Aircraft aluminum alloy plate aging evaluation method based on equivalent circuit model

Abstract

The invention relates to the technical field of aircraft part processing, testing or inspection and the like, and provides an aircraft aluminum alloy plate aging evaluation method based on an equivalent circuit model, and the method comprises the following steps: collecting electrochemical impedance spectrums of samples with different exposure age limits, and extracting electrochemical impedance spectrum characteristics of the samples; establishing an equivalent circuit model comprising solution resistance, coating resistance, coating capacitance, Warburg impedance, anodic oxide film charge transfer resistance, interface capacitance, aluminum alloy matrix charge transfer resistance, interface electric double-layer capacitance, inductance and corresponding resistance of the inductance based on the characteristics, wherein the equivalent circuit model comprises the solution resistance, the coating resistance, the coating capacitance, the Warburg impedance, the anodic oxide film charge transfer resistance, the interface capacitance, the aluminum alloy matrix charge transfer resistance and the interface electric double-layer capacitance; and analyzing a resistance curve and a capacitance curve obtained by fitting the model to complete the evaluation of the corrosion and aging degree. According to the method, systematicness and accuracy of aging evaluation are improved, an electrochemical mechanism in the corrosion process can be disclosed, time correlation modeling of the aging process can be achieved, and the method is suitable for long-term service performance monitoring and service life prediction of the aviation aluminum alloy structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of processing, testing or inspection of aircraft components, and in particular to an aging evaluation method for aircraft aluminum alloy panels based on an equivalent circuit model. BACKGROUND

[0002] Aluminum alloy is widely used in the manufacture of aerospace structural components due to its light weight, high strength and good processing performance. However, aluminum alloy materials are susceptible to the combined effects of moisture, chloride ions, sulfur oxides and ultraviolet light in the atmosphere during long-term service, resulting in aging phenomena such as corrosion, coating degradation and interface debonding, which reduces their mechanical properties and protective properties, and in severe cases, even affects the structural safety and service life of the aircraft. To slow down the corrosion process of aluminum alloy panels, the existing technology generally uses epoxy coating as a protective coating. However, the epoxy coating may still have problems such as coating aging, crack formation and reduced coating resistance when exposed to complex service environments for a long time, which allows corrosion medium to penetrate into the aluminum alloy substrate, triggering interfacial corrosion and even pitting corrosion and other damage mechanisms. Therefore, how to accurately evaluate the corrosion aging degree of aluminum alloy panels with epoxy coating under different service life is a key technical problem in the safety monitoring of aviation materials. The existing technology for evaluating the aging degree of the coating mainly includes visual inspection, weight loss analysis, contact angle testing and spectral analysis, etc. However, these methods generally have the following technical problems: the evaluation results are highly subjective, lack quantitative indicators, most methods only focus on surface changes and ignore the electrochemical reaction process at the interface under the coating, some methods are only suitable for short-term accelerated testing and cannot reflect the aging law under real service conditions, and most methods lack parameters related to the service life of the material, making it difficult to achieve quantitative prediction of corrosion aging.

[0003] In summary, the existing technology has the technical problems of highly subjective evaluation results, lack of quantitative indicators, inability to reveal the corrosion behavior at the interface between the coating and the substrate, difficulty in applying to long-term corrosion trend tracking analysis, and inability to establish a correlation model between corrosion characteristics and service time. SUMMARY

[0004] To overcome the deficiencies of the existing technology, the present application provides an aging evaluation method for aircraft aluminum alloy panels based on an equivalent circuit model, which can quantitatively and systematically evaluate the corrosion aging degree of aluminum alloy panels, improve the accuracy and objectivity of the evaluation, and support time-related modeling of the aging process, suitable for long-term health monitoring and failure warning of aviation aluminum alloy structural components.

[0005] The aging evaluation method for aircraft aluminum alloy panels based on an equivalent circuit model provided by the present application comprises: Epoxy-coated aluminum alloy plate samples with different exposure years were obtained, and electrochemical impedance spectra of the epoxy-coated aluminum alloy plate samples with different exposure years were collected to obtain the electrochemical impedance spectral characteristics of the collected samples. Based on the electrochemical impedance spectroscopy characteristics of the collected samples, an equivalent circuit model was established, which includes solution resistance, coating resistance, coating capacitance, Warburg impedance, anodic oxide film charge transfer resistance, anodic oxide film interface capacitance, aluminum alloy substrate corrosion charge transfer resistance, interface double layer capacitance, inductance, and the corresponding resistance of the inductance. The electrochemical impedance spectrum of the sample was fitted using the equivalent circuit model, and the fitted resistance and capacitance curves were obtained. By comparing and analyzing the resistance and capacitance curves of the sample under different exposure years, the corrosion aging degree of the epoxy-coated aluminum alloy plate was comprehensively evaluated.

[0006] Compared with the prior art, the beneficial effects of this invention are as follows: This invention provides an aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model. The method includes: acquiring epoxy-coated aluminum alloy plate samples exposed for different years; collecting electrochemical impedance spectroscopy (EIS) data of the epoxy-coated aluminum alloy plate samples at different exposure years to obtain the EIS characteristics of the collected samples; establishing an equivalent circuit model based on the EIS characteristics of the collected samples, including solution resistance, coating resistance, coating capacitance, Warburg impedance, anodic oxide film charge transfer resistance, anodic oxide film interface capacitance, aluminum alloy substrate corrosion charge transfer resistance, interface double-layer capacitance, inductance, and the corresponding resistance of the inductance; fitting the EIS of the samples using the equivalent circuit model to obtain the fitted resistance and capacitance curves; and comprehensively assessing the corrosion aging degree of the epoxy-coated aluminum alloy plates by comparing and analyzing the resistance and capacitance curves of the samples under different exposure years. This method obtains electrochemical impedance spectroscopy under different exposure years, and constructs an equivalent circuit model by combining key electrochemical parameters such as solution resistance, coating resistance, capacitance, and anodic oxide film charge transfer resistance. It then fits the resistance and capacitance curves closely related to corrosion aging, thereby achieving a quantitative and systematic assessment of the corrosion aging degree of aluminum alloy plates. This not only improves the accuracy and objectivity of the assessment, but also supports time-related modeling of the aging process, making it suitable for long-term health monitoring and failure early warning of aerospace aluminum alloy structural components. Attached Figure Description

[0007] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. Some specific embodiments of the invention will be described in detail below with reference to the accompanying drawings in an exemplary and non-limiting manner. The same reference numerals in the drawings designate the same or similar parts or components. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the drawings: Figure 1 This is a schematic flowchart of an aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model, according to an embodiment of the present invention. Detailed Implementation

[0008] To enable those skilled in the art to better understand the present invention, the technical solutions of this embodiment will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely 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 should fall within the scope of protection of the present invention.

[0009] See Figure 1 This embodiment provides an aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model, including the following steps: S101. Obtain epoxy-coated aluminum alloy plate samples with different exposure years, and collect electrochemical impedance spectra of epoxy-coated aluminum alloy plate samples with different exposure years to obtain the electrochemical impedance spectrum characteristics of the collected samples. S102. Based on the electrochemical impedance spectroscopy characteristics of the collected samples, establish an equivalent circuit model containing solution resistance, coating resistance, coating capacitance, Warburg impedance, anodic oxide film charge transfer resistance, anodic oxide film interface capacitance, aluminum alloy substrate corrosion charge transfer resistance, interface double layer capacitance, inductance, and the corresponding resistance of the inductance. S103. The electrochemical impedance spectrum of the sample is fitted using the equivalent circuit model, and the fitted resistance curve and capacitance curve are obtained. By comparing and analyzing the resistance curve and capacitance curve of the sample under different exposure years, the corrosion aging degree of the epoxy-coated aluminum alloy plate is comprehensively evaluated.

[0010] It should be noted that in this embodiment, epoxy-coated aluminum alloy plate samples with different exposure years are obtained, and electrochemical impedance spectroscopy (EIS) spectra of these samples are collected at different exposure years to obtain the EIS characteristics of the collected samples. This enables quantitative detection of coating aging and provides key response data of the coating during the aging process in actual service environments. By collecting the responses of samples with different exposure years through EIS, the evolution process of the coating material and interface can be quantitatively characterized using frequency domain features. This provides electrochemical fingerprint information on coating degradation and interface corrosion development, exhibiting time correlation and providing prerequisite data for modeling aging patterns. Furthermore, in this embodiment, based on the electrochemical impedance spectroscopy characteristics of the collected samples, an equivalent circuit model is established, incorporating solution resistance, coating resistance, coating capacitance, Warburg impedance, anodic oxide film charge transfer resistance, anodic oxide film interface capacitance, aluminum alloy substrate corrosion charge transfer resistance, interface double-layer capacitance, inductance, and the corresponding resistance of the inductance. This allows the complex electrochemical aging process to be transformed into calculable and fitable structural parameters, quantifying the impedance effects of each interface (coating, oxide film, substrate) in different corrosion stages, while simultaneously expressing the diffusion control behavior and charge transfer process of the corrosion reaction. The equivalent circuit model organically integrates coating behavior, anodic oxide film behavior, and aluminum alloy substrate corrosion behavior into a unified electrochemical model framework, comprehensively describing the multi-level reaction mechanism of aluminum alloy plates during corrosion. Based on this, a Warburg impedance element is introduced to model the diffusion behavior of the corrosive medium within the coating and at the interface, further enhancing the model's ability to describe the medium transport process. Simultaneously, the addition of an inductor and its series resistor in the circuit effectively characterizes the reaction delay and phase lag effect caused by the formation of adsorbed intermediate substances during corrosion, thereby more comprehensively simulating multiple coupled processes such as mass transfer, charge transfer, and adsorption in the corrosion system, improving the accuracy and depth of corrosion behavior analysis. Furthermore, in this embodiment, the equivalent circuit model is used to fit the electrochemical impedance spectroscopy of the sample, obtaining the fitted resistance and capacitance curves. By comparing and analyzing the resistance and capacitance curves of samples under different exposure years, the corrosion aging degree of epoxy-coated aluminum alloy plates is comprehensively evaluated, thus achieving a direct reflection of the aging degree using electrical parameters and quantitative modeling of the time-related correlation of corrosion trends. Changes in the resistance curve can reflect processes such as decreased coating shielding ability, oxide film damage, and substrate corrosion activation; the capacitance curve can capture aging indicators such as increased coating porosity and enhanced interfacial activity. In this embodiment, by comparing the curves of samples with different ages, the key turning points of the aging process are revealed, allowing for quantitative prediction of coating life. This systematically solves the core problems of existing corrosion aging assessment technologies, such as strong subjectivity, difficulty in revealing interface mechanisms, and lack of time-dimensional modeling, achieving a quantitative, systematic, and traceable assessment of the service health of structural components.

[0011] It should also be noted that solution resistance refers to the bulk resistance of the electrolyte solution between the aluminum alloy sample and the reference electrode in the corrosion system, used to characterize the conductivity of the electrolyte medium. Its value depends on the conductivity of the solution, temperature, and the distance between the sample and the reference electrode. In the equivalent circuit, solution resistance is the impedance term that the input signal first passes through, representing the basic impedance of the solution layer to the entire electrochemical reaction process. Coating resistance refers to the resistive effect of the epoxy coating on the penetration behavior of ions and charges, used to simulate the insulation and shielding performance of the coating. When the coating is dense and defect-free, the resistance is relatively large; as the coating ages, cracks, or absorbs water, the resistance gradually decreases. The trend of coating resistance can directly reflect the degradation process of the coating. Coating capacitance is used to simulate the polarization energy storage characteristics of epoxy coatings under external AC excitation. Its capacitance is affected by factors such as coating thickness, dielectric constant, and water content. As the coating absorbs moisture and the dielectric constant increases, the coating capacitance will increase over time, which can be used as an indirect criterion for the coating's water content and aging degree. Warburg impedance is an equivalent circuit element used in electrochemical impedance spectroscopy (EIS) analysis to simulate and characterize the diffusion process of corrosive media at the electrode / coating interface. It is a parameter with a clear physical meaning, primarily used to describe the controlled electrochemical behavior of ion or molecule diffusion from solution to the aluminum alloy surface or defect region. Anodic oxide film charge transfer resistance refers to the resistance of the anodic oxide film interface to electron or ion transfer during the corrosion reaction, used to characterize the shielding properties of the oxide film and its ability to hinder charge migration. A higher anodic oxide film charge transfer resistance indicates higher oxide film density and integrity, and a stronger inhibitory effect on the corrosion process. Anodic oxide film interfacial capacitance reflects the polarization ability at the interface between the oxide film and the coating or electrolyte, mainly affected by ion exchange and charge distribution at the interface. Changes in capacitance can reveal early signs of oxide film penetration or localized failure. Aluminum alloy substrate corrosion charge transfer resistance refers to the resistance encountered by electrons flowing from the anodic dissolution region to the cathodic reduction region during the corrosion electrochemical reaction on the aluminum alloy substrate surface. The charge transfer resistance of the aluminum alloy matrix corrosion reflects the rate of corrosion; a smaller value indicates a more intense corrosion reaction. The interfacial double-layer capacitance represents the capacitive characteristics of the charge separation layer formed between the aluminum alloy surface and the electrolyte interface. It reflects changes in interfacial polarization and active surface area; in actively corroded regions, the interfacial double-layer capacitance typically increases significantly. Interfacial double-layer capacitance can be used to determine whether the corrosion process has entered a stable or accelerated phase. Inductance characterizes the slow reaction or hysteresis behavior of adsorbed intermediate products (such as oxygen, hydroxyl groups, aluminum salts, etc.) at the interface during corrosion. The presence of inductance indicates a dynamic response delay in the system, serving as an equivalent simulation of the temporal nature of the reaction mechanism and improving the model's fitting accuracy for low-frequency impedance. The resistance corresponding to the inductance is the series resistance of the inductive element, used to characterize energy loss during adsorption delay or dissipation behavior during interfacial ion exchange. This resistance term can adjust the phase angle and response decay rate of the inductive unit in the fit.

[0012] Preferably, in the equivalent circuit model, the solution resistance is used to simulate the conductivity of the electrolyte in the solution; the coating resistance and coating capacitance are combined in parallel and connected in series with the solution resistance to simulate the shielding effect of the epoxy coating; the coating resistance and coating capacitance are combined in parallel and connected to the Warburg impedance to characterize the diffusion behavior of the corrosive medium in the coating and interface; the Warburg impedance is connected in series with the parallel combination of the anodic oxide film charge transfer resistance and the anodic oxide film interface capacitance to simulate the charge transfer and energy storage characteristics of the anodic oxide film interface; the parallel combination of the anodic oxide film charge transfer resistance and the anodic oxide film interface capacitance is connected in series with the parallel combination of the aluminum alloy substrate corrosion charge transfer resistance and the interface double-layer capacitance to simulate the charge transfer reaction and double-layer capacitance behavior at the interface during the corrosion of the aluminum alloy substrate; the parallel combination of the aluminum alloy substrate corrosion charge transfer resistance and the interface double-layer capacitance is connected in series with an inductor and its corresponding resistor to characterize the reaction delay effect caused by the formation of intermediate adsorption products during the corrosion process.

[0013] It should be noted that by constructing an equivalent circuit model with a clear hierarchical structure, a systematic modeling and accurate evaluation of the entire corrosion and aging process of epoxy-coated aluminum alloy plates can be achieved. This model not only starts with solution resistance, sequentially connecting multiple electrochemical response units of the coating layer, anodic oxide film layer, and aluminum alloy substrate layer, but also uses the parallel combination of coating resistance and capacitance to reflect the degradation of coating shielding performance. Warburg impedance effectively simulates the diffusion behavior of corrosive media in defect paths, and the series connection of charge transfer resistance and interfacial capacitance of the anodic oxide film reproduces the buffering effect of the oxide film in the early stages of corrosion. Furthermore, the model further characterizes the corrosion process of the aluminum alloy substrate as a response of charge transfer resistance and double-layer capacitance, and at the end, uses inductance and its corresponding resistive element to accurately capture the reaction delay phenomenon caused by adsorbed intermediate products, enhancing the model's analytical capability for low-frequency dynamic corrosion characteristics.

[0014] Preferably, nano-cerium oxide is added to the epoxy coating, and the content of the nano-cerium oxide is between 0.5 wt% and 2.0 wt%. It should be noted that controlling the content of the nano-cerium oxide between 0.5 wt% and 2.0 wt% can significantly enhance the corrosion resistance of the coating. As a rare earth oxide, cerium oxide possesses excellent redox slow-release properties, and can release Ce³⁺ / Ce when the coating is damaged. 4 ⁺ ions repair local defects and passivate corrosion points, thereby delaying further penetration of corrosive media.

[0015] Preferably, graphene nanosheets are added to the epoxy coating, and the content of the graphene nanosheets is between 0.5 wt% and 2.0 wt%. Controlling the addition ratio of graphene nanosheets between 0.5 wt% and 2.0 wt% can improve the density and shielding performance of the coating. Due to its highly sheet-like structure and excellent mechanical and electrical properties, graphene can construct a labyrinthine barrier in the coating, extending the penetration path of corrosive media. Simultaneously, its high specific surface area is beneficial for filling microscopic pores and defects, blocking corrosion channels. Furthermore, graphene has excellent electrical conductivity, which can be manifested in the impedance spectrum as phase changes in charge transfer processes and changes in diffusion hysteresis terms. This makes the charge transfer impedance and Warburg impedance parameters in the equivalent circuit model more sensitive, enhancing the monitorability of the aging process.

[0016] Preferably, the graphene nanosheets form imino groups through cross-linking with amino radicals. The graphene nanosheets can undergo cross-linking reactions with amino radicals in the coating to form imino group structures, thereby enhancing the interfacial adhesion between the coating and the substrate at the molecular level. This cross-linked structure not only improves the adhesion and peel resistance of the coating but also delays the migration and accumulation of corrosive media at the coating / aluminum alloy interface by stabilizing the interfacial structure. In the electrochemical impedance response, the improved interfacial adhesion can be manifested as a stable trend in the interfacial bilayer capacitance and a delayed interfacial polarization phenomenon, thus improving the fit and reliability of the impedance spectrum.

[0017] Preferably, carbon nanotubes are added to the epoxy coating, and polydopamine is coated on the surface of the carbon nanotubes to increase the carboxyl and amino groups at the interface between the epoxy coating and the substrate. Adding carbon nanotubes to the epoxy coating and coating them with polydopamine allows for functional modification. The polydopamine layer introduces abundant carboxyl and amino functional groups, enabling chemical cross-linking with the epoxy resin matrix and enhancing the interfacial bonding strength between the coating and the aluminum alloy substrate. The strengthened interfacial bonding structure significantly reduces the risk of cracking, blistering, and peeling in the interfacial region during corrosion, improving the overall stability of the coating system. In electrochemical response, this strengthened interfacial structure leads to more stable responses in the anodic oxide film interfacial capacitance and the substrate bilayer capacitance, resulting in higher fitting accuracy.

[0018] Preferably, the polydopamine-coated carbon nanotube content is 5%–15% of the carbon nanotube mass, to enable the functional groups at the interface to undergo a cross-linking reaction with the epoxy resin. The polydopamine coating layer accounts for 5%–15% of the carbon nanotube mass, ensuring that it provides sufficient active functional groups for cross-linking without causing agglomeration or a decrease in electrical properties due to excessive polydopamine. This coating ratio directly affects the low-frequency stability and model convergence of the coating system in electrochemical impedance spectroscopy, thereby improving the accuracy and robustness of corrosion aging state analysis.

[0019] Preferably, the environmental conditions under which the samples are exposed include a coastal atmospheric environment to simulate real corrosion and aging conditions after different exposure years. The coastal atmospheric environment simulates typical high salt spray, high humidity, and strong oxidizing conditions in actual service, effectively improving the representativeness and practicality of the aging assessment. In a coastal environment, Cl⁻ and SO₂... x The synergistic effect of corrosive agents such as H2O creates a more complex erosion mechanism on the coating and aluminum alloy substrate, which can promote the exposure of coating defects, charge transfer imbalance, and intensified interfacial polarization. Electrochemical impedance spectroscopy data obtained in high-corrosion environments can more significantly reflect the mapping characteristics of corrosion behavior in circuit model parameters, improving the model's sensitivity to subtle parameter changes.

[0020] Preferably, the electrochemical impedance spectroscopy (EIS) acquisition frequency range is 0.01 Hz to 100 kHz to ensure accurate capture of microscopic changes in the resistance, capacitance, and impedance of the sample coating. Setting the acquisition frequency range to 0.01 Hz to 100 kHz covers the entire frequency domain, from diffusion processes (low frequency) to charge transfer and interfacial reactions (mid-to-high frequency) and solution resistance response (high frequency), effectively enhancing the EIS's ability to capture various corrosion mechanisms. Especially in the low-frequency range, it can characterize dynamic features such as intermediate product adsorption and charge accumulation delay, providing data support for inductors and Warburg devices; while in the high-frequency range, it can accurately reflect the solution conductivity and the initial state of the coating. This wideband acquisition strategy ensures sufficient density and coverage of impedance spectroscopy data, enhancing the accuracy and stability of equivalent circuit model fitting.

[0021] Preferably, in the fitting process of the electrochemical impedance spectrum of the sample using the equivalent circuit model, Zsimp-Win software is used for equivalent circuit model fitting, and electrochemical impedance data is obtained at a scan rate of 0.5 mV / s. Using Zsimp-Win software as a dedicated equivalent circuit fitting tool and performing experimental operations at a scan rate of 0.5 mV / s effectively improves the computational accuracy of model construction and the stability of data acquisition. Zsimp-Win has flexible circuit structure setting functions and a stable nonlinear fitting algorithm, capable of handling multi-parameter high-order models, while the low-speed frequency sweep setting of 0.5 mV / s avoids fitting errors caused by excessively fast polarization or response lag, improving the realism of the impedance spectrum in each frequency band.

[0022] Preferably, the capacitance curves include capacitance trend curves showing the changes in coating capacitance and interfacial bilayer capacitance over exposure years. When comparing and analyzing the capacitance curves of samples with different exposure years, the capacitance trend curves are used to assess changes in coating density and interfacial corrosion. The coating capacitance reflects the overall density and polarization capability of the coating, while the interfacial bilayer capacitance reflects the degree of corrosion activation and interfacial ion exchange capacity. The long-term evolution trends of both can reveal the rate of decline in coating protective capability and the evolution of interfacial corrosion degree. By constructing a trend curve model, not only can the critical time point of corrosion be identified, but mathematical support can also be provided for service life prediction.

[0023] Preferably, the resistance curves include trend curves showing the change in coating resistance and aluminum alloy substrate charge transfer resistance over exposure years. When comparing and analyzing the resistance curves of samples under different exposure years, the corrosion status of the coating and substrate is assessed using these trend curves. A decrease in coating resistance indicates a decline in its shielding performance, while a decrease in the charge transfer resistance of the aluminum alloy substrate directly reflects an intensified corrosion reaction. By plotting the trend curves of resistance change over time, the evolution of the corrosion degree of the coating and substrate under different exposure periods can be quantified, enabling service life estimation based on electrical parameters.

[0024] Preferably, the aging assessment method for aircraft aluminum alloy plates based on the equivalent circuit model also includes determining the glass transition temperature and thermal stability of the epoxy coating material using DSC (Differential Scanning Calorimetry) and TGA (Thermogravimetric Analysis). Analyzing the glass transition temperature and thermal stability of the epoxy coating material using DSC and TGA helps to assess the degree of aging of the coating from a thermal performance perspective. With increasing corrosion and environmental aging, the glass transition temperature of the coating may decrease, and its thermogravimetric behavior may change, manifested as a decrease in crosslinking density and structural degradation. These changes can serve as auxiliary criteria when changes in electrochemical parameters are not significant, enhancing the multi-dimensional characteristics of aging identification.

[0025] Preferably, the aging assessment method for aircraft aluminum alloy plates based on the equivalent circuit model also includes determining the elemental composition and oxidation state changes of the epoxy coating surface using X-ray photoelectron spectroscopy (XPS) to aid in the analysis of the coating's aging mechanism. XPS technology provides high-precision characterization of the elemental composition and oxidation state changes of the epoxy coating surface, revealing corrosion-induced chemical reaction pathways and the evolution mechanism of the coating's chemical structure. XPS can identify aging phenomena such as element migration, functional group changes, and surface aluminum alloy ion enrichment in the coating, providing chemical-level mechanistic support for phenomena such as charge transfer changes and abnormal interfacial capacitance in electrochemical impedance parameters. This cross-validation with electrochemical response parameters constructs a corrosion aging model from a systematic perspective of structure, performance, and mechanism, effectively enhancing the scientific rigor of the assessment results.

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for aging assessment of aircraft aluminum alloy plates based on an equivalent circuit model, characterized in that, include: Epoxy-coated aluminum alloy plate samples with different exposure years were obtained, and electrochemical impedance spectra of the epoxy-coated aluminum alloy plate samples with different exposure years were collected to obtain the electrochemical impedance spectral characteristics of the collected samples. Based on the electrochemical impedance spectroscopy characteristics of the collected samples, an equivalent circuit model was established, which includes solution resistance, coating resistance, coating capacitance, Warburg impedance, anodic oxide film charge transfer resistance, anodic oxide film interface capacitance, aluminum alloy substrate corrosion charge transfer resistance, interface double layer capacitance, inductance, and the corresponding resistance of the inductance. The electrochemical impedance spectrum of the sample was fitted using the equivalent circuit model, and the fitted resistance and capacitance curves were obtained. By comparing and analyzing the resistance and capacitance curves of the sample under different exposure years, the corrosion aging degree of the epoxy-coated aluminum alloy plate was comprehensively evaluated.

2. The aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model according to claim 1, characterized in that, The epoxy coating contains nano-cerium oxide, the content of which is between 0.5wt% and 2.0wt%.

3. The aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model according to claim 1, characterized in that, The epoxy coating contains graphene nanosheets, the content of which is between 0.5wt% and 2.0wt%.

4. The aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model according to claim 3, characterized in that, The graphene nanosheets form imino groups through cross-linking with amino free radicals.

5. The aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model according to claim 1, characterized in that, Carbon nanotubes are added to the epoxy coating, and polydopamine is coated on the surface of the carbon nanotubes to increase the carboxyl and amino groups at the interface between the epoxy coating and the substrate.

6. The aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model according to claim 5, characterized in that, The polydopamine-coated carbon nanotubes contain 5% to 15% of the carbon nanotube mass, so that the functional groups at the interface can undergo a cross-linking reaction with the epoxy resin.

7. The aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model according to claim 1, characterized in that, The environmental conditions in which the samples were exposed included coastal atmospheric environments, in order to simulate real corrosion and aging conditions after exposure for different years.

8. The aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model according to claim 1, characterized in that, The electrochemical impedance spectroscopy sampling frequency range is 0.01 Hz to 100 kHz to ensure accurate capture of the microscopic changes in the resistance, capacitance, and impedance of the sample coating.

9. The aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model according to claim 1, characterized in that, In the process of fitting the electrochemical impedance spectrum of the sample using the equivalent circuit model, Zsimp-Win software was used to fit the equivalent circuit model, and electrochemical impedance data were obtained at a scan rate of 0.5 mV / s.

10. The aging assessment method for aircraft aluminum alloy plates based on an equivalent circuit model according to claim 1, characterized in that, The capacitance curves include the capacitance trend curves of the coating capacitance and the interfacial bilayer capacitance as a function of exposure years. When comparing and analyzing the capacitance curves of samples under different exposure years, the capacitance trend curves are used to evaluate the changes in coating density and interfacial corrosion.

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