Connection structure

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

[0001] The present disclosure relates to a connection structure. This application claims priority to Japanese Patent Application No. 2023-200226, filed on November 27, 2023. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] Patent Document 1 discloses a fastening structure including 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 the first fastened member and the second fastened member together. A protrusion protruding toward the second fastened member is integrally formed on the surface of the first fastened member facing 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. Hereinafter, the first fastened member will be referred to as a terminal, the second fastened member as an attachment target, and the fastening member as a bolt.

[0003] JP 2023-82637 A

[0004] The connection structure disclosed herein comprises a terminal, an attachment object to which the terminal is attached, and a bolt connecting the terminal and the attachment object. The terminal comprises a first surface facing the attachment object when connected to the attachment object, and a notch through which the bolt passes. The first surface has an uneven portion formed around the notch. The terminal and the attachment object are made of pure aluminum or an aluminum alloy. The terminal has a Vickers hardness of 50 HV or higher. When the first surface and the attachment object are connected by tightening the bolt, the ratio S1 / S2 of a first area S1 to a second area S2 is 0.66 or less. The first area S1 is the area of ​​the region where the first surface contacts the attachment object at a pressure of 25 MPa or higher. The second area S2 is the area of ​​an annular region with 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 That's all.

[0005] FIG. 1 is a schematic side view showing a connection structure of an embodiment. FIG. 2 is a schematic plan view showing a terminal provided in the connection structure of an embodiment. FIG. 3 is a schematic plan view showing a terminal different from that of FIG. 2. FIG. 4 is a cross-sectional view showing an example of a concave-convex portion of a terminal provided in the connection structure of an embodiment. FIG. 5 is a cross-sectional view showing another example of a concave-convex portion of a terminal provided in the connection structure of an embodiment. FIG. 6 is a cross-sectional view showing yet another example of a concave-convex portion of a terminal provided in the connection structure of an embodiment. FIG. 7 is a cross-sectional view showing yet another example of a concave-convex portion of a terminal provided in the connection structure of an embodiment. FIG. 8 is a schematic plan view of a terminal used in a fastening test. FIG. 9 is an explanatory diagram illustrating an overview of the fastening test.

[0006] [Problem to be Solved by the Present Disclosure] When a terminal is made of pure aluminum or an aluminum alloy and an attachment object is made of copper or a copper alloy, galvanic corrosion can occur if water adheres to the connection portion between the terminal and the attachment object.

[0007] Galvanic corrosion can be prevented when the terminal and the attachment object are made of pure aluminum or an aluminum alloy. However, because aluminum is a highly reactive 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 a terminal and an attachment object are fastened with a bolt and a compressive force is applied, the aluminum oxide film formed on the protrusion is destroyed due to 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, the aluminum oxide film may not be destroyed by the protrusion.

[0008] Furthermore, if the linear expansion coefficients of the terminal, the attachment object, and the bolt are different, thermal shock caused by repeated heating and cooling can apply shear force to the interface between the terminal and the 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, shear at the interface caused by thermal shock can easily cause the interface to slide, leading to the accumulation of an oxide film.

[0009] 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 attachment object. [Advantages of the present disclosure] The connection structure of the present disclosure can suppress an increase in contact resistance over time at the interface between a terminal and an attachment object.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0011] (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 terminal and the attachment object are made of pure aluminum or an aluminum alloy. The terminal has a Vickers hardness of 50 HV or higher. When the first surface and the attachment object are connected by tightening the bolt, the ratio S1 / S2 of a first area S1 to a second area S2 is 0.66 or less. The first area S1 is the area of ​​a region where the first surface contacts the attachment object at a pressure of 25 MPa or higher. The second area S2 is the area of ​​an annular 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 mm ２ That's all.

[0012] Since the material of the terminal and the material of the object to be attached are pure aluminum or aluminum alloy, the occurrence of galvanic corrosion can be suppressed even if water adheres to the connection portion between the terminal and the object to be attached.

[0013] The terminal has a Vickers hardness of 50 HV or more. The protrusions of the concave-convex portion of the terminal having such hardness easily bite into the attachment target when the terminal and the attachment target are connected with a bolt. The protrusions that bite into the attachment target are deformed by the attachment target. The deformation of the protrusions destroys the oxide coatings on the surfaces of the terminal and the attachment target near the protrusions, establishing electrical continuity between the terminal and the attachment target. The protrusions bite into the attachment target and deform, thereby firmly mechanically fixing the terminal and the attachment target. The protrusions having a Vickers hardness of 50 HV or more are resistant to deformation by thermal shock and vibration after the terminal and the attachment target are connected. Therefore, the connection strength between the terminal and the attachment target is less likely to be reduced by thermal shock and vibration. In other words, the fastening between the terminal and the attachment target is less likely to loosen, and the terminal and the attachment target are less likely to rub against each other at the interface between the terminal and the attachment target. As a result, new aluminum surfaces are less likely to be formed 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.

[0014] The first area S1 is the area where the first surface comes into contact with the attachment target 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 the first area S1 to the second area S2, the greater the pressure acting on the area of ​​the first area S1. Because the ratio S1 / S2 is 0.66 or less, the pressure acting on the area of ​​the first area S1 increases, making it easier for the protrusions of the terminal's concave-convex portion to bite into the attachment target.

[0015] The first area S1 is 5 mm ２ Since the ratio S1 / S2 is 0.66 or less and the first area S1 is 5 mm ２ If the above conditions are met, the terminal and the object to which it is attached are mechanically connected firmly, and the strength of the connection is likely to be maintained over a long period of time, making it difficult for the contact resistance between the terminal and the object to increase over time.

[0016] (2) In the connection structure of (1) above, the first area S1 may be the area of ​​the specific color-developing region of the pressure-sensitive sheet, which is 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 to a size of 138 × (D1) ２ The clamping force is ±50 N. The specific color-forming region is a region that has a color that indicates that the clamping force is 25 MPa or more.

[0017] The ratio S1 / S2 can be determined appropriately and reproducibly by the fastening test. (3) In the connection structure of (1) or (2), pure aluminum or an aluminum alloy, which is the material of the terminal, may be exposed to the outside in at least a part of the first surface.

[0018] In this disclosure, "pure aluminum or aluminum alloy 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 attachment object. Therefore, "artificially formed coating" does not include natural oxide films. Natural oxide films are not artificially formed and are not conductive. A natural oxide film is, for example, an aluminum oxide film. In addition, "artificially formed coating" does not include unavoidable surface contamination, specifically organic matter, hydrates, or moisture.

[0019] A coating artificially formed on a terminal can reduce the contact resistance between the terminal and the object to which it is attached. However, artificially forming a coating requires time and cost. The terminal of the present disclosure can reduce the contact resistance with the object to which it is attached by having a predetermined Vickers hardness and unevenness, even without an artificially formed coating. A terminal without an artificially formed coating has excellent productivity.

[0020] If the terminal does not have an artificially formed coating, the terminal and the object to which it is attached are likely to come into contact with the same metal, making it easier to suppress the occurrence of galvanic corrosion.

[0021] (4) In any of the connection structures (1) to (3) above, the material of the attachment object, pure aluminum or aluminum alloy, may be exposed to the outside on at least a portion of the surface facing the first surface of the attachment object.

[0022] In the connection structure of the present disclosure, 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. Attachment targets that do not have an artificially formed coating are superior in productivity. Attachment targets that do not have an artificially formed coating tend to have contact between the terminal and the attachment target as they are made of the same metal, making it easier to suppress the occurrence of galvanic corrosion.

[0023] (5) In any of the connection structures (1) to (4) above, the terminal may have a Vickers hardness of less than 80 HV.

[0024] If the Vickers hardness of the terminal is less than 80 HV, the terminal's bending workability is improved, making it easier to form terminals with complex shapes. If the Vickers hardness of the terminal is less than 80 HV, the convex parts of the terminal's concave-convex part are easily crushed when connecting the terminal to an attachment object. As a result, the oxide coating near the convex parts of the concave-convex part is easily destroyed, making it easier to ensure conductivity between the terminal and the attachment object.

[0025] (6) In any of the connection structures (1) to (5) above, the object to be attached may have a Vickers hardness of 50 HV or more.

[0026] If the Vickers hardness of the attachment object is 50 HV or more, the convex portions of the concave and convex portions of the terminal are easily deformed when connecting the terminal to the attachment object. If the Vickers hardness of the attachment object is 50 HV or more, the contact resistance between the terminal and the attachment object is less likely to increase even when subjected to thermal shock.

[0027] (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.

[0028] When the terminal and the attachment object are made of specific materials and the ratio V1 / V2 satisfies a specific range, the occurrence of galvanic corrosion can be suppressed, and the contact resistance between the terminal and the attachment object is less likely to increase over time or even when subjected to thermal shock.

[0029] [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 the convenience of explanation, some of the configuration may be exaggerated or simplified. The dimensional ratios of each part in the drawings may also differ from the actual ratios. Note that the present invention is not limited to these examples, but is defined by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0030] A connection structure 1 according to an embodiment will be described with reference to Figures 1 to 7. As shown in Figure 1, the connection structure 1 according to 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 according to the embodiment is that it satisfies the following requirements (a) to (e).

[0031] (a) As shown in FIGS. 2 and 3, the terminal 2 has an uneven portion 25 formed around the notch 2h on the first surface 21.

[0032] (b) The material of the terminal 2 and the material of the attachment object 3 are pure aluminum or an aluminum alloy.

[0033] (c) The Vickers hardness of the terminal 2 is 50 HV or more. (d) The ratio S1 / S2 of the first area S1 to the second area S2, which will be described later, is 0.66 or less.

[0034] (e) The first area S1 is 5 mm ２That's all. <Terminal> 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. As shown in FIG. 1 , the terminal 2 in this example is part of a terminal-attached electric wire 10. The terminal-attached electric wire 10 is composed of an electric wire 5 and a terminal 2 that is independent of the electric wire 5. The electric wire 5 includes a conductor 50 and an insulating coating 51 that covers 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 0.4 mm to 30 mm. The conductor 50 in this example is a stranded wire made of multiple strands. The conductor 50 is made of, for example, pure copper, a copper alloy, pure aluminum, or an aluminum alloy. The thickness of the insulating coating 51 may be, for example, 0.1 mm to 10 mm, or 0.2 mm to 5 mm. The material of the insulating coating 51 is, for example, primarily composed of a polyolefin-based resin. The polyolefin-based resin is, for example, polyethylene or polypropylene. The insulating coating 51 may be made of a silicone-based resin.

[0035] 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 portion formed on the bus bar. The connection portion is a part of the bus bar formed into a terminal shape. Furthermore, unlike this example, the terminal 2 may be, for example, a part of a single-core wire, i.e., a connection portion formed on the tip of the single-core wire.

[0036] 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 with the attachment target 3. The second surface 22 is a surface opposite the first surface 21. The terminal 2 has a notch 2h that opens to the first surface 21 and the second surface 22. A bolt 4 passes through the notch 2h. The notch 2h here includes a through hole and a slit. A 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, such as the left end surface, the top end surface, and the bottom 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 circular hole shape as shown in FIG. 2 or an elongated hole shape (not shown). A slit is a region that, although not shown, is open not only to the first surface 21 and the second surface 22 but also to a surface perpendicular to the first surface 21 and the second surface 22, for example, to one of the left end surface, the upper end surface, and the 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.

[0037] The terminal 2 of 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 to another surface perpendicular to both the first surface 21 and the second surface 22. Instead of using the wire barrel 29, the electric wire 5 may be connected to the terminal 2 by welding or solid-state welding. Examples of such joining methods include resistance welding, laser welding, ultrasonic welding, and friction stir welding.

[0038] The size of the terminal 2 is determined depending on 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.

[0039] 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.

[0040] <Uneven Portion> The terminal 2 has an uneven portion 25 at a position on the first surface 21 that overlaps with the attachment target 3. The uneven portion 25 is formed in the cross-hatched region in FIG. 2 , i.e., around the notch 2h on the first surface 21. The uneven portion 25 serves to strengthen the connection between the terminal 2 and the attachment target 3. The outer peripheral contour of the uneven portion 25 is rectangular. The inner peripheral contour of this uneven portion 25 is circular. In the example of FIG. 2 , the inner peripheral contour of the uneven portion 25 coincides with the notch 2h. Unlike the example of FIG. 2 , the inner peripheral contour of the uneven portion 25 may not coincide with the notch 2h and may be larger than the notch 2h. The uneven portion 25 may also be ring-shaped, as shown in FIG. 3 . In the example of FIG. 3 , the inner peripheral contour of the ring-shaped uneven portion 25 does not coincide with the notch 2h and may be larger than the notch 2h. Unlike the example in 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 or may not be rectangular or circular. The concave-convex portion 25 can be formed by, for example, cutting or rolling.

[0041] As shown in FIGS. 4 to 7 , the uneven portion 25 of this example is composed of a first surface 21 and multiple grooves 25g formed in the first surface 21. FIGS. 4 to 7 are cross-sectional views of the terminal 2 cut along a plane perpendicular to the direction along the grooves 25g. The multiple grooves 25g may be arranged in parallel or cross-hatched fashion. The multiple parallel grooves 25g may be aligned along a first length of the terminal 2 or along a second length, specifically, a width, of the terminal 2. The multiple annular grooves 25g may be arranged concentrically in the uneven portion 25. Unlike this example, the uneven portion 25 may have multiple protrusions protruding from the first surface 21. In this 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, which will be 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 apexes of the convex portions of the concave-convex 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 concave-convex portion 25 has, for example, a first configuration shown in FIG. 4, a second configuration shown in FIG. 5, a third configuration shown in FIG. 6, or a fourth configuration shown in FIG. 7.

[0042] [First Form] In the first form, 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 easily bites into the attachment object 3. Therefore, the uneven portion 25 having the V-groove easily reduces the contact resistance between the terminal 2 and the attachment object 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 an imaginary line that passes through the bottom of the V-groove and is perpendicular to the first surface 21 is taken, the angles formed by the imaginary line and the left side wall and the right side wall of the V-groove are equal.

[0043] 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 with 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 with a mountain-shaped cross section, constitutes a 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 also corresponds to 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 distance 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 with 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.

[0044] The angle θ between the side walls of two adjacent grooves 25g shown in Figure 4 is 90°. The angle θ is not limited to 90° and may be 60° or greater and 170° or less. The angle θ may be 80° or greater and 160° or less, or may be greater 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 processing precision, which makes it easier to reduce production costs.

[0045] The bottom shape of the groove 25g may be a curved surface or a flat surface connected to the sidewalls by a smooth R-shape. When the bottom shape of the groove 25g is a curved surface or a flat surface, stress due to vibration, thermal shock, etc. on the terminal 2 is less likely to concentrate around the V-shaped bottom surface of the groove 25g, making it less likely to damage the terminal 2. In addition, since there is no need to increase the processing precision of the groove 25g excessively, the production cost of the terminal 2 can be easily reduced.

[0046] [Second Configuration] In the second configuration, as shown in Fig. 5, the tops of the convex portions of the concave-convex portion 25 are flat. This flat surface is the first surface 21. The joint between the first surface 21 and the groove 25g forms the corner 25c of the concave-convex portion 25. In this example, the corner 25c is sharp. The cross-sectional shape of the groove 25g is V-shaped, as in the first configuration.

[0047] The width W2 of the flat surface, i.e., the distance between two adjacent grooves 25g, is, for example, more than 0 mm and not more than 5 mm. The width W2 may be 0.01 mm or more and 2 mm or less. The width W1 between the opening edges of the grooves 25g is, for example, 0.01 mm or more and 3 mm or less. The width W1 may be 0.02 mm or more and 1 mm or less. The depth of the grooves 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.

[0048] The angle φ formed between the side wall of the groove 25g and the first surface 21 is, for example, greater than 90° and not greater than 170°. The angle φ may also be greater than 90° and not greater than 160°. The angles φ of the multiple grooves 25g do not have to be the same. If the angles φ are not the same, there is no need to excessively increase the processing precision, which makes it easier to reduce production costs.

[0049] 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.

[0050] [Third Configuration] In the third configuration, as shown in Figure 6, the tops of the convex portions of the uneven portion 25 are rounded. In other words, the corners 25c at the joints between two adjacent grooves 25g, i.e., the corners 25c that form 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 to 0.8 mm. The radius of curvature R of the corners 25c may be 0.01 mm to 0.6 mm, 0.02 mm to 0.5 mm, or 0.03 mm to 0.3 mm. The smaller the radius of curvature R of the corners 25c, the more easily the corners 25c will bite into the attachment target 3.

[0051] The depth of the groove 25g, i.e., the height h1 of the convex portion, is, for example, 0.005 mm to 1 mm. The height h1 may be 0.01 mm to 0.5 mm, 0.05 mm to 0.5 mm, or 0.1 mm to 0.5 mm.

[0052] The bottom surface of the groove 25g may also be rounded. In other words, the bottom surface of the groove 25g may be curved. The radius of curvature R of the bottom surface of the 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 the groove 25g may 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.

[0053] [Fourth Form] In the fourth form, 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.

[0054] The width W3 of the convex portion, i.e., the distance between two adjacent grooves 25g, is, for example, more than 0 mm and not more than 5 mm. The width W3 may be 0.01 mm or more and 2 mm or less. The width W1 between the opening edges of the grooves 25g is, for example, 0.01 mm or more and 3 mm or less. The width W1 may be 0.02 mm or more and 1 mm or less. The depth of the grooves 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 0.6 mm or less, 0.05 mm or more and 0.6 mm or less, or 0.1 mm or more and 0.6 mm or less.

[0055] 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 0.7 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 formed between the side wall of the groove 25g and the first surface 21 shown in FIG. 7 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.

[0056] 4 to 7 bite into the attachment object 3 when the terminal 2 and the attachment object 3 are connected. At that time, the corner 25c is deformed by the attachment object 3. This deformation destroys the oxide film on the surface of the corner 25c and on the surface of the attachment object 3 corresponding to the corner 25c, thereby establishing electrical continuity between the terminal 2 and the attachment object 3. By pressing the corner 25 against the attachment object 3 with a specified pressure or more, the terminal 2 and the attachment object 3 are firmly connected for a long period of time.

[0057] <Material> The material of the terminal 2 is pure aluminum or an aluminum alloy. Pure aluminum is an aluminum alloy with an aluminum content of 99% by mass or more. An aluminum alloy is an alloy with the highest aluminum content. 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 to 1.50% by mass of silicon and 0.01% by mass to 2.00% by mass of magnesium. The silicon and magnesium contents are values ​​when the entire aluminum alloy is taken as 100% by mass. This also applies to the contents 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 copper content is, for example, 0% by mass to 1.2% by mass or 0.1% by mass to 1.2% by mass. 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 or less. 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 has, for example, International Registered Alloy Number 6101 or 6061.

[0058] The pure aluminum or aluminum alloy material of the terminal 2 may be exposed to the outside on at least a portion of the first surface 21 of the terminal 2. In other words, at least a portion of the first surface 21 does not need to have a coating artificially formed on the outer periphery of the pure aluminum or aluminum alloy. The aluminum or aluminum alloy material of the terminal 2 may be exposed to the outside over the entire first surface 21. Although the coating serves to reduce the contact resistance between the terminal 2 and the attachment target 3, forming the coating requires effort and cost. Since the terminal 2 has the uneven portion 25 described above and has a Vickers hardness described below, the contact resistance with the attachment target 3 can be reduced even without the coating. A terminal 2 without the coating has excellent productivity.

[0059] <Vickers Hardness> The Vickers hardness of the terminal 2 is 50 HV or higher. The Vickers hardness is measured in accordance with JIS Z 2244-1:2020. The higher the Vickers hardness, the more easily the corners 25c of the convex portions of the uneven portion 25 bite into the attachment object 3 when the terminal 2 and the attachment object 3 are fastened by the bolt 4. The corners 25c that bite into the attachment object 3 are deformed by the attachment object 3. The deformation of the corners 25c destroys the oxide coating on the surfaces of the terminal 2 and the attachment object 3 in the vicinity of the corners 25c, thereby establishing electrical continuity between the terminal 2 and the attachment object 3. The corners 25c bite into the attachment object 3 and deform, thereby mechanically and firmly fixing the terminal 2 and the attachment object 3. A convex portion with a Vickers hardness of 50 HV or higher is less likely to deform due to thermal shock and vibration after the terminal 2 and the attachment object 3 are connected. Therefore, the connection strength between the terminal 2 and the attachment object 3 is less likely to decrease due to thermal shock and vibration. That is, the connection between the terminal 2 and the attachment object 3 is less likely to loosen, and the terminal 2 and the attachment object 3 are less likely to rub against each other at the interface between them. As a result, new aluminum surfaces are less likely to be formed on the surfaces of the terminal 2 and the attachment object 3 at the interface due to friction, etc., and the contact resistance between the terminal 2 and the attachment object 3 is less likely to increase. The Vickers hardness of the terminal 2 may be 55 HV or more, or 60 HV or more.

[0060] The Vickers hardness of the terminal 2 is, for example, less than 80 HV. If the Vickers hardness of the terminal 2 is less than 80 HV, the bending workability 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, for example, a Z-shaped bent portion. If the Vickers hardness of the terminal 2 is less than 80 HV, the corners 25c of the uneven portion 25 are easily crushed when connecting the terminal 2 to the attachment object 3. As a result, the oxide film near the corners 25c of the uneven portion 25 is easily destroyed, and conductivity between the terminal 2 and the attachment object 3 is easily ensured. The Vickers hardness of the terminal 2 may be 75 HV or less, or 70 HV or less.

[0061] The Vickers hardness of the terminal 2 may be, for example, 50 HV or more and less than 80 HV, 55 HV or more and 75 HV or less, or 60 HV or more and 70 HV or less.

[0062] <<Conductivity>> The conductivity of the terminal 2 is, for example, 40% IACS or more and 63% IACS or less. The conductivity is measured in accordance with JIS H 0505:1975. Aluminum alloys containing silicon and magnesium easily meet the above conductivity. When the terminal 2 has the above conductivity, the amount of heat generated by the terminal 2 is reduced. As a result, thermal damage to the wire 5 connected to the terminal 2 and the attachment object 3 is reduced. The conductivity may be 41% IACS or more and 60% IACS or less, or 42% IACS or more and 58% IACS or less. Alternatively, the conductivity may be 40% IACS or more and 50% IACS or less.

[0063] <Attachment 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.

[0064] 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 portion 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. Both the material of the terminal 2 and the material of the attachment object 3 may be pure aluminum. Both the material of the terminal 2 and the material of the attachment object 3 may be aluminum alloy. When both the material of the terminal 2 and the material of the attachment object 3 are 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 aluminum alloy and the material of the attachment object 3 may be pure aluminum.

[0065] The material of the mounting object 3, pure aluminum or aluminum alloy, may be exposed to the outside on at least a portion of the surface of the mounting object 3 facing the first surface 21. In other words, at least a portion of the surface of the mounting object 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 mounting object 3, aluminum or aluminum alloy, may be exposed to the outside on the entire surface of the mounting object 3. Even if the mounting object 3 does not have the coating, the terminal 2 has a predetermined Vickers hardness and the uneven portion 25, so that the contact resistance between the terminal 2 and the mounting object 3 is unlikely to increase. The mounting object 3 without the coating has excellent productivity.

[0066] The attachment target 3 may have a coating layer 31 on its surface. The coating layer 31 is typically a metal layer formed by plating. In this example, the coating layer 31 is a plated layer. The coating layer 31 fills gaps at the interface between the terminal 2 and the attachment target 3 when the terminal 2 and the attachment target 3 rub against each other. This prevents oxidation of the newly formed aluminum surface of the terminal 2, and reduces the increase in contact resistance between the terminal 2 and the attachment target 3. The coating layer 31 need only be provided on at least the portion that contacts the terminal 2. The coating layer 31 may contain at least one element 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 body of the attachment target 3, the increase in contact resistance at the interface between the terminal 2 and the attachment target 3 is likely to be suppressed. The coating layer 31 is not essential.

[0067] The Vickers hardness of the attachment object 3 is, for example, 50 HV or higher. The Vickers hardness of the attachment object 3 is measured by pressing a mirror-polished surface within 300 μm from the surface of the attachment object 3 with an indenter. If the Vickers hardness of the attachment object 3 is 50 HV or higher, the corners 25 c of the uneven portion 25 are likely to deform when connecting the terminal 2 to the attachment object 3. The deformation of the corners 25 c destroys the oxide film near the corners 25 c, facilitating electrical continuity between the terminal 2 and the attachment object 3. If the Vickers hardness of the attachment object 3 is 50 HV or higher, the contact resistance between the terminal 2 and the attachment object 3 is unlikely to increase even when subjected to thermal shock. The Vickers hardness of the attachment object 3 may be 55 HV or higher, or 60 HV or higher.

[0068] 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 corners 25 c can easily bite into the attachment object 3. The biting of the corners 25 c into the attachment object 3 can easily mechanically securely fix the terminal 2 and the attachment object 3. The Vickers hardness of the attachment object 3 may be 110 HV or less, or 80 HV or less.

[0069] The Vickers hardness of the attachment 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.

[0070] 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.

[0071] <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 shank 40 and a head 41. The bolt 4 in this example further includes a flange 42. The flange 42 abuts against the second surface 22 of the terminal 2. A nut 4n is fitted onto the shank 40. The nut 4n abuts against the attachment object 3. The terminal 2 and the attachment object 3 are tightened between the flange 42 of the bolt 4 and the nut 4n. In the case of a bolt 4 that does not include a flange 42, a washer is disposed between the head 41 and the terminal 2. The bolt 4 is made of, for example, steel. The bolt 4 may be made of, for example, SNB7 steel specified in JIS G 4107:2010. The bolt 4 may also be made of an aluminum alloy.

[0072] <First Area S1 / Second Area S2> When the first surface 21 having the concave-convex portion 25 is connected to the attachment object 3 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 or greater connection strength. 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 greater. Therefore, the range of the ratio S1 / S2 is, for example, 0.05 or greater and 0.66 or less, 0.10 or greater and 0.60 or less, 0.15 or greater and 0.50 or less, or 0.20 or greater and 0.40 or less.

[0073] The first area S1 is the area of ​​the region where the first surface 21 comes into contact with 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 tightening test shown in the test example described later. The first area S1 is 5 mm ２The first area S1 is 5 mm ２ If the first area S1 is 6 mm or more, the terminal 2 and the attachment object 3 are mechanically connected firmly, and the connection strength is likely to be maintained for a long period of time. The larger the first area S1, the higher the connection strength. ２ or more, or 7 mm ２ 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.

[0074] The second area S2 is the area of ​​a predetermined circular region. The circular 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. In other words, S2 = π(D2 / 2) ２ −π(D1 / 2) ２The bolt 4 is selected so that it can properly fasten the terminal 2 and the attachment object 3 when placed in the notch 2h with an inner diameter D3. The nominal diameter D1 and bearing surface diameter D2 of the bolt 4 can be selected appropriately depending on the location where the terminal 2 is to be 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 shank 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. When fastening using the bolt 4, a bolt 4 having a flange portion 42 below the head portion 41 is used. When fastening using a bolt 4 without a flange portion, a washer is used. The outer diameter of the flange portion 42 appropriate for the nominal diameter D1 can be determined by referring to Appendix JA.3 of JIS B 1189:2014. For a bolt 4 having a flange portion 42, the bearing surface diameter D2 can be determined by multiplying the outer diameter of the flange portion 42 by 0.929. If a washer is disposed between the bolt 4 and the terminal 2, the bearing surface diameter D2 can be determined by multiplying the outer diameter of the washer by 0.929. 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 greater but less than 5 mm, the nominal diameter D1 is 4 mm and the bearing surface diameter D2 is 9.8 mm. Note that 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 an appropriate nominal diameter D1 and bearing surface diameter D2 depending on the application.

[0075] 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. ２ If the above conditions are met, 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.

[0076] [Test Example 1] In Test Example 1, test structures simulating the connection structure of the embodiment were fabricated, and a salt spray test was performed to examine the presence or absence of galvanic corrosion at the connection portion between the terminals of the test structure and the attachment object. After the salt spray test, the contact resistance between the terminals of the test structure and the attachment object was measured. In Test Example 1, test structures of Sample No. 1-1 to Sample No. 1-20 were fabricated.

[0077] <<Description of Samples>> <Terminals>> The terminals 2 of each sample have the shape shown in Fig. 8. Each terminal 2 is a rectangular plate measuring 14 mm x 40 mm. The thickness of each terminal 2 is 2.0 mm. Each terminal 2 has a circular hole-shaped notch 2h that is concentric with the center of the surface area of ​​the terminal 2. The inner diameter D3 of each notch 2h is 7 mm.

[0078] The material of each terminal 2 is as shown in Table 1. The material column in Table 1 indicates not only the material but also the temper. In the material column of Table 1, the material is shown to the left of the "-" and the temper to the right. The material is indicated by the international 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.

[0079] The samples marked with P1, P2, C1, or C2 in the column for textured surface in Table 1 have linear textured portions 25 on the surface of the terminal 2.

[0080] In the unevenness processing indicated as P1, the uneven portion 25 was formed by low-load press processing. As shown in FIG. 5, the uneven portion 25 formed 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 uneven portion 25 are flat surfaces. The corners 25c are rounded to a radius of curvature of 0.2 mm. The bottom surfaces of the grooves 25g are rounded to a radius of curvature of 0.3 mm. The width W1 of the grooves 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 instrument VR-5000 manufactured by Keyence Corporation. All dimensions of the uneven portion 25 in the following description were measured in the same manner.

[0081] In the unevenness processing indicated as P2, the uneven portion 25 was formed by high-load press processing. As shown in FIG. 6, the uneven portion 25 formed by the unevenness processing indicated as P2 has multiple V-shaped grooves 25g arranged in parallel, and the corners 25c where two adjacent grooves 25g join are rounded. The radius of curvature of the corners 25c is 0.2 mm. The bottom surface of the grooves 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.

[0082] In the unevenness processing indicated as C1, the uneven portion 25 was formed by cutting. As shown in FIG. 5, the uneven portion 25 formed by the unevenness processing indicated as C1 has multiple V-shaped grooves 25g arranged in parallel, and the tops of the convex portions of the uneven portion 25 are flat surfaces. The corners 25c are rounded to have a radius of curvature of 0.2 mm. The bottom surfaces of the grooves 25g are rounded to have a radius of curvature of 0.3 mm. The width W1 of the grooves 25g is 0.4 mm. The width W2 of the flat surface is 0.65 mm. The angle φ is 160°. The height h1 is 0.05 mm.

[0083] In the unevenness processing indicated as C2, the unevenness portion 25 was formed by cutting. The unevenness portion 25 by the unevenness processing indicated as C2 is the same as the unevenness portion 25 by the unevenness processing indicated as P2.

[0084] The samples marked with "-" in the "textured" column in Table 1 do not have the textured portion 25 on the surface of each terminal 2.

[0085] 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 value of 20 measured values. All Vickers hardness values ​​in the following description were determined in the same manner.

[0086] <Mounting Object> The mounting object 3 of each sample has the shape shown in FIG. 8. Each mounting object 3 is an annular plate with a thickness of 1.5 mm. The inner diameter of the mounting object 3 is equal to the nominal diameter D1 of the bolt 4 (FIG. 1). The outer diameter D4 of the mounting object 3 is the length of the diagonal of a square circumscribing the circle with the bearing surface diameter D2 shown by the two-dot chain line, i.e., √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. The relationship between the inner diameter D3, nominal diameter D1, bearing surface diameter D2, and outer diameter D4 is shown in Table 2. The values ​​in Table 2 were set based on the selection criteria already described.

[0087] The material of each attachment target 3 is as shown in Table 1. As mentioned above, the material column in Table 1 indicates the temper as well as the material. The material of the attachment target 3 of Sample No. 1-20 is indicated by the number in the Copper Development Association standard. C1020 is oxygen-free copper. A coating layer is provided on the surface of each attachment target 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 consisting 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 includes a coating layer made of tin, the material column in Table 1 indicates "+Sn plating." Samples No. 1-1 to 1-6 and Sample No. 1-10 to 1-9 are marked "+Sn plating." The surface of each of the attachment targets 3 of Nos. 1 to 20 does not have an artificially formed coating. In other words, the material of each attachment target 3 is exposed to the outside on the surface of each attachment target 3.

[0088] The surface of the attachment target 3 of Sample No. 1-18 has linear uneven portions 25 formed by the uneven processing indicated as P1 above. In Sample No. 1-18, the uneven portions 25 of the attachment target 3 have the same configuration as the uneven portions 25 of the terminal 2. The surface of the attachment target 3 of Sample No. 1-19 has linear uneven portions 25 formed by the uneven processing indicated as P2 above. In Sample No. 1-19, the uneven portions 25 of the attachment target 3 have the same configuration as the uneven portions 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.

[0089] The Vickers hardness of each mounting object 3 was as shown in Table 1. The Vickers hardness of the mounting object 3 was measured by pressing an indenter against a cross section of the mounting object 3 within 300 μm from its surface, which had been mirror-polished with diamond abrasive grains having an average grain size of 1 / 2 μm until the influence of the processing-affected layer disappeared. 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.

[0090]

[0091]

[0092] <<Fastening Test>> The first area S1 was determined by a fastening test. Fig. 9 is a schematic diagram of the fastening test. In the fastening test, a pressure-sensitive sheet 7 was prepared in addition to the terminal 2 and the attachment target 3 of each sample. As shown by the dashed line in Fig. 8, the attachment target 3 was placed on top of the terminal 2 during the fastening test.

[0093] The clamping device 8 shown in Figure 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 seating surface 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 seating surface diameter D2. The inner diameter of the lower punch 82 is smaller than the nominal diameter D1. In this example, a positioning pin 83 is arranged 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.

[0094] The attachment target 3, pressure-sensitive sheet 7, and terminal 2 were set in this order on the end face of the lower punch 82 of the clamping device 8. As a result, a laminate 9 in which the pressure-sensitive sheet 7 was placed between the terminal 2 and attachment target 3 was placed on the end face of the lower punch 82. The pressure-sensitive sheet 7 was a "Pre-sheet (pressure measurement film) for medium pressure MS PS" manufactured by Fujifilm Corporation. The uneven portion 25 of the terminal 2 faced the pressure-sensitive sheet 7.

[0095] The upper punch 81 was compressed and moved downward by the crosshead of the universal testing machine, and pressure was applied to the laminate 9, simulating a state in which an axial force was applied to the bolt 4. The final value L1 of the applied pressure was 138 × (D1).２ ±50 N. The applied pressure is measured by a load cell of a universal testing machine and controlled by the displacement of the crosshead. The final value L1 is uniquely determined according to the inner diameter D3 of the notch 2h, although there may be some error. The final value L1 was reached 5 seconds after the start of application of the axial force. Tightening at the final value L1 was maintained for 5 seconds, after which the load was removed. The temperature during measurement was 25°C and the relative humidity was 40%.

[0096] The pressure-sensitive sheet 7 was collected from between the terminal 2 and the attachment target 3, and image analysis was performed to calculate the area of ​​the specific color-producing region of the pressure-sensitive sheet 7. The area of ​​the specific color-producing region was the first area S1.

[0097] 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 simultaneously with the pressure-sensitive sheet 7. The color chart shows the correspondence between the pressure applied to the pressure-sensitive sheet 7 and the color density of the pressure-sensitive sheet 7. The resolution of the scanner was 300 dpi (dots per inch), 24-bit color.

[0098] The scanned image data was analyzed using Image J. Image J is open-source image analysis software. The software version was 1.53k. The image data was converted into an 8-bit monochrome image. Using the software, a histogram of the brightness of the color-producing area of ​​the pressure-sensitive sheet 7 was created, along with a histogram of the brightness of the color chart. With the pressure-sensitive sheet 7, the higher the contact pressure, the darker the color produced. In monochrome images, 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 was determined. Meanwhile, from the histogram of the color-producing area of ​​the pressure-sensitive sheet 7, the number N of pixels showing a contact pressure of 25 MPa or more was determined. In a 300 dpi image, the area per pixel was 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 for each sample.

[0099] <Salt Spray Test and Contact Resistance> Before the salt spray test, the masses of the terminal 2 and the attachment object 3 were measured. Next, the terminal 2 and attachment object 3 of each sample were fastened together again with a bolt and nut to create a test structure. The bolt material was SNB7 steel, with a Vickers hardness of 360 HV. The nut material was SWRCH10R, with a Vickers hardness of 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 attachment object 3 was 6 mm, and the outer diameter was 18.4 mm. The bolt and nut were fastened together with a 138 x 6 bolt set screw, with an axial force of approximately 5 kN (L1). ２ The relationship between torque and axial force was measured in advance using an axial force bolt with a strain gauge, and the tightening torque of the test structure was set based on this.

[0100] 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 a four-terminal method. In the four-terminal method, alligator clips for supplying current were clamped between the terminal 2 of each sample and the attachment target 3. Also, alligator clips for measuring voltage were clamped between the terminal 2 of each sample and the attachment target 3. A measurement current of 1 A was applied under 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.

[0101] After measuring the contact resistance, the bolts and nuts were removed, and the masses of the terminal 2 and the attachment object 3 were measured. The mass change of the terminal 2 and attachment object 3 of each sample was determined before and after the salt spray test. The results are shown in Table 1. In the mass change column of Table 1, "0" indicates that there was no mass change in either the terminal 2 or the attachment object 3. If there was a mass change in at least one of the terminal 2 or 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 no mass measurement was performed after the salt spray test, a "-" is shown in the mass change column of Table 1.

[0102] As shown in Table 1, if the material of terminal 2 and the material of attachment object 3 are aluminum-based, there is no mass change or only a small mass change even if water adheres to the connection between the terminal and the attachment object. It can be seen that if the material of terminal 2 and the material of attachment 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 attachment object 3 is exposed on the surface of attachment object 3, there is no mass change even if water adheres to the connection between the terminal and the attachment object.

[0103] As shown in Table 1, it was found that by satisfying all of the requirements (a) to (e) described at the beginning of the embodiment column, it is possible to suppress an increase in contact resistance between the terminal and the object to be attached.

[0104] Samples No. 1-1, 1-4, 1-7, 1-10, and 1-13 had no irregularities on the terminal surface, resulting in a large S1 / S2 ratio. Samples No. 1-14 and 1-16 had irregularities on the terminal surface, but the width W2 of the flat surface was large, resulting in a large S1 / S2 ratio. It is believed that the large S1 / S2 ratio reduced the contact pressure and increased the contact resistance. Sample No. 1-17 had a low Vickers hardness of 45 HV, resulting in the convex portions of the irregularities being plastically deformed and collapsed. The plastic deformation of the convex portions reduced the axial force of the bolt, resulting in a decrease in contact pressure and increased contact resistance. It is also believed that Sample No. 1-16 had a low Vickers hardness of 45 HV, resulting in the high contact resistance due to the plastic deformation of the convex portions of the irregularities.

[0105] [Test Example 2] In Test Example 2, test structures simulating the connection structure of the embodiment were fabricated, and the contact resistance after a thermal shock test was measured. In Test Example 2, test structures of Sample No. 2-1 to Sample No. 2-28 were fabricated.

[0106] <<Sample Description>> <Terminal>> The terminal 2 of each sample was the same as in Test Example 1. The material, texture, and Vickers hardness of each terminal 2 were as shown in Table 3. The "P1," "P2," "C1," and "C2" columns in Table 3 were the same as those in Test Example 1. The "P3" column in Table 3 indicated a case in which a linear textured portion 25 was formed by pressing with a different load than P1 and P2. The textured portion 25 marked "P3" had multiple V-shaped grooves 25g arranged in parallel, as shown in FIG. 5, with the tops of the convex portions of the textured portion 25 being flat. The corners 25c were rounded to a radius of curvature of 0.2 mm. The bottom surfaces of the grooves 25g were rounded to a radius of curvature of 0.3 mm. The width W1 of the grooves 25g was 0.5 mm. The width W2 of the flat surface was 0.5 mm. The angle φ is 160°. The height h1 is 0.06 mm.

[0107] <Mounting object> The mounting object 3 of each sample was the same as in Test Example 1. The material, textured finish, and Vickers hardness of each mounting object 3 are as shown in Table 3. A coating layer made of nickel was provided on the surface of each mounting object 3 of Samples No. 2-14 to 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 included a coating layer made of nickel, "+Ni plating" was written in the material column of Table 3.

[0108]

[0109] <<Tightening Test>> The first area S1 was determined by a tightening test in the same manner as in Test Example 1. The results are shown in Table 3 together with the ratio S1 / S2.

[0110] <<Thermal Shock Test and Contact Resistance>> A test structure was fabricated by fastening the terminal 2 of each sample to the attachment target 3 with a bolt and nut. The materials, Vickers hardness, and fastening conditions of the bolt and nut were the same as those in 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 involves holding the sample in an atmosphere at 150°C for 30 minutes. Step B involves cooling the atmosphere to -40°C within 5 minutes of completing step A. Step C involves holding the sample in an atmosphere at -40°C for 30 minutes after completing step B. Step D involves heating the atmosphere to 150°C within 5 minutes of completing step C.

[0111] After the thermal shock test, the contact resistance of the connection structure was measured by the four-terminal method in the same manner as in Test Example 1. The results are shown in Table 3.

[0112] As shown in Table 3, if all of the requirements (a) to (e) described at the beginning of the embodiment column are met, and in addition there is no coating on the attachment object, and the ratio V1 / V2 is 0.6 or more and 1.8 or less, it was found that the contact resistance between the terminal and the attachment object is unlikely to increase even when subjected to thermal shock.

[0113] [Test Example 3] In Test Example 3, a plurality of test structures were fabricated with different shapes of the uneven portion 25 of the terminal 2, and the electrical resistance was measured immediately after the terminal and the attachment object in the test structure were fastened with a bolt, and after a thermal shock test. In Test Example 3, test structures No. 3-1 to No. 3-5 were fabricated.

[0114] <<Sample Description>> <Terminal>> The terminal 2 of each sample is a rectangular plate measuring 20 mm x 40 mm. The thickness of each terminal 2 is 2.0 mm. Each terminal 2 has 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.

[0115] 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 corners 25c where two adjacent grooves 25g join are rounded. The radius of curvature of the corners 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.

[0116] The surface of 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 opening edge of notch 2h. The surface of 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 and concentric with the center of notch 2h. The surface of 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 and concentric with the center of notch 2h. The number of protrusions is indicated as "B1," "B4," or "B6" in the "texture processing" column of Table 4.

[0117] The surface of each terminal 2 of sample No. 3-5 does not have an uneven portion 25. <Mounting object> The mounting object 3 of each sample is a rectangular plate of 20 mm x 40 mm, similar to the terminal 2. The thickness of each mounting object 3 is 2.0 mm. A round hole equal to the nominal diameter D1 of the bolt is provided in the mounting object 3. 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.

[0118]

[0119] <Electrical Resistance Immediately After Tightening> A test structure was prepared by fastening the terminal 2 of each sample to the attachment object 3 with a bolt and a nut. The bolt and nut materials were both steel, SWRHN12. The nominal diameter D1 of the bolt and the nominal diameter D1 of the nut were 6 mm. The bolt bearing surface diameter D2 was 13 mm, and the bolt axial length was 14 mm. The terminal 2 and the attachment object 3 were fastened using this bolt and nut with a tightening torque of 8 N m. Immediately after fastening the terminal 2 and the attachment object 3 with the bolt and nut, the electrical resistance of the test structure was measured using the four-terminal method. The measurement method was the same as that described in Patent Document 1. The results are shown in Table 4.

[0120] <Electrical Resistance After Thermal Shock Test> The above test structures of each sample were subjected to 200 cycles of thermal shock testing. One cycle comprises steps A to D. Step A involves holding in an atmosphere of 160°C for 60 minutes. Step B involves cooling the atmosphere to -40°C within 5 minutes of completing step A. Step C involves holding in an atmosphere of -40°C for 60 minutes after completing step B. Step D involves heating the atmosphere to 160°C within 5 minutes of completing step C. After the thermal shock test, the electrical resistance of the connection structure was measured using a four-terminal method. The measurement method was the same as that described in Patent Document 1. The results are shown in Table 4.

[0121] <<Tightening 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 was the first area S1. The results are shown in Table 4 together with the ratio S1 / S2.

[0122] As shown in Table 4, Sample No. 3-1 was found to be resistant to an increase in contact resistance between the terminal and the attachment 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, when an aluminum oxide film formed on the surface of the terminal 2 or the surface of the attachment object 3, it is believed that the oxide film was destroyed at the corners 25c.

[0123] For Samples 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 hemispherical convex portions 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 attachment object 3, the oxide film could not be destroyed.

[0124] [Test Example 4] In Test Example 4, aluminum-based plate materials simulating the terminal 2 of the embodiment were prepared, and the bending workability of the plate materials was examined. In Test Example 4, Samples 4-1 to 4-6 were prepared using the materials shown in Table 5. Samples 4-2, 4-3, and 4-5 were overaged to reduce their hardness below that of tempered T6 materials. Overaging treatment involves a higher treatment temperature or a longer treatment time than T6 treatment. Samples 4-2, 4-3, and 4-5 differ in at least one of the temperature and time of the aging treatment. Each plate material was a 30 mm x 50 mm rectangular plate cut by electrical discharge machining. The plate material thickness was 2 mm.

[0125] The bending test was performed using a V-block method in accordance with JIS Z 2248:2014. The specimens were bent at a 90° angle so that the bending ridge was parallel to the longitudinal direction of each specimen. After bending, the outer surface of each specimen was visually inspected for cracks. The results are shown in Table 5.

[0126]

[0127] As shown in Table 5, no cracks occurred in the plate material having a Vickers hardness of less than 80 HV. Therefore, it can be said that terminals having a Vickers hardness of less than 80 HV have excellent bending workability and can be easily formed into complex shapes.

[0128] 1 Connection structure, 10 Electric 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 Shank portion, 41 Head portion, 42 Flange portion, 5 Electric wire, 50 Conductor, 51 Insulating coating, 7 Pressure-sensitive sheet, 8 Fastening device, 81 Upper punch, 82 Lower punch, 83 Positioning pin, 9 Laminated body, D2 Bearing surface diameter, D3 Inner diameter, D4 Outer diameter, P1 Pitch, W1, W2, W3 Width, h1 Height, θ, φ Angle.

Claims

1. A connection structure comprising a terminal, an attachment object to which the terminal is attached, and a bolt connecting the terminal and the attachment object, wherein the terminal comprises: a first surface facing the attachment object when connected to the attachment object; and a notch through which the bolt passes, the first surface having 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, 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 tightening the bolt is 0.66 or less, the first area S1 is the area of ​​an area where the first surface comes into contact with 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, and the first area S1 is 5 mm ２ That's it, the connection structure.

2. The first area S1 is the area of ​​a specific color-developing region of the pressure-sensitive sheet obtained by a clamping test that satisfies the following condition, and in the clamping test, a laminate in which the pressure-sensitive sheet is disposed between the first surface and the mounting target is subjected to a clamping test of 138×(D1) ２ The connection structure according to claim 1 , wherein the connection structure is fastened with an axial force of ±50 N, and the specific color-producing region is a region having a color indicating that the connection structure is pressed with a pressure of 25 MPa or more.

3. A connection structure as claimed in claim 1 or 2, wherein the material of said terminal, pure aluminum or aluminum alloy, is exposed to the outside on at least a portion of said first surface.

4. A connection structure as described in any one of claims 1 to 3, wherein 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.

5. A connection structure according to any one of claims 1 to 4, wherein the terminal has a Vickers hardness of less than 80 HV.

6. A connection structure according to any one of claims 1 to 5, wherein the Vickers hardness of the attachment object is 50 HV or more.

7. A connection structure according to any one of claims 1 to 6, wherein the ratio V1 / V2 of the Vickers hardness V1 of the terminal to the Vickers hardness V2 of the attachment object is 0.6 or more and 1.8 or less, and the material of the terminal and the material of the attachment object are International Registered Alloy Numbers 6101 or 6061.

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