Composite powder preparation and forming method for laser additive manufacturing high-performance multifunctional aluminum alloy

Abstract

The invention discloses a laser additive manufacturing-oriented high-performance multifunctional aluminum alloy composite powder preparation and forming method, which comprises the following steps of: preparing a SiO2 coated carbon material by a solution-gel method, and uniformly mixing the SiO2 coated carbon material and aluminum powder by a planetary ball mill, and the high-performance multifunctional aluminum alloy material fused and formed by the laser powder bed is obtained by controlling the process interval. In order to solve the problems of poor reinforcing phase dispersity, weak interface bonding force and the like in the existing aluminum alloy preparation process, the comprehensive performance of the high-performance multifunctional aluminum alloy formed through additive manufacturing is improved, and the manufacturing method is simple and high in operability.

Description

Technical Field

[0001] The present invention belongs to the field of additive manufacturing of high thermal conductivity aluminum alloys, and specifically relates to a method for preparing and forming a composite powder for a high-performance and multifunctional aluminum alloy for laser additive manufacturing. Background Art

[0002] Due to the advantages of aluminum matrix composites such as low density, light weight, good thermal and electrical conductivity, high specific strength and specific stiffness, etc., they are widely used in the fields of aerospace, automotive, electronics and electrical, etc.

[0003] Laser powder bed fusion (LPBF) technology can directly manufacture components with complex internal structures, thin-wall features and high precision by layer-by-layer melting and solidifying metal powders according to the design model. LPBF requires no mold or only a simple support structure, which can greatly shorten the R & D cycle and reduce production costs. Currently, it has been widely used in the field of manufacturing aerospace precision components. With the development trend of integrated, integrated and lightweight design of components in the fields of aerospace and others, higher requirements for heat dissipation performance are put forward for various components. LPBF can integrally form complex configuration aluminum alloy heat dissipation structures, and has important application prospects in the field of aerospace heat dissipation. However, in terms of the material forming process, the current LPBF forming of high thermal conductivity aluminum alloys still faces bottleneck technical problems. Currently, adding fine carbon materials to composite aluminum alloy materials is an effective way to improve the thermal conductivity of aluminum alloy components, such as diamond, carbon nanotubes (CNTs), graphene, etc. However, the introduction of carbon materials brings a series of process problems in the LPBF process of laser additive manufacturing. One is the wetting behavior between the carbon material and the aluminum alloy melt during the laser melting process. Due to the poor wetting effect of carbon / Al, defects such as pores and cracks are likely to initiate. The other is that the interface bonding between the fine carbon material and the aluminum alloy matrix significantly affects the thermal conductivity of the macroscopic component. Under the action of a high-energy laser beam, the carbon material is prone to local melting to form a harmful phase of Al4C3 at the interface, significantly reducing the strength and thermal conductivity of the formed specimen.

[0004] In summary, the laser additive manufacturing LPBF forming of carbon-modified high thermal conductivity aluminum alloy materials has important applications in the field of integrated forming of aerospace heat dissipation components and has become a hot research direction in current technology. However, there are still technical problems such as poor wettability at the carbon material / aluminum matrix interface and easy generation of interface harmful phases, which reduce the strength and thermal conductivity of the components. It is urgent to develop a method to improve the interface bonding and formability of laser additive manufacturing carbon-modified high thermal conductivity aluminum alloys. Summary of the Invention

[0005] Objective of the Invention: The technical problem to be solved by the present invention is to address the problems existing in the existing laser additive manufacturing LPBF formed carbon material reinforced high thermal conductivity aluminum alloy material, such as insufficient dispersion stability, low wettability, and poor interfacial bonding. A composite powder preparation and forming method for high-performance and multifunctional aluminum alloy for laser additive manufacturing is proposed to improve the formability and comprehensive performance.

[0006] In order to achieve the above-mentioned invention objective, the technical solutions adopted by the present invention are as follows: A method for preparing a composite powder for high-performance and multifunctional aluminum alloy for laser additive manufacturing, comprising the following steps: S1. Prepare SiO2 uniformly coated carbon material by solution gel method; S2. Use a planetary ball mill to uniformly mix the SiO2 coated carbon material prepared in step (1) with aluminum powder to obtain the product.

[0007] Specifically, the method for preparing SiO2 uniformly coated carbon material by solution gel method in step S1 is as follows: (1) Put the carbon material into an acid solution for acidification, then wash and vacuum dry. (2) Disperse the carbon material treated in step (1) in a mixed solution of sodium dodecyl sulfate and absolute ethanol, add tetraethyl orthosilicate and mix evenly, then slowly add deionized water to hydrolyze tetraethyl orthosilicate, form a silica gel on the surface of the carbon material, add ammonia as a catalyst after ultrasonic treatment to accelerate the formation of silica nanoparticles until a homogeneous gel is formed. (3) Vacuum dry the gel obtained in step (2) to dehydrate silicon hydroxide and form a SiO2 coating on the surface of the carbon material; finally, calcine the product to further densify and crystallize the SiO2 coating to obtain the product.

[0008] Preferably, in step (1), the carbon material is any one of carbon nanotubes, graphene, carbon nanofibers, and carbon fibers, and the average particle size does not exceed 2 μm.

[0009] Preferably, in step (1), the acid solution is a mixed aqueous solution of nitric acid and sulfuric acid, wherein the volume concentration of nitric acid is 65 - 68%, and the volume concentration of sulfuric acid is 97 - 99%; the mixed mass-volume ratio of the carbon material to the acid solution is 30 - 50 g / ml; the acidification is carried out by magnetic stirring for 6 - 8 h; after acidification, it is washed with deionized water until the pH value is 6 - 7; the temperature of the vacuum drying is 70 - 90 °C, and the time is 22 - 24 h.

[0010] Preferably, in step (2), in the mixed solution of sodium dodecyl sulfate and absolute ethanol, the concentration of sodium dodecyl sulfate is 1-4 wt%; the mass-volume ratio of the carbon material to the mixed solution used for dispersion is 30-50 g / ml; the molar ratio of tetraethyl orthosilicate to the carbon material is 0.6-1.0 mol.

[0011] Preferably, in step (2), deionized water is slowly added dropwise at a rate of 0.2-0.4 ml / min to promote the hydrolysis of tetraethyl orthosilicate; after ultrasonic treatment for 90-110 minutes, ammonia is added as a catalyst at a rate of 0.01-0.02 ml / min, and then homogenized for 3-4 hours until a gel is formed.

[0012] Preferably, in step (3), the gel obtained in step (2) is placed in a vacuum dryer at 75-80 °C for 24-25 hours to form a SiO2 coating on the surface of the carbon material; the calcination treatment is carried out at 430-450 °C for 2-4 hours.

[0013] Preferably, in step S2, the aluminum powder used is near-spherical aluminum powder with a particle diameter not greater than 30 μm and a purity not less than 99.8%; the mixing mass ratio of the SiO2-coated carbon material to the aluminum powder is 0.4-0.6%.

[0014] Preferably, the planetary ball mill uses medium-low energy ball milling, and the ball milling process is dry milling. The rotational speed of the ball mill is set at 230-260 rpm, and the time is 3-5 h, during which it rotates for 10-20 min and stops to cool for 3-6 min. Ceramic balls are selected as the grinding balls, and the ball-to-material ratio is selected as 1:1-1:3.

[0015] Furthermore, the composite powder prepared by the above preparation method is also within the protection scope of the present invention.

[0016] Furthermore, the present invention also claims the application of the above composite powder in the laser powder bed fusion forming of carbon material-reinforced high thermal conductivity aluminum alloy materials.

[0017] Specifically, argon protection is used during the laser powder bed fusion forming process. Before powder spreading, the forming substrate is preheated to 100-150 °C. Its main processing parameters are: laser power 375-450 W, preferably 400-425 W, scanning speed: 800-1200 mm / s, preferably 800-1000 mm / s, scanning spacing: 50-60 μm, powder spreading layer thickness: 30-50 μm, and the scanning path is island-shaped, rotating 37°.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1)The present invention uses SiO2-coated carbon materials, which increases the density of the carbon materials, making it closer to the density of aluminum powder, reducing the van der Waals force, and thus significantly improving the uniformity of the dispersion of the reinforcement during the powder processing and reducing the agglomeration phenomenon of the carbon materials.

[0019] (2)The SiO2 coating of the present invention improves the compatibility between the carbon materials and the aluminum powder as well as the wettability with the aluminum matrix (the contact angle of the Al-SiO2 system is about 76°, much smaller than 104.5° of the Al-carbon material system), enabling more reinforcements to enter the interior of the aluminum grains during ball milling and processing, and improving the strength and plasticity of the aluminum alloy.

[0020] (3)The presence of the SiO2 coating in the present invention makes the carbon materials more stable in the aluminum matrix, and the fracture mode changes from the pull-out of the carbon materials to the bridging and fracture of the carbon materials, more effectively transmitting the load and improving the load-bearing capacity of the aluminum alloy.

[0021] (4)During the processing of the present invention, the SiO2-coated carbon materials react in-situ with the aluminum matrix and are transformed into Al4O4C nanoparticles, inhibiting the large generation of Al4C3 and enhancing the comprehensive performance of the aluminum alloy. Description of the Drawings

[0022] The following further specifically describes the present invention in conjunction with the drawings and specific embodiments, and the above and / or other advantages of the present invention will become clearer.

[0023] Figure 1 SEM image of the original powder of the SiO2-coated carbon materials prepared by the sol-gel method in Example 1 after ball milling treatment.

[0024] Figure 2 SEM image of the original powder of the SiO2-coated carbon materials prepared by the sol-gel method in Example 5 after ball milling treatment.

[0025] Figure 3 Optical image of the cross-section of the formed aluminum alloy test block in Example 1.

[0026] Figure 4 Optical image of the cross-section of the formed aluminum alloy test block in Example 2.

[0027] Figure 5 Optical image of the cross-section of the formed aluminum alloy test block in Example 3.

[0028] Figure 6 Optical image of the cross-section of the formed aluminum alloy test block in Example 4.

[0029] Figure 7 Optical image of the cross-section of the formed aluminum alloy test block in Example 5. Detailed Description of the Invention

[0030] The present invention can be better understood according to the following embodiments. Embodiment 1

[0031] Combined with Figure 1 , a method for preparing and forming powders for a high-performance and multifunctional aluminum alloy for laser additive manufacturing according to the present invention includes the following steps: (1) Put 1 g of carbon material into a mixed solution of nitric acid aqueous solution (65 v / v%) and sulfuric acid aqueous solution (98 v / v) with a volume ratio of 1:3, and stir magnetically for 6 h for acidification. After taking it out, wash it with deionized water to adjust the pH value to 7, and dry it in a vacuum furnace at 80 °C for 24 h.

[0032] (2) Disperse the carbon material obtained in step (1) with absolute ethanol and sodium dodecyl sulfate in an ultrasonic probe for 45 minutes. The dispersant is an appropriate amount of absolute ethanol and 2 wt% of sodium dodecyl sulfate (SDS). Add 2.44 mol of TEOS to the solution and continue ultrasonic for 15 min. Then, slowly drop deionized water into the solution at a rate of 0.2 ml / min to promote the hydrolysis of TEOS and form silicon hydroxide (Si(OH)4) colloid on the surface of the carbon nanotubes. Keep the mixture in an ultrasonic environment for another 90 minutes, and then add 0.27 mol of ammonia to the solution at a rate of 0.01 ml / min as a catalyst to accelerate the formation of silica nanoparticles. The whole homogenization process lasts for 3 hours until a gel is formed.

[0033] (3) Place the gel obtained in step (2) in a vacuum furnace at 75 °C and dry it for 24 hours. After the dehydration of silicon hydroxide, a SiO2 coating will be formed on the surface of the carbon material. Finally, calcine the carbon material / SiO2 mixture at 450 °C for 2 hours to further densify and crystallize the silica layer. The obtained carbon material has a mass ratio of carbon material to SiO2 of 1:4.

[0034] (4) Mix the above-mentioned SiO2-coated carbon material with aluminum powder at a mass ratio of 0.5%, and then put it into a planetary ball mill for low-energy ball milling. The ball milling process is dry milling. The rotation speed of the ball mill is set at 250 rpm and the time is set at 4 h, where it rotates for 15 min and stops for 5 min to cool. The grinding balls are selected as ceramic balls and the ball-to-material ratio is selected as 1:2. After low-energy ball milling, the SiO2-coated carbon material and aluminum powder are evenly dispersed.

[0035] (5) LPBF forming, during which argon protection is adopted. Before powder spreading, preheat the forming substrate to 100 - 150 °C. Its main processing parameters are: laser power 400 W, scanning speed 1000 mm / s, scanning spacing: 50 μm, powder spreading layer thickness: 30 μm, and the scanning path is island-shaped, rotating 37°.

[0036] The SEM observation of the prepared powder is as follows Figure 1 shown. It can be seen that the powder is in the shape of uniform spheres, the surface coating layer is uniform and the particle size distribution is normal, starting from the laser additive manufacturing of high-performance multifunctional aluminum alloys. Example 2

[0037] The difference between this example and Example 1 is that: In step (1), the weight of the carbon material is 1 g. In step (2), 1.83 mol of TEOS is added. For the obtained carbon material, the mass ratio of the carbon material to SiO2 is 1:3. Example 3

[0038] The difference between this example and Example 1 is that: In step (1), the weight of the carbon material is 1 g. In step (2), 3.05 mol of TEOS is added. For the obtained carbon material, the mass ratio of the carbon material to SiO2 is 1:5. Example 4

[0039] The difference between this example and Example 1 is that: In step (4), the ball milling time is set to 3 h and the ball milling speed is 200 rpm. Example 5

[0040] The difference between this example and Example 1 is that: In step (4), the ball milling time is set to 5 h and the ball milling speed is 300 rpm.

[0041] The SEM of the mixed powder is observed as Figure 2 shown. It is observed that a large number of fractures and defects appear in the composite powder, destroying its original aspect ratio and structural integrity, and there is an agglomeration phenomenon.

[0042] The density, strength and thermal conductivity of the formed specimens under different process parameters are measured. The test results of different examples are shown in Table 1.

[0043] Table 1 Properties of different aluminum alloys

[0044] Comparing Examples 1-5 shows that the method of the present invention can improve the mechanical properties and thermal conductivity of the aluminum alloy formed by laser additive manufacturing. The cross-section grinding and polishing tests are carried out on the aluminum alloys formed in different examples. The optical pictures of the typical specimens formed in Examples 1-5 are as Figures 3-7 shown.

[0045] Figure 3 , Figure 4 , Figure 5 are the cross-section optical images of the SiO2-coated carbon material formed specimens prepared by the sol-gel method in Example 1, Example 2 and Example 3 respectively. FromFigure 3 It can be seen that the cross-section of the specimen in Example 1 formed by using the method of the present invention is continuous and dense, without obvious metallurgical defects. In comparison Figure 4 、 Figure 5 shows that the mass ratio of SiO2 to the carbon material can affect the coating situation of SiO2. If the mass ratio is too small, SiO2 cannot completely coat the carbon material, which will lead to a decrease in the wettability of the prepared powder and easily cause metallurgical defects such as pores due to the introduction of the carbon material. If the mass ratio is too large, an excessive amount of SiO2 particles will be formed, which will lead to particle inclusions and affect the performance of the aluminum alloy. The optimized mass ratio is 1:4.

[0046] Figure 6 、 Figure 7 are the optical images of the cross-sections of the specimens formed in Example 4 and Example 5, indicating that the ball milling parameters can affect the powder quality and thus the forming quality. If the ball milling time is too short and the rotation speed is too low, the powder particle size will be too large to meet the expected fine particle size requirements, and the porosity of the formed specimen will increase. If the ball milling time is too long and the rotation speed is too large, a large number of fractures and defects will appear in the original powder, and both too low and too high ball milling speeds will cause carbon material agglomeration, which will lead to an increase in the number of defects in the formed specimen and a decrease in the comprehensive performance of the aluminum alloy. The optimized rotation speed and ball milling time are 250 rpm and 4 h.

[0047] The present invention provides an idea and method for preparing and forming a composite powder for laser additive manufacturing of high-performance and multifunctional aluminum alloys. There are many methods and ways to specifically implement this technical solution. The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. Each component not clearly defined in this embodiment can be realized by the prior art.

Claims

1. A method for preparing composite powder for laser additive manufacturing of high-performance multifunctional aluminum alloy, characterized in that: The steps include: S1. Prepare SiO2 uniformly coated carbon material by solution gel method; S2. Use a planetary ball mill to evenly mix the SiO2-coated carbon material prepared in step (1) with aluminum powder to obtain.

2. The method for preparing composite powder for laser additive manufacturing of high-performance multifunctional aluminum alloy according to claim 1, characterized in that: Step S1: The method for preparing SiO2 uniformly coated carbon material by solution gel method is as follows: (1) The carbon material is placed in an acid solution for acidification, then washed and vacuum dried; (2) dispersing the carbon material treated in step (1) in a mixed solution of sodium dodecyl sulfate and anhydrous ethanol, adding tetraethyl orthosilicate and mixing evenly, then slowly adding deionized water to hydrolyze the tetraethyl orthosilicate to generate silica gel on the surface of the carbon material, and then adding ammonia as a catalyst after ultrasonic treatment to accelerate the formation of silica nanoparticles until a homogeneous gel is formed; (3) vacuum drying the gel obtained in step (2) to dehydrate the silicon hydroxide and form a SiO2 coating on the surface of the carbon material; finally, calcining the product to further densify and crystallize the SiO2 coating.

3. The method for preparing composite powder for laser additive manufacturing of high-performance multifunctional aluminum alloy according to claim 2, characterized in that: In step (1), the carbon material is any one of carbon nanotubes, graphene, carbon nanofibers, and carbon fibers, and the average particle size of the particles does not exceed 2 μm.

4. The method for preparing composite powder for laser additive manufacturing of high-performance multifunctional aluminum alloy according to claim 2, characterized in that: In step (1), the acid solution is a mixed aqueous solution of nitric acid and sulfuric acid, wherein the volume concentration of nitric acid is 65-68%, and the volume concentration of sulfuric acid is 97-99%; the mixed mass volume ratio of carbon material and acid solution is 30-50g / ml; acidification is performed by magnetic stirring for 6-8 hours; after acidification, washing is performed with deionized water to a pH value of 6-7; the temperature of vacuum drying is 70-90°C, and the time is 22-24 hours.

5. The method for preparing composite powder for laser additive manufacturing of high-performance multifunctional aluminum alloy according to claim 2, characterized in that: In step (2), in the mixed solution of sodium dodecyl sulfate and anhydrous ethanol, the concentration of sodium dodecyl sulfate is 1-4wt%; the mass volume ratio of the carbon material to the mixed solution used for dispersion is 30-50g / ml; and the molar ratio of tetraethyl orthosilicate to carbon material is 0.6-1.0mol.

6. The method for preparing composite powder for laser additive manufacturing of high-performance multifunctional aluminum alloy according to claim 2, characterized in that: In step (2), deionized water is slowly added at a rate of 0.2-0.4 ml / min to promote the hydrolysis of ethyl orthosilicate; after ultrasonication for 90-110 minutes, ammonia is added as a catalyst at a rate of 0.01-0.02 ml / min, and then homogenized for 3-4 hours until a gel is formed.

7. The method for preparing composite powder for laser additive manufacturing of high-performance multifunctional aluminum alloy according to claim 2, characterized in that: In step (3), the gel obtained in step (2) is placed in a vacuum dryer at 75-80°C for 24-25 hours to form a SiO2 coating on the surface of the carbon material; the calcination treatment is performed at 430-450°C for 2-4 hours.

8. The method for preparing composite powder for laser additive manufacturing of high-performance multifunctional aluminum alloy according to claim 1, characterized in that: In step S2, the aluminum powder is nearly spherical aluminum powder, with a particle diameter of no more than 30 μm and a purity of no less than 99.8%; the mixing mass ratio of the SiO2-coated carbon material to the aluminum powder is 0.4-0.6%; The planetary ball mill adopts medium and low energy ball milling, the ball milling process is dry milling, the ball mill speed is set to 230-260rpm, the time is 3-5, wherein the rotation time is 10-20min and the cooling time is 3-6min, the grinding balls are ceramic balls, and the ball-to-material ratio is 1:1-1:

3.

9. The composite powder prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the composite powder according to claim 9 in laser powder bed melting forming of carbon material reinforced high thermal conductivity aluminum alloy material, characterized in that: Argon gas protection is used during the laser powder bed fusion forming process. Before spreading the powder, the forming substrate is preheated to 100-150°C, the laser power is 375-450W, the scanning speed is 800-1200mm / s, the scanning spacing is 50-60μm, the powder layer thickness is 30-50μm, the scanning path is island-shaped, and rotated 37°.

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