Protective coating for aluminum alloy heat exchange tubes and method for producing same

Abstract

The application discloses a protective coating for an aluminum alloy heat exchange pipe and a preparation method thereof, and relates to the technical field of coating materials.The protective coating for the aluminum alloy heat exchange pipe comprises the following raw materials in mass parts: 100 parts of bisphenol A type epoxy resin; 28-32 parts of polyetheramine D230; 8-12 parts of modified MgAlCe-BTC-LDH filler; 4-6 parts of polydopamine modified hexagonal boron nitride; 35-45 parts of propylene glycol methyl ether acetate; and 1-2 parts of dispersant.The modified MgAlCe-BTC-LDH filler prepared by the application realizes the triple functions of Ce element antioxidation, BTC corrosion inhibition and layer barrier.The polydopamine modified hexagonal boron nitride prepared by the application effectively improves the heat conduction performance, solves the contradiction between insulation and heat conduction, and meets the protection requirements of the aluminum alloy heat exchange pipe.

Description

Technical Field

[0001] This invention relates to the field of coating materials technology, specifically to a protective coating for aluminum alloy heat exchange tubes and its preparation method. Background Technology

[0002] Heat exchange tubes are components of a heat exchanger, housed within a cylindrical shell, used for heat exchange between two media. They possess high thermal conductivity and excellent isothermal properties. As a device capable of rapidly transferring heat energy from one point to another with virtually no heat loss, they are known as heat transfer superconductors, with a thermal conductivity thousands of times that of copper. Commonly used materials include carbon steel, low-alloy steel, stainless steel, copper, copper-nickel alloys, aluminum alloys, and titanium. Aluminum alloy heat exchange tubes are industrial heat transfer elements using aluminum-based alloys as the core material. High hardness, elongation, and acid and corrosion resistance are achieved through optimized alloy composition and heat treatment processes. This product employs precision manufacturing processes such as casting, extrusion molding, and spinning fins, achieving a 100% yield rate. No cracks are found in the curved sections during bending. Due to their lightweight and high thermal conductivity, aluminum alloy heat exchange tubes are widely used in automotive radiators, industrial condensers, and other fields.

[0003] When aluminum alloys are exposed to natural environments, a dense aluminum oxide film spontaneously forms. This film acts as a natural barrier, providing a considerable degree of corrosion protection in neutral or near-neutral environments. However, when aluminum alloys face extreme or harsh environments, such as the high humidity and high salinity of marine atmospheres and underwater seawater, or environments rich in halide ions, especially chloride ions (Cl), corrosion can occur. - In environments with such corrosive ions, the protective effect of the alumina film is limited. These corrosive agents can easily penetrate the weak points of the alumina film, directly contacting the aluminum alloy substrate, leading to pitting corrosion, other more widespread localized corrosion, and severely damaging the material's structure and properties. To overcome this challenge, the industry employs various complex surface treatment technologies to enhance the corrosion resistance of aluminum alloys. Among these, methods such as anodizing, electroless plating, and conversion coatings construct a more robust protective layer on the aluminum alloy surface through physical or chemical means. In existing technologies, protective coatings often use silicone resin, epoxy resin, or zinc-aluminum composite coatings: organic coatings, while exhibiting good corrosion resistance, are prone to aging and cracking at high temperatures and have low thermal conductivity, significantly reducing heat exchange efficiency; metal coatings (such as zinc-aluminum coatings) have excellent thermal conductivity, but their corrosion resistance depends on the sacrificial anode effect, leading to rapid depletion in highly corrosive environments, and insufficient interfacial bonding with the aluminum alloy substrate, resulting in easy peeling; ceramic coatings are heat-resistant but brittle, have poor thermal shock resistance, and cannot withstand the thermal cycling stress of heat exchange tubes. Therefore, developing a single-layer protective coating that combines high thermal conductivity, strong corrosion resistance, and excellent interfacial adhesion has become the key to solving the failure problem of aluminum alloy heat exchange tubes. Summary of the Invention

[0004] The purpose of this invention is to provide a protective coating for aluminum alloy heat exchange tubes and its preparation method, thereby solving the following technical problems:

[0005] Existing protective coatings for aluminum alloy heat exchange tubes suffer from insufficient thermal conductivity, poor corrosion resistance, and easy peeling.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A protective coating for aluminum alloy heat exchange tubes comprises at least the following raw materials by weight:

[0008] 100 parts of bisphenol A type epoxy resin; 28-32 parts of polyetheramine D230; 8-12 parts of modified MgAlCe-BTC-LDH filler; 4-6 parts of polydopamine-modified hexagonal boron nitride; 35-45 parts of propylene glycol methyl ether acetate; 1-2 parts of dispersant.

[0009] As a further aspect of the present invention: the preparation method of the modified MgAlCe-BTC-LDH filler includes at least the following steps:

[0010] Magnesium, aluminum and cerium nitrates are dissolved in deionized water to obtain a mixed nitrate solution;

[0011] Sodium hydroxide and BTC were dissolved in deionized water, and after the reaction, an intercalation solution was obtained.

[0012] The intercalation solution was added dropwise to the nitrate mixture, and sodium hydroxide solution was added to maintain the pH at 10-12. After the reaction, the solution was filtered, washed and dried to obtain MgAlCe-BTC-LDH.

[0013] The MgAlCe-BTC-LDH was added to the hydrolysate of γ-aminopropyltriethoxysilane. After the reaction, the mixture was filtered, washed, dried and ground to obtain the modified MgAlCe-BTC-LDH filler.

[0014] As a further aspect of the present invention: the molar ratio of magnesium ions, aluminum ions and cerium ions in the nitrate mixed solution is 3:0.8-1.2:0.1-0.3, and the total concentration of magnesium ions, aluminum ions and cerium ions is 0.3-0.5 mol / L.

[0015] As a further aspect of the present invention: the concentration of BTC in the intercalation solution is 0.08-0.12 mol / L, and the volume ratio of the nitrate mixed solution to the intercalation solution is 1:1.

[0016] As a further aspect of the present invention: the mass ratio of the MgAlCe-BTC-LDH and the γ-aminopropyltriethoxysilane is 1:0.3-0.5.

[0017] As a further aspect of the present invention, the preparation method of the polydopamine-modified hexagonal boron nitride includes the following steps:

[0018] Tris(hydroxymethyl)aminomethane was added to deionized water, and dilute hydrochloric acid was added to adjust the pH to 8-9. Dopamine hydrochloride was added, and hexagonal boron nitride was added while stirring. After ultrasonic treatment, the mixture was filtered, washed, and dried to obtain polydopamine-modified hexagonal boron nitride.

[0019] As a further aspect of the present invention: the concentration of the dilute hydrochloric acid is 0.1 mol / L, and the mass ratio of the tris(hydroxymethyl)aminomethane, the dopamine hydrochloride, and the hexagonal boron nitride is 0.4-0.5:0.7-0.9:1-3.

[0020] As a further aspect of the present invention: the dispersant is one or a mixture of BYK-2155, BYK-307 or BYK-088.

[0021] A method for preparing a protective coating for an aluminum alloy heat exchanger tube as described in any one of the above claims, comprising at least the following preparation steps:

[0022] Bisphenol A type epoxy resin and propylene glycol methyl ether acetate were mixed, a dispersant was added and ultrasonically dispersed, then modified MgAlCe-BTC-LDH filler and polydopamine-modified hexagonal boron nitride were added and ball-milled, followed by the addition of polyetheramine D230, stirring and degassing to obtain the coating slurry.

[0023] The aluminum alloy heat exchange tube is subjected to sandblasting and acetone degreasing, then coated with the coating slurry. After curing, a protective coating for the aluminum alloy heat exchange tube is obtained.

[0024] As a further aspect of the present invention, the thickness of the protective coating for the aluminum alloy heat exchange tube is 70-80 μm.

[0025] The beneficial effects of this invention are:

[0026] The protective coating for aluminum alloy heat exchange tubes prepared in this invention uses bisphenol A type epoxy resin as a base material and adds polyetheramine D230. The benzene ring structure of bisphenol A epoxy gives the coating high hardness, and combined with a three-dimensional cross-linked network, the surface wear resistance is significantly improved. The polyether segments of polyetheramine D230 can absorb impact energy through segment movement, making the aluminum alloy heat exchange tube less prone to cracking due to collisions during installation and transportation. Modified MgAlCe-BTC-LDH filler and polydopamine-modified hexagonal boron nitride are also added as functional fillers, giving the coating long-term salt spray resistance, high thermal conductivity, and strong adhesion. It is suitable for harsh environments such as automotive radiators and offshore platform heat exchangers, extending the service life of aluminum alloy heat exchange tubes. Among them, the modified MgAlCe-BTC-LDH filler achieves the triple functions of Ce element anti-oxidation, BTC corrosion inhibition and layered barrier, which can be directly adapted to the protection requirements of aluminum alloy heat exchange tubes, further improving the coating's high temperature oxidation resistance and long-term salt spray resistance, and is more suitable for harsh heat exchange environments such as automobiles and oceans; at the same time, the addition of polydopamine modified hexagonal boron nitride gives the coating excellent thermal conductivity and high adhesion, and synergistically improves the coating's corrosion resistance with the modified MgAlCe-BTC-LDH filler.

[0027] The MgAlCe-BTC-LDH filler prepared in this invention is a typical layered double hydroxide. Modified with a silane coupling agent, it is uniformly dispersed in an epoxy matrix, forming a dense, stacked barrier. This structure significantly reduces the penetration rate of corrosive media in the coating, effectively delaying the time it takes for the media to reach the aluminum alloy surface. When a small amount of corrosive media penetrates the physical barrier, BTC between the LDH layers is slowly released through anion exchange. The carboxyl groups in the BTC molecules can form a stable chelate film with aluminum ions on the aluminum alloy surface, inhibiting the dissolution of aluminum ions. Simultaneously, cerium ions in the LDH hydrolyze at corrosion sites to generate cerium hydroxide, further transforming into a dense composite oxide film, blocking the continued corrosion reaction.

[0028] The polydopamine-modified hexagonal boron nitride prepared in this invention utilizes the catechol groups of polydopamine to form hydrogen and covalent bonds with the hydroxyl groups of the epoxy matrix and the aluminum alloy surface. This results in a tighter interface between the coating and the substrate, preventing interfacial gaps from becoming channels for corrosive media penetration, thereby improving the adhesion and density of the coating. Simultaneously, the lamellar structure of hexagonal boron nitride fills the micropores generated during epoxy matrix curing, forming a "cross-barrier network" with the layered structure of LDH, further extending the penetration path of corrosive media. Furthermore, cubic boron nitride itself possesses excellent thermal conductivity; after polydopamine modification, the compatibility of its surface amino groups with the epoxy matrix is ​​enhanced, forming continuous thermal conductive pathways in the matrix and improving the coating's thermal conductivity. Additionally, the cerium element in MgAlCe-BTC-LDH reduces phonon scattering within the coating, decreasing thermal resistance. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: The preparation method of modified MgAlCe-BTC-LDH filler includes the following steps:

[0031] Add 36.64g magnesium nitrate hexahydrate, 17.86g aluminum nitrate nonahydrate and 4.13g cerium nitrate hexahydrate to 500mL of deionized water, place in a three-necked flask, and stir vigorously at 80℃ to obtain a nitrate mixed solution.

[0032] Dissolve 9.56 g BTC and 19.2 g sodium hydroxide in 500 mL of deionized water at 45 °C, and react at 45 °C for 20 min to obtain the intercalation solution.

[0033] The above intercalation solution was added dropwise to the above nitrate mixed solution. The pH value was maintained at 11 using 2 mol / L NaOH solution. The mixture was stirred at 80°C for 1.5 h under a nitrogen atmosphere. Then it was transferred to an autoclave, heated to 130°C and held for 24 h. After washing with deionized water at 4000 rpm and filtering for 4 min, the mixture was dried in an oven at 70°C to obtain MgAlCe-BTC-LDH.

[0034] γ-aminopropyltriethoxysilane was prepared into a 100 ml solution with water and anhydrous ethanol at a volume ratio of 5:45:50. 1 ml of glacial acetic acid was added, and the mixture was hydrolyzed at 60 °C for 4 h. Then, 10 g of the above MgAlCe-BTC-LDH powder was added, and the mixture was stirred and reacted for another 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, filtered, dried, and ground into powder to obtain the modified MgAlCe-BTC-LDH filler.

[0035] Example 2: The preparation method of modified MgAlCe-BTC-LDH filler includes the following steps:

[0036] Add 44.46 g magnesium nitrate hexahydrate, 21.01 g aluminum nitrate nonahydrate and 6.52 g cerium nitrate hexahydrate to 500 mL of deionized water, place in a three-necked flask, and stir vigorously at 80 °C to obtain a nitrate mixed solution.

[0037] 11.47 g BTC and 19.2 g sodium hydroxide were dissolved in 500 mL of deionized water at 45 °C and reacted at 45 °C for 20 min to obtain the intercalation solution.

[0038] The above intercalation solution was added dropwise to the above nitrate mixed solution. The pH value was maintained at 11 using 2 mol / L NaOH solution. The mixture was stirred at 80°C for 1.5 h under a nitrogen atmosphere. Then it was transferred to an autoclave, heated to 130°C and held for 24 h. After washing with deionized water at 4000 rpm and filtering for 4 min, the mixture was dried in an oven at 70°C to obtain MgAlCe-BTC-LDH.

[0039] γ-aminopropyltriethoxysilane was prepared into a 100 ml solution with water and anhydrous ethanol at a volume ratio of 5:45:50. 10 ml of glacial acetic acid was added, and the mixture was hydrolyzed at 60 °C for 4 h. Then, 10 g of the above MgAlCe-BTC-LDH powder was added, and the mixture was stirred and reacted for another 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, filtered, dried, and ground into powder to obtain the modified MgAlCe-BTC-LDH filler.

[0040] Example 3: The preparation method of polydopamine-modified hexagonal boron nitride includes the following steps:

[0041] 4.8 g of tris(hydroxymethyl)aminomethane was added to 3000 mL of deionized water, and 0.1 mol / L dilute hydrochloric acid was slowly added to adjust the pH to 8.5. 8 g of dopamine hydrochloride was added while stirring continuously, followed by 20 g of hexagonal boron nitride powder under rapid stirring. The mixture was sonicated for 3 h and equilibrated at 60 °C for 24 h. The mixture was centrifuged and filtered, and washed several times with deionized water until the filtrate became colorless. Solid-liquid separation was performed, and the mixture was dried under vacuum at 60 °C for 24 h to obtain polydopamine-modified hexagonal boron nitride.

[0042] Example 4: The preparation method of the protective coating for aluminum alloy heat exchange tubes includes the following steps:

[0043] 100 parts by weight of bisphenol A type epoxy resin (E44) and 40 parts by weight of propylene glycol methyl ether acetate were mixed, and 1.5 parts by weight of dispersant BYK-2155 were added. The mixture was ultrasonically dispersed at 300W for 10 min. Then, 10 parts by weight of modified MgAlCe-BTC-LDH filler prepared in Example 1 and 5 parts by weight of polydopamine modified hexagonal boron nitride prepared in Example 3 were added. The mixture was ball-milled at 200 r / min for 2 h with a ball-to-material ratio of 5:1. Then, 30 parts by weight of polyetheramine D230 were added. The mixture was stirred at 40℃ for 30 min and degassed under vacuum at -0.09 MPa for 20 min to obtain the coating slurry.

[0044] The aluminum alloy heat exchange tube was sandblasted with 7075 aluminum alloy to a thickness of 3 μm, degreased with acetone, and then the above-mentioned coating slurry was sprayed under high pressure of 0.3 MPa, with a wet film thickness of 120 μm. The coating was leveled at room temperature for 2 hours, cured at 80°C for 2 hours, and then cured at 120°C for 4 hours to obtain a protective coating for aluminum alloy heat exchange tubes with a dry film thickness of 70 μm.

[0045] Example 5: The preparation method of the protective coating for aluminum alloy heat exchange tubes includes the following steps:

[0046] 100 parts by weight of bisphenol A type epoxy resin (E44) and 40 parts by weight of propylene glycol methyl ether acetate were mixed, and 1.5 parts by weight of dispersant BYK-2155 were added. The mixture was ultrasonically dispersed at 300W for 10 min. Then, 10 parts by weight of modified MgAlCe-BTC-LDH filler prepared in Example 2 and 5 parts by weight of polydopamine modified hexagonal boron nitride prepared in Example 3 were added. The mixture was ball-milled at 200 r / min for 2 h with a ball-to-material ratio of 5:1. Then, 30 parts by weight of polyetheramine D230 were added. The mixture was stirred at 40°C for 30 min and degassed under vacuum at -0.09 MPa for 20 min to obtain the coating slurry.

[0047] The aluminum alloy heat exchange tube was sandblasted with 7075 aluminum alloy to a thickness of 3 μm, degreased with acetone, and then the above-mentioned coating slurry was sprayed under high pressure of 0.3 MPa, with a wet film thickness of 120 μm. The coating was leveled at room temperature for 2 hours, cured at 80°C for 2 hours, and then cured at 120°C for 4 hours to obtain a protective coating for aluminum alloy heat exchange tubes with a dry film thickness of 70 μm.

[0048] Example 6: The preparation method of the protective coating for aluminum alloy heat exchange tubes includes the following steps:

[0049] 100 parts by weight of bisphenol A type epoxy resin (E44) and 42 parts by weight of propylene glycol methyl ether acetate were mixed, and 1.8 parts by weight of dispersant BYK-2155 were added. The mixture was ultrasonically dispersed at 300W for 10 min. Then, 12 parts by weight of modified MgAlCe-BTC-LDH filler prepared in Example 1 and 6 parts by weight of polydopamine modified hexagonal boron nitride prepared in Example 3 were added. The mixture was ball-milled at 200 r / min for 2 h with a ball-to-material ratio of 5:1. Then, 32 parts by weight of polyetheramine D230 were added. The mixture was stirred at 40℃ for 30 min and degassed under vacuum at -0.09 MPa for 20 min to obtain the coating slurry.

[0050] The aluminum alloy heat exchange tube was sandblasted with 7075 aluminum alloy to a thickness of 3 μm, degreased with acetone, and then the above-mentioned coating slurry was sprayed under high pressure of 0.3 MPa, with a wet film thickness of 120 μm. The coating was leveled at room temperature for 2 hours, cured at 80°C for 2 hours, and then cured at 120°C for 4 hours to obtain a protective coating for aluminum alloy heat exchange tubes with a dry film thickness of 70 μm.

[0051] Example 7: The preparation method of the protective coating for aluminum alloy heat exchange tubes includes the following steps:

[0052] 100 parts by weight of bisphenol A type epoxy resin (E44) and 42 parts by weight of propylene glycol methyl ether acetate were mixed, and 1.8 parts by weight of dispersant BYK-2155 were added. The mixture was ultrasonically dispersed at 300W for 10 min. Then, 12 parts by weight of modified MgAlCe-BTC-LDH filler prepared in Example 2 and 6 parts by weight of polydopamine modified hexagonal boron nitride prepared in Example 3 were added. The mixture was ball-milled at 200 r / min for 2 h with a ball-to-material ratio of 5:1. Then, 32 parts by weight of polyetheramine D230 were added. The mixture was stirred at 40℃ for 30 min and degassed under vacuum at -0.09 MPa for 20 min to obtain the coating slurry.

[0053] The aluminum alloy heat exchange tube was sandblasted with 7075 aluminum alloy to a thickness of 3 μm, degreased with acetone, and then the above-mentioned coating slurry was sprayed under high pressure of 0.3 MPa, with a wet film thickness of 120 μm. The coating was leveled at room temperature for 2 hours, cured at 80°C for 2 hours, and then cured at 120°C for 4 hours to obtain a protective coating for aluminum alloy heat exchange tubes with a dry film thickness of 70 μm.

[0054] Comparative Example 1: The preparation method of the modified MgAl-BTC-LDH filler includes the following steps:

[0055] Add 38.5g magnesium nitrate hexahydrate and 15.0g aluminum nitrate nonahydrate to 500mL of deionized water, place in a three-necked flask, and stir vigorously at 80℃ to obtain a nitrate mixed solution;

[0056] Dissolve 9.56 g BTC and 19.2 g sodium hydroxide in 500 mL of deionized water at 45 °C, and react at 45 °C for 20 min to obtain the intercalation solution.

[0057] The above intercalation solution was added dropwise to the above nitrate mixed solution. The pH value was maintained at 11 using 2 mol / L NaOH solution. The mixture was stirred at 80°C for 1.5 h under a nitrogen atmosphere. Then it was transferred to an autoclave, heated to 130°C and held for 24 h. The mixture was then washed with deionized water at 4000 rpm and filtered for 4 min until a neutral pH value was reached. Finally, it was dried in an oven at 70°C to obtain MgAl-BTC-LDH.

[0058] γ-aminopropyltriethoxysilane was prepared into a 100 ml solution with water and anhydrous ethanol at a volume ratio of 5:45:50. 10 ml of glacial acetic acid was added, and the mixture was hydrolyzed at 60 °C for 4 h. Then, 10 g of the above MgAl-BTC-LDH powder was added, and the mixture was stirred and reacted for another 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, filtered, dried, and ground into powder to obtain the modified MgAl-BTC-LDH filler.

[0059] Comparative Example 2: The preparation method of the modified MgAlCe-NO3-LDH filler includes the following steps:

[0060] Add 38.5g magnesium nitrate hexahydrate, 15.0g aluminum nitrate nonahydrate and 4.3g cerium nitrate hexahydrate to 500mL of deionized water, place in a three-necked flask, and stir vigorously at 80℃ to obtain a nitrate mixed solution.

[0061] Dissolve 3.4g of sodium nitrate and 19.2g of sodium hydroxide in 500ml of deionized water at 45℃ and react at 45℃ for 20min to obtain the intercalation solution.

[0062] The above intercalation solution was added dropwise to the above nitrate mixed solution. The pH value was maintained at 11 using 2 mol / L NaOH solution. The mixture was stirred at 80°C for 1.5 h under a nitrogen atmosphere. Then it was transferred to an autoclave, heated to 130°C and held for 24 h. After washing with deionized water at 4000 rpm and filtering for 4 min, the mixture was dried in an oven at 70°C to obtain MgAlCe-NO3-LDH.

[0063] γ-aminopropyltriethoxysilane was prepared into a 100 ml solution with water and anhydrous ethanol at a volume ratio of 5:45:50. 10 ml of glacial acetic acid was added, and the mixture was hydrolyzed at 60 °C for 4 h. Then, 10 g of the above MgAlCe-NO3-LDH powder was added, and the mixture was stirred and reacted for another 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, filtered, dried, and ground into powder to obtain the modified MgAlCe-NO3-LDH filler.

[0064] Compared with Example 4, Comparative Example 3 only replaced the modified MgAlCe-BTC-LDH filler prepared in Example 1 with the modified MgAl-BTC-LDH filler prepared in Comparative Example 1 by the same mass. The remaining components and preparation methods were completely the same as those in Example 4.

[0065] Compared with Example 4, Comparative Example 4 only replaced the modified MgAlCe-BTC-LDH packing prepared in Example 1 with the modified MgAlCe-NO3-LDH packing prepared in Comparative Example 2 by the same mass. The remaining components and preparation methods were completely the same as those in Example 4.

[0066] Compared with Example 4, Comparative Example 5 only replaced the modified MgAlCe-BTC-LDH filler prepared in Example 1 with the unmodified MgAlCe-BTC-LDH prepared in Example 1 by the same mass. The remaining components and preparation methods were completely the same as those in Example 4.

[0067] Compared with Example 4, Comparative Example 6 did not include the polydopamine-modified hexagonal boron nitride prepared in Example 3, while the remaining components and preparation methods were completely consistent with Example 4.

[0068] Compared with Example 4, Comparative Example 7 did not include the modified MgAlCe-BTC-LDH filler prepared in Example 1, but the remaining components and preparation methods were completely consistent with Example 4.

[0069] Performance testing

[0070] Thermal conductivity testing: The thermal diffusivity α of the coating was measured using a Netzsch laser thermal conductivity meter (NETZSCH, LFA447), and the specific heat capacity C of the coating was measured using a Netzsch analytical thermal synchrotron (NETZSCH, STA449). p Finally, the thermal conductivity λ of the coating is calculated using the following formula:

[0071] λ=C p ·ρ·α;

[0072] Where: λ - thermal conductivity of the coating; C p - Specific heat capacity of the coating; ρ - density of the coating; α - thermal diffusivity of the coating; test results are shown in Table 1;

[0073] Adhesion test: Following the single-sided column test method in section 9.4.2 of the national standard GB / T 5210—2006, the coatings of the aluminum alloy heat exchange tubes obtained in Examples 4-7 and Comparative Examples 3-7 were fixed to the surface of a prepared coated test plate with a steel plate as the substrate using adhesive. After the adhesive cured, a serrated cutting device was used to cut through the outer edge of the column to the substrate. After sample treatment, the adhesion was tested using a pull-off adhesion tester. During the test, the tensile force direction should be kept perpendicular to the test plate surface, and the stress increase rate should not exceed 1 MPa / s. One set of test combinations should be completed within 90 seconds, and each set of test data should consist of at least 6 sets of data. The test results are shown in Table 1.

[0074] Salt spray resistance test: Salt spray corrosion test was conducted using a salt spray corrosion test chamber (LYW-025 type, Shanghai Yiheng Scientific Instruments Co., Ltd.). A 5wt.% NaCl solution was continuously sprayed inside the chamber at a test temperature of 25℃, a spray rate of 1-2 mL / h, and a pH value maintained at 6.5-7.2. The scratched coating was placed in the salt spray chamber, and after 5000 hours, the corrosion of the coating and substrate was characterized and evaluated; the test results are shown in Table 1.

[0075] Chloride ion penetration resistance test: According to national standard GB / T 35490—2017, the coatings obtained in Examples 4-7 and Comparative Examples 3-7 were prepared into coating test pieces. The coated side of the test piece faced the 3% sodium chloride aqueous solution, and the paper substrate side faced the distilled water. After being placed at room temperature for 30 days, the chloride ion content in the distilled water was detected by ultraviolet spectroscopy, and the chloride ion penetration through the coating test piece [mg / (cm³)] was calculated. 2 The arithmetic mean of [d] was used to quantify the coating's resistance to chloride ion penetration; the test results are shown in Table 1.

[0076] Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves of the coated samples were measured using an electrochemical workstation (Zennium, Germany) to investigate the corrosion behavior of the coating in 3.5 wt% NaCl solution. A classic three-electrode testing system was employed, with a 1 cm × 1 cm platinum sheet as the auxiliary electrode, a saturated calomel electrode as the reference electrode, and the coated sample as the working electrode. The coated electrode was immersed in 3.5 wt% NaCl solution until the open-circuit potential stabilized, and then the EIS was measured. The frequency scan range was 10⁵–10² Hz, and the scan amplitude was 20 mA. The potentiodynamic polarization curve scan rate was 2 mV / s, and the scan range was ±0.2 V. The results are shown in Table 1.

[0077] Table 1: Statistical table of performance test data of specimens from Examples 4-7 and Comparative Examples 3-7

[0078]

[0079] As shown in Table 1, the coating material prepared by this invention, when applied to the surface of the aluminum alloy heat exchanger tube, imparts excellent thermal conductivity and corrosion resistance, significantly extending the service life of the aluminum alloy heat exchanger tube. In Comparative Example 3, the modified filler added contained no Ce, resulting in a significantly reduced corrosion resistance of the coating. In Comparative Example 4, the modified filler added was free of BTC, leading to edge cracks in the resulting coating. - As the penetration rate increased, the filler added in Comparative Example 5 was not modified with silane coupling agent, resulting in a decrease in coating adhesion and a decrease in corrosion resistance. In Comparative Example 6, no polydopamine-modified cubic boron nitride was added, resulting in a sharp drop in the thermal conductivity of the coating. In Comparative Example 7, no modified filler was added, resulting in a decrease in corrosion resistance and a reduction in thermal conductivity.

[0080] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0081] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A protective coating for aluminum alloy heat exchange tubes, characterized in that, It shall include at least the following parts by weight of raw materials: 100 parts of bisphenol A type epoxy resin; 28-32 parts of polyetheramine D230; 8-12 parts of modified MgAlCe-BTC-LDH filler; 4-6 parts of polydopamine-modified hexagonal boron nitride; 35-45 parts of propylene glycol methyl ether acetate; 1-2 parts of dispersant; The preparation method of the modified MgAlCe-BTC-LDH filler includes at least the following steps: Magnesium, aluminum and cerium nitrates are dissolved in deionized water to obtain a mixed nitrate solution; Sodium hydroxide and BTC were dissolved in deionized water, and after the reaction, an intercalation solution was obtained. The intercalation solution was added dropwise to the nitrate mixture, and sodium hydroxide solution was added to maintain the pH at 10-12. After the reaction, the solution was filtered, washed and dried to obtain MgAlCe-BTC-LDH. The MgAlCe-BTC-LDH was added to the hydrolysate of γ-aminopropyltriethoxysilane. After the reaction, the mixture was filtered, washed, dried, and ground to obtain the modified MgAlCe-BTC-LDH filler.

2. The protective coating for aluminum alloy heat exchange tubes according to claim 1, characterized in that, The molar ratio of magnesium ions, aluminum ions and cerium ions in the nitrate mixed solution is 3:0.8-1.2:0.1-0.3, and the total concentration of magnesium ions, aluminum ions and cerium ions is 0.3-0.5 mol / L.

3. The protective coating for aluminum alloy heat exchange tubes according to claim 1, characterized in that, The concentration of BTC in the intercalation solution is 0.08-0.12 mol / L, and the volume ratio of the nitrate mixed solution to the intercalation solution is 1:

1.

4. The protective coating for aluminum alloy heat exchange tubes according to claim 1, characterized in that, The mass ratio of MgAlCe-BTC-LDH to γ-aminopropyltriethoxysilane is 1:0.3-0.

5.

5. The protective coating for aluminum alloy heat exchange tubes according to claim 1, characterized in that, The preparation method of the polydopamine-modified hexagonal boron nitride includes the following steps: Tris(hydroxymethyl)aminomethane was added to deionized water, and dilute hydrochloric acid was added to adjust the pH to 8-9. Dopamine hydrochloride was added, and hexagonal boron nitride was added while stirring. After ultrasonic treatment, the mixture was filtered, washed, and dried to obtain polydopamine-modified hexagonal boron nitride.

6. The protective coating for aluminum alloy heat exchange tubes according to claim 5, characterized in that, The concentration of the dilute hydrochloric acid is 0.1 mol / L, and the mass ratio of the tris(hydroxymethyl)aminomethane, the dopamine hydrochloride, and the hexagonal boron nitride is 0.4-0.5:0.7-0.9:1-3.

7. The protective coating for aluminum alloy heat exchange tubes according to claim 1, characterized in that, The dispersant is one or a mixture of BYK-2155, BYK-307, or BYK-088.

8. A method for preparing a protective coating for an aluminum alloy heat exchanger tube as described in any one of claims 1-7, characterized in that, It includes at least the following preparation steps: Bisphenol A type epoxy resin and propylene glycol methyl ether acetate were mixed, a dispersant was added and ultrasonically dispersed, then modified MgAlCe-BTC-LDH filler and polydopamine-modified hexagonal boron nitride were added and ball-milled, followed by the addition of polyetheramine D230, stirring and degassing to obtain the coating slurry. The aluminum alloy heat exchange tube is subjected to sandblasting and acetone degreasing, then coated with the coating slurry. After curing, a protective coating for the aluminum alloy heat exchange tube is obtained.

9. A method for preparing a protective coating for an aluminum alloy heat exchanger tube according to claim 8, characterized in that, The thickness of the protective coating on the aluminum alloy heat exchange tube is 70-80 μm.

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