High-gd rare earth magnesium alloy micro-arc oxidation electrolyte and film forming method

Abstract

This invention belongs to the field of metal surface treatment technology, specifically relating to a micro-arc oxidation electrolyte and a high-power segmented rapid film formation method for high-Gd rare-earth magnesium alloys. It is particularly suitable for the preparation and processing of efficient, dense, and corrosion-resistant ceramic films on the surface of rare-earth magnesium alloys with a Gd content of 3-15 wt%. The micro-arc oxidation electrolyte for high-Gd rare-earth magnesium alloys described in this invention significantly improves electrolyte stability through the synergistic design of specialized electrolyte components and optimized process parameters, achieving rapid and high-quality film formation. The micro-arc oxidation film formation method for high-Gd rare-earth magnesium alloys described in this invention is based on a specialized electrolyte and a segmented process forming an organic whole. This method aims to achieve rapid formation of a dense, uniform, and highly corrosion-resistant ceramic film layer within 3-5 minutes, while significantly improving electrolyte stability and reducing energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a micro-arc oxidation electrolyte and a high-power segmented rapid film formation method for high-Gd rare earth magnesium alloys. It is particularly suitable for the preparation and processing of efficient, dense, and corrosion-resistant ceramic films on the surface of rare earth magnesium alloys with a Gd content of 3-15wt%. Background Technology

[0002] Magnesium alloys, due to their low density, high specific strength, good electromagnetic shielding, and dimensional stability, have broad application prospects in aerospace, automotive, and other fields. The addition of the rare earth element Gd can significantly improve the mechanical properties and high-temperature stability of magnesium alloys. Micro-arc oxidation technology is an advanced surface treatment technique that uses high-voltage discharge to grow ceramic oxide films in situ on the surface of metals and their alloys in an electrolyte. The resulting ceramic films possess high hardness, excellent wear resistance, good thermal shock resistance, and high insulation. However, some problems still exist in the preparation of high-Gd rare earth magnesium alloy micro-arc oxidation films in existing technologies.

[0003] For example, Chinese patent CN118497863A reports a method to improve the interlayer bonding force of micro-arc oxidation and electrophoretic coating of rare earth magnesium alloys. Although this method can obtain micro-arc oxidation film for high Gd rare earth magnesium alloys, the process is complicated, the intermediate links are difficult to control, the electrolyte has poor stability for rare earth ions, poor conductivity uniformity, and the resulting micro-arc oxidation coating is prone to local ablation and peeling. For example, Chinese patent CN116103722A discloses a method for preparing a micro-arc oxidation film layer for large surface area rare earth magnesium alloy parts. Although this method can prepare large-area rare earth micro-arc oxidation coatings, the electrolyte used has a complex composition and excessively high chemical concentration, which easily leads to poor uniformity and localized loose micro-arc oxidation coatings. At the same time, the processing time is as long as 30-120 minutes, which consumes a lot of energy, and the electrolyte is prone to volatilization due to long-term continuous operation, resulting in component failure. In addition, this method is prone to causing alloying elements (such as Gd, Y, etc.) to dissolve and react with the electrolyte components during the processing of high Gd rare earth magnesium alloys, resulting in precipitation, which leads to instability of the electrolyte composition and rapid failure.

[0004] Furthermore, traditional micro-arc oxidation processes often employ a single static parameter mode of constant current or constant voltage, as reported in Chinese patent CN118854410A. This not only results in long processing times (typically 10-30 minutes or more) and high energy consumption, but also easily leads to uneven film growth, incomplete initial nucleation, or later energy overload, causing film ablation, unevenness, high porosity, and insufficient density, thus affecting corrosion resistance. In addition, traditional micro-arc oxidation processes often introduce cerium oxide nanoparticles as a hard filler phase, as in the scheme of Chinese patent CN118727096A. However, during the instantaneous high temperature and rapid cooling process of micro-arc discharge, the nanoparticles of cerium oxide exhibit poor dispersion and are prone to unfavorable crystal transformations and volumetric stress, introducing micro-defects into the film, leading to uneven distribution and poor corrosion resistance.

[0005] Therefore, there is a need in the field to develop a micro-arc oxidation electrolyte and process suitable for high-Gd rare-earth magnesium alloys, which can efficiently suppress ion dissolution and achieve rapid and high-quality film formation, and has important industrial application value. Summary of the Invention

[0006] The first objective of this invention is to provide an electrolyte for the micro-arc oxidation process of high-Gd rare-earth magnesium alloys, which effectively solves the problems of electrolyte instability caused by Gd ion dissolution, long process time, and poor film uniformity in the traditional micro-arc oxidation process. The second objective of this invention is to provide a method for micro-arc oxidation film formation of high-Gd rare-earth magnesium alloys. The method employs a high-power segmented rapid preparation method, which aims to rapidly form a dense, uniform, and highly corrosion-resistant ceramic film within 3-5 minutes, while significantly improving electrolyte stability and reducing energy consumption.

[0007] To address the aforementioned technical problems, this invention provides a high-Gd rare-earth magnesium alloy micro-arc oxidation electrolyte, wherein the electrolyte is an aqueous solution comprising the following concentrations: sodium silicate (Na2SiO3) 12-20 g / L, potassium hydroxide (KOH) 1-2 g / L, hydroxyethyl ethylenediamine triacetic acid (HEDTA) 3-5 g / L, potassium fluorotitanate (K2TiF6) 1-3 g / L, yttrium oxide stabilized zirconia nanoparticles (YSZ) 5-10 g / L, and polyvinylpyrrolidone (PVP) 0.5-1.5 g / L.

[0008] Specifically, the high-Gd rare-earth magnesium alloy micro-arc oxidation electrolyte: The yttrium oxide-stabilized zirconium oxide nanoparticles have a particle size of 50-300 nm; and / or, In the yttrium oxide-stabilized zirconium oxide nanoparticles, the doping amount of yttrium oxide is 5-8 mol.

[0009] The yttrium oxide stabilized zirconia nanoparticles (YSZ) are stable crystalline phase nanoparticles formed by doping 5-8 mol% yttrium oxide with zirconia as the main body. The particle size range is 50-300 nm, preferably 100 nm.

[0010] The present invention also discloses a method for preparing a micro-arc oxidation electrolyte for high-Gd rare-earth magnesium alloys, comprising the steps of mixing sodium silicate, potassium hydroxide, hydroxyethyl ethylenediamine triacetic acid, potassium fluorotitanate, yttrium oxide-stabilized zirconia nanoparticles and polyvinylpyrrolidone with deionized water in selected proportions.

[0011] Preferably, the mixing step employs mechanical stirring and ultrasonic-assisted dispersion to achieve uniformity.

[0012] This invention also discloses a method for micro-arc oxidation film formation of high-Gd rare-earth magnesium alloys, comprising the following steps: (1) Take the high Gd rare earth magnesium alloy substrate to be processed for pretreatment; (2) The substrate is subjected to micro-arc oxidation treatment using the high Gd rare earth magnesium alloy micro-arc oxidation electrolyte as described in claim 1 or 2.

[0013] Specifically, in the micro-arc oxidation film formation method for high Gd rare earth magnesium alloy, in step (2), the temperature of the electrolyte is controlled to be 30±2℃ in the micro-arc oxidation treatment step.

[0014] In step (2), a special electrolyte is used to perform a micro-arc oxidation reaction on rare earth magnesium alloy to prepare a micro-arc oxidation film. During the micro-arc oxidation reaction process, the workpiece is immersed in the electrolyte for 3-5 minutes, and the electrolyte temperature is precisely controlled at 30±2℃ by a cooling system.

[0015] Specifically, the micro-arc oxidation film formation method for high-Gd rare-earth magnesium alloys includes the following stages based on the film growth mechanism: (21) High-voltage, low-frequency nucleation stage: control voltage 450-500V, frequency 1500-2000Hz, duty cycle 10%-20%; (22) Medium-voltage high-frequency rapid growth stage: control voltage 400-450V, frequency 2000-2500Hz, duty cycle 20%-30%; (23) Low-voltage high duty cycle densification stage: control voltage 350-400V, frequency 1000-1500Hz, duty cycle 30%-50%.

[0016] Specifically, in the micro-arc oxidation film formation method for high-Gd rare-earth magnesium alloys, the total time for the micro-arc oxidation treatment is 3-5 minutes; wherein, The high-pressure, low-frequency nucleation stage accounts for 20%-30% of the total processing time; The processing time for the medium-voltage high-frequency rapid growth stage accounts for 50%-60% of the total time; The processing time for the low-pressure, high-duty-cycle densification stage accounts for 20%-30% of the total time.

[0017] Specifically, in the micro-arc oxidation film formation method for high Gd rare earth magnesium alloys, in step (2), the thickness of the film formed by the micro-arc oxidation process is controlled to be 10-20 μm.

[0018] Specifically, in the high Gd rare earth magnesium alloy micro-arc oxidation film formation method, step (1) includes the pretreatment step of grinding, cleaning and drying the substrate; Preferably, the polishing step involves sequentially polishing the substrate with 800-grit, 1000-grit, 1500-grit, and 2000-grit sandpaper; Preferably, the cleaning step is ultrasonic cleaning; Preferably, the drying step is performed at a temperature of 50-60°C for 2-3 hours.

[0019] Specifically, the method for forming a film by micro-arc oxidation of high-Gd rare-earth magnesium alloy further includes a post-treatment step for the prepared micro-arc oxidation film, which specifically includes ultrasonic cleaning and drying with distilled water and alcohol. Preferably, the drying temperature is 50-60℃ and the drying time is 2 hours.

[0020] Specifically, in the micro-arc oxidation film formation method for high-Gd rare-earth magnesium alloy, the Gd content in the high-Gd rare-earth magnesium alloy substrate is 3-15 wt%.

[0021] The high-Gd rare-earth magnesium alloy micro-arc oxidation electrolyte of this invention is composed of sodium silicate, potassium hydroxide, hydroxyethyl ethylenediamine triacetic acid, potassium fluorotitanate, yttrium oxide-stabilized zirconium oxide nanoparticles, and polyvinylpyrrolidone, through the synergistic design of specialized electrolyte components and optimized process parameters. The HEDTA used is specifically designed to stabilize Gd... 3+ With strong complexing ability and good alkaline stability, combined with the assistance of potassium fluorotitanate and the use of polymeric dispersants to achieve long-term stable suspension of nanoparticles, the nanoparticles are ensured to be uniformly distributed and efficiently filled in the film layer, which fundamentally inhibits precipitation formation. The electrolyte can be used continuously and stably, greatly improving the stability of the electrolyte and achieving rapid and high-quality film formation.

[0022] The high-Gd rare-earth magnesium alloy micro-arc oxidation electrolyte of this invention uses yttrium oxide-stabilized zirconia nanoparticles instead of traditional nanoparticles. YSZ is a stabilized zirconia formed by doping yttrium oxide (Y₂O₃) into zirconia (ZrO₂), possessing high ionic conductivity, excellent thermal stability, mechanical strength, and corrosion resistance. YSZ not only has higher hardness and thermal stability to effectively fill pores, but its unique phase transformation toughening effect can absorb energy through microscopic phase transformation during film formation, resulting in uniform distribution and improved corrosion resistance. It also significantly improves the hardness, heat resistance, and thermal shock resistance of the film.

[0023] The micro-arc oxidation film formation method for high-Gd rare-earth magnesium alloys described in this invention is a high-power, segmented, rapid film formation method closely integrated with the micro-arc oxidation growth mechanism. Based on the film growth mechanism, the voltage, frequency, and duty cycle are adjusted, sequentially undergoing three stages: high-voltage, low-frequency nucleation; medium-voltage, high-frequency rapid growth; and low-voltage, high-duty-cycle densification. This system can efficiently suppress Gd ion dissolution and achieve precise matching between energy and film growth, thereby forming a dense, uniform, and corrosion-resistant ceramic film on the surface of high-Gd rare-earth magnesium alloys in a very short time. This solves the problems of low efficiency, uneven film quality, and rapid electrolyte instability associated with traditional processes.

[0024] The micro-arc oxidation film formation method for high-Gd rare-earth magnesium alloys described in this invention features a three-stage process design based on the growth mechanism. The energy input is precisely matched to the requirements of each growth stage, reducing the total film formation time to 3-5 minutes and increasing efficiency by more than 60%. The prepared film layer is uniformly grown, has a dense structure, and can reach a thickness of 10-20 μm. The porosity is significantly reduced, and it is firmly bonded to the substrate. The corrosion resistance and wear resistance are greatly improved, resulting in a significant improvement in film formation efficiency and quality.

[0025] The micro-arc oxidation film formation method for high-Gd rare-earth magnesium alloys described in this invention is based on a dedicated electrolyte and a segmented process forming an organic whole. The high voltage during the nucleation stage creates conditions for a stable interface in the HEDTA complex system; the high frequency during the growth stage matches the uniform entrainment of YSZ nanoparticles; and the densification stage fully utilizes the high melting point of YSZ to achieve high-temperature "sintering" densification. This method aims to achieve rapid formation of a dense, uniform, and highly corrosion-resistant ceramic film within 3-5 minutes, while significantly improving electrolyte stability and reducing energy consumption. Attached Figure Description

[0026] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This is a scanning electron microscope image of the micro-arc oxidation film layer of the high-Gd rare-earth magnesium alloy prepared in Example 1; Figure 2This is a scanning electron microscope image of the micro-arc oxidation film layer of the high-Gd rare-earth magnesium alloy prepared in Comparative Example 1. Figure 3 This is a scanning electron microscope image of the micro-arc oxidation film layer of the high-Gd rare-earth magnesium alloy prepared in Comparative Example 2. Figure 4 The image shows a scanning electron microscope (SEM) image of the micro-arc oxidation film layer of the high-Gd rare-earth magnesium alloy prepared in Comparative Example 3. Detailed Implementation

[0027] The present invention will be further described below with reference to embodiments. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples.

[0028] In the following embodiments of the present invention, an electrolyte for micro-arc oxidation of high Gd rare earth magnesium alloys is provided. The electrolyte is an aqueous solution comprising the following concentrations: sodium silicate (Na2SiO3) 12-20 g / L, potassium hydroxide (KOH) 1-2 g / L, hydroxyethyl ethylenediamine triacetic acid (HEDTA) 3-5 g / L, potassium fluorotitanate (K2TiF6) 1-3 g / L, yttrium oxide stabilized zirconia nanoparticles (YSZ) 5-10 g / L, and polyvinylpyrrolidone (PVP) 0.5-1.5 g / L.

[0029] The present invention also provides a method for preparing a micro-arc oxidation film layer in the following embodiments, comprising the following steps: (1) Prepare a micro-arc oxidation electrolyte for high Gd rare earth magnesium alloy and pretreat the high Gd rare earth magnesium alloy substrate to be treated. (2) The above electrolyte was used to carry out micro-arc oxidation reaction on rare earth magnesium alloy to quickly prepare micro-arc oxidation film layer, and the sample was post-processed.

[0030] Specifically, the micro-arc oxidation process includes the following stages based on the film growth mechanism: (21) High-voltage low-frequency nucleation stage: control voltage 450-500V, frequency 1500-2000Hz, duty cycle 10%-20%, processing time accounts for 20%-30% of the total micro-arc oxidation processing time; (22) Medium-voltage high-frequency rapid growth stage: control voltage 400-450V, frequency 2000-2500Hz, duty cycle 20%-30%, processing time accounts for 50%-60% of the total micro-arc oxidation processing time; (23) Low-pressure high-duty-cycle densification stage: control voltage 350-400V, frequency 1000-1500Hz, duty cycle 30%-50%, processing time accounts for 20%-30% of the total micro-arc oxidation processing time.

[0031] Example 1 In 500 mL of deionized water, the following components were added and dissolved sequentially: 15.0 g sodium silicate (Na₂SiO₃), 1.5 g potassium hydroxide (KOH), 4.0 g hydroxyethyl ethylenediamine triacetic acid (HEDTA), and 2.0 g potassium fluorotitanate (K₂TiF₆). After addition, the mixture was mechanically stirred until clear. Then, 8.0 g of yttrium oxide-stabilized zirconia nanoparticles (YSZ, average particle size 100 nm, Y₂O₃ doping 5 mol%) and 1.0 g polyvinylpyrrolidone (PVP, K₃₀) were added. Deionized water was added to a total volume of 1 L, and mechanical stirring was continued for 30 minutes, supplemented with ultrasonic dispersion (300 W power, 20 minutes) to obtain a uniform and stable milky white electrolyte.

[0032] Take a rare earth magnesium alloy sheet with a Gd content of 10wt% and dimensions of 50mm×25mm×2mm. Polish it sequentially with 800-grit, 1000-grit, 1500-grit, and 2000-grit sandpaper using a wet polishing method until a mirror finish is achieved. Then, ultrasonically clean it for 5 minutes each with deionized water and anhydrous ethanol, and finally dry it with hot air for later use.

[0033] This embodiment employs a segmented micro-arc oxidation process to treat the aforementioned alloy sheet. Using the pretreated magnesium alloy sample as the anode and a 316L stainless steel tank as the cathode, the sample is immersed in the electrolyte and a high-frequency pulsed micro-arc oxidation power supply is used. The total treatment time is set to 4 minutes, and the process runs automatically according to the following program: Stage 1: High-voltage, low-frequency nucleation stage (nucleation, 0-60 seconds): Voltage 480V, frequency 1800Hz, duty cycle 15%; Phase Two: Medium-Voltage High-Frequency Rapid Growth Phase (Growth, 60-180 seconds): Voltage 420V, Frequency 2200Hz, Duty Cycle 25%; Phase 3: Low-voltage, high-duty-cycle densification phase (densification, 180-240 seconds): Voltage 380V, frequency 1200Hz, duty cycle 45%; The electrolyte temperature is controlled at 30±1℃ by an external circulating water cooling system, and magnetic stirring is performed at a speed of 200rpm throughout the process.

[0034] Remove the sample, rinse it with flowing deionized water, then immerse it in anhydrous ethanol for ultrasonic cleaning for 3 minutes, and finally place it in a 55℃ forced-air drying oven to dry for 2 hours.

[0035] Figure 1The image shows a scanning electron microscope (SEM) image of the micro-arc oxidation film on the high-Gd rare-earth magnesium alloy prepared in this embodiment. The SEM image shows a film thickness of 18.3 μm, exhibiting a uniform and dense surface with small and evenly distributed pores and no obvious cracks. Yttrium-stabilized zirconia (YSZ) particles effectively filled the micro-arc oxidation pores, reducing the pore size. A 48-hour immersion corrosion test in 3% NaCl solution showed an average corrosion rate of only 0.192 mg / (cm²). 2 •d) exhibits excellent corrosion resistance. After 20 cycles of water quenching from 150℃ to room temperature, the film layer showed no peeling or cracking, demonstrating excellent heat resistance and thermal shock resistance.

[0036] Example 2 The preparation method of the electrolyte in this embodiment is the same as that in Embodiment 1, except that the concentrations of each component of the electrolyte are as follows: sodium silicate 12g / L, potassium hydroxide 2g / L, hydroxyethyl ethylenediamine triacetic acid 3g / L, potassium fluorotitanate 3g / L, yttrium oxide stabilized zirconia nanoparticles 5g / L, and polyvinylpyrrolidone 1.5g / L.

[0037] Take a rare earth magnesium alloy sheet with dimensions of 50mm × 25mm × 2mm and a Gd content of 3wt%. Polish it sequentially using 800-grit, 1000-grit, 1500-grit, and 2000-grit sandpaper using a wet polishing method until a mirror finish is achieved. Then, ultrasonically clean it for 5 minutes each with deionized water and anhydrous ethanol, and finally dry it with hot air for later use.

[0038] This embodiment employs a segmented micro-arc oxidation process to treat the alloy sheet. Using the pre-treated magnesium alloy sample as the anode and a 316L stainless steel tank as the cathode, the sample is immersed in the aforementioned electrolyte and a high-frequency pulsed micro-arc oxidation power supply is used. The total treatment time is set to 3 minutes, and the process runs automatically according to the following program: Stage 1: High-voltage, low-frequency nucleation stage (nucleation, 0-54 seconds): Voltage 450V, frequency 1500Hz, duty cycle 10%; Phase Two: Medium-Voltage High-Frequency Rapid Growth Phase (Growth, 54-144 seconds): Voltage 400V, Frequency 2000Hz, Duty Cycle 20%; Phase 3: Low-voltage, high-duty-cycle densification phase (densification, 144-180 seconds): Voltage 350V, frequency 1000 Hz, duty cycle 30%; The electrolyte temperature is controlled at 30±1℃ by an external circulating water cooling system, and magnetic stirring is performed at a speed of 200rpm throughout the process.

[0039] Remove the sample, rinse it with flowing deionized water, then immerse it in anhydrous ethanol for ultrasonic cleaning for 3 minutes, and finally place it in a 55℃ forced-air drying oven to dry for 2 hours.

[0040] Example 3 The preparation method of the electrolyte in this embodiment is the same as that in Embodiment 1, except that the concentrations of each component of the electrolyte are as follows: sodium silicate 20 g / L, potassium hydroxide 1 g / L, hydroxyethyl ethylenediamine triacetic acid 5 g / L, potassium fluorotitanate 1 g / L, yttrium oxide stabilized zirconia nanoparticles 10 g / L, and polyvinylpyrrolidone 0.5 g / L.

[0041] Take a rare earth magnesium alloy sheet with a Gd content of 15wt% and dimensions of 50mm×25mm×2mm. Polish it sequentially with 800-grit, 1000-grit, 1500-grit, and 2000-grit sandpaper using a wet polishing method until a mirror finish is achieved. Then, ultrasonically clean it for 5 minutes each with deionized water and anhydrous ethanol, and finally dry it with hot air for later use.

[0042] This embodiment employs a segmented micro-arc oxidation process to treat the alloy sheet. Using the pre-treated magnesium alloy sample as the anode and a 316L stainless steel tank as the cathode, the sample is immersed in the aforementioned electrolyte and a high-frequency pulsed micro-arc oxidation power supply is used. The total treatment time is set to 5 minutes, and the process runs automatically according to the following program: Stage 1: High-voltage, low-frequency nucleation stage (nucleation, 0-60 seconds): Voltage 450V, frequency 1500Hz, duty cycle 10%; Phase Two: Medium-Voltage High-Frequency Rapid Growth Phase (Growth, 60-240 seconds): Voltage 400V, Frequency 2000Hz, Duty Cycle 20%; Phase 3: Low-voltage, high-duty-cycle densification phase (densification, 240-300 seconds): Voltage 350V, frequency 1000 Hz, duty cycle 30%; The electrolyte temperature is controlled at 30±1℃ by an external circulating water cooling system, and magnetic stirring is performed at a speed of 200rpm throughout the process.

[0043] Remove the sample, rinse it with flowing deionized water, then immerse it in anhydrous ethanol for ultrasonic cleaning for 3 minutes, and finally place it in a 55℃ forced-air drying oven to dry for 2 hours.

[0044] Example 3 The electrolyte preparation method described in this embodiment is the same as that in Embodiment 1. The concentrations of each component of the electrolyte are as follows: sodium silicate 15 g / L, potassium hydroxide 1.5 g / L, hydroxyethyl ethylenediamine triacetic acid 4 g / L, potassium fluorotitanate 2 g / L, yttrium oxide stabilized zirconium oxide nanoparticles 8 g / L, and polyvinylpyrrolidone 1 g / L.

[0045] Take a rare earth magnesium alloy sheet with a Gd content of 8wt% and dimensions of 50mm×25mm×2mm. Polish it sequentially with 800-grit, 1000-grit, 1500-grit, and 2000-grit sandpaper using a wet polishing method until a mirror finish is achieved. Then, ultrasonically clean it for 5 minutes each with deionized water and anhydrous ethanol, and finally dry it with hot air for later use.

[0046] This embodiment employs a segmented micro-arc oxidation process to treat the alloy sheet. Using the pre-treated magnesium alloy sample as the anode and a 316L stainless steel tank as the cathode, the sample is immersed in the aforementioned electrolyte and a high-frequency pulsed micro-arc oxidation power supply is used. The total treatment time is set to 5 minutes, and the process runs automatically according to the following program: Stage 1: High-voltage, low-frequency nucleation stage (nucleation, 0-60 seconds): Voltage 480V, frequency 1800Hz, duty cycle 15%; Phase Two: Medium-Voltage High-Frequency Rapid Growth Phase (Growth, 60-210 seconds): Voltage 430V, Frequency 2300Hz, Duty Cycle 25%; Phase 3: Low-voltage, high-duty-cycle densification phase (densification, 210-300 seconds): Voltage 370V, frequency 1300 Hz, duty cycle 40%; The electrolyte temperature is controlled at 30±1℃ by an external circulating water cooling system, and magnetic stirring is performed at a speed of 200rpm throughout the process.

[0047] Remove the sample, rinse it with flowing deionized water, then immerse it in anhydrous ethanol for ultrasonic cleaning for 3 minutes, and finally place it in a 55℃ forced-air drying oven to dry for 2 hours.

[0048] Comparative Example 1 The micro-arc oxidation film formation method described in this comparative example is the same as that in Example 1, except that in the preparation of the electrolyte, the YSZ nanoparticles (8.0 g / L) in the electrolyte are replaced with an equal mass of cerium oxide (CeO2) nanoparticles (average particle size 100 nm), while other components, concentrations and process parameters remain unchanged.

[0049] Figure 2 This is a scanning electron microscope (SEM) image of the micro-arc oxidation film of a high-Gd rare-earth magnesium alloy with added cerium oxide nanoparticles, as shown in this comparative example. SEM reveals obvious microcracks and significant particle agglomeration in the film, with a significantly higher porosity than in Example 1. The cerium oxide particles fill the micro-arc oxidation pores, reducing the pore size. The coating thickness reaches 16.5 μm, and a 48-hour immersion corrosion test in 3% NaCl solution shows an average corrosion rate of only 0.205 mg / (cm²). 2 •d) exhibits good corrosion resistance. However, after 10 thermal shock cycles, localized peeling of the film occurred, indicating poor performance.

[0050] As can be seen, the electrolyte of the present invention uses yttrium oxide stabilized zirconia nanoparticles instead of traditional nanoparticles. YSZ not only has higher hardness and thermal stability to effectively fill pores, but its unique phase transformation toughening effect can absorb energy through microscopic phase transformation during film formation, uniformly distribute and improve corrosion resistance, and significantly improve the hardness, heat resistance and thermal shock resistance of the film.

[0051] Comparative Example 2 The micro-arc oxidation film formation method described in this comparative example is the same as that in Example 1, except that the micro-arc oxidation process is set to a constant parameter mode, wherein the voltage is 420 V, the frequency is 1800 Hz, the duty cycle is 30%, the processing time is 4 minutes, and other conditions (temperature, stirring) are the same as in Example 1.

[0052] Figure 3 This is a scanning electron microscope (SEM) image of the micro-arc oxidation film on a high-Gd rare-earth magnesium alloy under constant micro-arc oxidation parameters in this comparative scheme. SEM images show numerous large, unclosed discharge pores on the film surface, poor uniformity, and slight cracks. The porosity is significantly higher than the previous two experimental groups, indicating poor compactness. The micro-arc oxidation coating thickness is relatively low, at 12.1 μm, and the growth efficiency is lower than that of the segmented process. In the 48-hour immersion experiment, the mass loss was 0.472 mg / (cm³). 2 d) Poor corrosion resistance. Slight turbidity appeared in the electrolyte during the later stages of treatment, indicating a higher concentration of Gd. 3+ The dissolved substances were not effectively complexed.

[0053] As can be seen, the micro-arc oxidation film formation method for high-Gd rare-earth magnesium alloys described in this invention adjusts the voltage, frequency, and duty cycle according to the film growth mechanism, sequentially undergoing three stages: high-voltage low-frequency nucleation, medium-voltage high-frequency rapid growth, and low-voltage high-duty-cycle densification. This system can efficiently suppress Gd ion dissolution and achieve precise matching between energy and film growth, thereby forming a dense, uniform, and corrosion-resistant ceramic film on the surface of high-Gd rare-earth magnesium alloys in a very short time, solving the problems of low efficiency, uneven film quality, and rapid electrolyte instability in traditional processes.

[0054] Comparative Example 3 The micro-arc oxidation film formation method described in this comparative example is the same as that in Example 1, except that the total micro-arc oxidation time is set to 10 minutes and distributed to each film formation stage according to the same rule, while other components, concentrations and process parameters remain unchanged.

[0055] Figure 4 This is a scanning electron microscope (SEM) image of the micro-arc oxidation film on a high-Gd rare-earth magnesium alloy with a total micro-arc oxidation time of 10 minutes, as shown in this comparative example. The comparison results indicate that the SEM reveals severe localized ablation on the film surface, with obvious cracks, significant particle agglomeration, and an unevenly distributed micro-arc oxidation coating with large pores and a thickness of 7.2 μm. During the 48-hour immersion experiment, the mass loss was 0.836 mg / (cm³). 2 d), poor corrosion resistance.

[0056] As can be seen, the micro-arc oxidation film formation method for high Gd rare earth magnesium alloys described in this invention, based on a three-stage process design of growth mechanism, precisely matches the energy input to the requirements of each growth stage, shortening the total film formation time to 3-5 minutes and improving efficiency by more than 60%. The prepared film layer is uniformly grown, has a dense structure, and can reach a thickness of 10-20 μm. The porosity is significantly reduced, and it is firmly bonded to the substrate. The corrosion resistance and wear resistance are greatly improved, and the film formation efficiency and quality are significantly enhanced.

[0057] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A micro-arc oxidation electrolyte for high-Gd rare-earth magnesium alloys, characterized in that, The electrolyte is an aqueous solution comprising the following concentrations: Sodium silicate 12-20 g / L, potassium hydroxide 1-2 g / L, hydroxyethyl ethylenediamine triacetic acid 3-5 g / L, potassium fluorotitanate 1-3 g / L, yttrium oxide stabilized zirconia nanoparticles 5-10 g / L, polyvinylpyrrolidone 0.5-1.5 g / L.

2. The high-Gd rare-earth magnesium alloy micro-arc oxidation electrolyte according to claim 1, characterized in that: The yttrium oxide-stabilized zirconium oxide nanoparticles have a particle size of 50-300 nm; and / or, In the yttrium oxide-stabilized zirconium oxide nanoparticles, the doping amount of yttrium oxide is 5-8 mol.

3. A method for preparing the high-Gd rare-earth magnesium alloy micro-arc oxidation electrolyte as described in claim 1 or 2, characterized in that, The process includes the step of mixing sodium silicate, potassium hydroxide, hydroxyethyl ethylenediamine triacetic acid, potassium fluorotitanate, yttrium oxide-stabilized zirconia nanoparticles and polyvinylpyrrolidone with deionized water in a selected ratio.

4. A method for micro-arc oxidation film formation of high-Gd rare-earth magnesium alloy, characterized in that, Includes the following steps: (1) Take the high Gd rare earth magnesium alloy substrate to be processed for pretreatment; (2) The substrate is subjected to micro-arc oxidation treatment using the high Gd rare earth magnesium alloy micro-arc oxidation electrolyte as described in claim 1 or 2.

5. The micro-arc oxidation film formation method for high-Gd rare-earth magnesium alloys according to claim 4, characterized in that, In step (2), the temperature of the electrolyte is controlled to be 30±2℃ in the micro-arc oxidation treatment step.

6. The method for micro-arc oxidation film formation of high-Gd rare-earth magnesium alloy according to claim 4 or 5, characterized in that, The micro-arc oxidation process includes the following stages based on the film growth mechanism: (21) High-voltage, low-frequency nucleation stage: control voltage 450-500V, frequency 1500-2000Hz, duty cycle 10%-20%; (22) Medium-voltage high-frequency rapid growth stage: control voltage 400-450V, frequency 2000-2500Hz, duty cycle 20%-30%; (23) Low-voltage high duty cycle densification stage: control voltage 350-400V, frequency 1000-1500Hz, duty cycle 30%-50%.

7. The method for micro-arc oxidation film formation of high-Gd rare-earth magnesium alloy according to claim 6, characterized in that, The total time for the micro-arc oxidation treatment is 3-5 minutes; among which... The high-pressure, low-frequency nucleation stage accounts for 20%-30% of the total processing time; The processing time for the medium-voltage high-frequency rapid growth stage accounts for 50%-60% of the total time; The processing time for the low-pressure, high-duty-cycle densification stage accounts for 20%-30% of the total time.

8. The method for micro-arc oxidation film formation of high-Gd rare-earth magnesium alloy according to any one of claims 4-7, characterized in that, In step (2), the thickness of the film layer formed in the micro-arc oxidation process is controlled to be 10-20 μm.

9. The method for micro-arc oxidation film formation of high-Gd rare-earth magnesium alloy according to any one of claims 4-8, characterized in that, In step (1), the pretreatment step includes grinding, cleaning and drying the substrate; Preferably, the polishing step involves sequentially polishing the substrate with 800-grit, 1000-grit, 1500-grit, and 2000-grit sandpaper; Preferably, the cleaning step is ultrasonic cleaning; Preferably, the drying step is performed at a temperature of 50-60°C for 2-3 hours.

10. The method for micro-arc oxidation film formation of high-Gd rare-earth magnesium alloy according to any one of claims 4-9, characterized in that, The high-Gd rare earth magnesium alloy substrate contains 3-15 wt% Gd.

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