Preparation method of EDTA-assisted low-temperature water bath MAO / LDH hybrid coating on magnesium alloy substrate surface

Abstract

This invention relates to a biodegradable magnesium alloy surface coating technology integrating structure and function, and more particularly to a method for preparing an EDTA-assisted low-temperature water bath MAO / LDH hybrid coating on a magnesium alloy substrate. The method comprises three steps: magnesium alloy pretreatment, MAO substrate preparation, and low-temperature water bath deposition of metal ion-doped LDH. Using a Mg-Al magnesium alloy after micro-arc oxidation as the substrate, an LDH coating doped with functionalized metal ions is synthesized on the MAO coating using a low-temperature water bath method. The process is green, environmentally friendly, simple, easy to control, and has low production costs. The resulting coating exhibits characteristics such as dense structure, strong adhesion, excellent corrosion resistance, and ion exchangeability. Different metal ions are introduced into the LDH coating using the chelating effect of EDTA, and different properties are achieved by loading different metal ions into the LDH coating.

Description

Technical Field

[0001] This invention relates to a coating technology that integrates structure and function on the surface of biodegradable magnesium alloys, and more particularly to a method for preparing an EDTA-assisted low-temperature water bath MAO / LDH hybrid coating on the surface of a magnesium alloy substrate. Background Technology

[0002] Orthopedic diseases caused by population aging have gradually become a major threat to human health, leading to a growing demand for bone implant materials. Magnesium alloys, due to their excellent mechanical properties, biocompatibility, and biodegradability, are outstanding candidates for biodegradable implant materials. Currently, medical-grade magnesium alloys are available on the market in Germany and South Korea. However, the degradation rate of magnesium alloys is uncontrollable; excessively rapid degradation can cause the magnesium alloy to lose its mechanical integrity, leading to alkalization of the lesion site and inducing a series of inflammations. Therefore, developing a functional, integrated coating that can improve the corrosion resistance of magnesium alloys while enhancing the antibacterial properties of the coating is particularly important.

[0003] Traditional magnesium alloy surface coatings such as calcium phosphate coatings, hydroxyapatite coatings, chemical conversion films, and MAO coatings have limited functionality and certain performance limitations. For example, micro-arc oxidation technology generates a ceramic-like metal oxide film on the magnesium alloy surface under high pressure. Although this coating has high adhesion to the magnesium alloy surface, its porous structure limits its application, allowing corrosive media to corrode the magnesium alloy substrate through its pores. MAO coatings exhibit good corrosion resistance in the early stages of corrosion, but in later stages, they actually accelerate the corrosion rate of the base magnesium metal.

[0004] Therefore, existing research has proposed some methods to improve the density of MAO coatings, such as:

[0005] Chinese patent application CN116288597A discloses a voltage regulation method for preparing a high-density MAO thin film on the surface of AZ91D magnesium alloy, including the following steps: a) pretreatment of magnesium alloy surface: sanding and cleaning; b) immersing the sample in a phosphate + silicate composite electrolyte; c) preparing the MAO coating using a bipolar pulse power supply in constant voltage mode.

[0006] Although the MAO coatings prepared by the above techniques optimize various parameters of micro-arc oxidation and improve film uniformity, thickness (0–40 μm), and corrosion resistance (neutral salt spray test corrosion time >500 h), porosity still exists. The risk of corrosive media contacting the magnesium alloy substrate through the through-holes and causing galvanic corrosion remains.

[0007] Therefore, we believe that sealing MAO with appropriate post-processing methods is a common strategy to improve the protective performance of MAO.

[0008] Hydrotalcite (LDH) coatings possess ion exchange capabilities, providing not only a physical barrier against corrosive media but also allowing the exchange of chloride ions (Cl-) within the corrosive medium. - This reduces its aggression on the surface oxide film, thereby extending the corrosion resistance of the magnesium alloy coating.

[0009] Currently, the preparation of biomedical hydrotalcite on magnesium alloy surfaces mainly falls into two categories: single hydrotalcite coating preparation and hydrotalcite composite coating preparation. The preparation of single hydrotalcite coatings includes in-situ growth, co-precipitation, electrochemical deposition, spin coating, and anion exchange. In-situ growth technology is considered a promising alternative method due to its simplicity and versatility in practice, as well as the strong adhesion of the coating to the metal surface through chemical bonds. Its main methods include one-step in-situ growth, two-step in-situ growth, hydrothermal treatment, urea hydrolysis, and steam methods.

[0010] However, the corrosion resistance and functionality of a single hydrotalcite coating are insufficient to solve the problems of magnesium alloy applications in harsh environments. Therefore, it is necessary to develop novel hydrotalcite composite coatings. Composite hydrotalcite coatings possess different functions due to their unique structure and ion exchange capabilities.

[0011] Besides the challenges of corrosion resistance, when magnesium alloys are used as implant materials, the issues of bacterial infection and the growth of surface microbial films must also be considered. Although magnesium ions themselves have some antibacterial properties, they are insufficient to prevent bacterial infection at the implantation site. Furthermore, common magnesium alloy antibacterial coatings (electrophoretic deposition of drug suspensions (CN115305544A), drug composite coatings (CN114306740A)) often involve complex preparation processes and high drug prices. Positively charged LDH layers make it possible to synthesize LDHs with various electronic structures and specific surface properties, such as introducing Gd into LDHs. 3+ It allows for simultaneous MRI imaging and ischemia-reperfusion therapy. Furthermore, LDH exhibits good biocompatibility and cell adhesion (Duan Xue et al., Intercalation Assembly Chemistry of Inorganic Supramolecular Materials, Science Press, 2009). Therefore, we considered incorporating functional metal ions into hydrotalcite to address the issue of coating antibacterial properties.

[0012] Typically, the metal ions that can be introduced into coatings as antibacterial agents mainly include Ag. + Cu 2+ Zn 2+ For example, Zn can be introduced into montmorillonite (MMT) via hydrothermal ion exchange. 2+After loading onto the surface of AZ31 magnesium alloy, the magnesium alloy exhibited significant resistance to *Escherichia coli* and *Staphylococcus aureus* (YHZou, et al., *Acta Biomater.* 98 (2019) 196-214). Additionally, the magnesium alloy surface was coated with a hydroxyapatite / Cu-ZIF-8 composite coating. 2+ The release of [the substance] also exhibits significant antibacterial properties (L. Ling, et al., Colloids Surf. B ​​Biointerfaces 219(2022)112810-112810). However, these coatings contain metal ions (Ag) with electrode potentials higher than those of magnesium. + Cu 2+ Zn 2+ During the corrosion process of magnesium, it gains electrons and is reduced to metal atoms, which causes galvanic corrosion between the magnesium alloy matrix and the metal. In addition, the introduction of heavy metal ions such as copper can also have a certain impact on human health.

[0013] Compared to the aforementioned metal ions, gallium's electrode potential is closer to that of magnesium and its alloys, thus avoiding galvanic corrosion between different metals. Furthermore, studies have indicated that gallium ions possess certain osteogenic and antibacterial properties. For instance, gallium-containing mesoporous bioglass nanoparticles synthesized via the sol-gel method exhibit high resistance to both Gram-positive and Gram-negative bacteria; adding an appropriate amount of gallium ions to zinc oxide nanoparticles enhances their antibacterial properties (F. Kurtuldu, et al., Mater. Sci. Eng. C124 (2021) 112050).

[0014] Therefore, it is proposed that gallium-containing LDH may be a novel MAO sealing coating, which can improve both corrosion resistance and antibacterial properties of the coating.

[0015] However, while preparing LDH coatings on magnesium alloy substrates is relatively simple and easy to achieve, it is difficult on MAO coatings because MAO coatings are very sensitive to the solution environment in which LDH is generated. For example, high temperatures and low pH levels have adverse effects on MAO coatings. Excessive dissolution of the MAO coating reduces its corrosion resistance. There are three methods for growing LDH on MAO coatings:

[0016] (1) If the dissolution rate of MAO is faster than the formation rate of LDH, the corrosion resistance of the composite coating may be relatively lower than that of the single MAO coating. For example, Chen Junfeng et al. prepared Mg-Al-LDH on MAO coating by hydrothermal treatment for 1 h in a solution containing 0.1M aluminum nitrate and 0.6M ammonium nitrate at pH 7 at 95℃. Their electrochemical results showed that the corrosion current density of the MAO / LDH composite coating was an order of magnitude higher than that of the pure MAO sample.

[0017] (2) If the dissolution rate of MAO is approximately equal to the formation rate of LDH, the corrosion resistance of the composite coating may remain unchanged. Peng Feng et al. prepared a MAO / LDH composite coating by hydrothermal treatment in a solution at 120℃ and pH 12.8 for 12 h. The corrosion current density of the composite coating did not change significantly compared with the single MAO coating.

[0018] (3) If the MAO dissolution rate is less than the LDH formation rate, the corrosion resistance of the composite coating is improved. Based on the MAO coating of AZ91 magnesium alloy, Jiang Dan et al. prepared magnesium-aluminum LDH using a hydrothermal co-precipitation method at 120℃ and pH 11. The corrosion current density of the composite coating increased from 1.27 × 10⁻⁶. -6 A·cm -2 Reduced to 1.03×10 -7 A·cm -2 .

[0019] The changes in corrosion resistance of the composite coating under the above three conditions indicate that optimizing the solution temperature and pH is crucial for the growth of LDH on MAO surfaces and the improvement of corrosion resistance.

[0020] In summary, unlike existing hydrotalcite systems, this study innovatively proposes a novel strategy for synthesizing composite hydrotalcite coatings with antibacterial properties. The antibacterial properties of the cations involved in the formation of this hydrotalcite can be manifested in the composite coating. Summary of the Invention

[0021] The technical problem to be solved by this invention is to provide a method for preparing an EDTA (ethylenediaminetetraacetic acid) assisted low-temperature water bath MAO (micro-arc oxidation) / LDH (hydrotalcite) hybrid coating on the surface of a magnesium alloy substrate. The method utilizes the chelating effect of EDTA to control the participation of metal ions in the solution in the formation of the LDH coating. A novel composite hydrotalcite coating is developed under low-temperature water bath conditions. The prepared coating has a dense structure, good stability, and excellent corrosion resistance.

[0022] The technical solution adopted is as follows:

[0023] A method for preparing an EDTA-assisted low-temperature water bath MAO / LDH hybrid coating on a magnesium alloy substrate includes the following steps:

[0024] The first step is to pre-treat the surface of the magnesium alloy substrate by grinding to remove the surface oxide layer;

[0025] The second step is the preparation of the MAO coating;

[0026] Step 3, LDH coating preparation:

[0027] (1) Weigh out sodium hydroxide, disodium ethylenediaminetetraacetate and metal nitrate salt respectively;

[0028] (2) Mix the weighed materials from step (1), add deionized water to prepare a solution, and test the solution with a pH meter to find that it is 13.0 to 14.0.

[0029] (3) Place the solution in a beaker and add a stirring magnet, and place it in a constant temperature water bath; suspend the magnesium alloy substrate in the solution prepared in step (2), set the water bath temperature to 60°C, stir and keep warm, then take out the magnesium alloy substrate and dry it in an oven, and the surface of the magnesium alloy substrate will be coated with MAO / LDH hybrid coating.

[0030] Preferably, the magnesium alloy substrate is a Mg-Al alloy.

[0031] Preferably, the first step of pretreatment of the magnesium alloy substrate surface includes: selecting a magnesium alloy substrate, sanding it with sandpaper to remove the surface oxide layer until there are no obvious corrosion marks and scratches on the surface, cleaning it with deionized water and anhydrous ethanol, drying it with cold air, and setting it aside for later use.

[0032] Preferably, the second step, the specific method for preparing the MAO coating, includes:

[0033] An electrolyte solution of phytic acid and sodium hydroxide was prepared and placed in a micro-arc oxidation electrolytic cell. The anode of the micro-arc oxidation was a pretreated magnesium alloy substrate, and the cathode was a stainless steel plate.

[0034] The positive and negative electrodes of the micro-arc oxidation power supply were connected to the electrolytic cell respectively. The MAO coating was prepared using a manual constant voltage method. After micro-arc oxidation, the magnesium alloy substrate was cleaned with deionized water, dried with warm air, and stored in a clean petri dish.

[0035] Preferably, the voltage for micro-arc oxidation is controlled between 330V and 380V.

[0036] Preferably, the prepared MAO coating has a thickness of 3.59±0.46μm and an impedance value of 4.00×10⁻⁶. 4 Ω·cm 2 ~4.50×10 4 Ω·cm 2 .

[0037] Preferably, in the third step, the metal ion in the nitrate metal salt is Ga. 3+ .

[0038] Preferably, in the third step, the concentration of sodium hydroxide is 0.80–1.20 mol / L, the concentration of nitrate metal salt is 0.03–0.05 mol / L, and the concentration of disodium ethylenediaminetetraacetate is 10.0–20.0 g / L.

[0039] Preferably, in the third step, the water bath is kept at a constant temperature for 36–48 hours.

[0040] Preferably, the prepared hybrid coating exhibits a self-corrosion current density that can be reduced to 4.00 × 10⁻⁶. -8 A·cm -2 Its impedance value reaches 2.00 × 10⁻⁶. 5 Ω·cm 2 .

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] Compared with existing technologies, this invention features a simple and controllable preparation process, is environmentally friendly, and has low production costs. The MAO / LDH hybrid coating loaded with different metal ions prepared on a magnesium alloy substrate exhibits ion exchangeability and good corrosion resistance. When using gallium nitrate, Ga is chelated via EDTA. 3+ The doped coating has excellent antibacterial properties and biocompatibility.

[0043] The LDH synthesis method proposed in this invention is not limited to Ga 3+ It is not limited to trivalent cations, but includes metal ions of various valence states (Ga). 3+ Ag + Zn 2+ Cu 2+ Fe 3+ (e.g., etc.) can all participate in the formation of LDH. That is, this technology can achieve different performance characteristics by loading LDH with different metal ions. Attached Figure Description

[0044] Figure 1 The XRD pattern of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1;

[0045] Figure 2 This is a SEM image of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1.

[0046] Figure 3 The image shows the FT-IR image of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1.

[0047] Figure 4 The image shows the polarization curve of the MAO / Mg-Al-Ga-LDH hybrid coating on the surface of the magnesium alloy prepared in Example 1.

[0048] Figure 5 The image shows the Nyquist plot of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1.

[0049] Figure 6This is a cross-sectional view of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1;

[0050] Figure 7 XPS spectrum of MAO / Mg-Al-Ga-LDH hybrid coating on magnesium alloy surface prepared in Example 1;

[0051] Figure 8 The Mg1s spectrum of the MAO / Mg-Al-Ga-LDH hybrid coating on the surface of the magnesium alloy prepared in Example 1;

[0052] Figure 9 The hydrogen evolution rate curve is shown for the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1.

[0053] Figure 10 This is a test image of the anti-E. coli test of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1;

[0054] Figure 11 This is a cytotoxicity test diagram of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1. Detailed Implementation

[0055] The present invention will now be described in detail with reference to the embodiments.

[0056] Example 1

[0057] Step 1: Removal of oxide film from magnesium alloy surface

[0058] After the magnesium alloy is processed into a block of 20mm×20mm×5mm, its surface is polished with 150#-2500# sandpaper until there are no obvious corrosion marks or scratches on the surface.

[0059] The polished magnesium alloy was washed with deionized water and anhydrous ethanol, dried with warm air, and stored in a clean petri dish.

[0060] The second step is the preparation of the MAO coating.

[0061] (1) Weigh out 6 g / L phytic acid and 10 g / L sodium hydroxide respectively, and set aside;

[0062] (2) Mix the phytic acid and sodium hydroxide, add deionized water, and prepare a mixed solution;

[0063] (3) Pour the prepared solution into the PMMA electrolytic cell. The anode is a polished magnesium alloy block, and the cathode is a stainless steel plate. Connect the positive and negative terminals of the micro-arc oxidation power supply to the electrolytic cell respectively.

[0064] (4) Set the parameters of the micro-arc oxidation power supply as follows: frequency 500Hz, duty cycle 20%, current density 83.3mA / cm, oxidation time 3 minutes to prepare MAO coating;

[0065] (5) After micro-arc oxidation, the sample is washed with deionized water, dried with warm air, and stored in a clean petri dish.

[0066] Step 3: LDH coating preparation

[0067] (1) Weigh out 40 g / L sodium hydroxide, 10 g / L disodium ethylenediaminetetraacetate and 1.28 g / L gallium nitrate respectively, and set aside;

[0068] (2) Weigh the medicines, mix them, add deionized water to prepare a solution, and test the pH of the solution with a pH meter. The pH is about 13.

[0069] (3) Place the solution in a beaker, add a magnetic stir bar, and place the beaker in a constant temperature water bath. Suspend the sample in the solution. Set the water bath temperature to 60℃, turn on the magnetic stir bar, and maintain the temperature for 48 hours. A MAO / Mg-Al-Ga-LDH coating is then obtained on the surface of the magnesium alloy substrate.

[0070] Mg-rich 2+ And Al 3+ The dissolution of the MAO membrane can provide metal ions for the synthesis of hydrotalcite (LDH). The pH of the solution can be adjusted by adding NaOH, and Ga can be added externally. 3+ This allows for the incorporation of EDTA into hydrotalcite coatings. The innovative low-temperature water bath in-situ growth technique theoretically enables cations on the host layer to be chemically bonded to the metal substrate, thereby enhancing the film's adhesion. Furthermore, an EDTA-induced Ga... 3+ The method for forming LDH, based on the existing water bath method for LDH preparation, achieves successful participation of functional metal ions in the LDH formation process by rationally adjusting the temperature and pH value of the LDH solution. Compared with existing corrosion-resistant and antibacterial coatings on magnesium alloy surfaces, this hydrotalcite composite coating has excellent corrosion resistance (i corr ≈4.00×10 -8 A·cm -2Compared to the calcium-phosphorus coating of chlorophyll copper loaded on the surface of magnesium alloy (after 72h co-culture, the proliferation rate of MC3T3E1 cells reached 120%) (ZY Zhang, et al., Bioact. Mater. 18(2022) 284-299.), the proliferation rate of rat spinal cord mesenchymal stem cells reached 116% after 3h co-culture with this composite coating, demonstrating that the coating has good biocompatibility; compared to the copper ion-containing antibacterial coating with good antibacterial effect (the antibacterial effect is about 96% after 12h co-culture) (J. Chen, et al. Colloids Surf. B, 179(2019) 77-86.), the antibacterial effect of this coating is also relatively excellent (the antibacterial effect is about 76.6% after 5h co-culture).

[0071] The basic principle of the above technical solution is as follows: First, a layer of MAO is prepared on the surface of the magnesium alloy. The porous surface of MAO is conducive to the growth of the LDH coating. Then, the chelating effect of EDTA is used to bind the Al in the solution. 3+ Ga 3+ Chelated to the MAO coating surface, Mg is reacted in a low-temperature water bath under a strongly alkaline environment. 2+ Al 3+ Ga 3+ and OH - The reaction produces a Mg-Al-Ga-LDH coating. Throughout the entire process, EDTA complexes the free metal ions. This is because EDTA has a strong affinity for Mg... 2+ Its complexing ability is stronger, therefore magnesium hydroxide is rapidly formed in the initial stage of soaking. With the increase of Mg... 2+ The content decreased, Al 3+ As the relative concentration continues to increase, EDTA has a greater effect on Al. 3+ Increased complexing ability, Al 3+ The EDTA complex is adsorbed onto the generated magnesium hydroxide and undergoes isomeric substitution to form Mg-Al-LDH. The formation mechanism of Mg-Ga-LDH is similar. The in-situ generated LDH acts as a pore-sealing agent in the MAO coating, reducing coating defects. The ion exchange effect of LDH weakens the resistance to corrosive ions such as Cl-. - The role of Ga during corrosion. 3+ The release of [something] will have a certain antibacterial effect.

[0072] Ga 3+ There may be two antibacterial mechanisms: one is Ga 3+ The penetration and intercellular diffusion of Ga increases the content of reactive oxygen species between cells, thereby inhibiting bacterial growth; another reason is that Ga... 3+ with Fe 3+ There are certain similarities; bacterial iron-binding proteins bind to Ga. 3+ However, Ga3+ It cannot be reduced, thus interrupting the bacteria's iron metabolism process.

[0073] To better understand the above technical solution, its chemical reaction mechanism is briefly explained below:

[0074] The main functions of each component in the LDH precursor solution are as follows: Sodium hydroxide and gallium nitrate ionize in aqueous solution to produce hydroxide ions and gallium ions, providing the necessary ions for LDH formation. At the same time, hydroxide ions can adjust the pH. The magnesium ions and aluminum ions required for LDH formation come from the dissolution of the MAO coating.

[0075] Mg 2+ and very small amounts of Al 3+ Adsorbed onto the magnesium alloy surface and reacting with OH - I combine to form hydroxides,

[0076] Mg 2+ +3OH - →Mg(OH)2↓ (1)

[0077] Al 3 + + 3OH - →Al(OH)3↓ (2)

[0078] In the initial soaking stage, the amount of Al(OH)3 is much lower than that of Mg(OH)2. As the soaking time increases, the amount of CO3... 2- In the presence of Mg(OH)2, some of the Mg 2+ By Al 3+ and Ga 3+ Alternative, with Ga 3+ The reaction equation is expressed as follows:

[0079] Ga 3+ +3OH - →Ga(OH)3 (3)

[0080]

[0081] 2Mg(OH)2+Ga 3+ +3OH - →Mg2Ga(OH)7 (5)

[0082]

[0083]

[0084] During the magnesium alloy film formation process, the pH level is maintained at a high level to effectively prevent the dissolution of the magnesium alloy matrix.

[0085] The technical effect of the above solution is that it cleverly combines the MAO coating and the LDH coating, and utilizes the chelating effect of EDTA to bond Ga... 3+ When introduced into the LDH coating, LDH not only acts as a pore sealer but also imparts Ga to the composite coating. 3+ Some of its biological properties, such as antibacterial and osteogenic properties.

[0086] In the above technical solution, both the raw materials and products are non-toxic and harmless, and are either compatible with or essential to the human body, exhibiting good biocompatibility. On the one hand, the process is green and environmentally friendly; on the other hand, the obtained MAO / Mg-Al-Ga-LDH coating has characteristics such as ion exchangeability, good corrosion resistance, excellent antibacterial properties, and biocompatibility.

[0087] Both gallium nitrate and sodium hydroxide were of analytical grade, and the gallium nitrate was gallium nitrate nonahydrate.

[0088] Example 2

[0089] In Example 1, gallium nitrate was replaced with ferric nitrate, and everything else was the same as in Example 1.

[0090] Example 3

[0091] In Example 1, gallium nitrate was replaced with copper nitrate, and everything else was the same as in Example 1.

[0092] Example 4

[0093] In Example 1, gallium nitrate was replaced with zinc nitrate, and everything else was the same as in Example 1.

[0094] Example 5

[0095] In Example 1, gallium nitrate was replaced with silver nitrate, and everything else was the same as in Example 1.

[0096] Product testing and inspection:

[0097] Example 1 was selected as a representative example. The prepared coating was subjected to XRD test, scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) detection, electrochemical test (polarization curve and AC impedance Nyquist plot), X-ray photoelectron spectroscopy (XPS) test, hydrogen evolution test, antibacterial test and cytotoxicity test. The results are as follows.

[0098] Figure 1 The X-ray diffraction pattern of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1 is shown below.

[0099] like Figure 1As shown, an LDH coating was successfully synthesized on the surface of a magnesium alloy using a low-temperature water bath method. The Mg-Al-Ga-LDH coating exhibited three diffraction characteristic peaks: (003), (006), and (009).

[0100] The coating exhibits typical LDH layered structure characteristics.

[0101] Figure 2 This is a scanned image of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1. Figure 2 As shown, the LDH nanosheets of the MAO / Mg-Al-Ga-LDH hybrid coating prepared in Example 1 are compactly and uniformly covered on the magnesium alloy surface through mutual cross-connection, and grow perpendicularly on the surface, thus exhibiting a porous structure. The nanosheets of the MAO / Mg-Al-Ga-LDH hybrid coating grow perpendicular to the substrate surface in an oriented manner, which is consistent with the orientation distribution of the LDH coating on the magnesium alloy surface in the X-ray diffraction results, indicating that the coating has high crystallinity and good bonding strength with the substrate.

[0102] Figure 3 The image shows the infrared spectrum of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1. Figure 3 As shown, 3697 and 3450cm -1 The peaks at 1351 and 1384 cm⁻¹ are attributed to the Mg-OH and OH stretching vibrations, confirming the formation of Mg(OH)₂ and other metal hydroxides. Furthermore, the peaks at 1351 and 1384 cm⁻¹... -1 The double peaks and 1114cm -1 The double peak at that point corresponds to CO3 2- And CO, this is because CO3 is present in LDH. 2- Embedded. 1640cm -1 The peak at 767 cm⁻¹ is attributed to crystalline H₂O molecules. Additionally, the peak at 767 cm⁻¹... -1 and 620cm -1 The two peaks are metal oxide peaks, which may be due to small amounts of Al-O and Mg-O bonds. Compared with the MAO coating, the MAO / Mg-Al-LDH and MAO / Mg-Al-Ga-LDH coatings show higher activity at 3697 cm⁻¹. -1 A significant Mg-OH peak was observed, which also proves the successful preparation of the LDH coating.

[0103] Figure 4 This is a polarization curve of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1. Figure 4 As shown, the corrosion current density (i) in the polarization curve corr ), self-corrosion potential (E) corrThe corrosion current density is an important standard for evaluating the corrosion resistance of a sample. The lower the corrosion current density and the higher the self-corrosion potential, the better the corrosion resistance of the magnesium alloy. Comparative results show that the self-corrosion current density is significantly reduced when the MAO / Mg-Al-Ga-LDH hybrid coating is compared to the uncoated magnesium alloy substrate. Furthermore, the passivation range is large, and the polarization curves exhibit a stepped pattern to varying degrees in the anodic region, indicating a repeated passivation-re-passivation-re-passivation process, demonstrating the self-healing properties of the LDH coating. This indicates that the coating possesses self-healing or self-repairing capabilities. The results show that, compared to the uncoated magnesium alloy AZ31, the LDH coating on the magnesium alloy surface exhibits excellent corrosion resistance.

[0104] Figure 5 The image shows the Nyquist plot of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1. Figure 5 As shown, a larger arc resistance in the Nyquist plot indicates better corrosion resistance of the sample. Experimental results show that the MAO / Mg-Al-Ga-LDH hybrid coating can significantly improve the corrosion resistance of the magnesium alloy substrate.

[0105] Figure 6 This is a cross-sectional scan of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1. Figure 6 As shown, for the MAO / Mg-Al-Ga-LDH hybrid coating, the thickness of the LDH coating is 1.61±0.17 μm, and it is completely embedded in the MAO coating, proving the successful preparation of the MAO / Mg-Al-Ga-LDH hybrid coating.

[0106] Figure 7 and Figure 8 The images show the XPS spectra and Mg1s peak spectra of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1. Figure 7 and 8 As shown, Ga 2p, O 1s, N 1s, Al 2p, Ga 3 / 2p, and Mg 1s peaks were observed in the XPS spectrum. The Mg 1s spectrum ( Figure 8 The Mg(OH)₂ (1302.7 eV), Mg-Al-LDH (1304 eV), and Mg-Ga-LDH (1304.8 eV) groups were assigned. The formation of Mg-Al-LDH and Mg-Ga-LDH was demonstrated. Figure 9 The figure shows the hydrogen evolution rate curve of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1. Figure 9As shown, the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface effectively reduced the hydrogen evolution rate of the magnesium alloy substrate. During the immersion process of 168h, the hydrogen evolution rate of the coated magnesium alloy substrate remained at a low level.

[0107] Figure 10 The image shows the antibacterial test curve of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1. The coating maintained an inhibition rate of 75.0%–80.0% against Staphylococcus aureus and Escherichia coli within 5 hours. Figure 10 As shown, the number of colonies in the MAO / Mg-Al-Ga-LDH hybrid coating group on the magnesium alloy surface was significantly reduced, indicating that the coating prepared in Example 1 improved the resistance of the magnesium alloy substrate to Escherichia coli.

[0108] Figure 11 This image shows the cytotoxicity test results of the MAO / Mg-Al-Ga-LDH hybrid coating on the magnesium alloy surface prepared in Example 1. The coating showed a proliferative effect on rat spinal cord mesenchymal stem cells (SDBMSCs) of 110.0%–120.0% after 72 hours of co-culture. Figure 11 As shown, the number of cells in the MAO / Mg-Al-Ga-LDH hybrid coating group on the magnesium alloy surface was significantly increased compared with the blank group, indicating that the coating did not exhibit obvious cytotoxicity and showed a cell growth-promoting effect.

[0109] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing an EDTA-assisted low-temperature water bath MAO / LDH hybrid coating on a magnesium alloy substrate, characterized in that, Includes the following steps: The first step is to pre-treat the surface of the magnesium alloy substrate by grinding to remove the surface oxide layer; The second step is the preparation of the MAO coating; the specific methods for preparing the MAO coating include: An electrolyte solution of phytic acid and sodium hydroxide was prepared and placed in a micro-arc oxidation electrolytic cell. The anode of the micro-arc oxidation was a pretreated magnesium alloy substrate, and the cathode was a stainless steel plate. The positive and negative terminals of the micro-arc oxidation power supply were connected to the electrolytic cell, and the MAO coating was prepared using a manual constant voltage method. After micro-arc oxidation, the magnesium alloy substrate was washed with deionized water, dried with warm air, and stored in a clean petri dish. The voltage of the micro-arc oxidation was controlled between 330V and 380V. The prepared MAO coating had a thickness of 3.59 ± 0.46 μm and an impedance of 4.00 × 10⁻⁶ μm. 4 Ω·cm 2 ~4.50×10 4 Ω·cm 2 ; Step 3, LDH coating preparation: (1) Weigh out sodium hydroxide, disodium ethylenediaminetetraacetate and metal nitrate salt respectively; (2) Mix the weighed materials from step (1), add deionized water to prepare a solution, and test the solution with a pH meter to find that it is 13.0~14.

0. (3) Place the solution in a beaker and add a stirring magnet. Place it in a constant temperature water bath and keep it warm for 36~48h. Suspend the magnesium alloy substrate in the solution prepared in step (2), set the water bath temperature to 60℃, stir and keep it warm. Then take out the magnesium alloy substrate and dry it in an oven. The surface of the magnesium alloy substrate will then have a MAO / LDH hybrid coating. The magnesium alloy substrate is selected from Mg-Al alloys; the metal ion in the nitrate metal salt is Ga. 3+ ; The concentration of sodium hydroxide was 0.80~1.20 mol / L, the concentration of nitrate metal salt was 0.03~0.05 mol / L, and the concentration of disodium ethylenediaminetetraacetate was 10.0~20.0 g / L.

2. The method for preparing an EDTA-assisted low-temperature water bath MAO / LDH hybrid coating on a magnesium alloy substrate according to claim 1, characterized in that, The first step of the pretreatment of the magnesium alloy substrate surface includes: selecting the magnesium alloy substrate, sanding it with sandpaper to remove the surface oxide layer until there are no obvious corrosion marks and scratches on the surface, cleaning it with deionized water and anhydrous ethanol, drying it with cold air, and setting it aside for later use.

3. The method for preparing an EDTA-assisted low-temperature water bath MAO / LDH hybrid coating on a magnesium alloy substrate according to claim 1, characterized in that, The prepared hybrid coating exhibits a self-corrosion current density that can be reduced to 4.00 × 10⁻⁶. -8 A·cm -2 Its impedance value reaches 2.00 × 10⁻⁶. 5 Ω·cm 2 .

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