Magnesium alloy surface flame-retardant heat-insulating coating and preparation method thereof

Abstract

The invention belongs to the technical field of coatings, and particularly relates to a magnesium alloy surface flame-retardant heat-insulating coating and a preparation method thereof. The composite material is characterized by comprising the following raw materials in parts by weight: 40-55 parts of modified phenolic resin, 10-20 parts of aerogel, 10-20 parts of reinforced fibers, 10-20 parts of a flame retardant, 2-5 parts of nano flame-retardant synergistic powder, 2-4 parts of a curing agent, 1-3 parts of a defoaming agent, 2-6 parts of a wetting agent and 60-80 parts of an ethanol water solution. The flame-retardant heat-insulating coating formed on the surface of the magnesium alloy has excellent flame retardance, heat insulation, corrosion resistance and adhesive force, can be used in the fields of aerospace, rail transit, 3C electronics and the like, and has a wide market prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings, and specifically relates to a flame retardant and heat-insulating coating on the surface of a magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium alloys have significant advantages such as low density, high specific strength and specific stiffness, strong damping and vibration reduction, good electromagnetic shielding performance, and easy recycling. They have important application value in the fields of aerospace, transportation, electronic information, etc. Especially in the aviation field, components such as engine casings, oil pump housings, and battery pack housings made of magnesium alloys can greatly reduce weight, reduce energy consumption, and improve maneuverability. However, due to safety considerations, the aviation field has very strict requirements on the ignition properties of selected materials. In view of the active chemical properties of magnesium at high temperatures and the poor density of the oxide film formed, the ignition properties of magnesium alloy components are an important consideration for their application in the aviation field. In terms of flame retardant protection of magnesium alloy components, although alloying method is currently the most commonly used method to improve the flame retardant properties of magnesium alloy components, when designing alloys, it is also necessary to comprehensively consider the effects of added flame retardant elements on processability, mechanical properties, and corrosion resistance, and these factors are often contradictory and cannot be taken into account. The use of surface flame retardant protective coating is another effective way to solve this problem, but most of the current flame retardant coatings require a high thickness (>1mm) and sufficient space to form an expanding thermal insulation layer; at the same time, magnesium alloys have high thermal conductivity and fast heat transfer and dissipation. In order to maintain the stability of the internal temperature of magnesium alloy structural parts, magnesium alloy components are often required to have both flame retardant properties and thermal insulation effects. However, there are few reports on magnesium alloy flame retardant thermal insulation coatings, and the compatibility of flame retardant thermal insulation coatings with magnesium alloy substrates is also unknown. Therefore, it is urgent to develop flame retardant thermal insulation protective coatings suitable for magnesium alloys. Summary of the invention

[0003] In view of the application requirements of magnesium alloys in the aerospace field, the present invention provides a flame retardant and heat-insulating coating on the surface of a magnesium alloy and a preparation method thereof, aiming to make lightweight magnesium alloy materials have excellent flame retardant and heat-insulating properties.

[0004] To achieve the above invention, the present invention provides the following technical solutions:

[0005] A flame retardant and heat-insulating coating on the surface of a magnesium alloy, wherein the raw materials thereof are composed of the following in parts by weight:

[0006] 40-55 parts of modified phenolic resin;

[0007] Aerogel 10-20 parts;

[0008] Reinforcement fiber 10-20 parts;

[0009] Flame retardant 10-20 parts;

[0010] 2-5 parts of nano flame retardant synergistic powder;

[0011] 2-4 parts of curing agent;

[0012] 1-3 parts of defoaming agent;

[0013] Wetting agent 2-6 parts;

[0014] 60-80 parts of ethanol aqueous solution.

[0015] Preferably, the modified phenolic resin is prepared according to the following steps: phenol, formaldehyde and oxalic acid are added in sequence to a three-necked flask filled with distilled water, the temperature is raised to 70-80°C, and the mixture is stirred at 800-1000r / min for reaction for 2-3h, then diphenylphosphoric acid is added, the mixture is stirred and reacted for 2-3h, a high-speed centrifuge is used for centrifugation at 6000-7500r / min for 8-10min, the precipitate is dried in an oven at 120-130°C for 3-4h, and the modified phenolic resin powder is ground for standby use; wherein the dosage ratio of distilled water, phenol, formaldehyde, oxalic acid and diphenylphosphoric acid is 250-300mL: 90-100g: 20-30g: 10-15g: 15-20g.

[0016] Preferably, the aerogel is modified SiO 2 The aerogel is prepared according to the following steps: adding a silicon source, ethanol and distilled water to a reaction container in sequence, stirring at 700-800r / min for 2-3h, then adding dilute hydrochloric acid (mass concentration is 5%-10%) to adjust the pH to 4-5, heating to 50-60°C and continuing to stir for 6-8h, then adding ammonia water, continuing to stir for 10-20min, then adding nano powder, continuing to stir for 12-14h, sealing the reaction container with a plastic wrap, aging in a 50-55°C drying oven for 10-12h to obtain a wet gel; adding n-hexane to the reaction container to submerge the wet gel, reacting in a 50-60°C water bath for 3-4h, placing in an 80-90°C oven to dry for 4-5h, then heating to 110-120°C, continuing to dry for 7-8h, and grinding to obtain a modified SiO 2 Aerogel powder; wherein the amount ratio of silicon source, ethanol, distilled water, ammonia water, and nano powder is 50-80g, 150-200mL: 25-50mL: 3-5mL: 5-8g. Further preferably: the silicon source is any one of methyl orthosilicate, ethyl orthosilicate, isopropyl orthosilicate, calcium silicate, and sodium silicate, or a mixture of any two in any mass ratio. The nano powder is Al 2 O 3 Powder, TiO 2 Powder, ZrO 2 Any one of powder, MgO powder, and BN powder, or a mixture of any two of them in any mass ratio.

[0017] Preferably, the flame retardant is prepared according to the following steps: adding terephthalaldehyde and ethanol to a three-necked flask, mixing and stirring at 800-1000r / min at 25°C for 0.5-1h, then adding phenylphosphoryl dichloride and ethyl acetate, heating to 65-75°C, continuing stirring for 2-3h, then adding 9,10-dihydro-9-oxygen-10-phosphoric acid-10-oxide (DOPO), continuing stirring and reacting for 8-9h, centrifuging at a speed of 6000-7000r / min using a high-speed centrifuge to obtain a precipitate, washing the precipitate with toluene 2-3 times, drying at 80-85°C for 4-5h, and grinding the dried solid to obtain a flame retardant; wherein the amount ratio of terephthalaldehyde, ethanol, phenylphosphoryl dichloride, ethyl acetate, and DOPO is 6-8g:180-210mL:30-35g:100-120mL:35-45g.

[0018] Preferably, the nano flame retardant synergistic powder is any one of titanium dioxide, montmorillonite, silicon dioxide, magnesium hydroxide, and aluminum hydroxide, or a mixture of any two of them in any mass ratio.

[0019] Preferably, the reinforcing fiber is any one of glass fiber, ceramic fiber, basalt fiber, carbon fiber, polyester fiber, or a mixture of any two of them in any mass ratio.

[0020] Preferably: the curing agent is any one of 4-4′-diaminodiphenylmethane DDM, hexamethylenetetramine HMTA, and 4,4′-diaminodiphenyl sulfone DDS, or a mixture of any two of them in any mass ratio; the defoamer is any one of defoamer DF-285, defoamer DF-210, defoamer DF-212, defoamer BYK-A515, and defoamer BYK-A501, or a mixture of any two of them in any mass ratio; the wetting agent is any one of polyoxyethylene ether, fluorocarbon alkyl silicone oil, fluorocarbon alkyl polyoxyethylene alcohol, and fluorocarbon alkyl amine, or a mixture of any two of them in any mass ratio.

[0021] Preferably, the ethanol aqueous solution consists of ethanol and water in a volume ratio of 1:1.

[0022] The method for preparing the flame retardant and heat-insulating coating on the surface of the magnesium alloy of the present invention comprises the following steps:

[0023] S1: Weigh each raw material by weight;

[0024] S2: Add reinforcing fibers to the ethanol aqueous solution, add a wetting agent while stirring, mix and stir at 600 - 800 r / min for 0.5 - 1 h, then sequentially add modified phenolic resin, aerogel and defoaming agent, continue to stir for 1 - 2 h, then add a flame retardant, nano flame retardant synergistic powder and curing agent, raise the temperature to 60 - 75 °C, increase the rotation speed to 1200 - 1300 r / min and mix and stir for 2 - 3 h to obtain a treatment solution;

[0025] S3: After polishing the magnesium alloy substrate to be treated with sandpaper until the surface is bright, clean it with acetone and dry it. Apply the treatment solution evenly on the surface of the magnesium alloy substrate by brushing process; or adopt the dipping process, at room temperature, completely immerse the magnesium alloy substrate in the treatment solution for 5 - 8 min, take it out and hang it vertically for 0.5 - 1 h, and scrape off the remaining paint at the bottom with a scraper. After the surface is dry, put the magnesium alloy substrate into a drying oven and dry it at 100 - 150 °C for 5 - 6 h to obtain a flame retardant and heat insulation coating on the magnesium alloy surface.

[0026] The flame retardant and heat insulation coating on the magnesium alloy surface of the present invention can be applied to the aviation field.

[0027] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0028] (1) The present invention takes modified silica aerogel as the main component of the heat insulation filler. During the preparation process of the modified silica aerogel, nano powders with high melting point and high thermal stability are added. While improving the thermal stability of the silica aerogel, these nano powders can form a physical barrier layer inside the silica aerogel, increase the porosity, effectively prevent heat transfer, and significantly reduce the thermal conductivity of the coating.

[0029] (2) The present invention takes the DOPO system as the main flame retardant. The nano flame retardant synergistic powder can improve the structural stability and compactness of the protective carbon layer formed by the main flame retardant at high temperature, thereby isolating oxygen, preventing the spread of flames, and improving the fire protection grade of the coating.

[0030] (3) In the embodiments of the present invention, the thickness of the flame retardant and heat insulation coating on the magnesium alloy surface prepared is 70 - 80 μm, the UL 94 fire protection grade is V - 0, the thermal conductivity is 0.0233 W / (m·k), the neutral salt spray test is 720 h, and the adhesion is grade 0. Therefore, the flame retardant and heat insulation coating of the present invention has excellent flame retardancy, heat insulation, corrosion resistance and adhesion. Specific embodiments

[0031] The present invention will be described in detail below in conjunction with embodiments to clarify the features and advantages of the present invention. The following embodiments are not limitations of the present invention. The formulations sorted out by those skilled in the art according to the ideas and raw material ratios of the present invention also fall within the protection scope of the present invention.

[0032] The modified phenolic resin, aerogel, flame retardant and flame retardant thermal insulation coating on the surface of magnesium alloy involved in the following examples and comparative examples are prepared according to the following steps:

[0033] Preparation of modified phenolic resin: In a three-necked flask filled with 300 mL of distilled water, add 100 g of phenol, 30 g of formaldehyde, and 15 g of oxalic acid in sequence, heat to 80°C, stir and react at 1000 r / min for 3 h, then add 20 g of diphenylphosphoric acid, continue stirring and react for 2 h, use a high-speed centrifuge to centrifuge at 6000 r / min for 10 min, dry the precipitate in an oven at 130°C for 3 h, and grind to obtain the modified phenolic resin powder for stand-alone use.

[0034] Preparation of aerogel: 50 g of isopropyl orthosilicate, 150 mL of ethanol and 25 mL of distilled water were added to a beaker in sequence, stirred at 800 r / min for 2 h, then diluted hydrochloric acid (8 wt%) was added to adjust the pH to 4, heated to 60 ° C and stirred for 6 h, then 3 mL of ammonia was added, stirred for 10 min, and then nano-Al was added. 2 O 3 8g of powder was added, and stirring was continued for 12h. The beaker was sealed with plastic wrap and placed in a 55℃ drying oven for aging for 10h to obtain a wet gel. n-Hexane was added to the beaker to submerge the wet gel. After reacting in a 60℃ water bath for 3h, the gel was placed in an 80℃ oven for drying for 4h, and then heated to 120℃ and continued to dry for 8h. The modified SiO 2 The aerogel powder is set aside for use.

[0035] Preparation of flame retardant: Add 8 g of terephthalaldehyde and 210 mL of ethanol to a three-necked flask, stir at 25°C and 800 r / min for 0.5 h, then add 35 g of phenylphosphoryl dichloride and 120 mL of ethyl acetate, raise the temperature to 65°C, continue stirring for 2 h, then add 45 g of DOPO, continue stirring and react for 8 h, centrifuge at 7000 r / min with a high-speed centrifuge to obtain a precipitate, wash the precipitate twice with toluene, dry at 85°C for 4 h, grind the dried solid to obtain a flame retardant for use.

[0036] Preparation of flame retardant and thermal insulation coating on magnesium alloy surface:

[0037] S1: Weigh each component by weight.

[0038] S2: Add reinforcing fiber (glass fiber is used in the following embodiments) to a beaker filled with ethanol aqueous solution (composed of ethanol and water in a volume ratio of 1:1), add a wetting agent (fluorocarbon alkyl silicone oil is used in the following embodiments) while stirring, mix and stir at 800 r / min for 0.5 h, then add modified phenolic resin, aerogel and defoamer (BYK-A515 defoamer is used in the following embodiments) in sequence, continue stirring for 2 h, then add flame retardant, nano flame retardant synergistic powder (titanium dioxide is used in the following embodiments) and curing agent (hexamethylenetetramine is used in the following embodiments), raise the temperature to 60°C, increase the speed to 1200 r / min, mix and stir for 2 h, and obtain a treated liquid.

[0039] S3: After sanding the AZ91D magnesium alloy substrate (75*40*2mm) to a bright surface, clean it with acetone and dry it. Using the immersion process, the magnesium alloy substrate is completely immersed in the treatment liquid for 8 minutes at room temperature, taken out and hung vertically for 0.5 hours, and the remaining paint on the bottom is scraped off with a scraper. After the surface is dry, it is placed in a drying oven and dried at 120℃ for 2 hours, and then dried at 150℃ for 3 hours to obtain a flame retardant and heat-insulating coating on the magnesium alloy surface.

[0040] Example 1

[0041] A flame retardant and heat-insulating coating on the surface of a magnesium alloy, wherein the raw materials are composed of 55 parts of modified phenolic resin, 20 parts of aerogel, 20 parts of reinforcing fiber, 20 parts of flame retardant, 5 parts of nano flame retardant synergistic powder, 4 parts of curing agent, 3 parts of defoaming agent, 6 parts of wetting agent and 60 parts of ethanol aqueous solution in parts by weight.

[0042] Example 2

[0043] A flame retardant and heat-insulating coating on the surface of a magnesium alloy, wherein the raw materials thereof are composed by weight: 50 parts of modified phenolic resin, 15 parts of aerogel, 15 parts of reinforcing fiber, 15 parts of flame retardant, 3 parts of nano flame retardant synergistic powder, 3 parts of curing agent, 2 parts of defoaming agent, 4 parts of wetting agent and 65 parts of ethanol aqueous solution.

[0044] Example 3

[0045] A flame retardant and heat-insulating coating on the surface of a magnesium alloy, wherein the raw materials thereof are composed by weight: 40 parts of modified phenolic resin, 10 parts of aerogel, 10 parts of reinforcing fiber, 10 parts of flame retardant, 2 parts of nano flame retardant synergistic powder, 2 parts of curing agent, 1 part of defoaming agent, 3 parts of wetting agent and 75 parts of ethanol aqueous solution.

[0046] Comparative Example 1

[0047] The components of the flame-retardant and heat-insulating coating on the surface of the magnesium alloy prepared in this comparative example are the same as those in Example 1, except that the weight fraction of the aerogel is 0.

[0048] Comparative Example 2

[0049] The components of the flame retardant and heat-insulating coating on the surface of the magnesium alloy prepared in this comparative example are the same as those in Example 1, except that the amount of nano powder added during the preparation of the aerogel is 0.

[0050] Comparative Example 3

[0051] The components of the flame retardant and heat-insulating coating on the surface of the magnesium alloy prepared in this comparative example are the same as those in Example 1, except that the nano-Al 2 O 3 Powder replaced with nano ZrO 2 powder.

[0052] Comparative Example 4

[0053] The components of the flame retardant and heat-insulating coating on the surface of the magnesium alloy prepared in this comparative example are the same as those in Example 1, except that the weight fraction of the flame retardant is 0.

[0054] Comparative Example 5

[0055] The components of the flame retardant and heat-insulating coating on the surface of the magnesium alloy prepared in this comparative example are the same as those in Example 1, except that the weight fraction of the nano flame retardant synergistic powder is 0.

[0056] Comparative Example 6

[0057] The components of the flame retardant and heat-insulating coating on the surface of the magnesium alloy prepared in this embodiment are the same as those in Embodiment 1, except that the nano flame retardant synergistic powder is replaced by montmorillonite.

[0058] The thickness, UL-94 fire rating, thermal conductivity, adhesion, and corrosion resistance of the flame retardant and thermal insulation coatings on the magnesium alloy surfaces prepared in Examples 1 to 3 and Comparative Examples 1 to 6 are tested as follows:

[0059] Coating thickness: GB / T 13452.2-2008 "Determination of film thickness of paints and varnishes"

[0060] UL 94 fire rating: GB / T 2408-2021 "Determination of combustion performance of plastics - Horizontal and vertical methods"

[0061] Thermal conductivity: GB / T 10297-2015 "Determination of thermal conductivity of non-metallic solid materials - Hot wire method"

[0062] Adhesion: GB / T 9286-2021 "Scratch test for paints and varnishes"

[0063] Corrosion resistance: GB / T1771-2007 "Determination of neutral salt spray resistance of paints and varnishes" After 720 hours of neutral salt spray test, if there is no obvious rust, bubbles and cracks on the surface, it is qualified; if there is obvious rust, bubbles and cracks, it is unqualified.

[0064] The test results of the coating properties formed on the surface of the magnesium alloy substrate by the treatment solutions configured in the above-mentioned embodiments and comparative examples are shown in Table 1.

[0065] Table 1 Coating performance test results

[0066]

[0067] According to Table 1, we can see that:

[0068] It can be seen from Examples 1 to 3 that the flame retardant and thermal insulation coating on the surface of the magnesium alloy prepared in the present invention has a high UL-94 fire protection rating, low thermal conductivity, excellent corrosion resistance and adhesion, so that the magnesium alloy components have better flame retardant and thermal insulation functions.

[0069] It can be seen from Example 1 and Comparative Example 1 that the present invention selects modified silica aerogel as a thermal insulation filler, which reduces the thermal conductivity of the coating and greatly improves the thermal insulation performance. This is because the modified silica aerogel with low thermal conductivity and high porosity can block the continuous transfer of heat flow inside the phenolic resin.

[0070] It can be seen from Example 1 and Comparative Example 2 that the present invention selects nanopowder to modify the silica aerogel, which reduces the thermal conductivity of the coating. This is because the addition of nanopowder with a high melting point and high thermal stability to the silica aerogel forms a physical barrier layer inside the silica aerogel, increases the porosity, and effectively prevents heat transfer.

[0071] It can be seen from Example 1 and Comparative Examples 2 and 3 that the present invention adds nano-Al in the process of preparing modified silica aerogel. 2 O 3 Powder and nano ZrO 2 The powder can reduce the thermal conductivity of the coating and improve the thermal insulation performance of magnesium alloy components. 2 O 3 Powder has better performance.

[0072] It can be seen from Example 1 and Comparative Examples 4 and 5 that the present invention selects the DOPO system as the main flame retardant, and adds the nano flame retardant synergistic powder to work synergistically with the main flame retardant, which greatly improves the UL-94 fire rating of the coating. This is because the addition of the nano flame retardant synergistic powder enhances the structural stability and density of the protective carbon layer formed by the main flame retardant under high temperature conditions, isolates oxygen, prevents the spread of flames, and protects the substrate.

[0073] It can be seen from Example 1 and Comparative Examples 5 and 6 that the present invention selects titanium dioxide and montmorillonite as nano flame retardant synergistic powders, both of which can improve the UL-94 fire rating of the coating, and titanium dioxide has better performance.

[0074] 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 present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0075] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A flame retardant and heat-insulating coating on the surface of a magnesium alloy, characterized in that: The composition of each raw material in parts by weight is as follows: 40-55 parts of modified phenolic resin; Aerogel 10-20 parts; Reinforcement fiber 10-20 parts; Flame retardant 10-20 parts; 2-5 parts of nano flame retardant synergistic powder; 2-4 parts of curing agent; 1-3 parts of defoaming agent; Wetting agent 2-6 parts; 60-80 parts of ethanol aqueous solution.

2. The flame retardant and heat-insulating coating on the surface of magnesium alloy according to claim 1, characterized in that: The modified phenolic resin is prepared according to the following steps: Phenol, formaldehyde and oxalic acid are added to a three-necked flask filled with distilled water in sequence, the temperature is raised to 70-80°C, and the mixture is stirred at 800-1000 r / min for 2-3 hours, then diphenylphosphoric acid is added, and the mixture is stirred for 2-3 hours, and a high-speed centrifuge is used to centrifuge the mixture at 6000-7500 r / min for 8-10 minutes, and the precipitate is dried in an oven at 120-130°C for 3-4 hours, and the precipitate is ground to obtain a modified phenolic resin powder; wherein the amount ratio of distilled water, phenol, formaldehyde, oxalic acid and diphenylphosphoric acid is 250-300 mL: 90-100 g: 20-30 g: 10-15 g: 15-20 g.

3. The flame retardant and heat-insulating coating on the surface of magnesium alloy according to claim 1, characterized in that: The aerogel is a modified SiO2 aerogel, which is prepared according to the following steps: Add silicon source, ethanol and distilled water to the reaction container in sequence, stir at 700-800r / min for 2-3h, then add dilute hydrochloric acid with a mass concentration of 5%-10% to adjust the pH to 4-5, heat to 50-60℃ and continue stirring for 6-8h, then add ammonia water, continue stirring for 10-20min, then add nano powder, continue stirring for 12-14h, seal the reaction container with plastic wrap, and age in a drying oven at 50-55℃ for 10-12h. Obtain wet gel; add n-hexane into the reaction container to submerge the wet gel, react in a water bath at 50-60°C for 3-4 hours, place in an oven at 80-90°C for drying for 4-5 hours, then heat to 110-120°C, continue drying for 7-8 hours, and grind to obtain modified SiO2 aerogel powder; wherein the amount ratio of silicon source, ethanol, distilled water, ammonia water, and nano powder is 50-80g, 150-200mL: 25-50mL: 3-5mL: 5-8g.

4. The flame retardant and heat-insulating coating on the surface of magnesium alloy according to claim 3, characterized in that: In the aerogel preparation process, the silicon source is any one of methyl orthosilicate, ethyl orthosilicate, isopropyl orthosilicate, calcium silicate, and sodium silicate, or a mixture of any two of them in any mass ratio.

5. The flame retardant and heat-insulating coating on the surface of magnesium alloy according to claim 3, characterized in that: In the aerogel preparation process, the nano powder is any one of Al2O3 powder, TiO2 powder, ZrO2 powder, MgO powder, and BN powder, or a mixture of any two of them in any mass ratio.

6. The flame retardant and heat-insulating coating on the surface of magnesium alloy according to claim 1, characterized in that: The flame retardant is prepared according to the following steps: Add terephthalaldehyde and ethanol to a three-necked flask, stir at 800-1000 r / min for 0.5-1h at 25°C, then add phenylphosphoryl dichloride and ethyl acetate, heat to 65-75°C, continue stirring for 2-3h, then add 9,10-dihydro-9-oxygen-10-phosphoric acid-10-oxide DOPO, continue stirring and reacting for 8-9h, centrifuge at 6000-7000 r / min with a high-speed centrifuge to obtain a precipitate, wash the precipitate with toluene 2-3 times, dry at 80-85°C for 4-5h, grind the dried solid to obtain a flame retardant; wherein the amount ratio of terephthalaldehyde, ethanol, phenylphosphoryl dichloride, ethyl acetate and DOPO is 6-8g:180-210mL:30-35g:100-120mL:35-45g.

7. The flame retardant and heat-insulating coating on the surface of magnesium alloy according to claim 1, characterized in that: The nano flame retardant synergistic powder is any one of titanium dioxide, montmorillonite, silicon dioxide, magnesium hydroxide, and aluminum hydroxide, or a mixture of any two of them in any mass ratio.

8. The flame retardant and heat-insulating coating on the surface of magnesium alloy according to claim 1, characterized in that: The reinforcing fiber is any one of glass fiber, ceramic fiber, basalt fiber, carbon fiber, polyester fiber, or a mixture of any two of them in any mass ratio.

9. The flame retardant and heat-insulating coating on the surface of magnesium alloy according to claim 1, characterized in that: The curing agent is any one of 4-4,-diaminodiphenylmethane DDM, hexamethylenetetramine HMTA, and 4,4′-diaminodiphenyl sulfone DDS, or a mixture of any two of them in any mass ratio; the defoamer is any one of defoamer DF-285, defoamer DF-210, defoamer DF-212, defoamer BYK-A515, and defoamer BYK-A501, or a mixture of any two of them in any mass ratio; the wetting agent is any one of polyoxyethylene ether, fluorocarbon alkyl silicone oil, fluorocarbon alkyl polyoxyethylene alcohol, and fluorocarbon alkyl amine, or a mixture of any two of them in any mass ratio; the ethanol aqueous solution is composed of ethanol and water in a volume ratio of 1:

1.

10. A method for preparing a flame retardant and heat-insulating coating on a magnesium alloy surface as claimed in any one of claims 1 to 9, characterized in that: The steps include: S1: Weigh each raw material by weight; S2: Add reinforcing fiber to the ethanol aqueous solution, add a wetting agent while stirring, mix and stir at 600-800 r / min for 0.5-1h, then add modified phenolic resin, aerogel and defoamer in sequence, continue stirring for 1-2h, then add flame retardant, nano flame retardant synergistic powder and curing agent, raise the temperature to 60-75°C, increase the speed to 1200-1300 r / min, mix and stir for 2-3h, and obtain a treated liquid; S3: grinding the magnesium alloy substrate to be treated with sandpaper until the surface is bright, then cleaning with acetone and drying; Use a brushing process to evenly apply the treatment liquid on the surface of the magnesium alloy substrate; or use an immersion process to completely immerse the magnesium alloy substrate in the treatment liquid for 5-8 minutes at room temperature, take it out and hang it vertically for 0.5-1 hour, and scrape off the remaining paint on the bottom with a scraper; After the surface is dried, the magnesium alloy substrate is placed in a drying oven and dried at 100-150° C. for 5-6 hours to obtain a flame retardant and heat-insulating coating on the surface of the magnesium alloy.

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