Connection structure

Abstract

To provide a connection structure capable of suppressing a time-dependent increase in contact resistance on a boundary surface between a terminal and an attachment object.SOLUTION: A connection structure comprises: a terminal, an attachment object to which the terminal is attached; and a bolt that connects the terminal with the attachment object. The terminal includes: a first surface that faces the attachment object in a state of being connected to the attachment object; and a notch which is penetrated by the bolt. The first surface comprises an uneven part that is formed around the notch. A material of the terminal is aluminum or aluminum alloy, and a Vickers hardness of the terminal is 50HV or more and less than 80HV. The attachment object comprises: a main body part made of copper or a copper alloy; a conductive layer that covers the surface that faces the first surface of the main body part; and the notch to which is penetrated by the bolt. A ratio S1 / S2 of an area of a first surface S1 and an area of a second surface S2 in a state where the first surface and the attachment object are connected by fastening the volt is 0.8 or less, and the area of the first surface S1 is 5 mm2 or larger.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a connection structure. [Background technology]

[0002] Patent Documents 1 and 2 disclose an electric wire with a terminal that is connected to an attachment object by a bolt. The terminal has a through hole. A bolt that connects the terminal and the attachment object passes through the through hole. The terminal and the attachment object are fastened to each other by the bolt and the nut, so that the terminal and the attachment object are mechanically fixed to each other and electrically connected to each other.

[0003] The terminal of the electric wire with terminal is made of, for example, aluminum or an aluminum alloy, which is lightweight and contributes to reducing the weight of the terminal and the electric wire with terminal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-11128 [Patent Document 2] Patent Publication No. 2022-22609 Summary of the Invention [Problem to be solved by the invention]

[0005] In a connection structure in which a terminal is connected to an attachment object, there is a risk that the contact resistance at the interface between the terminal and the attachment object will increase over time. For example, when vibration and thermal shock act on the connection structure, the fastening between the terminal and the attachment object will loosen, or the terminal and the attachment object will rub against each other at the interface. In particular, when the terminal and the attachment object are made of different materials, the difference in thermal expansion coefficient between the terminal and the attachment object makes the interface more susceptible to thermal shock. A new aluminum surface is formed on the surface of the terminal at the interface due to friction, etc. When the new aluminum surface oxidizes, the contact resistance between the terminal and the attachment object increases.

[0006] An object of the present disclosure is to provide a connection structure capable of suppressing an increase in contact resistance over time at the interface between a terminal and an object to which it is attached. [Means for solving the problem]

[0007] The connection structure of the present disclosure includes a terminal, an attachment target to which the terminal is attached, and a bolt connecting the terminal and the attachment target. The terminal includes a first surface facing the attachment target when connected to the attachment target, and a notch through which the bolt passes. The first surface includes an uneven portion formed around the notch. The material of the terminal is pure aluminum or an aluminum alloy. The Vickers hardness of the terminal is 50 HV or more and less than 80 HV. The attachment target includes a main body portion made of pure copper or a copper alloy, a conductive layer covering a surface of the main body portion facing the first surface, and a notch through which the bolt passes. The ratio S1 / S2 of the first area S1 and the second area S2 in a state in which the first surface and the attachment target are connected by tightening the bolt is 0.42 or less. The first area S1 is the area of ​​a region where the first surface contacts the attachment target 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. 2 That's all. Effect of the Invention

[0008] 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. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic side view showing a connection structure according to an embodiment. [Diagram 2] FIG. 2 is a schematic plan view showing an end portion of a terminal and an electric wire provided in the connection structure of the embodiment. [Diagram 3] FIG. 3 is a schematic plan view showing a terminal different from that in FIG. [Figure 4] FIG. 4 is a cross-sectional view showing a concave-convex portion of a terminal provided in the connection structure of the embodiment. [Diagram 5] FIG. 5 is a cross-sectional view showing a projection and recess portion different from that in FIG. [Figure 6] FIG. 6 is a schematic plan view showing an attachment target provided in the connection structure of the embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view showing an interface between a terminal provided in the connection structure of the embodiment and an object to which the terminal is attached. [Figure 8] FIG. 8 is an explanatory diagram showing measurement points for measuring the thickness of a conductive layer of a mounting target provided in the connection structure of the embodiment. [Figure 9] FIG. 9 is a schematic plan view of a terminal used in a fastening test. [Figure 10] FIG. 10 is an explanatory diagram for explaining an outline of the fastening test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Description of the embodiments of the present disclosure First, the 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 target to which the terminal is attached, and a bolt connecting the terminal and the attachment target. The terminal includes a first surface facing the attachment target when connected to the attachment target, and a notch through which the bolt passes. The first surface includes an uneven portion formed around the notch. The material of the terminal is pure aluminum or an aluminum alloy. The Vickers hardness of the terminal is 50 HV or more and less than 80 HV. The attachment target includes a main body portion made of pure copper or a copper alloy, a conductive layer covering a surface of the main body portion facing the first surface, and a notch through which the bolt passes. A ratio S1 / S2 of a first area S1 and a second area S2 in a state in which the first surface and the attachment target are connected by tightening the bolt is 0.42 or less. The first area S1 is an area of ​​a region where the first surface contacts the attachment target 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. 2 That's all.

[0012] In the case where the attachment target is composed only of a main body without a conductive layer, if the Vickers hardness of the terminal is less than 80 HV, when thermal shock or vibration acts after the terminal and the attachment target are connected by a bolt, the convex part of the uneven part of the terminal is likely to be excessively deformed. When the convex part is excessively deformed, a new aluminum surface is formed on the surface of the terminal, and the new surface is oxidized. In addition, stress relaxation of the terminal occurs, the axial force of the bolt is released, and the terminal and the attachment target are likely to rub against each other. As a result, a new aluminum surface is formed on the surface of the terminal, and the new surface is oxidized. In addition, the surface of the attachment target is likely to be oxidized. Therefore, the contact resistance between the terminal and the attachment target is likely to increase.

[0013] In contrast, in the connection structure of (1) above, the attachment target has a conductive layer. The fact that the Vickers hardness, the ratio S1 / S2, and the first area S1 of the terminal each satisfy the above ranges is equivalent to indicating that the conductive layer is soft enough that the convex portion of the uneven portion of the terminal can easily bite into the conductive layer of the attachment target. By having a soft conductive layer on the attachment target, even if the Vickers hardness of the terminal is less than 80HV, the convex portion can easily bite into the conductive layer when the terminal and the attachment target are connected by a bolt. Since the Vickers hardness of the terminal is less than 80HV, the convex portion is easily deformed by biting into the conductive layer. The terminal and the attachment target are mechanically and firmly fixed by the biting into the conductive layer and deformation of the convex portion. In addition, the deformation of the convex portion destroys the oxide coating in the vicinity of the convex portion, and the terminal and the attachment target are electrically connected. In addition, since the mounting object has a soft conductive layer, and the Vickers hardness of the terminal is 50HV or more, when thermal shock or vibration is applied after the terminal and the mounting object are connected by a bolt, the convex part of the uneven part of the terminal does not deform too much. Therefore, the connection strength between the terminal and the mounting object is not easily reduced by thermal shock and vibration. That is, 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, a new aluminum surface is not easily formed on the surface of the terminal at the interface due to friction, etc., and the contact resistance between the terminal and the mounting object is not easily increased. Therefore, the terminal and the mounting object are mechanically firmly connected, and the connection strength is easily maintained for a long period of time. That is, the contact resistance between the terminal and the mounting object is not easily increased over time.

[0014] The first area S1 is the area of ​​the region where the first surface comes into contact with the object to be attached 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 region of the first area S1. However, if the absolute value of the first area S1 is too small, the connection strength between the terminal and the object to be attached is not sufficiently ensured. When the ratio S1 / S2 is 0.42 or less and the first area S1 is 5 mm 2If the above conditions are met, the terminal and the object to which the terminal is attached are mechanically connected firmly, and the connection strength is likely to be maintained over a long period of time, so that the contact resistance between the terminal and the object to which the terminal is attached is unlikely to increase over time.

[0015] (2) In the connection structure of (1) above, the first area S1 may be an area of ​​a specific color-developing region of a pressure-sensitive sheet that 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 conductive layer is clamped to a thickness of 138×(D1). 2 The clamp is tightened with an axial force of ±50 N. The specific color-developing region is a region having a color that indicates that the clamp has been pressed with a pressure of 25 MPa or more.

[0016] The connection structure of (2) above allows the ratio S1 / S2 to be determined appropriately with good reproducibility.

[0017] (3) In the connection structure of (1) or (2) above, a hardness ratio obtained by dividing a Vickers hardness of the terminal by a Vickers hardness of the main body may be 0.50 or more.

[0018] If the hardness ratio is 0.50 or more, the contact resistance between the terminal and the attachment object is likely to be reduced.

[0019] (4) In any one of the connection structures (1) to (3) above, the object to be attached may have a Vickers hardness of 40 HV or more and 150 HV or less.

[0020] If the Vickers hardness of the attachment target is 40HV or more, the convex portion of the uneven portion of the terminal is likely to deform. The deformation of the convex portion destroys the oxide coating in the vicinity of the convex portion, and the terminal and the attachment target are likely to be electrically connected. If the Vickers hardness of the attachment target is 150HV or less, the convex portion is likely to bite into the attachment target. Biting into the attachment target tends to mechanically fix the terminal and the attachment target firmly.

[0021] (5) In any one of the connection structures (1) to (4) above, the main body may have a Vickers hardness of 60 HV or more and 150 HV or less.

[0022] When the Vickers hardness of the main body is in the above range, the Vickers hardness of the attachment object easily satisfies the requirement of 60 HV to 150 HV. In addition, since the mechanical strength of the attachment object is increased, the connection structure of (5) above has excellent mechanical strength of the entire connection structure.

[0023] (6) In any one of the connection structures (1) to (5) above, the conductive layer may be made of pure tin, an alloy containing tin and copper, pure silver, or an alloy containing silver and copper.

[0024] The conductive layer made of the above-mentioned material tends to prevent the surface oxidation of the main body made of copper or a copper alloy, and therefore the connection structure of (6) tends to prevent an increase in contact resistance at the interface between the terminal and the object to which it is attached.

[0025] (7) In any one of the connection structures (1) to (6) above, the conductive layer may have an average thickness of 0.5 μm or more and 3 μm or less.

[0026] When the average thickness of the conductive layer is 0.5 μm or more, the convex parts of the uneven part of the terminal are less likely to deform excessively and are more likely to bite into the conductive layer. When the average thickness of the conductive layer is 3 μm or less, the convex parts of the uneven part of the terminal are more likely to deform.

[0027] (8) In any one of the connection structures described above in (1) to (7), the uneven portion may have a plurality of grooves, and each of the plurality of grooves may be a V-shaped groove.

[0028] The V-groove means a groove whose contour shape in a cross section perpendicular to the direction along the groove is V-shaped. The opening edge of the V-groove is likely to bite into the mounting object. Even if there is a difference in hardness between the terminal and the mounting object, the opening edge of the V-groove deforms and breaks its own oxide film, while the valley of the V-groove restrains the excessive plastic flow of the opening edge of the V-groove, so that the opening edge of the V-groove and the side wall of the V-groove are likely to bite into the mounting object. The side wall of the V-groove generates shear stress between the terminal and the conductive layer due to the axial load. Therefore, the oxide film present on the surface of the terminal and the conductive layer is likely to be destroyed, which tends to promote metal contact between the terminal and the conductive layer. Therefore, the uneven portion having the V-groove is likely to reduce the contact resistance between the terminal and the mounting object.

[0029] (9) In the connection structure of (8) above, an angle between side walls of two adjacent V-shaped grooves in the plurality of grooves may be greater than 90° and equal to or less than 140°.

[0030] If the above angle is greater than 90° and less than 140°, the opening edge of the V-groove is likely to bite into the attachment target.

[0031] (10) In any one of the connection structures (1) to (9) above, the material of the main body may be oxygen-free copper, tough pitch copper, C18661 in the Copper Development Association standard, C10850 in the Copper Development Association standard, C19210 in the Copper Development Association standard, or JC100 in the Japan Automotive Engineering Society standard.

[0032] The connection structure of (10) above can suppress an increase in contact resistance at the interface between the terminal and the object to which it is attached over a long period of time.

[0033] (11) In any one of the connection structures (1) to (10) above, the material of the terminal may be International Registered Alloy Number 6101.

[0034] The connection structure of (11) above can suppress an increase in contact resistance at the interface between the terminal and the object to which it is attached over a long period of time.

[0035] Details of the embodiments of the present disclosure Hereinafter, 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 objects. Note that the present invention is not limited to the configurations shown in the embodiments, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0036] <<Embodiment>> [Connection structure] A connection structure 1 of the embodiment will be described with reference to Fig. 1 to Fig. 8. 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). As shown in (A) and (B) of FIG. 2 and FIG. 3, the terminal 2 has an uneven portion 25 formed around the notch 2h in the first surface 21. (B) The material of the terminal 2 is pure aluminum or an aluminum alloy, and the Vickers hardness of the terminal 2 is not less than 50 HV and less than 80 HV. 7C, the attachment target 3 includes a main body 30 made of pure copper or a copper alloy, and a conductive layer 31 covering the surface of the main body 30 facing the first surface 21. (D) The ratio S1 / S2 of a first area S1 to a second area S2 described later is 0.42 or less. (E) The first area S1 is 5 mm 2 That's all.

[0037] [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. The terminal 2 in this example is a part of the electric wire with terminal 10. 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 0.4 mm to 30 mm. The conductor 50 in this example is a stranded wire in which a plurality of wires are twisted together. The conductor 50 is made of, for example, 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 0.2 mm to 5 mm. The material of the insulating coating 51 is, for example, mainly composed of a polyolefin resin. The polyolefin resin is, for example, polyethylene or polypropylene. The insulating coating 51 may be a silicone resin. The terminal 2 is not limited to the embodiment in 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.

[0038] 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 object 3 when the terminal 2 is connected to the attachment object 3. The first surface 21 has a portion that overlaps with the attachment object 3 and a portion that does not overlap with the attachment object 3. 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. A bolt 4 passes through the notch 2h. The notch 2h is a concept that includes not only a notch that is usually considered, but also a through hole. The notch 2h 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 surface perpendicular to the first surface 21 and the second surface 22, such as the left end surface, the upper end surface, and the lower end surface of the terminal 2 in FIG. 2. That is, the 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. The slit is a region that opens not only to the first surface 21 and the second surface 22, but also to any one of the surfaces perpendicular to the first surface 21 and the second surface 22, such as the left end surface, the upper end surface, and the lower end surface of the terminal 2 in FIG. 2, although not shown. That is, the slit is a region whose cross section along the first surface 21 has an open cross section.

[0039] The terminal 2 in this example includes a wire barrel 29 that holds the conductor 50 of the electric wire 5. The terminal 2 may further include an insulation barrel that holds 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.

[0040] The size of the terminal 2 is determined depending on the application of the terminal 2. For example, the length of the terminal 2, i.e., the length along the extending direction of the electric wire 5, is 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, i.e., the distance between the first surface 21 and the second surface 22, is, for example, 0.1 mm or more and 7 mm or less. The thickness of the terminal 2 may be, for example, 0.3 mm or more and 4 mm or less, or 0.5 mm or more and 3 mm or less.

[0041] The shape of the notch 2h shown in FIG. 2 is a round hole shape as described above. That is, the notch 2h 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.

[0042] 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 not be rectangular or circular, but may be elliptical. The concave-convex portion 25 can be formed by, for example, cutting or rolling.

[0043] As shown in FIG. 4 and FIG. 5, 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. FIG. 4 and FIG. 5 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 length of the terminal 2, or in a direction along the width of the terminal 2, i.e., in a direction perpendicular to the length. The plurality of annular grooves 25g may be arranged concentrically in the uneven portion 25. 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 protrusion may be, for example, a prism, a pyramid, a truncated pyramid, a cylinder, a cone, a truncated cone, or a hemisphere. The apex of the protrusion may have a curved surface with an arbitrary radius of curvature R.

[0044] 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, this V-groove is a V-groove in which, 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.

[0045] Each groove 25g constitutes a recess of the uneven portion 25. The interval 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 a corner 25c. The corner 25c may be rounded. The interval between two adjacent corners 25c, i.e., the pitch P1, is, for example, 0.4 mm or more and 5 mm or less. The pitch P1 in this example is also the width W1 of the opening of the groove 25g. The pitch P1 may be, for example, 0.5 mm or more and 3 mm or less. The depth of the groove 25g, which is the length from the bottom of the groove 25g to the corner 25c in the direction perpendicular to the first surface 21, 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, for example, 0.01 mm or more and 0.5 mm or less.

[0046] The radius of curvature R of the corner 25c may be, for example, 0.01 mm or more and 1 mm or less. The radius of curvature R of the corner 25c may be 0.01 mm or more and 0.05 mm or less. The angle θ between the side walls of the 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 the V-groove having the above angle, i.e., the corner 25c, is likely to bite into the mounting object 3. The individual angles θ 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 accuracy, which makes it easier to reduce production costs.

[0047] 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 excessively increase the processing accuracy of groove 25g, which makes it easy to reduce the production cost of terminal 2.

[0048] As shown in Fig. 5, groove 25g may have a uniform width toward the bottom of groove 25g. The cross-sectional shape of groove 25g in Fig. 5 is rectangular. Each groove 25g constitutes a concave portion of uneven portion 25, and first surface 21 constitutes a convex portion of uneven portion 25. The joint between first surface 21 and groove 25g constitutes corner 25c of uneven portion 25. Corner 25c may be rounded.

[0049] The width W2 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 W2 may be, for example, 0.01 mm or more and 2 mm or less. The width W1 of the opening of the groove 25g is, for example, 0.01 mm or more and 3 mm or less. The width W1 may be, for example, 0.02 mm or more and 1 mm or less. 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 0.6 mm or less.

[0050] The radius of curvature R of the corner 25c may be, for example, 0.01 mm or more and 1 mm or less. The radius of curvature R of the corner 25c may be 0.01 mm or more and 0.8 mm or less. The angle φ between the side wall of the groove 25g shown in FIG. 5 and the first surface 21 is 90°. The angle φ may be 90° or more and 160° or less. The angle φ may be 90° or more and 150° or less. The individual angles φ do not have to be consistent. If the individual angles φ are not consistent, there is no need to excessively increase the processing accuracy, which makes it easier to reduce production costs.

[0051] The bottom surface of the groove 25g does not have to be flat, and may be curved. The bottom surface of the groove 25g may be connected to the sidewall by a smooth R-shape. When the bottom surface of the groove 25g is curved or connected to the sidewall by a smooth R-shape, stress due to vibration, thermal shock, etc. on the terminal 2 is unlikely to concentrate around the bottom surface or sidewall of the groove 25g, and the terminal 2 is unlikely to be damaged. In addition, since there is no need to excessively increase the processing accuracy of the groove 25g, the production cost of the terminal 2 is likely to be reduced.

[0052] When the terminal 2 and the attachment object 3 are connected, the corner 25c of the uneven portion 25 in Figs. 4 and 5 bites into the conductive layer 31 as shown in Fig. 7. At that time, the corner 25c is deformed by the attachment object 3. This deformation destroys the oxide film of the corner 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 to each other for a long period of time. As shown in Fig. 7, not only the conductive layer 31 but also the main body portion 30 may be recessed by the corner 25c.

[0053] The material of the terminal 2 is pure aluminum or an aluminum alloy. The surface of the terminal 2 is not provided with a conductive layer. Pure aluminum is an alloy containing 99% or more by mass of aluminum. An aluminum alloy is an alloy containing the most aluminum. The content of aluminum contained in the aluminum alloy is, for example, 80% or more by mass when the entire aluminum alloy is taken as 100% by mass. The aluminum alloy is allowed to contain unavoidable impurities. The aluminum alloy contains, for example, 0.01% to 1.50% by mass of silicon and 0.01% to 2.00% by mass 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 also true 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, 0.1% 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 is, for example, International Registered Alloy Number 6101. When the aluminum alloy contains the above-mentioned additive elements, at least one of copper and manganese may be essential.

[0054] The Vickers hardness of the terminal 2 is equal to or greater than 50HV and less than 80HV. The Vickers hardness is measured in accordance with JIS Z 2244-1:2020. The Vickers hardness may be, for example, equal to or greater than 55HV and less than 75HV, or equal to or greater than 60HV and less than 70HV.

[0055] The Vickers hardness of the terminal 2 is 50HV or more and less than 80HV, the ratio S1 / S2 of the first area S1 to the second area S2 described later is 0.42 or less, and the first area S1 is 5 mm 2 The above is equivalent to indicating that the conductive layer 31 of the attachment object 3 is soft enough that the corner 25c of the uneven portion 25 of the terminal 2 can easily bite into the conductive layer 31 of the attachment object 3. By providing the soft conductive layer 31 of the attachment object 3, even if the Vickers hardness of the terminal 2 is less than 80 HV, the corner 25c can easily bite into the conductive layer 31 when the terminal 2 and the attachment object 3 are connected by the bolt 4. Since the Vickers hardness of the terminal 2 is less than 80 HV, the corner 25c can easily deform by biting into the conductive layer 31. The corner 25c bites into the conductive layer 31 and deforms, and the terminal 2 and the attachment object 3 are mechanically and firmly fixed. In addition, the deformation of the corner 25c destroys the oxide coating in the vicinity of the corner 25c, and the terminal 2 and the attachment object 3 are electrically connected. In addition, since the mounting object 3 has a soft conductive layer 31, and the Vickers hardness of the terminal 2 is 50HV or more, when thermal shock or vibration is applied after the terminal 2 and the mounting object 3 are connected by the bolt 4, the corner 25c does not deform too much. Therefore, the connection strength between the terminal 2 and the mounting object 3 is not easily reduced by thermal shock and vibration. That is, the fastening between the terminal 2 and the mounting object 3 is not easily loosened, and the terminal 2 and the mounting object 3 are not easily rubbed against each other at the interface between the terminal 2 and the mounting object 3. As a result, a new aluminum surface is not easily formed on the surface of the terminal 2 at the interface due to friction, etc., and the contact resistance between the terminal 2 and the mounting object 3 is not easily increased. Therefore, the terminal 2 and the mounting object 3 are mechanically firmly connected, and the connection strength is easily maintained for a long period of time. That is, the contact resistance between the terminal 2 and the mounting object 3 is not easily increased over time.

[0056] 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. Aluminum alloys containing silicon and magnesium easily satisfy 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.

[0057] [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 Figs. 1 and 6, the attachment target 3 has a notch 3h through which the bolt 4 passes. The notch 3h is a concept that includes not only a notch that is usually thought of, but also a through hole. The notch 3h, like the notch 2h, includes a through hole and a slit. The notch 3h in this example is a through hole. As shown in Fig. 7, the attachment target 3 has a main body portion 30 and a conductive layer 31.

[0058] (Main body) The material of the main body 30 is, for example, pure copper or a copper alloy. Pure copper or a copper alloy is relatively easy to deform. Therefore, the corners 25c of the uneven portion 25 of the terminal 2 are easily inserted into the attachment object 3, and the connection between the terminal 2 and the attachment object 3 is strong. Specific materials of the main body 30 are oxygen-free copper, tough pitch copper, C18661 in the Copper Development Association standard, C10850 in the Copper Development Association standard, C19210 in the Copper Development Association standard, or JC100 in the Japan Automotive Engineering Society standard.

[0059] The Vickers hardness of the main body 30 is, for example, 60HV or more and 150HV or less. If the Vickers hardness of the main body 30 is 60HV or more and 150HV or less, the Vickers hardness of the attachment target 3 is likely to satisfy 60HV or more and 150HV or less. The Vickers hardness of the main body 30 may be 65HV or more and 140HV or less, or 70HV or more and 130HV or less.

[0060] (Conductive layer) The conductive layer 31 is provided on the surface of the main body 30. The conductive layer 31 may be provided at least on a portion that contacts the terminal 2. The conductive layer 31 is disposed between the corner 25c and the main body 30. When the terminal 2 and the attachment object 3 rub against each other, the conductive layer 31 fills the gap at the interface between the opening edge of the uneven portion 25 of the terminal 2 and the attachment object 3. Therefore, the newly formed aluminum surface of the terminal 2 is unlikely to oxidize, and the contact resistance between the terminal 2 and the attachment object 3 is unlikely to increase. In addition, the conductive layer 31 suppresses oxidation of the surface of the main body 30. The conductive layer 31 is not broken by the pressure and sliding contact of the corner 25c.

[0061] The material of the conductive layer 31 is, for example, pure tin, an alloy containing tin and copper, pure silver, or an alloy containing silver and copper. Pure tin has a tin content of 99% by mass or more. The tin content of the alloy containing tin and copper is, for example, 5% by mass or more and less than 99% by mass, 10% by mass or more and 98% by mass or less, or 15% by mass or more and 97% by mass or less, when the entire alloy containing tin and copper is taken as 100% by mass. The copper content of the alloy containing tin and copper is, for example, 1% by mass or more and 95% by mass or less, 2% by mass or more and 90% by mass or less, or 3% by mass or more and 85% by mass or less, when the entire alloy containing tin and copper is taken as 100% by mass. Pure silver has a silver content of 92.5% by mass or more. The content of silver in the alloy containing silver and copper is, for example, 10% by mass or more and less than 92.5% by mass, 50% by mass or more and less than 91% by mass, or 80% by mass or more and less than 90% by mass, when the entire alloy containing silver and copper is taken as 100% by mass. The content of copper in the alloy containing silver and copper is, for example, 7.5% by mass or more and less than 92.5% by mass, 9% by mass or more and less than 90% by mass, or 10% by mass or more and less than 50% by mass, when the entire alloy containing silver and copper is taken as 100% by mass. The conductive layer 31 made of these materials is easily adhered to the main body 30 made of copper or a copper alloy. Therefore, an increase in the contact resistance at the interface between the terminal 2 and the attachment target 3 is easily suppressed. The composition of the conductive layer 31 is determined by high-frequency inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0062] The conductive layer 31 made of an alloy containing tin and copper may contain a compound of tin (Sn) and copper (Cu). The compound may be, for example, a Cu6Sn5 phase, a Cu3Sn phase, or a CuSn 0.8 phase may be used. By including the above-mentioned compound, the Vickers hardness of the conductive layer 31 is appropriately improved, and the terminal 2 and the attachment object 3 are easily and mechanically fixed firmly to each other. The above-mentioned compound can be identified by analyzing the chemical composition using an energy dispersive X-ray spectrometer (SEM-EDX) attached to a scanning electron microscope or by analyzing the crystal structure using an X-ray diffraction device (XRD).

[0063] The average thickness of the conductive layer 31 is, for example, 0.5 μm or more and 3 μm or less. If the average thickness of the conductive layer 31 is 0.5 μm or more, the corners 25c of the uneven portion 25 are unlikely to deform excessively and are likely to bite into the conductive layer 31. If the average thickness of the conductive layer 31 is 3 μm or less, the corners 25c of the uneven portion 25 are likely to deform. The average thickness of the conductive layer 31 may be 1 μm or more and 2.5 μm or less, or 1.5 μm or more and 2 μm or less.

[0064] A method for determining the average thickness of the conductive layer 31 will be described with reference to FIG. 8. FIG. 8 is a plan view of the surface of the attachment target 3 facing the terminal 2. The thickness of the conductive layer 31 is measured at least at one point from the first intersection β1 to the eighth intersection β8 on the contour line of the imaginary square α. The imaginary square α is a square that envelops the first imaginary circle γ1. The first imaginary circle γ1 is a circle that passes through the middle between the notch 3h and the second imaginary circle γ2. The second imaginary circle γ2 is a circle that is concentric with the notch 3h and has a diameter that is the same length as the width of the attachment target 3.

[0065] The first intersection β1 is an intersection between the first virtual line δ1 and the fifth virtual line δ5. The second intersection point β2 is an intersection point between the first imaginary line δ1 and the sixth imaginary line δ6. The third intersection β3 is an intersection between the second virtual line δ2 and the third virtual line δ3. The fourth intersection point β4 is an intersection point between the second virtual line δ2 and the fourth virtual line δ4. The fifth intersection β5 is an intersection between the third virtual line δ3 and the fifth virtual line δ5. The sixth intersection β6 is an intersection of the fourth virtual line δ4 and the fifth virtual line δ5. The seventh intersection β7 is an intersection of the third virtual line δ3 and the sixth virtual line δ6. The eighth intersection point β8 is an intersection point between the fourth virtual line δ4 and the sixth virtual line δ6.

[0066] The first imaginary line δ1 is a straight line that passes through the center of the notch 3h and is perpendicular to the direction along the width of the attachment target 3. The second imaginary line δ2 is a straight line that passes through the center of the notch 3h and is perpendicular to the first imaginary line δ1. The third virtual line δ3 is one side of the virtual square α, is a straight line parallel to the first virtual line δ1 and perpendicular to the second virtual line δ2. The fourth virtual line δ4 is one side of the virtual square α and is a straight line parallel to the third virtual line δ3. The fifth virtual line δ5 is one side of the virtual square α, and is a straight line perpendicular to the first virtual line δ1 and parallel to the second virtual line δ2. The sixth virtual line δ6 is one side of the virtual square α and is a straight line parallel to the fifth virtual line δ5.

[0067] A cross section is taken along the width of the attachment target 3 at least at one of the first intersection point β1 to the eighth intersection point β8. The cross section is mirror-polished and imaged using an electron microscope. The imaging magnification is 5,000 times or more and 50,000 times or less. The field of view size is 12 μm × 9 μm. In the captured photograph, the thickness of the conductive layer 31 is measured. Three or more measurements of the thickness of the conductive layer 31 in each photograph are taken. The average value of all the measured thicknesses is regarded as the average thickness of the conductive layer 31.

[0068] The conductive layer 31 is typically a metal layer formed by a plating method. In this example, the conductive layer 31 is a plated layer. Examples of the plating method include electroplating, electroless plating, and hot-dip plating. The Vickers hardness of the attachment target 3 can be adjusted depending on the type of plating method and the conditions of the plating method.

[0069] The hardness ratio obtained by dividing the Vickers hardness of the terminal 2 by the Vickers hardness of the main body 30 is, for example, 0.50 or more. If the hardness ratio is 0.50 or more, the contact resistance between the terminal 2 and the attachment object 3 is likely to be reduced. The hardness ratio may be 0.51 or more, 0.52 or more. The hardness ratio may be 1.40 or less, 1.35 or less, or 1.30 or less. That is, the hardness ratio may be 0.50 or more and 1.40 or less, 0.51 or more and 1.35 or less, or 0.52 or more and 1.30 or less.

[0070] The Vickers hardness of the attachment target 3 is, for example, 40HV or more and 150HV or less. The Vickers hardness of the attachment target 3 is not the hardness measured by pressing the surface of the main body 30 on which the conductive layer 31 is not provided with an indenter, but the hardness measured by pressing the surface of the conductive layer 31 on the main body 30 with an indenter. If the Vickers hardness of the attachment target 3 is 40HV or more, the corner 25c is easily deformed. The deformation of the corner 25c destroys the oxide coating in the vicinity of the corner 25c, and the terminal 2 and the attachment target 3 are easily electrically connected. If the Vickers hardness of the attachment target 3 is 150HV or less, the corner 25c is easily embedded in the attachment target 3. The embedding of the corner 25c in the attachment target 3 easily mechanically fixes the terminal 2 and the attachment target 3 firmly. The Vickers hardness of the mounting object 3 may be 65 HV or more and 140 HV or less, or 70 HV or more and 130 HV or less.

[0071] Although not shown in the drawings, the attachment target 3 may have an intermediate layer between the main body 30 and the conductive layer 31. The material of the intermediate layer may be, for example, nickel or an alloy containing nickel and copper. The presence of the intermediate layer tends to suppress the reaction between the copper contained in the main body 30 and the conductive layer 31. This tends to suppress oxidation of the surface of the main body 30. In addition, excessive increase in hardness of the conductive layer 31 tends to be suppressed.

[0072] [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 include 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.

[0073] [First area S1 / Second area S2] In a state where the first surface 21 having the concave and convex portions 25 and the attachment object 3 are connected by fastening the bolt 4, the ratio S1 / S2 of the first area S1 to the second area S2 is 0.42 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, for example, 0.40 or less, 0.38 or less, 0.36 or less, or 0.34 or less. The lower limit of the ratio S1 / S2 is, for example, 0.10. Therefore, the range of the ratio S1 / S2 is, for example, 0.10 or more and 0.42 or less, 0.10 or more and 0.40 or less, 0.10 or more and 0.38 or less, 0.10 or more and 0.36 or less, or 0.10 or more and 0.34 or less.

[0074] The first area S1 is the area of ​​the region where the first surface 21 contacts the attachment target 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 the test example described later. The first area S1 is 5 mm 2 That is all. The first area S1 is 5 mm 2 If the first area S1 is larger than the above, 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. The first area S1 is, for example, 6 mm 2 More than 7mm is fine 2The 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.

[0075] 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) 2 The bolt 4 is selected so that the terminal 2 and the object 3 to be attached can be properly fastened when the bolt 4 is placed in the notch 2h having the inner diameter D3. The nominal diameter D1 and the bearing surface diameter D2 of the bolt 4 can be appropriately selected according to 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. When fastening with the bolt 4, a bolt 4 having a flange portion 42 below the head portion 41 is used. When fastening with 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 the attached table JA.3 of JIS B 1189:2014. In the case of 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. In the case of a washer 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 more but 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 an appropriate nominal diameter D1 and bearing surface diameter D2 depending on the application.

[0076] 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 is the case, 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. As a result, the contact resistance between the terminal 2 and the attachment object 3 is unlikely to increase over time.

[0077] Test Example 1 In the test example, members simulating the terminal 2 and the attachment target 3 of the embodiment were prepared, and the ratio S1 / S2 was obtained by a fastening test. In addition, a test structure simulating the connection structure 1 of the embodiment was fabricated, and a thermal shock test was performed using the test structure.

[0078] [Samples No. 1 to No. 13, Samples No. 101 to No. 107] [Terminal] The terminal 2 of each sample has the shape shown in Fig. 9. 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.

[0079] The material, temper, and Vickers hardness of each terminal 2 were as shown in Table 1. The material column in Table 1 shows the internationally registered alloy number. 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 points. All Vickers hardness values ​​in the following description were determined in the same manner. None of the terminals 2 have a conductive layer formed by a plating method or the like. This point is the same for all terminals 2 in the following description.

[0080] Each terminal 2 has a concave-convex portion 25. The shape of each concave-convex portion 25 is as shown in Table 1. The shape in Table 1 indicates the overall shape of the concave-convex portion 25. In the column for shape in Table 1, "parallel" refers to a concave-convex portion 25 in which a plurality of V-shaped grooves 25g are arranged in parallel. In the same column, "cross" refers to a concave-convex portion 25 in which a plurality of V-shaped grooves 25g are perpendicular to each other in a cross-hatched pattern. "Cross" refers to a concave-convex portion 25 having a so-called square knurled shape. The pitch P1 (mm) of each concave-convex portion 25 and the radius of curvature R (mm) of the corner 25c are as shown in Table 1. The height h1 of each concave-convex portion 25 was 0.2 mm, and the angle θ between the side walls of two adjacent grooves 25g was 140°.

[0081] [Installation target] The mounting target 3 of each sample has a shape shown in FIG. 9. Each mounting target 3 is a circular plate having a thickness of 1.5 mm. The mounting targets 3 of Samples No. 1 to No. 13 and Samples No. 101 to No. 106 have a main body and a conductive layer. The mounting target 3 of Sample No. 107 does not have a conductive layer and is composed only of a main body. Each conductive layer covers the surface of the main body that faces the terminal 2. The material, temper, and Vickers hardness of each main body and the material of each conductive layer are as shown in Table 1. The column for the material of the main body in Table 1 shows the number specified in JIS H 3100:2018 or the number in the Copper Development Association standard. C1020 is oxygen-free copper. The "Cu-Sn alloy" in the column for the material of the conductive layer in Table 1 is an alloy that contains 61 mass% tin and 39 mass% copper when the entire alloy is 100 mass%, and the remainder is made of unavoidable impurities. Each conductive layer was formed by a plating method. The Vickers hardness of the attachment target 3 was as shown in Table 1. The Vickers hardness of the attachment target 3 having the conductive layer 31 was measured by pressing the surface of the conductive layer 31 on the main body part 30 with an indenter. The Vickers hardness of the attachment target 3 not having the conductive layer 31 was the Vickers hardness of the main body part 30, and was measured by pressing the surface of the main body part 30 with an indenter.

[0082] The inner diameter of the attachment object 3 is equal to the nominal diameter D1 of the bolt 4 (FIG. 1). As shown in FIG. 9, the outer diameter D4 of the attachment object 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, i.e., √2 times the bearing surface diameter D2. In the example shown in FIG. 9, 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 were set based on the selection criteria already mentioned.

[0083] [Table 1]

[0084] [Table 2]

[0085] [Tightening test] Fig. 10 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. 9, the attachment target 3 was placed on top of the terminal 2 in the fastening test.

[0086] The fastening device 8 shown in FIG. 10 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 was the same as the seat diameter D2, and the inner diameter was 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 was 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, 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.

[0087] The attachment target 3, the pressure-sensitive sheet 7, and the 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 disposed between the terminal 2 and the attachment target 3 was placed on the end face of the lower punch 82. The pressure-sensitive sheet 7 was "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.

[0088] The upper punch 81 was compressed by the crosshead of the universal testing machine and moved downward, simulating a state in which an axial force was applied to the bolt 4, and the laminate 9 was pressurized. The final value L1 of the pressing force was 138×(D1). 2 ±50N. The applied pressure is measured by the load cell of the universal testing machine and is 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. The tightening at the final value L1 was maintained for 5 seconds, after which the load was removed. The temperature during the measurement was 25°C and the relative humidity was 40%.

[0089] The pressure-sensitive sheet 7 was collected from between the terminal 2 and the attachment 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 was the first area S1.

[0090] 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) and 24-bit color.

[0091] The scanned image data was analyzed using Image J. Image J is an open source image analysis software. The software version was 1.53k. The image data was converted to an 8-bit monochrome image. The software was used to create a histogram of the brightness of the color-producing area of ​​the pressure-sensitive sheet 7, as well as 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. With 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 can be obtained. 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 can be obtained. With 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 for each sample.

[0092] [Thermal shock test] A test structure was created in which the terminal 2 of each sample and the mounting object 3 were fastened with a bolt and nut. The bolt material was SNB7 steel, with a Vickers hardness of 360HV. The nut material was SWRCH10R, with a Vickers hardness of 210HV. Since the inner diameter D3 of the notch 2h of the terminal 2 was 7mm, the nominal diameter D1 of the bolt and the nominal diameter D1 of the nut were 6mm. The inner diameter of the mounting object 3 was 6mm, and the outer diameter was 18.4mm. The bolt and nut were fastened to a specimen with an axial load of approximately 5kN (138×6 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.

[0093] The test structures were subjected to 200 cycles of thermal shock testing. One cycle includes steps A through D. Step A is a 30 minute hold in an atmosphere at 150°C. Step B is cooling the atmosphere to -40°C within 5 minutes of completing step A. Step C is a 30 minute hold in an atmosphere at -40°C from the completion of step B. Step D is heating the atmosphere to 150°C within 5 minutes of completing step C.

[0094] After the thermal shock test, the contact resistance of the test specimens was measured using the four-terminal method. In the four-terminal method, alligator clips for supplying current were clamped between terminal 2 of each sample and mounting target 3. In addition, alligator clips for measuring voltage were clamped between terminal 2 of each sample and mounting target 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.

[0095] As shown in Table 1, the contact resistance of Sample No. 1 to Sample No. 13 was 0.20 mΩ or less. The contact resistance of Sample No. 101 to Sample No. 107 was more than 0.20 mΩ. This test example shows that by satisfying all of the requirements (A) to (E) described at the beginning of the embodiment section, it is possible to suppress an increase in contact resistance over time at the interface between the terminal and the attachment object. [Explanation of symbols]

[0096] 1 Connection structure 10 Wire with terminal 2 terminals, 2h notch, 21 first side, 22 second side 25 uneven part, 25c square, 25g groove, 29 wire barrel 3 mounting object, 3h notch, 30 main body, 31 conductive layer 4 bolts, 4n nuts 40 shaft portion, 41 head portion, 42 flange portion 5 Electric wire, 50 Conductor, 51 Insulation 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 width, h1 height, θ, φ angle α Virtual square β1 First intersection, β2 Second intersection, β3 Third intersection, β4 Fourth intersection β5 Fifth intersection, β6 Sixth intersection, β7 Seventh intersection, β8 Eighth intersection γ1: First virtual circle, γ2: Second virtual circle δ1 first virtual line, δ2 second virtual line, δ3 third virtual line δ4 fourth virtual line, δ5 fifth virtual line, δ6 sixth virtual line

Claims

1. 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 is made of pure aluminum or an aluminum alloy. The Vickers hardness of the terminal is 50 HV or more and less than 80 HV, The attachment target is: A body portion made of pure copper or a copper alloy; a conductive layer covering a surface of the main body portion facing the first surface; a notch through which the bolt passes; 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 0.42 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 mm ２ That's all. Connection structure.

2. 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 in which the pressure-sensitive sheet was disposed between the first surface and the conductive layer was fastened to a clamping plate having a thickness of 138×(D1) ２ Tighten with an axial force of ±50N. 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.

3. 3. The connection structure according to claim 1, wherein a hardness ratio obtained by dividing a Vickers hardness of said terminal by a Vickers hardness of said main body is 0.50 or more.

4. 4. The connection structure according to claim 3, wherein the Vickers hardness of the attachment object is 40 HV or more and 150 HV or less.

5. The connection structure according to claim 4 , wherein the body portion has a Vickers hardness of 60 HV or more and 150 HV or less.

6. 3. The connection structure according to claim 1, wherein the conductive layer is made of pure tin, an alloy containing tin and copper, pure silver, or an alloy containing silver and copper.

7. 3. The connection structure according to claim 1, wherein the conductive layer has an average thickness of 0.5 μm or more and 3 μm or less.

8. The uneven portion has a plurality of grooves, The connection structure according to claim 1 or 2, wherein each of the plurality of grooves is a V-groove.

9. The connection structure according to claim 8 , wherein an angle between side walls of two adjacent V-grooves in the plurality of grooves is greater than 90° and is equal to or smaller than 140°.

10. The connection structure according to claim 1 or 2, wherein the material of the main body is oxygen-free copper, tough pitch copper, C18661 in the Copper Development Association standard, C10850 in the Copper Development Association standard, C19210 in the Copper Development Association standard, or JC100 in the Japan Automotive Engineering Society standard.

11. 3. The connection structure according to claim 1, wherein the material of the terminal is International Registered Alloy Number 6101.

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