Magnesium alloy surface rare earth element doped high-corrosion-resistance self-healing PEO / LDHs composite coating and preparation method thereof

Abstract

The invention discloses a preparation method of a rare earth element doped high-corrosion-resistance self-healing PEO / LDHs composite coating on the surface of a magnesium alloy. The preparation method comprises the following specific steps: firstly, putting a pretreated base material into a micro-arc oxidation electrolyte to obtain a micro-arc oxidation (PEO) layer; then the PEO layer is placed in a rare earth salt solution for a hydrothermal reaction, then ultrasonic treatment is carried out in absolute ethyl alcohol to prepare a rare earth doped PEO layer, and finally the rare earth doped PEO layer is immersed in an LDHs growth solution for hydrothermal treatment to obtain the composite coating. According to the method, the problems that single rare earth modified PEO is poor in binding force and long in cycle period can be effectively solved, the PEO / LDHs composite coating prepared through the hydrothermal method has high corrosion resistance, rare earth cations with corrosion inhibition performance can be released when the coating is exposed to a corrosion environment, LDH nanosheet reconstruction covers the defects in the coating, and the corrosion resistance of the coating is improved. The magnesium alloy has an obvious self-repairing effect, and the service life of the magnesium alloy can be remarkably prolonged.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy surface treatment technology, specifically to a rare earth element-doped, highly corrosion-resistant, and self-healing PEO / LDHs composite coating for magnesium alloy surfaces and its preparation method. Background Technology

[0002] Magnesium alloys are currently the lightest metallic structural materials, with broad application prospects, including communications, automotive, aerospace, biomedical implants, and energy storage. However, their low standard electrode potential makes them highly susceptible to corrosion in environments such as humid air, sulfur-containing atmospheres, and the ocean, exhibiting high corrosion susceptibility. This characteristic severely limits the widespread application of magnesium alloys.

[0003] Micro-arc oxidation (PEO) is an effective method for modifying metal surfaces, forming a porous, dense ceramic layer that prevents corrosive media from contacting the substrate. Electrolyte substances react to generate oxides, which melt and solidify within the discharge channels, repeatedly accumulating on the surface. However, the inherent micropores and microcracks on the PEO coating surface allow corrosive media to easily penetrate the substrate. Therefore, a method is needed to seal the pores in the PEO coating to further improve its corrosion resistance.

[0004] Rare earth elements have been widely studied and applied in the field of magnesium alloy surface treatment. Rare earth ions are often used as corrosion inhibitors, releasing themselves at damaged areas of the coating to form insoluble oxides or hydroxides, thus endowing the coating with self-healing properties and effectively extending its service life. However, the methods for incorporating rare earth elements into coatings are often complex, requiring multiple cycles and the use of chelating agents, which can easily dissolve the PEO layer and severely affect its corrosion resistance.

[0005] In summary, the current research focus is on how to achieve efficient sealing of PEO coating pores and simultaneously impart stable self-healing properties to magnesium alloys using a simple process, thereby improving the corrosion resistance of magnesium alloys. Summary of the Invention

[0006] This invention addresses the problems of cumbersome rare earth element doping processes and poor corrosion resistance in coatings by proposing a rare earth element-doped, highly corrosion-resistant, and self-healing PEO / LDHs composite coating for magnesium alloy surfaces, along with its preparation method. The composite coating provides superior corrosion protection for magnesium alloys.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A method for preparing a rare earth element-doped, highly corrosion-resistant, and self-healing PEO / LDHs composite coating on a magnesium alloy surface includes the following steps: (1) Pretreatment: The surface of the magnesium alloy substrate is sanded with sandpaper, then cleaned with deionized water and anhydrous ethanol, and dried to obtain the pretreated magnesium alloy substrate. (2) Preparation of micro-arc oxidation layer: The pretreated magnesium alloy substrate obtained in step (1) is immersed in the electrolyte and micro-arc oxidation is performed to form a PEO layer; (3) Ultrasonic treatment after sealing with rare earth salt solution: The sample obtained in step (2) was placed in a rare earth salt aqueous solution for hydrothermal reaction, and after being taken out and dried, it was ultrasonicated in anhydrous ethanol for 30 minutes to obtain a rare earth element doped PEO coating. (4) Growth of LDHs: The rare earth element-doped PEO coating is placed in the LDHs growth solution for hydrothermal reaction to obtain a rare earth element-doped PEO / LDHs composite coating.

[0008] Further, the magnesium alloy substrate in step (1) is AZ31B magnesium alloy.

[0009] Furthermore, the sanding process in step (1) specifically involves sanding the substrate surface with 240#, 400#, 800#, and 1200# sandpaper in sequence.

[0010] Furthermore, the electrolyte in step (2) contains an aqueous solution of 15 g / L Na3PO4, 2 g / L NaOH and 2 g / L NaF.

[0011] Furthermore, the micro-arc oxidation process in step (2) is as follows: a magnesium alloy is used as the anode, a stainless steel plate is used as the cathode, the operating mode is constant current mode, and the current density is 2 A / dm³. 2 The frequency was 800 Hz, the duty cycle was 40%, the reaction time was 20 min, the electrolyte temperature was kept at 25℃, and the electrolyte was continuously stirred with a magnetic rotor.

[0012] Further, the concentration of the rare earth salt aqueous solution in step (3) is 0.03 mol / L, and the rare earth salt is selected from one of Ce(NO3)3·6H2O, La(NO3)3·6H2O and Y(NO3)3·6H2O; the hydrothermal reaction temperature is 110℃ and the reaction time is 1 h.

[0013] Further, the preparation steps of the LDHs growth solution in step (4) are as follows: the pH of the deionized water containing 0.08 mol / L Mg(NO3)2·6H2O, 0.02 mol / L Al(NO3)3·9H2O and 0.08 mol / L NaNO3 is adjusted to 12 with 5 mol / L NaOH, then aged at 75℃ for 6 hours, and then left to stand for 4 hours.

[0014] Furthermore, the hydrothermal reaction in step (4) is carried out at a temperature of 120°C for 12 hours.

[0015] A rare earth element-doped, highly corrosion-resistant, and self-healing PEO / LDHs composite coating on the surface of a magnesium alloy obtained by the above preparation method.

[0016] The beneficial effects of this invention are as follows: (1) This invention prepares a PEO layer on the surface of a magnesium alloy and incorporates rare earth elements into the PEO layer. The self-healing behavior of rare earth elements in a corrosive environment and the resulting particles seal the pores of the PEO layer to extend the service life of the magnesium alloy. At the same time, it has good adhesion to the magnesium alloy substrate. Among the rare earth elements, cerium salts form a new rare earth oxide phase, while lanthanum salts and yttrium salts cannot form a new rare earth oxide phase. They are not incorporated into the micro-arc oxidation layer in the form of a film, but rather fill the micropores and defects in the micro-arc oxidation film layer through chemical bonding.

[0017] (2) In this invention, LDHs, as a type of functional nanomaterial, not only act as a physical barrier to seal the micropores and microcracks on the PEO layer, but also, due to their unique interlayer anion exchange properties, allow ions, small inorganic molecules, and organic macromolecules to insert into the LDHs layer through ion exchange. Furthermore, they can capture Cl in corrosive environments. - , reduce Cl - The concentration on the coating surface is adjusted to achieve a protective effect. It also acts as a nano-container for anionic corrosion inhibitors, actively releasing interlayer corrosion inhibitors when the LDH layer is damaged, thus protecting the substrate.

[0018] (3) When the coating is exposed to a corrosive environment, it can release more and more rare earth cations to reach the coating defects for repair, which significantly improves the corrosion resistance of magnesium alloy and broadens the application range of magnesium alloy.

[0019] (4) Compared with the prior art, the present invention has a simpler preparation process, is environmentally friendly and pollution-free, lowers the technical threshold in the production process, has strong scalability, and can significantly reduce the corrosion current density of magnesium alloy substrates, thus having good economic benefits.

[0020] (5) In this invention, the release of rare earth ions and the surface reconstruction of LDH when the composite coating is damaged endow the coating with a dual self-healing effect. When the composite coating is exposed to a corrosive environment, the rare earth ions doped into PEO can be released to form a hydroxide self-healing layer covering the coating defects; secondly, the LDH grown on PEO can capture Cl in the corrosive environment. - Release some or all of the interlayer NO3 - This reduces the corrosive effect of chloride ions on the metal substrate, while achieving self-repair at the damaged coating site through surface reconstruction. Attached Figure Description

[0021] Figure 1 This invention discloses a process flow diagram of a rare earth element-doped, highly corrosion-resistant, and self-healing PEO / LDHs composite coating for magnesium alloy surfaces and its preparation method.

[0022] Figure 2 Cross-sectional SEM and EDS images of PEO.

[0023] Figure 3 (a) XRD patterns of PEO doped with different rare earth ions; (b) XRD patterns of PEO / LDHs doped with different rare earth ions.

[0024] Figure 4 : Test diagram of the bonding force of PEO doped with different rare earth ions.

[0025] Figure 5 High-resolution XPS spectra of PEO with different rare earth ions: (a) Ce 3d, (b) O 1s, (c) La 3d, (d) O 1s, (e) Y 3d, and (f) O 1s.

[0026] Figure 6 SEM images of PEO / LDH composite coatings doped with different rare earth ions, where (a1)~(a2) are PEO layers at different magnifications, (b1)~(b2) are the morphologies of La-PEO and LDH after growth, (c1)~(c2) are the morphologies of Ce-PEO and LDH after growth, and (d1)~(d2) are the morphologies of Y-PEO and LDH after growth.

[0027] Figure 7 Potentiodynamic polarization curves of PEO and PEO / LDHs composite coatings with different rare earth ion doping.

[0028] Figure 8 Metallographic micrographs of the scratched area of ​​the sample after immersion in 3.5% NaCl solution for 24-72 hours.

[0029] Figure 9 SEM images and micro-area XRD patterns of the scratched areas of Y-PEO / LDHs samples. Detailed Implementation

[0030] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0031] Example 1 A method for preparing a Ce-doped, highly corrosion-resistant, and self-healing PEO / LDHs composite coating on the surface of a magnesium alloy, comprising the following specific steps: (1) Pretreatment: The surface of the AZ31B magnesium alloy substrate was polished with sandpaper of 240#, 400#, 800# and 1200# in sequence, then rinsed with deionized water and anhydrous ethanol, and dried with cold air to obtain the pretreated magnesium alloy substrate. (2) Preparation of micro-arc oxidation (PEO) layer: The AZ31B magnesium alloy substrate pretreated in step (1) was placed in a 3L deionized aqueous solution (electrolyte) composed of 15g / L Na3PO4, 2g / L NaOH and 2g / L NaF for micro-arc oxidation. The AZ31B magnesium alloy substrate was used as the anode and the stainless steel plate was used as the cathode. The working mode was constant current mode and the current density was 2 A / dm. 2 The frequency was 800 Hz, the duty cycle was 40%, the reaction time was 20 min, and the electrolyte temperature was kept at 25℃ under the water cooling system. At the same time, the electrolyte was continuously stirred with a magnetic rotor to obtain the PEO layer. Figure 2 The images show cross-sectional SEM and EDS images of PEO. The thickness produced by the micro-arc oxidation process of this invention can reach 26.4 μm.

[0032] (3) Ultrasonic treatment after sealing with rare earth salt solution: The PEO layer was placed in a 0.03 mol / L Ce(NO3)3·6H2O aqueous solution and hydrothermally heated at 110℃ for 1 hour. After being taken out and dried, it was ultrasonically treated in anhydrous ethanol for 30 min to obtain a rare earth ion Ce-doped PEO layer (Ce-PEO). (4) Growth of LDHs: The rare earth ion Ce-doped PEO layer was placed in the LDHs growth solution. The composition of the MgAl-LDHs growth solution was 0.08 mol / L Mg(NO3)2·6H2O, 0.02 mol / L Al(NO3)3·9H2O, and 0.08 mol / L NaNO3 in deionized water. The pH of the solution was adjusted to 12 with 5 mol / L NaOH. The solution was then aged at 75°C for 6 hours and then allowed to stand at the same temperature for 4 hours to obtain the MgAl-LDHs growth solution. The Ce-doped PEO layer was placed in the MgAl-LDHs growth solution and hydrothermally reacted at 120°C for 12 hours to obtain the coating as a Ce-doped PEO / LDHs composite coating (Ce-PEO / LDH).

[0033] Example 2 A rare earth element La-doped, highly corrosion-resistant, and self-healing PEO / LDHs composite coating for magnesium alloy surfaces and its preparation steps are as follows: (1) Pretreatment: The surface of the AZ31B magnesium alloy substrate was polished with sandpaper of 240#, 400#, 800# and 1200# in sequence, then rinsed with deionized water and anhydrous ethanol, and dried with cold air to obtain the pretreated magnesium alloy substrate. (2) Preparation of micro-arc oxidation (PEO) layer: The AZ31B magnesium alloy substrate pretreated in step (1) was placed in a 3L deionized water solution (electrolyte) composed of 15g / L Na3PO4, 2g / L NaOH and 2g / L NaF for micro-arc oxidation. The AZ31B magnesium alloy substrate was used as the anode and the stainless steel plate was used as the cathode. The working mode was constant current mode and the current density was 2A / dm. 2 The reaction was conducted at a frequency of 800 Hz, a duty cycle of 40%, and a reaction time of 20 min. The entire reaction system was kept at an electrolyte temperature of 25°C under a water-cooling system, while the electrolyte was continuously stirred using a magnetic rotor to obtain a PEO layer. Figure 2 The images show cross-sectional SEM and EDS images of PEO, demonstrating that the micro-arc oxidation process of this invention can produce a thickness of up to 26.4 μm. (3) Ultrasonic treatment after sealing with rare earth salt solution: The PEO layer was placed in a 0.03 mol / L La(NO3)3·6H2O aqueous solution and hydrothermally heated at 110℃ for 1 hour. After being taken out and dried, it was ultrasonically treated in anhydrous ethanol for 30 min to obtain a rare earth ion La-doped PEO layer (La-PEO). (4) Growth of LDHs: The rare earth ion La-doped PEO layer was placed in the LDHs growth solution. The composition of the MgAl-LDHs growth solution was 0.08 mol / L Mg(NO3)2·6H2O, 0.02 mol / L Al(NO3)3·9H2O, and 0.08 mol / L NaNO3 in deionized water. The pH of the solution was adjusted to 12 with 5 mol / L NaOH. The solution was then aged at 75°C for 6 hours and then allowed to stand at the same temperature for 4 hours to obtain the MgAl-LDHs growth solution. The La-doped PEO layer was placed in the MgAl-LDHs growth solution and hydrothermally reacted at 120°C for 12 hours. The resulting coating was a La-doped PEO / LDHs composite coating (La-PEO / LDH).

[0034] Example 3 A rare earth element Y-doped, highly corrosion-resistant, and self-healing PEO / LDHs composite coating for magnesium alloy surfaces and its preparation steps are as follows: (1) Pretreatment: The surface of the AZ31B magnesium alloy substrate was polished with sandpaper of 240#, 400#, 800# and 1200# in sequence, then rinsed with deionized water and anhydrous ethanol, and dried with cold air to obtain the pretreated magnesium alloy substrate. (2) Preparation of micro-arc oxidation (PEO) layer: The AZ31B magnesium alloy substrate pretreated in step (1) was placed in a 3L deionized aqueous solution (electrolyte) composed of 15g / L Na3PO4, 2g / L NaOH and 2g / L NaF for micro-arc oxidation. The AZ31B magnesium alloy substrate was used as the anode and the stainless steel plate was used as the cathode. The working mode was constant current mode and the current density was 2 A / dm. 2 The reaction was conducted at a frequency of 800 Hz, a duty cycle of 40%, and a reaction time of 20 min. The entire reaction system was kept at an electrolyte temperature of 25°C under a water-cooling system, while the electrolyte was continuously stirred using a magnetic rotor to obtain a PEO layer. Figure 2 The images show cross-sectional SEM and EDS images of PEO, demonstrating that the micro-arc oxidation process of this invention can produce a thickness of up to 26.4 μm. (3) Ultrasonic treatment after sealing with rare earth salt solution: The PEO layer was placed in a 0.03 mol / LY(NO3)3·6H2O aqueous solution and hydrothermally heated at 110℃ for 1 hour. After being taken out and dried, it was ultrasonically treated in anhydrous ethanol for 30 min to obtain a rare earth ion Y-doped PEO layer (Y-PEO). (4) Growth of LDHs: The rare earth ion Y-doped PEO layer was placed in the LDHs growth solution. The composition of the MgAl-LDHs growth solution was deionized water containing 0.08 mol / L Mg(NO3)2·6H2O, 0.02 mol / L Al(NO3)3·9H2O, and 0.08 mol / L NaNO3. The pH of the solution was adjusted to 12 with 5 mol / L NaOH. The solution was then aged at 75℃ for 6 hours and then allowed to stand at the same temperature for 4 hours to obtain the MgAl-LDHs growth solution. The Y-ion doped PEO layer was placed in the MgAl-LDHs growth solution and hydrothermally reacted at 120℃ for 12 hours. The resulting coating was a Y-ion doped PEO / LDHs composite coating (Y-PEO / LDH).

[0035] Figure 1 This is a process flow diagram of the preparation method of a rare earth element-doped, highly corrosion-resistant, and self-healing PEO / LDHs composite coating on the surface of a magnesium alloy according to the present invention.

[0036] The prepared rare-earth element-doped PEO / LDHs composite coating was subjected to XRD diffraction analysis, such as... Figure 3 As shown in (a), the main components of the PEO coating are MgO and Mg3(PO4)2, with the strongest Mg matrix peak visible. The peaks of the La-PEO sample are indistinguishable from those of PEO because the La doped into PEO may be amorphous or too thin to be detected. The Ce-PEO sample shows a peak at 28.5°C. oNew diffraction peaks appeared, corresponding to typical CeO2 peaks; the Y-PEO sample showed a peak at 9.7. o The presence of a peak in Y(NO3)3·nH2O indicates the presence of incompletely decomposed yttrium nitrate hydrate during the hydrothermal process. Figure 3 (b) It can be seen that the LDH peak of Y-PEO growth is the strongest, followed by Ce-PEO, but both exhibit peak envelopment. This indicates that the doping of rare earth ions with larger ionic radii into the LDH interlayer will disrupt the LDH lattice. Y ions have a relatively small ionic radius (0.089 nm) and are more easily doped into the LDH interlayer. In addition, Y has the lowest electronegativity, which enhances the electrostatic interaction between the host layer and the interlayer anions.

[0037] According to ASTM D3359 standard, adhesion testing was performed on Re-PEO films with a thickness not exceeding 50 μm. Eleven cuts were made at 1 mm intervals, and the cuts were checked to see if they penetrated the substrate. 3M tape was then applied flat to the cut surfaces, and the tape was peeled off at approximately 180° within 90±30 seconds. Figure 4 As shown, the Ce-PEO group showed slight peeling at the tangent of the membrane layer, with a peeling area of ​​less than 5%, and the adhesion rating was 4B. The La-PEO and Y-PEO groups showed complete and smooth tangents without peeling, and the adhesion rating was 5B for both groups.

[0038] Figure 5 The XPS spectra of PEO doped with different rare earth elements show that ten peaks can be fitted to the Ce 3d nuclear energy levels, corresponding to Ce 3d 3 / 2 and Ce 3d 5 / 2 Furthermore, it exists in two valence states, Ce(III) and Ce(IV). Under the same conditions, two peaks can be fitted to the high-resolution spectrum of O1s. One peak corresponds to the Ce-O bond in CeO2, and the other peak corresponds to the OH group of water absorbed on the surface. - The La 3d nuclear energy levels can be fitted with seven peaks, corresponding to La 3d 3 / 2 and La 3d 5 / 2 Two peaks can be fitted to Y3d, corresponding to Y3d 3 / 2 and Y 3d 5 / 2 In both groups, no O1s except OH were observed. - Other peaks besides those shown indicate that rare earth elements have been successfully incorporated into the PEO layer.

[0039] Figure 6Figures (b1-d1) show the SEM morphology of rare earth ion-doped PEO. Compared to PEO (a1), the Ce-PEO group shows a large number of particulate materials, while the Y-PEO group also shows particulate materials, but in smaller quantities, which can provide some sealing effect on the PEO pores. The La-PEO group shows no difference in morphology from PEO, possibly because La element is doped into PEO in other amorphous forms. Figures (b2-d2) show the morphology after LDH growth. It can be seen that the LDH grown in Ce-PEO is relatively sparse, while the LDH grown in La-PEO is amorphous and curled, with large pores between the flakes, which cannot delay the corrosion of the magnesium alloy substrate. The Y-PEO group grows a large number of thin-plate LDH flakes, and the LDH flakes grow densely, effectively sealing the PEO pores and increasing Cl... - The difficulty of penetration is related to the radius of these rare earth ions. The ion radii, from largest to smallest, are La>Ce>Y. The larger the ion radius, the greater the lattice disruption of LDH by rare earth ions. Y ions, on the other hand, have a smaller radius and are more likely to undergo isomorphous substitution with Al ions, resulting in a denser LDH growth.

[0040] Figure 7 Table 1 shows the potentiodynamic polarization curves of seven different coatings after immersion in a 3.5% NaCl aqueous solution. The fitting parameters are shown in Table 1. Compared with PEO, the self-corrosion current of rare earth-doped PEO is reduced to a certain extent. The self-corrosion current of Ce-PEO and Y-PEO is reduced by an order of magnitude. The LDH wafers grown by the Y-PEO group are more dense, and the self-corrosion current density can reach 5.557 × 10⁻⁶. -8 It exhibits the best corrosion resistance and can provide superior corrosion protection for magnesium alloys.

[0041] Figure 8 The images show the microstructure of the scratched areas of each sample after artificial scratch treatment and immersion in solution for 24, 48, and 72 hours, respectively. It can be seen that the Y-PEO / LDHs sample exhibited a significant self-healing effect after immersion for 48 hours, and after 72 hours, significant repair product deposition appeared in the scratched area, covering the exposed magnesium alloy substrate.

[0042] Figure 9 The magnified image of the scratched area of ​​Y-PEO / LDHs shows the self-healing products in the shape of nanoflowers. Micro-area XRD analysis of the scratched area revealed characteristic peaks of the (003) and (006) crystal planes of LDHs nanosheets, indicating that the self-healing effect of the composite coating is due to the reconstruction of LDH nanosheets in the scratched area. The self-healing products cover the damaged coating and provide corrosion protection for the magnesium alloy.

[0043] Table 1. Fitting parameters for the potentiodynamic polarization curves of LDH grown with different RE-PEOs. The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a rare earth element-doped, highly corrosion-resistant, and self-healing PEO / LDHs composite coating on a magnesium alloy surface, characterized in that: Includes the following steps: (1) Pretreatment: The surface of the magnesium alloy substrate is sanded with sandpaper, and then rinsed with deionized water and anhydrous ethanol and dried to obtain the pretreated substrate; (2) Preparation of micro-arc oxidation layer: The pretreated substrate obtained in step (1) is immersed in electrolyte and micro-arc oxidation is performed to form a PEO layer; (3) Ultrasonic treatment after sealing with rare earth salt solution: The sample obtained in step (2) was placed in a rare earth salt aqueous solution for hydrothermal reaction, and after being taken out and dried, it was ultrasonicated in anhydrous ethanol for 30 minutes to obtain a rare earth element doped PEO coating. (4) Growth of LDHs: The rare earth element-doped PEO coating is placed in the LDHs growth solution for hydrothermal reaction to obtain a rare earth element-doped PEO / LDHs composite coating.

2. The preparation method according to claim 1, characterized in that: The magnesium alloy substrate in step (1) is AZ31B magnesium alloy.

3. The preparation method according to claim 1, characterized in that: In step (1), the sanding process involves sanding the substrate surface with 240#, 400#, 800#, and 1200# sandpaper in sequence.

4. The preparation method according to claim 1, characterized in that: The electrolyte in step (2) is an aqueous solution of 15 g / L Na3PO4, 2 g / L NaOH and 2 g / L NaF.

5. The preparation method according to claim 1, characterized in that: The micro-arc oxidation process in step (2) is as follows: magnesium alloy is used as the anode, stainless steel plate is used as the cathode, the working mode is constant current mode, and the current density is 2 A / dm. 2 The frequency was 800 Hz, the duty cycle was 40%, the reaction time was 20 min, the electrolyte temperature was kept at 25℃, and the electrolyte was stirred with a magnetic rotor.

6. The preparation method according to claim 1, characterized in that: The concentration of the rare earth salt aqueous solution in step (3) is 0.03 mol / L, and the rare earth salt is selected from Ce(NO3)3·6H2O, La(NO3)3·6H2O and Y(NO3)3·6H2O; the hydrothermal reaction temperature is 110℃ and the reaction time is 1 h.

7. The preparation method according to claim 1, characterized in that: The preparation steps of the LDHs growth solution in step (4) are as follows: the pH of the deionized water containing 0.08 mol / L Mg(NO3)2·6H2O, 0.02 mol / L Al(NO3)3·9H2O and 0.08 mol / L NaNO3 is adjusted to 12 with 5 mol / L NaOH, then aged at 75℃ for 6 hours, and then left to stand for 4 hours.

8. The preparation method according to claim 1, characterized in that: The hydrothermal reaction in step (4) is carried out at a temperature of 120°C for 12 hours.

9. A rare earth element-doped, highly corrosion-resistant, and self-healing PEO / LDHs composite coating on the surface of a magnesium alloy, obtained by the preparation method according to any one of claims 1 to 8.

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