A brazing plate for fluxless brazing, its preparation method and application

Abstract

The present invention relates to the technical field of brazing materials, and in particular, to a brazing plate for fluxless brazing, a preparation method thereof, and an application thereof. The brazing plate comprises a composite plate in a sandwich foil structure and rupture layers located on both sides of the composite plate. The rupture layers contain Ge. The composite plate comprises a core layer and solder layers located on both sides of the core layer. By mass percentage, the solder layers contain not less than 0.9% of La and not less than 0.9% of Ce. The brazing plate provided by the present invention does not need to be coated with a brazing flux during brazing, can realize fluxless brazing of a radiator, and has high joint strength after brazing. The method of the present invention first rolls out a brazing plate without rupture layers, and then dip-coats a layer of rupture metal powder on its upper and lower surfaces to form a brazing plate with a rupture metal layer through in-situ melting reaction, overcoming the problem that it is difficult to prepare a brazing plate with a Ge-containing rupture layer by the traditional rolling method. Moreover, the rupture layer is metallurgically bonded to the composite plate, with high bonding strength and not easy to fall off.

Description

Technical Field

[0001] The present invention relates to the technical field of brazing materials, and in particular, to a brazing plate for fluxless brazing, a preparation method thereof, and an application thereof. Background Art

[0002] A brazing plate is composed of a base material at the core and a brazing filler metal layer on the surface layer, and is commonly used for gas shielded furnace welding of radiators or sealed shielding boxes of various specifications and complete assemblies.

[0003] Currently, when brazing a radiator, the brazing plate used is a conventional brazing filler metal pressed on the surface of the base material substrate, with single-sided pressing or double-sided pressing. The conventional brazing method is to first cut the brazing plate into the same size as the part to be welded, evenly spray a layer of brazing flux on its upper and lower surfaces, dry it, assemble it with the workpiece to be welded, and then put it into the furnace for nitrogen shielded brazing. However, during the subsequent assembly of the brazing plate, the brazing flux layer on its surface is easily touched or collided and partially falls off, resulting in uneven brazing flux layer and affecting the welding consistency; more seriously, the brazing flux cannot be completely decomposed and volatilized during the brazing process, causing a large amount of residues and pores in the brazing seam, seriously affecting the airtightness and welding quality of the radiator.

[0004] In addition, due to the relatively complex and dense oxide film on the surface of die-cast aluminum alloy, it is necessary to use brazing flux when performing nitrogen shielded brazing with a conventional brazing plate, otherwise it is difficult to effectively weld.

[0005] Therefore, there is an urgent need to develop a brazing plate for fluxless brazing of die-cast aluminum alloy radiators and a preparation method thereof.

[0006] In view of this, the present invention is specifically proposed. Summary of the Invention

[0007] The first object of the present invention is to provide a brazing plate for fluxless brazing, so as to solve the technical problems that the traditional brazing plate needs to spray brazing flux before brazing, the sprayed brazing flux is easy to fall off during the assembly process, and the brazing flux is easy to remain in the brazing seam after brazing, affecting the welding quality. The present invention realizes fluxless brazing by providing a film-breaking layer on the brazing plate and using Ge in the film-breaking layer to rapidly diffuse into the grain boundaries of the base material to be welded during brazing, tearing or breaking the surface oxide film.

[0008] The second object of the present invention is to provide a preparation method of the brazing plate for fluxless brazing as described above. The preparation method of the present invention has a simple process and high efficiency, and prepares the film-breaking layer by dip-coating film-breaking metal powder and in-situ melting, overcoming the technical problems that the film-breaking layer containing Ge is brittle and difficult to roll and process.

[0009] The third object of the present invention is to provide an application of the brazing plate for fluxless brazing as described above or the brazing plate prepared by the preparation method of the brazing plate for fluxless brazing as described above in the fluxless brazing of radiators.

[0010] To achieve the above object of the present invention, the following technical solutions are specifically adopted:

[0011] A brazing plate for fluxless brazing, comprising a composite plate in a sandwich foil structure and rupture layers on both sides of the composite plate. The rupture layers contain Ge. The composite plate includes a core layer and solder layers on both sides of the core layer. By mass percentage, the solder layer contains not less than 0.9% of La and not less than 0.9% of Ce.

[0012] Preferably, in the rupture layer, the mass percentage content of Ge is 25%-60%.

[0013] Preferably, the composition of the rupture layer includes Al-55Ge eutectic and / or Al-25.6Ge-5.6Si alloy.

[0014] Preferably, the thickness of one side of the rupture layer accounts for 0.45%-1% of the total thickness of the brazing plate.

[0015] Preferably, the thickness of the composite plate is 2-2.2 mm, and the thickness of the rupture layer is 10-20 μm.

[0016] Preferably, the thickness of one side of the solder layer accounts for 7%-10% of the total thickness of the composite plate.

[0017] Preferably, the core layer is an aluminum alloy. By mass parts, the solder layer includes the following components:

[0018] 8.0-10 parts of Si, 0.9-1.5 parts of La, 0.9-1.5 parts of Ce, and 80-91 parts of Al.

[0019] Preferably, in the solder layer, the mass ratio of La to Ce is 0.8-1.2:1.

[0020] The preparation method of the brazing plate for fluxless brazing according to any one of the foregoing embodiments includes the following steps:

[0021] S1. Stack and fix a core substrate and a solder metal plate in the order of solder metal plate-core substrate-solder metal plate to form an integrated composite metal block;

[0022] S2. Roll the composite metal block to obtain a composite plate with a sandwich foil structure;

[0023] S3. Pass the composite plate through a suspension containing rupture metal powder and a solvent at a constant speed and air-dry it, so that the rupture metal powder adheres to the surface of the composite plate;

[0024] S4. Heat the composite plate with the film-breaking metal powder attached thereto under an inert atmosphere to melt the film-breaking metal powder, so as to form a film-breaking layer on the surface of the composite plate.

[0025] Preferably, the core substrate is an aluminum alloy substrate, and the filler metal plate comprises the following components by mass percentage: 8.0 - 10 parts of Si, 0.9 - 1.5 parts of La, 0.9 - 1.5 parts of Ce, and 80 - 91 parts of Al.

[0026] Preferably, the thickness of a single layer of the filler metal plate accounts for 7% - 10% of the total thickness of the composite metal block.

[0027] Preferably, the film-breaking metal powder comprises Al-55Ge eutectic powder and / or Al-25.6Ge-5.6Si alloy powder.

[0028] Preferably, the particle size of the film-breaking metal powder is 30 - 44 μm.

[0029] Preferably, the solvent comprises at least one of carbon tetrachloride, alcohol, acetone, and isopropanol.

[0030] Preferably, the mass concentration of the suspension is 8% - 20%.

[0031] Preferably, the speed of the composite plate passing through the suspension is 3 - 10 mm / s.

[0032] Preferably, in step S4, the heating temperature is 420 - 530 °C.

[0033] Application of the filler metal plate for fluxless brazing according to any one of the foregoing embodiments or the filler metal plate prepared by the method for preparing the filler metal plate for fluxless brazing according to any one of the foregoing embodiments in fluxless brazing of a radiator.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] (1) In the present invention, a film-breaking layer is provided on the filler metal plate. Ge in the film-breaking layer will rapidly diffuse into the grain boundaries of the base metal to be brazed at a low-temperature brazing temperature. Since the condensation volume expansion rate of Ge is 5.5%, the volume will expand rapidly, "tearing or bursting" the surface oxide film. In the presence of Si, Ge can also form germanium-silicon compounds with Si. The germanium-silicon compounds will also rapidly diffuse into the grain boundaries of the base metal to be brazed during low-temperature brazing to break the oxide film; Ge can also form a large number of low-melting eutectic phases and low-melting alloy phases with Al. The metal liquid of these alloy phases first wets, spreads, scours, and removes the broken oxide film, and then reaches the brazing temperature, driving the wetting and spreading of the filler alloy liquid to achieve fluxless brazing, thereby solving the problem of defects in the brazing seam caused by flux residue.

[0036] (2) The filler metal layer of the present invention contains a relatively high content of La and Ce. La and Ce generate high-pressure steam, which penetrates into the grain boundaries of the base metal, helping to break the film and achieve fluxless brazing. Moreover, in the aluminum brazing sheet, La and Ce also have a good deoxidation effect and can react with Al and O to form LaCeAlO 3 compounds, which are dispersed in the brazing seam as hard particles, refining the brazing seam structure and improving the strength of the brazed joint.

[0037] (3) Since the film-breaking metal layer containing Ge is extremely brittle and prone to fragmentation during the rolling process, it is difficult to prepare a coiled brazing sheet with a film-breaking layer by traditional rolling methods. The method of the present invention first rolls out a brazing sheet without a film-breaking layer, and then coats a layer of film-breaking metal powder on its upper and lower surfaces. By in-situ melting reaction at a certain temperature, a coiled brazing sheet with a film-breaking metal layer is formed, overcoming the problem that is difficult to prepare by traditional rolling methods. Moreover, the film-breaking layer is metallurgically bonded to the composite plate, with high bonding strength and not easy to fall off. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] 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 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, without creative efforts, other drawings can also be obtained based on these drawings.

[0039] Figure 1 It is a schematic structural diagram of the brazing sheet provided by the embodiment of the present invention;

[0040] Figure 2 It is the weld seam metallographic photo of the die-cast aluminum radiator brazed with the brazing sheet in each embodiment of the present invention. Among them, (a) is for Embodiment 1, (b) is for Embodiment 2, (c) is for Embodiment 3, (d) is for Embodiment 4, (e) is for Embodiment 5, (f) is for Embodiment 6, and (g) is for Embodiment 7;

[0041] Figure 3 It is the weld seam metallographic photo of the die-cast aluminum radiator brazed with the brazing sheet in each comparative example of the present invention. Among them, (a) is for Comparative Example 1, (b) is for Comparative Example 2, (c) is for Comparative Example 3, (d) is for Comparative Example 4, and (e) is for Comparative Example 5;

[0042] Figure 4 It is the energy spectrum scanning result of the weld seam slag hole after brazing the brazing sheet in Comparative Example 1 of the present invention;

[0043] Figure 5 It is the filler metal flow spreading morphology on the surface of the die-cast aluminum without flux brazed with the brazing sheet in Embodiment 1 and Comparative Example 1 of the present invention;

[0044] Figure 6This is the surface morphology diagram of the brazing plate prepared in Comparative Example 2 of the present invention.

[0045] Reference numerals:

[0046] 1 - Film-breaking layer; 2 - Brazing filler metal layer; 3 - Core material layer. Detailed implementation manners

[0047] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings and specific implementation manners. However, those skilled in the art will understand that the following described embodiments are part of the embodiments of the present invention, rather than all the embodiments, and are only used to illustrate the present invention and should not be regarded 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 belong to 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.

[0048] As Figure 1 shown, a brazing plate for fluxless brazing provided by the first aspect of the present invention includes a composite plate in a sandwich foil structure and film-breaking layers 1 located on both sides of the composite plate. The film-breaking layer 1 contains Ge. The composite plate includes a core material layer 3 and brazing filler metal layers 2 located on both sides of the core material layer 3. By mass percentage, the brazing filler metal layer contains not less than 0.9% of La and not less than 0.9% of Ce.

[0049] The present invention is provided with a Ge-containing film-breaking layer on the brazing plate. Ge can react with Si to form germanium-silicon compounds. Ge and germanium-silicon compounds will rapidly diffuse into the grain boundaries of the base material to be brazed at a low brazing temperature. Since the condensation volume expansion rate of Ge is 5.5%, the volume expands rapidly, which will tear or break the surface oxide film. Ge can also form a large number of eutectic phases and low-melting alloy phases. For example, in an aluminum brazing plate, an Al-Ge eutectic phase (425 °C) and an Al-Si-Ge low-melting alloy phase (425 °C - 530 °C) can be formed. The metal liquids of these alloy phases first wet, spread, wash and remove the broken oxide film, and then reach the brazing temperature, driving the wetting and spreading of the brazing filler metal liquid, thereby realizing fluxless brazing. In addition, the brazing filler metal layer contains a relatively high content of La and Ge. During the brazing process, La and Ce generate high-pressure vapors, which penetrate into the grain boundaries of the base material, helping to break the film and realizing fluxless brazing. When the content of La and Ce is less than 0.9%, the effect of assisting in film breaking is not good.

[0050] In some specific embodiments of the present invention, in the film-breaking layer 1, the mass percentage content of Ge is 25% - 60%. For example, it can be any value among 25.6%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or a range value composed of any two of these values. If the Ge content is too low, the film-breaking effect is poor; if the Ge content is too high, it will cause a change in the solder composition, resulting in a decrease in joint strength. In addition, too high a Ge content will also lead to an increase in cost.

[0051] In some specific embodiments of the present invention, the composition of the film-breaking layer 1 includes Al-55Ge eutectic (55wt% Ge and the balance Al) and / or Al-25.6Ge-5.6Si alloy (5.6wt% Si, 25.6wt% Ge and the balance Al). In the brazing plate of the present invention, the components that play the role of film-breaking are Ge and / or germanium-silicon compounds, and the film-breaking is achieved by the diffusion of Ge and germanium-silicon compounds at the grain boundaries.

[0052] In some specific embodiments of the present invention, the single-side thickness of the film-breaking layer 1 accounts for 0.45% - 1% of the total thickness of the brazing plate. For example, it can be any value among 0.45%, 0.5%, 0.54%, 0.6%, 0.7%, 0.74%, 0.8%, 0.88%, 0.95%, 1% or a range value composed of any two of these values. If the film-breaking layer is too thin, the content of the film-breaking components is too low, and the film-breaking effect is poor; if the film-breaking layer is too thick, the content of the film-breaking components is too high, which will cause a change in the solder composition, a decrease in joint strength, and an increase in cost.

[0053] In some specific embodiments of the present invention, the thickness of the composite plate is 2.0 - 2.2 mm. For example, it can be any value among 2.0 mm, 2.05 mm, 2.1 mm, 2.15 mm, 2.2 mm or a range value composed of any two of these values; the thickness of the film-breaking layer 1 is 10 - 20 μm. For example, it can be any value among 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or a range value composed of any two of these values.

[0054] In some specific embodiments of the present invention, the single-side thickness of the solder layer 2 accounts for 7% - 10% of the total thickness of the composite plate. For example, it can be any value among 7%, 8%, 9%, 10% or a range value composed of any two of these values.

[0055] In some specific embodiments of the present invention, the core material layer 3 is an aluminum alloy, such as 3003 alloy, 6061 alloy or 6063 alloy, etc.; by mass, the solder layer 2 includes the following components:

[0056] Si 8.0 - 10 parts, La 0.9 - 1.5 parts, Ce 0.9 - 1.5 parts and Al 80 - 91 parts.

[0057] This embodiment provides an aluminum brazing sheet. The brazing filler metal composition used is an aluminum-silicon-based brazing filler metal, in which a relatively high content of La and Ce is added. During brazing, it can react with Al and oxygen to form LaCeAlO 3 compounds, which are dispersed in the brazing seam, refining the brazing seam structure. The formed LaCeAlO 3 can serve as a strengthening phase, and this reaction process consumes oxygen, having a good deoxidation effect and being able to improve the strength of the brazed joint. At the same time, part of La and Ce generate high-pressure steam, which penetrates into the grain boundaries of the aluminum base material, helping to break the film and achieve fluxless brazing.

[0058] The aluminum brazing sheet provided by the present invention can be used for fluxless brazing of die-cast aluminum alloys. Compared with ordinary aluminum alloys, the oxide film on the surface of die-cast aluminum alloys is more complex and dense, and it is more difficult to remove. Flux must be used during brazing. Moreover, some die-cast aluminum alloys have a high Si content and silicon ash on the surface, which will react with the flux, resulting in the failure of the flux and great welding difficulty. However, the aluminum brazing sheet provided by the present invention can overcome the above problems and achieve fluxless brazing of die-cast aluminum alloys.

[0059] In some embodiments, typically but not restrictively, for example, in the brazing filler metal layer 2, the mass fraction of Si can be any point value or a range value composed of any two point values among 8.0 parts, 8.5 parts, 9.0 parts, 9.5 parts, and 10 parts; the mass fraction of La can be any point value or a range value composed of any two point values among 0.9 parts, 1.0 parts, 1.2 parts, 1.4 parts, and 1.5 parts; the mass fraction of Ce can be any point value or a range value composed of any two point values among 0.9 parts, 1.0 parts, 1.2 parts, 1.4 parts, and 1.5 parts; the mass fraction of Al can be any point value or a range value composed of any two point values among 80 parts, 82 parts, 85 parts, 87 parts, 89 parts, and 90 parts.

[0060] In some specific embodiments of the present invention, in the brazing filler metal layer 2, the mass ratio of La to Ce is 0.8 - 1.2:1. For example, it can be any point value or a range value composed of any two point values among 0.8:1, 0.9:1, 1:1, 1.1:1, and 1.2:1. Controlling the ratio within the above range is to obtain a better deoxidation effect and brazing quality because when the mass ratio of La to Ce is 1:1, La and Ce can just completely react to form LaCeAlO 3 compounds, and the deoxidation effect is the best. If the ratio is too high or too low, it will cause an excessive amount of La or Ce, forming inclusions and at the same time increasing the brittleness of the material and reducing the joint strength.

[0061] The second aspect of the present invention provides a preparation method of a brazing sheet for fluxless brazing according to any one of the foregoing embodiments, including the following steps:

[0062] S1. Stack the core substrate and the filler metal plate in the order of filler metal plate - core substrate - filler metal plate and fix them into one body to obtain a composite metal block;

[0063] S2. Perform hot rolling and multi-pass rolling on the composite metal block to obtain a composite plate with a sandwich foil structure;

[0064] S3. Pass the composite plate through a suspension containing film-breaking metal powder and solvent at a constant speed and air-dry it, so that the film-breaking metal powder adheres uniformly to the surface of the composite plate;

[0065] S4. Heat the composite plate with the film-breaking metal powder attached in an inert atmosphere to melt the film-breaking metal powder and form a film-breaking layer by in-situ reaction on the surface of the composite plate.

[0066] Since the Ge-containing alloy foil is extremely brittle and prone to fragmentation during the rolling process, it is difficult to obtain a brazing plate with a Ge-containing film-breaking layer by traditional rolling methods. The method of the present invention first rolls the core substrate and the filler metal plate into a traditional brazing plate (composite plate), and then coats a layer of film-breaking metal powder on its upper and lower surfaces and melts it in an inert atmosphere to form a brazing plate with a Ge-containing film-breaking layer in-situ. Moreover, a metallurgical bond can be formed between the film-breaking layer and the composite plate, with high bond strength and not easy to fall off. In addition, a rolled brazing plate can be produced, overcoming the technical problem that it is difficult to prepare a brazing plate with a Ge-containing film-breaking layer by traditional rolling methods; and the preparation process of the method of the present invention is simple and efficient.

[0067] In some specific embodiments of the present invention, the filler metal plate is obtained by melting, casting, and rolling, and its length and width are the same as those of the core substrate. Its initial thickness can be calculated according to the ratio of the single-side filler layer to the total thickness of the composite plate.

[0068] In some specific embodiments of the present invention, in step S1, the core substrate and the filler metal plate are fixed by using rivets to fix the four corners; in other embodiments, spot welding can also be used.

[0069] In some specific embodiments of the present invention, the core substrate is an aluminum alloy substrate, and the filler metal plate includes the following components by mass percentage: 8.0 - 10 parts of Si, 0.9 - 1.5 parts of La, 0.9 - 1.5 parts of Ce, and 80 - 91 parts of Al. This embodiment provides a method for preparing an aluminum brazing plate. Among them, the raw materials for preparing the filler metal plate include Al-20Si, Al-10La, Al-10Ce, and Al.

[0070] In some specific embodiments of the present invention, the thickness of the single-layer filler metal plate accounts for 7% - 10% of the total thickness of the composite metal block. For example, it can be any value among 7%, 8%, 9%, 10% or a range value composed of any two of these values.

[0071] In some specific embodiments of the present invention, the film-breaking metal powder includes Al-55Ge eutectic powder and / or Al-25.6Ge-5.6Si alloy powder; wherein, by mass percentage, the composition of the Al-55Ge eutectic powder is 55% Ge and the balance Al, and the composition of the Al-25.6Ge-5.6Si alloy powder is 5.6% Si, 25.6% Ge and the balance Al.

[0072] In some specific embodiments of the present invention, the particle size of the used film-breaking metal powder is 30-44 μm. For example, it can be any point value or a range value composed of any two point values among 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 42 μm, 44 μm; if the particle size of the film-breaking metal powder is too large, the in-situ reaction is uneven and the formed metallurgical bonding layer is uneven; if the particle size of the film-breaking metal powder is too small, it is easy to agglomerate, the dip coating is uneven, and the cost of crushing the metal powder with too small particle size is high.

[0073] In some specific embodiments of the present invention, the solvent used for preparing the suspension includes at least one of carbon tetrachloride, alcohol, acetone and isopropyl alcohol. The used solvent has good volatility and no residue, which is convenient for the removal of the solvent and enables the composite metal powder to adhere to the composite plate.

[0074] In some specific embodiments of the present invention, the preparation method of the suspension includes: adding the film-breaking metal powder into a solution tank filled with the solvent and stirring for 3-5 min to obtain it; during dip coating, the composite plate passes through the solution tank filled with the suspension.

[0075] In some specific embodiments of the present invention, the mass concentration of the suspension is 8%-20%. For example, it can be any point value or a range value composed of any two point values among 8%, 10%, 12%, 15%, 18%, 20%.

[0076] In some specific embodiments of the present invention, the speed of the composite plate passing through the suspension is 3-10 mm / s. For example, it can be any point value or a range value composed of any two point values among 3 mm / s, 5 mm / s, 6 mm / s, 8 mm / s, 10 mm / s. The thickness of the film-breaking layer can be adjusted by adjusting the speed of the composite plate passing through the suspension.

[0077] In some specific embodiments of the present invention, in step S4, the heating method of the composite plate is that the composite plate passes through a nitrogen-protected tunnel furnace with a certain temperature at a certain speed, and an in-situ reaction forms a brazing plate containing a film-breaking layer. The heating temperature is 420-530 °C. For example, it can be any point value or a range value composed of any two point values among 420 °C, 450 °C, 480 °C, 500 °C, 520 °C, 530 °C.

[0078] The third aspect of the present invention provides an application of the brazing plate for fluxless brazing described in any one of the foregoing embodiments or the brazing plate prepared by the method for preparing the brazing plate for fluxless brazing described in any one of the foregoing embodiments in the fluxless brazing of radiators. For example, the aluminum brazing plate prepared by the method of the present invention can be used for the fluxless brazing of die-cast aluminum alloy radiators.

[0079] The embodiments of the present invention will be described in detail below in conjunction with specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0080] Example 1

[0081] This example provides an aluminum brazing plate for fluxless brazing, which is a five-layer plate structure, including a composite plate and a film-breaking layer on both sides of the composite plate. The composite plate includes a 3003 alloy layer and a brazing filler metal layer on both sides of the 3003 alloy layer; wherein, the thickness of the single-sided brazing filler metal layer accounts for 7% of the total thickness of the composite plate, and the single-sided thickness of the film-breaking layer is 10 μm;

[0082] The mass parts of each element in the brazing filler metal layer are as follows: 8.0 parts of Si, 0.9 parts of La, 0.9 parts of Ce, and 90.2 parts of Al;

[0083] The component of the film-breaking layer is an Al-55Ge eutectic reaction layer.

[0084] The preparation method of the brazing plate includes the following steps:

[0085] S1. Given the size specification of the 3003 plate as 500 mm × 400 mm × 20 mm, calculate the initial thickness of the single-layer brazing filler metal plate as 1.6 mm according to the fact that the thickness of the single-sided brazing filler metal layer accounts for 7% of the composite plate; weigh the brazing filler metal raw materials Al-20Si (aluminum-silicon master alloy containing 20 wt% Si and 80 wt% Al), Al-10La (aluminum-lanthanum master alloy containing 10 wt% La and 90 wt% Al), Al-10Ce (aluminum-cerium master alloy containing 10 wt% cerium and 90 wt% aluminum) and Al by mass parts, and obtain the brazing filler metal foil with the required initial thickness through melting, casting and rolling, and cut it into brazing filler metal plates with the same length and width as the 3003 plate; take a 3003 alloy plate and two brazing filler metal plates, stack them in the order of brazing filler metal plate - 3003 alloy plate - brazing filler metal plate, and fix the four corners with four rivets to obtain a composite metal block;

[0086] S2. Perform hot rolling composite and multi-pass rolling on the composite metal block to obtain a rolled composite plate with a thickness of 2 mm;

[0087] S3. Take the Al-55Ge eutectic block, and through crushing, grinding, and screening, obtain the film-breaking metal powder with a particle size of 30 μm; take an appropriate amount of the film-breaking metal powder and add it to the solution tank filled with carbon tetrachloride, stir for 3 min to obtain a suspension with a mass concentration of 10%, and pass the composite plate prepared in step S2 through the solution tank at a speed of 10 mm / s and air-dry it;

[0088] S4. After air-drying, the composite plate with the film-breaking metal powder attached passes through a nitrogen-protected tunnel furnace at a temperature of 420 °C to obtain a brazing plate with a film-breaking layer through in-situ reaction.

[0089] Example 2

[0090] This example provides an aluminum brazing plate for fluxless brazing, which is a five-layer plate structure, including a composite plate and film-breaking layers on both sides of the composite plate. The composite plate includes a 3003 alloy layer and brazing layers on both sides of the 3003 alloy layer; wherein, the thickness of the single-sided brazing layer accounts for 8% of the total thickness of the composite plate, and the single-sided thickness of the film-breaking layer is 12 μm;

[0091] The mass fractions of each element in the brazing layer are as follows: 9.0 parts of Si, 1.0 part of La, 1.0 part of Ce, and 89 parts of Al;

[0092] The composition of the film-breaking layer is an Al-25.6Ge-5.6Si alloy reaction layer.

[0093] The preparation method of the brazing plate is similar to that of Example 1, and the differences are as follows:

[0094] In step S1, the initial thickness of the single-layer brazing metal plate is 1.9 mm;

[0095] In step S2, the thickness of the composite plate is 2.2 mm;

[0096] In step S3, the raw material of the film-breaking metal powder is an Al-25.6Ge-5.6Si alloy block, the stirring time for preparing the suspension is 4 min, and the speed of the composite plate passing through the suspension is 8 mm / s;

[0097] In step S4, the temperature of the nitrogen-protected tunnel furnace is 450 °C;

[0098] The remaining process conditions are the same as those in Example 1.

[0099] Example 3

[0100] This example provides an aluminum brazing plate for fluxless brazing, which is a five-layer plate structure, including a composite plate and film-breaking layers on both sides of the composite plate. The composite plate includes a 3003 alloy layer and brazing layers on both sides of the 3003 alloy layer; wherein, the thickness of the single-sided brazing layer accounts for 9% of the total thickness of the composite plate, and the single-sided thickness of the film-breaking layer is 15 μm;

[0101] The mass fractions of the elements in the solder layer are as follows: 10.0 parts of Si, 1.2 parts of La, 1.2 parts of Ce, and 87.6 parts of Al;

[0102] The composition of the film-breaking layer is an Al-55Ge eutectic alloy reaction layer.

[0103] The preparation method of the brazing plate is similar to that of Example 1, with the differences being:

[0104] In step S1, the initial thickness of the single-layer solder metal plate is 2.2 mm;

[0105] In step S3, the stirring time for preparing the suspension is 5 min, and the speed of the composite plate passing through the suspension is 6 mm / s;

[0106] In step S4, the temperature of the nitrogen protection tunnel furnace is 500 °C;

[0107] The remaining process conditions are the same as those in Example 1.

[0108] Example 4

[0109] This example provides a fluxless brazing aluminum brazing plate, which is a five-layer plate structure, including a composite plate and film-breaking layers on both sides of the composite plate. The composite plate includes a 3003 alloy layer and solder layers on both sides of the 3003 alloy layer; wherein, the thickness of the single-side solder layer accounts for 10% of the total thickness of the composite plate, and the single-side thickness of the film-breaking layer is 18 μm;

[0110] The mass fractions of the elements in the solder layer are as follows: 8.0 parts of Si, 1.5 parts of La, 1.5 parts of Ce, and 89 parts of Al;

[0111] The composition of the film-breaking layer is an Al-55Ge eutectic alloy reaction layer.

[0112] The preparation method of the brazing plate is similar to that of Example 1, with the differences being:

[0113] In step S1, the initial thickness of the single-layer solder metal plate is 2.5 mm;

[0114] In step S2, the thickness of the composite plate is 2.2 mm;

[0115] In step S3, the speed of the composite plate passing through the suspension is 5 mm / s.

[0116] In step S4, the temperature of the nitrogen protection tunnel furnace is 520 °C;

[0117] The remaining process conditions are the same as those in Example 1.

[0118] Example 5

[0119] This embodiment provides an aluminum brazing sheet for fluxless brazing, which is a five-layer plate structure, including a composite plate and film-breaking layers on both sides of the composite plate. The composite plate includes a 3003 alloy layer and brazing filler metal layers on both sides of the 3003 alloy layer. Among them, the thickness of the brazing filler metal layer on one side accounts for 8% of the total thickness of the composite plate, and the thickness of the film-breaking layer on one side is 20 μm.

[0120] The mass fractions of each element in the brazing filler metal layer are as follows: 10.0 parts of Si, 1.5 parts of La, 1.5 parts of Ce, and 87 parts of Al.

[0121] The film-breaking layer is composed of an Al-55Ge eutectic alloy reaction layer.

[0122] The preparation method of the brazing sheet is similar to that of Example 1, with the differences being:

[0123] In step S1, the initial thickness of the single-layer brazing filler metal plate is 1.9 mm.

[0124] In step S3, the stirring time for preparing the suspension is 5 min, and the speed of the composite plate passing through the suspension is 3 mm / s.

[0125] In step S4, the temperature of the nitrogen-protected tunnel furnace is 530 °C.

[0126] The remaining process conditions are the same as those in Example 1.

[0127] Example 6

[0128] Example 6 is similar to Example 2, with the only difference being that Ce in the brazing filler metal layer is 1.25 parts and aluminum is 88.75 parts, and the remaining conditions are the same as those in Example 2.

[0129] Example 7

[0130] Example 7 is similar to Example 2, with the only difference being that La in the brazing filler metal layer is 1.2 parts and aluminum is 88.8 parts, and the remaining conditions are the same as those in Example 2.

[0131] Comparative Example 1

[0132] Comparative Example 1 is similar to Example 1, with the only difference being that it does not include a film-breaking layer, and the remaining conditions are the same as those in Example 1.

[0133] Comparative Example 2

[0134] Comparative Example 2 is similar to Example 1, with the only difference being that the film-breaking layer is prepared by the traditional rolling method, that is, the 3003 alloy plate, the filler metal plate, and the Al-55Ge alloy plate are stacked and fixed together in the order of "Al-55Ge alloy plate - filler metal plate - 3003 alloy plate - filler metal plate - Al-55Ge alloy plate", and then the brazing plate is prepared by the rolling method. Since the outermost Al-55Ge alloy plate is too brittle, only 2 passes of rolling are carried out, and the surface alloy film-breaking metal plate layer cracks into pieces, resulting in a large area of the brazing plate without a film-breaking layer (see Figure 6 ).

[0135] Comparative Example 3

[0136] Comparative Example 3 is similar to Example 1, with the only difference being that the thickness of the film-breaking layer is 5 μm, and the other conditions are the same as those in Example 1.

[0137] Comparative Example 4

[0138] Comparative Example 4 is similar to Example 1, with the only difference being that the thickness of the film-breaking layer is 25 μm, and the other conditions are the same as those in Example 1.

[0139] Comparative Example 5

[0140] Comparative Example 5 is similar to Example 1, with the only difference being that in the filler layer, La is 0.5 parts, Ce is 0.5 parts, and Al is 91 parts, and the other conditions are the same as those in Example 1.

[0141] Test Example

[0142] The brazing plates in each example and each comparative example were respectively used for in-furnace brazing of die-cast aluminum radiators (tunnel furnace brazing, brazing furnace temperature 595 °C, chain speed 400 mm / min). The welded samples of each brazing plate were made into standard test pieces, and the joint strength was tested according to GB / T 11363 and the weld metal microstructure was compared (Note: Since Comparative Example 1 does not contain a film-breaking layer, a brazing flux needs to be coated before brazing, and the coated brazing flux is a mixture of potassium hexafluoroaluminate:cesium hexafluoroaluminate = 5:1). The test results of the joint strength are shown in Table 1.

[0143] Table 1

[0144]

[0145] Figure 2 are the weld metal microstructure photos after brazing of the brazing plates in each example of the present invention, Figure 3 are the weld metal microstructure photos after brazing of the brazing plates in each comparative example of the present invention. From the data in Table 1 and Figure 2 , Figure 3It can be seen that the joint strength of the brazed plates in the examples is much higher than that of the brazed plates in the comparative examples. The joint strength after brazing of the filler metals in the examples is all above 58 MPa. In particular, for Example 4, its shear strength is as high as 74.5 MPa. Compared with the shear strength of 45.1 Mpa of the joint brazed with the ordinary brazed plate without a film-breaking layer coated with a brazing flux in Comparative Example 1, it is increased by about 65.2%. This is because there are no pores or brazing flux residues in the brazing seams in the examples, and the density of the brazing seams is high. However, there are a large amount of brazing flux residues, slag holes and pores in the brazing seams of Comparative Example 1, and the actual welding rate is low, resulting in a low joint strength. In Comparative Example 2, a brazed plate with a film-breaking layer was prepared by a traditional method. Since the film-breaking metal is brittle, there is no film-breaking layer on a large area of the surface of the brazed plate, resulting in a large area of the brazing seam not being welded, and the joint strength is low, about 38.4 MPa. In Example 6, the mass ratio of La to Ce is 0.8:1, and Ce is in excess. In Example 7, the mass ratio of La to Ce is 1.2:1, and La is in excess. A small amount of inclusions are generated in both cases. Compared with Example 2, the joint strength is reduced, but it is still better than that of the comparative examples.

[0146] Figure 4 Figure 4 shows the energy spectrum scanning results of the slag holes in the weld seam after brazing of the brazed plate in Comparative Example 1. In the figure, the large area of blue is the Al element, the green is the fluorine element, the bright yellow is the oxygen element, the red is the potassium element, the dark yellow is the silicon element, and the purple is the strontium element. The content of each element is provided in the table, where the atomic fraction is expressed in at%, and the mass fraction is expressed in wt%. It can be seen from the figure that there are F and K elements in the weld seam of Comparative Example 1, which confirms that there are a large amount of brazing flux residues in the brazing seam.

[0147] Figure 5 Figure 8 shows the spreading morphology of the filler metal on the surface of the die-cast aluminum plate after fluxless brazing under nitrogen protection in a tunnel furnace using the brazed plates in Example 1 and Comparative Example 1 respectively. The left figure is Comparative Example 1, and the right figure is Example 1. It can be seen from the figure that there is no spreading of any filler metal on the surface of the die-cast aluminum plate in Comparative Example 1, and fluxless gas protection brazing cannot be achieved.

[0148] Figure 6 Figure 12 shows the rolling morphology of the brazed plate in Comparative Example 2, and the dark black film-breaking metal layer on the surface is brittle and cracked into pieces.

[0149] Although the present invention has been illustrated and described with reference to specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; 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 can be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A brazing sheet for fluxless brazing, characterized in that: The composite plate is composed of a sandwich foil structure and a broken film layer located on both sides of the composite plate, wherein the broken film layer contains Ge, and the composite plate includes a core material layer and a solder layer located on both sides of the core material layer, wherein the solder layer contains 0.9%-1.5% La and 0.9%-1.5% Ce by mass percentage; The composition of the film-breaking layer is Al-55Ge eutectic and / or Al-25.6Ge-5.6Si alloy; The core material layer is an aluminum alloy, and the brazing material layer includes the following components by mass: Si 8.0-10 parts, La 0.9-1.5 parts, Ce 0.9-1.5 parts and Al 80-91 parts; The thickness of one side of the film-breaking layer accounts for 0.45%-1% of the total thickness of the brazing plate; The thickness of the solder layer on one side accounts for 7%-10% of the total thickness of the composite plate.

2. The brazing sheet for fluxless brazing according to claim 1, characterized in that: The thickness of the composite plate is 2.0-2.2 mm, and the thickness of the film-breaking layer is 10-20 μm.

3. The brazing sheet for fluxless brazing according to claim 1, characterized in that: In the solder layer, the mass ratio of La to Ce is 0.8-1.2:

1.

4. The method for preparing a brazing sheet for fluxless brazing according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. The core substrate and the brazing metal plate are stacked and fixed in the order of the brazing metal plate - the core substrate - the brazing metal plate to obtain a composite metal block; Wherein, the core material substrate is an aluminum alloy substrate, and the brazing filler metal plate comprises the following components by mass percentage: 8.0-10 parts of Si, 0.9-1.5 parts of La, 0.9-1.5 parts of Ce and 80-91 parts of Al; The thickness of the single-layer brazing metal plate accounts for 7%-10% of the total thickness of the composite metal block; S2. The composite metal block is rolled to obtain a composite plate having a sandwich foil structure; S3. The composite plate is passed through a suspension containing a film-breaking metal powder and a solvent at a uniform speed and air-dried so that the film-breaking metal powder is attached to the surface of the composite plate; S4. The composite plate attached with the broken film metal powder is heated under an inert atmosphere to melt the broken film metal powder to form a broken film layer on the surface of the composite plate; The film-breaking metal powder is Al-55Ge eutectic powder and / or Al-25.6Ge-5.6Si alloy powder.

5. The method for preparing a brazing sheet for fluxless brazing according to claim 4, characterized in that: In step S3, at least one of the following characteristics is met: (1) The particle size of the film-breaking metal powder is 30-44 μm; (2) The solvent includes at least one of carbon tetrachloride, alcohol, acetone and isopropanol; (3) The mass concentration of the suspension is 8%-20%; (4) The speed at which the composite plate passes through the suspension is 3-10 mm / s.

6. The method for preparing a brazing sheet for fluxless brazing according to claim 4, characterized in that: In step S4, the heating temperature is 420-530°C.

7. Use of the brazing sheet for fluxless brazing according to any one of claims 1 to 3 or the brazing sheet prepared by the method for preparing the brazing sheet for fluxless brazing according to any one of claims 4 to 6 in fluxless brazing of radiators.

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