Corrosion-resistant radar wave-absorbing coating and preparation method thereof

Abstract

The invention provides a corrosion-resistant radar wave-absorbing coating and a preparation method thereof, and belongs to the technical field of functional composite materials. The coating is of a three-layer structure composed of a bottom layer, a middle layer and a surface layer. The bottom layer is prepared from the following raw materials: fluorinated polyurethane, modified FeSiCr, modified graphene nanoplatelets, zinc phosphate and propylene glycol methyl ether acetate; the middle layer is prepared from the following raw materials: fluorinated polyurethane, a mixture of modified FeSiCr and modified FeSiAl, hydroxyl functionalized multi-walled carbon nanotubes and propylene glycol methyl ether acetate; the surface layer is prepared from the following raw materials: UV cured polyurethane, glass flakes, hydroxylated nano boron nitride, an ultraviolet light absorber, modified fumed silica and propylene glycol methyl ether acetate. According to the invention, L / S / C wave band broadband wave-absorbing performance is realized through gradient composite structure design, and the obtained coating has excellent salt mist resistance, ultraviolet resistance and humidity and heat resistance through component and structure optimization.

Description

Technical Field

[0001] The present invention relates to the technical field of functional composite materials, and particularly to a corrosion-resistant radar absorbing coating and a preparation method thereof. Background Art

[0002] Wind power equipment in the marine environment (such as wind power towers, blades, offshore platforms, etc.) has a large electromagnetic wave reflection area. Coating absorbing materials on wind power towers and blades can significantly reduce the electromagnetic reflectivity in the L, S, and C bands. However, being exposed to extreme conditions such as high salt fog, high humidity, strong ultraviolet radiation, and damp heat cycling for a long time poses severe challenges to the corrosion resistance, weather resistance, and functionality of the materials.

[0003] Currently, the application of traditional protective radar absorbing materials (RAM) in the marine environment has the following key problems: (1) Salt fog corrosion: Chloride ions in seawater penetrate the coating, accelerating the electrochemical corrosion of the metal substrate, resulting in coating blistering and peeling. (2) Ultraviolet aging: Long-term ultraviolet irradiation causes the degradation of the polymer matrix, manifested as coating powdering, discoloration, and a decline in mechanical properties.

[0004] At the same time, the existing radar absorbing coatings have a narrow frequency band coverage: A single absorber (such as FeSiAl) is only effective for specific frequency bands (such as the L / S band), and it is difficult to cover the wide-frequency requirements of L / S / C (1 - 8 GHz). Poor environmental adaptability: Magnetic alloy powders (such as FeSiAl) are easily oxidized, and carbon fibers are prone to galvanic corrosion in a high salt fog environment, resulting in coating failure. Thick coatings and low efficiency: To achieve broadband absorption, traditional solutions require an increase in coating thickness (>4 mm), and at the same time rely on a thermal curing process (time-consuming >4 hours), making it difficult to meet the requirements of rapid offshore construction.

[0005] Therefore, there is an urgent need for an absorbing coating that can achieve strong broadband absorption in the L / S / C bands and at the same time has strong salt fog and corrosion resistance. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a corrosion-resistant radar absorbing coating and a preparation method thereof. The present invention uses FeSiCr / FeSiAl magnetic alloy powder as the core absorber, realizes broadband absorption performance in the L / S / C bands through gradient composite structure design, and realizes excellent salt fog resistance, ultraviolet resistance, and damp heat resistance of the obtained coating through component and structure optimization.

[0007] To achieve the above object, the present invention provides the following technical solutions: One of the technical solutions of the present invention is a corrosion-resistant radar absorbing coating, and the coating consists of a bottom layer, an intermediate layer and a surface layer to form a three-layer structure; the raw materials of the bottom layer are fluorinated polyurethane, modified FeSiCr, modified graphene microflakes, zinc phosphate and propylene glycol methyl ether acetate; the raw materials of the intermediate layer are a mixture of fluorinated polyurethane, modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes and propylene glycol methyl ether acetate; the raw materials of the surface layer are UV-cured polyurethane, glass flakes, hydroxylated nano-boron nitride, ultraviolet absorber, modified fumed silica and propylene glycol methyl ether acetate.

[0008] Another technical solution of the present invention is a preparation method of the above corrosion-resistant radar absorbing coating, comprising the following steps: After uniformly mixing modified FeSiCr, modified graphene microflakes, zinc phosphate, propylene glycol methyl ether acetate and fluorinated polyurethane, coat them on a substrate and cure for 1 to obtain the bottom layer; After uniformly mixing a mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, propylene glycol methyl ether acetate and fluorinated polyurethane, coat them on the surface of the bottom layer and cure for 2 to obtain the intermediate layer; After uniformly mixing glass flakes, hydroxylated nano-boron nitride, ultraviolet absorber, modified fumed silica, propylene glycol methyl ether acetate and UV-cured polyurethane, coat them on the surface of the intermediate layer and cure for 3 to obtain the radar absorbing coating.

[0009] The present invention discloses the following technical effects: The present invention adopts a three-layer structure, a gradient structure of a bottom layer (high FeSiCr content), an intermediate layer (FeSiCr / FeSiAl mixture), and a surface layer (protective / conductive layer). Through the synergistic effect of FeSiCr and FeSiAl, impedance gradual change and wide-band absorption in L, S, and C bands are achieved; at the same time, the surface layer not only plays the role of impedance transition but also enhances the weather resistance of the entire structure.

[0010] The alloy absorbent selected by the present invention itself has strong salt spray resistance and corrosion resistance; fluorinated modified polyurethane (hydrolysis-resistant, salt spray-resistant) is used, and nano-boron nitride (h-BN) is added to improve thermal conductivity; glass flakes are introduced to extend the corrosion path, and ultraviolet absorbers are used to inhibit photoaging, comprehensively realizing the enhancement of weather resistance.

[0011] The spraying process is adopted for the bottom layer and the intermediate layer of the present invention, and ultraviolet light curing is carried out for the surface layer (completed within 60 seconds), meeting the requirements of on-site construction at sea. Detailed implementation manners

[0012] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0013] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0014] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0015] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0016] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0017] Unless otherwise specified, room temperature in the present invention refers to 25±5°C.

[0018] A first aspect of the present invention provides a corrosion-resistant radar absorbing coating, comprising a three-layer structure consisting of a base layer, an intermediate layer, and a surface layer; the base layer is made of fluorinated polyurethane, modified FeSiCr, modified graphene microplatelets, zinc phosphate, and propylene glycol methyl ether acetate; the intermediate layer is made of fluorinated polyurethane, a mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, and propylene glycol methyl ether acetate; and the surface layer is made of UV-cured polyurethane, glass flakes, hydroxylated nano-boron nitride, an ultraviolet absorber, modified fumed silica, and propylene glycol methyl ether acetate.

[0019] In a preferred embodiment of the present invention, the modified FeSiCr is FeSiCr modified by a silane coupling agent; the modified FeSiAl is FeSiAl modified by a silane coupling agent; the modified graphene microplate is a graphene microplate modified by a silane coupling agent; the modified fumed silica is fumed silica that has been hydrophobic treated; and the silane coupling agent is silane coupling agent KH-550.

[0020] In the present invention, the preparation method of the modified FeSiCr is as follows: The pretreated FeSiCr is added to an aqueous solution of a silane coupling agent (KH-550) and stirred for reaction; the pretreatment is washing and drying; the concentration of the aqueous solution of the silane coupling agent is 1.0-2.0 wt%; the mass-to-volume ratio of the FeSiCr to the aqueous solution of the silane coupling agent is 1 g:10 mL; the temperature of the stirring reaction is 50 °C, the time is 90 min, and the rotation speed is 300 rpm; after the stirring reaction is completed, the steps of washing and drying the obtained product in sequence are further included; the particle size of the FeSiCr is 2-5 μm, and the morphology is irregular particles, spherical-like.

[0021] The preparation method of the modified FeSiAl is as follows: The pretreated FeSiAl is added to an aqueous solution of a silane coupling agent (KH-550) and stirred for reaction; the pretreatment is washing and drying; the concentration of the aqueous solution of the silane coupling agent is 1.0-2.0 wt%; the mass-to-volume ratio of the FeSiAl to the aqueous solution of the silane coupling agent is 1 g:10 mL; the temperature of the stirring reaction is 50 °C, the time is 90 min, and the rotation speed is 300 rpm; after the stirring reaction is completed, the steps of washing and drying the obtained product in sequence are further included; the sheet diameter of the FeSiAl is 1-3 μm, and the morphology is flaky.

[0022] The preparation method of the modified graphene microplate is as follows: The graphene microplate is added to an aqueous solution of a silane coupling agent (KH-550) and refluxed; the concentration of the aqueous solution of the silane coupling agent is 1.0-2.0 wt%; the mass-to-volume ratio of the graphene microplate to the aqueous solution of the silane coupling agent is 1 g:500 mL; the temperature of the reflux reaction is 120 °C, the time is 4 h, and the inert gas protection atmosphere; after the reflux reaction is completed, the steps of washing and drying the obtained product are further included; the thickness of the graphene microplate is 2-5 nm.

[0023] The preparation method of the modified fumed silica is as follows: silica is added to a mixed solution of ethanol and water, and ultrasonic treatment is carried out to obtain mixture 1; a silane coupling agent (KH-550) is added to mixture 1 for reaction 1, and then spray drying is carried out to obtain the modified fumed silica; in the mixed solution of ethanol and water, the volume ratio of ethanol to water is 9:1; the silica accounts for 15-20 wt% of the mixed solution of ethanol and water; the power of the ultrasonic treatment is 500 W and the time is 30 min; the silane coupling agent accounts for 10-25 wt% of the mass of the silica; the temperature of reaction 1 is 60 °C and the time is 3 h; the particle size of the modified fumed silica is 5-20 nm.

[0024] The preparation method of the hydroxyl-functionalized multi-walled carbon nanotubes is as follows: the multi-walled carbon nanotubes spread out thinly are treated with low-temperature plasma of steam radio frequency discharge with a power of 100 W for 10-15 minutes to achieve hydroxyl functionalization; the particle size of the hydroxyl-functionalized multi-walled carbon nanotubes is 10-20 nm and the length is 1-10 μm.

[0025] The sheet diameter of the hydroxylated nano boron nitride is 200 nm and the thickness is 5-20 nm.

[0026] In a preferred embodiment of the present invention, by mass percentage, in the bottom layer, it includes 40% fluorinated polyurethane, 45% modified FeSiCr, 8% modified graphene microflakes, 3% zinc phosphate, and the balance of propylene glycol methyl ether acetate.

[0027] In a preferred embodiment of the present invention, in the mixture of modified FeSiCr and modified FeSiAl, the mass ratio of modified FeSiCr to modified FeSiAl is 3:(2-7).

[0028] Optionally, the mass ratio of modified FeSiCr to modified FeSiAl is 3:2, 3:3, 3:4, 3:5, 3:6, 3:7 or any value between the aforementioned two ratios.

[0029] In a preferred embodiment of the present invention, by mass percentage, in the intermediate layer, it includes 35% fluorinated polyurethane, 50% mixture of modified FeSiCr and modified FeSiAl, 5% hydroxyl-functionalized multi-walled carbon nanotubes, and the balance of propylene glycol methyl ether acetate.

[0030] In a preferred embodiment of the present invention, by mass percentage, in the surface layer, it includes 45% UV-curable polyurethane, 25%-30% glass flakes, 15% hydroxylated nano boron nitride, 5% ultraviolet absorber, 0.8% modified fumed silica, and the balance of propylene glycol methyl ether acetate.

[0031] In a preferred embodiment of the present invention, the thickness of the glass flakes is 1-3 μm; the ultraviolet absorber is Tinuvin 1130.

[0032] In a preferred embodiment of the present invention, the thickness of the bottom layer is 1.8-2.0 mm, the thickness of the intermediate layer is 1.3-1.5 mm, and the thickness of the surface layer is 0.5 mm.

[0033] In a preferred embodiment of the present invention, the thickness of the bottom layer is 1.8 mm, the thickness of the intermediate layer is 1.5 mm, and the thickness of the surface layer is 0.5 mm.

[0034] In a preferred embodiment of the present invention, the thickness of the bottom layer is 1.9 mm, the thickness of the intermediate layer is 1.3 mm, and the thickness of the surface layer is 0.5 mm.

[0035] In a preferred embodiment of the present invention, the thickness of the bottom layer is 2.0 mm, the thickness of the intermediate layer is 1.5 mm, and the thickness of the surface layer is 0.5 mm.

[0036] The second aspect of the present invention provides a method for preparing the above corrosion-resistant radar absorbing coating, comprising the following steps: After uniformly mixing modified FeSiCr, modified graphene microflakes, zinc phosphate, propylene glycol methyl ether acetate, and fluorinated polyurethane, coat it onto a substrate and cure for 1 hour to obtain the bottom layer; After uniformly mixing a mixture of modified FeSiCr and modified FeSiAl, hydroxy-functionalized multi-walled carbon nanotubes, propylene glycol methyl ether acetate, and fluorinated polyurethane, coat it onto the surface of the bottom layer and cure for 2 hours to obtain the intermediate layer; After uniformly mixing glass flakes, hydroxylated nano-boron nitride, ultraviolet absorber, modified fumed silica, propylene glycol methyl ether acetate, and UV-curable polyurethane, coat it onto the surface of the intermediate layer and cure for 3 hours to obtain the radar absorbing coating.

[0037] In a preferred embodiment of the present invention, the parameters for curing 1 are set as: curing at 50-60 °C for 10-15 minutes; the parameters for curing 2 are set as: curing at room temperature for 25-30 minutes; the parameters for curing 3 are set as: ultraviolet light curing with a wavelength of 365 nm and an intensity of 80 mW / cm² for 30-60 seconds.

[0038] The present invention does not make special limitations on the above-mentioned method of uniform mixing, and conventional technical means of those skilled in the art can be selected, such as stirring and ultrasonic treatment.

[0039] The present invention does not make special limitations on the above-mentioned coating method, and conventional technical means of those skilled in the art can be selected, such as high-pressure spraying and roller coating.

[0040] The technical solutions described in the present invention are conventional solutions in the art unless otherwise specified. The reagents or raw materials used are purchased from commercial channels or are publicly available unless otherwise specified.

[0041] In the examples of the present invention, the preparation method of modified FeSiCr is as follows: 10 g of FeSiCr powder that has been ultrasonically cleaned with anhydrous ethanol is dried and then put into 100 mL of an aqueous KH550 solution with a concentration of 2.0 wt%. Under the condition of maintaining the temperature at 50 °C, it is stirred at 300 rpm for 90 minutes, then filtered by suction and rinsed once with 5 mL of anhydrous ethanol per gram of powder. After centrifuging to remove the residual liquid, it is dried at 80 °C for 1 hour.

[0042] The preparation method of modified FeSiAl is as follows: 10 g of FeSiAl powder that has been ultrasonically cleaned with anhydrous ethanol is dried and then put into 100 mL of an aqueous KH550 solution with a concentration of 2.0 wt%. Under the condition of maintaining the temperature at 50 °C, it is stirred at 300 rpm for 90 minutes, then filtered by suction and rinsed once with 5 mL of anhydrous ethanol per gram of powder. After centrifuging to remove the residual liquid, it is dried at 80 °C for 1 hour.

[0043] The preparation method of modified graphene microflakes is as follows: 1 g of graphene microflakes is added to 500 mL of an aqueous KH550 solution with a concentration of 1.5 wt%. Under the condition of nitrogen protection, it is refluxed and reacted at 120 °C for 4 hours, then washed with ethanol three times, 15 minutes each time, and finally dried at 60 °C for 10 hours.

[0044] The preparation method of hydroxyl-functionalized multi-walled carbon nanotubes is as follows: The multi-walled carbon nanotubes spread out thinly are treated with a low-temperature plasma of water vapor radio frequency discharge with a power of 100 W for 15 minutes to achieve hydroxyl functionalization.

[0045] The preparation method of modified fumed silica is as follows: Silica is put into an alcohol-water solvent with ethanol:water = 9:1 (volume ratio) at a ratio of 20 wt%. After ultrasonic treatment at a power of 500 W for 30 minutes, KH550 (25 wt% of silica) is added, and the reaction is carried out at 60 °C for 3 hours, and then spray-dried to obtain modified fumed silica.

[0046] The preparation method of hydroxylated nano-boron nitride is as follows: The nano-boron nitride is ultrasonically cleaned in ethanol for 30 minutes, vacuum-dried at 80 °C for 12 hours, spread out thinly, and then treated with a low-temperature plasma of water vapor radio frequency discharge with a power of 100 W for 30 minutes. After turning off the plasma, Ar gas is continuously introduced for 5 minutes.

[0047] In the embodiments of the present invention, the test of microwave reflection loss follows GJB 2038-94, and the vector network analyzer and the bow method are adopted; the salt spray test follows ASTM B117, and at the same time, the electrochemical workstation is used to test the 0.1 Hz low-frequency impedance of the coating; the ultraviolet aging follows ISO 11507, and the experimental is carried out by using the box-type ultraviolet aging test chamber combined with the color difference tester; the damp heat cycle test follows GJB150.9A, and the test is carried out by using the high and low temperature damp heat test chamber.

[0048] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments. Embodiment 1

[0049] The coating in this embodiment adopts a gradient three-layer wave-absorbing coating structure, with the bottom layer thickness of 1.8 mm, the middle layer thickness of 1.5 mm, the surface layer thickness of 0.5 mm, and the total thickness of 3.8 mm. The corresponding formula for each layer is shown in Table 1.

[0050] Table 1 Corresponding components of each layer ,

[0051] The preparation steps of the coating are as follows: Bottom layer spraying: After uniformly mixing modified FeSiCr, modified graphene microflakes, zinc phosphate, propylene glycol methyl ether acetate, and fluorinated polyurethane, it is spray-coated onto the substrate under high pressure and cured at 60 °C for 10 minutes; Middle layer spraying: After uniformly mixing the mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, propylene glycol methyl ether acetate, and fluorinated polyurethane, it is spray-coated onto the surface of the bottom layer and cured at room temperature for 30 minutes; Surface layer ultraviolet curing: After uniformly mixing hydroxylated nano boron nitride, glass flakes, Tinuvin 1130, modified fumed silica, propylene glycol methyl ether acetate, and UV-curable polyurethane, it is roll-coated onto the surface of the middle layer, and then cured with ultraviolet light with a wavelength of 365 nm and an intensity of 80 mW / cm² for 40 seconds.

[0052] The total curing time of this embodiment is < 2 hours, which is suitable for on-site operation.

[0053] For the obtained coating, its microwave reflection loss, corrosion resistance, and weather resistance are tested. The results are as follows: 1) Reflection loss (Table 2): Table 2

[0054] L - band (1 - 2 GHz): The effective bandwidth with return loss less than or equal to - 10 dB is greater than or equal to 300 MHz; S - band (2 - 4 GHz): The effective bandwidth with return loss less than or equal to - 10 dB is greater than or equal to 800 MHz; C - band (4 - 8 GHz): The effective bandwidth with return loss less than or equal to - 10 dB is greater than or equal to 2.2 GHz.

[0055] 2) Corrosion resistance: Salt spray test (2000 h, ASTM B117): No blistering, no peeling, adhesion loss < 3%; Electrochemical impedance (EIS, 0.1 Hz): |Z| > 5×10 8 Ω·cm².

[0056] 3) Weather resistance: UV aging (2500 h, ISO 11507): Color difference ΔE < 1.2, no chalking on the surface; Humid heat cycling (70°C / 95% RH, 30 days): No delamination, adhesion ≥ 7 MPa. Example 2

[0057] The difference from Example 1 is only that the thickness of the bottom layer is 1.9 mm, the thickness of the middle layer is 1.3 mm, the thickness of the surface layer is 0.5 mm, the total thickness is 3.7 mm, the mass ratio of modified FeSiCr to modified FeSiAl is 3:7, and the curing time during the spraying of the middle layer is 35 min. Other steps and parameters are the same as those in Example 1.

[0058] The total curing time of this example < 2 hours, which is suitable for on - site operation.

[0059] For the obtained coating, its microwave reflection loss, corrosion resistance and weather resistance were tested. The results are as follows: 1) Wave absorption performance (Table 3): Table 3

[0060] L - band (1 - 2 GHz): The effective bandwidth with return loss less than or equal to - 10 dB is greater than or equal to 380 MHz; S - band (2 - 4 GHz): The effective bandwidth with return loss less than or equal to - 10 dB is greater than or equal to 800 MHz.

[0061] 2) Corrosion resistance: Salt spray test (2000 h, ASTM B117): Adhesion loss < 2%, no blistering on the surface.

[0062] Electrochemical impedance (0.1 Hz): |Z| = 6×10 8Ω·cm².

[0063] 3) Weather resistance: UV aging (2500 h): Color difference ΔE = 1.0, no chalking on the surface.

[0064] Damp heat cycling (30 days): Adhesion ≥ 7.5 MPa.

[0065] It can be seen from the above results that increasing the FeSiAl ratio enhances the low-frequency absorption (RL in the L band is increased to -28 dB), but the high-frequency performance (C band) decreases. Example 3

[0066] The difference from Example 1 is only that the thickness of the bottom layer is 2.0 mm, the thickness of the middle layer is 1.5 mm, the thickness of the surface layer is 0.5 mm, the total thickness is 4.0 mm, the mass percentage of glass flakes is 30%, and the curing time in the surface layer UV curing is 60 min. Other steps and parameters are the same as those in Example 1.

[0067] The total curing time of this example < 2 hours, which is suitable for on-site operation.

[0068] For the obtained coating, its microwave reflection loss, corrosion resistance and weather resistance are tested. The results are as follows: 1) Wave absorption performance (Table 4): Table 4

[0069] L band (1 - 2 GHz): The effective bandwidth with return loss ≤ -10 dB ≥ 290 MHz; S band (2 - 4 GHz): The effective bandwidth with return loss ≤ -10 dB ≥ 900 MHz; C band (4 - 8 GHz): The effective bandwidth with return loss ≤ -10 dB ≥ 2.2 GHz.

[0070] 2) Results of enhanced corrosion resistance: Salt spray test (2500 h, ASTM B117): Adhesion loss < 1%, no corrosion penetration.

[0071] 3) Results of enhanced weather resistance: UV aging (3000 h): ΔE = 0.8, surface gloss retention > 90%.

[0072] It can be seen from the above results that by increasing the proportion of glass flakes, the corrosion resistance and UV protection are significantly improved, but the wave absorption performance decreases slightly.

[0073] Comparative Example 1 The coating of this comparative example is a single-layer structure with a thickness of 4.0 mm, and the corresponding coating formulation is shown in Table 5.

[0074] Table 5

[0075] The preparation steps of the coating are as follows: After mixing polyurethane, modified FeSiCr, modified fumed silica and propylene glycol methyl ether acetate evenly, it is spray-coated onto the substrate under high pressure and cured at 80 °C for 2 hours. The construction period is long (>4 hours).

[0076] For the obtained coating, its microwave reflection loss and corrosion resistance are tested. The results are as follows: 1) Wave absorption performance: L band: -9 dB @ 1.2 GHz (failed); S band: -12 dB @ 2.8 GHz; C band: -13 dB @ 5.5 GHz.

[0077] 2) Salt spray test (500 h, ASTM B117): Surface powdering, adhesion decreased by 40%.

[0078] It can be seen from the above results that the low-frequency performance is poor, and at the same time, the salt spray resistance performance is poor.

[0079] Comparative Example 2 The difference from Example 1 is only that the surface layer is omitted, and other steps and parameters are the same as those in Example 1.

[0080] The total curing time of this comparative example is about 1 hour.

[0081] For the obtained coating, its microwave reflection loss, corrosion resistance and weather resistance are tested. The results are as follows: 1) Wave absorption performance (Table 6): Table 6

[0082] L band (1 - 2 GHz): The effective bandwidth with return loss less than or equal to -10 dB is greater than or equal to 280 MHz; S band (2 - 4 GHz): The effective bandwidth with return loss less than or equal to -10 dB is greater than or equal to 750 MHz; C band (4 - 8 GHz): The RL ≤ -10 dB bandwidth only covers up to 5.0 GHz. Due to the lack of the surface conductive layer and impedance transition structure, the high-frequency absorption ability is significantly reduced, and the C-band performance does not meet the standard.

[0083] 2) Corrosion resistance: Salt spray test (2000 h, ASTM B117): Slight blistering on the surface, adhesion loss up to 8% (compared with <3% in Example 1); Electrochemical impedance (0.1 Hz): |Z| = 1×10 8 Ω·cm² (greater than 5×10 8 Ω·cm² of Comparative Example 1).

[0084] Due to the lack of glass flakes and nano boron nitride on the surface layer, the corrosion path is shortened and the protective performance is greatly reduced.

[0085] 3) Weather resistance: UV aging (2500 h): Color difference ΔE = 2.5, slight surface powdering (ΔE < 1.2 in Comparative Example 1); Humid heat cycle (30 days): Adhesion drops to 5 MPa (≥7 MPa in Comparative Example 1).

[0086] Due to the lack of ultraviolet absorber (Tinuvin 1130) and dense surface layer, the weather resistance deteriorates significantly.

[0087] Comparative Example 3 The coating of this comparative example adopts a gradient three-layer wave-absorbing coating structure, with the middle layer thickness of 1.8 mm, the bottom layer thickness of 1.5 mm, and the surface layer thickness of 0.5 mm, and the total thickness of 3.8 mm. The corresponding formula for each layer is shown in Table 7 (the difference from Example 1 is that the bottom layer of Example 1 is set as the middle layer, and the middle layer of Example 1 is set as the bottom layer).

[0088] Table 7 Corresponding components of each layer ,

[0089] The preparation steps of the coating are as follows: Bottom layer spraying: Mix the mixture of modified FeSiCr and modified FeSiAl, hydroxy-functionalized multi-walled carbon nanotubes, propylene glycol methyl ether acetate, and fluorinated polyurethane evenly, and then spray it onto the substrate surface and cure it at room temperature for 30 minutes; Middle layer spraying: Mix modified FeSiCr, modified graphene microflakes, zinc phosphate, propylene glycol methyl ether acetate, and fluorinated polyurethane evenly, and then spray it onto the bottom layer under high pressure and cure it at 60°C for 10 minutes; Surface layer UV curing: Mix hydroxylated nano boron nitride, glass flakes, Tinuvin 1130, modified fumed silica, propylene glycol methyl ether acetate, and UV-curable polyurethane evenly, roll-coat it on the surface of the middle layer, and then cure it with ultraviolet light with a wavelength of 365 nm and an intensity of 80 mW / cm² for 40 seconds.

[0090] For the obtained coating, its microwave reflection loss and corrosion resistance are tested. The results are as follows: Wave-absorbing performance (Table 8): Table 8

[0091] 2) Corrosion resistance: Salt spray test (2000 h, ASTM B117): No blistering, 5% adhesion loss.

[0092] Electrochemical impedance (0.1 Hz): |Z| = 3×10 8 Ω·cm².

[0093] Comparative Example 4 The difference from Example 1 is only that in the bottom layer, the modified FeSiCr and modified graphene microflakes are replaced by unmodified FeSiCr and graphene microflakes, and other steps and parameters are the same as those in Example 1.

[0094] The properties of the microwave absorption material obtained in this comparative example are as shown in Table 9 below: Table 9

[0095] Comparative Example 5 The difference from Example 1 is only that in the surface layer, the hydroxylated nano-boron nitride is replaced by non-hydroxylated nano-boron nitride, and other steps and parameters are the same as those in Example 1.

[0096] The properties of the microwave absorption material obtained in this comparative example are as shown in Table 10 below: Table 10

[0097] Comparative Example 6 The difference from Example 1 is only that in the bottom layer, the proportion of the modified graphene microflakes is adjusted from 8% to 12%, and the modified FeSiCr is adjusted from 45% to 41%. During the high-pressure spraying of the bottom layer, sagging occurred, and the surface roughness Ra = 3.8 μm after curing at 60°C (Ra < 1.5 μm in Example 1). The properties of the microwave absorption material obtained are as shown in Table 11 below: Table 11

[0098] Comparative Example 7 The difference from Example 1 is only that in the surface layer, the proportion of the glass flakes is adjusted from 25% to 35%, and the proportion of the hydroxylated nano-boron nitride is adjusted from 15% to 5%. When UV curing the surface layer, the time needs to be extended to 70 seconds (40 seconds in Example 1), and there is still partial incomplete curing; the properties of the microwave absorption material obtained are as shown in Table 12 below: Table 12

[0099] Comparative Example 8 The difference from Example 1 is only that in the intermediate layer, the mass ratio of modified FeSiCr to modified FeSiAl is adjusted from 6:4 to 8:2, and other steps and parameters are the same as those in Example 1. After spraying the intermediate layer, it is cured at room temperature for 30 minutes, and the coating hardness is 2H (the coating hardness in Example 1 is 3H). The performance of the obtained microwave absorbing material is as shown in Table 13 below: Table 13

[0100] Comparative Example 9 The difference from Example 1 is only that in the intermediate layer, the mass ratio of modified FeSiCr to modified FeSiAl is adjusted from 6:4 to 2:8, and other steps and parameters are the same as those in Example 1. After spraying the intermediate layer, poor leveling occurs, and at the same time, it is found that the toughness of the cured coating decreases, and the elongation at break changes from 25% in Example 1 to 15%. The performance of the obtained microwave absorbing material is as shown in Table 14 below: Table 14

[0101] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A corrosion-resistant radar-absorbing coating, characterized in that, The coating consists of a three-layer structure composed of a bottom layer, an intermediate layer, and a surface layer; the raw materials of the bottom layer are fluorinated polyurethane, modified FeSiCr, modified graphene microflakes, zinc phosphate, and propylene glycol methyl ether acetate; the raw materials of the intermediate layer are a mixture of fluorinated polyurethane, modified FeSiCr, and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, and propylene glycol methyl ether acetate; the raw materials of the surface layer are UV-curable polyurethane, glass flakes, hydroxylated nano boron nitride, ultraviolet absorber, modified fumed silica, and propylene glycol methyl ether acetate.

2. The corrosion-resistant radar absorbing coating according to claim 1, characterized in that, The modified FeSiCr is FeSiCr modified by a silane coupling agent; the modified FeSiAl is FeSiAl modified by a silane coupling agent; the modified graphene microflakes are graphene microflakes modified by a silane coupling agent; the modified fumed silica is fumed silica treated by a hydrophobic treatment; the silane coupling agent is silane coupling agent KH-550.

3. The corrosion-resistant radar absorbing coating according to claim 1, characterized in that, By mass percentage, in the bottom layer, it includes 40% fluorinated polyurethane, 45% modified FeSiCr, 8% modified graphene microflakes, 3% zinc phosphate, and the balance of propylene glycol methyl ether acetate.

4. The corrosion-resistant radar absorbing coating according to claim 1, characterized in that, In the mixture of modified FeSiCr and modified FeSiAl, the mass ratio of modified FeSiCr to modified FeSiAl is 3:(2 - 7).

5. The corrosion-resistant radar absorbing coating according to claim 1 or 4, characterized in that, By mass percentage, in the intermediate layer, it includes 35% fluorinated polyurethane, 50% mixture of modified FeSiCr and modified FeSiAl, 5% hydroxyl-functionalized multi-walled carbon nanotubes, and the balance of propylene glycol methyl ether acetate.

6. The corrosion-resistant radar absorbing coating according to claim 1, wherein By mass percentage, in the surface layer, it includes 45% UV-curable polyurethane, 25% - 30% glass flakes, 15% hydroxylated nano boron nitride, 5% ultraviolet absorber, 0.8% modified fumed silica, and the balance of propylene glycol methyl ether acetate.

7. The corrosion-resistant radar absorbing coating according to claim 1 or 6, characterized in that, The thickness of the glass flakes is 1 - 3 μm; the ultraviolet absorber is Tinuvin 1130.

8. The corrosion-resistant radar absorbing coating according to claim 1, wherein, The thickness of the bottom layer is 1.8 - 2.0 mm, the thickness of the intermediate layer is 1.3 - 1.5 mm, and the thickness of the surface layer is 0.5 mm.

9. A method for preparing the corrosion-resistant radar absorbing coating according to any one of claims 1-8, characterized in that, It includes the following steps: After uniformly mixing modified FeSiCr, modified graphene microflakes, zinc phosphate, propylene glycol methyl ether acetate, and fluorinated polyurethane, coat it onto the substrate and cure 1 to obtain the bottom layer; After uniformly mixing the mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, propylene glycol methyl ether acetate, and fluorinated polyurethane, coat it on the surface of the bottom layer and cure 2 to obtain the intermediate layer; After uniformly mixing glass flakes, hydroxylated nano boron nitride, ultraviolet absorber, modified fumed silica, propylene glycol methyl ether acetate, and UV-curable polyurethane, coat it on the surface of the intermediate layer and cure 3 to obtain the radar absorbing coating.

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