Aluminum soldering flux and preparation method thereof

Abstract

The invention provides an aluminum soldering flux and a preparation method thereof, and the method comprises the following steps: (1) adding ammonium bifluoride and / or ammonium fluoride into water for dissolving to obtain a mixture A; (2) anhydrous rubidium carbonate, cesium carbonate and an aluminum compound are added into the mixture A to be evenly mixed, a mixture B is obtained, and the aluminum compound is selected from aluminum oxide and / or aluminum hydroxide; and (3) the mixture B is stirred, heated and reacted until the materials do not flow, then high-temperature heating reaction is conducted, and the aluminum soldering flux is obtained. The method provided by the invention is simple in process, the adopted raw material components are simple, the cost is low, hydrofluoric acid and other low-safety raw materials are avoided, and the method is environment-friendly. The aluminum soldering flux obtained through the method has the advantages of being excellent in film removing, wetting and spreading performance, high in activity, not prone to water absorption and free of corrosion after welding, and particularly the melting point of the aluminum soldering flux ranges from 460 DEG C to 510 DEG C.

Description

Technical Field

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

[0002] Aluminum and its alloys possess excellent physical and chemical properties, good processing and corrosion resistance, and are widely used in aerospace, automotive, and machinery manufacturing. With the increasing demand for aluminum alloys, the demand for aluminum alloy welding has also increased. Brazing, with its advantages of minimal weld deformation and high dimensional accuracy, has become widely adopted in the aluminum alloy welding field.

[0003] Aluminum brazing flux primarily removes the oxide film on the aluminum alloy surface during brazing. Based on their post-weld effects on the material, brazing fluxes are categorized into two main types: corrosive and non-corrosive. Corrosive brazing fluxes primarily refer to chloride brazing fluxes, composed of alkali metal chloride salts. These fluxes are inexpensive and have a long history of use. However, the chloride residues left after welding are susceptible to moisture absorption and corrosive to the alloy, requiring additional cleaning steps. Consequently, non-corrosive brazing fluxes, also known as fluoride brazing fluxes, have been developed.

[0004] Fluoride fluxes can be prepared by various methods, the most common and widely used being the wet method. There are two types of wet methods. One involves using hydrofluoric acid with metal oxides or hydroxides such as cesium carbonate, rubidium carbonate, aluminum hydroxide, and potassium hydroxide. However, hydrofluoric acid is a highly corrosive acid and reacts violently with metal salts such as rubidium hydroxide, aluminum hydroxide, rubidium carbonate, and cesium carbonate. Large-scale production poses significant safety risks and places high demands on reaction vessels and exhaust emissions, increasing production costs and environmental risks. Another wet method involves mixing fluoride in water in a proportional manner, or using water as the medium, to form a slurry or suspension. The resulting solution is then dried at high temperature or air-dried to form the final flux. However, direct fluoride preparation methods are expensive, and fluoride salts such as cesium fluoride are highly hygroscopic, easily absorbing moisture at room temperature, which can affect the flux composition ratio.

[0005] Furthermore, most current aluminum brazing flux patents focus on optimizing the composition and ratio of the flux to achieve a more suitable melting point. However, these patents and methods often add multiple substances to the formula, increasing raw material costs and hindering quality control in actual production. Summary of the Invention

[0006] The present invention aims to solve one of the technical problems in the prior art to at least a certain extent. To this end, one object of the present invention is to provide an aluminum brazing flux and a preparation method thereof.

[0007] In a first aspect of the present invention, a method for preparing an aluminum brazing flux is provided, the method comprising: (1) adding ammonium bifluoride and / or ammonium fluoride into water and dissolving them to obtain a mixture A; (2) adding anhydrous rubidium carbonate, cesium carbonate and an aluminum compound to the mixed material A and mixing them uniformly to obtain a mixed material B, wherein the aluminum compound is selected from aluminum oxide and / or aluminum hydroxide; (3) The mixed material B is stirred and heated to react until the material stops flowing, and then heated at high temperature to react to obtain aluminum brazing flux.

[0008] According to the preparation method of the aluminum brazing flux provided by the present invention, ammonium bifluoride and / or ammonium fluoride are reacted with anhydrous rubidium carbonate, cesium carbonate and an aluminum compound to produce an aluminum brazing flux with excellent film removal, wetting and spreading properties, high activity, low water absorption, and no corrosion after welding. At the same time, the raw material composition of the aluminum brazing flux is simple, the preparation process is simple, and the use of low-safety raw materials such as hydrofluoric acid is avoided. It is environmentally friendly and does not add other complex and high-cost components, which is conducive to quality control and suitable for mass production. Specifically, the prepared aluminum brazing flux has a melting point between 460 and 510°C and is suitable for aluminum alloy brazing at around 500°C.

[0009] Furthermore, the following reactions may occur during the above preparation process: Al2O3+6NH4F=2AlF3+3H2O+6NH3↑ Cs2CO3+2NH4F=2CsF+CO2↑+2NH3↑+H2O Rb2CO3+2NH4F=2RbF+CO2↑+2NH3↑+H2O Al2O3+3NH4HF2=2AlF3+3H2O+3NH3↑ Cs2CO3+NH4HF2=2CsF+CO2↑+NH3↑+H2O Rb2CO3+NH4HF2=2RbF+CO2↑+NH3↑+H2O.

[0010] In some embodiments of the present invention, in step (1), the ammonium bifluoride and / or the ammonium fluoride is used as a dry material, and the mass ratio of the dry material to the water is 1:(0.5-1.5).

[0011] In some embodiments of the present invention, the mixed material A consists of a first mixed material A and a second mixed material A, the first mixed material A reacts with the aluminum compound, and the second mixed material A reacts with the anhydrous rubidium carbonate and the cesium carbonate.

[0012] Preferably, when the ammonium fluoride is added to water and dissolved to obtain the mixture A, the molar ratio of the aluminum element in the mixture B to the ammonium fluoride in the first mixture A is 1:(3-4), and the molar ratio of the total amount of rubidium and cesium elements in the mixture B to the ammonium fluoride in the second mixture A is 1:(1-1.25).

[0013] When the ammonium bifluoride is added to water and dissolved to obtain the mixture A, the molar ratio of the aluminum element in the mixture B to the ammonium bifluoride in the first mixture A is 1:(1.5-2), and the molar ratio of the total amount of rubidium and cesium elements in the mixture B to the ammonium bifluoride in the second mixture A is 1:(0.5-0.625).

[0014] It should be noted that when preparing the mixture A, the addition amounts of anhydrous rubidium carbonate, cesium carbonate, and the aluminum compound are first calculated, and the amount of ammonium bifluoride or ammonium fluoride required is calculated based on the reaction relationship. When calculating the reaction relationship again, the amount of ammonium bifluoride or ammonium fluoride is calculated and weighed according to the above-mentioned molar ratio. After weighing, the separately weighed ammonium bifluoride or ammonium fluoride is mixed together and dissolved in water to obtain the mixture A.

[0015] In some embodiments of the present invention, in step (3), the high-temperature heating temperature is 280-400°C and the time is 1-3 hours. The high-temperature heating temperature and time must be controlled within the above ranges to reach the reaction temperature of the aluminum raw material and ammonium fluoride / ammonium bifluoride, and the reaction time must be sufficient to ensure that the reaction proceeds fully, so that the melting point of the prepared flux is in the medium temperature range.

[0016] In some embodiments of the present invention, the temperature of the heating reaction is 90-140°C.

[0017] In some embodiments of the present invention, cesium carbonate and an aluminum compound are heated and maintained to remove water of crystallization. Specifically, the temperature for removing water of crystallization from cesium carbonate is 150-300°C for 2-4 hours, and argon is passed through the solution. The temperature for removing water of crystallization from the aluminum compound is 300-400°C for 2-4 hours, and argon is passed through the solution.

[0018] It should be noted that the anhydrous rubidium carbonate, cesium carbonate and aluminum compound are all analytically pure, for example, the purity of cesium carbonate is above 99.5%; ammonium bifluoride and ammonium fluoride are also analytically pure.

[0019] In a second aspect of the present invention, another method for preparing an aluminum brazing flux is provided, the method comprising: (a) adding ammonium bifluoride and / or ammonium fluoride to water and dissolving them to obtain a first mixed material; (b) adding aluminum oxide and / or aluminum hydroxide to water and mixing uniformly to obtain a second mixed material; (c) adding the first mixture to the second mixture and stirring to react to obtain a third mixture; (d) drying the third mixed material until it does not flow and then heating it at high temperature to react, thereby obtaining the first material; (e) adding anhydrous rubidium carbonate and cesium carbonate to the first mixture and stirring to react to obtain a fourth mixture; (f) adding the first material to the fourth mixed material and stirring the mixture until the mixture becomes viscous and does not flow, and then continuing to heat the mixture to obtain an aluminum brazing flux.

[0020] According to the preparation method of the aluminum brazing flux provided by the present invention, ammonium bifluoride and / or ammonium fluoride are reacted with anhydrous rubidium carbonate, cesium carbonate and an aluminum compound respectively, and then mixed and further reacted. The step-by-step process can be used to prepare an aluminum brazing flux with excellent film removal, wetting and spreading properties, high activity, low water absorption, and no corrosion after welding. At the same time, the raw material composition of the aluminum brazing flux is simple, the preparation process is simple, and the use of low-safety raw materials such as hydrofluoric acid is avoided. It is environmentally friendly and does not add other complex and high-cost components, which is conducive to quality control and suitable for mass production. Specifically, the prepared aluminum brazing flux has a melting point between 460 and 510°C and is suitable for aluminum alloy brazing at around 500°C.

[0021] Furthermore, the following reactions may occur during the above preparation process: Al2O3+6NH4F=2AlF3+3H2O+6NH3↑ Cs2CO3+2NH4F=2CsF+CO2↑+2NH3↑+H2O Rb2CO3+2NH4F=2RbF+CO2↑+2NH3↑+H2O Al2O3+3NH4HF2=2AlF3+3H2O+3NH3↑ Cs2CO3+NH4HF2=2CsF+CO2↑+NH3↑+H2O Rb2CO3+NH4HF2=2RbF+CO2↑+NH3↑+H2O.

[0022] In some embodiments of the present invention, in step (a), the ammonium bifluoride and / or the ammonium fluoride is used as a dry material, and the mass ratio of the dry material to the water is 1:(0.5-1.5).

[0023] In some embodiments of the present invention, in step (b), the aluminum oxide and / or aluminum hydroxide is used as the aluminum material, and the mass ratio of the aluminum material to the water is 1:(0.5-1.5).

[0024] In some embodiments of the present invention, in step (c), when the ammonium fluoride is dissolved in the water to obtain the first mixture, the molar ratio of the aluminum element in the second mixture to the ammonium fluoride in the first mixture is 1:(3-4). Controlling the molar ratio of the aluminum element in the second mixture to the ammonium fluoride in the first mixture within the above range allows the aluminum material to completely react to form the brazing flux.

[0025] In some embodiments of the present invention, in step (c), when the ammonium bifluoride is dissolved in the water to obtain the first mixture, the molar ratio of the aluminum element in the second mixture to the ammonium bifluoride in the first mixture is 1:(1.5-2). Controlling the molar ratio of the aluminum element in the second mixture to the ammonium bifluoride in the first mixture within the above range can ensure sufficient and complete reaction.

[0026] In some embodiments of the present invention, in step (c), the stirring reaction comprises: stirring the reaction at room temperature for 30 min-40 min, then continuously heating the mixture to the boiling point and continuing the reaction for 0.5 h-2 h.

[0027] In some embodiments of the present invention, in step (d), the high-temperature reaction is carried out at a temperature of 280-450°C and for a time of 1-3 hours. For example, the temperature is 280°C, 300°C, 320°C, 350°C, 380°C, 400°C, 420°C, 450°C, or any range between any two of the foregoing values. Controlling the high-temperature reaction temperature and time within these ranges ensures a thorough reaction without residual high-melting-point materials or intermediates. (Insufficient reaction temperature and time can lead to the formation of high-melting-point AlF3, resulting in a high amount of unmelted residue during actual use of the flux, which can affect the performance of the weld joint and hinder practical use.)

[0028] In some embodiments of the present invention, in step (d), the drying temperature is 90-140° C., thereby removing the water generated in the reaction and previously added, and obtaining a relatively dry material for convenient subsequent operations.

[0029] In some embodiments of the present invention, in step (e), when the ammonium fluoride is dissolved in the water to obtain the first mixture, the molar ratio of the total amount of rubidium and cesium to the ammonium fluoride in the first mixture is 1:(1-1.25). Controlling the molar ratio of rubidium and cesium to the ammonium fluoride in the first mixture within the above range can ensure complete fluorination of rubidium and cesium.

[0030] In some embodiments of the present invention, in step (e), when the ammonium bifluoride is dissolved in the water to obtain the first mixture, the molar ratio of the total amount of rubidium and cesium to the ammonium bifluoride in the first mixture is 1:(0.5-0.625). Controlling the molar ratio of rubidium and cesium to the ammonium bifluoride in the first mixture within the above range can achieve a good fluorination effect, ensuring complete fluorination of rubidium and cesium, as demonstrated by process experiments.

[0031] In some embodiments of the present invention, in step (e), the stirring reaction time is 30 min-40 min at room temperature. In step (e), the stirring reaction is accompanied by gas generation.

[0032] In some embodiments of the present invention, in step (f), the stirring reaction temperature is 90-140°C.

[0033] In some embodiments of the present invention, in step (f), the temperature of the elevated temperature reaction is 280-350°C, and the time is 1-3 hours. For example, the temperature is 280°C, 300°C, 320°C, 350°C, or any range between any two of the aforementioned values. Controlling the elevated temperature and time within the aforementioned ranges allows for complete reaction of ammonium fluoride and ammonium bifluoride, eliminating residual raw materials and producing no high-melting-point byproducts.

[0034] In some embodiments of the present invention, cesium carbonate and an aluminum compound are heated and maintained to remove water of crystallization. Specifically, the temperature for removing water of crystallization from cesium carbonate is 150-300°C for 2-4 hours, and argon is passed through the solution. The temperature for removing water of crystallization from the aluminum compound is 300-400°C for 2-4 hours, and argon is passed through the solution.

[0035] It should be noted that the anhydrous rubidium carbonate, cesium carbonate and aluminum compound are all analytically pure, for example, the purity of cesium carbonate is above 99.5%; ammonium bifluoride and ammonium fluoride are also analytically pure.

[0036] In a third aspect, the present invention provides an aluminum brazing flux prepared using the aforementioned method. This aluminum brazing flux exhibits excellent film removal, wetting, and spreading properties, is highly active, is non-hydroscopic, and exhibits no post-weld corrosion. Specifically, the aluminum brazing flux has a melting point of 460-510°C.

[0037] Preferably, the mass ratio of rubidium, cesium, and aluminum in the aluminum brazing flux is (20-32):(27-32):(10-13). Controlling the mass ratio of rubidium, cesium, and aluminum in the aluminum brazing flux within the aforementioned range can produce a brazing flux with an ideal melting point. When the mass ratio of rubidium to cesium in the raw material composition is lower than this mass ratio, the resulting brazing flux has a high melting point and is impractical. When the mass ratio of rubidium to cesium in the raw material composition is higher than this mass ratio, two scenarios arise: increasing the cesium ratio results in a lower melting point but a significant increase in cost. Increasing the rubidium ratio results in no significant decrease in melting point, but rather an increase in melting point, which also increases cost (rubidium salts are more expensive than cesium salts), which does not meet actual production requirements.

[0038] The present invention has at least the following beneficial effects: The method for preparing an aluminum brazing flux provided by the present invention features a simple process, employs simple raw material components, is low-cost, and avoids the use of unsafe raw materials such as hydrofluoric acid, resulting in environmental friendliness. The aluminum brazing flux obtained by this method exhibits excellent film removal, wetting, and spreading properties, is highly active, is not susceptible to water absorption, and exhibits no post-weld corrosion. Specifically, the aluminum brazing flux has a melting point between 460°C and 510°C, making it suitable for brazing aluminum alloys at temperatures around 500°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 The DSC, dissolution and spreading test, and XRD pattern of the aluminum brazing flux of Example 1 of the present invention are shown; Figure 2 1. DSC, dissolution and spreading test and XRD pattern of the aluminum brazing flux of Example 2 of the present invention; Figure 3 1. DSC, dissolution and spreading test, and XRD pattern of the aluminum brazing flux of Example 3 of the present invention; Figure 4 1. DSC, dissolution and spreading test, and XRD pattern of the aluminum brazing flux of Example 4 of the present invention; Figure 5 1. DSC, dissolution and spreading test, and XRD pattern of the aluminum brazing flux of Example 5 of the present invention; Figure 6 1. DSC, dissolution and spreading test, and XRD pattern of the aluminum brazing flux of Example 6 of the present invention; Figure 7 The DSC, dissolution and spreading test and XRD pattern of the aluminum brazing flux of Comparative Example 1 of the present invention are shown; Figure 8 The DSC, dissolution and spreading test and XRD pattern of the aluminum brazing flux of Comparative Example 2 of the present invention are shown; Figure 9 The DSC, dissolution and spreading test and XRD pattern of the aluminum brazing flux of Comparative Example 3 of the present invention are shown; Figure 10 1. The DSC, dissolution and spreading tests and XRD diagram of the aluminum brazing flux of Comparative Example 4 of the present invention are shown. DETAILED DESCRIPTION

[0041] Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative work shall fall within the scope of protection of the present invention. The present invention will be described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0042] Example 1 This embodiment provides an aluminum brazing flux, and the specific preparation process is as follows: (1) Cesium carbonate and rubidium carbonate were kept at 250°C for 4 hours to remove the crystal water, and aluminum oxide was kept at 350°C for 4 hours to remove the crystal water.

[0043] (2) Weigh 42.00 g of ammonium fluoride and dissolve it in 40 mL of water to obtain the first mixture.

[0044] (3) Weigh 19.27 g of aluminum oxide and add 20 ml of water to make a paste to obtain the second mixture.

[0045] (4) Slowly add the first mixture into the paste-like second mixture, stir at room temperature for 0.5 h, then continue to heat until the mixture boils and continue to react for 1 h to obtain the third mixture.

[0046] (5) The third mixture obtained in step 4 was dried on a hot plate at 90°C until it did not flow, then transferred to a crucible and reacted at 380°C for 2 h to obtain powder A.

[0047] (6) Weigh 27.63 g of ammonium fluoride and dissolve it in 20 mL of water.

[0048] (7) Weigh 44.55 g of rubidium carbonate and 34.37 g of cesium carbonate, add them to the ammonium fluoride solution obtained in step (6), stir and react at room temperature for 30 min, then add powder A, stir and react at 90 °C until it becomes viscous and does not flow, then react at 350 °C for 1 h, while removing excess ammonia.

[0049] (8) Grinding the material obtained in step (7) to obtain aluminum brazing flux.

[0050] The mass ratio of rubidium, cesium and aluminum in the aluminum brazing flux obtained in Example 1 is 32:27:10.

[0051] Example 2 This embodiment provides an aluminum brazing flux, and the specific preparation process is as follows: (1) Cesium carbonate and rubidium carbonate were kept at 250°C for 4 hours to remove the crystal water, and aluminum oxide was kept at 350°C for 4 hours to remove the crystal water.

[0052] (2) Weigh 64.80 g of ammonium fluoride and dissolve it in 60 mL of water to obtain the first mixture.

[0053] (3) Weigh 25.48 g of aluminum oxide and add 20 ml of water to make a paste to obtain the second mixture.

[0054] (4) Slowly add the first mixture into the paste-like second mixture, stir at room temperature to allow for full reaction for 0.5 h, then continue to heat the mixture until it boils and continue to react for 1 h to obtain the third mixture.

[0055] (5) The third mixture obtained in step 4 was dried on a hot plate at 90°C until it did not flow, and then transferred to a crucible and reacted at 450°C for 1 hour to obtain powder A.

[0056] (6) Weigh 20.18 g of ammonium fluoride and dissolve it in 20 mL of water.

[0057] (7) Weigh 30.48 g of rubidium carbonate and 41.54 g of cesium carbonate, add them to the ammonium fluoride solution obtained in step (6), stir and react at room temperature for 30 min, then add powder A, stir and react at 90 ° C until it becomes viscous and does not flow, then dry at 280 ° C for 3 h to remove excess ammonia.

[0058] (8) Grinding the material obtained in step (7) to obtain aluminum brazing flux.

[0059] The mass ratio of rubidium, cesium and aluminum in the aluminum brazing flux obtained in Example 2 is 20.8:31.3:12.5.

[0060] Example 3 This embodiment provides an aluminum brazing flux, and the specific preparation process is as follows: (1) Cesium carbonate and rubidium carbonate were kept at 250°C for 4 hours to remove the crystal water, and aluminum oxide was kept at 350°C for 4 hours to remove the crystal water.

[0061] (2) Weigh 50.17 g of ammonium bifluoride and dissolve it in 50 mL of water to obtain the first mixture.

[0062] (3) Weigh 22.42 g of aluminum oxide and add 20 ml of water to make a paste to obtain the second mixture.

[0063] (4) Slowly add the first mixture into the paste-like second mixture, stir at room temperature to allow for full reaction for 0.5 h, then continue to heat the mixture until it boils and continue to react for 1 h to obtain the third mixture.

[0064] (5) The third mixture obtained in step 4 was dried on a hot plate at 90°C until it did not flow, and then transferred to a crucible and reacted at 400°C for 1 hour to obtain powder A.

[0065] (6) Weigh 15.98 g of ammonium bifluoride and dissolve it in 25 mL of water.

[0066] (7) Weigh 37.41 g of rubidium carbonate and 38.48 g of cesium carbonate, add them to the ammonium bifluoride solution obtained in step (6), stir and react at room temperature for 30 min, then add powder A, stir and react at 90 °C until it becomes viscous and does not flow, then react at 300 °C for 2 h, while removing excess ammonia.

[0067] (8) Grinding the material obtained in step (7) to obtain aluminum brazing flux.

[0068] The mass ratio of rubidium, cesium and aluminum in the aluminum brazing flux obtained in Example 3 is 26.0:29.4:11.1.

[0069] Example 4 This embodiment provides an aluminum brazing flux, and the specific preparation process is as follows: (1) Cesium carbonate and rubidium carbonate were kept at 250℃ for 4 hours to remove crystal water, and aluminum oxide was kept at 350℃ for 4 hours to remove crystal water.

[0070] (2) Weigh 72.30 g of ammonium fluoride and dissolve it in 65 mL of water.

[0071] (3) Weigh 40.88 g of rubidium carbonate, 38.45 g of cesium carbonate, and 20.90 g of aluminum oxide, and add them to the ammonium fluoride solution in step 2 in sequence. Stir thoroughly to obtain a mixture.

[0072] (4) The mixture obtained in step 3 was stirred and heated to 140°C for sufficient reaction until the material stopped flowing, and then reacted at 280°C for 3 hours. After grinding, aluminum brazing flux was obtained.

[0073] The mass ratio of rubidium, cesium and aluminum in the aluminum brazing flux obtained in Example 4 is 28.2:29.2:10.3.

[0074] Example 5 This embodiment provides an aluminum brazing flux, and the specific preparation process is as follows: (1) Cesium carbonate and rubidium carbonate were kept at 250°C for 4 hours to remove the crystal water, and aluminum oxide was kept at 350°C for 4 hours to remove the crystal water.

[0075] (2) Weigh 75.00 g of ammonium fluoride and dissolve it in 70 mL of water.

[0076] (3) Weigh 35.10 g of anhydrous rubidium carbonate, 38.45 g of cesium carbonate, and 23.45 g of aluminum oxide, and add them to the ammonium fluoride solution in step 2 in sequence. Stir thoroughly to obtain a mixture.

[0077] (4) The mixture obtained in step 3 was dried at 120°C until it did not flow, reacted at 350°C for 2h, and ground to obtain aluminum brazing flux.

[0078] The mass ratio of rubidium, cesium and aluminum in the aluminum brazing flux obtained in Example 5 is 24.5:29.5:11.7.

[0079] Example 6 This embodiment provides an aluminum brazing flux, and the specific preparation process is as follows: (1) Cesium carbonate was kept at 250°C for 4 hours to remove the crystal water, and aluminum hydroxide was kept at 350°C for 4 hours to remove the crystal water.

[0080] (2) Weigh 64.17 g of ammonium bifluoride and dissolve it in 60 mL of water.

[0081] (3) Weigh 30.49 g of anhydrous rubidium carbonate, 38.45 g of cesium carbonate, and 39.00 g of aluminum hydroxide, and add them to the ammonium bifluoride solution in step 2 in sequence, stirring thoroughly to obtain a mixture.

[0082] (4) The mixture obtained in step 3 was dried at 90°C until it did not flow, reacted at 400°C for 1.5 hours, and ground to obtain an aluminum brazing flux.

[0083] The mass ratio of rubidium, cesium and aluminum in the aluminum brazing flux obtained in Example 6 is 21.4:29.7:12.8.

[0084] Comparative Example 1 This comparative example provides an aluminum brazing flux, and the specific preparation process is as follows: (1) Cesium carbonate and rubidium carbonate were kept at 250℃ for 4 hours to remove crystal water, and aluminum oxide was kept at 350℃ for 4 hours to remove crystal water.

[0085] (2) Weigh 53.34 g of ammonium fluoride and dissolve it in 50 mL of water.

[0086] (3) Weigh 53.12 g of anhydrous rubidium carbonate, 9.77 g of cesium carbonate, and 24.47 g of aluminum oxide and add them to the ammonium fluoride solution in step 2 in sequence, stir to allow for sufficient reaction, and obtain a mixture.

[0087] (4) The mixture obtained in step 3 was dried at 90°C until it did not flow, and then reacted at 350°C. 2h, and aluminum brazing flux is obtained after grinding.

[0088] The mass ratio of rubidium element, cesium element and aluminum element in the aluminum brazing flux obtained in Comparative Example 1 is 40.3:8.2:13.3.

[0089] Comparative Example 2 (1) Cesium carbonate and rubidium carbonate were kept at 100°C for 4 hours to remove the crystal water, and aluminum oxide was kept at 350°C for 4 hours to remove the crystal water.

[0090] (2) Weigh 66.15 g of ammonium bifluoride and dissolve it in 60 mL of water to obtain the first mixture.

[0091] (3) Weigh 37.41 g of rubidium carbonate, 38.48 g of cesium carbonate, and 22.42 g of aluminum oxide and add them to the ammonium bifluoride solution in step 2 in sequence, stir to allow for sufficient reaction, and obtain a mixture.

[0092] (4) The mixture obtained in step 3 was dried at 100°C until it did not flow, reacted at 200°C for 3 hours, and ground to obtain an aluminum brazing flux.

[0093] Comparative Example 3 Take 38.76g of cesium fluoride, 27.58g of rubidium fluoride and 41.97g of aluminum fluoride in a container, stir and mix them evenly to obtain aluminum brazing flux.

[0094] Comparative Example 4 Commercially available potassium fluoroaluminate flux.

[0095] The performance of the aluminum brazing fluxes of the examples and comparative examples was tested as follows: The aluminum brazing flux was subjected to XRD, DSC, dissolution and spreading tests, and moisture content testing. The dissolution and spreading tests were conducted at 510°C. The substrate used for the dissolution and spreading tests was 6061 aluminum alloy, and the brazing filler metal was Zn-Al. The test method involved placing 0.10g of the test sample on a 40mm x 40mm x 2mm 6063 aluminum plate and heating it with a hydrogen flame for 50 seconds. The film removal ability and flowability of the test sample on the 6061 aluminum plate were then observed. The moisture content test, which examined the moisture absorption of the finished aluminum brazing flux, involved weighing the dried aluminum brazing flux into an open watch glass at 75% humidity for 24 hours before testing the flux for moisture.

[0096] The performance test results of the aluminum brazing fluxes of the embodiments and comparative examples are shown in Tables 1 and Figure 1-10 .

[0097] Table 1

[0098] As can be seen in Table 1, the flux examples prepared according to the patented method all have melting points below 495°C, exhibit good clearing without residue, exhibit excellent fluidity at high temperatures, exhibit good film removal properties, exhibit high flux activity, exhibit no moisture absorption, and exhibit no post-weld corrosion, effectively meeting the requirements for medium-temperature aluminum brazing. In Comparative Example 1, the high Rb:Cs:Al ratio raises the flux melting point to above 500°C. Furthermore, the flux exhibits a high residue during clearing and a low wetting and spreading area, demonstrating that the ratio significantly influences both the flux melting point and activity. In Comparative Example 2, the high-temperature heating reaction temperature is 200°C, which is relatively low, resulting in incomplete reaction. This is reflected in the flux's poor clearing performance, small spreading area, and low flux activity. Furthermore, the flux absorbs moisture, posing a risk of post-weld corrosion. Comparative Example 3 was prepared according to the method of direct mixing of fluorides mentioned in other materials. Because the fluoride salts of rubidium and cesium are highly hygroscopic, they absorb moisture severely during preparation. The resulting flux absorbs moisture severely, and no obvious melting point can be measured. When the melting and spreading tests were carried out at 500°C, the results were poor, and the use effect was not good. Comparative Example 4 is a commercially available ordinary potassium fluoroaluminate flux. Because it does not contain rubidium and cesium, it has a higher melting point and average activity.

[0099] The accompanying drawings are DSC, melt clear photographs and XRD patterns of the examples and comparative examples. Figure 1 The figures are test images of the aluminum brazing flux prepared in Example 1, (a) is the DSC analysis curve, (b) is the actual image after the clearing test, and (c) is the XRD spectrum. Figure 2 The figures are test images of the aluminum brazing flux prepared in Example 2, (a) is the DSC analysis curve, (b) is the actual image after the clearing test, and (c) is the XRD spectrum; Figure 3 The figures are the test graphs of the aluminum brazing flux prepared in Example 3, (a) is the DSC analysis curve, (b) is the actual image after the clearing test, and (c) is the XRD spectrum; Figure 4 The figures are test images of the aluminum brazing flux prepared in Example 4, (a) is the DSC analysis curve, (b) is the actual image after the clearing test, and (c) is the XRD spectrum. Figure 5 The figures are test images of the aluminum brazing flux prepared in Example 5, (a) is the DSC analysis curve, (b) is the actual image after the clearing test, and (c) is the XRD spectrum; Figure 6 The figures are test images of the aluminum brazing flux prepared in Example 6, (a) is the DSC analysis curve, (b) is the actual image after the clearing test, and (c) is the XRD spectrum; Figure 7 The test diagram of the aluminum brazing flux prepared in Comparative Example 1 is shown in FIG. (a) is the DSC analysis curve, (b) is the actual image after the clearing test, and (c) is the XRD spectrum. Figure 8The test diagram of the aluminum brazing flux prepared in Comparative Example 2 is shown in FIG. 1 , where (a) is the DSC analysis curve, (b) is the actual image after the clearing test, and (c) is the XRD spectrum. Figure 9 The test diagram of the aluminum brazing flux prepared in Comparative Example 3 is shown in FIG. (a) is the DSC analysis curve, (b) is the actual image after the clearing test, and (c) is the XRD spectrum. Figure 10 The test diagram of the aluminum brazing flux prepared in Comparative Example 4 is shown in FIG. 1 , where (a) is the DSC analysis curve, (b) is the actual image after the clearing test, and (c) is the XRD spectrum. The DSC analysis curve in the accompanying figure shows that the flux prepared in the example has a melting point and a narrow melting range, while the flux prepared in the comparative example has a high melting point and a wide melting range. The actual image after melting and clearing shows that the aluminum flux prepared in the example is completely melted and cleared, with essentially no obvious residue on the aluminum substrate. The wetting ring indicates that the oxide film on the surface of the aluminum substrate has been removed, while the comparative example has obvious white residue on the aluminum plate surface after melting and clearing, a small wetting ring area, and low flux activity.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing an aluminum brazing flux, characterized in that: include: (1) adding ammonium bifluoride and / or ammonium fluoride into water and dissolving them to obtain a mixture A; (2) adding anhydrous rubidium carbonate, cesium carbonate and an aluminum compound to the mixed material A and mixing them uniformly to obtain a mixed material B, wherein the aluminum compound is selected from aluminum oxide and / or aluminum hydroxide; (3) The mixed material B is stirred and heated to react until the material stops flowing, and then heated at high temperature to react to obtain aluminum brazing flux.

2. The method according to claim 1, characterized in that In step (1), the ammonium bifluoride and / or the ammonium fluoride is used as a dry material, and the mass ratio of the dry material to the water is 1: (0.5-1.5); And / or, in step (3), the high temperature heating temperature is 280-400°C and the time is 1h-3h; And / or, in step (3), the temperature of the heating reaction is 90-140°C.

3. The method according to claim 1 or 2, characterized in that The mixed material A consists of a first mixed material A and a second mixed material A, the first mixed material A reacts with the aluminum compound, and the second mixed material A reacts with the anhydrous rubidium carbonate and the cesium carbonate; Preferably, when the ammonium fluoride is added to water and dissolved to obtain the mixture A, the molar ratio of the aluminum element in the mixture B to the ammonium fluoride in the first mixture A is 1:(3-4), and the molar ratio of the total amount of rubidium and cesium elements in the mixture B to the ammonium fluoride in the second mixture A is 1:(1-1.25); When the ammonium bifluoride is added to water and dissolved to obtain the mixture A, the molar ratio of the aluminum element in the mixture B to the ammonium bifluoride in the first mixture A is 1:(1.5-2), and the molar ratio of the total amount of rubidium and cesium elements in the mixture B to the ammonium bifluoride in the second mixture A is 1:(0.5-0.625).

4. A method for preparing an aluminum brazing flux, characterized in that: include: (a) adding ammonium bifluoride and / or ammonium fluoride to water and dissolving them to obtain a first mixed material; (b) adding aluminum oxide and / or aluminum hydroxide to water and mixing uniformly to obtain a second mixed material; (c) adding the first mixture to the second mixture and stirring to react to obtain a third mixture; (d) drying the third mixed material until it does not flow and then heating it at high temperature to react, thereby obtaining the first material; (e) adding anhydrous rubidium carbonate and cesium carbonate to the first mixture and stirring to react to obtain a fourth mixture; (f) adding the first material to the fourth mixed material and stirring the mixture until the mixture becomes viscous and does not flow, and then continuing to heat the mixture to obtain an aluminum brazing flux.

5. The method according to claim 4, characterized in that: In step (a), the ammonium bifluoride and / or the ammonium fluoride is used as a dry material, and the mass ratio of the dry material to the water is 1: (0.5-1.5); And / or, in step (b), the aluminum oxide and / or aluminum hydroxide is used as the aluminum material, and the mass ratio of the aluminum material to the water is 1:(0.5-1.5).

6. The method according to claim 4, characterized in that: In step (c), when the ammonium fluoride is added to the water and dissolved to obtain the first mixture, the molar ratio of the aluminum element in the second mixture to the ammonium fluoride in the first mixture is 1:(3-4); And / or, in step (c), when the ammonium bifluoride is added to the water and dissolved to obtain the first mixture, the molar ratio of the aluminum element in the second mixture to the ammonium bifluoride in the first mixture is 1:(1.5-2); And / or, in step (c), the stirring reaction comprises: stirring the reaction at room temperature for 30 min-40 min, then continuously heating the mixture until the mixture boils and continuing the reaction for 0.5 h-2 h.

7. The method according to claim 4, characterized in that: In step (d), the heating temperature is 280-400°C and the time is 1h-3h; And / or, in step (d), the drying temperature is 90-140°C.

8. The method according to claim 4, characterized in that: In step (e), when the ammonium fluoride is added to the water and dissolved to obtain the first mixture, the molar ratio of the total amount of rubidium and cesium elements to the ammonium fluoride in the first mixture is 1:(1-1.25); And / or, in step (e), when the ammonium bifluoride is added to the water and dissolved to obtain the first mixture, the molar ratio of the total amount of rubidium and cesium elements to the ammonium bifluoride in the first mixture is 1:(0.5-0.625); And / or, in step (e), the stirring reaction time is 30 min-40 min, and the temperature is room temperature.

9. The method according to claim 4, characterized in that: In step (f), the stirring reaction temperature is 90-140°C; And / or, in step (f), the temperature of the temperature-raising reaction is 280-350° C., and the time is 1 h-3 h.

10. An aluminum brazing flux, characterized in that: Prepared by the method according to any one of claims 1 to 3 or the method according to any one of claims 4 to 9; Preferably, in the aluminum brazing flux, the mass ratio of rubidium, cesium and aluminum is (20-32): (27-32): (10-13); And / or, the melting point of the aluminum brazing flux is 460-510°C.

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