Protective coating for aluminum alloy heat exchange tube and preparation method of protective coating

Abstract

The invention discloses a protective coating for an aluminum alloy heat exchange tube and a preparation method of the protective coating, and relates to the technical field of coating materials. The protective coating for the aluminum alloy heat exchange tube at least comprises the following raw materials in parts by mass: 100 parts of bisphenol A epoxy resin; 28 to 32 parts of polyether amine D230; 8 to 12 parts of a modified MgAlCe-BTC-LDH filling material; 4 to 6 parts of polydopamine modified hexagonal boron nitride; 35 to 45 parts of propylene glycol methyl ether acetate; and 1-2 parts of a dispersant. The modified MgAlCe-BTC-LDH filler prepared by the invention realizes triple functions of Ce element oxidation resistance, BTC corrosion inhibition and layered barrier, and the polydopamine modified hexagonal boron nitride prepared by the invention effectively improves the heat-conducting property, solves the contradiction between insulation and heat conduction, and adapts to the protection requirement of an aluminum alloy heat exchange tube.

Description

Technical Field

[0001] The present invention relates to the technical field of coating materials, and in particular to a protective coating for an aluminum alloy heat exchange tube and a preparation method thereof. Background Art

[0002] Heat exchange tubes are one of the components of a heat exchanger, placed within the cylinder and used to exchange heat between two media. They possess high thermal conductivity and excellent isothermal properties. They can rapidly transfer heat from one point to another with virtually no heat loss, earning them the name "heat transfer superconductor," with a thermal conductivity thousands of times greater than that of copper. Common 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 components with an aluminum-based alloy as their core material. Through optimized alloy composition and heat treatment, they achieve high hardness, elongation, and acid and corrosion resistance. Utilizing precision manufacturing processes such as melt casting, extrusion molding, and fin spinning, these tubes achieve a 100% yield rate, with no cracks in the curved areas during bending. Due to their lightweight and high thermal conductivity, aluminum alloy heat exchange tubes are widely used in applications such as automotive radiators and industrial condensers.

[0003] When aluminum alloys are exposed to the natural environment, they will spontaneously form a dense aluminum oxide film. This film acts as a natural barrier and can provide a considerable degree of corrosion protection in neutral or near-neutral environments. However, when aluminum alloys face extreme or harsh environments, such as high humidity, high salinity marine atmosphere and seawater underwater environment, or rich in halogen ions, especially chloride ions Cl - In the presence of such aggressive ions, the protective aluminum oxide film has limited effectiveness. These corrosive agents can easily penetrate weak points in the aluminum oxide film and directly contact the aluminum alloy substrate, causing pinhole corrosion, pitting, or other more extensive localized corrosion, severely damaging the material's structure and performance. To overcome this challenge, the industry has adopted a variety of complex surface treatment technologies to enhance the corrosion resistance of aluminum alloys. Among them, methods such as anodizing, electroless plating, and conversion coatings use physical or chemical means to build a more robust protective layer on the aluminum alloy surface. Existing protective coatings often use silicone resins, epoxy resins, or zinc-aluminum composite coatings. While organic coatings offer good corrosion resistance, they are susceptible to aging and cracking at high temperatures and have low thermal conductivity, significantly reducing heat transfer efficiency. Metallic coatings (such as zinc-aluminum coatings) offer excellent thermal conductivity, but their corrosion resistance relies on the sacrificial anode effect, which degrades rapidly in highly corrosive environments. Furthermore, their interfacial bonding with the aluminum alloy substrate is weak, leading to flaking. Ceramic coatings are resistant to high temperatures but are brittle and have poor thermal shock resistance, making them unable to withstand the thermal cycling stresses of heat exchange tubes. Therefore, developing a single-layer protective coating with high thermal conductivity, strong corrosion resistance and excellent interface bonding strength has become the key to solving the failure problem of aluminum alloy heat exchange tubes. Summary of the Invention

[0004] The purpose of the present invention is to provide a protective coating for aluminum alloy heat exchange tubes and a preparation method thereof, to solve the following technical problems: The existing protective coatings for aluminum alloy heat exchange tubes have problems such as insufficient thermal conductivity, poor corrosion resistance and easy falling off.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A protective coating for an aluminum alloy heat exchange tube comprises at least the following raw materials in parts by weight: 100 parts of bisphenol A 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.

[0006] As a further embodiment of the present invention, the preparation method of the modified MgAlCe-BTC-LDH filler comprises at least the following steps: dissolving nitrates of magnesium, aluminum and cerium in deionized water to obtain a nitrate mixed solution; Sodium hydroxide and BTC are dissolved in deionized water and reacted to obtain an intercalation solution; The intercalation solution is dropped into the nitrate mixed solution, and a sodium hydroxide solution is added to maintain the pH at 10-12. After the reaction, the mixture is filtered, washed, and dried to obtain MgAlCe-BTC-LDH; The MgAlCe-BTC-LDH is added to the hydrolyzed solution of γ-aminopropyltriethoxysilane, and after reaction, the mixture is filtered, washed, dried and ground to obtain a modified MgAlCe-BTC-LDH filler.

[0007] As a further embodiment 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.

[0008] As a further embodiment 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.

[0009] As a further embodiment of the present invention, the mass ratio of the MgAlCe-BTC-LDH to the γ-aminopropyltriethoxysilane is 1:0.3-0.5.

[0010] As a further embodiment of the present invention: the preparation method of the polydopamine-modified hexagonal boron nitride comprises the following steps: Tris(hydroxymethyl)aminomethane) is added to deionized water, and diluted hydrochloric acid is added to adjust the pH to 8-9, dopamine hydrochloride is added, and hexagonal boron nitride is added under stirring. After ultrasonic treatment, the mixture is filtered, washed and dried to obtain polydopamine-modified hexagonal boron nitride.

[0011] As a further embodiment 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.

[0012] As a further embodiment of the present invention, the dispersant is a mixture of one or more of BYK-2155, BYK-307 or BYK-088.

[0013] A method for preparing a protective coating for an aluminum alloy heat exchange tube as described in any one of the above, comprising at least the following preparation steps: Bisphenol A epoxy resin and propylene glycol methyl ether acetate were mixed, a dispersant was added and ultrasonically dispersed, and then modified MgAlCe-BTC-LDH filler and polydopamine-modified hexagonal boron nitride were added and ball-milled, and then polyetheramine D230 was added and stirred for degassing to obtain a coating slurry; The aluminum alloy heat exchange tube is subjected to sandblasting and acetone degreasing treatment, and then the coating slurry is sprayed on the tube. After curing, a protective coating for the aluminum alloy heat exchange tube is obtained.

[0014] As a further solution of the present invention: the thickness of the protective coating for the aluminum alloy heat exchange tube is 70-80 μm.

[0015] Beneficial effects of the present invention: The protective coating for aluminum alloy heat exchange tubes prepared by the present invention is based on a bisphenol A epoxy resin with polyetheramine D230 added. The benzene ring structure of the bisphenol A epoxy imparts high hardness to the coating, and combined with a three-dimensional cross-linked network, it significantly improves surface wear resistance. The polyether segments of the polyetheramine D230 absorb impact energy through chain movement, making the aluminum alloy heat exchange tubes less susceptible 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 demanding applications such as automotive radiators and offshore platform heat exchangers, extending the service life of the aluminum alloy heat exchange tubes. Among them, the modified MgAlCe-BTC-LDH filler realizes the triple functions of Ce element anti-oxidation, BTC corrosion inhibition and layered barrier, which can directly adapt to the protection needs of aluminum alloy heat exchange tubes, further improve 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 corrosion resistance of the coating with the modified MgAlCe-BTC-LDH filler.

[0016] The MgAlCe-BTC-LDH filler prepared in this invention is a typical layered double hydroxide, modified with a silane coupling agent and uniformly dispersed within an epoxy matrix, forming a dense, stacked barrier. This structure significantly reduces the penetration rate of corrosive media into 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, the BTC between the LDH layers is slowly released through an anion exchange mechanism. The carboxyl groups in the BTC molecules form a stable chelate film with the aluminum ions on the aluminum alloy surface, inhibiting the dissolution of the aluminum ions. Simultaneously, the cerium ions in the LDH hydrolyze at the corrosion site to form cerium hydroxide, which is further converted into a dense composite oxide film, blocking the continued corrosion reaction.

[0017] The polydopamine-modified hexagonal boron nitride prepared by the present invention has catechol groups in the polydopamine that can form hydrogen bonds and covalent bonds with the hydroxyl groups in the epoxy matrix and the hydroxyl groups on the aluminum alloy surface, thereby strengthening the interface between the coating and the substrate and preventing interfacial gaps from becoming penetration channels for corrosive media, thereby improving the adhesion between the coating and the substrate and the density of the coating. At the same time, the flaky structure of the hexagonal boron nitride can fill the micropores generated during the curing process of the epoxy matrix, forming a "cross-barrier network" with the layered structure of the LDH, further extending the penetration path of the corrosive media. Cubic boron nitride itself has excellent thermal conductivity. After modification with polydopamine, the compatibility of its surface amino groups with the epoxy matrix is ​​improved, forming a continuous thermal conductive path in the matrix, improving the thermal conductivity of the coating. Furthermore, the cerium element in the MgAlCe-BTC-LDH can reduce phonon scattering within the coating, reducing thermal resistance. DETAILED DESCRIPTION

[0018] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0019] Example 1 The preparation method of the modified MgAlCe-BTC-LDH filler comprises the following steps: 36.64 g of magnesium nitrate hexahydrate, 17.86 g of aluminum nitrate nonahydrate, and 4.13 g of cerium nitrate hexahydrate were added to 500 mL of deionized water in a three-necked flask and vigorously stirred at 80° C. to obtain a nitrate mixed solution; 9.56 g of BTC and 19.2 g of sodium hydroxide were dissolved in 500 ml of deionized water at 45 °C and reacted at 45 °C for 20 min to obtain an intercalation solution; The intercalation liquid was added dropwise to the nitrate mixed solution, and the pH value was maintained at 11 using a 2 mol / L NaOH solution. The mixture was stirred at 80°C for 1.5 h under a nitrogen atmosphere, and then transferred to an autoclave. The mixture was heated to 130°C and maintained for 24 h, and then centrifuged and filtered with deionized water at 4000 rpm for 4 min until a neutral pH value was reached. The mixture was then dried in an oven at 70°C to obtain MgAlCe-BTC-LDH. γ-Aminopropyltriethoxysilane, water and anhydrous ethanol were prepared into a 100 ml solution in a volume ratio of 5:45:50, and 1 ml of glacial acetic acid was added. After hydrolysis at 60°C for 4 hours, 10 g of the above-mentioned MgAlCe-BTC-LDH powder was added and the reaction was continued with stirring for 1 hour. After the reaction, the mixture was centrifuged and washed three times, then filtered, dried and ground into powder to obtain a modified MgAlCe-BTC-LDH filler.

[0020] Example 2 The preparation method of the modified MgAlCe-BTC-LDH filler comprises the following steps: 44.46 g of magnesium nitrate hexahydrate, 21.01 g of aluminum nitrate nonahydrate, and 6.52 g of cerium nitrate hexahydrate were added to 500 mL of deionized water in a three-necked flask and vigorously stirred at 80° C. to obtain a nitrate mixed solution; 11.47 g of BTC and 19.2 g of sodium hydroxide were dissolved in 500 ml of deionized water at 45°C and reacted at 45°C for 20 min to obtain an intercalation solution; The intercalation liquid was added dropwise to the nitrate mixed solution, and the pH value was maintained at 11 using a 2 mol / L NaOH solution. The mixture was stirred at 80°C for 1.5 h under a nitrogen atmosphere, and then transferred to an autoclave. The mixture was heated to 130°C and maintained for 24 h, and then centrifuged and filtered with deionized water at 4000 rpm for 4 min until a neutral pH value was reached. The mixture was then dried in an oven at 70°C to obtain MgAlCe-BTC-LDH. γ-Aminopropyltriethoxysilane, water and anhydrous ethanol were prepared into a 100 ml solution in a volume ratio of 5:45:50, and 10 ml of glacial acetic acid was added. After hydrolysis at 60°C for 4 hours, 10 g of the above-mentioned MgAlCe-BTC-LDH powder was added and the reaction was continued with stirring for 1 hour. After the reaction, the mixture was centrifuged and washed three times, filtered and dried, and ground into powder to obtain a modified MgAlCe-BTC-LDH filler.

[0021] Example 3 The preparation method of polydopamine-modified hexagonal boron nitride comprises the following steps: 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 under constant stirring, followed by 20 g of hexagonal boron nitride powder under rapid stirring. The mixture was ultrasonically treated 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. The solid and liquid were separated, and the mixture was dried at 60 ° C under vacuum for 24 h to obtain polydopamine-modified hexagonal boron nitride.

[0022] Example 4 A method for preparing a protective coating for an aluminum alloy heat exchange tube comprises the following steps: 100 parts by mass of bisphenol A epoxy resin (E44) and 40 parts by mass of propylene glycol methyl ether acetate were mixed, 1.5 parts by mass of dispersant BYK-2155 were added, and ultrasonic dispersion was performed at 300W for 10 minutes. Then, 10 parts by mass of the modified MgAlCe-BTC-LDH filler prepared in Example 1 and 5 parts by mass of polydopamine-modified hexagonal boron nitride prepared in Example 3 were added. The mixture was ball-to-material ratio was 5:1 and ball milling was performed at 200 r / min for 2 hours. Then, 30 parts by mass of polyetheramine D230 was added, and the mixture was stirred at 40°C for 30 minutes. The mixture was vacuum degassed at -0.09 MPa for 20 minutes to obtain a coating slurry. The aluminum alloy heat exchange tube was sandblasted with 7075 aluminum alloy to an Ra of 3 μm and degreased with acetone. The above coating slurry was sprayed at a high pressure of 0.3 MPa with a wet film thickness of 120 μm. The tube 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 the aluminum alloy heat exchange tube with a dry film thickness of 70 μm.

[0023] Example 5 A method for preparing a protective coating for an aluminum alloy heat exchange tube comprises the following steps: 100 parts by mass of bisphenol A epoxy resin (E44) and 40 parts by mass of propylene glycol methyl ether acetate were mixed, 1.5 parts by mass of dispersant BYK-2155 were added, and ultrasonic dispersion was performed at 300W for 10 minutes. Then, 10 parts by mass of the modified MgAlCe-BTC-LDH filler prepared in Example 2 and 5 parts by mass of polydopamine-modified hexagonal boron nitride prepared in Example 3 were added. The mixture was ball-to-material ratio was 5:1 and ball milling was performed at 200 r / min for 2 hours. Then, 30 parts by mass of polyetheramine D230 was added, and the mixture was stirred at 40°C for 30 minutes. The mixture was vacuum degassed at -0.09 MPa for 20 minutes to obtain a coating slurry. The aluminum alloy heat exchange tube was sandblasted with 7075 aluminum alloy to an Ra of 3 μm and degreased with acetone. The above coating slurry was sprayed at a high pressure of 0.3 MPa with a wet film thickness of 120 μm. The tube 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 the aluminum alloy heat exchange tube with a dry film thickness of 70 μm.

[0024] Example 6 A method for preparing a protective coating for an aluminum alloy heat exchange tube comprises the following steps: 100 parts by mass of bisphenol A epoxy resin (E44) and 42 parts by mass of propylene glycol methyl ether acetate were mixed, 1.8 parts by mass of dispersant BYK-2155 were added, and ultrasonic dispersion was performed at 300W for 10 minutes. Then, 12 parts by mass of the modified MgAlCe-BTC-LDH filler prepared in Example 1 and 6 parts by mass of polydopamine-modified hexagonal boron nitride prepared in Example 3 were added. The mixture was ball-to-material ratio was 5:1 and ball milling was performed at 200 rpm for 2 hours. Then, 32 parts by mass of polyetheramine D230 was added, and the mixture was stirred at 40°C for 30 minutes. The mixture was vacuum degassed at -0.09 MPa for 20 minutes to obtain a coating slurry. The aluminum alloy heat exchange tube was sandblasted with 7075 aluminum alloy to an Ra of 3 μm and degreased with acetone. The above coating slurry was sprayed at a high pressure of 0.3 MPa with a wet film thickness of 120 μm. The tube 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 the aluminum alloy heat exchange tube with a dry film thickness of 70 μm.

[0025] Example 7 A method for preparing a protective coating for an aluminum alloy heat exchange tube comprises the following steps: Mix 100 parts by mass of bisphenol A type epoxy resin (E44) and 42 parts by mass of propylene glycol methyl ether acetate, add 1.8 parts by mass of dispersant BYK-2155, ultrasonic dispersion for 10 min at 300 W, then add 12 parts by mass of modified MgAlCe-BTC-LDH filler prepared in Example 2 and 6 parts by mass of polydopamine modified hexagonal boron nitride prepared in Example 3, ball milling treatment for 2 h at a ball-to-material ratio of 5:1 and a rotation speed of 200 r / min, then add 32 parts by mass of polyetheramine D230, stirring at 40℃ for 30 min, vacuum degassing at -0.09 MPa for 20 min, to obtain a coating slurry; Sandblast the aluminum alloy heat exchange pipe to Ra of 3 μm, acetone degreasing treatment, high pressure spraying of the above coating slurry at 0.3 MPa, wet film thickness of 120 μm; room temperature leveling for 2 h, first curing at 80℃ for 2 h, then curing at 120℃ for 4 h, to obtain a dry film thickness of 70 μm of the protective coating for the aluminum alloy heat exchange pipe.

[0026] The preparation method of the modified MgAl-BTC-LDH filler of Comparative Example 1 comprises the following steps: Add 38.5 g of magnesium nitrate hexahydrate and 15.0 g of aluminum nitrate nonahydrate to 500 mL of deionized water, place in a three-necked flask, and stir vigorously at 80℃ to obtain a mixed nitrate solution; Dissolve 9.56 g of BTC and 19.2 g of sodium hydroxide in 500 mL of deionized water at 45℃, and react at 45℃ for 20 min to obtain an intercalation solution; Add the above intercalation solution dropwise to the above mixed nitrate solution, maintain the pH value at 11 using 2 mol / L NaOH solution, stir at 80℃ for 1.5 h under a nitrogen atmosphere, then transfer to an autoclave, heat to 130℃ and maintain for 24 h, then centrifuge and wash with deionized water at a rotation speed of 4000 r / min and filter for 4 min until the pH value reaches neutral, then dry in an oven at 70℃ to obtain MgAl-BTC-LDH; Prepare a 100 ml solution of γ-aminopropyltriethoxysilane, water and anhydrous ethanol in a volume ratio of 5:45:50, add 10 ml of glacial acetic acid, hydrolyze at 60℃ for 4 h, then add 10 g of the above MgAl-BTC-LDH powder and continue to stir for 1 h, after the reaction is completed, centrifuge and wash the mixture three times, then suction filter, dry and grind into powder to obtain the modified MgAl-BTC-LDH filler.

[0027] The preparation method of the modified MgAlCe-NO3-LDH filler of Comparative Example 2 comprises the following steps: 38.5 g of magnesium nitrate hexahydrate, 15.0 g of aluminum nitrate nonahydrate, and 4.3 g of cerium nitrate hexahydrate were added to 500 mL of deionized water in a three-necked flask and vigorously stirred at 80° C. to obtain a nitrate mixed solution; Dissolve 3.4 g of sodium nitrate and 19.2 g of sodium hydroxide in 500 ml of deionized water at 45°C and react at 45°C for 20 min to obtain an intercalation solution; The intercalation liquid was added dropwise to the nitrate mixed solution, and the pH value was maintained at 11 using a 2 mol / L NaOH solution. The mixture was stirred at 80°C for 1.5 h under a nitrogen atmosphere, and then transferred to an autoclave. The mixture was heated to 130°C and maintained for 24 h, and then centrifuged and filtered with deionized water at 4000 rpm for 4 min until a neutral pH value was reached. The mixture was then dried in an oven at 70°C to obtain MgAlCe-NO3-LDH. γ-Aminopropyltriethoxysilane was mixed with water and anhydrous ethanol in a volume ratio of 5:45:50 to prepare a 100 ml solution, and 10 ml of glacial acetic acid was added. After hydrolysis at 60°C for 4 h, 10 g of the above-mentioned MgAlCe-NO3-LDH powder was added and the reaction was continued with stirring for 1 h. After the reaction, the mixture was centrifuged and washed three times, filtered, dried, and ground into powder to obtain a modified MgAlCe-NO3-LDH filler.

[0028] Comparative Example 3 Compared with Example 4, Comparative Example 3 only replaces the modified MgAlCe-BTC-LDH filler prepared in Example 1 added in Example 4 with the modified MgAl-BTC-LDH filler prepared in Comparative Example 1, and the other components and preparation methods are exactly the same as those in Example 4.

[0029] Comparative Example 4 Compared with Example 4, Comparative Example 4 only replaces the modified MgAlCe-BTC-LDH filler prepared in Example 1 added in Example 4 with the modified MgAlCe-NO3-LDH filler prepared in Comparative Example 2. The other components and preparation methods are exactly the same as those in Example 4.

[0030] Comparative Example 5 Compared with Example 4, Comparative Example 5 only replaces the modified MgAlCe-BTC-LDH filler prepared in Example 1 added in Example 4 with the unmodified MgAlCe-BTC-LDH prepared in Example 1, and the other components and preparation methods are exactly the same as those in Example 4.

[0031] Comparative Example 6 Compared with Example 4, in Comparative Example 6, the polydopamine-modified hexagonal boron nitride prepared in Example 3 was not added, and the remaining components and preparation method were completely consistent with those in Example 4.

[0032] Comparative Example 7 Compared with Example 4, in Comparative Example 7, the modified MgAlCe-BTC-LDH filler prepared in Example 1 was not added, and the remaining components and preparation method were completely consistent with those in Example 4.

[0033] Performance testing Thermal conductivity test: The thermal diffusivity α of the coating was tested using a NETZSCH laser thermal conductivity meter (NETZSCH, LFA447), and the specific heat capacity C of the coating was tested using a NETZSCH thermal analyzer (NETZSCH, STA449). p , and finally the thermal conductivity λ of the coating is calculated by the following formula: λ=C p ·ρ·α; Where: λ-thermal conductivity of coating; C p -Specific heat capacity of the coating; ρ-density of the coating; α-thermal diffusivity of the coating; the test results are shown in Table 1; Adhesion test: In accordance with the single-sided test column test method in Section 9.4.2 of the national standard GB / T 5210-2006, the aluminum alloy heat exchange tube coatings obtained in Examples 4-7 and Comparative Examples 3-7 were fixed to the surface of a prepared coating test plate with a steel plate as the substrate using an adhesive. After the adhesive solidified, a sawtooth cutting device was used to cut through the outer periphery of the test column to the substrate. After the sample was processed, adhesion was tested using a pull-off adhesion tester. During the test, the tensile force direction should be maintained perpendicular to the test plate surface, and the stress increase rate should not exceed 1 MPa / s. A set of test combinations should be tested within 90 seconds. Each set of test data consists of at least 6 sets of data. The test results are shown in Table 1. Salt spray resistance test: A salt spray corrosion test chamber (LYW-025, Shanghai Yiheng Scientific Instrument Co., Ltd.) was used for salt spray testing. A 5 wt.% NaCl solution was continuously sprayed inside the chamber at a temperature of 25°C, a spray rate of 1-2 mL / h, and a pH value maintained between 6.5 and 7.2. The scratched coating was placed in the chamber for 5,000 hours, and the corrosion of the coating and substrate was characterized and evaluated. The test results are shown in Table 1. Chloride ion penetration resistance test: In accordance with the 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 a 3% sodium chloride aqueous solution, and the paper substrate side faced distilled water. After standing at room temperature for 30 days, the chloride ion content in the distilled water was measured by ultraviolet spectroscopy, and the chloride ion penetration rate through the coating test piece was calculated [mg / (cm 2 ·d)] is used to quantitatively characterize the coating's resistance to chloride ion permeability; the test results are shown in Table 1; Electrochemical impedance spectroscopy: An electrochemical workstation (Zennium, Germany) was used to measure the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves of the coating samples to study the corrosion behavior of the coating in a 3.5wt% NaCl solution. A classic three-electrode test system was used, with a 1cm×1cm platinum sheet as the auxiliary electrode, a saturated calomel electrode as the reference electrode, and the coating sample as the working electrode. The coating electrode was immersed in a 3.5wt% NaCl solution and the open circuit potential was stabilized before the EIS of the coating was measured. The frequency sweep range was 105-102Hz, and the sweep amplitude was 20mA. The potentiodynamic polarization curve sweep rate was 2mV / s, and the sweep range was ±0.2V. The test results are shown in Table 1. Table 1: Statistical table of performance test data of test pieces of Examples 4-7 and Comparative Examples 3-7 As shown in Table 1, the coating material prepared by the present invention is coated on the surface of the aluminum alloy heat exchange tube, giving the aluminum alloy heat exchange tube excellent thermal conductivity and corrosion resistance, greatly extending the service life of the aluminum alloy heat exchange tube. In Comparative Example 3, the modified filler added did not contain Ce, and the corrosion resistance of the obtained coating was significantly reduced. In Comparative Example 4, the modified filler added did not contain BTC, and the edge cracks of the obtained coating were small. - The permeability increased. The filler added in Comparative Example 5 was not modified with a silane coupling agent, and the adhesion of the obtained coating decreased, resulting in a decrease in corrosion resistance. In Comparative Example 6, polydopamine-modified cubic boron nitride was not added, and the thermal conductivity of the obtained coating dropped sharply. In Comparative Example 7, no modified filler was added, and the corrosion resistance and thermal conductivity were also reduced.

[0034] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these 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 any one or more embodiments or examples.

[0035] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A protective coating for aluminum alloy heat exchange tubes, characterized in that: At least include the following raw materials by mass: 100 parts of bisphenol A 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.

2. The protective coating for aluminum alloy heat exchange tube according to claim 1, characterized in that: The preparation method of the modified MgAlCe-BTC-LDH filler comprises at least the following steps: dissolving nitrates of magnesium, aluminum and cerium in deionized water to obtain a nitrate mixed solution; Sodium hydroxide and BTC are dissolved in deionized water and reacted to obtain an intercalation solution; The intercalation solution is dropped into the nitrate mixed solution, and a sodium hydroxide solution is added to maintain the pH at 10-12. After the reaction, the solution is filtered, washed, and dried to obtain MgAlCe-BTC-LDH; The MgAlCe-BTC-LDH is added to the hydrolyzed solution of γ-aminopropyltriethoxysilane, and after reaction, the mixture is filtered, washed, dried and ground to obtain a modified MgAlCe-BTC-LDH filler.

3. The protective coating for aluminum alloy heat exchange tube according to claim 2, 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 the magnesium ions, aluminum ions and cerium ions is 0.3-0.5 mol / L.

4. The protective coating for aluminum alloy heat exchange tube according to claim 2, 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.

5. The protective coating for aluminum alloy heat exchange tube according to claim 2, characterized in that: The mass ratio of the MgAlCe-BTC-LDH to the γ-aminopropyltriethoxysilane is 1:0.3-0.

5.

6. The protective coating for aluminum alloy heat exchange tube according to claim 1, characterized in that: The preparation method of the polydopamine-modified hexagonal boron nitride comprises the following steps: Tris(hydroxymethyl)aminomethane) is added to deionized water, and diluted hydrochloric acid is added to adjust the pH to 8-9, dopamine hydrochloride is added, and hexagonal boron nitride is added under stirring. After ultrasonic treatment, the mixture is filtered, washed and dried to obtain polydopamine-modified hexagonal boron nitride.

7. The protective coating for aluminum alloy heat exchange tube according to claim 6, 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.

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

9. A method for preparing a protective coating for an aluminum alloy heat exchange tube according to any one of claims 1 to 8, characterized in that: The method comprises at least the following preparation steps: Bisphenol A epoxy resin and propylene glycol methyl ether acetate were mixed, a dispersant was added and ultrasonically dispersed, and then modified MgAlCe-BTC-LDH filler and polydopamine-modified hexagonal boron nitride were added and ball-milled, and then polyetheramine D230 was added and stirred for degassing to obtain a coating slurry; The aluminum alloy heat exchange tube is subjected to sandblasting and acetone degreasing treatment, and then the coating slurry is sprayed on the tube. After curing, a protective coating for the aluminum alloy heat exchange tube is obtained.

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

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