阅读说明：本技术 一种于微弧氧化镁合金表面一步原位生成Zn-MOF涂层及其制备方法 (One-step in-situ generation Zn-MOF coating on surface of micro-arc magnesium oxide alloy and preparation method thereof ) 是由 尚伟 蒋世权 金苏丹 李秋凤 易兰 温玉清 于 2021-07-15 设计创作，主要内容包括：本发明公开了一种微弧氧化镁合金表面Zn-MOF涂层及其制备方法。该镁合金表面MAO/ZIF-8涂层具体包括依次附着于镁合金表面的微弧氧化层和Zn-MOF层。对镁合金基体依次进行打磨抛光、除油、超声清洗,而后进行微弧氧化处理,在表面形成微弧氧化膜之后；将其置于聚四氟乙烯反应釜中高温高压反应,以形成Zn-MOF涂层,干燥后获得镁合金表面MAO/ZIF-8涂层。本发明制备方法工艺简易,该Zn-MOF涂层一步原位生长,与镁合金基材有着良好的结合力,并能够均匀分布于镁合金表面,具有良好的耐腐蚀性能。(The invention discloses a Zn-MOF coating on the surface of a micro-arc magnesium oxide alloy and a preparation method thereof. The MAO/ZIF-8 coating on the surface of the magnesium alloy specifically comprises a micro-arc oxidation layer and a Zn-MOF layer which are sequentially attached to the surface of the magnesium alloy. Sequentially polishing, degreasing and ultrasonically cleaning a magnesium alloy matrix, and then performing micro-arc oxidation treatment to form a micro-arc oxidation film on the surface; placing the magnesium alloy into a polytetrafluoroethylene reaction kettle for high-temperature high-pressure reaction to form a Zn-MOF coating, and drying to obtain the MAO/ZIF-8 coating on the surface of the magnesium alloy. The preparation method has simple process, the Zn-MOF coating grows in situ in one step, has good binding force with the magnesium alloy substrate, can be uniformly distributed on the surface of the magnesium alloy, and has good corrosion resistance.)

1. A micro-arc magnesium oxide alloy surface Zn-MOF coating and a preparation method thereof are characterized in that: the MAO/ZIF-8 coating on the surface of the magnesium alloy comprises a micro-arc oxidation layer and a Zn-MOF layer which are sequentially attached to the surface of the magnesium alloy.

2. The Zn-MOF coating on the surface of the micro-arc magnesium oxide alloy and the preparation method thereof according to claim 1 are characterized by comprising the following specific steps:

(1) magnesium alloy pretreatment

In order to remove stains and oxides on the surface of the magnesium alloy, metallographic abrasive paper of #180, #600, #1000 and #1500 is selected for grinding and polishing, and then a large amount of deionized water is used for washing residues; carrying out oil removal treatment for 60s at the temperature of 60-80 ℃; finally, performing ultrasonic treatment for 10-15 min by using ethanol and water respectively, and drying to obtain a treated magnesium alloy; the deoiling liquid comprises the following components: 15-20 g/LNaOH, 30-40 g/LNa₂CO₃、15～20g/LNa₃PO₄；

(2) Micro arc oxidation treatment

At room temperature, placing the treated magnesium alloy obtained in the step (1) as an anode and a stainless steel sheet as a cathode in a micro-arc oxidation solution for micro-arc oxidation treatment by using pulse voltage to obtain a micro-arc oxidation treated magnesium alloy carrier; the electrical parameters were set as: the frequency is 50-200 Hz, the duty ratio is 30-50%, the termination voltage is 180-220V, and the micro-arc oxidation time is 30-40 min; the micro-arc oxidation solution comprises the following components: 10-15 g/LNaOH, 5-10 g/LNa₂SiO₃、5～10g/LNaF、4～6g/LNa₂B₄O₇、1～5g/LNa₂WO₄、3～5mL/LC₃H₈O₃And 3-5 mL/LC₆H₁₅NO₃；

(3) Zn-MOF coating preparation

0.59g of zinc nitrate hexahydrate, 0.245g of 2-methylimidazole and 0.135g of sodium formate were dissolved in 30mL of methanol; then pouring the magnesium alloy into a polytetrafluoroethylene reaction kettle containing the micro-arc oxidation treatment magnesium alloy carrier obtained in the step (2), wherein the magnesium alloy is vertically suspended in the reaction kettle and is subjected to constant-temperature synthesis reaction at 180 ℃ for 24 hours; naturally cooling to room temperature in the air after the reaction is finished, taking out, washing for 5-10 times by using deionized water, and drying at 50 ℃ to obtain the MAO/ZIF-8 coating on the surface of the magnesium alloy;

the sodium hydroxide, sodium carbonate, sodium phosphate, sodium silicate, sodium fluoride, sodium tetraborate, sodium tungstate, triethanolamine, glycerol, zinc nitrate hexahydrate, 2-methylimidazole, sodium formate, methanol and ethanol are all chemically pure or above.

Technical Field

The invention belongs to a corrosion-resistant composite coating of a metal material, and particularly relates to a Zn-MOF coating on the surface of a micro-arc magnesium oxide alloy and a preparation method thereof.

Background

Magnesium and its alloy are used as green engineering material in 21 st century. In recent years, magnesium alloys have a wide application prospect in the fields of new energy automobiles, aerospace, biomedicine, electronic products and the like due to excellent physical properties such as small density, excellent electromagnetic shielding property, better die-casting processing and recycling property and the like. Especially, the constant development progress of the national automobile industry and the 3C industry nowadays, and the light weight has attracted extensive attention. Magnesium alloys, as the lightest known engineering materials of application, are well able to solve the problem of weight reduction of automobiles and 3C products. However, magnesium alloys have a very negative potential, which makes them susceptible to corrosion in humid air, a drawback that severely limits their large-scale use. To address this problem, researchers have introduced a number of treatments. Micro-arc oxidation (MAO) is more commonly used in a number of coating preparation methods. This is due to its satisfactory coating properties, including high adhesion to the substrate, high microhardness, and high corrosion resistance.

As a novel nano material film, the Metal Organic Framework (MOF) film has the advantages of surface grafting modification capability, adjustable shape and large selectable space, and shows good application value in many fields. However, the MOF film layer and the support have a large difference in material properties, and have many problems in connectivity, and it is difficult to form a strong high-performance film layer. During the formation of the film, factors such as carrier species, surface roughness, pore size, surface chemical composition, etc., can greatly influence the processes of nucleation, crystallization and intergrown densification of MOF grains on the surface thereof. And then, a continuous and compact Zn-MOF film layer is grown in a one-step in-situ solvothermal mode. The micro-arc oxidation film surface can better promote the nucleation and crystallization of the MOF film layer, the ligand and the carrier form hydrogen bonds or other bond energy under the conditions of high temperature and high pressure to strengthen the bonding force between the film layer and the carrier and promote the continuous growth of the film layer. The method aims to combine the surface of the micro-arc oxidation film with one-step in-situ solvothermal construction of the Zn-MOF coating, thereby providing active and passive protection capability for the magnesium alloy substrate and inhibiting the occurrence of a corrosion process.

Disclosure of Invention

The invention aims to provide a Zn-MOF coating on the surface of a micro-arc magnesium oxide alloy and a preparation method thereof.

The preparation method of the Zn-MOF coating on the surface of the micro-arc magnesium oxide alloy comprises the following specific steps:

(1) magnesium alloy pretreatment

In order to remove stains and oxides on the surface of the magnesium alloy, metallographic abrasive paper of #180, #600, #1000 and #1500 is selected for grinding and polishing, and then a large amount of deionized water is used for washing residues; carrying out oil removal treatment for 60s at the temperature of 60-80 ℃; finally, performing ultrasonic treatment for 10-15 min by using ethanol and water respectively, and drying to obtain a treated magnesium alloy; the deoiling liquid comprises the following components: 15-20 g/L NaOH, 30-40 g/L Na₂CO₃、15～20g/L Na₃PO₄。

(2) Micro arc oxidation treatment

At room temperature, placing the treated magnesium alloy obtained in the step (1) as an anode and a stainless steel sheet as a cathode in a micro-arc oxidation solution for micro-arc oxidation treatment by using pulse voltage to obtain a micro-arc oxidation treated magnesium alloy carrier; the electrical parameters were set as: the frequency is 50-200 Hz, the duty ratio is 30-50%, the termination voltage is 180-220V, and the micro-arc oxidation time is 30-40 min; the micro-arc oxidation solution comprises the following components: 10-15 g/L NaOH, 5-10 g/L Na₂SiO₃、5～10g/L NaF、4～6g/L Na₂B₄O₇、1～5g/L Na₂WO₄、3～5mL/L C₃H₈O₃And 3-5 mL/L C₆H₁₅NO₃。

(3) Zn-MOF coating preparation

0.59g of zinc nitrate hexahydrate, 0.245g of 2-methylimidazole and 0.135g of sodium formate were dissolved in 30mL of methanol. And (3) then pouring the magnesium alloy into a polytetrafluoroethylene reaction kettle containing the micro-arc oxidation treatment magnesium alloy carrier obtained in the step (2), wherein the magnesium alloy is vertically suspended in the reaction kettle, and carrying out constant-temperature synthesis reaction at 180 ℃ for 24 hours. And after the reaction is finished, naturally cooling the mixture to room temperature in the air, taking the mixture out, washing the mixture for 5-10 times by using deionized water, and drying the mixture at 50 ℃ to obtain the MAO/ZIF-8 coating on the surface of the magnesium alloy.

The sodium hydroxide, sodium carbonate, sodium phosphate, sodium silicate, sodium fluoride, sodium tetraborate, sodium tungstate, triethanolamine, glycerol, zinc nitrate hexahydrate, 2-methylimidazole, sodium formate, methanol and ethanol are all chemically pure or above.

The preparation method has simple process, the Zn-MOF coating grows in situ in one step, has good binding force with the magnesium alloy substrate, and can be uniformly distributed on the surface of the magnesium alloy. The coating is found to have good corrosion resistance through electrochemical performance tests.

Drawings

FIG. 1 is an SEM image of the MAO coating and MAO/ZIF-8 coating prepared in example 1.

Figure 2 is a phase characterization XRD pattern of example 1.

FIG. 3 is a zeta potential polarization curve for the MAO coating and the MAO/ZIF-8 coating prepared in example 1.

Detailed Description

Example (b):

(1) magnesium alloy pretreatment

In order to remove stains and oxides on the surface of the magnesium alloy, metallographic abrasive paper of #180, #600, #1000 and #1500 is selected for grinding and polishing, and then a large amount of deionized water is used for washing residues; degreasing treatment was carried out at 70 ℃ for 60 seconds (20g/L NaOH, 30g/L Na)₂CO₃、20g/L Na₃PO₄) (ii) a Finally, respectively carrying out ultrasonic treatment on the mixture for 10min by using ethanol and water, and drying the mixture for later use;

(2) micro arc oxidation treatment

The micro-arc oxidation is carried out in a silicate system by adopting pulse voltage, at room temperature, the magnesium alloy treated in the step (1) is used as an anode, a stainless steel sheet is used as a cathode, the magnesium alloy is placed in a micro-arc oxidation solution to be subjected to micro-arc oxidation treatment by adopting the pulse voltage, and the set electrical parameters are as follows: frequency 50Hz, duty cycle 30%, end voltage 220V, micro-arcThe oxidation time is 30 min; the micro-arc oxidation solution used in the process comprises the following components: 11g/L NaOH, 5g/L Na₂SiO₃，8g/L NaF，4g/L Na₂B₄O₇，1g/L Na₂WO₄，5mL/L C₃H₈O₃，4mL/L C₆H₁₅NO₃。

(3) Zn-MOF coating preparation

0.59g of zinc nitrate hexahydrate, 0.245g of 2-methylimidazole and 0.135g of sodium formate were dissolved in 30mL of methanol. And (3) then pouring the mixture into a polytetrafluoroethylene reaction kettle vertically suspending the micro-arc oxidation treatment magnesium alloy carrier obtained in the step (2), and carrying out constant-temperature synthesis reaction at 180 ℃ for 24 hours. And after the reaction is finished, naturally cooling the mixture to room temperature in the air, taking the mixture out, washing the mixture for 10 times by using deionized water, and drying the mixture at 50 ℃ to obtain the MAO/ZIF-8 coating on the surface of the magnesium alloy.

The sodium hydroxide, sodium carbonate, sodium phosphate, sodium silicate, sodium fluoride, sodium tetraborate, sodium tungstate, triethanolamine, glycerol, zinc nitrate hexahydrate, 2-methylimidazole, sodium formate, methanol and ethanol are all chemically pure or above.

The MAO/ZIF-8 coating on the surface of the magnesium alloy prepared by the embodiment is represented by SEM, and the surface of the coating is densely and uniformly distributed on the surface of the magnesium alloy and can completely cover micropores of a micro-arc oxidation film on a bottom layer. The surface of the sample is scanned by X-ray, and the XRD pattern obtained shows that MgSiO is mainly present in the coating₃And ZIF-8. The MAO/ZIF-8 coating of this example was characterized for corrosion resistance, and tested in a three-electrode system (calomel electrode as a reference electrode, platinum electrode as an auxiliary electrode, and magnesium alloy surface coating as a working electrode) using a CHI760 electrochemical workstation, and 3.5 wt.% sodium chloride solution was used as an electrolyte. And (3) selecting a potentiodynamic polarization curve to research the corrosion resistance of the magnesium alloy surface coating, and testing by adopting a scanning rate of 5mV/s after the open circuit potential is stable. The corrosion current density of the MAO/ZIF-8 coating on the surface of the magnesium alloy obtained in the embodiment is 7.995 multiplied by 10^-7A·cm^-2Specific micro-arc oxidation film corrosion current density of 2.136X 10^-6A·cm^-2Reduced by one order of magnitude compared with AZ91 magnesium alloyCorrosion current density of gold matrix 1.137X 10^-5A·cm^-2The corrosion resistance of the magnesium alloy is improved by two orders of magnitude.