can easily lead to slip and instability of the interface contact area, resulting in poor composite conditions.

[0085] Figure 5 This is the appearance of the silver-copper composite strip obtained by the method of Example 1 of the present invention.Figure 5 It can be seen that the silver-copper composite strip prepared by the method of the present invention is not restricted by pressure and there is no interface instability phenomenon, realizing the stable and precise composite of multiple interfaces.

[0086] Test Example 2

[0087] This test example examines the bonding strength and resistivity of the silver-copper composite strips of Examples 1-5 and Comparative Examples 1-5. The composite strips of Examples 1-5 and Comparative Examples 1-5 were respectively sampled as test samples, and the resistivity and interface bonding strength of the samples were measured. The interface bonding strength was carried out in accordance with GB / T 228.1. A strip with a size of 5 mm×10 mm was taken as the standard specimen (one end was silver and the other end was copper), and the transverse tensile strength of the strip was measured. The resistivity test was carried out in an experimental environment of 20 °C, and the resistance of the composite strip with the same size and specification as above was measured using a QJ84 type digital DC bridge. The results of three tests were taken as the average value. The test results are shown in Table 1 below.

[0088] Table 1 Test results of the bonding strength and resistivity of the silver-copper composite strips of the examples and comparative examples

[0089]

[0090]

[0091] As can be seen from Table 1, in the mixed solution of Comparative Example 1, since no carbon nanotubes were added, the interface bonding strength of the obtained silver-copper composite strip was low and the resistivity was high, which could not meet the use requirements. In Comparative Examples 2 and 3, nano-graphite powder and nano-cubic boron nitride were respectively added to the mixed solution. The nano-graphite powder and nano-cubic boron nitride could be embedded in the brazing seam to play a skeleton role, thereby enhancing the interface bonding strength. However, the electrical conductivity of these two materials themselves was not good, which would cause the resistivity of the composite strip to increase and also could not meet the use requirements. In Comparative Example 4, the matching gap between the silver bar and the groove was too large, which was equivalent to too large a brazing seam gap. When the brazing seam gap was too large, it was difficult for the brazing filler metal liquid to fill the brazing seam, resulting in low interface bonding strength. At the same time, the too wide brazing seam led to an increase in resistivity. In Comparative Example 5, the matching gap between the silver bar and the groove was too small, which was equivalent to too small a brazing seam gap. During the dip brazing process, it was difficult for the brazing filler metal liquid to fill into the too narrow brazing seam, also resulting in relatively low interface bonding strength and unable to meet the use requirements.

[0092] Through comprehensive comparison, it can be known that when the silver-copper composite strip is prepared in the examples of the present invention, the mixed solution contains carbon nanotubes with good electrical conductivity and can increase the interface bonding strength. At the same time, the brazing seam gap is moderate and the filling quality of the brazing filler metal liquid is good. The overall application effect makes the composite strip not only have high interface bonding strength, but also small resistivity and good comprehensive quality, and is very suitable for use as the melt material for fuses.

[0093] In summary, the preparation method of the large-size and multi-interface silver-copper composite strip provided by the present invention can enable the number of silver bars and the bandwidth in the composite strip to be unrestricted by pressure, and there is no need for multi-pass rolling. The method is simple and efficient, truly realizing the integrated preparation of the large-size and multi-interface silver-copper composite strip. Moreover, the interface bonding strength of the prepared composite strip is as high as 166-170 MPa, and the resistivity is only (1.85-1.88)×10 -8 Ω·m. The comprehensive quality is excellent, and it has broad application prospects in the field of preparing melt materials for large-voltage DC circuits.

Claims

1. A preparation method of a large-sized and multi-interface silver-copper composite strip, characterized in that, it includes the following steps: (1) Uniformly cut a preset number of blind hole grooves along the length direction of the oxygen-free copper plate, and brush a brazing flux on the inner wall of the blind hole grooves; Take pure silver strips with the same number and matching dimensions as the blind hole grooves, and heat-treat the pure silver strips and the oxygen-free copper plate after brushing the brazing flux; Melt a BAg72Cu alloy block into a metal liquid, add carbon nanotubes to the metal liquid and mix evenly to obtain a mixed liquid; (2) Immerse the heated pure silver strips obtained in step (1) into the mixed liquid, then sequentially embed the pure silver strips into the blind hole grooves of the oxygen-free copper plate obtained after heating, and cool to obtain a silver-copper composite strip preform; (3) Cut the silver-copper composite strip preform to obtain a finished large-sized and multi-interface silver-copper composite strip.

2. The preparation method of the large-sized and multi-interface silver-copper composite strip as described in claim 1, characterized in that, in step (1), the type of the brazing flux is any one of FB102, FB103, FB104, and FB302.

3. The preparation method of the large-sized and multi-interface silver-copper composite strip as described in claim 1, characterized in that, in step (1), the dimensional fit clearance between the pure silver strip and the blind hole groove is 0.05 - 0.2 mm.

4. The preparation method of the large-sized and multi-interface silver-copper composite strip as described in claim 1, characterized in that, in step (1), the temperature of the heat treatment is 780 - 850 °C, and the time of the heat treatment is 25 - 40 min.

5. The preparation method of the large-sized and multi-interface silver-copper composite strip as described in claim 1, characterized in that, in step (1), the temperature for melting the BAg72Cu alloy block into a metal liquid is 780 - 800 °C; the addition amount of the carbon nanotubes is 0.03 - 0.06% of the mass of the metal liquid.

6. The preparation method of the large-sized and multi-interface silver-copper composite strip as described in any one of claims 1 - 5, characterized in that, in step (2), the immersion is to completely immerse the pure silver strip into the metal liquid, and the immersion time is 8 - 10 s.

7. The preparation method of the large-sized and multi-interface silver-copper composite strip as described in any one of claims 1 - 5, characterized in that, after step (2), the cooling further includes the steps of mechanically removing the excess brazing flux and the excess oxygen-free copper.

8. The preparation method of the large-sized and multi-interface silver-copper composite strip as described in any one of claims 1 - 5, characterized in that, in step (3), the cutting is performed using a picosecond laser; the output power of the picosecond laser is 3 - 5 W, the focusing optical plate is 4 - 6 μm, and the moving speed is 400 - 600 mm / s.

9. A large-sized and multi-interface silver-copper composite strip prepared by using the preparation method of the large-sized and multi-interface silver-copper composite strip as described in any one of claims 1 - 8, characterized in that, The silver-copper composite strip is mainly formed by arranging pure silver strips and oxygen-free copper strips in sequence along the width direction; a BAg72Cu material layer is formed at the interface between the pure silver strip and the oxygen-free copper strip; the number of the oxygen-free copper strips is 1 more than the number of the pure silver strips, and the outermost side of the silver-copper composite strip is an oxygen-free copper strip.

10. The large-size, multi-interface silver-copper composite strip according to claim 9, characterized in that the width of the silver-copper composite strip ≥ 120 mm, and the number of pure silver strips in the silver-copper composite strip ≥ 6; the lengths and thicknesses of the oxygen-free copper strips and the pure silver strips in the silver-copper composite strip are equal; the thickness of the silver-copper composite strip is 0.1 - 0.3 mm.

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