A preparation method of a far infrared ray emitting coating with a thickness of 8-14 microns on a surface of a dual-phase magnesium-lithium alloy based on jet powdering

Abstract

A method for preparing an 8-14 μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray-applied powder. This invention relates to the field of material surface treatment technology, specifically to a method for preparing an 8-14 μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray-applied powder. This invention aims to solve the problems of poor corrosion resistance, low far-infrared emissivity of the alloy surface, and inability to effectively generate far-infrared radiation in magnesium-lithium alloys. The method includes: 1. Powder weighing; 2. Ball milling and powder mixing; 3. Pretreatment of the magnesium-lithium alloy surface; 4. Preparation of a sodium silicate-based micro-arc oxidation electrolyte; 5. Spray-applied powder preparation; 6. Micro-arc oxidation process. This invention is suitable for alloy materials such as aluminum, magnesium, and titanium, and the resulting coating exhibits good far-infrared radiation performance and a long service life.

Description

Technical Field

[0001] This invention relates to the field of material surface treatment technology, specifically to a method for preparing an 8-14μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray powder addition. Background Technology

[0002] Magnesium-lithium alloys are the lightest alloys, with a density of 1.30–1.65 g / cm³. 3 Magnesium-lithium alloys possess excellent properties such as high specific strength and specific stiffness, good damping performance, and resistance to high-energy particle penetration. They also exhibit good cold and hot working properties, making them ideal materials for lightweight components. They have broad application prospects in aerospace, automotive, electronics, and military fields. The addition of lithium can reduce the density of magnesium alloys, increase their plasticity, and decrease their strength. However, lithium has a lower electronegativity than magnesium, significantly reducing the corrosion resistance of magnesium alloys. Magnesium-lithium alloys are highly chemically reactive; magnesium and lithium readily react with oxygen, hydrogen, and nitrogen in the air, resulting in extremely low corrosion resistance. This poor corrosion resistance limits the application of magnesium-lithium alloys.

[0003] Infrared radiation is an inherent property of materials. Infrared radiation materials have wide applications in aerospace, aviation, remote sensing, military, construction, furnace heating, rescue monitoring, medical care and other fields. At present, the preparation methods of metal far-infrared radiation materials are: (1) Surface compound generation method: compounds are generated on the surface by heating or contact with other oxidizing elements. The compound generation is unstable; (2) Alloying method: elements with strong infrared radiation are added to the alloy. The cost is high; (3) Surface coating method: a coating method to generate a certain thickness of coating on the metal surface by coating. A variety of compounds with high infrared radiation are mixed to form a bonding coating. Some coatings are easy to peel off; (4) A coating with certain infrared emission performance is formed on the alloy surface by chemical conversion, anodizing, micro-arc oxidation and electrodeposition technology. Some coatings use Al2O3, SiC and TiO2 particles to improve infrared radiation performance; most patented technologies are to prepare coatings to prevent the release of infrared rays and form thermal control coatings.

[0004] Infrared detection primarily focuses on two atmospheric window bands: 3-5μm and 8-14μm. Far-infrared radiation with wavelengths of 5.6-15μm plays a vital role in human survival and the growth of all things, possessing molecular resonance penetration properties that promote plant and animal growth. Among these, far-infrared radiation in the 8-14μm band resonates with water molecules in the human body, exerting the greatest effect on the human body and possessing the highest application value; it is known as the "lifeline." Magnesium-lithium alloys have low density and can be used as outer shells for infrared decoys or ground-based false targets. However, the metal itself has a weak infrared radiation capability, and the infrared radiation it produces is insufficient for applications requiring high infrared emissivity. Furthermore, as a device for human rehabilitation, it cannot produce far-infrared radiation easily absorbed by the skin surface, thus failing to effectively accelerate blood circulation. Summary of the Invention

[0005] This invention aims to address the problems of poor corrosion resistance and low far-infrared emissivity of magnesium-lithium alloys, which prevent the effective generation of far-infrared rays. It provides a method for preparing an 8-14 μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray-applied powder.

[0006] A method for preparing an 8-14 μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray powder addition is specifically carried out according to the following steps:

[0007] 1. Powder weighing: Mix tourmaline powder, MgO powder, Al2O3 powder and suspending agent in a mortar until homogeneous as raw material powder;

[0008] 2. Ball milling and powder mixing: Place the raw material powder into the ball mill jar of the planetary ball mill and add anhydrous ethanol to the ball mill jar; transfer the ball mill jar to the ball mill and place the empty jar counterweight in the corresponding position, and lock the ball mill jar; turn on the ball mill power to ball mill and mix. After mixing, take out the powder, let it air dry, put it into the mortar and grind it again, pour the ground powder into a transparent plastic tube, seal both ends with caps, and obtain the raw material powder encapsulation tube;

[0009] III. Surface pretreatment of magnesium-lithium alloy: The magnesium-lithium alloy is cut into round samples. The two surfaces of the round samples are sandblasted and then polished with silicon carbide wet sandpaper. Then, they are placed in a beaker containing anhydrous ethanol and cleaned in an ultrasonic cleaner. After air drying, the magnesium-lithium alloy samples are obtained.

[0010] IV. Preparation of sodium silicate-based micro-arc oxidation electrolyte: Sodium silicate, potassium hydroxide, glycerol, phytic acid and colorant are added sequentially to deionized water. Each chemical reagent is stirred with a magnetic stirrer to ensure complete dissolution, thus obtaining the micro-arc oxidation electrolyte.

[0011] V. Preparation for spraying powder: Prepare two electromagnetic air compressor oxygen pumps. Connect a clean plastic tube to the outlet of one oxygen pump and insert an air stone. Open one end of the raw material powder packaging tube and insert it into the outlet of the other oxygen pump.

[0012] VI. Micro-arc oxidation process: Pour the micro-arc oxidation electrolyte into a stainless steel tank. Use a bipolar pulsed micro-arc oxidation power supply, connecting the stainless steel tank to the negative terminal of the power supply as the cathode. Clamp the magnesium-lithium alloy sample with a special clamp and connect it to the positive terminal of the power supply as the anode. Place the magnesium-lithium alloy sample into the electrolyte and stabilize it for 180 seconds. Then, place the plastic tube with air bubbles into the electrolyte and turn on the oxygen pump. Turn on the micro-arc oxidation power supply and open the cap at the other end of the raw material powder packaging tube, placing it into the electrolyte. Turn on the oxygen pump power supply, and spray the raw material powder inside the packaging tube into the micro-arc oxidation electrolyte. At the same time, use a powerful stirrer to stir. The outside of the stainless steel tank is cooled with circulating water to control the electrolyte temperature below 38℃. After the micro-arc oxidation coating preparation is completed, turn off the micro-arc oxidation power supply, the oxygen pump power supply, and the stirrer power supply. Take out the sample, rinse it with deionized water, dry the sample with a hair dryer, and place it in a sealed bag for later use.

[0013] The beneficial effects of this invention are:

[0014] This invention employs micro-arc oxidation technology, where a ball-milled mixed powder is injected into an electrolyte solution under gas pressure. Then, under high voltage, the gas in the electrolyte ionizes, generating a micro-arc discharge on the surface of a magnesium-lithium alloy. This promotes the embedding of tourmaline particles from the electrolyte into an in-situ oxide ceramic coating formed on the magnesium-lithium alloy surface. The result is a self-generated coating on the magnesium-lithium alloy surface with tourmaline doping. This coating exhibits high bonding strength with the substrate, improving the corrosion resistance and far-infrared emissivity (8-14 μm) of the magnesium-lithium alloy. This method is simple, suitable for alloys such as aluminum, magnesium, and titanium, and produces a coating with good far-infrared radiation performance and a long service life. Attached Figure Description

[0015] Figure 1 The image shows the SEM surface morphology of the micro-arc oxidation coating on the magnesium-lithium alloy surface obtained in the example.

[0016] Figure 2 The image shows the SEM cross-sectional morphology of the micro-arc oxidation coating on the magnesium-lithium alloy surface obtained in the example.

[0017] Figure 3 The wetting angle test diagram for Mg-7Li alloy is shown.

[0018] Figure 4 The image shows the wetting angle test results of the micro-arc oxidation coating on the magnesium-lithium alloy surface obtained in the example.

[0019] Figure 5The image shows a comparison of the polarization curves of the micro-arc oxidation coating on the surface of the Mg-7Li alloy and the magnesium-lithium alloy obtained in the examples; where 1 represents the Mg-7Li alloy and 2 represents the micro-arc oxidation coating on the surface of the magnesium-lithium alloy obtained in the examples.

[0020] Figure 6 The image shows a comparison of the infrared emissivity of the micro-arc oxidation coating on the surface of the Mg-7Li alloy and the magnesium-lithium alloy obtained in the example; where 1 represents the Mg-7Li alloy and 2 represents the micro-arc oxidation coating on the surface of the magnesium-lithium alloy obtained in the example. Detailed Implementation

[0021] Specific Implementation Method 1: This implementation method describes a method for preparing an 8-14μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray powder addition, specifically following these steps:

[0022] 1. Powder weighing: Mix tourmaline powder, MgO powder, Al2O3 powder and suspending agent in a mortar until homogeneous as raw material powder;

[0023] 2. Ball milling and powder mixing: Place the raw material powder into the ball mill jar of the planetary ball mill and add anhydrous ethanol to the ball mill jar; transfer the ball mill jar to the ball mill and place the empty jar counterweight in the corresponding position, and lock the ball mill jar; turn on the ball mill power to ball mill and mix. After mixing, take out the powder, let it air dry, put it into the mortar and grind it again, pour the ground powder into a transparent plastic tube, seal both ends with caps, and obtain the raw material powder encapsulation tube;

[0024] III. Surface pretreatment of magnesium-lithium alloy: The magnesium-lithium alloy is cut into round samples. The two surfaces of the round samples are sandblasted and then polished with silicon carbide wet sandpaper. Then, they are placed in a beaker containing anhydrous ethanol and cleaned in an ultrasonic cleaner. After air drying, the magnesium-lithium alloy samples are obtained.

[0025] IV. Preparation of sodium silicate-based micro-arc oxidation electrolyte: Sodium silicate, potassium hydroxide, glycerol, phytic acid and colorant are added sequentially to deionized water. Each chemical reagent is stirred with a magnetic stirrer to ensure complete dissolution, thus obtaining the micro-arc oxidation electrolyte.

[0026] V. Preparation for spraying powder: Prepare two electromagnetic air compressor oxygen pumps. Connect a clean plastic tube to the outlet of one oxygen pump and insert an air stone. Open one end of the raw material powder packaging tube and insert it into the outlet of the other oxygen pump.

[0027] VI. Micro-arc oxidation process: Pour the micro-arc oxidation electrolyte into a stainless steel tank. Use a bipolar pulsed micro-arc oxidation power supply, connecting the stainless steel tank to the negative terminal of the power supply as the cathode. Clamp the magnesium-lithium alloy sample with a special clamp and connect it to the positive terminal of the power supply as the anode. Place the magnesium-lithium alloy sample into the electrolyte and stabilize it for 180 seconds. Then, place the plastic tube with air bubbles into the electrolyte and turn on the oxygen pump. Turn on the micro-arc oxidation power supply and open the cap at the other end of the raw material powder packaging tube, placing it into the electrolyte. Turn on the oxygen pump power supply, and spray the raw material powder inside the packaging tube into the micro-arc oxidation electrolyte. At the same time, use a powerful stirrer to stir. The outside of the stainless steel tank is cooled with circulating water to control the electrolyte temperature below 38℃. After the micro-arc oxidation coating preparation is completed, turn off the micro-arc oxidation power supply, the oxygen pump power supply, and the stirrer power supply. Take out the sample, rinse it with deionized water, dry the sample with a hair dryer, and place it in a sealed bag for later use.

[0028] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the tourmaline powder used in step one has a mesh size of 150-200 mesh. Everything else is the same as in Specific Implementation Method One.

[0029] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 2 in that the weight ratio of tourmaline powder, MgO powder, and Al2O3 powder in step one is 18:1:1. Everything else is the same as in Specific Implementation Method 2.

[0030] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method One in that the amount of suspending agent added in step one is 5-10%. Everything else is the same as in Specific Implementation Method One.

[0031] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method One in that the anhydrous ethanol level in step two is 2-3 mm above the raw material powder. Everything else is the same as in Specific Implementation Method One.

[0032] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method One in that the ball milling parameters in step two are: rotation speed of 300 r / min, forward and reverse mixing settings, and mixing time of 40–60 min. Everything else is the same as in Specific Implementation Method One.

[0033] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method One in that the grinding time in step two is 3-5 minutes. Everything else is the same as in Specific Implementation Method One.

[0034] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method One in that the inner diameter of the transparent plastic tube mentioned in step two is 4.5–5 mm, the wall thickness is 0.5 mm, and the length is 40–80 mm. Everything else is the same as in Specific Implementation Method One.

[0035] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method One in that the magnesium-lithium alloy described in step three is a cast Mg-7Li alloy, composed of 92.04% Mg, 7% Li, 0.4% Al, and 0.56% Zn by weight, and has an α+β dual-phase structure. Everything else is the same as in Specific Implementation Method One.

[0036] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method One in that the diameter of the circular sample in step three is 30±0.1mm, and the thickness is 3-5mm. Everything else is the same as in Specific Implementation Method One.

[0037] Specific Implementation Method Eleven: This implementation method differs from Specific Implementation Method One in that, in step three, the surface is polished using silicon carbide wet sandpaper at grits of 180, 400, 600, 800, 1000, and 1200 grits in sequence. Everything else is the same as in Specific Implementation Method One.

[0038] Specific Implementation Method Twelve: This implementation method differs from Specific Implementation Method One in that the sandblasting time in step three is 5-10 minutes. Everything else is the same as in Specific Implementation Method One.

[0039] Specific Implementation Method Thirteen: This implementation method differs from Specific Implementation Method One in that the cleaning time in the ultrasonic cleaner in step three is 3-5 minutes. Everything else is the same as in Specific Implementation Method One.

[0040] Specific Implementation Method Fourteen: This implementation method differs from Specific Implementation Method One in that the sodium silicate in the micro-arc oxidation electrolyte described in step four is 20-40 g / L, potassium hydroxide is 5-8 g / L, glycerol is 10-20 mL / L, phytic acid is 1-3 mL / L, and colorant is 1-3 g / L. Everything else is the same as in Specific Implementation Method One.

[0041] Specific Implementation Method Fifteen: This implementation method differs from Specific Implementation Method One in that the process parameters for micro-arc oxidation in step six are: frequency 200–600 Hz, duty cycle 8–15%, voltage 300–450 V, and oxidation time 20–30 min. All other parameters are the same as in Specific Implementation Method One.

[0042] Specific Implementation Method Sixteen: This implementation method differs from Specific Implementation Method One in that the concentration of the raw material powder sprayed into the micro-arc oxidation electrolyte in step six is ​​20 g / L to 25 g / L. Everything else is the same as in Specific Implementation Method One.

[0043] Specific Implementation Method Seventeen: This implementation method differs from Specific Implementation Method One in that: the suspending agent in step one is sodium alginate; and the colorant in step four is ferrous sulfate. Everything else is the same as in Specific Implementation Method One.

[0044] The effectiveness of the present invention was verified through the following experiments:

[0045] Example 1: A method for preparing an 8-14 μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray powder addition is specifically carried out according to the following steps:

[0046] 1. Powder weighing: Place 18g of tourmaline powder (passed through a 150-200 mesh sieve), 1g of MgO powder, 1g of Al2O3 powder, and 1-2g of suspending agent into a mortar and mix evenly to obtain the raw material powder.

[0047] II. Ball Milling and Powder Mixing: Place the raw material powder into the ball mill jar of the planetary ball mill, and add anhydrous ethanol to the jar to a level 2-3 mm above the raw material powder. Transfer the ball mill jar to the ball mill, place the empty jar counterweight in the corresponding position, and lock the ball mill jar. Turn on the ball mill power, set the process parameters to 300 r / min, set forward and reverse mixing, and mix for 40-60 min. After mixing, remove the powder, let it air dry naturally, and grind it again in the mortar for 3-5 min. Pour the ground powder into a transparent plastic tube with an inner diameter of 4.5-5 mm, a wall thickness of 0.5 mm, and a length of 40-80 mm. Seal both ends with caps to obtain the raw material powder encapsulation tube.

[0048] III. Surface Pretreatment of Magnesium-Lithium Alloy: The magnesium-lithium alloy is cut into circular samples. Both surfaces of the circular samples are sandblasted for 5-10 minutes, and then polished sequentially with silicon carbide wet sandpaper of 180 mesh, 400 mesh, 600 mesh, 800 mesh, 1000 mesh, and 1200 mesh. The samples are then placed in a beaker containing anhydrous ethanol and cleaned in an ultrasonic cleaner for 3-5 minutes, followed by natural air drying to obtain the magnesium-lithium alloy samples. The magnesium-lithium alloy is a cast Mg-7Li alloy, composed of 92.04% Mg, 7% Li, 0.4% Al, and 0.56% Zn by weight, exhibiting an α+β dual-phase structure. The diameter of the circular samples is 30±0.1 mm, and the thickness is 3-5 mm.

[0049] IV. Preparation of sodium silicate-based micro-arc oxidation electrolyte: Sodium silicate, potassium hydroxide, glycerol, phytic acid, and colorant are added sequentially to deionized water. Each chemical reagent is stirred with a magnetic stirrer until completely dissolved to obtain the micro-arc oxidation electrolyte. The micro-arc oxidation electrolyte contains 20–40 g / L sodium silicate, 5–8 g / L potassium hydroxide, 10–20 mL / L glycerol, 1–3 mL / L phytic acid, and 1–3 g / L colorant.

[0050] V. Preparation for spraying powder: Prepare two electromagnetic air compressor oxygen pumps. Connect a clean plastic tube to the outlet of one oxygen pump and insert an air stone. Open one end of the raw material powder packaging tube and insert it into the outlet of the other oxygen pump.

[0051] VI. Micro-arc oxidation process: Pour the micro-arc oxidation electrolyte into a stainless steel tank. Use a bipolar pulsed micro-arc oxidation power supply, connecting the stainless steel tank to the negative terminal of the power supply as the cathode. Clamp the magnesium-lithium alloy sample with a special clamp and connect it to the positive terminal of the power supply as the anode. Place the magnesium-lithium alloy sample in the electrolyte and stabilize it for 180 seconds. Then, place the plastic tube with air bubbles into the electrolyte and turn on the oxygen pump. Turn on the micro-arc oxidation power supply and open the cap at the other end of the raw material powder packaging tube, placing it into the electrolyte. Turn on the oxygen pump power supply, and the raw material powder inside the packaging tube will be sprayed into the micro-arc oxidation electrolyte. Simultaneously, a powerful stirrer is used for stirring, and the stainless steel tank is cooled by circulating water to control the electrolyte temperature below 38℃. After the micro-arc oxidation coating preparation is completed, the micro-arc oxidation power supply, oxygen pump power supply, and stirrer power supply are turned off. The sample is taken out, rinsed with deionized water, dried with a hair dryer, and placed in a sealed bag for later use. The process parameters of the micro-arc oxidation are: frequency 200-600Hz, duty cycle 8-15%, voltage 300-450V, oxidation time 20-30min; the concentration of raw material powder sprayed into the micro-arc oxidation electrolyte is 20-25g / L.

[0052] A tourmaline-doped ceramic coating is formed on the surface of a magnesium-lithium alloy using a micro-arc oxidation technique via a spray powder addition method. This coating has a strong bond with the substrate, high hardness, and easily controllable thickness, and exhibits a high far-infrared emissivity of 8-14μm. Figure 1 The surface morphology of the micro-arc oxidation ceramic coating on Mg-7Li magnesium alloy is shown. It can be seen that the micro-arc oxidation coating exhibits a porous, crater-like honeycomb structure with numerous embedded particles on the surface, visible within the micropores. During micro-arc oxidation, the generated high voltage breaks down the double layer of the alloy surface, forming numerous micro-arcs. Under high temperature and pressure, magnesium and lithium react with oxygen to form a relatively thick oxide film on the surface. Simultaneously, the electrolyte doped with tourmaline powder, MgO powder, and Al2O3 powder, driven by the electric arc, promotes particle embedding into the generated ceramic coating. The micro-arc oxidation coating is formed in situ on the surface of the Mg-7Li magnesium alloy substrate. This coating has a strong bond with the substrate, high hardness, and easily controllable thickness. Tourmaline particles are visible distributed within the coating. The tourmaline powder in the coating is a boron-dominant cyclic silicate mineral with permanent spontaneous electrodes that generate an electrostatic field. It possesses permanent electric field and self-polarization properties, enabling the electrolysis of adsorbed water molecules on the surface through a weak current. Figure 2 The cross-sectional morphology of the Mg-7Li magnesium alloy micro-arc oxidation ceramic coating shows that the coating thickness is 15-20 μm.

[0053] Figure 3 and Figure 4The wetting angle test results are for the Mg-7Li magnesium alloy matrix and the alloy with micro-arc oxidation ceramic coating, respectively. The wetting angle of the Mg-7Li alloy is 23°, which is relatively small. The wetting angle of the alloy with micro-arc oxidation ceramic coating is 38.48°, which is higher than the wetting angle of the alloy itself, making it difficult for the corrosive medium to spread on the alloy surface.

[0054] Figure 5 Polarization curve analysis was performed on magnesium-lithium alloys and alloys with micro-arc oxidation coatings. Table 1 shows the polarization curve fitting results. Figure 5 As shown in Table 1, the corrosion electrode potential of the magnesium-lithium alloy matrix is ​​-1.5857V, and the corrosion current density is 2.235×10⁻⁶. -4 A·cm -2 The corrosion electrode potential of the alloy with the micro-arc oxidation coating is -1.4202V, and the corrosion current density is 5.666×10⁻⁶. -6 A·cm -2 Compared to the substrate, the alloy with micro-arc oxidation coating exhibits increased corrosion electrode potential and a two-order-of-magnesium reduction in corrosion current density, effectively improving the corrosion resistance of magnesium-lithium alloys.

[0055] Table 1. Results of Polarization Curve Fitting Data

[0056]

[0057] Figure 6 The far-infrared emissivity of Mg-7Li alloys and alloys with micro-arc oxidation coatings in the 8-14 μm range. (From...) Figure 6 As can be seen, the infrared emissivity of the substrate is between 0.08 and 0.45 in the 4-20 μm wavelength range, with an average infrared emissivity of 0.18 in the 4-7 μm wavelength range and 0.25 in the 7-20 μm wavelength range. Maximum infrared emissivity peaks occur at 7 μm and 18.5 μm, at 0.35 and 0.45, respectively. The coated alloy surface has a porous coating, increasing the radiative surface area. The infrared emissivity of the coated alloy is between 0.6 and 0.95, with a minimum infrared emissivity of approximately 0.6 at 8 μm. In the 8-14 μm wavelength range, the infrared emissivity of the substrate is between 0.15 and 0.3, while the infrared emissivity of the coated alloy is between 0.7 and 0.92. Compared with the Mg-7Li magnesium alloy substrate, the far-infrared radiation emissivity of the micro-arc oxidation coating prepared by this invention is improved, which effectively increases the far-infrared emissivity of the magnesium alloy surface in the 8-14μm wavelength range. Far-infrared rays in this band can resonate with water molecules in the human body, which can accelerate blood circulation and metabolism, produce a warming effect, and soothe nerves, thus having other therapeutic and health care effects.

Claims

1. A method for preparing an 8-14 μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray-applied powder, characterized in that... The preparation method of the 8-14μm far-infrared emitting coating on the surface of the dual-phase magnesium-lithium alloy based on spray powder addition is carried out according to the following steps:

1. Powder weighing: Mix tourmaline powder, MgO powder, Al2O3 powder and suspending agent in a mortar until homogeneous as raw material powder; the tourmaline powder has a mesh size of 150-200 mesh; the weight ratio of tourmaline powder, MgO powder and Al2O3 powder is 18:1:

1.

2. Ball milling and powder mixing: Place the raw material powder into the ball mill jar of the planetary ball mill and add anhydrous ethanol to the ball mill jar; transfer the ball mill jar to the ball mill and place the empty jar counterweight in the corresponding position, and lock the ball mill jar; turn on the ball mill power to ball mill and mix. After mixing, take out the powder, let it air dry, put it into the mortar and grind it again, pour the ground powder into a transparent plastic tube, seal both ends with caps, and obtain the raw material powder encapsulation tube; III. Surface Pretreatment of Magnesium-Lithium Alloy: The magnesium-lithium alloy was cut into circular samples. Both surfaces of the circular samples were sandblasted, and then the surfaces were polished with silicon carbide wet sandpaper. The samples were then placed in a beaker containing anhydrous ethanol and cleaned in an ultrasonic cleaner. After air drying, the magnesium-lithium alloy samples were obtained. The magnesium-lithium alloy was a cast Mg-7Li alloy, which was composed of 92.04% Mg, 7% Li, 0.4% Al and 0.56% Zn by weight percentage, and had an α+β dual-phase structure. IV. Preparation of sodium silicate-based micro-arc oxidation electrolyte: Sodium silicate, potassium hydroxide, glycerol, phytic acid and colorant are added sequentially to deionized water. Each chemical reagent is stirred with a magnetic stirrer to ensure complete dissolution, thus obtaining the micro-arc oxidation electrolyte. V. Preparation for spraying powder: Prepare two electromagnetic air compressor oxygen pumps. Connect a clean plastic tube to the outlet of one oxygen pump and insert an air stone. Open one end of the raw material powder packaging tube and insert it into the outlet of the other oxygen pump. VI. Micro-arc oxidation process: Pour the micro-arc oxidation electrolyte into a stainless steel tank, and use a bipolar pulsed micro-arc oxidation power supply to connect the stainless steel tank to the negative terminal of the power supply as the cathode. Clamp the magnesium-lithium alloy sample with a special chuck, connect it to the positive terminal of the power supply as the anode, place the magnesium-lithium alloy sample in the electrolyte and stabilize it for 180 seconds, then put the plastic tube with air bubbles into the electrolyte and turn on the oxygen pump. Turn on the micro-arc oxidation power supply and open the cap at the other end of the raw material powder packaging tube, place it in the electrolyte, turn on the oxygen pump power supply, and spray the raw material powder inside the raw material powder packaging into the micro-arc oxidation electrolyte; at the same time, use a powerful stirrer to stir, and use circulating water to cool the outside of the stainless steel tank to control the electrolyte temperature below 38℃; after the micro-arc oxidation coating preparation is completed, turn off the micro-arc oxidation power supply, oxygen pump power supply and stirrer power supply, take out the sample, rinse it with deionized water, dry the sample with a hair dryer and put it in a sealed bag for later use; the process parameters of the micro-arc oxidation are: frequency 200~600Hz, duty cycle 8~15%, voltage 300~450V, oxidation time 20~30min.

2. The method for preparing an 8-14 μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray-applied powder, as described in claim 1, is characterized in that... The amount of suspending agent added in step one is 5-10%.

3. The method for preparing an 8-14 μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray-applied powder, as described in claim 1, is characterized in that... The parameters for the ball mill described in step two are: rotation speed of 300 r / min, forward and reverse mixing, and mixing time of 40~60 min.

4. The method for preparing an 8-14 μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray-applied powder, as described in claim 1, is characterized in that... The transparent plastic tube mentioned in step two has an inner diameter of 4.5~5mm, a wall thickness of 0.5mm, and a length of 40~80mm.

5. The method for preparing an 8-14 μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray-applied powder, as described in claim 1, is characterized in that... In step four, the micro-arc oxidation electrolyte contains 20-40 g / L sodium silicate, 5-8 g / L potassium hydroxide, 10-20 mL / L glycerol, 1-3 mL / L phytic acid, and 1-3 g / L colorant.

6. The method for preparing an 8-14 μm far-infrared emitting coating on the surface of a dual-phase magnesium-lithium alloy based on spray-applied powder, as described in claim 1, is characterized in that... In step six, the concentration of the raw material powder sprayed into the micro-arc oxidation electrolyte is 20 g / L to 25 g / L.

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