Metal interconnection structure and method for producing a metal interconnection structure

Abstract

Metal connection structure comprising: an iron alloy part; an aluminum alloy part; and a bonding intermediate layer disposed between the iron alloy part and the aluminum alloy part and comprising: an iron-silicon sublayer in solid solution phase in contact with the iron alloy part, an aluminum-silicon sublayer in eutectic phase in contact with the aluminum alloy part, and a silicon sublayer arranged between the iron-silicon sublayer in solid solution phase and the aluminum-silicon sublayer in eutectic phase.

Description

Technical FieldThe present disclosure relates to a metal joint structure manufactured by welding alloy parts having different melting points, and a method of manufacturing the metal joint structure.Prior ArtFor parts used for the body of an automobile and the like, a joining structure made by joining alloy parts having different melting points is employed. For example, an aluminum alloy part having a low specific gravity is used for weight reduction and an iron alloy part is used for realizing high rigidity. Accordingly, a portion is formed in which a part made of an iron alloy and a part made of an aluminum alloy are joined by welding.However, since the melting point and specific gravity of iron alloys are greatly different from those of aluminum alloys, it is generally difficult to weld them together. Therefore, a special welding method is required to weld an iron alloy part to an aluminum alloy part.US 2011 / 0 020 666 A1 discloses a metal compound structure and a metal compound method, in which the structure includes an iron-based metal body, an intermetallic compound layer, and a compound layer.DE 10 2014 107 693 A1 discloses resistance spot welding of steel to a workpiece made of aluminum or made of aluminum alloy. The weld joint includes an aluminum alloy weld tip and an Fe-Al intermetallic layer.EP 3 068 574 B1 discloses welding two metallic workpieces by applying a layer of weld modifying material to a surface of one or each of the metallic workpieces using a cold spray process prior to welding, wherein the weld modifying material is a metallic material and wherein the weld modifying material, the first metallic workpiece and the second metallic workpiece each have a majority elementary component.Patent Document 1 discloses a method of manufacturing a welding structure of different materials, in which an aluminum material or an aluminum alloy material is joined to a steel that is an iron alloy type. A welding structure of different materials disclosed in Patent Document 1 is manufactured using a filler material for joining different materials, the filler material including silicon and titanium, and the rest of the filler material being made of aluminum and aluminum alloy, which is an inevitable impurity.Prior Art DocumentsPatent DocumentsPatent Document 1: Unexamined Published Patent Application JP 2014-180685 A.The different material welding structure described in Patent Document 1 is manufactured by welding a steel that is an iron alloy type with an aluminum alloy using a different material joining filler that contains aluminum and an aluminum alloy, the filler being disposed between the steel and the aluminum alloy; aluminum components contained in the different material joining filler react with the iron alloy to form an intermediate joining layer. However, there is a risk that a brittle intermetallic iron-aluminum compound forms on the intermediate connecting layer, which reduces the welding factor. Therefore, when a welding structure made of different materials is applied to automobile frames, there is a problem that the welding structure made of different materials easily causes cracks.The present disclosure has been made to solve the above-described problem and provide a metal joining structure having an improved joining strength of a part manufactured by welding an iron alloy to an aluminum alloy, and a method for manufacturing such a metal joining structure.Solution of Problem SettingIn order to solve the above-described problems and achieve the object, a metal joining structure according to the present disclosure includes: an iron alloy part; an aluminum alloy part; and an intermediate joining layer that is disposed between the iron alloy part and the aluminum alloy part and includes a mixed crystal phase iron-silicon sublayer in contact with the iron alloy part, a eutectic phase aluminum-silicon sublayer in contact with the aluminum alloy part, and a silicon sublayer that is disposed between the mixed crystal phase iron-silicon sublayer and the eutectic phase aluminum-silicon sublayer.The metal joint structure according to the present disclosure includes, between the iron alloy part and the aluminum alloy part, a joint interlayer including a silicon sublayer made of only silicon whose melting point is lower than the melting point of the iron alloy and higher than the melting point of the aluminum alloy; therefore, the structure can prevent both the iron alloy and the aluminum alloy from melting, thereby improving the strength of the joint.Brief Description of the FiguresFIG. 1 is a cross-sectional view showing a metal interconnection structure according to Embodiment 1. FIG. 2 is a view showing a concrete example of an intermediate interconnection layer of the metal interconnection structure shown in FIG. 1. FIG. 3 is a view for explaining the state of the metal interconnection structure before manufacturing. FIG. 4 is a view for explaining a method of joining the metal joining structure.EmbodimentsMetal interconnection structures according to embodiments of the present invention will be described in detail below with reference to the figures.Embodiment 1FIG. 1 is a cross-sectional view of a metal interconnection structure according to the present embodiment. The metal joint structure 100 includes an iron alloy part 1, an aluminum alloy part 2, and an intermediate joining layer 3 disposed between the iron alloy part and the aluminum alloy part.The type of the iron alloy constituting the iron alloy part 1 and the type of the aluminum alloy constituting the aluminum alloy part 2 are not particularly limited; for the iron alloy part 1, for example, a low-carbon cold-rolled steel sheet (SPCC), a high-strength steel sheet, or a stainless steel sheet may be used; For the aluminum alloy member 2, for example, JIS (Japanese Industrial Standard) A1000 series (pure aluminum series), JIS-A2000 series (aluminum-copper alloy series), JIS-A3000 series (aluminum-manganese alloy series), JIS-A4000 series (aluminum-silicon alloy series), JIS-A5000 series (aluminum-magnesium alloy series), JIS-A6000 series (aluminum-magnesium-silicon alloy series) or JIS-A7000 series (aluminum-zinc-magnesium alloy series) can be used.FIG. 2 is a view showing a concrete example of an intermediate compound layer shown in FIG. 1. Referring to FIG. 2, the structure of the intermediate interconnection layer 3 of the metal interconnection structure 100 according to the present embodiment will be described. The intermediate bonding layer 3 includes a mixed crystal phase iron-silicon sublayer 4, a eutectic phase aluminum-silicon sublayer 5, and a silicon sublayer 6 interposed between the mixed crystal phase iron-silicon sublayer 4 and the eutectic phase aluminum-silicon sublayer 5. By incompletely melting the silicon layer 7, the silicon sublayer 6 is formed as an unmelted silicon layer which is not fused with other metals. It is noted that silicon has a lower melting point than iron and a higher melting point than aluminum.Here, the solid solution phase (solid solution) is a phase in which some of atoms in the crystal are replaced with atoms of another element but the original crystal structure remains unchanged, or some atoms of another element have been inserted; the eutectic phase is a phase in which a crystal containing two or more elements is uniformly mixed with a crystal having a component ratio different from that of the aforementioned crystal.The mixed crystal phase iron-silicon sublayer 4 is in a phase in which silicon particles have been incorporated into an iron matrix, whereby the matrix becomes hard and thereby the strength of the joint is improved. The aluminum-silicon eutectic-phase sublayer 5 is in a phase in which silicon particles are dispersed in an aluminum matrix, whereby the matrix becomes hard and thereby the strength of the joint is improved. When a mixed crystal containing various elements becomes hard, the lattice constant changes, but the crystal structure remains unchanged from that of the matrix. On the other hand, an iron-aluminum intermetallic compound formed by crystallization has a crystal structure different from that of the matrix and hardly agrees with the matrix, and its crystals are coarse and difficult to disperse. Therefore, it is rather a starting point for cracks in the metal interconnection structure. Accordingly, there is a possibility that the strength of the joint is lowered. In the metal joint structure 100, therefore, there are a mixed crystal phase iron-silicon sublayer 4, an eutectic phase aluminum-silicon sublayer 5, and a silicon sublayer 6 between the iron alloy part 1 and the aluminum alloy part 2, thereby significantly improving the strength of the joint between the iron alloy part 1 and the aluminum alloy part 2. Since grain boundaries of the silicon grains in the aluminum-silicon eutectic phase sublayer 5 poorly conform to the iron matrix and the aluminum matrix, it is desirable that the silicon grains be small in order to improve the strength of the joint.Above, the structure of the intermediate compound layer 3 in the present embodiment has been described using a combination of a mixed crystal phase iron-silicon sublayer, a silicon sublayer, and an eutectic phase aluminum-silicon sublayer as an example. Of course, the same advantage can be obtained with a combination of a mixed crystal phase iron-silicon sublayer, a silicon sublayer and a mixed crystal phase aluminum-silicon sublayer or a combination of a eutectic phase iron-silicon sublayer, a silicon sublayer and a eutectic phase aluminum-silicon sublayer.Next, a manufacturing method of the metal interconnection structure 100 will be described with reference to FIGS. 3 and 4. FIG. 4 shows a region where an iron alloy member 1 is placed on an aluminum alloy member 2 on which a silicon layer 7 to be described later is formed. The iron alloy part 1 (melting point of iron: 1538 degrees C.), the aluminum alloy part 2 (melting point of aluminum: 660 degrees C.), and a silicon layer 7 (melting point of silicon: 1414 degrees C.) are used for the production of the metal joint structure 100; for implementation and comparison examples, a cold-rolled steel sheet (SPCC) is used for the iron alloy constituting the iron alloy part 1, and A6063 is used for the aluminum alloy constituting the aluminum alloy part 2. A YAG laser is used as a light source for a high energy beam 8.First, a silicon coating for forming a silicon layer 7 is formed on a joining surface of the aluminum alloy member 2 by a cold spraying method. The silicon constituting the silicon layer 7 preferably has a high purity, preferably 95 wt % to 99.99 wt %. In the present embodiment, the silicon layer 7 is formed on the joining surface of the aluminum alloy member 2 by the cold spraying method using 99.99% by weight of silicon powder having a thickness of 1.0 μm.The cold spraying method is a technique for forming a coating in which a powder material is applied in a solid state below its melting temperature by collision with a carrier material without the powder material being melted or without the material being brought into the gaseous state. By the use of the cold spraying method, the silicon layer 7 can be formed uniformly without melting the aluminum alloy member 2 having a melting point lower than the silicon layer 7.The aluminum alloy member 2 has a strong oxide film (Al 2 O 3- film) on its surface; the oxide film prevents the surface from being welded. However, by the use of the cold spraying method, the oxide film is broken by the collision of the powder material grains, whereby a silicon layer 7 can be formed on the surface of the aluminum alloy member 2 whose oxide film has been removed.Next, under the condition shown in FIG. 3 that the iron alloy member 1 overlaps with the aluminum alloy member 2 on which the silicon layer 7 has been formed, the center of the overlapping portion is irradiated with a high energy beam 8 from the side of the iron alloy member 1. As irradiation conditions for the high energy beam 8, the spot diameter φ at the irradiation point of the high energy beam 8, the laser power, and the irradiation time are set so as to generate a temperature distribution that causes no melting of the aluminum alloy part 2 but only melting of the silicon layer 7.Specifically, an iron alloy part 1 having an area of 80 mm x 20 mm and a thickness of 0.5 mm and an aluminum alloy part 2 on which a silicon layer 7 is formed and having an area of 80 mm x 20 mm and a thickness of 1.0 mm are used, the alloy parts being superposed with an overlap 20 mm wide. Using an oscillator which generates a high energy beam 8 having a maximum output power of 3 kW and a lens having a focal length of 100 mm, the high energy beam 8 at the target point of the beam on the ferrous alloy member 1 is defocusing to a spot diameter φ of 6 mm, and the ferrous alloy member is irradiated for 2 seconds with a laser power of 1 kW. During irradiation with the high energy beam 8, argon gas is blown at a flow rate of 20 L / min from a nozzle (not shown in the figure) disposed coaxially with the laser beam axis to protect the alloy parts.Next, it will be described how the state of the joint surface changes during the joining process. As shown in FIG. 3, when the high energy beam 8 is irradiated from the iron alloy part 1 side, heat dissipated from the iron alloy part 1 melts silicon and aluminum, forming an aluminum-silicon eutectic-phase sublayer 5. Via the aluminum-silicon eutectic-phase sublayer 5, a silicon sublayer 6 prepared by partially melting the silicon layer 7 itself is firmly bonded to the aluminum alloy part 2. The iron alloy member 1 having a higher melting point than the silicon layer 7 melts only in a very flat part of its surface bonded to the silicon layer 7, thereby forming a mixed crystal phase iron-silicon sub-layer 4. Via the mixed crystal phase iron-silicon sublayer 4, the silicon sublayer 6 formed by melting the silicon layer 7 itself is firmly bonded to the iron alloy part 1. In this method, the mixed crystal phase iron-silicon sublayer 4 and the eutectic phase aluminum-silicon sublayer 5 are sequentially formed by mutual diffusion between iron and silicon and inter-diffusion between aluminum and silicon, respectively. Therefore, each of these sub-layers becomes thicker as compared with the silicon layer 7, thereby increasing the thickness of the intermediate compound layer 3.The irradiation with the high energy beam 8 should preferably be adjusted so that the heating is performed at a temperature equal to or higher than the melting point of the silicon layer 7 and at a temperature equal to or lower than the melting point of the iron alloy part 1. Note that when the lower surface side of the aluminum alloy part 2 is irradiated with the high energy beam 8, the aluminum alloy part 2 first completely melts without melting the iron alloy part 1, so that these two parts cannot be joined.As described so far, by irradiating the upper surface of the iron alloy member 1 with the high energy beam 8, the metal compound structure 100 shown in FIG. 1 can be obtained. In the description of the present embodiment, a YAG laser was used as an example of the light source of the high energy beam 8. However, the light source that can be used here is not limited to the YAG laser, and a CO 2- laser, a fiber laser, a disc laser, a semiconductor laser, or the like can also be used.Since the joining method of the present embodiment does not require plating, it can be easily applied to materials that are difficult to plate. As a result, a plating process can be avoided.In the following description, the welding factors of metal joining structures 100 obtained by the above joining method and those of comparative examples are evaluated. A welding factor is a value that indicates how strong a welded joint is relative to the strength of its base material.(Evaluation method)As for the thicknesses of the intermediate bonding layers 3, the samples are mirror-polished by mechanical polishing to prepare test samples of the cross sections of the bonding surfaces; then, measurements are performed using a scanning electron microscope (SEM).Regarding the presence or absence of the mixed crystal phase iron-silicon sublayer 4, the eutectic phase aluminum-silicon sublayer 5, and the silicon sublayer 6, crystal structure analyses based on X-ray diffraction (XRD) are performed on the cross sections of the joint surfaces of the samples under examination; the ratios of the peak intensities derived from the mixed crystal phase iron-silicon sublayer 4, the eutectic phase aluminum-silicon sublayer 5, and the silicon sublayer 6 are used to determine their respective presence or absence.The weld factors are calculated from the tensile shear strengths measured by conducting tensile tests on the metal joint structures. The evaluations of the welding factors are classified as follows: a sample having a welding factor of 80% or more is referred to as "good"; a sample having a welding factor of 60% or more and less than 80% is referred to as "medium"; and a sample having a welding factor of less than 60% is referred to as "poor". Table 1 summarizes the evaluation results of the implementation examples and the comparative examples. [Table 1] Table 1] [Table 1] Table 1]Comparative Example 1A6063SPCC0,2lackinglackinglackinglackingpoor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor 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present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present presentpresent present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present presentpresent present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present presentgood good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good 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present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present presentpresent present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present presentpresent present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present presentgood good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good 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present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present presentpresent present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present presentpresent present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present present presentagentsComparative Example 2A6063SPCC700874 (No intermediate bonding layer formed)lackinglackinglackingpoor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poor poorIt is understood from Table 1 that the silicon layer 7 for forming a partial layer composed of only silicon by melting the silicon layer 7 should preferably have a thickness of 1.0 μm to 300 μm from the viewpoint of the welding factor. The reason why the silicon layer 7 should preferably have a thickness of 1.0 μm to 300 μm is that a thickness of less than 1.0 μm causes iron to diffuse into aluminum, and that a thickness of more than 300 μm causes a peeling problem. In Comparative Example 1, the silicon layer 7 is thin, whereby the aluminum alloy member 2 melts upon welding. As a result, no mixed crystal sublayer, no silicon sublayer and no eutectic sublayer are formed in the joint surface, but a coarse intermetallic iron-aluminum compound, whereby the welding factor deteriorates. In Comparative Example 2, on the other hand, the silicon layer 7 is extremely thick, so that a large amount of heat is required for melting. This results in overheating of the silicon layer 7, thereby melting surface layers of the iron alloy part 1 and the aluminum alloy part 2 and thereby forming a coarse iron-aluminum intermetallic compound, resulting in a decrease in the strength of the joint between the intermediate joining layer 3 and the iron alloy part 1 and a decrease in the strength of the joint between the intermediate joining layer 3 and the aluminum alloy part 2, thereby degrading the welding factor.Table 1 shows that the welding factor is satisfactory when the thickness of the intermediate bonding layer 3 is in the range of 1.0 μm to 360 μm. This is because it is difficult to stably form an intermediate compound layer 3 having a thickness of less than 1.0 μm which is uniform simultaneously while maintaining the uniformity, and also because a silicon layer 7 required for forming such an intermediate compound layer peels off, it is difficult to form an intermediate compound layer 3 having a thickness of more than 360 μm.By the manufacturing method described so far, the metal interconnection structure according to the present embodiment shown in FIG. 1 is obtained. According to the metal compound structure of the present embodiment, by the presence of the silicon sublayer 6 formed by melting the silicon layer 7 itself, the iron alloy part 1 can be prevented from flowing into the aluminum-silicon eutectic phase sublayer 5 side and the aluminum alloy part 2 can be prevented from flowing into the iron-silicon mixed crystal phase sublayer 4 side. Therefore, it is possible to prevent the direct melting of the iron alloy part 1 and the aluminum alloy part 2, thereby preventing the formation of a coarse iron-aluminum intermetallic compound, which brings about an advantage that the strength of the joint between various kinds of metals, i.e., the iron alloy part 1 and the aluminum alloy part 2, can be improved.By using the metal joint structure according to the present embodiment, it is possible to apply an aluminum alloy part that is lighter than an iron alloy part to some of the parts used for a vehicle body or the like, particularly for its chassis, its trunk, and its frame, whereby its weight can be reduced.Description of the Symbols1 Iron alloy part, 2 Aluminum alloy part, 3 Intermediate compound layer, 4 Mixed crystal phase iron-silicon part layer, 5 Eutectic phase aluminum-silicon part layer, 6 Silicon part layer, 7 Silicon layer, 8 High energy beam, 100 Metal compound structure.

Claims

A metal joining structure comprising: an iron alloy part; an aluminum alloy part; and a joining interlayer disposed between the iron alloy part and the aluminum alloy part, and comprising: a mixed crystal phase iron-silicon sublayer in contact with the iron alloy part, a eutectic phase aluminum-silicon sublayer in contact with the aluminum alloy part, and a silicon sublayer disposed between the mixed crystal phase iron-silicon sublayer and the eutectic phase aluminum-silicon sublayer.The metal interconnection structure of claim 1, wherein the thickness of the intermediate interconnection layer is in the range of 1.0 μm to 360 μm.A method for manufacturing a metal joint structure, comprising: a step of forming a silicon layer on a joining surface of an aluminum alloy part; a step of overlapping an iron alloy part with the aluminum alloy part with the silicon layer interposed therebetween; and a step of bonding the iron alloy part to the aluminum alloy part by heating the iron alloy part with a high energy beam incident on a side of the iron alloy part, whereby heat dissipated from the side of the iron alloy causes a bonding surface between the iron alloy part and the silicon layer to be melted to form a mixed crystal phase iron-silicon sublayer, a bonding surface between the aluminum alloy part and the silicon layer to form an eutectic phase aluminum-silicon sublayer, and the silicon layer to be melted to form a silicon sublayer.The method for manufacturing a metal interconnection structure according to claim 3, wherein the thickness of the silicon layer is in the range of 1.0 μm to 300 μm.The method for manufacturing a metal interconnection structure according to claim 3 or 4, wherein the silicon layer is formed by depositing a silicon coating on the joining surface of the aluminum alloy part by a cold spraying method.

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