Composite bar and welding method

Abstract

The application provides a composite rod and a welding method, and comprises the following steps: performing chemical and mechanical composite treatment on the surfaces of 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod; placing the TU1 oxygen-free copper rod in a liquid nitrogen medium, and performing assembly after the TU1 oxygen-free copper rod is cooled to-150 DEG C; placing the assembled 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod in a furnace cavity of a current-assisted vacuum diffusion welding device, performing axial loading on a pressure head assembly, and connecting a pulse current instrument with the pressure head assembly; performing current-assisted vacuum diffusion welding processing on the assembled 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod, and obtaining a 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod composite rod. The interface diffusion behavior is synergistically regulated by a pressure field-temperature field-current field, so that the heterogeneous welding of the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod is realized. The microstructure of the composite rod obtained by the method shows that no pores, inclusions and other defects are observed in the weld area, so that the process is simplified and the energy consumption is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of functional composite materials, and particularly relates to a composite rod and a welding method. BACKGROUND

[0002] Under the background of rapid development of electronic components and chip technology in modern society, electronic components generate more and more heat in the running process. Under this background, electronic packaging materials need to have more excellent comprehensive performance to overcome the slow heat dissipation and other shortcomings while having excellent performance.

[0003] Copper (Cu) is the research focus in the field of high-performance electronic packaging materials due to its excellent thermal conductivity. Kovar alloy (4J29), also known as "constant expansion alloy", can maintain a low and stable thermal expansion coefficient below the Curie point. Therefore, the Kovar alloy and Cu composite material can overcome the shortcomings of insufficient thermal conductivity of Kovar alloy, and can retain its low thermal expansion coefficient and good weldability, and is an ideal electronic packaging material.

[0004] At present, the common method for preparing Kovar alloy and Cu composite material is welding. However, the melting points of Kovar alloy and Cu are quite different, and ordinary welding methods are difficult to apply. For example, in vacuum brazing, large residual stress is easily generated at the welded joint, which further causes the mechanical properties of the welded joint to decrease. Although hot isostatic pressing diffusion welding can effectively realize the welding of Cu and Kovar alloy, and the weld is defect-free, this process has the problems of complex process, high energy consumption, high cost, and difficult to guarantee the air tightness and electrical properties after sealing.

[0005] In summary, the existing preparation process of Kovar-Cu composite material has the problems of complex process, high energy consumption, long process, high cost, etc., and there is still a lack of effective solution. SUMMARY

[0006] In view of the above technical problems, the present application provides a composite rod welding method, which is an innovative process based on current-assisted vacuum diffusion welding. The method realizes the heterogeneous welding of 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod by precisely controlling the axial pressure, gradient temperature and pulse current parameters in a vacuum environment through multi-field coupling mechanism (pressure field-temperature field-current field) synergistic regulation of interface diffusion behavior. The microstructure of the composite rod obtained by the method shows that no pores, inclusions and other defects are observed in the weld area, and the generation of micro-cracks caused by thermal stress concentration is inhibited. The welding cycle is shortened to 1 hour, which ensures the interface metallurgical quality, simplifies the process and reduces the energy consumption.

[0007] The application further provides a composite rod prepared by the composite rod welding method, and the welding seam surface is smooth and free of obvious defects such as visible cracks.

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

[0009] The application performs chemical and mechanical composite treatment on the surfaces of the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod, places the TU1 oxygen-free copper rod in a liquid nitrogen medium, cools the TU1 oxygen-free copper rod to-150 DEG C, and then assembles; places the assembled 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod in a furnace cavity of a current-assisted vacuum diffusion welding device, axially loads a pressure head assembly, and connects a pulse current instrument with the pressure head assembly; performs current-assisted vacuum diffusion welding processing on the assembled 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod, and obtains a 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod composite rod. The application cooperatively regulates interface diffusion behavior through a pressure field-temperature field-current field, realizes dissimilar welding of the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod, and the composite rod obtained by the method does not observe pores, inclusions and other defects in the welding seam area, thereby simplifying the process and reducing energy consumption.

[0010] A composite rod welding method, comprising the following steps:

[0011] Step S1: performing chemical and mechanical composite treatment on the surfaces of a 4J29 Kovar alloy pipe and a TU1 oxygen-free copper rod;

[0012] Step S2: placing the TU1 oxygen-free copper rod after the composite treatment in step S1 in a liquid nitrogen medium, cooling the TU1 oxygen-free copper rod to-150 DEG C, and then assembling the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod;

[0013] Step S3: placing the assembled 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod in step S2 in a furnace cavity of a current-assisted vacuum diffusion welding device, axially loading a pressure head assembly of the current-assisted vacuum diffusion welding device to make the workpiece to be welded strictly contact with the pressure head, and connecting a pulse current instrument of the current-assisted vacuum diffusion welding device with the pressure head assembly;

[0014] Step S4: accurately regulating thermal coupling parameters by a control system of the current-assisted vacuum diffusion welding device in a vacuum environment, performing current-assisted vacuum diffusion welding processing on the assembled 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod in step S3, and combining pressure loading of the pressure head and pulse current to jointly activate metal molecular diffusion, thereby realizing high-efficiency metallurgical combination of the 4J29 Kovar alloy and the TU1 oxygen-free copper;

[0015] Step S5: After completing step S4, current-assisted vacuum diffusion welding, 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℃ / min until the furnace temperature drops to room temperature to obtain 4J29 Kovar alloy pipe and TU1 oxygen-free copper rod composite bar. The interface of the composite bar exhibits continuous and dense metallurgical bonding characteristics, and no obvious defects such as voids or cracks are observed.

[0016] In the above scheme, the chemical and mechanical composite treatment in step S1 is as follows: First, the inner wall surface of the 4J29 Kovar alloy pipe is soaked in acetone solution for 10 minutes to remove surface machining oil stains, ultrasonically cleaned for 8 minutes to remove residual particles in the pipe cavity, and soaked in 18% to 20% hydrochloric acid solution at room temperature for 8 minutes to remove the surface oxide film; second, the surface of the TU1 oxygen-free copper rod is sandblasted and its 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, and inner diameter 4.9mm-5.1mm.

[0018] In the above scheme, the TU1 oxygen-free copper rod has a length of 38mm-40mm and a diameter of 5.0mm-5.1mm.

[0019] In the above scheme, after the composite treatment in step S2, the TU1 oxygen-free copper rod is tied tightly with metal wire and placed in a liquid nitrogen container for cryogenic assembly. Its 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. Taking advantage of the large thermal expansion coefficient of copper, the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod are cold-assembled together.

[0020] Preferably, the TU1 oxygen-free copper rod is removed after cooling to -150℃ to -170℃.

[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 are in strict contact, the contact surface of the pressure head and the workpiece to be welded form a stable closed loop, and the current is evenly distributed.

[0022] In the above scheme, the vacuum degree of the welding furnace cavity in the step S4 current-assisted vacuum diffusion welding is controlled at -2 MPa, the gradient temperature rising mode is heated to 950-1050 DEG C at a temperature rising rate of 10 DEG C / min, and kept in a constant temperature state for 1 hour, the current-assisted synchronous application frequency is 50 Hz, the current intensity is 1950 A, the current density is 10 A / mm

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

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

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

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

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

[0028] Compared with the prior art, the beneficial effects of the present application are:

[0029] The application innovatively adopts current-assisted vacuum diffusion welding technology to solve the problem of traditional welding failure caused by the large difference in thermal expansion coefficient between Kovar alloy and copper. By accurately controlling the auxiliary current, servo pressure and thermodynamic parameters, the metallurgical combination of 4J29 Kovar alloy and TU1 oxygen-free copper dissimilar alloy is successfully realized, and the composite rod with Kovar alloy cladding copper core is prepared. Compared with traditional fusion welding or brazing, this process has the following advantages: no macroscopic crack and pore defects at the welding interface; atomic diffusion is promoted by the current field; the method process is simplified, energy consumption is reduced, and it is suitable for precision manufacturing fields such as aerospace conductive components and nuclear reactor seals. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a flowchart of the composite rod welding method of the application.

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

[0032] Figure 3 It is a temperature-time curve diagram of the current-assisted vacuum diffusion welding of the application.

[0033] Figure 4 It is a 2000 times scanning electron microscope microstructure photo of the composite rod prepared in Example 1 of the application.

[0034] Figure 5 It is a 2000 times scanning electron microscope microstructure photo of the composite rod prepared in Example 2 of the application.

[0035] Figure 6 It is a 2000 times scanning electron microscope microstructure photo of the composite rod prepared in Example 3 of the application.

[0036] Figure 7 It is a 2000 times scanning electron microscope microstructure photo of the composite rod prepared in the comparative example. DETAILED DESCRIPTION

[0037] The embodiments of the application are described in detail below, and examples of the embodiments are shown in the drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the application, and cannot be understood as a limitation of the application.

[0038] Example 1

[0039] Figure 1 It is a flowchart of the composite rod welding method of the application, Figure 2A preferred embodiment of the current-assisted vacuum diffusion welding device for realizing the composite rod welding method is adopted for the application, the current-assisted vacuum diffusion welding device is added with a pulse current instrument on the basis of an existing vacuum diffusion welding device, and comprises upper and lower graphite pressure heads of a pressure head assembly, a graphite plate, an experimental tooling, a pulse current instrument and a control system; the pressure head assembly is connected with a servo motor, and the servo motor drives the pressure head assembly to realize axial loading; the positive and negative poles of the pulse current instrument are connected with the upper and lower graphite pressure heads respectively, and the current is transmitted to the workpiece to be processed placed in the experimental tooling through the upper and lower graphite pressure heads, so that the workpiece to be processed is subjected to the action of heat coupling and current at the same time, and high-efficiency metallurgical bonding is realized.

[0040] During the experiment, the upper graphite plate is pressed, the tooling sample and the graphite plate are tightly attached under the action of the pressure, and the mica sheet placed in the middle of the graphite plate plays a role in ensuring that all the current passes through the tooling.

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

[0042] Step S1: the surfaces of the Kovar alloy pipe with a brand of 4J29 and the oxygen-free copper rod with a brand of TU1 are subjected to chemical and mechanical composite treatment;

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

[0044] Step S3: the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod assembled in step S2 are placed in a current-assisted vacuum diffusion welding furnace cavity, and the control system of the current-assisted vacuum diffusion welding device controls the servo motor to drive the pressure head assembly to realize axial loading, so that the workpiece to be welded and the pressure head are kept in strict contact;

[0045] Step S4: the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod assembled in step S3 are subjected to vacuum diffusion welding processing by accurately regulating and controlling the thermal coupling parameters through a numerical control system in a vacuum environment, the metal molecular diffusion is activated by the combined action of the pressure head pressure and the current-assisted pulse current, the workpiece to be welded is subjected to the action of heat coupling and current, and high-efficiency metallurgical bonding of the 4J29 Kovar alloy and the TU1 oxygen-free copper is realized;

[0046] Step S5: after the current-assisted vacuum diffusion welding process in step S4 is completed, the temperature rising system is turned off and the vacuum system continues to run, the cooling rate is ≤4 DEG C / min, and the temperature of the furnace body is reduced to room temperature until a 4J29 Kovar alloy pipe and a TU1 oxygen-free copper rod composite rod are obtained; the interface of the composite rod presents continuous and dense metallurgical bonding characteristics, and no obvious defects such as cavities and cracks are found.

[0047] The specific steps of the chemical and mechanical composite treatment in step S1 are as follows: First, the inner wall surface of the 4J29 Kovar alloy pipe is soaked in acetone solution for 10 minutes to remove surface machining oil stains, ultrasonically cleaned for 8 minutes to remove residual particles in the pipe cavity, and then soaked in a hydrochloric acid solution with a mass fraction of 18% to 20% at room temperature for 8 minutes to remove the surface oxide film; second, the surface of the TU1 oxygen-free copper rod is sandblasted and its two ends are chamfered (30°) to eliminate stress concentration.

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

[0049] After the composite treatment in step S2, the TU1 oxygen-free copper rod is tied tightly with metal wire and placed in a liquid nitrogen container for cryogenic assembly. Its temperature is tested with an industrial thermometer. After the TU1 oxygen-free copper rod cools to -150°C, it is taken out and slowly placed inside the 4J29 Kovar alloy pipe. Taking advantage of the large thermal expansion coefficient of copper, the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod are cold-assembled together.

[0050] In step S3, before starting the vacuum diffusion welding furnace, the temperature measuring thermocouple is installed on the sample fixture. 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 in strict contact. 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 cavity for current-assisted vacuum diffusion welding is controlled at -2MPa. The temperature is increased to 950℃ at a gradient heating rate of 10℃ / min and held at this constant temperature for 1 hour. The current-assisted synchronous application is performed at a frequency of 50Hz, a current intensity of 1950A, a duty cycle of 70%, and a current density of 10A / mm². 2 An auxiliary voltage of 4.47V is used to promote current diffusion, while an axial hot-pressing pressure of 0.25Mpa is applied.

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

[0053] Example 2

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

[0055] In step S4, the vacuum degree of the welding furnace cavity for current-assisted vacuum diffusion welding is controlled at -2MPa, and the temperature is increased to 1000℃ at a gradient heating rate of 10℃ / min (e.g., Figure 3and kept in constant temperature state for 1 hour, current auxiliary synchronous application frequency 50 Hz, current intensity 1950 A, duty cycle 70%, current density 11 A / mm 2 , auxiliary voltage 4.05 V to promote current diffusion, while cooperating with 0.25 Mpa axial hot pressing pressure.

[0056] The metallographic structure of the composite rod prepared by the parameters of the embodiment is dense, and no visible cracks and other defects are observed, as shown in Figure 5 .

[0057] Example 3

[0058] The specific preparation steps are the same as those of Example 1, and the difference between this embodiment and Example 1 is that:

[0059] The vacuum degree of the welding furnace cavity of the step S4 current auxiliary vacuum diffusion welding is controlled at -2 MPa, and the gradient heating mode is heated to 1050℃ at a heating rate of 10℃ / min (as shown in Figure 3 ), and kept in constant temperature state for 1 hour, current auxiliary synchronous application frequency 50 Hz, current intensity 1950 A, duty cycle 70%, current density 12 A / mm 2 , auxiliary voltage 3.62 V to promote current diffusion, while cooperating with 0.25 Mpa axial hot pressing pressure.

[0060] The metallographic structure of the composite rod prepared by the parameters of the embodiment is dense, and no visible cracks and other defects are observed, as shown in Figure 6 .

[0061] Comparative Example 1

[0062] A conventional welding process of a Kovar alloy and copper rod composite rod is as follows:

[0063] Step S1: The surfaces of a Kovar alloy pipe with a brand of 4J29 and a copper rod without oxygen with a brand of TU1 are subjected to chemical and mechanical composite treatment;

[0064] Step S2: The Kovar alloy pipe and the copper rod are assembled, and the TU1 copper rod without oxygen is placed in the inner cavity of the 4J29 Kovar alloy pipe;

[0065] Step S3: The assembled workpiece in step S2 is placed in a vacuum diffusion welding furnace, and the pressure head is vertically placed on the workpiece under the action of the pressure;

[0066] Step S4: The workpiece in step S3 is subjected to vacuum diffusion welding processing, and the workpiece is subjected to thermal and mechanical coupling under the action of the pressure, thereby preparing a Kovar alloy and copper composite rod;

[0067] Step S5: After being cooled to room temperature, the Kovar alloy and copper composite rod is taken out.

[0068] The step S1 chemical and mechanical composite treatment is specifically: first, the inner wall surface of the 4J29 Kovar alloy pipe is soaked in an acetone solution for 10 min to remove surface machining oil stains, ultrasonic cleaning is performed for 8 min to remove residual particles in the pipe cavity, and a 18%-20% mass fraction hydrochloric acid solution is used to soak at room temperature for 8 min to remove the surface oxide film; second, sand blasting treatment is performed on the surface of the TU1 oxygen-free copper rod, and chamfering (30°) is performed on both ends of the rod to eliminate stress concentration.

[0069] The size of the Kovar alloy pipe is: an outer diameter of 20 mm, an inner diameter of 7 mm, and a length of 50 mm. The size of the copper rod is: a diameter of 7 mm and a length of 50 mm.

[0070] The vacuum diffusion welding process parameters of the step S4 are: the vacuum degree of the welding furnace cavity is controlled at -2 MPa, the gradient temperature rising mode is to rise the temperature to 1000℃ at a temperature rising rate of 10℃ / min, and the temperature is kept constant for 3 hours, and the vertical hot pressing pressure is 2.5 MPa.

[0071] The conventional vacuum diffusion welding process is used to prepare the Kovar alloy and copper composite rod, the holding time is 3 h, the holding time is only 1 h by using the process of the application, the process flow is greatly shortened, the energy consumption of the comparative example is large, the pressure is 2.5 MPa, the hot pressing pressure of the application is 0.2-0.25 MPa, it can be seen that the application is more energy-saving, and the metallographic structure of the prepared composite rod is dense and has no obvious weld defect, while the metallographic structure of the comparative example has obvious weld defects and is not welded, as shown in Figure 7 .

[0072] The application uses current-assisted vacuum diffusion welding to prepare the 4J29 Kovar alloy and TU1 oxygen-free copper composite rod, heats to the bonding temperature by using a vacuum diffusion welding furnace, and pressurizes by using a pressure head and radiative heating at the same time, so as to achieve metallurgical bonding under the joint action of thermal coupling and current. The application fully utilizes the advantages of current-assisted vacuum diffusion welding technology, cooperatively controls the interface diffusion behavior by using a multi-field coupling mechanism (pressure field-temperature field-current field), accurately controls the axial pressure, gradient temperature and pulse current parameters in a vacuum environment, realizes the dissimilar welding of the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper rod. The microstructure of the composite rod obtained by the method shows that no pores, inclusions and other defects are observed in the weld area, the generation of micro-cracks caused by thermal stress concentration is inhibited, the welding cycle is shortened to 1 h, the interface metallurgical quality is ensured, the process is simplified, and the energy consumption is reduced.

[0073] It should be understood that although the present specification is described in terms of various embodiments, each of which describes only one implementation, the specification is intended to cover all possible implementations that are within the scope of the application, which is defined by the claims. One skilled in the art will readily recognize from the disclosure herein, that alternative embodiments of the present application can be constructed from a number of approaches already known in the art, which do not depart from the spirit and scope of the present application. The individual features of the various embodiments of this application each will be recognized by one of ordinary skill in the art to be an innovative application that alone would entitle the applicant to a patent, but the present application is intended to cover each and every combination of the individual features disclosed herein and any other innovative feature that would be recognized by those of ordinary skill in the art to be an innovative application that alone would entitle the applicant to a patent.

[0074] The foregoing detailed description has set forth various embodiments of the devices and / or processes via the use of specific terminology. However, embodiments thereof can be practiced without the specific details (e.g., dimensions, times, direction, order of sequence, etc.) that are described herein. It is to be understood that the foregoing detailed description of the devices and / or processes is susceptible to various modifications, adaptations, and implementations by one of ordinary skill in the art. It is to be understood that such modifications, adaptations, and implementations are intended to fall within the scope of the present application.

Claims

1. A method of welding a composite bar, characterized by, The method comprises the following steps: Step S1: chemically and mechanically composite processing the surface of the Kovar alloy pipe with a brand of 4J29 and the oxygen-free copper bar with a brand of TU1; Step S2: placing the TU1 oxygen-free copper bar after the composite processing in step S1 in a liquid nitrogen medium, and after the TU1 oxygen-free copper bar is cooled, assembling the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper bar; Step S3: placing the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper bar assembled in step S2 in a furnace cavity of a current-assisted vacuum diffusion welding device, axially loading a pressure head assembly of the current-assisted vacuum diffusion welding device, so that the workpieces to be welded are in strict contact with the pressure head, and connecting a pulse current instrument of the current-assisted vacuum diffusion welding device with the pressure head assembly; Step S4: current-assisted vacuum diffusion welding processing the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper bar assembled in step S3 in a vacuum environment, activating the metals by combining the pressure of the pressure head and the pulse current to realize high-efficiency metallurgical combination of the 4J29 Kovar alloy and the TU1 oxygen-free copper; Step S5: after the current-assisted vacuum diffusion welding in step S4 is completed, closing a temperature rising system of the current-assisted vacuum diffusion welding device and keeping a vacuum system continuously running until the temperature of the furnace body is reduced to room temperature, and obtaining the composite bar of the 4J29 Kovar alloy pipe and the TU1 oxygen-free copper bar.

2. The composite bar welding method according to claim 1, characterized by, The chemical and mechanical composite processing in step S1 is specifically as follows: first, immersing the inner wall surface of the 4J29 Kovar alloy pipe in an acetone solution for 10 min to remove surface machining oil stains, ultrasonic cleaning for 8 min to remove residual particles in the pipe cavity, and immersing in a hydrochloric acid solution with a mass fraction of 18%-20% at room temperature for 8 min to remove the surface oxide film; second, sandblasting the surface of the TU1 oxygen-free copper bar and chamfering the two ends to eliminate stress concentration.

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

4. The composite bar welding method according to claim 3, characterized by, The TU1 oxygen-free copper bar is taken out after being cooled to-170 DEG C to-150 DEG C.

5. The composite bar welding method according to claim 1, characterized by, In step S3, before starting the current-assisted vacuum diffusion welding device, a temperature measuring thermocouple is installed on the sample tooling, the pressure head assembly is driven by a servo motor to realize axial loading, so that the workpieces to be welded are in strict contact with the pressure head of the pressure loading system, and a stable closed loop is formed on the contact surface of the pressure head and the workpieces to be welded.

6. The composite bar welding method according to claim 1, characterized by, In the current-assisted vacuum diffusion welding in step S4, the gradient temperature rising mode is raised to 950-1050 DEG C at a temperature rising rate of 10 DEG C / min, and kept in a constant temperature state for 1 hour, the current assistance is synchronously applied at a frequency of 50 Hz and a current intensity of 1950 A, and at the same time, an axial hot pressing pressure of 0.2-0.25 Mpa is matched.

7. The composite rod welding method of claim 6, wherein In the step S4, the gradient heating mode is used to heat the sample to 950℃ at a heating rate of 10℃ / min, and then keep the temperature constant for 1 hour. The current assisted synchronous application frequency is 50Hz, the current intensity is 1950A, the duty cycle is 70%, the current density is 10A / mm2, the auxiliary voltage is 4.47V to promote current diffusion, and the axial hot pressing pressure is 0.25Mpa.

8. The composite rod welding method of claim 6, wherein In the step S4, the gradient heating mode is used to heat the sample to 1000℃ at a heating rate of 10℃ / min, and then keep the temperature constant for 1 hour. The current assisted synchronous application frequency is 50Hz, the current intensity is 1950A, the duty cycle is 70%, the current density is 11A / mm2, 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 of claim 6, wherein In the step S4, the gradient heating mode is used to heat the sample to 1050℃ at a heating rate of 10℃ / min, and then keep the temperature constant for 1 hour. The current assisted synchronous application frequency is 50Hz, the current intensity is 1950A, the duty cycle is 70%, the current density is 12A / mm2, the auxiliary voltage is 3.62V to promote current diffusion, and the axial hot pressing pressure is 0.25Mpa.

10. A composite bar, characterized by The composite rod prepared by the method according to any one of claims 1-9. The composite rod prepared by the method according to any one of claims 1-9.

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