Joined structure and method for manufacturing the joined structure

Abstract

A joined structure (1) according to one embodiment 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), wherein the aluminum member (11) has one or more protrusions (111), the plated steel member (12) has one or more through holes (121), the protrusions (111) are inserted into the through holes (121) and are crimped, the base steel member (122) is exposed on the inner surface of the through hole (121), and a transition plating layer (124) having substantially the same composition as the surface plating layer (123) is provided on a portion 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

[Technical Field]

[0001] The present invention relates to a joint structure and a method for manufacturing the joint structure. This application claims priority based on Japanese Patent Application No. 2024-177807, filed on October 10, 2024, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, aluminum die casting has been increasingly applied to various mechanical structural parts. Aluminum die casting refers to an aluminum alloy casting or a casting method that is obtained by filling a molten aluminum alloy into a mold under high pressure and then rapidly cooling the aluminum alloy. Aluminum die casting is used, for example, as a material for automobile front shock towers, rear shock towers, and subframes.

[0003] In recent years, a manufacturing technology known as Gigacast has also been developed. Gigacast is a technology that uses large casting equipment to mold multiple aluminum parts into a single part, producing huge components. By casting the components that make up an automobile body into large parts, it is possible to reduce the weight of the automobile, manufacturing costs, and manufacturing processes. For this reason, the application of Gigacast is expected to expand in the future. Furthermore, with the advancement of automobile electrification, aluminum die casting is beginning to be used in inverter cases, battery modules, and battery packs.

[0004] The aluminum die-cast member exemplified above needs to be joined to another member. The other member may be, for example, a press-formed steel plate, an aluminum extrusion material, etc. For example, Patent Documents 1 to 5 disclose various methods for joining an aluminum die-cast member to another member. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 3-86381 [Patent Document 2] Japanese Patent Application Publication No. 11-77192 [Patent Document 3] Japanese Patent Application Publication No. 59-166330 [Patent Document 4] Japanese Patent Application Publication No. 56-111529 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-21249 Summary of the Invention [Problem to be solved by the invention]

[0006] Welding is difficult to use as a means of joining aluminum die-cast and steel. For example, when aluminum die-cast and steel are welded together, brittle intermetallic compounds form in the weld metal. These brittle intermetallic compounds significantly reduce the joint strength of the weld.

[0007] Another possible method for joining aluminum die castings and steel materials is mechanical joining using fasteners, etc. However, aluminum die castings have the problem that the joints formed by mechanical joining are prone to cracking. The joints are prone to deformation due to stress concentration. Because aluminum die castings have low ductility, deformation at the joints is likely to cause cracks in the aluminum die castings.

[0008] Furthermore, when joining aluminum die castings and steel materials, galvanic corrosion becomes a problem. Galvanic corrosion is corrosion that occurs when dissimilar metals are directly connected and a battery is formed between them. Galvanic corrosion can be mitigated by providing a plating layer on the surface of the steel material. However, if through holes are provided in the plated steel member to mechanically join the aluminum die castings 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 the plated steel member.

[0009] By forming a plating layer after drilling a steel material, a plating layer can also be formed on the inner surface of the through hole. However, by performing a plating process after drilling, the manufacturing cost of the joined structure increases.

[0010] In view of the above circumstances, the present disclosure provides a joined structure including aluminum members that can be manufactured inexpensively and in a short time without cracking and that can suppress galvanic corrosion at the joint, and a method for manufacturing the same. [Means for solving the problem]

[0011] The gist of the present disclosure is as follows.

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

[0013] (10) Another aspect of the present disclosure provides a method for manufacturing a joined structure having an aluminum member and one or more plated steel members having a base steel member and a surface plating layer formed on the surface thereof, the method comprising the steps of forming a through hole in the plated steel member, inserting a protrusion of the aluminum member into the through hole, and deforming the tip of the protrusion while heating it to crimp the protrusion into the through hole. When forming the through hole in the plated steel member, the surface plating layer of the plated steel member is transferred to the inner surface of the through hole to form a transition plating layer, and when crimping the protrusion into the through hole, the transition plating layer on the inner surface of the through hole is maintained. (11) Preferably, in the joining method for a joined structure described in (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 a joined structure described in (11) above, the mold to be inserted into the through hole is pushed toward the inside of the plated steel member from the surface of the plated steel member that contacts the aluminum member. (13) Preferably, in the joining method for a joined structure described in any one of (10) to (12) above, when the tip of the protrusion is heated and deformed, the maximum temperature of the protrusion is set to be less than the melting point of the surface plating layer. (14) Preferably, in the method for joining a joined structure according to any one of (10) to (13) above, the protrusion is heated using a spot welding electrode, and the tip of the protrusion is deformed. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a joined structure including aluminum members that can be manufactured inexpensively and in a short time without cracking and that can suppress galvanic corrosion at the joint, and a method for manufacturing the same. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. [Figure 2] FIG. 4 is an enlarged cross-sectional view of the inner surface of a through hole. [Figure 3] 10 is a cross-sectional view of a joined structure in which the cross-sectional area of ​​the base end of the protrusion is larger than the area of ​​the side of the through hole facing the aluminum member. FIG. [Figure 4] 10 is a cross-sectional view of a joined structure in which the cross-sectional area of ​​the base end of the protrusion is larger than the area of ​​the side of the through hole facing the aluminum member. FIG. [Figure 5] 5A to 5C are schematic diagrams illustrating a step of forming a through hole. [Figure 6] 10A and 10B are schematic diagrams illustrating a step of inserting a protrusion into a through-hole. [Figure 7] 10A and 10B are schematic diagrams illustrating a process of deforming the tip of a protrusion using a direct spot welding machine. [Figure 8] FIG. 10 is a schematic diagram illustrating a process of deforming the tip of a protrusion using an indirect spot welding machine. [Figure 9] 10 is a cross-sectional photograph of a joint structure in which the amount of heat input during crimping was appropriate. [Figure 10] 10 is a cross-sectional photograph of a joint structure in which the amount of heat input during crimping was inappropriate. [Figure 11] This figure is taken from Figure 2.9 "Typical macroscopic solidification structures" on page β-3 of Volume β3 "Processing Science and Processing Equipment" in the "Mechanical Engineering Handbook β. Design Edition" (edited by the Japan Society of Mechanical Engineers, Maruzen Co., Ltd., published April 30, 2008). DETAILED DESCRIPTION OF THE INVENTION

[0016] (1.Joint structure 1) A joined structure 1 according to one embodiment of the present disclosure includes 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, wherein the aluminum member 11 has one or more protrusions 111, the plated steel members 12 have one or more through holes 121, the protrusions 111 are inserted into the through holes 121 and are crimped, the base steel member 122 is exposed on the inner surface of the through holes 121, and a transition plating layer 124 having substantially the same composition as the surface plating layer 123 is provided on a portion 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 inside of the through holes 121. The joined structure 1 according to this embodiment will be described in detail below with reference to FIG. 1 and other figures.

[0017] (Aluminum component 11) The joined structure 1 has an aluminum member 11. The aluminum member 11 is a mechanical structural member made of an aluminum alloy. Specific examples of aluminum alloys will be described later.

[0018] The aluminum member 11 can be applied in various shapes depending on its application. Suitable examples of applications of the aluminum member 11 include front shock towers, rear shock towers, bumpers, and subframes of automobiles. The aluminum member 11 can also be used as a component constituting the electrical system of an electric vehicle, such as an inverter case, a battery module, and a battery pack. Note that one joined structure 1 may include two or more aluminum members 11.

[0019] (Plated steel member 12) The joined structure 1 further includes one or more plated steel members 12. The plated steel members 12 are mechanical structural members manufactured from plated steel material. The plated steel members 12 can also be applied to various shapes depending on their applications. The plated steel members 12 are applied to various shapes mainly 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 the present 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 cold-rolled steel sheet for hot stamping having a plating layer and then hot-stamping the press material, the rolled surface of the plated steel member 12 is the "surface." The rolled surface is the surface that comes into contact with a cold-rolling mill roll during the production 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 a through hole 121, which will be described later.

[0021] In this disclosure, for ease of explanation, the plating layer provided on the surface of the base steel member 122 is referred to as the "surface plating layer 123" to distinguish it from the transition plating layer 124 described below. 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 protrusion 111. The plated steel member 12 has a through hole 121. The protrusion 111 of the aluminum member 11 is inserted into the through hole 121 of the plated steel member 12. The protrusion 111 is also crimped. Specifically, the protrusion 111 has a tip 1112 and a shaft 1111, and the tip 1112 is plastically deformed by crimping. The shaft 1111 is the portion of the protrusion 111 that is arranged inside the through hole 121. The tip 1112 is the portion of the protrusion 111 on the tip side that is arranged outside the through hole 121.

[0023] When the protrusion 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 shank 1111 in the cross section is the same as or smaller than the diameter of the through hole 121. The diameter of the tip 1112 is enlarged by plastic deformation to be larger than the diameter of the outlet of the through hole 121. The outlet of the through hole 121 refers to the end of the through hole on the tip 1112 side. The tip 1112 prevents the protrusion 111 from coming off the through hole 121. The protrusion 111 functions to join the aluminum member 11 and the plated steel member 12, like a rivet. However, the protrusion 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 crimping. Hot crimping is performed while the tip portion 1112 is thermally softened. This prevents cracking of the protrusion 111. However, it is not preferable to overheat the protrusion 111 during hot crimping. This is because excessive heating of the protrusion 111 will cause the transition plating layer 124, which will be described later, to disappear.

[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 the multiple protrusions 111 are inserted into the multiple through holes 121 and crimped. When the protrusions 111 and the 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 the through holes 121 may be, for example, circular, elliptical, or polygonal.

[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 through hole 121 is formed with the base steel member 122 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 protrusion 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 joined 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 above-described surface plating layer 123 lies in the location where they are disposed. The surface plating layer 123 is disposed on the surface of the base steel member 122. The transition plating layer 124 is disposed on the inner surface of the through hole 121, i.e., on part of the end face of the base steel member 122. The transition plating layer 124 is present between the inner surface of the through hole 121 in the plated steel member 12 and the protrusion 111 in the aluminum member 11, preventing contact between the two.

[0029] The transition plating layer 124 is formed by the plating layer provided on the surface of the plated steel member 12 migrating to the inner surface of the through hole 121. Therefore, the composition of the transition plating layer 124 is substantially the same as that of the plating layer provided on the surface of the plated steel member 12. Small amounts of iron components from the base steel member 122 or aluminum components from the aluminum member 11 may be mixed into the transition plating layer 124. A plating layer containing these impurities originating from the base steel member 122 or the 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 toward the inside of the through hole 121. A surface plating layer 123 is present on the surface of the plated steel member 12 on the side where the transition plating layer 124 is present.

[0030] An example of a transfer plating layer 124 is a sag 1211 formed during punching. Punching is the cutting of material by applying shear force between a pair of blades (mold 3). The sag 1211 is a shrinkage of the material caused by pressing a tool such as the mold 3 into the material. Figure 2 shows a schematic diagram of the inner surface of a through hole 121 in which a sag 1211 has been formed by punching. The mold 3 on the left side of the drawing is pressed downward into the plated steel member 12 shown in Figure 2. As a result, the mold 3 on the left side of the drawing cuts off a portion of the plated steel member 12 to form the through hole 121.

[0031] When the through hole 121 is formed, the end surface of the plated steel member 12 is plastically deformed in the direction in which the left-side mold 3 is pressed in. The downward arrow in FIG. 2 indicates the direction in which the left-side mold 3 is pressed in. As a result, a sag 1211 is formed on the upper side of the plated steel member 12 in FIG. 2. Furthermore, a burr 1212 is formed on the lower side of the plated steel member 12 in FIG. 2.

[0032] The inventors have found that when the clearance C, which is the distance between a pair of dies 3, is within a specific range, the dies 3 transfer 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 toward the inside of the through hole 121. Suitable conditions for punching will be described later.

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

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

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

[0036] Furthermore, in the joined structure 1 according to this embodiment, the protrusion 111 is part of the aluminum member 11. Therefore, in the operation of joining the aluminum member 11 and the plated steel member 12, it is not necessary to assemble the protrusion 111 to the aluminum member 11. Therefore, the joined structure 1 according to this embodiment can be easily manufactured.

[0037] 6 and 7, which will be described later, the tip of the protrusion 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 device. The spot welding machine includes a spot welding electrode 2, a pressure device that moves the spot welding electrode 2, and a transformer that applies current to the spot welding electrode 2. The spot welding electrode 2 applies pressure while locally heating the material to be welded by passing current through it.

[0038] A spot welding machine can be easily adapted for use in crimping the protrusion 111 of the aluminum member 11. The spot welding machine can apply electrical heat to the protrusion 111 of the aluminum member 11 inserted into the through hole 121 of the plated steel member 12. This heats the tip of the protrusion 111 and thermally softens the protrusion 111. The spot welding machine can also apply pressure to the protrusion 111 of the aluminum member 11. By applying pressure to the tip 1112 of the thermally softened protrusion 111, the tip 1112 can be easily plastically deformed. Therefore, manufacturing the joined structure 1 according to the present disclosure does not require dedicated equipment for joining. Joining can be performed using a spot welding machine, which is a general-purpose welding equipment. However, as described below, when crimping the protrusion 111 into the through hole 121, heat input conditions must be selected that maintain the transfer plating layer 124 on the inner surface of the through hole 121.

[0039] Furthermore, the crimping operation using a spot welder can be performed inexpensively and in a short time, and does not cause cracks in the protrusions 111. Resistive heating using an electrode can thermally soften the tip 1112 of the protrusions 111 of the aluminum member 11 within a few seconds. Therefore, the crimping operation can be completed in an extremely short time and at low cost. Furthermore, although the aluminum alloy that constitutes 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 joined structure 1 according to this embodiment, the transition plating layer 124 suppresses galvanic corrosion. If the transition plating layer 124 were not present on the inner surface of the through hole 121, the base steel member 122 exposed on the inner surface of the through hole 121 would come into contact with the protrusion 111 of the aluminum member 11. There is a high possibility of galvanic corrosion occurring at the contact area. However, the transition plating layer 124 disposed on the inner surface of the through hole 121 reduces the contact area between the base steel member 122 and the aluminum member 11, suppressing galvanic corrosion.

[0041] Additionally, when manufacturing the bonded structure 1, there is no need to add an additional step for forming the transition plating layer 124. For example, punching with the clearance C amount within a predetermined range allows for simultaneous formation of both the through hole 121 and the transition plating layer 124. Therefore, the transition plating layer 124 of the bonded structure 1 according to this embodiment does not complicate the manufacturing process.

[0042] For the reasons described above, the joint structure 1 according to this embodiment can be manufactured inexpensively and in a short time without cracking, and can also suppress galvanic corrosion at the joint.

[0043] The most basic aspect of the joined structure 1 according to this embodiment has been described above. A more preferred aspect will now be described.

[0044] (aluminum die-cast parts) A suitable example of the aluminum member 11 is an aluminum die-cast member. An aluminum die-cast member is a mechanical structural member made of aluminum die-cast. Aluminum die-casting is an aluminum alloy casting obtained by filling a molten aluminum alloy into a mold under high pressure and then rapidly cooling the aluminum alloy. Aluminum die-cast members have excellent strength and can be manufactured in a short time.

[0045] When observing the cross section of an aluminum die-cast member, a fibrous metal structure called metal flow can be observed. Metal flow is a trace of the flow of molten aluminum during casting. An aluminum member 11 having metal flow is considered to be an aluminum die-cast member. It is desirable to form a cross section for observing the metal flow parallel to the surface of the aluminum member 11.

[0046] Specific examples of the aluminum alloy that can be used to form the aluminum member 11 include ADC10, ADC12, AC4CH, AC4C, Al-Si-Mg alloys, and Al-Mg-Si-Mn alloys.

[0047] (Metal flow of protrusion 111) There is no limitation on the method for manufacturing the protrusions 111. For example, the protrusions 111 can be formed by cutting the aluminum member 11, or by 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 protrusions 111 of the aluminum member 11 are formed during die-casting. This reduces the number of steps required to form the protrusions 111 and suppresses cracks in the protrusions 111 and their surroundings.

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

[0050] The shapes of chill crystals, columnar crystals, and equiaxed crystals are shown, for example, in Figure 2.9, "Typical Macroscopic Solidification Structure," on page β-3 of Volume β3, "Processing Science and Processing Equipment," of the "Mechanical Engineering Handbook, β. Design Edition" (edited by the Japan Society of Mechanical Engineers, Maruzen Co., Ltd., published April 30, 2008). For reference, this figure is cited as Figure 11 in this disclosure. Chill crystals, columnar crystals, and equiaxed crystals can be identified by observing the etched cross section. Furthermore, the protrusions 111 in which crystals are arranged, as shown in (a) and (b) of this figure, are considered to be protrusions 111 formed during die casting.

[0051] Furthermore, the protrusions 111 formed during die casting are integrally formed with the aluminum member 11. Therefore, the protrusions 111 that have metal flow lines extending along the surface of the protrusions 111 and are integrally formed with the aluminum member 11 are considered to be protrusions 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 machined, such as by cutting, the chill crystals may disappear by cutting. In that case, the protrusion 111 is composed of only columnar crystals, or of columnar crystals and equiaxed crystals. Furthermore, 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 observing the surface and cross section.

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

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

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

[0056] (Position of the transition plating layer 124) 1, the transfer plating layer 124 preferably extends from the surface of the plated steel member 12 facing the aluminum member 11 toward the inside of the through hole 121. The "surface of the plated steel member 12 facing the aluminum member 11" refers to the surface of the plated steel member 12 at the mating interface between the plated steel member 12 and the aluminum member 11.

[0057] Galvanic corrosion tends to be more severe on the surface of the plated steel member 12 on the aluminum member 11 side than on the surface of the plated steel member 12 on the side opposite the aluminum member 11. Therefore, by providing a transition plating layer 124 on the surface of the plated steel member 12 on the aluminum member 11 side, galvanic corrosion can be further suppressed.

[0058] (Tapered shape of through-hole 121 and / or protrusion 111) Preferably, the through hole 121 has a tapered shape that narrows from the base end 1113 of the protrusion 111 toward the tip. By applying a tapered shape to the through hole 121, the transfer plating layer 124 is more easily formed on the inner surface of the through hole 121. This makes it easier to leave the transfer plating layer 124 after hot caulking. This further suppresses galvanic corrosion in the joined structure 1.

[0059] 3, the protrusion 111 preferably has a tapered shape that narrows from the base end 1113 of the protrusion 111 toward the tip end. In this case, it is more preferable that the cross-sectional area of ​​the base end 1113 of the protrusion 111 is larger than the area of ​​the through hole 121 on the surface of the plated steel member 12 facing the aluminum member 11. Furthermore, it is preferable that the transfer plating layer 124 extends from the surface of the plated steel member 12 facing the aluminum member 11 toward the inside of the through hole 121.

[0060] The "cross-sectional area of ​​the base end 1113 of the protrusion 111" refers to the area of ​​the cut surface when the protrusion 111 is cut from the aluminum member 11 along the surface on which the protrusion 111 is provided. The cross-sectional area of ​​the base end 1113 of the protrusion 111 can be measured by cutting the protrusion 111 along the dashed line marked with symbol A in FIG. 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 on 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 marked with symbol B in FIG. 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] 3, the contact area between the protrusion 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. In addition, a transition plating layer 124 is provided in this area. Therefore, according to the configuration illustrated in FIG. 3, the transition plating layer 124 is provided in the contact area between the protrusion 111 and the through hole 121, which is an area where galvanic corrosion is likely to occur. This further suppresses galvanic corrosion.

[0062] As shown in FIG. 4, a tapered shape can be applied to both the protrusion 111 and the through hole 121. In this case, it is more preferable that the cross-sectional area of ​​the base end 1113 of the protrusion 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 more 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 inside of the through hole 121. In this case, the transition plating layer 124 can more easily flow into the through hole 121, which makes it easier to reduce the area of ​​the exposed base material. This further suppresses galvanic corrosion.

[0063] (hot crimping) Preferably, the protrusion 111 is hot-caulked. The tip 1112 of the protrusion 111 is a hot-caulked portion. Hot-caulking can prevent the protrusion 111 from cracking during the caulking operation. Furthermore, hot-caulking does not cause work hardening of the tip 1112.

[0064] Whether the manufacturing method of the protrusion 111 is hot crimping or cold crimping can be determined based on the presence or absence of work hardening at the tip 1112. A work-hardened portion is significantly formed at the tip 1112 of the cold crimped protrusion 111. If the hardness H1 of the tip 1112 of the protrusion 111 and the hardness H2 of the aluminum member 11 at a location 10 mm or more away from the protrusion 111 satisfy H1≦1.1×H2, the protrusion 111 is considered to have been hot crimped.

[0065] The hardness H1 of the tip 1112 of the protrusion 111 is measured on a cross section of the protrusion 111. The cross section passes through approximately the center of the protrusion 111 and is parallel to the surface of the aluminum member 11. The maximum value of the Vickers hardness measured at any five points on the cross section of the tip 1112 of the protrusion 111 is regarded as H1. The hardness H2 of the aluminum member 11 is measured in a cross section perpendicular to the surface of the aluminum member 11. The "surface" refers to the surface on which the protrusions 111 are provided. The measurement position for H2 is any point that satisfies the following requirements. (1) The center of the thickness of the aluminum member 11 or a position at a depth equivalent thereto. (2) A position 10 mm or more away from the protrusion 111 along the surface of the aluminum member 11. Regarding (1) above, for example, if the aluminum member 11 is a plate-like member with a thickness of t, the measurement position for H2 is set at a depth of t / 2 from the surface of the aluminum member 11. Next, regarding (2) above, for example, when measuring H2 in a cross section that passes through the center of the protrusion 111 and is perpendicular to the surface of the aluminum member 11 as shown in FIG. 1, the measurement position for H2 is set at a distance of 10 mm or more from 1113 to the left of the page. The average value of the Vickers hardness of the aluminum member 11 measured at any five points that satisfy the above requirements is regarded as H2. The test force used in measuring the Vickers hardness is the same for all points.

[0066] (2. Method for manufacturing the bonded structure 1) Another embodiment of the present disclosure provides a method for manufacturing a joined structure 1, which includes an aluminum member 11 and one or more plated steel members 12 having a base steel member 122 and a surface-plated layer 123 formed thereon. The method includes the steps of forming a through hole 121 in the plated steel member 12, inserting a protrusion 111A of the aluminum member 11 into the through hole 121, and deforming the tip of the protrusion 111A while heating it to crimp the protrusion 111A into the through hole 121. When forming the through hole 121 in the plated steel member, the surface-plated layer 123 of the plated steel member is transferred to the inner surface of the through hole 121 to form a transition plating layer 124. When crimping the protrusion 111A into the through hole 121, the transition plating layer 124 on the inner surface of the through hole 121 is maintained. The following describes the details of the method for manufacturing the joined structure 1 according to this embodiment. Note that the preferred embodiments of the joined structure 1 described above can also be applied to the method for manufacturing the joined 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, an aluminum member 11 and a plated steel member 12 are joined together. The aluminum member 11 has one or more protrusions 111A. Before being crimped, the protrusions 111A do not have tip portions 1112. In the joined structure 1, the protrusions 111A are inserted into the through holes 121. Therefore, it is necessary to appropriately select the position of the protrusions 111A.

[0068] (S1 Formation of through-holes 121) First, as shown in Fig. 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 protrusion 111A. When forming the through hole 121 in the plated steel member, the surface plating layer 123 of the plated steel member is transferred to the inner surface of the through hole 121 to form a transfer plating layer 124. The means for forming the through hole 121 is not particularly limited. However, when forming the through hole 121, the processing conditions must be optimized so that a sufficient amount of the surface plating layer 123 is transferred into the inside of the through hole 121.

[0069] As shown in FIG. 2, when punching is used to form the through hole 121, the clearance C, which is the distance between a pair of dies 3, is set to 10 to 40% of the thickness of the base steel member. If the clearance C is less than 10%, the amount of transfer of the surface plating layer 123 is small, and a sufficient amount of the transfer 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 exceeds 40%, it becomes difficult to form the through hole 121. More preferably, the upper limit is 35% or less, 30% or less.

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

[0071] 6, an adhesive may be provided between the plated steel member 12 and the aluminum member 11 to bond them together. In this case, before inserting the protrusion 111A into the through-hole 121, the adhesive is applied to one or both of the aluminum member 11 and the plated steel member 12. Then, while inserting the protrusion 111A into the through-hole 121, the area of ​​one member to which the adhesive 13 is 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 the protrusion 111A) 7 or 8, the tip of the protrusion 111A is deformed, thereby crimping the protrusion 111A into the through-hole 121. By crimping the protrusion 111A into the through-hole 121, a tip 1112 is formed, and the aluminum member 11 and the plated steel member 12 are joined together.

[0073] When deforming the tip of the protrusion 111A, the protrusion 111A is heated. This softens the protrusion 111A, reducing its deformation resistance. The reduced deformation resistance prevents the protrusion 111A from cracking during crimping.

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

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

[0076] Furthermore, the maximum temperature of the protrusion 111A can be estimated by simulation. Therefore, when the tip of the protrusion 111A is heated and deformed, conditions may be estimated and adopted such that the maximum temperature of the protrusion 111A is lower than the melting point of the surface plating layer 123.

[0077] A suitable example of a heating means for the protrusion 111A is a spot welding electrode 2. The spot welding electrode 2 is a rod-shaped electrode made of a copper alloy that, during spot welding, directly contacts the base material to pass a welding current and transmit a pressing force. However, in the manufacturing method for the joined structure 1 according to this embodiment, the spot welding electrode 2 is not used to weld the plated steel member 12 and the aluminum member 11. The spot welding electrode 2 applies pressure to the protrusion 111A while passing current through it. The resistance heat generated by the current passing through the electrode 2 thermally softens the protrusion 111A. By applying pressure to the protrusion 111A in its thermally softened state, the tip of the protrusion 111A is easily deformed, forming a tip 1112 that crimps the through hole 121.

[0078] The crimping of the protrusion 111A using the spot welding electrode 2 may be performed using either a direct spot welding machine or an indirect spot welding machine. JIS Z 3001-6:2013, "Welding Terminology - Part 6: Resistance Welding," defines direct spot welding as spot welding performed by applying pressure directly to the weld joint with an electrode and passing a welding current in the plate thickness direction. In this standard, indirect spot welding is defined as spot welding in which a current is passed through the electrode in a manner similar to series current, creating a single nugget in the base material directly below the electrode. Below, specific examples of crimping performed using a direct spot welding machine or an indirect spot welding machine are described.

[0079] (Crimping work using a direct spot welder) When crimping the protrusion 111A using a direct spot welding machine, as illustrated in FIG. 7 , the protrusion 111A is sandwiched between a pair of spot welding electrodes 2. The tip of one of the spot welding electrodes 2 is placed at the tip of the protrusion 111A. The tip of the other spot welding electrode 2 is placed on the surface of the aluminum member 11 opposite the protrusion 111A. The central axes of the pair of spot welding electrodes 2 are aligned. Then, while a current is passed between the pair of spot welding electrodes 2, the spot welding electrodes 2 are moved to narrow the distance between the electrodes. This crushes the tip of the protrusion 111A, forming a tip portion 1112 having a diameter larger than that of the through hole 121.

[0080] (Crimping work using an indirect spot welder) When crimping the protrusion 111A using an indirect spot welding machine, a pair of spot welding electrodes 2 are arranged in parallel, as illustrated in FIG. 8 . The tip of one of the spot welding electrodes 2 is placed at the tip of the protrusion 111A. The tip of the other spot welding electrode 2 is placed on the surface of the aluminum member 11 on which the protrusion 111A is provided. The central axes of the pair of spot welding electrodes 2 do not coincide. Then, while a current is passed between the pair of spot welding electrodes 2, the spot electrode placed at the tip of the protrusion 111A is pressed against the protrusion 111A. This crushes the tip of the protrusion 111A, forming a tip portion 1112 having a diameter larger than that of the through hole 121.

[0081] Crimping using a direct spot welder is preferable because it can be performed easily and reliably. However, when performing crimping using a direct spot welder, it is necessary to place the spot welding electrode 2 on the surface of the aluminum member 11 opposite the protrusion 111A. For example, if the aluminum member 11 has a closed cross-sectional structure, crimping using a direct spot welder may not be possible. Crimping using an indirect spot welder is suitable for such cases because, when performing crimping using an indirect spot welder, both of the pair of spot welding electrodes 2 are placed on the surface on which the protrusion 111A is provided.

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

[0083] The optimal current flow conditions vary depending on the size of the protrusion 111A of the aluminum member 11 before crimping, the diameter and depth of the through hole 121 in 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, etc.

[0084] (Action and effect) In the manufacturing method of the joined structure 1 according to this embodiment, the transition plating layer 124 for preventing galvanic corrosion can be formed simultaneously with the through hole 121. Furthermore, in the manufacturing method of the joined structure 1 according to this embodiment, the protrusion 111A can be crimped without cracking using a spot welder, which is a general-purpose manufacturing equipment. For the above reasons, the manufacturing method of the joined structure 1 according to this embodiment can manufacture the joined structure 1 inexpensively and in a short time without cracking, and can suppress galvanic corrosion at the joint.

[0085] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited thereto and can be appropriately modified without departing from the technical spirit thereof. A more preferred example of the joined structure 1 according to the present embodiment and the method for manufacturing the same 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 refers to the diameter of the through hole 121 when the through hole 121 is circular, and refers to the maximum diameter when the through hole 121 is elliptical or polygonal. When the through hole 121 has a tapered shape, the maximum and minimum diameters of the through hole 121 preferably fall within the above-mentioned ranges.

[0087] The larger the through hole 121, the easier it is to insert the protrusion 111 into the through hole 121. Furthermore, the larger the through hole 121, the thicker the diameter of the shaft 1111 that ensures the joining strength can be made. This increases the joining strength at the time of joining. On the other hand, the smaller the through hole 121, the thinner the protrusion 111 can be made. This makes it easier to deform the protrusion 111A.

[0088] The depth of the through hole 121 can be selected appropriately depending on 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 position where the through hole 121 is provided. From the viewpoint of facilitating the crimping operation, the depth of the through hole 121 is preferably 5.0 mm or less. From the viewpoint of ensuring bonding strength, the depth of the through hole 121 is preferably 0.6 mm or more. When the plated steel member 12 is plate-shaped, the through hole 121 can be provided at any position in the plated steel member 12. On the other hand, when the plated steel member 12 is non-plate-shaped, a plate-shaped flange portion can be provided on the plated steel member 12, and the through hole 121 can be provided in the flange portion.

[0089] (Diameter of shaft 1111 of protrusion 111) In the joined structure 1, the maximum diameter of the shank 1111 of the protrusion 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 shank 1111 expands when the tip of the protrusion 111 is deformed. However, as shown in FIGS. 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 shank 1111 and the inner wall of the through hole 121, causing the diameter of the shank 1111 of the protrusion 111 to become smaller than the diameter of the through hole 121. In the joined structure 1, preferred examples of the diameter and length of the shank 1111 of the protrusion 111 correspond to the diameter and depth of the through hole 121 described above.

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

[0091] More preferably, the diameter of the protrusion 111 before the tip is deformed is smaller than the diameter of the through hole 121, with the difference between the two being within a range of 0.5 to 2.5 mm. This allows the adhesive 13 to flow between the protrusion 111 and the through hole 121. The adhesive 13 disposed between the protrusion 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 protrusion 111 refers to the diameter of the protrusion 111 when the protrusion 111 is circular, and refers to the maximum diameter when the protrusion 111 is elliptical or polygonal.

[0092] (Protrusion amount of protrusion 111 before deformation of the tip) The protrusion amount of the protrusion 111 before the tip is deformed is preferably 3.0 to 15.0 mm. The protrusion amount 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 the protrusion 111 when the protrusion 111 before the tip is deformed is inserted into the through hole 121. If the plated steel member 12 and the aluminum member 11 come into contact around the protrusion 111 when the protrusion 111 is inserted into the through hole 121, the protrusion amount of the protrusion 111 is the length of the protrusion 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 the protrusion 111 when the protrusion 111 is inserted into the through hole 121 as illustrated in FIG. 4, the protrusion amount of the protrusion 111 is the length of the protrusion 111 minus the depth of the through hole 121 and the thickness of the gap.

[0093] Note that the adhesive 13 is not applied when measuring the protrusion amount of the protrusion 111 before deforming the tip. That is, the thickness of the adhesive 13 is not taken into consideration when determining the protrusion amount of the protrusion 111 before deforming the tip. 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 amount, the easier it is to deform the tip of protrusion 111. On the other hand, the greater the protrusion amount, the larger the diameter of tip 1112, and the stronger the bonding strength.

[0095] (Shape of tip 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 preferably 1.5 mm or more. If the tip portion 1112 is circular when viewed in a plane along the axial direction of the through hole 121, the diameter of the tip portion 1112 is its diameter. If the tip portion 1112 is elliptical or polygonal when viewed in a plane along the axial direction of the through hole 121, the diameter of the tip portion 1112 is the diameter of the smallest circle circumscribing the tip portion 1112. In addition, 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 protrusion 111 in the joined structure 1.

[0096] The larger the diameter and thickness of the tip portion 1112, the stronger the bonding strength. The smaller the diameter and thickness of the tip portion 1112, the easier it is to deform the tip of the protrusion 111.

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

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

[0099] The exposed amount of the base steel member 122 is evaluated using 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 center of gravity of the through hole 121 is considered to be the center of the through hole 121. Next, the cross section is observed using an optical microscope or an electron microscope. If necessary, an element distribution mapping image of the cross section is taken. Based on the cross-sectional observation results, the position of the transfer plating layer 124 and the position where the base steel member 122 is exposed are identified. Then, the length of the area where the base steel member 122 is exposed along the thickness direction of the plated steel member 12 is measured. The value obtained by dividing the length of the area where the base steel member 122 is exposed by the thickness of the plated steel member 12 is considered to be the exposed amount of the base steel member 122. [Example]

[0100] The effects of one embodiment of the present disclosure will be explained in more detail using examples. However, the conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effects of the present disclosure. The present disclosure is not limited to this example of conditions. Various conditions may be adopted in the present disclosure as long as they do not deviate from the gist of the disclosure and achieve the purpose.

[0101] Two bonded structures were produced, each having an aluminum member and one or more plated steel members each having a base steel member and a surface-plated layer formed on the surface of the base steel member. The surface-plated layer was a Zn-plated layer.

[0102] The manufacturing method includes the steps of forming a through hole in a plated steel member, inserting a protrusion of an aluminum member into the through hole, and deforming the tip of the protrusion while heating it to crimp the protrusion into the through hole. In addition, when forming the through hole in the plated steel member, the surface plating layer of the plated steel member is transferred to the inner surface of the through hole to form a transfer plating layer.

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

[0104] [Table 1]

[0105] Fig. 9 shows a cross-sectional photograph of the protrusion and through hole of the joined structure obtained under crimping condition 1. Fig. 10 shows a cross-sectional photograph of the protrusion and through hole of the joined structure obtained under crimping condition 2. In both the examples of Fig. 9 and Fig. 10, the plated steel member 12 was punched from the top to the bottom of the paper. 9 and 10, (A) is a low-magnification SEM cross-sectional photograph. (B) is a high-magnification SEM cross-sectional photograph of the region surrounded by the dashed line in (A). (C) is a mapping image of the Zn concentration in the region surrounded by the dashed line in (A). (D) is a mapping image of the Fe concentration in the region surrounded by the dashed line in (A). The cross-sectional photographs were taken under the following conditions: Device model number: JSM-IT300 (manufactured by JEOL) EDS detector: JED-2300 x 2 (manufactured by JEOL) 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 transfer plating layer was formed on the inner surface of the through hole obtained under crimping condition 1. The Zn concentration mapping image shown in Figure 9(C) shows a high Zn concentration region extending vertically. This high Zn concentration region is located at the boundary between the shaft of the protrusion and the base steel member of the plated steel member. This high Zn concentration region is the transfer plating layer.

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

[0108] 1 Joined structure 11 Aluminum components 111 Protrusion 111A Protrusion before crimping 1111 Shaft 1112 Tip 1113 Proximal end 12 Plated steel members 121 Through hole 1211 Dare 1212 Bali 122 Base steel members 123 Surface plating layer 124 Transition plating layer 13 Adhesive 2 Spot welding electrodes 3. Mold C Clearance

Claims

1. Aluminum members, one or more plated steel members having a base steel member and a surface plating layer provided on a surface of the base steel member; A joint structure comprising: The aluminum member has one or more protrusions, the plated steel member has one or more through holes; the protrusion is inserted into the through hole and is crimped; The base steel member is exposed on the inner surface of the through hole, a transition plating layer having substantially the same components as the surface plating layer is provided on a portion of the inner surface of the through hole; The transition plating layer extends from one surface of the plated steel member toward the inside of the through hole. bonded structure.

2. 2. The joined structure according to claim 1, wherein the aluminum member is an aluminum die-cast member.

3. 3. The joined structure according to claim 2, wherein the protrusions of the aluminum member are formed during die casting.

4. 4. The joint structure according to claim 1, wherein the surface plating layer of the plated steel member is a zinc-based plating layer.

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

6. A joint structure described in 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 inside of the through hole.

7. 4. The joint structure according to claim 1, wherein the through hole has a tapered shape that narrows from the base end side of the protrusion toward the tip end side.

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

9. The hardness H1 of the tip of the protrusion and the hardness H2 of the aluminum member at a point 10 mm or more away from the protrusion satisfy H1≦1.1 × H2.

10. A method for manufacturing a joined structure having an aluminum member and one or more plated steel members having a base steel member and a surface plating layer provided on the surface of the base steel member, forming a through hole in the plated steel member; a step of inserting a protrusion of the aluminum member into the through hole; a step of deforming a tip of the protrusion while heating it to caulk the protrusion into the through hole; Equipped with When forming the through hole in the plated steel member, the surface plating layer of the plated steel member is transferred to the inner surface of the through hole to form a transfer plating layer; When the protrusion is crimped into the through hole, the transition plating layer on the inner surface of the through hole is maintained. A method for manufacturing a bonded structure.

11. The through hole is formed by punching using a set of dies, The clearance between the pair of dies is set to 10 to 40% of the thickness of the base steel member. The method for manufacturing a bonded structure according to claim 10 .

12. The die to be inserted into the through hole is pushed toward the inside of the plated steel member from the surface of the plated steel member that contacts the aluminum member. The method for manufacturing a bonded structure according to claim 11 .

13. When the tip of the protrusion is deformed while being heated, the maximum temperature of the protrusion is set to be lower than the melting point of the surface plating layer. The method for manufacturing the bonded structure according to any one of claims 10 to 12.

14. The method for manufacturing a joint structure according to claim 12, wherein the protrusion is heated and the tip of the protrusion is deformed using a spot welding electrode.

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