Method for regulating and controlling heterogeneous growth of layered double-metal hydroxide film in friction stir welding seam area

Abstract

The invention discloses a method for regulating and controlling heterogeneous growth of a layered double-metal hydroxide film in a friction stir welding seam area, and relates to the technical field of friction stir welding corrosion protection. The method comprises the following steps: performing friction stir welding on two magnesium alloy plates to obtain a weld zone; and placing the weld zone in an LDHs growth solution for hydrothermal reaction. The reaction time is regulated and controlled through a hydrothermal method, and an MgAl-LDHs film layer grows in a weld zone. More electrochemical active sites are formed in a welding seam area due to severe plastic deformation in the welding process, more precursors are promoted to be formed in the initial growth stage, and the LDHs structure is induced to grow more compactly and more uniformly due to inherent defects of the welding seam area, so that structural optimization of an LDHs film layer is realized, and the welding seam area is better protected from being corroded.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of friction stir welding corrosion protection, and particularly relates to a method for regulating the heterogeneous growth of a layered double hydroxide film in a friction stir welding weld zone. BACKGROUND

[0002] As the lightest metal material in engineering applications, magnesium alloys have high specific strength and specific stiffness, good fire resistance, easy processing, and easy recycling, and play an important role in the industrial low-carbon green transformation. Welding is an important technical means to ensure the industrial application of magnesium alloys. Traditional fusion welding applied to magnesium alloy materials is prone to cause coarse grains in the weld, and defects such as oxidation, porosity, and cracks, which reduce the performance of the weld area. As a solid-phase welding technology, friction stir welding (FSW) realizes mechanical connection before melting through intense stirring, effectively preventing embrittlement and the formation of weakened phases. However, due to the severe plastic deformation and heat input experienced by the weld zone, the microstructure of the weld zone is significantly different from that of the base material zone, and the residual stress between the weld zone and the base material zone makes the corrosion behavior of the magnesium alloy FSW weld zone more complex and severe than that of the base material zone.

[0003] Currently, a common method for preventing corrosion of the substrate is to prepare a protective film on the surface. Layered double hydroxide (LDHs) is a compound similar in structure to brucite. Due to its excellent physical barrier properties, corrosion-inhibiting layered structure, and environmental protection characteristics, it is increasingly being applied to the corrosion protection of magnesium alloys. Its chemical formula can be represented as [Mg 2+ 1-x M 3+ x (OH)2] x+ (A) n- x / n ·mH2O], where M 2+ and M 3+ represent divalent and trivalent metal cations, respectively, A n- represents an interlayer anion, n represents the corresponding charge number of the anion, x is the molar ratio of M 3+ / (M 2+ +M 3+ ), and m represents the number of interlayer water molecules. The LDHs film layer not only acts as a physical barrier, but also as a smart nano-container to capture aggressive chloride ions, achieving an automatic protection effect and effectively improving the corrosion resistance of the substrate. Currently, research on the growth of LDHs and its corrosion resistance mainly focuses on the protection of magnesium alloy surfaces, and there is little research on LDHs film layers on complex substrates in the friction stir welding weld zone. SUMMARY

[0004] The application aims to provide a method for regulating the hetero-growth of a layered double hydroxide film in a friction stir welding weld zone, so as to solve the problem of serious corrosion in the weld zone of a magnesium alloy friction stir welding weld zone due to severe plastic deformation and heat input.

[0005] The application aims to provide a method for regulating the hetero-growth of a layered double hydroxide film in a friction stir welding weld zone, so as to solve the problem of serious corrosion in the weld zone of a magnesium alloy friction stir welding weld zone due to severe plastic deformation and heat input. A method for regulating the hetero-growth of a layered double hydroxide film in a friction stir welding weld zone, comprising the following steps: S1. Friction stir welding two magnesium alloy plates to obtain a weld zone; S2. Placing the weld zone in an LDH growth solution for hydrothermal reaction.

[0006] Further, in S1, the magnesium alloy plate is a magnesium alloy plate with a ZK60 brand.

[0007] Further, in S1, the welding speed of the friction stir welding is 90-110 mm / min, and the pressing amount is 0.2±0.01 mm.

[0008] Further, in S2, before the hydrothermal reaction, the weld zone needs to be pretreated, specifically polished with 500#, 800#, 1500# and 2000# SiC sandpaper, and then cleaned with anhydrous ethanol and deionized water, and dried with cold air.

[0009] Further, in S2, the configuration method of the LDH growth solution comprises the following steps: adding Al(NO3)3 and NaNO3 into deionized water, mixing uniformly, and adjusting the pH to 10.6.

[0010] Further, the amount ratio of Al(NO3)3, NaNO3 and deionized water is 0.015 mol:0.3 mol:1 L.

[0011] Further, the pH is adjusted by using a NaOH solution with a concentration of 1-3 mol / L.

[0012] Further, in S2, the hydrothermal reaction temperature is 373-393 K.

[0013] Further, the hydrothermal reaction temperature is 383 K.

[0014] Further, in S2, the hydrothermal reaction growth time is 13-16 h.

[0015] Compared with the prior art, the application has the following beneficial effects: 1. The present application provides a method for regulating the growth of layered double hydroxide film heterostructure in the weld zone of friction stir welding, which grows MgAl-LDHs film layer in the weld zone by in-situ hydrothermal growth method. The structure of the obtained LDHs film layer has good corrosion protection for the weld base. Due to the severe plastic deformation during welding, more electrochemically active sites are formed in the weld area, which promotes the formation of more precursors in the early stage, and acts as an efficient ion adsorption site in the middle stage, so that the LDHs film layer grown in the weld area is more dense. The dense nanosheet structure prolongs the erosion path of the corrosion medium to the weld base, and the weld area has better corrosion resistance, which more effectively protects the weld area from corrosion.

[0016] 2. By regulating the hydrothermal growth time, the weld area obtains a more dense film layer, the nanosheet of the obtained MgAl LDHs film layer is complete, uniform, regularly arranged, and all distributed perpendicular to the sample surface, the nanosheet edge is clear, the surface is smooth, the ab axis direction is much larger than the c axis, and a typical LDHs nanosheet layer structure is presented.

[0017] 3. The present application utilizes the inherent defects formed in the weld area during the welding process, and the obtained enriched active sites promote the formation of more dense nanosheets, and the increased layer charge density effectively blocks the Cl - erosion, which realizes the structure optimization of the LDHs film layer and better protects the weld area from corrosion by the corrosion medium.

[0018] 4. The present application has simple and environmentally friendly process, and realizes the structure optimization and performance improvement of the LDHs film layer through the triple synergistic mechanism of "weld defect-electrochemical activity-film formation kinetics". The weld defect is used to induce the densification of the film layer, which improves the active corrosion protection performance of the weld area and increases the service life of the FSW magnesium alloy connecting piece. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is the morphology characterization diagram of MgAl LDHs film layer in Example 1 of the present application, wherein the left graph is a scanning electron microscope photo, and the right graph is an energy spectrum diagram;

[0020] Figure 2 It is the XRD spectrum of MgAl LDHs film layer in Example 1; Figure 3 It is the FT-IR spectrum of MgAl LDHs film layer in Example 1; Figure 4 It is the morphology characterization diagram of MgAl LDHs film layer in Example 2, wherein the left graph is a scanning electron microscope photo, and the right graph is an energy spectrum diagram; Figure 5The left picture is a scanning electron microscope photograph, and the right picture is an energy spectrum diagram. Figure 6 The Tafel polarization curves of the weld base and the MgAl LDHs film layer with different growth times are shown in the same coordinate system. DETAILED DESCRIPTION

[0021] The specific embodiments of the present application are described in detail below, but it should be understood that the scope of protection of the present application is not limited by the specific embodiments.

[0022] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0023] It should be understood that in various embodiments of the present application, the size of the sequence number of each process does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0024] The weight of the related components mentioned in the embodiments of the present application can not only refer to the specific content of each component, but also represent the weight ratio between each component, therefore, as long as the content of the related components in the embodiments of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the embodiments of the present application. Specifically, the mass mentioned in the embodiments of the present application can be μg, mg, g, kg and other mass units commonly known in the chemical field.

[0025] Unless otherwise defined, all professional terms used below have the same meaning as generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application.

[0026] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0027] The embodiments of the present application provide a method for regulating the heterogeneous growth of a layered double hydroxide film in a friction stir welding weld zone, specifically comprising the following steps: S1. Two magnesium alloy plates are friction stir welded to obtain a weld zone; S2. The weld zone is placed in an LDH growth solution for hydrothermal reaction.

[0028] The plate is subjected to friction stir welding, and the plastic deformation and high heat input during the welding process drive the generation and movement of dislocations in the metal lattice of the weld zone, so that the dislocation density of the weld zone is higher than that of the base material zone. The obtained friction stir welded joint is placed in the LDHs growth solution, and the high dislocation density brings high internal energy storage, so that more electrochemically active sites are formed in the weld zone; by controlling the hydrothermal growth conditions, the LDHs are nucleated and grown in the weld zone with high electrochemically active sites, and the structure-optimized dense LDH nanosheets are formed on the surface of the weld zone, so that the in-situ controllable heterogeneous growth of the layered double hydroxide film on the weld zone of the magnesium alloy plate is realized.

[0029] In a specific embodiment, the magnesium alloy plate is a ZK60 magnesium alloy plate. The ZK60 magnesium alloy belongs to the Mg-Zn-Zr alloy system, and the main components are magnesium, zinc and zirconium, wherein the zinc content is usually 6%, and the zirconium content is about 0.5%. By adjusting the ratio of zinc and zirconium, the alloy realizes the balance of high strength and good corrosion resistance. In use, a ZK60 with a size of 25 cm x 6 cm x 6 mm is selected for friction stir welding.

[0030] In a specific embodiment, the welding speed of friction stir welding is 90-110 mm / min, and the pressing amount is 0.2±0.01 mm, preferably the welding speed is 100 mm / min, to realize firm welding.

[0031] In a specific embodiment, before the hydrothermal reaction, the weld zone needs to be pretreated, specifically polished with 500#, 800#, 1500# and 2000# SiC sandpaper in turn, then cleaned with anhydrous ethanol and deionized water in turn, and dried with cold air. By pretreatment, the impurities on the surface of the magnesium alloy are removed to prevent interference with the hydrothermal reaction process.

[0032] In a specific embodiment, the configuration method of the LDHs growth solution includes the following steps: adding Al(NO3)3 and NaNO3 into deionized water, mixing uniformly, and adjusting the pH to 10.6. The alkaline environment provides a growth environment, and the growth of LDHs nanosheets in the growth solution can be divided into three stages of dissolution-nucleation-expansion growth. Due to the severe plastic deformation and heat input during the welding process, the weld zone generates and runs dislocations, so that there are a large number of dislocations in the weld zone, and the higher the dislocation density, the higher the internal energy storage, so that the weld zone has more electrochemically active microenvironments.

[0033] In the initial stage of the growth of the weld zone LDHs, the active microenvironment promotes the rapid dissolution of the weld zone matrix, forming more precursor structures of LDHs nanosheets, and in the middle stage, these active microenvironments act as high-efficiency ion adsorption sites, so that Al 3+The preferential diffusion into the precursor structure, together with the high electrochemical activity of the weld zone, drives a unique micro-zone autocatalytic cycle, making the NO 3- Rapid interlamination into the precursor structure, triggering instantaneous nucleation, forms typical LDHs nanosheets.

[0034] The weld zone, as the growth time is prolonged, due to the evolutionary selection in the growth process, LDHs grow stably along the larger ab plane size, the c axis is perpendicular to the substrate surface, the interlamination is spontaneously close-packed through hydrogen bonding and van der Waals force, forming a locally continuous coating layer, until all the Al 3+ is gradually consumed, the LDHs nanosheets intersect or connect with each other, the surface lamella is three-dimensionally stacked in order, forming a structure-optimized dense LDHs coating layer.

[0035] The weld zone is enriched with active sites due to the formation of defects, which makes the nanosheets densify, and the lamella charge density increases, effectively blocking the Cl - erosion, achieving the structural optimization of the LDHs film layer and better protecting the weld zone from the erosion of corrosive media.

[0036] In a specific embodiment, the amount ratio of Al(NO3)3, NaNO3 and deionized water is 0.015 mol:0.3 mol:1 L. At this concentration, further realization of the controlled growth of the LDHs film layer.

[0037] In a specific embodiment, a NaOH solution with a concentration of 1-3 mol / L is used to adjust the pH, which can avoid introducing additional impurities.

[0038] In a specific embodiment, the hydrothermal reaction temperature is 373K-393K; preferably, the hydrothermal reaction temperature is 383K. The hydrothermal reaction is carried out at an appropriate temperature in a constant-temperature air drying oven to ensure complete growth.

[0039] In a specific embodiment, the hydrothermal reaction growth time is 13-16h. The growth time is controlled during the growth of LDHs to promote the uniform distribution of LDHs crystal nucleus and further improve the denseness of LDHs nanosheets.

[0040] The following will be further illustrated with specific embodiments.

[0041] Example 1

[0042] A method for regulating the heterogenous growth of a layered double hydroxide film in a friction stir welding weld zone, comprising the following steps: S1. Two pieces of ZK60 magnesium alloy plates with a size of 25 cm x 6 cm x 6 mm were subjected to friction stir welding at a welding speed of 100 mm / min and a downward pressure of 0.2 mm. After the welding was completed, the plates were cut to obtain a 20 mm x 20 mm x 5 mm weld zone sample with the center of the weld seam as the reference point. The sample was then polished with 500#, 800#, 1500# and 2000# SiC sandpaper, respectively, and then cleaned with anhydrous ethanol and deionized water, respectively, and dried with cold air; S2. 0.015 mol of Al(NO3)3 and 0.3 mol of NaNO3 were added to 1 L of deionized water, mixed uniformly, and the pH was adjusted to 10.6 with a 2 mol / L NaOH solution to obtain an LDHs growth solution. The weld zone sample was placed horizontally in a polytetrafluoroethylene inner tank, and the LDHs growth solution was poured into the tank. The inner tank was placed in a specially designed stainless steel reactor and sealed, and then the reactor was placed in a constant temperature air drying oven at 383 K for hydrothermal reaction. After 13 hours of hydrothermal growth, the sample was cleaned and dried to obtain a ZK60 magnesium alloy friction stir welding seam surface MgAl LDHs film layer, denoted as MgAl LDHs-13h.

[0043] The sample was characterized and tested as follows: (1) Appearance: The appearance of MgAl LDHs-13h was tested by scanning electron microscopy (SEM), as shown in Figure 1 , it can be seen from the left image of Figure 1 that the ZK60 magnesium alloy friction stir welding seam surface MgAl LDHs film layer is distributed entirely perpendicular to the sample surface, with clear nanosheet edges and a smooth surface. The ab axis direction is much larger than the c axis, showing a typical LDHs nanosheet layer structure. From the EDS spectrum in the right image of Figure 1 , it can be seen that there is N element, indicating the presence of NO 3- between the LDHs layers. (2) Structure analysis: The crystallinity of MgAl LDHs-13h was tested by XRD, and the XRD spectrum is shown in Figure 2 . From the figure, it can be seen that the (003) and (006) crystal planes are characteristic diffraction crystal planes of LDHs, and MgAl LDHs has been successfully grown on the surface of the ZK60 magnesium alloy friction stir welding seam.

[0044] (3) Chemical composition: The chemical composition of MgAl LDHs-13h was tested by infrared spectroscopy (FT-IR), and the FT-IR spectrum is shown in Figure 3 . From the figure, it can be seen that the absorption peaks in the range of 400-700 cm -1 correspond to the stretching vibration of metal hydroxide (M-OH). The absorption peak at a wave number of 3696 cm-1 and 3440cm -1 The nearby absorption peaks correspond to the vibrations of HOH and OH, respectively, and can be attributed to water molecules between the LDH layers or hydroxyl groups on the layers. At a wavenumber of 1660 cm⁻¹... -1 The absorption peaks appearing nearby correspond to the stretching vibrations of H₂O, and may be related to the water of crystallization within the LDHs interlayer. At a wavenumber of 1367 cm⁻¹... -1 The absorption peak that appears nearby corresponds to NO3. - Or CO3 2- The stretching vibrations indicate that NO3- is involved in the growth of LDHs. - It enters the middle layer of LDHs to balance the charge and maintain the electroneutrality of LDHs, while CO3... 2- The stretching vibrations may be due to CO2 pollution in the air. The absorption peaks corresponding to the wavenumbers indicated in the FT-IR spectra are all related to the functional groups of the LDH structure.

[0045] Example 2

[0046] A method for controlling the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding is different from Example 1 in that only the hydrothermal growth time is replaced with 14h; a MgAlLDHs film layer is obtained on the surface of the ZK60 magnesium alloy friction stir weld, denoted as MgAl LDHs-14h.

[0047] The morphology of MgAl LDHs-14h was tested by scanning electron microscopy (SEM), such as... Figure 4 As shown, from Figure 4 The left image shows that the MgAl LDHs film on the surface of the ZK60 magnesium alloy friction stir weld is entirely perpendicular to the sample surface, with clear nanosheet edges and a smooth surface, exhibiting a typical LDHs nanosheet structure. However, fine particles are attached to the surface of the LDHs film. Figure 4 The EDS energy spectrum on the right shows the presence of N element, indicating the presence of NO3 in the interlayer of LDHs. - Meanwhile, the Al content in the EDS results was higher than that in Example 1. This may be due to the fine particles attached to the surface of the LDHs film, which may be Al oxides or hydroxides.

[0048] Example 3

[0049] A method for controlling the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding is different from Example 1 in that only the hydrothermal growth time is replaced with 16h; a MgAlLDHs film layer is obtained on the surface of the ZK60 magnesium alloy friction stir weld, denoted as MgAl LDHs-16h.

[0050] The morphology of MgAl LDHs-16h was tested by scanning electron microscopy (SEM), such as... Figure 5 As shown, from Figure 5 As shown in the left image, the MgAl LDHs film on the surface of the ZK60 magnesium alloy friction stir weld is entirely perpendicular to the sample surface, with clear edges and a smooth surface, exhibiting a typical LDHs nanosheet structure. However, some LDHs nanosheets show breakage and collapse, resulting in an uneven surface morphology. Additionally, some particles adhere to the surface of the LDHs film. Figure 5 The EDS spectrum on the right shows the presence of N, indicating the presence of NO3 in the interlayer of LDHs. - Meanwhile, the Al content in the EDS results was higher than that in Examples 1 and 2. This may be due to the fine particles attached to the surface of the LDHs film, which may be Al oxides or hydroxides.

[0051] Example 4

[0052] A method for controlling the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding is different from Example 1 in that only the hydrothermal growth time is replaced with 15h; a MgAlLDHs film layer is obtained on the surface of the ZK60 magnesium alloy friction stir weld, denoted as MgAl LDHs-15h.

[0053] Comparative Example 1

[0054] This comparative example uses the weld zone sample (weld substrate) from Example 1, without subjecting it to hydrothermal reaction.

[0055] Comparative Example 2

[0056] A method for controlling the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding is different from Example 1 in that only the hydrothermal growth time is replaced with 4h; a MgAl LDHs film layer is obtained on the surface of the ZK60 magnesium alloy friction stir weld, denoted as MgAl LDHs-4h.

[0057] Comparative Example 3

[0058] A method for controlling the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding is different from Example 1 in that only the hydrothermal growth time is replaced with 8h; a MgAl LDHs film layer is obtained on the surface of the ZK60 magnesium alloy friction stir weld, denoted as MgAl LDHs-8h.

[0059] Comparative Example 4

[0060] A method for controlling the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding is different from Example 1 in that only the hydrothermal growth time is replaced with 12h; a MgAlLDHs film layer is obtained on the surface of the ZK60 magnesium alloy friction stir weld, denoted as MgAl LDHs-12h.

[0061] Comparative Example 5

[0062] A method for controlling the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding is different from Example 1 in that only the hydrothermal growth time is replaced with 17h; a MgAlLDHs film layer is obtained on the surface of the ZK60 magnesium alloy friction stir weld, denoted as MgAl LDHs-17h.

[0063] Example 5

[0064] Performance testing: Electrochemical corrosion tests were conducted on the weld area samples containing MgAl LDHs film in Examples 1-4, the weld area sample without MgAl LDHs film in Comparative Example 1, the weld area samples containing MgAl LDHs film in Comparative Examples 2-5, and the base material samples. The corrosion resistance test results were represented by electrochemical polarization curves (equipment was P4000a). The test results of Examples 1-4 and Comparative Examples 1-5 are summarized in Table 1.

[0065] Table 1

[0066] As shown in Table 1, the corrosion current density at the ZK60 magnesium alloy friction stir weld seam coated with a dense MgAl LDHs-13h film decreased most significantly. This is because in the initial stage of LDHs growth in the weld region, the active microenvironment promotes the rapid dissolution of the matrix in the weld region, forming more precursor structures for LDHs nanosheets. Subsequently, these active microenvironments act as highly efficient ion adsorption sites, allowing Al in the solution to... 3+ Preferential diffusion into the precursor structure, coupled with the high electrochemical activity of the weld zone, drives a unique micro-regional autocatalytic cycle, enabling NO3 to... - Rapid intercalation into the interlaminar layer triggers instantaneous nucleation. In the weld region, due to evolutionary selection during growth, LDHs grow stably along a larger ab plane with the c-axis perpendicular to the matrix surface. The lamellar layers spontaneously pack together through hydrogen bonds and van der Waals forces, forming a locally continuous overlay until all Al in the solution is reached. 3+ As they are gradually consumed, LDH nanosheets intersect or connect with each other, and the surface layers are stacked in an orderly three-dimensional manner to form a dense LDH capping layer with optimized structure.

[0067] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0068] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for regulating the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding, characterized in that, Includes the following steps: S1. Two magnesium alloy plates are subjected to friction stir welding to obtain the weld zone; S2. Place the weld zone in the LDHs growth solution for hydrothermal reaction.

2. The method for regulating the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding according to claim 1, characterized in that, In S1, the magnesium alloy sheet is a magnesium alloy sheet with the grade ZK60.

3. The method for regulating the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding according to claim 1, characterized in that, In S1, the welding speed of friction stir welding is 90-110 mm / min, and the pressure is 0.2±0.01 mm.

4. The method for regulating the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding according to claim 1, characterized in that, In S2, before the hydrothermal reaction, the weld area needs to be pretreated: after grinding with 500#, 800#, 1500# and 2000# SiC sandpaper in sequence, it is then cleaned with anhydrous ethanol and deionized water in sequence, and then dried with cold air.

5. The method for regulating the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding according to claim 1, characterized in that, In S2, the preparation method of LDHs growth medium includes the following steps: add Al(NO3)3 and NaNO3 to deionized water, mix evenly, and adjust the pH to 10.

6.

6. The method for regulating the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding according to claim 5, characterized in that, The pH was adjusted using a NaOH solution with a concentration of 1-3 mol / L.

7. The method for regulating the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding according to claim 5, characterized in that, The ratio of Al(NO3)3, NaNO3, and deionized water is 0.015 mol: 0.3 mol: 1 L.

8. The method for regulating the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding according to claim 1, characterized in that, In S2, the hydrothermal reaction temperature is 373-393K.

9. The method for regulating the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding according to claim 8, characterized in that, The hydrothermal reaction temperature is 383K.

10. The method for regulating the heterogeneous growth of layered bimetallic hydroxide films in the weld zone of friction stir welding according to claim 1, characterized in that, In S2, the hydrothermal growth time is 13-16 hours.

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