ZK61M magnesium alloy surface corrosion-resistant coating as well as preparation method and application thereof

Abstract

The invention relates to a ZK61M magnesium alloy surface corrosion-resistant coating and a preparation method and application thereof. The ZK61M magnesium alloy surface corrosion-resistant coating comprises a ZK61M magnesium alloy matrix and a magnesium-aluminum layered double hydroxide (MgAl-LDH) coating attached to the surface of the ZK61M magnesium alloy matrix.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal surface treatment, and particularly relates to a corrosion-resistant coating on the surface of ZK61M magnesium alloy, a preparation method thereof, and an application thereof. Background Art

[0002] As one of the lightest metals, magnesium alloy is the first choice for the lightweight development of the equipment manufacturing industry. It has the characteristics of high specific strength, excellent electrical and thermal conductivity, good damping performance, good castability, machinability, and easy recycling. In recent years, it has been widely used in the fields of automobile manufacturing, aerospace, electronics, and military industry. ZK61M magnesium alloy belongs to the Mg-Zn-Zr series. Due to the presence of zirconium in its composition, ZK61M magnesium alloy has high strength and good toughness. At the same time, the corrosion resistance and high-temperature resistance of the alloy have also been greatly improved, and it is widely used in the fields of aerospace, military, transportation, and 3C (computers, communications, and consumer electronics).

[0003] Although magnesium alloy has excellent properties, magnesium has high electrochemical activity and poor stability, and its standard electrode potential is about -2.37V, making it prone to oxidation and corrosion. During the spraying process of the coating-type thermal control coating on the heat dissipation surface of magnesium alloy, due to the action of the binder, the above corrosion problem is more prominent, which greatly shortens the service life and application fields of magnesium alloy. At the same time, the occurrence of corrosion will also bring problems such as economic losses and environmental pollution. Therefore, how to improve the corrosion resistance of magnesium alloy has become an urgent problem to be solved in the application of magnesium alloy.

[0004] At present, the methods for improving the corrosion resistance of magnesium alloy are mainly divided into two categories: one is to improve the corrosion resistance of magnesium alloy by increasing its purity and improving its microstructure; the other is to adopt surface treatment technology to improve the corrosion resistance of magnesium alloy. Among them, increasing the purity of magnesium alloy and improving its microstructure have very limited effects on improving the corrosion resistance of magnesium alloy; the surface protective layer constructed by surface treatment technology can play a shielding role, hinder the contact between magnesium alloy and corrosive medium, delay the penetration of corrosive medium, and thus slow down its corrosion rate, playing a good protective role. Among them, the surface treatment technologies for improving the corrosion resistance of magnesium alloy mainly include chemical conversion, micro-arc oxidation, laser treatment, spraying, etc. However, these methods often have the disadvantages of complex process, high cost, and high energy consumption. For example, although the micro-arc oxidation coating has a simple process and little pollution, the porous coating provides a path for the intrusion of corrosive medium; the chemical conversion film has high bonding strength and rich varieties, but it causes great environmental pollution and high waste liquid treatment cost; the spraying requires strict requirements on the size and shape of metal powder, has a high raw material cost, and the bonding strength between the coating and the substrate interface is weak, and it is easy to fall off, etc. Summary of the Invention

[0005] Aiming at the deficiencies and drawbacks of the existing technologies for preparing corrosion-resistant coatings on magnesium alloys, the purpose of the present invention is to provide a corrosion-resistant coating on the surface of ZK61M magnesium alloy, its preparation method and application. The surface coating of magnesium alloy provided by the present invention has excellent corrosion resistance. The MgAl-LDH coating grown by in-situ coprecipitation has a strong bonding force with the magnesium alloy, and is a stable corrosion-resistant coating with a long service life. This method can improve the corrosion resistance of the magnesium alloy surface, provide long-term protection for the magnesium alloy surface, and extend the service life of the magnesium alloy.

[0006] In the first aspect, the present invention provides a corrosion-resistant coating on the surface of ZK61M magnesium alloy, and the corrosion-resistant coating on the surface of ZK61M magnesium alloy includes: a ZK61M magnesium alloy substrate, and a magnesium-aluminum layered double hydroxide MgAl-LDH coating attached to the surface of the ZK61M magnesium alloy substrate.

[0007] Preferably, in the magnesium-aluminum layered double hydroxide MgAl-LDH coating, the mass ratio of magnesium hydroxide is 14-33%, and the mass ratio of aluminum hydroxide is 14-17%.

[0008] Preferably, the thickness of the magnesium-aluminum layered double hydroxide MgAl-LDH coating is 5-10 μm.

[0009] Preferably, the self-corrosion potential of the corrosion-resistant coating on the surface of ZK61M magnesium alloy is -1.52~-1.26V / SCE, preferably -1.45~-1.26V / SCE, and the self-corrosion current density is 2.28×10 -5 ~1.89×10 -7 Acm -2 .

[0010] In the second aspect, the present invention provides a preparation method of the above-mentioned corrosion-resistant coating on the surface of ZK61M magnesium alloy, and the preparation method includes the following steps: (1) Polish the ZK61M magnesium alloy with SiC sandpaper, then clean and dry it to obtain a pretreated ZK61M magnesium alloy; (2) Add the pretreated ZK61M magnesium alloy into a precursor solution containing a chelating agent, an Al 3+ salt, and NaNO 3 for a water bath coprecipitation reaction to obtain the corrosion-resistant coating on the surface of ZK61M magnesium alloy.

[0011] Preferably, in step (1), the mesh numbers of the SiC sandpaper are 800 mesh and 1200 mesh respectively, and the cleaning method is ultrasonic cleaning for 10-30 min.

[0012] Preferably, in step (2), the chelating agent is EDTA or DTPA; the Al 3+The salt is Al(NO 3 ) 3 ·9H 2 O; In the precursor solution, the concentration ratio of the chelating agent, Al 3+ salt, and NaNO 3 is 0.01 - 0.1 M: 0.05 - 0.1 M: 0.2 - 0.3 M.

[0013] Preferably, in step (2), the pH value of the precursor solution is 9 - 11; preferably, a 1 - 2 M NaOH solution is used to adjust the pH value of the precursor solution.

[0014] Preferably, in step (2), the temperature of the water bath co - precipitation reaction is 80 - 120 °C, preferably 95 °C; the time of the water bath co - precipitation reaction is 6 - 36 h.

[0015] In a third aspect, the present invention provides an application of the above - mentioned corrosion - resistant coating on the surface of ZK61M magnesium alloy in the field of metal surface treatment.

[0016] Beneficial effects (1) The MgAl - LDH coating of the present invention has excellent corrosion - resistant performance, and the grown coating has a strong bonding force with the magnesium alloy; (2) The present invention prepares the corrosion - resistant coating by chelating agent - assisted in - situ co - precipitation on the magnesium alloy substrate, without the need for high - temperature and high - pressure conditions, reducing energy consumption; in a solution containing Al 3+ , directly using the magnesium alloy as the magnesium source for the growth of MgAl - LDH, the preparation process is simple and easy to operate, with low cost, environmental protection, and has the possibility of wide application; (3) Based on the layered characteristics of MgAl - LDH of the present invention, the layered structure is beneficial to hinder the contact between the corrosion medium and the substrate, playing a shielding role, thereby improving the corrosion - resistant performance of the magnesium alloy; (4) The layered double - hydroxide prepared by the present invention has the characteristics of layered double - hydroxide layers, and the subsequent modification of the coating can be carried out by utilizing the anion exchangeability between the layers. Description of the drawings

[0017] Figure 1 It is a schematic structural diagram of the corrosion - resistant coating on the surface of ZK61M magnesium alloy prepared in Example 1; Figure 2 It is an X - ray diffraction pattern of the pre - treated magnesium alloy and the layered double - hydroxide prepared in Example 3; Figure 3 It is a SEM photograph of the surface of the pre - treated magnesium alloy (a) and the MgAl - LDH coating in - situ grown on the surface of the magnesium alloy in Example 1 (b - c); Figure 4 Infrared spectrum diagram (a) of the MgAl-LDH coating on the magnesium alloy surface in Example 3 and X-ray photoelectron spectroscopy diagram (b) of the coating sample; Figure 5 Polarization curve diagram (3.5wt% NaCl solution) of the pre-treated magnesium substrate provided by the present invention and the magnesium-aluminum layered double hydroxide prepared in Example 1; Reference numerals: 1. ZK61M magnesium alloy substrate; 2. MgAl-LDH coating. Detailed implementation manners

[0018] The present invention will be further described below through the following implementation manners. It should be understood that the following implementation manners are only used to illustrate the present invention and do not limit the present invention.

[0019] First, the present invention provides a corrosion-resistant coating on the surface of ZK61M magnesium alloy. Among them, the corrosion-resistant coating on the surface of ZK61M magnesium alloy may include: a ZK61M magnesium alloy substrate, and a magnesium-aluminum layered double hydroxide MgAl-LDH coating attached to the surface of the ZK61M magnesium alloy substrate.

[0020] In some implementation manners, in the magnesium-aluminum layered double hydroxide MgAl-LDH coating, the mass ratio of magnesium hydroxide may be 14-33%, and the mass ratio of aluminum hydroxide is 14-17%.

[0021] Research shows that as the molar ratio of magnesium to aluminum increases from 2:1 to 4:1, the layer spacing of LDHs decreases from 0.888 nm to 0.796 nm, which leads to a decrease in the number of anions loaded by LDHs and a decrease in the adsorption capacity for chloride ions. The increase in the magnesium-aluminum ratio may affect the anion exchange ability of LDHs, and thus affect its performance. Therefore, controlling the mass ratio of magnesium and aluminum within a specific range is crucial for optimizing the performance of MgAl-LDHs. If one side is too large or too small, it may cause changes in the layer spacing, thereby affecting the adsorption performance and rust inhibition effect of the material.

[0022] In some implementation manners, the thickness of the magnesium-aluminum layered double hydroxide MgAl-LDH coating may be 5-10 μm. If the coating is too thin, it cannot provide sufficient protection, resulting in easy penetration of corrosive media, thereby reducing the protection effect of the coating; if the coating is too thick, it will cause cracking and peeling of the coating due to increased interlayer stress, which also affects its protection performance.

[0023] The corrosion-resistant coating on the surface of ZK61M magnesium alloy provided by the present invention has excellent corrosion resistance, and the magnesium-aluminum layered double hydroxide MgAl-LDH coating has good adhesion to the substrate.

[0024] In some embodiments, the self-corrosion potential of the corrosion-resistant coating on the surface of the ZK61M magnesium alloy can be -1.52 to -1.26 V / SCE, preferably -1.45 to -1.26 V / SCE; the self-corrosion current density can be 2.28×10 -5 ~1.89×10 -7 Acm -2 .

[0025] In the corrosion-resistant coating on the surface of the ZK61M magnesium alloy provided by the present invention, the MgAl-LDH layered structure is beneficial to hindering the contact between the corrosion medium and the substrate, playing a shielding role, thereby improving the corrosion resistance of the magnesium alloy; moreover, the layered double hydroxide prepared by the present invention has the characteristics of a layered double hydroxide layer, and the interlayer anion exchangeability thereof can be used for further subsequent modification of the coating.

[0026] Hereinafter, the preparation method of the corrosion-resistant coating on the surface of the ZK61M magnesium alloy will be exemplarily described. Among them, the preparation method may include the following steps: (1) The ZK61M magnesium alloy is polished with SiC sandpaper, then cleaned and dried to obtain a pretreated ZK61M magnesium alloy; (2) The pretreated ZK61M magnesium alloy is added to a precursor solution containing a chelating agent, an Al 3+ salt, and NaNO 3 for a water bath coprecipitation reaction to obtain the corrosion-resistant coating on the surface of the ZK61M magnesium alloy.

[0027] In some embodiments, in step (1), the mesh numbers of the SiC sandpaper can be 800 mesh and 1200 mesh respectively, and the cleaning method can be ultrasonic cleaning for 10 to 30 min. The polishing treatment and cleaning of the surface are to remove the chips, grease, macroscopic corrosion points and corrosion products on the surface of the magnesium alloy; at the same time, the surface of the polished magnesium alloy has a certain roughness, which is beneficial to providing chemical reaction active sites for subsequent in-situ coprecipitation.

[0028] In some embodiments, in step (2), the chelating agent can be EDTA or DTPA. The chelating agent promotes the substitution of part of the Mg 3+ in Mg(OH) 2 by Al 2+ to generate Mg-Al LDHs and has a significant complexing ability with Mg 2+ / Al 3+ cations, playing a key role in the nucleation and deposition of the MgAl-LDH film.

[0029] EDTA and DTPA are aminocarboxylic acid chelating agents. They provide coordination sites through the amino and carboxyl groups in their molecular structures to form chelates with metal ions. They have strong coordination ability, stability in aqueous solution, better controllability of chelation reaction, and improve the crystallinity, stability and functionality of LDH. They are widely used in the preparation of LDH. Magnesium alloy is dissolved in the solution to produce Mg 2+ cations, the chelating agent in the solution combines with these dissolved cations to form stable and soluble chelates. 2+ and Al 3+ The cation also reacts with OH - The anions combine to form a metal hydroxide precipitate on the substrate surface, thereby forming a film. These combined reactions promote the dissolution of the magnesium alloy into the solution. When the surface is completely covered by the precipitate film, the dissolution of the substrate is inhibited. 3+ Replacement of Mg(OH) 2 Part of Mg 2+ , thus generating Mg-Al LDHs.

[0030] In some embodiments, in step (2), the Al 3+ The salt can be Al(NO 3 ) 3 9H 2 O.

[0031] Sodium nitrate can participate in the reaction and exist between the layers of LDH as an interlayer anion, while preventing a large amount of carbon dioxide in the air from dissolving into the solution under alkaline solution conditions to form carbonate intercalation.

[0032] In some embodiments, in step (2), the chelating agent, Al 3+ Salt, NaNO 3 The concentration ratio can be 0.01~0.1M:0.05~0.1M:0.2~0.3M.

[0033] Al 3+ Improper concentration of salt and sodium nitrate will affect the formation and performance of LDHs membrane: Al 3+ The amount of salt used will affect the magnesium-aluminum ratio of LDH. Too little salt may cause Al 3+ Insufficient deposition of Mg-Al LDHs film may affect the formation of Mg-Al LDHs film; excessive sodium nitrate may affect the pH value of the solution, thereby affecting Mg 2+ The concentration of the chelating agent will affect the formation and thickness of the LDH coating: too little will result in insufficient thickness of the LDHs film, affecting its protective effect; too much will result in too thick a LDHs film, affecting its adhesion and uniformity.

[0034] In some embodiments, in step (2), the pH value of the precursor solution may be 9 to 11; preferably, a 1 to 2 M NaOH solution is used to adjust the pH value of the precursor solution.

[0035] pH has a significant impact on the crystallization and corrosion resistance of the LDHs coating. When the solution pH value is 10.0, the obtained LDH coating has the best crystallization. However, too high or too low pH values may have an adverse effect on the formation and properties of the Mg-Al LDHs film: too high pH value may cause alkaline corrosion; too low pH value may damage the protective oxide film on the metal surface and accelerate the corrosion of the metal.

[0036] In some embodiments, in step (2), the temperature of the water bath co-precipitation reaction may be 80 - 120 °C, preferably 95 °C; the time of the water bath co-precipitation reaction may be 6 - 36 h.

[0037] When the temperature is too low, the reaction rate slows down, resulting in incomplete reaction, and the crystallinity and purity of the product may be affected, thus affecting the film-forming effect and properties of Mg-Al LDHs; when the temperature is too high, side reactions will occur, such as an increase in the oxidation tendency of some metal hydroxides, thus affecting the precipitation rate and the quality of the product. If the reaction time is too short, the crystallization of the Mg-Al LDHs film layer is insufficient, affecting its protective performance and adhesion; if the reaction time is too long, the LDHs film layer may be too thick, affecting its adhesion and uniformity, and at the same time side reactions will occur, such as excessive growth or decomposition of LDHs, thus affecting its properties.

[0038] The preparation method provided by the present invention first pretreats the magnesium alloy to make the magnesium alloy reach a certain roughness, and then places it in a growth solution containing a chelating agent and grows it under water bath stirring. Using the magnesium alloy as a magnesium source, it forms a chelate with the foreign Al 3+ Under the action of the chelating agent, and in-situ co-precipitation growth of the MgAl-LDH coating occurs on the surface of the magnesium alloy. During the growth process, by controlling the concentration of the chelating agent, reaction time, reaction temperature, pH, etc., the generated MgAl-LDH has high purity and a complete structure, effectively providing corrosion protection for the surface of the magnesium alloy.

[0039] The present invention prepares a corrosion-resistant coating by chelating agent-assisted in-situ co-precipitation on a magnesium alloy substrate, without the need for high-temperature and high-pressure conditions, reducing energy consumption. In a solution containing Al 3+ Directly using the magnesium alloy as a magnesium source for the growth of MgAl-LDH, the preparation process is simple and easy to operate, with low cost, environmental protection, and has the possibility of wide application.

[0040] The corrosion-resistant coating on the surface of the ZK61M magnesium alloy provided by the present invention can be applied to the field of metal surface treatment.

[0041] The following are further examples to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, rather than being limited to the specific values in the following examples. Unless otherwise specified, the technical means used in the examples are conventional means well-known to those skilled in the art.

[0042] Example 1

[0043] The preparation method of the corrosion-resistant coating on the surface of ZK61M magnesium alloy provided in this example includes the following steps (1) Pretreatment steps on the surface of magnesium alloy: including surface polishing treatment and surface cleaning; the surface polishing treatment uses 800-mesh and 1200-mesh SiC sandpapers. After polishing, it is ultrasonically cleaned with absolute ethanol for 10 min, and dried with cold air to obtain the pretreated magnesium alloy; (2) Growth of MgAl-LDH: Dissolve 0.1 mol / L DTPA in 200 ml of deionized water, then add 0.05 mol / L Al(NO 3 ) 3 ·9H 2 O and 0.2 mol / L NaNO 3 , and use 2 M NaOH solution to adjust the pH value of the obtained solution to 10 ± 0.1; Immerse the pretreated magnesium alloy specimen into the prepared precursor solution, heat it to 95 °C and react for 22 h under continuous stirring in a water bath. After the reaction, take it out, ultrasonically clean it with deionized water for 10 min, and dry it with hot air to obtain the layered double hydroxide corrosion-resistant coating on the surface of the ZK61M magnesium alloy.

[0044] Example 2

[0045] The preparation method of the corrosion-resistant coating on the surface of ZK61M magnesium alloy provided in this example refers to Example 1, and the main difference is that: In step (2), the concentration of the chelating agent is 0.01 mol / L; the reaction time is 24 h.

[0046] Example 3

[0047] The preparation method of the corrosion-resistant coating on the surface of ZK61M magnesium alloy provided in this example refers to Example 1, and the main difference is that: In step (2), the chelating agent is EDTA, the concentration is 0.015 mol / L; the reaction time is 14 h.

[0048] Example 4

[0049] The preparation method of the corrosion-resistant coating on the surface of ZK61M magnesium alloy provided in this example refers to Example 1, and the main difference is that: In step (2), the chelating agent is EDTA, and the concentration is 0.01 mol / L; the reaction time is 16 h.

[0050] Example 5

[0051] The preparation method of the corrosion-resistant coating on the surface of ZK61M magnesium alloy provided in this example refers to Example 1, and the main difference is that: In step (2), the concentration of the chelating agent is 0.01 mol / L; the temperature of water bath heating is 80 °C, and the reaction time is 36 h.

[0052] Example 6

[0053] The preparation method of the corrosion-resistant coating on the surface of ZK61M magnesium alloy provided in this example refers to Example 1, and the main difference is that: In step (2), the chelating agent is EDTA, and the concentration is 0.01 mol / L; the temperature of water bath heating is 120 °C, and the reaction time is 14 h.

[0054] Example 7

[0055] The preparation method of the corrosion-resistant coating on the surface of ZK61M magnesium alloy provided in this example refers to Example 1, and the main difference is that: In step (2), the chelating agent is EDTA, and the concentration of aluminum nitrate is 0.1 mol / L; the reaction time is 24 h.

[0056] Comparative Example 1

[0057] The preparation method of the surface coating of ZK61M magnesium alloy provided in this comparative example refers to Example 1, and the main difference is that: in step (2), no chelating agent is used; the reaction time is 24 h.

[0058] Comparative Example 2

[0059] The preparation method of the surface coating of ZK61M magnesium alloy provided in this comparative example refers to Example 1, and the main difference is that: in step (2), the chelating agent is EDTA, the concentration is 0.01 mol / L; the pH of the reaction solution is 12 ± 0.1, and the reaction time is 14 h.

[0060] Comparative Example 3

[0061] The preparation method of the ZK61M magnesium alloy surface coating provided in this comparative example refers to Example 1, and the main differences are as follows: In step (2), the chelating agent is EDTA with a concentration of 0.01 mol / L; the pH of the reaction solution is 8 ± 0.1, and the reaction time is 14 h.

[0062] Table 1 below shows the reaction parameters of Examples 1-7 and Comparative Examples 1-3, and the electrochemical parameters of the coatings and magnesium alloys prepared therefrom: "-" indicates no data; for a typical polarization curve, the higher the self-corrosion potential (E corr ), the lower the corrosion thermodynamic tendency, and the better the thermodynamic stability of the material; the smaller the self-corrosion current density (I corr ), the slower the corrosion rate of the material, and the better the corrosion resistance.

[0063] Figure 1 Figure 15 is a schematic structural diagram of the corrosion-resistant coating on the surface of the ZK61M magnesium alloy prepared in Example 1. As can be seen from the figure, the coating is composed of a ZK61M magnesium alloy substrate and a MgAl-LDH coating on the surface.

[0064] Figure 2 Figure 19 is an X-ray diffraction pattern of the pretreated magnesium alloy and the layered double hydroxide prepared in Example 3. As can be seen from the figure, an LDH phase is formed on the surface of the coating.

[0065] Figure 3 Figure 23 is a SEM photograph of the surface of the pretreated magnesium alloy (a) and the MgAl-LDH coating in-situ grown on the surface of the magnesium alloy in Example 1 (b-c). As can be seen from the figure, there are many scratches on the surface of the pretreated sample, and the MgAl-LDH formed after water bath growth has a flaky nanostructure.

[0066] Figure 4 Figure 27 is an infrared spectrum of the MgAl-LDH coating on the surface of the magnesium alloy in Example 3 (a) and an X-ray photoelectron spectrum of the coating sample (b). As can be seen from the figure, MgAl-LDH is formed on the surface of the reacted sample.

[0067] Figure 5 Figure 31 is a polarization curve of the pretreated magnesium substrate and the magnesium-aluminum layered double hydroxide prepared in Example 1 (3.5 wt% NaCl solution). As can be seen from the figure, the corrosion potential of the coating is higher than that of the magnesium alloy substrate, and the corrosion current is smaller than that of the magnesium alloy, indicating that the coating has better corrosion resistance than the magnesium alloy.

[0068] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be construed as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and alternatives to the present invention will be obvious. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A ZK61M magnesium alloy surface corrosion-resistant coating, characterized in that: The ZK61M magnesium alloy surface corrosion-resistant coating comprises: a ZK61M magnesium alloy substrate, and a magnesium-aluminum layered double hydroxide MgAl-LDH coating attached to the surface of the ZK61M magnesium alloy substrate.

2. The ZK61M magnesium alloy surface corrosion-resistant coating according to claim 1, characterized in that: In the magnesium-aluminum layered double hydroxide MgAl-LDH coating, the mass proportion of magnesium hydroxide is 14-33%, and the mass proportion of aluminum hydroxide is 14-17%.

3. The ZK61M magnesium alloy surface corrosion-resistant coating according to claim 1 or 2, characterized in that: The thickness of the magnesium aluminum layered double hydroxide MgAl-LDH coating is 5-10 μm.

4. The corrosion-resistant coating on the surface of ZK61M magnesium alloy according to any one of claims 1 to 3, characterized in that: The self-corrosion potential of the corrosion-resistant coating on the surface of the ZK61M magnesium alloy is -1.52 to -1.26 V / SCE, preferably -1.45 to -1.26 V / SCE, and the self-corrosion current density is 2.28×10 -5 ~1.89×10 -7 Acm -2 .

5. A method for preparing a corrosion-resistant coating on the surface of a ZK61M magnesium alloy according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: (1) polishing the ZK61M magnesium alloy with SiC sandpaper, and then cleaning and drying the ZK61M magnesium alloy to obtain a pretreated ZK61M magnesium alloy; (2) Add the pretreated ZK61M magnesium alloy to a mixture containing a chelating agent, Al 3+ A water bath coprecipitation reaction is carried out in a precursor solution of salt and NaNO3 to obtain the corrosion-resistant coating on the surface of the ZK61M magnesium alloy.

6. The preparation method according to claim 5, characterized in that: In step (1), the mesh sizes of the SiC sandpaper are 800 mesh and 1200 mesh respectively, and the cleaning method is ultrasonic cleaning for 10 to 30 minutes.

7. The preparation method according to claim 5 or 6, characterized in that: In step (2), the chelating agent is EDTA or DTPA; the Al 3+ The salt is Al(NO3)3·9H2O; In the precursor solution, the chelating agent, Al 3+ The concentration ratio of salt and NaNO3 is 0.01~0.1M:0.05~0.1M:0.2~0.3M.

8. The preparation method according to any one of claims 5 to 7, characterized in that: In step (2), the pH value of the precursor solution is 9 to 11; preferably, a 1 to 2 M NaOH solution is used to adjust the pH value of the precursor solution.

9. The preparation method according to any one of claims 5 to 8, characterized in that: In step (2), the temperature of the water bath co-precipitation reaction is 80-120° C., preferably 95° C.; and the time of the water bath co-precipitation reaction is 6 to 36 hours.

10. Use of the corrosion-resistant coating on the surface of the ZK61M magnesium alloy according to any one of claims 1 to 4 in the field of metal surface treatment.

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