A copper-aluminum base NbTi superconducting wire and a preparation method thereof

Abstract

This invention belongs to the field of superconducting wire technology and relates to a copper-aluminum matrix NbTi superconducting wire and its preparation method. This invention provides a copper-aluminum matrix NbTi superconducting wire, comprising grooved wires and superconducting circular wires; the grooved wires are aluminum grooved wires with copper-coated surfaces; the superconducting circular wires are NbTi / Cu / Al composite wires with copper-coated surfaces. This invention uses an NbTi / Cu / Al / Cu superconducting circular wire structure and aluminum grooved wires with copper-coated surfaces to prepare copper-aluminum matrix NbTi superconducting wires, solving the technical problem that conventional copper-based NbTi superconducting wires cannot simultaneously achieve both cost and performance.

Description

Technical Field

[0001] This invention belongs to the field of superconducting wire technology and relates to a copper-aluminum matrix NbTi superconducting wire and its preparation method. Background Technology

[0002] NbTi superconducting wire is currently the most widely used practical low-temperature superconducting material. It enters a superconducting state at extremely low liquid helium temperatures (4.2K, approximately -269°C), exhibiting zero resistance and perfect diamagnetism, and can carry extremely high currents without loss. This material possesses excellent machinability, stable superconducting properties, and relatively economical cost, making it a core choice for applications requiring strong magnetic fields. NbTi superconducting wire is inextricably linked to magnetic resonance imaging (MRI) systems; it is a core component of MRI, accounting for over 30% of the total cost of the superconducting magnet. The superconducting magnet needs to generate an extremely strong, highly uniform, and long-term stable static magnetic field (typically 0.5T to 3.0T) during patient examinations. Coils wound from NbTi superconducting wire achieve superconductivity under liquid helium cooling, thus maintaining this strong magnetic field with almost zero energy consumption, ensuring high resolution and stability of MRI images.

[0003] Typical NbTi superconducting wires consist of grooved wires and superconducting round wires. The grooved wires are usually made of pure copper or pure aluminum, while the superconducting round wires typically have a structure of NbTi / barrier layer / Cu. Currently, the common method to reduce the cost of NbTi superconducting wires is to completely replace the copper substrate with an aluminum substrate. However, the material properties (hardness, elongation, etc.) of NbTi and aluminum differ significantly, posing various difficulties when processing them together, requiring specialized fabrication equipment. Furthermore, while completely replacing the copper substrate with an aluminum substrate or removing the barrier layer can effectively reduce costs, it also drastically degrades the performance of NbTi superconducting wires, leading to decreased magnet stability, reduced reliability, shortened lifespan, and even direct failure. Summary of the Invention

[0004] The purpose of this invention is to provide a copper-aluminum matrix NbTi superconducting wire, which is made by partially replacing copper with aluminum, thereby reducing costs while maintaining high performance and stability.

[0005] To address this need, the present invention provides a copper-aluminum matrix NbTi superconducting wire and its preparation method.

[0006] On one hand, the present invention relates to a copper-aluminum matrix NbTi superconducting wire, wherein the assembly structure of the copper-aluminum matrix NbTi superconducting wire includes a grooved wire and a superconducting circular wire, wherein the superconducting circular wire is placed in the groove of the grooved wire; the grooved wire is an aluminum grooved wire with a copper-coated surface.

[0007] The superconducting circular wire is an NbTi / Cu / Al composite wire with a copper-coated surface;

[0008] The NbTi rod used in the NbTi / Cu / Al composite line is an NbTi rod with Ni plated on its surface.

[0009] Furthermore, in the copper-aluminum matrix NbTi superconducting wire provided by the present invention, the mass fraction of copper in the grooved wire is 20-70%.

[0010] Furthermore, in the copper-aluminum matrix NbTi superconducting wire provided by the present invention, the thickness of the copper plating layer on the surface of the NbTi / Cu / Al composite wire is 2~3μm, and the thickness of the Ni plating layer on the surface of the Ni-plated NbTi rod is 2~3μm.

[0011] Furthermore, in the copper-aluminum matrix NbTi superconducting wire provided by the present invention, the area ratio of NbTi, Cu and Al in the NbTi / Cu / Al composite wire is 1:2~33:8~32.

[0012] Furthermore, in the copper-aluminum matrix NbTi superconducting wire provided by the present invention, the assembly structure of the NbTi / Cu / Al composite wire includes: a circular porous aluminum ingot, wherein the holes in the circular porous aluminum ingot are evenly distributed in concentric circles with symmetrical hole centers, and each hole is filled with a circular NbTi / Cu single-core composite rod.

[0013] Furthermore, in the copper-aluminum matrix NbTi superconducting wire provided by the present invention, the gap distance between the circular NbTi / Cu single-core composite rod and the hole is no higher than 0.5 mm.

[0014] Furthermore, in the copper-aluminum matrix NbTi superconducting wire provided by the present invention, the assembly structure of the NbTi / Cu / Al composite wire includes: multiple hexagonal NbTi / Cu / Al single-core composite rods closely arranged in an aluminum tube, and small-sized aluminum rods filling the gaps between the hexagonal NbTi / Cu / Al single-core composite rods and the aluminum tube.

[0015] Furthermore, in the copper-aluminum matrix NbTi superconducting wire provided by the present invention, the gap area in the aluminum tube after the small-size aluminum rod is filled is not higher than 5%.

[0016] On the other hand, the present invention provides a method for preparing copper-aluminum matrix NbTi superconducting wire, which includes: coating and welding copper strip onto the surface of aluminum rod, annealing after multiple cold drawing to eliminate cold working stress, and then obtaining the grooved wire after flattening, die passing, multiple rolling and shaping die finishing.

[0017] The NbTi / Cu / Al composite wire was prepared by multiple drawing passes and multiple aging heat treatments.

[0018] The superconducting circular wire was prepared by electroplating copper onto the surface of the NbTi / Cu / Al composite wire.

[0019] The copper-aluminum matrix NbTi superconducting wire is obtained by inserting the superconducting round wire into the grooved wire and then induction heating and online tin melting.

[0020] Furthermore, in the method for preparing copper-aluminum matrix NbTi superconducting wires provided by the present invention, the parameters for electroplating copper include: electroplating solution temperature of 40℃~60℃, coating deposition rate of 100μm / h~200μm / h, and trace speed of 0.5m / min~1.0m / min.

[0021] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0022] This invention significantly reduces material costs while maintaining excellent superconducting performance and long-term stability. By employing a matrix design that partially replaces copper with aluminum, combined with surface copper plating protection, composite structure assembly using the "tube-through method" or "drilling method," and a strictly controlled multi-stage aging heat treatment process, the prepared copper-aluminum matrix NbTi superconducting wire achieves a critical current density (Jc) of 3076~3108 A / mm² under conditions of 4.2K and 5T. 2 The performance is comparable to that of traditional pure copper-based wires, while the unit cost can be reduced by about 30% to 35%. The preparation process involved in this invention is highly compatible with existing superconducting wire processing equipment, requires no special equipment, and is easy to achieve large-scale continuous production. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 Metallographic image of copper-aluminum matrix NbTi superconducting wires prepared by drilling method.

[0025] Figure 2 Metallographic image of copper-aluminum matrix NbTi superconducting wires prepared by the tube-through method. Detailed Implementation

[0026] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental and detection methods described in each embodiment are conventional methods; the reagents and materials described are commercially available unless otherwise specified. Unless otherwise specified, all percentages in the following embodiments refer to mass percentages. Unless otherwise specified, all proportions in the following embodiments refer to mass ratios.

[0027] In the following examples, the copper used is oxygen-free copper, grade TU00; the aluminum used is pure aluminum with an aluminum content >99.95%.

[0028] Example 1

[0029] This embodiment provides a process for preparing copper-aluminum matrix NbTi superconducting wires using the tube-through method.

[0030] Step 1: Clean, assemble, weld, extrude, draw in multiple passes, form, cut to length and straighten the Ni-plated NbTi rod, copper tube, aluminum tube and aluminum top cover and aluminum bottom cover to obtain a hexagonal NbTi / Cu / Al single-core composite rod.

[0031] In step 1, to reduce the cost of a single-core rod, the Nb cylinder barrier layer was eliminated compared to the NbTi / barrier layer / Cu single-core rod, and a thin-walled copper tube was used. The NbTi rod surface was chemically plated with Ni, with a plating thickness of 2μm~3μm, which effectively prevents the reaction between Cu and Ti. Simultaneously, the Ni layer interdiffused with Cu during the aging heat treatment to form a CuNi alloy, further reducing AC losses.

[0032] Step 2: Multiple hexagonal NbTi / Cu / Al single-core composite rods are tightly arranged inside an aluminum tube, with the gaps filled using small-diameter aluminum rods. The area of ​​the gaps in the aluminum tube after filling with small-diameter aluminum rods is no more than 5%. After assembly, the rods are drawn to the required specifications through multiple passes and subjected to multiple aging heat treatments to form the NbTi superconducting phase, thus obtaining the NbTi / Cu / Al composite wire. The area ratio of NbTi, Cu, and Al in the NbTi / Cu / Al composite wire is 1:(2~33):(8~32).

[0033] In step 2, the multiple aging heat treatments employ a low-temperature, short-time, and multiple-time method to prevent the diffusion reaction between Cu and Ti during prolonged holding, which would form brittle Cu-Ti compounds and affect the long-line processing of the composite wire. The parameters for the multiple aging heat treatments are: aging temperature of 200℃~600℃, holding time of 10h~20h per treatment, and 6~8 aging cycles.

[0034] Step 3: Electroplat Cu onto the surface of NbTi / Cu / Al composite wires of a certain specification. The coating thickness is determined according to the design requirements to obtain NbTi / Cu / Al / Cu composite wires, i.e., superconducting round wires.

[0035] Copper plating is performed on the aluminum surface of the NbTi / Cu / Al composite wire. The plating thickness is uniform and non-eccentric, ranging from 2μm to 3μm. The electroplating bath temperature is 40℃ to 60℃, the plating deposition rate is 100μm / h to 200μm / h, and the wire speed is 0.5m / min to 1.0m / min. Visual inspection is required throughout the electroplating process to ensure uniform copper plating and no aluminum leakage.

[0036] Step 4: Copper strip and aluminum rod are used for cladding welding, multi-pass drawing and annealing to obtain copper-clad aluminum round rod; copper-clad aluminum round rod of a certain specification is rolled in multiple passes and finished by a sizing die to obtain U-shaped copper-clad aluminum groove line, i.e. groove line;

[0037] The copper mass fraction in the grooved line is 20-70% to prevent aluminum leakage inside the U-shaped groove during subsequent multi-pass rolling. When the copper strip is welded onto the surface of the aluminum rod, the weld should be free of defects such as porosity and cracks. After multiple cold drawing passes, a short-time annealing is required, mainly to eliminate cold working stress. The copper-clad aluminum round rod is flattened, passed through a die, rolled in multiple passes, and finished with a shaping die to obtain the copper-clad aluminum grooved line. After forming, eddy current testing and online visual inspection are required to ensure that the surface of the copper-clad aluminum grooved line is free of defects such as inclusions, cracks, and aluminum leakage.

[0038] Step 5: In-line embedding and welding of multi-core NbTi / Cu / Al / Cu composite wire and U-shaped copper-clad aluminum channel wire to obtain rectangular copper-clad aluminum-based NbTi superconducting wire. Then, in-line braided insulation is performed to finally obtain extremely low-cost and highly stable NbTi superconducting wire.

[0039] The surfaces of the copper-plated NbTi superconducting core wire and the copper-clad aluminum groove wire are all copper, and the surfaces are strictly required to be free of aluminum defects. The purpose is to use molten tin for welding during the subsequent inlay welding process to ensure that the rectangular wire surface is uniformly tin-plated and free of inlay defects.

[0040] Before copper-plated NbTi superconducting core wires and copper-clad aluminum channel wires are soldered into molten solder, they must undergo ultrasonic cleaning to remove surface foreign matter. Simultaneously, fluxing is used to eliminate surface tension. Throughout the inlay soldering process, online dimensional inspection, eddy current testing, and visual inspection are required to ensure stable bare wire dimensions, no missing inlays or copper areas, and uniform tin plating. After inlay soldering, the bare wires undergo online insulation braiding. The insulation material can be polyester or glass fiber, depending on the wire's operating environment. During the braiding process, online withstand voltage testing is required to prevent defects caused by missed braiding.

[0041] Example 2

[0042] This embodiment provides a process for preparing copper-aluminum matrix NbTi superconducting wires by drilling.

[0043] Step 1: Clean, assemble, weld, extrude, draw in multiple passes, form, cut to length and straighten the Ni-plated NbTi rod, copper tube and copper top cover and bottom cover to obtain a circular NbTi / Cu single-core composite rod.

[0044] Step 2: Drill holes in the aluminum ingot to obtain a circular porous aluminum ingot with the holes evenly distributed in concentric circles to maintain central symmetry; place the circular NbTi / Cu single-core composite rod into the hole of the circular porous aluminum ingot, and then use aluminum top and bottom covers for assembly, welding, extrusion, multi-pass drawing and multiple aging heat treatments to obtain NbTi / Cu / Al composite wire.

[0045] In step 2, the multiple aging heat treatments employ a low-temperature, short-time, and multiple-stage method to prevent the diffusion reaction between Cu and Ti during prolonged holding, which could lead to the formation of brittle Cu-Ti compounds and affect the long-line processing of the composite wire. The aging temperature is 200℃, each holding time is 10 hours, and the aging process is repeated 6 times.

[0046] Step 3: Electroplat Cu onto the surface of NbTi / Cu / Al composite wires of a certain specification. The thickness of the plating layer is determined according to the design requirements to obtain NbTi / Cu / Al / Cu composite wires, i.e., superconducting round wires.

[0047] The remaining steps are the same as in Example 1.

[0048] Example 3

[0049] This embodiment provides a process for preparing copper-aluminum matrix NbTi superconducting wires using the tube-through method.

[0050] A Φ180mm Ni-plated NbTi rod, a 5mm thick thin-walled high-purity oxygen-free copper tube, and a 15mm thick high-purity aluminum tube are cleaned, assembled, welded, and extruded to obtain a Φ55mm NbTi / Cu / Al single-core composite rod. This is then subjected to multiple drawing passes, hexagonal forming, length cutting, and straightening to H15mm to obtain the final NbTi / Cu / Al single-core composite rod. Fifty-five NbTi / Cu / Al single-core composite rods are neatly arranged within a 10mm thick high-purity aluminum tube, with the gaps between the single-core rods and the copper tube filled with Φ2mm aluminum rods. This is followed by welding and extrusion to obtain a Φ62mm NbTi / Cu / Al composite rod. This rod then undergoes multiple drawing passes and multiple aging heat treatments at 300℃ for eight cycles. Each heat treatment lasted 15 hours, resulting in a Φ0.798mm NbTi / Cu / Al composite wire. This composite wire was then electroplated with copper to a thickness of 2μm, yielding a copper-plated Φ0.800mm NbTi / Cu / Al composite wire. A Φ3.5mm copper-clad aluminum rod (50% copper by mass) was subjected to multiple rolling, annealing, and die forming to obtain a 2mm wide and 1mm high copper-clad aluminum channel wire. The Φ0.800mm NbTi / Cu / Al composite wire and the copper-clad aluminum channel wire were then in-line inlay welded together to obtain a 1.9mm wide and 0.8mm high rectangular bare wire. Finally, polyester filament was used for in-line braiding insulation to obtain a 2.1mm wide and 1.0mm high copper-aluminum matrix NbTi superconducting wire. The Jc(4.2K,5T) of this wire is 3108A / mm². 2 It has performance comparable to conventional oxygen-free copper-based wires, but the unit cost is reduced by about 30%.

[0051] Example 4

[0052] This embodiment provides a process for preparing copper-aluminum matrix NbTi superconducting wires by drilling.

[0053] A Φ210mm Ni-plated NbTi rod and a 7mm thick thin-walled high-purity oxygen-free copper tube are cleaned, assembled, welded, and extruded to obtain a Φ70mm NbTi / Cu single-core composite rod. This is then subjected to multiple drawing passes, length cutting, and straightening until it reaches Φ20mm, yielding the NbTi / Cu single-core composite rod. Twenty Φ20.4mm deep holes are drilled from a Φ200mm high-purity aluminum ingot using a deep-hole drilling method. Twenty NbTi / Cu single-core composite rods are placed into the drilled aluminum ingot, followed by welding and extrusion to obtain a Φ60mm NbTi / Cu / Al composite rod. This is then subjected to multiple drawing passes and... Multiple aging heat treatments were performed at 280℃ for six cycles, with each cycle lasting 10 hours, to obtain a Φ0.978mm NbTi / Cu / Al composite wire. The composite wire was then electroplated with copper to a thickness of 2μm, resulting in a copper-plated Φ0.980mm NbTi / Cu / Al composite wire. A Φ5mm copper-clad aluminum rod (70% copper by mass) was subjected to multiple rolling, annealing, and die forming to obtain a 4mm wide and 2mm high copper-clad aluminum channel wire. The Φ0.980mm NbTi / Cu / Al composite wire and the copper-clad aluminum channel wire were then in-line inlay welding. Figure 1 The diagram shows the process of obtaining a rectangular bare wire with a width of 3.9 mm and a height of 1.9 mm. Finally, glass fiber is used for in-line braiding insulation to obtain a copper-aluminum matrix NbTi superconducting wire with a width of 4.15 mm and a height of 2.15 mm. The Jc(4.2K,5T) of this wire is 3088 A / mm². 2 It has performance comparable to conventional oxygen-free copper-based wires, but the unit cost is reduced by about 35%.

[0054] Example 5

[0055] This embodiment provides a process for preparing copper-aluminum matrix NbTi superconducting wires by drilling.

[0056] A Φ140mm Ni-plated NbTi rod and a 5mm thick thin-walled high-purity oxygen-free copper tube were cleaned, assembled, welded, and extruded to obtain a Φ40mm NbTi / Cu single-core composite rod. This was then subjected to multiple drawing passes, length cutting, and straightening until Φ14mm was obtained, yielding the NbTi / Cu single-core composite rod. Thirty-nine Φ14.3mm deep holes were drilled from a Φ100mm high-purity aluminum ingot using a deep-hole drilling method. Thirty-nine NbTi / Cu single-core composite rods were placed into the drilled aluminum ingot, followed by welding and extrusion to obtain a Φ45mm NbTi / Cu / Al composite rod. This was then subjected to multiple drawing passes and multiple aging heat treatments at 320℃ for seven aging cycles, each with a holding time of 20 hours, to obtain the Φ A 0.778mm NbTi / Cu / Al composite wire was first prepared, then surface-plated with copper to a thickness of 2μm to obtain a copper-plated 0.780mm NbTi / Cu / Al composite wire. A 3.8mm copper-clad aluminum rod (60% copper by mass) was then subjected to multi-pass rolling, annealing, and die forming to obtain a 2.8mm wide and 1.8mm high copper-clad aluminum channel wire. The 0.780mm NbTi / Cu / Al composite wire and the copper-clad aluminum channel wire were then in-line inlay welded together to obtain a 2.7mm wide and 1.8mm high rectangular bare wire. Finally, polyester filament was used for in-line braiding insulation to obtain a 3mm wide and 2.1mm high copper-aluminum matrix NbTi superconducting wire. The Jc(4.2K,5T) of this wire is 3076A / mm². 2 It has performance comparable to conventional oxygen-free copper-based wires, but the unit cost is reduced by about 32%.

[0057] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate preferred embodiments. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A copper-aluminum matrix NbTi superconducting wire, wherein the assembly structure of the copper-aluminum matrix NbTi superconducting wire includes a grooved wire and a superconducting circular wire, wherein the superconducting circular wire is placed in the groove of the grooved wire; characterized in that, The groove line is an aluminum groove line with a copper-coated surface; The superconducting circular wire is an NbTi / Cu / Al composite wire with a copper-coated surface; The NbTi rod used in the NbTi / Cu / Al composite line is an NbTi rod with Ni plated on its surface; The mass fraction of copper in the grooved lines is 20-70%; The thickness of the copper plating layer on the surface of the NbTi / Cu / Al composite wire is 2~3μm, and the thickness of the Ni plating layer on the surface of the NbTi rod with Ni plating is 2~3μm; The assembly structure of the NbTi / Cu / Al composite line includes: a circular porous aluminum ingot, wherein the holes in the circular porous aluminum ingot are evenly distributed in concentric circles with central symmetry, and each hole is filled with a circular NbTi / Cu single-core composite rod, wherein the gap between the circular NbTi / Cu single-core composite rod and the hole is no higher than 0.5 mm.

2. A copper-aluminum matrix NbTi superconducting wire, wherein the assembly structure of the copper-aluminum matrix NbTi superconducting wire includes a grooved wire and a superconducting circular wire, wherein the superconducting circular wire is placed in the groove of the grooved wire; characterized in that, The groove line is an aluminum groove line with a copper-coated surface; The superconducting circular wire is an NbTi / Cu / Al composite wire with a copper-coated surface; The NbTi rod used in the NbTi / Cu / Al composite line is an NbTi rod with Ni plated on its surface; The mass fraction of copper in the grooved lines is 20-70%; The thickness of the copper plating layer on the surface of the NbTi / Cu / Al composite wire is 2~3μm, and the thickness of the Ni plating layer on the surface of the NbTi rod with Ni plating is 2~3μm; The assembly structure of the NbTi / Cu / Al composite line includes: multiple hexagonal NbTi / Cu / Al single-core composite rods arranged closely in an aluminum tube; the gap between the hexagonal NbTi / Cu / Al single-core composite rods and the aluminum tube is filled with small-sized aluminum rods; the gap area in the aluminum tube after the small-sized aluminum rods are filled is no more than 5%.

3. The copper-aluminum matrix NbTi superconducting wire according to claim 1 or 2, characterized in that, The area ratio of NbTi, Cu and Al in the NbTi / Cu / Al composite line is 1:2~33:8~32.

4. A method for preparing a copper-aluminum matrix NbTi superconducting wire, characterized in that, The preparation of the copper-aluminum matrix NbTi superconducting wire according to any one of claims 1 to 3 includes: welding copper strip onto the surface of an aluminum rod, annealing after multiple cold drawing to eliminate cold working stress, and then obtaining the grooved wire after flattening, die passing, multiple rolling and finishing with a shaping die. The NbTi / Cu / Al composite wire was prepared by multiple drawing passes and multiple aging heat treatments. The superconducting circular wire was prepared by electroplating copper onto the surface of the NbTi / Cu / Al composite wire. The copper-aluminum matrix NbTi superconducting wire is obtained by inserting the superconducting round wire into the grooved wire and then induction heating and online tin melting.

5. The method for preparing copper-aluminum matrix NbTi superconducting wire according to claim 4, characterized in that, The parameters for the electroplating of copper include: electroplating solution temperature of 40℃~60℃, coating deposition rate of 100μm / h~200μm / h, and trace speed of 0.5m / min~1.0m / min.

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