A method for preparing a green ceramic film on a magnesium alloy surface

Abstract

This invention belongs to the field of surface treatment methods for magnesium alloy materials, specifically relating to a method for preparing a green ceramic film on the surface of magnesium alloys. The method uses a phosphate system as the main salt, with iron salts reacting with triethanolamine to form a coloring metal salt. A coloring electrolyte is prepared under a strongly alkaline environment. This electrolyte does not contain harmful elements such as vanadium and chromium, reducing environmental pollution. A two-step constant-current micro-arc oxidation process with reduced voltage is employed to obtain a uniformly colored, strongly adhered, and dense green ceramic film on the magnesium alloy surface, exhibiting excellent properties such as high wear resistance and corrosion resistance. The process of this invention is simple and efficient, and the electrolyte is environmentally friendly and energy-efficient.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment methods for magnesium alloy materials, and specifically relates to a method for preparing a green ceramic film on the surface of a magnesium alloy. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials, possess a series of advantages, including high specific strength and specific stiffness, good damping and vibration reduction performance, high electromagnetic shielding performance, and easy recyclability. As a new generation of green, high-strength, and lightweight metallic materials with great development potential, magnesium alloys have immense application value in aerospace, weaponry, automotive industry, and electronics. However, magnesium alloys exhibit high chemical and electrochemical reactivity, poor corrosion resistance, and are mostly soft with low hardness, resulting in poor wear resistance. These factors hinder their widespread application. Surface treatment of magnesium alloys to improve their corrosion and wear resistance is one of the simplest and most effective methods, while also meeting the decorative requirements of civilian industries and the camouflage requirements of the military industry.

[0003] Micro-arc oxidation, also known as plasma electrolytic oxidation or anodic spark precipitation, is a novel technique for directly growing ceramic layers in situ on the surfaces of valve metals such as Mg, Al, and Ti. Due to the complexity of the ceramic film formation process, there is currently no authoritative theoretical model to explain the phenomena observed during experiments and the formation mechanism of the film. Ceramic films prepared using micro-arc oxidation coloring technology exhibit strong adhesion to the substrate and high hardness, resulting in good corrosion and wear resistance. However, most magnesium alloy ceramic films prepared using this technique are white or off-white; research on green ceramic films is relatively limited, which fails to meet the requirements of military products used in field operations for wear resistance, corrosion resistance, and camouflage.

[0004] The existing technologies for preparing green ceramic films on magnesium alloy surfaces using micro-arc oxidation technology have the following shortcomings: (1) The most reported electrolytes for preparing green ceramic films in micro-arc oxidation are metal oxides such as vanadium salts and chromium salts. However, vanadium salts and chromium salts are highly toxic and have a certain degree of environmental pollution. (2) Most micro-arc oxidation processes use a one-stage constant current or constant voltage process, which leads to intense discharge in the later stage of micro-arc oxidation. The film surface is relatively rough and porous and cracks will be generated. For example, application publication number CN202010512259.X discloses a method for preparing green corrosion-resistant ceramic films grown in situ on the surface of aluminum-based composite materials. The green corrosion-resistant ceramic film prepared using a one-stage constant current process has cracks and ablation on its surface. Summary of the Invention

[0005] To address the problems in the background art, this invention provides a method for preparing a green ceramic film on the surface of a magnesium alloy. The coloring electrolyte prepared in this invention does not contain harmful elements such as vanadium and chromium, thus achieving the greening function of the magnesium alloy surface. While ensuring that the green ceramic coating of the magnesium alloy has good corrosion resistance and wear resistance, by optimizing the micro-arc oxidation process and adopting a two-step constant current micro-arc oxidation treatment with reduced voltage, energy consumption and production costs can be greatly reduced.

[0006] The present invention relates to a method for preparing a green ceramic film on a magnesium alloy surface, comprising the following steps:

[0007] Using a polished and cleaned magnesium alloy as the anode and a stainless steel plate as the cathode, the anode is immersed in a coloring electrolyte and subjected to a two-step constant current micro-arc oxidation process with reduced voltage. After the micro-arc oxidation is completed, the anode is immersed in warm water and then dried to obtain a magnesium alloy with a green ceramic film on its surface.

[0008] The colored electrolyte includes 15–25 g / L phosphate, 10–15 g / L sodium fluoride, 2–10 g / L iron salt, 22.5–90 g / L triethanolamine and deionized water; the pH value is adjusted to 10–12.

[0009] The current density of the step-down two-step constant current micro-arc oxidation process is 3–10 A / dm³. 2 The oxidation voltage for the first step of constant current micro-arc oxidation treatment is 450-550V; the oxidation voltage for the second step of constant current micro-arc oxidation treatment is 300-450V; during the micro-arc oxidation process, a circulating cooling device is used to keep the temperature of the coloring electrolyte below 20℃ to avoid the electrolyte temperature from rising during the micro-arc oxidation process, which would cause the surface film to be ablated.

[0010] Furthermore, as a preferred method, the specific method for grinding and cleaning is as follows: after the magnesium alloy is ground step by step with SiC sandpaper of 400#, 800#, 1500# and 2000#, it is polished with a polishing cloth, then cleaned for 5 minutes under anhydrous ethanol and ultrasonic conditions, then rinsed with deionized water, and finally dried for later use.

[0011] Furthermore, as a preferred embodiment, the method for preparing the colored electrolyte is as follows: First, phosphate and sodium fluoride in a mass ratio of 2:1 are placed in deionized water and stirred continuously to ensure complete dissolution, thereby obtaining the main salt electrolyte; then, triethanolamine, an organic additive, is added to the iron salt solution and stirred continuously to allow the triethanolamine to fully undergo a complexation reaction with the iron salt, thereby obtaining the metal salt electrolyte; finally, the metal salt electrolyte and the main salt electrolyte are mixed, and the pH value of the solution is adjusted to 10-12 using an alkaline pH adjuster to obtain the colored electrolyte.

[0012] The phosphate is any one of sodium phosphate, sodium hexametaphosphate, or sodium polyphosphate.

[0013] The iron salt is either ferric ammonium sulfate or ferric ammonium oxalate;

[0014] Alkaline pH adjusters are potassium hydroxide or sodium hydroxide.

[0015] Furthermore, as a preferred embodiment, the parameters for the first step of constant current micro-arc oxidation treatment are: oxidation voltage of 450–550V and current density of 3–10A / dm³. 2 The first step, constant current micro-arc oxidation, has the following parameters: positive duty cycle 10–20%, negative duty cycle 5–10%, frequency 400–500 Hz, and oxidation time 5–10 min; the second step, constant current micro-arc oxidation, has the following parameters: oxidation voltage 300–450 V, current density 3–10 A / dm³. 2 The positive duty cycle is 10-20%, the negative duty cycle is 5-10%, the frequency is 400-500Hz, and the oxidation time is 5-10min.

[0016] Understandably, in the two-step constant current micro-arc oxidation process with reduced pressure, the present invention first performs a high-pressure constant current micro-arc oxidation process, which can shorten the arc initiation time of micro-arc oxidation and increase the reaction time for film formation. Then, through the second step of low-pressure constant current micro-arc oxidation, the oxide film layer at the micropores is repeatedly melted and regenerated, thereby repairing the large-diameter micropores formed in the first constant current stage, so as to obtain a more dense ceramic layer with better resistance to corrosion media and improved corrosion resistance of the ceramic layer.

[0017] Furthermore, as a preferred method, the specific method of soaking in warm water is as follows: immerse the processed magnesium alloy sample in warm water at 20-50°C for 13-17 minutes to make the green ceramic film formed on the surface of the magnesium alloy more dense.

[0018] Furthermore, as a preferred method, the drying method after soaking in warm water is as follows: first, dry with a hair dryer, then place in a drying oven for 27 to 33 minutes at a temperature of 45 to 55°C to obtain a green ceramic film on the magnesium alloy surface with a film thickness of 10 to 20 μm.

[0019] The beneficial effects of this invention are:

[0020] 1. Avoid using toxic coloring metals in electrolyte preparation. Use triethanolamine as a metal chelating agent to react with iron salts as colorants to form iron metal complexes that are not easily hydrolyzed and condensed. This prevents iron ions from precipitating as ferric hydroxide in strongly alkaline solutions, thus dispersing the coloring iron ions. This not only improves color uniformity but also ensures the stability of the solution, allowing for long-term use without precipitation and extending the electrolyte's lifespan.

[0021] 2. The present invention sets process parameters adapted to the coloring electrolyte to perform a two-step constant current micro-arc oxidation treatment on magnesium alloy with reduced voltage. The two work together to obtain a uniform green ceramic film on the surface of magnesium alloy. The surface of the green film layer is dense and almost without pores. The process has low energy consumption, high production efficiency and is conducive to industrial production. Attached Figure Description

[0022] Figure 1 Cross-sectional SEM images of the green ceramic film on the magnesium alloy surface in Example 1(a) and Comparative Example 3(b);

[0023] Figure 2 The images show surface SEM images of the green ceramic film on the magnesium alloy surface in Example 2(a) and Comparative Example 7(b);

[0024] Figure 3 The polarization curves were obtained by immersing untreated AZ91 magnesium alloy and magnesium alloys with green ceramic films formed on the surface in Examples 1-3 in 3.5% NaCl solution for 0.5 h. Detailed Implementation

[0025] Example 1

[0026] (1) Cut AZ91 magnesium alloy wire into samples with a length × width × height of 30mm × 30mm × 2mm. Use 400#, 800#, 1500# and 2000# SiC sandpaper to grind the sample step by step to remove the surface passivation film. Polish with polishing cloth, then clean with anhydrous ethanol and ultrasonic for 5 minutes to remove stains. Then rinse with deionized water and finally blow dry for later use.

[0027] (2) First, pour 2L of deionized water into the oxidation tank. Weigh 80g of sodium hexametaphosphate and 40g of sodium fluoride and add them to the deionized water. Stir continuously to ensure complete dissolution, thus obtaining the main salt electrolyte. Then, dissolve 32g of ammonium oxalate ferric salt in 2L of deionized water. Simultaneously, while stirring, pour in 134.9g of triethanolamine and heat in a constant temperature water bath for 20 minutes to allow for a complete complexation reaction, thus obtaining the metal salt electrolyte. Mix the metal salt electrolyte with the main salt electrolyte, and then add a 4g / L potassium hydroxide solution to the mixed solution to adjust the pH to 12, thus obtaining the colored electrolyte.

[0028] (3) Using the magnesium alloy treated in step (1) as the anode and the stainless steel plate as the cathode, the anode is immersed in the prepared coloring electrolyte. A two-step constant current micro-arc oxidation process with a step-down voltage is adopted, and the process parameters are set. The first step is as follows: oxidation voltage is 500V, and current density is 8A / dm³. 2The positive duty cycle is 20%, the negative duty cycle is 10%, the frequency is 450Hz, and the oxidation time is 8 minutes. After voltage reduction, the second step is performed, specifically: the oxidation voltage is 350V, and the current density is 8A / dm³. 2 The positive duty cycle was 20%, the negative duty cycle was 10%, the frequency was 450 Hz, and the oxidation time was 6 min. During the micro-arc oxidation process, a circulating cooling device was used to keep the temperature of the coloring electrolyte below 20℃.

[0029] (4) Immerse the processed magnesium alloy sample in warm water at 40°C for 15 minutes, then take it out and dry it with a hair dryer, and then put it in a drying oven for 30 minutes at a temperature of 50°C to obtain a magnesium alloy with a green ceramic film on the surface. The thickness of the green coating on the surface is about 18 μm.

[0030] Example 2

[0031] (1) Cut AZ91 magnesium alloy wire into samples with a length × width × height of 30mm × 30mm × 2mm. Use 400#, 800#, 1500# and 2000# SiC sandpaper to grind the sample step by step to remove the surface passivation film. Polish with polishing cloth, then clean with anhydrous ethanol and ultrasonic for 5 minutes to remove stains. Then rinse with deionized water and finally blow dry for later use.

[0032] (2) First, pour 2L of deionized water into the oxidation tank. Weigh out 96g of sodium hexametaphosphate and 48g of sodium fluoride and add them to the deionized water. Stir continuously until fully dissolved to obtain the main salt electrolyte. Then, dissolve 20g of ammonium oxalate ferric salt in 2L of deionized water. While stirring, pour in 112.4g of triethanolamine and heat in a constant temperature water bath for 20min to allow the complexation reaction to occur fully, thus obtaining the metal salt electrolyte. Mix the metal salt electrolyte with the main salt electrolyte, and then add a 4g / L potassium hydroxide solution to the mixed solution to adjust the pH to 12, thus obtaining the colored electrolyte.

[0033] (3) Using the magnesium alloy treated in step (1) as the anode and the stainless steel plate as the cathode, the anode is immersed in the prepared coloring electrolyte. A two-step constant current micro-arc oxidation process with a step-down voltage is adopted, and the process parameters are set. The first step is as follows: oxidation voltage is 550V, and current density is 6A / dm³. 2 The positive duty cycle is 15%, the negative duty cycle is 10%, the frequency is 500Hz, and the oxidation time is 5 minutes. After voltage reduction, the second step is performed, specifically: the oxidation voltage is 400V, and the current density is 6A / dm³. 2 The positive duty cycle was 15%, the negative duty cycle was 10%, the frequency was 500 Hz, and the oxidation time was 8 min. During the micro-arc oxidation process, a circulating cooling device was used to keep the temperature of the coloring electrolyte below 20℃.

[0034] (4) Immerse the processed magnesium alloy sample in warm water at 40°C for 15 minutes, then take it out and dry it with a hair dryer, and then put it in a drying oven for 30 minutes at a temperature of 50°C to obtain a magnesium alloy with a green ceramic film on the surface. The thickness of the green coating on the surface is about 14 μm.

[0035] Example 3

[0036] (1) Cut AZ91 magnesium alloy wire into samples with a length × width × height of 30mm × 30mm × 2mm. Use 400#, 800#, 1500# and 2000# SiC sandpaper to grind the sample step by step to remove the surface passivation film. Polish with polishing cloth, then clean with anhydrous ethanol and ultrasonic for 5 minutes to remove stains. Then rinse with deionized water and finally blow dry for later use.

[0037] (2) First, pour 2L of deionized water into the oxidation tank. Weigh out 96g of sodium hexametaphosphate and 48g of sodium fluoride and add them to the deionized water. Stir continuously to ensure complete dissolution, thus obtaining the main salt electrolyte. Then, dissolve 40g of ammonium oxalate ferric salt in 2L of deionized water. Simultaneously, while stirring, pour in 134.9g of triethanolamine and heat in a constant temperature water bath for 20 minutes to allow for a complete complexation reaction, thus obtaining the metal salt electrolyte. Mix the metal salt electrolyte with the main salt electrolyte, and then add a 4g / L sodium hydroxide solution to the mixed solution to adjust the pH to 12, thus obtaining the colored electrolyte.

[0038] (3) Using the magnesium alloy treated in step (1) as the anode and the stainless steel plate as the cathode, the anode is immersed in the prepared coloring electrolyte. A two-step constant current micro-arc oxidation process with a step-down voltage is adopted, and the process parameters are set. The first step is as follows: oxidation voltage is 500V, and current density is 10A / dm³. 2 The positive duty cycle is 20%, the negative duty cycle is 10%, the frequency is 400Hz, and the oxidation time is 6 minutes. After voltage reduction, the second step is performed, specifically: the oxidation voltage is 300V, and the current density is 10A / dm³. 2 The positive duty cycle was 20%, the negative duty cycle was 10%, the frequency was 400 Hz, and the oxidation time was 10 min. During the micro-arc oxidation process, a circulating cooling device was used to keep the temperature of the coloring electrolyte below 20℃.

[0039] (4) Immerse the processed magnesium alloy sample in warm water at 40°C for 15 minutes, then take it out and dry it with a hair dryer, and then put it in a drying oven for 30 minutes at a temperature of 50°C to obtain a magnesium alloy with a green ceramic film on the surface. The thickness of the green coating on the surface is about 15 μm.

[0040] Comparative Example 1

[0041] Compared with Example 1, the difference lies in step (2): 4L of deionized water is poured into the oxidation tank, and 80g of sodium hexametaphosphate, 40g of sodium fluoride, 32g of ferric ammonium oxalate, and 134.9g of triethanolamine additive are weighed and added to the deionized water. The mixture is then heated in a constant temperature water bath for 20 minutes to ensure complete dissolution. A 4g / L potassium hydroxide solution is then added to the mixed solution to adjust the pH to 12, thus obtaining the colored electrolyte. Other operations are the same as in Example 1. The electrolyte prepared under these conditions contains ferric hydroxide precipitate and does not produce an arc during micro-arc oxidation, resulting in no green film on the magnesium alloy surface.

[0042] Comparative Example 2

[0043] Compared with Example 1, the difference is that in step (2), 2L of deionized water is first poured into the oxidation tank, and 80g of sodium hexametaphosphate and 40g of sodium fluoride are weighed and added to the deionized water. The mixture is stirred continuously to ensure complete dissolution, thus obtaining the main salt electrolyte. Then, 32g of ammonium oxalate ferric salt is dissolved in 2L of deionized water to obtain the metal salt electrolyte. The metal salt electrolyte is mixed with the main salt electrolyte, and then a potassium hydroxide solution with a concentration of 4g / L is added to the mixed solution to adjust the pH to 12, thus obtaining the colored electrolyte. Other operations are the same as in Example 1. Because the complexing agent triethanolamine was not added when preparing the metal salt electrolyte, the solution contained a large amount of flocculent precipitate, which affected the arc initiation during the micro-arc oxidation process, and no green film was obtained on the magnesium alloy surface.

[0044] Comparative Example 3

[0045] Compared with Example 1, the difference is that step (3) adopts a one-step constant current micro-arc oxidation treatment, and the specific process parameters are: oxidation voltage of 500V and current density of 8A / dm³. 2 The positive duty cycle was 20%, the negative duty cycle was 10%, the frequency was 450 Hz, and the oxidation time was 14 min. After micro-arc oxidation, the magnesium alloy sample was removed and placed in a drying oven at 50 ℃ for 30 min to obtain a magnesium alloy sample with a green surface. Other operations were the same as in Example 1. However, this process exhibited a violent discharge reaction in the later stage of micro-arc oxidation, and severe ablation was found at the edges of the magnesium alloy sample, resulting in large pores and cracks on the film surface and poor density.

[0046] Comparative Example 4

[0047] Compared with Example 1, the difference is that in step (2), potassium hydroxide solution is not added to adjust the pH value of the mixed electrolyte, while other operations are the same as in Example 1. The mixed electrolyte without pH adjustment is weakly acidic, and a tip discharge phenomenon occurs during the micro-arc oxidation process. At the same time, there are obvious ablation marks on the surface of the magnesium alloy, and the prepared micro-arc oxidation ceramic film has obvious cracks.

[0048] Comparative Example 5

[0049] Compared to Example 1, the difference lies in that the pH of the coloring electrolyte in step (2) is adjusted to 8. All other operations are the same as in Example 1. Under these conditions, the green ceramic film on the magnesium alloy surface is lighter in color.

[0050] Comparative Example 6

[0051] Compared with Example 1, the difference is that the pH value of the coloring electrolyte in step (2) is adjusted to 14. Other operations are the same as in Example 1. At this time, the mixed electrolyte contains a large number of hydroxide ions, which accumulate in large quantities on the magnesium alloy surface during the micro-arc oxidation process, resulting in a violent micro-arc oxidation arc reaction, large pores in the ceramic film layer, and the generation of cracks.

[0052] Comparative Example 7

[0053] Compared with Example 2, the difference lies in that the oxidation voltage of the first constant current micro-arc oxidation treatment in step (3) is 600V, and the oxidation voltage of the second constant current micro-arc oxidation treatment is 200V. Other operations are the same as in Example 2. During the first constant current micro-arc oxidation treatment, the voltage is high, which greatly shortens the arc initiation time on the magnesium alloy surface. However, due to the high energy, the reaction is violent, which eventually generates large pores on the magnesium alloy surface. During the second constant current micro-arc oxidation treatment, the voltage is low, which prevents the oxide film layer at the pores from repeatedly melting and regenerating. This makes it impossible to repair the large-diameter micropores formed in the first constant current stage, and even the phenomenon of arc extinguishing may occur. Ultimately, this results in high porosity on the ceramic film surface and large pores that cannot block the erosion of the corrosive medium.

[0054] Comparative Example 8

[0055] The difference between Comparative Example 8 and Example 3 is that the current density of the two-step constant current micro-arc oxidation treatment in step (3) is set to 14 A / dm. 2 The other operations are the same as in Example 3. During the first step of constant current micro-arc oxidation, the high current density directly caused large-area ablation marks on the ceramic film layer formed on the magnesium alloy surface, making it impossible to perform the second step of constant current micro-arc oxidation.

[0056] Comparative Example 9

[0057] Compared with Example 3, Comparative Example 9 differs in that the current density of the two-step constant current micro-arc oxidation treatment in step (3) is set to 1.5 A / dm. 2The other operations are the same as in Example 3. During the first step of constant current micro-arc oxidation, the low current density leads to an increased arc initiation time on the magnesium alloy surface, a weaker arc reaction, and a thinner ceramic film. Arc extinction may even occur in the later stages of the first phase. During the second step of constant current micro-arc oxidation, the further reduction in voltage prevents micro-arc oxidation from occurring on the magnesium alloy surface, resulting in a thinner and less dense ceramic film.

[0058] Performance Analysis:

[0059] Figure 1 The images show cross-sectional SEM images of the green ceramic films on the magnesium alloy surface in Example 1(a) and Comparative Example 3(b). It can be seen that the film prepared by the two-step constant-current micro-arc oxidation process with reduced voltage is relatively dense, without large pores or cracks, while the film prepared by the one-step constant-current micro-arc oxidation process clearly shows large pores and cracks.

[0060] Figure 2 The images show surface SEM images of the green ceramic film on the magnesium alloy surface in Example 2(a) and Comparative Example 7(b). It can be seen that in the two-step constant current micro-arc oxidation process using a step-down method, the voltage setting of the first micro-arc oxidation process parameter was too high, and the voltage setting of the second micro-arc oxidation process parameter was too low, ultimately resulting in larger pores in the ceramic film layer on the magnesium alloy surface and reduced corrosion resistance.

[0061] Figure 3 The polarization curves obtained by immersing untreated AZ91 magnesium alloy and magnesium alloys with green ceramic films formed on the surface of Examples 1-3 in a 3.5% NaCl solution for 0.5 h show that the corrosion potential of the magnesium alloy samples obtained after micro-arc oxidation is significantly higher than that of the magnesium alloy substrate, and the corrosion current density and corrosion rate are lower than those of the substrate. This indicates that the green ceramic film obtained on the surface of the magnesium alloy after micro-arc oxidation can greatly improve the corrosion resistance of the magnesium alloy substrate.

[0062] It should be noted that specific conditions are not specified in the embodiments, and conventional conditions are followed. The above are merely preferred embodiments of the present invention, but the present invention is not limited to the above specific embodiments. Those skilled in the art can make obvious improvements, changes, and modifications to some technical features of the foregoing embodiments without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a green ceramic film on a magnesium alloy surface, characterized in that, Includes the following steps: Using a polished and cleaned magnesium alloy as the anode and a stainless steel plate as the cathode, the anode is immersed in a coloring electrolyte and subjected to a two-step constant current micro-arc oxidation process with reduced voltage. After the micro-arc oxidation is completed, the anode is immersed in warm water and then dried to obtain a magnesium alloy with a green ceramic film on the surface. The colored electrolyte includes 15-25 g / L phosphate, 10-15 g / L sodium fluoride, 2-10 g / L iron salt, 22.5-90 g / L triethanolamine and deionized water; the pH value is adjusted to 10-12. The current density of the step-down two-step constant current micro-arc oxidation process is 3~10A / dm³. 2 The oxidation voltage for the first step of constant current micro-arc oxidation treatment is 450~550V; the oxidation voltage for the second step of constant current micro-arc oxidation treatment is 300~450V; during the micro-arc oxidation process, a circulating cooling device is used to keep the temperature of the coloring electrolyte below 20℃. The parameters for the first step of constant current micro-arc oxidation treatment are: oxidation voltage of 450~550V, and current density of 3~10A / dm³. 2 Positive duty cycle 10~20%, negative duty cycle 5~10%, frequency 400~500Hz, oxidation time 5~10min; The parameters for the second step, constant current micro-arc oxidation, are: oxidation voltage of 300~450V, and current density of 3~10A / dm³. 2 Positive duty cycle 10~20%, negative duty cycle 5~10%, frequency 400~500Hz, oxidation time 5~10min.

2. The method for preparing a green ceramic film on a magnesium alloy surface according to claim 1, characterized in that, The specific method for grinding and cleaning is as follows: After grinding the magnesium alloy with SiC sandpaper of 400#, 800#, 1500# and 2000# in stages, polish it with a polishing cloth, clean it for 5 minutes under anhydrous ethanol and ultrasonic conditions, rinse it with deionized water, and finally blow it dry for later use.

3. The method for preparing a green ceramic film on a magnesium alloy surface according to claim 1, characterized in that, The method for preparing the colored electrolyte is as follows: First, phosphate and sodium fluoride in a mass ratio of 2:1 are added to deionized water and stirred continuously to ensure complete dissolution, thus obtaining the main salt electrolyte; then, triethanolamine, an organic additive, is added to the iron salt solution and stirred continuously to ensure that the triethanolamine fully complexes with the iron salt, thus obtaining the metal salt electrolyte; finally, the metal salt electrolyte and the main salt electrolyte are mixed, and the pH value of the solution is adjusted to 10-12 using an alkaline pH adjuster to obtain the colored electrolyte; wherein the alkaline pH adjuster is potassium hydroxide or sodium hydroxide.

4. The method for preparing a green ceramic film on a magnesium alloy surface according to claim 1, characterized in that, The phosphate is any one of sodium phosphate, sodium hexametaphosphate, or sodium polyphosphate; the iron salt is any one of ferric ammonium sulfate or ferric ammonium oxalate.

5. The method for preparing a green ceramic film on a magnesium alloy surface according to claim 1, characterized in that, The specific method for soaking in warm water is as follows: Immerse the processed magnesium alloy sample in warm water at 20~50℃ for 13~17 minutes.

6. The method for preparing a green ceramic film on a magnesium alloy surface according to claim 1, characterized in that, The drying method after soaking in warm water is as follows: first dry with a hair dryer, then put it in a drying oven for 27~33 minutes at a temperature of 45~55℃.

7. The method for preparing a green ceramic film on a magnesium alloy surface according to any one of claims 1 to 6, characterized in that, The thickness of the green ceramic film on the magnesium alloy surface is 10~20μm.

Images