An electrolyte for preparing an amorphous matte coating on a magnesium-lithium alloy surface and its application

Abstract

This invention belongs to the field of magnesium-lithium alloy surface treatment technology, specifically relating to an electrolyte for preparing an amorphous matte coating on the surface of magnesium-lithium alloys and its application. The electrolyte of this invention consists of the following components: sodium orthovanadate 20g / L~30g / L, sodium metagermanate 5g / L~10g / L, ammonium dihydrogen phosphate 5g / L~10g / L, ammonium fluoride 2g / L~4g / L, sodium tripolyphosphate 5g / L~10g / L, triethanolamine 5mL / L~10mL / L, and glacial acetic acid 10mL / L~20mL / L. The magnesium-lithium alloy is first pretreated, then placed in the electrolyte for micro-arc oxidation, and finally post-treated to prepare a dense and uniform amorphous, highly corrosion-resistant matte coating on the surface of the magnesium-lithium alloy. The coating exhibits excellent corrosion resistance and matte properties. By controlling the composition and content of the electrolyte, this invention ensures that the electrolyte pH is approximately neutral, improving the stability and safety of the electrolyte and facilitating industrial production.

Description

Technical Field

[0001] This invention belongs to the field of magnesium-lithium alloy surface treatment technology, specifically relating to an electrolyte for preparing an amorphous matte coating on the surface of magnesium-lithium alloy and its application. Background Technology

[0002] With increasing demands for information volume and imaging quality in the exploration of Earth and other celestial bodies, space optical remote sensors not only need high resolution and good image quality, but also high reliability while maintaining a lightweight structure. During on-orbit operation, sunlight reflected from the optical structure surface may reach the sensor's image plane, forming stray light that is not an imaging source. This can reduce the imaging contrast of the optical system, blur the image, and even prevent the system from retrieving the target, severely impacting the overall monitoring and identification capabilities. Therefore, it is necessary to prepare a black matte coating on the optical structure surface. This coating, with its high absorption rate of sunlight in the space environment, can absorb and weaken non-imaging sensitive light within the optical detector's path, thereby eliminating stray light and improving the sensor's imaging quality.

[0003] Magnesium-lithium alloys are the lightest alloys, possessing high specific strength, specific stiffness, electromagnetic shielding properties, and excellent formability, making them ideal materials for lightweight components. Therefore, they have attracted significant attention in aerospace, electronics, military, and many other high-tech fields. The application of magnesium-lithium alloys in space optical systems can reduce weight by 20% to 30%, which is of great significance for the lightweighting of these systems. However, magnesium-lithium alloys themselves have low solar absorption rates, lack anti-glare properties, and exhibit very poor corrosion resistance, leading to corrosion during transportation and storage. Therefore, a coating with high corrosion resistance and anti-glare properties is needed on their surface to meet operational requirements.

[0004] Micro-arc oxidation technology is simple, low-cost, has minimal environmental impact, and is highly applicable to complex workpieces. Micro-arc oxidation coatings exhibit good film-substrate adhesion and a rough, porous surface, resulting in a large specific surface area and strong adsorption capacity. In particular, black ceramic coatings prepared using micro-arc oxidation technology show great promise for matte coating applications. Current reports on magnesium-lithium alloy matte coatings mainly focus on high-absorption black paints; however, these paints suffer from poor adhesion, easy decomposition, and poor corrosion resistance, significantly limiting their application. Summary of the Invention

[0005] The technical problem this invention aims to solve is to address the shortcomings of the prior art by providing an electrolyte for preparing an amorphous, highly corrosion-resistant, matte coating on the surface of a magnesium-lithium alloy and its application. This electrolyte maintains a near-neutral pH by controlling the composition and content of each component, which is both environmentally friendly and improves the electrolyte's stability. The application of this electrolyte involves preparing an amorphous, highly corrosion-resistant, matte coating in situ on the surface of a magnesium-lithium alloy using a micro-arc oxidation process. This electrolyte and process enhance the corrosion resistance and matte finish of the coating.

[0006] The electrolyte for the amorphous, high-corrosion-resistant, matte coating on the surface of magnesium-lithium alloys described in this invention comprises the following components and contents: sodium orthovanadate 20g / L~30g / L, sodium metagermanate 5g / L~10g / L, ammonium dihydrogen phosphate 5g / L~10g / L, ammonium fluoride 2g / L~4g / L, sodium tripolyphosphate 5g / L~10g / L, triethanolamine 5mL / L~10mL / L, glacial acetic acid 10mL / L~20mL / L, and the remainder is deionized water; the pH of this electrolyte is 6.5~7.5.

[0007] This invention improves the stability and safety of the electrolyte by controlling the composition and content of each component, ensuring a near-neutral pH, which is beneficial for industrial production. The micro-arc oxidation arc discharge in this electrolyte exhibits a softer, more uniform, and denser spark, thus enhancing the coating's density and corrosion resistance. Magnesium alloys are inherently reactive; if the ion concentration in the electrolyte is too high or unevenly distributed (resulting in precipitation or suspended matter), severe localized heat accumulation can occur during micro-arc oxidation, leading to ablation pits on the coating surface. The electrolyte formulation of this invention, containing ammonium dihydrogen phosphate, sodium tripolyphosphate, and triethanolamine, all have the effect of complexing metal cations, thereby promoting the dissolution of vanadium and germanium salts, resulting in a solution free of precipitation and suspended matter, with a uniform ion concentration distribution, effectively inhibiting ablation. This electrolyte can improve the ablation phenomenon of magnesium-lithium alloy substrates during micro-arc oxidation, preventing white ablation pits in the black coating, promoting the formation of a dense and uniform coating, thereby improving the coating's corrosion resistance and matting properties, and ensuring a high yield of black coatings.

[0008] The application of the electrolyte for the amorphous, highly corrosion-resistant, matte coating on the surface of magnesium-lithium alloys described in this invention includes the following steps:

[0009] Step 1: After polishing the magnesium-lithium alloy, activate it with a surface activation solution.

[0010] Step 2: Prepare the electrolyte. The components and concentrations of the electrolyte are as follows: sodium orthovanadate 20g / L~30g / L, sodium metagermanate 5g / L~10g / L, ammonium dihydrogen phosphate 5g / L~10g / L, ammonium fluoride 2g / L~4g / L, sodium tripolyphosphate 5g / L~10g / L, triethanolamine 5mL / L~10mL / L, and glacial acetic acid 10mL / L~20mL / L. Add each reagent to deionized water in sequence and stir continuously until completely dissolved to prepare a near-neutral solution. Then, place the near-neutral solution in the electrolytic cell and let it stand before using it as the electrolyte.

[0011] Step 3: Immerse the magnesium-lithium alloy treated in Step 1 completely in the electrolyte as the anode, use a stainless steel sheet as the cathode, and then process it according to the micro-arc oxidation process to prepare a coating on the surface of the magnesium-lithium alloy.

[0012] Step 4: Immerse the magnesium-lithium alloy that has undergone micro-arc oxidation treatment in Step 3 in the post-treatment solution and then perform ultrasonic treatment to obtain an amorphous, highly corrosion-resistant matte coating on the surface of the magnesium-lithium alloy.

[0013] Step one includes the following specific steps: The magnesium-lithium alloy is polished step by step using water-resistant abrasive paper of 320#, 600#, 800#, 1000#, 1500#, and 2000# and metallographic abrasive paper in sequence. The magnesium-lithium alloy is then activated with a surface activation solution at room temperature for 30 seconds. After that, the surface of the magnesium-lithium alloy is rinsed clean with deionized water, ultrasonically cleaned in anhydrous ethanol for 10 minutes, and then dried for later use, thus completing the pretreatment.

[0014] The surface activation solution described in step one consists of 5%–10% nitric acid, 20%–30% citric acid, and the remainder is deionized water. Because magnesium-lithium alloys have high activity and poor corrosion resistance, oxide scale will form on their surface when stored in an atmospheric environment. Therefore, a surface activation solution is used to activate the surface of the magnesium-lithium alloy substrate to obtain a fresh substrate surface.

[0015] The electrolyte in step two has a pH of 6.5-7.5, and glacial acetic acid is used to adjust the pH. Firstly, glacial acetic acid is an organic acid, and its addition to the electrolyte will not introduce new impurities, thus maintaining the stability of the electrolyte composition. Secondly, the electrolyte is a near-neutral solution that is harmless to human skin, making it more environmentally friendly and safer. Finally, a near-neutral solution can effectively prevent the precipitation of metal ions, resulting in better stability.

[0016] The micro-arc oxidation process described in step three is as follows: the micro-arc oxidation treatment uses a constant voltage DC pulse power supply with a voltage of 400V~450V, a frequency of 1500Hz~2000Hz, a duty cycle of 10%~20%, and an oxidation time of 15min~20min. During the micro-arc oxidation treatment, a chiller is used to control the temperature of the electrolyte at 10℃~15℃.

[0017] The specific operation process is as follows: the voltage is boosted from 0V to 220V and held for 1 minute, then boosted at a rate of 30V / min to reach the target voltage for micro-arc oxidation treatment. After the micro-arc oxidation treatment is completed, the voltage is first reduced to 30V and held for 1 minute, then reduced to 0V.

[0018] By controlling the micro-arc oxidation process, it is possible to ensure that the coating grows densely, avoid coating ablation caused by excessively high voltage, and avoid coating thickness and insufficient blackness caused by excessively low voltage, thus affecting its performance. This ensures that all properties of the coating reach their optimal levels. This invention also avoids coating ablation and excessively large surface pores at high temperatures by controlling the temperature of the electrolyte during the micro-arc oxidation process, thereby preventing the coating from affecting its corrosion resistance.

[0019] The post-treatment solution in step four consists of 40 g / L to 50 g / L sodium fluoride, with the remainder being deionized water. The ultrasonic treatment lasts for 20 to 30 minutes at a temperature of 40°C to 50°C. After removal, the solution is rinsed thoroughly with deionized water and dried to complete the post-treatment. By immersing the solution in the post-treatment solution and subjecting it to ultrasonic vibration, the sodium fluoride solution can enter the through-pores of the micro-arc oxidation coating and react with the magnesium-lithium alloy substrate, forming a dense magnesium fluoride film that blocks the through-pores, preventing corrosive media from contacting the substrate. This process does not alter the porous surface morphology of the micro-arc oxidation coating, thereby improving the corrosion resistance of the amorphous, high-corrosion-resistant matte coating.

[0020] This invention employs a near-neutral electrolyte to perform micro-arc oxidation treatment on the surface of a magnesium-lithium alloy, resulting in an in-situ grown amorphous, highly corrosion-resistant, matte coating. By using a constant-voltage DC pulse power supply and maintaining stable voltage control in the low-voltage region, the amorphous, highly corrosion-resistant, matte coating grows more densely in the early stages of micro-arc oxidation.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. This invention ensures that the pH of the electrolyte is near neutral by controlling the composition and content of each component. Near-neutral electrolyte is environmentally friendly and highly stable, which improves the economy of the electrolyte and is beneficial to industrial production.

[0023] 2. When the electrolyte of the present invention is used to perform micro-arc oxidation treatment on magnesium-lithium alloy samples, the arc discharge on the sample surface is in a soft spark state and is more uniform and dense. This can improve the phenomenon of ablation of the magnesium-lithium alloy substrate during micro-arc oxidation, avoid the formation of ablation points in the coating, and facilitate the formation of a dense and uniform micro-arc oxidation coating. This improves the corrosion resistance and matting performance of the coating and ensures the coating yield.

[0024] 3. This invention employs a micro-arc oxidation process and post-treatment to grow an amorphous, highly corrosion-resistant matte coating in situ on the surface of magnesium-lithium alloys. The coating structure is continuous and dense without through-holes. The amorphous nature of the coating significantly improves corrosion resistance, achieving a corrosion current density of 7.247 × 10⁻⁶ in a 3.5% NaCl solution. -8 A / cm 2 Compared to magnesium-lithium alloy substrates, the corrosion current density decreased by four orders of magnitude. Post-treatment of the micro-arc oxidation coating with sodium fluoride resulted in a continuous, dense coating structure without through-holes. This invention first adds ammonium fluoride to the electrolyte, and then uses sodium fluoride in the subsequent treatment, achieving better results compared to micro-arc oxidation coatings without post-treatment.

[0025] 4. Using the electrolyte and micro-arc oxidation process of this invention, an amorphous, highly corrosion-resistant, matte coating can be prepared on the surface of magnesium-lithium alloys. The coating has a high V content and introduces Ge, greatly improving the solar absorption rate to 0.98. Existing technologies often use sodium metavanadate as a colorant. This invention discovers that using a combination of sodium orthovanadate and sodium metagermanate as a colorant has better results than using sodium metavanadate alone. The electrolyte is clearer, without flocculent precipitates, and its stability is much higher than that of sodium metavanadate. The electrolyte in this invention uses sodium orthovanadate and sodium metagermanate as the main coloring salts. Under the action of an electric field, VO 3- and Ge 2+ The electrolyte migrates into the discharge channel and participates in the micro-arc oxidation reaction. Through a combination of plasma thermochemical and electrochemical reactions, the reactants undergo further phase transformation at high temperatures, forming a complex composite salt. This salt then reacts with the magnesium-lithium matrix material to form a black coating of V₂O₅-GeO₂-MgO-MgF₂. Compared to using sodium metavanadate or sodium germanate alone, this microstructure exhibits superior solar absorption and significantly improved corrosion resistance. Using sodium metavanadate or sodium germanate alone results in some white or gray substances in the coating, affecting film integrity. The coating obtained by combining sodium orthovanadate and sodium germanate has a better matting effect, greatly improving solar absorption, with less color difference and a uniform, smooth surface. Furthermore, using sodium metavanadate alone results in many flocculent precipitates, which is detrimental to the recycling of the electrolyte.

[0026] 5. The amorphous high corrosion-resistant matting coating prepared on the surface of magnesium-lithium alloy using the electrolyte, micro-arc oxidation process and post-treatment process of the present invention improves the corrosion resistance of the coating while maintaining its excellent matting performance. Attached Figure Description

[0027] Figure 1 This is a macroscopic morphology diagram of the LA103Z magnesium-lithium alloy with an amorphous, highly corrosion-resistant, matte coating in Example 1 of the present invention.

[0028] Figure 2 This is a scanning electron microscope image of the surface of the LA103Z magnesium-lithium alloy with an amorphous, highly corrosion-resistant, matte coating in Example 1 of the present invention.

[0029] Figure 3 This is a cross-sectional scanning electron microscope image of the LA103Z magnesium-lithium alloy with an amorphous, highly corrosion-resistant, matte coating, as described in Example 1 of the present invention.

[0030] Figure 4 The X-ray diffraction patterns are those of the amorphous, highly corrosion-resistant matting coatings prepared on the surface of LA103Z magnesium-lithium alloy in Examples 1 and 2 of this invention.

[0031] Figure 5 XPS spectra of the amorphous high corrosion-resistant matting coating prepared on the surface of LA103Z magnesium-lithium alloy in Example 1 of this invention; wherein, (a) represents MgO and MgF2, (b) represents V2O5 and MgO, (c) represents V2O5, (d) represents MgF2, (e) represents GeO2, and (f) represents different elements.

[0032] Figure 6 Electrochemical polarization curves of the amorphous, highly corrosion-resistant matting coatings prepared on the surface of the LA103Z magnesium-lithium alloy substrate and in 3.5% NaCl solution for Examples 1 and 2. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. It should be noted that the embodiments described in this invention are only for further explanation and illustration, and not for limiting their application scope. Based on this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.

[0034] Example 1

[0035] The electrolyte in this embodiment consists of the following components: sodium orthovanadate 30 g / L, sodium germanate 10 g / L, ammonium dihydrogen phosphate 10 g / L, ammonium fluoride 4 g / L, sodium tripolyphosphate 10 g / L, triethanolamine 10 mL / L, glacial acetic acid 10 mL / L, and the remainder is deionized water.

[0036] The application method of the electrolyte in this embodiment includes the following steps:

[0037] Step 1: Select an LA103Z magnesium-lithium alloy sheet with dimensions (length × width × thickness) of 15mm × 15mm × 3mm as the substrate. Use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy in stages. Then, activate the magnesium-lithium alloy for 30 seconds at room temperature with a surface activation solution composed of 10% nitric acid, 30% citric acid, and the remainder deionized water. After that, rinse the surface of the magnesium-lithium alloy with deionized water, and then place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes. Blow it dry and set it aside for later use. This completes the pretreatment.

[0038] Step 2: Prepare the electrolyte. The components and their contents of the electrolyte are as follows: sodium orthovanadate 30g / L, sodium germanate 10g / L, ammonium dihydrogen phosphate 10g / L, ammonium fluoride 4g / L, sodium tripolyphosphate 10g / L, triethanolamine 10mL / L, and glacial acetic acid 10mL / L. Add each reagent to deionized water in sequence and stir continuously until completely dissolved to prepare a near-neutral solution with a pH of 7.5. Then, place the near-neutral solution in the electrolytic cell and let it stand before using it as the electrolyte.

[0039] Step 3: The pretreated magnesium-lithium alloy from Step 1 is clamped in an electrolytic cell and completely immersed in the electrolyte as the anode. A stainless steel sheet is used as the cathode. Then, a micro-arc oxidation process is performed to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. The micro-arc oxidation process is as follows: a constant voltage DC pulse power supply is used, with a voltage of 450V, a frequency of 2000Hz, a duty cycle of 10%, and an oxidation time of 20 minutes. During the micro-arc oxidation process, a chiller is used to control the electrolyte temperature at 10℃~15℃. Specifically, the voltage is increased from 0V to 220V and held for 1 minute, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is reduced to 30V and held for 1 minute, then reduced back to 0V.

[0040] Step 4: Immerse the magnesium-lithium alloy treated with micro-arc oxidation in Step 3 completely in the post-treatment solution, which is prepared with 50g / L sodium fluoride and the remainder deionized water. Then place it in an ultrasonic bath and vibrate and sonicate for 30 minutes at 50℃. After that, take it out, rinse it with deionized water, and dry it to complete the post-treatment. An amorphous high corrosion-resistant matte coating is obtained on the surface of the magnesium-lithium alloy substrate.

[0041] Energy dispersive spectroscopy (EDS) analysis was performed on the amorphous high corrosion resistance matting coating prepared on the surface of LA103Z magnesium-lithium alloy in this embodiment. The results are shown in Table 1.

[0042] Table 1. EDS analysis results of the matte coating prepared in Example 1:

[0043] element V Ge Mg O F Total Atom percentage (%) 17.35 7.22 28.60 42.78 4.05 100 .

[0044] As shown in Table 1, the amorphous, high-corrosion-resistant matting coating prepared on the surface of LA103Z magnesium-lithium alloy in this embodiment is composed of elements such as V, Ge, Mg, O, and F. The coating contains transition metal elements V and Ge, which contain unsaturated d orbitals, facilitating the transfer of electrons from the outermost electron shell to the second outermost electron shell, thereby absorbing light and improving the matting performance of the coating.

[0045] from Figure 1 It is known that the coating is black with uniform color and complete morphology, without defects such as ablation, peeling, or cracking. The black coating has a high solar absorption rate and excellent matting performance. The solar absorption rate of this amorphous high corrosion-resistant matting coating is 0.98 (refer to GJB 2502.2-2015).

[0046] from Figure 2 It can be seen that this amorphous, highly corrosion-resistant matting coating exhibits a typical micro-arc oxidation surface morphology, which increases the specific surface area of ​​the coating and is beneficial to improving the coating's absorption rate of sunlight. From Figure 3 It can be seen that the amorphous high corrosion-resistant matte coating is tightly bonded to the LA103Z magnesium-lithium alloy substrate, and the coating is highly dense and free of through-pores, which is beneficial to enhancing the corrosion resistance of the coating. From Figure 4 The results of Example 1 show that the high corrosion-resistant matte coating prepared on the surface of LA103Z magnesium-lithium alloy exhibits a typical amorphous state, and the amorphous coating has stronger corrosion resistance. Figure 5 As can be seen from (a), (b), (c), (d), (e), and (f) in the figure, the main components of the amorphous high corrosion-resistant matte coating in this embodiment are V2O5, GeO2, MgO, and MgF2.

[0047] from Figure 6 The results of Example 1 show that, in electrochemical testing in 3.5% NaCl solution, the corrosion current I of the amorphous high corrosion-resistant matte coating prepared on the surface of LA103Z magnesium-lithium alloy is... corr =7.247×10 -8 A / cm 2 The corrosion current of the LA103Z magnesium-lithium alloy matrix is ​​1.526 × 10⁻⁶. -4 A / cm 2 The corrosion current of this amorphous, highly corrosion-resistant matte coating was reduced by four orders of magnitude, indicating a significant improvement in corrosion resistance and providing excellent corrosion protection for the LA103Z magnesium-lithium alloy substrate.

[0048] Example 2

[0049] The electrolyte in this embodiment consists of the following components: 20 g / L sodium orthovanadate, 5 g / L sodium germanate, 5 g / L ammonium dihydrogen phosphate, 2 g / L ammonium fluoride, 5 g / L sodium tripolyphosphate, 5 mL / L triethanolamine, 20 mL / L glacial acetic acid, and the remainder is deionized water.

[0050] The application method of the electrolyte in this embodiment includes the following steps:

[0051] Step 1: Select an LA103Z magnesium-lithium alloy sheet with dimensions (length × width × thickness) of 15mm × 15mm × 3mm as the substrate. Use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy in stages. Then, activate the magnesium-lithium alloy for 30 seconds at room temperature with a surface activation solution composed of 5% nitric acid, 20% citric acid, and the remainder deionized water. After that, rinse the surface of the magnesium-lithium alloy with deionized water, and then place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes. Blow it dry and set it aside for later use. This completes the pretreatment.

[0052] Step 2: Prepare the electrolyte. The components and concentrations of the electrolyte are as follows: sodium orthovanadate 20 g / L, sodium germanate 5 g / L, ammonium dihydrogen phosphate 5 g / L, ammonium fluoride 2 g / L, sodium tripolyphosphate 5 g / L, triethanolamine 5 mL / L, and glacial acetic acid 20 mL / L. Add each reagent to deionized water in sequence and stir continuously until completely dissolved to prepare a near-neutral solution with a pH of 6.5. Then, place the near-neutral solution in the electrolytic cell and let it stand before using it as the electrolyte.

[0053] Step 3: The pretreated magnesium-lithium alloy from Step 1 is clamped in an electrolytic cell and completely immersed in the electrolyte as the anode. A stainless steel sheet is used as the cathode. Then, a micro-arc oxidation process is performed to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. The micro-arc oxidation process is as follows: a constant voltage DC pulse power supply is used, with a voltage of 400V, a frequency of 1500Hz, a duty cycle of 20%, and an oxidation time of 15min. During the micro-arc oxidation process, a chiller is used to control the electrolyte temperature at 10℃~15℃. Specifically, the voltage is increased from 0V to 220V and held for 1min, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is reduced to 30V and held for 1min, then reduced back to 0V.

[0054] Step 4: The magnesium-lithium alloy treated by micro-arc oxidation in Step 3 is completely immersed in the post-treatment solution, which is prepared by 40 g / L sodium fluoride and the remainder is deionized water. Then, it is placed in an ultrasonic bath and ultrasonically vibrated for 20 minutes at a temperature of 40°C. After that, it is taken out, rinsed with deionized water, and dried to complete the post-treatment. An amorphous high corrosion-resistant matte coating is obtained on the surface of the magnesium-lithium alloy substrate.

[0055] from Figure 4 The results of Example 2 show that the high corrosion-resistant matte coating prepared on the surface of LA103Z magnesium-lithium alloy using the process of Example 2 also exhibits a typical amorphous state, which improves the corrosion resistance of the coating.

[0056] from Figure 6 The calculation results of Example 2 show that the corrosion current I of the amorphous high corrosion-resistant matte coating prepared on the surface of LA103Z magnesium-lithium alloy using the process of Example 2 is... corr =9.659×10 -8 A / cm 2 In Example 2, the amorphous high corrosion-resistant matting coating has a solar absorption rate of 0.95.

[0057] Example 3

[0058] The electrolyte in this embodiment consists of the following components: sodium orthovanadate 25 g / L, sodium germanate 8 g / L, ammonium dihydrogen phosphate 8 g / L, ammonium fluoride 3 g / L, sodium tripolyphosphate 8 g / L, triethanolamine 8 mL / L, glacial acetic acid 15 mL / L, and the remainder is deionized water.

[0059] The application method of the electrolyte in this embodiment includes the following steps:

[0060] Step 1: Select an LA103Z magnesium-lithium alloy sheet with dimensions (length × width × thickness) of 15mm × 15mm × 3mm as the substrate. Use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy in stages. Then, activate the magnesium-lithium alloy for 30 seconds at room temperature with a surface activation solution composed of 8% nitric acid, 25% citric acid, and the remainder deionized water. After that, rinse the surface of the magnesium-lithium alloy with deionized water, and then place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes. Blow it dry and set it aside for later use. This completes the pretreatment.

[0061] Step 2: Prepare the electrolyte. The components and their contents of the electrolyte are as follows: sodium orthovanadate 25 g / L, sodium germanate 8 g / L, ammonium dihydrogen phosphate 8 g / L, ammonium fluoride 3 g / L, sodium tripolyphosphate 8 g / L, triethanolamine 8 mL / L, and glacial acetic acid 15 mL / L. Add each reagent to deionized water in sequence and stir continuously until completely dissolved to prepare a near-neutral solution with a pH of 7.2. Then, place the near-neutral solution in the electrolytic cell and let it stand before using it as the electrolyte.

[0062] Step 3: The pretreated magnesium-lithium alloy from Step 1 is clamped in an electrolytic cell and completely immersed in the electrolyte as the anode. A stainless steel sheet is used as the cathode. Then, a micro-arc oxidation process is performed to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. The micro-arc oxidation process is as follows: a constant voltage DC pulse power supply is used, with a voltage of 430V, a frequency of 1800Hz, a duty cycle of 15%, and an oxidation time of 18 minutes. During the micro-arc oxidation process, a chiller is used to control the electrolyte temperature at 10℃~15℃. Specifically, the voltage is increased from 0V to 220V and held for 1 minute, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is reduced to 30V and held for 1 minute, then reduced back to 0V.

[0063] Step 4: The magnesium-lithium alloy treated with micro-arc oxidation in Step 3 is completely immersed in the post-treatment solution, which is prepared with 45g / L sodium fluoride and the remainder deionized water. Then, it is placed in an ultrasonic bath and vibrated for 25 minutes at a temperature of 45℃. After that, it is taken out, rinsed with deionized water, and dried to complete the post-treatment. An amorphous high corrosion-resistant matte coating is obtained on the surface of the magnesium-lithium alloy substrate.

[0064] The corrosion current I of the amorphous, highly corrosion-resistant matte coating prepared on the surface of LA103Z magnesium-lithium alloy using the process of Example 3. corr =8.746×10 -8 A / cm 2 In Example 3, the amorphous high corrosion-resistant matting coating has a solar absorption rate of 0.96.

[0065] Comparative Example 1

[0066] The electrolyte in this comparative example does not contain sodium germanate, and the rest of the methods are the same as in Example 1.

[0067] The electrolyte consists of the following components: sodium orthovanadate 30 g / L, ammonium dihydrogen phosphate 10 g / L, ammonium fluoride 4 g / L, sodium tripolyphosphate 10 g / L, triethanolamine 10 mL / L, glacial acetic acid 10 mL / L, and the remainder is deionized water.

[0068] The application method of electrolyte includes the following steps:

[0069] Step 1: Select an LA103Z magnesium-lithium alloy sheet with dimensions (length × width × thickness) of 15mm × 15mm × 3mm as the substrate. Use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy in stages. Then, activate the magnesium-lithium alloy for 30 seconds at room temperature with a surface activation solution composed of 10% nitric acid, 30% citric acid, and the remainder deionized water. After that, rinse the surface of the magnesium-lithium alloy with deionized water, and then place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes. Blow it dry and set it aside for later use. This completes the pretreatment.

[0070] Step 2: Prepare the electrolyte. The components and concentrations of the electrolyte are as follows: sodium orthovanadate 30 g / L, ammonium dihydrogen phosphate 10 g / L, ammonium fluoride 4 g / L, sodium tripolyphosphate 10 g / L, triethanolamine 10 mL / L, and glacial acetic acid 10 mL / L. Add each reagent to deionized water in sequence and stir continuously until completely dissolved to prepare a near-neutral solution with a pH of 7.5. Then, place the near-neutral solution in the electrolytic cell and let it stand before using it as the electrolyte.

[0071] Step 3: The pretreated magnesium-lithium alloy from Step 1 is clamped in an electrolytic cell and completely immersed in the electrolyte as the anode. A stainless steel sheet is used as the cathode. Then, a micro-arc oxidation process is performed to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. The micro-arc oxidation process is as follows: a constant voltage DC pulse power supply is used, with a voltage of 450V, a frequency of 2000Hz, a duty cycle of 10%, and an oxidation time of 20min. During the micro-arc oxidation process, a chiller is used to control the electrolyte temperature at 10℃~15℃. Specifically, the voltage is increased from 0V to 220V and held for 1min, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is reduced to 30V and held for 1min, then reduced back to 0V.

[0072] Step 4: The magnesium-lithium alloy treated by micro-arc oxidation in Step 3 is completely immersed in the post-treatment solution, which is prepared by 50 g / L sodium fluoride and the remainder is deionized water. Then, it is placed in an ultrasonic bath and vibrated for 30 minutes at a temperature of 50°C. After that, it is taken out, rinsed with deionized water, dried and post-treated to obtain a matte coating of Comparative Example 1 on the surface of the magnesium-lithium alloy substrate.

[0073] Comparative Example 2

[0074] This comparative example does not undergo post-treatment in the post-treatment solution; the remaining methods are the same as in Example 2.

[0075] The electrolyte consists of the following components: sodium orthovanadate 20 g / L, sodium germanate 5 g / L, ammonium dihydrogen phosphate 5 g / L, ammonium fluoride 2 g / L, sodium tripolyphosphate 5 g / L, triethanolamine 5 mL / L, and glacial acetic acid 20 mL / L.

[0076] The application method of electrolyte includes the following steps:

[0077] Step 1: Select an LA103Z magnesium-lithium alloy sheet with dimensions (length × width × thickness) of 15mm × 15mm × 3mm as the substrate. Use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy in stages. Then, activate the magnesium-lithium alloy for 30 seconds at room temperature with a surface activation solution composed of 5% nitric acid, 20% citric acid, and the remainder deionized water. After that, rinse the surface of the magnesium-lithium alloy with deionized water, and then place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes. Blow it dry and set it aside for later use. This completes the pretreatment.

[0078] Step 2: Prepare the electrolyte. The components and concentrations of the electrolyte are as follows: sodium orthovanadate 20 g / L, sodium germanate 5 g / L, ammonium dihydrogen phosphate 5 g / L, ammonium fluoride 2 g / L, sodium tripolyphosphate 5 g / L, triethanolamine 5 mL / L, and glacial acetic acid 20 mL / L. Add each reagent to deionized water in sequence and stir continuously until completely dissolved to prepare a near-neutral solution with a pH of 6.5. Then, place the near-neutral solution in the electrolytic cell and let it stand before using it as the electrolyte.

[0079] Step 3: The pretreated magnesium-lithium alloy from Step 1 is clamped in an electrolytic cell and completely immersed in the electrolyte as the anode. A stainless steel sheet is used as the cathode. Then, a micro-arc oxidation process is performed to prepare a micro-arc oxidation coating on the magnesium-lithium alloy surface. The micro-arc oxidation process is as follows: a constant voltage DC pulse power supply is used, with a voltage of 400V, a frequency of 1500Hz, a duty cycle of 20%, and an oxidation time of 15min. During the micro-arc oxidation process, a chiller is used to control the electrolyte temperature at 10℃~15℃. Specifically, the voltage is increased from 0V to 220V and held for 1min, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is reduced to 30V and held for 1min, then reduced back to 0V. A matte coating (Comparative Example 2) is obtained on the magnesium-lithium alloy substrate surface.

[0080] Comparative Example 3

[0081] In this comparative example, sodium orthovanadate in the electrolyte was replaced with sodium metavanadate, and the rest of the preparation method was the same as in Example 2.

[0082] The electrolyte consists of the following components: sodium metavanadate 20 g / L, sodium metagermanate 5 g / L, ammonium dihydrogen phosphate 5 g / L, ammonium fluoride 2 g / L, sodium tripolyphosphate 5 g / L, triethanolamine 5 mL / L, glacial acetic acid 20 mL / L, and the remainder is deionized water.

[0083] The application method of electrolyte includes the following steps:

[0084] Step 1: Select an LA103Z magnesium-lithium alloy sheet with dimensions (length × width × thickness) of 15mm × 15mm × 3mm as the substrate. Use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy in stages. Then, activate the magnesium-lithium alloy for 30 seconds at room temperature with a surface activation solution composed of 5% nitric acid, 20% citric acid, and the remainder deionized water. After that, rinse the surface of the magnesium-lithium alloy with deionized water, and then place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes. Blow it dry and set it aside for later use. This completes the pretreatment.

[0085] Step 2: Prepare the electrolyte. The components and their contents of the electrolyte are as follows: sodium metavanadate 20 g / L, sodium metagermate 5 g / L, ammonium dihydrogen phosphate 5 g / L, ammonium fluoride 2 g / L, sodium tripolyphosphate 5 g / L, triethanolamine 5 mL / L, and glacial acetic acid 20 mL / L. Add each reagent to deionized water in sequence and stir continuously until completely dissolved to prepare a near-neutral solution with a pH of 6.5. Then, place the near-neutral solution in the electrolytic cell and let it stand before using it as the electrolyte.

[0086] Step 3: The pretreated magnesium-lithium alloy from Step 1 is clamped in an electrolytic cell and completely immersed in the electrolyte as the anode. A stainless steel sheet is used as the cathode. Then, a micro-arc oxidation process is performed to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. The micro-arc oxidation process is as follows: a constant voltage DC pulse power supply is used, with a voltage of 400V, a frequency of 1500Hz, a duty cycle of 20%, and an oxidation time of 15min. During the micro-arc oxidation process, a chiller is used to control the electrolyte temperature at 10℃~15℃. Specifically, the voltage is increased from 0V to 220V and held for 1min, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is reduced to 30V and held for 1min, then reduced back to 0V.

[0087] Step 4: The magnesium-lithium alloy treated by micro-arc oxidation in Step 3 is completely immersed in the post-treatment solution, which is prepared by 40 g / L sodium fluoride and the remainder is deionized water. Then, it is placed in an ultrasonic bath and ultrasonically vibrated for 20 minutes at a temperature of 40°C. After that, it is taken out, rinsed with deionized water, dried and post-treated to obtain a matte coating of Comparative Example 3 on the surface of the magnesium-lithium alloy substrate.

[0088] Comparative Example 4

[0089] In this comparative example, sodium germanate was used to replace sodium orthovanadate in the electrolyte in an equal amount, and the rest of the methods were the same as in Example 2.

[0090] The electrolyte consists of the following components: sodium germanate 25 g / L, ammonium dihydrogen phosphate 5 g / L, ammonium fluoride 2 g / L, sodium tripolyphosphate 5 g / L, triethanolamine 5 mL / L, glacial acetic acid 20 mL / L, and the remainder is deionized water.

[0091] The application method of electrolyte includes the following steps:

[0092] Step 1: Select an LA103Z magnesium-lithium alloy sheet with dimensions (length × width × thickness) of 15mm × 15mm × 3mm as the substrate. Use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy in stages. Then, activate the magnesium-lithium alloy for 30 seconds at room temperature with a surface activation solution composed of 5% nitric acid, 20% citric acid, and the remainder deionized water. After that, rinse the surface of the magnesium-lithium alloy with deionized water, and then place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes. Blow it dry and set it aside for later use. This completes the pretreatment.

[0093] Step 2: Prepare the electrolyte. The components and concentrations of the electrolyte are as follows: sodium germanate 25 g / L, ammonium dihydrogen phosphate 5 g / L, ammonium fluoride 2 g / L, sodium tripolyphosphate 5 g / L, triethanolamine 5 mL / L, and glacial acetic acid 20 mL / L. Add each reagent to deionized water in sequence and stir continuously until completely dissolved to prepare a near-neutral solution with a pH of 6.5. Then, place the near-neutral solution in the electrolytic cell and let it stand before using it as the electrolyte.

[0094] Step 3: The pretreated magnesium-lithium alloy from Step 1 is clamped in an electrolytic cell and completely immersed in the electrolyte as the anode. A stainless steel sheet is used as the cathode. Then, a micro-arc oxidation process is performed to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. The micro-arc oxidation process is as follows: a constant voltage DC pulse power supply is used, with a voltage of 400V, a frequency of 1500Hz, a duty cycle of 20%, and an oxidation time of 15min. During the micro-arc oxidation process, a chiller is used to control the electrolyte temperature at 10℃~15℃. Specifically, the voltage is increased from 0V to 220V and held for 1min, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is reduced to 30V and held for 1min, then reduced back to 0V.

[0095] Step 4: The magnesium-lithium alloy treated by micro-arc oxidation in Step 3 is completely immersed in the post-treatment solution, which is prepared by 40 g / L sodium fluoride and the remainder is deionized water. Then, it is placed in an ultrasonic bath and ultrasonically vibrated for 20 minutes at a temperature of 40°C. After that, it is taken out, rinsed with deionized water, dried and post-treated to obtain a matte coating of Comparative Example 4 on the surface of the magnesium-lithium alloy substrate.

[0096] Comparative Example 5

[0097] In this comparative example, 40 g / L sodium fluoride was added to the electrolyte, and the post-treatment solution in step four was not treated. The rest of the methods were the same as in Example 2.

[0098] The electrolyte consists of the following components: 40 g / L sodium fluoride, 20 g / L sodium orthovanadate, 5 g / L sodium germanate, 5 g / L ammonium dihydrogen phosphate, 2 g / L ammonium fluoride, 5 g / L sodium tripolyphosphate, 5 mL / L triethanolamine, 20 mL / L glacial acetic acid, and the remainder is deionized water.

[0099] The application method of electrolyte includes the following steps:

[0100] Step 1: Select an LA103Z magnesium-lithium alloy sheet with dimensions (length × width × thickness) of 15mm × 15mm × 3mm as the substrate. Use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy in stages. Then, activate the magnesium-lithium alloy for 30 seconds at room temperature with a surface activation solution composed of 5% nitric acid, 20% citric acid, and the remainder deionized water. After that, rinse the surface of the magnesium-lithium alloy with deionized water, and then place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes. Blow it dry and set it aside for later use. This completes the pretreatment.

[0101] Step 2: Prepare the electrolyte. The components and their contents of the electrolyte are as follows: 40 g / L sodium fluoride, 20 g / L sodium orthovanadate, 5 g / L sodium germanate, 5 g / L ammonium dihydrogen phosphate, 2 g / L ammonium fluoride, 5 g / L sodium tripolyphosphate, 5 mL / L triethanolamine, and 20 mL / L glacial acetic acid. Add each reagent to deionized water in sequence and stir continuously until completely dissolved to prepare a near-neutral solution with a pH of 6.5. Then, place the near-neutral solution in the electrolytic cell and let it stand before using it as the electrolyte.

[0102] Step 3: The pretreated magnesium-lithium alloy from Step 1 is clamped in an electrolytic cell and completely immersed in the electrolyte as the anode. A stainless steel sheet is used as the cathode. Then, a micro-arc oxidation process is performed to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. The micro-arc oxidation process is as follows: a constant voltage DC pulse power supply is used, with a voltage of 400V, a frequency of 1500Hz, a duty cycle of 20%, and an oxidation time of 15min. During the micro-arc oxidation process, a chiller is used to control the electrolyte temperature at 10℃~15℃. Specifically, the voltage is increased from 0V to 220V and held for 1min, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is reduced to 30V and held for 1min, then reduced back to 0V.

[0103] Comparative Example 6

[0104] In this comparative example, the post-treatment solution in step four uses 10 wt% polyborosilazane diluent (xylene as solvent) instead of sodium fluoride, and the rest of the method is the same as in Example 2.

[0105] The electrolyte consists of the following components: sodium orthovanadate 20 g / L, sodium germanate 5 g / L, ammonium dihydrogen phosphate 5 g / L, ammonium fluoride 2 g / L, sodium tripolyphosphate 5 g / L, triethanolamine 5 mL / L, glacial acetic acid 20 mL / L, and the remainder is deionized water.

[0106] The application method of electrolyte includes the following steps:

[0107] Step 1: Select an LA103Z magnesium-lithium alloy sheet with dimensions (length × width × thickness) of 15mm × 15mm × 3mm as the substrate. Use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy in stages. Then, activate the magnesium-lithium alloy for 30 seconds at room temperature with a surface activation solution composed of 5% nitric acid, 20% citric acid, and the remainder deionized water. After that, rinse the surface of the magnesium-lithium alloy with deionized water, and then place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes. Blow it dry and set it aside for later use. This completes the pretreatment.

[0108] Step 2: Prepare the electrolyte. The components and concentrations of the electrolyte are as follows: sodium orthovanadate 20 g / L, sodium germanate 5 g / L, ammonium dihydrogen phosphate 5 g / L, ammonium fluoride 2 g / L, sodium tripolyphosphate 5 g / L, triethanolamine 5 mL / L, and glacial acetic acid 20 mL / L. Add each reagent to deionized water in sequence and stir continuously until completely dissolved to prepare a near-neutral solution with a pH of 6.5. Then, place the near-neutral solution in the electrolytic cell and let it stand before using it as the electrolyte.

[0109] Step 3: The pretreated magnesium-lithium alloy from Step 1 is clamped in an electrolytic cell and completely immersed in the electrolyte as the anode. A stainless steel sheet is used as the cathode. Then, a micro-arc oxidation process is performed to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. The micro-arc oxidation process is as follows: a constant voltage DC pulse power supply is used, with a voltage of 400V, a frequency of 1500Hz, a duty cycle of 20%, and an oxidation time of 15min. During the micro-arc oxidation process, a chiller is used to control the electrolyte temperature at 10℃~15℃. Specifically, the voltage is increased from 0V to 220V and held for 1min, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is reduced to 30V and held for 1min, then reduced back to 0V.

[0110] Step 4: The magnesium-lithium alloy treated by micro-arc oxidation in Step 3 is completely immersed in a post-treatment solution, which is a 10wt% polyborosilicate dilution prepared with xylene as the solvent. Then, it is placed in an ultrasonic bath and ultrasonically vibrated for 20 minutes at a temperature of 40°C. After that, it is taken out and dried in an oven (held at 120°C for 90 minutes). After the post-treatment, a matte coating of Comparative Example 6 is obtained on the surface of the magnesium-lithium alloy substrate.

[0111] Examples 1-3 were used as the test group, and Comparative Examples 1-6 were used as the control group. Corrosion resistance and solar absorption rate were tested. The test results are as follows:

[0112] 1. Corrosion resistance test:

[0113] Polarization curves were tested at room temperature using a Gamry electrochemical workstation from the United States, employing a three-electrode system (platinum electrode as counter electrode and saturated calomel electrode as reference electrode), a scan rate of 1 mV / s, and a 3.5% NaCl solution as the corrosive medium. The experimental results are shown in Table 2.

[0114] Table 2 Corrosion current of the coatings in the test group and the control group:

[0115] Group <![CDATA[Corrosion current (I corr ) <!-- 10 -->]]> Example 1 <![CDATA[7.247×10 -8 A / cm 2 ]]> Example 2 <![CDATA[9.659×10 -8 A / cm 2 ]]> Example 3 <![CDATA[8.746×10 -8 A / cm 2 ]]> Comparative Example 1 <![CDATA[3.356×10 -7 A / cm 2 ]]> Comparative Example 2 <![CDATA[5.424×10 -6 A / cm 2 ]]> Comparative Example 3 <![CDATA[5.867×10 -6 A / cm 2 ]]> Comparative Example 4 <![CDATA[7.264×10 -5 A / cm 2 ]]> Comparative Example 5 <![CDATA[3.756×10 -6 A / cm 2 ]]> Comparative Example 6 <![CDATA[6.483×10 -6 A / cm 2 ]]> LA103Z magnesium-lithium alloy matrix <![CDATA[1.526×10 -4 A / cm 2 ]]> .

[0116] As shown in Table 2, under the same experimental conditions, the corrosion currents of Examples 1-3 were 7.247 × 10⁻⁶, respectively. -8 A / cm 2 9.659×10 -8 A / cm 2 8.746×10 -8 A / cm 2The corrosion resistance of the coating was significantly lower than that of the control group, indicating that Examples 1-3 have better corrosion resistance. Comparative Example 1 shows that adding sodium metagermanate to the electrolyte helps improve the corrosion resistance of the coating. Comparative Example 2 shows that the corrosion resistance of the coating sample treated with the post-treatment solution is significantly improved. Comparative Examples 3 and 4 show that, compared to using sodium metavanadate in combination with sodium metagermanate or using sodium metagermanate alone, the coating obtained by the electrolyte system of sodium orthovanadate combined with sodium metagermanate in this invention has better corrosion resistance. This invention first adds ammonium fluoride to the electrolyte, and then uses sodium fluoride in the post-treatment solution. As shown in Comparative Example 5, the two steps have a synergistic effect, which is better than directly adding ammonium fluoride and sodium fluoride to the electrolyte. The coating structure is continuous, dense and without through holes. Comparative Example 6 also proves that the two steps have a synergistic effect. In Comparative Example 6, ammonium fluoride is added to the electrolyte first and polyborosilazane is used in the post-treatment solution. The coating formed in Comparative Example 6 does not have the same corrosion resistance as this invention. The polyborosilazane has poor adhesion to the oxide layer, is easy to peel off, and the film integrity is insufficient.

[0117] 2. Solar absorption rate test:

[0118] The solar absorptivity was tested in accordance with GJB 2502.2-2015, and the test results are shown in Table 3.

[0119] Table 3. Solar absorption rates of the coatings in the test and control groups:

[0120] Group Solar absorption rate Example 1 0.98 Example 2 0.95 Example 3 0.96 Comparative Example 1 0.87 Comparative Example 2 0.93 Comparative Example 3 0.85 Comparative Example 4 0.76 Comparative Example 5 0.83 Comparative Example 6 0.78 .

[0121] As can be seen from Table 3, under the same experimental conditions, the solar absorption rates of Examples 1 to 3 were 0.98, 0.95, and 0.96, respectively, while the solar absorption rates of the control group all decreased significantly, indicating that Examples 1 to 3 have better extinction performance.

[0122] Existing technologies often use sodium metavanadate as a colorant. This invention discovers that using a combination of sodium orthovanadate and sodium metagermanate as a colorant yields better results compared to using sodium metavanadate alone. The electrolyte is clearer, free of flocculent precipitates, and exhibits significantly higher stability than sodium metavanadate alone. In this invention, the electrolyte uses sodium orthovanadate and sodium metagermanate as the main coloring salts, and under the influence of an electric field, VO 3- and Ge 2+The material migrates into the discharge channel and participates in the micro-arc oxidation reaction. Through a combination of plasma thermochemical and electrochemical reactions, the reactants undergo further phase transformation at high temperatures, forming a complex composite salt. This salt reacts with the magnesium-lithium matrix material to form a black coating composed of V₂O₅, GeO₂, MgO, and MgF₂. Compared to Comparative Example 1 using sodium orthovanadate alone or Comparative Example 3 using sodium metavanadate in combination with sodium metagermanate, this microstructure exhibits superior solar absorption and significantly improved corrosion resistance. In Comparative Example 4, using sodium metagermanate alone, the coating contains some white or gray substances and is relatively porous with poor film integrity, thus affecting its corrosion resistance and matting properties. The coating obtained after combining sodium orthovanadate and sodium metagermanate shows improved solar absorption, better matting effect, less color difference, and a uniform and smooth surface.

[0123] In this invention, ammonium fluoride is first added to the electrolyte, and then sodium fluoride is used in the post-treatment solution. Compared with Comparative Example 2, which does not use post-treatment solution, and Comparative Example 5, which directly adds sodium fluoride to the electrolyte, this invention has better results, with a continuous and dense coating structure without through-holes. In Comparative Example 6, ammonium fluoride is first added to the electrolyte, and polyborosilicate is used in the subsequent treatment. The microstructure formed in Comparative Example 6 has a lower solar light absorption rate and is not as corrosion resistant as this invention, which also shows that the use of sodium fluoride in the post-treatment solution has a synergistic effect with the electrolyte of this invention.

[0124] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. An electrolyte for preparing an amorphous matte coating on the surface of a magnesium-lithium alloy, characterized in that, The electrolyte comprises the following components and contents: sodium orthovanadate 20g / L~30g / L, sodium metagermanate 5g / L~10g / L, ammonium dihydrogen phosphate 5g / L~10g / L, ammonium fluoride 2g / L~4g / L, sodium tripolyphosphate 5g / L~10g / L, triethanolamine 5mL / L~10mL / L, glacial acetic acid 10mL / L~20mL / L, and the remainder is deionized water; the pH of the electrolyte is 6.5~7.5; after being subjected to micro-arc oxidation treatment in the electrolyte, an amorphous matte coating is formed on the surface of the magnesium-lithium alloy.

2. The application of the electrolyte for preparing an amorphous matte coating on the surface of a magnesium-lithium alloy as described in claim 1, characterized in that, Includes the following steps: Step 1: After polishing the magnesium-lithium alloy, activate it with a surface activation solution. Step 2: Prepare the electrolyte, the components and their contents of which are as follows: sodium orthovanadate 20g / L~30g / L, sodium metagermanate 5g / L~10g / L, ammonium dihydrogen phosphate 5g / L~10g / L, ammonium fluoride 2g / L~4g / L, sodium tripolyphosphate 5g / L~10g / L, triethanolamine 5mL / L~10mL / L, glacial acetic acid 10mL / L~20mL / L; Step 3: Immerse the magnesium-lithium alloy treated in Step 1 completely in the electrolyte as the anode, use a stainless steel sheet as the cathode, and then process it according to the micro-arc oxidation process to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. Step 4: Immerse the magnesium-lithium alloy that has undergone micro-arc oxidation in Step 3 in a post-treatment solution until completely submerged. After ultrasonic treatment, an amorphous matte coating is obtained on the surface of the magnesium-lithium alloy.

3. The application according to claim 2, characterized in that, The surface activation solution components and their mass percentages mentioned in step one are: 5%~10% nitric acid, 20%~30% citric acid, and the remainder is deionized water.

4. The application according to claim 2, characterized in that, Step one includes the following specific steps: The magnesium-lithium alloy is polished step by step using 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper in sequence. The magnesium-lithium alloy is then activated at room temperature with a surface activation solution for 30 seconds. After that, the surface of the magnesium-lithium alloy is rinsed clean with deionized water and then ultrasonically cleaned in anhydrous ethanol for 10 minutes.

5. The application according to claim 2, characterized in that, The electrolyte in step two has a pH of 6.5 to 7.5, and the pH is adjusted using glacial acetic acid.

6. The application according to claim 2, characterized in that, The micro-arc oxidation process described in step three is as follows: the micro-arc oxidation treatment uses a constant voltage DC pulse power supply with a voltage of 400V~450V, a frequency of 1500Hz~2000Hz, a duty cycle of 10%~20%, an oxidation time of 15min~20min, and the temperature of the electrolyte during the micro-arc oxidation process is 10℃~15℃.

7. The application according to claim 2, characterized in that, Step 3 includes the following operation process: boost the voltage from 0V to 220V and hold for 1 minute, then boost the voltage at a rate of 30V / min to reach the target voltage, perform micro-arc oxidation treatment, and after the micro-arc oxidation treatment is completed, first reduce the voltage by 30V and hold for 1 minute, then reduce the voltage to 0V.

8. The application according to claim 2, characterized in that, The composition and content of the post-treatment solution mentioned in step four are: 40 g / L to 50 g / L sodium fluoride, with the remainder being deionized water.

9. The application according to claim 2, characterized in that, The ultrasonic treatment in step four lasts for 20 to 30 minutes at a temperature of 40 to 50 degrees Celsius.

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