Joined body and joining method

Abstract

An objective of the present invention is to provide a joined body obtained by joining, with high strength, a separate member to an iron material having an Fe-Al layer containing an intermetallic compound.　An aspect for solving the problem is a joined body obtained by joining a separate member to an iron material having an Fe-Al layer containing an intermetallic compound, wherein the separate member is joined to a solid solution layer in which aluminum contained in the Fe-Al layer is solid-dissolved in the base material of the iron material. The joined body is obtained by a joining method including a heating step for heating, on the joining part of the iron material to which the separate member is to be joined, the Fe-Al layer to at least the melting point and at most the boiling point by means of a heat source and heating the base material of the iron material to least the melting point and at most the boiling point.

Description

Joint and joining method

[0001] The present invention relates to a bonded body and a bonding method.

[0002] In recent years, CO ２ There is a demand for reducing emissions and improving energy efficiency. One way to achieve this is to reduce the weight of various components. For example, one way to reduce the weight of components is to use dissimilar material joints, in which some components made of relatively high-strength, heavy materials such as steel plates are replaced with relatively light materials such as aluminum or magnesium.

[0003] As a technique for joining dissimilar materials, for example, a method of hybrid welding an aluminum-based workpiece and an iron-based workpiece without using a brazing filler metal or flux has been disclosed (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2006-281279

[0005] Patent Document 1 discloses that when welding an aluminum-based workpiece to an iron-based workpiece having a zinc-based coating layer on its surface, a first heat source that heats the surface of the iron-based workpiece is first applied to melt only the zinc-based coating layer, and then a second heat source that heats the end of the aluminum-based coated workpiece is applied to melt and join the zinc-based coating layer and the aluminum-based workpiece. It also discloses that the heat quantity of the second heat source is lower than that of the first heat source, thereby suppressing the formation of an intermetallic compound of aluminum and iron.

[0006] However, when the technology disclosed in Patent Document 1 is applied to a zinc alloy plated steel plate containing iron, the molten zinc alloy plate contains iron, and therefore aluminum and iron may form an intermetallic compound in the molten zone of the aluminum-based welded material, potentially reducing the strength of the joint.

[0007] Furthermore, when a high-tensile steel sheet having an aluminum-based plating (e.g., an Al-Si alloy) on its surface is hot stamped, the heat generated during the process forms an Fe-Al layer containing intermetallic compounds between the iron base material and the aluminum-based plating. The melting point of this Fe-Al layer is higher than that of zinc or zinc alloy plating and close to that of iron. For this reason, it is difficult to melt only the Fe-Al layer using the technology of Patent Document 1. Furthermore, even if only the Fe-Al layer can be melted, as with the zinc alloy-plated steel sheet described above, the presence of iron within the plating may similarly cause the aluminum and iron to form intermetallic compounds in the molten zone, potentially reducing the strength of the joint.

[0008] The present invention has been made in view of the above, and has an object to provide a joined body in which a separate member is joined with high strength to a steel material having an Fe—Al layer containing an intermetallic compound.

[0009] (1) The present disclosure relates to a joined body in which a separate member is joined to an iron material having an Fe—Al layer containing an intermetallic compound, in which the separate member is joined to a solid solution layer in which aluminum contained in the Fe—Al layer is solid-solved in a base material of the iron material.

[0010] According to (1), it is possible to provide a joined body in which a separate member is joined with high strength to a steel material having an Fe—Al layer containing an intermetallic compound.

[0011] (2) The joined body according to (1), wherein the separate member is made of a material different from the iron material, and an intermetallic compound layer is formed at the interface between the solid solution layer and the separate member.

[0012] According to (2), the iron material and another member that is a different material can be diffusion-bonded, and the generation of intermetallic compounds at locations other than the interface with the solid solution layer can be prevented.

[0013] (3) A joined body according to (1) or (2), in which a second iron material is joined to the surface of the iron material opposite to the surface to which the separate member is joined, the solid solution layer is a layer that reaches from the iron material to the second iron material in the thickness direction, and the separate member, the iron material, and the second iron material are joined in this order.

[0014] According to (3), a joined body can be produced without adding a step of joining iron materials together. In addition, the joining flange can be made shorter than with other welding methods.

[0015] (4) The present disclosure also relates to a joining method for joining a separate member to an iron material having an Fe—Al layer containing an intermetallic compound, the joining method including a heating step of heating the Fe—Al layer to a temperature between a melting point and a boiling point by a heat source at a joining portion of the iron material to be joined to the separate member, and heating a base material of the iron material to a temperature between a melting point and a boiling point.

[0016] According to (4), aluminum contained in the Fe-Al layer dissolves in the base material of the iron material, and no Fe-Al layer exists at the interface between the iron material and the other member, making joining easy.

[0017] (5) The joining method according to (4), wherein in the heating step, the base material is melted by the heat source in a volume that allows aluminum of the Fe—Al layer melted by the heat source to form a solid solution.

[0018] According to (5), the generation of intermetallic compounds can be suppressed, and the strength of the iron material can be maintained.

[0019] (6) The joining method according to (4) or (5), wherein the separate member is a material different from the iron material, and further includes a cooling step of lowering the temperature of the surface of the iron material to a melting point of the iron material or lower after the heating step, and a joining step of joining the separate member to the surface of the iron material after the cooling step.

[0020] According to (6), it is possible to suppress the generation of intermetallic compounds between the iron material and another member that is a different material. In addition, it is possible to suppress the generation of intermetallic compounds even when another member that is a different material is joined to an iron material that has been subjected to aluminum-based plating.

[0021] (7) The joining method according to (6), wherein the melting point of the separate member is lower than the melting point of the iron material, and the cooling step lowers the surface of the iron material to near the melting point of the separate member, and then the joining step joins the separate member to the iron material.

[0022] According to (7), it is possible to suppress the generation of intermetallic compounds between the iron material and the other dissimilar material. In addition, by making maximum use of the heat generated by the heating step, it is possible to ensure wettability of the other materials at the initial stage of joining, which contributes to speeding up the construction and stabilizing the quality.

[0023] (8) A joining method according to any one of (4) to (7), in which, before the heating step, a second iron material is placed in contact with the surface of the iron material opposite to the surface to be joined with the separate member, and the iron material and the second iron material are melted and joined by the heating step.

[0024] According to (8), a joined body can be produced without adding a step of joining iron materials together. In addition, the joining flange can be made shorter than with other welding methods.

[0025] FIG. 1 is a cross-sectional view showing an outline of a bonded body according to the first embodiment. FIG. 2 is a view showing a manufacturing process of a bonded body according to the first embodiment. FIG. 3 is a view showing a manufacturing process of a bonded body according to the first embodiment. FIG. 4 is a view showing a manufacturing process of a bonded body according to the first embodiment. FIG. 5 is a cross-sectional view showing an outline of a bonded body according to a second embodiment. FIG. 6 is a view showing a manufacturing process of a bonded body according to the second embodiment. FIG. 7 is a view showing a manufacturing process of a bonded body according to the second embodiment. FIG. 8 is a view showing a manufacturing process of a bonded body according to the second embodiment. FIG. 9 is a cross-sectional view showing an outline of a bonded body according to a comparative example. FIG. 10 is a microscope photograph showing a cross-section of a bonded body according to an example.

[0026] 1, a joined body 1 according to this embodiment has a separate member 3 joined to an iron material 2 having an Fe—Al layer 22 on its surface. Specifically, the separate member 3 is joined to a solid-solution layer 23 formed by the aluminum contained in the Fe—Al layer 22 being solid-solved in a base material 21 of the iron material 2. With the above configuration, the Fe—Al layer 22 is not present at the interface between the iron material 2 and the separate member 3, and therefore the iron material 2 and the separate member 3 are firmly joined together.

[0027] (Iron Material) The iron material 2 is not particularly limited as long as it is an iron material having an Fe—Al layer 22 on the surface of the base material 21. Examples of the iron material 2 include iron materials in which the Fe—Al layer 22 is formed on the surface by heating an iron material such as a high-tensile steel plate having an aluminum-based plating (Al—Si alloy or the like) on the surface by hot stamping or the like. In addition to the above, the iron material may be an iron material in which the Fe—Al layer 22 is formed in advance on the surface of the base material 21.

[0028] The Fe—Al layer 22 is a layer containing an intermetallic compound. The intermetallic compound may be any intermetallic compound containing iron (Fe) and aluminum (Al), and is not particularly limited, but examples thereof include Al—Si—Fe-based intermetallic compounds. The Fe—Al layer 22 may contain an alloy other than the intermetallic compound, for example, an Fe—Al alloy. The thickness of the Fe—Al layer 22 in the iron material 2 other than the joint portion is not particularly limited. The thickness of the Fe—Al layer 22 may be, for example, 10 to 50 μm, or 20 to 40 μm.

[0029] The melting point of the Fe—Al layer 22 is not particularly limited, but is, for example, approximately 1280 to 1480°C. The melting point of the Fe—Al layer 22 is closer to the melting point of iron (base material 21) (approximately 1560°C) than, for example, the melting point of zinc-based plating. Therefore, when attempting to melt only the Fe—Al layer 22 to join it to the separate member 3, it is necessary to adjust the melting temperature to a temperature between the melting points of the Fe—Al layer 22 and the base material 21, making temperature control difficult. In this embodiment, the Fe—Al layer 22 melts together with the base material 21 to form a solid-solution layer 23, which is then joined to the separate member 3. This facilitates temperature control during the manufacture of the joined body 1.

[0030] The solid-solution layer 23 is a layer in which aluminum contained in the Fe—Al layer 22 is dissolved in the base material 21. The solid-solution layer 23 is a layer that reaches the position where the base material 21 is present in the thickness direction of the iron material 2. The proportion of aluminum that is dissolved in iron in the solid-solution layer 23, i.e., the proportion of aluminum to iron in the solid-solution layer 23, is preferably 10 mass % or less. By setting the proportion of aluminum in the solid-solution layer 23 within the above range, it is possible to prevent aluminum from being unable to dissolve and generating an intermetallic compound, which would otherwise reduce the strength of the iron material 2.

[0031] The solid solution layer 23 is formed by a heating step described below. The heating step melts the Fe—Al layer 22 at the joining portion of the iron material 2 together with the base material 21, forming a solidified solid solution layer 23. Then, when the separate member 3 is joined to the solid solution layer 23, a thin intermetallic compound 4 can be generated between the iron material 2 and the separate member 3. The thickness of this intermetallic compound 4 is thinner than the thickness of the Fe—Al layer 22 in locations other than the joining portion. The above-described thickness difference is particularly evident at the toe 32 a and root 32 b of the separate member 3 in FIG. 1 . From the above, it can be inferred that the aluminum contained in the Fe—Al layer 22 has dissolved in the base material 21.

[0032] 1, the separate member 3 includes a base material 31 and a joint 32. The separate member 3 may be made of the same material as the iron material 2, or may be made of a different material. When the separate member 3 is made of a different material, examples of the material constituting the separate member 3 include aluminum, magnesium, and alloys thereof.

[0033] The joint 32 is a portion that is melted and joined to the solid solution layer 23. The joint 32 may be a part of the base material 31, or may be made of a material different from that of the base material 31. The joint 32 may be, for example, a brazing material (such as a flux-cored wire).

[0034] 1, it is preferable that only a thin intermetallic compound layer 4 exists at the interface between the joint 32 and the solid solution layer 23. That is, it is preferable that the solid solution layer 23 and the joint 32 are diffusion bonded by a diffusion reaction. If an Fe—Al layer 22 of the same thickness as that of the portion other than the joint exists at the interface between the joint 32 and the solid solution layer 23, the diffusion reaction (atomic movement) is inhibited, making it difficult to achieve diffusion bonding.

[0035] 1, an intermetallic compound layer 4 is preferably formed at the interface between the joint 32 of the separate member 3 and the solid solution layer 23. That is, in the joined body 1, the layers are formed in the following order when viewed from the thickness direction: the base material 21 of the iron material 2, the solid solution layer 23, the intermetallic compound layer 4, and the joint 32 of the separate member 3.

[0036] Since the Fe contained in the Fe—Al layer 22 is contained in the solid solution layer 23, the intermetallic compound layer 4 is formed relatively thinly only at the interface between the solid solution layer 23 and the joint 32 of the separate member 3. As a result, it is possible to prevent the intermetallic compound layer 4 from being formed in other locations (for example, inside the joint 32 other than the interface with the solid solution layer 23). Furthermore, the thickness of the intermetallic compound layer 4 at the toe 32a and the root 32b is sufficiently thin, thereby ensuring the joining strength of the joined body 1. The thickness of the intermetallic compound layer 4 at the toe 32a and the root 32b is preferably thinner than the thickness of the Fe—Al layer 22 at locations other than the joint of the iron material 2. The thickness of the intermetallic compound layer 4 is, for example, ½ or less, and may be ⅓ or less, of the thickness of the Fe—Al layer 22.

[0037] Second Embodiment Next, the configuration of a bonded body 1a according to a second embodiment will be described with reference to Fig. 3. The same components as those in the first embodiment are denoted by the same reference numerals in the drawing, and the description thereof may be omitted.

[0038] 3, in the joined body 1a, a second iron material 2a is joined to the surface of the iron material 2 opposite to the surface to which the separate member 3 is joined. The second iron material 2a is joined to the iron material 2 by a solid solution layer 23b.

[0039] The second iron material 2a is not particularly limited as long as it is an iron material. For example, it may be an iron material having an Fe—Al layer 22 like the iron material 2, or an iron material having other plating layers or the like.

[0040] The solid-solution layer 23b is a layer formed so as to reach the position where the second iron material 2a is present in the thickness direction. The other configuration of the solid-solution layer 23b may be the same as that of the solid-solution layer 23. For example, in the solid-solution layer 23b, the ratio of aluminum to iron is preferably 10 mass % or less.

[0041] 2A to 2D , a joining method for joining the iron material 2 and the separate member 3 to obtain the joined body 1 will be described. The joining method according to this embodiment includes a heating step in which the Fe—Al layer 22 is heated by a heat source to a temperature between the melting point and the boiling point at the joining portion of the iron material 2 to be joined to the separate member 3 (the positions of the molten layers 21 m and 22 m in FIG. 2A ), and the base material 21 is heated to a temperature between the melting point and the boiling point at a position adjacent in the thickness direction to the heated Fe—Al layer 22. This converts the Fe—Al layer 22 at the joining portion into a solid solution layer 23, thereby facilitating joining and improving joining strength.

[0042] The heat source in the heating step is not particularly limited, but is preferably a laser beam B1, as shown in Fig. 2A. The laser beam B1 is irradiated onto the joint of the iron materials 2 from a laser beam irradiation device 51, for example. In the following description, the heat source is described as the laser beam B1, but the heat source is not limited to the above, and any known heat source used in welding, such as an arc or an electron beam, can be used.

[0043] The heating step causes the Fe—Al layer 22 at the joint to become a molten layer 22m. Similarly, the base material 21 at the joint becomes a molten layer 21m. As a result, as shown in FIG. 2B , a molten layer 23a is generated in which the molten layers 21m and 22m are mixed. At this time, it is preferable to adjust the volumes of the molten layers 21m and 22m so that the content of aluminum derived from the Fe—Al layer 22 is within 10 mass% of the Fe contained in the molten layer 23a. This suppresses the generation of intermetallic compounds and improves strength. The above adjustment can be made, for example, by adjusting the temperature and irradiation time of the laser beam B1 in the heating step.

[0044] In particular, when the separate member 3 is made of a material different from the iron material 2, the joining method according to this embodiment preferably includes, after the heating step, a cooling step of lowering the surface temperature of the iron material 2 to a melting point or lower of the iron material 2 (molten layer 23 a). As a result of the cooling step, the molten layer 23 a solidifies at the joining portion of the iron material 2 to form a solid solution layer 23, as shown in FIG. 2C . In the joining step described below, by joining the separate member 3 to the solid solution layer 23, it is possible to prevent an excessively thick intermetallic compound from being generated between the iron material 2 and the separate member 3.

[0045] In the cooling step, it is preferable to lower the surface temperature of the iron material 2 to near the melting point of the separate member 3 (for example, about 660° C. when the separate member 3 is made of aluminum), particularly when the separate member 3 is made of a material different from the iron material 2 and has a lower melting point than the iron material 2 (for example, aluminum or magnesium). In this state, by joining the separate member 3 to the solid solution layer 23 in the joining step described below, it is possible to more preferably prevent an intermetallic compound of excessive thickness from being generated between the iron material 2 and the separate member 3.

[0046] In the cooling step, joining is possible even if the surface temperature of the iron material 2 is lowered below the melting point of the separate member 3, but it is preferable to lower the temperature to near the melting point of the separate member 3. This makes it possible to make maximum use of the heat in the heating step and ensure wettability of the separate member 3 at the initial stage of joining, contributing to faster construction and more stable quality.

[0047] 2D , the joining step is a step of joining the separate member 3 to the solid solution layer 23 after the cooling step. In the joining step, the joining portion 32 of the separate member 3 is heated and melted, and joined to the solid solution layer 23. The heating temperature of the joining portion 32 in the joining step can be, for example, equal to or higher than the melting point of the separate member 3 and equal to or lower than the melting point of the solid solution layer 23. By not heating the joining portion 32 in the joining step too high, the time for the diffusion reaction can be shortened. This makes it possible to sufficiently thin the thickness of the intermetallic compound layer 4, particularly the thickness of the intermetallic compound layer 4 at the toe 32 a and the root 32 b, and ensure the joining strength of the joined body 1.

[0048] The heat source for heating the joint 32 is not particularly limited, but is preferably a laser beam B2. Like the laser beam B1, the laser beam B2 is irradiated onto the joint 32 from, for example, a laser beam irradiation device 52. Instead of a laser beam, a known heat source used in welding, such as an arc or an electron beam, may also be used. The joining step is preferably performed under a shielding gas to prevent oxidation of the surface of the iron material 2.

[0049] Second Embodiment Next, a joining method for joining an iron material 2, a second iron material 2a, and a separate member 3 to obtain a joined body 1a will be described with reference to Figures 4A to 4D. Configurations similar to those in the first embodiment are denoted by the same reference numerals in the drawings, and descriptions thereof may be omitted.

[0050] 4A , in the joining method according to the present embodiment, a second iron material 2a is placed in contact with the surface of the iron material 2 opposite to the surface to be joined to the separate member 3. Then, in the heating step, the base material 21 at a position adjacent to the heated Fe—Al layer 22 is heated to a temperature not lower than the melting point but not higher than the boiling point, and the second iron material 2a at a position adjacent to the heated base material 21 in the thickness direction is heated to a temperature not lower than the melting point but not higher than the boiling point.

[0051] The heating step forms molten layer 21m in the thickness direction up to a position where it reaches second iron material 2a. As a result, as shown in FIG. 4B, molten layer 23c is formed, in which molten layer 21m and molten layer 22m are mixed. At this time, it is preferable to adjust the volume of molten layer 21m so that the aluminum content is within 10 mass% of the Fe contained in molten layer 23c. The aluminum originates from Fe-Al layer 22 and may also originate from second iron material 2a.

[0052] The molten layer 23c is cooled and solidified, forming a solid solution layer 23b, thereby joining the iron material 2 and the iron material 2a. Therefore, the joining can be performed without a separate process for joining the iron materials (the iron material 2 and the iron material 2a). If the iron materials were to be welded together by another method, such as spot welding, they would need to be welded at a different position in the horizontal direction from the welding position of the separate member 3. However, by using the heating step, the joining position between the iron materials can be made the same position in the horizontal direction as the welding position of the separate member 3. Therefore, the joining flange (the portion where the iron materials overlap) can be made shorter than when welding by the other method.

[0053] The joining method according to this embodiment preferably includes a cooling step similar to that of the first embodiment, particularly when the separate member 3 is made of a material different from the iron material 2 .

[0054] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0055] Next, an example of the present invention will be described, but the present invention is not limited to this example.

[0056] Example 1 A joined body 1 was produced by the joining method described in the first embodiment. The iron material used was a hot-stamped high-tensile steel plate having an Al-Si-Fe intermetallic compound. Aluminum was used as the separate member. A laser beam was used as the heat source in the heating step and the joining step. Specifically, a Laser Line LDM4500 oscillator and a processing head OTS-3 were used in the heating step. A Trump TruDisk 8001 oscillator and a processing head Processing Optics D70 were used in the joining step. As a result of the joining, a thin Al-Si-Fe intermetallic compound was formed only at the interface between the iron material and the separate member, and good joinability was obtained.

[0057] Figure 6 is a photomicrograph of a cross section of the joined body 1 according to Example 1. The reference numerals in Figure 6 correspond to the reference numerals in the above-described embodiment. As shown in Figure 6, the intermetallic compound layer 4 (Al-Si-Fe intermetallic compound) does not migrate into the inside of the joint 32. Furthermore, the thickness of the intermetallic compound layer 4 (Al-Si-Fe intermetallic compound) is sufficiently thin at the toe 32a and the root 32b. Therefore, it is clear that the joined body 1 has a desirable joining strength.

[0058] Comparative Example 1: A joined body 1b according to Comparative Example 1 was fabricated using the same iron material and separate member as in Example 1, but with a joining method in which an Al-Si-Fe intermetallic compound was dispersed in the aluminum separate member. Specifically, the joining portion of the iron material 2 was heated with a laser beam to a temperature above the melting point of aluminum but below the melting point of iron. The surface of the iron material 2 was then cooled to near the melting point of aluminum, and the aluminum separate member was joined. The joining portion was then heated with a laser beam to a temperature above the melting point of aluminum but below the melting point of iron. As a result, an Fe-Al layer 22 was solid-dissolved in the joint 32, as shown in FIG. 5 (note that the symbols in FIG. 5 have the same meanings as in the above embodiment). However, when a cross section of the joined body 1b was observed after joining, the Fe component 22a of the Fe-Al layer 22 had migrated into the joint 32, and Al-Si-Fe intermetallic compounds were formed inside the joint 32, in areas other than the interface between the iron material and the separate member. As a result, sufficient joint strength was not obtained.

[0059] From the above results, it is clear that the bonded body produced by the bonding method according to this embodiment can obtain a preferable bonding strength by bonding another member to the solid solution layer.

[0060] REFERENCE SIGNS LIST 1, 1a Joint 2 Iron material 21 Base material 22 Fe—Al layer 23, 23b Solid solution layer 3 Separate member 4 Intermetallic compound layer

Claims

1. A joined body in which another member is joined to an iron material having an Fe-Al layer containing an intermetallic compound, wherein the other member is joined to a solid-solution layer in which the aluminum contained in the Fe-Al layer is dissolved in the base material of the iron material.

2. The joined body according to claim 1, wherein the separate member is made of a material different from the iron material, and an intermetallic compound layer is formed at the interface between the solid solution layer and the separate member.

3. The joined body described in claim 1, wherein a second iron material is joined to the surface of the iron material opposite to the surface to which the other component is joined, the solid solution layer is a layer that reaches from the iron material to the second iron material in the thickness direction, and the other component, the iron material, and the second iron material are joined in this order.

4. A method for joining another member to an iron material having an Fe-Al layer containing intermetallic compounds, comprising a heating step of heating the Fe-Al layer to a temperature between the melting point and the boiling point using a heat source at the joint of the iron material to be joined to the other member, and heating the base material of the iron material to a temperature between the melting point and the boiling point.

5. The joining method according to claim 4, wherein in said heating step, said base material is melted by said heat source in a volume that allows aluminum of said Fe-Al layer to form a solid solution.

6. The joining method according to claim 4, wherein the separate member is a material different from the iron material, and further comprising: a cooling step, after the heating step, of lowering the temperature of the surface of the iron material to a melting point of the iron material or lower; and a joining step, after the cooling step, of joining the separate member to the surface of the iron material.

7. The joining method according to claim 6, wherein the melting point of the separate member is lower than the melting point of the iron material, and in the cooling step, the surface of the iron material is cooled to near the melting point of the separate member, and then in the joining step, the separate member is joined to the iron material.

8. The joining method according to claim 4, wherein, prior to the heating step, a second iron material is placed in contact with the surface of the iron material opposite to the surface to be joined with the other component, and the iron material and the second iron material are melted and joined together by the heating step.

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