CN115255606A - A kind of copper and graphite diffusion connection method containing aluminum intermediate layer - Google Patents

Abstract

A copper and graphite diffusion connection method with an aluminum intermediate layer belongs to the technical field of connection of dissimilar materials. The invention adopts the magnetron sputtering technology to prepare the micron-level aluminum intermediate layer on the graphite surface, and then performs vacuum diffusion connection with the copper assembly; in the connection process, the "two-stage method" process is adopted, and the copper matrix and the aluminum intermediate layer are first made of each other. The CuAl alloy layer is formed by diffusion, and then diffusion connection is performed with the graphite matrix, and finally a connection joint of the copper/CuAl alloy layer/Al ₄ C ₃ compound/graphite structure is formed. The advantages of the present invention are: (1) greatly reducing the diffusion bonding temperature of copper and graphite, and reducing welding stress; (2) promoting the reaction of the connection interface to ensure that each interface of the joint is a good metallurgical bond.

Description

Copper and graphite diffusion connection method of an aluminum-containing interlayer

technical field

The invention belongs to the technical field of dissimilar material welding, and in particular provides a diffusion connection method suitable for low connection temperature and good interface bonding of copper and graphite.

Background technique

Graphite has the advantages of good thermal conductivity, electrical conductivity, high melting point, good thermal shock resistance, thermal fatigue resistance, corrosion resistance, etc., and has been used more and more in metallurgy, electronics, automobiles, nuclear power, aerospace and other fields. Wide range of applications. However, due to the problems of low strength, high brittleness, and easy blackening of the surface of graphite, it is difficult to use it alone, and it is usually necessary to connect it with metal to prepare parts. Due to its excellent electrical and thermal conductivity, ductility and radiation resistance, copper is the most promising metal material for connecting with graphite to prepare structural and functional components. Graphite and copper connectors have been widely used in the first wall of nuclear fusion reactors and commutators of automobile motors. Due to the large difference in the melting points of graphite and copper, it is difficult to use fusion welding to connect. Currently, the connection between graphite and copper is generally connected by diffusion connection. However, the diffusion connection between graphite and copper is more difficult, which is mainly reflected in (1) in order to promote the diffusion between graphite and copper during the connection process, the current diffusion connection temperature is generally high, and the thermal expansion coefficient difference between graphite and copper is very different , the joint will produce a large residual thermal stress under the condition of high temperature connection; (2) The interaction between graphite (carbon) and copper is weak, neither solid solution with each other nor intermetallic compound can be formed, so the connection interface is often only in the A "mechanical occlusion" state rather than a metallurgical bond results in poor interfacial bonding. Therefore, research and development of a diffusion bonding method for copper and graphite with low bonding temperature and good interfacial bonding has become one of the key issues in the field of bonding dissimilar materials.

Contents of the invention

The purpose of the present invention is to propose a copper alloy with an aluminum-containing intermediate layer for the problems that the high connection temperature in the current copper/graphite diffusion connection leads to large joint thermal stress, and the weak interaction between graphite and copper leads to poor interfacial bonding. Diffusion connection method with graphite, which can greatly reduce the diffusion connection temperature of copper and graphite, reduce welding stress, and promote the reaction of the connection interface to ensure good metallurgical bonding at all interfaces of the joint.

A copper-graphite diffusion connection method for an aluminum-containing interlayer, characterized in that a micron-sized aluminum interlayer is prepared on the graphite surface by magnetron sputtering technology, and then assembled with copper for vacuum diffusion connection; during the connection process, " The two-stage method" process firstly makes the copper substrate interdiffused with the aluminum intermediate layer to form a CuAl alloy layer, and then diffuses and connects with the graphite substrate, finally forming a connection joint of copper/CuAl alloy layer/Al ₄ C ₃ compound/graphite structure.

Concrete technological process of the present invention comprises the following steps:

Step 1, place the graphite and aluminum targets after grinding, polishing, ultrasonic cleaning and drying in the sample chamber and target stage of the magnetron sputtering system respectively, and vacuum the sample chamber to 1×10 ^-3 Pa～5× 10 ^-4 Pa;

Step 2: Infuse high-purity argon gas into the sample chamber until the pressure in the sample chamber is 0.5-0.8 Pa, and stabilize the temperature of the sample chamber at 20°C-30°C, turn on the magnetron sputtering switch, and sputter Al coating on the graphite surface. layer, the sputtering time is 45min~60min, the sputtering power is 60W~85W, and the sputtering coating thickness is 15~20μm;

Step 3, after grinding, polishing, ultrasonic cleaning, and drying the sputtered Al-coated graphite obtained in step 2, assemble it with the copper surface to be connected, and place the copper on the magnetron sputtered Al-coated graphite and placed in the vacuum diffusion connection mold to obtain the assembled pre-welded parts;

Step 4, put the assembled pre-welded parts into the hearth of the high-vacuum diffusion welding furnace and evacuate it. When the vacuum degree reaches 1×10 ^-4 Pa, start heating and pressurizing at a pressure of 4-8 MPa/min. Load the pressure rate to 40~60MPa and keep the pressure all the time, raise the temperature to 500~550℃ at a rate of 5~10℃/min and keep it for 10~20min, and then increase the temperature at a rate of 5~10℃/min to 650-700° C., keep warm for 10-20 minutes, and then cool with the furnace to obtain a connection joint of copper/CuAl alloy layer/Al ₄ C ₃ compound/graphite structure.

Further, the grinding, polishing, ultrasonic cleaning, and drying treatment described in step 1 are to grind and polish the surface of graphite and aluminum laser pulse sputtering targets, and then use acetone, alcohol, and deionized water to perform ultrasonic cleaning for 15 to 20 minutes, Put it into a drying oven with a constant temperature of 40-50°C for 20-30 minutes.

Further, the grinding, polishing, ultrasonic cleaning, and drying treatment described in step 3 are to grind and polish the graphite and copper surfaces coated with magnetron sputtering Al, and then use acetone, alcohol, and deionized water to perform ultrasonic cleaning for 15 minutes. ~20min, put it into a drying oven with a constant temperature of 40~50°C for 20~30min.

The present invention has the following advantages:

(1) Copper and graphite are diffused and connected using the "two-stage method" process with aluminum as the intermediate layer. With the help of the strong interaction between aluminum and copper elements, aluminum and carbon elements, the connection can be realized at a relatively low temperature , greatly reducing the welding stress of the connecting joint;

(2) Copper and graphite are diffused and connected with aluminum as the intermediate layer. In the first stage, interdiffusion of elements occurs at the copper/aluminum interface, so that the aluminum intermediate layer is transformed into a CuAl alloy layer; in the second stage, the CuAl alloy layer/graphite A reaction occurs at the interface to generate Al ₄ C ₃ compound. With the help of the aluminum interlayer, it is avoided that the connection interface between copper and graphite is only "mechanically occluded" due to the weak interaction, and each interface of the connection joint has achieved good metallurgical bonding.

Description of drawings

Fig. 1 is a scanning electron microscope image of the structure of the copper/graphite diffusion bonded joint with an aluminum interlayer in Example 1. Graphite on the left and copper on the right. The Al ₄ C ₃ compound layer is on the side close to the graphite in the connection interface structure, and the CuAl alloy layer is on the side close to the copper. The interfaces of the connection joints are dense and defect-free, forming a good metallurgical bond.

Detailed ways

Example 1

This embodiment is a welding method of copper and graphite. The copper involved is T1 red copper, which is machined into a cylinder of Φ15mm×3mm; the graphite involved is cylindrical graphite of Φ15mm×3mm.

The specific process of this embodiment includes the following steps:

Step 1. After grinding and polishing the surface of the copper, graphite and aluminum magnetron sputtering targets, ultrasonically clean them with acetone, alcohol, and deionized water for 15 minutes, and then dry them in a drying oven with a constant temperature of 50°C for 25 minutes. Place the dried graphite and aluminum targets in the sample chamber and target stage of the magnetron sputtering system respectively, and evacuate the sample chamber to 5×10 ^-4 Pa;

Step 2: Infuse high-purity argon gas into the sample chamber until the pressure in the sample chamber is 0.6Pa, and stabilize the temperature of the sample chamber at 24°C, turn on the magnetron sputtering switch, and sputter Al coating on the graphite surface. 50min, sputtering power 65W;

Step 3: Grinding and polishing the Al-coated graphite and copper surfaces by magnetron sputtering, followed by ultrasonic cleaning with acetone, alcohol, and deionized water for 15 minutes, and drying in a drying oven at a constant temperature of 50°C for 25 minutes. Assembling the graphite coated with magnetron sputtered Al and the copper surface to be connected, placing the copper above the graphite coated with magnetron sputtered Al and placing it in a vacuum diffusion connection mold;

Step 4, put the assembled pre-welded parts into the hearth of the high-vacuum diffusion welding furnace and evacuate it. When the vacuum degree reaches 1×10 ^-4 Pa, start heating and pressurizing at a pressurization rate of 4MPa/min Load to 40MPa and maintain the pressure all the time, raise the temperature to 550°C at a rate of 10°C/min and keep it for 10 minutes, then raise it to 650°C at a rate of 8°C/min, keep it for 10 minutes and then cool it with the furnace to get Connection joint of copper/CuAl alloy layer/Al ₄ C ₃ compound/graphite structure.

Step 5: Cut the T1 red copper and graphite joint obtained in step 4 along the axial section by machining, polish the interface with sandpaper, prepare a metallographic sample, and observe the microstructure of the joint with a scanning electron microscope, as shown in Figure 1 As shown, the final connection joint is a copper/CuAl alloy layer/Al ₄ C ₃ compound/graphite structure, and each interface of the joint is dense and defect-free, forming a good metallurgical bond. The highest diffusion connection temperature of copper and graphite in this method is 650°C, which is far lower than the connection temperature of 870°C in the existing copper/graphite diffusion connection technology, effectively reducing welding stress.

Example 2

This embodiment is a welding method of copper and graphite. The copper involved is T1 red copper, which is machined into a cylinder of Φ15mm×3mm; the graphite involved is cylindrical graphite of Φ15mm×3mm.

The specific process of this embodiment includes the following steps:

Step 1. After grinding and polishing the surface of the copper, graphite and aluminum magnetron sputtering targets, ultrasonically clean them with acetone, alcohol, and deionized water for 20 minutes, and then dry them in a drying oven with a constant temperature of 50°C for 30 minutes. Place the dried graphite and aluminum targets in the sample chamber and target stage of the magnetron sputtering system respectively, and evacuate the sample chamber to 5×10 ^-4 Pa;

Step 2: Infuse high-purity argon gas into the sample chamber until the pressure in the sample chamber is 0.7 Pa, and stabilize the temperature of the sample chamber at 26°C, turn on the magnetron sputtering switch, and sputter Al coating on the graphite surface, the sputtering time is 55min, sputtering power 75W;

Step 3: Grinding and polishing the Al-coated graphite and copper surfaces by magnetron sputtering, followed by ultrasonic cleaning with acetone, alcohol, and deionized water for 20 minutes, and drying in a drying oven at a constant temperature of 50°C for 20 minutes. Assembling the graphite coated with magnetron sputtered Al and the copper surface to be connected, placing the copper above the graphite coated with magnetron sputtered Al and placing it in a vacuum diffusion connection mold;

Step 4, put the assembled pre-welded parts into the hearth of the high-vacuum diffusion welding furnace and vacuumize it. When the vacuum degree reaches 1×10 ^-4 Pa, start heating and pressurizing at a pressurization rate of 5MPa/min Load to 45MPa and maintain the pressure all the time, raise the temperature to 520°C at a rate of 10°C/min and keep it for 15 minutes, then raise it to 680°C at a rate of 5°C/min, keep it for 15 minutes and then cool it with the furnace to get Connection joint of copper/CuAl alloy layer/Al ₄ C ₃ compound/graphite structure.

In step 5, the T1 red copper and graphite joint obtained in step 4 is cut along the axial section by machining, the interface is polished with sandpaper and then polished to prepare a metallographic sample, and the microstructure of the joint is observed with a scanning electron microscope.

Example 3

This embodiment is a welding method of copper and graphite. The copper involved is T1 red copper, which is machined into a cylinder of Φ15mm×3mm; the graphite involved is cylindrical graphite of Φ15mm×3mm.

The specific process of this embodiment includes the following steps:

Step 1. After grinding and polishing the surface of the copper, graphite and aluminum magnetron sputtering targets, ultrasonically clean them with acetone, alcohol, and deionized water for 20 minutes, and then dry them in a drying oven with a constant temperature of 50°C for 20 minutes. Place the dried graphite and aluminum targets in the sample chamber and target stage of the magnetron sputtering system respectively, and evacuate the sample chamber to 5×10 ^-4 Pa;

Step 2: Infuse high-purity argon gas into the sample chamber until the pressure in the sample chamber is 0.8 Pa, and stabilize the temperature of the sample chamber at 28°C, turn on the magnetron sputtering switch, and sputter Al coating on the graphite surface, the sputtering time is 60min, sputtering power 85W;

Step 3: Grinding and polishing the Al-coated graphite and copper surfaces by magnetron sputtering, followed by ultrasonic cleaning with acetone, alcohol, and deionized water for 15 minutes, and drying in a drying oven at a constant temperature of 50°C for 30 minutes. Assembling the graphite coated with magnetron sputtered Al and the copper surface to be connected, placing the copper above the graphite coated with magnetron sputtered Al and placing it in a vacuum diffusion connection mold;

Step 4, put the assembled pre-welded parts into the hearth of the high-vacuum diffusion welding furnace and vacuumize it. When the vacuum degree reaches 1×10 ^-4 Pa, start heating and pressurizing at a pressurization rate of 5MPa/min Load to 50MPa and maintain the pressure all the time, raise the temperature to 500°C at a rate of 10°C/min and keep it for 20 minutes, then raise it to 700°C at a rate of 5°C/min, keep it for 20 minutes and then cool with the furnace to get Connection joint of copper/CuAl alloy layer/Al ₄ C ₃ compound/graphite structure.

In step 5, the T1 red copper and graphite joint obtained in step 4 is cut along the axial section by machining, the interface is polished with sandpaper and then polished to prepare a metallographic sample, and the microstructure of the joint is observed with a scanning electron microscope.

Claims (3)

1. A copper and graphite diffusion connection method containing an aluminum intermediate layer is characterized in that a magnetron sputtering technology is adopted to prepare a micron-sized aluminum intermediate layer on the surface of graphite, and then the micron-sized aluminum intermediate layer is assembled with copper to be subjected to vacuum diffusion connection; in the connection process, a two-stage process is adopted, firstly, the copper matrix and the aluminum intermediate layer are mutually diffused to form a CuAl alloy layer, then, the CuAl alloy layer and the graphite matrix are subjected to diffusion connection, and finally, the copper/CuAl alloy layer/Al is formed₄C₃The specific process of the connecting joint of the compound/graphite structure comprises the following steps:

step 1, respectively placing graphite and an aluminum target material which are polished, ultrasonically cleaned and dried in a sample chamber and a target material table of a magnetron sputtering system, and vacuumizing the sample chamber to 1 multiplied by 10^-3Pa～5×10^-4Pa；

Step 2, introducing high-purity argon into the sample chamber until the pressure in the sample chamber is 0.5-0.8 Pa, stabilizing the temperature of the sample chamber at 20-30 ℃, opening a magnetron sputtering switch, sputtering an Al coating on the surface of the graphite for 45-60 min, wherein the sputtering power is 60-85W, and the thickness of the sputtering coating is 15-20 mu m;

step 3, after the graphite sputtered with the Al coating obtained in the step 2 is ground, polished, cleaned by ultrasonic waves and dried again, the graphite is assembled with a to-be-connected surface of copper, the copper is placed above the graphite subjected to magnetron sputtering of the Al coating and is placed in a vacuum diffusion connection die, and an assembled preset welding part is obtained;

step 4, placing the assembled preset welding part into a hearth of a high vacuum diffusion welding furnace and vacuumizing until the vacuum degree reaches 1 multiplied by 10^-4When Pa is needed, heating and pressurizing are started, 40-60 MPa is loaded at a pressurizing rate of 4-8 MPa/min and the pressure is kept all the time, the temperature is increased to 500-550 ℃ at a heating rate of 5-10 ℃/min and is kept for 10-20 min, then the temperature is increased to 650-700 ℃ at a heating rate of 5-10 ℃/min, and is kept for 10-20 min and then is cooled along with the furnace, and a copper/CuAl alloy layer/Al is obtained₄C₃A compound/graphite structure connection joint.

2. The method for diffusion bonding of copper and graphite with an aluminum interlayer according to claim 1, wherein the grinding, polishing, ultrasonic cleaning and drying treatment in step 1 are carried out by grinding and polishing the surfaces of the graphite and aluminum laser pulse sputtering target, then sequentially carrying out ultrasonic cleaning for 15-20 min with acetone, alcohol and deionized water, and drying treatment for 20-30 min in a drying oven with a constant temperature of 40-50 ℃.

3. The method for diffusion bonding of copper and graphite with an aluminum-containing interlayer according to claim 1, wherein the polishing, burnishing, ultrasonic cleaning and drying treatment in step 3 is to polish and polish the surfaces of graphite and copper with a magnetron sputtering Al coating, then sequentially perform ultrasonic cleaning for 15-20 min with acetone, alcohol and deionized water, and dry in a drying oven at a constant temperature of 40-50 ℃ for 20-30 min.

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