Magnesium alloy surface protection material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of metal surface protection materials, in particular to a magnesium alloy surface protection material, a preparation method and application of the magnesium alloy surface protection material, and the magnesium alloy surface protection material comprises 40-60 parts of fluorocarbon-containing resin matrix, 30-50 parts of functional filler, 5-10 parts of corrosion inhibitor, 3-8 parts of cross-linking agent, 0.5-2 parts of catalyst and 1-3 parts of assistant. The functional filler is modified to form a core-shell structure, nano-zinc oxide is loaded on graphene, and rare earth cerium salt is coated with calcium fluorophosphate whiskers; the preparation process comprises the steps of 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 adhesive force is less than or equal to grade 1, 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 The coating is comprehensive in protection performance, good in adhesive force and weather resistance, high in high and low temperature resistance and corrosion resistance and stable in process, has a synergistic effect of physical shielding, chemical corrosion inhibition and self-repairing, and provides reliable and long-acting protection for magnesium alloy.

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 to the surface of the substrate 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 solution of 1 mg / mL, 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, hydrothermal reaction is carried out at 90-100℃ for 6-12 hours, then hydrazine hydrate is added for reduction treatment, and graphene nanosheets loaded with nano zinc oxide are obtained.

[0018] Preferably, the calcium fluorophosphate whiskers are prepared by the following method: calcium fluorophosphate whiskers are dispersed in a cerium nitrate solution, the pH value is adjusted to 8-10 with ammonia water, and stirring reaction is carried out at 60-80℃ for 2-4 hours, then Ce 3+ and PO4 3- on the surface of the calcium fluorophosphate whiskers occur coordination adsorption reaction to form 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 surface of the magnesium alloy, the mercapto group in the 2-mercaptobenzothiazole molecule reacts with magnesium ions to form an insoluble chelate protective film, covering the surface of the cracks and preventing further intrusion of corrosive media.

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

[0021] S1: Prepare a mixed resin: add hydroxyl fluorocarbon resin and fluorosilicon modified acrylic resin into a reaction kettle in proportion, stir at 50-60℃ for 1-2 hours to fully mix the two resins and form an interpenetrating network structure;

[0022] S2: Pretreat the fillers: add nano silicon dioxide, graphene nanosheets, and calcium fluorophosphate whiskers into a high-speed shearing machine in proportion, add a dispersant BYK-163 at the same time, shear and disperse at a speed of 5000-10000 rpm for 30-60 minutes, then perform ultrasonic assisted dispersion for 15-30 minutes to ensure uniform dispersion of the fillers;

[0023] S3: Prepare a slurry: add the mixed resin prepared in step S1 into a reaction kettle, slowly add the pretreated fillers in step S2 under stirring, stir at 60-70℃ for 2-4 hours to fully immerse and disperse the fillers in the resin; then sequentially add 2-mercaptobenzothiazole, rare earth cerium salt, and a crosslinking agent, and perform pre-crosslinking reaction at 50-60℃ for 1-2 hours, control the degree of pre-crosslinking by real-time monitoring of the viscosity change of the reaction system, and stop the pre-crosslinking reaction when the viscosity reaches 1.5-2.0 times the initial value;

[0024] S4 catalytic crosslinking: the temperature of the reaction system is reduced to 40-50 DEG C, the catalyst dibutyl tin dilaurate and triethylamine are added, and the stirring is continued for 30-60 minutes, so that the crosslinking reaction is fully carried out; then the material is ground through a sand mill, the zirconium beads are used as the grinding medium, the grinding rate is 1500-2000 rpm, and the material is circularly ground for 3-5 times, so that the particle size of the material is less than or equal to 10 microns; finally, the leveling agent EFKA-3034 is added, and the stirring is uniform, so that the magnesium alloy surface protection material is obtained.

[0025] Preferably, the end point of the pre-crosslinking reaction in the step S3 is determined by monitoring the viscosity change in real time, and the specific method is that an online viscometer is installed in the reaction kettle, the viscosity value is recorded every 5 minutes, when the viscosity value reaches 1.5-2.0 times of the initial viscosity value, the pre-crosslinking reaction is considered to be completed, and the heating is stopped immediately and the temperature is reduced; the sand mill grinding in the step S4 adopts a multi-stage grinding process, the zirconium beads with a diameter of 1 mm are used for the first-stage grinding for 2 hours, so that the particle size of the material is reduced to 20-30 microns; the zirconium beads with a diameter of 0.5 mm are used for the second-stage grinding for 1-2 hours, so that the particle size of the material is further reduced to less than or equal to 10 microns; the particle size of the ground material is analyzed by a laser particle size analyzer, and it is ensured that more than 90% of the particles have a particle size less than or equal to 10 microns.

[0026] Preferably, the magnesium alloy surface protection material is applied to the surface protection of magnesium alloy parts such as automobile engine cylinder blocks, unmanned aerial vehicle landing gears and electronic equipment housings; and the specific application method is that the surface of the magnesium alloy part is pretreated by degreasing, pickling and phosphating, so that the surface oil stains and oxide layers are removed; then the protection material is coated on the surface of the magnesium alloy part by air spraying or electrostatic spraying, and the coating thickness is 20-50 microns; and after the coating, the protection material is cured at 120-150 DEG C for 1-2 hours, so that a firm coating is formed.

[0027] (Three) beneficial technical effects

[0028] Compared with the prior art, the beneficial effects of the present application are:

[0029] 1. By adopting the interpenetrating network matrix formed by fluorocarbon resin and fluorosilicon modified acrylic resin, excellent weather resistance and adhesion are achieved, and the performance short board of the traditional single resin matrix is overcome; the multi-element functional filler cooperatively constructs the "core-shell" composite structure, realizes the synergistic effect of physical shielding and chemical protection, and effectively blocks the penetration of corrosion medium.

[0030] 2. The introduction of functional additives endows the material with multiple protection functions. Carbon quantum dots modified nano zinc oxide forms a photocatalytic antibacterial network, improving the cleanliness of the coating surface; polydopamine coated montmorillonite constructs a labyrinth barrier structure, significantly reducing the permeability of aggressive media. The corrosion inhibitor system realizes intelligent response through synergistic effect, quickly releases and forms a protective film when microcracks appear on the coating, realizes self-repairing function, and prolongs the service life of the material.

[0031] 3. Through pre-crosslinking control, ultrasonic assisted dispersion and multi-stage grinding and other optimization methods, the uniform dispersion of fillers is ensured, and the compactness and performance stability of the coating are improved. The coating is firmly combined with the magnesium alloy substrate, effectively resists thermal stress and mechanical stress, and can still maintain good integrity under high and low temperature cycle conditions, avoiding the failure of protection due to cracking. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a preparation method flow chart of a magnesium alloy surface protection material according to the present application;

[0033] Figure 2 is a salt spray test corrosion resistance time fold line comparison chart of the examples and the comparative examples;

[0034] Figure 3 is a high and low temperature cycle resistance number columnar comparison chart of the examples and the comparative examples;

[0035] Figure 4 is a self-repairing efficiency and water absorption rate columnar fold line comparison chart of the examples and the comparative examples. DETAILED DESCRIPTION

[0036] According to Figures 1 to 4 , the specific embodiments of the present application are as follows:

[0037] Example 1

[0038] Raw material preparation

[0039] Hydroxyl fluorocarbon resin: number average molecular weight 40,000, hydroxyl value 75 mgKOH / g, fluorine content 25wt%, take 45 parts; fluorosilicon modified acrylic resin: siloxane content 10wt%, number average molecular weight 25,000, take 15 parts; nano silicon dioxide: particle size 30nm, specific surface area 200m 2 / g, modified by KH-570, grafting rate 10wt%, take 15 parts; graphene nanosheet: sheet diameter 3 pm, thickness 5 nm, surface load 10wt% nano zinc oxide, take 7 parts; calcium fluorophosphate whisker: aspect ratio 20, diameter 0.5 pm, surface coated with 10wt% cerium nitrate, take 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: dibutyl tin dilaurate 0.8 parts, triethylamine 0.4 parts; auxiliary agent: dispersant BYK-163 1 part, leveling agent EFKA-3034 1 part.

[0040] Preparation process

[0041] Mixed resin preparation: hydroxyl fluorocarbon resin and fluorosilicon modified acrylic resin are added to the reaction kettle, the temperature is set to 55°C, and stirring is carried out for 1.5 hours to form an interpenetrating network structure;

[0042] Filler pretreatment: nano silicon dioxide, graphene nanosheet, and calcium fluorophosphate whisker are mixed, BYK-163 dispersant is added, and the mixture is put into a high-speed shearing machine at a speed of 8000 rpm for shearing for 45 minutes, and then an ultrasonic device with a power of 500 W is used for dispersion for 20 minutes;

[0043] Slurry preparation: the pretreated filler is slowly added to the mixed resin, the temperature is raised to 65°C, and stirring is carried out for 3 hours; 2-mercaptobenzothiazole, cerium nitrate, isocyanate trimer, and KH-550 are sequentially added, the temperature is raised to 55°C, and pre-crosslinking reaction is carried out for 1.5 hours; the viscosity is monitored by an online viscometer, and the reaction is stopped when the viscosity reaches 1.8 times the initial value;

[0044] Catalytic crosslinking: the reaction system is cooled to 45°C, dibutyl tin dilaurate and triethylamine are added, and stirring is carried out for 45 minutes; the material is put into a sand mill, first ground with zirconium beads with a diameter of 1 mm for 2 hours, then ground with zirconium beads with a diameter of 0.5 mm for 1.5 hours, until the particle size of the material is ≤10 pm; finally, leveling agent EFKA-3034 is added and stirred uniformly.

[0045] Coating process

[0046] Magnesium alloy test piece (AZ31B) pretreatment: degreasing by ultrasonic cleaning with acetone for 15 minutes, pickling by immersing in 10% H2SO4 solution at room temperature for 5 minutes, phosphating by immersing in Zn-Mn series phosphating solution at 60°C for 10 minutes;

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

[0048] Curing: the coated test piece is put into an oven and cured at 135°C for 1.5 hours.

[0049] Example 2

[0050] Raw material preparation

[0051] Hydroxyl fluorocarbon resin: number average molecular weight 35,000, hydroxyl value 60 mgKOH / g, fluorine content 22wt%, take 38 parts; fluorosilicon modified acrylic resin: siloxane content 8wt%, number average molecular weight 22,000, take 12 parts; nanometer silicon dioxide: particle size 20nm, specific surface area 250m 2 / g, modified by KH-570, grafting rate 8wt%, take 12 parts; graphene nanosheet: sheet diameter 2μm, thickness 3nm, surface loaded with 8wt% nanometer zinc oxide, take 6 parts; fluorophosphoric calcium whisker: aspect ratio 15, diameter 0.3μm, surface coated with 8wt% cerium nitrate, take 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; auxiliary agent: dispersant BYK-163 0.8 parts, leveling agent EFKA-303 40.8 parts; carbon quantum dot modified nanometer zinc oxide: 1.5 parts (carbon quantum dot particle size 5-10nm, zinc oxide particle size 20-50nm).

[0052] Preparation process

[0053] Mixed resin preparation: hydroxyl fluorocarbon resin and fluorosilicon modified acrylic resin are added to the reaction kettle, stirred at 55℃ for 1.5 hours to form an interpenetrating network;

[0054] Filler pretreatment: nanometer silicon dioxide, graphene nanosheet, fluorophosphoric calcium whisker, carbon quantum dot modified nanometer zinc oxide are mixed, BYK-163 is added, sheared at 8000rpm for 45 minutes, and ultrasonically dispersed at 500W for 20 minutes;

[0055] Slurry preparation: the pretreated filler is added to the mixed resin, stirred at 65℃ for 3 hours; the corrosion inhibitor and crosslinking agent are added, and pre-crosslinked at 55℃ for 1.5 hours, and the viscosity is stopped when it reaches 1.6 times the initial value;

[0056] Catalytic crosslinking: the temperature is lowered to 45℃, the catalyst is added and stirred for 45 minutes, 1mm zirconium bead is used for sanding for 2 hours, 0.5mm zirconium bead is used for sanding for 1.5 hours until the particle size is ≤10μm, and the leveling agent is stirred evenly.

[0057] Coating process

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

[0059] Air spray: the protective material is coated on the surface of the pretreated test piece by air spraying, and the coating thickness is controlled to be 30 μm;

[0060] Curing: the coated test piece is placed in an oven and cured 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 mgKOH / g, fluorine content 28 wt%, take 50 parts; fluorosilicon modified acrylic resin: siloxane content 12 wt%, number average molecular weight 28,000, take 15 parts; nanometer silicon dioxide: particle size 40 nm, specific surface area 180 m 2 / g, KH-570 modified, grafting rate 12 wt%, take 18 parts; graphene nanosheet: sheet diameter 4 μm, thickness 7 nm, loaded with 12 wt% nanometer zinc oxide, take 8 parts; fluorophosphoric calcium whisker: aspect ratio 25, diameter 0.7 μm, coated with 12 wt% cerium nitrate, take 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 part; auxiliary agent: BYK-163 1.2 parts, EFKA-3034 1.2 parts; polydopamine coated montmorillonite: coating amount 15 wt%, interlayer spacing 2.8 nm, take 1 part.

[0064] Preparation process

[0065] Mixed resin: hydroxyl fluorocarbon resin and fluorosilicon modified acrylic resin are added to the reaction kettle, stirred at 55℃ for 1.5 hours to form an interpenetrating network;

[0066] Filler pretreatment: nanometer silicon dioxide, graphene nanosheet, fluorophosphoric calcium whisker, and polydopamine coated montmorillonite are mixed, BYK-163 is added, sheared at 8000 rpm for 45 minutes, and ultrasonically dispersed at 500 W for 20 minutes;

[0067] Slurry preparation: the pretreated filler is added to the mixed resin, stirred at 65℃ for 3 hours; the corrosion inhibitor and crosslinking agent are added, and pre-crosslinked at 55℃ for 1.5 hours, and the stirring is stopped when the viscosity reaches 1.9 times the initial value;

[0068] Catalytic crosslinking: the temperature is lowered to 45℃, the catalyst is added and stirred for 45 minutes, 1 mm zirconium bead is used for sanding for 2 hours, 0.5 mm zirconium bead is used for sanding for 1.5 hours until the particle size is ≤10 μm, and the leveling agent is stirred evenly.

[0069] Coating process

[0070] Magnesium alloy pretreatment: degreasing with acetone ultrasonic cleaning for 15 minutes, soaking in 10% H2SO4 solution at room temperature for 5 minutes, phosphating in Zn-Mn series phosphating solution at 60°C for 10 minutes;

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

[0072] Curing: the coated test piece is placed in an oven and cured at 140°C for 1.2 hours.

[0073] Example 4

[0074] Raw material preparation

[0075] Hydroxyl fluorocarbon resin: 50,000 molecular weight, 100 mgKOH / g hydroxyl value, 30 wt% fluorine, 55 parts; fluorosilicon modified acrylic resin: 15 wt% siloxane, 30,000 molecular weight, 15 parts; nanometer silicon dioxide: 50 nm particle size, 150 m 2 / g, 15 wt% grafting rate, 20 parts; graphene: 5 μm flake diameter, 10 nm thickness, 15 wt% zinc oxide loading, 10 parts; fluorophosphoric calcium whisker: 30 aspect ratio, 1 μm diameter, 15 wt% cerium coating, 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; auxiliary agent: BYK-163 1.5 parts, EFKA-3034 1.5 parts; carbon quantum dot zinc oxide 3 parts, polydopamine montmorillonite (20 wt% coating, 3.0 nm interlayer spacing) 2 parts.

[0076] Preparation process

[0077] Mixed resin: hydroxyl fluorocarbon resin and fluorosilicon modified acrylic resin are added to the reaction kettle, stirred at 55°C for 1.5 hours to form an interpenetrating network;

[0078] Filler pretreatment: nanometer silicon dioxide, graphene, fluorophosphoric calcium whisker, carbon quantum dot zinc oxide, and polydopamine montmorillonite are mixed, BYK-163 is added, sheared at 8000 rpm for 45 minutes, and ultrasonically dispersed at 500 W for 20 minutes;

[0079] Slurry preparation: pretreated fillers are added to the mixed resin, stirred at 65°C for 3 hours; corrosion inhibitor and crosslinking agent are added, and pre-crosslinking is carried out at 55°C for 1.5 hours, and the viscosity is stopped when it reaches 2.0 times the initial value;

[0080] Catalytic crosslinking: cooling to 45℃, adding catalyst and stirring for 45 minutes, putting the material into a sand mill, first grinding with zirconium beads of 1mm in diameter for 2 hours, then grinding with zirconium beads of 0.5mm in diameter for 1.5 hours until the particle size of the material is ≤10μm; finally adding leveling agent EFKA-3034 and stirring uniformly.

[0081] Coating process

[0082] Magnesium alloy pretreatment: degreasing by ultrasonic cleaning with acetone for 15 minutes, pickling by immersing in 10% H2SO4 solution at room temperature for 5 minutes, phosphating by immersing in Zn-Mn series phosphating solution at 60℃ for 10 minutes;

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

[0084] Curing: the coated test piece is put into an oven and cured at 150℃ for 1 hour.

[0085] Comparative example

[0086] Raw material preparation

[0087] Hydroxyl fluorocarbon resin: 60 parts; nano-silicon dioxide: unmodified, particle size 30nm, 30 parts; 2-mercaptobenzothiazole 5 parts; isocyanate trimer 5 parts; dibutyltin dilaurate 1 part; BYK-163 1 part, EFKA-3034 1 part.

[0088] Preparation process

[0089] Hydroxyl fluorocarbon resin and nano-silicon dioxide are stirred at 65℃ for 3 hours; 2-mercaptobenzothiazole, isocyanate trimer, and dibutyltin dilaurate are added and stirred for 1 hour; sand grinding to a particle size ≤10μm, and adding additives and stirring uniformly.

[0090] Coating process

[0091] Magnesium alloy pretreatment: degreasing by ultrasonic cleaning with acetone for 15 minutes, pickling by immersing in 10% H2SO4 solution at room temperature for 5 minutes, phosphating by immersing in Zn-Mn series phosphating solution at 60℃ for 10 minutes; air spraying: the protective material is coated on the surface of the pretreated test piece by air spraying, and the coating thickness is controlled to be 35μm; curing: the coated test piece is put into an oven and cured at 135℃ for 1.5 hours.

[0092] The basic protection performance of the examples and the comparative example is compared as follows:

[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 embodiment is 2.5-3 times that of the comparative example, and the hardness and adhesion are significantly better. The functional filler synergizes with process optimization to improve the basic protection performance. The comparative example has insufficient performance due to single composition.

[0096] The functional property indicators of the embodiment and the comparative example are compared as follows:

[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 has high-efficiency self-repairing capability and high and low temperature cycle resistance, and low water absorption. The multi-element functional additive and the barrier structure play a key role. The comparative example has no functional design, and the performance gap is significant.

[0100] 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, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A magnesium alloy surface protective material, characterized in that: The invention 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, auxiliary agent: 1-3 parts; The fluorocarbon resin matrix is ​​composed of a hydroxyl fluorocarbon resin and a 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 trifluoroethyl methacrylate, γ-methacryloyloxypropyltrimethoxysilane and butyl acrylate in a weight ratio of (30-40):(10-20):(40-60) under the action of azobisisobutyronitrile initiator; the functional filler is composed of nano-difluoromethane Silicon oxide, graphene nanosheets, and calcium fluorophosphate whiskers are composed in a weight ratio of (2-4):(1-2):(2-4); wherein the surface of the nano-silicon dioxide is modified with a silane coupling agent KH-570, and methacrylate groups are grafted onto the surface after modification; the graphene nanosheets have a sheet diameter of 1-5 μm, a thickness of 1-10 nm, and are loaded with 5-15 wt% of nano-zinc oxide on the surface; and 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 5-15wt% of a rare earth cerium salt; the corrosion inhibitor consists of 2-mercaptobenzothiazole and a rare earth cerium salt; the crosslinking agent consists of an isocyanate trimer and a silane coupling agent KH-550 in a weight ratio of (2-5):(1-3); the catalyst consists of dibutyltin dilaurate and triethylamine in a weight ratio of (1-3):1; and the auxiliary agent consists of a dispersant BYK-163 and a 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: The invention 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 in a molar ratio of 1:2, and pyrolysis reaction is carried out at 200°C for 4 hours to obtain carbon quantum dots with a particle size of 5-10nm; 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, ultrasonic treatment is performed for 2 hours to uniformly attach the carbon quantum dots to the surface of zinc oxide, 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: The invention 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 5wt% 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, so that dopamine is oxidatively polymerized on the surface of the montmorillonite to form a polydopamine coating layer, and the coating amount is 10-20wt%.

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 or more -CF2- repeating units in the 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-methacryloxypropyltrimethoxysilane, and butyl acrylate are mixed in a weight ratio of (30-40):(10-20):(40-60), 0.5-1 wt% of azobisisobutyronitrile (azobisisobutyronitrile) as an initiator based on the total weight of the monomers is added, and the mixture is reacted at 70-80° C. for 4-6 hours to obtain a 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 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, and the molar ratio of urea to zinc nitrate is 3:1, the reaction is hydrothermally reacted at 90-100° C. for 6-12 hours, and then hydrazine hydrate is 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: dispersing the calcium fluorophosphate whiskers in a cerium nitrate solution, adjusting the pH value to 8-10 with ammonia water, stirring and reacting at 60-80° C. for 2-4 hours, and then 3+ PO4 on the surface of calcium fluorophosphate whiskers 3- A coordination adsorption reaction occurs to form a stable coating layer.

7. The magnesium alloy surface protective material according to claim 6, characterized in that: The weight ratio of the 2-mercaptobenzothiazole to the 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 mercapto groups in the 2-mercaptobenzothiazole molecules react with magnesium ions to form an insoluble chelate protective film, which covers the crack surface and prevents further intrusion of the corrosive medium.

8. A method for preparing the magnesium alloy surface protective material according to claim 7, characterized in that: The following steps are involved: S1: preparing a mixed resin: adding a hydroxy fluorocarbon resin and a fluorosilicone modified acrylic resin into a reaction kettle in proportion, stirring at 50-60°C for 1-2 hours to fully mix the two resins to form an interpenetrating network structure; S2 Pretreatment of filler: Add nano-silica, graphene nanosheets, and calcium fluorophosphate whiskers in proportion to a high-speed shearing machine, and add dispersant BYK-163. 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: preparing a slurry: adding the mixed resin prepared in step S1 to a reactor, slowly adding the filler pretreated in step S2 while stirring, and stirring at 60-70°C for 2-4 hours to allow the filler to be fully infiltrated and dispersed in the resin; then, adding 2-mercaptobenzothiazole, a rare earth cerium salt, and a crosslinking agent in sequence, and performing a pre-crosslinking reaction at 50-60°C for 1-2 hours. The degree of pre-crosslinking is controlled by real-time monitoring of the viscosity change of the reaction system. When the viscosity reaches 1.5-2.0 times the initial value, the pre-crosslinking reaction is stopped; S4 catalytic crosslinking: lower the temperature of the reaction system to 40-50°C, add catalysts dibutyltin dilaurate and triethylamine, and continue stirring for 30-60 minutes to allow the crosslinking reaction to proceed fully; then grind the material through a sand mill using zirconium beads as grinding media at a grinding rate of 1500-2000 rpm, and cycle grinding 3-5 times to make the material particle size ≤10μm; finally, add the leveling agent EFKA-3034 and stir evenly to obtain a magnesium alloy surface protection material.

9. The method for preparing a 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. The specific method is as follows: 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 regarded as 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, and the first stage grinding uses zirconium beads with a diameter of 1 mm, and grinds for 2 hours to reduce the material particle size to 20-30 μm; the second stage grinding uses zirconium beads with a diameter of 0.5 mm, and grinds for 1-2 hours to further reduce the material particle size to ≤10 μm; the ground material is subjected to particle size analysis by a laser particle size analyzer to ensure that more than 90% of the particles have a particle size of ≤10 μm.

10. An application of the magnesium alloy surface protective material according to claim 7, characterized in that: Used for surface protection of magnesium alloy components such as automobile engine cylinder blocks, drone landing gears, and electronic equipment casings; the specific application method is: first degrease, pickle, and phosphate the surface of the magnesium alloy component to remove surface oil and oxide layer; then use air spraying or electrostatic spraying to coat the protective material on the surface of the magnesium alloy component with a coating thickness of 20-50μm; after coating, cure at 120-150℃ for 1-2 hours to form a solid coating for the protective material.

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