A self-fluxing soft solder and its preparation method and application

Abstract

The present invention relates to the technical field of soldering, and in particular, to a self-fluxing soft solder and its preparation method and application. The self-fluxing soft solder mainly consists of a tin-based solder and a soldering flux with a mass ratio of 75-94:6-25; wherein, the tin-based solder is mainly made of the following components by mass percentage: 7%-9% of Sb, 4%-6% of Cu, 0.2%-2% of Ni, and the balance is Sn; the soldering flux includes zinc chloride and / or ammonium chloride. The melting point of the self-fluxing soft solder is 230-250°C, which completely avoids the sensitization temperature range of stainless steel and the problem of intergranular corrosion after soldering; at the same time, this soft solder can greatly improve the shear strength of the joint after soldering; using this soft solder does not require additional addition of a soldering flux and can be directly soldered.

Description

Technical Field

[0001] The present invention relates to the technical field of soldering, and in particular, to a self-fluxing soft solder and its preparation method and application. Background Art

[0002] Stainless steel has good formability, corrosion resistance, heat resistance and other properties, and is widely used in the fields of aerospace, rail transit, nuclear energy devices, refrigeration, etc., such as honeycomb structures, heat exchangers, casing structures, etc. It is also widely used in industries such as food, medical, and kitchenware, and is an important pin material for electronic product connectors. These products often have complex structures and many welding positions, and soldering is a very efficient connection method. According to the melting point of the solder, soldering can be divided into hard soldering and soft soldering. Soldering with a solder liquidus temperature higher than 450 °C is hard soldering, and soldering with a temperature lower than 450 °C is soft soldering.

[0003] Common solders for stainless steel hard soldering include Ni-based, Cu-based, and Ag-based solders. The melting points of these solders are all above 600 °C, and the soldering temperature is within the sensitization range (450 - 800 °C) of austenitic stainless steel. For common austenitic stainless steels (such as 304, 316, etc.), staying in the sensitization range will cause Cr23C6 to form at the grain boundaries, and a Cr-depleted zone will appear near the grain boundaries, resulting in serious intergranular corrosion problems. Therefore, using soft soldering is an important measure to avoid stainless steel sensitization. For occasions with relatively low working temperatures, low strength requirements, but good sealing and beautiful appearance requirements, stainless steel soft soldering has outstanding advantages.

[0004] Soldering requires the use of a soldering flux to remove the oxide film on the surface of stainless steel and improve the wetting performance of the solder on the stainless steel base material. Common soft solders for stainless steel soldering include Sn92AgCuSb, Pb58Sn40Sb2, Sn99, Sn96BiSbCuNi, Pb97Ag, etc., and common soft soldering fluxes include aqueous orthophosphoric acid solution, zinc chloride hydrochloric acid aqueous solution, zinc chloride ammonium chloride aqueous solution, hydrochloric acid diethylamine orthophosphoric acid ethylene glycol solution, etc.

[0005] However, the shear strength of the joint after soldering with the existing stainless steel soft solder is relatively low (about 40 MPa), and the solder and soldering flux are used separately. It is difficult to quantitatively add the soldering flux. To ensure the soldering quality, the soldering flux is usually added in excess. On the one hand, this causes waste of the soldering flux, and on the other hand, the residual soldering flux has certain corrosiveness, increasing the cleaning process.

[0006] For example, patent document CN100592958C discloses a Sn-Cu soft solder for stainless steel soldering. By adding alloy elements lithium and titanium with deoxidizing effects, it has a certain deoxidizing and oxide film removing effect at the soldering temperature, but this technology still needs to be used in combination with a soldering agent to achieve a better soldering effect.

[0007] In addition, a self-fluxing filler metal refers to a filler metal that itself contains components for removing oxide films and preventing secondary oxidation, and can be directly brazed without the need for additional brazing fluxes. There are two forms of self-fluxing filler metals. One is that the constituent elements of the filler metal have the ability to remove oxide films, such as copper-phosphorus and copper-silver-phosphorus filler metals containing phosphorus, and copper-based and silver-based filler metals containing lithium. The other is the combination of the filler metal and the brazing flux, such as cored, coated, and powder-synthesized filler metals. Soft soldering mainly uses tin-based filler metals. As the largest application scenario, electronic packaging mostly uses composite solder pastes or rosin-cored filler metals. However, it is only suitable for brazing materials mainly composed of Cu and Ni.

[0008] Moreover, the rosin-cored self-fluxing tin-based soft solder in the prior art has the following problems: the distribution of the brazing flux is uneven and it is easy to leak out; the types of base metals applicable are few, and it cannot remove the oxide film on the surface of stainless steel.

[0009] In view of this, the present invention is specifically proposed. Summary of the Invention

[0010] The first object of the present invention is to provide a self-fluxing soft solder, the melting point of the self-fluxing soft solder is 230 - 250 °C, which completely avoids the sensitization temperature range of stainless steel and the problem of intergranular corrosion occurring after brazing; at the same time, the self-fluxing soft solder can greatly improve the shear strength of the joint after brazing; in addition, using this self-fluxing soft solder does not require additional brazing flux and can be directly brazed.

[0011] The second object of the present invention is to provide a preparation method of the self-fluxing soft solder, which has the advantages that the prepared self-fluxing soft solder is not easy to absorb moisture, is simple and easy to operate, has a short process flow, and is suitable for mass production.

[0012] The third object of the present invention is to provide the application of the self-fluxing soft solder in the brazing of stainless steel.

[0013] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0014] The present invention provides a self-fluxing soft solder, which is mainly composed of a tin-based filler metal and a brazing flux with a mass ratio of 75 - 94:6 - 25;

[0015] Among them, the tin-based filler metal is mainly made of the following components by mass percentage: 7% - 9% of Sb, 4% - 6% of Cu, 0.2% - 2% of Ni, and the balance is Sn;

[0016] The brazing flux includes zinc chloride and / or ammonium chloride.

[0017] Preferably, the mass ratio of the tin-based filler metal to the brazing flux is 80 - 92:8 - 20.

[0018] Preferably, the brazing flux includes zinc chloride and ammonium chloride with a mass ratio of 2 - 5:1.

[0019] Preferably, the melting point of the self-fluxing soft solder is 230 to 250 °C.

[0020] The present invention also provides a method for preparing the self-fluxing soft solder as described above, comprising the following steps:

[0021] After the mixed material containing Sb, Cu, Ni and Sn is smelted into an ingot, it is made into powder to obtain solder powder;

[0022] The solder powder is uniformly mixed with a soldering flux and then plastically formed to obtain a self-fluxing soft solder;

[0023] Wherein, the soldering flux includes zinc chloride and / or ammonium chloride.

[0024] Preferably, the particle size of the solder powder is 30 to 200 mesh, preferably 50 to 150 mesh.

[0025] Preferably, the particle size of the soldering flux is 100 to 300 mesh;

[0026] Preferably, the particle size of the soldering flux is smaller than that of the solder powder.

[0027] Preferably, the method of plastic forming includes at least one of extrusion, drawing and rolling;

[0028] Preferably, the extrusion includes cold extrusion and / or hot extrusion;

[0029] Preferably, the temperature of the hot extrusion is 100 to 150 °C.

[0030] Preferably, the method of plastic forming includes the following steps: after the solder powder is uniformly mixed with the soldering flux, cold extrusion, hot extrusion and drawing are carried out in sequence.

[0031] The present invention also provides the use of the self-fluxing soft solder as described above or the self-fluxing soft solder prepared by the method for preparing the self-fluxing soft solder as described above in stainless steel brazing.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] (1) The melting point of the self-fluxing soft solder provided by the present invention is maintained at 230 to 250 °C, completely avoiding the sensitization temperature range of stainless steel and avoiding the problem of intergranular corrosion after brazing.

[0034] (2) The self-fluxing soft solder provided by the present invention forms fine and uniformly distributed (Cu,Ni) 6 Sn 5The strengthening phase significantly improves the shear strength of the soldered joint after soldering. Especially when the mass percentage of Ni is 0.5%, the shear strength of the soldered joint reaches 66.9 MPa, which is 60% higher than that without adding Ni.

[0035] (3) The self-fluxing soft solder provided by the present invention can effectively remove the oxide film on the surface of stainless steel by adding zinc chloride and / or ammonium chloride.

[0036] (4) The self-fluxing soft solder provided by the present invention can be directly used for soldering without the need to additionally add a soldering flux, which is more convenient to use.

[0037] (5) The preparation method of the self-fluxing soft solder provided by the present invention can effectively avoid moisture absorption by dispersing and firmly wrapping the soldering flux - zinc chloride and / or ammonium chloride in the solder powder.

[0038] (6) The preparation method of the self-fluxing soft solder provided by the present invention adopts the powder extrusion forming method, in which the soldering flux is evenly distributed and not easy to leak out, facilitating use. Description of the Drawings

[0039] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0040] Figure 1 It is the DSC curve graph of Examples 1 - 5 provided by the present invention;

[0041] Figure 2 It is the SEM-EDS test result graph of the self-fluxing soft solder prepared in Example 2 provided by the present invention;

[0042] Figure 3 It is the SEM-EDS test result graph of the solder prepared in Comparative Example 1 provided by the present invention. Detailed Embodiments

[0043] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0044] In a first aspect, the present invention provides a self-fluxing soft solder that can be used for ferroalloys, especially stainless steel, which is mainly composed of a tin-based solder and a soldering flux with a mass ratio of 75-94 (including but not limited to any point value among 76, 77, 78, 79, 80, 82, 84, 85, 87, 89, 90, 91, 92, 93 or the range value between any two of them): 6-25 (including but not limited to any point value among 7, 8, 9, 10, 12, 14, 15, 17, 19, 20, 21, 22, 23, 24 or the range value between any two of them).

[0045] For example, the mass ratio of the tin-based solder to the soldering flux can be 75:25, 78:22, 80:20, 82:18, 84:16, 85:15, 86:14, 88:12, 90:10, 92:8 or 94:6.

[0046] Among them, the tin-based solder is mainly made of the following components by mass percentage: 7% - 9% of Sb, 4% - 6% of Cu, 0.2% - 2% of Ni, and the balance is Sn.

[0047] Among them, the mass percentage of Sb includes but not limited to any point value among 7.2%, 7.4%, 7.5%, 7.7%, 7.9%, 8.0%, 8.2%, 8.5%, 8.5%, 8.7%, 8.9% or the range value between any two of them; the mass percentage of Cu includes but not limited to any point value among 4.2%, 4.4%, 4.5%, 4.7%, 4.9%, 5.0%, 5.2%, 5.5%, 5.5%, 5.7%, 5.9% or the range value between any two of them; the mass percentage of Ni includes but not limited to any point value among 0.3%, 0.4%, 0.5%, 0.7%, 0.9%, 1.0%, 1.2%, 1.4%, 1.5%, 1.7%, 1.9% or the range value between any two of them.

[0048] The soldering flux includes zinc chloride and / or ammonium chloride.

[0049] The present invention uses Sn-Sb-Cu as the matrix. By controlling the amounts of alloying elements, the melting point of the self-fluxing soft solder is maintained at 230-250 °C, completely avoiding the sensitization temperature range of stainless steel and the problem of intergranular corrosion occurring after brazing.

[0050] Furthermore, for the lead-free solder Sn-Sb-Cu-Ni provided by the present invention, by adding Ni element to the Sn-Sb-Cu matrix, fine and uniformly distributed (Cu,Ni) 6 Sn 5 strengthening phases are formed, greatly improving the shear strength of the brazed joint after welding. Especially when the mass percentage of Ni is 0.5%, the shear strength of the brazed joint reaches 66.9 MPa, which is 60% higher than that without adding Ni. The problem of low shear strength of the joint after brazing with conventional stainless steel soft solders is solved.

[0051] Even further, for the self-fluxing soft solder provided by the present invention, by adding zinc chloride and / or ammonium chloride, the oxide film on the surface of stainless steel can be effectively removed. The problem that the traditional rosin-core self-fluxing tin-based soft solder cannot remove the oxide film on the surface of stainless steel is solved.

[0052] Still further, in the prior art, when traditional solders are used for brazing stainless steel, a brazing flux needs to be added separately. It is difficult to accurately quantify the brazing flux, resulting in waste of the brazing flux and an increase in subsequent cleaning processes. However, the self-fluxing soft solder provided by the present invention can be directly used for brazing without the need to add an additional brazing flux, making it more convenient to use.

[0053] Preferably, the mass ratio of the tin-based solder to the brazing flux is 80-92 (including but not limited to any point value among 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91 or the range value between any two of them): 8-20 (including but not limited to any point value among 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or the range value between any two of them).

[0054] In order to comprehensively consider the melting point of the self-fluxing soft solder and the strength of the welded joint after welding, the composition of the brazing flux is optimized in this application. Preferably, the brazing flux includes zinc chloride and ammonium chloride with a mass ratio of 2-5:1, where the mass ratio includes but not limited to any point value among 2:1, 3:1, 4:1, 5:1 or the range value between any two of them.

[0055] Preferably, the melting point of the self-fluxing soft solder is 230-250 °C, including but not limited to any point value among 231 °C, 233 °C, 235 °C, 237 °C, 238 °C, 239 °C, 240 °C, 241 °C, 242 °C, 245 °C, 248 °C or the range value between any two of them.

[0056] The self-fluxing soft solder provided by the present invention has a specific composition and specific proportion, and its melting point is maintained at 230-250 °C, completely avoiding the sensitization temperature range of stainless steel and solving the problem of intergranular corrosion occurring after brazing.

[0057] Second, the present invention provides a method for preparing the self-fluxing soft solder as described above, including the following steps:

[0058] After the mixed material containing Sb, Cu, Ni and Sn is melted to obtain an ingot, the ingot is made into powder to obtain solder powder;

[0059] The solder powder is mixed with a brazing flux evenly and then plastically formed to obtain a self-fluxing soft solder;

[0060] Wherein, the brazing flux includes zinc chloride and / or ammonium chloride.

[0061] By plastically forming after evenly mixing the solder powder with the brazing flux, the present invention obtains a self-fluxing soft solder that does not require the addition of a brazing flux and can be directly used for brazing, which is easy to use.

[0062] Moreover, by dispersing and firmly wrapping the brazing flux - zinc chloride and / or ammonium chloride in the Sn-Sb-Cu-Ni solder powder, while effectively removing the oxide film on the surface of stainless steel, moisture absorption can be effectively avoided.

[0063] In some specific embodiments of the present invention, the method for making the powder includes at least one of mechanical physical method, ball milling method and atomization method.

[0064] In some specific embodiments of the present invention, after making the powder, a screening step is further included.

[0065] In some specific embodiments of the present invention, the brazing flux is dried and / or ground. Preferably, the drying temperature is 120-150 °C. Preferably, the grinding includes ball milling.

[0066] In order to comprehensively consider the formability and moisture absorption performance of the self-fluxing soft solder, the particle sizes of the solder powder and the brazing flux are optimized in this application. Preferably, the particle size of the solder powder is 30-200 mesh, including but not limited to the point values of any one of 40 mesh, 50 mesh, 60 mesh, 80 mesh, 100 mesh, 120 mesh, 150 mesh, 180 mesh or the range values between any two of them; preferably 50-150 mesh.

[0067] Preferably, the particle size of the brazing flux is 100-300 mesh; including but not limited to the point values of any one of 120 mesh, 150 mesh, 180 mesh, 200 mesh, 230 mesh, 250 mesh, 280 mesh or the range values between any two of them.

[0068] Preferably, the particle size of the soldering flux is smaller than that of the solder powder. This is conducive to the dispersed distribution of the soldering flux and it being firmly wrapped within the solder powder, thereby avoiding moisture absorption.

[0069] Preferably, the method of plastic forming includes at least one of extrusion, drawing, and rolling.

[0070] Preferably, the extrusion includes cold extrusion and / or hot extrusion.

[0071] Preferably, the temperature of the hot extrusion is 100 - 150 °C, including but not limited to any point value such as 110 °C, 120 °C, 130 °C, 140 °C or the range value between any two of them.

[0072] Preferably, the method of plastic forming includes the following steps: after the solder powder and the soldering flux are mixed evenly, cold extrusion, hot extrusion, and drawing are carried out in sequence.

[0073] By using the powder extrusion forming method to prepare the Sn - Sb - Cu - Ni self - fluxing soft solder, the present invention has the soldering flux evenly distributed, not easily leaking out, and convenient for use. Moreover, the soldering flux is dispersed and firmly wrapped in the solder, effectively avoiding moisture absorption.

[0074] In some specific embodiments of the present invention, the plastic forming specifically includes the following steps: the mixed material after the solder powder and the soldering flux are mixed evenly is cold - extruded into a powder blank with a diameter of Φ60 - 90 mm and a height of 30 - 50 mm; then the powder blank is hot - extruded into a thick wire with a diameter of 1.8 - 3.6 mm; and then, by using the waste heat of the hot extrusion, the thick wire is drawn into a thin - wire - shaped self - fluxing soft solder (finished product) with a diameter of 1.6 - 3.2 mm.

[0075] In a third aspect, the present invention provides the application of the self - fluxing soft solder as described above or the self - fluxing soft solder prepared by the preparation method of the self - fluxing soft solder as described above in stainless steel soldering.

[0076] The rosin - cored solder in the prior art is suitable for soldering materials mainly composed of Cu and Ni and cannot remove the oxide film on the surface of stainless steel. However, the Sn - Sb - Cu - Ni self - fluxing soft solder with a specific composition provided by the present invention can effectively remove the oxide film on the surface of stainless steel. Moreover, the strength of the welded joint obtained after soldering is high.

[0077] The following will describe the implementation scheme of the present invention in detail with reference to the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0078] Example 1

[0079] This example provides a self - fluxing soft solder, which is composed of a tin - based solder and a soldering flux with a mass ratio of 88:12. Among them, the tin - based solder is mainly made of the following components by mass percentage: Sb 7%, Cu 4%, Ni 0.2%, and the balance is Sn. The soldering flux includes zinc chloride and ammonium chloride with a mass ratio of 2:1.

[0080] This example also provides a preparation method for the self - fluxing soft solder, including the following steps:

[0081] (1) Weigh Sb, Cu, Ni, and Sn according to the above - mentioned ratio. After melting them into an Sn - Sb - Cu - Ni ingot, use the atomization method to make it into Sn - Sb - Cu - Ni powder, and then perform screening to obtain a solder powder with a particle size of 30 - 50 mesh.

[0082] (2) Weigh, dry zinc chloride and ammonium chloride, and then perform ball - milling to obtain a soldering flux powder with a particle size of 100 - 120 mesh. Then mix the soldering flux powder with the solder powder obtained in step (1) according to the above - mentioned ratio and stir evenly.

[0083] (3) Put the evenly - stirred mixed powder in step (2) into a mold for cold extrusion to obtain a composite powder blank with a diameter of Φ60mm and a height of 30mm. Hot - extrude the composite powder blank at 120°C to obtain a wire with a diameter of 1.8mm. Then, using the waste heat of hot extrusion, perform hot drawing on the above - mentioned wire to obtain a finished self - fluxing soft solder wire with a diameter of 1.6mm.

[0084] Example 2

[0085] The self - fluxing soft solder provided in this example is composed of a tin - based solder and a soldering flux with a mass ratio of 86:14. Among them, the tin - based solder is mainly made of the following components by mass percentage: Sb 8%, Cu 4%, Ni 0.5%, and the balance is Sn. The soldering flux includes zinc chloride and ammonium chloride with a mass ratio of 2.5:1.

[0086] The preparation method of the self - fluxing soft solder provided in this example is basically the same as that of Example 1, with the differences being: in step (1), the solder powder obtained after screening has a particle size of 50 - 100 mesh; in step (2), the soldering flux powder obtained after ball - milling has a particle size of 100 - 150 mesh; in step (3), the diameter of the composite powder blank is the height is 35mm, and the temperature of hot extrusion is 150°C.

[0087] Example 3

[0088] The self-fluxing soft solder provided by this embodiment is composed of a tin-based solder and a soldering flux with a mass ratio of 85:15. Among them, the tin-based solder is mainly made of the following components by mass percentage: 8% Sb, 5% Cu, 1% Ni, and the balance is Sn. The soldering flux includes zinc chloride and ammonium chloride with a mass ratio of 4:1.

[0089] The preparation method of the self-fluxing soft solder provided by this embodiment is basically the same as that of Example 1, except that: in step (1), the solder powder with a particle size of 100-150 mesh is obtained after screening; in step (2), the soldering flux powder with a particle size of 120-150 mesh is obtained after ball milling; in step (3), the diameter of the composite powder blank is 35 mm in height, the temperature of hot extrusion is 130 °C, the diameter of the wire obtained after hot extrusion is 2.3 mm, and the diameter of the finished self-fluxing soft solder obtained after drawing is 2.0 mm.

[0090] Example 4

[0091] The self-fluxing soft solder provided by this embodiment is composed of a tin-based solder and a soldering flux with a mass ratio of 84:16. Among them, the tin-based solder is mainly made of the following components by mass percentage: 8.5% Sb, 4.5% Cu, 2% Ni, and the balance is Sn. The soldering flux includes zinc chloride and ammonium chloride with a mass ratio of 3:1.

[0092] The preparation method of the self-fluxing soft solder provided by this embodiment is basically the same as that of Example 1, except that: in step (1), the solder powder with a particle size of 150-200 mesh is obtained after screening; in step (2), the soldering flux powder with a particle size of 200-300 mesh is obtained after ball milling; in step (3), the diameter of the composite powder blank is 40 mm in height, the temperature of hot extrusion is 130 °C, the diameter of the wire obtained after hot extrusion is 2.7 mm, and the diameter of the finished self-fluxing soft solder obtained after drawing is 2.4 mm.

[0093] Example 5

[0094] The self-fluxing soft solder provided by this embodiment is composed of a tin-based solder and a soldering flux with a mass ratio of 82:18. Among them, the tin-based solder is mainly made of the following components by mass percentage: 9% Sb, 6% Cu, 1.5% Ni, and the balance is Sn. The soldering flux includes zinc chloride and ammonium chloride with a mass ratio of 5:1.

[0095] The preparation method of the self-fluxing soft solder provided by this embodiment is basically the same as that of Example 4, except that: in step (3), the diameter of the composite powder blank is 50 mm in height, the diameter of the wire obtained after hot extrusion is 3.6 mm, and the diameter of the finished self-fluxing soft solder obtained after drawing is 3.2 mm.

[0096] Comparative Example 1

[0097] The chemical composition of the solder provided in this comparative example is basically the same as that of Example 2, except that 0.5% of Ni by mass fraction is replaced with 0.5% of Sn (i.e., Ni is not added).

[0098] The preparation method of the solder provided in this comparative example is the same as that of Example 2.

[0099] Experimental Example 1

[0100] The melting points of the self-fluxing soft solders prepared in each of the above examples and the solders prepared in each of the comparative examples were respectively detected, and the self-fluxing soft solders prepared in each of the above examples and the solders prepared in each of the comparative examples were used to braze stainless steel, and then the strength of the brazed joints obtained after each group of brazing was detected. The results are shown in Table 1 below.

[0101] Table 1 Melting points of each group of solders and strength of brazed joints

[0102]

[0103]

[0104] The DSC curves of Examples 1 to 5 are as Figure 1 shown. Among them, Figure 1 the numbers 1 to 5 in

[0105] correspond to the DSC curves of Examples 1 to 5 respectively. Figure 1 As can be seen from

[0106] and Table 1, the melting point of the self-fluxing soft solder prepared by the present invention is 239 - 241 °C, completely avoiding the sensitization temperature range of stainless steel and avoiding the problem of intergranular corrosion after brazing.

[0107] Experimental Example 2

[0108] SEM-EDS analysis was respectively performed on the self-fluxing soft solder prepared in Example 2 and the solder prepared in Comparative Example 1, and the results are respectively as Figure 2 and Figure 3 shown.

[0109] As can be seen from Figure 2 the self-fluxing soft solder prepared in Example 2 forms fine and uniformly distributed (Cu,Ni) 6 Sn 5 strengthening phases. While in Comparative Example 1, (Cu,Ni) 6 Sn5 Reinforcing phase

[0110] Although the present invention has been illustrated and described with reference to specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the same; those of ordinary skill in the art should understand that without departing from the spirit and scope of the present invention, the technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A self-fluxing soft solder for brazing stainless steel, characterized in that, it is mainly composed of a tin-based solder and a brazing flux with a mass ratio of 75~94:6~25; wherein, the tin-based solder is made of the following components by mass percentage: Sb 7%~9%, Cu 4%~6%, Ni 0.2%~2%, and the balance is Sn; the brazing flux includes zinc chloride and ammonium chloride with a mass ratio of 2~5:1; the preparation method of the self-fluxing soft solder includes the following steps: After the mixed material containing Sb, Cu, Ni and Sn is melted into an ingot, it is made into powder to obtain solder powder; The solder powder and the brazing flux are mixed evenly and then plastically formed to obtain the self-fluxing soft solder; the particle size of the brazing flux is smaller than that of the solder powder, and the brazing flux is dispersed and wrapped in the solder powder.

2. The self-fluxing soft solder according to claim 1, characterized in that, the mass ratio of the tin-based solder to the brazing flux is 80~92:8~20.

3. The self-fluxing soft solder according to claim 1, characterized in that, the melting point of the self-fluxing soft solder is 230~250 °C.

4. The self-fluxing soft solder according to claim 1, characterized in that, the particle size of the solder powder is 30~200 mesh.

5. The self-fluxing soft solder according to claim 1, characterized in that, the particle size of the solder powder is 50~150 mesh.

6. The self-fluxing soft solder according to claim 1, characterized in that, the particle size of the brazing flux is 100~300 mesh.

7. The self-fluxing soft solder according to claim 1, characterized in that, the method of plastic forming includes at least one of extrusion, drawing and rolling.

8. The self-fluxing soft solder according to claim 7, characterized in that, the extrusion includes cold extrusion and / or hot extrusion.

9. The self-fluxing soft solder according to claim 8, characterized in that, the temperature of the hot extrusion is 100~150 °C.

10. The self-fluxing soft solder according to claim 1, characterized in that, the method of plastic forming includes the following steps: after the solder powder and the brazing flux are mixed evenly, cold extrusion, hot extrusion and drawing are carried out in sequence.

11. The self-fluxing soft solder according to any one of claims 1~10 is used in the brazing of stainless steel.

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