A method for preparing a high corrosion-resistant coating of magnesium-lithium alloy by PECVD technology

Abstract

This invention discloses a method for preparing a high corrosion-resistant coating of magnesium-lithium alloy using PECVD technology, belonging to the field of magnesium-lithium alloy corrosion protection technology. The invention includes: (1) mechanically grinding a magnesium-lithium alloy substrate; (2) ultrasonically cleaning the magnesium-lithium alloy; (3) pretreating the magnesium-lithium alloy in a sodium hydroxide solution; (4) performing PECVD treatment on the pretreated alloy, wherein the PECVD treatment atmosphere includes a mixture of carbon tetrafluoride and nitrogen; (5) ultrasonically cleaning the corrosion-resistant coating magnesium-lithium alloy, followed by heating and drying to accelerate the stabilization of the corrosion-resistant coating until the corrosion-resistant coating is completely cured and stabilized, thus completing the preparation of the high corrosion-resistant coating of magnesium-lithium alloy and obtaining a magnesium-lithium alloy with a stable corrosion-resistant coating. The magnesium-lithium alloy corrosion-resistant coating prepared by the method of this invention has excellent density and uniformity, high bonding strength with the substrate, high corrosion resistance, and long protection duration.

Description

Technical Field

[0001] This invention belongs to the field of magnesium-lithium alloy corrosion protection technology, and relates to a method for preparing a highly corrosion-resistant coating for magnesium-lithium alloys using PECVD technology. Background Technology

[0002] Magnesium-lithium alloys, due to their extremely low density and excellent specific strength, have become the preferred lightweight structural materials and are widely used in aerospace, automotive manufacturing, and portable electronic devices. Magnesium-lithium alloys have a density approximately 30% lower than aluminum alloys, making them ideal for applications with extremely high weight reduction requirements. However, magnesium-lithium alloys have a significant drawback: poor corrosion resistance. Especially when operating in humid and saline environments, they are highly susceptible to pitting corrosion, crevice corrosion, and stress corrosion cracking, leading to surface damage, affecting mechanical properties, and thus shortening their service life.

[0003] Corrosion protection of magnesium-lithium alloys is mainly achieved by coating the alloy surface with an anti-corrosion film. Traditional methods for forming this film include chemical conversion, electroplating, and anodizing. While these methods improve the corrosion resistance of magnesium-lithium alloys to some extent, they still have some drawbacks. For example, the protective capabilities of chemical conversion and anodizing films are limited and difficult to maintain stability over long-term use; electroplating is a complex process and can easily cause environmental pollution.

[0004] Plasma-enhanced chemical vapor deposition (PECVD), as an emerging coating preparation technology, has attracted widespread attention due to its ability to deposit denser and more uniform films compared to traditional film formation methods, while also minimizing environmental pollution. The density, uniformity, and adhesion strength of the anti-corrosion film are directly proportional to its protective effect. Improving the density, uniformity, and adhesion strength of the film to the substrate all contribute to enhancing the protective effect and extending the duration of protection. Therefore, further optimizing film performance, improving protective efficacy, and extending the duration of protection based on PECVD coatings is of great significance.

[0005] Therefore, it is necessary to provide a method for preparing a high corrosion-resistant coating of magnesium-lithium alloy using PECVD technology, thereby enhancing the protective effect and duration of the corrosion-resistant coating prepared by PECVD technology. Summary of the Invention

[0006] To overcome the problems in the prior art, the present invention pre-treats the magnesium-lithium alloy to form a hydroxide film layer, and deposits a highly chemically inert fluorocarbon coating on the hydroxide film layer. Based on the coating prepared using PECVD technology, the uniformity, stability, and adhesion strength of the film layer to the substrate are further improved, thereby enhancing the protective effect and protection duration of the film layer on the magnesium-lithium alloy.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] The method includes the following steps:

[0009] (1) Mechanically polish the magnesium-lithium alloy substrate;

[0010] (2) The magnesium-lithium alloy after mechanical polishing in step (1) is subjected to ultrasonic washing;

[0011] (3) The magnesium-lithium alloy after ultrasonic washing in step (2) is placed in sodium hydroxide solution for pretreatment, and a uniform hydroxide film is formed on the surface of the magnesium-lithium alloy to obtain the pretreated alloy.

[0012] (4) The pretreated alloy is subjected to PECVD treatment. The PECVD treatment atmosphere includes a mixture of carbon tetrafluoride and nitrogen. Under the action of plasma, a dense fluorocarbon coating is formed on the surface of the hydroxide film, which is a corrosion-resistant coating, and a corrosion-resistant magnesium-lithium alloy is obtained.

[0013] (5) After ultrasonic cleaning of the corrosion-resistant coating magnesium-lithium alloy, heat drying is performed to accelerate the stabilization of the corrosion-resistant coating until the corrosion-resistant coating is completely cured and stabilized, thus completing the preparation of the high corrosion-resistant coating of magnesium-lithium alloy and obtaining a magnesium-lithium alloy with a stable corrosion-resistant coating.

[0014] Preferably, in step (1), the magnesium-lithium alloy substrate is mechanically polished using 3000-7000 grit sandpaper, and the surface roughness of the magnesium-lithium alloy substrate is polished to 1.5-2.0 μm.

[0015] Preferably, in step (2), the magnesium-lithium alloy substrate is placed in acetone for ultrasonic cleaning, the ultrasonic cleaning frequency is 40-60kHz, and the cleaning time is 30min.

[0016] Preferably, in step (3), the sodium hydroxide solution has a mass concentration of 20%, the pretreatment temperature is 30-50℃, and the pretreatment time is 30min.

[0017] Preferably, in step (4), the deposition temperature is 150-200℃, the deposition pressure is 4.0-5.0 Torr, the plasma power is 100-300W, and the deposition time is 45-90min.

[0018] Preferably, in step (4), the flow rate of carbon tetrafluoride gas is 30-60 sccm and the flow rate of nitrogen gas is 40-80 sccm.

[0019] Preferably, in step (5), alcohol is used for ultrasonic cleaning, the ultrasonic cleaning frequency is 40-60kHz, and the cleaning time is 30min.

[0020] Preferably, in step (5), the heating and drying temperature is 40-60℃, and the heating and drying method is intermittent heating and drying. After each heating and drying for 30-60 minutes, the corrosion-resistant coated magnesium-lithium alloy is placed in the air for natural air cooling for 6 hours, and then the next heating and drying is carried out. This process is repeated until the corrosion-resistant coating is completely cured and stable.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention forms a hydroxide film on the surface of a magnesium-lithium alloy through pretreatment, and deposits a corrosion-resistant coating on the hydroxide film. Utilizing the principle of interfacial chemistry, it effectively improves the bonding strength between the corrosion-resistant coating and the magnesium-lithium alloy substrate. At the same time, the chemically active interface provided by the hydroxide film promotes uniform deposition of the corrosion-resistant coating and enhances its stability. As a result, the corrosion-resistant coating has high density, uniformity, and high bonding strength with the alloy substrate, improving the protective effect of the corrosion-resistant coating on the magnesium-lithium alloy substrate and extending the protection time.

[0023] 2. This invention uses a mixture of carbon tetrafluoride and nitrogen as the reaction gas to deposit a fluorocarbon coating as a corrosion-resistant coating. Fluorocarbon coatings are inorganic coatings with high chemical inertness, and the coating itself has good stability and corrosion resistance.

[0024] 3. This invention can complete the deposition of corrosion-resistant coatings at lower temperatures and in a shorter time, which helps to reduce the energy consumption in preparing corrosion-resistant coatings. Furthermore, the process is relatively simple, highly controllable, and suitable for industrial application.

[0025] 4. The intermittent heating and drying method of the present invention can gradually release the internal stress of the corrosion-resistant coating, prevent the corrosion-resistant coating from cracking or peeling due to prolonged heating, and improve the overall quality and protective effect of the finally obtained corrosion-resistant coating. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments.

[0028] The chemical composition of the magnesium-lithium alloy used in the embodiments and comparative examples of this invention is shown in Table 1. All chemical reagents not specifically described in the embodiments and comparative examples of this invention were commercially available analytical grade reagents.

[0029] Table 1

[0030] Approximately 85% Approximately 10% Approximately 5%

[0031] Example 1

[0032] This embodiment prepares a magnesium-lithium alloy corrosion-resistant coating using the following method:

[0033] (1) Use sandpaper to mechanically polish the magnesium-lithium alloy substrate until the surface roughness of the magnesium-lithium alloy substrate is 1.5μm.

[0034] (2) After polishing, the magnesium-lithium alloy substrate is placed in acetone and washed with an ultrasonic frequency of 60kHz for 30 minutes to remove oil and impurities from the surface of the magnesium-lithium alloy and obtain a clean washed sample.

[0035] (3) The shaken sample was placed in a sodium hydroxide solution with a mass concentration of 20% and pretreated at 50°C for 30 minutes. After treatment, a uniform hydroxide film was formed on the surface of the magnesium-lithium alloy, and the pretreated sample was obtained.

[0036] (4) The pretreated sample was placed in a PECVD reactor. The reaction atmosphere was set to a mixture of carbon tetrafluoride (CF4) and nitrogen (N2), with a carbon tetrafluoride flow rate of 60 sccm, a nitrogen flow rate of 80 sccm, a deposition temperature of 200℃, and a deposition pressure of 5.0 Torr. The plasma power was set to 300W, and the processing time was 90 min, in order to deposit a dense fluorocarbon corrosion-resistant coating on the surface of the magnesium-lithium alloy, thus obtaining a corrosion-resistant coated magnesium-lithium alloy.

[0037] (5) The corrosion-resistant coated magnesium-lithium alloy was placed in alcohol for ultrasonic cleaning at a frequency of 60 kHz for 30 min. Then it was heated and dried for 60 min at a temperature of 60 °C. After the first heating and drying, the corrosion-resistant coated magnesium-lithium alloy was placed in the air for natural air cooling. After 6 h, it was heated and dried again. This heating and drying was repeated 4 times with 3 intervals in between, for a total of 18 h, to ensure that the coating was completely cured and stabilized, and to obtain a magnesium-lithium alloy with a stable corrosion-resistant coating.

[0038] The magnesium-aluminum alloy corrosion-resistant coating prepared in this embodiment is dense and uniform, with a coating thickness of approximately 5-7 μm. The coating exhibits good adhesion and is firmly bonded to the magnesium-lithium alloy substrate.

[0039] In this embodiment, the magnesium-lithium alloy sample showed no significant corrosion after a 72-hour salt spray test, demonstrating excellent corrosion resistance. Furthermore, after mechanical friction and corrosion resistance tests, the corrosion-resistant coating remained stable and fully cured, without any peeling or flaking.

[0040] Example 2

[0041] This embodiment prepares a magnesium-lithium alloy corrosion-resistant coating using the following method:

[0042] (1) Use sandpaper to mechanically polish the magnesium-lithium alloy substrate until the surface roughness of the magnesium-lithium alloy substrate is 1.8μm.

[0043] (2) After polishing, the magnesium-lithium alloy substrate is placed in acetone and washed with an ultrasonic frequency of 50kHz for 30 minutes to remove oil and impurities from the surface of the magnesium-lithium alloy and obtain a clean washed sample.

[0044] (3) The shaken sample was placed in a sodium hydroxide solution with a mass concentration of 20% and pretreated at 40°C for 30 minutes. After treatment, a hydroxide film was formed on the surface of the magnesium-lithium alloy, and the pretreated sample was obtained.

[0045] (4) The pretreated sample was placed in a PECVD reactor. The reaction atmosphere was set to a mixture of carbon tetrafluoride (CF4) and nitrogen (N2), with a carbon tetrafluoride flow rate of 40 sccm, a nitrogen flow rate of 60 sccm, a deposition temperature of 170℃, and a deposition pressure of 4.5 Torr. The plasma power was set to 200W, and the processing time was 55 min, in order to deposit a dense fluorocarbon corrosion-resistant coating on the surface of the magnesium-lithium alloy, thus obtaining a corrosion-resistant coated magnesium-lithium alloy.

[0046] (5) The corrosion-resistant coated magnesium-lithium alloy was placed in alcohol for ultrasonic cleaning at a frequency of 50 kHz for 30 min. Then it was heated and dried for 40 min at a temperature of 50 °C. After the first heating and drying, the corrosion-resistant coated magnesium-lithium alloy was placed in the air for natural air cooling. After 6 h, it was heated and dried again. This heating and drying was repeated 4 times with 3 intervals in between, for a total of 18 h, to ensure that the coating was completely cured and stabilized, and to obtain a magnesium-lithium alloy with a stable corrosion-resistant coating.

[0047] The magnesium-aluminum alloy corrosion-resistant coating prepared in this embodiment is dense and uniform, with a coating thickness of approximately 4-6 μm. The coating exhibits good adhesion and is firmly bonded to the magnesium-lithium alloy substrate.

[0048] In this embodiment, the magnesium-lithium alloy sample showed slight corrosion after a 72-hour salt spray test. The corrosion resistance of the coating decreased slightly compared to Example 1, but its corrosion resistance remained at a good level. Furthermore, after mechanical friction and corrosion resistance tests, the coating remained stably and fully cured without significant peeling.

[0049] Example 3

[0050] This embodiment prepares a magnesium-lithium alloy corrosion-resistant coating using the following method:

[0051] (1) Use sandpaper to mechanically grind the magnesium-lithium alloy substrate until the surface roughness of the magnesium-lithium alloy substrate is 2.0μm.

[0052] (2) After polishing, the magnesium-lithium alloy substrate is placed in acetone and washed with an ultrasonic frequency of 40kHz for 30 minutes to remove oil and impurities from the surface of the magnesium-lithium alloy and obtain a clean washed sample.

[0053] (3) The shaken sample was placed in a sodium hydroxide solution with a mass concentration of 20% and pretreated at 30°C for 30 minutes. After treatment, a thick hydroxide film was formed on the surface of the magnesium-lithium alloy, and the pretreated sample was obtained.

[0054] (4) The pretreated sample was placed in a PECVD reactor. The reaction atmosphere was set to a mixture of carbon tetrafluoride (CF4) and nitrogen (N2), with a carbon tetrafluoride flow rate of 30 sccm, a nitrogen flow rate of 40 sccm, a deposition temperature of 150℃, and a deposition pressure of 4.0 Torr. The plasma power was set to 100W, and the processing time was 45 min, in order to deposit a dense fluorocarbon corrosion-resistant coating on the surface of the magnesium-lithium alloy, thus obtaining a corrosion-resistant coated magnesium-lithium alloy.

[0055] (5) The corrosion-resistant coated magnesium-lithium alloy was placed in alcohol for ultrasonic cleaning at a frequency of 40 kHz for 30 min. Then it was heated and dried for 30 min at a temperature of 40 °C. After the first heating and drying, the corrosion-resistant coated magnesium-lithium alloy was placed in the air for natural air cooling. After 6 h, it was heated and dried again. This heating and drying was repeated 4 times with 3 intervals in between, for a total of 18 h. The coating was completely cured and stabilized, and a magnesium-lithium alloy with a stable corrosion-resistant coating was obtained.

[0056] The magnesium-aluminum alloy corrosion-resistant coating prepared in this embodiment is dense and uniform, with a coating thickness of approximately 6-8 μm. Minor cracks appear in some areas of the coating.

[0057] In this embodiment, after a 72-hour salt spray test, the magnesium-lithium alloy sample showed only minor corrosion at the crack locations, and the overall corrosion resistance of the coating remained at a high level. After mechanical friction and corrosion resistance tests, the overall stability of the corrosion-resistant coating was good, with only slight peeling of the coating occurring in the crack areas.

[0058] Comparative Example 1

[0059] This comparative example uses the same preparation method as Example 1 to prepare a corrosion-resistant coating on a magnesium-lithium alloy. The difference is that this comparative example does not use sodium hydroxide solution to pretreat the magnesium-lithium alloy substrate, but directly deposits the corrosion-resistant coating on the surface of the magnesium-lithium alloy substrate. That is, the corrosion-resistant coating is not deposited on the hydroxide film layer.

[0060] The corrosion-resistant coating of the magnesium-lithium alloy prepared in this comparative example showed severe peeling after mechanical friction and corrosion resistance tests, and the magnesium-lithium alloy that lost the protection of the corrosion-resistant coating was severely corroded.

[0061] Comparative Example 2

[0062] This comparative example uses the same method as Example 1 to prepare a magnesium-lithium alloy corrosion-resistant coating, the difference being that a mixture of carbon tetrafluoride and methane gas is used in the PECVD process of this comparative example.

[0063] Compared to Example 1, the corrosion resistance of the corrosion-resistant coating in this comparative magnesium-lithium alloy sample is significantly reduced.

[0064] Comparative Example 3

[0065] This comparative example uses the same method as Example 1 to prepare a magnesium-lithium alloy corrosion-resistant coating, the difference being that the magnesium-lithium alloy of the corrosion-resistant coating in this comparative example is continuously dried.

[0066] Compared to Example 1, the magnesium-lithium alloy sample of this comparative example showed corrosion spots and localized peeling in the early stages of the salt spray test, indicating a significant decrease in the performance of the corrosion-resistant coating.

[0067] Comparative Example 4

[0068] The magnesium-lithium alloy corrosion-resistant coating in this comparative example was prepared using the same method as in Example 1, except that the PECVD treatment temperature in this comparative example was 400°C.

[0069] The corrosion-resistant coating of the comparative magnesium-lithium alloy sample developed cracks and pores immediately after preparation.

[0070] As can be seen from Examples 1-3, the adjustment of process parameters during the preparation of corrosion-resistant coatings has a significant impact on the final performance of the corrosion-resistant coating.

[0071] Compared to Example 1, the bonding strength between the magnesium-lithium alloy corrosion-resistant coating and the magnesium-lithium alloy substrate in Comparative Example 1 was significantly reduced, resulting in severe peeling of the corrosion-resistant coating. This was mainly due to the lack of appropriate interfacial chemical reactions and the participation of hydroxyl groups between the magnesium-lithium alloy and the corrosion-resistant coating in Comparative Example 1. In Example 1, the pretreatment with sodium hydroxide formed a uniform hydroxide film. The hydroxide film formed stable chemical bonds with the metal atoms on the surface of the magnesium-lithium alloy substrate through chemical reactions. For example, oxygen atoms in the hydroxide formed strong metal-oxygen bonds (MO bonds) with magnesium or lithium elements on the substrate surface, allowing the hydroxide film to adhere firmly to the magnesium-lithium alloy surface and providing good adhesion. At the same time, this hydroxide film strengthened the surface polarity of the magnesium-lithium alloy substrate and introduced a large number of hydroxyl groups (–OH). These polar groups can chemically combine with chemical reactants in the corrosion-resistant coating material (such as decomposition products of fluorinated gas) to form strong chemical bonds, thereby enhancing the bonding strength between the corrosion-resistant coating and the hydroxide film, and further strengthening the bonding strength between the corrosion-resistant coating and the magnesium-lithium alloy substrate through the hydroxide film. Conversely, in Comparative Example 1, due to the lack of a hydroxide film, the magnesium-lithium alloy surface is relatively smooth and lacks active sites. The corrosion-resistant coating and the magnesium-lithium alloy substrate mainly rely on physical adsorption rather than chemical bonding. This physical adsorption bonding force is much weaker than the chemical bonding force, resulting in a significant reduction in the bonding strength between the corrosion-resistant coating and the magnesium-lithium substrate, thus affecting the protective effect of the corrosion-resistant coating on the magnesium-lithium alloy.

[0072] Compared to Example 1, the corrosion resistance of the magnesium-lithium alloy corrosion-resistant coating in Comparative Example 2 significantly decreased. This was mainly because the coating produced using a mixture of carbon tetrafluoride and nitrogen as the reaction atmosphere for PECVD treatment exhibited good density and uniformity, and the presence of fluorides enhanced the coating's corrosion resistance and adhesion. Although the addition of methane in Comparative Example 2 increased the carbon content in the coating, improving its hardness, it also led to increased brittleness and decreased density. This irregular carbon distribution made the coating more prone to cracking under stress, significantly affecting its adhesion and corrosion resistance. Furthermore, the presence of methane may have resulted in more porosity and defects in the coating, further weakening its protective capabilities.

[0073] Compared to Example 1, the corrosion resistance and bonding strength with the magnesium-lithium alloy substrate of the magnesium-lithium alloy corrosion-resistant coating in Comparative Example 3 were significantly reduced. This was mainly due to the significant negative impact of continuous drying on the performance of the corrosion-resistant coating. Although continuous drying shortens the total drying time, the corrosion-resistant coating deposited by PECVD technology is prone to accumulating residual internal stress at high temperatures. Continuous drying leads to a large temperature difference between the inside and outside of the corrosion-resistant coating, making it difficult to completely remove solvents and volatile substances from the coating and effectively eliminate residual internal stress. These residual internal stresses easily induce microcracks and voids, weakening the density and adhesion of the corrosion-resistant coating. In addition, the difficulty of temperature control during continuous drying increases, easily leading to local overheating or uneven curing of the corrosion-resistant coating. Ultimately, this resulted in the magnesium-lithium alloy corrosion-resistant coating in Comparative Example 3 showing corrosion spots and localized peeling earlier in the salt spray test. In contrast, by using intermittent drying, the corrosion-resistant coating can be stabilized under milder conditions, thereby enhancing the bonding strength between the corrosion-resistant coating and the magnesium-lithium alloy substrate, removing residual solvents, and improving the coating's corrosion resistance and durability.

[0074] Compared to Example 1, the magnesium-lithium alloy corrosion-resistant coating prepared in Comparative Example 4 has more defects. This is mainly because the PECVD deposition temperature in Comparative Example 4 is too high, leading to a decrease in the thermal stability of the fluorocarbon coating, making it prone to cracks and porosity, thus reducing the coating's density and corrosion resistance. Furthermore, the magnesium-lithium alloy substrate is sensitive to high temperatures; high temperatures exacerbate oxidation on the substrate surface, weakening the adhesion between the corrosion-resistant coating and the substrate, resulting in poor adhesion and easy peeling or detachment. Simultaneously, excessively high processing temperatures may also cause changes in the chemical composition within the corrosion-resistant coating. The molecular structure of the fluorocarbon coating may be destroyed by thermal decomposition, resulting in an uneven distribution of the coating's components, which further weakens the coating's protective performance.

[0075] In summary, this invention, through reasonable control of process parameters and a targeted preparation method, produces a magnesium-lithium alloy corrosion-resistant coating with high density, uniformity, bonding strength with the substrate, and stability. This effectively enhances the corrosion resistance and protective duration of the magnesium-lithium alloy corrosion-resistant coating. The process is simple, highly controllable, and suitable for industrial application.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a high corrosion-resistant coating of magnesium-lithium alloy using PECVD technology, characterized in that: The method includes the following steps: (1) Mechanically polish the magnesium-lithium alloy substrate; (2) The magnesium-lithium alloy after mechanical polishing in step (1) is subjected to ultrasonic washing; (3) The magnesium-lithium alloy after ultrasonic washing in step (2) is placed in sodium hydroxide solution for pretreatment, and a uniform hydroxide film is formed on the surface of the magnesium-lithium alloy to obtain the pretreated alloy. (4) The pretreated alloy is subjected to PECVD treatment. The PECVD treatment atmosphere includes a mixture of carbon tetrafluoride and nitrogen. Under the action of plasma, a dense fluorocarbon coating is formed on the surface of the hydroxide film, which is a corrosion-resistant coating, and a corrosion-resistant magnesium-lithium alloy is obtained. (5) After ultrasonic cleaning of the corrosion-resistant coating magnesium-lithium alloy, heat drying is performed to accelerate the stabilization of the corrosion-resistant coating until the corrosion-resistant coating is completely cured and stabilized, thus completing the preparation of the high corrosion-resistant coating of magnesium-lithium alloy and obtaining a magnesium-lithium alloy with a stable corrosion-resistant coating. In step (3), the sodium hydroxide solution has a mass concentration of 20%, the pretreatment temperature is 30-50℃, and the pretreatment time is 30min. In step (4), the deposition temperature is 150-200℃, the deposition pressure is 4.0-5.0 Torr, the plasma power is 100-300W, the deposition time is 45-90min, the carbon tetrafluoride gas flow rate is 30-60sccm, and the nitrogen gas flow rate is 40-80sccm. In step (5), the heating and drying temperature is 40-60℃, and the heating and drying method is intermittent heating and drying. After each heating and drying for 30-60 minutes, the corrosion-resistant coated magnesium-lithium alloy is placed in the air for natural air cooling for 6 hours, and then the next heating and drying is carried out. This process is repeated until the corrosion-resistant coating is completely cured and stable.

2. The method for preparing a high corrosion-resistant coating of magnesium-lithium alloy using PECVD technology according to claim 1, characterized in that: In step (1), the magnesium-lithium alloy substrate is mechanically polished using 3000-7000 grit sandpaper, and the surface roughness of the magnesium-lithium alloy substrate is polished to 1.5-2.0μm.

3. The method for preparing a high corrosion-resistant coating of magnesium-lithium alloy using PECVD technology according to claim 1, characterized in that: In step (2), the magnesium-lithium alloy substrate is placed in acetone for ultrasonic cleaning. The ultrasonic cleaning frequency is 40-60kHz and the cleaning time is 30min.

4. The method for preparing a high corrosion-resistant coating of magnesium-lithium alloy using PECVD technology according to claim 1, characterized in that: In step (5), alcohol is used for ultrasonic cleaning. The ultrasonic cleaning frequency is 40-60kHz and the cleaning time is 30min.

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