A method for refining primary silicon of Al-Si alloy based on laser additive manufacturing and nanoceramic synergistic modification

Abstract

This invention discloses a method for refining primary silicon in Al-Si alloys through synergistic modification with nano-ceramics based on laser additive manufacturing. The method involves uniformly mixing Al-Si alloy powder with TiB2 and Al2O3 nano-ceramics using a ball mill under inert gas protection to obtain a ceramic-reinforced nano-Al-Si alloy composite powder. This nano-ceramic-modified Al-Si alloy powder is then melted and solidified layer by layer using a laser powder bed melting and forming equipment to create the desired target part. In this method, during the solidification of the nano-ceramic-reinforced Al-Si alloy melt, Al2O3 nanoparticles, due to their similarity to the Si crystal structure and the existence of a good interfacial coherence relationship, act as heterogeneous nucleation sites for primary silicon, increasing the nucleation rate and refining the size of primary silicon. TiB2 nanoparticles, distributed at the solid-liquid interface, can to a certain extent prevent the diffusion and aggregation of Si atoms into Si-Si atom clusters, thereby inhibiting the growth of the primary silicon phase, promoting the regularization of the primary silicon morphology and refining its size, and effectively reducing matrix grain size, significantly improving the mechanical properties of the Al-Si alloy.

Description

Technical Field

[0001] This invention belongs to the field of Al-Si alloy materials, specifically relating to a method for refining primary silicon in Al-Si alloys through synergistic modification with nano-ceramics based on laser additive manufacturing. Background Technology

[0002] Al-Si alloys with a silicon content exceeding 22 wt.% are classified as high-silicon aluminum alloys. These alloys possess excellent thermal stability and wear resistance, making them promising candidates for applications in transportation, power machinery, portable electronic device packaging, and high-end hermetically sealed packaging. However, the coarse primary silicon in the microstructure of high-Si content Al-Si alloys reduces the strength and plasticity of the material, thus degrading its performance. Therefore, refining the primary silicon and improving its microstructure are essential for enhancing the overall performance of high-Si content Al-Si aluminum alloys. Compared to conventional casting, laser powder bed melting technology offers unparalleled advantages in preparing Al-Si alloys. Laser powder bed melting (LBD) is an unsteady solidification process that can improve heat dissipation during solidification, thereby increasing the cooling rate and supercooling, shortening crystal growth time, and refining grains. Therefore, LBD can refine the primary silicon phase and matrix grains in the microstructure of high-Si content Al-Si alloys, showing potential for preparing high-Si content Al-Si alloys with excellent properties. However, the degree of refinement of primary silicon in high-Si content Al-Si alloys formed solely by LBD is limited, and the primary silicon morphology in the microstructure of LBD-formed Al-Si alloys still exhibits sharp edges and distinct angular features, which can adversely affect the material's mechanical properties. Therefore, adding nucleating agents or modifiers to high-Si content Al-Si alloys can increase the heterogeneous nucleation sites of primary silicon and inhibit its continuous growth, thereby improving the microstructure and distribution of primary silicon and enhancing the material's mechanical properties. This method is not limited by production processes or scale and has broad application prospects.

[0003] According to solidification theory, the formation of primary silicon involves two processes: nucleation and growth. Phase fluctuations are the basis for nucleation. In the original high-Si-content Al-Si alloy, the formation of silicon phase nuclei mainly originates from Si-Si atom clusters frozen in the supercooled melt. Large-sized Si-Si atom clusters that meet the critical nucleation conditions can become stable nuclei, while some Si atom clusters will redissolve in the aluminum melt through Si atom diffusion. The silicon phase growth process is mainly achieved through the continuous migration of Si atoms from the melt to the surface of Si-Si atom clusters and the continuous advancement of the liquid-solid interface. During the solidification of aluminum alloys, Si atoms diffuse faster than Al atoms, and due to energy differences, the diffusion rate of Si atoms differs on crystal planes with different crystal indices. Atoms diffuse faster on crystal planes with higher crystal indices than on crystal planes with lower crystal indices. Primary silicon always diffuses along the twin plane {111}. <112> or <110> Directional nucleation and preferential growth via small planar growth inevitably lead to atomic misalignment during crystal growth, causing a change in the growth direction of the silicon crystal. As a result, the primary silicon phase exhibits a polygonal and angular morphology, appearing as an irregular polygon or petal shape under a microscope, which affects the mechanical properties of Al-Si alloys. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to address the existing problems in the preparation technology of Al-Si alloy materials, and to provide a method for refining primary silicon in Al-Si alloys by synergistic modification of nano-ceramics based on laser additive manufacturing, so as to significantly improve the mechanical properties of Al-Si alloys.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for refining primary silicon in Al-Si alloys through synergistic modification with nano-ceramics based on laser additive manufacturing includes the following steps:

[0007] (1) Disperse TiB2 nano-ceramic powder and Al2O3 nano-ceramic powder in anhydrous ethanol and then dry to obtain a uniformly dispersed mixed nano-ceramic powder.

[0008] (2) Mix the Al-Si alloy powder with the mixed nano-ceramic powder from step (1) until uniform, to obtain nano-ceramic particle-reinforced Al-Si alloy composite powder;

[0009] (3) Establish a three-dimensional solid geometric model of the target part, then slice the model into layers and plan the laser scanning path, discretize the three-dimensional solid into a series of two-dimensional data, save this file and import it into the laser powder bed melting and forming equipment;

[0010] (4) The laser powder bed melting and forming equipment melts and solidifies the nano-ceramic particle reinforced Al-Si alloy composite powder in step (2) layer by layer according to the file saved in step (3), and finally forms the target part to be built.

[0011] Specifically, in step (1), the TiB2 nano-ceramic powder used is an irregular TiB2 ceramic powder with a purity greater than 99.9% and a particle size distribution range of 30 to 75 nm.

[0012] Specifically, in step (1), the Al2O3 nano-ceramic powder used is an irregular Al2O3 ceramic powder with a purity greater than 99.9% and a particle size distribution range of 25 to 60 nm.

[0013] Preferably, in step (1), the mass ratio of TiB2 ceramic powder to Al2O3 ceramic powder is 3:1 to 3:2. If the content of nano-ceramic particles is too low, the refining effect of primary silicon in the Al-Si alloy is not good; if the content of nano-ceramic particles is too high, the metallurgical defects in the Al-Si alloy structure increase, the laser forming quality decreases, and the performance of the composite material is affected.

[0014] Specifically, in step (1), TiB2 ceramic powder and Al2O3 ceramic powder are dispersed in anhydrous ethanol at a solute:solvent mass ratio of 10:(1~2), and then placed in an ultrasonic oscillator for oscillation. Subsequently, the resulting mixture is placed in a vacuum drying oven for drying to obtain uniformly dispersed nano-ceramic powder. The ultrasonic power of the ultrasonic oscillator is 1000~1200W, and the ultrasonic oscillation time is 8~12h. The drying temperature of the vacuum drying oven is 70~90℃, and the drying time is 10~14h.

[0015] Specifically, in step (2), the Al-Si alloy powder has a particle size distribution range of 20~48 μm, with a silicon content of 22~55 wt.%, an iron content of 0.08~0.17%, a copper content of 2.3~3.0%, and the balance being aluminum.

[0016] Preferably, in step (2), the mixed nano-ceramic powder accounts for 1.5 to 6 wt.% of the mass of the Al-Si alloy powder.

[0017] Preferably, in step (2), the Al-Si alloy powder and the mixed nano-ceramic powder are uniformly mixed using a QM series planetary ball mill under inert gas protection. A ceramic jar is used in this process, and the grinding media are ceramic grinding balls with diameters of 6 mm and 8 mm. The ball milling process parameters are set as follows: ball-to-material ratio of 2:1; simultaneously, to prevent excessively high temperatures inside the grinding jar, the equipment operates in an intermittent mode during ball milling, with a rotation speed of 150–250 rpm, a grinding time of 3–5 h, a grinding time of 14–20 min per cycle, and an interval of 4–6 min.

[0018] Specifically, in step (4), the laser power used in the laser powder bed melting and forming equipment is 350~450 W, the scanning speed is 1600-2400 mm / s, the scanning spacing is 40~60 μm, the powder thickness is 40~60 μm, and a partitioned island scanning strategy is adopted.

[0019] Preferably, the laser powder bed fusion molding equipment uses the SLM-150 type laser powder bed fusion molding equipment, which mainly includes a YLR-500 type fiber laser, a laser forming chamber, an automatic powder spreading system, a protective atmosphere device, a computer control circuit system, and a cooling circulation system. Before forming, the sandblasted aluminum substrate is fixed on the worktable of the laser powder bed fusion molding equipment and leveled. Then, the forming chamber is sealed by a sealing device, evacuated, and an inert gas protective atmosphere is introduced. The typical laser powder bed fusion molding process is as follows: (a) The powder spreading device evenly spreads the powder to be processed on the forming substrate. The laser beam scans the slicing area line by line according to the pre-designed scanning path, causing the powder layer to melt and solidify rapidly, thereby obtaining the first two-dimensional plane of the part; (b) The computer control system lowers the forming substrate by one powder layer thickness, and conversely, raises the piston of the powder supply cylinder by one powder layer thickness. The powder spreading device lays a new layer of powder to be processed. The laser beam completes the second powder layer scan according to the slicing information to obtain the second two-dimensional plane of the part; (c) The above steps are repeated, and the powder to be processed is formed layer by layer until the part is processed. In step (4), the laser powder bed melting parameters were determined after process optimization. Beneficial effects

[0020] (1) In this invention, the nucleation and growth process of primary silicon in the microstructure of Al-Si alloy reinforced with nano-ceramic particles is different from that described above. When there is a good interfacial coherence relationship between the two phases, one of the phases can serve as the core for heterogeneous nucleation of the other phase. Moreover, when the lattice mismatch between the two crystal forms is less than 6%, it can effectively promote heterogeneous nucleation. Si has a face-centered cubic structure with a lattice constant of 0.54 nm, and Al2O3 has a cubic crystal structure with a lattice constant of 0.79 nm. The crystal structures of Si and Al2O3 are similar, and the lattice mismatch is 3%. The Al2O3 phase can serve as a suitable substrate for heterogeneous nucleation of primary silicon, promoting the nucleation of the primary silicon phase, increasing its nucleation rate, and achieving the effect of refining the size of primary silicon. TiB2 nanoceramic particles, located at the solid-liquid interface of the aluminum alloy melt, can, to some extent, prevent the diffusion and aggregation of Si atoms into Si-Si atom clusters. This leads to changes in the anisotropy of primary silicon and inhibits silicon phase growth, thereby regularizing the morphology and refining the size of the primary silicon, while also refining the matrix grains. Therefore, adding an appropriate amount of TiB2+Al2O3 nanoceramic phase to Al-Si alloys can refine the matrix grains and primary silicon phase, and adjust the morphology and distribution of the hard and brittle Si phase. The combined effect of the two nanoceramic particles can significantly improve the mechanical properties of high-Si content Al-Si alloys.

[0021] (2) In this invention, nano-ceramic particles and Al-Si alloy powder are mixed and then placed in a QM series planetary ball mill for ball milling and powder mixing. Through ball milling process optimization, nano-ceramic particles with uniform distribution, good flow properties and suitable for laser powder bed melting and forming are obtained. This process is simple to operate and saves costs.

[0022] (3) In this invention, compared with Al-Si alloy powder, the laser absorption rate of the composite powder is significantly increased after adding an appropriate amount of nano-ceramic particles to Al-Si alloy. During the laser powder bed melting and forming process, the laser energy input of the powder bed is increased, so that the powder layer can be fully melted, thereby improving the forming quality and mechanical properties of the parts.

[0023] (4) This invention utilizes laser powder bed melting technology to prepare Al-Si alloy materials, which not only shortens the production cycle and improves product production efficiency, but also allows for the formation of parts with complex geometries with almost no subsequent machining. The cooling rate of the molten pool during laser powder bed melting is extremely high, reaching 10... 3 ~10 8 K / s increases the undercooling of the Al-Si alloy melt, avoiding the formation of coarse dendrites in traditional processing and improving the mechanical properties of the parts.

[0024] (5) In this invention, Si and Al2O3 have similar crystal structures and a good interfacial coherence relationship. Al2O3 particles can act as heterogeneous nucleation sites for primary silicon, improving the nucleation rate and refining the size of primary silicon. TiB2 nanoparticles are distributed on the solid-liquid interface, which can, to a certain extent, prevent Si atoms from diffusing and aggregating into Si-Si atom clusters, thereby inhibiting silicon phase growth and promoting the regularization of the morphology and refinement of the size of primary silicon. Therefore, adding appropriate amounts of Al2O3 and TiB2 nano-ceramic phases to Al-Si alloy can refine primary silicon and adjust its morphology and distribution, significantly improving the mechanical properties of Al-Si alloy. Attached Figure Description

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0026] Figure 1 This is a cross-sectional microstructure diagram of the (TiB2+Al2O3) / Al-Si composite powder in Example 1.

[0027] Figure 2 This is a photograph of the (TiB2+Al2O3) / Al-Si composite material sample obtained by laser powder bed melting in Example 1.

[0028] Figure 3 The image shows the cross-sectional OM image of the (TiB2+Al2O3) / Al-Si composite material sample obtained by laser powder bed melting in Example 1.

[0029] Figure 4 The image shows the cross-sectional OM image of the (TiB2+Al2O3) / Al-Si composite material in Example 2, obtained by laser powder bed melting.

[0030] Figure 5 The image shows the cross-sectional OM image of the laser powder bed molten Al-Si alloy sample in Comparative Example 1. Detailed Implementation

[0031] The present invention can be better understood from the following embodiments.

[0032] In the following examples, the raw materials used are irregularly shaped Al2O3 ceramic powder with a particle size distribution ranging from 25 to 60 nm and a purity greater than 99.9%; irregularly shaped TiB2 ceramic powder with a particle size distribution ranging from 30 to 75 nm and a purity greater than 99.9%; and Al-Si alloy powder with a particle size distribution ranging from 20 to 48 μm, wherein the silicon content is 22 to 55 wt.%, the iron content is 0.08 to 0.17%, the copper content is 2.3 to 3.0%, and the balance is aluminum. Example 1

[0033] (1) TiB2 and Al2O3 with a mass ratio of 3:1 were dispersed in anhydrous ethanol at a solute:solvent mass ratio of 10:1. The mixture was then subjected to ultrasonic vibration at a power of 1000 W for 10 h. The mixture was then dried in a vacuum drying oven at 80 °C for 12 h to obtain uniformly dispersed nano-ceramics. The ceramic powder was mixed with Al-Si alloy powder at a ratio of 1.5 wt.% to prepare composite powder. The ball milling and mixing operation was carried out in a QM series planetary ball mill. The process used a ceramic jar and ceramic grinding balls with diameters of 6 mm and 8 mm. The ball milling process parameters were set as follows: ball-to-material ratio of 2:1, ball milling speed of 150 rpm, and ball milling time of 5 h. To prevent the temperature inside the ball mill jar from getting too high, the equipment was operated in an intermittent mode during ball milling, i.e., the equipment was paused for 5 min of air cooling after every 15 min of operation. The ball milling process requires argon protection to prevent oxidation or contamination of the aluminum alloy powder. The cross-sectional microstructure of the (TiB2+Al2O3) / Al-Si composite powder obtained in this embodiment is shown below. Figure 1 As shown.

[0034] (2) Modeling and slicing of target parts

[0035] A three-dimensional solid geometric model of the target part was created using Solidworks software on a computer. Then, Magics software was used to perform layer slicing and scan path planning on the three-dimensional solid model, discretizing the three-dimensional solid into a series of two-dimensional data. This file was saved and imported into the laser powder bed melting forming equipment. The laser process parameters were set as follows: laser power of 350 W, laser scanning speed of 1600 mm / s, scanning interval of 50 μm, powder thickness of 50 μm, using a partitioned island scanning strategy, and the laser scanning direction rotation angle between adjacent layers was 37°.

[0036] (3) Laser powder bed melting process

[0037] The nano-ceramic particle-reinforced Al-Si alloy composite powder obtained in step (1) was used for laser powder bed melting. An SLM-150 laser powder bed melting system was used, which mainly includes a YLR-500 fiber laser, a laser forming chamber, an automatic powder spreading system, a protective atmosphere device, a computer control circuit system, and a cooling circulation system. Before forming, the sandblasted aluminum substrate was fixed on the worktable of the laser powder bed melting system and leveled. Then, the forming chamber was sealed by a sealing device, evacuated, and argon protective atmosphere was introduced. A typical laser powder bed melting process is as follows: (a) The powder spreading device evenly spreads the powder to be processed on the forming substrate. The laser beam scans the slicing area line by line according to the pre-designed scanning path, causing the powder layer to melt and solidify rapidly, thereby obtaining the first two-dimensional plane of the part; (b) The computer control system lowers the forming substrate by one powder layer thickness, and conversely, raises the piston of the powder supply cylinder by one powder layer thickness. The powder spreading device then spreads a new layer of powder to be processed. The laser beam scans the second powder layer according to the slicing information to obtain the second two-dimensional plane of the part; (c) The above steps are repeated, and the powder to be processed is formed layer by layer until the part is processed.

[0038] After cooling, remove the molded substrate from the equipment (e.g.) Figure 2 As shown in the figure, the part was separated from the substrate using wire cutting to obtain a (TiB2+Al2O3) / Al-Si composite material sample. The (TiB2+Al2O3) / Al-Si composite material bulk sample was ground, polished, and etched according to standard metallographic sample preparation methods. It was found that the primary silicon was significantly refined after the addition of the nano-ceramic reinforcing phase. Large snowflake-shaped primary silicon crystals in the coarse-grained region were significantly reduced or even disappeared, and the morphology of the primary silicon crystals changed from snowflake-shaped to polygonal or irregular, with the average size reduced to approximately 6.58 μm, a decrease of 27%. However, the morphology of the bulk primary silicon crystals in the fine-grained region of the nano-ceramic modified Al-Si alloy did not change significantly, with an average size of approximately 2.14 μm. (See [reference needed]). Figure 3 The obtained (TiB2+Al2O3) / Al-Si composite standard compression specimens were subjected to room temperature compression tests, and their compressive strength reached 741 MPa, which is 21% higher than that of the Al-Si alloy without ceramic reinforcement. Example 2

[0039] (1) TiB2 and Al2O3 with a mass ratio of 2:1 were dispersed in anhydrous ethanol at a solute:solvent mass ratio of 10:1. The mixture was then subjected to ultrasonic vibration at a power of 1000 W for 10 h. The mixture was then dried in a vacuum drying oven at 80 °C for 12 h to obtain uniformly dispersed nano-ceramics. The ceramic powder was mixed with Al-Si alloy powder at a ratio of 3.5 wt.% to prepare composite powder. The ball milling and mixing operation was carried out in a QM series planetary ball mill. The process used a ceramic jar and ceramic grinding balls with diameters of 6 mm and 8 mm. The ball milling process parameters were set as follows: ball-to-material ratio of 2:1, ball milling speed of 200 rpm, and ball milling time of 4 h. To prevent the temperature inside the ball mill jar from becoming too high, the equipment was operated in an intermittent mode during ball milling, i.e., the equipment was paused for 5 min of air cooling after every 15 min of operation. The ball milling process must be carried out under argon protection to prevent the aluminum alloy powder from being oxidized or contaminated.

[0040] (2) Modeling and slicing of target parts

[0041] A three-dimensional solid geometric model of the target part was created using Solidworks software on a computer. Then, Magics software was used to perform layer slicing and scan path planning on the three-dimensional solid model, discretizing the three-dimensional solid into a series of two-dimensional data. This file was saved and imported into the laser powder bed melting forming equipment. The laser process parameters were set as follows: laser power of 450 W, laser scanning speed of 2400 mm / s, scanning interval of 50 μm, powder thickness of 50 μm, using a partitioned island scanning strategy, and the laser scanning direction rotation angle between adjacent layers was 37°.

[0042] (3) Laser powder bed melting process

[0043] The nano-ceramic particle-reinforced Al-Si alloy composite powder obtained in step (1) was used for laser powder bed melting. An SLM-150 laser powder bed melting system was used, which mainly includes a YLR-500 fiber laser, a laser forming chamber, an automatic powder spreading system, a protective atmosphere device, a computer control circuit system, and a cooling circulation system. Before forming, the sandblasted aluminum substrate was fixed on the worktable of the laser powder bed melting system and leveled. Then, the forming chamber was sealed by a sealing device, evacuated, and argon protective atmosphere was introduced. The laser powder bed melting process is as follows: (a) The powder spreading device evenly spreads the powder to be processed on the forming substrate. The laser beam scans the slicing area line by line according to the pre-designed scanning path, so that the powder layer melts and solidifies rapidly, thereby obtaining the first two-dimensional plane of the part; (b) The computer control system lowers the forming substrate by one powder layer thickness, and conversely, raises the piston of the powder supply cylinder by one powder layer thickness. The powder spreading device spreads a new layer of powder to be processed. The laser beam completes the second powder layer scanning according to the slicing information to obtain the second two-dimensional plane of the part; (c) Repeat the above steps, and the powder to be processed is formed layer by layer until the part is processed.

[0044] After cooling, the formed substrate was removed from the equipment, and the part was separated from the substrate using wire cutting to obtain a (TiB2+Al2O3) / Al-Si composite material sample. The (TiB2+Al2O3) / Al-Si composite material bulk sample was ground, polished, and etched according to standard metallographic sample preparation methods. The addition of nano-ceramic reinforcing phase significantly refined the primary silicon. The large, snowflake-shaped primary silicon crystals that were originally prominent in the coarse-grained region were essentially eliminated, their morphology changing from snowflake-like to polygonal, with the average size significantly reduced to ~6.43 μm, a 29% reduction compared to the primary silicon size in the alloy. In the fine-grained region, the morphology of the bulk primary silicon crystals in the nano-ceramic modified Al-Si alloy remained essentially unchanged, with an average size of approximately 2.20 μm, showing no significant change. (See [link to relevant documentation]). Figure 4 The obtained (TiB2+Al2O3) / Al-Si composite standard compression specimens were subjected to room temperature compression tests, and their compressive strength reached 755 MPa, which is 23% higher than that of the Al-Si alloy without ceramic reinforcement. Example 3

[0045] (1) TiB2 and Al2O3 with a mass ratio of 3:2 were dispersed in anhydrous ethanol at a solute:solvent mass ratio of 10:1. The mixture was then subjected to ultrasonic vibration at a power of 1000 W for 10 h. The mixture was then dried in a vacuum drying oven at 80 °C for 12 h to obtain uniformly dispersed nano-ceramics. The ceramic powder was mixed with Al-Si alloy powder at a ratio of 6 wt.% to prepare composite powder. The ball milling and mixing operation was carried out in a QM series planetary ball mill. The process used a ceramic jar and ceramic grinding balls with diameters of 6 mm and 8 mm. The ball milling process parameters were set as follows: ball-to-material ratio of 2:1, ball milling speed of 250 rpm, and ball milling time of 3 h. To prevent the temperature inside the ball mill jar from becoming too high, the equipment was operated in an intermittent mode during ball milling, i.e., the equipment was paused for 5 min of air cooling after every 15 min of operation. The ball milling process must be carried out under argon protection to prevent the aluminum alloy powder from being oxidized or contaminated.

[0046] (2) Modeling and slicing of target parts

[0047] A three-dimensional solid geometric model of the target part was created using Solidworks software on a computer. Then, Magics software was used to perform layer slicing and scan path planning on the 3D solid model, discretizing the 3D solid into a series of two-dimensional data. This file was saved and imported into a laser powder bed fusion molding equipment. The laser process parameters were set as follows: laser power of 400 W, laser scanning speed of 2000 mm / s, scanning interval of 50 μm, powder thickness of 50 μm, using a partitioned island scanning strategy, and a 37° rotation angle in the laser scanning direction between adjacent layers.

[0048] (3) Laser powder bed melting process

[0049] The nano-ceramic particle-reinforced Al-Si alloy composite powder obtained in step (1) was used for laser powder bed melting. An SLM-150 laser powder bed melting system was used, which mainly includes a YLR-500 fiber laser, a laser forming chamber, an automatic powder spreading system, a protective atmosphere device, a computer control circuit system, and a cooling circulation system. Before forming, the sandblasted aluminum substrate was fixed on the worktable of the laser powder bed melting system and leveled. Then, the forming chamber was sealed by a sealing device, evacuated, and argon protective atmosphere was introduced. The laser powder bed melting process is as follows: (a) The powder spreading device evenly spreads the powder to be processed on the forming substrate. The laser beam scans the slicing area line by line according to the pre-designed scanning path, so that the powder layer melts and solidifies rapidly, thereby obtaining the first two-dimensional plane of the part; (b) The computer control system lowers the forming substrate by one powder layer thickness, and conversely, raises the piston of the powder supply cylinder by one powder layer thickness. The powder spreading device spreads a new layer of powder to be processed. The laser beam completes the second powder layer scanning according to the slicing information to obtain the second two-dimensional plane of the part; (c) Repeat the above steps, and the powder to be processed is formed layer by layer until the part is processed.

[0050] After cooling, the formed substrate was removed from the equipment, and the part was separated from the substrate using wire cutting to obtain a (TiB2+Al2O3) / Al-Si composite material sample. The (TiB2+Al2O3) / Al-Si composite material bulk sample was ground, polished, and etched according to standard metallographic sample preparation methods. After adding the nano-ceramic reinforcing phase, the microstructure of primary silicon changed significantly. The primary silicon in the coarse-grained region changed noticeably, with large-sized primary silicon significantly reduced or even completely disappeared. Its morphology changed from a complex snowflake-like shape to an irregular shape, and the average size decreased sharply to ~6.60 μm, a 27% reduction compared to Al-Si without the addition. The obtained (TiB2+Al2O3) / Al-Si composite material standard compression test was conducted at room temperature, and its compressive strength reached 735 MPa, a 20% improvement compared to the Al-Si alloy without the ceramic reinforcing phase. Comparative Example 1

[0051] The specific steps of this comparative example are basically the same as those of Example 1, except that in step (1) of this comparative example, no nano-ceramic powder is added to the Al-Si alloy and no composite powder is prepared by ball milling. Instead, near-spherical Al-Si alloy powder prepared by gas atomization is used as the raw material for laser powder bed melting and forming. Its microstructure is as follows: Figure 5 As shown. Comparison Figure 3 and Figure 5It was observed that the primary silicon in the coarse-grained region of the Al-Si alloy was snowflake-shaped with an average size of ~9.02 μm, while the blocky primary silicon in the fine-grained region had an average size of ~2.86 μm. The obtained Al-Si alloy standard compression specimen was subjected to a room temperature compression test, and its compressive strength was 612 MPa. Comparative Example 2

[0052] The specific steps of this comparative example are basically the same as those of Example 1, except that in step (1) of this comparative example, only Al2O3 nano-ceramic powder is added to the Al-Si alloy to prepare composite powder, which is then subjected to laser powder bed melting. It was found that the refining effect of primary silicon in the laser-formed sample was not obvious, and large-sized snowflake-shaped primary silicon still existed in the coarse-grained region, with an average size of ~8.94 μm. In the fine-grained region, the morphology of the blocky primary silicon in the nano-ceramic modified Al-Si alloy remained basically unchanged, with an average size of ~2.78 μm, and no significant change was observed. The standard compression test of the obtained Al2O3 / Al-Si composite material was carried out at room temperature, and its compressive strength reached 627 MPa, which was an improvement compared to the Al-Si alloy without the addition of nano-ceramic reinforcing phase, but not significantly. Comparative Example 3

[0053] The specific steps of this comparative example are basically the same as those of Example 1, except that in step (1) of this comparative example, the content of TiB2+Al2O3 nano-ceramics added to the Al-Si alloy is less than 1 wt.% to prepare composite powder, which is then subjected to laser powder bed melting. It was found that the refining effect of primary silicon in the coarse-grained region of the laser-formed sample was not obvious, and a large amount of large-sized primary silicon still existed, with an average size of ~9.01 μm. The morphology of primary silicon in the fine-grained region was almost unchanged, and the average size remained at ~2.80 μm. The obtained (TiB2+Al2O3) / Al-Si composite material standard compression test was carried out at room temperature, and its compressive strength was 618 MPa. Compared with the compressive strength of Al-Si alloy without ceramic reinforcement, the change was not obvious. This is because the content of added nano-ceramics was too low, and the refining effect on coarse primary silicon and matrix was not obvious, so the performance did not change significantly. Comparative Example 4

[0054] The specific steps of this comparative example are basically the same as those of Example 1, except that in step (1) of this comparative example, TiB2+Al2O3 nano-ceramic content is added to the Al-Si alloy to prepare composite powder, which is then subjected to laser powder bed melting. It was found that the addition of nano-ceramic reinforcing phase significantly refined the primary silicon. In the coarse-grained region, the large-sized snowflake-shaped primary silicon crystals that were originally formed were basically eliminated, and their morphology changed from the original snowflake-shaped to an irregular shape, with the average size reduced to ~6.18 μm, which is 31% smaller than the size of the primary silicon crystals in the alloy. In the fine-grained region, the morphology of the blocky primary silicon crystals in the nano-ceramic modified Al-Si alloy remained basically unchanged, with an average size of about 2.05 μm. The obtained (TiB2+Al2O3) / Al-Si composite standard compression specimen was subjected to a room temperature compression test. Its compressive strength was only 523 MPa, which was 15% lower than that of the Al-Si alloy without ceramic reinforcement. The compression performance was significantly reduced. This is because the high content of nano-ceramics increased the brittleness of the laser-formed sample, causing the specimen to fracture prematurely during the compression test, resulting in low mechanical properties.

[0055] As can be seen from Examples 1-3 and the comparative examples, laser powder bed fusion forming of (TiB2+ Al2O3) / AlSi 40 The compressive strength of the composite material samples increased significantly, and the mechanical properties were significantly improved. Si and Al2O3 have similar crystal structures and a good interfacial coherence relationship. Al2O3 particles can be rapidly captured and absorbed by Si atom clusters, thereby increasing the Al2O3 particle content within the Si grains. In the method of this invention, during the solidification of the nano-ceramic-reinforced Al-Si alloy melt, TiB2 nano-ceramic particles are located at the solid-liquid interface of the aluminum alloy melt. To a certain extent, this prevents the diffusion and aggregation of Si atoms into Si-Si atom clusters, leading to changes in the anisotropy of primary silicon and inhibiting silicon phase growth. This results in a more regular morphology and finer size of the primary silicon. Al2O3 particles act as heterogeneous nucleation sites for primary silicon, increasing the nucleation rate and refining the size of primary silicon. Therefore, the nano-ceramic particles can effectively improve the morphology of primary silicon in the Al-Si alloy composite material microstructure and fully refine the primary silicon distributed in the aluminum matrix.

[0056] This invention provides a method and approach for refining primary silicon in Al-Si alloys through synergistic modification with nano-ceramics based on laser additive manufacturing. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for refining primary silicon in Al-Si alloys through synergistic modification with nano-ceramics based on laser additive manufacturing, characterized in that, Includes the following steps: (1) Disperse TiB2 nano-ceramic powder and Al2O3 nano-ceramic powder in anhydrous ethanol and then dry to obtain a uniformly dispersed mixed nano-ceramic powder. (2) Mix the Al-Si alloy powder with the mixed nano-ceramic powder from step (1) until uniform, to obtain nano-ceramic particle-reinforced Al-Si alloy composite powder; (3) Establish a three-dimensional solid geometric model of the target part, then slice the model into layers and plan the laser scanning path, discretize the three-dimensional solid into a series of two-dimensional data, save this file and import it into the laser powder bed melting and forming equipment; (4) The laser powder bed melting and forming equipment melts and solidifies the nano-ceramic particle reinforced Al-Si alloy composite powder in step (2) layer by layer according to the file saved in step (3), and finally forms the target part to be built. In step (1), the mass ratio of TiB2 ceramic powder to Al2O3 ceramic powder is 3:1 to 3:2; the particle size distribution range of the TiB2 nano-ceramic powder used is 30 to 75 nm; the particle size distribution range of the Al2O3 nano-ceramic powder used is 25 to 60 nm. In step (2), the mixed nano-ceramic powder accounts for 1.5 to 6 wt.% of the mass of the Al-Si alloy powder; the particle size distribution of the Al-Si alloy powder is in the range of 20 to 48 μm, wherein the silicon content is 22 to 55 wt.%, the iron content is 0.08 to 0.17%, the copper content is 2.3 to 3.0%, and the balance is aluminum; In step (4), the laser power used in the laser powder bed melting and forming equipment is 350~450 W, the scanning speed is 1600-2400 mm / s, the scanning spacing is 40~60 μm, the powder thickness is 40~60 μm, and a partitioned island scanning strategy is adopted.

2. The method for refining primary silicon in Al-Si alloys through synergistic modification with nano-ceramics based on laser additive manufacturing, as described in claim 1, is characterized in that... In step (1), the TiB2 nano-ceramic powder used is an irregular TiB2 ceramic powder with a purity greater than 99.9%.

3. The method for refining primary silicon in Al-Si alloys through synergistic modification with nano-ceramics based on laser additive manufacturing according to claim 1, characterized in that, In step (1), the Al2O3 nano-ceramic powder used is an irregular Al2O3 ceramic powder with a purity greater than 99.9%.

4. The method for refining primary silicon in Al-Si alloys through synergistic modification with nano-ceramics based on laser additive manufacturing, as described in claim 1, is characterized in that... In step (1), TiB2 ceramic powder and Al2O3 ceramic powder are dispersed in anhydrous ethanol at a solute:solvent mass ratio of 10:(1~2), and then subjected to ultrasonic oscillation. The resulting mixture is then placed in a vacuum drying oven for drying to obtain uniformly dispersed nano-ceramic powder. The ultrasonic power of the ultrasonic oscillator is 1000~1200 W, and the ultrasonic oscillation time is 8~12h. The drying temperature of the vacuum drying oven is 70~90℃, and the drying time is 10~14h.

5. The method for refining primary silicon in Al-Si alloys through synergistic modification with nano-ceramics based on laser additive manufacturing according to claim 1, characterized in that, In step (2), Al-Si alloy powder and mixed nano-ceramic powder are mixed uniformly using a QM series planetary ball mill under inert gas protection.

6. The method for refining primary silicon in Al-Si alloys through synergistic modification with nano-ceramics based on laser additive manufacturing according to claim 5, characterized in that, The ball milling is carried out intermittently, with a rotation speed of 150-250 rpm and a milling time of 3-5 hours. Each milling session lasts 14-20 minutes, with an interval of 4-6 minutes.

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