Magnesium alloy material with gradient structure ceramic film layer as well as preparation method and application of magnesium alloy material

Abstract

The invention relates to the technical field of metal surface treatment, and particularly discloses a magnesium alloy material with a gradient-structure ceramic film layer and a preparation method and application of the magnesium alloy material. The ceramic membrane layer provided by the invention comprises a membrane base layer, a transition layer and a surface layer, from the membrane base layer to the surface functional layer, the contents of zirconium oxide and magnesium silicate in the ceramic membrane layer are gradually reduced, and the contents of the rare earth compound and the nano titanium dioxide are gradually increased. The film base layer contains relatively high content of zirconium oxide and magnesium silicate, can effectively reduce high heat transfer to the substrate and reduce heat loss of the substrate, has good compatibility with the substrate and enhances the binding force with the substrate, and the middle transition layer is used as a buffer area, so that the mechanical property of the film layer is in smooth transition, the stress of the film layer is relieved, and the film layer is not easy to peel off. The content of rare earth composite oxide and nano titanium dioxide in the surface layer is high, and the rare earth composite oxide and the nano titanium dioxide cooperate to jointly improve the heat insulation performance and the corrosion resistance. The invention provides a novel magnesium alloy material with excellent performance for the fields of aerospace, automobile manufacturing and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of metal surface treatment, and in particular to a magnesium alloy material with a gradient structure ceramic film layer, a preparation method thereof, and an application thereof. Background Art

[0002] Magnesium alloys, with their low density, high specific strength, and excellent shock absorption properties, hold great potential for application in numerous fields, particularly in aerospace and automotive manufacturing, where lightweight materials are crucial. However, their inherent flammability is a key factor limiting their widespread use in high-temperature environments. Under high-temperature conditions, magnesium reacts violently with oxygen, posing a risk of combustion. This not only threatens the safe operation of related equipment but also significantly hinders the expansion of magnesium alloy applications in these environments.

[0003] As an advanced metal surface treatment method, micro-arc oxidation technology can form a ceramic film with a certain hardness, wear resistance and corrosion resistance on the surface of magnesium alloys, providing an effective way to improve the surface properties of magnesium alloys. However, the current traditional micro-arc oxidation technology still faces many problems that need to be solved when applied to magnesium alloys. On the one hand, the density and thermal insulation performance of the ceramic film prepared by traditional electrolytes are difficult to meet the stringent requirements of high-end application scenarios. In the aerospace field, when the spacecraft re-enters the atmosphere, the surface will be subjected to extremely high temperatures. The existing magnesium alloy micro-arc oxidation ceramic film cannot provide reliable thermal insulation protection, resulting in the risk of high-temperature damage to the substrate material. On the other hand, the ceramic film layer has poor bonding with the substrate, which makes the film layer prone to shedding, delamination and other phenomena under long-term complex stress, and the stability and service life of the film layer cannot be guaranteed.

[0004] In order to solve the above problems, a new method for preparing micro-arc oxidation thermal insulation ceramic film layer on the surface of magnesium alloy is developed, which has important practical significance for breaking the bottleneck of magnesium alloy in high-temperature application field, expanding its application scope and improving the technical level of related industries. Summary of the Invention

[0005] In view of the fact that the density and thermal insulation performance of the existing magnesium alloy micro-arc oxidation ceramic film layer are difficult to meet the stringent requirements of high-end application scenarios, and problems such as easy falling off and stratification occur, the present invention provides a method for preparing a gradient ceramic film layer on the surface of a magnesium alloy, aiming to improve the comprehensive performance of the magnesium alloy in a high-temperature environment and meet the application needs of high-end fields such as aerospace, automobile manufacturing, etc.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0007] A magnesium alloy material with a gradient structure ceramic film layer, comprising a magnesium alloy substrate and a gradient structure ceramic film layer formed on the surface of the magnesium alloy substrate, wherein the ceramic film layer comprises a base layer, a transition layer, and a surface layer; from the base layer to the surface functional layer, the content of zirconium oxide and magnesium silicate in the ceramic film layer gradually decreases, while the content of the rare earth compound and nano-titanium dioxide gradually increases;

[0008] Wherein, the rare earth compound includes lanthanum oxide, neodymium oxide and erbium oxide.

[0009] Compared with the prior art, the surface of the magnesium alloy material provided by the present invention contains a ceramic film layer with a gradient structure, wherein the film base layer contains a high content of zirconium oxide and magnesium silicate. Zirconium oxide has excellent high-temperature resistance and low thermal conductivity. Its relatively high content in the base layer helps to initially block a large amount of heat; magnesium silicate has good high-temperature resistance and can improve the stability of the ceramic film layer in a high-temperature environment. It can synergize with zirconium oxide to withstand higher temperatures, reduce the adverse effects of high temperature on the film layer structure and performance, further enhance the thermal insulation effect, and significantly reduce the risk of high-temperature damage to the substrate.

[0010] The transition layer acts as a buffer zone between the magnesium alloy substrate and the surface functional layer. The gradual change in composition of the ceramic film from the base layer to the surface layer allows for a smooth transition in mechanical properties. The base layer's composition is more compatible with the magnesium alloy substrate, forming a strong chemical and physical bond with the substrate. As the composition gradually changes from the base to the surface, the mechanical properties of the film also gradually change, which helps to alleviate the stress generated during the film's formation and use. This stress relief effect significantly strengthens the bond between the ceramic film and the magnesium alloy substrate, ensuring that the film is not easily peeled off even under long-term use or complex operating conditions.

[0011] The surface functional layer contains a high content of rare earth composite oxides and nano-titanium dioxide. Rare earth oxides can scatter and absorb thermal radiation, and nano-titanium dioxide can significantly reduce heat transfer with its unique nanostructure. The rare earth composite oxides and nano-titanium dioxide work together to achieve a multi-level, efficient thermal insulation effect, effectively improving the overall thermal insulation performance of the magnesium alloy material. The surface layer is in direct contact with the external environment and needs to have a certain degree of protection. The surface layer formed by nano-titanium dioxide and rare earth composite oxides can, to a certain extent, resist the erosion of external chemicals and prevent the film layer from being corroded. In addition, it can also provide antioxidant protection for the internal film layer and the magnesium alloy substrate, slowing the oxidation rate of the magnesium alloy in the air and extending the service life of the material.

[0012] Furthermore, the rare earth composite oxide introduced into the film layer of the present invention can improve the density, structural stability, thermal insulation and bonding strength between the film layer and the substrate; the surface of the introduced nano-titanium dioxide has abundant active sites, which can adsorb a large amount of ions in the electrolyte and actively participate in the formation reaction of the film layer, which can not only refine the grains of the film layer, but also fill the tiny pores inside the film layer, significantly improving the density and thermal insulation of the film layer.

[0013] Furthermore, the mass ratio of the lanthanum oxide, neodymium oxide and erbium oxide is (3-5):(1-3):(1-2).

[0014] Lanthanum oxide lowers the film formation temperature, promoting crystal growth and densification, and enhancing the film's structural stability and thermal shock resistance. Neodymium oxide refines grain size, improving film density, thermal insulation, and adhesion to the substrate. Erbium oxide, with its unique light absorption and emission properties, forms a unique microstructure within the film, enhancing thermal insulation and synergizing with other components to enhance the film's overall performance. These three components work together to stabilize the film's structure, maintaining its structural integrity and overall performance when subjected to external forces, high temperatures, and chemical corrosion.

[0015] In the present invention, nano-titanium dioxide has a significant synergistic effect with lanthanum oxide, neodymium oxide, and erbium oxide. In terms of grain refinement, nano-titanium dioxide forms a large number of nuclei by virtue of its high specific surface area and abundant active sites to adsorb ions. Lanthanum oxide lowers the film-forming temperature to help ions aggregate on its surface, and neodymium oxide affects the growth of nuclei. The three work together to increase the number of nuclei and make them grow evenly, effectively refining the grains. In terms of pore filling, nano-titanium dioxide adsorbs ions to participate in the reaction, lanthanum oxide promotes the rapid migration of ions to the pores for deposition, neodymium oxide makes the structure compact and conducive to filling, and the microstructure constructed by erbium oxide provides a stable environment for pore filling. Together, they reduce the porosity of the film layer and improve the density, thermal insulation and other comprehensive properties of the film layer.

[0016] The present invention also provides a method for preparing a magnesium alloy material having a gradient structure ceramic film layer, which comprises the following steps:

[0017] S1. preparing solutions A, B, and C of different concentrations; wherein the solutions A, B, and C all comprise potassium fluorozirconate, sodium silicate, potassium hydroxide, and potassium fluoride; and the concentrations of potassium fluorozirconate and sodium silicate in the solutions A, B, and C decrease in sequence;

[0018] S2. Preparation of porous ceramic microspheres loaded with rare earth composite oxides and nano-titanium dioxide;

[0019] S3, adding the porous ceramic microspheres loaded with rare earth composite oxides and nano-titanium dioxide into an electrolyte tank, and at the same time, introducing solution A, solution B, and solution C into the electrolyte tank at a first preset flow ratio, using the magnesium alloy as the anode of micro-arc oxidation and the inert electrode as the cathode of micro-arc oxidation, performing a first stage of micro-arc oxidation, and simultaneously performing a first ultrasonic treatment on the electrolyte tank during the micro-arc oxidation to form a film base layer on the surface of the magnesium alloy;

[0020] S4, adjusting the flow rates of solution A, solution B, and solution C to a second preset flow rate ratio, performing a second stage of micro-arc oxidation, and simultaneously performing a second ultrasonic treatment on the electrolyte to form a transition layer on the surface of the membrane base layer;

[0021] S5, adjusting the flow rates of solution A, solution B, and solution C to a third preset flow rate ratio, performing a third stage of micro-arc oxidation, and simultaneously performing a third ultrasonic treatment on the electrolyte to form a surface functional layer on the surface of the transition layer, thereby obtaining a magnesium alloy material having a gradient structure ceramic film layer;

[0022] In the process from the first stage of micro-arc oxidation to the third stage of micro-arc oxidation, the flow rate ratio of solution A gradually decreases, and the flow rate ratio of solution C gradually increases, so that the concentrations of potassium fluorozirconate and sodium silicate in the final electrolyte gradually decrease;

[0023] From the first stage of micro-arc oxidation to the third stage of micro-arc oxidation, the voltage of micro-arc oxidation gradually decreases and the pulse frequency gradually increases;

[0024] During the first ultrasonic treatment to the third ultrasonic treatment, the ultrasonic frequency gradually increases and the ultrasonic power gradually decreases.

[0025] The preparation method of the magnesium alloy material with a gradient structure ceramic film layer provided by the present invention adopts a higher concentration of electrolyte in the initial stage of micro-arc oxidation. The higher concentration of potassium fluorozirconate in the electrolyte can promote the formation of more zirconium oxide, which is tightly accumulated on the surface of the substrate to form a dense zirconium oxide enriched layer, thereby improving the thermal shock resistance of the entire film layer. At the same time, the silicate ions produced by the hydrolysis of a higher concentration of sodium silicate react with magnesium ions to form magnesium silicate, which fills the gaps between the zirconium oxide particles, further enhancing the density of the base layer and the bonding strength with the substrate. The higher concentrations of potassium hydroxide and potassium fluoride can promote better bonding between the film layer and the substrate and the rapid formation of the initial film layer. The concentrations of potassium fluorozirconate and sodium silicate are gradually reduced in the intermediate transition layer, so that the composition, structure and performance of the film layer gradually change, thereby improving the bonding strength between the base layer and the surface functional layer of the film layer and ensuring the stability of the overall structure of the film layer. Near the membrane surface, the concentrations of potassium fluorozirconate and sodium silicate are relatively reduced. At the same time, with the passage of time, rare earth composite oxides and nano-titanium dioxide are gradually released from the porous ceramic balls. The rare earth composite oxides and nano-titanium dioxide released from the porous ceramic balls in the electrolyte increase significantly, and more rare earth composite oxides and nano-titanium dioxide participate in the formation reaction of the surface functional layer. Through the synergistic effect of rare earth composite oxides and nano-titanium dioxide, the surface functional layer has the advantages of high density, good thermal insulation performance and high corrosion resistance, which significantly improves the comprehensive performance of the magnesium alloy.

[0026] It should be noted that the magnesium alloy was pretreated before micro-arc oxidation: the surface of the magnesium alloy was polished using 400 mesh, 600 mesh, 800 mesh, 1000 mesh, 1200 mesh and 1500 mesh sandpaper in sequence. Each time the sandpaper was changed, the polishing direction was changed by 90° to ensure a smooth surface and effectively remove oxide scale and impurities. The polished magnesium alloy was rinsed with deionized water to remove residual debris on the surface. Subsequently, the magnesium alloy was placed in an ultrasonic cleaning tank filled with anhydrous ethanol and ultrasonically cleaned for 15 minutes to thoroughly remove oil stains and fine impurities. After cleaning, the sample was removed with clean tweezers, placed on dry filter paper, and naturally blown dry for use.

[0027] As a specific embodiment of the present invention, in S1, the solution A comprises: 20 g / L to 30 g / L potassium fluorozirconate, 20 g / L to 25 g / L sodium silicate, 4 g / L to 6 g / L potassium hydroxide, and 4 g / L to 6 g / L potassium fluoride;

[0028] The solution B comprises: 12 g / L to 15 g / L of potassium fluorozirconate, 10 g / L to 15 g / L of sodium silicate, 3 g / L to 4 g / L of potassium hydroxide, and 3 g / L to 4 g / L of potassium fluoride;

[0029] The solution C comprises: 8 g / L to 10 g / L of potassium fluorozirconate, 5 g / L to 8 g / L of sodium silicate, 1 g / L to 2 g / L of potassium hydroxide and 1 g / L to 2 g / L of potassium fluoride.

[0030] Furthermore, S2 specifically includes the following steps:

[0031] Dispersing nano-titanium dioxide in water to obtain a nano-titanium dioxide dispersion;

[0032] The rare earth composite oxide is dispersed in anhydrous ethanol to obtain a rare earth composite oxide dispersion;

[0033] The nano-titanium dioxide dispersion and the rare earth composite oxide dispersion are evenly mixed, and porous ceramic microspheres are added and immersed to obtain porous ceramic microspheres loaded with rare earth composite oxide and nano-titanium dioxide.

[0034] Furthermore, the mass ratio of the rare earth composite oxide, nano-titanium dioxide and porous ceramic microspheres is (1.2-1.8):(1.2-1.8):(18-22).

[0035] Furthermore, the average pore size of the porous ceramic microspheres is 10 μm to 20 μm, and the porosity is 60% to 70%.

[0036] Furthermore, the immersion temperature is 20° C. to 30° C., and the immersion time is 20 h to 25 h.

[0037] Specifically, the inert electrode is a stainless steel plate.

[0038] Preferably, in S3, the concentration of the porous ceramic microspheres loaded with rare earth composite oxides and nano-titanium dioxide in the electrolyte is 8 g / L to 12 g / L.

[0039] Furthermore, in S3, the flow rate of solution A is 75% to 85% of the total flow rate, the flow rate of solution B is 5% to 15% of the total flow rate, and the flow rate of solution C is 5% to 15% of the total flow rate.

[0040] Furthermore, in S3, in the first ultrasonic treatment, the ultrasonic frequency is 20kHz~25kHz, and the power is 200W~400W; the voltage of the first stage micro-arc oxidation is 370V~380V, the pulse frequency is 500Hz~700Hz, and the duty cycle is 20%~40%; the treatment time of the first stage micro-arc oxidation is 8min~12min.

[0041] In the first micro-arc oxidation stage, a higher micro-arc oxidation voltage is used to enable the ions in the electrolyte to quickly migrate to the workpiece surface and react, forming an initial film layer. A lower pulse frequency gives the ions sufficient time to deposit on the substrate surface, helping to form a uniform initial film layer and laying a good foundation for the growth of subsequent film layers. In addition, the use of lower frequency and medium power ultrasonic waves can further promote the diffusion of ions in the electrolyte and accelerate the film formation speed.

[0042] Furthermore, in S4, the flow rate of solution A is 35% to 45% of the total flow rate, the flow rate of solution B is 35% to 45% of the total flow rate, and the flow rate of solution C is 15% to 25% of the total flow rate.

[0043] Furthermore, in S4, in the second ultrasonic treatment, the ultrasonic frequency is 30kHz~35kHz, and the power is 150W~300W; the voltage of the second stage micro-arc oxidation is 350V~360V, the pulse frequency is 700Hz~900Hz, and the duty cycle is 20%~40%; the treatment time of the second stage micro-arc oxidation is 8min~12min.

[0044] Using a lower voltage can slow the growth of the membrane, allowing ions more time to deposit and react within the membrane, leading to gradual densification and improved membrane quality. Simultaneously, using a higher ultrasonic frequency and appropriately reducing the ultrasonic power can more precisely promote ion diffusion and distribution, aiding in the densification of the membrane. Furthermore, a higher ultrasonic frequency and reduced ultrasonic power facilitate the release of rare earth oxides and nano-titanium dioxide from the porous ceramic membrane, increasing their concentrations in the electrolyte and, consequently, their content in the resulting transition layer.

[0045] Furthermore, in S5, the flow rate of solution A is 15% to 25% of the total flow rate, the flow rate of solution B is 25% to 35% of the total flow rate, and the flow rate of solution C is 45% to 55% of the total flow rate.

[0046] Furthermore, in S5, in the third ultrasonic treatment, the ultrasonic frequency is 35kHz~40kHz, and the power is 100W~200W; the voltage of the third stage micro-arc oxidation is 320V~330V, the pulse frequency is 900Hz~1000Hz, and the duty cycle is 20%~40%; the treatment time of the third stage micro-arc oxidation is 8min~12min.

[0047] In the later stage of film formation, further reducing the voltage of micro-arc oxidation can make the growth of the film layer slower and more stable, which is beneficial to the adjustment and optimization of the internal structure of the film layer and increase the bonding force between the film layer and the substrate; at this stage, the use of high-frequency, low-power ultrasound can further promote the diffusion and migration of ions in the electrolyte in the film layer, fill the tiny pores in the film layer, and help to further increase the content of rare earth composite oxides and nano-titanium dioxide in the electrolyte, thereby further improving the density and hardness of the film layer.

[0048] It should be noted that during the entire micro-arc oxidation process, a high-precision temperature control system is used to accurately control the temperature of the electrolyte at 25-30°C, effectively avoiding the occurrence of unstable film quality problems caused by temperature fluctuations and ensuring the consistency of film quality prepared in different batches.

[0049] The present invention also provides the application of the magnesium alloy material with the gradient structure ceramic film layer in the fields of aerospace or automobile manufacturing.

[0050] The present invention forms a multilayer ceramic film with a gradient structure on the surface of a magnesium alloy material. The base layer contains high levels of zirconium oxide and magnesium silicate, effectively reducing the transfer of high heat to the substrate and reducing heat loss from the substrate. The base layer also exhibits good compatibility with the substrate, forming a strong chemical and physical bond, enhancing adhesion to the substrate. The intermediate transition layer acts as a buffer zone, ensuring a smooth transition in the mechanical properties of the film, relieving stress and ensuring that the film is resistant to peeling. The surface layer contains high levels of rare earth composite oxides and nano-titanium dioxide, which synergistically improve thermal insulation and corrosion resistance. This invention provides a novel magnesium alloy material with excellent performance for fields such as aerospace and automotive manufacturing, with high potential application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Polarization curves of the magnesium alloy substrate of the present invention and the magnesium alloy material with a gradient structure ceramic film layer prepared in Example 1. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0053] In order to better illustrate the present invention, further examples are given below.

[0054] The preparation method of the porous ceramic microspheres loaded with rare earth composite oxides and nano-titanium dioxide used in the following examples and comparative examples is as follows:

[0055] Ultrasonic dispersion of 1.5 g of nano-titanium dioxide in 100 mL of deionized water was performed to obtain a nano-titanium dioxide dispersion.

[0056] 1.5 g of rare earth composite oxide was ultrasonically dispersed in 100 mL of anhydrous ethanol to obtain a rare earth composite oxide dispersion; the rare earth composite oxide was lanthanum oxide, neodymium oxide, and erbium oxide in a mass ratio of 3:1:1;

[0057] Under stirring conditions, the rare earth composite oxide dispersion was slowly added to the nano-titanium dioxide dispersion, and stirring was continued for 1 hour. Then, 10 g of porous ceramic microspheres were added and immersed at room temperature for 24 hours. During this period, stirring was performed every 4 hours. After the immersion was completed, the mixture was filtered, washed with deionized water, and dried to obtain porous ceramic microspheres loaded with rare earth composite oxides and nano-titanium dioxide.

[0058] The average diameter of the ceramic microspheres used is 10-20 μm, and the porosity is 60-70%.

[0059] In the embodiments of the present invention, porous ceramic microspheres loaded with rare earth composite oxides and nano-titanium dioxide prepared under other conditions specified in the present invention can also achieve comparable technical effects on the performance of the prepared gradient multilayer ceramic membrane.

[0060] Example 1

[0061] This embodiment provides a method for preparing a magnesium alloy material having a gradient structure ceramic film layer:

[0062] S1. Select a ZM6 magnesium alloy specimen with a size of 30 mm × 20 mm × 3 mm and polish the surface of the magnesium alloy using 400-mesh, 600-mesh, 800-mesh, 1000-mesh, 1200-mesh, and 1500-mesh sandpaper in sequence. Each time the sandpaper is changed, the polishing direction is changed by 90°. The polished magnesium alloy is rinsed with deionized water. Subsequently, the magnesium alloy is placed in an ultrasonic cleaning tank filled with anhydrous ethanol and ultrasonically cleaned for 15 minutes. The specimen is removed with clean tweezers, placed on dry filter paper, and naturally dried for later use.

[0063] S2. Weigh 20 g of potassium fluorozirconate, 20 g of sodium silicate, 4 g of potassium hydroxide, and 4 g of potassium fluoride, add them to a beaker filled with 800 mL of deionized water, and stir magnetically at 300 rpm. After complete dissolution, add deionized water to 1 L and continue stirring for 10 min to obtain solution A. Place solution A into chamber A.

[0064] Weigh 12 g of potassium fluorozirconate, 13 g of sodium silicate, 3 g of potassium hydroxide, and 3 g of potassium fluoride, add them to a beaker filled with 800 mL of deionized water, and stir magnetically at 300 rpm. Once completely dissolved, add deionized water to 1 L and continue stirring for 10 min to obtain solution B. Place solution B into chamber B.

[0065] Weigh 8 g of potassium fluorozirconate, 5 g of sodium silicate, 2 g of potassium hydroxide, and 2 g of potassium fluoride, add them to a beaker filled with 800 mL of deionized water, and stir magnetically at 300 rpm. Once completely dissolved, add deionized water to 1 L and continue stirring for 10 min to obtain Solution C. Place Solution C into Chamber C.

[0066] S3, select an aluminum alloy conductive rod and make it well connected to the micro-arc oxidation power supply, fix the pretreated magnesium alloy on the conductive rod, connect the conductive rod with the magnesium alloy to the anode of the micro-arc oxidation power supply, and connect the stainless steel plate as the cathode to the power supply. The peristaltic pump is used to deliver the electrolyte to a 3L electrolyte tank at the initial set flow rate (80% in chamber A, 10% each in chambers B and C). At the same time, 30g of porous ceramic balls loaded with nano-titanium dioxide and rare earth composite oxides are evenly dispersed in the electrolyte tank;

[0067] S4, setting the process parameters of the membrane base layer, ultrasonic frequency 20kHz, power 200W, micro-arc oxidation process parameters as voltage 370V, pulse frequency 500Hz, duty cycle 30%, and turning on the temperature sensor to monitor the electrolyte temperature in real time, so that the electrolyte temperature is controlled at 25-30°C, turning on the micro-arc oxidation device and ultrasonic wave, and treating for 10 minutes to form a membrane base layer on the surface of the magnesium alloy;

[0068] S5, the voltage of micro-arc oxidation was reduced to 350V, the pulse frequency was increased to 700Hz, the ultrasonic frequency was increased to 30kHz, and the power was reduced to 150W. The other parameters remained unchanged. At the same time, the electrolyte flow rate was adjusted by a peristaltic pump so that the flow rate ratio of the electrolyte in chambers A, B, and C became 40%, 40%, and 20%. Micro-arc oxidation was performed for 10 minutes to form a transition layer on the surface of the membrane base layer.

[0069] S5, the voltage of micro-arc oxidation was reduced to 320V, the pulse frequency was increased to 900Hz, the ultrasonic frequency was increased to 35kHz, and the power was reduced to 100W. The other parameters remained unchanged. At the same time, the electrolyte flow rate was adjusted by a peristaltic pump so that the flow rate ratio of the electrolyte in chambers A, B, and C became 20%, 30%, and 50%. Micro-arc oxidation was carried out for 10 minutes to form a surface functional layer on the surface of the transition layer.

[0070] S6. After the micro-arc oxidation treatment is completed, the magnesium alloy is immediately taken out with tweezers, quickly placed in deionized water, and gently shaken for 1 to 2 minutes to remove the electrolyte on the surface of the magnesium alloy. Then, the moisture is absorbed with filter paper, and the magnesium alloy is placed in a 60°C oven for 2 hours. After being taken out and cooled to room temperature, a magnesium alloy material with a gradient structure ceramic film layer is obtained.

[0071] Performance Testing

[0072] 1. Thermal insulation performance test

[0073] An infrared emissivity meter (AE1-RD1) was preheated for 30 minutes. Hemispherical emissivity was measured at five different locations on the surface of the magnesium alloy with the gradient ceramic coating at room temperature and within a wavelength range of 2 to 20 μm. The average value was used to evaluate the thermal insulation performance. The test results showed that the hemispherical emissivity of the untreated magnesium alloy substrate was approximately 0.15. The emissivity of the magnesium alloy with the gradient ceramic coating reached 0.91, indicating a significant improvement in the thermal insulation performance of the coating.

[0074] 2. Bonding strength test

[0075] The sample was heated to 600°C in a muffle furnace at a rate of 10°C / min. After holding for 3 minutes, it was quickly cooled in room-temperature cooling water. This thermal cycle was repeated 50 times. After each cycle, the sample surface was observed with a microscope and the naked eye, noting any damage such as cracks, peeling, and blistering to assess the adhesion between the film and the substrate. Test results: The thermal cycle test cycled between 600°C and room temperature 50 times. Stereoscopic microscopy revealed no visible cracks or peeling after 50 cycles, indicating good thermal shock resistance, indicating strong adhesion between the substrate and the film.

[0076] 3. Hardness test

[0077] A Vickers hardness tester was calibrated according to GB / T 4340.1-2009, using a test force of 0.2 kgf and a loading time of 15 seconds. Hardness was measured at five different locations on the surface of the magnesium alloy with the gradient ceramic film prepared above, with the test points spaced at least 0.5 mm apart. The average hardness value was recorded and used as the film hardness value. The test result: a hardness of 650 HV.

[0078] 4. Corrosion resistance test

[0079] The magnesium alloy material with the gradient structure ceramic film prepared above was polished at the edge and sealed with epoxy resin, leaving only the test surface as the working electrode. A three-electrode system was formed with a saturated calomel reference electrode and a platinum auxiliary electrode. A 3.5wt% NaCl solution was prepared and poured into the electrolytic cell. The three-electrode system was placed in the electrolytic cell and stabilized at the open circuit potential for 30 minutes. A polarization curve test was then performed at a scan rate of 0.5mV / s and a scan range of -2V to +1V (relative to the open circuit potential). The corrosion potential and corrosion current density were obtained from the curve to evaluate the corrosion resistance of the film layer. The results are as follows: Figure 1 shown.

[0080] Test results: The corrosion potential of magnesium alloy without micro-arc oxidation treatment in this solution is about -1.582V, and the corrosion current density is as high as 7.755×10 -4 A / cm 2The corrosion potential of the magnesium alloy material with a gradient structure ceramic film prepared in the embodiment shifted to 0.131 V, and the corrosion current density decreased to 2.221×10 -8 A / cm 2 The positive shift of the corrosion potential and the significant reduction of the corrosion current density indicate that the micro-arc oxidation film in the embodiment significantly improves the corrosion resistance of the magnesium alloy.

[0081] Example 2

[0082] This embodiment provides a method for preparing a magnesium alloy material having a gradient structure ceramic film layer:

[0083] S1. Select a ZM6 magnesium alloy specimen with a size of 30 mm × 20 mm × 3 mm and polish the surface of the magnesium alloy using 400-mesh, 600-mesh, 800-mesh, 1000-mesh, 1200-mesh, and 1500-mesh sandpaper in sequence. Each time the sandpaper is changed, the polishing direction is changed by 90°. The polished magnesium alloy is rinsed with deionized water. Subsequently, the magnesium alloy is placed in an ultrasonic cleaning tank filled with anhydrous ethanol and ultrasonically cleaned for 15 minutes. The specimen is removed with clean tweezers, placed on dry filter paper, and naturally dried for later use.

[0084] S2. Weigh 30 g of potassium fluorozirconate, 25 g of sodium silicate, 5 g of potassium hydroxide, and 5 g of potassium fluoride, add them to a beaker filled with 800 mL of deionized water, and stir magnetically at 300 rpm. After complete dissolution, add deionized water to 1 L and continue stirring for 10 min to obtain solution A. Place solution A into chamber A.

[0085] Weigh 15 g of potassium fluorozirconate, 15 g of sodium silicate, 4 g of potassium hydroxide, and 3 g of potassium fluoride, add them to a beaker filled with 800 mL of deionized water, and stir magnetically at 300 rpm. After they are completely dissolved, add deionized water to 1 L and continue stirring for 10 min to obtain solution B. Place solution B into chamber B.

[0086] Weigh 9 g of potassium fluorozirconate, 8 g of sodium silicate, 1 g of potassium hydroxide, and 2 g of potassium fluoride, add them to a beaker filled with 800 mL of deionized water, and stir magnetically at 300 rpm. Once completely dissolved, add deionized water to 1 L and continue stirring for 10 min to obtain Solution C. Place Solution C into Chamber C.

[0087] S3, select an aluminum alloy conductive rod and make it well connected to the micro-arc oxidation power supply, fix the pretreated magnesium alloy on the conductive rod, connect the conductive rod with the magnesium alloy to the anode of the micro-arc oxidation power supply, and connect the stainless steel plate as the cathode to the power supply. The electrolyte is transported to a 3L electrolyte tank by a peristaltic pump at the initial set flow rate (75% in chamber A, 10% in chamber B, and 15% in chamber C). At the same time, 36g of porous ceramic balls loaded with nano-titanium dioxide and rare earth composite oxides are evenly dispersed in the electrolyte tank;

[0088] S4, set the process parameters of the membrane base layer, ultrasonic frequency 22kHz, power 300W, micro-arc oxidation process parameters as voltage 375V, pulse frequency 600Hz, duty cycle 40%, and turn on the temperature sensor to monitor the electrolyte temperature in real time, so that the electrolyte temperature is controlled at 25-30°C, turn on the micro-arc oxidation device and ultrasonic wave, and process for 8 minutes to form a membrane base layer on the surface of the magnesium alloy;

[0089] S5, the voltage of micro-arc oxidation was reduced to 360V, the pulse frequency was increased to 800Hz, the ultrasonic frequency was increased to 33kHz, and the power was reduced to 200W. The other parameters remained unchanged. At the same time, the electrolyte flow rate was adjusted by a peristaltic pump so that the flow rate ratio of the electrolyte in chambers A, B, and C became 35%, 45%, and 20%. Micro-arc oxidation was carried out for 12 minutes to form a transition layer on the surface of the membrane base layer.

[0090] S5, the voltage of micro-arc oxidation was reduced to 325V, the pulse frequency was increased to 950Hz, the ultrasonic frequency was increased to 40kHz, and the power was reduced to 150W. The other parameters remained unchanged. At the same time, the electrolyte flow rate was adjusted by a peristaltic pump so that the flow rate ratio of the electrolyte in chambers A, B, and C became 15%, 35%, and 50%. Micro-arc oxidation was performed for 10 minutes to form a surface functional layer on the surface of the transition layer.

[0091] S6. After the micro-arc oxidation treatment is completed, the magnesium alloy is immediately taken out with tweezers, quickly placed in deionized water, and gently shaken for 1 to 2 minutes to remove the electrolyte on the surface of the magnesium alloy. Then, the moisture is absorbed with filter paper, and the magnesium alloy is placed in a 60°C oven for 2 hours. After being taken out and cooled to room temperature, a magnesium alloy material with a gradient structure ceramic film layer is obtained.

[0092] The performance test was carried out in exactly the same manner as in Example 1. The infrared emissivity of the ceramic film prepared in this comparative example was measured in the 2-20 μm band using an infrared emissivity meter. The infrared emissivity was 0.89. After 50 thermal shock tests at 600°C, the film had no obvious cracks or peeling. The film hardness was measured to be 630 HV using a Vickers hardness tester. In a 3.5% NaCl solution, the corrosion potential was measured to be 0.042 V using an electrochemical workstation, and the corrosion current density was 1.245×10 -7 A / cm2 .

[0093] Example 3

[0094] This embodiment provides a method for preparing a magnesium alloy material having a gradient structure ceramic film layer:

[0095] S1. Select a ZM6 magnesium alloy specimen with a size of 30 mm × 20 mm × 3 mm and polish the surface of the magnesium alloy using 400-mesh, 600-mesh, 800-mesh, 1000-mesh, 1200-mesh, and 1500-mesh sandpaper in sequence. Each time the sandpaper is changed, the polishing direction is changed by 90°. The polished magnesium alloy is rinsed with deionized water. Subsequently, the magnesium alloy is placed in an ultrasonic cleaning tank filled with anhydrous ethanol and ultrasonically cleaned for 15 minutes. The specimen is removed with clean tweezers, placed on dry filter paper, and naturally dried for later use.

[0096] S2. Weigh 25 g of potassium fluorozirconate, 23 g of sodium silicate, 6 g of potassium hydroxide, and 6 g of potassium fluoride, add them to a beaker filled with 800 mL of deionized water, and stir magnetically at 300 rpm. After complete dissolution, add deionized water to 1 L and continue stirring for 10 min to obtain solution A. Place solution A into chamber A.

[0097] Weigh 14 g of potassium fluorozirconate, 10 g of sodium silicate, 3 g of potassium hydroxide, and 4 g of potassium fluoride, add them to a beaker filled with 800 mL of deionized water, and stir magnetically at 300 rpm. After complete dissolution, add deionized water to 1 L and continue stirring for 10 min to obtain solution B. Place solution B into chamber B.

[0098] Weigh 10 g of potassium fluorozirconate, 6 g of sodium silicate, 2 g of potassium hydroxide, and 1 g of potassium fluoride, add them to a beaker filled with 800 mL of deionized water, and stir magnetically at 300 rpm. Once completely dissolved, add deionized water to 1 L and continue stirring for 10 min to obtain Solution C. Place Solution C into Chamber C.

[0099] S3, select an aluminum alloy conductive rod and make it well connected to the micro-arc oxidation power supply, fix the pretreated magnesium alloy on the conductive rod, connect the conductive rod with the magnesium alloy to the anode of the micro-arc oxidation power supply, and connect the stainless steel plate as the cathode to the power supply. The peristaltic pump is used to deliver the electrolyte to a 3L electrolyte tank at the initial set flow rate (85% in chamber A, 5% in chamber B, and 10% of the total flow rate in chamber C). At the same time, 24g of porous ceramic balls loaded with nano-titanium dioxide and rare earth composite oxides are evenly dispersed in the electrolyte tank;

[0100] S4, setting the process parameters of the membrane base layer, ultrasonic frequency 25kHz, power 400W, micro-arc oxidation process parameters as voltage 380V, pulse frequency 700Hz, duty cycle 20%, and turning on the temperature sensor to monitor the electrolyte temperature in real time, so that the electrolyte temperature is controlled at 25-30°C, turning on the micro-arc oxidation device and ultrasonic wave, and treating for 10 minutes to form a membrane base layer on the surface of the magnesium alloy;

[0101] S5, the voltage of micro-arc oxidation was reduced to 330V, the pulse frequency was increased to 900Hz, the ultrasonic frequency was increased to 35kHz, and the power was reduced to 300W. The other parameters remained unchanged. At the same time, the electrolyte flow rate was adjusted by a peristaltic pump so that the flow rate ratio of the electrolyte in chambers A, B, and C became 40%, 45%, and 15%. Micro-arc oxidation was carried out for 12 minutes to form a transition layer on the surface of the membrane base layer.

[0102] S5, the voltage of micro-arc oxidation was reduced to 320V, the pulse frequency was increased to 1000Hz, the ultrasonic frequency was increased to 38kHz, and the power was reduced to 200W. The other parameters remained unchanged. At the same time, the electrolyte flow rate was adjusted by a peristaltic pump so that the flow rate ratio of the electrolyte in chambers A, B, and C became 20%, 25%, and 55%. Micro-arc oxidation was performed for 8 minutes to form a surface functional layer on the surface of the transition layer.

[0103] S6. After the micro-arc oxidation treatment is completed, the magnesium alloy is immediately taken out with tweezers, quickly placed in deionized water, and gently shaken for 1 to 2 minutes to remove the electrolyte on the surface of the magnesium alloy. Then, the moisture is absorbed with filter paper, and the magnesium alloy is placed in a 60°C oven for 2 hours. After being taken out and cooled to room temperature, a magnesium alloy material with a gradient structure ceramic film layer is obtained.

[0104] The performance test was carried out in exactly the same manner as in Example 1. The infrared emissivity of the ceramic film prepared in this comparative example was measured in the 2-20 μm band using an infrared emissivity meter. The infrared emissivity was 0.92. After 50 thermal shock tests at 600°C, the film had no obvious cracks or peeling. The film hardness was measured to be 663HV using a Vickers hardness tester. In a 3.5% NaCl solution, the corrosion potential was measured to be 0.062V using an electrochemical workstation using a three-electrode system, and the corrosion current density was 0.66×10 -8 A / cm 2 .

[0105] Comparative Example 1

[0106] This comparative example provides a method for preparing a ceramic film layer on a magnesium alloy surface by micro-arc oxidation. The only difference from Example 1 is that porous ceramic microspheres loaded with rare earth composite oxides and nano-titanium dioxide are not added to the electrolyte tank. The rest is exactly the same and will not be repeated here.

[0107] The performance test was carried out in exactly the same manner as in Example 1. The infrared emissivity of the ceramic film prepared in this comparative example was measured in the 2-20 μm band using an infrared emissivity meter. After 50 thermal shock tests at 600°C, a small number of fine cracks appeared on the surface of the film. The hardness of the film was measured to be 480 HV using a Vickers hardness tester. In a 3.5% NaCl solution, the corrosion potential was measured to be -1.382 V using an electrochemical workstation using a three-electrode system, and the corrosion current density was 2.212×10 -5 A / cm 2 .

[0108] Comparative Example 2

[0109] This comparative example provides a method for preparing a ceramic film layer on a magnesium alloy surface by micro-arc oxidation. The only difference from Example 1 is that ultrasonic treatment is not performed during the entire micro-arc oxidation process. The rest is exactly the same and will not be repeated here.

[0110] The performance test was carried out in exactly the same manner as in Example 1. The infrared emissivity of the ceramic film prepared in this comparative example was measured in the 2-20 μm band using an infrared emissivity meter. After 50 thermal shock tests at 600°C, a small number of slight cracks appeared on the surface of the film. The hardness of the film was measured to be 600 HV using a Vickers hardness tester. In a 3.5% NaCl solution, the corrosion potential was measured to be -1.285 V using an electrochemical workstation using a three-electrode system, and the corrosion current density was 1.422×10 -5 A / cm 2 .

[0111] Comparative Example 3

[0112] This comparative example provides a method for preparing a ceramic film layer on a magnesium alloy surface by micro-arc oxidation. The only difference from Example 1 is that the same concentration of electrolyte is used throughout the micro-arc oxidation process. The specific steps are as follows:

[0113] This embodiment provides a method for preparing a magnesium alloy material having a gradient structure ceramic film layer:

[0114] S1. Select a ZM6 magnesium alloy specimen with a size of 30 mm × 20 mm × 3 mm and polish the surface of the magnesium alloy using 400-mesh, 600-mesh, 800-mesh, 1000-mesh, 1200-mesh, and 1500-mesh sandpaper in sequence. Each time the sandpaper is changed, the polishing direction is changed by 90°. The polished magnesium alloy is rinsed with deionized water. Subsequently, the magnesium alloy is placed in an ultrasonic cleaning tank filled with anhydrous ethanol and ultrasonically cleaned for 15 minutes. The specimen is removed with clean tweezers, placed on dry filter paper, and naturally dried for later use.

[0115] S2. Weigh 20 g of potassium fluorozirconate, 10 g of sodium silicate, 4 g of potassium hydroxide, and 4 g of potassium fluoride, add them to a beaker filled with 800 mL of deionized water, and stir magnetically at 300 rpm. After complete dissolution, add deionized water to 1 L and continue stirring for 10 min to obtain solution A. Place solution A into chamber A.

[0116] S3, select an aluminum alloy conductive rod and make it well connected to the micro-arc oxidation power supply. Fix the pretreated magnesium alloy on the conductive rod. Connect the conductive rod with the magnesium alloy to the anode of the micro-arc oxidation power supply. Connect the stainless steel plate as the cathode to the power supply. The electrolyte in chamber A is transported to a 3L electrolyte tank by a peristaltic pump. At the same time, 30g of porous ceramic balls loaded with nano-titanium dioxide and rare earth composite oxides are evenly dispersed in the electrolyte tank.

[0117] S4, setting the process parameters of the membrane base layer, ultrasonic frequency 20kHz, power 200W, micro-arc oxidation process parameters as voltage 370V, pulse frequency 500Hz, duty cycle 30%, and turning on the temperature sensor to monitor the electrolyte temperature in real time, so that the electrolyte temperature is controlled at 25-30°C, turning on the micro-arc oxidation device and ultrasonic wave, and treating for 30 minutes to form a membrane base layer on the surface of the magnesium alloy;

[0118] S5. After the micro-arc oxidation treatment is completed, the magnesium alloy is immediately taken out with tweezers, quickly placed in deionized water, and gently shaken for 1 to 2 minutes to remove the electrolyte on the surface of the magnesium alloy. Then, the moisture is absorbed with filter paper, and the magnesium alloy is placed in a 60°C oven for 2 hours. After being taken out and cooled to room temperature, a magnesium alloy material with a gradient structure ceramic film layer is obtained.

[0119] The performance test was carried out in exactly the same manner as in Example 1. The infrared emissivity of the ceramic film prepared in this comparative example was measured in the 2-20 μm band using an infrared emissivity meter. After 50 thermal shock tests at 600°C, a small number of fine cracks appeared on the surface of the film. The hardness of the film was measured to be 550 HV using a Vickers hardness tester. In a 3.5% NaCl solution, the corrosion potential was measured to be -1.331 V using an electrochemical workstation using a three-electrode system, and the corrosion current density was 1.723×10 -5 A / cm 2 .

[0120] Comparative Example 4

[0121] This comparative example provides a method for preparing a ceramic film layer on a magnesium alloy surface by micro-arc oxidation. The only difference from Example 1 is that the rare earth composite oxide is replaced by a single lanthanum oxide. The rest is exactly the same and will not be repeated here.

[0122] The performance test was carried out in exactly the same manner as in Example 1. The infrared emissivity of the ceramic film prepared in this comparative example was measured in the 2-20 μm band using an infrared emissivity meter. After 50 thermal shock tests at 600°C, there were no cracks on the surface of the film. The hardness of the film was measured to be 525 HV using a Vickers hardness tester. In a 3.5% NaCl solution, the corrosion potential was measured to be 0.051 V using an electrochemical workstation using a three-electrode system, and the corrosion current density was 1.652×10 -6 A / cm 2 .

[0123] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A magnesium alloy material with a gradient structure ceramic film layer, characterized in that: The invention relates to a magnesium alloy substrate and a ceramic film layer with a gradient structure formed on the surface of the magnesium alloy substrate, wherein the ceramic film layer comprises a base layer, a transition layer and a surface functional layer; from the base layer to the surface functional layer, the content of zirconium oxide and magnesium silicate in the ceramic film layer gradually decreases, and the content of rare earth compound and nano-titanium dioxide gradually increases; Wherein, the rare earth compound includes lanthanum oxide, neodymium oxide and erbium oxide.

2. The magnesium alloy material with a gradient structure ceramic film layer according to claim 1, characterized in that: The mass ratio of the lanthanum oxide, neodymium oxide and erbium oxide is (3-5):(1-3):(1-2).

3. A method for preparing a magnesium alloy material having a gradient structure ceramic film layer according to claim 1 or 2, characterized in that: The following steps are involved: S1. preparing solutions A, B, and C of different concentrations; wherein the solutions A, B, and C all comprise potassium fluorozirconate, sodium silicate, potassium hydroxide, and potassium fluoride; and the concentrations of potassium fluorozirconate and sodium silicate in the solutions A, B, and C decrease in sequence; S2. Preparation of porous ceramic microspheres loaded with rare earth composite oxides and nano-titanium dioxide; S3, adding the porous ceramic microspheres loaded with rare earth composite oxides and nano-titanium dioxide into an electrolyte tank, and at the same time, introducing solution A, solution B, and solution C into the electrolyte tank at a first preset flow ratio, using the magnesium alloy as the anode of micro-arc oxidation and the inert electrode as the cathode of micro-arc oxidation, performing a first stage of micro-arc oxidation, and simultaneously performing a first ultrasonic treatment on the electrolyte tank during the micro-arc oxidation to form a film base layer on the surface of the magnesium alloy; S4, adjusting the flow rates of solution A, solution B, and solution C to a second preset flow rate ratio, performing a second stage of micro-arc oxidation, and simultaneously performing a second ultrasonic treatment on the electrolyte to form a transition layer on the surface of the membrane base layer; S5, adjusting the flow rates of solution A, solution B, and solution C to a third preset flow rate ratio, performing a third stage of micro-arc oxidation, and simultaneously performing a third ultrasonic treatment on the electrolyte to form a surface functional layer on the surface of the transition layer, thereby obtaining a magnesium alloy material having a gradient structure ceramic film layer; In the process from the first stage of micro-arc oxidation to the third stage of micro-arc oxidation, the flow rate ratio of solution A gradually decreases, and the flow rate ratio of solution C gradually increases, so that the concentrations of potassium fluorozirconate and sodium silicate in the final electrolyte gradually decrease; From the first stage of micro-arc oxidation to the third stage of micro-arc oxidation, the voltage of micro-arc oxidation gradually decreases and the pulse frequency gradually increases; During the first ultrasonic treatment to the third ultrasonic treatment, the ultrasonic frequency gradually increases and the ultrasonic power gradually decreases.

4. The method for preparing a magnesium alloy material having a gradient structure ceramic film layer according to claim 3, wherein: In S1, the solution A comprises: 20 g / L to 30 g / L potassium fluorozirconate, 20 g / L to 25 g / L sodium silicate, 4 g / L to 6 g / L potassium hydroxide, and 4 g / L to 6 g / L potassium fluoride; The solution B comprises: 12 g / L to 15 g / L of potassium fluorozirconate, 10 g / L to 15 g / L of sodium silicate, 3 g / L to 4 g / L of potassium hydroxide, and 3 g / L to 4 g / L of potassium fluoride; The solution C comprises: 8 g / L to 10 g / L of potassium fluorozirconate, 5 g / L to 8 g / L of sodium silicate, 1 g / L to 2 g / L of potassium hydroxide and 1 g / L to 2 g / L of potassium fluoride.

5. The method for preparing a magnesium alloy material having a gradient structure ceramic film layer according to claim 3, wherein: S2 specifically includes the following steps: Dispersing nano-titanium dioxide in water to obtain a nano-titanium dioxide dispersion; The rare earth composite oxide is dispersed in anhydrous ethanol to obtain a rare earth composite oxide dispersion; The nano-titanium dioxide dispersion and the rare earth composite oxide dispersion are evenly mixed, and porous ceramic microspheres are added and immersed to obtain porous ceramic microspheres loaded with rare earth composite oxide and nano-titanium dioxide.

6. The method for preparing a magnesium alloy material having a gradient structure ceramic film layer according to claim 5, characterized in that: The mass ratio of the rare earth composite oxide, nano-titanium dioxide and porous ceramic microspheres is (1.2-1.8):(1.2-1.8):(18-22); and / or The porous ceramic microspheres have an average pore size of 10 μm to 20 μm and a porosity of 60% to 70%; and / or The immersion temperature is 20° C. to 30° C., and the immersion time is 20 hours to 25 hours.

7. The method for preparing a magnesium alloy material having a gradient structure ceramic film layer according to claim 3, characterized in that: In S3, the concentration of the porous ceramic microspheres loaded with rare earth composite oxides and nano-titanium dioxide in the electrolyte is 8 g / L to 12 g / L; and / or In S3, the flow rate of solution A is 75% to 85% of the total flow rate, the flow rate of solution B is 5% to 15% of the total flow rate, and the flow rate of solution C is 5% to 15% of the total flow rate; and / or In S3, in the first ultrasonic treatment, the ultrasonic frequency is 20kHz~25kHz, and the power is 200W~400W; the voltage of the first stage micro-arc oxidation is 370V~380V, the pulse frequency is 500Hz~700Hz, and the duty cycle is 20%~40%; the treatment time of the first stage micro-arc oxidation is 8min~12min.

8. The method for preparing a magnesium alloy material having a gradient structure ceramic film layer according to claim 3, wherein: In S4, the flow rate of solution A is 35% to 45% of the total flow rate, the flow rate of solution B is 35% to 45% of the total flow rate, and the flow rate of solution C is 15% to 25% of the total flow rate; and / or In S4, in the second ultrasonic treatment, the ultrasonic frequency is 30kHz~35kHz, and the power is 150W~300W; the voltage of the second stage micro-arc oxidation is 350V~360V, the pulse frequency is 700Hz~900Hz, and the duty cycle is 20%~40%; the treatment time of the second stage micro-arc oxidation is 8min~12min.

9. The method for preparing a magnesium alloy material having a gradient structure ceramic film layer according to claim 3, wherein: In S5, the flow rate of solution A is 15% to 25% of the total flow rate, the flow rate of solution B is 25% to 35% of the total flow rate, and the flow rate of solution C is 45% to 55% of the total flow rate; and / or In S5, in the third ultrasonic treatment, the ultrasonic frequency is 35kHz~40kHz, and the power is 100W~200W; the voltage of the third stage micro-arc oxidation is 320V~330V, the pulse frequency is 900Hz~1000Hz, and the duty cycle is 20%~40%; the treatment time of the third stage micro-arc oxidation is 8min~12min.

10. Use of the magnesium alloy material with a gradient structure ceramic film layer according to claim 1 or 2 in the fields of aerospace or automobile manufacturing.

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