Brazing method for large-size graphite and copper

Abstract

The invention relates to the technical field of material connection, and discloses a large-size graphite and copper brazing method which comprises the following steps: S1, performing mechanical polishing treatment on the surface of graphite by using abrasive paper from coarse to fine, and then cleaning the graphite by using acetone; the copper part is soaked in a chemical nickel plating solution, and chemical nickel plating treatment on the copper surface is completed; s2, selecting a titanium-containing active brazing filler metal; s3, clamping and positioning the treated graphite and the copper piece by using a positioning fixture to ensure that a gap between the graphite and the copper piece is uniform so as to meet the brazing requirement; s4, the assembled graphite and copper piece are placed in a vacuum brazing furnace, brazing is carried out in a brazing segmented heating mode, and heat preservation is carried out for 10-30 minutes after brazing; and S5, after brazing is completed, furnace cooling is conducted, and the cooling speed needs to be controlled to be 5 DEG C / min. By conducting special treatment on the surfaces of graphite and copper, the wettability of the brazing filler metal to the graphite and the copper is improved, and the problem that in the prior art, the wettability of the brazing filler metal is poor is effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of material connection, and in particular to a brazing method for large-size graphite and copper. Background Art

[0002] Graphite has the advantages of good electrical conductivity, thermal conductivity, high temperature resistance and chemical stability. It is widely used in electronics, aerospace, metallurgy, chemical industry and other fields. Copper, as an excellent electrical and thermal conductive material, also occupies an important position in many industrial fields. Connecting graphite with copper can combine the advantages of both and expand its application range. However, due to the large differences in the physical and chemical properties of graphite and copper, such as the special crystal structure of graphite, low surface energy, poor wettability with most metals, and the large difference in thermal expansion coefficients between graphite and copper, the connection between graphite and copper, especially the connection between large-sized graphite and copper, faces many challenges.

[0003] Traditional connection methods such as mechanical connection have problems such as low connection strength and large contact resistance; diffusion connection requires high temperature and high pressure conditions, and has strict requirements on equipment, making it difficult to achieve large-scale industrial application; and the existing brazing methods often have defects such as poor brazing wettability, low joint strength, and easy generation of pores and cracks during welding when dealing with the connection of large-size graphite and copper. They cannot meet the requirements of connection quality and reliability in actual engineering applications. Therefore, it is necessary to develop a new method suitable for brazing large-size graphite and copper to overcome the shortcomings of the existing technology.

[0004] Based on this, a brazing method for large-size graphite and copper is proposed. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems and to propose a brazing method for large-sized graphite and copper.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A method for brazing large-size graphite and copper comprises the following steps: S1: Use sandpaper from coarse to fine to mechanically polish the graphite surface to remove the oxide layer and impurities on the surface, and then clean it with acetone; The copper part is immersed in a chemical nickel plating solution to form a uniform nickel layer on the copper surface, thereby completing the chemical nickel plating treatment on the copper surface; S2: Select an active solder containing titanium, the composition of which needs to include 70% silver, 25% copper, and 5% titanium; S3: Using a positioning fixture to clamp and position the processed graphite and copper parts to ensure that the gap between them is uniform so as to meet the brazing requirements; S4: Place the assembled graphite and copper parts in a vacuum chamber at a brazing temperature of 360°C and a vacuum degree of 1x10 -1 Pa-1x10 -3 Pa vacuum brazing furnace, brazing is carried out by means of staged heating, and the heat preservation after brazing is 10-30 minutes; S5: After brazing, cool down with the furnace, and the cooling rate needs to be controlled at 5℃ / min.

[0007] Preferably, during the nickel plating process in which the copper part is immersed in a nickel plating solution, the thickness of the nickel plating layer needs to be ensured to be 0.05-0.1 mm.

[0008] Preferably, in the clamping positioning, the gap size between the graphite and the copper part ranges from 0.05 to 0.1 mm.

[0009] Preferably, the staged heating method is to first heat from room temperature to 360°C at a heating rate of 20°C / min; Then keep at 360℃ for 20 minutes; Then the temperature was raised to 560°C at a rate of 25°C / min; Finally, the temperature was kept at 560°C for 30 minutes, and then the temperature was increased to 830°C at a rate of 25°C / min; Finally, the temperature was kept at 830°C for 15 minutes until the final brazing temperature of 890°C was reached.

[0010] Preferably, after the brazing part is cooled to room temperature, it is necessary to heat the brazing part to 450° C. at 20° C. / min, keep the temperature for 2 hours, and then cool it to room temperature at 5° C. / min.

[0011] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. The present application improves the wettability of the solder to the graphite and copper surfaces by performing special treatment on the surfaces of the graphite and copper, thereby effectively solving the problem of poor wettability of the solder in the prior art.

[0012] 2. This application avoids the generation of defects such as pores and cracks during welding and improves welding quality by adopting titanium-containing active brazing filler metal and reasonably designing brazing process parameters, such as staged heating method, appropriate insulation time and vacuum degree.

[0013] 3. The brazing method of the present application is suitable for connecting large-sized graphite and copper, has good operability and repeatability, and can meet the requirements of large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of the structure of the brazing process of graphite and copper provided according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] See also Figure 1 , the present invention provides a technical solution: A method for brazing large-size graphite and copper comprises the following steps: S1: Use sandpaper from coarse to fine to mechanically polish the graphite surface to remove the oxide layer and impurities on the surface, and then clean it with acetone to improve the roughness and cleanliness of the graphite surface and enhance the wettability of the brazing material to the graphite surface; The copper parts are immersed in a chemical nickel plating solution and reacted under certain temperature and time conditions to form a uniform nickel layer on the copper surface, completing the chemical nickel plating treatment on the copper surface. The chemical nickel plating treatment can improve the wettability of the copper surface and serve as an intermediate transition layer during the brazing process, which is beneficial to improving the joint strength. S2: Select an active solder containing titanium, the composition of which needs to include 70% silver, 25% copper, 5% titanium and other trace elements. The addition of titanium is to improve the wettability of the solder to graphite, and to form chemical bonds by chemically reacting with carbon atoms on the surface of graphite, thereby enhancing the bonding force between the solder and graphite; S3: Assemble the treated graphite and copper parts according to the design requirements, and use a positioning fixture to clamp and position the treated graphite and copper parts to prevent displacement during the brazing process and ensure that the gap between the two is uniform so as to meet the brazing requirements; S4: Place the assembled graphite and copper parts in a vacuum chamber at a brazing temperature of 360°C and a vacuum degree of 1x10 -1 Pa-1x10 -3 Pa vacuum brazing furnace, brazing is carried out by brazing segmented heating method, and the heat preservation after brazing is 10-30 minutes. During the brazing process, the brazing material melts at high temperature and fills into the gap between graphite and copper, and reacts chemically with the graphite and copper surfaces to form a firm joint; S5: After brazing, the furnace is cooled, and the cooling rate needs to be controlled at 5℃ / min. Slow cooling can prevent the cooling rate from being too fast, causing stress concentration at the interface between graphite and copper brazing, resulting in graphite cracking.

[0017] Specifically, during the nickel plating process in which the copper part is immersed in the nickel plating solution, it is necessary to ensure that the thickness of the nickel plating layer is 0.05-0.1 mm.

[0018] Specifically, during the clamping and positioning, the gap between the graphite and the copper part is in the range of 0.05-0.1 mm.

[0019] Specifically, the stepwise heating method is to first heat from room temperature to 360°C at a heating rate of 20°C / min; Then keep at 360℃ for 20 minutes; Then the temperature was raised to 560°C at a rate of 25°C / min; Finally, the temperature was kept at 560°C for 30 minutes, and then the temperature was increased to 830°C at a rate of 25°C / min; Finally, keep the temperature at 830°C for 15 minutes until the final brazing temperature of 890°C is reached; Staged heating can avoid solder splashing and welding defects caused by sudden temperature rise.

[0020] Specifically, after the brazed parts are cooled to room temperature, they need to be heated to 450°C at 20°C / min, kept at that temperature for 2 hours, and then cooled to room temperature at 5°C / min. Repeated cooling can eliminate residual stress in the brazed parts.

[0021] The joint formed between graphite and copper brazed in this way has high strength and can withstand large external forces and loads, meeting the requirements for connection strength in practical applications. The joint also has good electrical and thermal conductivity. Compared with unconnected graphite and copper, the performance loss is small, and the combined advantages of graphite and copper can be effectively utilized.

[0022] The above description of the embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for brazing large-size graphite and copper, characterized in that: The following steps are involved: S1: Use sandpaper from coarse to fine to mechanically polish the graphite surface to remove the oxide layer and impurities on the surface, and then clean it with acetone; The copper part is immersed in a chemical nickel plating solution to form a uniform nickel layer on the copper surface, thereby completing the chemical nickel plating treatment on the copper surface; S2: Select an active solder containing titanium, the composition of which needs to include 70% silver, 25% copper, and 5% titanium; S3: Using a positioning fixture to clamp and position the processed graphite and copper parts to ensure that the gap between them is uniform so as to meet the brazing requirements; S4: Place the assembled graphite and copper parts in a vacuum chamber at a brazing temperature of 360°C and a vacuum degree of 1x10 -1 Pa-1x10 -3 Pa vacuum brazing furnace, brazing is carried out by means of staged heating, and the heat preservation after brazing is 10-30 minutes; S5: After brazing, cool down with the furnace, and the cooling rate needs to be controlled at 5℃ / min.

2. A method for brazing large-size graphite and copper according to claim 1, characterized in that: During the nickel plating process in which the copper part is immersed in the nickel plating solution, it is necessary to ensure that the thickness of the nickel plating layer is 0.05-0.1 mm.

3. A method for brazing large-size graphite and copper according to claim 1, characterized in that: In the clamping and positioning, the gap between the graphite and the copper piece ranges from 0.05 to 0.1 mm.

4. The brazing method of large-size graphite and copper according to claim 1, characterized in that: The stepwise heating method is to first heat from room temperature to 360°C at a heating rate of 20°C / min; Then keep at 360℃ for 20 minutes; Then the temperature was raised to 560°C at a rate of 25°C / min; Finally, the temperature was kept at 560°C for 30 minutes, and then the temperature was increased to 830°C at a rate of 25°C / min; Finally, the temperature was kept at 830°C for 15 minutes until the final brazing temperature of 890°C was reached.

5. The brazing method of large-size graphite and copper according to claim 1, characterized in that: After the brazing part is cooled to room temperature, it is necessary to heat the brazing part to 450° C. at 20° C. / min, keep the temperature for 2 hours, and then cool it to room temperature at 5° C. / min.

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