Magnetostrictive member and method for manufacturing a magnetostrictive member

Abstract

To provide a magnetostrictive member with environmental resistance and a method for manufacturing a magnetostrictive member. [Solution] The magnetostrictive member is a plate-like body having a longitudinal direction and a transverse direction, and is made of crystals of an iron-based alloy having magnetostrictive properties, and the surface of the magnetostrictive member is covered with a single layer of plating.

Description

Technical Field

[0001] The present invention relates to a magnetostrictive member and a method for manufacturing the magnetostrictive member.

Background Art

[0002] Magnetostrictive materials have attracted attention as functional materials. For example, an Fe-Ga alloy, which is an iron-based alloy, is a material that exhibits a magnetostrictive effect and an inverse magnetostrictive effect and shows a large magnetostriction of about 100 to 350 ppm. Therefore, in recent years, it has attracted attention as a material for vibration power generation in the energy harvesting field, and applications to wearable terminals and sensors are expected.

[0003] For example, a magnetostrictive vibration power generation device is composed of a magnetostrictive member such as an Fe-Ga alloy wound around a coil, a yoke, and a permanent magnet for a bias magnetic field (Patent Document 2, Non-Patent Document 1). In this magnetostrictive vibration power generation device, when the yoke of the movable part of the device is vibrated, the magnetostrictive member fixed to the center of the yoke vibrates in conjunction, and the magnetic flux density of the coil wound around the magnetostrictive member changes due to the inverse magnetostrictive effect, generating an electromagnetic induction electromotive force to generate electricity. In a magnetostrictive vibration power generation device, since a force is applied in the longitudinal direction of the yoke to cause vibration, it is desirable to process a magnetostrictive member such as an Fe-Ga alloy used for the device so that <100>, which is the easy magnetization axis, is in the longitudinal direction.

[0004] The magnetostrictive characteristics of the Fe-Ga alloy are considered to affect the magnetostrictive / inverse magnetostrictive effect and the characteristics of the magnetostrictive vibration power generation device, and are important parameters in device design (Non-Patent Document 1). In particular, the magnetostriction constant depends on the Ga composition of the Fe-Ga alloy single crystal, and it is known that the magnetostriction constant becomes maximum when the Ga composition is 18 to 19 at% and 27 to 28 at% (Non-Patent Document 2), and it is considered desirable to use an Fe-Ga alloy having such a Ga concentration for the device. Furthermore, in recent years, in addition to a large magnetostriction constant, it has been reported that the larger the parallel magnetostriction amount, the higher the device characteristics such as the output voltage tend to be (Non-Patent Document 3).

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] International Publication No. 2021 / 100467 [Patent Document 2] International Publication No. 2011 / 158473 [Patent Document 3] Patent No. 7084620 [Non-patent literature]

[0006] [Non-Patent Document 1] Toshiyuki Ueno, Journal of the Japan Society for Precision Engineering, Vol. 79, No. 4, (2013) 305-308. [Non-Patent Document 2] AE Clark et al., Appl. Phys. 93(2003)8621. [Non-Patent Document 3] Jung Jin Park, Suok-Min Na, Ganesh Raghunath, and Alison B. Flatau., AIP ADVANCES 6, 056221(2016) [Overview of the project] [Problems that the invention aims to solve]

[0007] As described above, the device characteristics of magnetostrictive vibration power generation devices and the like are affected by the magnetostrictive properties of the magnetostrictive member. Therefore, the magnetostrictive member is required to have high magnetostrictive properties and low variation in magnetostrictive properties. In this context, the crystal orientation of the Fe-Ga alloy single crystal is <100> It was previously thought that if the Ga concentration was uniform, a magnetostrictive member with a uniform magnetostrictive constant could be obtained. However, device characteristics are affected not only by the magnetostrictive constant but also by the parallel magnetostriction. Patent Document 1 discloses that by adding multiple grooves, such as grinding marks, extending in the longitudinal direction of the magnetostrictive member, a magnetostrictive member with a high magnetostrictive constant and parallel magnetostriction, and with little variation in magnetostrictive constant and parallel magnetostriction between members, can be obtained. When this magnetostrictive member was incorporated into the magnetostrictive vibration power generation device and the device characteristics were confirmed, it was found that a predetermined device output (e.g., power generation amount such as force coefficient) could be obtained, and that there was little variation in device output between devices.

[0008] Measuring the parallel magnetostriction of a magnetostrictive component requires attaching strain gauges to the magnetostrictive material, which constitutes destructive testing. In contrast, evaluating the force coefficient can be done by measuring impedance by inserting and removing a measuring coil, making it a non-destructive test. Therefore, impedance measurement is preferred for product inspection.

[0009] Furthermore, prior to the present invention, the inventors of this invention discovered that the amount of parallel magnetostriction of a magnetostrictive member is positively correlated with the force coefficient calculated from impedance measurements. The force coefficient is also positively correlated with the device output (Patent Document 2). Prior to the present invention, the inventors of this invention also discovered that increasing the device output increases not only the amount of parallel magnetostriction but also the force coefficient (Japanese Patent Application: JP 2023-037128, International Patent Application: PCT / JP2024 / 4133).

[0010] Furthermore, in order for the device output (power generation) to be maximized, it is necessary to appropriately set the magnetic flux density of the magnet incorporated into the device. Specifically, the magnetic flux density (hereinafter referred to as the optimal magnetic field strength) must be approximately half of the maximum parallel magnetostriction of the magnetostrictive material incorporated into the device. Therefore, prior to the present invention, the inventors added an annealing treatment (heat treatment) to increase the force coefficient so as to increase the device output and to suppress variations in the optimal magnetic field strength (Japanese Patent Application: JP 2023-037128, International Patent Application: PCT / JP2024 / 4133).

[0011] Incidentally, magnetostrictive vibration power generation devices are being considered not only for indoor use but also for outdoor applications, such as vibrations from bridge piers. Therefore, the magnetostrictive components incorporated into these devices require environmental resistance. Corrosion resistance is particularly important for devices used outdoors.

[0012] Therefore, the present invention aims to provide a magnetostrictive member with environmental resistance and a method for manufacturing a magnetostrictive member. [Means for solving the problem]

[0013] According to an aspect of the present invention, a magnetostrictive member is provided, which is a plate-like body having a longitudinal direction and a transverse direction, and is made of crystals of an iron-based alloy having magnetostrictive properties, wherein the surface of the magnetostrictive member is covered with a single layer of plating.

[0014] Furthermore, at least a portion of each edge of the plate-like body may be a chamfered surface. The chamfered surface may also be a curved surface. Additionally, the plating layer of the magnetostrictive member may be a zinc plating layer.

[0015] Furthermore, according to an aspect of the present invention, a method for manufacturing a magnetostrictive member is provided, comprising the steps of preparing a magnetostrictive member cut into individual pieces, and a plating step of forming a single-layer plating layer on the surface of the prepared magnetostrictive member, wherein the plating step does not include strike plating.

[0016] Moreover, it may be configured to have a step of chamfering the prepared magnetostrictive member. Further, the plating step may be configured to be zinc plating. Further, the plating bath for the zinc plating may be configured to be an alkaline plating bath. Further, the chamfering may be configured to be barrel polishing.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a magnetostrictive member having environmental resistance and a method for manufacturing the magnetostrictive member.

Brief Description of the Drawings

[0018] [Figure 1] It is a diagram showing an example of a magnetostrictive member according to an embodiment, where (A) is a perspective view and (B) is a cross-sectional view taken along line A-A shown in (A). [Figure 2] It is a diagram showing examples of single crystals and thin plate members. [Figure 3] It is a diagram showing an example of an impedance measuring device. [Figure 4] It is a diagram showing an electrical-mechanical equivalent circuit of a measurement coil.

Modes for Carrying Out the Invention

[0019] Hereinafter, specific embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments and can be appropriately changed without changing the gist of the present invention. In each drawing, part or all may be schematically described and the scale may be changed. Further, in the following description, the description "A to B" means "A or more and B or less". Also, in the drawings, the directions in the figure may be described using the XYZ coordinate system. In this XYZ coordinate system, the direction perpendicular to the XY plane is denoted as the Z direction. Each of the X direction, Y direction, and Z direction is described such that the direction of the arrow in the figure is the + direction and the direction opposite to the direction of the arrow is the - direction.

[0020] [Embodiment] The magnetostrictive member and the method for manufacturing the magnetostrictive member according to this embodiment will be described below.

[0021] (Magnetostrictive member) First, the magnetostrictive member of this embodiment will be described. Figures 1(A) and 1(B) show an example of the magnetostrictive member according to this embodiment.

[0022] The magnetostrictive member 1 is a plate-like body having a longitudinal direction D1 and a transverse direction D2, as shown in Figures 1(A) and (B). The plate-like body is preferably rectangular in plan view. The plate-like body has a front surface 3 and a back surface 4. The front surface 3 and the back surface 4 are preferably parallel to each other, but do not have to be parallel. The magnetostrictive member 1 has a single layer of plating C on the front surface 3, the back surface 4 and the sides (XZ plane and YZ plane in the example of Figure 1(A)). The front surface 3, the back surface 4 and the sides of the plate-like body are covered with a single layer of plating C (see Figure 1(B)). In particular, in this embodiment, it is preferable that no undercoat plating layer, such as strike plating described later, is provided between the front surface 3, the back surface 4 and the sides and the single layer of plating C.

[0023] A portion of each side 5 of the magnetostrictive member 1 may optionally be provided with a chamfered surface 6. In the magnetostrictive member 1, at least a portion of each side 5 of the plate-like body may optionally be provided with a chamfered surface 6 (chamfered portion). Furthermore, the magnetostrictive member 1 may optionally be provided with a plurality of grooves 2 extending in the longitudinal direction D1, such as those described in Patent Document 1.

[0024] The magnetostrictive member 1 is made of a crystal of an iron-based alloy. Multiple magnetostrictive members 1 can be obtained, for example, from the same crystal. The iron-based alloy is not particularly limited as long as it has magnetostrictive properties. Magnetostrictive properties refer to the property of undergoing a change in shape when a magnetic field is applied. Examples of iron-based alloys include Fe-Ga, Fe-Ni, Fe-Al, Fe-Co, Tb-Fe, Tb-Dy-Fe, Sm-Fe, and Pd-Fe alloys. Alternatively, an alloy may be one in which a third component has been added to the above alloys. For example, an alloy may be an Fe-Ga alloy in which Ba, Cu, etc. have been added. Among these iron-based alloys, Fe-Ga alloy has high magnetostrictive properties and is easy to process compared to other alloys, and is therefore applied to materials for vibration power generation in the energy harvesting field, as well as wearable terminals and sensors. In the following description, as an example of a magnetostrictive member 1, an example in which the magnetostrictive member 1 is made of a single crystal of Fe-Ga alloy will be described. Figure 2 shows examples of single crystals and thin plate members.

[0025] Fe-Ga alloy single crystals have a body-centered cubic lattice structure, and among the directional indices in Miller indices, the first to third... <100> This is based on the principle that the axes (see Figure 2) are equivalent, and the first to third {100} planes (see Figure 2) among the plane indices in Miller indices are equivalent (i.e., (100), (010), and (001) are equivalent). Furthermore, Fe-Ga alloys have the property of exhibiting large magnetic strain in specific crystal orientations. When utilizing this property in a magnetostrictive vibration power generation device, it is desirable to match the direction in which magnetostrictive member 1 is required in the device with the orientation (direction) in which the magnetic strain of the crystal is maximum. Specifically, as described above, this is the easy magnetization direction in a single crystal. <100> It is desirable to set the direction to the longitudinal direction D1 of the magnetostrictive member 1. This is the easy magnetization direction in a single crystal. <100> Setting the direction to the longitudinal direction D1 of the magnetostrictive member 1 can be achieved, for example, by calculating the crystal orientation of the single crystal using a known crystal orientation analysis and cutting the single crystal based on the calculated crystal orientation.

[0026] The crystal that can be used in the magnetostrictive member 1 of this embodiment may be a single crystal or a polycrystalline crystal. <100> To increase the degree of orientation concentration and improve the properties of the material as a magnetostrictive material, the use of single crystals is more advantageous than that of polycrystalline materials. However, although polycrystalline materials have lower magnetostrictive properties than single crystals, they can be produced at a lower cost, so polycrystalline materials are sometimes used.

[0027] The magnetostrictive member 1 is used, for example, as a material (component) for vibration power generation devices in the energy harvesting field, or as a material (component) for wearable terminals and sensors. For example, the magnetostrictive vibration power generation device shown in the above-mentioned Patent Document 2 is composed of a coil, a magnetostrictive member made of Fe-Ga alloy wound around the coil, a yoke, and a permanent magnet for the field. In this magnetostrictive vibration power generation device, when the yoke, which is the movable part of the device, is vibrated, the magnetostrictive member fixed to the center of the yoke vibrates in conjunction, and the magnetic flux density of the coil wound around the magnetostrictive member changes due to the inverse magnetostrictive effect, generating an electromagnetic induction electromotive force and thus generating electricity. When used in such a mechanism, the shape of the magnetostrictive member 1 is preferably a thin plate, and preferably set to an elongated rectangular shape in plan view. There are no particular limitations on the thickness of the magnetostrictive member 1. For example, 0.3 mm to 5 mm is preferred. The shape and size of the magnetostrictive member 1 are appropriately set according to the size of the target device. For example, the length of one side of the magnetostrictive member 1 may be 5 mm or more, 10 mm or more, or 30 mm or more. For example, the magnetostrictive member 1 may have a length (dimension) of 25 mm in the longitudinal direction D1, a width (dimension) of 4 mm in the transverse direction D2, and a thickness of 0.5 mm.

[0028] The shape and dimensions of the magnetostrictive member 1 are not particularly limited. For example, the magnetostrictive member 1 does not have to be rectangular in plan view. For example, the shape of the magnetostrictive member 1 may be elliptical, track-shaped, or irregular in plan view. When the shape of the magnetostrictive member 1 is other than rectangular in plan view, the longitudinal direction D1 is the direction of the major axis, the direction of the major axis, etc., and the short direction D2 is the direction perpendicular to the longitudinal direction D1.

[0029] As mentioned above, magnetostrictive vibration power generation devices are being considered not only for indoor use but also for outdoor use, such as vibrations from bridge piers. For this reason, the magnetostrictive members incorporated into magnetostrictive vibration power generation devices must have high and stable magnetostrictive properties as well as environmental resistance. In particular, corrosion resistance is important for devices used outdoors. However, as mentioned above, iron-based alloys such as Fe-Ga alloys have high magnetostrictive properties but poor corrosion resistance. Generally, some materials can have their corrosion resistance improved by plating, but the inventors of this application have found that plating can cause a decrease in magnetostrictive properties in magnetostrictive members.

[0030] Therefore, the inventors of the present invention, after examining plating methods and the like, found that the magnetostrictive properties of a magnetostrictive member are affected by the characteristics of the plating, and further found that they are affected by strike plating and other aspects of the plating process, thus completing the embodiments of the present invention. The manufacturing method of a magnetostrictive member according to the embodiments of the present invention is a method for manufacturing a magnetostrictive member, comprising the steps of preparing a magnetostrictive member cut into individual pieces and a plating step of forming a single layer of plating on the surface of the prepared magnetostrictive member, wherein the plating step does not include strike plating. Furthermore, the magnetostrictive member according to the embodiments of the present invention is a plate-like body made of a crystal of an iron-based alloy having magnetostrictive properties, having a longitudinal direction and a transverse direction, and the surface of the magnetostrictive member is covered with a single layer of plating. A detailed explanation follows below.

[0031] Magnetostrictive members are produced by processing single crystals grown using methods such as the Cz method or VB method into thin plate-like members by cutting the crystal using methods such as electrical discharge wire cutting, and then cutting the thin plate members into predetermined shapes using a cutting device to produce individual pieces of magnetostrictive members. During such cutting, burrs are generated, and these burrs can cause fluctuations in the magnetostrictive properties. For this reason, the magnetostrictive member 1 may have chamfered surfaces 6 on at least some of the edges of each side of the plate-like body, and by providing chamfered surfaces 6, the fluctuations in magnetostrictive properties caused by the burrs generated during cutting are suppressed.

[0032] The plating layer C on the magnetostrictive member 1 is applied to improve corrosion resistance, and therefore it is preferable to cover the entire surface of the magnetostrictive member 1. Thus, it is important that the plating layer C is formed on the magnetostrictive member 1 after it has been cut into individual pieces. Plating the magnetostrictive member before it is cut into individual pieces is undesirable because the cut portions are not plated, which can lead to corrosion. While there are no particular limitations on the plating method, barrel plating or rack plating is preferred from the viewpoint that the magnetostrictive member 1 is an individual piece. Barrel plating is a method in which the magnetostrictive member is placed in a container called a barrel, and the plating is performed while the barrel itself is rotated. Barrel plating is preferred because it allows for the simultaneous plating of many individual pieces, thus enabling efficient processing of a large quantity of individual pieces.

[0033] In the plating layer C, the type of plating is not particularly limited as long as it is corrosion-resistant. For example, zinc plating, tin plating, nickel plating, etc. are preferred.

[0034] Generally, in plating, strike plating is performed as an undercoat to improve the adhesion between the material to be plated and the plated layer. Strike plating, for example, can be made denser and improve adhesion by applying a higher current and processing for a shorter time than when forming the main plating. Nickel strike plating is often used for iron-based alloys. However, as shown in the comparative example described later, it has been found that when zinc plating is performed after nickel strike plating on magnetostrictive members, the magnetostrictive properties before plating, such as the force coefficient, decrease or the optimal magnetic field strength fluctuates. This is thought to be because the plating stress from the strike plating is generated on the main surface (front and back) of the magnetostrictive member, affecting the main surface and changing the magnetostrictive properties. In particular, for magnetostrictive members obtained by stabilizing the magnetostrictive properties by forming multiple grooves 2 extending in the longitudinal direction of the magnetostrictive member, such as grinding marks, as shown in Patent Document 1, it has been found that the influence of the fluctuation in magnetostrictive properties due to the above-mentioned strike plating is significant. Therefore, an embodiment of the present invention is characterized by a manufacturing process flow for magnetostrictive members that does not perform this strike plating. In other words, in the magnetostrictive member 1 of this embodiment, the plating layer C is a single layer and does not undergo strike plating. The causes of the change in magnetostrictive properties due to plating are not limited to those described above and may include other causes.

[0035] In plating the magnetostrictive member 1, it is important not to change the stress and surface roughness on both main surfaces of the magnetostrictive member. For example, the magnetostrictive properties are also affected by the thickness of the plating and the type of plating solution. There are two types of plating baths: acidic baths (acidic plating baths) and alkaline baths (alkaline plating baths). In this embodiment, as shown in the example, it was found that in the case of an acidic bath, the surface of the magnetostrictive member is more easily etched compared to an alkaline bath, and therefore the magnetostrictive properties are more likely to change. From this viewpoint, an alkaline bath is preferable. As the plating thickness increases, the plating stress tends to increase, and the magnetostrictive properties tend to change. The thickness of the plating layer C is preferably, for example, 1 μm to 10 μm, and more preferably 2 μm to 8 μm. When the thickness of the plating layer C is within the above range, changes in magnetostrictive properties due to plating can be more reliably suppressed, and corrosion resistance can be more reliably provided. For example, by setting the thickness of the plating layer C within the above range, fluctuations in magnetostrictive properties can be suppressed as shown in the examples, and when compared with the reference value, the force coefficient can be limited to within ±10% and the optimal magnetic field strength to within ±20%, preferably within ±5% for both the force coefficient and the optimal magnetic field strength. The force coefficient and the optimal magnetic field strength can be evaluated using the same method as described in the Japanese Patent Application No. 2023-037128 and the international patent application PCT / JP2024 / 4133, and details are described in the examples.

[0036] The plating process is performed after the magnetostrictive member has been diced, but the chamfering process may be performed before the plating process. The magnetostrictive member 1 is diced, for example, using an outer blade or a dicing device. When dicing with either of the above devices, a burr of up to approximately 60 μm is generated on the cut exit side (sometimes referred to as the burr side). Even if the processing conditions for dicing are changed, the size of the burr will be reduced, but a burr will always be generated. In the magnetostrictive member 1, it is preferable to remove this burr by chamfering to create a chamfered surface 6 (C-surface or curved surface). Although the chamfering process can also be performed after the plating process, the chamfered portion 6 is exposed without a plating layer C, making it prone to corrosion, so it is preferable to perform the plating process after the chamfering process.

[0037] The method of chamfering is not particularly limited as long as it is possible to chamfer the edges (edge ​​portions) of the magnetostrictive member 1. For example, the chamfering method may be performed using a bevel polishing device with a chamfered grinding wheel, or it may be performed using a jig with a cutter, grinder, sandpaper, etc. Each edge (all edges) may be chamfered by barrel polishing using a barrel polishing machine, etc. It is preferable to perform chamfering on the parts where burrs are generated when the magnetostrictive member 1 is separated into individual pieces. For example, it is preferable to perform chamfering on the cut exit side where burrs are likely to be generated when the magnetostrictive member 1 is separated into individual pieces. It is preferable to perform chamfering on at least four sides of the side of the magnetostrictive member 1: two sides in the longitudinal direction and two sides in the short direction on the cut exit side. Alternatively, all edges of the magnetostrictive member 1 may be chamfered. For example, the magnetostrictive member 1 in one aspect of the present invention includes removing at least one portion of the burrs. In one aspect of the present invention, the magnetostrictive member 1 is a plate-like body, and at least a portion of each edge of the plate-like body is a chamfered surface (chamfered portion). In other words, the magnetostrictive member 1 is a plate-like body, and may be configured to have chamfered surfaces 6 on at least a portion of each edge of the plate-like body. In the example shown in Figure 1, the edges include the portions of each edge (12 edges in total) in the rectangular parallelepiped shape, and the portions near the edges. In this specification, "edge portion" may be abbreviated as "edge". The amount of chamfering by the chamfering process is not particularly limited, as long as it does not depart from the spirit of the present invention.

[0038] In particular, chamfering by barrel polishing is preferable because it can be processed continuously with barrel plating, making it efficient. Furthermore, barrel polishing and barrel plating are preferable because they allow for the processing of a large number of magnetostrictive components at once by placing them in a container, resulting in high production efficiency. Barrel polishing is a method in which magnetostrictive components are placed in a container called a barrel, polishing stones, compound, and water are added, and the container is moved or vibrated so that the magnetostrictive components inside the container come into contact with the polishing stones and are polished. As a result, all sides of the magnetostrictive component become curved chamfered surfaces. In addition, the main surface of the magnetostrictive component also comes into contact with the polishing stones and is polished to a smaller extent than the other sides. This makes it possible to remove deposits from the surface of the magnetostrictive component and improve the adhesion of the plating when a plating process is performed after barrel polishing. For this reason, it is more preferable to perform the plating process after the barrel polishing process.

[0039] The characteristics of the magnetostrictive member 1 of this embodiment will be further described. For example, as shown in the example, the plating adhesion of the magnetostrictive member 1 of this embodiment is good, without peeling of the plating, when evaluated using the tape test method (15.1) of the plating adhesion test (JIS H8504) specified in the Japanese Industrial Standards. In addition, the magnetostrictive member 1 of this embodiment has corrosion resistance, for example, and shows no visible corrosion in a 5-day immersion test at room temperature.

[0040] As described above, the magnetostrictive member according to this embodiment is a plate-like body having a longitudinal and transverse direction, made of crystals of an iron-based alloy having magnetostrictive properties, and the surface of the magnetostrictive member is covered with a single layer of plating. The magnetostrictive member according to this embodiment suppresses the problem of reduced magnetostrictive properties due to plating and has excellent environmental resistance.

[0041] (Manufacturing method for magnetostrictive members) Next, the method for manufacturing the magnetostrictive member of this embodiment will be described. The method for manufacturing the magnetostrictive member of this embodiment is the method for manufacturing the magnetostrictive member 1 of this embodiment described above. In the following description, the method for manufacturing the magnetostrictive member 1 from a single crystal ingot of Fe-Ga alloy will be described as an example, but the method for manufacturing the magnetostrictive member of this embodiment is not limited to the following description. Furthermore, any descriptions in this specification that are applicable to the method for manufacturing the magnetostrictive member of this embodiment will also be applicable to the method for manufacturing the magnetostrictive member of this embodiment. Furthermore, in the method for manufacturing the magnetostrictive member of this embodiment described below, any descriptions that are applicable to the magnetostrictive member of this embodiment described above will also be applicable to the magnetostrictive member of this embodiment.

[0042] A method for manufacturing a magnetostrictive member according to an aspect of the present invention is a method for manufacturing a magnetostrictive member comprising the steps of preparing a magnetostrictive member cut into individual pieces, and a plating step of forming a single layer of plating on the surface of the prepared magnetostrictive member, wherein the plating step does not include strike plating. One aspect of the method for manufacturing a magnetostrictive member according to the present invention includes forming and coating a single layer of plating on the surface of a magnetostrictive member which is a plate-like body made of crystals of an iron-based alloy having magnetostrictive properties and having longitudinal and transverse directions.

[0043] In the process of preparing individual magnetostrictive members, for example, magnetostrictive members manufactured and individually prepared by a conventional method are prepared. Generally, magnetostrictive members are made by processing single crystals grown by methods such as the Cz method or VB method into thin plate members by electrical discharge wire cutting, etc., and then cutting the thin plate members into predetermined shapes using a cutting device, etc., to produce individual magnetostrictive members. Alternatively, as shown in Patent Document 1, a magnetostrictive member may have a grinding surface, to which a plurality of grooves 2 extending in the longitudinal direction D1 of the magnetostrictive member are added, such as grinding marks (e.g., grinding marks from surface grinding), in order to obtain a magnetostrictive member with a high magnetostrictive constant and parallel magnetostriction and low variation in magnetostrictive constant and parallel magnetostriction between members. Extending in the longitudinal direction D1 includes the angle of intersection with the longitudinal direction D1 being within 45°. Note that the magnetostrictive member does not have to have the above grooves 2.

[0044] Next is the process of chamfering the individual pieces of magnetostrictive material. As described above, the magnetostrictive material cut into individual pieces will have burrs of varying sizes at the cut edges. The chamfering process is the process of removing these burrs. As described above, the chamfering process chamfers at least a portion of the edges of the plate-like material. The edges of the plate-like material on which the chamfering process is performed are as described above. Furthermore, in the chamfering process, the shape of the chamfered surface 6 can be any of the various chamfered shapes described above. In the chamfering process, the shape of the chamfered surface 6 can be, for example, a chamfered surface, a curved surface (e.g., a rounded surface, a barrel-polished surface), or a fine chamfered surface. The chamfering process can be carried out by, for example, a known method. As described above, the chamfering process is preferably barrel polishing. Note that the chamfering process is an optional process.

[0045] Next is a plating process in which a single layer of plating is formed on the surface of the chamfered magnetostrictive member. As mentioned above, this plating process does not involve strike plating. The plating process is carried out, for example, using the plating method, type of plating bath, and formation of the plating layer thickness as described above. For example, in the plating process, the type of plating (material) is not particularly limited as long as it is a corrosion-resistant plating, and zinc plating, tin plating, nickel plating, etc. are preferred. Also, in the plating process, the plating bath may be an acidic bath (acidic plating bath) or an alkaline bath (alkaline plating bath), and as mentioned above, an alkaline bath is more preferred. Furthermore, the thickness of the plating layer C is preferably, for example, 1 μm or more and 10 μm or less, and more preferably 2 μm or more and 8 μm or less. When the thickness of the plating layer C is within the above range, changes in magnetostrictive properties due to plating can be suppressed more reliably, and corrosion resistance can be more reliably imparted.

[0046] In the method for manufacturing a magnetostrictive member according to an embodiment of the present invention, as described above, it is more preferable that the chamfering process is performed by barrel polishing and the plating process is barrel plating. Barrel polishing is preferable because it can be performed continuously with barrel plating, thus providing good efficiency. Furthermore, barrel polishing and barrel plating are preferable because they allow a large number of magnetostrictive members to be placed in a container and processed at once, resulting in good production efficiency. In addition, when the plating process is performed after barrel polishing, as described above, it is preferable because it can remove deposits from the surface of the magnetostrictive member and improve the adhesion of the plating. [Examples]

[0047] The present invention will be described in detail below using examples, but the present invention is not limited in any way by these examples.

[0048] [Example 1] The magnetostrictive members were manufactured based on the manufacturing method of this embodiment described above. Magnetostrictive members were prepared by processing and cutting individual pieces from cylindrical Fe-Ga alloy single crystals grown by the vertical Bridgman (VB) method, which had a gallium content of 17.2 to 19.8 at%.

[0049] The fragmentation from the single crystal was performed using the following procedure. First, a thin plate was prepared by cutting the single crystal parallel to the crystal growth direction using a free abrasive wire saw. Next, the obtained thin plate was subjected to surface grinding using a #100 flat grinding wheel on a surface grinding machine to adjust the thickness of the thin plate and to form multiple grooves (grinding marks) on the front and back surfaces. After that, the cutting position was set so that the longitudinal direction of the magnetostrictive material was the same as the grinding direction during surface grinding, i.e., the direction of the grinding marks, and a magnetostrictive material with dimensions of 25 mm in the longitudinal direction × 4 mm in the transverse direction × 0.5 mm in thickness was cut out using an outer blade cutting device.

[0050] Next, chamfering was performed. Chamfering was carried out on each side (all sides) by barrel polishing using a barrel polishing machine. A magnetic benchtop barrel polishing machine was used for barrel polishing. Stainless steel pins were used as polishing stones, and liquid compound and pure water were added. The rotation speed was 350 rpm and the processing time was 30 minutes. In this example of barrel polishing, the corners of the magnetostrictive member were polished, then the sides parallel to the short direction D2, and then the sides parallel to the long direction D1. The amount of polishing was smallest near the center of the long direction D1. The chamfer width at the center of the long direction D1 was measured to be 30-50 μm. The chamfer width was determined by measuring five arbitrary points in an image obtained from observation with an optical microscope.

[0051] Next, zinc plating was performed using a barrel plating apparatus. Pre- and post-plating treatments were set using conventional techniques. However, nickel strike plating, which is performed before the main plating, was omitted. The plating bath used was an acidic zinc plating bath. The plating thickness was 3 μm. Ten magnetostrictive members of this embodiment were manufactured using the above method.

[0052] Next, the fabricated magnetostrictive members were evaluated. First, a water immersion test was conducted to evaluate the corrosion resistance of the magnetostrictive members. The water immersion test was performed at room temperature for 5 days, and the appearance of the magnetostrictive members was observed after the test. If no corrosion occurred after 5 days under the above conditions, it was considered good and marked with a "○". If corrosion occurred after 5 days, it was considered poor and marked with a "×".

[0053] To evaluate the adhesion of the plating, the tape test method (15.1) of the plating adhesion test (JIS H8504) specified in the Japanese Industrial Standards was used. If there was no peeling of the plating, it was marked as good ("○"), and if there was peeling of the plating, it was marked as poor ("×").

[0054] The magnetostrictive properties were evaluated using the same method as described in Japanese Patent Application No. 2023-037128 and International Patent Application No. PCT / JP2024 / 4133, determining the maximum force coefficient and the maximum optimal magnetic field strength. For comparison, the average force coefficient and optimal magnetic field strength of 10 magnetostrictive members that were not chamfered and had burrs of 20 μm or less at the time of cutting were used as a baseline.

[0055] Regarding the evaluation of the maximum force coefficient and the maximum optimal magnetic field strength, the same method as described in Japanese Patent Application No. 2023-037128 and International Patent Application No. PCT / JP2024 / 4133 will be described below. The evaluation of the maximum force coefficient and the maximum optimal magnetic field strength was performed using an evaluation method based on electromechanical equivalent circuit analysis (impedance measurement). The electromechanical equivalent circuit analysis (impedance measurement) will be described below. Figure 3 shows an overview of the impedance measurement device. A bias magnetic field is generated in the excitation coil using a DC (direct current) power supply, and the magnetostrictive material is magnetized. With the magnetostrictive material placed inside the measurement coil, the impedance of the measurement coil is measured. The equivalent circuit of the measurement coil is shown in Figure 4, and the equivalent impedance of this circuit can be expressed by the following equation (1). The force coefficient α is the degree of coupling between the mechanical system and the electrical system, and is an indicator of the energy conversion efficiency from mechanical energy to electrical energy, and has a positive correlation with the power output of the vibration power generation device.

[0056]

number

[0057] The measured impedance loop is converted to a dynamic impedance loop by subtracting the component obtained by removing the electrical circuit component, and the force coefficient α is calculated from equations (2) and (3) below.

number

number

[0058] The impedance measurement described above is performed multiple times while changing the bias magnetic field generated by the excitation coil by varying the current of the DC power supply. When the force coefficient α is measured while the magnetic field strength is varied from 0 kA / m to the saturation magnetic field, the force coefficient α is maximized at around half the saturation magnetic field strength, and decreases elsewhere. The magnetic field strength at which the force coefficient α is maximized is the optimal magnetic field strength. The force coefficient α at the optimal magnetic field strength is defined as the force coefficient αmax (note that the force coefficient αmax is sometimes abbreviated as force coefficient). In other words, by generating a bias magnetic field to magnetize the magnetostrictive material, and placing the magnetostrictive material inside the measuring coil, the impedance of the measuring coil is measured multiple times while varying the bias magnetic field strength up to the saturation magnetic field strength. Based on the obtained measurement results of the impedance of the measuring coil, the optimal magnetic field strength, which is the magnetic field strength at which the force coefficient α is maximized, and the characteristics of the magnetostrictive member, including the force coefficient αmax at the optimal magnetic field strength, can be determined.

[0059] In this example, the magnetostrictive properties were measured using an impedance measuring device as shown in Figure 3, and the force coefficient and optimal magnetic field strength were determined. The impedance measurement was performed as follows: A measuring coil was fabricated so that the manufactured magnetostrictive member fit perfectly inside, and impedance measurement equivalent to that described in Patent Document 3 (Patent No. 7084620) was performed. The excitation current was set to 10-70 mA, and the current was applied at 5 mA intervals. Converting this to magnetic field strength, 1 mA = 78.4 A / m, and a bias magnetic field was applied at 0.392 kA / m intervals in the range of 0.784-5.488 kA / m. An impedance analyzer was used to perform impedance measurements at frequencies of 50-150 kHz, and the force coefficient α at each magnetic field strength was calculated. The optimal magnetic field strength at which the force coefficient α was maximized and the force coefficient αmax at that time were calculated.

[0060] Table 1 shows the manufacturing conditions and evaluation results. In Example 1, both corrosion resistance and plating adhesion were good. Furthermore, the force coefficient and optimal magnetic field strength were within ±5% of the standard, and the change in magnetostrictive properties was small and good.

[0061] [Example 2] In Example 2, the plating thickness was 6 μm. Other conditions were the same as in Example 1. The manufacturing conditions and evaluation results are shown in Table 1. In Example 2, both corrosion resistance and plating adhesion were good. In addition, the force coefficient was good, within ±10% of the standard, but the optimal magnetic field strength tended to be slightly higher, ranging from 0% to +15% of the standard.

[0062] [Example 3] In Example 3, an alkaline bath was used for the Zn plating. Other conditions were the same as in Example 1. The manufacturing conditions and evaluation results are shown in Table 1. In Example 3, both corrosion resistance and plating adhesion were good. In addition, the force coefficient was good, within ±3% of the standard, and the optimal magnetic field strength was also good, within ±5% of the standard.

[0063] In Example 4, an alkaline Zn plating bath was used, and the plating thickness was 6 μm. Other conditions were the same as in Example 1. The manufacturing conditions and evaluation results are shown in Table 1. In Example 4, both corrosion resistance and plating adhesion were good. In addition, the force coefficient was good, within ±6% of the standard, and the optimal magnetic field strength was also good, within ±5% of the standard.

[0064] [Comparative Example 1] Comparative Example 1 involved nickel strike plating before Zn plating. The nickel strike plating was performed for 10 minutes. Other conditions were the same as in Example 1. The manufacturing conditions and evaluation results are shown in Table 1. In Comparative Example 1, the plating layer consisted of two layers: a strike plating layer and a Zn plating layer. Comparative Example 1 showed good corrosion resistance and plating adhesion. In addition, the force coefficient was within ±10% of the standard, and the optimal magnetic field strength tended to be 0% to +35% higher than the standard.

[0065] [Comparative Example 2] Comparative Example 2 prepared magnetostrictive members cut into pieces similar to those in Example 1 and barrel-polished. However, plating was not performed. Comparative Example 2 was the same as Example 1 except that plating was not performed. The manufacturing conditions and evaluation results are shown in Table 1. In Comparative Example 2, corrosion occurred across the entire surface after 24 hours of immersion in water during the corrosion resistance evaluation.

[0066] [Table 1]

[0067] (summary) From the results of Examples 1-4 and Comparative Example 1, it can be seen that when strike plating is performed as in Comparative Example 1, the variation in magnetostrictive properties is greater compared to when strike plating is not performed as in Examples 1-4. From the results of Examples 1-4 and Comparative Examples 1-2, it is confirmed that the magnetostrictive member and the method for manufacturing the magnetostrictive member of this embodiment suppress the problem of reduced magnetostrictive properties due to plating and also have environmental resistance.

[0068] Furthermore, the technical scope of the present invention is not limited to the embodiments described above. One or more of the requirements described above may be omitted. Also, the requirements described above may be combined as appropriate. In addition, to the extent permitted by law, all disclosures of the documents cited above shall be incorporated as part of the description herein. [Explanation of Symbols]

[0069] 1: Magnetostrictive member 2:Groove 3: Surface 4: Back side 5: Edge (edge ​​part) 6: Chamfered surface (chamfered part) C: Plating layer D1: Longitudinal direction D2: Lateral direction

Claims

1. A magnetostrictive member is a plate-like body made of crystals of an iron-based alloy having magnetostrictive properties, and having longitudinal and transverse directions, A magnetostrictive member wherein the surface of the magnetostrictive member is covered with a single layer of plating.

2. The magnetostrictive member according to claim 1, wherein at least a portion of each edge of the plate-like body is a chamfered surface.

3. The chamfered surface is a curved surface, according to claim 2, for the magnetostrictive member.

4. The magnetostrictive member according to claim 1, wherein the plating layer of the magnetostrictive member is a zinc plating layer.

5. A method for manufacturing a magnetostrictive member, The process of preparing magnetostrictive members cut into individual pieces, The process includes a plating step of forming a single layer of plating on the surface of the prepared magnetostrictive member, The aforementioned plating step is a method for manufacturing a magnetostrictive member, which does not involve strike plating.

6. The method for manufacturing a magnetostrictive member according to claim 5, further comprising the step of performing chamfering on the prepared magnetostrictive member.

7. The method for manufacturing a magnetostrictive member according to claim 5, wherein the plating step is zinc plating.

8. The method for manufacturing a magnetostrictive member according to claim 7, wherein the zinc plating bath is an alkaline plating bath.

9. The method for manufacturing a magnetostrictive member according to claim 6, wherein the chamfering process is barrel polishing.

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