Metal bar with gradient laminated heterogeneous fiber structure and preparation method of metal bar

Abstract

The invention belongs to the field of material preparation, and particularly relates to a metal bar of a gradient laminated heterogeneous fiber structure and a preparation method of the metal bar. The preparation method comprises the following specific steps: respectively cutting a copper plate and a bronze plate into slices; a raw wire of which the base material is austenitic stainless steel is drawn into a microwire. The copper sheets, the microwires and the bronze sheets are alternately stacked and then placed into diffusion welding equipment, and diffusion welding is carried out in an argon shield furnace. And the welded thin plate is further turned up from the edge to the center to be rolled into a rod shape, and then diffusion welding is conducted under the same condition. And wrapping the processed bar with a stainless steel pipe, and then carrying out multi-pass rotary forging and pressing to finally obtain the gradient heterogeneous fiber structure solid bar with a fine grain layer on the surface and coarse grains on the core part. The preparation method is easy to operate, diffusion welding and rotary forging are combined, the bar with the heterostructure is finally obtained, the strength of the alloy bar is remarkably improved, and certain plasticity is reserved.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation, specifically relating to a gradient laminated heterofiber structure metal rod and its preparation method. It can significantly improve the ultimate tensile strength and yield strength of metal materials at the expense of a small elongation, while at the same time without a significant decrease in ductility and toughness. Background Technology

[0002] Copper and its alloys possess excellent machinability, allowing them to be formed into parts of various shapes and sizes through forging, rolling, and stretching. Copper alloys have relatively low strength, are easily plastically deformed, are relatively fatigue-resistant, have an attractive appearance, and possess good electrical and thermal conductivity and corrosion resistance, making them an important branch of heavy non-ferrous metals. Copper alloys are widely used in industrial fields, and their production volume is second only to steel and aluminum, making them the third largest alloy category among metallic materials.

[0003] Diffusion welding refers to the process where the surfaces of materials in contact are brought close together under the influence of temperature and pressure, resulting in localized plastic deformation and interatomic diffusion. This leads to the formation of a new diffusion layer at the interface, achieving a reliable bond. Diffusion-welded joints exhibit stable quality, high connection strength, and excellent high-temperature performance and corrosion resistance. They do not cause macroscopic deformation, melting, or relative movement of the parts. Diffusion-assisted materials (i.e., intermediate layer materials) may or may not be used between the two mating surfaces. Diffusion welding can be used to prepare heterogeneous laminate composite materials with good interfacial adhesion.

[0004] Rotary forging, also known as radial forging, is a forming process for long-axis rolled parts. The workpiece is struck with a high-frequency radial reciprocating motion, causing it to rotate and move axially. Under the impact of the hammer, the workpiece undergoes radial compression and length extension deformation. Rotary forging combines the characteristics of pulse loading and multi-directional forging, which is beneficial for uniform deformation and improved plasticity of the metal. Because the forging material is subjected to biaxial compression and uniaxial tensile stress, forging is considered a plasticity-enhancing process that can effectively refine grains and improve the mechanical properties of metallic materials. Due to its low strain and excellent grain refinement ability, forging is used to manufacture workpieces with ultrafine grain structures or even nanocrystalline structures.

[0005] In recent years, the design of gradient and laminated structures for copper and its alloys to improve their overall performance has attracted widespread attention. Nanocrystals generated by intense plastic deformation offer high strength but low ductility, while coarse grains offer high ductility but low strength. Recent research on heterostructured materials has shown that the combination of soft coarse grains and hard nanoscale grains can produce a synergistic effect, enabling materials to achieve higher strength with less loss of ductility. Faced with the dilemma of balancing strength and ductility in metallic materials, it is necessary to explore new metallic materials and their preparation methods.

[0006] Heterogeneous materials have emerged as a novel class of materials due to their superior mechanical properties. Heterogeneous materials are defined as materials with significant differences in mechanical properties between their micro-regions, and the interactions between these regions can produce a significant synergistic optimization effect on macroscopic mechanical properties. The synergistic strengthening effect of materials can be altered or even enhanced by adjusting the microscopic heterogeneity. For example, nanocrystals have high strength but low ductility, while coarse grains have low strength but high ductility. However, combining low-strength coarse grains with high-strength nanocrystals can overcome the limitations of traditional mixing principles, achieving a simultaneous improvement in both macroscopic high strength and high ductility in heterogeneous materials.

[0007] Zhongchen Zhou et al. were the first to use copper-brass heterostructures as model materials and fabricate a set of high-density copper-brass heterofibers with well-bonded heterostructure interfaces through diffusion welding and rotational oscillation processing. The density of the heterostructure interfaces in the heterofibers is twice that of the heterolaminates. This microstructure is conducive to accumulating a higher geometrically necessary dislocation density, thereby achieving a stronger synergistic strengthening effect during heterogeneous strengthening and realizing an excellent combination of strength and ductility.

[0008] Yunlai Zhao et al. prepared pure copper heterograin composite laminates composed of fine / coarse / fine grains using roll bonding and annealing techniques. Compared with the tensile results of non-composite laminates, the well-bonded interface helped achieve ductility and strength exceeding the expectations of the mixing rules.

[0009] Chongxiang Huang et al. compared the strength and ductility of copper-bronze laminates with those of traditional homogeneous copper-bronze.

[0010] The results show that by adjusting the interfacial spacing of the laminates, the balance between strength and ductility can be further optimized. The key principle is to maximize back stress and work hardening. When the interfacial spacing is too large, insufficient back stress is generated. However, when the interfacial spacing is too small, the interfacial affected zones overlap, leaving insufficient space for dislocation accumulation, thus limiting the work hardening ability to maintain ductility. Therefore, for heterogeneous structures, an optimal interfacial spacing equivalent to twice the width of the interfacial affected zone should be designed.

[0011] Researchers have made materials stronger by manipulating their composition and microstructure dimensions. This design inspiration comes from the microstructure of biomaterials in nature, as the mechanical properties of materials are essentially regulated by their microstructure. Emerging microstructures mainly include gradient structures, layered structures, bimodal structures, and harmonic structures. Numerous experiments have shown that these carefully designed structural materials exhibit a superior combination of strength and ductility compared to homogeneous materials.

[0012] Using high-melting-point, high-elongation 316 and 316L metal microfilaments as metal fibers and copper and bronze as the metal matrix phases, a set of composite laminates with heterogeneous copper / stainless steel / bronze components were obtained through diffusion welding and rotary forging processes, with carefully customized microstructures. Austenitic stainless steel metal fibers possess high tensile strength, excellent plasticity and toughness, while the copper / bronze heterostructure exhibits excellent ductility. For example, the heterostructured pure titanium laminate prepared by Danyang Li et al. exhibits very high yield strength, characterized by alternating coarse and fine grain layers, achieving a good combination of strength and ductility, far exceeding the predicted values ​​of the Hall-Petch relation and the mixing law. Introducing austenitic stainless steel metal fibers as reinforcing phases into copper and its alloys is an effective means of achieving alloy strength and toughness. During the preparation of metal fiber reinforced copper-based rods, rotary forging dies (usually 2 to 8) perform short-duration, high-frequency (6800 to 12000 times per minute) hammering on the rods, while simultaneously moving radially and applying compressive force to the closed workpiece. With each hammer blow from the mold, the workpiece begins to move radially and is shaped with good precision. Summary of the Invention

[0013] This invention provides a metal rod with a gradient laminated heterostructure fiber and its preparation method.

[0014] The technical solution provided to achieve the present invention is as follows:

[0015] This invention first uses diffusion welding to obtain a heterogeneous laminate, and then uses rotary forging to prepare a gradient fiber heterogeneous metal rod or cable that significantly improves the ultimate tensile strength and yield strength of the metal material, while maintaining its ductility and toughness. The process includes the following steps:

[0016] Step (1): Cut the copper and bronze plates into pieces with dimensions of 100×100×1mm. 3 The thin sheets are mechanically ground with #1200# SiC sandpaper to remove surface contaminants, then ultrasonically cleaned, and finally air-dried to thoroughly clean the surfaces of the copper and bronze sheets.

[0017] Step (2): The raw filament of austenitic stainless steel is drawn into microfilaments and the stainless steel microfilaments are subjected to bright heat treatment.

[0018] Step (3): Copper sheets, stainless steel microwires and bronze sheets are stacked alternately and then diffusion welded in an argon-protected furnace to obtain a copper / stainless steel / bronze heterolaminate with good interfacial bonding.

[0019] Step (4): The welded sheet is further rolled from the edge to the center into a rod shape, and then diffusion welding is performed under the same conditions. After two diffusion welding processes, a well-bonded rod material with a copper / stainless steel / bronze heterostructure is obtained.

[0020] Step (5): Wrap the processed bar with a 304L stainless steel tube, and then perform multiple rotations.

[0021] Forging is performed with a diameter reduction of 0.5 mm per pass. During repeated forging, lubricating oil is used to protect the forging hammer, ultimately resulting in a solid bar with a diameter of 10 mm, a fine-grained surface, and a coarse-grained core, exhibiting a gradient heterostructure fiber structure.

[0022] Furthermore, the metal matrix phase is copper / bronze or other metal materials with excellent plasticity but low strength, specifically copper with a purity of 99.9% or higher and Cu-5wt%Zn-5wt%Sn bronze, and the metal fibers are austenitic stainless steel 316, 316L metal microwires or other metal microwires with high melting point, strength and elongation, with a diameter range of 0.5-1mm.

[0023] Furthermore, the diffusion welding between the laminates is carried out at temperatures below 700°C, with a delay time of 5 seconds. The laminate thickness obtained by the first diffusion welding is 5 mm. The rolled laminates result in rod-shaped materials with unstable interfacial bonding. The second diffusion welding ensures good adhesion between the rod interfaces.

[0024] Furthermore, the alloy bar wrapped in stainless steel tube is subjected to multi-pass rotary forging at room temperature, with a diameter reduction of 0.5 mm per pass. During the repeated forging process, lubricating oil is used to protect the forging hammer, ultimately resulting in a solid bar with a diameter of 10 mm, a fine-grained surface, and a coarse-grained core, exhibiting a gradient heterostructure.

[0025] Compared with the prior art, the significant advantages of this invention are:

[0026] 1. This invention carefully designs the component materials, using copper / bronze as the matrix phase material and austenitic stainless steel microwires as the reinforcing phase material. It employs diffusion welding technology to achieve good adhesion between the metal interfaces, thus obtaining a set of copper / stainless steel / bronze component laminate composite materials with heterogeneous fiber structures.

[0027] 2. This invention features a meticulously designed microstructure and employs a rotary forging process. By striking the workpiece with high-frequency radial reciprocating motion, the resulting alloy exhibits an ultrafine-grained outer layer with strong high-temperature stability.

[0028] Qualitatively, the inner layer is a high-strength and tough gradient fiber heterogeneous metal rod with fine or coarse grains and good plasticity, elongated along the axial direction.

[0029] 3. The processing technology involved in this invention is mature, the experimental equipment is complete, the investment cost is low, the safety factor is high, and the production efficiency is high. Attached Figure Description

[0030] Figure 1 (a) is a schematic diagram of the copper / bronze plate cutting design of the present invention.

[0031] Figure 1 (b) is a schematic diagram of the stainless steel raw wire drawing method designed in this invention.

[0032] Figure 1 (c) is a schematic diagram of diffusion welding of the laminate designed in this invention.

[0033] Figure 1 (d) is a schematic diagram of the rod diffusion welding method designed in this invention.

[0034] Figure 1 (e) is a process flow diagram of the metal rod with gradient laminated heterofiber structure prepared by rotary forging according to the present invention.

[0035] Figure 2 This is a schematic diagram of the cross-section of the gradient laminated fiber heterogeneous metal rod of the present invention.

[0036] Explanation of reference numerals in the attached figures:

[0037] 1- Rotary forging mill housing, 2- Rotary forging die system, 3- Metal bar material undergoing rotary forging deformation 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] The copper used in this invention is commercially pure copper (99.9% Cu), which has excellent electrical and thermal conductivity, excellent plasticity, and is easy to hot-press and cold-press. The copper alloy used is bronze, with a main elemental composition of Cu-Zn-Sn. Bronze has good casting performance, wear resistance, and stable chemical properties. The metal fibers used are austenitic stainless steel microwires with high melting point, strength, and elongation. Ultra-low carbon austenitic stainless steel with a carbon content of less than 0.03% can fundamentally prevent intergranular chromium-depleted corrosion in microwire products. The reduction in carbon content reduces the hardness during drawing, and nickel can effectively reduce the cold work hardening tendency of steel and improve cold workability, giving stainless steel high plasticity and toughness at both room temperature and low temperature. Introducing austenitic stainless steel microwires as a reinforcement into the copper and its alloy matrix phase is an effective means of achieving alloy strengthening and toughening. In the preparation of metal fiber reinforced copper matrix composites, blocky materials with good surface adhesion can be successfully obtained through diffusion welding technology.

[0040] This invention first uses diffusion welding to obtain a copper / austenitic stainless steel / bronze laminate composite material, and then uses rotary forging to prepare a gradient laminated heterofiber structure metal rod with simple process and high strength and high toughness in the final product, including the following steps:

[0041] The copper and bronze plates were cut into pieces with dimensions of 100×100×1mm. 3 The thin sheets are mechanically ground with up to #1200# SiC sandpaper to remove surface contaminants, ultrasonically cleaned, and then air-dried to thoroughly clean the surfaces of the copper and bronze sheets.

[0042] Raw filaments made of austenitic stainless steel are drawn into microfilaments, and the stainless steel microfilaments are then subjected to bright heat treatment.

[0043] Copper sheets, stainless steel microwires, and bronze sheets are stacked alternately and then placed in a diffusion welding device. Diffusion welding is performed in an argon-protected furnace to obtain a copper / stainless steel / bronze heterolaminate with good interfacial adhesion.

[0044] The welded sheet is further rolled from the edge to the center into a rod shape, and then diffusion welding is performed under the same conditions. After two-step diffusion welding process, a well-bonded rod material with a copper / stainless steel / bronze heterostructure is obtained.

[0045] The processed bar is wrapped in a 304L stainless steel tube and then subjected to multiple rotary forging passes, with a diameter reduction of 0.5 mm per pass. During the repeated forging process, lubricating oil is used to protect the forging hammer, ultimately resulting in a solid bar with a diameter of 10 mm, a fine-grained surface, and a coarse-grained core, exhibiting a gradient heterostructure fiber structure.

[0046] The surface of the bar is a fine-grained structure layer that is distinct from the matrix material. The grain size in this fine-grained structure layer is significantly smaller than that in the matrix material. Therefore, there is a gradient change from fine grains to coarse grains from the surface to the core. Fine grains have high strength but low ductility, while coarse grains have low strength but high ductility. The gradient laminated heterofiber structure metal bar prepared by the above method has a fine-grained surface that significantly improves the strength of the alloy bar, while the coarse-grained core retains a certain degree of plasticity.

Claims

1. A method of producing a metal rod of a gradient-laminated heterogeneous fiber structure, characterized by, A high melting point and high elongation metal fiber is used as a reinforcing phase, and copper and bronze are used as a metal matrix phase, including the following steps: Step (1): Copper and bronze plates were cut into 100 x 100 x 1 mm pieces, and the surfaces of the pieces were mechanically polished with up to #1200 SiC paper to remove surface contamination, ultrasonically cleaned, and then dried in air to thoroughly clean the surfaces of the copper and bronze pieces. 3 Step (1): Copper and bronze plates were cut into 100 x 100 x 1 mm pieces, and the surfaces of the pieces were mechanically polished with up to #1200 SiC paper to remove surface contamination, ultrasonically cleaned, and then dried in air to thoroughly clean the surfaces of the copper and bronze pieces. Step (2): the raw wire of the base material of austenitic stainless steel is drawn into a micro wire, and the stainless steel micro wire is subjected to bright heat treatment to ensure the smooth surface of the micro wire; Step (3): copper sheet, stainless steel micro wire and bronze sheet are alternately stacked, and then diffusion welding is carried out in an argon protection furnace to obtain a copper / stainless steel / bronze heterogeneous laminated plate with good interface bonding; Step (4): the thin plate after welding is further rolled from the edge to the center to form a rod, and then diffusion welding is carried out under the same conditions; Step (5): the processed rod is wrapped in a 304L stainless steel tube, and then multi-pass rotary forging is carried out to obtain a gradient heterogeneous fiber structure solid rod with a fine crystal layer on the surface and a coarse crystal in the core.

2. The production method according to claim 1, characterized by, In step (1), the metal matrix phase is copper / bronze or other metal materials with excellent plasticity but low strength, specifically copper with a purity of more than 99.9% and Cu-5wt%Zn-5wt%Sn bronze.

3. The preparation method according to claim 2, characterized in that, In step (2), the metal fiber is austenitic stainless steel 316, 316L or other metal micro wires with high melting point, strength and elongation, with a diameter of 0.5-1mm.

4. The production method according to claim 3, characterized by, In step (3), the diffusion welding between the laminated plates is carried out at 700℃ or below, including 700℃, with a delay time of 5s, and the thickness of the laminated plate obtained by diffusion welding is 5mm.

5. The preparation method according to claim 4, characterized in that, In step (4), the rolled laminated plate is a rod-shaped material with unstable interface bonding state, and the second diffusion welding makes the laminated plate interface well bonded.

6. The preparation method according to claim 5, characterized in that, In step (5), the alloy rod wrapped in a stainless steel tube is subjected to multi-pass rotary forging at room temperature, with a diameter reduction of 0.5mm per pass. In the repeated forging process, lubricating oil is used to protect the forging hammer, and finally a gradient heterogeneous fiber structure solid rod with a diameter of 10mm and a fine crystal layer on the surface and a coarse crystal in the core is obtained.

7. A gradient laminated heterogeneous fiber structure metal rod prepared by the preparation method of any one of claims 1-6.

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