In-situ detection method for state of oxidation film on surface of aluminum alloy

Abstract

The invention provides an in-situ detection method for the state of an oxidation film on the surface of an aluminum alloy, and relates to the field of corrosion and protection research. The method comprises the following steps: an aluminum alloy to be detected is used as a working electrode, the working electrode and an auxiliary electrode are alternately arranged, adjacent electrodes are separated by an insulating spacer, the working electrode and the auxiliary electrode are respectively connected to a wiring terminal, and the aluminum alloy galvanic corrosion sensor is obtained through packaging; the current collector is connected to the micro-galvanometer and arranged in a target environment to collect current signals; when the sensor works, a galvanic corrosion current value generated by the sensor is closely related to an aluminum alloy surface state and an environmental medium; based on the characteristic, the current value and the change rate serve as characterization parameters of the aluminum alloy surface oxidation film, and the damage process of the aluminum alloy oxidation film is monitored in real time by monitoring galvanic corrosion current. The method has the advantages of being easy and convenient to operate, rapid in response, capable of achieving in-situ monitoring and the like, and an effective means is provided for in-situ monitoring and early warning of the aluminum alloy surface corrosion behavior.

Description

Technical Field

[0001] This application relates to the field of corrosion and protection research, and in particular to an in-situ detection method for the oxide film state on the surface of aluminum alloys. Background Technology

[0002] Aluminum alloys are widely used in aerospace, transportation, and other fields due to their high strength, low density, and excellent machinability. However, aluminum alloys are susceptible to corrosion, and the oxide film formed on their surface is their main protective barrier. When the oxide film breaks down, the internal aluminum alloy matrix is ​​exposed to the environment and is prone to corrosion, affecting material properties and service life. Especially under chlorine-containing media, strong acid and alkali environments, or mechanical stress, the surface oxide film is prone to localized cracking, leading to pitting corrosion, crevice corrosion, and other localized corrosion. If not monitored in time, this will result in deterioration of component performance or even failure.

[0003] Existing technologies for monitoring the condition of aluminum alloy passivation films mainly include electrochemical impedance spectroscopy (EIS), linear polarization resistance method, and ultrasonic testing. Among them, although electrochemical impedance spectroscopy can reflect the compactness of the oxide film, the testing equipment is complex and the operation is cumbersome, making it difficult to achieve on-site online monitoring; the linear polarization resistance method has strict requirements for the testing environment, is easily affected by solution resistance interference, and has limited monitoring accuracy; the ultrasonic testing method is mainly suitable for film thickness detection and cannot effectively identify early film rupture signals.

[0004] In view of the above, this application is hereby submitted. Summary of the Invention

[0005] The purpose of this application is to provide an in-situ detection method for the oxide film state on the surface of aluminum alloys, so as to solve the above-mentioned problems.

[0006] To achieve the above objectives, this application adopts the following technical solution: An in-situ detection method for the oxide film state on the surface of aluminum alloy includes: The aluminum alloy to be tested is used as the working electrode, and the working electrode and the auxiliary electrode are arranged alternately and the adjacent electrodes are separated by insulating pads. The working electrode and the auxiliary electrode are respectively connected to the wiring terminals and encapsulated to obtain an aluminum alloy galvanic corrosion sensor. The aluminum alloy galvanic corrosion sensor is connected to a microammeter and placed in the target environment to collect current signals. When the current value is less than 2000nA and the current increases by less than 20nA every 100 minutes, the aluminum alloy under test is in the oxide film protection period, and it is determined that the aluminum alloy under test is not corroded. When the current value is 2000-4000 nA and the current increases by 50-100 nA every 100 minutes, the aluminum alloy under test is in the metastable pitting corrosion stage, and it is determined that the aluminum alloy under test is in the early corrosion stage. When the current value is greater than 4000nA and the current increases by more than 150nA every 100 minutes, the aluminum alloy under test is in the steady-state pitting formation and development stage, and it is determined that the aluminum alloy under test has been corroded.

[0007] Preferably, the temperature of the target environment is 20-40℃ and the humidity is 70-90%.

[0008] Preferably, the environmental medium is the atmosphere or an aqueous solution of sodium chloride with a mass concentration of 0%-3.5%.

[0009] Preferably, the environmental medium is a sodium chloride aqueous solution with a mass concentration of 0.5%-1%.

[0010] Preferably, the encapsulation uses epoxy resin to fill the electrode gaps.

[0011] Preferably, the aluminum alloy galvanic corrosion sensor comprises multiple sets arranged in parallel.

[0012] Preferably, the aluminum alloy includes any one of aluminum-magnesium alloy, aluminum-magnesium-silicon alloy, and aluminum-zinc-magnesium-copper alloy.

[0013] Preferably, the material of the auxiliary electrode is selected from stainless steel and / or graphite.

[0014] Compared with the prior art, the beneficial effects of this application include: The in-situ detection method for the oxide film state of aluminum alloy surfaces provided in this application is based on the principle of galvanic corrosion. An aluminum alloy galvanic corrosion sensor is designed and fabricated using aluminum alloy and a passivating metal. When the sensor is turned on, the magnitude of the galvanic corrosion current generated is closely related to the surface state of the aluminum alloy and the environmental medium. The formation of an oxide film on the aluminum alloy surface can significantly inhibit the corrosion activity of the metal substrate, while the destruction of the oxide film leads to the exposure of the metal substrate, triggering a sudden change in the galvanic corrosion current. Based on this characteristic, the monitoring of the galvanic corrosion current is correlated with the oxide film destruction process. The magnitude and rate of change of the galvanic corrosion current are used as characterization parameters of the oxide film state on the aluminum alloy surface, thereby achieving real-time monitoring of the aluminum alloy oxide film damage process. This invention has the advantages of simple operation, rapid response, and in-situ monitoring capability, providing an effective technical means for in-situ monitoring and early warning of aluminum alloy surface corrosion behavior.

[0015] The in-situ detection method for the oxide film state of aluminum alloy surfaces provided in this application can achieve a monitoring frequency on the order of minutes, and monitor the dynamic evolution process of the oxide film on the aluminum alloy surface under environmental influences in real time and with high sensitivity. It can be used to monitor the protection-damage process of the oxide film on the aluminum alloy surface under different experimental conditions, and the monitored corrosion current waveform corresponds to different states of the aluminum alloy surface. Compared with traditional weight loss methods or electrochemical impedance spectroscopy, this method not only achieves in-situ and continuous monitoring, but also captures the important early failure information of metastable pitting corrosion, providing more direct data support for early warning and life prediction of aluminum alloy corrosion. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0017] Figure 1 This is a schematic diagram of the structure of a 7A04 aluminum alloy galvanic corrosion sensor. Figure 2 For different Cl - Current-time curve of galvanic corrosion of 7A04 aluminum alloy sensor at different concentrations; Figure 3 For different Cl - Potentiodynamic polarization curves of 7A04 aluminum alloy pad samples at different concentrations; Figure 4 The graph shows the corrosion current variation of the 7A04 aluminum alloy galvanic corrosion sensor under atmospheric exposure. Figure 5 The graph shows the corrosion current variation of a Q235 carbon steel galvanometer corrosion sensor probe under atmospheric exposure. Figure 6 The image shows the galvanic corrosion current-time curve of the 7A04 aluminum alloy sensor obtained in Example 3. Detailed Implementation

[0018] To better illustrate the technical solution provided in this application, the technical solution will be described in its entirety before the embodiments, as follows: An in-situ detection method for the oxide film state on the surface of aluminum alloy includes: The aluminum alloy to be tested is used as the working electrode, and the working electrode and the auxiliary electrode are arranged alternately and the adjacent electrodes are separated by insulating pads. The working electrode and the auxiliary electrode are respectively connected to the wiring terminals and encapsulated to obtain an aluminum alloy galvanic corrosion sensor. The aluminum alloy galvanic corrosion sensor is connected to a microammeter and placed in the target environment to collect current signals. When the current value is less than 2000nA and the current increases by less than 20nA every 100 minutes, the aluminum alloy under test is in the oxide film protection period, and it is determined that the aluminum alloy under test is not corroded. When the current value is 2000-4000 nA and the current increases by 50-100 nA every 100 minutes, the aluminum alloy under test is in the metastable pitting corrosion stage, and it is determined that the aluminum alloy under test is in the early corrosion stage. When the current value is greater than 4000nA and the current increases by more than 150nA every 100 minutes, the aluminum alloy under test is in the steady-state pitting formation and development stage, and it is determined that the aluminum alloy under test has been corroded.

[0019] Galvanic corrosion is an electrochemical corrosion phenomenon that occurs when two metals with different electrode potentials come into contact. The magnitude of the galvanic current generated is closely related to the potential difference between the two metals, their surface state, and the surrounding medium. The formation of an oxide film on aluminum alloys significantly alters their surface electrochemical activity, while the rupture of the oxide film exposes the fresh metal substrate, triggering a sudden change in the galvanic corrosion current. Based on this characteristic, a simple, fast-responding, and in-situ real-time galvanic corrosion current sensor was developed to overcome the shortcomings of existing technologies and achieve real-time and accurate monitoring of the passivation film state of aluminum alloys.

[0020] The fabricated aluminum alloy galvanic corrosion sensor was connected to a microammeter (with an accuracy of nA and a monitoring frequency of minutes) and placed in an experimental environment. When a liquid film forms on the surface, the working electrode and the counter electrode form a conductive electrochemical circuit, allowing for real-time acquisition of the galvanic current signal. Since this current value is directly proportional to the instantaneous corrosion rate of the aluminum alloy anode, continuous monitoring of changes in the corrosion current allows for a direct and quantitative evaluation of the dynamic process of protection and damage to the aluminum alloy oxide film.

[0021] In one optional implementation, the target environment has a temperature of 20-40°C and a humidity of 70-90%.

[0022] Optionally, the temperature of the target environment can be any value between 20°C, 30°C, 40°C, or 20-40°C, and the humidity can be any value between 70%, 80%, 90%, or 70-90%.

[0023] In one optional implementation, the environmental medium is the atmosphere or an aqueous solution of sodium chloride with a mass concentration of 0%-3.5%.

[0024] It should be noted that 0% sodium chloride aqueous solution refers to deionized water.

[0025] Optionally, the mass concentration of the sodium chloride aqueous solution can be 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or any value between 0% and 3.5%.

[0026] In one optional embodiment, the environmental medium is an aqueous solution of sodium chloride with a mass concentration of 0.5%-1%.

[0027] The current characteristics of damage to the oxide film on aluminum alloy surfaces include the following three stages: (1) Stage I: Oxide film protection period After the sample entered the experimental environment, due to the spontaneous formation of the oxide film on the aluminum alloy surface, the galvanic corrosion current stabilized at a low current level (<2000 nA), and the rate of change of current per unit time approached 0 (current increase <20 nA per 100 min), with no significant fluctuations. This stable low current plateau indicates that the oxide film completely covers the surface, effectively isolating the substrate from the corrosive environment and providing good protection.

[0028] (2) Stage II: Metastable pitting corrosion period During the metastable stage, the galvanic corrosion current fluctuates between 2000 and 4000 nA, exhibiting a periodic fluctuation characteristic of "peak + fall" (individual values ​​may exceed 4000 nA, but will immediately fall back; this is still considered within the range), but the overall rate of change is a slow positive value (e.g., the current increases by an average of 50-100 nA every 100 minutes). These phenomena correspond to the occurrence period of metastable pitting corrosion, which is a precursor to steady-state pitting corrosion. Its frequency and intensity are important indicators for evaluating the stability of the passivation film.

[0029] (3) Stage III: Steady-state pitting formation and development period When a metastable pitting corrosion fails to passivate successfully, it develops into a stable pitting corrosion. The galvanic corrosion current exceeds 4000 nA, which manifests as an irreversible current surge on the current curve. The rate of change of current shows a "continuous positive growth" trend, with a significant increase in the rate of change per unit time (current increase >150 nA per 100 min), and no obvious drop back to the low amplitude range. This indicates that the oxide film has undergone permanent rupture, forming a stable macroscopic pit. The aluminum substrate within the pit acts as a large anode, forming a strong galvanic couple with the large-area cathode, driving a continuous anodic dissolution current. The fluctuations in current reflect the dynamic processes such as the accumulation, diffusion, and bubble escape of corrosion products within the pit.

[0030] (4) The effect of environmental corrosivity on current characteristics The evolution rate and morphological characteristics of the aforementioned current features are significantly regulated by environmental corrosivity. The stronger the environmental corrosivity (e.g., increased chloride ion concentration, increased humidity, increased temperature), the faster the oxide film transitions from the "protective period" to the "metastable pitting period," manifested as a shortened duration of the "low current plateau" in stage I. Simultaneously, the frequency and intensity of metastable pitting also increase, with current peaks becoming more concentrated and significant. In highly corrosive environments, metastable pitting easily overcomes the repassivation limit, rapidly evolving into the "steady-state pitting period," leading to an earlier current surge in stage III, and ultimately, a higher and more volatile steady-state current value. Therefore, by comparing current curves under different environments, the impact of environmental factors on the service performance of aluminum alloys can be quantitatively assessed.

[0031] In an alternative embodiment, the encapsulation uses epoxy resin to fill the electrode gaps.

[0032] Conduct the same type of electrodes separately using conductive silver paste or by welding, and connect copper wires to the terminals; encapsulate the electrode assembly in a cylindrical 3D printed PLA shell, fill the electrode gaps with epoxy resin potting compound (perform vacuum degassing for 30 minutes before potting to ensure the resin is fully filled and free of air bubbles), cure at room temperature for more than 48 hours, leaving only the terminal interface exposed, to make an aluminum alloy galvanic corrosion sensor; generally, prepare 4 parallel probes to ensure test repeatability.

[0033] After encapsulation, an aluminum alloy galvanic corrosion sensor similar to a probe is formed; during the experiment, the end face is exposed to the test environment.

[0034] In one alternative embodiment, the aluminum alloy galvanic corrosion sensor comprises multiple sets arranged in parallel.

[0035] In one optional embodiment, the aluminum alloy includes any one of aluminum-magnesium alloy, aluminum-magnesium-silicon alloy, and aluminum-zinc-magnesium-copper alloy; Corrosion-resistant alloys of the 5 series (aluminum-magnesium alloy), 6 series (aluminum-magnesium-silicon alloy) and 7 series (aluminum-zinc-magnesium-copper alloy).

[0036] The auxiliary electrode is made of stainless steel and / or graphite.

[0037] The auxiliary electrode, as the cathode, is required to have a potential difference with the aluminum alloy being tested. Stable materials with correct electrode potential, such as stainless steel and graphite, should be selected.

[0038] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0039] Example 1 This embodiment provides an in-situ detection method for the oxide film state on the surface of aluminum alloys, including the following steps: 1. Electrode Selection and Assembly: Seven 7A04 aluminum alloy sheets are used as the anode (A), and seven 2507 stainless steel sheets are used as the cathode (B). These are arranged alternately. Each electrode sheet is 1 mm thick. A 0.1 mm thick PTFE insulating gasket separates each pair of electrodes (to prevent direct contact and short circuits). The electrode assembly is secured with nylon bolts. A schematic diagram is shown below. Figure 1 As shown.

[0040] 2. Electrode conduction and encapsulation: Conductive silver paste was used to conduct the same type of electrodes (7 pieces of 7A04 aluminum alloy and 7 pieces of 2507 stainless steel) to the terminals, and copper wires were connected to the terminals. The electrode assembly was encapsulated in a cylindrical 3D printed PLA shell, and epoxy resin potting compound was used to fill the electrode gaps (vacuum degassing was performed for 30 minutes before potting to ensure that the resin was fully filled without air bubbles). The mixture was cured at room temperature for more than 48 hours, leaving only the terminal interface exposed, to create a 7A04 aluminum alloy thermocouple sensor probe. Four parallel probes were prepared to ensure experimental repeatability.

[0041] 3. Monitoring system connection: Connect the fabricated sensor probe to a micro-ammeter (accuracy in the nA range, monitoring frequency in the minute range) and place it in the experimental environment. When a liquid film forms on the probe surface, the working electrode and the counter electrode form a conductive electrochemical circuit, which can collect the galvanic current signal in real time and capture the protection and damage process of the aluminum alloy oxide film.

[0042] 4. Experimental Environment Setup: The probe was placed in a humid heat chamber at 30℃ and 90% relative humidity. The solutions introduced were deionized water, 0.5%, 1%, and 3.5% NaCl solutions, respectively. Each experiment lasted for 72 hours. This allows us to investigate the effect of Cl⁻ concentration on oxide film damage behavior.

[0043] 5. Monitoring results and analysis of oxide film damage characteristics (e.g.) Figure 2 (as shown) In a deionized water medium humid and hot environment: after the sample entered the experimental environment, due to the relatively mild ambient medium, the protective effect of the oxide film and the environmental erosion rate reached a dynamic balance. The corrosion current remained stable overall, with only brief and low-peak local spikes that quickly returned to the baseline level. After 72 hours of experimentation, the current value stabilized at around 900 nA. This stable current plateau indicates that the oxide film has effectively isolated the substrate from the ambient medium, demonstrating good protective performance.

[0044] In a 0.5 wt% NaCl humid heat solution environment, the current showed a slow, gradual increase, with fluctuations ≤500 nA within 2000 min, corresponding to the overall protective function of the oxide film. Subsequently, the curve was accompanied by a series of current spikes, with the corrosion current value gradually increasing until reaching the metastable pitting corrosion stage. After 72 h, the current value fluctuated around 2500 nA, indicating that a small amount of Cl⁻ could induce film defects and reduce the protective performance of the oxide film.

[0045] In a 1 wt% NaCl humid heat solution environment: the current stabilized at around 1000 nA for the first 1000 min, consistent with "Stage I," indicating a relatively stable oxide film. Later, the current exhibited several significant spikes (peak increase ≥ 2000 nA), followed by a slight drop back to baseline, with the overall current value ranging from 2000-4000 nA. This characteristic corresponds to the current characteristics of "Stage II," characterized by frequent metastable pitting corrosion. - As the concentration increases, the frequency of localized ruptures in the oxide film increases, and defects in the film continue to accumulate. However, the current value gradually increases in the later stages, and the rate of passivation film rupture is generally greater than the repair rate, indicating that the aluminum alloy is developing towards steady-state pitting corrosion.

[0046] In a 3.5 wt% NaCl humid heat solution environment, the current showed a rapid and continuous upward trend to 15000 nA, and the current growth rate was 350 nA / 100 min, with no "low current plateau period". This is because under high Cl⁻ concentration, the passivation film rupture rate far exceeds the repassivation rate; the integrity of the film layer is rapidly lost, and the protective function is basically ineffective.

[0047] This embodiment clarifies Cl through thermocouple current monitoring. - Quantitative relationship between concentration and oxide film rupture behavior of 7A04 aluminum alloy: Cl - Higher concentrations result in more frequent peaks and greater fluctuations in the galvanic corrosion current, a shorter corresponding "low-current plateau period," and more severe oxide film rupture. This is largely consistent with the electrochemical test results of the sample in Comparative Example 1, verifying that the current monitoring method of this invention can accurately capture different Cl- concentrations. - The dynamic rupture process of oxide film at certain concentrations provides an effective technical means for evaluating the service performance of aluminum alloys in chlorine-containing environments.

[0048] Comparative Example 1 The experiment was conducted following the method and steps of Example 1. The difference from Example 1 is that the experimental material in Comparative Example 1 was a 7A04 aluminum alloy hanging plate with a size of 25×50×3mm. 3 Corrosion tests were also conducted under humid and hot conditions with different salt concentrations. Aluminum alloy plate samples with different placement times (1h, 2h, 6h, 12h, 24h and 72h) were taken out of the test chamber in sequence and electrochemical tests were performed.

[0049] The potentiodynamic polarization curves of the samples were measured using a CHI660D electrochemical workstation. A standard three-electrode system was employed, with the experimental sample as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum sheet as the auxiliary electrode. Electrochemical measurements were performed using a 3.5 wt% NaCl solution at 20°C. The determination of the potentiodynamic polarization curves was performed according to standard GB / T17899-1999. The sample was immersed in the electrolyte solution for 20 min, and measurements were started after the open-circuit potential stabilized. The scan rate was 1 mV / s, and the potential range was -0.3 to 0.8 V (relative to Eocp). To ensure the stability of the experimental data, each electrochemical test was repeated at least three times.

[0050] In a humid and hot environment with deionized water as the medium, the polarization curves at 2h, 12h, and 24h all show passivation regions, and the current density in the passivation regions remains consistently at 10. -8 ~10 -7 A・cm -2 The low current density corresponds to a stable low plateau of the galvanic current, which is consistent with the current curve characteristics in Example 1. This indicates that the oxide film mainly provides steady-state protection under the humid and hot environment of deionized water medium, with very little metastable pitting corrosion.

[0051] In a 0.5 wt.% NaCl humid heat solution environment: during the initial exposure period (within 12 hours), the polarization curve showed a clear passivation zone, and the corrosion current density remained at a low level (10 wt.%). -8 ~10 -7 A・cm -2 This is similar to the characteristics under deionized water conditions, indicating that the oxide film remains intact and still provides good protection to the substrate. However, as the exposure time extends to 24 hours, the passivation zone essentially disappears, signifying that the protective performance of the oxide film has begun to deteriorate. This transformation is dynamically confirmed in the galvanic corrosion current monitoring chart. The current curve clearly shows a composite characteristic of "Stage I: Oxide Film Protection Period" and "Stage II: Metastable Pitting Corrosion Period".

[0052] In a 1 wt.% NaCl humid heat solution environment: after 2 hours, the passivation region of the polarization curve began to narrow, and after 12 hours, the passivation characteristics disappeared. The corresponding current showed multiple brief sharp peaks, which may be due to local damage to the oxide film and metastable pitting corrosion leading to current peaks.

[0053] In a 3.5 wt.% NaCl humid hot solution environment: after 1 hour, the passivation zone of the polarization curve basically disappeared, and the current of the corrosion current curve continued to rise over time, showing the characteristics of "active dissolution". This is completely consistent with the current characteristics of "permanent rupture of the passivation film in stage III and formation of steady-state pitting corrosion", indicating that the metastable pitting corrosion under 3.5 wt.% NaCl has developed into a steady-state macro-corrosion pit, and the aluminum alloy substrate is continuously exposed and undergoes strong anodic dissolution.

[0054] Different Cl - The potentiodynamic polarization curves of 7A04 aluminum alloy pads at various concentrations are shown below. Figure 3 As shown.

[0055] Example 2 This embodiment provides an in-situ detection method for the oxide film state on the surface of aluminum alloys, including the following steps: 1. The corrosion sensor consists of seven pairs of galvanic electrodes, each 1 mm thick, made of 7A04 aluminum alloy (anode) and 2507 stainless steel (cathode). These electrodes are isolated by thin plastic gaskets and secured with nylon bolts. These insulating gaskets prevent internal short circuits, and the thin gaskets (0.1 mm) ensure a sufficiently close gap between adjacent electrodes to promote galvanic corrosion. Both types of electrodes are connected to an interface, which is then wired to a microammeter and a data logger. Four parallel probe samples were prepared to ensure experimental accuracy.

[0056] 2. An aluminum alloy probe was placed at the Qionghai Atmospheric Test Station in Hainan Province for a one-year exposure experiment, from May 2024 to April 2025. Galvanic corrosion current data was monitored using a micro-ammeter, with a detection frequency of one data point per minute. Statistical analysis was performed using the hourly average. Real-time meteorological and environmental data from the test station were also monitored simultaneously.

[0057] Figure 4As can be seen, when the aluminum alloy probe sample is initially placed, due to the protective effect of the surface oxide film, the current value remains at a very low level, around 50 nA, and the current change rate is less than 20 nA / 100min. This indicates that the aluminum alloy surface film has good integrity and stable protective performance. The aluminum alloy surface can maintain a balance between passivation film rupture and repair. The galvanic corrosion current remains at a low amplitude because the electrochemical activity of the substrate is isolated by the film. As exposure time increased, the current began to show a significant surge in peak values, with the frequency and amplitude of peaks gradually increasing (from 2000 nA to 18000 nA). This is likely due to the adsorption and penetration of Cl⁻ from the atmospheric environment (from tropical marine particulate matter, chlorine-containing precipitation, etc.) into the film defects, inducing local film dissolution. After exposure, the aluminum alloy substrate forms a large potential difference with the counter electrode, resulting in a surge in galvanic current. The current fluctuations after the peak value decreased (the baseline between peak values ​​in the figure rose to around 4000 nA, with a current change rate of 100 nA / 100 min), reflecting that the re-repair capability of the passivation film after rupture gradually decreased over time, and film defects continued to accumulate. By February 2025, the density and amplitude of the current peaks further increased, and the baseline current rose significantly, with an average value of around 10 μA and a current change rate much greater than 150 nA / 100 min, indicating that the accumulation of contaminants on the aluminum alloy surface reached saturation, and the electrolyte film thickened and its conductivity increased. Metastable pitting corrosion breaks through the repassivation limit and develops into steady-state pitting, with a significant increase in corrosion rate, and the oxide film on the aluminum alloy surface no longer exists.

[0058] This embodiment provides a current monitoring process of an aluminum alloy probe that has been in service in an atmospheric environment for one year. It studies the evolution of the surface state of the aluminum alloy probe during long-term service in a real environment, providing data support for the practical application of the invention.

[0059] Comparative Example 2 Referring to the test method of Example 2, the test sample of Comparative Example 2 was made of Q235 carbon steel and the corrosion current value collected was changed after long-term exposure in an atmospheric environment.

[0060] 1. The corrosion sensor consists of a pair of electrodes made of Q235 carbon steel (anode) and graphite (cathode), each 1 mm thick, isolated by a thin plastic gasket (0.1 mm) and secured with nylon bolts. Both types of electrodes are connected to a single interface, which is then connected by wires to a microammeter and a data logger. Four parallel probe samples are prepared to ensure experimental accuracy.

[0061] 2. The Q235 steel-graphite probe was placed at the Qingdao Atmospheric Test Station for a one-year exposure experiment. The corrosion current was monitored by a micro-ammeter, and real-time data of meteorological and environmental factors at the test station were monitored simultaneously.

[0062] from Figure 5 As can be seen from the curve, in the initial stage (0~1000h), the current rapidly climbs from nearly 0 nA to a peak range of 25000~30000 nA. This is because the surface oxide film of Q235 carbon steel (mainly Fe2O3 and Fe(OH)) is loose and discontinuous, unable to form a dense passivation film to isolate the electrochemical activity of the substrate. Surface iron atoms continuously undergo anodic dissolution with the environmental medium, forming a stable large potential difference with the counter electrode, thus maintaining a high current amplitude. In the middle stage (1000~2000h), the current consistently fluctuates within a high range of 5000~25000 nA. This is due to the "random coverage-removal" of the loose corrosion product layer on the carbon steel surface: when corrosion products temporarily cover the substrate, the current decreases slightly; when the corrosion products are eroded by the medium and loosen and detach, fresh iron substrate is exposed, and the current surges again. This is similar to the "local rupture-removal" phenomenon of the passivation film on aluminum alloys. The regular peak value of "rapid repair" is completely different and is a typical current characteristic of metallic materials without passivation film. In the later stage (after 2000h), the current generally drops back to the range of 0~5000 nA. This is because a thick layer of loose corrosion products accumulates on the surface, which to some extent hinders the contact between the corrosive medium and the substrate, reducing the electrochemical reaction rate. However, the product layer lacks the density and stability of a passivation film and will still fall off with environmental changes (such as humidity fluctuations or slight external forces), so the current fluctuation continues.

[0063] Example 3 The experiment was conducted in a 0.5% sodium chloride aqueous solution environment. Unlike Example 1, the monitoring time was extended to 8000 min, and the results are as follows: Figure 6 As shown.

[0064] Figure 6 The corrosion process can be clearly characterized by three distinct stages: protection of the aluminum alloy oxide film, metastable pitting corrosion, and steady-state pitting corrosion.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 this application.

Claims

1. An in-situ detection method for the oxide film state on the surface of aluminum alloy, characterized in that, include: The aluminum alloy to be tested is used as the working electrode, and the working electrode and the auxiliary electrode are arranged alternately and the adjacent electrodes are separated by insulating pads. The working electrode and the auxiliary electrode are respectively connected to the wiring terminals and encapsulated to obtain an aluminum alloy galvanic corrosion sensor. The aluminum alloy galvanic corrosion sensor is connected to a microammeter and placed in the target environment to collect current signals. When the current value is less than 2000nA and the current increases by less than 20nA every 100 minutes, the aluminum alloy under test is in the oxide film protection period, and it is determined that the aluminum alloy under test is not corroded. When the current value is 2000-4000 nA and the current increases by 50-100 nA every 100 minutes, the aluminum alloy under test is in the metastable pitting corrosion stage, and it is determined that the aluminum alloy under test is in the early corrosion stage. When the current value is greater than 4000nA and the current increases by more than 150nA every 100 minutes, the aluminum alloy under test is in the steady-state pitting formation and development stage, and it is determined that the aluminum alloy under test has been corroded.

2. The in-situ detection method for the oxide film state of aluminum alloy surface according to claim 1, characterized in that, The target environment has a temperature of 20-40℃ and a humidity of 70-90%.

3. The in-situ detection method for the oxide film state of aluminum alloy surface according to claim 1, characterized in that, The environmental medium is the atmosphere or a sodium chloride aqueous solution with a mass concentration of 0%-3.5%.

4. The in-situ detection method for the oxide film state of aluminum alloy surface according to claim 3, characterized in that, The environmental medium is a sodium chloride aqueous solution with a mass concentration of 0.5%-1%.

5. The in-situ detection method for the oxide film state of aluminum alloy surface according to claim 1, characterized in that, The encapsulation uses epoxy resin to fill the electrode gaps.

6. The in-situ detection method for the oxide film state of aluminum alloy surface according to claim 1, characterized in that, The aluminum alloy galvanic corrosion sensor comprises multiple sets arranged in parallel.

7. The in-situ detection method for the oxide film state of aluminum alloy surface according to claim 1, characterized in that, The aluminum alloy includes any one of aluminum-magnesium alloy, aluminum-magnesium-silicon alloy, and aluminum-zinc-magnesium-copper alloy.

8. The in-situ detection method for the oxide film state of aluminum alloy surface according to any one of claims 1-7, characterized in that, The auxiliary electrode is made of stainless steel and / or graphite.

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