Silver-based multi-element near-eutectic medium-temperature vacuum brazing filler metal and preparation method thereof

Abstract

The invention relates to silver-based multi-element near-eutectic medium-temperature vacuum brazing filler metal and a preparation method thereof, and belongs to the field of non-ferrous metal brazing. The brazing filler metal is prepared from the following components in percentage by weight: 19.5 to 21.0 weight percent of Cu, 9.0 to 10.0 weight percent of In, 4.5 to 5.5 weight percent of Ge, 4.2 to 4.8 weight percent of Sn, 1.8 to 2.2 weight percent of Ni, 1.7 to 2.0 weight percent of Si, 0.05 to 0.2 weight percent of Co and the balance of Ag. The preparation method comprises the steps of intermediate alloy preparation, vacuum medium-frequency induction melting, centrifugal rapid cooling casting, vacuum heat treatment regulation and control, hot rolling cogging, surface treatment and precise cold rolling. The alloy is low in melting point, low in required vacuum brazing temperature, excellent in wetting characteristic for stainless steel, high in joint strength after brazing and capable of meeting the requirements for medium-temperature vacuum brazing packaging, gradient brazing and repair welding of 316L stainless steel base materials in vacuum electronic devices.

Description

Technical Field

[0001] The invention relates to a silver-based multi-element near-eutectic medium-temperature vacuum solder and a preparation method thereof, which mainly solves the problem of medium-temperature vacuum brazing of a 316L stainless steel substrate in vacuum electronic devices and belongs to the field of nonferrous metal brazing. Background Art

[0002] Vacuum electronic devices are devices for transmitting and converting light or electrical signals (energy). They are widely used in key areas such as national defense industry, power grid energy, medical science, etc. Vacuum electronic devices are components made of many metal and non-metal materials connected by welding methods. Since the device needs to maintain an ultra-high vacuum for a long time when working, it has high standard requirements for the physical properties of brazing packaging materials. Silver solder has high physical properties such as thermal conductivity and electrical conductivity, and its brazing performance is very excellent. It has always been the main packaging material in the field of vacuum electronic device manufacturing. Common silver solder is mainly Ag-28Cu eutectic alloy. The solid-liquid phase temperature of this solder is 779℃, and it has good brazing properties for metals such as copper and nickel. With the complexity of device shapes and the diversification of application environments, some structures in vacuum electronic devices require materials such as Kovar and stainless steel. Secondly, the structure needs graded brazing, which involves silver-based solders with different melting points and different brazing temperatures. Currently, the mature silver-based solders are mainly AgCuPd series (810-900℃), AgCuNi series (780-830℃), AgCuIn series (600-710℃), AgCuSn series (630-720℃), etc. There is basically no mature silver-based medium-temperature solder products with a melting point below 600℃ and a brazing temperature below 630℃.

[0003] 316L stainless steel has excellent corrosion resistance and is widely used in aerospace, radar electronics, new energy and other fields. 316L stainless steel has become the preferred material for key parts of vacuum electronic devices, but 316L stainless steel contains a high content of Cr (16.00-18.00wt%), a small amount of Mo (2.00-3.00wt%) and a trace amount of Ti elements, and has a complex oxide film (TiOx, Cr2O3, MoO) on its surface. When using silver-based solder for vacuum brazing, it often needs to exceed 900℃. Common silver-based medium-temperature solders such as AgCuIn28-10, AgCuSn30-10, AgCuInSn22-13-7 cannot wet 316L stainless steel in a vacuum environment below 700℃, resulting in metallurgical results. The AgCuInSnNi series solders reported in the literature can wet 316L stainless steel to a certain extent at 700℃, but the metallurgical bonding is weak and the brazed joint strength is less than 80MPa; AgCuGeSnNi24-25-4-0.1 solder can braze 316L stainless steel at 680℃ in a vacuum environment, but the material has very poor plasticity due to the 25wt% Ge content, and foil strips can basically not be processed. Secondly, the presence of a large amount of Ge causes the joint strength to be less than 100MPa, and the material vapor pressure is high, which cannot meet the needs of vacuum electronic devices. Other silver-based medium-temperature solders such as AgCuZn cannot be used in a vacuum environment.

[0004] In summary, the surface of 316L stainless steel is mainly composed of oxide films containing Cr, Mo, and Ti. The mechanism of metallurgical action is basically to break the oxide film on the surface of 316L stainless steel T, and form a metallurgical reaction with basic Fe, Ni, Cr and other elements to form a bonding layer. First of all, considering the application scenarios and costs of vacuum electronic devices, and the solid phase temperature of the first-level brazing filler metal of vacuum electronic devices is 680℃, the brazing temperature of the designed brazing filler metal is required to be lower than 650℃. Secondly, vacuum electronic devices need to be baked at 500℃ for a long time, and the melting point of the brazing filler metal needs to be higher than 530℃. Therefore, the melting point of the brazing filler metal needs to be designed between 550 and 600℃, preferably eutectic solder. Summary of the invention

[0005] Therefore, in response to the above technical problems, the present invention designs and develops a medium-temperature high-strength silver-based alloy vacuum solder with a melting point between 550 and 600°C and a brazing temperature of about 630°C, which has good metallurgical effect on medium-temperature vacuum brazing of 316L stainless steel, and can meet the high reliability requirements, high strength, good airtightness requirements of vacuum electronic device connections, as well as the service needs of long-term baking.

[0006] The main purpose of the present invention is to provide a silver-based multi-element near-eutectic medium-temperature vacuum solder. The alloy eutectic melting point is 552-562°C, and the recommended brazing temperature is 630°C (316L stainless steel). It mainly solves the medium-temperature vacuum brazing packaging of 316L stainless steel in vacuum electronic devices, and has the advantages of high strength after welding, low vapor pressure, good airtightness, etc., and has excellent wettability on Cu, Ni, Kovar alloy and other stainless steel substrates.

[0007] Another object of the present invention is to provide a method for preparing a silver-based multi-element near-eutectic medium-temperature vacuum solder. The preparation method and process flow solve the problem of forming brittle silver-based medium-temperature alloy materials, and can prepare ultra-thin foil strips that meet industrial needs. The prepared foil strips have uniform alloy composition, consistent grain orientation, fine IMC, clean surface, high yield rate, and can be processed into any preformed products, meeting the multi-level packaging requirements of vacuum electronic devices for vacuum solder.

[0008] To achieve the above object, the present invention adopts the following design scheme:

[0009] A silver-based multi-element near-eutectic medium-temperature vacuum solder comprises, by weight percentage, 19.5-21.0wt% Cu, 9.0-10.0wt% In, 4.5-5.5wt% Ge, 4.2-4.8wt% Sn, 1.8-2.2wt% Ni, 1.7-2.0wt% Si, 0.05-0.2wt% Co, and the balance being Ag.

[0010] The silver-based multi-element near-eutectic medium-temperature vacuum solder has a near-eutectic melting point of 552-562°C.

[0011] The innovation of the present invention is mainly to design a medium-low temperature and high-strength silver-based alloy vacuum solder that meets the requirements of medium-temperature vacuum brazing of 316L stainless steel. The main design idea is based on the Ag-28Cu eutectic, and by eliminating high vapor pressure elements such as Zn, Cd, Ga, etc., In, Sn, Ge and other melting point reducing elements are selectively added. Through the study of silver-based medium-temperature solders such as AgCuInSn, AgCuGeSnNi, etc., it is found that when the In element is added in excess of 10%, the alloy will have a low melting point phase of 480-490°C, so the In content is controlled within 10%, and the addition of In is beneficial to increasing the wetting power of the brazing material under vacuum; the design addition of the Ge element can not only play a melting point reducing role, but also be beneficial to the alloy in a vacuum environment to break the oxide film on the surface of the 316L stainless steel, but the solid solubility of Ge in the Cu element is limited, and when it exceeds 10%, a large amount of intermetallic compounds will precipitate, affecting the plasticity of the alloy. Further experiments have found that when the Ge element is 4.5-5.5wt%, it is guaranteed to exist in the form of Cu solid solution, and also to ensure an effective film breaking effect during the brazing process. Sn element is designed to be added to further reduce the melting point of the alloy. In order to avoid the large-scale appearance of CuSn intermetallic compounds that affect the alloy plasticity and the precipitation of low-melting-point phases, it needs to be controlled within 5.0wt%. In order to achieve better metallurgical effects on 316L stainless steel and avoid the large-scale production of CuTi intermetallic compounds at the reaction interface, Ni element is designed to be added. Ni element can preferentially participate in metallurgical effects and generate Ni-based solid solutions at the interface, which can also play a role in refining grains. Si is a reducing element in the flux. A small amount of Si can reduce Cr2O3, and its vapor pressure is lower than that of Li. In order to improve the brazing activity and wettability of the alloy (for stainless steel), and to form Ni3Si strengthening phase during brazing and improve the strength of the brazing material, Si addition should be 1.7-2.0wt%. Considering that the strength of the brazing material itself determines the strength of the intermediate layer of the weld, by screening and designing the addition of trace Co elements, the grains can be further refined and the high-temperature service performance of the brazing material can be improved to ensure that the performance of the alloy material does not decrease when it is baked for a long time. However, the addition of Co content will increase the melting point, so the content needs to be controlled at 0.05-0.2wt%. The study also found that when the Cu content is high, the Cu element diffuses into the 316L substrate during brazing, which will cause intergranular corrosion problems. When the Cu content is low, the metallurgical effect decreases. Therefore, the Cu content needs to be strictly controlled at 19.5-21.0wt% to ensure the existence of solid solution in the alloy and avoid the formation of intermetallic compounds.

[0012] A method for preparing a silver-based multi-element near-eutectic medium-temperature vacuum solder material, the method comprising the following steps:

[0013] (1) Raw material selection and master alloy preparation

[0014] According to the composition of the silver-based multi-element near-eutectic medium-temperature vacuum solder, Ag, Cu, In, Ge, Sn, Ni, Si and Co are used as raw materials;

[0015] Ag-In master alloy, Cu-Sn master alloy, Cu-Ge master alloy, Cu-Ni master alloy, Cu-Si master alloy and Cu-Co master alloy were prepared by vacuum medium frequency induction melting.

[0016] (2) Vacuum medium frequency induction melting

[0017] The master alloy prepared in step (1) is subjected to the weight percentage of each element in the silver-based multi-element near-eutectic medium-temperature vacuum solder to calculate the weight of each element and the weight of the master alloy; a vacuum induction melting furnace is used to put all the weighed pure Ag, pure Cu and the master alloy into an alumina crucible, the lid is closed, and the furnace is evacuated; heating is turned on, and when the initial liquid phase is seen from the observation port, high-purity argon gas is filled in, and heating is continued until all of the liquid is molten, and the power is reduced to perform refining;

[0018] (3) Centrifugal rapid cooling casting

[0019] The molten alloy melt obtained in step (2) is cast by centrifugal rapid cooling, and the melt is filled into a horizontal graphite casting mold by rotating centrifugal force to obtain an alloy slab with uniform composition;

[0020] (4) Vacuum heat treatment to control crystal orientation

[0021] The alloy slab obtained in step (3) is subjected to crystal orientation control in a high vacuum heat treatment furnace to obtain an alloy ingot with uniform grain orientation;

[0022] (5) Precision rolling

[0023] The alloy ingot obtained in step (4) is subjected to rough rolling on a hot rolling mill to obtain a strip material, which is then rolled into a coil; the strip material is double-sided polished to a bright silver color; and a cold rolling mill is used to perform multiple cold rolling processes until a foil material is obtained, which is then rolled into a coil.

[0024] In step (1), when selecting raw materials, Ag, Cu, In, Ge, Sn, Ni, Si and Co raw materials are all high-purity, with a purity of 99.999% (wt.%).

[0025] In step (1), a vacuum medium-frequency induction melting method is adopted to prepare Ag-20In master alloy, Cu-50Sn master alloy, Cu-40Ge master alloy, Cu-20Ni master alloy, Cu-20Si master alloy and Cu-10Co master alloy respectively; wherein the content of In in the Ag-In master alloy is 20wt%, and the balance is Ag; the content of Sn in the Cu-Sn master alloy is 50wt%, and the balance is Cu; the content of Ge in the Cu-Ge master alloy is 40wt%, and the balance is Sb; the content of Ni in the Cu-Ni master alloy is 20wt%, and the balance is Cu; the content of Si in the Cu-Si master alloy is 20wt%, and the balance is Cu; the content of Co in the Cu-Co master alloy is 10wt%, and the balance is Cu.

[0026] In step (2), the smelting method is vacuum medium frequency induction smelting, the refining temperature is 650-700°C, and the refining time is 5-10 minutes. When performing vacuum smelting, the furnace is evacuated to 10 -2 Pa; the heating power is 20-30kw; after filling with high-purity argon, the vacuum in the furnace is 0.8MPa.

[0027] In step (3), the casting method is centrifugal pressure rapid cooling casting, the centrifugal casting temperature is 650-700°C, and the centrifugal speed is 500-1000n / min. The thickness of the alloy slab is 10-15mm, and the width is 80-250mm.

[0028] In step (4), vacuum heat treatment is used to adjust the crystal orientation of the structure, and the vacuum degree is <5.0×10 -3 Pa, temperature is 520~530℃, and holding time is 12~16h.

[0029] In step (5), the hot rolling mill is a 250 two-roller reversible hot rolling mill, the rolling mill roll temperature is 420-450°C, and the hot rolling pass processing rate is 5%-10%; the cold rolling mill is a 50-type four-roller reversible cold rolling mill, the intermediate vacuum annealing temperature is 480-500°C, and the vacuum degree is 10 -2 Pa, the processing rate of each cold rolling pass in the annealing interval is 15% to 30%, and the tension is 0 to 10 kN.

[0030] In step (5), the strip material has a thickness of 0.8 to 1.0 mm and a width of 80 to 250 mm; the foil material has a thickness of 0.05 to 0.1 mm and a width of 80 to 250 mm.

[0031] The alloy composition of the solder of the present invention and the silver-based multi-element near-eutectic medium-temperature vacuum solder foil strip prepared by the above-mentioned preparation method, the solder alloy is a near-eutectic melting point of 552-562°C, and the recommended brazing temperature is 630°C (316L stainless steel). It mainly solves the medium-temperature vacuum brazing packaging of 316L stainless steel in vacuum electronic devices, and has the advantages of high strength, low vapor pressure, good air tightness after welding, and has excellent wettability on Cu, Ni, Kovar alloy and other stainless steel substrates. It meets the multi-level packaging requirements of complex structures of vacuum electronic devices. The preparation method is "intermediate alloy preparation + vacuum medium-frequency induction melting + centrifugal pressure rapid cooling casting + vacuum heat treatment to control crystal orientation + hot rolling blanking + surface polishing + precision cold rolling". This processing flow solves the problems of segregation of silver-based multi-element alloy components, coarse grains, inconsistent crystal orientation, etc. From the perspective of component design and processing path, it inhibits the growth of brittle compounds, controls the consistency of grain orientation during phase nucleation, etc., and is suitable for stable batch production. The preparation method can obtain foil strips with uniform alloy composition, consistent grain orientation, fine IMC, clean surface, high yield rate, and can be processed into any preformed products, thus meeting the multi-level packaging requirements of vacuum electronic devices for vacuum solder.

[0032] Advantages of the present invention:

[0033] 1. The silver-based multi-element near-eutectic medium-temperature vacuum solder manufactured by the method of the present invention mainly solves the medium-temperature vacuum brazing packaging of 316L stainless steel in vacuum electronic devices, and has the advantages of high strength after welding, low vapor pressure, good air tightness, etc.

[0034] 2. The silver-based multi-element near-eutectic medium-temperature vacuum solder manufactured by the method of the present invention has a low melting point of 552-562°C, a short melting range, and is close to the eutectic.

[0035] 3. The silver-based multi-element near-eutectic medium-temperature vacuum solder manufactured by the method of the present invention has excellent brazing processability, good wettability and high strength, and has excellent wettability for Cu, Ni, Kovar alloy and stainless steel substrates.

[0036] 4. The silver-based multi-element near-eutectic medium-temperature vacuum solder manufactured by the method of the present invention can achieve interfacial metallurgical bonding with 316L stainless steel at a relatively low brazing temperature, and the reaction layer is dense and has high strength after welding. Compared with gold-based and aluminum-based solders in the same temperature range, it has more practical application value.

[0037] 5. The processing and preparation process of the method of the present invention is novel, which fundamentally solves the problems of macroscopic component segregation, coarse grains, inconsistent crystal orientation, etc. caused by more elements in multi-element alloys, inhibits the growth of brittle compounds, controls the consistency of grain orientation during phase nucleation, etc., and is suitable for stable batch production.

[0038] 6. The preparation method can obtain foil strips with uniform alloy composition, consistent grain orientation, fine IMC, clean surface, high yield rate, and can be processed into any preformed products, meeting the multi-level packaging requirements of vacuum electronic devices for vacuum solder.

[0039] The silver-based multi-element near-eutectic medium-temperature vacuum solder of the invention has scientific design and reasonable preparation process, is a low-silver brazing material, has an alloy melting point of 552-562° C., and a recommended brazing temperature of 630° C. (316L stainless steel).

[0040] Suitable for medium-temperature packaging of vacuum electronic devices. The solder is a multi-element eutectic alloy with a moderate melting temperature and excellent wettability to Cu, Ni, Kovar alloy and stainless steel substrates; it meets the medium-temperature vacuum brazing packaging requirements of 316L stainless steel in vacuum electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The differential thermal analysis spectrum of the silver-based multi-element near-eutectic medium-temperature vacuum solder prepared in Example 1 of the present invention;

[0042] Figure 2 This is an electron microscope photograph of the joint structure of a 316L stainless steel substrate brazed (6030°C) with a silver-based multi-element near-eutectic medium-temperature vacuum solder prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0043] The silver-based multi-component near-eutectic medium-temperature vacuum solder and the preparation method thereof of the present invention will be further described below in conjunction with an example of specific ingredient calculation.

[0044] The silver-based multi-element near-eutectic medium-temperature vacuum solder of the invention consists of the following components by weight percentage: Cu 19.5-21.0wt%, In 9.0-10.0wt%, Ge 4.5-5.5wt%, Sn 4.2-4.8wt%, Ni 1.8-2.2wt%, Si 1.7-2.0wt%, Co 0.05-0.2wt%, Ag being the remainder, and the total amount of the above components is 100%.

[0045] The method for preparing the eutectic medium-temperature solder foil strip of the present invention is obtained by preparing an intermediate alloy, performing non-vacuum medium-frequency refining, performing rapid cooling horizontal casting, and performing isothermal rolling, and includes the following specific steps:

[0046] (1) Raw material selection and master alloy preparation: Ag, Cu, In, Ge, Sn, Ni, Si, and Co raw materials are all 99.999%. Ag-20In master alloy, Cu-50Sn master alloy, Cu-40Ge master alloy, Cu-20Ni master alloy, Cu-20Si master alloy, and Cu-10Co master alloy are prepared by vacuum medium frequency induction melting.

[0047] (2) Vacuum medium frequency induction melting: The master alloy prepared in step (1) is subjected to the weight percentage of each element in the silver-based multi-element near-eutectic medium-temperature vacuum solder, and the weight of each element and the weight of the master alloy are calculated; a vacuum induction melting furnace is used to put all the weighed pure Ag, pure Cu and the master alloy into an alumina crucible, the lid is closed, and the furnace is evacuated to 10 -2 Pa or less; turn on the heating with a heating power of 20 to 30 kW, and when the initial liquid phase is seen from the observation port, fill in high-purity argon gas until the vacuum in the furnace reaches 0.8 MPa, continue heating until all the liquid is molten, reduce the power, control the refining temperature to 650 to 700 ° C, and maintain for 5 to 10 minutes.

[0048] (3) Centrifugal rapid cooling casting: The molten alloy melt obtained in step (2) is subjected to centrifugal rapid cooling casting. The melt is filled into a horizontal graphite casting mold by rotating centrifugal force. The centrifugal casting temperature is 650-700°C and the centrifugal speed is 500-1000n / min to obtain an alloy slab with a thickness of 10-15mm, a width of 80-250mm and uniform composition.

[0049] (4) Crystal orientation control by vacuum heat treatment: The alloy slab obtained in step (3) is subjected to crystal orientation control in a high vacuum heat treatment furnace with a vacuum degree of <5.0×10 -3 Pa, the temperature is 530℃, the holding time is 12 to 16h, and an alloy ingot with consistent grain orientation is obtained.

[0050] (5) Precision rolling: The alloy ingot obtained in step (4) is subjected to rough rolling by a 250 two-roller reversible hot rolling mill, the rolling mill roll temperature is 420-450°C, the hot rolling pass processing rate is 5%-10%, and a strip with a thickness of 0.8-1.0 mm and a width of 80-250 mm is obtained and rolled; the strip is double-sided polished to a bright silver color; a 50-type four-roller reversible cold rolling mill is used, the intermediate vacuum annealing temperature is 480-500°C, the vacuum degree is 10 -2 Pa, the processing rate of each cold rolling pass in the annealing room is 15% to 30%, the tension is 0 to 10kN, and multiple cold rolling passes are performed until a foil with a thickness of 0.05 to 0.1mm and a width of 80 to 250mm is obtained and rolled.

[0051] Embodiment 1:

[0052] Step 1: Raw material preparation and master alloy preparation

[0053] According to the alloy composition of Example 1 in Table 1, raw materials were prepared and weighed according to the designed component ratio, the total feeding amount of a single furnace was 100 kg, and vacuum medium frequency induction melting was adopted to prepare Ag-20In master alloy, Cu-50Sn master alloy, Cu-40Ge master alloy, Cu-20Ni master alloy, Cu-20Si master alloy, and Cu-10Co master alloy respectively;

[0054] Step (2) Vacuum medium frequency induction melting

[0055] The weight of each element and the weight of the master alloy prepared in step (1) are calculated according to the weight percentage of each element in the silver-based multi-element near-eutectic medium-temperature vacuum solder, as shown in Table 2; a vacuum induction melting furnace is used to put all the weighed pure Ag, pure Cu and master alloy into an alumina crucible, cover it, and evacuate the furnace to 10 -2 Pa or less; turn on the heating with a heating power of 25kw, and when the initial liquid phase is seen from the observation port, fill in high-purity argon gas until the vacuum in the furnace is 0.8MPa, continue heating until all is molten liquid, reduce the power, control the refining temperature to 680℃, and maintain for 8min.

[0056] Step (3) Centrifugal rapid cooling casting

[0057] The molten alloy melt obtained in step (2) is subjected to centrifugal rapid cooling casting. The melt is filled into a horizontal graphite casting mold by rotating centrifugal force. The centrifugal casting temperature is 680°C and the centrifugal speed is 800n / min to obtain an alloy slab with a thickness of 12mm, a width of 150mm and uniform composition.

[0058] Step (4) Vacuum heat treatment to adjust crystal orientation

[0059] The alloy slab obtained in step (3) is subjected to crystal orientation control in a high vacuum heat treatment furnace with a vacuum degree of <5.0×10 -3 Pa, the temperature is 530℃, the holding time is 14h, and an alloy ingot with consistent grain orientation is obtained.

[0060] Step (5) Precision rolling

[0061] The alloy ingot obtained in step (4) is subjected to rough rolling on a 250 two-roller reversible hot rolling mill, the rolling mill roll temperature is 430°C, the hot rolling pass processing rate is 10%, and a strip with a thickness of 1.0 mm and a width of 150 mm is obtained and rolled; the strip is double-sided polished to a bright silver color; a 50-type four-roller reversible cold rolling mill is used, the intermediate vacuum annealing temperature is 490°C, the vacuum degree is 10 -2Pa, the processing rate of each cold rolling pass in the annealing room is 20%, the tension is 5kN, and multiple cold rolling passes are performed until a foil with a thickness of 0.05mm and a width of 150mm is obtained and rolled.

[0062] Embodiment 2:

[0063] Step 1: Raw material preparation and master alloy preparation

[0064] According to the alloy composition of Example 2 in Table 1, raw materials were prepared and weighed according to the designed component ratio, the total feeding amount of a single furnace was 100 kg, and vacuum medium frequency induction melting was adopted to prepare Ag-20In master alloy, Cu-50Sn master alloy, Cu-40Ge master alloy, Cu-20Ni master alloy, Cu-20Si master alloy, and Cu-10Co master alloy respectively;

[0065] Step (2) Vacuum medium frequency induction melting

[0066] The weight of each element and the weight of the master alloy prepared in step (1) are calculated according to the weight percentage of each element in the silver-based multi-element near-eutectic medium-temperature vacuum solder, as shown in Table 2; a vacuum induction melting furnace is used to put all the weighed pure Ag, pure Cu and master alloy into an alumina crucible, cover it, and evacuate the furnace to 10 -2 Pa or less; turn on the heating with a heating power of 30 kW, and when the initial liquid phase is seen from the observation port, fill in high-purity argon gas until the vacuum in the furnace reaches 0.8 MPa, continue heating until all is molten liquid, reduce the power, control the refining temperature to 700 ° C, and maintain for 5 minutes.

[0067] Step (3) Centrifugal rapid cooling casting

[0068] The molten alloy melt obtained in step (2) is cast by centrifugal rapid cooling. The melt is filled into a horizontal graphite casting mold by rotating centrifugal force. The centrifugal casting temperature is 700°C and the centrifugal speed is 500n / min to obtain an alloy slab with a thickness of 10mm, a width of 80mm and uniform composition.

[0069] Step (4) Vacuum heat treatment to adjust crystal orientation

[0070] The alloy slab obtained in step (3) is subjected to crystal orientation control in a high vacuum heat treatment furnace with a vacuum degree of <5.0×10 -3 Pa, the temperature is 530℃, the holding time is 12h, and an alloy ingot with consistent grain orientation is obtained.

[0071] Step (5) Precision rolling

[0072] The alloy ingot obtained in step (4) is subjected to rough rolling on a 250 two-roller reversible hot rolling mill, the rolling mill roll temperature is 450°C, the hot rolling pass processing rate is 5%, and a strip with a thickness of 0.8 mm and a width of 80 mm is obtained, which is rolled; the strip is double-sided polished to a bright silver color; a 50-type four-roller reversible cold rolling mill is used, the intermediate vacuum annealing temperature is 500°C, the vacuum degree is 10 -2 Pa, the processing rate of each cold rolling pass in the annealing room is 15%, the tension is 0kN, and multiple cold rolling passes are performed until a foil with a thickness of 0.1mm and a width of 80mm is obtained and rolled.

[0073] Embodiment 3:

[0074] Step 1: Raw material preparation and master alloy preparation

[0075] According to the alloy composition of Example 3 in Table 1, raw materials were prepared and weighed according to the designed component ratio, the total feeding amount of a single furnace was 100 kg, and vacuum medium frequency induction melting was adopted to prepare Ag-20In master alloy, Cu-50Sn master alloy, Cu-40Ge master alloy, Cu-20Ni master alloy, Cu-20Si master alloy, and Cu-10Co master alloy respectively;

[0076] Step (2) Vacuum medium frequency induction melting

[0077] The weight of each element and the weight of the master alloy prepared in step (1) are calculated according to the weight percentage of each element in the silver-based multi-element near-eutectic medium-temperature vacuum solder, as shown in Table 2; a vacuum induction melting furnace is used to put all the weighed pure Ag, pure Cu and master alloy into an alumina crucible, cover it, and evacuate the furnace to 10 -2 Pa or less; turn on the heating with a heating power of 20 kW, and when the initial liquid phase is seen from the observation port, fill in high-purity argon gas until the vacuum in the furnace reaches 0.8 MPa, continue heating until all is molten liquid, reduce the power, control the refining temperature to 650 ° C, and maintain for 10 minutes.

[0078] Step (3) Centrifugal rapid cooling casting

[0079] The molten alloy melt obtained in step (2) is cast by centrifugal rapid cooling. The melt is filled into a horizontal graphite casting mold by rotating centrifugal force. The centrifugal casting temperature is 650°C and the centrifugal speed is 1000n / min to obtain an alloy slab with a thickness of 15mm, a width of 250mm and uniform composition.

[0080] Step (4) Vacuum heat treatment to adjust crystal orientation

[0081] The alloy slab obtained in step (3) is subjected to crystal orientation control in a high vacuum heat treatment furnace with a vacuum degree of <5.0×10-3 Pa, the temperature is 520℃, the holding time is 16h, and an alloy ingot with consistent grain orientation is obtained.

[0082] Step (5) Precision rolling

[0083] The alloy ingot obtained in step (4) is subjected to rough rolling on a 250 two-roller reversible hot rolling mill, the rolling mill roll temperature is 420°C, the hot rolling pass processing rate is 10%, and a strip with a thickness of 1.0 mm and a width of 250 mm is obtained, which is rolled; the strip is double-sided polished to a bright silver color; a 50-type four-roller reversible cold rolling mill is used, the intermediate vacuum annealing temperature is 480°C, the vacuum degree is 10 -2 Pa, the processing rate of each cold rolling pass in the annealing room is 30%, the tension is 10kN, and multiple cold rolling passes are performed until a foil with a thickness of 0.05mm and a width of 250mm is obtained and rolled.

[0084] Embodiment 4:

[0085] Step 1: Raw material preparation and master alloy preparation

[0086] According to the alloy composition of Example 4 in Table 1, raw materials were prepared and weighed according to the designed component ratio, the total feeding amount of a single furnace was 100 kg, and vacuum medium frequency induction melting was adopted to prepare Ag-20In master alloy, Cu-50Sn master alloy, Cu-40Ge master alloy, Cu-20Ni master alloy, Cu-20Si master alloy, and Cu-10Co master alloy respectively;

[0087] Step (2) Vacuum medium frequency induction melting

[0088] The weight of each element and the weight of the master alloy prepared in step (1) are calculated according to the weight percentage of each element in the silver-based multi-element near-eutectic medium-temperature vacuum solder, as shown in Table 2; a vacuum induction melting furnace is used to put all the weighed pure Ag, pure Cu and master alloy into an alumina crucible, cover it, and evacuate the furnace to 10 -2 Pa or less; turn on the heating with a heating power of 20 kW, and when the initial liquid phase is seen from the observation port, fill in high-purity argon gas until the vacuum in the furnace reaches 0.8 MPa, continue heating until all is molten liquid, reduce the power, control the refining temperature to 700 ° C, and maintain for 10 minutes.

[0089] Step (3) Centrifugal rapid cooling casting

[0090] The molten alloy melt obtained in step (2) is subjected to centrifugal rapid cooling casting. The melt is filled into a horizontal graphite casting mold by rotating centrifugal force. The centrifugal casting temperature is 700°C and the centrifugal speed is 1000n / min to obtain an alloy slab with a thickness of 10mm, a width of 200mm and uniform composition.

[0091] Step (4) Vacuum heat treatment to adjust crystal orientation

[0092] The alloy slab obtained in step (3) is subjected to crystal orientation control in a high vacuum heat treatment furnace with a vacuum degree of <5.0×10 -3 Pa, the temperature is 530℃, the holding time is 12h, and an alloy ingot with consistent grain orientation is obtained.

[0093] Step (5) Precision rolling

[0094] The alloy ingot obtained in step (4) is subjected to rough rolling on a 250 two-roller reversible hot rolling mill, the rolling mill roll temperature is 450°C, the hot rolling pass processing rate is 5%, and a strip with a thickness of 0.8 mm and a width of 200 mm is obtained, which is rolled; the strip is double-sided polished to a bright silver color; a 50-type four-roller reversible cold rolling mill is used, the intermediate vacuum annealing temperature is 500°C, the vacuum degree is 10 -2 Pa, the processing rate of each cold rolling pass in the annealing room is 30%, the tension is 10kN, and multiple cold rolling passes are performed until a foil with a thickness of 0.08mm and a width of 200mm is obtained and rolled.

[0095] Embodiment 5:

[0096] Step 1: Raw material preparation and master alloy preparation

[0097] According to the alloy composition of Example 5 in Table 1, raw materials were prepared and weighed according to the designed component ratio, the total feeding amount of a single furnace was 100 kg, and vacuum medium frequency induction melting was adopted to prepare Ag-20In master alloy, Cu-50Sn master alloy, Cu-40Ge master alloy, Cu-20Ni master alloy, Cu-20Si master alloy, and Cu-10Co master alloy respectively;

[0098] Step (2) Vacuum medium frequency induction melting

[0099] The weight of each element and the weight of the master alloy prepared in step (1) are calculated according to the weight percentage of each element in the silver-based multi-element near-eutectic medium-temperature vacuum solder, as shown in Table 2; a vacuum induction melting furnace is used to put all the weighed pure Ag, pure Cu and master alloy into an alumina crucible, cover it, and evacuate the furnace to 10 -2 Pa or less; turn on the heating with a heating power of 30 kW, and when the initial liquid phase is seen from the observation port, fill in high-purity argon gas until the vacuum in the furnace reaches 0.8 MPa, continue heating until all is molten liquid, reduce the power, control the refining temperature to 650 ° C, and maintain for 8 minutes.

[0100] Step (3) Centrifugal rapid cooling casting

[0101] The molten alloy melt obtained in step (2) is subjected to centrifugal rapid cooling casting. The melt is filled into a horizontal graphite casting mold by rotating centrifugal force. The centrifugal casting temperature is 680°C and the centrifugal speed is 750n / min to obtain an alloy slab with a thickness of 12mm, a width of 100mm and uniform composition.

[0102] Step (4) Vacuum heat treatment to adjust crystal orientation

[0103] The alloy slab obtained in step (3) is subjected to crystal orientation control in a high vacuum heat treatment furnace with a vacuum degree of <5.0×10 -3 Pa, the temperature is 520℃, the holding time is 16h, and an alloy ingot with consistent grain orientation is obtained.

[0104] Step (5) Precision rolling

[0105] The alloy ingot obtained in step (4) is subjected to rough rolling on a 250 two-roller reversible hot rolling mill, the rolling mill roll temperature is 440°C, the hot rolling pass processing rate is 8%, and a strip with a thickness of 1.0 mm and a width of 100 mm is obtained and rolled; the strip is double-sided polished to a bright silver color; a 50-type four-roller reversible cold rolling mill is used, the intermediate vacuum annealing temperature is 490°C, the vacuum degree is 10 -2 Pa, the processing rate of each cold rolling pass in the annealing room is 20%, the tension is 5kN, and multiple cold rolling passes are performed until a foil with a thickness of 0.05mm and a width of 100mm is obtained and rolled.

[0106] Table 1 The proportion of each element in the alloy in Examples 1 to 5

[0107]

[0108] Table 2 Weight of each element and master alloy in Examples 1 to 5

[0109]

[0110]

[0111] The silver-based multi-element near-eutectic medium-temperature vacuum solder foil strips prepared in Examples 1-5 were tested for melting point, specification size, wettability (316L), joint tensile strength, etc., and the test data obtained are shown in Table 3.

[0112] Table 3 Properties of silver-based multi-element near-eutectic medium-temperature vacuum solder foil strips of Examples 1 to 5

[0113]

[0114] like Figure 1As shown, it is a differential thermal curve of the silver-based multi-element near-eutectic medium-temperature vacuum solder prepared in Example 1. It can be seen from the figure that the melting temperature of the AgCuInGeSnNiSiCo alloy obtained by adopting the alloy proportion and preparation method designed by the present invention is 553.35-558.04°C, the melting range is only 6°C, the endothermic peak and the exothermic peak curve are obvious, and there is no low melting point phase precipitation and phase change.

[0115] like Figure 2 As shown, the joint structure electron microscope photograph of the brazing 316L stainless steel substrate (630°C) obtained by brazing the silver-based multi-element near-eutectic medium-temperature vacuum brazing filler metal prepared in Example 1 is obtained. It can be seen from the figure that the silver-based multi-element near-eutectic medium-temperature vacuum brazing filler metal developed by the present invention has an obvious brazing metallurgical effect on the 16L stainless steel substrate, the metallurgical bonding at the welding weld is dense, there are few intermetallic compounds in the reaction interface, and solid solution is mainly present.

[0116] The eutectic medium-temperature solder of the present invention has a moderate melting temperature and has excellent wettability to Cu, Ni, Kovar alloy and stainless steel substrates; it meets the medium-temperature vacuum brazing packaging requirements of 316L stainless steel material in vacuum electronic devices.

[0117] The silver-based multi-element near-eutectic medium-temperature vacuum solder and preparation method of the present invention mainly solve the problem of no reliable solder for vacuum brazing of 316L stainless steel medium-temperature substrate and medium-temperature vacuum brazing of 316L stainless steel in vacuum electronic devices. The melting point of the multi-element alloy solder is 552-562°C, the melting range is less than 10°C, and the recommended brazing temperature is 630°C. Its preparation method includes intermediate alloy preparation, vacuum medium-frequency induction melting, centrifugal rapid cooling casting, vacuum heat treatment regulation, hot rolling blanking, surface treatment, and precision cold rolling. The alloy has a low melting point, the required vacuum brazing temperature is low, and it has excellent wetting properties for stainless steel. The joint strength after brazing is high, which meets the requirements of medium-temperature vacuum brazing packaging, gradient brazing and repair welding of 316L stainless steel substrates in vacuum electronic devices.

[0118] The above embodiments only illustrate the silver-based multi-component near-eutectic medium-temperature vacuum solder part of the present invention. In the above technical scheme of the present invention: the content of metal elements in the solder alloy can be freely selected within the prescribed range, and they are no longer listed here one by one. Therefore, the technical scheme contained in the above description should be regarded as illustrative, rather than used to limit the protection scope of the patent application of the present invention.

Claims

1. A silver-based multi-element near-eutectic medium-temperature vacuum solder, characterized in that: Calculated by weight percentage, it contains: Cu 19.5-21.0wt%, In 9.0-10.0wt%, Ge 4.5-5.5wt%, Sn 4.2-4.8wt%, Ni 1.8-2.2wt%, Si 1.7-2.0wt%, Co 0.05-0.2wt%, and Ag is the balance.

2. The method for preparing the silver-based multi-element near-eutectic medium-temperature vacuum solder according to claim 1, characterized in that: The following steps are involved: (1) Raw material selection and master alloy preparation According to the composition of the silver-based multi-element near-eutectic medium-temperature vacuum solder, Ag, Cu, In, Ge, Sn, Ni, Si and Co are used as raw materials; Ag-In master alloy, Cu-Sn master alloy, Cu-Ge master alloy, Cu-Ni master alloy, Cu-Si master alloy and Cu-Co master alloy were prepared by vacuum medium frequency induction melting. (2) Vacuum medium frequency induction melting The master alloy prepared in step (1) is subjected to the weight percentage of each element in the silver-based multi-element near-eutectic medium-temperature vacuum solder to calculate the weight of each element and the weight of the master alloy; a vacuum induction melting furnace is used to put all the weighed pure Ag, pure Cu and master alloy into an alumina crucible, the lid is closed, and the furnace is evacuated; heating is turned on, and when the initial liquid phase is seen from the observation port, high-purity argon gas is filled in, and heating is continued until all of the liquid is molten, and the power is reduced to perform refining; (3) Centrifugal rapid cooling casting The molten alloy melt obtained in step (2) is cast by centrifugal rapid cooling, and the melt is filled into a horizontal graphite casting mold by rotating centrifugal force to obtain an alloy slab with uniform composition; (4) Vacuum heat treatment to control crystal orientation The alloy slab obtained in step (3) is subjected to crystal orientation control in a high vacuum heat treatment furnace to obtain an alloy ingot with uniform grain orientation; (5) Precision rolling The alloy ingot obtained in step (4) is subjected to rough rolling on a hot rolling mill to obtain a strip material, which is then rolled into a coil; the strip material is double-sided polished to a bright silver color; and a cold rolling mill is used to perform multiple cold rolling processes until a foil material is obtained, which is then rolled into a coil.

3. The method for preparing the silver-based multi-element near-eutectic medium-temperature vacuum solder according to claim 2, characterized in that: The purity of the raw materials Ag, Cu, In, Ge, Sn, Ni, Si and Co is 99.999wt.%.

4. The method for preparing the silver-based multi-element near-eutectic medium-temperature vacuum solder according to claim 2, characterized in that: Ag-20In master alloy, Cu-50Sn master alloy, Cu-40Ge master alloy, Cu-20Ni master alloy, Cu-20Si master alloy and Cu-10Co master alloy were prepared by vacuum medium frequency induction melting.

5. The method for preparing the silver-based multi-element near-eutectic medium-temperature vacuum solder according to claim 2, characterized in that: The smelting method is vacuum medium frequency induction smelting, the refining temperature is 650-700°C, and the refining time is 5-10 minutes; when performing vacuum smelting, the furnace is evacuated to 10 -2 Pa; the heating power is 20-30kw; after filling with high-purity argon, the vacuum in the furnace is 0.8MPa.

6. The method for preparing the silver-based multi-element near-eutectic medium-temperature vacuum solder according to claim 5, characterized in that: The casting method is centrifugal pressure rapid cooling casting, the centrifugal casting temperature is 650-700° C., and the centrifugal speed is 500-1000 n / min.

7. The method for preparing the silver-based multi-element near-eutectic medium-temperature vacuum solder according to claim 2, characterized in that: The alloy slab has a thickness of 10 to 15 mm and a width of 80 to 250 mm.

8. The method for preparing the silver-based multi-element near-eutectic medium-temperature vacuum solder according to claim 2, characterized in that: Vacuum heat treatment is used to control the crystal orientation of the structure, and the vacuum degree is <5.0×10 -3 Pa, temperature is 520~530℃, and holding time is 12~16h.

9. The method for preparing the silver-based multi-element near-eutectic medium-temperature vacuum solder according to claim 2, characterized in that: The hot rolling mill is a 250 two-roller reversible hot rolling mill, the rolling mill roll temperature is 420-450°C, and the hot rolling pass processing rate is 5%-10%; the cold rolling mill is a 50-type four-roller reversible cold rolling mill, the intermediate vacuum annealing temperature is 480-500°C, the vacuum degree is 10 -2 Pa, the processing rate of each cold rolling pass in the annealing interval is 15% to 30%, and the tension is 0 to 10 kN.

10. The method for preparing the silver-based multi-element near-eutectic medium-temperature vacuum solder according to claim 2, characterized in that: The strip material has a thickness of 0.8-1.0 mm and a width of 80-250 mm; the foil material has a thickness of 0.05-0.1 mm and a width of 80-250 mm.

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