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CN-122007707-A - Synthesis method of nanoscale potassium/sodium hydroxyl fluoride metal acid brazing flux for aluminum brazing

CN122007707ACN 122007707 ACN122007707 ACN 122007707ACN-122007707-A

Abstract

The invention belongs to the technical field of brazing materials, and particularly relates to a method for synthesizing nanoscale potassium/sodium hydroxyl fluoride metal acid brazing flux for aluminum brazing. The novel aluminum brazing flux is prepared by taking aluminum hydroxide, potassium hydroxide/sodium hydroxide/calcium hydroxide/magnesium hydroxide and the like and hydrofluoric acid aqueous solution as main raw materials in the presence of a mixed system of an organic solvent and water, has the characteristics of low melting point, small particle size, concentrated distribution and strong dispersion stability, and has the comprehensive performance obviously superior to that of the brazing flux prepared by the traditional method, and the brazing flux prepared by the method has the advantages of low cost, convenience in use, good film forming effect, low consumption and high surface smoothness after brazing.

Inventors

  • ZHOU HAO
  • LI KE
  • Ding ce
  • BI JINGGUO
  • GAO LUHAN
  • MING WENYONG

Assignees

  • 山东明瑞新材料科技有限公司

Dates

Publication Date
20260512
Application Date
20260331

Claims (10)

  1. 1. A method for synthesizing nanoscale potassium/sodium hydroxide fluorometallate brazing flux for aluminum brazing, which is characterized by comprising the following steps of: s1, adding aluminum hydroxide into hydrofluoric acid aqueous solution for dissolution, and stirring for reaction for 0.5-3h to obtain fluoroaluminate solution; S2, adding an organic solvent into the fluoroaluminate solution prepared in the step S1, and uniformly stirring to obtain an alcohol solution; And S3, adding an aqueous solution of metal hydroxide into the alcohol solution prepared in the step S2, uniformly stirring, regulating the pH value of the system to 5.0, stirring for reaction, and concentrating by rotary evaporation to obtain the nanoscale potassium/sodium hydroxide fluometallate brazing flux.
  2. 2. The method of synthesizing nano-sized potassium/sodium hydroxide fluorometallate flux for aluminum brazing according to claim 1, wherein the molar ratio of hydrofluoric acid to aluminum hydroxide in the aqueous hydrofluoric acid solution in step S1 is (4-6): 1.
  3. 3. The method for synthesizing nano-sized potassium/sodium hydroxide fluorometallate flux for aluminum brazing according to claim 2, wherein the molar ratio of hydrofluoric acid to aluminum hydroxide in the aqueous hydrofluoric acid solution in step S1 is (4.1-4.2): 1.
  4. 4. The method for synthesizing nano-sized potassium/sodium hydroxide fluorometallate flux for aluminum brazing according to claim 1, wherein the mass percentage of the aqueous hydrofluoric acid solution in the step S1 is 5% to 100%.
  5. 5. The method for synthesizing nano-sized potassium/sodium hydroxide fluorometallate flux for aluminum brazing according to claim 4, wherein the mass percentage of the aqueous hydrofluoric acid solution in the step S1 is 20% to 50%.
  6. 6. The method for synthesizing nano potassium/sodium hydroxide flux for aluminum brazing according to claim 1, wherein the stirring reaction in the step S1 is performed at a temperature of 0 to 80 ℃ for a time of 1 to 3 hours.
  7. 7. The method for synthesizing nano-sized potassium/sodium hydroxide flux for aluminum brazing according to claim 6, wherein the temperature of the stirring reaction in step S1 is 5 to 20 ℃.
  8. 8. The method for synthesizing nanoscale potassium/sodium hydroxide fluorometallate brazing flux for aluminum brazing according to claim 1, wherein in the step S2, the organic solvent is one or more of methanol, ethanol, ethylene glycol, propylene glycol, butanediol and methylpentanediol, and the addition amount of the organic solvent is 2-6 times of the mass of aluminum hydroxide.
  9. 9. The method for synthesizing nano-sized potassium/sodium hydroxide fluorometallate flux for aluminum brazing according to claim 8, wherein the organic solvent in the step S2 is methylpentanediol, and the addition amount of the organic solvent is 3 to 5 times the mass of aluminum hydroxide.
  10. 10. The method for synthesizing nanoscale potassium/sodium hydroxide fluorometallate flux for aluminum brazing according to claim 1, wherein in the step S3, the metal hydroxide is one or more of potassium hydroxide, sodium hydroxide, calcium hydroxide and magnesium hydroxide, and the molar ratio of the metal hydroxide to hydrofluoric acid is (0.061-0.134) (0.41-0.42).

Description

Synthesis method of nanoscale potassium/sodium hydroxyl fluoride metal acid brazing flux for aluminum brazing Technical Field The invention belongs to the technical field of brazing materials, and particularly relates to a method for synthesizing nanoscale potassium/sodium hydroxyl fluoride metal acid brazing flux for aluminum brazing. Background Conventional flux "Nokolock" nominally composed of potassium fluoroaluminate K 1.14AlF4.14 is used in many industrial applications as a flux. Hundreds of thousands of tons per year are being used in the manufacture of heat exchangers for air conditioning systems, automobiles, and refrigeration equipment. K 1.14AlF4.14 is in fact a mixture of KAlF 4 with small amounts of AlF 3 and K 2AlF5 and a minor amount of K 3AlF6. In the chemical phase diagram of the KF-AlF3 system, the molar ratio of 1.14KF to 1AlF 3 represents the eutectic composition, at which the melting point of the system is lowest. In the brazing process of aluminum, a layer of compact aluminum oxide film exists on the surface of the aluminum, the layer of compact aluminum oxide film prevents molten solder from wetting and flowing, the quality of a brazing joint is seriously influenced, and the main application of brazing flux potassium fluoroaluminate is that the brazing flux potassium fluoroaluminate can react with the aluminum oxide film in a molten (liquid) state, and the main reaction equation is as follows: al 2O3+6KAlF4→8AlF3+3K2 O type 1a Al 2O3+3K2AlF5→5AlF3+3K2 O type 1b Al 2O3+2K3AlF6→4AlF3+3K2 O formula 1c. In actual use, since the melting point of the metal aluminum material is about 660.3 ℃, and the melting points of both the pure potassium fluoroaluminates KAlF 4、K2AlF5 and K 3AlF6 are higher than 660.3 ℃, it is not possible to use either pure potassium fluoroaluminate during the brazing process. But at the eutectic point, the melting points of 1.14KF and 1AlF 3 are only about 565-572 ℃, so that potassium fluoroaluminate nominally of composition K 1.14AlF4.14 is useful as a flux in aluminum brazing processes. However, in the application, where the reaction is carried out according to formula 1, the powdered brazing flux must be suspended in water or an alcohol/water mixture, and it is often necessary to add a so-called binder to adhere it to the surface of the aluminum material. At this stage, nokolock needs to be uniformly coated on the surface of the aluminum material to ensure the continuity of brazing. The traditional brazing flux potassium fluoroaluminate synthesis process mainly comprises the following two steps of 1, dissolving aluminum hydroxide in a hydrofluoric acid solution with the mass concentration of 40%, wherein the molar ratio of hydrofluoric acid to aluminum hydroxide is 4.14:1, forming fluochloric acid after complete dissolution, wherein the reaction formula is as follows, 4.14HF+Al (OH) 3→H1.14AlF4.14+3H2 O (formula 2), and 2, adding a potassium hydroxide aqueous solution with the stoichiometric required amount (quantitative) to neutralize the system after complete dissolution of aluminum hydroxide in the hydrofluoric acid solution, and the reaction formula is as follows, H 1.14AlF4.14+1.14KOH→K1.14AlF4.14+1.14H2 O (formula 3). The two steps of reaction form a product with the total component of K 1.14AlF4.14, and the white solid powder product is obtained after cleaning, filtering, drying and crushing. The preparation method comprises the steps of (1) melting aluminum-based alloy after smelting and purifying treatment to obtain molten liquid, cooling, collecting and screening the molten liquid after being impacted by inert gas to obtain brazing filler metal, (2) adding aluminum hydroxide into hydrofluoric acid, adding potassium hydroxide for coprecipitation, drying, crushing and screening a product obtained by coprecipitation to obtain brazing flux, (3) uniformly mixing the brazing filler metal obtained in the step (1) and the brazing flux obtained in the step (2), pressing to obtain a pressed compact, heating and variable-speed extruding the pressed compact to obtain the aluminum-based flux-cored wire. However, the conventional synthesis process has the problems that 1, even if a surface or an active agent is added in an aqueous phase reaction environment, ostwald ripening and agglomeration of powder particles are very easy to occur, and products with small particle sizes and uniform distribution are difficult to obtain, 2, the process is complicated by removing impurity ions through complicated steps such as cleaning after reaction, and 3, the reaction products are high in post-treatment cost and not environment-friendly through procedures such as filtering, drying, crushing and grinding. Therefore, a new reaction control strategy is needed, which can control the reaction process more precisely in a non-aqueous environment to synthesize a novel aluminum brazing flux with more uniform particle size, better stability and direct use. Disclosure of Invention In order to