Same metal welding method

Abstract

The invention discloses a same metal welding method, and relates to the technical field of welding, and the same metal welding method comprises the following steps: selecting a welding flux, selecting a copper-tin welding flux based on a melting point and a welding area, forming an eutectic through copper and tin, and pretreating an oxygen-free copper workpiece to be welded, the method comprises the steps that abrasive paper one-way polishing, absolute ethyl alcohol ultrasonic cleaning and drying treatment are sequentially conducted, base metal is formed, the welding face of the base metal is evenly coated with copper-tin solder, brazing is conducted on the base metal, hydrogen and nitrogen generated through ammonia decomposition serve as a reducing atmosphere and a protective atmosphere respectively, and through cooperative regulation and control over temperature, pressure and time, the copper-tin solder is obtained. And performing diffusion reaction on tin in the copper-tin solder and the base material to form a copper-tin intermetallic compound bonding layer. The copper-tin solder is combined with brazing, base metal does not need to be melted, energy loss caused by high heat conduction of oxygen-free copper is prevented, effective combination can be achieved without multiple times of bottoming, the welding efficiency and the welding quality are improved, and the welding quality of the medium-thickness plate is excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding, in particular to a same metal welding method. BACKGROUND

[0002] The battery liquid cooling plate in a new energy vehicle is a key component for a battery thermal management system, mainly dissipating heat through liquid circulation. It circulates the cooling liquid through the internal flow channel to absorb the heat generated during the operation of the battery, so as to maintain the working temperature of the battery pack within a safe range.

[0003] The liquid cooling plate includes an upper plate, a lower plate and fins. Oxygen-free copper, as a high-purity copper material with extremely low oxygen content, has excellent electrical conductivity, thermal conductivity, corrosion resistance and processing performance, and has a wide range of application scenarios. Therefore, the upper plate, the lower plate and the fins of the liquid cooling plate usually use oxygen-free copper as the material. The upper plate, the lower plate and the fins need to be welded during the manufacturing process, and the welding quality directly affects the product reliability, so the copper and oxygen-free copper welding technology has always been the focus of research in the industrial manufacturing field. However, the characteristics of high thermal conductivity and high laser reflectivity (≥90%) of oxygen-free copper make its welding a technical bottleneck in the industry. The existing process cannot balance the joint quality, welding efficiency and production cost, which restricts its large-scale application in the industrial production field. SUMMARY

[0004] The present application provides a same metal welding method, which can solve the problem that the copper and oxygen-free copper welding process in the prior art cannot balance the joint quality, welding efficiency and production cost.

[0005] A same metal welding method, comprising: Selecting the solder, selecting copper-tin solder based on the melting point and the welding area, and forming eutectic by copper and tin; Pretreating the oxygen-free copper workpiece to be welded, sequentially through sandpaper one-way polishing, anhydrous ethanol ultrasonic cleaning and drying treatment, to form a base material; Uniformly applying copper-tin solder on the welding surface of the base material, and naturally air-drying or drying after application; Clamping the base material with an adjustable spacing clamp to realize assembly; Brazing the base material, placing the assembled base material in an ammonia decomposition furnace, using hydrogen and nitrogen generated by ammonia decomposition as reducing atmosphere and protective atmosphere respectively, and cooperatively controlling temperature, pressure and time to make tin in the copper-tin solder diffuse with the base material to form a copper-tin intermetallic compound bonding layer, and the copper-tin solder fills the gap between the base materials through capillary action after melting to form a dense composite metal bonding layer.

[0006] The same metal welding method provided by the present application has the following beneficial effects compared with the prior art, but is not limited thereto: The method adopts copper-tin solder combined with brazing, brazing does not need to melt the base material, prevents energy loss caused by high thermal conductivity of oxygen-free copper, does not need multiple priming to achieve effective bonding, improves welding efficiency and welding quality, makes the welding quality of the medium plate excellent, the welded joint is not easy to oxidize and discolor, has no obvious pores and solder accumulation, has no obvious weld appearance, has good air tightness and mechanical properties, and can meet the scene demand of new energy automobile battery electric control cooling system and other strict welding quality requirements.

[0007] Through the synergistic design of copper-tin solder composition and ammonia decomposition atmosphere, and the synergistic control of temperature, pressure and time process parameters, a stable welding reaction path is formed to ensure the consistency of welding quality and process stability. The synergistic design of solder and atmosphere balances quality and cost.

[0008] Avoid using high-end devices such as laser and electron beam, and auxiliary devices such as mechanical vibration and ultrasonic, reduce post-processing procedures, improve welding efficiency, and the protective atmosphere generated by ammonia decomposition is lower in cost than mixed gas containing helium, effectively reducing equipment investment and comprehensive production cost, and adapting to large-scale production.

[0009] Further, the oxygen-free copper workpiece includes a liquid cooling plate upper plate, a liquid cooling plate lower plate, and a fin.

[0010] Further, the welding surface roughness Ra of the base material is ≤1.6 μm.

[0011] Further, the ultrasonic cleaning time of anhydrous ethanol is 5 min, and the oven drying time is 10 min.

[0012] Further, the ammonia decomposition furnace includes four functional cavities, namely a preheating cavity, a heating cavity, a welding cavity, and a cooling cavity, and the base material is placed on the four times speed chain of the ammonia decomposition furnace for transmission welding.

[0013] Further, during the brazing process of the base material, the temperature, pressure and time are synergistically controlled, the copper-tin solder adopts a reaction path of low-temperature melting, medium-temperature diffusion and pressure densification, the low-temperature melting temperature is 227℃~850℃, the medium-temperature diffusion temperature is 600℃~900℃, and the pressure for pressure densification is 0.1MPa~0.5MPa.

[0014] Further, in the copper-tin solder, the mass fraction of tin is 12%~15%, and the particle size of copper and tin needs to be optimized to match the diffusion reaction between the base material and the copper-tin solder.

[0015] Further, phosphorus and zinc can be added to the copper-tin solder, or silver and indium can be added to adjust the welding performance.

[0016] Further, after brazing, the welding area needs to be cut open and the welding quality needs to be detected.

[0017] Further, the welding quality is detected by appearance detection and CCD camera observation, to confirm that there is no oxidation discoloration, no solder accumulation, and no obvious weld in the welding area. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 A flow chart of a same metal welding method of the present application; Figure 2 An image of the welding area between the upper plate and the lower plate of the liquid cooling plate observed by the CCD camera after cutting the welded piece; Figure 3 An image of the welding area between the upper plate and the fin of the liquid cooling plate, and the welding area between the lower plate and the fin of the liquid cooling plate observed by the CCD camera after cutting the welded piece. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings which show the embodiments according to the present application. It should be understood that the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments described in the present application, all other embodiments obtained by those skilled in the art without creative labor shall fall within the scope of protection of the present application.

[0020] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application; the terms "include", "contain", "have", "with", "contain", "contain" and the like in the specification and claims of the present application and the above description of drawings are open-ended terms. Therefore, a method or device "including", "containing", "having" one or more steps or elements has one or more steps or elements, but is not limited to only having the one or more elements. The terms "first", "second" and the like in the specification and claims of the present application or the above description of drawings are used to distinguish different objects, and are not used to describe a specific order or primary and secondary relationship. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more features. In the description of the present application, unless otherwise stated, the meaning of "multiple" is two or more.

[0021] In the description of the present application, it should be understood that the terms "upper", "lower", "left", "right", "front", "back", etc. indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0022] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "attaching" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0023] It should be emphasized that when the term "comprising / including" is used in the present specification, it is used to explicitly indicate the presence of the features, integers, steps or components described, but does not exclude the presence or addition of one or more other features, integers, steps, components or groups of features, integers, steps, components.

[0024] The term "and / or" in the present application is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In addition, the character " / " in the present application generally represents that the front and rear associated objects have an "or" relationship.

[0025] The upper plate and the lower plate respectively refer to the upper heat conduction panel and the lower heat conduction panel of the liquid cooling plate. The two plates are the main structure of the liquid cooling plate, and are usually made of oxygen-free copper with high thermal conductivity. In the process of heat conduction, the heat generated by the battery module is first conducted to the lower plate, and then conducted to the inner flow channel wall through the material in the plate, and finally taken away by the cooling liquid flowing through. The upper and lower plates jointly constitute the shell and the main heat conduction path of the liquid cooling plate. The fins are thin sheet structures with irregular geometric shapes filled between the upper and lower heat conduction panels. The main function of the fins is to greatly increase the heat exchange area inside the liquid cooling plate. By introducing fins in the fluid (cooling liquid) path, the contact area with the cooling liquid is increased, thereby significantly improving the heat conduction efficiency, so that the liquid cooling plate can take away heat more quickly and effectively.

[0026] In the process of welding the upper plate, the lower plate and the fins of the liquid cooling plate, the welding of oxygen-free copper workpieces is involved. The existing oxygen-free copper welding processes generally include high-energy beam welding processes (including laser welding and electron beam welding), arc welding processes (melting welding processes using an electric arc as a heat source, such as argon arc welding), and traditional brazing processes (welding processes using filler metal as a medium without melting the base material).

[0027] Specifically, the high-energy beam welding process relies on a high-energy beam such as a laser or an electron beam as a heat source. Due to its high energy density, it can theoretically quickly melt the base material to achieve bonding. However, oxygen-free copper has a high laser reflectivity (≥90%), and a large amount of energy is reflected during laser welding. Although the reflectivity of electron beam welding is lower, it requires a vacuum environment. At the same time, due to the high thermal conductivity of oxygen-free copper, energy is quickly conducted and lost, resulting in insufficient penetration when welding medium-thick plates (3mm≤plate thickness≤5mm). Multiple passes must be made to achieve effective bonding, which not only reduces welding efficiency but also increases the risk of joint defects (such as interlayer incomplete fusion and porosity). This process not only has limited energy utilization efficiency but also has poor adaptability to medium-thick plates, making it difficult to balance efficiency and quality.

[0028] The arc welding process generally uses argon arc welding. Before welding, anhydrous alcohol and CJ301 flux are mixed in a certain proportion and applied to the surface of the workpiece joint, and then argon arc welding is performed. During welding, the protective medium is configured with 25%-35% nitrogen, 25%-35% argon, and 35%-50% helium by mass ratio, and the welding environment temperature is maintained above 20℃. This welding method can significantly improve the welding quality of oxygen-free copper workpieces, but it also has some drawbacks.

[0029] Firstly, argon arc welding has high heat input, and oxygen-free copper has high thermal conductivity, which can easily cause heat to diffuse to the heat-affected zone, resulting in coarse grains in the heat-affected zone. Under vibration conditions (such as automotive parts), there is a risk of cracks due to residual stress.

[0030] Moreover, argon arc welding has high costs, with a high helium content of 35%-50% in the protective medium. Helium is a scarce resource and is expensive to obtain, which significantly increases the material cost of mass production.

[0031] The inventors found that helium is an inert gas that can only isolate oxygen and cannot remove the oxide film, resulting in joint oxidation and porosity defects, insufficient mechanical properties, and poor temperature resistance and stability.

[0032] In addition, the argon arc welding process has poor adaptability. The matching window of the thickness and volume of the oxygen-free copper workpiece plate with key parameters such as gas flow and welding current is narrow, making it difficult to accurately control. Some medium-thick plates are prone to incomplete fusion defects during welding.

[0033] In traditional brazing processes, copper is prone to oxidation at high temperatures. During brazing, the oxide film on the copper surface hinders solder wetting, leading to wider and more numerous weld seams. To avoid oxidation, conventional methods involve introducing complex protective gases (such as high-purity argon) during brazing, or using vacuum welding equipment to isolate oxygen. However, the preparation and proportioning of argon is costly, and using vacuum welding equipment requires a large initial investment and high energy consumption, resulting in high overall costs.

[0034] See Figure 1 The present invention provides a method for welding identical metals, comprising: S1. Select the solder type. Based on the melting point and welding area, choose copper-tin solder to form a eutectic through copper and tin.

[0035] In the selected copper-tin solder, tin accounts for 12% to 15% of the total mass, and the particle sizes of copper and tin need to be optimized to match the diffusion reaction between the base material and the copper-tin solder. Compared with expensive silver-based solder and ordinary copper-based solder with high melting points, copper-tin solder forms a low-melting-point eutectic (melting point of 227°C) through copper (Cu) and tin (Sn), which can effectively reduce the welding temperature and reduce the impact of high temperature on the thermal deformation of the base material during subsequent welding. It is also suitable for applications with larger welding areas.

[0036] S2. The oxygen-free copper workpiece to be welded is pretreated by sequentially undergoing unidirectional sanding, ultrasonic cleaning with anhydrous ethanol, and drying to form the base material.

[0037] In this embodiment, the oxygen-free copper workpiece includes an upper liquid cooling plate, a lower liquid cooling plate, and fins. Grinding is performed to remove oxide scale from the workpiece surface; the surface roughness Ra of the base material after grinding is ≤1.6μm. Anhydrous ethanol ultrasonic cleaning is performed for 5 minutes to remove oil and dust. Drying in an 80℃ oven for 10 minutes prevents moisture from causing porosity during welding, providing a clean and dry welding surface for subsequent welding.

[0038] It should be noted that the order of S1 and S2 can be interchanged, depending on the actual situation. When the welding area or overall volume of the workpiece is large, more time and economic costs are required for pre-processing, which can be prioritized until the solder is selected before welding.

[0039] S3. Apply copper-tin solder evenly to the welding surface of the base material. After application, allow it to air dry or bake to evaporate any residual alcohol and moisture, and avoid residual impurities affecting the subsequent welding quality.

[0040] In this embodiment, the copper-tin solder is in paste form, which is easy to apply.

[0041] S4. The base material is clamped using adjustable-pitch fixtures to achieve assembly.

[0042] The assembly process uses adjustable-spacing cast iron blocks, ceramic or silicon carbide clamps to clamp the base material. The clamping spacing is flexibly adjusted according to the size of the base material to ensure accurate positioning of the base material during welding and avoid welding deformation.

[0043] S5. Brazing of the base material: The assembled base material is placed in an ammonia decomposition furnace. 75% hydrogen and 25% nitrogen generated from ammonia decomposition are used as the reducing and protective atmospheres, respectively. Through coordinated control of temperature, pressure, and time, the tin in the copper-tin solder undergoes a diffusion reaction with the base material. Under the protection of the ammonia decomposition atmosphere, the tin in the copper-tin solder paste and the copper in the oxygen-free copper base material undergo atomic-level interdiffusion and chemical reaction through heating and heat preservation processes, ultimately forming a uniform and dense copper-tin intermetallic compound bonding layer. After melting, the copper-tin solder fills the gaps between the base materials through capillary action, forming a dense composite metal bonding layer. This ensures the uniformity of the bonding layer and avoids grain coarsening caused by high temperatures.

[0044] The ammonia decomposition furnace comprises four functional chambers: a preheating chamber, a heating chamber, a welding chamber, and a cooling chamber. The base material is placed on a high-speed conveyor belt within the furnace for welding. Inside the furnace, ammonia gas is heated and decomposed into nitrogen and hydrogen using a catalyst. Nitrogen, acting as a protective gas, prevents oxidation of the base material, protecting the oxygen-free copper surface from oxidation during welding. Hydrogen's reducing properties remove trace amounts of oxide film from the base material surface. The combination of nitrogen and hydrogen effectively integrates pre-weld rust removal with in-weld protection.

[0045] Specifically, although the oxygen content of oxygen-free copper in the base material (upper and lower plates of the liquid cooling plate, and fins) is extremely low, trace amounts of CuO oxide film may still exist on the surface (especially when exposed to air after pretreatment). Hydrogen has strong reducing properties and can undergo a reduction reaction with the oxide film during welding preheating and heating processes, with the chemical formula: CuO + H2 → Cu + H2O. Hydrogen decomposes the oxide film into elemental copper and water vapor. The water vapor is discharged from the furnace with the atmosphere, thereby completely removing oxidation interference from the base material surface. This directly solves the problem of oxide film hindering solder wetting in existing technologies, ensuring that copper-tin solder can be evenly spread on the base material surface, laying the foundation for subsequent metallurgical bonding. In addition, the water vapor produced by the reduction reaction of hydrogen and the unreacted hydrogen can create slight airflow disturbances in the furnace, which helps to expel trace gases generated during the welding process (such as water vapor evaporated due to residual moisture during the pretreatment of oxygen-free copper workpieces, and impurity gases volatilized from the solder paste), reduce weld porosity defects, and improve the tightness and airtightness of the welded joint.

[0046] During welding, oxygen-free copper base material and copper-tin solder readily react with oxygen in the air to generate oxidation products (such as CuO and SnO2), leading to oxidation discoloration, porosity, and slag inclusions in the weld. Hydrogen, as a reducing atmosphere, preferentially reacts with residual oxygen in the furnace or oxygen that has seeped into the air, while simultaneously forming a reducing protective layer on the surface of the base material and solder, isolating oxygen from contact and fundamentally preventing oxidation in the welding area, thus ensuring the purity of the joint.

[0047] Nitrogen produced by ammonia decomposition is an auxiliary protective component in this protective atmosphere. Its main function is to work synergistically with hydrogen to optimize the protective effect. Specifically, it includes inert isolation to enhance the protective effect, stabilizing the furnace atmosphere to regulate the process environment, reducing safety risks, and balancing atmosphere costs.

[0048] Specifically, nitrogen is a chemically stable inert gas that does not react chemically with the base material (oxygen-free copper), copper-tin solder, or reaction products. It constitutes 25% of the atmosphere, filling the furnace space, further diluting and isolating it from outside air, especially oxygen, reducing hydrogen consumption, and avoiding the risk of oxidation caused by excessively high local oxygen concentrations within the furnace, thus forming a double protection with hydrogen.

[0049] The presence of nitrogen helps maintain stable pressure within the furnace, preventing excessive pressure fluctuations under a pure hydrogen atmosphere. It also slows down hydrogen diffusion, allowing the reduction reaction to proceed more smoothly and preventing localized temperature fluctuations caused by excessively rapid hydrogen reaction, thus avoiding coarse grains in the base material. Furthermore, nitrogen's low specific heat capacity means it does not significantly affect the temperature field distribution within the furnace, ensuring precise control of welding temperature and time process parameters.

[0050] Pure hydrogen poses a flammable and explosive risk (explosion limits 4%~75%). Nitrogen, as an inert diluent, can control the hydrogen concentration within a safe range. While 75% hydrogen does not exceed the explosion limit, the sealed design of the ammonia decomposition furnace, combined with the inert buffering effect of nitrogen, can further reduce the risk of combustion and explosion. Furthermore, nitrogen is widely available and inexpensive, significantly reducing the overall cost of the protective atmosphere compared to the scarce helium used in existing technologies.

[0051] In summary, the synergistic effect of hydrogen and nitrogen produces a protective effect superior to that of a simple additive approach. Hydrogen's reducing properties address the core issues of oxide film removal and oxidation prevention, while nitrogen's inertness addresses the auxiliary issues of atmosphere stability, safety, and cost. This synergistic approach avoids the high safety risks and cost waste associated with a pure hydrogen atmosphere, while also compensating for the lack of reducing properties and inability to remove oxide films in a pure nitrogen atmosphere. Ultimately, this achieves welding quality characterized by no oxidation discoloration, no porosity, and uniform solder spread, while also meeting the cost control requirements of large-scale production.

[0052] In this embodiment, during the brazing process of the base material, the temperature, pressure and time are coordinated and controlled, and the copper-tin solder adopts a reaction path of low-temperature melting-medium-temperature diffusion-pressure densification.

[0053] In copper-tin solder, tin undergoes a diffusion reaction with the base material. This diffusion reaction is essentially a synergistic effect of atomic thermal motion and chemical reaction. Atomic diffusion is a cross-boundary movement after gaining energy. During soldering, the ammonia decomposition furnace heats the material, increasing the temperature. Sn atoms in the solder paste and Cu atoms on the surface of the oxygen-free copper base material gain sufficient energy to overcome the binding forces between their atoms and begin to diffuse into each other. Sn atoms penetrate from the molten solder paste into the base material, while Cu atoms migrate from the base material into the liquid solder paste, forming an atomic mixing zone at the interface between the solder and the base material. The chemical reaction forms a stable bonding bridge. The diffused Sn and Cu atoms do not simply mix but react chemically in a specific ratio to generate Cu-Sn intermetallic compounds (including but not limited to Cu3Sn and Cu6Sn4). These compounds are structurally stable, high-strength, and thermally conductive intermediate phases that act like a bridge, firmly bonding the two pieces of oxygen-free copper base material together to form a metallurgical bond. This metallurgical bond differs from physical bonding, and its bonding strength is close to that of the base material itself.

[0054] In essence, diffusion reactions are a synergistic adaptation of processes and materials. First, precise matching of solder composition is crucial, limiting the Sn mass percentage in the solder paste to 12-15% and optimizing the particle size distribution of Cu and Sn. This ratio precisely matches the Cu content in the base material, ensuring an appropriate Sn-Cu atomic ratio during diffusion. This prevents an excess or deficiency of any element, which could lead to uneven bonding layer composition, such as a pure Sn layer or an unreacted Cu layer, affecting solder strength. Second, coordinated temperature and time control is essential, employing a reaction path of low-temperature melting – medium-temperature diffusion – pressurized densification. The low temperature melts the solder paste, providing a liquid channel for atomic diffusion; the medium temperature provides sufficient energy for atomic diffusion; and the holding time ensures sufficient atomic diffusion depth and a complete reaction, while avoiding high temperatures that could cause coarse grains in the base material. Then, a reducing atmosphere is used to clear obstacles. The 75% H2 and 25% N2 atmosphere generated by ammonia decomposition removes the trace oxide film on the surface of the base material (the oxide film will hinder atomic diffusion) and isolates oxygen to prevent the oxidation of Sn and Cu atoms (oxidation will reduce the atomic activity and prevent effective diffusion reaction), thus providing a clean and undisturbed environment for the diffusion reaction.

[0055] The diffusion reaction directly determines the weld quality. Without a diffusion reaction, the solder can only fill the gaps between the base materials, forming a physical bond, making the joint prone to detachment and leakage. However, the copper-tin intermetallic compound bonding layer formed by the diffusion reaction makes the solder and the base material a unified whole, ensuring that the weld joint has good mechanical properties and airtightness. To ensure uniform weld quality, the diffusion reaction occurs synchronously across the entire weld surface through process parameter control, avoiding localized lack of diffusion (leading to incomplete fusion) or uneven diffusion (leading to inconsistent bonding layer thickness), ultimately achieving an effect with no obvious weld seam.

[0056] The diffusion reaction does not require auxiliary means such as ultrasound or mechanical vibration. It can occur stably simply by coordinating the design of solder composition, temperature and atmosphere, which reduces the operating threshold and equipment investment and meets the needs of large-scale production.

[0057] Existing argon arc welding technology mainly relies on the melting and fusion of the base material, which results in high heat input and easily leads to coarse grains. This invention achieves metallurgical bonding at a lower temperature through diffusion reaction and the formation of intermetallic compounds. This avoids high-temperature damage to the base material and ensures joint quality, solving the industry problem of balancing high quality and low cost.

[0058] In this embodiment, the low-temperature melting temperature is 227℃~850℃, the medium-temperature diffusion temperature is 600℃~900℃, and the pressure for pressurization is 0.1MPa~0.5MPa.

[0059] S6. After brazing is completed, the welded area needs to be cut open and the weld quality needs to be inspected. Before cutting open the welded area, a helium mass spectrometer leak detector can be used to test the sealing performance of the welded parts.

[0060] Welding quality is inspected through visual inspection and CCD camera observation to confirm that the weld is free of oxidation and discoloration and solder accumulation. The images captured by the CCD camera show that the welded area between the oxygen-free copper is full and there are no obvious weld seams.

[0061] See Figure 2 There are no obvious weld seams on the welding surfaces of the upper and lower plates of the liquid cooling plate.

[0062] See Figure 3 There are no obvious welds on the welding surfaces of the upper plate and fins of the liquid cooling plate, and on the welding surfaces of the lower plate and fins of the liquid cooling plate.

[0063] It is understood that in some embodiments, other alternative methods may be used, as follows: Solder composition substitution: Adding phosphorus and zinc to copper-tin solder reduces raw material costs and simplifies pretreatment, but increases the soldering temperature by 100°C, making it unsuitable for heat-sensitive components. Furthermore, phosphorus has slight toxicity, requiring enhanced ventilation and protection in the workshop. Alternatively, silver and indium can be added. Silver forms a low-melting-point silver-copper eutectic (melting point <780°C), indium improves solder paste wettability, and the ammonia decomposition atmosphere prevents silver oxidation, ultimately forming a uniform bonding layer containing a silver-reinforced phase. This effectively improves joint strength and solderability in the soldering area, but at a higher cost.

[0064] Solder form alternative: Copper-tin solder paste is pre-formed into solder sheets with dimensions matching the welding surface of the base material. Pre-alloyed solder sheets reduce coating process errors and ensure uniform solder usage. Customized solder sheet stamping dies are required. This method offers high production efficiency, good consistency, and less material waste.

[0065] Welding alternatives: While vacuum brazing, as used in this application, can completely isolate oxygen, prevent oxidation of the base material surface, eliminate the need for flux, and ensure high surface cleanliness, its cost is relatively high. An alternative solution uses an induction heating coil instead of resistance heating, coupled with an ammonia decomposition atmosphere sealing hood (partially sealed, covering only the welding area). Although this provides higher heating efficiency, the induction coil needs to be customized according to the shape of the base material, resulting in poor versatility and making it unsuitable for welding complex structural components.

[0066] The welding method of this invention produces excellent welding quality, free from defects such as oxidation and porosity, and has good airtightness. It does not require high-end equipment or complex auxiliary means, and the cost is controllable. It is suitable for oxygen-free copper homogeneous metal plates with a thickness of 1mm to 5mm and irregular welding areas, and is especially suitable for the manufacturing field of new energy vehicle battery electronic control cooling systems.

[0067] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for welding identical metals, characterized in that, include: Solder selection is based on melting point and welding area, copper-tin solder is selected, and copper and tin form a eutectic. The oxygen-free copper workpiece to be welded is pretreated by sequentially undergoing unidirectional sanding, ultrasonic cleaning with anhydrous ethanol, and drying to form the base material. Apply copper-tin solder evenly to the welding surface of the base material, and allow it to air dry or bake dry after application. The base material is clamped using adjustable-pitch fixtures to achieve assembly; The base material is brazed by placing the assembled base material in an ammonia decomposition furnace. Hydrogen and nitrogen produced by ammonia decomposition are used as reducing and protective atmospheres, respectively. Through the coordinated control of temperature, pressure and time, the tin in the copper-tin solder diffuses with the base material to form a copper-tin intermetallic compound bonding layer. After the copper-tin solder melts, it fills the gaps between the base materials through capillary action to form a dense composite metal bonding layer.

2. The same metal welding method as described in claim 1, characterized in that, Oxygen-free copper workpieces include the upper plate of the liquid cooling plate, the lower plate of the liquid cooling plate, and fins.

3. The method for welding the same metal as described in claim 1, characterized in that, The surface roughness Ra of the base material for welding is ≤1.6μm.

4. The same metal welding method as described in claim 1, characterized in that, The ultrasonic cleaning time with anhydrous ethanol is 5 minutes, and the drying time in the oven is 10 minutes.

5. The method for welding the same metal as described in claim 1, characterized in that, The ammonia decomposition furnace includes four functional chambers: a preheating chamber, a heating chamber, a welding chamber, and a cooling chamber. The base material is placed on the high-speed conveyor belt of the ammonia decomposition furnace for conveying and welding.

6. The method for welding the same metal as described in claim 1, characterized in that, During the brazing process of the base material, the temperature, pressure and time are coordinated and controlled. The copper-tin solder adopts a reaction path of low temperature melting - medium temperature diffusion - pressure densification. The low temperature melting temperature is 227℃~850℃, the medium temperature diffusion temperature is 600℃~900℃, and the pressure densification pressure is 0.1MPa~0.5MPa.

7. The method for welding the same metal as described in claim 1, characterized in that, In copper-tin solder, tin accounts for 12% to 15% of the mass, and the particle sizes of copper and tin need to be optimized to match the diffusion reaction between the base material and the copper-tin solder.

8. The method for welding identical metals as described in claim 1, characterized in that, Phosphorus and zinc, or silver and indium, can be added to copper-tin solder to adjust its soldering properties.

9. The method for welding the same metal as described in claim 1, characterized in that, After brazing is completed, the welded area needs to be cut open and the weld quality needs to be inspected.

10. The method for welding the same metal as described in claim 9, characterized in that, Welding quality was inspected by visual inspection and CCD camera observation to confirm that the weld was free of oxidation and discoloration, had no solder accumulation, and that there were no obvious weld seams in the welded area.

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