Preparation method and application of magnesium alloy micro-arc oxidation film surface Mg-MOF-74 film layer

Abstract

The application discloses a preparation method of a Mg-MOF-74 film layer on a magnesium alloy micro-arc oxidation film surface, and comprises the following steps: 1) immersing the magnesium alloy into a micro-arc oxidation growth solution to perform micro-arc oxidation treatment, and obtaining the magnesium alloy covered with a MAO layer; 2) immersing the magnesium alloy covered with the MAO layer into an in-situ growth solution to perform in-situ solvothermal reaction, cleaning and drying, and obtaining the magnesium alloy covered with the Mg-MOF-74 film layer. The preparation method is characterized in that: the magnesium alloy is first subjected to micro-arc oxidation treatment, and then the magnesium alloy subjected to the micro-arc oxidation treatment is subjected to in-situ growth reaction by using a traditional reaction kettle one-step in-situ solvothermal method, so that the uniform and dense Mg-MOF-74 film layer is obtained, and the corrosion resistance of the magnesium alloy is effectively improved; the reagents used in the whole preparation process are simple, easy to obtain, and pollution-free to the environment, the whole process is simple and green, the preparation method can meet the needs of industrial development and mass production, and the application range of the magnesium alloy is expanded.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal surface protection treatment, and particularly relates to a preparation method of a Mg-MOF-74 film layer on a magnesium alloy micro-arc oxidation film surface and application thereof. BACKGROUND

[0002] Magnesium and magnesium alloys are the lightest structural metals, with a hexagonal crystal structure, and are the eighth most abundant element in the earth's crust. Magnesium alloys are used in the telecommunications, battery, torpedo, automotive, aerospace, biomedical, and electronics industries due to their high specific strength, low weight, recyclability, low density, high damping capacity, good thermal conductivity, and good castability. However, due to their low standard electrode potential, the corrosion rate in water and humid environments is high, and the application is very limited.

[0003] Currently, there are two solutions to solve the high corrosion rate of magnesium: the first is to alloy it with other elements by adding different weight ratios of Mn, Zr, Al, Zn, Li, Sr, and rare earth elements; the second is to provide a suitable protective film layer on its surface. The protective film layer can form an additional layer on the surface without changing the inherent properties of the alloy itself.

[0004] Micro-arc oxidation film (MAO) is the most common surface treatment method for magnesium alloys due to its simple preparation technology and reliable method. However, during the discharge breakdown process of micro-arc oxidation, the surface of the film layer is in contact with the electrolyte, and the melt will rapidly solidify and release gas, forming micropores. These inherent micropores on the surface of the MAO film layer are the connecting channels for the corrosion medium to invade the substrate, causing the MAO film layer to degrade over time, thereby significantly reducing the fatigue life of the magnesium alloy. Therefore, subsequent treatment of the MAO film layer is required.

[0005] Metal-organic frameworks (MOFs) are a new type of material that is a porous network structure self-assembled from inorganic metal ions and organic ligands (heterocyclic compounds containing N and O heteroatoms); they are known for their extremely high specific surface area, excellent thermal stability, and chemical stability. However, MOFs have satisfactory performance in the corrosion prevention field, mainly because MOF particles are integrated as nanofillers in a polymer matrix. This method is limited by the compatibility of MOF crystals, resulting in poor dispersion stability of MOFs during the coating preparation process. Experiments have shown that MOFs cannot be directly grown into a film on the magnesium alloy substrate due to their poor adhesion. Therefore, pretreatment of the magnesium alloy AZ31 is required before growing the MOF film layer.

[0006] The Mg-MOF-74 can only be prepared in the form of powder by the solvothermal method in the prior art. For example, patent CN 118165284A discloses a method for synthesizing Mg-MOF-74, in which a soluble magnesium salt and an organic ligand are dissolved in a mixed solvent composed of different proportions of N,N-dimethylformamide and a first low-carbon alcohol to obtain a mixed solution 1; then water and the mixed solution 1 are mixed in different proportions, and a solvothermal reaction is performed. The sample (crude product) after the reaction needs to be subjected to solid-liquid separation, washing, soaking in a second low-carbon alcohol for 48-96 hours, and high-temperature (200-300 DEG C) vacuum drying for 2-8 hours to obtain the final Mg-MOF-74 powder product with different morphologies. This method is complex, requires a vacuum device, and takes a long time; and patent CN 115216025 A discloses a method for preparing a defect type Mg-MOF-74 by a hydrothermal reaction method, in which MgCl2.6H2O and 2,5-dihydroxyterephthalic acid are dissolved in a mixed solvent of N,N-dimethylformamide, anhydrous ethanol and deionized water, and then a precipitate (crude product) is obtained by heating and standing; then a fresh methanol solution is fully stirred and allowed to stand for 12 hours, and the filtered product is added to a fresh methanol solution again, and the above operation is repeated for 6 times (3 days); and finally the Mg-MOF-74 powder crystal is obtained after washing and drying. The methanol solution used in this method is toxic and has potential harm to the human body, and the method takes a long time and is complicated to operate, which is not conducive to the popularization and application of Mg-MOF-74. SUMMARY

[0007] The present application aims to at least solve one of the technical problems in the related art. To this end, the main purpose of the present application is to provide a method for preparing a Mg-MOF-74 film layer on the surface of a magnesium alloy micro-arc oxidation film, which aims to solve the problems that the existing MOFs are not widely used in magnesium alloy corrosion protection, the types of raw materials for preparation are various, the consumption is large, and the safety, environmental protection and energy saving performance are poor.

[0008] The purpose of the present application is achieved by the following technical solutions:

[0009] A method for preparing a Mg-MOF-74 film layer on the surface of a magnesium alloy micro-arc oxidation film, comprising the following steps:

[0010] 1) immersing a magnesium alloy in a micro-arc oxidation growth solution to perform micro-arc oxidation treatment, to obtain a magnesium alloy covered with a MAO layer;

[0011] 2) immersing the magnesium alloy covered with the MAO layer in an in-situ growth solution to perform an in-situ solvothermal reaction, washing and drying, to obtain a magnesium alloy covered with a Mg-MOF-74 film layer, i.e., a magnesium alloy MAO film surface Mg-MOF-74 film layer.

[0012] In some specific embodiments, the micro-arc oxidation growth solution comprises 0.03-0.06M of trisodium phosphate dodecahydrate, and 0.1-0.3M of sodium hydroxide in water.

[0013] In some specific embodiments, the process parameters of the micro-arc oxidation treatment are as follows: the temperature of the micro-arc oxidation growth solution is 5-10℃, the reaction voltage is 300-400V, and the reaction time is 2-8min.

[0014] In some specific embodiments, the in-situ growth solution comprises a mixed solution of 0.2-0.4mM of magnesium nitrate and 0.3-0.5mM of trimesic acid; and the mixed solution is a mixture of N,N-dimethylformamide, anhydrous ethanol and deionized water in a volume ratio of 15:1:1.

[0015] In some specific embodiments, the process parameters of the in-situ solvothermal reaction are as follows: the reaction temperature is 100-140℃, and the reaction time is 16-32h.

[0016] In some specific embodiments, the magnesium alloy is further pretreated before the micro-arc oxidation treatment, specifically: the magnesium alloy substrate is first polished, and then the polished magnesium alloy substrate is degreased and oil-removed.

[0017] In some specific embodiments, the polishing treatment specifically comprises: the magnesium alloy substrate is polished using 150, 600, 800, 1200 and 2000# sandpaper respectively, and then ultrasonic cleaning is performed using alcohol and drying is performed.

[0018] In some specific embodiments, the degreasing and oil-removing solution used in the degreasing and oil-removing process is an aqueous solution comprising 40g / L of sodium hydroxide, 25g / L of sodium carbonate and 40g / L of sodium phosphate, in terms of mass volume concentration.

[0019] The application also provides applications of the magnesium alloy micro-arc oxidation film surface Mg-MOF-74 film layer in the fields of aerospace, automobiles, medical devices and 3C digital devices.

[0020] Compared with the prior art, the application has at least the following advantages:

[0021] 1) The preparation method of the magnesium alloy micro-arc oxidation film surface Mg-MOF-74 film layer provided by the application uses a micro-arc oxidation growth solution with specific components, the components are simple and easy to obtain, the micro-arc oxidation treatment time is greatly shortened, only 2-8min, and the production efficiency is greatly improved; meanwhile, in the preparation of the Mg-MOF-74 film layer, a mixed solution of N,N-dimethylformamide: anhydrous ethanol: deionized water = 15:1:1 is used as the medium, no additional metal cations are introduced, and the production is safer, more environmentally friendly and energy-saving;

[0022] 2) The preparation method of the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film provided by the application, by first performing micro-arc oxidation treatment on the magnesium alloy, and then performing in-situ growth reaction on the magnesium alloy subjected to the micro-arc oxidation treatment by using a traditional reaction kettle one-step in-situ solvothermal method, a uniform and dense Mg-MOF-74 film layer is obtained; the reagents used in the entire preparation process are simple, easy to obtain, and environmentally friendly, the overall process is simple and green, and can meet the needs of industrial development and mass production, and can further expand the application range of the magnesium alloy. The traditional one-step solvothermal method is used on the surface of the magnesium alloy MAO film layer, the reaction conditions are mild, and the process is stable; the metal cations in the magnesium alloy and the MAO will participate in the formation of the Mg-MOF-74 film layer in the solvothermal process, so that the preparation method of the application is more mature, has the advantages of energy saving, industrial production practicability, simple operation and the like, and provides a new technical route for industrial production;

[0023] 3) The Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film prepared by the application is in-situ grown, and the film layer prepared has firm combination; the Mg-MOF-74 film layer grown on the micro-arc oxidation film layer has good combination and film forming property, and the pores of the MAO film are closed; without introducing additional metal cations, the Mg 2+ in the magnesium alloy substrate and the MAO film layer jointly participate in the generation of the Mg-MOF-74 film layer, effectively block and prevent the corrosion of corrosive ions (such as Cl- and the like) in the outside world on the magnesium substrate, and play a role in protecting the substrate; and is suitable for popularization and application in the fields of aerospace, automobiles, medical devices, 3C digital devices and the like. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the application, the drawings needed in the specific embodiments or prior art description will be briefly introduced below.

[0025] Figure 1 is a scanning electron microscope photo of the Mg-MOF-74 film layer on the surface of the magnesium alloy in Example 1;

[0026] Figure 2 is a metallographic microscope photo of the Mg-MOF-74 film layer on the surface of the magnesium alloy in Example 1;

[0027] Figure 3 is an XRD spectrum of the Mg-MOF-74 film layer on the surface of the magnesium alloy in Example 1;

[0028] Figure 4Tafel polarization curves of AZ31 magnesium alloy, AZ31 magnesium alloy coated with MAO film and AZ31 magnesium alloy coated with Mg-MOF-74 film in the same coordinate measured by electrochemical workstation in Example 1;

[0029] Figure 5 Scanning electron microscope photos of Mg-MOF-74 film layer on the surface of magnesium alloy in Example 2;

[0030] Figure 6 Tafel polarization curves of AZ31 magnesium alloy, AZ31 magnesium alloy coated with MAO film and AZ31 magnesium alloy coated with Mg-MOF-74 film in the same coordinate measured by electrochemical workstation in Example 2;

[0031] Figure 7 Scanning electron microscope photos of Mg-MOF-74 film layer on the surface of magnesium alloy in Example 3;

[0032] Figure 8 Tafel polarization curves of AZ31 magnesium alloy, AZ31 magnesium alloy coated with MAO film and AZ31 magnesium alloy coated with Mg-MOF-74 film in the same coordinate measured by electrochemical workstation in Example 3. DETAILED DESCRIPTION

[0033] The application will be further described in conjunction with the accompanying drawings and examples, which are only illustrative and not restrictive, and should not be used to limit the scope of the application.

[0034] When expressing a quantity, concentration or other value or parameter either as an amount, a range, or a preferred range or as a limit of a range or a preferred value, unless otherwise indicated, it is understood that any and every range or value between the recited values should be considered as the literarily and structurally disclosed. Unless otherwise stated, the numerical values listed in the specification and claims are inclusive of the endpoints, and all integers and fractions within the range.

[0035] All percentages, parts, ratios, etc. as used herein are by weight, unless otherwise specified.

[0036] The materials, methods, and examples herein are illustrative only and, except as specifically stated, are not intended to be limiting.

[0037] In the following examples, magnesium nitrate, trimesic acid, N-,N-dimethylformamide, anhydrous ethanol, deionized water were purchased from Shanghai Roder Scientific Co., Ltd., China;

[0038] The test methods used in the following examples include:

[0039] The corrosion resistance and the bonding force are embodied by testing the Tafel polarization curve of each test sample and observing the metallographic microstructure at the scratch, respectively.

[0040] 1) Bonding force test;

[0041] A metallographic microscope (Zeiss, Germany) is used to form a cross pattern on the surface of the coating at different coating surfaces by using a QFH reticle, and the cut reaches the Mg substrate. Then the surface is carefully cleaned five times with a brush, and the cut is adhered with adhesive tape and pulled off. The adhesion between the coating and the AZ31 substrate is evaluated according to the GB / T 9286-1998 standard.

[0042] Example 1

[0043] The preparation method of the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film provided in the embodiment comprises the following steps:

[0044] 1) degreasing and oil removal

[0045] 11) an aqueous solution containing 40 g / L of sodium hydroxide, 25 g / L of sodium carbonate and 40 g / L of sodium phosphate is prepared;

[0046] 12) magnesium alloy pretreatment: the magnesium alloy is basically polished by using 150, 600, 800, 1200 and 2000# sandpaper respectively, and then ultrasonic cleaning is performed with alcohol for five minutes, and then dried for standby;

[0047] 13) the polished magnesium alloy AZ31 is immersed in the above-mentioned degreasing and oil-removing aqueous solution, water bath is kept at 50℃, and after 60s, 1M sodium hydroxide aqueous solution is used for alkaline washing for 30s, and then 400g / L nitric acid (ρ=1.42g / ml) is used for polishing at room temperature 25℃ for 2min; then deionized water is used for cleaning once, and cold air is used for drying;

[0048] 2) micro-arc oxidation film (MAO for short)

[0049] 21) an aqueous solution of 0.049M of trisodium phosphate dodecahydrate and 0.18M of sodium hydroxide is prepared by using deionized water;

[0050] 22) first, the magnesium alloy sample after degreasing and oil removal in step 1) is fixed with a copper wire in a polymethyl methacrylate electrolytic cell containing a stainless steel plate, and then the micro-arc oxidation growth solution in step 21) is poured; the anode is AZ31 magnesium alloy, and the cathode is a stainless steel plate; the micro-arc oxidation growth solution has a temperature of 8℃, a reaction voltage of 350V, and a reaction time of 5min, and a magnesium alloy covered with a MAO film is obtained;

[0051] 3) in-situ growth of Mg-MOF-74 film (Mg-MOF-74 for short)

[0052] 31) Preparation with a mixed solution of N-,N-dimethylformamide: anhydrous ethanol: deionized water = 15:1:1 (volume ratio); and dissolving magnesium nitrate and trimesic acid in the aforementioned mixed solution by mass concentration, mixing uniformly to obtain an in-situ growth solution; wherein the molar concentration of magnesium nitrate is 0.2 mM, and the molar concentration of trimesic acid is 0.4 mM;

[0053] 32) The magnesium alloy coated with the MAO film prepared in step 2) is placed in a polytetrafluoroethylene liner, then the in-situ growth solution prepared in step 31) is poured into the liner, and the liner is placed in a reaction kettle, tightened, and finally placed in a drying box for in-situ growth, with a reaction temperature of 120°C and a reaction time of 24 h, and then washed and dried to obtain a magnesium alloy coated with a Mg-MOF-74 film;

[0054] wherein the washed and dried, specifically, the magnesium alloy coated with the Mg-MOF-74 film layer after the reaction in step 3) is first washed with flowing deionized water to remove the in-situ growth solution attached to the surface, then placed in an ultrasonic cleaning machine for ultrasonic cleaning in anhydrous ethanol for 7 min, and then washed with deionized water and dried to obtain the Mg-MOF-74 film layer on the magnesium alloy micro-arc oxidation film surface (Mg-MOF-74 film layer).

[0055] The present application tests the morphology, structure, and performance of the Mg-MOF-74 film layer on the magnesium alloy micro-arc oxidation film surface prepared in the present embodiment, specifically:

[0056] 1) Appearance and morphology

[0057] The present application tests the appearance and morphology of the Mg-MOF-74 film on the magnesium alloy surface in Example 1, and the scanning electron microscope image is as shown in Figure 1 From the figure, it can be seen that the Mg-MOF-74 film on the magnesium alloy surface has completely covered the MAO film layer, the Mg-MOF-74 nanoparticles grow in the horizontal direction, are rod-shaped, are closely connected to each other, and there are some impurities, which may be related to the dissolved Mg 2+ ions in the magnesium matrix and the MAO film layer.

[0058] In addition, the metallographic micrograph of the Mg-MOF-74 film layer on the magnesium alloy micro-arc oxidation film surface is as shown in Figure 2 From the figure, it can be seen that the Mg-MOF-74 film layer on the magnesium alloy micro-arc oxidation film surface has clear and smooth cutting edges, and no obvious large-scale detachment is observed, and the small detachment area in the cross-sectional area is not more than 5%, which indicates that the bonding force degree of the Mg-MOF-74 film layer on the micro-arc oxidation film surface to the magnesium alloy is evaluated as level 1 according to the bonding force classification standard.

[0059] 2) Structure analysis

[0060] The crystallinity of the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film in Example 1 was tested, and the XRD pattern is shown in Figure 3 From the figure, it can be seen that the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film appears multiple characteristic diffraction peaks at 7.6°, 9.2°, 27.9°, 28.5° and 29.5°. Most of these peaks are sharp and have high intensity, indicating that the Mg-MOF-74 film layer has good crystallinity.

[0061] 3) Electrochemical performance

[0062] The electrochemical performance of the film layer on the surface of the magnesium alloy in Example 1 was tested by an electrochemical workstation, specifically:

[0063] The Tafel polarization curves of the magnesium alloy AZ31, the magnesium alloy covered with the MAO film (curve MAO) and the magnesium alloy covered with the Mg-MOF-74 film (curve Mg-MOF-74) were measured by the electrochemical workstation under the same coordinate, and the results are shown in Figure 4 Specifically:

[0064] The corrosion resistance test of the magnesium alloy protective film is represented by the electrochemical polarization curve (the equipment model is Princeton4000A), and the corrosion voltage of the AZ31 magnesium alloy is-1.37V, the corrosion voltage of the AZ31 magnesium alloy covered with the MAO film after the treatment under the conditions of Example 1 is-1.55V, and the corrosion voltage of the AZ31 magnesium alloy covered with the Mg-MOF-74 film is-1.51V, which is obviously improved compared with the corrosion voltage of the magnesium alloy substrate, and the corrosion tendency is reduced. The corrosion speed, corrosion resistance and corrosion current density are directly related. The corrosion current density of the pure AZ31 magnesium alloy is 1.02×10 -5 Acm -2 , the corrosion current density of the magnesium alloy covered with the MAO film is 7.31×10 -7 A cm -2 , but the corrosion current density of the magnesium alloy covered with the Mg-MOF-74 film after the treatment under the conditions of Example 1 is 1.21×10 -7 A cm -2 , which is reduced by half an order of magnitude compared with the magnesium alloy covered with the MAO film; and is reduced by two orders of magnitude compared with the AZ31 magnesium alloy sample. The above results can fully illustrate that the Mg-MOF-74 film has an effective corrosion inhibition effect on the AZ31 magnesium alloy, and the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film of the present application has excellent corrosion resistance and can effectively protect the magnesium substrate.

[0065] Example 2

[0066] The preparation method of the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film provided by the embodiment comprises the following steps:

[0067] 1) degreasing and deoiling

[0068] 11) prepare an aqueous solution containing 40 g / L of sodium hydroxide, 25 g / L of sodium carbonate and 40 g / L of sodium phosphate;

[0069] 12) magnesium alloy pretreatment: respectively use 150, 600, 800, 1200 and 2000# sandpaper to polish the magnesium alloy, and then perform ultrasonic cleaning with alcohol for five minutes and dry for standby;

[0070] 13) immerse the polished magnesium alloy AZ31 in the above-mentioned degreasing and deoiling aqueous solution, perform water bath heat preservation at 50℃ for 60s, then perform alkali washing with 1M aqueous solution of sodium hydroxide for 30s, and then perform polishing with 400 g / L of nitric acid (ρ = 1.42 g / ml) at room temperature 25℃ for 2 min; then clean once with deionized water, and dry with cold air.

[0071] 2) micro-arc oxidation film (MAO for short)

[0072] 21) prepare a micro-arc oxidation growth solution of 0.049M of trisodium phosphate dodecahydrate and 0.18M of sodium hydroxide by weight concentration with deionized water;

[0073] 22) first fix the magnesium alloy sample after degreasing and deoiling in step 1) with a copper wire in a polymethyl methacrylate electrolytic cell containing a stainless steel plate, and then pour the micro-arc oxidation growth solution in step 21) into the cell; the anode is the magnesium alloy AZ31, and the cathode is the stainless steel plate; the micro-arc oxidation growth solution has a temperature of 8℃, a reaction voltage of 350V and a reaction time of 5 min, and the magnesium alloy covered with the MAO film is obtained;

[0074] 3) in-situ growth of Mg-MOF-74 film (Mg-MOF-74 for short)

[0075] 31) prepare an in-situ growth solution of 0.3mM of magnesium nitrate and 0.3mM of trimesic acid by weight concentration with a mixed solution of N-, N-dimethylformamide: anhydrous ethanol: deionized water = 15:1:1 (volume ratio);

[0076] 32) place the magnesium alloy with the surface MAO layer prepared in step 2) into a polytetrafluoroethylene inner liner sleeve, then pour the in-situ growth solution prepared in step 31) into the liner and place the liner into a reaction kettle, tighten, and finally place in a drying box for in-situ growth, with a reaction temperature of 110℃ and a reaction time of 18h, and the magnesium alloy covered with the Mg-MOF-74 film is obtained;

[0077] wherein the washing and drying, specifically, the Mg-MOF-74 film layer coated on the magnesium alloy sample after the reaction in step 3) is washed with flowing deionized water to remove the in-situ growth solution attached on the surface, then the sample is placed in an ultrasonic cleaning machine for ultrasonic cleaning in anhydrous ethanol for 6 min, followed by washing with deionized water and drying, to obtain the Mg-MOF-74 film layer on the magnesium alloy micro-arc oxidation film surface.

[0078] The application tests the morphology and performance of the Mg-MOF-74 film layer on the magnesium alloy micro-arc oxidation film surface prepared in the embodiment, specifically:

[0079] 1) Appearance morphology

[0080] The application tests the appearance morphology of the Mg-MOF-74 film layer on the magnesium alloy micro-arc oxidation film surface in Example 2, and the scanning electron microscope image is as shown in Figure 5 From the figure, it can be seen that the surface of the Mg-MOF-74 film layer on the magnesium alloy micro-arc oxidation film surface is still completely covered with the MAO film layer, and the rod-shaped Mg-MOF-74 grows in multiple directions, with a small part growing perpendicular to the alloy substrate.

[0081] 2) Electrochemical performance

[0082] The application tests the electrochemical performance of the magnesium alloy surface film layer in Example 2 by an electrochemical workstation, specifically:

[0083] The Tafel polarization curves of the magnesium alloy AZ31, the magnesium alloy coated with the MAO film (curve MAO) and the magnesium alloy coated with the Mg-MOF-74 film (curve Mg-MOF-74) in the same coordinate are measured by the electrochemical workstation, and the results are as shown in Figure 6 , specifically:

[0084] The corrosion resistance test of the magnesium alloy protective film is represented by the electrochemical polarization curve (the equipment model is Princeton4000A), wherein the corrosion voltage of the AZ31 magnesium alloy is-1.37V, the corrosion voltage of the AZ31 magnesium alloy coated with the MAO film after the treatment in Example 2 is-1.55V, and the corrosion voltage of the AZ31 magnesium alloy coated with the Mg-MOF-74 film is-1.49V, which is obviously improved relative to the corrosion voltage of the magnesium alloy substrate, and the corrosion tendency is reduced. The corrosion speed, corrosion resistance and corrosion current density are directly related. The corrosion current density of the pure AZ31 magnesium alloy is 1.02×10 -5 Acm -2 , the corrosion current density of the magnesium alloy coated with the MAO film is 7.31×10 -7 A cm -2However, the corrosion current density of the magnesium alloy coated with the Mg-MOF-74 film after the treatment of Example 2 is 2.19 x 10 -7 A cm -2 The corrosion current density of the treated magnesium alloy is reduced by one order of magnitude relative to the magnesium alloy coated with the MAO film, and is reduced by two orders of magnitude relative to the sample of the AZ31 magnesium alloy. The above results fully demonstrate that the Mg-MOF-74 film has an effective corrosion inhibition effect on the AZ31 magnesium alloy, and the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film has excellent corrosion resistance, which can effectively protect the magnesium matrix.

[0085] Example 3

[0086] The preparation method of the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film provided in the example includes the following steps:

[0087] 1) degreasing and oil removal

[0088] 11) prepare an aqueous solution containing 40 g / L of sodium hydroxide, 25 g / L of sodium carbonate, and 40 g / L of sodium phosphate;

[0089] 12) magnesium alloy pretreatment: and respectively use 150, 600, 800, 1200, and 2000# sandpaper to polish the magnesium alloy, and then perform ultrasonic cleaning with alcohol for five minutes and dry for standby;

[0090] 13) immerse the polished magnesium alloy AZ31 in the above-mentioned degreasing and oil removal aqueous solution, water bath at 50℃ for 60s, then wash with 1M sodium hydroxide aqueous solution for 30s, and then polish with 400g / L nitric acid (ρ=1.42g / ml) at room temperature 25℃ for 2min; then wash once with deionized water, and dry with cold air.

[0091] 2) micro-arc oxidation film (MAO for short)

[0092] 21) prepare a micro-arc oxidation growth solution of 0.049M of trisodium phosphate dodecahydrate and 0.18M of sodium hydroxide by weight concentration with deionized water;

[0093] 22) first fix the magnesium alloy sample after degreasing and oil removal in step 1) with a copper wire in a polymethyl methacrylate electrolytic cell containing a stainless steel plate, and then pour the micro-arc oxidation growth solution in step 21) into the cell; the anode is AZ31 magnesium alloy, and the cathode is a stainless steel plate; the micro-arc oxidation growth solution has a temperature of 8℃, a reaction voltage of 350V, and a reaction time of 5min, and a MAO layer is obtained on the surface of the magnesium alloy;

[0094] 3) in-situ growth of Mg-MOF-74 film (Mg-MOF-74 for short)

[0095] 31) Preparation of in-situ growth solution of magnesium nitrate 0.4 mM, trimesic acid 0.5 mM by using a mixed solution of N-, N-dimethylformamide: anhydrous ethanol: deionized water = 15:1:1 (volume ratio) as solvent;

[0096] 32) The magnesium alloy with surface MAO layer prepared in step 2) is placed in a polytetrafluoroethylene liner, then the in-situ growth solution prepared in step 31) is poured into the liner, and the liner is placed in a reaction kettle, tightened, and finally placed in a drying box for in-situ growth, with a reaction temperature of 140°C and a reaction time of 30h, to obtain a magnesium alloy micro-arc oxidation film surface Mg-MOF-74 film layer, i.e. a magnesium alloy micro-arc oxidation film surface Mg-MOF-74 film layer;

[0097] wherein the washing and drying are carried out by first washing the magnesium alloy sample with Mg-MOF-74 film layer prepared in step 3) after the reaction is completed with flowing deionized water to remove the in-situ growth solution adhered to the surface, then placing it in an ultrasonic cleaning machine for ultrasonic cleaning in anhydrous ethanol for 8 min, and then washing it with deionized water and drying, to obtain a magnesium alloy micro-arc oxidation film surface Mg-MOF-74 film layer.

[0098] The present application tests the morphology and performance of the magnesium alloy micro-arc oxidation film surface Mg-MOF-74 film layer prepared in this embodiment, specifically:

[0099] 1) Appearance and morphology

[0100] The present application tests the appearance and morphology of the magnesium alloy micro-arc oxidation film surface Mg-MOF-74 film layer in Example 3, and the scanning electron microscope image is as shown in Figure 7 From the figure, it can be seen that the magnesium alloy micro-arc oxidation film surface Mg-MOF-74 film layer grows substantially perpendicular to the substrate surface, which may be related to the concentration of Mg 2+ .

[0101] 2) Electrochemical performance

[0102] The present application tests the electrochemical performance of the magnesium alloy surface film layer in this embodiment 3 by an electrochemical workstation, specifically:

[0103] The Tafel polarization curves of magnesium alloy AZ31, magnesium alloy with MAO film (curve MAO) and magnesium alloy with Mg-MOF-74 film (curve Mg-MOF-74) in the same coordinate measured by the electrochemical workstation are as shown in Figure 8 , specifically:

[0104] The corrosion resistance test of the magnesium alloy protective film is represented by electrochemical polarization curve (the equipment model is Princeton 4000A), the corrosion voltage of the AZ31 magnesium alloy is -1.37V, the corrosion voltage of the AZ31 magnesium alloy covered with the MAO film after the condition treatment of example 1 is -1.55V, the corrosion voltage of the AZ31 magnesium alloy covered with the Mg-MOF-74 film is -1.42V, which is obviously improved relative to the corrosion voltage of the magnesium alloy substrate, the corrosion tendency is reduced, and the corrosion speed, the corrosion resistance and the corrosion current density are directly related. The corrosion current density of the pure AZ31 magnesium alloy is 1.02×10 -5 A cm -2 The corrosion current density of the magnesium alloy covered with the MAO film is 7.31×10 -7 A cm -2 But the corrosion current density of the sample covered with the Mg-MOF-74 film after the condition treatment of example 3 is 2.78×10 -7 A cm -2 The corrosion current density of the treated sample is reduced by half an order of magnitude relative to the magnesium alloy covered with the MAO film, and is reduced by two orders of magnitude relative to the sample of the AZ31 magnesium alloy. The above results can fully illustrate that the Mg-MOF-74 film has an effective corrosion inhibition effect on the AZ31 magnesium alloy, the Mg-MOF-74 film layer on the magnesium alloy micro-arc oxidation film has excellent corrosion resistance, and can effectively protect the magnesium substrate.

[0105] Comparative example 1

[0106] The preparation method of the Mg-MOF-74 film layer on the magnesium alloy micro-arc oxidation film provided by the comparative example is basically the same as that of example 2, and the difference is only that the magnesium alloy is not subjected to micro-arc oxidation treatment, but is directly subjected to in-situ growth of the Mg-MOF-74 film, and specifically includes the following steps:

[0107] 1) degreasing and deoiling

[0108] 11) preparing an aqueous solution containing 40g / L of sodium hydroxide, 25g / L of sodium carbonate and 40g / L of sodium phosphate;

[0109] 12) magnesium alloy pretreatment: and respectively using 150, 600, 800, 1200 and 2000# sandpaper to polish the magnesium alloy, and then ultrasonic cleaning with alcohol for five minutes and drying for standby;

[0110] 13) After polishing the magnesium alloy AZ31, immerse it in the above-mentioned water solution for removing grease and oil, and keep it in water bath at 50℃ for 60s, then wash it with 1M sodium hydroxide aqueous solution for 30s, and then polish it with 400g / L nitric acid (p=1.42g / ml) at room temperature 25℃ for 1-2min; then wash it with deionized water once, and dry it with cold air.

[0111] 2) In-situ growth of Mg-MOF-74 film (referred to as Mg-MOF-74)

[0112] 21) Prepare an in-situ growth solution of magnesium nitrate 0.3mM and trimesic acid 0.3mM by using a mixed solution of N-,N-dimethylformamide: anhydrous ethanol: deionized water = 15:1:1 (volume ratio), and prepare it according to the molar concentration;

[0113] 22) Put the magnesium alloy pretreated in step 1) into a polytetrafluoroethylene liner, then pour the in-situ growth solution prepared in step 21) into the liner, and put the liner into a reaction kettle, tighten it, and finally put it in a drying box for in-situ growth, with a reaction temperature of 110℃ and a reaction time of 20h, and as a result, Mg-MOF-74 nanoparticles are dispersed in clusters on the surface of the magnesium alloy, and the magnesium alloy covered with a continuous Mg-MOF-74 film cannot be obtained.

[0114] It can be known from the comparison between Example 2 and Comparative Example 1 that in the preparation method of the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film provided in the application, the magnesium alloy is first treated with a MAO film, which is a prerequisite for preparing the Mg-MOF-74 film layer by a solvothermal method, that is, the micro-arc oxidation treatment and the in-situ solvothermal reaction are synergistic, the preparation of the Mg-MOF-74 film layer is successfully realized, and the Mg-MOF-74 film layer has excellent adhesion with the magnesium alloy AZ31.

[0115] In summary, the preparation method of the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film provided in the application is based on the magnesium alloy MAO film, and a layer of Mg-MOF-74 film layer is grown in-situ by a solvothermal method, the micropores of the MAO are filled with Mg-MOF-74 nanoparticles, so that the film layer is more dense and has more excellent corrosion resistance; and no additional metal cations need to be introduced, and the Mg 2+In addition, since the Mg-MOF-74 is grown in situ, the Mg-MOF-74 is directly formed on the surface of the magnesium alloy MAO film, the binding force between the film layer and the substrate and the film forming performance are improved, and the feasibility of application in the industrial field is improved. The Mg-MOF-74 film layer not only seals the pores of the MAO film layer, but also has the characteristics of corrosion resistance, and the performance is much better than that of the untreated magnesium alloy AZ31. The inventor finds through a large number of experiments that the purpose can be achieved by using a traditional and mature reaction kettle on the MAO film layer through a solvothermal reaction, and a Mg-MOF-74 film layer with good binding force and good corrosion resistance is generated; the operation steps of the present application are simple, the raw materials are environmentally friendly and non-toxic, the time consumption is short, and a good Mg-MOF-74 film layer can be obtained by adding a small amount of additional elements, and the energy consumption is lower.

[0116] The above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the description of the present application.

Claims

1. A method for preparing a Mg-MOF-74 film layer on the surface of a magnesium alloy micro-arc oxidation film, characterized in that, Includes the following steps: 1) A magnesium alloy is immersed in a micro-arc oxidation growth solution for micro-arc oxidation treatment to obtain a magnesium alloy coated with a MAO layer; wherein the micro-arc oxidation growth solution includes an aqueous solution of 0.03-0.06M trisodium dodecahydrate and 0.1-0.3M sodium hydroxide; the process parameters of the micro-arc oxidation treatment are: the temperature of the micro-arc oxidation growth solution is 5-10℃, the reaction voltage is 300-400V, and the reaction time is 2-8min; 2) The magnesium alloy coated with MAO layer is immersed in the in-situ growth solution for a one-step in-situ solvothermal reaction, washed and dried to obtain a magnesium alloy coated with Mg-MOF-74 film, namely the Mg-MOF-74 film on the surface of the magnesium alloy MAO film; wherein the in-situ growth solution includes 0.2~0.4mM magnesium nitrate, 0.3~0.5mM trimesic acid, and a mixed solution of N-,N-dimethylformamide, anhydrous ethanol and deionized water in a volume ratio of 15:1:1; the process parameters of the one-step in-situ solvothermal reaction are: reaction temperature of 100-140℃ and reaction time of 16-32h.

2. The method for preparing the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film according to claim 1, characterized in that, It also includes pretreatment before micro-arc oxidation of magnesium alloys, specifically: first grinding the magnesium alloy substrate, and then degreasing and deoiling the ground magnesium alloy substrate.

3. The method for preparing the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film according to claim 2, characterized in that, The polishing process specifically involves polishing the magnesium alloy substrate with 150, 600, 800, 1200, and 2000# sandpaper, followed by ultrasonic cleaning with alcohol and drying.

4. The method for preparing the Mg-MOF-74 film layer on the surface of the magnesium alloy micro-arc oxidation film according to claim 2, characterized in that, The degreasing and oil removal solution used in the degreasing and oil removal process is an aqueous solution comprising 40 g / L sodium hydroxide, 25 g / L sodium carbonate, and 40 g / L sodium phosphate, based on mass-volume concentration.

5. The application of a Mg-MOF-74 film layer on the surface of a magnesium alloy micro-arc oxidation film prepared by any one of the preparation methods of claims 1-4 in the fields of aerospace, automotive, medical devices and 3C digital products.

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