WO2025115295A1 - Connection structure - Google Patents

Abstract

The present invention provides a connection structure comprising a terminal, a mounting object to which the terminal is to be mounted, and a bolt connecting the terminal and the mounting object, wherein the terminal has a first surface that faces the mounting object when the terminal is connected to the mounting object and a notch through which the bolt is passed, the first surface has an uneven portion formed around the notch, the material of the terminal and the material of the mounting object is pure aluminum or aluminum alloy, the terminal has a Vickers hardness of 50 HV or higher, the ratio S1/S2 of a first area S1 to a second area S2 is 0.66 or less when the first surface and the mounting object are connected by tightening the bolt, and the first area S1 is 5 mm² or greater.

Description

Connection structure

This disclosure relates to a connection structure. This application claims priority to Japanese Patent Application No. 2023-200226, filed on November 27, 2023. All contents of said Japanese Patent Application are incorporated herein by reference.

Patent Document 1 discloses a fastening structure that includes a first fastened member, a second fastened member, and a fastening member. The first fastened member is made of pure aluminum or an aluminum alloy. The second fastened member is made of pure copper, a copper alloy, pure aluminum, or an aluminum alloy. The fastening member fastens and fixes the first fastened member and the second fastened member to each other. A protrusion that protrudes toward the second fastened member is integrally formed on the surface of the first fastened member that faces the second fastened member. A specific example of the shape of the protrusion is a hemisphere with a radius of curvature of 1 mm. When the first fastened member and the second fastened member are fastened with the fastening member and a compressive force is applied, the pure aluminum or aluminum alloy inside the protrusion comes into direct contact with the metal of the second fastened member. In the following, the first fastened member is called a terminal, the second fastened member is called an attachment target, and the fastening member is called a bolt.

JP 2023-82637 A

The connection structure of the present disclosure includes a terminal, an attachment object to which the terminal is attached, and a bolt connecting the terminal and the attachment object. The terminal includes a first surface facing the attachment object when connected to the attachment object, and a notch through which the bolt passes. The first surface includes an uneven portion formed around the notch. The material of the terminal and the material of the attachment object are pure aluminum or an aluminum alloy. The Vickers hardness of the terminal is 50 HV or more. The ratio S1/S2 of the first area S1 to the second area S2 in a state in which the first surface and the attachment object are connected by tightening the bolt is 0.66 or less. The first area S1 is the area of an area where the first surface contacts the attachment object under a pressure of 25 MPa or more. The second area S2 is the area of an annular area with the nominal diameter D1 of the bolt as the inner diameter and the bearing surface diameter D2 of the bolt as the outer diameter. The first area S1 is 5 ^mm2 or more.

FIG. 1 is a schematic side view showing a connection structure according to an embodiment. FIG. 2 is a schematic plan view showing a terminal provided in the connection structure of the embodiment. FIG. 3 is a schematic plan view showing a terminal different from that in FIG. FIG. 4 is a cross-sectional view showing an example of a concave-convex portion of a terminal provided in the connection structure of the embodiment. FIG. 5 is a cross-sectional view showing another example of the concave and convex portions of the terminal provided in the connection structure of the embodiment. FIG. 6 is a cross-sectional view showing still another example of the concave-convex portion of the terminal provided in the connection structure of the embodiment. FIG. 7 is a cross-sectional view showing still another example of the concave-convex portion of the terminal provided in the connection structure of the embodiment. FIG. 8 is a schematic plan view of a terminal used in a fastening test. FIG. 9 is an explanatory diagram for explaining an outline of the fastening test.

[Problem that this disclosure aims to solve]
In the case where the terminal is made of pure aluminum or an aluminum alloy and the attachment target is made of copper or a copper alloy, galvanic corrosion may occur if water adheres to the connection portion between the terminal and the attachment target.

When the terminal and the attachment object are made of pure aluminum or an aluminum alloy, the occurrence of galvanic corrosion can be suppressed. However, because aluminum is a very active metal, an aluminum oxide film can form on each surface of the terminal and the attachment object. This aluminum oxide film increases the contact resistance between the terminal and the attachment object. Patent Document 1 describes that when the terminal and the attachment object are fastened with a bolt and a compressive force is applied, the aluminum oxide film formed on the protrusion is destroyed by the plastic deformation of the protrusion. However, in the technology of Patent Document 1, the tip of the protrusion is configured with a relatively gentle curve, and depending on the axial force of the bolt, there is a risk that the aluminum oxide film will not be destroyed by the protrusion.

Furthermore, if the linear expansion coefficients of the terminal, attachment object, and bolt are different, the thermal shock caused by repeated heating and cooling can apply a shear force to the interface between the terminal and attachment object, causing the interface to slide. This sliding causes repeated formation and oxidation of new aluminum surfaces, resulting in the accumulation of an oxide film and increased contact resistance. In the technology of Patent Document 1, the tip of the protrusion is configured with a relatively gentle curve, and depending on the axial force of the bolt, the interface can easily slide due to the shear of the interface caused by thermal shock, making it easy for an oxide film to accumulate.

An object of the present disclosure is to provide a connection structure that can suppress an increase in contact resistance over time at the interface between a terminal and an object to which it is attached.
[Effects of this disclosure]
The connection structure of the present disclosure can suppress an increase in contact resistance over time at the interface between the terminal and the attachment object.

[Description of the embodiments of the present disclosure]
First, the embodiments of the present disclosure will be listed and described.

(1) A connection structure according to an embodiment of the present disclosure includes a terminal, an attachment object to which the terminal is attached, and a bolt connecting the terminal and the attachment object. The terminal includes a first surface facing the attachment object when connected to the attachment object, and a notch through which the bolt passes. The first surface includes an uneven portion formed around the notch. The material of the terminal and the material of the attachment object are pure aluminum or an aluminum alloy. The Vickers hardness of the terminal is 50 HV or more. The ratio S1/S2 of the first area S1 to the second area S2 in a state in which the first surface and the attachment object are connected by tightening the bolt is 0.66 or less. The first area S1 is the area of an area where the first surface contacts the attachment object under a pressure of 25 MPa or more. The second area S2 is the area of an annular area having an inner diameter equal to the nominal diameter D1 of the bolt and an outer diameter equal to the bearing surface diameter D2 of the bolt. The first area S1 is 5 ^mm2 or more.

The terminal and the material of the object to which it is attached are made of pure aluminum or an aluminum alloy, so even if water adheres to the connection between the terminal and the object to which it is attached, the occurrence of galvanic corrosion can be suppressed.

The terminal has a Vickers hardness of 50 HV or more. The convex portion of the uneven portion of the terminal having such hardness is likely to bite into the mounting object when the terminal and the mounting object are connected by a bolt. The convex portion that bites into the mounting object is deformed by the mounting object. The deformation of the convex portion destroys the oxide film on the surface of the terminal and the surface of the mounting object in the vicinity of the convex portion, and the terminal and the mounting object are electrically connected. The convex portion bites into the mounting object and deforms, and the terminal and the mounting object are mechanically and firmly fixed. The convex portion having a Vickers hardness of 50 HV or more is not easily deformed by thermal shock and vibration after the terminal and the mounting object are connected. Therefore, the connection strength between the terminal and the mounting object is not easily reduced by thermal shock and vibration. In other words, the fastening between the terminal and the mounting object is not easily loosened, and the terminal and the mounting object are not easily rubbed against each other at the interface between the terminal and the mounting object. As a result, new aluminum surfaces are less likely to form on the surfaces of the terminal and the object at the interface due to friction, etc., and the contact resistance between the terminal and the object is less likely to increase.

First area S1 is the area where the first surface comes into contact with the attachment object when pressure equal to or greater than a specified value is applied. When the axial force of the bolt is constant, the smaller the ratio of first area S1 to second area S2, the greater the pressure acting on the area of first area S1. Because the ratio S1/S2 is 0.66 or less, the pressure acting on the area of first area S1 increases, and the convex portions of the terminal's concave-convex portion tend to bite into the attachment object.

Since the first area S1 is 5 ^mm2 or more, the connection strength between the terminal and the attachment object is sufficiently ensured. If the ratio S1/S2 is 0.66 or less and the first area S1 is 5 ^mm2 or more, the terminal and the attachment object are mechanically firmly connected, and the connection strength is likely to be maintained over a long period of time. As a result, the contact resistance between the terminal and the attachment object is unlikely to increase over time.

(2) In the connection structure of (1) above, the first area S1 may be the area of a specific color-developing region of the pressure-sensitive sheet determined by a clamping test that satisfies the following condition: In the clamping test, a laminate in which the pressure-sensitive sheet is disposed between the first surface and the attachment target is clamped with an axial force of 138×(D1) ² ±50 N. The specific color-developing region is a region having a color that indicates that it has been pressed with a pressure of 25 MPa or more.

By the above fastening test, the ratio S1/S2 can be appropriately determined with good reproducibility.
(3) In the connection structure of (1) or (2) above, the material of the terminal, that is, pure aluminum or an aluminum alloy, may be exposed to the outside on at least a part of the first surface.

In this disclosure, "pure aluminum or aluminum alloy is exposed to the outside" means that there is no artificially formed coating on the outer periphery of the pure aluminum or aluminum alloy. This "artificially formed coating" is a conductive coating, such as a conductive plating layer, formed for the purpose of reducing the contact resistance between the terminal and the object to which it is attached. Therefore, "artificially formed coating" does not include natural oxide films. Natural oxide films are not artificially formed, and are not conductive. Natural oxide films are, for example, aluminum oxide films. In addition, "artificially formed coatings" do not include unavoidable surface dirt, specifically organic matter, hydrates, or moisture.

A coating artificially formed on a terminal can reduce the contact resistance between the terminal and the object to which it is attached. On the other hand, artificially forming a coating requires time and cost. The terminal disclosed herein can reduce the contact resistance with the object to which it is attached, even without an artificially formed coating, due to its predetermined Vickers hardness and unevenness. Terminals that do not have an artificially formed coating have excellent productivity.

If the terminal does not have an artificially formed coating, the terminal and the object to which it is attached are more likely to come into contact with the same metal, making it easier to prevent galvanic corrosion.

(4) In any of the connection structures (1) to (3) above, the material of the attachment target, pure aluminum or aluminum alloy, may be exposed to the outside on at least a portion of the surface of the attachment target facing the first surface.

In the connection structure disclosed herein, even if the attachment target does not have an artificially formed coating, the terminal has a predetermined Vickers hardness and unevenness, so that the contact resistance between the terminal and the attachment target is unlikely to increase. An attachment target that does not have an artificially formed coating is highly productive. If the attachment target does not have an artificially formed coating, the terminal and attachment target are more likely to come into contact with the same type of metal, making it easier to suppress the occurrence of galvanic corrosion.

(5) In any of the connection structures (1) to (4) above, the Vickers hardness of the terminal may be less than 80 HV.

If the Vickers hardness of the terminal is less than 80HV, the terminal's bending workability is improved, and it is easy to form terminals with complex shapes. If the Vickers hardness of the terminal is less than 80HV, the convex parts of the uneven part of the terminal are easily crushed when connecting the terminal to the object to which it is attached. As a result, the oxide film near the convex parts of the uneven part is easily destroyed, making it easier to ensure electrical continuity between the terminal and the object to which it is attached.

(6) In any of the connection structures (1) to (5) above, the Vickers hardness of the attachment object may be 50 HV or more.

If the Vickers hardness of the attachment object is 50HV or more, the convex parts of the terminal's unevenness are likely to deform when connecting the terminal and attachment object. If the Vickers hardness of the attachment object is 50HV or more, the contact resistance between the terminal and attachment object is unlikely to increase even when subjected to thermal shock.

(7) In any of the connection structures (1) to (6) above, the ratio V1/V2 of the Vickers hardness V1 of the terminal to the Vickers hardness V2 of the attachment object may be 0.6 or more and 1.8 or less, and the material of the terminal and the material of the attachment object may be International Registered Alloy Number 6101 or 6061.

　By making the terminal and the object to be attached from specific materials and making the ratio V1/V2 fall within a specific range, the occurrence of galvanic corrosion can be suppressed, and the contact resistance between the terminal and the object to be attached is unlikely to increase over time or even when subjected to thermal shock.

[Details of the embodiment of the present disclosure]
An embodiment of the connection structure of the present disclosure will be described with reference to the drawings. The same reference numerals in the drawings indicate the same or equivalent parts. In each drawing, for convenience of explanation, some of the configurations may be exaggerated or simplified. The dimensional ratios of each part in the drawings may also differ from the actual ones. Note that the present invention is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

The connection structure 1 of the embodiment will be described with reference to Figs. 1 to 7. As shown in Fig. 1, the connection structure 1 of the embodiment includes a terminal 2, an attachment object 3, and a bolt 4. The terminal 2 and the attachment object 3 are connected by the bolt 4. One of the features of the connection structure 1 of the embodiment is that it satisfies the following requirements (a) to (e).

(a) As shown in Figures 2 and 3, the terminal 2 has an uneven portion 25 formed around the notch 2h on the first surface 21.

(b) The material of the terminal 2 and the material of the attachment object 3 are pure aluminum or an aluminum alloy.

(c) The Vickers hardness of the terminal 2 is 50 HV or more.
(d) The ratio S1/S2 of a first area S1 to a second area S2 described later is 0.66 or less.

(e) the first area S1 is 5 ^mm2 or more;
<Terminals>
The form of the terminal 2 is not particularly limited as long as it is configured to be connected to the attachment object 3 by the bolt 4. The terminal 2 of this example is a part of the electric wire with terminal 10 as shown in FIG. 1. The electric wire with terminal 10 is configured with an electric wire 5 and a terminal 2 independent of the electric wire 5. The electric wire 5 includes a conductor 50 and an insulating coating 51 covering the outer periphery of the conductor 50. The outer diameter of the conductor 50 may be, for example, 0.1 mm to 50 mm or less, or 0.4 mm to 30 mm or less. The conductor 50 of this example is a stranded wire in which a plurality of wires are twisted together. The conductor 50 is, for example, made of pure copper, copper alloy, pure aluminum, or aluminum alloy. The thickness of the insulating coating 51 may be, for example, 0.1 mm to 10 mm or less, or 0.2 mm to 5 mm or less. The material of the insulating coating 51 is, for example, mainly made of a polyolefin-based resin. The polyolefin-based resin is, for example, polyethylene or polypropylene. The insulating coating 51 may be a silicone-based resin.

The terminal 2 is not limited to the form of this example in which it is connected to the electric wire 5. Unlike this example, the terminal 2 may be, for example, a part of a bus bar, i.e., a connection part formed on the bus bar. The connection part is a part of the bus bar formed into a terminal shape. Additionally, unlike this example, the terminal 2 may be, for example, a part of a single-core wire, i.e., a connection part formed on the tip of the single-core wire.

The terminal 2 in this example is a CB-type terminal. Unlike this example, the terminal 2 may be a U-type terminal, a Y-type terminal, or an R-type terminal. The terminal 2 has a first surface 21 and a second surface 22. The first surface 21 is a surface that faces the attachment target 3 when the terminal 2 is connected to the attachment target 3. The first surface 21 has a portion that overlaps with the attachment target 3 and a portion that does not overlap. The second surface 22 is a surface opposite to the first surface 21. The terminal 2 has a notch 2h that opens to the first surface 21 and the second surface 22. The bolt 4 passes through the notch 2h. The notch 2h here includes a through hole and a slit. The through hole is a hole that opens only to the first surface 21 and the second surface 22 as shown in FIG. 2, and does not open to any of the surfaces perpendicular to the first surface 21 and the second surface 22, for example, the left end surface, the upper end surface, and the lower end surface of the terminal 2 in FIG. 2. That is, a through hole is a hole whose cross section along the first surface 21 has a closed cross section. The shape of the through hole is, for example, a round hole shape as shown in FIG. 2 or an elongated hole shape (not shown). A slit is a region that is open not only to the first surface 21 and the second surface 22 (not shown) but also to a surface perpendicular to the above-mentioned first surface 21 and second surface 22, for example, any one of the left end surface, upper end surface, and lower end surface of the terminal 2 in FIG. 2. That is, a slit is a region whose cross section along the first surface 21 has an open cross section.

The terminal 2 in this example includes a wire barrel 29 that grips the conductor 50 of the electric wire 5. The terminal 2 may further include an insulation barrel that grips the insulating coating 51 of the electric wire 5. The position of the surface of the terminal 2 to which the electric wire 5 is connected is not particularly limited. In this example, the electric wire 5 is connected to the second surface 22. Unlike this example, the electric wire 5 may be connected to the first surface 21, or may be connected to another surface perpendicular to both the first surface 21 and the second surface 22. The electric wire 5 may be connected to the terminal 2 by welding or solid-state welding instead of the wire barrel 29. Such a joining method is, for example, resistance welding, laser welding, ultrasonic welding, or friction stir welding.

The size of the terminal 2 is determined according to the application of the terminal 2. The length of the terminal 2 is, for example, 5 mm or more and 200 mm or less. The length of the terminal 2 may be 10 mm or more and 50 mm or less. The thickness of the terminal 2 is, for example, 0.1 mm or more and 7 mm or less. The thickness of the terminal 2 is the distance between the first surface 21 and the second surface 22. The thickness of the terminal 2 may be 0.3 mm or more and 4 mm or less, or 0.5 mm or more and 3 mm or less.

The shape of the notch 2h shown in FIG. 2 is a round hole shape as described above. The notch 2h shown in FIG. 2 is a circular through hole. The inner diameter D3 of the notch 2h is, for example, 4 mm or more and 20 mm or less. Unlike this example, the shape of the notch 2h may be an elongated hole shape. The inner diameter D3 of the elongated hole-shaped notch 2h is the diameter of the smallest circle inscribed in the notch 2h. The shape of the notch 2h may be a slit shape that reaches the left end of the terminal 2 in FIG. 2.

≪Uneven portion≫
The terminal 2 has a concave-convex portion 25 at a position on the first surface 21 that overlaps with the attachment target 3. The concave-convex portion 25 is formed in the area shown by cross-hatching in FIG. 2, that is, around the notch 2h on the first surface 21. The concave-convex portion 25 serves to strengthen the connection between the terminal 2 and the attachment target 3. The outer peripheral contour of the concave-convex portion 25 is rectangular. The inner peripheral contour of the concave-convex portion 25 is circular. In the example of FIG. 2, the inner peripheral contour of the concave-convex portion 25 coincides with the notch 2h. Unlike the example of FIG. 2, the inner peripheral contour of the concave-convex portion 25 may not coincide with the notch 2h and may be larger than the notch 2h. The concave-convex portion 25 may be annular, as shown in FIG. 3. In the example of FIG. 3, the inner peripheral contour of the annular concave-convex portion 25 does not coincide with the notch 2h and may be larger than the notch 2h. Unlike the example of Fig. 3, the inner peripheral contour of the annular concave-convex portion 25 may coincide with the notch 2h. The outer peripheral contour of the concave-convex portion 25 may be elliptical, not necessarily rectangular or circular. The concave-convex portion 25 may be formed by, for example, cutting or rolling.

The uneven portion 25 of this example is composed of a first surface 21 and a plurality of grooves 25g formed in the first surface 21, as shown in Figures 4 to 7. Figures 4 to 7 are cross-sectional views of the terminal 2 cut along a plane perpendicular to the direction along the grooves 25g. The plurality of grooves 25g may be arranged in parallel, or may cross each other in a cross-hatched pattern. The parallel grooves 25g may be arranged in a direction along the first length of the terminal 2, or in a direction along the second length, specifically the width, of the terminal 2. In the uneven portion 25, a plurality of annular grooves 25g may be arranged in a concentric pattern. Unlike this example, the uneven portion 25 may have a plurality of protrusions protruding from the first surface 21. In that case, the protrusions form the convex portions of the uneven portion 25, and the first surface 21 forms the concave portions. The shape of the protrusions is not particularly limited as long as the ratio S1/S2 between the first area S1 and the second area S2 described later can be realized. The shape of the protrusions may be, for example, a prism, a pyramid, a truncated pyramid, a cylinder, a cone, or a truncated cone. The corners of the tops of the protrusions of the uneven portion 25 may be sharp or may be rounded so that the radius of curvature R is 0.01 mm or more and 0.8 mm or less. The radius of curvature R may be 0.01 mm or more and 0.6 mm or less, 0.02 mm or more and 0.5 mm or less, or 0.03 mm or more and 0.3 mm or less. The uneven portion 25 has, for example, a first form shown in FIG. 4, a second form shown in FIG. 5, a third form shown in FIG. 6, or a fourth form shown in FIG. 7.

[First form]
In the first embodiment, as shown in Fig. 4, the groove 25g narrows toward the bottom of the groove 25g. The cross-sectional shape of the groove 25g in Fig. 4 is V-shaped. That is, the groove 25g is a V-groove. The opening edge of the V-groove is likely to bite into the attachment target 3. Therefore, the uneven portion 25 having the V-groove is likely to reduce the contact resistance between the terminal 2 and the attachment target 3. This V-groove is a V-groove in which the bisector of the angle of the V-groove is perpendicular to the first surface 21. That is, when a virtual line is taken that passes through the bottom of the V-groove and is perpendicular to the first surface 21, the angles that the virtual line makes with the left side wall and the right side wall of the V-groove are equal.

Each groove 25g constitutes a recess in the uneven portion 25. In this example, the distance between two adjacent grooves 25g is 0 mm. In this case, a convex portion having a mountain-shaped cross section is formed in the uneven portion 25. The joint between two adjacent grooves 25g, i.e., the apex of the convex portion having a mountain-shaped cross section, constitutes the corner 25c. In this example, the corner 25c is sharp. The distance between two adjacent corners 25c, i.e., the pitch P1, is, for example, 0.4 mm or more and 5 mm or less. In this example, the pitch P1 is also the width W1 between the opening edges of the grooves 25g. The pitch P1 may be 0.5 mm or more and 3 mm or less. The depth of the groove 25g, which is the length from the straight line connecting the opening edges of the grooves 25g to the bottom of the groove 25g, i.e., the height h1 of the convex portion having a mountain-shaped cross section, is, for example, 0.005 mm or more and 1 mm or less. The height h1 may be 0.01 mm or more and 0.5 mm or less.

The angle θ between the side walls of two adjacent grooves 25g shown in FIG. 4 is 90°. The angle θ is not limited to 90°, and may be 60° or more and 170° or less. The angle θ may be 80° or more and 160° or less, or may be more than 90° and 140° or less. The opening edge of a V-groove having the above angles, i.e., the corner 25c, is likely to bite into the attachment target 3. The angles θ of the multiple grooves 25g do not have to be the same. If the individual angles θ are not the same, there is no need to excessively increase the processing precision, which makes it easier to reduce production costs.

The bottom shape of groove 25g may be a curved surface, or a flat surface connected to the sidewalls by a smooth R-shape. When groove 25g has a curved or flat bottom shape, stress due to vibration, thermal shock, etc. on terminal 2 is less likely to concentrate around the bottom of the V-shape of groove 25g, making terminal 2 less likely to be damaged. In addition, there is no need to increase the processing precision of groove 25g excessively, which makes it easier to reduce the production costs of terminal 2.

[Second form]
In the second embodiment, as shown in Fig. 5, the tops of the convex portions of the uneven portion 25 are flat. This flat surface is the first surface 21. The joint between the first surface 21 and the groove 25g constitutes the corner 25c of the uneven portion 25. In this embodiment, the corner 25c is sharp. The cross-sectional shape of the groove 25g is V-shaped, similar to the first embodiment.

The width W2 of the flat surface, i.e., the distance between two adjacent grooves 25g, is, for example, greater than 0 mm and equal to or less than 5 mm. The width W2 may be 0.01 mm or greater and equal to or less than 2 mm. The width W1 between the opening edges of the grooves 25g is, for example, 0.01 mm or greater and equal to or less than 3 mm. The width W1 may be 0.02 mm or greater and equal to or less than 1 mm. The depth of the grooves 25g, i.e., the height h1 of the convex portion, is, for example, 0.005 mm or greater and equal to or less than 1 mm. The height h1 may be 0.01 mm or greater and equal to or less than 0.5 mm, 0.05 mm or greater and equal to or less than 0.5 mm, or 0.1 mm or greater and equal to or less than 0.5 mm.

The angle φ between the side wall of the groove 25g and the first surface 21 is, for example, greater than 90° and less than 170°. The angle φ may be greater than 90° and less than 160°. The angles φ of the multiple grooves 25g do not have to be the same. If the individual angles φ are not the same, there is no need to excessively increase the processing precision, which makes it easier to reduce production costs.

The corners 25c may be rounded. The radius of curvature R of the corners 25c is, for example, 0.01 mm or more and 0.8 mm or less. The radius of curvature R of the corners 25c may be 0.01 mm or more and 0.6 mm or less, 0.02 mm or more and 0.5 mm or less, or 0.03 mm or more and 0.3 mm or less. The bottom surface of the groove 25g may be a curved surface. The bottom surface and the side wall of the groove 25g may be connected by a smooth R shape.

[Third form]
In the third embodiment, as shown in Fig. 6, the tops of the convex portions of the uneven portion 25 are rounded. In other words, the corners 25c that form the joints between two adjacent grooves 25g, i.e., the convex portions with a mountain-shaped cross section, are rounded. The radius of curvature R of the corners 25c is, for example, 0.01 mm or more and 0.8 mm or less. The radius of curvature R of the corners 25c may be 0.01 mm or more and 0.6 mm or less, 0.02 mm or more and 0.5 mm or less, or 0.03 mm or more and 0.3 mm or less. The smaller the radius of curvature R of the corners 25c, the more easily the corners 25c will bite into the attachment target 3.

The depth of the groove 25g, i.e., the height h1 of the convex portion, is, for example, 0.005 mm or more and 1 mm or less. The height h1 may be 0.01 mm or more and 0.5 mm or less, 0.05 mm or more and 0.5 mm or less, or 0.1 mm or more and 0.5 mm or less.

The bottom surface of groove 25g may also be rounded. In other words, the shape of the bottom surface of groove 25g may be curved. The radius of curvature R of the bottom surface of groove 25g is, for example, 0.01 mm or more and 0.8 mm or less. The radius of curvature R of the bottom surface of groove 25g may also be 0.01 mm or more and 0.1 mm or less, 0.02 mm or more and 0.08 mm or less, or 0.03 mm or more and 0.07 mm or less.

[Fourth form]
In the fourth embodiment, as shown in Fig. 7, the groove 25g has a uniform width toward the bottom of the groove 25g. The cross-sectional shape of the groove 25g in Fig. 7 is rectangular. Each groove 25g constitutes a concave portion of the uneven portion 25, and the first surface 21 constitutes a convex portion of the uneven portion 25. The joint between the first surface 21 and the groove 25g constitutes a corner 25c of the uneven portion 25. In this example, the corner 25c is sharp.

The width W3 of the convex portion, i.e., the distance between two adjacent grooves 25g, is, for example, greater than 0 mm and equal to or less than 5 mm. The width W3 may be equal to or greater than 0.01 mm and equal to or less than 2 mm. The width W1 between the opening edges of the grooves 25g is, for example, equal to or greater than 0.01 mm and equal to or less than 3 mm. The width W1 may be equal to or greater than 0.02 mm and equal to or less than 1 mm. The depth of the grooves 25g, i.e., the height h1 of the convex portion, is, for example, equal to or greater than 0.005 mm and equal to or less than 1 mm. The height h1 may be equal to or greater than 0.01 mm and equal to or less than 0.6 mm, equal to or greater than 0.05 mm and equal to or less than 0.6 mm, or equal to or greater than 0.1 mm and equal to or less than 0.6 mm.

The corner 25c may be rounded. The radius of curvature R of the corner 25c is, for example, 0.01 mm or more and 0.8 mm or less. The radius of curvature R of the corner 25c may be 0.01 mm or more and 0.7 mm or less, 0.02 mm or more and 0.6 mm or less, or 0.03 mm or more and 0.5 mm or less. The angle φ between the side wall of the groove 25g shown in FIG. 7 and the first surface 21 is 90°. The bottom surface of the groove 25g may be a curved surface. The bottom surface and the side wall of the groove 25g may be connected by a smooth R shape.

The corners 25c of the uneven portion 25 shown in Figures 4 to 7 bite into the attachment object 3 when the terminal 2 and the attachment object 3 are connected. At that time, the corners 25c are deformed by the attachment object 3. This deformation destroys the oxide film on the surface of the corners 25c and on the surface of the attachment object 3 corresponding to the corners 25c, and the terminal 2 and the attachment object 3 are electrically connected. The uneven portion 25 is pressed against the attachment object 3 with a specified pressure or more, so that the terminal 2 and the attachment object 3 are firmly connected for a long period of time.

≪Material≫
The material of the terminal 2 is pure aluminum or an aluminum alloy. Pure aluminum means an aluminum content of 99% by mass or more. An aluminum alloy is an alloy containing the most aluminum. The aluminum content of the aluminum alloy is, for example, 80% by mass or more when the entire aluminum alloy is taken as 100% by mass. The aluminum alloy is allowed to contain inevitable impurities. The aluminum alloy contains, for example, 0.01% by mass or more and 1.50% by mass or less of silicon and 0.01% by mass or more and 2.00% by mass or less of magnesium. The content ratios of silicon and magnesium are values when the entire aluminum alloy is taken as 100% by mass. This point is the same for the content ratios of each of the following elements. The aluminum alloy may further contain one or more additive elements selected from the group consisting of copper, manganese, iron, chromium, zirconium, and titanium. The content ratio of copper is, for example, 0% by mass or more and 1.2% by mass or less, or 0.1% by mass or more and 1.2% by mass or less. The manganese content is, for example, 0% by mass or more and 1.5% by mass or less. The iron content is, for example, 0% by mass or more and 0.8% by mass. The chromium content is, for example, 0% by mass or more and 0.4% by mass or less. The zirconium content is, for example, 0% by mass or more and 0.8% by mass or less. The titanium content is, for example, 0% by mass or more and 0.2% by mass or less. The total content of titanium and zirconium is, for example, 0% by mass or more and 0.3% by mass or less. The aluminum alloy is, for example, 6101 or 6061 in the International Registered Alloy Number.

In at least a part of the first surface 21 of the terminal 2, the pure aluminum or aluminum alloy that is the material of the terminal 2 may be exposed to the outside. In other words, at least a part of the first surface 21 may not have a coating artificially formed on the outer periphery of the pure aluminum or aluminum alloy. In the entirety of the first surface 21, the aluminum or aluminum alloy that is the material of the terminal 2 may be exposed to the outside. Although the coating serves to reduce the contact resistance between the terminal 2 and the attachment target 3, forming the coating requires time and cost. Since the terminal 2 has the uneven portion 25 described above and has a Vickers hardness described later, the contact resistance with the attachment target 3 can be reduced even without the coating. A terminal 2 that does not have the coating has excellent productivity.

<Vickers hardness>
The Vickers hardness of the terminal 2 is 50 HV or more. The Vickers hardness is measured in accordance with JIS Z 2244-1:2020. The higher the Vickers hardness, the easier it is for the corner 25c of the convex portion of the uneven portion 25 to bite into the mounting object 3 when the terminal 2 and the mounting object 3 are fastened by the bolt 4. The corner 25c that bites into the mounting object 3 is deformed by the mounting object 3. The deformation of the corner 25c destroys the oxide film on the surface of the terminal 2 and the surface of the mounting object 3 in the vicinity of the corner 25c, and the terminal 2 and the mounting object 3 are electrically connected. The corner 25c bites into the mounting object 3 and the corner 25c deforms, so that the terminal 2 and the mounting object 3 are mechanically and firmly fixed. A convex portion having a Vickers hardness of 50 HV or more is less likely to be deformed by thermal shock and vibration after the terminal 2 and the mounting object 3 are connected. Therefore, the connection strength between the terminal 2 and the attachment object 3 is unlikely to decrease due to thermal shock and vibration. That is, the fastening between the terminal 2 and the attachment object 3 is unlikely to loosen, and the terminal 2 and the attachment object 3 are unlikely to rub against each other at the interface between the terminal 2 and the attachment object 3. As a result, new aluminum surfaces are unlikely to be formed on the surfaces of the terminal 2 and the attachment object 3 at the above-mentioned interfaces due to friction, etc., and the contact resistance between the terminal 2 and the attachment object 3 is unlikely to increase. The Vickers hardness of the terminal 2 may be 55 HV or more, or 60 HV or more.

The Vickers hardness of the terminal 2 is, for example, less than 80HV. If the Vickers hardness of the terminal 2 is less than 80HV, the bending processability of the terminal 2 is improved, and it is easy to form the terminal 2 into a complex shape. The terminal 2 may be formed to have multiple bent portions for convenience of wiring. The terminal 2 may have a portion bent into, for example, a Z-shape. If the Vickers hardness of the terminal 2 is less than 80HV, the corner 25c of the uneven portion 25 is easily crushed appropriately when the terminal 2 and the attachment object 3 are connected. As a result, the oxide film near the corner 25c of the uneven portion 25 is easily destroyed, and the electrical continuity between the terminal 2 and the attachment object 3 is easily ensured. The Vickers hardness of the terminal 2 may be 75HV or less, or 70HV or less.

The Vickers hardness of terminal 2 may be, for example, 50 HV or more and less than 80 HV, 55 HV or more and less than 75 HV, or 60 HV or more and less than 70 HV.

Conductivity
The electrical conductivity of the terminal 2 is, for example, 40% IACS or more and 63% IACS or less. The electrical conductivity is measured in accordance with JIS H 0505:1975. An aluminum alloy containing silicon and magnesium easily meets the above electrical conductivity. When the terminal 2 has the above electrical conductivity, the amount of heat generated by the terminal 2 is suppressed. As a result, thermal damage to the electric wire 5 connected to the terminal 2 and the attachment target 3 is reduced. The electrical conductivity may be 41% IACS or more and 60% IACS or less, or 42% IACS or more and 58% IACS or less. Alternatively, the electrical conductivity may be 40% IACS or more and 50% IACS or less.

<Installation target>
The shape of the attachment target 3 is not particularly limited as long as it is configured to be connectable to the terminal 2 by the bolt 4. The attachment target 3 in this example has a terminal shape. As shown in Fig. 1, the attachment target 3 has a notch 3h through which the bolt 4 passes. The notch 3h includes a through hole and a slit, similar to the notch 2h provided in the terminal 2. The notch 3h in this example is a circular through hole.

The material of the attachment object 3 is pure aluminum or an aluminum alloy. If the material of the terminal 2 and the material of the attachment object 3 are pure aluminum or an aluminum alloy, the occurrence of galvanic corrosion can be suppressed even if water adheres to the connection part between the terminal 2 and the attachment object 3. The material of the terminal 2 and the material of the attachment object 3 may be the same or different. The material of the terminal 2 and the material of the attachment object 3 may both be pure aluminum. The material of the terminal 2 and the material of the attachment object 3 may both be an aluminum alloy. If the material of the terminal 2 and the material of the attachment object 3 are both aluminum alloys, the compositions may be the same or different. The material of the terminal 2 may be pure aluminum and the material of the attachment object 3 may be an aluminum alloy. The material of the terminal 2 may be an aluminum alloy and the material of the attachment object 3 may be pure aluminum.

The material of the attachment target 3, pure aluminum or aluminum alloy, may be exposed to the outside on at least a portion of the surface of the attachment target 3 facing the first surface 21. In other words, at least a portion of the above surface of the attachment target 3 does not need to have a coating artificially formed on the outer periphery of the pure aluminum or aluminum alloy. The material of the attachment target 3, aluminum or aluminum alloy, may be exposed to the outside on the entire surface of the attachment target 3. Even if the attachment target 3 does not have the above coating, the contact resistance between the terminal 2 and the attachment target 3 is unlikely to increase because the terminal 2 has a predetermined Vickers hardness and an uneven portion 25. An attachment target 3 without the above coating has excellent productivity.

The mounting object 3 may have a coating layer 31 on the surface of the mounting object 3. The coating layer 31 is typically a metal layer formed by plating. In this example, the coating layer 31 is a plating layer. The coating layer 31 fills the gap at the interface between the terminal 2 and the mounting object 3 when the terminal 2 and the mounting object 3 rub against each other. Therefore, the newly formed aluminum surface of the terminal 2 is less likely to oxidize, and the contact resistance between the terminal 2 and the mounting object 3 is less likely to increase. The coating layer 31 may be provided at least on the portion that contacts the terminal 2. The coating layer 31 may contain at least one type selected from the group consisting of gold, silver, tin, and nickel. If the Vickers hardness of the coating layer 31 is lower than the Vickers hardness of the pure aluminum or aluminum alloy that constitutes the main body of the mounting object 3, the increase in the contact resistance at the interface between the terminal 2 and the mounting object 3 is easily suppressed. The coating layer 31 is not essential.

The Vickers hardness of the attachment object 3 is, for example, 50 HV or more. The Vickers hardness of the attachment object 3 is measured by pressing a mirror-finished surface, within 300 μm of the surface of the attachment object 3, with an indenter until the effect of the processing-induced alteration layer disappears. If the Vickers hardness of the attachment object 3 is 50 HV or more, the corner 25c of the uneven portion 25 is easily deformed when connecting the terminal 2 and the attachment object 3. The deformation of the corner 25c destroys the oxide film near the corner 25c, and the terminal 2 and the attachment object 3 are easily electrically connected. If the Vickers hardness of the attachment object 3 is 50 HV or more, the contact resistance between the terminal 2 and the attachment object 3 is unlikely to increase even when subjected to a thermal shock. The Vickers hardness of the attachment object 3 may be 55 HV or more, or 60 HV or more.

The Vickers hardness of the attachment object 3 is, for example, 160 HV or less. If the Vickers hardness of the attachment object 3 is 160 HV or less, the corner 25c easily bites into the attachment object 3. The bite of the corner 25c into the attachment object 3 makes it easy for the terminal 2 and the attachment object 3 to be firmly fixed mechanically. The Vickers hardness of the attachment object 3 may be 110 HV or less, or 80 HV or less.

The Vickers hardness of the mounting object 3 may be, for example, 50 HV or more and 160 HV or less, or 55 HV or more and 110 HV or less, or 60 HV or more and 80 HV or less.

The ratio V1/V2 of the Vickers hardness V1 of the terminal 2 to the Vickers hardness V2 of the attachment object 3 is, for example, 0.6 or more and 1.8 or less. If the ratio V1/V2 is 0.6 or more and 1.8 or less, the contact resistance between the terminal 2 and the attachment object 3 is unlikely to increase over time or even when subjected to thermal shock. The ratio V1/V2 may be 0.65 or more and 1.70 or less, 0.7 or more and 1.6 or less, or 0.75 or more and 1.50 or less.

<Bolt>
The bolt 4 tightens the terminal 2 and the attachment object 3 to connect the terminal 2 and the attachment object 3. The bolt 4 includes a shaft portion 40 and a head portion 41. The bolt 4 in this example further includes a flange portion 42. The flange portion 42 abuts against the second surface 22 of the terminal 2. A nut 4n is fitted onto the shaft portion 40. The nut 4n abuts against the attachment object 3. The terminal 2 and the attachment object 3 are tightened between the flange portion 42 of the bolt 4 and the nut 4n. In the case of a bolt 4 that does not have a flange portion 42, a washer is disposed between the head portion 41 and the terminal 2. The material of the bolt 4 is, for example, steel. The bolt 4 may be made of, for example, SNB7 steel as specified in JIS G 4107:2010. The bolt 4 may be made of an aluminum alloy.

<First area S1/second area S2>
In a state in which the first surface 21 having the uneven portion 25 and the attachment object 3 are connected by tightening the bolt 4, the ratio S1/S2 of the first area S1 to the second area S2 is 0.66 or less. The ratio S1/S2 is an index indicating that the terminal 2 and the attachment object 3 are connected with a predetermined connection strength or more. The ratio S1/S2 may be 0.60 or less, 0.50 or less, or 0.40 or less. The ratio S1/S2 is, for example, 0.05 or more. Therefore, the range of the ratio S1/S2 is, for example, 0.05 or more and 0.66 or less, 0.10 or more and 0.60 or less, 0.15 or more and 0.50 or less, or 0.20 or more and 0.40 or less.

The first area S1 is the area of the region where the first surface 21 contacts the attachment object 3 at a pressure equal to or greater than a specified value. The specified value is, for example, 25 MPa. The first area S1 is determined by a fastening test shown in a test example described later. The first area S1 is 5 ^mm2 or more. If the first area S1 is 5 ^mm2 or more, the terminal 2 and the attachment object 3 are mechanically firmly connected, and the connection strength is likely to be maintained over a long period of time. The larger the first area S1, the higher the connection strength. The first area S1 may be 6 ^mm2 or more, or 7 ^mm2 or more. The upper limit of the first area S1 is limited by the ratio S1/S2. In other words, the lower limit of the ratio S1/S2 is limited by the first area S1.

The second area S2 is the area of a predetermined annular region. The annular region is a virtual region with the nominal diameter D1 of the bolt 4 as the inner diameter and the bearing surface diameter D2 of the bolt 4 as the outer diameter. That is, S2=π(D2/2) ² -π(D1/2) ^2. The bolt 4 is selected so that the terminal 2 and the attachment target 3 can be appropriately fastened when placed in the notch 2h with the inner diameter D3. The nominal diameter D1 and bearing surface diameter D2 of the bolt 4 can be appropriately selected depending on the location where the terminal 2 is applied. The selection criteria are exemplified as follows. The nominal diameter D1 is determined based on the inner diameter D3 of the notch 2h. The nominal diameter D1 corresponds to the diameter of the shaft portion 40 of the bolt 4 corresponding to the inner diameter D3. The bearing surface diameter D2 corresponds to the outer diameter of the range where the axial force of the bolt 4 substantially acts on the second surface 22 of the terminal 2. In fastening with the bolt 4, a bolt 4 having a flange portion 42 below the head portion 41 is used. A washer is used when fastening with a bolt 4 that does not have a flange portion. The outer diameter of the flange portion 42 appropriate for the nominal diameter D1 can be determined by referring to Attachment JA.3 of JIS B 1189:2014. In the case of a bolt 4 having a flange portion 42, the outer diameter of the flange portion 42 multiplied by 0.929 can be regarded as the bearing surface diameter D2. In the case of a washer disposed between the bolt 4 and the terminal 2, the outer diameter of the washer multiplied by 0.929 can be regarded as the bearing surface diameter D2. The nominal diameter D1 may be the same as the inner diameter D3. The bearing surface diameter D2 is larger than the inner diameter D3 and the nominal diameter D1. For example, if the inner diameter D3 is 4 mm or more and less than 5 mm, the nominal diameter D1 is 4 mm and the bearing surface diameter D2 is 9.8 mm. The nominal diameter D1 and the bearing surface diameter D2 may be changed depending on the application of the terminal 2. A person skilled in the art can select the appropriate nominal diameter D1 and bearing surface diameter D2 depending on the application.

When the axial force of the bolt 4 is constant, the smaller the ratio of the first area S1 to the second area S2, the greater the pressure acting on the region having the first area S1. If the ratio S1/S2 is 0.66 or less and the first area S1 is 5 ^mm2 or more, the terminal 2 and the attachment object 3 are mechanically connected firmly, and the connection strength is likely to be maintained over a long period of time. As a result, the contact resistance between the terminal 2 and the attachment object 3 is unlikely to increase over time.

[Test Example 1]
In Test Example 1, a test structure simulating the connection structure of the embodiment was fabricated, and a salt spray test was performed to check for the presence or absence of galvanic corrosion at the connection portion between the terminal in the test structure and the mounting object. In addition, after the salt spray test, the contact resistance between the terminal in the test structure and the mounting object was measured. In Test Example 1, test structures of Sample No. 1-1 to Sample No. 1-20 were fabricated.

Sample Description
<Terminals>
The terminal 2 of each sample has the shape shown in Fig. 8. Each terminal 2 is a rectangular plate of 14 mm x 40 mm. The thickness of each terminal 2 is 2.0 mm. Each terminal 2 is provided with a circular hole-shaped notch 2h concentric with the areal center of the terminal 2. The inner diameter D3 of each notch 2h is 7 mm.

The material of each terminal 2 is as shown in Table 1. The material column in Table 1 indicates the temper in addition to the material. In the material column of Table 1, the material is indicated to the left of the "-" and the temper to the right. The material is indicated by the internationally registered alloy number. The surface of each terminal 2 does not have an artificially formed coating. In other words, the material of the terminal 2 is exposed to the outside on the surface of each terminal 2.

　Samples marked P1, P2, C1, or C2 in the uneven processing column of Table 1 have linear uneven portions 25 on the surface of the terminal 2.

In the unevenness processing indicated as P1, the unevenness portion 25 was formed by low-load press processing. As shown in FIG. 5, the unevenness portion 25 by the unevenness processing indicated as P1 has multiple V-shaped grooves 25g arranged in parallel, and the tops of the convex portions of the unevenness portion 25 are flat surfaces. The corners 25c are rounded so that the radius of curvature is 0.2 mm. The bottom surface of the groove 25g is rounded so that the radius of curvature is 0.3 mm. The width W1 of the groove 25g is 0.4 mm. The width W2 of the flat surface is 0.6 mm. The angle φ is 160°. The height h1 is 0.05 mm. These dimensions were measured using a one-shot shape measuring machine VR-5000 manufactured by Keyence Corporation. All dimensions of the unevenness portion 25 in the following description were measured in the same manner.

In the unevenness processing labeled P2, uneven portion 25 was formed by high-load press processing. As shown in FIG. 6, uneven portion 25 by unevenness processing labeled P2 has multiple V-shaped grooves 25g arranged in parallel, and corner 25c, which is the joint between two adjacent grooves 25g, is rounded. The radius of curvature of corner 25c is 0.2 mm. The bottom surface of groove 25g is rounded so that the radius of curvature is 0.3 mm. The angle θ is 140°. The height h1 is 0.15 mm.

In the unevenness processing labeled C1, unevenness portion 25 was formed by cutting processing. As shown in FIG. 5, unevenness portion 25 by unevenness processing labeled C1 has multiple V-shaped grooves 25g arranged in parallel, and the tops of the convex portions of unevenness portion 25 are flat surfaces. Corners 25c are rounded to have a radius of curvature of 0.2 mm. The bottom surface of groove 25g is rounded to have a radius of curvature of 0.3 mm. Width W1 of groove 25g is 0.4 mm. Width W2 of the flat surface is 0.65 mm. Angle φ is 160°. Height h1 is 0.05 mm.

In the uneven processing indicated as C2, uneven portion 25 was formed by cutting. The uneven portion 25 formed by the uneven processing indicated as C2 is the same as the uneven portion 25 formed by the uneven processing indicated as P2.

　Samples marked with "-" in the uneven processing column in Table 1 do not have uneven portions 25 on the surface of each terminal 2.

The Vickers hardness of each terminal 2 was as shown in Table 1. The Vickers hardness was measured in accordance with JIS Z 2244-1:2020. The Vickers hardness measurement load was 50 gf (≒0.49 N). The Vickers hardness was the median of the measured values at 20 points. All Vickers hardness values in the following explanation were determined in the same manner.

<Installation target>
The mounting target 3 of each sample has a shape shown in FIG. 8. Each mounting target 3 is an annular plate having a thickness of 1.5 mm. The inner diameter of the mounting target 3 is equal to the nominal diameter D1 of the bolt 4 (FIG. 1). The outer diameter D4 of the mounting target 3 is the length of the diagonal of a square circumscribing the circle of the bearing surface diameter D2 shown by the two-dot chain line, that is, √2 times the bearing surface diameter D2. In the example shown in FIG. 8, the square and the outer shape of the uneven portion 25 coincide with each other. The relationship between the inner diameter D3, the nominal diameter D1, the bearing surface diameter D2, and the outer diameter D4 is shown in Table 2. The values in Table 2 are set based on the selection criteria already described.

The material of each mounting object 3 is as shown in Table 1. As mentioned above, the material column in Table 1 indicates the quality as well as the material. The material of the mounting object 3 of sample No. 1-20 is indicated by a number in the Copper Development Association standard. C1020 is oxygen-free copper. A coating layer is provided on the surface of each mounting object 3 of sample No. 1-7, sample No. 1-8, and sample No. 1-9. The coating layer was formed by plating. The coating layer had a two-layer structure of a base layer made of nickel and a finishing layer made of tin. The thickness of the base layer was 1 μm. The thickness of the finishing layer was 2 μm. When the finishing layer has a coating layer made of tin, the material column in Table 1 indicates "+Sn plating". For sample No. 1-1 to sample No. 1-6, and sample No. 1-10 to sample No. The surface of each of the attachment targets 3, 1-20, does not have an artificially formed coating. In other words, the surface of each attachment target 3 exposes the material of the attachment target 3 to the outside.

The surface of the attachment target 3 of sample No. 1-18 has a linear uneven portion 25 formed by the uneven processing indicated as P1 above. In sample No. 1-18, the uneven portion 25 of the attachment target 3 has the same configuration as the uneven portion 25 of the terminal 2. The surface of the attachment target 3 of sample No. 1-19 has a linear uneven portion 25 formed by the uneven processing indicated as P2 above. In sample No. 1-19, the uneven portion 25 of the attachment target 3 has the same configuration as the uneven portion 25 of the terminal 2. The surfaces of the attachment targets 3 of sample No. 1-1 to sample No. 1-17 and sample No. 1-20 do not have uneven portions 25.

The Vickers hardness of each mounting object 3 is as shown in Table 1. The Vickers hardness of the mounting object 3 is measured by pressing an indenter against a cross section within 300 μm from the surface of the mounting object 3 that has been mirror-finished with diamond abrasive grains of an average grain size of 1/2 μm until the effect of the processing-affected layer disappears. Table 1 also shows the ratio V1/V2 of the Vickers hardness V1 of the terminal 2 to the Vickers hardness V2 of the mounting object 3.

Fastening test
The first area S1 was obtained by the fastening test. Fig. 9 is a schematic diagram of the fastening test. In the fastening test, in addition to the terminal 2 and the attachment target 3 of each sample, a pressure-sensitive sheet 7 was prepared. As shown by the dashed line in Fig. 8, the attachment target 3 is overlapped with the terminal 2 in the fastening test.

The fastening device 8 shown in FIG. 9 comprises an upper punch 81, a lower punch 82, and a positioning pin 83. The upper punch 81 has a cylindrical shape. The material of the upper punch 81 was S50C. The outer diameter of the upper punch 81 is the same as the seat diameter D2, and the inner diameter is the same as the nominal diameter D1. The lower punch 82 has a cylindrical shape. The material of the lower punch 82 was S50C. The outer diameter of the lower punch 82 is the same as the seat diameter D2. The inner diameter of the lower punch 82 is smaller than the nominal diameter D1. In this example, the positioning pin 83 is disposed on the end face of the lower punch 82. The positioning pin 83 may be press-fitted into a hole in the lower punch 82.

The attachment object 3, pressure-sensitive sheet 7, and terminal 2 were set in this order on the end face of the lower punch 82 of the fastening device 8. As a result, a laminate 9 in which the pressure-sensitive sheet 7 was placed between the terminal 2 and attachment object 3 was placed on the end face of the lower punch 82. The pressure-sensitive sheet 7 was a "Press Sheet (Pressure Measurement Film) for Medium Pressure MS PS" manufactured by Fujifilm Corporation. The uneven portion 25 of the terminal 2 faces the pressure-sensitive sheet 7.

The upper punch 81 was compressed and moved downward by the crosshead of the universal testing machine, and the laminate 9 was pressurized by simulating a state in which an axial force was applied to the bolt 4. The final value L1 of the pressure force was 138×(D1) ² ±50N. The pressure force was measured by the load cell of the universal testing machine and controlled by the displacement of the crosshead. The final value L1 was determined uniquely according to the inner diameter D3 of the notch 2h, although there was some error. The final value L1 was reached 5 seconds after the start of application of the axial force. The tightening at the final value L1 was maintained for 5 seconds, and then the load was removed. The temperature during the measurement was 25° C., and the relative humidity was 40%.

The pressure-sensitive sheet 7 was collected from between the terminal 2 and the mounting target 3, and the area of the specific color-producing region of the pressure-sensitive sheet 7 was calculated by image analysis. The area of the specific color-producing region is the first area S1.

The color-developing surface of the pressure-sensitive sheet 7 is scanned. At this time, the color chart attached to the pressure-sensitive sheet 7 is scanned at the same time as the pressure-sensitive sheet 7. The color chart shows the correspondence between the pressure acting on the pressure-sensitive sheet 7 and the color density of the pressure-sensitive sheet 7. The scanner resolution was 300 dpi (dots per inch), 24-bit color.

The scanned image data was analyzed by Image J. Image J is an open source image analysis software. The version of the software was 1.53k. The image data was converted to an 8-bit monochrome image. The software created a histogram of the brightness of the color-developing area of the pressure-sensitive sheet 7, as well as a histogram of the brightness of the color chart. In the pressure-sensitive sheet 7, the higher the contact pressure, the darker the color. In the monochrome image, the higher the contact pressure, the lower the brightness. From the histogram of the color chart, the brightness corresponding to a contact pressure of 25 MPa or more is obtained. Meanwhile, from the histogram of the color-developing area of the pressure-sensitive sheet 7, the number N of pixels showing a contact pressure of 25 MPa or more is obtained. In a 300 dpi image, the area per pixel is 0.007168 mm ^2. Therefore, the first area S1 is 0.007168×N. Once the first area S1 is obtained, the ratio S1/S2 can be calculated. Table 1 shows the size of the first area S1 and the ratio S1/S2 of each sample.

<Salt spray test and contact resistance>
Before the salt spray test, the masses of the terminal 2 and the mounting object 3 were measured. Next, the terminal 2 and the mounting object 3 of each sample were fastened again with a bolt and a nut to prepare a test structure. The material of the bolt was SNB7 steel, and the Vickers hardness was 360 HV. The material of the nut was SWRCH10R, and the Vickers hardness was 210 HV. Since the inner diameter D3 of the terminal 2 was 7 mm, the nominal diameter D1 of the bolt and the nominal diameter D1 of the nut were 6 mm. The inner diameter of the mounting object 3 was 6 mm, and the outer diameter was 18.4 mm. The bolt and the nut were fastened so that the final reaching value L1 of the axial force was about 5 kN (138 x 6 ² N). The relationship between the torque and the axial force was measured in advance using an axial force bolt with a strain gauge, and the fastening torque of the test structure was set based on this.

The above test structures of each sample were subjected to a salt spray test. In this test, the salt water concentration was 5% by mass, the test temperature was 35°C, and the test time was 20 days. After the salt spray test, the contact resistance of the test structures was measured using the four-terminal method. In the four-terminal method, alligator clips for supplying current are clamped between the terminal 2 of each sample and the mounting object 3. Also, alligator clips for measuring voltage are clamped between the terminal 2 of each sample and the mounting object 3. A measurement current of 1 A was applied under the condition of a clamping voltage of 12 V. The measured voltage was divided by the applied current to calculate the contact resistance. The unit of contact resistance is mΩ (milliohms). The calculated contact resistance results are shown in Table 1.

After measuring the contact resistance, the bolts and nuts were removed and the mass of the terminal 2 and the attachment object 3 were measured. The mass change before and after the salt spray test was determined for the terminal 2 and attachment object 3 of each sample. The results are shown in Table 1. In the mass change column of Table 1, "0" indicates that there was no mass change in both the terminal 2 and the attachment object 3. If there was a mass change in at least one of the terminal 2 and the attachment object 3, the mass change of the terminal 2 is shown to the left of the "/" in the mass change column of Table 1, and the mass change of the attachment object 3 is shown to the right. If mass measurement was not performed after the salt spray test, "-" is shown in the mass change column of Table 1.

As shown in Table 1, if the material of terminal 2 and the material of mounting object 3 are aluminum-based, there is no mass change, or the mass change is small, even if water adheres to the connection between the terminal and the mounting object. It can be seen that if the material of terminal 2 and the material of mounting object 3 are aluminum-based, galvanic corrosion can be suppressed. In particular, if the material of terminal 2 is exposed to the outside on the surface of terminal 2 and the material of mounting object 3 is exposed on the surface of mounting object 3, there is no mass change even if water adheres to the connection between the terminal and the mounting object.

As shown in Table 1, it was found that by satisfying all of the requirements (a) to (e) explained at the beginning of the embodiment column, it is possible to suppress an increase in the contact resistance between the terminal and the object to which it is attached.

Sample No. 1-1, Sample No. 1-4, Sample No. 1-7, Sample No. 1-10, and Sample No. 1-13 had no unevenness on the terminal surface, and the ratio S1/S2 was large. Sample No. 1-14 and Sample No. 1-16 had unevenness on the terminal surface, but the width W2 of the flat surface was large, and so the ratio S1/S2 was large. It is believed that the large ratio S1/S2 reduced the contact pressure and increased the contact resistance. Sample No. 1-17 had a low Vickers hardness of 45 HV for the terminal, and so the convex parts of the uneven parts were plastically deformed and collapsed. It is believed that the axial force of the bolt was reduced due to the plastic deformation of the convex parts, and this reduced the contact pressure and increased the contact resistance. Note that in Sample No. In the case of 1-16, the Vickers hardness of the terminal is low at 45 HV, and it is believed that the high contact resistance is due to the convex parts of the uneven part undergoing plastic deformation.

[Test Example 2]
In Test Example 2, test structures simulating the connection structure of the embodiment were fabricated, and the contact resistance after the thermal shock test was measured. In Test Example 2, test structures of Sample No. 2-1 to Sample No. 2-28 were fabricated.

Sample Description
<Terminals>
The terminal 2 of each sample is the same as that of Test Example 1. The material, uneven processing, and Vickers hardness of each terminal 2 are as shown in Table 3. "P1", "P2", "C1", and "C2" shown in the uneven processing column of Table 3 are the same as those of Test Example 1. "P3" shown in the uneven processing column of Table 3 indicates a case in which a linear uneven portion 25 is formed by pressing with a load different from that of P1 and P2. As shown in FIG. 5, the uneven portion 25 by uneven processing indicated as "P3" has a plurality of V-shaped grooves 25g arranged in parallel, and the top of the convex portion of the uneven portion 25 is a flat surface. The corner 25c is rounded so that the radius of curvature is 0.2 mm. The bottom surface of the groove 25g is rounded so that the radius of curvature is 0.3 mm. The width W1 of the groove 25g is 0.5 mm. The width W2 of the flat surface is 0.5 mm. The angle φ is 160°. The height h1 is 0.06 mm.

<Installation target>
The mounting target 3 of each sample was the same as in Test Example 1. The material, uneven processing, and Vickers hardness of each mounting target 3 are as shown in Table 3. A coating layer made of nickel is provided on the surface of each mounting target 3 of Sample No. 2-14 to Sample No. 2-16. This coating layer had a single-layer structure with a finishing layer made of nickel. The thickness of the coating layer was 2 μm. When the finishing layer has a coating layer made of nickel, "+Ni plating" is written in the material column of Table 3.

Fastening test
The first area S1 was determined by a fastening test in the same manner as in Test Example 1. The results are shown in Table 3 together with the ratio S1/S2.

Thermal shock test and contact resistance
A test structure was fabricated in which the terminal 2 of each sample and the mounting target 3 were fastened with a bolt and a nut. The material, Vickers hardness, and fastening conditions of the bolt and nut were the same as those of Test Example 1. The fabricated test structure was subjected to 200 cycles of thermal shock testing. One cycle includes steps A to D. Step A is to hold the atmosphere at 150°C for 30 minutes. Step B is to cool the atmosphere to -40°C within 5 minutes from the completion of step A. Step C is to hold the atmosphere at -40°C for 30 minutes from the completion of step B. Step D is to heat the atmosphere to 150°C within 5 minutes from the completion of step C.

After the thermal shock test, the contact resistance of the connection structure was measured using the four-terminal method. The measurement method was the same as in Test Example 1. The results are shown in Table 3.

As shown in Table 3, if all of the requirements (a) to (e) explained at the beginning of the embodiment column are met, and in addition there is no coating on the attachment target, and the ratio V1/V2 is 0.6 to 1.8, the contact resistance between the terminal and the attachment target is unlikely to increase even when subjected to thermal shock.

[Test Example 3]
In Test Example 3, a plurality of test structures having different shapes of the uneven portion 25 of the terminal 2 were prepared, and the electrical resistance immediately after the terminal and the mounting object in the test structure were fastened with a bolt and the electrical resistance after the thermal shock test were measured. In Test Example 3, test structures of Sample No. 3-1 to Sample No. 3-5 were prepared.

Sample Description
<Terminals>
The terminal 2 of each sample is a rectangular plate of 20 mm × 40 mm. The thickness of each terminal 2 is 2.0 mm. Each terminal 2 is provided with a circular hole-shaped notch 2h with an inner diameter D3 of 6.4 mm. The material and Vickers hardness of each terminal 2 are as shown in Table 4.

The surface of the terminal 2 of sample No. 3-1 has a linear uneven portion 25 formed by cutting. As shown in FIG. 6, this uneven portion 25 has multiple V-shaped grooves 25g arranged in parallel, and the corner 25c where two adjacent grooves 25g join is rounded. The radius of curvature of the corner 25c is 0.3 mm. The angle θ is 140°. The height h1 is 0.18 mm. This uneven processing is indicated as "P4" in the uneven processing column of Table 4.

The surface of the terminal 2 of sample No. 3-2 has one hemispherical protrusion with a radius of curvature of 1 mm. This one protrusion is located 6.3 mm away from the edge of the opening of the notch 2h. The surface of the terminal 2 of sample No. 3-3 has four hemispherical protrusions with a radius of curvature of 1 mm. These four protrusions are equally spaced on a circle with a diameter of 12.6 mm concentric with the center of the notch 2h. The surface of the terminal 2 of sample No. 3-4 has six hemispherical protrusions with a radius of curvature of 1 mm. These six protrusions are equally spaced on a circle with a diameter of 12.6 mm concentric with the center of the notch 2h. The number of protrusions is indicated in the uneven processing column of Table 4 as "B1", "B4", or "B6".

The surface of each terminal 2 of sample No. 3-5 does not include the uneven portion 25.
<Installation target>
The mounting object 3 of each sample is a rectangular plate of 20 mm × 40 mm, similar to the terminal 2. The thickness of each mounting object 3 is 2.0 mm. The mounting object 3 is provided with a round hole equal to the nominal diameter D1 of the bolt. The material and Vickers hardness of each mounting object 3 are as shown in Table 4. The surface of each mounting object 3 does not have an uneven portion 25.

<Electrical resistance immediately after tightening>
A test structure was prepared by fastening the terminal 2 and the mounting object 3 of each sample with a bolt and a nut. The material of the bolt and the material of the nut were both steel, SWRHN12. The nominal diameter D1 of the bolt and the nominal diameter D1 of the nut were 6 mm. The bearing surface diameter D2 of the bolt was 13 mm, and the axial length of the bolt was 14 mm. The terminal 2 and the mounting object 3 were fastened with the bolt and the nut at a fastening torque of 8 N·m. Immediately after the terminal 2 and the mounting object 3 were fastened with the bolt and the nut, the electrical resistance of the test structure was measured by the four-terminal method. The measurement method was the same as that described in Patent Document 1. The results are shown in Table 4.

<Electrical resistance after thermal shock test>
The above test structures of each sample were subjected to 200 cycles of thermal shock testing. One cycle includes steps A to D. Step A is held in an atmosphere of 160°C for 60 minutes. Step B is cooled to -40°C within 5 minutes from the completion of step A. Step C is held in an atmosphere of -40°C for 60 minutes from the completion of step B. Step D is heated to 160°C within 5 minutes from the completion of step C. After the thermal shock testing, the electrical resistance of the connection structure was measured by a four-terminal method. The measurement method was the same as that described in Patent Document 1. The results are shown in Table 4.

Fastening test
After the above two electrical resistance tests were completed, the bolts were removed, the pressure-sensitive sheet was sandwiched and compressed with an axial force of 5 kN, and the area of the colored region of the pressure-sensitive sheet was calculated in the same manner as in Test Example 1. The area of this colored region is the first area S1. The results are shown in Table 4 together with the ratio S1/S2.

As shown in Table 4, it was found that sample No. 3-1 was unlikely to increase the contact resistance between the terminal and the mounting object, not only immediately after fastening, but also when subjected to thermal shock. Sample No. 3-1 has an uneven portion 25 consisting of multiple V-shaped grooves 25g and corners 25c with a curvature radius of 0.3 mm. Therefore, it is believed that when an aluminum oxide film was formed on the surface of the terminal 2 or the surface of the mounting object 3, the oxide film was destroyed at the corners 25c.

In Samples No. 3-2, 3-3, and 3-4, the contact resistance increased after the thermal shock test compared to immediately after fastening. In the case of a hemispherical convex portion with a curvature radius of 1 mm, the tip of the convex portion is configured with a relatively gentle curve. Therefore, regardless of the number of convex portions, it is believed that when an aluminum oxide film formed on the surface of the terminal 2 or the surface of the mounting object 3, the oxide film could not be destroyed.

[Test Example 4]
In Test Example 4, an aluminum-based plate material simulating the terminal 2 of the embodiment was prepared, and the bending workability of the plate material was examined. In Test Example 4, Sample No. 4-1 to Sample No. 4-6 were prepared from the materials shown in Table 5. Sample No. 4-2, Sample No. 4-3, and Sample No. 4-5 were overaged to reduce the hardness to less than that of the material of temper T6. The overaging treatment is performed at a higher treatment temperature or for a longer treatment time than the T6 treatment. Sample No. 4-2, Sample No. 4-3, and Sample No. 4-5 are different in at least one of the temperature and time of the aging treatment. Each plate material is a rectangular plate of 30 mm x 50 mm cut by electric discharge machining. The thickness of the plate material is 2 mm.

The bending test was conducted using a V-block method in accordance with JIS Z 2248:2014. The specimens were bent at 90° so that the bending ridge was parallel to the length of the specimen. After bending, the outer surface of each specimen was visually inspected for cracks. The results are shown in Table 5.

As shown in Table 5, no cracks occurred in plate materials with a Vickers hardness of less than 80HV. Therefore, it can be said that terminals with a Vickers hardness of less than 80HV have excellent bending workability and are easy to form into complex shapes.

1 Connection structure, 10 Wire with terminal, 2 Terminal, 2h Notch, 21 First surface, 22 Second surface, 25 Concave and convex portion, 25c Corner, 25g Groove, 29 Wire barrel, 3 Mounting object, 3h Notch, 31 Coating layer, 4 Bolt, 4n Nut, 40 Shaft portion, 41 Head portion, 42 Flange portion, 5 Wire, 50 Conductor, 51 Insulating coating, 7 Pressure-sensitive sheet, 8 Fastening device, 81 Upper punch, 82 Lower punch, 83 Positioning pin, 9 Laminate, D2 Seat diameter, D3 Inner diameter, D4 Outer diameter, P1 Pitch, W1, W2, W3 Width, h1 Height, θ, φ Angle.

Claims (7)

A connection structure including a terminal, an attachment object to which the terminal is attached, and a bolt that connects the terminal and the attachment object,
The terminal is
A first surface facing the attachment target in a state where the attachment target is connected to the first surface;
a notch through which the bolt passes;
The first surface includes an uneven portion formed around the notch,
the terminal and the object are made of pure aluminum or an aluminum alloy;
The terminal has a Vickers hardness of 50 HV or more,
a ratio S1/S2 of a first area S1 to a second area S2 in a state in which the first surface and the attachment object are connected by fastening the bolt is 0.66 or less;
The first area S1 is an area of a region where the first surface contacts the attachment object at a pressure of 25 MPa or more,
The second area S2 is an area of a circular region having an inner diameter equal to the nominal diameter D1 of the bolt and an outer diameter equal to the bearing surface diameter D2 of the bolt,
The first area S1 is 5 ^mm2 or more;
Connection structure. The first area S1 is the area of the specific color-developing region of the pressure-sensitive sheet obtained by a clamping test that satisfies the following conditions:
In the fastening test, a laminate having the pressure-sensitive sheet disposed between the first surface and the attachment target is fastened with an axial force of 138×(D1) ² ±50 N,
The connection structure according to claim 1 , wherein the specific color-producing region is a region having a color indicating that the region has been pressed with a pressure of 25 MPa or more. The connection structure according to claim 1 or claim 2, in which the material of the terminal, pure aluminum or aluminum alloy, is exposed to the outside on at least a portion of the first surface. The connection structure according to any one of claims 1 to 3, in which the material of the attachment object, pure aluminum or aluminum alloy, is exposed to the outside on at least a portion of the surface of the attachment object facing the first surface. The connection structure according to any one of claims 1 to 4, wherein the terminal has a Vickers hardness of less than 80 HV. The connection structure according to any one of claims 1 to 5, wherein the Vickers hardness of the attachment object is 50 HV or more. a ratio V1/V2 of a Vickers hardness V1 of the terminal to a Vickers hardness V2 of the attachment target is 0.6 or more and 1.8 or less;
7. The connection structure according to claim 1, wherein the material of the terminal and the material of the object to be attached are International Registered Alloy Numbers 6101 or 6061.