CN113549971B

CN113549971B - Superconducting strip welded joint and strengthening treatment method thereof

Info

Publication number: CN113549971B
Application number: CN202010337608.9A
Authority: CN
Inventors: 薛济萍; 薛驰; 黄勇; 田波; 蔡玲玲
Original assignee: Zhongtian Group Shanghai Superconducting Technology Co ltd; Jiangsu Zhongtian Technology Co Ltd
Current assignee: Zhongtian Group Shanghai Superconducting Technology Co ltd; Jiangsu Zhongtian Technology Co Ltd
Priority date: 2020-04-26
Filing date: 2020-04-26
Publication date: 2022-09-30
Anticipated expiration: 2040-04-26
Also published as: CN113549971A

Abstract

The outer layer of the superconducting tape welding joint is wrapped with a metal strengthening layer in an omnibearing and seamless mode. On the premise of not influencing the electrical performance and the mechanical performance of a welding point of a welding joint, the upper surface, the lower surface and the two side surfaces of the superconducting strip joint are simultaneously subjected to strengthening treatment, so that the welding resistance of the welding point is reduced, and the mechanical strength of the joint is increased; a welding flux layer is avoided between the generated metal strengthening layer and the superconducting tape, and the thickness of the metal strengthening layer can be accurately controlled according to working conditions, so that the mechanical property of the position of a welding joint can be automatically adjusted. In addition, the method has simple process and convenient operation, and does not need special equipment.

Description

Superconducting strip welded joint and strengthening treatment method thereof

Technical Field

The invention relates to the field of metal surface treatment, in particular to a superconducting strip welding joint and a strengthening treatment method thereof.

Background

With the development of the application technology of superconduction, the superconducting materials are applied to the fields of scientific research, medical treatment, electric power, industry and the like more and more. At present, the length of a single commercial superconducting tape in mass production is only kilometer magnitude, and the use requirement of an engineering project cannot be met at all, so that the length of the superconducting tape is usually required to be prolonged by welding in the current practical engineering application. The fabrication of the welding joint of the superconducting tape is an important technique in the application of the superconducting tape, and since the joint is usually welded by using a conventional conductor solder, the welding resistance is generated, and the welding resistance is one of the main sources of the heat load of the superconducting component, in order to reduce the heat loss of the joint, the welding resistance of the joint must be reduced as much as possible.

The commonly used method for reducing the joint resistance is as follows: firstly, the welding area of a welding point is increased, namely the relative welding length between two superconducting tapes is increased; secondly, performing single-sided or double-sided secondary stitch welding on the upper surface and the lower surface of the welding spot joint. In the second generation of high temperature superconducting tapes (coated conductor structure superconducting tapes), a method is also provided, in which the base tapes of two welded superconducting tapes are peeled off and extended by a certain length, and the joints are covered with the base tapes and welded to the surfaces of the superconducting tapes together.

The methods can reduce the welding resistance of the welding point and increase the mechanical strength of the joint to a certain extent, but the welding length is lengthened, the bending performance of the joint position is reduced due to the surface stitch welding of the superconducting strip or the base band, the mechanical performance of the welding point is reduced, the use of the strip is influenced, and particularly, the use amount and the number of layers of the welding material are increased in the stitch welding mode, so that the hardness of the joint is increased, and the bending performance is further reduced. Moreover, the method can only strengthen the upper surface and the lower surface of the joint, the two side surfaces of the strip are welded and packaged by using the solder, and when the joint is in the stress working conditions of twisting, bending and the like, the hidden danger risks of unsoldering, tearing and the like are easy to occur.

In summary, how to strengthen the upper surface, the lower surface and the two side surfaces of the superconducting strip joint on the premise of not influencing the mechanical performance of the welding point is important for research on reducing the welding resistance of the welding point and increasing the mechanical strength of the joint.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a superconducting tape welded joint and a strengthening method thereof, which can reduce the welding resistance of the welded joint and increase the mechanical strength of the joint.

The first purpose of the invention is to provide a superconducting tape welding joint, wherein the outer layer of the superconducting tape welding joint is wrapped with a metal strengthening layer in an omnibearing and seamless mode.

Specifically, the metal of the metal strengthening layer includes, but is not limited to, gold, silver, copper or copper-zinc alloy.

Specifically, the thickness range of the metal reinforcing layer is as follows: 5um to 40 um.

The second purpose of the invention is to provide a method for coating metal on the outer layer of the superconducting tape welding joint, wherein the metal strengthening layer is formed by coating metal on the outer layer of the superconducting tape welding joint by using a method for coating metal on the outer layer.

Specifically, the method for plating the metal includes but is not limited to electroplating or electroless plating.

Specifically, the electroplating is to form the metal reinforcing layer by placing the welded joint as a cathode in a plating solution containing the metal and depositing cations of the metal in the plating solution on the surface of the welded joint through electrolysis.

Preferably, the electroplating of the welded joint comprises the following specific steps:

(1) pretreatment: polishing, degreasing, acid washing and then ultrasonically cleaning a welding joint of the superconducting strip;

(2) placing the pretreated welding joint part serving as a cathode in a plating solution containing the metal, placing an anode in the plating solution of the metal, and introducing direct current between the anode and the welding joint to deposit metal cations in the plating solution on the surface of the welding joint so as to form the metal strengthening layer;

(3) and carrying out post-treatment on the welding joint with the surface formed with the metal strengthening layer.

Further preferably, the polishing is to polish the welding spot of the welding joint and the surface of the peripheral strip by using sand paper to remove burrs, tin nodules and residual soldering flux on the surface, the degreasing is to remove surface grease by using alcohol, and the pickling is to remove a surface oxide film by using citric acid or oxalic acid.

Compared with the prior art, the superconducting tape welding joint and the strengthening treatment method thereof strengthen the upper surface, the lower surface and two side surfaces of the superconducting tape welding joint on the premise of not influencing the electrical performance and the mechanical performance of a welding point of the welding joint, thereby reducing the welding resistance of the welding point and increasing the mechanical strength of the joint; a solder layer is avoided between the generated metal strengthening layer and the superconducting tape, and the thickness of the metal strengthening layer can be accurately controlled according to working conditions, so that the mechanical property of the position of a welding joint can be automatically adjusted. In addition, the method has simple process and convenient operation, and does not need to use special equipment.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the prior art descriptions will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a schematic view of the appearance of a weld joint of the present invention before strengthening treatment;

FIG. 2 is a schematic view of the appearance of a weld joint after strengthening treatment according to the present invention;

fig. 3 is a cross-sectional view of fig. 2.

Reference numerals and component parts description referred to in the drawings:

1. a superconducting tape; 2. a solder layer; 3. a metal strengthening layer.

Detailed Description

The common method for reducing the resistance of the joint is to increase the relative welding length between two superconducting tapes, increase the conductive sectional area by the method, reduce the welding resistance and increase the mechanical property, and has the defects that the bending property of a welding point is reduced along with the increase of the welding length, and a large-length welding point is broken when the bending radius is small, so that the method is not suitable for certain specific working conditions.

And performing single-side or double-side secondary stitch welding on the upper surface and the lower surface of the welding point joint. For the superconducting tapes with the coated conductor structure, the base bands of two welded superconducting tapes can be stripped and prolonged by a certain length, and the joints are covered by the base bands and welded to the surfaces of the superconducting tapes together.

In other processes, a certain relative pressure is applied to two strips at the welding point position in the welding process, so that the solder layer becomes thin (the conductive path is shortened, the resistance is reduced), and the contact between the solder and the surface of the strips is more sufficient (the welding strength is improved). However, the pressure has a saturation value, and when the pressure reaches a certain value, the welding resistance cannot be reduced, the superconducting tape can be damaged, the performance of a welding point is reduced, and even the circuit is broken.

Although the welding resistance of the welding point can be reduced and the mechanical strength of the joint can be increased to a certain extent by the methods, the welding length is lengthened, the bending performance of the joint position is reduced due to the surface stitch welding of the superconducting tape or the base tape, the mechanical performance of the welding point is reduced, the use of the tape is affected, and particularly, the use amount and the number of layers of the solder are increased in the stitch welding mode, so that the hardness of the joint is increased, and the bending performance is further reduced. In addition, the method can only strengthen the upper surface and the lower surface of the joint, and the two side surfaces of the strip are in an open state, so that hidden risks such as welding and tearing are easy to occur when the joint is in stress working conditions such as twisting and bending.

Therefore, in order to solve the above problems, the present invention provides a new method for strengthening a welding joint of a superconducting tape based on a conventional welding method, which can effectively reduce the welding resistance of the welding joint of the superconducting tape, improve the mechanical strength of the joint, and the like, and can avoid the influence on the bending performance of the joint.

The technical solution of the present invention will be clearly and completely described by the following detailed description. It should be apparent that the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in figures 1-3, a superconducting tape welding joint, a superconducting tape 1 is welded with another superconducting tape 1, a solder layer 2 is arranged in the middle, and a metal strengthening layer 3 is wrapped on the outer layer of the superconducting tape welding joint in an omnibearing and seamless mode. The metal of the metal strengthening layer 3 includes, but is not limited to, gold, silver, copper or copper-zinc alloy. Thickness range of the metal reinforcing layer 3: 5um to 40 um.

One of the welding methods of the superconducting tapes of the present invention is as follows: and brazing in a lap joint mode.

(1) Polishing and cleaning the strip, and removing an oxide layer and impurities on the surface of the strip to ensure that the strip has better wettability;

(2) preheating a welding workbench to enable the temperature of the welding workbench to be higher than the melting point of the solder, wherein the general welding temperature is slightly higher than the melting point of the solder by 5-10 ℃, and the highest temperature is lower than the temperature recommended in a strip specification;

(3) the strip is spread on a welding plane, and a proper amount of soldering flux and welding flux are added;

(4) applying a preset pressure to the strip by adopting a pressure tool, and keeping the pressure constant;

(5) and closing the heater, and cooling the joint to room temperature to obtain the welded superconducting strip.

And then strengthening the obtained welded superconducting strip, and carrying out omnibearing seamless wrapping on the welding joint of the superconducting strip by using an electroplating method, a chemical plating method or other outer plating methods to obtain a metal strengthening layer 3 wrapped on the welding joint and the periphery. The specific outer plating method only explains the specific steps of the electroplating process, and other outer plating methods are not specifically described as long as the metal strengthening layer 3 can be wrapped outside the welding joint of the superconducting strip.

The main process flow of the metal strengthening layer 3 of the superconducting strip welding joint is as follows: pretreatment, metal layer electroplating and post-treatment. The following is set forth in detail:

1. pretreatment

The surface of the strip around the welding point machine of the superconducting strip needs to be pretreated before plating, and the aim is to finish the surfaces of the welding point and the strip, remove grease, oxide films and the like on the surfaces of the welding point and the strip and provide a needed plating surface for the deposition of a subsequent plating layer.

(1) Polishing the surfaces of the welding spots and the peripheral strips by using sand paper with the mesh number larger than 600 meshes, removing various macroscopic defects such as burrs, tin welding nodules, residual scaling powder and the like on the surfaces, and improving the flatness and the electroplating quality of the surfaces.

(2) Degreasing and oil removal the surface lipids are removed by using alcohol.

(3) And (4) removing the surface oxidation film by using weak corrosive solution such as citric acid or oxalic acid.

(4) Ultrasonic cleaning: further removing residual grease and acid pickling solution on the surface.

2. Electroplating of

The welding joint part of the prepared welded superconducting strip is used as a cathode and is placed in a plating solution containing metal, an anode is placed in the metal plating solution, and direct current is introduced between the anode and the welding joint of the superconducting strip, so that metal cations in the plating solution are deposited on the surface of the welding joint, and a metal strengthening layer is formed.

3. Post-treatment

After electroplating, the plating layer needs to be subjected to post-treatment so as to improve the corrosion resistance, the tarnish resistance, the oxidation resistance and the like of the plating layer. The quality of the post-treatment process directly influences the quality of the function of the coating.

Such as: after copper plating, ultrasonic cleaning is firstly carried out to remove residual plating solution on the surface, and then a copper protective agent is sprayed to prevent the surface plating layer from being quickly oxidized.

Embodiment 1 the invention provides a superconducting tape welded joint and a strengthening treatment method thereof, wherein an electroplating method is adopted, the metal of a metal strengthening layer is copper, the thickness of the metal strengthening layer is 20um, and the method comprises the following specific steps:

(1) pretreatment: polishing the welding point of the welding joint and the surface of the peripheral strip by using 800-mesh abrasive paper, cleaning the polished surface by using commercially available alcohol to remove grease, and finally removing an oxide layer on the surface by using commercially available citric acid;

(2) electroplating: placing the pretreated welding joint as a cathode in a plating solution containing metal copper, placing a copper electrode in the plating solution containing the metal copper as an anode, and depositing copper ions in the plating solution on the surfaces of the welding joint and peripheral strips by passing direct current between the anode and the cathode, wherein the thickness of a metal strengthening layer is controlled to be 20 microns;

(3) and (3) post-treatment: and carrying out ultrasonic cleaning to remove residual plating solution on the surface to obtain the welding joint with the metal strengthening layer formed on the surface.

Embodiment 2 the present invention provides a superconducting tape welded joint and a reinforcement processing method thereof, which are substantially the same as those of embodiment 1 except that: the metal of the metal strengthening layer is silver.

Embodiment 3 the present invention provides a superconducting tape welded joint and a reinforcement processing method thereof, which are substantially the same as those of embodiment 1 except that: the metal of the metal strengthening layer is gold.

Embodiment 4 the present invention provides a superconducting tape welded joint and a reinforcement processing method thereof, which are substantially the same as those of embodiment 1 except that: the metal of the metal strengthening layer is copper-zinc alloy.

Embodiment 5 the present invention provides a superconducting tape welded joint and a reinforcement processing method thereof, which are substantially the same as those of embodiment 1 except that: the thickness of the metal strengthening layer is 40 um.

Embodiment 6 the present invention provides a superconducting tape welded joint and a reinforcement processing method thereof, which are substantially the same as embodiment 2 except that: the thickness of the metal strengthening layer is 40 um.

Embodiment 7 the present invention provides a superconducting tape welded joint and a strengthening treatment method thereof, which are substantially the same as those of embodiment 3 except that: the thickness of the metal strengthening layer is 40 um.

Embodiment 8 the present invention provides a superconducting tape welded joint and a strengthening treatment method thereof, which are substantially the same as those of embodiment 4 except that: the thickness of the metal strengthening layer is 40 um.

Embodiment 9 the present invention provides a superconducting tape welded joint and a strengthening treatment method thereof, which are substantially the same as those of embodiment 1, except that: the thickness of the metal strengthening layer is 5 um.

Comparative example 1 the present invention provides a welded joint of superconducting tapes which has not been subjected to the above-mentioned strengthening treatment, and the welding method is identical to that of example 1 except that the strengthening treatment of the present application has not been performed.

Comparative example 2 the present invention provides a superconducting tape welded joint and a reinforcement treatment method thereof, which are substantially the same as in example 1 except that: the thickness of the metal strengthening layer is 2 um.

Comparative example 3 the present invention provides a superconducting tape welded joint and a reinforcement treatment method thereof, which are substantially the same as in example 1 except that: the thickness of the metal strengthening layer is 50 um.

Table 1: the above examples 1 to 9 and comparative examples 1 to 3 were subjected to performance tests:

as shown in table 1 above:

an outer copper-plated strengthening layer is adopted, when the thickness of a plating layer is 5 mu m, the welding resistance of a welding spot is reduced by 4%, and the maximum mechanical strain is reduced by 55.9%; when the thickness of the plating layer is 20um, the welding resistance of the welding spot is reduced by 8.5%, and the maximum mechanical strain is reduced by 67.1%; when the thickness of the plating layer is 40um, the welding resistance of the welding spot is reduced by 13.8%, and the maximum mechanical strain is reduced by 70.4%.

The outer silver plating strengthening layer is adopted, when the thickness of the plating layer is 20um, the welding resistance of the welding spot is reduced by 8.9%, and the maximum mechanical strain is reduced by 67.3%; when the thickness of the plating layer is 40um, the welding resistance of the welding spot is reduced by 14.2 percent, and the maximum mechanical strain is reduced by 72.7 percent.

An outer gold-plated strengthening layer is adopted, when the thickness of a plating layer is 20 mu m, the welding resistance of a welding spot is reduced by 7.1%, and the maximum mechanical strain is reduced by 67.1%; when the thickness of the plating layer is 40um, the welding resistance of the welding spot is reduced by 11.4%, and the maximum mechanical strain is reduced by 73.7%.

The outer copper-zinc alloy plated strengthening layer is adopted, and when the thickness of the plating layer is 20 mu m, the welding resistance of a welding spot is reduced by 3.8%, and the maximum mechanical strain is reduced by 67.3%; when the thickness of the plating layer is 40um, the welding resistance of the welding spot is reduced by 5.4%, and the maximum mechanical strain is reduced by 72.7%.

In summary, the coating layer is added outside the welding spot, so that the sectional area of a transmission current path can be increased, and the larger the sectional area is, the smaller the welding resistance is; the metal protective layer is added outside the welding spot, namely a layer of fully-coated armor is added outside the welding spot, and the mechanical strength of the plating layer can be adjusted by changing the material and the thickness of the plated armor according to the tensile strength, the shearing strength and the like of the plated material, so that the mechanical performance of the welding spot is indirectly enhanced.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A strengthening treatment method for a welding joint of a superconducting strip is characterized by comprising the following steps: coating metal on the outer layer of the welding joint of the superconducting tapes by using an outer metal coating method to form the metal reinforcing layer; the method of the external plating technology comprises electroplating; the electroplating of the welding joint comprises the following specific steps:

(1) pretreatment: polishing, degreasing, acid washing and then ultrasonically cleaning the welding joint of the superconducting strip;

(3) and carrying out post-treatment on the welding joint with the metal strengthening layer formed on the surface.

2. The method for strengthening a welded joint of superconducting tapes according to claim 1, wherein: the method for plating the metal comprises electroplating or chemical plating.

3. The method for strengthening a welded joint of superconducting tapes according to claim 1, wherein: and the polishing is to polish the welding spots of the welding joints and the surfaces of peripheral strips by using sand paper to remove burrs, tin nodules and residual soldering flux on the surfaces, the degreasing and oil removal is to remove surface grease by using alcohol, and the acid cleaning is to remove surface oxide films by using citric acid or oxalic acid.

4. A superconducting tape welded joint formed by the method of strengthening a superconducting tape welded joint according to any one of claims 1 to 3, characterized in that: the outer layer of the welding joint of the superconducting strip is wrapped with a metal strengthening layer in an omnibearing and seamless mode.

5. The superconducting tape weld joint according to claim 4, wherein: the metal of the metal strengthening layer comprises gold, silver, copper or copper-zinc alloy.

6. The superconducting tape weld joint according to claim 4, wherein: the thickness range of the metal reinforcing layer is as follows: 5um to 40 um.