An aluminum alloy surface corrosion process prediction method considering residual strain

Abstract

The application discloses a kind of aluminum alloy surface corrosion process prediction methods considering residual strain, specifically related to the field of aero-engine protection.It includes: obtaining the composition of the oxide film on the surface of aluminum alloy and the corresponding crystal structure under the corrosion environment, extracting the corrosion medium ions, and constructing a surface model; Determine the tensile and compressive strength of the surface model; Build multiple adsorption configurations; According to the tensile and compressive strength, determine the residual strain range; Within the residual strain range, apply tension or compression strain to any adsorption configuration, determine the adsorption energy of the current corrosion medium ions in the adsorption configuration under different strains; Determine the diffusion barrier of the corrosion medium ions in the oxide film under different strains; Determine the adsorption energy-diffusion barrier ratio of the corrosion medium ions in the adsorption configuration under each strain; According to the adsorption energy-diffusion barrier ratio under each strain, predict the corrosion process of the aluminum alloy surface. Through the above method, the corrosion behavior under complex working conditions can be accurately predicted.

Description

TECHNICAL FIELD

[0001] The application relates to the field of protection of an aero-engine, in particular to an aluminum alloy surface corrosion process prediction method considering residual strain. BACKGROUND

[0002] Aluminum alloy is widely used in the research and manufacture of key components such as fan blades of an aero-engine due to its high strength-weight ratio and excellent corrosion resistance. When the aircraft operates in the marine atmospheric environment, the accumulated residual stress or strain of the fan blade during long-term service causes high-concentration chlorine ions in the air to effectively penetrate the oxide film on the surface of the aluminum alloy, accelerates the corrosion process, significantly weakens the structural strength of the key components of the aircraft, reduces the service life thereof, increases the risk of catastrophic accidents and causes huge economic losses.

[0003] The corrosion process directly affects the long-term service performance of the aluminum alloy. For the existing aluminum alloy surface corrosion process prediction method, a corrosion kinetics model is established depending on experiments. However, the dependence on experiments has significant limitations: the establishment of tests under different working conditions is time-consuming and labor-consuming, the research and development cost is high, macroscopic experiments combined with characterization analysis are difficult to reveal the micro-mechanism of the adsorption and inward diffusion of the corrosion medium on the surface, cannot comprehensively analyze the corrosion mechanism of the aluminum alloy from the atomic level and multiple scales, and results in low prediction accuracy. SUMMARY

[0004] The main purpose of the application is to provide an aluminum alloy surface corrosion process prediction method considering residual strain, aiming to solve the problem of low prediction accuracy of the existing prediction method.

[0005] To achieve the purpose, the application provides an aluminum alloy surface corrosion process prediction method considering residual strain, which comprises the following steps: obtaining the composition and corresponding crystal structure of the oxide film on the surface of the aluminum alloy in a corrosion environment, and extracting corrosion medium ions; constructing a surface model according to the composition and crystal structure of the oxide film; determining the tensile and compressive strength of the surface model; adsorbing the corrosion medium ions on the adsorption sites of the surface model to obtain a plurality of adsorption configurations; determining the residual strain range according to the tensile and compressive strength; applying tensile or compressive strain to any adsorption configuration within the residual strain range to determine the adsorption energy of the corrosion medium ions in the adsorption configuration under different strains; determining the final state structure and initial state structure among the plurality of adsorption configurations, and simultaneously applying tensile or compressive strain to the final state structure and initial state structure within the residual strain range to determine the diffusion barrier of the corrosion medium ions in the oxide film under different strains; determining the ratio of the absolute value of the adsorption energy of the corrosion medium ions in the adsorption configuration to the diffusion barrier of the corrosion medium ions in the oxide film under each strain, and taking it as the adsorption energy-diffusion barrier ratio under each strain; and predicting the corrosion process of the aluminum alloy surface according to the adsorption energy-diffusion barrier ratio under each strain.

[0006] Optionally, the corrosion process of the aluminum alloy surface is predicted according to the adsorption energy-diffusion barrier ratio under each strain, including: determining the ratio of the absolute value of the adsorption energy of the corrosion medium ion in the adsorption configuration and the diffusion barrier of the corrosion medium ion in the oxide film under no applied strain, and taking the ratio as a reference value; comparing the adsorption energy-diffusion barrier ratio with the reference value, and determining the control stage of the aluminum alloy corrosion process and the corresponding macro corrosion characteristics according to the comparison result.

[0007] Optionally, the corrosion process of the aluminum alloy surface is predicted according to the adsorption energy-diffusion barrier ratio under each strain, including: determining the ratio of the absolute value of the adsorption energy of the corrosion medium ion in the adsorption configuration and the diffusion barrier of the corrosion medium ion in the oxide film under no applied strain, and taking the ratio as a reference value; comparing the adsorption energy-diffusion barrier ratio with the reference value, and determining the control stage of the aluminum alloy corrosion process and the corresponding macro corrosion characteristics according to the comparison result.

[0008] Optionally, after obtaining a plurality of adsorption configurations, the method further includes: determining the adsorption energy of each corrosion medium ion in the adsorption configuration, and taking the adsorption configuration with the lowest adsorption energy as the most stable adsorption configuration.

[0009] Optionally, the adsorption energy of the corrosion medium ion in the adsorption configuration under different strains is determined by applying tensile or compressive strain to any adsorption configuration within the residual strain range, including: applying tensile or compressive strain to the most stable adsorption configuration within the residual strain range to determine the adsorption energy of the corrosion medium ion in the most stable adsorption configuration under different strains.

[0010] Optionally, the final state structure and the initial state structure are determined in the plurality of adsorption configurations, and the diffusion barrier of the corrosion medium ion in the oxide film under different strains is determined by simultaneously applying tensile or compressive strain to the final state structure and the initial state structure within the residual strain range, including: taking the most stable adsorption configuration as the final state structure and the metastable adsorption configuration as the initial state structure; applying tensile or compressive strain to the final state structure and the initial state structure within the residual strain range; and using the CI-NEB method to determine the diffusion barrier of the corrosion medium ion on the surface of the adsorption configuration under different strains, which migrates from the metastable adsorption site to the most stable adsorption site.

[0011] Optionally, the surface model is constructed according to the composition and crystal structure of the oxide film, including: constructing a unit cell model according to the composition and crystal structure of the oxide film, and performing structure optimization on the unit cell model by first principles; and constructing a surface model using the surface with the largest exposed area in the unit cell model.

[0012] Optionally, the first principle is realized by VASP software; wherein, the interaction between the electron and the ion is characterized by a projection enhanced wave method; the energy cutoff value of the plane wave basis set is 520 eV, the energy convergence threshold of the self-consistent calculation is 1*10 - 6 eV, the force convergence threshold of the crystal structure optimization of the oxide film is 0.01 eV / Å; for the van der Waals force in the adsorption process, the DFT-D3 dispersion correction method is used to describe the weak interaction.

[0013] Optionally, the tensile and compressive strengths of the surface model are determined, including: determining the volume and total energy of the surface model as functions of strain based on the first principle, and determining the tensile and compressive strengths based on the Nielson-Martin model in combination with the volume and total energy as functions of strain.

[0014] Optionally, after predicting the corrosion process of the aluminum alloy surface, the method further comprises: performing a corrosion experiment on the aluminum alloy, and drawing a corrosion kinetics curve by using the surface or cross-section corrosion morphology of the aluminum alloy under different residual strains; and comparing the corrosion kinetics curve with the predicted corrosion process under each strain to verify the accuracy of the predicted corrosion process.

[0015] Compared with the prior art, the application has the following beneficial effects:

[0016] The aluminum alloy surface corrosion process prediction method considering residual strain of the application can realize the prediction of the corrosion process by constructing a surface model based on the composition of the oxide film on the surface of the aluminum alloy and the corresponding crystal structure, and constructing an adsorption configuration in combination with the corrosion medium ions, without the need for macroscopic experiments; the adsorption energy and diffusion barrier of the corrosion medium ions on the surface of the oxide film under different strains are calculated, the adsorption and diffusion behaviors are quantified, the microcorrosion mechanism of the corrosion medium elements under different stress states is quickly analyzed, the control stage of the corrosion process is determined by the ratio of the adsorption energy and the diffusion barrier, the corrosion behavior under complex working conditions is accurately predicted, and the range of the pre-applied residual stress is determined according to the tensile and compressive strengths of the surface model, so that the calculation efficiency and the rationality of the results can be balanced. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a flowchart of the aluminum alloy surface corrosion process prediction method considering residual strain of the application;

[0018] Figure 2 It is the γ-Al2O3 (110) surface model constructed in embodiment 1 and the γ-Al2O3 (110) surface model adsorbed with Cl ions;

[0019] Figure 3 It is the strain-stress curve of the γ-Al2O3 (110) surface model in embodiment 1.

[0020] Figure 4 Structure diagram of four adsorption configurations constructed in Example 1;

[0021] Figure 5 Adsorption energy column chart of adsorption configuration Al Ⅲa under different strains in Example 1;

[0022] Figure 6 Curve diagram of adsorption energy and diffusion barrier with strain in Example 1;

[0023] Figure 7 Curve diagram of R value with strain in Example 1;

[0024] Figure 8 Corrosion kinetics curve of 2A70 aluminum alloy under different erosion angles in Example 1.

[0025] The purposes, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0026] In order to make the purposes, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below with reference to the drawings in the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0027] The first embodiment of the present application provides an aluminum alloy surface corrosion process prediction method considering residual strain, specifically comprising the following steps:

[0028] Step S1, obtaining the composition and corresponding crystal structure of the oxide film on the surface of the aluminum alloy under the corrosion environment, and extracting the corrosion medium ions; constructing a surface model according to the composition and crystal structure of the oxide film;

[0029] Specifically, the aluminum alloy after corrosion is detected by X-ray diffraction detection and energy spectrum analysis to determine the main components and crystal structure of the protective oxide film on the surface; a unit cell model is constructed according to the composition and crystal structure of the oxide film, and the structure of the unit cell model is optimized by the first principle; a surface model is constructed by using the largest exposed surface in the unit cell model.

[0030] In this embodiment, the first principle is realized by VASP (Vienna Abinitio Simulation Package); wherein the interaction between electrons and ions is characterized by the projection augmented wave method; the energy cutoff value of the plane wave basis set is 520 eV, the energy convergence threshold of the self-consistent calculation is 1x10 -6 eV, the relaxation is performed using the conjugate gradient algorithm, the force convergence threshold for optimizing the crystal structure of the oxide film is 0.01 eV / Å, and the fixed cell volume and lattice parameters are used for optimization; for the van der Waals force in the adsorption process, the DFT-D3 (Density Functional Theory with Dispersion correction of the 3rd generation) is used to describe the weak interaction.

[0031] Step S2, determine the tensile and compressive strength of the surface model; in order to balance the calculation efficiency and the rationality of the results, the tensile and compressive calculation of the clean surface (surface model) is necessary to obtain the tensile and compressive strength.

[0032] Specifically, step S21, based on the first principle, the volume and total energy of the surface model are determined as functions of strain, respectively;

[0033] The surface model is subjected to strain, and the strain is gradually increased along the direction perpendicular to the interface without changing the lattice parameters; and through the first principle, the strain-volume and strain-total energy functions of the surface model are calculated, respectively, and the stress-strain curve is drawn according to the strain-volume and strain-total energy functions, and the deformation energy distribution is obtained according to the stress-strain curve. For example, in the tensile simulation process, the engineering strain is applied in a quasi-static manner, and the increment step of the engineering strain is set to 2%. In this process, the lateral Poisson effect is ignored, and only the atomic position is relaxed. The tensile strain can be expressed as: wherein and represent the initial length and deformed length of the surface model, respectively. By calculating the stress value corresponding to different strain variables, the relationship between strain and surface structure is converted into the relationship between stress and surface structure, so as to determine the influence of different stress values on the surface.

[0034] Step S22, based on the Nielson Martin model, the volume and total energy as functions of strain are combined to determine the tensile and compressive strength, and the tensile or compressive strength is determined by the following formula:

[0035]

[0036] wherein, , V and E are the volume and total energy of the surface model, respectively, as a function of strain The distribution of deformation energy and the corresponding volume distribution obtained in step S21 are substituted into the above formula, and the tensile or compressive strength is obtained.

[0037] In step S3, the surface model is subjected to corrosion medium ion adsorption to obtain a plurality of adsorption configurations.

[0038] After obtaining a plurality of adsorption configurations, one adsorption configuration can be arbitrarily selected as a reference state to determine the corrosion medium ion adsorption tendency, but in order to ensure the accuracy of subsequent prediction, the most stable adsorption configuration needs to be selected as the reference state in the embodiment. The lower the adsorption energy, the more conducive to the adsorption of corrosion medium ions on the surface, and the optimal adsorption site is determined accordingly. Therefore, the specific selection method is to determine the adsorption energy of each corrosion medium ion in the adsorption configuration, and the adsorption configuration with the lowest adsorption energy is selected as the most stable adsorption configuration. The calculation formula of the adsorption energy is:

[0039]

[0040] In the formula, and E and E' are the total energies of the adsorption configuration before and after adsorption, respectively, Ei is the energy of the adsorbed ion, which is calculated in a 15x15x15 Å box.

[0041] In step S4, the residual strain range is determined according to the tensile and compressive strength; in the residual strain range, the adsorption energy of the current corrosion medium ion in the adsorption configuration under different strains is determined by applying tensile or compressive strain to any adsorption configuration.

[0042] Specifically, according to the tensile and compressive strength obtained in step S2, a suitable strain range is selected. In this range, the most stable adsorption configuration is subjected to tensile or compressive strain to determine the adsorption energy of the current corrosion medium ion in the adsorption configuration under different strains.

[0043] In step S5, the final state structure and the initial state structure are determined in the plurality of adsorption configurations, and the diffusion barrier of the corrosion medium ion in the oxide film under different strains is determined by simultaneously applying tensile or compressive strain to the final state structure and the initial state structure in the residual strain range.

[0044] Specifically, the most stable adsorption configuration is taken as the final state structure, and the metastable adsorption configuration is taken as the initial state structure; within the range of residual strain, the initial state structure and the final state structure are simultaneously subjected to tensile or compressive strain; the CI-NEB (Climbing Image Nudged Elastic Band) method is used to determine the corrosion medium ions on the surface of the adsorption configuration under different strains, and the diffusion barrier of the corrosion medium ions migrating from the metastable adsorption site to the most stable adsorption site. The CI-NEB method inserts equal number of intermediate states between the initial state and the final state for each diffusion configuration under each strain, simulates the diffusion path of the corrosion medium ions on the surface of the oxide film, and takes the maximum energy value in the diffusion path as the final diffusion barrier.

[0045] Step S6, the ratio of the absolute value of the adsorption energy of the corrosion medium ions in the adsorption configuration to the diffusion barrier of the corrosion medium ions in the oxide film under each strain is determined, and is taken as the adsorption energy-diffusion barrier ratio under each strain, and the expression is:

[0046]

[0047] In the formula, is the diffusion barrier of the corrosion medium ions in the oxide film, is the adsorption energy-diffusion barrier ratio.

[0048] Step S7, according to the adsorption energy-diffusion barrier ratio under each strain, the corrosion process on the surface of the aluminum alloy is predicted.

[0049] Specifically, step S71, the ratio of the absolute value of the adsorption energy of the corrosion medium ions in the adsorption configuration to the diffusion barrier of the corrosion medium ions in the oxide film under each strain is determined, and is taken as the reference value;

[0050] Step S72, the adsorption energy-diffusion barrier ratio is compared with the reference value, and according to the comparison result, the control stage of the corrosion process of the aluminum alloy under different strains and the corresponding macroscopic corrosion characteristics are determined; wherein, the control stage includes an adsorption dominant control stage and a diffusion dominant control stage.

[0051] Further, when the adsorption energy-diffusion barrier ratio under the current strain is greater than the reference value, the corrosion process is in the adsorption dominant control stage, and the macroscopic corrosion characteristic corresponding to the early stage of corrosion is that the corrosion medium is adsorbed on the surface; when the adsorption energy-diffusion barrier ratio under the current strain is less than the reference value, the corrosion process is in the element diffusion dominant control stage, and the macroscopic corrosion characteristic corresponding to the middle and late stages of corrosion is that the corrosion medium diffuses into the aluminum alloy matrix.

[0052] Step S8, corrosion experiments are performed on the aluminum alloy, and the corrosion kinetics curves are drawn by using the surface or cross-section corrosion morphology of the aluminum alloy under different residual strains; the corrosion kinetics curves are compared with the predicted corrosion process under each strain to verify the accuracy of the predicted corrosion process.

[0053] Specifically, the corrosion experiment adopts a neutral salt spray test, and the experimental temperature is set to 650-980℃; during the experiment, an electronic analytical balance with a precision of 0.1 mg is used to measure the corrosion weight gain, and the corrosion kinetics curves under different strains are drawn, and a scanning electron microscope is used to observe the surface / cross-section morphology of the oxide film to judge the failure state of the oxide film. In order to facilitate comparison, a strain-R curve can be established, and the corrosion kinetics curve is compared with the strain-R curve to determine whether the oxide film failure state in the corrosion kinetics curve under the same stress corresponds to the corrosion process corresponding to R, that is, the accuracy of the prediction method of the present embodiment can be verified.

[0054] In the present embodiment, the first-principle is used to respectively optimize the aluminum alloy bulk structure, optimize the surface structure and adsorb and diffuse, which can ensure the reliability of the theoretical calculation results; the adsorption and diffusion behavior of the corrosion medium ions on the surface of the oxide film under different strains is quantified to obtain the adsorption energy-diffusion barrier ratio, and the adsorption energy-diffusion barrier ratio without applying strain is used as a reference to determine the control stage of the corrosion process, and the precise prediction of the corrosion process under residual stress is realized; by constructing a surface model of the aluminum alloy surface oxide film composition and corresponding crystal structure, and combining with the corrosion medium ions to construct an adsorption configuration, the first-principle calculation can realize the prediction of the corrosion process, without the need for macroscopic experiments, avoiding the limitations and high cost of prediction; constructing the adsorption configuration and calculating the adsorption energy and diffusion barrier can reveal the microscopic mechanism of the adsorption and inward diffusion of the corrosion medium particles on the surface, and further comprehensively analyze the corrosion mechanism of the aluminum alloy from the atomic level.

[0055] Example 1

[0056] Step S10, select the sample, and perform energy spectrum analysis on the sample to determine that the main component of the surface protective oxide film is Al2O3, and in combination with the low-temperature and humid environment, it is determined that the crystal structure of Al2O3 is γ-Al2O3, and the corrosion medium ions are Cl ions and H ions. In the MaterialsProject database, the initial unit cell of γ-Al2O3 is obtained, and modeling and visualization are performed by using MaterialsStudio and VESTA (Visualization for Electronic and Structural Analysis) to obtain the γ-Al2O3 unit cell model, and the structure of the unit cell model is optimized by first principles. Under the actual catalytic conditions, the largest exposed area is the (110) surface, and the γ-Al2O3 (110) surface is modeled in a supercell with a size of 8.404 Å x 8.077 Å x 24.989 Å. The vacuum layer thickness along the Z direction is set to 15 Å, and the structure of the γ-Al2O3 (110) surface model is optimized to obtain a clean surface (surface model) as shown in Figure 2 , and a top view as shown in Figure 2 (c).

[0057] Step S20, strain is applied to the γ-Al2O3 (110) surface model, and the strain is gradually increased along the direction perpendicular to the interface without changing the lattice parameters, and the strain includes tensile strain and compressive strain; the strain-stress curve of the γ-Al2O3 (110) surface model is calculated by first principles, as shown in Figure 3 From the figure, it can be seen that when the applied compressive strain is 16%, the compressive stress reaches the compressive limit, i.e. the compressive strength is 67.15 GPa; the tensile stress gradually increases with the increase of strain, until the strain reaches 24% and reaches the peak value, i.e. the tensile strength is 18.80 GPa, and then the bonding degree of the γ-Al2O3 (110) surface atoms decreases sharply.

[0058] Step S30, Cl ions are adsorbed on the Al sites of the γ-Al2O3 (110) surface model, and H ions are adsorbed on the O sites to balance the charge, and in all calculations, the bottom four layers are frozen, while the remaining four layers of adsorbed Cl ions and hydroxyl groups are allowed to relax. The γ-Al2O3 (110) surface with adsorbed Cl ions is shown in Figure 2 (b), wherein the top view is shown in Figure 2 (d), O 3a , O 3b , O 2a , and O 2bAlIIIa, AlIVa, and AlIVb are the surface-layer tricoordinate and dicoordinate O atoms, respectively; AlIIIa, AlIVa, and AlIVb are the surface-layer tricoordinate and tetracoordinate Al atoms, respectively. Atoms of the same type and with the same letter have the same chemical environment. AlIIIb is the subsurface-layer tricoordinate Al atom. Cl ions were adsorbed onto the surface AlIIIa, AlIVa, and AlIVb sites, and the subsurface AlIIIb site, respectively, resulting in four adsorption configurations. The Cl ion adsorption energy for each adsorption configuration was calculated. The results of the adsorption configuration and adsorption energy calculations are as follows: Figure 4 As shown. Specifically, Figure 4 In the middle (a), Al is the adsorption configuration. Ⅲa Its top view is shown Figure 4 In the middle (e), the adsorption energy is -3.45 eV. Figure 4 (b) represents the adsorption configuration of Al. Ⅲb Its top view is shown Figure 4 In the middle (f), the adsorption energy is -1.92 eV, and the adsorption configuration is Al. Ⅲa and adsorption configuration Al Ⅲb This indicates different adsorption configurations at the three coordination sites. Figure 4 (c) represents the adsorption configuration of Al. Ⅳa Its top view is shown Figure 4 In the middle (g), the adsorption energy is -2.52 eV. Figure 4 In the middle (d), Al is the adsorption configuration. Ⅳb Its top view is shown Figure 5 In the middle (h), the adsorption energy is -2.72 eV, and the adsorption configuration is Al. Ⅳa and adsorption configuration Al Ⅳb This represents the different adsorption configurations at the four-coordinate sites. Based on the calculated adsorption energies of ions in different corrosive media at each adsorption configuration, the most stable adsorption configuration was determined to be Al. Ⅲa .

[0059] Step S40: Based on the tensile and compressive strengths, and considering the efficiency of equilibrium calculations, the adsorption configuration Al is... Ⅲa Apply -6% to 0% compressive strain and 0% to 10% tensile strain, and calculate the adsorption energy. The results are as follows: Figure 6The adsorption energy values at zero strain (0%) are taken as the reference. The compression strain region shows significant changes in adsorption energy: the adsorption energy is only 1.509 eV at a strain of -6%, which is the lowest among all strains; the adsorption energy rises sharply to 3.459 eV at a strain of -4%, reaching a peak; and the adsorption energy decreases to 3.277 eV at a strain of -2%, still at a relatively high level, indicating that compression strain can significantly enhance the adsorption energy, and the enhancement effect of -4% compression strain is the most prominent. In the tensile strain region, the adsorption energy decreases to 2.699 eV at a strain of 4%, which is the lowest in the tensile strain region, indicating that Cl ions are not easily adsorbed on the surface of γ-Al2O3 (110) at this strain; the adsorption energy values at the remaining tensile strains are relatively high, and the overall adsorption energy values are maintained in a relatively high interval of 3.2-3.4 eV.

[0060] Step S50, selecting adsorption configuration Al Ⅲa as the final state structure, and selecting adsorption configuration Al Ⅳa as the initial state structure, the CI-NEB method was used to calculate the diffusion barrier of Cl ions on the surface of γ-Al2O3 (110) under different strains by inserting 5 intermediate states between the initial state and the final state structure for each strain, and the calculation results are shown in Figure 7 From the figure, it can be seen that the diffusion barrier at zero strain (0%) is taken as the reference, which is only 2.311 eV, the lowest among all strains, which indicates that the diffusion resistance of Cl ions in the surface of γ-Al2O3 (110) without strain is extremely small, and the diffusion behavior is extremely easy to occur, and can quickly penetrate into the film. When compression strain is applied, the diffusion barrier is maintained at 3.0-3.4 eV, which is higher than that without strain, indicating that compression strain can greatly increase the diffusion barrier and increase the diffusion resistance, and the diffusion resistance under 4% compression strain is the largest; when tensile stress is applied, within the range of 2%-6% tensile strain, the diffusion barrier gradually increases, while within the range of 8%-10% tensile strain, the diffusion barrier gradually decreases. It shows that small tensile stress helps to hinder the diffusion of Cl ions in the surface of γ-Al2O3 (110), while larger tensile stress will reduce this hindering effect.

[0061] However, only from the single dimension of adsorption energy or diffusion barrier, the corrosion effect of Cl ions on the surface of γ-Al2O3 (110) cannot be comprehensively and accurately judged. As mentioned above, the absolute values of adsorption energy under -4% and -2% compression strain are relatively high, being 3.459 eV and 3.277 eV respectively, indicating that Cl ions are extremely easy to adsorb under these conditions, and it seems that γ-Al2O3 (110) has almost no resistance to the corrosion behavior of Cl ions, but when the actual influence of the strain on corrosion is comprehensively evaluated, the diffusion barriers are as high as 3.365 eV and 3.171 eV respectively, which specifically shows that adsorption and diffusion are cooperatively controlled, and the actual corrosion rate is stable, therefore, the adsorption energy or diffusion barrier alone cannot obtain accurate results.

[0062] Step S60, in order to clarify the effect of Cl ion on the corrosion behavior of aluminum alloy under pre-strain, the adsorption and diffusion synergistic effect of Cl ion on the surface of γ-Al2O3 (110) under different strains in the elastic strain range is calculated, that is, the adsorption energy-diffusion barrier ratio R under each strain is determined, and the results are shown in Figure 8 From the figure, it can be seen that under the compression strain of-6%, the adsorption energy is the lowest and the diffusion barrier is relatively high, and the R value is less than the reference value (R value when the strain is 0), indicating that the Cl ion is not easy to adsorb on the surface of γ-Al2O3 (110) when the early adsorption occurs; and when the corrosion proceeds to the later stage, it is also difficult to penetrate due to its high diffusion barrier, indicating that the corrosion effect under this strain is the best. When the strain decreases to-4% and-2% compression strain, the R value is close to 1, at this time the adsorption energy and the diffusion barrier are in a relatively high and basically flat state, which means that the adsorption driving and diffusion hindering reach a balance, and the corrosion process is controlled by both, the rate is stable, and only considering the adsorption energy under this strain may lead to fast corrosion start, but the R value reveals the balancing effect of diffusion hindering. In addition, under the condition of low tensile stress of 0%-8%, the R value first decreases and then increases, and is less than the reference value, indicating that low tensile stress is beneficial to improve the corrosion resistance of the alloy to a certain extent. It is worth noting that the minimum value is 0.876 under the tensile stress of 4%, which is much lower than the reference value, indicating that the corrosion resistance of the alloy under this strain is the strongest. However, these results cannot be obtained from a single adsorption or diffusion behavior.

[0063] Step S70, 2A70 aluminum alloy is prepared into un-erosion samples, and 2A70 aluminum alloy samples under the erosion of erosion time 30s, erosion speed 0.5MPa, and typical erosion angles (30°, 45°, 90°). Neutral salt spray test is carried out by using salt spray corrosion tester. The environmental temperature of the salt spray test box is 35℃±2℃, the saturation barrel temperature is 47℃, the pH is 6.5~7.2, the test solution is NaCl aqueous solution, water is deionized water, and salt is analytical pure NaCl. The national standard shows that 24h spray wetting 24h drying is one corrosion cycle, and the salt spray test is carried out for 2 cycles, 4 cycles and 6 cycles respectively.

[0064] The corrosion kinetics curves under different erosion angles are obtained by weighing method. The results are shown in ​As shown, it can be seen that the weight loss rate of the eroded 2A70 aluminum alloy sample is relatively large in the initial stage of salt spray corrosion (2 corrosion cycles), and is obviously higher than that of the aluminum alloy sample without erosion; in the middle stage of corrosion (4 corrosion cycles), the weight loss rate of the aluminum alloy sample with an erosion angle of 45° and 90° begins to decrease; in the late stage of corrosion (6 corrosion cycles), the weight loss rate of the aluminum alloy sample with an erosion angle of 90° is the smallest. In addition, the change rule of the weight loss of the aluminum alloy sample with an erosion angle of 30° is the same as that of the aluminum alloy sample without erosion, and the weight loss rate of the aluminum alloy sample with an erosion angle of 30° is slightly larger than that of the aluminum alloy sample without erosion; overall, the corrosion weight loss of the 2A70 aluminum alloy under 90° erosion is the smallest, and the corrosion weight loss of the 2A70 aluminum alloy under 30° erosion is the largest. It can be seen that after six corrosion cycles, the ranking of the corrosion resistance of the 2A70 aluminum alloy samples under different erosion conditions is: 90°> 45°> without erosion> 30°.

[0065] Different erosion angles are directly related to the residual stress on the surface of the alloy. When high-angle (90°) erosion occurs, there is no transverse shear stress because it is perpendicular to the surface of the alloy, and the high-pressure stress downward perpendicular to the surface of the alloy can offset the outward thrust generated by the growth of corrosion products inside the alloy, and the surface of the alloy finally presents residual compressive stress. Similarly, when medium-angle (45°) erosion occurs, the compressive stress perpendicular to the surface of the alloy can offset the outward thrust generated by the growth of corrosion products inside the alloy, but the transverse shear stress cannot be offset, and the transverse shear stress will eventually make the surface of the alloy present low residual tensile stress. When low-angle (30°) erosion occurs, the transverse shear stress is large, which will cause greater residual tensile stress.

[0066] The corrosion kinetics conclusion obtained through the test is that the residual compressive stress caused by high-angle (90°) erosion helps to improve the corrosion resistance of the surface of the alloy, the low residual tensile stress caused by medium-angle (45°) erosion can slow down the corrosion rate of the alloy to a certain extent, and the high residual tensile stress caused by low-angle (30°) erosion increases the corrosion rate of the alloy and reduces the corrosion resistance of the alloy. Therefore, the corrosion kinetics conclusion obtained through the test is consistent with the conclusion predicted in step S60, which verifies the feasibility and reliability of the prediction method of the present application.

[0067] The above is only a preferred embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation using the content of the specification and drawings of the present application, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for predicting surface corrosion progression of an aluminum alloy taking into account residual strain, characterized by, The method comprises the following steps: acquiring the composition and corresponding crystal structure of the oxide film on the surface of the aluminum alloy under a corrosive environment, and extracting ions of a corrosive medium; constructing a unit cell model according to the composition and the crystal structure of the oxide film, and performing structural optimization on the unit cell model by using a first principle; constructing a surface model by using a surface with the largest exposed area in the unit cell film type; determining the tensile and compressive strengths of the surface model; performing adsorption of the ions of the corrosive medium on the adsorption sites of the surface model to obtain a plurality of adsorption configurations; determining the adsorption energies of the ions of the corrosive medium in the adsorption configurations, and taking the adsorption configuration with the lowest adsorption energy as the most stable adsorption configuration; determining a residual strain range according to the tensile and compressive strengths; applying tensile or compressive strain to any adsorption configuration within the residual strain range to determine the adsorption energies of the ions of the corrosive medium in the adsorption configuration under different strains; taking the most stable adsorption configuration as a final state structure and a metastable adsorption configuration as an initial state structure; applying tensile or compressive strain to the final state structure and the initial state structure within the residual strain range; determining the diffusion barrier of the ions of the corrosive medium from the metastable adsorption site to the most stable adsorption site on the surface of the adsorption configuration under different strains by using a CI-NEB method; determining the ratio of the absolute value of the adsorption energy of the ions of the corrosive medium in the adsorption configuration under each strain to the diffusion barrier of the ions of the corrosive medium in the oxide film, and taking the ratio as the adsorption energy-diffusion barrier ratio under each strain; predicting the corrosion process of the surface of the aluminum alloy according to the adsorption energy-diffusion barrier ratio under each strain.

2. The method of claim 1, wherein the method is characterized by: The method for predicting the corrosion process of the surface of the aluminum alloy according to the adsorption energy-diffusion barrier ratio under each strain comprises the following steps: determining the ratio of the absolute value of the adsorption energy of the ions of the corrosive medium in the adsorption configuration without applying strain to the diffusion barrier of the ions of the corrosive medium in the oxide film, and taking the ratio as a reference value; comparing the adsorption energy-diffusion barrier ratio with the reference value, and determining the control stage of the corrosion process of the aluminum alloy and the corresponding macroscopic corrosion feature according to the comparison result.

3. The method of predicting the surface corrosion progression of an aluminum alloy taking into account residual strain according to claim 2, characterized by, The method for comparing the adsorption energy-diffusion barrier ratio with the reference value and determining the control stage of the corrosion process of the aluminum alloy and the corresponding macroscopic corrosion feature according to the comparison result comprises the following steps: when the adsorption energy-diffusion barrier ratio under the current strain is greater than the reference value, the corrosion process is in an adsorption-dominant control stage, and the macroscopic corrosion feature is that the corrosive medium is adsorbed on the surface in the early stage of corrosion; when the adsorption energy-diffusion barrier ratio under the current strain is less than the reference value, the corrosion process is in an element diffusion-dominant control stage, and the macroscopic corrosion feature is that the corrosive medium diffuses into the aluminum alloy matrix in the middle and later stages of corrosion.

4. The method of predicting the surface corrosion progression of an aluminum alloy taking into account residual strain according to claim 1, characterized by, The method for applying tensile or compressive strain to any adsorption configuration within the residual strain range to determine the adsorption energies of the ions of the corrosive medium in the adsorption configuration under different strains comprises the following steps: applying tensile or compressive strain to the most stable adsorption configuration within the residual strain range to determine the adsorption energies of the ions of the corrosive medium in the most stable adsorption configuration under different strains.

5. The method of claim 1, wherein the method is characterized by: The first principle is realized by using VASP software; wherein the interaction between electrons and ions is characterized by a projection augmented wave method; The energy cutoff of the plane wave basis set is 520 eV, the energy convergence threshold of the self-consistent calculation is 1x10 -6 eV, and the force convergence threshold of the oxide film crystal structure optimization is 0.01 eV / Å; for the van der Waals force in the adsorption process, a DFT-D3 dispersion correction method is used to describe the weak interaction.

6. The method of predicting the surface corrosion progression of an aluminum alloy considering residual strain according to claim 1, characterized by, Determine the tensile and compressive strength of the surface model, comprising: Based on the first principle, the volume and total energy of the surface model as a function of strain are determined respectively, and based on the Nielson-Martin model, the tensile and compressive strength are determined by combining the volume and total energy as a function of strain.

7. The method of predicting the surface corrosion progression of an aluminum alloy considering residual strain according to claim 1, characterized by, After predicting the corrosion process of the aluminum alloy surface, the method further comprises: Carrying out corrosion experiment on the aluminum alloy, and using the surface or cross-section corrosion morphology of the aluminum alloy under different residual strains to draw the corrosion kinetics curve; Comparing the corrosion kinetics curve with the predicted corrosion process under each strain to verify the accuracy of the predicted corrosion process.

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