Dissimilar material joining method and composite member

Abstract

To provide a novel method for joining dissimilar materials, in which a raw material for joining and a material to be joined can be joined with superior bonding strength according to access (single side access) from one direction relative to the raw material for joining, regardless of a rear surface structure and thickness of the raw material for joining and the height of a joint part, and to provide a composite member according to the method.SOLUTION: In a state that a raw material 3 for joining is abutted against one surface of a material 2 to be joined, a tip side of a friction agitation tool 1 is press-fitted to the raw material 3 for joining in order to apply friction and agitation thereto under rotation of the friction agitation tool, through an open hole 21 from the other surface side of the material 2 to be joined, and a part of the raw material 3 for joining is fluidized to the other surface side of the material 2 to be joined, through a gap between an inner peripheral edge part of the material 2 to be joined forming the open hole 21 and the friction agitation tool 1, thereby forming a joint part 31 engaging with the inner peripheral edge part of the material 2 to be joined.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for joining dissimilar materials using friction stir forming, and to a composite member. [Background technology]

[0002] In recent years, in order to reduce the weight of automobiles, aircraft, and other such components, it is predicted that the use of multi-material parts will progress rapidly over the next 20 years. This calls for the establishment of dissimilar material (dissimilar metal) joining technologies that provide excellent joining strength and appearance without increasing weight.

[0003] Conventionally, there are known methods for joining dissimilar materials, namely, mechanical joining methods which are applicable to any materials to be joined, and metallurgical joining methods such as resistance spot welding.

[0004] Conventional mechanical joining methods include screws, conventional rivets, self-piercing rivets and blind rivets, but there is a problem that fasteners (rivets) increase the weight.

[0005] In recent years, research has been conducted into the use of friction stir welding (FSW) and friction stir spot welding (FSSW) as metallurgical methods for joining dissimilar materials. However, there is a problem in that there are restrictions on the thermal conditions for suppressing the thickness of the intermetallic compound layer at the interface between the materials to be joined, which reduces the joint strength.

[0006] In addition, friction stir welding has the restriction that when overlapping and joining dissimilar materials, the friction stir tool must be pressed in from the side of the material to be joined, which has a relatively low melting point. Therefore, although it is suitable for joining plate materials, it is difficult to apply it to joining thick aluminum alloy casting parts or aluminum alloy shaped materials to steel plates, as the back structure and large thickness of the aluminum alloy casting parts or aluminum alloy extrusions get in the way.

[0007] On the other hand, the present inventor has proposed a method for joining dissimilar materials using friction stir forming (FSF) (Patent Document 1). Specifically, the joining method of Patent Document 1 uses a friction stir tool having a protrusion at the tip shoulder of a cylindrical shape, (a) a plate-shaped joining material is placed on the upper surface of a plate-shaped workpiece material with a pilot hole drilled therein, and a molding die is placed on the lower surface, and (b) the friction stir tool is rotated and lowered relative to the joining material, and while feeding it in a predetermined horizontal direction, it is pressed in and friction stirred. As a result, the flowed joining material is deformed and filled in the cavity of the molding die, forming a bulge in the rivet-like joint, and the joining material is mechanically joined to the plate-shaped workpiece material. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2018-51606 A Summary of the Invention [Problem to be solved by the invention]

[0009] However, even in the joining method of Patent Document 1, there is a constraint that the friction stir tool must be pressed in from the joining material side, so if the back surface structure of the joining material gets in the way or if the material is thick, it is not necessarily easy to form a rivet-like joint.

[0010] Furthermore, in the joining method of Patent Document 1, it is necessary to place a plate-shaped joining material on the top surface of the plate-shaped joined materials, place a forming die on the bottom surface, and press in a friction stir tool from the joining material side. In other words, in the case of the joining method of Patent Document 1, access from two directions (front and back) of the joining material is required (double-side access), so it was thought that the difficulty in mounting it on, for example, an industrial robot arm was an area that needed to be improved.

[0011] Furthermore, in the joining method of Patent Document 1, when attempting to form a riveted joint with a large height, it is necessary to press the friction stir tool deeply into the joining materials. In this case, the bottom of the press mark of the friction stir tool and the vicinity of the base of the riveted joint come close to each other, which may reduce the strength of the joint, and this was considered to be an area that should be improved.

[0012] The present invention has been made in consideration of the above-mentioned circumstances, and has an objective of providing a new method for joining dissimilar materials that can join a joining material and a joined material with excellent joining strength by accessing the joining material from one direction (single side access) regardless of the back structure and thickness of the joining material or the height of the joint portion to be formed, and a composite member made using this method. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides a dissimilar material joining method for joining a workpiece and a joining material using a friction stir tool, comprising the steps of: The workpiece is a plate having a through hole into which the tip of the friction stirring tool can be inserted, The process is as follows: a friction stirring step in which, while rotating the friction stirring tool, in a state in which the joining material is in contact with one surface of the workpiece, the tip side of the friction stirring tool is pressed into the joining material from the other surface side of the workpiece through the through hole to frictionally stir, and a part of the joining material flows to the other surface side of the workpiece through a gap between the friction stirring tool and the inner peripheral edge of the workpiece that forms the through hole, thereby forming a joint portion that meshes with the inner peripheral edge of the workpiece The present invention is characterized in that it includes:

[0014] The composite member of the present invention is a composite member in which a joined material and a joining material are joined, The workpiece is a plate having a through hole, The joining material is in contact with one surface of the workpiece, a joint portion is formed in which a part of the joining material is engaged with an inner peripheral edge portion of the joined material that forms at least the through hole, The joint portion located inside the through hole is characterized in that a substantially cylindrical recess is formed on the other surface side of the workpieces as a press-fit mark of a friction stir tool. Effect of the Invention

[0015] The method for joining dissimilar materials of the present invention can join a joining material and a joined material with excellent joining strength by accessing the joining material from one side (single side access) regardless of the thickness of the joining material or the height of the joint to be formed. Furthermore, the composite member of the present invention has excellent joining strength. [Brief description of the drawings]

[0016] [Figure 1] 1(A) and 1(B) are schematic diagrams illustrating a first embodiment of a method for joining dissimilar materials according to the present invention. [Diagram 2] (A) is a schematic diagram showing the mechanism by which a through hole is formed by a punching process (press shearing process) using a punch and a die, and (B) is a schematic diagram showing the sagging and fracture surface formed on the inner surface of the through hole. [Diagram 3] 1 is a schematic diagram illustrating a third embodiment of the method for joining dissimilar materials of the present invention, in which an aluminum alloy is used as a joining material. [Figure 4] 1 is a schematic diagram illustrating a fourth embodiment of the method for joining dissimilar materials of the present invention, in which an aluminum alloy is used as a joining material. [Diagram 5] 11A and 11B are a front view and a sectional view illustrating a star-shaped shape of the communication holes of the blank holder when viewed from the front. [Figure 6] 1 is a schematic diagram illustrating another embodiment of the dissimilar material joining method of the present invention. [Figure 7] FIG. 1 is a front view showing the test specimens used for cross tensile strength (CTS) and shear tensile strength (TSS). [Figure 8]FIG. 2 is a diagram showing the appearance and cross-sectional macrostructure of a joint formed in an example. [Figure 9] 1 is an enlarged photograph of a joint between a joint portion and a workpiece. [Figure 10] This is a photograph showing the state of a joint that was destroyed during CTS and TSS evaluation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A first embodiment of the method for joining dissimilar materials of the present invention will be described below. Figures 1(A) and (B) are cross-sectional views illustrating the first embodiment of the method for joining dissimilar materials of the present invention.

[0018] The method for joining dissimilar materials of the present invention uses a friction stir tool 1 to join a workpiece 2 and a raw material 3 to be joined.

[0019] The friction stir tool 1 may be any tool that can be used for friction stir forming (FSF), and the specific form is not limited thereto, but an example of the friction stir tool 1 is the friction stir tool 1 described in Patent Document 1. Specifically, as illustrated in Fig. 1(A) and (B), the friction stir tool 1 preferably includes a substantially cylindrical main body 11, a shoulder portion 12 located at the tip of the main body 11, and a protrusion 13 protruding from the shoulder portion 12.

[0020] Moreover, the friction stirring tool 1 is preferably made of a heat-resistant alloy or the like that is hard and has high heat resistance.

[0021] The shape of the protrusion 13 is not particularly limited, and examples of the shape include a disk shape, a cylindrical shape, a cone shape, a hemispherical shape, a screw shape, etc. In the embodiment illustrated in Fig. 1, the friction stirring tool 1 has a cylindrical protrusion 13.

[0022] The height and volume of the protrusion 13 are not particularly limited, and can be appropriately set in consideration of the embodiments described later.

[0023] The shoulder portion 12 may be provided, as a whole or in part, with an inclination angle θ of, for example, about 45° or less, which is deeply inclined toward the center of the rotation axis of the friction stirring tool 1. The magnitude of this inclination angle θ is preferably determined in consideration of the flow state of the joining material 3 laterally with respect to the rotation axis, the occurrence of burrs, the aesthetic state, and the like.

[0024] The workpieces 2 are in the form of a plate having a through hole 21 into which the tip (projection 13) of the friction stirring tool 1 can be inserted.

[0025] The material of the workpieces 2 is not particularly limited, and examples thereof include hard steel plate, titanium, glass, and CFRP.

[0026] The number of through holes 21 formed in the workpiece 2 may be one or two or more, and when there are two or more, the sizes of the through holes 21 may be the same or different diameters.

[0027] The shape of the through hole 21 is not particularly limited, and may be a circle, a rectangle, a polygon, a substantially long hole, a slit, a curved hole, etc. in a front view. In the embodiment illustrated in Fig. 1, a circular through hole 21 is formed in the workpiece 2.

[0028] The thickness of the workpiece 2 is not particularly limited, and can be designed taking into consideration the cross-sectional area of ​​the through hole 21, the conditions under which the joining material 3 becomes fluid, the design and operation conditions of the friction stir tool 1, etc. Specifically, for example, the thickness of the workpiece 2 is t, the depth to which the tip of the friction stir tool 1 is pressed into the joining material 3 is h, p [mm], the diameter of the protrusion 13 is d [mm], the diameter of the through hole 21 is D [mm], and the shear strength of the joining material 3 is τ [MPa]. From the law of constancy of the volume of plastic deformation,

number

number

number

[0029] Needless to say, it is desirable to design each of the above design values ​​with a margin of error in order to accommodate positional errors between the friction stirring tool 1 and the through hole 21 during construction and variations due to softening of the joining material 3 by heat.

[0030] In addition, if the tip of the friction stirring tool 1 is too close to the back surface of the joining material 3, the joining material 3 may be pulled and cracked. In order to prevent cracking, depending on the material and temperature of the joining material 3, p A preferable guideline for the thickness is, for example, within about 90% of the thickness of the bonding material 3 .

[0031] The material of the joining material 3 is not particularly limited, and may be, for example, aluminum and its alloys, magnesium alloys, copper and its alloys, titanium and its alloys, steel, etc., with aluminum being a preferred example.

[0032] The method for joining dissimilar materials of the present invention includes a friction stir step.

[0033] In the friction stirring process, while the friction stirring tool 1 is rotating in a state where the joining material 3 is in contact with one surface 2A of the workpiece 2, its tip (projection 13) is pressed into the joining material 3 from the other surface 2B side of the workpiece 2 through the through hole 21 to perform friction stirring. As a result, a part of the joining material 3 flows to the other surface 2B side of the workpiece 2 (friction stirring tool 1 side) through the gap between the inner peripheral edge 22 of the workpiece 2 that forms the through hole 21 and the friction stirring tool 1 (projection 13), forming a joint 31 that joins with the inner peripheral edge 22 of the workpiece 2.

[0034] More specifically, in this embodiment, when the shoulder portion 12 and the workpieces 2 are spaced apart, the protrusion 13 is designed to have a height that reaches the joining material 3 located on one surface 2A of the workpieces 2. With the shoulder portion 12 and the workpieces 2 spaced apart, the protrusion 13 is pressed into the joining material 3 through the through hole 21 and frictionally stirred, whereby a part of the joining material 3 flows from the one surface 2A of the workpieces 2 to between the workpieces 2 located on the other surface 2B and the shoulder portion, forming the head 31a of the joint portion 31.

[0035] The method for joining dissimilar materials of the present invention allows access (single-side access) to the joining material 3 from one direction, the side of the joined material 2. Therefore, regardless of the thickness of the joining material 3 or the height of the joint portion 31 to be formed, the joining material 3 and the joined material 2 can be joined with excellent joining strength.

[0036] In this embodiment, the composite member has a flange-shaped head 31a formed by wrapping around the through hole 21 located on the other surface 2B side of the workpiece 2, and is engaged with the flange-shaped head 31a. More preferably, in the composite member in which the workpiece 2 and the workpiece 3 are joined by the dissimilar material joining method of this embodiment, the strength of the joint portion 31 can be improved by metallurgically bonding a part of the workpiece 3 to the inner peripheral portion 22 of the workpiece 2 that forms the through hole 21. In addition, a recess (a press-fit mark of the friction stir tool 1) that is recessed in a substantially cylindrical shape from the other surface 2B side of the workpiece 2 is formed in the region located inside the through hole 21. In addition, in this embodiment, the composite member has a flange-shaped head 31a formed by wrapping around the through hole 21 located on the other surface 2B side of the workpiece 2, and is formed by wrapping around the through hole 21.

[0037] Furthermore, by providing the side surface of the through hole 21 with a slope that widens outward toward the other surface 2B of the workpieces 2 (the friction stir tool 1 side), the shear area in the pulling direction of the rivet-like joint part 31 can be increased to obtain better joint strength. In this case, by abutting the shoulder part 12 against the other surface 2B of the workpieces 2, the rivet-like joint part 31 can be formed so as not to protrude toward the surface 2B of the workpieces 2.

[0038] In the composite member of the present invention, the structure of the rivet-like joint portion 31 maintains its strength by being connected to the joining material 3 via the flange-like head 31a, so that the friction stir tool 1 can be pressed in deeper and excellent joining strength can be maintained even if the bottom of the recess becomes thin.

[0039] The design and operating conditions of the friction stirring tool 1 may take into consideration the description in Patent Document 1, for example.

[0040] Specifically, for example, the area of ​​the shoulder portion of the rotating friction stirring tool 1, the volume of the protrusions, the rotation speed, the horizontal movement distance and movement speed, the pressing force and the pressing amount when pressing are as follows: 1) Type (softening temperature) and thickness of bonding material 3, 2) the thickness of the workpiece 2 and the diameter of the through hole 21; 3) Burrs generated at the contact area between the outer edge of the friction stirring tool 1 and the joining material 3 Taking these factors into consideration, the conditions for fluidizing the bonding material 3 can be determined.

[0041] A second embodiment of the method for joining dissimilar materials according to the present invention will be described.

[0042] The method for joining dissimilar materials of the present invention can include a punching step of forming the through holes 21 in the materials to be joined 2 by a punching process using a punch and a die.

[0043] FIG. 2 is a schematic diagram showing the mechanism by which a through hole 21 is formed by a punching process (press shearing process) using a punch and a die.

[0044] In the hole punching process, shear cracks are generated in the material from the contact area between the shoulder 41 of the die 4 and the edge 51 of the punch 5, and these cracks connect to form the through hole 21. As a result, an inclined fracture surface 21a is formed in the shear direction at the inner peripheral edge 22 of the through hole 21 due to the difference (clearance) between the outer diameter of the punch 5 and the inner diameter of the die 4. In addition, a sag 21b is also formed depending on the clearance conditions.

[0045] In the method for joining dissimilar materials of this embodiment, in the friction stir process, the joint portion 31 is joined to the inner peripheral edge portion 22 via a sagging or fracture surface. Therefore, the joint portion 31 of this embodiment can achieve excellent joining strength even without forming a head.

[0046] In the case where the head of the joint portion 31 is not formed in the composite member obtained by the dissimilar material joining method of this embodiment, the joint portion 31 and the other surface 2B of the workpiece 2 can be formed flat (excluding recesses due to the pressing marks of the friction stir tool 1).

[0047] Also, for example, a face-stripping punch can be used as the punch to provide a step or inclination around the through-hole 21 on the other surface 2B side of the workpieces 2 in FIG. 1, thereby achieving even better joining strength.

[0048] A third embodiment of the method for joining dissimilar materials according to the present invention will be described.

[0049] FIG. 3 is a schematic diagram illustrating one embodiment of the method for joining dissimilar materials of the present invention.

[0050] In the method for joining dissimilar materials of the present invention, in the friction stir process, a blank holder 6 having a communicating hole 61 is placed around the through hole 21 located on the other surface 2B side of the workpiece 2, and a friction stirring tool 1 can be inserted into this communicating hole 61 to perform friction stirring.

[0051] In the embodiment illustrated in FIG. 3, the friction stirring tool 1 has a generally cylindrical body 11, a flat shoulder 12 located at one end of the body 11, and a protrusion 13 protruding from the shoulder 12.

[0052] The communication hole 61 of the blank holder 6 is generally cylindrical and communicates in the vertical direction, and the diameter D of the communication hole 61 is formed slightly larger than the outer diameter D' of the main body of the friction stirring tool 1. The diameter D of the communication hole 61 is also formed larger than the diameter of the through hole 21, and the center of the communication hole 61 and the center of the through hole 21 generally coincide in the vertical direction. The material of the blank holder 6 is not particularly limited, and it can be made of various metals, etc.

[0053] In this embodiment, in the friction stirring process, the tip side (main body 11, shoulder 12, protrusion 13) of the friction stirring tool 1 is inserted into the communication hole 61, and in a state in which the shoulder 12 and the workpiece 2 are separated, the protrusion is pressed into the joining material 3 through the through hole 21 to perform friction stirring. At this time, the inner peripheral surface of the blank holder 6 forming the communication hole 61 and the outer peripheral surface of the main body 11 of the friction stirring tool 1 face each other closely with almost no gap. A part of the joining material 3 is made to flow by friction stirring and filled between the workpiece 2 and the shoulder 12, thereby forming the head 31a of the joint part 31.

[0054] In the dissimilar material joining method of this embodiment, the joining material 3 can also be accessed from one direction (single-side access) on the side of the joined material 2. Therefore, regardless of the thickness of the joining material 3 or the height of the joint portion 31 to be formed, the joining material 3 and the joined material 2 can be joined with excellent joining strength.

[0055] In addition, the blank holder 6 provides a sealed structure that restricts the lateral flow range of the joining material 3, making it possible to stably obtain a taller joint 31. Furthermore, by providing such a blank holder 6, it is possible to suppress the workpieces 2 from floating up or deforming.

[0056] Therefore, the distance H between the workpieces 2 and the shoulder portion 12 can be appropriately set in consideration of the joining strength due to the thickness of the head 31a of the joint portion 31. In addition, the height and press-fit depth of the protrusion 13 (the distance hp from one surface 2A of the workpieces 2 to the tip of the protrusion 13) can be appropriately designed in consideration of the desired size and strength of the joint portion 31.

[0057] A fourth embodiment of the method for joining dissimilar materials according to the present invention will now be described. Fig. 4 is a schematic diagram illustrating one embodiment of the method for joining dissimilar materials according to the present invention.

[0058] 4, the friction stirring tool 1 has a tip portion 14 having a substantially cylindrical shape. The communication hole 61 of the blank holder 6 is substantially cylindrical and communicates in the vertical direction, and the diameter d' of the communication hole 61 is slightly larger than the diameter d of the tip portion 14 of the friction stirring tool 1. The diameter d' of the communication hole 61 is substantially equal to the diameter of the through hole 21.

[0059] The blank holder 6 is provided with a head forming space 62 at the end of the communicating hole 61 located on the side of the workpieces 2, the head forming space 62 extending outward from the inner peripheral surface forming the communicating hole 61. In this embodiment, the head forming space 62 is formed in a disk shape, and its diameter D is designed to be larger than the diameter d' of the communicating hole 61 and the diameter of the through hole 21.

[0060] In this embodiment, in the friction stirring process, the tip 14 of the friction stirring tool 1 is inserted into the communication hole 61, passed through the head forming space 62, and pressed into the joining material 3 through the through hole 21 to perform friction stirring. At this time, the inner peripheral surface of the blank holder 6 that forms the communication hole 61 and the outer peripheral surface of the tip 14 of the friction stirring tool 1 face each other closely with almost no gap. Part of the joining material 3 is caused to flow by friction stirring, and part of the joining material 3 is filled in the head forming space 62, whereby the head 31a of the joint part 31 can be formed.

[0061] In the dissimilar material joining method of this embodiment, the joining material 3 can also be accessed from one direction (single-side access) on the side of the joined material 2. Therefore, regardless of the thickness of the joining material 3 or the height of the joint portion 31 to be formed, the joining material 3 and the joined material 2 can be joined with excellent joining strength.

[0062] In addition, the blank holder 6 provides a sealed structure that restricts the lateral flow range of the joining material 3, making it possible to stably obtain a taller joint 31. Furthermore, by providing such a blank holder 6, it is possible to suppress the workpieces 2 from floating upward or becoming deformed.

[0063] Therefore, the height H of the head forming space 62 can be appropriately set in consideration of the joining strength due to the thickness of the head 31a of the joint part 31. Also, the press-fit depth of the tip part 14 of the friction stirring tool 1 (the distance hp from the one surface 2A of the workpieces 2 to the tip of the tip part 14) can be appropriately designed in consideration of the desired size and strength of the joint part 31.

[0064] The dissimilar material joining method and composite member of the present invention are not limited to the above-described embodiments, and include, for example, the following embodiments.

[0065] (A) If the joining material is thin, a backing plate can be provided on the joining material.

[0066] (B) The shape of the communication hole 61 of the blank holder, which determines the outer peripheral shape of the head of the rivet-like joint, may be various shapes other than a round hole, but in order to prevent deformation of the workpieces 2, it is also preferable to have claw portions 63 that approach the through hole of the workpieces 2, such as a star shape when viewed from the front as shown in Fig. 5. In this case, it is more preferable that the imaginary tangent circle C connecting the inward tips of the claw portions 63 has the same diameter as the through hole of the workpieces 2, but it may be larger or smaller taking into consideration the joint strength to be secured.

[0067] (C) The shape of the tip of the friction stirring tool (projection 13 in FIG. 1 and the area of ​​tool 14 in FIG. 4 that is pressed into material 3 at the tip) can be appropriately designed so that the joining materials can easily flow upward. By providing a screw-shaped groove on the outer surface, the joining materials can be rolled up, so that the joining materials can flow upward more efficiently.

[0068] (D) It is also preferable to move the rotating tool in a circular orbit so that the side of the friction stir tool abuts against the side of the through hole in the workpieces. This makes it easier to remove the oxide film on the workpiece surfaces and form a mechanical joint with a rivet-like structure while simultaneously achieving metallurgical joining of the workpiece sides.

[0069] (E) It is also preferable to use a friction stirring tool with an eccentric protrusion, and rotate the tool while the protrusion is in contact with the side of the through hole in the workpiece. This makes it easier to remove the oxide film on the surface of the workpiece, form a mechanical joint with a rivet-like structure, and simultaneously achieve metallurgical joining of the side of the workpiece (hard material).

[0070] (F) Fig. 6 is a schematic diagram illustrating another embodiment of the method for joining dissimilar materials of the present invention. As illustrated in Fig. 6, an embodiment using a head holding plate 7 having an opening 71 and a cylindrical friction stirring tool 1 having no protrusion at its tip can be exemplified.

[0071] 6(A), the opening 71 of the head holding plate 7 has a diameter slightly larger than the diameter of the friction stirring tool 1. The head holding plate 7 is disposed in contact with the other surface 2B of the workpieces 2, and the center of the through hole 21 and the center of the opening 71 are approximately aligned in the up-down direction. The diameter of the opening 71 is designed to be slightly smaller than the diameter of the through hole 21.

[0072] 6(B), while the workpieces 4 are held down by the head holding plate 7 so as not to float up, the friction stir tool 1 is inserted into the raw material 3 through the opening 71 and the through hole 21. At this time, a gap is formed between the friction stir tool 1 and the through hole 21, whereas the friction stir tool 1 and the inner peripheral surface of the head holding plate 7 that forms the opening 71 closely face each other. Then, the insertion of the friction stir tool 1 causes the raw material 3 to flow and fill the through hole 21.

[0073] 6(C), the head holding plate 7 is then moved upward to a predetermined position, and the friction stirring tool 1 is further inserted, causing the fluidized joining material 3 to rise further through the through hole 21. The fluidized joining material 3 is then held down from above by the head holding plate 7, so that the upward movement of the fluidized joining material 3 is restricted while it is moved sideways, forming a mechanical joint between the vicinity of the inner peripheral edge portion 22 of the workpieces 2 and the rivet-like joint portion 3 having the head 31a.

[0074] In this embodiment as well, the joining material 3 and the workpiece 2 can be joined with excellent joining strength by accessing the joining material 3 from one side (single side access) regardless of the thickness of the joining material 3 or the height of the joint part 31 to be formed. In addition, by adjusting the position of the head holding plate 7, the height and diameter of the head 31a of the joint part 31 can be easily adjusted.

[0075] In addition, when the deformation of the workpieces 2 is not large, the head holding plate 7 can be left fixed in a specified position as shown in Figure 6 (C) without being movable, and the holding of the workpieces 4 by the head holding plate 7 can be omitted. EXAMPLES

[0076] The method for joining dissimilar materials and the composite member of the present invention will be described in more detail below with reference to examples. However, the method for joining dissimilar materials and the composite member of the present invention are in no way limited to the following examples.

[0077] <Example 1> Molding of joint part A 1 mm thick SPCE steel plate (joining material) with a drilled hole of 10 mm diameter was joined to a 3 mm thick A5083-O aluminum alloy plate (joining material). Specifically, as shown in Figure 3, the top of the materials to be joined was held down with a blank holder (plate holder) with a through hole of 13.5 mm inner diameter, and the SKD61 tool shown in Figure 3 was inserted into the through hole to perform friction stir forming, and the impression formed by the through hole of the blank holder and the shoulder part of the tool was completely filled with the aluminum alloy. Note that no release agent or lubricant was used during forming.

[0078] <Example 2> Test of joint strength The cross tensile strength (CTS) and shear tensile strength (TSS) were evaluated using the test specimen shown in Figure 6. The test equipment used was a SHIMADZU AUTOGRAPH AG-10TB (RX), and the crosshead speed was 1 mm / min.

[0079] <Example 3> Results Figure 7 shows the appearance of the formed joint and a cross-sectional macrostructure photograph. It was observed that the material at the bottom of the aluminum alloy plate had been recessed, leaving a recess of about 0.6 mm deep on the back side. It was confirmed that the aluminum alloy had wrapped around to the top of the steel plate to form an interlock. A star zone was observed near the contact surface with the tool, and although it was prominent near the base of the probe, it was localized. Due to thermal effects, the Vickers hardness was softer overall than that of the base material (107 Hv) before forming (Figure 8).

[0080] In addition, the steel plate around the through hole was deformed due to the flow of the aluminum alloy, so the shear surface area of ​​the aluminum alloy that broke during the joint strength evaluation test was actually smaller than if the steel plate had not deformed.

[0081] Figure 9 shows the appearance of the joints that were destroyed during the CTS and TSS evaluations. In both cases, the head of the rivet-like structure made of aluminum alloy was destroyed.

[0082] The CTS was 2.03 kN (N=5, 1σ=214 N) and the TSS was 4.12 kN (N=5, 1σ=431 N), confirming that the joint had excellent joint strength.

[0083] Therefore, it was confirmed that the dissimilar material joining method of the present invention makes it possible to join the joining material and the joined material with excellent joining strength by accessing the joining material from one direction (single side access) regardless of the thickness of the joining material or the height of the joint portion to be formed. [Explanation of symbols]

[0084] 1 Friction stirring tool 2 Material to be joined 2A First side 2B 2nd side part 21 Through hole 22 Inner periphery 3 Joining material 31 Joint 31a head 4 Die 5 Punch 6 Blank holder 61 Communication hole 62 Head formation space 7 Head support plate 71 Opening

Claims

1. A method for joining dissimilar materials, which joins a workpiece and a joining material using a friction stir tool, comprising the steps of: The workpiece is a plate having a through hole into which the tip of the friction stirring tool can be inserted, The following steps: a friction stirring step in which, while rotating the friction stirring tool, in a state in which the joining material is in contact with one surface of the workpiece, the tip side of the friction stirring tool is pressed into the joining material from the other surface side of the workpiece through the through hole to frictionally stir, and a part of the joining material flows to the other surface side of the workpiece through a gap between the friction stirring tool and the inner peripheral edge of the workpiece that forms the through hole, thereby forming a joint portion that meshes with the inner peripheral edge of the workpiece Including, A method for joining dissimilar materials, characterized in that in the friction stir process, a blank holder having a communicating hole is placed around the through hole located on the other side of the workpieces, and the friction stirring tool is inserted into this communicating hole to perform friction stirring.

2. A piercing process is included in which the through hole of the workpiece is formed by a piercing process using a punch and a die, In the piercing step, a sagging or inclined fracture surface is formed on the inner peripheral edge of the through hole, 2. The method for joining dissimilar materials according to claim 1, wherein in the friction stir step, the joint portion meshes with the inner peripheral edge portion via the sag or the fracture surface.

3. The friction stirring tool includes a substantially cylindrical body, a flat shoulder portion located at one end of the body, and a protrusion portion protruding from the shoulder portion. The communication hole of the blank holder is larger than an outer diameter of the main body of the friction stirring tool, 2. The method for joining dissimilar materials according to claim 1, characterized in that in the friction stirring process, the friction stirring tool is inserted into the communicating hole, and while the shoulder portion and the workpiece are separated, the protrusion is pressed into the joining material through the through hole and friction stirred, thereby causing a part of the joining material to flow between the workpiece and the shoulder portion to form a head of the joint portion.

4. The friction stirring tool has a tip portion having a substantially cylindrical shape, The communication hole of the blank holder is larger than an outer diameter of the tip portion of the friction stirring tool, the blank holder is provided with a head forming space at an end side of the communicating hole located on the workpiece side, the head forming space extending outward from an inner surface of the communicating hole and larger than a diameter of the through hole of the workpiece, 2. The method for joining dissimilar materials according to claim 1, characterized in that, in the friction stirring process, the friction stirring tool is inserted into the communicating hole, and the tip end is pressed into the joining material through the through hole to frictionally stir, thereby causing a portion of the joining material to flow into the head formation space to form a head of the joint portion.

5. A method for joining dissimilar materials, comprising the steps of: joining a workpiece and a joining material using a friction stirring tool, the method comprising the steps of: The workpiece is a plate having a through hole into which the tip of the friction stirring tool can be inserted, The following steps: a friction stirring step in which, while rotating the friction stirring tool, in a state in which the joining material is in contact with one surface of the workpiece, the tip side of the friction stirring tool is pressed into the joining material from the other surface side of the workpiece through the through hole to frictionally stir, and a part of the joining material flows to the other surface side of the workpiece through a gap between the friction stirring tool and the inner peripheral edge of the workpiece that forms the through hole, thereby forming a joint portion that meshes with the inner peripheral edge of the workpiece Including, In the friction stirring process, a head holding plate having an opening having a diameter larger than an outer diameter of the tip of the friction stirring tool is brought into contact with the other surface side of the workpiece, and the opening and the through hole of the workpiece are aligned; The friction stirring tool is inserted into the joining material through the opening and the through hole, thereby filling the through hole with the fluidized joining material; A method for joining dissimilar materials, characterized in that the head holding plate is moved upward to a predetermined position and the friction stirring tool is further inserted into the joining material, thereby causing the head holding plate to restrict the upward movement of the flowing joining material while moving it sideways, thereby forming a head of the joint portion.

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