Magnesium alloy micro-arc oxidation-electrophoretic deposition composite film layer and preparation method and application thereof

Abstract

The invention relates to a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film layer which comprises a magnesium alloy substrate, a micro-arc oxidation middle layer and an electrophoretic deposition layer. The magnesium alloy micro-arc oxidation-electrophoretic deposition composite film layer finally prepared by adjusting the parameters of micro-arc oxidation, electrophoretic deposition and sintering has super-hydrophobicity and excellent corrosion shielding performance, can be applied to the field of ships, and prolongs the service life of a ship body.

Description

Technical Field

[0001] This invention relates to magnesium alloy surface treatment technology, and more particularly to a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film, its preparation method, and its application. Background Technology

[0002] Magnesium alloys possess characteristics such as low density, high specific strength, good heat dissipation and shock absorption, good electrical conductivity, ease of processing and forming, and certain corrosion resistance. They are among the lightest practical metals. Due to their lightweight and high strength, magnesium alloys are widely used in automobiles, aerospace, and electronics. For marine magnesium alloys, during service, the presence of surrounding moisture and the splashing of waves generated by the interaction between the sea and the vessel cause water to adhere to the surface of the magnesium alloy, resulting in surface corrosion. To improve the corrosion resistance of magnesium alloys and extend the service life of the hull, surface modification of the metal material is a common method.

[0003] Surface modification of metallic materials often involves methods such as anodizing, laser surface pretreatment, and chemical etching. Micro-arc oxidation, as a green and environmentally friendly method, applies high voltage to metallic materials through a special electrolyte, and generates oxides in situ through a series of complex physicochemical reactions such as plasma discharge. This process endows the materials with properties such as corrosion resistance, wear resistance, and thermal shock resistance. However, the performance improvement achieved by micro-arc oxidation cannot fully meet the needs of application scenarios. Therefore, researchers often use subsequent processing methods to improve the corresponding performance.

[0004] PTFE (polytetrafluoroethylene), also known as "King of Plastics" or "Teflon", has excellent high and low temperature resistance (-180~260℃), outstanding chemical stability (resistant to acids, alkalis and most solvents), low coefficient of friction and self-lubricating properties, excellent non-stick properties, good electrical insulation properties, and good weather resistance and wear resistance.

[0005] PTFE's hydrophobic properties are manifested in its extremely low surface energy and lack of affinity for water molecules, allowing gas to pass through while preventing liquids from passing through. This characteristic makes it an excellent waterproof and dustproof material, and it is widely used in filtration, electronics, medical and other fields.

[0006] Currently, although there are reports on the preparation of superhydrophobic composite films on magnesium alloy surfaces by combining micro-arc oxidation with electrophoretic deposition, these methods often involve complex post-processing steps in addition to micro-arc oxidation and electrophoretic deposition. Therefore, obtaining superhydrophobic composite films through simple processes is the current research focus. Summary of the Invention

[0007] To address the technical problems existing in the background art, the present invention proposes a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film, wherein the composite film comprises a magnesium alloy substrate, a micro-arc oxidation intermediate layer, and an electrophoretic deposition surface layer; Preferably, the micro-arc oxidation intermediate layer has a protrusion-microporous structure, and the protrusion-microporous structure is composed of magnesium orthosilicate and magnesium oxide; Preferably, the electrophoretic deposition surface layer has a nanoparticle-micropore interlocking hierarchical structure, and the hierarchical structure is composed of polytetrafluoroethylene.

[0008] The present invention also proposes a method for preparing the above-mentioned magnesium alloy micro-arc oxidation-electrophoretic deposition composite film, comprising the following steps: S1. Magnesium alloy samples are obtained by cutting, grinding and degreasing magnesium alloy plates; S2. The magnesium alloy sample is subjected to micro-arc oxidation to obtain a magnesium alloy micro-arc oxidation sample. S3. Magnesium alloy micro-arc oxidation sample was electrophoretically deposited in a non-aqueous medium to obtain magnesium alloy micro-arc oxidation-electrophoretic deposition sample. S4. The magnesium alloy micro-arc oxidation-electrophoretic deposition sample was sintered to obtain a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film.

[0009] Preferably, in step S2, the micro-arc oxidation electrolyte is a silicate-based electrolyte, which includes 10-20 g / L sodium silicate, 2-5 g / L potassium hydroxide, and the remaining component is deionized water; More preferably, the sodium silicate concentration is 15 g / L and the potassium hydroxide concentration is 2 g / L.

[0010] More preferably, in step S2, the micro-arc oxidation is in constant voltage mode, with a positive voltage of 400V, a negative voltage of 0-30V, a duty cycle of 10-30%, a power frequency of 300-1000Hz, an oxidation time of 10min, and a solution temperature of 20-50℃.

[0011] Preferably, in step S3, the electrolyte for electrophoretic deposition includes 2-10 g / L of polytetrafluoroethylene, 0.01-0.1 g / L of dispersant, and 0.01-0.05 g / L of inorganic acid; More preferably, the polytetrafluoroethylene is 5 g / L, the dispersant is 0.05 g / L, and the inorganic acid is 0.039 g / L; More preferably, the dispersant is polyethyleneimine, and the inorganic acid is nitric acid.

[0012] More preferably, in step S3, the interelectrode distance of the electrophoretic deposition is 8-15 mm, the constant voltage is 100-150 V, and the deposition time is 5-10 min; More preferably, the electrophoretic deposition has an inter-electrode distance of 10 mm, a constant voltage of 120 V, and a deposition time of 5 min.

[0013] Preferably, in step S4, the sintering temperature is 300-400℃, the sintering time is 1-3h, and the heating rate is 8-15℃ / min; More preferably, the sintering temperature is 300℃, the sintering time is 2h, and the heating rate is 10℃ / min.

[0014] In this invention, if traditional sintering parameters are used, such as 180-250℃, 0.5h, and a heating rate of 5℃ / min, the final product will have significantly reduced performance in terms of hydrophobicity, corrosion resistance, and wear resistance.

[0015] The present invention also proposes the application of the above-mentioned magnesium alloy micro-arc oxidation-electrophoretic deposition composite film or the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film prepared by the above preparation method in ships.

[0016] Beneficial effects of this invention: This invention has made "directional" modifications to three key aspects: electrolyte formulation, charging method, and deposition-sintering coupling parameters. A large number of PTFE nanoparticles with low surface energy are grown on the originally rough micro-arc oxidation surface. Without destroying the micro-morphology, the PTFE layer can form a hierarchical multi-scale micro-nano structure on the micro-arc oxidation (MAO) ceramic layer, namely a "nanoparticle-micropore interlocking" hierarchical structure. The two work together to enable the composite coating to capture a large amount of air. When in contact with water, it forms an air layer and transforms into a Cassie-Baxter state, which has superhydrophobic properties. (2) During the sintering process in the muffle furnace, as the temperature rises, the low surface energy PTFE particles will sinter and fuse with each other to form a denser and more continuous coating structure, which improves its adhesion, mechanical strength and corrosion resistance, and can also increase the contact angle of the coating. (3) The magnesium alloy micro-arc oxidation-electrophoretic deposition composite film of the present invention has a good dense barrier effect. In corrosive environments such as seawater (such as in the shipbuilding field), only a few electrons pass through the dense layer to reach the substrate, and it can maintain excellent corrosion shielding performance for a long time. Attached Figure Description

[0017] Figure 1 The graphs show the polarization curves of the composite films in Example 1, Comparative Example 1, and Comparative Example 2. Figure 2 Impedance spectra of the composite films in Example 1, Comparative Example 1, and Comparative Example 2; Figure 3 Bode plots of the composite films in Example 1, Comparative Example 1, and Comparative Example 2; Figure 4 This is an electron microscope image of the magnesium alloy micro-arc oxidation sample in Example 1; Figure 5 This is an electron microscope image of the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film in Example 1; Figure 6 This is a side view of the contact angle of the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film in Example 1; Figure 7 This is a side view of the contact angle of the magnesium alloy matrix in Comparative Example 1; Figure 8 This is a side view of the contact angle of the magnesium alloy micro-arc oxidation sample of Comparative Example 2. Figure 9 This is a side view of the contact angle of the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film in Comparative Example 3. Detailed Implementation

[0018] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0020] The technical solution of the present invention will now be described more clearly and completely with reference to specific embodiments and comparative examples.

[0021] Example 1 This embodiment proposes a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film, the preparation method of which is shown below: S1. Use a wire EDM machine to cut a 100mm×100mm×2mm magnesium alloy sheet (AZ31) into 20mm×20mm×2mm magnesium alloy samples. Use SiC sandpaper to polish the magnesium alloy samples step by step. The sandpaper size is 400#-1000#. After polishing, rinse the magnesium alloy with deionized water, then place it in anhydrous ethanol for ultrasonic cleaning to remove oil, and then dry it to obtain the pretreated magnesium alloy sample for later use. S2. The pretreated magnesium alloy sample (considered as the anode) is placed in a stainless steel tank (considered as the cathode) and micro-arc oxidation is performed using an FL7-MAO30G micro-arc oxidation power supply. After washing with deionized water, it is dried to obtain a magnesium alloy micro-arc oxidation sample. The electrical parameters for micro-arc oxidation are as follows: constant voltage mode: positive voltage 400V, negative voltage 10V, duty cycle 10%, power frequency 500Hz, oxidation time 10min, and solution temperature 45℃. The electrolyte formulation for micro-arc oxidation is as follows: sodium silicate 15g / L, potassium hydroxide 2g / L, and deionized water as the electrolyte matrix. S3. Place the magnesium alloy micro-arc oxidation sample (considered as the cathode) and graphite (considered as the anode) in an electrolytic cell and perform electrophoretic deposition treatment to obtain a uniformly distributed PTFE deposition layer on the surface of the magnesium alloy micro-arc oxidation sample, thus obtaining a magnesium alloy micro-arc oxidation-electrophoretic deposition sample. The parameters for electrophoretic deposition were: interelectrode distance of 10 mm, constant voltage of 120 V, and deposition time of 5 min. The electrolyte formulation for electrophoretic deposition is as follows: 5 g / L polytetrafluoroethylene (particle size less than 1 μm), 0.05 g / L polyethyleneimine, 0.039 g / L nitric acid, and anhydrous ethanol as the electrolyte matrix for electrophoretic deposition. S4. Place the magnesium alloy micro-arc oxidation-electrophoretic deposition sample in a quartz crucible, and then sinter the quartz crucible containing the sample in the center of a muffle furnace to form a uniformly deposited PTFE nanoparticle deposition layer on the surface of the magnesium alloy micro-arc oxidation-electrophoretic deposition sample, thus obtaining a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film. The sintering parameters are: heating rate 10℃ / min, sintering temperature 300℃, and sintering time 2h.

[0022] Example 2 This embodiment proposes a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film, the preparation method of which is shown below: S1. Use a wire EDM machine to cut a 100mm×100mm×2mm magnesium alloy sheet (AZ31) into 20mm×20mm×2mm magnesium alloy samples. Use SiC sandpaper to polish the magnesium alloy samples step by step. The sandpaper size is 400#-1000#. After polishing, rinse the magnesium alloy with deionized water, then place it in anhydrous ethanol for ultrasonic cleaning to remove oil, and then dry it to obtain the pretreated magnesium alloy sample for later use. S2. The pretreated magnesium alloy sample (considered as the anode) is placed in a stainless steel tank (considered as the cathode) and micro-arc oxidation is performed using an FL7-MAO30G micro-arc oxidation power supply. After washing with deionized water, it is dried to obtain a magnesium alloy micro-arc oxidation sample. The electrical parameters for micro-arc oxidation are as follows: constant voltage mode: positive voltage 400V, negative voltage 15V, duty cycle 30%, power frequency 300Hz, oxidation time 10min, and solution temperature 30℃. The electrolyte formulation for micro-arc oxidation is as follows: sodium silicate 10g / L, potassium hydroxide 3g / L, and deionized water as the electrolyte matrix. S3. Place the magnesium alloy micro-arc oxidation sample (considered as the cathode) and graphite (considered as the anode) in an electrolytic cell and perform electrophoretic deposition treatment to obtain a uniformly distributed PTFE deposition layer on the surface of the magnesium alloy micro-arc oxidation sample, thus obtaining a magnesium alloy micro-arc oxidation-electrophoretic deposition sample. The parameters for electrophoretic deposition were: interelectrode distance of 10 mm, constant voltage of 120 V, and deposition time of 5 min. The electrolyte formulation for electrophoretic deposition is as follows: 8 g / L polytetrafluoroethylene (particle size less than 1 μm), 0.1 g / L polyethyleneimine, 0.05 g / L nitric acid, and anhydrous ethanol as the electrolyte matrix for electrophoretic deposition. S4. Place the magnesium alloy micro-arc oxidation-electrophoretic deposition sample in a quartz crucible, and then sinter the quartz crucible containing the sample in the center of a muffle furnace to form a uniformly deposited PTFE nanoparticle deposition layer on the surface of the magnesium alloy micro-arc oxidation-electrophoretic deposition sample, thus obtaining a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film. The sintering parameters are as follows: heating rate 12℃ / min, sintering temperature 350℃, and sintering time 1.5h.

[0023] Example 3 This embodiment proposes a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film, the preparation method of which is shown below: S1. Use a wire EDM machine to cut a 100mm×100mm×2mm magnesium alloy sheet (AZ31) into 20mm×20mm×2mm magnesium alloy samples. Use SiC sandpaper to polish the magnesium alloy samples step by step. The sandpaper size is 400#-1000#. After polishing, rinse the magnesium alloy with deionized water, then place it in anhydrous ethanol for ultrasonic cleaning to remove oil, and then dry it to obtain the pretreated magnesium alloy sample for later use. S2. The pretreated magnesium alloy sample (considered as the anode) is placed in a stainless steel tank (considered as the cathode) and micro-arc oxidation is performed using an FL7-MAO30G micro-arc oxidation power supply. After washing with deionized water, it is dried to obtain a magnesium alloy micro-arc oxidation sample. The electrical parameters for micro-arc oxidation are as follows: constant voltage mode: positive voltage 400V, negative voltage 30V, duty cycle 25%, power frequency 1000Hz, oxidation time 10min, and solution temperature 50℃. The electrolyte formulation for micro-arc oxidation is as follows: sodium silicate 15g / L, potassium hydroxide 5g / L, and deionized water as the electrolyte matrix. S3. Place the magnesium alloy micro-arc oxidation sample (considered as the cathode) and graphite (considered as the anode) in an electrolytic cell and perform electrophoretic deposition treatment to obtain a uniformly distributed PTFE deposition layer on the surface of the magnesium alloy micro-arc oxidation sample, thus obtaining a magnesium alloy micro-arc oxidation-electrophoretic deposition sample. The parameters for electrophoretic deposition were: interelectrode distance of 12 mm, constant voltage of 100 V, and deposition time of 8 min. The electrolyte formulation for electrophoretic deposition is as follows: 8 g / L polytetrafluoroethylene (particle size less than 1 μm), 0.1 g / L polyethyleneimine, 0.02 g / L nitric acid, and anhydrous ethanol as the electrolyte matrix for electrophoretic deposition. S4. Place the magnesium alloy micro-arc oxidation-electrophoretic deposition sample in a quartz crucible, and then sinter the quartz crucible containing the sample in the center of a muffle furnace to form a uniformly deposited PTFE nanoparticle deposition layer on the surface of the magnesium alloy micro-arc oxidation-electrophoretic deposition sample, thus obtaining a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film. The sintering parameters are: heating rate 15℃ / min, sintering temperature 300℃, and sintering time 2.5h.

[0024] Example 4 This embodiment proposes a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film, the preparation method of which is shown below: S1. Use a wire EDM machine to cut a 100mm×100mm×2mm magnesium alloy sheet (AZ31) into 20mm×20mm×2mm magnesium alloy samples. Use SiC sandpaper to polish the magnesium alloy samples step by step. The sandpaper size is 400#-1000#. After polishing, rinse the magnesium alloy with deionized water, then place it in anhydrous ethanol for ultrasonic cleaning to remove oil, and then dry it to obtain the pretreated magnesium alloy sample for later use. S2. The pretreated magnesium alloy sample (considered as the anode) is placed in a stainless steel tank (considered as the cathode) and micro-arc oxidation is performed using an FL7-MAO30G micro-arc oxidation power supply. After washing with deionized water, it is dried to obtain a magnesium alloy micro-arc oxidation sample. The electrical parameters for micro-arc oxidation are as follows: constant voltage mode: positive voltage 400V, negative voltage 10V, duty cycle 15%, power frequency 800Hz, oxidation time 10min, and solution temperature 40℃. The electrolyte formulation for micro-arc oxidation is as follows: sodium silicate 20g / L, potassium hydroxide 4g / L, and deionized water as the electrolyte matrix. S3. Place the magnesium alloy micro-arc oxidation sample (considered as the cathode) and graphite (considered as the anode) in an electrolytic cell and perform electrophoretic deposition treatment to obtain a uniformly distributed PTFE deposition layer on the surface of the magnesium alloy micro-arc oxidation sample, thus obtaining a magnesium alloy micro-arc oxidation-electrophoretic deposition sample. The parameters for electrophoretic deposition were: interelectrode distance of 10 mm, constant voltage of 120 V, and deposition time of 5 min. The electrolyte formulation for electrophoretic deposition is as follows: 3 g / L polytetrafluoroethylene (particle size less than 1 μm), 0.02 g / L polyethyleneimine, 0.05 g / L nitric acid, and anhydrous ethanol as the electrolyte matrix for electrophoretic deposition. S4. Place the magnesium alloy micro-arc oxidation-electrophoretic deposition sample in a quartz crucible, and then sinter the quartz crucible containing the sample in the center of a muffle furnace to form a uniformly deposited PTFE nanoparticle deposition layer on the surface of the magnesium alloy micro-arc oxidation-electrophoretic deposition sample, thus obtaining a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film. The sintering parameters are: heating rate 10℃ / min, sintering temperature 300℃, and sintering time 2h.

[0025] Comparative Example 1 This comparative example presents a composite film layer, the preparation method of which is the same as that of Example 1, except that steps S2-S4 are omitted.

[0026] Comparative Example 2 This comparative example presents a composite film layer, the preparation method of which is the same as that of Example 1, except that steps S3-S4 are omitted.

[0027] Comparative Example 3 This comparative example presents a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film, which is prepared in the same way as in Example 1, except that the electrophoretic deposition formula in step S3 is replaced with "polytetrafluoroethylene (particle size less than 1 μm) 49.86 g / L, sodium dodecylbenzenesulfonate 2.77 g / L, and the electrolyte matrix for electrophoretic deposition is deionized water".

[0028] Performance testing The composite films prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to performance tests, including hydrophobicity and corrosion resistance. Hydrophobicity: The static contact angle of the prepared superhydrophobic sample surface was measured using a contact angle meter; Corrosion resistance: Electrochemical experiments were conducted using a 3.5 wt% sodium chloride solution as the corrosive medium in a three-electrode system.

[0029] Figure 1 The graphs shown are polarization curves of the composite films in Example 1, Comparative Example 1, and Comparative Example 2. Figure 1 It can be seen that the self-corrosion current density of the sample in Example 1 is 2.27 × 10⁻⁶. -8 A / cm 2 The self-corrosion current density of Comparative Example 2 (4.17 × 10⁻⁶) was compared to that of Comparative Example 2. -7 A / cm 2 Reduce by an order of magnitude; Figure 2 The impedance spectra of the composite films in Example 1, Comparative Example 1, and Comparative Example 2 are shown. Figure 3 The Bode plots are for the composite films in Example 1, Comparative Example 1, and Comparative Example 2; by Figure 2 and Figure 3 It can be seen that the impedance modulus of Example 1 in the low-frequency region is two orders of magnitude higher than that of Comparative Example 2, and Example 1 has the largest capacitive arc and good corrosion shielding performance, indicating that very few electrons pass through the dense layer to reach the substrate, thanks to the dense barrier effect of the superhydrophobic coating.

[0030] Figure 4 The image shown is an electron microscope image of the magnesium alloy micro-arc oxidation sample from Example 1. Figure 4 It is known that specific micro-arc oxidation electrolytes and electrical parameters result in a unique three-dimensional structure on the magnesium alloy surface, namely a protrusion-micropore structure, which exists on the magnesium alloy surface.

[0031] Figure 5 The image shows an electron microscope image of the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film in Example 1. The electrophoretically deposited PTFE particles partially or completely fill the micropores generated by micro-arc oxidation, which not only forms a denser surface and improves the corrosion resistance of the material, but also does not completely cover the protruding structure generated by micro-arc oxidation. Instead, it forms a hierarchical structure of "nanoparticle-micropore interlocking". This unique hierarchical structure and the low friction of polytetrafluoroethylene (PTFE) can further improve the wear resistance and friction reduction of the material. Through this nanoparticle-micropore interlocking hierarchical structure design, the surface properties of magnesium alloys are significantly improved, enabling them to perform well in a variety of applications, especially in environments requiring high wear resistance, corrosion resistance and friction reduction. Figure 6 This is a side view of the contact angle of the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film in Example 1, with a contact angle of 153.2°. Figure 7 The image shows a side view of the contact angle of the magnesium alloy matrix in Comparative Example 1, with a contact angle of 82.3°. Figure 8 The contact angle side view of the magnesium alloy micro-arc oxidation sample of Comparative Example 2 is 75.5°. Although its surface is rough, due to the introduction of more hydrophilic groups such as hydroxyl groups by plasma discharge during the micro-arc oxidation process, its surface is hydrophilic, and the contact angle is smaller than that of Example 1. Figure 9 The image shows a side view of the contact angle of the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film in Comparative Example 3, with a contact angle of 85.2°.

[0032] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A magnesium alloy micro-arc oxidation-electrophoretic deposition composite film, characterized in that, The composite film layer includes a magnesium alloy substrate, a micro-arc oxidation intermediate layer, and an electrophoretic deposition surface layer.

2. The magnesium alloy micro-arc oxidation-electrophoretic deposition composite film according to claim 1, characterized in that, The micro-arc oxidation intermediate layer has a protrusion-microporous structure, which is composed of magnesium orthosilicate and magnesium oxide.

3. The magnesium alloy micro-arc oxidation-electrophoretic deposition composite film according to claim 1 or 2, characterized in that, The electrophoretic deposition surface layer has a nanoparticle-micropore interlocking hierarchical structure, and the hierarchical structure is composed of polytetrafluoroethylene.

4. A method for preparing a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Magnesium alloy samples are obtained by cutting, grinding and degreasing magnesium alloy plates; S2. The magnesium alloy sample is subjected to micro-arc oxidation to obtain a magnesium alloy micro-arc oxidation sample. S3. Magnesium alloy micro-arc oxidation sample was electrophoretically deposited in a non-aqueous medium to obtain magnesium alloy micro-arc oxidation-electrophoretic deposition sample. S4. The magnesium alloy micro-arc oxidation-electrophoretic deposition sample was sintered to obtain a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film.

5. The method for preparing the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film according to claim 4, characterized in that, In step S2, the micro-arc oxidation electrolyte is a silicate-based electrolyte, which includes 10-20 g / L sodium silicate, 2-5 g / L potassium hydroxide, and the remaining component is deionized water. Preferably, the sodium silicate concentration is 15 g / L and the potassium hydroxide concentration is 2 g / L.

6. The method for preparing the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film according to claim 4 or 5, characterized in that, In step S2, the micro-arc oxidation is performed in constant voltage mode, with a positive voltage of 400V, a negative voltage of 0-30V, a duty cycle of 10-30%, a power frequency of 300-1000Hz, an oxidation time of 10min, and a solution temperature of 20-50℃.

7. The method for preparing the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film according to any one of claims 4-6, characterized in that, In step S3, the electrolyte for electrophoretic deposition includes 2-10 g / L of polytetrafluoroethylene, 0.01-0.1 g / L of dispersant, and 0.01-0.05 g / L of inorganic acid; Preferably, the polytetrafluoroethylene is 5 g / L, the dispersant is 0.05 g / L, and the inorganic acid is 0.039 g / L; Preferably, the dispersant is polyethyleneimine and the inorganic acid is nitric acid.

8. The method for preparing the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film according to any one of claims 4-7, characterized in that, In step S3, the interelectrode distance of the electrophoretic deposition is 8-15 mm, the constant voltage is 100-150 V, and the deposition time is 5-10 min; Preferably, the electrophoretic deposition involves an electrode distance of 10 mm, a constant voltage of 120 V, and a deposition time of 5 min.

9. The method for preparing the magnesium alloy micro-arc oxidation-electrophoretic deposition composite film according to any one of claims 4-8, characterized in that, In step S4, the sintering temperature is 300-400℃, the sintering time is 1-3h, and the heating rate is 8-15℃ / min; Preferably, the sintering temperature is 300℃, the sintering time is 2h, and the heating rate is 10℃ / min.

10. The application of a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film as described in any one of claims 1-3 or a magnesium alloy micro-arc oxidation-electrophoretic deposition composite film prepared by the preparation method described in any one of claims 4-9 in ships.

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