A welding method for enhancing the bonding strength of a graphite film to a metal

Abstract

The application discloses a welding method for enhancing the bonding strength of graphite film and metal, and belongs to the technical field of welding of connecting pieces, and comprises the following steps: S1, parallel arrangement and lamination of flexible graphite film, surface treatment of the welding part at the end of the graphite film laminated body, then putting the upper and lower two layers of the graphite film laminated body into metal solder to obtain a graphite film-solder laminated body; S2, putting the graphite film-solder laminated body into a metal end with a roughened inner surface, and obtaining a graphite film-metal composite end with extremely high bonding strength through vacuum hot-pressing brazing. The application fully combines the characteristics of inorganic non-metal and metal, considers the influence of the interface, vacuum degree and mechanical pressure on the welding strength, and significantly improves the bonding strength of the graphite film and the metal end.

Description

Technical Field

[0001] This invention relates to the field of welding technology for connectors, and in particular to a welding method for enhancing the bonding strength between graphite film and metal. Background Technology

[0002] High thermal conductivity carbon fibers, graphite ropes, and graphite films are a class of flexible carbon materials with a high degree of graphitization, playing an increasingly important role in aerospace, intelligent manufacturing, and mobile communication equipment. In many applications, these highly graphitized carbon materials need to be bonded to other materials, especially metals. However, their inherent flexibility, multiple interfaces, and self-lubricating properties make it difficult to bond them tightly with metals, resulting in numerous thermally resistive interfaces. This severely impacts the utilization and application of their high thermal conductivity.

[0003] Currently, the main methods for welding graphite materials to metals are brazing or vacuum brazing. These methods only connect the graphite surface to the metal using solder, but as the graphene sheets slip, it is difficult to guarantee a long-term bond. Some researchers have explored welding graphite to metals by machining grooves on the surface of the graphite block. The solder filling the grooves acts as an anchor, thereby increasing the bonding strength between the graphite and the metal.

[0004] However, this method is difficult to implement for flexible carbon materials with a high degree of graphitization, such as carbon fibers, graphite ropes, and graphite films, because they are inherently very thin or fine, making it impractical to groove their surfaces; furthermore, their extreme softness makes it impossible to fix the processed surface. To maximize the flexibility, high strength, high electrical conductivity, and excellent thermal conductivity of these carbon materials, exploring an effective welding method to improve the bonding performance between graphite materials and metals is crucial. Summary of the Invention

[0005] The purpose of this invention is to provide a welding method that enhances the bonding strength between graphite film and metal, thereby solving the problems in the prior art.

[0006] To achieve the above objectives, the present invention provides a welding method for enhancing the bonding strength between graphite film and metal, comprising the following steps:

[0007] S1. Arrange flexible graphite films in parallel and stack them. Perform surface treatment on the welding part at the end of the graphite film stack. Then, put metal solder into the upper and lower layers at the end of the graphite film stack to obtain a graphite film-solder stack.

[0008] S2. Place the graphite film-solder laminate into the metal end with the inner surface roughened. Then place the metal end with the graphite film-solder laminate in between the graphite electrode blocks for diffusion welding. After evacuating the welding cavity, heat the electrode to above the melting point of the solder. At the same time, apply vertical pressure to the metal end to make the solder completely wet the surface of the graphite film. Allow it to cool naturally to room temperature to obtain the graphite film-metal composite end.

[0009] Preferably, in S1, the graphite film is one of polyimide-based graphite film, natural graphite film, and graphene film, with a thickness of 10~600 μm and a thermal conductivity of 400~2000 W / (m·K).

[0010] Preferably, the thickness of the graphite film is 10~300 μm.

[0011] Preferably, in S1, the surface treatment process is one or a combination of oxidation etching and surface metal film deposition.

[0012] Preferably, in the surface metal coating operation, the thickness of the metal film layer is 10~3000 nm, and the metal film layer is one or more of titanium film, molybdenum film, nickel film, tin film, copper film, silver film, and gold film.

[0013] Preferably, in S1, the metal solder is one of tin-based, silver-based, gold-based, aluminum-based, copper-based, cadmium-based, and nickel-based, and the metal solder is in powder or foil form, with a melting and welding temperature of 100~1200℃.

[0014] Preferably, in step S2, the surface roughening process involves roughening the metal end using a carbide rotary file, a diamond cutting disc, or a tapping tool; the metal end is one of copper, copper alloy, aluminum, aluminum alloy, silver, or silver alloy.

[0015] Preferably, in step S2, the vacuum level of the welding cavity is less than 10. -1 Pa; the pressure applied vertically to the metal end is 0.5~10.0 MPa.

[0016] Therefore, the welding method for enhancing the bonding strength between graphite film and metal according to the present invention has the following beneficial effects:

[0017] (1) In this invention, the welding surface of the graphite film is oxidized and etched to form micro-nano pits, and then a metal film layer is deposited on the surface, which can increase the physical bonding and affinity between the flexible graphite material and the metal and solder. Some active metal film layers will also react with the graphite material surface to form chemical bonds during high-temperature brazing, further enhancing the interface bonding strength.

[0018] (2) In this invention, the inner surface of the metal end is roughened to increase the contact area of ​​the solder and thus increase the bonding strength. Then, vacuum hot pressing brazing is used. Vacuum can effectively remove the gas in the solder during brazing and avoid the generation of interlayer welding defects. Hot pressing can wet the solder to the graphite film and metal to the greatest extent, which can enhance the bonding strength of the connector. In this process, graphite block electrodes are used as the carrier for heating and applying pressure, which achieves two goals at once, and the heat transfer is uniform and the welding efficiency is high.

[0019] (3) The method protected by the present invention effectively solves the problem of tight connection between graphite film and metal end, and can meet the actual needs of multiple scenarios such as aerospace, artificial intelligence, new energy, and mobile communication.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a flowchart of the graphite film-metal composite end welding method of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0024] Example 1

[0025] like Figure 1 As shown, this embodiment provides a welding method to enhance the bonding strength between graphite film and metal, as detailed below:

[0026] S1. Take 5 flexible polyimide-based graphite films with a width of 30 mm, a thickness of 300 μm, and a thermal conductivity of 1500 W / (m·K), arrange them in parallel and stack them, perform micro-oxygen etching on the welding part, and micro-oxygen etching on the part that needs to be welded to the metal in a self-made muffle furnace at 700℃ for 30 min. After forming micro-nano pits by ultrasonication with deionized water, electroplate a 100 nm thick titanium film and nickel film on its surface in sequence.

[0027] Gold-tin solder sheets (Au80Sn20) smaller than the welding area are placed on the upper and lower layers of the treated graphite film laminate to obtain a graphite film-solder laminate.

[0028] S2. Machining a copper metal end with internal dimensions comparable to the laminate size, roughening its inner surface with a tungsten carbide rotary file, placing the graphite film-solder laminate into the copper metal end, and then placing the metal end with the graphite film-solder laminate placed between the graphite electrode blocks for diffusion bonding. Vacuuming is performed to achieve a vacuum level of 1.0 × 10⁻⁶ in the welding chamber. -2 Pa; then heat the graphite block electrode to 300℃, and at the same time apply a pressure of 1.0 MPa vertically to the metal end to make the solder completely wet the surface of the graphite film;

[0029] Finally, it is naturally cooled to room temperature to obtain a graphite film-metal composite end with extremely high bonding strength.

[0030] Example 2

[0031] The specific steps are the same as in Example 1, except that the five flexible polyimide-based graphite films with a width of 30 mm and a thickness of 300 μm are replaced with five graphene films with a width of 30 mm and a thickness of 300 μm.

[0032] Example 3

[0033] The specific steps are the same as in Example 1, except that the five flexible polyimide-based graphite films with a width of 30 mm, a thickness of 300 μm, and a thermal conductivity of 1500 W / (m·K) are replaced with ten flexible polyimide-based graphite films with a width of 30 mm, a thickness of 150 μm, and a thermal conductivity of 1800 W / (m·K).

[0034] Example 4

[0035] The specific steps are the same as in Example 1, except that the micro-oxygen etching operation is removed.

[0036] Example 5

[0037] The specific steps are the same as in Example 1, except that the surface metal coating operation is removed.

[0038] Example 6

[0039] The specific steps are the same as in Example 1, except that instead of electroplating a 100 nm thick titanium film and a nickel film on the graphite film surface in sequence, a 100 nm thick titanium film and a molybdenum film are electroplated in sequence.

[0040] Example 7

[0041] The specific steps are the same as in Example 1, except that the gold-tin solder sheet (Au80Sn20) is replaced with a copper-nickel solder sheet (90CuNi), and the corresponding graphite block electrode temperature is adjusted to 450°C.

[0042] Example 8

[0043] The specific steps are the same as in Example 1, except that the gold-tin solder sheet (Au80Sn20) is replaced with silver-copper-zinc-manganese brazing filler metal (BAg49M), and the temperature of the graphite block electrode is adjusted to 780°C.

[0044] Example 9

[0045] The specific steps are the same as in Example 1, except that the roughening method of the inner surface of the copper metal end is changed from grinding with a tungsten carbide rotary file to creating threads using a tapping tool.

[0046] Example 10

[0047] The specific steps are the same as in Example 1, the only difference being that the copper metal end is replaced with the aluminum metal end.

[0048] Example 11

[0049] The specific steps are the same as in Example 1, the only difference being that the copper metal end is replaced with the manganese steel metal end.

[0050] Example 12

[0051] The specific steps are the same as in Example 1, the only difference being that the vacuum degree of the welding cavity is reduced from 1.0 × 10⁻⁶. -2 Pa increased to 5.2 × 10 -4 Pa.

[0052] Example 13

[0053] The specific steps are the same as in Example 1, the only difference being that the vacuum degree of the welding cavity is reduced from 1.0 × 10⁻⁶. -4 Pa decreased to 2.3 × 10 -1 Pa.

[0054] Example 14

[0055] The specific steps are the same as in Example 1, except that the pressure applied vertically to the metal end is increased from 1.0 MPa to 3.0 MPa.

[0056] Example 15

[0057] The specific steps are the same as in Example 1, except that the pressure applied vertically to the metal end is increased from 1.0 MPa to 6.0 MPa.

[0058] Example 16

[0059] The specific steps are the same as in Example 1, except that the pressure applied vertically to the metal end is reduced from 1.0 MPa to 0.5 MPa.

[0060] Comparative Example 1

[0061] 1) The flexible graphite film material is cut. The flexible section is made of 30 layers of graphite film with a single layer thickness of 25 μm. The flexible section is 150 mm long and 20 mm wide.

[0062] 2) An underlayer (Ti) is prepared by ion plating on the surface and sides of the welding area at both ends of each flexible graphite film. Then, a solder barrier layer (Mo) and a surface layer (Ni) are deposited sequentially by magnetron sputtering to obtain an ultra-thin, highly bonded Ti\Mo\Ni metallized film layer, in which the titanium layer is about 0.1 μm, the molybdenum layer is 0.3 μm, and the nickel layer is about 1 μm.

[0063] 3) A gold-based solder layer is deposited on the surface of the graphite film metallization layer using magnetron sputtering. The thickness of the solder layer is controlled at 6-8 μm to ensure uniform thickness.

[0064] 4) Process aluminum alloy parts according to the design drawings for brazing and assembling heat conduction cables, and perform alkaline degreasing, chemical cleaning, and surface electroplating with nickel.

[0065] 5) Prepare Au-20Sn solder foil with a thickness of 30 μm and Pb-3Ag soft solder sheet with a thickness of 200 μm, cut them and stack them to form a composite solder sheet with a sandwich layer.

[0066] 6) Assembly: A specially designed fixed clamping fixture is used to stack 30 layers of graphite film, and a "sandwich" composite brazing filler metal is inserted into the gap between the graphite film stack and the aluminum alloy.

[0067] 7) Place the assembled graphite heat-conducting cable and welding fixture into a vacuum brazing furnace, evacuate, heat, and hold at the brazing temperature of 320℃ for no more than 10 minutes. The heating and cooling rate should be less than 30℃ / min. Throughout the process, ensure that the vacuum level inside the furnace is better than 10. -3 Pa·m 3 / s.

[0068] Comparative Example 2

[0069] A material with a thickness of 20 μm and a thermal conductivity of 1500 W·m -1 ·K -1 The flexible, highly thermally conductive graphite film was cut into strips with a length of 110 mm and a width of 20 mm. Fifty strips of graphite film were stacked together, and the two ends of the graphite film were heat-treated at 700℃ in an oxygen-containing atmosphere for 1 h, followed by thermal reduction at 2800℃ in an inert atmosphere for 30 min. Then, 300 nm thick copper was deposited on both ends of the graphite film by chemical plating.

[0070] Prepare two aluminum alloy shells with a groove length of 22 mm, a groove width of 1.5 mm, a groove depth of 10 mm, and a wall thickness of 2 mm. Then, place the stacked graphite film in the groove and fill it with a low melting point gallium alloy. Hot press the shell at 200℃ and 0.5 MPa. After cooling to room temperature, a flexible graphite film / metal composite heat-conducting cable with high thermal conductivity is obtained.

[0071] The tensile strength of the welded composite ends of the above embodiments and comparative examples was tested, and the tensile strengths are shown in the table below:

[0072] Table 1 Tensile Strength

[0073]

[0074] As can be seen from the data in the table above, the tensile strength of graphite materials welded to metals using the method protected by this invention is higher than that of the comparative example.

[0075] In this invention, a metal brazing filler (which can be in the form of foil or powder) is superimposed or mixed with a high-performance graphite film or fiber. A certain voltage and current are applied to melt the metal brazing filler and tightly bond it with the graphite material, thereby connecting the flexible graphite material and the metal composite together. This method can further enhance the interfacial bonding strength between the two and effectively solve the problem of tight connection between the graphite film and the metal end.

[0076] Therefore, the present invention provides a welding method to enhance the bonding strength between graphite film and metal. This method involves oxidizing and etching the welding portion of the graphite film stack to form micro-nano pits and / or depositing a metal film layer on the surface. Subsequently, metal solder is placed at both ends of the surface-treated graphite film stack. The graphite film-solder stack is then placed into the metal end with a roughened inner surface. Vacuum hot-press brazing is then performed to obtain a graphite film-metal composite end with extremely high bonding strength. This method fully combines the characteristics of inorganic non-metals and metals, and considers the influence of interface, vacuum degree, and mechanical pressure on welding strength, significantly improving the bonding strength between the graphite film and the metal end.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A welding method for enhancing the bonding strength between graphite film and metal, characterized in that, Includes the following steps: S1. Flexible graphite films are stacked in parallel. The welding portion at the end of the graphite film stack is surface-treated. Then, metal solder is placed into the upper and lower layers at the end of the graphite film stack to obtain a graphite film-solder stack. The graphite film is one of polyimide-based graphite film, natural graphite film, and graphene film, with a thickness of 10-600 μm and a thermal conductivity of 400-2000 W / (m·K). The surface treatment process is one or a combination of oxidation etching and surface metal film deposition. S2. Place the graphite film-solder laminate into the metal end with the inner surface roughened, and then place the metal end with the graphite film-solder laminate into the graphite electrode block for diffusion welding. After evacuating the welding cavity, heat the electrode to above the melting point of the solder, and at the same time apply vertical pressure to the metal end to make the solder completely wet the surface of the graphite film. After completion, the material is allowed to cool naturally to room temperature to obtain the graphite film-metal composite end. The surface roughening process involves using a carbide rotary file, diamond cutting disc, or tapping tool to roughen the metal end. The metal end is one of copper, copper alloy, aluminum, aluminum alloy, silver, or silver alloy. The vacuum degree of the welding chamber is less than 10. -1 Pa; the pressure applied vertically to the metal end is 0.5 to 10.0 MPa.

2. The welding method for enhancing the bonding strength between graphite film and metal according to claim 1, characterized in that: The thickness of the graphite film is 10–300 μm.

3. The welding method for enhancing the bonding strength between graphite film and metal according to claim 1, characterized in that: In the surface metal coating operation, the thickness of the metal film layer is 10-3000 nm, and the metal film layer is one or more of titanium film, molybdenum film, nickel film, tin film, copper film, silver film, and gold film.

4. The welding method for enhancing the bonding strength between graphite film and metal according to claim 1, characterized in that: In S1, the metal solder is one of tin-based, silver-based, gold-based, aluminum-based, copper-based, cadmium-based, and nickel-based, and the metal solder is in powder or foil form, with a melting and welding temperature of 100–1200°C.

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