Member joining method

Abstract

To provide a member joining method capable of suppressing the generation of a deep recessed part in a joining part even when using a joining tool of a simple constitution.SOLUTION: A member joining method according to the embodiment includes: a step of forming a first layer including a fine crystal grain structure on a surface of a first member on a side opposite to a first backing side by performing a friction stirring process using a rotating joining tool; a step of placing a second member on a surface of the first member on a side on which the first layer is formed; and a step of pressurizing and heating a surface of the second member opposite to the first member side in a region facing the first layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a method for joining members. [Background technology]

[0002] For example, friction stir spot welding (FSSW) has been proposed as a method for overlap welding of metal-containing components. Friction stir spot welding has the advantage of requiring less power than resistance welding (spot welding), for example, when joining low-electrical resistance metals such as aluminum.

[0003] In friction stir spot welding, a joining tool having a shoulder and a stirring pin protruding from the shoulder is generally used. When performing friction stir spot welding, a rotating joining tool is pressed against overlapping metal sheets so that the shoulder is positioned inside the upper metal sheet and the stirring pins are positioned inside the upper and lower metal sheets. Therefore, when friction stir spot welding is performed, the shape of the tip of the joining tool is transferred to the joint. In other words, a shallow recess is formed in the joint where the shoulder was pressed in, and a deep recess is formed where the stirring pin was pressed in.

[0004] In addition, in friction stir spot welding, techniques have been proposed in which a fine-grained sheet is sandwiched between metal plates or a fine-grained layer is provided between metal plates. However, these techniques also use a joining tool having a shoulder and a stirring pin protruding from the shoulder, which results in the formation of a deep recess in the joint where the stirring pin was pressed in.

[0005] Deep recesses in the joint area detract from the aesthetics of the product. Furthermore, deep recesses in the joint area tend to trap moisture and other contaminants, which take time to evaporate, resulting in problems such as reduced reliability of the joint and the product. In this case, simply eliminating the stirring pin would eliminate the deep recess in the center of the joint, but it would be difficult for the stirring area to reach the contact point between the metal sheets, making it difficult to achieve the required joint strength. To achieve the required joint strength with a joining tool without a stirring pin, the shoulder would need to be inserted deeply into the upper sheet, ultimately leaving a deep recess in the joint.

[0006] Another proposed technique involves using a separate stirring pin and shoulder, driving them separately, and filling the deep recesses with softened metal. However, driving the stirring pin and shoulder separately complicates the structure of the welding tool, resulting in increased costs. Furthermore, because the shoulder is inserted to a depth greater than the thickness of the upper metal plate, the welding load increases, necessitating a highly rigid friction stir welding device. This increases the cost of the friction stir welding device. Furthermore, because the stirring pin and shoulder are slid separately, softened metal can enter the gap between the stirring pin and shoulder, easily causing wear on the sides of the stirring pin and shoulder. This can lead to a decrease in the strength of the welding tool over time (see Non-Patent Document 1).

[0007] Therefore, there has been a demand for the development of a method for joining members that can prevent deep recesses from occurring in the joining portion even when a joining tool with a simple configuration is used. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 6505618 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-94475 [Patent Document 3] Japanese Patent Application Publication No. 2023-152110 [Non-patent literature]

[0009] [Non-Patent Document 1] Camila C. de Castro et al.: Tool wear mechanisms and effects on refill friction stir spot welding of AA2198-T8 sheets, Journal of Materials Research and Technology, vol.20 (2022), 857-866. Summary of the Invention [Problem to be solved by the invention]

[0010] The problem that the present invention aims to solve is to provide a method for joining components that can prevent deep recesses from occurring in the joining portion even when a joining tool with a simple configuration is used. [Means for solving the problem]

[0011] A method for joining members according to an embodiment includes the steps of: performing friction stir processing on a surface of a first member opposite a first backing side using a rotating joining tool to form a first layer containing a fine crystalline grain structure; placing a second member on the surface of the first member on which the first layer is formed; and applying pressure and heat to a region of the surface of the second member opposite the first member side that faces the first layer. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram illustrating a joining device. [Figure 2] 1(a) to 1(d) are schematic process diagrams illustrating the method for joining members according to the present embodiment. [Figure 3]6(a) to 6(c) are schematic process drawings illustrating a method for joining members according to another embodiment. [Figure 4] 6(a) to 6(d) are schematic process drawings illustrating a method for joining members according to another embodiment. [Figure 5] This is a photograph of a layer formed by friction stir processing. [Figure 6] This is a photograph of the components being joined by applying pressure and heat to the components using a rotating joining tool. [Figure 7] This is a photograph of a cross section of a joint between components. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments will be illustrated with reference to the drawings. In the drawings, like components are designated by like reference numerals and detailed descriptions thereof will be omitted where appropriate.

[0014] First, an example of a joining device 100 capable of carrying out the method for joining members according to this embodiment will be described. FIG. 1 is a schematic diagram illustrating a bonding apparatus 100. As shown in FIG. 1, arrows X, Y, and Z represent three mutually orthogonal directions. For example, arrow Z represents the vertical direction, and arrows X and Y represent the horizontal direction. The joining device 100 shown in FIG. 1 overlaps a member 301 (corresponding to an example of a first member) and a member 302 (corresponding to an example of a second member), and joins the members 301 and 302 together by spot joining or line joining.

[0015] As shown in FIG. 1, the welding apparatus 100 includes, for example, a moving unit 101, a holding unit 102, a backing 103 (which corresponds to an example of a first backing), a processing unit 104, a welding tool 105, and a frame 106.

[0016] The moving unit 101 can be provided on a frame 106. A backing 103 and at least one of a member 301 and a member 302 can be provided on the moving unit 101. The joining device 100 illustrated in FIG. 1 is provided with the backing 103 and the member 301 and the member 302 that are provided one on top of the other. The moving unit 101 can move in at least one of the X direction and the Y direction. The moving unit 101 is, for example, a single-axis table or a two-axis table (XY table).

[0017] The holding unit 102 can be provided, for example, on the moving unit 101. The holding unit 102 holds the backing 103 and at least one of the member 301 and the member 302 provided on the backing 103. The holding unit 102 is, for example, a chuck.

[0018] At least one of a member 301 and a member 302 is provided on the backing 103 . The surface 103a of the backing 103 opposite to the moving part 101 side can be a flat surface. As will be described later, a backing 113 (corresponding to an example of a second backing) may be used instead of the backing 103. A recess 113a1 is provided on the surface 113a of the backing 113 facing the member 301 (member 302). The recess 113a1 is open to the surface 113a.

[0019] The backing 103 and the backing 113 may be, for example, a metal plate. For example, the backing 103 and the backing 113 are formed from tool steel, carbon steel, etc. However, the materials of the backing 103 and the backing 113 are not limited to those exemplified above.

[0020] The processing unit 104 holds the welding tool 105. The processing unit 104 rotates the welding tool 105 around a central axis 104a. The processing unit 104 also changes the position of the rotated welding tool 105. For example, the processing unit 104 changes the position of the rotated welding tool 105 in the Z direction to press the end surface 105a of the welding tool 105 against the member 301 or the member 302. The processing unit 104 includes a control motor 104b such as a servo motor.

[0021] The welding tool 105 has, for example, a cylindrical shape. A typical welding tool used in friction stir welding has a stirring pin protruding from the end face (also called a shoulder, etc.) of the welding tool. However, the end face 105a of the welding tool 105 is flat and does not have a stirring pin. It is also possible to provide a spiral groove on the end face 105a of the welding tool 105. However, providing a spiral groove on the end face 105a of the welding tool 105 may increase the manufacturing cost of the welding tool 105 or increase the likelihood of wear on the end face 105a. It is more preferable that the end face 105a of the welding tool 105 be a flat surface. The material of the welding tool 105 may be, for example, tool steel, tungsten alloy, ceramic, etc. However, the material of the welding tool 105 is not limited to the examples given above.

[0022] The frame 106 is provided with, for example, a processing unit 104 and a moving unit 101. The frame 106 can be installed on the floor of a factory or the like, for example.

[0023] Members 301 and 302 include metal. In this case, the material of member 302 may be the same as or different from the material of member 301. The material of members 301 and 302 may be, for example, aluminum, aluminum alloy, copper, copper alloy, titanium, titanium alloy, magnesium, magnesium alloy, iron, etc. However, the materials of members 301 and 302 are not limited to those exemplified above. There are no particular limitations on the shape of the members 301 and 302, but the members 301 and 302 may be, for example, plate-shaped.

[0024] Next, a method for joining members according to this embodiment will be described. 2(a) to 2(d) are schematic process diagrams illustrating the method for joining members according to this embodiment.

[0025] First, as shown in FIG. 2(a), a layer 301a1 (corresponding to an example of a first layer) is formed on one surface 301a of the member 301. The layer 301a1 includes a fine crystalline grain structure. The fine crystalline grain structure includes, for example, crystal grains having a smaller grain size than the grain size of the crystal grains on the surface 301a of the member 301. For example, when the member 301 is an aluminum alloy (e.g., A5083), the average grain size of the crystal grains on the surface 301a of the member 301 is, for example, approximately 30 μm to 100 μm. The average grain size of the crystal grains in the layer 301a1 can be, for example, 5 μm or less.

[0026] 2(a), the layer 301a1 can be formed by friction stir processing (FSP). For example, when a rotating welding tool 105 is pressed against one surface 301a of the member 301 and held for a certain period of time, a fine grain structure with large residual strain is formed in the region of the surface 301a of the member 301 where the welding tool 105 is pressed.

[0027] When the members 301 are made of an aluminum alloy (e.g., A5083), the rotation speed of the welding tool 105 can be, for example, about 600 rpm, and the holding time can be 3 seconds. The diameter of the end face 105a of the welding tool 105 can be, for example, about 10 mm. The distance by which the end face 105a of the welding tool 105 is pressed from the surface 301a of the members 301 (insertion depth of the welding tool 105) is, for example, about 0.1 mm.

[0028] Here, increasing the rotation speed of the welding tool 105 during friction stir processing increases the temperature of the area of the members 301 where the welding tool 105 is pressed. When the temperature of this area increases, the material softens, reducing deformation resistance and residual strain. As a result, it becomes difficult for the crystal grain diameter to become small. The rotation speed of the welding tool 105 can be changed as appropriate depending on, for example, the material of the members 301. The relationship between the material of the members 301 and the appropriate rotation speed of the welding tool 105 can be determined as appropriate, for example, by conducting experiments or simulations.

[0029] Next, as shown in FIG. 2(b), a member 302 to be joined is placed on the surface 301a of the member 301.

[0030] Next, as shown in FIG. 2(c), pressure and heat are applied to the surface 302a of the member 302 opposite to the member 301 side. For example, a rotating welding tool 105 is pressed against the region of the surface 302a of the member 302 facing the layer 301a1. In this case, the rotation speed of the welding tool 105 can be, for example, the same as the rotation speed of the welding tool 105 when forming the layer 301a1. The insertion depth of the welding tool can be, for example, 0.3 mm.

[0031] With member 301 and member 302 overlapped, if pressure and heat are applied to surface 302a of member 302 opposite to member 301, member 301 and member 302 will be bonded at the position where layer 301a1 was formed, as shown in Figure 2(d).

[0032] The process and mechanism by which the members 301 and 302 are joined together are not entirely clear, but can be considered as follows. When layer 301a1, which includes a fine crystalline grain structure with large residual strain, is pressurized and heated, the temperature increase and pressure cause recrystallization in the fine crystalline grain structure with large residual strain. As recrystallization progresses, the fine crystalline grain structure attempts to form irregularities on its surface. The force that attempts to form these irregularities causes minute deformations at the contact points between layer 301a1 and member 302, causing the oxide films on layer 301a1 and member 302 to break, bringing the clean surfaces of the materials into contact. The contact between the clean surfaces of the materials firmly bonds member 301 and member 302.

[0033] Although FIG. 2(d) illustrates a case where the layer 301a1 containing the fine crystalline grain structure remains after the joining of the member 301 and the member 302, the layer 301a1 containing the fine crystalline grain structure may disappear or become almost completely absent due to recrystallization.

[0034] In the method for joining members according to this embodiment, as shown in Fig. 2(c), the end surface 105a of the joining tool 105 is flat and is not provided with a stirring pin. Therefore, as shown in Fig. 2(d), even if a shallow recess 302a1 with a depth of about 0.45 mm remains on the surface 302a of the member 302, a deep recess with a depth corresponding to the shape of the stirring pin is not formed (see Figs. 6 and 7).

[0035] That is, according to the method for joining members according to this embodiment, even when a joining tool 105 with a simple configuration is used, it is possible to prevent deep recesses from being formed in the joining portion.

[0036] If it is possible to prevent deep recesses from forming in the joints, it is possible to prevent the joints from damaging the aesthetic appearance of the product. Furthermore, shallow recesses are less likely to retain moisture than deep recesses, and the contact area between moisture and the outside air is larger, shortening the time required for evaporation, thereby preventing a decrease in the reliability of the joints and the product.

[0037] 3(a) to 3(c) are schematic process diagrams illustrating a method for joining members according to another embodiment.

[0038] First, a layer 301a1 is formed on one surface 301a of a member 301 in the same manner as in FIG. 2(a) described above. Similarly to FIG. 2(a), a layer 302b1 (corresponding to an example of the second layer) is formed on one surface 302b of the component 302. The layer 302b1 includes a fine crystalline grain structure. The fine crystalline grain structure includes, for example, crystal grains having a smaller grain size than the crystal grains on the surface 302b of the component 302b. For example, when the component 302 is an aluminum alloy (e.g., A5083), the average grain size of the crystal grains on the surface 302b of the component 302 is, for example, approximately 30 μm to 100 μm. The average grain size of the crystal grains in the layer 302b1 can be, for example, 5 μm or less. The method and conditions for forming the layer 302b1 may be the same as those for forming the layer 301a1, for example.

[0039] 3(a), the component 302 to be joined is placed on the surface 301a of the component 301. At this time, the surface 302b of the component 302 on which the layer 302b1 is formed faces the surface 301a of the component 301. When the component 302 is viewed from the direction in which it is to be superimposed on the component 301, at least a partial region of the layer 302b1 formed on the component 302 overlaps with the layer 301a1 formed on the component 301.

[0040] Next, as shown in FIG. 3(b), pressure and heat are applied to the surface 302a of the component 302 opposite to the component 301 side. For example, a rotating joining tool 105 is pressed against the area of the surface 302a of the component 302 facing the layer 301a1 and the layer 302b1. In this case, the rotation speed of the joining tool 105 can be, for example, the same as the rotation speed of the joining tool 105 when forming the layer 301a1. The insertion depth of the joining tool 105 can be, for example, 0.45 mm.

[0041] With the members 301 and 302 superimposed on each other, applying pressure and heat to the surface 302a of the member 302 opposite to the member 301 side will bond the members 301 and 302 at the positions where at least one of the layers 301a1 and 302b1 was formed, as shown in Figure 3(c). The process and mechanism of bonding the layer 302b1 can be considered to be similar to those described above.

[0042] In this case, in the region where the layer 301a1 and the layer 302b1 overlap, recrystallization progresses in each of the layer 301a1 and the layer 302b1, so that more reliable bonding can be achieved.

[0043] Furthermore, in the region where the layers 301a1 and 302b1 do not overlap but are misaligned, for example, the layer 301a1 and the surface 302b of the member 302 come into contact, and recrystallization progresses in the layer 301a1, resulting in bonding. For example, the layer 302b1 and the surface 301a of the member 301 come into contact, and recrystallization progresses in the layer 302b1, resulting in bonding. Therefore, even in the region where the layers 301a1 and 302b1 do not overlap but are misaligned, bonding similar to that shown in FIG. 2(d) can be achieved.

[0044] That is, with the method for joining members according to this embodiment, joining can be performed even if the positions of layer 301a1 and layer 302b1 are misaligned. This improves the reliability of the joint. It also makes it possible to increase the joint area and the joint strength.

[0045] Although FIG. 3(c) illustrates a case where the layer 301a1 and the layer 302b1 containing the fine crystalline grain structure remain after the joining of the member 301 and the member 302, the layer 301a1 and the layer 302b1 containing the fine crystalline grain structure may disappear or become almost completely absent due to recrystallization.

[0046] In the method for joining members according to this embodiment, the end surface 105a of the joining tool 105 is flat and is not provided with a stirring pin, as shown in Fig. 3(b). Therefore, even if shallow recesses 302a1 remain on the surface 302a of the member 302, deep recesses corresponding to the shape of the stirring pin are not formed (see Figs. 6 and 7).

[0047] That is, according to the method for joining members according to this embodiment, even when a joining tool 105 with a simple configuration is used, it is possible to prevent deep recesses from being formed in the joining portion.

[0048] If it is possible to prevent deep recesses from forming in the joints, it is possible to prevent the joints from damaging the aesthetic appearance of the product. Furthermore, shallow recesses are less likely to retain moisture than deep recesses, and the contact area between moisture and the outside air is larger, shortening the time required for evaporation, thereby preventing a decrease in the reliability of the joints and the product.

[0049] 4(a) to 4(d) are schematic process diagrams illustrating a method for joining members according to another embodiment.

[0050] First, a layer 301a1 is formed on one surface 301a of a member 301 in the same manner as in FIG. 2(a) described above.

[0051] Furthermore, as shown in FIG. 4(a), a layer 302b1 is formed on one surface 302b of the member 302. 4(a), the layer 302b1 can be formed by friction stir processing. For example, when a rotating welding tool 105 is pressed against one surface 302b of the member 302, a fine grain structure with large residual strain is formed in the region of the surface 302b of the member 302 against which the welding tool 105 is pressed. The conditions for forming the layer 302b1 can be, for example, a rotation speed of the welding tool 105 of 600 rpm and an insertion depth of the welding tool 105 of 0.3 mm.

[0052] 2 and 3, the surface 103a of the backing 103 on which the component 301 (component 302) is placed is flat. In contrast, as shown in FIG. 4(a), the surface 113a of the backing 113 on which the component 302 is placed is provided with a recess 113a1. The opening dimension of the recess 113a1 can be equal to or slightly larger than the diameter of the end surface 105a of the joining tool 105. The depth of the recess 113a1 can be approximately the same as the insertion depth of the joining tool 105.

[0053] As shown in FIG. 4(a), if a recess 113a1 is provided on the surface 113a of the backing 103 on which the member 302 is placed, when the joining tool 105 is inserted into the member 302, the surface 302a side of the member 302 is pushed into the recess 113a1, forming a protrusion 302a2. That is, a layer 302b1 is formed on a surface 302b of the member 302, and a convex portion 302a2 is formed on a surface 302a opposite to the surface 302b. The convex portion 302a2 is formed at a position opposite to the layer 302b1. The conditions for forming the layer 302b1 may be, for example, the same as the conditions for forming the layer 301a1, in terms of the rotation speed of the welding tool 105, and the insertion depth of the welding tool 105 may be, for example, 0.3 mm.

[0054] 4(b), a member 301 is placed on a backing 103 having a flat surface 103a. A member 302 to be joined is placed on the surface 301a of the member 301. At this time, the surface 302b of the member 302 on which the layer 302b1 is formed faces the surface 301a of the member 301. When the member 302 is viewed from the direction in which the member 302 is superimposed on the member 301, at least a partial region of the layer 302b1 formed on the member 302 overlaps with the layer 301a1 formed on the member 301. Furthermore, by placing the member 302 in this manner, the convex portion 302a2 provided on the surface 302a of the member 302 faces the layer 301a1 formed on the member 301.

[0055] Next, as shown in FIG. 4(c), pressure and heat are applied to the protrusion 302a2 provided on the surface 302a of the member 302. For example, a rotating welding tool 105 is pressed against the top surface of the protrusion 302a2. In this case, the rotation speed of the welding tool 105 can be the same as the rotation speed of the welding tool 105 when forming the layer 302b1, for example. The insertion depth of the welding tool 105 can be 0.4 mm from the surface of the member 302a2.

[0056] As described above, the insertion depth of the welding tool 105 can be set to be approximately the same as the sum of the depth of the recess 113a1 of the backing 113 and the depth of the recess 301a1 of the member 301. In other words, the insertion depth of the welding tool 105 can be set to be approximately the same as the sum of the height of the protrusion 302a2 and the depth of the recess 301a1 of the member 301.

[0057] If the insertion depth of the joining tool 105 is approximately the same as the combined value of the height of the convex portion 302a2 and the depth of the concave portion 301a1, when the convex portion 302a2 is pressed in with the rotating joining tool 105, the distance between the top surface of the convex portion 302a2 and the surface 302a of the member 302 in the thickness direction of the member 302 can be set to approximately 0.1 mm, which is equivalent to the depth of the concave portion 301a1 of the member 301, as shown in Figure 4(d).

[0058] That is, according to the method for joining members according to the present embodiment, it is possible to prevent a deep recess from being formed in the joining portion even when using a joining tool 105 with a simple configuration. Moreover, it is possible to further reduce the depth of the recess 302a1 described above.

[0059] Therefore, it is possible to further prevent the aesthetic appearance of the product from being impaired by the joint. Furthermore, even if a recess 302a1 is formed, the depth of the recess 302a1 can be made shallower, making it even less likely for moisture to accumulate. Therefore, it is possible to further prevent a decrease in the reliability of the joint and the product.

[0060] In the above, an example has been given of forming layer 301a1 on one surface 301a of member 301, but it is also possible to join member 301 on which layer 301a1 is not formed, similar to member 302 in Figure 2(b) described above.

[0061] Furthermore, although the case where the layer 302b1 and the convex portion 302a2 are formed on the member 302 has been described, the layer 301a1 and the convex portion may also be formed on the member 301. The formation method and conditions for forming the convex portion on the member 301 may be the same as, for example, the formation method and conditions for forming the convex portion 302a2 on the member 302.

[0062] As described above, the material of the member 301 may be different from the material of the member 302. If the materials are different, the difference in melting point between the material of the member 301 and the material of the member 302 may be large. If the difference in melting point between the materials is large, when the members 301 and 302 are pressurized and heated to cause recrystallization in the fine crystal grain structure, the material with the lower melting point may melt, making joining difficult.

[0063] In this case, recrystallization occurs in the fine grain structure at a temperature approximately half the melting point of the base material. Therefore, it is preferable that the melting point of one of the materials of the member 301 and the member 302 be at least half the melting point of the other material. In this way, good joining can be achieved even when the materials of the member 301 and the member 302 are different. Note that an appropriate joining temperature when the materials of the member 301 and the member 302 are different can be determined appropriately, for example, by conducting experiments or simulations. The temperature can also be adjusted, for example, by the rotation speed of the joining tool 105. For example, the temperature can be lowered by slowing down the rotation speed of the joining tool 105.

[0064] In addition, in the above, an example has been given of joining members 301 and 302 by applying pressure and heat to members 301 and 302 using a rotating joining tool 105, but the method of applying pressure and heat is not limited to this.

[0065] For example, a rod-shaped body having a heating device such as a heater can be used to apply pressure and heat to the members 301 and 302. In this manner, recrystallization can be caused in the layer 301a1 or the layer 302b1, which includes a fine crystal grain structure with large residual strain.

[0066] Alternatively, a rod-shaped body having an ultrasonic vibration device can be used to apply pressure and heat to member 301 and member 302. In this case, frictional heat generated between the rod-shaped body and member 302 by ultrasonic vibration heats layer 301a1 or layer 302b1, which includes a fine crystal grain structure with large residual strain. Therefore, even in this case, recrystallization can be caused in layer 301a1 or layer 302b1, which includes a fine crystal grain structure with large residual strain.

[0067] However, if the members 301 and 302 are pressurized and heated using a rotating welding tool 105, it is possible to use the same welding tool 105 to form the layer 301a1 or the layer 302b1 that includes a fine crystal grain structure with large residual strain, and to pressurize and heat the members 301 and 302. In other words, the same welding apparatus 100 and manufacturing process can be used for both purposes, which reduces manufacturing costs and shortens the manufacturing period.

[0068] FIG. 5 is a photograph showing a case where the layer 301a1 or the layer 302b1 is formed by friction stir processing. The material is an aluminum alloy (A5083). The rotation speed of the welding tool 105 is 600 rpm. The diameter of the end face 105a of the welding tool 105 is 10 mm. The insertion depth of the welding tool 105 is 0.1 mm.

[0069] 5, when layer 301a1 or layer 302b1 is formed by friction stir processing, a shallow recess is formed in the region where layer 301a1 or layer 302b1 is formed. Layer 301a1 or layer 302b1 containing a fine crystal grain structure with large residual strain is formed on the surface of this recess.

[0070] FIG. 6 is a photograph showing a case where members 301 and 302 are joined together by applying pressure and heat to members 301 and 302 using a rotating joining tool 105. 6 shows the case where the rotating welding tool 105 is pressed against the member 302. The material is an aluminum alloy (A5083). The rotation speed of the welding tool 105 is 600 rpm. The diameter of the end face 105a of the welding tool 105 is 10 mm. The insertion depth of the welding tool 105 is 0.45 mm.

[0071] 6, shallow recesses 302a1 are formed on surface 302a of member 302. However, the bottom surface of recesses 302a1 is flat, and no deep recesses are formed that resemble the shape of the stirring pins.

[0072] FIG. 7 is a photograph of a cross section of the joint between member 301 and member 302. The material is an aluminum alloy (A5083). The thickness of the members 301 and 302 is 2 mm. The rotation speed of the welding tool 105 is 600 rpm. The diameter of the end face 105a of the welding tool 105 is 10 mm. The insertion depth of the welding tool 105 is 0.45 mm.

[0073] 7, shallow recesses 302a1 are formed on surface 302a of member 302. However, the bottom surface of recesses 302a1 is flat, and no deep recesses with the shape of the stirring pins are formed.

[0074] As can be seen from FIG. 7, burrs 302a3 may occur around the periphery of the recess 302a1. Such burrs 302a3 can be removed as necessary. For example, in the joining apparatus 100 illustrated in FIG. 1, if a cutting tool such as an end mill is used instead of the joining tool 105, the burrs 302a3 can be easily removed. That is, if the members 301 and 302 are pressurized and heated using the rotating joining tool 105, the burrs 302a3 can be removed using the joining apparatus 100 to which the joining tool 105 is attached. That is, the joining apparatus 100 can be used as both a joining apparatus and a burr removal apparatus.

[0075] As described above, the method for joining members according to this embodiment can include the following steps. A process of forming a layer 301a1 including a fine crystal grain structure by performing friction stir processing on a surface 301a of the member 301 opposite to the backing 103 side using a rotating welding tool 105. A process of placing a member 302 on the surface 301a of the member 301 on which the layer 301a1 is formed. A step of applying pressure and heat to a surface 302a of the member 302 opposite to the member 301 side, in a region facing the layer 301a1.

[0076] The method may further include a step of performing friction stir processing on a surface 302b of the member 302 opposite to the backing 103 side using a rotating welding tool 105 to form a layer 302b1 containing a fine crystal grain structure. In this case, in the step of placing the member 302 described above, the side of the member 302 on which the layer 302b1 is formed can be placed on the side of the member 301 on which the layer 301a1 is formed.

[0077] Furthermore, in the process of forming layer 302b1 containing a fine crystalline grain structure, backing 113 having a recess 113a1 opening on the surface on the member 302 side can be used instead of backing 103, and layer 302b1 can be formed on surface 302b of member 302 opposite to the backing 113 side, and protrusion 302a2 can be formed on the portion of member 302 facing recess 113a1 on the backing 113 side. In the step of applying pressure and heat to the surface 302a of the member 302 opposite to the member 301 side, which is an area facing the layer 301a1, the protrusion 302a2 of the member 302 can be applied with pressure and heat.

[0078] In the process of applying pressure and heat to the surface 302a of the component 302 opposite the component 301 side, in the area facing the layer 301a1, the rotating joining tool 105 can be pressed against the area of the component 302 facing the layer 301a1.

[0079] In the above, an example has been given in which the rotating welding tool 105 is pressed against the member 301 or the member 302, but the rotating welding tool 105 can also be pressed against the member 301 or the member 302 while being moved in a direction intersecting the central axis of the welding tool 105. In this way, a strip-shaped layer 301a1 or a layer 302b1 extending in the moving direction of the welding tool 105 can be formed.

[0080] Furthermore, when pressurizing and heating the members 301 and 302, recrystallization can be caused in the belt-like layer 301a1 or the layer 302b1 by moving the welding tool 105 in a direction intersecting the central axis of the welding tool 105. Therefore, a belt-like bonded portion can be formed between the members 301 and 302.

[0081] In this case, a joining tool having stirring pins with a height lower than the thickness of the members 301 and 302 may be used. As described above, when forming a layer containing a dot-like fine crystal grain structure, it is preferable to use a welding tool 105 having a flat end surface 105a and not provided with a stirring pin. On the other hand, when forming a layer containing a band-shaped fine crystal grain structure, a welding tool equipped with a columnar stirring pin protruding from the end surface 105a of the welding tool 105 can also be used. In this case, the length of the stirring pin in the height direction (protruding direction) can be made shorter than the length in the thickness direction of the thinner of the members 301 and 302. In other words, the welding tool is equipped with a stirring pin at its tip, and the length of the stirring pin in the height direction can be made shorter than the length in the thickness direction of the members 301 and 302 to be subjected to friction stir processing. The length of the stirring pin in the height direction is the dimension between the end face of the welding tool and the tip (projecting end) of the stirring pin in the direction along the central axis of the welding tool.

[0082] In the step of applying pressure and heat to a region of the surface 302a of the component 302 opposite to the component 301 side, which region faces the layer 301a1, the rotating joining tool 105 can be moved along the band-shaped fine crystal grain structure layer in a direction intersecting the central axis of the joining tool 105. In this case, a joining tool equipped with a stirring pin whose height is shorter than the thickness of the components 301 and 302 may be used.

[0083] In addition, in the process of joining members 301 and 302, in addition to the method of applying pressure with a rotating joining tool 105, a method of applying ultrasonic vibrations to the joining tool 105 while pressing members 301 and 302 with the joining tool 105 to generate frictional heat and join them may also be used.

[0084] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other. [Explanation of symbols]

[0085] 103 backing, 103a surface, 105 joining tool, 105a end surface, 113 backing, 113a1 recess, 301 member, 301a surface, 301a1 layer, 302 member, 302a surface, 302a1 recess, 302a2 protrusion, 302b surface, 302b1 layer

Claims

1. performing a friction stir treatment on a surface of the first member opposite the first backing side using a rotating welding tool to form a first layer including a fine grain structure; placing a second member on a surface of the first member on which the first layer is formed; applying pressure and heat to a region of the second member opposite to the first member side, the region facing the first layer; A method for joining members comprising the steps of:

2. The method further includes a step of performing a friction stir treatment on a surface of the second member opposite to the first backing side using the rotating welding tool to form a second layer including a fine grain structure, 2. The method for joining members according to claim 1, wherein in the step of placing the second member, the side of the second member on which the second layer is formed is placed on the side of the first member on which the first layer is formed.

3. In the step of forming the second layer including the fine crystal grain structure, a second backing having a recessed portion opening on a surface facing the second member is used instead of the first backing, and the second layer is formed on a surface of the second member opposite to the second backing side, and a convex portion is formed on a portion of the second member facing the recessed portion on the second backing side; 3. A method for joining members according to claim 2, wherein in the process of pressurizing and heating the area of the second member on the side opposite the first member side and facing the first layer, the convex portion of the second member is pressurized and heated.

4. 4. The method for joining members according to claim 1, wherein in the step of pressurizing and heating a region of the second member on a surface opposite to the first member side and facing the first layer, the rotating joining tool is pressed against the region of the second member facing the first layer.

5. The method for joining members according to any one of claims 1 to 3, wherein at least a portion of the end surface of the joining tool on the side of the first member or the side of the second member, including the center of rotation of the end surface, is a flat surface.

6. The method for joining members according to any one of claims 1 to 3, wherein the rotating welding tool is moved in a direction intersecting a central axis of the welding tool when performing the friction stir treatment.

7. 5. The method for joining members according to claim 4, wherein in the step of applying pressure and heat to a region of the second member on the side opposite to the first member side and facing the first layer, the rotating joining tool is moved in a direction intersecting a central axis of the joining tool.

8. The method for joining members according to claim 6 or 7, wherein at least a portion of the end surface of the joining tool on the side of the first member or the side of the second member, including the center of rotation of the end surface, is a flat surface.

9. The method for joining members described in any one of claims 1 to 3, wherein the joining tool has a stirring pin at its tip, and the height direction length of the stirring pin is shorter than the thickness direction length of the first member or the second member to be subjected to the friction stir treatment.

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