Composite bar and welding method

Abstract

The invention provides a composite bar and a welding method. The welding method comprises the following steps that chemical and mechanical composite treatment is conducted on the surfaces of a 4J29 kovar alloy pipe and a TU1 oxygen-free copper bar; the TU1 oxygen-free copper rod is placed in a liquid nitrogen medium, and after the TU1 oxygen-free copper rod is cooled to-150 DEG C, assembling is conducted; the assembled 4J29 kovar alloy pipe and TU1 oxygen-free copper bar are placed in a furnace cavity of current-assisted vacuum diffusion welding equipment, a pressure head assembly is used for axial loading, and a pulse current meter is connected with the pressure head assembly; and the assembled 4J29 kovar alloy pipe and TU1 oxygen-free copper bar are subjected to current-assisted vacuum diffusion welding machining, and the 4J29 kovar alloy pipe and TU1 oxygen-free copper bar composite bar is obtained. According to the method, the interface diffusion behavior is regulated and controlled through cooperation of the pressure field, the temperature field and the current field, dissimilar welding of the 4J29 kovar alloy pipe and the TU1 oxygen-free copper bar is achieved, the microstructure of the composite bar obtained through the method shows that defects such as air holes and inclusions are not observed in a weld joint area, the process is simplified, and energy consumption is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of functional composite materials, and in particular relates to a composite rod and a welding method. Background Art

[0002] In the context of the rapid development of electronic components and chip technology in modern society, the heat generated by electronic components during operation is increasing. Under this background, electronic packaging materials need to have more outstanding comprehensive performance to meet excellent performance while overcoming many shortcomings such as slow heat dissipation.

[0003] Copper (Cu) has excellent thermal conductivity, which makes Cu-based composite materials the research focus in the field of high-performance electronic packaging materials. Kovar alloy (4J29), also known as "constant expansion alloy", can maintain a low and stable thermal expansion coefficient below the Curie point. Therefore, Kovar alloy and Cu composite materials can overcome the shortcomings of Kovar alloy's insufficient thermal conductivity while retaining its low thermal expansion coefficient and good weldability, making it an ideal electronic packaging material.

[0004] At present, welding methods are commonly used to prepare Kovar alloy and Cu composite materials. However, the melting points of Kovar alloy and Cu are quite different, and ordinary welding methods are difficult to apply. Taking vacuum brazing as an example, it is very easy to generate large residual stress at the welded joint, which in turn causes the mechanical properties of the welded joint to decrease. Although hot isostatic diffusion welding can effectively realize the welding of Cu and Kovar alloy, and the weld is defect-free, the process has the problems of complex process, high energy consumption and high cost, and its air tightness and electrical properties after sealing are also difficult to guarantee.

[0005] In summary, the existing Kovar-Cu composite material preparation process generally has problems such as complex process, high energy consumption, lengthy process, and high cost, and there is still a lack of effective solutions. Summary of the invention

[0006] In view of the above technical problems, the present invention provides a composite rod welding method, which is an innovative process based on current-assisted vacuum diffusion welding. Through the multi-field coupling mechanism (pressure field-temperature field-current field), the interface diffusion behavior is coordinated and regulated, and the axial pressure, gradient temperature and pulse current parameters are accurately controlled in a vacuum environment to achieve the dissimilar welding of 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod. The microstructure of the composite rod obtained by this method shows that no defects such as pores and inclusions are observed in the weld area, and the generation of microcracks caused by thermal stress concentration is suppressed. The welding cycle is shortened to 1 hour, which simplifies the process and reduces energy consumption while ensuring the metallurgical quality of the interface.

[0007] The present invention also provides a composite rod, which is prepared by the composite rod welding method, has a smooth weld surface and has no obvious defects such as cracks visible to the naked eye.

[0008] The present invention achieves the above technical objectives through the following technical means.

[0009] The present invention performs chemical and mechanical composite treatment on the surface of 4J29 Kovar alloy tube and TU1 oxygen-free copper rod; the TU1 oxygen-free copper rod is placed in a liquid nitrogen medium, and after the TU1 oxygen-free copper rod is cooled to -150°C, it is assembled; the assembled 4J29 Kovar alloy tube and TU1 oxygen-free copper rod are placed in the furnace chamber of a current-assisted vacuum diffusion welding device, the pressure head assembly is axially loaded, and the pulse current meter is connected to the pressure head assembly; the assembled 4J29 Kovar alloy tube and TU1 oxygen-free copper rod are processed by current-assisted vacuum diffusion welding to obtain a composite rod of 4J29 Kovar alloy tube and TU1 oxygen-free copper rod. The present invention realizes heterogeneous welding of 4J29 Kovar alloy tube and TU1 oxygen-free copper rod by synergistically regulating interface diffusion behavior through pressure field-temperature field-current field, and the microstructure of the composite rod obtained by the method shows that no defects such as pores and inclusions are observed in the weld area, thereby simplifying the process and reducing energy consumption.

[0010] A composite bar welding method comprises the following steps:

[0011] Step S1: chemically and mechanically treating the surfaces of a 4J29 Kovar alloy tube and a TU1 oxygen-free copper rod;

[0012] Step S2: placing the oxygen-free copper rod of TU1 after the composite treatment in step S1 in a liquid nitrogen medium, and after the oxygen-free copper rod of TU1 is cooled to, assembling the 4J29 Kovar alloy tube and the oxygen-free copper rod of TU1;

[0013] Step S3: placing the 4J29 Kovar alloy tube and TU1 oxygen-free copper rod assembled in step S2 in a furnace chamber of a current-assisted vacuum diffusion welding device, axially loading the pressure head assembly of the current-assisted vacuum diffusion welding device so that the workpiece to be welded is in strict contact with the pressure head, and connecting a pulse current meter of the current-assisted vacuum diffusion welding device to the pressure head assembly;

[0014] Step S4: in a vacuum environment, the thermomechanical coupling parameters are precisely controlled by the control system of the current-assisted vacuum diffusion welding equipment, and the 4J29 Kovar alloy tube and the TU1 oxygen-free copper rod assembled in step S3 are processed by current-assisted vacuum diffusion welding, and the metal molecules are diffused by activating the pressure of the pressure head and the pulse current, so as to achieve efficient metallurgical bonding of the 4J29 Kovar alloy and the TU1 oxygen-free copper;

[0015] Step S5: After completing the current-assisted vacuum diffusion welding in step S4, turn off the heating system of the current-assisted vacuum diffusion welding equipment and keep the vacuum system running continuously. Preferably, cool at a cooling rate of ≤4°C / min until the furnace temperature drops to room temperature, to obtain a composite rod of 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod; the interface of the composite rod presents continuous and dense metallurgical bonding characteristics, without obvious defects such as voids and cracks.

[0016] In the above scheme, the chemical and mechanical composite treatment in step S1 is specifically as follows: first, the inner wall surface of the 4J29 Kovar alloy pipe is soaked in acetone solution for 10 minutes to remove the surface machining oil, ultrasonic cleaning is performed for 8 minutes to remove the residual particles in the tube cavity, and a hydrochloric acid solution with a mass fraction of 18% to 20% is used to soak at room temperature for 8 minutes to remove the surface oxide film; secondly, the surface of the TU1 oxygen-free copper rod is sandblasted, and the two ends are chamfered (30°) to eliminate stress concentration.

[0017] In the above scheme, the dimensions of the 4J29 Kovar alloy pipe are: length 38mm-40mm, outer diameter 18mm-20mm, inner diameter 4.9mm-5.1mm.

[0018] In the above solution, the size of the TU1 oxygen-free copper rod is 38mm-40mm in length and 5.0mm-5.1mm in diameter.

[0019] In the above scheme, the TU1 oxygen-free copper rod after the composite treatment in step S2 is tied with metal filaments and placed in a liquid nitrogen pot for deep cold assembly. The temperature is tested with an industrial thermometer. After the TU1 oxygen-free copper rod is cooled to below -150°C, it is taken out and slowly placed inside the 4J29 Kovar alloy pipe. The 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod are cold assembled together by utilizing the large thermal expansion coefficient of copper.

[0020] Preferably, the TU1 oxygen-free copper rod is taken out after being cooled to -150°C to -170°C.

[0021] In the above scheme, in step S3, before starting the current-assisted vacuum diffusion welding equipment, the temperature measuring thermocouple is installed on the sample fixture, and the pressure head assembly is driven by a servo motor to achieve axial loading, so that the workpiece to be welded and the pressure head of the pressure loading system maintain strict contact, and the contact surface between the pressure head and the workpiece to be welded forms a stable closed loop, and ensures that the current is evenly distributed.

[0022] In the above scheme, the vacuum degree of the welding furnace chamber of the current-assisted vacuum diffusion welding in step S4 is controlled at -2MPa, and the gradient heating mode is heated to 950-1050°C at a heating rate of 10°C / min, and the constant temperature is maintained for 1 hour. The current-assisted synchronous application frequency is 50Hz and the current intensity is 1950A to promote current diffusion, and at the same time, the axial hot pressing pressure of 0.2-0.25Mpa is used to achieve dense connection of the materials.

[0023] Furthermore, in step S4, the vacuum degree of the welding furnace chamber of the current-assisted vacuum diffusion welding is controlled at -2MPa, the temperature is raised to 950°C at a heating rate of 10°C / min in the gradient heating mode, and the temperature is kept constant for 1 hour, and the current-assisted synchronous application frequency is 50Hz, the current intensity is 1950A, the duty cycle is 70%, and the current density is 10A / mm 2 , the auxiliary voltage is 4.47V to promote current diffusion, and the axial hot pressing pressure is 0.25Mpa.

[0024] Furthermore, in step S4, the vacuum degree of the welding furnace chamber of the current-assisted vacuum diffusion welding is controlled at -2MPa, the temperature is raised to 1000°C at a heating rate of 10°C / min in the gradient heating mode, and the temperature is kept constant for 1 hour, and the current-assisted synchronous application frequency is 50Hz, the current intensity is 1950A, the duty cycle is 70%, and the current density is 11A / mm 2 , the auxiliary voltage is 4.05V to promote current diffusion, and the axial hot pressing pressure is 0.25Mpa.

[0025] Furthermore, in step S4, the vacuum degree of the welding furnace chamber of the current-assisted vacuum diffusion welding is controlled at -2MPa, the temperature is increased to 1050°C at a heating rate of 10°C / min in the gradient heating mode, and the temperature is kept constant for 1 hour, and the current-assisted synchronous application frequency is 50Hz, the current intensity is 1950A, the duty cycle is 70%, and the current density is 12A / mm 2 , the auxiliary voltage is 3.62V to promote current diffusion, and the axial hot pressing pressure is 0.25Mpa.

[0026] A composite bar is prepared according to the composite bar welding method.

[0027] In the above scheme, the 4J29 Kovar alloy and TU1 oxygen-free copper composite rod has a dense structure, and no defects such as pores and inclusions are observed in the weld area, and no thermal stress cracks are generated.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention innovatively adopts current-assisted vacuum diffusion welding technology to solve the problem of traditional welding failure caused by the large difference in thermal expansion coefficients between Kovar and copper. By precisely controlling the auxiliary current, servo pressure and thermodynamic parameters, the metallurgical bonding of 4J29 Kovar and TU1 oxygen-free copper dissimilar alloys is successfully achieved to prepare composite rods with Kovar coated copper core. Compared with traditional fusion welding or brazing, this process has significant advantages: there are no macro cracks and pore defects at the welding interface; atomic diffusion is promoted by the current field; the method process is streamlined and energy consumption is reduced, which is suitable for precision manufacturing fields such as aerospace conductive components and nuclear reactor seals. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the process flow of the composite rod welding method of the present invention.

[0031] Figure 2 It is a schematic diagram of the current-assisted vacuum diffusion welding equipment of the present invention.

[0032] Figure 3 This is a temperature-time curve of current-assisted vacuum diffusion welding of the present invention.

[0033] Figure 4 This is a 2000x scanning electron microscope microstructure photograph of the composite rod prepared in Example 1 of the present invention.

[0034] Figure 5 This is a 2000x scanning electron microscope microstructure photograph of the composite rod prepared in Example 2 of the present invention.

[0035] Figure 6 This is a 2000x scanning electron microscope microstructure photograph of the composite rod prepared in Example 3 of the present invention.

[0036] Figure 7 The microstructure photograph of the composite rod prepared for the comparative example was taken with a scanning electron microscope at 2000 times magnification. DETAILED DESCRIPTION

[0037] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0038] Example 1

[0039] Figure 1 is a schematic diagram of the process of the composite rod welding method of the present invention, Figure 2The invention discloses a preferred embodiment of a current-assisted vacuum diffusion welding device for realizing a composite rod welding method adopted by the present invention. The current-assisted vacuum diffusion welding device adds a pulse ammeter on the basis of the existing vacuum diffusion welding device, including an upper graphite pressure head and a lower graphite pressure head of a pressure head assembly, a graphite plate, an experimental tooling, a pulse ammeter and a control system; the pressure head assembly is connected to a servo motor, and the servo motor drives the pressure head assembly to realize axial loading; the positive and negative poles of the pulse ammeter are respectively connected to the upper graphite pressure head and the lower graphite pressure head, and the current is transmitted to the workpiece to be processed placed in the experimental tooling through the upper graphite pressure head and the lower graphite pressure head, so that the workpiece to be processed is subjected to thermal coupling and the action of the current at the same time, thereby realizing efficient metallurgical bonding.

[0040] During the experiment, pressure was applied to the upper graphite plate to ensure that the tooling sample and the graphite plate were in close contact under the action of pressure. The mica sheet placed in the middle of the graphite plate ensured that all current passed through the tooling.

[0041] The composite bar welding method comprises the following steps:

[0042] Step S1: chemically and mechanically treating the surfaces of a 4J29 Kovar alloy tube and a TU1 oxygen-free copper rod;

[0043] Step S2: placing the oxygen-free copper rod of TU1 after the composite treatment in step S1 in a liquid nitrogen medium for ten minutes, and after the oxygen-free copper rod of TU1 is cooled to -150°C, placing the oxygen-free copper rod of TU1 into the inner cavity of the 4J29 Kovar alloy tube for assembly;

[0044] Step S3: placing the 4J29 Kovar alloy tube and TU1 oxygen-free copper rod assembled in step S2 in a current-assisted vacuum diffusion welding furnace chamber, and the control system of the current-assisted vacuum diffusion welding equipment controls the servo motor to drive the pressure head assembly to achieve axial loading, so that the workpiece to be welded maintains strict contact with the pressure head;

[0045] Step S4: in a vacuum environment, the thermomechanical coupling parameters are precisely controlled by a numerical control system, and the 4J29 Kovar alloy tube and the TU1 oxygen-free copper rod assembled in step S3 are subjected to vacuum diffusion welding. The metal molecules are diffused by combining the pressure of the pressure head and the pulse current assisted by the current, and the efficient metallurgical bonding of the 4J29 Kovar alloy and the TU1 oxygen-free copper is achieved under the action of thermomechanical coupling and current.

[0046] Step S5: After completing the current-assisted vacuum diffusion welding process in step S4, turn off the heating system and keep the vacuum system running continuously, and cool at a cooling rate of ≤4°C / min until the furnace temperature drops to room temperature, thereby obtaining a composite rod of 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod; the interface of the composite rod presents continuous and dense metallurgical bonding characteristics, and no obvious defects such as voids and cracks are observed.

[0047] The chemical and mechanical composite treatment in step S1 is specifically as follows: first, the inner wall surface of the 4J29 Kovar alloy pipe is soaked in acetone solution for 10 minutes to remove the surface machining oil, ultrasonic cleaning is performed for 8 minutes to remove the residual particles in the tube cavity, and a hydrochloric acid solution with a mass fraction of 18% to 20% is used to soak at room temperature for 8 minutes to remove the surface oxide film; secondly, the surface of the TU1 oxygen-free copper rod is sandblasted, and the two ends thereof are chamfered (30°) to eliminate stress concentration.

[0048] The dimensions of the 4J29 Kovar alloy tube are: outer diameter 20 mm, inner diameter 5.0 mm, length 40 mm. The dimensions of the TU1 oxygen-free copper rod are: diameter 5.1 mm, length 40 mm.

[0049] The TU1 oxygen-free copper rod after the composite treatment in step S2 is tied with metal filaments and placed in a liquid nitrogen pot for deep cold assembly. The temperature is tested with an industrial thermometer. After the TU1 oxygen-free copper rod is cooled to -150°C, it is taken out and slowly placed inside the 4J29 Kovar alloy pipe. The 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod are cold assembled together by utilizing the large thermal expansion coefficient of copper.

[0050] In step S3, before starting the vacuum diffusion welding furnace, a temperature measuring thermocouple is installed on the sample fixture, and the pressure head assembly is axially loaded through a high-precision servo control system, so that the workpiece to be welded and the pressure head are kept in strict contact, and the contact surface between the pressure head and the workpiece to be welded forms a stable closed loop, and ensures that the current is evenly distributed.

[0051] In step S4, the vacuum degree of the welding furnace chamber of the current-assisted vacuum diffusion welding is controlled at -2MPa, and the temperature is increased to 950°C at a heating rate of 10°C / min in a gradient heating mode, and the temperature is kept constant for 1 hour. The current-assisted synchronous application frequency is 50Hz, the current intensity is 1950A, the duty cycle is 70%, and the current density is 10A / mm 2 , the auxiliary voltage is 4.47V to promote current diffusion, and the axial hot pressing pressure is 0.25Mpa.

[0052] In this embodiment, the prepared Kovar alloy and copper composite rod has no defects such as cracks visible to the naked eye. Figure 4 shown.

[0053] Example 2

[0054] The specific preparation steps are the same as those in Example 1. The difference between this example and Example 1 is that:

[0055] In step S4, the vacuum degree of the welding furnace chamber of the current-assisted vacuum diffusion welding is controlled at -2 MPa, and the temperature is raised to 1000° C. (eg, Figure 3The current was assisted synchronously with a frequency of 50 Hz, a current intensity of 1950 A, a duty cycle of 70%, and a current density of 11 A / mm2. 2 , the auxiliary voltage is 4.05V to promote current diffusion, and the axial hot pressing pressure is 0.25Mpa.

[0056] The composite rod prepared by the parameters of this embodiment has a dense metallographic structure and no defects such as cracks visible to the naked eye. Figure 5 shown.

[0057] Example 3

[0058] The specific preparation steps are the same as those in Example 1. The difference between this example and Example 1 is that:

[0059] In step S4, the vacuum degree of the welding furnace chamber of the current-assisted vacuum diffusion welding is controlled at -2 MPa, and the temperature is raised to 1050°C (such as 10°C / min) at a heating rate of 10°C / min in a gradient heating mode. Figure 3 The current was assisted by synchronous application of 50Hz frequency, 1950A current intensity, 70% duty cycle, and 12A / mm2 current density. 2 , the auxiliary voltage is 3.62V to promote current diffusion, and the axial hot pressing pressure is 0.25Mpa.

[0060] The composite rod prepared by the parameters of this embodiment has a dense metallographic structure and no defects such as cracks visible to the naked eye. Figure 6 shown.

[0061] Comparative Example 1

[0062] A conventional welding process of Kovar alloy and copper rod composite rod comprises the following steps:

[0063] Step S1: Step S1: chemical and mechanical composite treatment is performed on the surfaces of the Kovar alloy tube with the grade of 4J29 and the oxygen-free copper rod with the grade of TU1;

[0064] Step S2: Assemble the Kovar alloy tube and the copper rod, and place the TU1 oxygen-free copper rod in the inner cavity of the 4J29 Kovar alloy tube;

[0065] Step S3: placing the workpiece assembled in step S2 into a vacuum diffusion welding furnace, ensuring that the pressure head is placed vertically on the workpiece;

[0066] Step S4: vacuum diffusion welding is performed on the workpiece to be processed in step S3, and the workpiece is subjected to thermal coupling under the pressure of the pressure head, so as to prepare a composite rod of Kovar alloy and copper;

[0067] Step S5: After the temperature drops to room temperature, take out the Kovar alloy and copper composite rod.

[0068] The chemical and mechanical composite treatment in step S1 is specifically as follows: first, the inner wall surface of the 4J29 Kovar alloy pipe is soaked in acetone solution for 10 minutes to remove the surface machining oil, ultrasonic cleaning is performed for 8 minutes to remove the residual particles in the tube cavity, and a hydrochloric acid solution with a mass fraction of 18% to 20% is used to soak at room temperature for 8 minutes to remove the surface oxide film; secondly, the surface of the TU1 oxygen-free copper rod is sandblasted, and the two ends thereof are chamfered (30°) to eliminate stress concentration.

[0069] The dimensions of the Kovar alloy tube are: outer diameter 20 mm, inner diameter 7 mm, length 50 mm. The dimensions of the copper rod are: diameter 7 mm, length 50 mm.

[0070] The processing parameters of the vacuum diffusion welding in step S4 are: the vacuum degree of the welding furnace chamber is controlled at -2MPa, the temperature is increased to 1000°C at a heating rate of 10°C / min in a gradient heating mode, and the temperature is maintained at a constant temperature for 3 hours, and the vertical hot pressing pressure is 2.5Mpa.

[0071] The conventional vacuum diffusion welding process is used to prepare the Kovar alloy and copper composite rod, and the insulation time is as long as 3 hours. The insulation time of the process of the present invention is only 1 hour, which greatly shortens the process flow. The energy consumption of the comparative example is large and the pressure is 2.5MPa. The hot pressing pressure of the present invention is 0.2-0.25MPa. It can be seen that the present invention is more energy-efficient, and the prepared composite rod has a dense metallographic structure without obvious weld defects, while the metallographic structure of the comparative example has obvious weld defects and is not welded. Figure 7 shown.

[0072] The present invention prepares 4J29 Kovar alloy and TU1 oxygen-free copper composite rods by current-assisted vacuum diffusion welding, and uses a vacuum diffusion welding furnace to heat to the bonding temperature, and simultaneously pressurizes the pressure head and heats by radiation through current-assisted, so as to achieve metallurgical bonding under the joint action of thermal coupling and current. The present invention gives full play to the advantages of current-assisted vacuum diffusion welding technology, coordinates and regulates the interface diffusion behavior through a multi-field coupling mechanism (pressure field-temperature field-current field), accurately controls the axial pressure, gradient temperature and pulse current parameters under a vacuum environment, and realizes the heterogeneous welding of 4J29 Kovar alloy pipes and TU1 oxygen-free copper rods. The microstructure of the composite rod obtained by the method shows that no defects such as pores and inclusions are observed in the weld area, and the generation of microcracks caused by thermal stress concentration is suppressed, and the welding cycle is shortened to 1h, while ensuring the metallurgical quality of the interface, the process is simplified and the energy consumption is reduced.

[0073] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0074] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A composite bar welding method, characterized in that: The following steps are involved: Step S1: chemically and mechanically treating the surfaces of a 4J29 Kovar alloy tube and a TU1 oxygen-free copper rod; Step S2: placing the oxygen-free copper rod of TU1 after the composite treatment in step S1 in a liquid nitrogen medium, and after the oxygen-free copper rod of TU1 is cooled, assembling the 4J29 Kovar alloy tube and the oxygen-free copper rod of TU1; Step S3: placing the 4J29 Kovar alloy tube and TU1 oxygen-free copper rod assembled in step S2 in a furnace chamber of a current-assisted vacuum diffusion welding device, axially loading the pressure head assembly of the current-assisted vacuum diffusion welding device so that the workpiece to be welded is in strict contact with the pressure head, and connecting a pulse current meter of the current-assisted vacuum diffusion welding device to the pressure head assembly; Step S4: performing current-assisted vacuum diffusion welding on the 4J29 Kovar alloy tube and TU1 oxygen-free copper rod assembled in step S3 under a vacuum environment, combining the pressure of the pressure head with the pulse current to activate the diffusion of metal molecules, so as to achieve efficient metallurgical bonding of the 4J29 Kovar alloy and the TU1 oxygen-free copper; Step S5: After completing the current-assisted vacuum diffusion welding in step S4, turn off the heating system of the current-assisted vacuum diffusion welding equipment and keep the vacuum system running continuously until the furnace temperature drops to room temperature, thereby obtaining a 4J29 Kovar alloy tube and a TU1 oxygen-free copper rod composite rod.

2. The composite bar welding method according to claim 1, characterized in that: The chemical and mechanical composite treatment in step S1 is specifically as follows: first, the inner wall surface of the 4J29 Kovar alloy pipe is soaked in acetone solution for 10 minutes to remove the surface machining oil, ultrasonic cleaning is performed for 8 minutes to remove the residual particles in the tube cavity, and a hydrochloric acid solution with a mass fraction of 18% to 20% is used to soak at room temperature for 8 minutes to remove the surface oxide film; secondly, the surface of the TU1 oxygen-free copper rod is sandblasted, and the two ends thereof are chamfered to eliminate stress concentration.

3. The composite bar welding method according to claim 1, characterized in that: The TU1 oxygen-free copper rod after the composite treatment in step S2 is tied tightly with metal filaments and placed in a liquid nitrogen pot for deep cold assembly. After the TU1 oxygen-free copper rod is cooled to below -150°C, it is taken out and slowly placed inside the 4J29 Kovar alloy pipe, and the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod are cold assembled together.

4. The composite bar welding method according to claim 3, characterized in that: Take out the TU1 oxygen-free copper rod after it cools to -150℃~-170℃.

5. The composite bar welding method according to claim 1, characterized in that: In step S3, before starting the current-assisted vacuum diffusion welding equipment, the temperature measuring thermocouple is installed on the sample fixture, and the pressure head assembly is driven by a servo motor to achieve axial loading, so that the workpiece to be welded and the pressure head of the pressure loading system maintain strict contact, and the contact surface between the pressure head and the workpiece to be welded forms a stable closed loop.

6. The composite bar welding method according to claim 1, characterized in that: In step S4, the vacuum degree of the welding furnace chamber of the current-assisted vacuum diffusion welding is controlled at -2MPa, and the gradient heating mode is heated to 950-1050°C at a heating rate of 10°C / min, and the constant temperature is maintained for 1 hour. The current-assisted synchronous application frequency is 50Hz and the current intensity is 1950A to promote current diffusion, while the axial hot pressing pressure is 0.2-0.25Mpa.

7. The composite bar welding method according to claim 6, characterized in that: In step S4, the vacuum degree of the welding furnace chamber of the current-assisted vacuum diffusion welding is controlled at -2MPa, and the temperature is increased to 950°C at a heating rate of 10°C / min in a gradient heating mode, and the temperature is kept constant for 1 hour. The current-assisted synchronous application frequency is 50Hz, the current intensity is 1950A, the duty cycle is 70%, and the current density is 10A / mm 2 , the auxiliary voltage is 4.47V to promote current diffusion, and the axial hot pressing pressure is 0.25Mpa.

8. The composite bar welding method according to claim 6, characterized in that: In step S4, the vacuum degree of the welding furnace chamber of the current-assisted vacuum diffusion welding is controlled at -2MPa, and the temperature is increased to 1000°C at a heating rate of 10°C / min in the gradient heating mode, and the temperature is kept constant for 1 hour. The current-assisted synchronous application frequency is 50Hz, the current intensity is 1950A, the duty cycle is 70%, and the current density is 11A / mm 2 , the auxiliary voltage is 4.05V to promote current diffusion, and the axial hot pressing pressure is 0.25Mpa.

9. The composite bar welding method according to claim 6, characterized in that: The vacuum degree of the welding furnace chamber of the step S4 current-assisted vacuum diffusion welding is controlled at -2MPa, and the temperature is raised to 1050°C at a heating rate of 10°C / min in a gradient heating mode, and the temperature is kept constant for 1 hour. The current-assisted synchronous application frequency is 50Hz, the current intensity is 1950A, the duty cycle is 70%, and the current density is 12A / mm 2 , the auxiliary voltage is 3.62V to promote current diffusion, and the axial hot pressing pressure is 0.25Mpa.

10. A composite rod, characterized in that: Prepared by the composite bar welding method according to any one of claims 1-9.

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