Composite brazing sheet containing multiple diffusion interlayers and manufacturing process of composite brazing sheet

Abstract

The invention discloses a composite brazing sheet containing multiple diffusion interlayers and a manufacturing process of the composite brazing sheet, the composite brazing sheet sequentially comprises a core material, a first collaborative diffusion interlayer, a second collaborative diffusion interlayer and a brazing filler metal layer, the first collaborative diffusion interlayer is in contact with the core material, and the second collaborative diffusion interlayer is in contact with the brazing filler metal layer. The second cooperative diffusion middle layer is located between the first cooperative diffusion middle layer and the brazing filler metal layer. The phase change reaction occurs in the brazing temperature zone, theta-Al2Cu + beta-Si eutectic melt with high wettability and high fluidity is separated out in situ, and the interface wettability and the brazing filler metal spreading capacity are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite brazing sheets, in particular to a composite brazing sheet containing multiple diffusion intermediate layers and a manufacturing process thereof. Background Art

[0002] With the widespread application of high-performance aluminum alloy materials in structural parts, aluminum alloy brazing sheets have become a key type of composite materials. In order to achieve stable connection of different functional layers in aluminum alloy brazing sheets, improve welding performance and service reliability, the existing technology uses a multi-layer composite structure to tightly combine the core material, brazing layer and transition intermediate layer through rolling or explosive composite methods.

[0003] During the brazing thermal cycle, the traditional single-layer intermediate layer structure is difficult to effectively prevent the low-melting-point elements in the brazing filler metal from deeply penetrating into the core material, which can easily lead to obvious dissolution and mechanical property degradation of the core material. At the same time, the diffusion of elements may also form a brittle eutectic phase on the surface of the core material, thereby affecting the density and fatigue resistance of the joint.

[0004] At the same time, due to the certain electrochemical potential difference between the core material and the brazing material, galvanic corrosion is easily caused in a complex service environment. Traditional brazing sheets do not have a galvanic adjustment layer with clear functions, so the corrosion behavior is particularly serious in the weld area, shortening the service life of the material. Summary of the Invention

[0005] One object of the present invention is to provide a composite brazing sheet containing a multi-layer diffusion intermediate layer and a manufacturing process thereof. The present invention undergoes a phase change reaction in the brazing temperature zone, and in situ precipitates a θ-Al2Cu+β-Si eutectic melt with high wettability and high fluidity, effectively improving the interface wettability and the solder spreading ability.

[0006] According to an embodiment of the present invention, a composite brazing sheet containing multiple diffusion intermediate layers includes, in sequence: a core material, a first collaborative diffusion intermediate layer, a second collaborative diffusion intermediate layer, and a brazing material layer. The first collaborative diffusion intermediate layer contacts the core material, and the second collaborative diffusion intermediate layer is located between the first collaborative diffusion intermediate layer and the brazing material layer.

[0007] Optionally, the core material is 3003 or 6061 aluminum alloy, with a thickness of 0.3 mm to 1.0 mm and a surface roughness of 0.3 μm to 0.8 μm.

[0008] Optionally, the first cooperative diffusion intermediate layer is a galvanic harmonic blocking layer, which is composed of an aluminum-manganese-zinc alloy, wherein the mass fraction of manganese is 1.0% to 1.5%, the mass fraction of zinc is 0.3% to 0.7%, and the thickness is 15μm to 35μm.

[0009] Optionally, the second cooperative diffusion intermediate layer is a heat-activated micro-melted island layer, which is composed of an Al-Si-Cu-Ti multi-element eutectic alloy, wherein the Si mass fraction is 5% to 6.5%, the Cu mass fraction is 1% to 2%, the Ti mass fraction is 0.05% to 0.15%, and the thickness is 10μm to 30μm.

[0010] Optionally, when the brazing temperature reaches 630-650° C., a distributed θ-Al 2 Cu + β-Si micro-melting island structure is formed inside the heat-activated micro-melting island layer.

[0011] Optionally, the brazing material layer is an Al-10Si alloy layer with a thickness of 25 μm to 50 μm, and the brazing material layer and the second cooperative diffusion intermediate layer form a continuous brazing seam after metallurgical fusion.

[0012] A manufacturing process for a composite brazing sheet containing a multi-layer diffusion intermediate layer, for manufacturing a composite brazing sheet containing a multi-layer diffusion intermediate layer, comprising:

[0013] Material preparation and surface pretreatment: 3003 or 6061 aluminum alloy with a thickness of 0.3mm to 1.0mm was selected as the core material. The surface of the core material was mechanically drawn and alkaline degreased to obtain a surface roughness of 0.3μm to 0.8μm.

[0014] Preparation of multi-layer diffusion intermediate layer alloy: the first synergistic diffusion intermediate layer is prepared by direct melting-casting and rolling method, the second synergistic diffusion intermediate layer is prepared by directional rapid solidification method, and the distribution of spheroidization precursor phase is refined by cold rolling;

[0015] Multi-layer lamination and vacuum packaging: lamination is carried out according to the core material / aluminum-manganese-zinc alloy slab / aluminum-silicon-copper-titanium alloy sheet / Al-10Si alloy layer, and vacuum packaging is carried out. The vacuum degree is higher than 1.0×10-2P a , packaging pressure is controlled at 5~12MPa;

[0016] Zoned temperature-controlled multi-pass rolling: the encapsulated laminated structure is sent to the zoned temperature-controlled rolling line with three temperature zones: T1 is 320-350°C, T2 is 370-410°C, and T3 is 410-440°C. The total deformation rate is controlled at 40%-55%, the thickness difference of each rolling pass is controlled at ±3%, and the rolling speed is 5-15m / min.

[0017] Online short-time uniform temperature diffusion: The rolled sheet is subjected to short-time uniform temperature diffusion treatment at a temperature of 470-510°C for 2-6 minutes in a controlled atmosphere of N2+0.5% H2 mixed protective gas. Pre-stabilized θ-Al2Cu and β-Si pre-melted island phase nuclei are formed during the diffusion process.

[0018] Finished product cooling and straightening: Use air cooling to cool the sheet to room temperature, with a cooling rate greater than 20℃ / s, and control the finished product warpage to ≤0.5mm / 300mm, and the overall thickness deviation of the sheet to ≤±3μm.

[0019] Optionally, the thermally activated micro-melting island layer is prepared as follows:

[0020] Alloy smelting and casting and rolling: Aluminum ingots are used as the base material and melted in a medium frequency induction furnace to a temperature of 740-780°C. Si is first added and, after uniform melting, Al-Cu master alloy and Al-Ti master alloy are added in sequence. After stirring evenly, the melt is refined and degassed for 10-15 minutes. After filtering through a ceramic filter, the melt is cast and rolled into alloy billets with a thickness of 2-5 mm using a horizontal continuous casting and rolling mill.

[0021] Homogenization treatment: The cast-rolled alloy billet is subjected to homogenization treatment, heated to 520-540°C, kept at this temperature for 6-10 hours, and slowly cooled to room temperature at a cooling rate of 10-15°C / h. A uniform α-Al matrix and dispersed Si-rich and Cu-rich phases are initially formed inside the alloy billet.

[0022] Multi-pass temperature-controlled rolling: The alloy billet after homogenization treatment is subjected to multi-pass zoned temperature-controlled rolling. The temperature of the first rolling pass is controlled at 420-450°C, the reduction of a single pass is 25%-30%, and the total deformation of the passes is 50%-60%. The temperature of the second rolling pass is controlled at 350-380°C, and the reduction of a single pass is controlled at 15%-20%. Fine particles or island-like clusters are dispersed in the matrix to obtain alloy sheets with a thickness of 10-30μm.

[0023] Online short-time rapid temperature diffusion treatment: The rolled alloy sheet is superimposed on the composite brazing sheet system, vacuum-encapsulated to form a laminated structure, the laminated structure is heated to 480-520°C, kept warm for 1-3 minutes to form a metastable solid solution structure, and then cooled to room temperature.

[0024] The beneficial effects of the present invention are:

[0025] The composite brazing sheet containing multiple diffusion intermediate layers and the manufacturing process thereof proposed in the present invention form a multi-layer structural system with a functional synergistic mechanism by sequentially arranging a first synergistic diffusion intermediate layer and a second synergistic diffusion intermediate layer between the core material and the brazing material layer. The first synergistic diffusion intermediate layer is composed of an aluminum-manganese-zinc alloy to form a galvanic harmonizing and blocking platform, which is used to control the potential difference between the core material and the brazing material in the brazing hot zone, slow down the corrosion reaction caused by the galvanic difference, and avoid the formation of local electrochemical corrosion paths; the second synergistic diffusion intermediate layer adopts Al-Si-Cu-Ti eutectic alloy material, has a controllable thermally activated micro-melting island effect, undergoes a phase change reaction in the brazing temperature zone, and precipitates in situ a θ-Al2Cu+β-Si eutectic melt with high wettability and high fluidity, effectively improving the interface wettability and brazing material spreading ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 The present invention provides the microscopic morphology characteristics of the θ-Al2Cu+β-Si eutectic structure of a composite brazing sheet containing a multi-layer diffusion intermediate layer.

[0028] Among them, the bright dendritic phase (marked as a) is the θ phase (Al2Cu), which is a copper-rich phase and appears as dendritic or feather-like crystals. The dark base phase (marked as β) is the β-Si phase, which appears as irregular particles or islands. DETAILED DESCRIPTION

[0029] The present invention will now be described in further detail with reference to the accompanying drawings, which are simplified schematic diagrams that illustrate the basic structure of the present invention in a schematic manner.

[0030] Example 1: Preparation of aluminum composite brazing sheet containing two diffusion intermediate layers

[0031] This embodiment provides an aluminum alloy composite brazing sheet with two diffusion intermediate layers. The structure includes an aluminum alloy core layer, two diffusion intermediate layers located on one side of the core layer, and an outermost brazing cladding layer. The core layer material is a high-strength aluminum alloy, the diffusion intermediate layers are composed of two aluminum alloy thin layers with different compositions, and the brazing filler metal layer is a low-melting-point aluminum-based brazing alloy. The composition ratios of the materials of each layer are as follows:

[0032] Core layer alloy: 3xxx series aluminum alloy is selected, with the mass composition of: Mn 1.0%, Cu 0.6%, Si 0.2%, Fe0.3%, Zn 0.1%, Ti 0.05%, and the balance is Al and inevitable impurities. The aluminum alloy has medium strength and good plasticity. An appropriate amount of Cu is added to improve the strength after brazing, Mn improves the corrosion resistance of the alloy, and Ti refines the grains.

[0033] First intermediate layer alloy: industrial pure aluminum foil (1xxx series, AA1050) with a thickness of 50 μm is selected. The purity of the first intermediate layer is not less than 99.5%, which acts as a diffusion barrier layer to isolate the elements of the core layer and the solder layer from interdiffusion.

[0034] Second intermediate layer alloy: A zinc-containing aluminum alloy foil (AA7072, Zn content of about 1.0%) with a thickness of about 40 μm is selected. The second intermediate layer and the pure aluminum layer together form a multi-layer diffusion barrier, in which a small amount of Zn element improves the electrochemical anode performance and preferentially sacrifices the protective core layer in a corrosive environment.

[0035] Brazing filler metal alloy: Use traditional aluminum-silicon brazing filler metal alloy (4xxx series, AA4343) with a thickness of about 60μm. The main component is Si 7.5%, and the balance is Al (Mg content is controlled below 0.05%). The brazing filler metal has a low melting point (eutectic temperature is about 577℃) and good wetting fluidity, making it suitable for vacuum or flux brazing of aluminum alloys.

[0036] The first intermediate layer alloy, the second intermediate layer alloy and the brazing filler metal alloy are obtained by melting and casting ingots or commercial thin plates / foils are selected. The core layer and brazing filler metal layer ingots are cast according to the ratio and the intermediate layer aluminum foil of the required thickness is prepared. After the material preparation is completed, the composite brazing sheet is prepared according to the following steps:

[0037] S1. Surface treatment: Mill or grind the surface of the core layer ingot to be composited to remove the oxide layer and impurities, so that the surface roughness is controlled at 1.6-3.2μm. Clean and degrease the surface of the middle layer aluminum foil and the solder layer ingot with acetone, and lightly brush the surface of the pure aluminum foil with a stainless steel brush to activate the metal surface. After cleaning, the surface of each layer should be free of oil, oxide film and dust.

[0038] S2. Lamination assembly: The treated core layer ingot is placed on the lower pedestal of the composite rolling mill, with the upper surface serving as the composite interface. The first intermediate layer of pure aluminum foil is laid on the core layer to make it close to the core layer surface and flattened without wrinkles. The second intermediate layer of zinc-containing aluminum foil and the solder layer ingot are laid in sequence on the pure aluminum foil to ensure that the layers are aligned without misalignment or air bubbles being entangled, thereby obtaining a four-layer laminated structure of core layer / pure aluminum foil / Zn-containing aluminum foil / solder layer. In order to prevent interlayer sliding during rolling, spot welding or narrow welds are used to locally weld and fix the layers at the edges on both sides of the laminate.

[0039] S3. Composite heating: Place the assembled composite billet in a heating furnace and preheat it under inert atmosphere or vacuum conditions. A two-stage heating process is adopted: homogenize and keep warm at 520℃ for 5 hours to eliminate the casting stress of the core layer ingot and improve the interface diffusion performance, cool to 480℃ and keep warm for another 2 hours to make the middle layer of pure aluminum foil begin to soften but not melt, and remove residual water vapor and oxides on the interface. After preheating, immediately take the composite billet out of the furnace for hot rolling.

[0040] S4. Hot rolling composite: The heated composite billet is quickly fed into the rolling mill for hot rolling composite, and the rolled sheet is subjected to a short-time temperature diffusion treatment at a temperature of 470°C for 2 minutes in a controlled atmosphere of N2+0.5% H2 mixed protective gas. Pre-stabilized θ-Al2Cu and β-Si pre-melted island phase nuclei are formed during the diffusion process.

[0041] S5. Cooling and intermediate annealing: After hot rolling, the multi-layer composite plate is quickly cooled to room temperature to retain the fiber structure, and intermediate annealing is performed to reduce the hardness for cold rolling. The hot-rolled plate is placed in a 300℃ air furnace for 2 hours and then cooled in the furnace to eliminate the work hardening stress. After annealing, the interfaces of each layer of the composite plate have been fully diffused and there is no obvious stratification.

[0042] S6. Cold rolling to finished product thickness: The annealed composite plate is cold rolled in multiple passes, gradually reducing the thickness from about 5 mm to the target thickness of 0.50 mm. The reduction rate of the last pass is controlled within 20% to obtain the required thickness tolerance and improve the surface finish of the plate. The thickness of each layer is proportionally thinned during the cold rolling process. The thickness of the finished composite brazing sheet is distributed as follows: the core layer is about 0.35 mm, and the total thickness of the middle layer is about 0.081 mm. After cold rolling, the material is in a hard or semi-hard state. Slight stretching and straightening can be performed to correct the plate shape as needed.

[0043] Performance verification: Take the prepared composite brazing sheet to test its brazing performance and corrosion resistance;

[0044] First, a brazing wettability test was conducted: the composite plate of this embodiment was cut into 20mm×30mm specimens, and two specimens were placed with the brazing layers overlapping each other, with an angle of 5° to form a simulated lap joint. The brazing was completed in a nitrogen-protected furnace at 600°C for 3 minutes. The results showed that the brazing layer was completely melted after heating and fully wetted the surface of the core layer. The molten brazing material spread evenly along the interface, forming a continuous and bright brazing seam at the joint.

[0045] The solder spreading length and joint filling rate were measured: the spreading length was 100% of the sample length, and the solder joint filling rate was 100%, indicating that the sheet of the present invention had good solder fluidity and strong wetting ability during the brazing process, forming a strong brazing joint.

[0046] Further metallographic microscopic observations showed that two thin intermediate layer transition zones were still visible between the core layer and the solder layer after brazing. The thickness was slightly reduced but still continuous. Only limited element diffusion occurred in the intermediate layer, and no core layer was found to be dissolved or thinned. Energy spectrum line scanning was used to analyze the distribution of Si elements in the cross section of the brazed joint. The results showed that Si was mainly distributed in the solder layer and the adjacent intermediate layer area, and the diffusion depth into the core layer matrix was less than 20μm. In comparison, in the sample without an intermediate layer, the diffusion depth of Si into the core layer exceeded 50μm, and a brittle eutectic structure rich in Si phase was formed locally. It can be seen that the multi-layer intermediate layer of the present invention effectively blocks the excessive diffusion of Si into the core material.

[0047] In addition, a post-brazing corrosion performance test was conducted: the samples after brazing were immersed in a 3.5% sodium chloride solution for 7 days, and the corrosion conditions were observed every day. The sample of Example 1 only had slight uniform corrosion spots on the surface and no through-corrosion was found. The cross-section observation showed that the intermediate layer was intact and there was no obvious intergranular corrosion in the core layer matrix. However, the control sample without an intermediate layer developed deep corrosion grooves along the grain boundaries of the core layer after immersion for 3 days, and corrosion penetrated the thickness in some areas. The results show that the provision of a multi-layer diffusion intermediate layer improves the corrosion resistance of the brazing sheet after the brazing thermal cycle.

[0048] Example 2: Composite brazing sheet composed of high-strength core material and thick intermediate layer

[0049] This example provides another aluminum composite brazing sheet with two diffusion intermediate layers. The main difference from Example 1 lies in the core layer alloy composition and intermediate layer thickness ratio. The structure includes a core layer, two diffusion intermediate layers, and a brazing filler metal layer. The specific materials and process conditions are as follows:

[0050] Core layer alloy: An improved 3xxx series aluminum alloy is selected, with the following mass composition: Mn 1.2%, Cu 0.8%, Mg 0.3%, Zr 0.10%, Ti 0.05%, Fe 0.3%, and Si 0.2%. Compared with Example 1, the Cu content is increased to improve the alloy strength, and a trace amount of Zr is added to refine the grains and improve the structural stability after brazing. The Mg content is controlled at 0.3%, which ensures that excessive oxides are not generated at the brazing temperature while improving the room temperature strength.

[0051] The first intermediate layer alloy is industrial high-purity aluminum foil, with a thickness of 60 μm and a purity of more than 99.6%. The first intermediate layer is slightly thicker than that in Example 1 and is mainly used to isolate the high content of Cu and Mg in the core layer from diffusing into the solder layer, preventing them from entering the molten pool during brazing and affecting the performance of the solder.

[0052] Second intermediate layer alloy: Zn-containing aluminum alloy foil, 50μm thick, 2.0% Zn content. Appropriately increasing the Zn content and thickness allows the second intermediate layer to provide stronger cathodic protection after brazing. On the one hand, the presence of Zn further reduces the electrode potential of this layer, making it more easily dissolved in the corrosive medium than the core layer; on the other hand, during brazing, the Zn layer contacts the brazing filler metal, forming a trace Al-Zn solid solution at the interface. Fine crystals are formed after the brazing filler metal solidifies, which is beneficial to the mechanical properties of the joint.

[0053] Solder layer alloy: Aluminum silicon solder with a slightly higher melting point is selected, with a thickness of 70 μm and a Si content of 10%. The increased Si content provides a larger melting temperature range and sufficient liquid phase volume during brazing, which adapts to the presence of a thicker intermediate layer in this embodiment, so that the solder can still fully melt and wet the core layer surface.

[0054] The preparation process is basically the same as that of Example 1. Since the core layer of this embodiment contains Zr element, the temperature needs to be appropriately increased and the holding time needs to be extended during melting, homogenization and heat treatment to ensure a fully uniform distribution of the alloy elements.

[0055] In Example 2, the core layer ingot can be homogenized at 560°C for 12 hours to form a fine dispersed phase of Zr. Before lamination, the surfaces of the core layer and the solder layer are milled to remove the oxide scale. The first layer of high-purity aluminum foil is finely polished and purified like the core layer surface. The four-layer structure is also adopted during lamination: core layer / high-purity aluminum foil / Zn-containing aluminum foil / solder layer and fixed by spot welding at the edges. The initial pressure in the hot rolling stage is more moderate to ensure that the thicker pure aluminum intermediate layer can gradually transition and deform without folding and cracking; the final hot rolling thickness is about 6mm, and the cold rolling is to a finished product thickness of 0.50mm (of which the core layer is about 0.32mm, the total thickness of the two intermediate layers is about 0.12mm, and the solder layer is 0.06mm). Due to the high strength of the core layer, it is delivered in the finished annealing state O state, and is furnace cooled after being kept at 450°C for 2 hours to obtain the maximum elongation for subsequent forming.

[0056] Performance Verification: The composite brazing sheet obtained in Example 2 was subjected to the same brazing joint and corrosion performance tests as in Example 1. The results showed that the sheet in Example 2 performed equally well during the brazing process. The brazing filler metal layer was fully wetted after melting and had good filling. Due to the higher Si content in the brazing filler metal, a wider spreading range was observed than in Example 1. The molten brazing filler metal even formed a thin film overflow at the edge of the overlapping sample, indicating that the wetting angle was extremely small (close to 0°). The microstructure of the brazed joint showed that the two intermediate layers were still clearly distinguishable and the thickness ratio was basically maintained. The total thickness of the pure aluminum layer and the Zn-containing layer after brazing was 90 μm, only slightly less than the original thickness. Overall, the intermediate layer was intact and continuous without being melted through. The core layer matrix did not show any dissolution thinning, and no brittle compounds caused by Cu and Mg diffusion were found at the interface. In contrast, without the protection of multiple intermediate layers, the high Cu content core layer easily formed an Al-Cu-Si eutectic with Si during brazing, and a low-melting-point eutectic liquid film appeared at the adjacent grain boundaries, weakening the matrix. This embodiment effectively avoided such phenomena by isolating the intermediate layer.

[0057] After 168 hours of salt spray accelerated corrosion testing (35°C, 5% NaCl, continuous spray of neutral salt spray), only uniform passivation spots were observed on the surface of the sample in Example 2, with no deep pitting pits. Metallographic corrosion inspection of the sample cross-section showed slight thinning of the intermediate layer near the core layer (presumably because the second Zn-containing intermediate layer was partially dissolved first in the corrosive environment), but the core layer was intact and free of holes. In contrast, the single-layer intermediate layer sample under the same salt spray conditions showed a small amount of pitting invading the core layer surface, while the sample without the intermediate layer suffered severe overall corrosion and perforation failure. This shows that the higher strength core material combined with the thicker multi-layer diffusion intermediate layer design in this embodiment further improves the corrosion resistance life of the brazed joint after brazing while maintaining mechanical properties.

[0058] Comparative Example 1: Composite brazing sheet with a single intermediate layer

[0059] In order to evaluate the superiority of the multi-layer diffusion intermediate layer, a comparative test of a single-layer intermediate layer composite brazing sheet was conducted. The structure of the comparative sample was a traditional three-layer composite: core layer / single-layer intermediate liner / brazing material layer. The core layer alloy used the same 3xxx series composition as in Example 1, and the brazing material layer used AA4343 aluminum-silicon alloy (thickness of about 0.08 mm) as in Example 1, except that only a pure aluminum intermediate layer (1xxx series, not including the second layer of Zn aluminum) with a thickness of about 80 μm was set between the core layer and the brazing material layer. According to the embodiment Similar rolling, compounding and heat treatment processes were used to produce a three-layer brazing sheet. Testing showed that the brazing material of the comparative sample melted and spread well during brazing. However, due to the lack of a second Zn-containing barrier layer, some Si could still diffuse through the single-layer pure aluminum into the core layer. A small amount of eutectic Si precipitation was observed on the surface of the core layer on the cross-section after brazing, and the core material was corroded to a depth of about 30 μm. After 120 hours of salt spray testing, pitting pits appeared on the surface of the comparative example 1 sample and some of them penetrated into the core layer, indicating that the single-layer intermediate layer has limited corrosion protection.

[0060] Comparative Example 2: Non-diffusion intermediate layer using Al-Si-Cu-Ti eutectic alloy material

[0061] The samples were subjected to joint tests under the same brazing conditions. The results showed that after the solder melted, a large amount of Si diffused into the core layer, resulting in a decrease in the actual available liquid phase of the solder, affecting the wetting and spreading. The joint was not completely filled after brazing, and a small amount of weld defects occurred. Cross-sectional observation showed that the surface of the core layer was obviously melted, forming a depression about 50 to 100 μm deep, and the core layer thickness became thinner. Corrosion tests further showed that the corrosion resistance of the core layer was significantly reduced without the protection of the intermediate layer: multiple penetrating corrosion occurred on the sample within 48 hours of salt spraying, and the internal organization was aggravated by the corrosion sensitivity due to the Si enrichment during the previous brazing.

[0062] The key performance indicators of the samples of Examples 1-3 and Comparative Examples 1-2 are summarized and compared, as shown in Table 1 below.

[0063] Table 1 Comparison of brazing performance and corrosion resistance of different sheet structures

[0064]

[0065]

[0066] As can be seen from the data in Table 1, Examples 1 and 2 of the present invention, due to the provision of a multi-layer diffusion interlayer, exhibit significantly superior performance to the comparative materials. Specifically, the solder wetting and spreading rate of Examples 1 and 2 during brazing is close to or exceeds 100%, far higher than the approximately 80% achieved without an interlayer. This indicates that the multi-layer interlayer effectively prevents Si from diffusing into the core layer, maintaining sufficient solder wetting and fluidity. Regarding the core layer corrosion depth, no significant corrosion was observed in Examples 1 and 2 (less than 5 μm, considered zero). In contrast, the core layer of Comparative Example 2 without an interlayer was the most severely corroded, reaching a depth of more than 20% of its original thickness. While Comparative Example 1 with a single interlayer showed some improvement, it still had an erosion depth of approximately 30 μm. This demonstrates that the dual-layer interlayer of the present invention can completely isolate the core material from solder corrosion. In terms of corrosion resistance, Example 1 showed only slight spot corrosion after 168 hours of salt spray exposure, while Example 2 showed almost no corrosion. In contrast, the material without the protection of the multi-layer interlayer suffered significant corrosion and even perforation failure. This is mainly due to the fact that the pure aluminum + Zn-containing multi-layer intermediate layer in the present invention not only prevents the diffusion of harmful elements during brazing but also acts as a sacrificial anode in a corrosive environment, thereby doubly improving the corrosion resistance.

[0067] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A composite brazing sheet containing multiple diffusion intermediate layers, characterized in that: The composite brazing sheet comprises: a core material, a first collaborative diffusion intermediate layer, a second collaborative diffusion intermediate layer and a brazing material layer in sequence. The first collaborative diffusion intermediate layer contacts the core material, and the second collaborative diffusion intermediate layer is located between the first collaborative diffusion intermediate layer and the brazing material layer.

2. The composite brazing sheet containing multiple diffusion intermediate layers according to claim 1, characterized in that: The core material is 3003 or 6061 aluminum alloy, has a thickness of 0.3 mm to 1.0 mm, and a surface roughness of 0.3 μm to 0.8 μm.

3. The composite brazing sheet containing multiple diffusion intermediate layers according to claim 1, characterized in that: The first cooperative diffusion intermediate layer is a galvanic harmonic blocking layer, which is composed of an aluminum-manganese-zinc alloy, wherein the mass fraction of manganese is 1.0% to 1.5%, the mass fraction of zinc is 0.3% to 0.7%, and the thickness is 15μm to 35μm.

4. The composite brazing sheet containing multiple diffusion intermediate layers according to claim 1, characterized in that: The second cooperative diffusion intermediate layer is a heat-activated micro-melted island layer, which is composed of an Al-Si-Cu-Ti multi-element eutectic alloy, wherein the Si mass fraction is 5% to 6.5%, the Cu mass fraction is 1% to 2%, the Ti mass fraction is 0.05% to 0.15%, and the thickness is 10μm to 30μm.

5. The composite brazing sheet containing multiple diffusion intermediate layers according to claim 4, characterized in that: When the brazing temperature reaches 630-650° C., a distributed θ-Al 2 Cu + β-Si micro-melting island structure is formed inside the heat-activated micro-melting island layer.

6. The composite brazing sheet containing multiple diffusion intermediate layers according to claim 1, characterized in that: The brazing material layer is an Al-10Si alloy layer with a thickness of 25 μm to 50 μm. The brazing material layer and the second cooperative diffusion intermediate layer form a continuous brazing seam after metallurgical fusion.

7. A process for manufacturing a composite brazing sheet containing multiple diffusion intermediate layers, characterized in that: A composite brazing sheet material containing a multi-layer diffusion intermediate layer as claimed in any one of claims 1 to 6, comprising: Material preparation and surface pretreatment: 3003 or 6061 aluminum alloy with a thickness of 0.3mm to 1.0mm was selected as the core material. The surface of the core material was mechanically drawn and alkaline degreased to obtain a surface roughness of 0.3μm to 0.8μm. Preparation of multi-layer diffusion intermediate layer alloy: the first synergistic diffusion intermediate layer is prepared by direct melting-casting and rolling method, the second synergistic diffusion intermediate layer is prepared by directional rapid solidification method, and the distribution of spheroidization precursor phase is refined by cold rolling; Multi-layer lamination and vacuum packaging: lamination is carried out according to the core material / aluminum-manganese-zinc alloy slab / aluminum-silicon-copper-titanium alloy sheet / Al-10Si alloy layer, and vacuum packaging is carried out. The vacuum degree is higher than 1.0×10-2P a , packaging pressure is controlled at 5~12MPa; Zoned temperature-controlled multi-pass rolling: the encapsulated laminated structure is sent to the zoned temperature-controlled rolling line with three temperature zones: T1 is 320-350°C, T2 is 370-410°C, and T3 is 410-440°C. The total deformation rate is controlled at 40%-55%, the thickness difference of each rolling pass is controlled at ±3%, and the rolling speed is 5-15m / min. Online short-time uniform temperature diffusion: The rolled sheet is subjected to short-time uniform temperature diffusion treatment at a temperature of 470-510°C for 2-6 minutes in a controlled atmosphere of N2+0.5% H2 mixed protective gas. Pre-stabilized θ-Al2Cu and β-Si pre-melted island phase nuclei are formed during the diffusion process. Finished product cooling and straightening: Use air cooling to cool the sheet to room temperature, with a cooling rate greater than 20℃ / s, and control the finished product warpage to ≤0.5mm / 300mm, and the overall thickness deviation of the sheet to ≤±3μm.

8. The manufacturing process of a composite brazing sheet containing a multi-layer diffusion intermediate layer according to claim 7, characterized in that: The method for preparing the thermally activated micro-melting island layer is as follows: Alloy smelting and casting and rolling: Aluminum ingots are used as the base material and melted in a medium frequency induction furnace to a temperature of 740-780°C. Si is first added and, after uniform melting, Al-Cu master alloy and Al-Ti master alloy are added in sequence. After stirring evenly, the melt is refined and degassed for 10-15 minutes. After filtering through a ceramic filter, the melt is cast and rolled into alloy billets with a thickness of 2-5 mm using a horizontal continuous casting and rolling mill. Homogenization treatment: The cast-rolled alloy billet is subjected to homogenization treatment, heated to 520-540°C, kept at this temperature for 6-10 hours, and slowly cooled to room temperature at a cooling rate of 10-15°C / h. A uniform α-Al matrix and dispersed Si-rich and Cu-rich phases are initially formed inside the alloy billet. Multi-pass temperature-controlled rolling: The alloy billet after homogenization treatment is subjected to multi-pass zoned temperature-controlled rolling. The temperature of the first rolling pass is controlled at 420-450°C, the reduction of a single pass is 25%-30%, and the total deformation of the passes is 50%-60%. The temperature of the second rolling pass is controlled at 350-380°C, and the reduction of a single pass is controlled at 15%-20%. Fine particles or island-like clusters are dispersed in the matrix to obtain alloy sheets with a thickness of 10-30μm. Online short-time rapid temperature diffusion treatment: The rolled alloy sheet is superimposed on the composite brazing sheet system, vacuum-encapsulated to form a laminated structure, the laminated structure is heated to 480-520°C, kept warm for 1-3 minutes to form a metastable solid solution structure, and then cooled to room temperature.

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