An extrusion method for a silver-based brazing strip

Abstract

A method for extruding silver-based brazing strip includes the following steps: 1) Weighing raw material powder according to the following weight percentages: Cu: 20-28%, Ti: 1-5%, with the balance being Ag; 2) Reducing silver and copper powder in a hydrogen atmosphere at a temperature range of 300-450℃ for 20-30 minutes; 3) Mixing silver, copper, and titanium powder in a ball mill jar under inert gas protection; 4) Pre-pressing and shaping the powder under a pressure of 2-5 MPa for 10-15 seconds; followed by cold isostatic pressing. 5) The blank is obtained by holding the pressure at 180-250 MPa for 30-90 seconds; 6) The blank is sintered at 450℃-650℃ for 30-60 minutes; 7) The blank is placed in an extruder and hot-extruded at 500-650℃ with an extrusion ratio of 5-15 to obtain an alloy long strip; 8) The alloy long strip is continuously hot-rolled in a protective atmosphere at 400-500℃, with each rolling deformation not exceeding 20%, until a strip with a thickness of 0.04-0.05 mm is obtained.

Description

Technical Field

[0001] This invention relates to the field of metal material preparation, and specifically to an extrusion molding method for silver-based brazing strip. Background Technology

[0002] In fields such as electronic packaging, aerospace, and high-temperature power devices, ceramic / metal heterostructures are key components for achieving efficient heat dissipation, reliable insulation, and vacuum sealing. Their core performance lies in achieving a high-strength, highly airtight interface connection between the ceramic and metal, and the quality of this interface connection directly depends on the performance and consistency of the active solder strip used.

[0003] Currently, active brazing filler metals suitable for ceramic bonding are mainly titanium (Ti)-containing silver-copper based alloys. However, producing strips with uniform microstructure, precise thickness, and good flexibility from these alloys faces significant technical challenges. Traditional smelting and rolling processes have inherent drawbacks when preparing high-titanium alloys: titanium readily forms various high-hardness, brittle intermetallic compounds such as CuTi2 and AgTi with matrix elements like copper and silver. These hard and brittle phases easily induce processing brittleness during subsequent hot or cold rolling of ingots, leading to problems such as rolling cracks and edge breakage, significantly reducing yield and making it difficult to achieve the industrial manufacturing of long, stable strips.

[0004] Existing technologies address these issues by employing powder metallurgy. However, when powder metallurgy is applied to complex systems such as silver-copper-molybdenum-nickel-titanium, the following problems still exist:

[0005] 1) Metal powders, especially silver powder and copper powder, inevitably have oxide films on their surfaces, which can become sources of defects in subsequent sintering and rolling processes, severely deteriorating the bonding strength between powders, exacerbating the tendency to crack during rolling, and resulting in low strip ductility and yield.

[0006] 2) The billets obtained by conventional single pressing or sintering processes often have problems with porosity and uneven density, which can easily become crack sources during rolling deformation, directly affecting the stability of the rolling process and the final pass rate of the strip.

[0007] 3) Existing processes are mostly limited to intermittent production in the laboratory, making it difficult to achieve a stable and efficient continuous rolling process. The instability of billet properties and the frequent strip breakage during the rolling process hinder its large-scale industrial application.

[0008] Therefore, there is an urgent need for a preparation process that can systematically improve the quality of billets and enable large-scale production. Summary of the Invention

[0009] To address the aforementioned problems, this invention provides an extrusion molding method for silver-based brazing strips. By controlling the oxide content of the raw materials and employing a stepwise approach of cold isostatic pressing, sintering, and extrusion to increase the density of the blank, the density and uniformity of the blank are significantly improved, thus providing a reliable foundation for the stable preparation and large-scale production of high-quality active brazing strips.

[0010] The technical solution of this invention is: a method for extruding and molding silver-based brazing strip, comprising the following steps:

[0011] 1) Ingredients: Weigh the raw material powder according to the following weight percentages: Cu: 20-28%, Ti: 1-5%, with the balance being Ag;

[0012] 2) Raw material pretreatment: Silver powder and copper powder are reduced in a hydrogen atmosphere at a temperature range of 300℃~450℃ for 20min~30min.

[0013] 3) Mixing: Under inert gas protection, the pretreated silver powder, copper powder and titanium powder are placed in a ball mill jar for mixing;

[0014] 4) Molding; The mixed powder is loaded into the molding mold of the hydraulic press and pre-pressed under a pressure of 2-5 MPa for 10-15 seconds; then a cold isostatic press is used for cold isostatic pressing at a pressure of 180-250 MPa for 30-90 seconds to obtain the blank.

[0015] 5) Sintering; The billet is sintered under vacuum or protective atmosphere at a temperature of 450℃~650℃ for 30min~60min.

[0016] 6) Extrusion; The sintered billet is placed in an extruder and hot-extruded at a temperature range of 500℃ to 650℃, with the extrusion ratio controlled at 5 to 15, to obtain alloy long strips;

[0017] 7) Hot rolling: Under a protective atmosphere of 400℃~500℃, the alloy strip is continuously hot rolled, with the deformation amount in each rolling pass not exceeding 20%, until a strip with a thickness of 0.04mm~0.05mm is obtained.

[0018] Preferably, in step 1), the ingredients may optionally include Mo and / or Ni.

[0019] Preferably, the weight percentage of Mo is 0.5-2% and the weight percentage of Ni is 5-10%.

[0020] Preferably, in step 1), the particle size range of the raw material powder is 250 mesh to 500 mesh, and the purity is not less than 99.9%.

[0021] Preferably, in step 2), the silver powder and copper powder are both sieved through a 250-mesh sieve after reduction.

[0022] Preferably, in step 3), copper balls are added during mixing, and the ratio of the weight of the raw material to the weight of the copper balls is 1:0.5 to 1.

[0023] Preferably, in step 7), the deformation amount of the first rolling pass is less than 15%.

[0024] Preferably, the method further includes the following steps:

[0025] 8) Annealing: The hot-rolled strip is annealed in a vacuum or protective atmosphere at a temperature of 450-480℃.

[0026] 9) Surface treatment; use a soft brush to polish the surface of the strip to remove surface impurities.

[0027] The advantages of this invention are:

[0028] 1. This invention employs a combined process of hydraulic press pre-pressing and cold isostatic pressing, effectively reducing internal porosity and density gradient in the billet. Subsequent sintering and high-temperature extrusion processes further enhance rheological densification and compositional homogenization. This gradual increase in density through cold isostatic pressing-sintering-extrusion, compared to the method of repeatedly pressing with a hydraulic press (which is prone to cracking during subsequent rolling), results in higher billet homogenization, significantly reducing the risk of cracking due to internal defects during rolling and greatly improving the rolling yield.

[0029] 2. This invention purifies the raw material powder through hydrogen reduction pretreatment. The billet prepared by this invention possesses excellent and consistent plastic deformation capacity, effectively improving the rollability and production qualification rate of the strip. Examples show that the rolling yield can reach over 94%, far exceeding the comparative example, demonstrating the method's effect on improving forming stability and production qualification rate.

[0030] 3. The method described in this invention has less stringent requirements on the particle size of the raw material powder, which can be purchased directly. Continuous alloy strips are obtained through extrusion. Compared to the existing technology of hot-rolling individual billets after sintering, the continuous alloy strips of this application make the hot rolling process seamless and easier to scale up production. Compared to special processes such as rapid solidification and sputtering coating, equipment investment and manufacturing costs are significantly reduced, resulting in extremely high cost-effectiveness and market competitiveness. Attached Figure Description

[0031] Figure 1 This is a flowchart of the present invention;

[0032] Figure 2 These are physical images of embodiments of the present invention;

[0033] Figure 3 This is a graph showing the melting point test results of Embodiment 1 of the present invention;

[0034] Figure 4 This is a graph showing the melting point test results of Embodiment 2 of the present invention;

[0035] Figure 5 This is a graph showing the melting point test results of Embodiment 3 of the present invention;

[0036] Figure 6 This is a cracking diagram during the rolling process of a comparative embodiment of the present invention. Detailed Implementation

[0037] See Figures 1 to 6 A method for extruding silver-based brazing strip includes the following steps:

[0038] 1) Ingredients: Weigh the raw material powder according to the following weight percentages: Cu: 20-28%, Ti: 1-5%, and optionally add Mo and / or Ni: Mo: 0.5-2%, Ni: 5-10%, with the balance being Ag; The particle size range of the raw material powder is 250 mesh to 500 mesh, and the purity is not less than 99.9%. The particle size requirement of the raw material powder is lenient, making it easy to prepare or to purchase directly.

[0039] 2) Raw material pretreatment: Silver and copper powders are reduced in a hydrogen atmosphere at a temperature range of 300℃ to 450℃ for 20 to 30 minutes. Reduction of the silver and copper powders removes the surface oxide film, preventing deterioration of the powder bonding strength during subsequent sintering and rolling, which could exacerbate rolling cracking and lead to low strip ductility and yield. After reduction, the silver and copper powders are sieved through a 250-mesh sieve to prevent agglomeration and improve their purity, thus enhancing subsequent processing performance.

[0040] 3) Mixing: Under inert gas protection, pretreated silver powder, copper powder and titanium powder are placed in a ball mill jar for mixing. Copper balls are added during mixing, and the ratio of raw material weight to copper ball weight is 1:0.5~1.

[0041] 4) Molding; The mixed powder is loaded into the molding mold of the hydraulic press and pre-pressed under a pressure of 2-5 MPa for 10-15 seconds; then a cold isostatic press is used for cold isostatic pressing at a pressure of 180-250 MPa for 30-90 seconds to obtain the blank.

[0042] 5) Sintering; sinter the billet under vacuum or a protective atmosphere at a temperature of 450℃~650℃ for 30min~60min; ensure that the density of the billet after sintering is higher than 80%.

[0043] 6) Extrusion; The sintered billet is placed in an extruder and hot-extruded at a temperature range of 500℃ to 650℃, with the extrusion ratio controlled at 5 to 15, to obtain alloy long strips; the density of the alloy long strips is guaranteed to be higher than 92%;

[0044] 7) Hot rolling: Under a protective atmosphere of 400℃~500℃, the alloy long strip is continuously hot rolled, wherein the deformation of the first rolling pass is less than 15%, and the deformation of each rolling pass is not greater than 20% to avoid rolling cracks, until a strip with a thickness of 0.04mm~0.05mm is obtained.

[0045] 8) Annealing: The hot-rolled strip is annealed in a vacuum or protective atmosphere at a temperature of 450-480℃.

[0046] 9) Surface treatment; use a soft brush to polish the surface of the strip to remove surface impurities.

[0047] Example 1: Preparation of AgCu 28 Ti2 solder strip:

[0048] 1) Ingredients: Weigh out 1.5 kg of copper powder, 4 kg of silver powder, and 0.15 kg of titanium powder respectively.

[0049] 2) Raw material pretreatment: Silver powder and copper powder were placed in a hydrogen roasting furnace for reduction. The roasting temperature was 350℃, the hydrogen flow rate was 5L / min, and the temperature was maintained for 20min. After being taken out of the furnace, they were both passed through a 250-mesh sieve.

[0050] 3) Mixing: Weigh 1.4 kg of reduced and sieved copper powder and 3.5 kg of silver powder, and then put them together with 0.1 kg of titanium powder into a copper ball mill jar for mixing. Add copper balls during mixing, rotate at 90 r / min, mix for 24 h, and the material:ball ratio (by weight) = 1:0.5. Argon gas is introduced for protection.

[0051] 4) Molding: After ball milling, the powder is placed in a rectangular metal mold and shaped using a 500T hydraulic press at a pressure of 5MPa for 15s. After demolding, the powder is removed. Then, the shaped blank is placed into a rectangular rubber mold and cold isostatically pressed using a cold isostatic press at a pressure of 225MPa for 60s to obtain the blank.

[0052] 5) Sintering: The formed billet was placed in a high-temperature chamber and sintered under argon protection at a temperature of 650℃ for 30 minutes, with the temperature increased and decreased during furnace heating and cooling. The density after sintering was measured to be 85.8%.

[0053] 6) Extrusion: The sintered billet is placed in an 800T extruder and extruded at 650℃ with an extrusion ratio of 12 to produce a 25mm×5mm alloy strip. The density after extrusion is measured to be 96.4%.

[0054] 7) Hot Continuous Rolling: The two ends of the extruded alloy strip are connected to iron strips of similar specifications and placed in a mesh belt reduction furnace. During rolling, an argon atmosphere is introduced, and the iron strip is used as traction to slowly pass through a four-high rolling mill at 450°C for continuous hot rolling. The holding time for the first pass is 30 minutes, and the deformation is 8.6%. The deformation of the remaining passes is controlled to be no more than 20%, and the holding time is controlled to be 20 minutes. After multiple passes of rolling, a strip with a thickness of 0.05 mm is obtained.

[0055] 8) Annealing: Annealing is performed under an argon atmosphere at a temperature of 480℃ for 1 hour.

[0056] 9) Surface treatment: Use a soft brush to polish the surface of the strip to remove surface impurities.

[0057] AgCu obtained using the method of this embodiment 28 Ti2 brazing filler strip, after pressing-isostatic pressing-extrusion, achieves a density of 96.4% and a melting point of 755.6℃. No fractures due to internal defects in the billet occurred during the rolling process. The rolling yield was approximately 96.5% (weight of qualified strip / weight of feed material) based on weighing calculations.

[0058] Example 2: Preparation of AgCu 28 Ni8Ti2 solder strip:

[0059] 1) Ingredients: Weigh out 1.5kg of copper powder, 3.5kg of silver powder, 0.15kg of titanium powder, and 0.4kg of nickel powder respectively;

[0060] 2) Raw material pretreatment: Silver powder and copper powder were placed in a hydrogen roasting furnace for reduction. The roasting temperature was 350℃, the hydrogen flow rate was 5L / min, and the temperature was maintained for 20min. After being taken out of the furnace, they were both passed through a 250-mesh sieve.

[0061] 3) Mixing: Weigh 1.4 kg of reduced and sieved copper powder and 3.1 kg of silver powder, and then mix them together with 0.1 kg of titanium powder and 0.4 kg of nickel powder in a copper ball mill jar. Add copper balls during mixing, rotate at 90 r / min, mix for 24 hours, and the material:ball ratio (by weight) = 1:0.5. Argon gas is introduced for protection.

[0062] 4) Molding: After ball milling, the powder is placed in a rectangular metal mold and shaped using a 500T hydraulic press at a pressure of 5MPa and a holding time of 12s. After demolding, the powder is removed. Then, the shaped blank is loaded into a rectangular rubber mold and cold isostatically pressed using a cold isostatic press at a pressure of 235MPa and a holding time of 60s to obtain the blank.

[0063] 5) Sintering: The formed billet was placed in a high-temperature chamber and sintered under argon protection at a temperature of 600℃ for 30 minutes, with the temperature increased and decreased in the furnace. The density after sintering was measured to be 86.5%.

[0064] 6) Extrusion: The sintered billet was placed in an 800T extruder and extruded at 620℃ with an extrusion ratio of 12 to produce a 25mm × 5mm alloy strip. The density after extrusion was measured to be 95.8%.

[0065] 7) Hot Continuous Rolling: The two ends of the extruded alloy strip are connected to iron strips of similar specifications and placed in a mesh belt reduction furnace. During rolling, an argon atmosphere is introduced, and the iron strip is used as traction to slowly pass through a four-high rolling mill at 450°C for continuous hot rolling. The holding time for the first pass is 30 minutes, and the deformation is 7.4%. The deformation of the remaining passes is controlled to be no more than 20%, and the holding time is controlled to be 20 minutes. After multiple passes of rolling, a strip with a thickness of 0.045 mm is obtained.

[0066] 8) Annealing: Annealing is performed under an argon atmosphere at a temperature of 450℃ for 1 hour.

[0067] 9) Surface treatment: Polish and grind the surface of the hot-rolled strip with a soft brush to remove surface impurities;

[0068] AgCu obtained using the method of this embodiment 28 The Ni8Ti2 brazing filler strip achieves a density of 95.8% after pressing, isostatic pressing, and extrusion, with a melting point of 713.6℃. No fractures due to internal defects in the billet occurred during the rolling process. The rolling yield (weight of qualified strip / weight of feed material) was approximately 95.7% based on weighing calculations.

[0069] Example 3: Preparation of AgCu 28 Mo1Ni8Ti2 solder strip:

[0070] 1) Ingredients: Weigh out 1.5kg copper powder, 3.5kg silver powder, 0.15kg titanium powder, 0.4kg nickel powder, and 0.1kg molybdenum powder respectively;

[0071] 2) Raw material pretreatment: Silver powder and copper powder were placed in a hydrogen roasting furnace for reduction. The roasting temperature was 350℃, the hydrogen flow rate was 5L / min, and the temperature was maintained for 20min. After being taken out of the furnace, they were both passed through a 250-mesh sieve.

[0072] 3) Mixing: Weigh 1.4 kg of reduced and sieved copper powder and 3.05 kg of silver powder, and then mix them together with 0.1 kg of titanium powder, 0.4 kg of nickel powder and 0.05 kg of molybdenum powder in a copper ball mill jar. Add copper balls during mixing, rotate at 90 r / min, mix for 24 hours, and the material:ball ratio (by weight) = 1:0.5. Argon gas is introduced for protection.

[0073] 4) Molding: After ball milling, the powder is placed in a rectangular metal mold and shaped using a 500T hydraulic press at a pressure of 5MPa and a holding time of 12s. After demolding, the powder is removed. Then, the shaped blank is loaded into a rectangular rubber mold and cold isostatically pressed using a cold isostatic press at a pressure of 233MPa and a holding time of 60s to obtain the blank.

[0074] 5) Sintering: The formed billet was placed in a high-temperature chamber and sintered under argon protection at a temperature of 600℃ for 30 minutes, with the temperature increased and decreased in the furnace. The density after sintering was measured to be 81.2%.

[0075] 6) Extrusion: The sintered billet is placed in an 800T extruder and extruded at 600℃ with an extrusion ratio of 12 to produce a 25mm × 5mm alloy strip. The density after extrusion is measured to be 95.5%.

[0076] 7) Hot Continuous Rolling: The two ends of the extruded alloy strip are connected to iron strips of similar specifications and placed in a mesh belt reduction furnace. During rolling, an argon atmosphere is introduced, and the iron strip is used as traction to slowly pass through a four-high rolling mill at 450°C for continuous hot rolling. The holding time for the first pass is 30 minutes, and the deformation is 6.5%. The deformation of the remaining passes is controlled to be no more than 20%, and the holding time is controlled to be 20 minutes. After multiple passes of rolling, a strip with a thickness of 0.05 mm is obtained.

[0077] 8) Annealing: Annealing is performed under an argon atmosphere at a temperature of 450℃ for 1 hour.

[0078] 9) Surface treatment: Use a soft brush to polish and grind the surface of the hot-rolled strip to remove surface impurities.

[0079] AgCu obtained using the method of this embodiment 28The Mo1Ni8Ti2 brazing filler strip achieves a density of 95.5% after pressing, isostatic pressing, and extrusion, with a melting point of 719.0℃. No fractures due to internal defects in the billet occurred during the rolling process. The rolling yield was approximately 94.6% (weight of qualified strip / weight of feed material) based on weighing calculations.

[0080] Comparative Example 1: This comparative example uses AgCu 28 The preparation of Mo1Ni8Ti2 solder is explained:

[0081] In contrast, instead of using the multi-stage densification process of this invention, a hydraulic press is used for unidirectional pressing followed by sintering, and then rolling with the same parameters.

[0082] Blank density: The relative density of the sintered blank after unidirectional pressing is approximately 79.8%.

[0083] Rolling yield: During the rolling process, large-area cracking can occur due to uneven porosity and density within the billet. Figure 6 Since continuous rolling cannot be completed, the yield cannot be calculated.

[0084] The sintering density, extrusion density, rolling yield, and melting point of the alloy powders in Examples 1, 2, 3, and Comparative Example 1 are shown in the table below.

[0085]

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for extruding silver-based brazing strip, characterized in that, Includes the following steps: 1) Ingredients: Weigh the raw material powder according to the following weight percentages: Cu: 20-28%, Ti: 1-5%, balance Ag; the particle size range of the raw material powder is 250 mesh to 500 mesh, and the purity is not less than 99.9%. Add Mo and Ni, wherein the weight percentage of Mo is 0.5-2% and the weight percentage of Ni is 5-10%. 2) Raw material pretreatment: Silver powder and copper powder are reduced in a hydrogen atmosphere at a temperature range of 300℃~450℃ for 20min~30min; after reduction, the silver powder and copper powder are sieved through a 250-mesh sieve. 3) Mixing: Under inert gas protection, the pretreated silver powder, copper powder and titanium powder are placed in a ball mill jar for mixing; 4) Molding; The mixed powder is loaded into the molding mold of the hydraulic press and pre-pressed under a pressure of 2-5 MPa for 10-15 seconds; then a cold isostatic press is used for cold isostatic pressing at a pressure of 180-250 MPa for 30-90 seconds to obtain the blank. 5) Sintering; The billet is sintered under vacuum or protective atmosphere at a temperature of 450℃~650℃ for 30min~60min. 6) Extrusion; The sintered billet is placed in an extruder and hot-extruded at a temperature range of 500℃ to 650℃, with the extrusion ratio controlled at 5 to 15, to obtain alloy long strips. 7) Hot continuous rolling; Under a protective atmosphere of 400℃~500℃, the alloy long strip is continuously hot rolled, with the deformation amount in each rolling pass not exceeding 20%, until a strip with a thickness of 0.04mm~0.05mm is obtained. 8) Annealing: The hot-rolled strip is annealed in a vacuum or protective atmosphere at a temperature of 450-480℃. 9) Surface treatment; use a soft brush to polish the surface of the strip to remove surface impurities.

2. The method according to claim 1, characterized in that: In step 3), copper balls are added during mixing, with the ratio of raw material weight to copper ball weight being 1:0.5 to 1.

3. The method according to claim 1, characterized in that: In step 7), the deformation amount of the first rolling pass is less than 15%.

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