A trivalent element doped anticorrosion coating on a magnesium-zinc alloy surface and a method of making the same

Abstract

This invention relates to a trivalent element-doped anti-corrosion coating on the surface of a magnesium-zinc alloy and its preparation method. The trivalent element-doped anti-corrosion coating comprises: a magnesium-zinc alloy substrate, and a trivalent element-doped anti-corrosion coating formed in situ on the surface of the magnesium-zinc alloy substrate; wherein the anti-corrosion coating is a layered bimetallic hydroxide anti-corrosion coating doped with a trivalent element; the trivalent element in the trivalent element-doped anti-corrosion coating includes at least one of aluminum, iron, nickel, and lanthanum; the method involves first placing at least one of the trivalent element's elemental form, oxide, and hydroxide into deionized water, heating, and introducing CO2 gas to obtain a trivalent element carbonate solution; then immersing the magnesium-zinc alloy substrate in the trivalent element carbonate solution; finally, adding an alkaline solution dropwise to the carbonate solution for a second immersion treatment and drying to obtain the trivalent element-doped anti-corrosion coating on the surface of the magnesium-zinc alloy.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation and relates to a trivalent element-doped anti-corrosion coating on the surface of a magnesium-zinc alloy and its preparation method. Specifically, it relates to a method for preparing a trivalent element-doped layered hydroxide anti-corrosion coating on the surface of a magnesium-zinc alloy using a carbonate solution, and particularly to a method for preparing a trivalent element-doped layered hydroxide anti-corrosion coating on the surface of a ZK61M magnesium-zinc alloy. Background Technology

[0002] Magnesium alloys, with their high specific strength, low density, high thermal conductivity, electromagnetic shielding, and excellent machinability, have gradually replaced aluminum or titanium alloys in certain parts of the automotive, shipbuilding, aerospace, and other fields. However, magnesium has a very low standard electrode potential, approximately -2.372V, making it highly susceptible to corrosion in humid or water-containing environments. Therefore, protective coatings are required on the surfaces of magnesium alloy parts to reduce corrosion. ZK61M is a magnesium-zinc-zirconium alloy with high strength, good plasticity, and corrosion resistance. It is one of the most widely used wrought magnesium alloys in the aerospace field, exhibiting no stress corrosion cracking tendency, simple heat treatment process, good machinability, and the ability to manufacture large forgings with complex shapes.

[0003] Methods for preparing anti-corrosion coatings on magnesium alloy surfaces include electroplating, anodizing, chemical vapor deposition, physical vapor deposition, laser / ion or electron beam treatment, micro-arc oxidation, and chemical conversion. Among these, layered bimetallic hydroxides, with their two-dimensional layered structure, possess inherent ion exchange properties that can capture corrosive anions while releasing corrosion inhibitors, thereby delaying corrosion and improving the corrosion protection capability of magnesium alloys. This has become a research hotspot in recent years and is considered the most effective process for preparing protective chemical conversion coatings on magnesium alloy surfaces. Traditionally, layered bimetallic hydroxides are prepared using a hydrothermal method. The high temperature and high pressure conditions limit the application scenarios of layered bimetallic hydroxides, and the pollution from reaction products and energy consumption are also significant factors restricting their use. Summary of the Invention

[0004] To address the above problems, this invention provides an environmentally friendly layered bimetallic hydroxide anti-corrosion coating doped with trivalent elements on the surface of magnesium-zinc alloys and its preparation method.

[0005] In a first aspect, the present invention provides a trivalent element-doped anti-corrosion coating on the surface of a magnesium-zinc alloy, comprising: a magnesium-zinc alloy substrate, and a trivalent element-doped anti-corrosion coating formed in situ on the surface of the magnesium-zinc alloy substrate; wherein the anti-corrosion coating is a trivalent element-doped layered bimetallic hydroxide anti-corrosion coating; the trivalent element in the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating includes at least one of aluminum, iron, nickel, and lanthanum. A trivalent element carbonate solution is prepared by first placing at least one of the following: a trivalent element element, a trivalent element oxide, and a trivalent element hydroxide, into deionized water, heating, and then introducing CO2 gas. A magnesium-zinc alloy substrate is then immersed in the trivalent element carbonate solution for further treatment. Finally, an alkaline solution is added dropwise to the carbonate solution for a second immersion treatment, followed by drying, to obtain a trivalent element-doped anti-corrosion coating on the surface of the magnesium-zinc alloy.

[0006] Preferably, the Zn content in the magnesium-zinc alloy matrix is ​​2-9 mol%, with the balance being Mg.

[0007] Preferably, the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating comprises Mg-Zn layered bimetallic hydroxide and trivalent elements doped in the Mg-Zn layered bimetallic hydroxide; the trivalent elements exist in the form of hydroxides (e.g., aluminum hydroxide, iron hydroxide, nickel hydroxide, lanthanum hydroxide, etc.). The trivalent element doping content in the layered bimetallic hydroxide anti-corrosion coating is 20-70 mol% (e.g., 20 mol%, 30 mol%, 40 mol%, 45 mol%, 50 mol%, 55 mol%, 60 mol%, 65 mol%, 70 mol%, etc., i.e., the molar ratio of trivalent element to (trivalent element + Mg element + Zn element)). Preferably, the molar ratio of Mg to Zn in the Mg-Zn layered bimetallic hydroxide is (4-6):1, more preferably 5:1.

[0008] Preferably, the thickness of the trivalent element-doped anti-corrosion coating is 5–20 μm.

[0009] Preferably, the corrosion potential of the trivalent element-doped anti-corrosion coating is > -1.4645 eV.

[0010] Secondly, the present invention provides a method for preparing a trivalent element-doped anti-corrosion coating on the surface of a magnesium-zinc alloy, comprising: (1) Place at least one of the elements, oxides and hydroxides of the trivalent element into deionized water and heat to 20-90°C. Continuously pass CO2 gas through the water to carry out the reaction. After the reaction is completed, filter the solution to obtain a carbonate solution of the trivalent element. (2) CO2 gas was continuously introduced into the carbonate solution of the obtained trivalent element, and the magnesium-zinc alloy matrix was immersed in the carbonate solution to obtain the sample. (3) After the soaking treatment is completed, an alkaline solution is added dropwise to the carbonate solution for a second soaking treatment, and then dried to obtain a trivalent element doped anti-corrosion coating.

[0011] In this invention, excess trivalent elements, trivalent oxides, and trivalent hydroxides first react with carbonic acid to generate a saturated carbonate solution of trivalent elements (reaction equations: M + H₂CO₃ → M₂(CO₃)₃, M₂O₃ + H₂CO₃ → M₂(CO₃)₃ + H₂O, M(OH)₃ + H₂CO₃ → M₂(CO₃)₃ + H₂O). Under carbonic acid conditions, the saturated carbonate solution of trivalent elements undergoes a displacement reaction with magnesium and zinc elements in the magnesium alloy to generate magnesium carbonate and zinc carbonate (reaction equations: M₂(CO₃)₃ + Mg → MgCO₃ + M, M₂(CO₃)₃ + Zn → ZnCO₃ + M, M + H₂CO₃ → M₂(CO₃)₃). Finally, it reacts with an alkaline solution to generate trivalent metal hydroxides that immerse themselves on the surface of the magnesium alloy (reaction equation: M₂(CO₃)₃ + MgCO₃ + ZnCO₃ + NaOH → [MgCO₃](MgCO₃) ... (1-x-m) Zn x M m [(OH)2](CO3) m / 2 ·nH2O+Na2CO3) yields a layered double hydroxide anti-corrosion coating doped with trivalent elements.

[0012] Preferably, the magnesium-zinc alloy substrate is pretreated before immersion treatment; the pretreatment includes grinding and cleaning. Preferably, the polishing is performed by sequentially using 120-grit, 500-grit, and 2000-grit grinding wheels; The cleaning method is ultrasonic cleaning.

[0013] Preferably, in step (1), the molar ratio of at least one of the trivalent element, the oxide of the trivalent element, and the hydroxide of the trivalent element to the carbonic acid solution is not less than 0.1:1; preferably, the carbonate solution of the trivalent element is a saturated solution.

[0014] Preferably, in step (2), the parameters of the soaking treatment include: atmospheric pressure, temperature of 20 to 90°C, and time of more than 1 hour, preferably 1 to 12 hours, and most preferably 8 to 12 hours.

[0015] Preferably, in step (3), an alkaline solution is added dropwise until the pH value of the solution is greater than 8, preferably 9 to 12, and most preferably 10 to 11; The temperature of the secondary soaking treatment is 20-90℃, preferably 50℃; the time of the secondary soaking treatment is more than 1 hour, preferably 2-8 hours, and most preferably 3-4 hours. The drying temperature is 40–60°C (e.g., 50°C), and the time is no less than 1 hour.

[0016] Preferably, in step (3), the pH value of the alkaline solution (meaning the alkaline solution to be added) (NaOH) is greater than 8, preferably 9 to 12, and most preferably 10 to 11; the composition of the alkaline solution includes at least one of NaOH, KOH, LiOH, NH4OH, Ca(OH)2, Ba(OH)2, Sr(OH)2, CsOH, and FrOH.

[0017] Thirdly, the present invention provides a method for preparing a trivalent element-doped anti-corrosion coating on the surface of a magnesium-zinc alloy, comprising: (1) Place at least one of the elements, oxides and hydroxides of the trivalent element into deionized water and heat to 20-90°C. Continuously pass CO2 gas through the water to carry out the reaction. After the reaction is completed, filter the solution to obtain a carbonate solution of the trivalent element. (2) CO2 gas was continuously introduced into the carbonate solution of the obtained trivalent element, and the magnesium-zinc alloy matrix was immersed in the carbonate solution to obtain the sample. (3) The obtained sample was transferred to an alkaline solution for a second soaking treatment, and then dried to obtain a trivalent element doped anti-corrosion coating.

[0018] Preferably, the magnesium-zinc alloy substrate is pretreated before immersion treatment; the pretreatment includes grinding and cleaning. Preferably, the polishing is performed by sequentially using 120-grit, 500-grit, and 2000-grit grinding wheels; The cleaning method is ultrasonic cleaning.

[0019] Preferably, in step (1), the molar ratio of at least one of the trivalent element, the oxide of the trivalent element, and the hydroxide of the trivalent element to the carbonic acid solution is not less than 0.1:1; preferably, the carbonate solution of the trivalent element is a saturated solution.

[0020] Preferably, in step (2), the parameters of the soaking treatment include: atmospheric pressure, temperature of 20 to 90°C, and time of more than 1 hour, preferably 1 to 12 hours, and most preferably 8 to 12 hours.

[0021] Preferably, in step (3), the pH value of the alkaline solution (meaning the alkaline solution used for transfer) (NaOH) is greater than 8, preferably 9-12, and most preferably 10-11; the composition of the alkaline solution includes at least one of NaOH, KOH, LiOH, NH4OH, Ca(OH)2, Ba(OH)2, Sr(OH)2, CsOH, and FrOH. The temperature of the secondary soaking treatment is 20-90℃, preferably 50℃; the time of the secondary soaking treatment is more than 1 hour, preferably 2-8 hours, and most preferably 3-4 hours. The drying temperature is 40–60°C (e.g., 50°C), and the time is no less than 1 hour.

[0022] Compared with the prior art, the present invention first puts at least one of the trivalent element, the oxide of the trivalent element, and the hydroxide of the trivalent element into deionized water heated to 20-90°C and continuously purged with CO2 gas to react, thereby obtaining a carbonate solution of the trivalent element. Then, the magnesium-zinc alloy substrate is immersed in the carbonate solution for treatment. It has the following advantages: (1) The trivalent element can react directly and fully with the magnesium alloy in the solution in ionic form, avoiding the influence of uneven local concentration of the trivalent element on the preparation of the trivalent element-doped layered double hydroxide; (2) The ratio of the trivalent element to the magnesium-zinc alloy can be effectively and accurately controlled by controlling the solution concentration and the amount of solution used; (3) It prevents the trivalent element, the oxide of the trivalent element, and the hydroxide of the trivalent element from being deposited directly on the surface of the magnesium-zinc alloy without participating in the reaction, or the trivalent element, the oxide of the trivalent element, and the hydroxide of the trivalent element from being deposited directly on the surface of the magnesium-zinc alloy due to excessive amount, so that the trivalent element-doped layered hydroxide cannot be obtained. This invention enables effective control of the doping ratio of trivalent elements, improves the uniformity of element distribution, and precisely controls the composition of layered hydroxides doped with trivalent elements.

[0023] Beneficial effects: (1) The trivalent element-doped layered bimetallic hydroxide anti-corrosion coating prepared by the present invention has good anti-corrosion performance and can be applied to automobiles, ships, aviation, aerospace and other fields. (2) The method for preparing anti-corrosion coating on magnesium-zinc alloy surface provided by the present invention is simple to operate, low in cost, short in time, and easy to promote and apply in industrial applications. Attached Figure Description

[0024] Figure 1 SEM image of the surface of the anti-corrosion coating prepared in Example 1; Figure 2 The XRD pattern of the anti-corrosion coating prepared in Example 1; Figure 3 The image shows the XRD pattern of the ZK61M magnesium-zinc alloy in Comparative Example 1. Detailed Implementation

[0025] To further illustrate the invention's content, features, and practical effects, the invention will be described in detail below with reference to embodiments. It should be noted that the modification methods of the invention are not limited to these specific implementation methods. Equivalent substitutions and modifications made by those skilled in the art based on their reading of the invention's content, without departing from the spirit and essence of the invention, are also within the scope of protection claimed by this invention.

[0026] This invention provides a trivalent element-doped layered bimetallic hydroxide anti-corrosion coating for the surface of a magnesium-zinc alloy, comprising: a magnesium-zinc alloy substrate, and a trivalent element-doped layered bimetallic hydroxide anti-corrosion coating formed in situ on the surface of the magnesium-zinc alloy substrate. The trivalent element-doped layered bimetallic hydroxide anti-corrosion coating comprises magnesium hydroxide, zinc hydroxide, and hydroxides of doped trivalent elements (e.g., iron, nickel, lanthanum, etc.).

[0027] The following is an exemplary description of the preparation method of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating on the surface of magnesium-zinc alloy provided by the present invention.

[0028] Pretreatment of the magnesium alloy substrate. After grinding, the ZK61M magnesium-zinc alloy parts or samples are cleaned in ethanol and then dried. Grinding is performed using abrasive wheels, for example, sequentially using 120-grit, 500-grit, and 2000-grit wheels. Preferably, the samples are ultrasonically cleaned at 80–300 W for at least 1 hour. The drying temperature is 50°C, and the drying time is at least 1 hour.

[0029] Preparation of carbonate solution. An excess of at least one of the following: a trivalent element, an oxide of a trivalent element, and a hydroxide of a trivalent element, is placed in a certain amount of deionized water. The mixture is heated to 20–90°C, and CO2 gas is continuously introduced to carry out the reaction. After the reaction is complete, the mixture is filtered to obtain a carbonate solution of the trivalent element.

[0030] In an optional embodiment, the molar ratio of at least one of the trivalent element, the oxide of the trivalent element, and the hydroxide of the trivalent element to the carbonic acid solution is not less than 0.1:1; preferably, the carbonate solution of the trivalent element is a saturated solution.

[0031] CO2 gas was continuously passed through the carbonate solution of the obtained trivalent element, and the magnesium-zinc alloy matrix was immersed in the carbonate solution to obtain the sample.

[0032] In an optional embodiment, the parameters of the soaking treatment include: atmospheric pressure, temperature of 20-90°C, and time of more than 1 hour, preferably 1-12 hours, and most preferably 8-12 hours.

[0033] After the initial soaking treatment, an alkaline solution is added dropwise to the carbonate solution for a second soaking treatment, followed by drying to obtain a trivalent element-doped layered bimetallic hydroxide anti-corrosion coating. Alternatively, the obtained sample is transferred to an alkaline solution for a second soaking treatment, followed by drying to obtain a trivalent element-doped layered bimetallic hydroxide anti-corrosion coating.

[0034] In an optional embodiment, an alkaline solution is added dropwise until the pH value of the solution is greater than 8, preferably 9-12, and most preferably 10-11. The temperature of the secondary soaking treatment is 20-90°C, preferably 50°C; the time of the secondary soaking treatment is more than 1 hour, preferably 2-8 hours, and most preferably 3-4 hours. The drying temperature is 40-60°C (e.g., 50°C), and the time is not less than 1 hour. The alkaline solution comprises at least one of NaOH, KOH, LiOH, NH4OH, Ca(OH)2, Ba(OH)2, Sr(OH)2, CsOH, and FrOH.

[0035] In this invention, all steps are performed under heating and normal pressure.

[0036] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are all within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below. In the following examples and comparative examples, corrosion potential is used to represent the corrosion resistance of the coating. The higher this value, the stronger the corrosion resistance and the better the corrosion resistance effect. Generally, an electrochemical workstation is used to test the corrosion potential.

[0037] Example 1 (1) A 20×20mm ZK61M magnesium-zinc alloy (Zn content of 5.43%) sample was polished with 120 mesh, 500 mesh and 2000 mesh grinding wheels in sequence, then ultrasonically cleaned with ethanol for 60 minutes, and then dried in an oven at 50℃ for 1 hour. (2) Measure 1000 ml of deionized water, add 0.3 mol of Fe2O3 powder, heat to 50°C, and continuously react by passing CO2 gas at a rate of 1 L / min. Filter to obtain Fe2O3-containing solution. 3+ carbonate solution; (3) Immerse the treated ZK61M magnesium-zinc alloy sample in a carbonate solution (1000 mL) with CO2 gas continuously introduced at 1 L / min for 1 hour (with CO2 gas continuously introduced and the carbonate solution kept at 50°C). (4) Transfer the soaked ZK61M magnesium-zinc alloy sample to an alkaline solution (solute is NaOH, 0.0001mol / L) at 50℃ with pH 10 and soak for 4 hours; (5) Take out the ZK61M magnesium-zinc alloy sample after soaking in alkaline solution and dry it in an oven at 50°C for 1 hour to obtain a trivalent element-doped layered bimetallic hydroxide anti-corrosion coating.

[0038] Example 2

[0039] The preparation process of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating on the magnesium alloy surface in Example 2 is the same as in Example 1, except that: in step (2), Fe2O3 powder is replaced with aluminum powder (0.3 mol), and in step (4), the soaking time is 24 hours.

[0040] Example 3

[0041] The preparation process of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating on the magnesium alloy surface in Example 3 is the same as in Example 1, except that in step (2), Fe2O3 powder is replaced with Al2O3 powder (0.3 mol).

[0042] Example 4

[0043] The preparation process of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating on the magnesium alloy surface in Example 4 is the same as in Example 1, except that in step (2), Fe2O3 powder is replaced with La2O3 powder (0.3 mol).

[0044] Example 5

[0045] The preparation process of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating on the magnesium alloy surface in Example 5 is the same as in Example 1, except that in step (2), Fe2O3 powder is replaced with Ni2O3 powder (0.3 mol).

[0046] Example 6

[0047] The preparation process of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating on the magnesium alloy surface in Example 6 is the same as in Example 1, except that the temperature of the alkaline solution in step (4) is 90°C.

[0048] Example 7

[0049] The preparation process of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating on the magnesium alloy surface in Example 7 is the same as in Example 1, except that in step (4), the pH of the alkaline solution is 9 (the solute is NaOH, 0.00001mol / L).

[0050] Example 8

[0051] The preparation process of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating on the magnesium alloy surface in Example 8 is the same as in Example 1, except that the mass of Fe2O3 powder is 0.2 mol in step (2).

[0052] Example 9

[0053] The preparation process of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating on the magnesium alloy surface in Example 9 is the same as in Example 1, except that the mass of Fe2O3 powder is 0.4 mol in step (2).

[0054] Example 10

[0055] The preparation process of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating on the magnesium alloy surface in Example 10 is the same as in Example 1, except that the mass of Fe2O3 powder is 0.5 mol in step (2).

[0056] Comparative Example 1

[0057] In this Comparative Example 1, ZK61M magnesium-zinc alloy is used as an example.

[0058] Comparative Example 2

[0059] The preparation process of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating on the magnesium alloy surface in Comparative Example 2 is the same as that in Example 1, except that Fe2O3 powder is not added in step (2).

[0060] Corrosion potential tests were performed on Examples 1-10 and Comparative Examples 1-2. Table 1 lists the raw material composition, experimental parameters, and corrosion potentials of Examples 1-10 and Comparative Examples 1-2.

[0061] Table 1:

[0062] As shown in Table 1, the corrosion potential of the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating prepared by the present invention is significantly higher than that of Comparative Examples 1-2, indicating that it has a better anti-corrosion effect.

[0063] Figure 1 The image shows a SEM image of the anti-corrosion coating surface prepared in Example 1. As can be seen from the image, this method can prepare a coating with a typical layered double hydroxide morphology.

[0064] Figure 2 The image shows the XRD pattern of the anti-corrosion coating prepared in Example 1. Figure 3The image shows the XRD pattern of the ZK61M magnesium-zinc alloy in Comparative Example 1. As can be seen from the figure, compared with Comparative Example 1, the coating prepared by the method of the present invention has a distinct layered structure in the low-angle region, indicating the formation of layered double hydroxides.

Claims

1. A trivalent element doped corrosion resistant coating for a magnesium-zinc alloy surface, characterized in that, include: A magnesium-zinc alloy substrate, wherein a trivalent element-doped anti-corrosion coating is formed in situ on the surface of the magnesium-zinc alloy substrate; wherein the anti-corrosion coating is a trivalent element-doped layered bimetallic hydroxide anti-corrosion coating; wherein the trivalent element in the trivalent element-doped layered bimetallic hydroxide anti-corrosion coating includes at least one of aluminum, iron, nickel, and lanthanum. A trivalent element carbonate solution is prepared by first placing at least one of the following: a trivalent element element, a trivalent element oxide, and a trivalent element hydroxide, into deionized water, heating, and then introducing CO2 gas. A magnesium-zinc alloy substrate is then immersed in the trivalent element carbonate solution for further treatment. Finally, an alkaline solution is added dropwise to the carbonate solution for a second immersion treatment, followed by drying, to obtain a trivalent element-doped anti-corrosion coating on the surface of the magnesium-zinc alloy.

2. The trivalent element doped corrosion resistant coating of a magnesium zinc alloy surface according to claim 1, characterized in that, The Zn content in the magnesium-zinc alloy matrix is ​​2-9 mol%, with the balance being Mg.

3. The trivalent element doped corrosion resistant coating of a magnesium zinc alloy surface according to claim 1 or 2, characterized in that, The trivalent element-doped layered bimetallic hydroxide anti-corrosion coating comprises Mg-Zn layered bimetallic hydroxide and trivalent elements doped in Mg-Zn layered bimetallic hydroxide; the trivalent elements exist in the form of hydroxides. The trivalent element doping content in the layered bimetallic hydroxide anti-corrosion coating is 20-70 mol%. Preferably, the molar ratio of Mg to Zn in the Mg-Zn layered bimetallic hydroxide is (4-6):1, more preferably 5:

1.

4. The trivalent element-doped corrosion resistant coating of a magnesium-zinc alloy surface according to any one of claims 1 to 3, characterized in that The thickness of the trivalent element-doped anti-corrosion coating is 5–20 μm.

5. The trivalent element-doped corrosion resistant coating of a magnesium-zinc alloy surface according to any one of claims 1 to 4, characterized in that The corrosion potential of the trivalent element-doped anti-corrosion coating is >-1.4645eV.

6. A method for producing a trivalent element-doped anticorrosive coating layer on the surface of a magnesium-zinc alloy according to any one of claims 1 to 5, characterized by, include: (1) Place at least one of the elements, oxides and hydroxides of the trivalent element into deionized water and heat to 20-90°C. Continuously pass CO2 gas through the water to carry out the reaction. After the reaction is completed, filter the solution to obtain a carbonate solution of the trivalent element. (2) CO2 gas was continuously introduced into the carbonate solution of the obtained trivalent element, and the magnesium-zinc alloy matrix was immersed in the carbonate solution to obtain the sample. (3) After the soaking treatment is completed, an alkaline solution is added dropwise to the carbonate solution for a second soaking treatment, and then dried to obtain a trivalent element doped anti-corrosion coating; or, the obtained sample is transferred to an alkaline solution for a second soaking treatment, and then dried to obtain a trivalent element doped anti-corrosion coating.

7. The preparation method according to claim 6, characterized in that, Prior to the immersion treatment, the magnesium-zinc alloy substrate is pretreated; the pretreatment includes grinding and cleaning. Preferably, the polishing is performed by sequentially using 120-grit, 500-grit, and 2000-grit grinding wheels; The cleaning method is ultrasonic cleaning.

8. The production method according to claim 6 or 7, characterized by, In step (1), the molar ratio of at least one of the trivalent element, the oxide of the trivalent element, and the hydroxide of the trivalent element to the carbonic acid solution is not less than 0.1:1; preferably, the carbonate solution of the trivalent element is a saturated solution.

9. The production method according to any one of claims 6 to 8, characterized by, In step (2), the parameters of the soaking treatment include: atmospheric pressure, temperature of 20-90°C, and time of more than 1 hour, preferably 1-12 hours, and most preferably 8-12 hours.

10. The production method according to any one of claims 6 to 9, characterized by, In step (3), an alkaline solution is added dropwise until the pH value of the solution is greater than 8, preferably 9 to 12, and most preferably 10 to 11; The alkaline solution has a pH value greater than 8, preferably 9-12, and most preferably 10-11; the alkaline solution comprises at least one of NaOH, KOH, LiOH, NH4OH, Ca(OH)2, Ba(OH)2, Sr(OH)2, CsOH, and FrOH. The temperature of the secondary soaking treatment is 20-90℃, preferably 50℃; the time of the secondary soaking treatment is more than 1 hour, preferably 2-8 hours, and most preferably 3-4 hours. The drying temperature is 40-60℃, and the time is not less than 1 hour.

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