Aluminum-alloy brazing flux paste and preparation method therefor

Abstract

The present invention belongs to the technical field of aluminum-alloy brazing materials, and specifically relates to an aluminum-alloy brazing flux paste and a preparation method therefor. The method comprises: 1) mixing cetyltrimethylammonium bromide and / or modified urea and / or a modified silicate with water to prepare an additive; and 2) mixing the additive prepared in step 1) with a wet-process formulated cesium-series brazing flux until uniform, and aging same to obtain a flux paste. The flux paste of the present invention can adhere to a workpiece during welding, thereby overcoming the defect of it being inconvenient to apply a powdered brazing flux to a complicated workpiece or a ramp surface. Moreover, the flux paste of the present invention has good stability and a good flux effect, and forms a high-strength weld joint after fluxing.

Description

Aluminum alloy brazing flux paste and preparation method thereof Technical Field

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

[0002] Aluminum alloy workpieces are widely used in aerospace, automotive manufacturing, air conditioning radiators, and other fields. Most aluminum alloy workpieces are joined by welding, with brazing being the primary method for joining aluminum alloy workpieces. In recent years, the welding of aluminum alloy workpieces has gradually moved towards miniaturization and automation. Traditional powdered brazing fluxes are particularly inadequate for brazing aluminum alloy workpieces with complex structures and irregular joint shapes. However, paste flux not only allows for adhesion to complex and irregular workpieces but also offers advantages such as flexibility and precise placement, ensuring high-quality fluxing during aluminum alloy welding.

[0003] Common soldering flux paste is a paste-like flux material prepared by adding rosin, isopropyl alcohol, organic acid and special chemical substances. Its main function is to remove oxides on the surface of the base material, reduce surface tension and improve the wettability of the solder. It is mostly suitable for soft soldering of electronic components and electronic circuit boards, but is not very suitable for brazing of aluminum and aluminum alloys at higher temperatures.

[0004] Numerous studies have reported on the development of aluminum solder pastes. These pastes primarily consist of powdered brazing filler metal, brazing flux, thixotropic agents, thickeners, and organic solvents. These pastes are generally capable of meeting the welding requirements of relevant aluminum alloy workpieces. However, the preparation of these pastes requires specialized processing techniques for most powdered filler metals, significantly increasing the cost and difficulty of preparing these pastes compared to traditional powdered, filamentous, foil, and sheet forms. Furthermore, to ensure the stability of the paste, a significant amount of organic matter is used, accounting for approximately 15%-40% of the total volume. During welding operations such as flame brazing and induction brazing, excessive organic matter can carbonize and blacken the weld, leading to weld defects and compromising the aesthetics of the weld.

[0005] Common cesium fluoroaluminate products on the market typically come in powder form. Although they can be mixed with water or alcohol to form a paste, their stability is poor and they are prone to delamination. Adding common thickeners to improve paste stability can result in excessive organic matter, which can carbonize and blacken after brazing, causing weld defects. For example, the flux containing cesium fluoroaluminate products disclosed in CN201510776244.3 contains over 50% organic matter. Therefore, it is crucial to minimize the amount of organic matter added while ensuring flux paste stability. Related literature indicates that in some aqueous solutions, flake, rod, or needle-shaped crystals tend to form a framework with strong attraction at the edges and ends, resulting in a stable framework structure. By controlling the micromorphology of cesium fluoroaluminate flux crystals, modifying their surface with a small amount of additives, and then supplementing with appropriate additives, a flux paste with excellent stability, simple preparation, and superior fluxing performance can be developed. This is of great significance for promoting high-quality brazing of aluminum and aluminum alloy workpieces. Summary of the Invention

[0006] In order to overcome the current problems in the field of aluminum alloy brazing, namely that powdered brazing flux is not suitable for the brazing of complex workpieces, and existing liquid or paste-type cesium fluoroaluminate-based fluxes have challenges such as poor stability, excessive organic matter content and low weld strength, the present invention provides an aluminum alloy brazing flux paste and a preparation method thereof.

[0007] The objects of the present invention are:

[0008] 1. It can be used to remove the surface oxide film during aluminum alloy brazing, promote the wetting and spreading of the brazing material on the base material, and thus achieve reliable connection of aluminum and aluminum alloys;

[0009] 2. The preparation process is simple and easy to repeat;

[0010] 3. Wide range of applications and simple operation;

[0011] 4. The residue after brazing is easy to clean or there is no residue.

[0012] To achieve the above objectives, the present invention adopts the following technical solutions.

[0013] A method for preparing aluminum alloy brazing flux paste,

[0014] The method comprises:

[0015] 1) Two or three components of hexadecyltrimethylammonium bromide, modified urea, and modified silicate are mixed with water to prepare an additive;

[0016] 2) The additive prepared in step 1) is evenly mixed with the wet-process cesium-based flux, and subjected to aging treatment to obtain a soldering paste.

[0017] As a preference,

[0018] In the additives of step 1):

[0019] When containing cetyltrimethylammonium bromide, the concentration of cetyltrimethylammonium bromide is 0.01 to 0.06 mol / L;

[0020] When containing modified urea solution, the modified urea concentration is 0.05wt%-0.2wt%;

[0021] When modified silicate is contained, the concentration of the modified silicate is 0.05%-0.4wt%.

[0022] As a preference,

[0023] Step 2) The wet-process cesium flux is prepared by the following method:

[0024] Soluble cesium salt and aluminum hydroxide are mixed in a ratio of Al to Cs atoms of 1: (1-2), dispersed in water for pre-reaction, and then hydrofluoric acid is added and stirred to react until the precipitate no longer increases.

[0025] As a preference,

[0026] The hydrofluoric acid is used in an excess amount of 0.05 to 0.20 mol based on the standard dosage of metal atoms and fluorine atoms;

[0027] The standard dosage, i.e. the ratio of aluminum atoms to fluorine atoms, is 1:(4-5).

[0028] As a preference,

[0029] During the preparation process of the wet-process cesium-based flux, hydrofluoric acid is added and stirred at 65-90° C. for 0.5-3.0 hours.

[0030] As a preference,

[0031] Step 2) During the mixing process of the additive and the wet-process cesium-based flux, the molar amount of the wet-process cesium-based flux is calculated based on the molar amount of the aluminum element contained, and 70 to 165 mL of the additive is added per mole of the wet-process cesium-based flux, and the additive and the wet-process cesium-based flux are mixed uniformly.

[0032] As a preference,

[0033] In step 2), the process of mixing the additive with the wet-process cesium flux is as follows: while continuously stirring the additive, the wet-process cesium flux is slowly added to the additive in batches. For example, the wet-process cesium flux is slowly added in batches at a uniform rate over 5-100 minutes, preferably for 10-30 minutes.

[0034] As a preference,

[0035] Step 2) After the mixing, the mixture is rapidly stirred at a stirring speed of 1000-2000 rpm for 20-70 minutes; after the stirring is completed, the mixture is aged at 25-45° C. until it becomes a stable paste.

[0036] Aluminum alloy brazing flux paste.

[0037] A key aspect of this invention lies in the introduction of special additives to thicken and stabilize the cesium fluoroaluminate flux. Conventional cesium fluoroaluminate flux pastes typically contain organic additives such as triethanolamine, glycerol, methylcellulose, borate esters, and small alcohols. This invention uniquely utilizes hexadecyltrimethylammonium bromide, modified urea, and modified silicate as organic additives, avoiding the use of conventional ingredients to enhance the stability of the cesium fluoroaluminate flux paste.

[0038] In common cesium fluoroaluminate brazing flux pastes, the main purpose of organic additives is to thicken and improve the stability of the cesium fluoroaluminate brazing flux. Therefore, a large amount of organic additives is needed to "wrap" the brazing flux (i.e., cesium fluoroaluminate brazing flux) to achieve the dispersion of the brazing flux and protect the brazing flux to avoid the loss and failure of the active ingredients.

[0039] In addition, the present invention uses unique organic additives.

[0040] The unique feature of the organic additives in the present invention is that, upon application, they interact with the needle-shaped cesium fluoroaluminate brazing flux to impart a higher viscosity coefficient to the system, enabling effective thickening at relatively low dosages. Unlike conventional organic additives, the additives of the present invention interact with the brazing flux through intermolecular forces, protecting it and enhancing its stability and altering its thixotropic effect. Consequently, in practical use, the brazing flux paste of the present invention is convenient and flexible to apply, enabling precise application. After brazing, minimal residue remains on the weld surface, making it easy to clean.

[0041] The second core of the present invention lies in the use of a specially formulated wet-process cesium flux. Common cesium fluoroaluminate fluxes are composed of Cs2AlF5 or CsAlF4, and are often prepared by reacting fluoroaluminic acid with a cesium salt, or by reacting hydrogen fluoride with aluminum hydroxide (or similar aluminum compounds) before reacting with a cesium salt. The cesium fluoroaluminate flux produced by this method has a single component. In contrast, the present invention first mixes the cesium salt with aluminum hydroxide, pre-reacts, and then slowly adds hydrogen fluoride for a secondary reaction to produce the product. In the present invention, the target product is primarily composed of CsAlF4 and / or CsAlF4·2H2O and / or Cs2AlF5 and / or Cs2AlF5·H2O. Therefore, the present invention first requires strict control of the relative amounts of cesium and aluminum, as well as the relative amounts of the two metal atoms, cesium and aluminum, and fluorine, to achieve effective control of the product.

[0042] For the present invention, there are two important processes in the above process. First, the cesium salt and aluminum hydroxide are mixed, part of the aluminum hydroxide is reacted, and the reaction product is fully mixed with the remaining raw materials. This process is crucial for controlling the uniformity of the product and preventing the generation of by-products, ensuring that the subsequent preparation process proceeds smoothly. Secondly, a slightly excessive amount of hydrogen fluoride is slowly added to carry out subsequent reactions. In common processes, fluoroaluminate ions are formed by the reaction of aluminum hydroxide and hydrogen fluoride, and then reacted with the cesium salt to form a product. However, in this process, the reaction process is difficult to control and an amorphous product is easily formed. The present invention first pre-reacts the cesium salt and aluminum hydroxide, and then slowly adds a slightly excessive amount of hydrogen fluoride, which can effectively control the reaction process. This process can stably prepare cesium fluoroaluminate crystals with a needle-shaped micromorphology, and the cesium fluoroaluminate brazing flux can further promote the stability of the paste under the action of additives in the aqueous solution system.

[0043] Through the control of the above preparation process, the cesium fluoroaluminate-based flux prepared by the present invention has a uniform and stable crystal form, stable quality, is not prone to agglomeration, and covers the weld surface after welding to protect the weld.

[0044] On the other hand, when mixing the flux of the present invention and the additive, it is also important to note that the flux prepared in proportion should be slowly added to the additive, rather than directly mixing the two. This is because direct mixing can cause the flux to agglomerate, and this agglomeration of the flux will lead to rapid failure or a significant reduction in the effectiveness of the soldering paste. Common organic additives will actually absorb heat during the soldering process, and the agglomeration of the flux will cause very serious temperature unevenness during the soldering process. The agglomeration of the flux will cause the flux to be unevenly distributed, resulting in poor surface de-filming of the base material during the soldering process, making it impossible to effectively implement the soldering process. This is also a defect of existing cesium fluoroaluminate soldering pastes.

[0045] The invention also relates to the application of the soldering paste.

[0046] The soldering paste of the present invention contains no solder and contains very little organic matter. It requires a powdered or filamentary solder for soldering and can be used in brazing methods such as furnace brazing, induction brazing, and flame brazing. Specifically, the application method involves applying the soldering paste to the area to be soldered, adding a powdered, flaky, or filamentary solder, and heating the area to be soldered with a heat source until the soldering paste and the solder melt, completing the soldering process. Alternatively, a filamentary or flaky solder is dipped into the soldering paste and brazing is completed under heat from a heat source.

[0047] The beneficial effects of the present invention are:

[0048] The soldering paste of the present invention can adhere to the workpiece during the welding process, thereby solving the defect that powdered solder flux is inconvenient to use on complex workpieces or sloped surfaces. At the same time, the soldering paste of the present invention has good soldering effect, the formed weld has high strength, and the soldering paste can cover the weld surface after cooling after welding, thereby protecting the weld. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG1 is the TG-DSC characterization result of the wet-process cesium-based flux prepared in Example 1.

[0050] FIG2 is a schematic structural diagram of a lap joint assembly for lap joint welding according to an embodiment of the present invention. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below with reference to specific embodiments and the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only a portion of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0052] Unless otherwise specified, the raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art; unless otherwise specified, the methods used in the examples of the present invention are all methods known to those skilled in the art.

[0053] Example 1

[0054] An aluminum alloy brazing flux paste is prepared by the following method:

[0055] 1) preparing an additive using water as a solvent, wherein the concentration of cetyltrimethylammonium bromide in the prepared additive is 0.01 mol / L and the concentration of Laponite-RD (modified silicate) is 0.05 wt%;

[0056] 2) Preparation of wet-process cesium flux: Aluminum hydroxide [Al(OH)3], cesium carbonate (Cs2CO3) and hydrofluoric acid (HF) were weighed in a ratio of 1:1.5:4.5 among the atoms of Al, Cs and F, and the aluminum hydroxide and cesium carbonate were thoroughly mixed and dispersed in deionized water. The amount of cesium carbonate was 1 mol and the amount of water was 500 mL. The mixture was stirred at 120 rpm for 10 minutes to allow some of the aluminum hydroxide to react first, and the reaction product was thoroughly mixed with the remaining raw materials. The solution was then stirred slowly at 300 rpm and the weighed hydrofluoric acid was added slowly and uniformly within 10 minutes. The reaction temperature was controlled at 80°C. After the weighed hydrofluoric acid was added, 0.05 mol of hydrofluoric acid was added while stirring. The reaction was stirred for 3 hours until the precipitate no longer increased, the solution was evaporated to dryness, the product was ultrasonically cleaned with deionized water, and then dried at 60°C to obtain a wet-process cesium flux.

[0057] 3) The additive prepared in step 1) and the wet-configuration cesium flux prepared in step 2) were mixed uniformly at a ratio of 100 mL of the additive per mol of the wet-configuration cesium flux. The wet-configuration flux was slowly added to the additive at a uniform speed within 20 min. The molar amount of the wet-configuration cesium flux was calculated based on the molar amount of aluminum hydroxide used in step 2). The molar amount of aluminum hydroxide used was the molar amount of the product wet-configuration cesium flux. After mixing, the mixture was rapidly stirred at 1500 rpm for 60 min, and then aged at 40° C. to obtain a stable aluminum alloy brazing flux paste.

[0058] The wet-process cesium flux obtained above was subjected to TG-DSC characterization, and the results are shown in Figure 1. The upper line in Figure 1 is the TG curve on the left, and the lower line is the DSC curve on the right. Figure 1 clearly shows that when the wet-process cesium flux prepared by the present invention is heated, it experiences a small mass loss of only approximately 2.1014% at approximately 170°C as the temperature increases. Simultaneously, the DSC curve reveals an endothermic peak within this temperature range. This mass loss and endothermic peak are therefore determined to be caused by the absorption of heat by the crystallized water in the flux, which breaks the chemical bond between the water and the flux, transforming into free water and volatilizing it. Furthermore, the wet-process cesium flux prepared by the present invention exhibits distinct endothermic peaks at 445.5°C and 476.75°C, indicating that the flux has a wide melting temperature range, making it more adaptable to brazing operations while exhibiting no weight loss within this temperature range. It can be said that the wet-process cesium-based flux prepared by the present invention has little loss during brazing and has good fluxing performance and application prospects.

[0059] On this basis, the flux paste was also subjected to stability test, spreadability test, welding test and weld corrosion test.

[0060] in:

[0061] During the stability test, 15 mL of solder paste was centrifuged at 3000 rpm for 7 × 24 hours. After the centrifugation, the solder paste was observed for signs of solidification or sedimentation.

[0062] During the spreadability test, 1 mL of solder flux paste was applied to a 6061 aluminum plate measuring 40 × 40 × 2 mm (apply only to the 40 × 40 mm surface, and only one surface is sufficient, the same applies below). 0.1 g of 4047 aluminum-silicon alloy solder wire was placed on the solder flux as a solder. The aluminum plate was heated until the solder flux and solder melted. After cooling, the spread area of ​​the solder was measured.

[0063] During the welding test, 0.1g of 4047 aluminum-silicon alloy wire was used as the filler metal to lap-weld two 6061 aluminum plates, each measuring 50×20×2mm. Flux paste was applied to the weld joint and the surrounding area. The 6061 aluminum plates were heated until the flux and filler metal melted. After cooling, the lap joint was mechanically tested for shear strength and fracture location.

[0064] During the weld corrosion test, 0.1g of 4047 aluminum-silicon alloy welding wire was used as the brazing filler metal to lap-weld two 6061 aluminum plates, each measuring 50×20×2mm. Flux paste was applied to the weld joint and the surrounding area. The 6061 aluminum plates were heated until the flux paste and the brazing filler metal melted. After cooling, the lap joint was subjected to a corrosion test and placed in boiling hydrochloric acid (37wt%). The time required for the joint to be thinned to 50% of its original thickness was recorded. The maximum test duration was 12h.

[0065] During the welding test and weld corrosion test, the overlapping surface was a 50×20 mm surface of two 6061 aluminum plates, with a 4 mm overlap. The solder was placed at the overlap, and flux was applied to the outer surface of the solder and around the intersection with the two 6061 aluminum plates. A schematic diagram of the lap joint assembly for lap welding is shown in Figure 2 (i.e., the front view). The same applies below.

[0066] The above test results are shown in the following table.

[0067] It can be seen from the above characterization results that the flux paste of the present invention has very excellent stability, and there is no solidification or sedimentation phenomenon after centrifugation. In addition, the solder has good fluidity during the welding process, and can more effectively and well infiltrate the weld. The weld strength after welding is high, even higher than the strength of the original parent material. The fracture position in the shear resistance characterization is located in the parent material. In addition, the flux paste of the present invention can also cover and protect the weld after welding, and performs very well in subsequent corrosion tests.

[0068] Example 2

[0069] An aluminum alloy brazing flux paste is prepared by the following method:

[0070] 1) The additive was prepared using water as a solvent. In this example, the concentration of the modified urea BYK-420 was 0.1 wt %, and the concentration of the modified silicate Laponite-RD was 0.1 wt %;

[0071] 2) Preparation of wet-process cesium flux: Aluminum hydroxide [Al(OH)3], cesium carbonate (Cs2CO3) and hydrofluoric acid (HF) were weighed in a ratio of 1:1.4:4.4 among the atoms of Al, Cs and F, and the aluminum hydroxide and cesium carbonate were thoroughly mixed and dispersed in deionized water. The amount of cesium carbonate was 1 mol and the amount of water was 500 mL. The mixture was stirred at 120 rpm for 15 minutes to allow some of the aluminum hydroxide to react first, and the reaction product was thoroughly mixed with the remaining raw materials. The solution was then stirred slowly at 300 rpm and the weighed hydrofluoric acid was slowly added at a uniform rate within 10 minutes. The reaction temperature was controlled at 80°C. After the weighed hydrofluoric acid was added, 0.05 mol of hydrofluoric acid was added while stirring. The mixture was stirred for 3 hours until the precipitate no longer increased, the solution was evaporated to dryness, the precipitate was ultrasonically cleaned with deionized water, and then dried at 60°C to obtain a wet-process cesium flux.

[0072] 3) The additive prepared in step 1) and the wet-configuration cesium flux prepared in step 2) were uniformly mixed at a ratio of 100 mL of the additive per mol of the wet-configuration cesium flux. The wet-configuration flux was slowly added to the additive at a uniform speed within 20 minutes. The molar amount of the wet-configuration cesium flux was calculated based on the molar amount of aluminum hydroxide used in step 2). The molar amount of aluminum hydroxide used was the molar amount of the product wet-configuration cesium flux. After mixing, the mixture was rapidly stirred at 1500 rpm for 60 minutes, and then aged at 40° C. to obtain a stable aluminum alloy brazing flux paste.

[0073] The flux paste in this example was subjected to stability test, spreadability test, welding test and weld corrosion test.

[0074] in:

[0075] During the stability test, 15 mL of solder paste was centrifuged at 3000 rpm for 7 × 24 hours. After the centrifugation, the solder paste was observed for signs of solidification or sedimentation.

[0076] During the spreadability test, 1 mL of solder flux paste was applied to a 6061 aluminum plate measuring 40 × 40 × 2 mm. 0.1 g of 4047 aluminum-silicon alloy solder wire was placed on the solder paste as a filler metal. The aluminum plate was heated until the solder paste and filler metal melted. After cooling, the spread area of ​​the filler metal was measured.

[0077] During the welding test, 0.1g of 4047 aluminum-silicon alloy wire was used as the filler metal to lap-weld 6061 aluminum plates measuring 50×20×2mm. Flux paste was applied to the weld joint and the surrounding area. The 6061 aluminum plates were heated until the flux and filler metal melted. After cooling, the lap joints were mechanically tested for shear strength and fracture location.

[0078] During the weld corrosion test, 0.1g of 4047 aluminum-silicon alloy welding wire was used as the brazing filler metal to weld lap joints of 6061 aluminum plates measuring 50×20×2mm. Flux paste was applied to the weld joint and the surrounding area. The 6061 aluminum plate was heated until the flux paste and the brazing filler metal melted. After cooling, the lap joint was subjected to a corrosion test and placed in boiling hydrochloric acid (37wt% concentration). The time required for it to be thinned to 50% of its original thickness was recorded. The maximum test time was 12h.

[0079] The above test results are shown in the following table.

[0080] The above characterization results show that the flux paste of the present invention has excellent stability, without any solidification or sedimentation after centrifugation. In addition, the solder has good fluidity during the welding process, which can more effectively and well infiltrate the weld. The weld strength after welding is high, even higher than the strength of the original parent material. The fracture position in the shear resistance characterization is located in the parent material. In addition, the flux paste of the present invention can also cover and protect the weld after welding, and performs very well in subsequent corrosion tests.

[0081] Example 3

[0082] An aluminum alloy brazing flux paste is prepared by the following method:

[0083] 1) Prepare the additive using water as solvent. In this example, the concentration of cetyltrimethylammonium bromide is 0.03 mol / L, the concentration of modified urea BYK-420 is 0.2 wt%, and the concentration of modified silicate Laponite-RD is 0.2 wt%.

[0084] 2) Preparation of wet-process cesium flux: aluminum hydroxide [Al(OH)3], cesium carbonate (Cs2CO3) and hydrofluoric acid (HF) were weighed respectively according to the atomic ratio of Al, Cs and F of 1:1.3:4.3. The aluminum hydroxide and cesium carbonate were thoroughly mixed and then dispersed in deionized water. The amount of cesium carbonate was 1 mol and the amount of water was 500 mL. The mixture was stirred at 120 rpm for 10 min. First, part of the aluminum hydroxide was reacted, and the reaction product was thoroughly mixed with the remaining raw materials. Then, the solution was slowly stirred at 300 rpm and the weighed hydrofluoric acid was slowly and uniformly added within 10 min. The reaction temperature was controlled to 85°C. After the weighed hydrofluoric acid was added, 0.07 mol of hydrofluoric acid was added while maintaining stirring. The stirring state was maintained for 2 h. After the precipitate no longer increased, the solution was evaporated to dryness. The precipitate was ultrasonically cleaned with deionized water and dried at 60°C to obtain a wet-process cesium flux.

[0085] 3) The additive prepared in step 1) and the wet-configuration cesium flux prepared in step 2) were mixed uniformly at a ratio of 100 mL of the additive per mol of the wet-configuration cesium flux. The wet-configuration flux was slowly added to the additive at a uniform speed within 20 minutes. The molar amount of the wet-configuration cesium flux was calculated based on the molar amount of aluminum hydroxide used in step 2). The molar amount of aluminum hydroxide used was the molar amount of the product wet-configuration cesium flux. After mixing, the mixture was rapidly stirred at 1600 rpm for 40 minutes, and then aged at 40° C. to obtain a stable aluminum alloy brazing flux paste.

[0086] The flux paste in this example was subjected to stability test, spreadability test, welding test and weld corrosion test.

[0087] in:

[0088] During the stability test, 15 mL of solder paste was centrifuged at 3000 rpm for 7 × 24 hours. After the centrifugation, the solder paste was observed for signs of solidification or sedimentation.

[0089] During the spreadability test, 1 mL of solder flux paste was applied to a 6061 aluminum plate measuring 40 × 40 × 2 mm. 0.1 g of 4047 aluminum-silicon alloy solder wire was placed on the solder paste as a filler metal. The aluminum plate was heated until the solder paste and filler metal melted. After cooling, the spread area of ​​the filler metal was measured.

[0090] During the welding test, 0.1g of 4047 aluminum-silicon alloy wire was used as the filler metal to lap-weld 6061 aluminum plates measuring 50×20×2mm. Flux paste was applied to the weld joint and the surrounding area. The 6061 aluminum plates were heated until the flux and filler metal melted. After cooling, the lap joints were mechanically tested for shear strength and fracture location.

[0091] During the weld corrosion test, 0.1g of 4047 aluminum-silicon alloy welding wire was used as the brazing filler metal to weld lap joints of 6061 aluminum plates measuring 50×20×2mm. Flux paste was applied to the weld joint and the surrounding area. The 6061 aluminum plate was heated until the flux paste and the brazing filler metal melted. After cooling, the lap joint was subjected to a corrosion test and placed in boiling hydrochloric acid (37wt% concentration). The time required for it to be thinned to 50% of its original thickness was recorded. The maximum test time was 12h.

[0092] The above test results are shown in the following table.

[0093] From the above characterization results, it can be seen that the flux paste of the present invention has very excellent stability, and there is no solidification or sedimentation phenomenon after centrifugation. In addition, the solder has good fluidity during the welding process, and can more effectively and well infiltrate the weld. The weld strength after welding is high, even higher than the strength of the original parent material. The fracture position in the shear resistance characterization is located in the parent material. In addition, the flux paste of the present invention can also cover and protect the weld, and performs very well in subsequent corrosion tests.

[0094] Comparative Example 1

[0095] The experimental contents of Example 1 were followed, except that the additive prepared in step 1) of Example 1 was directly mixed with the wet-process brazing flux prepared in step 2) of Example 1 to prepare the soldering flux paste. The same experimental characterization as in Example 1 was performed, and the characterization results are shown in the following table.

[0096] From the comparison of the above characterization results with Example 1, it can be seen that the test spreading area and the shear strength of the weldment are significantly reduced when comparing the fluxing performance of the flux paste prepared by directly mixing the flux and the additive with the flux paste prepared by slowly adding the flux to the additive in the present invention.

[0097] Comparative Example 2

[0098] The experimental contents of Example 1 were followed, except that the order of adding aluminum hydroxide, cesium salt, and hydrofluoric acid in step 2) of Example 1 was changed to first preparing a cesium salt solution based on 1 mol of cesium carbonate and 500 mL of water, adding aluminum hydroxide to the hydrofluoric acid, and then slowly adding the prepared cesium salt solution to prepare a wet-process cesium-based flux. The wet-process flux was used to prepare a soldering flux paste, and the same experimental characterization as in Example 1 was performed. The characterization results are shown in the following table.

[0099] From the comparison of the above characterization results with Example 1, it can be seen that the wet-process brazing flux obtained by the raw material addition sequence of the present invention is more compatible with the additives used in the present invention and has better spreading performance and welding effect.

[0100] Comparative Example 3

[0101] The soldering flux was prepared according to the experimental contents of Example 1, except that commercially available cesium fluoroaluminate was used instead of the wet-process cesium-based flux prepared in step 2) of Example 1. The same experimental characterization as in Example 1 was performed. The characterization results are shown in the following table.

[0102] From the comparison of the above characterization results with Example 1, it can be seen that the wet-process cesium-based flux of the present invention has better compatibility with the organic additives used in the present invention than commercially available cesium fluoroaluminate, is less likely to settle, and has better spreadability and welding effect.

[0103] Comparative Example 4

[0104] The soldering flux paste was prepared according to the experimental contents of Example 1, except that an organic additive aqueous solution containing 30 wt % trimethyl borate and 25 wt % methanol was used instead of the additive in step 1). The same experimental characterization as in Example 1 was performed. The characterization results are shown in the following table.

[0105] Comparison of the above characterization results with those of Example 1 reveals that the use of borate esters and methanol as organic additives does improve the stability of the flux paste, albeit to a limited extent. While the spreadability is superior to that of the flux paste of Example 1, both the weld strength and weld corrosion test show a significant decrease, indicating relatively limited practical effectiveness. This is primarily due to the fact that conventional organic additives often contain excessive organic matter during welding, resulting in poor welding performance and difficulty forming a protective layer on the weld surface, significantly reducing corrosion resistance.

Claims

1. An aluminum alloy soldering flux and its preparation method, characterized in that, The method includes: 1) Mixing two or three components of cetyltrimethylammonium bromide, modified urea, and modified silicate with water to prepare an additive; 2) Mixing the additive prepared in step 1) uniformly with a wet-configuration cesium-based soldering flux, and obtaining a soldering paste after aging treatment.

2. The aluminum alloy brazing flux and its preparation method according to claim 1, characterized in that, In the additive described in step 1): When cetyltrimethylammonium bromide is contained, the concentration of cetyltrimethylammonium bromide is 0.01 - 0.06 mol / L; When modified urea is contained, the concentration of modified urea is 0.08 - 0.2 wt%; When modified silicate is contained, the concentration of modified silicate is 0.05% - 0.4 wt%.

3. A kind of aluminum alloy soldering flux and its preparation method according to claim 1, characterized in that, The wet-configuration cesium-based soldering flux described in step 2) is prepared by the following method: Dispersing soluble cesium salt and aluminum hydroxide in water in a ratio of Al and Cs atomic ratio of 1:(1 - 2) for pre-reaction, and then adding hydrofluoric acid and stirring until the precipitation no longer increases.

4. A kind of aluminum alloy soldering flux and its preparation method according to claim 3, characterized in that, The hydrofluoric acid is in an amount that is 0.05 - 0.20 mol in excess based on the standard amount of metal atoms and fluorine atoms; The standard amount is that the ratio of aluminum atoms to fluorine atoms is 1:(4 - 5).

5. The preparation method of a brazing flux for aluminum alloy brazing according to claim 3, characterized in that, During the preparation process of the wet-configuration cesium-based soldering flux, after adding hydrofluoric acid, stir and react at 65 - 90 °C for 0.5 - 3.0 h.

6. The aluminum alloy brazing flux paste according to claim 1 and its preparation method are characterized in that, During the mixing process of the additive and the wet-configuration cesium-based soldering flux in step 2), the molar amount of the wet-configuration cesium-based soldering flux is calculated based on the molar amount of the contained aluminum element, and the additive and the wet-configuration cesium-based soldering flux are mixed uniformly according to the ratio of adding 70 - 165 mL of the additive per mole of the wet-configuration cesium-based soldering flux.

7. A kind of aluminum alloy soldering flux and its preparation method according to claim 1, characterized in that The operation process of mixing the additive and the wet-configuration cesium-based soldering flux in step 2) is: while continuously stirring the additive, add the wet-configuration cesium-based soldering flux in batches slowly into the additive.

8. A kind of aluminum alloy brazing flux and its preparation method according to claim 7, characterized in that, The wet-configuration cesium-based soldering flux is added into the additive in batches at a uniform speed slowly within 5 - 100 min.

9. A kind of aluminum alloy brazing flux and its preparation method according to claim 7, characterized in that, After mixing in step 2), then stir rapidly at a stirring speed of 1000 - 2000 rpm for 20 - 70 min; after the stirring ends, perform aging treatment at 25 - 45 °C until it presents a stable paste state.

10. An aluminum alloy soldering paste for soldering prepared by any method according to claims 1 to 9.

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