Dissimilar material joining method and joined body used in the dissimilar material joining method

Abstract

An aluminum material (the first component) and a steel material (the second component) are placed overlapping, with a resin layer sandwiched between the front end of the aluminum rivet's shaft and the surface of the steel material. A pair of electrodes sandwich the rivet and the steel material, and current is applied between the electrodes while pressure is applied, spot welding the rivet and the steel material while removing the resin layer from between the electrodes. The rivet's connection to the shaft on the back side of the head is provided with an annular step formed circumferentially and protruding axially.

Description

Technical Field

[0001] The invention relates to a dissimilar material joining method and a rivet used for the dissimilar material joining method. Background Art

[0002] In recent years, in response to global environmental issues caused by exhaust gases and other factors, research has been underway to improve fuel efficiency by reducing the weight of vehicles such as automobiles. To minimize obstacles to vehicle weight reduction and improve collision safety, there is an increasing use of lightweight alloys, such as aluminum alloys, in vehicle body structures, replacing some of the traditionally used steel with materials that are lighter and have excellent energy absorption properties.

[0003] Unless the entire vehicle body is composed entirely of aluminum alloy, these aluminum alloys must be used in combination with steel materials (steel components) such as steel plates and steel sections, which are commonly used in conventional vehicle bodies. Therefore, dissimilar metal joining (dissimilar material joining) is essential. Patent Document 1 discloses such a dissimilar material joining method.

[0004] Furthermore, an adhesive layer is often provided between aluminum alloy materials and steel members to prevent corrosion (galvanic corrosion) caused by the potential difference between the two and to ensure joint strength. Patent Document 2 discloses a joining method using such an adhesive layer.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-207898

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2015-24436 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] However, in the joining method of Patent Document 2, the metals do not contact each other in the portion where the adhesive is present, so the adhesive must be removed from the portion where the rivet is welded in advance. This adhesive removal process is very time-consuming and impractical.

[0011] Therefore, it is preferable to use the so-called weld bonding method, which involves removing the adhesive during spot welding while the adhesive remains. However, directly using weld bonding can easily cause sparks to fly from the weld, making it difficult to achieve the desired nugget shape, resulting in reduced joint strength. This problem is not limited to dissimilar bonding between aluminum and steel, but also occurs with other combinations of dissimilar materials.

[0012] The present invention solves the above-mentioned problems and aims to provide a method for joining dissimilar materials and a rivet used in the adhesive spot welding method using a rivet, which can suppress the generation of spatter and the like and perform good spot welding.

[0013] Solutions to Problems

[0014] The present invention includes the following structures.

[0015] (1) A method for joining dissimilar materials, comprising the steps of: driving a rivet having a head and a shaft into and penetrating a first member; arranging the first member through which the rivet is installed and a second member capable of being welded to the rivet in an overlapping manner with a resin layer sandwiched between the front end side of the rivet's shaft of the first member and the second member; and performing spot welding while sandwiching the rivet and the second member using a pair of electrodes, applying a current while applying pressure between the electrodes, and removing the resin layer from between the electrodes.

[0016] The rivet has an annular step portion formed along the circumferential direction and protruding in the axial direction at a connection portion with the shaft portion on the back side of the head.

[0017] When the rivet is driven into and mounted on the first member, the annular step portion presses the first member to form an annular protrusion that causes the inner peripheral edge of the through hole of the shaft portion in the first member to protrude toward the second member.

[0018] By applying pressure between the electrodes during the spot welding, a gap is formed between the radially outer side of the annular protrusion of the first member and the second member, and spot welding is performed while the resin layer is discharged into the gap.

[0019] (2) A method for joining dissimilar materials, comprising the steps of: placing a first member having a pre-hole and an annular protrusion on the periphery of the pre-hole in an overlapping manner with a second member with a resin layer interposed therebetween; passing the shaft of a rivet having a head and a shaft that can be welded to the second member through the pre-hole of the first member; and clamping the rivet and the second member with a pair of electrodes, applying electricity while applying pressure between the electrodes, and spot welding while excluding the resin layer from between the electrodes, wherein:

[0020] The rivet has an annular step portion formed along the circumferential direction and protruding in the axial direction at a connection portion with the shaft portion on the back side of the head.

[0021] By applying pressure between the electrodes during the spot welding, a gap is formed between the radially outer side of the annular protrusion of the first member and the second member, and spot welding is performed while the resin layer is discharged into the gap.

[0022] (3) A rivet having a head and a shaft, wherein:

[0023] The rivets are used for joining dissimilar materials as follows:

[0024] A first member having the shaft portion inserted therethrough and a second member capable of being welded to the rivet are arranged in an overlapping manner with a resin layer sandwiched between the front end side of the shaft portion of the rivet of the first member and the second member. The rivet and the second member are sandwiched by a pair of electrodes, and current is applied between the electrodes while pressurizing the electrodes to perform spot welding while removing the resin layer from between the electrodes.

[0025] The rivet includes an annular step portion formed along the circumferential direction and protruding in the axial direction at a connection portion with the shaft portion on the back side of the head portion.

[0026] Effects of the Invention

[0027] According to the present invention, in the adhesive spot welding method using rivets, it is possible to join dissimilar materials by good spot welding while suppressing the generation of spatter and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1A This is a perspective view of the appearance of a rivet used in the method for joining dissimilar materials of the present invention.

[0029] Figure 1B This is a perspective view of the appearance of a rivet used in the method for joining dissimilar materials of the present invention.

[0030] Figure 2 This is a process diagram showing the rivet driving process in stages (A) to (C).

[0031] Figure 3A This is a cross-sectional view of an aluminum material with rivets driven into it.

[0032] Figure 3B It is from Figure 3A Bottom view viewed from below.

[0033] Figure 4 This is a process explanatory diagram showing a state in which an aluminum material with rivets driven therein is overlapped with a steel material with a resin layer interposed therebetween.

[0034] Figure 5 This is a process explanatory diagram showing the state of resistance spot welding between an aluminum material and a steel material using rivets.

[0035] Figure 6 These are explanatory diagrams showing the state from pressurization between electrodes to energization in stages (A) to (C).

[0036] Figure 7 (A) and (B) are process explanatory diagrams showing another method of fixing a rivet to an aluminum material.

[0037] Figure 8 It shows Figure 6 A cross-sectional view of another structure of a dissimilar metal joint shown.

[0038] Figure 9A This is a partially enlarged cross-sectional view showing another shape of the annular step portion of the rivet.

[0039] Figure 9B This is a partially enlarged cross-sectional view showing another shape of the annular step portion of the rivet.

[0040] Figure 9C This is a partially enlarged cross-sectional view showing another shape of the annular step portion of the rivet. DETAILED DESCRIPTION

[0041] The following describes embodiments of the present invention in detail with reference to the accompanying drawings. In the dissimilar material joining method of the present invention, an annular step portion protruding axially is provided on the back side of the head of the rivet used. While the dissimilar material joining method using a steel rivet to join aluminum and steel is exemplified herein, the combination of materials of the joined components is arbitrary.

[0042] <Rivet Structure>

[0043] Figure 1A 、 Figure 1B This is a perspective view of the appearance of a rivet used in the method for joining dissimilar materials of the present invention.

[0044] The rivet 11 is made of steel and has a disc-shaped head 13 and a shaft 15 coaxially connected to the center of the head 13. The rivet 11 has an annular step 17 formed circumferentially around the shaft 15 and projecting in the axial direction at the connection point between the head 13 and the shaft 15 (the inner circumference of the annular head back surface 13a). The step-shaped corners and corners of the annular step 17—namely, corner 17a connected to the head back surface 13a, corner 17b connected to the shaft side surface 15b, and corner 17c forming the outer peripheral edge of the projecting tip—are chamfered to form curved surfaces in an axial cross-section.

[0045] It should be noted that Figure 1A 、 Figure 1B The shaft portion 15 shown is a cylindrical shape with a constant diameter, but may also be a shape that gradually increases in size from the base end toward the tip end on the head 13 side, and the shaft cross section may be an ellipse.

[0046] The front end surface (shaft front end surface) 15a of the shaft portion 15 is a curved surface that protrudes in the axial direction. The top 19 of the curve of the shaft front end surface 15a is aligned with the central axis L of the shaft portion 15. Alternatively, the top 19 may be a conical protrusion (projection) instead of a curved surface.

[0047] <Steps for joining dissimilar materials>

[0048] Next, a procedure for joining dissimilar materials between an aluminum material and a steel material using the rivet 11 will be described.

[0049] Figure 2 These are process explanatory diagrams showing the driving process of the rivet 11 in stages from (A) to (C).

[0050] like Figure 2 As shown in FIG. 2 (A), an aluminum material 23 is placed on a die head 21 having a cylindrical upper portion, and a rivet 11 is placed on top of the die head 21. An annular recess 21a is formed on the inner circumference of the upper surface of the die head 21. Then, a punch 25 is used to drive the head 13 of the rivet 11 into the aluminum material 23.

[0051] As the aluminum material 23, aluminum alloys of the 2000, 3000, 4000, 5000, 6000, or 7000 series, or ductile materials of pure aluminum of the 1000 series, can be used. From the perspective of weldability, aluminum alloys of the 5000, 6000, or 7000 series are particularly preferred. Furthermore, the aluminum material 23 is not limited to sheet materials; it can also be extruded components (tubes or hollow, solid, or profiled cross-sections) or forged materials (sheet materials or ribbed materials). Furthermore, the surface of the aluminum material 23 can be subjected to various surface treatments such as shot peening, etching, and brush polishing as pretreatment. In this case, organic matter on the surface of the aluminum material is removed, improving the quality of the joint.

[0052] like Figure 2 As shown in (B), when the punch 25 is lowered to press the rivet 11 into the aluminum material 23, the portion of the aluminum material 23 facing the shaft 15 is blanked by the shaft 15, and this blanked portion (blank) 23A falls toward the inside of the die head 21. Furthermore, the rivet 11 is pressed toward the aluminum material 23 by the punch 25, and the aluminum material 23 is sandwiched between the head 13 and the die head 21. As a result, the annular step 17 of the rivet 11 is pressed into the aluminum material 23, and the aluminum material 23 plastically flows into the recess 21a formed on the upper surface of the die head 21.

[0053] In this way, Figure 2As shown in (C), the shaft portion 15 of the rivet 11 penetrates the aluminum material 23, and the front end surface 15a of the shaft portion is exposed on the lower surface of the aluminum material 23. In addition, the annular step portion 17 formed on the head portion 13 enters the aluminum material 23, and the rivet 11 is riveted and fixed to the aluminum material 23. In addition, the inner peripheral edge of the through hole through which the shaft portion 15 of the aluminum material 23 penetrates is formed with an annular protrusion 26 that protrudes forward in the insertion direction of the shaft portion 15.

[0054] The rivet 11 can also be driven simultaneously with the stamping process (finishing process) of the aluminum material 23 during the stamping process. Specifically, during the stamping process of the aluminum material 23, a punch is provided on the stamping die, or the stamping die itself is used in place of the punch, and the rivet 11 is punched out simultaneously with the lowering of the stamping die. This ensures that the rivet 11 is riveted and fixed to the aluminum material 23. In this state, the rivet 11 remains riveted and fixed to the aluminum material 23 during transportation along the resistance spot welding line, preventing it from falling during transportation. This improves the workability of the joining process.

[0055] Figure 3A This is a cross-sectional view of an aluminum material 23 with a rivet 11 driven into it. Figure 3B It is from Figure 3A Bottom view viewed from below.

[0056] Figure 3A The annular protrusion 26 of the aluminum material 23 shown is formed to be at the same height as or lower than the outer peripheral edge 31 of the shaft portion front end surface 15a of the rivet 11 in the axial direction. In other words, the annular protrusion 26 does not protrude from the shaft portion 15. Furthermore, the radial outer side of the annular protrusion 26 of the aluminum material 23 is not pressed by the annular step 17 of the rivet 11 and is not subjected to the concave portion 21a of the die head 21 (see FIG. 1 ). Figure 2 ) is affected by the plastic flow of the aluminum material 23, and the flat surface 23a is formed into the original shape. That is, the flat surface 23a of the aluminum material 23 is recessed from the annular protrusion 26 by a distance S.

[0057] Therefore, the rivet 11 and the aluminum material 23 Figure 3A The axial positions in the diagram are, from the bottom, the top 19 of the shaft front end surface 15a, the outer peripheral edge 31, the annular protrusion 26, and the flat surface 23a.

[0058] Figure 4 This is a process explanatory diagram showing a state in which the aluminum material 23 into which the rivet 11 is driven is overlapped with the steel material 29 with the resin layer 27 interposed therebetween.

[0059] A resin layer 27 is formed on one surface of the steel material 29. The resin layer 27 serves as an adhesive that bonds the aluminum material 23 and the steel material 29. The resin layer 27 also has electrical insulating properties, thereby preventing galvanic corrosion caused by contact between the aluminum material 23 and the steel material 29 and firmly bonding the two.

[0060] Steel material 29 can be made of mild steel, high-tensile steel, or the like. A resin layer 27 is formed on one surface of steel material 29. Resin layer 27 serves as an adhesive that bonds aluminum material 23 and steel material 29. Resin layer 27 also has electrical insulating properties, thereby preventing galvanic corrosion caused by contact between aluminum material 23 and steel material 29 and firmly bonding them.

[0061] The adhesive used for resin layer 27 can be applied to steel 29 or aluminum 23 in a liquid or viscous state. Furthermore, resin layer 27 is not limited to being applied with an adhesive; a sheet-like adhesive sheet may also be provided. When using an adhesive sheet, it can be pre-bonded to either steel 29 or aluminum 23, or both. Alternatively, the aluminum 23 and steel 29 can be bonded together when the two materials are stacked. Thus, resin layer 27 is sandwiched between the surface of the rivet 11's shaft tip in aluminum 23 and the surface of steel 29.

[0062] Figure 5 This is a process explanatory diagram showing how the aluminum material 23 and the steel material 29 are resistance spot welded using the rivet 11 .

[0063] At the position of the rivet 11, the aluminum material 23 on which the rivet 11 is installed and the steel material 29 overlapping the aluminum material 23 are sandwiched by a pair of electrodes 33 and 35. Then, while one of the electrodes 33 and 35 is pressed toward the other by a pressure device (not shown), a current (current I) is passed between the electrodes by a power supply device (not shown). As a result, a nugget 37 of a desired size is formed between the front end surface 15a of the shaft portion of the rivet 11 and the steel material 29 (see Figure 6 ).

[0064] Here, a detailed description will be given of the process of pressurizing the aluminum material 23 and the steel material 29 between electrodes and passing electricity between the electrodes until the nugget 37 is formed.

[0065] Figure 6 These are explanatory diagrams showing the state from pressurization between electrodes to energization in stages (A) to (C).

[0066] like Figure 6 As shown in (A), the front end face 15a of the shaft portion of the rivet 11 passes through Figure 4The electrodes 33 and 35 shown are sandwiched between the electrodes and pressed against the resin layer 27, forcing the resin layer 27 radially outward, centered around the top 19 of the rivet 11. Furthermore, the current flowing between the electrodes heats and melts the resin layer 27 in contact with the shaft front end 15a of the rivet 11, causing it to flow radially outward (arrow M) or partially sublime. At this point, a small gap forms between the annular protrusion 26 and the steel material 29, allowing the resin layer 27 to smoothly discharge radially outward through this gap. This allows the resin layer 27 to be substantially completely discharged, at least from the vicinity of the center axis L of the shaft front end 15a.

[0067] Moreover, if Figure 6 As shown in (B), near the central axis L, the shaft front end surface 15a and the steel material 29 are in close contact without the resin layer 27 interposed therebetween. The heating caused by the passage of electricity causes both to melt, forming a nugget 37. The nugget 37 grows with the central axis L as the starting point. At this time, the annular protrusion 26 is strongly pressed against the steel material 29 (arrow F) by the pressure applied between the electrodes.

[0068] like Figure 6 As shown in (C), the nugget 37 grows by energizing, but the annular protrusion 26 continues to strongly press the steel material 29 radially outside the shaft 15 of the rivet 11, so the molten body (molten steel) of the nugget 37 is blocked, and splashing can be prevented.

[0069] Thus, the nugget 37 grows from the central axis L of the shaft 15 as current is applied, and can grow to a size that provides sufficient joining strength between the rivet 11 and the steel material 29 while suppressing deviation from the central axis L and generation of spatter.

[0070] As described above, rivet 11 includes an annular step 17. When rivet 11 is driven into aluminum material 23 for installation, annular step 17 forms an annular protrusion 26 on the inner circumference of the through-hole in shaft portion 15 of aluminum material 23. During spot welding, pressure is applied between electrodes to create a gap radially outside annular protrusion 26 between aluminum material 23 and steel material 29, allowing resin layer 27 to be smoothly discharged through this gap. Furthermore, the passage of current between the electrodes generates a nugget 37 starting from the center of shaft portion 15, where resin layer 27 is absent. On the radially outer side of shaft portion 15, annular protrusion 26 acts as a weir, preventing spatter.

[0071] Thus, even when dissimilar materials are joined via the resin layer 27 by resistance spot welding, a nugget of a desired size can be stably formed at the center of the shaft portion 15 without generating sparks or spatter, thereby achieving a desired sufficient joining strength.

[0072] Furthermore, by utilizing the annular step 17 to rivet the rivet 11 to the aluminum material 23, work hardening occurs at the spot weld between the rivet 11 and the steel material 29, resulting from the riveting of the aluminum material 23 and the rivet 11. This further increases the mutual joining force (mechanical joining force). Consequently, the synergistic effect of spot welding and riveting achieves high joint strength for the dissimilar material joint. Furthermore, when the rivet 11 is pressed into the aluminum material 23 and riveted, cracks can be prevented from forming on the aluminum material 23 side.

[0073] <Other structural examples>

[0074] In the above example, the rivet 11 is fixed to the aluminum material 23 by riveting by driving the rivet 11 into the aluminum material 23 . However, the method of fixing the rivet 11 to the aluminum material 23 is not limited thereto.

[0075] Figure 7 (A) and (B) are process explanatory views showing another method of fixing the rivet 11 to the aluminum material 23 .

[0076] like Figure 7 As shown in (A), a pre-hole 23b with an inner diameter that allows the shaft 15 of the pre-rivet 11 to pass through is pre-set at the location where the rivet 11 is set on the aluminum material 23. When forming the pre-hole 23b, for example, the aforementioned Figure 2 The die head 21 shown and the punch having the outer shape of the annular step portion 17 of the rivet 11 are as shown in FIG. Figure 7 As shown in (A), an annular protrusion 26 is pre-formed on the periphery of the pre-hole 23b. Figure 7 As shown in FIG. 2 (B), the shaft portion 15 of the rivet 11 is passed through the pre-hole 23 b by punching or the like, thereby fixing the rivet 11 to the aluminum material 23 .

[0077] The annular protrusion 26 of the pilot hole 23 b may be formed so as to protrude from the aluminum material 23 after the rivet 11 is fixed, and the forming method is not limited.

[0078] The rivet 11 can be riveted to the aluminum material 23 by stamping, for example, when the aluminum material 23 is a vehicle body structural member, during the vehicle body stamping process. Alternatively, the rivet 11 can be riveted to the aluminum material 23 by stamping, separately from the stamping process, in a process before or after the stamping process, such as an aluminum plate manufacturing process.

[0079] Figure 8 It shows Figure 6 A cross-sectional view of another structure of a dissimilar metal joint shown.

[0080] Here, another steel material 30 is further overlapped on the side of the steel material 29 opposite to the aluminum material 23. According to this structure, by overlapping multiple steel materials 29 and 30 and spot welding them with the rivet 11, three pieces of material can be simply joined by a single welding. Moreover, by providing multiple pieces of steel materials 29 and 30, the strength of the joint body can be improved, and the applicable range of joining dissimilar materials can be expanded. It should be noted that the number of steel sheets is more than 3, and the plate thicknesses can be the same or different. Similarly, with respect to the aluminum material 23, the number of sheets and the plate thickness are arbitrary within the range that the annular protrusion 26 can be formed.

[0081] Figure 9A 、 Figure 9B 、 Figure 9C This is a partially enlarged cross-sectional view showing another shape of the annular step portion of the rivet.

[0082] The annular step portion 17 of the rivet 11 is not limited to Figure 1B The shape shown. Figure 9A As shown, the annular step portion 17A may be configured such that the annular corner portions 17a, 17b and the annular corner portion 17c are each formed at a right angle in the axial cross section. In this case, the engagement of the aluminum material with the rivet 11 is optimized, and the riveting strength can be increased.

[0083] And, as Figure 9B As shown, the annular step portion 17B may also be an annular protrusion having a corner portion 17b on the head back surface 13a side of the shaft side surface 15b, an inclined surface 17d that expands radially outward toward the shaft front end surface 15a of the rivet 11, and a cylindrical surface 17e extending axially from the head back surface 13a and having a corner portion 17c formed at the front end. In this case, as shown in FIG. Figure 7 As shown in (B), when the annular step portion 17B is pressed against the aluminum material 23, the aluminum material plastically flows into the space between the cylindrical surface 17e and the shaft side surface 15b. Furthermore, the portion of the protrusion including the corner portion 17c deforms radially outward and bites into the aluminum material 23. This allows the rivet 11 and the aluminum material 23 to be more securely connected.

[0084] Moreover, if Figure 9C As shown, the annular step portion 17C may also be an annular protrusion having the aforementioned inclined surface 17d and an inclined surface 17f extending axially from the head back surface 13a and expanding radially outward toward the shaft front end surface 15a, with a corner portion 17c formed at the front end. In this case, the angle of the corner portion 17c in the axial cross section is smaller than that of the annular step portion 17B, which improves the engagement with the aluminum material 23 and achieves a more secure riveted state.

[0085] <Surface treatment of rivets>

[0086] Next, a process of forming a film on the surface of the rivet 11 will be described.

[0087] It is preferable to provide a zinc high eutectic nickel plating film having a nickel eutectic ratio of 13 to 18%, for example, on the surface of the rivet 11 .

[0088] The zinc eutectic nickel plating film preferably has a thickness of 5 to 10 μm, which can provide excellent corrosion resistance and heat resistance, thereby effectively preventing electrolytic corrosion.

[0089] It is also preferable to further provide a chemical conversion film on the zinc eutectic nickel plating film of the rivet 11. The chemical conversion film may be a chromate film obtained by subjecting the surface of the zinc eutectic nickel plated rivet to a chromate treatment (JIS H0201).

[0090] Chromate films are thinner than paint and can ensure high corrosion resistance and heat resistance. In addition, they improve the adhesion of paint in electrodeposition coating after joining dissimilar materials.

[0091] Alternatively, a zircon-based chemical conversion coating can be formed instead of a chromate coating. Examples of zircon-based chemical conversion treatments include those using zircon phosphate. Using a zircon-based chemical conversion coating allows for chromium-free treatment.

[0092] The present invention is not limited to the above-mentioned embodiments. Combining the various structures of the embodiments with each other, and making changes and applications based on the description in the specification and known technologies by those skilled in the art are also intended contents of the present invention and are included in the scope of protection required.

[0093] As described above, the following matters are disclosed in this specification.

[0094] (1) A method for joining dissimilar materials, comprising the steps of: driving a rivet having a head and a shaft into and penetrating a first member; arranging the first member through which the rivet is installed and a second member capable of being welded to the rivet in an overlapping manner with a resin layer sandwiched between the front end side of the rivet's shaft of the first member and the second member; and performing spot welding while sandwiching the rivet and the second member using a pair of electrodes, applying a current while applying pressure between the electrodes, and removing the resin layer from between the electrodes.

[0095] The rivet has an annular step portion formed along the circumferential direction and protruding in the axial direction at a connection portion with the shaft portion on the back side of the head.

[0096] When the rivet is driven into and mounted on the first member, the annular step portion presses the first member to form an annular protrusion that causes the inner peripheral edge of the through hole of the shaft portion in the first member to protrude toward the second member.

[0097] By applying pressure between the electrodes during the spot welding, a gap is formed between the radially outer side of the annular protrusion of the first member and the second member, and spot welding is performed while the resin layer is discharged into the gap.

[0098] According to this dissimilar material joining method, the resin layer can be reliably removed from the interface between the rivet and the second member, thereby enabling the rivet and the second member to be spot welded smoothly without causing splashing. In addition, by driving the rivet into the first member, the rivet can be prevented from falling out, thereby improving operability and welding workability.

[0099] (2) A method for joining dissimilar materials, comprising the steps of: placing a first member having a pre-hole and an annular protrusion on the periphery of the pre-hole in an overlapping manner with a second member with a resin layer interposed therebetween; passing the shaft of a rivet having a head and a shaft that can be welded to the second member through the pre-hole of the first member; and clamping the rivet and the second member with a pair of electrodes, applying electricity while applying pressure between the electrodes, and spot welding while excluding the resin layer from between the electrodes, wherein:

[0100] The rivet has an annular step portion formed along the circumferential direction and protruding in the axial direction at a connection portion with the shaft portion on the back side of the head.

[0101] By applying pressure between the electrodes during the spot welding, a gap is formed between the radially outer side of the annular protrusion of the first member and the second member, and spot welding is performed while the resin layer is discharged into the gap.

[0102] This dissimilar material joining method reliably removes the resin layer from the interface between the rivet and the second member, enabling excellent spot welding between the rivet and the second member without spattering. Furthermore, the rivet can be inserted into the pre-hole of the first member at any time, such as during the stamping process of the first member or in a process separate from or before or after the stamping process, thereby increasing the degree of process flexibility.

[0103] (3) The method for joining dissimilar materials according to (1) or (2), wherein:

[0104] A member of the same type as the second member is further overlapped on the side of the second member opposite to the first member and spot welded.

[0105] According to this dissimilar material joining method, by providing a plurality of steel materials, the strength of the joined body can be increased, and the application range of the dissimilar material joining can be expanded.

[0106] (4) The method for joining dissimilar materials according to any one of (1) to (3), wherein:

[0107] The rivet is provided with a zinc eutectic nickel plating film.

[0108] According to this method of joining dissimilar materials, it is possible to provide a rivet with excellent corrosion resistance and heat resistance.

[0109] (5) The method for joining dissimilar materials according to (4), wherein:

[0110] In the dissimilar material joining method, a chemical conversion film is further provided covering the zinc eutectic nickel plating film of the rivet.

[0111] According to this method for joining dissimilar materials, high corrosion resistance and heat resistance can be ensured, and the adhesion of the coating material is improved in electrodeposition coating or the like after joining the dissimilar materials.

[0112] (6) The method for joining dissimilar materials according to (5), wherein:

[0113] The chemical conversion film is a chromate film.

[0114] According to this dissimilar material joining method, since it is a widely known process, a good coating can be stably obtained even under various conditions.

[0115] (7) The method for joining dissimilar materials according to (5), wherein:

[0116] The chemical conversion film is a zirconium-based chemical conversion film.

[0117] According to this dissimilar material joining method, a chemical conversion film can be formed by a chromium-free treatment.

[0118] (8) A rivet having a head and a shaft, wherein:

[0119] The rivets are used for joining dissimilar materials as follows:

[0120] A first member having the shaft portion inserted therethrough and a second member capable of being welded to the rivet are arranged in an overlapping manner with a resin layer interposed between the front end side of the shaft portion of the rivet of the first member and the second member. The rivet and the second member are sandwiched by a pair of electrodes, and current is applied between the electrodes while pressurizing the electrodes, and spot welding is performed while the resin layer is removed from between the electrodes.

[0121] The rivet includes an annular step portion formed along the circumferential direction and protruding in the axial direction at a connection portion with the shaft portion on the back side of the head portion.

[0122] According to this rivet, the resin layer can be reliably removed from the interface with the second member, thereby enabling good spot welding with the second member without generating splashes.

[0123] Note that this application is based on Japanese patent application No. 2020-144619 filed on August 28, 2020, the contents of which are incorporated herein by reference.

[0124] Description of reference numerals:

[0125] 11 Rivets

[0126] 13 Head

[0127] 13a Back of head

[0128] 15 Shaft

[0129] 15a Front end of shaft

[0130] 15b Shaft side

[0131] 17, 17A, 17B, 17C Annular step

[0132] 17a Corner

[0133] 17b corner part

[0134] 17c Corner

[0135] 17d inclined surface

[0136] 17e cylindrical surface

[0137] 17f Inclined surface

[0138] 19 Top

[0139] 21 Die Head

[0140] 21a recess

[0141] 23 Aluminum (first component)

[0142] 23a Flat surface

[0143] 23b Pre-hole

[0144] 25 punch

[0145] 26 annular protrusion

[0146] 27 Resin layer

[0147] 29 Steel (Second Component)

[0148] 30 Steel (same type of components)

[0149] 31 outer periphery

[0150] 33, 35 electrodes

[0151] 37 nugget.

Claims

1. A method for joining dissimilar materials, comprising the steps of: driving a shaft portion of a rivet having a head and a shaft portion into and penetrating a first member; overlapping the first member through which the rivet is installed and a second member capable of being welded to the rivet so that a resin layer is sandwiched between the front end side of the shaft portion of the rivet of the first member and the second member; and performing spot welding while sandwiching the rivet and the second member using a pair of electrodes, applying electricity while applying pressure between the electrodes, and removing the resin layer from between the electrodes. The rivet has an annular step portion formed along the circumferential direction and protruding in the axial direction at a connection portion with the shaft portion on the back side of the head. When the rivet is driven into and mounted on the first member, the annular step portion presses the first member to form an annular protrusion that causes the inner peripheral edge of the through hole of the shaft portion in the first member to protrude toward the second member. By applying pressure between the electrodes during the spot welding, a gap is formed between the radially outer side of the annular protrusion of the first member and the second member, and spot welding is performed while the resin layer is discharged into the gap.

2. The method for joining dissimilar materials according to claim 1, wherein: A member of the same type as the second member is further overlapped on the side of the second member opposite to the first member and spot welded.

3. A method for joining dissimilar materials, comprising the steps of: placing a first member having a pre-hole and an annular protrusion on the periphery of the pre-hole in an overlapping manner with a second member with a resin layer interposed therebetween; passing the shaft of a rivet having a head and a shaft that can be welded to the second member through the pre-hole of the first member; and using a pair of electrodes to sandwich the rivet and the second member, applying electricity while applying pressure between the electrodes, and spot welding while removing the resin layer from between the electrodes, wherein The rivet has an annular step portion formed along the circumferential direction and protruding in the axial direction at a connection portion with the shaft portion on the back side of the head. By applying pressure between the electrodes during the spot welding, a gap is formed between the radially outer side of the annular protrusion of the first member and the second member, and spot welding is performed while the resin layer is discharged into the gap.

4. The method for joining dissimilar materials according to claim 3, wherein: A member of the same type as the second member is further overlapped on the side of the second member opposite to the first member and spot welded.

5. The method for joining dissimilar materials according to any one of claims 1 to 4, wherein: The rivet is provided with a zinc eutectic nickel plating film.

6. The method for joining dissimilar materials according to claim 5, wherein: In the dissimilar material joining method, a chemical conversion film is further provided covering the zinc eutectic nickel plating film of the rivet.

7. The method for joining dissimilar materials according to claim 6, wherein: The chemical conversion film is a chromate film.

8. The method for joining dissimilar materials according to claim 6, wherein: The chemical conversion film is a zirconium-based chemical conversion film.

9. A joined body used in the dissimilar materials joining method according to any one of claims 1 to 8, comprising: the rivet having a head and a shaft; and the first member penetrating the shaft to which the rivet is attached, wherein: The rivet has an annular step portion formed along the circumferential direction and protruding in the axial direction at a connection portion between the back side of the head and the shaft portion. The first member has an annular protrusion protruding forward in the insertion direction of the shaft portion at an inner peripheral edge portion of a through hole through which the shaft portion of the first member passes. The rivet is fixed by the pressure between the electrodes during the spot welding so as to form a gap between the radially outer side of the annular protrusion of the first member and the second member.

10. A joined body used in the dissimilar materials joining method according to any one of claims 1 to 8, comprising: the rivet having a head and a shaft; and the first member penetrating the shaft to which the rivet is attached, wherein: The rivet has an annular step portion formed along the circumferential direction and protruding in the axial direction at a connection portion between the back side of the head and the shaft portion. The first member has an annular protrusion protruding forward in the insertion direction of the shaft portion at an inner peripheral edge portion of a through hole through which the shaft portion of the first member passes. The annular protrusion is formed to be equal to or lower than the outer peripheral edge of the shaft front end surface of the shaft portion, The radially outer side of the annular protrusion has a surface recessed from the annular protrusion.

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