A highly corrosion-resistant laser-welded exhaust manifold and its preparation method

Abstract

The present invention relates to the field of exhaust manifolds, and is used to solve the problem that the existing exhaust manifolds are prone to oxidation and corrosion, resulting in damage to the exhaust manifolds. Specifically, it relates to a highly corrosion-resistant laser-welded exhaust manifold and a preparation method thereof. In this method, a polyamic acid solution, that is, a highly corrosion-resistant coating, is formed by the polymerization reaction of the amino group on the organophosphorus reactant and the anhydride group on the fluorine-containing reactant. After the highly corrosion-resistant coating is attached to the laser-welded exhaust manifold, thermal imidization treatment is carried out to dehydrate and form a polyimide coating, which is the highly corrosion-resistant coating. This highly corrosion-resistant coating has good high-temperature resistance and corrosion resistance. After wrapping the laser-welded exhaust manifold, it is difficult for the manifold to be oxidized and corroded. Moreover, the highly corrosion-resistant coating has excellent high-temperature resistance and will not crack or fall off at high temperatures, thereby being able to provide long-term protection for the laser-welded exhaust manifold and improving the service life of the laser-welded exhaust manifold.

Description

Technical Field

[0001] The present invention relates to the field of exhaust manifolds, and particularly to a highly corrosion-resistant laser-welded exhaust manifold and a preparation method thereof. Background Art

[0002] An exhaust manifold is a pipeline connected to an engine cylinder block. The exhaust manifold is usually segmented, and each segment of the exhaust manifold is connected to one cylinder block of the engine. The adjacent two segments of the exhaust manifold are hermetically connected through a piston ring. However, as the exhaust manifold expands and contracts thermally during use, a gap is generated between the piston ring and the exhaust pipe, resulting in air leakage. Air leakage is prohibited in the new emission law. Therefore, a corrugated pipe is sleeved on the adjacent two segments of the exhaust manifold. Since the corrugated pipe is a stainless steel pipe and the exhaust manifold is a cast iron pipe, and their materials are different, laser welding is required to connect the exhaust manifold and the corrugated pipe.

[0003] A circumferential weld is formed at the connection between the exhaust manifold and the corrugated pipe. With the continuous increase of the power of the automotive engine and the increase of the exhaust temperature, the exhaust manifold is subjected to the thermal cycle impact of the discharged high-temperature gas flow and the harsh climate conditions during driving. The exhaust manifold is prone to oxidation and corrosion, resulting in damage to the exhaust manifold, affecting its tightness with the corrugated pipe, and causing air leakage. Summary of the Invention

[0004] In order to overcome the above technical problems, the purpose of the present invention is to provide a highly corrosion-resistant laser-welded exhaust manifold and a preparation method thereof: by mixing an organophosphorus reactant and a fluorine-containing reactant and then adding them together with N-methylpyrrolidone into a three-necked flask for stirring reaction, after the reaction is completed, the solid content of the solution is adjusted to obtain a highly corrosion-resistant coating. The laser-welded exhaust manifold is cleaned, then naturally drained, dried, immersed in the highly corrosion-resistant coating, taken out and dried, and then heat-treated. After the highly corrosion-resistant coating is cured to form a highly corrosion-resistant coating, the highly corrosion-resistant laser-welded exhaust manifold is obtained, solving the problem that the existing exhaust manifold is prone to oxidation and corrosion, resulting in damage to the exhaust manifold.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A preparation method of a highly corrosion-resistant laser-welded exhaust manifold includes the following steps:

[0007] Step 1: Mix an organophosphorus reactant and a fluorine-containing reactant according to a molar ratio of 1:1, and then add them together with N-methylpyrrolidone into a three-necked flask equipped with a stirrer, a thermometer, and a gas guide tube. Nitrogen protection is introduced, and the mixture is stirred and reacted at a temperature of 25-30 °C and a stirring rate of 750-950 r / min for 5-6 h. After the reaction is completed, N-methylpyrrolidone is added and stirring is continued to adjust the solid content of the solution to 20-25%, obtaining a highly corrosion-resistant coating;

[0008] Step 2: Wash the laser-welded exhaust manifold with absolute ethanol and distilled water 2 - 3 times, then drain it naturally. After drying, immerse it in a highly corrosion-resistant coating. Then, take it out and dry it at a temperature of 60 - 70 °C for 1 - 2 h until the surface is dry. Then, raise the temperature to 90 - 100 °C and keep it warm for 4 - 5 h. Then, raise the temperature to 130 - 150 °C and keep it warm for 2 - 3 h. Then, raise the temperature to 250 - 260 °C and keep it warm for 1 - 2 h. Then, raise the temperature to 280 - 300 °C and keep it warm for 1 - 2 h. Then, cool it naturally to room temperature, and the highly corrosion-resistant coating cures to form a highly corrosion-resistant coating layer, obtaining the highly corrosion-resistant laser-welded exhaust manifold.

[0009] As a further solution of the present invention: The organophosphorus reactant is prepared by the following steps:

[0010] A1: Add p-nitrobenzaldehyde, p-phenylenediamine, anhydrous magnesium sulfate, and absolute ethanol into a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Stir at a temperature of 25 - 30 °C and a stirring rate of 450 - 550 r / min for 15 - 25 min. Then, raise the temperature to reflux, control the heating rate at 1 - 2 °C / min, and continue to stir and react for 3 - 5 h. After the reaction is completed, cool the reaction product to 3 - 5 °C, then perform vacuum filtration. Wash the filter cake with absolute ethanol 2 - 3 times, and then place it in a vacuum drying oven and dry it at a temperature of 70 - 80 °C for 4 - 5 h to obtain Intermediate 1;

[0011] The reaction process is as follows:

[0012]

[0013] A2: Add Intermediate 1, DOPO, sodium hydride, and N,N-dimethylformamide into a three-necked flask equipped with a stirrer, a thermometer, and a gas guide tube. Introduce nitrogen for protection. Stir at a temperature of 25 - 30 °C and a stirring rate of 450 - 550 r / min for 10 - 15 min. Then, raise the temperature to 100 - 105 °C and continue to stir and react for 20 - 30 h. After the reaction is completed, cool the reaction product to room temperature, and then rotate and evaporate to remove the solvent to obtain Intermediate 2;

[0014] The reaction process is as follows:

[0015]

[0016] A3: Add intermediate 2, 10% palladium carbon, and absolute ethanol into a four-necked flask equipped with a stirrer, a thermometer, a constant-pressure dropping funnel, and a reflux condenser. While stirring at a stirring rate of 450 - 550 r / min, heat up to reflux, control the heating rate at 2 - 3 °C / min. Then, while stirring, gradually add the hydrazine hydrate solution dropwise, control the dropping rate at 1 - 2 drops / s. After the dropping is completed, continue stirring and reacting for 10 - 15 h. After the reaction ends, filter the reaction product while it is hot. Add the filtrate into ice water to precipitate a solid. Filter it under vacuum, wash the filter cake with distilled water 2 - 3 times, and then place it in a vacuum drying oven and dry it at a temperature of 55 - 65 °C for 5 - 7 h to obtain the organophosphorus reactant.

[0017] The reaction process is as follows:

[0018]

[0019] As a further scheme of the present invention: The dosage ratio of the p-nitrobenzaldehyde, p-phenylenediamine, anhydrous magnesium sulfate, and absolute ethanol in step A1 is 0.2 mol: 0.1 mol: 0.22 - 0.25 mol: 120 - 150 mL.

[0020] As a further scheme of the present invention: The dosage ratio of intermediate 1, DOPO, sodium hydride, and N,N-dimethylformamide in step A2 is 0.1 mol: 0.2 mol: 0.25 - 0.30 mol: 130 - 160 mL.

[0021] As a further scheme of the present invention: The dosage ratio of intermediate 2, 10% palladium carbon, absolute ethanol, and hydrazine hydrate solution in step A3 is 15 mmol: 1.0 - 1.5 g: 150 - 180 mL: 15 - 18 mL, and the mass fraction of the hydrazine hydrate solution is 85%.

[0022] As a further scheme of the present invention: The fluorine-containing reactant is prepared by the following steps:

[0023] B1: Add naphthylethylene, ethyl acetate, sodium bromide, and cerium chloride into a three-necked flask equipped with a stirrer, a thermometer, and a constant-pressure dropping funnel. Stir at a temperature of 25 - 30 °C and a stirring rate of 450 - 550 r / min for 30 - 40 min. Then, while stirring, gradually add hydrogen peroxide dropwise, control the dropping rate at 1 - 2 drops / s. After the dropping is completed, continue stirring and reacting for 3 - 5 h. After the reaction ends, filter the reaction product under vacuum, wash the filter cake with distilled water and absolute ethanol 2 - 3 times in sequence, and then place it in a vacuum drying oven and dry it at a temperature of 25 - 30 °C for 6 - 8 h to obtain intermediate 3;

[0024] The reaction process is as follows:

[0025]

[0026] B2: Add intermediate 3, cobalt acetate, manganese acetate, N-hydroxyphthalimide, and glacial acetic acid into a three-necked flask equipped with a stirrer, a thermometer, and a gas inlet tube. Introduce oxygen, control the flow rate of oxygen to be 1.0 - 1.2 L / min, and stir and react for 5 - 6 h under the conditions of a temperature of 110 - 115 °C and a stirring rate of 450 - 550 r / min. After the reaction is completed, cool the reaction product to room temperature, then perform vacuum filtration. Wash the filter cake with distilled water 2 - 3 times, then place it in a vacuum drying oven and dry it for 2 - 3 h under the condition of a temperature of 30 - 35 °C. Then recrystallize with glacial acetic acid to obtain intermediate 4;

[0027] The reaction process is as follows:

[0028]

[0029] B3: Add intermediate 4, 4,4'-(hexafluoroisopropylidene)diphenol, anhydrous potassium carbonate, and N,N-dimethylformamide into a three-necked flask equipped with a stirrer, a thermometer, and a gas inlet tube. Introduce nitrogen for protection, and stir and react for 60 - 70 h under the conditions of a temperature of 110 - 120 °C and a stirring rate of 450 - 550 r / min. After the reaction is completed, cool the reaction product to room temperature, then add the reaction product into anhydrous ether, wash it with distilled water 2 - 3 times, then let it stand for liquid separation. Dry the organic phase with anhydrous magnesium sulfate, then perform suction filtration. Rotate and evaporate the filtrate to remove the solvent, then wash the evaporation product with anhydrous tetrahydrofuran 2 - 3 times, and then place it in a vacuum drying oven and dry it for 5 - 6 h under the condition of a temperature of 50 - 55 °C to obtain intermediate 5;

[0030] The reaction process is as follows:

[0031]

[0032] B4: Add intermediate 5 and acetic anhydride into a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Stir for 10 - 15 min under the conditions of a temperature of 25 - 30 °C and a stirring rate of 450 - 550 r / min, then raise the temperature to reflux, control the heating rate to be 3 - 5 °C / min, and then continue to stir and react for 6 - 8 h. After the reaction is completed, filter the reaction product while it is hot, cool the filtrate to 3 - 5 °C to precipitate, then perform vacuum filtration. Place the filter cake in a vacuum drying oven and dry it for 8 - 10 h under the condition of a temperature of 35 - 45 °C to obtain the fluorine-containing reactant.

[0033] The reaction process is as follows:

[0034]

[0035] As a further solution of the present invention: the dosage ratio of the naphthalene ethyl ring, ethyl acetate, sodium bromide, cerium chloride and hydrogen peroxide in step B1 is 0.1 mol: 180 - 200 mL: 0.11 - 0.15 mol: 0.05 - 0.08 mol: 100 - 120 mL, and the mass fraction of the hydrogen peroxide is 25 - 30%.

[0036] As a further solution of the present invention: the dosage ratio of the intermediate 3, cobalt acetate, manganese acetate, N-hydroxyphthalimide and glacial acetic acid in step B2 is 0.1 mol: 3.0 - 3.5 g: 1.3 - 1.6 g: 2.0 - 2.5 g: 300 - 350 mL.

[0037] As a further solution of the present invention: the dosage ratio of the intermediate 4, 4,4'-(hexafluoroisopropylidene)diphenol, anhydrous potassium carbonate, N,N-dimethylformamide and anhydrous diethyl ether in step B3 is 0.22 - 0.25 mol: 0.1 mol: 0.25 - 0.3 mol: 250 - 300 mL: 450 - 500 mL.

[0038] As a further solution of the present invention: the dosage ratio of the intermediate 5 and acetic anhydride in step B4 is 1 g: 30 - 40 mL.

[0039] As a further solution of the present invention: a highly corrosion-resistant laser-welded exhaust manifold, which is prepared by the preparation method of the highly corrosion-resistant laser-welded exhaust manifold.

[0040] The beneficial effects of the present invention:

[0041] A highly corrosion-resistant laser-welded exhaust manifold and its preparation method according to the present invention. An organic phosphorus reactant and a fluorine-containing reactant are mixed and then added together with N-methylpyrrolidone to a three-necked flask for stirring reaction. After the reaction ends, the solid content of the solution is adjusted to obtain a highly corrosion-resistant coating. The laser-welded exhaust manifold is cleaned, then naturally drained, dried, immersed in the highly corrosion-resistant coating, taken out and dried, and then heat-treated. After the highly corrosion-resistant coating is cured to form a highly corrosion-resistant coating layer, the highly corrosion-resistant laser-welded exhaust manifold is obtained. In this method, the amino group on the organic phosphorus reactant and the anhydride group on the fluorine-containing reactant undergo a polymerization reaction to generate a polyamic acid solution, that is, the highly corrosion-resistant coating. After the highly corrosion-resistant coating is attached to the laser-welded exhaust manifold, a thermal imidization treatment is carried out to dehydrate and form a polyimide coating layer, which is the highly corrosion-resistant coating layer. This highly corrosion-resistant coating layer has good high-temperature resistance and corrosion resistance. After wrapping the laser-welded exhaust manifold, it is difficult for it to be oxidized and corroded. Moreover, this highly corrosion-resistant coating layer has excellent high-temperature resistance and will not crack or fall off at high temperatures, thereby being able to provide long-term protection for the laser-welded exhaust manifold and improving the service life of the laser-welded exhaust manifold.

[0042] In the process of preparing this highly corrosion-resistant laser-welded exhaust manifold, an organic phosphorus reactant is first prepared. The aldehyde group on p-nitrobenzaldehyde reacts with the amino group on p-phenylenediamine to form a C=N bond, obtaining intermediate 1. Then, DOPO uses the P-H bond on it to undergo an addition reaction with the C=N bond to introduce an organic phosphorus group, obtaining intermediate 2. Then, hydrazine hydrate is used to reduce the nitro group on intermediate 2 to an amino group, obtaining the organic phosphorus reactant. In the process of preparing this highly corrosion-resistant laser-welded exhaust manifold, a fluorine-containing reactant is also prepared. Sodium bromide is used to brominate naphthalene ethyl ring, introducing a bromine atom on its naphthalene ring, obtaining intermediate 3. Then, using cobalt acetate, manganese acetate, N-hydroxyphthalimide, and oxygen as oxidants on intermediate 3, an anhydride group is introduced on intermediate 3, obtaining intermediate 4. Then, the bromine atom on intermediate 4 undergoes a nucleophilic substitution reaction with the hydroxyl group on 4,4,4'-(hexafluoroisopropylidene)diphenol, obtaining intermediate 5. Then, the carboxyl group on intermediate 5 is dehydrated to form an anhydride, obtaining the fluorine-containing reactant. The molecular structure of this organic phosphorus reactant contains a large number of benzene rings, as well as organic phosphorus and organic nitrogen. The molecular structure of the fluorine-containing reactant contains a large number of benzene rings, C-F bonds, and naphthalene rings. The reaction product of the two has all the above groups. The naphthalene ring and the benzene ring endow it with good thermal stability and improve its high-temperature resistance. Under the synergistic action of organic phosphorus and organic nitrogen, it exhibits good flame-retardant high-temperature resistance and further improves its high-temperature resistance. The C-F bond endows it with good chemical stability and improves its corrosion resistance, thereby making the prepared highly corrosion-resistant laser-welded exhaust manifold excellent in high-temperature oxidation resistance and corrosion resistance. Specific embodiments

[0043] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0044] Example 1:

[0045] This embodiment is a preparation method of an organophosphorus reactant, including the following steps:

[0046] A1: Add 0.2 mol of p-nitrobenzaldehyde, 0.1 mol of p-phenylenediamine, 0.22 mol of anhydrous magnesium sulfate, and 120 mL of anhydrous ethanol into a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Stir at a temperature of 25 °C and a stirring rate of 450 r / min for 15 min, then heat up to reflux, control the heating rate at 1 °C / min, and then continue to stir and react for 3 h. After the reaction is completed, cool the reaction product to 3 °C, then perform vacuum filtration. Wash the filter cake with anhydrous ethanol twice, and then place it in a vacuum drying oven and dry it at a temperature of 70 °C for 4 h to obtain Intermediate 1;

[0047] A2: Add 0.1 mol of Intermediate 1, 0.2 mol of DOPO, 0.25 mol of sodium hydride, and 130 mL of N,N-dimethylformamide into a three-necked flask equipped with a stirrer, a thermometer, and a gas pipe. Introduce nitrogen for protection. Stir at a temperature of 25 °C and a stirring rate of 450 r / min for 10 min, then continue to stir and react at a temperature of 100 °C for 20 h. After the reaction is completed, cool the reaction product to room temperature, and then remove the solvent by rotary evaporation to obtain Intermediate 2;

[0048] A3: Add 15 mmol of Intermediate 2, 1.0 g of 10% palladium-carbon, and 150 mL of anhydrous ethanol into a four-necked flask equipped with a stirrer, a thermometer, a constant-pressure dropping funnel, and a reflux condenser. While stirring, heat up to reflux at a stirring rate of 450 r / min, control the heating rate at 2 °C / min, and then gradually add 15 mL of 85% hydrazine hydrate solution dropwise while stirring, control the dropping rate at 1 drop / s. After the dropping is completed, continue to stir and react for 10 h. After the reaction is completed, filter the reaction product while it is hot, add the filtrate to ice water to precipitate, perform vacuum filtration, wash the filter cake with distilled water twice, and then place it in a vacuum drying oven and dry it at a temperature of 55 °C for 5 h to obtain the organophosphorus reactant.

[0049] Example 2:

[0050] This example is a preparation method of an organophosphorus reactant, comprising the following steps:

[0051] A1: Add 0.2 mol of p-nitrobenzaldehyde, 0.1 mol of p-phenylenediamine, 0.25 mol of anhydrous magnesium sulfate, and 150 mL of anhydrous ethanol into a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Stir at 30 °C and a stirring rate of 550 r / min for 25 min, then heat up to reflux, control the heating rate at 2 °C / min, and continue to stir and react for 5 h. After the reaction is completed, cool the reaction product to 5 °C, then perform vacuum filtration. Wash the filter cake with anhydrous ethanol three times, and then place it in a vacuum drying oven and dry it at 80 °C for 5 h to obtain Intermediate 1;

[0052] A2: Add 0.1 mol of Intermediate 1, 0.2 mol of DOPO, 0.30 mol of sodium hydride, and 160 mL of N,N-dimethylformamide into a three-necked flask equipped with a stirrer, a thermometer, and a gas pipe. Introduce nitrogen for protection. Stir at 30 °C and a stirring rate of 550 r / min for 15 min, then heat up to 105 °C and continue to stir and react for 30 h. After the reaction is completed, cool the reaction product to room temperature, and then remove the solvent by rotary evaporation to obtain Intermediate 2;

[0053] A3: Add 15 mmol of Intermediate 2, 1.5 g of 10% palladium on carbon, and 180 mL of anhydrous ethanol into a four-necked flask equipped with a stirrer, a thermometer, a constant pressure dropping funnel, and a reflux condenser. While stirring, heat up to reflux at a stirring rate of 550 r / min, control the heating rate at 3 °C / min, then while stirring, gradually add dropwise 18 mL of a hydrazine hydrate solution with a mass fraction of 85%, control the dropping rate at 2 drops / s. After the dropping is completed, continue to stir and react for 15 h. After the reaction is completed, filter the reaction product while it is hot, add the filtrate to ice water to precipitate, perform vacuum filtration, wash the filter cake with distilled water three times, and then place it in a vacuum drying oven and dry it at 65 °C for 7 h to obtain the organophosphorus reactant.

[0054] Example 3:

[0055] This example is a preparation method of a fluorine-containing reactant, comprising the following steps:

[0056] B1: Add 0.1 mol of naphthyl ethyl ring, 180 mL of ethyl acetate, 0.11 mol of sodium bromide, and 0.05 mol of cerium chloride into a three-necked flask equipped with a stirrer, a thermometer, and a constant-pressure dropping funnel. Stir for 30 min at a temperature of 25 °C and a stirring rate of 450 r / min. Then, while stirring, gradually add 100 mL of 25% hydrogen peroxide dropwise, controlling the dropping rate at 1 drop / s. After the addition is complete, continue stirring and reacting for 3 h. After the reaction is completed, vacuum filter the reaction product, wash the filter cake with distilled water and absolute ethanol twice each, then place it in a vacuum drying oven and dry it at a temperature of 25 °C for 6 h to obtain intermediate 3;

[0057] B2: Add 0.1 mol of intermediate 3, 3.0 g of cobalt acetate, 1.3 g of manganese acetate, 2.0 g of N-hydroxyphthalimide, and 300 mL of glacial acetic acid into a three-necked flask equipped with a stirrer, a thermometer, and a gas pipe. Pass in oxygen and control the oxygen flow rate at 1.0 L / min. Stir and react at a temperature of 110 °C and a stirring rate of 450 r / min for 5 h. After the reaction is completed, cool the reaction product to room temperature, then vacuum filter it. Wash the filter cake with distilled water twice, then place it in a vacuum drying oven and dry it at a temperature of 30 °C for 2 h. Then, recrystallize it with glacial acetic acid to obtain intermediate 4;

[0058] B3: Add 0.22 mol of intermediate 4, 0.1 mol of 4,4'-(hexafluoroisopropylidene)diphenol, 0.25 - 0.3 mol of anhydrous potassium carbonate, and 250 mL of N,N-dimethylformamide into a three-necked flask equipped with a stirrer, a thermometer, and a gas pipe. Protect it with nitrogen. Stir and react at a temperature of 110 °C and a stirring rate of 450 r / min for 60 h. After the reaction is completed, cool the reaction product to room temperature, then add the reaction product into 450 mL of anhydrous ether, wash it with distilled water twice, then let it stand for liquid separation. Dry the organic phase with anhydrous magnesium sulfate, then filter it. Rotate and evaporate the filtrate to remove the solvent, then wash the evaporation product with anhydrous tetrahydrofuran twice, and then place it in a vacuum drying oven and dry it at a temperature of 50 °C for 5 h to obtain intermediate 5;

[0059] B4: Add 1 g of intermediate 5 and 30 mL of acetic anhydride into a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Stir at a temperature of 25 °C and a stirring rate of 450 r / min for 10 min, then heat up to reflux, control the heating rate at 3 °C / min, and then continue stirring and reacting for 6 h. After the reaction is completed, filter the reaction product while it is hot, cool the filtrate to 3 °C to precipitate a solid, then vacuum filter it. Place the filter cake in a vacuum drying oven and dry it at a temperature of 35 °C for 8 h to obtain the fluorine-containing reactant.

[0060] Example 4:

[0061] This example is a preparation method of a fluorine-containing reactant, comprising the following steps:

[0062] B1: Add 0.1 mol of naphthalene ethyl ring, 200 mL of ethyl acetate, 0.15 mol of sodium bromide, and 0.08 mol of cerium chloride into a three-necked flask equipped with a stirrer, a thermometer, and a constant-pressure dropping funnel. Stir at 30 °C and a stirring rate of 550 r / min for 40 min. Then, while stirring, gradually add 120 mL of 30% hydrogen peroxide dropwise, controlling the dropping rate at 2 drops / s. After the addition is complete, continue stirring and reacting for 5 h. After the reaction is completed, vacuum filter the reaction product, wash the filter cake with distilled water and anhydrous ethanol three times each, and then place it in a vacuum drying oven and dry it at 30 °C for 8 h to obtain intermediate 3;

[0063] B2: Add 0.1 mol of intermediate 3, 3.5 g of cobalt acetate, 1.6 g of manganese acetate, 2.5 g of N-hydroxyphthalimide, and 350 mL of glacial acetic acid into a three-necked flask equipped with a stirrer, a thermometer, and a gas pipe. Pass in oxygen, controlling the oxygen flow rate at 1.2 L / min. Stir and react at 115 °C and a stirring rate of 550 r / min for 6 h. After the reaction is completed, cool the reaction product to room temperature, then vacuum filter it, wash the filter cake with distilled water three times, and then place it in a vacuum drying oven and dry it at 35 °C for 3 h. Then, recrystallize it with glacial acetic acid to obtain intermediate 4;

[0064] B3: Add 0.25 mol of intermediate 4, 0.1 mol of 4,4'-(hexafluoroisopropylidene)diphenol, 0.3 mol of anhydrous potassium carbonate, and 300 mL of N,N-dimethylformamide into a three-necked flask equipped with a stirrer, a thermometer, and a gas pipe. Protect it with nitrogen. Stir and react at 120 °C and a stirring rate of 550 r / min for 70 h. After the reaction is completed, cool the reaction product to room temperature, then add the reaction product into 500 mL of anhydrous ether, wash it with distilled water three times, then let it stand for liquid separation. Dry the organic phase with anhydrous magnesium sulfate, then filter it. Rotate and evaporate the filtrate to remove the solvent, then wash the evaporation product with anhydrous tetrahydrofuran three times, and then place it in a vacuum drying oven and dry it at 55 °C for 6 h to obtain intermediate 5;

[0065] B4: Add 1 g of intermediate 5 and 40 mL of acetic anhydride to a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Stir for 15 min at a temperature of 30 °C and a stirring rate of 550 r / min. Then, raise the temperature to reflux, control the heating rate at 5 °C / min, and continue stirring and reacting for 8 h. After the reaction is completed, filter the reaction product while it is hot. Cool the filtrate to 5 °C to precipitate a solid. Then, perform vacuum filtration. Place the filter cake in a vacuum drying oven and dry it at a temperature of 45 °C for 10 h to obtain a fluorine-containing reactant.

[0066] Example 5:

[0067] This example is a method for preparing a highly corrosion-resistant laser-welded exhaust manifold, which includes the following steps:

[0068] Step 1: Mix the organophosphorus reactant from Example 1 and the fluorine-containing reactant from Example 3 in a molar ratio of 1:1, and then add them together with N-methylpyrrolidone to a three-necked flask equipped with a stirrer, a thermometer, and a gas duct. Introduce nitrogen for protection and stir and react at a temperature of 25 °C and a stirring rate of 750 r / min for 5 h. After the reaction is completed, add N-methylpyrrolidone and continue stirring to adjust the solid content of the solution to 20% to obtain a highly corrosion-resistant coating.

[0069] Step 2: Wash the laser-welded exhaust manifold twice with absolute ethanol and distilled water, then drain it naturally. After drying, immerse it in the highly corrosion-resistant coating. Then, take it out and dry it at a temperature of 60 °C for 1 h until the surface is dry. Then, raise the temperature to 90 °C and keep it warm for 4 h. Then, raise the temperature to 130 °C and keep it warm for 2 h. Then, raise the temperature to 250 °C and keep it warm for 1 h. Then, raise the temperature to 280 °C and keep it warm for 1 h. Then, naturally cool it to room temperature. The highly corrosion-resistant coating cures to form a highly corrosion-resistant coating layer, and the highly corrosion-resistant laser-welded exhaust manifold is obtained.

[0070] Example 6:

[0071] This example is a method for preparing a highly corrosion-resistant laser-welded exhaust manifold, which includes the following steps:

[0072] Step 1: Mix the organophosphorus reactant from Example 2 and the fluorine-containing reactant from Example 4 in a molar ratio of 1:1, and then add them together with N-methylpyrrolidone to a three-necked flask equipped with a stirrer, a thermometer, and a gas duct. Introduce nitrogen for protection and stir and react at a temperature of 30 °C and a stirring rate of 950 r / min for 6 h. After the reaction is completed, add N-methylpyrrolidone and continue stirring to adjust the solid content of the solution to 25% to obtain a highly corrosion-resistant coating.

[0073] Step 2: Wash the laser-welded exhaust manifold with absolute ethanol and distilled water three times, then drain it naturally. After drying, immerse it in a highly corrosion-resistant coating. Then take it out and dry it at 70°C for 2 hours until the surface is dry. Then raise the temperature to 100°C and keep it warm for 5 hours. Then raise the temperature to 150°C and keep it warm for 3 hours. Then raise the temperature to 260°C and keep it warm for 2 hours. Then raise the temperature to 300°C and keep it warm for 2 hours. Then cool it naturally to room temperature. The highly corrosion-resistant coating cures to form a highly corrosion-resistant coating, and the highly corrosion-resistant laser-welded exhaust manifold is obtained.

[0074] Comparative Example 1:

[0075] Comparative Example 1 is a laser-welded exhaust manifold without treatment.

[0076] Detect the performance of the highly corrosion-resistant laser-welded exhaust manifolds of Examples 5-6 and Comparative Example 1. Place the highly corrosion-resistant laser-welded exhaust manifold in a high-temperature electric furnace and place it at 600°C for 6 hours. Then take it out and weigh it to detect the oxidation weight gain of the highly corrosion-resistant laser-welded exhaust manifold. Place the highly corrosion-resistant laser-welded exhaust manifold in a 6% FeCl3 solution at 50°C and keep it warm for 48 hours. Take it out, remove the surface reaction products, and calculate the corrosion weight loss of the sample.

[0077] The test results are shown in the following table:

[0078] Sample Example 5 Example 6 Comparative Example 1 Coating condition at 600 °C No cracking, no peeling No cracking, no peeling / <![CDATA[Oxidation weight gain, g / cm 2 > 0.075 0.071 1.28 <![CDATA[Corrosion weight loss, g / cm 2 > 0.066 0.063 0.34

[0079] Referring to the data in the above table, it can be known that the untreated laser-welded exhaust manifold is prone to oxidation at high temperatures and is prone to corrosion under the condition of FeCl3 solution. However, the laser-welded exhaust manifold treated with the highly corrosion-resistant coating has good high-temperature oxidation resistance and corrosion resistance. Therefore, it can effectively improve the performance of the laser-welded exhaust manifold and extend its service life.

[0080] In the description of this specification, the description referring to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0081] The above content is only an example and explanation of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar methods to replace them. As long as they do not deviate from the invention or exceed the scope defined by this claim book, they should all belong to the protection scope of the present invention.

Claims

1. A preparation method of a highly corrosion-resistant laser-welded exhaust manifold, characterized in that, It includes the following steps: Step 1: Mix the organophosphorus reactant and the fluorine-containing reactant, and then add them together with N-methylpyrrolidone into a three-necked flask for stirring reaction. After the reaction is completed, adjust the solid content of the solution to obtain a highly corrosion-resistant coating. Step 2: Clean the laser-welded exhaust manifold, then drain it naturally, dry it in an oven, immerse it in the highly corrosion-resistant coating, then take it out and dry it, and then perform heat treatment until the highly corrosion-resistant coating cures to form a highly corrosion-resistant coating, thus obtaining the highly corrosion-resistant laser-welded exhaust manifold. Among them, the organophosphorus reactant is prepared by the following steps: A1: Add p-nitrobenzaldehyde, p-phenylenediamine, anhydrous magnesium sulfate, and absolute ethanol into a three-necked flask and stir. Then heat up to reflux and continue stirring the reaction. After the reaction is completed, cool the reaction product, then perform vacuum filtration. Wash and dry the filter cake to obtain Intermediate 1. The dosage ratio of p-nitrobenzaldehyde, p-phenylenediamine, anhydrous magnesium sulfate, and absolute ethanol in Step A1 is 0.2 mol: 0.1 mol: 0.22 - 0.25 mol: 120 - 150 mL. A2: Add Intermediate 1, DOPO, sodium hydride, and N,N-dimethylformamide into a three-necked flask and stir. Then heat up and continue stirring the reaction. After the reaction is completed, cool the reaction product to room temperature, and then perform rotary evaporation to obtain Intermediate 2. The dosage ratio of Intermediate 1, DOPO, sodium hydride, and N,N-dimethylformamide in Step A2 is 0.1 mol: 0.2 mol: 0.25 - 0.30 mol: 130 - 160 mL. A3: Add Intermediate 2, 10% palladium on carbon, and absolute ethanol into a four-necked flask, heat up to reflux while stirring, and then gradually add hydrazine hydrate solution drop by drop while stirring. After the addition is completed, continue stirring the reaction. After the reaction is completed, filter the reaction product while it is hot. Add the filtrate into ice water to precipitate, perform vacuum filtration, wash and dry the filter cake to obtain the organophosphorus reactant. The dosage ratio of Intermediate 2, 10% palladium on carbon, absolute ethanol, and hydrazine hydrate solution in Step A3 is 15 mmol: 1.0 - 1.5 g: 150 - 180 mL: 15 - 18 mL, and the mass fraction of the hydrazine hydrate solution is 85%. The fluorine-containing reactant is prepared by the following steps: B1: Add naphthylethylene ring, ethyl acetate, sodium bromide, and cerium chloride into a three-necked flask and stir. Then gradually add hydrogen peroxide drop by drop while stirring. After the addition is completed, continue stirring the reaction. After the reaction is completed, perform vacuum filtration on the reaction product. Wash and dry the filter cake to obtain Intermediate 3. The dosage ratio of naphthylethylene ring, ethyl acetate, sodium bromide, cerium chloride, and hydrogen peroxide in Step B1 is 0.1 mol: 180 - 200 mL: 0.11 - 0.15 mol: 0.05 - 0.08 mol: 100 - 120 mL, and the mass fraction of the hydrogen peroxide is 25 - 30%. B2: Add intermediate 3, cobalt acetate, manganese acetate, N-hydroxyphthalimide and glacial acetic acid into a three-necked flask, introduce oxygen and stir for reaction. After the reaction is completed, cool the reaction product, then carry out vacuum filtration. Wash and dry the filter cake to obtain intermediate 4; the dosage ratio of intermediate 3, cobalt acetate, manganese acetate, N-hydroxyphthalimide and glacial acetic acid in step B2 is 0.1 mol: 3.0 - 3.5 g: 1.3 - 1.6 g: 2.0 - 2.5 g: 300 - 350 mL; B3: Add intermediate 4, 4,4'-(hexafluoroisopropylidene)diphenol, anhydrous potassium carbonate and N,N-dimethylformamide into a three-necked flask and stir for reaction. After the reaction is completed, cool the reaction product, then add the reaction product into anhydrous ether, then wash with distilled water, then let it stand for layer separation, dry the organic phase, then carry out rotary evaporation, then wash and dry the evaporation product to obtain intermediate 5; the dosage ratio of intermediate 4, 4,4'-(hexafluoroisopropylidene)diphenol, anhydrous potassium carbonate, N,N-dimethylformamide and anhydrous ether in step B3 is 0.22 - 0.25 mol: 0.1 mol: 0.25 - 0.3 mol: 250 - 300 mL: 450 - 500 mL; B4: Add intermediate 5 and acetic anhydride into a three-necked flask and stir, then raise the temperature to reflux and continue stirring for reaction. After the reaction is completed, filter the reaction product while it is hot, cool the filtrate to precipitate, then carry out vacuum filtration, and dry the filter cake to obtain the fluorine-containing reactant; the dosage ratio of intermediate 5 and acetic anhydride in step B4 is 1 g: 30 - 40 mL.

2. A highly corrosion-resistant laser-welded exhaust manifold, characterized in that, The highly corrosion-resistant laser-welded exhaust manifold is prepared by the preparation method of the highly corrosion-resistant laser-welded exhaust manifold described in claim 1.

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