Flux-free brazing method for aluminum alloy and brazing paste

Abstract

The method for flux-free brazing of an aluminum alloy includes the steps of: (1) plating a surface of an aluminum alloy to be welded with zinc to form a zinc-plated layer; (2) applying a flux-free brazing paste to the zinc-plated layer, the flux-free brazing paste comprising a binder, 70-80 parts by weight of zinc-aluminum brazing material, and 6.0-8.0 parts by weight of rubidium iron boron magnetic particles; and (3) heating a portion to be welded to form a eutectic or near-eutectic brazing liquid between the zinc-plated layer and the zinc-aluminum brazing material, applying a rotating magnetic field, spinning the rubidium iron boron magnetic particles under the action of the rotating magnetic field, and brazing the aluminum alloy in a flux-free manner. The present invention realizes flux-free brazing of an aluminum alloy by diffusing the plating layer and the brazing material layer under the action of a concentration gradient, and by promoting the spin film breakage and flow of the ferromagnetic particles. The brazed joint obtained has few inclusions and pore defects, a relatively dense brazing seam, and high joint strength. A brazing filler paste for flux-free brazing is further disclosed.

Description

Technical Field

[0001] The present invention belongs to the field of soldering materials, and specifically relates to a flux-free soldering method for aluminum alloys and a soldering paste.

Background Art

[0002] Cast aluminum alloys have low manufacturing costs, are lightweight, have high strength, and have good low-temperature performance, and are widely used in aerospace, ships, automobiles, motorcycles, and large equipment. When casting aluminum alloys, defects such as oxide inclusions, pores, shrinkage, and cracks are likely to occur. Due to the inherent defects of cast aluminum alloys, welding defects such as inclusions, pores, and cracks are likely to occur during soldering.

[0003] Currently, the commonly used soldering method for cast aluminum alloys is to combine a CsF3Al flux with a Zn95Al solder and perform induction or torch soldering in the atmosphere. Zn95Al is a eutectic solder (a solder with a Zn content of 95% is a eutectic solder, and a solder with a Zn content of less than 95% is a hypoeutectic solder). It has good fluidity, a low soldering temperature, and is widely used for soldering cast aluminum alloys. However, the main components of the CsF3Al flux that is compatible with the Zn95Al eutectic solder are CsF and Al3F, which have a high viscosity, and it is difficult to remove its soldering residue. Furthermore, defects such as excessive slag entrainment and pores are formed at the soldering joint, resulting in low joint strength and affecting the service life of the casting.

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a flux-free soldering method for aluminum alloys that reduces inclusions and pores and improves joint strength.

[0005] A second object of the present invention is to provide a soldering paste suitable for use in the above method.

Means for Solving the Problem

[0006] In order to achieve the above object, the flux-free brazing method of the aluminum alloy of the present invention employs the following technical means.

[0007] The flux-free brazing method of an aluminum alloy is Step (1) of applying zinc plating to the brazed surface of the aluminum alloy to form a zinc plating layer; Applying a flux-free brazing material paste to the zinc plating layer, the flux-free brazing material paste comprising a binder and a zinc-aluminum brazing material and the weight ratio with neodymium iron boron magnetic particles is ( 70 - 80 ):( 6.0 - 8.0 ) components, and the components of the zinc-aluminum brazing material is Zn and the weight ratio with Al is ( 80.0 - 90.0 ):( 5.0 - 15.0 ) Step (2); Heating the brazed part to form a eutectic or near-eutectic brazing material liquid in the zinc plating layer and the zinc-aluminum brazing material, and applying a rotating magnetic field, Neodymium Step (3) in which iron-boron magnetic particles perform a spin motion under the action of the rotating magnetic field to perform flux-free brazing joining of the aluminum alloy.

[0008] The flux-free brazing method of the cast aluminum alloy of the present invention realizes flux-free brazing of the aluminum alloy under the action of the concentration gradient of the plating layer and the brazing material layer, and under the spin film breaking and flow promotion of the ferromagnetic particles. The obtained brazed joint has few inclusion and pore defects, the brazed joint is relatively dense, and the joint strength is high.

[0009] It should be understood that in step 2), applying the flux-free brazing material paste to the zinc plating layer means applying the flux-free brazing material paste to the zinc plating layer of one or both of the two aluminum alloys to be brazed.

[0010] Preferably, in step (1), the thickness of the zinc plating layer is 15 to 30 μm.

[0011] Preferably, the Neodymium particle diameter of the iron boron magnetic particles is 30 to 50 nm. Neodymium which are iron boron magnetic particles Neodymium The iron boron magnet (Nd2Fe14B) is Neodymium a tetragonal crystal composed of iron, boron, and is a ferromagnetic material, but Neodymium Another reason for selecting the iron boron magnetic particles is that they have good wettability with respect to the brazing material and do not affect the interfacial bonding property with the brazing material.

[0012] Preferably, the weight ratio of the zinc aluminum brazing material to the binder is (70.0 to 80.0):(3.0 to 6.0), and the binder is one or more selected from polyethylene glycol 200, terpineol, and isopropanol. More preferably, the coating thickness of the brazing material paste is 3 to 8 μm.

[0013] Preferably, in step (3), the rotating magnetic field is generated by an alternating current, the current intensity is 0.1 to 20 A, and the current frequency is 10 2 ~10 5 Hz.

[0014] Preferably, in step (3), the time for applying the rotating magnetic field is 8 to 15 s.

[0015] Preferably, in step (3), the heating temperature is 380 to 420 °C.

[0016] Preferably, the aluminum alloy is a cast aluminum alloy. Cast aluminum alloys are widely applied, and many defects are accompanied during casting, and the conventional brazing joint effect is poor. The brazing joint problem of the cast aluminum alloy can be successfully solved by using the method of the present invention.

[0017] The brazing paste of the present invention employs the following technical means. It is a brazing paste for flux-free brazing of aluminum alloys, comprising a binder and a zinc-aluminum brazing filler metal and the weight ratio with neodymium iron boron magnetic particles is ( 70 - 80 ):( 6.0 - 8.0 ) components, and the components of the zinc-aluminum brazing filler metal is Zn and the weight ratio with Al is ( 80.0 - 90 ):( 5.0 - 15.0 ) .

[0018] The brazing paste for flux-free brazing of aluminum alloys of the present invention is used in combination with the above brazing method to achieve rapid induction brazing of cast aluminum alloys in an air atmosphere, without polluting the environment and being environmentally friendly.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0020] The flux-free brazing method for aluminum alloys of the present invention mainly passes through the concentration gradient diffusion principle, NeodymiumUtilize the spin-breaking film mechanism under the action of a rotating magnetic field of iron-boron ferromagnetic particles to achieve highly reliable and highly dense flux-free brazing of aluminum alloys.

[0021] The following brazing method is mainly implemented in the following steps. Step 1) Apply a pure zinc layer to the surfaces of both of the cast aluminum alloys to be welded to obtain zinc-plated cast aluminum alloys. Step 2) Uniformly apply a brazing material paste to the plating layer of one of the zinc-plated cast aluminum alloys, composite it with the plated surface of the other cast aluminum alloy, assemble and fix it, then place it in a rotating magnetic field, and place the welded part inside the inductor. Step 3) Turn on the power supply and start heating, heat to 380 - 420 °C, the brazing material layer becomes liquid, and under the action of the concentration gradient, it diffuses and dissolves with the plating layers on both sides to form a eutectic or near-eutectic brazing material liquid. Step 4) Keep the brazing material in a liquid state, activate the spin magnetic field, and Neodymium make the iron-boron ferromagnetic particles in the brazing material layer perform spin motion, collide and rub, fill the gaps by the flow of the brazing material liquid, form a metallurgical bond, turn off the magnetic field power supply, stop the heating power supply, and the brazing is completed.

[0022] As shown in Figure 1, in the above method, a pure zinc layer 2 is plated on the surfaces of both of the cast aluminum alloys 1 to be welded, and a hypoeutectic Zn-Al brazing material paste 3 containing iron-boron ferromagnetic particles is applied to the plating layer of one of the cast aluminum alloys and assembled facing the plated surface of the other cast aluminum alloy. During brazing, the workpiece is placed in a spin magnetic field, and the welded part is placed inside the inductor. When heated to 380 - 420 °C, the brazing material layer melts into a brazing material liquid, and under the action of the concentration gradient, the brazing material liquid and the plating layer diffuse, causing a eutectic reaction to form a eutectic Zn95Al brazing material liquid. Activate the spin magnetic field, the ferromagnetic particles generate spin motion, rub and collide on the surface of the plating layer, break the film and can promote the flow, promote the flow of the brazing material liquid to fill the gaps, and achieve flux-free brazing of the cast aluminum alloy. Neodymium

[0023] ​ The solder alloy close to eutectic refers to a solder alloy close to the eutectic composition. The zinc-aluminum solder alloy component (Zn and the weight ratio with Al is ( 80.0 - 90.0 ):( 5.0 - 15.0 ) ) in the solder paste is a hypoeutectic solder alloy. When heated to a temperature of 380 - 420°C, Zn in the plating layer continues to diffuse into the solder layer, increasing the Zn content in the solder alloy and making the solder alloy composition approach the eutectic composition (95Zn5Al) more and more, potentially forming a solder alloy liquid close to eutectic.

[0024] The rotating magnetic field is generated by a transverse magnetic field generator and is designed based on the principle of generating a rotating magnetic field by a symmetrical three-phase alternating current in a symmetrical three-phase winding. It mainly consists of an iron core and a winding. The main feature of generating a rotating magnetic field is that the magnetic field strength does not change, and the direction rotates continuously.

[0025] Specifically, as shown in FIGS. 1 and 2, three pairs of magnetic poles 4 are evenly arranged on the same circumference (the brazed workpiece is arranged inside the magnetic field formed by the three pairs of magnetic poles), and the central axis of the circle on which the three pairs of magnetic poles 4 are evenly arranged passes through the center position of the weld bead. By supplying power to the exciting coil on the magnetic pole in a three-phase single-phase six-wire exciting sequence, a rotating magnetic field is generated. The current intensity is 0.1 - 20 A, the current frequency is 10 2 ~10 5 Hz, and the time is 8 - 15 s.

[0026] The rotating magnetic field rotates clockwise or counterclockwise in a plane perpendicular to the welded surface. In the left side view of FIG. 2, the rotation direction of the magnetic field may be clockwise or counterclockwise.

[0027] The present invention does not require the use of flux, and no flux remains at the brazed joint. Also, Neodymium The spin collision (reciprocating motion) of the iron-boron ferromagnetic particles further serves to discharge slag and remove gas, and the obtained joint is relatively dense and has high strength.

[0028] Hereinafter, embodiments of the present invention will be further described with specific examples. The following examples are for explaining the present invention and do not limit the scope of the present invention. For those where specific conditions are not described in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. When the manufacturer is not specified for the reagents or equipment used, they are all ordinary products available commercially.

[0029] 1. Specific Example of Flux-Free Brazing Method for Cast Aluminum Alloy (Example 1) The flux-free brazing method for the aluminum alloy in this example includes the following steps. (1) A pure zinc layer with a thickness of 15 - 30 μm is plated on the weld surfaces of both of the two cast aluminum alloys to obtain zinc-plated cast aluminum alloys. (2) A brazing paste with a thickness of 3 - 8 μm is uniformly applied to the plating layer of one of the zinc-plated cast aluminum alloys, relatively fitted to the plated surface of the other cast aluminum alloy, fixed, and then placed in a rotating magnetic field, and the welded part is placed in an inductor. Each component of the brazing paste is 75.0 parts by mass of brazing powder, Neodymium 6.0 parts by mass of iron boron ferromagnetic particles, and 3.0 parts by mass of a binder. Each component in the brazing powder is 80.0 parts by mass of Zn and 5.0 parts by mass of Al. Neodymium The particle size of the iron boron ferromagnetic particles is 30 nm. The binder is polyethylene glycol 200. (3) Turn on the power supply and start heating. Heat to 400 °C. Under the concentration gradient action, the brazing layer and the plating layers on both sides diffuse and dissolve to form a eutectic brazing liquid. (4) Keep the brazing material in a liquid state, activate the rotating magnetic field, spin the iron boron ferromagnetic particles in the brazing layer, fill the gaps by the flow of the brazing liquid, and form a metallurgical bond. Then turn off the magnetic field power supply and stop the heating power supply, and the brazing is completed. Neodymium

[0030] In this embodiment, three pairs of magnetic poles are evenly arranged on the same circumference, and the central axis of the three pairs of evenly arranged magnetic poles passes through the center position of the welding bead. By supplying power to the exciting coils on the magnetic poles in a three-phase single-phase six-wire exciting sequence, a rotating magnetic field is generated. The current intensity is 10 A, and the current frequency is 10 4 Hz, and the time is 10 s.

[0031] In other embodiments, depending on the case of welding, the current intensity may be 0.1, 0.5, 1, 3, 5, 8, 15, 20 A, etc., and the current frequency may be 10 2 , 10 3 , 10 5 Hz, etc., and the time may be 8, 12, 15 s, etc. It is preferable that the magnetic particles can reciprocate, promoting film breaking and fluidity.

[0032] (Example 2) In the flux-free welding method of aluminum alloy in this embodiment, each component of the welding material paste is 76.0 parts by mass of welding material powder, Neodymium 7.0 parts by mass of iron-boron ferromagnetic particles, and 5.0 parts by mass of binder. Each component in the welding material powder is 82.0 parts by mass of Zn and 8.0 parts by mass of Al. Neodymium The particle size of the iron-boron ferromagnetic particles is 40 nm, and it is substantially the same as Example 1 except that the binder is terpineol.

[0033] (Example 3) In the flux-free welding method of aluminum alloy in this embodiment, each component of the welding material paste is 77.0 parts by mass of welding material powder, Neodymium 8.0 parts by mass of iron-boron ferromagnetic particles, and 6.0 parts by mass of binder. Each component in the welding material powder is 85.0 parts by mass of Zn and 10.0 parts by mass of Al. Neodymium The particle size of the iron-boron ferromagnetic particles is 50 nm, and it is substantially the same as Example 1 except that the binder is isopropanol.

[0034] (Example 4) The fluxless soldering method of the aluminum alloy in this embodiment is such that each component of the solder paste is 78.0 parts by mass of solder powder, Neodymium 6.0 parts by mass of iron-boron ferromagnetic particles, and 3.0 parts by mass of a binder. Each component in the solder powder is 87.0 parts by mass of Zn and 12.0 parts by mass of Al. Neodymium The particle diameter of the iron-boron ferromagnetic particles is 30 nm, and it is substantially the same as Example 1 except that the binder consists of terpineol and isopropanol with a volume ratio of 1:1.

[0035] (Example 5) The fluxless soldering method of the aluminum alloy in this embodiment is such that each component of the solder paste is 79.0 parts by mass of solder powder, Neodymium 7.0 parts by mass of iron-boron ferromagnetic particles, and 5.0 parts by mass of a binder. Each component in the solder powder is 88.0 parts by mass of Zn and 14.0 parts by mass of Al. Neodymium The particle diameter of the iron-boron ferromagnetic particles is 50 nm, and it is substantially the same as Example 1 except that the binder consists of polyethylene glycol 200 and terpineol with a volume ratio of 1:1.

[0036] (Example 6) The fluxless soldering method of the aluminum alloy in this embodiment is such that each component of the solder paste is 70.0 parts by mass of solder powder, Neodymium 8.0 parts by mass of iron-boron ferromagnetic particles, and 6.0 parts by mass of a binder. Each component in the solder powder is 90.0 parts by mass of Zn and 15.0 parts by mass of Al. Neodymium The particle diameter of the iron-boron ferromagnetic particles is 40 nm, and it is substantially the same as Example 1 except that the binder consists of polyethylene glycol 200, terpineol, and isopropanol with a volume ratio of 1:1:1.

[0037] In other embodiments of the fluxless soldering method of the present invention, the soldering temperature may be 385 °C, 395 °C, 405 °C, 415 °C, 420 °C, etc., and all of these can achieve substantially equivalent experimental results.

[0038] 2. Specific Examples of Solder Paste (Example 7) The solder paste for aluminum alloy flux-free soldering in this example corresponds to the solder paste in the soldering method of Example 1.

[0039] Other examples of the solder paste correspond to the solder paste in the soldering methods of Examples 2 to 6 respectively.

[0040] 3. Experimental Examples (Experimental Example 1) When other conditions are the same, induction soldering with cesium fluoroaluminate flux using Zn95Al eutectic solder was performed on cast aluminum alloy, and flux-free induction soldering of cast aluminum alloy was performed using the soldering method of Example 5. The solder joint forms and joint strengths of the two joints were compared.

[0041] The form of the solder joint of flux-containing soldering is shown in Figure 3, and the form of the solder joint of flux-free soldering is shown in Figure 4.

[0042] From the comparison of the above solder joint forms, it can be seen that there are more inclusions and pores in the solder joints obtained by flux-containing soldering compared with the flux-free solder joints.

[0043] The base material for the welding test of cast aluminum alloy is a plate with a thickness of 2 mm, a width of 15 mm, and a length of 50 mm. After soldering, it is processed into a standard shear sample according to the provisions of GB / T11364-2008, and the shear strength of the joint is tested and compared. The results are shown in Table 1.

[0044] The comparison of the shear strengths of the two joints is shown in Table 1. The cases of the shear strengths of some test pieces are shown in Figure 5.

[0045]

Table 1

[0046] The average shear strength of the solder joint of Example 1, which is a flux-free solder joint, is 44.7 MPa. However, the average shear strength of the solder joint obtained by soldering with flux-containing solder is only 21.8 MPa, indicating that the former is much higher than the latter.

[0047] The shear strengths of the joints of Examples 1 to 6 are shown in Table 2.

[0048]

Table 2

[0049] As can be seen from Table 2, the shear strength of the joint obtained by the method of the example was significantly improved compared to soldering with Zn95Al solder with flux.

[0050] (Experimental Example 2) Energy spectrum analysis was performed on the inclusions in the soldering with flux, and the results are shown in Figure 6.

[0051] As can be seen from Figure 6, the energy spectrum analysis results at point A in the flux-containing solder joint show Cs and F components. There are many flux residues in the solder joint, which are difficult to remove, and it was found that the solder strength is also difficult to effectively improve.

[0052] (Supplementary Note) (Supplementary Note 1) A flux-free soldering method for aluminum alloy, Step (1) of applying zinc plating to the weld surface of the aluminum alloy to form a zinc plating layer; Applying a flux-free solder paste to the zinc plating layer, wherein the flux-free solder paste consists of a binder and a zinc-aluminum solder and the weight ratio with neodymium iron boron magnetic particles is ( 70 - 80 ):( 6.0 - 8.0 ) components, and the components of the zinc-aluminum solder are Zn and the weight ratio with Al is ( 80.0 - 90.0 ):( 5.0 - 15.0) Step (2), heating the welded part to form a eutectic or near-eutectic solder liquid in the zinc plating layer and the zinc-aluminum solder material, and applying a rotating magnetic field, Neodymium step (3) in which the iron-boron magnetic particles perform a spin motion under the action of the rotating magnetic field to perform flux-free soldering joining of the aluminum alloy, and A flux-free soldering method for an aluminum alloy, characterized by the above.

[0053] (Appendix 2) In step (1), the thickness of the zinc plating layer is 15 to 30 μm, The flux-free soldering method for an aluminum alloy according to Appendix 1, characterized by the above.

[0054] (Appendix 3) The Neodymium particle diameter of the iron-boron magnetic particles is 30 to 50 nm, The flux-free soldering method for an aluminum alloy according to Appendix 1, characterized by the above.

[0055] (Appendix 4) The weight ratio of the zinc-aluminum solder material to the binder is (70.0 to 80.0):(3.0 to 6.0), and the binder is one or more selected from polyethylene glycol 200, terpineol, and isopropanol, The flux-free soldering method for an aluminum alloy according to any one of Appendices 1 to 3, characterized by the above.

[0056] (Appendix 5) The coating thickness of the solder paste is 3 to 8 μm, The flux-free soldering method for an aluminum alloy according to Appendix 4, characterized by the above.

[0057] (Appendix 6) In step (3), the rotating magnetic field is generated by an alternating current, the current intensity is 0.1 to 20 A, and the current frequency is 10 2 ~10 5which is Hz The flux - free brazing method of the aluminum alloy according to Supplementary Note 1, characterized in that

[0058] (Supplementary Note 7) The rotating magnetic field rotates clockwise or counterclockwise in a plane perpendicular to the surface to be welded The flux - free brazing method of the aluminum alloy according to Supplementary Note 1 or 6, characterized in that

[0059] (Supplementary Note 8) In step (3), the time for applying the rotating magnetic field is 8 - 15 s The flux - free brazing method of the aluminum alloy according to Supplementary Note 6, characterized in that

[0060] (Supplementary Note 9) In step (3), the heating temperature is 380 - 420 °C The flux - free brazing method of the aluminum alloy according to Supplementary Note 1, characterized in that

[0061] (Supplementary Note 10) The aluminum alloy is a cast aluminum alloy The flux - free brazing method of the aluminum alloy according to Supplementary Note 1 or 6 or 8 or 9, characterized in that

[0062] (Supplementary Note 11) A brazing paste for flux - free brazing of aluminum alloy, comprising a binder and a zinc - aluminum brazing filler metal and the weight ratio with neodymium iron boron magnetic particles is ( 70 - 80 ):( 6.0 - 8.0 ) as components, and the components of the zinc - aluminum brazing filler metal are Zn and the weight ratio with Al is ( 80.0 - 90 ):( 5.0 - 15.0 ) and The brazing paste for flux - free brazing of aluminum alloy, characterized in that

Explanation of Reference Signs

[0063] 1 Cast aluminum alloy 2 Zinc layer 3 Brazing paste 4 Magnetic pole

Claims

1. A fluxless brazing method for aluminum alloy, comprising: Step (1) of applying zinc plating to the brazed surface of the aluminum alloy to form a zinc plating layer; Step (2) of applying a fluxless brazing material paste to the zinc plating layer, wherein the fluxless brazing material paste consists of a binder and a component with a weight ratio of zinc-aluminum brazing material to neodymium iron boron magnetic particles being (70-80):(6.0-8.0), and the component of the zinc-aluminum brazing material has a weight ratio of Zn to Al being (80.0-90.0):(5.0-15.0); Step (3) of heating the brazed part to form a eutectic or near-eutectic brazing liquid on the zinc plating layer and the zinc-aluminum brazing material, applying a rotating magnetic field, causing the neodymium iron boron magnetic particles to perform a spin motion under the action of the rotating magnetic field, and brazing and joining the aluminum alloy in a fluxless manner. A fluxless brazing method for aluminum alloy, characterized by the above.

2. In step (1), the thickness of the zinc plating layer is 15-30 μm. The fluxless brazing method for aluminum alloy according to claim 1, characterized by the above.

3. The particle size of the neodymium iron boron magnetic particles is 30-50 nm. The fluxless brazing method for aluminum alloy according to claim 1, characterized by the above.

4. The weight ratio of the zinc-aluminum brazing material to the binder is (70.0-80.0):(3.0-6.0), and the binder is one or more selected from polyethylene glycol 200, terpineol, and isopropanol. The fluxless brazing method for aluminum alloy according to any one of claims 1-3, characterized by the above.

5. The coating thickness of the brazing material paste is 3-8 μm. The fluxless brazing method for aluminum alloy according to claim 4, characterized by the above.

6. In step (3), the rotating magnetic field is generated by an alternating current, the current strength is 0.1-20 A, and the current frequency is 10 ２ ~10 ５ Hz, The fluxless brazing method for aluminum alloy according to claim 1, characterized by the above.

7. The rotating magnetic field rotates clockwise or counterclockwise in a plane perpendicular to the brazed surface. The fluxless brazing method for aluminum alloy according to claim 1 or 6, characterized by the above.

8. In step (3), the time for applying the rotating magnetic field is 8-15 s. The fluxless brazing method for aluminum alloy according to claim 6, characterized by the above. Claim 9 In step (3), the heating temperature is 380 to 420 °C, The flux-free soldering method for aluminum alloy according to claim 1, characterized in that. Claim 10 The aluminum alloy is a cast aluminum alloy, The flux-free soldering method for aluminum alloy according to claim 1 or 6 or 8 or 9, characterized in that. Claim 11 A solder paste for flux-free soldering of aluminum alloy, It consists of a binder and a component with a weight ratio of (70 to 80): (6.0 to 8.0) between a zinc-aluminum solder and neodymium iron boron magnetic particles. The composition of the zinc-aluminum solder has a weight ratio of Zn to Al of (80.0 to 90): (5.0 to 15.0). The solder paste for flux-free soldering of aluminum alloy, characterized in that.

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