A composite filler metal, a method of making the same, and a method for joining dissimilar alloys

Abstract

The application discloses a kind of composite filler metal and preparation method and method for connecting dissimilar alloys, belongs to dissimilar alloy connection technical field, with mass fraction, composite filler metal includes 60-70 parts Ag, 25-35 parts Cu, 3-4 parts Ti, 0.1-3 parts Cr.Ag, Cu, Ti, Cr metal powder is mixed, dry powder compacts, and composite filler metal is obtained, and composite filler metal is vacuum brazing again with dissimilar alloy.The application adopts the above-mentioned composite filler metal and preparation method and method for connecting dissimilar alloys, by optimizing Ag-Cu-Ti-Cr quaternary system solder component ratio, innovation preparation process and supporting vacuum brazing parameter, high quality, high stability brazing connection of stainless steel and high speed steel is realized, the mechanical properties of brazed joint are significantly improved, and production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of dissimilar alloy joining technology, and in particular to a composite brazing filler metal, its preparation method, and a method for joining dissimilar alloys. Background Technology

[0002] AgCuTi-based composite solders are key active materials for connecting ceramics, metal compounds, and dissimilar metals (such as titanium alloys / stainless steel and SiC / Al composites). The technology has evolved from basic Ag-Cu-Ti ternary alloys to composite material systems that enhance phase regulation performance by introducing TiC nanoparticles, Mo fibers, graphene, etc.

[0003] In the field of dissimilar alloy joining of 17-4PH stainless steel and N128 high-speed steel, vacuum brazing has become the preferred technology due to its low welding temperature and minimal thermal impact on the base materials. Furthermore, the weld gap, brazing temperature, and holding time are key parameters affecting joint performance. However, existing technologies still have significant drawbacks: Firstly, commonly used Ni-based brazing filler metals (such as BNi2) have high melting points, requiring brazing temperatures of around 1100℃. This not only causes coarsening of the 17-4PH austenite grains and aggregation or dissolution of N128 carbides, but also generates significant thermal stress due to the difference in thermal expansion coefficients between the two base materials, leading to component deformation. Secondly, 17-4PH and N128 differ greatly in composition and thermophysical properties. The interfacial reaction involves multi-component diffusion and the competitive formation of various intermetallic compounds. Existing research only focuses on the influence of a single parameter, failing to clarify the coupling effect of weld gap, temperature, and time, and their impact on the microstructure and mechanical properties of the weld joint, making it difficult to provide precise process guidance. Therefore, there is an urgent need to research a dedicated brazing solution that synergistically optimizes the composition and process for this dissimilar alloy. Summary of the Invention

[0004] The purpose of this invention is to provide a composite brazing filler metal, its preparation method, and a method for joining dissimilar alloys. By optimizing the composition ratio of the Ag-Cu-Ti-Cr quaternary brazing filler metal, innovating the preparation process, and setting up matching vacuum brazing parameters, high-quality and high-stability brazing connections between stainless steel and high-speed steel are achieved, significantly improving the mechanical properties of the brazed joints and reducing production costs.

[0005] To achieve the above objectives, the present invention provides a composite brazing filler metal comprising, by mass parts, 60-70 parts Ag, 25-35 parts Cu, 3-4 parts Ti, and 0.1-3 parts Cr.

[0006] This invention also provides a method for preparing composite solder, comprising the following steps: Ag, Cu, Ti, and Cr metal powders are mixed and pressed into a dry powder blank to obtain a composite brazing filler metal.

[0007] Preferably, the mixing time is 4-8 hours.

[0008] Preferably, the pressure for pressing dry powder into a compact is 200-300 MPa.

[0009] The present invention also provides a method for using composite brazing filler metal to join dissimilar alloys, comprising the following steps: S1. Dissimilar alloys are ultrasonically cleaned and dried using ethanol; S2. Assemble the dried alloy and brazing filler metal, perform vacuum brazing, and allow it to cool naturally after brazing to obtain the brazed joint.

[0010] Preferably, in S1, dissimilar alloys include stainless steel and high-speed steel.

[0011] Furthermore, stainless steel includes 17-4PH, and high-speed steel includes N128.

[0012] Preferably, in S1, the ultrasonic cleaning frequency is 30-50kHz, the ultrasonic cleaning power is 70-90W, the ultrasonic cleaning temperature is 20-30℃, and the ultrasonic cleaning time is 10-30min.

[0013] Preferably, in S1, the drying temperature is 60-100℃ and the drying time is 20-40 min.

[0014] Preferably, in S2, the lap length of the assembly is 8-12mm, and the gap between the brazing seams is 0.15-0.2mm.

[0015] Preferably, in S2, the vacuum degree of vacuum brazing is ≤6.67×10⁻⁶. -3 Pa, the heating rate of vacuum brazing is 3-7℃ / min. The heating process of vacuum brazing is as follows: first heat up to 330-370℃, hold for 10-20min, then continue to heat up to 880-920℃, and hold for 8-12min.

[0016] Therefore, the present invention, employing the aforementioned composite brazing filler metal, its preparation method, and the method for joining dissimilar alloys, has the following beneficial effects: (1) By optimizing the composition ratio of the brazing filler metal in the Ag-Cu-Ti-Cr quaternary system, innovating the preparation process and matching vacuum brazing parameters, this invention achieves high-quality and high-stability brazing connection between stainless steel and high-speed steel, significantly improving the mechanical properties of the brazed joint and reducing production costs.

[0017] (2) By precisely controlling the mass percentages of Ag, Cu, Ti and Cr, this invention utilizes Ti to form a thin-layer compound with elements such as C and Ti in the base material to strengthen the interface. Cr plays a synergistic role in solid solution strengthening and stress relief. While ensuring good wettability, it greatly improves the wetting ability and interface bonding strength of the brazing filler metal to stainless steel and high-speed steel. The resulting joint is dense and defect-free, with excellent mechanical properties and reliability.

[0018] (3) The present invention uses a three-dimensional mixer to mix powder and a 200-300MPa dry powder pressing technique to prepare a preformed blank that is easy to position and assemble. It is perfectly adapted to the brazing assembly process, and is flexible and highly reliable.

[0019] (4) The present invention constructs a complete process of “composition phase diagram calculation - uniform powder mixing - precise pressing and molding - customized brazing process”, which is controllable from raw material ratio to brazing process, ensuring that the composition of each batch of brazing filler metal is highly uniform, thereby ensuring the excellent stability and good repeatability of brazed joint performance.

[0020] (5) The present invention uses conventional metal powder as raw material, which significantly reduces the cost compared with imported special brazing filler metal. The integrated preparation process simplifies the production steps and provides a domestic solution for high-performance metal heterojunction with both high stability and good economy.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 These are XRD patterns of the brazing filler metal after brazing in Embodiments 1-3 of the present invention; Figure 2 These are metallographic microstructure images of the brazing filler metal after brazing in Examples 1-3 of this invention; Figure 3 These are EDS surface scan images and elemental surface scan distribution images of the brazing filler metal surface after brazing in Embodiment 3 of the present invention; Figure 4 These are EDS surface scan images and elemental surface scan distribution images of the brazing filler metal surface after brazing in Embodiment 1 of the present invention; Figure 5 These are EDS surface scan images and elemental surface scan distribution images of the brazing filler metal surface after brazing, as shown in Embodiment 2 of the present invention. Figure 6 These are SEM images and EDS point analysis images of the brazing filler metal after brazing in Embodiment 3 of the present invention; Figure 7 These are SEM images and EDS point analysis images of the brazing filler metal after brazing in Embodiment 1 of the present invention; Figure 8 These are SEM images and EDS point analysis images of the brazing filler metal after brazing in Embodiment 2 of the present invention; Figure 9 This is a diagram showing the shear strength of the brazed joints after brazing in Embodiments 1-3 of the present invention. Detailed Implementation

[0023] The phase diagram of Ag-Cu-Ti-Cr solder was calculated using the thermodynamic software packages Pandat or Thermo-Calc to determine its solid-liquid phase temperature. Based on the simulated phase content-temperature relationship curve, the optimal Cr addition ratio and brazing temperature were determined.

[0024] A composite brazing filler metal, comprising, by mass parts, 60-70 parts Ag, 25-35 parts Cu, 3-4 parts Ti, and 0.1-3 parts Cr.

[0025] The above-mentioned ratio of Ag, Cu, Ti, and Cr metal powders is the basis for achieving good wetting and high-strength bonding, among which the content of Ti and Cr is the core to ensure activity.

[0026] The preparation method of the above-mentioned composite solder includes the following steps: Ag, Cu, Ti, and Cr metal powders are mixed and pressed into a dry powder blank to obtain a composite brazing filler metal.

[0027] The mixing time is 4-8 hours. Mixing ensures that the powder has a highly uniform composition at the microscopic scale, preventing the agglomeration of active elements.

[0028] The pressure of dry powder compaction is 200-300 MPa. Dry powder compaction is used to press uniformly mixed metal powder into green compacts.

[0029] The method for using the above-mentioned composite brazing filler metal to join dissimilar alloys includes the following steps: S1. Dissimilar alloys are ultrasonically cleaned and dried using ethanol; S2. Assemble the dried alloy and brazing filler metal, perform vacuum brazing, and allow it to cool naturally after brazing to obtain the brazed joint.

[0030] In S1, dissimilar alloys include stainless steel and high-speed steel.

[0031] In S1, the ultrasonic cleaning frequency is 30-50kHz, the ultrasonic cleaning power is 70-90W, the ultrasonic cleaning temperature is 20-30℃, and the ultrasonic cleaning time is 10-30min.

[0032] In S1, the drying temperature is 60-100℃ and the drying time is 20-40 minutes.

[0033] In S2, the lap length of the assembly is 8-12mm, and the brazing gap of the assembly is 0.15-0.2mm.

[0034] During assembly, a ceramic plate is used to support and ensure the weldment is level. A ceramic block is used to apply pressure to maintain the predetermined gap between the composite brazing filler metal and the base material. The brazing gap is controlled to the set value (deviation ≤ 0.02 mm) using a micrometer.

[0035] In S2, the vacuum degree of vacuum brazing is ≤6.67×10⁻⁶. -3 Pa, the heating rate of vacuum brazing is 3-7℃ / min. The heating process of vacuum brazing is as follows: first heat up to 330-370℃, hold for 10-20min, then continue to heat up to 880-920℃, and hold for 8-12min.

[0036] The stainless steel used in this application is 17-4PH, and the high-speed steel is N128. The main chemical compositions of 17-4PH and N128 are shown in Table 1 and Table 2, respectively.

[0037] Table 1. Main chemical components of 17-4PH

[0038] Table 2. Main chemical components of N128

[0039] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0041] In this invention, unless otherwise specified, the test materials and instruments are all conventional test materials in the field and can be purchased through commercial channels.

[0042] Example 1 A composite brazing filler metal, by mass parts, comprises 60 parts Ag, 35 parts Cu, 3.5 parts Ti, and 1.5 parts Cr, denoted as 60Ag-35Cu-3.5Ti-1.5Cr.

[0043] The preparation method of the above-mentioned composite solder includes the following steps: Ag, Cu, Ti, and Cr metal powders were weighed and mixed. The mixture was then mixed for 6 hours using a three-dimensional mixer to ensure that the powder composition was highly uniform at the microscale and to prevent the agglomeration of active elements. The uniformly mixed metal powders were then pressed into a green blank under a pressure of 250 MPa to obtain the composite brazing filler metal.

[0044] The method for using the above-mentioned composite brazing filler metal to join dissimilar alloys includes the following steps: S1. Cut 17-4PH and N128 into plates with dimensions of 10mm×10mm×3mm, and then perform ultrasonic cleaning with anhydrous ethanol to thoroughly remove oil stains. The parameters are set as follows: frequency 40kHz, power 80W, temperature 25℃, and time 20min. Then, place the cleaned alloy in an 80℃ forced-air drying oven to dry for 30min to avoid residual moisture. Use graded sandpaper of 240#, 400#, 600#, and 800# in sequence to polish the surface of the base material to remove the oxide layer, thus completing the surface pretreatment of the base material. S2. Assemble the pretreated alloy and brazing filler metal with an overlap length of 10mm and a brazing gap of 0.15mm. During assembly, use a ceramic plate to support and ensure the weldment is level, apply pressure with a ceramic block to maintain the predetermined gap between the composite brazing filler metal and the base material, and control the brazing gap to the set value (deviation ≤ 0.02mm) using a micrometer. Vacuum brazing was then performed in an SLG1400-100A vacuum tube furnace, maintaining a vacuum level of 6.67 × 10⁻⁶. -3 To prevent oxidation, the temperature was first increased to 350℃ at a rate of 5℃ / min and held for 15min, then increased to 900℃ and held for 10min. Finally, the furnace was allowed to cool naturally to reduce residual stress, resulting in a brazed joint.

[0045] Example 2 A composite brazing filler metal, by mass parts, comprises 65 parts Ag, 28 parts Cu, 4 parts Ti, and 3 parts Cr, denoted as 65Ag-28Cu-4Ti-3Cr.

[0046] The preparation method of the above-mentioned composite solder is the same as that in Example 1.

[0047] The method of using the above-mentioned composite brazing filler metal to join dissimilar alloys is the same as that in Example 1, except that in S2, the brazing gap is 0.2 mm, and the vacuum brazing process is as follows: first heat up to 350°C at a heating rate of 5°C / min, hold for 15 min, and then continue to heat up to 920°C and hold for 10 min.

[0048] Example 3 A composite brazing filler metal, by mass parts, comprises 70 parts Ag, 25 parts Cu, 4 parts Ti, and 1 part Cr, denoted as 70Ag-25Cu-4.0Ti-1.0Cr.

[0049] The preparation method of the above-mentioned composite solder is the same as that in Example 1.

[0050] The method of using the above-mentioned composite brazing filler metal to connect dissimilar alloys is the same as that in Example 1, except that in S2, the vacuum brazing process is as follows: first heat up to 350°C at a heating rate of 5°C / min, hold for 15 minutes, and then continue to heat up to 880°C and hold for 10 minutes.

[0051] Phase analysis of the brazing filler metal (brazing seam) after brazing in Examples 1-3 was performed using X-ray diffraction. A Cu target was used for X-ray diffraction, the scanning speed was 5° / min, and the range was 10°-90°. The results are as follows: Figure 1 As shown, where Figure 1 (a) in the figure is the temperature-phase content simulation curve of the AgCuTiCr solder system. Figure 1 (b) in the figure shows the XRD patterns of the brazing seam surface at different brazing temperatures.

[0052] from Figure 1 As can be seen from (a) in the figure, in the low temperature range below 800℃, the alloy system is in the solid state, mainly composed of face-centered cubic (FCC) phases such as FCC_L12 and FCC_L12#2, as well as Cu4Ti1 intermetallic compound phase, exhibiting a multiphase coexistence state. When the temperature reaches 600℃, the intermetallic compound Cu4Ti1 disappears. When the temperature rises above 800℃, various solid phases gradually disappear, while the proportion of liquid phase (LIQUID) begins to increase, which means that the solder changes from solid to liquid.

[0053] from Figure 1 As shown in (b), diffraction peaks of the face-centered cubic Ag-rich phase (FCC-Ag), the Cu-rich phase (FCC-Cu), and the body-centered cubic Cr phase (BCC-Cr) were detected at all temperatures. The diffraction peak intensity of TiC (FCC-TiC) was high at 880℃, weakened at 900℃, and increased at 920℃. This is because the FCC phase was retained after rapid cooling following complete melting of the alloy, confirming the... Figure 1 (a) Prediction of FCC phase dominance at high temperature.

[0054] The brazing filler metal (brazing seam) after brazing in Examples 1-3 was observed using field emission scanning electron microscopy, and elemental distribution analysis was performed. The results are as follows: Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, where Figure 2 Image (a) in Example 3 shows the metallographic microstructure of the brazing filler metal under a 50 μm scale. Figure 2 Image (b) shows the metallographic microstructure of the brazing filler metal after brazing in Example 3 under a 20 μm scale. Figure 2 Image (c) in the figure shows the metallographic microstructure of the brazing filler metal after brazing in Example 1 under a 50 μm scale. Figure 2 Image (d) in the figure is a metallographic microstructure of the brazing filler metal after brazing in Example 1, displayed on a 20 μm scale. Figure 2 Image (e) in Example 2 shows the metallographic microstructure of the brazing filler metal under a 50 μm scale. Figure 2 (f) is a metallographic microstructure of the brazing filler metal after brazing in Example 2, displayed on a 20 μm scale. Figure 3 Image (a) is an EDS surface scan of the brazing filler metal surface after brazing in Example 3. Figure 3 Image (b) shows the EDS elemental surface scan distribution of Ag in the brazing filler metal after brazing in Example 3. Figure 3 Image (c) shows the EDS elemental surface scan distribution of Cu in the brazing filler metal after brazing in Example 3. Figure 3 Image (d) shows the EDS elemental surface scan distribution of Ti in the brazing filler metal after brazing in Example 3. Figure 3 (e) is an EDS elemental surface scan distribution diagram of Cr element in the brazing filler metal after brazing in Example 3; Figure 4 Image (a) is an EDS surface scan of the brazing filler metal surface after brazing in Example 1. Figure 4 Image (b) shows the EDS elemental surface scan distribution of Ag in the brazing filler metal after brazing in Example 1. Figure 4 Image (c) shows the EDS elemental surface scan distribution of Cu in the brazing filler metal after brazing in Example 1. Figure 4 Image (d) shows the EDS elemental surface scan distribution of Ti in the brazing filler metal after brazing in Example 1. Figure 4 Image (e) shows the EDS elemental surface scan distribution of Cr in the brazing filler metal after brazing in Example 1. Figure 5 Image (a) is an EDS surface scan of the brazing filler metal surface after brazing in Example 2. Figure 5 Image (b) shows the EDS elemental surface scan distribution of Ag in the brazing filler metal after brazing in Example 2. Figure 5 Image (c) shows the EDS elemental surface scan distribution of Cu in the brazing filler metal after brazing in Example 2. Figure 5 Image (d) shows the EDS elemental surface scan distribution of Ti in the brazing filler metal after brazing in Example 2. Figure 5 (e) is an EDS elemental surface scan distribution diagram of Cr element in the brazing filler metal after brazing in Example 2.

[0055] from Figure 2As can be seen, at 880℃ (Example 3), the matrix is ​​a continuous light-colored phase, in which small, irregularly shaped dark-colored second-phase particles are distributed. At this temperature, the solder has fully melted and undergone a eutectic reaction, but atomic diffusion may not be sufficient, and element migration is somewhat restricted, thus forming a dense metastable structure. When the temperature rises to 900℃ (Example 1), phase coarsening and aggregation begin to appear in the eutectic layer, the interlamellar spacing increases, the number of dark-colored particles increases, and local particle aggregation occurs, indicating that the structure enters a coarsening stage as the temperature increases. When the temperature is increased to 920℃ (Example 2), the eutectic structure further coarsens, the phase interface becomes clearer, radial eutectic clusters appear, and dark-colored particles grow into spherical shapes, leading to local component segregation and the formation of new phases.

[0056] from Figure 3 As can be seen, Ag and Cu, as the main elements, are continuously and widely distributed in the matrix, while Ti and Cr exhibit local enrichment characteristics. This indicates that at 880℃, Ti and Cr are not completely dissolved in the Ag-Cu liquid phase, but tend to combine with themselves or other elements to form Ti / Cr precipitates.

[0057] from Figure 4 As can be seen, the elemental distribution pattern changes. Cu is distributed throughout the entire matrix and is absent along with Ag in the particle region, indicating that Cu is dissolved in the Ag matrix. A small portion of Ti exists only weakly in the Ag-Cu matrix, while most Ti is wrapped in a ring shape around the Cr particles, forming a Cr@Ti (titanium shell covering chromium core) core-shell structure. This phenomenon indicates that Ti tends to agglomerate on the surface of Cr particles.

[0058] from Figure 5 As can be seen, the distribution of Ag and Cu elements is similar to that at 880℃ (Example 3), but the enrichment range of Ti and Cr expands, and their concentration gradient becomes gentler. Dark gray Cr-rich particles are distributed in the matrix. Unlike at 880℃ and 900℃ (Example 1), Cr elements exhibit shrinkage defects in the precipitated phase, indicating that Cr has significantly agglomerated at 920℃. Light gray Ti particles are attached to the periphery of the Cr-rich particles.

[0059] The morphology and EDS points of the brazing filler metal (brazing seam) after brazing in Examples 1-3 were analyzed using scanning electron microscopy. The results are as follows: Figure 6-8 As shown, where Figure 6 Image (a) is an SEM image of the brazing filler metal after brazing in Example 3. Figure 6 (b) is an EDS point analysis diagram of the brazing filler metal after brazing in Example 3; Figure 7 Image (a) is an SEM image of the brazing filler metal after brazing in Example 1. Figure 7 (b) is an EDS point analysis diagram of the brazing filler metal after brazing in Example 1; Figure 8Image (a) is an SEM image of the brazing filler metal after brazing in Example 2. Figure 8 (b) is an EDS point analysis diagram of the brazing filler metal after brazing in Example 2.

[0060] from Figure 6 As can be seen, the surface of the solder is a eutectic phase at 880℃. This indicates that the solder has good fluidity at this temperature and can achieve complete spreading and bonding. EDS point analysis of typical locations shows that points 1 and 3 are Ag-Cu eutectic phases rich in Ag solid solution, while point 2 is where Ti element reacts with C element in the parent material N128 to form TiC particles.

[0061] from Figure 7 As can be seen, the microstructure coarsens, the size of the black particles decreases, and their number increases. The interface structure is well-dense, tending to be smooth and clear. Aggregation of second-phase particles is visible in region 4, and the atomic percentage of Cr element is 96.49% as shown by spot analysis.

[0062] from Figure 8 As can be seen, the large-area Ag-Cu eutectic matrix exhibits a lamellar substructure. Compared to the conditions at 880℃ and 900℃, the sharpness of the matrix phase boundaries is reduced, and more Ti and Cr atoms dissolve into the liquid phase and precipitate outwards before solidification. This process promotes atomic bonding at the interface, homogenizes the composition within the brazing seam, and contributes to the formation of a more stable interface. High-magnification observation and EDS point analysis show that the eutectic lamellar structure remains intact at high temperatures, and the Ag-Cu eutectic distribution at the interface is uniform.

[0063] The shear strength of the brazing filler metal (brazing seam) after brazing in Examples 1-3 was tested using a universal testing machine. The maximum applied load was 5 kN, and the loading rate was 0.5 mm / min. The results are as follows: Figure 9 As shown. From Figure 9As can be seen, when the holding time is fixed at 10 min, the shear strength of the 17-4PH / Ag-Cu-Ti-Cr / N128 brazed joint increases with the increase of brazing temperature. When the brazing temperature is 880℃, the joint shear strength is 116.63 MPa; when the brazing temperature is gradually increased to 900℃, the joint shear strength is 130.09 MPa; when the brazing temperature is further increased to 920℃, the joint shear strength increases to a maximum of 187.88 MPa. The magnitude of the shear strength directly reflects the load-bearing capacity and structural reliability of the brazed joint. This result shows that under the optimized Ag-Cu-Ti-Cr quaternary composite brazing alloy composition and matching vacuum brazing process of this invention, as the brazing temperature increases, the brazing alloy can fully melt and spread. The active element Ti reacts fully with C in the base material to generate TiC reinforced interface phase, and the Cr element effectively plays a role in solid solution strengthening and interface stress relief, making the brazed joint structure more compact and significantly improving the interface bonding strength, ultimately achieving a significant increase in the shear strength of the brazed joint.

[0064] Therefore, this invention employs the aforementioned composite brazing filler metal and its preparation method, as well as a method for joining dissimilar alloys. By optimizing the composition ratio of the Ag-Cu-Ti-Cr quaternary brazing filler metal, innovating the preparation process, and implementing matching vacuum brazing parameters, it achieves high-quality, high-stability brazing connections between stainless steel and high-speed steel, significantly improving the mechanical properties of the brazed joints and reducing production costs.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A composite brazing filler metal, characterized in that: By mass, it includes 60-70 parts Ag, 25-35 parts Cu, 3-4 parts Ti, and 0.1-3 parts Cr.

2. The method for preparing a composite solder according to claim 1, characterized in that: Includes the following steps: Ag, Cu, Ti, and Cr metal powders are mixed and pressed into a dry powder blank to obtain a composite brazing filler metal.

3. The method for preparing a composite solder according to claim 2, characterized in that: The mixing time is 4-8 hours.

4. The method for preparing a composite solder according to claim 2, characterized in that: The pressure for dry powder compaction is 200-300 MPa.

5. The method for using a composite brazing filler metal as described in claim 1 to join dissimilar alloys, characterized in that: Includes the following steps: S1. Dissimilar alloys are ultrasonically cleaned and dried using ethanol; S2. Assemble the dried alloy and brazing filler metal, perform vacuum brazing, and allow it to cool naturally after brazing to obtain the brazed joint.

6. A method for joining dissimilar alloys using a composite brazing filler metal according to claim 5, characterized in that: In S1, dissimilar alloys include stainless steel and high-speed steel.

7. A method for joining dissimilar alloys using a composite brazing filler metal according to claim 6, characterized in that: Stainless steel includes 17-4PH, and high-speed steel includes N128.

8. A method for using a composite brazing filler metal to join dissimilar alloys according to claim 5, characterized in that: In S1, the ultrasonic cleaning frequency is 30-50kHz, the ultrasonic cleaning power is 70-90W, the ultrasonic cleaning temperature is 20-30℃, and the ultrasonic cleaning time is 10-30min.

9. A method for joining dissimilar alloys using a composite brazing filler metal according to claim 5, characterized in that: In S2, the lap length of the assembly is 8-12mm, and the brazing gap of the assembly is 0.15-0.2mm.

10. A method for using a composite brazing filler metal according to claim 5 to join dissimilar alloys, characterized in that: In S2, the vacuum degree of vacuum brazing is ≤6.67×10⁻⁶. -3 Pa, the heating rate of vacuum brazing is 3-7℃ / min. The heating process of vacuum brazing is as follows: first heat up to 330-370℃, hold for 10-20min, then continue to heat up to 880-920℃, and hold for 8-12min.

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