Processing method of high-quality copper-aluminum transition wire clamp

Abstract

This invention discloses a method for processing high-quality copper-aluminum transition clamps. The method involves first pre-treating the copper and aluminum plates to remove surface contaminants and oxide films. Then, flux is applied to the surfaces of the aluminum and copper plates to be welded. Next, sheet-shaped brazing filler metal is placed on the aluminum plate's welding surface and then bonded and fixed to the copper plate's welding surface. Pressure is applied for induction brazing. Finally, nano-graphite-modified EVA hot melt adhesive is coated around the transition area. After cooling, the high-quality copper-aluminum transition clamp is obtained. The copper-aluminum transition clamp obtained by this invention exhibits low solder joint failure rate, high bonding strength, and good corrosion resistance. Furthermore, this method requires no special production equipment, is simple, and has low cost, making it suitable for industrial application.

Description

Technical Field

[0001] This invention belongs to the technical field of copper-aluminum transition clamps, and specifically relates to a processing method for high-quality copper-aluminum transition clamps. Background Technology

[0002] In power conversion systems, connections between copper and aluminum are involved in many places, requiring the use of copper-aluminum transition clamps. Copper-aluminum transition clamps play an important role in power conversion systems and are widely used in the wiring terminals of electrical equipment such as transformers, disconnect switches, and circuit breakers.

[0003] Copper-aluminum transition clamps come in two types: butt-joint and lap-joint. Butt-joint clamps are often manufactured using flash welding and friction welding processes, which are complex and prone to welding defects such as cracks, misalignment, and incomplete fusion at the weld. Therefore, butt-joint clamps are being rapidly phased out due to their inherent structural and performance defects. Lap-joint clamps, on the other hand, are becoming increasingly widely used. Lap-joint clamps are often manufactured using brazing, which not only meets electrical performance requirements well but also provides a large bonding area and high mechanical strength. Compared to other brazing methods, induction brazing requires simple equipment, is easy to operate, and has low cost, making it a significant advantage for brazing copper-aluminum clamps.

[0004] Because copper and aluminum are both highly susceptible to oxidation, commonly used zinc-aluminum brazing filler metals exhibit poor wetting properties on copper and aluminum base materials. This results in a high rate of incomplete welds, low joint strength, and susceptibility to electrochemical corrosion at the brazed joints, leading to high failure rates and short service lives for copper-aluminum wire clamps. Therefore, developing a new processing method for high-quality copper-aluminum transition wire clamps to address these current problems is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a processing method for high-quality copper-aluminum transition clamps, which results in copper-aluminum transition clamps with low solder joint rate and good corrosion resistance, thus solving the problems existing in the current production of copper-aluminum transition clamps.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for processing a high-quality copper-aluminum transition clamp includes the following steps:

[0008] (1) Pretreatment of aluminum plate: Immerse the aluminum plate in a NaOH solution with a concentration of 100g / L at 15~35℃ for 3~4min, then rinse with running cold water, then immerse in a HNO3 solution with a volume concentration of 10%~15% for 3~4min, then rinse with running cold water, then rinse with ethanol and dry.

[0009] (2) Pretreatment of copper plate: Immerse the copper plate in H2SO4 solution with a volume concentration of 8-12% for 3-4 minutes, then rinse with running cold water, then rinse with ethanol and dry.

[0010] (3) Apply flux; apply a 0.1 mm thick layer of flux evenly to the surfaces of the pretreated aluminum and copper plates to be soldered;

[0011] (4) Brazing: Place brazing filler metal on the aluminum plate to be brazed, then attach and fix it to the copper plate to be brazed, and then apply pressure to perform induction brazing.

[0012] (5) Sealing treatment: Apply nano-graphite sheet modified EVA hot melt adhesive around the welding transition part in step (4), and let it cool naturally to obtain the copper-aluminum transition clamp.

[0013] Further, the flux in step (3) is composed of the following raw materials in parts by mass: 15-20 parts of CsF, 35-45 parts of AlF3, and 30-40 parts of isopropanol (C3H8O).

[0014] Furthermore, the brazing filler metal used in step (4) is in the form of a long sheet, the length of which is equal to the length of the area to be welded, the width is 2 mm, and the thickness is 0.1~0.2 mm. When placing the filler metal, the length direction of the filler metal is consistent with the length direction of the area to be welded, and the sheets are spaced 0.2 mm apart so that gas can escape during the welding process.

[0015] Furthermore, the brazing filler metal is composed of the following parts by weight of raw materials: 70-98 parts Zn and 2-30 parts Al.

[0016] Furthermore, in step (4), the induction brazing uses a planar coil; 430 stainless steel sheet is used as the induction heating pad, which covers the copper-aluminum overlap area during welding; the brazing temperature is 550~570℃, the time is 8~12s, and the applied pressure is 20.0~30.0KPa.

[0017] Further, the nano-graphite sheet modified EVA hot melt adhesive mentioned in step (5) is obtained by mixing EVA hot melt adhesive and nano-graphite sheets in a torque rheometer according to the formula, and then pouring the mixed adhesive onto a polytetrafluoroethylene film and cooling it.

[0018] Furthermore, by weight, 97-98 parts of EVA hot melt adhesive and 3-4 parts of nano-graphite sheets are used.

[0019] Furthermore, the mixing temperature is 160°C, the rotor speed is 60 rpm, and the time is 15 min.

[0020] The flux used in this invention is a mixture of CsF, AlF3, and C3H8O. CsF and AlF3 are highly reactive, while F... + Ions can remove the oxide film on the surface of the plate through chemical adsorption and displacement reactions on the oxide film surface. C3H8O, acting as a solvent, reacts with copper oxide during brazing heating, further removing the copper oxide film on the copper substrate surface. Its volatiles also protect the copper plate and weld from oxidation. Removing the oxide film from the base material and protecting the base material significantly improves the wettability of the brazing filler metal to the base material.

[0021] This invention employs a nano-graphite sheet-modified EVA hot melt adhesive to seal the weld transition area around the copper-aluminum transition clamp. The nano-graphite sheet-modified EVA hot melt adhesive consists of EVA hot melt adhesive and nano-graphite sheets. EVA hot melt adhesive features rapid adhesion, high strength, aging resistance, non-toxicity, and corrosion resistance, effectively isolating the copper-aluminum transition clamp joint from the service environment. The nano-graphite sheets, dispersed within the EVA hot melt adhesive, undergo covalent cross-linking with the EVA hot melt adhesive molecular chains, forming a network structure that increases the coating's density. Furthermore, the large aspect ratio of the two-dimensional graphite sheets embedded within the coating further provides a physical shield against corrosive media, effectively enhancing the coating's impermeability and corrosion resistance. In addition, the uniform dispersion of the nano-graphite sheets in the EVA hot melt adhesive significantly improves the thermal conductivity of the sealed coating. Simultaneously, the preparation process of the nano-graphite sheet-modified EVA hot melt adhesive is short, low-cost, and exhibits good microstructure consistency.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. The copper-aluminum transition clamp provided by the present invention has a low rate of false welding in the copper-aluminum welding area, a large copper-aluminum contact area, and good copper-aluminum joint performance.

[0024] 2. In the preparation process of the copper-aluminum transition clamp provided by the present invention, the isopropanol component in the flux can further remove the oxide film on the surface of the base material, and its volatiles can protect the base material and weld from oxidation, thereby improving the spreading performance of the brazing filler metal on the surface of the base material.

[0025] 3. The copper-aluminum transition clamp provided by the present invention uses a segmented thin sheet of brazing filler metal during the manufacturing process. The spacing between the sheets is conducive to the escape of gas, which can reduce defects such as porosity, bulge, and slag inclusion at the weld joint and reduce the rate of incomplete soldering.

[0026] 4. The copper-aluminum transition clamp provided by this invention uses nano-graphite sheet modified EVA hot melt adhesive to seal the joint area, which greatly improves the corrosion resistance of the copper-aluminum transition clamp and extends its service life. Attached Figure Description

[0027] Figure 1 Photographs of the surface morphology of the brazing area at the tensile shear fracture of the copper-aluminum welded joint prepared in Example 1 (A) and Comparative Example 1 (B). Detailed Implementation

[0028] A method for processing a high-quality copper-aluminum transition clamp includes the following steps:

[0029] (1) Pretreatment of aluminum plate: Immerse the aluminum plate in a NaOH solution with a concentration of 100g / L at 15~35℃ for 3~4min, then rinse with running cold water, then immerse in a HNO3 solution with a volume concentration of 10%~15% for 3~4min, then rinse with running cold water, then rinse with ethanol and dry.

[0030] (2) Pretreatment of copper plate: Immerse the copper plate in H2SO4 solution with a volume concentration of 8-12% for 3-4 minutes, then rinse with running cold water, then rinse with ethanol and dry.

[0031] (3) Apply flux; apply a 0.1 mm thick layer of flux evenly to the surfaces of the pretreated aluminum and copper plates to be soldered;

[0032] (4) Brazing: Place a sheet of brazing filler metal (its length is equal to the length of the area to be welded, its width is 2mm, and its thickness is 0.1~0.2mm) on the surface of the aluminum plate to be welded. When placing the filler metal, the length direction of the filler metal is consistent with the length direction of the area to be welded, and the sheet is spaced 0.2mm apart. Then attach and fix it to the surface of the copper plate to be welded, and then apply pressure for induction brazing. A planar coil is used for induction brazing. 430 stainless steel sheet is used as an induction heating pad to cover the copper-aluminum overlap area during welding. The brazing temperature is 550~570℃, the time is 8~12s, and the applied pressure is 20.0~30.0KPa.

[0033] (6) Sealing treatment: Preheat the nano-graphite sheet modified EVA hot melt adhesive at 80°C for 3 minutes, and then heat it to 130~180°C to melt it; apply the melted hot melt adhesive to the welding transition part in step (4), and after it cools naturally, the copper-aluminum transition clamp is obtained.

[0034] The flux in step (3) is composed of the following raw materials in parts by mass: 15-20 parts of CsF, 35-45 parts of AlF3, and 30-40 parts of isopropanol (C3H8O).

[0035] The brazing filler metal used in step (4) consists of the following parts by weight: 70-98 parts Zn and 2-30 parts Al.

[0036] The nano-graphite sheet modified EVA hot melt adhesive mentioned in step (5) is prepared by pouring 97-98 parts of EVA hot melt adhesive and 3-4 parts of nano-graphite sheets into a torque rheometer, mixing at 160°C for 15 minutes (rotor speed of 60 rpm), and then pouring the mixed adhesive onto a polytetrafluoroethylene film and cooling it.

[0037] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0038] In the following examples, the aluminum plate used is 1060 pure aluminum, and the copper plate is T2 pure copper.

[0039] Example 1

[0040] 1. Remove oil and oxide film from the surfaces of copper and aluminum plates to be welded: Immerse the aluminum plate in a 100g / L NaOH solution at 15℃ for 4 minutes, then rinse with running cold water, and then immerse in a 10% HNO3 solution for 4 minutes for gloss treatment. After treatment, rinse with running cold water, then rinse with ethanol and dry. Immerse the copper plate in an 8% H2SO4 solution for 4 minutes, then rinse with running cold water, then rinse with ethanol and dry.

[0041] 2. Apply flux to the surfaces of the aluminum and copper plates to be soldered: Prepare a flux by weight of 15 parts CsF, 335 parts AlF3, and 40 parts isopropanol. After mixing them evenly, apply the flux to the surfaces of the aluminum and copper plates to be soldered, with a coating thickness of 0.1 mm.

[0042] 3. By weight, mix and melt 98 parts of Zn and 2 parts of Al to form a thin plate of brazing filler metal with a thickness of 0.2 mm. Then, cut the filler metal into long strips according to the size of the area to be brazed. The length of the strips should be equal to the length of the area to be brazed, and the width should be 2 mm. Lay the strips flat on the surface of the aluminum base material coated with flux, and make sure that the length direction of the filler metal is consistent with the length direction of the area to be brazed. The strips should be spaced 0.2 mm apart to allow the gas generated during the brazing heating process to escape easily.

[0043] 4. Fix the above-mentioned base material, brazing filler metal, flux, and heating pad with a clamp, apply a pressure of 30.0 kPa to the welding area, and use a planar coil for induction brazing; use 430 stainless steel sheet as induction heating pad, and cover the copper-aluminum overlap part during welding; the temperature of induction brazing is 550℃, and the heating time of induction brazing is 12s;

[0044] 5. Preparation of nano-graphite sheet modified EVA hot melt adhesive: According to the mass ratio, pour 97 parts of EVA hot melt adhesive and 4 parts of nano-graphite sheets into the torque rheometer through the feeding port, mix at 160℃ for 15 minutes (rotor speed is 60 rpm), then turn on the torque rheometer, pour the mixed adhesive onto a polytetrafluoroethylene film, and after cooling, the nano-graphite sheet modified EVA hot melt adhesive is obtained.

[0045] 6. Sealing treatment around the weld: Preheat the nano-graphite sheet modified EVA hot melt adhesive at 80°C for 3 minutes, and then heat it to 130°C to melt it; apply the melted hot melt adhesive to the area around the weld of the copper-aluminum transition clamp that has been brazed above, and after it cools naturally, the finished copper-aluminum transition clamp is obtained.

[0046] Example 2

[0047] 1. Remove oil and oxide film from the surfaces of copper and aluminum plates to be welded: Immerse the aluminum plate in a 100g / L NaOH solution at 25℃ for 3 minutes, then rinse with running cold water, and then immerse in a 12% HNO3 solution for 4 minutes for gloss treatment. After treatment, rinse with running cold water, then rinse with ethanol and dry. Immerse the copper plate in a 12% H2SO4 solution for 3 minutes, then rinse with running cold water, then rinse with ethanol and dry.

[0048] 2. Apply flux to the surfaces of the aluminum and copper plates to be soldered: Prepare a flux by weight of 20 parts CsF, 340 parts AlF, and 30 parts isopropanol. Mix the flux evenly and apply it to the surfaces of the aluminum and copper plates to be soldered, with a coating thickness of 0.1 mm.

[0049] 3. By weight, mix and melt 85 parts of Zn and 15 parts of Al to form a thin plate of brazing filler metal with a thickness of 0.1 mm. Then, cut the filler metal into long strips according to the size of the area to be brazed. The length of the strips should be equal to the length of the area to be brazed, and the width should be 2 mm. Lay the strips flat on the surface of the aluminum base material coated with flux, and make sure that the length direction of the filler metal is consistent with the length direction of the area to be brazed. The strips should be spaced 0.2 mm apart to allow the gas generated during the brazing heating process to escape easily.

[0050] 4. Fix the above-mentioned base material, brazing filler metal, flux, and heating pad with a clamp, apply a pressure of 25.0 kPa to the welding area, and use a planar coil for induction brazing; use 430 stainless steel sheet as induction heating pad, and cover the copper-aluminum overlap part during welding; the temperature of induction brazing is 560℃, and the heating time of induction brazing is 10s;

[0051] 5. Preparation of nano-graphite sheet modified EVA hot melt adhesive: According to the mass ratio, pour 97 parts of EVA hot melt adhesive and 3 parts of nano-graphite sheets into the torque rheometer through the feeding port, mix at 160℃ for 15 minutes (rotor speed is 60 rpm), then turn on the torque rheometer, pour the mixed adhesive onto a polytetrafluoroethylene film, and after cooling, you will get nano-graphite sheet modified EVA hot melt adhesive.

[0052] 6. Sealing treatment around the weld: Preheat the nano-graphite sheet modified EVA hot melt adhesive at 80°C for 3 minutes, and then heat it to 150°C to melt it; apply the melted hot melt adhesive to the area around the brazed copper-aluminum transition clamp weld, and after it cools naturally, the finished copper-aluminum transition clamp is obtained.

[0053] Example 3

[0054] 1. Remove oil and oxide film from the surfaces of copper and aluminum plates to be welded: Immerse the aluminum plate in a 100g / L NaOH solution at 35℃ for 3 minutes, then rinse with running cold water, and then immerse in a 15% HNO3 solution for 3 minutes for gloss treatment. After treatment, rinse with running cold water, then rinse with ethanol and dry. Immerse the copper plate in a 10% H2SO4 solution for 4 minutes, then rinse with running cold water, then rinse with ethanol and dry.

[0055] 2. Apply flux to the surfaces of the aluminum and copper plates to be soldered: Prepare a flux by weight of 18 parts CsF, 345 parts AlF, and 35 parts isopropanol. Mix the flux evenly and apply it to the surfaces of the aluminum and copper plates to be soldered, with a coating thickness of 0.1 mm.

[0056] 3. By weight, mix and melt 70 parts of Zn and 30 parts of Al to form a thin plate of brazing filler metal with a thickness of 0.1 mm. Then, cut the filler metal into long strips according to the size of the area to be brazed. The length of the strips should be equal to the length of the area to be brazed, and the width should be 2 mm. Lay the strips flat on the aluminum plate base material coated with flux, and make sure that the length direction of the filler metal is consistent with the length direction of the area to be brazed. The strips should be spaced 0.2 mm apart to allow the gas generated during the brazing heating process to escape easily.

[0057] 4. Fix the above-mentioned base material, brazing filler metal, flux, and heating pad with a clamp, apply a pressure of 20.0 kPa to the welding area, and use a planar coil for induction brazing; use 430 stainless steel sheet as induction heating pad, and cover the copper-aluminum overlap part during welding; the temperature of induction brazing is 570℃, and the heating time of induction brazing is 8s;

[0058] 5. Preparation of nano-graphite sheet modified EVA hot melt adhesive: According to the mass ratio, pour 97 parts of EVA hot melt adhesive and 4 parts of nano-graphite sheets into the torque rheometer through the feeding port, mix at 160℃ for 15 minutes (rotor speed is 60 rpm), then turn on the torque rheometer, pour the mixed adhesive onto a polytetrafluoroethylene film, and after cooling, the nano-graphite sheet modified EVA hot melt adhesive is obtained.

[0059] 6. Sealing treatment around the weld: Preheat the nano-graphite sheet modified EVA hot melt adhesive at 80°C for 3 minutes, and then heat it to 180°C to melt it; apply the melted hot melt adhesive to the area around the weld of the copper-aluminum transition clamp that has been brazed above, and after it cools naturally, the finished copper-aluminum transition clamp is obtained.

[0060] Comparative Example 1

[0061] In Example 1, the flux used in step 2 does not contain isopropanol, and the rest of the operation is the same as in Example 1.

[0062] Comparative Example 2

[0063] In Example 1, step 2, isopropanol in the flux composition is replaced with the same number of parts by weight of ethanol, and the remaining operations are the same as in Example 1.

[0064] Comparative Example 3

[0065] In step 3 of Example 2, the brazing filler metal is cut into a whole piece with the same size as the area to be soldered, and the rest of the operation is the same as in Example 2.

[0066] Comparative Example 4

[0067] After brazing, no hot melt adhesive is used to seal the weld perimeter; the remaining operations are the same as in Example 3.

[0068] Comparative Example 5

[0069] After brazing, seal the area directly with EVA hot melt adhesive, and perform the remaining operations as in Example 3.

[0070] For the copper-aluminum brazed joints prepared in the examples and comparative examples, surface morphology photographs of the brazed area at the tensile shear fracture were taken using a digital camera. Metallographic image processing software was used to analyze the surface morphology photographs and test the rate of incomplete welds in the welded area. Simultaneously, an electrochemical workstation was used to determine the polarization curve of the coating, with a 3.5 wt% NaCl solution as the test medium, to obtain the corrosion current density (Ig). corr The results are shown in Tables 1 and 2.

[0071] Table 1. Test results of the poor solder joint rate of copper-aluminum brazed joints obtained in Examples 1-3 and Comparative Examples 1-3.

[0072]

[0073] Table 2. Electrochemical performance test results of copper-aluminum brazed joints obtained in Examples 1-3 and Comparative Examples 4 and 5.

[0074]

[0075] As can be seen from the test results in Table 1, the rate of incomplete soldering in the copper-aluminum brazing areas of Examples 1-3 is much lower than that of Comparative Examples 1-3. This is because, during the brazing heating process, the addition of isopropanol to the flux removes the oxide film on the surface of the base material and protects the surface from oxidation, which helps the brazing filler metal spread during heating. Ethanol, under the same conditions, does not have this effect. Simultaneously, the improved brazing filler metal gas escape channel promotes gas discharge during heating, reducing defects such as porosity, bulging, and slag inclusions at the weld joint, thereby improving the spread of the brazing filler metal and reducing incomplete soldering (e.g., Figure 1 ).

[0076] As can be seen from the electrochemical performance test results in Table 2, the corrosion current density of the copper-aluminum brazed joints treated with nano-graphite sheet modified EVA hot melt adhesive in Examples 1-3 is much lower than that of the copper-aluminum brazed joint in Comparative Example 4 without weld perimeter sealing treatment, and is also significantly lower than that of the copper-aluminum brazed joint in Comparative Example 5 directly sealed with EVA hot melt adhesive. This is because the nano-graphite sheet modified EVA hot melt adhesive plays an effective shielding role against corrosive media, and the addition of nano-graphite sheets further improves the shielding and protective effect of EVA hot melt adhesive.

[0077] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for processing a high-quality copper-aluminum transition clamp, characterized in that, Includes the following steps: (1) Pretreatment of aluminum plate: Immerse the aluminum plate in a NaOH solution with a concentration of 100g / L at 15~35℃ for 3~4min, then rinse with running cold water, then immerse in a HNO3 solution with a volume concentration of 10%~15% for 3~4min, then rinse with running cold water, then rinse with ethanol and dry. (2) Pretreatment of copper plate: Immerse the copper plate in H2SO4 solution with a volume concentration of 8-12% for 3-4 minutes, then rinse with running cold water, then rinse with ethanol and dry. (3) Apply flux; apply a 0.1 mm thick layer of flux evenly to the surfaces of the pretreated aluminum and copper plates to be soldered; (4) Brazing: Place brazing filler metal on the aluminum plate to be brazed, then attach and fix it to the copper plate to be brazed, and then apply pressure to perform induction brazing. (5) Sealing treatment: Coat the weld transition area of ​​step (4) with nano-graphite sheet modified EVA hot melt adhesive and let it cool naturally to obtain copper-aluminum transition clamp. The flux mentioned in step (3) is composed of the following raw materials in parts by mass: 15-20 parts of CsF, 35-45 parts of AlF3, and 30-40 parts of isopropanol.

2. The processing method of the high-quality copper-aluminum transition clamp according to claim 1, characterized in that, The brazing filler metal used in step (4) is in the form of a long sheet, the length of which is equal to the length of the area to be soldered, the width is 2mm, and the thickness is 0.1~0.2mm. When placing the filler metal, the length direction of the filler metal is consistent with the length direction of the area to be soldered, and the sheet is spaced 0.2mm apart.

3. The high-quality copper-aluminum transition fitting processing method according to claim 1 or 2, characterized in that, The brazing filler metal is composed of the following raw materials in parts by weight: 70-98 parts Zn and 2-30 parts Al.

4. The method of processing high-quality copper-aluminum transition fittings according to claim 1, characterized in that, In step (4), a planar coil is used for induction brazing; 430 stainless steel sheet is used as an induction heating pad to cover the copper-aluminum overlap area during welding; the brazing temperature is 550~570℃, the time is 8~12s, and the applied pressure is 20.0~30.0kPa.

5. The method of processing high-quality copper-aluminum transition fittings according to claim 1, characterized in that, The nano-graphite sheet modified EVA hot melt adhesive mentioned in step (5) is prepared by mixing EVA hot melt adhesive and nano-graphite sheets in a torque rheometer according to the formula, and then pouring the mixed adhesive onto a polytetrafluoroethylene film and cooling it.

6. The method of processing high-quality copper-aluminum transition fittings according to claim 5, characterized in that, By weight, 97-98 parts of EVA hot melt adhesive and 3-4 parts of nano-graphite sheets are used.

7. The method of processing high-quality copper-aluminum transition fittings according to claim 5, characterized in that, The mixing temperature was 160℃, the rotor speed was 60rpm, and the time was 15min.

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