A corrosion resistant coating on a magnesium-zinc alloy surface and a method of making the same

Abstract

This invention relates to an anion-modified anti-corrosion coating on the surface of a magnesium-zinc alloy and its preparation method. The anion-modified anti-corrosion coating on the magnesium-zinc alloy surface comprises: a magnesium-zinc alloy substrate, and an anion-modified anti-corrosion coating formed in situ on the surface of the magnesium-zinc alloy substrate; wherein the anion-modified anti-corrosion coating is an anion-modified layered bimetallic hydroxide anti-corrosion coating; and the anions in the anion-modified layered bimetallic hydroxide anti-corrosion coating include NO3. ‑ Ions, SO4 2‑ Ions, MoO4 2‑ Ions, VO3 2‑ Ions, WO4 2‑ At least one of the ions; the magnesium-zinc alloy substrate is first immersed in a weakly acidic solution, then an alkaline solution is added dropwise to the weakly acidic solution for a second immersion treatment, and then dried to obtain the anion-modified anti-corrosion coating on the surface of the magnesium-zinc alloy.

Description

Technical Field

[0001] This invention belongs to the field of material preparation and relates to a method for preparing anion-modified anti-corrosion coatings on magnesium alloy surfaces. Specifically, it relates to a method for preparing anion-modified layered hydroxide anti-corrosion coatings on magnesium-zinc alloy surfaces using a carbonate solution, and particularly to a method for preparing anion-modified layered hydroxide anti-corrosion coatings on ZK61M magnesium-zinc alloy surfaces. 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 anion-modified anti-corrosion coating for magnesium-zinc alloy surfaces and its preparation method.

[0005] In a first aspect, the present invention provides an anion-modified anti-corrosion coating for a magnesium-zinc alloy surface, comprising: a magnesium-zinc alloy substrate, and an anion-modified anti-corrosion coating formed in situ on the surface of the magnesium-zinc alloy substrate; wherein the anion-modified anti-corrosion coating is an anion-modified layered bimetallic hydroxide anti-corrosion coating; and the anions in the anion-modified layered bimetallic hydroxide anti-corrosion coating include NO3. - Ions, SO4 2- Ions, MoO4 2-Ions, VO3 2- Ions, WO4 2- At least one of the ions; The magnesium-zinc alloy substrate is first immersed in a weakly acidic solution, then an alkaline solution is added dropwise to the weakly acidic solution for a second immersion treatment, and finally dried to obtain an anion-modified 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 layered bimetallic hydroxide anti-corrosion coating is a Mg-Zn layered bimetallic hydroxide; the molar ratio of Mg to Zn in the Mg-Zn layered bimetallic hydroxide is (4-6):1, preferably 5:1.

[0008] Preferably, the thickness of the anion-modified anti-corrosion coating is 5–20 μm.

[0009] Preferably, the corrosion potential of the anion-modified anti-corrosion coating is > -1.4645 eV.

[0010] Secondly, the present invention provides a method for preparing anion-modified anti-corrosion coating on the surface of a magnesium-zinc alloy, comprising: (1) The magnesium-zinc alloy matrix was immersed in a weakly acidic solution to obtain a sample; (2) After the soaking treatment is completed, an alkaline solution is added dropwise to the weak acid solution for a second soaking treatment, and then dried to obtain an anion-modified anti-corrosion coating.

[0011] 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.

[0012] Preferably, in step (1), the pH of the weakly acidic solution is 1 to 6; and the concentration of the weakly acidic solution is 0.000001 to 0.1 mol / L. The method for preparing the weakly acidic solution includes: adding deionized water to an acidic solution, heating to 20-90°C, and adjusting the pH to 1-6 to obtain a weakly acidic solution; wherein the acidic solution is at least one of HNO3, H2SO4, H3MoO4, H3MoVO7, and H2WO4. The parameters for 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.

[0013] Preferably, in step (2), 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.

[0014] Preferably, in step (2), 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.

[0015] Thirdly, the present invention provides a method for preparing anion-modified anti-corrosion coating on the surface of a magnesium-zinc alloy, comprising: (1) The magnesium-zinc alloy matrix was immersed in a weakly acidic solution to obtain a sample; (2) After the soaking treatment is completed, the obtained sample is placed in an alkaline solution for a second soaking treatment, and then dried to obtain an anion-modified anti-corrosion coating.

[0016] 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.

[0017] Preferably, in step (1), the pH of the weakly acidic solution is 1 to 6; and the concentration of the weakly acidic solution is 0.000001 to 0.1 mol / L. The method for preparing the weakly acidic solution includes: adding deionized water to an acidic solution, heating to 20-90°C, and adjusting the pH to 1-6 to obtain a weakly acidic solution; wherein the acidic solution is at least one of HNO3, H2SO4, H3MoO4, H3MoVO7, and H2WO4. The parameters for 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.

[0018] Preferably, in step (2), 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.

[0019] In this invention, when a magnesium-zinc alloy is immersed in a weakly acidic solution at normal pressure and 20–90°C, the cathodic reaction of the magnesium alloy in the weakly acidic solution is: 2e - +2H + (aq)→H2(g), the anodic reaction is: Mg(s)-2e - →Mg 2+ (aq), Zn(s)-2e - →Zn 2+ (aq), and the anions (NO3) in the solution. - Ions, SO4 2- Ions, MoO4 2- Ions, VO3 2- Ions, WO4 2- At least one of the ions combines to form magnesium and zinc salts. After adding an alkaline solution or transferring the sample to an alkaline solution, OH... - The addition of these components gradually transforms the magnesium and zinc salts into a dense film of magnesium hydroxide and zinc hydroxide, improving corrosion resistance. More importantly, this invention utilizes strong acid anions (NO3-). - Ions, SO4 2- Ions, MoO4 2- Ions, VO3 2- Ions, WO4 2-At least one of the ions is used as an intercalation material to modify the layered bimetallic hydroxide anti-corrosion coating, which has good anti-corrosion ability. However, strong acids have stronger corrosiveness and are prone to causing more severe corrosion to magnesium alloys in the reaction of step (1), and are usually not used directly to react with magnesium alloys to prepare coatings. This invention controls the reaction of the strong acid solution with the magnesium alloy by precisely controlling the pH value, reaction time and reaction temperature of the strong acid solution, thereby reducing the direct corrosive effect on the magnesium alloy, while providing sufficient precursor material for the preparation of layered bimetallic hydroxides in step (2). In addition, compared with weak acid radicals, the strong acid radical anions used in this invention have stronger ion replacement ability and are more difficult to be replaced by chloride ions in corrosive media (such as salt spray), so they can better protect the metal substrate from contact with corrosive chloride ions and have better anti-corrosion performance.

[0020] In this invention, the corrosion protection mechanism of the layered double hydroxide is as follows: During corrosion, the corrosive medium (usually chloride ions) displaces the anions in the layered double hydroxide through ion exchange, allowing them to enter the interior of the layered double hydroxide and gradually displace layer by layer until the chloride ions reach the junction of the layered double hydroxide and the metal, where they react with the metal and cause corrosion. Therefore, the displacement capacity of the anions determines the corrosion protection capability of the layered double hydroxide; the stronger the displacement capacity, the less easily it is replaced by chloride ions, and the more difficult it is for chloride ions to react with the metal, resulting in stronger corrosion protection. The coating prepared using a weakly acidic solution containing strong acid anions in this invention exhibits improved corrosion protection.

[0021] Beneficial effects: (1) The anion-modified anti-corrosion coating on the surface of magnesium-zinc alloy 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 described in this invention is simple to operate, low in cost, short in time, and easy to promote and apply in industrial applications. Attached Figure Description

[0022] Figure 1 SEM image of the surface of the anti-corrosion coating prepared in Example 1; Figure 2 The image shows the XRD pattern of the anti-corrosion coating prepared in Example 1. Detailed Implementation

[0023] 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.

[0024] This invention provides an anion-modified anti-corrosion coating for a magnesium-zinc alloy surface, comprising: a magnesium-zinc alloy substrate, and an anion-modified layered bimetallic hydroxide anti-corrosion coating formed in situ on the surface of the magnesium-zinc alloy substrate; the anion-modified layered bimetallic hydroxide anti-corrosion coating comprises magnesium hydroxide, zinc hydroxide, and anions (e.g., NO). 3- Ions, SO4 2- Ions, MoO4 2- Ions, VO3 2- Ions, WO4 2- (Ions, etc.)

[0025] In this invention, the layered bimetallic hydroxide anti-corrosion coating is modified by adjusting the concentration of the weakly acidic solution and the reaction conditions, thereby successfully preparing a bimetallic hydroxide coating with different anion intercalations and a layered structure on the surface of a magnesium alloy.

[0026] The following is an exemplary description of the preparation method of the anion-modified anti-corrosion coating on the surface of magnesium-zinc alloy provided by the present invention.

[0027] 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.

[0028] A certain amount of deionized water is added to an acidic solution (e.g., HNO3, H2SO4, H3MoO4, H3MoVO7, H2WO4), heated to 20–90°C (e.g., 50°C), and the pH is adjusted to 1–6 (e.g., pH=4) to obtain a weakly acidic solution. Preferably, the pH of the weakly acidic solution is 1–6. The concentration of the weakly acidic solution is 0.000001–0.1 mol / L.

[0029] The pretreated ZK61M magnesium-zinc alloy parts or samples are immersed in a weakly acidic solution to obtain samples.

[0030] 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.

[0031] After the initial soaking treatment, a second soaking treatment is performed by adding an alkaline solution dropwise to a weakly acidic solution, followed by drying to obtain an anion-modified layered bimetallic hydroxide anti-corrosion coating. Alternatively, the obtained sample is placed in an alkaline solution for a second soaking treatment, followed by drying to obtain an anion-modified layered bimetallic hydroxide anti-corrosion coating.

[0032] 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.

[0033] In this invention, all the above steps are performed under heating and normal pressure.

[0034] 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.

[0035] 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 1000ml of deionized water, add HNO3 dropwise, adjust the pH value to 4, and heat to 50℃; (3) Place the treated ZK61M magnesium-zinc alloy sample in the weakly acidic solution (concentration of 0.0001 mol / L) obtained in step (2) and soak for 1 hour; (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 and dry it in a 50℃ oven for 1 hour to obtain HNO3 on the surface of the magnesium-zinc alloy. - Ion-modified anti-corrosion coating.

[0036] Example 2

[0037] The preparation process of the anion-modified anti-corrosion coating on the magnesium-zinc alloy surface in Example 2 is the same as that in Example 1, except that in step (2), HNO3 is replaced with H2SO4.

[0038] Example 3

[0039] The preparation process of the anion-modified anti-corrosion coating on the magnesium-zinc alloy surface in Example 3 is the same as that in Example 1, except that in step (2), HNO3 is replaced with H2MoO4.

[0040] Example 4

[0041] The preparation process of the anion-modified anti-corrosion coating on the magnesium-zinc alloy surface in Example 4 is the same as that in Example 1, except that in step (2), HNO3 is replaced with H2VO3.

[0042] Example 5

[0043] The preparation process of the anion-modified anti-corrosion coating on the magnesium-zinc alloy surface in Example 5 is the same as that in Example 1, except that in step (2), HNO3 is replaced with H2WO4.

[0044] Example 6

[0045] The preparation process of the anion-modified anti-corrosion coating on the magnesium-zinc alloy surface in Example 6 is the same as that in Example 1, except that the temperature of the alkaline solution in step (4) is 90°C.

[0046] Example 7

[0047] The preparation process of the anion-modified anti-corrosion coating on the magnesium-zinc alloy surface in Example 7 is the same as that in Example 1, except that in step (4), the pH of the alkaline solution is 9 (the solute is NaOH, 0.00001mol / L).

[0048] Example 8

[0049] The preparation process of the anion-modified anti-corrosion coating on the magnesium-zinc alloy surface in Example 8 is the same as that in Example 1, except that in step (2), the pH value is adjusted to 1.

[0050] Example 9

[0051] The preparation process of the anion-modified anti-corrosion coating on the magnesium-zinc alloy surface in Example 9 is the same as that in Example 1, except that in step (2), the pH value is adjusted to 2.

[0052] Example 10

[0053] The preparation process of the anion-modified anti-corrosion coating on the magnesium-zinc alloy surface in Example 10 is the same as that in Example 1, except that in step (2), the pH value is adjusted to 3.

[0054] Comparative Example 1

[0055] In this Comparative Example 1, ZK61M magnesium-zinc alloy is used as an example.

[0056] Corrosion potential tests were performed on Examples 1-10 and Comparative Example 1. Table 1 lists the raw material composition, experimental parameters, and corrosion potentials of Examples 1-10 and Comparative Example 1. Table 1 lists the raw material composition, morphology, and corrosion potentials of Examples 1-10 and Comparative Example 1.

[0057] Table 1:

[0058] As shown in Table 1, the corrosion potential of the anion-modified anti-corrosion coating on the magnesium-zinc alloy surface prepared by the present invention is significantly higher than that of Comparative Example 1, indicating that it has a better anti-corrosion effect.

[0059] 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.

[0060] Figure 2 The image shows the XRD pattern of the anti-corrosion coating prepared in Example 1. As can be seen from the image, the coating prepared by this method exhibits a distinct layered structure in the low-angle region, indicating the formation of layered double hydroxides.

Claims

1. An anion-modified anti-corrosion coating for magnesium-zinc alloy surfaces, characterized in that, include: A magnesium-zinc alloy substrate, and an anion-modified anti-corrosion coating formed in situ on the surface of the magnesium-zinc alloy substrate; wherein the anion-modified anti-corrosion coating is an anion-modified layered bimetallic hydroxide anti-corrosion coating; the anions in the anion-modified layered bimetallic hydroxide anti-corrosion coating include NO3. - Ions, SO4 2- Ions, MoO4 2- Ions, VO3 2- Ions, WO4 2- At least one of the ions; The magnesium-zinc alloy substrate is first immersed in a weakly acidic solution, then an alkaline solution is added dropwise to the weakly acidic solution for a second immersion treatment, and finally dried to obtain an anion-modified anti-corrosion coating on the surface of the magnesium-zinc alloy.

2. The anion-modified anti-corrosion coating on the 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 anion-modified anti-corrosion coating on the surface of magnesium-zinc alloy according to claim 1 or 2, characterized in that, The layered bimetallic hydroxide anti-corrosion coating is a Mg-Zn layered bimetallic hydroxide; the molar ratio of Mg to Zn in the Mg-Zn layered bimetallic hydroxide is (4-6):1, preferably 5:

1.

4. The anion-modified anti-corrosion coating on the surface of magnesium-zinc alloy according to any one of claims 1-3, characterized in that, The thickness of the anion-modified anti-corrosion coating is 5–20 μm.

5. The anion-modified anti-corrosion coating on the surface of magnesium-zinc alloy according to any one of claims 1-4, characterized in that, The corrosion potential of the anion-modified anti-corrosion coating is >-1.4645eV.

6. A method for preparing an anion-modified anti-corrosion coating on the surface of a magnesium-zinc alloy according to any one of claims 1-5, characterized in that, include: (1) The magnesium-zinc alloy matrix was immersed in a weakly acidic solution to obtain a sample; (2) After the soaking treatment is completed, add alkaline solution to the weak acid solution for a second soaking treatment, and then dry to obtain an anion-modified anti-corrosion coating; or, place the obtained sample in an alkaline solution for a second soaking treatment, and then dry to obtain an anion-modified 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 preparation method according to claim 6 or 7, characterized in that, In step (1), the pH of the weakly acidic solution is 1 to 6; the concentration of the weakly acidic solution is 0.000001 to 0.1 mol / L. The method for preparing the weakly acidic solution includes: adding deionized water to an acidic solution, heating to 20-90°C, and adjusting the pH to 1-6 to obtain a weakly acidic solution; wherein the acidic solution is at least one of HNO3, H2SO4, H3MoO4, H3MoVO7, and H2WO4. The parameters for 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.

9. The preparation method according to any one of claims 6-8, characterized in that, In step (2), 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 comprises at least one of NaOH, KOH, LiOH, NH4OH, Ca(OH)2, Ba(OH)2, Sr(OH)2, CsOH, and FrOH.

10. The preparation method according to any one of claims 6-9, characterized in that, In step (2), 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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