Electrolyte for preparing amorphous matt coating on surface of magnesium-lithium alloy and application

Abstract

The invention belongs to the technical field of magnesium-lithium alloy surface treatment, and particularly relates to an electrolyte for preparing an amorphous matt coating on the surface of a magnesium-lithium alloy and application of the electrolyte. The electrolyte is prepared from the following components: 20 g / L-30 g / L of sodium orthovanadate, 5 g / L-10 g / L of sodium metagermanate, 5 g / L-10 g / L of ammonium dihydrogen phosphate, 2 g / L-4 g / L of ammonium fluoride, 5 g / L-10 g / L of sodium tripolyphosphate, 5 mL / L-10 mL / L of triethanolamine and 10 mL / L-20 mL / L of glacial acetic acid. According to the preparation method, the magnesium-lithium alloy is firstly pretreated and then placed in electrolyte for micro-arc oxidation treatment, and finally post-treatment is performed, so that the compact and uniform amorphous high-corrosion-resistance matting coating is prepared on the surface of the magnesium-lithium alloy, and the coating has excellent corrosion resistance and matting performance. By controlling the components and content of the electrolyte, the pH of the electrolyte is ensured to be about neutral, the stability and safety of the electrolyte are improved, and industrial production is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnesium-lithium alloy surface treatment, and particularly relates to an electrolyte for preparing an amorphous matte coating on the surface of a magnesium-lithium alloy and its application. Background Art

[0002] As the amount of information and imaging quality required for exploring the Earth or other celestial bodies increases, space optical remote sensors must not only have high resolution and good image quality, but also high reliability while being lightweight. During the on-orbit operation of a remote sensor, sunlight reflected from the surface of the optical structure may be transmitted to the remote sensor image plane, forming stray light from non-imaging light sources, resulting in reduced imaging contrast and blurred imaging in the optical system, and even making the system unable to extract the target, seriously affecting the monitoring and recognition capabilities of the entire device. Therefore, it is necessary to prepare a black matte coating on the surface of the optical structure. In a space environment, this coating can utilize its own high absorption rate of sunlight to absorb and weaken non-imaging sensitive light in the optical detector optical path, thereby eliminating stray light and improving the imaging quality of the remote sensor.

[0003] Magnesium-lithium alloy is the lightest alloy, boasting high specific strength, specific stiffness, electromagnetic shielding properties, and excellent formability. It is an ideal material for lightweight components and, therefore, has attracted considerable attention in aerospace, electronics, military, and other high-tech fields. Its use in space optical systems can reduce weight by 20% to 30%, which is crucial for lightweighting these systems. However, magnesium-lithium alloy itself has a low solar absorption rate, lacks extinction capability, and exhibits very poor corrosion resistance. Corrosion can occur during transportation and storage, necessitating the application of a coating with high corrosion resistance and extinction properties to meet operational requirements.

[0004] Micro-arc oxidation technology offers simple processes, low costs, minimal environmental impact, and strong applicability for complex workpieces. Micro-arc oxidation coatings possess excellent membrane-substrate bonding and a rough, porous surface, resulting in a large specific surface area and strong adsorption capacity. Black ceramic coatings produced using micro-arc oxidation technology, in particular, hold great promise for matte coating applications. Existing reports on matte coatings for magnesium-lithium alloys primarily focus on highly absorbent black coatings, but these coatings suffer from poor bonding, easy decomposition, and poor corrosion resistance, significantly limiting their use. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the above-mentioned prior art and provide an electrolyte and its application for preparing an amorphous, highly corrosion-resistant matte coating on the surface of a magnesium-lithium alloy. By controlling the composition and content of each component, the electrolyte maintains a near-neutral pH, which is both environmentally friendly and improves the stability of the electrolyte. The electrolyte is used to prepare an amorphous, highly corrosion-resistant matte coating in situ on the surface of a magnesium-lithium alloy using a micro-arc oxidation process. The amorphous, highly corrosion-resistant matte coating prepared using this electrolyte and process improves the corrosion resistance and matte properties of the coating.

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

[0007] The present invention controls the components and contents of the electrolyte to ensure a near-neutral pH, improving electrolyte stability and safety, and facilitating industrial production. The arc discharge during micro-arc oxidation in this electrolyte exhibits a soft spark state and is more uniform and dense, thereby improving the coating's density and corrosion resistance. Magnesium alloys are inherently reactive. If the ion concentration in the electrolyte is too high or the ion concentration distribution is uneven (presence of precipitates or suspended matter), severe heat accumulation can occur in localized areas during the micro-arc oxidation process, leading to ablation pits on the surface of the micro-arc oxidation coating. The ammonium dihydrogen phosphate, sodium tripolyphosphate, and triethanolamine in the electrolyte formulation of the present invention all act to complex metal cations, promoting the dissolution of vanadium and germanium salts. This eliminates precipitates and suspended matter in the solution, maintains a uniform ion concentration, and effectively inhibits ablation. This electrolyte can mitigate ablation of magnesium-lithium alloy substrates during micro-arc oxidation, preventing the appearance of white ablation pits in black coatings. This facilitates the production of a dense and uniform coating, thereby improving the coating's corrosion resistance and matte properties and ensuring a high yield of black coatings.

[0008] The application of the electrolyte for the amorphous high corrosion-resistant matte coating on the surface of the magnesium-lithium alloy of the present invention comprises the following steps: Step 1: After polishing, the magnesium-lithium alloy is activated with a surface activation solution; Step 2: Prepare an electrolyte. The components and contents of the electrolyte are as follows: 20 g / L to 30 g / L sodium orthovanadate, 5 g / L to 10 g / L sodium metagermanate, 5 g / L to 10 g / L ammonium dihydrogen phosphate, 2 g / L to 4 g / L ammonium fluoride, 5 g / L to 10 g / L sodium tripolyphosphate, 5 mL / L to 10 mL / L triethanolamine, and 10 mL / L to 20 mL / L glacial acetic acid. Each reagent is sequentially added to deionized water and stirred continuously until completely dissolved to prepare a nearly neutral solution. The nearly neutral solution is then placed in an electrolytic cell and allowed to stand as the electrolyte. Step 3: The magnesium-lithium alloy treated in step 1 is completely immersed in an electrolyte as an anode, a stainless steel sheet is used as a cathode, and then treated according to a micro-arc oxidation process to prepare a coating on the surface of the magnesium-lithium alloy; Step 4: The magnesium-lithium alloy treated by micro-arc oxidation in step 3 is completely immersed in a post-treatment solution, and an amorphous high-corrosion-resistant matte coating is obtained on the surface of the magnesium-lithium alloy after ultrasonic treatment.

[0009] Step 1 includes the following specific contents: 320#, 600#, 800#, 1000#, 1500#, 2000# water-resistant abrasive paper and metallographic sandpaper are used to polish the magnesium-lithium alloy step by step, and the magnesium-lithium alloy is activated for 30 seconds using a surface activation liquid at room temperature. Then, the surface of the magnesium-lithium alloy is rinsed with deionized water, and then ultrasonically cleaned in anhydrous ethanol for 10 minutes, and then blown dry for standby use to complete the pretreatment; The surfactant solution described in step 1 contains 5% to 10% nitric acid, 20% to 30% citric acid, and the remainder deionized water. Because magnesium-lithium alloys are highly reactive and have poor corrosion resistance, they can form oxide scale on their surfaces when stored in atmospheric conditions. Therefore, the surfactant solution is used to activate the surface of the magnesium-lithium alloy substrate to create a fresh substrate surface.

[0010] The pH of the electrolyte in step 2 is between 6.5 and 7.5, and glacial acetic acid is used to adjust the pH. First, glacial acetic acid is an organic acid, and its addition to the electrolyte does not introduce new impurities, maintaining the electrolyte's composition. Second, the electrolyte is a near-neutral solution that is harmless to human skin, making it more environmentally friendly and safe. Finally, a near-neutral solution effectively prevents metal ion precipitation, resulting in better stability.

[0011] The micro-arc oxidation process described in step three is: the micro-arc oxidation treatment adopts 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, and a refrigerator is used during the micro-arc oxidation treatment to control the temperature of the electrolyte to 10℃~15℃.

[0012] The specific operation process is: increase the voltage from 0V to 220V and maintain it for 1 minute, then increase the voltage at a rate of 30V / min to reach the target voltage, and perform micro-arc oxidation treatment. After the micro-arc oxidation treatment is completed, first reduce the voltage by 30V and maintain it for 1 minute, and then reduce the voltage to 0V.

[0013] By controlling the micro-arc oxidation process, the coating can be guaranteed to grow densely, avoiding coating ablation caused by too high voltage, and thin coating thickness and insufficient blackness caused by too low voltage, which affect its performance, ensuring that all performance of the coating reaches the best; the present invention controls the temperature of the electrolyte during the micro-arc oxidation process to avoid coating ablation at high temperature and excessive surface holes, which in turn affect the corrosion resistance of the coating.

[0014] The composition and content of the post-treatment liquid in step four are: 40g / L~50g / L sodium fluoride, and the rest is deionized water. The time of the ultrasonic treatment is 20min~30min, the temperature is 40℃~50℃, and after taking out, it is rinsed with deionized water and dried for post-treatment. By immersing the ultrasonic oscillation in the post-treatment liquid, the sodium fluoride solution can enter the through-holes of the micro-arc oxidation coating and react with the magnesium-lithium alloy matrix to generate a dense magnesium fluoride film layer to block the through-holes, prevent the corrosive medium from contacting the matrix, and do not change the porous surface morphology of the micro-arc oxidation coating, thereby improving the corrosion resistance of the amorphous high-corrosion-resistant matte coating.

[0015] The present invention adopts a near-neutral electrolyte to perform micro-arc oxidation treatment on the surface of the magnesium-lithium alloy, thereby obtaining an in-situ grown amorphous high-corrosion-resistant matte coating on the surface of the magnesium-lithium alloy. By adopting a constant-voltage DC pulse power supply and voltage stabilization control in the low-voltage area, the amorphous high-corrosion-resistant matte coating grows more densely in the initial stage of micro-arc oxidation.

[0016] Compared with the prior art, the present invention has the following advantages: 1. The present invention ensures that the pH of the electrolyte is near neutral by controlling the composition and content of each component. The near-neutral electrolyte is environmentally friendly and highly stable, thereby improving the economy of the electrolyte and facilitating industrial production.

[0017] 2. When the magnesium-lithium alloy sample is subjected to micro-arc oxidation treatment using the electrolyte of the present invention, the arc discharge on the sample surface is in a soft spark state and is more uniform and dense, which can improve the phenomenon of ablation of the magnesium-lithium alloy matrix during the micro-arc oxidation process, avoid the occurrence of ablation points in the coating, and is conducive to the generation of a dense and uniform micro-arc oxidation coating, thereby improving the corrosion resistance and matte properties of the coating and ensuring the coating yield.

[0018] 3. The present invention adopts micro-arc oxidation process and post-treatment to grow an amorphous high corrosion-resistant matte coating on the surface of magnesium-lithium alloy in situ. The coating structure is continuous and dense without through holes. The amorphous coating significantly improves the corrosion resistance. The corrosion current density in 3.5% NaCl solution reaches 7.247×10-8 A / cm 2 Compared with the magnesium-lithium alloy substrate, the corrosion current density is reduced by 4 orders of magnitude. The micro-arc oxidation coating is post-treated with sodium fluoride, resulting in a continuous, dense coating structure without through-holes. The present invention first adds ammonium fluoride to the electrolyte and then uses sodium fluoride in the subsequent treatment. This method achieves better results than the micro-arc oxidation coating without post-treatment.

[0019] 4. By using the electrolyte and micro-arc oxidation process of the present invention, an amorphous high-corrosion-resistant matte coating can be prepared on the surface of magnesium-lithium alloy. The coating has a high V content and the introduction of Ge element greatly improves the solar light absorption rate, which can reach 0.98. The existing technology often uses sodium metavanadate as a colorant. The present invention has found that using a combination of sodium orthovanadate and sodium metagermanate as a colorant has better effects than using sodium metavanadate alone. The electrolyte is clearer, there is no flocculent precipitate, and the stability is much higher than that of sodium metavanadate. The electrolyte in the present invention uses sodium orthovanadate and sodium metagermanate as the main coloring salts. Under the action of the electric field, VO 3- and Ge 2+ They migrate into the discharge channel and participate in the micro-arc oxidation reaction. After a combined plasma thermochemical and electrochemical reaction, the reactants undergo further phase transformation at high temperatures, forming a complex salt composition. These salts then react with the magnesium and lithium matrix materials to form a black coating composed of V2O5-GeO2-MgO-MgF2. Compared to sodium metavanadate or sodium metagermanate alone, this microstructure exhibits superior solar light absorption and significantly improved corrosion resistance. When sodium metavanadate or sodium metagermanate is used alone, the coating will contain some white or gray matter, affecting film integrity. However, the coating obtained by combining sodium orthovanadate and sodium metagermanate exhibits superior matting, significantly improving solar light absorption, minimizing color difference, and achieving a uniform and smooth surface. Furthermore, when sodium metavanadate is used alone, a large amount of flocculent precipitate forms, hindering electrolyte recycling.

[0020] 5. The amorphous high corrosion-resistant matte 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 on the basis of the excellent matte performance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a macroscopic morphology of the LA103Z magnesium-lithium alloy with an amorphous high corrosion-resistant matte coating in Example 1 of the present invention.

[0022] Figure 2 This is a surface scanning electron microscope image of the LA103Z magnesium-lithium alloy with an amorphous high corrosion-resistant matte coating in Example 1 of the present invention.

[0023] Figure 3This is a cross-sectional scanning electron microscope image of the LA103Z magnesium-lithium alloy with an amorphous high corrosion-resistant matte coating in Example 1 of the present invention.

[0024] Figure 4 This is the X-ray diffraction analysis pattern of the amorphous high corrosion-resistant matte coating prepared on the surface of LA103Z magnesium-lithium alloy in Examples 1 and 2 of the present invention.

[0025] Figure 5 This is the XPS spectrum of the amorphous high corrosion-resistant matte coating prepared on the surface of LA103Z magnesium-lithium alloy in Example 1 of the present invention; wherein, (a) is MgO and MgF2, (b) is V2O5 and MgO, (c) is V2O5, (d) is MgF2, (e) is GeO2, and (f) is different elements.

[0026] Figure 6 The electrochemical polarization curves of the LA103Z magnesium-lithium alloy substrate and the amorphous high corrosion-resistant matte coating prepared on the surface of the LA103Z magnesium-lithium alloy in Examples 1 and 2 in 3.5% NaCl solution. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is clearly and completely described below in conjunction with the embodiments and drawings. It should be noted that the embodiments described in the present invention are only used to further explain and illustrate, and are not intended to limit the scope of its application. Based on the present invention, all other embodiments obtained by those skilled in the art without making any creative work are within the scope of protection of the present invention.

[0028] Example 1 The electrolyte of this embodiment is composed of the following components: 30 g / L sodium orthovanadate, 10 g / L sodium metagermanate, 10 g / L ammonium dihydrogen phosphate, 4 g / L ammonium fluoride, 10 g / L sodium tripolyphosphate, 10 mL / L triethanolamine, 10 mL / L glacial acetic acid, and the rest is deionized water.

[0029] The application method of the electrolyte in this embodiment includes the following steps: Step 1: Select an LA103Z magnesium-lithium alloy sheet with a size (length × width × thickness) of 15 mm × 15 mm × 3 mm as the substrate, and use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy step by step. Then, use a surfactant solution composed of 10% nitric acid, 30% citric acid, and the rest deionized water to activate the magnesium-lithium alloy at room temperature for 30 seconds. Then, rinse the surface of the magnesium-lithium alloy with deionized water, place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes, blow dry it for standby use, and complete the pretreatment; Step 2: Prepare an electrolyte. The components and contents of the electrolyte are as follows: 30 g / L sodium orthovanadate, 10 g / L sodium metagermanate, 10 g / L ammonium dihydrogen phosphate, 4 g / L ammonium fluoride, 10 g / L sodium tripolyphosphate, 10 mL / L triethanolamine, and 10 mL / L glacial acetic acid. Each reagent is sequentially added to deionized water and stirred continuously until completely dissolved to obtain a nearly neutral solution with a pH of 7.5. The nearly neutral solution is then placed in an electrolytic cell and allowed to stand as the electrolyte. Step 3: Use a fixture to clamp the magnesium-lithium alloy that has been pretreated in step 1 and place it in an electrolytic cell. The alloy is completely immersed in the electrolyte as the anode, and a stainless steel sheet is used as the cathode. The alloy is then treated according to the micro-arc oxidation process to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. The micro-arc oxidation process is as follows: the micro-arc oxidation process uses a constant voltage DC pulse power supply 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 refrigerator is used to control the temperature of the electrolyte at 10°C to 15°C. The specific operation process is as follows: increase the voltage from 0V to 220V and maintain it for 1min, then increase the voltage at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is first reduced by 30V and maintained for 1min, and then reduced to 0V.

[0030] Step 4: The magnesium-lithium alloy treated with micro-arc oxidation in step 3 is completely immersed in a post-treatment liquid, wherein the post-treatment liquid is prepared by 50 g / L sodium fluoride and the rest is deionized water. The magnesium-lithium alloy is then placed in an ultrasonic tank for 30 minutes at a temperature of 50°C, and then taken out and rinsed with deionized water. After drying and post-treatment, an amorphous, highly corrosion-resistant matte coating is obtained on the surface of the magnesium-lithium alloy substrate.

[0031] The amorphous high corrosion-resistant matte coating prepared on the surface of the LA103Z magnesium-lithium alloy in this embodiment was subjected to energy spectrum EDS analysis, and the results are shown in Table 1.

[0032] Table 1 EDS analysis results of the matte coating prepared in Example 1: element V Ge Mg O F Total Atom ratio (%) 17.35 7.22 28.60 42.78 4.05 100 .

[0033] As shown in Table 1, the amorphous, highly corrosion-resistant matte coating prepared on the surface of the LA103Z magnesium-lithium alloy in this example is composed of elements such as V, Ge, Mg, O, and F. The coating contains transition metal elements V and Ge, which have unsaturated d orbitals, facilitating the transfer of electrons from the outermost electron shell to the next outermost electron shell, thereby absorbing light and improving the coating's matte performance.

[0034] from Figure 1The coating is black and uniform in color, with a complete morphology and no defects such as ablation, peeling, or cracking. The black coating has high solar absorptivity and excellent matting properties. The solar absorptivity of this amorphous, highly corrosion-resistant matte coating is 0.98 (refer to GJB 2502.2-2015).

[0035] from Figure 2 It can be seen that the amorphous high corrosion resistance matte coating has 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. 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 has no through holes, which is beneficial to enhancing the corrosion resistance of the coating. Figure 4 From the results of Example 1, it can be seen that the high corrosion resistant matte coating prepared on the surface of LA103Z magnesium-lithium alloy presents a typical amorphous state, and the amorphous coating has stronger corrosion resistance. Figure 5 From (a), (b), (c), (d), (e) and (f) in the figure, it can be seen that the main components of the amorphous high corrosion-resistant matte coating in this embodiment are V2O5, GeO2, MgO and MgF2.

[0036] from Figure 6 The results of Example 1 show that 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 , compared with the corrosion current of LA103Z magnesium-lithium alloy substrate of 1.526×10 -4 A / cm 2 It is reduced by 4 orders of magnitude. The amorphous high corrosion-resistant matte coating has a lower corrosion current, which means that the corrosion resistance of the coating is greatly improved, and it plays a good corrosion protection role for the LA103Z magnesium-lithium alloy substrate.

[0037] Example 2 The electrolyte of this embodiment is composed of the following components: 20 g / L sodium orthovanadate, 5 g / L sodium metagermanate, 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 rest is deionized water.

[0038] The application method of the electrolyte in this embodiment includes the following steps: Step 1: Select an LA103Z magnesium-lithium alloy sheet with a size (length × width × thickness) of 15 mm × 15 mm × 3 mm as the substrate, and polish the magnesium-lithium alloy step by step using 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper. Activate the magnesium-lithium alloy at room temperature for 30 seconds using a surfactant solution consisting of 5% nitric acid, 20% citric acid, and the rest deionized water. Rinse the surface of the magnesium-lithium alloy with deionized water, ultrasonically clean it in anhydrous ethanol for 10 minutes, blow dry it, and then complete the pretreatment. Step 2: Prepare an electrolyte. The components and contents of the electrolyte are as follows: 20 g / L sodium orthovanadate, 5 g / L sodium metagermanate, 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. Each reagent is sequentially added to deionized water and stirred continuously until completely dissolved to obtain a nearly neutral solution with a pH of 6.5. The nearly neutral solution is then placed in an electrolytic cell and allowed to stand as the electrolyte. Step 3: Use a fixture to clamp the magnesium-lithium alloy that has undergone pretreatment in Step 1 and place it in an electrolytic cell. The alloy is completely immersed in the electrolyte as the anode, and a stainless steel sheet is used as the cathode. The alloy is then treated according to a micro-arc oxidation process to prepare a micro-arc oxidation coating on the surface of the alloy. The micro-arc oxidation process is as follows: the micro-arc oxidation process uses a constant-voltage DC pulse power supply with a voltage of 400V, a frequency of 1500Hz, a duty cycle of 20%, and an oxidation time of 15 minutes. During the micro-arc oxidation process, a refrigerator is used to control the temperature of the electrolyte at 10°C to 15°C. The specific operation process is as follows: the voltage is increased from 0V to 220V and maintained for 1 minute, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is first reduced by 30V and maintained for 1 minute, and then reduced to 0V.

[0039] Step 4: The magnesium-lithium alloy treated with micro-arc oxidation in step 3 is completely immersed in a post-treatment liquid, wherein the post-treatment liquid is prepared by 40 g / L sodium fluoride and the rest is deionized water. The magnesium-lithium alloy is then placed in an ultrasonic tank for 20 minutes at a temperature of 40°C, and then taken out and rinsed with deionized water. After drying and post-treatment, an amorphous, highly corrosion-resistant matte coating is obtained on the surface of the magnesium-lithium alloy substrate.

[0040] from Figure 4 It can be seen from the results of Example 2 that the high corrosion-resistant matte coating prepared on the surface of LA103Z magnesium-lithium alloy using the process of Example 2 also presents a typical amorphous state, thereby improving the corrosion resistance of the coating.

[0041] from Figure 6The 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 The solar light absorptivity of the amorphous high corrosion-resistant matte coating in Example 2 is 0.95.

[0042] Example 3 The electrolyte of this embodiment is composed of the following components: 25 g / L sodium orthovanadate, 8 g / L sodium metagermanate, 8 g / L ammonium dihydrogen phosphate, 3 g / L ammonium fluoride, 8 g / L sodium tripolyphosphate, 8 mL / L triethanolamine, 15 mL / L glacial acetic acid, and the rest is deionized water.

[0043] The application method of the electrolyte in this embodiment includes the following steps: Step 1: Select an LA103Z magnesium-lithium alloy sheet with a size (length × width × thickness) of 15 mm × 15 mm × 3 mm as the substrate, and use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy step by step. Then, use a surfactant solution composed of 8% nitric acid, 25% citric acid, and the rest deionized water to activate the magnesium-lithium alloy at room temperature for 30 seconds. Then, rinse the surface of the magnesium-lithium alloy with deionized water, place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes, blow dry it for standby use, and complete the pretreatment; Step 2: Prepare an electrolyte. The components and contents of the electrolyte are as follows: 25 g / L sodium orthovanadate, 8 g / L sodium metagermanate, 8 g / L ammonium dihydrogen phosphate, 3 g / L ammonium fluoride, 8 g / L sodium tripolyphosphate, 8 mL / L triethanolamine, and 15 mL / L glacial acetic acid. Each reagent is sequentially added to deionized water and stirred continuously until completely dissolved to obtain a nearly neutral solution with a pH of 7.2. The nearly neutral solution is then placed in an electrolytic cell and allowed to stand as the electrolyte. Step 3: Use a fixture to clamp the magnesium-lithium alloy that has undergone pretreatment in Step 1 and place it in an electrolytic cell. The alloy is completely immersed in the electrolyte as the anode, and a stainless steel sheet is used as the cathode. The alloy is then treated according to a micro-arc oxidation process to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. The micro-arc oxidation process is as follows: the micro-arc oxidation process uses a constant-voltage DC pulse power supply 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 refrigerator is used to control the temperature of the electrolyte at 10°C to 15°C. The specific operation process is as follows: the voltage is increased from 0V to 220V and maintained for 1 minute, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is first reduced by 30V and maintained for 1 minute, and then reduced to 0V.

[0044] Step 4: The magnesium-lithium alloy treated with micro-arc oxidation in step 3 is completely immersed in a post-treatment liquid, wherein the post-treatment liquid is prepared by 45 g / L sodium fluoride and the rest is deionized water. The magnesium-lithium alloy is then placed in an ultrasonic tank for 25 minutes at a temperature of 45°C, and then taken out and rinsed with deionized water. After drying and post-treatment, an amorphous, highly corrosion-resistant matte coating is obtained on the surface of the magnesium-lithium alloy substrate.

[0045] 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 3 corr =8.746×10 -8 A / cm 2 The solar light absorptivity of the amorphous high corrosion-resistant matte coating in Example 3 is 0.96.

[0046] Comparative Example 1 The electrolyte of this comparative example does not contain sodium metagermanate, and the rest of the method is the same as that of Example 1.

[0047] The electrolyte consists of the following ingredients: 30 g / L sodium orthovanadate, 10 g / L ammonium dihydrogen phosphate, 4 g / L ammonium fluoride, 10 g / L sodium tripolyphosphate, 10 mL / L triethanolamine, 10 mL / L glacial acetic acid, and the rest is deionized water.

[0048] The method for applying the electrolyte comprises the following steps: Step 1: Select an LA103Z magnesium-lithium alloy sheet with a size (length × width × thickness) of 15 mm × 15 mm × 3 mm as the substrate, and use 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper to polish the magnesium-lithium alloy step by step. Then, use a surfactant solution composed of 10% nitric acid, 30% citric acid, and the rest deionized water to activate the magnesium-lithium alloy at room temperature for 30 seconds. Then, rinse the surface of the magnesium-lithium alloy with deionized water, place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes, blow dry it for standby use, and complete the pretreatment; Step 2: Prepare an electrolyte. The components and contents of the electrolyte are as follows: 30 g / L sodium orthovanadate, 10 g / L ammonium dihydrogen phosphate, 4 g / L ammonium fluoride, 10 g / L sodium tripolyphosphate, 10 mL / L triethanolamine, and 10 mL / L glacial acetic acid. Each reagent is sequentially added to deionized water and stirred continuously until completely dissolved to obtain a nearly neutral solution with a pH of 7.5. The nearly neutral solution is then placed in an electrolytic cell and allowed to stand as the electrolyte. Step 3: Use a fixture to clamp the magnesium-lithium alloy that has undergone pretreatment in Step 1 and place it in an electrolytic cell. The alloy is completely immersed in the electrolyte as the anode, and a stainless steel sheet is used as the cathode. The alloy is then treated according to a micro-arc oxidation process to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy. The micro-arc oxidation process is as follows: the micro-arc oxidation process uses a constant-voltage DC pulse power supply 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 refrigerator is used to control the temperature of the electrolyte at 10°C to 15°C. The specific operation process is as follows: the voltage is increased from 0V to 220V and maintained for 1 minute, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is first reduced by 30V and maintained for 1 minute, and then reduced to 0V.

[0049] Step 4: The magnesium-lithium alloy treated with micro-arc oxidation in step 3 is completely immersed in a post-treatment liquid, wherein the post-treatment liquid is prepared by 50 g / L sodium fluoride and the rest is deionized water. The magnesium-lithium alloy is then placed in an ultrasonic tank and ultrasonically vibrated for 30 minutes at a temperature of 50°C. The alloy is then taken out and rinsed with deionized water. After drying and post-treatment, a matte coating of comparative example 1 is obtained on the surface of the magnesium-lithium alloy substrate.

[0050] Comparative Example 2 This comparative example does not undergo treatment in a post-treatment solution, and the remaining methods are the same as those in Example 2.

[0051] The electrolyte consists of the following ingredients: sodium orthovanadate 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, and glacial acetic acid 20 mL / L.

[0052] The method for applying the electrolyte comprises the following steps: Step 1: Select an LA103Z magnesium-lithium alloy sheet with a size (length × width × thickness) of 15 mm × 15 mm × 3 mm as the substrate, and polish the magnesium-lithium alloy step by step using 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper. Activate the magnesium-lithium alloy at room temperature for 30 seconds using a surfactant solution consisting of 5% nitric acid, 20% citric acid, and the rest deionized water. Rinse the surface of the magnesium-lithium alloy with deionized water, ultrasonically clean it in anhydrous ethanol for 10 minutes, blow dry it, and then complete the pretreatment. Step 2: Prepare an electrolyte. The components and contents of the electrolyte are as follows: 20 g / L sodium orthovanadate, 5 g / L sodium metagermanate, 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. Each reagent is sequentially added to deionized water and stirred continuously until completely dissolved to obtain a nearly neutral solution with a pH of 6.5. The nearly neutral solution is then placed in an electrolytic cell and allowed to stand as the electrolyte. Step 3: Use a fixture to clamp the magnesium-lithium alloy that has been pretreated in step 1 and place it in an electrolytic cell. The alloy is completely immersed in the electrolyte as the anode, and a stainless steel sheet is used as the cathode. The alloy is then treated according to the micro-arc oxidation process 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 for micro-arc oxidation treatment, 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 treatment, a refrigerator is used to control the temperature of the electrolyte to 10°C to 15°C. The specific operation process is as follows: the voltage is increased from 0V to 220V and maintained for 1min, then increased at a rate of 30V / min to reach the target voltage, and after the oxidation time is over, the voltage is first reduced by 30V and maintained for 1min, and then reduced to 0V. The matte coating of Comparative Example 2 is obtained on the surface of the magnesium-lithium alloy substrate.

[0053] Comparative Example 3 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 that in Example 2.

[0054] The electrolyte consists of the following ingredients: 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 rest is deionized water.

[0055] The method for applying the electrolyte comprises the following steps: Step 1: Select an LA103Z magnesium-lithium alloy sheet with a size (length × width × thickness) of 15 mm × 15 mm × 3 mm as the substrate, and polish the magnesium-lithium alloy step by step using 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper. Activate the magnesium-lithium alloy at room temperature for 30 seconds using a surfactant solution consisting of 5% nitric acid, 20% citric acid, and the rest deionized water. Rinse the surface of the magnesium-lithium alloy with deionized water, ultrasonically clean it in anhydrous ethanol for 10 minutes, blow dry it, and then complete the pretreatment. Step 2: Prepare an electrolyte. The components and contents of the electrolyte are as follows: 20 g / L sodium metavanadate, 5 g / L sodium metagermanate, 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. Each reagent is sequentially added to deionized water and stirred continuously until completely dissolved to obtain a nearly neutral solution with a pH of 6.5. The nearly neutral solution is then placed in an electrolytic cell and allowed to stand as the electrolyte. Step 3: Use a fixture to clamp the magnesium-lithium alloy that has undergone pretreatment in Step 1 and place it in an electrolytic cell. The alloy is completely immersed in the electrolyte as the anode, and a stainless steel sheet is used as the cathode. The alloy is then treated according to a micro-arc oxidation process to prepare a micro-arc oxidation coating on the surface of the alloy. The micro-arc oxidation process is as follows: the micro-arc oxidation process uses a constant-voltage DC pulse power supply with a voltage of 400V, a frequency of 1500Hz, a duty cycle of 20%, and an oxidation time of 15 minutes. During the micro-arc oxidation process, a refrigerator is used to control the temperature of the electrolyte at 10°C to 15°C. The specific operation process is as follows: the voltage is increased from 0V to 220V and maintained for 1 minute, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is first reduced by 30V and maintained for 1 minute, and then reduced to 0V.

[0056] Step 4: The magnesium-lithium alloy treated with micro-arc oxidation in step 3 is completely immersed in a post-treatment liquid, wherein the post-treatment liquid is prepared by 40 g / L sodium fluoride and the rest is deionized water. The magnesium-lithium alloy is then placed in an ultrasonic tank and ultrasonically vibrated for 20 minutes at a temperature of 40°C. The alloy is then taken out and rinsed with deionized water. After drying and post-treatment, a matte coating of comparative example 3 is obtained on the surface of the magnesium-lithium alloy substrate.

[0057] Comparative Example 4 In this comparative example, an equal amount of sodium metagermanate was used to replace the sodium orthovanadate in the electrolyte, and the rest of the method was the same as that of Example 2.

[0058] The electrolyte consists of the following ingredients: 25 g / L sodium metagermanate, 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 rest is deionized water.

[0059] The method for applying the electrolyte comprises the following steps: Step 1: Select an LA103Z magnesium-lithium alloy sheet with a size (length × width × thickness) of 15 mm × 15 mm × 3 mm as the substrate, and polish the magnesium-lithium alloy step by step using 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper. Activate the magnesium-lithium alloy at room temperature for 30 seconds using a surfactant solution consisting of 5% nitric acid, 20% citric acid, and the rest deionized water. Rinse the surface of the magnesium-lithium alloy with deionized water, ultrasonically clean it in anhydrous ethanol for 10 minutes, blow dry it, and then complete the pretreatment. Step 2: Prepare an electrolyte. The components and contents of the electrolyte are as follows: 25 g / L sodium metagermanate, 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. Each reagent is sequentially added to deionized water and stirred continuously until completely dissolved to obtain a nearly neutral solution with a pH of 6.5. The nearly neutral solution is then placed in an electrolytic cell and allowed to stand as the electrolyte. Step 3: Use a fixture to clamp the magnesium-lithium alloy that has undergone pretreatment in Step 1 and place it in an electrolytic cell. The alloy is completely immersed in the electrolyte as the anode, and a stainless steel sheet is used as the cathode. The alloy is then treated according to a micro-arc oxidation process to prepare a micro-arc oxidation coating on the surface of the alloy. The micro-arc oxidation process is as follows: the micro-arc oxidation process uses a constant-voltage DC pulse power supply with a voltage of 400V, a frequency of 1500Hz, a duty cycle of 20%, and an oxidation time of 15 minutes. During the micro-arc oxidation process, a refrigerator is used to control the temperature of the electrolyte at 10°C to 15°C. The specific operation process is as follows: the voltage is increased from 0V to 220V and maintained for 1 minute, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is first reduced by 30V and maintained for 1 minute, and then reduced to 0V.

[0060] Step 4: The magnesium-lithium alloy treated with micro-arc oxidation in step 3 is completely immersed in a post-treatment liquid, wherein the post-treatment liquid is prepared by 40 g / L sodium fluoride and the rest is deionized water. The magnesium-lithium alloy is then placed in an ultrasonic tank and ultrasonically vibrated for 20 minutes at a temperature of 40°C. The alloy is then taken out and rinsed with deionized water. After drying and post-treatment, a matte coating of comparative example 4 is obtained on the surface of the magnesium-lithium alloy substrate.

[0061] Comparative Example 5 In this comparative example, 40 g / L sodium fluoride was added to the electrolyte, and the electrolyte was not treated in the post-treatment solution of step 4. The rest of the method was the same as that of Example 2.

[0062] The electrolyte consists of the following ingredients: 40 g / L sodium fluoride, 20 g / L sodium orthovanadate, 5 g / L sodium metagermanate, 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 rest is deionized water.

[0063] The method for applying the electrolyte comprises the following steps: Step 1: Select an LA103Z magnesium-lithium alloy sheet with a size (length × width × thickness) of 15 mm × 15 mm × 3 mm as the substrate, and polish the magnesium-lithium alloy step by step using 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper. Activate the magnesium-lithium alloy at room temperature for 30 seconds using a surfactant solution consisting of 5% nitric acid, 20% citric acid, and the rest deionized water. Rinse the surface of the magnesium-lithium alloy with deionized water, ultrasonically clean it in anhydrous ethanol for 10 minutes, blow dry it, and then complete the pretreatment. Step 2: Prepare an electrolyte. The components and contents of the electrolyte are as follows: 40 g / L sodium fluoride, 20 g / L sodium orthovanadate, 5 g / L sodium metagermanate, 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. Each reagent is sequentially added to deionized water and stirred continuously until completely dissolved to obtain a nearly neutral solution with a pH of 6.5. The nearly neutral solution is then placed in an electrolytic cell and allowed to stand as the electrolyte. Step 3: Use a fixture to clamp the magnesium-lithium alloy that has undergone pretreatment in Step 1 and place it in an electrolytic cell. The alloy is completely immersed in the electrolyte as the anode, and a stainless steel sheet is used as the cathode. The alloy is then treated according to a micro-arc oxidation process to prepare a micro-arc oxidation coating on the surface of the alloy. The micro-arc oxidation process is as follows: the micro-arc oxidation process uses a constant-voltage DC pulse power supply with a voltage of 400V, a frequency of 1500Hz, a duty cycle of 20%, and an oxidation time of 15 minutes. During the micro-arc oxidation process, a refrigerator is used to control the temperature of the electrolyte at 10°C to 15°C. The specific operation process is as follows: the voltage is increased from 0V to 220V and maintained for 1 minute, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is first reduced by 30V and maintained for 1 minute, and then reduced to 0V.

[0064] Comparative Example 6 In this comparative example, the post-treatment liquid in step 4 uses 10 wt % polyborosilazane diluent (the solvent is xylene) instead of sodium fluoride, and the rest of the method is the same as that in Example 2.

[0065] The electrolyte consists of the following ingredients: sodium orthovanadate 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 rest is deionized water.

[0066] The method for applying the electrolyte comprises the following steps: Step 1: Select an LA103Z magnesium-lithium alloy sheet with a size (length × width × thickness) of 15 mm × 15 mm × 3 mm as the substrate, and polish the magnesium-lithium alloy step by step using 320#, 600#, 800#, 1000#, 1500#, and 2000# water-resistant abrasive paper and metallographic sandpaper. Activate the magnesium-lithium alloy at room temperature for 30 seconds using a surfactant solution consisting of 5% nitric acid, 20% citric acid, and the rest deionized water. Rinse the surface of the magnesium-lithium alloy with deionized water, ultrasonically clean it in anhydrous ethanol for 10 minutes, blow dry it, and then complete the pretreatment. Step 2: Prepare an electrolyte. The components and contents of the electrolyte are as follows: 20 g / L sodium orthovanadate, 5 g / L sodium metagermanate, 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. Each reagent is sequentially added to deionized water and stirred continuously until completely dissolved to obtain a nearly neutral solution with a pH of 6.5. The nearly neutral solution is then placed in an electrolytic cell and allowed to stand as the electrolyte. Step 3: Use a fixture to clamp the magnesium-lithium alloy that has undergone pretreatment in Step 1 and place it in an electrolytic cell. The alloy is completely immersed in the electrolyte as the anode, and a stainless steel sheet is used as the cathode. The alloy is then treated according to a micro-arc oxidation process to prepare a micro-arc oxidation coating on the surface of the alloy. The micro-arc oxidation process is as follows: the micro-arc oxidation process uses a constant-voltage DC pulse power supply with a voltage of 400V, a frequency of 1500Hz, a duty cycle of 20%, and an oxidation time of 15 minutes. During the micro-arc oxidation process, a refrigerator is used to control the temperature of the electrolyte at 10°C to 15°C. The specific operation process is as follows: the voltage is increased from 0V to 220V and maintained for 1 minute, then increased at a rate of 30V / min to reach the target voltage. After the oxidation time, the voltage is first reduced by 30V and maintained for 1 minute, and then reduced to 0V.

[0067] Step 4: The magnesium-lithium alloy treated with micro-arc oxidation in step 3 is completely immersed in a post-treatment liquid, where the post-treatment liquid is a 10wt% polyborosilazane dilution prepared with xylene as a solvent, and then placed in an ultrasonic tank for 20 minutes at 40°C. The alloy is then taken out and dried in an oven (120°C for 90 minutes) to complete the post-treatment, and a matte coating of comparative example 6 is obtained on the surface of the magnesium-lithium alloy substrate.

[0068] Examples 1 to 3 were used as test groups, and Comparative Examples 1 to 6 were used as control groups to conduct corrosion resistance tests and solar light absorption rate tests. The test results are as follows: 1. Corrosion resistance test: Polarization curve tests were performed at room temperature using a Gamry electrochemical workstation in the United States. A three-electrode system (platinum electrode as counter electrode, saturated calomel electrode as reference electrode) was used. The scan rate was 1 mV / s, and the corrosion medium was 3.5% NaCl solution. The test results are shown in Table 2.

[0069] Table 2 Corrosion current of coatings in the test group and the control group: 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 ]]> .

[0070] It can be seen from Table 2 that under the same test conditions, the corrosion currents of Examples 1 to 3 are 7.247×10 -8 A / cm 2 , 9.659×10 -8 A / cm 2 , 8.746×10 -8 A / cm 2 , which is significantly lower than that of the control group, indicating that Examples 1 to 3 have better corrosion resistance. As can be seen from Comparative Example 1, the addition of sodium metagermanate to the electrolyte has a certain help in improving the corrosion resistance of the coating. As can be seen from Comparative Example 2, the corrosion resistance of the coating sample treated with the post-treatment liquid is significantly improved. As can be seen from Comparative Examples 3 and 4, compared with the use of sodium metavanadate combined with sodium metagermanate or sodium metagermanate alone, the coating obtained by the electrolyte system of sodium orthovanadate combined with sodium metagermanate in the present invention has better corrosion resistance. The present invention first adds ammonium fluoride to the electrolyte and then uses sodium fluoride in the post-treatment liquid. As can be seen from Comparative Example 5, the above two steps have a synergistic effect. Compared with directly adding ammonium fluoride and sodium fluoride to the electrolyte, the effect is better, the coating structure is continuous and dense and has no through holes, and Comparative Example 6 also proves that the above two steps have a synergistic effect. In Comparative Example 6, ammonium fluoride is first added to the electrolyte and polyborosilazane is used in the post-treatment liquid. The corrosion resistance of the coating formed in Comparative Example 6 is not as good as that of the present invention. The bonding strength of polyborosilazane with the oxide layer is poor, it is easy to peel off, and the film integrity is insufficient.

[0071] 2. Solar absorption rate test: The solar absorption rate test was carried out with reference to GJB 2502.2-2015. The test results are shown in Table 3.

[0072] Table 3 Solar light absorption rate of the coatings in the test group and the control group: 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 .

[0073] It can be seen from Table 3 that under the same test conditions, the solar light absorptivity of Examples 1 to 3 are 0.98, 0.95, and 0.96, respectively, while the solar light absorptivity of the control group is significantly decreased, indicating that Examples 1 to 3 have better extinction performance.

[0074] The existing technology often uses sodium metavanadate as a colorant. The present invention has found that the use of a combination of sodium orthovanadate and sodium metagermanate as a colorant has better effects than using sodium metavanadate alone. The electrolyte is clearer, has no flocculent precipitates, and is much more stable than sodium metavanadate. The electrolyte in the present invention uses sodium orthovanadate and sodium metagermanate as the main coloring salts. Under the action of the electric field, VO 3- and Ge 2+ Migrate into the discharge channel, participate in the micro-arc oxidation reaction, and undergo plasma thermochemical and electrochemical composite reactions. During the reaction, the reactants undergo further phase transformation at high temperature to form a complex salt with complex components, and react with the matrix material magnesium lithium to form a black coating composed of V2O5, GeO2, MgO, and MgF2. Compared with the comparative example 1 using sodium orthovanadate alone or the comparative example 3 using sodium metavanadate in combination with sodium metagermanate, the microstructure has a better solar light absorption rate and the corrosion resistance has also been significantly improved. When comparative example 4 uses sodium metagermanate alone, there will be some white or gray matter in the coating, and the coating is relatively loose, and the film-forming integrity is poor, thereby affecting its corrosion resistance and extinction performance. The coating obtained by the reaction after the sodium orthovanadate and sodium metagermanate are compounded has an improved solar light absorption rate, a better extinction effect, small color difference, and a uniform and smooth surface.

[0075] In the present invention, ammonium fluoride is first added to the electrolyte, and then sodium fluoride is used in the post-treatment liquid. Compared with Comparative Example 2 in which no treatment is performed in the post-treatment liquid and Comparative Example 5 in which sodium fluoride is directly added to the electrolyte, the present invention has better effect, and the coating structure is continuous and dense without through holes. In Comparative Example 6, ammonium fluoride is first added to the electrolyte, and polyborosilazane is used in the subsequent treatment. The microstructure formed in Comparative Example 6 has a low solar light absorption rate and is not as good as the present invention in corrosion resistance, which also shows that the use of sodium fluoride in the post-treatment liquid has a synergistic effect with the electrolyte of the present invention.

[0076] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution 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: 20 g / L to 30 g / L of sodium orthovanadate, 5 g / L to 10 g / L of sodium metagermanate, 5 g / L to 10 g / L of ammonium dihydrogen phosphate, 2 g / L to 4 g / L of ammonium fluoride, 5 g / L to 10 g / L of sodium tripolyphosphate, 5 mL / L to 10 mL / L of triethanolamine, 10 mL / L to 20 mL / L of glacial acetic acid, and the remainder is deionized water; the pH of the electrolyte is 6.5 to 7.

5.

2. The use of the electrolyte for preparing an amorphous matte coating on the surface of a magnesium-lithium alloy according to claim 1, characterized in that: The following steps are involved: Step 1: After polishing, the magnesium-lithium alloy is activated with a surface activation solution; Step 2: prepare an electrolyte, wherein the components and contents of the electrolyte are as follows: 20 g / L to 30 g / L sodium orthovanadate, 5 g / L to 10 g / L sodium metagermanate, 5 g / L to 10 g / L ammonium dihydrogen phosphate, 2 g / L to 4 g / L ammonium fluoride, 5 g / L to 10 g / L sodium tripolyphosphate, 5 mL / L to 10 mL / L triethanolamine, and 10 mL / L to 20 mL / L glacial acetic acid; Step 3: The magnesium-lithium alloy treated in step 1 is completely immersed in an electrolyte as an anode, and a stainless steel sheet is used as a cathode, and then treated according to a micro-arc oxidation process to prepare a micro-arc oxidation coating on the surface of the magnesium-lithium alloy; Step 4: The magnesium-lithium alloy treated by micro-arc oxidation in step 3 is completely immersed in a post-treatment solution, and an amorphous matte coating is obtained on the surface of the magnesium-lithium alloy after ultrasonic treatment.

3. The use according to claim 2, characterized in that The components and mass percentages of the surfactant solution described in step 1 are: 5% to 10% nitric acid, 20% to 30% citric acid, and the remainder is deionized water.

4. The use according to claim 2, characterized in that Step 1 includes the following specific contents: 320#, 600#, 800#, 1000#, 1500#, 2000# water-resistant abrasive paper and metallographic sandpaper are used to polish the magnesium-lithium alloy step by step, and the magnesium-lithium alloy is activated for 30 seconds using a surface activation liquid at room temperature. Then, the surface of the magnesium-lithium alloy is rinsed with deionized water and then ultrasonically cleaned in anhydrous ethanol for 10 minutes.

5. The use according to claim 2, characterized in that The pH of the electrolyte in step 2 is 6.5-7.5, and glacial acetic acid is used to adjust the pH.

6. The use according to claim 2, characterized in that The micro-arc oxidation process in step three is as follows: the micro-arc oxidation treatment adopts 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 use according to claim 2, characterized in that Step three includes the following operation process: boosting the voltage from 0V to 220V and maintaining it for 1 minute, then boosting the voltage to the target voltage at a rate of 30V / min, and performing micro-arc oxidation treatment. After the micro-arc oxidation treatment is completed, the voltage is first reduced by 30V and maintained for 1 minute, and then reduced to 0V.

8. The use according to claim 2, characterized in that The composition and content of the post-treatment liquid in step 4 are: 40g / L~50g / L sodium fluoride, and the rest is deionized water.

9. The use according to claim 2, characterized in that The ultrasonic treatment time in step 4 is 20 min to 30 min, and the temperature is 40° C. to 50° C.

Images