Aluminum-based composite brazing material, preparation method thereof and heat exchanger component

Abstract

The invention discloses an aluminum-based composite brazing material, a preparation method of the aluminum-based composite brazing material and a heat exchanger component. The preparation method of the aluminum-based composite brazing material comprises the steps that brazing flux powder and inorganic filler are mixed through a dry method; mixing a binder mother solution, a polymer binder emulsion and the mixed dry material; coating the surface of the brazing filler metal layer aluminum alloy base material with the polymer reinforced slurry, and performing curing treatment; the brazing filler metal layer aluminum alloy base material with the brazing flux composite layer formed on the surface and the structural core layer aluminum alloy base material with the high solidus temperature are oppositely placed, so that the brazing flux composite layer is located on the side, away from the structural core layer aluminum alloy base material, of the brazing filler metal layer aluminum alloy base material, and cast-rolling compounding is conducted; and the brazing filler metal layer aluminum alloy base material wraps the structural core layer aluminum alloy base material. In the preparation method, after the polymer reinforced slurry is coated and cured, a tough, compact and firmly attached brazing flux composite layer can be formed on the surface of the brazing filler metal layer, and the interface bonding strength of the brazing flux composite layer and a matrix is superior to that of loose brazing flux particle accumulation in a traditional process.

Description

Technical Field

[0001] This application relates to the field of metal matrix composite technology, specifically to an aluminum-based composite brazing material and its preparation method, and a heat exchanger component. Background Technology

[0002] Composite brazing aluminum alloys are core materials for evaporators, condensers, and industrial heat exchangers in refrigeration equipment. Their brazing performance directly determines the sealing integrity and long-term operational reliability of the heat exchange system. In key areas such as cold chain logistics, thermal management of new energy vehicles, and industrial waste heat recovery, the quality of this material affects equipment energy efficiency and service life. The key technology for this type of material lies in the pre-preparation of a stable and uniform flux layer on the substrate surface. During the brazing process, this layer needs to effectively dissolve the oxide film on the surface of the base material using the active ingredient potassium fluoroaluminate. Simultaneously, precise control of the flux particle size distribution promotes the wetting and spreading of the brazing filler metal, and avoids defects such as incomplete welds or missed welds caused by uneven flux distribution or poor bonding. In complex flow channel structures of thin-walled irregular parts, the stability of the flux layer becomes a core factor restricting the product qualification rate.

[0003] Currently, the main industrial process for preparing flux-embedded layers is powder metallurgy combined with hot isostatic pressing (HIP). This involves mixing flux powder with silicon-aluminum alloy powder in a specific ratio, filling the mixture into a 4-series aluminum alloy shell to form a sheath, and then pressing it under high temperature and pressure in a HIP apparatus after vacuum degassing to form the internal embedded structure. While this traditional process can achieve high-concentration flux embedding, it has a lengthy process chain (including multiple steps such as powder mixing, sheath welding, and vacuum degassing), resulting in a long production cycle and high investment in HIP equipment, leading to a significant increase in energy consumption per unit product. Furthermore, the product thickness is limited by the sheath size, and when subsequently cold-rolled to thin-walled specifications, delamination is prone to occur due to differences in the bonding strength between the flux and the substrate interface. In addition, during the shell welding and encapsulation process, microcracks are easily generated in the heat-affected zone of laser welding, and the high-concentration flux design leads to material cost waste in conventional applications. At the same time, residual flux can easily cause intergranular corrosion.

[0004] As the refrigeration and heat exchange industry moves towards higher integration and lower leakage rates, stringent requirements are being placed on flux pre-embedded layers for three-dimensional precision control, process efficiency, and optimization of life-cycle costs. Traditional powder metallurgy processes, due to large equipment investments and low production flexibility, struggle to meet the demands of industries such as home appliances and automobiles for multi-variety, small-batch customized production. These technological bottlenecks urgently require innovative breakthroughs in material systems and preparation processes to achieve precise control and efficient production of flux pre-embedded layers. Summary of the Invention

[0005] In view of this, this application provides an aluminum-based composite brazing material and its preparation method, as well as a heat exchanger component, to solve the above-mentioned technical problems.

[0006] To achieve the above objectives, in a first aspect, this application provides a method for preparing an aluminum-based composite brazing material. The method includes: dry mixing flux powder with inorganic filler to prepare a mixed dry material; mixing a binder mother liquor, a polymer binder emulsion, and the mixed dry material to prepare a polymer-reinforced slurry; coating the polymer-reinforced slurry onto the surface of the aluminum alloy substrate of the brazing filler layer, followed by curing treatment to form a flux composite layer on the surface; placing the aluminum alloy substrate of the brazing filler layer with the flux composite layer on its surface opposite to the aluminum alloy substrate of the structural core layer, such that the flux composite layer is located on the side of the aluminum alloy substrate of the brazing filler layer away from the aluminum alloy substrate of the structural core layer, and performing casting and rolling composite bonding, so that the aluminum alloy substrate of the brazing filler layer covers the aluminum alloy substrate of the structural core layer, wherein the solidus temperature of the aluminum alloy of the brazing filler layer is lower than the solidus temperature of the aluminum alloy of the structural core layer, thereby preparing the aluminum-based composite brazing material.

[0007] Based on the first aspect, in some embodiments, the viscosity of the polymer-reinforced slurry is from 100 mPa·s to 250 mPa·s.

[0008] Based on the first aspect, in some embodiments, the mass ratio of flux powder to inorganic filler is (60~80):(20~40).

[0009] Based on the first aspect, in some embodiments, the average particle size of the flux powder is 20 μm to 50 μm.

[0010] Based on the first aspect, in some embodiments, the average particle size of the inorganic filler is 20 μm to 50 μm.

[0011] Based on the first aspect, in some embodiments, the flux powder includes fluoroaluminate.

[0012] Based on the first aspect, in some embodiments, the inorganic filler includes at least one of aluminum silicate and aluminum silicate.

[0013] Based on the first aspect, in some embodiments, the polymer binder emulsion includes polytetrafluoroethylene.

[0014] Based on the first aspect, in some embodiments, the binder masterbatch includes at least one of isopropanol, cellulose-based binders, and polyether-based binders.

[0015] Based on the first aspect, in some embodiments, the coating method includes roll coating.

[0016] Based on the first aspect, in some embodiments, the curing temperature is 140 °C to 180 °C, and the curing time is 1.5 h to 3 h.

[0017] Based on the first aspect, in some embodiments, the casting and rolling temperature is 680 °C to 720 °C.

[0018] Secondly, this application provides an aluminum-based composite brazing material, prepared by the above-described preparation method. The aluminum-based composite brazing material includes a structural core layer aluminum alloy substrate and a solder layer aluminum alloy substrate located outside the structural core layer, wherein flux powder is embedded in the surface layer of the solder layer aluminum alloy substrate away from the structural core layer.

[0019] Based on the second aspect, in some embodiments, the aluminum alloy substrate of the brazing filler layer includes an aluminum-silicon alloy, and the aluminum alloy substrate of the structural core layer includes an aluminum-manganese alloy.

[0020] Based on the second aspect, in some embodiments, the thickness of the flux composite layer is 0.08 mm to 0.15 mm.

[0021] Thirdly, this application provides a heat exchanger component comprising the aforementioned aluminum-based composite brazing material.

[0022] Based on the third aspect, in some embodiments, the heat exchanger components include at least one of an evaporator tube, a condenser fin, and a battery cooling plate.

[0023] In the preparation method of the aluminum-based composite brazing material of this application, a dry mixture of flux powder and inorganic filler is combined with a binder masterbatch and a polymer binder emulsion. The polymer binder emulsion enhances the adhesion between the flux layer and the aluminum substrate. Simultaneously, by combining the rheological properties and viscosity coefficient provided by the binder masterbatch, a polymer-reinforced slurry with excellent stability and high adhesion performance is prepared. After coating and curing, this slurry forms a strong, dense, and firmly adhered flux composite layer on the surface of the flux layer. Its interfacial bonding strength with the substrate is superior to that of loose flux particle accumulation in traditional processes. This fundamentally solves the problem of flux layer delamination and uneven distribution during subsequent processing or thermal cycling, improving the integrity and consistency of the flux pre-embedded coating. Therefore, this application achieves a simplified operation by using a dry mixing method to combine flux powder and inorganic filler, replacing the lengthy and complex processes of powder metallurgy-hot isostatic pressing, such as powder mixing, encapsulation welding, vacuum degassing, and high-pressure pressing. This shortens the production cycle, reduces equipment investment and energy consumption, and demonstrates excellent process economy. Furthermore, by employing efficient casting and rolling, the solder layer coated with the flux composite layer, placed according to a predetermined positional relationship, is metallurgically composited with a structural core layer having a higher solidus temperature. This achieves a high-strength bond of multi-layer materials in one step, which is beneficial for improving production efficiency and adapting to the requirements of large-scale continuous production lines. Moreover, the predetermined difference in melting points between the solder layer and the core layer ensures that the composite material can ensure the solder layer melts and connects during brazing while the core layer maintains structural integrity. The aluminum-based composite brazing material prepared by the method of this application exhibits excellent performance in brazing, including high joint strength, good sealing, and low flux residue. This provides key material support for the mass production of long-life, high-reliability heat exchange components in fields such as refrigeration and new energy vehicles. Attached Figure Description

[0024] Figure 1 Images showing the surface morphology and surface element distribution of the composite brazed aluminum alloy substrate provided in Embodiment 1 of this application.

[0025] Figure 2 This is a microscopic image of the aluminum-based composite brazing material provided in Embodiment 1 of this application before brazing.

[0026] Figure 3 This is a microscopic image of the aluminum-based composite brazing material provided in Embodiment 1 of this application after brazing. Detailed Implementation

[0027] To facilitate understanding of the technical solutions of this application, a more comprehensive description of the technical solutions of this application will be provided below with reference to the accompanying drawings, which illustrate preferred embodiments of the technical solutions of this application. However, the technical solutions of this application can be implemented in many different forms and are not limited to the embodiments described herein. Rather, these embodiments are provided to enable a more thorough and comprehensive understanding of the disclosure of the technical solutions of this application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] To address the core shortcomings of traditional powder metallurgy-hot isostatic pressing processes, such as lengthy procedures, high costs, uneven flux distribution, and insufficient interfacial bonding strength, this application proposes a novel pre-embedded flux aluminum alloy material and its preparation method. This simplifies the process flow and reduces overall costs, allows for control over flux layer thickness and distribution, achieves high-strength interfacial bonding with the core layer, and adapts to large-scale continuous production to ensure product consistency. Ultimately, this provides a high-performance, highly reliable composite brazing material suitable for mass production in the refrigeration, heat exchange, and new energy fields, promoting its widespread application.

[0030] Based on this, one embodiment of this application provides a method for preparing an aluminum-based composite brazing material, the method comprising:

[0031] Step 1: Dry mix the flux powder with the inorganic filler to prepare a mixed dry material.

[0032] The above steps involve dry mixing of flux powder and inorganic filler, followed by compounding the dry mixture of flux powder and inorganic filler with binder mother liquor and polymer binder emulsion to prepare a polymer-reinforced slurry with excellent stability and high bonding performance. This process simplifies the traditional powder metallurgy-hot isostatic pressing process by using dry mixing of flux powder and inorganic filler, replacing the lengthy and complex processes of powder mixing, cladding welding, vacuum degassing, and high-pressure pressing. This shortens the production cycle, reduces equipment investment and energy consumption, and demonstrates excellent process economy.

[0033] In some embodiments, the mass ratio of flux powder to inorganic filler is (60~80):(20~40). For example, the mass fraction of flux powder can be 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, or any value within the range of any two of the above values, and the mass fraction of inorganic filler can be 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, or any value within the range of any two of the above values. By optimizing the balance between the active component of the flux and the inorganic carrier, controlling the mass ratio of flux powder to inorganic filler in the mixed dry material within the above range helps to further improve the unity of functionality and processability. Within this range, sufficient flux powder ensures that the coating has sufficient film removal ability and brazing activity, while the appropriate introduction of inorganic filler can not only effectively adjust the rheological properties of the slurry and prevent sedimentation, but also serve as a skeleton support after drying and curing, reducing coating cracking and maintaining structural stability at high temperatures. This ratio reduces the risk of cost waste and residual corrosion when there is too much flux, and also reduces the risk of insufficient activity when there is too much filler.

[0034] In some embodiments, the average particle size of the flux powder is between 20 μm and 50 μm. For example, the average particle size of the flux powder can be 20 μm, 23 μm, 26 μm, 29 μm, 32 μm, 35 μm, 38 μm, 41 μm, 44 μm, 47 μm, 50 μm, or any value within the range of any two of the above values. Controlling the average particle size of the flux powder within the above range helps to ensure uniform mixing in the polymer-reinforced slurry, promotes the formation of a flux composite layer with high bonding strength, and also helps to improve the uniformity of the distribution of the active flux components in the subsequently formed flux composite layer.

[0035] In some embodiments, the average particle size of the inorganic filler is from 20 μm to 50 μm. For example, the average particle size of the inorganic filler can be 20 μm, 23 μm, 26 μm, 29 μm, 32 μm, 35 μm, 38 μm, 41 μm, 44 μm, 47 μm, 50 μm, or any value within the range of any two of the above values. Controlling the average particle size of the inorganic filler within the above range helps to ensure uniform mixing in the polymer-reinforced slurry, promotes the formation of a flux composite layer with high bonding strength, and also helps to improve the uniformity of the distribution of the flux active ingredients in the subsequently formed flux composite layer.

[0036] In some embodiments, the flux powder comprises fluoroaluminate. For example, fluoroaluminate includes, but is not limited to, potassium fluoroaluminate. Understandably, potassium fluoroaluminate, as a flux, has a good cleaning effect on oxide films.

[0037] In some embodiments, the inorganic filler includes at least one of aluminum silicate and aluminum silicate. The aforementioned inorganic filler helps to regulate rheology, prevent slurry sedimentation, promote uniform subsequent coating, and reduce shrinkage stress in the flux composite layer during subsequent drying and sintering, thereby reducing the risk of cracking in the flux composite layer. Furthermore, it maintains a stable structure at brazing temperatures, providing a high-temperature framework for the flux and aiding in the regulation of flux release.

[0038] Step 2: Mix the binder masterbatch, polymer binder emulsion and dry mixed materials to prepare polymer-reinforced slurry.

[0039] The above steps involve combining a dry mixture of flux powder and inorganic filler with a binder masterbatch and a polymer binder emulsion. The polymer binder emulsion enhances the adhesion between the flux layer and the aluminum substrate. Simultaneously, by combining the rheological properties and viscosity coefficient provided by the binder masterbatch, a polymer-reinforced slurry with excellent stability and high adhesion performance is prepared. After coating and curing, this slurry forms a strong, dense, and firmly adhered flux composite layer on the surface of the flux layer. Its interfacial bonding strength with the substrate is superior to that of loose flux particle accumulation in traditional processes. This fundamentally solves the problem of flux layer delamination and uneven distribution during subsequent processing or thermal cycling, and improves the integrity and consistency of the flux pre-embedded coating.

[0040] In some embodiments, the viscosity of the polymer-reinforced slurry is between 100 mPa·s and 250 mPa·s. For example, the viscosity of the polymer-reinforced slurry can be 100 mPa·s, 120 mPa·s, 140 mPa·s, 160 mPa·s, 180 mPa·s, 200 mPa·s, 210 mPa·s, 230 mPa·s, 250 mPa·s, or any value within the range of any two of the above values. Controlling the viscosity of the polymer-reinforced slurry within the above range helps to further improve the coating quality and the adhesion of the coating to the metal substrate surface, reduces the risk of slurry flow, uneven coating, or substrate exposure when the viscosity is low, and reduces the risk of coating difficulties, excessive coating thickness, and defects when the viscosity is high. With the above viscosity range, the polymer-reinforced slurry has good leveling and shaping ability, and can form a continuous, uniform, and thickness-controllable wet film by rolling, scraping, etc., which is beneficial for obtaining a dense, defect-free solid flux composite layer.

[0041] In some embodiments, the polymer binder emulsion includes polytetrafluoroethylene (PTFE). PTFE, as the core material of the polymer binder emulsion, effectively ensures excellent adhesion between the flux layer and the aluminum substrate.

[0042] In some embodiments, the binder stock comprises at least one of isopropanol, a cellulose binder, and a polyether binder. For example, cellulose binders include, but are not limited to, carboxymethyl cellulose, and polyether binders include, but are not limited to, polyethylene oxide. In the binder stock, isopropanol can act as an auxiliary dispersant, helping to reduce the viscosity of the slurry; cellulose binders can act as thickeners, helping to adjust the stability of the slurry; and polyether binders can assist in thickening and binding, helping to improve the ductility of the slurry. Understandably, the above-mentioned binder stock may also include water as a base solvent and used to adjust the initial moisture content of the slurry.

[0043] Step 3: Apply polymer-reinforced slurry to the surface of the aluminum alloy substrate of the solder layer, and cure it to form a flux composite layer on the surface.

[0044] The above steps, by coating the polymer-reinforced slurry onto the surface of the solder layer substrate and drying and curing it to form a continuous flux composite layer, realize the transformation of the flux from discrete particles to a dense and firmly adhered layer. This is beneficial for promoting the uniform distribution of the flux at the nano / micro level in the two-dimensional plane, and also helps the flux composite layer to form a strong physicochemical bond with the substrate. This helps to improve the thickness uniformity and adhesion of the flux composite layer, and also helps to improve the bonding force between the flux and the metal interface in the flux composite layer, reducing the risk of peeling.

[0045] In some embodiments, the coating method includes roll coating. Roll coating ensures stable production line operation speed, helps meet the demands of modern industrial continuous and automated production, and facilitates the organic unity of high quality and high efficiency.

[0046] In some embodiments, the curing temperature is between 140 °C and 180 °C, and the curing time is between 1.5 h and 3 h. For example, the curing temperature can be 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, or any value within the range of any two of the above values. The curing time can be 1.5 h, 1.8 h, 2 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, 3 h, or any value within the range of any two of the above values. Controlling the curing temperature and time within the above range helps to better remove solvent and regulate the arrangement of flux particles, which is beneficial for promoting the formation of a continuous, dense, and structurally stable flux composite layer between particles through interfacial forces.

[0047] Step 4: Place the aluminum alloy substrate with the flux composite layer on its surface opposite the aluminum alloy substrate with the structural core layer, so that the flux composite layer is located on the side of the aluminum alloy substrate away from the structural core layer, and perform casting and rolling composite to make the aluminum alloy substrate with the flux layer cover the aluminum alloy substrate with the structural core layer. The solidus temperature of the aluminum alloy with the flux layer is lower than that of the aluminum alloy with the structural core layer, thus preparing the aluminum-based composite brazing material.

[0048] The above steps employ efficient casting and rolling to metallurgically combine the solder layer coated with the flux composite layer, which is placed according to a preset positional relationship, with the structural core layer, which has a higher solidus temperature. This achieves a high-strength bond of multi-layer materials in one step, which is beneficial to improving production efficiency and is suitable for the requirements of large-scale continuous production lines. Moreover, the preset difference in melting points between the solder layer and the core layer ensures that the composite material can ensure that the solder layer melts and connects during the brazing process while the core layer maintains its structural integrity.

[0049] In some embodiments, the casting temperature is between 680 °C and 720 °C. For example, the casting temperature can be 680 °C, 685 °C, 690 °C, 695 °C, 700 °C, 705 °C, 710 °C, 715 °C, 720 °C, or any value within the range of any two of the above values. Controlling the casting temperature within the above range helps to further improve the bonding strength of the formed composite interface and regulate the reasonable pre-embedded structure of the flux within the material.

[0050] In some embodiments, after casting-rolling composite to obtain a composite plate, the above preparation method further includes: hot rolling or cold rolling the composite plate. Hot rolling or cold rolling helps to control the thickness of the composite plate.

[0051] In some embodiments, after casting-rolling composite to obtain a composite plate, the above preparation method further includes annealing the composite plate. Annealing helps to eliminate processing stress and stabilize the microstructure.

[0052] An embodiment of this application also provides an aluminum-based composite brazing material, prepared by the above-described preparation method. The aluminum-based composite brazing material includes a structural core layer aluminum alloy substrate and a solder layer aluminum alloy substrate located outside the structural core layer, wherein flux powder is embedded in the surface layer of the solder layer aluminum alloy substrate away from the structural core layer.

[0053] The aluminum-based composite brazing material prepared by the method of this application exhibits excellent properties such as high joint strength, good sealing performance, and low flux residue during the brazing process, providing key material support for the mass production of long-life and high-reliability heat exchange components in fields such as refrigeration and new energy vehicles.

[0054] In some embodiments, the aluminum alloy substrate of the solder layer includes an aluminum-silicon alloy, and the aluminum alloy substrate of the structural core layer includes an aluminum-manganese alloy. When the above-mentioned aluminum alloy substrates are selected for the solder layer and the structural core layer, the flux-embedded aluminum matrix composite material of this application can use its own solder layer as a source of solder and flux to braze the entire flux-embedded aluminum matrix composite material to the target part.

[0055] In some embodiments, the thickness of the flux composite layer is from 0.08 mm to 0.15 mm. For example, the thickness of the flux composite layer can be 0.08 mm, 0.09 mm, 0.1 mm, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, 0.15 mm, or any value within the range of any two of the above values. Controlling the thickness of the flux composite layer within the above range helps to minimize the amount of flux used and its residue while ensuring sufficient brazing capability, achieving a balance between the reliability, durability, and economy of the brazed joint; it reduces the risk of insufficient flux dosage leading to insufficient film removal or incomplete filler metal filling when the thickness is small, affecting the joint sealing strength; and it reduces the risk of excessive flux when the thickness is large, increasing costs, easily causing corrosion due to increased residue, and potentially affecting filler metal flow and joint formation.

[0056] One embodiment of this application also provides a heat exchanger component, including the aforementioned aluminum-based composite brazing material.

[0057] The aluminum-based composite brazing material prepared in this application is applied to heat exchanger components. Components manufactured based on this material can achieve high-quality self-brazing connections in a brazing furnace without the need for additional flux after assembly. This simplifies the component manufacturing process, improves production efficiency, and enhances the uniformity and reliability of brazing quality. The resulting heat exchangers feature high joint strength, low leakage rate, and long corrosion resistance, meeting the requirements of refrigeration, automotive, and new energy fields for efficient and reliable thermal management components.

[0058] In some embodiments, the heat exchanger components include at least one of an evaporator tube, a condenser fin, and a battery cooling plate.

[0059] The present application will be described below through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0060] Example 1:

[0061] An aluminum-based composite brazing material, the preparation method of which includes:

[0062] Step 1: Dry material mixing. According to the mass percentage, add 71.4% potassium fluoroaluminate (particle size 20 μm to 50 μm) and 28.6% aluminum silicate (particle size 20 μm to 50 μm) to a stainless steel mixer and stir at 200 r / min for 18 min until the materials are evenly dispersed and there is no agglomeration.

[0063] Step 2: Slurry Preparation. Binder stock solution: By mass percentage, it consists of 50% pure water (approximately 2 L), 25% carboxymethyl cellulose (CMC), and 25% polyethylene oxide (PEO). After stirring at 52 °C for 12 min, 5 L of isopropanol is added. Composite Process: The binder stock solution is mixed with 5 L of polytetrafluoroethylene (PTFE) emulsion, and the above-mentioned dry mixture is added. The mixture is stirred at 130 r / min for 10 min to obtain a homogeneous slurry with a viscosity of 180 mPa·s.

[0064] Step 3: Roller Coating. A 4045 aluminum alloy plate (0.12 mm thick) was selected as the substrate for the flux layer. It was wiped with alcohol and then air-dried. The roller press parameters were set as follows: roller gap 0.12 mm, travel speed 3 m / min, and flux layer thickness 0.1 mm after coating.

[0065] Step 4: Drying and curing. The coating is dried at 160 ℃ for 2 hours using a medium-speed blower to form a flux composite layer on the coated surface of the substrate.

[0066] Step 5: Casting and Rolling Composite and Post-treatment. The 3003 aluminum-manganese alloy core substrate (1.5 mm thick) and the brazing filler layer substrate are composited in a double-strip casting and rolling mill, with the casting and rolling temperature controlled between 690 ℃ and 710 ℃. The composite sheet undergoes hot rolling, cold rolling, and annealing to eliminate processing stress and stabilize the microstructure.

[0067] Example 2:

[0068] An aluminum-based composite brazing material, the preparation method of which includes:

[0069] Step 1: Dry material mixing. According to the mass percentage, add 71.4% potassium fluoroaluminate (particle size 20 μm to 50 μm) and 28.6% aluminum silicate (particle size 20 μm to 50 μm) to a stainless steel mixer and stir at 180 r / min for 20 min until the materials are evenly dispersed and there is no agglomeration.

[0070] Step 2: Slurry Preparation. Binder Masterbatch: By mass percentage, it consists of 47.4% deionized water, 26.3% carboxymethyl cellulose (CMC), and 26.3% polyethylene oxide (PEO). After stirring at 55 °C for 15 min, 4.5 L of isopropanol is added (to reduce the total solvent volume). Composite Process: The binder masterbatch is mixed with 5 L of polytetrafluoroethylene (PTFE) emulsion, and the above-mentioned dry mixture is added. The mixture is stirred at 120 r / min for 15 min to obtain a homogeneous slurry with a viscosity of 220 mPa·s.

[0071] Step 3: Roller Coating. 4343 aluminum alloy sheet (0.15 mm thick) was selected as the substrate for the flux layer. It was wiped with alcohol and then air-dried. The roller press parameters were set as follows: roller gap 0.15 mm, speed 2.5 m / min (adjusted for high-viscosity slurry), resulting in a flux layer thickness of 0.13 mm.

[0072] Step 4: Drying and curing. The coating is kept at 170 ℃ for 1.5 h (the drying cycle is shortened by increasing the temperature to adapt to the thermal conductivity of the thick coating), and a medium-speed blower is used to dry the coating, forming a flux composite layer on the coated surface of the substrate.

[0073] Step 5: Casting and Rolling Composite and Post-treatment. The 3003 aluminum-manganese alloy core substrate (1.5 mm thick) and the brazing filler layer substrate are composited in a double-strip casting and rolling mill, with the casting and rolling temperature controlled between 690 ℃ and 710 ℃. The composite sheet undergoes hot rolling, cold rolling, and annealing to eliminate processing stress and stabilize the microstructure.

[0074] Example 3:

[0075] An aluminum-based composite brazing material, the preparation method of which includes:

[0076] Step 1: Dry material mixing. According to the mass percentage, add 71.4% potassium fluoroaluminate (particle size 20 μm to 50 μm) and 28.6% diatomaceous earth (particle size 20 μm to 50 μm) to a stainless steel mixer and stir at a speed of 220 r / min for 15 min (shorten the mixing time by increasing the speed) until the materials are evenly dispersed and there is no agglomeration.

[0077] Step 2: Slurry Preparation. Binder Masterbatch: Composed of 52.4% deionized water, 23.8% carboxymethyl cellulose (CMC), and 23.8% polyethylene oxide (PEO) by mass percentage. After stirring at 50 °C for 10 min, isopropanol is added. Composite Process: The binder masterbatch and polytetrafluoroethylene (PTFE) emulsion are mixed at a mass ratio of 1:1, and the above-mentioned dry mixture is added. The mixture is stirred at 150 r / min for 8 min to obtain a homogeneous slurry with a viscosity of 130 mPa·s.

[0078] Step 3: Roller Coating. A 4045 aluminum alloy plate (0.10 mm thick) was selected as the substrate for the flux layer. It was wiped with alcohol and then air-dried. The roller press parameters were set as follows: roller gap 0.10 mm, travel speed 3.5 m / min, and flux layer thickness 0.08 mm after coating.

[0079] Step 4: Drying and curing. The coating is kept at 150 ℃ for 2.5 h (by extending the curing time by lowering the temperature, thin-layer cracking is suppressed), and a medium-speed blower is used to dry the coating, forming a flux composite layer on the coated surface of the substrate.

[0080] Step 5: Casting and Rolling Composite and Post-treatment. The 3003 aluminum-manganese alloy core substrate (1.5 mm thick) and the brazing filler layer substrate are composited in a double-strip casting and rolling mill, with the casting and rolling temperature controlled between 690 ℃ and 710 ℃. The composite sheet undergoes hot rolling, cold rolling, and annealing to eliminate processing stress and stabilize the microstructure.

[0081] Example 4:

[0082] An aluminum-based composite brazing material, the preparation method of which includes:

[0083] Step 1: Dry material mixing. According to the mass percentage, add 71.4% potassium fluoroaluminate (particle size 20 μm to 50 μm) and 28.6% aluminum silicate (particle size 20 μm to 50 μm) to a stainless steel mixer and stir at 200 r / min for 18 min (by increasing the speed to shorten the mixing time) until the materials are evenly dispersed and there is no agglomeration.

[0084] Step 2: Slurry Preparation. Binder Masterbatch: Composed of 50% deionized water, 25% carboxymethyl cellulose (CMC), and 25% polyethylene oxide (PEO) by mass percentage. After stirring at 52 °C for 12 min, add 5 L of isopropanol. Composite Process: Mix the binder masterbatch with 5 L of polytetrafluoroethylene (PTFE) emulsion, then add the above-mentioned dry mixture. Stir at 130 r / min for 10 min to obtain a homogeneous slurry with a viscosity of 180 mPa·s.

[0085] Step 3: Roller Coating. A 4343 aluminum alloy plate (0.12 mm thick) was selected as the substrate for the flux layer. It was wiped with alcohol and then air-dried. The roller press parameters were set as follows: roller gap 0.12 mm, travel speed 3 m / min, and flux layer thickness 0.1 mm after coating.

[0086] Step 4: Drying and curing. A stepped temperature increase program is used: 120 ℃ for 30 min, 160 ℃ for 1 h, and 180 ℃ for 30 min. A flux composite layer is formed on the coating surface of the above substrate.

[0087] Step 5: Casting and Rolling Composite and Post-treatment. The 3003 aluminum-manganese alloy core substrate (1.5 mm thick) and the brazing filler layer substrate are composited in a double-strip casting and rolling mill, with the casting and rolling temperature controlled between 690 ℃ and 710 ℃. The composite sheet undergoes hot rolling, cold rolling, and annealing to eliminate processing stress and stabilize the microstructure.

[0088] Comparative Example 1:

[0089] Traditional spraying process: The substrate is AA3003 / AA4045 aluminum alloy foil. The foil surface is wiped with alcohol and fully dried. The flux suspension is directly applied to the aluminum foil surface using a dry powder spraying method to obtain aluminum-based composite brazing material. During the coating process, flux accumulation was observed in some areas. The drying process uses room temperature natural evaporation or non-temperature controlled heating.

[0090] This application conducted performance tests on the aluminum-based composite brazing materials of Examples 1-4 and Comparative Example 1, including: coverage rate, layer thickness ratio, and flux coating thickness uniformity.

[0091] The coating ratio utilizes the difference in microstructure between the cladding metal and the core metal, and the thickness of the cladding and core layers is measured using a metallographic microscope (AxioObserver.Z1m). The testing method for the coating ratio is similar to that for metallographic microstructure testing, referring to standards GB / T 3246.1—2024 and GB / T 13298—2015. The layer thickness ratio test (coating ratio stability test) measures the ratio of the solder layer thickness to the substrate thickness to ensure that the filler metal filling capacity meets the standards, referring to standard GB / T 3246.1-2012. The flux coating thickness uniformity, i.e., the standard deviation of the flux coating thickness, refers to standard GB / T 6462-2005, where five fields of view are randomly selected, the coating thickness is measured, and the standard deviation is calculated. The test results are shown in Table 1.

[0092] Table 1. Performance test results of aluminum-based composite brazing materials of Examples 1-4 and Comparative Example 1 of this application

[0093]

[0094] Please refer to Table 1. The coverage rate of Examples 1-4 of this application is 8.5%~8.9%, which is higher than 7.1% of Comparative Example 1. This is because Examples 1-4 achieve uniform coverage of the flux layer on the structural core layer through the coating of polymer-reinforced slurry, resulting in tight interface bonding. In contrast, the traditional spraying process of Comparative Example 1 results in incomplete coverage due to coating accumulation and insufficient bonding force. The layer thickness ratio of Examples 1-4 is 12.15%~12.74%, which is lower than 14.94% of Comparative Example 1. This is because the polymer-reinforced slurry of Examples 1-4 can precisely control the thickness of the flux composite layer (0.08~0.15mm) through roll coating, resulting in a stable layer thickness ratio. In contrast, Comparative Example 1 suffers from uneven spraying, leading to excessively thick local coatings and a large and high layer thickness ratio fluctuation. The standard deviation of the flux coating thickness of Examples 1-4 is lower than that of Comparative Example 1. This is because the polymer-reinforced slurry of Examples 1-4 can be roll coated and cured, ensuring uniform flux layer thickness. In contrast, the dry powder spraying process of Comparative Example 1 is prone to local accumulation and pinholes, resulting in uneven thickness distribution. Therefore, the embodiments of this application, by preparing polymer-reinforced slurry and combining it with the "roll coating + casting and rolling composite" process, comprehensively outperform the traditional spraying process of Comparative Example 1 in terms of coverage rate, layer thickness ratio stability and coating uniformity, thus verifying the advantages of this application in improving material structure consistency and process controllability.

[0095] This application also analyzed the surface morphology and elemental distribution characteristics of the composite brazed aluminum alloy substrate treated with coating technology (obtained in the third step) using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) (GeminiSEM300) under the conditions of accelerating voltage 10-20 kV, working distance 5-15 mm, and EDS acquisition time 5-10 min. Please refer to [link to relevant documentation]. Figure 1 Taking Example 1 as an example, the white strip-shaped precipitates and some clustered aggregates in the figure are KAlF4 compounds, with the strip-shaped phases being diffusely distributed. SEM morphology analysis results show that the aluminum alloy substrate surface is covered with a continuous and uniform flux coating, and its microstructure exhibits a fine network or granular feature, with no obvious local voids, agglomerations, or accumulation observed. High-magnification microscopic observation shows that the coating and substrate interface are densely bonded, with good surface smoothness, and no local protrusions or depressions caused by uneven coating are observed, indicating that the flux is uniformly spread on the substrate surface, confirming the precise control capability of the patented technology for flux distribution. In the elemental distribution diagram, key elements such as Si, F, and K show a uniform distribution across the entire region, proving that the flux components did not undergo stratification or agglomeration during the coating process, thus ensuring that the flux activity, melting point, and fluidity of each region of the substrate remain consistent during subsequent brazing; the absence of abnormal element diffusion behavior indicates that uniform flux coating ensures the consistency of the reaction kinetics between the base material and the flux, effectively avoiding performance fluctuations caused by uneven coating.

[0096] This application also analyzed the microstructure of the obtained flux-embedded aluminum matrix composite material before and after brazing using a scanning electron microscope (GeminiSEM 300). Please refer to the relevant documentation. Figure 2 and Figure 3 Taking Example 1 as an example, Figure 2 The magnification of (a) to (c) gradually increases. Combined with the microstructures at different magnifications, it can be seen that the aluminum-based composite brazing material prepared by the method of this application, through optimized coating, achieves complete coverage of the flux on a macroscopic scale and uniform particle dispersion and size on a microscopic scale, effectively avoiding problems such as localized accumulation, uneven dispersion, and coating cracking that are prone to occur in traditional coating processes. During the brazing process, the Al-Si eutectic transforms from an equiaxed structure to a needle-like structure, and the thickness increases, indicating diffusion. After brazing, Figure 3 In the images (a) to (e), (b) is a magnified view of the brazing area in (a), (c) is the upper brazing area, (d) is the central brazing area, and (e) is the lower brazing area. It can be observed from each different area that the flux does not remain on the material surface. This uniformity advantage can directly improve the flux activity release efficiency in the subsequent welding process, reduce welding defects caused by excessively high / low local flux concentration, and provide key microstructure protection for the welding performance stability of the material.

[0097] Based on the above analysis results, the preparation method of the aluminum-based composite brazing material of this application involves combining a dry mixture of flux powder and inorganic filler with a binder masterbatch and a polymer binder emulsion. The polymer binder emulsion enhances the adhesion between the flux layer and the aluminum substrate. Simultaneously, by combining the rheological properties and viscosity coefficient provided by the binder masterbatch, a polymer-reinforced slurry with excellent stability and high adhesion performance is prepared. After coating and curing, this slurry can form a strong, dense, and firmly adhered flux composite layer on the surface of the flux layer. Its interfacial bonding strength with the substrate is superior to that of loose flux particle accumulation in traditional processes. This fundamentally solves the problem of flux layer easy delamination and uneven distribution during subsequent processing or thermal cycling, and improves the integrity and consistency of the flux pre-embedded coating. Therefore, this application achieves a simplified operation by using dry mixing of flux powder and inorganic fillers, replacing the lengthy and complex processes of powder metallurgy-hot isostatic pressing, such as powder mixing, cladding welding, vacuum degassing, and high-pressure pressing, which is beneficial for shortening the production cycle and reducing equipment investment and energy consumption, demonstrating excellent process economy. Furthermore, efficient casting and rolling are used to metallurgically composite the solder layer coated with this flux composite layer, placed according to a preset positional relationship, with a structural core layer having a higher solids temperature, achieving high-strength bonding of multi-layer materials in one step. This improves production efficiency and is suitable for large-scale continuous production lines. Moreover, the preset melting point difference between the solder layer and the core layer ensures that the composite material can maintain the structural integrity of the core layer while the solder layer melts and connects during brazing. The aluminum-based composite brazing material prepared by this application exhibits excellent performance in brazing, including high joint strength, good sealing, and low flux residue, providing key material support for the mass production of long-life, high-reliability heat exchange components in fields such as refrigeration and new energy vehicles.

[0098] Compared to the embodiments of this application, Comparative Example 1 uses a traditional spraying process. When the flux suspension is directly applied to the aluminum foil surface using a dry powder spraying method, flux accumulation is observed in localized areas during the coating process. The resulting flux film has the following defects: uneven thickness distribution, significant localized accumulation, high pinhole density, and large flux residue.

[0099] In summary, this application achieves high-precision and uniform flux coating by optimizing the flux preparation and coating methods, providing a key guarantee for the interfacial bonding strength and overall performance stability of composite materials after brazing.

[0100] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0101] The embodiments described above are merely illustrative of several implementations of the technical solution of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the technical solution of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for preparing an aluminum-based composite brazing material, characterized in that, The preparation method includes: The flux powder and inorganic filler are dry-mixed to prepare a mixed dry material; A polymer-reinforced slurry is prepared by mixing the binder masterbatch, the polymer binder emulsion, and the aforementioned dry mixture. The polymer-reinforced slurry is coated onto the surface of the aluminum alloy substrate of the solder layer, and after curing, a flux composite layer is formed on the surface. The aluminum alloy substrate with the flux composite layer formed on its surface is placed opposite to the aluminum alloy substrate of the structural core layer, such that the flux composite layer is located on the side of the aluminum alloy substrate away from the aluminum alloy substrate of the structural core layer, and then cast and rolled to composite the aluminum alloy substrate of the solder layer, so that the aluminum alloy substrate of the solder layer covers the aluminum alloy substrate of the structural core layer, wherein the solidus temperature of the aluminum alloy of the solder layer is lower than the solidus temperature of the aluminum alloy of the structural core layer, thus preparing the aluminum-based composite brazing material.

2. The preparation method according to claim 1, characterized in that, The viscosity of the polymer-reinforced slurry is from 100 mPa·s to 250 mPa·s.

3. The preparation method according to claim 1, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The mass ratio of the flux powder to the inorganic filler is (60~80):(20~40); (2) The average particle size of the flux powder is 20 μm to 50 μm; (3) The average particle size of the inorganic filler is 20 μm to 50 μm.

4. The preparation method according to claim 1, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The flux powder includes fluoroaluminate; (2) The inorganic filler includes at least one of aluminum silicate and aluminum silicate; (3) The polymer binder emulsion includes polytetrafluoroethylene; (4) The adhesive masterbatch includes at least one of isopropanol, cellulose adhesive and polyether adhesive.

5. The preparation method according to claim 1, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The coating method includes roll coating; (2) The curing temperature is 140 ℃ to 180 ℃, and the curing time is 1.5 h to 3 h; (3) The casting and rolling temperature is 680 ℃ to 720 ℃.

6. An aluminum-based composite brazing material, characterized in that, Prepared by the preparation method according to any one of claims 1 to 5; The aluminum-based composite brazing material includes the structural core layer aluminum alloy substrate and the brazing filler layer aluminum alloy substrate located outside the structural core layer, wherein the brazing flux powder is embedded in the surface layer of the brazing filler layer aluminum alloy substrate away from the structural core layer.

7. The aluminum-based composite brazing material as described in claim 6, characterized in that, The brazing filler layer aluminum alloy substrate includes an aluminum-silicon alloy, and the structural core layer aluminum alloy substrate includes an aluminum-manganese alloy.

8. The aluminum-based composite brazing material as described in claim 6, characterized in that, The thickness of the flux composite layer is 0.08 mm to 0.15 mm.

9. A heat exchanger component, characterized in that, Includes the aluminum-based composite brazing material according to any one of claims 6 to 8.

10. The heat exchanger component as claimed in claim 9, characterized in that, The heat exchanger components include at least one of automotive air conditioning evaporator flat tubes, radiator chips, and new energy vehicle battery cooling plates.

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