A high-purity aluminum rod material for a superconducting cable aluminum stabilizer and a preparation method thereof

Abstract

The present invention discloses a high-purity aluminum rod material for a superconducting cable aluminum stabilizer and a preparation method thereof, belonging to the technical field of industrial high-purity aluminum. The method of the present invention uses ultra-high-purity aluminum as a raw material, and through Ni and Be for composition optimization design and microalloying method to control the morphology and distribution of the Al-Ni-Be phase, so as to strengthen the high-purity aluminum matrix and at the same time reduce the influence of impurity elements on the conductivity of high-purity aluminum; the yield strength of the high-purity aluminum rod material is greater than 75 MPa, and the RRR value is greater than 400.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial high-purity aluminum, and particularly relates to a high-purity aluminum rod material for a superconducting cable aluminum stabilizer and a preparation method thereof. Background Art

[0002] Industrial high-purity aluminum is mainly used as the anode foil for electrolytic capacitors, capacitor leads, integrated circuit wires, vacuum evaporation materials, stable conductors for superconductors, matrix metals for disk alloys and high fracture toughness aluminum alloys, as well as for special purposes in scientific research, chemical engineering, etc. Ultra-high-purity aluminum has many excellent properties and wide applications. It has better electrical conductivity, ductility, reflectivity and corrosion resistance than primary aluminum, and has wide applications in the fields of the electronic industry, aerospace, etc. 96% of 5N5-6N ultra-high-purity aluminum (the maximum content of each impurity is 0.4 ppm) is used in the semiconductor device manufacturing industry, and 4% is used as the stabilization material for superconducting cables.

[0003] The key component detector magnet of a large-scale positron-electron collider mainly provides a uniform and stable magnetic field environment and is a large-caliber magnet. The key component high-purity aluminum material for the aluminum stabilizer superconducting cable of the detector magnet and its preparation technology are currently blank in China. The core of the aluminum stabilizer superconducting cable is NbTi wire, and the outside is wrapped with high-purity aluminum material. The main function is that if the current distribution is uneven or too large and the core wire undergoes a quench phenomenon, the external aluminum stabilizer can shunt so that the core wire will not have excessive heat leading to attenuation. Since the aluminum stabilizer superconducting cable needs to carry a large current and requires good mechanical properties to resist strong electromagnetic forces, the aluminum stabilizer material needs to have two key indicators of RRR value (room temperature resistivity / low temperature resistivity) and mechanical properties, that is, it should have a high RRR value and a certain yield strength, which requires improving the performance of the aluminum stabilizer base material and developing the extrusion rolling process technology and specific heat treatment process for the subsequent aluminum stabilizer superconducting cable.

[0004] For high-purity aluminum, when the impurity content is at the 10 -6 order of magnitude, the addition of each new impurity can increase the resistivity by 10 -11Ω·m. The influence of impurity elements on the resistivity of high-purity aluminum is relatively small above room temperature, but increases significantly below zero degrees Celsius. The RRR value of 99.96% pure high-purity aluminum is 200, that is, the resistivity at 273K is 200 times that at 4.2K. The RRR of high-purity aluminum with a purity of 99.998% reaches over 3000, and the RRR of high-purity aluminum with a purity of 99.99998% reaches 45000. Therefore, aluminum with a purity above 99.99% becomes a superconductor at extremely low temperatures (1.1 - 1.2K). Thus, high-purity aluminum is an indispensable key material for preparing the stabilizer of superconducting cables. However, in addition to ensuring the RRR value of the aluminum stabilizer material for superconducting cables, it must also have a certain mechanical strength. However, almost all impurity elements will cause an increase in the resistivity of high-purity aluminum materials. Therefore, it is necessary to prepare and develop high-purity aluminum rod materials for the stabilizer of superconducting cables with both RRR value and yield strength through microalloying means, appropriate casting and processing methods, and specific heat treatment processes.

[0005] Prior art 1 discloses an aluminum alloy superconducting cable and its preparation method (CN201810205004.1). The aluminum alloy superconducting cable includes: a conductor, and concentrically and sequentially provided on the outer layer of the conductor are: a graphene composite high semi-conductive conductor shielding layer, an XLPE insulating layer, a graphene composite high semi-conductive insulating shielding layer, a copper tape shielding layer, a non-woven fabric, and a sheath. The chemical composition weight ratio of the conductor is as follows: graphene 1 - 5%, silicon 2%, iron 0.55 - 0.8%, magnesium 0.01 - 0.05%, zinc 0.05%, copper 0.1 - 0.2%, boron 0.04%, and the balance is aluminum. The preparation method is simple. The cable is light in weight, low in loss, can not only increase the current-carrying capacity of the line but also reduce losses, is pollution-free, and can reduce the power operation cost.

[0006] However, what this technology describes is the preparation of an Al-Si-Mg-Fe aluminum alloy superconducting cable, mainly adding 1 - 5% graphene to enhance the electrical conductivity of the Al-Si-Mg-Fe aluminum alloy rod. Secondly, the continuous rolling and drawing production method is adopted. However, the cost of graphene is relatively high, and there is no cost advantage if it is popularized and applied in power cables, and it cannot be industrially applied in the short term.

[0007] The prior art 1 discloses an aluminum alloy superconducting cable and its preparation method (202010720621.2). Its aluminum rod achieves the effects of high tensile strength and high conductivity, and solves the disadvantage that the tensile strength and conductivity of the existing aluminum rod cannot be satisfied simultaneously. Its superconducting cable includes an aluminum alloy cable core, and the outside of the aluminum alloy cable core is wrapped with a protective layer, and at least one aluminum alloy cable core is arranged inside the protective layer; the aluminum alloy cable core includes an aluminum alloy superconductor, and the outside of the aluminum alloy superconductor is coated with a composite high semi-conductive conductor shielding layer and a cross-linked polyethylene insulating layer. The aluminum alloy superconductor includes the following components by mass percentage: yttrium barium copper oxide 1-3%, magnesium 0.05-0.1%, zinc 0.02-0.07%, chromium 0.08-0.15%, strontium: 0.05-0.1%, boron 0.02-0.06%, manganese 0.5-1.0%, zirconium: 0.02-0.07%, and the balance is aluminum. The elongation rate of the aluminum alloy single wire of its aluminum alloy superconducting cable is ≥35%, the tensile strength is >115 MPa, the number of 90° bending times is more than 38 times, the DC resistivity at 20°C is ≤0.026, the conductivity is ≥64.0% IACS, the bending radius is ≥7D, and the rebound performance is reduced by 40% compared with the copper cable, and the anti-creep performance is increased by 300% compared with the aluminum core cable.

[0008] The prior art 2 aluminum alloy superconducting cable solves the problems of low strength, high self-weight, and high loss of the existing aluminum alloy cable. The strength and conductivity of the aluminum rod are mainly improved through the alloying treatment of various elements such as Mg, Zn, Cr, Sr, B, Mn, Zr, etc.; however, its complex alloying treatment process is difficult, and the material cost is high, and the tensile strength of 115 MPa has no obvious advantage, so it is difficult to be popularized and applied in the power cable industry. Summary of the Invention

[0009] Since the aluminum stabilizer superconducting cable needs to carry a large current and requires good mechanical properties to resist strong electromagnetic forces, the aluminum stabilizer material needs to have two key indicators, namely the RRR value (room temperature resistivity / low temperature resistivity) and mechanical properties. Almost any element doping will affect the resistivity of ultra-high purity aluminum to varying degrees, especially the low temperature resistivity is more sensitive to impurity elements, which in turn affects its RRR index. In order to enhance the mechanical properties of the ultra-high purity aluminum rod material, microalloying treatment must be carried out. Therefore, the mechanical properties of the ultra-high purity aluminum rod material for the aluminum stabilizer of the superconducting cable are contradictory to the RRR index. The purpose of the present invention is to provide an ultra-high purity aluminum rod material for the aluminum stabilizer of a superconducting cable and its preparation method. By means of the excellent ultra-low temperature conductivity of 4N8-5N ultra-high purity aluminum, through the microalloying treatment of doping trace elements such as Ni and Be that have relatively little influence on the conductivity of ultra-high purity aluminum, and after adopting a specific extrusion and drawing process and aging treatment process, an ultra-high purity aluminum rod material with both mechanical properties and low temperature conductivity is obtained.

[0010] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] A preparation method of high-purity aluminum rod material for superconducting cable aluminum stabilizer. The method uses ultra-high-purity aluminum as raw material, and through Ni and Be for composition optimization design and microalloying method to control the morphology and distribution of Al-Ni-Be phase, so as to strengthen the high-purity aluminum matrix and reduce the influence of impurity elements on the conductivity of high-purity aluminum. The method specifically includes the following steps:

[0012] (1) Batching and melting: After adding refined aluminum ingots into a high-purity graphite crucible and melting them, high-purity Ni and high-purity AlBe3 master alloy are added in sequence for melting. After refining and casting, an aluminum ingot blank is obtained. After sawing and milling the surface, it is processed into a round bar with a diameter of...

[0013] (2) Extrusion: The round bar prepared in step (1) is put into a soaking furnace for segmented soaking treatment. The soaking treatment temperature is 320 - 360 °C, and the holding time is more than 720 min. After the soaking treatment is completed, extrusion deformation is carried out, and finally the round bar sample is extruded into a high-purity aluminum rod with a diameter of 9.5 - 12 mm.

[0014] (3) Drawing: The high-purity aluminum rod prepared in step (2) is drawn and deformed to a diameter of 6.0 - 8.0 mm.

[0015] (4) Aging heat treatment: The drawn aluminum rod is subjected to aging heat treatment in an electric resistance furnace. The aging treatment temperature is 120 - 150 °C, and the aging time is 10 - 15 h.

[0016] In the above step (1), the refined aluminum ingot is 4N8 - 5N high-purity aluminum prepared by the three-layer liquid electrolysis method, and its purity is 99.998 - 99.999%; the purity of the high-purity Ni is 99.99%.

[0017] In the above step (1), the addition amounts of the high-purity Ni and the high-purity AlBe3 master alloy in the aluminum liquid are proportioned according to the chemical composition of the prepared high-purity aluminum rod.

[0018] In the above step (1), the melting process of the refined aluminum ingot is as follows: Add the refined aluminum ingot into a high-purity graphite crucible and melt and heat it up. When the aluminum liquid is heated to 750 - 800 °C, add high-purity Ni, and then hold for 3 - 5 min; after mechanical stirring, let it stand for 3 min, skim off the surface scum, heat it up again to make the temperature reach 720 - 760 °C, add the high-purity AlBe3 master alloy wrapped in aluminum foil, and then hold for 5 - 10 min.

[0019] In the above step (1), the refining process is as follows: control the temperature of the molten aluminum at 730 - 750 °C, and use a refining device to carry out refining in a high-purity argon atmosphere. Set the rotor speed at 350 - 400 r / min, and set the argon flow rate at 0.25 - 1.0 m 3 / h. The refining time is 10 - 30 min. After refining, let it stand for 3 - 5 min, and then skim the slag.

[0020] In the above step (1), the casting process is as follows: control the temperature of the molten aluminum at 720 - 750 °C, and bake the launder and semi-continuous tooling in advance to reduce the temperature drop of the molten aluminum; set the casting speed at 120 - 150 mm / min, and set the cooling water flow rate at 50 - 80 m 3 / h, and then carry out casting.

[0021] In the above step (2), the extrusion deformation is carried out by an extruder. Set the temperature of the extrusion cylinder at 350 - 380 °C, the extrusion pressure at 125 - 150 MPa, and control the cooling water temperature at 15 - 30 °C;

[0022] Using the above method, a high-purity aluminum rod material for superconducting cable aluminum stabilizer is prepared. By weight percentage, the chemical composition of the high-purity aluminum rod material is as follows:

[0023] Fe < 0.0008%, Si < 0.0008%, Cu < 0.0005%, Zn < 0.0003%, Ti < 0.0001%, Mg < 0.0001%, Mn < 0.0001%, Ni 0.01 - 0.10%, Be 0.005% - 0.05%, and the balance is Al and other impurity elements; the content of other single impurity elements < 0.0001%.

[0024] The purity of the high-purity aluminum rod material is greater than 99.85%; its yield strength is greater than 75 MPa, and the RRR value is greater than 400.

[0025] The design principle and beneficial effects of the present invention are as follows:

[0026] 1) The present invention uses 4N8 - 5N ultra-high purity aluminum prepared by the three-layer liquid electrolysis method as the raw material, and adopts the microalloying means of high-purity Ni and AlBe3 master alloy to carry out composition optimization design and melting treatment. Since the chemical properties of Be and Al are similar, and their electrode potentials are also similar, the AlBe compound has relatively little influence on the conductivity of high-purity aluminum. By optimizing the design of the Ni and Be components and the microalloying method, the morphology and distribution of the Al-Ni-Be phase are controlled, so as to strengthen the high-purity aluminum matrix to a certain extent, and at the same time minimize the influence of impurity elements on the room temperature / low temperature resistivity of high-purity aluminum.

[0027] 2) The present invention adopts a semi - continuous casting process method. By controlling appropriate casting speed, cooling intensity, and casting temperature, the uniformity of the composition and structure of the high - purity aluminum billet doped with Ni and Be elements is ensured. Then, through a specific extrusion and drawing process, including extrusion speed, extrusion temperature, and cooling intensity, etc., the uniformity of the extrusion structure of the high - purity aluminum rod is ensured. Through the design of the aging heat treatment process, including reasonable aging temperature and aging time, the yield strength of the high - purity aluminum rod is appropriately increased. At the same time, the adverse impact of the extrusion and drawing process on the resistivity of the high - purity aluminum rod material is controlled at a low level and the normal - temperature resistivity is appropriately reduced. Finally, a high - purity aluminum rod material with a yield strength exceeding 75 Mpa and an RRR value exceeding 400 is obtained.

[0028] 3) The high - purity aluminum rod material developed by the present invention for high - strength superconducting cables has both mechanical properties and electrical properties. It can be used as a key basic material for the aluminum stabilizer of superconducting cables in the later stage. After successful application, it has important guarantee significance for the preparation of key materials of superconducting cables in future large - scale particle colliders. Specific embodiments

[0029] To further understand the present invention, the following describes the present invention in combination with examples. However, the examples are only for further elaborating the characteristics and advantages of the present invention, rather than limiting the claims of the present invention.

[0030] The present invention is based on the experimental research of the aluminum stabilizer material for superconducting cables. Since the aluminum - stabilized superconducting cable needs to carry a large current and requires good mechanical properties to resist strong electromagnetic forces, it is necessary to consider two key indicators, namely the RRR value (normal - temperature resistivity / low - temperature resistivity) and mechanical properties. It is necessary to have both a high RRR value and a certain yield strength. This requires micro - alloying means, appropriate casting and processing methods, and specific heat treatment means to produce a high - purity aluminum rod material with both RRR and mechanical properties, providing a basic material support for the subsequent application research of the aluminum stabilizer of superconducting cables.

[0031] The preparation method of the high - purity aluminum rod material for the aluminum stabilizer of superconducting cables provided by the present invention is as follows:

[0032] 1. Equipment resources: 300 kg intermediate - frequency furnace, refining device, graphite stirring rod, slag - skimming spoon, single - root semi - continuous casting tooling, water - cooled mold with a diameter of 125 mm, boron nitride coating, thermocouple. To prevent composition pollution, a high - purity graphite crucible is required for melting. Before casting, the graphite ring of the mold is treated with graphite powder and castor oil, and the flow trough and tools are coated with boron nitride coating.

[0033] 2. Batching and melting

[0034] 2.1 Melting: The refined aluminum ingots with Al content of 99.998 - 99.999% are added into a high-purity graphite crucible according to the proportion requirements and melted with temperature rising. When the aluminum liquid temperature rises to 750℃ - 800℃, high-purity Ni is added, then keep warm for 3 - 5 min, conduct mechanical stirring, stand for 3 min, skim off the surface dross, raise the temperature again to 720 - 760℃, add the high-purity AlBe3 master alloy wrapped with aluminum foil, and then keep warm for 5 - 10 min.

[0035] 2.2 Refining: Control the aluminum liquid temperature at 730 - 750℃, and use a refining device to conduct high-purity argon gas refining. Set the rotor speed at 350 - 400 r / min and the argon gas flow rate at 0.25 - 1.0 m 3 / h, refine for 10 - 30 min, stand for 3 - 5 min, and conduct slag skimming.

[0036] 2.3 Casting: Control the aluminum liquid temperature at 720 - 750℃, pre-bake the launder and semi-continuous tooling in advance to reduce the temperature drop of the aluminum liquid. Set the casting speed at 120 - 150 mm / min and the cooling water flow rate at 50 - 80 m 3 / h, and conduct casting. Saw and mill the high-purity casting billet into a round bar with a diameter of .

[0037] 3. Extrusion: Put the round bar into a soaking furnace for segmented soaking treatment. The soaking treatment temperature is 320 - 360℃, and keep warm for more than 720 min. After soaking, use an 880T horizontal extrusion press for extrusion deformation. Set the extrusion cylinder temperature at 350℃ - 380℃ and the extrusion pressure at 125 - 150 Mpa. Control the cooling water temperature at 15 - 30℃. Finally, extrude the sample into a high-purity aluminum rod with a diameter of 9.5 mm.

[0038] 4. Drawing: Draw the 9.5 mm high-purity aluminum rod to deform it to 8.0 mm.

[0039] 5. Aging heat treatment: Use an electric resistance furnace to conduct aging heat treatment on the drawn aluminum rod. The aging treatment temperature is 120 - 150℃, and the aging time is 10 - 15 h to improve the strength of the high-purity aluminum rod and obtain a high-purity aluminum rod with a diameter of 8.0 mm and certain strength.

[0040] 6. Performance testing: Remove 2 m from the head and tail of the aluminum rod, take samples to conduct tests on indicators such as room temperature resistivity, tensile strength, yield strength, elongation, and low-temperature resistivity (4.2 k).

[0041] In the following examples and comparative examples, the purity of the high-purity Ni used is 99.99%.

[0042] Comparative Example 1:

[0043] 1) Ingot preparation:

[0044] Melting: Add refined aluminum ingots with 99.996% Al into a high-purity graphite crucible and melt while heating up according to the ratio requirements. When the aluminum liquid temperature rises to 780 °C, add high-purity Ni (with concentrations of 500 ppm and 1000 ppm respectively), then keep warm for 5 min, conduct mechanical stirring, let it stand for 3 min, skim off the surface scum, and then keep warm for 5 min;

[0045] Refining: Control the aluminum liquid temperature at 740 °C, and use a refining device to conduct high-purity argon gas refining. Set the rotor speed at 370 r / min and the argon gas flow rate at 0.50 m 3 / h, refine for 10 - 30 min, let it stand for 3 min, and conduct slag skimming;

[0046] Casting: Control the aluminum liquid temperature at 730 °C, pre-bake the launder and semi-continuous tooling in advance to reduce the temperature drop of the aluminum liquid. Set the casting speed at 150 mm / min and the cooling water flow rate at 50 m 3 / h, and conduct casting. Saw and mill the high-purity ingot into a round bar with a diameter specified.

[0047] 2) Extrusion and drawing:

[0048] Put 6 round bars into a soaking furnace for segmented soaking treatment. The soaking treatment temperature is 330 °C, and keep warm for more than 720 min. After soaking, use an 880T horizontal extrusion press for extrusion deformation. Set the extrusion cylinder temperature at 360 °C and the extrusion pressure at 125 MPa. Control the cooling water temperature at 20 °C. Finally, extrude the sample into a high-purity aluminum rod with a diameter of 9.5 mm; Drawing: Draw the 9.5 mm high-purity aluminum rod to 8.0 mm by drawing deformation.

[0049] 3) Aging treatment: Use an electric resistance furnace to conduct aging heat treatment on the drawn aluminum rod. The aging treatment temperature is 120 °C and the aging time is 13 h to improve the strength of the high-purity aluminum rod and obtain a high-purity aluminum rod with a diameter of 8.0 mm and certain strength.

[0050] 4) Performance testing: Remove 2 m from the head and tail of the aluminum rod, and take two groups of samples respectively. The first group has a high-purity Ni concentration of 500 ppm, numbered AN1-1, AN1-2, AN1-3, and the second group has a high-purity Ni concentration of 1000 ppm, numbered AN1-4, AN1-5, AN1-6. Conduct tests on indicators such as room-temperature resistivity, tensile strength, yield strength, elongation, and low-temperature resistivity (4.2 K).

[0051] Example 2:

[0052] 1) Ingot preparation: Melting: Add refined aluminum ingots with 99.998% Al into a high-purity graphite crucible and melt while heating up. When the aluminum liquid reaches 780 °C, add high-purity Ni (theoretical concentration value is 1000 ppm), then keep it warm for 5 min, conduct mechanical stirring, let it stand for 3 min, skim off the surface scum, and then keep it warm for 5 min; Refining: Control the temperature of the aluminum liquid at 740 °C, and use a refining device to conduct high-purity argon gas refining. Set the rotor speed at 370 r / min and the argon gas flow rate at 0.50 m 3 / h, refine for 10 - 30 min, let it stand for 3 min, and conduct slag skimming; Casting: Control the temperature of the aluminum liquid at 730 °C, pre-bake the chute and semi-continuous tooling in advance to reduce the temperature drop of the aluminum liquid. Set the casting speed at 150 mm / min and the cooling water flow rate at 50 m 3 / h, and conduct casting. Saw and mill the high-purity ingot into a round bar with a diameter of .

[0053] 2) Extrusion and drawing: Put 3 round bars into a soaking furnace for segmented soaking treatment. The soaking treatment temperature is 330 °C, and keep it warm for more than 720 min. After soaking, use an 880T horizontal extrusion press for extrusion deformation. Set the temperature of the extrusion cylinder at 360 °C and the extrusion pressure at 125 Mpa. Control the cooling water temperature at 20 °C. Finally, extrude the sample into a high-purity aluminum rod with a diameter of 9.5 mm; Drawing: Draw the 9.5 mm high-purity aluminum rod to 8.0 mm by drawing deformation.

[0054] 3) Aging treatment: Use an electric resistance furnace to conduct aging heat treatment on the drawn aluminum rod. The aging treatment temperature is 120 °C and the aging time is 13 h to improve the strength of the high-purity aluminum rod and obtain a high-purity aluminum rod with a diameter of 8.0 mm and certain strength.

[0055] 4) Performance testing: Cut off 2 m from the head and tail of the aluminum rod, and number the samples as AN2-1, AN2-2, and AN2-3. Test the indicators such as room-temperature resistivity, tensile strength, yield strength, elongation, and low-temperature resistivity (4.2 K) respectively.

[0056] Example 3:

[0057] 1) Ingot preparation: Melting: Add refined aluminum ingots with 99.998% Al into a high-purity graphite crucible according to the ratio requirements and melt while raising the temperature. When the aluminum liquid temperature rises to 780 °C, add high-purity Ni (theoretical value 250 ppm), then keep it warm for 5 min, carry out mechanical stirring, let it stand for 3 min, skim off the surface scum, raise the temperature again to 730 °C, and add high-purity AlBe3 master alloy wrapped in aluminum foil (theoretical Be concentration 250 ppm), then keep it warm for 5 min; Refining: Control the aluminum liquid temperature at 740 °C, use a refining device to carry out high-purity argon gas refining, set the rotor speed at 370 r / min, set the argon gas flow rate at 0.50 m 3 / h, refine for 10 - 30 min, let it stand for 3 min, and carry out slag skimming; Casting: Control the aluminum liquid temperature at 730 °C, pre-bake the launder and semi-continuous tooling in advance to reduce the temperature drop of the aluminum liquid, set the casting speed at 150 mm / min, and set the cooling water flow rate at 50 m 3 / h, and carry out casting. Saw and mill the high-purity ingot into a round bar with a diameter .

[0058] 2) Extrusion and drawing: Put 3 round bars into a soaking furnace for segmented soaking treatment. The soaking treatment temperature is 330 °C, and keep it warm for more than 720 min. After soaking, use an 880T horizontal extrusion press for extrusion deformation, set the extrusion cylinder temperature at 360 °C, and the extrusion pressure at 125 Mpa. Control the cooling water temperature at 20 °C. Finally, extrude the sample into a high-purity aluminum rod with a diameter of 9.5 mm; Drawing: Draw the 9.5 mm high-purity aluminum rod to 8.0 mm for deformation.

[0059] 3) Aging treatment: Use an electric resistance furnace to carry out aging heat treatment on the drawn aluminum rod. The aging treatment temperature is 120 °C, and the aging time is 13 h to improve the strength of the high-purity aluminum rod and obtain a high-purity aluminum rod with a diameter of 8.0 mm having a certain strength. The purity of the high-purity aluminum rod material is greater than 99.85%.

[0060] 4) Performance testing: Remove 2 m from the head and tail of the aluminum rod, and number the samples as ANB1-1, ANB1-2, and ANB1-3, and respectively conduct tests on indicators such as room temperature resistivity, tensile strength, yield strength, elongation, and low-temperature resistivity (4.2 k).

[0061] The component parameters of Examples 1 - 3 are shown in Table 1:

[0062] Table 1:

[0063]

[0064]

[0065] The test results of mechanical properties and electrical properties are shown in Table 2:

[0066] Table 2:

[0067]

[0068]

[0069] By comparative analysis of Table 1 and Table 2:

[0070] 1. Comparative Example 1 shows that when the microalloying element Ni increases from 500 ppm to about 1000 ppm, the yield strength of the high-purity aluminum rod slightly increases and the RRR slightly decreases. This proves that Ni element microalloying is beneficial to increasing the strength of the high-purity aluminum rod and has little effect on the RRR value.

[0071] 2. In Comparative Examples 1-2, the Ni element is about 1000 ppm. Comparative Example 2 uses Al99.996% high-purity aluminum, and Example 1 uses Al99.998% high-purity aluminum. The total sum of impurity elements such as Fe and Si in Comparative Example 2 exceeds 44.8 ppm, while the impurity elements such as Fe and Si in Example 1 are about 16.3 ppm. The yield strength of the high-purity aluminum rod in Example 1 is slightly lower than that in Comparative Example 2, but the RRR value of Example 1 is 13.4% higher than that in Comparative Example 2, indicating that the reduction of trace impurity elements such as Fe and Si is beneficial to the RRR value of the high-purity aluminum rod.

[0072] 3. It can be seen from Comparative Examples 1-2 that the highest value of the yield strength is 70 Mpa, while the highest value of the RRR is only 250. Thus, with single doping of Ni element, the yield strength has reached the highest and cannot be increased further, and the RRR value cannot be further improved. In Example 1, the content of Ni element is reduced, and an appropriate amount of Be element is doped for microalloying treatment, achieving good results. The yield strength of the high-purity aluminum rod is increased to 76 Mpa, especially the RRR value is greatly improved, and the highest RRR value reaches 408.

[0073] In summary, for the high-purity aluminum rod to have both yield strength and RRR value, Example 1 is preferred, that is, Fe: 5.8 ppm, Si: 4.9 ppm, Cu: 4 ppm, Ni: 230 ppm, Be: 230 ppm, with the balance being Al and inevitable impurity elements as the preferred components. Through the conductivity advantage of ultra-high-purity aluminum, while retaining its original high-conductivity characteristics, through the action of Ni and Be microalloying, the yield strength and RRR index of the high-purity aluminum rod are improved simultaneously. In addition, the extrusion and drawing process and the aging heat treatment process play a key role in further increasing the yield strength of the high-purity aluminum rod, and finally a high-purity aluminum rod material for superconducting cable aluminum stabilizer with both mechanical properties and electrical conductivity is obtained.

[0074] The advantages of the present invention are as follows:

[0075] 1) High-quality high-purity raw material guarantee: The present invention uses Al99.998 - Al99.999% high-purity aluminum purified by three-layer electrolysis, high-quality pure Ni99.99% metal, and high-purity AlBe master alloy as raw materials. High-quality raw materials can largely avoid the introduction of unnecessary impurity elements, minimize the influence of impurity elements on the resistivity at normal and low temperatures, especially the elements that have a greater impact on the resistivity of pure aluminum. At the same time, microalloying means need to be used to accurately control the content of alloying elements such as Ni and Be. Therefore, high requirements are placed on the purity and composition stability of high-purity aluminum, high-purity nickel, and high-purity AlBe master alloy raw materials.

[0076] 2) Microalloying composition design and billet preparation technology: The key indicators of the high-purity aluminum rod material of the present invention are the RRR value and the yield strength. Therefore, the key of the present invention is to experimentally study the composition ratio of different microalloying elements added to the high-purity aluminum substrate and the melting and casting preparation process of the billet. Using an intermediate frequency furnace for melting can ensure the full alloying of Ni and Be elements, with a relatively high melting efficiency. At the same time, the melt can be fully stirred, which is beneficial to composition uniformity and slag floating. Using high-purity argon for refining, the melt purity is relatively high. Through composition optimization ratio tests and microalloying means, the morphology and distribution of Al-Ni-Be compounds are controlled, so as to ensure the uniformity of the high-purity aluminum billet structure and the yield strength and RRR value indicators of the final high-purity aluminum rod. Finally, the optimal composition of the high-purity aluminum rod is determined: Fe: <0.0008%, Si <0.0008%, Cu <0.0005%, Zn: <0.0003%, Ti: <0.0001%, Mg: <0.0001%, Mn: <0.0001%, Ni: 0.01 - 0.10%, Be: 0.005% - 0.05%, other single <0.0001%.

[0077] 3) Specific extrusion, drawing and heat treatment processes: Based on a 120-mm diameter high-purity billet with stable composition and structure, the present invention develops specific extrusion, drawing and heat treatment processes. Using a suitable extrusion and drawing process, the 120-mm billet is extruded to 9.5 mm and then drawn to 8.0 mm, and finally age heat treatment is carried out. The yield strength of the high-purity aluminum rod prepared by this process is improved, and at the same time, the RRR value can also be controlled within a certain range. Finally, the yield strength of the 8.0-mm high-purity aluminum rod can reach more than 75 MPa, and the RRR value exceeds 400.

[0078] It should be explained that the above is only the preferred implementation mode 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 preparation method of a high-purity aluminum rod material for a superconducting cable aluminum stabilizer, characterized in that: This method uses ultra-high purity aluminum as raw material, optimizes the composition design with Ni and Be, and strengthens the high-purity aluminum matrix through process control while reducing the influence of impurity elements on the electrical conductivity of high-purity aluminum; The chemical composition of the high-purity aluminum rod material is as follows: Fe < 0.0008%, Si < 0.0008%, Cu < 0.0005%, Zn < 0.0003%, Ti < 0.0001%, Mg < 0.0001%, Mn < 0.0001%, Ni 0.01 - 0.10%, Be 0.005% - 0.05%, and the balance is Al and other impurity elements; the content of other single impurity elements < 0.0001%; This method includes the following steps: (1) Batching and melting: After adding refined aluminum ingots into a high-purity graphite crucible and melting, successively add high-purity Ni and high-purity AlBe3 master alloy for melting, obtain aluminum cast blanks through refining and casting, and process them into round bars with a diameter of φ110 - 130 mm after sawing and milling the surface; (2) Extrusion: Put the round bars prepared in step (1) into a soaking furnace for segmented soaking treatment, the soaking treatment temperature is 320 - 360 °C, and keep warm for more than 720 min; after the soaking treatment is completed, perform extrusion deformation, and finally extrude the round bar specimens into high-purity aluminum rods with a diameter of 9.5 - 12 mm; (3) Drawing: Perform drawing deformation on the high-purity aluminum rods prepared in step (2) until the diameter reaches 6.0 - 8.0 mm; (4) Aging heat treatment: Use an electric resistance furnace to perform aging heat treatment on the drawn aluminum rods, the aging treatment temperature is 120 - 150 °C, and the aging time is 10 - 15 h.

2. The preparation method of the high-purity aluminum rod material for the aluminum stabilizer of the superconducting cable according to claim 1, characterized in that: In step (1), the refined aluminum ingots are high-purity aluminum with a purity of 99.998 - 99.999%, and the high-purity Ni has a purity of 99.99%.

3. The preparation method of the high-purity aluminum rod material for the aluminum stabilizer of the superconducting cable according to claim 1, wherein: In step (1), the addition amounts of the high-purity Ni and the high-purity AlBe3 master alloy in the aluminum liquid are proportioned according to the chemical composition of the prepared high-purity aluminum rods.

4. The preparation method of the high-purity aluminum rod material for the aluminum stabilizer of the superconducting cable according to claim 1, wherein: In step (1), the melting process of the refined aluminum ingots is as follows: Add the refined aluminum ingots into a high-purity graphite crucible and melt and heat up. When the aluminum liquid is heated to 750 - 800 °C, add high-purity Ni, and then keep warm for 3 - 5 min; after mechanical stirring, let it stand for 3 min, skim off the surface floating slag, heat up again to make the temperature reach 720 - 760 °C, and add the high-purity AlBe3 master alloy wrapped in aluminum foil, and then keep warm for 5 - 10 min.

5. The preparation method of the high-purity aluminum rod material for the aluminum stabilizer of the superconducting cable, according to claim 1 or 4, characterized in that: In step (1), the refining process is as follows: control the temperature of the molten aluminum at 730 - 750 °C, use a refining device to carry out refining in an atmosphere of high-purity argon, set the rotor speed at 350 - 400 r / min, set the argon flow rate at 0.25 - 1.0 m 3 / h, the refining time is 10 - 30 min, after refining, let it stand for 3 - 5 min, and then skim the slag.

6. The preparation method of the high-purity aluminum rod material for the aluminum stabilizer of the superconducting cable according to claim 1, characterized in that: In step (1), the casting process is as follows: control the temperature of the molten aluminum to be 720 - 750 °C, bake the launder and the semi-continuous tooling in advance to reduce the temperature drop of the molten aluminum; set the casting speed to 120 - 150 mm / min and the cooling water flow rate to 50 - 80 m 3 / h for casting.

7. The preparation method of the high-purity aluminum rod material for the aluminum stabilizer of the superconducting cable, as claimed in claim 1, wherein: In step (2), the extrusion deformation is carried out by an extruder, the temperature of the extrusion cylinder is set at 350 - 380 °C, the extrusion pressure is 125 - 150 MPa, and the cooling water temperature is controlled at 15 - 30 °C.

8. A high-purity aluminum rod material for a superconducting cable aluminum stabilizer prepared by the method according to claim 1, characterized in that: The purity of this high-purity aluminum rod material is greater than 99.85%.

9. The high-purity aluminum rod material for the aluminum stabilizer of the superconducting cable according to claim 8, characterized in that: The yield strength of this high-purity aluminum rod material is greater than 75 MPa, and the RRR value is greater than 400.

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