Dissimilar metal material joining structure, dissimilar metal material joining method

Abstract

The dissimilar metal material bonding structure (1) is mainly composed of a first bonding material (3), a second bonding material (5), and a three-dimensional structure (7). The three-dimensional structure (7) is bonded to the first bonding material (3). The second bonding material (5) fills the space (9b) of the three-dimensional structure (7) and is geometrically integrated with the three-dimensional structure (7). As described above, the three-dimensional structure (7) and the first bonding material (3) are bonded through an interface (11). In addition, the second bonding material (5) fills the space (9b) of the three-dimensional structure (7) and is integrated. The first bonding material (3) and the second bonding material (5) are bonded through the three-dimensional structure (7). At this time, since the second bonding material (5) fills the space (9b) of the three-dimensional structure (7), it is firmly bonded and integrated through an anchoring effect. In addition, by inducing a metallurgical reaction at the interface between the first bonding material and the second bonding material, the bonding (tensile) strength can be improved.

Description

Technical Field

[0001] This invention relates to a dissimilar metal material joint structure formed by joining dissimilar metals together, and a method thereof. Background Technology

[0002] Previously, methods were proposed to join dissimilar materials together without using mechanical fasteners such as bolts. However, in such joint structures, the joint strength near the interface between the joining materials often becomes problematic, relative to the individual strengths of each material. Therefore, for joint structures of dissimilar materials, it is necessary to further improve the joint strength.

[0003] As a method for joining dissimilar materials, one example is to pre-form a fine concave-convex shape on the surface of one of the joining materials, thereby improving the joining strength through the anchoring effect of the concave-convex shape (e.g., Patent Documents 1 and 2).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2020-124910

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-081191 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] Patent documents 1 and 2 describe a method of bonding metal and resin firmly by forming fine irregularities on a metal surface, immersing resin in these irregularities, and using the anchoring effect of the irregularity to bond the metal and resin together. However, while this method is effective to some extent when bonding metal and resin materials, the anchoring effect caused by the irregularity of the metal surface is insufficient when bonding metal materials to each other, making it difficult to adequately ensure the bond strength.

[0010] The present invention was made in view of these problems, and its object is to provide a joint structure of dissimilar metal materials that can achieve high bonding strength and a jointing method thereof.

[0011] Solution for solving the problem

[0012] To achieve the above objectives, the first invention is a joint structure of dissimilar metal materials, characterized in that it comprises: a first metal joint material; a three-dimensional metal structure joined to the first joint material and having a spatial portion; and a second metal joint material filling the spatial portion of the three-dimensional structure, wherein the first joint material and the second joint material are joined through the three-dimensional structure.

[0013] Preferably, an intermetallic compound is formed at the interface between the three-dimensional structure and the second bonding material, and in cross-sectional view, the formation length of the intermetallic compound relative to the interface length between the three-dimensional structure and the second bonding material is more than 5% and less than 60%.

[0014] Preferably, the three-dimensional structure has a sloping section, the cross-sectional area of ​​which decreases as it moves away from the first bonding material.

[0015] Preferably, the three-dimensional structure is formed at a substantially seamless interface with the first bonding material, and the spatial portion is formed at a location away from the first bonding material.

[0016] Preferably, the three-dimensional structure is lattice-shaped, and the formation direction of at least a portion of the spatial portion of the three-dimensional structure is not a continuous straight line direction perpendicular to the bonding surface of the first bonding material.

[0017] In this case, the formation direction of at least a portion of the space of the three-dimensional structure may also be inclined relative to the bonding direction with the first bonding material.

[0018] Alternatively, the forming direction of at least a portion of the spatial portion of the three-dimensional structure may also be bent relative to the bonding direction with the first bonding material.

[0019] According to the first invention, by forming a three-dimensional structure on a first bonding material and bonding a second bonding material with the three-dimensional structure made of metal, a sufficient anchoring effect can be obtained.

[0020] Furthermore, by filling the three-dimensional structure with a metallic second bonding material through high-pressure casting, the metallurgical reaction at the interface between the three-dimensional structure and the second bonding material can be promoted, and the bonding strength can be improved. In addition, since the metal is in a completely liquid phase during high-pressure casting, even three-dimensional structures with lower viscosity and narrower space than molten resin, or large products with long filling distances, can be adequately filled with the second bonding material.

[0021] Furthermore, if the three-dimensional structure has a sloping section with a cross-sectional area that decreases with distance from the first bonding material, the bonding strength can be further improved. Additionally, since the area ratio of the second bonding material to the three-dimensional structure gradually changes, localized stress concentration is difficult to occur even under conditions such as thermal cycling or repeated stress.

[0022] Furthermore, the three-dimensional structure is formed at the interface with the first bonding material with approximately no gap. By forming a spatial portion in the three-dimensional structure at a position away from the first bonding material, the bonding strength between the three-dimensional structure and the first bonding material can be improved.

[0023] Furthermore, when the three-dimensional structure is lattice-shaped, if the formation direction of the spatial portion is a continuous straight line, this direction may become a weak direction for the bonding strength. That is, when this direction coincides with a continuous straight line perpendicular to the bonding surface with the first bonding material, the bonding strength relative to the bonding direction between the first and second bonding materials may become weaker. In contrast, by making the formation direction of the spatial portion of the three-dimensional structure not a continuous straight line perpendicular to the bonding surface with the first bonding material, the bonding strength relative to the bonding direction between the first and second bonding materials can be further improved.

[0024] For example, by forming a three-dimensional structure such that the direction of forming the space between the lattices of the three-dimensional structure is inclined relative to the direction of bonding with the first bonding material, the bonding strength relative to the bonding direction of the first bonding material and the second bonding material can be improved.

[0025] Furthermore, by forming the three-dimensional structure such that the forming direction of at least a portion of the spatial portion of the three-dimensional structure is bent relative to the bonding direction with the first bonding material, it is possible to suppress the formation of weak directions relative to the first bonding material in all directions.

[0026] The second invention is a method for joining dissimilar metal materials, characterized by comprising: step a, forming a three-dimensional metal structure having a spatial portion on a first metal joining material; and step b, filling the spatial portion of the three-dimensional structure with a second metal joining material by high-pressure casting, wherein the first joining material and the second joining material are joined through the three-dimensional structure.

[0027] Preferably, step c involves filling the mold with the second bonding material and then maintaining a reaction layer formation holding time at the interface between the three-dimensional structure and the second bonding material before mold opening.

[0028] The three-dimensional structure may also have a sloping section, the cross-sectional area of ​​which is parallel to the interface of the three-dimensional structure and decreases as it moves away from the first bonding material.

[0029] Alternatively, the three-dimensional structure may be lattice-shaped, and the formation direction of at least a portion of the spatial portion of the three-dimensional structure is not a continuous straight line direction perpendicular to the bonding surface of the first bonding material.

[0030] Preferably, the three-dimensional structure is formed using a 3D printer.

[0031] According to the second invention, a sufficient anchoring effect can be obtained. Furthermore, by filling the three-dimensional structure with a metallic second bonding material through high-pressure casting, the metallurgical reaction at the interface between the three-dimensional structure and the second bonding material can be promoted, and the bonding strength can be improved.

[0032] Furthermore, if the three-dimensional structure has a sloping section where the cross-sectional area decreases with distance from the first bonding material, a section with the maximum bonding strength can be formed within the joint structure of the three-dimensional structure and the second bonding material. Therefore, without pre-calculating and setting the optimal cross-sectional area ratio, a dissimilar metal joint structure with high bonding strength can be easily obtained.

[0033] Furthermore, by making the formation direction of the spatial portion of the three-dimensional structure not a continuous straight line direction perpendicular to the joint surface of the first joint material, it is possible to obtain a dissimilar metal joint structure with high joint strength relative to the joint direction of the first joint material and the second joint material.

[0034] In addition, by using a 3D printer to form three-dimensional structures, it is possible to form three-dimensional structures of arbitrary shapes with high precision.

[0035] Invention Effects

[0036] According to the present invention, a joint structure of dissimilar metal materials capable of achieving high bonding strength and a jointing method thereof can be provided. Attached Figure Description

[0037] Figure 1 This is a three-dimensional cross-sectional view showing a dissimilar metal material joint structure 1.

[0038] Figure 2A This is a diagram showing the state in which the three-dimensional structure 7 has been formed.

[0039] Figure 2B This is a diagram showing the state in which the second bonding material 5 is filled into the three-dimensional structure 7.

[0040] Figure 3 This is a three-dimensional cross-sectional view showing the dissimilar metal material joint structure 1a.

[0041] Figure 4 This is a side view (perspective view of the second bonding material 5) showing the dissimilar metal material bonding structure 1a.

[0042] Figure 5A This is a top view concept diagram of structure 1, which is a joint structure of dissimilar metal materials.

[0043] Figure 5B yes Figure 5AEE line section view.

[0044] Figure 6 This is a conceptual diagram showing the positional relationship between the three-dimensional structure 7 (space part 9b) of the dissimilar metal material bonding structure 1 and the second bonding material 5.

[0045] Figure 7A This is a cross-sectional concept diagram of structure 1a, which is a joint structure of dissimilar metal materials.

[0046] Figure 7B This is a conceptual diagram showing the positional relationship between the three-dimensional structure 7a (space part 9b) of the dissimilar metal material bonding structure 1a and the second bonding material 5.

[0047] Figure 8A This is a side view (perspective view of the second bonding material 5) of a three-dimensional structure 7 showing a dissimilar metal material bonding structure 1.

[0048] Figure 8B This is a side view (perspective view of the second bonding material 5) of a three-dimensional structure 7b showing a dissimilar metal material bonding structure 1b.

[0049] Figure 9 This is a conceptual diagram showing the formation direction of the space portion 9b in each embodiment.

[0050] Figure 10A This is a side view (perspective view of the second bonding material 5) showing the dissimilar metal material bonding structure 1c.

[0051] Figure 10B This is a side view (perspective view of the second bonding material 5) showing the dissimilar metal material bonding structure 1d.

[0052] Figure 11A yes Figure 10A TT line sectional view.

[0053] Figure 11B yes Figure 10A UU-line sectional view.

[0054] Figure 11C yes Figure 10A VV-line sectional view.

[0055] Figure 12 This is a conceptual diagram showing the positional relationship between the three-dimensional structure 7c (space part 9b) of the dissimilar metal material bonding structure 1c and the second bonding material 5.

[0056] Figure 13A This is a side view (perspective view of the second bonding material 5) showing the dissimilar metal material bonding structure 1e.

[0057] Figure 13BThis is a side view (perspective view of the second bonding material 5) showing the dissimilar metal material bonding structure 1f.

[0058] Figure 14A It is a photo of the interface of the joint.

[0059] Figure 14B yes Figure 14A Enlarged photo of part C.

[0060] Figure 15 yes Figure 14B The schematic diagram. Detailed Implementation

[0061] (First Implementation)

[0062] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a partial three-dimensional sectional view showing the dissimilar metal material bonding structure 1. The dissimilar metal material bonding structure 1 is mainly composed of a first bonding material 3, a second bonding material 5, and a three-dimensional structure 7.

[0063] The first bonding material 3 is made of metal and is formed into a predetermined shape. The material of the first bonding material 3 is not particularly limited; for example, tool steel can be used.

[0064] Furthermore, the forming method of the first bonding material is not particularly limited, and can be any of the following methods: rolling, extrusion, casting, forging, or machining. In addition, for simplicity, the illustrated example shows a cylindrical shape for the dissimilar metal bonding structure 1, but the shape of the dissimilar metal bonding structure 1 can be any shape, and the shapes of the first bonding material 3, the second bonding material 5, and the three-dimensional structure 7 are determined according to the final shape.

[0065] A three-dimensional structure 7 is bonded to a first bonding material 3. The three-dimensional structure 7 is made of metal, and the material is not particularly limited; for example, maraging steel can be used. The first bonding material 3 and the three-dimensional structure 7 can be made of different materials, but materials with similar coefficients of thermal expansion are preferred. The three-dimensional structure 7 is formed by a 3D printer or similar means. That is, the three-dimensional structure 7 is layered and bonded to the surface (interface 11) of the first bonding material 3. Furthermore, the interface 11 does not necessarily have to be planar.

[0066] Among these methods, 3D printers can utilize well-known techniques such as powder bed deposition, directed energy deposition, and thermofusion lamination. Powder bed deposition involves, for example, spreading metal powder and then irradiating only the desired areas with a laser to melt and solidify it. Directed energy deposition involves spraying molten metal for deposition and solidification. Thermofusion lamination involves using thermoplastic resin as a binder to deposit metal powder, and then removing the binder to form the final shape. The methods for forming the three-dimensional structure 7 are not limited to these, but by using a 3D printer, the bonding strength can be designed by setting the desired morphology (porosity, area ratio, described later).

[0067] In this embodiment, the three-dimensional structure 7 is lattice-shaped. Furthermore, in the following description, the wall portion constituting the lattice of the three-dimensional structure 7 is referred to as the lattice portion 9a, and the portion outside the lattice portion 9a surrounded by it is referred to as the space portion 9b. That is, the lattice shape of the three-dimensional structure 7 is composed of the lattice portion 9a and the space portion 9b. Furthermore, the lattice shape is not limited to the square lattice shown in the figure; it can also be a triangular lattice or a honeycomb shape, etc. Additionally, the three-dimensional structure 7 does not necessarily have to be lattice-shaped; if it has at least a space portion 9b communicating with the outside, its shape is not limited. Hereinafter, an example of a regular lattice shape for the three-dimensional structure 7 will be described.

[0068] The second bonding material 5 fills the space 9b of the three-dimensional structure 7 and is integrated with the three-dimensional structure 7. That is, the space 9b is completely connected to the outside of the three-dimensional structure 7 and is not an independent space. The second bonding material 5 is made of metal, for example, a non-ferrous metal (aluminum, copper, magnesium, etc.) different from the first bonding material 3.

[0069] As described above, the three-dimensional structure 7 is joined to the first bonding material 3 via the interface 11. Furthermore, the second bonding material 5 fills the space 9b of the three-dimensional structure 7, thus achieving integration. Therefore, the first bonding material 3 and the second bonding material 5 are joined through the three-dimensional structure 7. At this time, since the second bonding material 5 fills the space 9b of the three-dimensional structure 7, they are firmly joined and integrated through an anchoring effect. Moreover, since the second bonding material is metal, a more robust connection can be achieved by causing a metallurgical reaction between the first and second bonding materials during the manufacturing process.

[0070] Next, the manufacturing method of the dissimilar metal material joint structure 1 (dissimilar metal material jointing method) will be described. First, as follows... Figure 2AAs shown, a three-dimensional structure 7 is formed on the surface of the first bonding material 3 using a 3D printer or similar means. The three-dimensional structure 7 is constructed from a material different from the first bonding material 3. Before constructing the three-dimensional structure 7, the surface of the first bonding material 3 (corresponding to the surface of interface 11) can be pre-treated. For example, an uneven or porous shape can be formed on the surface of the first bonding material 3, or an oxide coating removal process or a bonding agent (such as flux) can be applied. Alternatively, surface treatments such as electroplating or coating using PVD or CVD can be performed. For example, by forming a metal layer on the surface of the three-dimensional structure 7 that reacts metallurgically with or promotes a metallurgical reaction with the metal of the second bonding material 5, or by attaching fine metal powder to the surface of the three-dimensional structure 7, the bonding strength can be further improved.

[0071] Furthermore, in this embodiment, the three-dimensional structure 7 is composed of a square grid, and the orientation of the grid portion 9a is composed of a direction A perpendicular to the interface 11 and a direction B orthogonal to it (the direction perpendicular to the plane of the paper is omitted. The same applies below). The orientation of the grid will be explained in detail later.

[0072] Next, as Figure 2B As shown, a second bonding material 5 is filled into the space 9b of the three-dimensional structure 7. Furthermore, when filling the space 9b of the three-dimensional structure 7 with the second bonding material 5, this manufacturing method utilizes necessary molds, etc., but these are not shown in the diagram.

[0073] The method for filling the space 9b of the three-dimensional structure 7 with the second bonding material 5 is not particularly limited; for example, general casting methods such as melt forging, high-pressure casting, die casting, and gravity casting can be used. However, to improve quality by fully filling every corner of the space 9b with the second bonding material 5, melt forging, high-pressure casting, and die casting are particularly preferred. Furthermore, to achieve a stronger bond through the metallurgical reaction between the three-dimensional structure 7 and the second bonding material 5, melt forging and high-pressure casting, which maintain the interface between the second bonding material 5 and the three-dimensional structure 7 at high temperatures for a long time and facilitate reaction, are preferred.

[0074] The formation of a reaction layer at the interface between the second bonding material 5 and the three-dimensional structure 7 is promoted by prolonged close contact between the molten second bonding material 5 and the three-dimensional structure 7 at high temperature. The reaction layer is an intermetallic compound formed at the interface between the second bonding material 5 and the three-dimensional structure 7. For example, if the three-dimensional structure 7 is an iron-based material such as maraging steel and the second bonding material 5 is an aluminum alloy, the reaction layer is formed by intermetallic compounds such as FeAl3 and Fe2Al3. Alternatively, if the three-dimensional structure 7 is a Ni-based alloy and the second bonding material 5 is an aluminum alloy, the reaction layer is formed by intermetallic compounds such as NiAl3, Ni2Al3, NiAl, and Ni5Al3. Thus, it is preferable that a reaction layer is formed at the interface between the three-dimensional structure 7 and the second bonding material 5. Furthermore, the reaction layer (intermetallic compound) is not limited to these types; various intermetallic compounds can be used, depending on the type of metal used in the three-dimensional structure 7 and the second bonding material 5.

[0075] Generally, intermetallic compounds are more brittle than the base metal, and the formation of large intermetallic compounds has always been avoided in the field of metal processing (casting). However, the inventors have discovered that the presence of a certain amount of intermetallic compound (reaction layer) can improve the bonding strength of dissimilar metals. For example, the inventors have found that the bonding strength of the interface varies depending on the size of the reaction layer, and the bonding strength tends to increase to a certain extent when the amount of reaction layer at the interface increases. More specifically, cross-sectional observations have shown that high bonding strength can be obtained when the formation length of the intermetallic compound relative to the interface length between the three-dimensional structure 7 and the second bonding material 5 (hereinafter referred to as the reaction layer ratio) is 5% to 60%.

[0076] When the reaction layer ratio is less than 5%, the increased bonding strength due to the presence of intermetallic compounds cannot be fully obtained. On the other hand, if the formation length of the intermetallic compound relative to the interface length between the three-dimensional structure 7 and the second bonding material 5 is greater than 60%, as described above, a decrease in the strength of the material itself due to the intermetallic compound may occur.

[0077] Furthermore, as a method for measuring the reaction layer ratio, for example, firstly, from a metal optical photograph (e.g., at approximately 100x magnification) that allows confirmation of the cross-section of the intermetallic compound, an interface range of 300 μm or more (more preferably 500 μm or more) is arbitrarily selected. For this interface range (interface length), the reaction layer ratio can be calculated by measuring the length of the intermetallic compound formed on the interface. Additionally, it is preferable that during measurement, areas with complex interface shapes (outliers) are excluded, and areas that are as flat as possible and close to the average reaction layer ratio are selected, and the average value of at least three measurements is taken.

[0078] As described above, the longer the molten second bonding material 5 and the three-dimensional structure 7 are in close contact at high temperature, the easier it is for the reaction layer to form and grow. Therefore, the formation state of the reaction layer can be controlled by casting conditions such as the melting temperature (solution temperature) of the second bonding material 5, the contact time in the molten state (solidification time), and the preheating temperature of the three-dimensional structure 7. For example, it is preferable to maintain the intermetallic compound formation holding time for forming an intermetallic compound at the interface between the three-dimensional structure 7 and the second bonding material 5 after filling the mold with the second bonding material 5 and before opening the mold. By appropriately setting the intermetallic compound formation holding time, the formation length of the intermetallic compound relative to the interface length between the three-dimensional structure 7 and the second bonding material 5 can be adjusted.

[0079] Furthermore, generally speaking, in metal casting, increasing the cooling rate can refine the grains, stabilize quality, and shorten cycle time, thus reducing manufacturing costs. For example, in aluminum die casting, multiple internal cooling mechanisms are incorporated into the mold, and the mold temperature is low at the start of casting. Therefore, the solidification time is very short, ranging from a few seconds to tens of seconds, and even for large products, it rarely exceeds one minute, making it difficult to form a reaction layer. Additionally, in gravity mold casting and low-pressure casting, the solidification time is extended by about 10 minutes, but the casting pressure is reduced to 0.1 MPa. This insufficient pressure to bring the molten metal into close contact with the three-dimensional structure 7 further hinders the formation of a reaction layer.

[0080] On the other hand, melt forging or high-pressure casting methods involve a long contact time (solidification time) in the molten state, and the casting pressure is as high as about 100 MPa. This allows the molten liquid to be pressurized and continuously adhered to the three-dimensional structure 7, thus easily forming a reaction layer, making them preferred casting methods. In this way, after filling the molten liquid under high pressure (e.g., 50 MPa or more, more preferably 80 MPa or more), the holding time until mold opening is extended (at least 1 minute, more preferably 2 minutes or more, more preferably 4 minutes or more), thereby obtaining the desired intermetallic compound.

[0081] Furthermore, the surface of the three-dimensional structure 7 can be subjected to the surface treatment described above before the second bonding material 5 is filled into the three-dimensional structure 7. Additionally, after the three-dimensional structure 7 is formed, a heat treatment to relieve stress or tempering of the three-dimensional structure 7 can be performed. Through the above, a dissimilar metal material bonded structure 1 can be obtained.

[0082] As described above, according to the first embodiment, the two materials can be firmly bonded by joining the first bonding material 3 and the second bonding material 5 through the three-dimensional structure 7. For example, when the second bonding material 5 is formed directly on the surface of the first bonding material 3 by casting or the like, it is sometimes impossible to sufficiently ensure the bonding strength at the interface 11 of the two materials. In this case, by integrating the three-dimensional structure 7 that bonds the first bonding material 3 with the second bonding material 5, the two materials can be bonded with high bonding strength. That is, in this embodiment, it is effective when the bonding strength between the first bonding material 3 and the three-dimensional structure 7 is greater than the bonding strength between the first bonding material 3 and the second bonding material.

[0083] Furthermore, the bonding strength between the three-dimensional structure 7 and the second bonding material 5 can be adjusted by the shape of the three-dimensional structure 7 (the shape and volume ratio of the lattice portion 9a, and the shape and volume ratio of the spatial portion 9b). At this time, by constructing the three-dimensional structure 7 using a 3D printer, the three-dimensional structure 7 can be designed in any shape. Therefore, by designing a three-dimensional structure 7 of the desired shape based on the material of the three-dimensional structure 7 or the second bonding material 5, sufficient bonding strength can be ensured.

[0084] Furthermore, the three-dimensional structure 7 is not only disposed near the interface of the first bonding material 3, but also inside the second bonding material 5. Therefore, the three-dimensional structure 7 can mitigate the effects of differences in mechanical properties such as rigidity and hardness, and differences in thermal expansion rates between the first bonding material 3 and the second bonding material 5. For example, by appropriately designing the shape and structure of the three-dimensional structure 7, and the filling depth of the second bonding material 5, damage at the interface 11 can be suppressed and prevented, and the mechanical and thermal properties of the dissimilar metal bonding structure 1 can be freely designed and controlled.

[0085] Furthermore, by forming a reaction layer at the interface between the three-dimensional structure 7 and the second bonding material 5, a higher bonding strength can be obtained.

[0086] (Second Implementation)

[0087] Next, the second embodiment will be described. Figure 3 This is a partial cross-sectional perspective view showing the dissimilar metal material bonding structure 1a according to the second embodiment. Figure 4 This is a side view (perspective view of the second bonding material 5) of the dissimilar metal material bonding structure 1a. Furthermore, in the following description, structures that achieve the same function as in the first embodiment are labeled with... Figures 1-2B The same reference numerals are used in the accompanying drawings, and repeated descriptions are omitted.

[0088] The dissimilar metal bonding structure 1a is substantially the same as the dissimilar metal bonding structure 1, but differs in that it employs a three-dimensional structure 7a. The three-dimensional structure 7a is also lattice-shaped like the three-dimensional structure 7, but the orientation of its lattice is different. As described above, in the first embodiment, the orientation of the lattice portion 9a of the three-dimensional structure 7 is a direction A perpendicular to the interface 11 of the first bonding material 3 and a direction B perpendicular to it (see reference). Figure 2A ).

[0089] On the other hand, in the second embodiment, the direction of the lattice portion 9a of the three-dimensional structure 7a is a direction C or D that is inclined relative to the direction A perpendicular to the interface 11 of the first bonding material 3 (the direction perpendicular to the paper is omitted) (see reference). Figure 4 ).

[0090] In the case of a square grid, the interior of a cube constituting a unit of the grid, formed by the grid section 9a, becomes a space section 9b. Therefore, the cube of this space section 9b is continuous in a continuous direction. That is, the continuous direction of the space section 9b is aligned with the axis of any grid section 9a.

[0091] Furthermore, in this embodiment, the continuous direction of the basic unit structure of the lattice (the axial direction of the lattice portion 9a) is set as the lattice formation direction, and the continuous direction of the resulting spatial portion 9b is set as the spatial portion 9b formation direction. That is, the formation direction of at least a portion of the spatial portion 9b of the lattice-shaped three-dimensional structure 7a is not perpendicular to the continuous straight line direction of the interface 11 with the first bonding material 3 (the bonding direction between the first bonding material 3 and the second bonding material 5, A in the figure), but is inclined relative to the direction perpendicular to the interface 11 (i.e., not 0° or 90°).

[0092] Next, the effect of tilting the formation direction of the lattice will be explained. First, for comparison, the dissimilar metal material bonding structure 1 of the first embodiment will be explained. Figure 5A This is a conceptual planar diagram of structure 1, which is a joint structure made of dissimilar metal materials. Figure 5B yes Figure 5A The EE line sectional view. In addition, for simplicity, the layout of the grid shape is shown in the following description. To make it easier to understand the orientation of the grid part 9a, the cross-sectional shape of the grid part 9a is represented by a rectangle.

[0093] like Figure 5B As shown, in a cross-section perpendicular to the axial direction of the grid portion 9a, the grid portion 9a is arranged relative to the joining direction A of the first joining material 3 and the second joining material 5 and the direction perpendicular to it, B. At this time, as described above, the forming direction of the space portion 9b also becomes the joining direction A of the first joining material 3 and the second joining material 5 and the direction perpendicular to it, B.

[0094] Figure 6 This is a conceptual diagram showing the positional relationship of the second bonding material 5 filling the grid portion 9a and the space portion 9b. The study examines the case where a load F is applied to the bonding direction (perpendicular to the interface 11) between the first bonding material 3 and the second bonding material 5.

[0095] In cases where the aforementioned reaction layer is insufficient, the bonding strength at the interface between the three-dimensional structure 7 and the second bonding material 5 is low. Therefore, it is assumed that if the bonding strength at the interface between the three-dimensional structure 7 and the second bonding material 5 is excluded, the bonding strength between the three-dimensional structure 7 and the second bonding material 5 is mainly obtained through the tensile strength of the individual components of the three-dimensional structure 7 and the second bonding material 5, as well as the anchoring effect brought about by the integration of the second bonding material 5 and the three-dimensional structure 7. Furthermore, in order to easily fill the space 9b of the three-dimensional structure 7 with the second bonding material 5, a material with a lower melting point than the first bonding material 3 or the three-dimensional structure 7 is usually selected. Therefore, generally speaking, the second bonding material 5 is a material with lower strength than the first bonding material 3 or the three-dimensional structure 7.

[0096] As shown in the figure, the area above the three-dimensional structure 7 (range G in the figure) is only the second bonding material 5, thus becoming the tensile strength of the second bonding material 5 itself. Therefore, the material of the second bonding material 5 needs to be selected to have the strength required for the dissimilar metal bonding structure 1.

[0097] On the other hand, at the location where it intersects with the three-dimensional structure 7 (range H in the figure), the cross-sectional area of ​​the second bonding material 5 (the sum of K in the figure) is smaller than that of range G (J in the figure) due to the grid portion 9a. Furthermore, below the grid portion 9a, an anchoring effect is expected (L in the figure). Therefore, in the location lower than range H in the figure, the shear force between the grid portions 9a acts through the anchoring effect, thereby increasing the bonding strength.

[0098] Therefore, the design of the cross-sectional area of ​​the second bonding material 5 (i.e., the cross-sectional area of ​​the space portion 9b in the section parallel to the interface 11) and the shear force (anchoring effect) of the grid portion 9a is very important in the bonding strength between the first bonding material 3 and the second bonding material 5.

[0099] Among them, Figure 6 In the example shown, the grid sections 9a are arranged in a continuous straight line, approximately perpendicular to the interface 11. That is, the formation direction of the space section 9b is a continuous straight line, approximately perpendicular to the interface 11. In this case, the cross-sectional area K between the grid sections 9a repeats in a continuous straight line, approximately perpendicular to the interface 11. In this situation, it is not possible to efficiently obtain the anchoring effect of each layer in the depth direction of the three-dimensional structure 7.

[0100] Figure 7A , Figure 7B This is a diagram showing the dissimilar metal material bonding structure 1a according to the second embodiment. Figure 7A Corresponding to Figure 5B , Figure 7B Corresponding to Figure 6 In contrast to the first embodiment, in the second embodiment, as shown in the figure, the forming direction of the grid portion 9a (space portion 9b) is tilted from the direction perpendicular to the interface 11 (45° in the illustrated example).

[0101] like Figure 7B As shown, in the three-dimensional structure 7a of the dissimilar metal material bonding structure 1a, the fracture strength is determined by the cross-sectional area N of the second bonding material 5 within range I. That is, it is the same as the three-dimensional structure 7 of the dissimilar metal material bonding structure 1. In addition, when the range is less than M, in addition to the fracture strength based on the cross-sectional area O, an effect of improved fracture strength based on the anchoring effect P can also be obtained.

[0102] Even when the three-dimensional structure 7 and the three-dimensional structure 7a have the same grid spacing, by arranging the grid at an angle, the cross-sectional area O of the second bonding material 5 in the section parallel to the interface 11 can be increased in the three-dimensional structure 7a compared to the three-dimensional structure 7. Furthermore, since the spatial portion 9b (i.e., the minimum cross-sectional area O) is not formed as a continuous straight line in the direction perpendicular to the interface 11, the anchoring effect can be obtained more efficiently in each layer in the depth direction of the three-dimensional structure 7. Therefore, the bonding strength between the first bonding material 3 and the second bonding material 5 can be improved.

[0103] According to the second embodiment, the same effect as the first embodiment can be obtained. In addition, by tilting the formation direction of the spatial portion 9b of the three-dimensional structure 7a relative to the bonding direction with the first bonding material 3 (the direction perpendicular to the interface 11), the anchoring effect of tensile load relative to that direction can be obtained more efficiently.

[0104] (Third implementation method)

[0105] Next, the third embodiment will be described. For comparison purposes, Figure 8A This is a side view (perspective view of the second bonding material 5) showing the dissimilar metal material bonding structure 1 of the first embodiment. Figure 8B This is a side view (perspective view of the second bonding material 5) showing the dissimilar metal material bonding structure 1b of this embodiment.

[0106] The dissimilar metal joint structure 1b is roughly the same as the dissimilar metal joint structure 1, but differs in that it employs a three-dimensional structure 7b. The three-dimensional structure 7b is, for example, obtained by applying a twist to the three-dimensional structure 7 about the center line perpendicular to the interface 11 towards the lattice section 9a (space section 9b).

[0107] Figure 9 This is a conceptual diagram showing the formation direction of the lattice in the three-dimensional structures 7, 7a, and 7b (the formation direction of the spatial part 9b). As described above, in the three-dimensional structure 7, the formation direction of the spatial part 9b is a continuous straight line in the direction perpendicular to the interface 11 (Q in the figure).

[0108] On the other hand, as described above, in the three-dimensional structure 7a of the second embodiment, the forming direction of the space portion 9b is a continuous straight line in a direction inclined from the direction perpendicular to the interface 11 (R in the figure). Thus, in the three-dimensional structure 7a, by making the forming direction of the space portion 9b inclined relative to the bonding direction with the first bonding material 3, the anchoring effect against loads in the bonding direction with the first bonding material 3 can be more efficient. However, since the space portion 9b is formed as a continuous straight line, the same problem as with the three-dimensional structure 7 arises for loads parallel to the forming direction of the space portion 9b.

[0109] In this embodiment, the spatial portion 9b is formed in a spiral shape with an axis perpendicular to the interface 11 as its rotation center (S in the figure). That is, the spatial portion 9b of the three-dimensional structure 7b of the dissimilar metal material bonding structure 1b is curved relative to the bonding direction with the first bonding material 3. Thus, by forming the lattice in a spiral shape, and by not forming a continuous straight line in part of the spatial portion 9b, an anchoring effect can be efficiently achieved in any direction.

[0110] Furthermore, if the formation direction of the space portion 9b is curved, it is not necessarily limited to a spiral twisted shape. In addition, at the rotation center of the interface 11, there may be a portion of the space portion 9b that is formed as a continuous straight line, but as long as at least a portion of the formation direction of the space portion 9b is curved relative to the bonding direction with the first bonding material 3, the effect of this embodiment can be obtained.

[0111] According to the third embodiment, the same effects as those of the first embodiment can be obtained. Furthermore, by bending the formation direction of the spatial portion 9b of the three-dimensional structure 7b, an anchoring effect can be obtained more efficiently for tensile loads in any direction.

[0112] (Fourth Implementation)

[0113] Next, the fourth embodiment will be described. Figure 10AThis is a side view (perspective view of the second bonding material 5) of the dissimilar metal material bonding structure 1c according to the fourth embodiment. Figure 11A yes Figure 10A TT line sectional view, Figure 11B yes Figure 10A UU-line sectional view, Figure 11C yes Figure 10A VV-line sectional view.

[0114] The dissimilar metal bonding structure 1c is substantially the same as the dissimilar metal bonding structure 1, but differs in that it employs a three-dimensional structure 7c. The three-dimensional structure 7c is composed of a generally square grid, but the thickness of the grid portions 9a varies depending on the location. Specifically, the three-dimensional structure 7c has a section with an inclined cross-section, the cross-sectional area of ​​which (the cross-sectional area of ​​the grid portion 9a, hereinafter the same) decreases as it moves away from the first bonding material 3. That is, as the three-dimensional structure 7c moves away from the first bonding material 3, the cross-sectional area of ​​the grid portion 9a parallel to the interface 11 decreases, while the cross-sectional area of ​​the space portion 9b increases.

[0115] The inclined section of the cross-section is not necessarily limited to a part where the cross-sectional area changes continuously. For example, the thickness of the grid section 9a may not change gradually, but rather... Figure 10B As shown in the three-dimensional structure 7d of the dissimilar metal material bonding structure 1d, the thickness of the lattice portion 9a varies in stages. Thus, the cross-sectional area of ​​the lattice portion 9a constituting the lattice can also vary in stages. That is, the cross-sectional area of ​​the inclined portion only needs to vary continuously or intermittently; as needed, the average cross-sectional area at predetermined intervals can be calculated, and the average cross-sectional area within a predetermined range can be formed to decrease as it moves away from the first bonding material 3.

[0116] Preferably, the cross-sectional area of ​​the lattice portion 9a of the three-dimensional structures 7c and 7d is predetermined or greater at the interface 11 with the first bonding material 3. For example, it is preferable that the cross-sectional area of ​​the lattice portion 9a at the interface 11 is 80% or more of the total cross-sectional area (the sum of the lattice portion 9a and the space portion 9b), and it is particularly preferable that there is no space portion 9b at the interface 11 (i.e., the cross-sectional area of ​​the lattice portion 9a is 100%). In this case, the space portion 9b is formed at a position away from the first bonding material 3. In addition, the cross-sectional area of ​​the uppermost part of the three-dimensional structures 7c and 7d (the cross-sectional area of ​​the lattice portion 9a) is preferably 30% or less. With this setting, the effect of changing the cross-sectional area can be obtained more reliably.

[0117] As described above, the bonding force between the second bonding material 5 and the first bonding material 3 at the contact portion is small. Therefore, even when the second bonding material 5 is in contact with the first bonding material 3 at interface 11, the impact on the bonding strength is relatively small. In contrast, if the bonding area between the three-dimensional structures 7c and 7d and the first bonding material is large at interface 11, the bonding force between them becomes higher. Therefore, it is preferable that the three-dimensional structures 7c and 7d are formed at the interface 11 with the first bonding material 3 with approximately no gaps.

[0118] Figure 12 This is a conceptual diagram showing the positional relationship between the lattice portion 9a and the second bonding material 5 of the dissimilar metal bonding structure 1c. As described above, the fracture strength of the second bonding material 5 depends on its cross-sectional area (the cross-sectional area parallel to the interface 11), but in range X, since the cross-sectional area of ​​the lattice portion 9a is small, the cross-sectional area of ​​the second bonding material 5 is large. Therefore, the reduction in bonding strength in range X can be controlled. On the other hand, in the deeper part than range X, the cross-sectional area of ​​the second bonding material 5 gradually decreases, but the anchoring effect (shear force) of the lattice portion 9a increases, thus ensuring sufficient bonding strength.

[0119] Furthermore, since the cross-sectional area ratio of the second bonding material 5 to the lattice portion 9a gradually changes, it is possible to suppress and disperse locally applied thermal stress caused by the difference in the coefficients of thermal expansion between the second bonding material 5 and the lattice portion 9a. Additionally, since mechanical stress is dispersed through bending deformation of the joint of the three-dimensional structure, fatigue strength can be improved. Therefore, the reliability of the bonding material can be further improved.

[0120] Furthermore, as a way to form the inclined section of the cross-section, it could be... Figure 13A The dissimilar metal material joint structure 1e shown, or Figure 13B The dissimilar metal bonding structure 1f is shown. Similarly, in the three-dimensional structure 7e of the dissimilar metal bonding structure 1a, the lattice portion 9a (spatial portion 9b) is formed at an angle perpendicular to the interface 11. Furthermore, it has an inclined cross-sectional area, the cross-sectional area of ​​which decreases with distance from the first bonding material 3. This arrangement allows for the simultaneous achievement of both the effect of forming the lattice portion 9a (spatial portion 9b) at an angle and the effect of forming the inclined cross-sectional area.

[0121] Furthermore, the three-dimensional structure 7f of the dissimilar metal bonding structure 1f, like the three-dimensional structure 7b of the dissimilar metal bonding structure 1b, is formed in a spiral shape by twisting a lattice, with the lattice portion 9a (spatial portion 9b) bent. It also has a section with an inclined cross-sectional area, the cross-sectional area of ​​which decreases as it moves away from the first bonding material 3. This arrangement allows for the simultaneous achievement of both the bending effect of the lattice portion 9a (spatial portion 9b) and the effect of forming an inclined cross-sectional area. Moreover, as long as it has an inclined cross-sectional area where the cross-sectional area of ​​the section parallel to the interface 11 decreases as it moves away from the first bonding material 3, the three-dimensional structure does not necessarily have to be lattice-shaped; in particular, its shape is not limited.

[0122] According to the fourth embodiment, the same effects as in the first embodiment can be obtained. Furthermore, since the three-dimensional structure has a sloping section where the cross-sectional area decreases with distance from the first bonding material 3, the bonding strength can be further improved. Additionally, since the area ratio of the second bonding material 5 to the three-dimensional structure gradually changes, localized stress concentration is difficult to occur even under conditions such as thermal cycling. Furthermore, since mechanical stress is dispersed through bending deformation of the joint of the three-dimensional structure, fatigue strength can be improved. Moreover, since the three-dimensional structure 7 has a sloping section where the cross-sectional area decreases with distance from the first bonding material 3, a cross-sectional area ratio with maximum bonding strength can be formed within the joint structure of the three-dimensional structure 7 and the second bonding material 5. Therefore, without pre-calculating and setting the optimal cross-sectional area ratio, a dissimilar metal joint structure with high bonding strength can be easily obtained.

[0123] Example

[0124] First, the formation morphology of the reaction layer (intermetallic compound) relative to casting conditions was evaluated. In the evaluation, a φ25 × 105 mm DH2F (free-machining hot-rolled tool steel) round bar was used as the first bonding material. At the end face of the first bonding material, martensitic aging steel particles (particle size 10~30 μm) were laser-melted and laminated using a metal 3D lamination machine (powder bed method: Concept-Laser) to form a 10 mm high layer. Figure 2A The three-dimensional structure shown is a first embodiment. The cross-sectional area of ​​each part (the cross-sectional area of ​​the grid part parallel to the interface) is fixed at 45%. That is, the cross-sectional area ratios of the grid part and the space part formed by the martensitic aging steel are the same, forming a three-dimensional structure in which the space part extends in the vertical direction relative to the end face of the first bonding material.

[0125] After preheating the first bonding material and the three-dimensional structure in a furnace with a varied preheating temperature for 2 hours, they were placed into a mold. As the second bonding material, aluminum alloy (A2017) melted at a predetermined temperature was filled and infiltrated into the space of the three-dimensional structure using high-pressure casting at a casting pressure of 100 MPa and varying solidification holding time (time from filling the molten metal to mold opening). The resulting dissimilar metal bonded structure was subjected to T4 heat treatment (solution treatment at 500℃ for 4 hours → water quenching → natural aging). Then, the formation of a reaction layer at the interface between the three-dimensional structure and the second bonding material was confirmed.

[0126] Figure 14A This is a diagram showing an example of an observation section. Figure 14B yes Figure 14A Enlarged view of part C. Figure 14A , Figure 14B In the middle, part A is a three-dimensional structure, and part B is the second bonding material. Additionally, in... Figure 14B In the middle, part X is the reaction layer. Furthermore, Figure 15 yes Figure 14B The schematic diagram.

[0127] Elemental analysis of the reaction layer revealed that Fe content was above 10 mass%, which is much higher than the Fe content standard of the A2017 aluminum alloy in the second bonding body (below 0.7 mass%). This indicates that the intermetallic compound was generated through the metallurgical reaction between the three-dimensional structure (martensitic aging steel) and the A2017 aluminum alloy in the second bonding body.

[0128] Next, within the cross-section, the boundary length La is defined, and the sum of the lengths Lb of the intermetallic compounds between them is calculated. Furthermore, in... Figure 14B The measured results were: measurement length = 390 μm, total length of intermetallic compound = 230 μm, and reaction layer ratio = 59%. This measurement was performed at any 30 locations, and the reaction layer ratio was calculated as the sum of Lb / boundary length La × 100%.

[0129] Within the scope of this experiment, no reaction layer ratio exceeded 60%. Therefore, the evaluation methods shown in Table 1 were used to evaluate each condition. The evaluation results are shown in Tables 2 and 3.

[0130] Table 1

[0131]

[0132] Table 2

[0133]

[0134] Table 3

[0135]

[0136] Table 2 shows the results at a preheating temperature of 450°C, and Table 3 shows the results at a preheating temperature of 350°C. The results indicate that, under either condition, sufficient intermetallic compounds were not formed when the holding time was 30 seconds. Furthermore, a higher preheating temperature and melt temperature yielded better results, as did a longer solidification holding time. However, excessively long holding times increased cycle times and reduced productivity. Additionally, excessive formation of intermetallic compounds could lead to a greater reduction in material strength. Therefore, a solidification holding time of 10 minutes or less is preferred.

[0137] Next, the first bonding material and the second bonding material were joined using different bonding structures, and the bonding strength (tensile strength) at this time was evaluated.

[0138] (Example 1)

[0139] DH2F (free-cutting hot-rolled tool steel) round bars with a diameter of φ25 × 105 mm were used as the first bonding material. At the end face of the first bonding material, martensitic aging steel particles (particle size 10~30 μm) were laminated using a 3D metal lamination machine (powder bed method: Concept-Laser) with a laser to melt and laminate, forming a 10 mm high layer. Figure 2A The three-dimensional structure shown is a first embodiment. The cross-sectional area of ​​each part (the cross-sectional area of ​​the grid part parallel to the interface) is fixed at 45%. That is, the cross-sectional area ratios of the grid part and the space part formed by the martensitic aging steel are the same, forming a three-dimensional structure in which the space part extends in the vertical direction relative to the end face of the first bonding material.

[0140] After preheating the first bonding material and the three-dimensional structure in a furnace at 450°C for 2 hours, they were placed into a mold. As the second bonding material, aluminum alloy (A2017) molten at 800°C was filled and infiltrated into the space of the three-dimensional structure using high-pressure casting at a casting pressure of 100 MPa and a solidification holding time (time from filling the molten metal to mold opening) of 8 minutes. The resulting dissimilar metal bonded structure underwent T4 heat treatment (solution treatment at 500°C for 4 hours → water quenching → natural aging treatment). Tensile test specimens (φ 20 mm) were then fabricated, and their tensile strength was measured.

[0141] (Example 2)

[0142] SKD61 (hot-rolled tool steel) round bars with a diameter of φ25×105mm were used as the first bonding material. At the end face of the first bonding material, martensitic aging steel particles (particle size 10~30μm) were laminated using a metal 3D lamination machine (powder bed method: Concept-Laser) with laser melting to form a 10mm high layer. Figure 4 The three-dimensional structure shown is a second embodiment. Furthermore, the cross-sectional area of ​​each part (the cross-sectional area of ​​the grid portion parallel to the interface) is fixed at 50%. That is, by making the cross-sectional area ratios of the grid portion and the space portion formed from martensitic aging steel the same, a three-dimensional structure is formed in which the space portion extends in an inclined direction relative to the end face of the first bonding material.

[0143] After preheating the first bonding material and the three-dimensional structure in a furnace at 450°C for 2 hours, they were placed into a mold. As the second bonding material, aluminum alloy (A2017) molten at 800°C was filled and infiltrated into the space of the three-dimensional structure using high-pressure casting at a casting pressure of 100 MPa and a solidification holding time of 8 minutes. The resulting dissimilar metal bonded structure underwent T4 heat treatment (solution treatment at 500°C for 4 hours → water quenching → natural aging treatment). Tensile test specimens (φ20 mm) were then prepared, and their tensile strength was measured.

[0144] (Example 3)

[0145] DH2F (free-cutting hot-rolled tool steel) round bars with a diameter of φ25 × 105 mm were used as the first bonding material. At the end face of the first bonding material, martensitic aging steel particles (particle size 10~30 μm) were laser-melted and laminated using a metal 3D lamination machine (powder bed method: EOS Corporation) to form a 10 mm high layer. Figure 8B The three-dimensional structure shown is a third embodiment. The cross-sectional area of ​​each part (the cross-sectional area of ​​the grid part parallel to the interface) is fixed at 45%. That is, the cross-sectional area ratios of the grid part and the space part formed by the martensitic aging steel are the same, forming a three-dimensional structure in which the space part extends in a spiral shape relative to the end face of the first bonding material.

[0146] After preheating the first bonding material and the three-dimensional structure in a furnace at 450°C for 2 hours, they were placed into a mold. As the second bonding material, aluminum alloy (AC4C) molten at 800°C was filled and infiltrated into the space of the three-dimensional structure using high-pressure casting at a casting pressure of 100 MPa and a solidification holding time of 8 minutes. The resulting dissimilar metal bonded structure underwent T4 heat treatment (solution treatment at 500°C for 4 hours → water quenching → natural aging). Tensile test specimens (φ 20 mm) were then prepared, and their tensile strength was measured.

[0147] (Example 4)

[0148] SKD61 (hot-rolled tool steel) round bars with a diameter of φ25×105mm were used as the first bonding material. At the end face of the first bonding material, martensitic aging steel particles (particle size 10~30μm) were laser-melted and laminated using a metal 3D lamination machine (powder bed method: EOS Corporation) to form a 10mm high layer. Figure 13A The three-dimensional structure shown is a fourth embodiment. Furthermore, the cross-sectional area of ​​the lattice portion near the interface is 80% or more, and the cross-sectional area of ​​the uppermost lattice portion of the three-dimensional structure is 30% or less. That is, the cross-sectional areas of the lattice portion and the space portion formed by the martensitic aging steel are formed to decrease with increasing distance from the first bonding material.

[0149] After preheating the first bonding material and the three-dimensional structure in a furnace at 450°C for 2 hours, they were placed into a mold. As the second bonding material, aluminum alloy (AC4C) molten at 800°C was filled and infiltrated into the space of the three-dimensional structure using high-pressure casting at a casting pressure of 100 MPa and a solidification holding time of 8 minutes. The resulting dissimilar metal bonded structure underwent T4 heat treatment (solution treatment at 500°C for 4 hours → water quenching → natural aging treatment). Tensile test specimens (φ20 mm) were then fabricated, and their tensile strength was measured.

[0150] (Example 5)

[0151] DH2F (free-machining hot-rolled tool steel) round bars with a diameter of φ25 × 105 mm were used as the first bonding material. At the end face of the first bonding material, martensitic aging steel particles (particle size 10~30 μm) were laminated using a metal 3D lamination machine (powder bed method: Concept-Laser) with laser melting to form a 10 mm high layer. Figure 2A The three-dimensional structure shown is a first embodiment. The cross-sectional area of ​​each part (the cross-sectional area of ​​the grid part parallel to the interface) is fixed at 45%. That is, the cross-sectional area ratios of the grid part and the space part formed by the martensitic aging steel are the same, forming a three-dimensional structure in which the space part extends in the vertical direction relative to the end face of the first bonding material.

[0152] After preheating the first bonding material and the three-dimensional structure in a furnace at 450°C for 2 hours, they were placed into a mold. As the second bonding material, aluminum alloy (A2017) molten at 800°C was filled and infiltrated into the space of the three-dimensional structure using a die-casting method with a solidification holding time of 30 seconds and a casting pressure of 80 MPa. The resulting dissimilar metal bonded structure underwent T4 heat treatment (solution treatment at 500°C for 4 hours → water quenching → natural aging treatment). Tensile test specimens (φ 20 mm) were then fabricated, and their tensile strength was measured.

[0153] (Example 6)

[0154] DH2F (free-cutting hot-rolled tool steel) round bars with a diameter of φ25 × 105 mm were used as the first bonding material. At the end face of the first bonding material, martensitic aging steel particles (particle size 10~30 μm) were laminated using a metal 3D lamination machine (powder bed method: Concept-Laser) with laser melting to form a 10 mm high layer. Figure 2A The three-dimensional structure shown is a first embodiment. The cross-sectional area of ​​each part (the cross-sectional area of ​​the grid part parallel to the interface) is fixed at 45%. That is, the cross-sectional area ratios of the grid part and the space part formed by the martensitic aging steel are the same, forming a three-dimensional structure in which the space part extends in the vertical direction relative to the end face of the first bonding material.

[0155] After preheating the first bonding material and the three-dimensional structure in a furnace at 350°C for 2 hours, they were placed into a mold. As the second bonding material, aluminum alloy (A2017) molten at 700°C was filled and infiltrated into the space of the three-dimensional structure using high-pressure casting at a casting pressure of 100 MPa and a solidification holding time of 8 minutes. The resulting dissimilar metal bonded structure underwent T4 heat treatment (solution treatment at 500°C for 4 hours → water quenching → natural aging). Tensile test specimens (φ 20 mm) were then fabricated, and their tensile strength was measured.

[0156] (Comparative Example 1)

[0157] A 30×105mm SKD61 (hot-rolled tool steel) round bar was used as the first bonding material. A recess (1-3 μm deep) was formed on the end face of the first bonding material by etching (NMT or T-liquid method). The bonding material was preheated in a furnace at 450°C for 2 hours and then placed into a mold. As the second bonding material, aluminum alloy (A2017) melted at 800°C was used to fill and infiltrate the recess of the first bonding material by high-pressure casting at a casting pressure of 100 MPa and a solidification holding time of 8 minutes. The resulting dissimilar metal bonded structure was subjected to the same T4 heat treatment as in Examples 1 and 2 (solution treatment at 500°C for 4 hours → water quenching → natural aging treatment). As a result, all test pieces fractured from the bonding surface during water quenching. Therefore, tensile testing was not possible. Furthermore, the interface between the first and second bonding materials was evaluated as a reaction layer.

[0158] (Comparative Example 2)

[0159] SKD61 (hot-rolled tool steel) round bars with a diameter of φ30×105mm were used as the first bonding material. Recesses (groove width 10μm~20μm, groove depth 100μm~500μm) were formed on the end face of the first bonding material using a laser dimple forming method (DLAMP). The bonding material was preheated in a furnace at 450°C for 2 hours and then placed into a mold. As the second bonding material, aluminum alloy (A2017) melted at 800°C was used to fill and impregnate the recesses of the first bonding material using high-pressure casting at a casting pressure of 100MPa and a solidification holding time of 8 minutes. The resulting dissimilar metal bonded structure underwent the same T4 heat treatment as in Examples 1 and 2 (solution treatment at 500°C for 4 hours → water quenching → natural aging treatment). As a result, most of the test specimens fractured at the bonding surface during water quenching. Tensile test pieces (φ20mm) were made from the unfractured specimens, and tensile strength was measured. Furthermore, the interface between the first bonding material and the second bonding material was evaluated as a reactive layer.

[0160] (Comparative Example 3)

[0161] DH2F (free-cutting hot-rolled tool steel) round bars with a diameter of φ30×105mm were used as the first bonding material. A spray-welded layer (10~30μm thick) with a Zn•SUS•Fe alloy was formed on the end face of the first bonding material using a spray welding method. This bonding material was preheated in a furnace at 450°C for 2 hours and then placed into a mold. As the second bonding material, aluminum alloy (AC4C) molten at 800°C was filled and infiltrated into the uneven portion of the first bonding material using a high-pressure casting method with a casting pressure of 100MPa and a solidification holding time of 8 minutes. The resulting dissimilar metal bonded structures were subjected to the same T4 heat treatment as in Examples 1 and 2 (solution treatment at 500°C for 4 hours → water quenching → natural aging treatment). As a result, all test pieces fractured at the bonding surface during water quenching. Therefore, tensile tests could not be performed. Furthermore, the interface between the first and second bonding materials was evaluated as a reaction layer.

[0162] The results are shown in Table 4.

[0163] Table 4

[0164]

[0165] Based on the results, the joint structure using a three-dimensional structure can ensure high tensile strength. In particular, for a given cross-sectional area, the tensile strength of Example 2, in which the lattice direction of the three-dimensional structure is inclined relative to the joint surface, is increased compared to Example 1, in which the lattice direction of the three-dimensional structure is perpendicular to the joint surface. Furthermore, by setting the lattice direction of the three-dimensional structure to a spiral shape, the tensile strength is further increased. In addition, Example 4, which forms an inclined section in the cross-sectional area, can ensure high tensile strength compared to Examples 1 and 2.

[0166] Furthermore, since Example 5 uses die casting, the reaction layer is smaller, resulting in lower tensile strength. Thus, in a casting method where metallurgical bonding strength is reduced, the tensile strength increases to some extent due to the anchoring effect of the beam structure of the three-dimensional structure, but it is still lower than in Example 1 where the reaction layer is larger in the same structure. Therefore, by forming the reaction layer through sufficient solidification holding time (reaction layer formation holding time), the tensile strength can be improved.

[0167] Furthermore, although Example 6 uses high-pressure casting, the reaction layer is rated "good" due to the low preheating temperature and low melt temperature. Therefore, compared to Example 1, which has the same bonding structure, the metallurgical bonding force is smaller, and the tensile strength is slightly reduced compared to Example 1.

[0168] In contrast, in comparative examples with conventionally formed surface irregularities, almost all test specimens fractured during water quenching. This can be attributed to weak bond strength, which was unable to withstand the stress of thermal shrinkage during water quenching. Furthermore, even if fracture did not occur during water quenching, the bond strength was significantly reduced. The comparative examples had small surface irregularities, resulting in very weak anchoring effects; therefore, no increase in bond strength was observed due to the strong anchoring effect generated by the beams, as seen in the three-dimensional structure of this invention.

[0169] Furthermore, the reaction layer in the comparative example was significantly smaller compared to Example 1, which was cast under the same conditions. In Example 1, the fine beam portion of the three-dimensional structure was encased in molten metal and maintained at a high temperature for an extended period, easily leading to the formation of a reaction layer. In contrast, in the comparative example, because the first and second joints were in interfacial contact, the heat at the interface shifted towards the base material (root) of the first joint, making it difficult to maintain a high interface temperature; therefore, the reaction was not considered to have occurred. Moreover, all the examples described above were obtained after T4 treatment, but even other tempering processes showed the same tendency.

[0170] The embodiments of the present invention have been described above with reference to the accompanying drawings, but the technical scope of the present invention is not limited to the above embodiments. Those skilled in the art will obviously be able to conceive of various modifications or alterations within the scope of the technical concept described in the claims, and it should be understood that these modifications or alterations also fall within the technical scope of the present invention.

[0171] Explanation of reference numerals in the attached figures:

[0172] 1, 1a, 1b, 1c, 1d, 1e, 1f: Dissimilar metal joint structures

[0173] 3: First bonding material

[0174] 5: Second bonding material

[0175] 7, 7a, 7b, 7c, 7d, 7e, 7f: Three-dimensional structures

[0176] 9a: Grid section

[0177] 9b: Space Department

[0178] 11: Interface

Claims

1. A joint structure made of dissimilar metal materials, characterized in that, have: The first bonding material is made of metal; A three-dimensional metallic structure, which is bonded to the first bonding material and has a spatial portion; and A second bonding material made of metal, which fills the space portion of the three-dimensional structure; The first bonding material and the second bonding material are bonded together through the three-dimensional structure. An intermetallic compound is formed at the interface between the three-dimensional structure and the second bonding material. In cross-sectional observation, the formation length of the intermetallic compound relative to the interface length between the three-dimensional structure and the second bonding material is more than 10% and less than 60%. The first bonding material and the three-dimensional structure are made of steel, and the second bonding material is made of aluminum alloy.

2. The joint structure of dissimilar metal materials according to claim 1, characterized in that, The three-dimensional structure is lattice-shaped, and at least a portion of the spatial portion of the three-dimensional structure is formed in a direction that is not a continuous straight line perpendicular to the bonding surface of the first bonding material, but rather curved relative to the bonding direction of the first bonding material.

3. A method for joining dissimilar metal materials, characterized in that, have: Step a: Forming a three-dimensional metal structure with a spatial portion on a first bonding material made of metal; Step b involves filling the spatial portion of the three-dimensional structure with a second metal bonding material through high-pressure casting. as well as In step c, after filling the mold with the second bonding material, a reaction layer formation holding time is maintained before mold opening for forming a reaction layer at the interface between the three-dimensional structure and the second bonding material. In step c, an intermetallic compound is formed at the interface between the three-dimensional structure and the second bonding material, and the formation length of the intermetallic compound relative to the interface length between the three-dimensional structure and the second bonding material is 10% to 60%. The first bonding material and the second bonding material are bonded together through the three-dimensional structure. The first bonding material and the three-dimensional structure are made of steel, and the second bonding material is made of aluminum alloy.

4. The method for joining dissimilar metal materials according to claim 3, characterized in that, The three-dimensional structure is lattice-shaped, and at least a portion of the spatial portion of the three-dimensional structure is curved relative to the bonding direction with the first bonding material.

5. The method for joining dissimilar metal materials according to claim 3, characterized in that, In step a, the three-dimensional structure is formed using a 3D printer.

Images