Welding method for enhancing bonding strength of graphite film and metal

Abstract

The invention discloses a welding method for enhancing the bonding strength of graphite films and metal, which belongs to the technical field of connecting piece welding and comprises the following steps of: S1, arranging and stacking flexible graphite films in parallel, performing surface treatment on a welding part at the end part of a graphite film stacking body, then putting metal solder into the upper layer and the lower layer of the end part of the graphite film stacking body, and welding the upper layer and the lower layer of the end part of the graphite film stacking body; a graphite film-solder laminated body is obtained; and S2, the graphite film-solder laminated body is put into the metal end with the inner surface roughened, and a graphite film-metal composite end part with extremely high bonding strength is obtained through vacuum hot-pressing brazing. According to the method, the characteristics of inorganic nonmetal and metal are fully combined, the influence of an interface, the vacuum degree and mechanical pressure on the welding strength is considered, and the bonding strength of the graphite film and the metal end is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of connecting piece welding, and in particular to a welding method for enhancing the bonding strength between a graphite film and a metal. Background Art

[0002] High thermal conductivity carbon fiber, graphite rope, graphite film, etc. are a type of flexible carbon materials with a high degree of graphitization, which play an increasingly important role in aerospace, intelligent manufacturing, mobile communication equipment and other fields. In many scenarios, such highly graphitized carbon materials need to be used together with other materials, especially metal materials, but they have the characteristics of flexibility, multiple interfaces, and self-lubrication, which makes it difficult to combine closely with metal materials, resulting in a large number of thermal resistance interfaces, which seriously affects the high thermal conductivity and application of these carbon materials.

[0003] At present, the main method for welding graphite materials to metal materials is brazing or vacuum brazing. This method can only connect the graphite surface and metal together through solder, but with the slip of graphene sheets, it is difficult to ensure a long-term bonding effect. Some researchers have welded the graphite block to the metal by machining grooves on the surface of the graphite block. The solder filled into the groove can play an anchoring role, thereby increasing the bonding strength between the graphite and the metal.

[0004] However, this method is difficult to implement for flexible and highly graphitized carbon materials such as carbon fiber, graphite rope, and graphite film, because they are very thin or fine, and it is not realistic to groove their surfaces; in addition, they are very soft and cannot be fixed on the processing surface. In order to maximize the flexibility and excellent properties of these carbon materials such as high strength, high electrical conductivity and heat transfer, it is crucial to explore a welding method that effectively improves the bonding performance of graphite materials and metals. Summary of the invention

[0005] The purpose of the present invention is to provide a welding method for enhancing the bonding strength between a graphite film and a metal, so as to solve the problems in the background technology.

[0006] To achieve the above object, the present invention provides a welding method for enhancing the bonding strength between a graphite film and a metal, comprising the following steps: S1, stacking the flexible graphite films in parallel, performing surface treatment on the welding part at the end of the graphite film stack, and then placing the upper and lower layers at the end of the graphite film stack into metal solder to obtain a graphite film-solder stack; S2. Place the graphite film-solder laminate into the metal end with a roughened inner surface, and then place the metal end of the graphite film-solder laminate between the graphite electrode blocks of diffusion welding. After evacuating the welding cavity, heat the electrode to above the melting point of the solder, and apply vertical pressure to the metal end to allow the solder to completely infiltrate the surface of the graphite film; cool naturally to room temperature to obtain a graphite film-metal composite end.

[0007] Preferably, in S1, the graphite film is one of a polyimide-based graphite film, a natural graphite film and a graphene film, has a thickness of 10 to 600 μm, and a thermal conductivity of 400 to 2000 W / (m·K).

[0008] Preferably, the thickness of the graphite film is 10-300 μm.

[0009] Preferably, in S1, the surface treatment process is one of oxidation etching and surface metal coating, or a combination of the two.

[0010] Preferably, in the surface metal film plating 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.

[0011] Preferably, in S1, the metal solder is one of tin-based, silver-based, gold-based, aluminum-based, copper-based, cadmium-based, and nickel-based, the metal solder is in powder or foil form, and the melting welding temperature is 100-1200°C.

[0012] Preferably, in S2, the surface roughening process is to roughen the metal end using a carbide rotary file, a diamond cutting blade or a tapping tool; the metal end is one of copper, copper alloy, aluminum, aluminum alloy, silver and silver alloy.

[0013] Preferably, in S2, the vacuum degree of the welding chamber is less than 10 -1 Pa; the pressure applied vertically to the metal end is 0.5~10.0 MPa.

[0014] Therefore, the welding method of the present invention for enhancing the bonding strength between graphite film and metal has the following beneficial effects: (1) In the present invention, the welding surface of the graphite film is oxidized and etched to form micro-nano pits, and then a metal film layer is plated on the surface, which can increase the physical bonding effect and affinity between the flexible graphite material and the metal and solder. Part of the active metal film layer will also react with the surface of the graphite material to form chemical bonds during high-temperature brazing, further enhancing the interface bonding strength.

[0015] (2) In the present invention, the inner surface of the metal end is roughened to increase the contact area of ​​the solder, thereby increasing the bonding strength. Vacuum hot pressing brazing is then used. The vacuum can effectively remove the gas in the solder during brazing, thereby avoiding the generation of interlayer welding defects. Hot pressing can maximize the uniform wetting of the solder with the graphite film and the metal, thereby enhancing the bonding strength of the connector. In this process, a graphite block electrode is used as a carrier for heating and applying pressure, thereby achieving two goals at one stroke, with uniform heat transfer and high welding efficiency.

[0016] (3) The method protected by the present invention effectively solves the problem of tight connection between the graphite film and the metal end, and can meet the actual needs of multiple scenarios such as aerospace, artificial intelligence, new energy, and mobile communications.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of the graphite film-metal composite end welding method of the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0020] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0021] Example 1 like Figure 1 As shown, this embodiment provides a welding method for enhancing the bonding strength between a graphite film and a metal, which is specifically as follows: 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 parts, and micro-oxygen etch the parts to be welded with metal in a homemade muffle furnace at 700°C for 30 min. After using deionized water ultrasound to form micro-nano pits, a 100 nm thick titanium film and a nickel film are electroplated on the surface in sequence.

[0022] Gold-tin solder sheets (Au80Sn20) smaller than the soldering area are placed in the upper and lower layers of the end of the processed graphite film stack to obtain a graphite film-solder stack.

[0023] S2. Process a copper metal end with the same internal dimensions as the laminate, roughen its inner surface with a tungsten steel rotary file, place the graphite film-solder laminate into the copper metal end, place the metal end with the graphite film-solder laminate between the graphite electrode blocks for diffusion welding, and evacuate the welding chamber to a vacuum degree of 1.0×10 -2 Pa; then the graphite block electrode is heated to 300°C, and a pressure of 1.0 MPa is applied vertically to the metal end to make the solder completely infiltrate the surface of the graphite film; Finally, the graphite film-metal composite end is naturally cooled to room temperature to obtain a graphite film-metal composite end with extremely high bonding strength.

[0024] Example 2 The specific steps are the same as those 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.

[0025] Example 3 The specific steps are the same as those 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).

[0026] Example 4 The specific steps are the same as those in Example 1, except that the micro-oxygen etching operation is removed.

[0027] Example 5 The specific steps are the same as those in Example 1, the only difference being that the surface metal coating operation is removed.

[0028] Example 6 The specific steps are the same as those in Example 1, with the only difference being that the process of sequentially electroplating a layer of 100 nm thick titanium film and a layer of nickel film on the surface of the graphite film is replaced by sequentially electroplating a layer of 100 nm thick titanium film and a layer of molybdenum film.

[0029] Example 7 The specific steps are the same as those 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.

[0030] Example 8 The specific steps are the same as those in Example 1, except that the gold-tin solder sheet (Au80Sn20) is replaced with silver-copper-zinc-manganese solder (BAg49M), and the corresponding graphite block electrode temperature is adjusted to 780°C.

[0031] Example 9 The specific steps are the same as those in Example 1, with the only difference being that the method of roughening the inner surface of the copper metal end is replaced by a tapping tool to manufacture the thread instead of a tungsten steel rotary file.

[0032] Example 10 The specific steps are the same as those in Example 1, except that the copper metal end is replaced by the aluminum metal end.

[0033] Embodiment 11 The specific steps are the same as those in Example 1, the only difference being that the copper metal end is substituted for the manganese steel metal end.

[0034] Example 12 The specific steps are the same as those in Example 1. The only difference is that the vacuum degree of the welding chamber is increased from 1.0×10 -2 Pa increased to 5.2×10 -4 Pa.

[0035] Embodiment 13 The specific steps are the same as those in Example 1. The only difference is that the vacuum degree of the welding chamber is increased from 1.0×10 -4 Pa is reduced to 2.3×10 -1 Pa.

[0036] Embodiment 14 The specific steps are the same as those in Example 1, except that the pressure vertically applied to the metal end is increased from 1.0 MPa to 3.0 MPa.

[0037] Embodiment 15 The specific steps are the same as those in Example 1, except that the pressure vertically applied to the metal end is increased from 1.0 MPa to 6.0 MPa.

[0038] Example 16 The specific steps are the same as those in Example 1, except that the pressure vertically applied to the metal end is reduced from 1.0 MPa to 0.5 MPa.

[0039] Comparative Example 1 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. 2) The surface and side surfaces of the welded areas at both ends of each layer of flexible graphite film are ion-plated to prepare a base layer (Ti), and then the solder barrier layer molybdenum (Mo) and the surface layer nickel (Ni) are deposited in sequence by magnetron sputtering to obtain an ultra-thin, high-bonding 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.

[0040] 3) A gold-based soft solder layer is deposited on the surface of the graphite film metallization layer using a magnetron sputtering process. The thickness of the solder layer is controlled at 6-8 μm to ensure uniform thickness.

[0041] 4) Process the aluminum alloy parts according to the requirements of the thermal wire brazing assembly design drawings, perform alkaline degreasing, chemical cleaning, and surface nickel electroplating treatment.

[0042] 5) Prepare a 30 μm thick Au-20Sn solder foil and a 200 μm thick Pb-3Ag soft solder sheet, cut them and stack them to form a sandwich composite solder sheet.

[0043] 6) Assembly: Use specially designed fixed clamping tooling to stack 30 layers of graphite film, and insert a "sandwich" composite brazing material stack into the contact gap between the graphite film stack and the aluminum alloy.

[0044] 7) Put the assembled graphite heat conducting wire and welding tooling into the vacuum brazing furnace, evacuate, heat, and keep the temperature at 320℃ for no more than 10 minutes. The heating and cooling rate is less than 30℃ / min. During the whole process, the vacuum degree in the furnace is better than 10 -3 Pa·m 3 / s.

[0045] Comparative Example 2 The thickness is 20 μm and the thermal conductivity is 1500 W·m -1 ·K -1 The flexible high thermal conductivity graphite film was cut into strips with a length of 110 mm and a width of 20 mm. 50 graphite films were stacked together, and both ends of the graphite film were heat treated at 700°C in an oxygen-containing atmosphere for 1 h, and thermally reduced at 2800°C in an inert atmosphere for 30 min, and then 300 nm thick copper was plated on both ends of the graphite film by chemical plating.

[0046] 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 were prepared. Then, the stacked graphite films were placed in the grooves and filled with low-melting-point gallium alloy. The resulting films were hot-pressed at 200°C and 0.5 MPa. After cooling to room temperature, a highly thermally conductive flexible graphite film / metal composite thermal cable was obtained.

[0047] The tensile strength of the welded composite end portions of the above-mentioned embodiment and comparative example was tested, and the tensile strengths thereof are shown in the following table: Table 1 Tensile strength

[0048] It can be seen from the data in the above table that the tensile strength of the graphite material and the metal welded by the method protected by the present invention is higher than that of the comparative example.

[0049] In the present invention, a metal brazing material (which can be in the form of foil or powder) is superimposed or mixed with a high-performance graphite film or fiber, and a certain voltage and current are applied to melt the metal brazing material and tightly combine with the graphite material, thereby compositely connecting the flexible graphite material and the metal. This method can further enhance the interface bonding strength between the two and effectively solve the problem of tight connection between the graphite film and the metal end.

[0050] Therefore, the present invention provides a welding method for enhancing the bonding strength between graphite film and metal, which comprises the following steps: oxidizing and etching the welding part of the graphite film stack to form micro-nano pits and / or a metal film layer on the surface, then placing metal solder on the upper and lower ends of the surface-treated graphite film stack, placing the graphite film-solder stack 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 method fully combines the characteristics of inorganic non-metals and metals, takes into account the effects of interface, vacuum degree and mechanical pressure on welding strength, and significantly improves the bonding strength between the graphite film and the metal end.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A welding method for enhancing the bonding strength between a graphite film and a metal, characterized in that: The following steps are involved: S1, stacking the flexible graphite films in parallel, performing surface treatment on the welding part at the end of the graphite film stack, and then placing the upper and lower layers at the end of the graphite film stack into metal solder to obtain a graphite film-solder stack; S2, placing the graphite film-solder laminate into the metal end with the roughened inner surface, and then placing the metal end of the graphite film-solder laminate between the graphite electrode blocks of diffusion welding, after evacuating the welding cavity, heating the electrode to above the melting point of the solder, and applying vertical pressure to the metal end at the same time, so that the solder completely infiltrates the surface of the graphite film; After completion, the graphite film-metal composite end is obtained by naturally cooling to room temperature.

2. A welding method for enhancing the bonding strength between a graphite film and a metal according to claim 1, characterized in that: In S1, the graphite film is one of a polyimide-based graphite film, a natural graphite film and a graphene film, has a thickness of 10 to 600 μm, and a thermal conductivity of 400 to 2000 W / (m·K).

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

4. A welding method for enhancing the bonding strength between a graphite film and a metal according to claim 1, characterized in that: In S1, the surface treatment process is one of oxidation etching and surface metal film coating, or a combination of the two.

5. A welding method for enhancing the bonding strength between a graphite film and a metal according to claim 4, characterized in that: In the surface metal film plating 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.

6. A welding method for enhancing the bonding strength between a graphite film and a 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, the metal solder is in powder or foil form, and the melting welding temperature is 100-1200°C.

7. A welding method for enhancing the bonding strength between a graphite film and a metal according to claim 1, characterized in that: In S2, the surface roughening process is to roughen the metal end using a carbide rotary file, a diamond cutting blade or a tapping tool; the metal end is one of copper, copper alloy, aluminum, aluminum alloy, silver, and silver alloy.

8. A welding method for enhancing the bonding strength between a graphite film and a metal according to claim 1, characterized in that: In S2, the vacuum degree of the welding chamber is less than 10 -1 Pa; the pressure applied vertically to the metal end is 0.5~10.0 MPa.

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