A chromium-free passivation agent for magnesium alloy workpieces and a preparation method thereof

Abstract

This invention belongs to the field of passivating agent technology, specifically relating to a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces and its preparation method. The chromium-free passivating agent comprises the following components by weight: 4-5 parts film-forming agent; 8-10 parts functional acrylic resin; 0.8-1 parts vanadate; 3-5 parts coupling agent; 1-2 parts corrosion inhibitor; and 70-80 parts water. The chromium-free passivating agent provided by this invention uses zirconium fluoride and titanium fluoride as film-forming agents, and is modified by adding functional acrylic resin, which improves the density and corrosion resistance of the passivation film. This results in a chromium-free passivating agent with good corrosion resistance, adhesion, high-temperature resistance, and antibacterial properties. When used in magnesium alloy workpieces, it exhibits good corrosion resistance and helps extend the service life of the magnesium alloy workpieces.

Description

Technical Field

[0001] This invention belongs to the field of passivating agent technology, specifically relating to a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces and its preparation method. Background Technology

[0002] Magnesium alloy workpieces are alloy materials made from magnesium as the base and with the addition of elements such as aluminum, zinc, manganese, zirconium, and rare earth elements. They have significant advantages such as low density, high specific strength, good vibration damping, excellent electromagnetic shielding, good machinability, good heat dissipation, and good recyclability, and are widely used in aerospace, automotive industry, electronic communications, medical devices, sports equipment, and many other fields. Magnesium alloy workpieces are chemically active and easily react with oxygen and moisture in the air, leading to surface corrosion or oxidation discoloration. Their corrosion resistance is relatively poor, and a dense and stable passivation film is usually formed on the surface of magnesium alloys to significantly improve their corrosion resistance. Magnesium alloy passivating agents can be divided into chromate passivating agents and chromium-free passivating agents (such as phosphate-based, permanganate-based, silicate / tungstate-based, molybdate-based, zirconium-titanium-based, silane-based, and rare earth-based). Among them, chromate passivating agents have been restricted in use due to the strong toxicity and carcinogenicity of hexavalent chromium, and chromium-free passivating agents are gradually replacing chromate passivating agents as a new development direction.

[0003] Chinese Patent Application No. CN202310951403.3 discloses a corrosion-resistant magnesium alloy chromium-free passivation solution and its preparation method, comprising the following raw materials by weight percentage: 2-10% coupling agent; 0.2-1.6% cerium nitrate; 0.5-5% ammonium fluorotitanate; 0.2-3% lauryl betaine; 0.4-1.4% ammonium zirconium carbonate; the balance being water. This chromium-free passivation solution can effectively improve the corrosion resistance and coating adhesion of magnesium alloys, forming a stable, uniform, and corrosion-resistant protective film through chemical reaction, significantly extending the service life of magnesium alloys. Chinese Patent Application No. CN202410398483.9 discloses a self-healing passivation solution for magnesium alloys. The chromium passivation solution and its preparation method are disclosed. The raw materials include 6-9 parts phytic acid solution, 20-60 parts functionalized nano-polypyrrole aqueous dispersion, 0.6-1.0 parts vanadate, 1-3 parts silane coupling agent, and the balance deionized water. The raw materials can improve the corrosion resistance level of the chromium-free passivation technology, improve the adhesion of the coating, and enhance the self-healing ability of the magnesium alloy after passivation through synergistic effects. Although the passivation solutions disclosed in the above patents can avoid the use of hexavalent chromium, reducing potential harm to the environment and human body, the corrosion resistance of the passivation solutions is insufficient. Therefore, it is necessary to develop a chromium-free passivating agent with excellent corrosion resistance for magnesium alloy workpieces. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces and its preparation method. This invention uses zirconium fluoride and titanium fluoride as film-forming agents and adds functional acrylic resin for modification, which improves the density and corrosion resistance of the passivation film. This results in a chromium-free passivating agent with good corrosion resistance, adhesion, high-temperature resistance, and antibacterial properties. When used in magnesium alloy workpieces, it exhibits good corrosion resistance and helps extend the service life of magnesium alloy workpieces.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows: A corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, the chromium-free passivating agent comprising the following components by weight: 4-5 parts film-forming agent; 8-10 parts functional acrylic resin; 0.8-1 parts vanadate; 3-5 parts coupling agent; 1-2 parts corrosion inhibitor; and 70-80 parts water.

[0006] Furthermore, the film-forming agent is composed of zirconium fluoride and titanium fluoride in a mass ratio of 1:0.8-1.

[0007] Furthermore, the vanadate is ammonium metavanadate or sodium metavanadate.

[0008] Furthermore, the coupling agent is 3-glycidyl etheroxypropyltrimethoxysilane.

[0009] Furthermore, the corrosion inhibitor is phytic acid.

[0010] Further, the preparation method of the functional acrylic resin is as follows: under nitrogen protection, methyl methacrylate, acrylic acid, butyl acrylate and functional benzotriazole are added to deionized water, placed at 75-80℃, and ammonium persulfate aqueous solution is added dropwise. After the addition is completed, the temperature is raised to 85-90℃, and the reaction is stirred for 1.5-2 hours to obtain the functional acrylic resin.

[0011] Further, the mass ratio of methyl methacrylate, acrylic acid, butyl acrylate, functional benzotriazole, and deionized water is 1:0.3-0.4:1.8-2:0.4-0.5:4-5.

[0012] Further, the amount of ammonium persulfate used is 0.2-0.3% of the total mass of methyl methacrylate, acrylic acid, butyl acrylate, and functional benzotriazole; the concentration of the ammonium persulfate aqueous solution is 30-40 wt%.

[0013] Furthermore, the preparation method of the functional benzotriazole is as follows: S1. Add 6-chloro-1-hydroxybenzotriazole and triethylamine to chloroform, stir until homogeneous, slowly add epoxide butene dropwise, and after the addition is complete, place at 50-60℃ and stir for 3-4 hours to obtain alkenylbenzotriazole. S2. Add alkenylbenzotriazole, 5,5-dimethylhydantoin, and potassium hydroxide to acetonitrile, stir until homogeneous, place at 70-80℃, stir and react for 5-6 hours, cool to room temperature, add sodium hypochlorite, and continue stirring for 1-2 hours to obtain modified benzotriazole. S3. Add modified benzotriazole and guanidinoacetic acid to toluene, stir well, slowly add concentrated sulfuric acid dropwise, and after the addition is complete, place at 110℃ and reflux for 7-8 hours to obtain functional benzotriazole.

[0014] Further, the molar ratio of 6-chloro-1-hydroxybenzotriazole, epoxide, and triethylamine in step S1 is 1:1.1-1.2:1.2-1.3.

[0015] Further, in step S2, the molar ratio of alkenylbenzotriazole, 5,5-dimethylhydantoin, potassium hydroxide, and sodium hypochlorite is 1:1.1-1.2:1.2-1.3:1.2-1.3.

[0016] Further, the molar ratio of modified benzotriazole, guanidinoacetic acid, and concentrated sulfuric acid in step S3 is 1:1.1-1.2:0.05-0.08.

[0017] The present invention also provides a method for preparing a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, comprising the following steps: adding a film-forming agent, functional acrylic resin, vanadate, coupling agent, and corrosion inhibitor to water according to the weight ratio, stirring for 0.5-1 h at a stirring speed of 800-1000 r / min to obtain a chromium-free passivating agent.

[0018] The present invention has the following beneficial effects: This invention uses 6-chloro-1-hydroxybenzotriazole as a raw material, reacting it sequentially with epoxide, 5,5-dimethylhydantoin, sodium hypochlorite, and guanidinoacetic acid to obtain a functional benzotriazole containing benzotriazole, dimethylhydantoin chloride, guanidino, and butenyl groups. This invention further polymerizes the butenyl group of the functional benzotriazole with methyl methacrylate, acrylic acid, and butyl acrylate to obtain a functional acrylic resin. The polyacrylic acid molecule in the functional acrylic resin obtained by this invention has good film-forming properties and adhesion, and can synergistically work with film-forming agents to improve the adhesion and density of passivation films. The functional benzotriazole in the functional acrylic resin... Benzotriazole, consisting of a benzotriazole group, a dimethylhydantoin chloride group, and a guanidine group, exhibits superior high-temperature resistance, enhancing the high-temperature performance of chromium-free passivators. It can also form a film through coordination adsorption, further improving the density of the passivation film. Combined with phytic acid, it enhances corrosion resistance. Both the dimethylhydantoin chloride group and the guanidine group possess antibacterial properties, working together to significantly improve the antibacterial activity of the chromium-free passivator. Simultaneously, the amino group in the guanidine group can interact with the hydroxyl and phosphate groups in phytic acid through hydrogen bonding, thereby increasing the bonding force between the passivator components and contributing to enhanced passivation film density and overall performance.

[0019] The chromium-free passivating agent provided by this invention uses zirconium fluoride and titanium fluoride as film-forming agents and adds functional acrylic resin for modification, which improves the density and corrosion resistance of the passivation film. This results in a chromium-free passivating agent with good corrosion resistance, adhesion, high temperature resistance and antibacterial properties. When used in magnesium alloy workpieces, it has good corrosion resistance and helps to extend the service life of magnesium alloy workpieces. Attached Figure Description

[0020] Figure 1 The image shows the corrosion resistance test results for die-cast magnesium alloy workpieces. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. The technical features designed in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] In the technical solution of this invention, all chemical reagents used are commercially available, including zirconium fluoride (CAS number 7783-64-4), titanium fluoride (CAS number 13470-08-1), ammonium metavanadate (CAS number 7803-55-6), sodium metavanadate (CAS number 13718-26-8), 3-glycidyl etheroxypropyltrimethoxysilane (CAS number 2530-83-8), phytic acid (CAS number 83-86-3), methyl methacrylate (CAS number 80-62-6), butyl acrylate (CAS number 141-32-2), acrylic acid (CAS number 79-10-7), and chlorinated paraffin. Ammonium sulfate CAS number 7727-54-0, 6-chloro-1-hydroxybenzotriazole CAS number 26198-19-6, glycidene CAS number 930-22-3, 5,5-dimethylhydantoin CAS number 77-71-4, potassium hydroxide CAS number 1310-58-3, sodium hypochlorite CAS number 7681-52-9, guanidinoacetic acid CAS number 352-97-6, concentrated sulfuric acid CAS number 7664-93-9, chloroform CAS number 67-66-3; acetonitrile CAS number 75-05-8; toluene CAS number 108-88-3.

[0023] Example 1 This embodiment provides a method for preparing functional benzotriazole: ; S1. Add 17.0 g of 6-chloro-1-hydroxybenzotriazole and 12.2 g of triethylamine to 500 mL of chloroform, stir well, and slowly add 7.7 g of epoxide. After the addition is complete, place at 50 °C and stir for 4 h. After the reaction is complete, remove chloroform, and extract and concentrate to obtain 21.4 g of alkenylbenzotriazole; wherein the molar ratio of 6-chloro-1-hydroxybenzotriazole, epoxide, and triethylamine is 1:1.1:1.2. Alkenylbenzotriazole: ESI (m / z): 240.7 [M+H] + , 1 H-NMR (600MHz, DMSO-d6, δppm): 7.99 (s, 1H), 7.90 (d, J=8.5Hz, 1H), 7.46 (d, J=8.5Hz, 1H) , 6.19 (s, 1H), 5.89-5.92 (m, 1H), 5.28-5.30 (m, 2H), 4.28-4.31 (m, 1H), 3.73-3.75 (m, 2H); S2. Add 21.4g of alkenylbenzotriazole, 12.6g of 5,5-dimethylhydantoin, and 6.0g of potassium hydroxide to 450mL of acetonitrile. Stir well and place at 80℃ for 5h. Cool to room temperature, add 8.0g of sodium hypochlorite, and continue stirring for 2h. After the reaction is complete, remove the acetonitrile, and extract and concentrate to obtain 25.8g of modified benzotriazole. The molar ratio of alkenylbenzotriazole, 5,5-dimethylhydantoin, potassium hydroxide, and sodium hypochlorite is 1:1.1:1.2:1.2. Modified benzotriazole: ESI (m / z): 366.8 [M+H] + , 1 H-NMR (600MHz, DMSO-d6, δppm): 8.24 (s, 1H), 8.06 (d, J=8.5Hz, 1H), 7.70 (d, J=8.5Hz, 1H), 6.18 ( s, 1H), 5.90-5.93 (m, 1H), 5.28-5.31 (m, 2H), 4.28-4.30 (m, 1H), 3.72-3.75 (m, 2H), 1.75 (s, 6H); S3. Add 25.8g of modified benzotriazole and 9.1g of guanidinoacetic acid to 350mL of toluene, stir well, and slowly add 0.35g of concentrated sulfuric acid dropwise. After the addition is complete, reflux at 110℃ for 7h. After the reaction is complete, remove the toluene, and extract and concentrate to obtain 26.5g of functional benzotriazole; wherein the molar ratio of modified benzotriazole, guanidinoacetic acid and concentrated sulfuric acid is 1:1.1:0.05. Functional benzotriazole: ESI (m / z): 465.9 [M+H] + , 1 H-NMR (600MHz, DMSO-d6, δppm): 8.23 ​​(s, 1H), 8.05 (d, J=8.5Hz, 1H), 7.84 (s, 1H), 7.70 (d, J=8.5Hz, 1H), 6. 64 (s, 2H), 5.89-5.93 (m, 1H), 5.30-5.35 (m, 3H), 4.32 (s, 2H), 3.75-3.79 (m, 2H), 2.50 (s, 1H), 1.74 (s, 6H).

[0024] Example 2 This embodiment provides a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, comprising the following components by weight: 5 parts film-forming agent; 10 parts functional acrylic resin; 0.9 parts vanadate; 5 parts coupling agent; 2 parts corrosion inhibitor; and 80 parts water. The film-forming agent is composed of zirconium fluoride and titanium fluoride in a 1:1 mass ratio; the vanadate is ammonium metavanadate; the coupling agent is 3-glycidyl etheroxypropyltrimethoxysilane; and the corrosion inhibitor is phytic acid.

[0025] The preparation method of functional acrylic resin is as follows: Under nitrogen protection, methyl methacrylate, acrylic acid, butyl acrylate and functional benzotriazole are added to deionized water, and the mixture is placed at 80°C. An aqueous solution of ammonium persulfate is added dropwise. After the addition is complete, the temperature is raised to 90°C, and the mixture is stirred for 1.5 hours. After the reaction is complete, the mixture is cooled to obtain the functional acrylic resin. The mass ratio of methyl methacrylate, acrylic acid, butyl acrylate, functional benzotriazole and deionized water is 1:0.4:1.9:0.5:5. The amount of ammonium persulfate is 0.3% of the total mass of methyl methacrylate, acrylic acid, butyl acrylate and functional benzotriazole. The concentration of the ammonium persulfate aqueous solution is 30 wt%.

[0026] This embodiment also provides a method for preparing a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, comprising the following steps: adding a film-forming agent, functional acrylic resin, vanadate, coupling agent, and corrosion inhibitor to water according to the weight ratio, stirring for 0.5 h at a stirring speed of 1000 r / min to obtain the chromium-free passivating agent.

[0027] Example 3 This embodiment provides a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, comprising the following components by weight: 4.5 parts film-forming agent; 9 parts functional acrylic resin; 1 part vanadate; 4 parts coupling agent; 1.5 parts corrosion inhibitor; and 70 parts water. The film-forming agent is composed of zirconium fluoride and titanium fluoride in a mass ratio of 1:0.9; the vanadate is ammonium metavanadate; the coupling agent is 3-glycidyl etheroxypropyltrimethoxysilane; and the corrosion inhibitor is phytic acid.

[0028] The preparation method of functional acrylic resin is as follows: Under nitrogen protection, methyl methacrylate, acrylic acid, butyl acrylate and functional benzotriazole are added to deionized water, and the mixture is placed at 78°C. An aqueous solution of ammonium persulfate is added dropwise. After the addition is complete, the temperature is raised to 87°C, and the mixture is stirred for 1.8 hours. After the reaction is complete, the mixture is cooled to obtain the functional acrylic resin. The mass ratio of methyl methacrylate, acrylic acid, butyl acrylate, functional benzotriazole and deionized water is 1:0.35:1.8:0.45:4.5. The amount of ammonium persulfate is 0.25% of the total mass of methyl methacrylate, acrylic acid, butyl acrylate and functional benzotriazole. The concentration of the aqueous solution of ammonium persulfate is 35 wt%.

[0029] This embodiment also provides a method for preparing a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, comprising the following steps: adding a film-forming agent, functional acrylic resin, vanadate, coupling agent, and corrosion inhibitor to water according to the weight ratio, stirring for 0.8 hours at a stirring speed of 900 r / min to obtain the chromium-free passivating agent.

[0030] Example 4 This embodiment provides a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, comprising the following components by weight: 4 parts film-forming agent; 8 parts functional acrylic resin; 0.8 parts vanadate; 3 parts coupling agent; 1 part corrosion inhibitor; and 75 parts water. The film-forming agent is composed of zirconium fluoride and titanium fluoride in a mass ratio of 1:0.8; the vanadate is sodium metavanadate; the coupling agent is 3-glycidyl etheroxypropyltrimethoxysilane; and the corrosion inhibitor is phytic acid.

[0031] The preparation method of functional acrylic resin is as follows: Under nitrogen protection, methyl methacrylate, acrylic acid, butyl acrylate and functional benzotriazole are added to deionized water, placed at 75°C, and ammonium persulfate aqueous solution is added dropwise. After the addition is complete, the temperature is raised to 85°C, and the mixture is stirred for 2 hours. After the reaction is complete, the mixture is cooled to obtain functional acrylic resin. The mass ratio of methyl methacrylate, acrylic acid, butyl acrylate, functional benzotriazole and deionized water is 1:0.3:2:0.4:4; the amount of ammonium persulfate is 0.2% of the total mass of methyl methacrylate, acrylic acid, butyl acrylate and functional benzotriazole; the concentration of ammonium persulfate aqueous solution is 40 wt%.

[0032] This embodiment also provides a method for preparing a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, comprising the following steps: adding a film-forming agent, functional acrylic resin, vanadate, coupling agent, and corrosion inhibitor to water according to the weight ratio, stirring for 1 hour at a stirring speed of 800 r / min to obtain a chromium-free passivating agent.

[0033] Comparative Example 1 This comparative example provides a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, comprising the following components by weight: 5 parts film-forming agent; 10 parts functional acrylic resin; 0.9 parts vanadate; 5 parts coupling agent; 2 parts corrosion inhibitor; and 80 parts water. The film-forming agent is composed of zirconium fluoride and titanium fluoride in a 1:1 mass ratio; the vanadate is ammonium metavanadate; the coupling agent is 3-glycidyl etheroxypropyltrimethoxysilane; and the corrosion inhibitor is phytic acid.

[0034] The preparation method of functional acrylic resin is as follows: Under nitrogen protection, methyl methacrylate, acrylic acid, butyl acrylate and modified benzotriazole are added to deionized water, and the mixture is placed at 80°C. An aqueous solution of ammonium persulfate is added dropwise. After the addition is complete, the temperature is raised to 90°C, and the mixture is stirred for 1.5 hours. After the reaction is complete, the mixture is cooled to obtain the functional acrylic resin. The mass ratio of methyl methacrylate, acrylic acid, butyl acrylate, modified benzotriazole and deionized water is 1:0.4:1.9:0.5:5. The amount of ammonium persulfate is 0.3% of the total mass of methyl methacrylate, acrylic acid, butyl acrylate and modified benzotriazole. The concentration of the ammonium persulfate aqueous solution is 30 wt%.

[0035] This comparative example also provides a method for preparing a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, which is the same as in Example 2.

[0036] Comparative Example 2 This comparative example provides a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, comprising the following components by weight: 5 parts film-forming agent; 10 parts acrylic resin; 0.9 parts vanadate; 5 parts coupling agent; 2 parts corrosion inhibitor; and 80 parts water. The film-forming agent is composed of zirconium fluoride and titanium fluoride in a 1:1 mass ratio; the vanadate is ammonium metavanadate; the coupling agent is 3-glycidyl etheroxypropyltrimethoxysilane; and the corrosion inhibitor is phytic acid.

[0037] The preparation method of acrylic resin is as follows: Under nitrogen protection, methyl methacrylate, acrylic acid, and butyl acrylate are added to deionized water, and the mixture is placed at 80°C. An aqueous solution of ammonium persulfate is then added dropwise. After the addition is complete, the temperature is raised to 90°C, and the mixture is stirred for 1.5 hours. After the reaction is complete, the mixture is cooled to obtain acrylic resin. The mass ratio of methyl methacrylate, acrylic acid, butyl acrylate, and deionized water is 1:0.4:1.9:5. The amount of ammonium persulfate is 0.3% of the total mass of methyl methacrylate, acrylic acid, and butyl acrylate. The concentration of the ammonium persulfate aqueous solution is 30 wt%.

[0038] This comparative example also provides a method for preparing a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, which is the same as in Example 2.

[0039] Comparative Example 3 This comparative example provides a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, comprising the following components by weight: 5 parts film-forming agent; 0.9 parts vanadate; 5 parts coupling agent; 2 parts corrosion inhibitor; and 80 parts water. The film-forming agent is composed of zirconium fluoride and titanium fluoride in a mass ratio of 1:1; the vanadate is ammonium metavanadate; the coupling agent is 3-glycidyl etheroxypropyltrimethoxysilane; and the corrosion inhibitor is phytic acid.

[0040] This comparative example also provides a method for preparing a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, which is the same as in Example 2.

[0041] Test case The performance of the chromium-free passivating agents provided in Examples 2 to 4 and Comparative Examples 1 to 3 was tested. Die-cast magnesium alloy workpieces were selected, cleaned, immersed in the chromium-free passivating agent, dried, and then subjected to corrosion resistance testing. The corrosion resistance was tested according to GB / T 10125-2021 standard at 35°C using continuous spraying of NaCl aqueous solution (50 g / L), pH 7.0, and a salt spray deposition rate of 1.5 mL / h·80 cm. 2The salt spray resistance time was 520 hours, and the appearance of black rust spots or white corrosion on the surface was observed. The adhesion test was conducted according to GB / T 9286-2021 standard. The chromium-free passivator was stored at 80℃ in a dark environment for 90 days, and its high-temperature stability was observed. The antibacterial rate of the chromium-free passivator against Staphylococcus aureus, Escherichia coli, and Bacillus subtilis was tested. The test results are shown in Table 1 below.

[0042] Table 1 As shown in Table 1, the chromium-free passivating agents provided in Examples 2 to 4 of the present invention have high adhesion, good high-temperature stability, and high inhibition rates against Staphylococcus aureus, Escherichia coli, and Bacillus subtilis, indicating that the chromium-free passivating agents provided in the present invention have good adhesion, high-temperature resistance, and antibacterial properties.

[0043] Figure 1 The figures in the middle, from left to right, show the corrosion resistance test results for Examples 2, 3, and 4. Figure 1 As can be seen from the examples, when the chromium-free passivating agents provided in Examples 2 to 4 are used in die-cast magnesium alloy workpieces, no black rust spots or white corrosion products appear on their surfaces, and no corrosion occurs, indicating that the chromium-free passivating agents provided by the present invention have good corrosion resistance.

[0044] Compared with Comparative Examples 1 and 3, Example 2 of this invention adds functional acrylic resin to the chromium-free passivator. The polyacrylic acid molecular structure in the functional acrylic resin has good film-forming properties and adhesion, and can synergistically work with the film-forming agent to improve the adhesion and density of the passivation film. The functional benzotriazole in the functional acrylic resin, namely the benzotriazole group, dimethylhydantoin chloride group, and guanidine group, has good high-temperature resistance, which can improve the high-temperature resistance of the chromium-free passivator. It can also form a film through coordination adsorption, further improving the density of the passivation film. Together with phytic acid, it enhances corrosion resistance. The dimethylhydantoin chloride group and guanidine group both have certain antibacterial effects. The two can work together to significantly improve the antibacterial properties of the chromium-free passivator. At the same time, the amino group in the guanidine group can also interact with the hydroxyl and phosphate groups in the phytic acid through hydrogen bonding, thereby improving the binding force between the passivator components, which helps to enhance the density of the passivation film and improve its overall performance.

[0045] It should be noted that, in this document, terms such as "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces, characterized in that, The chromium-free passivating agent comprises the following components in parts by weight: 4-5 parts film-forming agent; 8-10 parts functional acrylic resin; 0.8-1 part vanadate; 3-5 parts coupling agent; and 1-2 parts corrosion inhibitor. 70-80 parts water; The preparation method of the functional acrylic resin is as follows: under nitrogen protection, methyl methacrylate, acrylic acid, butyl acrylate and functional benzotriazole are added to deionized water, and the mixture is placed at 75-80℃. Ammonium persulfate aqueous solution is added dropwise. After the addition is complete, the temperature is raised to 85-90℃ and the mixture is stirred for 1.5-2 hours to obtain the functional acrylic resin.

2. The corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces according to claim 1, characterized in that, The mass ratio of methyl methacrylate, acrylic acid, butyl acrylate, functional benzotriazole, and deionized water is 1:0.3-0.4:1.8-2:0.4-0.5:4-5.

3. The corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces according to claim 1, characterized in that, The amount of ammonium persulfate used is 0.2-0.3% of the total mass of methyl methacrylate, acrylic acid, butyl acrylate, and functional benzotriazole; the concentration of the ammonium persulfate aqueous solution is 30-40 wt%.

4. The corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces according to claim 1, characterized in that, The preparation method of the functional benzotriazole is as follows: S1. Add 6-chloro-1-hydroxybenzotriazole and triethylamine to chloroform, stir until homogeneous, slowly add epoxide butene dropwise, and after the addition is complete, place at 50-60℃ and stir for 3-4 hours to obtain alkenylbenzotriazole. S2. Add alkenylbenzotriazole, 5,5-dimethylhydantoin, and potassium hydroxide to acetonitrile, stir until homogeneous, place at 70-80℃, stir and react for 5-6 hours, cool to room temperature, add sodium hypochlorite, and continue stirring for 1-2 hours to obtain modified benzotriazole. S3. Add modified benzotriazole and guanidinoacetic acid to toluene, stir well, slowly add concentrated sulfuric acid dropwise, and after the addition is complete, place at 110℃ and reflux for 7-8 hours to obtain functional benzotriazole.

5. The corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces according to claim 4, characterized in that, The molar ratio of 6-chloro-1-hydroxybenzotriazole, epoxide, and triethylamine in step S1 is 1:1.1-1.2:1.2-1.

3.

6. The corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces according to claim 4, characterized in that, The molar ratio of alkenylbenzotriazole, 5,5-dimethylhydantoin, potassium hydroxide, and sodium hypochlorite in step S2 is 1:1.1-1.2:1.2-1.3:1.2-1.

3.

7. The corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces according to claim 4, characterized in that, The molar ratio of modified benzotriazole, guanidinoacetic acid, and concentrated sulfuric acid in step S3 is 1:1.1-1.2:0.05-0.

08.

8. The corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces according to claim 1, characterized in that, The film-forming agent is composed of zirconium fluoride and titanium fluoride in a mass ratio of 1:0.8-1; the vanadate is ammonium metavanadate or sodium metavanadate.

9. The corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces according to claim 1, characterized in that, The coupling agent is 3-glycidyl etheroxypropyltrimethoxysilane; the corrosion inhibitor is phytic acid.

10. A method for preparing a corrosion-resistant, high-temperature-resistant, chromium-free passivating agent for magnesium alloy workpieces as described in any one of claims 1-9, characterized in that, The process includes the following steps: according to the weight ratio, add film-forming agent, functional acrylic resin, vanadate, coupling agent, and corrosion inhibitor to water, stir for 0.5-1h at a stirring speed of 800-1000r / min to obtain chromium-free passivating agent.

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