JPH0416888B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing an aluminum stabilized superconductor, and in particular improves the bondability between the superconductor and aluminum without deteriorating the properties of the superconductor. [Prior art and problems to be solved by the invention] In general, as superconductors, superconductors having a stranded or assembled wire structure coated with high-purity copper to stabilize them have been put into practical use. A superconductor stabilized with aluminum is desired because high-purity aluminum has lower residual resistance and magnetic resistance than copper at the cryogenic temperatures actually used. Conventionally, a method of extrusion coating aluminum around the superconductor has been proposed as a method for manufacturing aluminum-stabilized superconductors, but superconducting materials such as Nb-Ti,
Since the deformation resistance during processing of V ₃ Ga, Nb ₃ Sn, etc. and aluminum is extremely different, it is extremely difficult to integrate them into a composite body through normal processing.Extrusion coating is an attempt to improve the bonding between superconductors and aluminum. However, there were problems such as breakage of the superconductor wires. Also, unlike other composite materials, such as aluminum-coated steel wire and steel-core aluminum trolley wire, aluminum-stabilized superconductors have the disadvantage that their properties deteriorate due to the effects of heat and processing during aluminum coating. Ta. [Means for Solving the Problems] In view of this, the present invention has been developed based on various researches to improve the bondability between superconductors and aluminum without deteriorating the properties of superconductors. A method for manufacturing aluminum stabilized superconductors with excellent bondability has been developed. That is, the present invention provides a method for extrusion coating aluminum as a stabilizing material on the outer periphery of a superconductor having a structure in which stranded wires, assembled wires, or the outer periphery thereof is coated with copper.
After polishing and degreasing the surface of the superconductor, a pure aluminum billet with a purity of 99.99 wt% or more, which is held in a non-oxidizing atmosphere and heated from both sides to a temperature of 480 to 350°C, is passed through a pair of opposed rams. After extrusion and pressure welding, the product is cooled to a temperature of 300°C or less within 20 minutes, and then heat treated at a temperature of 180 to 250°C for 4 to 200 hours. [Function] In the present invention, the surface of the stranded wire, the assembled wire, or the superconductor (hereinafter abbreviated as the core wire) having a structure in which the outer periphery thereof is coated with high-purity copper is polished and degreased to remove the oxide or / This is to remove stains such as fats and oils and make the metal surface active, thereby facilitating metal bonding with aluminum in the next extrusion coating process. The reason why this is kept in a non-oxidizing atmosphere such as an inert gas (argon, nitrogen gas, etc.) is to maintain the activated metal surface until it is coated with aluminum. Therefore, if polishing and degreasing are insufficient, or if a non-oxidizing atmosphere is insufficiently maintained, the bond between the core wire and aluminum will deteriorate, causing problems in practical use as a superconductor. The purity of the aluminum extruded onto the core wire
The reason why it is 99.99wt% or more is to reduce the residual resistance.
This is because it functions as a current bypass, that is, a stabilizing agent, when the superconducting properties are impaired, and if the purity is below this level, sufficient effects cannot be obtained. In addition, the extrusion temperature of the aluminum billet was set to 480
The temperature was limited to ~350°C in order to obtain a superconductor with good bonding between the core wire and the aluminum coating without deteriorating the superconducting properties, and the billet temperature was set at 480°C.
If it is higher, the core wire will be affected by heat during extrusion coating, resulting in deterioration of superconducting properties, and furthermore, a thick alloy layer will be formed between the aluminum and the core wire, resulting in deterioration of bending workability and mechanical properties. In particular, during billet addition and press-splicing when manufacturing long products, the core wire is kept at a high temperature, resulting in severe deterioration of superconducting properties. On the other hand, if the billet temperature is lower than 350°C, the bonding between the core wire and aluminum will be insufficient, and in order to improve this, the extrusion speed must be lowered, which reduces productivity and makes it impractical. The reason why the aluminum billet is extruded from both sides of the core wire by a pair of opposing rams is to provide pressure contact to both sides of the core wire, thereby improving the bonding between the aluminum and the core wire. In addition, cooling to a temperature below 300°C within 20 minutes after extrusion welding is important because it may cause deterioration of superconducting properties, including the parts that are kept at high temperatures during billet jointing, and damage the interface between the core wire and aluminum. This is to prevent the alloy layer from becoming thicker, and secondly, to stop or slow down the recrystallization of the aluminum material. If such cooling is not provided, the 480
When a billet heated to ~350°C is extruded, the temperature of the extruded material will exceed 400°C due to the heat generated during processing. And the high purity aluminum used in aluminum stabilized superconductors is thus
At temperatures above 400°C, recrystallization progresses rapidly and ends before impurities dissolved in aluminum, which contribute to improving the residual resistance ratio, begin to precipitate. Therefore, since the precipitation of impurities is promoted by the process in which processing strains (dislocations, etc.) inside the material are moved and disappeared by recrystallization due to heating, once recrystallization is completed as described above, Precipitation is no longer promoted. In order to prevent this, in the present invention, recrystallization is stopped or slowed down after aluminum is extruded and pressed, and then a new heat treatment is performed at 180 to 250°C for 4 to 200 hours to balance the recrystallization rate and precipitation rate. The residual resistance ratio is improved by promoting precipitation to the maximum extent possible. The reason why the heat treatment conditions were set as above is that when the temperature exceeds 250℃ and the time exceeds 200 hours, an Al-Cu alloy layer grows and the bonding strength between the two decreases. This is because the recrystallization rate becomes too fast and the residual resistance ratio is not improved, and if the temperature is less than 180°C and the time is less than 4 hours, the effect of improving the residual resistance ratio is insufficient. [Example] Hereinafter, the present invention will be described in detail with reference to Examples. Gather 1500 Nb-Ti superconducting wires with a diameter of 50μ,
This peripheral surface is coated with high purity copper, width 3.0mm, thickness 2.0mm
Using a core wire of
As shown in Fig. 1, an aluminum stabilized superconductor with a width of 20 mm and a thickness of 4 mm has a structure in which superconducting wires 2 are assembled and a copper coating layer 3 is provided on the circumferential surface of the core wire 1. An aluminum stabilizing layer 4 is formed around the outer periphery of the core wire 1. was manufactured. Extrusion coating of aluminum was carried out using an extruder shown in FIG. The extruder has a barrel 5 filled with heated aluminum billets 4a and 4b on the left and right sides, and a core wire 1 is attached to one wall in the middle in the axial direction.
A nipple 6 is provided to insert the core wire into the extruder, and a die 7 is provided on the other wall to take out the core wire from inside the extruder.
1. The billets 4a and 4b filled in the barrel 5 are pressed against both sides of the core wire 1 that crosses inside the extruder.
It has a pair of opposing rams 8a and 8b, and billet supply ports 9 on both left and right sides of the barrel 5 (only one side is shown in the figure).
It has been established. Although the core wire 1 is not shown in the figure, after its surface is polished and degreased, it is held in a non-oxidizing atmosphere, passed through a nipple 6, inserted into an extruder, traverses the inside of the extruder, and exits from a die 7. At this time, no tension is applied to the core wire 1 from the front, and only a repetitive force is applied from the rear. Billet 4a, 4b
When the rams 8a, 8b are retreated and fed into the barrel 5 from the supply port 9, and the rams 8a, 8b are moved forward toward each other, the billets 4a, 4b are compressed toward both sides of the core wire 1, The core wire 1 is pressed and extruded through a die 7, and aluminum 4 is extruded and coated around the core wire 1, as shown in FIG. The superconducting properties (critical current value Ic) of the aluminum stabilized superconductor produced in this manner were determined under the conditions of a temperature of 4.2〓 and 7T. In addition, as an evaluation of bondability at the interface between aluminum and core wire,
An aluminum stabilized superconductor was held in a jig with a curved surface of 4 mm radius, and flatwise it was
A 90-degree repeated bending test was conducted to determine the number of bending cycles until the interface peeled off. These results are the first
Also listed in the table. For comparison, an aluminum-stabilized superconductor was produced by extrusion coating aluminum through an extruder without polishing or degreasing the surface of the core wire, and the same tests were conducted on this superconductor. Similar tests were also conducted on an aluminum stabilized superconductor in which the outer periphery of a polished and degreased core wire was extruded and coated with aluminum using a conventional single-sided extruder. These results are also listed in Table 1.

【table】

[Table] (2) Heat treatment conditions after extrusion coating

〓 Electrical resistance at 300K〓
(3) Residual resistance ratio of coated aluminum stabilizing material

Claims (1)

[Claims] 1 In a method of extrusion coating aluminum as a stabilizing material on the outer periphery of a superconductor having a structure of stranded wires, assembled wires, or copper coating on the outer periphery, the surface of the superconductor is polished and degreased, and then held in a non-oxidizing atmosphere. and heated to a temperature of 480 to 350℃ from both sides.
Within 20 minutes after a pure aluminum billet of 99.99wt% or more is extruded and pressure welded by a pair of opposed rams.
Cool to a temperature below 300℃ and then heat this to 180~250℃
1. A method for producing an aluminum stabilized superconductor, comprising heat treatment at a temperature of 4 to 200 hours.