Method for joining dissimilar metal materials

Abstract

To provide a bonding method for dissimilar metals, capable of preventing a sealing agent from intruding into the area in which a weld metal is formed and of preventing a moisture intrusion after bonding and thereby, capable of preventing occurrence of poor weld and corrosion in a weld zone to improve a bonding strength.SOLUTION: A bonding method for dissimilar metals comprises: a process of forming on an upper plate 2, a recessed area 21 having a form separating from a lower plate 1 so as to surround at least a first through hole 2a provided on the upper plate 2 before the process of arranging the upper plate 2 above the lower plate 1; and a process of applying a sealing agent 3 on at least one of a face of the upper plate 2 facing the lower plate 1, and the face of the lower plate 1 facing the upper plate 2 so as to surround at least the first through hole 2a. The area on which the sealing agent 3 is applied is made to be an area of the recessed area separating from the first through hole 2a in the recessed area 21 except the internal face of the area 21 and the area facing the recessed area 21 in the lower plate 1.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The present invention relates to a method for joining dissimilar metal materials capable of joining plate materials made of different materials with high strength.

Background Art

[0002] In transportation equipment represented by automobiles, improvement of fuel efficiency is constantly required for the purpose of suppressing (a) consumption of petroleum fuel which is a finite resource, (b) CO which is a greenhouse gas generated by combustion, and (c) running costs. As means therefor, in addition to improvement of power system technologies such as utilization of electric drive, weight reduction of the vehicle body is also one of the improvement measures. As a means for weight reduction, there is a method of replacing steel which is the current main material with aluminum or an aluminum alloy, magnesium or a magnesium alloy, carbon fiber or the like which are lightweight materials. However, replacing all of them with these lightweight materials has problems such as increased cost and insufficient strength, and a design method called so-called multi-material in which steel and lightweight materials are combined in appropriate places has attracted attention. Hereinafter, aluminum or an aluminum alloy, magnesium or a magnesium alloy may be simply referred to as an aluminum alloy or a magnesium alloy. 2 、(c) running costs. As means therefor, in addition to improvement of power system technologies such as utilization of electric drive, weight reduction of the vehicle body is also one of the improvement measures. As a means for weight reduction, there is a method of replacing steel which is the current main material with aluminum or an aluminum alloy, magnesium or a magnesium alloy, carbon fiber or the like which are lightweight materials. However, replacing all of them with these lightweight materials has problems such as increased cost and insufficient strength, and a design method called so-called multi-material in which steel and lightweight materials are combined in appropriate places has attracted attention. Hereinafter, aluminum or an aluminum alloy, magnesium or a magnesium alloy may be simply referred to as an aluminum alloy or a magnesium alloy.

[0003] By the way, when steel and the above lightweight materials are combined and joined, it is known that corrosion called galvanic corrosion occurs in the contact area of dissimilar metals. For example, when an aluminum alloy material having a low natural potential and a steel material having a high natural potential are brought into contact with each other in water, a corrosion circuit is formed and corrosion occurs in the aluminum alloy material. This corrosion circuit is formed by the presence of a medium through which an aluminum alloy and steel are energized, that is, water.

[0004] Therefore, as methods for preventing corrosion due to contact of dissimilar metal materials as described above, the following methods (1) to (3) can be mentioned. (1) Prevent water from entering the contact area of dissimilar metal materials. (2) Reduce the potential difference between dissimilar metals. (3) Cut off the energization path.

[0005] Among the methods (1) to (3) for preventing the above corrosion, as a method for preventing water from entering the contact area of dissimilar metal materials, for example, a method of disposing a water immersion prevention sealant around the contact area can be mentioned.

[0006] Figs. 9A to 9C are cross-sectional views showing the arc spot welding method in which a sealant is disposed between plates in the order of processes. As shown in Fig. 9A, a sealant 53 is disposed on the surface of an aluminum alloy plate 52 serving as a lower plate so as to surround the joining planned positions of the two plates. Next, as an upper plate, a steel plate 51 provided with a through hole 51a at the joining planned position is prepared, and the steel plate 51 is positioned so that the through hole 51a overlaps with the joining planned position in the aluminum alloy plate 52. Thereafter, as shown in Fig. 9B, the steel plate 51 is disposed on the upper surface of the aluminum alloy plate 52. Thereafter, as shown in Fig. 9C, the steel plate 51 is pressed toward the aluminum alloy plate 52 to bring the sealant 53 into close contact with the aluminum alloy plate 52 and the steel plate 51. Thereafter, although not shown, arc welding is performed through the through hole 51a to melt a part of the aluminum alloy plate 52 and form a weld metal that fills the through hole 51a, and further form a reinforcement on the upper surface of the steel plate 51, thereby joining the aluminum alloy plate 52 and the steel plate 51.

[0007] The above Figs. 9A to 9C are an example of an arc spot welding method that does not use an element, but also in arc spot welding using an element, a sealant can be similarly disposed between two plates.

[0008] Figs. 10A to 10C are cross-sectional views showing the process sequence of an element arc spot welding method in which a sealant is disposed between plate materials. As shown in Fig. 10A, a sealant 53 is disposed on the surface of a steel plate 61 serving as a lower plate so as to surround the joining position of two plate materials. Next, as an upper plate, an aluminum alloy plate 62 provided with a through hole 62a at a planned joining position is prepared, and the aluminum alloy plate 62 is positioned such that the through hole 62a and the planned joining position in the steel plate 61 overlap. Further, an element 64 having a through hole 64a in the same direction as the through hole 62a is inserted into the through hole 62a of the aluminum alloy plate 62. Note that a head having an outer diameter larger than the diameter of the through hole 62a of the aluminum alloy plate 62 is formed at the upper portion of the element 64. Thereafter, as shown in Fig. 10B, the aluminum alloy plate 62 is disposed on the upper surface of the steel plate 61. Thereafter, as shown in Fig. 10C, the aluminum alloy plate 62 is pressed toward the steel plate 61 to bring the sealant 53 into close contact with the steel plate 61 and the aluminum alloy plate 62. Thereafter, although illustration is omitted, arc welding is performed through the through hole 64a of the element 64 to melt a part of the steel plate 61 and a part of the element 64 and to form a weld metal that fills the through hole 64a of the element 64, thereby joining the steel plate 61 and the aluminum alloy plate 62.

[0009] According to the above-described joining method, it is possible to prevent moisture from entering between the upper plate and the lower plate. However, depending on the amount of the sealant 53 used, the pressing force of the upper plate against the lower plate, etc., the sealant 53 may enter the planned joining position. Taking the element arc welding shown in Figs. 10A to 10C as an example, when arc welding is performed in a state where the sealant 53 exists at the planned joining position, as shown in Fig. 11, blowholes 68 are formed in the weld metal 65 due to volatilization of the sealant 53, resulting in a welding defect.

[0010] Incidentally, a joining method of lap-welding dissimilar metal materials using a sealant is disclosed in, for example, Patent Document 1. Patent Document 1 describes a joining method in which a concave or convex portion surrounding a joining planned site is formed on at least one joining surface of both materials, and welding is performed in a state where a sealant is disposed around the joining planned site between the overlapped both materials.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] However, according to the joining method described in Patent Document 1, since a steel plate and an aluminum alloy plate are joined by, for example, resistance spot welding or resistance seam welding, an intermetallic compound (IMC) having extremely brittle properties is generated in the molten mixing portion of both plate materials, and there is a problem that the strength against tension and impact is extremely low.

[0013] In addition, in the conventional joining method, it is not possible to sufficiently suppress the intrusion of the sealant into the welding portion between both plates. When an arc welding joining method is applied to the joining method described in Patent Document 1, as shown in FIG. 11, welding defects may occur due to the presence of the sealant. As a result, the joining strength decreases.

[0014] The present invention has been made in view of such problems, and when joining plate materials made of different materials by arc welding, it is possible to prevent the sealant from entering the region where the welding metal is formed, and it is possible to prevent the intrusion of moisture after joining. Accordingly, an object of the present invention is to provide a joining method for dissimilar metal materials that can prevent the occurrence of welding defects and corrosion in the welded portion and improve the joining strength.

Means for Solving the Problems

[0015] The above object of the present invention is achieved by the configuration of the following [1] related to a method for joining dissimilar metal materials.

[0016] [1] A step of disposing a lower plate and an upper plate made of a material different from that of the lower plate and having a first through hole on a surface orthogonal to the thickness direction of the lower plate; A method for joining dissimilar metal materials, comprising a step of melting a part of the lower plate through the first through hole by arc spot welding and forming a welding metal having the same main components as the lower plate. Before the step of disposing the upper plate, a step of forming a recess in the upper plate in a shape separated from the lower plate so as to surround at least the first through hole; A step of applying a sealant to at least one of the surface of the upper plate facing the lower plate and the surface of the lower plate facing the upper plate so as to surround at least the first through hole. The region where the sealant is applied is a region separated from the first through hole with respect to the recess, excluding the inner wall surface of the recess and the region of the lower plate facing the recess. A method for joining dissimilar metal materials, characterized by this.

[0017] Further, a preferred embodiment of the present invention related to a method for joining dissimilar metal materials relates to the following [2] to [6].

[0018] [2] In the step of forming the welding metal, while filling the first through hole, a surplus having a diameter larger than the diameter of the first through hole is formed on the upper surface of the upper plate, and the lower plate and the upper plate are joined. The method for joining dissimilar metal materials according to [1], characterized by this.

[0019] [3] Before the step of forming the welding metal, A step of inserting an element having a second through hole into the first through hole is included. The element has an insertion portion formed on one axial end side of the second through hole and having a diameter that can be inserted into the first through hole, and a head portion formed on the other axial end side of the second through hole and having a diameter larger than that of the first through hole. The method for joining dissimilar metal materials according to [1], characterized in that, in the step of forming the welding metal, a step of melting a part of the lower plate and at least a part of the element and forming a welding metal that fills the second through hole is included.

[0020] [4] The recess has a hole side wall portion on the side of the first through hole and a sealant side wall portion on the side opposite to the hole side wall portion. The method for joining dissimilar metal materials according to any one of [1] to [3], characterized in that, in the step of forming the recess in the upper plate, the recess is formed such that the hole side wall portion is higher than the sealant side wall portion.

[0021] [5] The method for joining dissimilar metal materials according to any one of [1] to [4], characterized in that the surface to which the sealant is applied is the surface of the upper plate facing the lower plate.

[0022] [6] The method for joining dissimilar metal materials according to any one of [1] to [5], characterized in that the lower plate is one of an aluminum or aluminum alloy plate and a steel plate, and the upper plate is the other. [Advantages of the Invention]

[0023] According to the present invention, when joining plates made of different materials by arc welding, it is possible to prevent the sealant from entering the region where the welding metal is formed, and it is possible to prevent the intrusion of moisture after joining. Thereby, it is possible to provide a method for joining dissimilar metal materials that can prevent the occurrence of welding defects and corrosion at the welded portion and improve the joining strength. [Brief Description of the Drawings]

[0024]

Figure 1A

Figure 1B

Figure 1C

Figure 2

Figure 3A

Figure 3B

Figure 4A

Figure 4B

Figure 5

Figure 6

Figure 7A

Figure 7B

Figure 7C

Figure 8A

Figure 8B

Figure 8C

Figure 9A

Figure 9B

Figure 9C

Figure 10A

Figure 10B

Figure 10C

Figure 11

[0025] Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as "the present embodiments") will be described in detail. Note that the present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

[0026] [Method for Joining Dissimilar Metal Materials] When the present inventor was joining dissimilar metal materials by arc spot welding, in order to prevent a sealant for preventing the intrusion of moisture into the welded part from entering the region where the welded metal is formed, intensive studies were conducted. As a result, it was found that it is effective to provide a recess for retaining the sealant so as to surround the through hole provided in the upper plate, and to apply the sealant to a region outside this recess. Hereinafter, the method for joining dissimilar metal materials according to the present embodiment will be described in detail with reference to the drawings.

[0027] <First Embodiment> Figs. 1A to 1C are cross-sectional views showing the method for joining dissimilar metal materials according to the first embodiment of the present invention in the order of steps. Further, Fig. 2 is a drawing substitute photograph showing a joint joined by the method for joining dissimilar metal materials according to the first embodiment of the present invention. The present embodiment is a method for joining a steel plate (lower plate) 1 and an aluminum alloy plate (upper plate) 2 by element arc spot welding.

[0028] As shown in Fig. 1A, a cylindrical first through hole 2a is formed at the planned joining position of the aluminum alloy plate 2 with the steel plate 1, and a recess 21 is formed by press working so as to surround the first through hole 2a. The recess 21 has a shape that is recessed in a direction away from the aluminum alloy plate 2 when the aluminum alloy plate 2 is disposed on the upper surface of the steel plate 1. Therefore, when the aluminum alloy plate 2 is disposed on the upper surface of the steel plate 1, a gap 22 is formed at the location where the recess 21 is formed.

[0029] Next, on the surface (lower surface) of the aluminum alloy plate 2 facing the steel plate 1, a sealing agent 3 is applied in a region outside the recess 21, that is, a region separated from the first through-hole 2a with respect to the recess 21 so as to surround the first through-hole 2a. At this time, the sealing agent 3 is not applied to the inner wall surface of the recess 21. Next, a steel element 4 is inserted into the first through-hole 2a. A second through-hole 4a is formed in the element 4, and an insertion portion 4b having a diameter that can be inserted into the first through-hole 2a of the aluminum alloy plate 2 is formed on one end side in the axial direction of the second through-hole 4a. Further, a head portion 4c having a diameter larger than the diameter of the first through-hole 2a is formed on the other end side in the axial direction of the second through-hole 4a of the element 4. Note that it is preferable that the axial length of the insertion portion 4b is equal to the plate thickness of the aluminum alloy plate 2.

[0030] Thereafter, as shown in FIG. 1B, the aluminum alloy plate 2 is positioned so that the second through-hole 4a overlaps with the planned joining position in the steel plate 1, and the aluminum alloy plate 2 is disposed on a plane orthogonal to the thickness direction of the steel plate 1. Note that the timing of inserting the element 4 into the first through-hole 2a may be after the aluminum alloy plate 2 is disposed on the upper surface of the steel plate 1.

[0031] Thereafter, as shown in FIG. 1C, the aluminum alloy plate 2 is pressed toward the steel plate 1 to bring the sealing agent 3 into close contact with the steel plate 1 and the aluminum alloy plate 2. At this time, since the distance between the aluminum alloy plate 2 and the steel plate 1 becomes narrow, the sealing agent 3 applied to the lower surface of the aluminum alloy plate 2 is spread in a direction approaching the second through-hole 4a and a direction away from the second through-hole 4a. However, the sealing agent 3 that has moved in the direction approaching the second through-hole 4a stays in the gap 22 of the recess 21 and does not penetrate into the direction of the second through-hole 4a from the recess 21.

[0032] Thereafter, as shown in FIG. 2, arc welding is performed using a steel welding wire (not shown) through the second through-hole 4a of the element 4, melting a part of the steel plate 1 and at least a part of the element 4, and forming a weld metal 5 that fills the second through-hole 4a. Thereby, the element 4 and the steel plate 1 are firmly welded together by welding, and the aluminum alloy plate 2 is physically fixed to the steel plate 1 by the head 4c of the element 4, so that the steel plate 1 and the aluminum alloy plate 2 are joined together.

[0033] According to the joining method according to the present embodiment as described above, since the recess 21 is formed in the aluminum alloy plate 2, even when the aluminum alloy plate 2 is pressed toward the steel plate 1, the sealant 3 stays in the gap 22 of the recess 21 and can be prevented from entering the second through-hole 4a. Therefore, in the step of performing arc welding thereafter, it is possible to prevent blowholes from occurring in the weld metal 5 due to the vaporization of the sealant 3, and it is possible to prevent the occurrence of welding defects. Note that the sealant 3 that has moved in the direction away from the second through-hole 4a can be ignored because it does not affect the subsequent arc welding process.

[0034] In addition, since the first through-hole 2a and the recess 21 of the aluminum alloy plate 2 can be formed by a single pressing process, the processing of the aluminum alloy plate 2 does not become complicated. The sealant 3 may be applied to at least one of the surface of the aluminum alloy plate 2 facing the steel plate 1 and the surface of the steel plate 1 facing the aluminum alloy plate 2. However, if it is applied to the aluminum alloy plate 2 side, the recess 21 and the first through-hole 2a can be visually confirmed. Therefore, it can be applied so as to surround the first through-hole 2a in a region separated from the first through-hole 2a excluding the inner wall surface of the recess 21, and the position where the sealant 3 is applied can be easily determined.

[0035] Furthermore, in the present embodiment, a welding wire having the same main components as the steel plate 1 is used, and the steel plate 1 and the aluminum alloy plate 2 are joined by arc spot welding using a steel element 4. Therefore, dissimilar metals of a steel material and an aluminum alloy material do not melt simultaneously to form a brittle intermetallic compound, and a weld metal having the same main components as the steel plate 1 is formed, enabling a high-strength joint to be obtained. Further, since the periphery of the weld metal 5 obtained by welding is completely sealed by the sealant 3, it is possible to prevent moisture from entering the weld metal 5 or the contact portion between the steel plate 1 and the aluminum alloy plate 2. Therefore, it is possible to prevent a corrosion circuit from being formed between the steel plate 1 and the aluminum alloy plate 2 and corrosion from occurring in the aluminum alloy material.

[0036] <Second Embodiment> FIGS. 3A and 3B are cross-sectional views showing the method for joining dissimilar metal materials according to the second embodiment of the present invention in the order of steps. In FIGS. 3A and 3B, the same or equivalent parts as those in the first embodiment shown in FIGS. 1A to 1C are denoted by the same reference numerals in the drawings, and the description thereof is omitted or simplified.

[0037] As shown in FIG. 3A, in the second embodiment, the recess 21 is press-worked so that a step is formed between the side closer to the first through-hole 2a than the recess 21 and the side on which the sealant is applied rather than the recess 21. That is, the recess 21 has a hole side wall portion 21a on the side closer to the first through-hole 2a and a sealant side wall portion 21b on the side opposite to this hole side wall portion, that is, on the sealant side, and the recess 21 is formed such that the hole side wall portion 21a is higher than the sealant side wall portion 21b. Thereafter, in the same manner as in the first embodiment, the sealant 3 is applied to the lower surface of the aluminum alloy plate 2 so as to surround the first through-hole 2a in a region outside the recess 21.

[0038] Thereafter, as shown in FIG. 3B, the aluminum alloy plate 2 is positioned so that the second through-hole 4a of the element 4 overlaps with the planned joining position on the steel plate 1. The aluminum alloy plate 2 is placed on the upper surface of the steel plate 1 and pressed toward the steel plate 1. Thereafter, arc welding is performed through the second through-hole 4a of the element 4 to melt a part of the steel plate 1 and at least a part of the element 4, and to form a weld metal 5 that fills the second through-hole 4a. As a result, the element 4 and the steel plate 1 are firmly welded together by welding, and the steel plate 1 and the aluminum alloy plate 2 are joined.

[0039] Also in the joining method according to the second embodiment as described above, similar to the first embodiment, it is possible to prevent the occurrence of welding defects and corrosion at the welded portion, and to improve the joining strength. Further, in the present embodiment, since the hole side wall portion 21a is formed to be higher than the sealant side wall portion 21b, when the aluminum alloy plate 2 is placed on the steel plate 1, a gap G is formed between the aluminum alloy plate 2 and the steel plate 1 in the region where the sealant is applied. Therefore, the sealant 3 can be disposed between the aluminum alloy plate 2 and the steel plate 1 in a state having a thickness, and the water intrusion prevention effect by the sealant 3 can be further enhanced.

[0040] In the present embodiment, in order to arrange the region where the first through-hole 2a of the aluminum alloy plate 2 is formed to be in contact with the steel plate 1, the height difference between the hole side wall portion 21a and the sealant side wall portion 21b becomes the distance of the gap G. The distance of the gap G is not particularly limited, but if it is too large, the required amount of the sealant 3 increases to fill the gap G between the aluminum alloy plate 2 and the steel plate 1. Also, if the gap G is too small, it becomes difficult to ensure the thickness of the sealant 3. Therefore, it is preferable to perform press working so that the distance of the gap G is 0.1 mm or more and 2.0 mm or less.

[0041] <Third Embodiment> Figures 4A and 4B are cross-sectional views showing the method for joining dissimilar metal materials according to the third embodiment of the present invention in the order of steps. Further, FIG. 5 is a drawing substitute photograph showing the shape of the aluminum alloy plate used in the method for joining dissimilar metal materials according to the third embodiment of the present invention. In FIGS. 4A and 4B, the same or equivalent parts as those in the second embodiment shown in FIGS. 3A and 3B are denoted by the same reference numerals in the drawings, and the description thereof is omitted or simplified.

[0042] Also in the third embodiment, similar to the second embodiment, the recess 21 is formed such that the hole side wall portion 21a is higher than the sealant side wall portion 21b. Further, as shown in FIGS. 4B and 5, when the aluminum alloy plate 2 is disposed on the steel plate 1, the aluminum alloy plate 2 is processed so that the region including the first through hole 2a of the aluminum alloy plate 2 is separated from the surface of the steel plate 1. That is, a convex portion 6 protruding in a direction opposite to the recess 21 is formed at the tip of the hole side wall portion 21a in the recess 21, and the region including the through hole 2a has a shape recessed in the same direction as the recess 21. Therefore, when the aluminum alloy plate 2 is disposed on the steel plate 1, a gap portion 7 is formed between the region including the first through hole 2a and the steel plate 1.

[0043] Also in the joining method according to the third embodiment as described above, similar to the first embodiment, the occurrence of welding defects and corrosion at the welded portion can be prevented, and the joining strength can be improved. Further, similar to the second embodiment, since a gap G is formed between the aluminum alloy plate 2 and the steel plate 1 in the region where the sealant is applied, the thickness of the sealant 3 to be applied can be ensured, and the water intrusion prevention effect by the sealant 3 can be further enhanced. Furthermore, in the present embodiment, when performing arc welding inside the second through hole 4a of the element 4, since there is a gap portion 7 between the aluminum alloy plate 2 and the steel plate 1, deep penetration of the arc can be obtained, and the joining strength can be further improved.

[0044] Note that, also in this embodiment, in order to arrange the tip of the convex portion 6 in contact with the steel plate 1, the height difference between the hole side wall portion 21a and the sealant side wall portion 21b in the concave portion 21 becomes the distance of the gap G. The preferable distance of the gap G is as described above.

[0045] <Fourth Embodiment> FIG. 6 is a cross-sectional view showing a joint obtained by the method for joining dissimilar metal materials according to the fourth embodiment of the present invention. In the fourth embodiment shown in FIG. 6, the differences from the first embodiment shown in FIGS. 1A to 1C are only the presence or absence of the element 4 and the materials of the upper plate and the lower plate, and thus the drawings showing the process sequence are omitted. In FIG. 6, the same or equivalent parts as those in the second embodiment shown in FIGS. 1A to 1C are denoted by the same reference numerals in the drawings, and the description thereof is omitted or simplified.

[0046] In this embodiment, an aluminum alloy plate 32 is used as the lower plate and a steel plate 31 is used as the upper plate, and the two are joined by element arc spot welding. That is, a first through hole 31a is formed at the planned joining position of the steel plate 31 with the aluminum alloy plate 32, and a concave portion 21 is formed by pressing so as to surround the first through hole 31a. Thereafter, in the same manner as in the first embodiment, a sealant 3 is applied to the surface of the steel plate 31 on the upper plate side facing the aluminum alloy plate 32. Thereafter, as shown in FIG. 1B, the steel plate 31 is positioned so that the first through hole 31a and the planned joining position in the aluminum alloy plate 32 overlap, and the steel plate 31 is disposed on the upper surface of the aluminum alloy plate 32.

[0047] Thereafter, the steel plate 31 is pressed toward the aluminum alloy plate 32 to bring the sealant 3 into close contact with the steel plate 31 and the aluminum alloy plate 32. Note that, in this embodiment, the element 4 is not used. Thereafter, arc welding is performed using a welding wire (not shown) made of an aluminum alloy through the first through-hole 31a to melt a part of the aluminum alloy plate 32 and form a weld metal 15 that fills the first through-hole 31a. At this time, a surplus 15a having a diameter larger than that of the first through-hole 31a is formed on the upper surface of the steel plate 31. Thereby, the steel plate 31 and the aluminum alloy plate 32 are joined.

[0048] As shown in the fourth embodiment, the materials of the upper plate and the lower plate are not particularly limited, and the lower plate can be either an aluminum or aluminum alloy plate or a steel plate, and the upper plate can be the other. In the present embodiment, a recess 21 is formed in the steel plate 31 which is the upper plate, and a sealant 3 is applied to the outside of the recess 21 excluding the inner wall surface of the recess 21. Therefore, even when the steel plate 31 is pressed toward the aluminum alloy plate 32, it is possible to prevent the sealant from entering the location where the arc is generated, and the same effect as in the first embodiment can be obtained. Further, in the present embodiment, without using an element, a weld metal 15 made of an aluminum alloy is formed using the same welding material as the aluminum alloy plate 32 which is the lower plate. Therefore, the weld metal 15 and the aluminum alloy plate 32 are firmly joined by welding. Also, a surplus 15a is formed on the upper surface of the steel plate 31, and this surplus 15a corresponds to the head 4c of the element 4 in the first embodiment. Therefore, since the steel plate 31 is physically fixed to the steel plate 1 by the surplus 15a of the weld metal 15, the steel plate 31 and the aluminum alloy plate 32 are joined.

[0049] Note that even when the aluminum alloy plate 32 is used as the lower plate and the steel plate 31 is used as the upper plate as in the fourth embodiment, an aluminum alloy element can be used and a welding material made of an aluminum alloy can be used to join the aluminum alloy plate 32 and the steel plate 31. However, since the aluminum alloy element is almost melted by welding, the cross-sectional shape of the obtained joint becomes the same shape as that shown in FIG. 6.

[0050] Also, in the fourth embodiment, similar to the second embodiment, the wall on the side of the first through-hole in the recess 21 is formed to be higher than the wall on the side where the sealant is applied, and a gap G may be formed between the aluminum alloy plate 32 and the steel plate 31 in the region where the sealant is applied. Thereby, the thickness for applying the sealant 3 can be ensured. Furthermore, even when adopting a joining method without using an element with the aluminum alloy plate 32 as the lower plate and the steel plate 31 as the upper plate, the region including the first through-hole 31a can be formed in a shape recessed in the same direction as the recess 21. With such a configuration, when the steel plate 31 is disposed on the aluminum alloy plate 32, a gap portion 7 is formed between the region including the first through-hole 31a and the aluminum alloy plate 32, and the penetration of the arc can be deepened.

[0051] In the second to fourth embodiments, similar to the first embodiment, the sealant 3 may be applied to the upper plate side, the lower plate side, or both. However, when the sealant 3 is applied to the inner wall surface of the recess 21 of the upper plate or the region of the lower plate facing the recess 21, before placing the upper plate on the lower plate and pressing the upper plate toward the lower plate, the volume of the gap 22 is in a small state. Therefore, when the upper plate is pressed toward the lower plate, it becomes difficult to retain the sealant 3 in the gap 22 of the recess 21, and there is a possibility that the sealant 3 may penetrate into the welded portion. Therefore, when the sealant 3 is applied to the lower plate side, it is important not to apply it to the region facing the recess 21.

[0052] FIG. 7A is a plan view showing the shape of an aluminum alloy plate applicable to the first embodiment, FIG. 7B is a cross-sectional view taken along line A-A in FIG. 7A, and FIG. 7C is a perspective view thereof. Note that FIGS. 7A and 7C show the surface facing the steel plate 1. As described above, since the recess 21 is formed on the surface of the aluminum alloy plate 2 facing the steel plate 1, it is possible to prevent the sealant from entering the region where the arc is generated. The region where the sealant is applied may be a region outside the recess 21 excluding the inner wall surface of the recess 21, and may be applied so as to surround the first through hole 2a. For example, it may be applied to the region A1 near the recess 21, or may be applied to the region A2 near the four end faces of the aluminum alloy plate 2.

[0053] FIG. 8A is a top view showing a joint obtained by applying the fourth embodiment using a steel plate having a hat-shaped cross-sectional shape, FIG. 8B is a cross-sectional view taken along line B-B in FIG. 8A, and FIG. 8C is a perspective view thereof. FIGS. 8A to 8C show an example in which the upper plate shape shown in the third embodiment is adopted, the lower plate is an aluminum alloy plate, the upper plate is a steel plate, and the elements are joined by a method without using elements. In FIGS. 8A to 8C, the same or equivalent parts as those in the third embodiment shown in FIGS. 4A and 4B are denoted by the same reference numerals in the drawings, and the description thereof is omitted or simplified.

[0054] As shown in FIGS. 8A to 8C, the steel plate 41 is formed with ribs 43 extending in the longitudinal direction, and the cross-sectional shape thereof is hat-shaped. A plurality of first through holes 41a are provided on both sides of the rib 43. In FIG. 8A, the regions A3 and A4 where the sealant is applied are shown by broken lines and alternate long and short dash lines, but the regions A3 and A4 shown in FIG. 8A are the surfaces facing the aluminum alloy plate 42, not the upper surface of the steel plate 41. Thus, even when a plurality of first through holes 41a are provided on the same plane, the region where the sealant is applied may be a region outside the recess 21 excluding the inner wall surface of the recess 21, and may be a region surrounding at least one first through hole 2a. For example, it may be applied to the region A3 surrounding each recess 21 outside each recess 21, or may be applied to the region A4 surrounding all the recesses 21 provided on the same plane.

Description of Reference Numerals

[0055] 1, 31, 41, 51, 61 Steel plate (lower plate) 2, 32, 42, 52, 62 Aluminum alloy plate (upper plate) 2a, 31a, 41a, 51a First through-hole 3, 53 Sealing agent 4 Element 4a Second through-hole 5, 15 Weld metal 6 Protrusion 7 Gap portion 21 Recess 22 Gap

Claims

1. A step of disposing an upper plate made of a material different from that of the lower plate and having a first through hole on a surface orthogonal to the thickness direction of the lower plate; A method for joining dissimilar metal materials, comprising: a step of melting a part of the lower plate through the first through hole by arc spot welding and forming a welding metal having the same main components as the lower plate; Before the step of disposing the upper plate, a step of forming a recess in the upper plate in a shape separated from the lower plate so as to surround at least the first through hole; A step of applying a sealant to at least one of the surface of the upper plate facing the lower plate and the surface of the lower plate facing the upper plate so as to surround at least the first through hole; The method for joining dissimilar metal materials, wherein the region where the sealant is applied is a region separated from the first through hole with respect to the recess, excluding the inner wall surface of the recess and the region of the lower plate facing the recess.

2. In the step of forming the welding metal, the first through hole is filled, and an excess having a diameter larger than the diameter of the first through hole is formed on the upper surface of the upper plate, and the lower plate and the upper plate are joined. The method for joining dissimilar metal materials according to Claim 1.

3. Before the step of forming the welding metal, A step of inserting an element having a second through hole into the first through hole is included, The element has an insertion portion formed at one axial end side of the second through hole and having a diameter that can be inserted into the first through hole, and a head portion formed at the other axial end side of the second through hole and having a diameter larger than the diameter of the first through hole, In the step of forming the welding metal, a step of melting at least a part of the lower plate and at least a part of the element and forming a welding metal that fills the second through hole is included. The method for joining dissimilar metal materials according to Claim 1.

4. The recess has a hole side wall portion on the first through hole side and a sealant side wall portion on the side facing the hole side wall portion, In the step of forming the recess in the upper plate, the recess is formed such that the hole side wall portion is higher than the sealant side wall portion. The method for joining dissimilar metal materials according to any one of Claims 1 to 3.

5. The surface to which the sealant is applied is the surface of the upper plate facing the lower plate, and the method for joining dissimilar metal materials according to any one of claims 1 to 3 is characterized in that.

6. The method for joining dissimilar metal materials according to any one of claims 1 to 3, wherein the lower plate is made of either an aluminum or aluminum alloy plate or a steel plate, and the upper plate is made of the other.

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