JP2012166270A - Spot friction stir welding method of bimetallic metals - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spot friction stir welding method of bimetallic metals capable of welding the bimetallic metals with a stable high welding strength without deforming the metals by using the spot friction stir welding method.SOLUTION: The metals are superposed on a backing material 3 successively from the lower side from the metal material 1 of higher melting point, and the metal materials are subjected to the spot friction stir welding by using a friction tool 5 rotating from its upper side. A heat insulating layer 4 is formed between the backing material 3 and the metal material 1 of higher melting point, and the heat insulating layer 4 is a ceramic layer 4b formed of a ceramic material.

Description

  The present invention relates to a spot friction stir welding method for dissimilar metal materials in which different metal materials having different melting points are overlapped and bonded by spot friction stir welding, more specifically, spot friction stir welding by overlapping iron-based materials and aluminum-based materials. The present invention relates to a spot friction stir welding method for dissimilar metal materials to be joined together.

  Welded joints made by stacking and joining dissimilar metal materials with different melting points such as iron-based materials and aluminum-based materials are used in a wide range of transportation fields such as automobiles and railway vehicles, machine parts, and buildings. . In particular, a welded joint using an aluminum-based material on one side is suitably used in the transportation field of automobiles, railway vehicles, and the like because the aluminum-based material is lightweight.

  However, when dissimilar metal materials with different melting points such as iron-based materials and aluminum-based materials are joined by resistance spot welding, which has been widely used in the past, high power energy is required and dust is scattered during welding. Instead of this resistance spot welding, the adoption of a new welding method that does not require high power energy and does not harm the work environment has been studied.

  Therefore, a welding method using spot friction stir welding has begun to be adopted in recent years. This welding method is an excellent welding method that does not require high power energy unlike resistance spot welding when joining dissimilar metal materials and that dust does not scatter during welding.

  However, this spot friction stir welding method can be adopted without any problem for joining the same kind of metal such as joining of aluminum materials, but different metal materials having different melting points such as iron materials and aluminum materials. When it is used for joining, stable and high joining strength cannot be obtained. Therefore, in joining actual dissimilar metal materials with different melting points, various improvements and improvements have been made at actual welding sites, but no method has been established that can stably obtain high joint strength. Is the current situation.

  When dissimilar metal materials such as iron-based materials and aluminum-based materials are joined together by a welding method using spot friction stir welding, the reason why a stable high joint strength cannot be obtained is that the melting points of the metal materials to be joined are different. .

  For example, an important requirement when welding iron-based materials and aluminum-based materials by spot friction stir welding is to push the probe at the tip of a rotating friction tool into the aluminum-based material to cause the aluminum-based material to plastically flow, while The surface (interface) temperature of the iron-based material is increased to a temperature at which diffusion bonding can be performed by heat generated by friction and plastic flow between the material and the iron-based material.

  However, in the conventional welding method using spot friction stir welding, an aluminum-based material having a low melting point immediately softens and plastically flows, but an iron-based material having a high melting point immediately stabilizes the temperature at the joint interface when the friction time is insufficient. Thus, since the temperature range where bonding is possible is not reached, a good bonding portion cannot be obtained. On the other hand, when the friction time is lengthened and the friction tool is rotated and the probe at the tip is pushed right above the iron-based material, the temperature of the iron-based material rises to an appropriate temperature. As a result, the pressure is not applied to the bonding interface, and as a result, a stable bonded portion cannot be obtained.

  In recent years, Patent Documents 1 to 4 and the like have proposed a method in which dissimilar metal materials such as an iron-based material and an aluminum-based material are overlapped and welded. Among these proposals, Patent Document 1 and Patent Document 2 are proposals related to a method of welding by spot friction stir welding. Patent Document 3 and Patent Document 4 are proposals relating to a technique for joining an iron-based material and an aluminum-based material by arc welding.

  Patent Document 1 discloses a lap joint friction stir welding method in which a plurality of members having different melting points are stacked, an upper member having a low melting point is pressed with a rotating joining tool (friction tool), and joined by friction stirring. A friction stir welding method for a lap joint is described in which the vicinity of the surface of a member pressed by a tool is stirred by frictional heat, the temperature of the overlapping surface is increased by the frictional heat, and the members are joined by diffusion bonding between opposing members. .

  Further, in Patent Document 2, when a dissimilar metal plate is subjected to friction point bonding using a rotary tool (friction tool) having a pin portion (probe) at the tip, a receiving surface for receiving a metal plate material having a high melting point is provided. A receiving tool with a recess having a larger outer diameter than the tip of the pin, receiving a metal plate with a high melting point that is a stack of metal plates with a low melting point, and pushing from a metal plate with a low melting point while rotating the rotary tool By softening the metal plate material having a low melting point by the generated frictional heat and plastically flowing the portion corresponding to the concave portion of the metal plate material having a high melting point to the concave portion side, and joining the metal plate materials to each other The method of forming the concave portion corresponding to the pin portion in the metal plate material having a high melting point is described.

  These methods are proposals of a technique for welding dissimilar metal materials such as iron-based material and aluminum-based material by spot friction stir welding, and are effective proposals regarding a spot friction stir welding method for welding dissimilar metal materials. It is considered. However, the method described in Patent Document 1 is a method in which an upper member having a low melting point is pressed with a rotating welding tool to closely adhere the bonding interface between the upper plate and the lower plate by diffusion bonding. It is not clearly different from the prior art only by clarification specifically, and it cannot be said that a stable and high bonding strength can be obtained. Further, the method described in Patent Document 2 merely forms a concave portion having a small diameter corresponding to the pin portion (probe) on a metal plate material having a high melting point, and it can be said that stable bonding strength can always be obtained. Absent. Moreover, it is a technique in which a recess has to be formed in a metal material, and a problem still remains in that respect.

  That is, in these patent documents 1 to 4, there is a spot friction stir welding method that can join dissimilar metal materials with stable high joint strength without deforming the metal material using the spot friction stir welding method. Not listed. Patent Documents 3 and 4 describe techniques relating to joining of different materials by arc welding, and are proposals relating to techniques different from the present invention.

JP 2005-28378 A JP 2006-95585 A JP 2006-21249 A JP 2006-150439 A

  The present invention has been made as a solution to the above-described conventional problems, and it is not necessary to use high power energy for dissimilar metal materials having different melting points, and dust is not scattered during welding and the work environment is also harmed. Spot friction stir welding method for dissimilar metal materials that can join dissimilar metal materials with stable and high joint strength without deforming the metal materials using the spot friction stir welding method, which is an excellent welding method It is a problem to provide.

  The invention according to claim 1 is a spot friction stir welding method for dissimilar metal materials formed by overlapping and joining dissimilar metal materials having different melting points, and the metal material having a high melting point is laminated on the backing material in order from the bottom. In the spot friction stir welding using a friction tool rotating from above, a heat insulating layer is formed on the backing material between the backing material and the metal material having a high melting point, and the heat insulating layer is A spot friction stir welding method for dissimilar metal materials, characterized in that the layer is a ceramic layer formed of a ceramic material.

  According to a second aspect of the present invention, among the different metal materials having different melting points, the metal material having a higher melting point is an iron-based material, and the metal material having a lower melting point is an aluminum-based material. Stir welding method.

  According to the spot friction stir welding method for dissimilar metal materials of the present invention, it is not necessary to use high power energy for dissimilar metal materials having different melting points such as iron-based materials and aluminum-based materials, and dust is scattered during welding. In addition, the spot friction stir welding method, which is an excellent welding method that does not harm the work environment, can be joined with stable and high joint strength without deforming the metal material.

  The inventors of the present invention do not need to use high power energy for dissimilar metal materials having different melting points such as iron-based material and aluminum-based material, and dust does not scatter during welding, and the work environment is not harmed. Research and development were conducted in order to find a method capable of joining with a stable and high joint strength without deforming the metal material by using the spot friction stir welding method which is an excellent welding method.

  As a result, in the conventional spot friction stir welding method, the metal material having a high melting point is in contact with the metal backing material at the welding joint position, so that the metal material having a low melting point is made to stir plastically flow the metal material having a low melting point. When the surface temperature of a metal material with a high melting point is raised due to friction between the metal material with a high melting point and heat generated by plastic flow, it was found that most of the generated thermal energy flows to the backing material. . That is, when a metal material having a low melting point is in an appropriate temperature state for joining, the surface temperature of the metal material having a high melting point has not increased to a sufficient temperature for joining, and as a result, the metal The materials could not be bonded with a stable and high bonding strength.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings. In the following description, a metal material having a high melting point is described as an iron-based material, and a metal material having a low melting point is described as an aluminum-based material. The aluminum-based material indicates pure aluminum or an aluminum alloy. In addition to iron-based materials and aluminum-based materials, nickel-based materials, copper-based materials, and other various metal materials may be used as the metal material.

  FIG. 1 shows a welded joint of an iron-based material and an aluminum-based material, in which (a) is a plan view and (b) is a side view thereof. In addition, the numerical value shown to a figure shows each part dimension of the welded joint used in the Example mentioned later. FIG. 2 shows a friction tool used in the spot friction stir welding method for dissimilar metal materials of the present invention, and FIG. 3 shows an embodiment of a backing material used in the spot friction stir welding method for dissimilar metal materials of the present invention. FIG. 4 shows a backing material used in a conventional spot friction stir welding method.

  FIG. 5 shows a state in which an iron-based material and an aluminum-based material are welded together by a spot friction stir welding method according to an embodiment of the present invention. FIG. 6 shows a state in which the joining strength of a welded joint of an iron-based material and an aluminum-based material is confirmed in an embodiment described later, and FIG. 7 shows a state in which the probe at the tip of the friction tool is pushed into the aluminum-based material. Show. FIG. 8 shows a state in which an iron-based material and an aluminum-based material are welded together by a spot friction stir welding method according to a different embodiment of the present invention.

  In order to eliminate the problem that much of the generated thermal energy flows to the backing material 3 when raising the surface temperature of the iron-based material 1, the inventors of the columnar backing material 3 The heat insulation layer 4 was formed in the upper part in the position which was in contact with the iron-based material 1 in the conventional spot friction stir welding method. The heat insulating layer 4 shown in FIGS. 4 and 5 is an air layer 4a, and the heat insulating layer 4 shown in FIG. 8 is a ceramic layer 4b formed using a ceramic material. When the heat insulating layer 4 is the ceramic layer 4b, the ceramic layer 4b is in contact with the iron-based material 1. However, since the ceramic layer 4b has high heat insulating properties, heat energy is prevented from flowing to the backing material 3. Can do.

  When the heat insulating layer 4 is the air layer 4a, the air layer 4a has a circular plan view, and its diameter is 0.6 to 1.4 times the tool diameter of the rotating friction tool 5 shown in FIGS. The range. Moreover, the thickness of the air layer 4a shall be 0.20 mm or more.

  If the diameter of the air layer 4a is less than 0.6 times the tool diameter of the friction tool 5, the area where the backing material 3 around the air layer 4a is in contact with the iron-based material 1 will be excessive. A good heat insulation effect cannot be obtained. On the other hand, when the diameter of the air layer 4a is more than 1.4 times the tool diameter of the friction tool 5, the bent iron-based material 1 pushed by the friction tool 5 comes into contact with the backing material 3, so that it is sufficient. A good heat insulation effect cannot be obtained. It is more desirable that the diameter of the air layer 4a and the tool diameter of the friction tool 5 are the same.

  Further, even when the thickness of the air layer 4a is less than 0.20 mm, the bent iron-based material 1 pushed by the friction tool 5 comes into contact with the backing material 3, so that a sufficient heat insulating effect cannot be obtained. . Although there is no upper limit of the thickness of the air layer 4a, it is a matter of course that even if it is thick, it does not exceed the length of the cylindrical backing material 3.

  Moreover, it is desirable that the diameter of the columnar backing material 3 be equal to or larger than the tool diameter of the friction tool 5. This is because when the friction tool 5 is pushed in, the backing material 3 reliably receives the pushing force.

  Furthermore, it is desirable that the diameter of the backing material 3 is 1.1 to 2.2 times the diameter of the air layer 4a. If the diameter of the backing material 3 is less than 1.1 times the diameter of the air layer 4a, the contact area between the backing material 3 and the iron-based material 1 becomes too small, and the iron-based material pushed in by the friction tool 5 1 cannot be fully supported. On the other hand, if the diameter of the backing material 3 is more than 2.2 times the diameter of the air layer 4a, the contact area with the iron-based material 1 becomes too large to obtain a sufficient heat insulating effect. In this case, the contact position of the iron-based material 1 and the backing material 3 is a position away from the welding joint position, and since the influence on the reduction of the heat insulation effect is small, it is not an essential requirement of the present invention.

  When the heat insulating layer 4 is a ceramic layer 4b formed using a ceramic material, the upper portion of the backing material 3 is a ceramic layer 4b formed using a ceramic material as shown in FIG. . Since the iron-based material 1 is in contact with the ceramic layer 4b, the iron-based material 1 does not bend unlike the case where the air layer 4a is the heat insulating layer 4. Accordingly, the ceramic layer 4b may have any thickness as long as heat insulation can be ensured.

  Next, a method of joining the iron-based material 1 and the aluminum-based material 2 by the spot friction stir welding method for dissimilar metal materials of the present invention using the backing material 3 having the heat-insulating layer 4 formed thereon is referred to as a heat-insulating layer. A description will be given based on FIG. 5 which is an embodiment in which 4 is an air layer 4a.

  First, the iron-based material 1 and the aluminum-based material 2 are overlapped on the backing material 3 in this order from the bottom in the order of the iron-based material 1 and the aluminum-based material 2. Next, while the friction tool 5 is rotated from above on the surface of the aluminum-based material 2, the aluminum-based material 2 is plastically flowed by being pushed from the probe 5 a at the tip thereof. In this state, the surface (interface) temperature of the iron-based material 1 is increased by friction between the aluminum-based material 2 and the iron-based material 1 and heat generated by plastic flow. Since the air layer 4 a is formed in the upper part, most of the heat energy does not flow to the backing material 3. Although the iron-based material 1 and the backing material 3 are in contact with each other around the welded joint position, heat energy does not flow directly from the welded joint position to the backing material 3, so The surface (interface) temperature can be maintained at an appropriate temperature at which diffusion bonding can be performed.

  In this state, since the iron-based material 1 and the aluminum-based material 2 are friction stir welded, the iron-based material 1 and the aluminum-based material 2 which are dissimilar metal materials having different melting points are weld-bonded with a stable and high bonding strength.

Example 1
A spot friction stir welding test of the iron-based material 1 and the aluminum-based material 2 was performed using a spot friction stir welding apparatus (manufactured by Kawasaki Heavy Industries: FSJ stationary system). As a test body, 590 MPa class hot-dip galvanized high-tensile steel plate (plate thickness: 1.2 mm) was used as the iron-based material 1, and AA6022-equivalent aluminum alloy plate (plate thickness: 1.0 mm) was used as the aluminum-based material 2. The shape of a welded joint obtained by welding the iron-based material 1 and the aluminum-based material 2 is shown in FIGS. Specific dimensions of each part of the welded joint are as shown in FIGS. The unit of the numerical value is mm.

  The friction tool 5 of the spot friction stir welding apparatus used for the test of the invention example and the comparative example is shown in FIG. 2, and the heat insulating layer 4 ( The backing material 3 on which the air layer 4a) is formed is shown in FIG. 3, and the back of the spot friction stir welding apparatus used in the test of the comparative example is not formed with the heat insulating layer 4 (air layer 4a) with the iron-based material 1. The pad 3 is shown in FIG.

  In FIG. 2, Ds is the tool diameter of the friction tool 5 and φ10 mm, Dp is the diameter of the probe 5a at the tip of the friction tool 5 and φ2 mm, and Hp is the length of the probe 5a and 0.5 mm. 3, Du is the diameter of the backing material 3 and φ16 mm, Dk is the diameter of the air layer 4a and φ8 mm, and Hk is the thickness of the air layer 4a and is 0.25 mm. In FIG. Is the diameter of the backing material 3 and is φ16 mm. In addition, Dt shown in FIG. 7 shows the pressing depth of the probe 5a at the tip of the friction tool 5.

  That is, in the example of the invention, among the conditions shown in claim 1, the diameter of the air layer 4a (Dk) / the tool diameter of the friction tool 5 (Ds) = 0.8 times, and the thickness (Hk) of the air layer 4a is 0. 25 mm, which satisfies the conditions shown in claim 1. Further, among the conditions shown in claim 2, the diameter of the backing material 3 (Du) ≧ the tool diameter (Ds) of the friction tool 5, the diameter of the backing material 3 (Du) / the diameter of the air layer 4a (Dk) = It is 2.0 times, and the condition shown in claim 2 is also satisfied.

  In FIG. 5, the state which weld-joins the iron-type material 1 and the aluminum-type material 2 with the spot friction stir welding method of the example of an invention is shown. A shear tensile test based on JIS Z3136 was performed by the method shown in FIG. 6 using a welded joint in which the iron-based material 1 and the aluminum-based material 2 were welded and joined by this spot friction stir welding method. Similarly, for the comparative example, a welded joint was prepared by welding the iron-based material 1 and the aluminum-based material 2 by the spot friction stir welding method, and a shear tensile test in accordance with JIS Z3136 was performed by the method shown in FIG. Carried out.

  The shear tensile test was carried out with the number of samples set to N = 3 by changing the pressing force, the number of rotations, the pressing time, and the indentation depth of the friction tool 5 in both the inventive example and the comparative example. The acceptance criteria were all that the shear force obtained by each sample was 3200 N or more and the average shear force was 3500 N or more. The test results are shown in Tables 1 and 2.

  In the comparative example shown in Table 1, a sample having a shearing force exceeding 3200N or 3500N can be confirmed in part, but the heat insulating layer 4 (air layer 4a) is not formed between the backing material 3 and the iron-based material 1 In the example, the conditions under which stable high strength (shearing force) was obtained could not be confirmed. On the other hand, in the invention example shown in Table 2, each sample satisfies all the acceptance criteria, and the insulating layer 4 (air layer 4a) is provided between the backing material 3 and the iron-based material 1 under the conditions of claim 1. It was confirmed that, if formed, a high strength (shearing force) can be stably obtained without variation.

(Example 2)
In the same manner as in Example 1, a spot friction stir welding test of the iron-based material 1 and the aluminum-based material 2 was performed using a spot friction stir welding apparatus (manufactured by Kawasaki Heavy Industries: FSJ stationary system). In the same manner as in Example 1, the iron-based material 1 is a 590 MPa class hot-dip galvanized high-tensile steel plate (plate thickness: 1.2 mm), and the aluminum-based material 2 is an AA6022-equivalent aluminum alloy plate (plate thickness: 1. 0 mm) was used.

  In Example 2, the pressure of the friction tool 5 is fixed at 2.0 kN, the rotation speed is 2000 rpm, the pressurization time is 5 s, the indentation depth is 0.7 mm, the diameter (Dk) of the air layer 4a, the air layer 4a By changing the thickness (Hk) of each, a shear tensile test was performed to confirm the appropriate dimensions of the air layer 4a. Moreover, the diameter (Du) of some backing materials 3 was also changed according to the diameter (Dk) of the air layer 4a. The acceptance criterion is the same as in Example 1.

  Each comparative example does not satisfy any of the conditions shown in claim 1, and No. 18 is 0.4 times the diameter (Dk) of the air layer 4a / the tool diameter (Ds) of the friction tool 5. In No. 19, the diameter (Dk) of the air layer 4a / the tool diameter (Ds) of the friction tool 5 is 0.5 times. On the other hand, no. No. 20, the diameter (Dk) of the air layer 4a / the tool diameter (Ds) of the friction tool 5 is 1.6 times. No. No. 21 has a thickness (Hk) of the air layer 4a of 0.10 mm. No. 22 has a thickness (Hk) of the air layer 4a of 0.15 mm.

  On the other hand, in each invention example, the diameter (Dk) of the air layer 4a / the tool diameter (Ds) of the friction tool 5 is 0.6 to 1.4 times, and the thickness (Hk) of the air layer 4a is 0.20 mm or more. Satisfy the condition. Table 3 shows the results of a shear tensile test based on JIS Z3136.

  No. 18 and No. 19 is a comparative example in which the diameter (Dk) of the air layer 4a / the tool diameter (Ds) of the friction tool 5 is less than 0.6 times. In these comparative examples, since the area where the backing material 3 around the air layer 4a is in contact with the iron-based material 1 is excessive, a sufficient heat insulating effect by the air layer 4a cannot be obtained, and the acceptance criterion is satisfied. It is thought that it was not possible.

  On the other hand, no. 20 is a comparative example in which the diameter (Dk) of the air layer 4a / the tool diameter (Ds) of the friction tool 5 exceeds 1.4 times. In this comparative example, since the bent iron-based material 1 pushed by the friction tool 5 has come into contact with the backing material 3, a sufficient heat insulating effect by the air layer 4a cannot be obtained, and the acceptance criterion cannot be satisfied. It is thought.

  No. 21 and no. 22 is a comparative example that does not satisfy the condition that the thickness (Hk) of the air layer 4a is 0.20 mm or more. In these comparative examples, since the air layer 4a is too thin and the bent iron-based material 1 pushed in by the friction tool 5 has come into contact with the backing material 3, a sufficient heat insulating effect cannot be obtained, and the acceptance criterion is It seems that he was not satisfied.

  For these comparative examples, no. In the invention examples 23 to 28, the diameter (Dk) of the air layer 4a / the tool diameter (Ds) of the friction tool 5 is 0.6 to 1.4 times, and the thickness (Hk) of the air layer 4a is 0.20 mm or more. Since the conditions are satisfied, a sufficient heat insulating effect can be obtained by the air layer 4a, and it is considered that the acceptance criterion is satisfied. That is, the proper dimension of the air layer 4a could be confirmed by the above test.

(Example 3)
In the same manner as in Example 1, a spot friction stir welding test of the iron-based material 1 and the aluminum-based material 2 was performed using a spot friction stir welding apparatus (manufactured by Kawasaki Heavy Industries: FSJ stationary system). In the same manner as in Example 1, the iron-based material 1 is a 590 MPa class hot-dip galvanized high-tensile steel plate (plate thickness: 1.2 mm), and the aluminum-based material 2 is an AA6022-equivalent aluminum alloy plate (plate thickness: 1. 0 mm) was used. The difference from Example 1 is that, as shown in FIG. 8, the heat insulating layer 4 is a ceramic layer 4b formed using alumina-based ceramics.

  In Example 3, the shear tensile test based on JIS Z3136 was performed by changing the pressing force, rotation speed, pressing time, and indentation depth of the friction tool 5 respectively. The acceptance criterion is the same as in Example 1. The test results are shown in Table 4.

  According to the test results of Table 4, all passed the acceptance criteria. From this result, even when the heat insulating layer is a ceramic layer formed of a ceramic material, a sufficient heat insulating effect can be obtained, and high strength (shearing force) can be stably obtained without variation. It could be confirmed.

The welded joint of the iron-type material and aluminum-type material produced with the spot friction stir welding method of the dissimilar metal material of this invention is shown, (a) is the top view, (b) is the side view. It is a longitudinal cross-sectional view which shows the friction tool used for the spot friction stir welding method of the dissimilar metal material of this invention. It is a longitudinal cross-sectional view which shows one Embodiment of the backing material used for the spot friction stir welding method of the dissimilar metal material of this invention. It is a longitudinal cross-sectional view which shows the backing material used for the conventional spot friction stir welding method. In one Embodiment of this invention, it is a longitudinal cross-sectional view which shows the state which weld-joined the iron-type material and the aluminum-type material with the spot friction stir welding method. It is a top view which shows the state which has confirmed the joint strength of the welded joint of an iron-type material and an aluminum-type material by a shear tension test. It is a longitudinal cross-sectional view which shows the state which has pushed the probe of the friction tool front-end | tip into aluminum-type material. It is a longitudinal cross-sectional view which shows the state which weld-joined the iron-type material and the aluminum-type material with the spot friction stir welding method in different embodiment of this invention.

1 ... Iron-based materials (metal materials with high melting points)
2… Aluminum material (metal material with low melting point)
3 ... Backing material 4 ... Heat insulation layer 4a ... Air layer 4b ... Ceramic layer 5 ... Friction tool 5a ... Probe

Claims (2)

In the spot friction stir welding method of dissimilar metal materials formed by overlapping and joining dissimilar metal materials having different melting points,
When the spot friction stir welding is carried out using a friction tool that rotates from the top on the backing material in order from the metal material with the high melting point in order from the bottom,
Forming a heat insulating layer on the backing material between the backing material and the metal material having a high melting point;
A spot friction stir welding method for dissimilar metal materials, wherein the heat insulating layer is a ceramic layer formed of a ceramic material.   The spot friction stir welding method for dissimilar metal materials according to claim 1, wherein, among the dissimilar metal materials having different melting points, the metal material having a high melting point is an iron-based material, and the metal material having a low melting point is an aluminum-based material.

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