Gradient composite rod containing high density crimped metal fibers and method of making

Abstract

This invention relates to a gradient composite material rod containing high-density crimped metal fibers and its preparation method. The method includes the following steps: (1) preparing crimped metal fibers using selective laser melting; (2) preparing crimped metal fiber bundles; (3) placing the metal fiber bundles into a casting mold and pouring in an aluminum alloy solution to obtain an alloy rod containing crimped metal fibers; (4) heating and holding the alloy rod at a certain temperature followed by rotary forging to obtain an elongated composite rod; (5) mechanically grinding the surface of the elongated composite rod to obtain a gradient composite material rod containing high-density crimped metal fibers with a fine-grained surface and a coarse-grained core. This invention combines selective laser melting and hot rotary forging to obtain a rod with a heterogeneous structure, significantly improving the strength of the alloy rod while retaining its plasticity. Simultaneously, the high-density crimped metal fibers inside the rod can improve the fracture resistance of the rod or cable.

Description

Technical Field

[0001] This invention belongs to the field of composite materials, specifically relating to a gradient composite rod containing high-density crimped metal fibers and its preparation method. Background Technology

[0002] Ti6Al4V (TC4) titanium alloy is a material that has attracted much attention and experienced rapid development both domestically and internationally. It is also a widely used material in the aerospace field. A typical α+β type titanium alloy, it possesses excellent comprehensive properties and is the most widely used titanium alloy, making it highly favored in the aerospace, marine, and defense industries. TC4 titanium alloy is frequently used to manufacture various precision parts required for aircraft, such as tail fin mounting plates and rotor blade mounts for Black Hawk helicopters. Experiments and practical applications have shown that parts made of titanium alloy can extend the service life of components and significantly improve their fatigue limit.

[0003] Selective laser melting (SLM) is a powder bed melting technique in additive manufacturing. It has been used to fabricate complex and intricate structures and can solve problems encountered in the casting and forging of titanium alloys. This technology primarily uses a high-energy laser to melt thin layers of powder based on a computer-aided design model of the part to be processed. Through layer-by-layer powder deposition and melting, high-density parts of arbitrary shapes are formed. Due to its unique advantages in manufacturing complex and precise structures, SLM technology has shown enormous application potential in the aerospace field.

[0004] 7xxx series aluminum alloys, based on the Al-Zn-Mg-Cu elemental system, are precipitation-hardening deformation aluminum alloys with high specific strength, good formability, excellent thermal conductivity, and corrosion resistance. As a high-strength aluminum alloy, 7xxx series aluminum alloys have demonstrated unique advantages in aerospace, automotive, and defense industries. In aerospace, 7xxx series aluminum alloys are mainly used to manufacture aircraft structures, wings, fuselages, and engine parts; in automotive manufacturing, they are widely used in automotive components such as engine housings and wheels; and in defense, they are mainly used to manufacture structural components for military equipment such as rockets and missiles. To further improve the overall performance of 7xxx series aluminum alloys, we can use severe plastic deformation (SPD) technology to prepare ultrafine-grained materials. This is currently recognized as the most effective, promising, and widely used method for preparing ultrafine-grained materials. SPD mainly improves the material's performance in various ways by applying single or multiple shear strains to the material, causing the grains to break down and refine, increasing the defect density. As research into SPD (Special Purpose Processing) deepens, many SPD processes have been developed. Common methods for processing intense plastic deformation include equal channel extrusion, high-pressure torsion, torsional extrusion, cyclic expansion extrusion, simple shear extrusion, multi-directional forging, cumulative rolling, cryogenic rolling, and cryogenic asynchronous rolling. These processing methods, under certain temperature and strain rate conditions, apply various forms of external force to overcome the metal's deformation resistance, causing intense plastic deformation. This results in aluminum alloy profiles of various shapes, dimensions, and microstructures, significantly improving strength but reducing ductility and toughness. Tang et al. used a process of solution treatment (475℃ / 2h) + ECAP (300℃ / 16 passes) + room temperature cold rolling + aging at 110℃ for 22h to increase the yield strength and tensile strength of Al-Zn-Mg-Sc-Zr alloy from 456MPa and 469MPa to 594MPa and 606MPa, respectively, but the elongation decreased from 16.7% to 10%. Although the tensile strength increased by 30.3% and the yield strength increased by 29.2%, the elongation decreased. Wang et al. studied 1060 aluminum alloy and found that under low-temperature cumulative rolling conditions, as the number of rolling passes increased, the tensile strength and yield strength of the material increased rapidly from the annealed state to the first rolling pass, but the elongation decreased significantly. Summary of the Invention

[0005] The purpose of this invention is to provide a gradient composite material rod containing high-density crimped metal fibers and its preparation method. Because the rod contains high-density crimped metal fibers, which are interwoven and distributed to form a complex and ordered fiber system, even if some fibers have tiny cracks, the adjacent crimped fibers can prevent the cracks from extending further. At the same time, it can significantly improve the ultimate tensile strength and yield strength of the metal material at the cost of a smaller elongation, but without a significant decrease in ductility and toughness.

[0006] The technical solution for achieving the objective of this invention is: a method for preparing a gradient composite rod containing high-density crimped metal fibers, comprising the following steps:

[0007] Step (1): Using alloy powder with a melting point higher than 800℃ as raw material, laser selective melting is used to prepare several coiled metal fibers;

[0008] Step (2): Twist several coiled metal fibers together to obtain a loose bundle of coiled metal fibers;

[0009] Step (3): Melt the aluminum alloy into a liquid state, put the coiled metal fiber bundle into the casting mold, pour the aluminum alloy solution, and obtain an alloy rod containing coiled metal fibers;

[0010] Step (4): After heating and holding the alloy bar from step (3) at a certain temperature, perform rotary forging to obtain an elongated composite bar;

[0011] Step (5): The elongated composite rod obtained in step (4) is subjected to surface mechanical grinding to obtain a gradient composite material rod containing high-density crimped metal fibers with a fine-grained surface and a coarse-grained core.

[0012] Furthermore, step (1) specifically includes the following steps:

[0013] Step (11): Use TC4 alloy powder with a particle size range of 15-53μm as raw material;

[0014] Step (12): Construct a three-dimensional model of the curled metal fiber, place the axis of the metal fiber perpendicular to the Z-axis of the printing platform, slice the three-dimensional model of the curled metal fiber to generate the metal fiber printing path; select a tree-shaped support structure according to the size and shape of the suspended area of ​​the curled metal fiber, add it to the suspended part of the three-dimensional model of the curled metal fiber, and generate the support path.

[0015] Step (13): Set the printing parameters and perform laser selective melting printing to obtain curled metal fibers with a diameter of 0.5mm-1mm.

[0016] Furthermore, in step (12), the powder layer thickness is set to 0.02 mm, and the three-dimensional model of the curled metal fiber is sliced ​​according to the powder layer thickness to generate the metal fiber printing path.

[0017] In step (12), the branch angle of the tree-shaped support structure is 30°-60°, and the branch spacing is 0.5mm-1mm;

[0018] The specific printing parameters for step (13) are as follows:

[0019] The laser power is 300±10W, the scanning speed is 800mm / s-1200mm / s, the scanning spacing is 0.1±0.01mm, the spot diameter is 0.2±0.02mm, the substrate temperature is 100±5℃, and the printing process is protected by an argon atmosphere.

[0020] Furthermore, the powder is austenitic stainless steel powder or ferritic stainless steel powder.

[0021] Further, step (2) specifically involves: using a manual twisting method, clamping one end of a curled metal fiber with tweezers or pliers, taking another metal fiber, crossing one end of it with one end of the first metal fiber, rotating the tweezers or pliers to make the two metal fibers intertwine and form a twisted fiber bundle; repeating the above steps, adding more metal fibers, and continuously twisting until the desired high-density fiber bundle is achieved.

[0022] Further, step (3) specifically involves: using 7055 aluminum alloy, casting at 680℃~720℃, with a delay time of 5±0.5s, to cast an aluminum alloy-titanium alloy composite rod with a diameter of 8±1mm.

[0023] Furthermore, molten droplet composite arc additive manufacturing is used to replace the casting in step (3) to combine aluminum alloy and titanium alloy coiled metal fiber bundles.

[0024] Further, step (4) specifically involves heating and holding the aluminum alloy-titanium alloy composite bar from step (3) at 7055 molten aluminum alloy for 10 ± 1 min. After holding, the bar is subjected to rotary forging with a diameter reduction of 1%-3% per pass and a total deformation of 10-20% to obtain an elongated composite bar.

[0025] Furthermore, in step (5), the surface mechanical grinding uses a ball bearing head with a grinding speed of 0.1m / s-0.3m / s, a reduction of 5μm-50μm per pass, and a total reduction of 25μm-250μm, ultimately obtaining a gradient composite material rod containing high-density crimped metal fibers with a fine-grained surface and a coarse-grained core.

[0026] A gradient composite rod containing high-density crimped metal fibers is prepared using the method described above.

[0027] Compared with the prior art, the significant advantages of this invention are:

[0028] (1) The present invention incorporates high-density crimped metal fiber bundles. Metal fibers themselves have high strength, and after many metal fibers are gathered to form high-density fiber bundles, the fibers support and cooperate with each other, which further enhances the strength of the overall structure. In application scenarios that need to withstand large tensile, compressive or impact forces, high-density crimped metal fiber bundles can maintain the stability and integrity of the structure. When the material generates defects such as cracks during severe plastic deformation, the presence of high-density crimped metal fibers can change the path of crack propagation. When cracks propagate in composite materials, they will deflect and branch when they encounter fibers, consuming more energy and thus improving the toughness of the material.

[0029] (2) The composite material of aluminum alloy and high-density crimped titanium alloy metal fiber can reduce the weight of the structure while ensuring strength and performance. Compared with traditional solid aluminum alloy materials, this composite material has a higher strength-to-weight ratio, thus better achieving material lightweighting.

[0030] (3) Hot rotary forging of the aluminum alloy-titanium alloy composite bar in step (3) can further reduce the porosity generated during the casting process; hot rotary forging can make the interface of the two alloys more tightly bonded, improve the bonding strength of the interface, and thus improve the overall performance of the composite material; during hot rotary forging, the material is subjected to strong plastic deformation at high temperature, which refines the grains; refined grains can improve the strength, toughness and plasticity of the material. In terms of strength, fine-grained materials have more grain boundaries, which can hinder the movement of dislocations, thereby improving the strength of the material. In terms of toughness, the crack propagation path of fine-grained materials is more tortuous and requires more energy, thus having better toughness; at the same time, hot rotary forging can precisely control the size and shape of the material; by adjusting the rotary forging process parameters, composite bars with high-precision dimensions can be obtained to meet the needs of different application fields.

[0031] (4) The present invention uses surface mechanical grinding technology to prepare gradient composite rods containing high-density crimped metal fibers, which can obtain heterogeneous alloys with excellent bonding between inner and outer layers; wherein, the outer layer of the rod exhibits an ultrafine crystalline structure, and the inner layer is a coarse crystalline structure elongated along the axis, thereby achieving high strength and high toughness of the gradient fiber heterogeneous metal rod; at the same time, surface nano-sizing can adjust the ratio of the inner and outer layers of the conductor by changing the inner and outer radii, thereby adjusting the strength and plasticity matching of the high strength and high toughness alloy.

[0032] (5) The processing technology involved in this invention is mature, the experimental equipment is complete, the investment cost is low, it is safe and environmentally friendly, the production efficiency is high, and it is easy to realize industrial production. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the laser selective melting process in this invention, wherein (a) is a schematic diagram of the laser selective melting equipment printing titanium alloy coiled metal fibers; and (b) is a schematic diagram of the coiled metal fiber bundle.

[0034] Figure 2 The diagram shows the pouring of molten aluminum, where (a) is a casting diagram and (b) is the initial composite rod containing curled metal fibers obtained by casting.

[0035] Figure 3 The diagram shows a hot rotary forging process; (a) is a schematic diagram of hot rotary forging, and (b) is a composite material bar obtained by hot rotary forging.

[0036] Figure 4 This is a schematic diagram illustrating the fabrication process of a gradient composite rod containing high-density crimped metal fibers using surface nanostructuring.

[0037] Figure 5 Figure (a) shows a cross-sectional view of the gradient structure composite rod of the present invention, and Figure (b) shows a cross-sectional view of the composite rod after hot spinning and forging, and Figure (c) shows a cross-sectional view of the composite rod after surface nano-sizing. Detailed Implementation

[0038] The specific embodiments of the present invention will be described in further detail below, but the embodiments of the present invention are not limited thereto.

[0039] This invention provides a gradient composite rod containing high-density crimped metal fibers and its preparation method. The specific solution is as follows:

[0040] This invention combines laser selective melting, casting, hot forging, and surface mechanical grinding technologies to obtain a gradient composite rod containing high-density crimped metal fibers with a fine-grained surface and a coarse-grained core. The process includes the following steps:

[0041] TC4 titanium alloy powder was prepared as raw material and dried in a vacuum drying oven at a temperature of 80℃-180℃ for 2 hours. After drying, it was vacuum cooled for 2 hours before being removed.

[0042] Design a complete 3D solid model of the required curled metal fiber with a diameter of 0.5mm-1mm using 3D modeling software on a computer. Convert the 3D model file to STL format. Rotate the model in slicing software, aligning the axis of the metal fiber perpendicular to the Z-axis of the printing platform. Set the powder layer thickness to 0.02mm and let the slicing software slice the model according to the set layer thickness to generate the printing path. Select a suitable support structure based on the size and shape of the suspended area. Choose a tree-shaped support, set the branch angle to 30°-60°, and the branch spacing to 0.5mm-1mm. Add the selected support structure to the suspended part of the model in the software.

[0043] Select a titanium alloy substrate and fix it on the liftable worktable in the SLM equipment. Then, level the SLM equipment and spread the dried titanium alloy powder thinly and evenly on the powder feeding platform. Evacuate the SLM equipment and fill it with argon gas for atmosphere protection. Then, perform selective laser melting with the following process parameters: laser power of 300W, scanning speed of 800mm / s-1200mm / s, scanning spacing of 0.1mm, spot diameter of 0.2mm, substrate temperature of 100℃, and argon atmosphere protection during the printing process; the diameter of the coiled metal fiber is 0.5mm-1mm. A horizontal scraper first evenly spreads a thin layer of metal powder onto the substrate. A high-energy laser beam selectively melts the powder on the substrate according to the data information of the current layer in the 3D digital model, forming the shape of the current layer of the part. Then, the horizontal scraper spreads another layer of metal powder on the already processed layer, and the high-energy laser beam selectively melts it according to the data information of the next layer in the digital model. After each layer of the forming material is melted, the work platform is lowered by one layer thickness, and the forming material is then flattened on the work platform. Selective melting continues, and this cycle of selective melting is repeated until several coiled metal fibers with a diameter of 0.5mm-1mm are gradually accumulated, such as... Figure 1 As shown in (a).

[0044] Several curled metal fibers are twisted together. One end of a metal fiber is held by fine tweezers or small pliers. Another metal fiber is selected, and its end is crossed with the end of the first fiber. The tweezers or pliers are slowly rotated, causing the two fibers to intertwine and gradually form a twisted fiber bundle. The above steps are repeated, adding more metal fibers and twisting continuously, until a loose bundle of curled metal fibers is obtained, such as... Figure 1 As shown in (b).

[0045] This invention sets up a casting mold, into which a bundle of curled metal fibers is placed; 7055 aluminum alloy is smelted at a melting temperature of 700°C using an electromagnetic induction heating furnace; when the alloy solution temperature reaches 500°C, a refining agent is added to refine and remove slag from the alloy; after this step is completed, the heating frequency of the induction coil is adjusted to keep the molten aluminum alloy at the casting temperature, ready for casting.

[0046] like Figure 2 As shown in (a), molten aluminum alloy is poured into a casting mold for casting, which firmly bonds the aluminum alloy matrix and the coiled metal fiber bundles, thereby obtaining an alloy rod containing coiled metal fibers. The formed alloy rod is as follows: Figure 2 (b) As shown, the aluminum alloy casting is carried out at 680℃~720℃ with a delay time of 5s. After casting, it is cooled and then taken out from the casting mold. The diameter of the cast bar is about 8mm.

[0047] The obtained aluminum-titanium alloy composite bar was heated and held at 70% of the melting point of 7055 aluminum alloy for 10 minutes. After holding, it was subjected to rotary forging with a diameter reduction of 1%-3% per pass and a total deformation of 10-20%. The schematic diagram of rotary forging is shown below. Figure 3 As shown in (a), an elongated composite rod is obtained, and the elongated composite rod is as follows: Figure 3 As shown in (b), its internal grain structure is as follows Figure 5 As shown in (a).

[0048] like Figure 4 As shown, the obtained elongated composite rods were subjected to surface mechanical grinding using a ball bearing indenter at a grinding speed of 0.1 m / s–0.3 m / s. The reduction per pass was 5 μm–50 μm, with a total reduction of 25 μm–250 μm. This resulted in a gradient composite rod containing high-density crimped metal fibers, with a fine-grained surface and a coarse-grained core. Its internal grain structure is as follows: Figure 5 As shown in (b).

[0049] In summary, the gradient composite rod containing high-density crimped metal fibers prepared by this invention exhibits excellent performance, with a superior balance between strength and toughness. Furthermore, the high-density crimped metal fibers within the rod are interwoven and distributed to form a complex and ordered fiber system, thereby further enhancing the strength and fracture resistance of the composite rod.

Claims

1. A method for preparing a gradient composite rod containing high-density crimped metal fibers, characterized in that, Includes the following steps: Step (1): Using alloy powder with a melting point higher than 800℃ as raw material, laser selective melting is used to prepare several coiled metal fibers; Step (2): Twist several coiled metal fibers together to obtain a loose bundle of coiled metal fibers; Step (3): Melt the aluminum alloy into a liquid state, put the coiled metal fiber bundle into the casting mold, pour the aluminum alloy solution, and obtain an alloy rod containing coiled metal fibers; Step (4): After heating and holding the alloy bar from step (3) at a certain temperature, perform rotary forging to obtain an elongated composite bar; Step (5): The elongated composite rod obtained in step (4) is subjected to surface mechanical grinding to obtain a gradient composite rod containing high-density crimped metal fibers with a fine-grained surface and a coarse-grained core. Step (1) specifically includes the following steps: Step (11): Use TC4 alloy powder with a particle size range of 15-53μm as raw material; Step (12): Construct a three-dimensional model of the curled metal fiber, place the axis of the metal fiber perpendicular to the Z-axis of the printing platform, and slice the three-dimensional model of the curled metal fiber to generate the metal fiber printing path. Based on the size and shape of the suspended area of ​​the curled metal fiber, a tree-shaped support structure is selected and added to the suspended part of the 3D model of the curled metal fiber, and a support path is generated. Step (13): Set the printing parameters and perform laser selective melting printing to obtain curled metal fibers with a diameter of 0.5mm-1mm; In step (12), the powder layer thickness is set to 0.02 mm. The three-dimensional model of the curled metal fiber is sliced ​​according to the powder layer thickness to generate the metal fiber printing path. In step (12), the branch angle of the tree-shaped support structure is 30°-60°, and the branch spacing is 0.5mm-1mm; The specific printing parameters for step (13) are as follows: The laser power is 300±10W, the scanning speed is 800mm / s-1200mm / s, the scanning spacing is 0.1±0.01mm, the spot diameter is 0.2±0.02mm, the substrate temperature is 100±5℃, and the printing process is protected by an argon atmosphere.

2. The method according to claim 1, characterized in that, Step (2) is as follows: Using a manual twisting method, use tweezers or pliers to hold one end of a curled metal fiber, take another metal fiber, cross one end of it with one end of the first metal fiber, rotate the tweezers or pliers to make the two metal fibers intertwine to form a twisted fiber bundle; repeat the above steps, add more metal fibers, and twist continuously until the desired high-density fiber bundle is achieved.

3. The method according to claim 2, characterized in that, Step (3) specifically involves using 7055 aluminum alloy, casting at 680℃~720℃, with a delay time of 5±0.5s, to cast aluminum alloy-titanium alloy composite rods, with a diameter of 8±1mm.

4. The method according to claim 1, characterized in that, The aluminum alloy and titanium alloy coiled metal fiber bundles are combined by using molten droplet composite electric arc additive manufacturing instead of casting in step (3).

5. The method according to claim 3, characterized in that, Step (4) specifically involves heating and holding the aluminum alloy-titanium alloy composite bar from step (3) at 7055 molten aluminum alloy for 10 ± 1 min. After holding, the bar is subjected to rotary forging with a diameter reduction of 1%-3% per pass and a total deformation of 10-20% to obtain an elongated composite bar.

6. The method according to claim 5, characterized in that, In step (5), the surface mechanical grinding uses a ball bearing head with a grinding speed of 0.1m / s-0.3m / s, a reduction of 5μm-50μm per pass, and a total reduction of 25μm-250μm. Finally, a gradient composite material rod containing high-density crimped metal fibers with a fine-grained surface and a coarse-grained core is obtained.

7. A gradient composite rod containing high-density crimped metal fibers, characterized in that, Prepared using the method described in any one of claims 1-6.

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