Preparation method of high corrosion and wear resistant magnesium alloy anodic oxidation composite coating

Abstract

The application discloses a preparation method of a high-corrosion-resistance and wear-resistance magnesium alloy anodic oxidation composite coating. The method is characterized in that: a magnesium alloy is used as an anode, and an anodic oxidation coating is prepared by using an electrochemical method; then, a hydrothermal method is used, and zinc nitrate is used as a zinc ion source to prepare a rice flower-shaped zinc oxide intermediate layer on the sample subjected to anodic oxidation treatment, so as to serve as a growth site of a metal organic framework; finally, the sample containing the anodic oxidation layer and the transition layer is placed in a methanol solution containing dimethyl imidazole to perform a secondary solvothermal reaction, a zeolite imidazolate framework is synthesized on the surface of the sample, and a novel composite coating is obtained. The zeolite imidazolate framework can be uniformly distributed on the surface of the coating, and has strong combination capacity with the coating; the composite coating can not only improve the corrosion resistance of the material, but also significantly improve the wear resistance of the material, and has positive significance for promoting the application of the magnesium alloy as a medical degradable implant material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal corrosion inhibition coating and medical degradable implant materials, and particularly relates to a preparation method of a high-corrosion-resistant and wear-resistant magnesium alloy anodized composite coating. BACKGROUND

[0002] Magnesium and its alloys have been considered as a promising material for biomedical applications due to their biodegradability, non-toxicity and similar elastic modulus to natural bone. However, the high activity of magnesium alloys easily causes corrosion, which limits the use requirements of the corresponding materials. And the substrate defects (such as cracks and pits) caused by rapid corrosion lead to premature material fracture, which affects the material to play its due role. Therefore, it is necessary to use surface coating technology to control the degradation rate in the physiological environment.

[0003] In related surface treatment, anodized coating is widely used due to its high hardness, high wear resistance and corrosion resistance. The coating is usually deposited in the form of a porous ceramic layer on the alloy surface, and the corrosion medium in the environment can further corrode the substrate through the coating defects to cause the failure of the coating.

[0004] Metal organic frameworks (MOFs) are coordination polymers with three-dimensional porous structure, which are connected and extended by metal center units and organic ligands. The most representative one is zeolitic imidazolate framework-8 (ZIF-8), which has been studied in the field of biomedicine due to its good biocompatibility, adjustable size and porosity, drug loading rate and other characteristics. On the one hand, the biocompatibility of the material can be further improved; on the other hand, the introduced ZIF-8 can act as a zinc-rich coating, which has the special ability to protect the metal in harsh environmental conditions, and its corrosion products can prevent the corrosion medium from further penetrating into the coating, thereby improving the protective effect of the coating. The method reported in the literature is to introduce ZIF-8 into the coating by physical means, which is complicated and has the disadvantage of weak combination with the coating, so it is difficult to form a uniform and stable coating. Considering the above limitations, a method of using homologous metal oxide induction to construct a stable MOF composite coating in situ is proposed to obtain a magnesium alloy anodized composite coating material with corrosion resistance and wear resistance. SUMMARY

[0005] The purpose of the present application is to use the method of homologous metal oxide induction, combined with the principles of hydrothermal and solvothermal, to provide a method for preparing a ZIF-8 / magnesium alloy anodized layer composite coating material.

[0006] The object of the present application is achieved in that a preparation method of a high corrosion and wear resistant magnesium alloy anodization composite coating is characterized in that: 1) a magnesium alloy is used as an anode to prepare a sample containing an anodization layer by an anodization method; 2) a zinc oxide transition layer is prepared on the sample containing the anodization layer by a hydrothermal method; and 3) the sample containing the anodization layer and the zinc oxide transition layer is placed in a dimethyl imidazole-containing methanol solution to perform a secondary solvothermal reaction, and ZIF-8 is synthesized on the surface of the sample containing the anodization layer and the zinc oxide transition layer to form a novel composite coating material.

[0007] Further, the method for preparing the anodization layer on the magnesium alloy by anodization is that a magnesium alloy is used as an anode, a platinum sheet is used as a cathode, anodization is performed in a fluoride-containing alkaline electrolyte solution at 150-220 V, an anode current of 0.5-1 A, a duty cycle of 55%, and a temperature of 30±5 ℃ for 50-120 s.

[0008] Further, the zinc oxide transition layer is prepared by a hydrothermal method: zinc nitrate is dissolved in ultrapure water as a zinc ion source, ammonia water is used to adjust the pH value, and the transition layer solution is obtained by rapid stirring for 5 min; the magnesium alloy substrate containing the anodization layer prepared in step 1) is placed in the transition layer solution, and then is transferred into a polytetrafluoroethylene hydrothermal inner container, sealed, and placed in a temperature-controlled oven; the reaction is performed at 70-100 ℃ in a temperature-controlled environment for 6-12 h; after the reaction is completed, the magnesium alloy substrate containing the anodization layer and the zinc oxide transition layer is taken out after being cooled to room temperature, washed with water and alcohol to remove impurities, and dried to obtain the magnesium alloy containing the anodization layer and the zinc oxide transition layer.

[0009] Further, the magnesium alloy containing the anodization layer and the zinc oxide transition layer is placed in a dimethyl imidazole-containing methanol solution to perform a solvothermal treatment, reacted at 100-120 ℃ for 6-12 h, cooled to room temperature, taken out, washed with water and alcohol to remove impurities, and dried to obtain the composite coating material.

[0010] Specifically, the present application adopts the following technical scheme: a preparation method of a high corrosion and wear resistant magnesium alloy anodization composite coating is characterized in that: a pretreated magnesium alloy is used as an anode, a platinum sheet is used as a cathode, and an anodization film is formed on the surface of the magnesium alloy in a fluoride-containing alkaline electrolyte solution environment by an anodization method; the sample after anodization treatment is placed in a zinc nitrate-containing alkaline solution, and a zinc oxide transition layer is constructed on the surface of the anodization layer by a hydrothermal method; and finally a ZIF-8 / magnesium alloy anodization composite coating material is formed by a solvothermal reaction. The specific steps are as follows:

[0011] 1) Magnesium alloy pretreatment: the surface layer of the magnesium alloy is polished, the surface organic impurities are removed by ethanol and acetone, the oil is removed by alkaline and acidic cleaning solutions, and finally the magnesium alloy is rinsed with ultrapure water and dried.

[0012] 2) Preparation of anodic oxidation layer: the pretreated magnesium alloy is anode, platinum sheet is cathode, in the alkaline electrolyte solution containing potassium fluoride, the treatment time is 50 s-120 s, the voltage range is 150 V-220 V, the current range is 0.5 A-1.5 A, the duty cycle is 55%, the electrolysis temperature is 30±5 DEG C, and the anodic oxidation coating is obtained.

[0013] 3) Preparation of zinc oxide transition layer: the sample after anodic oxidation treatment is placed in a growth solution, sealed in a hydrothermal kettle, reacted at 70 DEG C-100 DEG C for 6-12 h, naturally cooled to room temperature, washed with water and alcohol, and dried to obtain a sample containing a zinc oxide transition layer.

[0014] 4) Preparation of ZIF-8 composite coating: the sample containing the zinc oxide transition layer is placed in a dimethyl imidazole methanol solution, and a solvothermal reaction is carried out at 100 DEG C-120 DEG C for 6-12 h, and the composite coating material is obtained after cooling to room temperature, washing with water and alcohol, and drying.

[0015] In the preparation step of the zinc oxide transition layer, the sample after anodic oxidation treatment is placed in a growth solution, and hydrothermal treatment is carried out at 70 DEG C-100 DEG C. The growth solution mainly refers to zinc nitrate as a zinc ion source, dispersed in ultrapure water, and the pH of the solution is adjusted to 10-13 with ammonia water.

[0016] The composite material coating obtained by the above scheme has the following characteristics: the zinc oxide transition layer and ZIF-8 can fill the coating defects generated in the anodic oxidation process to some extent, reduce the corrosion of the substrate caused by the corrosion medium through the defects, increase the overall corrosion potential of the coating and reduce the corrosion current, and further improve the corrosion resistance of the material; the zinc oxide transition layer can provide growth sites for ZIF-8, which is helpful for the uniform growth of ZIF-8 on the surface of the coating and better combination with the coating; ZIF-8 can improve the overall wear resistance of the coating to some extent, so that the material can maintain good mechanical properties and reduce the adverse effects of material wear; ZIF-8 has good biocompatibility, adjustable porosity and size, and can be used as a carrier to load bioactive molecules or drug media for biological treatment. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a scanning electron microscope image of the magnesium alloy anodic oxidation coating obtained by anodic oxidation in the specific embodiment 1 of the application.

[0018] Figure 2 It is a scanning electron microscope image of the anodic oxidation layer in the specific embodiment 1 of the application, which generates a zinc oxide transition layer on the surface in a hydrothermal environment after hydrothermal treatment.

[0019] Figure 3A scanning electron microscope image of the ZIF-8 / magnesium alloy anodic oxidation composite coating obtained after the solvothermal treatment in Embodiment 1 of the present application.

[0020] Figure 4 A polarization curve diagram obtained by electrochemical corrosion test in Embodiment 1 of the present application; (sample mark in the figure: ZG11-magnesium alloy comparative sample, PEO-anodic oxidation layer, PZ-anodic oxidation layer containing zinc oxide transition layer, PZM-ZIF-8 / ZnO / anodic oxidation composite coating).

[0021] Fig. 5(a) is a micro-morphology diagram of the anodic oxidation layer sample in Embodiment 2 of the present application under external force abrasion conditions.

[0022] Fig. 5(b) is a micro-morphology diagram of the anodic oxidation layer sample containing zinc oxide transition layer in Embodiment 2 of the present application under external force abrasion conditions.

[0023] Fig. 5(c) is a micro-morphology diagram of the ZIF-8 composite coating in Embodiment 2 of the present application under external force abrasion conditions. DETAILED DESCRIPTION

[0024] Embodiment 1

[0025] 1) The magnesium alloy was used as the substrate, the surface oxide layer was polished by the metallographic sandpaper, and then the treated magnesium alloy was obtained by alkali washing, acid washing and drying. The treated magnesium alloy was used as the anode, and the platinum sheet was used as the cathode. The anodic oxidation was carried out in the alkaline fluorine-containing electrolyte solution (20 g / L KOH, 58.1 g / L KF) under the voltage of 200 V for 50 s. After that, the sample was taken out, cleaned with ultrapure water, and dried at room temperature. The micro-morphology diagram is shown in Fig. 1, and the coating presents the ceramic phase characteristics, covering the anodic oxidation layer on the surface of the substrate. Figure 1

[0026] 2) The zinc oxide transition layer growth solution was prepared by dissolving 0.0035 mol of zinc nitrate in ultrapure water, and adjusting the pH of the solution with ammonia water to make the solution pH=11. After rapid stirring for 5 min, the sample containing the anodic oxidation layer after the anodic oxidation treatment in step 1) was put into the growth solution, and then the hydrothermal treatment was carried out at 70℃ for 12 h. After the reaction was completed, the sample was cooled to room temperature and taken out. The sample containing the anodic oxidation layer containing the zinc oxide transition layer was obtained after cleaning with ultrapure water and ethanol and drying. The micro-morphology is shown in Fig. 2, and the surface is covered with a layer of rice flower-like zinc oxide transition layer. Figure 2

[0027] ​​3) The anolyte sample containing the zinc oxide transition layer after hydrothermal treatment in step 2) was transferred to a methanol solution containing 0.01 mol of dimethylimidazole and subjected to solvothermal treatment at 100℃ for 12 hours. After treatment, it was cooled to room temperature, washed with ultrapure water and ethanol respectively, and then dried. The surface morphology is shown in the figure. Figure 3 As shown, a polyhedral ZIF-8 crystal was formed on the surface and successfully bonded to the zinc oxide transition layer surface to form a sample.

[0028] 4) Electrochemical corrosion tests were performed on the samples obtained in step 3) above to evaluate the corrosion resistance of the coating material (polyhedral ZIF-8). The experimental results are as follows: Figure 4 As shown in Table 1, the specific experimental data are as follows: ZG11—magnesium alloy control sample, PEO—anodic oxide layer, PZ—anodic oxide layer with zinc oxide transition layer, PZM—ZIF-8 / ZnO / anodic oxide composite coating. Compared with the magnesium alloy substrate, the corrosion potential of the coated material gradually increases, and the corrosion current decreases significantly. This indicates that both the anodic oxide layer and the prepared composite coating (PZM, i.e., the product obtained in step 3) can improve the corrosion resistance of magnesium alloy. The composite coating containing ZIF-8 has the best effect, and the corrosion current of the material decreases by 4 orders of magnitude.

[0029] Table 1. Tafel fitting data for polarization curves

[0030]

[0031] Example 2

[0032] 1) Using a magnesium alloy as a substrate, the surface of the magnesium alloy was polished with metallographic sandpaper to remove the oxide layer, followed by alkaline washing, acid treatment, and drying to obtain the treated magnesium alloy. Using the treated magnesium alloy as the anode and a platinum sheet as the cathode, anodizing was performed for 50 s in an alkaline fluorine-containing electrolyte solution (20 g / L KOH, 58.1 g / L KF) at 200 V. After removal, the sample was rinsed with ultrapure water and dried at room temperature.

[0033] 2) The zinc oxide transition layer growth solution was prepared by dissolving 0.017 mol of zinc nitrate in ultrapure water and adjusting the pH of the solution with ammonia to pH=11. The solution was stirred rapidly for 5 min. Then, the sample containing the anodic oxide layer after the anodizing treatment in step 1) was placed in the growth solution and hydrothermally treated at 70℃ for 12 h. After the reaction was completed, the sample was cooled to room temperature and removed. It was washed with ultrapure water and ethanol respectively and dried to obtain the sample containing the anodic oxide layer of zinc oxide transition layer.

[0034] 3) The sample of the anodic oxidation layer with zinc oxide transition layer after hydrothermal treatment in step 2) was transferred into a methanol solution containing 0.01 mol of dimethyl imidazole, and was subjected to a solvothermal treatment at 100°C for 12 h. After cooling to room temperature, the sample was taken out, washed with ultrapure water and ethanol, and dried to obtain a sample of ZIF-8 composite coating.

[0035] 4) The wear resistance of the three coating materials obtained above was tested under a load of 20 N. The micrographs after the test are shown in FIG. 5(a), FIG. 5(b), and FIG. 5(c). FIG. 5(a), FIG. 5(b), and FIG. 5(c) correspond to the sample of the anodic oxidation layer (product prepared in step 1), the sample of the anodic oxidation layer with zinc oxide transition layer (product prepared in step 2), and the sample of the ZIF-8 composite coating (product prepared in step 3), respectively. During the friction process, it was observed that there were great differences among the three samples. The coating duration of the sample of the anodic oxidation layer and the sample of the anodic oxidation layer with zinc oxide transition layer under a load of 20 N was 55 s and 75 s, respectively. Subsequently, the coating lost its protective effect, and it was observed that there were residual debris on the edges of the tracks, and the wear marks in the friction area penetrated into the magnesium alloy substrate, indicating that the coating in the area was severely worn. However, under the same load conditions, the sample of the ZIF-8 composite coating was slightly damaged on the surface after 300 s, but no wear marks penetrating into the magnesium alloy substrate were observed. This indicates that the addition of ZIF-8 can further improve the wear resistance of the coating.

Claims

1. A method for preparing a highly corrosion-resistant and wear-resistant anodized composite coating on magnesium alloy, characterized in that: The steps are as follows: 1) Using magnesium alloy as the anode, a sample containing an anodic oxide layer is prepared by anodizing; 2) A zinc oxide transition layer is prepared on the sample containing the anodic oxide layer by hydrothermal method. The zinc oxide transition layer is prepared by hydrothermal method: zinc nitrate is used as the zinc ion source and dissolved in ultrapure water, the pH value is adjusted by ammonia water, and the mixture is stirred rapidly for 5 min to obtain the transition layer solution. The magnesium alloy substrate containing the anodic oxide layer obtained in step 1) is placed in the transition layer solution, and then transferred to a polytetrafluoroethylene hydrothermal liner, sealed, and placed in a temperature-controlled oven. The reaction is carried out at a temperature of 70-100℃ for 6-12 h. After the reaction is completed, the sample is taken out after cooling to room temperature, washed with water and alcohol to remove impurities, and dried to obtain a zinc oxide transition layer on the anodic oxide layer of magnesium alloy; 3) The sample containing the anodic oxide layer and the zinc oxide transition layer is placed in a methanol solution containing dimethylimidazole for a secondary solvothermal reaction to synthesize ZIF-8 on the surface of the sample containing the anodic oxide layer and the zinc oxide transition layer, forming a composite coating material.

2. The method for preparing a highly corrosion-resistant and wear-resistant anodized composite coating of magnesium alloy as described in claim 1, characterized in that: The method for preparing anodized layers on magnesium alloys by anodizing is as follows: using magnesium alloy as the anode and platinum sheet as the cathode, anodizing is performed in a fluorine-containing alkaline electrolyte solution at 150-220 V, anodic current 0.5-1 A, duty cycle 55%, and temperature 30±5℃ for 50-120 s.

3. The method for preparing a highly corrosion-resistant and wear-resistant anodized composite coating of magnesium alloy as described in claim 1, characterized in that: Magnesium alloys with zinc oxide transition layers on anodized layers are subjected to solvothermal treatment in a methanol solution containing dimethylimidazole at 100-120℃ for 6-12 h. After cooling to room temperature, the alloys are removed, washed with water and alcohol to remove impurities, and dried to obtain the composite coating material.

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