A magnesium alloy surface protection material, a preparation method and application thereof

Abstract

The application relates to the technical field of metal surface protection materials, in particular to a magnesium alloy surface protection material, a preparation method and application thereof, which contains 40-60 parts of a fluorocarbon resin matrix, 30-50 parts of functional fillers, 5-10 parts of corrosion inhibitors, 3-8 parts of cross-linking agents, 0.5-2 parts of catalysts and 1-3 parts of additives; the functional fillers are modified to form a 'core-shell' structure, graphene is loaded with nano zinc oxide, and fluorophosphoric calcium whiskers are coated with rare earth cerium salt; the preparation process comprises resin interpenetrating network formation, filler pretreatment, pre-crosslinking, catalytic crosslinking and grinding; the material forms a three-dimensional protection system, the hardness is greater than or equal to 3H, the adhesion is less than or equal to 1 grade, the salt mist resistance is greater than or equal to 1000h, the self-repairing efficiency is greater than or equal to 90%, and the high-low temperature cycle resistance is excellent. The application has comprehensive protection performance, synergistic effects of physical shielding, chemical corrosion inhibition and self-repairing, good adhesion and weather resistance, strong high-low temperature resistance and corrosion resistance, and stable process, and can provide reliable and long-acting protection for magnesium alloys.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal surface protection materials, in particular to a magnesium alloy surface protection material, a preparation method and applications thereof. BACKGROUND

[0002] As the lightest metal structural material, magnesium alloy has high specific strength, good thermal conductivity and excellent electromagnetic shielding performance, and has broad application prospects in the fields of automobiles, aerospace, electronic equipment and the like. However, magnesium alloy has a low standard electrode potential (-2.37 V) and is chemically active, and is prone to corrosion in humid environments, high-temperature and high-humidity environments or environments containing chloride ions. A loose and porous oxide film is easily formed on the surface of magnesium alloy, which cannot effectively prevent the further invasion of corrosive media, thereby severely restricting the engineering application range of magnesium alloy.

[0003] Current magnesium alloy surface protection technologies mainly include chemical conversion film, anodic oxidation, electroplating and coating protection. Although chemical conversion film and anodic oxidation technologies can improve corrosion resistance to some extent, the film layer is usually thin and brittle, and cracks and peeling are easily generated under complex working conditions. The electroplating process has environmental pollution problems, and the adhesion between the plating layer and the magnesium alloy substrate is poor, which is difficult to meet the long-term protection requirements. Coating protection has become one of the most widely used magnesium alloy protection technologies due to its advantages such as simple operation, low cost and good protection effect.

[0004] Existing coating protection materials have many technical defects. Traditional organic coatings such as epoxy resin and polyurethane have certain physical shielding effect, but have poor weather resistance and corrosion resistance, and are prone to aging and failure after long-term use. Fluorocarbon coatings have excellent weather resistance, but have poor adhesion to the magnesium alloy substrate, and lack self-repairing function. Once scratches or cracks occur, corrosive media will quickly penetrate the substrate surface to cause local corrosion.

[0005] The selection and dispersion of functional fillers are the key to the protection performance of the coating. Single fillers such as silicon dioxide and graphene commonly used in existing technologies are difficult to form an effective synergistic protection system. The addition of corrosion inhibitors can improve the chemical protection performance, but traditional corrosion inhibitors have problems such as difficult to control the release rate and poor compatibility with the resin matrix, resulting in unstable coating performance. In addition, the coating has poor high-low temperature cycle performance, and is prone to cracking due to thermal stress when the temperature changes sharply, which affects the protection effect.

[0006] With the rapid development of new energy vehicles, high-end equipment and other fields, higher requirements are put forward for the comprehensive performance of magnesium alloy protective materials, not only excellent corrosion resistance, adhesion and wear resistance, but also self-repairing, high and low temperature resistance, antibacterial and other multi-functional requirements. Therefore, it has important theoretical significance and engineering application value to develop a high-performance magnesium alloy surface protective material with physical shielding, chemical corrosion inhibition and self-repairing functions, to solve the problems of insufficient corrosion resistance, single function and short service life in the prior art. SUMMARY

[0007] (I) Technical problems solved

[0008] In view of the deficiencies of the prior art, the present application provides a magnesium alloy surface protective material, a preparation method and applications thereof.

[0009] (II) Technical solutions

[0010] A magnesium alloy surface protective material, consisting of the following components by weight: fluorocarbon resin matrix: 40-60 parts, functional filler: 30-50 parts, corrosion inhibitor: 5-10 parts, crosslinking agent: 3-8 parts, catalyst: 0.5-2 parts, auxiliary agent: 1-3 parts;

[0011] The fluorocarbon resin matrix is composed of hydroxyl fluorocarbon resin and fluorosilicon modified acrylic resin in a mass ratio of (2-4.5):1; wherein the number average molecular weight of the hydroxyl fluorocarbon resin is 30000-50000; the fluorosilicon modified acrylic resin is prepared by methyl trifluoroacetate, gamma-methacryloxypropyl trimethoxysilane and butyl acrylate in a weight ratio of (30-40):(10-20):(40-60) under the action of azobis isobutyronitrile initiator; the functional filler is composed of nano silicon dioxide, graphene nanosheet and fluorophosphoric acid calcium whisker in a weight ratio of (2-4):(1-2):(2-4); wherein the surface of the nano silicon dioxide is modified by silane coupling agent KH-570, and the modified surface is grafted with methacrylate groups; the graphene nanosheet has a sheet diameter of 1-5 μm and a thickness of 1-10 nm, and the surface is loaded with 5-15 wt% of nano zinc oxide; the fluorophosphoric acid calcium whisker has an aspect ratio of 10-30 and a diameter of 0.1-1 μm, and is prepared by the following reaction:

[0012] 5Ca(NO3)2+3(NH4)2HPO4+NH4F+3NH3H2O→Ca5(PO4)3F↓+10NH4NO3+3H2O

[0013] And the surface is coated with 5-15wt% of rare earth cerium salt; the corrosion inhibitor is composed of 2-mercaptobenzothiazole and rare earth cerium salt; the crosslinking agent is composed of isocyanate trimer and silane coupling agent KH-550 in a weight ratio of (2-5):(1-3); the catalyst is composed of dibutyltin dilaurate and triethylamine in a weight ratio of (1-3):1; and the auxiliary agent is composed of dispersant BYK-163 and leveling agent EFKA-3034 in a weight ratio of 1:1.

[0014] Preferably, 1-3 parts of carbon quantum dot modified nano zinc oxide are further included, the carbon quantum dots are prepared by mixing citric acid and ethylenediamine in a molar ratio of 1:2, pyrolyzing the mixture at 200℃ for 4 hours to obtain carbon quantum dots with a particle size of 5-10nm; and the carbon quantum dot modified nano zinc oxide is prepared by dispersing the carbon quantum dots in ethanol, adding nano zinc oxide, ultrasonic treatment for 2 hours to make the carbon quantum dots uniformly adhere to the surface of the zinc oxide, and then heat treatment at 150℃ for 1 hour to make the hydroxyl groups on the surface of the carbon quantum dots form Zn-O-C bonds with the zinc atoms on the surface of the zinc oxide.

[0015] Preferably, 0.5-2 parts of polydopamine coated montmorillonite are further included, the polydopamine coated montmorillonite is prepared by dispersing sodium-based montmorillonite in deionized water to prepare a 5wt% suspension, adding dopamine hydrochloride, adjusting the pH to 8.5 with a tris-hydroxymethyl aminomethane buffer solution, and stirring at room temperature for 24 hours to make the dopamine oxidize and polymerize on the surface of the montmorillonite to form a polydopamine coating layer with a coating amount of 10-20wt%.

[0016] Preferably, the hydroxyl fluorocarbon resin has a hydroxyl value of 50-100mgKOH / g, a fluorine content of 20-30wt%, and ≥8-CF2-repeating units in the molecular chain; the fluorosilicon modified acrylic resin has a siloxane content of 5-15wt% and is prepared by mixing trifluoroethyl methacrylate, γ-methacryloyloxypropyl trimethoxysilane, and butyl acrylate in a weight ratio of (30-40):(10-20):(40-60), adding 0.5-1wt% of azobisisobutyronitrile as an initiator based on the total mass of the monomers, and reacting at 70-80℃ for 4-6 hours to obtain the fluorosilicon modified acrylic resin; the siloxane segments in the fluorosilicon modified acrylic resin condense with the hydroxyl groups in the fluorocarbon resin to form Si-O-C covalent bonds.

[0017] Preferably, the graphene nanosheets are prepared by the following hydrothermal method: graphene oxide is dispersed in deionized water to prepare a 1 mg / mL solution, zinc nitrate and urea are added, the mass ratio of zinc nitrate to graphene oxide is 1:2, the molar ratio of urea to zinc nitrate is 3:1, the hydrothermal reaction is carried out at 90-100℃ for 6-12 hours, and then hydrazine hydrate is added for reduction treatment to obtain graphene nanosheets loaded with nano-zinc oxide.

[0018] Preferably, the calcium fluorophosphate whiskers are prepared by the following method: dispersing calcium fluorophosphate whiskers in a cerium nitrate solution, adjusting the pH to 8-10 with ammonia, and stirring the reaction at 60-80°C for 2-4 hours to allow the Ce to react. 3+ PO4 on the surface of calcium fluorophosphate whiskers 3- A coordination adsorption reaction occurs, forming a stable coating layer.

[0019] Preferably, the weight ratio of 2-mercaptobenzothiazole to rare earth cerium salt is (1-2):1, forming a synergistic corrosion inhibition system in the coating; when microcracks appear on the magnesium alloy surface, the thiol group in the 2-mercaptobenzothiazole molecule undergoes a complexation reaction with magnesium ions to generate an insoluble chelate protective film, which covers the crack surface and prevents the corrosive medium from further penetrating.

[0020] Preferably, the preparation method of the magnesium alloy surface protective material includes the following steps:

[0021] S1 Preparation of mixed resin: Add hydroxyl fluorocarbon resin and fluorosilicone modified acrylic resin to the reaction vessel in proportion, stir at 50-60℃ for 1-2 hours to fully mix the two resins and form an interpenetrating network structure.

[0022] S2 pretreated filler: Add nano-silica, graphene nanosheets, and calcium fluorophosphate whiskers to a high-speed shearing machine in proportion, and add dispersant BYK-163 at the same time. Shear and disperse at a speed of 5000-10000 rpm for 30-60 minutes, and then perform ultrasonic-assisted dispersion for 15-30 minutes to ensure uniform dispersion of the filler.

[0023] S3 Preparation of slurry: Add the mixed resin obtained in step S1 to the reactor, and slowly add the filler pretreated in step S2 under stirring. Stir at 60-70℃ for 2-4 hours to fully impregnate and disperse the filler in the resin. Then add 2-mercaptobenzothiazole, rare earth cerium salt and crosslinking agent in sequence, and carry out pre-crosslinking reaction at 50-60℃ for 1-2 hours. The degree of pre-crosslinking is controlled by monitoring the viscosity change of the reaction system in real time. When the viscosity reaches 1.5-2.0 times the initial value, the pre-crosslinking reaction is stopped.

[0024] S4 Catalytic Crosslinking: The reaction system temperature is lowered to 40-50℃, and the catalysts dibutyltin dilaurate and triethylamine are added. Stirring is continued for 30-60 minutes to ensure the crosslinking reaction is fully carried out. Then, the material is ground in a sand mill using zirconium beads as the grinding media at a grinding speed of 1500-2000 rpm. The mill is circulated and ground 3-5 times to make the particle size ≤10μm. Finally, the leveling agent EFKA-3034 is added and stirred evenly to obtain the magnesium alloy surface protection material.

[0025] Preferably, the endpoint of the pre-crosslinking reaction in step S3 is determined by real-time monitoring of viscosity changes. Specifically, an online viscometer is installed in the reactor, and the viscosity value is recorded every 5 minutes. When the viscosity value reaches 1.5-2.0 times the initial viscosity value, it is considered the endpoint of the pre-crosslinking reaction, and heating is immediately stopped and the temperature is lowered. In step S4, the sand mill grinding adopts a multi-stage grinding process. The first stage of grinding uses zirconium beads with a diameter of 1 mm and grinds for 2 hours to reduce the particle size of the material to 20-30 μm. The second stage of grinding uses zirconium beads with a diameter of 0.5 mm and grinds for 1-2 hours to further reduce the particle size of the material to ≤10 μm. The particle size of the ground material is analyzed by a laser particle size analyzer to ensure that more than 90% of the particles have a diameter of ≤10 μm.

[0026] Preferably, the magnesium alloy surface protective material is applied to the surface protection of magnesium alloy components such as automobile engine blocks, drone landing gear, and electronic device housings. The specific application method is as follows: first, the surface of the magnesium alloy component is pretreated by degreasing, pickling, and phosphating to remove surface oil and oxide layers; then, the protective material is coated onto the surface of the magnesium alloy component by air spraying or electrostatic spraying, with a coating thickness of 20-50 μm; after coating, it is cured at 120-150℃ for 1-2 hours to form a strong coating.

[0027] (III) Beneficial Technical Effects

[0028] Compared with existing technologies, the beneficial effects of this invention are:

[0029] 1. By using fluorocarbon resin and fluorosilicone modified acrylic resin to form an interpenetrating network matrix, it has both excellent weather resistance and adhesion, overcoming the shortcomings of traditional single resin matrix performance; multi-functional fillers synergistically construct a "core-shell" composite structure, realizing the synergistic effect of physical shielding and chemical protection, effectively blocking the penetration of corrosive media.

[0030] 2. The introduction of functional additives endows the material with multiple protective functions. Carbon quantum dot-modified nano-zinc oxide forms a photocatalytic antibacterial network, improving the surface cleanliness of the coating; polydopamine-coated montmorillonite constructs a labyrinthine barrier structure, significantly reducing the permeability of corrosive media. The corrosion inhibitor system achieves intelligent response through synergistic action, rapidly releasing and forming a protective film when microcracks appear in the coating, achieving self-repair function and extending the material's service life.

[0031] 3. Through optimization methods such as pre-crosslinking control, ultrasonic-assisted dispersion, and multi-stage grinding, the filler is uniformly dispersed, improving the coating's density and performance stability. The coating bonds firmly to the magnesium alloy substrate, effectively resisting thermal and mechanical stresses, and maintaining good integrity even under high and low temperature cycling conditions, preventing protective failure due to cracking. Attached Figure Description

[0032] Figure 1 This is a flowchart of a method for preparing a magnesium alloy surface protective material proposed in this invention;

[0033] Figure 2 This is a line graph comparing the corrosion resistance time of the salt spray test between the examples and the comparative examples;

[0034] Figure 3 This is a bar chart comparing the number of high and low temperature cycles of the examples and comparative examples;

[0035] Figure 4 This is a bar graph comparing the self-healing efficiency and water absorption rate of the examples and comparative examples. Detailed Implementation

[0036] according to Figures 1 to 4 The specific embodiments of the present invention are as follows:

[0037] Example 1

[0038] Raw material preparation

[0039] Hydroxyl fluorocarbon resin: number average molecular weight 40,000, hydroxyl value 75 mg KOH / g, fluorine content 25 wt%, 45 parts; Fluorosilicone modified acrylic resin: siloxane content 10 wt%, number average molecular weight 25,000, 15 parts; Nano silica: particle size 30 nm, specific surface area 200 m² / g. 2 / g, modified with KH-570, grafting rate 10wt%, 15 parts; Graphene nanosheets: 3μm diameter, 5nm thickness, surface loaded with 10wt% nano zinc oxide, 7 parts; Calcium fluorophosphate whiskers: aspect ratio 20, diameter 0.5μm, surface coated with 10wt% cerium nitrate, 18 parts; Corrosion inhibitor: 2-mercaptobenzothiazole 4 parts, cerium nitrate 3 parts; Crosslinking agent: isocyanate trimer 3.5 parts, silane coupling agent KH-550 1.5 parts; Catalyst: dibutyltin dilaurate 0.8 parts, triethylamine 0.4 parts; Additives: dispersant BYK-163 1 parts, leveling agent EFKA-303 4 parts.

[0040] Preparation process

[0041] Preparation of mixed resins: Hydroxyfluorocarbon resin and fluorosilicone modified acrylic resin were added to a reaction vessel, the temperature was set at 55℃, and the mixture was stirred for 1.5 hours to form an interpenetrating network structure.

[0042] Filler pretreatment: Mix nano-silica, graphene nanosheets and calcium fluorophosphate whiskers, add dispersant BYK-163, put it into a high-speed shear machine and shear at 8000 rpm for 45 minutes, and then disperse it with a 500W ultrasonic device for 20 minutes.

[0043] Slurry preparation: The pretreated filler was slowly added to the mixed resin, the temperature was raised to 65℃ and stirred for 3 hours; 2-mercaptobenzothiazole, cerium nitrate, isocyanate trimer and KH-550 were added in sequence, the temperature was raised to 55℃ and the pre-crosslinking reaction was carried out for 1.5 hours. The reaction was stopped when the viscosity reached 1.8 times the initial value by monitoring with an online viscometer.

[0044] Catalytic crosslinking: Cool the reaction system to 45°C, add dibutyltin dilaurate and triethylamine, and stir for 45 minutes; put the material into a sand mill, first grind with zirconium beads with a diameter of 1 mm for 2 hours, then replace with zirconium beads with a diameter of 0.5 mm and grind for 1.5 hours until the particle size of the material is ≤10μm; finally add leveling agent EFKA-3034 and stir evenly.

[0045] Coating process

[0046] Magnesium alloy specimen (AZ31B) pretreatment: ultrasonic cleaning with acetone for 15 minutes to degrease, soaking in 10% H2SO4 solution at room temperature for 5 minutes for acid washing, and then soaking in Zn-Mn phosphating solution at 60℃ for 10 minutes for phosphating.

[0047] Air spraying: The protective material is applied to the surface of the pretreated test piece by air spraying, and the coating thickness is controlled to be 35μm;

[0048] Curing: Place the coated test piece in an oven and cure at 135℃ for 1.5 hours.

[0049] Example 2

[0050] Raw material preparation

[0051] Hydroxyl fluorocarbon resin: number average molecular weight 35,000, hydroxyl value 60 mg KOH / g, fluorine content 22 wt%, 38 parts; Fluorosilicone modified acrylic resin: siloxane content 8 wt%, number average molecular weight 22,000, 12 parts; Nano silica: particle size 20 nm, specific surface area 250 m² / g. 2 / g, modified with KH-570, grafting rate 8wt%, 12 parts; graphene nanosheets: sheet diameter 2μm, thickness 3nm, surface loaded with 8wt% nano zinc oxide, 6 parts; calcium fluorophosphate whiskers: aspect ratio 15, diameter 0.3μm, surface coated with 8wt% cerium nitrate, 15 parts; corrosion inhibitor: 2-mercaptobenzothiazole 3.5 parts, cerium nitrate 2.5 parts; crosslinking agent: isocyanate trimer 3 parts, silane coupling agent KH-550 1 part; catalyst: dibutyltin dilaurate 0.6 parts, triethylamine 0.3 parts; additives: dispersant BYK-163 0.8 parts, leveling agent EFKA-3034 0.8 parts; carbon quantum dot modified nano zinc oxide: 1.5 parts (carbon quantum dot particle size 5-10nm, zinc oxide particle size 20-50nm).

[0052] Preparation process

[0053] Preparation of mixed resins: Hydroxyfluorocarbon resin and fluorosilicone modified acrylic resin were added to a reaction vessel and stirred at 55°C for 1.5 hours to form an interpenetrating network;

[0054] Filler pretreatment: Mix nano-silica, graphene nanosheets, calcium fluorophosphate whiskers, and carbon quantum dot modified nano-zinc oxide, add BYK-163, shear at 8000 rpm for 45 minutes, and ultrasonically disperse at 500W for 20 minutes.

[0055] Slurry preparation: Add the pretreated filler to the mixed resin and stir at 65°C for 3 hours; add corrosion inhibitor and crosslinking agent, and pre-crosslink at 55°C for 1.5 hours, stopping when the viscosity reaches 1.6 times the initial value;

[0056] Catalytic crosslinking: Cool to 45℃, add catalyst and stir for 45 minutes, mill with 1mm zirconium beads for 2 hours, then replace with 0.5mm zirconium beads and mill for 1.5 hours until the particle size is ≤10μm, add leveling agent and stir well.

[0057] Coating process

[0058] Magnesium alloy pretreatment: ultrasonic cleaning with acetone for 15 minutes to degrease, soaking in 10% H2SO4 solution at room temperature for 5 minutes for acid pickling, and then soaking in Zn-Mn phosphating solution at 60℃ for 10 minutes for phosphating.

[0059] Air spraying: The protective material is applied to the surface of the pretreated test piece by air spraying, and the coating thickness is controlled to be 30μm.

[0060] Curing: Place the coated test piece in an oven and cure at 130℃ for 1.8 hours.

[0061] Example 3

[0062] Raw material preparation

[0063] Hydroxyl fluorocarbon resin: number average molecular weight 45,000, hydroxyl value 90 mg KOH / g, fluorine content 28 wt%, 50 parts; Fluorosilicone modified acrylic resin: siloxane content 12 wt%, number average molecular weight 28,000, 15 parts; Nano silica: particle size 40 nm, specific surface area 180 m² / g. 2 / g, KH-570 modified, grafting rate 12wt%, 18 parts; Graphene nanosheets: sheet diameter 4μm, thickness 7nm, loaded with 12wt% nano zinc oxide, 8 parts; Calcium fluorophosphate whiskers: aspect ratio 25, diameter 0.7μm, coated with 12wt% cerium nitrate, 20 parts; Corrosion inhibitor: 2-mercaptobenzothiazole 4.5 parts, cerium nitrate 3.5 parts; Crosslinking agent: isocyanate trimer 4 parts, KH-550 2 parts; Catalyst: dibutyltin dilaurate 1 part, triethylamine 0.5 parts; Additives: BYK-163 1.2 parts, EFKA-3034 1.2 parts; Polydopamine coated montmorillonite: coating amount 15wt%, interlayer spacing 2.8nm, 1 part.

[0064] Preparation process

[0065] Mixed resins: Hydroxyfluorocarbon resin and fluorosilicone modified acrylic resin are added to a reaction vessel and stirred at 55°C for 1.5 hours to form an interpenetrating network;

[0066] Filler pretreatment: Mix nano-silica, graphene nanosheets, calcium fluorophosphate whiskers, and polydopamine-coated montmorillonite, add BYK-163, shear at 8000 rpm for 45 minutes, and ultrasonically disperse at 500W for 20 minutes.

[0067] Slurry preparation: Add the pretreated filler to the mixed resin and stir at 65°C for 3 hours; add corrosion inhibitor and crosslinking agent, and pre-crosslink at 55°C for 1.5 hours, stopping when the viscosity reaches 1.9 times the initial value;

[0068] Catalytic crosslinking: Cool to 45℃, add catalyst and stir for 45 minutes, mill with 1mm zirconium beads for 2 hours, then replace with 0.5mm zirconium beads and mill for 1.5 hours until the particle size is ≤10μm, add leveling agent and stir well.

[0069] Coating process

[0070] Magnesium alloy pretreatment: ultrasonic cleaning with acetone for 15 minutes to degrease, soaking in 10% H2SO4 solution at room temperature for 5 minutes for acid pickling, and then soaking in Zn-Mn phosphating solution at 60℃ for 10 minutes for phosphating.

[0071] Air spraying: The protective material is applied to the surface of the pretreated test piece by air spraying, and the coating thickness is controlled to be 40μm;

[0072] Curing: Place the coated test piece in an oven and cure at 140℃ for 1.2 hours.

[0073] Example 4

[0074] Raw material preparation

[0075] Hydroxyl fluorocarbon resin: 50,000 molecular weight, 100 mg KOH / g hydroxyl value, 30 wt% fluorine, 55 parts; Fluorosilicone modified acrylic resin: 15 wt% siloxane, 30,000 molecular weight, 15 parts; Nano silica: 50 nm particle size, 150 μm 2 / g, 15wt% grafting rate, take 20 parts; Graphene: 5μm sheet diameter, 10nm thickness, 15wt% zinc oxide loading, take 10 parts; Calcium fluorophosphate whiskers: 30 aspect ratio, 1μm diameter, 15wt% cerium coating, take 20 parts; Corrosion inhibitor: 2-mercaptobenzothiazole 5 parts, cerium nitrate 5 parts; Crosslinking agent: isocyanate trimer 5 parts, KH-550 3 parts; Catalyst: dibutyltin dilaurate 1.2 parts, triethylamine 0.6 parts; Additives: BYK-163 1.5 parts, EFKA-3034 1.5 parts; Carbon quantum dot zinc oxide 3 parts, polydopamine montmorillonite (20wt% coating, 3.0nm interlayer spacing) 2 parts.

[0076] Preparation process

[0077] Mixed resins: Hydroxyfluorocarbon resin and fluorosilicone modified acrylic resin are added to a reaction vessel and stirred at 55°C for 1.5 hours to form an interpenetrating network;

[0078] Filler pretreatment: Mix nano silica, graphene, calcium fluorophosphate whiskers, carbon quantum dot zinc oxide, and polydopamine montmorillonite, add BYK-163, shear at 8000 rpm for 45 minutes, and ultrasonically disperse at 500W for 20 minutes.

[0079] Slurry preparation: Add the pretreated filler to the mixed resin and stir at 65°C for 3 hours; add corrosion inhibitor and crosslinking agent, and pre-crosslink at 55°C for 1.5 hours, stopping when the viscosity reaches 2.0 times the initial value;

[0080] Catalytic crosslinking: Cool to 45℃, add catalyst and stir for 45 minutes. Put the material into a sand mill and grind it for 2 hours with 1mm diameter zirconium beads, then replace with 0.5mm diameter zirconium beads and grind for 1.5 hours until the material particle size is ≤10μm. Finally, add leveling agent EFKA-3034 and stir evenly.

[0081] Coating process

[0082] Magnesium alloy pretreatment: ultrasonic cleaning with acetone for 15 minutes to degrease, soaking in 10% H2SO4 solution at room temperature for 5 minutes for acid pickling, and then soaking in Zn-Mn phosphating solution at 60℃ for 10 minutes for phosphating.

[0083] Air spraying: The protective material is applied to the surface of the pretreated test piece by air spraying, and the coating thickness is controlled to be 50μm;

[0084] Curing: Place the coated test piece in an oven and cure at 150°C for 1 hour.

[0085] Comparative Example

[0086] Raw material preparation

[0087] Hydroxyfluorocarbon resin: 60 parts; Nano silica: unmodified, particle size 30nm, 30 parts; 2-mercaptobenzothiazole 5 parts; Isocyanate trimer 5 parts; Dibutyltin dilaurate 1 part; BYK-163 1 part; EFKA-303 4 1 parts.

[0088] Preparation process

[0089] Hydroxyfluorocarbon resin and nano-silica were stirred at 65°C for 3 hours; 2-mercaptobenzothiazole, isocyanate trimer, and dibutyltin dilaurate were added and stirred for 1 hour; the mixture was then milled until the particle size was ≤10μm, and the additives were added and stirred evenly.

[0090] Coating process

[0091] Magnesium alloy pretreatment: ultrasonically clean with acetone for 15 minutes to degrease, soak in 10% H2SO4 solution at room temperature for 5 minutes for pickling, and then soak in Zn-Mn phosphating solution at 60℃ for 10 minutes for phosphating; air spraying: apply the protective material to the surface of the pretreated test piece by air spraying, and control the coating thickness to 35μm; curing: place the coated test piece in an oven and cure at 135℃ for 1.5 hours.

[0092] The basic protection performance of the examples and comparative examples is compared in the table below:

[0093] Table 1

[0094] Item Example 1 Example 2 Example 3 Example 4 Comparative Example Salt spray test corrosion resistance time (h) 1200 1150 1300 1400 450 Hardness (pencil hardness) 4H 3H 4H 5H 2H Adhesion (crosshatch method) 0 level 0 level 0 level 0 level 2 level

[0095] The salt spray resistance time of the example is 2.5-3 times that of the comparative example, and the hardness and adhesion are significantly better. The synergistic effect of functional fillers and process optimization improves the basic protective performance, while the comparative example has insufficient performance due to its single composition.

[0096] The functional characteristics of the embodiments and comparative examples are compared in the table below:

[0097] Table 2

[0098] Item Example 1 Example 2 Example 3 Example 4 Comparative Example Self-repairing efficiency (%) 90 92 95 97 0 High-low temperature cycle resistance (times) 500 500 600 600 200 Water absorption rate (24 h, %) 0.3 0.25 0.2 0.15 1.2

[0099] The embodiment exhibits high self-healing capabilities and resistance to high and low temperature cycling, with low water absorption. Multifunctional additives and barrier structures play a crucial role, while the comparative embodiment lacks functional design and shows a significant performance difference.

[0100] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A magnesium alloy surface protective material, characterized in that, It is composed of the following components in parts by weight: fluorocarbon resin matrix: 40-60 parts, functional filler: 30-50 parts, corrosion inhibitor: 5-10 parts, crosslinking agent: 3-8 parts, catalyst: 0.5-2 parts, and additives: 1-3 parts. The fluorocarbon resin matrix is ​​composed of hydroxyl fluorocarbon resin and fluorosilicone modified acrylic resin in a mass ratio of (2-4.5):1; wherein the number average molecular weight of the hydroxyl fluorocarbon resin is 30,000-50,000; the fluorosilicone modified acrylic resin is prepared by reacting trifluoroethyl methacrylate, γ-methacryloyloxypropyltrimethoxysilane and butyl acrylate in a weight ratio of (30-40):(10-20):(40-60) with an azobisisobutyronitrile initiator; the functional filler is composed of nano-di(2-4.5)-butyl acrylate. The composition comprises silicon dioxide, graphene nanosheets, and calcium fluorophosphate whiskers in a weight ratio of (2-4):(1-2):(2-4); wherein the surface of the nano-silica is modified with silane coupling agent KH-570, and the modified surface is grafted with methacrylate groups; the graphene nanosheets have a diameter of 1-5 μm, a thickness of 1-10 nm, and are loaded with 5-15 wt% nano-zinc oxide; the calcium fluorophosphate whiskers have an aspect ratio of 10-30 and a diameter of 0.1-1 μm, and are prepared by the following reaction: 5Ca(NO3)2+3(NH4)2+HPO4+NH4F+3NH3H2O→Ca5(PO4)3F↓+10NH4NO3+3H2O The surface is coated with 5-15 wt% rare earth cerium salt; the corrosion inhibitor is composed of 2-mercaptobenzothiazole and rare earth cerium salt; the crosslinking agent is composed of isocyanate trimer and silane coupling agent KH-550 in a weight ratio of (2-5):(1-3); the catalyst is composed of dibutyltin dilaurate and triethylamine in a weight ratio of (1-3):1; the additives are composed of dispersant BYK-163 and leveling agent EFKA-3034 in a weight ratio of 1:

1.

2. The magnesium alloy surface protective material according to claim 1, characterized in that, It also includes 1-3 parts of carbon quantum dot modified nano zinc oxide, wherein the carbon quantum dots are prepared by the following method: citric acid and ethylenediamine are mixed at a molar ratio of 1:2 and pyrolyzed at 200°C for 4 hours to obtain carbon quantum dots with a particle size of 5-10 nm; the carbon quantum dot modified nano zinc oxide is prepared by the following steps: carbon quantum dots are dispersed in ethanol, nano zinc oxide is added, and ultrasonic treatment is performed for 2 hours to make the carbon quantum dots uniformly adhere to the zinc oxide surface, and then heat treatment is performed at 150°C for 1 hour to form Zn-OC bonds between the hydroxyl groups on the surface of the carbon quantum dots and the zinc atoms on the surface of the zinc oxide.

3. The magnesium alloy surface protective material according to claim 2, characterized in that, It also includes 0.5-2 parts of polydopamine-coated montmorillonite, which is prepared by the following method: dispersing sodium montmorillonite in deionized water to prepare a 5 wt% suspension, adding dopamine hydrochloride, adjusting the pH to 8.5 with tris(hydroxymethyl)aminomethane buffer solution, stirring and reacting at room temperature for 24 hours to allow dopamine to oxidatively polymerize on the surface of montmorillonite to form a polydopamine coating layer with a coating amount of 10-20 wt%.

4. The magnesium alloy surface protective material according to claim 3, characterized in that, The hydroxyl fluorocarbon resin has a hydroxyl value of 50-100 mgKOH / g, a fluorine content of 20-30 wt%, and contains ≥8 -CF2- repeating units in its molecular chain; the fluorosilicone-modified acrylic resin has a siloxane content of 5-15 wt% and is prepared by the following method: trifluoroethyl methacrylate, γ-methacryloyloxypropyltrimethoxysilane, and butyl acrylate are mixed in a weight ratio of (30-40):(10-20):(40-60), and 0.5-1 wt% of azobisisobutyronitrile is added as an initiator. The mixture is reacted at 70-80℃ for 4-6 hours to obtain the fluorosilicone-modified acrylic resin; the siloxane segments in the fluorosilicone-modified acrylic resin undergo a condensation reaction with the hydroxyl groups in the fluorocarbon resin to form Si-OC covalent bonds.

5. The magnesium alloy surface protective material according to claim 4, characterized in that, The graphene nanosheets were prepared by the following hydrothermal method: graphene oxide was dispersed in deionized water to prepare a 1 mg / mL solution, zinc nitrate and urea were added, the mass ratio of zinc nitrate to graphene oxide was 1:2, and the molar ratio of urea to zinc nitrate was 3:

1. The hydrothermal reaction was carried out at 90-100℃ for 6-12 hours, and then hydrazine hydrate was added for reduction treatment to obtain graphene nanosheets loaded with nano-zinc oxide.

6. The magnesium alloy surface protective material according to claim 5, characterized in that, The calcium fluorophosphate whiskers are prepared by the following method: calcium fluorophosphate whiskers are dispersed in a cerium nitrate solution, the pH is adjusted to 8-10 with ammonia, and the mixture is stirred at 60-80°C for 2-4 hours to allow the Ce2 phosphate to react. 3+ PO4 on the surface of calcium fluorophosphate whiskers 3- A coordination adsorption reaction occurs, forming a stable coating layer.

7. The magnesium alloy surface protective material according to claim 6, characterized in that, The weight ratio of 2-mercaptobenzothiazole to rare earth cerium salt is (1-2):1, forming a synergistic corrosion inhibition system in the coating. When microcracks appear on the surface of the magnesium alloy, the thiol group in the 2-mercaptobenzothiazole molecule undergoes a complexation reaction with magnesium ions to generate an insoluble chelate protective film that covers the crack surface and prevents further intrusion of corrosive media.

8. A method for preparing the magnesium alloy surface protective material according to claim 7, characterized in that, Includes the following steps: S1 Preparation of mixed resin: Add hydroxyl fluorocarbon resin and fluorosilicone modified acrylic resin to the reaction vessel in proportion, stir at 50-60℃ for 1-2 hours to fully mix the two resins and form an interpenetrating network structure. S2 pretreated filler: Add nano-silica, graphene nanosheets, and calcium fluorophosphate whiskers to a high-speed shearing machine in proportion, and add dispersant BYK-163 at the same time. Shear and disperse at a speed of 5000-10000 rpm for 30-60 minutes, and then perform ultrasonic-assisted dispersion for 15-30 minutes to ensure uniform dispersion of the filler. S3 Preparation of slurry: Add the mixed resin obtained in step S1 to the reactor, and slowly add the filler pretreated in step S2 under stirring. Stir at 60-70℃ for 2-4 hours to fully impregnate and disperse the filler in the resin. Then add 2-mercaptobenzothiazole, rare earth cerium salt and crosslinking agent in sequence, and carry out pre-crosslinking reaction at 50-60℃ for 1-2 hours. The degree of pre-crosslinking is controlled by monitoring the viscosity change of the reaction system in real time. When the viscosity reaches 1.5-2.0 times the initial value, the pre-crosslinking reaction is stopped. S4 Catalytic Crosslinking: The reaction system temperature is lowered to 40-50℃, and the catalysts dibutyltin dilaurate and triethylamine are added. Stirring is continued for 30-60 minutes to ensure the crosslinking reaction is fully carried out. Then, the material is ground in a sand mill using zirconium beads as the grinding media at a grinding speed of 1500-2000 rpm. The mill is circulated and ground 3-5 times to make the particle size ≤10μm. Finally, the leveling agent EFKA-3034 is added and stirred evenly to obtain the magnesium alloy surface protection material.

9. The method for preparing the magnesium alloy surface protective material according to claim 8, characterized in that, The endpoint of the pre-crosslinking reaction in step S3 is determined by real-time monitoring of viscosity changes. Specifically, an online viscometer is installed in the reactor, and the viscosity value is recorded every 5 minutes. When the viscosity value reaches 1.5-2.0 times the initial viscosity value, it is considered the endpoint of the pre-crosslinking reaction, and heating is immediately stopped and the temperature is lowered. In step S4, the sand mill grinding adopts a multi-stage grinding process. The first stage of grinding uses zirconium beads with a diameter of 1 mm and grinds for 2 hours to reduce the particle size of the material to 20-30 μm. The second stage of grinding uses zirconium beads with a diameter of 0.5 mm and grinds for 1-2 hours to further reduce the particle size of the material to ≤10 μm. The particle size of the ground material is analyzed by a laser particle size analyzer to ensure that more than 90% of the particles have a diameter of ≤10 μm.

10. An application of the magnesium alloy surface protective material according to claim 7, characterized in that, This material is used for surface protection of magnesium alloy components such as automotive engine blocks, drone landing gear, and electronic device housings. The specific application method is as follows: First, the surface of the magnesium alloy component is pretreated by degreasing, pickling, and phosphating to remove surface oil and oxide layers. Then, the protective material is applied to the surface of the magnesium alloy component by air spraying or electrostatic spraying, with a coating thickness of 20-50μm. After coating, it is cured at 120-150℃ for 1-2 hours to form a strong coating.

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