Preparation method of brazing filler metal

Abstract

The invention belongs to the field of preparation of brazing filler metal, and particularly relates to a preparation method of brazing filler metal. The preparation method of the brazing filler metal comprises the following steps that the upper brazing filler metal strip, the at least one middle brazing filler metal strip and the lower brazing filler metal strip are welded together under the action of an electrode roller; the components of at least one middle brazing filler metal belt are different from those of the upper brazing filler metal belt and the lower brazing filler metal belt, and the upper brazing filler metal belt, the at least one middle brazing filler metal belt and the lower brazing filler metal belt are fused into the whole alloy brazing filler metal during brazing. According to the preparation method of the brazing filler metal, after the multiple brazing filler metal strips enter the electrode roller, the composite interfaces of every two adjacent brazing filler metal strips are melted under the action of resistance heat and form metallurgical bonding under the pressure of the electrode roller, and the functional composite brazing filler metal with extremely high integrity is obtained; on the basis of metallurgical bonding, the brazing filler metal can be conveniently fused into an integral alloy, the deviation design or instability condition of brazing filler metal composition is reduced, and it is guaranteed that the expected welding seam function is achieved.

Description

Technical Field

[0001] The invention belongs to the field of solder preparation, and in particular relates to a method for preparing the solder. Background Art

[0002] Brazing filler metals are widely used in aerospace, electrical and mechanical, automotive, electronic information, refrigeration and household appliances, and other fields, and can be called the "universal glue" of the industry. Different joint performance is required for different service environments of welding joints. For example: for use environments that require high sealing, the brazed joints need to have good flowability; for long-term use in high-salt corrosion environments such as the ocean, the joints must have very good corrosion resistance; for long-term use in impact service environments, the joints need to have very high impact resistance. To obtain such joints with different functional characteristics, it is necessary to prepare welding rods with certain functionality.

[0003] Silver-based solders with Ag, Cu, and Zn as main alloying elements have been widely used in machinery, home appliances, tools and other industries. In order to meet different performance requirements, low melting point elements such as Sn are usually added to significantly reduce the melting point of the solder and improve its wetting properties. Traditional AgCuZnSn solders are produced by adding Sn elements to AgCuZn alloy solders through batching, and then using smelting, casting, rolling, extrusion, drawing and other processes to form BAg25CuZnSn, BAg30CuZnSn, BAg40CuZnSn, BAg45CuZnSn, BAg56CuZnSn and other varieties. However, the Sn content of the AgCuZnSn solder produced by the above method should not be too high (generally below 2%), otherwise the plasticity of the solder will be significantly reduced, and problems such as processing difficulties, low efficiency, and low yield will occur, which will significantly increase the production cost of this type of solder. Other alloy elements, such as Ni, Co, Mn, etc., can play a corresponding performance adjustment role (corrosion resistance, impact resistance) by adding appropriate amounts to the basic solder (silver-copper-zinc solder), but they also have similar problems as mentioned above, which leads to the overall industrial production of various functional solders facing problems such as low production efficiency and high production costs.

[0004] In order to solve the production problem of the above functional solder, the applicant has proposed a composite solder structure design (CN106181124A) in the early stage. The composite solder includes a composite rolled tin layer and a solder alloy layer. The flux layer is sprayed on the outer surface of the tin layer and the solder alloy layer to form a four-layer composite solder product. The focus of the composite solder is the composite rolling of the tin layer and the solder alloy layer. Compared with the traditional methods of depositing the tin layer by electroplating, hot dip plating, thermal spraying, chemical plating, etc., the composite rolling scheme using a precision rolling mill can form a tin layer with uniform thickness and beautiful shape.

[0005] The scheme of composite rolling using precision rolling mills requires a large rolling force to form a good mechanical bond. At the same time, during use, due to the low melting point of the Sn layer, the Sn layer will melt first and easily separate from the solder alloy layer. The amount of Sn that fuses with the solder alloy layer to form the overall alloy is reduced or unstable, which makes it difficult to ensure that the composition of the functional composite solder during brazing meets the design, which in turn causes the weld function to be less than expected. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a solder, so as to solve the problem that the composition of the existing functional composite solder is easily deviated from the design during brazing, thus affecting the function of the weld.

[0007] In order to achieve the above purpose, the technical solution adopted by the present invention is: A method for preparing solder comprises the following steps: an upper solder strip, at least one middle solder strip, and a lower solder strip are welded together under the action of an electrode roller; the composition of at least one middle solder strip is different from that of the upper solder strip and the lower solder strip, and the upper solder strip, at least one middle solder strip, and the lower solder strip are fused into an integral alloy solder during brazing.

[0008] The method for preparing the solder provided by the present invention comprises the following steps: after a plurality of solder strips enter an electrode roller, the composite interface of two adjacent solder strips melts under the action of resistance heat and forms a metallurgical bond under the pressure of the electrode roller, thereby obtaining a functional composite solder with extremely high integrity; during brazing, the solder can be conveniently fused into an integral alloy on the basis of the metallurgical bond, thereby reducing the deviation of the solder composition from the design or the occurrence of instability, thereby ensuring the realization of the expected weld function.

[0009] Preferably, the upper solder band and the lower solder band are silver-based solder or copper-based solder, and the middle solder band is a metal single-element strip or an alloy strip. The upper solder band and the lower solder band are both basic solders, and the middle solder band is a metal single-element strip or an alloy strip. The performance of the basic solder is optimized by using the middle solder band. The components of the upper solder band and the lower solder band can be the same or different. With this design, the basic solder is divided into two. During brazing, the components of the middle solder band can be more evenly fused, thereby further improving the uniformity and stability of the brazing effect.

[0010] Further preferably, the metal single substance strip is a pure copper strip or a pure silver strip, the alloy strip is a copper alloy strip, and the alloy elements in the copper alloy strip are selected from one or a combination of two or more of Sn, Ni, Co, Mn, Zn, and Ag. The middle solder strip combined with the upper and lower solder strips can quickly produce the required composite solder. At the same time, the introduction of alloy elements such as Sn, Ni, Co, and Mn is generally to prepare composite solders with special uses. For example, Sn can significantly improve the flowability of the solder; Ni, Mn, and Co can improve the toughness of the brazed joint, and Mn also has the effect of reducing the melting point of the solder. Of course, alloy strips such as CuZn and AgCu related to the elemental composition of the upper and lower solder strips can also be selected to achieve the composition adjustment of the composite solder and simplify the preparation of new solders. This method can be used to form silver-based solders with various functions as the silver-based solders of the upper and lower solder strips. The processing process is mature, and commercially available finished products that meet the specifications can be directly purchased for use. The middle solder strip is made of copper alloy, which is easy to disperse the alloy elements and has a good composite effect with the upper solder strip and the lower solder strip.

[0011] Preferably, before entering the electrode roller, low melting point metal powder is added to the composite interface of the upper solder strip, the lower solder strip and the middle solder strip, and the melting point of the low melting point metal powder is not higher than 450°C. By adding low melting point metal powder to the composite interface, the interface resistance can be increased, which is conducive to promoting the heat melting welding between the strips during electrode roller rolling and improving the bonding strength of the composite solder product. Low melting point metal powder can be added between all composite interfaces as needed, and can also be selectively added between certain composite interfaces according to the characteristics of different solder strips.

[0012] Further preferably, the added thickness of the low melting point metal powder is not greater than 0.1 mm.

[0013] Further preferably, the low melting point metal powder is one or a combination of two or more of Sn powder, SnAg alloy powder, and CnSn alloy powder; the mass content of Sn in the SnAg alloy powder and CnSn alloy powder is above 90%. Sn powder, SnAg alloy powder, and CuSn alloy powder are all high Sn content (>93 wt%) powders with a melting temperature below 400°C. The main purpose is to increase the Sn content of the overall composite solder, which solves the problems of difficult processing, low efficiency, and low yield in the production of high Sn (>5 wt%) solder by traditional methods.

[0014] Preferably, before entering the electrode roller, the surface to be composited of the middle solder strip or the surface to be composited of the upper solder strip and the lower solder strip is laser roughened. Laser roughening can not only remove impurities on the solder strip surface, but also provide favorable conditions for the resistance contact between the solder strips.

[0015] Further preferably, the laser texturing controls the surface roughness Ra≤1 μm.

[0016] Preferably, the voltage applied by the electrode roller is 220-380V, the current is 1-3A, and the pressure is 10-25MPa. With the above conditions, a good welding effect can be easily achieved.

[0017] In summary, the core beneficial effects of the present invention are mainly reflected in the following aspects: 1) The basic solder and functional solder are processed separately to reduce the processing difficulty.

[0018] 2) The roller electrode method, resistance heating, and full-process computer control are used to achieve continuous production of functional composite solder strips. The processability of the solder is significantly improved, which is conducive to improving production efficiency and reducing production costs.

[0019] 3) Adding a gas protection cover during resistance heating can prevent oxidation problems during resistance heating; the composite wide band after welding can be directly prepared into a finished composite brazing electrode through a cutting machine and a rolling machine.

[0020] 4) Use one basic material and match it with various functional welding rods to achieve rapid switching of multiple types of functional solder strips without affecting the normal production process of the enterprise.

[0021] 5) Both the basic solder strip and the functional solder strip can be purchased from the market, realizing the separation of smelting and processing. The final solder formula is well kept confidential and has little environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of a device for preparing a functional composite solder according to the present invention; Among them, 1-upper unwinding wheel; 2-lower unwinding wheel; 3-middle unwinding wheel; 4-electrode roller; 5-gas protection box; 6-cutting machine; 7-rolling machine; 8-finished functional composite solder electrode; Figure 2 This is a microscopic interface structure diagram of the functional composite solder prepared in Example 1 of the present invention; Figure 3 This is a microscopic interface structure diagram of the functional composite solder prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0023] In order to solve the problem that existing functional composite solders are difficult to prepare and have high production costs, the present invention proposes a method for continuously preparing functional composite solders, which mainly includes welding an upper solder band, at least one middle solder band, and a lower solder band together under the action of an electrode roller; the composition of at least one of the middle solder bands is different from that of the upper solder band and the lower solder band, and the upper solder band, at least one middle solder band, and the lower solder band are fused into an integral alloy solder during brazing.

[0024] The above method is applicable to different series of solders such as silver-based and copper-based solders, and can obtain components with different compositions and properties, which is not only beneficial to solder production, but also to solder use. The method is also conducive to fast switching of different varieties and batch production, thereby reducing production costs.

[0025] The schematic diagram of the device for preparing the functional composite solder of the present invention is as follows Figure 1 As shown, it includes an unwinding device, an electrode roller, a cutting machine and a rolling cutter.

[0026] The unwinding device includes an upper unwinding wheel 1, a lower unwinding wheel 2 and a middle unwinding wheel 3, which are used to unwind the upper solder strip, the lower solder strip and the middle solder strip respectively. The electrode roller 4 is arranged in a gas protection box 5 to prevent the surface of the solder from being oxidized during the heating process. The protective gas can use an inert gas or a reducing gas. The cutting machine 6 and the rolling cutter 7 are arranged downstream of the electrode roller in sequence to cut the formed composite solder strip to obtain a finished functional composite solder electrode 8.

[0027] Preferably, the electrode roller is a hollow structure, and a coolant can be passed into the interior to cool the electrode roller. The coolant can be selected from one or more of water, methoxy-nonafluorobutane, 2-(trifluoromethyl)-3-ethoxy dodecafluorohexane, nonafluoroisobutyl ethyl ether, and C5-18-perfluoroalkane electronic fluorination liquid.

[0028] The following is a detailed description of the solder production method based on the above device, which adopts the following steps: (1) Production of conventional solder strips (upper and lower solder strips) a. Place the raw materials with the basic components in a smelting furnace for smelting and cast into ingots.

[0029] b. After the ingot is heated, it is placed in an extruder and extruded into a thick plate through a die; c. The solder strip of specified thickness and width is obtained by rolling, and the surface is cleaned and then wound into a coil for use. Here, the thickness of the upper and lower solder strips can be 4~10mm and the width can be 30~100mm.

[0030] (2) Production of functional solder strip (middle solder strip) a. Place the raw materials with basic functional components in a smelting furnace for smelting and cast into ingots.

[0031] b. After the ingot is heated, it is placed in an extruder and extruded into a thick plate through a die; c. The specified thickness and width of the solder strip is obtained by rolling, and the surface is cleaned and then wound into a coil for use. Here, the thickness of the middle solder strip can be 1~8mm and the width can be 30~100mm. The widths of the upper and lower solder strips and the middle solder strip are the same to achieve synchronous electrode composite solder strips; the thickness of the middle solder strip is generally not greater than that of the upper and lower solder strips to prevent the upper and lower solder strips from being too thin, resulting in side slip when the upper and lower rollers are pressurized.

[0032] (3) Preparation of composite welding strip a. Place two conventional solder strips on two outer unwinding wheels, and place one or more functional solder strips on the corresponding intermediate unwinding wheels; b. The surfaces of the upper and lower solder strips to be composited are laser-textured and then placed between two electrode rollers. The two electrode rollers shrink toward the middle, compacting the three layers of solder strips. The current and pressure between the electrodes are controlled by a computer system. c. According to Ampere's law, the resistance increases due to the gap between the middle solder strip and the upper and lower solder strips. According to Q=I 2 RT, the heat generation increases, and the interface composite will heat up and melt; d. Due to the pressure between the two roller electrodes, the middle solder strip is metallurgically bonded with the upper and lower solder strips and welded together to form a composite solder strip.

[0033] e. The overall resistance heating device is placed in a gas protection box, which can effectively prevent the solder surface from being oxidized during the heating process and affecting the composite effect. The protective gas can be an inert gas or a reducing gas.

[0034] (4) Cutting of composite welding strip a. The composite welding strip is cut and rolled, and different cutters are replaced according to the required width to roll and cut into composite welding rods of corresponding width; b. After deburring and quality inspection, the composite welding rod can be packaged and shipped out.

[0035] The implementation process of the present invention is described in detail below in conjunction with specific embodiments. In the following embodiments, the width of the upper and lower solder strips and the middle solder strip is 100 mm.

[0036] 1. The specific embodiment of the method for preparing the solder of the present invention is as follows: Example 1 The method for preparing the solder of this embodiment comprises the following steps: (1) Production of conventional solder strips a. The raw materials with the basic components are placed in a smelting furnace for smelting and cast into ingots.

[0037] b. After the ingot is heated, it is placed in an extruder and extruded into a thick plate through a special die.

[0038] c. The BAg35Cu32Zn33 welding strip with a thickness of 4.2 mm is obtained by rolling, and is wound into a coil for use after surface cleaning.

[0039] In other implementations, other conventional silver-based solders may also be selected, such as BAg50Cu30Zn20 as the conventional solder strip.

[0040] (2) Production of functional solder strips a. Place the raw materials with basic functional components in a smelting furnace for smelting and cast into ingots.

[0041] b. After the ingot is heated, it is placed in an extruder and extruded into a thick plate through a special die.

[0042] c. A CuSn welding strip (Cu90Sn10, i.e., Sn mass content is 10% and the remainder is Cu) with a specified thickness of 1.6 mm is obtained by rolling, and is wound into a coil for standby use after surface cleaning.

[0043] (3) Preparation of composite welding strip a. Place two conventional solder BAgCuZn solder strips (as the upper and lower solder strips) on two unwinding wheels, and place a CuSn functional solder strip (as the middle solder strip) on the unwinding wheel.

[0044] b. Before entering the electrode roller, the surfaces of the upper and lower solder strips to be composited are laser roughened respectively. Laser roughening can not only remove impurities on the solder strip surface, but also provide favorable conditions for the resistance contact between the upper and lower solder strips. Laser roughening can control the surface roughness Ra≤1μm. The upper and lower solder strips and the middle solder strip are combined in sequence and enter between the two electrode rollers of the gas protection box. The two electrode rollers shrink toward the middle and press the three layers of solder strips. The computer system controls: the electrode voltage is 380V, the current is 2A, the pressure between the electrodes is 2kN, the contact surface between the electrode roller and the solder strip is 2mm*100mm, and the solder strip is under pressure of 10MPa.

[0045] c. According to Ampere's law, the resistance increases due to the gap between the middle solder strip and the upper and lower solder strips. According to Q=I 2 RT, the heat generation increases, and the interface composite will heat up and melt.

[0046] d. Due to the pressure between the two roller electrodes, the middle solder strip is metallurgically bonded with the upper and lower solder strips and welded together to form a composite solder strip.

[0047] e. The overall resistance heating device is placed in a gas protection box, which can effectively prevent the solder surface from being oxidized during the heating process and affecting the composite effect. The protective gas can be an inert gas or a reducing gas.

[0048] (4) Cutting of composite welding strip a. The composite welding strip is cut and rolled, and different cutters are replaced according to the required width to roll-cut into composite welding rods of corresponding width.

[0049] b. After deburring and quality inspection, the composite welding rod can be packaged and shipped out.

[0050] On the basis of Example 1, in order to increase the composite efficiency and the uniformity of melting of the finished composite solder during use, multiple middle solder strips can be used, and the middle solder strips are stacked up and down. The composition of each middle solder strip can be the same or different, for example, it can be pure metals such as silver and copper, or it can be in the form of an alloy.

[0051] Example 2 The difference between the preparation method of the solder of this embodiment and that of embodiment 1 is as follows: (1) Production of conventional solder strips The BAgCuZn welding strip (BAg35Cu32Zn33) with a thickness of 6 mm is obtained by rolling, and is wound into a coil for use after surface cleaning.

[0052] (2) Production of functional solder strips A CuNi welding strip (Cu90Ni10, i.e., Ni content is 10% by mass and the balance is Cu) with a thickness of 5 mm is obtained by rolling, and is wound into a coil for use after surface cleaning.

[0053] (3) Preparation of composite welding strip Controlled by computer system: electrode voltage is 380V, current is 3A, pressure between electrodes is 4kN, and pressure on welding strip is 20MPa.

[0054] Example 3 The difference between the preparation method of the solder of this embodiment and that of embodiment 1 is as follows: (1) Production of conventional solder strips The BAg95Cu welding strip with a thickness of 6 mm is obtained by rolling, and is wound into a coil for use after surface cleaning.

[0055] (2) Production of functional solder strips Pure copper strip with a thickness of 4 mm is obtained by rolling, and after surface cleaning, it is wound into a coil for use.

[0056] (3) Preparation of composite welding strip Controlled by computer system: electrode voltage is 380V, current is 2.7A, pressure between electrodes is 5kN, and pressure on welding strip is 25MPa.

[0057] Example 4 The difference between the method for preparing the solder of this embodiment and that of Embodiment 1 is as follows: (1) Production of conventional solder strips The BAgCuZn welding strip (BAg35Cu32Zn33) with a thickness of 6 mm is obtained by rolling, and is wound into a coil for use after surface cleaning.

[0058] (2) Production of functional solder strips The CuSn welding strip (Cu90Sn10) with a thickness of 5 mm is obtained by rolling, and is wound into a coil for use after surface cleaning.

[0059] (3) Preparation of composite welding strip a. Place two conventional solder BAgCuZn strips on two unwinding wheels and a CuSn functional solder strip on the unwinding wheel.

[0060] b. At the front angle where the three-layer welding strip enters the roller, Cu5Sn95 alloy powder (i.e., Sn mass content is 95%, and the remainder is Cu) is sprayed at a constant flow and speed to the two contact surfaces through the nozzle to ensure that the added thickness of Cu5Sn95 alloy powder is not more than 0.1mm. This can reduce the welding current to a certain extent and increase the welding speed. The added Sn can also reduce the melting point of the solder and improve the wetting performance.

[0061] c. The two electrode rollers shrink toward the middle, compressing the three layers of solder strips. The computer system controls: electrode voltage 380V, current 1.7A, pressure between electrodes 3 kN, and solder strip pressure 15MPa.

[0062] d. According to Ampere's law, there is a gap between the middle solder strip and the upper and lower solder strips, and due to the presence of alloy powder, the resistance is relatively large. According to Q=I 2 RT, the heat generation increases, and the alloy powder has a low melting point, so it will heat up and melt quickly.

[0063] e. Due to the pressure between the two roller electrodes, the middle solder strip, CuSn alloy powder and the outer solder are metallurgically combined and welded together to form a composite solder strip.

[0064] The composition of the composite solder product prepared in this way is shown in Table 1 below.

[0065] Table 1 Composite solder product composition description 2. Experimental Examples Experimental Example 1 The interface bonding of the functional composite solders obtained in Example 1 and Example 2 was observed, and the results were as follows: Figure 2 and Figure 3 As shown in the figure, the three layers of the functional composite solder obtained in the embodiment are tightly bonded to each other, showing a typical metallurgical bonding state.

[0066] Experimental Example 2 On the basis of Example 3, the pressure of the welding strip was adjusted to 10 MPa, 15 MPa and 20 MPa respectively, and the interlayer tensile strength of the composite welding strip under different pressures was investigated (GB / T 228-2002 Room temperature tensile test method for metal materials). The results are shown in Table 2.

[0067] Table 2 Interlayer tensile strength of composite welding strip under different pressures As shown in Table 2, the interlayer tensile strength of the composite welding strip produced by the method of the present invention reaches 104-173 MPa, showing good interlayer bonding. In addition, due to the use of a sandwich-like core structure, the integrity of the material is significantly improved, which is also conducive to improving the uniformity of melting when the welding strip is used.

[0068] Example 3 On the basis of Example 4, other conditions remained the same, and the current and welding speed required for the welding process of the composite solder without adding alloy powder were compared. The results are shown in Table 3.

[0069] Table 3 Comparison of the composite effects of adding / not adding alloy powder It can be seen from Table 3 that after adding the alloy powder, the surface roughness between the upper and lower welding strips and the middle layer increases, the required current is reduced from 1.9A to 1.7A, and the welding speed is reduced from 2s to 1.5s, which improves the welding rate of the composite solder. Moreover, the interface bonding effect of the prepared composite welding strip is also better than that without adding alloy powder.

Claims

1. A method for preparing a solder, characterized in that: The following steps are involved: The upper solder band, at least one middle solder band and the lower solder band are welded together under the action of the electrode roller; the composition of at least one middle solder band is different from that of the upper solder band and the lower solder band, and the upper solder band, at least one middle solder band and the lower solder band are fused into a whole alloy solder during brazing.

2. The method for preparing the solder according to claim 1, characterized in that: The upper solder strip and the lower solder strip are silver-based solder or copper-based solder, and the middle solder strip is a metal single-element strip or an alloy strip.

3. The method for preparing the solder according to claim 2, characterized in that: The metal strip is a pure copper strip or a pure silver strip, the alloy strip is a copper alloy strip, and the alloy elements in the copper alloy strip are selected from one or a combination of two or more of Sn, Ni, Co, Mn, Zn, and Ag.

4. The method for preparing the solder according to claim 1, characterized in that: Before entering the electrode roller, low melting point metal powder is added to the composite interface of the upper solder band, the lower solder band and the middle solder band, and the melting point of the low melting point metal powder is not higher than 450°C.

5. The method for preparing the solder according to claim 4, characterized in that: The added thickness of the low melting point metal powder is not more than 0.1 mm.

6. The method for preparing the solder according to claim 4, characterized in that: The low melting point metal powder is one or a combination of two or more of Sn powder, SnAg alloy powder, and CnSn alloy powder; the mass content of Sn in the SnAg alloy powder and the CnSn alloy powder is above 90%.

7. The method for preparing the solder according to claim 1, characterized in that: Before entering the electrode roller, the surface to be composited of the middle solder strip or the surface to be composited of the upper solder strip and the lower solder strip is laser roughened.

8. The method for preparing the solder according to claim 7, characterized in that: The laser texturing controls the surface roughness Ra≤1 μm.

9. The method for preparing the solder according to claim 1, characterized in that: The voltage applied by the electrode roller is 220~380V, the current is 1~3A, and the pressure is 10~25MPa.

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