Aluminum alloy brazing filler metal and method of making and using the same

Abstract

The application discloses a brazing flux capable of enhancing the radiation resistance of aluminum alloy brazing joints, and a preparation method and application thereof. The brazing flux is composed of 5-18% of an organic mixture and the balance of an inorganic mixture. The organic mixture is composed of 7-15% of EP-12 epoxy resin, 8-16% of EP-16 epoxy resin, 5-8% of F-51A high-temperature-resistant flame-retardant thermosetting phenolic resin, 5-8% of F-52A high-temperature-resistant flame-retardant thermosetting phenolic resin, 5-8% of resorcinol, 5-8% of hydroquinone and the balance of phthalic anhydride. The inorganic mixture is composed of 40-55% of CsF, 20-30% of AlF3, 0.005-0.01% of GaF3 and the balance of Al(OH)3. The brazing flux matches Zn-Al filler metal, can make the aluminum alloy brazing joint have good radiation resistance, and can significantly improve the shearing strength of the brazing joint.

Description

Technical Field

[0001] This invention belongs to the field of brazing materials technology, and relates to a flux that can enhance the radiation resistance of aluminum alloy brazing joints, its preparation method and application. Background Technology

[0002] As is well known, the metal material used to connect the base metals in brazing is called brazing filler metal. However, in most cases, brazing filler metal must be supplemented with flux to achieve a reliable brazing connection. Therefore, flux is one of the important auxiliary materials in the brazing process. Generally, after the brazing connection is completed, the flux residue needs to be cleaned up using appropriate methods to prevent it from corroding the brazed joint metal or the base metal or causing other adverse effects.

[0003] In recent years, there have been many inventions of Nocolok fluxes such as K3AlF6 flux, KAlF4 flux, or their improved fluxes such as CsF-AlF3 flux for brazing aluminum and aluminum alloys, and they have been widely used in brazing of the same or different materials, such as aluminum alloy + aluminum alloy and aluminum alloy + copper alloy.

[0004] With the widespread adoption of aluminum alloy structural components in the aerospace field, brazing technology is playing an increasingly important role. For specialized applications such as aluminum alloy antennas and waveguide devices in spacecraft, brazed joints need to possess a certain level of radiation resistance. Current technologies can only achieve this by modifying the brazing structure or physical reinforcement. However, these methods significantly increase costs and weight, seriously hindering the development of the aerospace industry. Therefore, there is an urgent need to develop new fluxes that can enhance the radiation resistance of aluminum alloy brazed joints.

[0005] A search revealed that Chinese patent application CN115922150A discloses a novel flux that enhances the radiation resistance and low-temperature resistance of solder joints. This flux is matched with BAg40CuZnCdNi solder for brazing Q345 steel and 304 stainless steel of the same or different materials, or matched with BCu80SnPAg solder for brazing copper and brass of the same or different materials. Since the inorganic mixture in the above flux consists of 4%–13% KBF4, 5%–12% KF, 5%–10% Bi2O3, and the balance being B2O3, fluxes containing "borides" are generally unsuitable for brazing aluminum alloys. Therefore, it is necessary to explore alternative approaches and develop novel fluxes that enhance the radiation resistance of aluminum alloy brazed joints to meet the needs of aerospace manufacturing. Summary of the Invention

[0006] The purpose of this invention is to provide a flux that enhances the radiation resistance of aluminum alloy brazed joints, its preparation method, and its application. The residue left after brazing with this flux forms a dense, thin, and uniform "plastic-glass" protective layer with radiation resistance, meeting the requirements of brazed joints in aerospace devices such as aluminum alloy antennas and aluminum alloy waveguides.

[0007] The technical solution for achieving the objective of this invention is as follows:

[0008] A flux that enhances the radiation resistance of brazed joints in aluminum alloys is formulated as follows: 5%–18% organic mixture, with the balance being an inorganic mixture; the organic mixture is formulated as follows: 7%–15% EP-12 epoxy resin, 8%–16% EP-16 epoxy resin, 5%–8% F-51A high-temperature flame-retardant thermosetting phenolic resin, 5%–8% F-52A high-temperature flame-retardant thermosetting phenolic resin, 5%–8% resorcinol, 5%–8% hydroquinone, with the balance being phthalic anhydride; the inorganic mixture is formulated as follows: 40%–55% CsF, 20%–30% AlF3, 0.005%–0.01% GaF3, with the balance being Al(OH)3.

[0009] The preparation method of the above-mentioned flux that can enhance the radiation resistance of aluminum alloy brazing joints includes the following steps:

[0010] (1) EP-12 epoxy resin, EP-16 epoxy resin, F-51A high temperature flame retardant thermosetting phenolic resin, F-52A high temperature flame retardant thermosetting phenolic resin, resorcinol, hydroquinone, and phthalic anhydride are mixed evenly in a stainless steel container according to the formula to obtain an organic mixture.

[0011] (2) CsF, AlF3, GaF3 and Al(OH)3 are mixed evenly in a stainless steel container according to the proportion to obtain an inorganic mixture;

[0012] (3) Mix the above organic mixture and inorganic mixture evenly in a stainless steel container according to the ratio to obtain flux.

[0013] Preferably, in the above preparation method, the purity of each raw material used is greater than 99.5%.

[0014] Furthermore, the present invention also provides the application of the above-mentioned flux, specifically the application method of matching the above-mentioned flux with Zn-Al brazing filler metal for brazing connections of the same or different materials such as aluminum alloy + aluminum alloy or aluminum alloy + copper alloy.

[0015] Unlike the flux reported in Chinese patent application CN115922150A, whose brazing method is limited to induction brazing, the flux obtained in this invention is applicable to various brazing processes such as furnace brazing, flame brazing, and induction brazing. After brazing, the flux residue forms a dense, thin, and uniform "plastic-glass" protective layer on the surface of the weld joint, which has radiation resistance. In addition, the shear strength of the brazed joint is more than 15% higher than that of the brazed joint with the existing commercially available CsF-AlF3 flux, meeting the urgent needs of aerospace product manufacturing. Detailed Implementation

[0016] Compared with traditional Nocolok fluxes such as K3AlF6, KAlF4, and CsF-AlF3, the technical solution adopted in this invention creatively solves the following key technical problems:

[0017] 1) Since K3AlF6 and KAlF4 fluxes are not suitable for brazing aluminum alloys and copper alloys, CsF-AlF3 flux, a "modified" Nocolok flux, is the best choice for brazing aluminum alloys and copper alloys. Similarly, traditional CsF-AlF3 flux mainly works by reacting the compounds in the flux with the oxides on the surface of the base metal and the filler metal at a selected brazing temperature, removing the oxide film and cleaning the surface of the base metal and the filler metal, thus facilitating the wetting, spreading, and filling of the gaps by the liquid filler metal. Although CsF-AlF3 flux residue is less corrosive, in most cases, flux residue still needs to be cleaned after brazing. Given the special properties of the flux of this invention and the requirement that the brazing seams of many aluminum alloy structures cannot be cleaned, it is necessary to enable the flux residue after brazing to organically combine with the "organic mixture" to form a thin and dense "plastic-glass" layer. Therefore, in addition to considering that the combination of "epoxy resin + phenolic resin" should not have a negative effect on the flux formulation (i.e., the inorganic mixture), the selection and combination of resins must also meet the requirements of high temperature resistance and higher curing temperature (600℃~700℃).

[0018] Extensive research and experimentation revealed that a novel resin combination was developed: EP-12 and EP-16 epoxy resins, which possess excellent radiation resistance, were paired with F-51A and F-52A high-temperature resistant flame-retardant thermosetting phenolic resins, which exhibit high temperature resistance. Resorcinol, hydroquinone, and phthalic anhydride were used as curing agents and accelerators, respectively. This combination allowed the organic mixture to cure smoothly during brazing at 600℃–700℃, forming a thin and uniform plastic-glass body with the CsF-AlF3 flux residue. This body evenly covered the surface of the aluminum alloy brazing joint, resulting in excellent radiation resistance and significantly improved shear strength.

[0019] 2) Traditional cesium-containing Nocolok aluminum alloy fluxes (such as CsF-AlF3 flux) mainly consist of CsAlF4, CsF, and AlF3. When used with Zn-Al brazing filler metal in the 500-700℃ range for brazing aluminum alloy + aluminum alloy and aluminum alloy + copper alloys, they effectively protect the base material from oxidation and promote filler metal flow. However, the resulting aluminum alloy brazed joints lack radiation resistance. Experiments show that... 60 Under the condition that the radiation dose rate of the Co-γ radiation source is 0.25 Gy(Si) / s, after 720 hours of radiation, the shear strength of the brazed joint decreases by more than 20%.

[0020] Traditional CsF-AlF3 fluxes primarily consist of CsAlF4, typically achieved by directly mixing CsF and AlF3 in a 1:1 molar ratio. However, due to the high F ion content (up to 32%) in CsAlF4 fluxes, the resulting residue is essentially powdery. To ensure that the residue of traditional CsAlF4 fluxes, while maintaining good film removal capabilities, can form a thin and dense "glassy body" that organically combines with the "epoxy resin + phenolic resin" mixture to form a "plastic-glassy body," its composition must be improved and optimized. To this end, the inventors, through extensive exploratory experiments, component selection, and content optimization, obtained a new inorganic combination of CsF, AlF3, GaF3, and Al(OH)3 that meets the above requirements. The key to this combination is a significant reduction in CsF and AlF3 fluorides and an increase of approximately 20% in Al(OH)3 (because Al(OH)3, upon high-temperature heating, forms Al2O3, which readily forms transparent alumina ceramics). This novel combination allows the brazing residue to form a thin and dense plastic-glass body + alumina ceramic, and the residue is essentially non-corrosive and requires no cleaning.

[0021] It is important to emphasize that the organic mixture formulation reported in CN115922150A is incompatible with the inorganic mixture of this invention—that is, it easily causes delamination and caking, making it impossible to prepare a flux with uniform texture and excellent brazing performance. Therefore, it is necessary to optimize and select the components and contents of epoxy resin, curing agent, and accelerator to solve the delamination and caking problems that may occur in the new flux.

[0022] The flux-matched Zn-Al brazing filler metal obtained by uniformly mixing the optimized organic mixture with the inorganic mixture described in this invention can be used for brazing connections of the same or different materials, such as aluminum alloy + aluminum alloy or aluminum alloy + copper alloy.

[0023] The flux of this invention, when heated within a temperature range of 600℃ to 700℃ and subjected to various brazing processes such as furnace brazing, flame brazing, and induction brazing, when matched with Zn-Al filler metal, can produce brazed joints with excellent radiation resistance when brazing aluminum alloy + aluminum alloy and aluminum alloy + copper alloy. Furthermore, the shear strength of the brazed joints can be increased by more than 10% compared to the shear strength of brazed joints obtained using commercially available CsAlF4 flux.

[0024] The present invention will be further described in detail below with reference to specific embodiments.

[0025] Example 1

[0026] A flux that enhances the radiation resistance of aluminum alloy brazed joints comprises, by mass percentage: 5% organic mixture, with the balance being an inorganic mixture; the organic mixture comprises, by mass percentage: 7% EP-12 epoxy resin, 16% EP-16 epoxy resin, 5% F-51A high-temperature flame-retardant thermosetting phenolic resin, 8% F-52A high-temperature flame-retardant thermosetting phenolic resin, 5% resorcinol, 8% hydroquinone, with the balance being phthalic anhydride; the inorganic mixture comprises, by mass percentage: 40% CsF, 30% AlF3, 0.005% GaF3, with the balance being Al(OH)3. The above flux is prepared through the following steps:

[0027] (1) EP-12 epoxy resin, EP-16 epoxy resin, F-51A high temperature flame retardant thermosetting phenolic resin, F-52A high temperature flame retardant thermosetting phenolic resin, resorcinol, hydroquinone, and phthalic anhydride are mixed evenly in a stainless steel container according to the formula to obtain an organic mixture.

[0028] (2) CsF, AlF3, GaF3 and Al(OH)3 are mixed evenly in a stainless steel container according to the proportion to obtain an inorganic mixture;

[0029] (3) Mix the above organic mixture and inorganic mixture evenly in a stainless steel container according to the ratio to obtain flux.

[0030] The above-mentioned flux, matched with Zn85-Al15 brazing filler metal, was used to braze 6063 aluminum alloy + 6063 aluminum alloy (plate thickness 3mm, lap width 5mm, the same below) using a furnace heating method with lap joint. The shear strength of the brazed joint (all data are the average of 5 experimental data, the same below) was 135±10MPa (fracture at the brazing seam). The above-mentioned flux, matched with Zn85-Al15 brazing filler metal, was used to braze 6063 aluminum alloy + H58 copper alloy (plate thickness 3mm, lap width 5mm, the same below). The shear strength of the brazed joint (all data are the average of 5 experimental data, the same below) was 135±10MPa (fracture at the brazing seam).

[0031] Brazed joint test pieces in 60 Under the condition of a Co-γ radiation source radiation dose rate of 0.25 Gy(Si) / s, after 720 hours of radiation, the shear strength of the 6063 aluminum alloy + 6063 aluminum alloy brazed joint decreased slightly to 130±10 MPa (fracture at the brazing seam). The shear strength of the 6063 aluminum alloy + H58 copper alloy brazed joint remained basically unchanged, at 133±10 MPa (fracture at the brazing seam).

[0032] Example 2

[0033] A flux that enhances the radiation resistance of aluminum alloy brazed joints comprises, by mass percentage: 18% organic mixture, with the balance being an inorganic mixture; the organic mixture comprises, by mass percentage: 15% EP-12 epoxy resin, 8% EP-16 epoxy resin, 8% F-51A high-temperature flame-retardant thermosetting phenolic resin, 5% F-52A high-temperature flame-retardant thermosetting phenolic resin, 8% resorcinol, 5% hydroquinone, with the balance being phthalic anhydride; the inorganic mixture comprises, by mass percentage: 55% CsF, 20% AlF3, 0.01% GaF3, with the balance being Al(OH)3. The preparation method is the same as in Example 1.

[0034] The above flux, matched with Zn85-Al15 brazing filler metal, was used to braze 6063 aluminum alloy + 6063 aluminum alloy (plate thickness 3mm, overlap width 5mm, the same below) using induction heating in a lap joint configuration. The shear strength of the brazed joint (all data are the average of 5 experimental data, the same below) was 135±10MPa (fracture at the brazing seam). The above flux, matched with Zn85-Al15 brazing filler metal, was also used to braze 6063 aluminum alloy + H58 copper alloy (plate thickness 3mm, overlap width 5mm, the same below). The shear strength of the brazed joint (all data are the average of 5 experimental data, the same below) was 135±10MPa (fracture at the brazing seam).

[0035] Brazed joint test pieces in 60 Under the condition of a Co-γ radiation source radiation dose rate of 0.25 Gy(Si) / s, after 720 hours of radiation, the shear strength of the 6063 aluminum alloy + 6063 aluminum alloy brazed joint decreased slightly to 130±10 MPa (fracture at the brazing seam). The shear strength of the 6063 aluminum alloy + H58 copper alloy brazed joint remained basically unchanged, at 133±10 MPa (fracture at the brazing seam).

[0036] Example 3

[0037] A flux that enhances the radiation resistance of aluminum alloy brazed joints comprises, by mass percentage: 12% organic mixture, with the balance being an inorganic mixture; the organic mixture comprises, by mass percentage: 11% EP-12 epoxy resin, 12% EP-16 epoxy resin, 6.5% F-51A high-temperature flame-retardant thermosetting phenolic resin, 7% F-52A high-temperature flame-retardant thermosetting phenolic resin, 7% resorcinol, 6% hydroquinone, with the balance being phthalic anhydride; the inorganic mixture comprises, by mass percentage: 50% CsF, 25% AlF3, 0.008% GaF3, with the balance being Al(OH)3. The preparation method is the same as in Example 1.

[0038] The above flux, matched with Zn85-Al15 brazing filler metal, was used to braze 6063 aluminum alloy + 6063 aluminum alloy (plate thickness 3mm, lap width 5mm, the same below) using an oxypropane flame heating method with a lap joint. The shear strength of the brazed joint (all data are the average of 5 experimental data, the same below) was 135±10MPa (fracture at the brazing seam). The above flux, matched with Zn85-Al15 brazing filler metal, was used to braze 6063 aluminum alloy + H58 copper alloy (plate thickness 3mm, lap width 5mm, the same below). The shear strength of the brazed joint (all data are the average of 5 experimental data, the same below) was 135±10MPa (fracture at the brazing seam).

[0039] Brazed joint test pieces in 60 Under the condition of a Co-γ radiation source radiation dose rate of 0.25 Gy(Si) / s, after 720 hours of radiation, the shear strength of the 6063 aluminum alloy + 6063 aluminum alloy brazed joint decreased slightly to 130±10 MPa (fracture at the brazing seam). The shear strength of the 6063 aluminum alloy + H58 copper alloy brazed joint remained basically unchanged, at 133±10 MPa (fracture at the brazing seam).

[0040] Comparative Example 1

[0041] Commercially available CsF-AlF3 flux was used to braze Zn85-Al15 solder using an induction heating method with a lap joint. The brazing of 6063 aluminum alloy + 6063 aluminum alloy (3mm plate thickness, 5mm lap width, same below) using an induction heating method with a lap joint yielded a shear strength of 110±10MPa (all data are averages of 5 experimental data, same below) (fracture at the brazing seam). The same flux-matched Zn85-Al15 solder was used to braze 6063 aluminum alloy + H58 copper alloy (3mm plate thickness, 5mm lap width, same below), yielding a shear strength of 110±10MPa (all data are averages of 5 experimental data, same below) (fracture at the brazing seam).

[0042] Brazed joint test pieces in 60 Under a Co-γ radiation source with a dose rate of 0.25 Gy(Si) / s, after 720 hours of radiation, the shear strength of the brazed joints of 6063 aluminum alloy + 6063 aluminum alloy significantly decreased, with an average of 85 ± 10 MPa (fracture at the brazing seam) based on five experimental data. The shear strength of the brazed joints of 6063 aluminum alloy + H58 copper alloy also significantly decreased, with an average of 88 ± 10 MPa (fracture at the brazing seam) based on five experimental data.

[0043] Comparative Example 2

[0044] The inorganic mixture described in Example 3, with a mass percentage ratio of 50% CsF, 25% AlF3, 0.008% GaF3, and the balance being Al(OH)3, was used to braze the flux-matched Zn85-Al15 brazing filler metal. The Zn85-Al15 filler metal was brazed using an oxypropane flame heating method with an lap joint. 6063 aluminum alloy + 6063 aluminum alloy (plate thickness 3mm, lap width 5mm, the same below) was also brazed using a furnace heating method with an lap joint. The shear strength of the brazed joint (all data are the average of 5 experimental data, the same below) was 115±10MPa (breakage at the brazing seam). The above flux was matched with Zn85-Al15 brazing filler metal to braze 6063 aluminum alloy + H58 copper alloy (plate thickness 3mm, overlap width 5mm, the same below). The shear strength of the brazed joint (all data are the average of 5 experimental data, the same below) was 115±10MPa (break at the brazing seam).

[0045] Brazed joint test pieces in 60 Under a Co-γ radiation source with a dose rate of 0.25 Gy(Si) / s, after 720 hours of radiation, the shear strength of the brazed joints of 6063 aluminum alloy + 6063 aluminum alloy significantly decreased, with an average of 90 ± 10 MPa (fracture at the brazing seam) based on five experimental data points. The shear strength of the brazed joints of 6063 aluminum alloy + H58 copper alloy also significantly decreased, with an average of 92 ± 10 MPa (fracture at the brazing seam) based on five experimental data points.

[0046] Comparative Example 3

[0047] When the 82.5% inorganic mixture described in Example 3 (the specific ratio of the inorganic mixture is: 50% CsF, 25% AlF3, 0.008% GaF3, with the balance being Al(OH)3) and the 17.5% organic mixture described in Example 3 reported in CN115922150A (the specific ratio of the organic mixture is: 20% E-51 epoxy resin, 15% F-51B high-temperature flame-retardant thermosetting phenolic resin, 15% F-52B high-temperature flame-retardant thermosetting phenolic resin, 13% resorcinol, with the balance being phthalic anhydride) are mixed in a stainless steel container for 10-20 minutes, the resulting flux resembles a "porridge-like" mixture and cannot form a homogeneous mixture.

[0048] The above-mentioned flux was matched with Zn85-Al15 brazing filler metal. Before brazing, the flux was stirred again for 5-10 minutes using an experimental stirrer. The above-mentioned flux-matched Zn85-Al15 brazing filler metal was brazed using an oxypropane flame heating method with a lap joint. The brazing of 6063 aluminum alloy + 6063 aluminum alloy (plate thickness 3mm, lap width 5mm, the same below) using a furnace heating method with a lap joint resulted in a shear strength of 75±10MPa (all data are averages of 5 experimental data, the same below) (fracture at the brazing seam). The above-mentioned flux-matched Zn85-Al15 brazing filler metal was used to braze 6063 aluminum alloy + H58 copper alloy (plate thickness 3mm, lap width 5mm, the same below), resulting in a shear strength of 65±10MPa (all data are averages of 5 experimental data, the same below) (fracture at the brazing seam), significantly lower than the shear strength of the brazed joint in the example.

[0049] Under a 60Co-γ radiation source with a dose rate of 0.25 Gy(Si) / s, after 720 hours of irradiation, the shear strength of the 6063 aluminum alloy + 6063 aluminum alloy brazed joints significantly decreased, with an average of 40 ± 10 MPa (fracture at the brazing seam) across five experimental data points. The shear strength of the 6063 aluminum alloy + H58 copper alloy brazed joints also significantly decreased, with an average of 30 ± 10 MPa (fracture at the brazing seam) across five experimental data points, significantly lower than the shear strength of the brazed joints in the example.

[0050] The experimental data from Examples 1 to 3 show that, using the flux of the present invention matched with Zn85-Al15 brazing filler metal, regardless of whether furnace heating, flame heating, or induction heating is used to braze 6063 aluminum alloy + 6063 aluminum alloy or 6063 aluminum alloy + H58 copper alloy joints, the brazed joints are... 60After 720 hours of radiation at a Co-γ radiation source dose rate of 0.25 Gy(Si) / s, the shear strength of the 6063 aluminum alloy + 6063 aluminum alloy brazed joint only decreased slightly, while the shear strength of the 6063 aluminum alloy + H58 copper alloy brazed joint remained almost unchanged, indicating that the flux of the present invention has significant radiation resistance in its flux residue.

[0051] A comparison of the three examples with the three comparative examples shows that the shear strength of the aluminum alloy + aluminum alloy or aluminum alloy + copper alloy brazed joints obtained by using the flux matched with Zn85-Al15 solder of the present invention is significantly improved (by about 18%) compared with the aluminum alloy + aluminum alloy or aluminum alloy + copper alloy brazed joints obtained by using commercially available CsF-AlF3 flux or the flux matched with Zn85-Al15 solder with the inorganic mixture ratio described in Example 3; the brazed joints of Comparative Example 1 and Comparative Example 2 show that... 60 Under a Co-γ radiation source dose rate of 0.25 Gy(Si) / s, after 720 hours of radiation, the shear strength of the brazed joint decreased significantly (by approximately 20%). In Comparative Example 3, due to the inability of the organic and inorganic mixtures to organically match, the fluxing performance was extremely poor. Although the filler metal remained unchanged and was particularly suitable for brazing aluminum alloys with or without copper alloys, the shear strength of the resulting brazed joint was only about 50% of that in the examples. 60 Under the condition of a Co-γ radiation source with a radiation dose rate of 0.25 Gy(Si) / s, after 720 hours of radiation, the shear strength of the brazed joint decreased by more than 45%. This is because the flux residue on the brazed joint was unevenly distributed, and therefore had almost no effect on radiation protection.

[0052] The comparison with Comparative Examples 1 and 2 shows that the technical solution of the present invention can not only enhance the radiation resistance of aluminum alloy brazed joints, but also significantly improve the shear strength of brazed joints. The comparison with Comparative Example 3 shows that in different inorganic mixture systems, the addition of organic mixtures such as epoxy resin systems requires "specific analysis of specific situations", and the components and composition of resin, curing agent and accelerator should be reasonably selected, and the amount added should also be reasonably adjusted.

Claims

1. A flux that enhances the radiation resistance of brazed joints in aluminum alloys, characterized in that, The organic mixture is formulated by mass percentage as follows: 5%–18% organic mixture, with the balance being an inorganic mixture; the organic mixture is formulated by mass percentage as follows: 7%–15% EP-12 epoxy resin, 8%–16% EP-16 epoxy resin, 5%–8% F-51A high-temperature flame-retardant thermosetting phenolic resin, 5%–8% F-52A high-temperature flame-retardant thermosetting phenolic resin, 5%–8% resorcinol, 5%–8% hydroquinone, with the balance being phthalic anhydride; the inorganic mixture is formulated by mass percentage as follows: 40%–55% CsF, 20%–30% AlF3, 0.005%–0.01% GaF3, with the balance being Al(OH)3.

2. The method for preparing flux according to claim 1, characterized in that, Includes the following steps: (1) EP-12 epoxy resin, EP-16 epoxy resin, F-51A high temperature flame retardant thermosetting phenolic resin, F-52A high temperature flame retardant thermosetting phenolic resin, resorcinol, hydroquinone, and phthalic anhydride are mixed evenly in a stainless steel container according to the formula to obtain an organic mixture. (2) Mix CsF, AlF3, GaF3 and Al(OH)3 evenly in a stainless steel container according to the proportion to obtain an inorganic mixture; (3) Mix the above organic mixture and inorganic mixture evenly in a stainless steel container according to the ratio to obtain flux.

3. The preparation method according to claim 2, characterized in that, The purity of each raw material is greater than 99.5%.

4. The application of the flux according to claim 1, characterized in that, The specific application method is as follows: the flux described in claim 1 is matched with Zn-Al brazing filler metal for brazing of the same or different materials, such as aluminum alloy + aluminum alloy or aluminum alloy + copper alloy.

5. The application according to claim 4, characterized in that, The brazing process is selected from furnace brazing, flame brazing or induction brazing.