A magnesium alloy high-pressure-resistant surface treatment liquid and a preparation method thereof

Abstract

This invention belongs to the field of insulating and heat-dissipating coating technology, specifically relating to a high-pressure-resistant surface treatment liquid for magnesium alloys and its preparation method. The raw materials, by weight, are as follows: 30-40 parts of organosilicon-modified waterborne epoxy resin, 9-12 parts of modified hexagonal boron nitride, 10-15 parts of modified graphene, 2-4 parts of curing agent, 0.5-2 parts of leveling agent, 1-2 parts of defoamer, and 25-50 parts of acetone. The high-pressure-resistant surface treatment liquid for magnesium alloys of this invention forms a coating on the surface of a magnesium alloy substrate with high volume resistivity, high breakdown voltage, high corrosion resistance, and high thermal conductivity. Besides its application in the new energy field, the high-pressure-resistant surface treatment liquid for magnesium alloys obtained by this invention can also be applied in aerospace, 3C electronics, and other fields, possessing broad market prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of insulating heat dissipation coatings, and particularly relates to a magnesium alloy high-voltage-resistant surface treatment liquid and a preparation method thereof. BACKGROUND

[0002] The energy storage battery mainly consists of a battery module, a battery management system (BMS) and a shell. The battery module includes positive and negative electrode materials, electrolyte, a separator and the like, and is the core of the battery; the battery management system (BMS) is responsible for monitoring the state of the battery and ensuring its safe and reliable operation; the shell is a protective layer of the energy storage battery and plays a role in protecting the internal structure of the battery and needs to have the functions of insulation, corrosion resistance, heat dissipation and the like. The battery shell, as a bearing body of the battery module, plays a key role in the safety and protection of the battery module.

[0003] At present, the common materials of the energy storage battery shell include aluminum alloy, stainless steel, ABS flame-retardant plastic and the like, which can all play a certain role in protecting the battery. However, with the increase of the energy density of the battery and the increase of the battery module, the proportion of the battery shell structure is also rising, which causes the overall weight of the energy storage battery to continuously increase. Therefore, under the development trend of energy saving and carbon reduction "lightweight" and the implementation of the related development policy of "lightweight" material-magnesium alloy, the magnesium alloy material with the characteristics of small density, light weight, high specific strength and specific stiffness, strong impact resistance and electromagnetic shielding has a broad market prospect in the application field of the energy storage battery shell. According to market research, the total weight of the aluminum alloy structural parts used by a certain brand of battery is about 125 kg, and if all the magnesium alloy is used, the weight is expected to be reduced to 80 kg, with a weight reduction effect of 30%. However, the magnesium alloy material is active and is prone to corrosion. At the same time, due to the particularity of the application scene in the field of the energy storage battery shell, the magnesium alloy material also needs to have good insulation and heat dissipation effects, and the main way to realize these functions is to coat a heat-conducting and insulating composite material on the surface thereof. At present, the heat-conducting and insulating composite material is divided into intrinsic heat-conducting and insulating composite material and filled heat-conducting and insulating composite material. The intrinsic heat-conducting and insulating composite material has a complex preparation process, high technical difficulty and limited improvement of the heat dissipation effect; the filled heat-conducting and insulating composite material has a simple preparation process and is easy to be used in industrialized mass production, and is a future research direction. However, the current filled heat-conducting and insulating composite material has a reverse relationship between heat conduction and breakdown voltage resistance; and the increase of the energy density and the charging and discharging power of the battery makes the existing filled heat-conducting and insulating composite material unable to meet the market requirements of insulation and the like. SUMMARY

[0004] The application provides a magnesium alloy high-voltage-resistant surface treatment liquid and a preparation method thereof aiming at the application requirements of the magnesium alloy in the field of energy storage batteries, and is intended to enable the lightweight magnesium alloy material to have excellent voltage resistance, corrosion resistance, heat dissipation and the like.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A high-pressure-resistant surface treatment liquid for magnesium alloys, wherein the raw materials are composed of the following components by weight:

[0007] 30-40 parts of organosilicon-modified waterborne epoxy resin;

[0008] 9-12 parts of modified hexagonal boron nitride;

[0009] 10-15 parts of modified graphene;

[0010] 2-4 parts of curing agent;

[0011] Leveling agent 0.5-2 parts;

[0012] 1-2 parts of defoamer;

[0013] 25-50 parts acetone.

[0014] Preferably, the organosilicon-modified waterborne epoxy resin is prepared according to the following steps:

[0015] S1. Add polyethylene glycol, catalyst, maleic anhydride, and propylene glycol methyl ether acetate to a three-necked flask. Purge air with nitrogen and, under nitrogen protection, heat to 80-90℃ and stir magnetically at 600-800 r / min for 8-10 hours. Then add epoxy resin, heat to 100-120℃, and continue stirring for 2-3 hours to obtain epoxy resin emulsifier. The ratio of polyethylene glycol, catalyst, maleic anhydride, propylene glycol methyl ether acetate, and epoxy resin is 40-50 g: 0.5-1.5 g: 5-8 g: 200-250 mL: 16-21 g.

[0016] S2. Add epoxy resin and epoxy resin emulsifier to a three-necked flask, heat to 65-75℃, and disperse using a high-speed dispersing shear machine at a rate of 1000-1200 r / min while simultaneously adding high-purity water dropwise at a rate of 1-2 mL / min. After the addition is complete, increase the dispersion rate to 1500-1600 r / min and continue dispersing for 1-2 hours to obtain an aqueous epoxy resin dispersion. The ratio of epoxy resin, epoxy resin emulsifier, and high-purity water is 70-80 g: 7-8 g: 130-150 mL.

[0017] S3. Add butyl acetate to the aqueous epoxy resin dispersion, and stir at a rate of 400-600 r / min in a constant temperature oil bath at 35-50℃ until fully dissolved. Then, add organosilane, dibutyltin dilaurate, and triethylamine in sequence, raise the temperature to 70-80℃, and continue stirring for 5-6 hours to obtain organosilicon-modified aqueous epoxy resin. The ratio of aqueous epoxy resin dispersion, butyl acetate, organosilane, dibutyltin dilaurate, and triethylamine is 50-60 g: 150-180 mL: 1.5-2.5 g: 0.3-0.6 g: 10-15 g.

[0018] Preferably, in step S1, the catalyst is any one or any two of potassium persulfate, boron trifluoride ether, and triphenylphosphine in any mass ratio.

[0019] Preferably, in the preparation step of the organosilicon-modified waterborne epoxy resin, the organosilicon is any one or any two of methyltriethoxysilane, dimethyldichlorosilane, phenyltrichlorosilane, and diphenyldichlorosilane in any mass ratio.

[0020] Preferably, the modified hexagonal boron nitride is prepared according to the following steps:

[0021] (1) Add hexagonal boron nitride (h-BN) powder to isopropanol solvent, and sonicate in a water bath for 10-12 h at room temperature. Then add NaOH, heat to 110-130℃, and stir at a constant temperature for 22-24 h to obtain hydroxylated h-BN-OH. Wash with high-purity water and filter until the filtrate is neutral. Dry the filter cake under vacuum at 65-70℃ for 22-24 h to obtain hydroxylated hexagonal boron nitride solid h-BN-OH, and grind it into powder for later use. The ratio of hexagonal boron nitride, isopropanol and NaOH is 10-14 g: 200-250 mL: 20-28 g.

[0022] (2) Add h-BN-OH powder and mercaptopropyltrimethoxysilane MPMS to a three-necked flask, and ultrasonically disperse in toluene at room temperature for 20-30 min. Under N2 protection, heat to 100-110℃ and stir and reflux in an oil bath for 6-8 h. Filter the solid product obtained by vacuum filtration, wash with anhydrous ethanol, filter 3-5 times, and vacuum dry at 65-70℃ for 22-24 h to obtain grafted h-BN-MPMS. The ratio of h-BN-OH powder, MPMS and toluene is 1.5-2 g: 1-3 mL: 200-250 mL.

[0023] (3) Add h-BN-MPMS, glycidyl methacrylate (GMA), and dimethylformamide (DMF) sequentially to a three-necked flask. Stir at 600-800 r / min under N2 atmosphere until homogeneous. Heat to 55-65℃ and quickly add benzoyl peroxide (BPO). Continue stirring at a constant temperature for 10-12 h to obtain modified hexagonal boron nitride, denoted as h-BN–PGMA. The ratio of h-BN-MPMS, GMA, DMF, and BPO is 1-2 g: 10-20 mL: 150-200 mL: 0.08-0.1 g.

[0024] Preferably, the modified graphene is prepared according to the following steps:

[0025] Step 1: Add graphene oxide and organosilane to anhydrous ethanol, ultrasonically disperse at room temperature for 1-2 hours, then heat to 100-110℃ and reflux in an oil bath for 10-12 hours. After cooling to room temperature, filter by suction. Wash the filter residue with ethanol three times by suction filtration, and finally dry in an oven at 65-75℃ for 0.5-1 hours to obtain silane-modified graphene oxide. The ratio of graphene oxide, organosilane and anhydrous ethanol is 2-4 g: 4-8 mL: 100-150 mL.

[0026] Step 2: Add silane-modified graphene oxide to an ethanol-water solution and ultrasonically disperse at room temperature for 1-2 hours. Add ammonia and continue ultrasonic dispersion for 1-2 hours. Slowly add an ethanol-water solution of tetraethoxysilane (TEOS). Stir magnetically at 60-65°C for 10-12 hours. Centrifuge at 7000-8000 r / min for 5-10 minutes using a high-speed centrifuge. Wash and filter the precipitate with high-purity water and dry in an oven at 70-75°C for 2-3 hours to obtain modified graphene. The volume ratio of silane-modified graphene oxide, ethanol-water solution, ammonia, and TEOS ethanol-water solution is 1-2 g: 400-500 mL: 100-150 mL: 12-24 mL. The ethanol-water solution is composed of ethanol and water in a volume ratio of 1:1. The volume ratio of TEOS to ethanol-water solution in the TEOS ethanol-water solution is 1:2.

[0027] Preferably, in the modified graphene preparation step, the organosilane is at least one selected from 3-(2-aminoethylamino)propyltrimethoxysilane (AAPTS), N,N-diethyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane.

[0028] Preferably, the curing agent is any one or a mixture of any two of succinic anhydride, ethylenediamine, and 4,4′-diaminodiphenyl sulfone in any mass ratio; the leveling agent is any one or a mixture of any two of polymethylalkylsiloxane, dimethylpolysiloxane, polyether-modified polydimethylsiloxane, and polyether-modified polymethylalkylsiloxane in any mass ratio; and the defoamer is any one or a mixture of any two of DF-2162, W-052, DF6800, BASF-1293, and A-10 defoamers in any mass ratio.

[0029] The preparation method of the high pressure resistance surface treatment liquid for magnesium alloys according to the present invention includes the following steps:

[0030] Step 1: Weigh each ingredient according to its weight.

[0031] Step 2: Add modified hexagonal boron nitride to acetone, then add modified graphene, and ultrasonically disperse for 1-2 hours. Then add organosilicon-modified waterborne epoxy resin, curing agent, leveling agent, and defoamer in sequence. Heat to 60-70℃ and stir at a constant temperature of 1200-1500 r / min for 0.5-1 hours. After cooling to room temperature, a high pressure-resistant surface treatment liquid for magnesium alloy is obtained.

[0032] The high-pressure-resistant surface treatment liquid for magnesium alloys of the present invention can be used in the casing of energy storage batteries.

[0033] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0034] (1) The present invention uses silicone-modified waterborne epoxy resin as the base film-forming liquid, and adds free radical polymerized graft modified hexagonal boron nitride and modified graphene oxide. Modified hexagonal boron nitride and graphene oxide have significant effects on improving the high pressure resistance and heat dissipation of the coating, and the two have a synergistic effect.

[0035] (2) This invention improves the dispersibility of epoxy resin by using epoxy resin emulsifier, increases the water-based and organosilicon modification pathways, introduces organosilicon active groups into water-based epoxy resin to form a cross-linking network, improves the adhesion and anti-aging properties of water-based epoxy resin, reduces the interfacial tension between epoxy resin and filler, and improves the corrosion resistance and adhesion of coating.

[0036] (3) The coating thickness formed by the treatment liquid on the surface of the magnesium alloy substrate in the embodiments of the present invention is 60-80 μm, and the volume resistivity is 1.42 × 10⁻⁶. 15The magnesium alloy high-pressure resistant surface treatment liquid of this invention forms a coating on the surface of a magnesium alloy substrate with high volume resistivity, high breakdown voltage, high corrosion resistance, and high thermal conductivity, solving the problems of poor corrosion resistance, poor heat dissipation, and poor pressure resistance existing in materials used for energy storage battery casings. The coating exhibits high volume resistivity, high breakdown voltage, high corrosion resistance, and high thermal conductivity.

[0037] (4) The high pressure resistance surface treatment liquid for magnesium alloys obtained by the present invention can be applied not only to the new energy field, but also to aerospace, 3C electronics and other fields, and has a broad market prospect. Detailed Implementation

[0038] The present invention will be described in detail below with reference to the embodiments, so as to illustrate the features and advantages of the present invention. The following embodiments are not intended to limit the present invention. Formulas prepared by those skilled in the art based on the ideas and raw material ratios of the present invention are also within the protection scope of the present invention.

[0039] The silicone-modified waterborne epoxy resin, modified hexagonal boron nitride, modified graphene, and magnesium alloy high-pressure-resistant surface treatment liquid involved in the following examples and comparative examples were prepared according to the following steps:

[0040] Preparation of silicone-modified waterborne epoxy resin:

[0041] S1. Add 50g of polyethylene glycol, 0.5g of potassium persulfate, 5g of maleic anhydride, and 200mL of propylene glycol methyl ether acetate to a three-necked flask. Purge the air with nitrogen and heat to 90℃ under nitrogen protection. Stir magnetically at 800r / min for 10h. Then add 21g of epoxy resin (bisphenol A type E-44, epoxy value 0.47), heat to 120℃, and continue stirring for 2h to obtain epoxy resin emulsifier.

[0042] S2. Add 80g of epoxy resin (bisphenol A type E-44) and 8g of epoxy resin emulsifier to a three-necked flask, heat to 65℃, and disperse at a rate of 1200r / min using a high-speed dispersing shear machine. At the same time, add 150mL of high-purity water (resistivity (25℃) ≥18MΩ·cm) dropwise at a rate of 1-2mL / min. After the addition is complete, increase the dispersion rate to 1500r / min and continue dispersing for 1h to obtain an aqueous epoxy resin dispersion.

[0043] S3. Take 50g of aqueous epoxy resin dispersion, add 150mL of butyl acetate, and stir at 400r / min in a constant temperature oil bath at 35℃ until fully dissolved. Then add 2.5g of methyltriethoxysilane, 0.6g of dibutyltin dilaurate, and 15g of triethylamine in sequence, heat to 70℃, and stir continuously for 5h to obtain organosilicon modified aqueous epoxy resin.

[0044] Modified hexagonal boron nitride was prepared according to the following steps:

[0045] (1) Add 10g of h-BN powder (purity > 99%, particle size 1μm) to 200mL of isopropanol solvent, and sonicate in a water bath for 12h at room temperature. Then add 20g of NaOH, heat to 130℃, and stir at a constant temperature for 24h to obtain hydroxylated h-BN-OH. Wash with high-purity water (resistivity (25℃) ≥ 18MΩ·cm) and filter until the filtrate is neutral. Dry the filter cake under vacuum at 70℃ for 24h to obtain hydroxylated hexagonal boron nitride solid (h-BN-OH), and grind it into powder for later use.

[0046] (2) Add 2g of h-BN-OH powder and 1mL of MPMS to a three-necked flask. At room temperature, ultrasonically disperse in 250mL of toluene for 20min. Under N2 protection, heat to 110℃ and stir and reflux in an oil bath for 8h. The solid product obtained by vacuum filtration is washed with anhydrous ethanol, filtered 3 times, and vacuum dried at 70℃ for 24h to obtain grafted h-BN-MPMS.

[0047] (3) Add 2g of h-BN-MPMS, 20mL of GMA and 200mL of DMF to a three-necked flask in sequence. Stir at 800r / min under N2 atmosphere until homogeneous. Heat to 55℃ and quickly add 0.1g of BPO. Continue stirring at constant temperature for 12h to obtain h-BN–PGMA.

[0048] Modified graphene is prepared according to the following steps:

[0049] Step 1: Take 2g of GO (purity >99wt%, flake diameter 20μm) and 4mL of 3-aminopropyltrimethoxysilane, add them to 100mL of anhydrous ethanol, sonicate at room temperature for 1h, then heat to 110℃, reflux in oil bath for 12h, cool to room temperature and filter, wash the filter residue with ethanol three times, and finally dry in an oven at 75℃ for 30min to obtain silane-modified graphene oxide.

[0050] Step 2: Take 1g of silane-modified graphene oxide, add 400mL of ethanol-water solution (composed of ethanol and water in a volume ratio of 1:1), and ultrasonically disperse at room temperature for 1h. Add 100mL of ammonia water and continue ultrasonic dispersion for 1h. Slowly add 12mL of tetraethoxysilane (TEOS) ethanol-water solution (the volume ratio of TEOS to ethanol-water solution is 1:2, and the ethanol-water solution is composed of ethanol and water in a volume ratio of 1:1). Stir magnetically at 60℃ for 12h. Centrifuge at 8000r / min for 10min using a high-speed centrifuge. Wash and filter the precipitate with high-purity water and dry it in an oven at 75℃ for 2h to obtain modified graphene.

[0051] The high-pressure-resistant surface treatment solution for magnesium alloys is prepared according to the following steps:

[0052] Step 1: Weigh each ingredient according to its weight.

[0053] Step 2: Add modified hexagonal boron nitride to acetone, then add modified graphene, and ultrasonically disperse for 1 hour. Then add organosilicon-modified waterborne epoxy resin, curing agent, leveling agent, and defoamer in sequence. Heat to 60°C and stir at 1500 r / min for 30 minutes. After cooling to room temperature, a high pressure-resistant surface treatment liquid for magnesium alloy is obtained.

[0054] Example 1

[0055] A high-pressure-resistant surface treatment liquid for magnesium alloys, wherein the raw materials are composed of the following components by weight: 40 parts of silicone-modified waterborne epoxy resin, 12 parts of modified hexagonal boron nitride, 15 parts of modified graphene, 4 parts of succinic anhydride, 2 parts of polyether-modified polydimethylsiloxane, 2 parts of W-052 defoamer, and 25 parts of acetone.

[0056] Example 2

[0057] A high-pressure-resistant surface treatment liquid for magnesium alloys, wherein the raw materials are composed of the following components by weight: 35 parts of silicone-modified waterborne epoxy resin, 10 parts of modified hexagonal boron nitride, 12 parts of modified graphene, 3 parts of succinic anhydride, 1 part of polyether-modified polydimethylsiloxane, 1 part of W-052 defoamer, and 38 parts of acetone.

[0058] Example 3

[0059] A high-pressure-resistant surface treatment liquid for magnesium alloys, wherein the raw materials are composed of the following components by weight: 30 parts of silicone-modified waterborne epoxy resin, 9 parts of modified hexagonal boron nitride, 10 parts of modified graphene, 2 parts of succinic anhydride, 0.5 parts of polyether-modified polydimethylsiloxane, 1 part of W-052 defoamer, and 47.5 parts of acetone.

[0060] Comparative Example 1

[0061] The components of the high-pressure-resistant magnesium alloy surface treatment liquid prepared in this comparative example are the same as those in Example 1, except that the silicone-modified waterborne epoxy resin is replaced with epoxy resin (bisphenol A type E-44).

[0062] Comparative Example 2

[0063] The composition of the high-pressure-resistant magnesium alloy surface treatment liquid prepared in this comparative example is the same as that in Example 1, except that the amount of modified hexagonal boron nitride added is 0.

[0064] Comparative Example 3

[0065] The components of the high-pressure-resistant magnesium alloy surface treatment liquid prepared in this comparative example are the same as those in Example 1, except that the amount of modified graphene added is 0.

[0066] Comparative Example 4

[0067] The composition of the high pressure-resistant surface treatment liquid for magnesium alloy prepared in this comparative example is the same as that in Example 1, except that the modified hexagonal boron nitride is replaced with hexagonal boron nitride (purity > 99%, particle size 1 μm).

[0068] Comparative Example 5

[0069] The composition of the high pressure-resistant surface treatment liquid for magnesium alloy prepared in this comparative example is the same as that in Example 1, except that the modified graphene is replaced with graphene oxide (purity >99wt%, sheet diameter 20μm).

[0070] The high pressure-resistant surface treatment liquids for magnesium alloys prepared in Examples 1-3 and Comparative Examples 1-5 were used to form coatings on the surface of magnesium alloy substrates according to the following method, and their performance was tested.

[0071] The magnesium alloy substrate (AZ91D, 70*40*2mm) was sanded until the surface was glossy and then cleaned with acetone. After drying, an immersion process was used. At room temperature, the magnesium alloy substrate was completely immersed in the treatment solution for 3 minutes, then removed and hung vertically for 30 minutes. Excess paint on the bottom was scraped off with a scraper. The magnesium alloy substrate treated with the treatment solution was then placed in a 120℃ oven and dried for 4 hours. The testing methods for coating thickness, volume resistivity, breakdown voltage, thermal conductivity, corrosion resistance, and adhesion performance are as follows.

[0072] Coating thickness: GB / T 13452.2-2008 "Determination of film thickness of paints and varnishes"

[0073] Volume resistivity: GB / T 31838.2–2019 "Dielectric and resistive properties of solid insulating materials - Part 2: Resistive properties (DC method) - Volume resistivity and volume resistivity"

[0074] Breakdown voltage: GB / T 1408.1-2016 "Electrical strength test methods for insulating materials - Part 1: Tests at power frequency"

[0075] Thermal conductivity: GB / T 10297-2015 "Determination of thermal conductivity of non-metallic solid materials - hot wire method"

[0076] Corrosion resistance: According to GB / T1771-2007 "Determination of resistance to neutral salt spray of paints and varnishes", after 720 hours of neutral salt spray test, the surface is qualified if there are no obvious rust marks, bubbles and cracks; if there are obvious rust marks, bubbles and cracks, it is unqualified.

[0077] Adhesion: GB / T 9286-2021 "Paints and Varnishes - Cross-cut Test"

[0078] The coating performance test results of the treatment solutions prepared in the above embodiments and comparative examples on the surface of magnesium alloy substrates are shown in Table 1.

[0079] Table 1. Coating performance test results

[0080] Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Coating thickness, μm 71 69 78 76 72 72 73 71 Volume resistance, Ω-cm 1.42 x 10 15 ]]> 1.39 x 10 15 ]] 1.35 x 10 15 ]]> 1.31 x 10 15 ]]> 1.22 x 10 14 ]]> 1.31 x 10 13 ]]> 1.33 x 10 14 ]] 1.96 x 10 13 ]] Breakdown voltage, V 6213 6135 6093 6034 5733 5336 5866 5574 Thermal conductivity, W / (m-k) 1.413 1.398 1.362 0.910 0.742 0.812 0.864 0.902 Corrosion resistance (NSS, 720 h) Pass Pass Pass Fail Fail Pass Pass Pass Adhesion, grade 0 0 0 2 0 0 0 0

[0081] According to Table 1:

[0082] As shown in Examples 1 to 3, the high-pressure resistant surface treatment liquid for magnesium alloys prepared in this invention forms coatings on the surface of magnesium alloy substrates with high breakdown voltage, volume resistivity, and thermal conductivity, as well as excellent surface adhesion and corrosion resistance. As shown in Example 1 and Comparative Example 1, this invention selects organosilicon to modify the waterborne epoxy resin, improving the corrosion resistance and adhesion of the coating. This is because the introduction of active groups of organosilicon into the waterborne epoxy resin forms a cross-linked network, improving the adhesion and anti-aging properties of the waterborne epoxy resin. As shown in Example 1, Comparative Examples 1 and 2, this invention selects modified hexagonal boron nitride as a thermally conductive filler, improving the thermal conductivity of the coating. This is because the organosilicon-modified waterborne epoxy resin and the modified hexagonal boron nitride improve their compatibility and reduce interfacial tension. Simultaneously, the modified hexagonal boron nitride constructs a three-dimensional thermally conductive network structure in the epoxy resin system, enhancing the thermal conductivity. As shown in Examples 1 and Comparative Examples 1 and 3, the present invention selects insulating modified graphene as the insulating filler, which improves the volume resistivity and breakdown voltage of the coating. This is because the organosilicon-modified waterborne epoxy resin and the modified graphene improve their compatibility, while the modified graphene shields its conductivity. As shown in Examples 1 and Comparative Examples 2 and 3, the present invention selects organosilicon to modify the waterborne epoxy resin, and uses modified hexagonal boron nitride and modified graphene as insulating and thermally conductive fillers, which improves the insulation and thermal conductivity of the coating. This is because the synergistic effect of the modified hexagonal boron nitride and graphene gives the coating superior insulation and heat dissipation effects. As shown in Examples 1 and Comparative Example 4, the present invention selects to modify hexagonal boron nitride, which improves the thermal conductivity of the coating. This is because polymer chains are grafted onto the surface of the hexagonal boron nitride, forming an interconnected thermally conductive network inside. As can be seen from Example 1 and Comparative Example 5, the present invention selects to modify graphene oxide, which improves the volume resistivity and breakdown voltage of the coating. This is because the modification causes graphene oxide to form an insulating sealing layer, thereby improving its insulation performance.

[0083] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0084] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A high-pressure-resistant surface treatment liquid for magnesium alloys, characterized in that, The composition of each raw material by weight is as follows: 30-40 parts of organosilicon-modified waterborne epoxy resin; 9-12 parts of modified hexagonal boron nitride; 10-15 parts of modified graphene; 2-4 parts of curing agent; Leveling agent 0.5-2 parts; 1-2 parts of defoamer; 25-50 parts acetone; The organosilicon-modified waterborne epoxy resin is prepared according to the following steps: S1. Add polyethylene glycol, catalyst, maleic anhydride, and propylene glycol methyl ether acetate to a three-necked flask. Purge air with nitrogen and, under nitrogen protection, heat to 80-90℃ and stir magnetically at 600-800 r / min for 8-10 hours. Then add epoxy resin, heat to 100-120℃, and continue stirring for 2-3 hours to obtain epoxy resin emulsifier. The ratio of polyethylene glycol, catalyst, maleic anhydride, propylene glycol methyl ether acetate, and epoxy resin is 40-50 g: 0.5-1.5 g: 5-8 g: 200-250 mL: 16-21 g. S2. Add epoxy resin and epoxy resin emulsifier to a three-necked flask, heat to 65-75℃, and disperse using a high-speed dispersing shear machine at a rate of 1000-1200 r / min while simultaneously adding high-purity water dropwise at a rate of 1-2 mL / min. After the addition is complete, increase the dispersion rate to 1500-1600 r / min and continue dispersing for 1-2 hours to obtain an aqueous epoxy resin dispersion. The ratio of epoxy resin, epoxy resin emulsifier, and high-purity water is 70-80 g: 7-8 g: 130-150 mL. S3. Add butyl acetate to the aqueous epoxy resin dispersion, and stir at a rate of 400-600 r / min in a constant temperature oil bath at 35-50℃ until fully dissolved; then add organosilane, dibutyltin dilaurate, and triethylamine in sequence, raise the temperature to 70-80℃, and continue stirring for 5-6 hours to obtain organosilicon-modified aqueous epoxy resin; wherein, the ratio of aqueous epoxy resin dispersion, butyl acetate, organosilane, dibutyltin dilaurate, and triethylamine is 50-60g: 150-180mL: 1.5-2.5g: 0.3-0.6g: 10-15g; The modified hexagonal boron nitride is prepared according to the following steps: (1) Add hexagonal boron nitride (h-BN) powder to isopropanol solvent, and sonicate in a water bath for 10-12 h at room temperature. Then add NaOH, heat to 110-130℃, and stir at a constant temperature for 22-24 h to obtain hydroxylated h-BN-OH. Wash with high-purity water and filter until the filtrate is neutral. Dry the filter cake under vacuum at 65-70℃ for 22-24 h to obtain hydroxylated hexagonal boron nitride solid h-BN-OH, and grind it into powder for later use. The ratio of hexagonal boron nitride, isopropanol and NaOH is 10-14 g: 200-250 mL: 20-28 g. (2) Add h-BN-OH powder and mercaptopropyltrimethoxysilane MPMS to a three-necked flask, and ultrasonically disperse in toluene at room temperature for 20-30 min. Under N2 protection, heat to 100-110℃ and stir and reflux in an oil bath for 6-8 h. Filter the solid product obtained by vacuum filtration, wash with anhydrous ethanol, filter 3-5 times, and vacuum dry at 65-70℃ for 22-24 h to obtain grafted h-BN-MPMS. The ratio of h-BN-OH powder, MPMS and toluene is 1.5-2 g: 1-3 mL: 200-250 mL. (3) Add h-BN-MPMS, glycidyl methacrylate (GMA), and dimethylformamide (DMF) sequentially to a three-necked flask. Stir at 600-800 r / min under N2 atmosphere until homogeneous. Heat to 55-65℃ and quickly add benzoyl peroxide (BPO). Continue stirring at a constant temperature for 10-12 h to obtain modified hexagonal boron nitride, denoted as h-BN-PGMA. The ratio of h-BN-MPMS, GMA, DMF, and BPO is 1-2 g: 10-20 mL: 150-200 mL: 0.08-0.1 g. The modified graphene is prepared according to the following steps: Step 1: Add graphene oxide and organosilane to anhydrous ethanol, ultrasonically disperse at room temperature for 1-2 hours, then heat to 100-110℃ and reflux in an oil bath for 10-12 hours. After cooling to room temperature, filter by suction. Wash the filter residue with ethanol three times, and finally dry in an oven at 65-75℃ for 0.5-1 hours to obtain silane-modified graphene oxide. The ratio of graphene oxide, organosilane, and anhydrous ethanol is 2-4 g: 4-8 mL: 100-150 mL. Step 2: Add silane-modified graphene oxide to an ethanol-water solution, ultrasonically disperse at room temperature for 1-2 hours, add ammonia, continue ultrasonic dispersion for 1-2 hours, and slowly add tetraethoxysilane. The TEOS ethanol aqueous solution was magnetically stirred at 60-65℃ for 10-12 hours, centrifuged at 7000-8000 r / min for 5-10 minutes using a high-speed centrifuge, the precipitate was washed and filtered with high-purity water, and dried in an oven at 70-75℃ for 2-3 hours to obtain modified graphene. The ratio of silane-modified graphene oxide, ethanol aqueous solution, ammonia water, and TEOS ethanol aqueous solution was 1-2 g: 400-500 mL: 100-150 mL: 12-24 mL. The ethanol aqueous solution was composed of ethanol and water in a volume ratio of 1:1, and the volume ratio of TEOS to ethanol aqueous solution in the TEOS ethanol aqueous solution was 1:

2.

2. The high-pressure-resistant surface treatment liquid for magnesium alloys according to claim 1, characterized in that, In step S1, the catalyst is any one or any two of potassium persulfate, boron trifluoride ether, and triphenylphosphine in any mass ratio.

3. The high-pressure-resistant surface treatment liquid for magnesium alloys according to claim 1, characterized in that, In step S3, the organosilane is any one or any two of methyltriethoxysilane, dimethyldichlorosilane, phenyltrichlorosilane, and diphenyldichlorosilane in any mass ratio.

4. The high-pressure-resistant surface treatment liquid for magnesium alloys according to claim 1, characterized in that, In the modified graphene preparation step, the organosilane is at least one of 3-(2-aminoethylamino)propyltrimethoxysilane (AAPTS), N,N-diethyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane.

5. The high-pressure-resistant surface treatment liquid for magnesium alloys according to claim 1, characterized in that: The curing agent is any one or a mixture of any two of succinic anhydride, ethylenediamine, and 4,4′-diaminodiphenyl sulfone in any mass ratio; the leveling agent is any one or a mixture of any two of polymethylalkylsiloxane, dimethylpolysiloxane, polyether-modified polydimethylsiloxane, and polyether-modified polymethylalkylsiloxane in any mass ratio; the defoamer is any one or a mixture of any two of DF-2162, W-052, DF6800, BASF-1293, and A-10 defoamers in any mass ratio.

6. A method for preparing the high-pressure-resistant surface treatment liquid for magnesium alloys according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Weigh each ingredient according to its weight. Step 2: Add modified hexagonal boron nitride to acetone, then add modified graphene, and ultrasonically disperse for 1-2 hours. Then add organosilicon-modified waterborne epoxy resin, curing agent, leveling agent, and defoamer in sequence. Heat to 60-70℃ and stir at a constant temperature of 1200-1500 r / min for 0.5-1 hours. After cooling to room temperature, a high pressure-resistant surface treatment liquid for magnesium alloy is obtained.