An aluminum alloy brazing flux and a method for preparing the same

Abstract

The present application belongs to the technical field of aluminum alloy brazing material, and particularly relates to an aluminum alloy brazing flux and a preparation method thereof, the method comprising: 1) mixing and preparing two or three components of cetyltrimethylammonium bromide, modified urea and modified silicate with water to obtain an additive; 2) mixing the additive prepared in step 1) with a wet configuration cesium series brazing agent, and performing aging treatment to obtain the flux. The flux can adhere to the workpiece during the welding process, solving the defect that the powdery brazing agent is not convenient to use on complex workpieces or inclined surfaces. Meanwhile, the flux has good stability and good fluxing effect, and the weld formed after fluxing has high strength.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum alloy brazing materials, and particularly relates to an aluminum alloy brazing flux and a preparation method thereof. BACKGROUND

[0002] Aluminum alloy workpieces are widely used in the fields of aerospace, automobile manufacturing, air conditioner radiators, etc. Most of the aluminum alloy workpieces are connected by welding, and brazing is the main method for connecting the aluminum alloy workpieces at present. In recent years, the workpieces for welding the aluminum alloy workpieces gradually develop towards miniaturization and automation, and especially for some workpieces with complex structures and irregular joint shapes, the traditional powdery flux cannot meet the requirements of modern aluminum alloy workpiece brazing. However, the paste flux not only can adhere to the complex and irregular workpieces, but also has the advantages of convenience, flexibility and accurate distribution, and plays a high-quality fluxing role in the welding of aluminum alloy workpieces.

[0003] The common flux paste is a paste fluxing material prepared by mixing rosin, isopropyl alcohol, organic acid and special chemicals, and its main functions are to remove the oxides on the surface of the base material, reduce the surface tension and improve the wettability of the filler metal. The flux paste is mainly suitable for soft soldering of electronic components and electronic circuit boards, but is not suitable for brazing of aluminum and aluminum alloy at high temperatures.

[0004] A large number of literatures have reported the research on aluminum brazing paste. The composition of the aluminum brazing paste mainly includes powdery filler metal, flux, thixotropic agent, thickening agent, organic solvent, etc. These aluminum brazing pastes can basically meet the welding requirements of related aluminum alloy workpieces. However, most of the powdery filler metals still need special processing technology during the preparation of the aluminum brazing paste. Compared with the traditional powdery, filamentous, foiled and sheet-shaped filler metals, this greatly increases the cost and preparation difficulty of the aluminum brazing paste. At the same time, in order to ensure the stability of the aluminum brazing paste, a large amount of organic matter is used, accounting for about 15%-40% of the total amount of the aluminum brazing paste. In the welding operations such as flame brazing and induction brazing, too much organic matter will be carbonized and blackened, resulting in defects in the weld, and also affecting the appearance after welding.

[0005] The common fluorine aluminum cesium product in the market is usually in powder form, although it can be mixed with water or alcohol in proportion to make paste, but its stability is poor and easy to separate. In order to improve the stability of the paste, the addition of common thickening agent may cause excessive addition of organic matter, and then the carbonization of organic matter after brazing produces black weld defects. For example, the soldering flux containing the fluorine aluminum cesium product disclosed in CN201510776244.3 has an organic matter content of more than 50%. Therefore, it is very important to reduce the addition amount of organic matter while ensuring the stability of the soldering paste. Related documents show that in some aqueous solution systems, the framework structure stable system is easily formed by the strong attraction of the framework edge and the end of the sheet, rod or needle-shaped crystal morphology. By controlling the micro-morphology of the cesium solder crystal and using a small amount of additives for surface modification, a brazing flux soldering paste with good stability, simple preparation and excellent soldering effect can be developed, which has great significance for promoting high-quality brazing of aluminum and aluminum alloy workpieces. SUMMARY

[0006] In order to overcome the problems existing in the field of aluminum alloy brazing at present, that is, the powder brazing agent cannot be used for soldering of complex workpieces, and the existing liquid or paste type cesium fluoride aluminum soldering agent has the challenges of poor stability, excessive organic matter content and low weld strength, the present application provides an aluminum alloy brazing soldering paste and a preparation method thereof.

[0007] The purpose of the present application is:

[0008] I. It can be used for removing the surface oxide film during aluminum alloy brazing, promoting the wetting and spreading of the filler metal on the base material, and thus realizing reliable connection of aluminum and aluminum alloy;

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

[0010] III. Wide application range and simple operation;

[0011] IV. Easy to clean or no residue after brazing.

[0012] In order to achieve the above purpose, the following technical solutions are adopted in the present application.

[0013] A preparation method of an aluminum alloy brazing soldering paste,

[0014] The method comprises:

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

[0016] 2) The additive prepared in step 1) is mixed with a wet configuration cesium soldering agent, and a soldering paste is obtained after aging treatment.

[0017] As a preferred,

[0018] The additive in step 1) is:

[0019] When the additive contains cetyl trimethyl ammonium bromide, the concentration of cetyl trimethyl ammonium bromide is 0.01-0.06 mol / L;

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

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

[0022] Preferably,

[0023] The wet-type cesium flux in step 2) is prepared by the following method:

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

[0025] Preferably,

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

[0027] The standard amount is a ratio of 1: (4-5) of aluminum atoms and fluorine atoms.

[0028] Preferably,

[0029] In the preparation process of the wet-type cesium flux, the hydrofluoric acid is stirred at 65-90°C for 0.5-3.0h after being added.

[0030] Preferably,

[0031] In the mixing process of the additive and the wet-type cesium flux in step 2), the molar amount of the wet-type cesium flux is calculated based on the molar amount of aluminum elements contained, and the additive is mixed with the wet-type cesium flux uniformly in a ratio of 70-165 mL of additive per mole of wet-type cesium flux.

[0032] Preferably,

[0033] The operation process of mixing the additive and the wet-type cesium flux in step 2) is that the wet-type cesium flux is slowly added to the additive in batches under continuous stirring of the additive. For example, the wet-type cesium flux is slowly added in batches at a uniform speed within 5-100 min, and the addition time is preferably 10-30 min.

[0034] Preferably,

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

[0036] An aluminum alloy brazing flux paste.

[0037] One of the core points of the present application is to introduce special additives to thicken and stabilize the cesium fluoroaluminate brazing agent composition. In traditional cesium fluoroaluminate flux paste, the organic additives / additives are usually triethanolamine, glycerol, methyl cellulose, borate ester, and small molecule alcohol. However, the present application uniquely uses cetyltrimethylammonium bromide, modified urea, and modified silicate as organic additives, avoiding the use of traditional components to improve the stability of the cesium fluoroaluminate flux paste.

[0038] In common cesium fluoroaluminate brazing flux paste, the purpose of organic additives is mainly to thicken and improve the stability of the cesium fluoroaluminate brazing agent, so a large amount of organic additives are needed to "wrap" the brazing agent (i.e. cesium fluoroaluminate brazing agent), achieve the dispersion and protection of the brazing agent, to avoid the loss and failure of the effective components.

[0039] In addition, the unique organic additives used in the present application.

[0040] In the present application, the unique feature of the organic additive is that after its use, it interacts with the needle-like cesium fluoroaluminate brazing agent, resulting in a higher viscosity coefficient of the system, which can achieve effective thickening with a smaller amount. Unlike traditional organic additives, the additive of the present application contacts the brazing agent through intermolecular forces to protect it, improve the stability of the brazing agent, and change the thixotropic effect. Therefore, in actual use, the brazing agent paste of the present application is convenient and flexible to use, can be accurately laid out, and after brazing, the surface of the welded part has less residue and is easy to clean.

[0041] The second core of the present application is to use the special wet configuration cesium series flux prepared by the present application. The common cesium fluoroaluminate flux composition is Cs2AlF5 or CsAlF4, and the preparation process is to react fluoroaluminate with cesium salt, or to react hydrogen fluoride with aluminum hydroxide (and similar aluminum compounds) and then react with cesium salt. The composition of the prepared cesium fluoroaluminate flux is single. In contrast, the present application first mixes cesium salt and aluminum hydroxide, pre-reacts, and then slowly adds hydrogen fluoride for secondary reaction to prepare the product. For the present application, the target product is mainly composed of CsAlF4 and / or CsAlF4·2H2O and / or Cs2AlF5 and / or Cs2AlF5·H2O. Therefore, the present application first strictly controls the relative amount of cesium and aluminum elements, and the relative amount of cesium and aluminum atoms and fluorine atoms, to effectively control the product.

[0042] For the present application, there are two important processes in the above process. First, mix cesium salt and aluminum hydroxide to react part of the aluminum hydroxide, and mix the reaction product with the remaining raw materials. This process is crucial to control the uniformity of the product and prevent the generation of by-products, ensuring the smooth progress of the subsequent preparation process. Secondly, slowly add a slight excess of hydrogen fluoride for subsequent reaction. In the common process, the reaction of aluminum hydroxide and hydrogen fluoride forms fluoroaluminate ions, which then react with cesium salt to form the product. However, in this process, the reaction progress control is difficult, and the product is prone to form indefinite crystal form. The present application first pre-reacts cesium salt and aluminum hydroxide, and then slowly adds a slight excess of hydrogen fluoride, which effectively controls the reaction progress. This process can stably prepare cesium fluoroaluminate crystals with needle columnar micro-morphology, and the cesium fluoroaluminate flux can further promote the stability of the paste in the aqueous solution system under the action of the additive.

[0043] Through the control of the above preparation process, the cesium fluoroaluminate flux prepared by the present application has a uniform and stable crystal form, stable quality, and is not prone to agglomeration. After welding, it covers the surface of the weld, protecting the weld.

[0044] On the other hand, when the flux and the additive of the present application are mixed, the flux prepared in proportion should be slowly added to the additive, rather than directly mixed. This is because direct mixing will cause the flux to agglomerate, which will cause the soldering paste to fail quickly or significantly reduce its effectiveness. Common organic additives will actually produce endothermic phenomena during soldering, and the agglomeration of the flux will cause very serious temperature non-uniformity during the soldering process. The agglomeration of the flux will cause uneven distribution of the flux, poor film removal effect on the surface of the base material during the soldering process, and cannot effectively realize the soldering process. This is a defect of the existing cesium fluoroaluminate soldering paste.

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

[0046] The soldering flux paste of the present application does not contain solder and has a small amount of organic matter, and needs to be matched with powder or wire solder for welding; it can be used for furnace brazing, induction brazing, flame brazing and other brazing methods. Specifically, the application method is as follows: the soldering flux paste is applied to the welding position, and is matched with powder, sheet, wire and other solder, and the welding position is heated by a heat source until the soldering flux paste and the solder melt, and the welding is completed; or the soldering flux paste is dipped with wire or sheet solder, and the brazing is completed under the heating of the heat source.

[0047] The present application has the following advantages:

[0048] The soldering flux paste of the present application can be adhered to the workpiece during the welding process, solving the defect that the powder soldering agent is not convenient to use on complex workpieces or inclined surfaces. At the same time, the soldering flux paste of the present application has good soldering effect, the formed weld has high strength, and the soldering flux paste can cover the surface of the weld after cooling, achieving protection of the weld. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 TG-DSC characterization results of the wet configuration cesium series soldering agent prepared in Example 1.

[0050] Figure 2 The structure diagram of the lap assembly for lap joint welding in the embodiment of the present application. DETAILED DESCRIPTION

[0051] The present application will be further described and illustrated in detail in the following combined with specific embodiments and the accompanying drawings of the specification. Those skilled in the art will be able to implement the present application based on these descriptions. In addition, the embodiments of the present application involved in the following description are generally only a part of the embodiments of the present application, not all the embodiments. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments in the present application without creative labor should belong to the scope of protection of the present application.

[0052] Unless otherwise specified, the raw materials used in the embodiments of the present application are commercially available or can be obtained by those skilled in the art; unless otherwise specified, the methods used in the embodiments of the present application are the methods mastered by those skilled in the art.

[0053] Example 1

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

[0055] 1) An additive is prepared with water as a solvent, and 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) Wet configuration cesium series flux preparation: according to the proportion of Al, Cs and F atom ratio is 1:1.5:4.5, aluminum hydroxide [Al(OH)3], cesium carbonate (Cs2CO3) and hydrofluoric acid (HF) are weighed respectively, the aluminum hydroxide and cesium carbonate are mixed uniformly and then dispersed in deionized water, the water is 500 mL based on 1 mol of cesium carbonate, the solution is continuously stirred at 120 rpm for 10 min, part of the aluminum hydroxide is reacted first, and the reaction product is mixed with the remaining raw materials. Then the solution is continuously stirred at 300 rpm and the weighed hydrofluoric acid is slowly and uniformly added within 10 min, the reaction temperature is controlled at 80℃, after the addition of the weighed hydrofluoric acid is completed, 0.05 mol of hydrofluoric acid is added while stirring, and the solution is stirred for 3 h, then the solution is evaporated to dryness, the product is washed with deionized water under ultrasonic, and then dried at 60℃ to obtain the wet configuration cesium series flux;

[0057] 3) The additive prepared in step 1) is mixed with the wet configuration cesium series flux prepared in step 2) according to the proportion of 100 mL of additive per mole of wet configuration cesium series flux, the wet configuration flux is slowly and uniformly added to the additive within 20 min, the molar amount of the wet configuration cesium series flux is calculated based on the molar amount of aluminum hydroxide used in step 2), and the molar amount of the wet configuration cesium series flux is the molar amount of the product, then the mixture is stirred at 1500 rpm for 60 min, and then aged at 40℃ to obtain the stable aluminum alloy brazing flux paste.

[0058] The wet configuration cesium series flux obtained above is characterized by TG-DSC, and the characterization results are shown in Figure 1 Figure 1 The upper line is the left TG curve, and the lower line is the right DSC curve. Figure 1 From the above, it can be seen that when the wet configuration cesium series flux prepared by the present application is heated, there is a small mass loss at about 170℃, only about 2.1014%. At the same time, the DSC curve shows that there is an endothermic peak in this temperature range, so it can be determined that the mass loss and the appearance of the endothermic peak are caused by the process of destroying the chemical bond between the water and the flux by the endothermic destruction of the crystal water in the flux, and the free water is volatilized. In addition, the wet configuration cesium series flux prepared by the present application forms obvious endothermic peaks at 445.5℃ and 476.75℃, the temperature range of the melting of the flux is large, which can better adapt to the operation of brazing, and there is no weight loss in the corresponding temperature range. It can be said that the wet configuration cesium series flux prepared by the present application has little loss during brazing, and has good brazing performance and application prospect.

[0059] ​On this basis, the soldering paste of the example is also subjected to stability test, spreading test, welding test and weld corrosion test.

[0060] wherein:

[0061] During the stability test, 15 mL of the soldering paste is placed in a centrifuge for 3000 rpm centrifugal treatment, the centrifugal treatment lasts for 7 x 24 h, and after the centrifugal treatment, it is observed whether the soldering paste appears solidification or sedimentation or the like;

[0062] During the spreading test, 1 mL of the soldering paste is dropped on a 6061 aluminum plate with a size of 40 x 40 x 2 mm (only dropped on the 40 x 40 mm surface, and the same applies below), 0.1 g of 4047 aluminum-silicon alloy wire is placed on the soldering paste as filler metal, the aluminum plate is heated to melt the soldering paste and the filler metal, and after cooling, the spreading area of the filler metal is measured;

[0063] During the welding test, 0.1 g of 4047 aluminum-silicon alloy wire is used as filler metal to weld two 6061 aluminum plates with a size of 50 x 20 x 2 mm, the soldering paste is applied to the welding joint and the surrounding area, the 6061 aluminum plate is heated to melt the soldering paste and the filler metal, and after cooling, the mechanical properties of the lap joint are tested to test the shear strength and the fracture position;

[0064] During the welding test, 0.1 g of 4047 aluminum-silicon alloy wire is used as filler metal to weld two 6061 aluminum plates with a size of 50 x 20 x 2 mm, the soldering paste is applied to the welding joint and the surrounding area, the 6061 aluminum plate is heated to melt the soldering paste and the filler metal, and after cooling, the mechanical properties of the lap joint are tested to test the shear strength and the fracture position;

[0065] During the welding test and the weld corrosion test, the 50 x 20 mm surfaces of the two 6061 aluminum plates are arranged in parallel and close to each other, and a gap is left between them, the lap length is 4 mm (i.e. the length of the two aluminum plates in alignment is 4 mm), the filler metal is arranged at the edge of the gap between the two aluminum plates to form a welding joint to be welded, the soldering paste is applied to the welding joint and the surrounding area (i.e. the edge of the gap between the two 6061 aluminum plates and the surrounding area of the filler metal), and the structure diagram of the lap joint welding assembly is shown in Figure 2 (i.e. front view), the same applies below. The 6061 aluminum plate is heated to melt the soldering paste and the filler metal, and under the action of the soldering paste, the filler metal can enter the gap between the two plates, so as to have better bonding strength and gap filling property.

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

[0067]

[0068] From the above characterization results, it can be seen that the soldering paste of the application has very excellent stability, and there is no solidification or sedimentation phenomenon after centrifugation. The solder has good fluidity during welding, can more effectively and well wet the weld, and the weld strength after welding is high, even higher than the original base material strength. The fracture position in the shear resistance characterization is located in the base material. In addition, the soldering paste of the application can also cover and protect the weld after welding, and performs very well in the subsequent corrosion test.

[0069] Example 2

[0070] An aluminum alloy soldering paste is prepared by the following method:

[0071] 1) An additive is prepared with water as a solvent. In this example, the concentration of modified urea BYK-420 in the prepared additive is 0.1wt%, and the concentration of modified silicate Laponite-RD is 0.1wt%;

[0072] 2) Wet configuration cesium series solder preparation: aluminum hydroxide [Al(OH)3], cesium carbonate (Cs2CO3) and hydrofluoric acid (HF) are weighed according to the atomic ratio of Al, Cs and F of 1:1.4:4.4, respectively. The aluminum hydroxide and cesium carbonate are mixed uniformly and then dispersed in deionized water. Taking the amount of cesium carbonate as 1 mol, the amount of water is 500 mL. Stir at a speed of 120 rpm for 15 min. First, part of the aluminum hydroxide reacts. The reaction product is mixed with the remaining raw materials. Then continuously stir the solution at a speed of 300 rpm and slowly add the weighed hydrofluoric acid at a uniform speed within 10 min. Control the reaction temperature at 80℃. After the addition of the weighed hydrofluoric acid is completed, 0.05 mol of hydrofluoric acid is added while stirring. Keep stirring for 3h. After the precipitation no longer increases, the solution is evaporated to dryness. The precipitate is washed with ultrasonic deionized water and then dried at 60℃. The wet configuration cesium series solder is obtained.

[0073] 3) The additive prepared in step 1) and the wet configuration cesium series solder prepared in step 2) are mixed uniformly according to the proportion of 100 mL of additive per mole of wet configuration cesium series solder. The wet configuration cesium series solder is slowly and uniformly added to the additive within 20 min. The molar amount of the wet configuration cesium series solder is calculated based on the molar amount of aluminum hydroxide used in step 2). The molar amount of the wet configuration cesium series solder is the molar amount of the product. After mixing, stir at a speed of 1500 rpm for 60 min. Then, after aging treatment at 40℃, the stable aluminum alloy soldering paste is obtained.

[0074] The stability test, spreading test, welding test and weld corrosion test are carried out on the soldering paste of this example.

[0075] wherein:

[0076] During the stability test, 15 mL of the flux was placed in a centrifuge for 3000 rpm centrifugal treatment, and the centrifugal treatment lasted for 7x24 h. After the centrifugal treatment, it was observed whether the flux appeared to be solidified or settled, etc.

[0077] During the spreadability test, 1 mL of the flux was dropped on a 6061 aluminum plate with a size of 40x40x2 mm. 0.1 g of 4047 aluminum-silicon alloy welding wire was placed on the flux as a filler metal. The aluminum plate was heated until the flux and the filler metal were melted. After cooling, the spread area of the filler metal was measured.

[0078] During the welding test, 0.1 g of 4047 aluminum-silicon alloy welding wire was used as a filler metal to weld a 6061 aluminum plate with a size of 50x20x2 mm. The flux was coated on the welding joint and the surrounding area. The aluminum plate was heated until the flux and the filler metal were melted. After cooling, the mechanical properties of the lap joint were tested, and the shear strength and the fracture position were tested.

[0079] During the weld corrosion test, 0.1 g of 4047 aluminum-silicon alloy welding wire was used as a filler metal to weld a 6061 aluminum plate with a size of 50x20x2 mm. The flux was coated on the welding joint and the surrounding area. The aluminum plate was heated until the flux and the filler metal were melted. After cooling, the lap joint was subjected to corrosion test, and was placed in boiling hydrochloric acid (37wt% concentration). The time required for the thickness to be reduced to 50% of the original thickness was recorded, and the maximum test duration was 12 h.

[0080] The test results are shown in the following table.

[0081]

[0082] From the above characterization results, it can be seen that the flux of the present application has very excellent stability, and there is no solidification or settlement phenomenon after centrifugation. In addition, the flux of the present application has good flowability of the filler metal during welding, can more effectively and well wet the weld, the weld strength after welding is high, even higher than the original base material strength, and the fracture position in the shear test is located in the base material. In addition, the flux of the present application can also protect the weld after welding, and performs very well in the subsequent corrosion test.

[0083] Example 3

[0084] An aluminum alloy brazing flux is prepared by the following method:

[0085] 1) The additive is prepared with water as solvent, the concentration of cetyltrimethylammonium bromide in the prepared additive 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%

[0086] 2) Preparation of wet-type cesium-based flux: aluminum hydroxide [Al(OH)3], cesium carbonate (Cs2CO3) and hydrofluoric acid (HF) are weighed according to the atomic ratio of Al, Cs and F being 1:1.3:4.3, the aluminum hydroxide and cesium carbonate are mixed uniformly and then dispersed in deionized water, the amount of water is 500 mL based on 1 mol of cesium carbonate, the solution is continuously stirred at a speed of 120 rpm for 10 min, part of the aluminum hydroxide is allowed to react first, the reaction product is mixed with the remaining raw materials, then the solution is continuously stirred at a speed of 300 rpm, and the weighed hydrofluoric acid is slowly and uniformly added within 10 min, the reaction temperature is controlled at 85°C, after the addition of the weighed hydrofluoric acid is completed, 0.07 mol of hydrofluoric acid is added while stirring, and the solution is stirred for 2 h, then the solution is evaporated to dryness, the precipitate is washed with ultrasonic deionized water and dried at 60°C to obtain the wet-type cesium-based flux;

[0087] 3) The additive prepared in step 1) is mixed with the wet-type cesium-based flux prepared in step 2) according to the proportion of 100 mL of additive per mole of wet-type cesium-based flux, the wet-type cesium-based flux is slowly and uniformly added to the additive within 20 min, the molar amount of the wet-type cesium-based flux is calculated based on the molar amount of aluminum hydroxide used in step 2), the molar amount of the wet-type cesium-based flux is the molar amount of the product, the mixture is stirred at a speed of 1600 rpm for 40 min, and then the stable aluminum alloy brazing flux paste is obtained after aging treatment at 40°C.

[0088] The stability test, spreadability test, welding test and weld corrosion test are carried out on the paste.

[0089] Wherein:

[0090] During the stability test, 15 mL of the paste is placed in a centrifuge for 3000 rpm centrifugation for 7×24 h, and then the paste is observed for solidification or sedimentation;

[0091] During the spreadability test, 1 mL of the paste is dropped on a 40×40×2 mm 6061 aluminum plate, 0.1 g of 4047 aluminum-silicon alloy wire is placed on the paste as filler metal, the aluminum plate is heated until the paste and the filler metal melt, and then the spread area of the filler metal is measured after cooling;

[0092] During the welding test, 0.1 g of 4047 aluminum-silicon alloy welding wire is taken as the filler metal to weld the 6061 aluminum plate with a size of 50*20*2 mm into a lap joint, the flux cored wire is coated on the welding joint and the surrounding, the 6061 aluminum plate is heated until the flux cored wire and the filler metal are melted, and after cooling, the lap joint is tested for mechanical properties to test its shear strength and fracture position;

[0093] During the welding test, 0.1 g of 4047 aluminum-silicon alloy welding wire is taken as the filler metal to weld the 6061 aluminum plate with a size of 50*20*2 mm into a lap joint, the flux cored wire is coated on the welding joint and the surrounding, the 6061 aluminum plate is heated until the flux cored wire and the filler metal are melted, and after cooling, the lap joint is tested for mechanical properties to test its shear strength and fracture position;

[0094] The above test results are shown in the following table.

[0095]

[0096] From the above characterization results, it can be seen that the flux cored wire of the application has very excellent stability, and there is no solidification or sedimentation phenomenon after centrifugation, and the filler metal has good fluidity during welding, which can more effectively and well wet the weld, the weld strength after welding is high, even higher than the original base material strength, the fracture position in the shear test is located in the base material, in addition, the flux cored wire of the application can also cover and protect the weld, and performs very well in the subsequent corrosion test.

[0097] Comparative Example 1

[0098] According to the experimental content of Example 1, the difference is only that the additive prepared in step 1) of Example 1 is directly mixed with the wet type brazing agent prepared in step 2) of Example 1 to prepare the flux cored wire, and the same test characterization as Example 1 is carried out, and the characterization results are shown in the following table.

[0099]

[0100] From the above characterization results compared with Example 1, it can be seen that the test spreading area and the shear strength of the welded part of the flux cored wire prepared by directly mixing the brazing agent and the additive are greatly reduced compared with the flux cored wire prepared by slowly adding the brazing agent to the additive in the application.

[0101] Comparative Example 2

[0102] According to the experimental content of Example 1, the difference is only that the addition sequence of aluminum hydroxide, cesium salt and hydrofluoric acid in step 2) of Example 1 is changed to first prepare a cesium salt solution with a water dosage of 500 mL based on a cesium carbonate dosage of 1 mol, add aluminum hydroxide to hydrofluoric acid, and then slowly add the prepared cesium salt solution to prepare a wet-type cesium-based flux. The wet-type flux is used to prepare a soldering paste, and the same test characterization as Example 1 is performed, and the characterization results are shown in the following table.

[0103]

[0104] From the above characterization results compared with Example 1, it can be seen that the wet-type cesium-based flux obtained by the raw material addition sequence is more suitable for the organic additive used in the present application, and has better spreading performance and welding effect.

[0105] Comparative Example 3

[0106] According to the experimental content of Example 1, the difference is only that the commercially available cesium fluoroaluminate is used instead of the wet-type cesium-based flux prepared in step 2) of Example 1 to prepare a soldering paste, and the same test characterization as Example 1 is performed, and the characterization results are shown in the following table.

[0107]

[0108] From the above characterization results compared with Example 1, it can be seen that the wet-type cesium-based flux of the present application is more suitable for the organic additive used in the present application than the commercially available cesium fluoroaluminate, and is not easy to settle, and has better spreading performance and welding effect.

[0109] Comparative Example 4

[0110] According to the experimental content of Example 1, the difference is only that the organic additive aqueous solution containing 30 wt% trimethyl borate and 25 wt% methanol is used instead of the additive of step 1) to prepare a soldering paste, and the same test characterization as Example 1 is performed, and the characterization results are shown in the following table.

[0111]

[0112] From the above characterization results compared with Example 1, it can be seen that the use of borate ester and methanol as organic additives actually helps the stability of the soldering paste, but is still limited. Although the spreading performance is better than that of the soldering paste of Example 1, the welding strength and weld corrosion test are significantly decreased, indicating that the actual use effect is relatively limited. This is mainly because the existing conventional organic additives generally have too much organic matter content during welding, resulting in poor welding effect, and it is difficult to form a protective layer on the surface of the weld, and the corrosion resistance is significantly decreased.

Claims

1. A method for preparing an aluminum alloy brazing flux, characterized in that, The method includes: 1) Prepare an additive by mixing hexadecyltrimethylammonium bromide, modified urea, and modified silicate with water; 2) Mix the additives obtained in step 1) with wet-process cesium-based flux evenly, and then age them to obtain solder paste. In step 1), the additive contains: The concentration of hexadecyltrimethylammonium bromide is 0.01–0.06 mol / L; The modified urea concentration is 0.08–0.2 wt%; The concentration of modified silicate is 0.05%-0.4 wt%. Step 2) The wet-process cesium-based flux is prepared by the following method: Soluble cesium salt and aluminum hydroxide were dispersed in water for pre-reaction according to an Al to Cs atomic ratio of 1:(1~2), and then hydrofluoric acid was added and stirred until the precipitate no longer increased. The process of mixing the additive with the wet-process cesium-based flux in step 2) is as follows: while continuously stirring the additive, the wet-process cesium-based flux is slowly added to the additive in batches. After mixing as described in step 2), stir rapidly at a stirring speed of 1000-2000 rpm for 20-70 minutes; after stirring, age at 25-45 ℃ until it becomes a stable paste.

2. The method for preparing an aluminum alloy brazing flux according to claim 1, characterized in that, The hydrofluoric acid is added in excess of 0.05–0.20 mol of metal atoms and fluorine atoms, based on the standard dosage. The standard dosage is defined as an aluminum atom to fluorine atom ratio of 1:(4-5).

3. The method for preparing an aluminum alloy brazing flux according to claim 1, characterized in that, In the preparation of the wet-process cesium-based flux, hydrofluoric acid is added and the mixture is stirred and reacted at 65–90 °C for 0.5–3.0 h.

4. The method for preparing an aluminum alloy brazing flux according to claim 1, characterized in that, In 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 aluminum element contained therein. The additive is mixed evenly with the wet-process cesium-based flux at a ratio of 70 to 165 mL of additive per mole of wet-process cesium-based flux.

5. The method for preparing an aluminum alloy brazing flux according to claim 1, characterized in that, The wet-process cesium-based flux is added to the additive in batches at a uniform and slow rate over a period of 5-100 minutes.

6. An aluminum alloy brazing flux prepared by any one of claims 1 to 5.

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