LDH / ZIF-8 composite protective film for surface of micro-arc oxidation film of magnesium-lithium alloy, and preparation method therefor and use thereof

Abstract

The present invention belongs to the technical field of metal surface protection, and provides an LDH / ZIF-8 composite protective film for a surface of a micro-arc oxidation film of a magnesium-lithium alloy, and a preparation method therefor and the use thereof. The objective of the present invention is to solve the current technical problems of poor stability and compactness of a composite film for a surface of a micro-arc oxidation film of a magnesium-lithium alloy, and a complex preparation process therefor. The method of the present invention comprises: mixing zinc nitrate hexahydrate, aluminum nitrate nonahydrate, 2-methylimidazole and water and magnetically stirring same, then adjusting the pH until the resulting mixture is alkaline, subsequently adding a magnesium-lithium alloy sample having a micro-arc oxidation film, and performing a hydrothermal reaction, so as to obtain a composite protective film. The present invention provides a one-step method for preparing an LDH / ZIF-8 composite film on a surface of a micro-arc oxidation film of a magnesium-lithium alloy, which method effectively enhances the ability of the film to protect a substrate in a long-term corrosion environment. The method of the present invention greatly reduces the operation steps for preparation, is convenient to operate, and has improved industrial applicability.

Description

A magnesium-lithium alloy micro-arc oxidation film surface LDH / ZIF-8 composite protective film, its preparation method and application Technical Field

[0001] This invention belongs to the field of metal surface protection technology, specifically relating to an LDH / ZIF-8 composite protective film on the surface of a magnesium-lithium alloy micro-arc oxidation film, its preparation method, and its application. Background Technology

[0002] Magnesium-lithium alloys, as the lightest structural metals, are widely favored in the automotive and aerospace industries, but their poor corrosion resistance limits their industrial applications. Micro-arc oxidation technology has attracted widespread attention due to its environmentally friendly electrolyte and the excellent corrosion resistance and good adhesion to the substrate in the resulting film. However, the high-voltage discharge and gas escape during the micro-arc oxidation process cause pores and cracks on the film surface. Corrosive solutions can penetrate into the substrate through these pores and cracks, causing corrosion. Therefore, the micro-arc oxidation film cannot provide long-term protection for the substrate. Thus, developing a post-treatment technology to seal the surface of the magnesium-lithium alloy micro-arc oxidation film is necessary.

[0003] Currently, the main method for sealing the surface of magnesium-lithium alloy micro-arc oxidation films is to prepare layered double hydroxides (LDHs). However, the stability of MAO-LDH composite films is poor, and their density still needs improvement. Another approach involves preparing composite films of LDH and MOFs on the MAO film surface to improve the overall performance of the protective film on the alloy surface. However, this method typically involves first preparing an LDH film on the MAO film surface, then immersing the composite film in a MOF solution to grow a MOF film on the LDH surface. The disadvantage of this method is its cumbersome steps and multiple reactions, which are not conducive to industrial applications. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems of poor stability and density of composite films on the surface of magnesium-lithium alloy micro-arc oxidation films, and to provide an LDH / ZIF-8 composite protective film on the surface of magnesium-lithium alloy micro-arc oxidation films, its preparation method and application.

[0005] The technical solution of the present invention is as follows:

[0006] One objective of this invention is to provide a method for preparing an LDH / ZIF-8 composite protective film on the surface of a magnesium-lithium alloy micro-arc oxidation film, the method comprising the following steps:

[0007] Zinc nitrate hexahydrate, aluminum nitrate nonahydrate, 2-methylimidazole and water were mixed and magnetically stirred. The pH was then adjusted to alkaline and placed in a reaction vessel with a polytetrafluoroethylene liner. A magnesium-lithium alloy sample with a micro-arc oxidation film was added, and the mixture was subjected to hydrothermal reaction. After cooling, the mixture was washed and dried to obtain the MAO-LDH / ZIF-8 composite protective film.

[0008] Further specifying, the molar ratio of zinc nitrate hexahydrate, aluminum nitrate nonahydrate, and 2-methylimidazole is (1-2):1:(70-80).

[0009] Further specified, the molar ratio of 2-methylimidazole to water is 1:(1.5-2).

[0010] Further specify, magnetic stirring for 8-12 minutes.

[0011] Further limit the pH to 10-10.5.

[0012] Further, the preparation of the micro-arc oxidation film on the surface of the magnesium-lithium alloy sample is as follows: the magnesium-lithium alloy sample is first surface treated, and then it is used as the anode, the stainless steel water tank is used as the cathode, and micro-arc oxidation is carried out in the electrolyte using a constant current method.

[0013] To be further specified, the surface treatment involves first polishing with silicon carbide sandpaper, and then ultrasonically treating with acetone and ethanol in sequence.

[0014] Furthermore, the electrolyte composition is specified as follows: 8-12 g / L Na2SiO3, 4-6 g / L NaF, and 1-3 g / L NaOH.

[0015] Further, the hydrothermal reaction temperature is 60-80℃ and the time is 10-14h.

[0016] The second objective of this invention is to provide a MAO-LDH / ZIF-8 composite protective film prepared by the above method.

[0017] The third objective of this invention is to provide an application of the MAO-LDH / ZIF-8 composite protective film prepared by the above method in the protection of metal surfaces.

[0018] The advantages of this invention compared to existing technologies are:

[0019] (1) This invention provides a one-step method for preparing an LDH / ZIF-8 composite film on the surface of a magnesium-lithium alloy micro-arc oxidation film, which fully utilizes the synergistic effect of the composite film's ion exchange capacity and stability to construct a robust physical barrier layer on the surface of the MAO film, thereby effectively enhancing the film's ability to protect the substrate under long-term corrosion conditions.

[0020] The existing methods for sealing magnesium-lithium alloy micro-arc oxidation films have many problems, such as poor film density, poor stability, complex production process, and poor adhesion to the film.

[0021] (2) This invention utilizes the affinity between LDH membrane and ZIF-8, and uses the preferentially grown LDH as a sacrificial layer in the hydrothermal process to obtain a composite membrane of LDH / ZIF-8, which not only achieves the purpose of sealing defects in MAO membrane, but also enhances the overall stability and compactness of the membrane, while having excellent bonding force with the membrane.

[0022] (3) The method of the present invention greatly reduces the preparation steps, is convenient to operate, and is environmentally friendly. It is a green, efficient, and safe micro-arc oxidation sealing process for magnesium-lithium alloys, thus improving its industrial applicability. Attached Figure Description

[0023] Figure 1 shows the SEM images of the MAO membrane and the MAO-LDH / ZIF-8 composite membrane in Example 1, where (a) is the MAO membrane, (b) is the MAO-LDH / ZIF-8 composite membrane, and (cd) is an enlarged view of (b).

[0024] Figure 2 shows the XRD patterns of the MAO membrane and the MAO-LDH / ZIF-8 composite membrane in Example 1;

[0025] Figure 3 shows the FT-IR images of the MAO membrane and the MAO-LDH / ZIF-8 composite membrane in Example 1;

[0026] Figure 4 shows the polarization curves of the MAO film and the MAO-LDH / ZIF-8 composite film in Example 1;

[0027] Figure 5 shows the corrosion rate curves of the MAO membrane and the MAO-LDH / ZIF-8 composite membrane obtained after 14 days of hydrogen evolution in Example 1. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0030] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used in the following embodiments, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus.

[0031] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. In this specification and claims, range definitions may be combined and / or interchanged, unless otherwise stated, these ranges include all ranges contained therein.

[0032] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0033] In this invention, "an embodiment" or "embodiment" refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments.

[0034] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] Example 1: The preparation method of the LDH / ZIF-8 composite protective film on the surface of the magnesium-lithium alloy micro-arc oxidation film in this example is carried out according to the following steps:

[0036] (1) Preparation of micro-arc oxidation film on the surface of Mg-9Li-3Al alloy:

[0037] The surface of the Mg-9Li-3Al alloy was polished sequentially using 320#, 800#, and 2000# silicon carbide sandpaper to remove the oxide film and stains. Then, it was ultrasonically treated with acetone and ethanol sequentially, each for 10 minutes, and dried to obtain the treated magnesium-lithium alloy.

[0038] The treated magnesium-lithium alloy was used as the anode, and a stainless steel water tank was used as the cathode. Micro-arc oxidation was performed using a constant current method with an electrical parameter of 5 A / dm². 2 The oxidation process was carried out at a frequency of 600 Hz, a duty cycle of 20%, and an oxidation time of 10 min. The electrolyte composition was 10 g / L Na₂SiO₃, 5 g / L NaF, and 2 g / L NaOH. A sample with a micro-arc oxidation film was obtained, and its SEM is shown in Figure 1(a).

[0039] (2) In-situ growth of LDH / ZIF-8 composite membrane:

[0040] A mixed solution was prepared according to the molar ratio of zinc nitrate hexahydrate: aluminum nitrate nonahydrate: 2-methylimidazole: water of 3:2:150:278, and then magnetically stirred for 10 min. Subsequently, 2 mol·L⁻¹ water was used. -1 The pH value was adjusted to 10.3 using NaOH solution.

[0041] The solution was transferred to a polytetrafluoroethylene (PTFE) liner, and the micro-arc oxidation sample from step (1) was placed vertically inside the PTFE liner. The reactor was placed in an oven at 70°C for hydrothermal reaction for 12 hours. After the reaction, it was cooled to room temperature in air, removed, cleaned with deionized water and ethanol, and dried to obtain an LDH / ZIF-8 composite film layer grown in situ on the surface of the magnesium-lithium alloy micro-arc oxidation film layer, namely the MAO-LDH / ZIF-8 composite protective film.

[0042] The SEM images of the LDH / ZIF-8 composite film grown in situ on the surface of the magnesium-lithium alloy micro-arc oxidation film prepared in this embodiment are shown in Figures 1(b)-(d). It can be seen that LDH / ZIF-8 grows uniformly and densely on the surface of the micro-arc oxidation film, and the defects in the micro-arc oxidation film are sealed by the LDH / ZIF-8 composite film.

[0043] As shown in Figure 2, the XRD diffraction pattern indicates that the main components of the composite film are Mg-Zn-Al-NO3(LDH), ZIF-8, MgO and Mg2SiO4.

[0044] As shown in Figure 3, the FT-IR spectrum indicates that the composite film layer at 3442 cm⁻¹... -1 and 1362cm -1 OH appeared respectively - broad peak and NO3 - The absorption vibration peak at 995 cm⁻¹ confirms the successful preparation of LDH on the surface of the MAO film. -1 1146cm -1 1575cm -1 and 2922cm -1The peaks correspond to the planar bending and planar vibration of the imidazole ring and the stretching vibration of the CH bond in ZIF-8. The simultaneous appearance of absorption bands for both the imidazole ring and nitrate in the composite membrane indicates the successful preparation of the LDH / ZIF-8 composite membrane.

[0045] The corrosion resistance of the MAO film and the MAO-LDH / ZIF-8 composite film in this embodiment was characterized using a Zahner IM6ex electrochemical workstation in a three-electrode system (saturated calomel electrode as reference electrode, platinum electrode as counter electrode, and sample as working electrode). Potentiodynamic polarization curves were performed at 1 mV / s scan rate in a 3.5 wt.% NaCl solution at room temperature to study the corrosion resistance of the film. The results are shown in Figure 4. The results show that the corrosion current density of the MAO-LDH / ZIF-8 composite film obtained in this embodiment is 3.098 × 10⁻⁶. -9 Compared to the corrosion current density of 1.986 × 10⁻⁶ for the MAO film... -7 This reduces the size by approximately two orders of magnitude.

[0046] Hydrogen evolution tests were conducted on the MAO film and the MAO-LDH / ZIF-8 composite film in this embodiment. The results are shown in Figure 5. The results show that the corrosion rate of the MAO film increased rapidly with time, then decreased after 4 days. This may be because the formation of the corrosion product Mg(OH)2 sealed the corrosion channels, thus blocking the penetration of the corrosive liquid. However, since the corrosion product Mg(OH)2 is loose and porous, it was quickly corroded and detached, thus accelerating the corrosion rate. The hydrogen evolution rate of the MAO-LDH / ZIF-8 film remained relatively stable, indicating that the film has good density and stability. The corrosion rates of the MAO film and the MAO-LDH / ZIF-8 composite film were 0.093 ml·cm⁻¹, respectively. -2 ·day -1 and 0.011 ml·cm -2 ·day -1 Compared with the MAO membrane, the average HER of the MAO-LDH / ZIF-8 membrane was significantly reduced over 14 days, demonstrating that the MAO-LDH / ZIF-8 composite membrane has good protective ability against the substrate under long-term conditions.

[0047] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a LDH / ZIF-8 composite protective film on the surface of a magnesium-lithium alloy micro-arc oxidation film, characterized in that, The method described: Zinc nitrate hexahydrate, aluminum nitrate nonahydrate, 2-methylimidazole and water were mixed and magnetically stirred. The pH was then adjusted to alkaline and placed in a reaction vessel with a polytetrafluoroethylene liner. A magnesium-lithium alloy sample with a micro-arc oxidation film was added, and the mixture was subjected to hydrothermal reaction. After cooling, the mixture was washed and dried to obtain the MAO-LDH / ZIF-8 composite protective film.

2. The method of claim 1, wherein, The molar ratio of zinc nitrate hexahydrate, aluminum nitrate nonahydrate, and 2-methylimidazole is (1-2):1:(70-80).

3. The method of claim 1, wherein, The molar ratio of 2-methylimidazole to water is 1:(1.5-2).

4. The method of claim 1, wherein, Stir magnetically for 8-12 minutes.

5. The method of claim 1, wherein, Adjust the pH to 10-10.

5.

6. The method according to claim 1, characterized in that, Preparation of micro-arc oxidation film on the surface of magnesium-lithium alloy sample: First, the magnesium-lithium alloy sample is surface treated, and then it is used as the anode and the stainless steel water tank is used as the cathode. Micro-arc oxidation is carried out in the electrolyte using the constant current method.

7. The method according to claim 6, characterized in that, Electrolyte composition: 8-12 g / L Na2SiO3, 4-6 g / L NaF and 1-3 g / L NaOH.

8. The method according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 60-80℃ for 10-14 hours.

9. The MAO-LDH / ZIF-8 composite protective film prepared by the method according to any one of claims 1-8.

10. The application of the MAO-LDH / ZIF-8 composite protective film prepared by the method according to any one of claims 1-8 in the protection of metal surfaces.

Images