Brazing plate for brazing flux-free brazing as well as preparation method and application of brazing plate

Abstract

The invention relates to the technical field of brazing materials, in particular to a brazing sheet for brazing flux-free brazing and a preparation method and application of the brazing sheet. The brazing sheet comprises a composite board of a sandwich foil structure and film breaking layers located on the two sides of the composite board, the film breaking layers contain Ge, the composite board comprises a core material layer and brazing filler metal layers located on the two sides of the core material layer, and the brazing filler metal layers contain, by mass, not lower than 0.9% of La and not lower than 0.9% of Ce. According to the brazing sheet, brazing flux does not need to be coated during brazing, brazing flux-free brazing of the radiator can be achieved, and the strength of a brazed connector is high. According to the method, the brazing plate without the broken film layer is rolled firstly, then the upper surface and the lower surface of the brazing plate are coated with the layer of broken film metal powder in a dip-coating mode, the brazing plate with the broken film metal layer is formed through the in-situ melting reaction, the problem that the brazing plate with the Ge broken film layer is difficult to prepare through a traditional rolling method is solved, the broken film layer and the composite plate are metallurgically bonded, the bonding strength is high, and the service life is long. The falling cannot easily occur.

Description

Technical Field

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

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

[0003] At present, when brazing a radiator, the brazing plate used is a base material substrate with a layer of conventional brazing material pressed on the surface, either single-sided or double-sided. The conventional brazing method is to first cut the brazing plate into the same size as the part to be welded, and evenly spray a layer of brazing flux on its upper and lower surfaces, assemble it with the workpiece to be welded after drying, and then put it into the furnace for nitrogen-shielded brazing. However, the brazing flux layer on the surface of the brazing plate is easily touched or partially detached during the subsequent assembly, resulting in an uneven brazing flux layer, affecting the welding consistency; more seriously, the brazing flux cannot be completely decomposed and volatilized during the brazing process, resulting in a large amount of residue and pores in the brazing seam, which seriously affects the air tightness and welding quality of the radiator.

[0004] In addition, since the oxide film on the surface of die-cast aluminum alloy is relatively complex and dense, brazing flux must be used when using conventional brazing plates for nitrogen shielded brazing, otherwise it will be difficult to weld effectively.

[0005] Therefore, it is urgent to develop a brazing plate and a preparation method thereof that can realize flux-free brazing of die-cast aluminum alloy radiators.

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

[0007] The first purpose of the present invention is to provide a brazing plate for flux-free brazing to solve the technical problems that the conventional brazing plate needs to be sprayed with flux before brazing, the flux sprayed is easy to fall off during the assembly process, and the flux is easy to remain in the brazing seam after brazing, which affects the welding quality. The present invention provides a film-breaking layer on the brazing plate, and utilizes the Ge in the film-breaking layer to rapidly diffuse into the grain boundary of the base material to be welded during brazing, tearing or breaking the surface oxide film, so as to achieve flux-free brazing.

[0008] The second purpose of the present invention is to provide a method for preparing a brazing plate for flux-free brazing as described above. The method of the present invention has a simple preparation process and high efficiency. The film-breaking layer is prepared by dipping the film-breaking metal powder and in-situ melting, which overcomes the technical difficulties of the Ge-containing film-breaking layer being brittle and difficult to roll.

[0009] A third object of the present invention is to provide a brazing sheet for fluxless brazing as described above or a brazing sheet prepared by the method for preparing a brazing sheet for fluxless brazing as described above, and use the brazing sheet in fluxless brazing of a radiator.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted: A brazing plate for flux-free brazing comprises a composite plate with a sandwich foil structure and film-breaking layers located on both sides of the composite plate, wherein the film-breaking layers contain Ge; the composite plate comprises a core material layer and brazing material layers located on both sides of the core material layer, wherein the brazing material layers contain not less than 0.9% La and not less than 0.9% Ce by mass percentage.

[0011] Preferably, in the film-breaking layer, the mass percentage of Ge is 25%-60%.

[0012] Preferably, the composition of the film-breaking layer includes Al-55Ge eutectic and / or Al-25.6Ge-5.6Si alloy.

[0013] Preferably, the thickness of the film-breaking layer on one side accounts for 0.45%-1% of the total thickness of the brazing sheet.

[0014] Preferably, the thickness of the composite plate is 2-2.2 mm, and the thickness of the film-breaking layer is 10-20 μm.

[0015] Preferably, the thickness of the solder layer on one side accounts for 7%-10% of the total thickness of the composite plate.

[0016] Preferably, the core material layer is an aluminum alloy, and the brazing material layer comprises 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.

[0017] Preferably, in the solder layer, the mass ratio of La to Ce is 0.8-1.2:1.

[0018] The method for preparing a brazing sheet for fluxless brazing according to any one of the aforementioned embodiments comprises the following steps: 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; 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. heating the composite plate to which the film-breaking metal powder is attached in an inert atmosphere to melt the film-breaking metal powder to form a film-breaking layer on the surface of the composite plate.

[0019] Preferably, the core 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.

[0020] Preferably, the thickness of a single layer of the brazing filler metal plate accounts for 7%-10% of the total thickness of the composite metal block.

[0021] Preferably, the film-breaking metal powder includes Al-55Ge eutectic powder and / or Al-25.6Ge-5.6Si alloy powder.

[0022] Preferably, the particle size of the film-breaking metal powder is 30-44 μm.

[0023] Preferably, the solvent comprises at least one of carbon tetrachloride, alcohol, acetone and isopropanol.

[0024] Preferably, the mass concentration of the suspension is 8%-20%.

[0025] Preferably, the speed at which the composite plate passes through the suspension is 3-10 mm / s.

[0026] Preferably, in step S4, the heating temperature is 420-530°C.

[0027] Use of the brazing sheet for fluxless brazing according to any one of the aforementioned embodiments or the brazing sheet produced by the method for producing the brazing sheet for fluxless brazing according to any one of the aforementioned embodiments in fluxless brazing of a radiator.

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a film-breaking layer on the brazing plate. Ge in the film-breaking layer will rapidly diffuse into the grain boundary of the base material to be welded at the low-temperature brazing temperature. Since the condensation volume expansion rate of Ge is 5.5%, the rapid volume expansion will "tear or break" the surface oxide film. In the presence of Si, Ge can also form a germanium-silicon compound with Si. During low-temperature brazing, the germanium-silicon compound will also rapidly diffuse into the grain boundary of the base material to be welded to break the oxide film. Ge can also form a large amount of low-melting eutectic phase and low-melting alloy phase with Al. The metal liquid of these alloy phases first wets, spreads, flushes and removes the broken oxide film, and then reaches the brazing temperature, driving the wetting and spreading of the solder alloy liquid, realizing flux-free brazing, thereby solving the problem of brazing seam defects caused by flux residues.

[0029] (2) The brazing material 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 boundary of the base material, helps to break the film, and realizes flux-free brazing. In addition, in the aluminum brazing plate, La and Ce also have a good deoxidation effect and can react with Al and O to generate LaCeAlO. 3 The compounds are dispersed in the brazing seam as hard particles, which refines the brazing seam structure and improves the strength of the brazed joint.

[0030] (3) Since the Ge-containing film-breaking metal layer is extremely brittle and easily broken during the rolling process, it is difficult to prepare a rolled brazing plate with a film-breaking layer by the traditional rolling method. The method of the present invention first rolls out a brazing plate without a film-breaking layer, and then dip-coats a layer of film-breaking metal powder on the upper and lower surfaces thereof. The rolled brazing plate containing the film-breaking metal layer is formed by an in-situ melting reaction at a certain temperature, thereby overcoming the difficulty of the traditional rolling method in preparation. In addition, the film-breaking layer is metallurgically bonded to the composite plate, has a high bonding strength, and is not easy to fall off. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 A schematic diagram of the structure of a brazing plate provided in an embodiment of the present invention; Figure 2 The metallographic photographs of the welds of the die-cast aluminum alloy heat sink brazed by the brazing plates in various embodiments of the present invention, wherein (a) is embodiment 1, (b) is embodiment 2, (c) is embodiment 3, (d) is embodiment 4, (e) is embodiment 5, (f) is embodiment 6, and (g) is embodiment 7; Figure 3 The metallographic photographs of the welds of the die-cast aluminum alloy radiators brazed by the brazing plates in the comparative examples of the present invention, wherein (a) is comparative example 1, (b) is comparative example 2, (c) is comparative example 3, (d) is comparative example 4, and (e) is comparative example 5; Figure 4 The energy spectrum scanning result of the weld slag hole after brazing of the brazing plate in Comparative Example 1 of the present invention; Figure 5 The solder flow morphology of the die-cast aluminum surface brazed by the brazing plate without flux in Example 1 of the present invention and Comparative Example 1; Figure 6 This is a surface morphology of the brazing plate prepared in Comparative Example 2 of the present invention.

[0033] Reference numerals: 1-Film breaking layer; 2-Brake layer; 3-Core material layer. DETAILED DESCRIPTION

[0034] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0035] like Figure 1 As shown, the first aspect of the present invention provides a brazing plate for flux-free brazing, comprising a composite plate with a sandwich foil structure and a film-breaking layer 1 located on both sides of the composite plate, the film-breaking layer 1 contains Ge, the composite plate comprises a core material layer 3 and a brazing material layer 2 located on both sides of the core material layer 3, and the brazing material layer contains not less than 0.9% La and not less than 0.9% Ce by mass percentage.

[0036] The present invention provides 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 diffuse rapidly into the grain boundaries of the base material to be welded at low-temperature brazing temperature. Since the condensation volume expansion rate of Ge is 5.5%, the volume expands rapidly, tearing or breaking the surface oxide film. Ge can also form a large number of low-melting eutectic phases and low-melting alloy phases. For example, Al-Ge eutectic phase (425°C) and Al-Si-Ge low-melting alloy phase (425°C-530°C) can be formed in the aluminum brazing plate. The metal liquid of these alloy phases first wets, spreads, flushes and removes the broken oxide film, and then reaches the brazing temperature to drive the wetting and spreading of the brazing alloy liquid, thereby realizing flux-free brazing. In addition, the brazing layer contains a relatively high content of La and Ge. During the brazing process, La and Ce generate high-pressure vapor, which penetrates into the base material grain boundaries, helps to break the film, and realizes flux-free brazing. When the content of La and Ce is lower than 0.9%, the effect of assisting the film breaking is not good.

[0037] In some specific embodiments of the present invention, in the film-breaking layer 1, the mass percentage of Ge is 25%-60%, for example, it can be any point value among 25.6%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or a range value composed of any two point values; if the Ge content is too low, the film-breaking effect is not good, and if the Ge content is too high, it will cause the solder composition to change, resulting in reduced joint strength. In addition, if the Ge content is too high, it will also increase the cost.

[0038] In some specific embodiments of the present invention, the composition of the film-breaking layer 1 includes Al-55Ge eutectic (55wt% Ge and balance Al) and / or Al-25.6Ge-5.6Si alloy (5.6wt% Si, 25.6wt% Ge and balance Al). In the brazing plate of the present invention, the components that play a film-breaking role are Ge and / or germanium-silicon compounds, and the film breaking is achieved by diffusion of Ge and germanium-silicon compounds at grain boundaries.

[0039] 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 point value among 0.45%, 0.5%, 0.54%, 0.6%, 0.7%, 0.74%, 0.8%, 0.88%, 0.95%, and 1%, or a range value composed of any two point values; if the film-breaking layer is too thin, the content of the film-breaking component is too low, and the film-breaking effect is not good; if the film-breaking layer is too thick, the content of the film-breaking component is too high, the composition of the solder will change, the joint strength will decrease, and the cost will increase.

[0040] 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 point value among 2.0 mm, 2.05 mm, 2.1 mm, 2.15 mm, and 2.2 mm, or a range value consisting of any two point values; the thickness of the film-breaking layer 1 is 10-20 μm, for example, it can be any point value among 10 μm, 12 μm, 15 μm, 18 μm, and 20 μm, or a range value consisting of any two point values.

[0041] 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 point value among 7%, 8%, 9%, 10% or a range value consisting of any two point values.

[0042] In some specific embodiments of the present invention, the core material layer 3 is an aluminum alloy, for example, 3003 alloy, 6061 alloy or 6063 alloy, etc.; the brazing material layer 2 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.

[0043] This embodiment provides an aluminum brazing plate. The brazing material used is an aluminum-silicon-based brazing material. A relatively high content of La and Ce is added to the brazing material. During brazing, La and Ce can react with Al and oxygen to generate LaCeAlO 3 Compounds are dispersed in the brazing seam, refining the brazing seam structure, and the generated LaCeAlO 3It can serve as a reinforcing phase, and the reaction process consumes oxygen, which has a good deoxidation effect and can improve the strength of the brazed joint. At the same time, part of La and Ce generates high-pressure steam, which penetrates into the grain boundaries of the aluminum base material, helps to break the film and realize flux-free brazing.

[0044] The aluminum brazing plate provided by the present invention can be used for flux-free 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 more difficult to remove. A flux must be used during brazing. In addition, some die-cast aluminum alloys have a high Si content and silicon ash on the surface, which will react with the flux, causing the flux to fail and making welding difficult. The aluminum brazing plate provided by the present invention can overcome the above difficulties and realize flux-free brazing of die-cast aluminum alloys.

[0045] In some embodiments, typically but not limiting, for example, in the solder layer 2, the mass fraction of Si can be any value among 8.0 parts, 8.5 parts, 9.0 parts, 9.5 parts, 10 parts, or a range value consisting of any two values; the mass fraction of La can be any value among 0.9 parts, 1.0 parts, 1.2 parts, 1.4 parts, 1.5 parts, or a range value consisting of any two values; the mass fraction of Ce can be any value among 0.9 parts, 1.0 parts, 1.2 parts, 1.4 parts, 1.5 parts, or a range value consisting of any two values; the mass fraction of Al can be any value among 80 parts, 82 parts, 85 parts, 87 parts, 89 parts, 90 parts, or a range value consisting of any two values.

[0046] In some specific embodiments of the present invention, the mass ratio of La to Ce in the brazing material layer 2 is 0.8-1.2:1, for example, it can be any point value among 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1 or a range value consisting of any two point values. The ratio is controlled within the above range in order 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 react completely to generate LaCeAlO 3 Compounds have the best deoxidation effect. Too high or too low a ratio will result in excessive La or Ce, forming inclusions, and at the same time increasing the brittleness of the material and reducing the strength of the joint.

[0047] A second aspect of the present invention provides a method for preparing a brazing sheet for fluxless brazing according to any one of the aforementioned embodiments, comprising the following steps: 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; S2. The composite metal block is hot rolled and rolled multiple times to obtain a composite plate having a sandwich foil structure; S3. The composite plate is passed through a suspension containing a broken metal powder and a solvent at a uniform speed and air-dried so that the broken metal powder is evenly attached to the surface of the composite plate; S4. The composite plate with the film-breaking metal powder attached thereto is heated in an inert atmosphere to melt the film-breaking metal powder and react in situ on the surface of the composite plate to form a film-breaking layer.

[0048] Since the alloy foil containing Ge is extremely brittle and is easily broken during the rolling process, it is difficult to obtain a brazing plate containing a Ge film-breaking layer by the traditional rolling method. The method of the present invention first rolls the core substrate and the brazing material metal plate into a traditional brazing plate (composite plate), and then dip-coats a layer of film-breaking metal powder on the upper and lower surfaces thereof, and melts them in an inert atmosphere to form a brazing plate containing a Ge film-breaking layer. The film-breaking layer and the composite plate can form a metallurgical bond with high bonding strength and are not easy to fall off. A rolled brazing plate can also be produced, thereby overcoming the technical difficulty that the traditional rolling method is difficult to prepare a brazing plate containing a Ge film-breaking layer. In addition, the method of the present invention has a simple preparation process and high efficiency.

[0049] In some specific embodiments of the present invention, the brazing filler metal plate is obtained by melting, casting and rolling, and its length and width are consistent with the core substrate. Its initial thickness can be calculated based on the ratio of the single-side brazing filler layer to the total thickness of the composite plate.

[0050] In some specific embodiments of the present invention, in step S1, the core substrate and the brazing metal plate are fixed by fixing the four corners with rivets; in other embodiments, spot welding can also be used.

[0051] In some specific embodiments of the present invention, the core 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. This embodiment provides a method for preparing an aluminum brazing plate, wherein the raw materials for preparing the brazing filler metal plate include Al-20Si, Al-10La, Al-10Ce, and Al.

[0052] In some specific embodiments of the present invention, the thickness of the single-layer brazing metal plate accounts for 7%-10% of the total thickness of the composite metal block. For example, it can be any point value among 7%, 8%, 9%, 10% or a range value consisting of any two point values.

[0053] 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 Al-55Ge eutectic powder is 55% Ge and the balance Al, and the composition of Al-25.6Ge-5.6Si alloy powder is 5.6% Si, 25.6% Ge and the balance Al.

[0054] In some specific embodiments of the present invention, the particle size of the film-breaking metal powder used is 30-44μm, for example, it can be any point value among 30μm, 32μm, 35μm, 38μm, 40μm, 42μm, 44μm, or a range value composed of any two point values; if the particle size of the film-breaking metal powder is too large, the in-situ reaction will be uneven, and the formed metallurgical bonding layer will be uneven; if the particle size of the film-breaking metal powder is too small, it will be easy to agglomerate, the dipping coating will be uneven, and the crushing cost of the metal powder with too small particle size will be high.

[0055] In some specific embodiments of the present invention, the solvent used to prepare the suspension includes at least one of carbon tetrachloride, alcohol, acetone and isopropanol. The solvent used has good volatility and no residue, which facilitates the removal of the solvent and allows the composite metal powder to adhere to the composite plate.

[0056] 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 containing a solvent and stirring for 3-5 minutes; during dip coating, the composite plate passes through the solution tank containing the suspension.

[0057] 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 among 8%, 10%, 12%, 15%, 18%, 20%, or a range value consisting of any two point values.

[0058] In some specific embodiments of the present invention, the speed at which the composite plate passes through the suspension is 3-10 mm / s. For example, it can be any point value among 3 mm / s, 5 mm / s, 6 mm / s, 8 mm / s, 10 mm / s or a range value composed of any two point values. The thickness of the membrane breaking layer can be adjusted by adjusting the speed at which the composite plate passes through the suspension.

[0059] In some specific embodiments of the present invention, in step S4, the composite plate is heated in such a way that the composite plate passes through a nitrogen-protected tunnel furnace with a certain temperature at a certain speed, and reacts in situ to form a brazing plate containing a broken film layer, and the heating temperature is 420-530°C, for example, it can be any point value among 420°C, 450°C, 480°C, 500°C, 520°C, 530°C, or a range value consisting of any two point values.

[0060] The third aspect of the present invention provides a brazing sheet for fluxless brazing as described in any one of the aforementioned embodiments or a brazing sheet prepared by the method for preparing a brazing sheet for fluxless brazing as described in any one of the aforementioned embodiments, and its application in fluxless brazing of a radiator. For example, the aluminum brazing sheet prepared by the method of the present invention can be used for fluxless brazing of a die-cast aluminum alloy radiator.

[0061] The embodiments of the present invention will be described in detail below in conjunction with specific examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If specific conditions are not specified in the examples, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0062] Example 1 This embodiment provides an aluminum brazing plate for fluxless brazing, which is a five-layer plate structure, including a composite plate and a film-breaking layer located on both sides of the composite plate, and the composite plate includes a 3003 alloy layer and a brazing material layer located on both sides of the 3003 alloy layer; wherein the thickness of the single-side brazing material layer accounts for 7% of the total thickness of the composite plate, and the single-side thickness of the film-breaking layer is 10 μm; The mass fractions of each element in the brazing material 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; The composition of the film-breaking layer is Al-55Ge eutectic reaction layer.

[0063] The method for preparing the brazing plate comprises the following steps: S1. Given the size of 3003 plate of 500mm×400mm×20mm, the initial thickness of the single-layer brazing filler metal plate is calculated to be 1.6mm, based on the thickness of the single-side brazing filler metal layer accounting for 7% of the composite plate; weigh the brazing filler raw materials Al-20Si (aluminum-silicon master alloy containing 20wt% Si and 80wt% Al), Al-10La (aluminum-lanthanum master alloy containing 10wt% La and 90wt% Al), Al-10Ce (aluminum-cerium master alloy containing 10wt% cerium and 90wt% aluminum) and Al by mass, obtain the brazing filler foil of the required initial thickness through smelting, casting and rolling, and cut it into brazing filler metal plates with the same length and width as the 3003 plate; take the 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; S2. The composite metal block is hot rolled and rolled multiple times to obtain a coiled composite plate having a thickness of 2 mm; S3. Take Al-55Ge eutectic block, by crushing, grinding, sieving, obtain a 30μm broken film metal powder; take an appropriate amount of broken film metal powder added to a solution tank containing carbon tetrachloride, stirred for 3min to obtain a suspension with a mass concentration of 10%, the composite plate obtained in step S2 was passed through the solution tank at a speed of 10mm / s and air-dried; S4. After air drying, the composite plate with the broken film metal powder attached thereto is passed through a nitrogen-protected tunnel furnace at a temperature of 420° C., and an in-situ reaction is performed to obtain a brazing plate containing a broken film layer.

[0064] Example 2 This embodiment provides an aluminum brazing plate for fluxless brazing, which is a five-layer plate structure, including a composite plate and a film-breaking layer located on both sides of the composite plate, and the composite plate includes a 3003 alloy layer and a brazing material layer located on both sides of the 3003 alloy layer; wherein the thickness of the single-side brazing material layer accounts for 8% of the total thickness of the composite plate, and the single-side thickness of the film-breaking layer is 12 μm; The mass fractions of each element in the brazing material layer are as follows: Si 9.0 parts, La 1.0 parts, Ce 1.0 parts, Al 89 parts; The composition of the film-breaking layer is Al-25.6Ge-5.6Si alloy reaction layer.

[0065] The preparation method of the brazing plate is similar to that of Example 1, except that: In step S1, the initial thickness of the single-layer brazing filler metal plate is 1.9 mm; In step S2, the thickness of the composite plate is 2.2 mm; In step S3, the raw material of the film-breaking metal powder is an Al-25.6Ge-5.6Si alloy block, the stirring time of the suspension is 4 minutes, and the speed at which the composite plate passes through the suspension is 8 mm / s; In step S4, the temperature of the nitrogen-protected tunnel furnace is 450° C.; The remaining process conditions are the same as in Example 1.

[0066] Example 3 This embodiment provides an aluminum brazing plate for fluxless brazing, which is a five-layer plate structure, including a composite plate and a film-breaking layer located on both sides of the composite plate, and the composite plate includes a 3003 alloy layer and a brazing material layer located on both sides of the 3003 alloy layer; wherein the thickness of the single-side brazing material layer accounts for 9% of the total thickness of the composite plate, and the single-side thickness of the film-breaking layer is 15 μm; The mass fractions of each element in the brazing material layer are as follows: Si 10.0 parts, La 1.2 parts, Ce 1.2 parts, Al 87.6 parts; The composition of the film-breaking layer is Al-55Ge eutectic alloy reaction layer.

[0067] The preparation method of the brazing plate is similar to that of Example 1, except that: In step S1, the initial thickness of the single-layer brazing filler metal plate is 2.2 mm; In step S3, the stirring time of the prepared suspension is 5 min, and the speed at which the composite plate passes through the suspension is 6 mm / s; In step S4, the temperature of the nitrogen-protected tunnel furnace is 500° C.; The remaining process conditions are the same as in Example 1.

[0068] Example 4 This embodiment provides an aluminum brazing plate for fluxless brazing, which is a five-layer plate structure, including a composite plate and a film-breaking layer located on both sides of the composite plate, and the composite plate includes a 3003 alloy layer and a brazing material layer located on both sides of the 3003 alloy layer; wherein the thickness of the single-side brazing material 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; The mass fractions of each element in the brazing material layer are as follows: Si 8.0 parts, La 1.5 parts, Ce 1.5 parts, Al 89 parts; The composition of the film-breaking layer is Al-55Ge eutectic alloy reaction layer.

[0069] The preparation method of the brazing plate is similar to that of Example 1, except that: In step S1, the initial thickness of the single-layer brazing filler metal plate is 2.5 mm; In step S2, the thickness of the composite plate is 2.2 mm; In step S3, the speed at which the composite plate passes through the suspension is 5 mm / s.

[0070] In step S4, the temperature of the nitrogen-protected tunnel furnace is 520° C.; The remaining process conditions are the same as in Example 1.

[0071] Example 5 This embodiment provides an aluminum brazing plate for fluxless brazing, which is a five-layer plate structure, including a composite plate and a film-breaking layer located on both sides of the composite plate, and the composite plate includes a 3003 alloy layer and a brazing material layer located on both sides of the 3003 alloy layer; wherein the thickness of the single-side brazing material layer accounts for 8% of the total thickness of the composite plate, and the single-side thickness of the film-breaking layer is 20 μm; The mass fractions of each element in the brazing material layer are as follows: Si 10.0 parts, La 1.5 parts, Ce 1.5 parts, Al 87 parts; The composition of the film-breaking layer is Al-55Ge eutectic alloy reaction layer.

[0072] The preparation method of the brazing plate is similar to that of Example 1, except that: In step S1, the initial thickness of the single-layer brazing filler metal plate is 1.9 mm; In step S3, the stirring time of the prepared suspension is 5 minutes, and the speed at which the composite plate passes through the suspension is 3 mm / s.

[0073] In step S4, the temperature of the nitrogen-protected tunnel furnace is 530° C.; The remaining process conditions are the same as those in Example 1.

[0074] Example 6 Example 6 is similar to Example 2, with the only difference being that the amount of Ce in the solder layer is 1.25 parts and the amount of aluminum is 88.75 parts. The other conditions are the same as those in Example 2.

[0075] Example 7 Example 7 is similar to Example 2, with the only difference being that the amount of La in the solder layer is 1.2 parts and the amount of aluminum is 88.8 parts. The other conditions are the same as those in Example 2.

[0076] Comparative Example 1 Comparative Example 1 is similar to Example 1, except that it does not contain a membrane breaking layer, and the other conditions are the same as those of Example 1.

[0077] Comparative Example 2 Comparative Example 2 is similar to Example 1, except that the film-breaking layer is prepared by a conventional rolling method, that is, the 3003 alloy plate, the brazing metal plate and the Al-55Ge alloy plate are stacked and fixed together in the order of "Al-55Ge alloy plate-brazing metal plate-3003 alloy plate-brazing metal plate-Al-55Ge alloy plate", and then the brazing plate is prepared by a rolling method. Since the outermost Al-55Ge alloy plate is too brittle, only two passes are rolled, and the surface alloy film-breaking metal plate layer is brittle and cracked into pieces, resulting in a large area of ​​the brazing plate without a film-breaking layer (see Figure 6 ).

[0078] Comparative Example 3 Comparative Example 3 is similar to Example 1, except that the thickness of the membrane breaking layer is 5 μm, and the other conditions are the same as those of Example 1.

[0079] Comparative Example 4 Comparative Example 4 is similar to Example 1, except that the thickness of the membrane-breaking layer is 25 μm, and the other conditions are the same as those of Example 1.

[0080] Comparative Example 5 Comparative Example 5 is similar to Example 1, with the only difference being that the solder layer contains 0.5 parts of La, 0.5 parts of Ce, and 91 parts of Al, and the other conditions are the same as those of Example 1.

[0081] Test example The brazing plates in each embodiment and each comparative example were respectively used for furnace brazing of the die-cast aluminum alloy radiator (tunnel furnace brazing, brazing furnace temperature of 595°C, chain speed of 400 mm / min), and each brazing plate welding sample was made into a standard test piece. The joint strength was tested according to GB / T 11363 and the weld metallographic morphology was compared (Note: since Comparative Example 1 does not contain a broken film layer, it is necessary to apply a brazing flux before brazing, and the applied brazing flux is a mixture of potassium fluoroaluminate: cesium fluoroaluminate = 5:1). The joint strength test results are shown in Table 1.

[0082] Table 1

[0083] Figure 2 The metallographic photographs of the welds after brazing of the brazing plates in each embodiment of the present invention are as follows: Figure 3 The metallographic photographs of the welds after brazing of the brazing plates in the comparative examples of the present invention are shown in Table 1. Figure 2 , Figure 3 It can be seen that the joint strength of the brazing plate brazed in the embodiment is much higher than that of the brazing plate brazed in the comparative example. The joint strength after brazing with the brazing filler in the embodiment is above 58MPa, especially in Example 4, whose shear strength is as high as 74.5MPa, which is about 65.2% higher than the shear strength of the joint brazed with the ordinary brazing plate coated with brazing flux without a broken film layer in Comparative Example 1, which is 45.1Mpa. This is because there are no pores or flux residues in the brazing seam in the embodiment, and the brazing seam has a high density, while there are a large number of flux residues, slag holes and pores in the brazing seam of Comparative Example 1, and the actual welding rate is low, resulting in low joint strength. In Comparative Example 2, a brazing plate containing a broken film layer is prepared by a traditional method. Because the broken film metal is brittle, a large area of ​​the brazing plate surface is free of a broken film layer, resulting in a large area of ​​the brazing seam not being welded, and the joint strength is low, about 38.4MPa. In Example 6, the mass ratio of La to Ce is 0.8:1, and Ce is excessive. In Example 7, the mass ratio of La to Ce is 1.2:1, and La is excessive. Both produce a small amount of inclusions. Compared with Example 2, the joint strength is reduced, but still better than the comparative example.

[0084] Figure 4 This is the energy spectrum scanning result of the slag hole in the weld after brazing of the brazing plate in Comparative Example 1. In the figure, the large area of ​​blue is Al element, green is fluorine element, bright yellow is oxygen element, red is potassium element, dark yellow is silicon element, and purple is strontium element. The table provides the content of each element, where the atomic fraction is expressed in at% and the mass fraction is expressed in wt%. It can be seen from the figure that F and K elements exist in the weld of Comparative Example 1, confirming that there is a large amount of flux residue in the brazing seam.

[0085] Figure 5 The figures show the solder flow morphology on the surface of the die-cast aluminum plate after flux-free brazing under nitrogen protection in a tunnel furnace using the brazing 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 figures that there is no solder flow on the surface of the die-cast aluminum plate in Comparative Example 1, and flux-free gas-protected brazing cannot be achieved.

[0086] Figure 6 This is the rolling morphology of the brazing plate of comparative example 2, and the dark black broken film metal layer on the surface is brittle and cracked into pieces.

[0087] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, 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 invention comprises a composite plate with a sandwich foil structure and a film-breaking layer located on both sides of the composite plate, wherein the film-breaking layer contains Ge. The composite plate comprises a core material layer and a solder layer located on both sides of the core material layer, wherein the solder layer contains not less than 0.9% La and not less than 0.9% Ce by mass percentage.

2. The brazing sheet for fluxless brazing according to claim 1, characterized in that: In the film-breaking layer, the mass percentage of Ge is 25%-60%; And / or, the composition of the film-breaking layer includes Al-55Ge eutectic and / or Al-25.6Ge-5.6Si alloy.

3. The brazing sheet for fluxless brazing according to claim 1, characterized in that: Meet at least one of the following characteristics: (1) The thickness of the broken film layer on one side accounts for 0.45%-1% of the total thickness of the brazing plate; (2) 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 thickness of the solder layer on one side accounts for 7%-10% of the total thickness of the composite plate.

4. The brazing sheet for fluxless brazing according to claim 1, characterized in that: 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.

5. 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.

6. The method for preparing a brazing sheet for fluxless brazing according to any one of claims 1 to 5, 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; 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. heating the composite plate to which the film-breaking metal powder is attached in an inert atmosphere to melt the film-breaking metal powder to form a film-breaking layer on the surface of the composite plate.

7. The method for preparing a brazing sheet for fluxless brazing according to claim 6, characterized in that: In step S1, at least one of the following characteristics is met: (1) The core 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; (2) The thickness of a single layer of the brazing filler metal plate accounts for 7%-10% of the total thickness of the composite metal block.

8. The method for preparing a brazing sheet for fluxless brazing according to claim 6, characterized in that: In step S3, at least one of the following characteristics is met: (1) The film-breaking metal powder includes Al-55Ge eutectic powder and / or Al-25.6Ge-5.6Si alloy powder; (2) The particle size of the film-breaking metal powder is 30-44 μm; (3) The solvent includes at least one of carbon tetrachloride, alcohol, acetone and isopropanol; (4) The mass concentration of the suspension is 8%-20%; (5) The speed at which the composite plate passes through the suspension is 3-10 mm / s.

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

10. Use of the brazing sheet for fluxless brazing according to any one of claims 1 to 5 or the brazing sheet prepared by the method for preparing the brazing sheet for fluxless brazing according to any one of claims 6 to 9 in fluxless brazing of a radiator.

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