A medium-strength and high-conductivity guide bar and its preparation method

Abstract

The present invention discloses a medium-strength and high-conductivity conductor bar and a preparation method thereof, belonging to the technical field of industrial high-purity aluminum. The conductor bar is obtained by doping Ni and rare earth Re elements into high-purity aluminum ingots, and the rare earth Re element is La and Ce; the present invention adopts the means of microalloying, and steps such as using mixed rare earth elements and extrusion deformation are adopted to refine the grains inside the aluminum bar, and greatly improve the strength index of the aluminum bar conductor. The tensile strength of the conductor bar can reach 107 MPa, and the conductivity can reach 64.21% IACS.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial high-purity aluminum, and particularly relates to a medium-strength and high-conductivity conductor bar and a preparation method thereof. Background Art

[0002] High-purity aluminum is being used as a functional material for cutting-edge technologies such as electronic intelligence due to its excellent properties. The conductivity, resistivity coefficient, thermal conductivity, etc. of high-purity aluminum and industrial pure aluminum are greatly affected by impurities. The higher the purity, the higher the conductivity and thermal conductivity, and the lower the resistivity coefficient. Due to a series of unique and excellent properties of high-purity aluminum, it has been widely used in various sectors of the national economy and has gradually become an indispensable material for some high-tech fields such as superconducting cable stabilization and integrated circuit wiring.

[0003] At the present stage, high-purity aluminum products support high-energy physics research and play an inestimable role in detecting the basic particles of matter. For example, the superconducting structures and cables of the detectors at the European Organization for Nuclear Research use a considerable amount of high-purity aluminum from Hydro Aluminium. Another example is that high-purity aluminum is also widely used in rectifier wire materials in China.

[0004] Although high-purity aluminum has high conductivity, making it have a large application area in high-precision products, its low strength greatly reduces its functionality in the large-share market. For example, due to its low strength, it is not suitable for use as an overhead line conductor. And highly alloyed conductors, due to their low conductivity, are not suitable for application in the field of line core conductors. Therefore, it is necessary to study a conductor with medium strength and high conductivity, which can effectively improve its strength without significantly reducing its component purity, so as to improve the application rate of high-purity aluminum in superconducting wires and cable cores.

[0005] The prior art one discloses the development of a high-conductivity boron-containing aluminum conductor (Liu Shunhua, Wang Guiqin, Gao Hongwu, Li Changmao, Liang Xiaoli, Xiang Xiaoli, Xiang Binglun, Wang Wenjun. Development of High-Conductivity Boron-Containing Aluminum Conductor [J]. Electric Wire & Cable, 2003(04):16 - 19. DOI:10.16105 / j.cnki.dxdl.2003.04.004.). The conductivity and strength of the aluminum conductor are improved through three aspects: optimizing the composition of the high-conductivity aluminum rod, purification process, and recovery treatment. Finally, the conclusion is obtained that in terms of composition optimization, it can be summarized as "adding boron, restricting silicon, and relaxing iron". For the purification treatment, it is necessary to remove the gas inclusions in the aluminum liquid as much as possible, filter with a foam ceramic filter plate, and use solvents such as C2Cl6, ZnCl2, and salts of chlorine for gas refining. In the recovery stage, annealing is carried out using the waste heat of the aluminum rod. Finally, the resistivity is stabilized at (2.73 - 2.76)×10 -8Ω·m, while ensuring that the strength eb of a single wire is 165 - 185 MPa, and reducing the fluctuation range of the strength to within 15% for an aluminum conductor.

[0006] This technology uses 99.7% aluminum as raw material, and through boronization treatment to reduce the influence of its impurity elements on the resistivity and performance. Although there is a large improvement in strength and the resistivity also increases to a certain extent, this conductor material has high requirements for its silicon - iron ratio, and the composition control is relatively complex. Moreover, the refining agent used in the process is a toxic substance, which does not conform to the principle of safe production.

[0007] The prior art two discloses a high - conductivity aluminum alloy single wire for overhead conductors and its preparation method (CN113862525A). The technical key points are as follows: calculated by mass percentage, the aluminum alloy single wire consists of the following components: B: 0.005% - 0.05%, La: 0.020% - 0.025%, Er: 0.050% - 0.055%, Fe: 0 - 0.095%, Si: 0 - 0.065%, Cr + Mn + V + Ti ≤ 0.008%, and the balance is aluminum and inevitable trace impurity elements. This technology uses 99.85% industrial pure aluminum ingots with low cost, and by adding trace alloying elements (B, La, Er) to optimize and control the composition of the alloy, it develops an aluminum alloy single wire material with a conductivity ≥ 63.2% IACS (20 °C), a tensile strength ≥ 170 MPa, and an elongation ≥ 2.0%.

[0008] This technology aims to develop an overhead conductor. By adding trace rare - earth elements, it improves the microstructure, refines the grains, removes in - body and harmful impurities in the aluminum alloy, and increases the strength. However, due to its relatively high content of iron and silicon impurity elements, it has a greater impact on its electrical conductivity. This technology first rolls an aluminum alloy round rod with a diameter of Ф9.5 mm on a 14 - roll continuous rolling mill, and then draws the Ф9.5 mm aluminum alloy round rod on a wire - drawing machine at a rate of 12 m / s - 15 m / s. The wire - drawing temperature is controlled at 30 °C - 45 °C, the deformation amount is controlled at 10% - 12%, the wire - drawing die is a wire - drawing die with a nano - diamond composite coating, and the number of drawing passes is 12 times. Finally, an aluminum alloy round single wire with a diameter of 3.50 mm - 3.60 mm is obtained. The process is relatively complex and not conducive to mass production. Summary of the Invention

[0009] The purpose of the present invention is to provide a medium - strength and high - conductivity guide rod and its preparation method by leveraging the characteristics of high - purity aluminum, such as high electrical conductivity, high ductility, high corrosion resistance, and high stability. Through micro - alloying means and specific heat treatment processes, a conductor or wire core with high electrical conductivity and medium strength is obtained, which is of great significance for improving the efficiency of electric energy transmission in circuits and reducing power transmission line losses.

[0010] To achieve the above - mentioned purpose, the technical solutions adopted by the present invention are as follows:

[0011] A medium-strength and high-conductivity conductor bar, which is obtained by doping Ni and rare earth Re elements into high-purity aluminum ingots, and the rare earth Re elements are La and Ce; the chemical composition of the conductor bar is as follows:

[0012] Ni = 500 - 2000 ppm, La = 100 - 500 ppm, Ce = 200 - 1500 ppm, Fe is 10 - 20 ppm, Si is 5 - 30 ppm, and the balance is Al and unavoidable impurities.

[0013] Among the impurity components contained in the conductor bar: Cu < 10 ppm, Zn < 5 ppm, Ti < 5 ppm, Mg < 5 ppm.

[0014] The preparation method of the medium-strength and high-conductivity conductor bar includes the following steps:

[0015] (1) Batching and melting: Add refined aluminum ingots into an intermediate frequency furnace to melt and raise the temperature, then add metal Ni and rare earth Re in sequence and keep warm for a period of time; then cast into a cylindrical specimen after refining;

[0016] (2) Extrusion processing: Obtain a specimen with a diameter through extrusion processing of the cylindrical specimen;

[0017] (3) Annealing treatment: Conduct segmented annealing in a soaking furnace; the first stage is to raise the temperature to 150 °C, and the heating time is 120 minutes; the second stage is to keep warm at 150 °C for 120 min; the third stage is to raise the temperature to 360 °C, and the heating time is 180 min; the fourth stage is to keep warm at 360 °C for 1000 min;

[0018] (4) Extrusion processing:

[0019] Extrude and deform the annealed specimen using an extruder. The temperature of the extrusion cylinder is set at 370 - 380 °C (the optimal is 375 °C), the extrusion pressure is 135 - 150 MPa, the cooling water temperature is controlled at 0 - 30 °C, and finally the specimen is extruded into an aluminum rod with a diameter of 9.5 mm;

[0020] (5) Drawing: Draw and deform the 9.5 mm aluminum rod to make its diameter reach 8.5 mm;

[0021] (6) Post heat treatment: Perform aging heat treatment on the drawn aluminum rod through a resistance furnace to obtain the medium-strength and high-conductivity conductor aluminum rod.

[0022] In the above step (1), the purity of the refined aluminum ingot is ≥99.996%, and the purity of the metal Ni is 99.99%; the rare earth Re elements are La and Ce, and the rare earth Re elements are added to the aluminum liquid in the form of Al-Re master alloy, and the addition amounts of La and Ce are calculated according to the chemical composition of the guide rod.

[0023] In the above step (1), the melting process is specifically as follows: Add the refined aluminum ingot into the furnace to melt and heat up. When the aluminum ingot is heated up to 780 - 800 °C, add the metal Ni, then keep it warm for 3 - 6 minutes, stir evenly, stand for 3 minutes, and skim the surface scum; Heat up again to make the temperature rise to 740 - 750 °C, add the high-purity Al-Re master alloy wrapped with aluminum foil, then keep it warm for 5 minutes and then carry out refining.

[0024] In the above step (1), during the refining process, after controlling the temperature of the aluminum liquid to 730 - 750 °C, add the environmentally friendly granular refining agent, refine for 5 - 8 minutes to make the refining agent fully react with the aluminum liquid, and skim the slag; Finally, carry out casting, and control the temperature of the aluminum liquid to 720 - 730 °C during casting.

[0025] In the above step (6), the holding temperature of the heat treatment process is 130 °C, and the holding time is 15 hours.

[0026] After heat treatment, the average grain size of the aluminum rod is 60.33 μm; the tensile strength of the guide rod can reach 107 MPa, and the conductivity can reach 64.21% IACS.

[0027] The design principle and beneficial effects of the present invention are as follows:

[0028] 1) The present invention uses Al99.996% refined aluminum prepared by the three-layer liquid electrolysis method, high-quality pure Ni99.99% metal, and high-purity Al-Re (La\Ce) master alloy as raw materials. The high-quality raw materials can largely avoid the introduction of impurity elements, which is beneficial to the conductivity of the conductor aluminum rod.

[0029] 2) The present invention uses an intermediate frequency furnace for melting, which can ensure the full alloying of the metal Ni, has a high melting efficiency, and at the same time the melt can be fully stirred, which is beneficial to the composition uniformity and scum removal. And an environmentally friendly granular refining agent is used to purify the aluminum liquid, making the bubbles sufficiently dispersed and fine, and the degassing and slag removal effects are good, and the melt purity is high.

[0030] 3) The product of the present invention uses the means of microalloying, and adopts steps such as mixed rare earth elements and extrusion deformation, so that the grains inside the aluminum rod are refined, and the strength index of the aluminum rod conductor is greatly improved.

[0031] 4) The heat treatment parameters adopted by the present invention are obtained through independent experiments and are only for the composition of the products of the present invention. It can effectively optimize the internal structure of the conductor and improve its mechanical properties. Brief Description of the Drawings

[0032] Figure 1 It is a 100 - fold view of the electron microscope of the sample No. 1 in Example 3.

[0033] Figure 2 It is a 100 - fold view of the electron microscope of the sample No. 3 in Example 3. Detailed Description of the Invention

[0034] To further understand the present invention, the present invention will be described below in conjunction with examples. However, the examples are only for further elaborating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0035] Adopting high - conductivity wires on transmission lines has the following advantages: First, high conductivity and energy conservation: Compared with the conductivity of conventional wires, the conductivity of high - conductivity wires has increased by about 0.71%, reducing resistance loss; Second, reducing short - distance tower investment: Since the wind load of the wire is reduced by about 10%, the tower weight can be reduced by about 0.5%; Third, strong operation reliability: It can relatively reduce the noise generated by corona discharge and line loss. Fourth, the strength is much higher than that of pure aluminum conductors, and it can meet the requirements for conductor strength in short - distance transmission. The conductivity of high - purity aluminum reaches 64.94% IACS, but its tensile strength is generally lower than 60 MPa, and it is restricted in actual applications. Therefore, researching and applying conductors or wire cores with high conductivity and medium strength through micro - alloying means and heat treatment process methods is of great significance for improving the power transmission efficiency of circuits and reducing transmission line losses.

[0036] The preparation method of the medium - strength and high - conductivity conductor rod provided by the present invention is as follows:

[0037] 1. Equipment resources: Resistance furnace, graphite stirrer, graphite ladle, slag - skimming ladle, round steel mold, boron nitride coating, thermocouple. Before casting, the mold and tools are pre - coated with boron nitride, and the tools are fully pre - heated.

[0038] 2. Batching and melting:

[0039] 2.1 Melting: Add refined aluminum ingots into the furnace according to the ratio requirements and heat up. When the aluminum ingots are heated to 780℃ - 800℃, add metal Ni, then keep warm for 3 - 6 minutes, stir, stand for 3 minutes, skim the surface scum, and heat up again to make the temperature rise to 740 - 750℃, add high - purity mixed rare earth Re (La and Ce) wrapped in aluminum foil, and then keep warm for 5 minutes.

[0040] 2.2 Refining: Control the temperature of the aluminum liquid at 730 - 750℃ and add an environmentally friendly granular refining agent (PROMAG RI granular refining agent). After the refining agent fully reacts with the aluminum liquid, skim the slag.

[0041] 2.3 Casting: Control the temperature of the molten aluminum at 720 - 730 °C and cast the round steel mold sample.

[0042] Processing: Process the head and tail parts and the skin of the prepared sample on a lathe. The final requirement is to extrude the sample diameter with a height of 200 mm.

[0043] 3. Extrusion: Put the processed sample with a diameter of and a height of 200 mm into a soaking furnace and perform staged annealing. In the first stage, heat up to 150 °C with a heating time of 120 minutes; in the second stage, keep the temperature at 150 °C for 120 min; in the third stage, heat up to 360 °C with a heating time of 180 min. In the fourth stage, keep the temperature at 360 °C for 1000 min. After annealing, perform extrusion deformation using an 880T horizontal extrusion press. The temperature of the extrusion cylinder is set at 370 - 380 °C, and the optimal temperature is 375 °C. The extrusion pressure is required to be carried out under 135 - 150 Mpa. Control the cooling water temperature at 0 - 30 °C. Finally, extrude the sample into a rod with a diameter of 9.5 mm.

[0044] 4. Drawing: Perform drawing deformation on the 9.5 mm rod to make its diameter reach 8.5 mm.

[0045] 5. Post - heat treatment: Perform aging heat treatment on the drawn aluminum rod through a resistance furnace to obtain a medium - strength and high - conductivity conductor aluminum rod.

[0046] In the following examples, the AlRe2% mixed rare earth refers to the mixture of Al - La master alloy and Al - Ce master alloy. The content of rare earth elements in both the Al - La master alloy and the Al - Ce master alloy is 2 wt.%. In the following examples and comparative examples, the grain refiner is PROMAG RI granular refiner.

[0047] Comparative Example 1:

[0048] Sample preparation: (Chemical composition of the aluminum rod: Fe: 12.20 ppm, Si: 8.40 ppm, Ni: 503.30 ppm, and the balance is Al and inevitable impurity elements.) Preheat the surface - smooth and dry Al99.996% aluminum ingot and pure metal Ni sufficiently, and add the refined aluminum ingot into the furnace to melt and heat up. When the aluminum ingot melts and heats up to 780 - 800 °C, skim off the surface oxide skin, immediately add metal Ni to make it fully contact with the molten aluminum, then keep warm for 3 - 6 min for stirring, let it stand for 3 min, skim off the surface scum, control the temperature of the molten aluminum at 730 - 750 °C and add the granular refiner. After the refiner reacts fully with the molten aluminum, skim the slag. Control the temperature of the molten aluminum at 720 - 730 °C and cast the round steel mold sample. (Mold diameter height: 220 mm).

[0049] Processing: The prepared sample is processed at the head and tail parts and the skin on a lathe. The final requirement is that the diameter of the extruded sample is 200 mm high.

[0050] Extrusion: The sample with a processed diameter and 200 mm high is placed in a soaking furnace and annealed in stages. In the first stage, it is heated to 150 °C with a heating time of 120 minutes; in the second stage, it is kept at 150 °C for 120 minutes; in the third stage, when it is heated to 360 °C, the heating time is 180 minutes. In the fourth stage, it is kept at 360 °C for 1000 minutes. After annealing, extrusion deformation is carried out using an 880T horizontal extrusion press. The temperature of the extrusion cylinder is set at 370 °C - 380 °C, and the optimal temperature is 375 °C. The extrusion pressure is required to be carried out under 135 - 150 Mpa. The cooling water temperature is controlled at 0 - 30 °C. Finally, the sample is extruded into a rod with a diameter of 9.5 mm.

[0051] Comparative Example 2:

[0052] Sample preparation: (Chemical composition of the aluminum rod: Fe: 14.60 ppm, Si: 8.70 ppm, Ni: 1033.80 ppm, the balance is AL and inevitable impurity elements) The surface of the Al99.996% aluminum ingot and pure metal Ni that are smooth and dry are fully preheated, and the refined aluminum ingot is added to the furnace to melt and heat up. When the aluminum ingot is melted and heated to 780 - 800 °C, the surface oxide skin is removed, and metal Ni is immediately added to make it fully contact with the aluminum liquid. Then, it is kept warm for 3 - 6 minutes for stirring, left standing for 3 minutes, the surface floating slag is removed, and the temperature of the aluminum liquid is controlled at 730 - 750 °C. Granular refining agent is added, and after the refining agent fully reacts with the aluminum liquid, the slag is removed. The temperature of the aluminum liquid is controlled at 720 - 730 °C, and the sample is cast into a round steel mold (mold diameter height: 220 mm).

[0053] Processing: The prepared sample is processed at the head and tail parts and the skin on a lathe. The final requirement is that the diameter of the extruded sample is 200 mm high.

[0054] Extrusion: The sample with a processed diameter and 200 mm high is placed in a soaking furnace and annealed in stages. In the first stage, it is heated to 150 °C with a heating time of 120 minutes; in the second stage, it is kept at 150 °C for 120 minutes; in the third stage, when it is heated to 360 °C, the heating time is 180 minutes. In the fourth stage, it is kept at 360 °C for 1000 minutes. After annealing, extrusion deformation is carried out using an 880T horizontal extrusion press. The temperature of the extrusion cylinder is set at 370 °C - 380 °C, and the optimal temperature is 375 °C. The extrusion pressure is required to be carried out under 135 - 150 Mpa. The cooling water temperature is controlled at 0 - 30 °C. Finally, the sample is extruded into a rod with a diameter of 9.5 mm.

[0055] Comparative Example 3:

[0056] Sample preparation: (Chemical composition of aluminum rod: Fe: 15.30 ppm, Si: 9.00 ppm, Ni: 1532.30 ppm, the balance is Al and inevitable impurity elements) Preheat the surface-smooth and dry Al99.996% aluminum ingot and pure metal Ni sufficiently, add the refined aluminum ingot into the furnace to melt and raise the temperature. When the aluminum ingot melts and the temperature rises to 780 - 800 °C, skim off the surface oxide skin, immediately add metal Ni to make it fully contact with the aluminum liquid, then keep warm for 3 - 6 min for stirring, stand for 3 min, and skim off the surface scum. Control the temperature of the aluminum liquid at 730 - 750 °C and add granular refining agent. After the refining agent reacts fully with the aluminum liquid, skim the slag. Control the temperature of the aluminum liquid at 720 - 730 °C and cast a round steel mold sample (mold diameter Height: 220 mm).

[0057] Processing: Process the head and tail parts and the skin of the prepared sample on a lathe. The final requirement is that the diameter of the extruded sample Height: 200 mm

[0058] Extrusion: Put the processed sample with a diameter Height: 200 mm into a soaking furnace and perform stepwise annealing. In the first stage, raise the temperature to 150 °C, and the heating time is 120 minutes; in the second stage, keep warm at 150 °C for 120 min; in the third stage, when raising the temperature to 360 °C, the heating time is 180 min. In the fourth stage, keep warm at 360 °C for 1000 min. After annealing, use an 880T horizontal extrusion press for extrusion deformation. The temperature of the extrusion cylinder is set at 370 - 380 °C, and the optimal temperature is 375 °C. The extrusion pressure is required to be carried out under 135 - 150 Mpa. Control the cooling water temperature at 0 - 30 °C. Finally, extrude the sample into a rod with a diameter of 9.5 mm

[0059] Comparative Example 4:

[0060] Sample preparation: (Chemical composition of aluminum rod: Fe: 20.00 ppm, Si: 9.80 ppm, Ni: 2008.30 ppm, the balance is Al and inevitable impurity elements) Preheat the surface-smooth and dry Al99.996% aluminum ingot and pure metal Ni sufficiently, add the refined aluminum ingot into the furnace to melt and raise the temperature. When the aluminum ingot melts and the temperature rises to 780 - 800 °C, skim off the surface oxide skin, immediately add metal Ni to make it fully contact with the aluminum liquid, then keep warm for 3 - 6 min for stirring, stand for 3 min, and skim off the surface scum. Control the temperature of the aluminum liquid at 730 - 750 °C and add granular refining agent. After the refining agent reacts fully with the aluminum liquid, skim the slag. Control the temperature of the aluminum liquid at 720 - 730 °C and cast a round steel mold sample. (Mold diameter Height: 220 mm)

[0061] Processing: The prepared sample is processed at the head and tail parts and the skin on a lathe. The final requirement is that the diameter of the extruded sample is 200 mm high.

[0062] Extrusion: The processed sample with a diameter of 200 mm high is placed in a soaking furnace and annealed in stages. In the first stage, it is heated to 150 °C with a heating time of 120 minutes; in the second stage, it is held at 150 °C for 120 minutes; in the third stage, when it is heated to 360 °C, the heating time is 180 minutes. In the fourth stage, it is held at 360 °C for 1000 minutes. After annealing, extrusion deformation is carried out using an 880T horizontal extrusion press, and the temperature of the extrusion cylinder is set at 375 °C. The extrusion pressure is required to be carried out under 135 - 150 Mpa. The cooling water temperature is controlled at 0 - 30 °C. Finally, the sample is extruded into a rod with a diameter of 9.5 mm.

[0063] Example 1:

[0064] Sample preparation: (Chemical composition of the aluminum rod: Fe: 13.5 ppm, Si: 11.2 ppm, Ni: 1029.9 ppm, La: 209.3 ppm, Ce: 472.2 ppm, the balance is Al and inevitable impurity elements) The surface of the aluminum ingot (purity 99.996%) which is smooth and dry, AlRe master alloy and pure metal Ni are fully preheated, and the refined aluminum ingot is added to the furnace for melting and heating up. The aluminum ingot is melted and heated up to 780 - 800 °C, the surface oxide skin is skimmed off, and immediately metal Ni is added to make it fully contact with the aluminum liquid. Then it is held for 3 - 6 minutes for stirring, left standing for 3 minutes, the surface scum is skimmed off, and it is heated up again to 740 - 750 °C and 2% of AlRe is added, and it is held for 5 minutes. The temperature of the aluminum liquid is controlled at 730 - 750 °C and a granular refining agent is added. After the refining agent fully reacts with the aluminum liquid, the slag is skimmed off. The temperature of the aluminum liquid is controlled at 720 - 730 °C and a round steel mold sample is cast (mold diameter height: 220 mm).

[0065] Processing: The prepared sample is processed at the head and tail parts and the skin on a lathe. The final requirement is that the diameter of the extruded sample is 200 mm high.

[0066] Extrusion: The processed sample with a diameter The specimen with a height of 200 mm is placed in a soaking furnace and subjected to step annealing. In the first stage, it is heated to 150 °C with a heating time of 120 minutes; in the second stage, it is held at 150 °C for 120 minutes; in the third stage, when it is heated to 360 °C, the heating time is 180 minutes. In the fourth stage, it is held at 360 °C for 1000 minutes. After annealing, extrusion deformation is carried out using an 880T horizontal extrusion press. The temperature of the extrusion cylinder is set at 370 °C - 380 °C, and the optimal temperature is 375 °C. The extrusion pressure is required to be carried out under 135 - 150 Mpa. The cooling water temperature is controlled at 0 - 30 °C. Finally, the specimen is extruded into a rod with a diameter of 9.5 mm.

[0067] Example 2:

[0068] Specimen preparation: (Chemical composition of the aluminum rod: Fe: 19.2 ppm, Si: 14.0 ppm, Ni: 1096.3 ppm, La: 673.969 ppm, Ce: 1500 ppm, with the balance being Al and inevitable impurity elements) The surface of the aluminum ingot (purity 99.996%), AlRe master alloy, and pure metal Ni with a smooth and dry surface are fully preheated, and the refined aluminum ingot is added to the furnace to melt and heat up. When the aluminum ingot is melted and heated to 780 - 800 °C, the surface oxide scale is skimmed off, and metal Ni is immediately added to make it fully contact with the aluminum liquid. Subsequently, it is held for 3 - 6 minutes for stirring, left standing for 3 minutes, the surface scum is skimmed off, and then heated to 740 - 750 °C again to add 2% of AlRe and held for 5 minutes. The temperature of the aluminum liquid is controlled at 730 - 750 °C, and a granular refining agent is added. After the refining agent fully reacts with the aluminum liquid, the slag is skimmed off. The temperature of the aluminum liquid is controlled at 720 - 730 °C, and a round steel mold specimen is cast (mold diameter height: 220 mm).

[0069] Processing: The prepared specimen is processed at the head, tail, and skin on a lathe. Finally, the diameter of the extruded specimen is required height 200 mm.

[0070] Extrusion: The specimen with a processed diameter height 200 mm is placed in a soaking furnace and subjected to step annealing. In the first stage, it is heated to 150 °C with a heating time of 120 minutes; in the second stage, it is held at 150 °C for 120 minutes; in the third stage, when it is heated to 360 °C, the heating time is 180 minutes. In the fourth stage, it is held at 360 °C for 1000 minutes. After annealing, extrusion deformation is carried out using an 880T horizontal extrusion press. The temperature of the extrusion cylinder is set at 370 °C - 380 °C, and the optimal temperature is 375 °C. The extrusion pressure is required to be carried out under 135 - 150 Mpa. The cooling water temperature is controlled at 0 - 30 °C. Finally, the specimen is extruded into a rod with a diameter of 9.5 mm.

[0071] The component parameters of Comparative Examples 1-4 and Examples 1-2 are shown in Table 1 (Fe and Si in the aluminum rod are introduced by the added Ni metal and AlRe master alloy):

[0072] Table 1:

[0073]

[0074] The performance test results are shown in Table 2:

[0075] Table 2:

[0076]

[0077]

[0078] It can be seen from the adjustment of the microalloying element Ni in Comparative Examples 1-4 in Table 2 that as the Ni element is added, the strength of the conductor rod tends to increase, and the conductivity decreases. The influence of Ni element on the conductivity is relatively small when the Ni element is in the range of 500 ppm - 1000 ppm, which meets the expectation. When it is above 1000 ppm, the change in conductivity is relatively large. Furthermore, by analyzing Example 1-2 and Comparative Example 2, it is found that due to the addition of rare earth elements La and Ce, the number of heterogeneous nucleation cores in the conductor rod increases. The intervention of a large number of new crystal nuclei restricts the growth of columnar crystals, playing a role in grain refinement and improving both the strength and plasticity. However, the increase in the number of heterogeneous nucleation points will also cause lattice distortion of the aluminum matrix, resulting in a decrease in the matrix conductivity.

[0079] Considering the final target value that the required conductor rod needs to achieve comprehensively, Example 1 is preferred, that is, Fe: 13.5 ppm, Si: 11.2 ppm, Ni: 1029.9 ppm, La: 209.3 ppm, Ce: 472.2 ppm, and the balance is Al and inevitable impurity elements as the preferred composition. The drawing and heat treatment processes are discussed for it.

[0080] Example 3:

[0081] Sample preparation: (Select the composition of the aluminum rod in Example 1, Fe: 13.5 ppm, Si: 11.2 ppm, Ni: 1029.9 ppm, La: 209.3 ppm, Ce: 472.2 ppm, and the balance is Al and inevitable impurity elements.) Preheat the Al99.996% aluminum ingot with a smooth and dry surface, 2% AlRe mixed rare earth, and pure metal Ni sufficiently. Add the refined aluminum ingot into the furnace to melt and raise the temperature. When the aluminum ingot melts and the temperature rises to 780 - 800 °C, skim off the surface oxide scale, immediately add metal Ni to make it fully contact with the aluminum liquid, then keep warm for 3 - 6 min and stir, let it stand for 3 min, skim off the surface scum, and raise the temperature again to 740 - 750 °C to add 2% AlRe, and keep warm for 5 min. Control the temperature of the aluminum liquid at 730 - 750 °C and add the granular refining agent. After the refining agent fully reacts with the aluminum liquid, skim the slag. Control the temperature of the aluminum liquid at 720 - 730 °C and cast a round steel mold sample (mold diameter height: 220 mm).

[0082] Processing: Process the head, tail, and skin of the prepared sample on a lathe. The final requirement is that the diameter of the extruded sample height is 200 mm.

[0083] Extrusion: Put the processed sample with a diameter height of 200 mm into a soaking furnace and perform segmented annealing. In the first stage, raise the temperature to 150 °C, and the heating time is 120 minutes; in the second stage, keep the temperature at 150 °C for 120 min; in the third stage, when raising the temperature to 360 °C, the heating time is 180 min. In the fourth stage, keep the temperature at 360 °C for 1000 min. After annealing, perform extrusion deformation using an 880T horizontal extrusion press. The temperature of the extrusion cylinder is set at 370 - 380 °C, and the optimal temperature is 375 °C. The extrusion pressure is required to be carried out at 135 - 150 Mpa. Control the cooling water temperature at 0 - 30 °C. Finally, extrude the sample into a rod with a diameter of 9.5 mm.

[0084] Drawing: Use a drawing machine to draw the rod sample with a wire diameter of 9.5 mm to 8.5 mm, and then perform heat treatment with different parameters. Table 3 below shows the changes in heat treatment parameters under the preferred composition in this example. The performance parameters measured from the samples in Table 3 are shown in Table 4.

[0085] Table 3:

[0086]

[0087] Table 4:

[0088]

[0089] It can be seen from the average values of all samples that, with the holding time extended at a constant holding temperature, the tensile strength first increases and then decreases, and the strength peak appears at 15 hours. With the holding time being the same, the conductivity shows high points at both 130°C and 150°C. However, the elongation of the conductor at 130°C is 31.3% higher than that of the sample without heat treatment, which is better than that at 150°C.

[0090] Therefore, we can obtain the optimal heat treatment process: holding temperature 130°C, holding time 15H.

[0091] Observation of the internal structure: Observation was carried out using an electron microscope. Figure 1-2 The high-magnification structures of the blank sample (sample No. 1) and the optimal sample (sample No. 3) were observed at 100 times magnification. It can be clearly seen that after microalloying and subsequent process treatments, the average internal grain size decreased from 92.24 μm to 60.33 μm, and the grain size was greatly improved.

[0092] Combining all technical and performance characteristics, the present invention takes advantage of high-purity aluminum. While retaining its original high-conductivity characteristics, through the microalloying effect of Ni and rare earth elements, the mechanical properties of the conductor are improved. In addition, extrusion deformation and heat treatment also play a key role in further refining the internal grains. Finally, a medium-strength and high-conductivity conductor is obtained under a complete set of processes.

[0093] Beneficial effects brought by the technical solution of the present invention:

[0094] 1) By adding microalloying elements and cooperating with process means such as extrusion heat treatment, the present invention effectively improves the strength of the aluminum matrix conductor. Finally, the optimal tensile strength obtained in the experiment can reach 107 Mp, which is much higher than the limit of 60 MPa of the pure aluminum matrix. It is even higher than the average strength of electrician's round aluminum rod 1A60 under H13.

[0095] 2) Although the limit value of 107 Mpa is much lower than that of alloy conductor rods, the conductivity of the conductor demonstrated by the present invention can reach 64.21% IACS, which is higher than the limit value of 63.5% IACS of all current electrician's round aluminum rods and aluminum conductors.

[0096] 3) If this conductor is used as the core material for short-distance cables, the energy consumption can be reduced by 0.71%. It should be noted that the above only applies to the preferred implementation manner of the present invention. For other technical personnel in the field, without departing from the principle of the present invention, several improvements and modifications made are also regarded as the protection scope of the present invention.

Claims

1. A medium-strength and high-conductivity guide rod, characterized in that: The guide rod is obtained by doping Ni and rare earth Re elements into high-purity aluminum ingots. The rare earth Re elements are La and Ce. The chemical composition of the guide rod is as follows: Ni = 500 - 2000 ppm, La = 100 - 500 ppm, Ce = 200 - 1500 ppm, Fe is 10 - 20 ppm, Si is 5 - 30 ppm, and the balance is Al and inevitable impurities; The preparation method of the medium-strength and high-conductivity guide rod includes the following steps: (1) Batching and melting: Add refined aluminum ingots into an intermediate frequency furnace to melt and raise the temperature, then sequentially add metal Ni and rare earth Re and keep warm for a period of time; then carry out refining and cast into a cylindrical sample; (2) Processing: Process the prepared sample on a lathe for the head and tail parts and the skin. Finally, the required extrusion sample has a diameter of φ100 mm and a height of 200 mm; (3) Annealing treatment: Carry out staged annealing in a soaking furnace; in the first stage, raise the temperature to 130 - 150 °C, and the heating time is 100 - 120 minutes; in the second stage, keep warm at 130 - 150 °C for 120 min; in the third stage, raise the temperature to 320 - 360 °C, and the heating time is 150 - 180 min; in the fourth stage, keep warm at 360 °C for 1000 min; (4) Extrusion processing: Extrude and deform the annealed sample using an extruder. The temperature of the extrusion cylinder is set at 370 - 380 °C, the extrusion pressure is 135 - 150 MPa, and the cooling water temperature is controlled at 0 - 30 °C. Finally, the sample is extruded into an aluminum rod with a diameter of 9.5 mm; (5) Drawing: Carry out drawing deformation on the 9.5 mm aluminum rod to make its diameter reach 8.5 mm; (6) Post heat treatment: Carry out aging heat treatment on the drawn aluminum rod through a resistance furnace to obtain the medium-strength and high-conductivity guide rod.

2. The medium-strength and high-conductivity guide bar according to claim 1, wherein: Among the impurity components contained in the guide rod: Cu < 10 ppm, Zn < 5 ppm, Ti < 5 ppm, Mg < 5 ppm.

3. The medium-strength and high-conductivity guide rod according to claim 1 or 2, wherein: The tensile strength of the guide rod reaches 107 MPa, and the conductivity reaches 64.21% IACS.

4. The preparation method of the medium-strength and high-conductivity guide rod according to claim 1, characterized in that: The method includes the following steps: (1) Batching and melting: Add refined aluminum ingots into an intermediate frequency furnace to melt and raise the temperature, then sequentially add metal Ni and rare earth Re and keep warm for a period of time; then carry out refining and cast into a cylindrical sample; (2) Processing: Process the prepared sample on a lathe for the head and tail parts and the skin. Finally, the required extrusion sample has a diameter of φ100 mm and a height of 200 mm; (3) Annealing treatment: Carry out staged annealing in a soaking furnace; in the first stage, raise the temperature to 130 - 150 °C, and the heating time is 100 - 120 minutes; in the second stage, keep warm at 130 - 150 °C for 120 min; in the third stage, raise the temperature to 320 - 360 °C, and the heating time is 150 - 180 min; in the fourth stage, keep warm at 360 °C for 1000 min; (4) Extrusion processing: Extrude and deform the annealed sample using an extruder. The temperature of the extrusion cylinder is set at 370 - 380 °C, the extrusion pressure is 135 - 150 MPa, and the cooling water temperature is controlled at 0 - 30 °C. Finally, the sample is extruded into an aluminum rod with a diameter of 9.5 mm; (5) Drawing: The 9.5 mm aluminum rod is drawn and deformed to make its diameter reach 8.5 mm; (6) Post heat treatment: The drawn aluminum rod is subjected to aging heat treatment through a resistance furnace to obtain the medium-strength and high-conductivity guide rod.

5. The preparation method of the medium-strength and high-conductivity guide rod according to claim 4, characterized in that: In step (1), the purity of the refined aluminum ingot is ≥99.996%, and the purity of the metal Ni is 99.99%; the rare earth Re element is La and Ce, and the rare earth Re element is added to the aluminum liquid in the form of an Al-Re master alloy. The addition amounts of La and Ce are calculated according to the chemical composition of the guide rod.

6. The preparation method of the medium-strength and high-conductivity guide rod according to claim 4, wherein: In step (1), the melting process is specifically as follows: The refined aluminum ingot is added to the furnace and melted with temperature increase. When the temperature of the aluminum ingot rises to 780 - 800 °C, metal Ni is added, and then it is kept warm for 3 - 6 minutes. After stirring evenly, it is left standing for 3 minutes, and the surface scum is removed; the temperature is increased again to 740 - 750 °C, and the high-purity Al-Re master alloy wrapped with aluminum foil is added, and then it is kept warm for 5 minutes and then refined.

7. The preparation method of the medium-strength and high-conductivity guide rod according to claim 6, characterized in that: In step (1), during the refining process, after controlling the temperature of the aluminum liquid to 730 - 750 °C, an environmentally friendly granular refining agent is added, and refining is carried out for 5 - 8 minutes to make the refining agent fully react with the aluminum liquid, and then the slag is removed; finally, casting is carried out, and the temperature of the aluminum liquid is controlled to 720 - 730 °C during casting.

8. The preparation method of the medium-strength and high-conductivity guide rod according to claim 4, characterized in that: In step (6), the holding temperature of the heat treatment process is 130 ± 10 °C, and the holding time is 15 hours.

9. The preparation method of the medium-strength and high-conductivity guide rod according to claim 8, characterized in that: The average grain size range of the aluminum rod after heat treatment: 60.33 - 72.50 μm.

Images