An aluminum-based composite sprayed coating and a method for producing the same

Abstract

This invention discloses an aluminum-based composite spray coating and its preparation method, belonging to the field of metal protective coating technology. The aluminum-based composite spray coating comprises bisphenol A type epoxy resin, an interface-confined silicon-boron modifier, 2,7-dihydroxyfluorene, flake alumina, boron nitride, zinc phosphate, a leveling agent, a wetting and dispersing agent, a silane adhesion promoter, a defoamer, and an organic solvent. The interface-confined silicon-boron modifier is formed by the synergistic modification of tetraethoxysilane, methyltriethoxysilane, boric acid, and dopamine through interface-confined polycondensation and dynamic boron-oxygen bond crosslinking. This invention, by constructing a silicon-oxygen confinement network and a synergistic structure of dynamic boron-oxygen bonds, and combining it with 2,7-dihydroxyfluorene to form an organic-inorganic interface bridging structure, can effectively improve the internal density, interface stability, and thermal cycling buffering capacity of the coating, thereby significantly improving the corrosion resistance, adhesion stability, crack resistance, and media penetration resistance of the aluminum-based composite spray coating.

Description

Technical Field

[0001] This invention relates to the field of metal protective coating technology, specifically to an aluminum-based composite spray coating and its preparation method. Background Technology

[0002] Aluminum-based spray coatings are widely used in marine engineering equipment, chemical storage tanks, bridge steel structures, aerospace components, and high-temperature metal parts due to their excellent corrosion resistance, low density, and good heat reflectivity. Currently, aluminum-based spray coatings typically use epoxy resin, silicone resin, or polyester resin as the film-forming system, combined with flake fillers, anti-corrosion pigments, and adhesion promoters to form a protective layer, thereby improving the salt spray resistance and service life of the metal substrate.

[0003] However, existing aluminum-based spray coatings still have many problems during long-term service. On the one hand, although traditional epoxy spray coating systems have good adhesion, they are prone to microcracks due to internal stress accumulation under high humidity and thermal cycling conditions. This leads to the penetration of corrosive media along the crack areas, causing interface peeling and localized corrosion propagation. On the other hand, existing inorganic silicon-oxygen modified systems mostly use single silane hydrolysis and condensation to form a dense network. Although this can improve the coating's hardness and heat resistance, the network structure is relatively rigid and prone to embrittlement under alternating temperature conditions, resulting in a decrease in the coating's thermal shock resistance.

[0004] Furthermore, most existing inorganic filler reinforcement methods rely on simple blending, which easily leads to problems such as uneven filler dispersion, insufficient interfacial compatibility, and local agglomeration, making it difficult to form a stable organic-inorganic synergistic structure. At the same time, traditional anti-corrosion systems lack sufficient control over the interfacial layer structure, making it difficult to effectively inhibit the continuous penetration of corrosive media such as water vapor and chloride ions. Therefore, coatings are still prone to decreased adhesion and protective failure in salt spray environments.

[0005] While some silicon-oxygen network-modified coatings exist in existing technologies, most focus only on improving single corrosion resistance properties. Research on the construction of dynamic interfacial buffer structures and organic-inorganic synergistic stabilization mechanisms is limited, particularly lacking technical solutions that utilize silicon-boron synergistic structures to jointly construct interfacial confined networks with specific rigid organic small molecules. This makes it difficult to simultaneously achieve corrosion resistance, thermal cycling stability, and crack resistance. Therefore, developing an aluminum-based composite spray coating with interfacial densification, dynamic buffering, and synergistic protection capabilities has significant research and application value. Summary of the Invention

[0006] To overcome the problems of insufficient interfacial adhesion stability, easy cracking under thermal cycling conditions, and decreased corrosion resistance in salt spray environments found in existing aluminum-based spray coatings, the present invention aims to provide an aluminum-based composite spray coating and its preparation method. The present invention employs an interface-confined silicon-boron modifier and 2,7-dihydroxyfluorene to synergistically construct an organic-inorganic composite protective network. The interface-confined silicon-boron modifier forms a stable composite structure through silicon-oxygen confined polycondensation and dynamic boron-oxygen bond crosslinking, and combines with functional components such as lamellar alumina, boron nitride, and zinc phosphate to construct a multi-scale protective system, thereby improving the internal interfacial density and structural stability of the coating. The aluminum-based composite spray coating of the present invention exhibits excellent corrosion resistance, thermal cycling stability, and interfacial crack resistance.

[0007] The objective of this invention can be achieved through the following technical solutions: An aluminum-based composite spray coating comprises the following raw materials in parts by weight: 80-160 parts of bisphenol A type epoxy resin; 15-60 parts of interface-confined boron silica modifier; 5-25 parts of 2,7-dihydroxyfluorene; 10-50 parts of flake alumina; 3-20 parts of boron nitride; 5-30 parts of zinc phosphate; 1-8 parts of leveling agent; 1-10 parts of wetting and dispersing agent; 2-12 parts of silane adhesion promoter; 0.5-5 parts of defoamer; and 30-120 parts of organic solvent. The interface-confined boron silica modifier is an organic-inorganic composite structure formed by the synergistic modification of tetraethoxysilane, methyltriethoxysilane, boric acid, and dopamine through interface-confined condensation polymerization and dynamic boron-oxygen bond crosslinking.

[0008] Optionally, the interface-confined silicon-boron modified material comprises the following raw materials in parts by weight: 10-40 parts of tetraethoxysilane; 5-30 parts of methyltriethoxysilane; 2-15 parts of boric acid; 1-10 parts of dopamine; and 30-120 parts of deionized water.

[0009] Optionally, the preparation method of the interface-confined silicon-boron modified material includes the following steps: (1) Tetraethoxysilane and methyltriethoxysilane were added to deionized water for mixed hydrolysis to obtain a silicon-oxygen prepolymer solution; (2) Add boric acid to the silicon-oxygen prepolymer solution to carry out a complexation reaction, so that the boric acid participates in the construction of the silicon-oxygen network and obtains a silicon-boron composite solution; (3) Add dopamine to the silicon-boron composite liquid to carry out interfacial deposition and synergistic cross-linking reaction. After the reaction is completed, the interfacial confined silicon-boron modified material is obtained.

[0010] Optionally, the reaction conditions in step (1) are to stir at 300-700 rpm for 1-3 hours at 25-45°C, followed by hydrolysis for 0.5-2 hours.

[0011] Optionally, the reaction conditions in step (2) are to react at 50-80°C for 1-4 hours, and the pH of the system is controlled at 7-9 during the reaction.

[0012] Optionally, the reaction conditions in step (3) are to react at 40–75 °C for 2–6 h under weakly alkaline conditions, followed by drying to obtain the interface-confined silicon-boron modified material.

[0013] Optionally, the leveling agent is a mixture of polyether-modified siloxane and acrylate leveling agent in a mass ratio of 1:1 to 3:1; the wetting and dispersing agent is a mixture of polycarboxylate dispersant and phosphate wetting agent in a mass ratio of 1:1 to 4:1; the silane adhesion promoter is a mixture of γ-glycidyl etheroxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane in a mass ratio of 1:1 to 2:1; the defoamer is a mixture of organosilicon defoamer and mineral oil defoamer in a mass ratio of 1:1 to 3:1; and the organic solvent is a mixture of xylene and n-butanol in a mass ratio of 2:1 to 5:1.

[0014] Optionally, a method for preparing an aluminum-based composite spray coating includes the following steps: S1, Bisphenol A type epoxy resin, organic solvent and wetting and dispersing agent are added to a dispersion container for premixing, and then 2,7-dihydroxyfluorene is added for dispersion and dissolution to obtain a basic resin dispersion; S2, add interface-confined silicon-boron modifier, flake alumina, boron nitride and zinc phosphate to the base resin dispersion and disperse at high speed to form a uniform composite slurry. S3. Leveling agent, silane adhesion promoter and defoamer are added to the composite slurry for adjustment. After being mixed evenly, it is sprayed onto the surface of the metal substrate and cured by gradient temperature increase to obtain aluminum-based composite spray coating.

[0015] Optionally, the reaction conditions for step S1 are stirring at 300-800 rpm for 1-3 hours at 25-50°C to fully disperse 2,7-dihydroxyfluorene in the base resin system. The reaction conditions for step S2 are high-speed dispersion at 1000-3000 rpm for 20-60 minutes, with the temperature controlled at 35-70°C during dispersion.

[0016] Optionally, the reaction conditions for step S3 are: after spraying, pre-curing at 60–90°C for 10–30 min, followed by curing at 120–180°C for 30–120 min.

[0017] The beneficial effects of this invention are: This invention constructs a synergistic structure of a silicon-oxygen confinement network and dynamic boron-oxygen bonds using interface-confined silicon-boron modifiers. Tetraethoxysilane and methyltriethoxysilane form a dense organic-inorganic silicon-oxygen network to improve the internal structural stability of the coating and reduce the penetration rate of corrosive media. The dynamic boron-oxygen bonds formed by boric acid buffer local stress generated during thermal cycling, thereby reducing the tendency for microcrack propagation. Dopamine enhances the interfacial bonding between the silicon-oxygen network and the epoxy resin and metal substrate. Simultaneously, 2,7-dihydroxyfluorene, utilizing its rigid conjugated structure and bisphenol hydroxyl properties, forms an interfacial bridging structure between the organic and inorganic phases, improving the internal density and interfacial stability of the coating and reducing the risk of interfacial failure under high-humidity salt spray conditions. Combined with a multi-scale synergistic protection system formed by lamellar alumina, boron nitride, and zinc phosphate, the resulting aluminum-based composite spray coating simultaneously possesses excellent corrosion resistance, thermal cycling stability, adhesion stability, and crack resistance. Attached Figure Description

[0018] The invention will now be further described with reference to the accompanying drawings.

[0019] Figure 1 The infrared spectra of the silicon-oxygen prepolymer and the interface-confined silicon-boron modified product are compared. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments. However, the present invention is not limited to the following embodiments. Equivalent adjustments made without departing from the spirit and essence of the present invention should also be considered to fall within the protection scope of the present invention.

[0021] Example 1: The purpose of this example is to obtain an aluminum-based composite spray coating with excellent interfacial bonding performance and good construction fluidity.

[0022] S1, 10 parts of tetraethoxysilane and 5 parts of methyltriethoxysilane were added to 30 parts of deionized water and stirred at 300 rpm for 1 h at 25 °C, followed by a hydrolysis reaction for 0.5 h to obtain a silicon-oxygen prepolymer solution; 2 parts of boric acid were added to the silicon-oxygen prepolymer solution and reacted at 50 °C for 1 h, with the pH of the system controlled at 7 to obtain a silicon-boron composite solution; then 1 part of dopamine was added to the silicon-boron composite solution and reacted at 40 °C for 2 h under weakly alkaline conditions, and after drying, an interface-confined silicon-boron modified product was obtained; S2, 80 parts of bisphenol A type epoxy resin, 30 parts of organic solvent and 1 part of wetting and dispersing agent are added to a dispersion container and stirred at 300 rpm for 1 h at 25℃. Then, 5 parts of 2,7-dihydroxyfluorene are added for dispersion and dissolution to obtain a basic resin dispersion. Then, 15 parts of interface-confined silicon boron modifier, 10 parts of flake alumina, 3 parts of boron nitride and 5 parts of zinc phosphate are added to the basic resin dispersion and dispersed at 1000 rpm for 20 min at 35℃ to form a uniform composite slurry. S3. Add 1 part leveling agent, 2 parts silane adhesion promoter and 0.5 parts defoamer to the composite slurry for adjustment. After mixing evenly, spray it onto the surface of the metal substrate. First, pre-cur it at 60℃ for 10 minutes, and then cure it at 120℃ for 30 minutes to obtain an aluminum-based composite spray coating.

[0023] Example 2: The purpose of this example is to obtain an aluminum-based composite spray coating with optimal overall performance in terms of corrosion resistance, thermal cycling stability and adhesion stability.

[0024] S1, 25 parts of tetraethoxysilane and 17 parts of methyltriethoxysilane were added to 75 parts of deionized water and stirred at 500 rpm for 2 h at 35 °C, followed by a 1 h hydrolysis reaction to obtain a silicon-oxygen prepolymer solution; 8 parts of boric acid were added to the silicon-oxygen prepolymer solution and reacted at 65 °C for 2.5 h, with the pH of the system controlled at 8, to obtain a silicon-boron composite solution; then 5 parts of dopamine were added to the silicon-boron composite solution and reacted at 58 °C for 4 h under weakly alkaline conditions, and dried to obtain an interface-confined silicon-boron modified product; Figure 1 Before modification, the sample mainly showed characteristic Si-O-Si absorption peaks at 1110 cm⁻¹ and 795 cm⁻¹, while a significant Si-OH absorption peak was observed at 960 cm⁻¹, indicating that a preliminary silicon-oxygen network had been formed in the system, but the degree of polycondensation was relatively limited. After modification, the sample showed significantly enhanced peaks at 3325 cm⁻¹, 1608 cm⁻¹, and 1515 cm⁻¹, indicating that dopamine successfully participated in the interfacial deposition reaction. Characteristic BO and BOC peaks appeared at 1385 cm⁻¹ and 1190 cm⁻¹, indicating that boric acid participated in the formation of a dynamic boron-oxygen bond structure. At the same time, the Si-O-Si peak at 1110 cm⁻¹ was significantly enhanced, while the peak at 960 cm⁻¹ was weakened, indicating that the silicon-oxygen network further condensed and densified, eventually forming a stable interfacial confined silicon-boron synergistic structure. S2, 120 parts of bisphenol A type epoxy resin, 75 parts of organic solvent and 5 parts of wetting and dispersing agent were added to a dispersion container and stirred at 550 rpm for 2 h at 38 °C. Then, 15 parts of 2,7-dihydroxyfluorene were added for dispersion and dissolution to obtain a basic resin dispersion. Then, 35 parts of interface-confined silicon boron modifier, 30 parts of flake alumina, 12 parts of boron nitride and 18 parts of zinc phosphate were added to the basic resin dispersion and dispersed at 2200 rpm for 40 min at 55 °C to form a uniform composite slurry. S3. Add 4 parts of leveling agent, 7 parts of silane adhesion promoter and 2.5 parts of defoamer to the composite slurry for adjustment. After mixing evenly, spray it onto the surface of the metal substrate. First, pre-cure at 75℃ for 20 minutes, and then cure at 150℃ for 75 minutes to obtain an aluminum-based composite spray coating.

[0025] Example 3: The purpose of this example is to obtain a highly dense aluminum-based composite spray coating with excellent heat resistance and stability in high salt spray environments.

[0026] S1, 40 parts of tetraethoxysilane and 30 parts of methyltriethoxysilane were added to 120 parts of deionized water and stirred at 700 rpm for 3 h at 45 °C, followed by a hydrolysis reaction for 2 h to obtain a silicon-oxygen prepolymer solution; 15 parts of boric acid were added to the silicon-oxygen prepolymer solution and reacted at 80 °C for 4 h, with the pH of the system controlled at 9 to obtain a silicon-boron composite solution; then 10 parts of dopamine were added to the silicon-boron composite solution and reacted at 75 °C for 6 h under weakly alkaline conditions, and after drying, an interface-confined silicon-boron modified product was obtained; S2, 160 parts of bisphenol A type epoxy resin, 120 parts of organic solvent and 10 parts of wetting and dispersing agent were added to a dispersion container and stirred at 800 rpm for 3 hours at 50°C. Then, 25 parts of 2,7-dihydroxyfluorene were added for dispersion and dissolution to obtain a basic resin dispersion. Then, 60 parts of interface-confined silicon-boron modifier, 50 parts of flake alumina, 20 parts of boron nitride and 30 parts of zinc phosphate were added to the basic resin dispersion and dispersed at 3000 rpm for 60 minutes at 70°C to form a uniform composite slurry. S3. Add 8 parts of leveling agent, 12 parts of silane adhesion promoter and 5 parts of defoamer to the composite slurry for adjustment. After mixing evenly, spray it onto the surface of the metal substrate. First, pre-cure at 90℃ for 30 minutes, and then cure at 180℃ for 120 minutes to obtain an aluminum-based composite spray coating.

[0027] Comparative Example 1: The purpose of this comparative example is to verify the influence of the dynamic boron-oxygen bond synergistic structure of boric acid in the interface-confined borosilicate modified product on the performance of aluminum-based composite spray coating. S1: 25 parts of tetraethoxysilane and 17 parts of methyltriethoxysilane were added to 75 parts of deionized water and stirred at 500 rpm for 2 hours at 35°C, followed by a 1-hour hydrolysis reaction to obtain a silica-oxygen prepolymer. Without adding boric acid, 5 parts of dopamine were directly added to the silica-oxygen prepolymer and reacted at 58°C for 4 hours under weakly alkaline conditions. After drying, a single silica-oxygen modified product was obtained. S2: 120 parts of bisphenol A type epoxy resin, 75 parts of organic solvent, and 5 parts of wetting and dispersing agent were added to a dispersion container and stirred at 550 rpm for 2 hours at 38°C, followed by the addition of 15 parts of 2,7-dihydroxyfluorene. The components were dispersed and dissolved to obtain a basic resin dispersion. Then, 35 parts of a single siloxane modifier, 30 parts of flake alumina, 12 parts of boron nitride, and 18 parts of zinc phosphate were added to the basic resin dispersion. The mixture was dispersed at 2200 rpm for 40 minutes at 55°C to form a uniform composite slurry. In step S3, 4 parts of leveling agent, 7 parts of silane adhesion promoter, and 2.5 parts of defoamer were added to the composite slurry for adjustment. After mixing evenly, the mixture was sprayed onto the surface of a metal substrate. It was pre-cured at 75°C for 20 minutes and then cured at 150°C for 75 minutes to obtain an aluminum-based composite spray coating.

[0028] Comparative Example 2: The purpose of this comparative example is to verify the effect of the dopamine interfacial deposition structure in the interface-confined silicon-boron modified material on the performance of aluminum-based composite spray coatings. S1: 25 parts of tetraethoxysilane and 17 parts of methyltriethoxysilane were added to 75 parts of deionized water and stirred at 500 rpm for 2 hours at 35°C, followed by a 1-hour hydrolysis reaction to obtain a silicon-oxygen prepolymer. 8 parts of boric acid were added to the silicon-oxygen prepolymer and reacted at 65°C for 2.5 hours, with the pH controlled at 8, to obtain a silicon-boron composite solution. No dopamine was added, and the mixture was directly dried after the reaction to obtain the silicon-boron modified material. S2: 120 parts of bisphenol A epoxy resin, 75 parts of organic solvent, and 5 parts of wetting and dispersing agent were added to a dispersion container and stirred at 550 rpm for 2 hours at 38°C, followed by the addition of… 15 parts of 2,7-dihydroxyfluorene were dispersed and dissolved to obtain a basic resin dispersion. Then, 35 parts of silicon boron modifier, 30 parts of flake alumina, 12 parts of boron nitride, and 18 parts of zinc phosphate were added to the basic resin dispersion. The mixture was dispersed at 2200 rpm for 40 minutes at 55°C to form a uniform composite slurry. In step S3, 4 parts of leveling agent, 7 parts of silane adhesion promoter, and 2.5 parts of defoamer were added to the composite slurry for adjustment. After mixing evenly, the mixture was sprayed onto the surface of a metal substrate. It was pre-cured at 75°C for 20 minutes and then cured at 150°C for 75 minutes to obtain an aluminum-based composite spray coating.

[0029] Comparative Example 3: The purpose of this comparative example is to verify the effect of 2,7-dihydroxyfluorene organic small molecules on the interfacial stability and corrosion resistance of aluminum-based composite spray coatings. S1: 25 parts of tetraethoxysilane and 17 parts of methyltriethoxysilane were added to 75 parts of deionized water and stirred at 500 rpm for 2 hours at 35°C, followed by a 1-hour hydrolysis reaction to obtain a silicon-oxygen prepolymer. 8 parts of boric acid were added to the silicon-oxygen prepolymer and reacted at 65°C for 2.5 hours, with the pH controlled at 8, to obtain a silicon-boron composite solution. Subsequently, 5 parts of dopamine were added to the silicon-boron composite solution and reacted at 58°C for 4 hours under weakly alkaline conditions. After drying, an interfacial confined silicon-boron modified product was obtained. S2: 120 parts of bisphenol A type epoxy resin, 75 parts of organic solvent, and 5 parts of wetting and dispersing agent were added to a dispersion container and stirred at 38°C... Stir at 550 rpm for 2 hours without adding 2,7-dihydroxyfluorene to obtain a basic resin dispersion. Then, add 35 parts of interface-confined borosilicate modifier, 30 parts of flake alumina, 12 parts of boron nitride, and 18 parts of zinc phosphate to the basic resin dispersion. Disperse at 2200 rpm for 40 minutes at 55°C to form a uniform composite slurry. In step S3, add 4 parts of leveling agent, 7 parts of silane adhesion promoter, and 2.5 parts of defoamer to the composite slurry for adjustment. After mixing evenly, spray it onto the surface of a metal substrate. Pre-cure at 75°C for 20 minutes, and then cure at 150°C for 75 minutes to obtain an aluminum-based composite spray coating.

[0030] Performance testing: 1. Salt spray corrosion resistance test The aluminum-based composite coatings obtained in the examples and comparative examples were uniformly sprayed onto the surface of an aluminum alloy substrate with dimensions of 150mm × 70mm × 2mm, and the coating thickness was controlled at 80–100 μm. The substrate was then left to stand at room temperature for 24 hours. The samples were then placed in a salt spray chamber and continuously sprayed with a 5% sodium chloride solution at a temperature of 35°C and a spray settling rate of 1–2 mL / h. After 480 hours of continuous testing, the blistering, cracking, and corrosion propagation of the coating surface were observed, and the corrosion spread width at the coating edge and surface integrity were recorded.

[0031] 2. Thermal cycling stability test The aluminum-based composite coatings obtained in the examples and comparative examples were sprayed onto the surface of an aluminum alloy substrate and cured under specified conditions. The samples were then placed in a thermal cycling test chamber, cycling between -20°C and 150°C, with each cycle lasting 30 minutes at the lower temperature and 30 minutes at the higher temperature. Each complete thermal cycling cycle was recorded as one period, and the total number of cycles was set to 100. After the test, the coating surface was observed for cracking, blistering, and peeling, and changes in coating integrity were recorded.

[0032] 3. Adhesion stability performance test The aluminum-based composite coatings obtained in the examples and comparative examples were sprayed onto the surface of an aluminum alloy substrate that had undergone surface polishing. After curing, the coatings were left at room temperature for 24 hours. The coating adhesion performance was then tested using a cross-cut test. Intersecting cuts were uniformly made on the coating surface, and then the coating was peeled off using special adhesive tape. The extent of coating detachment within the cut areas was observed, and the coating adhesion level was recorded. Simultaneously, the samples were placed at 85°C and 85% relative humidity for 120 hours, and then subjected to another adhesion test to evaluate the coating's adhesion stability under humid and hot conditions.

[0033] 4. Resistance to media penetration test The aluminum-based composite spray coatings obtained in the examples and comparative examples were sprayed onto the surface of an aluminum alloy substrate. After complete curing, the samples were immersed in a 3.5% sodium chloride solution at a controlled temperature of 45°C for 240 hours. After the test, the samples were removed, the coating surface was cleaned and dried, and the changes in surface gloss, blistering, and edge corrosion were observed. The percentage of the coating surface area that failed was recorded to evaluate the coating's barrier ability against corrosive media.

[0034] Table 1 Performance test results of aluminum-based composite spray coating

[0035] As shown in Table 1, the aluminum-based composite spray coatings obtained in Examples 1-3 are significantly superior to those in Comparative Examples 1-3 in terms of salt spray corrosion resistance, thermal cycling stability, adhesion stability, and resistance to media penetration. This indicates that the interface-confined silicon-boron modifier and 2,7-dihydroxyfluorene can effectively improve the overall protective performance of the spray coating. Among them, Example 2 exhibits the best overall performance, with a salt spray corrosion propagation width of only 0.6 mm, only one crack after thermal cycling, a wet heat adhesion rating of 0, and a media penetration failure area of ​​only 0.9%, indicating that this system has superior interface stability and corrosion resistance.

[0036] Although Example 1 achieved an interface-confined silicon-boron synergistic structure, the relatively low addition levels of each component resulted in a limited organic-inorganic synergistic network within the system. Consequently, five cracks still appeared during thermal cycling, and the media penetration failure area reached 3.6%. Example 3 increased the content of interface-confined silicon-boron modifier and inorganic filler, further improving the overall density of the coating and reducing the salt spray corrosion propagation width to 1.1 mm. However, due to the higher proportion of inorganic phase, local rigidity was enhanced, resulting in a slightly higher number of cracks after thermal cycling compared to Example 2.

[0037] In Comparative Example 1, no dynamic synergistic structure of boric acid was added, and only a single silicon-oxygen modified network was formed. This resulted in a lack of dynamic buffering capacity in the system, which easily led to internal stress concentration during thermal cycling. As a result, the number of cracks reached 14 after thermal cycling, and the salt spray corrosion propagation width reached 4.9 mm. This indicates that the dynamic boric-oxygen bond structure plays an important role in improving the crack resistance and corrosion resistance of the coating.

[0038] In Comparative Example 2, the absence of dopamine in the interfacial deposition structure reduced the interfacial bonding ability between the silicon-oxygen network and the epoxy resin and metal substrate, resulting in a decrease in the humid heat adhesion grade to level 2 and a media penetration failure area of ​​9.5%. This indicates that dopamine has a significant effect on improving interfacial bonding stability and inhibiting the penetration of corrosive media.

[0039] In Comparative Example 3, 2,7-dihydroxyfluorene was not added. Although the system still possessed a certain silicon-boron synergistic structure, the lack of rigid conjugated interface bridging led to a decrease in the internal density of the coating and a weakening of the interface stability under high humidity conditions. As a result, the salt spray corrosion propagation width increased to 3.2 mm, and the number of cracks increased to 9 after thermal cycling. This indicates that 2,7-dihydroxyfluorene can effectively improve the organic-inorganic interface stability and overall protective performance.

[0040] In summary, this invention utilizes an interface-confined silicon-boron modifier and 2,7-dihydroxyfluorene to synergistically construct an organic-inorganic composite protective network, which can significantly improve the corrosion resistance, thermal cycling stability, adhesion stability, and media penetration resistance of aluminum-based composite spray coatings. Among these, Example 2 exhibits the best overall performance.

Claims

1. An aluminum-based composite spray coating, characterized in that, The aluminum-based composite spray coating comprises the following raw materials in parts by weight: 80-160 parts of bisphenol A type epoxy resin; 15-60 parts of interface-confined boron silica modifier; 5-25 parts of 2,7-dihydroxyfluorene; 10-50 parts of flake alumina; 3-20 parts of boron nitride; 5-30 parts of zinc phosphate; 1-8 parts of leveling agent; 1-10 parts of wetting and dispersing agent; 2-12 parts of silane adhesion promoter; 0.5-5 parts of defoamer; and 30-120 parts of organic solvent. The interface-confined boron silica modifier is an organic-inorganic composite structure formed by the synergistic modification of tetraethoxysilane, methyltriethoxysilane, boric acid, and dopamine through interface-confined condensation polymerization and dynamic boron-oxygen bond crosslinking.

2. The aluminum-based composite spray coating according to claim 1, characterized in that, The interface-confined silicon-boron modified material comprises the following raw materials in parts by weight: 10-40 parts of tetraethoxysilane; 5-30 parts of methyltriethoxysilane; 2-15 parts of boric acid; 1-10 parts of dopamine; and 30-120 parts of deionized water.

3. An aluminum-based composite spray coating according to claim 1 or 2, characterized in that, The preparation method of the interface-confined silicon-boron modified material includes the following steps: (1) Tetraethoxysilane and methyltriethoxysilane were added to deionized water for mixed hydrolysis to obtain a silicon-oxygen prepolymer solution; (2) Add boric acid to the silicon-oxygen prepolymer solution to carry out a complexation reaction, so that the boric acid participates in the construction of the silicon-oxygen network and obtains a silicon-boron composite solution; (3) Add dopamine to the silicon-boron composite liquid to carry out interfacial deposition and synergistic cross-linking reaction. After the reaction is completed, the interfacial confined silicon-boron modified material is obtained.

4. The aluminum-based composite spray coating according to claim 3, characterized in that, The reaction conditions for step (1) are stirring at 300-700 rpm for 1-3 hours at 25-45°C, followed by hydrolysis for 0.5-2 hours.

5. The aluminum-based composite spray coating according to claim 3, characterized in that, The reaction conditions for step (2) are to react at 50-80℃ for 1-4 hours, and the pH of the system is controlled at 7-9 during the reaction.

6. The aluminum-based composite spray coating according to claim 3, characterized in that, The reaction conditions for step (3) are to react at 40-75°C for 2-6 hours under weakly alkaline conditions, followed by drying to obtain the interface-confined silicon-boron modified material.

7. The aluminum-based composite spray coating according to claim 1, characterized in that, The leveling agent is a mixture of polyether-modified siloxane and acrylate leveling agent in a mass ratio of 1:1 to 3:1; the wetting and dispersing agent is a mixture of polycarboxylate dispersant and phosphate wetting agent in a mass ratio of 1:1 to 4:1; the silane adhesion promoter is a mixture of γ-glycidyl etheroxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane in a mass ratio of 1:1 to 2:1; the defoamer is a mixture of organosilicon defoamer and mineral oil defoamer in a mass ratio of 1:1 to 3:1; and the organic solvent is a mixture of xylene and n-butanol in a mass ratio of 2:1 to 5:

1.

8. A method for preparing an aluminum-based composite spray coating, characterized in that, The preparation method includes the following steps: S1, Bisphenol A type epoxy resin, organic solvent and wetting and dispersing agent are added to a dispersion container for premixing, and then 2,7-dihydroxyfluorene is added for dispersion and dissolution to obtain a basic resin dispersion; S2, add interface-confined silicon-boron modifier, flake alumina, boron nitride and zinc phosphate to the base resin dispersion and disperse at high speed to form a uniform composite slurry. S3. Leveling agent, silane adhesion promoter and defoamer are added to the composite slurry for adjustment. After being mixed evenly, it is sprayed onto the surface of the metal substrate and cured by gradient temperature increase to obtain aluminum-based composite spray coating.

9. The method for preparing an aluminum-based composite spray coating according to claim 8, characterized in that, The reaction conditions for step S1 are: stirring at 300–800 rpm for 1–3 hours at 25–50°C to fully disperse 2,7-dihydroxyfluorene in the base resin system. The reaction conditions for step S2 are: high-speed dispersion at 1000–3000 rpm for 20–60 minutes, with the temperature controlled at 35–70°C during dispersion.

10. The method for preparing an aluminum-based composite spray coating according to claim 8, characterized in that, The reaction conditions for step S3 are: after spraying, pre-curing at 60-90℃ for 10-30 minutes, and then curing at 120-180℃ for 30-120 minutes.

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