Water-adding welding method for nickel-plated copper-aluminum dissimilar metal

Abstract

The invention relates to the technical field of new energy automobile battery pack manufacturing, and particularly discloses a nickel-plated copper-aluminum dissimilar metal water adding welding method which comprises the steps that S1, a cleaned nickel-plated copper sheet and a cleaned aluminum sheet are stacked and fixed in a tool jig provided with a flow channel; s2, water-based protection liquid containing a modified antioxidant additive is supplied to the welding area through a flow channel, a gas-phase protection layer is formed through in-situ vaporization of the water-based protection liquid, and the additive is prepared through a high-temperature condensation reaction of triethanolamine and boric acid; s3, starting the electrode to carry out resistance thermocompression welding on the welding area, continuously supplying protection liquid in the welding process, and controlling the flow, temperature and humidity of the protection liquid; and S4, after welding is completed, protection liquid is continuously supplied or quenching treatment is conducted. By means of the double mechanisms of water vapor physical isolation and auxiliary agent chemical reduction, high-temperature oxidation yellowing of a nickel plating layer is effectively restrained, a welded joint keeps silvery white gloss, and excellent corrosion resistance and connection strength are achieved.

Description

Technical Field

[0001] This invention belongs to the field of new energy vehicle battery pack manufacturing technology, specifically relating to a water-based welding method for nickel-plated copper-aluminum dissimilar metals. Background Technology

[0002] In the manufacturing of battery packs for new energy vehicles, nickel-plated copper sheets and aluminum sheets need to be firmly welded together to complete the electrical connection between the batteries. The reason for plating the surface of the copper sheet with a layer of nickel is mainly to improve the corrosion resistance of the copper sheet and enhance its compatibility with the aluminum sheet during welding.

[0003] When welding is performed using methods such as lasers or ultrasound, the welding area generates very high temperatures. This high temperature can cause the originally silvery-white nickel plating to change color, turning it yellow or brownish-yellow. This color change not only directly affects the product's appearance but may also indicate a decrease in the original protective properties of the nickel plating.

[0004] Currently, the industry practice is to blow inert gases such as argon into the welding area during welding in an attempt to isolate it from air and suppress this oxidation discoloration. However, this method is not very effective in solving the yellowing problem of nickel plating.

[0005] The yellowing of nickel plating may be related to nickel oxidation at high temperatures, diffusion between nickel and copper, and optical interference effects caused by changes in surface microstructure. Therefore, the industry needs a new process that can effectively solve the yellowing problem of nickel plating during welding while ensuring the quality of the welded joint and maintaining its proper metallic luster. Summary of the Invention

[0006] The purpose of this invention is to provide a water-based welding method for nickel-plated copper-aluminum dissimilar metals to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides a water-based welding method for nickel-plated copper-aluminum dissimilar metals, comprising the following steps: S1. Provide nickel-plated copper sheets and aluminum sheets to be welded, and perform surface cleaning treatment on the areas of the nickel-plated copper sheets and aluminum sheets to be welded; S2. The nickel-plated copper sheet and aluminum sheet are stacked and fixed in a welding fixture, the fixture being provided with a liquid guide channel extending toward the welding area; S3. A liquid protective medium is supplied to the welding area through the liquid guide channel, and the liquid protective medium vaporizes in situ under the action of the welding thermal field to form a gas phase protective layer; S4. Start the welding heat source to heat and pressurize the welding area, and continuously supply the liquid protective medium during the welding process, controlling the flow rate of the liquid protective medium to be 0.05-0.10 ml / s; S5. After welding is completed, stop heating and continue to supply the liquid protective medium or place the welded parts in a cooling liquid for cooling treatment; The liquid protective medium is a water-based solution, and its solvent is deionized water.

[0008] Preferably, the liquid protective medium also contains a modified antioxidant additive dissolved in it, and the preparation method of the modified antioxidant additive includes the following steps: P1. Add triethanolamine to the reaction vessel, heat to 60-70℃, and stir at 300-500 rpm; P2. Add boric acid to the triethanolamine in batches until the boric acid is completely dissolved to form a transparent viscous liquid; P3. Heat the reaction system to 110-120℃ and carry out the dehydration condensation reaction under vacuum conditions of -0.08MPa to -0.09MPa for 2-3 hours. P4. Cool to 80℃, add benzotriazole, and stir until completely dissolved; P5. Add deionized water to adjust the viscosity and cool to room temperature to obtain the modified antioxidant.

[0009] Preferably, the raw materials for preparing the modified antioxidant auxiliaries include, by mass parts: 100 parts triethanolamine, 40-50 parts boric acid, 2-5 parts benzotriazole, and 20-30 parts deionized water; the volume ratio of the modified antioxidant auxiliaries to deionized water in the liquid protective medium is 1:10 to 1:20.

[0010] Preferably, in step S3, the liquid protective medium is supplied in the following manner: The liquid protective medium is added by gravity dripping through a conduit, with the droplet diameter controlled to be less than 2 mm; or, the liquid protective medium is atomized into a micro-mist with an average particle size of less than 50 μm by an ultrasonic atomizing device and sprayed onto the welding area through a nozzle.

[0011] Preferably, in step S3, the supply of the liquid protective medium begins 0.5-1.0 seconds before the welding heat source is started; in step S4, the relative humidity of the welding process is controlled at 20%-30%.

[0012] Preferably, the welding heat source uses graphite electrodes for resistance thermo-press welding, the welding temperature is 600℃-650℃, the welding pressure is 0.3-0.5MPa, and the single-point welding time is 0.5-2.0 seconds.

[0013] Preferably, the horizontal distance between the outlet of the liquid guiding channel and the center of the welding area is 10-20mm, and the liquid guiding channel is sloping to guide the liquid protective medium to the interface between the nickel-plated copper sheet and the aluminum sheet.

[0014] Preferably, in step S5, the specific operation of the cooling treatment is as follows: after the welding heat source stops heating, the welded part is immediately immersed in room temperature deionized water or flowing tap water until the workpiece temperature drops to room temperature.

[0015] Preferably, the thickness of the nickel-plated copper sheet is 0.5-2.0 mm, the thickness of the aluminum sheet is 0.5-2.0 mm, and the thickness of the nickel plating layer is 2-10 μm.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention supplies a water-based protective liquid to the welding area. The volume expansion caused by the rapid vaporization of water at high temperatures displaces the air present in the welding area, forming a water vapor protective layer on the metal surface, physically isolating oxygen. Simultaneously, the vaporization process of the water removes excess heat, reducing the peak temperature of the nickel plating layer and inhibiting grain coarsening and surface oxidation discoloration. The resulting battery pack busbar welding joint maintains a silvery-white metallic luster in its nickel plating layer, with a color difference value ΔE controlled below 3, thus solving the problem of yellowing caused by high welding temperatures.

[0017] (2) In this invention, a modified antioxidant additive is dissolved in water. This additive is prepared by esterification of triethanolamine and boric acid. After the water evaporates, the remaining additive forms a flowing glassy film in situ at a high temperature of 600°C, covering the surface of the nickel plating layer and filling the protective gaps left by the dissipation of water vapor. Furthermore, the trace amounts of reducing gas generated by the high-temperature decomposition of the additive can reduce the slightly oxidized nickel. This mechanism of physical isolation from water vapor combined with the chemical reduction of the additive improves the stability of the welding process, enabling the nickel-plated copper and aluminum dissimilar metal welded parts to maintain good oxidation resistance and corrosion resistance even under complex working conditions. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] In the claims and description of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0020] This invention provides a water-based welding method for nickel-plated copper-aluminum dissimilar metals. The core of this method lies in utilizing the dual mechanisms of phase change endothermic reaction in the liquid medium and atmospheric protection to solve the problem of nickel plating oxidation and discoloration caused by high-temperature welding. The specific implementation process and principle are as follows: I. Welding Preparation and Tooling Design First, select nickel-plated copper sheets with a thickness of 0.5-2.0 mm (nickel plating thickness 2-10 μm) and aluminum sheets of the same thickness as the base materials to be welded. To ensure low contact resistance at the welding interface, the area to be welded must be cleaned beforehand to remove oil and oxide film.

[0021] In the clamping process, this invention features a dedicated welding fixture. This fixture not only secures the workpiece but, more importantly, integrates a liquid flow channel. This channel is designed with a sloping shape, its outlet precisely pointing towards the center of the welding area (horizontal distance controlled within 10-20mm). It utilizes gravitational potential energy or micro-pressure to guide the liquid protective medium precisely to the interface between the nickel-plated copper sheet and the aluminum sheet. This "directional flow guidance" design avoids ineffective liquid diffusion in non-welding areas, ensuring efficient utilization of the protective medium.

[0022] II. Introduction of Liquid Medium and Phase Change Protection during Welding 0.5-1.0 seconds before welding begins, liquid protective medium is supplied to the welding area through the guide channel. This lead time is crucial: it ensures that a liquid film or wetted zone has already formed at the welding interface the instant the electrodes are energized and heated.

[0023] Supply method: For conventional connections, gravity dripping can be used (droplet diameter <2mm); for precision connections, an ultrasonic atomizing device can be used to disperse the medium into micro-mist with a particle size of less than 50μm. Atomization can significantly increase the specific surface area of ​​the liquid, making its heat absorption and vaporization more rapid and the coverage more uniform.

[0024] Phase change principle: When the graphite electrode is heated (temperature rises to 600-650℃), the pre-existing liquid medium rapidly boils and vaporizes. Water has a very high latent heat of vaporization, and the phase change process removes a large amount of excess heat accumulated on the nickel plating surface, keeping the peak surface temperature below the severe oxidation temperature of nickel. Simultaneously, the volume expansion caused by liquid vaporization (water expands approximately 1700 times as it turns into water vapor) instantly creates a high-pressure outward airflow field, i.e., an "in-situ vapor phase protective layer," which effectively expels the surrounding air from the welding area, physically isolating oxygen.

[0025] III. Chemical Mechanism of Core Modified Antioxidant Auxiliaries To further enhance the protective effect, this invention incorporates a specially formulated modified antioxidant additive dissolved in deionized water (at a ratio of 1:10 to 1:20). The preparation and mechanism of action of this additive are the core chemical principles of this invention. 1. Raw material selection: Triethanolamine was selected as the skeleton, boric acid as the film-forming agent, and benzotriazole (BTA) as the corrosion inhibitor.

[0026] 2. Synthesis process: Esterification reaction (steps P1-P3): Triethanolamine and boric acid (mass ratio approximately 100:45) are mixed and subjected to a dehydration condensation reaction at 110-120℃ and a vacuum of -0.08MPa to -0.09MPa for 2-3 hours. Principle: The vacuum environment not only accelerates the removal of moisture, shifting the equilibrium towards the formation of borate esters, but also prevents the oxidation of amine groups at high temperatures. The resulting triethanolamine borate ester exhibits excellent high-temperature adhesion and film-forming properties.

[0027] Functionalization compounding (steps P4-P5): Benzotriazole is introduced after cooling to 80℃. The basic solubilizing effect of triethanolamine is used to uniformly disperse the water-insoluble BTA in the system.

[0028] 3. High-temperature protection mechanism: After the welding heat evaporates the moisture, the remaining borate polymer does not decompose immediately. Instead, it forms a flowing glassy melt film at around 600℃, tightly covering the nickel plating surface and filling the protective gaps left by the escape of water vapor. Simultaneously, the trace amounts of reducing gases (such as ammonia and hydrogen fragments) generated by the decomposition of the triethanolamine structure at high temperatures can actively reduce the slightly oxidized nickel atoms, achieving "self-repair."

[0029] IV. Welding Parameters and Cooling Control The welding process employs resistance thermoforming (welding pressure 0.3-0.5MPa, time 0.5-2.0 seconds), and the relative humidity of the environment is controlled at a low level of 20%-30% to prevent external moisture from interfering with the welding quality.

[0030] After welding, immediately stop heating and continue supplying protective medium or directly immerse the high-temperature workpiece in room temperature water for rapid cooling.

[0031] Cooling principle: Rapid cooling quickly freezes the metal lattice, preventing excessive growth of nickel plating grains during the high-temperature holding period (grain coarsening is one of the causes of yellowing). Simultaneously, when the temperature drops below 200℃, benzotriazole (BTA) in the additive begins to function. It adsorbs onto the metal surface to form a dense Cu / Ni-BTA complex passivation film, preventing secondary oxidation when the workpiece comes into contact with air after being exposed to water, ultimately ensuring a bright, silvery-white weld joint. Example

[0032] This embodiment provides a water-based welding method for nickel-plated copper-aluminum dissimilar metals.

[0033] I. Preparation of modified antioxidant auxiliaries: Prepare the following raw materials by weight: 110 parts triethanolamine, 45 parts boric acid, 3 parts benzotriazole (BTA), and 25 parts deionized water.

[0034] The specific preparation steps include: P1. Add 100 parts of triethanolamine to a reactor equipped with a mechanical stirrer and a reflux condenser, start stirring, set the speed to 400 rpm, and heat to 65°C.

[0035] P2. While stirring, slowly add 45 parts of boric acid in 3 portions, with an interval of 10 minutes between each addition, until the boric acid is completely dissolved and the reaction solution becomes transparent and viscous.

[0036] P3. Heat the reaction system to 115℃, start the vacuum pump to reduce the system pressure to -0.09MPa, and carry out the isothermal dehydration condensation reaction for 2.5 hours at this temperature and pressure.

[0037] P4. Stop heating and let the system cool naturally to 80°C. Add 3 parts of benzotriazole and stir continuously for 30 minutes until the solid is completely dissolved.

[0038] P5. Slowly add 25 parts of deionized water to adjust the viscosity of the system, continue stirring for 10 minutes, then discharge the material and cool it to room temperature to obtain a golden yellow transparent modified antioxidant.

[0039] II. Water Welding Process for Nickel-Plated Copper-Aluminum Dissimilar Metals Preparation of liquid protective medium: The modified antioxidant auxiliary agent (component A) prepared above was measured and mixed with deionized water at a volume ratio of 1:15. After stirring evenly, it was used as the liquid protective medium in this embodiment.

[0040] Welding steps: S1. Select a nickel-plated copper sheet with a thickness of 1.2mm (nickel plating layer thickness of 5μm) and an aluminum sheet with a thickness of 1.2mm. Wipe the area to be soldered with anhydrous ethanol to remove surface oil and dust.

[0041] S2. Place the cleaned nickel-plated copper sheet on top of the aluminum sheet and fix it in the graphite welding fixture. The fixture has a microchannel interface on its side, and the channel outlet is aligned with the center of the overlapping welding area of ​​the two metal sheets, with a distance of 15mm.

[0042] S3. Start the ultrasonic atomizing liquid supply device to atomize the prepared liquid protective medium into micro-mist with an average particle size of 30μm, and spray it onto the welding area through the microchannel interface.

[0043] S4. With the atomizing medium continuously supplied (supply rate equivalent to liquid volume of 0.08 ml / s), start the graphite electrode for resistance thermoforming welding. The welding parameters are set as follows: welding temperature 615℃, welding pressure 0.4 MPa, single-point welding time 1.2 seconds, and medium supply start time: 0.8 seconds before electrode pressing and heating.

[0044] S5. After welding is completed, lift the electrode, immediately stop heating, and immerse the welded component directly into flowing deionized water at 25°C for rapid cooling until the workpiece cools to room temperature, then remove and dry it. Example

[0045] This embodiment provides a water-based welding method for nickel-plated copper-aluminum dissimilar metals.

[0046] I. Preparation of Modified Antioxidant Additives Prepare the following ingredients by weight: 100 parts triethanolamine, 50 parts boric acid, 5 parts benzotriazole (BTA), and 30 parts deionized water.

[0047] The specific preparation steps include: P1. Add 100 parts of triethanolamine to a reactor equipped with a mechanical stirrer and a reflux condenser, start stirring, set the speed to 500 rpm, and heat to 70°C.

[0048] P2. While stirring, slowly add 50 parts of boric acid in 4 portions, 15 minutes apart each time, until the boric acid is completely dissolved and the reaction solution becomes transparent and viscous.

[0049] P3. Heat the reaction system to 120°C, start the vacuum pump to reduce the system pressure to -0.08MPa, and carry out the isothermal dehydration condensation reaction for 2.0 hours at this temperature and pressure.

[0050] P4. Stop heating and let the system cool naturally to 80°C. Add 5 parts of benzotriazole and stir continuously for 30 minutes until the solid is completely dissolved.

[0051] P5. Slowly add 30 parts of deionized water to adjust the viscosity of the system, continue stirring for 10 minutes, then discharge the material and cool it to room temperature to obtain a golden yellow transparent modified antioxidant.

[0052] II. Water Welding Process for Nickel-Plated Copper-Aluminum Dissimilar Metals Preparation of liquid protective medium: The modified antioxidant agent prepared above was measured and mixed with deionized water at a volume ratio of 1:10. After stirring evenly, it was used as the liquid protective medium in this embodiment.

[0053] Welding steps: S1. The steps are exactly the same as in Example 1.

[0054] S2. Place the cleaned nickel-plated copper sheet on top of the aluminum sheet and fix it in the graphite welding fixture. The fixture has a liquid guide channel at the top, and the channel outlet is sloping, aligned with the center of the overlapping welding area of ​​the two metal sheets, with a horizontal distance of 10mm.

[0055] S3. Start the gravity dripping liquid supply device and use the conduit to drip the prepared liquid protective medium into the liquid guide channel, with the droplet diameter controlled at about 1.5mm.

[0056] S4. With continuous droplet supply (flow rate controlled at 0.10 ml / s), initiate resistance thermoforming welding of the graphite electrode. Welding parameters are set as follows: welding temperature 650℃, welding pressure 0.3 MPa, single-point welding time 1.5 seconds, and medium supply start time: 1.0 second before electrode pressing and heating.

[0057] S5. The steps are exactly the same as in Example 1. Example

[0058] This embodiment provides a water-based welding method for nickel-plated copper-aluminum dissimilar metals.

[0059] Preparation of liquid protective medium: In this embodiment, the liquid protective medium is pure deionized water.

[0060] Welding steps: S1. The steps are exactly the same as in Example 1.

[0061] S2. Place the cleaned nickel-plated copper sheet on top of the aluminum sheet and fix it in the graphite welding fixture. The fixture has a guide tube at the top, with the tube outlet aligned with the center of the overlapping welding area of ​​the two metal sheets, at a horizontal distance of 20mm.

[0062] S3. Start the gravity dripping liquid supply device and add deionized water to the welding area through the conduit. The diameter of the droplets is controlled at about 2mm.

[0063] S4. With continuous droplet supply (flow rate controlled at 0.05 ml / s), initiate resistance thermoforming welding of the graphite electrode. Welding parameters are set as follows: welding temperature 600℃, welding pressure 0.5 MPa, single-point welding time 0.8 seconds, and medium supply start time: 0.5 seconds before electrode pressure heating.

[0064] S5. The steps are exactly the same as in Example 1.

[0065] Comparative Example 1 This comparative example provides a welding method for nickel-plated copper and aluminum dissimilar metals. Welding steps: S1. The steps are exactly the same as in Example 1.

[0066] S2. Place the cleaned nickel-plated copper sheet on top of the aluminum sheet and fix it in the graphite welding fixture.

[0067] S3. Start the graphite electrode to perform resistance thermoforming welding on the welding area. The welding parameters are set as follows: welding temperature 615℃, welding pressure 0.4MPa, and single-point welding time 1.2 seconds.

[0068] S4. After welding is completed, lift the electrodes and place the welded components in the air to cool naturally to room temperature.

[0069] Comparative Example 2 This comparative example provides a welding method for nickel-plated copper and aluminum dissimilar metals. Preparation of liquid protective medium: This comparative example uses pure anhydrous ethanol as the liquid protective medium.

[0070] Welding steps: S1. The steps are exactly the same as in Example 1.

[0071] S2. The steps are exactly the same as in Example 1.

[0072] S3. Start the ultrasonic atomizing liquid supply device to atomize pure anhydrous ethanol into micro-mist with an average particle size of 30μm, and spray it onto the welding area through the microchannel interface.

[0073] S4. With the atomizing medium continuously supplied (supply rate equivalent to liquid volume of 0.08 ml / s), start the graphite electrode for resistance thermoforming welding. The welding parameters are set as follows: welding temperature 615℃, welding pressure 0.4 MPa, single-point welding time 1.2 seconds, and medium supply start time: 0.8 seconds before electrode pressing and heating.

[0074] S5. The steps are exactly the same as in Example 1.

[0075] Comparative Example 3 This comparative example provides a welding method for nickel-plated copper and aluminum dissimilar metals. I. Preparation of Protective Fluid Additives Prepare the following raw materials by weight: 100 parts triethanolamine, 45 parts boric acid, 3 parts benzotriazole (BTA), and 25 parts deionized water.

[0076] The specific preparation steps include: P1. At room temperature, add 100 parts triethanolamine, 45 parts boric acid, and 3 parts benzotriazole to a mixing container.

[0077] P2. Turn on the mechanical stirrer, set the stirring speed to 400 rpm, and stir continuously for 30 minutes until all components are mixed and dissolved, resulting in a light yellow and transparent mixture.

[0078] II. Welding process for nickel-plated copper and aluminum dissimilar metals Preparation of liquid protective medium: The above-prepared mixture and deionized water were measured and mixed at a volume ratio of 1:15. After stirring evenly, it was used as the liquid protective medium in this comparative example.

[0079] Welding steps: S1. The steps are exactly the same as in Example 1.

[0080] S2. The steps are exactly the same as in Example 1.

[0081] S3. Start the ultrasonic atomizing liquid supply device to atomize the prepared liquid protective medium into micro-mist with an average particle size of 30μm, and spray it onto the welding area through the microchannel interface.

[0082] S4. With the atomizing medium continuously supplied (supply rate equivalent to liquid volume of 0.08 ml / s), start the graphite electrode for resistance thermoforming welding. The welding parameters are set as follows: welding temperature 615℃, welding pressure 0.4 MPa, single-point welding time 1.2 seconds, and medium supply start time: 0.8 seconds before electrode pressing and heating.

[0083] S5. The steps are exactly the same as in Example 1.

[0084] To verify the effectiveness of this invention, the test samples were prepared as follows: Nickel-plated copper sheets with a thickness of 1.2 mm and aluminum sheets with a thickness of 1.2 mm were selected and processed into standard strip-shaped samples of 100 mm × 25 mm. Following the complete welding processes of Examples 1, 2, and 3, and Comparative Examples 1, 2, and 3, the nickel-plated copper sheets and aluminum sheets were lap-welded together to obtain welded joint test samples that corresponded completely to each process scheme, and were sequentially labeled NAW-01 to NAW-06. Subsequently, the following performance tests were performed on all grouped samples.

[0085] All performance tests of this invention were conducted in accordance with the relevant Chinese national standards (GB / T), the specific standards of which are as follows: 1. Surface appearance and oxidation degree test The surface appearance and oxidation degree testing followed the Chinese national standards GB / T 11186.2-1989 "Methods for measuring the color of paint film - Part 2: Color Measurement" and GB / T 11186.3-1989 "Methods for measuring the color of paint film - Part 3: Color Difference Calculation". First, a precision colorimeter (D65 light source, 10° field of view) was used, with the unsoldered original nickel-plated copper sheet surface as the reference sample (set as standard white), to measure the color difference value ΔE in the weld center area of ​​each sample. Simultaneously, X-ray photoelectron spectroscopy (XPS) was used to perform a semi-quantitative analysis of the elemental composition of the weld area surface, focusing on scanning the characteristic peak areas of O1s (531 eV) and Ni2p (852 eV), and calculating the relative percentage content of oxygen atoms on the surface (Atomic %). The quantitative indicators for evaluation were the ΔE value and oxygen content. The smaller the ΔE value (usually required to be less than 3.0) and the lower the oxygen content, the less oxidation corrosion the weld heat-affected zone suffers, and the purer the nickel plating layer remains in a metallic state. This directly corresponds to the product having excellent appearance consistency and contact reliability in subsequent assembly.

[0086] 2. Microstructure and corrosion resistance testing The testing of microstructure and corrosion resistance followed the Chinese national standards GB / T 13298-2015 "Metallic Materials - Microstructural Testing Methods" and GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". First, the uniformity of grain size and the clarity of grain boundaries on the welded surfaces of each sample were observed using a scanning electron microscope (SEM, magnification 2000x-5000x). Then, the samples were placed in a neutral salt spray chamber and continuously sprayed with a 50±5 g / L sodium chloride solution mist at 35±2℃. Observations were taken every 4 hours, and the cumulative time from the first appearance of visible corrosion spots (such as red rust or white spots) was recorded. The quantitative evaluation indicators were grain morphology and salt spray resistance time (in hours). The finer and denser the grains, and the longer the salt spray resistance time (usually required to be greater than 48 hours), the more stable the microstructure of the welded joint and the stronger its resistance to electrochemical corrosion. This directly reflects that the welded component has a longer service life under harsh conditions such as high humidity and high salt spray inside the battery pack of new energy vehicles.

[0087] 3. Mechanical and electrical performance testing of welded joints The mechanical and electrical properties of the welded joints were tested in accordance with the Chinese national standards GB / T 39167-2020 "Tensive Shear Test Method for Resistance Spot Welded and Projection Welded Joints" and GB / T 15078-2021 "Method for Measurement of Contact Resistance of Precious Metal Electrical Contact Materials". First, an axial tensile force was applied to the welded specimen at a speed of 10 mm / min using a universal testing machine until fracture, and the maximum failure load (Peak Load, N) and fracture mode were recorded. Then, a 1A DC current was applied to the base material on both sides of the welded area at a fixed distance using a micro-ohmmeter (four-terminal method), and the voltage drop between the two points was measured and converted into a contact resistance value (μΩ). The quantitative indicators for evaluation were the maximum tensile shear force and the contact resistance. A higher tensile shear force and a failure mode of base material fracture, coupled with a lower contact resistance, indicate a stronger weld interface and a more unobstructed conductive path. This directly corresponds to the core performance requirements of low heat loss and high structural reliability of the battery pack busbar during high current transmission.

[0088] The performance of the test samples obtained from the above embodiments and comparative examples was tested, and the results are summarized in the table below:

[0089] 1. Surface appearance and oxidation degree analysis Based on the test results, the color difference value ΔE of the welded areas of the samples in Examples 1 to 3 was controlled between 1.8 and 2.9, meeting the appearance qualification requirement of ΔE < 3.0. Example 1, which combined atomization technology with modified additives, had a color difference value of 1.8 and a surface oxygen content of 2.1%, indicating that the protective layer constructed by this process effectively isolated oxygen contact. In contrast, Comparative Example 1, without protective measures, had a color difference value of 8.5 and a surface oxygen content of 15.6%, exhibiting a deeper degree of oxidation. Furthermore, Comparative Example 3, which used physically mixed additives, had a color difference value of 4.1, which was better than Comparative Example 1, but failed to reach the level of Example 1. This indicates that physical mixing failed to fully reproduce the film-forming and reduction characteristics of the polymer generated by the high-temperature condensation reaction.

[0090] 2. Microstructure and Corrosion Resistance Analysis Regarding corrosion resistance, Example 1 exhibited a salt spray resistance time exceeding 72 hours, superior to the less than 8 hours achieved by conventional welding (Comparative Example 1). This difference is primarily attributed to the in-situ protective film formed by the modified additive at high temperatures and the passivation effect of BTA molecules in the low-temperature region. Example 3 (pure water protection) demonstrated a salt spray resistance time of 36 hours, indicating that physical cooling and grain refinement contribute to improved corrosion resistance. Comparative Example 2 (pure ethanol) showed a salt spray resistance time of 12 hours, suggesting that single organic solvents evaporate too quickly at high temperatures and may leave residues, resulting in an insufficiently dense protective layer and limited effectiveness in blocking corrosive media.

[0091] 3. Mechanical and Electrical Performance Analysis of Welded Joints From the perspective of connection quality, the maximum tensile shear force of the welded joint in Example 1 was 1350 N, and the contact resistance was 3.5 μΩ. The failure mode in both cases was base metal fracture, indicating that the protective medium of the present invention did not negatively affect the weld strength, and the removal of the interface oxide layer resulted in a tighter metal bond. In Comparative Example 2 (pure ethanol), the tensile shear force was 950 N, lower than conventional welding levels, and the contact resistance was somewhat increased. This may be related to poor interface wetting or carbon buildup caused by the organic solvent. Comparing the data from the examples and comparative examples, it is clear that the solution of the present invention achieves improved appearance quality while maintaining stable welding mechanical and electrical properties.

[0092] The foregoing description of the specifications and embodiments is intended to explain the scope of protection of this invention, but does not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of this invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of this invention.

Claims

1. A water-based welding method for nickel-plated copper-aluminum dissimilar metals, characterized in that, Includes the following steps: S1. Provide nickel-plated copper sheets and aluminum sheets to be welded, and perform surface cleaning treatment on the areas of the nickel-plated copper sheets and aluminum sheets to be welded; S2. The nickel-plated copper sheet and aluminum sheet are stacked and fixed in a welding fixture, the fixture being provided with a liquid guide channel extending toward the welding area; S3. A liquid protective medium is supplied to the welding area through the liquid guide channel, and the liquid protective medium vaporizes in situ under the action of the welding thermal field to form a gas phase protective layer; S4. Start the welding heat source to heat and pressurize the welding area, and continuously supply the liquid protective medium during the welding process, controlling the flow rate of the liquid protective medium to be 0.05-0.10 ml / s; S5. After welding is completed, stop heating and continue to supply the liquid protective medium or place the welded parts in a cooling liquid for cooling treatment; The liquid protective medium is a water-based solution, and its solvent is deionized water.

2. The water-based welding method for nickel-plated copper-aluminum dissimilar metals according to claim 1, characterized in that, The liquid protective medium also contains a modified antioxidant additive dissolved in it, and the preparation method of the modified antioxidant additive includes the following steps: P1. Add triethanolamine to the reaction vessel, heat to 60-70℃, and stir at 300-500 rpm; P2. Add boric acid to the triethanolamine in batches until the boric acid is completely dissolved to form a transparent viscous liquid; P3. Heat the reaction system to 110-120℃ and carry out the dehydration condensation reaction under vacuum conditions of -0.08MPa to -0.09MPa for 2-3 hours. P4. Cool to 80℃, add benzotriazole, and stir until completely dissolved; P5. Add deionized water to adjust the viscosity and cool to room temperature to obtain the modified antioxidant.

3. The water-based welding method for nickel-plated copper-aluminum dissimilar metals according to claim 2, characterized in that, The raw materials for preparing the modified antioxidant auxiliaries include, by mass parts: 100 parts triethanolamine, 40-50 parts boric acid, 2-5 parts benzotriazole, and 20-30 parts deionized water; the volume ratio of the modified antioxidant auxiliaries to deionized water in the liquid protective medium is 1:10 to 1:

20.

4. The water-based welding method for nickel-plated copper-aluminum dissimilar metals according to claim 1, characterized in that, In step S3, the liquid protective medium is supplied in the following ways: The liquid protective medium is added by gravity dripping through a conduit, with the droplet diameter controlled to be less than 2 mm; or, the liquid protective medium is atomized into a micro-mist with an average particle size of less than 50 μm by an ultrasonic atomizing device and sprayed onto the welding area through a nozzle.

5. The water-based welding method for nickel-plated copper-aluminum dissimilar metals according to claim 1, characterized in that, In step S3, the supply of the liquid protective medium begins 0.5-1.0 seconds before the welding heat source is started; in step S4, the relative humidity of the welding process is controlled at 20%-30%.

6. The water-based welding method for nickel-plated copper-aluminum dissimilar metals according to claim 1, characterized in that, The welding heat source uses graphite electrodes for resistance thermo-press welding. The welding temperature is 600℃-650℃, the welding pressure is 0.3-0.5MPa, and the single-point welding time is 0.5-2.0 seconds.

7. The water-based welding method for nickel-plated copper-aluminum dissimilar metals according to claim 1, characterized in that, The outlet of the liquid guiding channel is 10-20mm away from the center of the welding area. The liquid guiding channel is sloping and guides the liquid protective medium to the interface between the nickel-plated copper sheet and the aluminum sheet.

8. The water-based welding method for nickel-plated copper-aluminum dissimilar metals according to claim 1, characterized in that, In step S5, the specific operation of the cooling treatment is as follows: after the welding heat source stops heating, the welded parts are immediately immersed in room temperature deionized water or flowing tap water until the workpiece temperature drops to room temperature.

9. The water-based welding method for nickel-plated copper-aluminum dissimilar metals according to claim 1, characterized in that, The thickness of the nickel-plated copper sheet is 0.5-2.0 mm, the thickness of the aluminum sheet is 0.5-2.0 mm, and the thickness of the nickel plating layer is 2-10 μm.

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