Preparation method and application of schiff base corrosion inhibitor for cooling liquid of AZ91D magnesium alloy

Abstract

This invention discloses a method for preparing a Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant. The method involves adding an ethanol or acetone solution of the ketone-containing heterocyclic compound dropwise to an aqueous solution of the alkaline amino acid at a molar ratio of 1:1 to 1.5. The reaction is carried out at 40–80°C for 4–36 hours, followed by concentration, extraction with glacial ethyl acetate, washing with glacial ethyl acetate, and drying to obtain the corrosion inhibitor. Further, the corrosion inhibitor is formulated into a coolant specifically for AZ91D magnesium alloy. This coolant is composed of a mixture of raw materials with the following weight percentages: 0.1–2% corrosion inhibitor, 39–60% deionized water, and 39–60% ethylene glycol. This invention features a simple preparation process, and the obtained corrosion inhibitor can be stored for a long time, exhibits good thermal stability, strong oxidation resistance, low conductivity, high corrosion inhibition efficiency, and good corrosion inhibition effect on AZ91D magnesium alloy.

Description

Technical Field

[0001] This invention belongs to the field of metal corrosion protection technology, and relates to a method for preparing nonionic organic corrosion inhibitors from heterocyclic compounds and amino acids. Specifically, it relates to a method for preparing and applying a Schiff base corrosion inhibitor for coolant used in AZ91D magnesium alloys. The corrosion inhibitor prepared using this invention is used to form a dense adsorption film on the metal surface of cooling system materials such as those in automotive engines by adding a small amount of the substance (i.e., the prepared corrosion inhibitor) to automotive coolant, thereby inhibiting corrosion of AZ91D magnesium alloys and effectively delaying metal corrosion. Background Technology

[0002] Magnesium alloys possess characteristics such as low density, high specific strength and specific stiffness, strong absorption of plastic deformation, and strong mechanical vibration resistance. AZ91D magnesium alloy is a high-performance magnesium alloy. In AZ91D, A represents aluminum, Z represents zinc, 9 indicates 9% aluminum content, 1 indicates 1% zinc content, and D is an identification code, conforming to the national standard GB / T5153-2003. Using magnesium alloys as materials for cooling systems in automobile engines is a superior lightweight material compared to aluminum alloys and plastics, significantly reducing vehicle weight and increasing range. However, magnesium and its alloys are reactive metals with extremely low standard electrode potential (-2.36V), making them prone to hydrogen evolution corrosion in coolants. Adding corrosion inhibitors to coolants to suppress magnesium alloy corrosion is currently a low-cost, convenient, and efficient anti-corrosion technology. Therefore, the development of a dedicated corrosion inhibitor technology for AZ91D magnesium alloy used in cooling systems for automobile engines has significant industrial value. In the prior art, there are few reports on corrosion inhibitors specifically for AZ91D magnesium alloy coolants. CN 111690936A discloses a compound corrosion inhibitor for AZ91D magnesium alloy suitable for neutral salt water corrosive media and its preparation method. This compound corrosion inhibitor is mainly composed of the organic corrosion inhibitor benzotriazole linseed oil amide derivative and the inorganic corrosion inhibitor sodium molybdate. CN 101922009B discloses a corrosion inhibitor formula for inhibiting the corrosion of magnesium alloys in automotive engine coolant. This formula is also composed of the organic corrosion inhibitor benzotriazole, hexamethylenetetramine, sodium dodecylbenzenesulfonate, and the inorganic corrosion inhibitors sodium molybdate and sodium fluoride. Similarly, CN105369256A discloses a magnesium alloy corrosion inhibitor in automotive coolant, the main components of which are also the organic corrosion inhibitor sodium lignosulfonate and the inorganic corrosion inhibitor disodium hydrogen phosphate. Patent 113818020A discloses a compound corrosion inhibitor for magnesium alloys in chlorine-containing media and its preparation method, the main components of which are also organic corrosion inhibitors (dicarboxylate) and inorganic corrosion inhibitors (sodium fluoride). The main drawback of the above-mentioned prior art is that the corrosion inhibitors are ionic organic or ionic inorganic corrosion inhibitors, resulting in coolant conductivity generally greater than 500 μS / cm. Using this in coolant for new energy vehicles poses a risk of short circuits and thermal runaway due to leakage. The new national standard GB29743.2-2025 requires a conductivity not exceeding 100 μS / cm; therefore, the above-mentioned prior art is not suitable for the coolant conductivity requirements of new energy vehicles. Developing a non-ionic organic corrosion inhibitor with low conductivity that provides special protection for AZ91D magnesium alloy is of great significance to the development of thermal management technology for new energy vehicles.

[0003] In existing technologies, most commonly used organic nonionic corrosion inhibitors accelerate the corrosion of AZ91D magnesium alloys. This is because the coordination space of these inhibitors is incompatible with AZ91D magnesium alloys, preventing the formation of a stable adsorption film. Furthermore, the unstable adsorption film on the surface of the magnesium hydroxide (Mg(OH)2) passivation film formed during corrosion is hindered by the presence of this passivation film, thus accelerating corrosion. For example, benzotriazole has good corrosion protection for copper alloys but accelerates the corrosion of AZ91D magnesium alloys.

[0004] In the prior art, the corrosion inhibitors used in the coolant for AZ91D magnesium alloy are all ionic organic corrosion inhibitors or ionic inorganic corrosion inhibitors, while there are no literature reports on non-ionic organic corrosion inhibitors that are effective in inhibiting the corrosion of AZ91D magnesium alloy. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems and shortcomings of existing organic nonionic corrosion inhibitors that accelerate the corrosion of AZ91D magnesium alloys, and to provide a method for preparing and applying a Schiff base corrosion inhibitor for AZ91D magnesium alloy coolants. This provides a method for preparing a dedicated organic Schiff base corrosion inhibitor for suppressing the corrosion of AZ91D magnesium alloys, and a method for applying it as a coolant corrosion inhibitor. This invention utilizes a nonionic organic corrosion inhibitor formed from amino acids and heterocyclic compounds, which contains a variety of heteroatom Schiff base coordination spatial structures to better chelate AZ91D magnesium alloys, forming a dense adsorption film that prevents corrosion particles from entering the surface and interior of the AZ91D magnesium alloy, thereby significantly slowing down the corrosion of the AZ91D magnesium alloy.

[0006] To achieve the purpose of this invention, the main technical solution adopted by this invention is as follows: the amino group of a basic amino acid reacts with the carbonyl group of a ketone-containing heterocyclic compound to form a Schiff base compound, and the Schiff base compound is mixed with water to form a coolant, which is then applied to the corrosion protection of AZ91D magnesium alloy.

[0007] Specifically, the present invention relates to a method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, characterized by comprising the following steps: a. Dissolve 100 parts by weight of basic amino acids in 80-250 parts by weight of deionized water (or distilled water) to form an aqueous solution of basic amino acids; b. Dissolve 100 parts by weight of the ketone-containing heterocyclic compound in 80 to 250 parts by weight of anhydrous ethanol or acetone to form an ethanol or acetone solution containing the ketone-containing heterocyclic compound. c. Place the alkaline amino acid aqueous solution into the reaction vessel, and place the ethanol or acetone solution containing the ketone heterocyclic compound into the (automatic) dropper; drop the ethanol or acetone solution containing the ketone heterocyclic compound into the reaction vessel, control the molar ratio of alkaline amino acid to ketone heterocyclic compound to be 1:1 to 1.5, and react at a temperature of 40 to 80°C for 4 to 36 hours to obtain the reacted material; d. Cool the reaction material to room temperature, concentrate the reaction material (solution) by vacuum distillation to obtain a concentrated solution, extract it with 1 to 3 times the volume of glacial ethyl acetate, continue to concentrate the aqueous phase by vacuum distillation, wash it with glacial ethyl acetate and dry it to obtain the Schiff base corrosion inhibitor (or amino acid heterocyclic Schiff base corrosion inhibitor) for the cooling liquid of AZ91D magnesium alloy.

[0008] Furthermore, the present invention comprises: a method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, characterized by including the following steps: a. Dissolve 100 parts by weight of basic amino acids in 80-250 parts by weight of deionized water (or distilled water) to form an aqueous solution of basic amino acids; The basic amino acid is any one or a mixture of two of L-histidine, L-lysine, and L-arginine. b. Dissolve 100 parts by weight of the ketone-containing heterocyclic compound in 80 to 250 parts by weight of anhydrous ethanol or acetone to form an ethanol or acetone solution containing the ketone-containing heterocyclic compound. c. Place the alkaline amino acid aqueous solution into the reaction vessel, and place the ethanol or acetone solution containing the ketone heterocyclic compound into the (automatic) dropper; drop the ethanol or acetone solution containing the ketone heterocyclic compound into the reaction vessel at a rate of 0.01-0.2 mL / s, control the molar ratio of alkaline amino acid to ketone heterocyclic compound to be 1-1.5, and react at a temperature of 40-80℃ for 4-36 h to obtain the reacted material; d. Cool the reacted material to room temperature, and concentrate the reacted material (solution) to 80-95% by mass distillation under reduced pressure to obtain a concentrated solution. Extract the solution with 1-3 times the volume of glacial ethyl acetate, and continue to concentrate the aqueous phase to 95-99% by reduced pressure distillation. Wash the solution with glacial ethyl acetate and dry it under vacuum at 50-80°C for 2-8 hours to obtain the Schiff base corrosion inhibitor (or amino acid heterocyclic Schiff base corrosion inhibitor) for the cooling liquid of AZ91D magnesium alloy.

[0009] In the above-described content of the present invention: the ketone-containing heterocyclic compound in step b is any one or a mixture of two of the following: tetrahydrofuran-3-one, 2-methyltetrahydrofuran-3-one, 3-hydroxytetrahydrofuran-2-one, tetrahydropyran-4-one, 3-methyltetrahydropyran-4-one, 2-imidazolium, 4-methylimidazolium-2-one, 2-piperazinone, 4-methyl-2-piperazinone, 1-methylpiperazin-2-one, 3,3-dimethyl-2-piperazinone, 2-pyrrolidone, 1-methyl-2-pyrrolidone, 5,5-dimethyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 3-morpholinone, 5-methylmorpholinone, 5-ethylmorpholinone, and 5-isopropylmorpholinone.

[0010] Another aspect of this invention is the application of a corrosion inhibitor prepared by a method for preparing Schiff base corrosion inhibitors for AZ91D magnesium alloy coolants (i.e., the Schiff base corrosion inhibitor for AZ91D magnesium alloy coolants, or amino acid heterocyclic Schiff base corrosion inhibitors), characterized in that: the prepared corrosion inhibitor is applied to automotive coolant (in a simulated corrosion environment) to inhibit corrosion of AZ91D magnesium alloy.

[0011] Furthermore, another aspect of the present invention is the application of a corrosion inhibitor prepared by a method for preparing Schiff base corrosion inhibitors for AZ91D magnesium alloy coolants (i.e., the Schiff base corrosion inhibitor for AZ91D magnesium alloy coolants, or amino acid heterocyclic Schiff base corrosion inhibitors), characterized in that: the (simulated corrosion environment) coolant is composed of raw materials mixed with the following components and their weight percentages: 0.1-2% corrosion inhibitor (i.e., the Schiff base corrosion inhibitor for AZ91D magnesium alloy coolants, or amino acid heterocyclic Schiff base corrosion inhibitors), 39-60% deionized water, and 39-60% ethylene glycol, and the total amount of each component raw material is 100%.

[0012] Another aspect of this invention relates to the application of the Schiff base corrosion inhibitor (i.e., the Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor) prepared by the method for preparing the Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, characterized in that: 0.05-5% sodium chloride by weight is also added to the (simulated corrosion environment) coolant.

[0013] Another aspect of this invention relates to the application of the Schiff base corrosion inhibitor (i.e., the Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor) prepared by the method for preparing the Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, characterized in that: a mixture of sodium sulfate, sodium chloride and sodium bicarbonate is also added to the (simulated corrosion environment) coolant. The concentrations of the mixture of sodium sulfate, sodium chloride, and sodium bicarbonate in the (simulated corrosive environment) coolant are as follows: sodium sulfate concentration is 130–160 mg / L, sodium chloride concentration is 150–180 mg / L, and sodium bicarbonate concentration is 120–150 mg / L.

[0014] Another aspect of this invention relates to the application of the Schiff base corrosion inhibitor (i.e., the Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor) prepared by the method for preparing the Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, characterized in that: the specific application method is to immerse the AZ91D magnesium alloy in a coolant (simulated corrosion environment) at a temperature of 20 to 80°C.

[0015] Compared with the prior art, the present invention has the following features and beneficial effects: (1) By using the present invention, the amino group of basic amino acid reacts with the carbonyl group of ketone heterocyclic compound through nucleophilic addition-elimination reaction to form Schiff base heterocyclic compound containing C=N double bond. By utilizing its Schiff base coordination space structure containing multiple heteroatoms, it can better chelate AZ91D magnesium alloy and form dense adsorption, thereby achieving high corrosion inhibition efficiency, good corrosion inhibition effect, obvious protection effect on AZ91D magnesium alloy, low conductivity (less than 100μS / cm), effectively reducing the risk of short circuit and thermal runaway. At room temperature, in a 0.5% sodium chloride coolant, after 7 days (d means day, the same below), the corrosion inhibition efficiency of AZ91D magnesium alloy can reach 94.64% (see Table 4); The present invention utilizes the non-ionic organic corrosion inhibitor formed by amino acid and heterocyclic compound, which contains Schiff base coordination space structure containing multiple heteroatoms, to better chelate AZ91D magnesium alloy and form dense adsorption film, preventing corrosion particles from entering the surface and interior of AZ91D magnesium alloy, thereby significantly slowing down the corrosion of AZ91D magnesium alloy; (2) The Schiff base corrosion inhibitor (or amino acid heterocyclic Schiff base corrosion inhibitor) for cooling liquid of AZ91D magnesium alloy prepared by the present invention is inexpensive to prepare, the synthesis process is simple, the purification efficiency is high, and the reaction can be carried out at low heating. Due to the C=N double bond conjugation effect and dynamic reversibility of the amino acid Schiff base heterocyclic compound corrosion inhibitor, the obtained corrosion inhibitor has good thermal stability (decomposition begins at 180℃), good stability at low temperature, and a wide applicable temperature range (-50~90℃). Moreover, the C=N double bond can effectively eliminate free radicals and has strong antioxidant capacity. (3) The Schiff base corrosion inhibitor (or amino acid heterocyclic Schiff base corrosion inhibitor) for cooling liquid of AZ91D magnesium alloy prepared by the present invention is simple to powder after drying, has a fine texture and can be stored for a long time. It is not picky about the use environment and use temperature, and can maintain good efficacy in both weak acid and weak alkali, especially under alkaline conditions. (4) The Schiff base corrosion inhibitor (or amino acid heterocyclic Schiff base corrosion inhibitor) for cooling liquid of AZ91D magnesium alloy prepared by the present invention has a relatively small molecular weight. The N, O and S in the heterocyclic molecules can be well adsorbed on the surface of AZ91D magnesium alloy and effectively block the continued corrosion of corrosive media such as sodium chloride, reduce the corrosion rate of magnesium alloy AZ91D, form a dense protective film, and have good performance at a temperature of 60 to 80℃. (5) The preparation process of this invention is simple. The Schiff base corrosion inhibitor (or amino acid heterocyclic Schiff base corrosion inhibitor) for cooling liquid of AZ91D magnesium alloy prepared by this invention is non-toxic and odorless. It has the advantages of good environmental compatibility, complete water solubility, convenient operation and good economy. It can be stored for a long time, has good thermal stability, strong anti-oxidation ability, low electrical conductivity, high corrosion inhibition efficiency for AZ91D magnesium alloy, good corrosion inhibition effect and strong practicality. Attached Figure Description

[0016] Figure 1 This is a photograph taken in Example 1, showing an AZ91D magnesium alloy block immersed in a 3.5% sodium chloride corrosion inhibitor coolant solution at 60°C for 7 days. Figure 1 (Left) Photograph of an AZ91D magnesium alloy block immersed in 3.5% sodium chloride blank coolant for 7 days. Figure 1 right); The figure illustrates that in Example 1, the AZ91D magnesium alloy block immersed in a 3.5% sodium chloride corrosion inhibitor coolant for 7 days had a glossy surface with few surface precipitates, while the AZ91D magnesium alloy block immersed in a 3.5% sodium chloride blank coolant for 7 days had a rough surface with a large amount of precipitates. This indicates that the coolant with added L-lysine-tetrahydropyran Schiff base corrosion inhibitor can effectively inhibit the corrosion of AZ91D magnesium alloy.

[0017] Figure 2 The images shown are from Example 1, specifically the surface SEM images of the AZ91D magnesium alloy block immersed in 3.5% sodium chloride corrosion inhibitor coolant for 7 days at 60°C (Figure a) and the surface SEM images of the AZ91D magnesium alloy block immersed in 3.5% sodium chloride blank coolant for 7 days (Figure b). The figure illustrates that in Example 1, the AZ91D magnesium alloy block immersed in 3.5% sodium chloride corrosion inhibitor coolant for 7 days had a dense film on its surface with little precipitate. In contrast, the AZ91D magnesium alloy block immersed in 3.5% sodium chloride blank coolant for 7 days had a large amount of precipitate on its surface and cracks appeared. This further demonstrates that the coolant with added L-lysine-tetrahydropyran Schiff base corrosion inhibitor can effectively inhibit the corrosion of AZ91D magnesium alloy.

[0018] Figure 3 This is the thermogravimetric diagram of the L-lysine-tetrahydropyran Schiff base corrosion inhibitor in Example 1; The figure illustrates that the L-lysine-tetrahydropyran Schiff base corrosion inhibitor in Example 1 exhibits excellent thermal stability and does not decompose before 180°C.

[0019] Figure 4 This is the XRD pattern of the AZ91D magnesium alloy block after it has been immersed in 3.5% sodium chloride corrosion inhibitor coolant for 7 days and then pickled, as described in Example 1. The figure illustrates that in Example 1, after the AZ91D magnesium alloy block was immersed in a 3.5% sodium chloride corrosion inhibitor coolant for 7 days and then pickled, the crystal phase structure of the AZ91D magnesium alloy did not change. This further demonstrates that the coolant containing L-lysine-tetrahydropyran Schiff base corrosion inhibitor does not affect the crystal phase structure of the AZ91D magnesium alloy. Detailed Implementation

[0020] The embodiments given below are intended to further illustrate the present invention, but should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0021] To verify the corrosion inhibition effect of the Schiff base corrosion inhibitor (or amino acid heterocyclic Schiff base corrosion inhibitor) prepared in this invention on AZ91D magnesium alloy in a simulated corrosion environment coolant, this invention uses the room temperature and high temperature static weight loss method to evaluate its corrosion inhibition effect. The room temperature and high temperature static weight loss method involves immersing the AZ91D magnesium alloy in a 0.05-5% sodium chloride coolant after degreasing and drying, and at 20-80℃ for 1-15 days. The corrosion inhibition efficiency is obtained by calculating the weight change of the AZ91D magnesium alloy before and after immersion. Corrosion inhibition efficiency = (blank weight loss - immersion coolant weight loss) / blank weight loss * 100%.

[0022] In the following embodiments, the unit of mass parts (parts by weight) is grams.

[0023] Example 1: A method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, comprising the following steps: a. Dissolve 100 parts by weight of L-lysine (basic amino acid) in 150 parts by weight of deionized water to form an L-lysine aqueous solution (basic amino acid aqueous solution). b. Dissolve 100 parts by mass of tetrahydropyran-4-one (containing ketone heterocyclic compound) in 100 parts by mass of anhydrous ethanol to form a tetrahydropyran-4-one ethanol solution (containing ketone heterocyclic compound). c. Control the molar ratio of L-lysine (basic amino acid) to tetrahydropyran-4-one (containing ketone heterocyclic compound) to be 1:1. Place the aqueous solution of L-lysine (basic amino acid aqueous solution) into the reaction vessel, and place the ethanol solution of tetrahydropyran-4-one (containing ketone heterocyclic compound) into a dropper. Add the ethanol solution of tetrahydropyran-4-one (containing ketone heterocyclic compound) to the reaction vessel at a rate of 0.02 mL / s. React at 40°C for 24 h to obtain the reaction product. d. After cooling the reaction material to room temperature, concentrate the reaction material (solution) to 85% by vacuum distillation, obtaining a concentrated solution. Extract the solution with 1.5 times the volume of glacial ethyl acetate. Continue to concentrate the aqueous phase to 95% by vacuum distillation, then wash with glacial ethyl acetate and vacuum dry at 60°C for 4 hours to obtain L-lysine-tetrahydropyran Schiff base corrosion inhibitor (i.e., Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor). Its characteristic infrared peak is detected at 3425.92 cm⁻¹. -1 2934.16cm -1 1580.86cm -1 1517.70cm -1 1406.82cm -1 1353.30cm -1 548.17cm -1 .

[0024] Furthermore, the application of the corrosion inhibitor prepared by the above-mentioned method for preparing a Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant (i.e., the L-lysine-tetrahydropyran Schiff base corrosion inhibitor, or the Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant, or the amino acid heterocyclic Schiff base corrosion inhibitor) is: to apply the prepared corrosion inhibitor to automotive coolant to inhibit the corrosion of AZ91D magnesium alloy. The coolant (or corrosion inhibitor coolant) is composed of raw materials with the following components and weight percentages: 1% corrosion inhibitor, 42% deionized water, and 57% ethylene glycol. A coolant without corrosion inhibitor is prepared by adding 43% deionized water and 57% ethylene glycol, which is defined as blank coolant. 3.5g of sodium chloride is added to the above coolant, and the two are named 3.5% sodium chloride corrosion inhibitor coolant and 3.5% sodium chloride blank coolant, respectively. Prepare AZ91D magnesium alloy blocks of 50*25*4mm and grind them sequentially with a constant speed grinder at 60 grit, 240 grit, 400 grit, 600 grit, and 1200 grit. After grinding, soak them in anhydrous ethanol and sonicate them for 3 minutes. Remove them and dry them for later use. Immerse the treated AZ91D magnesium alloy blocks in a coolant containing 3.5% sodium chloride corrosion inhibitor and a blank coolant containing 3.5% sodium chloride, respectively, and keep them at 60℃ for 1 day, 3 days, and 7 days. Calculate the corrosion inhibition efficiency based on the weight loss. The results are shown in Table 1.

[0025] Table 1: Static weight loss and corrosion inhibition efficiency of AZ91D magnesium alloy applied to 60℃ coolant containing 3.5% sodium chloride. The table shows that adding L-lysine-tetrahydropyran Schiff base corrosion inhibitor and immersing the alloy in 3.5% sodium chloride coolant at 60°C can effectively inhibit the corrosion of AZ91D magnesium alloy.

[0026] The conductivity of the corrosion inhibitor in the coolant containing L-lysine-tetrahydropyran Schiff base prepared in this example was found to be 65 μS / cm.

[0027] Example 2: A method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, comprising the following steps: a. Dissolve 100 parts by weight of L-lysine (basic amino acid) in 150 parts by weight of deionized water to form an L-lysine aqueous solution (basic amino acid aqueous solution). b. Dissolve 100 parts by mass of 2-pyrrolidone (containing ketone heterocyclic compounds) in 100 parts by mass of anhydrous ethanol to form a 2-pyrrolidone ethanol solution (an ethanol solution containing ketone heterocyclic compounds). c. Controlling the molar ratio of L-lysine (basic amino acid) to 2-pyrrolidone (containing ketone heterocyclic compound) to 1:1, the aqueous solution of L-lysine (basic amino acid) is placed in the reaction vessel, and the ethanol solution of 2-pyrrolidone (containing ketone heterocyclic compound) is placed in an automatic dropper; the ethanol solution of 2-pyrrolidone (containing ketone heterocyclic compound) is added dropwise to the reaction vessel at a rate of 0.02 mL / s, and the reaction is carried out at 40℃ for 24 h to obtain the reaction product; d. Cool the reacted material to room temperature, and concentrate the reacted material (solution) to 85% by mass distillation under reduced pressure to obtain a concentrated solution. Extract the solution with 1.5 times the volume of glacial ethyl acetate, and continue to concentrate the aqueous phase to 95% by reduced pressure distillation. Wash the solution with glacial ethyl acetate and dry it under vacuum at 60°C for 4 hours to obtain L-lysine-pyrrole Schiff base corrosion inhibitor (i.e., Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor).

[0028] Furthermore, the application of the corrosion inhibitor prepared by the above-mentioned method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy (i.e., the L-lysine-pyrrole Schiff base corrosion inhibitor, or the Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, or the amino acid heterocyclic Schiff base corrosion inhibitor) is: to apply the prepared corrosion inhibitor to automotive coolant to inhibit the corrosion of AZ91D magnesium alloy. The coolant (or corrosion inhibitor coolant) is composed of raw materials with the following components and weight percentages: 1% corrosion inhibitor, 42% deionized water, and 57% ethylene glycol. A coolant without corrosion inhibitor is prepared by adding 43% deionized water and 57% ethylene glycol. 3.5g of sodium chloride is added to the above coolant, resulting in a coolant containing 3.5% sodium chloride corrosion inhibitor and a blank coolant containing 3.5% sodium chloride, respectively. AZ91D magnesium alloy blocks of 50*25*4mm are prepared and polished sequentially with a constant-speed grinder at 60 grit, 240 grit, 400 grit, 600 grit, and 1200 grit. After polishing, the blocks are immersed in anhydrous ethanol and sonicated for 3 minutes, then removed and dried for later use. The treated AZ91D magnesium alloy blocks are immersed in the coolant containing 3.5% sodium chloride corrosion inhibitor and the blank coolant containing 3.5% sodium chloride, respectively, and kept at 60℃ for 1 day, 3 days, and 7 days. The corrosion inhibition efficiency is calculated based on the weight loss, and the results are shown in Table 2.

[0029] Table 2: Static weight loss test data and corrosion inhibition efficiency of AZ91D magnesium alloy applied to 60℃ coolant containing 3.5% sodium chloride: The table shows that adding L-lysine-pyrrole Schiff base corrosion inhibitor and immersing the alloy in 3.5% sodium chloride coolant at 60°C can effectively inhibit the corrosion of AZ91D magnesium alloy.

[0030] The conductivity of the corrosion inhibitor coolant containing L-lysine-pyrrole Schiff base prepared in this example was found to be 84 μS / cm.

[0031] Example 3: A method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, comprising the following steps: a. Dissolve 100 parts by weight of L-lysine (basic amino acid) in 150 parts by weight of deionized water to form an L-lysine aqueous solution (basic amino acid aqueous solution). b. Dissolve 100 parts by mass of 3-morpholinone (containing ketone heterocyclic compounds) in 100 parts by mass of anhydrous ethanol to form a 3-morpholinone ethanol solution (an ethanol solution containing ketone heterocyclic compounds). c. Control the molar ratio of L-lysine (basic amino acid) to 3-morpholinone (containing ketone heterocyclic compound) to be 1:1. Place the L-lysine aqueous solution (basic amino acid aqueous solution) into the reaction vessel, and place the 3-morpholinone ethanol solution (ethanol solution containing ketone heterocyclic compound) into an automatic dropper. Add the 3-morpholinone ethanol solution (ethanol solution containing ketone heterocyclic compound) dropwise into the reaction vessel at a rate of 0.02 mL / s. React at 40℃ for 24 h to obtain the reaction product. d. Cool the reacted material to room temperature, and concentrate the reacted material (solution) to 85% by mass distillation under reduced pressure to obtain a concentrated solution. Extract the solution with 1.5 times the volume of glacial ethyl acetate, and continue to concentrate the aqueous phase to 95% by reduced pressure distillation. Wash the solution with glacial ethyl acetate and dry it under vacuum at 60°C for 4 hours to obtain L-lysine-morpholine Schiff base corrosion inhibitor (i.e., Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor).

[0032] Furthermore, the application of the corrosion inhibitor prepared by the above-mentioned method for preparing a Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant (i.e., the L-lysine-morpholine Schiff base corrosion inhibitor, or the Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant, or the amino acid heterocyclic Schiff base corrosion inhibitor) is as follows: the prepared corrosion inhibitor is applied to automotive coolant to inhibit the corrosion of AZ91D magnesium alloy.

[0033] The coolant (or corrosion inhibitor-containing coolant) is composed of raw materials with the following components and weight percentages: 1% corrosion inhibitor, 42% deionized water, and 57% ethylene glycol. A corrosion inhibitor-free coolant is prepared by adding 43% deionized water and 57% ethylene glycol. 3.5g of sodium chloride is added to the above coolant, resulting in a coolant containing 3.5% sodium chloride corrosion inhibitor and a blank coolant containing 3.5% sodium chloride, respectively. AZ91D magnesium alloy blocks of 50*25*4mm are prepared and polished sequentially with a constant-speed grinder at 60 grit, 240 grit, 400 grit, 600 grit, and 1200 grit. After polishing, the blocks are immersed in anhydrous ethanol and sonicated for 3 minutes, then removed and dried for later use. The treated AZ91D magnesium alloy blocks are immersed in the 3.5% sodium chloride corrosion inhibitor coolant and the 3.5% sodium chloride blank coolant, respectively, and kept at 60℃ for 1 day, 3 days, and 7 days. The corrosion inhibition efficiency is calculated based on the weight loss, and the results are shown in Table 3.

[0034] Table 3: Static weight loss test data and corrosion inhibition efficiency of AZ91D magnesium alloy applied to 60℃ coolant containing 3.5% sodium chloride: The table shows that adding L-lysine-morpholine Schiff base corrosion inhibitor and immersing the alloy in 3.5% sodium chloride coolant at 60°C can effectively inhibit the corrosion of AZ91D magnesium alloy.

[0035] The conductivity of the corrosion inhibitor coolant containing L-lysine-morpholine Schiff base prepared in this example was found to be 78 μS / cm.

[0036] Example 4: The application of the corrosion inhibitor prepared by the above-described method for preparing a Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant (i.e., the L-lysine-tetrahydropyran Schiff base corrosion inhibitor, or the Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant, or the amino acid heterocyclic Schiff base corrosion inhibitor) is as follows: the prepared corrosion inhibitor is applied to automotive coolant to inhibit the corrosion of AZ91D magnesium alloy. The coolant (or corrosion inhibitor-containing coolant) is composed of raw materials mixed and formulated with the following components and their weight percentages: 2% corrosion inhibitor, 44.5% deionized water, and 53.5% ethylene glycol. A coolant without corrosion inhibitor is prepared by mixing 45% deionized water and 55% ethylene glycol. 0.5g of sodium chloride is added to the above coolant, and they are named 0.5% sodium chloride corrosion inhibitor coolant and 0.5% sodium chloride blank coolant, respectively. Prepare AZ91D magnesium alloy blocks of 50*25*4mm and grind them sequentially with a constant speed grinder at 60 grit, 240 grit, 400 grit, 600 grit, and 1200 grit. After grinding, soak them in anhydrous ethanol and sonicate them for 3 minutes. Remove them and dry them for later use. Immerse the treated AZ91D magnesium alloy blocks in a coolant containing 0.5% sodium chloride corrosion inhibitor and a blank coolant containing 0.5% sodium chloride, respectively, and keep them at 20℃ for 1 day, 3 days, and 7 days. Calculate the corrosion inhibition efficiency based on the weight loss. The results are shown in Table 4.

[0037] Table 4: Static weight loss test data and corrosion inhibition efficiency of AZ91D magnesium alloy applied to 20℃ coolant containing 0.5% sodium chloride: The table shows that the AZ91D magnesium alloy exhibits high corrosion inhibition efficiency when the L-lysine-tetrahydropyran Schiff base corrosion inhibitor is added and immersed in 0.5% sodium chloride coolant at 20°C.

[0038] The conductivity of the corrosion inhibitor in the coolant containing L-lysine-tetrahydropyran Schiff base prepared in this example was found to be 72 μS / cm.

[0039] Example 5: A method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, comprising the following steps: a. Dissolve 100 parts by weight of L-histidine (basic amino acid) in 150 parts by weight of deionized water to form an L-histidine aqueous solution (basic amino acid aqueous solution). b. Dissolve 100 parts by mass of 2-imidazolidineone (containing ketone heterocyclic compounds) in 100 parts by mass of anhydrous acetone to form a 2-imidazolidineone acetone solution (an acetone solution containing ketone heterocyclic compounds). c. Control the molar ratio of L-histidine (basic amino acid) to 2-imidazolidine (containing ketone heterocyclic compound) to be 1:1.5. Place the L-histidine aqueous solution (basic amino acid aqueous solution) into the reaction vessel, and place the 2-imidazolidine acetone solution (acetone solution containing ketone heterocyclic compound) into an automatic dropper. Add the 2-imidazolidine acetone solution (acetone solution containing ketone heterocyclic compound) dropwise into the reaction vessel at a rate of 0.01 mL / s. React at 50°C for 36 h to obtain the reaction product. d. Cool the reacted material to room temperature, and concentrate the reacted material (solution) to 90% by vacuum distillation according to mass percentage to obtain a concentrated solution. Extract the solution with 2 times the volume of glacial ethyl acetate, and continue to concentrate the aqueous phase to 96% by vacuum distillation. Wash the solution with glacial ethyl acetate and dry it under vacuum at 60°C for 8 hours to obtain L-histidine-imidazolium Schiff base corrosion inhibitor (i.e., Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor).

[0040] A 0.5% sodium chloride corrosion inhibitor coolant and a blank coolant containing 0.5% sodium chloride were prepared according to the method of Example 4. The AZ91D magnesium alloy was treated, immersed, and subjected to weight loss tests as described in Example 4. The corrosion inhibition efficiency was tested to be 92.58% after 7 days.

[0041] The conductivity of the corrosion inhibitor containing L-histidine-imidazol Schiff base prepared in this example was found to be 89 μS / cm.

[0042] Example 6: A method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, comprising the following steps: a. Dissolve 100 parts by weight of L-arginine (basic amino acid) in 150 parts by weight of deionized water to form an L-arginine aqueous solution (basic amino acid aqueous solution). b. Dissolve 100 parts by mass of 1-methyl-2-pyrrolidone (containing ketone heterocyclic compounds) in 100 parts by mass of anhydrous acetone to form a 1-methyl-2-pyrrolidone acetone solution (an acetone solution containing ketone heterocyclic compounds). c. Control the molar ratio of L-arginine (basic amino acid) to 1-methyl-2-pyrrolidone (containing ketone heterocyclic compound) to be 1-1.2. Place the L-arginine aqueous solution (basic amino acid aqueous solution) into the reaction vessel, and place the 1-methyl-2-pyrrolidone acetone solution (acetone solution containing ketone heterocyclic compound) into an automatic dropper. Add the 1-methyl-2-pyrrolidone acetone solution (acetone solution containing ketone heterocyclic compound) dropwise into the reaction vessel at a rate of 0.02 mL / s. React at 40°C for 12 h to obtain the reacted material. d. Cool the reacted material to room temperature, and concentrate the reacted material (solution) to 85% by mass distillation under reduced pressure to obtain a concentrated solution. Extract the solution with 3 times the volume of glacial ethyl acetate, and continue to concentrate the aqueous phase to 95% by reduced pressure distillation. Wash the solution with glacial ethyl acetate and dry it under vacuum at 60°C for 8 hours to obtain L-arginine-pyrrole Schiff base corrosion inhibitor (i.e., Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor).

[0043] Furthermore, a 3.5% sodium chloride corrosion inhibitor coolant and a blank coolant containing 3.5% sodium chloride were prepared according to the method of Example 2, and the AZ91D magnesium alloy was treated, immersed, and subjected to weight loss tests as described in Example 2. The corrosion inhibition efficiency was 89.97% after 7 days at 60°C.

[0044] The conductivity of the corrosion inhibitor containing L-arginine-pyrrole Schiff base prepared in this example was found to be 83 μS / cm.

[0045] Example 7: A method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, comprising the following steps: a. Dissolve 100 parts by weight of L-arginine (basic amino acid) in 150 parts by weight of deionized water to form an L-arginine aqueous solution (basic amino acid aqueous solution). b. Dissolve 100 parts by mass of 5-methylmorpholin-3-one (containing ketone heterocyclic compound) in 100 parts by mass of anhydrous ethanol to form a 5-methylmorpholin-3-one ethanol solution (containing ketone heterocyclic compound). c. Control the molar ratio of L-arginine (basic amino acid) to 5-methylmorpholin-3-one (containing ketone heterocyclic compound) to be 1:1. Place the L-arginine aqueous solution (basic amino acid aqueous solution) into the reaction vessel, and place the 5-methylmorpholin-3-one ethanol solution (containing ketone heterocyclic compound) into an automatic dropper. Add the 5-methylmorpholin-3-one ethanol solution (containing ketone heterocyclic compound) dropwise into the reaction vessel at a rate of 0.02 mL / s. React at 40°C for 24 h to obtain the reaction product. d. Cool the reacted material to room temperature, and concentrate the reacted material (solution) to 85% by mass distillation under reduced pressure to obtain a concentrated solution. Extract the solution with 1.5 times the volume of glacial ethyl acetate, and continue to concentrate the aqueous phase to 95% by reduced pressure distillation. Wash the solution with glacial ethyl acetate and dry it under vacuum at 60°C for 4 hours to obtain L-arginine-morpholine Schiff base corrosion inhibitor (i.e., Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor).

[0046] Furthermore, a 3.5% sodium chloride corrosion inhibitor coolant and a blank coolant containing 3.5% sodium chloride were prepared according to the method of Example 3, and the AZ91D magnesium alloy was treated, immersed, and subjected to weight loss tests as described in Example 3. The corrosion inhibition efficiency was 91.85% after 7 days at 60°C.

[0047] The conductivity of the corrosion inhibitor containing L-arginine-morpholine Schiff base prepared in this example was found to be 80 μS / cm.

[0048] Example 8: A method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, comprising the following steps: a. Dissolve 100 parts by weight of basic amino acids in one of 80 to 250 parts by weight of deionized water (or distilled water) to form an aqueous solution of basic amino acids. b. Dissolve 100 parts by mass of the ketone-containing heterocyclic compound in 80 to 250 parts by mass of anhydrous ethanol or acetone to form an ethanol or acetone solution containing the ketone-containing heterocyclic compound. c. Place the alkaline amino acid aqueous solution into the reaction vessel, and place the ethanol or acetone solution containing the ketone heterocyclic compound into the (automatic) dropper; drop the ethanol or acetone solution containing the ketone heterocyclic compound into the reaction vessel, control the molar ratio of the alkaline amino acid to the ketone heterocyclic compound to be one of 1:1 to 1.5, and react at a temperature of one of 40 to 80°C for a time of one of 4 to 36 hours to obtain the reacted material; d. Cool the reaction material to room temperature, concentrate the reaction material (solution) by vacuum distillation to obtain a concentrated solution, extract it with 1 to 3 times the volume of glacial ethyl acetate, continue to concentrate the aqueous phase by vacuum distillation, wash it with glacial ethyl acetate and dry it to obtain the Schiff base corrosion inhibitor (or amino acid heterocyclic Schiff base corrosion inhibitor) for the cooling liquid of AZ91D magnesium alloy.

[0049] Example 9: A method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, comprising the following steps: a. Dissolve 100 parts by weight of basic amino acids in 80 parts by weight of deionized water (or distilled water) to form an aqueous solution of basic amino acids; b. Dissolve 100 parts by mass of the ketone-containing heterocyclic compound in 80 parts by mass of anhydrous ethanol or acetone to form an ethanol or acetone solution containing the ketone-containing heterocyclic compound. c. Place the alkaline amino acid aqueous solution into the reaction vessel, and place the ethanol or acetone solution containing the ketone heterocyclic compound into the (automatic) dropper; drop the ethanol or acetone solution containing the ketone heterocyclic compound into the reaction vessel at a rate of 0.01 mL / s, control the molar ratio of alkaline amino acid to ketone heterocyclic compound to be 1:1, react at 40℃ for 36 h, and obtain the reacted material; d. Cool the reaction material to room temperature, and concentrate the reaction material (solution) to 95% by mass distillation under reduced pressure to obtain a concentrate. Extract the concentrate with 1 volume of glacial ethyl acetate, and continue to concentrate the aqueous phase to 99% by reduced pressure distillation. Wash with glacial ethyl acetate and vacuum dry at 50°C for 8 hours to obtain the Schiff base corrosion inhibitor (or amino acid heterocyclic Schiff base corrosion inhibitor) for the cooling liquid of AZ91D magnesium alloy.

[0050] Example 10: A method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, comprising the following steps: a. Dissolve 100 parts by weight of basic amino acids in 250 parts by weight of deionized water (or distilled water) to form an aqueous solution of basic amino acids; b. Dissolve 100 parts by mass of the ketone-containing heterocyclic compound in 250 parts by mass of anhydrous ethanol or acetone to form an ethanol or acetone solution containing the ketone-containing heterocyclic compound. c. Place the alkaline amino acid aqueous solution into the reaction vessel, and place the ethanol or acetone solution containing the ketone heterocyclic compound into the (automatic) dropper; drop the ethanol or acetone solution containing the ketone heterocyclic compound into the reaction vessel at a rate of 0.2 mL / s, control the molar ratio of alkaline amino acid to ketone heterocyclic compound to be 1:1.5, react at 80℃ for 4 hours, and obtain the reaction product; d. Cool the reacted material to room temperature, and concentrate the reacted material (solution) to 80% by vacuum distillation according to mass percentage to obtain a concentrated solution. Extract the solution with 3 times the volume of glacial ethyl acetate, and continue to concentrate the aqueous phase to 95% by vacuum distillation. Wash the aqueous phase with glacial ethyl acetate and dry it under vacuum at 80°C for 2 hours to obtain the Schiff base corrosion inhibitor (or amino acid heterocyclic Schiff base corrosion inhibitor) for the cooling liquid of AZ91D magnesium alloy.

[0051] Example 11: A method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, comprising the following steps: a. Dissolve 100 parts by weight of basic amino acids in 165 parts by weight of deionized water (or distilled water) to form an aqueous solution of basic amino acids; b. Dissolve 100 parts by mass of the ketone-containing heterocyclic compound in 165 parts by mass of anhydrous ethanol or acetone to form an ethanol or acetone solution containing the ketone-containing heterocyclic compound. c. Place the alkaline amino acid aqueous solution into the reaction vessel, and place the ethanol or acetone solution containing the ketone heterocyclic compound into the (automatic) dropper; drop the ethanol or acetone solution containing the ketone heterocyclic compound into the reaction vessel at a rate of 0.1 mL / s, control the molar ratio of alkaline amino acid to ketone heterocyclic compound to be 1:1.25, react at 60℃ for 20 h, and obtain the reacted material; d. Cool the reacted material to room temperature, and concentrate the reacted material (solution) to 87% by mass distillation under reduced pressure to obtain a concentrate. Extract the concentrate with 2 times the volume of glacial ethyl acetate, and continue to concentrate the aqueous phase to 97% by reduced pressure distillation. Wash with glacial ethyl acetate and dry under vacuum at 65°C for 5 hours to obtain the Schiff base corrosion inhibitor (or amino acid heterocyclic Schiff base corrosion inhibitor) for the cooling liquid of AZ91D magnesium alloy.

[0052] In the above embodiments 8 to 11: The basic amino acid mentioned in step a is any one or a mixture of two of L-histidine, L-lysine, and L-arginine; The ketone-containing heterocyclic compound mentioned in step b is any one or a mixture of two of the following: tetrahydrofuran-3-one, 2-methyltetrahydrofuran-3-one, 3-hydroxytetrahydrofuran-2-one, tetrahydropyran-4-one, 3-methyltetrahydropyran-4-one, 2-imidazolone, 4-methylimidazolone, 2-piperazinone, 4-methyl-2-piperazinone, 1-methylpiperazin-2-one, 3,3-dimethyl-2-piperazinone, 2-pyrrolidone, 1-methyl-2-pyrrolidone, 5,5-dimethyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 3-morpholinone, 5-methylmorpholinone, 5-ethylmorpholinone, and 5-isopropylmorpholinone.

[0053] Example 12: The application of the corrosion inhibitor prepared by the Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy (i.e., the Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor) according to one of the above embodiments 8-11 is: applying the prepared corrosion inhibitor to automotive coolant (simulating a corrosive environment) to inhibit corrosion of AZ91D magnesium alloy.

[0054] Example 13: The application of the corrosion inhibitor prepared by the method described in any of Examples 8-11 above (i.e., the Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor) is as follows: the prepared corrosion inhibitor is applied to automotive coolant in a (simulated corrosion environment) to inhibit corrosion of AZ91D magnesium alloy. The (simulated corrosion environment) coolant is composed of a mixture of raw materials with the following components and weight percentages: 0.1% corrosion inhibitor (i.e., the Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor), 39.9% deionized water, and 60% ethylene glycol.

[0055] Example 14: The application of the corrosion inhibitor prepared by the method described in any of Examples 8-11 above (i.e., the Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor) is as follows: the prepared corrosion inhibitor is applied to automotive coolant in a (simulated corrosion environment) to inhibit corrosion of AZ91D magnesium alloy. The (simulated corrosion environment) coolant is composed of a mixture of raw materials with the following weight percentages: 2% corrosion inhibitor (i.e., the Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor), 59% deionized water, and 39% ethylene glycol, and the total amount of each component is 100%.

[0056] Example 15: The application of the corrosion inhibitor prepared by the method described in any of Examples 8-11 above (i.e., the Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor) is as follows: the prepared corrosion inhibitor is applied to automotive coolant in a (simulated corrosion environment) to inhibit corrosion of AZ91D magnesium alloy. The (simulated corrosion environment) coolant is composed of a mixture of raw materials with the following weight percentages: 1% corrosion inhibitor (i.e., the Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, or amino acid heterocyclic Schiff base corrosion inhibitor), 50% deionized water, and 49% ethylene glycol, and the total amount of each component is 100%.

[0057] The above embodiments are merely illustrative of the results of the present invention and not intended to limit the technical solutions of the present invention. Although the embodiments of the present invention are described in detail and can be understood and reproduced by those skilled in the art, any modifications or partial substitutions that do not depart from the spirit and scope of the present invention are within the scope of the claims of the present invention.

[0058] In the above embodiments: unless otherwise specified, the percentage examples used are mass (weight) percentage examples or percentage examples known to those skilled in the art; unless otherwise specified, the proportions used are mass (weight) proportions; the weight parts can all be grams or kilograms.

[0059] In the above embodiments, the process parameters (temperature, time, speed, etc.) and the values ​​of each component dosage in each step are ranges, and any point can be applied.

[0060] The technical contents of this invention and the above embodiments that are not specifically described are the same as those of the prior art, and the raw materials are all commercially available products.

[0061] The present invention is not limited to the above embodiments; all embodiments described herein can be implemented and have the aforementioned good effects.

Claims

1. A method for preparing a Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy, characterized in that... Includes the following steps: a. Dissolve 100 parts by weight of basic amino acids in 80-250 parts by weight of deionized water to form an alkaline amino acid aqueous solution; b. Dissolve 100 parts by weight of the ketone-containing heterocyclic compound in 80 to 250 parts by weight of anhydrous ethanol or acetone to form an ethanol or acetone solution containing the ketone-containing heterocyclic compound. c. Place the alkaline amino acid aqueous solution into the reaction vessel, and place the ethanol or acetone solution containing the ketone heterocyclic compound into the dropper; drop the ethanol or acetone solution containing the ketone heterocyclic compound into the reaction vessel, controlling the molar ratio of alkaline amino acid to ketone heterocyclic compound to be 1:1 to 1.5, and react at a temperature of 40 to 80°C for 4 to 36 hours to obtain the reacted material; d. Cool the reaction material to room temperature, concentrate the reaction material by vacuum distillation to obtain a concentrate, extract with 1 to 3 times the volume of glacial ethyl acetate, continue to concentrate the aqueous phase by vacuum distillation, wash with glacial ethyl acetate and dry to obtain Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant.

2. The method for preparing the Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy according to claim 1, characterized in that... Includes the following steps: a. Dissolve 100 parts by weight of basic amino acids in 80-250 parts by weight of deionized water to form an alkaline amino acid aqueous solution; The basic amino acid is any one or a mixture of two of L-histidine, L-lysine, and L-arginine. b. Dissolve 100 parts by weight of the ketone-containing heterocyclic compound in 80 to 250 parts by weight of anhydrous ethanol or acetone to form an ethanol or acetone solution containing the ketone-containing heterocyclic compound. c. Place the alkaline amino acid aqueous solution into the reaction vessel, and place the ethanol or acetone solution containing the ketone heterocyclic compound into the dropper; add the ethanol or acetone solution containing the ketone heterocyclic compound dropwise into the reaction vessel at a rate of 0.01-0.2 mL / s, controlling the molar ratio of alkaline amino acid to ketone heterocyclic compound to be 1:1-1.5, and react at a temperature of 40-80℃ for 4-36 h to obtain the reacted material; d. Cool the reacted material to room temperature, concentrate the reacted material by vacuum distillation according to mass percentage, and extract the concentrate with 1 to 3 times the volume of glacial ethyl acetate. Continue to concentrate the aqueous phase by vacuum distillation, wash with glacial ethyl acetate, and vacuum dry at 50 to 80°C for 2 to 8 hours to obtain the Schiff base corrosion inhibitor for the coolant of AZ91D magnesium alloy.

3. The method for preparing Schiff base corrosion inhibitor for coolant of AZ91D magnesium alloy according to claim 1 or 2, characterized in that: The ketone-containing heterocyclic compound mentioned in step b is any one or a mixture of two of the following: tetrahydrofuran-3-one, 2-methyltetrahydrofuran-3-one, 3-hydroxytetrahydrofuran-2-one, tetrahydropyran-4-one, 3-methyltetrahydropyran-4-one, 2-imidazolone, 4-methylimidazolone, 2-piperazinone, 4-methyl-2-piperazinone, 1-methylpiperazin-2-one, 3,3-dimethyl-2-piperazinone, 2-pyrrolidone, 1-methyl-2-pyrrolidone, 5,5-dimethyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 3-morpholinone, 5-methylmorpholinone, 5-ethylmorpholinone, and 5-isopropylmorpholinone.

4. The application of the corrosion inhibitor prepared by the method for preparing Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant according to claim 1 or 2, characterized in that: The prepared corrosion inhibitor was applied to automotive coolant to inhibit corrosion of AZ91D magnesium alloy.

5. The application of the corrosion inhibitor prepared by the method for preparing Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant according to claim 4, characterized in that: The coolant is composed of a mixture of raw materials with the following weight percentages: 0.1-2% corrosion inhibitor, 39-60% deionized water, and 39-60% ethylene glycol, and the total of all raw materials is 100%.

6. The application of the corrosion inhibitor prepared by the method for preparing Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant according to claim 5, characterized in that: The coolant also contains 0.05% to 5% sodium chloride by weight.

7. The application of the corrosion inhibitor prepared by the method for preparing Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant according to claim 5 or 6, characterized in that: The coolant also contains a mixture of sodium sulfate, sodium chloride, and sodium bicarbonate.

8. The application of the corrosion inhibitor prepared by the method for preparing Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant according to claim 7, characterized in that: The concentrations of the mixture of sodium sulfate, sodium chloride, and sodium bicarbonate in the coolant are as follows: sodium sulfate concentration is 130–160 mg / L, sodium chloride concentration is 150–180 mg / L, and sodium bicarbonate concentration is 120–150 mg / L.

9. The application of the corrosion inhibitor prepared by the method for preparing Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant according to claim 5, 6 or 8, characterized in that: The specific application method involves immersing the AZ91D magnesium alloy in a coolant at a temperature of 20–80°C.

10. The application of the corrosion inhibitor prepared by the method for preparing Schiff base corrosion inhibitor for AZ91D magnesium alloy coolant according to claim 7, characterized in that: The specific application method involves immersing the AZ91D magnesium alloy in a coolant at a temperature of 20–80°C.

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