Brazing welding method and brazing system for copper-aluminum transition wire clamp

Abstract

The invention discloses a brazing method and system for a copper-aluminum transition wire clamp, and the method comprises the steps: firstly, carrying out the pretreatment of a copper plate and an aluminum plate, and removing the surface dirt and oxidation film; coating the brazing flux on the surface of the brazing filler metal, placing the brazing flux on the to-be-welded surface of the aluminum plate, attaching the brazing flux to the to-be-welded surface of the copper plate, fixing the brazing flux and the to-be-welded surface of the copper plate on a working table in a high-temperature test box of a brazing system, introducing inert gas, and starting integral preheating; and finally, a two-step induction brazing method is adopted for brazing, in the first stage, large-power heating is adopted for a period of time, in the second stage, small-power heating is adopted for continuous heating for a short time, then heating is stopped, and finally the copper-aluminum transition wire clamp can be manufactured after the copper-aluminum transition wire clamp is naturally cooled to the room temperature. According to the method, the total induction brazing time is shortened, the oxidation problem of the base metal and the brazing filler metal before the brazing flux is not melted in the welding process is avoided, the wettability of the brazing filler metal is improved, the generation of pore defects is reduced, meanwhile, the aluminum base metal is prevented from being too high in temperature and being corroded by the brazing filler metal, and the joint strength is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of copper-aluminum transition wire clamps, and in particular to a brazing welding process for copper-aluminum transition wire clamps. Background Art

[0002] Copper has excellent electrical conductivity, thermal conductivity, corrosion resistance, ductility and certain strength. Adding various alloy elements to copper can improve its corrosion resistance, strength and processing performance. Therefore, copper and copper alloys are widely used in electrical, electrical, aerospace, etc. Aluminum and its alloys occupy an important position in modern industrial materials due to their low density, high thermal conductivity and electrical conductivity. In order to reduce weight, reduce energy consumption and improve efficiency, aluminum is the preferred material to replace copper in many fields. For example, in the power industry, especially in the power conversion system, there are many cases of copper and aluminum connections, which require the use of copper-aluminum transition clamps.

[0003] Due to the large differences in physical and chemical properties between copper and aluminum, there are usually some problems when welding copper and aluminum: 1. The differences in thermal expansion coefficients and thermal conductivity between copper and aluminum lead to large residual stress after transition clamp welding, which is prone to microcracks; 2. The cooling speed of copper and aluminum after welding is fast, and the gas cannot escape completely, which easily produces porosity defects in the weld; 3. During the copper-aluminum induction brazing process, the temperature of aluminum is often too high and it is easily dissolved by the brazing material because the heat input speed is too fast and it is difficult to accurately control the temperature.

[0004] In order to solve the above problems and prepare a copper-aluminum transition clamp with excellent comprehensive performance, some researchers have conducted corresponding research. The "copper-aluminum brazing method for a copper-aluminum transition clamp" disclosed in patent CN 105742934 A first puts the aluminum alloy substrate into an annealing furnace for preheating and insulation, then takes it out and fits it with a copper sheet coated with solder paste, pre-presses it with a clamp, heats it with a flame gun at the welding position and welds the welding seam to the welding rod, presses it to shape, and obtains the copper-aluminum transition clamp after cooling. Although this method improves the welding efficiency to a certain extent, it preheats the aluminum alloy to 450-550°C in the annealing furnace. In an air environment, it is easy to cause oxidation of the parent material, thereby affecting the wettability of the brazing material to the substrate, resulting in a decrease in the joint strength, and the aluminum alloy substrate needs to be taken out of the annealing furnace after the preheating is completed. The inconvenient operation will also cause heat loss. Finally, the flame gun is used to heat a large area, which will also lead to a decrease in the joint strength. Patent CN 112338316B discloses a "brazing process for high-strength and tough copper-aluminum joints". High-frequency brazing is used. The copper base material to be welded is pre-chemically plated with a nickel-phosphorus layer. The nickel-phosphorus layer is discontinuous and has a row of evenly distributed dividing holes at the center of the width along the length direction. Although the harmful effects of a large number of brittle phases are eliminated to a certain extent, the brittleness of the joint is reduced and the strength and toughness of the joint are improved, the process is complicated and not conducive to mass production and industrial application. At the same time, it requires opening holes in the base material, which will affect its mechanical properties and corrosion resistance to a certain extent, and ultimately affect the use of copper-aluminum welded joints. Patent CN 117526034 A discloses a "processing method for a high-quality copper-aluminum transition wire clamp". First, remove dirt and oxides from the surface of the copper and aluminum plates, then apply a brazing flux composed of isopropyl alcohol, CsF and AlF3 on the copper and aluminum plates to be welded, place a long sheet of brazing material on the aluminum plate to be welded, and then attach and fix it to the copper plate to be welded, then apply pressure for induction brazing, and finally apply nano-graphite sheet modified EVA hot melt adhesive around the welding transition part, wait for it to cool naturally, and the copper-aluminum transition wire clamp is obtained. Although the wire clamp obtained by this method has a low false welding rate, high bonding strength and good corrosion resistance, it still cannot avoid the oxidation problem of part of the parent material when welding in the air, which reduces the wettability of the brazing material to the parent material, and it is difficult to accurately control the temperature, resulting in the parent material temperature being too high and easy to be dissolved by the brazing material, which ultimately leads to a decrease in performance.

[0005] In the existing copper-aluminum brazing process, the base material and the brazing material are usually oxidized before the brazing agent is melted, resulting in reduced brazing material wettability, and the base material is too hot during the welding process due to the high heat input speed and difficulty in temperature control, resulting in excessive aluminum temperature and being dissolved by the brazing material, which ultimately leads to reduced copper-aluminum joint strength. Therefore, how to solve the problems in the copper-aluminum welding process and prepare a copper-aluminum joint with higher strength has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0006] In view of the above problems, the present invention provides a brazing welding method and a brazing system for a copper-aluminum transition wire clamp, and the resulting copper-aluminum transition wire clamp has the performance characteristics of high shear strength.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] First, the present application provides a brazing welding method for a copper-aluminum transition clamp, which comprises the following steps:

[0009] (1) Pretreatment of the aluminum plate: polish the aluminum plate with sandpaper (e.g., 400-600 mesh), then clean it with ethanol; then put it into a 100 g / L NaOH solution (alkali solution) for alkaline washing for about 3-5 min, and then rinse it with deionized water; then immerse it in a 12% mass concentration dilute nitric acid solution for 2-3 min (acid solution I), and then rinse it with deionized water; finally, ultrasonically clean and dry it in sequence to obtain the pretreated aluminum plate for use;

[0010] (2) Pretreatment of the copper plate: polish the copper plate with sandpaper (e.g., 400-600 mesh), then wash it with deionized water and soak it in a 12% dilute sulfuric acid solution (acid solution II) for 2-3 minutes, and finally ultrasonically clean and dry it in turn to obtain the pretreated copper plate for later use;

[0011] The purpose of the pretreatment steps (1) and (2) is to remove dirt and oxide films on the surfaces of the aluminum and copper plates;

[0012] (3) Preparation before brazing: brazing is performed in a brazing system. First, the brazing flux is applied to the surface of the brazing material and then placed on the pre-treated aluminum plate to be welded. Then, it is bonded to the pre-treated copper plate to be welded and fixed on a workbench in a high-temperature test chamber. Then, flowing inert gas (such as argon) is introduced and the air pressure at the air inlet is maintained at 1.05-1.1 atm. Finally, the whole is preheated to 200-300°C in a high-temperature test chamber and kept warm for 10-15 minutes.

[0013] (4) Brazing: After preheating in the high-temperature test chamber, the two-step induction brazing method is used for brazing under the condition of continuous flow of inert gas: in the first stage, the high-power brazing is 20-24 kW, the brazing time is 10-14 s, and the heating temperature is 400-450°C; in the second stage, the low-power brazing is 16-18 kW, and the brazing is carried out until liquid phase appears at the edge of the weld (about 3-5 s).

[0014] Furthermore, the brazing system in step (3) includes an induction brazing machine, a high-temperature test chamber and a gas delivery device; a workbench and an induction coil are provided in the high-temperature test chamber, the induction coil is wound by a copper tube, both ends of the induction coil are fixedly connected to corresponding interfaces of the induction brazing machine, and is suspended above the workbench through a through hole of the high-temperature test chamber; the gas delivery device is connected to an air inlet located above a side wall of the high-temperature test chamber through a pipeline, and an air outlet is provided below the side wall of the high-temperature test chamber opposite to the air inlet.

[0015] Furthermore, the solder in step (3) is a ZnAl sheet with a thickness of 0.1 to 0.2 mm, and in terms of mass percentage, Zn: 78 to 88%, Al: 12 to 22%.

[0016] Furthermore, the flux in step (3) is a mixture of propylene glycol, CsF and AlF3, preferably propylene glycol: 10-25%, CsF: 25-30%, AlF3: 50-60% by mass percentage. The coating thickness is preferably 0.05-0.1 mm.

[0017] Secondly, the present application also provides a special brazing system for the brazing welding method of the above-mentioned copper-aluminum transition wire clamp, the brazing system includes an induction brazing machine, a high-temperature test chamber and a gas delivery device; the high-temperature test chamber is provided with a workbench and an induction coil; the induction coil is wound by a copper tube, and the two ends of the copper tube are fixedly connected to the corresponding interfaces of the induction brazing machine, and then suspended above the workbench through the through holes of the high-temperature test chamber; the gas delivery device is connected to the air inlet located above the side wall of the high-temperature test chamber through a pipeline, and an air outlet is provided below the side wall of the high-temperature test chamber opposite to the air inlet.

[0018] Furthermore, the gas delivery device is a gas cylinder provided with a gas control valve and a pressure sensor.

[0019] The above-mentioned induction brazing machine, high temperature test box (maximum operating temperature ≥ 500° C.), induction coil, and gas conveying device are all conventional devices in the art.

[0020] The present invention is prepared before brazing by first evenly coating the brazing flux on the surface of the brazing material and then placing it on the surface of the aluminum plate to be welded, then attaching it to the surface of the copper plate to be welded and fixing it on a workbench in a high-temperature test box, and then introducing flowing argon gas to start overall preheating. Preheating the base material, the brazing flux and the brazing material before brazing not only reduces the total time of induction brazing, but also introducing flowing inert gas (such as argon gas) before the brazing flux is melted can prevent the base material and the brazing material from being oxidized, thereby improving the wettability of the brazing material and effectively improving the strength of the joint.

[0021] The present invention adopts a two-step induction brazing method in the copper-aluminum transition clamp welding process. In the first stage, a large power is first used for heating for a period of time to heat the brazing flux and the brazing material to a temperature close to the melting temperature. In the second stage, a small power is used for heating for a short period of time to melt the brazing flux and the brazing material and keep them in the liquid phase for a certain period of time, which can not only make the brazing flux and the brazing material quickly reach the melting temperature, but also effectively prevent the aluminum base material from being too hot and being dissolved by the brazing material, and at the same time, the gas generated by the welding molten pool can be effectively discharged to reduce the false welding rate.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The brazing system provided by the present application can not only introduce flowing gas (such as argon), but also preheat the brazing material, flux and base material before induction brazing, and then perform induction welding. Firstly, the preheating step reduces the total time of induction brazing, and secondly, the inert gas atmosphere avoids the problem of the base material and brazing material being oxidized before the flux is melted, thereby improving the wettability of the brazing material and effectively improving the strength of the joint.

[0024] 2. The present invention adopts a two-step induction brazing method in the copper-aluminum transition clamp welding process, which reduces porosity defects, reduces the false welding rate, reduces the excessive temperature of the aluminum base material and the dissolution of the brazing material, and improves the shear strength of the joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the brazing system structure of the embodiment;

[0026] In the figure: 1-induction brazing machine; 2-high temperature test chamber; 3-air inlet; 4-induction coil; 5-copper plate; 6-brazing flux and brazing material; 7-aluminum plate; 8-support block; 9-workbench; 10-air outlet; 11-gas delivery device; 12-pipeline.

[0027] Figure 2 The figures are the physical pictures of the copper-aluminum brazing joints prepared in the examples and comparative examples;

[0028] Among them, (a) is a physical picture of the aluminum plate of the copper-aluminum brazing joint prepared in Example 2, and (b) is a physical picture of the aluminum plate of the copper-aluminum brazing joint prepared in Comparative Example 2.

[0029] Figure 3 To take photos of the surface morphology of the brazing area of ​​the shear fracture of the copper-aluminum brazing joint;

[0030] Among them, (a) is a photo of the fracture of the joint prepared in Example 3, and (b) is a photo of the fracture of the joint prepared in Comparative Example 3. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] The base materials used in the following examples are 1060 aluminum plate and T2 copper plate, the flux components are propylene glycol, CsF and AlF3, and the brazing filler metal is ZnAl brazing filler metal, all of which are conventional products available on the market.

[0033] The ultrasonic cleaning machine is an LC-UC-21 ultrasonic cleaning machine produced by China Laboratory Instrument Sales Center, and the electric blast drying oven is an SN-202-0A electric blast drying oven produced by China Laboratory Instrument Sales Center.

[0034] In the brazing system, the induction brazing machine used is the SY-30AB high-frequency induction brazing machine of Guangdong Saiyang Intelligent Equipment Technology Co., Ltd. (in actual applications, other conventional commercially available brazing machines can also be used); the high-temperature test chamber used is the DHG500-3 test chamber of Shenzhen Hengkuo Instrument Co., Ltd., with manually set air inlets and outlets (in actual applications, other conventional commercially available high-temperature test chambers can also be used and artificial holes can be made as needed). The test chamber includes heating tubes, insulation layers, high-temperature resistant sealing rings, air inlets, air outlets, temperature control instruments and other components, with timing and temperature control functions; the workbench used is the HYHTZ210 lifting workbench of Shenzhen Hengyu Laser Equipment (in actual applications, other conventional commercially available workbenches can also be used).

[0035] The copper / aluminum brazing joints prepared in the embodiment and comparative example were tested for tensile strength on a JHY-5000 series testing machine in accordance with the national standard GB11363-2008 "Test method for strength of brazing joints". The test temperature was room temperature and the tensile rate was 1.0 mm / min. Five joint samples under each process were selected for testing, and the results were averaged; a digital camera was used to take photos of the surface morphology of the brazing area of ​​the shear fracture, and metallographic image processing software was used to test the false soldering rate of the welding area.

[0036] The present invention is described in detail below through specific examples, but the use and purpose of these exemplary embodiments are only used to illustrate the present invention, and do not constitute any form of limitation on the actual protection scope of the present invention, nor limit the protection scope of the present invention to these.

[0037] The brazing system structure used in the following examples is as follows: Figure 1 As shown, the workbench 9 and the induction coil 4 are both arranged in the high temperature test box 2; the induction coil 4 is wound by a copper tube, and its two ends are fixedly connected to the corresponding interfaces of the induction brazing machine 1, and the copper tube is suspended above the workbench 9 through the through hole of the high temperature test box 2; the gas delivery device 11 is connected to the air inlet 3 above the side wall of the high temperature test box 2 through a pipeline, and a gas outlet 10 is provided below the side wall of the high temperature test box 2 opposite to the gas inlet 3, and the gas outlet 10 is connected to the exhaust pipe 12; the gas delivery device 11 is composed of a gas cylinder provided with a gas control valve and a pressure sensor, and the gas cylinder is filled with argon gas.

[0038] Example 1

[0039] 1. Pretreatment of aluminum plate: polish the aluminum plate with 400-mesh sandpaper, then clean it with ethanol; then put it into a 100g / L NaOH solution for alkaline washing for about 3 minutes, and then rinse it with deionized water; then immerse it in a 12% dilute nitric acid solution for 2 minutes, and then rinse it with deionized water; then use 80W ultrasonic cleaning for 180s, and finally place it in an electric blast drying oven and dry it at 80℃ for 15 minutes to obtain the pretreated aluminum plate for standby use;

[0040] 2. Pretreatment of the copper plate: polish the copper plate with sandpaper, then wash it with deionized water and soak it in 12% dilute sulfuric acid solution for 2 minutes, finally clean the copper plate with ultrasonic wave (80W cleaning for 180 seconds) and dry it (80℃ drying for 15 minutes) to obtain the pretreated copper plate for later use;

[0041] 3. Preparation before brazing: Figure 1 As shown, first, the brazing flux and the brazing material 6 (the brazing flux is evenly coated on the surface of the brazing material) are placed on the surface of the aluminum plate 7 to be welded after pretreatment in step 1, and then they are attached to the surface of the copper plate 5 to be welded after pretreatment in step 2 and fixed on the workbench 9 in the high temperature test box 2 of the brazing system; in this embodiment, a support block 8 is also provided under the copper plate 5 to ensure that the brazing flux and the brazing material 6 on the lower surface of the pretreated copper plate 5 and the surface of the pretreated aluminum plate 7 are at the same horizontal height; then the control valve of the gas cylinder is opened, the flowing argon gas is introduced, and the air pressure at the air inlet is maintained at 1.05atm, and finally the whole is preheated to 200℃ and kept warm for 10min.

[0042] The brazing material used in this embodiment is ZnAl sheet (Zn content 88wt%, Al content 12wt%, thickness 0.1mm), and the brazing agent (propylene glycol content 10wt%, CsF content 30wt%, AlF3 content 60wt%) is coated with a thickness of 0.05mm.

[0043] 4. Brazing: While continuing to flow argon, a two-step induction brazing method is used. In the first stage, the induction brazing machine uses a large power of 20kW to heat for 14s, and the heating temperature is 400-450℃. In the second stage, a small power of 18kW is used to continue heating for 5s until liquid overflow appears at the edge of the weld. Finally, after the heating is completed, wait for it to cool naturally to room temperature to obtain the copper-aluminum brazing joint.

[0044] Example 2

[0045] 1. Pretreatment of aluminum plate: polish the aluminum plate with sandpaper, then clean it with ethanol; then put it into a 100g / L NaOH solution for alkaline washing for about 5 minutes, and then rinse it with deionized water; then immerse it in a 12% dilute nitric acid solution for 3 minutes, and then rinse it with deionized water; finally, clean it with ultrasonic wave and dry it for use;

[0046] 2. Pretreatment of the copper plate: polish the copper plate with sandpaper, then wash it with deionized water and soak it in 12% dilute sulfuric acid solution for 3 minutes, finally clean the copper plate with ultrasonic wave and dry it for later use;

[0047] 3. Preparation before brazing: First, apply the brazing flux on the surface of the brazing material and place it on the pre-treated aluminum plate to be welded, then attach it to the pre-treated copper plate to be welded and fix it on the workbench in the high-temperature test chamber, then open the gas valve, let in flowing argon gas, and keep the gas pressure at the air inlet at 1.1atm, finally preheat the whole to 300℃ and keep warm for 10min;

[0048] The brazing material used in this embodiment is ZnAl sheet (Zn content 83wt%, Al content 17wt%, thickness 0.2mm), brazing agent (propylene glycol content 17wt%, CsF content 28wt%, AlF3 content 55wt%), and the coating thickness is 0.1mm.

[0049] 4. Brazing: While continuing to flow argon, a two-step induction brazing method is used. In the first stage, the induction brazing machine uses a large power of 22kW to heat for 12s, and the heating temperature range is 400-450℃. In the second stage, a small power of 17kW is used to continue heating for 4s until liquid overflow appears at the edge of the weld. Finally, after the heating is completed, wait for it to cool naturally to room temperature to obtain the copper-aluminum brazing joint.

[0050] The actual photo of the aluminum plate of the copper-aluminum brazing joint prepared in this example is as follows: Figure 2 As shown in (a), the fillet of the joint (the arc-shaped fillet formed by the solder overflowing from the gap outside the brazing seam) can be seen, and no corrosion is observed on the aluminum plate.

[0051] Example 3

[0052] 1. Pretreatment of aluminum plate: polish the aluminum plate with sandpaper, then clean it with ethanol; then put it into a 100g / L NaOH solution for alkaline washing for about 5 minutes, and then rinse it with deionized water; then immerse it in a 12% dilute nitric acid solution for 3 minutes, and then rinse it with deionized water; finally, clean it with ultrasonic wave and dry it for use;

[0053] 2. Pretreatment of the copper plate: polish the copper plate with sandpaper, then wash it with deionized water and soak it in 12% dilute sulfuric acid solution for 3 minutes, finally clean the copper plate with ultrasonic wave and dry it for later use;

[0054] 3. Preparation before brazing: First, apply the brazing flux on the surface of the brazing material and place it on the pre-treated aluminum plate to be welded, then attach it to the pre-treated copper plate and fix it on the workbench in the high-temperature test chamber, then open the gas valve to let in flowing argon gas, and keep the gas pressure at the air inlet at 1.1atm, and finally preheat the whole to 300℃ and keep it warm for 15min;

[0055] The solder composition used in this embodiment is ZnAl sheet (Zn content 78wt%, Al content 22wt%, thickness 0.2mm), and the flux (propylene glycol content 25wt%, CsF content 25wt%, AlF3 content 50wt%) is coated with a thickness of 0.1mm.

[0056] 4. Brazing: Under the condition of continuous flow of argon gas, a two-step induction brazing method is used. In the first stage, the induction brazing machine uses a large power of 24kW to heat for 10s, and the heating temperature is 400-450℃. In the second stage, a small power of 16kW is used to continue heating for 3s until liquid overflow appears at the edge of the weld. Finally, after the heating is completed, it is allowed to cool naturally to room temperature to obtain a copper-aluminum brazed joint. The fracture photo of the joint is shown in the figure. Figure 3 As shown in (a), it can be seen that there are fewer cold solder joints.

[0057] Comparative Example 1

[0058] The difference between Comparative Example 1 and Example 1 is that in step 3, argon gas is not passed in the preparation before brazing and the brazing material, brazing flux and base material are not preheated in advance, and the other steps are the same.

[0059] Comparative Example 2

[0060] The only difference between Comparative Example 2 and Example 2 is that in step 4 brazing, a single constant power of 22 kW is used to heat for 14 seconds until liquid overflow appears at the edge of the weld, and after heating is completed, it is allowed to cool naturally to room temperature; the other steps are the same.

[0061] The actual photo of the aluminum plate of the copper-aluminum brazing joint prepared in this comparative example is as follows: Figure 2 As shown in (b), the surface of the aluminum plate is dissolved by the molten solder to form depressions, indicating that corrosion has occurred.

[0062] Comparative Example 3

[0063] Comparative Example 3 is the same as steps 1 and 2 of Example 3; in step 3, argon gas is not passed in the preparation before brazing, and the brazing material, brazing flux and base material are not preheated in advance; step 4: directly use a constant 24kw heating for 12s until liquid overflow appears at the edge of the weld, and after the heating is completed, wait for it to cool naturally to room temperature, and then obtain the copper-aluminum brazing joint of Comparative Example 3, and the fracture photo of the joint is shown in Figure 3 As shown in (b), it can be seen that there are obviously more cold solder joints.

[0064] The shear strength and cold weld rate of the copper-aluminum brazing joints obtained in Examples 1-3 and Comparative Examples 1-3 were tested, and the results are shown in Tables 1 and 2 below.

[0065] Table 1 Shear strength test results of copper-aluminum brazing joints obtained in Examples 1 to 3 and Comparative Examples 1 to 3

[0066]

[0067]

[0068] Table 2 Test results of the cold welding rate of copper-aluminum brazing joints obtained in Examples 1 to 3 and Comparative Examples 1 to 3

[0069]

[0070] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A brazing welding method for a copper-aluminum transition clamp, characterized in that: The specific steps are as follows: (1) Pretreatment of aluminum plate: After the aluminum plate was polished with sandpaper, it was then cleaned with ethanol, alkali solution, deionized water, acid solution I, deionized water, and ultrasonic cleaning in sequence, and dried to obtain the pretreated aluminum plate for standby use; (2) Pretreatment of copper plate: The copper plate was polished with sandpaper, and then cleaned with deionized water, acid solution II, and ultrasonic cleaning in sequence, and dried to obtain the pretreated copper plate for later use; (3) Preparation before brazing: In the brazing system, the brazing flux is applied on the surface of the brazing material and then placed on the pre-treated aluminum plate to be welded, and then it is bonded with the pre-treated copper plate to be welded and fixed on the workbench in the high-temperature test box, and then inert gas is introduced and the air pressure at the air inlet is maintained at 1.05~1.1atm. Finally, the whole is preheated to 200~300℃ in the high-temperature test box and kept warm for 10~15min. The brazing system comprises an induction brazing machine, a high temperature test chamber and a gas delivery device; a workbench and an induction coil are provided in the high temperature test chamber, the induction coil is wound by a copper tube, both ends of the copper tube are fixedly connected to the corresponding interfaces of the induction brazing machine, and then suspended above the workbench through the through hole of the high temperature test chamber; the gas delivery device is connected to the air inlet located above the side wall of the high temperature test chamber through a pipeline, and an air outlet is provided below the side wall of the high temperature test chamber opposite to the air inlet; (4) Brazing: Under the condition of continuous inert gas flow, a two-step induction brazing method is used for brazing: in the first stage, the brazing power is 20~24kW, the brazing time is 10~14s, and the heating temperature is 400-450℃; in the second stage, the brazing power is 16~18kW, and the brazing is carried out until liquid phase appears at the edge of the weld.

2. The brazing welding method of the copper-aluminum transition clamp according to claim 1 is characterized in that: The solder is a ZnAl sheet, in which Zn accounts for 78-88% by mass and the remainder is Al.

3. The brazing welding method of the copper-aluminum transition clamp according to claim 1 is characterized in that: The flux is a mixture of propylene glycol, CsF and AlF3, wherein by mass percentage, propylene glycol accounts for 10-25%, CsF accounts for 25-30%, and AlF3 accounts for 50-60%.

4. The brazing welding method of the copper-aluminum transition clamp according to claim 1 is characterized in that: The coating thickness of the brazing agent is 0.05-0.1 mm.

5. The brazing welding method of the copper-aluminum transition clamp according to claim 1 is characterized in that: The alkaline solution is a NaOH solution, the acid solution I is a nitric acid solution, and the acid solution II is a sulfuric acid solution.

6. The brazing welding method of the copper-aluminum transition clamp according to claim 1 is characterized in that: The inert gas is argon.

7. The brazing welding method of the copper-aluminum transition clamp according to claim 2 is characterized in that: The thickness of the ZnAl sheet is 0.1-0.2 mm.

8. The dedicated brazing system for the brazing welding method of the copper-aluminum transition clamp as claimed in claim 1 is characterized in that: The brazing system includes an induction brazing machine, a high-temperature test chamber and a gas delivery device; the high-temperature test chamber is provided with a workbench and an induction coil; the induction coil is wound by a copper tube, and the two ends of the copper tube are fixedly connected to the corresponding interfaces of the induction brazing machine, and then suspended above the workbench through the through holes of the high-temperature test chamber; the gas delivery device is connected to the air inlet located above the side wall of the high-temperature test chamber through a pipeline, and an air outlet is provided below the side wall of the high-temperature test chamber opposite to the air inlet.

9. The brazing system according to claim 8, characterized in that: The gas delivery device is a gas cylinder provided with a gas control valve and a pressure sensor.

Images