A method for preparing solder stop used in aircraft processing

Abstract

The present invention provides a method for preparing a solder stopper used in aircraft processing, which belongs to the field of welding technology. The solder stopper ingredients include hexagonal boron nitride, Y-PSZ, lanthanum oxide, β-eucryptite powder, a rheology modifier, etc., which are applied in two layers, and the bottom layer additionally contains multilayer graphene. Y-PSZ is a product obtained by co-precipitating ZrOCl2·8H2O and Y(NO3)3·6H2O and sintering them at 600℃~650℃ and 1000℃~1050℃, respectively. The rheology modifier is a product obtained by treating α-cellulose with alkali to remove hemicellulose, TEMPO catalytic oxidation to convert the primary hydroxyl groups of cellulose into carboxyl groups, and surface modification using aluminum dimyristate and a silane coupling agent. The solder stopper can well control the release of volatilization and reaction, resist high-temperature flow, maintain good state and solder stop properties, is not prone to thermal stress cracking or peeling, is easy to penetrate by alkali immersion and mechanical stripping, and has little damage to the substrate.

Description

Technical Field

[0001] The invention belongs to the technical field of welding, and in particular relates to a method for preparing a solder stopper used in an aircraft processing process. Background Art

[0002] In the aviation manufacturing sector, with the widespread adoption of lightweight, high-strength materials like titanium alloys and high-temperature alloys, superplastic forming / diffusion bonding (SPF / DB) has become a core technology for constructing complex, lightweight components. In this process, solder stoppers, as key auxiliary materials, have a formula and performance that directly determine the component's forming accuracy and service reliability.

[0003] From a formulation perspective, early solder stoppers were mostly based on oxide ceramic powders, combined with binders and organic solvents. This traditional formulation has significant limitations: oxide ceramic powders are prone to micro-diffusion reactions with the metal matrix at high temperatures, leading to localized connection failure in the solder stop area; binders are mostly organic polymer materials, which decompose at high temperatures to produce gases, which can easily form pore defects on the component surface; and the evaporation rate of organic solvents is difficult to control, affecting the uniformity and stability of the coating. In recent years, researchers have begun to explore composite system formulations, improving the high-temperature chemical stability of solder stoppers by adding rare earth oxides, graphite, molybdenum disulfide, etc., and introducing nano-scale additives to improve powder dispersion and coating density.

[0004] The core performance requirements of solder stoppers are closely related to the rigorous processes of aviation manufacturing. First, high-temperature barrier performance is its key indicator. It is necessary to form a dense physical barrier within the superplastic forming temperature range of 800-1000°C to completely block the atomic diffusion at the metal interface, while maintaining stable chemical inertness to avoid reactions with the substrate. Secondly, coating and forming performance directly affect the accuracy of components. The solder stopper is required to have suitable rheological properties, which can not only accurately control the shape during coating, but also maintain the integrity of the coating at high temperatures to prevent peeling or cracking caused by thermal stress. In addition, removal performance is equally important. Traditional solder stoppers are firmly bonded to the metal matrix, and mechanical removal can easily damage the surface of the component, while chemical corrosion methods may introduce impurities. Therefore, the development of solder stoppers that can be decomposed at high temperatures or easily soluble in specific solvents has become a research hotspot.

[0005] At present, the following problems still need to be overcome in order to meet the requirements of solder paste for higher use:

[0006] (1) Difficulties in optimizing formula ingredients: Some traditional solder stoppers contain ingredients that are volatile or react with metals, forming defects such as pores on the surface of components; some ingredients react chemically with the metal matrix at high temperatures, affecting the solder stop effect and component performance.

[0007] (2) Severe challenges in high-temperature service performance: Aviation components are welded in high-temperature environments, and solder stoppers need to maintain good performance at high temperatures. However, existing solder stoppers may soften, flow, or even decompose at high temperatures, resulting in the failure of the solder stop effect. At high temperatures, the thermal expansion coefficients of the solder stopper and the metal substrate differ greatly, which can easily generate thermal stress, causing the coating to crack and peel, affecting the connection strength and overall performance of the component. In the superplastic forming / diffusion bonding process, the solder stopper's insufficient barrier properties and chemical stability at high temperatures can lead to unnecessary connections in non-connected areas, reducing the accuracy and reliability of the component.

[0008] (3) Technical difficulties in subsequent removal processes: After processing, the solder stop needs to be removed from the component surface. Traditional removal methods have many disadvantages. Mechanical grinding can easily cause scratches on the component surface, damaging the surface quality of the component and reducing fatigue life. Although sandblasting can remove the solder stop, it may damage the substrate and the dust generated pollutes the environment. Chemical corrosion uses corrosive chemical reagents such as strong acids and strong alkalis, which not only easily introduce impurities and affect component performance, but also pose environmental risks and high costs for wastewater and exhaust gas treatment.

[0009] At present, the solder stoppers used in aircraft processing mostly rely on imports. Therefore, it is urgent to develop independently developed solder stoppers that are highly efficient in resisting solder and can be removed without damage. Summary of the Invention

[0010] Solder stoppers used in aircraft processing still face problems such as volatilization or reaction of components, softening or flowing at high temperatures, thermal stress cracking or flaking, and damage to the substrate during removal. The present invention provides a method for preparing a solder stopper for use in aircraft processing. The method uses hexagonal boron nitride, Y-PSZ, lanthanum oxide, β-eucryptite powder, and other raw materials, utilizes yttrium oxide-doped stabilized zirconia, and adds a specially formulated rheology modifier. The resulting solder stopper is characterized by well-controlled release of volatilization and reaction, resistance to high-temperature flowing, maintaining good condition and solder-stopping properties, and being less susceptible to thermal stress cracking or flaking. Furthermore, the method controls the micropores of component reaction, making it easy for alkali immersion penetration and mechanical stripping. The specific technical solution is as follows:

[0011] A method for preparing a solder stopper used in an aircraft processing process comprises the following steps:

[0012] S1: Compound 8 to 12 parts of hexagonal boron nitride, 8 to 12 parts of Y-PSZ, 3 to 5 parts of lanthanum oxide, and 8 to 10 parts of β-eucryptite powder by mass, and mix them evenly to obtain a pretreated powder;

[0013] S2: 1.5 to 2 parts of dispersant are added to a solvent by mass and ultrasonically dispersed, followed by adding 0.3 to 0.5 parts of multilayer graphene for ultrasonic dispersion, followed by sequentially adding 65 wt% to 70 wt% of the total amount of pretreated powder and 1 to 2 parts of rheology modifier, homogenized by a high-speed disperser, and finally adding 8 to 10 parts of a binder dropwise, stirring and mixing, adjusting the viscosity to 4500 cP to 5000 cP with a solvent, vacuum defoaming, and filtering to obtain solder stop component A;

[0014] S3: Add 1.5 to 2 parts of dispersant by mass to the solvent and ultrasonically disperse. Then, add the remaining pre-treated powder and 1 to 2 parts of rheology modifier in sequence. Homogenize in a high-speed disperser for 30 to 40 minutes. Finally, add 8 to 10 parts of binder dropwise, stir and mix. Adjust the viscosity to 7500 to 8000 cP with solvent. Defoam under vacuum and filter through a filter to obtain solder stop component B.

[0015] S4: Apply solder stop component A to a designated area of ​​the substrate plate with a wet film thickness of 25±5μm, and dry with hot air at 80℃~85℃ for 10min~15min to obtain a base layer; then apply solder stop component B on the base layer with a wet film thickness of 25±5μm, and dry with hot air at 80℃~85℃ for 30min~40min to obtain a solder stop coating.

[0016] In the above preparation method, the purity of the hexagonal boron nitride is ≥99wt%, the free boron oxide is ≤0.5wt%, and the particle size D50 is between 1μm and 3μm; the particle size D50 of the lanthanum oxide is below 3μm; and the particle size D50 of the β-eucryptite powder is below 3μm.

[0017] In the above preparation method, the Y-PSZ is yttria partially stabilized zirconia, and the preparation method comprises the following steps: preparing a mixed solution at 60±2°C according to the mass ratio of deionized water: ZrOCl2·8H2O: Y(NO3)3·6H2O = (400~420): (170~180): (8~9); adding ammonia water dropwise to adjust the pH to 9.2±0.1, stirring the reaction to obtain a suspension; standing for aging, centrifuging, and washing the precipitate with deionized water at 50℃~60℃ until there is no Cl in the washing solution. - ; Disperse the precipitate in 5 to 6 times the mass of deionized water, add 1% to 3% of the mass of the precipitate as PAA dispersant, ultrasonicate, and freeze-dry to obtain a powder; Place the powder in a covered crucible, heat it to 600 to 650°C at a rate of 2°C / min to 3°C / min, and keep it warm for 1.5 to 2 hours, then heat it to 1000 to 1050°C at a rate of 3°C / min to 5°C / min, and keep it warm for 40 to 60 minutes to generate a tetragonal phase of >90wt%; After cooling naturally, sieve to obtain Y-PSZ.

[0018] In the above-mentioned preparation method of Y-PSZ, the dropping speed of the ammonia water is 8mL / min~10mL / min; the concentration of the ammonia water is 4mol / L~4.5mol / L; the stirring reaction is 400rpm~500rpm stirring reaction for 1.5h~2h; the static aging is 80±2℃ static aging for 24h~28h; the centrifugation is 4000rpm~5000rpm centrifugation for 10min~15min; the ultrasonic treatment is 300W~350W, 40kHz~45kHz ultrasonic treatment for 30min~40min; the mesh size of the sieving is 460 mesh~540 mesh.

[0019] In the above preparation method, the preparation method of the rheology modifier includes the following steps: adding α-cellulose to a 10-12 times by mass NaOH aqueous solution, stirring and soaking, and removing hemicellulose; adding 0.4% to 0.6% of TEMPO catalyst, 8% to 10% of NaBr, and 60% to 65% of NaClO in sequence, adjusting the pH to 10-11 with a hydrochloric acid aqueous solution, and stirring and reacting at room temperature for 3 hours to 4 hours; adding anhydrous ethanol in an amount of 4 times to 5 times the mass of the α-cellulose to terminate the reaction, then adjusting the pH to 6.5-7, and sequentially adding 4% to 6% of aluminum dimyristate and 3% to 5% of a silane coupling agent in an amount of α-cellulose by mass, stirring and mixing for 1 hour to 2 hours, centrifuging, washing the precipitate with a washing solution until it is neutral, and freeze-drying to obtain the rheology modifier.

[0020] In the preparation method of the above-mentioned rheology regulator, the particle size of the α-cellulose is below 200 mesh sieve; the concentration of the NaOH aqueous solution is 8wt% to 10wt%; the stirring and soaking is stirring and soaking at 70°C to 80°C for 3h to 4h; the concentration of the hydrochloric acid aqueous solution is 1mol / L to 1.5mol / L; the silane coupling agent is KH-560; the stirring speed is 300rpm to 400rpm; the centrifugation is 8000rpm to 10000rpm for 10min to 15min; and the washing liquid is an ethanol aqueous solution with a volume concentration of 30% to 40%.

[0021] In S2 of the above preparation method, the dispersant is ammonium polyacrylate and dodecyl phosphate in a mass ratio of 1:(0.4-0.5).

[0022] In S3 of the above preparation method, the dispersant is sodium polycarboxylate and dodecyl phosphate in a mass ratio of 1:(0.3-0.4).

[0023] In S2 and S3 of the above preparation method, the solvent is deionized water containing 0.1wt% to 0.2wt% of the non-ionic wetting agent PEG-400; the ultrasonic dispersion is 300W to 350W, 40kHz to 45kHz ultrasonic dispersion for 10min to 20min; the high-speed disperser homogenization is 8000rpm to 10000rpm high-speed disperser homogenization for 30min to 40min; the binder is a zirconium sol and aluminum sol mass ratio of 1: (1 to 1.5); the binder is preheated to 40°C to 50°C before dropwise addition, and the stirring and mixing is 300rpm to 400rpm stirring and mixing for 60min to 90min; the mesh size of the filter is 100 mesh to 150 mesh.

[0024] In S4 of the above preparation method, the material of the substrate plate is titanium alloy.

[0025] A solder stopper used in aircraft processing is obtained by adopting the above-mentioned preparation method.

[0026] The present invention provides a method for preparing a solder stopper used in aircraft processing, which has the following beneficial effects:

[0027] Hexagonal boron nitride (h-BN) has a typical layered crystal structure, with weak van der Waals forces holding the layers together. Under high-temperature conditions, this layered structure acts like a "molecular bearing," reducing friction within the coating and effectively suppressing flow and deformation. Furthermore, h-BN is extremely chemically stable. Within the superplastic forming temperature range of 800-1000°C, it undergoes virtually no chemical reaction with the titanium alloy substrate, forming a stable physical barrier that blocks atomic diffusion at the metal interface, ensuring effective solder stop.

[0028] Second, by precisely controlling the addition of yttrium oxide (Y2O3) and employing a specific preparation process, the hydroxide is coprecipitated to produce a zirconium-yttrium composite oxide. The resulting Y-PSZ is then pre-sintered at high temperatures to form a stable tetragonal phase structure. Tetragonal Y-PSZ possesses excellent mechanical properties, including high hardness and strength, enhancing the overall rigidity of the coating and resisting thermal stress deformation at high temperatures. Furthermore, under certain conditions, the tetragonal phase undergoes phase transformation and toughening. When the coating is subjected to thermal or mechanical stress, it transforms to a monoclinic phase, expanding in volume and absorbing energy, thereby inhibiting the initiation and propagation of cracks.

[0029] β-Eucryptite powder has an extremely low coefficient of thermal expansion, closely matching that of the titanium alloy substrate. During high-temperature heating and cooling, it effectively buffers thermal stresses between the coating and the substrate, reducing cracking and flaking caused by thermal expansion mismatch. Furthermore, its excellent chemical stability prevents adverse reactions with the titanium alloy substrate and other coating components.

[0030] 4. Lanthanum oxide, as a rare earth oxide, can form a dense protective film at the interface between the coating and the metal substrate, further inhibiting the diffusion of metal atoms and improving the reliability of the solder stop area.

[0031] 5. Solder Stop Component A (Base Layer): The base layer utilizes a lower-viscosity solder stop component A to enhance adhesion between the coating and the substrate. The low viscosity allows component A to better wet the substrate surface. During the coating process, components such as the dispersant and binder form chemical bonds or physical adsorption with atoms or molecules on the substrate surface, resulting in a strong bond. Furthermore, the appropriate amount of multilayer graphene and rheology modifier added to the base layer helps improve the microstructure of the coating. By adjusting the ratio of multilayer graphene and rheology modifier, oxidation or decomposition upon exposure to high temperatures creates partially controlled micropores, facilitating subsequent soaking and peeling of the coating without significantly affecting solder stop performance. Solder Stop Component B (Top Layer): The top layer utilizes a higher-viscosity solder stop component B, primarily to enhance the coating's stability at high temperatures. The high viscosity of component B allows it to maintain its shape at high temperatures and resist flow deformation caused by thermal stress. Among them, the binder (zirconium sol and aluminum sol mixed in a specific proportion) undergoes a curing reaction at high temperature to form a three-dimensional network structure, which tightly combines ceramic powder and other components together, enhancing the overall strength and deformation resistance of the coating.

[0032] 6. Multilayer graphene (which costs less than single-layer graphene and can be added in very low quantities) exhibits excellent thermal conductivity, creating efficient thermal paths within the coating. This allows for more uniform temperature distribution at high temperatures and reduces localized thermal stress concentrations. Furthermore, graphene's layered structure fills the pores between ceramic powder particles, increasing the coating's density and further enhancing its ability to block metal atom diffusion. Furthermore, the interaction between graphene and other components improves the coating's rheological properties, making it easier to control during the coating process.

[0033] 7. Through a specific modification process of α-cellulose, including alkaline treatment to remove hemicellulose, TEMPO-catalyzed oxidation to convert the primary hydroxyl groups of α-cellulose into carboxyl groups, and the addition of surface modifiers, the functionalized cellulose is achieved. The resulting rheology modifier exhibits unique rheological properties. At room temperature, it increases the viscosity of the coating, ensuring excellent shape retention during solder stop application and precise coating. At high temperatures, its molecular structure changes, releasing a certain lubricating effect, alleviating thermal stress within the coating and reducing flow deformation. Furthermore, the rheology modifier improves the dispersion of ceramic powder in the solvent, preventing agglomeration, thereby improving the uniformity and stability of the coating.

[0034] 8. Process parameters such as the mixing order of the ingredients, stirring speed, ultrasonic dispersion time, and drying temperature and time have been carefully designed and optimized. These parameters include first adding the dispersant to the solvent for ultrasonic dispersion, which fully activates the dispersant and allows it to better exert its dispersing effect. A high-speed disperser homogenizes the ingredients to ensure thorough mixing and a stable dispersion system. Precise control of drying temperature and time ensures that the solvent in the coating evaporates completely while preventing cracks or other defects in the coating caused by excessive temperatures or prolonged drying times. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to specific implementation cases, but the present invention is not limited to these embodiments.

[0036] Example 1

[0037] A method for preparing a solder stopper used in an aircraft processing process comprises the following steps:

[0038] S1: Compound 10 parts of hexagonal boron nitride, 10 parts of Y-PSZ, 4 parts of lanthanum oxide, and 9 parts of β-eucryptite powder by mass, and mix them evenly to obtain a pretreated powder;

[0039] The purity of hexagonal boron nitride is 99wt%, the free boron oxide is 0.5wt%, and the particle size D50 is 2.5μm; the particle size D50 of lanthanum oxide is 2.2μm; and the particle size D50 of β-eucryptite powder is 2.8μm.

[0040] S2: 1.8 parts of dispersant were added to the solvent by mass, and ultrasonically dispersed at 300W and 40kHz for 15 minutes. Then, 0.4 parts of multilayer graphene were added, and ultrasonically dispersed at 300W and 40kHz for 15 minutes. Then, 68wt% of the total amount of pretreated powder and 1.5 parts of rheology modifier were added in sequence. The mixture was homogenized in a 9000rpm high-speed disperser for 35 minutes. Finally, 9 parts of a binder preheated to 45°C was added dropwise. The binder was a zirconium sol and aluminum sol in a mass ratio of 1:1.3. The mixture was stirred at 350rpm for 70 minutes. The viscosity was adjusted to 4820cP (tested at room temperature) with a solvent. The mixture was vacuum defoamed and filtered through a 100-mesh filter to obtain solder stop component A.

[0041] The dispersant is ammonium polyacrylate and dodecyl phosphate in a mass ratio of 1:0.45; the solvent is deionized water containing 0.15 wt% of non-ionic wetting agent PEG-400.

[0042] S3: 1.8 parts of dispersant were added to the solvent by mass, and ultrasonic dispersion was performed at 300W and 40kHz for 15 minutes. Then, the remaining pretreated powder and 1.5 parts of rheology modifier were added in sequence. The mixture was homogenized in a high-speed disperser at 9000 rpm for 35 minutes. Finally, 9 parts of a binder preheated to 45°C was added dropwise. The binder was a zirconium sol and aluminum sol in a mass ratio of 1:1.3. The mixture was stirred at 350 rpm for 70 minutes. The viscosity was adjusted to 7750 cP with solvent (tested at room temperature). The mixture was vacuum defoamed and filtered through a 100-mesh filter to obtain solder stop component B.

[0043] The dispersant is sodium polycarboxylate and dodecyl phosphate in a mass ratio of 1:0.35; the solvent is deionized water containing 0.25 wt% non-ionic wetting agent PEG-400.

[0044] S4: Using titanium alloy as the substrate, the solder stop component A was coated on the specified area of ​​the substrate plate with a wet film thickness of 25 μm, and hot air dried at 82°C for 13 minutes to obtain a base layer; then the solder stop component B was coated on the base layer with a wet film thickness of 25 μm, and hot air dried at 82°C for 35 minutes to obtain a solder stop coating.

[0045] Among them, Y-PSZ is yttria partially stabilized zirconia, and the preparation method includes the following steps: preparing a 60°C mixed solution with deionized water: ZrOCl2·8H2O: Y(NO3)3·6H2O=410:175:8.5 by mass; adding ammonia water with a concentration of 4.2 mol / L at a rate of 9 mL / min, adjusting the pH to 9.2, and stirring at 450 rpm for 1.5 hours to obtain a suspension; aging at 80°C for 26 hours, centrifuging at 4500 rpm for 12 minutes, and washing the precipitate with 55°C deionized water until there is no Cl in the washing solution. - ; The precipitate was dispersed in 5.5 times the mass of deionized water, 2% of the mass of the precipitate was added as a PAA dispersant, ultrasonically treated at 300W and 40kHz for 35 minutes, and freeze-dried to obtain a powder; the powder was placed in a covered crucible, heated to 620℃ at 2℃ / min and kept warm for 1.5 hours, then heated to 1000℃ at 4℃ / min and kept warm for 50 minutes to generate a tetragonal phase of >90wt%; after natural cooling, the powder was passed through a 460-mesh sieve to obtain Y-PSZ.

[0046] The preparation method of the rheology modifier includes the following steps: adding α-cellulose passed through a 200-mesh sieve to a 9wt% NaOH aqueous solution at 11 times the mass, stirring and soaking at 75°C and 350 rpm for 3.5 hours to remove hemicellulose; adding 0.5% of the mass of the α-cellulose TEMPO catalyst, 9% of NaBr, and 62% of NaClO in sequence, adjusting the pH to 10.5 with a 1.2 mol / L hydrochloric acid aqueous solution, and stirring at 350 rpm for 3.5 hours at room temperature; adding 4.5 times the mass of the α-cellulose anhydrous ethanol to terminate the reaction, then adjusting the pH to 6.8, adding 5% of the mass of the α-cellulose aluminum dimyristate and 4% of the silane coupling agent KH-560 in sequence, stirring and mixing at 350 rpm for 1.5 hours, centrifuging at 9000 rpm for 12 minutes, washing the precipitate with a washing solution until it is neutral, the washing solution is a 35% volume concentration of ethanol aqueous solution, and freeze-drying to obtain the rheology modifier.

[0047] Example 2

[0048] A method for preparing a solder stopper used in an aircraft processing process comprises the following steps:

[0049] S1: 8 parts of hexagonal boron nitride, 12 parts of Y-PSZ, 3 parts of lanthanum oxide, and 10 parts of β-eucryptite powder were compounded and mixed uniformly to obtain a pretreated powder;

[0050] The purity of hexagonal boron nitride is 99.2 wt%, the free boron oxide is 0.4 wt%, and the particle size D50 is 3 μm; the particle size D50 of lanthanum oxide is 2.7 μm; and the particle size D50 of β-eucryptite powder is 1.8 μm.

[0051] S2: 1.5 parts of dispersant were added to the solvent by mass, and ultrasonic dispersion was performed at 350W and 40kHz for 20 minutes. Then, 0.3 parts of multilayer graphene was added, and ultrasonic dispersion was performed at 350W and 40kHz for 20 minutes. Then, 65wt% of the total amount of pretreated powder and 2 parts of rheology modifier were added in sequence. The mixture was homogenized in a high-speed disperser at 8000rpm for 40 minutes. Finally, 8 parts of a binder preheated to 50°C was added dropwise. The binder was a zirconium sol and aluminum sol in a mass ratio of 1:1. The mixture was stirred at 400rpm for 60 minutes. The viscosity was adjusted to 5000cP (tested at room temperature) with a solvent. The mixture was vacuum defoamed and filtered through a 100-mesh filter to obtain solder stop component A.

[0052] The dispersant is ammonium polyacrylate and dodecyl phosphate in a mass ratio of 1:0.5; the solvent is deionized water containing 0.1 wt% of non-ionic wetting agent PEG-400.

[0053] S3: Add 2 parts of dispersant to the solvent by mass, and ultrasonically disperse at 300W and 45kHz for 10 minutes. Then, add the remaining pretreated powder and 2 parts of rheology modifier in sequence, homogenize in a high-speed disperser at 8000rpm for 40 minutes, and finally add 8 parts of binder preheated to 50°C dropwise. The binder is a 1:1 ratio of zirconium sol to aluminum sol. Stir and mix at 400rpm for 60 minutes. Adjust the viscosity to 8000 cP (tested at room temperature) with solvent, defoam in vacuum, and filter through a 100-mesh filter to obtain solder stop component B.

[0054] The dispersant is sodium polycarboxylate and dodecyl phosphate in a mass ratio of 1:0.4; the solvent is deionized water containing 0.1 wt% of nonionic wetting agent PEG-400.

[0055] S4: Using titanium alloy as the substrate, apply solder stop component A to the specified area of ​​the substrate plate with a wet film thickness of 20 μm, and dry it with hot air at 85°C for 10 minutes to obtain a base layer; then apply solder stop component B on the base layer with a wet film thickness of 30 μm, and dry it with hot air at 80°C for 40 minutes to obtain a solder stop coating.

[0056] Among them, Y-PSZ is yttria partially stabilized zirconia, and the preparation method includes the following steps: preparing a 62°C mixed solution with a mass ratio of deionized water: ZrOCl2·8H2O: Y(NO3)3·6H2O = 400:180:8; adding ammonia water with a concentration of 4.5 mol / L at a rate of 8 mL / min, adjusting the pH to 9.1, and stirring at 500 rpm for 1.5 hours to obtain a suspension; aging at 82°C for 24 hours, centrifuging at 5000 rpm for 10 minutes, and washing the precipitate with 60°C deionized water until there is no Cl in the washing solution. - ; The precipitate was dispersed in 5 times the mass of deionized water, 3% of the mass of the precipitate was added as a PAA dispersant, ultrasonically treated at 300W and 45kHz for 30 minutes, and freeze-dried to obtain a powder; the powder was placed in a covered crucible, heated to 600℃ at 3℃ / min and kept warm for 2 hours, then heated to 1050℃ at 3℃ / min and kept warm for 40 minutes to generate a tetragonal phase of >90wt%; after natural cooling, the powder was passed through a 540-mesh sieve to obtain Y-PSZ.

[0057] The preparation method of the rheology modifier includes the following steps: adding α-cellulose passed through a 200-mesh sieve to a 10-fold 10wt% NaOH aqueous solution, stirring and soaking at 70°C and 400 rpm for 3 hours to remove hemicellulose; adding 0.6% of the mass of the α-cellulose TEMPO catalyst, 8% of NaBr, and 65% of NaClO in sequence, adjusting the pH to 11 with a 1 mol / L hydrochloric acid aqueous solution, and stirring at 300 rpm for 4 hours at room temperature; adding anhydrous ethanol 4 times the mass of the α-cellulose to terminate the reaction, then adjusting the pH to 7, adding 4% of the mass of the α-cellulose aluminum dimyristate and 5% of the silane coupling agent KH-560 in sequence, stirring and mixing at 300 rpm for 2 hours, centrifuging at 8000 rpm for 15 minutes, washing the precipitate with a washing solution until it is neutral, the washing solution is a 30% volume concentration of ethanol aqueous solution, and freeze-drying to obtain the rheology modifier.

[0058] Example 3

[0059] A method for preparing a solder stopper used in an aircraft processing process comprises the following steps:

[0060] S1: Compound 12 parts of hexagonal boron nitride, 8 parts of Y-PSZ, 5 parts of lanthanum oxide, and 8 parts of β-eucryptite powder by mass, and mix them evenly to obtain a pretreated powder;

[0061] The purity of hexagonal boron nitride is 99.3wt%, the free boron oxide is 0.3wt%, and the particle size D50 is 1μm; the particle size D50 of lanthanum oxide is 2.3μm; and the particle size D50 of β-eucryptite powder is 2.1μm.

[0062] S2: Add 2 parts of dispersant to the solvent by mass, and ultrasonically disperse at 300W and 45kHz for 10 minutes. Then add 0.5 parts of multilayer graphene, and ultrasonically disperse at 300W and 45kHz for 10 minutes. Then, add 70wt% of the pretreated powder and 1 part of rheology modifier in sequence. Homogenize in a high-speed disperser at 10000rpm for 30 minutes. Finally, add 10 parts of a binder preheated to 40°C dropwise. The binder is a zirconium sol and aluminum sol in a mass ratio of 1:1.5. Stir and mix at 300rpm for 90 minutes. Adjust the viscosity to 4500cP (test at room temperature) with a solvent. Defoam under vacuum and filter through a 150-mesh filter to obtain solder stop component A.

[0063] The dispersant is ammonium polyacrylate and dodecyl phosphate in a mass ratio of 1:0.4; the solvent is deionized water containing 0.2 wt% of non-ionic wetting agent PEG-400.

[0064] S3: Add 1.5 parts of dispersant to the solvent by mass, and disperse ultrasonically at 350W and 40kHz for 20 minutes. Then, add the remaining pretreated powder and 1 part of rheology modifier in sequence. Homogenize in a high-speed disperser at 10,000 rpm for 30 minutes. Finally, add dropwise 10 parts of a binder preheated to 40°C. The binder is a zirconium sol and aluminum sol in a mass ratio of 1:1.5. Mix at 300 rpm for 90 minutes. Adjust the viscosity to 7,500 cP with solvent (tested at room temperature). Defoam under vacuum and filter through a 150-mesh filter to obtain solder stop component B.

[0065] The dispersant is sodium polycarboxylate and dodecyl phosphate in a mass ratio of 1:0.3; the solvent is deionized water containing 0.2 wt% of nonionic wetting agent PEG-400.

[0066] S4: Using titanium alloy as the substrate, apply solder stop component A to the specified area of ​​the substrate plate with a wet film thickness of 30 μm, and dry it with hot air at 80°C for 15 minutes to obtain a base layer; then apply solder stop component B on the base layer with a wet film thickness of 20 μm, and dry it with hot air at 85°C for 30 minutes to obtain a solder stop coating.

[0067] Among them, Y-PSZ is yttria partially stabilized zirconia, and the preparation method includes the following steps: preparing a mixed solution at 58°C according to the mass ratio of deionized water: ZrOCl2·8H2O: Y(NO3)3·6H2O=420:170:9; adding ammonia water with a concentration of 4 mol / L at a rate of 10 mL / min, adjusting the pH to 9.3, stirring at 400 rpm for 2 hours to obtain a suspension; aging at 78°C for 28 hours, centrifuging at 4000 rpm for 15 minutes, and washing the precipitate with 50°C deionized water until there is no Cl in the washing solution. - ; The precipitate was dispersed in 6 times the mass of deionized water, 1% of the mass of the precipitate as PAA dispersant was added, ultrasonically treated at 350W and 40kHz for 40 minutes, and freeze-dried to obtain a powder; the powder was placed in a covered crucible, heated to 650℃ at 2℃ / min and kept warm for 1.5 hours, then heated to 1000℃ at 5℃ / min and kept warm for 60 minutes to generate a tetragonal phase of >90wt%; after natural cooling, the powder was passed through a 460-mesh sieve to obtain Y-PSZ.

[0068] The preparation method of the rheology modifier includes the following steps: adding α-cellulose passed through a 200-mesh sieve to an 8wt% NaOH aqueous solution at 12 times its mass, stirring and soaking at 80°C and 300 rpm for 4 hours to remove hemicellulose; adding 0.4% TEMPO catalyst, 10% NaBr, and 60% NaClO by mass of the α-cellulose in sequence, adjusting the pH to 10 with a 1.5 mol / L hydrochloric acid aqueous solution, and stirring at 400 rpm for 3 hours at room temperature; adding anhydrous ethanol 5 times the mass of the α-cellulose to terminate the reaction, then adjusting the pH to 6.5, adding 6% aluminum dimyristate by mass of the α-cellulose and 3% silane coupling agent KH-560 in sequence, stirring and mixing at 400 rpm for 1 hour, centrifuging at 10,000 rpm for 10 minutes, washing the precipitate with a washing solution until it is neutral, the washing solution is a 40% volume concentration ethanol aqueous solution, and freeze-drying to obtain the rheology modifier.

[0069] Sources of raw materials for the above examples: Lanthanum oxide (99.9% purity) was obtained from Shanghai Yaotian New Materials Technology Co., Ltd.; β-eucryptite powder was obtained from Zibo Zhengxin Ceramics Technology Co., Ltd.; multilayer graphene was obtained from Henan Wanshan New Materials Technology Co., Ltd.; zirconium sol (model YC-GRJ35) was obtained from Shanghai Yingcheng New Materials Co., Ltd.; aluminum sol (model ZTL-LJ-020) was obtained from Yangzhou Zhongtianli New Materials Co., Ltd.; ammonium polyacrylate was obtained from Henan Boyuan Chemical Products Co., Ltd.; dodecyl phosphate was obtained from Wuhan Qiaofeng Chemical Technology Co., Ltd.; sodium polycarboxylate was obtained from Guangzhou Baichuan Chemical Co., Ltd.; nonionic wetting agent PEG-400 was obtained from Jinan Jessie New Materials Co., Ltd.; ZrOCl2·8H2O was obtained from Shandong Desheng New Materials Co., Ltd.; Y(NO3)3·6H2O was obtained from Shandong Desheng New Materials Co., Ltd.; PAA dispersant was obtained from Hebei Annuo Environmental Protection Technology Co., Ltd.; α-cellulose was obtained from Wuhan Penglei Biotechnology Co., Ltd.; TEMPO catalyst was obtained from Beijing Green Baicao Technology Development Co., Ltd.; and NaBr was obtained from Suzhou Yingke Biotechnology Co., Ltd. NaClO was a 10 wt% solution sourced from Liaocheng Tongda Chemical Co., Ltd. Aluminum dimyristate was sourced from Jinjinle Chemical Co., Ltd. Silane coupling agent KH-560 was sourced from Shandong Yousuo Chemical Technology Co., Ltd.

[0070] Comparative Example 1

[0071] The difference from Example 1 is that the amount of hexagonal boron nitride is changed to 3 parts, and the amount of Y-PSZ is changed to 17 parts.

[0072] Comparative Example 2

[0073] The difference from Example 1 is that the amount of Y-PSZ is changed to 4 parts, and the amount of β-eucryptite powder is changed to 15 parts.

[0074] Comparative Example 3

[0075] The difference from Example 1 is that multilayer graphene is not added to the solder stop component A.

[0076] Comparative Example 4

[0077] The difference from Example 1 is that Y-PSZ is replaced by zirconium oxide (D50=1.2 μm).

[0078] Comparative Example 5

[0079] The difference from Example 1 is that no rheology regulator is added to the solder stop component A and the solder stop component B.

[0080] Comparative Example 6

[0081] The difference from Example 1 is that the rheology regulator is directly replaced by α-cellulose.

[0082] Comparative Example 7

[0083] The difference from Example 1 is that in the preparation of the rheology modifier, aluminum dimyristate and silane coupling agent KH-560 are not added for surface modification; that is, after adding anhydrous ethanol to terminate the reaction, the pH is adjusted to 6.8, and the mixture is directly centrifuged, washed, and freeze-dried.

[0084] Comparative Example 8

[0085] The difference from Example 1 is that aluminum dimyristate is not added in the preparation of the rheology regulator.

[0086] Sample size: Titanium alloy TC4 substrate size is 80 mm × 5 mm × 2 mm, original surface roughness is 0.85 μm, solder stop is applied from one end of the substrate, the coating area is 50 mm × 50 mm (thickness and curing are performed according to the corresponding embodiments and comparative examples), and the other end is blank with a size of 30 mm × 50 mm; 3 parallel samples of each type are prepared.

[0087] 1. High temperature coating flow deformation detection

[0088] Tilt the sample 30° (blank end facing downward) in a high-temperature furnace and heat to 1000°C at a rate of 5°C / min. Hold for 2 hours. Then cool to room temperature in the furnace. Scan and calculate the post-test area of ​​the coating. Calculate the flow deformation: flow deformation = (post-test area - pre-test area) / pre-test area × 100%.

[0089] 2. High temperature coating cracking detection

[0090] Surface cracks on high-temperature coating samples undergoing flow deformation testing were observed using a microscope (200x magnification). Crack ratings are as follows: Level 0 - No visible cracks on the coating surface; Level 1 - A small number of short cracks (single crack length <0.5mm), <5 cracks, with no cross-cutting; Level 2 - 5-10 cracks, 0.5-1mm long, with slight local cross-cutting; Level 3 - >10 cracks, >1mm long, with significant cross-cutting, forming a network structure but not penetrating the coating; Level 4 - Cracks penetrate the coating, resulting in large-scale flaking or loss of coating integrity.

[0091] 3. Difficulty test of chemical peeling combined with mechanical peeling

[0092] After the crack observation and rating is completed, the specimen is immersed in an aqueous solution containing 5wt% NaOH and 0.5wt% sodium gluconate at 80℃ for preliminary penetration and stripping. After soaking for 1 hour, the specimen is taken out and gently brushed with a soft brush. Then, it is mechanically polished with a polyurethane cloth at a low speed (500rpm) (polishing pressure of 0.1MPa), and the total time required to completely remove the solder stop coating is recorded.

[0093] 4. Surface roughness detection of substrate after peeling

[0094] The sample that has completed chemical peeling and mechanical peeling is used as the test object. The average roughness Ra of 5 points on the substrate surface is measured using a surface roughness meter.

[0095] Table 1 Test results (average value)

[0096]

[0097] In the test results, the fluctuation range of the flow deformation values ​​of three parallel samples was ≤±0.2; the fluctuation range of the peeling time values ​​of three parallel samples was ≤±6; and the fluctuation range of the substrate roughness values ​​of three parallel samples was ≤0.05.

[0098] Performance advantage analysis of Examples 1 to 3:

[0099] (1) Synergistic effect of ingredients:

[0100] 1. Hexagonal Boron Nitride (h-BN): In the examples, the h-BN content is 8-12 parts by weight. It has a typical layered crystal structure, with weak van der Waals forces between the layers. In high-temperature environments, this layered structure acts like a "molecular bearing," reducing frictional resistance within the coating and effectively inhibiting flow and deformation. Furthermore, h-BN is extremely chemically stable. Within the superplastic forming temperature range of 800-1000°C, it barely reacts chemically with the titanium alloy substrate, forming a stable physical barrier that blocks atomic diffusion at the metal interface, ensuring effective solder stop.

[0101] 2. Y-PSZ (yttria partially stabilized zirconia): Through precise control of the yttria (Y2O3) addition and a specific preparation process, Y-PSZ forms a stable tetragonal phase structure at high temperatures. Tetragonal Y-PSZ exhibits excellent mechanical properties, high hardness, and strength, enhancing the overall rigidity of the coating and resisting thermal stress deformation at high temperatures. Furthermore, under certain conditions, the tetragonal phase undergoes phase transformation toughening. When the coating is subjected to thermal or mechanical stress, the tetragonal phase transforms into a monoclinic phase, expanding in volume and absorbing energy, thereby inhibiting the initiation and propagation of cracks.

[0102] 3. β-Eucryptite Powder: β-Eucryptite powder has an extremely low coefficient of thermal expansion, closely matching that of the titanium alloy substrate. During high-temperature heating and cooling processes, it effectively buffers thermal stresses between the coating and the substrate, reducing cracking and spalling caused by thermal expansion mismatch. Furthermore, its excellent chemical stability prevents adverse reactions with the titanium alloy substrate and other coating components.

[0103] 4. Lanthanum oxide (La2O3): As a rare earth oxide, lanthanum oxide can form a dense protective film at the interface between the coating and the metal substrate, further inhibiting the diffusion of metal atoms and improving the reliability of the solder stop area.

[0104] (2) Gradient coating design:

[0105] 1. Solderstop Component A (Base Layer): The base layer utilizes a lower-viscosity solderstop component A to enhance adhesion between the coating and the substrate. The low viscosity allows component A to better wet the substrate surface. During the coating process, components such as the dispersant and binder form chemical bonds or physical adsorption with atoms or molecules on the substrate surface, resulting in a strong bond. Furthermore, the appropriate amount of multilayer graphene and rheology modifier added to the base layer helps improve the microstructure of the coating. By adjusting the ratio of multilayer graphene to rheology modifier, oxidation or decomposition upon exposure to high temperatures creates controlled micropores, facilitating subsequent soaking and peeling of the coating without significantly affecting solderstop performance.

[0106] 2. Solder Stop Component B (Top Coat): The top coat uses a high-viscosity solder stop component B, primarily to enhance the coating's stability at high temperatures. The high viscosity of component B allows it to maintain its shape at high temperatures and resist flow deformation caused by thermal stress. The binder (a specific mixture of zirconium sol and aluminum sol) cures at high temperatures, forming a three-dimensional network that tightly binds the ceramic powder and other components, enhancing the coating's overall strength and deformation resistance.

[0107] (3) Additives and process optimization:

[0108] 1. Multilayer graphene: Graphene exhibits excellent thermal conductivity and can create efficient thermal paths within the coating, resulting in more uniform temperature distribution at high temperatures and reducing localized thermal stress concentrations. Furthermore, the graphene layer structure can fill the pores between ceramic powder particles, increasing the coating's density and further enhancing its ability to block metal atom diffusion. Furthermore, the interaction between graphene and other components can improve the coating's rheological properties, making it easier to control during the coating process.

[0109] 2. Rheology Modifier: A rheology modifier, prepared through a specific modification process of α-cellulose (including alkaline treatment to remove hemicellulose, TEMPO-catalyzed oxidation, and the addition of surface modifiers), exhibits unique rheological properties. At room temperature, it increases the viscosity of the coating, ensuring excellent shape retention during solder stop application and precise coating. At high temperatures, its molecular structure changes, releasing a certain lubricating effect, alleviating thermal stress within the coating and reducing flow deformation. Furthermore, the rheology modifier improves the dispersion of ceramic powder in the solvent, preventing agglomeration, thereby enhancing the uniformity and stability of the coating.

[0110] 3. Preparation Process: The process parameters, including the mixing order of the ingredients, stirring speed, ultrasonic dispersion time, and drying temperature and time, have been carefully designed and optimized. These parameters include first adding the dispersant to the solvent and then ultrasonically dispersing it to fully activate the dispersant and maximize its dispersing effect. A high-speed disperser homogenizes the ingredients to achieve a uniform mixing and stable dispersion. Precise control of drying temperature and time ensures complete evaporation of the solvent from the coating while preventing cracks or other defects in the coating caused by excessive temperatures or prolonged drying times.

[0111] Analysis of data changes from Comparative Examples 1 to 9:

[0112] Comparative Example 1: The hexagonal boron nitride dosage was reduced from 10 parts to 3 parts, resulting in a significant reduction in the coating's key lubricating and barrier components. At high temperatures, the lack of h-BN's layered structure significantly reduces frictional resistance within the coating, making it more susceptible to flow and deformation. Furthermore, the reduced h-BN content weakens its ability to block metal atom diffusion, further impacting solder stop performance. The Y-PSZ dosage was increased to 17 parts. Although it has higher hardness and strength, its thermal expansion coefficient differs significantly from that of the titanium alloy substrate. Increasing the Y-PSZ content exacerbated the thermal expansion mismatch between the coating and substrate, significantly increasing the thermal stress generated during high-temperature heating and cooling, making the coating more susceptible to cracking. Furthermore, excessive Y-PSZ can create localized stress concentration areas within the coating, promoting crack initiation and propagation. The reduced h-BN content strengthens the bond between the coating and the titanium alloy substrate, making it difficult for alkaline solution to penetrate the coating-substrate interface during chemical stripping, thus prolonging the removal time. At the same time, due to the changes in the coating structure, particles are more likely to generate scratches during mechanical polishing, resulting in increased substrate roughness.

[0113] Comparative Example 2: The amount of Y-PSZ is reduced to 4 parts, resulting in insufficient content of stable tetragonal phase structure in the coating. At high temperatures, due to the reduction in the tetragonal phase content, the phase transformation toughening effect of Y-PSZ is weakened, the coating's ability to resist thermal and mechanical stresses decreases, and cracks are easily generated. The amount of β-eucryptite powder is increased to 10 parts. Although its low expansion properties help to alleviate some thermal stress, the increase in the proportion of ceramic phase reduces the toughness of the coating and increases its brittleness. Under the action of thermal stress, the coating is more likely to crack and the crack propagation rate is accelerated. β-eucryptite powder is easy to react with NaOH to a certain extent, which theoretically helps chemical stripping. However, due to the high proportion of ceramic phase in the coating, the porosity of the coating will change, causing some particles to fall off more easily during mechanical polishing, forming scratches, and increasing the roughness of the substrate. At the same time, the reaction of excessive β-eucryptite powder will change the structure of the coating, making it difficult to discharge the gas generated during the chemical stripping process, affecting the stripping effect.

[0114] Comparative Example 3: Multilayer graphene has extremely high thermal conductivity and can quickly conduct heat, making the coating temperature evenly distributed. When graphene is not added, the heat conduction path inside the coating is destroyed, and local overtemperature is likely to occur at high temperatures, leading to thermal stress concentration. Thermal stress concentration makes the coating more prone to cracks. In addition, thermal stress concentration will also affect the rheological properties of the coating, making the flow deformation of the coating at high temperatures higher than that of Example 1. The lamellar structure of graphene can play a certain lubricating role in the coating and improve the interface bonding state between the coating and the substrate; multilayer graphene is oxidized to form micropores after being subjected to high temperature, which helps the subsequent immersion and peeling of the coating. Without the presence of graphene, the bonding force between the coating and the substrate is enhanced, hindering the penetration of the alkali solution. During the mechanical polishing process, due to the lack of the lubricating effect of graphene, the friction between the particles and the coating increases, resulting in increased roughness.

[0115] Comparative Example 4: Y-PSZ was replaced with conventional zirconia. Conventional zirconia undergoes a phase transition from monoclinic to tetragonal to cubic at high temperatures, accompanied by a volume change (the monoclinic-tetragonal phase transition results in a volume expansion of approximately 4%-5%). Within the superplastic forming temperature range, this phase transition and volume change can generate significant internal stress within the coating, potentially inducing cracks. In contrast, Y-PSZ, stabilized by yttrium oxide, maintains a stable tetragonal structure at high temperatures, effectively avoiding the volume change and internal stress associated with the phase transition. Conventional zirconia is relatively weak in chemical stability and its ability to block metal atom diffusion. At high temperatures, atoms in the titanium alloy matrix are more likely to undergo diffusion bonding reactions through the conventional zirconia coating, resulting in reduced solder stop effectiveness and increased flow deformation. However, Y-PSZ, due to its stable tetragonal structure and excellent chemical stability, can better block metal atom diffusion, ensuring the reliability of the solder stop area. Conventional zirconia reacts with NaOH to form soluble zirconates, which theoretically facilitate chemical stripping. However, the phase transformation of ordinary zirconia affects the substrate, creating microcracks. This creates a tighter bond between the coating and the substrate, and some solder stoppers can become embedded in the microcracks on the substrate surface, making removal more difficult and time-consuming. Furthermore, these microcracks can affect mechanical polishing and increase substrate roughness.

[0116] Comparative Example 5: No rheology modifier added. Rheology modifiers play a key role in regulating viscosity and improving rheological properties in the coating. Without a rheology modifier, the coating's viscosity at room temperature cannot be effectively controlled, leading to sagging and uneven coating during the coating process. At high temperatures, due to the lack of a rheology modifier, the coating's viscosity drops sharply with increasing temperature, making it unable to maintain a good shape and causing significant flow deformation. Rheology modifiers also disperse and stabilize ceramic powder particles in the coating. Without them, the ceramic powder particles tend to agglomerate, resulting in an uneven internal structure of the coating. Under thermal stress, agglomerated areas are more susceptible to stress concentration, which can trigger the initiation and propagation of cracks, resulting in a distinct network of crack structures. Furthermore, the unevenness of the coating structure can affect its adhesion to the substrate, further reducing the coating's stability. The rheology modifier decomposes upon exposure to high temperatures, forming micropores that facilitate subsequent soaking and peeling of the coating; however, it does not significantly affect solder stop performance. The lack of rheology regulator deteriorates the coating structure, increasing the difficulty of polishing. At the same time, large flaking debris will leave scratches on the substrate surface, resulting in increased substrate roughness.

[0117] Comparative Example 6: α-cellulose is directly used as a rheology modifier. α-cellulose is more likely to undergo concentrated carbonization and decomposition at high temperatures, producing uneven gas, which accumulates into large bubbles inside the coating, causing bubbling and expansion of the coating, seriously damaging the structure of the coating, and increasing the flow deformation. The compatibility between unmodified α-cellulose and other ingredients is poor, and it is difficult to form a uniform and stable dispersion system. During the drying and curing process of the coating, phase separation is easily generated between α-cellulose and ceramic powder, resulting in an uneven internal structure of the coating and concentrated internal stress, which in turn causes cracks. The concentrated carbonized residues have a strong bond with the titanium alloy substrate, and chemical stripping is difficult to completely remove these residues, requiring longer mechanical polishing. At the same time, the carbonized particles have a high hardness and are prone to scratching the surface of the substrate during mechanical polishing, resulting in increased roughness.

[0118] Comparative Example 7: The rheology modifier was not modified with aluminum dimyristate and a silane coupling agent. Aluminum dimyristate and a silane coupling agent can form a good interfacial bond between the rheology modifier and the ceramic powder. Without these modifiers, the interfacial forces between the rheology modifier and the ceramic powder are weak, making debonding more likely at high temperatures. Debonding can damage the coating's internal structure, reduce its stability, and increase flow deformation. Modification with aluminum dimyristate and a silane coupling agent can control the decomposition of α-cellulose, preventing gas accumulation. Their absence can lead to the accumulation of large bubbles within the coating, causing expansion and increased flow deformation. The cellulose hydroxyl groups in the unmodified rheology modifier easily form chemical bonds, such as hydrogen bonds, with atoms on the surface of the titanium alloy substrate, resulting in a tighter bond between the coating and the substrate. During chemical stripping, alkali solution has difficulty breaking these chemical bonds, resulting in a prolonged removal time. Furthermore, due to the strong interfacial bonding, mechanical polishing can also more easily cause scratches on the substrate surface, increasing roughness.

[0119] Comparative Example 8: Rheology modifier without the addition of aluminum dimyristate. Aluminum dimyristate acts as a lubricant, which can reduce the internal friction resistance in the coating, and can also protect the cellulose from concentrated decomposition and carbonization, and avoid bubble aggregation and expansion. When aluminum dimyristate is not added, the viscosity of the coating at high temperature will increase significantly, the flow resistance will increase, and local thermal stress concentration will result. Local thermal stress concentration makes the coating more prone to deformation and cracking, and the flow deformation amount increases. Lacking the lubricating effect of aluminum dimyristate, the coating will become harder and more brittle after drying, and its toughness will decrease. Hard and brittle coatings are more likely to crack when subjected to thermal stress or mechanical stress, and the crack propagation rate is accelerated. Due to the increased hardness of the coating, the mechanical polishing process takes longer, and the particles are prone to scratches on the surface of the substrate.

Claims

1. A method for preparing a solder stopper used in aircraft processing, characterized in that: The steps include: S1: Compound 8 to 12 parts of hexagonal boron nitride, 8 to 12 parts of Y-PSZ, 3 to 5 parts of lanthanum oxide, and 8 to 10 parts of β-eucryptite powder by mass, and mix them evenly to obtain a pretreated powder; S2: 1.5 to 2 parts of dispersant are added to a solvent by mass and ultrasonically dispersed, followed by adding 0.3 to 0.5 parts of multilayer graphene for ultrasonic dispersion, followed by sequentially adding 65 wt% to 70 wt% of the total amount of pretreated powder and 1 to 2 parts of rheology modifier, homogenized by a high-speed disperser, and finally adding 8 to 10 parts of a binder dropwise, stirring and mixing, adjusting the viscosity to 4500 cP to 5000 cP with a solvent, vacuum defoaming, and filtering to obtain solder stop component A; S3: Add 1.5 to 2 parts of dispersant by mass to the solvent and ultrasonically disperse. Then, add the remaining pre-treated powder and 1 to 2 parts of rheology modifier in sequence. Homogenize in a high-speed disperser for 30 to 40 minutes. Finally, add 8 to 10 parts of binder dropwise, stir and mix. Adjust the viscosity to 7500 to 8000 cP with solvent. Defoam under vacuum and filter through a filter to obtain solder stop component B. S4: applying solder stop component A to a designated area of ​​the substrate plate with a wet film thickness of 25±5 μm, and drying with hot air at 80°C to 85°C for 10 to 15 minutes to obtain a base layer; then applying solder stop component B on the base layer with a wet film thickness of 25±5 μm, and drying with hot air at 80°C to 85°C for 30 to 40 minutes to obtain a solder stop coating; The Y-PSZ is a product obtained by co-precipitating ZrOCl2·8H2O and Y(NO3)3·6H2O and then sintering at 600°C to 650°C and 1000°C to 1050°C, respectively. The rheology modifier is a product obtained by treating α-cellulose with alkali to remove hemicellulose, oxidizing the primary hydroxyl groups of cellulose into carboxyl groups through TEMPO catalytic oxidation, and performing surface modification using aluminum dimyristate and a silane coupling agent.

2. The method for preparing a solder stopper used in aircraft processing according to claim 1, characterized in that: The purity of the hexagonal boron nitride is ≥99wt%, the free boron oxide is ≤0.5wt%, and the particle size D50 is between 1μm and 3μm; the particle size D50 of the lanthanum oxide is below 3μm; and the particle size D50 of the β-eucryptite powder is below 3μm.

3. The method for preparing a solder stopper used in aircraft processing according to claim 1, characterized in that: The Y-PSZ is yttria partially stabilized zirconia, and the preparation method comprises the following steps: preparing a mixed solution at 60±2°C according to the mass ratio of deionized water: ZrOCl2·8H2O: Y(NO3)3·6H2O = (400-420): (170-180): (8-9); adding ammonia water dropwise to adjust the pH to 9.2±0.1, stirring and reacting to obtain a suspension; standing for aging, centrifuging, and washing the precipitate with deionized water at 50°C to 60°C until the washing solution is free of Cl - ; Disperse the precipitate in 5 to 6 times the mass of deionized water, add 1% to 3% of the mass of the precipitate as PAA dispersant, ultrasonicate, and freeze-dry to obtain a powder; Place the powder in a covered crucible, heat it to 600 to 650°C at a rate of 2°C / min to 3°C / min, and keep it warm for 1.5 to 2 hours, then heat it to 1000 to 1050°C at a rate of 3°C / min to 5°C / min, and keep it warm for 40 to 60 minutes; After cooling naturally, sieve to obtain Y-PSZ.

4. The method for preparing a solder stopper used in aircraft processing according to claim 3, characterized in that: The dropping speed of the ammonia water is 8mL / min~10mL / min; the concentration of the ammonia water is 4mol / L~4.5mol / L; the stirring reaction is 400rpm~500rpm stirring reaction for 1.5h~2h; the static aging is 80±2℃ static aging for 24h~28h; the centrifugation is 4000rpm~5000rpm centrifugation for 10min~15min; the ultrasonic treatment is 300W~350W, 40kHz~45kHz ultrasonic treatment for 30min~40min; the mesh size of the sieving is 460mesh~540mesh.

5. The method for preparing a solder stopper used in aircraft processing according to claim 1, characterized in that: The preparation method of the rheology regulator comprises the following steps: adding α-cellulose to a NaOH aqueous solution with a mass of 10 to 12 times the mass of the α-cellulose, stirring and soaking the solution to remove hemicellulose; sequentially adding a TEMPO catalyst in an amount of 0.4 to 0.6% by mass of the α-cellulose, 8 to 10% by mass of NaBr, and 60 to 65% by mass of NaClO, adjusting the pH to 10 to 11 with a hydrochloric acid aqueous solution, and stirring and reacting at room temperature for 3 to 4 hours; adding anhydrous ethanol in an amount of 4 to 5 times by mass of the α-cellulose to terminate the reaction, then adjusting the pH to 6.5 to 7, sequentially adding aluminum dimyristate in an amount of 4 to 6% by mass of the α-cellulose and 3 to 5% by mass of a silane coupling agent, stirring and mixing for 1 to 2 hours, centrifuging, washing the precipitate with a washing solution until it becomes neutral, and freeze-drying to obtain the rheology regulator.

6. The method for preparing a solder stopper used in aircraft processing according to claim 5, characterized in that: The particle size of the α-cellulose is below 200 mesh sieve; the concentration of the NaOH aqueous solution is 8wt% to 10wt%; the stirring and soaking is stirring and soaking at 70°C to 80°C for 3h to 4h; the concentration of the hydrochloric acid aqueous solution is 1mol / L to 1.5mol / L; the silane coupling agent is KH-560; the stirring speed is 300rpm to 400rpm; the centrifugation is 8000rpm to 10000rpm for 10min to 15min; and the washing solution is an ethanol aqueous solution with a volume concentration of 30% to 40%.

7. The method for preparing a solder stopper used in aircraft processing according to claim 1, characterized in that: In S2, the dispersant is ammonium polyacrylate and dodecyl phosphate in a mass ratio of 1: (0.4-0.5).

8. The method for preparing a solder stopper used in aircraft processing according to claim 1, characterized in that: In S3, the dispersant is sodium polycarboxylate and dodecyl phosphate in a mass ratio of 1:(0.3-0.4).

9. The method for preparing a solder stopper used in aircraft processing according to claim 1, characterized in that: In S2 and S3, the solvent is deionized water containing 0.1wt% to 0.2wt% of the non-ionic wetting agent PEG-400; the ultrasonic dispersion is 300W to 350W, 40kHz to 45kHz ultrasonic dispersion for 10min to 20min; the high-speed disperser homogenization is 8000rpm to 10000rpm high-speed disperser homogenization for 30min to 40min; the binder is a zirconium sol and aluminum sol mass ratio of 1: (1 to 1.5); the binder is preheated to 40°C to 50°C before dropwise addition, and the stirring and mixing is 300rpm to 400rpm stirring and mixing for 60min to 90min; the mesh size of the filter is 100 mesh to 150 mesh.

10. The method for preparing a solder stopper used in aircraft processing according to claim 1, characterized in that: In S4, the substrate plate is made of titanium alloy.

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