A directional gradient columnar crystal structure copper pipe material and a preparation method thereof

Abstract

The application discloses a kind of directional gradient columnar crystal structure copper pipe material and preparation method thereof, material composition is expressed as percentage by weight: Cu is greater than or equal to 99.9%, impurity is less than or equal to 0.1%, and its preparation steps are: pure copper smelting, directional solidification.The copper pipe material has the characteristics of parallel arrangement gradient columnar crystal structure, the long axis direction of columnar crystal is parallel to the axial direction of copper pipe, and the width of columnar crystal gradually decreases from the edge of copper pipe to the inside of copper pipe, showing a gradient structure.The copper pipe material has excellent electrical conductivity and plasticity, with an electrical conductivity of 103% of the international annealed copper standard (IACS), an elongation of 58%, and is suitable for high-frequency AC power grid, high-frequency induction heating equipment, etc.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal material preparation, and particularly relates to a directional gradient columnar crystal structure copper pipe material and a preparation method thereof. BACKGROUND

[0002] With the rapid development of China's economy, super / ultra high voltage transmission lines have been built and put into operation, and the voltage level is continuously improved. As a core component of the power grid, the metal conductor directly affects the transmission efficiency. For super / ultra high voltage AC power grid, due to the "skin effect" of current, the current distribution in the conductor is uneven, and the current is concentrated in the thin layer of the conductor surface. The closer to the surface of the conductor, the greater the current density, while the current in the interior of the conductor is smaller, resulting in a decrease in the effective current-carrying area of the conductor, and an increase in the effective resistance of the conductor, and a corresponding increase in the power loss.

[0003] At present, hollow copper conductors are often used to replace solid copper conductors to reduce the skin effect resistance and make the skin effect area and the cross-sectional area of the wire as same as possible. The hollow copper conductor is prepared by high-purity copper (> 99.99%) through semi-continuous ingot casting, water-sealed extrusion, drawing, annealing process or horizontal continuous casting pipe blank, skinning, cold rolling, annealing process. The above method not only has complex process, but also causes a large number of grain boundaries, sub-grain boundaries, dislocations, vacancies and other defects in the conductor due to the deformation process such as extrusion and drawing, which causes electron scattering and affects the electrical conductivity. At the same time, in order to further improve the electrical conductivity of the hollow copper conductor, the surface of the conductor is plated with silver to reduce the resistance and power loss. However, this method has great difficulty in welding and high cost. Single crystal continuous casting technology is a common method for preparing single crystal copper or columnar crystal copper, and the convex or micro-convex solid-liquid interface is a necessary condition for the evolution of crystal from polycrystal to single crystal in the process of single crystal continuous casting. However, impurity elements tend to accumulate on the surface of the material, which needs to be removed by secondary processing. Therefore, it is urgent to develop a high-conductivity copper pipe material and a low-cost and efficient preparation method thereof. SUMMARY

[0004] The present application aims to provide a directional gradient columnar crystal structure copper pipe material and a preparation method thereof. The copper pipe material has the microstructure characteristics of parallel gradient columnar crystals, the long axis direction of the columnar crystal is parallel to the axial direction of the copper pipe, and the width of the columnar crystal gradually decreases from the edge of the copper pipe to the interior of the copper pipe, showing a gradient structure. The copper pipe has excellent performance, not only high electrical conductivity, but also high elongation, and is suitable for high-frequency AC power grid, high-frequency induction heating equipment and the like. The material preparation process is simple, low in cost, and easy to popularize and popularize.

[0005] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0006] In a first aspect, the present application provides a directional gradient columnar crystal structure copper pipe material, the composition of which is pure Cu, Cu≥99.9%, and impurities≤0.1% by weight percentage.

[0007] The oriented gradient columnar crystal structure copper pipe material has parallel arranged gradient columnar crystals, the long axis direction of the columnar crystals is parallel to the axial direction of the oriented gradient columnar crystal structure copper pipe material, and the width of the columnar crystals gradually decreases from the edge to the inside of the copper pipe, forming a gradient structure.

[0008] Further, the oriented gradient columnar crystal structure copper pipe material has a size of an outer diameter of 5-150 mm and a thickness of 0.5-25 mm.

[0009] Further, the oriented gradient columnar crystal structure copper pipe material has excellent electrical conductivity and plasticity, the electrical conductivity reaches 103% of the international annealed copper standard (IACS) electrical conductivity, and the elongation reaches 58%.

[0010] In a second aspect, the present application provides a device for preparing the oriented gradient columnar crystal structure copper pipe material of the first aspect, which comprises a furnace body, a thermocouple, a graphite crucible, a graphite mold, a cooling tank, a traction roller and a traction rod, the graphite crucible is arranged in the furnace body, a graphite runner is arranged at the bottom of the graphite crucible, a first end of the graphite runner is connected with the graphite crucible through an electromagnetic valve, a second end of the graphite runner is connected with a first end of the graphite mold, a graphite core is arranged in the cavity of the graphite mold, the axis of the graphite core is coincident with the axis of the graphite mold, a first end of the graphite core is connected with the inner wall of the graphite mold, a second end of the graphite core is flush with a second end of the graphite mold, the cooling tank is arranged at one side of the second end of the graphite mold, the solidified and formed copper pipe is connected with the traction rod, the traction rod is driven by the traction roller to pull the copper pipe to the cooling tank, an induction coil is arranged around the graphite crucible, the graphite runner and the graphite mold, and a thermocouple is arranged inside the graphite crucible, on the graphite runner and at the outlet of the graphite mold.

[0011] In a third aspect, the present application further provides a method for preparing the oriented gradient columnar crystal structure copper pipe material of the first aspect, which comprises the following steps:

[0012] In the first step, the pure copper raw material is added to the graphite crucible, the furnace cover is covered, vacuum is extracted to 1x10 -3 Pa, and high-purity argon gas with a pressure of 0.04-0.06 MPa is filled into the furnace body;

[0013] In the second step, the graphite crucible is heated by the induction coil, after the raw material is melted, the melt is kept at 1100-1150℃ for 30 minutes, then the electromagnetic valve is opened, the melt in the graphite crucible is introduced into the preheated graphite mold which is horizontally placed through the preheated graphite runner;

[0014] Third step: one end of the traction rod with jagged surface is inserted into the forming cavity of the graphite mold, the melt is solidified in the forming cavity to obtain a formed copper pipe, the formed copper pipe is connected with the traction rod, the traction rod is driven by the traction roller, and the formed copper pipe is pulled into the cooling water in the cooling tank at a certain pulling rate.

[0015] Further, in the first step, the purity of the high-purity argon gas is not less than 99.99%.

[0016] Further, in the second step, the temperature of the preheated graphite runner is consistent with the holding temperature of the melt.

[0017] Further, in the third step, the melt is solidified in the forming cavity to obtain a formed copper pipe, the grain competitive growth is carried out with a concave solid-liquid interface in the initial solidification stage, the epitaxial growth is carried out with a planar solid-liquid interface in the stable grain growth stage, a gradient columnar crystal structure with "outer thick and inner thin" is obtained, and meanwhile, the position of the solid-liquid interface is inside the graphite mold and close to the outlet position of the graphite mold, so as to reduce the surface defects of the prepared copper pipe, that is, the temperature of the melt entering the first end of the preheated graphite mold, that is, the inlet, is controlled to be 1100-1150 DEG C, the temperature of the copper pipe material at the second end of the graphite mold, that is, the outlet, is controlled to be 1090-1120 DEG C, one end of the traction rod is inserted into the forming cavity of the graphite mold by 3-8 mm, the other end of the traction rod is located on one side of the traction roller, so as to be pulled, and before pulling, it is ensured that part of the traction rod is in the cooling water. In order to realize the grain competitive growth, the formed copper pipe is pulled at an initial pulling rate of 500 mm / min when the melt contacts with the traction rod and starts to solidify and form. In order to realize the stable grain growth, the formed copper pipe is immediately pulled into the cooling water at a stable pulling rate of 1-100 mm / min when the formed copper pipe enters the cooling water. The flow rate of the cooling water is 0.5-20 m 3 / h, the above settings obtain the solid-liquid interface, and realize the continuous preparation of the copper pipe material with a directional gradient columnar crystal structure.

[0018] Compared with the prior art, the present application has the following obvious advantages: (1) the copper pipe material with a directional gradient columnar crystal structure is obtained, the defects such as transverse grain boundaries are eliminated, the gradient columnar crystals arranged in parallel greatly improve the electrical conductivity and plasticity, the electrical conductivity reaches 103% of the international annealed copper standard (IACS), and the elongation rate reaches 58%; (2) the traditional manufacturing processes such as extrusion, drawing, annealing and silver plating of the copper pipe conductor are avoided, the energy consumption and time are saved, the efficiency is improved, and the cost is reduced; (3) the purity requirement of the raw material is low, the directional solidification process reduces the impurity elements in the copper pipe, part of the impurity elements are segregated at the longitudinal grain boundaries in the core of the material, and the influence of the impurity on the electrical conductivity is reduced; (4) the material is clean and pollution-free after one-time net forming, the environment is friendly, and it is conducive to realize green manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1Crystal growth schematic of the solid-liquid interface of the concave and planar shape.

[0020] Figure 2 Schematic diagram of the process of the directional gradient columnar structure copper pipe material.

[0021] Figure 3 Schematic diagram of the process of the directional gradient columnar structure copper pipe material.

[0022] Figure 4 Three-dimensional structure diagram of different perspectives (a-b) of the graphite mold and core.

[0023] Figure 5 Microstructure diagram of the copper pipe material prepared in Example 1.

[0024] Figure 6 Performance diagram of the copper pipe material prepared in Example 1.

[0025] Wherein, 1 furnace body; 2-1 first thermocouple; 2-2 second thermocouple; 2-3 third thermocouple; 3 air inlet; 4 graphite crucible; 5 melt; 6 air outlet; 7 electromagnetic valve; 8-1 first heating coil; 8-2 second heating coil; 8-3 third heating coil; 9 graphite sprue; 10 graphite mold; 11 graphite core; 12 cooling tank; 13 formed copper pipe; 14 traction roller; 15 traction rod. DETAILED DESCRIPTION

[0026] The present application will be further described below in conjunction with specific embodiments.

[0027] It should be noted that the terms such as "upper", "lower", "left", "right", "intermediate" and the like cited in the present specification are only for the convenience of clear description, and are not intended to limit the scope of implementation, and the change or adjustment of the relative relationship is also regarded as the scope of implementation of the present application without substantial change of the technical content.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] The specific conditions not specified in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used without specifying the manufacturer are all conventional products that can be purchased on the market.

[0030] As used herein, the term "about" is used to provide flexibility to a given term, measurement, or value associated with a term, measurement, or value. One of ordinary skill in the art can readily determine the degree of flexibility afforded by the term "about" based on the context of the particular variable.

[0031] As used herein, the term "at least one of' is intended to mean one or more of. For example, "at least one of A, B and C" is intended to mean: A alone; B alone; C alone; as well as any combination of A, B and C.

[0032] Concentrations, amounts, and other numerical data can be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be construed as having been followed to the right of the recited range to indicate the inclusion of all individual numerical values and sub-ranges within the given ranges. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly recited values of 1 to about 4.5, but also include individual values and sub-ranges within the indicated range, such as 2, 3, and 4 and 1 to 3, 2 to 4, etc. The same principle applies to ranges reciting only one numerical value, such as "less than about 4.5," which should be interpreted to include all of the above-referenced values and ranges. Furthermore, such interpretations are meant to apply regardless of the specific breadth of the range being described.

[0033] The concepts and principles of the present invention are:

[0034] (1) In metal conductors, defects such as grain boundaries, sub-grain boundaries, dislocations, vacancies, etc. can cause electron scattering, hinder electron migration, and reduce electrical conductivity. The more defects, the lower the electrical conductivity of the conductor. The parallel arrangement of columnar crystal structure can greatly reduce the number of defects such as grain boundaries, sub-grain boundaries, dislocations, vacancies, etc. At the same time, the long axis of the columnar crystal is parallel to the axis of the conductor, eliminating the radial distribution of grain boundaries and other defects in the conductor. The grain boundaries are completely parallel to the axis of the conductor, obtaining excellent electron transmission channels. In addition, due to the "skin effect" of the current, the current is concentrated in the surface layer of the conductor. The wider the surface layer of the columnar crystal, the better the electrical conductivity. The gradient columnar crystal structure of "thick outside and thin inside", that is, from the edge to the inside of the copper pipe, the width of the columnar crystal gradually decreases, which can improve the electrical conductivity.

[0035] (2) Continuous directional solidification technology can be used to prepare long-size solid conductors, but for hollow copper pipes, the liquid surface is in a ring-shaped state, which is difficult to solidify and form, and is prone to deformation, scratching, and breaking. In addition, the temperature difference between the inner and outer diameters of the copper pipe during solidification generates a radial temperature field, which causes radial dendrite growth and destroys the axial columnar crystal structure. The present invention uses casting software to calculate the solidification interface characteristic parameters.

[0036] Firstly, the temperature field and solidification process of the hollow copper tube with different size specifications are simulated by Procast casting software, so as to solve the problems of ① leakage of the melt due to the action of gravity and static pressure and surface deformation of the copper tube; ② the surface of the copper tube is scratched, cracked and even pulled off due to the friction between the formed copper tube and the inner surface of the graphite mold. The position of the solid-liquid interface needs to meet the conditions of being inside the mold and being close to the outlet position of the mold. Inside the mold, the center part of the copper tube has been solidified, while the surface exists a liquid film layer, and solidifies rapidly after leaving the mold.

[0037] Secondly, the concave solid-liquid interface promotes the growth of the edge grain to the inside, forming the organization structure of edge coarse grain and middle fine grain. The planar solid-liquid interface maintains the grain organization and continues to grow by extension. In the initial stage of solidification, the concave solid-liquid interface competes for growth, and in the steady state, the planar solid-liquid interface grows by extension, so that the gradient columnar crystal structure of "coarse outside and fine inside" can be obtained. Figure 1 When the crystal grows in the concave solid-liquid interface, impurity elements such as O, C and Fe are easily discharged into the grain boundary of the core of the material, reducing the impurity content of the surface grain and improving the electrical conductivity.

[0038] When the heat dissipation is less than the heat source, the solid-liquid interface is concave, and when the heat dissipation is equal to the heat source, the solid-liquid interface is planar. According to the composition undercooling criterion: G L The larger the R value, the greater the temperature gradient and the smaller the pulling rate, and the more likely the solid-liquid interface to grow in a planar interface mode. Increasing the pulling rate or the melt temperature can obtain a concave solid-liquid interface. However, increasing the temperature gradient or the pulling rate, the solid-liquid interface moves to the second end of the graphite mold, i.e. the outlet direction, and is easy to leak; reducing the temperature gradient or the pulling rate, the solid-liquid interface moves to the inside of the mold, and the surface friction damage of the copper tube is increased.

[0039] Thirdly, in order to reduce the influence of the radial temperature gradient on the solid-liquid interface, the temperature difference between the surface temperature of the graphite core and the surface temperature of the graphite mold cavity at the same cross section is as small as possible, and the temperature difference is less than 50℃, so that the graphite material with high thermal conductivity is used as the core and the mold.

[0040] Finally, the solidification process is calculated by simulation software, so as to realize the grain competitive growth with concave solid-liquid interface in the initial solidification stage, realize the epitaxial growth with planar solid-liquid interface in the stable grain growth stage, and obtain the gradient columnar crystal structure with "outer coarse and inner fine", meanwhile, the position of the solid-liquid interface is in the inside of the casting mold and close to the position of the casting mold outlet, so as to reduce the surface defects of the prepared copper pipe, that is, the temperature of the melt entering the first end of the preheated graphite casting mold (the inlet) is 1100-1150 DEG C, the temperature of the copper pipe at the second end of the graphite casting mold (the outlet) is 1090-1120 DEG C, one end of the pulling rod is inserted into the forming cavity of the graphite casting mold by 3-8 mm, the other end of the pulling rod is at the side of the pulling roller, so as to be pulled, and the part of the pulling rod is ensured to be in the cooling water of the cooling tank before pulling. In order to realize the grain competitive growth, the forming copper pipe is pulled at the initial pulling speed of 500 mm / min when the melt in the forming cavity contacts with the pulling rod and the melt starts to solidify and form, after a certain distance (the distance from the graphite casting mold to the cooling tank is 10-100 mm), when the forming copper pipe reaches the first end of the cooling tank (the forming copper pipe enters the cooling water), in order to realize the stable grain growth, the forming copper pipe is pulled into the cooling water at the stable pulling speed of 1-100 mm / min, the flow of the cooling water is 0.5-20 m 3 / h, the solid-liquid interface is obtained, and the copper pipe material with the gradient columnar crystal structure of "outer coarse and inner fine" is continuously prepared. Figure 2

[0041] In combination Figure 3 , the application provides a device for preparing the copper pipe material with the gradient columnar crystal structure, which comprises a furnace body 1, a thermocouple, a graphite crucible 4, a graphite casting mold 10, a cooling tank 12, a pulling roller 14 and a pulling rod 15, the graphite crucible 4 is arranged in the furnace body 1, a graphite runner 9 is arranged at the bottom of the graphite crucible 4, the graphite crucible 4 and the first end of the graphite runner 9 are communicated through an electromagnetic valve 7, the second end of the graphite runner 9 is connected with the first end of the graphite casting mold 10, a graphite core 11 is arranged in the cavity of the graphite casting mold 10, the axis of the graphite core 11 is coincident with the axis of the graphite casting mold 10, the first end of the graphite core 11 is connected with the inner wall of the graphite casting mold 10, the second end of the graphite core 11 is flush with the second end of the graphite casting mold 10, the cooling tank 12 is arranged at one side of the second end of the graphite casting mold 10, the solidified and formed copper pipe 13 is connected with the pulling rod 15, the pulling rod 15 is driven by the pulling roller 14 to pull the copper pipe 13 to the cooling tank 12, the periphery of the graphite crucible 4, the graphite runner 9 and the graphite casting mold 10 is provided with an induction coil, and the inside of the graphite crucible 4, the graphite runner 9 and the outlet of the graphite casting mold 10 are provided with thermocouples.

[0042] ​In a preferred embodiment of the present application, the graphite core 11 is arranged in the cavity of the graphite casting mold 10, which is composed of a sprue and a forming cavity. In order to avoid the rupture of the copper pipe caused by insufficient melt supply during directional solidification, the diameter of the first end of the sprue is greater than that of the second end, and the difference between the diameters of the two ends is ≥1 times. The diameter of the first end of the forming cavity is the same as that of the second end. The diameter of the forming cavity of the graphite casting mold 10 is consistent with the outer diameter of the copper pipe to be prepared.

[0043] In combination Figure 4 In a more preferred embodiment of the present application, the cavity is composed of a sprue and a forming cavity. The diameter of the sprue gradually decreases from the first end to the second end, and the difference between the diameters of the two ends is ≥1 times. The diameter of the first end of the forming cavity is the same as that of the second end.

[0044] In combination Figure 4 In a preferred embodiment of the present application, the graphite core 11 is arranged in the forming cavity of the graphite casting mold 10. The axis of the graphite core 11 coincides with the axis of the graphite casting mold 10. The first end of the graphite core 11 is connected to the inner wall of the graphite casting mold 10 through a support (graphite reinforcing rib). The second end of the graphite core 11 is flush with the second end of the graphite casting mold 10.

[0045] In a preferred embodiment of the present application, the furnace body 1 is provided with an air inlet 3 and an air outlet 6 on both sides.

[0046] In a preferred embodiment of the present application, the second end of the graphite runner 9 is consistent with the inner diameter of the first end of the graphite casting mold 10.

[0047] In a preferred embodiment of the present application, the graphite core 11 is a cylindrical structure, and the outer diameter of the graphite core 11 is consistent with the inner diameter of the copper pipe to be prepared.

[0048] In a preferred embodiment of the present application, the distance from the second end of the graphite casting mold 10 to the cooling tank 12 is 10-100 mm.

[0049] In a preferred embodiment of the present application, the cooling tank 12 is filled with a cooling medium, and the cooling medium is water.

[0050] In a preferred embodiment of the present application, the graphite crucible 4 is provided with a first induction coil 8-1, the graphite runner 9 is provided with a second induction coil 8-2, and the graphite casting mold 10 is provided with a third induction coil 8-3.

[0051] In a preferred embodiment of the present application, the graphite crucible 4 is provided with a first thermocouple 2-1, the graphite runner 9 is provided with a second thermocouple 2-2, and the second end of the graphite casting mold 10 is provided with a third thermocouple 2-3.

[0052] In a preferred embodiment of the present application, the purity of the graphite runner, graphite mold and graphite core is not less than 99.99%.

[0053] In a preferred embodiment of the present application, the pulling rod is made of pure copper material, in order to ensure that the melt in the forming cavity solidifies when contacting with the pulling rod and the heat can be dissipated in time, the length of the pulling rod needs to be long enough so that a part of the pulling rod is in the cooling tank before pulling, in order to make the first end of the pulling rod have better connection effect with the solidified formed copper pipe, the first end of the pulling rod is provided as a hollow ring structure with sawtooth-shaped inner and outer surfaces, the remaining part is a solid structure, and the length of the hollow ring part is at least 8 mm.

[0054] Based on the above device, the working process is as follows:

[0055] The pure copper raw material is added into the graphite crucible 4, the furnace cover of the furnace body 1 is covered, vacuum is extracted to 1x10 -3 Pa, high-purity argon gas with a pressure of 0.04-0.06 MPa is filled into the furnace body 1;

[0056] The first induction coil 8-1 is used to heat the graphite crucible 4, after the raw material is melted, the melt is kept at 1100-1150℃ for 30 minutes, the second induction coil 8-2 is used to preheat the graphite runner 9, the preheating temperature is consistent with the melt temperature, the electromagnetic valve 7 is opened, the melt in the graphite crucible 4 is introduced into the cavity of the horizontally placed preheated graphite mold 10 through the preheated graphite runner 9;

[0057] The third induction coil 8-3 is used to heat the graphite mold 10, so that the melt temperature at the first end of the graphite mold 10, i.e. the inlet, is 1100-1150℃, the temperature of the formed copper pipe at the second end of the graphite mold 10, i.e. the outlet, is 1090-1120℃, the distance between the graphite mold 10 and the cooling tank 12 is set to 10-100 mm to establish a temperature gradient in the axial direction, one end of the pulling rod 15 with a sawtooth-shaped surface is inserted into the forming cavity of the graphite mold 10 by 3-8 mm, so that part of the pulling rod is in the cooling water of the cooling tank 12, the melt is solidified in the forming cavity of the graphite mold 10 to obtain the formed copper pipe 13, the formed copper pipe 13 is connected with the pulling rod 15, the pulling rod 15 is driven by the pulling roller 14, when the melt contacts with the pulling rod, the melt starts to solidify and form, the formed copper pipe 13 is pulled at an initial pulling rate of 500 mm / min, when one end of the formed copper pipe 13 is pulled into the cooling water of the cooling tank 12, it is immediately pulled at a stable pulling rate of 1-100 mm / min, and the flow rate of the cooling water is 0.5-20 m 3 / h.

[0058] Example 1

[0059] (1) Pure copper smelting

[0060] 99.9% pure copper raw material was added to a graphite crucible, the furnace cover was covered, vacuum was extracted to 1 x 10 -3 Pa, 0.04 MPa 99.99% pure argon was filled into the furnace, the graphite crucible was heated by an induction coil, after the raw material was melted, it was kept at 1130°C for 30 minutes and then was left to stand.

[0061] (2) Directional solidification

[0062] ①According to the size of the copper pipe to be prepared (outer diameter: 50 mm, thickness: 10 mm), the first end diameter of the graphite casting mold sprue was set to 100 mm, the second end diameter was set to 50 mm, the forming cavity diameter was set to 50 mm, a cylindrical graphite core with a diameter of 30 mm was arranged in the forming cavity of the graphite casting mold, the core axis was coincided with the graphite casting mold cavity axis, and the vertical distance between the core and the forming cavity was 10 mm.

[0063] ②The Procast casting software was used to simulate and calculate the solidification temperature field and process of the copper pipe in the graphite casting mold, the solid-liquid interface was selected at 5 mm inside the casting mold near the outlet, the solid-liquid interface first grew in a concave shape, and then grew in a flat interface stable epitaxial growth.

[0064] ③The electromagnetic valve was opened, and the melt in the crucible was introduced into the forming cavity of the preheated graphite casting mold which was placed horizontally by using the preheated graphite sprue at 1130°C.

[0065] ④The graphite casting mold was heated by an induction coil to ensure that the melt temperature entering the graphite casting mold was 1130°C, the copper pipe temperature at the outlet of the graphite casting mold was 1110°C, and the distance between the graphite casting mold and the cooling tank was 20 mm, so as to establish a temperature gradient in the axial direction.

[0066] ⑤A traction rod with a sawtooth surface was inserted into the forming cavity of the graphite casting mold by 5 mm, the length of the traction rod was 1000 mm, the other end of the traction rod was located at the right side of the traction roller, part of the traction rod was in the cooling water of the cooling tank, the melt in the forming cavity contacted with the traction rod to obtain a formed copper pipe, the formed copper pipe was connected with the traction rod for drawing, the initial drawing rate was 500 mm / min, when the first end of the formed copper pipe entered the cooling water after drawing for 20 mm, the formed copper pipe was immediately drawn into the cooling water at a drawing rate of 10 mm / min, the circulating water flow rate of the cooling water was 5 m 3 / h.

[0067] (3) Microstructure and property detection

[0068] A directional gradient columnar crystal structure copper pipe material was obtained, with an outer diameter of 50 mm and a thickness of 10 mm, as shown in Figure 5The microstructure features parallelly arranged columnar crystals, the long axis direction of the columnar crystals is parallel to the axial direction of the copper tube, and the width of the columnar crystals gradually decreases from the edge to the inside of the copper tube, showing a gradient structure. The prepared copper tube has excellent electrical conductivity and plasticity, the electrical conductivity reaches 103% of the international annealed copper standard (IACS), and the elongation reaches 58% (as shown in Table 1). Figure 6 ).

[0069] Example 2

[0070] In this example, the composition is 99.9% Cu (wt%), and the other steps are the same as in Example 1. The melting temperature is 1130°C, the cavity diameter of the graphite mold is 50 mm, a cylindrical graphite core with a diameter of 30 mm is arranged in the forming cavity of the graphite mold, the core axis is coincident with the cavity axis, and the vertical distance between the core and the cavity is 10 mm. The melt temperature in the mold is 1130°C, the copper tube temperature at the outlet of the mold is 1110°C, the distance between the graphite mold and the cooling water tank is 20 mm, the pulling rod is inserted into the cavity of the graphite mold by 5 mm, the initial drawing rate is 500 mm / min, the drawing is 20 mm, then the stable drawing rate is 20 mm / min, the circulating water flow is 5 m 3 / h, and a directional gradient columnar crystal structure copper tube material with an outer diameter of 50 mm and a thickness of 10 mm is obtained. The microstructure features parallelly arranged columnar crystals, the long axis direction of the columnar crystals is parallel to the axial direction of the copper tube, and the width of the columnar crystals gradually decreases from the edge to the inside of the copper tube, showing a gradient structure. The prepared copper tube has excellent electrical conductivity and plasticity, the electrical conductivity reaches 102% of the international annealed copper standard (IACS), and the elongation reaches 51%.

[0071] Example 3

[0072] In this example, the composition is 99.9% Cu (wt%), and the other steps are the same as in Example 1. The melting temperature is 1130°C, the cavity diameter of the graphite mold is 50 mm, a cylindrical graphite core with a diameter of 30 mm is arranged in the forming cavity of the graphite mold, the core axis is coincident with the cavity axis, and the vertical distance between the core and the cavity is 10 mm. The melt temperature in the mold is 1130°C, the copper tube temperature at the outlet of the mold is 1110°C, the distance between the graphite mold and the cooling water tank is 20 mm, the pulling rod is inserted into the cavity of the graphite mold by 5 mm, the initial drawing rate is 500 mm / min, the drawing is 20 mm, then the stable drawing rate is 5 mm / min, the circulating water flow is 5 m 3A copper tube with a directional gradient columnar crystal structure was obtained by [method name missing], with an outer diameter of 50 mm and a thickness of 10 mm. The microstructure consisted of parallel-arranged columnar crystals, with the long axis of the columnar crystals parallel to the axis of the copper tube. The width of the columnar crystals gradually decreased from the edge to the interior, exhibiting a gradient structure. The prepared copper tube possessed excellent electrical conductivity and ductility, achieving an electrical conductivity of 101% according to the International Association of Advanced Materials (IACS) standard for annealed copper, and an elongation of 48%.

[0073] Example 4

[0074] The composition prepared in this embodiment is 99.9% Cu (weight percentage). Other steps are the same as in Example 1. The melting temperature is 1130℃, the cavity diameter of the graphite mold is 50mm, and a cylindrical graphite core with a diameter of 30mm is placed inside the forming cavity of the graphite mold. The core axis coincides with the cavity axis, and the vertical distance between the core and the cavity is 10mm. The melt temperature inside the mold is 1130℃, the copper pipe temperature at the mold outlet is 1110℃, the distance between the graphite mold and the cooling water tank is 10mm, the traction rod is inserted 5mm into the cavity of the graphite mold, the initial pulling speed is 500mm / min, the pulling speed is 20mm, and then the stable pulling speed is 10mm / min. The circulating water flow rate is 10m³ / min. 3 A copper tube with a directional gradient columnar crystal structure was obtained by [method name missing], with an outer diameter of 50 mm and a thickness of 10 mm. The microstructure consisted of parallel-arranged columnar crystals, with the long axis of the columnar crystals parallel to the axis of the copper tube. The width of the columnar crystals gradually decreased from the edge to the interior, exhibiting a gradient structure. The prepared copper tube possessed excellent electrical conductivity and ductility, achieving an electrical conductivity of 103% according to the International Association of Advanced Materials (IACS) standard for annealed copper, and an elongation of 56%.

[0075] Example 5

[0076] The composition prepared in this embodiment is 99.9% Cu (weight percentage). Other steps are the same as in Example 1. The melting temperature is 1100℃, the cavity diameter of the graphite mold is 50mm, and a cylindrical graphite core with a diameter of 30mm is placed inside the forming cavity of the graphite mold. The core axis coincides with the cavity axis, and the vertical distance between the core and the cavity is 10mm. The melt temperature inside the mold is 1100℃, the copper pipe temperature at the mold outlet is 1090℃, the distance between the graphite mold and the cooling water tank is 20mm, the traction rod is inserted 5mm into the cavity of the graphite mold, the initial pulling speed is 500mm / min, the pulling speed is 20mm, and then the stable pulling speed is 10mm / min. The circulating water flow rate is 5m³ / min. 3mm, the microstructure feature is parallel arrangement of columnar crystal, the long axis direction of columnar crystal is parallel to the axial direction of copper tube, from the edge to the inside of copper tube, the width of columnar crystal gradually decreases, showing gradient structure. The prepared copper tube has excellent electrical conductivity and plasticity, the electrical conductivity reaches 101% of international annealed copper standard (IACS) electrical conductivity, and the elongation reaches 49%.

[0077] Example 6

[0078] In this example, the composition is 99.9% Cu (wt%), other steps are the same as example 1, the smelting temperature is 1150℃, the cavity diameter of graphite mold is 150mm, a cylindrical graphite core with a diameter of 50mm is arranged in the forming cavity of graphite mold, the core axis is coincided with the cavity axis, the vertical distance between the core and the cavity is 25mm, the melt temperature in the mold is 1150℃, the copper tube temperature at the outlet of mold is 1100℃, the distance between graphite mold and cooling water tank is 10mm, the pulling rod is inserted into the cavity of graphite mold by 8mm, the initial drawing rate is 500mm / min, drawing 10mm, then the stable drawing rate is 1mm / min, the circulating water flow is 20m 3 mm, the microstructure feature is parallel arrangement of columnar crystal, the long axis direction of columnar crystal is parallel to the axial direction of copper tube, from the edge to the inside of copper tube, the width of columnar crystal gradually decreases, showing gradient structure. The prepared copper tube has excellent electrical conductivity and plasticity, the electrical conductivity reaches 101% of international annealed copper standard (IACS) electrical conductivity, and the elongation reaches 49%.

[0079] Example 7

[0080] In this example, the composition is 99.9% Cu (wt%), other steps are the same as example 1, the smelting temperature is 1150℃, the cavity diameter of graphite mold is 5mm, a cylindrical graphite core with a diameter of 4mm is arranged in the forming cavity of graphite mold, the core axis is coincided with the cavity axis, the vertical distance between the core and the cavity is 0.5mm, the melt temperature in the mold is 1150℃, the copper tube temperature at the outlet of mold is 1100℃, the distance between graphite mold and cooling water tank is 100mm, the pulling rod is inserted into the cavity of graphite mold by 3mm, the initial drawing rate is 500mm / min, drawing 100mm, then the stable drawing rate is 100mm / min, the circulating water flow is 0.5m 3 / h, a directional gradient columnar crystal structure copper tube material is obtained, with an outer diameter of 5 mm and a thickness of 0.5 mm, and the microstructure features parallelly arranged columnar crystals, the long axis direction of the columnar crystals is parallel to the axial direction of the copper tube, and the width of the columnar crystals gradually decreases from the edge to the inside of the copper tube, showing a gradient structure. The prepared copper tube has excellent electrical conductivity and plasticity, with an electrical conductivity of 101% of the international annealed copper standard (IACS) and an elongation of 50%.

[0081] Example 8

[0082] In this example, the composition is 99.9% Cu (wt%), and the other steps are the same as in Example 1. The melting temperature is 1100°C, the cavity diameter of the graphite mold is 10 mm, a cylindrical graphite core with a diameter of 8 mm is arranged in the forming cavity of the graphite mold, the core axis is coincident with the cavity axis, the vertical distance between the core and the cavity is 1 mm, the melt temperature in the mold is 1100°C, the copper tube temperature at the outlet of the mold is 1090°C, the distance between the graphite mold and the cooling water tank is 10 mm, the pulling rod is inserted into the cavity of the graphite mold by 4 mm, the initial drawing rate is 500 mm / min, the drawing is 10 mm, then the stable drawing rate is 5 mm / min, the circulating water flow is 2 m 3 / h, a directional gradient columnar crystal structure copper tube material is obtained, with an outer diameter of 5 mm and a thickness of 0.5 mm, and the microstructure features parallelly arranged columnar crystals, the long axis direction of the columnar crystals is parallel to the axial direction of the copper tube, and the width of the columnar crystals gradually decreases from the edge to the inside of the copper tube, showing a gradient structure. The prepared copper tube has excellent electrical conductivity and plasticity, with an electrical conductivity of 101% of the international annealed copper standard (IACS) and an elongation of 50%.

[0083] Example 9

[0084] In this example, the composition is 99.9% Cu (wt%), and the other steps are the same as in Example 1. The melting temperature is 1130°C, the cavity diameter of the graphite mold is 20 mm, a cylindrical graphite core with a diameter of 16 mm is arranged in the forming cavity of the graphite mold, the core axis is coincident with the cavity axis, the vertical distance between the core and the cavity is 2 mm, the melt temperature in the mold is 1130°C, the copper tube temperature at the outlet of the mold is 1100°C, the distance between the graphite mold and the cooling water tank is 10 mm, the pulling rod is inserted into the cavity of the graphite mold by 4 mm, the initial drawing rate is 500 mm / min, the drawing is 10 mm, then the stable drawing rate is 10 mm / min, the circulating water flow is 5 m 3mm, thickness 2mm, microstructure feature is parallel arrangement of columnar crystal, the long axis direction of columnar crystal is parallel to the axial direction of copper tube, from the edge to the inside of copper tube, the width of columnar crystal gradually decreases, showing gradient structure. The prepared copper tube has excellent electrical conductivity and plasticity, the electrical conductivity reaches 103% of international annealed copper standard (IACS) electrical conductivity, and the elongation reaches 56%.

[0085] Example 10

[0086] The prepared composition is 99.9% Cu (wt%), and other steps are the same as those in Example 1. The melting temperature is 1130°C. The cavity diameter of the graphite mold is 20mm. A cylindrical graphite core with a diameter of 10mm is arranged in the forming cavity of the graphite mold, the core axis is coincided with the cavity axis, the vertical distance between the core and the cavity is 5mm. The melt temperature in the mold is 1130°C, the copper tube temperature at the outlet of the mold is 1100°C, the distance between the graphite mold and the cooling water tank is 20mm, the pulling rod is inserted into the cavity of the graphite mold by 5mm, the initial pulling rate is 500mm / min, the pulling is 20mm, then the stable pulling rate is 20mm / min, the circulating water flow is 10m 3 mm, thickness 5mm, microstructure feature is parallel arrangement of columnar crystal, the long axis direction of columnar crystal is parallel to the axial direction of copper tube, from the edge to the inside of copper tube, the width of columnar crystal gradually decreases, showing gradient structure. The prepared copper tube has excellent electrical conductivity and plasticity, the electrical conductivity reaches 101% of international annealed copper standard (IACS) electrical conductivity, and the elongation reaches 49%.

[0087] Comparative Example 1

[0088] In document 1 "Development of Single Crystal Continuous Casting Equipment for Vacuum Melting and Argon Protection and Preparation of Single Crystal Copper", 99.99% pure copper is used, and the process parameters are: copper liquid temperature 1135°C, mold temperature 1108°C, continuous casting speed 20mm / min, cooling distance 25mm, and a single crystal copper wire with a length of 6.3m is continuously cast, the electrical conductivity is 99.6% of international annealed copper standard (IACS) electrical conductivity, and the elongation reaches 48%.

[0089] Comparative Example 2

[0090] In document 2 "Research on a Short Process Thin-walled Copper Tube Preparation Technology", standard cathode copper Cu (Cu+Ag>99.95%) is used, and the process parameters are: copper liquid temperature 1150°C, continuous casting speed 100mm / min, cooling water flow 0.5m 3 / h, with concave solid-liquid interface growth, a single crystal copper tube with a length of 6.3m is prepared, the electrical conductivity is 99.6% of international annealed copper standard (IACS) electrical conductivity, and the elongation reaches 48%. ​The copper tube with thickness of 1.8 mm has columnar dendrite microstructure and transverse grain boundary, and has electrical conductivity of 101% of international annealed copper standard (IACS) and elongation of 48%.

[0091] Comparative Example 3

[0092] The blank copper tube prepared by semi-continuous ingot casting, water sealed extrusion, drawing, annealing and other processes using 99.95% pure copper, and then prepared into silver plated copper rod by pretreatment, electrolytic cleaning, silver immersion, fixation, electrolytic silver plating and post-treatment processes, has electrical conductivity of 100% of international annealed copper standard (IACS).

[0093] Table 1 shows the process parameters and performance test results of the copper tube materials prepared in each example and comparative example.

[0094] Table 1 shows the process parameters and performance test results of the copper tube materials prepared in each example and comparative example.

[0095]

[0096]

[0097] As shown in Table 1, the single crystal copper rod prepared by similar continuous directional solidification process parameters with convex interface growth has lower performance, and the copper tube prepared by concave interface growth has transverse grain boundary and columnar dendrite, and the electrical conductivity and plasticity are limited. In addition, the performance of the copper rod prepared by horizontal continuous casting + cold deformation + silver plating method is also low.

[0098] The above examples are only the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples. For example, various forms of combinations of the schemes in the examples, any changes, modifications, substitutions, combinations made without departing from the spirit and principles of the present application are equivalent replacement methods, which are within the protection scope of the present application.

Claims

1. A method of making a directionally graded, columnar-grained copper tube material, characterized by, The device for preparing copper pipe material with directional gradient columnar crystal structure comprises the following steps: First step: add pure copper raw material into graphite crucible, cover the furnace cover, vacuumize to 1x10 -3 Pa, fill high-purity argon gas of 0.04~0.06MPa into the furnace body; In the second step, the graphite pouring gate is preheated to the same temperature as the holding temperature of the melt. In the third step, one end of the pulling rod is inserted into the forming cavity of the graphite casting mold, the melt is solidified in the forming cavity to obtain a formed copper pipe, the formed copper pipe is connected with the pulling rod, the pulling rod is driven by the pulling roller, and the formed copper pipe is pulled into the cooling water in the cooling tank at a certain pulling rate. The temperature difference between the surface temperature of the graphite core at the same cross section and the surface temperature of the graphite casting mold cavity is reduced, and the temperature difference is less than 50 DEG C. In the third step, the temperature of the melt entering the preheated graphite mold at the first end, i.e. the inlet, is 1100-1150°C, the temperature of the copper pipe material at the second end of the graphite mold, i.e. the outlet, is 1090-1120°C, one end of the pulling rod is inserted into the forming cavity of the graphite mold by 3-8 mm, and before pulling, part of the pulling rod is ensured to be in the cooling water. When the melt contacts the pulling rod and the melt starts to solidify and form, the formed copper pipe is pulled at an initial pulling rate of 500 mm / min. When the formed copper pipe enters the cooling water, the formed copper pipe is immediately pulled into the cooling water at a stable pulling rate of 1-100 mm / min. The flow rate of the cooling water is 0.5-20 m 3 / h. In the third step, the temperature of the melt entering the preheated graphite mold at the first end, i.e. the inlet, is 1100-1150°C, the temperature of the copper pipe material at the second end of the graphite mold, i.e. the outlet, is 1090-1120°C, one end of the pulling rod is inserted into the forming cavity of the graphite mold by 3-8 mm, and before pulling, part of the pulling rod is ensured to be in the cooling water. When the melt contacts the pulling rod and the melt starts to solidify and form, the formed copper pipe is pulled at an initial pulling rate of 500 mm / min. When the formed copper pipe enters the cooling water, the formed copper pipe is immediately pulled into the cooling water at a stable pulling rate of 1-100 mm / min. The flow rate of the cooling water is 0.5- 2. The method of claim 1, wherein, In the second step, the temperature of the preheated graphite pouring gate is consistent with the holding temperature of the melt.

3. The method of claim 1, wherein, The device comprises a furnace body, a thermocouple, a graphite crucible, a graphite casting mold, a cooling tank, a pulling roller and a pulling rod. The graphite crucible is arranged in the furnace body, the bottom of the graphite crucible is provided with a graphite pouring gate, the graphite crucible and the first end of the graphite pouring gate are connected through an electromagnetic valve, the second end of the graphite pouring gate is connected with the first end of the graphite casting mold, a graphite core is arranged in the cavity of the graphite casting mold, the axis of the graphite core is coincident with the axis of the graphite casting mold, the first end of the graphite core is connected with the inner wall of the graphite casting mold, the second end of the graphite core is flush with the second end of the graphite casting mold, the cooling tank is arranged on one side of the second end of the graphite casting mold, the solidified formed copper pipe is connected with the pulling rod, the pulling rod is driven by the pulling roller, the formed copper pipe is pulled to the cooling tank, the graphite crucible, the graphite pouring gate and the graphite casting mold are all provided with induction coils, and the graphite crucible, the graphite pouring gate and the graphite casting mold are all provided with thermocouples. The distance from the second end of the graphite casting mold to the cooling tank is 10-100 mm. A graphite core is arranged in the cavity of the graphite casting mold, the cavity is composed of a sprue and a forming cavity, the first end of the sprue has a larger diameter than the second end, the difference between the diameters of the two ends is greater than or equal to 1 times, and the diameters of the first end and the second end of the forming cavity are the same. The diameter of the forming cavity of the graphite casting mold is consistent with the outer diameter of the copper pipe material.

4. The method of claim 3, wherein, A graphite core is arranged in the forming cavity of the graphite casting mold, the axis of the graphite core is coincident with the axis of the graphite casting mold, the first end of the graphite core is connected with the inner wall of the graphite casting mold through a support, and the second end of the graphite core is flush with the second end of the graphite casting mold.

5. The method of claim 3, wherein, The pulling rod is made of pure copper material, the first end of the pulling rod is provided with a hollow ring structure with sawtooth-shaped inner and outer surfaces, and the remaining part is a solid structure. The length of the hollow ring structure is at least 8 mm.

6. A copper pipe material of a columnar grain structure with a directional gradient prepared by the method according to any one of claims 1 to 5, characterized in that, The composition of the copper pipe material is pure Cu, Cu is greater than or equal to 99.9%, and impurities are less than or equal to 0.1% by weight percentage. The copper pipe material has parallel gradient columnar crystals, the long axis direction of the columnar crystals is parallel to the axial direction of the copper pipe material, the width of the columnar crystals gradually decreases from the edge to the inside of the copper pipe material, and the columnar crystals have a gradient structure.

7. The oriented gradient columnar grain structure copper tube material of claim 6 wherein, The copper pipe material has excellent electrical conductivity and plasticity, the electrical conductivity reaches 103% of the international annealed copper standard electrical conductivity, and the elongation rate reaches 58%.

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