SiCp / Al laser welding method for constructing gradient heterogeneous interface by matching high-entropy alloy with intermediate layer

Abstract

The application discloses a SiCp / Al laser welding method for constructing gradient heterogeneous interfaces by matching high-entropy alloy and intermediate layer, and relates to the technical field of metal matrix composite welding. The method comprises the following steps: S1, pretreating the surfaces to be welded and heterogeneous metal foils; S2, mixing 50%-80% of homogeneous aluminum alloy powder, 5%-30% of AlCoCrFeNi high-entropy alloy powder and active auxiliary components to prepare a pre-filled material; S3, coating the pre-filled material on the joint cross section and / or upper surface, and clamping and fixing the heterogeneous metal foils at the center position of the joint; and S4, performing laser welding. The core of the method is that when the content of the high-entropy alloy is 5%-20%, the titanium foils with a matching thickness of 20-100 microns or the zirconium foils with a matching thickness of 50-150 microns can actively construct the organizational structure with continuous composition transition and phase gradient distribution in the heterogeneous interface region. The application effectively alleviates the interface stress concentration caused by the mismatch of thermal physical properties, significantly inhibits the brittle fracture of the joint, and improves the comprehensive mechanical properties of the welded joint.

Description

Technical Field

[0001] This invention belongs to the field of metal matrix composite welding technology, and specifically discloses a SiCp / Al laser welding method for constructing a gradient heterogeneous interface by matching a high-entropy alloy with an intermediate layer. Background Technology

[0002] Silicon carbide particle-reinforced aluminum matrix composites (SiCp / Al) have broad application prospects in high-end equipment manufacturing fields such as aerospace structural components, precision instruments, electronic packaging, and rail transportation due to their high specific strength, high specific modulus, excellent thermal stability, and wear resistance. However, the significant differences in physicochemical properties between the SiC reinforcing phase and the Al matrix, especially the high mismatch between their melting points and coefficients of thermal expansion, make reliable bonding of SiCp / Al composites, particularly fusion welding, a key technical bottleneck restricting their engineering applications.

[0003] Joining SiCp / Al composites using traditional laser welding methods presents a series of severe metallurgical challenges. First, under the high temperatures of welding, SiC particles readily undergo interfacial reactions with the molten Al matrix, generating brittle, needle-like or lath-like Al4C3 phases. Al4C3 is not only highly brittle and prone to becoming crack initiation sites, but its formation also consumes beneficial SiC reinforcing phases, severely impairing the joint's mechanical properties and corrosion resistance. Second, the rapid solidification process of the weld pool easily leads to metallurgical defects such as particle segregation, porosity, and crystallization cracks, further reducing the joint's load-bearing capacity.

[0004] To improve the laser weldability of SiCp / Al composites, existing technologies often employ transition layer-assisted welding methods that introduce a dissimilar metal interlayer (such as Ti foil or Zr foil). This method utilizes the stronger chemical affinity of elements like Ti and Zr for C, preferentially reacting with C to form stable TiC or ZrC, thereby thermodynamically suppressing the formation of the harmful Al4C3 phase. However, there is also a significant difference in the coefficient of thermal expansion between the dissimilar metal interlayer (such as Ti or Zr) and the Al matrix. This inherent thermophysical property mismatch leads to significant residual thermal stress at the dissimilar interface during the rapid heating and cooling non-equilibrium thermal cycle of the weld. Furthermore, under conventional processes, the mixing of dissimilar components (Ti, Zr) with the Al matrix often results in a step-like distribution of composition and concentrated precipitation of brittle intermetallic compounds (such as TiAl3 and ZrAl3) at the interface, causing abrupt changes in microstructure. The superposition of abrupt changes in the microstructure and thermal stress concentration at the interface makes the heterogeneous interface extremely prone to becoming the source of crack initiation and propagation, ultimately leading to low-stress brittle fracture of the joint, which severely restricts the load-bearing reliability of the heterogeneous metal interlayer / SiCp / Al composite structure.

[0005] Existing research has also attempted to address these issues from the perspectives of filler material composition design and process parameter optimization, such as using mixed powders or intervening in molten pool behavior by adjusting the heat source mode or applying an external field. However, single-component filler materials are difficult to simultaneously control interfacial reactions and regulate microstructure gradients; while simple process parameter optimization mainly affects the macroscopic physical behavior of the molten pool and is unlikely to fundamentally intervene in the phase evolution path and microstructure distribution of heterogeneous interfaces.

[0006] In recent years, high-entropy alloys (HEAs) have shown great potential in controlling the microstructure of interfaces between dissimilar materials due to their unique hysteresis diffusion effect and excellent high-entropy effect. Theoretically, introducing HEAs is expected to reduce element activity and slow down diffusion rates through their multi-principal element properties, potentially enabling the construction of a gradient transition in composition and microstructure at the dissimilar interface. However, to date, there is a lack of effective technical solutions and clear understanding regarding how to effectively apply HEAs to the laser welding process of SiCp / Al composites with dissimilar metals, particularly how to establish a synergistic relationship between the HEAs and the intermediate layer to actively construct an ideal gradient interface structure. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a SiCp / Al laser welding method that uses a high-entropy alloy and an interlayer to construct a gradient heterogeneous interface. This method establishes a specific matching relationship between the high-entropy alloy content in the pre-filled material and the thickness of the heterogeneous metal interlayer. During laser welding, it actively controls the metallurgical reaction and element diffusion behavior in the heterogeneous interface region, thereby constructing a microstructure with a continuous compositional transition and a gradient phase distribution in the joint. This effectively buffers the interfacial thermal stress caused by thermophysical property mismatch, suppresses brittle fracture of the joint, and significantly improves the reliability of the welded joint.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A laser welding method for SiCp / Al to construct a gradient heterogeneous interface by matching a high-entropy alloy with an intermediate layer includes the following steps: S1. Pretreatment Steps: The surface of the area to be welded and the cross-section of the joint of the SiCp / Al composite substrate to be welded are ground to remove the surface oxide layer; the surface oxide layer of the dissimilar metal foil serving as the intermediate layer is also removed. The thickness of the SiCp / Al composite substrate to be welded can be 2~4mm, wherein the volume fraction of SiC particles is preferably 15%, and the matrix is ​​preferably 6xxx series aluminum alloy; the dissimilar metal foil is preferably titanium foil or zirconium foil with a purity of not less than 99.99%.

[0009] S2. Prefilling Material Preparation Steps: By mass percentage, 50%–80% of aluminum alloy powder homogeneous with the SiCp / Al composite matrix to be welded, 5%–30% of AlCoCrFeNi high-entropy alloy powder, and active auxiliary components are mixed uniformly to prepare a prefilling material. During preparation, the powder components can be mixed with anhydrous ethanol as a dispersion medium and milled into a paste using a ball milling process, or a suspension can be prepared using an ultrasonic oscillation process. In this way, after the prefilling material is coated, the anhydrous ethanol evaporates rapidly, forming a uniform powder coating with strong adhesion.

[0010] S3. Coating and assembly steps: The prefill material is coated on the joint section and / or the upper surface of the joint of the substrate to be welded, and the dissimilar metal foil is placed at the center of the joint between the substrates to be welded, and clamped and fixed by a fixture to form an assembly to be welded.

[0011] S4. Laser welding step: Perform laser welding on the assembly to be welded to form a welded joint. During welding, the laser welding power is preferably 1800~3800W, the welding speed is preferably 10~35mm / s, the defocusing amount is preferably 0~-2mm, and the shielding gas is argon gas with a purity of not less than 99.99%.

[0012] The core inventive point of this invention lies in the fact that the content of AlCoCrFeNi high-entropy alloy powder in the pre-filled material and the thickness of the heterogeneous metal foil satisfy a preset matching relationship, so as to actively construct a microstructure with continuous component transition and phase gradient distribution in the heterogeneous interface region. Specifically, the matching relationship is configured such that when the content of AlCoCrFeNi high-entropy alloy powder is 5%~20%, the heterogeneous metal foil is a titanium foil with a thickness of 20~100μm or a zirconium foil with a thickness of 50~150μm. When falling within this matching window, the hysteretic diffusion effect of the high-entropy alloy and the appropriate amount of heterogeneous components provided by the intermediate layer produce a synergistic effect. On the one hand, high-entropy alloys melt rapidly under the action of a laser heat source. Based on their multi-principal element characteristics, they reduce the activity of heterogeneous elements such as Ti and Zr by increasing the mixing entropy of the molten pool, suppressing the nucleation driving force and growth rate of brittle intermetallic compounds such as TiAl3 and ZrAl3, and avoiding the formation of coarse brittle phase grains in the weld center. At the same time, the Marangoni convection effect in the laser welding molten pool preferentially guides the Al matrix and heterogeneous metal interlayer to mix fully, promoting the formation of a compositional concentration gradient distribution along the weld width. On the other hand, the synergistic effect of the multi-principal elements of high-entropy alloys can induce the formation of complex solid solutions in the interface region, constructing a fine-grained zone transitioning from the heterogeneous metal enrichment region in the weld center to the Al matrix region, actively constructing a gradient structure from brittle phases such as TiAl3 and ZrAl3 to the Al matrix, and weakening abrupt changes in structure. Through the above synergistic effect, while effectively suppressing the formation of harmful interface reaction products such as Al4C3, the gradient structure evolution of the heterogeneous interface region is actively regulated, fundamentally solving the problems of stress concentration and brittle fracture caused by differences in thermophysical properties.

[0013] As a preferred technical solution, in step S2, the active auxiliary components, by mass percentage, include 2%~10% Cr2O3 powder, 5%~15% Na3AlF6 powder, and 2%~20% Si powder. Although these active auxiliary components are not the core components for constructing a gradient structure, they are crucial for ensuring weld density, reducing defect rate, and achieving stable welding. Specifically: Chromium trioxide (Cr2O3), as an oxide activator, can improve laser absorption rate to supplement heat input. At high temperatures, it decomposes into elemental chromium and oxygen, which not only avoids the powder morphology disturbing the molten pool but also provides a small amount of elemental chromium as a heterogeneous nucleation core, helping to refine weld grains; Sodium hexafluoroaluminate (Na3AlF6), as a common aluminum alloy flux, can reduce the alumina dissolution activation energy, reduce the influence of oxide film on molten pool fluidity, promote gas escape during welding, and significantly reduce joint porosity; The addition of elemental silicon (Si) powder can increase the Si element concentration in the molten pool, further inhibiting the formation of harmful Al4C3 phase from a thermodynamic perspective.

[0014] As a further technical solution, in step S2, the aluminum alloy powder homogeneous with the SiCp / Al composite matrix to be welded is a 6xxx series aluminum alloy powder. As a carrier for other functional components, it can improve the fluidity and wettability of the molten pool and replenish the molten pool with Al sources to reduce welding defects. The particle size of the AlCoCrFeNi high-entropy alloy powder is preferably 10~50μm; the particle size of the Cr2O3 powder and Na3AlF6 powder is preferably 20~50μm. Controlling the powder particle size within the above range is beneficial for the uniform mixing of the prefilling material and the stable melting and metallurgical reaction during laser welding. Furthermore, in addition to the aforementioned role in regulating interfacial reactions, the selected AlCoCrFeNi high-entropy alloy powder can also act as a reinforcing phase for the incompletely melted high-entropy alloy particles during welding, further enhancing the weld strength through load transfer, grain refinement, and dispersion strengthening mechanisms.

[0015] As a preferred technical solution, in step S2, the matching relationship is further optimized into any of the following combinations: The prefilled material contains 10% AlCoCrFeNi high-entropy alloy powder, and the heterogeneous metal foil is a 70μm thick titanium foil. Alternatively, the content of AlCoCrFeNi high-entropy alloy powder in the prefilled material is 10%, and the heterogeneous metal foil is a zirconium foil with a thickness of 50 μm; Alternatively, the content of AlCoCrFeNi high-entropy alloy powder in the prefilled material is 10%, and the heterogeneous metal foil is a zirconium foil with a thickness of 150 μm.

[0016] All of the above combinations fall within the optimal matching window, enabling the production of welded joints with a wide gradient microstructure and excellent tensile strength. For example, when a 10% high-entropy alloy is matched with a 70μm titanium foil, the resulting joint achieves a tensile strength of 225.5 MPa, and the gradient microstructure area accounts for 71% of the overall weld width.

[0017] The present invention also provides a welded joint prepared by the method described in any of the preceding claims. The welded joint has a microstructure with a continuous transition in composition and a gradient distribution of phases, wherein the width of the region with the gradient microstructure accounts for more than 65% of the overall weld width. This gradient structure effectively alleviates interfacial thermal stress, resulting in a significant increase in the tensile strength of the joint.

[0018] Furthermore, the present invention also relates to the application of the methods described in any of the foregoing in the manufacture of aerospace or precision instrument components.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The synergistic design scheme of high-entropy alloy prefilled material and heterogeneous metal interlayer provided by this invention achieves "multi-level control" of metallurgical reactions and proposes a heterogeneous interface control approach for gradient microstructure construction. Existing technologies mostly rely on a single alloying element to suppress Al4C3 formation and improve molten pool behavior through process optimization, but it is difficult to simultaneously achieve interface reaction control and microstructure uniformity. This invention uses a mixed prefilled powder with high-entropy alloy as the main functional component, working in conjunction with a heterogeneous metal interlayer. This forms a microstructure with continuous compositional transition and gradient phase distribution in the heterogeneous interface region, effectively alleviating interface stress concentration caused by differences in thermal expansion coefficients and reducing the risk of brittle fracture at the joint.

[0020] 2. This invention employs a high-entropy alloy as the main functional component of the pre-filled material, fully leveraging the unique retarded diffusion effect and synergistic effect of multiple principal components. The high-entropy alloy significantly reduces the element diffusion rate, slows down the interfacial reaction process, and provides sufficient kinetic conditions for the formation of gradient structures. Simultaneously, its multi-principal component characteristics effectively inhibit the heterogeneous nucleation and growth of brittle intermetallic compounds, promoting the formation of an ideal microstructure with continuous compositional transition and phase gradient distribution in the interfacial region. Compared to traditional single-component or fixed-ratio filler materials, the mixed pre-filled material offers greater freedom in composition design and processing methods, allowing for targeted control based on the specific combination of the base material and intermediate layer. Furthermore, the pre-filled material is applied in suspension or paste form, making operation simple, cost-effective, and highly compatible with existing laser welding processes.

[0021] 3. The welding method provided by this invention, through the synergistic effect of multiple components, achieves an improvement in the comprehensive mechanical properties of the welded joint, providing a technical solution for welding related material systems. The welded joint obtained by the method of this invention is improved in multiple performance dimensions. Furthermore, the applicability of this method is not limited to welding SiCp / Al composite materials alone with Ti or Zr interlayers; its design concept and process scheme for pre-filled material systems can be extended to laser welding systems of different aluminum alloy matrices, aluminum-based composite materials with different reinforcing phase ratios, and dissimilar metal materials, demonstrating significant technical promotion value. Attached Figure Description

[0022] Figure 1 A process flow diagram of the SiCp / Al laser welding method provided in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the welding assembly of the prefilled material and the intermediate foil provided in an embodiment of the present invention.

[0024] Figure 3This is a schematic diagram comparing the tissue evolution of the method in the embodiments of the present invention with that of the traditional method; wherein, (a) is direct welding without adding prefill material, (b) is welding with only adding intermediate layer metal foil, and (c) is welding with adding intermediate layer metal foil and prefill material containing high entropy alloy.

[0025] Figure 4 The images shown are metallographic structures and enlarged views of the welded joint cross sections obtained in some embodiments and comparative examples of the present invention; wherein, (a) is Example 1, (b) is Example 2, (c) is Example 3, (d) is Example 4, and (e) is Comparative Example 2.

[0026] Figure 5 The images are photographs and metallographic diagrams of some comparative examples of the present invention; wherein, (a) is a photograph of brittle fracture after welding of comparative example 3, (b) is a photograph of insufficient weld penetration of comparative example 4, and (c) is a metallographic diagram of a weld with a large number of pore defects inside comparative example 5. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of protection of the invention.

[0028] This invention, through systematic experimental research, reveals a significant synergistic matching effect between the content of high-entropy alloy in the prefiller and the thickness of the dissimilar metal interlayer in laser welding of SiCp / Al composite materials. This matching relationship directly determines the microstructure and mechanical properties of the weld joint. Specifically, when the combination of the two falls within a specific matching window, an ideal microstructure with continuous compositional transition and gradient phase distribution can be actively constructed in the dissimilar interface region, effectively buffering thermal stress and suppressing brittle fracture. Conversely, if the combination fails to meet the matching window, a series of problems will occur in the weld, such as excessively large Al4C3 acicular phase size, porosity defects, insufficient penetration depth, and excessive residual stress, significantly reducing the joint performance.

[0029] To clearly illustrate the technical effects of the aforementioned matching relationship, Table 1 summarizes the welding results and matching window level evaluations under different combinations of high-entropy alloy (AlCoCrFeNi) contents and different titanium (Ti) and zirconium (Zr) interlayer thicknesses. The patterns revealed in this table constitute the experimental basis for defining the specific matching range in the claims of this invention.

[0030] Table 1: Matching relationship between high-entropy alloy content and intermediate layer thickness and welding results As shown in Table 1, a high-quality weld joint with a "wide composition-microstructure gradient transition layer" can only be obtained when the high-entropy alloy content is between 5% and 20%, and when matched with a Ti foil with a thickness of 20 to 100 μm or a Zr foil with a thickness of 50 to 150 μm (i.e., process window number 3). This matching window is key to achieving the purpose of this invention.

[0031] To achieve the aforementioned preferred matching window, the present invention further provides an optimized pre-filled material formulation. This pre-filled material consists of a main functional component, an active auxiliary component, and a carrier component. The specific content, functional description, and mechanism of action of each component are summarized in Table 2.

[0032] Table 2 Summary of the composition and functions of prefilled materials Based on the matching window established in Table 1 and the prefilled material system defined in Table 2, the following will be combined with... Figure 1 The process flow diagram shown illustrates the preferred embodiments of each step of the method of the present invention in detail.

[0033] S1. Preprocessing steps The thickness of the SiC particle-reinforced 6xxx series Al-based composite material (SiCp / 6xxxAl) substrate used in this invention is preferably 2-4 mm. Specifically, the substrate can be a SiC / 6061Al plate with a SiC particle volume fraction of 15% that has undergone T6 heat treatment, for example, it can be purchased from Henan Hanyin Optoelectronic Technology Co., Ltd. Before welding, the surface of the substrate to be welded and the joint cross-section are pre-polished with 200-600 grit sandpaper to remove the surface oxide layer and obtain a clean surface for welding.

[0034] The intermediate layer metal foil is made of high-purity (preferably not less than 99.99%) titanium (Ti) foil or zirconium (Zr) foil with a thickness of 20~300 μm, and is cut into strips of equal width according to the thickness of the substrate to be soldered, so as to facilitate assembly.

[0035] For Ti foil, Keller's reagent is used for immersion at room temperature for 30-60 seconds to remove the surface oxide layer. For Zr foil, the surface is cleaned using a mixed pickling reagent consisting of 10%-45% nitric acid, 1%-5% hydrofluoric acid, and the remainder water, in accordance with the national standard GB / T 38986-2020 "Descaling and Cleaning Methods for Zirconium and Zirconium Alloy Surfaces". After pickling, both Ti and Zr foils must be thoroughly cleaned with anhydrous ethanol and dried with a hair dryer before use to ensure that there are no oxides or contaminants remaining on their surfaces.

[0036] S2. Prefilled material preparation steps This invention provides a prefill material specifically for SiC-reinforced aluminum matrix composites, the composition and content of which are as follows by mass percentage: 50%~80% of 6xxx series Al alloy powder, homogeneous with the base material to be welded; the aluminum alloy powder is preferably 6061Al alloy powder with the same composition as the base material, and can be purchased from Henan Hanyin Optoelectronic Technology Co., Ltd. or other commercially available channels. Chromium trioxide (Cr2O3) powder: 2%~10%; Elemental silicon (Si) powder: 2%~20%; Sodium hexafluoroaluminate (Na3AlF6) powder: 5%~15%; AlCoCrFeNi high-entropy alloy powder: 5%~30%. In the AlCoCrFeNi high-entropy alloy powder, the atomic ratio of the five elements Al, Co, Cr, Fe, and Ni is equiatomic, approximately 1:1:1:1:1. This powder can be a commercially available product, such as AlCoCrFeNi high-entropy alloy powder purchased from Beijing Gaoke New Materials Technology Co., Ltd., with a particle size of 10~50μm.

[0037] The prefilled material can be prepared using one of the following two methods to obtain a paste or suspension that is easy to apply: (1) Preparation of paste-like prefill material: Accurately weigh the powder of each component according to the above mass percentages, and add them together with the zirconia grinding balls into the grinding jar. It is preferable to use two sizes of grinding balls with diameters of 2 mm and 6 mm. After sealing the jar, perform ball milling for 2 hours. After ball milling, add anhydrous ethanol at a ratio of 0.8 mL per gram of mixed powder, stir evenly, and a paste that is easy to apply can be prepared.

[0038] (2) Preparation of suspension prefill material: Weigh each component powder accurately according to the above mass percentages and mix them evenly. Add anhydrous ethanol at a ratio of 2 mL of anhydrous ethanol per gram of mixed powder to prepare a suspension. After stirring the suspension evenly, place it in a sealed container, and then place the container in an ultrasonic cleaner for ultrasonic vibration treatment for more than 5 minutes to ensure that each component powder is fully dispersed in the suspension and obtain a uniform suspension for later use.

[0039] The anhydrous ethanol used in this invention is a powder dispersion medium. All functional components in the pre-filled material are insoluble in anhydrous ethanol, and no reaction occurs between the components during formulation. This facilitates thorough mixing and uniform dispersion of the components during ultrasonic oscillation or ball milling. When the suspension or paste is subsequently applied to the surface of the area to be soldered, the anhydrous ethanol evaporates rapidly, thereby forming a uniform powder coating with strong adhesion on the substrate surface.

[0040] S3. Coating and Assembly Steps The present invention provides an assembly method for pre-filling powder and dissimilar metal foil in a weld joint, wherein the pre-filling powder is a paste or powder suspension prepared in step S2 above, and the intermediate layer material is titanium foil or zirconium foil pretreated in step S1. Figure 2 A schematic diagram of the welding assembly of the prefill material and the intermediate foil layer is shown. The specific operating steps are as follows: (1) Coating inside the joint: Use a brush or scraper to take the prepared paste or suspension and apply it evenly to the two opposite joint sections of the SiCp / Al substrate to be soldered. Then, use a special clamp to initially clamp and fix the two substrates to be soldered to align the joints, but temporarily maintain a distance of more than 5 mm between the two sections to facilitate the subsequent placement of the intermediate layer foil.

[0041] (2) Pre-positioning of intermediate layer metal foil: Take a flat temporary support substrate and place it parallel to the bottom of the joint to be welded, close to the lower surface of the joint. Use tweezers to pick up the pre-treated intermediate layer metal foil and accurately place it at the center of the joint between the two substrates to be welded. Slowly and evenly rotate the clamp knob to gradually clamp the two ends of the welding joint until the intermediate layer metal foil is firmly fixed in the joint gap. Then, remove the temporary support plate below. Let the assembled parts stand for about 5 minutes to allow the anhydrous ethanol in the pre-filling material suspension or paste to evaporate naturally and the powder coating to dry. Then, use a brush or compressed air to gently remove the excess powder that overflows from the upper and lower surfaces of the joint due to compression.

[0042] (3) Coating the upper surface of the joint: Using the same method as the coating inside the joint, apply the paste or suspension evenly to the upper surface area of ​​the weld center. The width of the coated area should be greater than the expected width of the weld pool to ensure that there is sufficient pre-filling material to participate in the metallurgical reaction during the welding process. The coated and dried powder coating should be of uniform thickness and have a smooth surface, without lumps, cracks or peeling, to ensure the uniformity and stability of the metallurgical reaction during the subsequent laser welding process.

[0043] S4. Laser welding steps The fixture containing the SiCp / Al substrate, after being processed and dried in step S3, is placed on the laser welding stage. The position of the laser welding head is adjusted so that the laser beam is aligned with the weld centerline. The applicable laser welding process parameter range provided by this invention is as follows: Laser welding power: 1800~3800W; Welding speed: 10~35 mm / s; Laser defocusing: 0~-2 mm; Protective gas: pure argon with a purity of not less than 99.99% and a gas flow rate greater than 10 L / min; To prevent the high reflectivity of the aluminum substrate from damaging the laser's optical components, the deflection angle of the laser beam relative to the workpiece's normal direction is set to 5°~15°.

[0044] After confirming that the powder coating is completely dry, the laser is activated, and the assembly is welded according to the set welding path and process parameters to complete the weld formation.

[0045] After laser welding is completed, the joint undergoes necessary post-weld treatment. The specific steps are as follows: First, gently wipe the upper surface of the weld and the surrounding area with a clean cloth or wiping paper dampened with anhydrous ethanol to remove residual powder and fumes. For a small amount of black oxide or slight welding slag adhering to the weld surface, it can be gently polished with fine sandpaper or cleaned with a stainless steel wire brush until a bright weld metal surface is exposed.

[0046] Figure 3 This is a schematic diagram comparing the tissue evolution of the method of this invention with that of a traditional method. Figure 3 (a) shows the microstructure distribution when directly welded without prefill material. The SiC particles undergo a violent interfacial reaction with the Al matrix, generating a large number of large-sized needle-like Al4C3 harmful phases, which are concentrated in the center of the weld. In particular, the microstructure distribution is extremely uneven. Figure 3 (b) shows the microstructure distribution when only an intermediate layer of metal foil is added during welding. Although the formation of Al4C3 is suppressed to some extent, a step distribution of composition and concentrated precipitation of brittle intermetallic compounds are formed at the heterogeneous interface, resulting in abrupt changes in microstructure and stress concentration. Figure 3 (c) shows the microstructure distribution when welding using the method of the present invention (adding an intermediate layer metal foil and a prefill material containing a high-entropy alloy). A microstructure with continuous transition of composition and gradient distribution of phases was successfully constructed in the heterogeneous interface region, which effectively relieved thermal stress and avoided abrupt changes in microstructure.

[0047] Based on the matching window established in Table 1, the prefilled material system defined in Table 2, and the detailed process steps described above, the present invention will be further described in detail below through specific embodiments and comparative examples.

[0048] Example 1 A SiC / 6061Al plate (Henan Hanyin Optoelectronic Technology Co., Ltd.) with a SiC particle volume fraction of 15% and heat-treated to T6 was wire-cut to obtain a vertical plane. This plate, along with a 70 μm thick Ti foil, was prepared according to the pretreatment method for the surface to be welded and the intermediate layer of the metal foil. A suspension was prepared by mass percentage using 60% homogeneous 6-series Al alloy powder, 35% Cr2O, 15% Si powder, 10% Na3AlF6, and 10% AlCoCrFeNi (equal atomic ratio 1:1:1:1:1, Beijing Gaoke New Material Technology Co., Ltd.) high-entropy alloy powder, according to the pre-filling material preparation method. The workpiece to be welded was assembled onto the welding platform according to the coating and assembly method, and welding was performed according to the following laser parameters: laser power 2600W; welding speed 25mm / s; defocusing amount -2mm.

[0049] In this embodiment, the high-entropy alloy content is 10%, the Ti intermediate layer thickness is 70 μm, and the matching relationship between the two meets the high matching window shown in Table 1. The fracture location of the obtained weld is the weld center, the tensile strength is 225.5 MPa, and the width is 2.54 mm. The weld center contains small-sized Al4C3 and undecomposed SiC. Towards the remelting zone boundary, the acicular phase of Al4C3 gradually disappears, and the SiC particle size gradually increases, forming a gradient structure. The weld as a whole does not have obvious phase or structural abrupt changes. Figure 4 (a) The gradient structure area is 1.80 mm wide, accounting for 71% of the entire weld.

[0050] Example 2 Compared to Example 1, by mass percentage, a suspension was prepared using the following methods: 50% homogeneous Al 6-series alloy powder; 35% Cr2O; 15% Si powder; 10% Na3AlF6; and 20% AlCoCrFeNi high-entropy alloy powder. The laser parameters were changed to: laser power 2800W; welding speed 25mm / s; defocusing amount -2mm.

[0051] In this embodiment, the high-entropy alloy content is 20%, the Ti intermediate layer thickness is 70 μm, and the matching relationship between the two satisfies the matching window shown in Table 1. With increased laser power, the resulting weld fracture location is at the weld center, with a tensile strength of 192.0 MPa and a width of 2.93 mm. The weld center contains medium-sized Al4C3 and undecomposed SiC. Further outwards to the remelting zone boundary, the acicular phase of Al4C3 gradually disappears, and the SiC particle size gradually increases, forming a gradient structure. However, abrupt changes in structure occur at the boundary of the Al4C3 acicular phase enrichment zone, forming a fine-grained region without SiC particles and Al4C3. Figure 4(b) The overall gradient microstructure region is 2.14 mm wide, accounting for 72% of the entire weld. Due to the increased proportion of high-entropy alloy powder, the hysteresis diffusion effect excessively suppresses the interfacial reaction, and the Marangoni convection effect in the molten pool weakens due to viscosity changes. Therefore, Al4C3 concentrates in the center of the weld, resulting in an increase in Al4C3 size and the disappearance of the Al4C3 acicular phase and the formation of fine grains of SiC migration at the interface. This change has a smaller impact compared to other matching windows; apart from small-scale microstructural abrupt changes, a relatively wide gradient microstructure region can still be constructed.

[0052] Example 3 Compared to Example 1, the 70 μm Ti foil was replaced with a 50 μm Zr foil.

[0053] In this embodiment, the high-entropy alloy content is 10%, the Zr intermediate layer thickness is 50 μm, and the matching relationship between the two satisfies the high matching window shown in Table 1. The fracture location of the obtained weld is the weld center, the tensile strength is 195.9 MPa, and the width is 2.47 mm. The weld center contains small-sized Al4C3 and undecomposed SiC. Towards the remelting zone boundary, the acicular phase of Al4C3 gradually disappears, and the SiC particle size gradually increases, forming a gradient structure. The weld as a whole does not have obvious phase or structural abrupt changes. Figure 4 (c) The width of the overall gradient structure area is 1.60 mm, accounting for 65% of the overall weld.

[0054] Example 4 Compared to Example 1, the 70 μm Ti foil was changed to a 150 μm Zr foil.

[0055] In this embodiment, the high-entropy alloy content is 10%, the Zr intermediate layer thickness is 150 μm, and the matching relationship between the two satisfies the high matching window shown in Table 1. The fracture location of the obtained weld is the weld center, the tensile strength is 220.5 MPa, and the width is 2.55 mm. The weld center contains undecomposed SiC, the Al4C3 acicular phase has basically disappeared, and the SiC particle size gradually increases towards the remelting zone boundary, forming a gradient structure. The weld as a whole does not have obvious phase or microstructure abrupt changes. Figure 4 (d) The overall gradient structure region is 1.65 mm wide, accounting for 65% of the entire weld. Due to the increased Zr content, a large amount of C source required to form Al4C3 is consumed, so compared with Example 3, the Al4C3 in the weld region is significantly reduced.

[0056] Comparative Example 1 Compared to Example 1, by mass percentage, 70% of homogeneous 6-series Al alloy powder, 35% of Cr2O, 15% of Si powder, and 10% of Na3AlF6 were prepared into a suspension according to the pre-filled material preparation method described above.

[0057] In this comparative example, without the addition of a high-entropy alloy, the Ti interlayer thickness was 70 μm. The matching relationship between the two met the low matching window shown in Table 1. The resulting weld had a large number of pore defects penetrating the upper and lower surfaces of the weld, failing to achieve effective fusion between the base material and the interlayer. This resulted in a significant reduction in the effective load-bearing area of ​​the weld cross-section, and the weld joint fractured after welding. The fracture location was at the interlayer-Al matrix interface. Due to the delayed diffusion effect of the lack of a high-entropy alloy, Ti elements diffused rapidly towards the Al matrix side, causing uncontrolled interfacial reactions and generating a large number of low-melting-point eutectic phases and gaseous products. At the same time, under the influence of the active powder carrier, the molten pool had poor fluidity and a short solidification time, preventing bubbles from fully escaping and forming interconnected pores.

[0058] Comparative Example 2 Compared to Example 1, by mass percentage, a suspension was prepared using the same 6-series Al alloy powder (70%), Cr2O3 (5%), Si powder (15%), and Na3AlF6 (10%), according to the pre-filled material preparation method described above. The laser parameters were changed to: laser power 3000W; welding speed 25mm / s; defocusing amount -2mm.

[0059] In this comparative example, no high-entropy alloy was added, the Ti intermediate layer thickness was 70 μm, and the matching relationship between the two met the low matching window shown in Table 1. With increased laser power, the resulting weld width was 2.75 mm. In the central region of the weld, the metal foil and pre-filled powder did not fuse effectively, exhibiting obvious porosity defects and abrupt changes in microstructure, making the gradient transition region difficult to distinguish. Only within the fusion zone outside the Ti-enriched region boundary did a gradient distribution region of SiC particle size and density form. Figure 4 (e) The widths on both sides are 0.29 mm and 0.35 mm, respectively, accounting for 23% of the overall weld. Due to the increased heat input after increasing the laser power, the molten pool existence time is prolonged and the fluidity is slightly improved, allowing some bubbles to escape, thus reducing porosity defects. However, due to the lack of high-entropy alloy, the effect on interfacial reaction, element diffusion and molten pool control is insufficient, and the problem of prefill material fusion remains unresolved.

[0060] Comparative Example 3 Compared to Example 1, the 70 μm Ti foil was replaced with a 250 μm Zr foil.

[0061] In this comparative example, the high-entropy alloy content was 10%, and the Zr interlayer thickness was 250 μm. The matching relationship between the two met the low matching window shown in Table 1. The welded joint underwent brittle fracture due to thermal stress during cooling. No obvious metallurgical defects such as porosity or lack of fusion were observed at the fracture site. Figure 5 (a) The Zr interlayer is well bonded to the base material, which eliminates the influence of defects, unreasonable prefill material composition, and improper selection of welding process parameters. Therefore, it can be inferred that excessive Zr foil thickness leads to thermal stress concentration at the weld center, making effective connection impossible.

[0062] Comparative Example 4 Compared to Example 1, by mass percentage, 50% of homogeneous 6-series Al alloy powder, 35% of Cr2O, 15% of Si powder, 10% of Na3AlF6, and 20% of AlCoCrFeNi high-entropy alloy powder were prepared into a suspension according to the pre-filled material preparation method described above.

[0063] In this comparative example, the high-entropy alloy content was 20%, and the Ti interlayer thickness was 70 μm. The matching relationship between the two met the matching window shown in Table 1. However, the resulting weld penetration was insufficient, and effective fusion between the base material and the interlayer was not achieved. Figure 5 (b) When the proportion of high-entropy alloys increases while the laser power remains constant, the thermal conductivity of the molten pool decreases, the viscosity increases, and the effective downward transmission of laser energy decreases, resulting in insufficient melting depth and poor interlayer fusion.

[0064] Comparative Example 5 Compared to Example 1, by mass percentage, 80% of homogeneous 6-series Al alloy powder and 20% AlCoCrFeNi high-entropy alloy powder were prepared into a suspension according to the pre-filled material preparation method described above. The coating and assembly methods, as well as the welding process, are the same as those in the former example.

[0065] In this comparative example, the high-entropy alloy content was 20%, and the Ti interlayer thickness was 70 μm. The matching relationship between the two met the matching window shown in Table 1. Only when the welding parameters were changed to: laser power 3400W; welding speed 25mm / s; defocusing amount -2mm, the sample achieved effective penetration and good fusion between the base material and the interlayer. However, the weld width increased to 3.5 mm, and a large number of porosity defects were present. Figure 5 (c) Due to the lack of active components in the prefill material, the prefill material, which consists only of high-entropy alloy and aluminum alloy powder carrier, loses its regulatory function of improving laser absorption rate and reducing weld porosity. Therefore, it is necessary to significantly increase the heat input to ensure penetration depth and generate a large number of pores in the weld.

[0066] Test case To verify the technical effectiveness of the method of the present invention, the welded joints obtained in Examples 1-4 and Comparative Examples 1-5 were subjected to mechanical property testing and microstructure characterization to evaluate the influence of different high-entropy alloy contents and interlayer thickness matching relationships on the weld quality. The specific test methods and results are as follows.

[0067] 1. Testing Methods (1) Tensile strength test Standard tensile specimens were cut from the weld test plates of each embodiment and comparative example using a wire cutting method, perpendicular to the weld direction. The gauge length of the specimens included the complete weld and heat-affected zone. Room temperature tensile tests were conducted according to the national standard GB / T228.1-2021 "Metallic materials, tensile testing—Part 1: Tests at room temperature," with a tensile rate of 2 mm / min. At least three parallel specimens were tested for each parameter group, and the average value was taken as the tensile strength value of that group of joints.

[0068] (2) Measurement of the proportion of gradient tissue Metallographic observation of the weld joint cross-section was performed using optical microscopy (OM) and scanning electron microscopy (SEM). By observing the evolution of SiC particle size, distribution density, and Al4C3 acicular phase morphology in the weld cross-section, a gradient microstructure region characterized by continuous compositional transition and gradient phase distribution was defined. The proportion of gradient microstructure was calculated using the following formula: Gradient structure percentage = Gradient structure region width / Overall weld width × 100% (3) Fracture analysis After the tensile test, the fracture surface of the fractured specimen was collected, and the fracture morphology was observed using a scanning electron microscope (SEM) to determine the fracture location (weld center, heat-affected zone, or heterogeneous interface) and fracture type (ductile fracture, brittle fracture, or mixed fracture). The main metallurgical defect type leading to failure was determined by combining the metallographic analysis.

[0069] 2. Test Results The mechanical properties, gradient structure ratio, and fracture characteristics of the welded joints in each embodiment and comparative example are summarized in Table 3.

[0070] Table 3 Summary of performance test results of welded joints in various embodiments and comparative examples Note: "—" indicates that the joint fractured immediately after welding, had insufficient penetration, or had serious defects, making it impossible to prepare an effective tensile specimen or measure relevant data.

[0071] 3. Results Analysis and Discussion As can be seen from the comparative analysis in Table 3: (1) The necessity of adding high-entropy alloys (Example 1 compared with Comparative Examples 1 and 2) In Comparative Examples 1 and 2, where no high-entropy alloy was added, the welded joints either fractured immediately after welding or failed to form an effective connection due to severe lack of fusion and penetrating pores. The gradient microstructure in Comparative Example 2 was only 23%. This is because the lack of the retarded diffusion effect and molten pool regulation of the high-entropy alloy led to the rapid diffusion of Ti elements towards the Al matrix, resulting in uncontrolled interfacial reactions, generating a large amount of low-melting-point eutectic phases and gaseous products. Furthermore, the molten pool had poor fluidity, preventing bubbles from escaping. In contrast, Example 1, after adding 10% high-entropy alloy, showed a significant increase in tensile strength to 225.5 MPa and a substantial increase in the gradient microstructure to 71%, fully demonstrating the crucial role of introducing high-entropy alloy in improving weld formation quality and microstructure gradient.

[0072] (2) Comparison between high-matching windows and medium-matching windows (Example 1 vs. Example 2) Example 1 (10% high-entropy alloy + 70μm Ti) falls within the high-matching window shown in Table 1 (high-entropy alloy 5%~20% + Ti foil 20~100μm or Zr foil 50~150μm), while Example 2 (20% high-entropy alloy + 70μm Ti) falls within the medium-matching window. The tensile strength of Example 1 (225.5 MPa) is approximately 17.4% higher than that of Example 2 (192.0 MPa). This is because, in Example 2, when the high-entropy alloy content increases to 20%, the hysteresis diffusion effect excessively suppresses the interfacial reaction. Furthermore, the increased molten pool viscosity leads to weakened Marangoni convection, resulting in a concentrated distribution of Al4C3 acicular phases and abrupt fine-grained zonation at the weld center. Although the gradient microstructure proportions of the two are relatively close (71% vs 72%), the presence of abrupt microstructure weakens the load-bearing capacity of Example 2. This indicates that falling within the high-matching window is key to obtaining optimal overall performance.

[0073] (3) Influence of intermediate layer material and thickness (comparison of Examples 1, 3, 4 and Comparative Example 3) Comparing Example 1 (70 μm Ti), Example 3 (50 μm Zr), and Example 4 (150 μm Zr), all three fell within the high-matching window, with tensile strengths of 225.5 MPa, 195.9 MPa, and 220.5 MPa, respectively, achieving effective bonding and a high-strength gradient microstructure. In Example 4, due to the increased Zr content, the reaction with C to form ZrC significantly consumed the C source required for Al4C3 formation, resulting in a substantial reduction in the Al4C3 acicular phase in the weld region.

[0074] However, the thickness of the interlayer is highly sensitive. In Comparative Example 3, when the Zr foil thickness was increased from 150 μm to 250 μm, although the joint showed no obvious metallurgical defects, it spontaneously fractured during post-weld cooling due to excessive residual thermal stress at the weld center. This indicates that an excessively thick interlayer leads to an excess of heterogeneous components, exacerbating stress concentration caused by thermophysical property mismatch, exceeding the buffering capacity of the gradient structure. Therefore, controlling the interlayer thickness within a specific matching window is one of the decisive factors in ensuring weldability.

[0075] (4) The necessity of active auxiliary components (Example 1 vs. Comparative Example 5) The prefill material in Comparative Example 5 consisted only of 80% homogeneous Al alloy powder and 20% high-entropy alloy, completely lacking active auxiliary components such as Cr2O3, Na3AlF6, and Si powder. Under these conditions, to ensure sufficient penetration depth, the laser power needed to be significantly increased from the conventional 2600W to 3400W, but this still resulted in a large number of porosity defects inside the weld. Compared with Example 1, the weld quality was significantly deteriorated. This fully demonstrates that although active auxiliary components are not the core components for constructing a gradient microstructure, they play an indispensable auxiliary role in improving laser absorption, reducing weld porosity, and ensuring the stability of the welding process window.

[0076] 4. Conclusion Based on the above test results and analysis, the following conclusions can be drawn: (1) By establishing a specific matching relationship between the high-entropy alloy content in the prefilled material and the thickness of the heterogeneous metal interlayer (i.e., high matching window: 5%~20% high-entropy alloy matching 20~100μm Ti foil or 50~150μm Zr foil), the present invention can actively construct a microstructure with continuous composition transition and phase gradient distribution in the laser welding joint of SiCp / Al composite material, with the gradient microstructure accounting for more than 65%.

[0077] (2) The tensile strength of the welded joint obtained based on this matching relationship is significantly improved. The tensile strength of the optimal embodiment (Example 1) reaches 225.5 MPa, which effectively solves the problem of stress concentration and brittle fracture caused by thermophysical property mismatch.

[0078] (3) The active auxiliary components (Cr2O3, Na3AlF6, Si powder) in the prefill material are necessary components to ensure weld density, reduce defect rate and achieve stable welding process window.

[0079] The above description is merely a preferred embodiment and test example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser welding method for SiCp / Al to construct a gradient heterogeneous interface by matching a high-entropy alloy with an intermediate layer, characterized in that, Includes the following steps: S1. Pretreatment steps: Grind the surface of the area to be welded and the cross section of the joint of the SiCp / Al composite substrate to be welded; remove the surface oxide layer of the dissimilar metal foil used as the intermediate layer; S2. Prefill material preparation steps: By mass percentage, 50%~80% of aluminum alloy powder homogeneous with the SiCp / Al composite matrix to be welded, 5%~30% of AlCoCrFeNi high-entropy alloy powder, and active auxiliary components are mixed evenly to prepare a prefill material; S3. Coating and assembly steps: The prefill material is coated on the joint section and / or the upper surface of the joint of the substrate to be welded, and the dissimilar metal foil is placed at the center of the joint between the substrates to be welded, and clamped and fixed by a jig to form an assembly to be welded; S4. Laser welding step: Perform laser welding on the assembly to be welded to form a weld joint; The content of AlCoCrFeNi high-entropy alloy powder in the prefilled material and the thickness of the heterogeneous metal foil satisfy a preset matching relationship, so as to actively construct a microstructure with continuous component transition and phase gradient distribution in the heterogeneous interface region. The matching relationship is configured as follows: when the content of AlCoCrFeNi high-entropy alloy powder is 5%~20%, the heterogeneous metal foil is a titanium foil with a thickness of 20~100μm or a zirconium foil with a thickness of 50~150μm.

2. The SiCp / Al laser welding method for constructing a gradient heterogeneous interface by matching a high-entropy alloy with an intermediate layer according to claim 1, characterized in that, In step S1, the heterogeneous metal foil is a titanium foil or zirconium foil with a purity of not less than 99.99%.

3. The SiCp / Al laser welding method for constructing a gradient heterogeneous interface by matching a high-entropy alloy with an intermediate layer according to claim 1, characterized in that, In step S1, the volume fraction of SiC particles in the SiCp / Al composite substrate to be welded is 15%, and the matrix is ​​a 6xxx series aluminum alloy.

4. The SiCp / Al laser welding method for constructing a gradient heterogeneous interface by matching a high-entropy alloy with an intermediate layer according to claim 1, characterized in that, In step S2, the active auxiliary components, by mass percentage, include 2%~10% Cr2O3 powder, 5%~15% Na3AlF6 powder, and 2%~20% Si powder.

5. The SiCp / Al laser welding method for constructing a gradient heterogeneous interface by matching a high-entropy alloy with an intermediate layer according to claim 4, characterized in that, In step S2, the aluminum alloy powder that is homogeneous with the SiCp / Al composite matrix to be welded is a 6xxx series aluminum alloy powder, the particle size of the AlCoCrFeNi high-entropy alloy powder is 10~50μm, and the particle size of the Cr2O3 powder and Na3AlF6 powder is 20~50μm.

6. The SiCp / Al laser welding method for constructing a gradient heterogeneous interface by matching a high-entropy alloy with an intermediate layer according to claim 1, characterized in that, In step S2, the content of AlCoCrFeNi high-entropy alloy powder in the pre-filled material is 10%, and the heterogeneous metal foil is a titanium foil with a thickness of 70μm. Alternatively, the content of AlCoCrFeNi high-entropy alloy powder in the prefilled material is 10%, and the heterogeneous metal foil is a zirconium foil with a thickness of 50 μm; Alternatively, the content of AlCoCrFeNi high-entropy alloy powder in the prefilled material is 10%, and the heterogeneous metal foil is a zirconium foil with a thickness of 150 μm.

7. The SiCp / Al laser welding method for constructing a gradient heterogeneous interface by matching a high-entropy alloy with an intermediate layer according to claim 1, characterized in that, In step S2, the powders of each component are mixed with anhydrous ethanol and then formed into a paste by ball milling or into a suspension by ultrasonic oscillation.

8. The SiCp / Al laser welding method for constructing a gradient heterogeneous interface by matching a high-entropy alloy with an intermediate layer according to claim 1, characterized in that, In step S4, the laser welding power is 1800~3800W, the welding speed is 10~35mm / s, the defocusing amount is 0~-2mm, and the shielding gas is argon with a purity of not less than 99.99%.

9. A welded joint, characterized in that, The welded joint is prepared by the method according to any one of claims 1 to 8; the welded joint has a microstructure with continuous transition of composition and gradient distribution of phases, wherein the width of the region with gradient microstructure accounts for more than 65% of the overall width of the weld.

10. The application of the method as described in any one of claims 1 to 8 in the manufacture of aerospace or precision instrument components.

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