Joined structure and method for manufacturing joined structure

Abstract

A joined structure (1) according to one embodiment of the present disclosure comprises: an aluminum member (11); and one or more plated steel members (12) each having a base steel member (122) and a surface plating layer (123) provided on a surface of the base steel member (122). The aluminum member (11) has one or more protrusions (111), the plated steel member (12) has one or more through-holes (121), and the protrusions (111) are inserted into the through-holes (121) and caulked. At an inner surface of each through-hole (121), the base steel member (122) is exposed, a transition plating layer (124) having substantially the same component as the surface plating layer (123) is provided on a part of the inner surface of the through-hole (121), and the transition plating layer (124) extends from one surface of the plated steel member (12) toward the inside of the through-hole (121).

Description

Bonding structure and method for manufacturing the bonding structure

[0001] The present invention relates to a bonding structure and a method for manufacturing the bonding structure. This application claims priority based on Japanese Patent Application No. 2024-177807 filed in Japan on October 10, 2024, and incorporates its content herein by reference.

[0002] In recent years, the application of aluminum die-casting to various mechanical structural parts has been promoted. Aluminum die-casting refers to an aluminum alloy casting obtained by filling molten aluminum alloy into a mold at high pressure and then cooling the aluminum alloy at high speed, or the casting method thereof. Aluminum die-casting is used, for example, as a material for automotive front shock towers, rear shock towers, and subframes.

[0003] In addition, in recent years, a manufacturing technology called gigacasting has been developed. Gigacasting is a technology for manufacturing huge parts by molding a plurality of aluminum parts as one part using large-scale casting equipment. By making parts constituting an automobile body into large-scale cast parts, the weight, manufacturing cost, and manufacturing process of the automobile can be reduced. Therefore, it is expected that the application of gigacasting will expand in the future. Furthermore, with the progress of automotive electrification, aluminum die-casting has also begun to be applied to inverter cases, battery modules, and battery packs.

[0004] The members made of aluminum die-casting exemplified above need to be joined to other members. The other members are, for example, press-formed steel plates and aluminum extrusions. For example, Patent Documents 1 to 5 disclose various methods for joining an aluminum die-cast member and another member.

[0005] Japanese Patent Application Laid-Open No. 3-86381 Japanese Patent Application Laid-Open No. 11-77192 Japanese Patent Application Laid-Open No. 59-166330 Japanese Patent Application Laid-Open No. 56-111529 Japanese Patent Application Laid-Open No. 2006-21249

[0006] It is difficult to adopt welding as a joining means between aluminum die-casting and steel. For example, when an aluminum die-cast member and a steel material are welded, brittle intermetallic compounds are generated in the weld metal. The brittle intermetallic compounds significantly reduce the joining strength of the welded part.

[0007] Another possible method of joining aluminum die-cast materials to steel is mechanical joining using fastening members. However, aluminum die-cast materials have the problem that the joint formed by mechanical joining is prone to cracking. Stress concentration easily causes deformation at the joint. Since aluminum die-cast materials have low ductility, deformation at the joint easily causes cracking of the aluminum die-cast material.

[0008] Furthermore, when joining aluminum die-cast and steel materials, galvanic corrosion becomes a problem. Galvanic corrosion is a type of corrosion that occurs when dissimilar metals are directly connected, forming a galvanic cell between them. Galvanic corrosion can be mitigated by applying a plating layer to the surface of the steel material. However, if through holes are made in the plated steel member to mechanically join the aluminum die-cast and steel material, corrosion may occur in the through holes. This is because there is no plating on the inner surface of the through holes formed by punching in the plated steel member.

[0009] By drilling holes in the steel material and then forming a plating layer, a plating layer can be provided on the inner surface of the through-holes. However, adding a plating process after drilling significantly increases the manufacturing cost of the jointed structure.

[0010] In view of the above circumstances, this disclosure provides a joint structure comprising an aluminum member that can be manufactured inexpensively and quickly without cracking, and that can suppress dissimilar metal contact corrosion at the joint, and a method for manufacturing the same.

[0011] The gist of this disclosure is as follows:

[0012] (1) A joint structure according to one aspect of the present disclosure comprises an aluminum member, a base steel member, and one or more plated steel members having a surface plating layer provided on the surface of the base steel member, wherein the aluminum member has one or more protrusions, the plated steel member has one or more through holes, the protrusions are inserted into and crimped into the through holes, the base steel member is exposed on the inner surface of the through holes, a transition plating layer having substantially the same components as the surface plating layer is provided on a part of the inner surface of the through holes, and the transition plating layer extends from one surface of the plated steel member toward the interior of the through holes. (2) Preferably, in the joint structure described in (1) above, the aluminum member is an aluminum die-cast member. (3) Preferably, in the joint structure described in (2) above, the protrusions of the aluminum member are formed during die-casting. (4) Preferably, in the joining structure described in any one of (1) to (3) above, the surface plating layer of the plated steel member is a zinc-based plating layer. (5) Preferably, in the joining structure described in (4) above, the plated steel member has a coating or chromate-free treatment layer provided on the surface of the zinc-based plating layer. (6) Preferably, in the joining structure described in any one of (1) to (5) above, the transition plating layer extends from the surface of the plated steel member on the aluminum member side toward the interior of the through hole. (7) Preferably, in the joining structure described in any one of (1) to (6) above, the through hole has a tapered shape that narrows from the base end side of the projection toward the tip side. (8) Preferably, in the joint structure described in any one of (1) to (7) above, the projection has a tapered shape that narrows from the base end to the tip end of the projection, and the cross-sectional area of ​​the base end of the projection is larger than the area of ​​the through hole on the surface of the plated steel member on the aluminum member side. (9) Preferably, in the joint structure described in any one of (1) to (8) above, the hardness H1 of the tip of the projection and the hardness H2 of the aluminum member at a location 10 mm or more away from the projection satisfy H1 ≤ 1.1 × H2.

[0013] (10) A method for manufacturing a joint structure according to another aspect of the present disclosure is a method for manufacturing a joint structure comprising an aluminum member and one or more plated steel members having a surface plating layer provided on the surface of a base steel member, comprising the steps of: forming a through hole in the plated steel member; inserting a projection of the aluminum member into the through hole; and deforming the tip of the projection while heating it to crimp the projection into the through hole, wherein when forming the through hole in the plated steel member, the surface plating layer of the plated steel member is migrated to the inner surface of the through hole to form a migration plating layer, and when crimping the projection into the through hole, the migration plating layer on the inner surface of the through hole is maintained. (11) Preferably, in the method for joining a joint structure according to (10) above, the through hole is formed by punching using a set of dies, and the clearance of the set of dies is 10 to 40% of the plate thickness of the base steel member. (12) Preferably, in the joining method for the joining structure described in (11) above, the mold to be inserted into the through hole is pushed inward from the surface of the plated steel member on the side in contact with the aluminum member. (13) Preferably, in the joining method for the joining structure described in any one of (10) to (12) above, when the tip of the projection is heated and deformed, the maximum temperature of the projection is kept below the melting point of the surface plating layer. (14) Preferably, in the joining method for the joining structure described in any one of (10) to (13) above, the projection is heated and the tip of the projection is deformed using a spot welding electrode.

[0014] According to this disclosure, a joint structure comprising an aluminum member can be manufactured inexpensively and quickly without cracking, and a method for manufacturing the same can be provided, which can also suppress dissimilar metal contact corrosion at the joint.

[0015] This is a cross-sectional view of a jointed structure. This is an enlarged cross-sectional view of the inner surface of a through-hole. This is a cross-sectional view of a jointed structure in which the cross-sectional area of ​​the base end of the projection is larger than the area of ​​the through-hole facing the aluminum member. This is a cross-sectional view of a jointed structure in which the cross-sectional area of ​​the base end of the projection is larger than the area of ​​the through-hole facing the aluminum member. This is a schematic diagram of the process of forming a through-hole. This is a schematic diagram of the process of inserting the projection into the through-hole. This is a schematic diagram of the process of deforming the tip of the projection using a direct spot welding machine. This is a schematic diagram of the process of deforming the tip of the projection using an indirect spot welding machine. This is a cross-sectional photograph of a jointed structure in which the heat input during crimping was appropriate. This is a cross-sectional photograph of a jointed structure in which the heat input during crimping was inappropriate. This is a quoted figure from Figure 2.9 "Typical Macro-Solidification Structure" on page β-3 of β3 "Processing and Processing Equipment" in "Handbook of Mechanical Engineering β. Design Edition" (edited by the Japan Society of Mechanical Engineers, Maruzen Co., Ltd., published April 30, 2008).

[0016] (1. Joining Structure 1) A joining structure 1 according to one aspect of the present disclosure comprises an aluminum member 11, a base steel member 122, and one or more plated steel members 12 having a surface plating layer 123 provided on the surface of the base steel member 122. The aluminum member 11 has one or more protrusions 111, and the plated steel member 12 has one or more through holes 121. The protrusions 111 are inserted into and crimped into the through holes 121, and the base steel member 122 is exposed on the inner surface of the through holes 121. A transition plating layer 124 having substantially the same components as the surface plating layer 123 is provided on a part of the inner surface of the through holes 121, and the transition plating layer 124 extends from one surface of the plated steel member 12 toward the interior of the through hole 121. The details of the joining structure 1 according to this embodiment will be described below with reference to Figure 1, etc.

[0017] (Aluminum Member 11) The joint structure 1 includes an aluminum member 11. The aluminum member 11 is a mechanical structural member manufactured from an aluminum alloy. Specific examples of aluminum alloys will be described later.

[0018] Various shapes can be applied to the aluminum member 11 depending on its application. Suitable examples of applications for the aluminum member 11 include front shock towers, rear shock towers, bumpers, and subframes of automobiles. Components that constitute the electrical system of electric vehicles, such as inverter cases, battery modules, and battery packs, can also be made of aluminum member 11. A single joint structure 1 may comprise two or more aluminum members 11.

[0019] (Plated steel member 12) The joint structure 1 further comprises one or more plated steel members 12. A plated steel member 12 is a mechanical structural member manufactured from plated steel. Various shapes can be applied to the plated steel member 12 depending on its application. Plated steel members 12 are mainly applied to various shapes by cold or hot press forming (hot stamping).

[0020] (Plated layer and base steel member 122) The plated steel member 12 has a base steel member 122 and a surface plating layer 123 provided on one or both surfaces of the base steel member 122. Here, in this disclosure, the "surface" of the base steel member 122 and the plated steel member 12 is a concept that does not include the "end face". For example, if the plated steel member 12 is a hot-stamped member formed by cutting a press material from a hot-stamped cold-rolled steel sheet having a plating layer, and then hot-stamping the press material, then the rolled surface of the plated steel member 12 is the "surface". The rolled surface is the surface that the cold-rolling rolls contact during the manufacture of the cold-rolled steel sheet. The "end face" of the base steel member 122 and the plated steel member 12 is the surface that connects the two surfaces. The "end face" is formed, for example, by cutting the plated steel material. The "end face" is a concept that includes the inner surface of the through hole 121, which will be described later.

[0021] In this disclosure, for the sake of clarity, the plating layer provided on the surface of the base steel member 122 is referred to as the "surface plating layer 123" and distinguished from the transition plating layer 124 described later. Furthermore, in this disclosure, the term "plating layer" is a concept that includes both the "surface plating layer 123" and the "transition plating layer 124". Specific examples of the surface plating layer 123 of the plated steel member 12 will be described later.

[0022] (Protrusion 111 and through hole 121) The aluminum member 11 has a projection 111. The plated steel member 12 has a through hole 121. The projection 111 of the aluminum member 11 is inserted through the through hole 121 of the plated steel member 12. The projection 111 is also crimped. Specifically, the projection 111 has a tip portion 1112 and a shaft portion 1111, and the tip portion 1112 is plastically deformed by the crimping process. The shaft portion 1111 is the part of the projection 111 that is located inside the through hole 121. The tip portion 1112 is the tip-side part of the projection 111 that is located outside the through hole 121.

[0023] When the projection 111 and the through hole 121 are cut along a plane perpendicular to the axial direction of the through hole 121, the diameter of the shaft portion 1111 in the cross-section is the same as or smaller than the diameter of the through hole 121. The diameter of the tip portion 1112 is enlarged by plastic deformation to be larger than the diameter of the exit of the through hole 121. The exit of the through hole 121 is the end of the through hole on the side of the tip portion 1112. The tip portion 1112 prevents the projection 111 from detaching from the through hole 121. The projection 111 has the function of joining the aluminum member 11 and the plated steel member 12, like a rivet. However, the projection 111 differs from a rivet in that it is integral with the aluminum member 11.

[0024] The tip portion 1112 is preferably formed by hot riveting. Hot riveting is riveting performed while the tip portion 1112 is softened by heat. This prevents cracking of the projection 111. However, it is not preferable to overheat the projection 111 during hot riveting, because the transition plating layer 124, described later, will disappear due to excessive heating of the projection 111.

[0025] The aluminum member 11 may have two or more protrusions 111. The plated steel member 12 may have two or more through holes 121. In this case, it is preferable that each of the multiple protrusions 111 is inserted through and crimped into the multiple through holes 121. When the protrusions 111 and through holes 121 are cut along a plane perpendicular to the axial direction of the through holes 121, the cross-sectional shapes of the protrusions 111 and through holes 121 can be, for example, a circle, an ellipse, or a polygon.

[0026] (Inner surface of through hole 121) Unlike the surface of the plated steel member 12, the base steel member 122 is exposed on the inner surface of the through hole 121 of the plated steel member 12. By plating the steel material and then drilling the hole, a through hole 121 is formed in which the base steel member 122 is exposed. Processing marks formed during the drilling process may remain on the inner surface of the through hole 121. For example, if the drilling process is a punching process, fracture marks may be formed on the inner surface of the through hole 121. However, these processing marks may disappear when the projection 111 is crimped.

[0027] (Transition Plating Layer 124) A transition plating layer 124 is provided on a portion of the inner surface of the through hole 121 of the plated steel member 12. The transition plating layer 124 covers the base steel member 122 inside the through hole 121. Therefore, in the joint structure 1 according to this embodiment, the base steel member 122 is not exposed over the entire inner surface of the through hole 121.

[0028] The difference between the transition plating layer 124 and the surface plating layer 123 described above lies in their placement. The surface plating layer 123 is placed on the surface of the base steel member 122. The transition plating layer 124 is placed on the inner surface of the through hole 121, that is, on a part of the end face of the base steel member 122. The transition plating layer 124 exists between the inner surface of the through hole 121 of the plated steel member 12 and the projection 111 of the aluminum member 11, preventing contact between the two.

[0029] The transition plating layer 124 is formed when the plating layer provided on the surface of the plated steel member 12 migrates to the inner surface of the through hole 121. Therefore, the composition of the transition plating layer 124 is substantially the same as the plating layer provided on the surface of the plated steel member 12. A small amount of iron from the base steel member 122 and aluminum from the aluminum member 11 may be mixed into the transition plating layer 124. The plating layer containing these contaminants derived from the base steel member 122 and aluminum member 11 is also considered to be the transition plating layer 124. Furthermore, the transition plating layer 124 extends from one surface of the plated steel member 12 towards the interior of the through hole 121. A surface plating layer 123 exists on the surface of the plated steel member 12 on the side where the transition plating layer 124 exists.

[0030] An example of a transition plating layer 124 is a burr 1211 formed during punching. Punching is the cutting of a material by applying shear force between a set of blades (die 3). A burr 1211 is a shrinkage of the material caused by pressing a tool such as the die 3 into it. Figure 2 shows a schematic diagram of the inner surface of a through hole 121 in which a burr 1211 has been formed by punching. In the plated steel member 12 shown in Figure 2, the die 3 on the left side of the paper is pressed downwards. As a result, the die 3 on the left side of the paper cuts off a part of the plated steel member 12, forming a through hole 121.

[0031] During the formation of the through hole 121, the end face of the plated steel member 12 undergoes plastic deformation in the direction in which the mold 3 on the left side is pressed. The downward arrow in Figure 2 indicates the direction in which the mold 3 on the left side is pressed. As a result, a sag 1211 is formed on the upper side of the plated steel member 12 in Figure 2. Additionally, a burr 1212 is formed on the lower side of the plated steel member 12 in Figure 2.

[0032] The inventors have found that when the clearance C between a set of dies 3 is within a specific range, the die 3 transfers the surface plating layer 123 onto the sag 1211. This forms a transfer plating layer 124 that extends from one surface of the plated steel member 12 into the interior of the through hole 121. Preferred conditions for the punching process will be described later.

[0033] Furthermore, according to various experimental results by the inventors, the transition plating layer 124 formed during the drilling process may disappear when the tip of the projection 111 is hot-crimped. Figure 9 shows a cross-sectional photograph of an example where the amount of heat input during hot-crimping was appropriate, and Figure 10 shows a cross-sectional photograph of an example where the amount of heat input during hot-crimping was excessive. In the manufacturing of the example in Figure 10, the transition plating layer 124 was formed during the drilling process. However, in the example in Figure 10, the transition plating layer 124 disappeared during hot-crimping. Therefore, in the example in Figure 10, the transition plating layer 124 could not be confirmed in the cross-sectional analysis of the through-hole 121.

[0034] Therefore, in order to provide the transition plating layer 124 on the joint structure 1, it is necessary to (1) form a sufficient amount of the transition plating layer 124 during the drilling process, and (2) not lose the transition plating layer 124 during the crimping process.

[0035] (Effects) In the joint structure 1 according to this embodiment, the projection 111 of the aluminum member 11 and the through hole 121 of the plated steel member 12 form a joint by crimping. Therefore, welding between the aluminum member 11 and the plated steel member 12 is not required.

[0036] Furthermore, in the joining structure 1 according to this embodiment, the projection 111 is part of the aluminum member 11. Therefore, in the process of joining the aluminum member 11 and the plated steel member 12, it is not necessary to assemble the projection 111 to the aluminum member 11. Consequently, the manufacturing of the joining structure 1 according to this embodiment is easy.

[0037] Furthermore, as shown in Figures 6 and 7 described later, the tip of the projection 111A provided on the aluminum member 11 before it is joined to the plated steel member 12 can be crimped using a spot welding machine, which is a general-purpose piece of equipment. A spot welding machine has a spot welding electrode 2, a pressurizing device for moving the spot welding electrode 2, and a transformer for supplying current to the spot welding electrode 2. The spot welding electrode 2 applies pressure while locally heating the material to be welded by applying current.

[0038] A spot welding machine can be easily adapted for crimping the projection 111 of the aluminum member 11. The spot welding machine can electrically heat the projection 111 of the aluminum member 11 that has been inserted into the through hole 121 of the plated steel member 12. This heats the tip of the projection 111, allowing it to be thermally softened. The spot welding machine can also apply pressure to the projection 111 of the aluminum member 11. By applying pressure to the tip 1112 of the thermally softened projection 111, the tip 1112 can be easily plastically deformed. Therefore, in manufacturing the joined structure 1 according to this disclosure, no special equipment for joining is required. Joining can be performed using a spot welding machine, which is a general-purpose welding device. However, as will be described later, when crimping the projection 111 into the through hole 121, it is necessary to select heat input conditions that can maintain the transition plating layer 124 on the inner surface of the through hole 121.

[0039] Furthermore, crimping using a spot welding machine can be performed inexpensively and quickly, and does not cause cracks in the protrusions 111. Electrical heating using electrodes can cause thermal softening of the tip 1112 of the protrusions 111 of the aluminum member 11 within a few seconds. Therefore, the crimping work can be completed very quickly and inexpensively. In addition, although the aluminum alloy that makes up the aluminum member 11 is prone to cracking during plastic deformation, the thermally softened aluminum alloy does not crack due to plastic deformation.

[0040] Furthermore, in the joint structure 1 according to this embodiment, the transition plating layer 124 suppresses galvanic corrosion. If there is no transition plating layer 124 on the inner surface of the through hole 121, the exposed base steel member 122 on the inner surface of the through hole 121 and the protrusion 111 of the aluminum member 11 will come into contact. Galvanic corrosion is highly likely to occur at the contact point. However, the transition plating layer 124 arranged on the inner surface of the through hole 121 reduces the contact area between the base steel member 122 and the aluminum member 11, thereby suppressing galvanic corrosion.

[0041] In addition, when manufacturing the joining structure 1, there is no need to provide an additional procedure for forming the transition plating layer 124. For example, a punching process with the clearance C amount within a predetermined range can simultaneously perform both the formation of the through hole 121 and the formation of the transition plating layer 124. Therefore, the transition plating layer 124 of the joining structure 1 according to the present embodiment does not complicate its manufacturing process.

[0042] For the above reasons, the joining structure 1 according to the present embodiment can be manufactured at a low cost and without cracking in a short time, and can suppress the contact corrosion of dissimilar metals at the joint.

[0043] As described above, the most basic aspect of the joining structure 1 according to the present embodiment has been explained. Hereinafter, more preferable aspects will be explained.

[0044] (Aluminum die-cast member) A preferred example of the aluminum member 11 is an aluminum die-cast member. An aluminum die-cast member is a mechanical structure member composed of aluminum die-casting. Aluminum die-casting is an aluminum alloy casting obtained by filling a molten aluminum alloy into a mold at high pressure and then cooling the aluminum alloy at high speed. The aluminum die-cast member is excellent in strength and can be manufactured in a short time.

[0045] When observing the cross-section of the aluminum die-cast member, a fibrous metal structure called metal flow can be observed. The metal flow is a trace of the flow of molten aluminum during casting. The aluminum member 11 having the metal flow is regarded as an aluminum die-cast member. The cross-section for observing the metal flow is preferably formed parallel to the surface of the aluminum member 11.

[0046] Specific examples of the aluminum alloy constituting the aluminum member 11 are ADC10, ADC12, AC4CH, AC4C Al—Si—Mg-based alloy, and Al—Mg—Si—Mn-based alloy.

[0047] (Metal flow of the protrusion 111) The manufacturing method of the protrusion 111 is not limited. For example, the protrusion 111 can be formed by cutting the aluminum member 11 or welding a protrusion 111 product manufactured separately from the aluminum member 11 to the aluminum member 11.

[0048] When the aluminum member 11 is a die-cast member, it is preferable that the protrusion 111 of the aluminum member 11 is formed during die-casting. Thereby, the man-hour required for forming the protrusion 111 can be reduced, and cracks in the protrusion 111 and its periphery can be suppressed.

[0049] When the cross-section of the protrusion 111 of the aluminum member 11 formed during die-casting is corroded and observed, a metal flow can be visually recognized inside the protrusion 111. The cross-section is corroded using a mixture of water and ammonia at a volume ratio of 10% with respect to ammonia, or Keller's solution. The protrusion 111 having a metal flow has chill crystals on its surface layer and columnar crystals inside. Furthermore, equiaxed crystals may exist inside the metal flow. The columnar crystals are radially present from the inside to the outside of the protrusion 111. Note that the cross-section for observing the metal flow of the protrusion is preferably along the plate thickness direction of the plated steel member passing through the central axis of the protrusion. The cross-section is preferably observed at a magnification of 50 times using, for example, an optical microscope.

[0050] The shapes of the chill crystals, columnar crystals, and equiaxed crystals are schematically shown, for example, in FIG. 2.9, “Typical Macroscopic Solidification Structure” on page β-3 of Part β3, “Processing Science and Processing Equipment” of “Handbook of Mechanical Engineering, β. Design Edition” (edited by the Japan Society of Mechanical Engineers, Incorporated Association, published by Maruzen Co., Ltd. on April 30, 2008). For reference, this figure is cited in FIG. 11 of the present disclosure. By observing the corroded cross-section, the chill crystals, columnar crystals, and equiaxed crystals can be identified. Also, the protrusion 111 in which the crystals are arranged as shown in FIGS. (a) and (b) of the drawing is considered to be the protrusion 111 formed during die-casting.

[0051] Further, the protrusion 111 formed during die-casting is integrally formed with the aluminum member 11. Therefore, the protrusion 111 having a metal flow extending along the surface of the protrusion 111 and integrally formed with the aluminum member 11 is considered to be the protrusion 111 formed during die-casting.

[0052] Metal flow may also be observed in the cross-section of the protrusion 111 formed by cutting. However, if the protrusion is formed by casting and then subjected to machining such as cutting, the chill crystals may be removed by cutting. In that case, the protrusion 111 will consist only of columnar crystals, or of columnar crystals and equiaxed crystals. In addition, cutting marks may remain on the surface of the protrusion 111 formed by cutting. Therefore, the protrusion 111 formed by cutting and the protrusion 111 formed during die casting can be distinguished by surface observation and cross-sectional observation.

[0053] (Material of plated steel member 12) The material of the plated steel member 12 is not particularly limited. Preferred examples of plated steel member 12 are aluminum-based plated steel and zinc-based plated steel. Aluminum-based plated steel is a steel sheet having a base steel material and an aluminum-based plating layer provided on the surface of the base steel material, wherein the average concentration of aluminum in the plating layer is 20% by mass or more. Zinc-based plated steel is a steel sheet having a base steel material and a zinc-based plating layer provided on the surface of the base steel material, wherein the average concentration of zinc in the plating layer is 30% or more. Both the aluminum-based plating layer and the zinc-based plating layer exhibit the effect of further suppressing galvanic corrosion between the base steel material and the aluminum member 11.

[0054] A specific example of aluminum-plated steel is aluminum-plated hot-stamped steel sheet. Specific examples of zinc-plated steel are zinc-plated hot-stamped steel sheet, GA-plated (alloyed hot-dip galvanized) steel sheet, GI-plated (hot-dip galvanized) steel sheet, EG-plated (electro-galvanized) steel sheet, Zn-Ni-plated steel sheet, Zn-Al-Mg-plated steel sheet, and Zn-Mg-plated steel sheet.

[0055] The plated steel member 12 may further have a coating or chromate-free treatment layer provided on the surface of the zinc-based plating layer. Both the coating and the chromate-free treatment layer contribute to ensuring the corrosion resistance of the joint structure 1 and further suppressing galvanic corrosion between the base steel material and the aluminum member 11. A preferred example of the coating is an electrodeposited coating.

[0056] (Position of the transition plating layer 124) The transition plating layer 124 is preferably located on the surface of the plated steel member 12 on the side of the aluminum member 11, extending into the interior of the through hole 121, as shown in Figure 1. "The surface of the plated steel member 12 on the side of the aluminum member 11" refers to the surface of the plated steel member 12 at the mating surface between the plated steel member 12 and the aluminum member 11.

[0057] Dissimilar metal contact corrosion on the surface of the plated steel member 12 on the side of the aluminum member 11 tends to be more pronounced than on the surface of the plated steel member 12 on the side opposite to the aluminum member 11. Therefore, by applying a transition plating layer 124 to the surface of the plated steel member 12 on the side of the aluminum member 11, dissimilar metal contact corrosion can be further suppressed.

[0058] (Tapered shape of through hole 121 and / or projection 111) Preferably, the through hole 121 has a tapered shape that narrows from the base end 1113 of the projection 111 to the tip. By applying a tapered shape to the through hole 121, it becomes easier to form a migration plating layer 124 on the inner surface of the through hole 121. This makes it easier to leave an extra layer of migration plating layer 124 after hot riveting. As a result, dissimilar metal contact corrosion in the joined structure 1 is further suppressed.

[0059] Preferably, as shown in Figure 3, the projection 111 has a tapered shape that narrows from the base end 1113 towards the tip. In this case, it is even more preferable that the cross-sectional area of ​​the base end 1113 of the projection 111 is larger than the area of ​​the through hole 121 on the surface of the plated steel member 12 on the aluminum member 11 side. Furthermore, it is preferable that the transition plating layer 124 extends from the surface of the plated steel member 12 on the aluminum member 11 side towards the interior of the through hole 121.

[0060] "The cross-sectional area of ​​the base end 1113 of the projection 111" refers to the area of ​​the cut surface when the projection 111 is separated from the aluminum member 11 along the surface on which the projection 111 is provided. The cross-sectional area of ​​the base end 1113 of the projection 111 can be measured by cutting the projection 111 along the dashed line labeled A shown in Figure 3. "The area of ​​the through hole 121 on the surface of the plated steel member 12 on the aluminum member 11 side" refers to the area of ​​the through hole 121 at the mating surface between the plated steel member 12 and the aluminum member 11. The area of ​​the through hole 121 measured along the dashed line labeled B shown in Figure 3 is the area of ​​the through hole 121 on the surface of the plated steel member 12 on the aluminum member 11 side.

[0061] In the configuration illustrated in Figure 3, the contact portion between the projection 111 and the through hole 121 is the end of the through hole 121 on the surface of the plated steel member 12 on the aluminum member 11 side. Furthermore, a transition plating layer 124 is provided in this area. Therefore, in the configuration illustrated in Figure 3, the transition plating layer 124 is provided in the contact portion between the projection 111 and the through hole 121, which is an area where galvanic corrosion is likely to occur. As a result, galvanic corrosion is further suppressed.

[0062] Furthermore, as illustrated in Figure 4, a tapered shape can also be applied to both the projection 111 and the through hole 121. In this case as well, it is even more preferable that the cross-sectional area of ​​the base end 1113 of the projection 111 is larger than the area of ​​the through hole 121 on the surface of the plated steel member 12 on the aluminum member 11 side. It is also preferable that the transition plating layer 124 extends from the surface of the plated steel member 12 on the aluminum member 11 side toward the interior of the through hole 121. In this case, the transition plating layer 124 flows more easily into the interior of the through hole 121, and the area of ​​the exposed base material is reduced. This further suppresses galvanic corrosion.

[0063] (Hot riveting) Preferably, the projection 111 is hot riveted. The tip 1112 of the projection 111 is a hot riveted portion. Hot riveting can suppress cracking of the projection 111 during the riveting process. In addition, hot riveting prevents work hardening of the tip 1112.

[0064] Whether the projection 111 is manufactured by hot riveting or cold riveting can be determined based on the presence or absence of work hardening at the tip portion 1112. Work hardening is significantly observed at the tip portion 1112 of a cold-riveted projection 111. If the hardness H1 of the tip portion 1112 of the projection 111 and the hardness H2 of the aluminum member 11 at a location 10 mm or more away from the projection 111 satisfy H1 ≤ 1.1 × H2, the projection 111 is considered to have been hot-riveted.

[0065] The hardness H1 of the tip 1112 of the projection 111 is measured in the cross-section of the projection 111. The cross-section passes through approximately the center of the projection 111 and is formed parallel to the surface of the aluminum member 11. The maximum value of the Vickers hardness at any five locations in the cross-section of the tip 1112 of the projection 111 is considered to be H1. The hardness H2 of the aluminum member 11 is measured in a cross-section perpendicular to the surface of the aluminum member 11. "Surface" refers to the surface on which the projection 111 is provided. The measurement position for H2 is any location that satisfies the following requirements: (1) A position at the center of the thickness of the aluminum member 11, or a depth equivalent thereto. (2) A position at least 10 mm away from the projection 111 along the surface of the aluminum member 11. The above (1) will be explained. For example, if the aluminum member 11 is a plate-shaped member with thickness t, the measurement position for H2 will be at a depth of t / 2 from the surface of the aluminum member 11. Next, the above (2) will be explained. For example, when measuring H2 in a cross-section passing through the center of the projection 111 and perpendicular to the surface of the aluminum member 11, as shown in Figure 1, the measurement position for H2 should be at least 10 mm away from 1113 in the leftward direction of the paper. The average value of the Vickers hardness of the aluminum member 11 measured at any five locations that satisfy the above requirements shall be considered as H2. The test force used during Vickers hardness measurement shall be the same for all measurements.

[0066] (2. Method for Manufacturing Joined Structure 1) A method for manufacturing a joined structure 1 according to another aspect of the present disclosure is a method for manufacturing a joined structure 1 having an aluminum member 11 and one or more plated steel members 12 having a base steel member 122 and a surface plating layer 123 provided on its surface, comprising the steps of forming a through hole 121 in the plated steel member 12, inserting a projection 111A of the aluminum member 11 into the through hole 121, and deforming the tip of the projection 111A while heating it to crimp the projection 111A into the through hole 121, wherein when forming the through hole 121 in the plated steel member, the surface plating layer 123 of the plated steel member is migrated to the inner surface of the through hole 121 to form a migration plating layer 124, and when crimping the projection 111A into the through hole 121, the migration plating layer 124 on the inner surface of the through hole 121 is maintained. The details of the method for manufacturing a joined structure 1 according to this embodiment will be described below. Furthermore, the preferred embodiments of the joint structure 1 described above can also be applied to the manufacturing method of the joint structure 1 according to this embodiment.

[0067] (Aluminum member 11 and plated steel member 12) In the manufacturing method of the joined structure 1 according to this embodiment, the aluminum member 11 and the plated steel member 12 are joined together. The aluminum member 11 has one or more protrusions 111A. The protrusions 111A before crimping do not have a tip portion 1112. In the joined structure 1, the protrusions 111A are inserted through holes 121. Therefore, it is necessary to appropriately select the position of the protrusions 111A.

[0068] (S1 Formation of through hole 121) First, as shown in Figure 5, a through hole 121 is formed in the plated steel member 12. The position of the through hole 121 corresponds to the position of the projection 111A. When forming the through hole 121 in the plated steel member, the surface plating layer 123 of the plated steel member is migrated to the inner surface of the through hole 121 to form a migration plating layer 124. The means for forming the through hole 121 are not particularly limited. However, when forming the through hole 121, it is necessary to optimize the processing conditions so that a sufficient amount of the surface plating layer 123 is migrated into the interior of the through hole 121.

[0069] As shown in Figure 2, when the means for forming the through-hole 121 is punching, the clearance C, which is the distance between a set of dies 3, is set to 10 to 40% of the plate thickness of the base steel member. If the clearance C is less than 10%, the amount of surface plating layer 123 transferred will be small, and a sufficient amount of transferred plating layer 124 cannot be obtained. More preferably, the lower limit is 12% or more, 15% or more, 18% or more, or 20% or more. On the other hand, if the clearance C is greater than 40%, it becomes difficult to form the through-hole 121. More preferably, the upper limit is 35% or less, or 30% or less.

[0070] (S2 Insertion of projection 111A into through hole 121) Next, as shown in Figure 6, the projection 111A of the aluminum member 11 is inserted into the through hole 121.

[0071] As shown in Figure 6, an adhesive may be provided between the plated steel member 12 and the aluminum member 11 to bond them together. In this case, the adhesive is applied to one or both of the aluminum member 11 and the plated steel member 12 before inserting the projection 111A through the through hole 121. Then, while inserting the projection 111A through the through hole 121, the area on one member to which the adhesive 13 has been applied is pressed against the surface of the other member. This allows the two members to be bonded together.

[0072] (S3 Deformation of the tip of projection 111A) Then, the tip of projection 111A is deformed as shown in Figure 7 or Figure 8. This causes projection 111A to be crimped into the through hole 121. As projection 111A is crimped into the through hole 121, tip portion 1112 is formed, and the aluminum member 11 and plated steel member 12 are joined together.

[0073] When deforming the tip of the projection 111A, the projection 111A is heated. This softens the projection 111A and reduces its deformation resistance. The reduction in deformation resistance suppresses cracking of the projection 111A during crimping.

[0074] However, when crimping the projection 111A into the through hole 121, it is necessary to maintain the migration plating layer 124 on the inner surface of the through hole 121. For example, if the amount of heat input to the projection 111A is too large, the migration plating layer 124 provided in the through hole 121 will melt or evaporate and disappear. For example, in the joint structure 1 shown in Figure 10, the amount of heat input during hot crimping was excessive, causing the migration plating layer 124 to disappear. As a result, the migration plating layer 124 could not be confirmed in the cross-sectional analysis of the through hole 121.

[0075] From the viewpoint of reducing the deformation resistance of the tip of the projection 111A and preventing cracking of the projection 111A, a larger amount of heat input to the projection 111A is preferable. However, from the viewpoint of maintaining the transition plating layer 124, a smaller amount of heat input to the projection 111A is preferable. Therefore, it is preferable to determine the optimal amount of heat input by repeatedly performing crimping tests and cross-sectional observations under various conditions.

[0076] Furthermore, the maximum temperature of the projection 111A can be estimated through simulation. Therefore, when deforming the tip of the projection 111A while heating it, conditions can be estimated and adopted such that the maximum temperature of the projection 111A is below the melting point of the surface plating layer 123.

[0077] A preferred example of a heating means for the projection 111A is a spot welding electrode 2. The spot welding electrode 2 is a rod-shaped electrode made of copper alloy that directly contacts the base material during spot welding, conducting the welding current and transmitting the applied pressure. However, in the manufacturing method of the joint structure 1 according to this embodiment, the spot welding electrode 2 is not used for welding the plated steel member 12 and the aluminum member 11. The spot welding electrode 2 is applied while current is flowing through the projection 111A and pressure is applied. The projection 111A is softened by the resistive heat generated by the current. By applying pressure to the projection 111A in a softened state, the tip of the projection 111A is easily deformed, and a tip portion 1112 that crimps the through hole 121 is formed.

[0078] The crimping of the projection 111A using the spot welding electrode 2 may be performed by a direct spot welding machine or an indirect spot welding machine. In JIS Z 3001-6:2013 "Welding Terminology - Part 6: Resistance Welding", direct spot welding is defined as spot welding performed by directly applying pressure to the weld joint with an electrode and passing a welding current in the plate thickness direction. In the same standard, indirect spot welding is defined as spot welding that creates only one nugget in the base material directly below the electrode using a current flow method similar to series currenting. The following describes specific examples of crimping work performed by a direct spot welding machine or an indirect spot welding machine.

[0079] (Crimping operation using a direct spot welding machine) When crimping the projection 111A using a direct spot welding machine, the projection 111A is sandwiched between a pair of spot welding electrodes 2, as illustrated in Figure 7. The tip of one spot welding electrode 2 is positioned at the tip of the projection 111A. The tip of the other spot welding electrode 2 is positioned on the surface of the aluminum member 11 opposite to the projection 111A. The central axes of the pair of spot welding electrodes 2 are aligned. Then, while passing current between the pair of spot welding electrodes 2, the spot welding electrodes 2 are moved to narrow the distance between the electrodes. As a result, the tip of the projection 111A is crushed, and a tip portion 1112 having a diameter larger than the through hole 121 is formed.

[0080] (Crimping operation using an indirect spot welding machine) When crimping the projection 111A using an indirect spot welding machine, a pair of spot welding electrodes 2 are arranged in parallel, as illustrated in Figure 8. The tip of one spot welding electrode 2 is placed on the tip of the projection 111A. The tip of the other spot welding electrode 2 is placed on the surface of the aluminum member 11 on the side where the projection 111A is provided. The central axes of the pair of spot welding electrodes 2 are not aligned. Then, while passing current between the pair of spot welding electrodes 2, the spot electrode placed on the tip of the projection 111A is pressed against the projection 111A. As a result, the tip of the projection 111A is crushed, and a tip portion 1112 having a diameter larger than the through hole 121 is formed.

[0081] Crimping using a direct spot welding machine is preferable because it can be performed easily and reliably. However, when crimping using a direct spot welding machine, the spot welding electrode 2 must be positioned on the surface of the aluminum member 11 opposite to the projection 111A. For example, if the aluminum member 11 has a closed cross-sectional structure, crimping using a direct spot welding machine may not be possible. Crimping using an indirect spot welding machine is suitable in such cases. This is because when crimping using an indirect spot welding machine, both of the pair of spot welding electrodes 2 are positioned on the side where the projection 111A is provided.

[0082] The power supply for the spot welding machine is preferably a single-phase AC power supply, a DC inverter power supply, or an AC inverter power supply. The tip of the spot welding electrode 2 is preferably flat, but the tip may have curvature. The material of the tip of the spot welding electrode 2 is preferably chromium copper, alumina-dispersed copper, zirconium copper, chromium-zirconium copper, and beryllium copper.

[0083] The optimal energizing conditions vary depending on the size of the projection 111A of the aluminum member 11 before crimping, the diameter and depth of the through hole 121 of the plated steel member 12, the composition and thickness of the surface plating layer 123 of the plated steel member 12, and the clearance C when forming the through hole 121 in the plated steel member 12.

[0084] (Effects) In the manufacturing method of the jointed structure 1 according to this embodiment, a transition plating layer 124 for preventing dissimilar metal contact corrosion can be formed simultaneously with the through hole 121. Furthermore, in the manufacturing method of the jointed structure 1 according to this embodiment, the protrusion 111A can be crimped without cracking using a spot welding machine, which is a general-purpose manufacturing equipment. For these reasons, the manufacturing method of the jointed structure 1 according to this embodiment can be manufactured inexpensively and quickly without cracking, and dissimilar metal contact corrosion at the joint can be suppressed.

[0085] While embodiments of the present disclosure have been described above, the disclosure is not limited thereto and can be modified as appropriate without departing from the technical idea. Further preferred examples of the joint structure 1 and its manufacturing method according to the present embodiment will be described below.

[0086] (Diameter and depth of through-hole 121) The diameter of the through-hole 121 provided in the plated steel member 12 is preferably, for example, 3.0 to 25.0 mm. The diameter of the through-hole 121 is the diameter of the through-hole 121 if it is circular, and the maximum diameter if the through-hole 121 is elliptical or polygonal in shape. If the through-hole 121 has a tapered shape, it is preferable that the maximum and minimum diameters of the through-hole 121 are within the above range.

[0087] The larger the through hole 121, the easier it is to insert the projection 111 into the through hole 121. Also, the larger the through hole 121, the larger the diameter of the shaft portion 1111 that ensures the joint strength can be. This increases the joint strength during joining. On the other hand, the smaller the through hole 121, the thinner the projection 111 can be. This makes it easier to deform the projection 111A.

[0088] The depth of the through-hole 121 can be appropriately selected according to the shape of the plated steel member 12. The depth of the through-hole 121 is the same as the thickness of the plated steel member 12 at the location where the through-hole 121 is provided. From the viewpoint of facilitating the crimping work, it is preferable that the depth of the through-hole 121 be 5.0 mm or less. From the viewpoint of ensuring joint strength, it is preferable that the depth of the through-hole 121 be 0.6 mm or more. If the plated steel member 12 is plate-shaped, the through-hole 121 can be provided at any location on the plated steel member 12. On the other hand, if the plated steel member 12 is not plate-shaped, a plate-shaped flange portion can be provided on the plated steel member 12, and the through-hole 121 can be provided on the flange portion.

[0089] (Diameter of the shaft portion 1111 of the projection 111) In the joint structure 1, the maximum diameter of the shaft portion 1111 of the projection 111 provided on the aluminum member 11 may be the same as the diameter of the through hole 121. This is because the diameter of the shaft portion 1111 expands when the tip of the projection 111 is deformed. However, as shown in Figures 6 to 8, adhesive 13 may be applied between the aluminum member 11 and the plated steel member 12. In this case, the adhesive 13 may flow between the shaft portion 1111 and the inner wall of the through hole 121, and the diameter of the shaft portion 1111 of the projection 111 may become smaller than the diameter of the through hole 121. In the joint structure 1, preferred examples of the diameter and length of the shaft portion 1111 of the projection 111 are similar to the diameter and depth of the through hole 121 described above.

[0090] The diameter of the projection 111 before its tip is deformed is preferably smaller than the diameter of the through hole 121. The difference between the diameter of the projection 111 and the diameter of the through hole 121 is preferably 0.3 mm or more. This makes it easier to insert the projection 111 into the through hole 121.

[0091] More preferably, the diameter of the projection 111 before deformation of the tip is smaller than the diameter of the through hole 121, and the difference between the two is in the range of 0.5 to 2.5 mm. This allows the adhesive 13 to flow between the projection 111 and the through hole 121. The adhesive 13 placed between the projection 111 and the through hole 121 further suppresses galvanic corrosion between the plated steel member 12 and the aluminum member 11. Note that the diameter of the projection 111 is its diameter if the projection 111 is circular, and its maximum diameter if the projection 111 is elliptical or polygonal in shape.

[0092] (Amount of protrusion of projection 111 before deformation of the tip) The amount of protrusion of projection 111 before deformation of the tip is preferably 3.0 to 15.0 mm. The amount of protrusion is the distance between the surface of the plated steel member 12 that is not in contact with the aluminum member 11 and the tip of projection 111 when projection 111 is inserted into the through hole 121 before deformation of the tip. If the plated steel member 12 and the aluminum member 11 come into contact around projection 111 when projection 111 is inserted into the through hole 121, the amount of protrusion of projection 111 will be the length of projection 111 minus the depth of the through hole 121. If a gap is formed between the plated steel member 12 and the aluminum member 11 around projection 111 when projection 111 is inserted into the through hole 121, as illustrated in Figure 4, the amount of protrusion of projection 111 will be the length of projection 111 minus the depth of the through hole 121 and the thickness of the gap.

[0093] Furthermore, when measuring the amount of protrusion of the projection 111 before the tip is deformed, the adhesive 13 is not applied. In other words, the thickness of the adhesive 13 is not considered when determining the amount of protrusion of the projection 111 before the tip is deformed. This is because the thickness of the adhesive 13 varies depending on the pressure applied when bonding the plated steel member 12 and the aluminum member 11.

[0094] The smaller the protrusion, the easier it is to deform the tip of the projection 111. On the other hand, the larger the protrusion, the larger the diameter of the tip 1112, and the greater the joint strength.

[0095] (Shape of the tip portion 1112) The diameter of the tip portion 1112 is preferably larger than the diameter of the through hole 121, and the difference between the two is 1.5 mm or more. When the tip portion 1112 is circular when viewed in plan along the axial direction of the through hole 121, the diameter of the tip portion 1112 is its diameter. When the tip portion 1112 is elliptical or polygonal when viewed in plan along the axial direction of the through hole 121, the diameter of the tip portion 1112 is the diameter of the smallest circle that circumscribes the tip portion 1112. Furthermore, the thickness of the tip portion 1112 is preferably 1.0 to 9.0 mm. The thickness of the tip portion 1112 is the distance between the surface of the plated steel member 12 and the tip of the projection 111 in the joint structure 1.

[0096] The larger the diameter and thickness of the tip portion 1112, the greater the joint strength. The smaller the diameter and thickness of the tip portion 1112, the easier it is to deform the tip of the projection portion 111.

[0097] (Adhesive 13) The joint structure 1 may further include an adhesive 13 placed between the aluminum member 11 and the plated steel member 12. The adhesive further improves the joint strength between the aluminum member 11 and the plated steel member 12. The type of adhesive 13 is not particularly limited. Preferred examples of adhesive 13 are structural epoxy adhesives, rubber adhesives, and urethane adhesives. Adhesive 13 may also be a structural adhesive with excellent vibration damping properties, which is a composite of epoxy and rubber. Adhesive 13 may also be a rubber-based sealant that has airtight, dustproof, and waterproof functions.

[0098] (Amount of exposed base steel member 122 on the inner surface of the through hole 121) The base steel member 122 is exposed on the inner surface of the through hole 121. It is preferable that the amount of exposed base steel member 122 be small. For example, it is preferable that the amount of exposed base steel member 122 is 80% or less of the inner surface of the through hole 121. This further suppresses galvanic corrosion.

[0099] The amount of exposed base steel member 122 is evaluated by the following procedure. First, the through hole 121 is cut along a plane that passes through the center of the through hole 121 and is perpendicular to the mating surface between the plated steel member 12 and the aluminum member 11. If the through hole 121 is not circular, the centroid of the through hole 121 is considered to be the center of the through hole 121. Next, the cross section is observed with an optical microscope or electron microscope. If necessary, an elemental distribution mapping image of the cross section is taken. Based on the cross section observation results, the position of the transition plating layer 124 and the position where the base steel member 122 is exposed are identified. Then, the length of the region where the base steel member 122 is exposed is measured along the thickness direction of the plated steel member 12. The value obtained by dividing the length of the region where the base steel member 122 is exposed by the thickness of the plated steel member 12 is considered to be the amount of exposed base steel member 122.

[0100] The effects of one aspect of this disclosure will be further illustrated by the examples. However, the conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effectiveness of this disclosure. This disclosure is not limited to these examples of conditions. This disclosure may adopt various conditions as long as they do not depart from its gist and achieve its objectives.

[0101] Two jointed structures were manufactured, each comprising an aluminum member and one or more plated steel members having a surface plating layer applied to the surface of a base steel member. The surface plating layer was a Zn plating layer.

[0102] The manufacturing method comprises the steps of forming a through hole in a plated steel member, inserting a projection of an aluminum member into the through hole, and crimping the projection into the through hole by heating and deforming its tip. Furthermore, when forming the through hole in the plated steel member, the surface plating layer of the plated steel member was migrated to the inner surface of the through hole to form a migration plating layer.

[0103] In the manufacturing of the two jointed structures, the conditions for forming the through-holes were the same. However, the conditions for crimping the protrusions into the through-holes differed as follows. In both conditions, the crimping method was a direct spot welding device.

[0104]

[0105] Figure 9 shows cross-sectional photographs of the protrusions and through holes of the joint structure obtained under crimping condition 1. Figure 10 shows cross-sectional photographs of the protrusions and through holes of the joint structure obtained under crimping condition 2. In both examples in Figure 9 and Figure 10, the plated steel member 12 was punched out from the top to the bottom of the paper. In Figures 9 and 10, (A) is a low-magnification SEM cross-sectional photograph. (B) is a high-magnification SEM cross-sectional photograph of the area enclosed by the dashed line in (A). (C) is a mapping image of the Zn concentration in the area enclosed by the dashed line in (A). (D) is a mapping image of the Fe concentration in the area enclosed by the dashed line in (A). The conditions for taking the cross-sectional photographs were as follows. • Device model number: JSM-IT300 (JEOL Ltd.) • EDS detector: JED-2300 x 2 (JEOL Ltd.) • Acceleration voltage: 15kV • Current setting value: 70 • Working distance: 10mm

[0106] Under crimping condition 1, the amount of heat input to the protrusion was within the appropriate range. A transition plating layer was provided on the inner surface of the through hole obtained by crimping condition 1. The Zn concentration mapping image shown in Figure 9(C) shows a high Zn concentration region extending in the vertical direction. This high Zn concentration region is located at the boundary between the shaft portion of the protrusion and the base steel member of the plated steel member. This high Zn concentration region is the transition plating layer.

[0107] Under crimping condition 2, the heat input to the protrusion was excessive. No transition plating layer was present on the inner surface of the through-hole obtained under crimping condition 2. No high-Zn concentration regions were observed in the Zn concentration mapping image shown in Figure 10(C).

[0108] 1 Joining structure 11 Aluminum member 111 Projection 111A Projection before crimping 1111 Shaft 1112 Tip 1113 Base 12 Plated steel member 121 Through hole 1211 Sagging 1212 Burr 122 Raw steel member 123 Surface plating layer 124 Transition plating layer 13 Adhesive 2 Spot welding electrode 3 Mold C Clearance

Claims

1. A joint structure comprising: an aluminum member; a base steel member; and one or more plated steel members having a surface plating layer provided on the surface of the base steel member, wherein the aluminum member has one or more protrusions; the plated steel member has one or more through holes; the protrusions are inserted into and crimped into the through holes; the base steel member is exposed on the inner surface of the through holes; a transition plating layer having substantially the same components as the surface plating layer is provided on a part of the inner surface of the through holes; and the transition plating layer extends from one surface of the plated steel member toward the interior of the through holes.

2. The joint structure according to claim 1, characterized in that the aluminum member is an aluminum die-cast member.

3. The joint structure according to claim 2, characterized in that the projection of the aluminum member is formed during die casting.

4. The joint structure according to any one of claims 1 to 3, characterized in that the surface plating layer of the plated steel member is a zinc-based plating layer.

5. The joint structure according to claim 4, characterized in that the plated steel member has a coating or chromate-free treatment layer provided on the surface of the zinc-based plating layer.

6. The joining structure according to any one of claims 1 to 3, characterized in that the transition plating layer extends from the surface of the plated steel member on the aluminum member side toward the interior of the through hole.

7. The joint structure according to any one of claims 1 to 3, characterized in that the through hole has a tapered shape that narrows from the base end side to the tip side of the projection.

8. The joint structure according to claim 6, characterized in that the projection has a tapered shape that narrows from the base end to the tip, and the cross-sectional area of ​​the base end of the projection is larger than the area of ​​the through hole on the surface of the plated steel member on the aluminum member side.

9. The joint structure according to any one of claims 1 to 3, characterized in that the hardness H1 of the tip of the projection and the hardness H2 of the aluminum member at a location 10 mm or more away from the projection satisfy H1 ≤ 1.1 × H2.

10. A method for manufacturing a joint structure comprising an aluminum member and one or more plated steel members having a surface plating layer provided on the surface of a base steel member, the method comprising: forming a through hole in the plated steel member; inserting a projection of the aluminum member into the through hole; and deforming the tip of the projection while heating it to crimp the projection into the through hole, wherein when forming the through hole in the plated steel member, the surface plating layer of the plated steel member is migrated to the inner surface of the through hole to form a migration plating layer, and when crimping the projection into the through hole, the migration plating layer on the inner surface of the through hole is maintained.

11. The method for manufacturing a joint structure according to claim 10, characterized in that the through-hole is formed by punching using a set of dies, and the clearance of the set of dies is 10 to 40% of the plate thickness of the base steel member.

12. The method for manufacturing a joint structure according to claim 11, characterized in that the mold to be inserted into the through hole is pushed from the surface of the plated steel member on the side in contact with the aluminum member toward the interior of the plated steel member.

13. A method for manufacturing a jointed structure according to any one of claims 10 to 12, characterized in that when the tip of the projection is heated and deformed, the maximum temperature of the projection is kept below the melting point of the surface plating layer.

14. A method for manufacturing a joined structure according to 12, characterized in that the projection is heated using a spot welding electrode and the tip of the projection is deformed.

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