Method for preparing high-entropy alloy coating on magnesium alloy surface based on SLM technology

Abstract

The invention discloses a method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on an SLM technology, relates to the technical field of surface protection materials, and successfully overcomes the difficulty of preparing the coating on the surface of the magnesium alloy by using a selective laser melting technology. In the melting process of the high-entropy alloy powder, good metallurgical bonding is achieved between the high-entropy alloy powder and a magnesium alloy base material, a firm bonding interface is formed between a coating and a base body, the problems of coating falling, peeling and the like are effectively avoided, and the stability and long-acting protection performance of the coating are guaranteed. The maximum hardness of the high-entropy alloy coating prepared through the method can reach 452.2 HV, and compared with a magnesium alloy matrix, the hardness of the high-entropy alloy coating is greatly improved; the surface wear resistance of the magnesium alloy is obviously enhanced; an effective protective barrier is formed on the surface of the magnesium alloy, external friction, corrosion and the like can be resisted, the service life of a magnesium alloy product is greatly prolonged, and possibility is provided for application of the magnesium alloy in more fields with strict requirements for surface performance.

Description

Technical Field

[0001] The present invention relates to the technical field of surface protection materials, and particularly to a method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on SLM technology. Background Art

[0002] Due to characteristics such as low density, high specific strength and specific stiffness, good electromagnetic shielding, and easy recyclability, magnesium alloys are widely used in fields such as aerospace, automotive, and electronics. However, the properties of magnesium alloys such as hardness and wear resistance are relatively poor, which severely restricts their application in actual engineering. Therefore, it is extremely crucial to improve the hardness and other properties of magnesium alloys. High-entropy alloys possess high strength, high hardness, good wear resistance, corrosion resistance, and high-temperature stability. Preparing a high-entropy alloy coating on the surface of a magnesium alloy can significantly enhance the hardness, wear resistance, and other properties of the magnesium alloy.

[0003] Currently, there are many challenges in preparing coatings on the surface of magnesium alloys. From the perspective of material characteristics, magnesium as a substrate is significantly different from general materials such as aluminum, steel, and copper. Under the action of high-energy laser, magnesium is extremely easy to melt, volatilize, or even burn, which makes it extremely difficult to prepare coatings on the surface of magnesium alloys by laser. This is also the main reason why laser coating preparation is rarely used for magnesium alloys at present.

[0004] Therefore, the current mainstream surface treatment technologies for magnesium alloys include electroplating, electroless plating, thermal spraying, etc., but they have the following disadvantages respectively:

[0005] Electroplating technology deposits a metal coating on the surface of a magnesium alloy through an electrochemical method. It is often used to improve the corrosion resistance and decorative properties of magnesium alloys, and can obtain a uniform and delicate coating, and good coverage can also be achieved on the surface of workpieces with complex shapes. However, the electroplating process consumes a large amount of chemical reagents, which is easy to cause environmental pollution; and the bonding strength between the electroplated layer and the magnesium alloy substrate is relatively low, and the coating is easy to fall off when subjected to a large external force impact. From the perspective of cost analysis, the chemical reagent cost and wastewater treatment cost of electroplating are relatively high; in terms of production efficiency, the electroplating process is relatively cumbersome and the production cycle is long.

[0006] Electroless plating deposits a metal coating on the surface of a magnesium alloy based on an oxidation-reduction reaction. It does not require an external power supply, the operation is relatively simple, and the coating can be applied on non-conductive surfaces. However, electroless plating has a high cost, poor stability of the plating solution, and the plating solution needs to be frequently replaced. Moreover, the hardness improvement of the electroless plating layer is limited, and the effect on improving the wear resistance of magnesium alloys is not ideal enough. Electroless plating has obvious shortcomings in improving the comprehensive performance of magnesium alloys and cannot meet the application scenarios with high requirements for hardness and wear resistance.

[0007] Cold spraying technology is a new type of surface coating preparation technology. High-pressure gas is used to accelerate solid powder particles to supersonic speed, which impacts the substrate surface and causes plastic deformation to form a coating. Although it has advantages, it also has limitations. The equipment cost is high, requiring high-pressure gas sources, spray guns, powder feeding systems, etc., and the purchase and maintenance costs are expensive. There are strict requirements for materials. Not only should they have good toughness and deformability, but also requirements for particle size, shape, and fluidity, which limits material selection. The deposition efficiency is low. Compared with some thermal spraying technologies, it takes a long time to obtain a coating of a certain thickness, and large-scale production is likely to slow down the progress and increase costs. Moreover, the impact force of particles on the substrate is large, requiring high substrate strength and hardness. Repeated spraying to increase the coating thickness will increase stress, resulting in coating cracking and peeling, which limits the coating thickness. Summary of the Invention

[0008] In view of the above deficiencies of the prior art, the present invention provides a method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on SLM technology.

[0009] To achieve the above invention purpose, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on SLM technology is provided, which includes the following steps:

[0011] S1: The high-entropy alloy powder with a molar ratio of Al, Cr, Mn, Fe, Co, and Ni of 1:1:1:1:1:1 prepared by vacuum gas atomization is dried at 50°C in an endothermic atmosphere furnace to obtain dry high-entropy alloy powder;

[0012] S2: The high-entropy alloy powder is evenly laid on the surface of the magnesium alloy substrate;

[0013] S3: In an argon environment, the powder layer is scanned with a laser beam, the laser power is 175 - 300 W, and the scanning speed is 600 - 1100 mm / s, and a high-entropy alloy coating can be prepared on the surface of the magnesium alloy.

[0014] Furthermore, the particle size of the high-entropy alloy powder is 15 - 53 μm.

[0015] Furthermore, when performing the laser beam scanning in step S3, the ambient air pressure of the argon environment is maintained at 0.4 Pa.

[0016] Furthermore, the high-entropy alloy coating is prepared on the surface of the magnesium alloy in a multiple-layer and layer-by-layer manner. Specifically: after the high-entropy alloy powder is evenly laid on the surface of the magnesium alloy substrate, S3 is executed once, and then the high-entropy alloy powder is laid on the surface where the high-entropy alloy has already been formed again, and S3 is executed again, so that a multi-layer high-entropy alloy coating is formed on the surface of the magnesium alloy.

[0017] Furthermore, the laying thickness of the high-entropy alloy powder each time is 25 - 35 μm.

[0018] Furthermore, during each laser scan, the laser power is 300 W and the scanning speed is 900 mm / s.

[0019] Furthermore, the magnesium alloy substrate is AZ31 magnesium alloy.

[0020] The beneficial effects of the present invention are:

[0021] This invention successfully overcomes the difficulties of preparing coatings on magnesium alloy surfaces by utilizing selective laser melting technology. During the melting process of the high-entropy alloy powder, a good metallurgical bond is achieved with the magnesium alloy substrate, forming a strong interface between the coating and the substrate. This effectively prevents coating shedding and peeling, ensuring the coating's stability and long-term protective properties.

[0022] The high-entropy alloy coating prepared by the present invention has a maximum hardness of up to 452.2HV, which is a significant improvement compared to the hardness of the magnesium alloy substrate; and significantly enhances the wear resistance of the magnesium alloy surface; forms an effective protective barrier on the magnesium alloy surface, which can resist external friction, corrosion, etc., greatly extending the service life of magnesium alloy products, and providing possibilities for the application of magnesium alloys in more fields with stringent requirements on surface performance.

[0023] This invention precisely controls every step, from powder pretreatment to coating formation. Under specific process parameters, the resulting high-entropy alloy coating maintains a narrow tolerance to the desired coating height, ensuring a precise and controllable process. Furthermore, each step has clearly defined parameters, resulting in excellent repeatability and stability, facilitating industrialized, large-scale production and providing strong technical support for the development of the magnesium alloy industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Surface structure diagram of the high entropy alloy coating prepared in Example;

[0025] Figure 2 A diagram showing the interface between the high entropy alloy coating and the magnesium alloy substrate prepared in Example;

[0026] Figure 3 This is an enlarged view of the surface structure of the prepared high-entropy alloy coating after hardness testing. DETAILED DESCRIPTION

[0027] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0028] Example

[0029] A method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on SLM technology, which includes the following steps:

[0030] S1: Uniformly spread the high-entropy alloy powder with a molar ratio of Al, Cr, Mn, Fe, Co, and Ni of 1:1:1:1:1:1 prepared by true air atomization in a endothermic atmosphere furnace, set the temperature at 50 °C, dry for 0.5 hours, and then let it stand for half an hour to cool naturally to remove moisture and other impurities in the powder.

[0031] S2: Load the pretreated high-entropy alloy powder into the powder supply cylinder, and set the single-layer thickness of the powder to 30 μm. Select AZ31 magnesium alloy as the substrate, and perform cleaning treatments such as grinding and cleaning on its surface to remove the oxide layer and impurities to enhance the bonding force between the coating and the substrate. After fixing the magnesium alloy substrate, adjust the position of the piston in the forming cylinder for powder loading, and use a powder spreading blade to spread the powder evenly from one end to the other on the forming platform with uniform pressure and speed to ensure that the powder thickness is consistent; before loading the powder into the powder supply cylinder, screen the powder and select the powder with a particle size of 15 - 53 μm.

[0032] S3: Fill the forming cylinder with argon with a purity of 99.99%, and keep the inert gas pressure in the chamber at about 0.4 Pa. According to the preset scanning path, the laser power is 300 W, the scanning speed is 900 mm / s, and the laser beam scans the powder layer by layer for melting and forming. After each layer of scanning is completed, the forming cylinder descends 30 μm, the powder supply cylinder rises, and the powder spreading device spreads a new layer of powder until the coating thickness reaches 0.262 mm. Specifically, during implementation, the laser power can also be 175 W, 200 W, 225 W, 250 W, or 275 W, and the scanning speed can also be 600 mm / s, 700 mm / s, 800 mm / s, 1000 mm / s, or 1100 mm / s. The obtained coating and the substrate are as Figure 1 shown, where the circular area is the area containing the high-entropy alloy coating.

[0033] Use an electron microscope to scan and photograph the cross-section of the joint between the coating and the substrate, and the result is as Figure 2 shown. It can be seen from Figure 2 that the coating and the substrate are tightly bonded, and a firm bonding interface is formed between the coating and the substrate.

[0034] Perform performance tests on the prepared high-entropy alloy coating, including hardness tests. Specifically: wipe the surface of the coating with organic solvents such as alcohol to remove oil stains, dust, and impurities, ensuring that the surface is clean and smooth. Select a suitable diamond indenter and load, and according to the operating manual of the hardness tester, use a Vickers hardness tester with the product model HVS-1000Z to conduct multiple hardness tests on the sample and calculate the average value. The measured hardness of the coating is 452.2 HV. The surface of the coating after the hardness test is as Figure 3 shown. It can be seen from Figure 3 that although there are scratches on the prepared high-entropy alloy coating, the coating does not show peeling or flaking.

[0035] Wear resistance test. Specifically: use an MPX-2000 pin-on-disc friction and wear tester to conduct multiple hardness tests on each sample and calculate the average value. Fix the magnesium alloy specimens with and without the high-entropy alloy cladding layer, select a 6 mm tungsten carbide pin, apply a 5 N load, set the friction radius to 10 mm and the rotation speed to 200 r / min, and measure for 30 min at room temperature without lubrication. Record the frictional force when starting the machine, measure the wear mass loss after the test, calculate the wear volume, and calculate the wear resistance coefficient according to the formula. Measure each specimen 3 times and take the average value. The results show that the friction coefficient of the uncoated specimen is about 0.2, the friction coefficient of the specimen with the coating is 0.47, and the coating thickness is 0.262 mm.

Claims

1. A method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on SLM technology, characterized in that, It includes the following steps: S1: The high-entropy alloy powder with a molar ratio of Al, Cr, Mn, Fe, Co, and Ni of 1:1:1:1:1:1 prepared by vacuum gas atomization is dried at 50 °C in an endothermic atmosphere furnace to obtain dry high-entropy alloy powder; S2: The high-entropy alloy powder is evenly laid on the surface of the magnesium alloy substrate; S3: In an argon environment, the powder layer is scanned with a laser beam. The laser power is 175 - 300 W, and the scanning speed is 600 - 1100 mm / s, and a high-entropy alloy coating can be prepared on the surface of the magnesium alloy.

2. The method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on the SLM technology according to claim 1, wherein The particle size of the high-entropy alloy powder is 15 - 53 μm.

3. The method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on the SLM technology according to claim 2, wherein, When the laser beam scanning is performed in step S3, the ambient air pressure of the argon environment is maintained at 0.4 Pa.

4. The method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on the SLM technology according to claim 3, wherein, The high-entropy alloy coating is prepared on the surface of the magnesium alloy in a multi-layer-by-layer manner. Specifically: after the high-entropy alloy powder is evenly laid on the surface of the magnesium alloy substrate, S3 is executed once, and then the high-entropy alloy powder is laid on the surface where the high-entropy alloy has already formed again, and S3 is executed again, so that a multi-layer high-entropy alloy coating is formed on the surface of the magnesium alloy.

5. The method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on the SLM technology according to claim 4, wherein The laying thickness of the high-entropy alloy powder each time is 25 - 35 μm.

6. The method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on the SLM technology according to claim 5, wherein During each laser scanning, the laser power is 300 W, and the scanning speed is 900 mm / s.

7. The method for preparing a high-entropy alloy coating on the surface of a magnesium alloy based on the SLM technology according to claim 6, wherein, The magnesium alloy substrate is AZ31 magnesium alloy.

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