Composite brazing filler metal with reinforced foamy copper structure and preparation method of composite brazing filler metal

Abstract

The invention discloses composite brazing filler metal with a reinforced foamy copper structure and a preparation method of the composite brazing filler metal. The composite brazing filler metal is prepared by taking foamy copper as a framework and filling pores of the framework with composite powder composed of silver powder and copper-titanium nanoparticles. The composite brazing filler metal comprises, by mass, 1%-5% of titanium, 18%-44% of copper and the balance silver powder and inevitable trace impurities. Weighing silver powder and copper-titanium nanoparticles, and uniformly mixing the silver powder and the copper-titanium nanoparticles to obtain composite powder; filling the composite powder into pores of the foamy copper, compacting the composite powder through vibration or pressing, and pressing to prepare a brazing filler metal preform; and performing low-temperature sintering on the brazing filler metal preform to obtain the composite brazing filler metal. The capillary flow of the liquid alloy in the brazing process is promoted through the porous structure of the foamy copper, the spreadability and the interface reaction efficiency of materials difficult to wet such as ceramic are optimized by combining the uniformly distributed copper-titanium nanoparticles and the silver powder, and the overall strength, plasticity and crack propagation resistance of the composite brazing filler metal are improved.

Description

Technical Field

[0001] This invention relates to a composite solder and its preparation method, specifically to a composite solder reinforced with a foamed copper structure and its preparation method, belonging to the field of metal material joining technology. Background Technology

[0002] Metal joining technology, especially the joining of dissimilar materials such as ceramics to ceramics and ceramics to metals, plays a crucial role in high-end manufacturing fields such as aerospace, electronic information, and new energy equipment. These joining scenarios often place stringent requirements on the uniformity of the brazing filler metal's composition, its activity stability, and its comprehensive mechanical properties. Among these, Ag-Cu-Ti active brazing filler metals, due to their combination of good wettability to ceramics and reliable joining strength to metals, have become one of the most widely used types of brazing filler metals in this field. Currently, the preparation of Ag-Cu-Ti brazing filler metals mainly relies on two technical routes: traditional melting methods and conventional powder mixing methods. Traditional melting methods typically involve melting Ag, Cu, and Ti raw materials at high temperatures and then processing them into foil or filament brazing filler metals, which can meet basic joining requirements in low- to mid-range joining scenarios. Conventional powder brazing filler metals are prepared by mechanically mixing Ag powder, Cu powder, and Ti powder, providing some possibility for flexible adjustment of the brazing filler metal composition and finding applications in some customized joining needs. However, existing technical solutions still have several technical pain points that need optimization in practical applications. On the one hand, for brazing filler metals prepared by traditional smelting methods, Ti has high chemical reactivity and is prone to oxidation by reacting with oxygen in the air during the smelting process. Furthermore, Ti is also prone to segregation within the filler metal due to factors such as the smelting temperature field and cooling rate. This not only results in poor overall uniformity of the filler metal composition but also leads to uneven distribution of its activity, thus affecting the long-term reliability of the joint. On the other hand, in conventionally mechanically mixed powdered brazing filler metals, there is a significant difference in density between Ag powder, Cu powder, and Ti powder. This can easily lead to stratification during storage, transportation, and spreading. Moreover, the oxidizability of Ti powder has not been fundamentally improved. In addition, in conventional powder mixing methods, Ti has low solubility in Ag powder, making it difficult to form a uniformly distributed nanoscale reinforcing phase. This makes it difficult to further improve the mechanical properties of the filler metal, such as toughness and thermal shock resistance. Furthermore, both traditional molten brazing filler metals and conventional powder brazing filler metals are insufficient in terms of capillary flow capability and filling effect on microscopic unevenness of the base material when facing porous base materials or complex-shaped joints, making it difficult to meet the high-precision and high-reliability high-end connection requirements. Summary of the Invention

[0003] The purpose of this invention is to provide a composite brazing filler metal reinforced with a foamed copper structure and its preparation method. This invention promotes capillary flow during brazing through the porous structure of foamed copper, and, combined with uniformly distributed copper-titanium nanoparticles and silver powder, optimizes the spreadability and interfacial reaction efficiency of difficult-to-wet materials such as ceramics, thereby improving the overall strength, plasticity, and crack propagation resistance of the composite brazing filler metal.

[0004] The technical solution of the present invention is a composite solder reinforced with a foamed copper structure. The composite solder is prepared by using foamed copper as a skeleton and filling its pores with a composite powder composed of silver powder and copper-titanium nanoparticles. The mass percentage of each component in the composite solder is as follows: titanium is 1%-5%, copper is 18%-44%, and the balance is silver and unavoidable trace impurities.

[0005] In the aforementioned composite solder reinforced with a foamed copper structure, the titanium content is 2%-4% by mass.

[0006] The aforementioned composite solder with reinforced foamed copper structure has a porosity of 80%-95%.

[0007] The aforementioned composite solder with reinforced copper foam structure has copper-titanium nanoparticles with a particle size of 10-200 nm.

[0008] The aforementioned method for preparing the composite solder reinforced with copper foam structure includes the following steps: weighing silver powder and copper-titanium nanoparticles according to the target component ratio, mixing them uniformly under inert gas or vacuum conditions to obtain composite powder; filling the pores of copper foam with the composite powder, compacting it by vibration or pressing, and then pressing it to form a solder preform; and sintering the solder preform at low temperature in a vacuum or inert atmosphere to obtain the composite solder.

[0009] The aforementioned method for preparing the composite solder with reinforced copper foam structure involves mixing copper-titanium nanoparticles and silver powder in a vacuum environment or inert atmosphere at a stirring speed of 200-400 r / min for 20-40 min to obtain the composite powder.

[0010] In the aforementioned method for preparing composite solder with reinforced copper foam structure, the pressing is performed by cold isostatic pressing.

[0011] In the aforementioned method for preparing composite brazing filler metal with reinforced copper foam structure, the low-temperature sintering temperature is controlled between 580℃ and 620℃.

[0012] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes a structure with foamed copper as the framework and its pores filled with a composite powder composed of silver powder and copper-titanium nanoparticles. On one hand, the copper-titanium nanoparticles, isolated by the silver powder, significantly reduce oxidation and segregation, ensuring uniform release of activity during brazing and laying the foundation for long-term reliability of the joint. On the other hand, the dispersed copper-titanium nanoparticles pin dislocations and refine grains, producing dispersion strengthening and grain refinement effects, achieving a synergistic improvement in brazing alloy strength and toughness. Compared with traditional brazing alloy joints, this results in higher shear strength and less brittle fracture. Furthermore, the porous structure of the foamed copper provides flow channels for the copper-titanium nanoparticles and silver powder during brazing, promoting capillary flow to fully fill microscopic depressions in the base material and reduce voids and incomplete penetration defects. The uniformly distributed copper-titanium nanoparticles also allow titanium to be efficiently enriched at the ceramic / metal interface, reacting with the ceramic to form a stable interfacial bonding layer, significantly improving wettability. This invention also possesses extremely high process flexibility. The pressed brazing filler metal preform has a dense structure, high strength, and is not easily pulverized, making it easy to store, transport, and assemble. It is especially suitable for automated production lines and can ultimately meet the stringent requirements of high-precision and high-reliability connections of dissimilar materials in high-end manufacturing fields such as aerospace, electronic information, and new energy equipment, providing key material support for the upgrading of dissimilar material connection technology. Attached Figure Description

[0013] Figure 1 This is a flowchart of the preparation method of the present invention; Figure 2 This is a schematic diagram of the structure of the brazing filler metal preform of the present invention; Figure 3 This is a bar chart comparing the shear strength of brazed joints in Examples 1-4 and Comparative Examples 1-2; Figure 4 This is a scanning electron microscope image of the brazing seam in Embodiment 1 of the present invention; Figure 5 This is a scanning electron microscope image of the brazing seam in Embodiment 2 of the present invention; Figure 6 This is a scanning electron microscope image of the brazing seam in Embodiment 3 of the present invention; Figure 7 This is a scanning electron microscope image of the brazing seam in Embodiment 4 of the present invention. Detailed Implementation

[0014] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0015] Example 1: Preparation of a composite solder with a target composition of Ag-2.5Ti-23Cu (wt.%), such as... Figure 1 As shown, it includes the following steps: 1. Raw materials and parameters Target composition: Ti (titanium) content is 2.5 wt.%, Cu (copper) content is 23 wt.%, and Ag (silver) is the balance.

[0016] Copper foam parameters: porosity 90%, skeletal density 8.96 g / cm³.

[0017] Active phase raw material: Pre-alloyed CuTi nanoparticles (of which Ti mass fraction is 50%) are selected.

[0018] Silver powder: purity ≥ 99.9%.

[0019] 2. Ingredient Calculation and Weighing First, based on the target Ti content (2.5%) and the stoichiometry of CuTi nanoparticles (Ti accounts for 50%), the required mass of CuTi nanoparticles to account for 5% of the total mass was calculated. This portion of CuTi nanoparticles also incorporates 2.5% Cu.

[0020] Then, the Cu introduced by CuTi nanoparticles (2.5%) is subtracted from the target total Cu content (23%) to obtain the Cu content that needs to be provided by the foamed copper skeleton of 20.5%.

[0021] Finally, based on the porosity (90%) and skeleton density of the copper foam, the required mass of copper foam was precisely calculated, and it was ensured that its pore volume could be filled by the mixed powder of Ag powder and 5% CuTi nanoparticles. The raw materials were weighed according to this calculation.

[0022] 3. Preparation process (1) Mixing: Place the weighed Ag powder and CuTi nanoparticles in a vacuum mixer and mix for 30 minutes at a speed of 300 r / min to ensure that the nanoparticles are uniformly dispersed in the Ag powder.

[0023] (2) Filling: The uniformly mixed composite powder is filled into the three-dimensional interconnected pores of the copper foam through a vibration device to ensure dense filling.

[0024] (3) Molding: The filled foam copper is subjected to cold isostatic pressing at a pressure of 200MPa for 10 minutes to form a sheet-like brazing preform with a thickness of about 1mm.

[0025] (4) Sintering: The formed preform is sintered in a vacuum environment at a temperature of 600℃ for 60 minutes, followed by furnace cooling at a rate of 5℃ / min. The resulting composite brazing filler metal is as follows: Figure 1 As shown. This step aims to increase the strength of the prefabricated structure, making it easier to handle and assemble.

[0026] Example 2: Preparation of a composite solder with a target composition of Ag-1Ti-18Cu (wt.%), comprising the following steps: 1. Raw materials and parameters Target composition: Ti content 1 wt.%, Cu content 18 wt.%, Ag balance.

[0027] Copper foam parameters: porosity 85%, skeletal density 8.96 g / cm³.

[0028] Active phase raw material: Pre-alloyed CuTi nanoparticles (of which Ti mass fraction is 50%) are selected.

[0029] Silver powder: purity ≥ 99.9%.

[0030] 2. Ingredient Calculation and Weighing First, based on the target Ti content (1%) and the stoichiometric ratio of CuTi nanoparticles (Ti accounts for 50%), the required mass of CuTi nanoparticles, representing 2% of the total mass, is calculated. This portion of CuTi nanoparticles also introduces 1% Cu. Then, the Cu (1%) introduced by the CuTi nanoparticles is subtracted from the target total Cu content (18%), yielding a Cu content of 17% that needs to be provided by the copper foam framework. Finally, based on the porosity (85%) and framework density of the copper foam, the required mass of the copper foam is precisely calculated, ensuring that its pore volume is exactly filled by the mixed powder of Ag powder and 2% CuTi nanoparticles. The raw materials are then weighed according to this calculation.

[0031] 3. Preparation process (1) Mixing: Place the weighed Ag powder and CuTi nanoparticles in a vacuum mixer and mix for 30 minutes at a speed of 300 r / min to ensure that the nanoparticles are uniformly dispersed in the Ag powder.

[0032] (2) Filling: The uniformly mixed composite powder is filled into the three-dimensional interconnected pores of the copper foam through a vibration device to ensure dense filling.

[0033] (3) Molding: The filled foam copper is subjected to cold isostatic pressing at a pressure of 180MPa for 10 minutes to form a sheet-like brazing preform with a thickness of about 1mm.

[0034] (4) Sintering: The formed preform is sintered in a vacuum environment at a temperature of 580℃ for 60 minutes, followed by furnace cooling at a rate of 5℃ / min. The resulting composite brazing filler metal is as follows: Figure 1 As shown. This step aims to increase the strength of the prefabricated structure, making it easier to handle and assemble.

[0035] Example 3: Preparation of a composite solder with a target composition of Ag-5Ti-44Cu (wt.%), comprising the following steps: 1. Raw materials and parameters Target composition: Ti content 5 wt.%, Cu content 44 wt.%, Ag balance.

[0036] Copper foam parameters: porosity 85%, skeletal density 8.96 g / cm³.

[0037] Active phase raw material: Pre-alloyed CuTi nanoparticles (of which Ti mass fraction is 50%) are selected.

[0038] Silver powder: purity ≥ 99.9%.

[0039] 2. Ingredient Calculation and Weighing First, based on the target Ti content (5%) and the stoichiometric ratio of CuTi nanoparticles (Ti accounts for 50%), the required mass of CuTi nanoparticles, representing 10% of the total mass, is calculated. This portion of CuTi nanoparticles also introduces 5% Cu. Then, the Cu (5%) introduced by the CuTi nanoparticles is subtracted from the target total Cu content (44%), resulting in a Cu content of 39% that needs to be provided by the copper foam framework. Finally, based on the porosity (85%) and framework density of the copper foam, the required mass of copper foam is precisely calculated, ensuring that its pore volume is exactly filled by the mixed powder of Ag powder and 10% CuTi nanoparticles. The raw materials are then weighed according to this calculation.

[0040] 3. Preparation process (1) Mixing: Place the weighed Ag powder and CuTi nanoparticles in a vacuum mixer and mix for 30 minutes at a speed of 300 r / min to ensure that the nanoparticles are uniformly dispersed in the Ag powder.

[0041] (2) Filling: The uniformly mixed composite powder is filled into the three-dimensional interconnected pores of the copper foam through a vibration device to ensure dense filling.

[0042] (3) Molding: The filled foam copper is subjected to cold isostatic pressing at a pressure of 220MPa for 10 minutes to form a sheet-like brazing preform with a thickness of about 1mm.

[0043] (4) Sintering: The formed preform is sintered in a vacuum environment at a temperature of 620℃ for 60 minutes, followed by furnace cooling at a rate of 5℃ / min. The resulting composite brazing filler metal is as follows: Figure 1 As shown. This step aims to increase the strength of the prefabricated structure, making it easier to handle and assemble.

[0044] Example 4: Preparation of a composite solder with a target composition of Ag-3Ti-34Cu (wt.%), comprising the following steps: 1. Raw materials and parameters Target composition: Ti content 3 wt.%, Cu content 34 wt.%, Ag balance.

[0045] Copper foam parameters: porosity 92%, skeletal density 8.96 g / cm³.

[0046] Active phase raw material: Pre-alloyed CuTi nanoparticles (of which Ti mass fraction is 50%) are selected.

[0047] Silver powder: purity ≥ 99.9%.

[0048] 2. Ingredient Calculation and Weighing First, based on the target Ti content (3%) and the stoichiometric ratio of CuTi nanoparticles (Ti accounting for 50%), the required mass of CuTi nanoparticles, representing 6% of the total mass, was calculated. This portion of CuTi nanoparticles also introduces 3% Cu. Then, the Cu (3%) introduced by the CuTi nanoparticles was subtracted from the target total Cu content (34%), yielding a Cu content of 31% that needs to be provided by the copper foam framework. Finally, based on the porosity (92%) and framework density of the copper foam, the required mass of the copper foam was precisely calculated, ensuring that its pore volume could be precisely filled by the mixed powder of Ag powder and 6% CuTi nanoparticles. The raw materials were weighed according to this calculation.

[0049] 3. Preparation process (1) Mixing: Place the weighed Ag powder and CuTi nanoparticles in a vacuum mixer and mix for 30 minutes at a speed of 300 r / min to ensure that the nanoparticles are uniformly dispersed in the Ag powder.

[0050] (2) Filling: The uniformly mixed composite powder is filled into the three-dimensional interconnected pores of the copper foam through a vibration device to ensure dense filling.

[0051] (3) Molding: The filled foam copper is subjected to cold isostatic pressing at a pressure of 200MPa for 10 minutes to form a sheet-like brazing preform with a thickness of about 1mm.

[0052] (4) Sintering: The formed preform is sintered in a vacuum environment at a temperature of 600℃ for 60 minutes, followed by furnace cooling at a rate of 5℃ / min. The resulting composite brazing filler metal is as follows: Figure 1 As shown. This step aims to increase the strength of the prefabricated structure, making it easier to handle and assemble.

[0053] Comparative Example 1: Preparation of solder with a target composition of Ag-2.5Ti-23Cu (wt.%) using a conventional smelting method, including the following steps: 1. Raw materials and parameters Target composition: Ti content is 2.5 wt.%, Cu content is 23 wt.%, and Ag is the balance.

[0054] Raw materials: Ag powder, Cu powder, and Ti powder with a purity of ≥99.9% are selected.

[0055] 2. Ingredient Calculation and Weighing Based on the target composition of Ag-2.5Ti-23Cu, calculate the mass amounts of Ag powder, Cu powder, and Ti powder, and weigh them accurately for later use.

[0056] 3. Preparation process (1) Melting: Place the weighed Ag powder, Cu powder and Ti powder into a vacuum induction melting furnace, set the melting temperature to 850℃, keep it at that temperature for 20 minutes, and stir continuously during the process to ensure that the components are uniform.

[0057] (2) Casting billet: After the smelting is completed, the molten brazing filler metal is cast into a billet.

[0058] (3) Rolling: The casting billet is processed into foil-shaped brazing filler metal with a thickness of 1 mm through rolling process.

[0059] Comparative Example 2: Preparation of solder with target composition Ag-3Ti-34Cu (wt.%) using pure Ti powder instead of CuTi nanoparticles 1. Raw materials and parameters Target composition: Ti content 3 wt.%, Cu content 34 wt.%, Ag balance.

[0060] Raw materials: Ag powder, Cu powder, and pure Ti powder with a purity of ≥99.9% are selected.

[0061] 2. Ingredient Calculation and Weighing Based on the target composition of Ag-3Ti-34Cu, calculate the mass amounts of Ag powder, Cu powder, and pure Ti powder, and weigh them accurately for later use.

[0062] 3. Preparation process (1) Mixing: Under vacuum conditions, the weighed Ag powder, Cu powder and pure Ti powder are mixed evenly.

[0063] (2) Melting: Place the mixed powder into a vacuum induction melting furnace, set the melting temperature to 1000℃, keep it at that temperature for 20 minutes and stir it evenly.

[0064] (3) Casting billet: After smelting, the molten brazing filler metal is cast into a billet.

[0065] (4) Rolling: The billet is processed into foil-shaped brazing filler metal with a thickness of 1 mm through rolling process.

[0066] All embodiments and comparative examples were subjected to brazing experiments to test the spread area, brazed seam microstructure, joint shear strength, etc. Figure 3 It can be seen that the shear strengths of the brazed joints in Examples 1-4 are 27.21 MPa, 19.3 MPa, 22.2 MPa, and 37.62 MPa, respectively, while the shear strengths of Comparative Example 1 (conventional smelting method) and Comparative Example 2 (pure Ti powder substitution) are 15.63 MPa and 14.33 MPa, respectively. The shear strength of the examples is up to 161% higher than that of the comparative examples, proving the superior strength of the composite brazing alloy of the present invention; the microstructure and spread area of ​​the brazed joint are tested as follows. Figure 4-7 As shown, the spreading area of ​​alumina ceramics in Examples 1-4 increased by an average of 23% compared with Comparative Example 1, and the wettability of Example 4 was significantly improved.

[0067] This invention utilizes a structure with foamed copper as the framework and its pores filled with a composite powder composed of silver powder and copper-titanium nanoparticles. On one hand, the copper-titanium nanoparticles, isolated by the silver powder, significantly reduce oxidation and segregation, ensuring uniform release of activity during brazing and laying the foundation for long-term reliability of the joint. On the other hand, the dispersed copper-titanium nanoparticles pin dislocations and refine grains, producing dispersion strengthening and grain refinement effects, achieving a synergistic improvement in brazing alloy strength and toughness. Compared with traditional brazing alloy joints, this results in higher shear strength and less brittle fracture. Furthermore, the porous structure of the foamed copper provides flow channels for the copper-titanium nanoparticles and silver powder during brazing, promoting capillary flow to fully fill microscopic depressions in the base material and reduce voids and incomplete penetration defects. The uniformly distributed copper-titanium nanoparticles also allow titanium to be efficiently enriched at the ceramic / metal interface, reacting with the ceramic to form a stable interfacial bonding layer, significantly improving wettability. This invention also possesses extremely high process flexibility. The pressed brazing filler metal preform has a dense structure, high strength, and is not easily pulverized, making it easy to store, transport, and assemble. It is especially suitable for automated production lines and can ultimately meet the stringent requirements of high-precision and high-reliability connections of dissimilar materials in high-end manufacturing fields such as aerospace, electronic information, and new energy equipment, providing key material support for the upgrading of dissimilar material connection technology.

[0068] In summary, this invention promotes capillary flow of liquid alloy during brazing through the porous structure of foamed copper, and optimizes the spreadability and interfacial reaction efficiency of difficult-to-wet materials such as ceramics by combining uniformly distributed copper-titanium nanoparticles and silver powder, and improves the overall strength, plasticity and crack propagation resistance of the composite brazing filler metal.

Claims

1. A composite solder reinforced with a foamed copper structure, characterized in that: The composite solder is prepared by using copper foam as a skeleton and filling its pores with a composite powder composed of silver powder and copper-titanium nanoparticles. The mass percentage of each component in the composite solder is as follows: titanium 1%-5%, copper 18%-44%, and the balance is silver powder and unavoidable trace impurities.

2. The composite solder reinforced with foamed copper structure according to claim 1, characterized in that: The mass percentage of titanium is 2%-4%.

3. The composite solder reinforced with foamed copper structure according to claim 1, characterized in that: The porosity of the copper foam is 80%-95%.

4. The composite solder reinforced with foamed copper structure according to claim 1, characterized in that: The copper-titanium nanoparticles have a particle size of 10-200 nm.

5. The method for preparing the composite solder with foamed copper structure reinforcement according to any one of claims 1-4, characterized in that, The process includes the following steps: weighing silver powder and copper-titanium nanoparticles according to the target component ratio, mixing them evenly under inert gas or vacuum conditions to obtain composite powder; filling the pores of foamed copper with the composite powder, making it dense by vibration or pressing, and then pressing it to form a solder preform; and sintering the solder preform at low temperature in a vacuum or inert atmosphere to obtain the composite solder.

6. The method for preparing the composite solder reinforced with foamed copper structure according to claim 5, characterized in that: In a vacuum or inert atmosphere, copper-titanium nanoparticles and silver powder are mixed at a stirring speed of 200-400 r / min for 20-40 min to obtain composite powder.

7. The method for preparing the composite solder reinforced with foamed copper structure according to claim 5, characterized in that: The pressing is cold isostatic pressing.

8. The method for preparing the composite solder reinforced with foamed copper structure according to claim 5, characterized in that: The temperature of the low-temperature sintering is controlled between 580℃ and 620℃.

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