Copper-aluminum alloy transition connection terminal and production process thereof

Abstract

The present application relates to the technical field of cable connecting hardware, and particularly discloses a production process of a copper-aluminum alloy transition connecting terminal, which comprises the following steps: cleaning and removing oil stains and oxide films from the welding surfaces of a copper plate and an aluminum alloy plate; coating a brazing filler paste on the welding surface of the aluminum alloy plate; coating a brazing filler powder on the surface of the brazing filler paste; placing the welding surface of the copper plate on the brazing filler powder and fixing it with a clamp; and brazing the composite sheet. The present application innovatively stacks brazing filler pastes and brazing filler powders with different liquidus temperatures between the welding surfaces of the aluminum alloy connecting pipe and the copper plate, fully utilizes the excellent fluidity and wettability of the zinc-tin brazing filler in the first vacuum brazing stage to sufficiently wet the welding surfaces of the aluminum alloy plate and the copper plate, so as to ensure that the brazing filler can fully fill the gap between the brazing joints, and the brazing filler powder can be dispersed in the brazing filler alloy after the brazing filler alloy is melted, so as to realize diffusion and combination in the subsequent stage. The joint structure of the present application is refined, the stable phases are more, the intermetallic brittle compounds are significantly inhibited, the joint strength is enhanced, and the corrosion resistance is improved.

Description

Technical Field

[0001] This invention relates to the field of cable connection hardware technology, specifically to a copper-aluminum alloy transition connection terminal and its manufacturing process. Background Technology

[0002] In the traditional power and power equipment industry, copper-aluminum transition connections are mainly achieved through copper-aluminum transition plates, copper-aluminum transition clamps, and copper-aluminum terminals. Typically, copper-aluminum transition terminals are designed and manufactured consisting of a copper lug and a standard aluminum connecting tube. There are two main connection methods: one is neck friction butt welding, such as CN102683919A. Because the welding surface is entirely at the neck, the joint area is relatively small, resulting in insufficient tensile and bending mechanical strength at the copper-aluminum transition section, making it prone to breakage at the copper-aluminum transition weld. The other is composite sheet welding, such as CN 101841086 A, which uses explosive welding to achieve copper-aluminum lap welding. This method has a clear interface layer, belonging to a crystalline molecular fusion layer, resulting in high bonding strength.

[0003] In addition, brazing is also used for the joints of copper-aluminum transition connection terminals in composite sheet welded structures, such as gas brazing, furnace brazing, or gas shielded brazing. These brazing methods all require the use of flux to remove the oxide film on the surface of the base material so that the filler metal can fully wet the surface. However, the use of flux can easily generate porosity and inclusions in the weld, which greatly reduces the corrosion resistance of the joint. On the other hand, the residual flux residue is highly corrosive and can easily corrode the copper-aluminum joint, affecting the service life of the copper-aluminum joint.

[0004] Furthermore, to avoid the formation of brittle compounds at the aluminum-copper joint, silver-based brazing filler metals are generally used. However, silver-based filler metals are expensive and have poor conductivity, making them suitable only for thick welded joints. Zinc-aluminum filler metals are also used, but these tend to form a thicker layer of brittle copper-aluminum compounds on the copper side of the joint, which weakens the joint's mechanical properties and also results in poor corrosion resistance. Aluminum-silicon-copper-zinc filler metals are also used, which significantly improve fluidity and wettability, but the high content of CuAl2 brittle compounds makes the joint very brittle. Summary of the Invention

[0005] The purpose of this invention is to provide a copper-aluminum alloy transition connection terminal and its manufacturing process, which can enhance the joint strength and corrosion resistance.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] The manufacturing process for copper-aluminum alloy transition connection terminals includes the following steps:

[0008] S1. Clean and remove oil and oxide film from the surfaces of the copper plate and aluminum alloy plate to be welded, then wipe and dry them.

[0009] S2. Apply solder paste to the aluminum alloy plate surface to be soldered and smooth it out;

[0010] S3. Coat the surface of the solder paste with solder powder and smooth it out; the melting point of the solder powder is higher than that of the solder paste.

[0011] S4. Place the copper plate to be soldered flat on the brazing powder and fix the aluminum alloy plate and copper plate with clamps.

[0012] S5. Perform brazing of the composite sheet.

[0013] Preferably, the wiping in step S1 is done with alcohol or acetone.

[0014] Preferably, the thickness of the solder paste in step S2 is 0.2mm-0.3mm, and the thickness of the solder powder in step S3 is 0.15mm-0.25mm.

[0015] Preferably, the solder paste is composed of a binder and a solder alloy, wherein the solder alloy is a zinc-based solder with a liquidus temperature of 310℃-330℃.

[0016] Preferably, the chemical composition of the zinc-based brazing filler metal is: 35-40% zinc, 58-65% tin, 1-1.5% magnesium, and 0.2-0.25% zirconium.

[0017] Preferably, the brazing filler metal powder is an aluminum-based brazing filler metal with a liquidus temperature of 490℃-520℃.

[0018] Preferably, the chemical composition of the brazing filler metal powder is: 40-50% aluminum, 3.0-4.0% silicon, 45-55% zinc, and 0.3-0.4% scandium.

[0019] Preferably, the decomposition temperature of the adhesive and adhesive B is not higher than 450°C, and the melting temperature is not higher than 200°C.

[0020] Preferably, the composite sheet is brazed using vacuum brazing. The vacuum brazing conditions are: heating to 30°C-50°C above the melting point of the brazing filler metal paste and holding at that temperature for 30-60 minutes, with a vacuum degree of 9.5 × 10⁻⁶. -3 ~9.8×10 -3 Next, heat to 30°C-50°C above the melting point of the brazing filler metal powder and hold for 10-15 minutes, with a vacuum degree of 4.5 × 10⁻⁶. -3 ~4.8×10 -3 Then cool to 460℃-470℃ and hold for 10-20 minutes, with a vacuum degree of 6.0×10⁻⁶. -3 ~6.5×10 -3 Finally, the power is cut off to cool down the oven and the food is removed from the furnace.

[0021] The present invention also provides a copper-aluminum alloy transition connection terminal obtained by the above-described manufacturing process.

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

[0023] This invention relates to a copper-aluminum alloy transition connection terminal, comprising an aluminum alloy connecting tube and a copper plate. The copper plate and the aluminum alloy connecting tube employ a composite sheet brazing structure. The brazing process innovatively involves layering and coating brazing paste and brazing powder with different liquidus temperatures between the surfaces to be brazed on the aluminum alloy connecting tube and the copper plate. The brazing paste adheres to the aluminum alloy plate while the copper plate adheres to the brazing plate. During vacuum brazing, the temperature rise curve is controlled so that the brazing paste melts before the brazing powder in the first stage. This fully utilizes the excellent fluidity and wettability of zinc-tin brazing alloy to adequately wet the surfaces to be brazed on both the aluminum alloy plate and the copper plate, ensuring sufficient filling of the brazing gap. Furthermore, the brazing powder disperses within the brazing alloy after melting, facilitating diffusion and bonding in subsequent stages, eliminating the need for additional ultrasonic vibration or other pressure welding techniques to mix the brazing powder and brazing paste. On the other hand, the coexistence of zinc and tin in the brazing alloy and their solid solution bonding with aluminum result in the growth of numerous spiky solid solution whiskers from the aluminum surface, which are then embedded and bonded to the brazing alloy, significantly improving the joint strength.

[0024] In the second stage of vacuum brazing, silicon diffuses faster than aluminum, suppressing the formation of the copper-aluminum brittle compound CuAl2. A suitable amount of magnesium, having diffused to the copper and aluminum alloy plates during the first stage of fusion welding, inhibits aluminum oxidation, allowing the brazing filler powder and paste to wet and fill the weld surfaces. During continued heating, magnesium helps delay segregation transformation, preventing volume changes in the joint structure, and simultaneously promoting the formation of Al2CuMg and Mg2Si phases. These two intermetallic compounds are reinforcing phases and, like aluminum and copper, belong to the face-centered hexagonal lattice, resulting in strong bonding and enhanced joint strength and corrosion resistance. A magnesium content below 1% will result in the presence of brittle aluminum-copper compounds in the joint structure, while a content above 1.5% will reduce the amount of stabilizing phases and decrease joint strength.

[0025] In addition, the zirconium in the solder paste and the scandium in the solder powder can significantly refine the alloy grains and transform them into equiaxed grains in the alloy metallographic structure. This achieves the Al3(ScZr) phase dispersion toughening effect and the AlCu(Zr,Sc) phase hindering grain boundary sliding. Furthermore, the Al3(ScZr) phase interface is more stable, improving creep resistance, corrosion resistance, and joint strength.

[0026] This invention uses vacuum brazing technology, which eliminates the need to apply flux to the aluminum alloy plate to be welded, thus avoiding corrosion of the brazing seam by flux residue. Detailed Implementation

[0027] Example 1

[0028] This embodiment provides a manufacturing process for copper-aluminum alloy transition connection terminals, which specifically includes the following steps:

[0029] S1. Clean and remove oil and oxide film from the surfaces of the copper plate and aluminum alloy plate to be welded, then wipe with alcohol and let dry; the copper plate is 1350 brand and the aluminum alloy plate is 8030 aluminum alloy.

[0030] S2. Apply solder paste to the aluminum alloy plate surface to be soldered and smooth it to a thickness of 0.3 mm. The solder paste consists of a binder and a solder alloy: the binder has a decomposition temperature not exceeding 450℃ and a melting temperature not exceeding 200℃, and is specifically composed of ethyl cellulose, ethyl acetate, and ethanol in a mass ratio of 1.5:3:4. The solder alloy is a zinc-based solder with a liquidus temperature of 315℃, and its chemical composition is: 40% zinc, 58.3% tin, 1.5% magnesium, and 0.2% zirconium.

[0031] S3. Coat the surface of the solder paste with solder powder and smooth it to a thickness of 0.2 mm; the solder powder is an aluminum-based solder with a liquidus temperature of 515℃, and its chemical composition is as follows: 48.5% aluminum, 4.0% silicon, 47.2% zinc, and 0.3% scandium.

[0032] S4. Place the copper plate to be soldered flat on the solder paste and fix the aluminum alloy plate and copper plate with a clamp. The clamp is provided with a limiting post that can be adjusted according to the thickness of the solder paste and an elastic element that provides clamping force to make the two clamps clamp each other. The clamping gap defined by the limiting post is 0.3mm.

[0033] S5. Place in a vacuum furnace for vacuum brazing. The welding conditions are: heat to 350℃ and hold for 30 minutes, with a vacuum degree of 9.8 × 10⁻⁶. -3 Next, heat to 550℃ and hold for 10 minutes, with a vacuum degree of 4.8 × 10⁻⁶. -3 Then cool to 470℃ and hold for 10 minutes, with a vacuum degree of 6.0 × 10⁻⁶. -3 Finally, the power is cut off to cool down the oven and the food is removed from the furnace.

[0034] Example 2

[0035] This embodiment provides a manufacturing process for copper-aluminum alloy transition connection terminals, which specifically includes the following steps:

[0036] S1. Clean and remove oil and oxide film from the surfaces of the copper plate and aluminum alloy plate to be welded, then wipe with acetone and let dry; the copper plate is 1350 brand and the aluminum alloy plate is 8011 aluminum alloy.

[0037] S2. Apply solder paste to the aluminum alloy plate surface to be soldered and smooth it to a thickness of 0.25 mm. The solder paste consists of a binder and a solder alloy: the binder has a decomposition temperature not exceeding 450℃ and a melting temperature not exceeding 200℃, and is specifically composed of ethyl cellulose, ethyl acetate, and ethanol in a mass ratio of 1.5:3:4. The solder alloy is a zinc-based solder with a liquidus temperature of 330℃, and its chemical composition is: 36.75% zinc, 62% tin, 1% magnesium, and 0.25% zirconium.

[0038] S3. Coat the surface of the solder paste with solder powder and smooth it to a thickness of 0.15 mm; the solder powder is an aluminum-based solder with a liquidus temperature of 495°C and a chemical composition of: 41% aluminum, 3.6% silicon, 55% zinc, and 0.4% scandium.

[0039] S4. Place the copper plate to be soldered flat on the solder paste and fix the aluminum alloy plate and copper plate with a clamp. The clamp is provided with a limiting post that can be adjusted according to the thickness of the solder paste and an elastic element that provides clamping force to make the two clamps clamp each other. The clamping gap defined by the limiting post is 0.25mm.

[0040] S5. Place in a vacuum furnace for vacuum brazing. The welding conditions are: heating to 365℃ and holding for 45 minutes, with a vacuum degree of 9.5 × 10⁻⁶. -3 Next, heat to 540℃ and hold for 15 minutes, with a vacuum degree of 4.5 × 10⁻⁶. -3 Then cool to 470℃ and hold for 10 minutes, with a vacuum degree of 6.5 × 10⁻⁶. -3 Finally, the power is cut off to cool down the oven and the food is removed from the furnace.

[0041] Comparative Example 1

[0042] The only difference between this comparative example and Example 1 above is that the chemical composition of the brazing alloy is 40% zinc, 59.3% tin, 0.5% magnesium, and 0.2% zirconium.

[0043] Comparative Example 2

[0044] The only difference between this comparative example and Example 1 above is that the chemical composition of the solder powder is 49% aluminum, 4.0% silicon, and 47% zinc.

[0045] Comparative Example 3

[0046] The only difference between this comparative example and Example 1 above is that the chemical composition of the brazing alloy is 40% zinc, 59.8% tin, and 0.2% zirconium; and the chemical composition of the brazing powder is 48.5% aluminum, 2.5% silicon, 47.2% zinc, 0.3% scandium, and 1.5% magnesium.

[0047] Comparative Example 4

[0048] The only difference between this comparative example and Example 1 above is that the solder paste and solder powder are premixed together before being applied between the aluminum alloy plate and the copper plate.

[0049] The copper-aluminum transition connectors prepared in Examples 1-2 and Comparative Examples 1-4 were subjected to joint property tests. According to GB / T 11363-2008 "Test Method for Strength of Brazed Joints", the tensile strength of the joints in Examples 1-2 was above 110 MPa and the shear strength was above 65 MPa. In contrast, the tensile strength of Comparative Examples 1-4 decreased by 12.3%, 8.7%, 10.5%, and 13.9% respectively compared to Example 1.

[0050] The localized corrosion test of the joint involved immersing the treated, cleaned, and dried joint in a 3.5% sodium chloride aqueous solution at 60°C for 5 hours. The corrosion rates in Examples 1-2 were all less than 0.5 g / m². 2 Compared to Example 1, Comparative Examples 1-4 showed a decrease in joint corrosion of 5.1%, 10.2%, 2.5%, and 4.5%, respectively.

[0051] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope. All such changes and modifications fall within the scope of the present invention as claimed, which is defined by the appended claims and their equivalents.

Claims

1. A manufacturing process for copper-aluminum alloy transition connection terminals, characterized in that, Specifically, the steps include the following: S1. Clean and remove oil and oxide film from the surfaces of the copper plate and aluminum alloy plate to be welded, then wipe and dry them. S2. Apply solder paste to the aluminum alloy plate surface to be soldered and smooth it out; S3. Sprinkle brazing powder evenly over the brazing paste and smooth it out; the melting point of brazing powder is higher than that of brazing paste. S4. Place the copper plate to be soldered flat on the brazing powder and fix the aluminum alloy plate and copper plate with clamps. S5. Perform brazing of the composite sheet; The solder paste is composed of a binder and a solder alloy; the decomposition temperature of the binder is not higher than 450°C and the melting temperature is not higher than 200°C; the liquidus temperature of the solder alloy is 310°C-330°C, and the solder alloy is a zinc-based solder with the chemical composition of zinc, tin, magnesium and zirconium. The liquidus temperature of the brazing filler metal powder is 490℃-520℃, and the brazing filler metal powder is an aluminum-based brazing filler metal with the chemical composition of aluminum, silicon, zinc and scandium. In step S5, the heating curve is controlled so that the solder paste melts before the solder powder in the first stage, and then the solder powder melts in the second stage.

2. The manufacturing process of the copper-aluminum alloy transition connection terminal according to claim 1, characterized in that: The wiping in step S1 uses alcohol or acetone.

3. The manufacturing process of the copper-aluminum alloy transition connection terminal according to claim 1, characterized in that: The thickness of the solder paste in step S2 is 0.2mm-0.3mm, and the thickness of the solder powder in step S3 is 0.15mm-0.25mm.

4. The manufacturing process of the copper-aluminum alloy transition connection terminal according to claim 1, characterized in that: The chemical composition of the zinc-based brazing filler metal is: 35-40% zinc, 58-65% tin, 1-1.5% magnesium, and 0.2-0.25% zirconium.

5. The manufacturing process of the copper-aluminum alloy transition connection terminal according to claim 1, characterized in that: The chemical composition of the brazing filler metal powder is: 40-50% aluminum, 3.0-4.0% silicon, 45-55% zinc, and 0.3-0.4% scandium.

6. The manufacturing process of the copper-aluminum alloy transition connection terminal according to claim 1, characterized in that: The composite sheet is brazed using vacuum brazing. The vacuum brazing conditions are as follows: heating to 30°C-50°C above the melting point of the brazing filler paste and holding at that temperature for 30-60 minutes, with a vacuum degree of 9.5 × 10⁻⁶. -3 ~9.8×10 -3 Next, heat to 30°C-50°C above the melting point of the brazing filler metal powder and hold for 10-15 minutes, with a vacuum degree of 4.5 × 10⁻⁶. -3 ~4.8×10 -3 Then cool to 460℃-470℃ and hold for 10-20 minutes, with a vacuum degree of 6.0×10⁻⁶. -3 ~6.5×10 -3 Finally, the power is cut off to cool down the oven and the food is removed from the furnace.

7. A copper-aluminum alloy transition connection terminal manufactured by the production process described in claim 1.