Preparation method of magnesium alloy surface self-repairing high corrosion-resistant composite film

Abstract

The application discloses a preparation method of a magnesium alloy surface self-repairing high-corrosion-resisting composite film, and belongs to the technical field of metal material surface modification, and comprises the following steps: polishing a magnesium alloy to be bright, and cleaning the magnesium alloy with acetone; placing the polished and cleaned magnesium alloy in a composite oxidizing solution to obtain a magnesium alloy with an oxide film layer; dispersing graphene, adding the dispersed graphene into disulfide bond modified polyurethane, stirring to form a mixed solution, immersing the magnesium alloy with the oxide film layer in the solution, and solidifying to obtain a self-repairing intermediate layer; stirring tetrabutyl titanate, anhydrous ethanol, deionized water and hydrochloric acid, aging to obtain a sol, immersing the magnesium alloy with the oxide film and the self-repairing layer in the sol, and calcining. The application establishes a three-layer structure self-repairing high-corrosion-resisting film on the surface of the magnesium alloy through a composite oxidation, graphene loaded polyurethane and sol treatment approach, and the film has excellent corrosion resistance and friction resistance; the neutral salt spray of the composite film can reach 1000h, and the film can reach 120h after scratch treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of surface modification of metal materials, and particularly relates to a preparation method of a magnesium alloy surface self-repairing high-corrosion-resisting composite film. BACKGROUND

[0002] As the lightest metal structural material, magnesium alloy has high specific strength / stiffness, damping capacity, excellent biocompatibility and electromagnetic shielding performance, and has wide application potential in industry. However, magnesium is an active metal with a standard electrode potential of -2.37 V, which is prone to corrosion. At the same time, the MgO / Mg(OH)2 oxide film naturally formed on the surface of magnesium alloy is loose and porous, and cannot effectively protect the magnesium alloy. Therefore, the poor corrosion resistance of magnesium alloy to some extent hinders its practical application in the automobile, electronics, aerospace and other industries. In recent years, researchers have developed various magnesium alloy surface treatment and protection strategies to improve the corrosion resistance of magnesium alloy, such as micro-arc oxidation, electrochemical plating, organic coating and composite oxidation. One of the current research focuses is the development of surface composite films, and the synergistic effect of different components can significantly improve the corrosion resistance of magnesium alloy. However, magnesium alloy will produce cracks in the composite film layer during use due to wear, bumps and scratches, and it is difficult to detect and repair the initial micro-cracks, which will further expand the cracks and eventually lead to the failure of the protective film layer, thereby exposing the substrate to the environment and causing corrosion. Therefore, it is necessary to make the composite film layer have a self-repairing function.

[0003] At present, the self-repairing method for magnesium alloy surface treatment includes exogenous and intrinsic types. The exogenous self-repairing refers to loading a repair agent in the film layer through micro / nano containers such as microcapsules, so that when the surface film layer is damaged, the repair agent in the damaged area is automatically released to achieve self-repairing. The intrinsic self-repairing relies on the special properties and chemical bonds of the film layer material itself, such as reversible covalent bond, non-covalent bond, shape memory effect, etc. to achieve self-repairing. This method does not require additional repair agent and the operation steps are more simple. Therefore, in order to improve the multi-field applicability and actual service life of magnesium alloy, and simplify the preparation process, it is of great significance to develop a magnesium alloy surface self-repairing high-corrosion-resisting composite film based on the intrinsic self-repairing. SUMMARY

[0004] In order to solve the problems of poor corrosion resistance of magnesium alloy and easy wear and failure of the surface treatment and protection film layer during use, the application provides a preparation method of a magnesium alloy surface self-repairing high-corrosion-resisting composite film.

[0005] The purpose of the application can be achieved by the following technical solutions.

[0006] A preparation method of a magnesium alloy surface self-repairing high-corrosion-resisting composite film, comprising the following steps:

[0007] S1. Surface pretreatment of magnesium alloy: polish the magnesium alloy to bright and clean the surface with acetone;

[0008] S2. Preparation of composite oxidation primer: put the polished and cleaned magnesium alloy into the composite oxidation solution, stir at 80-100 r / min for 15-30 min at 20-40℃, so that the magnesium alloy surface forms an oxide film layer;

[0009] S3. Preparation of self-repairing intermediate layer: disperse graphene in DMF (N,N-dimethylformamide) by ultrasonic for 25-35 min to form a suspension, filter and wash the residue with ethanol, then add the residue into disulfide modified polyurethane, stir at 1000-1200 r / min for 30-40 min to remove ethanol, then stir at 300-500 r / min for 1-2 h to form a mixed solution; finally, immerse the magnesium alloy with oxide film layer in the mixed solution for 40-60 min, and then solidify in a drying oven at 70-120℃ for 3-5 h, so that the magnesium alloy surface forms a self-repairing intermediate layer;

[0010] S4. Preparation of friction-resistant topcoat: stir tetrabutyl titanate and anhydrous ethanol at 800-1000 r / min for 1-2 h at room temperature to form a mixed solution, slowly drop deionized water and 0.1 mol / L hydrochloric acid into the mixed solution under stirring, continue to stir for 3-4 h, stand for 12-18 h to get titanium dioxide sol; then immerse the magnesium alloy treated in step S3 in the sol for 1-2 h, take out and dry, and then calcine in a muffle furnace at 100-120℃ for 60-80 min at a heating rate of 0.5-1℃ / min, so that a self-repairing high corrosion-resistant composite film layer is formed on the surface of the magnesium alloy.

[0011] Further, the preparation method of the composite oxidation solution is as follows: add silane coupling agent to deionized water, stir at 400-500 r / min for 1-2 h at 25-35℃, then heat to 50-60℃, and then add silicate, tungstate, rare earth salt, complexing agent, benzotriazole and hydroxyethyl cellulose in sequence, continue to stir at 400-500 r / min for 6-8 h to get the composite oxidation solution base solution; finally, dilute the composite oxidation solution base solution in deionized water according to a mass fraction of 10%-20% to obtain the composite oxidation solution.

[0012] Further, the amount of silane coupling agent, silicate, tungstate, rare earth salt, complexing agent, benzotriazole, hydroxyethyl cellulose and deionized water is 25-45 g: 20-30 g: 15-25 g: 1.6-2.4 g: 3-5 g: 8-12 g: 6-8 g: 0.5 L.

[0013] Further, the silane coupling agent is any one of methyl triethoxysilane, 3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane.

[0014] Further, the silicate is any one of potassium silicate, sodium silicate, potassium metasilicate, sodium metasilicate or any two of them mixed in a mass ratio of 1:1.

[0015] Further, the tungstate is any one of sodium tungstate, sodium metatungstate, ammonium tungstate, ammonium metatungstate or any two of them mixed in a mass ratio of 1:1.

[0016] Further, the rare earth salt is any one of cerium chloride, rubidium chloride or a mixture of cerium chloride and rubidium chloride in a mass ratio of 1:1.

[0017] Further, the complexing agent is any one of disodium ethylenediaminetetraacetate, sodium gluconate, sodium citrate or any two of them mixed in a mass ratio of 1:1.

[0018] Further, in the preparation of the self-repairing interlayer in step S3, the mass ratio of graphene and disulfide bond modified polyurethane is 1:50-60.

[0019] Further, the preparation method of the disulfide bond modified polyurethane comprises the following steps:

[0020] Step A: Dissolve PTMEG (polytetramethylene ether glycol), IPDI (isophorone diisocyanate) and DBTDL (dibutyl tin dilaurate) in a mixed solvent of xylene and acetone in a volume ratio of 1:1, stir at 75-85°C and 200-250r / min for 1-2h to obtain a polyurethane prepolymer;

[0021] Step B: Dissolve polyethylene glycol and DTDA (4,4'-diamino diphenyl disulfide) in the same mixed solvent of xylene and acetone in a volume ratio of 1:1, then add dropwise to the polyurethane prepolymer; finally continue to stir the mixture at 75-85°C for 2-3h to obtain a disulfide bond modified polyurethane.

[0022] Further, in the preparation method of the disulfide bond modified polyurethane, the solid-liquid ratio of the amounts of PTMEG, IPDI, DBTDL, polyethylene glycol, DTDA, the mixed solvent used in step A and the mixed solvent used in step B is 160g-200g:100-120g:0.8-1.0g:48-64g:10-12g:100mL:100mL.

[0023] Further, in step S4, the volume ratio of the amounts of tetrabutyl titanate, anhydrous ethanol, deionized water and hydrochloric acid is 5:20-22:5-6:1-1.2.

[0024] Compared with the prior art, the present application has the following advantages:

[0025] 1. The present application provides a preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, which establishes a three-layer structure of self-repairing high corrosion-resistant film on the surface of magnesium alloy through composite oxidation, graphene loaded polyurethane and sol treatment, has excellent corrosion resistance and friction resistance, and the neutral salt spray of the composite film can reach 1000h, and after scratch treatment, it can reach 120h.

[0026] 2. The present application improves the corrosion resistance of the film layer through the film forming of silane coupling agent, inorganic corrosion inhibitor, rare earth salt and organic corrosion inhibitor.

[0027] 3. The present application establishes a disulfide bond modified polyurethane intermediate layer, which not only effectively fills the internal and external pores of the oxidation bottom layer, but also when the friction-resistant topcoat is damaged, the disulfide bond modified polyurethane elastomer can realize the high self-repairing performance of the composite film layer through multiple strategies such as its own elasticity, graphene sheet structure and regeneration of sulfur covalent bond in the repair process; controlling the curing temperature of the self-repairing intermediate layer to be 70-120℃ and the curing time to be 3-5h is beneficial to improve the hardness and density of the intermediate layer, and further improve the self-repairing ability.

[0028] 4. The present application establishes a friction-resistant topcoat through sol treatment, which can significantly improve the hardness and friction resistance of the composite film layer, and at the same time provides a protective barrier for the bottom layer and the intermediate layer, which is beneficial to improve the corrosion resistance of the composite film and better exert the self-repairing ability of the composite film. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0030] Example 1

[0031] The preparation method of the composite oxidation solution comprises the following steps:

[0032] To 0.5 L of deionized water, 35 g of methyl triethoxysilane was added, stirred at 30°C at 450 r / min for 2 h, then warmed to 55°C, and then 24 g of silicate (12 g of potassium silicate and 12 g of sodium silicate), 20 g of tungstate (10 g of sodium tungstate and 10 g of sodium metatungstate), 2.0 g of rare earth salt (1.0 g of cerium chloride and 1.0 g of rubidium chloride), 4 g of complexing agent (2 g of disodium ethylenediaminetetraacetate and 2 g of sodium citrate), 10 g of benzotriazole, and 8 g of hydroxyethyl cellulose were sequentially added, and stirring was continued at 450 r / min for 6 h to obtain a composite oxidizing liquid base solution. Finally, the composite oxidizing liquid base solution was added to deionized water at a mass fraction of 15% to obtain a composite oxidizing liquid.

[0033] Example 2-5

[0034] The preparation method of the composite oxidizing liquid was the same as that of Example 1, except that the amounts of the components in the composite oxidizing liquid base solution were different. See Table 1 for details.

[0035] Table 1 Composition of the composite oxidizing liquid base solution

[0036]

[0037] Comparative Example 1

[0038] The preparation method of the composite oxidizing liquid was the same as that of Example 1, except that the silane coupling agent was replaced by polyvinyl alcohol, and the other components and preparation process were unchanged.

[0039] Comparative Example 2

[0040] The preparation method of the composite oxidizing liquid was the same as that of Example 1, except that no rare earth salt was added, and the other components and preparation process were unchanged.

[0041] Comparative Example 3

[0042] The preparation method of the composite oxidizing liquid was the same as that of Example 1, except that no benzotriazole was added, and the other components and preparation process were unchanged.

[0043] Example 6

[0044] The preparation method of the disulfide bond modified polyurethane included the following steps:

[0045] Step A: 180 g of PTMEG, 120 g of IPDI, and 1.0 g of DBTDL were dissolved in 100 mL of a mixed solvent of xylene and acetone at a volume ratio of 1:1, and stirred at 80°C at 250 r / min for 1.5 h to obtain a polyurethane prepolymer;

[0046] Step B: 56 g of polyethylene glycol and 12 g of DTDA were dissolved in 100 mL of a mixed solvent of xylene and acetone in a volume ratio of 1:1, and then added dropwise into the above polyurethane prepolymer; finally, the mixture was continuously stirred and reacted at 80℃ for 2.5 h to obtain a disulfide bond modified polyurethane.

[0047] Comparative Example 4

[0048] The preparation method of the polyurethane was a control group of Example 6, and the difference was that no DTDA was added in Step B, and the rest of the components and the preparation process were unchanged.

[0049] Example 7

[0050] A preparation method of a self-repairing high corrosion-resistant composite film on a magnesium alloy surface, comprising the following steps:

[0051] S1. Surface pretreatment of magnesium alloy: polish the magnesium alloy to a bright finish and clean the surface with acetone;

[0052] S2. Preparation of composite oxide bottom layer: place the polished and cleaned magnesium alloy into the composite oxidation solution prepared in Example 1, and stir at 100 r / min under air at 30℃ for 25 min to form an oxide film layer on the surface of the magnesium alloy;

[0053] S3. Preparation of self-repairing intermediate layer: 3 g of graphene was dispersed in DMF by ultrasonic for 30 min to form a suspension, and the filter residue was washed with ethanol, then 150 g of disulfide bond modified polyurethane prepared in Example 6 was added, stirred at 1100 r / min for 35 min to remove ethanol, then stirred at 400 r / min for 1.5 h to form a mixed solution, and finally the magnesium alloy with an oxide film layer was immersed in the mixed solution for 60 min, and then dried in a 90℃ drying oven for 4 h to form a self-repairing intermediate layer on the surface of the magnesium alloy;

[0054] S4. Synthesis of friction-resistant outer coating: 40 mL of tetrabutyl titanate and 160 mL of anhydrous ethanol were stirred at 900 r / min at room temperature for 1.5 h to form a mixed solution, then slowly added dropwise into 45 mL of deionized water and 9 mL of 0.1 mol / L hydrochloric acid under stirring, and continued to stir for 4 h, and then aged for 16 h to obtain a titanium dioxide sol; then the magnesium alloy treated in S3 was immersed in the sol for 2 h, dried, and then taken out and calcined in a muffle furnace at 110℃ for 70 min at a heating rate of 1℃ / min to obtain a self-repairing high corrosion-resistant composite film layer on the surface of the magnesium alloy.

[0055] Example 8

[0056] A preparation method of a self-repairing high corrosion-resistant composite film on a magnesium alloy surface, comprising the following steps:

[0057] S1. Surface pretreatment of magnesium alloy: polish the magnesium alloy to bright and clean the surface with acetone;

[0058] S2. Preparation of composite oxide bottom layer: put the polished and cleaned magnesium alloy into the composite oxidation solution prepared in Example 1, stir at 100 r / min under air at 30℃ for 25 min, and form an oxide film layer on the surface of the magnesium alloy;

[0059] S3. Preparation of self-repairing intermediate layer: disperse 3 g of graphene in DMF for 30 min under ultrasonic to form a suspension, wash the filter residue with ethanol after filtration, add 150 g of disulfide bond modified polyurethane prepared in Example 6 to the filter residue, stir at 1000 r / min for 40 min to remove ethanol, then stir at 300 r / min for 2 h to form a mixed solution, finally immerse the magnesium alloy with the oxide film layer in the mixed solution for 60 min, and solidify in a drying oven at 70℃ for 5 h after taking out, so as to form a self-repairing intermediate layer on the surface of the magnesium alloy;

[0060] S4. Synthesis of friction-resistant outer coating: stir 40 mL of tetrabutyl titanate and 160 mL of anhydrous ethanol at 800 r / min at room temperature for 2 h to form a mixed solution, slowly drop 45 mL of deionized water and 9 mL of 0.1 mol / L hydrochloric acid under stirring, continue to stir for 4 h, stand for 12 h, and get titanium dioxide sol; then immerse the magnesium alloy treated in S3 in the sol for 2 h, take out after drying, and calcine in a muffle furnace at 100℃ for 80 min, with a heating rate of 0.5℃ / min, so as to obtain a self-repairing high corrosion-resistant composite film layer on the surface of the magnesium alloy.

[0061] Example 9

[0062] A method for preparing a self-repairing high corrosion-resistant composite film on the surface of a magnesium alloy, comprising the following steps:

[0063] S1. Surface pretreatment of magnesium alloy: polish the magnesium alloy to bright and clean the surface with acetone;

[0064] S2. Preparation of composite oxide bottom layer: put the polished and cleaned magnesium alloy into the composite oxidation solution prepared in Example 1, stir at 100 r / min under air at 30℃ for 25 min, and form an oxide film layer on the surface of the magnesium alloy;

[0065] S3. Self-repairing intermediate layer preparation: 3 g graphene was dispersed in DMF by ultrasonic for 30 min to form a suspension, and the filter residue was washed with ethanol after filtration. The filter residue was added into 150 g disulfide bond modified polyurethane prepared in Example 6, and stirred at 1200 r / min for 30 min to remove ethanol, and then stirred at 500 r / min for 1 h to form a mixed solution. Finally, the magnesium alloy with an oxidation film layer was immersed in the mixed solution for 60 min, and then dried in a 120℃ drying oven for 3 h to form a self-repairing intermediate layer on the surface of the magnesium alloy;

[0066] S4. Synthesis of friction-resistant top coating: 40 mL tetrabutyl titanate and 160 mL anhydrous ethanol were stirred at 1000 r / min at room temperature for 1 h to form a mixed solution, and 45 mL deionized water and 9 mL 0.1 mol / L hydrochloric acid were slowly added dropwise under stirring, and stirring was continued for 3 h. After standing for 18 h, a titanium dioxide sol was obtained. Then the magnesium alloy treated in S3 was immersed in the sol for 1.5 h, dried, and then taken out and calcined in a 120℃ muffle furnace for 60 min at a heating rate of 1℃ / min, to obtain a self-repairing high corrosion-resistant composite film layer on the surface of the magnesium alloy.

[0067] Example 10

[0068] A method for preparing a self-repairing high corrosion-resistant composite film on the surface of a magnesium alloy, comprising the following steps:

[0069] S1. Surface pretreatment of magnesium alloy: The magnesium alloy was polished to a bright finish, and then cleaned with acetone to obtain a clean surface;

[0070] S2. Preparation of composite oxidation bottom layer: The polished and cleaned magnesium alloy was placed in the composite oxidation solution prepared in Example 1, and stirred at 100 r / min in air at 30℃ for 25 min to form an oxidation film layer on the surface of the magnesium alloy;

[0071] S3. Self-repairing intermediate layer preparation: 3 g graphene was dispersed in DMF by ultrasonic for 30 min to form a suspension, and the filter residue was washed with ethanol after filtration. The filter residue was added into 150 g disulfide bond modified polyurethane prepared in Example 6, and stirred at 1050 r / min for 40 min to remove ethanol, and then stirred at 350 r / min for 2 h to form a mixed solution. Finally, the magnesium alloy with an oxidation film layer was immersed in the mixed solution for 60 min, and then dried in a 80℃ drying oven for 5 h to form a self-repairing intermediate layer on the surface of the magnesium alloy;

[0072] S4. Synthesis of the outer layer resistant to friction: 40 mL of tetrabutyl titanate and 160 mL of anhydrous ethanol were stirred at 850 r / min at room temperature for 1.5 h to form a mixed solution, 45 mL of deionized water and 9 mL of 0.1 mol / L hydrochloric acid were slowly dropped into the mixed solution under stirring, and stirring was continued for 4 h, and the solution was left to stand for aging for 14 h to obtain a titania sol; then the magnesium alloy treated in S3 was immersed in the sol for 2 h, taken out after drying, and calcined in a muffle furnace at 105°C for 75 min at a heating rate of 0.5°C / min, so that a self-repairing high corrosion-resistant composite film layer was obtained on the surface of the magnesium alloy.

[0073] Example 11

[0074] A method for preparing a self-repairing high corrosion-resistant composite film on the surface of a magnesium alloy, comprising the following steps:

[0075] S1. Surface pretreatment of the magnesium alloy: the magnesium alloy was polished to be bright, and cleaned with acetone until the surface was clean;

[0076] S2. Preparation of the composite oxide bottom layer: the polished and cleaned magnesium alloy was placed in the composite oxidation solution prepared in Example 1, and the surface of the magnesium alloy was allowed to form an oxide film layer under air stirring at 100 r / min at 30°C for 25 min;

[0077] S3. Preparation of the self-repairing intermediate layer: 3 g of graphene was dispersed in DMF by ultrasonic for 30 min to form a suspension, the filtrate was washed with ethanol after filtration, and the filtrate was added into 150 g of the disulfide bond modified polyurethane prepared in Example 6, stirred at 1150 r / min for 35 min to remove ethanol, then stirred at 450 r / min for 1 h to form a mixed solution, and finally the magnesium alloy with the oxide film layer was immersed in the mixed solution for 40 min, and taken out to be solidified in a drying oven at 100°C for 3.5 h, so that a self-repairing intermediate layer was formed on the surface of the magnesium alloy;

[0078] S4. Synthesis of the outer layer resistant to friction: 40 mL of tetrabutyl titanate and 160 mL of anhydrous ethanol were stirred at 850 r / min at room temperature for 1.5 h to form a mixed solution, 45 mL of deionized water and 9 mL of 0.1 mol / L hydrochloric acid were slowly dropped into the mixed solution under stirring, and stirring was continued for 4 h, and the solution was left to stand for aging for 14 h to obtain a titania sol; then the magnesium alloy treated in S3 was immersed in the sol for 2 h, taken out after drying, and calcined in a muffle furnace at 105°C for 75 min at a heating rate of 0.5°C / min, so that a self-repairing high corrosion-resistant composite film layer was obtained on the surface of the magnesium alloy.

[0079] Example 12

[0080] A method for preparing a self-repairing high corrosion-resistant composite film on the surface of a magnesium alloy, the specific experimental steps and parameter settings are the same as those in Example 7, except that the composite oxidation solution prepared in Example 2 is used in step S2.

[0081] Example 13

[0082] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, the specific experimental steps and parameter settings are the same as those of Example 7, and the difference lies in that the composite oxidation solution prepared in Example 3 is used in step S2.

[0083] Example 14

[0084] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, the specific experimental steps and parameter settings are the same as those of Example 7, and the difference lies in that the composite oxidation solution prepared in Example 4 is used in step S2.

[0085] Example 15

[0086] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, the specific experimental steps and parameter settings are the same as those of Example 7, and the difference lies in that the composite oxidation solution prepared in Example 5 is used in step S2.

[0087] Comparative Example 5

[0088] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, which is a control group of Example 7, and the difference lies in that the composite oxidation solution used in step S2 is prepared from Comparative Example 1, and the other components and experimental steps remain unchanged.

[0089] Comparative Example 6

[0090] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, which is a control group of Example 7, and the difference lies in that the composite oxidation solution used in step S2 is prepared from Comparative Example 2, and the other components and experimental steps remain unchanged.

[0091] Comparative Example 7

[0092] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, which is a control group of Example 7, and the difference lies in that the composite oxidation solution used in step S2 is prepared from Comparative Example 3, and the other components and experimental steps remain unchanged.

[0093] Comparative Example 8

[0094] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, which is a control group of Example 7, and the difference lies in that the drying oven curing temperature in step S3 is 60°C, and the other components and experimental steps remain unchanged.

[0095] Comparative Example 9

[0096] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, which is a control group of Example 7, and the difference lies in that the drying oven curing temperature in step S3 is 130°C, and the other components and experimental steps remain unchanged.

[0097] Comparative Example 10

[0098] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, which is a control group of Example 7, differs from Example 7 in that the curing time in the drying oven in step S3 is 2 h, and the other components and experimental steps remain unchanged.

[0099] Comparative Example 11

[0100] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, which is a control group of Example 7, differs from Example 7 in that the curing time in the drying oven in step S3 is 6 h, and the other components and experimental steps remain unchanged.

[0101] Comparative Example 12

[0102] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, which is a control group of Example 7, differs from Example 7 in that the disulfide bond modified polyurethane in step S3 is replaced by the polyurethane prepared in Comparative Example 4, and the other components and experimental steps remain unchanged.

[0103] Comparative Example 13

[0104] A preparation method of a magnesium alloy surface composite film, comprising the following steps:

[0105] S1. Magnesium alloy surface pretreatment: polish the magnesium alloy to a bright finish, and clean the surface with acetone;

[0106] S2. Preparation of composite oxide layer: place the polished and cleaned magnesium alloy into the composite oxidation solution prepared in Example 1, and stir at 100 r / min under air at 30°C for 25 min to form an oxide film layer on the surface of the magnesium alloy;

[0107] S3. Preparation of friction-resistant layer: stir 40 mL of tetrabutyl titanate and 160 mL of anhydrous ethanol at 900 r / min at room temperature for 1.5 h to form a mixed solution, slowly drop 45 mL of deionized water and 9 mL of 0.1 mol / L hydrochloric acid into the mixed solution under stirring, continue to stir for 4 h, and stand for 16 h to obtain a titanium dioxide sol; then immerse the magnesium alloy treated in S2 in the sol for 2 h, take it out after drying, and calcine it in a muffle furnace at 110°C for 70 min at a heating rate of 1°C / min.

[0108] Comparative Example 14

[0109] A preparation method of a magnesium alloy surface self-repairing high corrosion-resistant composite film, comprising the following steps:

[0110] S1. Magnesium alloy surface pretreatment: polish the magnesium alloy to a bright finish, and clean the surface with acetone;

[0111] S2. Preparation of a composite oxide layer: the polished and cleaned magnesium alloy was placed in the composite oxidation solution prepared in Example 1, and air stirring was performed at 100 r / min for 25 min at 30°C to form an oxide film layer on the surface of the magnesium alloy;

[0112] S3. Preparation of a self-repairing layer: 3 g of graphene was dispersed in DMF by ultrasonic treatment for 30 min to form a suspension, the filter residue was washed with ethanol, and the filter residue was added to 150 g of the disulfide bond modified polyurethane prepared in Example 6, and stirred at 1100 r / min for 35 min to remove ethanol, and then stirred at 400 r / min for 1.5 h to form a mixed solution, and finally the magnesium alloy with the oxide film layer was immersed in the mixed solution for 60 min, and after taking out, it was cured in a drying oven at 90°C for 4 h to form a self-repairing layer on the surface of the magnesium alloy.

[0113] Comparative Example 15

[0114] A method for preparing a composite film on the surface of a magnesium alloy, comprising the following steps:

[0115] S1. Surface pretreatment of the magnesium alloy: the magnesium alloy was polished to a bright finish, and cleaned with acetone to obtain a clean surface;

[0116] S2. Preparation of a composite oxide layer: the polished and cleaned magnesium alloy was placed in the composite oxidation solution prepared in Example 1, and air stirring was performed at 100 r / min for 25 min at 30°C to form an oxide film layer on the surface of the magnesium alloy.

[0117] Performance tests were performed on Examples 7-15 and Comparative Examples 5-15, as follows:

[0118] Corrosion resistance: neutral salt spray test (GB / T 10125-2021) was performed on the sample, and after 1000 h of testing, no rust appeared on the surface of the coating, which was qualified, otherwise it was unqualified;

[0119] Hardness: the Vickers hardness of the film layer was measured using a micro Vickers hardness tester;

[0120] Friction resistance: the film layer friction coefficient was obtained by ring-block sliding wear test (GB / T 12444-2006);

[0121] Self-repairing property: uniform specification scratches were made on the surface of each sample (to expose the magnesium substrate), and then neutral salt spray test was performed, and the width of the rust at the scratch was less than 2 mm, which was qualified; the rust condition at the scratch was observed every 24 h and the salt spray qualified time was recorded.

[0122] The test results are shown in Table 2:

[0123] Table 2

[0124]

[0125]

[0126] From Table 2, it can be seen that:

[0127] The test results of the magnesium alloy surface composite film layer obtained after preparing the self-repairing intermediate layer and the friction-resistant outer coating layer under different parameter settings after preparing the oxidation bottom layer by the same steps in Examples 7, 8, 9, 10, 11; the test results of the magnesium alloy surface composite film layer obtained after preparing the intermediate layer and the outer coating layer under the same experimental steps after preparing the oxidation bottom layer by different formula composite oxidation solutions (prepared by Examples 2, 3, 4, 5, respectively) in Examples 12, 13, 14, 15; the results show that the magnesium alloy surface composite film prepared by the surface modification treatment method of the application has high corrosion resistance, high hardness, excellent friction resistance and self-repairing performance.

[0128] From the comparison of Comparative Example 5 and Example 7, it can be seen that the silane coupling agent in the composite oxidation solution can improve the corrosion resistance of the composite film layer, which is attributed to the good film-forming effect of the silane coupling agent; from the comparison of Comparative Example 6, Comparative Example 7 and Example 7, it can be seen that the addition of rare earth salt and organic corrosion inhibitor in the composite oxidation solution can improve the corrosion resistance of the composite film layer, which is because the synergistic effect of inorganic corrosion inhibitor, rare earth salt and organic corrosion inhibitor can further enhance the corrosion resistance of the film layer. From the comparison of Comparative Examples 5, 6, 7 and Example 7, the oxidation bottom layer will directly affect the preparation effect of the subsequent intermediate layer and outer coating layer, thereby affecting the self-repairing ability and friction resistance of the composite film layer.

[0129] From the comparison of Comparative Examples 8, 9, 10, 11 and Example 7, it can be seen that during the preparation of the self-repairing intermediate layer, the immersion and solidification at 70-120℃ for 3-5h can make the hardness of the graphene-loaded modified polyurethane intermediate layer larger and the densification of the intermediate layer is improved, and the densified intermediate layer can effectively fill the internal and external pores of the oxidation bottom layer, thereby simultaneously improving the corrosion resistance, friction resistance and self-repairing property of the composite film. When the solidification temperature is reduced to 60℃ or the solidification time is reduced to 2h, the polyurethane molecular chain formed is incomplete, the molecular weight is small, and the mechanical property is poor, thereby resulting in the reduction of the hardness and the densification of the composite film; when the solidification temperature is increased to 130℃ or the solidification time is increased to 6h, the polyurethane molecules are crosslinked excessively, and part of the structure is damaged, which also reduces the hardness and the densification of the composite film; thereby further reducing the corrosion resistance, friction resistance and self-repairing ability.

[0130] It can be seen from the comparison of Comparative Example 12, Comparative Example 13 and Example 7 that the self-repairing effect of the composite film layer is mainly realized by graphene loading disulfide bond modified polyurethane intermediate layer. When the wear-resistant outer coating is damaged, the polyurethane elastomer of the intermediate layer can realize a certain self-repairing ability through its elasticity and graphene sheet structure; and on this basis, the polyurethane is modified by introducing reversible disulfide bond (S-S), which can regenerate sulfur covalent bond in the repair process, thereby further improving the self-repairing ability of the composite film.

[0131] It can be seen from the comparison of Comparative Example 14 and Example 7 that titanium dioxide sol treatment can significantly improve the hardness of the composite film layer and reduce the friction coefficient, and at the same time provides a protective barrier for the bottom layer and the intermediate layer, which is conducive to improving the corrosion resistance of the composite film and better exerting the self-repairing ability of the composite film; it can be seen from the comparison of Comparative Example 15 and Example 7 that only forming an oxide layer on the surface of the magnesium alloy has poor hardness, wear resistance and corrosion resistance, and under the synergistic action of the three-layer structure of the oxidation bottom layer, the self-repairing intermediate layer and the wear-resistant outer coating, the high corrosion resistance and self-repairing function of the composite film on the surface of the magnesium alloy can be maximized.

[0132] It should be noted that in this document, the relationship terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment.

[0133] Although the embodiments of the present application have been shown and described, it can be understood by those of ordinary skill in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a self-healing, highly corrosion-resistant composite film on a magnesium alloy surface, characterized in that, Includes the following steps: S1. Magnesium alloy surface pretreatment: Grind the magnesium alloy to a bright finish and clean it with acetone until the surface is clean; S2. Preparation of composite oxide underlayer: The polished and cleaned magnesium alloy is placed in the composite oxide solution and stirred in air at 80-100 r / min for 15-30 min at 20-40℃ to form an oxide film layer on the surface of the magnesium alloy. The preparation method of the composite oxidation liquid is as follows: A silane coupling agent is added to deionized water, and the mixture is stirred at 400-500 r / min for 1-2 hours at 25-35℃. Then, the temperature is raised to 50-60℃, and silicate, tungstate, rare earth salt, complexing agent, benzotriazole, and hydroxyethyl cellulose are added sequentially. The mixture is stirred at 400-500 r / min for 6-8 hours to obtain the composite oxidation liquid base solution. Finally, the composite oxidation liquid base solution is diluted with deionized water at a mass fraction of 10%-20% to obtain the composite oxidation liquid. When preparing the composite oxidation liquid base solution, the solid-liquid ratio of the silane coupling agent, silicate, tungstate, rare earth salt, complexing agent, benzotriazole, hydroxyethyl cellulose, and deionized water is 25-45g:20-30g:15-25g:1.6-2.4g:3-5g:8-12g:6-8g:0.5L. S3. Preparation of self-healing intermediate layer: Graphene is ultrasonically dispersed in N,N-dimethylformamide to form a suspension. After filtration, the filter residue is washed with ethanol. The filter residue is added to disulfide bond modified polyurethane and stirred at 1000-1200 r / min for 30-40 min to remove ethanol. Then, it is stirred at 300-500 r / min for 1-2 h to form a mixed solution. Finally, the magnesium alloy with oxide film is immersed in the mixed solution for 40-60 min. After removal, it is cured in a drying oven at 70-120℃ for 3-5 h to form a self-healing intermediate layer on the surface of the magnesium alloy. S4. Preparation of abrasion-resistant outer coating: Tetrabutyl titanate and anhydrous ethanol are stirred at 800-1000 r / min for 1-2 h at room temperature to form a mixed solution. Deionized water and 0.1 mol / L hydrochloric acid are slowly added dropwise while stirring, and stirring is continued for 3-4 h. The mixture is then allowed to stand for 12-18 h to obtain titanium dioxide sol. The volume ratio of tetrabutyl titanate, anhydrous ethanol, deionized water and hydrochloric acid is 5:20-22:5-6:1-1.

2. Then, the magnesium alloy treated in step S3 is immersed in the sol for 1-2 h, removed and dried, and then calcined in a muffle furnace at 100-120℃ for 60-80 min at a heating rate of 0.5-1℃ / min. This results in a self-healing, highly corrosion-resistant composite film on the surface of the magnesium alloy.

2. The method for preparing a self-healing, highly corrosion-resistant composite film on a magnesium alloy surface according to claim 1, characterized in that, The silane coupling agent is any one of methyltriethoxysilane, 3-aminopropyltriethoxysilane, and 3-aminopropyltrimethoxysilane.

3. The method for preparing a self-healing, highly corrosion-resistant composite film on a magnesium alloy surface according to claim 1, characterized in that, The silicate is formed by mixing any one or any two of potassium silicate, sodium silicate, potassium metasilicate, and sodium metasilicate in a mass ratio of 1:1; the tungstate is formed by mixing any one or any two of sodium tungstate, sodium metatungstate, ammonium tungstate, and ammonium metatungstate in a mass ratio of 1:1; the rare earth salt is formed by mixing any one of cerium chloride and rubidium chloride, or cerium chloride and rubidium chloride in a mass ratio of 1:

1.

4. The method for preparing a self-healing, highly corrosion-resistant composite film on a magnesium alloy surface according to claim 1, characterized in that, The complexing agent is any one or any two of disodium ethylenediaminetetraacetate, sodium gluconate, and sodium citrate mixed in a mass ratio of 1:

1.

5. The method for preparing a self-healing, highly corrosion-resistant composite film on a magnesium alloy surface according to claim 1, characterized in that, In step S3, the mass ratio of graphene to disulfide bond modified polyurethane is 1:50-60.

6. The method for preparing a self-healing, highly corrosion-resistant composite film on a magnesium alloy surface according to claim 1, characterized in that, The preparation method of the disulfide bond modified polyurethane includes the following steps: Step A: Dissolve polytetramethylene ether glycol, isophorone diisocyanate and dibutyltin dilaurate in a mixed solvent of xylene and acetone with a volume ratio of 1:1, and stir at 75-85℃ and 200-250 r / min for 1-2 h to obtain polyurethane prepolymer. Step B: Dissolve polyethylene glycol and 4,4'-diaminodiphenyl disulfide in a mixed solvent of xylene and acetone in the same volume ratio of 1:1, and then add it dropwise to the polyurethane prepolymer; finally, continue to stir the mixture at 75-85℃ for 2-3 hours to obtain disulfide-modified polyurethane.

7. The method for preparing a self-healing, highly corrosion-resistant composite film on a magnesium alloy surface according to claim 6, characterized in that, In the preparation method of the disulfide bond modified polyurethane, the solid-liquid ratio of polytetramethylene ether glycol, isophorone diisocyanate and dibutyltin dilaurate, polyethylene glycol, 4,4'-diaminodiphenyl disulfide, the mixed solvent used in step A and the mixed solvent used in step B is 160g-200g:100-120g:0.8-1.0g:48-64g:10-12g:100mL:100mL.

Images