A method for selective laser melting of homogeneous powder and preparation of composite materials

Abstract

This application provides a method for preparing homogeneous powder and composite materials through selective laser melting, comprising the following weight components: 85%–98.5% aluminum alloy powder, 0.5%–5% titanium powder, and 1–10% high-entropy alloy powder. The weighed powder is loaded into a ball mill jar, and a protective gas is introduced to purge air. High-efficiency mixing equipment is used, without adding any grinding media, for high-energy mixing. This invention utilizes a "ballless" mixing process, and subsequent processes work synergistically. The in-situ nucleation of Ti greatly refines the grains, the presence of the HEA phase pins grain boundaries, preheating at 150°C reduces the brittle temperature range, and rotation at 67°C disperses stress concentration, effectively managing the thermal gradient and stress field during selective laser melting. Multiple mechanisms work synergistically to solve the problem of hot cracking in aluminum-based composite materials during selective laser melting. The product requires no subsequent heat treatment, and the printed part can stably achieve a tensile strength of 500 MPa in the as-built state. This application features a simple preparation process, short cycle time, low cost, and high yield.

Description

Technical Field

[0001] This application belongs to the field of metal powder technology, and particularly relates to a method for selective laser melting of homogeneous powder and preparation of composite materials. Background Technology

[0002] Aluminum alloys are critical lightweight, high-strength materials for aerospace applications. Selective laser melting (SLM) technology is considered an ideal method for manufacturing complex structural components. However, limited by the wide solidification range of 7XXX aluminum alloys, SLM-formed parts (As-built state) generally suffer from severe hot cracking and poor mechanical properties (tensile strength is typically below 300 MPa). Existing technologies typically employ two approaches: one is compositional modification (such as adding Si, Zr, Ti): suppressing cracking through grain refinement, but the strength improvement in the As-built state is limited; the other is subsequent heat treatment: T6 heat treatment of the printed parts can improve strength, but this process is highly prone to causing warping deformation and microcrack propagation, and significantly increases manufacturing costs and cycle time. Summary of the Invention

[0003] To achieve the above objectives, this application provides a technical solution that simultaneously achieves "crack prevention" and "high strength" during selective laser melting "in-situ" forming without heat treatment. This invention combines an innovative powder homogenization method with specific process parameters (such as 150°C substrate preheating) to stably prepare crack-free 7075 aluminum-based composite material parts with a tensile strength of not less than 450 MPa (optimally up to 500 MPa) in an untreated (as-built) state.

[0004] The first aspect of this application provides a homogeneous powder for selective laser melting, comprising the following weight components: 85%–98.5% aluminum alloy powder, 0.5%–5% titanium powder, and 1–10% high entropy alloy (HEA) powder, wherein the aluminum alloy, Ti, and HEA powders are all spherical; the weighed powder is loaded into a ball mill jar, a protective gas is introduced to purge the air, and high-energy mixing is performed using a high-efficiency mixing device without adding any grinding media.

[0005] In any embodiment, the addition ratio of the aluminum alloy powder, titanium powder, and high entropy alloy (HEA) powder is as follows: the weight percentage of titanium powder is 0.5% to 5%; the weight percentage of HEA powder is 1% to 10%; and the balance is aluminum alloy powder.

[0006] In any embodiment, the mixing process parameters are 100-300 RPM for 4-8 hours.

[0007] In any embodiment, the aluminum alloy powder is a 7xxx series aluminum alloy powder with a particle size of 15-53μm.

[0008] In any embodiment, the aluminum alloy powder is 7075 series aluminum alloy powder.

[0009] In any embodiment, the high entropy alloy (HEA) powder has a particle size of 15-53 μm and a composition such as AlCoCrFeNi series.

[0010] In any embodiment, the high entropy alloy (HEA) powder is of the AlCoCrFeNi series.

[0011] In any embodiment, the titanium (Ti) powder has a particle size of 0-25 μm.

[0012] The second aspect of this application also provides a method for preparing composite materials by selective laser melting, wherein the above-mentioned homogeneous powder is laid on a forming substrate of a selective laser melting device, the substrate is preheated to 80°C to 200°C in a protective gas environment (e.g., argon), and the following parameters are set: laser power (P): 180 W to 260 W; scanning speed (v): 500 mm / s to 900 mm / s; powder layer thickness (t): 0.02 mm to 0.04 mm; scanning spacing (h): 0.08 mm to 0.10 mm; after printing, the component is cooled to room temperature in the furnace to obtain an untreated part.

[0013] In any embodiment, the substrate preheating temperature is 140°C to 160°C.

[0014] In any implementation, the scanning strategy of the selective laser melting device is as follows: a stripe scan strategy is adopted, with interlayer rotation of 67°.

[0015] In any embodiment, the volumetric energy density (VED) of the selective laser melting apparatus ranges from approximately 78 to 186 J / mm². 3 .

[0016] The beneficial effects of this application are as follows: The "ballless" mixing process adopted in this invention, through subsequent process synergy, including the combined effects of "homogeneous powder + 150℃ preheating + specific VED window + 67° interlayer rotation," effectively manages the thermal gradient and stress field during selective laser melting. The in-situ nucleation of Ti greatly refines the grains, the presence of the HEA phase pins the grain boundaries, the 150℃ preheating lowers the brittle temperature range, and the 67° rotation disperses stress concentration. These multiple mechanisms work together to fundamentally solve the problem of hot cracking during selective laser melting of aluminum-based composite materials. The product requires no subsequent heat treatment, and the printed part can stably achieve a tensile strength of 500 MPa in the as-built state. This application features a simple preparation process, short cycle time, low cost, and high yield. Attached Figure Description

[0017] Figure 1 The powders included were AA7075 powder (a), AlCoCrFeNi powder (b), titanium powder (c), and AA7075 + 5 wt.% AlCoCrFeNi from Example 1. 2.1 SEM morphology of + 2 wt.% Ti mixed powder (d);

[0018] Figure 2 Example 1: AA7075 + 5 wt.% AlCoCrFeNi 2.1 SEM morphology and EDS surface scan analysis of + 2 wt.% Ti mixed powder;

[0019] Figure 3 Optical microscope (OM) images of the selected laser melting composite material prepared according to the process parameters of Example 10 at different magnifications; where (a) is the morphology at 25x low magnification and (b) is the morphology at 200x high magnification.

[0020] Figure 4 SEM images of the selected laser melting composite material prepared according to the process parameters of Example 10 at different magnifications; where (a) is a 200x low magnification image and (b) is a 3000x high magnification image;

[0021] Figure 5 The room temperature tensile stress-strain curve of the selected laser-melted composite material prepared according to the process parameters of Example 10;

[0022] Figure 6 For Comparative Example 1, the room temperature tensile stress-strain curve of the pure AA7075 substrate in the selected laser melting printing state (without heat treatment) prepared using the process parameters of Example 10 in Table 1 is shown.

[0023] Figure 7The bar charts show the comparison of Vickers microhardness (HV0.5) of the AA7075 substrate in the printed state for Examples 1-15 and the corresponding selected area laser melting process parameters;

[0024] Figure 8 The image shows a comparison of the relative density of the AA7075 substrate printed with the corresponding selected area laser melting process parameters in Examples 1-15. Detailed Implementation

[0025] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the method for selective laser melting of homogeneous powder and preparation of composite materials according to this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0026] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0028] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0029] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0030] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0031] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0032] In one embodiment of this application, a homogeneous powder for selective laser melting is provided, comprising the following weight components: 85%–98.5% aluminum alloy powder, 0.5%–5% titanium powder, and 1–10% high entropy alloy (HEA) powder, wherein the aluminum alloy, titanium powder, and HEA powder are all spherical; the weighed powder is loaded into a ball mill jar, a protective gas is introduced to purge the air, and high-energy mixing is performed using a high-efficiency mixing device without adding any grinding media (i.e., in a "ball-free" state).

[0033] The "ballless" high-energy mixing step employed in this application is not for crushing or alloying, but rather utilizes the shearing and frictional action between powders to achieve uniform dispersion of HEA powder of the same particle size range between the aluminum alloy powder and the HEA powder without compromising the sphericity of the powder, using aluminum alloy powder with a particle size of 15-55μm as the main component. Simultaneously, titanium powder with a smaller particle size (0-25μm) fills the gaps between the aluminum alloy powder and the HEA powder, ultimately achieving a uniform overall mixing of the three powders to form a highly homogeneous mechanically mixed powder.

[0034] When the Ti content is too high (e.g., >5%), it easily forms a coarse or continuous network of excessive Al3Ti. The combination of phase boundary embrittlement and stress concentration significantly increases the susceptibility to hot cracking. When the HEA content is too high (e.g., >15%), the system deviates from the matrix composition framework of 7075, evolving into a new alloy system and easily inducing the precipitation of brittle phases such as intermetallic compounds, thereby weakening plasticity, toughness, and forming stability. Therefore, the addition of Ti and HEA should be controlled within the process window for achieving grain refinement / heterogeneous nucleation and load transfer, avoiding continuous brittle phase networks and compositional drift.

[0035] In some embodiments, the addition ratio of the aluminum alloy powder, titanium powder, and high entropy alloy (HEA) powder is as follows: the weight percentage of titanium powder is 0.5% to 5%; the weight percentage of HEA powder is 1% to 10%; and the balance is aluminum alloy powder.

[0036] In some embodiments, the mixing process parameters are 100–300 RPM for 4–8 hours.

[0037] When the rotation speed exceeds 300 RPM and / or the time is longer than 8 hours, the excessive mechanical energy will damage the oxide film on the surface of the aluminum powder and induce cold welding / neck bonding, generating satellite powder, out-of-round particles or flaky flocs. When the rotation speed is lower than 100 RPM and / or the time is shorter than 4 hours, the particle contact frequency and shear stress per unit time are insufficient, making it difficult to effectively disperse agglomerates and achieve the adhesion of microparticles to the surface of 7075 powder. Macroscopic component segregation and local agglomeration are likely to occur, resulting in fluctuations in loose packing density, angle of repose, and powder spreading stability, which in turn affects the densification and crack suppression effect of LPBF forming layers.

[0038] In some embodiments, the aluminum alloy powder is 7xxx series aluminum alloy powder with a particle size of 15-53 μm.

[0039] In some embodiments, the aluminum alloy powder is 7075 series aluminum alloy powder.

[0040] In some embodiments, the high entropy alloy (HEA) powder has a particle size of 15-53 μm and a composition such as AlCoCrFeNi series.

[0041] In some embodiments, the high entropy alloy (HEA) powder is of the AlCoCrFeNi series.

[0042] In some embodiments, the titanium (Ti) powder has a particle size of 0-25 μm.

[0043] In one embodiment of this application, a method for preparing composite materials by selective laser melting is proposed. The homogeneous powder is laid on a forming substrate in a selective laser melting apparatus. Under a protective gas atmosphere (e.g., argon), the substrate is preheated to 80°C–200°C, and the following parameters are set: laser power (P): 180 W–260 W (based on an epitaxial layer of [190, 220, 250 W]); scanning speed (v): 500 mm / s–900 mm / s (based on a range of [500–900 mm / s]); powder layer thickness (t): 0.02 mm–0.04 mm (based on an epitaxial layer of [0.03 mm]); scanning spacing (h): 0.08 mm–0.10 mm (based on an epitaxial layer of [0.09 mm]). After printing, the powder is cooled to room temperature in the furnace to obtain an untreated component.

[0044] Titanium powder and HEA powder were added to the 7075 aluminum alloy matrix powder. During the rapid melting and solidification of LPBF, Ti underwent a metal-metal reaction and diffusion, generating Al-Ti reaction phases (such as Al3Ti nucleation cores / dispersed phases) in situ within the molten pool. This significantly refined the grains, altered the solidification path, and suppressed hot cracking. Simultaneously, a thin diffusion layer was formed between the HEA particles and the matrix, providing metallurgical bonding and supporting load transfer and dislocation / Orowan strengthening.

[0045] This application utilizes an external reinforcing phase, HEA, which is a pinned reinforcing phase. The high entropy effect of HEA prevents it from easily bending and dissolving into the aluminum melt during the ultra-fast solidification process of selective laser melting (SLM), thus serving as a heterogeneous nucleation site to refine α-Al grains. The hard HEA particles themselves can also bear loads, strengthening the matrix and effectively pinning grain boundaries and dislocation movement. During the preparation process, Ti dissolves and reacts to form: 3Al + Ti → Al3Ti. The resulting compound is very fine, appearing as small flakes or blocks, and is widely distributed, providing a strong dispersion strengthening effect. This then transforms 7075 aluminum from columnar crystals into fine equiaxed crystals, obtaining an in-situ produced reinforcing phase that can also serve as a heterogeneous nucleation core, greatly refining the aluminum matrix grains. Furthermore, during SLM, it transforms into even smaller AlCoCrFeNi particles. 2.1 (HEA) particles precipitate, or partially dissolved HEA elements (such as Fe, Co, Ni) react with Al to form hard and brittle intermetallic compounds such as Al9(Fe,Ni)2 and Al3(Fe,Co,Ni), which also provide dispersion strengthening effect. However, their size and amount need to be controlled within the range specified in this application. Too much or too large an amount will become a crack source and affect product quality.

[0046] In some embodiments, the substrate preheating temperature is 140°C to 160°C.

[0047] In some embodiments, the scanning strategy of the selective laser melting device is: to use a strip scan strategy with interlayer rotation of 67°.

[0048] Rotation at this specific angle helps to interrupt the continuous growth of columnar crystals and distribute residual stress more evenly between different layers, further aiding in crack suppression.

[0049] In some embodiments, the volumetric energy density (VED) of the selective laser melting apparatus ranges from approximately 78 to 186 J / mm². 3 .

[0050] Example

[0051] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0052] Example 1

[0053] A method for preparing composite materials by selective laser melting includes the following steps:

[0054] (1) Preparation of homogeneous powder:

[0055] Commercially available spherical 7075 aluminum alloy powder (15-53 μm particle size), commercially available spherical high-entropy alloy (HEA) powder (15-53 μm particle size), and commercially available spherical titanium (Ti) powder (0-25 μm particle size) were selected. The three powders were weighed according to a predetermined mass percentage: 93% 7075 aluminum alloy powder, 2% Ti, and 5% high-entropy alloy (HEA) powder, with a total alloy composition of 100%. The weighed powders were then placed in a ball mill jar, and high-purity argon gas was introduced as a protective gas to purge air. A planetary ball mill was used for high-energy mixing at 100-300 RPM for 6 hours without adding any grinding media (i.e., in a "ball-free" state).

[0056] (2) Selective laser melting preparation of 7075 aluminum-based composite materials:

[0057] The homogeneous powder prepared in step (1) is laid on the forming substrate of the selective laser melting equipment. The substrate is preheated to 150°C under a protective gas atmosphere (e.g., argon). The selective laser melting process parameter window is set according to Table 1; the scanning strategy is strip scan with interlayer rotation of 67°. After printing, the part is cooled to room temperature in the furnace to obtain the untreated part.

[0058] Table 1. Selective Laser Melting (CEL) Process Parameters

[0059]

[0060] Comparative Example 1

[0061] Commercially available spherical 7075 aluminum alloy powder with a particle size of 15-53 μm was selected and deposited onto a forming substrate in a selective laser melting (SLM) apparatus. The substrate was preheated to 150°C under a protective gas atmosphere (e.g., argon). The SLM process parameters were set as follows: laser power (P): 250 W; scanning speed (v): 900 mm / s; powder layer thickness (t): 0.03 mm; scanning spacing (h): 0.09 mm; scanning strategy: strip scan with 67° interlayer rotation; the volumetric energy density (VED) of the SLM apparatus was approximately 102.88 J / mm². 3 After printing, the parts are cooled to room temperature in the oven to obtain the untreated parts.

[0062] Figure 1 , 2 In this application, the homogeneous powder high-entropy alloy and Ti are separate and not fused together, exhibiting a uniform distribution. Figure 2 The elemental spectrum shows that Al, Zn, Mg, and Cu (the main components of AA7075) are uniformly distributed in larger spherical particles. Ti (green) corresponds to smaller, independent particles. Co, Cr, Fe, and Ni (AlCoCrFeNi) are also present. 2.1 The components of the high-entropy alloy are concentrated on specific particles, confirming the uniform distribution of each component in the mixed powder.

[0063] As shown in Figure 1, the three original powders and their mixture exhibit a near-spherical morphology with a relatively smooth surface, meeting the requirements for flowability and bulk density of the laser selective melting process in this application. The AA7075 and AlCoCrFeNi used in this application... 2.1 The particle size range of high-entropy alloy powder is 15-53 μm, and that of titanium powder is 0-25 μm. In (a), the AA7075 powder has a relatively concentrated particle size distribution, with most particles having regular and round morphologies. Only a small amount of satellite powder adheres to the surface or gaps of larger particles, indicating that the original 7075 powder has good sphericity and loose packing properties, which is beneficial for obtaining a stable and continuous powder layer during the forming process. (b) shows AlCoCrFeNi... 2.1The high-entropy alloy powder also exhibits near-spherical particles, but with a slightly wider particle size distribution. Slightly rough protrusions and a small number of satellite particles can be observed on the particle surface, which is related to the solidification interface fluctuations caused by the multi-component composition of the high-entropy alloy. Overall, the powder maintains good sphericity and dispersibility, meeting the requirements for subsequent co-laying with aluminum alloy powder. In (c), the titanium powder particles are significantly finer, with some particles showing slightly irregular morphology and a small number of near-plate-like or short rod-shaped particles. These fine Ti particles mainly fill the gaps between large particles and provide a source of active elements in subsequent mixing, which is beneficial for the in-situ formation of dispersed strengthening phases (such as Al3Ti) during selective laser melting. However, their content needs to be controlled to avoid excessive Ti inducing brittle phases and cracking tendencies. (d) is AA7075 + 5 wt.% AlCoCrFeNi 2.1 The morphology of the +2 wt.% Ti mixed powder shows that the large spherical particles are still mainly composed of 7075 aluminum powder, and their sphericity is basically intact. No obvious cold welding agglomeration or severe plastic deformation was observed, indicating that the mixing process used was relatively mild and did not damage the morphology of the matrix powder. A large number of fine particles are evenly distributed between and near the surface of the coarse particles, presumably mainly high-entropy alloys and titanium powder. No obvious local enrichment or large-scale agglomeration areas were observed, indicating that the powder is uniformly dispersed after mixing. Overall, all three original powders have good sphericity and dispersibility. The morphology of the 7075 matrix powder is basically maintained after mixing, and the HEA and Ti particles are finely and evenly distributed in the gaps. This "coarse-fine composite" particle size structure not only helps to improve the packing density and interlayer compactness during the powder spreading process, but also provides good preconditions for the uniform distribution of HEA particles and Ti elements in the molten pool, interfacial reaction, and multi-scale strengthening during the subsequent selective laser melting forming process.

[0064] from Figure 2 The EDS surface scan results show that the spatial distribution of different elements in the mixed powder exhibits a clear correlation. Elements such as Al, Zn, Mg, and Cu are mainly enriched in larger, nearly spherical particles, and... Figure 1The morphological characteristics of the AA7075 powder are consistent, indicating that these particles are still mainly composed of 7075 aluminum alloy, and the mixing process did not change their composition and overall morphology. This result shows that there is no obvious element diffusion or pre-reaction during the powder pretreatment stage, and the matrix powder remains a typical Al-Zn-Mg-Cu alloy particle. Ti is distributed in the form of a large number of fine particles, and its signal does not overlap with the high-intensity regions of Al, Zn, Mg, and Cu, indicating that Ti mainly exists in the form of independent particles, rather than being significantly dissolved into AA7075 or HEA particles during the mixing process. This morphology of "independent fine Ti particles + coarse Al matrix particles" is conducive to in-situ reactions (such as the formation of dispersed Al3Ti phases) in the selective laser melting pool, while avoiding the generation of uncontrolled pre-alloying or large-sized brittle phases during the powder mixing stage. Co, Cr, Fe, Ni and other elements are represented as a group of particle clusters with different outlines from the matrix particles in the figure. Their high-intensity signals are concentrated on specific particles and are relatively uniformly distributed within the field of view. This indicates that AlCoCrFeNi 2.1 After mixing, the high-entropy alloy powder remains as independent HEA particles, without significant large-scale enrichment or "corner-off" separation in space. This indicates that the mixing process effectively avoids severe stratification based on density or particle size. Combining SEM morphology and EDS surface scan results, it can be concluded that the AA7075 powder forms a uniformly spread coarse matrix framework, with HEA particles and fine Ti particles evenly distributed as discrete phases within it, forming a relatively ideal multi-scale mixing state of "7075 matrix + HEA particles + fine Ti particles". This spatial distribution characteristic is beneficial for improving powder packing density and uniformity, and provides a favorable chemical and geometric prerequisite for the full participation of HEA particles and Ti elements in the molten pool, interfacial reactions, and multi-mechanism synergistic strengthening during subsequent selective laser melting forming.

[0065] Figure 3 The process parameters used in Example 10 were (P=220 W, v=900 mm / s, VED≈90.5 J / mm). 3 Optical microscopy (OM) images of the selected area laser melting state AA7075+5 wt.% AlCoCrFeNi+2 wt.% Ti composite material sample, showing its porosity (defect) distribution: (a) 25x low magnification morphology; (b) 200x high magnification morphology; It can be seen from the figures that the sample has good forming quality under this process parameter and no obvious metallurgical cracks were observed.

[0066] from Figure 3(a) The 25× low-magnification OM image shows that the sample cross-section has a uniform grayish-white matrix, with dark pores distributed in a dotted pattern. These pores are generally small in size and relatively uniformly distributed within the field of view. No obvious pore-rich zones or continuous defect zones are observed. This indicates that at P = 220 W and v = 900 mm / s (VED≈90.5 J / mm²), the surface temperature is suitable for microstructures. 3 Under these conditions, the molten pool overlaps sufficiently, the layers are well bonded together, and no large-scale unfused defects or sheet-like voids are formed, resulting in a high level of macroscopic density.

[0067] At 200x magnification Figure 3 In (b), the pore morphology and size characteristics can be observed more clearly. Most pores are nearly circular or elliptical with smooth boundaries, presumably formed by residual gas in the molten pool that could not escape in time; a small number of pores are slightly irregular in shape, possibly related to minor incomplete fusion or inclusions caused by local energy fluctuations. However, these irregular pores are limited in number and small in size, and do not form a connected network or obvious notch source morphology, so their weakening effect on the overall mechanical properties is relatively controllable. More importantly, no linear metallurgical defects such as hot cracks or shrinkage cracks propagating along the melt channel or grain boundaries were observed at either magnification. This indicates that under the current parameter combination and AlCoCrFeNi... 2.1 Under the +Ti composite design, the solidification shrinkage behavior and thermal stress level of the alloy system are effectively controlled. On the one hand, the selective laser melting process window avoids deep-melting bond holes and severe temperature gradients caused by excessively high energy density. On the other hand, HEA particles and fine Ti particles provide heterogeneous nucleation and grain refinement effects during solidification, jointly suppressing the hot cracking tendency commonly found in traditional selective laser melting of 7075. In summary, Figure 3 The cross-sectional morphology shown indicates that the AA7075+5wt.%AlCoCrFeNi prepared under the process parameters of Example 10... 2.1 The +2wt.%Ti composite material has fewer and more discrete fine pores, no obvious metallurgical cracks, and good overall forming quality, providing a dense matrix for obtaining higher strength and ductility in the future.

[0068] Figure 4 Selective laser-melted AA7075+5 wt.% AlCoCrFeNi was prepared using the process parameters of Example 10 (P=220 W, v=900 mm / s). 2.1 SEM images of the +2wt.% Ti composite sample: (a) 200x low magnification image, showing a highly dense and uniform microstructure with almost no macroscopic defects. (b) 3000x high magnification image, clearly showing the reinforcing phase particles (AlCoCrFeNi). 2.1The particles are dispersed within the AA7075 matrix. A good and continuous metallurgical interface is formed between the particles and the matrix, and no obvious interface separation or microcracks were observed, indicating that the composite material has excellent forming quality.

[0069] As can be seen from the 200× low-magnification SEM image in Figure 4(a), the sample surface is relatively smooth and dense, with only a very small number of dark pores or inclusions. Most areas do not exhibit identifiable large pores or incomplete fusion defects. This is consistent with the high density reflected in the previous OM results, indicating that under the parameter combination of P=220 W and v=900 mm / s, the molten pool overlaps sufficiently, the interlayer metallurgical bonding is good, and the overall forming quality is high. At 3000× magnification... Figure 4 In (b), several bright white second-phase particles can be clearly observed, with sizes ranging from submicron to several micrometers, and morphologies mostly irregular, near-blocky, or short strip-shaped. The interface between these high-contrast particles and the surrounding matrix is ​​clearly defined, but no obvious porosity, debonding, or microcracks are observed at the interface, nor are there any crack initiation features extending along the particle periphery. This indicates that the second phase can achieve continuous metallurgical bonding with the aluminum matrix during rapid solidification, rather than existing as mechanical inclusions. Combined with powder EDS surface scanning results, it can be inferred that these bright white particles are mainly Co / Cr / Fe / Ni-rich HEA particles and the secondary phases formed by their reaction with Al and Ti. From a field-view scale perspective, these second-phase particles are relatively dispersed in the matrix, without large-scale agglomeration areas, but rather exhibit a "dot-like dispersion + local small clusters" morphology. This spatial distribution pattern is beneficial for effective load transfer and dislocation pinning under tensile loads, contributing to dispersion strengthening and grain refinement effects. Furthermore, due to the limited particle size and good interfacial bonding, stress concentration is relatively controllable, without inducing obvious microcracks or early fracture sources. Combining the low-magnification and high-magnification SEM results in Figure 4, it can be concluded that the AA7075+5wt.% AlCoCrFeNi prepared under the process parameters of Example 10... 2.1 The +2wt.% Ti composite material not only has high overall density and very few macroscopic defects, but also has a dense and uniformly distributed interface between the HEA / Ti related second phase particles and the aluminum matrix. This provides a microstructure basis for obtaining higher yield strength and tensile strength while avoiding typical selective laser melting 7075 hot cracking failure.

[0070] Figure 5 Selective laser melting printing state (untreated) AA7075+5 wt.% AlCoCrFeNi was prepared using process parameters No. 1 (P=220 W, v=900 mm / s). 2.1The room temperature tensile stress-strain curves of the +2 wt.% Ti composite specimens are shown in the figure. The results of three repeated tests are presented. The ultimate tensile strength (UTS) of the specimens ranges from 460 to 505 MPa, with a maximum value of 505 MPa, and the elongation at break is approximately 2.6% to 2.9%. The three curves are basically consistent in shape, indicating that the printed specimens have good mechanical property stability.

[0071] from Figure 5 It can be seen that the elastic phases of the three stress-strain curves almost completely overlap, indicating that the elastic modulus and initial defect levels of the samples are very similar, and the macroscopic density and effective load-bearing capacity of the cross-sectional area are highly consistent during the printing process. After entering the yielding and subsequent strain hardening stages, the curves still maintain similar slopes and evolution trends, without obvious yield plateaus or sawtooth unstable deformations, reflecting the continuous yielding characteristics of typical high-strength aluminum alloys under rapid cooling and fine-grained microstructures. Before near fracture, the UTS of all three curves exceeded 460 MPa, with the highest sample reaching approximately 505 MPa, which is close to or even partially close to the strength level of traditional forged AA7075-T6 material, while this is still in the "printed state + untreated state". This indicates that under the process parameters of Example 10 and AlCoCrFeNi 2.1 Under the +Ti composite design, the selective laser melting (SLM) specimens achieved a considerably high load-bearing capacity without relying on subsequent T6 heat treatment. On the other hand, the elongation at break remained in the range of approximately 2.6%-2.9%. Although the plasticity was significantly lower than that of traditional T6 plates, this elongation level is still engineering-acceptable given the high strength requirements of the SLM 7075 system, which is prone to hot cracking and brittle fracture. The minimal dispersion of UTS and fracture strain in the three curves indicates that: (i) the melt pool overlap was stable and the defect level was consistent under the process parameters of Example 10; (ii) the volume fraction and distribution of HEA particles and Ti-related phases were highly repeatable across different specimens; and (iii) the fracture process was mainly controlled by the inherent microstructure of the material itself, rather than by accidental large pores or crack defects. This is consistent with the "high density, no through-cracks, and dispersed second-phase particles" observed in the OM / SEM section above. From the perspective of the strengthening mechanism, this performance of achieving a UTS of approximately 500 MPa under untreated conditions can be attributed to the synergistic effect of multiple mechanisms: 1) AlCoCrFeNi 2.11) Grains and fine Ti particles provide heterogeneous nucleation during rapid solidification, significantly refining the grains and increasing the contribution of Hall-Petch type fine grain strengthening; 2) A strong metallurgical interface is formed between the particles and the matrix, generating a significant load transfer effect under external load and strongly pinning dislocation motion, increasing dislocation strengthening; 3) The previous density results have shown that the porosity volume fraction is low under this parameter, and macroscopic cracks are effectively suppressed, allowing the above-mentioned fine grain strengthening and particle strengthening to be fully utilized in a relatively "clean" matrix. Therefore, Figure 5 The tensile curves not only demonstrate that under the parameters of Example 10, AA7075 + 5 wt.% AlCoCrFeNi 2.1 +2 wt.% Ti composite material can achieve a high strength of nearly 500 MPa in the as-built state, which also indirectly confirms the multi-scale synergistic strengthening mechanism of "high density + fine grains + dispersed particles" proposed earlier from the perspective of macroscopic mechanical response.

[0072] Figure 6 Room temperature tensile stress-strain curves of pure AA7075 matrix specimens in the selective laser melting printed state (without heat treatment) prepared using the process parameters (P=220 W, v=900 mm / s) corresponding to Example 10 in Table 1 are shown. This figure serves as a comparison group to highlight the role of the HEA+Ti reinforcing phase. The results show that the pure AA7075 specimens without added reinforcing particles exhibit severe hot cracking susceptibility during selective laser melting, resulting in extremely low mechanical properties: ultimate tensile strength (UTS) of only 51-66 MPa and elongation at break of less than 0.9%, exhibiting typical brittle fracture characteristics.

[0073] Figure 6 In stark contrast to the superior performance of the composite material in Figure 5 (with an ultimate tensile strength of up to 505 MPa and an elongation of ~2.8%), this demonstrates that Ti and HEA particles play a crucial role in suppressing cracks and strengthening the matrix.

[0074] from Figure 6 It can be seen that, under the process parameters corresponding to Example 10 in Table 1, the tensile stress-strain curve of the pure AA7075 matrix is ​​similar to... Figure 5The composite material exhibits completely different curve morphologies. All three curves show a near-linear increase in the low-strain stage, but fracture occurs abruptly before the stress reaches 70 MPa, with almost no obvious uniform plastic deformation stage. The corresponding UTS is only about 51-66 MPa, and the fracture strain is less than 0.9%, typically reflecting severe brittle failure behavior. It is noteworthy that although the peak stress and fracture strain of the three curves are very low, the differences between them are not significant, indicating that this low strength and low ductility do not stem from abnormally large pores or processing defects in individual samples, but rather from the inherent hot cracking sensitivity of the material system under this processing window. In other words, even if the nominal density is not significantly reduced, numerous through or semi-through hot cracks have already significantly weakened the load-bearing section, causing the sample to fracture prematurely at a relatively low stress level. Figure 6 and Figure 5 A comparison of the performance of HEA+Ti composite materials reveals that, under identical selective laser melting process parameters, the addition of 5 wt.% AlCoCrFeNi... 2.1 With the addition of 2 wt.% Ti, the UTS increased significantly from approximately 50-60 MPa to the 460-505 MPa range, and the fracture elongation also increased from <0.9% to approximately 2.6-2.9%. This order-of-magnitude increase in strength and significant plasticity recovery fully demonstrates that HEA particles and Ti elements play a crucial role in regulating the solidification behavior of the molten pool, refining grains, and alleviating stress concentration at the solid-liquid interface: 1) By providing a large number of heterogeneous nucleation sites and promoting the formation of equiaxed grains, they weaken the coarse columnar grains and high-stress grain boundaries that are easily generated in traditional selective laser melting of 7075; 2) Ti participates in the formation of dispersed strengthening phases and improves the wettability of the molten pool, making the interlayer metallurgical bonding more continuous and reducing macroscopic and microscopic crack initiation points; 3) HEA / Ti composite particles locally alter the thermal properties and stress distribution, making the thermal stress under rapid cooling more controllable and fundamentally reducing the susceptibility to hot cracking. Therefore, Figure 6 The extremely low strength and brittle fracture behavior of pure AA7075 shown are related to... Figure 5 The results of the composite material achieving a strength of ~500 MPa in the as-built state provide a stark contrast and offer direct and strong experimental evidence for the core conclusion that "HEA + Ti composite particle design can significantly suppress cracks and strengthen the selective laser melting 7075 matrix without heat treatment."

[0075] Figure 7 It is a selective laser melting printed AA7075 substrate and AA7075 + 5 wt.% AlCoCrFeNi 2.1The Vickers microhardness (HV0.5) of the +2wt.% Ti composite material under different process parameters in Examples 1-15 of Table 1 is compared. It can be seen that throughout the entire process parameter window, the microhardness of the composite material (blue bars) is consistently significantly higher than that of the pure AA7075 matrix (orange bars). For example, under the parameters corresponding to Example 10 in Table 1, the hardness of the composite material is approximately 175 HV0.5, almost twice that of the matrix (approximately 95 HV0.5). Figure 7 It can be seen that under 15 different selective laser melting process parameters, AA7075+5 wt.% AlCoCrFeNi 2.1 The microhardness of the +2 wt.% Ti composite material remained at a high level overall, while the hardness of the pure AA7075 matrix was generally in a lower range, showing a significant and stable hardness difference between the two. Overall, the hardness of the composite material was approximately 160-180 HV0.5 under various parameters, while the matrix samples were mostly concentrated around 90-110 HV0.5, representing a hardness increase of nearly 70-90%. This indicates that the HEA+Ti composite reinforcement design significantly strengthened the AA7075 matrix even in the as-built state. Comparisons of different parameter groups show that: 1) Both materials fluctuated slightly with process parameters, but the trends differed. Under some parameter groups with lower or higher energy densities, the hardness of the matrix samples decreased significantly, while the hardness of the composite material changed relatively little, remaining at a high level throughout the entire process parameter window. This indicates that after adding HEA and Ti, the material's sensitivity to stress-heat input decreased, exhibiting a wider "high hardness" process window. 2) The comparison of parameter number 10 is particularly typical. Figure 5 , Figure 6 Tensile specimens, under the same conditions of P = 220 W and v = 900 mm / s, showed that the composite material had a hardness of approximately 175 HV0.5, while pure AA7075 only had a hardness of approximately 95 HV0.5. This near-doubling increase in hardness corroborates the previous result of tensile strength increasing from 50-60 MPa to ~500 MPa, demonstrating a good correlation between microhardness and tensile strength. Combined with the previous OM / SEM results, the significant increase in hardness can be attributed to the synergistic effect of multiple strengthening mechanisms: on the one hand, AlCoCrFeNi... 2.1During rapid solidification, fine Ti particles provide numerous heterogeneous nucleation sites, significantly refining the grains and generating strong Hall-Petch grain refinement strengthening. On the other hand, some Ti reacts in situ with Al to form dispersed strengthening phases (such as Al3Ti), and the HEA particles themselves, as hard phases dispersed in the aluminum matrix, exert a strong pinning effect on dislocations, contributing to dispersion strengthening and load transfer strengthening. Simultaneously, the composite design also reduces the weakening of local hardness by softened regions and pores by increasing density and suppressing hot cracking, allowing the measured HV0.5 to more accurately reflect the intrinsic strength level of the matrix-particle system. In summary, Figure 7 The hardness comparison results shown not only quantitatively demonstrate that the HEA+Ti composite material is consistently superior to the matrix AA7075 throughout the entire process window, but also form a self-consistent chain of evidence with the results of density and tensile properties, further supporting the multi-scale strengthening mechanism that "HEA particles + Ti elements achieve as-built high strength through fine grain strengthening, dispersion strengthening and defect suppression".

[0076] Figure 8 It is AA7075 and AA7075+5 wt.% AlCoCrFeNi 2.1 The relative density of +2 wt.% Ti in Examples 1-15 is compared under different process parameters in Table 1. The scanning spacing and layer thickness of all samples remained constant, and different parameter sets were obtained by changing the laser power and scanning speed. It can be seen that the HEA+Ti composite reinforced material exhibits higher density and a wider high-density process window across all parameter ranges.

[0077] from Figure 8 As can be seen from the data, under all 15 sets of parameters, AA7075+5 wt.% AlCoCrFeNi 2.1 The relative density columnar bars of +2 wt.% Ti were all higher than those of AA7075 under the corresponding parameters, indicating that the overall density of the composite material was higher than that of the matrix. The density of the matrix alloy fluctuated around 94-96%, while that of the composite material was generally increased to around 97-99%, indicating that the HEA+Ti composite particle design significantly reduced the volume fraction of unfused voids and shrinkage defects.

[0078] Comparing the various parameter groups reveals that for AA7075, only a few parameter groups achieve near-high density, while most exhibit significant fluctuations. However, with the addition of HEA+Ti, most parameter groups (e.g., 1, 2, 4, 5, 9, 10, etc.) consistently achieve densities close to 98-99%, significantly widening the high-density range and reducing sensitivity to process fluctuations. This indicates that the introduction of composite particles, to some extent, "passivates" the sensitivity of process parameters to defect formation, resulting in more robust molding.

[0079] The increased density can be explained by the stability of the molten pool and the solidification behavior: i) High-entropy alloy particles and Ti, as heterogeneous nucleation sites, increase the nucleation rate during rapid solidification, which is conducive to the formation of fine equiaxed crystals and reduces the sensitivity to hot cracking when columnar crystals dominate; ii) Ti reacts with Al in the melt to generate dispersed Al3Ti particles, which can improve the wettability and flow behavior of the molten pool, making it easier for the molten pool to fill unmelted areas and reduce unfusion defects; iii) The presence of composite particles changes the local thermal properties (thermal conductivity, specific heat and viscosity, etc.), which helps to suppress excessively deep "keyholes" and violent splashing within a certain energy density range, thereby obtaining a more stable molten pool geometry.

[0080] In this application, the relatively high and less fluctuating relative density is the macroscopic basis for obtaining high strength and high fatigue performance: on the one hand, stress concentration sources such as pores and cracks are significantly weakened; on the other hand, microscopic mechanisms such as fine grain strengthening, load transfer strengthening and dislocation accumulation can be fully utilized in a matrix with "fewer defects", which is consistent with the high tensile strength of about 500 MPa in the as-built state reported later.

[0081] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A homogeneous powder for selective laser melting, characterized in that, The weight components include: the weight percentage of titanium powder is 0.5% to 5%, the weight percentage of high-entropy alloy powder is 1% to 10%, and the balance is 7XXX series aluminum alloy powder, and the aluminum alloy, Ti and high-entropy alloy powder are all spherical; the weighed powder is loaded into a ball mill tank, protective gas is introduced to exhaust air, high-efficiency mixing equipment is used to carry out high-energy mixing without adding any grinding ball medium, the shearing and friction between the powders are used to fill the titanium powder in the gap between the aluminum alloy powder and the high-entropy alloy powder, and a homogeneous mechanical mixed state is formed, wherein the titanium powder is filled in the accumulation gap between the aluminum alloy powder and the high-entropy alloy powder in the form of independent particles; the particle size range of the aluminum alloy powder and the high-entropy alloy powder is 15-55μm, and the particle size range of the titanium powder is 0-25μm.

2. The homogeneous powder for selective laser melting according to claim 1, characterized in that The mixing process parameters are mixing at 100-300 RPM for 4-8 hours.

3. The powder of claim 1, wherein, The aluminum alloy powder is a 7075 series aluminum alloy powder; and the high-entropy alloy powder has a particle size of an AlCoCrFeNi series.

4. A method for preparing a composite material by selective laser melting, wherein the homogeneous powder of any one of claims 1-3 is laid on a forming substrate of a selective laser melting device, the substrate is preheated to 150℃ under a protective gas environment, a strip scanning strategy is used, the substrate is rotated by 67° between layers, and the following parameter conditions are set: laser power: 180 W-260 W; scanning speed: 500 mm / s-900 mm / s; powder layer thickness: 0.02 mm-0.04 mm; scanning pitch: 0.08 mm-0.10 mm; after printing, the substrate is cooled to room temperature in the furnace, and a part in an un-heat-treated state is obtained.

5. The method of claim 4, wherein the laser is a fiber laser. The selective laser melting apparatus has a volumetric energy density range of 78-186 J / mm 3 .

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