Gradient fiber heterogeneous metal bar or cable and preparation method thereof

Abstract

The invention belongs to the field of material preparation, and particularly relates to a preparation method of a gradient fiber heterogeneous metal bar or cable. The preparation method comprises the following specific steps: (1) putting a plurality of metal fibers into a pouring mold; (2) molten aluminum is poured for casting, specifically, the molten aluminum and the molten aluminum are stably combined, and an alloy bar containing metal fibers is obtained; and (3) longitudinal surface nanocrystallization is carried out, specifically, surface grain refinement is carried out on the bar of the hard core gradient structure obtained in the step (2) through longitudinal surface nanocrystallization, a gradient fiber heterogeneous bar with a uniform surface nanocrystal layer and core coarse grains is obtained, lubricating oil is used for lubrication in the rolling process, and a thick gradient nanolayer is generated. The preparation method disclosed by the invention is simple to operate, a heterogeneous structure is finally obtained by combining rotary breaking and surface nanocrystallization, the strength of the alloy bar is remarkably improved, and certain plasticity is reserved.

Description

Technical Field

[0001] The present invention belongs to the field of material preparation, and particularly relates to a gradient fiber heterogeneous metal bar or cable and a preparation method thereof. Background Art

[0002] The used aluminum alloy is a high-strength and high-hardness aluminum alloy, and its main element composition is Al-Zn-Mg-Cu. It has the characteristics of high strength and good welding performance. At present, further improving the comprehensive performance of aluminum alloy is a very popular research direction. Ultra-fine grained materials with high strength and good plasticity can be prepared by severe plastic deformation (SPD) technology. Currently, the more common severe plastic deformation methods include high pressing torsion (HPT), accumulative rolling bonding (ARB), multi-axial compression (MAC), equal channel angular pressing (ECAP), cyclic extrusion and compression (CEC), and ultrasonic shot peening (USP), etc. The prepared aluminum alloy materials with excellent performance and light weight can be used in new energy vehicles, high-speed railway trains, aerospace and other fields. According to the Hall-Petch relationship, while SPD improves the strength of materials, it often sacrifices plasticity. Therefore, it is necessary to explore a plastic deformation method that sacrifices less plasticity while improving the strength of materials.

[0003] Heterogeneous metal materials are new structural materials composed of hard and soft structures, and have better mechanical properties and fatigue life compared with homogeneous structural materials. Heterogeneous nano-metal materials contain randomly distributed hard-phase nano-structures and soft-phase recrystallized grains. There are both coarse grains and fine grains inside heterogeneous metal materials. Coarse grains will undertake more plastic deformation, improving the strength-plasticity matching of materials. Since a strain gradient will be formed at the boundary between coarse grains and nano-grains, resulting in additional strengthening and hardening, the deformation mechanism of heterogeneous nano-metals is complex and there are many influencing factors.

[0004] Preparation of bimetallic composites by solid-liquid composite method. Its basic principle is to heat the solid metal with the higher temperature of the liquid metal, and even cause local remelting at the composite interface. The interface is combined together through metallurgical reaction and element interdiffusion to form bimetallic composites. A356 / 6085 aluminum alloy bimetallic composites can be prepared by the way of solid-liquid rolling composite. In addition, the solid-liquid casting and rolling composite process of bimetallic composite pipes can successfully prepare steel / aluminum composite pipes, copper / aluminum composite pipes, titanium / aluminum composite pipes and copper / aluminum composite pipes under the conditions of a molten pool height of 40 mm and a casting and rolling speed of 2.5 mm. For the impact jet solid-liquid composite method, it is not necessary to treat the surface of the base metal. Its principle is to pour the cladding metal melt on the surface of the base metal at a certain angle and speed, so as to carry out a heat flow impact on the surface of the base metal, remove the oxide film on the surface of the base metal, and thus realize the metallurgical bonding between the two metals.

[0005] Ling Cen et al. proposed that aluminum alloys represented by the 7xxx series are prone to high porosity, high crack sensitivity and mechanical property degradation in the laser molten pool, while Bunty Tomar et al. also mentioned that components fabricated by arc additive manufacturing often have non-negligible defects such as pores, tensile residual stresses and cracks, which will significantly reduce the mechanical properties of the materials. To solve the above defects, surface nanocrystallization technology is used. Among them, surface nanocrystallization is a new type of surface processing technology proposed by the team of Academician Lu Ke of the Chinese Academy of Sciences, which can improve the plasticity and strength of materials simultaneously, thereby improving the static load strength and dynamic load strength of materials. He believes that after the material surface is treated by the non-equilibrium method, the internal organizational structure changes, the coarse grains are refined into nanocrystals, forming a nanocrystalline structure, and thus a nanolayer is obtained. After the self-nanostrengthened layer is formed on the material surface, the grain sizes from the surface layer to the substrate are different. The closer to the surface layer, the smaller the grain size, and the nanolayer is tightly combined with the substrate and is not easy to peel off, and there is no obvious interface between the two. In practical applications, the main methods to realize surface nanocrystallization of materials are non-equilibrium thermodynamics method and surface mechanical treatment method.

[0006] After the material surface is treated by the non-equilibrium method, the internal organizational structure changes, the coarse grains are refined into nanocrystals, forming a nanocrystalline structure, and thus a nanolayer is obtained. After the self-nanostrengthened layer is formed on the material surface, the grain sizes from the surface layer to the substrate are different. The closer to the surface layer, the smaller the grain size, and the nanolayer is tightly combined with the substrate and is not easy to peel off, and there is no obvious interface between the two. In practical applications, the main methods to realize surface nanocrystallization of materials are non-equilibrium thermodynamics method and surface mechanical treatment method.

[0007] Huang H.W. et al. used surface mechanical rolling treatment (SMRT) to achieve surface nanocrystallization on 316 stainless steel, significantly improving the tensile and fatigue properties of the steel. Liu X.C. et al. used surface mechanical grinding treatment (SMGT) method to achieve surface gradient nanocrystallization on pure nickel and studied the evolution process of the gradient nanostructure; Xu W. et al. used the SMGT method to form a gradient nanostructure on the surface of pure aluminum at 77K and studied the mechanism of surface grain refinement; Long J.Z. et al. used the SMGT method to achieve a gradient nanostructure on pure copper and studied the grain coarsening phenomenon of pure copper during fatigue loading.

[0008] High melting point and high elongation metal fibers have high tensile strength, excellent plasticity and toughness. Introducing them as reinforcements into aluminum alloys is an effective means to strengthen and toughen aluminum alloys. During the preparation of metal fiber reinforced aluminum matrix composites, due to the high temperature and pressure, the reaction activity between the aluminum matrix and the metal fibers increases, resulting in severe interfacial reactions between the matrix and the fibers, thus generating complex reaction products. Most of these reaction products are hard and brittle, which will damage the mechanical properties of the composites. The surface nanocrystallization technology can solve the defects of hardness and brittleness of the materials. Summary of the Invention

[0009] The purpose of the present invention is to provide a gradient fiber heterogeneous metal bar or cable and its preparation method, which can significantly improve the ultimate tensile strength and yield strength of metal materials at the cost of sacrificing a small elongation rate, but the plasticity and toughness do not decrease significantly.

[0010] A preparation method of a gradient fiber heterogeneous metal bar or cable, and the preparation method is as follows:

[0011] Using high melting point and high elongation metal fibers as the reinforcement phase and aluminum or aluminum alloy as the metal matrix phase, including the following steps:

[0012] Step (1): Subject the high melting point and high elongation metal to multiple drawing operations and then place it in a casting mold. After melting, it is cooled to obtain metal fibers with a fibrous phase and a porous matrix.

[0013] Step (2): Melt aluminum or aluminum alloy to form a liquid state, and then pour the aluminum liquid into the casting mold for casting to firmly combine the aluminum matrix and the metal fibers, and obtain an alloy bar containing metal fibers.

[0014] Step (3): Longitudinal surface nanocrystallization: Refine the surface grains of the bar with a hard core gradient structure obtained in step (2) through longitudinal surface nanocrystallization to obtain a bar with a gradient fiber heterogeneity having a uniform surface nanocrystalline layer and a core coarse crystal; lubricating oil is used for lubrication during the rolling process to produce a relatively thick gradient nanolayer.

[0015] Further, the metal matrix phase is an aluminum or aluminum alloy solution, and the high melting point and high elongation metal is a metal fiber with a diameter of 0.1 - 0.5 mm.

[0016] Further, the metal fiber is a metal fiber of niobium, titanium, magnesium or zirconium.

[0017] Further, in step (2), the aluminum alloy casting is carried out at 700 - 720 °C, the delay time is 5 s, and the diameter of the cast bar is 5 mm.

[0018] Further, in step (3), the rolling head for surface nanocrystallization is a WC / Co small ball with a diameter of 14 mm, and the parameters are: the feeding speed of the rolling head is 0.1 mm / s, the single pressing depth is 50 μm, and it is repeated 5 times on the plate surface, with a total pressing depth of 250 μm.

[0019] Compared with the prior art, the remarkable advantages of the present invention are as follows:

[0020] 1. The present invention uses surface nanocrystallization to prepare high-strength and high-toughness gradient fiber heterogeneous metal bars or cables, and can obtain a heterogeneous alloy with good bonding between the inner and outer layers. Therefore, the outer layer part of the obtained alloy is in an ultrafine grain structure and has strong high-temperature stability; the inner layer part can be fine or coarse grains elongated along the axis, realizing that the gradient fiber heterogeneous metal bar has high strength and high toughness properties; 2. The present invention selects the surface nanocrystallization process, which can change the inner and outer radii to adjust the ratio of the inner and outer layers of the wire, so as to adjust the strength and plasticity matching of the high-strength and high-toughness alloy; 3. The equipment used in the present invention is mature, the material cost is low, it is close to net forming, is less restricted and easy to industrialize, and is at the same time green and pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a schematic diagram of the casting mold designed for the present invention and a schematic diagram of casting aluminum liquid for casting. Among them, Figure 1 (d) is a schematic diagram of the finished product of the gradient fiber heterogeneous metal bar.

[0022] Figure 2 The figure is a process flow chart for preparing high-strength and high-toughness gradient fiber heterogeneous metal bars or cables by using the surface nanocrystallization method in the present invention.

[0023] Figure 3 The figure is a schematic cross-sectional view of the gradient fiber heterogeneous metal bar in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The following further details the specific embodiments of the present invention, but the embodiments of the present invention are not limited thereto.

[0025] The present invention provides a gradient fiber heterogeneous metal bar or cable and a preparation method thereof. The specific scheme is as follows:

[0026] The present invention first obtains an aluminum alloy bar by casting, and then uses the surface nanocrystallization method to prepare a gradient fiber heterogeneous metal bar or cable with a simple process and high strength and high toughness characteristics of the final product, including the following steps:

[0027] The present invention sets up a set of casting molds, as Figure 1 shown, and the casting mold casts several metal fibers at the same time. Before casting, several metal bars are first placed in the casting mold, and the diameter range of the metal bars placed in the mold is between 0.1 and 0.5 mm.

[0028] High melting point and high elongation metals can dissolve sufficient oxygen at high temperatures, which destroys the ductility at normal working temperatures. For the present invention, dissolved oxygen is not desired. Therefore, the manufacture of these metal fibers is usually avoided at high temperatures.

[0029] The method for preparing metal fibers includes putting the pure metal after multiple drawing into a casting mold, heating it to form a molten structure, and then cooling it to form a porous matrix with a fiber phase.

[0030] According to the above method, materials of metal fibers with a diameter range between 0.1 and 0.5 mm can be prepared.

[0031] Melting aluminum or aluminum alloy, the melting temperature is 700 - 720 °C, using an electromagnetic induction heating furnace with the model of JMN - to melt aluminum or aluminum alloy. When the temperature of the alloy solution reaches 500 °C, adding a refining agent with a mass fraction of 0.5% of C2C l6 to refine and remove slag from the alloy. After this step is completed, adjust the heating frequency of the induction coil to keep the aluminum alloy melt at the pouring temperature and wait for casting.

[0032] Pour the aluminum liquid into the casting mold. The process of adding the aluminum liquid is as Figure 1 shown. The purpose of casting is to firmly combine the aluminum liquid and the metal fibers to prepare an aluminum alloy composite bar containing metal fibers.

[0033] The casting material is aluminum or aluminum alloy solution, the metal fiber material is high melting point and high elongation metal material. The casting of aluminum alloy is carried out at 500 - 630 °C, the delay time is 5 s, and the diameter of the cast bar is about 5 mm. After casting, it is also necessary to cool and then take it out from the casting mold.

[0034] The method for longitudinal surface nanocrystallization is surface mechanical rolling treatment. The schematic diagram of the method and operation of surface nanocrystallization is as Figure 2 shown. Carry out surface grain refinement on the prepared metal fiber bar with a hard core gradient structure to obtain a bar with a gradient fiber heterogeneous structure having a uniform surface nanocrystalline layer and a core coarse crystal.

[0035] The process of surface nanocrystallization needs to control the feed speed of the rolling head and the penetration depth of the rolling head, and reciprocate on the surface of the fiber metal bar containing aluminum or aluminum alloy to achieve gradient nanocrystallization of the bar surface.

[0036] For the above process of surface mechanical rolling treatment, lubricating oil needs to be used for lubrication, and the purpose is to produce a relatively thick gradient nanolayer.

[0037] For the process of surface nanocrystallization, when performing the rolling treatment, a WC / Co small ball with a rolling head diameter of 14 mm is used, the feeding speed of the rolling head is 0.1 mm / s, the single pressing depth is 50 μm, and it is repeated 5 times on the surface of the plate, with a total pressing depth of 250 μm.

[0038] For the gradient fiber heterogeneous metal bar or cable prepared by the above method, the grain structure of the prepared gradient fiber heterogeneous metal bar or cable is as Figure 3 shown.

[0039] The specific operation is as follows:

[0040] First, clean the pure metal with deionized water, and then perform drawing deformation on the pure metal; use metal fibers of niobium (Nb), titanium (Ti), magnesium (Mg), and zirconium (Zr) with high melting points and high ductility.

[0041] Put the deformed pure metal into a casting mold, melt it and then cool it to obtain a metal fiber with a porous matrix having a fiber phase;

[0042] Melt aluminum or aluminum alloy, with the melting temperature being 700 - 720 °C. Use an electromagnetic induction heating furnace with the model of JMN - to melt aluminum or aluminum alloy. When the temperature of the alloy solution reaches 500 °C, add a C2C refining agent with a mass fraction of 0.5% to refine and remove slag from the alloy. After this step is completed, adjust the heating frequency of the induction coil to keep the aluminum alloy melt at the casting temperature and wait for casting. l6 Pour the aluminum liquid into the casting mold to form a mixture of a fiber metal and a base metal, with the casting temperature in the range of 500 - 630 °C, and then cool the mixture to prepare an aluminum alloy composite bar containing metal fibers with both a fiber phase and a base phase.

[0043] Table 1 Chemical composition of aluminum alloy (mass fraction, %),

[0044]

[0045] Table 2 Mechanical properties of aluminum alloy,

[0046]

[0047] Pour the aluminum liquid into the casting mold to form a mixture of a fiber metal and a base metal, with the casting temperature in the range of 500 - 630 °C, and then cool the mixture to prepare an aluminum alloy composite bar containing metal fibers with both a fiber phase and a base phase.

[0048] Perform surface mechanical rolling treatment on the prepared aluminum alloy composite bar containing metal fibers. When performing the rolling treatment, use a WC / Co small ball with a rolling head diameter of 14 mm, the feeding speed of the rolling head is 0.1 mm / s, the single pressing depth is 50 μm, and it is repeated 5 times on the surface of the plate, with a total pressing depth of 250 μm. After surface grain refinement, a bar with a gradient fiber heterogeneity having a uniform surface nanocrystalline layer and a core coarse grain can be obtained.

[0049] The prepared gradient fiber heterogeneous aluminum alloy metal bars have excellent properties, with an excellent match between strength and plastic toughness. On the premise of sacrificing a relatively small elongation, the ultimate tensile strength and yield strength of the gradient fiber heterogeneous aluminum alloy metal bars are significantly improved, and the plastic toughness does not decrease significantly.

Claims

1. A method for preparing a gradient fiber heterogeneous metal bar or cable, characterized in that, Using a high melting point and high elongation metal fiber as the reinforcing phase and aluminum or an aluminum alloy as the metal matrix phase, the method includes the following steps: Step (1): Subject the high melting point and high elongation metal to multiple drawing processes, then place it in a casting mold, melt it, and then cool it to obtain metal fibers with a porous matrix having a fiber phase. Step (2): Melt aluminum or an aluminum alloy to form a liquid state, and cast the aluminum liquid into the casting mold to firmly bond the aluminum matrix and the metal fibers, and obtain an alloy bar containing metal fibers. Step (3): Longitudinal surface nanocrystallization: Refine the surface grains of the bar with a gradient structure of the hard core obtained in Step (2) through longitudinal surface nanocrystallization to obtain a bar with a gradient fiber structure having a uniform surface nanocrystalline layer and a coarse-grained core. During the rolling process, lubricating oil is used for lubrication to produce a relatively thick gradient nanolayer.

2. The preparation method according to claim 1, characterized in that The metal matrix phase is an aluminum or aluminum alloy solution, and the high melting point and high elongation metal is a metal fiber with a diameter of 0.1 - 0.5 mm.

3. The preparation method according to claim 1, characterized in that, The metal fiber is a metal fiber of niobium, titanium, magnesium or zirconium.

4. The preparation method according to claim 1, characterized in that, In Step (2), the aluminum alloy casting is carried out at 700 - 720 °C, the delay time is 5 s, and the diameter of the cast bar is 5 mm.

5. The preparation method according to claim 1, characterized in that, In Step (3), the diameter of the rolling head during surface nanocrystallization is a WC / Co ball with a diameter of 14 mm, and the parameters are: the feeding speed of the rolling head is 0.1 mm / s, the single indentation depth is 50 μm, and it is repeated 5 times on the surface of the plate, with a total indentation depth of 250 μm.

6. A gradient fiber structure metal bar or cable prepared by the preparation method according to any one of claims 1 - 5.

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