Dissimilar metal joint structure and battery pack

Abstract

Provided are: a dissimilar metal joint structure which, when an external force is applied thereto, allows a ductile fracture to occur not in a molten metal portion but in a base material portion; and a battery pack.　The dissimilar metal joint structure is characterized in that a molten metal part 3 satisfies conditions in which: (1) the depth D of the molten metal part 3 melted into a second member 2 from a superimposition interface 4 in a superimposed part is 0.1 mm or more; (2) the melting width dimension W of the molten metal part 3 in the longitudinal direction of a first member 1 and the second member 2 on the superimposition interface 4 between the first member 1 and the second member 2 is at least 1.2 times the plate thickness of the member having the shorter plate thickness when the plate thicknesses of the first member 1 and the second member 2 are different from each other, and is at least 1.2 times the plate thickness of either the first member or the second member when the plate thicknesses of the first member 1 and the second member 2 are the same; and (3) the area S of the molten metal part 3 on the superimposition interface 4 between the first member 1 and the second member 2 is greater than the sectional area, of the first member 1 or the second member 2, formed in the plate thickness direction along the outer periphery of the molten metal part 3.

Description

Dissimilar metal bonded structure and assembled battery

[0001] The present invention relates to a dissimilar metal bonded structure in which metals of different materials are bonded together, and to a battery pack using the same.

[0002] It is known that when dissimilar metal materials such as aluminum or copper are melted, there is a risk of a decrease in strength reliability due to brittle fracture of the molten metal part (the part where the dissimilar metals are melted together).

[0003] For example, Figure 39 shows a cross section of a lap joint (hereinafter also referred to as a dissimilar metal joint structure) in which an aluminum-based member 1 is arranged on the upper side (the side where heat is input by the laser beam) and a copper-based member 2 is arranged on the lower side, where a molten metal portion 3 formed by applying thermal energy such as a laser beam from above has penetrated the upper aluminum-based member 1 and melted into the lower copper-based member 2.

[0004] The metal structure of the welded metal portion 3 becomes a metallic compound consisting of a mixture of aluminum-based and copper-based metal components. In particular, when an intermetallic compound that becomes an embrittlement phase is formed, when an external force is applied to the lap joint, the fusion boundary 5 of the lap interface 4 where stress is concentrated becomes the starting point of fracture.

[0005] For example, when external forces are applied in opposite directions in the longitudinal direction of the lap joint, fracture 9 occurs at the lap interface of the welded metal portion 3, as shown in Figure 40. In this case, as can be seen from the load-displacement curve in the tensile test of the lap joint shown in Figure 41, brittle fracture with almost no plastic deformation is likely to occur at the time of fracture, making the fatigue strength unstable and potentially reducing the strength reliability of the dissimilar metal joint structure.

[0006] In order to avoid the concern of brittle fracture in such dissimilar metal bonded structures, for example, Japanese Patent Laid-Open Publication No. 2015-211981 (Patent Document 1) proposes a bonding method shown in Figures 42 and 43.

[0007] As shown in Figure 42, in a lap joint of an aluminum-based member 1 and a copper-based member 2, the dimensional specifications of the molten metal portion 3 that penetrates the aluminum-based member 1 and melts into the copper-based member 2 are such that the molten width dimension W1 at the lap interface 4 in the longitudinal direction of the lap joint is 10 to 50 μm and the depth dimension D1 is 5 to 30 μm, and the shape of the molten metal portion 3 is controlled to be extremely small, thereby suppressing the formation of harmful intermetallic compounds.

[0008] In addition, the number of fusion lines in a single bead with a small fusion width dimension W1 is increased, and multiple beads are overlapped to increase the total fusion width dimension W2, as shown in Figure 43, thereby improving the overall strength.

[0009] JP 2015-211981 A

[0010] Incidentally, in the conventional technology shown in Patent Document 1, the molten metal structure near lap interface 4, which is the starting point of fracture of the lap joint in molten metal portion 3 in Figure 42, becomes molten metal in which copper-based material and aluminum-based material are mixed, regardless of how small the melting ratio of the copper-based member to the aluminum-based member is, and therefore, there is a demand to reduce the risk of metallurgical brittle fracture.

[0011] Alternatively, during the actual production of products using mass-produced lap joints (dissimilar metal joint structures), it is necessary to reduce the risk of insufficient melting due to variations in the thickness, flatness, surface roughness, etc. of the dissimilar metal members, and variations in the processing point output and focal position of the irradiated laser beam, etc.

[0012] Alternatively, as shown in Figure 43, if the laser beam is irradiated multiple times to increase the number of fusion lines and overlap multiple beads, this increases the construction time and the total heat input, resulting in a decrease in production efficiency and a need to reduce concerns about the impact on product performance, such as deformation of the lap joint due to excessive heat input and thermal degradation of the resin part.

[0013] The object of the present invention is to solve at least one or more of the problems in the above-mentioned conventional technologies, and in particular to provide a novel dissimilar metal bonded structure and battery pack that, when an external force is applied, can undergo ductile fracture in the base material portion rather than brittle fracture in the molten metal portion.

[0014] The present invention provides a dissimilar metal joint structure having a first member made of a metallic material, a second member made of a metallic material different from the first member, an overlapping portion formed by the second member overlapping the first member on the heat-input side, and a molten metal portion formed at the overlapping portion and formed by melting and solidifying the first member and the second member, wherein the molten metal portion has the following characteristics: (1) a depth of the molten metal portion melting from the overlapping interface of the overlapping portion into the second member is 0.1 mm or more; (2) a depth of the molten metal portion melting from the overlapping interface of the first member and the second member is 0.1 mm or more; (3) The molten metal width dimension in the longitudinal direction of the first member and the second member is 1.2 times or more the thickness of the member with the shorter thickness when the plate thicknesses of the first member and the second member are different, or is 1.2 times or more the thickness of either member when the plate thicknesses of the first member and the second member are the same; and (4) the cross-sectional area of ​​the molten metal portion at the overlapping interface between the first member and the second member is larger than the cross-sectional area formed by the length along the outer edge of the molten metal portion at the overlapping interface and the plate thickness.

[0015] The present invention also provides a dissimilar metal joint structure having a first member made of a metallic material, a second member made of a metallic material different from the first member, an overlapping portion formed by the second member overlapping the first member on the heat-input side, and a molten metal portion formed at the overlapping portion and formed by melting and solidifying the first member and the second member, wherein the molten metal portion has the following characteristics: (1) a depth of the molten metal portion melting from the overlapping interface of the overlapping portion into the second member is 0.1 mm or more; (2) a depth of the molten metal portion melting from the overlapping interface of the overlapping portion into the second member is 0.1 mm or more; The molten metal width dimension at the interface in the longitudinal direction of the first member and the second member is 1.2 times or more the thickness of the member with the shorter plate thickness when the plate thicknesses of the first member and the second member are different, or is 1.2 times or more the thickness of either member when the plate thicknesses of the first member and the second member are the same; and (3) the cross-sectional area of ​​the molten metal portion at the overlapping interface between the first member and the second member is larger than the cross-sectional area formed by the plate width and plate thickness of the first member or the second member.

[0016] The present invention also provides a dissimilar metal joint structure having a first member made of a metallic material, a second member made of a metallic material different from the first member, an overlapping portion formed by the second member overlapping the first member on the heat-input side, and a molten metal portion formed at the overlapping portion and formed by melting and solidifying the first member and the second member, wherein a narrow portion is formed in the plate width direction by a notch penetrating in the plate thickness direction in the first member or the second member at the overlapping portion, and the molten metal portion is: (1) a molten metal portion melting into the second member from the overlapping interface of the overlapping portion (2) the melting width dimension of the molten metal in the longitudinal direction of the first member and the second member at the overlapping interface between the first member and the second member is 1.2 times or more the thickness of the member with the shorter thickness when the plate thicknesses of the first member and the second member are different, or is 1.2 times or more the thickness of either member when the plate thicknesses of the first member and the second member are the same; and (3) the cross-sectional area of ​​the molten metal portion at the overlapping interface between the first member and the second member is larger than the cross-sectional area formed by the plate width and plate thickness of the narrow portion of the first member or the second member.

[0017] The present invention also provides a dissimilar metal joint structure having a first member made of a metallic material, a second member made of a metallic material different from the first member, an overlapping portion formed by the second member overlapping the first member on the heat-input side, and a molten metal portion formed at the overlapping portion and formed by melting and solidifying the first member and the second member, wherein a thinned portion having a short length in the plate thickness direction is formed in the first member or the second member at the overlapping portion by a concave groove formed in the plate thickness direction, and the molten metal The part is characterized by satisfying the following conditions: (1) the depth of the molten metal part that melts from the overlapping interface of the overlapping part into the second member is 0.1 mm or more; (2) the melting width dimension of the molten metal in the longitudinal direction of the first member and the second member at the overlapping interface of the first member and the second member is 1.2 times or more the plate thickness of the thinned portion of the first member or the second member; and (3) the cross-sectional area of ​​the molten metal part at the overlapping interface of the first member and the second member is larger than the cross-sectional area formed by the plate thickness and plate width of the thinned portion of the first member or the second member.

[0018] According to the present invention, when an external force is applied, ductile fracture can occur not in the molten metal portion of the overlapping portion but in the base material portion of the plate member constituting the dissimilar metal bonded structure. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlapping interface of the molten metal portions of the dissimilar metals, and to obtain a dissimilar metal bonded structure with stable strength reliability.

[0019] 1 is a cross-sectional view showing the penetration depth, fusion width, fusion area, and plate thickness of the plate members constituting the lap joint of an embodiment of the present invention, in which one heat-input side is an aluminum-based plate member and the other side is a copper-based plate member. It is a structural diagram showing the fusion area at the lap interface of the lapped portion and the total length of the fusion metal portion at the lap interface, as viewed from the heat-input side (laser beam irradiation side) of the lap joint of FIG. 1. It is a cross-sectional view showing the penetration depth of the fusion metal portion formed in a lap joint made of dissimilar metals according to an embodiment of the present invention, when the fusion metal portion penetrates the plate member on the opposite side from the heat-input side. It is an explanatory diagram explaining a technique for advancing in the melting direction while repeatedly moving a laser beam at high speed within a predetermined region. It is a structural diagram showing the fusion area at the lap interface of the lapped portion and the total length of the fusion metal portion at the lap interface, as viewed from the heat-input side (laser beam irradiation side) of a lap joint having a fusion bead shape of an annular ellipse. It is an explanatory diagram showing the strength properties relative to the base material material and the area of ​​the molten metal structure. It is an explanatory diagram explaining the relationship between specific values ​​of the fusion width and fusion area and the fracture mode according to the present invention. FIG. 1 is an explanatory diagram showing a load-displacement curve due to ductile fracture occurring in a lap joint in an embodiment of the present invention. FIG. 1 is a cross-sectional view illustrating a state in which base material fracture occurs in a plate member having low strength when a tensile force is applied in the longitudinal direction of the lap joint. FIG. 2 is a cross-sectional view illustrating a state in which base material fracture occurs in a plate member having low strength when a tensile force is applied in a direction perpendicular to the longitudinal direction of the lap joint. FIG. 3 is a cross-sectional view illustrating a state in which base material fracture occurs in a plate member having a small plate thickness when a tensile force is applied in the longitudinal direction of the lap joint. FIG. 4 is an explanatory diagram illustrating a state in which base material fracture occurs in a plate member having a small plate thickness when a tensile force is applied in a direction perpendicular to the longitudinal direction of the lap joint. FIG. 5 is a structural diagram of the lap joint as viewed from the heat input side (laser beam irradiation side), showing the melted area at the overlapping interface of the overlapping portion and the plate width of the overlapping portion. FIG. 6 is a cross-sectional view illustrating a configuration in which the plate width in the short direction of the plate member on the heat input side of the overlapping portion is locally reduced, according to an embodiment of the present invention. 15 is a cross-sectional view illustrating the fracture of the base material at the portion where the plate thickness is locally reduced in FIG. 15. The cross-sectional view ...19 is a cross-sectional view showing a configuration in which a thin-walled portion consisting of a recess is formed in the short direction of the plate member on the heat-input side of the overlapping portion according to an embodiment of the present invention. 17 is a cross-sectional view illustrating base material fracture at the thin-walled portion in FIG. 17. 18 is a cross-sectional view showing a configuration in which a thin-walled portion consisting of a recess is formed in the short direction of the plate member on the opposite side of the overlapping portion from the heat-input side according to an embodiment of the present invention. 19 is a cross-sectional view showing the penetration depth, fusion width, fusion area, and plate thickness of the plate members constituting the lap joint of an embodiment of the present invention, in which one side to which heat is input is a copper-based plate member and the other side is an aluminum-based plate member. 21 is a structural diagram showing the fusion area at the overlapping interface of the overlapping portion and the total length of the fusion metal portion at the overlapping interface, as viewed from the heat-input side (laser beam irradiation side). 22 is a cross-sectional view showing the penetration depth, fusion width, fusion area, and plate thickness of the plate members constituting the lap joint of an embodiment of the present invention, in which one side to which heat is input is an aluminum-based plate member and the other side is a copper-based plate member having a plated layer. 25 is a schematic diagram of the lap joint of FIG. 23 as viewed from the heat input side (laser beam irradiation side), showing the molten area at the lap interface of the overlapping portion and the total length of the molten metal portion at the lap interface. FIG. 26 is a cross-sectional view showing an example of use of a lap joint in which one heat input side is an aluminum-based plate member and the other heat input side is a copper-based plate member with a plated layer as a bus bar, according to an embodiment of the present invention. FIG. 27 is a cross-sectional view of the bus bar of FIG. 25 as viewed from the heat input side (laser beam irradiation side), showing the molten area at the lap interface of the overlapping portion and the total length of the molten metal portion at the lap interface. FIG. 28 is a cross-sectional view showing an example of use of a lap joint in which one heat input side is a copper-based plate member with a plated layer as a bus bar, according to an embodiment of the present invention. FIG. 29 is a cross-sectional view showing an example of use of a lap joint in which one heat input side is a copper-based plate member with a plated layer as a bus bar, according to an embodiment of the present invention.30 is a structural diagram showing an example of an application form of the present invention, illustrating a configuration when electrode terminals made of dissimilar metals of two adjacent unit cells are connected to a bus bar made of an aluminum-based member. 30 is a structural diagram showing a configuration as viewed from the side in direction A in FIG. 30. 30 is a structural diagram showing a configuration as viewed from the side in direction B in FIG. 30. 30 is a structural diagram showing a configuration when the bus bar in FIG. 30 is laser beam welded to the positive electrode terminal and the negative electrode terminal, as viewed from the heat input side. 33 is a cross-sectional view showing the A-A cross section in FIG. 33. 33 is a structural diagram showing a configuration when the bus bar in FIG. 33 is laser beam welded to the negative electrode terminal, as viewed from the heat input side. 36 is a structural diagram showing an example of an application form of the present invention, illustrating a configuration when the bus bar and the voltage detection line terminal are laser beam welded, as viewed from the heat input side. 36 is a cross-sectional view showing the B-B cross section in FIG. 36. 36 is a structural diagram showing a configuration when the bus bar in FIG. 36 is laser beam welded to the voltage detection terminal, as viewed from the heat input side. 37 is a cross-sectional view showing the configuration of a molten metal portion in a conventional lap joint using dissimilar metals. Fig. 41 is a cross-sectional view showing a state in which brittle fracture has occurred in the direction of the lap interface of the welded metal portion in the lap joint shown in Fig. 39. Fig. 42 is an explanatory diagram showing an example of a load-displacement curve in brittle fracture occurring at the lap interface of the welded metal portion shown in Fig. 40. Fig. 43 is a cross-sectional view showing a cross section of the welded metal portion in which penetration into the lower member has been controlled to be small in Patent Document 1. Fig. 44 is a cross-sectional view showing a cross section of the welded metal portion in which penetration into the lower member has been controlled to be small in Patent Document 1, when the number of fusion lines has been increased to increase the fusion area of ​​the welded metal portion.

[0020] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiment, and various modifications and application examples within the technical concept of the present invention are also included within its scope.

[0021] Several embodiments of the present invention will be described with reference to the drawings. The basic idea of ​​the present invention is to propose a dissimilar metal bonded structure having a different configuration from that of Patent Document 1, which is capable of undergoing ductile fracture in the base material portion rather than the molten metal portion when an external force is applied.

[0022] First, a first embodiment of the present invention will be described with reference to FIGS. 1 to 12. FIGS. 1 and 2 show a lap joint (dissimilar metal joint structure) consisting of an elongated, flat, rectangular aluminum-based member (plate member) 1 and an elongated, flat, rectangular copper-based member (plate member) 2. In this embodiment, the side irradiated with the laser beam (the side where heat is input) is the aluminum-based member 1, and the opposite side is the copper-based member 2. In the following description, the side irradiated with the laser beam (the side where heat is input) may be referred to as the upper member or first member, and the opposite side as the lower member or second member, depending on the depiction of the drawings. The aluminum-based material may also be referred to as the first metal, and the copper-based material may also be referred to as the second metal.

[0023] The respective ends of the aluminum-based member 1 as a plate member made of a first metal and the copper-based member 2 as a plate member made of a second metal are overlapped at an overlapping portion Ov along the longitudinal direction Ld.

[0024] Here, the widths (lengths in the direction perpendicular to the longitudinal direction) L1 of the aluminum-based member 1 and the copper-based member 2 are set to the same length, and when they are stacked, the side surfaces of the aluminum-based member 1 and the copper-based member 2 in the longitudinal direction are dimensionally consistent.

[0025] The plate thickness of the aluminum-based member 1 and the copper-based member 2 is set to a range of 0.2 to 4 mm. The plate thickness of the aluminum-based member 1 and the copper-based member 2 is set to be the same, or one of them is set to be shorter. For example, it is expected that the plate thickness of the copper-based member 2 will be shorter in terms of strength. This will allow the strength of the aluminum-based member 1 and the copper-based member 2 to be closer.

[0026] A molten metal portion 3 is formed at the overlapping portion Ov of the aluminum-based member 1 and the copper-based member 2, for example, by irradiation with a laser beam. This molten metal portion 3 is a metal compound in which the metals of the aluminum-based member 1 and the copper-based member 2 are melted into each other. The molten metal portion 3 is formed near the center of the overlapping portion Ov in the longitudinal direction. The molten metal portion 3 penetrates the aluminum-based member 1 and melts into the copper-based member 2 to near the center in the plate thickness direction. The penetration depth D of this molten metal portion 3 can be controlled by the output power and scanning speed of the laser beam.

[0027] The inventors have found that the following dimensional relationship of the molten metal portion 3 is effective as a configuration that can cause ductile fracture in the base material portion rather than the molten metal portion when an external force is applied.

[0028] First, in this embodiment, the penetration depth D of the molten metal portion 3 is set to 0.1 mm or more on the copper-based member 2 side, based on the overlapping interface 4 where the aluminum-based member 1 and the copper-based member 2 come into contact, while taking into consideration variations in the flatness and surface roughness of each plate member, in order to ensure fusion between the aluminum-based member 1 and the copper-based member 2. It has been found that if the penetration depth D is less than 0.1 mm, sufficient fusion between the aluminum-based member 1 and the copper-based member 2 cannot be ensured.

[0029] In this way, the molten metal portion 3 is formed up to the inside of the copper-based member 2, thereby improving the fusion between the aluminum-based member 1 and the copper-based member 2. Here, the penetration depth D into the copper-based member 2 covers up to the surface of the copper-based member 2 opposite to the overlapping interface 4, and therefore the penetration depth D into the copper-based member 2 has the relationship "0.1 mm<D<T2".

[0030] Second, when the smaller of the thickness T1 of the aluminum-based member 1 and the thickness T2 of the copper-based member 2 is defined as the thickness Tmin, it is important that the molten width W of the molten metal portion 3 in the longitudinal direction of the aluminum-based member 1 and the copper-based member 2 at the overlapping interface 4 between the aluminum-based member 1 and the copper-based member 2 and the thickness Tmin satisfy the relationship "(1.2 × Tmin) ≦ W < L2." L2 is the longitudinal length of the overlapping portion Ov shown in Figures 1 and 2. Here, in order to form such a molten width W, it is necessary to control the heat input by the laser beam.

[0031] In laser beam welding, a laser beam that provides the above-mentioned melt width W for one bead (single bead) can be obtained by optimizing the output, focal position, scanning speed, etc., for a beam with a beam spot diameter of 100 μm or more in a multi-mode oscillation mode that is often used in welding work.

[0032] However, when the heat input is large in order to obtain the above-mentioned predetermined fusion width W, or when the plate thickness T2 of the copper-based member 2 is smaller than the plate thickness T1 of the aluminum-based member 1, the penetration depth D of the copper-based member 2 in the molten metal portion 3 may reach the plate thickness T2, causing the molten metal portion 3 to penetrate, as shown in FIG. 3 .

[0033] In this configuration in which it is not desirable for the molten metal portion 3 to penetrate the copper-based member 2, as shown in FIG. 1 , it is necessary to form a molten width W of the overlapping interface 4 that satisfies the above-mentioned relationship with one bead while keeping the penetration depth D of the copper-based member 2 within the plate thickness T2.

[0034] In this case, it is effective to use a method in which the laser beam moves repeatedly at high speed within a predetermined area while advancing in the melting direction. Figure 4 shows the ray trajectory 8 of the laser beam 6 as it moves in the melting direction while tracing a minute arc 7 at high speed, and the molten bead surface 9. Such repeated high-speed movement of the laser beam 6 may be in the form of a polygon, a cycloid curve, or two-dimensional movement such as a bi-directional movement, in addition to a minute arc.

[0035] In this way, at the overlap portion Ov of the aluminum-based member 1 and the copper-based member 2, in a cross section perpendicular to the direction of advancement of the weld bead, the metal fusion zone 3 is formed as a single bead that does not overlap partially in the direction of the weld width W of the overlap interface 4.

[0036] When a laser beam is irradiated multiple times to overlap multiple beads, as in Patent Document 1, this increases the construction time and the total heat input, which can result in concerns about adverse effects on product performance, such as reduced production efficiency and deformation of the lap joint due to excessive heat input and thermal degradation of the resin part.However, using a single bead can avoid these problems.

[0037] Furthermore, in order to obtain the above-mentioned penetration, it is effective for the laser beam 6 to be used to have a small beam diameter, for example, a single mode with a beam spot diameter of 80 μm or less, or a multimode oscillation mode. Alternatively, it is also effective to use oscillation specifications and optical system specifications that irradiate a laser beam with a wide rectangular intensity distribution.

[0038] By forming a molten metal portion 3 having a sufficiently large fusion width W that satisfies the above-mentioned relationship, the resistance to fracture from the fusion boundary 5 to the lap interface 4, i.e., in the direction of the fusion width W, which is likely to become the starting point of fracture when an external force is applied, becomes larger than the resistance in the thickness direction of the base material, and the fracture progresses in the thickness direction of the base material, leading to ductile fracture in the base material. Here, ductile fracture means that fracture occurs while stretching and plastically deforming at the time of fracture.

[0039] Third, in the molten metal portion 3 shown in Figures 1 and 2, when the area of ​​the molten molten metal portion 3 at the overlapping interface 4 is taken as molten area S and the total length (length of the outer periphery) of the molten metal portion 3 at the overlapping interface 4 is taken as AL, it is important to provide a molten area such that "(AL x Tmin) < S < SAL." Here, "SAL" is the area of ​​the overlapping portion Ov of the aluminum-based member 1 and the copper-based member 2 shown in Figures 1 and 2, and this also applies to other embodiments described below.

[0040] In other words, by making the area larger than the cross-sectional area of ​​the base material (AL x Tmin) taking into account the thickness of the base material on the smaller side from the fusion boundary 5 of the molten metal portion 3, which is the starting point of the fracture, it is possible to cause fracture of the base material, i.e., ductile fracture.

[0041] The total length AL of the periphery of the molten metal portion 3 at the overlap interface 4 means the length of the fracture initiation point when an external force is applied. For example, if the shape of the molten metal portion 3 at the overlap interface 4 is an annular ellipse as shown in Fig. 5, fracture occurs mainly on the outer diameter side of the molten metal portion 3 when stress is applied, so the length on the outer diameter side can be set as the total length AL so as to satisfy the above-mentioned relationship. Furthermore, the molten width W is obtained by adding the width Wc of the annular portion of the annular molten metal portion 3.

[0042] Here, when considering the mechanical strength per unit area, as shown in Figure 6, there is a difference in the strength of the aluminum-based base material and the copper-based base material, with the aluminum-based base material being smaller and the copper-based base material being larger.

[0043] However, in a metal compound of dissimilar materials in which the components of an aluminum-based base metal and a copper-based base metal are mixed, the strength of the compound itself that becomes the embrittlement phase is greater than that of the copper-based base metal, and in a phase structure that is rich in aluminum or copper, a strength tendency similar to that of the aluminum-based base metal or the copper-based base metal may be obtained. As a result, a weld metal part that has a mixed structure shows a strength distribution tendency with a range such as that shown in the hatched area in Figure 6, and in a metal structure in a weld metal part in which the embrittlement phase dominates at the interface fracture part, its mechanical strength may be greater than that of the copper-based base metal.

[0044] Therefore, if the fusion width and fusion area are ensured to satisfy the above-mentioned relationship so that the strength is greater than the base material strength, in order to avoid fracture paths that lead to brittle fracture, then the base material will fracture on the weaker side of either the aluminum-based or copper-based base material, i.e., ductile fracture will occur.

[0045] FIG. 7 illustrates the region of fracture mode when an external force is applied, based on the relationship between the molten width W and the molten area S obtained by the inventors, with the molten width correlation ratio [W / Tmin] between the molten width W of the molten metal portion 3 at the lap interface 4 and the plate thickness Tmin being plotted on the horizontal axis, and the molten area correlation ratio [S / (AL×Tmin)] between the molten area S at the lap interface 4 and the total length AL of the periphery of the molten metal portion and Tmin being plotted on the vertical axis.

[0046] In the region where the fusion width correlation ratio [W / Tmin] is "1.2 or more" and the fusion area correlation ratio [S / (L1 x Tmin)] is "1 or more," base material fracture (ductile fracture) occurs, while in the region where both are small, interfacial fracture (brittle fracture) occurs at the lap interface, and in the other region where the two are mixed, it is an indeterminate region where either type of fracture can occur. Therefore, by making the fusion width W have the relationship "(1.2 x Tmin) ≦ W < L2" and making the fusion area S have the relationship "(AL x Tmin) < S < SAL," it is possible to reliably induce base material fracture.

[0047] The interface fracture region is a region where brittle fracture occurs as shown in Figure 41, where fracture occurs instantaneously with almost no plastic deformation of the material. The base material fracture region is a ductile fracture where fracture progresses gradually while accompanied by plastic deformation of the base material, as shown in Figure 8.

[0048] In the relationship between the melt width W and the melt area S described above, the thickness of the plate members (aluminum-based member and copper-based member) is the thickness Tmin of the plate member with the shorter length, but even if the plate members (aluminum-based member and copper-based member) are determined to have the same thickness, a similar relationship can be applied.

[0049] Next, we will briefly explain the conditions for base material destruction due to differences in materials and the direction of external force application in lap joints that satisfy the above-mentioned conditions, and the conditions for base material destruction due to differences in plate thickness of plate members in lap joints and the direction of external force application.

[0050] 9 and 10 show the state of base material fracture when aluminum-based member 1 and copper-based member 2 are used and the plate thickness is the same. In this case, since the plate thickness is the same, the strength of the base material itself is smaller in aluminum-based member 1.

[0051] Figure 9 shows a case where a tensile force (external force) acts in the longitudinal direction of a lap joint, and base material fracture 10 occurs in the aluminum-based member 1, which has a lower base material strength. In this case, because the tensile force acts in the longitudinal direction, base material fracture occurs on the tension side, not the compression side.

[0052] 10 shows a case where a tensile force (external force) acts in a direction perpendicular to the longitudinal direction of the lap joint (the vertical direction in the drawing), and base material fracture 10 occurs in the aluminum-based member 1, which has a lower base material strength. In this case, the aluminum-based member 1 is pulled away, and base material fracture 10 occurs all around the periphery of the welded metal portion 3.

[0053] 11 and 12 show the state of base material fracture when an aluminum-based member 1 and a copper-based member 2 are used and the plate thickness of the copper-based member 2 is reduced. In this case, the plate thickness of the copper-based member 2 is thinner than that of the aluminum-based member 1, so the strength of the base material itself is smaller for the copper-based member 2.

[0054] 11 shows a case where a tensile force (external force) acts in the longitudinal direction of a lap joint, and base material fracture 10 occurs in the copper-based member 2, which has a lower base material strength. In this case, because the tensile force acts in the longitudinal direction, base material fracture occurs on the tension side, not the compression side.

[0055] 12 shows a case where a tensile force (external force) acts in a direction perpendicular to the longitudinal direction of the lap joint (the vertical direction in the drawing), and base material fracture 10 occurs in the copper-based member 2, which has a lower base material strength. In this case, the copper-based member 2 is pulled apart, and base material fracture 10 occurs all around the periphery of the welded metal portion 3.

[0056] As described above, the type of fracture that occurs varies depending on the way the load is applied, the thickness of each plate member, the material and physical properties, etc., but in any case, it becomes a ductile fracture accompanied by plastic deformation as shown in Figure 8, and there is no risk of brittle fracture.

[0057] As described above, in the first embodiment, the penetration depth D of the molten metal portion is set to "0.1 mm < D < T2", the molten width W of the molten metal portion 3 is set to "(1.2 × Tmin) ≦ W < L2", and the molten area S of the molten metal portion 3 is set to "(AL × Tmin) < S < SAL", so that when an external force is applied, ductile fracture will occur in the base material portion rather than brittle fracture in the molten metal portion 3.

[0058] In this way, it is possible to suppress the instability of fatigue strength due to brittle fracture at the overlapping interface of the molten metal portions of the dissimilar metals, and to obtain a dissimilar metal joint structure with stable strength reliability. Note that in other embodiments described below, unless otherwise specified, this first embodiment is the basis.

[0059] Furthermore, in the first embodiment and the other embodiments described below, a laser beam technique is used as the heat source for forming the molten metal portion, but electron beam welding, arc welding, etc. can also be used.

[0060] Electron beam welding achieves the same effect as laser beam welding by increasing the beam convergence and moving the beam in the melting direction while oscillating at high speed, making it possible to form a molten metal part with a large molten width in one bead. Arc welding, while inferior in convergence, can also form a molten metal part with a large molten width in one bead by melting while slightly oscillating the electrode.

[0061] Next, a second embodiment of the present invention will be described. The basic concept of this embodiment is the same as that of the first embodiment, but the method of calculating the fusion area S differs from that of the first embodiment. The second embodiment of the present invention will be described below with reference to FIG.

[0062] As described in the first embodiment, the penetration depth D of the molten metal portion 3 into the copper-based member 2 and the molten width W of the molten metal portion 3 in the longitudinal direction have the same relationship as in the first embodiment.

[0063] On the other hand, in the second embodiment, as shown in FIG. 13 , when the region where an external force acting on the molten metal portion 3 is applied on the thinner plate thickness side of the upper aluminum-based member 1 and the lower copper-based member 2 is defined as plate width L1, it is possible to provide a molten area S such that "(L1 × Tmin) < S < SAL".

[0064] That is, by making the area larger than the cross-sectional area (L1 × Tmin) of the base material taking into account the thickness of the base material on the thinner side from the fusion boundary 5 of the molten metal portion 3, which is the fracture initiation point, it is possible to lead to base material fracture, i.e., ductile fracture. In this case, in FIG. 7, the vertical axis shows the region of base material fracture as "S / (L1 × Tmin)." Base material fracture in this structure has the same form as base material fracture 10 shown in FIGS. 9 to 12, and is a ductile fracture accompanied by plastic deformation as in the first embodiment, eliminating the risk of brittle fracture.

[0065] In the second embodiment, too, by setting the penetration depth D of the molten metal portion to "0.1 mm < D < T2," the molten width W of the molten metal portion 3 to "(1.2 × Tmin) ≦ W < L2," and the molten area S of the molten metal portion 3 to "(L1 × Tmin) < S < SAL," it becomes possible to induce ductile fracture in the base material portion rather than brittle fracture in the molten metal portion 3 when an external force is applied. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlap interface of the molten metal portions of dissimilar metals, and to obtain a dissimilar metal bonded structure with stable strength reliability.

[0066] Next, a third embodiment of the present invention will be described. The basic concept of this embodiment is the same as that of the second embodiment, but differs in that a notch penetrating the plate member in the plate thickness direction is formed to locally shorten the plate width. The third embodiment of the present invention will be described below with reference to Figures 14 to 16. The penetration depth D of the molten metal portion 3 into the copper-based member 2 has the same relationship as that of the first embodiment.

[0067] 14 and 15, the upper aluminum-based member 1 has a locally narrow portion (hereinafter referred to as a narrow portion) 11. This narrow portion 11 is adjacent to the welded metal portion 3 of the aluminum-based member 1 and is formed within the overlapping portion Ov. Furthermore, this narrow portion 11 is formed by a notch 11n that extends inward from both side surfaces of the aluminum-based member 1 and penetrates the aluminum-based member 1 in the thickness direction. Therefore, the narrow portion 11 is weaker in strength.

[0068] Here, narrow width portion 11 is formed on the side where a tensile force acts on welded metal portion 3 (on the left side of welded metal portion 3 of aluminum-based member 1 in FIG. 14 ). In other words, the side opposite to the side where a tensile force acts is subjected to a compressive force, making it less likely for fracture to occur.

[0069] When the thickness of the narrow portion 11 of the aluminum-based member 1, where the width is locally small, is defined as "T1" and the thickness of the copper-based member 2 located below is defined as being equal to or less than the thickness T1, the melt width W at the overlapping interface 4 and the thickness T1 are determined to have the relationship "(1.2 × T1) ≦ W < L2".

[0070] Furthermore, when the plate width of the narrow portion 11 of the aluminum-based member 1, where the plate width is locally narrow, is defined as "Lmin," the melting area S at the overlapping interface 4 and the plate width Lmin are determined to have the relationship "(Lmin × T1) < S < SAL."

[0071] By setting the fusion width W and fusion area S in this way, it is possible to induce base material fracture 10 to occur in a locally narrow portion 11 of the aluminum-based member 1 where the plate width is small, as shown in Figure 16. In this case, in Figure 7, the vertical axis shows the region of base material fracture as "S / (Lmin x T1)."

[0072] In the embodiment shown in Figures 14 to 16, a narrow width portion 11 with a locally narrow plate width is provided in the aluminum-based member 1 located on the upper side, and an example is shown in which base material fracture occurs in the aluminum-based member 1 when an external force is applied, but the same action and effect can be obtained by conversely forming a similar narrow width portion 11 in the copper-based member 2 located on the lower side.

[0073] In the third embodiment, too, by setting the penetration depth D of the molten metal portion to "0.1 mm < D < T2," the molten width W of the molten metal portion 3 to "(1.2 × T1) ≦ W < L2," and the molten area S of the molten metal portion 3 to "(Lmin × T1) < S < SAL," it becomes possible to induce ductile fracture in the narrow width portion 11 of the base material when an external force is applied, rather than brittle fracture in the molten metal portion 3. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlap interface of the molten metal portions of the dissimilar metals, and to obtain a dissimilar metal bonded structure with stable strength reliability.

[0074] Next, a fourth embodiment of the present invention will be described. The basic concept of this embodiment is the same as that of the second embodiment, but it differs in that recessed grooves are formed along the width direction of the plate member to locally reduce the plate thickness. The fourth embodiment of the present invention will be described below with reference to Figures 17 and 18.

[0075] In the fourth embodiment, in a thick (long) plate member, the base material strength is naturally large, and it is difficult to ensure the molten width W and molten area S of the molten metal portion 3 that are sufficient to exceed the base material strength, or to avoid the risk of fracture at the overlapping interface and to increase the likelihood of base material fracture, a short (thin) portion is locally formed in the base material. Note that the penetration depth D of the molten metal portion 3 into the copper-based member 2 has the same relationship as in the first embodiment.

[0076] 17 and 18, the upper aluminum-based member 1 has a locally thin portion (hereinafter referred to as a thinned portion) 12. This thinned portion 12 is adjacent to the welded metal portion 3 of the aluminum-based member 1 and is formed in the range of the overlap portion Ov.

[0077] This thinned portion 12 extends inward in the plate thickness direction from the surface on the heat input side of the aluminum-based member 1, and is formed by a concave groove 12g that extends in the plate width direction of the aluminum-based member 1. Therefore, the thinned portion 12 is weakened in strength. Note that the groove 12g is formed across the entire plate width of the aluminum-based member 1, but it may also be formed as a groove 12g of a predetermined length only across a part of the plate width of the aluminum-based member 1, rather than across the entire plate width.

[0078] Here, similarly to the third embodiment, the thinned portion 12 is formed on the side where a tensile force acts on the molten metal portion 3 (on the left side of the molten metal 3 of the aluminum-based member 1 in FIG. 17 ). In other words, the side opposite to the side where the tensile force acts is subjected to a compressive force, making it less likely for fracture to occur.

[0079] When the thickness of the locally thinned portion 12 of the aluminum-based member 1 is defined as "Tgrv", the melt width W at the overlapping interface 4 and the thickness Tgrv are determined to have the relationship "(1.2 x Tgrv) ≦ W < L2".

[0080] Furthermore, when the plate width of the locally thinned portion 12 of the aluminum-based member 1 is defined as "L1" (see FIG. 13), the melting area S and the plate thickness Tgrv at the overlapping interface 4 are determined to satisfy the relationship "(L1 × Tgrv) < S < SAL."

[0081] By setting the fusion width W and fusion area S in this way, it is possible to induce base material fracture 10 to occur in a locally thinned portion 12 of the aluminum-based member 1 where the plate thickness is small, as shown in Figure 18. In this case, in Figure 7, the vertical axis shows the region of base material fracture as "S / (L1 x Ttgv)".

[0082] In the fourth embodiment, too, by setting the penetration depth D of the molten metal portion to "0.1 mm < D < T2," the molten width W of the molten metal portion 3 to "(1.2 × Ttgv) ≦ W < L2," and the molten area S of the molten metal portion 3 to "(L1 × Tgrv) < S < SAL," it becomes possible to lead to ductile fracture in the thinned portion 12 of the base metal when an external force is applied, rather than brittle fracture in the molten metal portion 3. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlap interface of the molten metal portions of dissimilar metals, and to obtain a dissimilar metal bonded structure with stable strength reliability.

[0083] 17 and 18 show an example in which a locally thinned portion 12 is provided in the upper aluminum-based member 1, thereby inducing base material fracture in the aluminum-based member 1 when an external force is applied. On the other hand, the same action and effect can be obtained by forming a similar thinned portion 12 in the lower copper-based member 2. A brief description will be given below with reference to FIGS. 19 and 20.

[0084] 19 , the copper-based member 2 below the overlapping interface 4 has a locally thin portion 12 (hereinafter referred to as a thinned portion). This thinned portion 12 is adjacent to the molten metal portion 3 of the copper-based member 2 and is formed within the overlapping portion Ov. The thinned portion 12 extends inward in the thickness direction from the surface on the overlapping interface 4 side, and is formed by a concave groove 12g extending in the width direction of the copper-based member 2. Therefore, the thinned portion 12 is weaker in strength.

[0085] Here, similarly to the third embodiment, the thinned portion 12 is formed on the side where a tensile force acts on the molten metal portion 3 (on the right side of the molten metal 3 of the copper-based member 2 in FIG. 19 ). In other words, the side opposite to the side where a tensile force acts is subjected to a compressive force, making it less likely for fracture to occur.

[0086] When the thickness of the locally thinned portion 12 of the copper-based member 2 is defined as "Tgrv", the melt width W at the overlapping interface 4 and the thickness Tgrv are determined to have the relationship "(1.2 x Tgrv) ≦ W < L2".

[0087] Furthermore, when the plate width of the thinned portion 12 of the copper-based member 2, where the plate thickness is locally small, is defined as "L1", the molten area S at the overlapping interface 4 and the plate thickness Tgrv are determined to have the relationship "(L1 × Tgrv) < S < SAL".

[0088] By setting the fusion width W and fusion area S in this way, it is possible to induce base material fracture 10 to occur in a locally thinned portion 12 of the copper-based member 2 where the plate thickness is small, as shown in Fig. 20. In this case, in Fig. 7, the vertical axis shows the region of base material fracture as "S / (L1 x Tgrv)".

[0089] In this modified example, by setting the penetration depth D of the molten metal portion to "0.1 mm < D < T2," the molten width W of the molten metal portion 3 to "(1.2 × Ttgv) ≦ W < L2," and the molten area S of the molten metal portion 3 to "(L1 × Tgrv) < S < SAL," it becomes possible to induce ductile fracture in the narrow width portion 11 of the base material when an external force is applied, rather than brittle fracture in the molten metal portion 3. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlap interface of the molten metal portions of the dissimilar metals, and to obtain a dissimilar metal bonded structure with stable strength reliability.

[0090] 19, the groove 12g is formed on the side of the overlapping interface 4, but it may also be formed on the surface opposite to the overlapping interface 4 (the lower side in the figure) as shown in Fig. 17. Even in this case, the same effects and advantages as those shown in Fig. 18 can be achieved.

[0091] The grooves 12g can be formed by mechanical thinning methods such as plastic working or cutting, thermal thinning methods such as electric discharge machining or laser irradiation, or chemical thinning methods such as local etching or reactive liquid.

[0092] Next, a fifth embodiment of the present invention will be described. The basic concept of this embodiment is the same as that of the first embodiment, but it differs in that the side to which heat is input by the laser beam is the copper-based member 2 and the opposite side is the aluminum-based member 1. The fifth embodiment of the present invention will be described below with reference to FIGS. 21 and 22.

[0093] 21 and 22 show a lap joint made of a long, thin, flat, rectangular copper-based member (plate member) 2 and a long, thin, flat, rectangular aluminum-based member (plate member) 1. In this embodiment, the side irradiated with the laser beam (the side receiving heat) is the copper-based member 2, and the opposite side is the aluminum-based member 1.

[0094] The respective end portions of the copper-based member 2 and the aluminum-based member 1, which are plate members, are overlapped at an overlapping portion Ov along the longitudinal direction Ld. Here, the widths L1 (lengths in a direction perpendicular to the longitudinal direction) of the copper-based member 2 and the aluminum-based member 1 are set to the same length, and in the overlapped state, the side surfaces of the copper-based member 1 and the aluminum-based member 1 in the longitudinal direction are dimensionally consistent.

[0095] The plate thickness of the copper-based member 2 and the aluminum-based member 1 is set to a range of 0.2 to 4 mm. The plate thickness of the copper-based member 2 and the aluminum member 1 is set to be the same, or one of them is set to be shorter. For example, it is expected that the plate thickness of the copper-based member 2 will be shortened in relation to tensile strength. This allows the strength of the aluminum-based member 1 and the copper-based member 2 to be closer.

[0096] A molten metal portion 3 is formed at the overlapping portion Ov of the copper-based member 2 and the aluminum-based member 1 by, for example, irradiation with a laser beam. This molten metal portion 3 is a metal compound in which the metals of the copper-based member 2 and the aluminum-based member 1 are melted into each other. The molten metal portion 3 is formed near the center of the overlapping portion 3 in the longitudinal direction. The molten metal portion 3 penetrates the copper-based member 2 and melts into the aluminum-based member 1 up to near the center in the plate thickness direction.

[0097] As a configuration that allows ductile fracture to occur in the base material portion rather than the molten metal portion when an external force is applied, similar to the first embodiment, the penetration depth D of the molten metal portion is set to "0.1 mm < D < T2", the molten width W of the molten metal portion 3 is set to "(1.2 × Tmin) ≦ W < L2", and the molten area S of the molten metal portion 3 is set to "(AL × Tmin) < S < SAL", so that when an external force is applied, ductile fracture can occur in the base material portion rather than brittle fracture in the molten metal portion 3.

[0098] In this way, in this embodiment as well, it is possible to suppress the instability of fatigue strength due to brittle fracture at the overlapping interface of the fused metal parts made of dissimilar metals, and to obtain a dissimilar metal joint structure with stable strength reliability. It goes without saying that the same can be applied to some of the above-mentioned embodiments.

[0099] In laser beam welding, the aluminum-based member 1 and the copper-based member 2 have different physical properties such as melting point, thermal conductivity, and light absorption rate, so the penetration behavior differs when the light is irradiated onto the surface of the aluminum-based member 1 and when the light is irradiated onto the surface of the copper-based member 2.

[0100] However, even if the melting ratios of the respective materials are different, the strength per unit area of ​​the weld metal portion 3 may be higher than the strength of either base material at the upper limit of the range, as shown in FIG.

[0101] In this way, even in a lap joint in which the copper-based member 2 is the heat input side, by ensuring the penetration depth D, fusion width W, and fusion area S, as in the first embodiment, the base material is induced to fracture on the side of one of the plate members with weaker strength.

[0102] Therefore, when an external force is applied, it is possible to induce ductile fracture in the base material portion rather than brittle fracture in the molten metal portion 3. This makes it possible to suppress destabilization of fatigue strength due to brittle fracture at the overlapping interface of the molten metal portions of dissimilar metals, and obtain a dissimilar metal bonded structure with stable strength reliability.

[0103] Next, a sixth embodiment of the present invention will be described. The basic concept of this embodiment is the same as that of the first embodiment, but differs in that a plating layer is formed on the surface of the copper-based member. The sixth embodiment of the present invention will be described below with reference to FIGS. 23 and 24.

[0104] 23 and 24, in a lap joint between an aluminum-based member 1 and a copper-based member 2, a plating layer 13 is formed by applying "nickel plating," "tin plating," or "plating consisting of both" to the surface of the copper-based member 2. Note that the plating layer 13 is exaggerated to be thicker for ease of understanding, and is different from the actual thickness.

[0105] In this embodiment, too, a configuration is provided in which ductile fracture can occur in the base material portion rather than the molten metal portion when an external force is applied, and similarly to the first embodiment, the penetration depth D of the molten metal portion is set to "0.1 mm < D < T2", the molten width W of the molten metal portion 3 is set to "(1.2 × Tmin) ≦ W < L2", and the molten area S of the molten metal portion 3 is set to "(AL × Tmin) < S < SAL". This makes it possible to lead to ductile fracture in the base material portion rather than brittle fracture in the molten metal portion 3 when an external force is applied. Note that the plate thickness includes the thickness of the plating layer 13.

[0106] In this embodiment, the molten metal portion 3 contains plating components (nickel and tin) in addition to aluminum-based and copper-based metallic materials, making the component composition of the molten metal structure more complex. However, since the amount of melting of the plating layer is sufficiently smaller than the amount of melting of the base metal, the strength properties of the molten metal structure still tend to be higher than the strength of the base metal, as in the first embodiment.

[0107] Therefore, in this sixth embodiment as well, the penetration depth D of the molten metal portion, the molten width W of the molten metal portion 3, and the molten area S of the molten metal portion 3 satisfy the above-mentioned relationship, so that when an external force is applied, ductile fracture can occur in the narrow width portion 11 of the base material, rather than brittle fracture in the molten metal portion 3. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlap interface of the molten metal portions of the dissimilar metals, and to obtain a dissimilar metal bonded structure with stable strength reliability.

[0108] Although FIG. 23 shows a configuration in which a plating layer is formed on the copper-based member 2, it is also possible to form a plating layer on the aluminum-based member 1, or on both the aluminum-based member 1 and the copper-based member 2, and the above-mentioned effects can also be achieved by melting the plating layer.

[0109] Next, an application example of the dissimilar metal bonded structure according to the above-described embodiment will be described. This dissimilar metal bonded structure is the dissimilar metal bonded structure with a plating layer formed thereon, as described in the sixth embodiment (Example 6). This embodiment is an example in which the dissimilar metal bonded structure is applied to a bus bar that connects the electrode terminals of unit cells in a battery pack. The penetration depth D, fusion width W, and fusion area S can be any of those of the above-described embodiments.

[0110] 25 and 26 show a longitudinal cross section of the bus bar as viewed from the side. Bus bar 14 is made of a dissimilar metal joint structure as described in Examples 1 to 6, and for example, the upper heat-receiving side is made of aluminum-based member 1, and the lower side is made of copper-based member 2 on which plating layer 13 is formed. The joint between aluminum-based member 1 and copper-based member 2 (the portion including molten metal portion 3) has a stepped shape (a shape that protrudes upward in the drawings) consisting of curved portion 15 for absorbing and mitigating external forces such as vibration and expansion of the battery pack.

[0111] A lap joint is formed on the protruding flat portion, and a laser beam is irradiated onto the surface of the upper aluminum-based member 1 to form a molten metal portion 3. In this case, the penetration depth D, molten width W, and molten area S are as described in the above-mentioned respective embodiments.

[0112] 27 shows a modified example of bus bar 14, which is made of a dissimilar metal joint structure, with the upper heat-receiving side being made of copper-based member 2 having plating layer 13 formed thereon, and the lower side being made of aluminum-based member 1. The joint (molten metal portion 3) between copper-based member 2 and aluminum-based member 1 has a stepped shape (a shape that protrudes upward in the drawing) made of curved portion 15 for absorbing and mitigating external forces such as vibration and expansion of the battery pack.

[0113] A lap joint is formed on the protruding flat portion, and a laser beam is irradiated onto the surface of the upper copper-based member 2 to form a molten metal portion 3. In this case, the penetration depth D, molten width W, and molten area S are as described in the above-mentioned respective embodiments.

[0114] 28 shows another modified example of bus bar 14, in which bus bar 14 is made of a dissimilar metal joint structure, with an upper heat-receiving side made of aluminum-based member 1 and a lower side made of copper-based member 2 formed with plating layer 13. The joint (molten metal portion 3) between aluminum-based member 1 and copper-based member 2 has a stepped shape (a shape that protrudes downward in the drawing) made of curved portion 15 for absorbing and mitigating external forces such as vibration and expansion of the battery pack.

[0115] A lap joint is formed on the flat portion protruding downward, and a laser beam is irradiated onto the surface of the upper aluminum-based member 1 to form a molten metal portion 3. In this case, the penetration depth D, molten width W, and molten area S are as described in the above-mentioned respective embodiments.

[0116] The bus bar 14 described above can be used, for example, as a bus bar for electrically connecting electrode terminals of different unit cells. Fig. 29 shows an example of a battery pack formed by combining adjacent unit cells.

[0117] 29 , a plurality of cells 16 are combined to form a battery pack 22. The cells 16 include a battery can and a battery lid, and the battery can contains a wound electrode body as an “electricity storage element” that outputs stored electricity, and the opening of the battery can is sealed by the battery lid.

[0118] The battery can contains an electrolyte solution, and the wound electrode body is immersed in the electrolyte solution. Note that an electrolyte other than a liquid electrolyte solution, such as a solid electrolyte, may also be used. The battery lid is provided with a positive electrode terminal 17 and a negative electrode terminal 18. The cell 16 charges the wound electrode body via the positive electrode terminal 17 and the negative electrode terminal 18, and supplies power to an external load.

[0119] A predetermined number of the cells 16 are stacked to form a battery pack, and the electrode terminals of adjacent cells 16 are connected by a bus bar. The bus bar electrically connects the positive electrode terminal 17 and the negative electrode terminal 18 of adjacent cells 16, and the cells 16 are connected in series.

[0120] 29 , each cell 16 has a pair of positive and negative electrode terminals 17 and 18, and when connecting the cells 16 in series, the positive and negative electrode terminals 17 and 18 of adjacent cells 16 are connected. The aluminum-based member 1 of the bus bar 14 is connected to the positive electrode terminal 17 of the cell 16, which is made of an aluminum-based material, and the copper-based member 2 of the bus bar 14, which has a nickel-plated or tin-plated plating layer 13, is connected to the negative electrode terminal 18 of the cell 16, which is also made of a copper-based material.

[0121] In this way, by using busbar 14 using the dissimilar metal bonded structure described in the first to sixth embodiments, even if a mechanical external force due to a temperature rise or the like in battery pack 22 acts on the busbar, it is possible to lead to ductile fracture in the base material portion rather than brittle fracture in molten metal portion 3. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlapping interface of the molten metal portions of dissimilar metals, and to provide a busbar with stable strength reliability.

[0122] Furthermore, by forming the molten metal part as a single bead when heat is input using a laser beam or the like, there is no increase in construction time or total heat input, which results in suppressing a decrease in production efficiency and avoiding adverse effects on product performance, such as deformation of the lap joint due to excessive heat input or thermal deterioration of the resin part.

[0123] Next, other application examples using the concept of the dissimilar metal bonded structure described above will be described with reference to Figures 30 to 35. In this embodiment, the above-described embodiment is applied to the joint between the electrode terminal of a cell and a bus bar in a battery pack. Note that, unlike the bus bar shown in Figure 29, the bus bar described below is made only of an aluminum-based material.

[0124] Here, sheet materials and resin members provided on the cells and battery pack, detailed configurations around the terminals, etc. are omitted. Also, Fig. 31 shows a side view seen from direction A shown in Fig. 30, and Fig. 32 shows a side view seen from direction B shown in Fig. 30.

[0125] 30 to 32 show the joints between the electrode terminals 17, 18 of two adjacent cells 16A, 16B that make up the battery pack and the bus bar 19. The cell 16A has a positive electrode terminal 17A made of an aluminum-based material and a negative electrode terminal 18A made of a copper-based material, and the cell 16B has a positive electrode terminal 17B made of an aluminum-based material and a negative electrode terminal 18B made of a copper-based material. Note that the symbols in parentheses after the reference numbers in the drawings indicate the materials.

[0126] 30 and 31 are the first members made of a first metal, and the negative electrode terminal 18B of the cell 16B and the negative electrode terminal 18A of the cell 16A, made of a second metal different from the first metal, are the second members. This combination forms the dissimilar metal bonded structures corresponding to Examples 1 to 6.

[0127] The positive electrode terminal 17A made of an aluminum-based material and the negative electrode terminal 18B made of a copper-based material are electrically connected by a bus bar 19-1 made only of an aluminum-based material. The negative electrode terminal 18A made of a copper-based material is electrically connected by a bus bar 19-2 made only of an aluminum-based material, and similarly, the positive electrode terminal 17B made of an aluminum-based material is electrically connected by a bus bar 19-3 made of an aluminum-based material.

[0128] The joining of dissimilar metals that is the subject of the present invention is the joining region between the negative electrode terminal 18B of the cell 16B and the bus bar 19-1, and the joining region between the negative electrode terminal 18A of the cell 16A and the bus bar 19-2. The molten metal portion 3 formed by any of the methods of the first to sixth embodiments described above is formed in these two joining regions.

[0129] Furthermore, the positive electrode terminal 17A of the battery 16A and the bus bar 19-1, and the positive electrode terminal 17B of the battery 16B and the bus bar 19-3 are both joined using an aluminum-based material, so no intermetallic compounds are generated and there is little risk of embrittlement.

[0130] FIG. 33 shows an extracted portion where a positive electrode terminal 17A made of an aluminum-based material and a negative electrode terminal 18B made of a copper-based material are electrically connected by a bus bar 19-1 made only of an aluminum-based material.

[0131] A molten metal portion 20 is formed at the joint between the positive electrode terminal 17A made of an aluminum-based material and the bus bar 19-1 made of an aluminum-based material, and as described above, this molten metal portion 20 is a joint made of the same type of aluminum-based metal. Note that, although the cross-sectional shape of the molten metal portion 20 along the overlapping interface is shown as a horizontal "U" shape in the figure, the bead shape itself is arbitrary.

[0132] Meanwhile, a molten metal portion 3 is formed at the joint between the negative electrode terminal 18B made of a copper-based material and the bus bar 19-1 made of an aluminum-based material, and as described above, this molten metal portion 3 is a joint between dissimilar metals, that is, an aluminum-based material and a copper-based material. Note that although the cross-sectional shape of the molten metal portion 3 along the overlapping interface is shown as a horizontal "U" shape in the figure, the bead shape itself is arbitrary.

[0133] Figure 34 shows a cross section taken along line A-A in Figure 33, and similarly to the embodiment shown in Figure 1, a molten metal portion 3 is formed penetrating the bus bar 19-1 toward the negative electrode terminal 18B made of a copper-based material. The penetration depth D of this molten metal portion 3 has the relationship shown in the above-mentioned embodiment. Figure 35 also shows the molten width W and molten area S of the molten metal portion 3, and in this example, the relationship also shows the relationship shown in the above-mentioned embodiment.

[0134] In this way, in the molten metal portion 3 formed in the joining region between the negative electrode terminal 18B of the battery 16B and the bus bar 19-1, and in the joining region between the negative electrode terminal 18A of the battery 16A and the bus bar 19-2, the penetration depth D of the molten metal portion, the molten width W of the molten metal portion 3, and the molten area S of the molten metal portion 3 are as described in the respective embodiments above.

[0135] Therefore, when an external force is applied, ductile fracture can occur in the base material, rather than brittle fracture in the molten metal portion 3. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlapping interface of the molten metal portion made of different metals, and to provide a battery pack with stable strength reliability.

[0136] Next, still another application example using the concept of the dissimilar metal bonded structure described above will be described with reference to Figures 36 to 38. In this embodiment, the above embodiment is applied to a joint between a bus bar made only of an aluminum-based material connected to the electrode terminal of a cell, and a voltage detection terminal made of a copper-based material that detects the voltage of the cell.

[0137] 36 to 38, a flat voltage detection terminal 21 made of a copper-based material is placed on a flat terminal portion 23 formed on a bus bar 19 made of an aluminum-based material connected to the electrode terminals of the cells that make up the battery pack, and a laser beam is irradiated onto the surface of this voltage detection terminal 21 to form a molten metal portion 3. A lead wire 24 is electrically connected to the voltage detection terminal 21, and is connected to control means (not shown).

[0138] 36 is the first member made of the first metal, and the voltage detection terminal 21 made of the second metal different from the first metal is the second member. This combination is a dissimilar metal joint structure corresponding to Examples 1 to 6.

[0139] The voltage detection terminal 21 is made of a copper-based material such as phosphor bronze, or a material such as nickel. When a copper-based material is used, the terminal may be nickel-plated or tin-plated, or both.

[0140] 36 shows an example in which the bus bar 19 is joined to the electrode terminal of the cell, and then the terminal portion 23 of the bus bar 19 is joined to the voltage detection terminal 21. In other words, the voltage detection terminal 21 is disposed on the front side of the terminal portion 23 of the bus bar 19, i.e., on the side opposite to the side where the bus bar 19 contacts the electrode terminal of the cell, and a laser beam is irradiated onto the voltage detection terminal 21.

[0141] On the other hand, if it is a process before joining the bus bar 19 and the electrode terminal of the single battery, a voltage detection terminal 21 can be placed on the back side of the bus bar 19, i.e., on the side where the bus bar 19 is joined to the electrode terminal of the single battery, and a laser beam can be irradiated onto the voltage detection terminal 21.

[0142] In this case, after the joining of the terminal portion 23 of the bus bar 19 and the voltage detection terminal 21 is completed, the bus bar 19 may be turned over so that the electrode terminal is joined to the back side of the bus bar 19. Here, Fig. 37 is a cross section taken along line B-B shown in Fig. 36, and Fig. 38 shows the cross-sectional shape of the molten metal portion 3 at the overlapping interface between the voltage detection terminal 21 and the terminal portion 23 of the bus bar 19.

[0143] In this way, the molten metal portion 3 formed in the joint region between the terminal portion 23 of the bus bar 19 and the voltage detection terminal 21 has the relationship described in the above embodiment in terms of the penetration depth D of the molten metal portion, the molten width W of the molten metal portion 3, and the molten area S of the molten metal portion 3, and therefore when an external force is applied, it can lead to ductile fracture in the base material rather than brittle fracture in the molten metal portion 3. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlapping interface of the molten metal portions made of dissimilar metals, and to provide a battery pack with stable strength reliability.

[0144] Furthermore, by forming the molten metal part as a single bead when applying heat using a laser beam or the like, there is no increase in construction time or total heat input, which in turn suppresses declines in production efficiency and avoids adverse effects on product performance, such as deformation of lap joints due to excessive heat input or thermal deterioration of resin parts.

[0145] If the voltage detection terminal 21 is made of a copper-based material, the functions and effects described in the above-described embodiment can be obtained. On the other hand, even if the voltage detection terminal 21 is made of a material containing nickel rather than copper, the strength is greater than that of an aluminum base material or a nickel-based terminal base material due to the properties of the compound phase of aluminum and nickel, and the same functions and effects as those described in the embodiment can be obtained.

[0146] The present invention is not limited to the above-described embodiments, but includes various modifications. The above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace other configurations with respect to the configuration of each embodiment.

[0147] 1...aluminum-based member, 2...copper-based member, 3...molten metal portion formed when dissimilar materials are melted, 4...lap interface of lap joint, 5...melting boundary of lap joint, 6...laser beam, 7...micro-arc motion of laser beam, 8...ray trajectory of laser beam, 9...portion of brittle fracture at lap interface, 10...portion of base material fracture, 11...narrow width portion, 12...thinned portion, 13...plated layer, 14...busbar made of aluminum-based member and copper-based member, 15...curved portion of busbar, 16...single cell, 17...positive electrode terminal of single cell, 18...negative electrode terminal of single cell, 19...busbar made of aluminum member, 20...molten metal portion in aluminum-based material, 21...voltage detection terminal, 23...terminal portion.

Claims

1. A dissimilar metal bonded structure having a first member made of a metallic material, a second member made of a metallic material different from the first member, an overlapping portion formed by the second member overlapping the first member on the heat input side, and a molten metal portion formed at the overlapping portion and formed by melting and solidifying the first member and the second member, wherein the molten metal portion has any of the following (A), (B), (C), and (D): (A) (1-A) the depth of the molten metal portion melting from the overlapping interface of the overlapping portion into the second member is 0.1 mm or more, (2-A) the molten width dimension of the molten metal portion in the longitudinal direction of the first member and the second member at the overlapping interface between the first member and the second member is 1.2 times or more the thickness of the member with the shorter thickness when the thicknesses of the first member and the second member are different, or is 1.2 times or more the thickness of either member when the thicknesses of the first member and the second member are the same, (3-A) the cross-sectional area of ​​the molten metal portion at the overlapping interface between the first member and the second member is larger than the cross-sectional area formed by the length along the outer edge of the molten metal portion at the overlapping interface and the plate thickness; (B) (1-B) the depth of the molten metal portion melting from the overlapping interface into the second member is 0.1 mm or more; (2-B) the molten width dimension of the molten metal portion at the overlapping interface between the first member and the second member in the longitudinal direction of the first member and the second member is 1.2 times or more the plate thickness of the member with a shorter plate thickness when the plate thicknesses of the first member and the second member are different, or is 1.2 times or more the plate thickness of either member when the plate thicknesses of the first member and the second member are the same; (3-B) the cross-sectional area of ​​the molten metal portion at the overlapping interface between the first member and the second member is larger than the cross-sectional area formed by the plate width and plate thickness of the first member or the second member; (C) A narrow portion is formed in the plate width direction by a notch penetrating in the plate thickness direction in the first member or the second member at the overlapping portion, and the molten metal portion has a depth of 0.1 mm or more from the overlapping interface of the overlapping portion to the second member.(2-C) the molten width dimension of the molten metal portion in the longitudinal direction of the first member and the second member at the overlapping interface between the first member and the second member is 1.2 times or more the thickness of the member having a shorter thickness when the plate thicknesses of the first member or the second member are different, or is 1.2 times or more the thickness of either member when the plate thicknesses of the first member or the second member are the same; (3-C) the cross-sectional area of ​​the molten metal portion at the overlapping interface between the first member and the second member is larger than the cross-sectional area formed by the plate width and plate thickness of the narrow portion of the first member or the second member; (D) a thinned portion having a short length in the plate thickness direction is formed in the first member or the second member at the overlapping portion by a concave groove formed in the plate thickness direction; and the molten metal portion is: (1-D) the depth of the molten metal portion melting from the overlapping interface of the overlapping portion into the second member is 0.1 mm or more. (2-D) A dissimilar metal bonded structure characterized by satisfying the following conditions: (2-D) A molten width dimension of the molten metal portion in the longitudinal direction of the first member and the second member at the overlapping interface between the first member and the second member is 1.2 times or more the plate thickness of the thinned portion of the first member or the second member; and (3-D) A cross-sectional area of ​​the molten metal portion at the overlapping interface between the first member and the second member is larger than the cross-sectional area formed by the plate thickness and plate width of the thinned portion of the first member or the second member.

2. A dissimilar metal bonded structure according to claim 1, characterized in that the molten bead forming the molten metal portion is formed as a single bead that does not overlap the molten metal portion in the direction of the molten width of the overlapping interface.

3. A dissimilar metal bonded structure according to claim 1, characterized in that the penetration depth of the molten metal portion from the overlapping interface into the second member is shorter than the plate thickness of the second member.

4. A dissimilar metal bonded structure according to claim 1, characterized in that the heat input to the first member is one of laser beam melting, electron beam melting, and arc melting.

5. A dissimilar metal bonded structure according to claim 1, characterized in that one of the first member and the second member is made of a copper-based material and the other is made of an aluminum-based material.

6. A dissimilar metal bonded structure according to claim 5, characterized in that at least one of the first member and the second member before bonding has a nickel plating layer, a tin plating layer, or both plating layers formed on the surface.

7. An assembled battery in which a plurality of unit cells, each including a battery can, a battery lid sealing the battery can, and an electrode terminal provided on the battery lid, are stacked, and the electrode terminals of adjacent unit cells are connected by a bus bar, wherein the bus bar comprises a dissimilar metal bonded structure joining a first member made of a first metal connected to the electrode terminal of one of the adjacent unit cells, and a second member made of a second metal different from the first metal connected to the electrode terminal of the other adjacent unit cell, and wherein the dissimilar metal bonded structure is the dissimilar metal bonded structure described in claim 1.

8. A battery pack according to claim 7, wherein the electrode terminal and the first member of one of the cells are made from the same type of metallic material, and the electrode terminal and the second member of the other of the cells are made from the same type of metallic material.

9. An assembled battery according to claim 8, wherein the electrode terminal and the first member of one of the cells are made of an aluminum-based metal, and the electrode terminal and the second member of the other of the cells are made of a copper-based metal.

10. A battery assembly in which a plurality of unit cells, each including a battery can, a battery lid sealing the battery can, and an electrode terminal provided on the battery lid, are stacked, and the electrode terminals of adjacent unit cells are connected by a bus bar, wherein the bus bar is a first member made of a first metal, and the electrode terminals of the unit cells are second members made of a second metal different from the first metal, forming a dissimilar metal bonding structure, wherein the dissimilar metal bonding structure is the dissimilar metal bonding structure described in claim 1.

11. A battery pack according to claim 10, wherein the second member of one of the adjacent cells is made from the same metal as the first member, and the second member of the other adjacent cell is made from a metal different from that of the first member.

12. A battery pack according to claim 11, wherein the second member and the first member of one of the cells are made of an aluminum-based metal, and the second member of the other of the cells is made of a copper-based metal.

13. A battery pack in which a plurality of unit cells, each including a battery can, a battery lid sealing the battery can, and an electrode terminal provided on the battery lid, are stacked, and the electrode terminals of adjacent unit cells are connected by a bus bar, wherein a voltage detection terminal is joined to the bus bar, and the bus bar is a first member made of a first metal, and the voltage detection terminal is a second member made of a second metal different from the first metal, in a dissimilar metal bonding structure, wherein the dissimilar metal bonding structure is the dissimilar metal bonding structure described in claim 1.

14. The battery pack according to claim 13, wherein the bus bars are made of an aluminum-based metal, and the voltage detection terminals are made of a copper-based metal.

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