Joining structure and method for manufacturing the same

Abstract

To provide a joining structure in which joined bodies formed from metal are strongly joined to each other using metal plating and a manufacturing method for the joining structure.SOLUTION: A joining structure 10 comprises: a first joined body 12 which is formed from a first metal; a second joined body 16 which is formed from a second metal; and a plating part 14 which is formed from plating metal between the first joined body 12 and the second joined body 16 and joins the first joined body 12 and the second joined body 16. The plating part 14 has a conjoining interface AI, at which the plating metal is conjoined, formed in a section substantially equidistant from the joined surfaces 12a, 16a of the first joined body 12 and the second joined body 16, and has a recrystallization region RC in which the metal plating has recrystallized in the vicinity of the conjoining interface AI, or has a first diffusion region MR1 in which the metal plating has diffused in the vicinity of the conjoining interface AI.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The technology disclosed in this specification relates to a joined structure and a method for manufacturing the same.

Background Art

[0002] As a technology related to a joined structure for joining metal materials as joined objects, technologies such as welding are widely used. However, there is no known example of using plating in a metal material joined structure such as a joined structure. On the other hand, for example, in Patent Document 1, in a semiconductor device, a technology for joining copper chip electrodes as joined objects or a copper chip electrode and a copper lead wire with plating mainly composed of nickel is disclosed. In the technology disclosed in Patent Document 1, for example, in a state where a chip electrode and a lead wire are partially in contact, plating is performed by flowing a plating solution around the contact portion, thereby forming a joining portion that joins them between the chip electrode and the lead wire.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] It is also conceivable to use the plating technology such as that in Patent Document 1 for joining joined objects formed of metals other than electrodes and lead wires. However, when using joining by plating for applications other than joining electrodes and the like, it is considered that the joining strength of the joined structure is insufficient.

[0005] The present invention has been created in view of the above points, and an object thereof is to provide a joined structure in which joined objects made of metal are firmly joined with a plating metal and a method for manufacturing the joined structure.

Means for Solving the Problems

[0006] The joined structure according to the present invention includes a first joined body made of a first metal, a second joined body made of a second metal, and a plating part made of a plating metal between the first joined body and the second joined body for joining the first joined body and the second joined body. The plating part has a joining interface where the plating metal meets at a portion substantially equidistant from each joined surface of the first joined body and the second joined body, and has a recrystallized region where the plating metal is recrystallized in the vicinity of the joining interface, or has a first diffusion region where the plating metal is diffused in the vicinity of the joining interface.

[0007] Another joined structure according to the present invention includes a first joined body made of a first metal, a second joined body made of a second metal, and a plating part made of a plating metal between the first joined body and the second joined body for joining the first joined body and the second joined body. The boundary portion between at least one of the first joined body and the second joined body and the plating part has a second diffusion region where the metal constituting at least one of the first joined body and the second joined body and the plating metal are diffused and mixed.

[0008] A method for manufacturing a joined structure according to the present invention includes an immersion step of immersing a plating solution between a first joined body made of a first metal and a second joined body made of a second metal, and forming a joining interface where plating metals grown from each joined surface of the first joined body and the second joined body meet between the first joined body and the second joined body, thereby joining the first joined body and the second joined body with the plating metal; and a heat treatment step of performing heat treatment on the plating metal after the joining step. The heat treatment step forms a recrystallized region where the plating metal is recrystallized at the joining interface.

[0009] The manufacturing method of another joining structure according to the present invention involves immersing a plating solution between a first joined body made of a first metal and a second joined body made of a second metal, and forming a joining interface where plating metals grown from the joined surfaces of the first joined body and the second joined body meet between the first joined body and the second joined body, thereby joining the first joined body and the second joined body with the plating metal. After the joining process, there is a heat treatment process of performing heat treatment on the plating metal. In the heat treatment process, when the melting point of the plating metal is T1 (K) and the heat treatment temperature is T2 (K), heat treatment is performed at a temperature where the relationship T2 ≥ T1 × 1 / 3 holds.

Advantages of the Invention

[0010] The joining structure of the present invention has a joining interface where plating metal meets at a portion substantially equidistant from each joined surface of a pair of joined bodies, and has a recrystallized region where the plating metal recrystallizes near the joining interface, or has a first diffusion region where the plating metal diffuses near the joining interface. Therefore, breakage starting from the joining interface can be prevented or suppressed, and a joining structure in which joined bodies made of metal are firmly joined with the plating metal can be realized.

Brief Description of the Drawings

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[0012] (First embodiment) As shown in FIG. 1, the bonded structure 10 is formed by bonding a wire-shaped first bonded body 12 and a plate-shaped second bonded body 16 with a plating portion 14, and includes the first bonded body 12, the second bonded body 16, and the plating portion 14. The first bonded body 12 and the second bonded body 16 are each formed of stainless steel, which is an iron-based alloy. The plating portion 14 is formed of nickel (Ni) as a plating metal between the first bonded body 12 and the second bonded body 16. This plating portion 14 is formed by plating using a plating solution. In this embodiment, the first metal forming the first bonded body 12 and the second metal forming the second bonded body 16 are the same metal, but they may be different metals.

[0013] In this embodiment, for convenience of explanation, a joined structure 10 in which a first joined body 12 in the form of an elongated wire with a circular cross section and a second joined body 16 in the form of a flat plate with a flat surface are joined will be described, but the shapes of the first joined body 12 and the second joined body 16 and the joined structure 10 formed by them are not limited to this. Examples of the joined structure 10 include joined pipes of a heat exchanger, joined pipes and a housing, joined pipes and a cooling fin, joined cooling fins and a housing, vacuum containers, joints for gas and liquid piping, wire meshes in which wires are joined together, honeycomb structures such as stainless steel catalyst carriers, and joined micro parts of members such as glasses can be mentioned. That is, structures that have been joined by welding or brazing in the past can be joined at low temperatures by plating instead of brazing. In this embodiment, the first and second joinable bodies 12 and 16, which are independent members, are described as a pair of joinable bodies. However, for example, the opposing portions of a roughly circular tubular body (C-shaped when viewed from the side) with a broken portion in between can be regarded as a pair of joinable bodies, and a plated portion can be formed between the portions to form a joined structure.

[0014] The first joined body 12 is fixed on the plate surface of the second joined body 16 in a form that extends along the plate surface of the second joined body 16. That is, the first joined body 12 is linearly in contact with the second joined body 16 along the extending direction in a form that the extending direction is orthogonal to the normal direction of the plate surface of the second joined body 16. A part of the surface of the first joined body 12 (the part facing the second joined body 16) serves as a joined surface 12a for joining with the second joined body 16, and a part of the surface of the second joined body 16 (the part facing the first joined body 12) serves as a joined surface 16a for joining with the first joined body 12.

[0015] The interval between the joined surface 12a of the first joined body 12 and the joined surface 16a of the second joined body 16 gradually widens outward from the contact portion C1 between the first joined body 12 and the second joined body 16. In other words, for both joined surfaces 12a, 16a, as the part regions of these joined surfaces 12a, 16a move away from the position of the contact portion C1 where they are in contact with each other, the interval between them continuously increases gradually. In this way, a plating portion 14 is formed between the joined surface 12a and the joined surface 16a where the interval increases gradually outward from the contact portion C1, and by the plating portion 14 binding to the first joined body 12 and the second joined body 16, the first joined body 12 and the second joined body 16 are joined together.

[0016] In this embodiment, an example is given of a mode in which the first joined body 12 and the second joined body 16 are in linear contact. However, for example, when joining a substantially spherical first joined body and a plate-shaped second joined body, the first joined body 12 and the second joined body 16 may be in point contact. Further, the first joined body 12 and the second joined body 16 may be close to each other in a point-like or linear manner. That is, the two joined surfaces may be such that the distance between them continuously and gradually increases as a part region of these joined surfaces moves away from a position where they are close to each other. Note that the fact that the joined bodies are close to each other in a point-like or linear manner means that the distance between the close parts of the joined surfaces of each joined body is small in a state where the close parts of the joined surfaces can be regarded as point-like or linear. The distance between the close parts of the joined surfaces is preferably 1 / 5 or less, and more preferably 1 / 10 or less, with respect to the maximum length from the close parts of the joined surfaces toward the outside, that is, the length from the close parts of the joined surfaces to the part that is farthest from the joined surfaces.

[0017] As described above, the configuration in which the distance between the joined surfaces is widened from the contact portion C1 of the joined surfaces 12a and 16a or from the close parts toward the outside prevents or suppresses the generation of voids at the portion where the columnar crystals that become the plating portions 14 growing from each joined surface meet. Thereby, the joining strength between the first joined body 12 and the second joined body 16 can be increased.

[0018] Note that, for example, when one surface of a prismatic first joined body is in contact with or opposed and close to the surface of a plate-shaped second joined body, a configuration in which a part of the joined bodies is in surface contact or a part of the joined bodies is close to each other in a surface-like manner may also be used. In this case, it is preferable to have a portion where the distance between the joined surfaces is widened from the contact portion of the joined surfaces or from the close parts toward the outside. In this case, the boundary between the surface-like contact or close part and the part where the distance gradually increases will be in linear contact or proximity. Therefore, even in such a configuration, the generation of voids is prevented or suppressed at the portion where the columnar crystals that become the plating portions growing from each joined surface whose distance gradually increases from the contact portion or the close part toward the outside meet.

[0019] As shown in FIG. 2, the plating portion 14 is formed without a void and without a gap between the joint surface 12a of the first joint body 12 and the joint surface 16a of the second joint body 16. Further, the plating portion 14 has a recrystallization region RC formed so as to straddle the joining interface AI in a part thereof. The recrystallization region RC is a granular crystal region in which columnar crystals of a plating metal (nickel in the present embodiment) grown from the respective joint surfaces 12a and 16a are recrystallized and become granular crystals in the manufacturing process of the joint structure 10 described later. As will be described later, when the metals constituting the first joint body 12 and the second joint body 16 diffuse into the plating portion 14, or when the plating metal of the plating portion 14 diffuses into the first joint body 12 and the second joint body 16, the boundaries between the first joint body 12 and the second joint body 16 and the plating portion 14, that is, the respective joint surfaces 12a and 16a may not be clear. However, in FIG. 2, the joint surfaces 12a and 16a are drawn for convenience.

[0020] In the manufacturing process of the joint structure 10, each columnar crystal grown from each joint surface 12a, 16a meets (collides) at a portion substantially equidistant from each joint surface 12a, 16a, and a joining interface AI between the columnar crystals extending from the joint surfaces 12a, 16a is formed at the portion. In the joint structure 10, by performing heat treatment in the manufacturing process, recovery (rearrangement of atoms) occurs at the joining interface, and a first diffusion region MR1 and a second diffusion region MR2 are formed.

[0021] By further performing heat treatment at a high temperature for a long time in the manufacturing process, in the joint structure 10, a recrystallization region RC in which the plating metal is recrystallized is formed in the plating portion 14 at a portion substantially equidistant from each of the joint surfaces 12a and 16a. That is, in the plating portion 14, granular crystals in which the plating metal is recrystallized so as to straddle the joining interface AI are formed. Therefore, the joining interface AI, which has a weak bonding strength and is a starting point for fracture of the plating portion 14, does not exist in the plating portion 14, and fracture starting from the joining interface AI can be prevented or suppressed. As a result, the joint structure 10 has a high joining strength between the first joint body 12 and the second joint body 16 and is firmly joined.

[0022] In the joining structure 10 of the present embodiment, although the recrystallization region RC is formed in a part of the plating portion 14, the recrystallization region RC may not be formed in the plating portion 14. Even if the recrystallization region RC is not formed, diffusion occurs at the joining interface at a temperature equal to or higher than the recovery temperature, and the interface strength increases. By performing heat treatment in the manufacturing process, in the joining structure 10, recovery of crystals (rearrangement of atoms) occurs in the plating portion 14. Thereby, the joining of the first joined body 12 and the second joined body 16 can be made stronger. The occurrence of crystal recovery can be confirmed, for example, by a decrease in the Vickers hardness of the plating portion 14, or by observing the formation of subgrain boundaries (or subcrystalline grain structures) in the plating portion 14 or a decrease in the dislocation density with an electron microscope or the like.

[0023] The recovery of crystals in the plating portion 14 may be formed only in the vicinity of the joining interface AI as shown, for example, as the first diffusion region MR1 in FIG. 2. The first diffusion region MR1 is a region where atoms (nickel atoms) of the plating metal constituting the plating portion 14 diffuse across the joining interface AI. That is, in the first diffusion region MR1, atoms of the plating metal constituting the crystal grown from the joined surface 12a of the first joined body 12 and atoms of the plating metal constituting the crystal grown from the joined surface 16a of the second joined body 16 are mixed.

[0024] Even if the recrystallization region RC is not formed, if the first diffusion region MR1 is formed in the vicinity of the joining interface AI as described above, the joining at the joining interface AI formed in the plating portion 14 becomes strong in the joining structure 10. Thereby, the joining of the first joined body 12 and the second joined body 16 can be made strong. If crystal recovery occurs throughout the plating portion 14, the joining of the first joined body 12 and the second joined body 16 can be made even stronger.

[0025] As described above, if a recrystallized region RC that straddles the joining interface AI generated during the manufacturing process of the joining structure 10 is formed at least in a part of the plating portion 14, the joining strength between the first joined body 12 and the second joined body 16 can be increased. For example, in the plating portion 14, a recrystallized region RC may be formed only in the vicinity of the joining interface AI, the joining interface AI may disappear, and a region that is not recrystallized (a region composed of columnar crystals) may be formed outside the recrystallized region RC (on the side of the joined surfaces 12a and 16a).

[0026] In addition, in the manufacturing process of the joining structure 10, even if heat treatment is not performed or as a result of heat treatment, the joining interface AI of the plating portion 14 has not disappeared, as long as the growth directions of the columnar crystals growing from the respective joined surfaces 12a and 16a are uniform, the generation of voids at the joining interface AI is prevented or suppressed, and the joining between the first joined body 12 and the second joined body 16 is less likely to deteriorate and can be made to have high strength and be good. Specifically, in the cross-section of the plating portion 14, if the area ratio of the plating portion 14 of columnar crystals with a length three times or more the width of one columnar crystal is 50% or more, good joining can be obtained between the first joined body 12 and the second joined body 16. More preferably, if it is 66% or more, the generation of voids can be effectively suppressed.

[0027] Regarding the crystal orientation of growth, in the case of nickel, <001> and <101> are the preferential growth directions. Even when they are mixed, columnar crystals are exhibited, and it is preferable that the above ratio by them is 50% or more, and it is preferable that it is 66% or more. Regarding the expression of crystal orientation, when the crystal is a cubic crystal, <101>, <110>, and <011> are equivalent to each other, and <100>, <010>, and <001> are also equivalent to each other and are treated as the same crystal orientation group.

[0028] Also, in the joining structure 10 by performing heat treatment at a temperature equal to or higher than the above-mentioned recovery temperature during the manufacturing process, second diffusion regions MR2 are formed at the boundary portions between the first joined body 12 and the plating portion 14 (near the joined surface 12a) and between the second joined body 16 and the plating portion 14 (near the joined surface 16a), respectively. In the second diffusion region MR2 formed at the boundary portion between the first joined body 12 and the plating portion 14, atoms such as iron of the stainless steel constituting the first joined body 12 and atoms of the plating metal (nickel atoms) constituting the plating portion 14 are mixed. In this second diffusion region MR2, the proportion of atoms such as iron of the stainless steel constituting the first joined body 12 continuously decreases gradually from the first joined body 12 toward the plating portion 14, and the proportion of nickel atoms of the plating metal continuously decreases gradually from the plating portion 14 toward the first joined body 12.

[0029] Similarly, in the second diffusion region MR2 formed at the boundary portion between the second joined body 16 and the plating portion 14, atoms such as iron of the stainless steel constituting the second joined body 16 and atoms of the plating metal (nickel atoms) constituting the plating portion 14 are mixed. In this second diffusion region MR2, the proportion of atoms such as iron of the stainless steel constituting the second joined body 16 continuously decreases gradually from the second joined body 16 toward the plating portion 14, and the proportion of nickel atoms of the plating metal continuously decreases gradually from the plating portion 14 toward the second joined body 16.

[0030] As described above, in the joining structure 10, second diffusion regions MR2 are respectively formed at the boundary between the first joined body 12 and the plating portion 14 and at the boundary between the second joined body 16 and the plating portion 14, so that the joining at the boundary between the first joined body 12 and the plating portion 14 and at the boundary between the second joined body 16 and the plating portion 14 is strengthened. For this reason, in the joining structure 10, the joining between the first joined body 12 and the second joined body 16 is stronger. For example, when each joined body is made of stainless steel and the plating metal is nickel, it is preferable that the thickness of the diffusion region is 5 nm or more (about 10 atoms). By having such a thickness in the diffusion region, a sufficient increase in joining strength can be obtained. The thickness of the diffusion region can be calculated from the heat treatment temperature and the heat treatment time based on the diffusion formula of each atom. Also, the thickness of the diffusion region can be confirmed by cross-sectional analysis using a transmission electron microscope (TEM) or the like.

[0031] In addition, in the joining structure 10, the first joined body 12 and the second joined body 16 are made of stainless steel, which is one of the iron-based alloys, and the plating portion 14 is made of nickel as the plating metal. And, since stainless steel contains nickel as an alloying element, it is considered that as long as the solubility limit is not exceeded, even if nickel diffuses to the stainless steel side, there are few changes in the crystal structure and deterioration due to precipitates. Also, copper and nickel are also complete solid solutions. Thus, when both joined bodies are complete solid solutions, since there are no different phases such as intermetallic compounds between different metals, excellent-strength joining can be realized between the first joined body 12 and the plating portion 14 and between the second joined body 16 and the plating portion 14, respectively. Also, both stainless steel and nickel are excellent in corrosion resistance. Therefore, in the joining structure 10, the excellent-strength joining is maintained for a long period.

[0032] In the joining structure 10, the first joined body 12 and the second joined body 16 are each made of stainless steel, but the metals constituting the first joined body 12 and the second joined body 16 are not limited to stainless steel. The metals constituting the joined bodies are preferably iron-based alloys including various stainless steels, copper, or copper alloys, etc. The iron-based alloy refers to those that are high-alloy steels such as ordinary steel, tool steel, stainless steel, and heat-resistant steel. Also, although the plating metal constituting the plating portion 14 is nickel, it is not limited to nickel. The plating metal constituting the plating portion 14 is preferably nickel alloy or copper etc. in addition to nickel. The nickel alloy refers to those such as zinc-nickel and copper-nickel alloy. It is preferable that the metal constituting the joined body and the plating metal constituting the plating portion 14 are a complete solid solution as described above, or metals with a relatively large solid solubility limit or the same metal. This is because if the metal constituting the joined body and the plating metal are the same, different phases will not be formed by diffusion. Examples of the complete solid solution include combinations of copper and nickel, gold and silver, etc.

[0033] Hereinafter, with reference to FIG. 3, the manufacturing method of the joining structure 10 according to the present embodiment will be described. First, in the smoothing step S2, the first joined body 12 and the second joined body 16 are prepared, and the outer surfaces including the joined surfaces 12a and 16a of the first joined body 12 and the second joined body 16 are machined or polished respectively to improve their surface roughness and smooth them. The surface roughness of the joined surfaces 12a and 16a of the first joined body 12 and the second joined body 16 after smoothing is preferably such that the value of the arithmetic surface roughness Ra is 5 μm or less, and more preferably 3 μm or less.

[0034] In addition, when using as the joined body those with a not-so-large surface roughness, such as a rolled plate or one in the state as it is after drawing process, the above smoothing treatment is not necessarily required.

[0035] By smoothing the joint surfaces 12a and 16a as described above, the growth directions of the columnar crystals of the plating metal growing from each of the joint surfaces 12a and 16a are made uniform. That is, the growth directions of the columnar crystals from each joint surface 12a and 16a are not made to be greatly different. As a result, locally, among the columnar crystals growing from one joint surface 12a, the columnar crystals growing from the outer portion do not meet the columnar crystals growing from the other joint surface 16a earlier than the columnar crystals growing from the inner portion. Therefore, it is possible to prevent or suppress the growth of the columnar crystals from the inner portion from stopping before they meet, and to prevent or suppress the generation of voids in the plating portion 14.

[0036] Next, in the pretreatment step S4, alkali degreasing and pickling are performed on the surface of the first joined body 12 and the surface of the second joined body 16 to remove dust, oil, etc. on the surface. Each treatment in the pretreatment step S4 may be performed in a state where the first joined body 12 is fixed to the second joined body 16 in the joining mode, or may be performed separately in a state where they are separated. This pretreatment step S4 may perform a treatment according to the material of the joined body, and may also be omitted.

[0037] In the joining step S6 after the pretreatment step S4, plating treatment is performed to form a plating portion 14 between the joint surface 12a of the first joined body 12 and the joint surface 16a of the second joined body 16, and the first joined body 12 and the second joined body 16 are joined. The plating treatment is performed by fixing both in a state where the first joined body 12 is linearly contacted with the second joined body 16 along its extending direction. That is, the plating treatment is performed in a state where the first joined body 12 and the second joined body 16 are fixed in a state to be joined. In the plating treatment performed on the first joined body 12 and the second joined body 16 formed of stainless steel, the main plating treatment is performed after the undercoat plating treatment.

[0038] In the undercoat plating process, a nickel thin film is formed on the surfaces of the first joined body 12 and the second joined body 16 while removing the passive films formed on their surfaces. As this undercoat plating process, for example, a Wood's bath (Ni strike plating) is used. The thin film formed by the undercoat plating process becomes a part of the plated portion 14. When it is not necessary for the joined body to remove the passive film, that is, when the joined surface has good plating properties, such an undercoat plating process is unnecessary.

[0039] In this plating process, for example, a sulfamic acid bath can be used. Thereby, a plated portion 14 is formed between the joined surface 12a of the first joined body 12 and the joined surface 16a of the second joined body 16. In this plating process, the temperature of the plating solution is preferably about 55°C. When performing the treatment by electrolytic plating such as a Wood's bath or a sulfamic acid bath, it is preferable that the first joined body 12 and the second joined body 16 are electrically connected and made equipotential, or that the first joined body 12 and the second joined body 16 are in contact or short-circuited at another location so as to be electrically conductive.

[0040] The plating solution used in this plating process is preferably one prepared so that columnar crystal aggregation occurs sequentially outward from the region where the distance between the joined surface 12a and the joined surface 16a is small. Also, the plating solution used in the plating process preferably does not contain additives that promote fine grain formation such as brighteners because the structure of the plated portion is likely to be columnar crystals. For the same reason, it is preferable to reduce the current density during this plating process. For example, a sample was prepared using a plating solution for nickel in which a brightener was added to refine the plated metal, and the above-mentioned shear test and observation of the joined cross-section were performed. As a result, the shear strength did not reach 50 Mpa, and the content of columnar crystals was 20%. On the other hand, when the brightener is not contained, the shear strength is, for example, 100 MPa or more, and the content of columnar crystals is, for example, 80% or more. Therefore, the addition (content) amount (including zero) of the brightener may be determined according to the target shear strength, the content of columnar crystals, gloss, etc.

[0041] When both of the metals constituting the two objects to be joined are aluminum, it is difficult to perform direct electrolytic plating. Therefore, after electroless nickel plating is deposited on the joining surfaces of the two objects to be joined to a thickness of about 0.1 to 10 μm, an appropriate gap is provided between the joining surfaces, and electrolytic nickel plating is grown in the gap to join the two objects to be joined. In the case of joining aluminum to aluminum, the heat treatment conditions after plating are preferably 200°C or higher and 600°C or lower.

[0042] Also, for example, when one of the first object to be joined and the second object to be joined is made of aluminum and the other is made of stainless steel, nickel is deposited on the object to be joined made of aluminum by electroless plating, and the object to be joined made of stainless steel is pretreated. After that, in a state where the two objects to be joined are brought into contact and fixed, a base plating treatment is performed in a Wood's bath, and a main plating treatment is performed in a sulfamic acid bath, whereby aluminum and stainless steel can be joined with a plating metal. In this case, the object to be joined made of stainless steel may be subjected to the base plating treatment up to that point, and then the two objects to be joined may be brought into contact and the main plating treatment may be performed to join the two objects to be joined.

[0043] In the present embodiment, plating treatment is performed on the entire surfaces of the first object to be joined 12 and the second object to be joined 16, but it is not necessary to perform plating treatment on portions that do not contribute to the joining. In this case, prior to the plating treatment, an organic film such as a resist film is applied in advance to portions of the surfaces of the first object to be joined 12 and the second object to be joined 16 that do not require plating treatment (portions excluding the joining surfaces 12a and 16a), so that selective plating treatment can be performed. Also, selective plating treatment can be performed by performing the plating treatment without removing the passive film on the portions of the surfaces of the first object to be joined 12 and the second object to be joined 16 that do not require plating treatment.

[0044] By performing the plating process as described above on the first joined body 12 and the second joined body 16, elongated columnar crystals of nickel grow from the joined surfaces 12a and 16a, respectively. The columnar crystals grown from the joined surface 12a of the first joined body 12 and the columnar crystals grown from the joined surface 16a of the second joined body 16 collide and join at their tips, forming a joining interface AI at a portion substantially equidistant from each of the joined surfaces 12a and 16a. This joining interface AI is formed in order from a location where the interval between the joined surfaces 12a and 16a is narrow to a location where it is wide. As a result, the generation of voids in the plated portion 14 is prevented or suppressed.

[0045] Next, in the heat treatment step S8, a heat treatment is performed to heat the structure in which the joined bodies 12 and 16 are joined at the plated portion 14 (hereinafter referred to as the pre-treatment joined structure) through the joining step S6 as described above. For example, the heat treatment is performed in the atmosphere under the conditions of 700°C and 90 minutes. Since the recrystallization temperature is generally about 1 / 3 of the melting point, when the melting point of the plating metal constituting the plated portion 14 is T1 (K) and the heat treatment temperature for the pre-treatment joined structure is T2 (K), it is preferable that the relationship T2 ≥ T1 × 1 / 3 holds. For example, when the plating metal is nickel, it is preferable to perform the heat treatment at a temperature of 576 K or higher, which is 1 / 3 of the melting point of nickel, 1728 K. The heat treatment temperature is more preferably T1 / 3 + 98 K or higher. Of course, the heat treatment temperature is preferably within a range where the performance of the joined bodies 12 and 16 and the plated portion 14 does not deteriorate. When the joined bodies 12 and 16 are made of stainless steel and the plating metal is nickel as in this embodiment, the heat treatment temperature is preferably 300°C or higher and 1150°C or lower.

[0046] By the above heat treatment, recovery (atomic rearrangement) occurs in the plating portion 14, a first diffusion region MR1 is formed in the vicinity of the joining interface AI, and a second diffusion region MR2 can be formed at the interface between the plating portion 14 and each joined body 12, 16. Further, in a high temperature range, columnar crystals can be recrystallized into granular crystals to form a recrystallized region RC. For example, when the plating metal is nickel, in the above heat treatment, by heating the pre-joined structure with the heat treatment temperature of 250 °C or higher, at the boundary portion between the first joined body 12 and the plating portion 14 (near the joined surface 12a), atoms such as iron of the stainless steel constituting the first joined body 12 diffuse to the plating portion 14 side, and atoms of the plating metal (nickel atoms) constituting the plating portion 14 diffuse to the first joined body 12 side. Also, at the boundary portion between the second joined body 16 and the plating portion 14 (near the joined surface 16a), atoms such as iron of the stainless steel constituting the second joined body 16 diffuse to the plating portion 14 side, and atoms of the plating metal (nickel atoms) constituting the plating portion 14 diffuse to the second joined body 16 side. Thereby, a second diffusion region MR2 can be formed at the boundary portion between the first joined body 12 and the plating portion 14 and at the boundary portion between the second joined body 16 and the plating portion 14, respectively.

[0047] Note that due to the occurrence of recovery (atomic rearrangement) at the joining interface of the plating portion 14, the Vickers hardness of the plating portion 14 decreases. For example, when the plating metal is nickel, when the hardness symbol is HV0.025, the Vickers hardness before heating is about 280 HV, whereas the Vickers hardness after the heat treatment is about 220 - 120 HV. The Vickers hardness of the plating portion 14 can be measured with a micro-Vickers by a known measurement method according to Japanese Industrial Standard JIS Z 2244.

[0048] Also, for example, when the plating metal is nickel, by heating the pre-treatment joint structure at a heat treatment temperature of 250°C or higher, columnar crystals can be recrystallized into granular crystals to form a recrystallized region RC. This change (recrystallization) to granular crystals starts from the joining interface AI where strong stress is applied in the plated portion 14, and the heating time can be lengthened and the recrystallized region can be expanded. The size of the recrystallized region can be adjusted by adjusting the heat treatment temperature, heating time, etc.

[0049] The joint structure 10 is manufactured by the above steps. In the manufactured joint structure 10, the joint between the first joined body 12 and the second joined body 16 is strong.

[0050] (Second Embodiment) As shown in FIG. 4, the joint structure 30 according to the second embodiment is formed by joining the first joined body 32 and the second joined body 36, which are arranged alternately and repeatedly bent in an M shape, by a plating portion 34. Note that it is the same as the first embodiment except as described in detail below.

[0051] The joint structure 30 is used, for example, as a honeycomb-shaped metal carrier for exhaust gas purification attached to the inside of an exhaust system pipe of an automobile or a motorcycle. For example, the first joined body 32 and the second joined body 36 are arranged alternately in the radial direction and wound concentrically. The first joined body 32 and the second joined body 36 are each formed by bending or curving a strip of ferritic stainless steel, which is one of iron-based alloys, into a predetermined shape. The plating portion 34 is formed of nickel (Ni) as the plating metal by plating using a plating solution between the first joined body 32 and the second joined body 36. In this embodiment, the first metal forming the first joined body 32 and the second metal forming the second joined body 36 are the same metal, but they may be different metals.

[0052] The first joined body 32 has bent portions that bend in an M shape and are each close to the second joined body 36 and fixed to the second joined body 36. Since the first joined body 32 and the second joined body 36 have a width in the depth direction of the drawing, the bent portions of the first joined body 32 are in linear contact with the second joined body 36. As shown in FIG. 5, the tip 32b of the bent portion of the first joined body 32 serves as a joined surface 32a for joining with the second joined body 36, and the surface of the portion of the second joined body 36 that contacts the first joined body 32 serves as a joined surface 36a for joining with the first joined body 32.

[0053] As shown in FIG. 5, the distance between the joined surface 32a of the first joined body 32 and the joined surface 36a of the second joined body 36 gradually widens outward from the tip 32b of the bent portion of the first joined body 32. In other words, the distance between the two joined surfaces 32a, 36a continuously increases gradually as the distance from the position of the tip 32b increases. In this way, a plating portion 34 is formed between the joined surface 32a and the joined surface 36a whose distance gradually increases outward from the tip 32b, and by the plating portion 34 binding to the first joined body 32 and the second joined body 36, the first joined body 32 and the second joined body 36 are joined.

[0054] The joined structure 30 is manufactured by the same procedure as the joined structure of the first embodiment, so that the joining strength between the first joined body 32 and the second joined body 36 is large and a strong joining is achieved. In the joining process, since the plating portion 34 is formed by circulating a plating solution between the first joined body 32 and the second joined body 36, the first joined body 32 and the second joined body 36 can be easily joined.

[0055] As for the metal carrier for exhaust gas purification described above, a joined structure in which joined bodies made of stainless steel are joined by brazing in a vacuum and a joined structure in which joined bodies made of ceramics are joined are known. However, those joined by brazing in a vacuum have a high manufacturing cost, and those using ceramics have a problem that the pressure loss increases. On the other hand, the joined structure 30 maintains the same joining strength as a metal carrier joined by conventional brazing, reduces the manufacturing cost, and prevents or suppresses the increase in pressure loss.

[0056] (Third Embodiment) In the third embodiment, a joined structure in which a metal wiring material and a solar cell whose joined surface is made of metal are joined at a plating portion will be described. As shown in FIGS. 6 and 7, the joined structure 50 is formed by joining a wiring material 52 as one joined body extending in a strip shape and an electrode 58 provided on the surface of a solar cell 56 as the other joined body by a plating portion 54. In FIG. 6, one solar cell 56 is depicted, but in reality, a plurality of solar cells 56 are joined to the wiring material 52 by the plating portion 54 to form a solar cell module. In this embodiment, one of the solar cell 56 and the wiring material 52 is the first joined body and the other is the second joined body. Except as will be described in detail below, it is the same as the first embodiment.

[0057] The wiring material 52 is made of copper and electrically connects a plurality of solar cells 56. The solar cell 56 is mainly made of silicon and has a flat plate shape. The plating portion 54 is formed of nickel (Ni) as a plating metal by plating using a plating solution between the wiring material 52 and the solar cell 56.

[0058] The solar cell 56 has a plurality of electrodes 58 formed on one surface thereof. The plurality of electrodes 58 each linearly extend in a direction orthogonal to the extending direction of the wiring member 52 and are arranged at a predetermined interval from each other in the extending direction of the wiring member 52. The wiring member 52 is not joined to the entire surface facing the solar cell 56, but only the portion intersecting the electrode 58 of the solar cell 56 is joined to the electrode 58. That is, the wiring member 52 is locally joined to the solar cell 56.

[0059] Since the wiring member 52 is locally joined in this way, the stress applied to the plating portion 54 is effectively relaxed as compared with a configuration in which the entire surface facing the solar cell 56 is joined. For this reason, the durability of the plating portion 54 is enhanced, and the life of the joined structure 50 as a solar cell module is extended as compared with a conventional solar cell module.

[0060] As shown in FIG. 7, the cross section of the wiring member 52 is in a mountain shape protruding toward the side in contact with the electrode 58 of the solar cell 56, and the top thereof is joined in a state of being in contact with the electrode 58. Since the top of the wiring member 52 linearly extends in the extending direction, the wiring member 52 and the electrode 58 are in linear contact. Note that even if a part or all of the top of the wiring member 52 is separated from the electrode 58 in the extending direction of the wiring member 52, there is no problem as long as it is within a range where it can be regarded as being close as described above. The surface around the top of the wiring member 52 serves as a joint surface 52a to be joined to the electrode 58 of the solar cell 56, and the surface of the electrode 58 of the solar cell 56 has a silver paste 60 sintered thereon, and a part of the surface serves as a joint surface 58a to be joined to the wiring member 52.

[0061] The interval between the joint surface 52a of the wiring member 52 and the joint surface 58a of the electrode 58 of the solar cell 56 gradually widens outward from the contact portion C2 where the top of the wiring member 52 contacts the electrode 58 of the solar cell 56. In other words, the interval between the two joint surfaces 32a and 36a continuously increases gradually as the distance from the position of the contact portion C2 increases.

[0062] The joining structure 50 is manufactured in the same procedure as the joining structure of the first embodiment except for the heat treatment process, thereby joining the wiring member 52 and each electrode 58 of the solar cell 56. Note that a Wood's bath is unnecessary. The plating portion 54 is formed in a state where generation of voids is prevented or suppressed between the joint surface 52a of the wiring member 52 and the joint surface 58a of the electrode 58 of the solar cell 56. As a result, the joining between the wiring member 52 and the solar cell 56 is good.

[0063] In this way, by replacing the joining of the wiring member 52 and the solar cell 56 from joining by solder, which is generally applied to the joining of the wiring member and the solar cell in a conventional solar cell module, with joining by the plating portion 54 of the plating metal formed of nickel, good joining between the wiring member 52 and the solar cell 56 is achieved. Further, the nickel used for the plating portion 54 has a smaller difference in the coefficient of thermal expansion from copper, which is the material of the wiring member 52, than the difference between solder and copper, and it is less likely that peeling of the wiring member 52 due to deterioration of the plating portion 54 occurs due to repeated temperature changes.

[0064] In the manufacturing process of the joining structure 50 that joins the wiring member 52 and the solar cell 56, it is preferable not to perform heat treatment or to perform heat treatment for the purpose of relaxing (removing or reducing) the strain of the plating portion 54. By relaxing the strain of the plating portion 54 by heat treatment, flexibility can be imparted to the joining of the plating portion 54, that is, the wiring member 52 and the electrode 58, and breakage of the plating portion 54 due to expansion and contraction caused by temperature changes between the wiring member 52 and the solar cell 56 during use is suppressed, and the life of the solar cell module can be improved.

[0065] The above heat treatment is preferably carried out at a temperature in the range of 250 to 800°C, for example, when the plating metal is nickel. The removal or relaxation of the strain in the plated portion 54 can be confirmed as a decrease in Vickers hardness. When the plating metal is nickel and the hardness symbol is HV0.025, the Vickers hardness before heating is about 280 HV, whereas the Vickers hardness after the heat treatment is about 220 to 120 HV. The Vickers hardness of the plated portion 54 can be measured with a micro-Vickers according to a known measurement method in accordance with Japanese Industrial Standard JIS Z 2244.

Example

[0066] (First Example) (1) Preparation of Samples In the first example, a plurality of samples of a joined structure in which a pair of joined bodies made of stainless steel were joined at a plated portion were prepared, and the joining strength was evaluated, and the joined cross section was observed and analyzed. A first joined body and a second joined body having the composition of SUS304 were prepared as the stainless steel. The first joined body was in the shape of a wire with a diameter of 0.5 mm and a length of 2 mm, and the second joined body was in the shape of a flat plate with a thickness of 0.5 mm. The plating metal constituting the plated portion was nickel. The method for preparing the samples was the same as the manufacturing method in the above first embodiment.

[0067] In the preparation of the samples, first, the first joined body and the second joined body were subjected to a smoothing treatment to improve the surface roughness of the first joined body and the second joined body. Next, as a pretreatment, the stainless steel on the surfaces of the first joined body and the second joined body was degreased with an alkali and pickled to remove dust, oil, etc. on the surface. Next, as a joining treatment, the first joined body was brought into linear contact with the second joined body and fixed, and a pre-plating treatment was performed in a Wood's bath, and then a main plating treatment was performed in a sulfamic acid bath to join the first joined body and the second joined body at the plated portion. The conditions for the plating treatment were a plating solution temperature of 55°C, a plating current density of 1.5 A / dm 2 and a plating width of 0.3 mm.

[0068] After plating, the samples were heat-treated in air. To verify the difference in bonding strength due to the difference in heat treatment temperature, samples were prepared by heat-treating for 90 minutes at the following temperatures: 400°C (673K), 500°C (773K), 600°C (873K), 700°C (973K), and 800°C (1073K) (hereafter referred to as single-temperature samples). In addition, samples that were not heat-treated and samples that were heat-treated sequentially at each heat treatment temperature from 400°C to 800°C in 100°C increments (hereafter referred to as cumulative heat-treated samples) were also prepared.

[0069] (2) Share Test To evaluate the bonding strength of each sample, a shear test was conducted to peel the first bonded body from the second bonded body, and the shear strength (MPa) was measured. A Nordson Shear Tester 4000Plus was used to measure the bonding strength. The shear test was conducted 10 times for each sample, and the average value was calculated. The measurement results of the shear strength of each sample are shown in Figure 8.

[0070] The above shear strength measurement results confirmed that for each single-temperature sample with a heat treatment temperature between 300°C and 800°C, the bonding strength increased compared to samples that were not heat treated. From these results, it was confirmed that by performing heat treatment at a temperature of 576K (303°C) or higher, which is one-third of the melting point of nickel, 1728K, a recrystallized region is effectively formed in the plated area, and the bonding between the first and second bonded bodies becomes strong. In addition, for the cumulative heat-treated sample, the bonding strength increased to about three times that of the sample that was not heat-treated, confirming the remarkable effect of the heat treatment.

[0071] (3) Observation of crystals on the bonded cross section First, for the samples without heat treatment, the cross-section (bonding cross-section) of the plated part and its vicinity was observed with a scanning electron microscope (SEM). For the observation, SU5000 manufactured by Hitachi was used, and the crystal orientation was measured by electron backscatter diffraction (EBSD). As shown in Fig. 9, it was confirmed that columnar crystals uniformly grew from each bonding surface of the first work piece to be joined and the second work piece to be joined. Also, it was confirmed that the crystal growth from the second bonded part was occupied by a crystal orientation of approximately <001> in the growth direction, and the area ratio was 80% or more. It has been confirmed that if the area ratio of such columnar crystals is 50% or more, preferably 66% or more, the generation of voids can be effectively suppressed and good bonding can be obtained.

[0072] Next, for each sample subjected to heat treatment, the cross-section (bonding cross-section) of the plated part and its vicinity was observed with a scanning electron microscope (SEM). As shown in Fig. 10, in the single-temperature sample heat-treated at 400 °C, columnar crystals could not be confirmed, and it was confirmed that most of the joining interface AI had disappeared. From this, it can be seen that the nickel constituting the plated part was recrystallized across the joining interface AI by heat treatment to form granular crystals, and the bonding was strengthened.

[0073] Also, as shown in Fig. 11, in the single-temperature sample heat-treated at 700 °C, the disappearance of the joining interface AI had progressed more than that of the sample heat-treated at 400 °C and had almost completely disappeared, and it was confirmed that recrystallization had progressed more than that of the single-temperature sample heat-treated at 400 °C. Also, in the single-temperature sample heat-treated at 700 °C, the boundary line between the first work piece to be joined and the plated part, and the boundary line between the second work piece to be joined and the plated part were less clear than those of the single-temperature sample heat-treated at 400 °C. From this, it can be seen that by performing heat treatment at a higher temperature, the diffusion of atoms such as iron constituting the first work piece to be joined and the second work piece to be joined into the plated part, and the diffusion of nickel atoms constituting the plated part into the first work piece to be joined and the second work piece to be joined had progressed more.

[0074] Also, as shown in Fig. 12, in the case of the cumulative heat treatment sample, the bonding interface AI has disappeared to the extent that it cannot be discriminated compared to the single-temperature sample heat-treated at 700°C, and it was confirmed that recrystallization has progressed more than in the single-temperature sample heat-treated at 700°C. Also, in the cumulative heat treatment sample, the boundary line between the first joined body and the plating part, and the boundary line between the second joined body and the plating part have become unclear and cannot be discriminated compared to the single-temperature sample heat-treated at 700°C. From this, it can be seen that the diffusion of atoms such as iron constituting the first joined body and the second joined body into the plating part, and the diffusion of nickel atoms constituting the plating part into the first joined body and the second joined body have further progressed.

[0075] (4) Analysis of the bonding cross-section For each sample subjected to heat treatment, the diffusion state of elements in the plating part and its vicinity cross-section (bonding cross-section) was measured by energy dispersive X-ray analysis (EDX), and elemental line analysis was performed. For energy dispersive X-ray analysis (EDX) and elemental line analysis, AZtecXmax50 manufactured by Oxford Instruments was used. The results are shown in Figs. 13 to 16. Fig. 13 shows the measurement results for the single-temperature sample heat-treated at 400°C, Fig. 14 shows the measurement results for the single-temperature sample heat-treated at 500°C, Fig. 15 shows the measurement results for the single-temperature sample heat-treated at 700°C, and Fig. 16 shows the measurement results for the cumulative heat treatment sample.

[0076] In the single-temperature sample heat-treated at 400°C, the slopes of the fluorescence X-ray intensities of atoms such as iron and nickel atoms in the boundary part between the first joined body and the plating part, and the boundary part between the second joined body and the plating part, that is, in the diffusion region MR, are almost perpendicular (the slope is large). From this, it can be seen that in the sample heat-treated at 400°C, although there is diffusion of atoms such as iron constituting the first joined body and the second joined body into the plating part, and diffusion of nickel atoms constituting the plating part into the first joined body and the second joined body, it has not progressed much.

[0077] In the single-temperature sample heat-treated at 500°C, it was confirmed that the slope of the fluorescence X-ray intensity of atoms such as iron and nickel atoms in the diffusion region MR was smaller than that of the single-temperature sample heat-treated at 400°C. It can be seen that the diffusion of atoms such as iron that make up the first and second joined bodies into the plating part and the diffusion of nickel atoms that make up the plating part into the first and second joined bodies are progressing. Also, in the single-temperature sample heat-treated at 700°C, it was confirmed that the slope of the fluorescence X-ray intensity of atoms such as iron and nickel atoms in the diffusion region MR was smaller than that of the single-temperature sample heat-treated at 500°C. It can be seen that the diffusion is progressing further than when heat-treated at a heat treatment temperature of 500°C.

[0078] Furthermore, in the case of the cumulative heat treatment sample, it was confirmed that the slope of the fluorescence X-ray intensity of atoms such as iron and nickel atoms in the diffusion region MR was smaller than that of the single-temperature sample heat-treated at 700°C. From this, it can be seen that in the cumulative heat treatment sample, compared with the sample heat-treated at 700°C, the diffusion of atoms such as iron that make up the first and second joined bodies into the plating part and the diffusion of nickel atoms that make up the plating part into the first and second joined bodies are progressing more.

[0079] (Second Embodiment) In the second embodiment, a sample of a joined structure in which a pipe-shaped first joined body made of stainless steel with both ends open and a lid-shaped second joined body that closes one end of the first joined body are joined at the plating part was produced. Vacuum pumping was performed from the other end of the open pipe, and a leak test was performed to evaluate the quality of the joining of the lid to the pipe. As the pipe-shaped first joined body, one with an outer diameter of 15 mm and an inner diameter of 8.3 mm was used, and the plating metal constituting the plating part was nickel.

[0080] The corner part on one end side closed by the lid-shaped second joined body was tapered with a length of 0.5 mm from the outside to the inside and a taper angle of 20°. Next, pretreatment was performed on the first joined body and the second joined body to remove dust, oil, etc. on the surface. The conditions of the pretreatment were the same as those in the first embodiment. Next, with one end of the first joined body closed by the second joined body, the sample was immersed in a plating solution for plating with nickel (Ni) as the plating metal, and a plating process was performed to form a plated portion in the gap formed by the taper processing. As this plating process, a first sample in which a sulfamic acid bath was continuously performed for 90 minutes and a second sample in which the sulfamic acid bath was performed for 60 minutes and then taken out of the plating solution once and the sulfamic acid bath was performed again for 30 minutes were each prepared. The conditions of the other plating processes were the same as those in the first embodiment.

[0081] The above leak test was performed on each of the prepared samples. As a result of the leak test, it was confirmed that sufficient joining strength was obtained for the first sample and the joining was good. Also, it was confirmed that the leak amount was further reduced for the second sample. From the results of this leak test, it can be seen that the joined structure joined by the plating process as described above can be applied not only to those that require joining strength but also to metal vacuum vessels, liquid containers, cooling pipes, etc. In addition, for the first sample and the second sample, the leak test was performed before and after the heat treatment, but no obvious change in the leak amount was observed before and after the heat treatment.

[0082] Note that, although not limited to the sample used in the second embodiment, the taper angle, which is the angle formed by the bonding surface of the first bonded body and the bonding surface of the second bonded body, is preferably in the range of 2° or more and 25° or less. If the taper angle is excessively large, the azimuth difference at the joining interface becomes large, voids are likely to occur, and the plating thickness may increase, resulting in a longer plating time. Therefore, setting the taper angle to 25° or less is preferable because it can shorten the time required to form the plating portion in the gap formed between the bonding surfaces during the manufacturing process. More preferably, it is 15° or less. On the other hand, if the taper angle is excessively small, it becomes difficult for the plating solution to flow in. Therefore, setting the taper angle to 2° or more is preferable because it can more reliably supply the plating solution to the gap portion and reduce the possibility of defects such as the generation of voids. More preferably, it is 5° or more.

[0083] (Third Embodiment) In the third embodiment, for the same first and second bonded bodies as in the second embodiment, before performing the pretreatment, for each bonding surface, samples with and without a smoothing process to improve the surface roughness were prepared. After performing the plating process on these samples, the difference in crystal growth was confirmed by observing the cross-section near the plating portion for each sample. In the smoothing process, the surface roughness of each bonding surface of the first and second bonded bodies was improved by planar polishing using an automatic polishing device AutoMet250 manufactured by Buehle, and the value of the arithmetic surface roughness Ra was set to 3 μm or less.

[0084] As a result of the observation, for the samples that were left as lathe - machined and not subjected to the smoothing process, as shown in Fig. 17, a plurality of voids were confirmed at the joining interface AI. On the other hand, for the samples that were subjected to the smoothing process, as shown in Fig. 18, no voids were confirmed at the joining interface AI. From these results, as shown in Fig. 19, when the surface roughness of the joint surfaces is not improved (when the surface roughness is large), even if the crystals growing from each joint surface are columnar crystals, it can be inferred that the growth directions of each crystal do not uniformly become parallel. Therefore, locally, among the columnar crystals growing from one joint surface, the columnar crystals growing from the outer part meet the columnar crystals growing from the other joint surface earlier than the columnar crystals growing from the inner part, and the growth of the columnar crystals from the inner part stops before meeting, and it can be inferred that voids are generated at the joining interface AI.

[0085] (Example 4) In Example 4, as shown in Fig. 20, a sample of a joined structure in which a flat plate - shaped first joined body and a second joined body made of stainless steel were joined at the plating part was fabricated, and the joining cross - section was observed and analyzed. First joined bodies and second joined bodies with the composition of SUS304 as stainless steel were prepared. Both the first joined body and the second joined body had a thickness of 0.2 mm, and the plating metal constituting the plating part was nickel. The method of fabricating the sample was the same as the manufacturing method in the above - mentioned first embodiment.

[0086] In the fabrication of the sample, first, one side surface of the first joined body and one side surface of the second joined body were each tapered so as to be inclined in a cross - sectional view. For the taper processing, when the tip of one side surface of the first joined body subjected to the taper processing and the tip of one side surface of the second joined body were brought into linear contact, the taper angle formed by the first joined body and the second joined body was set to 5 degrees. Next, as a pretreatment, the stainless steel on the surfaces of the first joined body and the second joined body was degreased with alkali and pickled to remove dust, oil, etc. on the surfaces.

[0087] Next, as the joining process, with the tip portions of one side surfaces of the first joined body and the second joined body in linear contact, both joined bodies were placed on a glass plate and fixed, a base plating process was performed in a wood bath, and then a main plating process was performed in a sulfamic acid bath to join the first joined body and the second joined body at the plated portion. The conditions of the plating process were that the temperature of the plating solution was 55°C, the current density of the plating was 1.5 A / dm 2 and the plating width was 0.2 mm, that is, the entire thickness direction was plated.

[0088] After the plating process, heat treatment of the sample was performed in the atmosphere. In order to verify the difference in joining strength depending on the presence or absence of the heat treatment temperature, samples without heat treatment and samples sequentially heat-treated for 90 minutes at each heat treatment temperature in 100°C increments from 400°C to 800°C were prepared.

[0089] First, for the sample without heat treatment, the plated portion and its vicinity cross-section (joining cross-section) were observed with a scanning electron microscope (SEM). For the observation, SU5000 manufactured by Hitachi was used, and the crystal orientation by electron backscatter diffraction (EBSD) was measured. As shown in FIG. 21, it was confirmed that columnar crystals were uniformly growing from each joined surface of the first joined body and the second joined body.

[0090] Next, for the samples subjected to heat treatment, the plated portion and its vicinity cross-section (joining cross-section) were observed with a scanning electron microscope (SEM). As shown in FIG. 22, in the samples subjected to heat treatment, columnar crystals could not be confirmed, granular crystals were confirmed, and it was confirmed that most of the joining interfaces had disappeared. From this, it can be seen that the nickel constituting the plated portion is recrystallized across the joining interface to form granular crystals by the heat treatment. When joining plate-shaped joined bodies adjacent to each other as in this embodiment, for example, one or both ends of both joined bodies may be projected so that the center in the thickness direction becomes the top of a mountain shape toward the other side and brought into contact or close proximity to join both joined bodies.

[0091] (Example 5) In the fifth embodiment, a plurality of samples of a joined structure in which a pair of joined members made of aluminum are joined at a plating portion were produced, and the joining strength was evaluated, and the joining cross-section was observed and analyzed. As the aluminum, a first joined member having a composition of 99% Al and a second joined member of 99.5% aluminum (A1050P) were prepared. The first joined member was in the form of a wire with a diameter of 0.5 mm and a length of 2 mm, and the second joined member was in the form of a flat plate with a thickness of 1 mm. The plating metal constituting the plating portion was nickel. The method for producing the sample was the same as the production method in the above-described first embodiment.

[0092] In the plating process, since all the joined members were aluminum and it was difficult to directly perform electrolytic nickel plating, samples with electroless Ni-10% P plating of 1 to 6 μm deposited on the surface were prepared. After joining the joined members by plating, the samples were heat-treated in the atmosphere. In order to verify the difference in joining strength due to the difference in heat treatment temperature, samples heat-treated for 30 minutes were prepared with the heat treatment temperatures set at 150 °C, 250 °C, 350 °C, and 450 °C. Also, a sample without heat treatment was prepared.

[0093] The evaluation of the joining strength was performed by the same method, conditions, and equipment as in the first embodiment. As a result of measuring the shear strength, in both the sample without heat treatment and the sample with a heat treatment temperature of 150 °C, fracture occurred at the interface between the joined member and the plating portion or at the joining interface of the plating portion. In the sample with a heat treatment temperature of 250 °C, fracture within the joined member was also observed. In both the sample with a heat treatment temperature of 350 °C and the sample with a heat treatment temperature of 450 °C, fracture occurred within all the joined members. From this, in each sample with a heat treatment temperature of 250 °C or higher, an increase in joining strength was confirmed compared to the sample without heat treatment and the sample with a heat treatment temperature of 150 °C.

[0094] (Sixth Embodiment) In the sixth embodiment, a plurality of samples of a joined structure in which a pair of joined bodies made of stainless steel were joined at a plating portion were prepared and subjected to a tensile test. As the stainless steel, a first joined body and a second joined body having the composition of SUS304 were prepared. The same samples as those in the fourth embodiment were prepared, and both the first joined body and the second joined body had a thickness of 0.2 mm, and the plating metal constituting the plating portion was nickel. For the tensile test, an autograph AG-X, a precision universal testing machine manufactured by Shimadzu Corporation, was used.

[0095] After the plating treatment, the samples were heat-treated in the air. In order to verify the difference in tensile strength depending on the presence or absence of joining and the presence or absence of the heat treatment temperature, a test piece sample of stainless steel without joining, a sample without heat treatment, and samples heat-treated at heat treatment temperatures of 200°C, 250°C, 300°C, 400°C, 500°C, and 600°C for 90 minutes each, and samples heat-treated sequentially at heat treatment temperatures in increments of 100°C from 400°C to 800°C were prepared. Three identical samples were prepared for each sample, and the average value of three tensile tests was calculated for each sample. The results are shown in FIG. 23.

[0096] In this embodiment, the maximum load of the test piece sample of stainless steel was set to 1.0, and the tensile strength was evaluated as a ratio to this. For the sample without heat treatment, the tensile strength was the lowest, at 0.81. The sample heat-treated at 200°C was 0.82 (not shown in the graph), the sample heat-treated at 250°C was 0.90 (not shown in the graph), at 300°C it was 0.95 (not shown in the graph), and at 400°C it was 0.97 (not shown in the graph). For the samples heat-treated at 500°C or higher and the samples heat-treated sequentially from 400°C to 800°C, fracture occurred on the joined bodies, so they were evaluated as 1.0. Also, it was confirmed that the samples heat-treated at 500°C or higher exhibited a joining strength equivalent to that of the test piece sample of stainless steel. From the above, it was confirmed that there was a clear increase in strength in the samples with a heat treatment temperature of 250°C or higher.

Explanation of Signs

[0097] 10, 30, 50 Joined structure 12, 32 First joined body 12a, 16a, 32a, 36a, 52a, 58a Joint surfaces 14, 34, 54 Plated parts 16, 36 Second joined body 52 Wiring material (joined body) 56 Solar cell (joined body) AI Joint interface MR1 First diffusion region MR2 Second diffusion region RC Recrystallization region

Claims

1. A first joined body made of a first metal, A second joined body made of a second metal, A plating part made of a plating metal between the first joined body and the second joined body, for joining the first joined body and the second joined body, Comprising, At least one of the first joined body and the second joined body is made of an iron-based alloy which is plain steel, tool steel, stainless steel or heat-resistant steel, The plating metal is made of nickel or a nickel alloy, The first joined body and the second joined body have a region where they are in point-like or linear contact, and the distance between the first joined body and the second joined body widens outward from the contacted region, The plating part has a recrystallization region of granular crystals in which the plating metal has recrystallized in a portion equidistant from each joined surface of the first joined body and the second joined body, Joined structure.

2. A second diffusion region in which the metal constituting at least one of the first joined body and the second joined body and the plating metal diffuse and mix is provided at a boundary portion between at least one of the first joined body and the second joined body and the plating part, The joined structure according to Claim 1.

3. A plating liquid is allowed to penetrate between a first joined body made of a first metal and a second joined body made of a second metal, and a joining step of joining the first joined body and the second joined body with the plating metal by forming a joining interface where the plating metals grown from each joined surface of the first joined body and the second joined body meet between the first joined body and the second joined body, A heat treatment step of performing heat treatment on the plating metal after the joining step, Comprising, At least one of the first joined body and the second joined body is made of an iron-based alloy which is plain steel, tool steel, stainless steel or heat-resistant steel, The plating metal is made of nickel or a nickel alloy, In the joining step, with a part of each joined surface of the first joined body and the second joined body in point-like or linear contact, the joining interface is formed in order from a narrow portion to a wide portion between each joined surface of the first joined body and the second joined body, The heat treatment step forms a recrystallization region of granular crystals in which the plating metal has recrystallized in a portion equidistant from each joined surface of the first joined body and the second joined body, Method for manufacturing a joined structure.

4. A plating solution is infiltrated between a first joined body made of a first metal and a second joined body made of a second metal, and a joining interface where plating metals grown from the joined surfaces of the first joined body and the second joined body meet is formed between the first joined body and the second joined body, thereby joining the first joined body and the second joined body with the plating metal in a joining step; a heat treatment step of performing heat treatment on the plating metal after the joining step; comprising; at least one of the first joined body and the second joined body is composed of an iron-based alloy which is plain steel, tool steel, stainless steel or heat-resistant steel; the plating metal is composed of nickel or a nickel alloy; in the joining step, with a part of each joined surface of the first joined body and the second joined body in a state of being in point-like or linear contact, the joining interface is formed in order from a narrow portion to a wide portion between the joined surfaces of the first joined body and the second joined body; in the heat treatment step, when the melting point of the plating metal is T1 (K) and the heat treatment temperature is T2 (K), heat treatment is performed at a temperature where the relationship of T2 ≧ T1 × 1 / 3 holds; A method for manufacturing a joined structure.

5. The heat treatment step eliminates the joining interface. The method for manufacturing a joined structure according to claim 3 or 4.

6. Before the joining step, a smoothing step of smoothing each joined surface of the first joined body and the second joined body is provided. The method for manufacturing a joined structure according to any one of claims 3 to 5.

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