Magnesium alloy corrosion-resistant micro-arc oxidation coating with self-repairing function and preparation method thereof

Abstract

The present application relates to magnesium alloy surface treatment technical field, especially to a kind of magnesium alloy corrosion-resistant micro-arc oxidation coating with self-repairing function and preparation method thereof.A kind of preparation method of magnesium alloy corrosion-resistant micro-arc oxidation coating with self-repairing function, comprising the following steps: step A, magnesium alloy pretreatment: the magnesium alloy is polished and polished;Step B, micro-arc oxidation treatment: stainless steel is used as cathode, magnesium alloy is used as anode and is placed into micro-arc oxidation electrolyte to carry out micro-arc oxidation treatment, and a porous micro-arc oxidation layer is formed in situ on the surface of magnesium alloy.The preparation method of the magnesium alloy corrosion-resistant micro-arc oxidation coating with self-repairing function, the magnesium alloy corrosion-resistant micro-arc oxidation coating prepared has long-lasting corrosion resistance and self-repairing performance, prolongs the service life of magnesium alloy, solves the problem that the protective performance of existing magnesium alloy protective coating is prone to sharp decline in use process, and the corrosion resistance effect is poor in long-term use, affects material service life.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy surface treatment technology, and in particular to a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating and its preparation method. Background Technology

[0002] With industrial development, environmental protection and carbon emission reduction have become hot topics of concern. The transportation industry, especially automobiles and new energy vehicles, can reduce energy consumption and thus carbon emissions by reducing their weight, which is a crucial method for controlling energy consumption. Magnesium alloys, due to their light weight, high specific strength, and excellent casting properties, have become a strong contender to replace steel in the future.

[0003] However, magnesium alloys are highly chemically reactive and prone to corrosion in the environment, which has become a major factor limiting their development. To improve the corrosion resistance of magnesium alloys, surface treatment technologies have been extensively developed. Existing surface treatment methods for magnesium alloys include anodizing, micro-arc oxidation, laser surface treatment, ion implantation and phosphating electrophoresis, and chemical conversion coatings. These methods can all improve the performance of magnesium alloys to some extent. It has been proven that micro-arc oxidation treatment results in the best performance improvement. However, the micropores inherent in micro-arc oxidation surface treatment technology and the microcracks formed during its preparation process cannot guarantee long-term corrosion resistance. Furthermore, mechanical damage encountered by the micro-arc oxidation film during service or installation, as well as corrosion damage during long-term service, can cause a sharp decline in the protective performance of the film, seriously affecting the service life of the material. Summary of the Invention

[0004] In response to the problems raised in the background art, the purpose of this invention is to propose a method for preparing a corrosion-resistant micro-arc oxidation coating for magnesium alloys with self-healing function. The prepared corrosion-resistant micro-arc oxidation coating for magnesium alloys has long-lasting corrosion resistance and self-healing properties, extending the service life of magnesium alloys. This solves the problem that the protective performance of existing magnesium alloy protective coatings is prone to rapid decline during use, and the corrosion resistance is poor after long-term use, affecting the service life of materials.

[0005] Another objective of this invention is to provide a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating prepared using the above-described preparation method, which has long-lasting corrosion resistance and self-healing properties.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] A method for preparing a corrosion-resistant micro-arc oxidation coating for magnesium alloys with self-healing function includes the following steps:

[0008] Step A, Magnesium alloy pretreatment: Grinding and polishing the magnesium alloy;

[0009] Step B, Micro-arc oxidation treatment: Stainless steel is used as the cathode and magnesium alloy is used as the anode. The magnesium alloy is placed in a micro-arc oxidation electrolyte for micro-arc oxidation treatment. A porous micro-arc oxidation layer is formed in situ on the surface of the magnesium alloy. The alloy is then cleaned and dried.

[0010] The micro-arc oxidation electrolyte comprises sodium tungstate and cerium oxide;

[0011] Step C, Hydroxylation treatment: The magnesium alloy is immersed in sodium hydroxide solution for hydroxylation treatment, and then cured after drying;

[0012] Step D, Preparation of silane agent: Tetraethyl orthosilicate silane and 3-aminopropyltrimethoxysilane are mixed evenly, 4-aminosalicylic acid is added and then ultrasonically dispersed evenly to obtain silane agent;

[0013] Step E, silanization treatment: The magnesium alloy after hydroxylation treatment is immersed in silane agent. After being pulled out of silane agent, a silane layer is formed on the surface of the micro-arc oxidation layer. The sample is then cleaned and dried to obtain the immersion sample.

[0014] Step F, Curing treatment: The extracted sample is dried and cured.

[0015] Step G, Epoxy Resin Sealing: Apply a layer of epoxy resin to the surface of the cured sample for sealing treatment. An epoxy layer is formed on the surface of the silane layer, and a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating consisting of a micro-arc oxidation layer, a silane layer and an epoxy layer is formed on the surface of the magnesium alloy.

[0016] To further explain, the composition of the micro-arc oxidation electrolyte is: sodium silicate 14-16 g / L, sodium fluoride 13-15 g / L, sodium hydroxide 2-3 g / L, glycerol 4-6 mL / L, sodium tungstate 2-6 g / L, and cerium oxide 2-10 g / L.

[0017] To further explain, in step D, tetraethyl orthosilicate silane and 3-aminopropyltrimethoxysilane are mixed evenly at a mass ratio of 1:1, and after adding 40 mg / L of 4-aminosalicylic acid, they are ultrasonically dispersed evenly to obtain a silane agent.

[0018] To further explain, in step E, the magnesium alloy after hydroxylation is placed in a silane agent and soaked at 25°C for 4-5 hours. After being pulled out of the silane agent at a speed of 1 mm / min, a silane layer is generated on the surface of the micro-arc oxidation layer. After rinsing with deionized water, it is dried at 30°C for 24-30 hours to obtain the extraction sample.

[0019] To further explain, in step C, the magnesium alloy is immersed in a sodium hydroxide solution for 2 minutes for hydroxylation treatment, dried in cold air, cured at 120°C for 2-3 hours, and then rinsed with deionized water. The concentration of the sodium hydroxide solution is 3-5 mol / L.

[0020] To further explain, in step A, the magnesium alloy is polished in sequence using sandpaper of 400#, 800#, 1200#, 1500# and 2000#.

[0021] To further explain, in step A, after grinding and polishing, holes are drilled in the magnesium alloy, and aluminum wires are tied to the drilled holes, which are then sealed with epoxy resin.

[0022] To further explain, in step F, the extracted sample is dried and cured at 100°C for 1 to 2 hours.

[0023] To further explain, in step G, the sample after drying and curing is placed on a spin coater and a layer of epoxy resin is spin-coated for sealing.

[0024] A self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating is prepared using the aforementioned method for preparing a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating.

[0025] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0026] The magnesium alloy treated by this invention can replace other alloys in harsh environments. By forming a triple self-healing layer, it possesses self-healing capabilities. When the film layer is damaged, it can react with the corrosive liquid to repair itself, preventing further corrosion of the substrate and protecting the magnesium alloy substrate from corrosion. Even if the surface epoxy layer is damaged, it can still protect the magnesium alloy from corrosion for a short period of time, exhibiting long-lasting corrosion resistance and self-healing properties. This significantly extends the service life of the magnesium alloy and has broad application prospects. Furthermore, the entire treatment process generates no harmful substances or gases, making it environmentally friendly. The preparation process is easy to operate, and the coating has good bonding strength, which can improve the effective and stable protection of the magnesium alloy. This solves the problems of existing magnesium alloy protective coatings, such as the rapid decline in protective performance during use, poor corrosion resistance over long-term use, and the impact on material lifespan. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope (SEM) image of the surface of the magnesium alloy before the micro-arc oxide layer is sealed in Example 1 of the present invention.

[0028] Figure 2 This is a scanning electron microscope (SEM) image of the surface of the magnesium alloy after the micro-arc oxide layer is sealed in the hole according to Example 1 of the present invention.

[0029] Figure 3 This is a scanning electron microscope (SEM) image of the surface of the coating after scratching in Embodiment 1 of the present invention;

[0030] Figure 4 This is a scanning electron microscope (SEM) image of the surface of the coating in Example 1 of the present invention when the repair time after scratch is 6 days.

[0031] Figure 5 The graphs show the evolution of open circuit potential over time after coating scratches in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0032] A method for preparing a corrosion-resistant micro-arc oxidation coating for magnesium alloys with self-healing function includes the following steps:

[0033] Step A, Magnesium alloy pretreatment: Grinding and polishing the magnesium alloy;

[0034] Step B, Micro-arc oxidation treatment: Stainless steel is used as the cathode and magnesium alloy is used as the anode. The magnesium alloy is placed in a micro-arc oxidation electrolyte for micro-arc oxidation treatment. A porous micro-arc oxidation layer is formed in situ on the surface of the magnesium alloy. The alloy is then cleaned and dried.

[0035] The micro-arc oxidation electrolyte comprises sodium tungstate and cerium oxide;

[0036] Step C, Hydroxylation treatment: The magnesium alloy is immersed in sodium hydroxide solution for hydroxylation treatment, and then cured after drying;

[0037] Step D, Preparation of silane agent: Tetraethyl orthosilicate silane and 3-aminopropyltrimethoxysilane are mixed evenly, 4-aminosalicylic acid is added and then ultrasonically dispersed evenly to obtain silane agent;

[0038] Step E, silanization treatment: The magnesium alloy after hydroxylation treatment is immersed in silane agent. After being pulled out of silane agent, a silane layer is formed on the surface of the micro-arc oxidation layer. The sample is then cleaned and dried to obtain the immersion sample.

[0039] Step F, Curing treatment: The extracted sample is dried and cured.

[0040] Step G, Epoxy Resin Sealing: Apply a layer of epoxy resin to the surface of the cured sample for sealing treatment. An epoxy layer is formed on the surface of the silane layer, and a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating consisting of a micro-arc oxidation layer, a silane layer and an epoxy layer is formed on the surface of the magnesium alloy.

[0041] This invention uses magnesium-based metal as the substrate. After pretreatment of the magnesium alloy by grinding and polishing, the magnesium alloy substrate is immersed in an electrolyte for micro-arc oxidation treatment, which grows a passivation film on the substrate surface. As the treatment time increases, the initially thin passivation film is continuously broken down, and the molten material is ejected at the breakdown site. Upon contact with the electrolyte, it cools and solidifies on the passivation film. With continuous breakdown and solidification of the molten material, the film layer continuously thickens, eventually forming a porous micro-arc oxidation layer. After the grinding and polishing pretreatment, a cleaner and smoother micro-arc oxidation film layer can be obtained. Then, the micro-arc oxidation layer is post-treated. The specific treatment method is to first perform hydroxylation treatment and silanization treatment, and finally coat an epoxy resin layer after the silane layer. This invention first adds sodium tungstate and cerium oxide as inorganic corrosion inhibitors to the electrolyte. Since the corrosive liquid enters through the pores of the film, sodium tungstate reacts with the corrosive liquid entering the pores to form a complex, blocking the corrosion channels (pores) and thus preventing further corrosion. This process occurs within the pores and serves as the first self-healing layer. Secondly, the simultaneous addition of sodium tungstate and cerium oxide to the electrolyte makes the resulting micro-arc oxidation layer more dense. This is manifested in cerium oxide filling the pores of the micro-arc oxidation layer, preventing the corrosive liquid from entering the film and causing corrosion, thus serving as the second self-healing layer. In addition, by adding 4-aminosalicylic acid as a corrosion inhibitor to the silane agent, the 4-aminosalicylic acid is uniformly dispersed in the silane agent. The silane agent is a mixture of tetraethyl orthosilicate silane (TEOS) and 3-aminopropyltrimethoxysilane (APTES). When the film is damaged, the corrosion inhibitor will react chemically with the entering corrosion liquid to generate insoluble substances to repair the damaged film, thereby preventing further corrosion. Macroscopically, it exhibits a certain self-healing function, serving as a third self-healing layer.

[0042] To further explain, by selecting tetraethyl orthosilicate silane (TEOS) and 3-aminopropyltrimethoxysilane (APTES) as silane agents, the physical bonding between the film layers is transformed into chemical bonding. By placing the hydroxylated magnesium alloy into the silane agent, the silane treatment allows the silane to form Si-O-Mg covalent bonds with the surface metal oxides, effectively enhancing the bonding force between the film layers (between the micro-arc oxidation layer and the silane layer).

[0043] The magnesium alloy treated by this invention can replace other alloys in harsh environments. By forming a triple self-healing layer, it possesses self-healing capabilities. When the film layer is damaged, it can react with the corrosive liquid to repair itself, preventing further corrosion of the substrate and protecting the magnesium alloy substrate from corrosion. Even if the surface epoxy layer is damaged, it can still protect the magnesium alloy from corrosion for a short period of time, exhibiting long-lasting corrosion resistance and self-healing properties. This significantly extends the service life of the magnesium alloy and has broad application prospects. Furthermore, the entire treatment process generates no harmful substances or gases, making it environmentally friendly. The preparation process is easy to operate, and the coating has good bonding strength, which can improve the effective and stable protection of the magnesium alloy. This solves the problems of existing magnesium alloy protective coatings, such as the rapid decline in protective performance during use, poor corrosion resistance over long-term use, and the impact on material lifespan.

[0044] To further explain, the composition of the micro-arc oxidation electrolyte is: sodium silicate 14-16 g / L, sodium fluoride 13-15 g / L, sodium hydroxide 2-3 g / L, glycerol 4-6 mL / L, sodium tungstate 2-6 g / L, and cerium oxide 2-10 g / L.

[0045] In the micro-arc oxidation electrolyte, sodium silicate serves as a film-forming agent, sodium fluoride as an auxiliary additive to improve the electrolyte's conductivity, sodium hydroxide as a pH adjuster, and glycerol as a performance improver. To enable the film to possess a certain self-healing function, sodium tungstate and cerium oxide inorganic salts are added to the electrolyte as inorganic corrosion inhibitors. Sodium tungstate can react with the corrosive solution to form a complex, blocking corrosion channels and preventing further corrosion, thus serving as the first layer of self-healing. Secondly, the simultaneous addition of sodium tungstate and cerium oxide to the electrolyte makes the resulting micro-arc oxidation layer more dense. Cerium oxide fills the pores of the micro-arc oxidation layer, preventing the corrosive solution from entering the film and causing corrosion, thus serving as the second layer of self-healing.

[0046] Furthermore, the main components of the micro-arc oxidation layer formed by this invention are magnesium silicate and magnesium fluoride, which have better strength and wear resistance than the magnesium matrix. Moreover, after sealing the pores with epoxy resin, the epoxy layer can provide good wear resistance and heat insulation. This makes the self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating not only have excellent corrosion resistance, but also good wear resistance, high hardness and good heat insulation.

[0047] Preferably, the composition of the micro-arc oxidation electrolyte is: sodium silicate 15g / L, sodium fluoride 14g / L, sodium hydroxide 2g / L, glycerol 5mL / L, sodium tungstate 3g / L and cerium oxide 3g / L.

[0048] Specifically, in step D, tetraethyl orthosilicate silane and 3-aminopropyltrimethoxysilane are mixed evenly at a mass ratio of 1:1, and 40 mg / L of 4-aminosalicylic acid is added and then ultrasonically dispersed evenly to obtain a silane agent.

[0049] Mixing tetraethyl orthosilicate silane and 3-aminopropyltrimethoxysilane in a 1:1 mass ratio results in a smoother silane layer with the best sealing effect. By adding 4-aminosalicylic acid as a corrosion inhibitor to the silane agent, the silane layer acts as a third self-healing layer. When the film is damaged, the corrosion inhibitor reacts chemically with the incoming corrosive solution to generate insoluble substances that repair the damaged film, thereby preventing further corrosion. Macroscopically, this exhibits a certain degree of self-healing function.

[0050] To further explain, in step E, the magnesium alloy after hydroxylation is placed in a silane agent and soaked at 25°C for 4-5 hours. After being pulled out of the silane agent at a speed of 1 mm / min, a silane layer is generated on the surface of the micro-arc oxidation layer. After rinsing with deionized water, it is dried at 30°C for 24-30 hours to obtain the extraction sample.

[0051] To enhance the bonding force between the film layers (between the micro-arc oxidation layer and the silane layer), tetraethyl orthosilicate silane (TEOS) and 3-aminopropyltrimethoxysilane (APTES) were selected as silane agents in a mass ratio of 1:1. This transformed the physical bonding between the film layers into a chemical bonding. The hydroxylated magnesium alloy was immersed in the silane agent and soaked at 25°C for 4–5 hours. The silane treatment allowed the silane to form Si-O-Mg covalent bonds with the surface metal oxides. Excess silane condensed to form a Si-O-Si three-dimensional network silane film. The film was then pulled at a speed of 1 mm / min. Due to the slow pulling speed, a denser film layer could be obtained.

[0052] Preferably, in step E, the magnesium alloy after hydroxylation is placed in a silane agent and soaked at 25°C for 4 hours. After being pulled out of the silane agent at a speed of 1 mm / min, a silane layer is generated on the surface of the micro-arc oxidation layer. After rinsing with deionized water, it is placed in a vacuum drying oven and dried at 30°C for 24 hours to obtain the extraction sample.

[0053] To further explain, in step C, the magnesium alloy is immersed in a sodium hydroxide solution for 2 minutes for hydroxylation treatment, dried in cold air, cured at 120°C for 2-3 hours, and then rinsed with deionized water. The concentration of the sodium hydroxide solution is 3-5 mol / L.

[0054] By immersing the magnesium alloy after micro-arc oxidation in a sodium hydroxide solution for hydroxylation, a large number of basic hydroxyl groups can be obtained on the surface. Hydroxylation makes the surface of the micro-arc oxidation layer more hydrophilic, which is beneficial for subsequent processing and obtaining a smoother and more uniform silane layer.

[0055] Preferably, in step C, the magnesium alloy is immersed in a sodium hydroxide solution for 2 minutes for hydroxylation treatment, dried in cold air, and then cured in an oven at 120°C for 2 hours. Finally, it is rinsed with deionized water. The concentration of the sodium hydroxide solution is 4 mol / L.

[0056] Preferably, in step A, the magnesium alloy is polished by sequentially using sandpaper of 400#, 800#, 1200#, 1500# and 2000#.

[0057] To obtain a cleaner and smoother micro-arc oxide film, the magnesium alloy was polished sequentially with sandpaper of 400#, 800#, 1200#, 1500# and 2000#. Preferably, silicon carbide wet sandpaper was used for mechanical polishing.

[0058] Preferably, in step A, after grinding and polishing, holes are drilled in the magnesium alloy, aluminum wires are attached to the drilled holes, and then the holes are sealed with epoxy resin.

[0059] Because magnesium alloys form an insulating film during micro-arc oxidation, which reduces or even eliminates their conductivity, thus preventing further micro-arc oxidation, holes are drilled in the magnesium alloy sample to ensure good conductivity during the micro-arc oxidation process. Aluminum wires are then attached to these holes to secure the magnesium alloy (aluminum wire was chosen over magnesium wire because it has better conductivity, better ductility, and is cheaper). Finally, the holes are sealed with epoxy resin (to prevent electrolyte from entering the holes and forming an insulating layer, which would cause poor conductivity during micro-arc oxidation). This pretreatment facilitates subsequent micro-arc oxidation. During micro-arc oxidation, the cathode of the micro-arc oxidation equipment is connected to stainless steel, and the anode is connected to the aluminum wires on the pretreated magnesium alloy. Preferably, after sealing the holes with epoxy resin, the sample is rinsed with deionized water after the epoxy resin has cured, then ultrasonically cleaned in anhydrous ethanol for 10 minutes, rinsed with deionized water, and dried with a hairdryer before use.

[0060] Specifically, in step B, 304 stainless steel is used as the cathode, and the magnesium alloy substrate is immersed in the electrolyte. A high-voltage power supply is applied, and a ceramic film (a porous micro-arc oxidation layer) is grown in situ on the surface of the magnesium alloy under high voltage (300V). After turning off the high-voltage power supply, the micro-arc oxidized magnesium alloy is removed, rinsed with deionized water, and dried with a hair dryer for later use.

[0061] To further explain, in step F, the extracted sample is dried and cured at 100°C for 1 to 2 hours.

[0062] Specifically, in step F, the extraction sample is placed in a vacuum drying oven, vacuumed, and dried and cured at 100°C for 1 hour to solidify the silane layer.

[0063] To further explain, in step G, the sample after drying and curing is placed on a spin coater and a layer of epoxy resin is spin-coated for sealing.

[0064] By placing the dried and cured sample on a spin coater to spin-coat a layer of epoxy resin with good coating uniformity, and then performing a sealing treatment, a corrosion-resistant micro-arc oxidation coating of magnesium alloy with self-healing function is obtained.

[0065] A self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating is prepared using the aforementioned method for preparing a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating.

[0066] The method for preparing a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating describes that produces a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating. This coating has a self-healing function; when the film is damaged, it can react with the corrosive liquid to repair itself, preventing further corrosion of the substrate and protecting the magnesium alloy substrate from corrosion. Even if the surface epoxy layer is damaged, it can still protect the magnesium alloy from corrosion in a short time, exhibiting long-lasting corrosion resistance and self-healing properties, thus greatly extending the service life of the magnesium alloy.

[0067] To facilitate understanding of the present invention, a more complete description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0068] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0069] Example 1

[0070] A method for preparing a corrosion-resistant micro-arc oxidation coating for magnesium alloys with self-healing function includes the following steps:

[0071] Step A, Magnesium Alloy Pretreatment: Using commercially available cast AZ91 magnesium alloy as the base material, the magnesium alloy is polished sequentially with 400#, 800#, 1200#, 1500# and 2000# sandpaper. Holes are drilled in the magnesium alloy, and aluminum wires are tied to the drilled holes. Then, the holes are sealed with epoxy resin. After the epoxy resin has cured, it is rinsed with deionized water, then ultrasonically cleaned in anhydrous ethanol for 10 minutes, rinsed with deionized water, and dried with a hair dryer for later use.

[0072] Step B, Micro-arc oxidation treatment: 304 stainless steel is used as the cathode and magnesium alloy is used as the anode. The magnesium alloy is placed in the micro-arc oxidation electrolyte for micro-arc oxidation treatment. A high voltage power supply is applied. Under the action of high voltage (300V), a porous micro-arc oxidation layer is formed in situ on the surface of the magnesium alloy. The high voltage power supply is turned off and the magnesium alloy after micro-arc oxidation is taken out. It is rinsed with deionized water and dried with a hair dryer for later use.

[0073] The composition of the micro-arc oxidation electrolyte is: sodium silicate 15g / L, sodium fluoride 14g / L, sodium hydroxide 2g / L, glycerol 5mL / L, sodium tungstate 3g / L and cerium oxide 3g / L;

[0074] Step C, Hydroxylation treatment: The magnesium alloy is immersed in sodium hydroxide solution for 2 minutes for hydroxylation treatment, dried in cold air, and then placed in an oven to cure at 120°C for 2 hours. Then it is rinsed with deionized water. The concentration of the sodium hydroxide solution is 4 mol / L.

[0075] Step D, Preparation of silane agent: Tetraethyl orthosilicate silane and 3-aminopropyltrimethoxysilane are mixed evenly at a mass ratio of 1:1, and 40 mg / L of 4-aminosalicylic acid is added and then ultrasonically dispersed evenly to obtain the silane agent.

[0076] Step E, silanization treatment: The magnesium alloy after hydroxylation treatment is placed in a silane agent and immersed at 25°C for 4 hours. After being pulled out of the silane agent at a speed of 1 mm / min, a silane layer is generated on the surface of the micro-arc oxidation layer. After rinsing with deionized water, it is placed in a vacuum drying oven and dried at 30°C for 24 hours to obtain the extraction sample.

[0077] Step F, Curing treatment: Place the extraction sample into a vacuum drying oven, evacuate the vacuum, and dry and cure at 100°C for 1 hour to cure the silane layer.

[0078] Step G, Epoxy Resin Sealing: Place the dried and cured sample on a spin coater and spin-coat a layer of epoxy resin for sealing. An epoxy layer is formed on the surface of the silane layer, and a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating consisting of a micro-arc oxidation layer, a silane layer, and an epoxy layer is formed on the surface of the magnesium alloy.

[0079] Example 2

[0080] A method for preparing a corrosion-resistant micro-arc oxidation coating for magnesium alloys with self-healing function includes the following steps:

[0081] Step A, Magnesium Alloy Pretreatment: Using commercially available forged AZ31 magnesium alloy as the base material, the magnesium alloy is polished in sequence with 400#, 800#, 1200#, 1500# and 2000# sandpaper. Holes are drilled in the magnesium alloy, and aluminum wires are tied to the drilled holes. Then, the holes are sealed with epoxy resin. After the epoxy resin has cured, it is rinsed with deionized water, then ultrasonically cleaned in anhydrous ethanol for 10 minutes, rinsed with deionized water, and dried with a hair dryer for later use.

[0082] Step B, Micro-arc oxidation treatment: 304 stainless steel is used as the cathode and magnesium alloy is used as the anode. The magnesium alloy is placed in the micro-arc oxidation electrolyte for micro-arc oxidation treatment. A high voltage power supply is applied. Under the action of high voltage (300V), a porous micro-arc oxidation layer is formed in situ on the surface of the magnesium alloy. The high voltage power supply is turned off and the magnesium alloy after micro-arc oxidation is taken out. It is rinsed with deionized water and dried with a hair dryer for later use.

[0083] The composition of the micro-arc oxidation electrolyte is: sodium silicate 15g / L, sodium fluoride 14g / L, sodium hydroxide 2g / L, glycerol 5mL / L, sodium tungstate 3g / L and cerium oxide 3g / L;

[0084] Step C, Hydroxylation treatment: The magnesium alloy is immersed in sodium hydroxide solution for 2 minutes for hydroxylation treatment, dried in cold air, and then placed in an oven to cure at 120°C for 2 hours. Then it is rinsed with deionized water. The concentration of the sodium hydroxide solution is 4 mol / L.

[0085] Step D, Preparation of silane agent: Tetraethyl orthosilicate silane and 3-aminopropyltrimethoxysilane are mixed evenly at a mass ratio of 1:1, and 40 mg / L of 4-aminosalicylic acid is added and then ultrasonically dispersed evenly to obtain the silane agent.

[0086] Step E, silanization treatment: The magnesium alloy after hydroxylation treatment is placed in a silane agent and immersed at 25°C for 4 hours. After being pulled out of the silane agent at a speed of 1 mm / min, a silane layer is generated on the surface of the micro-arc oxidation layer. After rinsing with deionized water, it is placed in a vacuum drying oven and dried at 30°C for 24 hours to obtain the extraction sample.

[0087] Step F, Curing treatment: Place the extraction sample into a vacuum drying oven, evacuate the vacuum, and dry and cure at 100°C for 1 hour to cure the silane layer.

[0088] Step G, Epoxy Resin Sealing: Place the dried and cured sample on a spin coater and spin-coat a layer of epoxy resin for sealing. An epoxy layer is formed on the surface of the silane layer, and a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating consisting of a micro-arc oxidation layer, a silane layer, and an epoxy layer is formed on the surface of the magnesium alloy.

[0089] Comparative Example 1

[0090] A method for preparing a micro-arc oxidation coating on a magnesium alloy includes the following steps:

[0091] Step A, Magnesium Alloy Pretreatment: Using commercially available cast AZ91 magnesium alloy as the base material, the magnesium alloy is polished sequentially with 400#, 800#, 1200#, 1500# and 2000# sandpaper. Holes are drilled in the magnesium alloy, and aluminum wires are tied to the drilled holes. Then, the holes are sealed with epoxy resin. After the epoxy resin has cured, it is rinsed with deionized water, then ultrasonically cleaned in anhydrous ethanol for 10 minutes, rinsed with deionized water, and dried with a hair dryer for later use.

[0092] Step B, Micro-arc oxidation treatment: 304 stainless steel is used as the cathode and magnesium alloy is used as the anode. The magnesium alloy is placed in the micro-arc oxidation electrolyte for micro-arc oxidation treatment. A high voltage power supply is applied. Under the action of high voltage (300V), a porous micro-arc oxidation layer is formed in situ on the surface of the magnesium alloy. The high voltage power supply is turned off and the magnesium alloy after micro-arc oxidation is removed. It is rinsed with deionized water and dried with a hair dryer.

[0093] The composition of the micro-arc oxidation electrolyte is: sodium silicate 15g / L, sodium fluoride 14g / L, sodium hydroxide 2g / L and glycerol 5mL / L.

[0094] like Figure 1 As shown, Figure 1 This is a scanning electron microscope (SEM) image of the surface of the magnesium alloy in Example 1 before epoxy resin sealing of the micro-arc oxide layer. Figure 2 The image shows a scanning electron microscope (SEM) image of the surface of the magnesium alloy micro-arc oxidation layer in Example 1 after epoxy resin sealing. The self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating prepared in Example 1 was scratched with a blade and placed in a 3.5% NaCl simulated seawater solution. After immersion for 4 days, it was removed and the surface morphology of the scratched area was observed and photographed using a scanning electron microscope at different repair times. It was found that when the repair time reached 6 days, the scratch in Example 1 was significantly repaired. Figure 3 This is a scanning electron microscope (SEM) image of the surface of the coating after scratches in Example 1. Figure 4 (SEM image of the surface of the coating in Example 1 after 6 days of repair following a scratch).

[0095] The self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating prepared in Example 1 and the micro-arc oxidation layer of Comparative Example 1 were scratched with a blade and placed in a 3.5% NaCl simulated seawater solution. After soaking for 4 days, they were removed and the open circuit potential evolution curves of Example 1 and Comparative Example 1 after the coating was scratched were tested using a Koster electrochemical workstation. Figure 5 As shown, in Example 1, the potential of the coating after scratching first decreases and then the repair potential shifts positively, that is, the self-corrosion potential of the coating sample gradually shifts positively, while in Comparative Example 1, the potential of the coating after scratching only partially shifts positively after the initial decrease.

[0096] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a corrosion-resistant micro-arc oxidation coating for magnesium alloys with self-healing function, characterized in that, Includes the following steps: Step A, Magnesium alloy pretreatment: Grinding and polishing the magnesium alloy; Step B, Micro-arc oxidation treatment: Stainless steel is used as the cathode and magnesium alloy is used as the anode. The magnesium alloy is placed in a micro-arc oxidation electrolyte for micro-arc oxidation treatment. A porous micro-arc oxidation layer is formed in situ on the surface of the magnesium alloy. The alloy is then cleaned and dried. Step C, Hydroxylation treatment: The magnesium alloy is immersed in sodium hydroxide solution for hydroxylation treatment, and then cured after drying; Step D, Preparation of silane agent: Tetraethyl orthosilicate silane and 3-aminopropyltrimethoxysilane are mixed evenly, 4-aminosalicylic acid is added and then ultrasonically dispersed evenly to obtain silane agent; Step E, silanization treatment: The magnesium alloy after hydroxylation treatment is immersed in silane agent. After being pulled out of silane agent, a silane layer is formed on the surface of the micro-arc oxidation layer. The sample is then cleaned and dried to obtain the immersion sample. Step F, Curing treatment: The extracted sample is dried and cured. Step G, Epoxy Resin Sealing: Apply a layer of epoxy resin to the surface of the cured sample for sealing treatment. An epoxy layer is formed on the surface of the silane layer, and a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating composed of a micro-arc oxidation layer, a silane layer and an epoxy layer is formed on the surface of the magnesium alloy. The micro-arc oxidation electrolyte consists of: sodium silicate 14-16 g / L, sodium fluoride 13-15 g / L, sodium hydroxide 2-3 g / L, glycerol 4-6 mL / L, sodium tungstate 2-6 g / L, and cerium oxide 2-10 g / L. In step D, tetraethyl orthosilicate silane and 3-aminopropyltrimethoxysilane are mixed evenly at a mass ratio of 1:1, and 40 mg / L of 4-aminosalicylic acid is added and then ultrasonically dispersed evenly to obtain a silane agent.

2. The method for preparing a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating according to claim 1, characterized in that, In step E, the hydroxylated magnesium alloy is placed in a silane agent and soaked at 25°C for 4–5 hours. After being pulled out of the silane agent at a speed of 1 mm / min, a silane layer is generated on the surface of the micro-arc oxidation layer. After rinsing with deionized water, it is dried at 30°C for 24–30 hours to obtain the extraction sample.

3. The method for preparing a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating according to claim 1, characterized in that, In step C, the magnesium alloy is immersed in a sodium hydroxide solution for 2 minutes for hydroxylation treatment, dried in cold air, cured at 120°C for 2-3 hours, and then rinsed with deionized water. The concentration of the sodium hydroxide solution is 3-5 mol / L.

4. The method for preparing a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating according to claim 1, characterized in that, In step A, the magnesium alloy is polished in sequence using sandpaper of 400#, 800#, 1200#, 1500# and 2000#.

5. The method for preparing a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating according to claim 4, characterized in that, In step A, after grinding and polishing, holes are drilled in the magnesium alloy, aluminum wires are tied to the drilled holes, and then the holes are sealed with epoxy resin.

6. The method for preparing a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating according to claim 1, characterized in that, In step F, the extracted sample is dried and cured at 100°C for 1-2 hours.

7. The method for preparing a self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating according to claim 1, characterized in that, In step G, the sample after drying and curing is placed on a spin coater and a layer of epoxy resin is spin-coated for sealing.

8. A self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating, prepared using the preparation method of the self-healing magnesium alloy corrosion-resistant micro-arc oxidation coating as described in any one of claims 1 to 7.

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