Joint structure, structural body, B-pillar, and method for manufacturing the joint structure

Abstract

To provide a joint structure which can restrict breakage originating in a HAZ softened part, and is obtained by bonding a high strength steel sheet to a corrosion-resistant material, and to provide a structure, a B pillar, and a manufacturing method of the joint structure.SOLUTION: A joint structure comprises: an internal structure having a plurality of steel members and a weld zone; and an external structure having a main body part and a folded part. The plurality of steel members of the internal structure is a non-plated steel member, an aluminum-based plated hot stamp steel member, and / or a galvanized hot stamp steel member. The external structure is a galvanized steel member or an aluminum alloy member. One or more tensile strengths out of the internal structure are 1180 MPa or higher. Tensile strength of the external structure is less than 440 MPa. The weld zone is a linear laser weld zone extending along an edge of the internal structure. An end of the internal structure is disposed between the main body part and the folded part of the external structure. An end of the internal structure is bonded to the external structure.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a joining structure, a structure, a B pillar, and a method for manufacturing a joining structure.

Background Art

[0002] A monocoque body that constitutes an automobile body is generally manufactured by overlapping steel plate members including high-strength steel plates at flange portions and resistance spot welding the overlapping portions. Thereby, it is possible to achieve both an improvement in the collision safety of the automobile and an improvement in fuel efficiency.

[0003] A reinforcement member, which is a skeletal member arranged inside an outer panel, uses a high-strength steel plate having a tensile strength of 980 MPa class. Furthermore, the application of a high-strength steel plate having a tensile strength of 1180 MPa class or more to the reinforcement member is also being studied.

[0004] In addition, the adoption of a technique for manufacturing a hot stamping member having a tensile strength of 1470 MPa or more by applying hot stamping to the forming process of a steel plate member of a laser welding member is also being advanced. Hot stamping is a forming method in which press forming and quenching of a steel plate are simultaneously performed in the same mold. In hot stamping, since the steel plate is heated to a high temperature and press formed in a highly ductile state, a skeletal member composed of a high-strength steel plate having a tensile strength of 1470 MPa or more can be efficiently manufactured. Furthermore, hot stamping also has an advantage that the dimensional accuracy after press forming is improved.

[0005] A hot stamping steel plate having a tensile strength of 1180 MPa or more obtained by hot stamping and forming generally contains a quenched structure. However, in a spot weld portion formed for joining members, a heat-affected zone (referred to as a HAZ softened portion) having a hardness lower than that of the base material is formed. In the HAZ softened portion, the quenched structure is tempered by the heat of resistance spot welding, so its hardness becomes lower than that of the base material portion.

[0006] HAZ softening is particularly pronounced in spot welds of high-tensile steel sheets (DP steel sheets) with a tensile strength of 1180 MPa or higher, martensitic steel sheets with a tensile strength of 1470 MPa or higher, and hot-stamped materials. For example, in a spot-welded joint obtained by spot-welding cold-rolled steel sheets with a tensile strength of 1180 MPa, HAZ softening reduces the Vickers hardness by approximately 90 HV compared to the base material. Furthermore, in a spot-welded joint manufactured from hot-stamped steel sheets with a tensile strength of 1800 MPa, HAZ softening reduces the Vickers hardness by approximately 240 HV compared to the base material.

[0007] When a spot weld with a HAZ (High-Area Softening) zone is subjected to in-plane tensile stress, strain concentrates locally in the soft HAZ zone. Therefore, even with a small amount of strain applied to the member, strain can concentrate in the HAZ zone, potentially leading to fracture. Fracture in the HAZ zone of a spot weld has been observed in members made of steel plates with a tensile strength of 1180 MPa or higher. Therefore, there is room to further improve the impact resistance of members made of high-strength steel plates by improving the concentration of strain in the HAZ zone.

[0008] For example, structural components of an automobile body, such as A-pillars, B-pillars, and roof rails, need to protect passengers in the cabin during a collision. Therefore, these structural components are constructed by overlapping multiple steel plate members with flanges and joining these overlapping sections using resistance spot welding, thereby forming a cylindrical closed cross-section. This suppresses deformation of the cabin during a collision. However, in severe collision modes, such as those reproduced in the Insurance Institute for Highway Safety (IIHS) SUV side-impact tests and Euro NCAP pole-side impact tests, strain can concentrate in the softened HAZ (Heat-Absorbing Zone) of the spot-welded area, potentially leading to fracture initiation.

[0009] Therefore, in order to further improve the performance of components made from high-strength steel plates, there is a need for technology that prevents the softened HAZ (heat-induced zone) of spot welds from becoming the fracture initiation point.

[0010] On the other hand, outer panels for automotive parts require both corrosion resistance and formability. Therefore, in the manufacturing of automotive parts, steel sheet members formed from steel sheets, including relatively low-strength zinc-plated steel sheets, are sometimes overlapped and joined at the overlapping parts by resistance spot welding or the like. For example, outer panels that make up the outer surface of a monocoque body are generally formed from steel sheets with zinc-based plating, such as alloyed hot-dip galvanizing or hot-dip galvanizing. In recent years, the use of aluminum alloy outer panels has also been considered in order to reduce the weight of the outer panels.

[0011] However, welding these corrosion-resistant materials to high-strength steel plates that form structural members results in various welding defects. For example, welding aluminum alloys to iron alloys generates brittle intermetallic compounds in the weld metal. Also, welding materials with zinc plating causes zinc to evaporate during welding, forming blowholes in the weld metal. Therefore, technologies that incorporate these difficult-to-weld materials into automotive parts while ensuring collision safety are increasingly in demand.

[0012] Patent Document 1 discloses a hemming structure in which a sealing member is interposed between the main body of an outer panel having a flange portion and the edge of an inner panel, and the flange portion of the outer panel is folded back until it makes surface contact with the edge of the inner panel to join the outer panel and the inner panel, characterized in that a space is provided between the edges of the outer panel and the inner panel to accumulate the extruded sealing member so that the sealing member extruded when the flange portion is folded back does not wrap around to the surface contact portion between the flange portion and the edge of the inner panel.

[0013] Patent Document 2 discloses a laser welding method in which a laser is intermittently irradiated along a welding plan line set on the overlapping portion of a workpiece to be welded to intermittently form a continuous welded portion of a predetermined length, characterized in that relief portions for releasing stress generated by welding are formed in advance in the portion of the workpiece corresponding to the continuous welded portion.

[0014] Patent Document 3 discloses a dissimilar material panel structure comprising: an outer panel made of a first metal material; an inner panel disposed on the lower side of the outer panel and made of a second metal material having a higher melting point than the first metal material; and a rivet made of the same material as the second metal material and having a head and a shaft, wherein the outer panel has a hem portion formed by bending its peripheral edge and holding the inner panel via an adhesive layer; the rivet has its head remaining on the surface of the outer panel, with its shaft portion penetrating from the lower side of the hem portion of the outer panel toward the inner panel, and the tip of the shaft portion being spot-welded to the inner panel; the inner panel is provided with a projection facing the rivet in the axial direction of the rivet; and a heat insulating portion consisting of an adhesive layer or an adhesive layer and a gap is formed between the projection of the inner panel and the outer panel after welding.

[0015] Patent Document 4 discloses a hem flange welding method for bending the edge of a thin plate-shaped workpiece and welding a sheet metal workpiece to the bent edge, characterized in that it comprises a laser welding step of performing linear welding of a predetermined length by laser welding at a low power level sufficient to prevent thermal distortion of the welded area, and a plasma welding step of intermittently performing plasma spot welding of a small diameter, sufficient to prevent thermal distortion of the welded area, along the laser-welded area. [Prior art documents] [Patent Documents]

[0016] [Patent Document 1] Japanese Patent Application Publication No. 8-155564 [Patent Document 2] Japanese Patent Application Publication No. 7-75888 [Patent Document 3] Japanese Patent Publication No. 2015-164840 [Patent Document 4] Japanese Patent Application Publication No. 7-309138 [Overview of the Initiative]

Problems to be Solved by the Invention

[0017] However, in any of the techniques described in the literature, no means has been provided that can incorporate a corrosion-resistant material that is difficult to weld as an outer member of the structure while ensuring the strength of the structure.

[0018] The present invention is capable of suppressing fracture starting from the HAZ softened portion, and provides a joining structure, a structure, and a B pillar obtained by joining a high-strength steel member and a member composed of a corrosion-resistant material not suitable for welding, and a method for manufacturing the joining structure.

Means for Solving the Problems

[0019] The gist of the present invention is as follows.

[0020] (1) A joining structure according to one aspect of the present invention includes an internal structure having a plurality of steel members with flange portions and a welding portion for joining the overlapping flange portions of the plurality of steel members, a main body portion, and an external structure having a folded-back portion formed at an end of the main body portion. The plurality of steel members of the internal structure are one or a combination of two or more of non-plated steel members, aluminum-based plated hot-stamp steel members, and zinc-based plated hot-stamp steel members. The external structure is a zinc-based plated steel member or an aluminum alloy member. The tensile strength of one or more of the plurality of steel members of the internal structure is 1180 MPa or more, and the tensile strength of the zinc-based plated steel member or the aluminum alloy member constituting the external structure is less than 440 MPa. The welding portion of the internal structure is a linear laser welding portion extending along the edge of the internal structure. The end of the internal structure is disposed between the main body portion and the folded-back portion of the external structure, and the end of the internal structure is adhered to the external structure.

[0021] (2) A structure according to another aspect of the present invention has the joining structure described in (1) above at a part or all of its ends. (3) The structure described in (2) above may be a B-pillar, an A-pillar, a roof rail, a side sill, a bumper, or a battery case of an automobile. (4) In the structure described in (2) or (3) above, the joining structure may be provided in a load-bearing region of the structure.

[0022] (5) A B-pillar according to another aspect of the present invention includes a skeletal member having an outer reinforcement, an inner reinforcement, and a welding portion that joins flange portions of the overlapped outer reinforcement and the inner reinforcement, a flange portion, and a folded-back portion formed on a part or all of an end of the flange portion, and an outer panel overlapped on the outer reinforcement, wherein the outer reinforcement and the inner reinforcement are one or a combination of two or more of a non-plated steel member, an aluminum-plated hot-stamped steel member, and a zinc-plated hot-stamped steel member, the outer panel is a zinc-plated steel member or an aluminum alloy member, the tensile strength of the outer reinforcement is 1180 MPa or more, the tensile strength of the inner reinforcement is 440 MPa or more, the tensile strength of the outer panel is less than 440 MPa, at least a part of the welding portion of the skeletal member is a linear laser welding portion extending along an edge of the flange portion of the skeletal member, an end of the flange portion of the skeletal member is disposed between the flange portion and the folded-back portion of the outer panel, and the end of the skeletal member is adhered to the outer panel. (6) In the B-pillar described in (5) above, the folded-back portion and the laser welding portion may be provided on at least a part of a flange portion between an upper door hinge attachment portion of the B-pillar and a roof rail coupling portion of the B-pillar.

[0023] (7) A method for manufacturing a joint structure according to another aspect of the present invention is a step of obtaining an internal structure by overlapping the flange portions of a plurality of steel members and laser welding them; a step of placing an adhesive on one or both of the ends of the internal structure and the ends of the external structure; a step of overlapping the ends of the internal structure and the ends of the external structure such that a part of the ends of the external structure protrudes from the ends of the internal structure; a step of folding back the ends of the external structure that protrude from the ends of the internal structure along the edge of the internal structure, thereby forming a main body portion and a folded portion in the external structure that sandwich the ends of the internal structure. The external structure is made of zinc-plated steel or aluminum alloy, the plurality of steel members of the internal structure are made of one or more types selected from unplated steel, aluminum-plated hot-stamped steel, and zinc-plated hot-stamped steel, the tensile strength of the external structure is less than 440 MPa, the tensile strength of one or more of the plurality of steel members of the internal structure is 1180 MPa or more, the laser welding is performed by irradiating a laser along the edges of the plurality of steel members of the internal structure, and the end of the internal structure is bonded to the external structure by the adhesive. [Effects of the Invention]

[0024] According to the present invention, it is possible to suppress fracture originating from the HAZ softened area and to provide a joint structure, a structural element, and a B-pillar obtained by joining a high-strength steel member and a member made of a corrosion-resistant material unsuitable for welding, as well as a method for manufacturing the joint structure. [Brief explanation of the drawing]

[0025] [Figure 1] This is a cross-sectional view of an example of a joint structure. [Figure 2] This is a plan view of an example of a joint structure included in a structural unit, as seen from the external structure side. [Figure 3] This is a cross-sectional view of another example of a joint structure. [Figure 4] This is a perspective view of the B-pillar and the impactor used in B-pillar collision simulations. [Figure 5] This is an exploded perspective view of the B-pillar. [Figure 6A] This diagram illustrates the process of welding multiple overlapping internal steel members. [Figure 6B] This is a diagram illustrating the process of applying adhesive. [Figure 6C] This diagram illustrates the process of layering the internal and external structures. [Figure 6D] This diagram illustrates the process of folding the ends of the external structure along the edges of the internal structure. [Figure 7] This graph compares the collision simulation results of B-pillars with various joint structures applied. [Figure 8] This is a strain distribution diagram of a B-pillar that was subjected to conventional spot welding, at the completion of impactor pressing. [Figure 9] This is a strain distribution diagram of the B-pillar to which the joint structure according to the first embodiment is applied, at the time of completion of impactor pressing. [Modes for carrying out the invention]

[0026] First, a joint structure 1 according to the first embodiment of the present invention will be described. As shown in Figures 1 and 2, the joint structure 1 according to the first embodiment of the present invention comprises an internal structure 11 having a plurality of steel members (internal steel members 112) having flange portions 1121, and a welded portion 111 that joins the overlapping flange portions 1121 of the plurality of steel members, and an external structure 12 having a main body portion 121 and a folded portion 122 formed at the end of the main body portion 121. Here, the plurality of steel members of the internal structure 11 are one or more types from unplated steel members, aluminum-plated hot-stamped steel members, and zinc-plated hot-stamped steel members. The external structure 12 is a zinc-plated steel member or an aluminum alloy member. The tensile strength of one or more of the plurality of steel members of the internal structure 11 is 1180 MPa or more. The tensile strength of the zinc-plated steel member or aluminum alloy member constituting the external structure 12 is less than 440 MPa. The welded portion 111 of the internal structure 11 is a linear laser welded portion 111 that extends along the edge of the internal structure 11. The end of the internal structure 11 is positioned between the main body portion 121 and the folded portion 122 of the external structure 12. The end of the internal structure 11 is bonded to the external structure 12. Note that "end of the internal structure 11" refers to a region with a certain width, consisting of the edge of the internal structure 11 and its vicinity. On the other hand, "edge of the internal structure 11" refers to the contour of the internal structure 11 itself, and refers to a region that has no width.

[0027] One of the main features of the joint structure 1 is that an external structure 12 is placed on the outside of the joint structure 1, and this external structure 12 is made of a corrosion-resistant material. The corrosion-resistant material is a zinc-plated steel sheet or an aluminum alloy sheet. The external structure 12 ensures the corrosion resistance of the joint structure 1.

[0028] Another feature of the joint structure 1 is that an internal structure 11 is located inside the joint structure 1, and this internal structure 11 includes high-strength steel members with a tensile strength of 1180 MPa or more. The internal structure 11 ensures the strength of the joint structure 1.

[0029] However, welding defects are likely to occur when welding corrosion-resistant members and high-strength steel members. Therefore, the inventors set the tensile strength of the external structure 12 to less than 440 MPa and bent its end to form a hem structure. Specifically, a folded portion 122 is formed at the end of the external structure 12, the end of the internal structure 11 is housed inside the folded portion 122, and the end of the internal structure 11 is further bonded to the external structure 12. In addition, the external structure 12 is excluded from the welded joint 111 that joins the flange portions 1121 of multiple steel members of the internal structure 11. The hem structure and adhesive 13 ensure the joint strength of the internal structure 11 and external structure 12, which are made of materials that are difficult to weld.

[0030] Furthermore, HAZ softening is more likely to occur in high-strength steel members. Therefore, the inventors have made the welded portion 111 of the internal structure 11, which is composed of multiple steel members including a high-strength steel member, a linear laser welded portion 111 that extends along the edge of the internal structure 11. As a result, the width of the HAZ softening portion along the direction perpendicular to the end of the joint structure is reduced, and the effect of plastic constraint on the HAZ softening portion from the surrounding non-softened portion is increased, making fracture in the HAZ softening portion less likely. In other words, the linear laser welded portion 111 that extends along the edge of the internal structure 11 ensures the joint strength between the multiple steel members that constitute the internal structure 11.

[0031] Based on the inventors' ideas, the joint structure 1 according to the first embodiment will be described in detail below. In this embodiment, the joint structure 1 refers to the joint portion in a structure 2 formed by joining multiple members. That is, the joint structure 1 is a part of the structure 2, which will be described later. The position, size, and extent of the joint structure 1 in the structure 2 are not particularly limited. A form suitable for the application of the joint structure 1 and structure 2 can be adopted. For example, if the structure 2 is a machine part formed by joining hot-stamped steel members, a part or all of the flange portion provided on its edge can be the joint structure 1 according to the first embodiment.

[0032] (Regarding internal structure 11) The internal structure 11 is composed of multiple steel members that are partially or entirely overlapped. For example, when the joint structure 1 according to the first embodiment is applied to the flange portion of the structure 2, the multiple steel members correspond to the flange portions of the multiple steel members that constitute the structure 2. Hereinafter, for convenience, the steel members that constitute the internal structure 11 will be referred to as internal steel members 112. All internal steel members 112 have flange portions 1121, and these flange portions 1121 are overlapped. Generally, a flange portion refers to a region that protrudes from the end of a member having a three-dimensional shape, but in this embodiment, the end of a flat plate is also considered a flange portion. For example, in a hat-shaped member obtained by joining the flange portion of a bent steel member to a flat plate, the end of the flat plate, i.e., the part that is joined to the flange portion of the steel member, is considered the flange portion of the flat plate.

[0033] The number of steel members in the internal structure 11 is not particularly limited, as long as there are two or more. In the joint structure 1 illustrated in Figure 1, the internal structure 11 is composed of two internal steel members 112, but the internal structure 11 may have three or more internal steel members 112.

[0034] One or more of the internal steel members 112 constituting the internal structure 11 are high-strength steel members with a tensile strength of 1180 MPa or higher. This ensures the strength of the joint structure 1 and the structure 2 to which it is applied. The tensile strength of the internal steel members 112 included in the internal structure 11 may be 1250 MPa or higher, 1350 MPa or higher, or 1550 MPa or higher. The tensile strength of other internal steel members 112 combined with the high-strength steel members is not particularly limited. The tensile strength of steel members may also be expressed in terms of Vickers hardness. In that case, conversion between Vickers hardness and tensile strength may be performed in accordance with SAE J417 (1983). For example, a steel member with a Vickers hardness of 372 HV or higher can be considered a steel member with a tensile strength of 1180 MPa or higher. A steel member with a Vickers hardness of 392 HV or higher can be considered a steel member with a tensile strength of 1250 MPa or higher. Steel members with a Vickers hardness of 412 HV or higher can be considered as having a tensile strength of 1340 MPa or higher. Steel members with a Vickers hardness of 458 HV or higher can be considered as having a tensile strength of 1530 MPa or higher.

[0035] The multiple internal steel members 112 constituting the internal structure 11 may be steel members without plating such as zinc plating, i.e., unplated steel members. This is because the corrosion resistance of the joint structure 1 according to the first embodiment is ensured by the external structure 12. On the other hand, the multiple internal steel members 112 of the internal structure 11 may have plating, to the extent that it does not adversely affect the welded parts 111 of the internal structure 11.

[0036] For example, the internal steel member 112 included in the internal structure 11 may be an aluminum-plated hot-stamped steel member or a zinc-plated hot-stamped steel member. The aluminum-plated hot-stamped steel member is obtained by hot-stamping an aluminum-plated steel sheet. The zinc-plated hot-stamped steel member is obtained by hot-stamping a zinc-plated steel sheet. The zinc-plated coating obtained through hot-stamping has a different film structure than ordinary zinc-plated coatings, has a high boiling point, and is less likely to evaporate during welding. Therefore, the zinc-plated coating obtained through hot-stamping is less likely to cause welding defects such as blowholes. The aluminum-plated coating also has a higher boiling point than the zinc-plated coating and is less likely to cause welding defects such as blowholes. Therefore, the aluminum-plated hot-stamped steel member and the zinc-plated hot-stamped steel member do not adversely affect the welded part 111 of the internal structure 11.

[0037] In aluminum-plated hot-stamped steel components, there are no specific regulations regarding the amount of aluminum-plated coating, but for example, 15 g / m² is used. 2 More than 120g / m 2 The following may also be used. The aluminum-based plating after hot stamping is composed of multiple aluminum-iron alloy layers. Examples of the chemical composition of the aluminum-based plating layer after hot stamping include the binary alloys of Al and Fe, such as the θ phase (FeAl3), η phase (Fe2Al5), ζ phase (FeAl2), Fe3Al, and the Fe-based BCC phase (α2, α). Examples of the chemical composition of the aluminum-iron alloy layer when the aluminum-based plating after hot stamping contains Si include τ1-Al2Fe3Si3, τ2-Al3FeSi, τ3-Al2FeSi, τ4-Al3FeSi2, τ5-Al8Fe2Si, τ6-Al9Fe2Si2, τ7-Al3Fe2Si3, τ8-Al2Fe3Si4, and τ10-Al4Fe 1.7 Examples include Si and τ11-Al5Fe2Si. Aluminum-based plating after hot stamping containing Si is often composed mainly of τ5. In addition, a layer of ZnO, Ti-based oxide, or Al-based oxide may be present on the surface of the plating layer.

[0038] In zinc-plated hot-stamped steel components, there are no specific regulations regarding the amount of zinc-plated coating applied after hot stamping, but for example, 10 g / m² 2 More than 80g / m 2 The following may also be applied: The composition of the zinc-based plating after hot stamping is, for example, Fe-Zn or Fe-Zn-Ni, and the average zinc concentration is, for example, about 25-45%. The zinc-based plating does not have to contain nickel, but if it does, the average nickel concentration is, for example, 25% or less. In addition, a layer of ZnO or TiO2 may be present on the surface of the zinc-based plating after hot stamping.

[0039] As described above, the internal steel members 112 are unplated steel members, aluminum-plated hot-stamped steel members, or zinc-plated hot-stamped steel members. All of the internal steel members 112 may be one of the unplated steel members, aluminum-plated hot-stamped steel members, and zinc-plated hot-stamped steel members, or the internal steel members 112 may be a combination of two or more of the unplated steel members, aluminum-plated hot-stamped steel members, and zinc-plated hot-stamped steel members.

[0040] In the internal structure 11, multiple internal steel members 112 have flange portions 1121, and these flange portions 1121 are overlapped. The internal structure 11 also has a welded portion 111 that joins these flange portions 1121. As shown in Figure 2, the welded portion 111 is a linear laser welded portion 111 that extends along the edge of the internal structure 11. For example, when the joining structure 1 is applied to the flange portion of the structure 2, the laser welded portion 111 extends linearly along the edge of the flange portion. This distributes the strain due to the in-plane tensile load applied to the internal structure 11 over a wide area, making it less likely for fracture to occur in the HAZ softened area. In other words, the linear laser welded portion 111 that extends along the edge of the internal structure 11 ensures the joint strength between the multiple internal steel members 112 that constitute the internal structure 11. The shape of the laser welded portion is not particularly limited. As a preferred example, the width of the laser welded portion is 0.4 mm to 3.0 m, and the length is 20 mm to 800 mm. Furthermore, the end of the laser-welded section may be treated with crater processing such as defocusing or adjusting the laser output and welding speed. This can reduce the risk of holes or cracks at the end of the weld.

[0041] (Regarding external structure 12) The external structure 12 has a plate-like structure with folded ends, as shown in Figure 1. The folded portion is referred to as the folded portion 122, and the remaining portion is referred to as the main body portion 121.

[0042] The material of the external structure 12 is either zinc-plated steel sheet or aluminum alloy sheet. Zinc-plated steel sheet is, for example, alloyed hot-dip galvanized steel sheet. Aluminum alloy sheet is, for example, 5000 series aluminum alloy or 6000 series aluminum alloy. This ensures that the external structure 12 has corrosion resistance to the joint structure 1. These corrosion-resistant materials can cause welding defects in conventional laser welding. If the material of the external structure 12 is zinc-plated steel sheet, blowhole defects will occur in the welded area. If the material of the external structure 12 is aluminum alloy sheet, a brittle intermetallic compound will form at the joint between the internal structure 11 and the external structure 12, resulting in insufficient joint strength. However, in the joint structure 1 according to the first embodiment, this problem is avoided by joining the internal structure 11 and the external structure 12 by means other than welding.

[0043] Furthermore, the tensile strength of the plates constituting the external structure 12 is set to less than 440 MPa. This is to facilitate the manufacturing of the folded portion 122 of the external structure 12. The tensile strength of the corrosion-resistant material constituting the external structure 12 may be 420 MPa or less, 400 MPa or less, or 380 MPa or less. The thickness of the plates constituting the external structure 12 may be 1.4 mm or less. This is to facilitate the manufacturing of the folded portion 122. The thickness of the plates constituting the external structure 12 is more preferably 0.5 mm to 1.2 mm. The number of materials constituting the external structure 12 is not particularly limited. In Figure 1, the external structure 12 is formed by folding back the flange portion of one member, but the external structure 12 may also be formed by overlapping and folding back the flange portions of two or more members. When the external structure 12 is composed of two or more members, it is preferable that the flange portions of these members are bonded together.

[0044] (Regarding the joining of the internal structure 11 and the external structure 12) The internal structure 11 and the external structure 12 are joined together by a hem structure provided at the end of the external structure 12 and by adhesive. The external structure 12 is provided with a main body portion 121 and a folded portion 122 as described above, and the end of the internal structure 11 is positioned between the main body portion 121 and the folded portion 122 of the external structure 12. In other words, the main body portion 121 and the folded portion 122 of the external structure 12 sandwich the end of the internal structure 11. The external structure 12 and the internal structure 11 are joined by this hem structure. In addition, the end of the internal structure 11 is adhesively bonded to the external structure 12.

[0045] By using a hem structure in combination with adhesive bonding, the joint strength of the internal structure 11 and the external structure 12 can be further increased. Normally, when welding a zinc-plated steel member or an aluminum alloy member to a steel member, welding defects such as blowholes and brittle intermetallic compounds occur, reducing the joint strength. On the other hand, in the joint structure 1 according to the first embodiment, the internal structure 11 and the external structure 12 are not welded. Neither the hem structure nor adhesive bonding causes any particular defects when joining a zinc-plated steel member or an aluminum alloy member to a steel member.

[0046] The joint structure 1 according to the first embodiment can take various forms as long as it has the above-described configuration. Preferred forms of the joint structure 1 according to the first embodiment will be described below.

[0047] (Example of laser weld shape) In the internal structure 11, multiple overlapping internal steel members 112 are joined by laser welding. This laser welding may be an overlap weld as shown in Figure 1, or a fillet weld as shown in Figure 3. An overlap weld is a weld composed of weld metal that penetrates from one surface of the internal structure 11 toward the other surface. A fillet weld is a weld composed of weld metal that welds one surface of the multiple internal steel members 112 to the remaining end faces. When the inventors performed FEM analysis, it was confirmed that the joint structure 1 has excellent strength regardless of the form of the weld. Furthermore, the penetration depth of the weld metal included in the weld is not particularly limited, and values ​​suitable for the thickness and tensile strength of the internal steel members 112 included in the internal structure 11 can be appropriately adopted.

[0048] (Example of the size of the folded portion 122) The size of the folded portion 122 is not particularly limited. The larger the folded portion 122, the better the joint strength between the internal structure 11 and the external structure 12, but if the folded portion 122 is too large, the effect saturates. On the other hand, the larger the folded portion 122, the greater the weight of the joint structure 1 and the material cost of the external structure 12. Therefore, it is preferable to consider the optimal size of the folded portion 122 by taking into account the thickness of the materials constituting the joint structure 1 and the application of the joint structure 1. An example of a suitable width for the folded portion 122 is 4 mm to 16 mm. The folded portion 122 may or may not cover the laser welded area. Here, the width of the folded portion 122 refers to the length of the folded portion 122 measured along a direction perpendicular to the edge of the joint structure 1.

[0049] (Example of an internal steel member 112 included in the internal structure 11) As described above, one or more of the internal steel members 112 included in the internal structure 11 are high-strength steel members, and the tensile strength of the internal steel members 112 combined with them is not particularly limited. For example, in the internal structure 11, a high-strength steel member with a tensile strength of 1180 MPa or more may be combined with a relatively low-strength steel member with a tensile strength of 440 MPa or more. The tensile strength of the internal steel members 112 combined with the high-strength steel member may be even lower. On the other hand, in the internal structure 11, two or more high-strength steel members with a tensile strength of 1180 MPa or more may be combined.

[0050] Furthermore, the internal steel members 112 are one or more selected from unplated steel members, aluminum-plated hot-stamped steel members, and zinc-plated hot-stamped steel members. All of the internal steel members 112 may be one of the unplated steel members, aluminum-plated hot-stamped steel members, and zinc-plated hot-stamped steel members, or the internal steel members 112 may be a combination of two or more of the unplated steel members, aluminum-plated hot-stamped steel members, and zinc-plated hot-stamped steel members.

[0051] (Example of heme structure) The end of the internal structure 11 is positioned between the main body 121 and the folded portion 122 of the external structure 12. The number of internal steel members 112 of the internal structure 11 positioned between the main body 121 and the folded portion 122 is not limited. For example, as shown in Figure 1, all of the internal steel members 112 of the internal structure 11 may be positioned between the main body 121 and the folded portion 122 of the external structure 12. On the other hand, as shown in Figure 3, only one of the internal steel members 112 of the internal structure 11 may be positioned between the main body 121 and the folded portion 122 of the external structure 12. In either case, the hem structure provided at the end of the external structure 12 can enhance the joint strength between the external structure 12 and the internal structure 11.

[0052] (Examples of bonding methods) The ends of the internal structure 11 are bonded to the external structure 12. Examples of adhesives 13 for bonding the internal structure 11 and the external structure 12 include epoxy, rubber, or urethane structural adhesives. Preferably, the adhesive 13 is an impact-resistant structural adhesive. In addition to the adhesive 13, a sealer may also be used to waterproof the ends of the joint structure 1. The zinc-plated steel or aluminum alloy members that constitute the external structure 12 are difficult to weld, but an adhesive 13 capable of bonding the external structure 12 to the internal structure 11 can be appropriately used.

[0053] The location where the adhesive 13 is applied is not particularly limited. For example, as shown in Figures 1 and 3, the adhesive may be applied to both the internal structure 11 and the main body 121, and to the folded portion 122. Alternatively, the adhesive may be applied only to the internal structure 11 and the main body 121 of the external structure 12. Alternatively, the adhesive may be applied only to the internal structure 11 and the folded portion 122 of the external structure 12. In any case, the adhesive may be applied to the entire contact area between the internal structure 11 and the external structure 12, or only to a part of it. The greater the bonding area, the greater the bonding strength between the internal structure 11 and the external structure 12. On the other hand, the greater the bonding area, the greater the amount of adhesive 13 required, and the greater the possibility of the adhesive overflowing onto the outside of the hem structure or into the gap between the external structure 12 and the internal structure 11. Also, the greater the area and location where the adhesive 13 is applied, the greater the time required to apply the adhesive 13. Depending on the intended use of the joint structure 1, it may be necessary to remove the excess adhesive 13. Therefore, it is preferable to optimize the placement and area of ​​the adhesive 13 while considering the intended use of the joint structure 1.

[0054] Furthermore, the joint structure 1 according to the first embodiment may further include components other than the internal structure 11 and the external structure 12. Within the limits that do not impair the effects described above, the joint structure 1 can take various configurations. For example, a member that does not have a folded portion 122 and is not welded to the internal steel member 112 may be placed between the internal structure 11 and the external structure 12.

[0055] Next, a structure 2 according to the second embodiment of the present invention will be described. The structure 2 according to the second embodiment comprises an internal member and an external member. The ends of the internal member and the external member are joined by the joining structure 1 according to the first embodiment. That is, the structure 2 according to the second embodiment has the joining structure 1 according to the first embodiment on part or all of the ends of the structure 2.

[0056] Multiple steel members included in the internal members of structure 2 correspond to multiple internal steel members 112 of the internal structure 11 in the joint structure 1 according to the first embodiment. The ends near the edges of the external members of structure 2 correspond to the external structure 12 in the joint structure 1 according to the first embodiment. In structure 2 according to the second embodiment, high strength is ensured by high-strength steel members, high corrosion resistance is ensured by zinc-plated steel members or aluminum alloy members, and high joint strength is ensured because each member is joined by the joint structure 1 according to the first embodiment.

[0057] Preferred examples of structure 2 include the B-pillar, A-pillar, roof rail, side sill, bumper, or battery case of an automobile. However, the applications of structure 2 are not particularly limited and can be applied to a variety of parts.

[0058] The joint structure 1 may be provided over the entire end of the structure 2. On the other hand, as shown in Figure 2, the joint structure 1 may be provided only on a part of the structure 2, and other joining means may be applied to the other parts. An example of a joining means that can be used in combination with the joint structure 1 is a spot weld 21 that joins all of the multiple steel members included in the internal member and the external member. As described above, in the spot weld 21, welding defects and stress concentration in the HAZ softened area occur, so the joint strength is lower than that of the joint structure 1 according to the first embodiment. On the other hand, the spot weld 21 has the advantage of requiring less time to form. Therefore, in the structure 2, the joint structure 1 may be applied only to the parts where joint strength is required, and the other parts may be joined by spot welding.

[0059] One example of a location where a joint structure 1 is preferable is the tensile load loading region within the steel plate surface. A load loading region is a region where tensile load is concentrated when an impact expected from its intended use is applied to the structure 2. For example, the B-pillar 3 of the automobile shown in Figure 4 is a window pillar located between the front and rear seats, and plays a role in protecting the interior of the vehicle from impacts applied to the vehicle from the side. Therefore, the impact expected to be applied to the B-pillar 3 is an impact applied perpendicularly to the B-pillar 3 to the lower end of the B-pillar 3 on the vehicle body. In FEM analysis, for example, by pressing the impactor i as shown in Figure 4, the impact expected to be applied to the B-pillar 3 can be simulated. Then, when an impact expected from the intended use of the B-pillar 3 is applied to the B-pillar 3, the region where the load is concentrated on the B-pillar 3 can be identified by FEM analysis. For example, in the B-pillar 3 shown in Figure 4, a portion of the flange between the upper door hinge mounting portion and the roof rail connection portion becomes a load-bearing area. However, the method for identifying the load-bearing area is not limited to FEM analysis. The load-bearing area can be identified by various methods, such as actually destroying various structures 2 and analyzing their failure modes. Also, in the B-pillar 3 shown in Figure 8, the dark-colored area with an arrow in the flange portion is the strain-bearing area. The strain-bearing area is a region of high strain that is formed when localized softening areas, such as HAZ softening areas, exist in the load-bearing area, and the strain-bearing area is likely to be the starting point of fracture. Here, in the B-pillar 3 shown in Figure 9, where the joint structure 1 is provided in the load-bearing area, the strain is distributed over a wide area of ​​the flange portion. The joint structure 1 provided in the load-bearing area suppresses the formation of a strain-bearing area in the load-bearing area, thereby more effectively suppressing fracture originating from HAZ softening areas.

[0060] Next, a B-pillar 3 according to the third embodiment of the present invention will be described. As shown in Figures 4 and 5, the B-pillar 3 according to the third embodiment is obtained by joining an outer panel 31, an outer reinforcement 32, and an inner reinforcement 34 by the joining structure 1 according to the first embodiment. That is, the B-pillar 3 according to the third embodiment is a B-pillar 3 comprising a skeletal member having an outer reinforcement 32, an inner reinforcement 34, and a welded portion that joins the flange portions of the overlapping outer reinforcement 32 and inner reinforcement 34, and an outer panel 31 that overlaps the outer reinforcement 32 and has a flange portion and a folded portion 122 formed on part or all of the end of the flange portion, wherein the outer reinforcement 32 and inner reinforcement 34 are unplated steel members, aluminum-plated hot-stamped steel members, or zinc-plated hot-stamped steel members. The outer panel 31 is a zinc-plated steel member or an aluminum steel member. The outer reinforcement force 32 has a tensile strength of 1180 MPa or more, the inner reinforcement force 34 has a tensile strength of 440 MPa or more, and the outer panel 31 has a tensile strength of less than 440 MPa. At least a portion of the welded portion of the skeletal member is a linear laser weld extending along the edge of the flange portion of the skeletal member. The end of the flange portion of the skeletal member is positioned between the flange portion and the folded portion 122 of the outer panel 31. The end of the skeletal member is bonded to the outer panel 31. In addition, as shown in Figure 5, a hinge reinforcement force 33 may be included in the B pillar 3.

[0061] The flange portion of the outer reinforcement force 32 and the flange portion of the inner reinforcement force 34 correspond to the multiple overlapping internal steel members 112 in the joint structure 1. The flange portion and folded portion 122 of the outer panel 31 correspond to the main body portion 121 and the folded portion 122 of the external structure 12 in the joint structure 1, respectively. In the B pillar 3 according to the third embodiment, high rigidity is ensured by the tensile strength of the outer reinforcement force 32 being 1180 MPa or more, and high corrosion resistance is ensured by the outer panel 31 being made of zinc-plated steel sheet or aluminum alloy sheet. Furthermore, high joint strength is ensured because laser welding and a hem structure are used in combination in at least a part of it.

[0062] Naturally, preferred embodiments of the joint structure 1 according to the first embodiment and the structure 2 according to the second embodiment can be applied to the B-pillar 3 as needed. For example, similar to structure 2, the folded portion 122 and the laser-welded portion may be provided in the load-bearing area of ​​the B-pillar 3. The load-bearing area of ​​the B-pillar 3 can be appropriately determined using the method for determining the load-bearing area of ​​structure 2 described above. In addition, in the B-pillar 3, a part of the flange portion between the upper door hinge mounting portion and the roof rail connection portion often becomes the load-bearing area. Therefore, the folded portion and the laser-welded portion may be provided in at least a part of the flange portion between the upper door hinge mounting portion and the roof rail connection portion.

[0063] The upper door hinge is the one of the two door hinges attached to the B-pillar that is closer to the vehicle's ceiling. For example, in the B-pillar illustrated in Figure 4, the area enclosed by the dashed line labeled X is the upper door hinge mounting area. Typically, the upper door hinge mounting area of ​​the B-pillar has through holes for fastening with bolts or screws. The roof rail refers to the lateral structural member of the outer frame of the car's ceiling. Therefore, the roof rail connection point of the B-pillar usually coincides with the end of the B-pillar on the vehicle's ceiling side. For example, in the B-pillar illustrated in Figure 4, the area enclosed by the dashed line labeled Y is the roof rail connection point.

[0064] Next, a method for manufacturing the joint structure 1 according to the fourth embodiment of the present invention will be described. The method for manufacturing the joint structure 1 according to the fourth embodiment of the present invention is: (S1) A step of overlapping the flange portions 1121 of multiple steel members (internal steel members 112) and laser welding them to obtain an internal structure 11, (S2) A step of applying adhesive 13 to one or both of the ends of the internal structure 11 and the ends of the external structure 12, (S3) A step of overlapping the end of the internal structure 11 and the end of the external structure 12 such that a part of the end of the external structure 12 protrudes from the end of the internal structure 11, (S4) The process of folding back the end of the external structure 12 that protrudes from the end of the internal structure 11 along the edge of the internal structure 11, thereby forming a main body portion 121 and a folded portion 122 on the external structure 12 that sandwich the end of the internal structure 11, It holds.

[0065] (S1) Welding First, as shown in Figure 6A, the flange portions 1121 of multiple internal steel members 112 are overlapped and laser-welded to obtain the internal structure 11. The welding S1 is a laser welding process in which a laser is irradiated along the edges of the multiple internal steel members 112 of the internal structure 11. This reduces strain concentration in the HAZ softened area when an in-plane tensile load is applied to the joint structure 1, thereby increasing the joint strength of the internal structure 11. The laser welding may be lap welding or fillet welding. In this embodiment, lap welding is a welding process that forms weld metal that melts from one surface to the other of the internal structure 11, as illustrated in Figure 1. Furthermore, it is not necessary to perform laser welding over the entire outer edge of the structure 2 to which the joint structure 1 is applied. It is sufficient to perform laser welding at least in the areas where the joint structure 1 is applied. The material and tensile strength of the multiple internal steel members 112 constituting the internal structure 11 are the same as those of the joint structure 1 according to the first embodiment.

[0066] (S2) Placement of adhesive 13 Next, as shown in Figure 6B, adhesive 13 is placed to bond the internal structure 11 and the external structure 12. The adhesive 13 may be placed on either the internal structure 11 or the external structure 12, or on both. The location of the adhesive 13 is not particularly limited. For example, as shown in Figure 1, the adhesive 13 may be placed both between the internal structure 11 and the main body 121 of the external structure 12, and between the internal structure 11 and the folded portion 122. The adhesive 13 may be placed only between the internal structure 11 and the main body 121 of the external structure 12. The adhesive 13 may be placed only between the internal structure 11 and the folded portion 122 of the external structure 12. In any case, the adhesive 13 may be placed over the entire contact area between the internal structure 11 and the external structure 12, or only on a part of it. It is preferable to optimize the location and area of ​​the adhesive 13 while considering the intended use of the joint structure 1. Note that the external structure 12 shown in Figure 6B is already folded 90° before being superimposed. This facilitates alignment between the external structure 12 and the internal structure 11. However, the external structure 12 and the internal structure 11 may also be superimposed with the external structure 12 in a flat state.

[0067] (S3) Superposition of internal structure 11 and external structure 12 Then, as shown in Figure 6C, the end of the internal structure 11 and the end of the external structure 12 are overlapped so that a portion of the end of the external structure 12 protrudes from the end of the internal structure 11. The direction in which the end of the external structure 12 protrudes is not particularly limited. Figure 6C shows an example in which the end of the external structure 12 protrudes downward from the paper, that is, in a direction that is substantially perpendicular to the external structure 12 and toward the internal structure 11. On the other hand, at the overlapping stage, the end of the external structure 12 may be made flat and protrude toward the right from the paper, that is, in a direction that is substantially parallel to the external structure 12 and toward the internal structure 11. In other words, the internal structure 11 and the external structure 12 should be overlapped so that a fold allowance that can become a folded portion 122 is provided at the end of the external structure 12. At this stage, the folded portion 122 has not been formed on the external structure 12. The protruding portion of the external structure 12 becomes the folded portion 122 in the subsequent folding process. However, the ends of the external structure 12 may be bent in advance, to the extent that it does not hinder the overlapping of the internal structure 11 and the external structure 12. The external structure 12 illustrated in Figure 6C is bent by approximately 90° at the overlapping stage to facilitate hemming.

[0068] (S4) Folding of the external structure 12 Furthermore, as shown in Figure 6D, the end of the external structure 12 that protrudes from the end of the internal structure 11 is folded back along the edge of the internal structure 11. This forms a main body portion 121 and a folded portion 122 on the external structure 12 that sandwich the end of the internal structure 11. In other words, the folding of the external structure 12 positions the end of the internal structure 11 between the main body portion 121 and the folded portion 122 of the external structure 12. Since the adhesive 13 is applied before overlapping and folding, the internal structure 11 and the external structure 12 are bonded together during overlapping S3 and / or folding S4. Normally, a process is required to hold the materials to be joined until the adhesive hardens. However, when the end of the internal structure 11 is sandwiched by the main body portion 121 and the folded portion 122, the holding process can be omitted. The adhesive may harden over time or by heating. For example, in the manufacturing process, it can be hardened by heating during the painting process.

[0069] Similar to the joint structure 1 of the first embodiment, in the fourth embodiment, the external structure 12 is a zinc-plated steel member or an aluminum alloy member, and the plurality of internal steel members 112 of the internal structure 11 are unplated steel members, aluminum-plated hot-stamped steel members, or zinc-plated hot-stamped steel members, the tensile strength of the external structure 12 is less than 440 MPa, and the tensile strength of one or more of the plurality of internal steel members 112 of the internal structure 11 is 1180 MPa or more. Naturally, preferred embodiments of the joint structure 1 of the first embodiment can also be applied to the manufacturing method of the joint structure 1 according to the fourth embodiment. [Examples]

[0070] The inventors evaluated the influence of the shape of the welded joint 111 on the joint strength of the internal structure 11 and the joint itself using finite element method simulations. A model simulating the B-pillar 3 was created with the shapes shown in Figures 4 and 5. Then, the displacement and strain of the impactor i when the B-pillar 3 was pressed down with the impactor i, as shown in Figure 4, were calculated using FEM analysis. Three methods were used to join the B-pillar 3. (A) The joint between the two steel members included in the internal structure 11 is made into an overlapping laser welded joint, a folded portion 122 is provided at the end of the external structure 12, the end of the internal structure 11 is placed inside the folded portion 122, and adhesive is applied to bond the entire contact surface of the external structure 12 and the internal structure 11 (see Figure 1). (B) The joint between the two steel members included in the internal structure 11 is made into a fillet laser weld, a folded portion 122 is provided at the end of the external structure 12, the end of the internal structure 11 is placed inside the folded portion 122, and adhesive is applied to bond the entire contact surface of the external structure 12 and the internal structure 11 (see Figure 3). (C) All of the internal structure 112 steel members and the external structure 12 are joined by spot welding. No folded-over portion 122 is provided at the end of the external structure 12.

[0071] Furthermore, the other simulation conditions were as follows: Outerline Force 32 was a so-called tailored blank material obtained by hot stamping after joining dissimilar materials. • Material of outer panel 31: GA plated steel sheet with a tensile strength of 270 MPa and a thickness of 0.7 mm. • Material of the upper part of Outerline Force 32: Aluminum-plated hot-stamped steel sheet with a tensile strength of 1800 MPa and a thickness of 1.6 mm. • Material of the lower part of Outerline Force 32: Aluminum-plated hot-stamped steel sheet with a tensile strength of 1300 MPa and a thickness of 1.2 mm. • Hinge Ring Force 33 Material: Aluminum-plated hot-stamped steel sheet with a tensile strength of 1800 MPa and a thickness of 1.6 mm. • Innarinforce 34 material: Unplated steel sheet with a tensile strength of 590 MPa and a thickness of 1.2 mm. • Method of joining the upper and lower parts of Outer Reinforce 32: Laser welding Note that the upper side of the outer force 32 is the left side of the page, and the lower side of the outer force 32 is the right side of the page. In other words, the vertical direction of the outer force 32 is the vertical direction of the vehicle to which the outer force 32 is assembled.

[0072] The test results are shown in Figure 7. In the conventional jointing condition (C) model, fracture occurred at impactor i displacements of approximately 170 mm, 190 mm, and 200 mm, starting from the HAZ softened area of ​​the spot weld of the flange of the 1800 MPa reinforcement material. As a result, the load decreased in the jointing condition (C) model. On the other hand, in the jointing conditions (A) and (B) models, no fracture occurred in the HAZ softened area of ​​the laser weld (the fracture criteria were not reached), so a high load was obtained even in the later stages of deformation after the impactor i displacement reached 200 mm. In addition, the adhesive of the flange hardly fractured in these models.

[0073] Figure 8 shows a simulation image of the model for joining condition (C) when the impactor i has been pressed down 250 mm. In the model for joining condition (C), localized strain concentration occurred in the spot weld 21 at three locations, indicated by arrows: the front seat side flange (upper side in Figure 8) of the bend at the top of the B-pillar, and the front and rear seat side flanges of the upper parallel section of the B-pillar, resulting in fracture of the HAZ softened area. These fracture locations are considered to be the strain load regions of the B-pillar 3.

[0074] Figure 9 shows a simulation image of the model for joining condition (B) when the impactor i has been pressed 250 mm. In the model for joining condition (B), the strain was distributed over a wide area of ​​the flange. [Explanation of Symbols]

[0075] 1 Joint structure 11 Internal structure 111 Welded parts (laser welded parts) 112 Internal steel parts 1121 Flange section 12 External structure 121 Main body 122 Turning section 13 Adhesive 2 structure 21 Spot welds 3 B-pillar 31 Outer Panel 32 Outerlinforce 33 Hinged Link Force 34 Inner Force i Impactor

Claims

1. An internal structure having a plurality of steel members having flange portions, and a welded portion that joins the overlapping flange portions of the plurality of steel members, An external structure having a main body and a folded portion formed at the end of the main body, A joint structure comprising, The multiple steel members of the internal structure are one or more combinations of unplated steel members, aluminum-plated hot-stamped steel members, and zinc-plated hot-stamped steel members. The external structure is made of zinc-plated steel or aluminum alloy. One or more of the multiple steel members of the internal structure have a tensile strength of 1180 MPa or more. The tensile strength of the zinc-plated steel member or aluminum alloy member constituting the external structure is less than 440 MPa. The welded portion of the internal structure is a linear laser welded portion that extends along the edge of the internal structure. The end of the internal structure is positioned between the main body and the folded portion of the external structure. The end of the internal structure is bonded to the external structure. The external structure is excluded from the welded joint that joins the flange portions of the multiple steel members of the internal structure. Joint structure.

2. A structure having the joint structure described in claim 1 in part or all of its end portion.

3. The structure according to claim 2, characterized in that it is a B-pillar, A-pillar, roof rail, side sill, bumper, or battery case of an automobile.

4. The structure according to claim 2 or 3, characterized in that the joint structure is provided in the load-bearing region of the structure.

5. A skeletal member having an outer reinforcement force, an inner reinforcement force, and a welded portion that joins the flange portions of the overlapping outer reinforcement force and the inner reinforcement force, An outer panel having a flange portion and a folded portion formed on part or all of the end of the flange portion, which is superimposed on the outer reinforcement, A B-pillar equipped with, The outer reinforcement and the inner reinforcement are one or more combinations of unplated steel members, aluminum-plated hot-stamped steel members, and zinc-plated hot-stamped steel members. The outer panel is made of zinc-plated steel or aluminum alloy. The tensile strength of the outer reinforcement force is 1180 MPa or more. The tensile strength of the aforementioned inner force is 440 MPa or more. The tensile strength of the outer panel is less than 440 MPa, At least a portion of the welded portion of the skeletal member is a linear laser welded portion that extends along the edge of the flange portion of the skeletal member, The end of the flange portion of the skeletal member is positioned between the flange portion and the folded portion of the outer panel. The end of the skeletal member is bonded to the outer panel. The outer panel is excluded from the welded joint that joins the flange portions of the multiple outer reinforcements and inner reinforcements of the skeletal member. B-pillar.

6. The B-pillar according to claim 5, characterized in that the folded portion and the laser-welded portion are provided on at least a part of the flange portion between the upper door hinge mounting portion of the B-pillar and the roof rail connecting portion of the B-pillar.

7. A process of overlapping the flange portions of multiple steel members and laser welding them to obtain the internal structure, A step of applying adhesive to one or both of the ends of the internal structure and the ends of the external structure, A step of overlapping the end of the internal structure and the end of the external structure such that a part of the end of the external structure protrudes from the end of the internal structure, The process of folding back the end of the external structure that protrudes from the end of the internal structure along the edge of the internal structure, thereby forming a main body portion and a folded portion in the external structure that sandwich the end of the internal structure, Equipped with, The external structure is made of zinc-plated steel or aluminum alloy. The plurality of steel members of the internal structure are one or more combinations of unplated steel members, aluminum-plated hot-stamped steel members, and zinc-plated hot-stamped steel members. The tensile strength of the external structure is less than 440 MPa. One or more of the multiple steel members of the internal structure have a tensile strength of 1180 MPa or more. The laser welding is a laser welding method in which a laser is irradiated along the edges of the multiple steel members of the internal structure. The end of the internal structure is bonded to the external structure by the adhesive. A method for manufacturing a bonded structure.

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